MARCH/APRIL 2012
www.industrial-printing.net
Getting in Touch with Conductive Films P. 14
UV-LED Curing Membrane-Switch Challenges Large-Format Pad Printing
contents
industrial + specialty printing March/April 2012 • Volume 03/Issue 02
FEATURES
10 Applications for Industrial Pad Printing Julian Joffee, Pad Print Machinery of Vermont
This article reviews capabilities and limitations of pad-printing equipment in demanding tasks.
14 Transparent Conductive Films for Touch-Key Applications Wolfgang Milner, PolyIC GmbH & Co.
Learn what’s expected from flexible, conductive, and transparent films in the near future.
18 Versatile Membrane Switches
Wim Zoomer and Neil Bolding, MacDermid Autotype
Market and design forces are rapidly changing the face of the classic membrane switch. See what’s being done now in the latest applications.
22 Developments in UV-LED Curing Karla Witt, INX Digital Int’l
This article offers insight into how some companies are approaching UV curing technology and examines current industry challenges and questions.
25 Pushing the Limits of Functional Printed Inks Don Banfield, Conductive Compounds, Inc.
The tests described here were designed to assess functional inks in extreme heat, humidity, and water.
30 Opportunities for Silver Inks and Pastes in a Declining Market Jill Simpson, Ph.D., NanoMarkets
Find out why silver is sliding and discover where profits may be found when working with inks based on this precious metal. INDUSTRIAL + SPECIALTY PRINTING, (ISSN 2125-9469) is published bi-monthly by ST Media Group International Inc., 11262 Cornell Park Dr., Cincinnati, OH 45242-1812. Telephone: (513) 421-2050, Fax: (513) 362-0317. No charge for subscriptions to qualified individuals. Annual rate for subscriptions to non-qualified individuals in the U.S.A.: $42 USD. Annual rate for subscriptions in Canada: $70 USD (includes GST & postage); all other countries: $92 (Int’l mail) payable in U.S. funds. Printed in the U.S.A. Copyright 2012, by ST Media Group International Inc. All rights reserved. The contents of this publication may not be reproduced in whole or in part without the consent of the publisher. The publisher is not responsible for product claims and representations. POSTMASTER: Send address changes to: Industrial + Specialty Printing, P.O. Box 1060, Skokie, IL 60076. Change of address: Send old address label along with new address to Industrial + Specialty Printing, P.O. Box 1060, Skokie, IL 60076. For single copies or back issues: contact Debbie Reed at (513) 421-9356 or Debbie.Reed@STMediaGroup.com. Subscription Services: ISP@halldata.com, Fax: (847) 763-9030, Phone: (847) 763-4938, New Subscriptions: www.industrial-printing.net/subscribe.
columns 34 Printed Electronics
Julia Goldstein, Ph.D. Learn about printed memory produced with either ferroelectric polymers or inorganic resistive materials in portable, flexible products.
36 Printing Methods
Richa Anand, Ph.D., Phoseon Technology UV-LED lamps are recognized for their lower energy consumption, longer lifetime, improved robustness, smaller form factor, and faster on/off switching. But how do they work?
38 Industry Insider
Jayna Sheats, Ph.D., TerePac This column talks about the role of printing in pervasive electronics.
40 Shop Tour
RSP, Inc. of Milwaukee, WI, handles a variety of printing and contract manufacturing services for membrane switches, touch screens, wire harnesses, and rubber and plastic molded products.
DEPARTMENTS 4 Editorial Response 6 Product Focus 32 Industry News 39 Advertising Index On the Cover
The cover photo is a close-up view of PolyIC’s latest transparent, conductive film for touchscreens and shows customer-specific patterns. Cover courtesy PolyIC. Cover design by Keri Harper.
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EDITORIAL RESPONSE
Energy for the Future
Industrial + Specialty Printing www.industrial-printing.net
GAIL FLOWER Editor
In President Obama’s State of the Union address in January 2012, he said that with America having only 2% of the world’s oil reserves, oil isn’t enough. And that “American oil production is the highest that it’s been in eight years.” At this rate, we have enough oil to last the U.S. 100 years. And then he promised that we would not walk away from the promise of clean energy. That’s a worldwide issue. At FlexTech Alliance this year in Phoenix, AZ, iSP magazine headed a panel discussion on PV that presented many interesting ideas. Most of the panel members saw organic solar (OPV) as the wave of the future, because it uses organic (carbon-based) electronics for light absorption and charge transport. Because the cells are made of plastic, they tend to be cheaper than silicon, and combined with the flexibility of organic molecules and the possibility of additive printing technologies for cell-material production, they are easier to make than silicon, thin-film cells. Many companies are involved in getting OPV from lab to fab. Bert Männig of Heliatek talked about how his company was spun off from the Technical University of Dresden and the University of Ulm in 2006, bringing together expertise in the fields of organic optoelectronics and organic oligomer synthesis. Right now, Heliatek is making the
transition from technology development to industrial manufacture. The company’s goal is to mass produce organic PV panels using vacuum-based, roll-to-roll, low-temperature processes. Männig said his company has set a record for cell efficiency at 9.8% for a 1.1-cm2 tandem cell manufactured using a low-temp deposition process. Jim Buntaine of Konarka talked about how his company spun out from the University of Massachusetts (Lowell) in 2001. He gave the history of PV, talking about how space power was needed in 1958 and that all satellites now use inorganic PV. From 1972 on, the energy crisis has motivated bringing PV to earth. In stage 3, from 1988, the global environmental impact of fossil fuel has begun to be recognized. The hope in phase 4 is for architectural power—PV power built into building materials. Konarka manufactures OPV cells using a roll-to-roll manufacturing technology and is capable of producing 250,000 ft2 (1 GW/year capability). Zheng Xu of Solarmer Energy talked about driving down the cost of flexible PV panels. Solarmer was founded in 2006, sprouting from technology licensed from UCLA and the University of Chicago. The company set world records for OPV efficiencies. Xu said that the killer app is power-converting windows. Solar still has a way to go in increasing efficiencies, lowering costs, getting materials accepted as normal building supplies. Still, it feels good to know that the research from universities actuPhoto: (L-R) Gail Flower, editor, iSP; Stephen Bedell, Research Staff, IBM; ally results in Jim Buntaine, executive VP and CTO, Konarka; Zheng Xu, manager of practical jobs and device engineering, Solarmer Energy Inc.; Bert Männing, Co-founder, Helireal products for atek; Jean-Noel Poirier, VP sales, Global Solar Energy; Miles Barr, MIT. clean energy. 4 | INDUSTRIAL + SPECIALTY PRINTING www.industrial-printing.net
STEVE DUCCILLI Group Publisher steve.duccilli@stmediagroup.com GREGORY SHARPLESS Associate Publisher gregory.sharpless@stmediagroup.com GAIL FLOWER Editor gail.flower@stmediagroup.com BEN P. ROSENFIELD Managing Editor ben.rosenfield@stmediagroup.com KERI HARPER Art Director keri.harper@stmediagroup.com LINDA VOLZ Production Coordinator linda.volz@stmediagroup.com BUSINESS DEVELOPMENT MANAGER Steve Duccilli steve.duccilli@stmediagroup.com EDITORIAL ADVISORY BOARD Joe Fjelstad, Brendan Florez, Dolf Kahle, Bruce Kahn, Ph.D., Rita Mohanty, Ph.D., Scott Moncrieff, Randall Sherman, Mike Young, Wim Zoomer
JERRY SWORMSTEDT Chairman of the Board TEDD SWORMSTEDT President KARI FREUDENBERGER Director of Online Media
CUSTOMER SERVICE Industrial + Specialty Printing Magazine Customer Service P.O. Box 1060 Skokie, IL 60076 ISP@halldata.com F: 847-763-9040
product focus
The latest equipment and materials for industrial printing
Electrically Conductive Adhesive Henkel Electronic Materials (www.henkel.com) recently developed a new, electrically conductive adhesive (ECA) compatible with lowercost, tin-terminated components to enable more cost-effective assembly processes. ABLESTIK ICP-3535M1 is a one-component, premixed ECA designed to provide low and stable contact resistance when used with 100% tin-terminated components. According to Henkel, the reliability of ABLESTIK ICP-3535M1 has been confirmed through various analyses, maintaining its stable contact resistance and good mechanical integrity after 3000 hr of temperature and humidity testing, 3000 cycles of thermal-shock evaluation, and 3000 hr of heat storage. Henkel says that, in each case, ABLESTIK ICP3535M1 exhibits excellent performance with very small components, such as 0402s, displaying absolutely zero bridging or wicking with highly miniaturized devices.
Flatbed UV Inkjet Printer Océ (www.oceusa.com) recently announced the availability of the Océ Arizona 318 GL printer, a system the company describes as a highly capable, introductory flatbed UV inkjet printer that offers smaller print producers high-quality imaging. The system print at speeds up to 194 sq ft/hr (18 sq m/hr) or more than 20 2 x 3-ft (0.6 x 0.9-m) boards/ hr. ONYX PosterShop X10 Océ Edition software is available to drive the printer. The Océ Arizona 318 GL can print on rigid media up to 49.2 in. (1250 mm) wide x 98.4 in. (2500 mm) long and up to 1.89 in. (48 mm) thick. Substrates are secured by a vacuum table, and the printer supports edge-to-edge printing, printing of multiple boards simultaneously, registered double-sided prints, and the printing of large displays tiled over several boards. Océ’s White Ink Option enables under-printing for non-white media or objects, over-printing for backlit applications on transparent media, and printing white as a spot color. An option for roll-fed media is also available. | Industrial + Specialty Printing www.industrial-printing.net
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Air-Filtration Closed-Loop QA Solution System Pad Print Machinery of Vermont (ppmovt.com) has added a new air-filtration system to its line of auxiliary equipment. This system uses a combination HEPA and carbon tray for removal of fumes and gases with high particulate content. Clean Air 300 features include 300-cfm airflow, a filter-monitor gauge, and swivel casters. The unit can connect to 2-, 2.5-, and 4-in.-diameter (51-, 63.5-, and 102-mm) hoses.
Double-Coated Tapes Polyonics (www. polyonics.com) bills its double-coated tapes as ideal for bonding materials that will be exposed to extremely high temperatures and harsh manufacturing environments. They include liners that are designed to be die cut and to assist in auto-application. The double-coated tapes are designed to resist chemicals typically found in PCB manufacturing, remain dimensionally stable at elevated temperatures, and provide excellent electrical properties, including dielectric strength. The double-coated polyimide tapes are offered in thicknesses of 1 and 2 mil and in high-temperature (up to 932°F, 500°C), ESD, and flame-retardant (tested for compliance with the UL94 VTM0 and FAR 25.853 flammability and BSS 7238/7239 smoke and toxicity standards) constructions.
Measurement Solutions
The N3 line of measurement solutions from Nanovea (www. nanovea.com) includes the M3, P3, and T3. The M3 is engineered to provide nanoindentation results under ASTM standards for use in R&D applications. Nanovea says its indentation method is fully automated with no need to observe the indent. The system features a touchscreen. The P3 is designed for 3D non-contact metrology and engineered to provide automatic nanometer ISO roughness and step data on nearly any material. The T3 is an automatic nano-wear tester using linear reciprocating, ASTM g133, for wear-rate study.
SEND US YOUR PRODUCT NEWS
Email gail.flower@stmediagroup.com
| Industrial + Specialty Printing www.industrial-printing.net
DEK (www.dek.com) calls its ProDEK an innovative and high-performance, closed-loop system tool designed to ensure print-performance optimization. It communicates between the DEK screen printer and solder-paste-inspection machine to identify any potential problems and is engineered to maintain consistent, repeatable, high-quality output. Features include proactive defect prevention; process optimization without manual intervention; interfaces to Koh Young, Parmi, and Cyber Optics; ability to retrofit to all DEK printers powered by the standard Instinctiv V9 user interface; and more. ProDEK monitors a configurable quantity of printed circuit boards (PCBs), sending an independently corrected, forward and reverse offset to the printer, which then adjusts paste-on-pad alignment in real time. ProDEK uses barcode-based tracking technology to ensure printed and inspected board synchronization.
Vacuum Motors ACI (www. aircontrolindustries.com) offers what it describes as an extensive range of vacuum pumps ideal for screenprinting applications and designed for easy retrofit. ACI units are driven by AC brushless motors and engineered for quiet operation. The brushless units are designed to ensure safe use in areas where solvents are present and low maintenance. ACI vacuum motors are multistage units of centrifugal design with impellers mounted directly on the motor shaft. The impellers are sheet aluminum and are balanced for optimum performance and minimal running stresses. They can be used for blowing and exhausting duties and support flow rates up to 500 cfm, pressures up to 64 in./SWG and 0.067-4 hp (0.05-3 kW). ACI’s vacuum motors conform to BS5000 Class B standard insulation and are C.S.A. approved.
Ink for Seiko Printers Films for Digital Imaging 3M Commercial Graphics (www.3m. com) and Seiko I Infotech Inc. (www. seiko-i.com) introduce GX 3M inks, billed as vibrant, flexible, colored inks made for use in Seiko I Infotech ColorPainter H Series printers and designed for printing onto many 3M brand opaque, translucent, and reflective graphics films. The solvent inks are formulated for excellent conformability and are available in eight colors (CMYKLcLm and two shades of W). According to the companies, GX 3M inks are suitable for graphics applied to compound curves, corrugations, and riveted and flat surfaces and, when protected with the proper 3M overlaminate, are also durable and weather resistant.
