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SMT-Guide

TA B L E O F C O N T E N T S

TA B L E O F C O N T E N T S

1

From THT to SMT – the evolution of PCB assembly

4

2

THR – the revolution in PCB assembly

5

3

The SMT process for modules with THR components

6

3.1 The process steps at a glance

6

3.2 Design of the PCB and stencil

6

3.3 Paste printing

10

3.4 Placement

12

3.5 Reflow soldering

14

3.6 Quality control

16

4

18

SL-SMT – Weidmüller’s innovative THR components for the SMT process

APPLICATION INFORMATION

3

1 FROM THT TO SMT

T H E E V O L U T I O N O F P C B A S S E M B LY

THT – assembly with leaded components