Sihl Digital Imaging (www.sihlusa.com) has developed what it describes as an easy to print, easy to apply, and easy to remove clear film for use with aqueous inkjet printers. Sihl ClearSTICK3166 is a 2-mil, clear, polyester film designed with and optically clear inkjet coating that Sihl says is ideal for interior application to virtually any substrate or surface. ClearSTICK-3166 is engineered for maximum inkload and fast drytimes with aqueous printers from HP, Epson, Canon, and others. Its white release liner allows for universal compatibility with media-feed and mediasensing systems. The film can be first- or second-surface printed. ClearSTICK-3166 is available in 75-ft (23-m) rolls and in widths of 17, 24, 36, and 50 in. (432, 610, 914, and 1270 mm).
Workflow Software Onyx Graphics (www.onyxgfx.com) recently unveiled ONYX Thrive, a scalable print-production solution based on Adobe PDF Print Engine technology. ONYX Thrive software manages the workflow associated with wide-format-print production and is designed to offer print-service providers accurate, predictable, and highquality results. Onyx Thrive workflow software is powered by Adobe technologies, including the Adobe PDF Print Engine, a renderingengine technology that Adobe partners use to build tailored solutions for their market segments. Onyx’s software features the Thrive Production Manager, a browserbased user interface that enables printservice providers to submit, control, and monitor jobs and devices from a Mac, PC, or mobile device.
Inkjet Ink Fujifilm (www.fujifilmusa.com) says its Color+ inkjet inks can help you achieve better color from your inkjet printer and make older printers run more efficiently. According to Fujifilm, Color+ inks are developed to provide optimal performance on a wide variety of inkjet printers from most of the leading suppliers. The ink features Fujifilm’s MicroV fine-pigment-dispersion technology, engineered to reduce printhead clogging and offer stronger, brighter colors.
march/april 2012 |
FEATURE STORY
APPLICATIONS FOR INDUSTRIAL PAD PRINTING The initial investment in pad printing can be high, but read on to discover the process’s many economies in industrial imaging.
Julian Joffe
Pad Print Machinery of Vermont
W
hen many of us think of pad printing, we automatically picture printing onto complex, three-dimensional products such as golf balls or medical devices (Figure 1). The reality is that certain products lend themselves well to pad printing while others do not; many others can be decorated with multiple different processes. The single most differentiating functional component of the pad-printing process is the silicone printing pad (Figure 2) and its unique characteristics. Its function is to transport the image from the etched cliche (plate) to the substrate being printed. Pad shapes, sizes, and durometer can be modified to suit the characteristics of the object being printed, but they also must comply with the laws of pad printing. That statement brings me to an observation: Many times, a client has asked why the pad shape cannot be flat or even concave. The answer is to pick up the image effectively, it must roll onto the cliche to allow the exclusion of air between the ink in the etched image area on the cliche and the pad surface (Figure 3). As a general rule, the harder a pad, the larger the radius can become. A very firm pad can have a less pointed shape than a
very soft pad. Another generality is that a harder pad prints a crisper image than a soft pad. Very firm pads tend to force ink to move within the etched areas and can cause problems that look like ghosting, particularly when larger ink surfaces are being printed/transferred. Very soft pads, in some cases, will not transfer or pick up an image in its entirety, leading to rough edges or voids.
LIMITATIONS OF PAD PRINTING While fairly large images can be printed, the cost of a machine for printing an image 8 in. in diameter in one color can approach $50,000. Large images require large pads, which in turn require large machines and, with them, a high price. In general, pad printing is highly suited to smaller images, but there are many exceptions involving highly successful
Figure 1 Variety of products where pad printing was used
10 | INDUSTRIAL + SPECIALTY PRINTING www.industrial-printing.net
imaging of very large graphics. Some other considerations follow. Ink coverage and opacity Large flooded background prints exceeding 2-3 in. in diameter do not always print well because of issues with uneven ink coverage and, very often, opacity. These types of images definitely lend themselves better to alternatives such as screen printing. Opacity can be challenging at times due to the fact that the wet ink being carried out of the etched cliche can be at maximum 0.0006 in. thick; therefore, multiple prints may be needed. The most notable issue with opacity comes into play when lighter colors are printed onto darker substrates. The dark substrate will often influence and change the color being printed—a red image on a black part is a good example of a situation where multiple prints often will not solve the problem. If you are forced to pad print the part, very often the best solution is to print a white underlay to solve the problem (Figure 4). If the product is flat, then by all means screen print it. Screen printing allows a large amount of ink to be deposited, thus eliminating the opacity issue. However, if, for example, the surface is rough or has odd surface topography, pad printing may be the only option. Machine speeds Most pad-printing systems that are manually fed can only accommodate throughput of approximately 1000-1500 cycles/hr. There are much faster systems, such as servo-driven and rotary pad printers, but if very high volumes are required, such as 3000 plus pieces/hr, the only way to meet these requirements is to print multiple parts per cycle. Once again, the larger print areas of multiple parts require a larger machine and automation dedicated to parts handling to meet those volumes. Once these types of volumes are a requirement, then one should look at alternatives such as high-speed rotary pad printing, inkjets, or offset printing (Figure 5). Once again, the part’s topography may present some obstacles to all other processes other than pad printing. Setup costs These are a relative thing and, in fact, only if the runs are extremely short can pad printing be viewed as expensive. Many times, clients ask for machines and, upon further investigation, it is revealed that they are printing variable data, such as serial numbers, in which case the setup time and cliche costs are in most
Figure 2 (Top) Sample of pad shapes and sizes Figure 3 (Bottom) A large pad is compressed over the substrate transferring the image.
cases prohibitive and an alternate type of printing must be found. Should this be a date code that changes daily, pad printing can be very viable, and the cost of a cliche is now relatively inexpensive and the few minutes of set up time inconsequential. Environmental variations Keep in mind that environmental conditions play a role in the drying speed of the inks; therefore, variations in humidity and temperature are an important consideration when implementing a pad-printing system. Under the same temperature and humidity conditions, the drying speed of the ink is determined by the amount of thinner and thinner type(s) added to the ink. The drying speed of the ink is a critical component to the quality of the imprint. Issues will arise when the ink dries too slowly or quickly for the conditions, which includes machine speed. Obviously, a faster machine will require an ink mixture that is slightly faster drying, and vise versa. Environmental changes that are small—for example, a temperature change from 60-70°—will, in most cases, have little effect on print quality. However, large swings in temperature and humidity require adjustments to inks. Trained personnel can get control of these issues quite easily, but a thorough understanding of the cause and effect are required.
Other processes, such as hot stamping and inkjet printing, are not that susceptible to environmental variations, but it’s very rarely worth investing in technology that is not that suitable for a process if it is merely a matter of enclosing an area and installing climate control to allow a more effective implementation of the pad-printing process. Strengths of pad printing The ability to follow rather complex shapes is the single most unique characteristic that has strengthened the market for pad printing and made it an ideal method for decorating items that otherwise would be close to impossible to print. Many medical devices, for example, would remain without critical markings if it were not for those relatively soft pads that conform so well to a variety of shapes. pad-printing systems are excellent for products that vary in shape during the print process—even fruit, vegetables, and eggs are being decorated effectively with pad printing. Setup With some training, even the most inexperienced of personnel can be up and running quickly. Depending upon the level of complexity of the handling systems and the number of colors, machines can go into a full production mode within a couple of days. Many of the newer multimarch/april 2012 | 11
Pad Printing Equipment and Supply Manufacturers and Distributors
Figure 4 (Top) White ink pad printed on a black irregular surface Figure 5 (Below) Rotary pad printer
All American Mfg. & Supply screenprintsupply.com
Cosmex Graphics Inc. cosmexgraphics.com
Diversified Printing Techniques Inc.
diverprint.com
Ever Bright Printing Machine Pty Ltd. everbrightprinting.en.alibaba.com
Inkcups Now inkcups.com
ITW Trans Tech itwtranstech.com
Microtec Technology Co. Ltd szmicrotec.com
Pad Print Machinery of Vermont padprintmachinery.com
Pemiagaan Hai Kuang Sdn Bhd
haikuang.com
Pentex Print Master Industries inkflexx.com
Printa Systems
printa.com
Reisch & Associates
reischpad.com
Serigraf Ltd. serigraf.ie
12 | Industrial + Specialty Printing www.industrial-printing.net
color systems have servo controls for image placement and can be set up with ease and speed. Many manufacturers fail to implement a prepress system that allows for very quick changeovers. The process may take a few extra minutes in the graphics department and in the platemaking process, but it can save hours per day in the print room. Preregistered artwork and positives with punch tabs are the well kept secret that many manufacturers and contract printers fail to note. Today, with new plate lasers being used, there is no excuse for not registering etchings on the cliches so the artwork is always in the correct position when changeovers take place. Autonomy through simplicity Ease of setup and platemaking allows small companies to create artwork and, in turn, make the cliches in house so that they can offer quick turnaround to customers. The advantages here are huge as the just-in-time mentality of many industries always views this capability as an essential part of doing business with chosen suppliers. The only other print process that is even simpler is inkjet, where direct-to-print comes to mind. The advent of the laser has further simplified the clichĂŠ-making process, and time to market can be reduced even further when you are prepared for the relatively high cost of entry to laser-based platemaking (Figure 6). One of the biggest advantages of pad printing is the fact that you could get a call in the morning and have a sample out to your customer that same day.
January/february 2012 www.industrial-printing.net
Materials and Methods for Printed OLeDs
Figure 6 Rapid fire laser etcher and plate etched within the laser
P. 20
Inkjets in Electronics Applications
Costs associated with set up The relatively low cost of cliches and inks allows the cost of production to remain low. Pad-printed labels commonly cost manufacturers tenths of a cent in larger production environments, making the return on investment way shorter than industry standards. However, fast ROI is not always the case, and some of the larger, more automated, systems will often have ROI numbers getting into the range of 18-24 months. There is no need for highly skilled personnel to set up equipment, thereby helping to keep production costs down (Figure 7). Low VOCs Closed-system pad printing is a process that, under normal conditions, does not require the use of extreme venting. You still should use air-carbon-filtration safety though. In most cases, due to the enclosed nature and structure of the pad-printing equipment, one air filtration unit can easily cover at least three machines. Pad printing almost always uses a solvent-based ink and of the solvent-based systems on the market, it is by far the easiest to control in terms of VOCs. I recall the complaints of one customer; and when I walked in to investigate the smell problem, I found that they had left solvent-soaked rags in open garbage cans in the production area. Once we exchanged them for sealed cans, the problem vanished. After 25 years in this business, I still feel pad printing is the most flexible and versatile decorating solution for many difficult-tomark applications. The initial investment in a pad printer can be high, but compared to other forms of product decorating—such as labeling garment tags using hot stamping and screen printing—pad printing cost per item is very economical. Pad-printing technology is continually evolving and more manufacturers are using pad printers within their production lines or adding automation to basic printers to reduce labor costs. There are always multiple ways to achieve the same objective. The key to success is selecting one that is the simplest, most flexible, cost effective, and will grow with your company. One last thing, find a supplier that knows the process and can and will service the systems they supply.
JULIAN JOFFE
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Extending Printing Capabilities 101 Membrane Switches Growing a Label Business
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Pad Print Machinery of Vermont Julian Joffe, founder and CEO of Pad Print Machinery of Vermont started his first company in the textile manufacturing field in Yonkers, NY. Joffe’s interest in engineering and his desire to help people has built the company into a 25,000-square-foot facility in East Dorset, Vermont. The company employs high-tech engineers designing and building industrial inkjet printers and automated pad-printing systems.
Already a subscriber to iSP? Lock in your subscription by visiting industrial-printing.net/renew MARCH/APRIL 2012 | 13
COVER STORY
TRANSPARENT, CONDUCTIVE FILMS FOR TOUCH-KEY APPLICATIONS Learn how specialized films will transform the way myriad printed-electronics products are manufactured. Wolfgang Mildner
PolyIC GmbH & Co.
Poly TC transparent conductive film 14 | INDUSTRIAL + SPECIALTY PRINTING www.industrial-printing.net
T
he form-follows-function design is all-important for modern car cockpits, cell phones, and electronic equipment in general. Purely functional design represents a thing of the past, while look and feel have become crucial selling points. Transparent, conductive films enable new design possibilities to be created—designs for controls and touch keys that are integrated into transparent surfaces or transparent touch keys on curved surfaces. Will you be able to control your car radio using buttons located directly on the dashboard in the future? Will we be able to move transparent side windows just by touching them? Will the controls on the center console be transparent touch keys instead of mechanical buttons? Will the hands-free keypad only appear when a driver wants to make a call and be invisible on the dashboard the rest of the time? These are visions of the future that will, for example, make car-interior designs even more attractive. However, transparent, conductive films are necessary for the implementation of such integrated controls. At present, these displays are manufactured using film that is coated with indium tin oxide (ITO), the most common material used for this purpose. As well as being transparent, these films also conduct electric current. ITO offers limited freedom of design; however, due to its restricted conductivity, relative fragility, and the complexity of the structuring process, it may not be used as often in future transparent, conductive films. FILMS FOR FUTURE CELL PHONES And what is in store for the future of the cell phone? What will follow smartphones? Cell phones are becoming ever lighter and slimmer. Using transparent and conductive fi lms, their shapes could become more ergonomic and devices could be considerably more flexible to make using them user-friendly. Alternatives to ITO are now available that compensate for its disadvantages. One option, based on printed-electronics-platform technology, is a type of cost-effective, flexible, electronic product that can be produced in high volumes. These fi lms are considerably flexible, transparent, and thin (Figure 1). They can either be used as a surface or be incorporated behind plastic, glass, and many other materials. PRINTED ELECTRONICS Printed electronics generally refers to electronic components or assemblies that are manufactured or partially manufactured using printing methods. These processes use electronic conducting and semiconducting functional materials instead of just graphics inks. Semiconducting materials are usually based on specialized plastics. Modern, high-volume, roll-to-roll printing methods reduce the cost of manufacturing and duration of production. In this way, they open new fields of application to which conventional (inorganic) electronics have hitherto had limited or no access. Thanks to printed electronics, new developments are emerging in largescale applications such as RFID tags, displays and solar cells. High production speed and the possibility of producing very large quantities using rapid, roll-to-roll processes are the starting point for printed electronics. Several layers of different materi-
als are laid on top of one another with great precision to create a continuous roll. This allows firms to manufacture functional films, such as electronic circuitry, that include all components (transistors, capacitors, diodes, etc.) using printed electronics. The production of electrode structures plays a major role and is the cornerstone of the process. It enables high-resolution, narrow conductor tracks to be produced on a large scale. The production of high-resolution structures at micron scale on thin, flexible, PET films can achieve both adequate conductivity and transparency of layers (Figure 2). TRANSPARENT, CONDUCTIVE FILMS Electrode-structure production can generally be used for any high-resolution structure on polyester film. The structure of the conductor tracks is so fine that the opaque metal can no longer be detected by the human eye and appears transparent. The conductor tracks are not created as wide lines on the film, but as a very fine conducting grid. The film is produced using a special rollto-roll printing process, a type of production that has its origins in printed electronics. This process allows large quantities to be produced and guarantees the flexibility of the film. Film structure and dimension can be adjusted to the particular field of application and to suit customers’ requirements. Companies market these flexible, conductive, and transparent films. That can be used in a diverse range of applications. Today, the touchscreen market is growing rapidly. Current conventional touch displays use films that are coated with ITO; however, ITO films are becoming more and more expensive due to the scarcity of indium, a rare metal. For this reason, manufacturers are looking for adequate alternatives to this type of film that can be used in a variety of touch applications, including screens and keys. Other fields of application can also be addressed. Transparent, conductive films could conceivably be used as a transparent, EMI-shielding film to block electromagnetic waves, as transparent heating films, or as electrodes.
Figure 1 High Resolution Image Conductive Area Example for Individual Layout Gap Width Pads & Wiring
Transparent PET Substrate
200µm
Example for a microscopic picture of conductive layer
MARCH/APRIL 2012 | 15
Figure 2 (Left) Flexible, conductive film with structured conductor tracks in a grid pattern so fine that it appears to be transparent to the human eye Figure 3 (Above) Transparent, conductive film for capacitive touch keys.
Transparent films for touchscreens What are resistive and capacitive touchscreens? Touch sensors differ with regard to their respective application in touch keys and touchscreens. They are the basis of modern, interactive input devices that have the advantage of being incredibly easy to use. Touchscreens are touch-sensitive surfaces. A distinction is made between capacitive and resistive touch. Resistive touch sensors use the pressure an object exerts on an input medium to establish a connection between two transparent conducting layers. The exact XY position of a touch point on a surface can be calculated from this electrical contact using the voltage gradients applied on the films in the X and Y directions. Capacitive touch sensors already recognize the proximity of electrically conducting objects, but can be regulated so that they have to be touched to react. In contrast to resistive technology, pressure is not required. The surfaces of capacitive touch sensors are electrically charged. When touched with a finger, a small transfer of charge is created. This small current can be measured on the surface where the uniform electrical field is established. Variations in its intensity in comparison to the areas that have not been touched allow the specific touch point to be precisely traced. Capacitive touch enables the use of applications that can detect the touch of one or more fingers on contact sites across the entire surface. Appropriate gestures made with one or more fingers can be recognized (multi-touch capability). Resistive touch sensors have set the touchscreen boom in motion; this process was additionally boosted by the multi-touch capability of capacitive sensors, a trend that is still going strong. Currently, for example, smartphones with multi-touch functionality are equipped with capacitive sensors. Transparent films for touch keys Touch keys are electronic switching devices operated by the touch of a finger and do not contain any mechanical moving parts. Ca16 | Industrial + Specialty Printing www.industrial-printing.net
pacitive touch keys are a predestined application for transparent, conductive films and are becoming more and more popular. Touch keys consist of conductive surfaces attached to a control chip. Capacitive keys recognize changes to the electrical capacitance caused, for example, by the touch of a finger. A change in the capacitance caused by a touch triggers a switching operation. Their great advantage is that they require no mechanical parts to function, which makes them very robust. The thin and flat design of keys of this type allow them to be seamlessly integrated into many kinds of applications. Their transparency enables them to be used as invisible keys, for example, that only appear when their contours are backlit. Transparent and conductive films can be used to create controls made of flat touch keys (Figure 3). The advantages of touch keys made of some films, such as transparency, ability to be backlit, thinness and flexibility, can be used anywhere where controls must be easy to clean and where a modern design without mechanical elements is desired. For instance, one possibility is mobile-communication keyboards on dashboards—ones that only become visible when the cell phone is activated. These keys are of particular interest to the automotive sector as they allow contemporary design concepts to be implemented as well as providing technical advantages. In addition to vehicle interiors, further applications for controls can be found in white goods (household devices such as cookers, refrigerators, and freezers), brown goods (electrical or electronic consumer goods), and in medical equipment. Curved surfaces One current trend towards using invisible keys in a diverse range of applications. Today, these elements are used in vehicle interiors, home appliances, and entertainment devices. The technical possibilities of these transparent controls enable implementation of previously impossible applications. Touch keys located directly on dashboards could be envisaged, for example. Their transparency would make them unnoticeable. They could also be integrated into the side windows or even the rear-view mirror. When combined with backlighting, the keys only become active when
Figure 4 It will be possible to dispense with conventional buttons and keys completely in the future. Flexible and conductive films can also be mounted on curved surfaces behind the dashboard.
required and are invisible the rest of the time. In addition to their high transparency and conductivity, the great flexibility of the films is a further advantage. Previously, transparent touch keys had the restriction that they could only be integrated into flat surfaces. Flexible controls, however, can now be built into surfaces that are curved or uneven (Figure 4). Touch keys can actually be positioned anywhere on the dynamic contours of a dashboard or center console. These new technologies open up unprecedented opportunities for creative design in vehicle interiors. In addition to their use in touch keys, transparent, conductive films can be used to implement further touch applications. Their ability to be structured in any desired form enables extensive grid structures to be created. This kind of transparent grid structure can be used to make larger touch applications, such as touch-sensitive screens. Resistive or capacitive single-touch or multi-touch applications of the kind used today in touch monitors and smartphones can be manufactured by combining two films. Touch sensors are becoming ever more popular as replacements for mechanical buttons and controls. The new trend is already clear: capacitive buttons and controls with attractive graphic designs integrated into surfaces. Attractive graphic surfaces are becoming increasingly important for equipment and controls particularly in the electronics, mobile communication and automotive sectors. Outstanding results can be achieved by combining transparent and conductive films with IMD (in-mold decoration) films. In this way, the surface in question is no longer disrupted by mechanical keys as the keys can be integrated behind the decoration. Non-conductive, metal IMD films can even be used to manufacture metallic surfaces and create, for example, brushed-metaleffect surfaces with integrated controls. The combination of touch sensors and IMD hints at the wealth of possibilities that can be achieved through the fusion of flexible design and application technologies, such as IMD, with the functional/electronic world. Product designers have been given a new dimension of creative freedom that is less and less restricted by conventional electronic standards and with graphic elements playing a more significant role. Further scope for transparent, conductive films Electrodes are electrical conductors, usually of metal, that are used to conduct electricity. Some film can be custom-printed with a conductive structure. It is even possible to print the conductors so finely that they become invisible to the human eye and enable transparent electrode grids to be manufactured. It is thus of particular use in applications requiring invisible current transport. Unlike other transparent conductors, such as ITO, the printed grid structures are a neutral shade so colors are not distorted. This opens up a multitude of application options for this type of film, including organic light-emitting diodes (OLED), organic solar cells (OPV), printed transistors, or as heating electrodes for
screens and mirrors. Further uses for electrodes Conductive structures can also be useful in any application that converts energy into heat. The extreme fineness of the conductive structures and layers places natural limitations on the heating elements. There are interesting perspectives for local heating elements—for example, to prevent windscreens and mirrors from misting up. The amount of energy required is so small that the structures necessary to transport it cause no optical impairment. Electrodes for EMC shielding The term EMC (electromagnetic compatibility) refers to electronic interference that can disturb electronic devices or even be produced by them. The increasing complexity of electronic circuits—for instance, in the automotive sector—has also caused an increase in disturbances triggered by electromagnetic waves. This risk can be curbed by using components that come under the category of EMC shielding. Some transparent, conductive films provide the following advantages for EMC shielding: • Customer-specific layouts, including grids in rhombic, rectangular, or hexagonal designs • Individual adjustment of the surface resistance and, therefore, the shielding effect and desired transparency • Customer-specific geometry can be used to set the EMC film cut-off frequency as desired Conclusion Printed electronics—the production of electronic components and products based on roll-to-roll processes—have left the laboratory and are displaying the first successful applications in the mass market. Products of this type pave the way for a whole spectrum of practical, large-scale applications They provide clear advantages with regards to both product design and integration into target applications. Finished products have become more economically priced for consumers. Flexibility and high conductivity in conductive films enable innovative touch keys to be manufactured that improve the look and function of modern vehicle interiors. Curved or transparent surfaces are no longer an obstacle for these thin films. Function follows design.
Wolfgang Mildner
Organic Electronics Association Wolfgang Mildner is managing director of PolyIC GmbH & Co. KG in Fürth, Germany. He studied computer science at the Technical University of Erlangen. He is member of the Board of the Organic Electronics Association/ VDMA and the German Flat Panel Foundation (DFF). For more information, visit polyic.com. march/april 2012 | 17
feature story
Versatile Membrane Switches Learn about the latest materials and methods for membrane-switch production. Neil Bolding and Wim Zoomer
A
membrane touch switch is a thin, integrated, front-panel assembly that has at least one flexible layer (Figure 1). The assembly typically comprises several layers of screen-printed polyester layers, spacers, polymer thick-film (silver) circuits, adhesive layers, and often a rigid backer. Often the whole assembly is incorporated into a metal or engineered plastic box to complete the control panel. Membrane touch switches have been used in electronics applications for almost 50 years. Since their introduction, membrane touch switches have evolved to become sophisticated, and often highly complex, electronic components. They are used in a broad spectrum of products, including industrial controllers, test equipment, critical medical devices, consumer appliances, and toys. Today, a membrane touch switch can feature multiple circuit layers, integrated display windows, embedded devices such as LED displays, high-definition graphics and even touch screen technologies. The challenge is to maintain consistency and quality while incorporating the latest materials and production processes to meet customer demands. Let’s take a quick look at the key components before looking at examples of the latest designs of some membrane switches. Components The graphic overlay is the top layer of the
membrane touch switch. It connects the operator to the device. Historically, the graphics are screen printed onto the second surface of the top layer. The material of choice has overwhelmingly become an engineered polyester film. The films typically range from a thickness of 0.005 to 0.010 in. Polyester, which is bi-axially oriented polyethylene terephthalate (PET), was introduced as a more durable alternative to polycarbonate. Polycarbonate was widely used for control panels, but now it tends to be used sparingly and primarily in applications with requirements for low actuations. Polyester keypads can be actuated more than three million times before showing any kind of wear. At present, digital printing is an option used to decorate the switch. Screen printing works well when larger volumes are required or high-performance, functional graphics are needed. Prototypes or small volumes may be printed using a digital printing technique. The primary advantage of digital printing is that an unlimited quantity of unique graphic overlays can be printed using this equipment. The specialty coating of the overlay and its thickness protects the graphics and circuitry from the environment and enables the operator to ensure visual appeal, haptic/tactile, response, and overall durability. The electrical circuits are primarily screen printed onto specialty heat-stabilized polyester film. By far the most commonly
18 | Industrial + Specialty Printing www.industrial-printing.net
used conductor is silver in the form of a conductive polymer thick-film (PTF) ink. Carbon-based inks are also used sometimes to give added protection to the silver when the switch is used in an extreme environmental condition. Membrane switches can be either tactile or non-tactile. Because operators of equipment often require feedback when pressing a key, domes can be assembled as a part of the membrane, to provide a tactile feedback and a positive snap-action response. Tactile membrane switches typically incorporate a metal dome embedded in the membrane switch. Alternative options are for polyester domes that are formed in the circuit or in the graphic-overlay layer. The dome’s size and material make up, in conjunction with the overlay, controls the actuation force and tactile response. Metal domes are available in a wide range of shapes and sizes. Different polyester-dome-actuation forces can be achieved by modifying the height and the diameter of the dome. Non-tactile membrane switches produces a low actuation force, determined by the circuit spacer thickness. Spacer layers and adhesive layers are used to separate the circuit layers (Figure 2) and to provide key openings to allow contacts for conductors and bind all the layers together to form a complete unit. Displays and backlighting are supplied predominantly by liquid-crystal displays (LCDs) and by relatively low-cost light-
Figure 2 Spacer and adhesive layers are used to separate circuit layers and to provide key contact openings for conductors in this circuit and backer.
Figure 3 Membrane switches used in a marine environment must be functional in adverse conditions. Photo courtesy of Electronic Imaging, NZ.
Figure 1 This membrane touch switch is an integrated, thin, assembly with at least one flexible layer.
emitting diodes (LEDs) when selective backlighting is required. Embossing is often required to provide a raised feature to embed surface-mount LEDs. Other options are fiber optics and electroluminescent lighting (EL). EL uses an indium-tin-oxide-coated (ITO) film, or a conductive polymer. The active light-emitting layer is a phosphorous or zinc-oxide printed layer to backlight the keypad, followed by a dielectric printed layer that separates the silver conductive ink printed rear electrode. Meeting the challenges After the recent downturns in the global economic climate, the manufacturer is being challenged to produce high-quality parts with fewer resources and reduced margins. The use of digital technologies is increasing; it is on the rise to produce prototypes and small production runs at the cost of traditional analog processes. They can do so at a reduced cost and often with an improved lead time. The issue at hand is the ability to provide the same performance levels of the analog process. To date this has not been readily achieved. The latest switch designs incorporating additional functionality will be reviewed to show the developments in the membrane switch industry and highlight the next generation of functional switches that are coming from established companies. To provide effective use over long service lives, membrane touch switches must be designed and manufactured carefully with
the conditions in mind and constructed from specialized materials to make them resistant to extreme mechanical or environmental stress. Membrane touch switches are routinely used in extreme conditions, such as high-temperature and high-humidity environments when used as spa (hot-tub) controllers or exposed to high heat and sun (UV irradiation) when used as oil-pumping switches or as sophisticated control panels in a marine environment (Figure 3) when exposed to tropical weather conditions. Other controllers may be found in potentially hazardous environments with a risk of explosion and high levels of dust and dirt, such as in mining. They are developed to withstand extremely harsh operating conditions with high levels of abrasive wear, high-pressure wash-down, and, in many applications, shock waves from coal-face blasting. The operator panels are essential components in the overall system. They provide control of specific functions at the coal face and local visual feedback of system status. Each panel is constructed from a robust stainless steel enclosure into which beveled LCD-display windows and membrane-key apertures are machined. The individual membrane keys provide a high degree of tactile response for operators wearing heavy-duty gloves. The membrane keys are protected by a single layer 0.006in.-thick hardcoated film, mounted and sealed directly beneath the open display windows and key apertures.
The sector for stylus-controlled devices is expanding. The outer film requirements are becoming more demanding, while the touch and visual appearance is critical. High impact resistance, combined with excellent optical clarity, is required. Bristol, UK-based Clue Trader Ltd, part of the BOM Group (Figure 4), and a software and hardware developer of IT systems for airlines, retailers, and government bodies, has developed a line of screen protectors using hardcoated polyester. The challenge was to find a solution that would offer additional protection to each TFT display without affecting its definition or tactile response. Kienzle Systems of Germany has developed the latest generation of heavy-duty tablet PCs (Figure 5) for extreme outdoor use with protection from vibration and water spray in areas such as land registry and surveying assignments, outdoor mapping, industrial and construction sites, and even rescue operations. High levels of UV light in such environments affects the performance of conventional membrane key pads, causing discoloration and embrittlement of the surface layers. Switches often must resist harsh chemical conditions and cleaning regimes as required in hospitals or commercial kitchens, or within an industrial workplace where aggressive solvents and cleaners may be used. The film substrate used to form the outer layer of the switch or keypad is critical to the product’s longevity. Therefore, march/april 2012 | 19
Figure 4 (Left) High impact resistance and excellent clarity are required for outer-layer films on a membrane switch. Photo courtesy Clue Trader Ltd, part of the BOM Group, Bristol, UK. Figure 5 (Right) This heavy-duty tablet PC must survive extreme outdoor use, vibration, impact, and water exposure. Photo courtesy Kienzle Systems GmbH.
it is important that membrane-keyboard manufacturers select the right film for each application. The latest generation of film substrates has been developed to provide manufacturers with a wide choice of film properties that can best be matched to their needs. Other applications dictate additional functionality, such as cleanliness requirements in a medical or hospital environment. To this extent, anti-microbial agents are available for use, and have been incorporated into film coatings. For example, antimicrobial overlay panels provide protection in a range of medical-gas area alarms. These alarms are used in hospitals to monitor the supply and condition of vital medical gasses. The hardcoated film incorporates a specially developed anti-microbial agent, ensuring that the microbial properties persist for the lifetime of the film. In addition, the film provides a scratch- and chemical-resistant surface that can withstand everyday rigors and the most aggressive cleaning methods. Aesthetics There is not just a need for functionality, but also a high degree of image aesthetics and feel to functional switches today. The aesthetics can be incorporated by the graphic image, the overlay film itself, and the functionality through design. In today’s challenging economic climate, businesses are developing new technologies and production methods to distinguish themselves from the competition and meet ever complex consumer demands. This is especially true of the design and manufacture of highquality electronics, such as membrane switches and keyboards and fascia panels. These applications now offer as standard a wide range of sophisticated functions, with multiple circuit layers, tactile keys, and integrated displays.
In particular, increasing focus has been placed on the aesthetic qualities of these electronic components as the demand for highly stylized parts continues to grow. Bex Design Services has pioneered the use of a combination of screen and digital printing with the use of flexible mirror inks and a specialty film designed to exhibit a stainless-steel finish at far lower costs than traditional metal overlays. This technology capitalizes on the high-definition capabilities of digital printing to manufacture multi-colored, reverse-printed, fine-line text and graphics. The digital print is overprinted using conventional screen techniques with the latest flexible mirror inks to complete the stainless-steel effect. A black print is finally added to give additional depth to the color to enhance the overall effect. Butler Technologies sees an opportunity within the emerging concept of graphics and printed circuitry being combined into a single, formed part. One such method to accomplish this is printing both decorative and functional inks onto the same formable polycarbonate film. The printed film is then thermoformed to shape, trimmed to size, and inserted into a plastic injection mold, where resin is shot behind the printed film. The result is a three-dimensional, fully functional part with conductive circuitry and the necessary in-molded connectors and mounting hardware. Examples of this are capacitive-touch user interfaces in the automotive and appliance industries. Butler Technologies also sees growth in the integration of silicone-rubber keypads and capacitive-touch technology into membrane-switch applications, as well as the change to digitally printed graphics to add appeal. This has forced them to learn and integrate new technologies and design capabilities.
20 | Industrial + Specialty Printing www.industrial-printing.net
Another capacitive-touch option being used by membrane-touch manufacturers is the MaxCap Touch. It can be used in similar ways as Capacitive-Plus and Field-Effect touch systems; however, it does not rely on predetermined threshold values. MaxCap Touch, instead, measures the actual touch event and, therefore, provides fast touch response. For a mature industry, this is a very exciting time in the history of membrane switches and many market and design forces are rapidly changing the face of the classic membrane switch.
neil bolding
MacDermid Autotype Inc. Neil Bolding has been employed by MacDermid Autotype for more than 25 years and involved in the printing industries for 30 years. He’s involved in customer-application support, regulatory compliance, quality management and product development support for screen printing and flexible electronics applications. He holds a bachelor’s degree in chemistry from London University and an M.B.A. from Roosevelt University, Chicago.
wim zoomer
Technical Language Wim Zoomer (wimzoomer@planet.nl) is owner of Nijmegen, Netherlands-based Technical Language, a consulting and communication business that focuses on flatbed and reel-to-reel rotary screen printing and other printing processes. He has written numerous articles for international screen-printing, art, and glass-processing magazines and is frequently called on to translate technical documents, manuals, books, advertisements, and other materials in English, French, German, Spanish, and Dutch. He is also the author of the book, “Printing Flat Glass,” as well as several case studies that appear online. He holds a degree in chemical engineering. You can visit his Website at www.technicallanguage.eu.
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Developments in UV-LED Curing
The benefits of converting to UV-LED include reduced operating costs and energy consumption, lower emissions, increased safety, and more. Karla Witte
INX Digital Int’l
W
hile the UV curing process has been in the printing industry for more than 30 years, LED- curing technology for UV printers has just begun to replace the older curing technology. This change offers compelling advantages, such as improved economics, system capabilities, and environmentally friendly benefits. Advanced UV-LED curing of inks is now available for screen printing, inkjet, offset, flexo, and other processes. Of course, without ink there can be no printing, so you can expect more developments and improved systems to continue in the future. This article offers insight on how some companies are approaching UV curing technology. It also examines current industry challenges and questions of interest posed by printers. Advantages of UV-LED curing UV curing is used for drying inks, coatings, adhesives, and other UV-sensitive materials through polymerization. The process can be defined as the hardening of a liquid material when exposed to ultraviolet energy. The ultraviolet curing of inks, coatings, and adhesives requires a high-intensity source of UV energy to initiate the chemical reaction that hardens and turns the liquid into a solid through chemical polymerization. Three key advantages that come to mind are economic, advanced capabilities, and environmental advantages. From an economic standpoint, UV-LED curing is energy efficient, long lasting, and can be regarded as low maintenance. Light-emitting diodes (LEDs) are solid-state devices that produce light when an electrical current flows from the positive (anode) side of the circuit to the negative (cathode) side. I have seen LEDs run well past 10,000 hours of working exposure without drift in Joules or Watts. Therefore, I’m not surprised to see vendors state the expected lifetime of UVLED systems to be up to 20,000 hours.
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The advanced capabilities available in the market today represent the newest developments allowing for heat-sensitive substrates, deep-through cure, small, compact machines with controlled curing intensity. Similar advancements have impacted the environment factor. The current emphasis is better than ever on workplace safety. Devices are now both mercury and ozone free, and there is greater interest in UV-A wavelength range. Looking at ink technology today, you can start by examining the challenges of current UV-LED light sources. From a simple point of view, power is a direct function of wavelength, so the lower the wavelength, the more difficult it is to achieve power output. It is also generally accepted that the power of the UV LED rapidly dissipates as the distance from the source increases. There is no established standard measurement of power output from UV LED; therefore, the output is often measured at the light source. For printing applications such as web and inkjet, it’s possible to get the source very close to the print surface, minimizing the loss of output power. For applications such as screen and sheetfed printing, the distance of the print surface from the light source is greatly increased, so understanding the energy output at the print surface becomes critical. To help overcome this, UV-LED light suppliers are studying the effect of peak intensity versus total UV exposure, and they are looking at ways of distributing the energy output over distances using proprietary and patent or patent pending techniques, much like during the initial development of mercury arc UV for printing. Current UV-LED light also produces a distinct, single-peak-intensity profile centered on a single wavelength. The major wavelength ranges emerging are at 385-395 nm (with some centering at 390 nm), and 365 nm. For printing ink, this presents obstacles that include the need to use photoinitiators that absorb into the visible light spectrum, affecting on-press stability as the visible light in a print operation can polymerize the ink on press.
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Wavelength in Nanometers (approximate) LED UV 365 LED UV 390 Mercury Lamp
Figure 1 Overlay of AMS 390 nm and 365nm UV-LED lamp intensity compared to standard, medium-pressure mercury-vapor arc UV. Photo courtesy of Air Motion Systems U.S.A.
The lack of energy in the UVB and UVC wavelength affects the ability to cure ink at the print surface, often due to oxygen inhibition. For coatings, additional challenges of yellowing from photo initiator can occur without using photo initiators that absorb in the UVB and UVC ranges. New developments aid screen printing These challenges have not stopped the use of LEDs with today’s printing technology. The advances in UV-LED power output were first used in commercial inkjet printing, with companies displaying the ability to produce narrow-web inkjet labels at speeds up to 80 ft/min. The advantages of UV-LED for inkjet include: a smaller footprint for the unit, the instant on/off or adjustable capability, no generation of IR for the light source, and no generation of ozone. The intensity of UV LED can be altered, just like a dimmer switch at home. This capability allows print shops to add specialty details such as matte or gloss or special effects. And the visible-light-stability challenges are minimized as the ink is not readily exposed to light prior to curing. As for screen printing, the advances in LED lamp technology and UV screen-printing ink formulations have proven LED curing as a viable alternative to medium-pressure mercury lamps. Chad Taggard, the VP of marketing for industry supplier Phoseon Technology, said recently that “printers using UV-curable inks should have units to measure the energy of any type of curing device.” This equipment will advise you to the amount of Watts and Joules that your ink/substrate achieves during exposure. A chemist then can create a formula that will cure based on this information. The print operator should then test the unit frequently to maintain the proper curing energy. It’s also important to use a testing device that works with UV LED, not just a UV device, because it would provide the wrong information. Not long ago, UV screen inks could not be used with LED curing because they did not have the processing latitude to overcome the restrictions of using LED lamps. Restrictions included lower wattage and single-nanometer output. The newest screen-ink technologies now formulate viable specialty inks that cure exceptionally well with 4- and 8-w LED 24 | Industrial + Specialty Printing www.industrial-printing.net
395-nm lamps at belt speeds of 30-120 ft/min. This curing-speed range relates to the ink’s color, the thickness of ink deposited, and the substrate color. As for applications that best fit this type of curing, films truly suit LED because the LED projects very little heat towards the substrate. LEDs are lightweight when mounted to the carriage, which is why smaller digital printers use LED. UV-LED lamps work well with any applications where the curing system can be within 25 mm of the curing substrate. Initial research has already shown that 365-nm UV provides better surface curing in a dark colored flexo ink, while having inferior cure at the print surface. Adding the higher energy output 385-nm UV-LED light source inline with the 365-nm light source had positive effects on the ink surface and substrate interface for curing (Figure 1). The belief is that as higher output UV-LED light sources are developed, the cure deficiencies may be overcome in the single-peak-irradiance-wavelength systems. Other ink developments include research into studying the impact of lack of IR heat on the curing process with UV LED and looking at how single-wavelength UV light may impact the overall adhesion of ink to a variety of substrates. Studies also are underway on the potential of photoinitiators specifically formulated to optimize curing with the UV-LED wavelengths, noting that getting regulatory approval on novel chemistries requires long-term development. Looking at the bottom line Overall, the market is starting to see the addition of practical lamps and inks. The benefits of converting to LED curing are numerous, including the reduction of operating costs, reduced emissions, and the use of mercury bulbs, as well as increased safety and a huge reduction in energy usage. It’s important to note that LED costs more than mercury-lamp systems. The up-side here is the consumable costs are eliminated, and so is the expense for blowers, ballasts, and other peripherals. If considering an investment in UV-LED curing, first prepare an ROI assessment to justify the cost of making a switch to LED from other curing types. Operating costs are significantly lower with UV LED. UV LED can be turned on or off instantly with no warm up time required. Printers who take advantage of this can significantly reduce their operating costs. Printers also need to keep in mind that thinner and/or heatsensitive substrates can be used with UV LED. Not only does this open the doors to potential new revenue streams, but it also reduces shipping and storage costs. It is possible that a print shop might save 30 % on shipping costs alone.
Karla Witte INX Digital Int’l
Karla Witte is the VP of product development for INX Digital Int’l Co. She has been involved in digital printing of fine and graphic art for 19 years and has also worked for Harvest Productions/BullDog Products. She can be contacted at karla.witte@inxdigital.com.
FEATURE STORY The tests performed here were intended to show how some commonly used functional inks fail when pushed to extremes in heat, humidity, and water in printed-electronic applications.
Don Banfield, Ryan Banfield, and Miranda Lawrence Conductive Compounds
A
s printed-electronics applications continue to expand and merge technologies between traditional, polymer thick-film, rigid/flex-circuit and electronic-assembly applications, the requirements for functional, printed inks are being pushed to new limits. Electrically conductive and resistive inks, UV-curable dielectric insulators, conductive adhesives, UV-curable encapsulants, and others that have been used in more traditional PTF-device manufacturing, such as membrane switches and EL panels, must be able to be adapted to the emerging, and often more stringent, requirements of the latest printed-electronics applications. New substrates and methods of application require changes to polymers and solvents traditionally used in PTF applications. To do this, it is essential to have an understanding of some of the practical limits these materials have when exposed to harsh environments and how to design devices around the limitations of the functional ink materials. OBJECTIVE Using a specially designed circuit configuration (Figure 1) that incorporates serpentine patterns, surface-mount pads, and crossover multilayer printed traces that are typically found in PTF printed devices, circuits were printed at three different printing facilities using different combinations of silver inks, UV dielectrics, low-temperature curable-surface-mount epoxies and encapsulants, and carbon inks. The three printing facilities were ECI Screenprint in Thompson, CT; GM Nameplate, Inc. in Seattle, WA; and Dawar Technologies in Pittsburgh, PA. After printing, surface-mount resistors were placed by Nicomatic LP in Warminster, PA. Final assembly was performed at ECI Screenprint and then product testing was performed at Conductive Compounds, Inc. in Hudson, NH. PET films used as substrates were standardized for all printers, and printers were instructed to use their best manufacturing practices that they would typically use for membrane-switch printing. All inks and materials were supplied by Conductive Compounds, Inc.
PROCEDURE Different copolymer combinations used in the silver inks included polyester, vinyl, and urethane. UV-curable dielectric insulating inks were urethane acrylate copolomers with matte and glossy finishes, and materials were evaluated as undercured and overcured with a Medium Pressure Mercury Vapor (MPMV) UV lamp. Surface-mount epoxies were two-part, low-temperature polymer systems typically used in PTF manufacturing, and epoxy evaluation was done with various ratios of part A to part B to investigate effects of incorrect mixing on polymeric properties. Because the materials selected are widely used in all areas of PTF-device manufacturing and have passed the rigors of appliance, medical, and automotive testing, it was necessary to push the conditioning and testing to further limits to force failures within the functional inks to try to see which component(s) of the inks would fall out first under adverse conditions. Typical conditioning of test samples were: • 85°C, 100% Rh, 1000 hours • Immersion in water at 40°C for seven days • 150°C bake at ambient Rh until failure Mechanical and electrical properties of test circuits were measured both before and after exposure. Two levels of testing were employed on the circuits and functional ink materials. First, testing and inspection of the circuits was performed using the following criteria: • Point-to-point electrical resistance on silver and carbon ink traces • Low-voltage resistance across 500 ohm surface-mount resistors • Destructive AC high-voltage-breakdown test through crossover multilayer patterns • Visual inspection of circuit materials and surface-mount joints Second, the functional ink materials were analyzed using sophisticated laboratory equipment to try to determine how the materials MARCH/APRIL 2012 | 25
Results The test results showed some expected and surprising results. Starting with an analysis of the performance of the UV curable, screen-printable dielectric/insulator inks, results indicated the need for two-pass applications of these materials to achieve reliable electrical insulation between two layers of conductors. Two different industry-standard acrylate function dielectric formulations (matte and glossy) were paired with silver inks made using more common polyester and vinyl copolymers to see if any interactions would show up during testing. Because the crossover-voltage test was destructive and failure ranges varied significantly, the results were tallied by percentage of failure of test samples at high voltage. Notice that the figure has two legends—one print pass and two print passes, yet there is only one set of bars on the chart for the two print passes. This is because every single sample of the one print pass dielectric failed at significant26 | Industrial + Specialty Printing www.industrial-printing.net
Figure 1 This specially designed circuit configuration incorporates patterns, pads, crossovers and traces typically found in PTH printed circuits. 50 Pre
45
Post
40 35
Resistance Ω
changed physically during testing and how these changes might lend themselves to potential failures in a printed electronics application. Below is a list and description of the test devices used as applicable: Thermogravimetric Analysis, TGA, measures weight loss very accurately at specified temperature ranges. This can be used to evaluate solvent and volatiles coming off of a material or at elevated temperatures up to 1000°C it is possible to burn off all polymeric material, leaving behind metal and inorganic fillers. Fourier Transform Infrared Spectroscopy, FTIR, gives a unique fingerprint of a polymer material by exposing it to a scan of the full wavelength infrared spectra. At different frequencies of IR, different combinations of atoms on a molecule will absorb the IR energy, so the fingerprint scan shows IR absorption by a polymer at different frequencies of energy. If a polymer undergoes any chemical changes at all, the FTIR scan will be different. Differential Scanning Calorimetry, DSC, measures the heat flowing into or out of a very small sample as it is heated by the instrument. This allows accurate measurement of properties such as melting points, activation time for epoxy curing, and crystallization points. The DSC can measure this by adding heat to a polymer or by exposing the polymer to specific bands of UV energy for UV-cured polymers. Thermomechanical Analysis, TMA, measures the expansion of a material accurately as it is exposed to heat. It can also measure the deflection of a fixed, constant weight into a polymer material as it is heated. This allows properties such as coefficient of thermal expansion (Cte) and glass-transition temperature (Tg) to be evaluated. This allows us to understand how functional inks and materials will work in an assembly as the device is heated and cooled and the various materials it contains expand and contract at different rates. Tensile/Elongation testing allows studying of the mechanical strength and elongation of materials. This testing is valuable not only as a benchmark to compare different materials, but also to look at the effects of undercuring materials and exposing them to heat and/or moisture. Scanning Electron Microscope, SEM, allows us to look at functional ink materials at exceptionally high magnifications—as high as 100,000x. This lets us see effects such as packing efficiency of filler materials and whether there is any evidence of fusing of the filler materials.
30 25 20 15 10 5 0
Vinyl, Matte
Vinyl, Glossy
Polyester, Matte
Polyester, Glossy
Figure 2 The effect of heat and moisture on conductive inks and UV dielectrics when exposed with and without graphic overlay materials laminated onto them.
10% overcure
9%
undercure
8% 7% 6% 5% 4% 3% 2% 1% 0%
UV 2530
UV 2531
UV 2534
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Figure 3 The weight loss percent by TGA of several different industry-standard UV materials.
Figure 4 A typical vinyl copolymer silver ink pattern before and after heat and humidity exposure
Figure 7 An FTIR scan of the polymer before and after exposure shows that the vinyl copolymer has undergone a significant chemical change in response to high temperature and humidity exposure.
Figure 5 A SEM surface scan of the two ink samples indicates that the surface of the silver particles do not appear to have undergone significant oxidation.
Figure 6 The base polymer used in the ink before and after humidity exposure
ly low voltages when tested. This reinforces the accepted industry standard of printing two layers of dielectric to build up to a final thickness of between 0.001-0.0012 in. total thickness rather than printing a single layer only to save materials and processing times. The first results showed the effects of heat and moisture on conductive inks and UV dielectrics when exposed with and without graphic-overlay materials laminated onto them, as well as the effect of using dielectrics for protection of printed circuitry instead of overlays only. When a vinyl copolymer and polyester copolymer silver conductive ink are paired on a test circuit with and without a PET-film overlay material laminated to the circuit surface, both the vinyl
and polyester inks show that even with laminated overlay film protection, the resistance of the ink traces increased greatly after heat and moisture exposure, presumably due to moisture wicking between the overlay and circuit substrate and causing swelling within the conductive ink polymer. Figure 2 shows the effect of heat and moisture with these same two conductive inks, but with matte and glossy UV dielectric covering the ink traces. Note the dramatic improvement to the polyester based conductive inks, and the slight improvement to the vinyl inks. This illustrates one of the reasons why vinyl-based conductive inks are not used for high-reliability printed-electronics applications. Vinyl copolymers do not have the long term stability with respect to heat and other factors that polyester copolymers and other thermoplastic polymer materials used to make conductive inks do. Our final data with respect to UV-curable dielectric/insulator inks address the issue of undercuring. Undercuring UV materials is probably the single largest factor with respect to crossover joint failure and surface-mount component placement. It is possible to cure a UV material to the point where it will marginally pass a cross hatch/tape adhesion test on a substrate, but the material will still be very vulnerable to moisture and solvent attack, as well as degradation from long term heating. Figure 3 shows the weight loss percent by TGA of several different industry standard UV materials, including acrylate functional urethane insulating inks, cationic epoxide insulating ink, and acrylate functional surface mount component attachment. Undercuring was accomplished by increasing belt speed to minimize time under the UV lamp until a level of approximately
10% undercuring, as verified by DSC analysis, was achieved. In all instances, the appearance of the undercured materials would pass standard crease and/or cross hatch tape adhesion testing. However, TGA analysis shows a dramatic increase in weight loss from volatiles on all undercured UV materials compared to those cured optimally. This is due to the fact that when undercured, many of the liquid polymer components are left unreacted in the dielectric film, so they can be removed much like a solvent can by heating. If these components have not reacted completely, this means that the hardened film created by the UV curing process is not optimized and is much weaker, leaving it prone to moisture or solvent attack. To illustrate this point, the percentage of elongation (stretch) of the component encapsulant and acrylate urethane matte and glossy dielectrics was evaluated on an Instron for both optimally cured and undercured configurations. Results showed a drastic difference in performance for undercured material vs. optimally cured for all three materials. Again, this indicates that unreacted polymer remains in the system and the crosslink density of the cured polymer is not optimal, leaving it prone to moisture and solvent absorption as well as heat degradation over time. Figures 4 – 7 illustrate a common misconception regarding silver conductive inks. Sometimes discoloration in these inks over time is attributed to silver oxidation, and there are concerns about electrical performance degradation over time because of oxidation. Even when completely surrounded by polymer binder in a conductive ink formulation, metal particles will gradually oxidize on their surfaces over time. The oxides that form on the surface of silver and march/april 2012 | 27
gold particles remain highly conductive compared to the oxides that form on other metals such as copper or aluminum. For this reason it is necessary to use the more expensive metals when formulating conductive inks. Even when exposed to ambient temperatures over time, many conductive inks will undergo a slight discoloration. This is more pronounced with vinyl and some urethane copolymer inks than with polyester or some other types of thermoplastics. A common perception is that this discoloration (usually a brownish or yellowish light coloration) is due to metal oxidation. Figure 4 shows a typical vinyl copolymer silver ink pattern before and after heat and humidity exposure. Note the light brown coloration after exposure. Figure 5 shows a SEM surface scan of the two ink samples, indicating that the surface of the silver particles do not appear to have undergone significant oxidation. Figure 6 shows the base polymer used in this ink both before and after heat and humidity exposure. There is a dark discoloration of the polymer after exposure. An FTIR scan of the polymer both before and after exposure (Figure 7) shows clearly that the vinyl copolymer has undergone a significant chemical change in response to the high temperature and humidity exposure. The final data sets presented focus on the surface-mount aspects of printed electronics. Because of the unique requirements of PE applications, often the substrates used are extremely thin and flexible, and cannot be exposed to high temperatures. Because most of these substrates are polymeric, adhesion of the surface-mount epoxy can be difficult. Temperature limitations of these polymeric substrates require that the vast majority of surface-mount applications in PE use two-part epoxy adhesives, which are able to cure at very low temperatures but have the disadvantage of short pot life (working time) after mixing. One of the frustrating aspects of trying to analyze surface-mount failures in printed electronic applications is that often the failure shows up as a latent defect, meaning that it passes testing after manufacturing but then shows up as a failure sometime after the customer receives it. Often the factors that contribute to this (incorrect curing of conductive epoxy, improper component placement, incorrect mixing of epoxy, and improper ink trace design) cannot be isolated and identified after manufacturing. It is nearly impossible to properly analyze a PE surface-mount joint to investigate means of failure. Often you will find a failed surface-mount joint, but the surface mount component sitting close to the failed joint does not fail, and often will even withstand an aggressive flex/crease test without failing. For this reason, it is essential to follow good manufacturing practices as recommended by suppliers in order to minimize the impact of these factors on potential surfacemount failure. Because of the potential for joint failure when attaching LEDs, resistors, or other components onto flexible thin films, it is advised to use center-stake adhesives such as one-part cyanoacrylates and clear, UV-curable encapsulants to cover the component completely after it has been surface mounted to the substrate. Figure 8 shows the results of four different construction methods after long-term immersion in hot water with respect to the number of extreme (out of spec) readings obtained when measuring resistance through a surface-mount joint and across a discrete resistor. The four construction methods used were conductive epoxy only, conductive epoxy with center stake adhesive, conductive epoxy with clear UV encapsulant 28 | Industrial + Specialty Printing www.industrial-printing.net
60%
% Extreme Surface Mount Resistance readings (Post Immersion Test) Sorted By Surface Mount Material Combinations
50%
Figure 8 The results of four different construction methods after long term hot water immersion
40% 30% 20% 10 % 0%
80%
Extreme Surface Mount Resistance Readings Coverlay Vs. No Coverlay
Figure 9 The effect of providing some protection to the surface-mount component and joints
60% 40% 20% 0%
Without Coverlay
With Coverlay
Figure 10
38%
Epoxy with Optimal, 5% Less And 5% More Cuting Agent The effect of a 14.2% Difference
36% 34% 32% 30% Optimal
-5% CA
+5% CA
common two-part conductive epoxy adhesive that has an abundance of curing agent added and a shortage of curing agent
only, and conductive epoxy with center-stake adhesive and clear UV encapsulant. Note the dramatic improvement in surface-mount joint reliability on the two construction methods that use the clear UV encapsulant to seal and protect the component and surface-mount joint from moisture. Figure 9 further illustrates the effect of providing some protection to the surface- mounted component and joints by comparing the number of failures on surface-mounted components both with and without a laminated polymer film overlay to protect them during long term water immersion. A common cause of surface-mount joint failure in printed electronics is incorrect mixing of resin to hardener. Most epoxy formulations require precise mix ratios with a tolerance of Âą1% by weight to optimize the mechanical properties of the conductive epoxy. Careless or incorrect weighing errors can easily push this tolerance out to Âą5% or more. Figure 10 shows the effect of a common two-part conductive epoxy adhesive that has both an abundance of curing agent added to it, and a shortage of curing agent. For this test, an optimal mix was prepared, as well as a mix with 5% less curing agent
and 5% more curing agent. The samples were cured to completeness, and the TGA was used to evaluate weight loss at very high temperature. Figure 10 shows the actual TGA scan to the left, and then a table of weight loss of the three different epoxies to the right. Note that the two configurations with less and more curing agent showed a significantly higher amount of weight loss during burn off in the TGA than the sample that was weighed and mixed correctly. This shows that if these two part epoxy materials are not weighed and mixed correctly, surfacemount joint integrity will be compromised because there is a lot of volatile, unreacted polymer in the materials that over time will act as solvents and begin to leach out of the material. To capitalize on the rapidly emerging opportunities within printed electronics, it is essential that manufacturers learn some of the material science behind these inks and have access to analytical equipment that can help them explore and understand the limits of the materials. Printed electronics continues to have a stigma of the Wild West attached to it, but collaborations between suppliers, printers, and OEM manufacturers can help push the boundaries of what functional ink materials and substrates are capable of accomplishing.
Don Banfield
Conductive Compounds Don Banfield is product manager and co-founder at Conductive Compounds, Inc., Hudson, NH. Conductive Compounds Inc. develops and manufactures materials for the global electronics assembly market. In addition to standard products, the company specializes in custom formulations for new high-tech applications in the printed electronics industry.
Ryan BanfielD
Conductive Compounds Ryan Banfield is a materials science engineer and sales engineer for Conductive Compounds, Inc.
miranda lawrence Conductive Compounds
Miranda Lawrence is a student intern at Conductive Compounds, Inc. from Northeastern University, Boston, MA. march/april 2012 | 29
feature story
Opportunities for Silver Inks and Pastes in a Declining Market Find out why silver is sliding and discover where profits may be found when working with inks based on this precious metal. Jill Simpson, Ph.D. NanoMarkets
S
uppliers of silver printing materials are facing a big problem today related to the high price of silver. Suppliers of silver inks and pastes to the electronics industry face the challenge of how to maintain profitability and market share in a world with persistently high silver prices with no clear end in sight. Average silver prices were higher than ever in 2011, at just more than $35 per ounce. A high level of investment offtake of silver for monetary hedging is keeping silver prices high. Silver prices rose more than 140% over the 2009-2011 timeframe, and some industry experts are predicting that the metal will go even higher in the next few years. It seems almost certain that low silver prices will not reappear any time soon. Fiscal uncertainty and high debt in important markets in the U.S. and Europe, along with lackluster economic growth, is keeping investment in silver metal high. In this new environment, NanoMarkets is in the unusual position of predicting a decline in global silver inks and paste consumption, in both value and volume terms. Specifically, our forecast for silver inks and pastes consumption for 2012 is about $7.5 billion, and we see the value of the market softening to about $7 billion by 2019. Suppliers of silver printing materials are facing a new world, one that is much different from the one they have been in for the last 50 years or so. Overall, this industry has had a very good run over the last several decades, in which the post World War II boom in consumer electronics, appliances, microwaves, refrigerators, etc. were the first big users of printed silver. When that market started to stabilize, the computing revolution arrived, and with it came a whole new addressable market for printed silver for microcircuitry in cell phones, computers, and the like (Figure 1). Then, in recent years, the crystalline-silicon PV mar30 | Industrial + Specialty Printing www.industrial-printing.net
ket emerged. The question now is: What’s next thing that will increase the size of your addressable market for silver? Changing markets for silver We believe that, eventually, the next big thing for printed silver will be printed, flexible, and perhaps transparent electronics applications, especially for applications that enable ubiquitous and/or wireless sensing and computing for the internet of things in both the medical and everyday consumer information spheres. The potential for these kinds of applications deserves some skepticism, but we think that the tide may be turning in their favor in the mid-term. We also think that these new applications are not going to develop quickly enough to offset declines. A breakdown of the market reveals that two applications dominate consumption: the traditional thick-film, printed-circuitry applications, and the photovoltaics market (Figure 2). In recent years, the photovoltaics market has overtaken traditional thick-film applications as the single biggest user of silver inks and pastes. But both of these applications are very cost sensitive, and both, in different ways, are facing difficult times ahead. The PV market had a very good year in 2010, with nearly 150% growth over 2009. For 2012 and forward, we anticipate, obviously, much lower growth rates, around 15% per year. Meanwhile, for a couple of reasons, we are also predicting a decline in consumption of silver in the PV market. First, there is an ongoing, gradual shift in relative importance of thin-film PV, which uses very little silver, compared to crystalline silicon PV, which uses a lot of printed silver. At the same time, the way that silver is consumed in crystalline-silicon PV is changing. While front-side printed silver grids appear safe, and even growing, backside electrodes are facing serious competition from aluminum, and printed silver tabbing strips are being increasingly replaced with solders. In addition, government support for PV is waning. Governments around the world are looking for ways to cut their budgets, and of course things like tax incentives, feed-in tariffs, and subsidies for PV are a natural target for the axe. Panel makers cannot be so certain anymore that governments around the world will continue to provide financing for PV. The other big consumer of printed silver is the thick-film ink and paste market. The thick-film printed-silver market is not in decline, but we are expecting relatively slow growth over the next decade. A contributing factor to the slow overall growth is that plasma display panels are in decline. They are being gradually displaced by LCDs, which will account for almost $300 million in lost revenue between now and 2019. Meanwhile, high silver prices do encourage substitution away from silver. In the past, when silver prices spiked, cheaper conductive alternatives have always increased in popularity, but they usually faded into the background when silver prices fell again. Today, however, persistently high silver prices may present a sustained opportunity for some of the cheaper alternatives to actually make a dent in silver inks. Opportunities amidst the trouble Of course, the news is all bad. First of all, there is no reasonable substitute for silver in most applications. Other metals with reasonable conductivity are available, but they are, for the most part, insufficiently conductive or too oxidation-prone for the most demanding printed silver applications. Nonmetallic conductors—
The case for nanosilver Nanosilver has been on the scene for a while now. When it first emerged, there was a lot of hype surrounding it, and the expectations were that it would revolutionize the electronics industry. The nanosilver revolution did not happen, and it became reasonable to ask whether it ever would. Thus far, economies of scale for nanosilver have not been achieved. Nanosilver also faces an uncertain and potentially complicated regulatory environment, especially in the EU, and, to a lesser extent, in the U.S. Market pull for printed-electronics applications for nanosilver has not materialized. There is good news for nanosilver, though (Figure 3). The aforementioned miniaturization trend and need for high resolution in electronics is tailor-made for nanosilver. In addition, the sustained high silver prices have a less negative effect on nanosilver than on conventional silver printing materials. These factors mean that there is an opportunity opening up for nanosilver to be more seriously evaluated in different kinds of applications. How to stay afloat In summary, the market for silver inks and pastes will decline over the next couple of years, but that doesn’t mean there aren’t places to make money. First, products that reduce costs through reductions in precious-metal usage are in demand, especially in the conventional thick-film and PV applications. Next, materials that enable miniaturization through high-resolution, fine-line printing will see increased demand, as will materials than that enable ubiquitous electronics, sensing, and computing. Finally, for suppliers that depend on the PV market, diversification into other markets may be necessary to maintain revenue levels.
$7.6 B
8000
Traditional Thick Film
$6.8 B
7000 6000
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RFIDs
4000 3000
OLED Lighting
2000
PDPs
1000
Photovoltaics
0
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Value ($Millions)
Figure 1 Silver Inks and Pastes 2012-2019 by Application ($ Millions)
2000 1500 1000 500 0
Value of Printed Silver in TFPV
- 200 - 180
4500 4000 3500 3000 2500
2012 2013 2014 2015 2016 2017 2018 2019
- 160 - 140 - 120 - 100 - 80 - 60 - 40 - 20 -0
Addressable Market ($Millions M2)
conductive polymers, carbon nanotubes, graphene, etc.—are also often cited for their potential in printed-circuitry applications. But all of these also are very small players, at least for now, and probably can only threaten printed silver on the fringes of the market. Second, the thick-film legacy applications will benefit from global industrialization that will drive growth in consumer electronics. And the general trend toward miniaturization in electronics provides new opportunities for suppliers to provide value-added materials that enable higher resolution. So, how does a supplier get into this market? Suppliers may also seek to offer drop-in replacements for the existing competition, but finding customers with sufficient incentive to switch to a me too product is difficult. Alternatively, they may offer products that require a change in process, but the costs and risks associated with switching existing production lines over to a new kind of process are often understated. Instead, NanoMarkets thinks that a better approach is to products that enable new applications, in markets that are not yet fully formed. Examples are: nanosilver inkjet inks that enable miniaturization for new kinds of sensors for pervasive electronics, inks that will enable flexible interconnection in flexible displays, or inks that enable larger panel sizes in the nascent OLED lighting market. There are also opportunities in new ink and paste markets that aren’t really fully formed yet. Supplying emerging markets is risky, but the rewards can be great, and the emerging nature of these markets also means that suppliers have time to work closely with customers to get into the development cycle.
Value of Printed Silver in c-Si PV c-Si Addressable Market TFPV Addressable Market
Figure 2 Silver Inks and Paste in PV by Application 2012-2019
500 450 400 350 300 250 200 150 100 50 0
Average Nanosilver ink/Paste Price
~12x
Average Conventional Silver ink/Paste Price Average Nanosilver ink/Paste Price
~2.4x ~3x ~1.7x 2012 2013 2014 2015 2016 2017 2018 2019
Figure 3 Average Ink and Paste Prices ($ / Troy Oz. Silver) Overall, the market for printed silver is entering a period of reduced volume. Suppliers will need to reorganize around newer businesses and newer applications, and marketing and business development strategies will require rethinking. Increased partnering and collaboration will be necessary to identify new applications, which may be increasingly found in riskier, yet higher value, products.
Jill Simpson, Ph.D. NanoMarkets
Jill Simpson, Ph.D., is senior analyst of NanoMarkets based in Glen Allen, VA. NanoMarkets is a market research and industry analysis firm that looks at opportunities within the advanced materials, energy, and electronics areas. march/april 2012 | 31
INDUSTRY NEWS
Market movements and association updates
AIXTRON Tools Installed at Graphene Research Lab AIXTRON SE installed two BM Pro, formerly known as Black Magic, 4-in.-wafer-deposition tolls to the Italian Institute of Technology (IIT) in Pisa, Italy, for the development and production of graphene in hydrogen storage systems. IIT Pisa will use one system to deposit graphene using chemical vapor deposition and plasma-enhanced chemical vapor deposition. The BM Pro system is for use in hightemperature (1800˚ C) processing, which forms graphene using sublimation. These two tools will assist the Institute’s research on graphene film for nanoelectronics and energy storage devices.
Auto Infotainment to Grow in 2012 Automotive infotainment revenue in 2011 amounted to $32.5 billion, up 3.4% from 2010, according to an IHS iSuppli Automotive Infotainment Semiconductor Market Tracker report. Revenue in 2012 is projected to surge to $33.5 billion, and growth will be even stronger in the next four years, ranging from 4.7-6.4 %. By 2016, the market will reach $41.2 billion, according to IHS. Automotive infotainment equipment represents a range of electronic devices concerned with a vehicle’s delivery of information and entertainment content to its occupants. The field includes areas like navigation systems, premium audio, telemetric, fuel efficiency, safety and connectivity solutions.
Roland DGA Announces Creative Awards Contest Results Roland DGA announced its top regional award winners of the Roland Creative Awards international design contest as well as Honorable Mention and January People’s Choice Award recipients for the North American region. All winning entries receive prizes and recognition, with the overall winners in each region going to Japan to compete for the worldwide grand prize, the Roland machine of their choice. A gallery of all winning entries worldwide can be viewed online at www.rolandcreativeawards.com/winners. Regional Award Winner: Gamut Media, Brea, CA—Saladish Honorable Mention Award Winners: AC Golden Design, Los Angeles, CA—Bonsey Pendant; Bennett Bean Studio, Blairstown, NJ—Ceramic Sculpture Monthly People’s Choice Award Winner: Loudmouth Printhouse, ONT—Devil Inside
BMG Forges Licensing Agreement with Kodak
Sarasota, FL-based Brand Management Group (BMG) will sell Kodak wide-format inkjet media products to imaging professionals in the wide-format print-for-pay, professional photography, fine-art reproduction, sign, in-house corporate graphics, point-of-purchase graphics, advertising, exhibit, and reprographics markets through a worldwide network of distributors and re-sellers. The trademark licensing agreement was signed in fourth quarter of 2011 and commenced effective January 2, 2012. 32 | Industrial + Specialty Printing www.industrial-printing.net
Soitec Secures Financing for Solar Plant in South Africa Bernin, France-based Soitec, manufacturer of semiconductor materials for the electronics and energy industries, has secured financing from Investec Bank Ltd. to build the company’s 50megawatt-peak solar-power plant in South Africa. Investec has committed to finance the project and raise the equity to construct the plant. All financial arrange are expected to be finalized by Q2 of 2012, the company says.
INX Partners with Giant Media INX Digital Int’l agreed to partner with Giant Media, LLC. In the wide-format industry Giant Media will sell INX Digital’s alternative line of products, including eco TRIANGLE EDX inks. Phoenix, AZ-based Giant Media provides equipment supplies, software, and consumables to the signage and graphics industry. Giant Media is in the process of securing an additional distribution facility in the Midwest to offer faster service to customers in that area. INX Digital introduced EDX inks in 2010. Since then, it has been used in the wide-format market.
LG Chem Starts Mass Production of OLED Panels
LG Chem finished the development phase of its OLED lighting panel and will begin mass production. The type 1 panel, the LG OLED-041 is a 100 x 100-mm panel that features 4,000K, CRI >80, 45 Im/W and 10,000-hr lifetime (LT70) at 3000 nits. The active emitting panel is 90 x 90 mm, and the whole panel is 2.44 mm thick. LG Chem is developing the second-generation panel, which will up the efficiency to 60 Im/W and the lifetime to 15,000 hr. The size will be the same, but the color will be 3,500K. LG is said to start mass production of type 2 panels in Q2 of 2012.
Blue Spark Opens BatteryPrinting Facility
Cleveland, OH-based Blue Spark Technologies, supplier of thin, flexible, eco-friendly printed batteries has opened a high-volume printing and production facility in West Bend, WI. The new facility extends Blue Spark’s capability to produce large volumes of its line of disposable, flexible, carbon-zinc batteries to meet growing demand for printed electronics that power innovations in commercial and industrial packaging. “Our investment in the new Wisconsin facility demonstrates our operational readiness to support wide range market adoption of thin printed batteries that bring power to packaging,” says company president and CEO John Gannon.
Ellsworth Continues Mexico Expansion Germantown, WI-based Ellsworth Adhesives has expanded to larger facilities in Tijuana and Guadalajara, Mexico. The company is a global distributor and provider specializing in adhesives, sealants, lubricants, coatings, encapsulants, tapes, soldering products, surface preparations, specialty chemicals, maintenance and repair products, and dispensing equipment. “Ellsworth has achieved explosive growth in Mexico in the past few years, and we are excited about the expansion in Tijuana and Guadalajara,” says Roger Lee, VP and general manager.
On the Move
Shiftman
Quadrant Engineered Plastic Products of Reading, PA, appointed Charlie Costello to regional sales manager in the Midwest region. Cincinnati, OH-based TAPPI has elected Steven J. Shiftman, president and CEO of Michelman, Inc., to serve on the 2012-2014 TAPPI board of directors.
Transparent Conductors for PV to Grow in 2012
The total market for transparent conductors (TC) in the photovoltaics (PV) industry is predicted to grow at a CAGR of more than 30% from a value of $90 million in 2012 to $300 million in 2016, according to a report from Nanomarkets, an industry forecast and analysis firm. PV markets are shifting, says the report. Major PV application markets covered include thin-film Si PV, CDTe PV, CIGS PV, OPV, and DSC. The report talks about decreased government support for the TFPV market. The largest prospect for TCs lie with solution-processable nanomaterials.
DuPont and Suntech Sign Strategic Agreement
DuPont and Suntech Power Holdings Co, Ltd., one of the world’s largest producers of solar panels, have signed a strategic agreement to help increase the supply of photovoltaic materials and technologies for the growing global market for solar energy. The agreement focuses on technology advancements, supply-chain optimization, cost-reduction initiatives, and DuPont’s Tedlar polyvinyl fluoride film supply. The companies also are pursuing co-marketing opportunities. The goal is to achieve faster and broader adoption of solar energy to reduce the world’s dependence on fossil fuels. They intend to achieve the goal by further improving the technology for solar energy and helping reduce its costs and building greater awareness of its benefits to consumers. “We’re partnering with leading PV-component suppliers around the world as we continue to make solar affordable for everyone, everywhere,” says Eric Luo, senior VP of global supply chain, Suntech. “Creating higher efficiency solar cells and further extending the long life of solar modules is critical to achieving affordable solar power, and we’ve worked closely and very successfully with DuPont in this regard. We’re taking our collaboration to the next level with this agreement.”
SEND US YOUR NEWS Email Gail.Flower@stmediagroup.com
march/april 2012 | 33
printed electronics
Printed Electronics with Memory Capability Julia Goldstein, Ph.D.
One advantage of flexible, printed electronics is the ability to incorporate electronics into portable products manufactured on any type of substrate. The array of possible applications is continually expanding. Flexible sensors can detect temperature, pressure, moisture content, acceleration, or chemical contamination. In some applications, the ability of a sensor-containing product to light up or otherwise indicate to the user that an unacceptable range has been detected is sufficient. A simple example is a temperature test strip attached to a home aquarium. A small region on the test strip glows brighter than the others, indicating current temperature. If the temperature displayed is too high or too low, the user knows to adjust the thermostat on the heater. The sensor will then return to showing an appropriate temperature, with no indication of the temperature history. In other applications, it may be important to have some record that a parameter is out of range. One example is a temperature sensor attached to a perishable food or medicine. The fact that the temperature is currently acceptable is not sufficient, because the product may have previously been exposed to a high temperature and become spoiled. This is where printed, flexible memory can play an important role. If sensor data can be stored and later retrieved, it can be used to determine whether a product is still usable and eliminate both the risks of using spoiled food or medicine and the cost of disposing of products that are still fresh. Many gigabytes of memory can be stored in a card the size of a coin. The problem for flexible-electronics applications is that the memory chip is produced on rigid silicon. It is small, but it’s not flexible. Memory devices
research focused on high-density memory, produced using organic materials are the but the greatest market opportunity is for most promising solution. They are printed simple products that are not computationally easily and can be processed at low temperaintensive and store a small amount of data. tures, making them compatible with a wide Thin Film Technologies (Figure 1) recrange of flexible substrates. Organics cannot compete with traditional silicon chips for ognized that opportunity and collaborated memory capacity, but they are a potential with Palo Alto Research Center (PARC) to low-cost option when flexibility is important produce demonstration products containing and only a small quantity of data needs to 20 bits of non-volatile memory using ferrobe stored. electric transistors. In the single-line design, Organic memory devices can be proone bottom electrode crosses multiple top duced using one of several technologies: electrodes. A grid architecture soon to be floating-gate transistors, resistive memory, or released incorporates two bottom electrodes ferroelectric polymers. Floating-gate transisin a passive grid, providing twice as many tors are not suitable for printing because intersection points in the same form factor of stringent processing requirements, but and capacity for 40 bits of data. research and development efforts using the For some applications, it may be useful other two approaches have yielded promising to be able to erase and reprogram the memresults. Ferroelectric-polymer technology is ory device for multiple uses. One advantage fairly well developed and suitable for either of ferroelectric transistors is that they are inkjet or roll-to-roll printing. not only non-volatile—they retain polarizaTo produce the devices, ferroelectric tion even after the applied electric field is polymer films are sandwiched between removed—but also are re-writeable. metal electrodes printed in a grid pattern. Inorganic, resistive technology is a posWhile the polymers are applied using spin sibility for memory applications in which coating, the electrodes are printed with silver inks. A layer of solvent printed between the two electrodes is patterned to produce connecting vias. Each location where the metal lines cross defines a memory cell, so it is possible to produce a design containPhoto courtesy of Thinfilm Technologies ing any quantity of memory cells. Initial Figure 1 Printed 20-bit memory sticker.
34 | Industrial + Specialty Printing www.industrial-printing.net
re-writeability is not important. VTT Technical Research Centre of Finland has produced write-once-read-many (WORM) memory devices using conductive nanoparticle inks. When a voltage is applied to the circuit, the nanoparticle structure undergoes rapid sintering and exhibits a corresponding drop in resistivity. Because the final resistance can be controlled precisely, the device can be designed as a multilevel operation to increase memory capacity. VTT produced a demonstration of this technology with electronic questionnaire cards, where a memory bit is sintered when a button on the card is pressed. Research efforts at Mid-Sweden University have resulted in an RFID moisture sensor with WORM memory functionality. The device, an array produced with silver nanoparticle inks printed on photo paper, exhibits a dramatic drop in resistance when exposed to 80% relative humidity. Researchers reported resistance stability during a 15-hour test, but further work is needed to demonstrate non-volatility over longer time periods. One issue with printed memory is how to read the stored data. Several options are
available, and the choice depends on the application. VTT envisions either contact or non-contact (wireless) readout options with an external coupling to each bit of data, or memory addressing logic printed into the device. Contact pads on the surface of the memory device can be connected to an external reader, but this may not be convenient for the customer. For example, a project incorporating memory into Pokemon cards to store character data was not marketable because users did not want to have to plug cards into an external reader. Thin Film’s current demonstration vehicle is a handheld video game that also functions as a card reader, designed to be more convenient for the user. The memory is built into a card that is inserted into the game module and stores data on the level achieved in the game. A sensor-plus-memory device that detects product spoilage may also work well with a reader placed in a location where perishable products are stored. A non-contact option for reading memory, such as a sweep-over wireless reader in the form of an electrically active barcode, would also be suited nicely to sensor applications. Readout
from a sensor could be linked directly to individual bits in the bar code. For the memory to be addressable, it is necessary to incorporate logic. In the Thin Film/PARC device, each memory cell includes one addressing and one memory transistor, allowing addressability in a fully printed device. Each cell has a separate readout line. For some applications, it may make sense to integrate printed sensors and memory with a small, thin Si chip. The addition of printed memory, produced with either ferroelectric polymers or inorganic resistive technology, holds many opportunities for the future of portable, flexible sensors and other products.
Julia Goldstein, Ph.D. Julia Goldstein, Ph.D., is a freelance writer with a background in materials science. She provides commercial writing for companies in the semiconductor and printed-electronics industries.
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march/april 2012 | 35
printing methods
UV-LED Curing for Industrial Printing Richa Anand, Ph.D. Phoseon Technology
UV-LED curing refers to a technique that uses energy output from light-emitting diodes (LEDs) in the ultraviolet (UV) spectrum to treat inks, coatings, adhesives, and other UV-curable materials. The energy generated by the ultraviolet light triggers the chain reaction, resulting in polymerization of the material and the hardening (or curing) of the material. Traditionally, mercury-based UV lamps have been used for curing, but now more energy efficient and environmentally friendly LED-based UV technology has proven a superior solution in the printing industry. LED curing technology uses semiconductor-based LEDs to project UV light when an electric current is passed through them. When an LED is forwardbiased, electrons are able to recombine with electron holes within the device, thus releasing energy in the form of photons. The color of the light emitted, or corresponding energy of the photon, is determined by the energy gap of the semiconductor material. LED lamps are recognized for their lower energy consumption, longer lifetime, improved robustness, smaller form factor, and faster on/off switching. But how do they work? UV-LED curing There are three key components of a UVLED curing system that, when optimized, provide an economically advantageous, high-throughput solution to the printing industry: materials (inks) that can absorb
energy in the UV spectrum to undergo polymerization process; LED curing lamps that provide energy in the UV spectrum of the spectrum; and a printing system in which a UV-LED lamp is integrated to cure material that passes underneath it. These elements together provide a longterm, sustainable printing method through green technology, eliminating ozone emissions and lowering energy consumption. UV LEDs have a narrow spectral output centered on a specific wavelength, ¹5 nm. LEDs are solid-state devices and can be built with diodes of various wavelengths, including—but not limited to— 395, 365, 385, 405, and 410 nm, unlike the broad spectrum of wavelength output by Hg-based lamps. This monochromatic distribution (Figure 1) requires new chemical formulations to ensure proper curing of
UV inks and coatings. Currently, the most popular wavelength is 395 nm, with 365 nm being used in specific applications. UV-LED curing lamps consist of multiple sub-components that, when combined optimally, can drive system performance. Key components of the UV LED light source can be summarized in four major categories. LEDs Light-emitting diodes consist of semiconducting material that is doped with impurities to create a p-n junction. Charge carriers, both electrons and holes, flow into the junction from electrodes (anode and cathode) with different voltages. When an electron meets the hole, it falls into a lower energy state, resulting in release of the energy in the form of a photon (Figure 2). The wavelength of the light emitted depends on the band-gap energy of the ma-
MERCURY LAMP 395 LED
UVC
100-280 MM
UVB
280-315 MM
UVA
VISIBLE LIGHT
INFRARED
315-400 MM
400-700 MM
700 - 1800 MM
Figure 1 Monochromatic distribution (wavelength)
36 | Industrial + Specialty Printing www.industrial-printing.net
terials (dopants) forming the p-n junction. The right combination of LEDs maximizes total UV energy. Arrays This term refers to a grouping or clustering of individual LEDs. The number, type, and size of LEDs—including the shape of the array and the method of connecting the LEDs electrically—all impact the array. Array architecture is targeted for air- and/or water-cooled systems. Optics Photons coming out of the light source are optimized by using various optical layouts. Optics are used in reflecting, molding, guiding and/or shaping the UV LED emission to maximize the energy reaching the media and cure the UV inks or coatings in various applications. The use of optics has three benefits to the user: increased efficiency of the UV energy irradiated on to the material; lower array-generated heat; and optimum system pricing. Temperatures UV LEDs last up to 20,000 hours and beyond if they are maintained at proper operating temperatures. As LEDs emit more energy, they also generate more heat, which needs to be managed. Thermal management removes excess heat from the system while providing a consistent operating temperature for the diodes to function at maximum performance. INK FORMULATIONS AND MATERIALS With advancements in the availability of UV-LED-optimized ink chemistry, UV LED sources have become a very viable curing solution for many in the industrial printing industry. Materials suppliers have noted the benefits of UV-LED curing (Table 1) in general and have responded to the demand and challenge in the printing world to formulate raw materials that absorb energy corresponding to the output wavelengths of LED-based UV curing units. Industrial screen printers, for example, have found that advancements in LED-lamp technology and UV-curable ink formulations make UV-LED curing a viable alternative to medium-pressure mercury lamps. Additionally, high-power, scalable, UV-LED curing systems are effective high-speed curing in screen printing applications. One of the key ingredients in the
chemical formulation is a photoinitiator that serves as a catalyst to start the polymerization process when exposed to narrow spectrum UV LED energy. And with the continued, widespread acceptance of UV LED systems, availability of suitable base materials continues to grow. The driving factors in advancement of chemistry of raw materials is increased capability and cost effectiveness of commercially available UV-LED curing lamps. APPLICATIONS IN INDUSTRIAL PRINTING AND DECORATING UV-LED curing allows the printing industry to explore new and challenging applications. The following represent just a few examples. Medical labeling The pharmaceutical industry demands exacting product development and production in a sterile and clean environment. The industry has continued to push the envelope of what is possible; enabling new advances in medicine. UV-LED technology brings inherent advantages to the world of printing, including the lack of IR radiation in heat-sensitive applications in cleanroom conditions. Bottle printing Today, UV-LED curing technology is integrated in printing units for a variety of label applications, including bottle-labeling machines and systems designed for direct printing on cylindrical beverage containers. The small size of the light sources makes them ideal for machines with limited space. It also allows for printing on heat-sensitive substrates without damaging the materials. These solutions enable users to process a variety of materials at maximum production speeds, with a fraction of the power requirements of a typical arc lamp. Printed electronics and photovoltaics Mass-produced consumer electronics and tight-tolerance photovoltaics applications benefit from the long life, reliability, and repeatability of UV-LED curing systems. The ability to function at optimum levels, even during long-lasting, high-volume jobs—and provide consistent output when curing very sensitive products—makes UV-LED technology an effective solution in these markets.
Forward Bias N Type
Junction
P Type
Photon emitted Figure 2 An example of a p-n junction as it applies to LED emissions
BENEFIT
FEATURE
ECONOMIC
• Energy Efficient • Long Lifetime • Low Maintenence • Low Operating Temperatures
ENVIRONMENTAL
• Mercury Free • Ozone Free • Workplace Safety • UV-A Wavelegnth
ADVANCED CAPABILITIES
• Heat Sensitive Substrates • Deep, Through Cure • Small, Compact Machines • Controlled Curing Intensity
Table 1 Benefits of UV-LED curing
CONCLUSION UV-LED curing is now an accepted tool in the printing industry. It opens challenging applications to industrial printers who specialize in a variety of imaging processes and push the formulation of advanced inks, coatings, and other consumables. At the same time, UV-LED curing units have become more efficient in delivering higher energy to the media, driving the engineering and implementation of environmentally clean, energy efficient, and compact curing units that increase throughput and support flexibility in a variety of production environments.
RICHA ANAND, PH.D. Phoseon Technology
Richa Anand, Ph.D., is product-marketing manager at Phoseon Technology, Hillsboro, OR. MARCH/APRIL 2012 | 37
industry insider
The Role of Printing in Pervasive Electronics Jayna Sheats, Ph.D. TerePac
The application of printing techniques to electronic devices has come a long way. Until about 1990, attempts to make semiconductor devices with printable materials had met little success. The discovery by Richard Friend and colleagues at Cambridge University of polymer light-emitting diodes in 1991, however, led to an explosion of activity in the synthesis of soluble semiconducting organic materials. In the same period, well-controlled procedures emerged for the preparation of inorganic nanocrystals in sufficient quantities for making active devices and conducting lines. Thereafter, researchers applied inkjet printing to fabrication of these devices, and it was quickly observed that conventional graphics printing techniques such as offset, gravure, etc., were potentially much faster. During this time, in parallel with the development of the Internet into a truly world-wide network, the vision articulated by the Auto-ID Labs at MIT of a global electronic identification system for objects of commerce evolved into the modern vision of the Internet of Things, in which every object is interconnected, and many of them have some awareness of their environment (i.e. sensors). However, realizing this vision clearly required far cheaper electronics than almost any self-standing units previously known; the target for simple, passive, RFID tags became $0.05 or less, including antennae. Using roll-to-roll printing, with the prospect of high throughput and low per-unit capital cost to make these products, attracted keen interest. Thus, we see several motive threads intermingled: printing, flexibility, large area, inexpensive, and pervasive. These share some common features but comprise distinct attributes. Printing can be done
on rigid substrates also, and First Solar has proven persuasively that inexpensive, thinfilm semiconductor products can be made (with vacuum processes) on rigid, large substrates. Most important, however, is the pervasive quality. A huge range of applications are commonly mentioned, such as medical, traffic, and chemical-flow sensors, food-freshness sensors, lab-on-a-chip, and intelligent packaging. Actual electronic requirements for these applications will differ substantially. High clock speed, vital for most consumer electronics, is not of great value for these distributed wireless sensors. However, lowpower consumption is absolutely paramount to avoid changing billions of batteries every few months; state-of-the-art energy harvesting limits device currents to the microamp regime with a small active duty cycle—most of the time spent dormant, at nanoamp or lower levels. At the same time, functions such as high data quality (no errors), strong security, and ease cannot be neglected. Texas Instruments (TI) introduced a product named SimpleLink, targeted to the Internet of Things, while ST Microelectronics has its GreenNet. The TI product has 6 kB of flash and 3 kB of RAM; GreenNet contains a 32-bit microcontroller and 2.4 GHz radio, along with autonomous power source. While these no doubt represent approaches that are not optimized for specific applications, they do give an indication of the kind of content that current customers are expecting, and are typical of units being offered by many companies for this purpose. Any printing approach to fabrication has to be prepared to provide solutions at this scale of complexity. The significance of Moore’s Law arises from the amenability of the logic transistor
38 | Industrial + Specialty Printing www.industrial-printing.net
to nearly indefinite shrinkage without loss of performance. Printing, developed with the human eye in mind, resolves spots at best a thousand times larger than ULSI microlithography. Because processing cost of planar devices is proportional to area, ones with smaller features are strongly favored to win despite higher patterningequipment costs. Techniques are now available for placing ultra-thin and tiny, inexpensive, silicon ICs into flexible packages. Where the product is intrinsically large area, with no high-resolution patterning, printing is most effective, and so should be expected to realize its greatest value in solar cells; companies such as Nanosolar, Solexant, and Konarka are demonstrating this now. Displays occupy an intermediate position. Pixels are matched to printing resolution, although requiring greater precision than conventional graphics. Backplane transistors must be smaller than the pixels, but there is no advantage in shrinkage to submicron dimensions; hence, the competition between printing and traditional lithographic processing for this application. For the circuits used by the Internet of Things, thin silicon will likely prevail. Printed interdevice interconnects, however, are essential. The integration of multiple printing techniques and nontraditional silicon assembly in an effective physical package will keep innovators busy for some time.
Jayna Sheats TerePac
Jayna Sheats, Ph.D. is president and CEO of TerePac.
SOURCE:
A Paid Advertising service of ISP magazine.
WHAT WE MAKE IS CLEARLY CONDUCTIVE, WHAT WE DO IS A LOT MORE The ORGACONTM product line consists of coating solutions, screenand inkjet printing inks for manufacturing transparent flexible electrodes for Electroluminescent lamps, Display devices, Capacitive Touch sensors, Organic Photovoltaics, and other Printed Electronics applications. Based on a water dispersible form of the intrinsic conductive polymer PEDOT, made and applied by Agfa for over 20 years now in the permanent antistatic treatment of polyester films. ORGACON products show a unique combination of high transparency, conductivity, flexibility and processability that is not matched by other organic or inorganic conductive based-materials. www.agfa.com/orgacon
ADVERTISING INDEX
March/April 2012
Advertiser
page
Advertiser
page
AGFA
39
Marabu North America
35
AGL
29
Mimaki USA
OBC
AWT World Trade Inc.
23
Novacentrix
IFC
Douthitt Corp.
3
Ohio Gravure
5
Dynamesh Inc.
9
RH Solutions
5
Graphic Parts International
23
Schober Technologies GMB
29
Industrial-Printing.net
21
Spartanics
23
Kammann USA Inc.
7
SGIA
IBC
Lintec of America
39
Xenon Corporation
7
MacDermid Autotype
1
shop tour 1
3
2
5
6
4
RSP, Inc.
location Milwaukee, WI other info RSP was founded 50 years ago as Ryan Screen Printing, Inc. It remains a family-owned operation, third generation, that manufactures membrane switches and control panels. The company offers contract manufacturing services, engineering, design, screen printing, digital printing, and assembly from its Milwaukee-based headquarters. The graphic-overlay and membrane-switch group in Milwaukee has a long history of experience in this area. RSP also does rubber molding, plastic molding, touch screens, and wire harnesses. In 2009, the company established RSP Electronics in PingDi, China to handle rubber and plastic molding, screen printing, and assembly production.
1
Automated screen-printing press
4 The screen-printing line
2 Laser cutting
5 Screen printing on silicone keypads
3 RSP owners and management team
6 Close-up view of a press operator in action
40 | Industrial + Specialty Printing www.industrial-printing.net
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Keyword: Expo2012
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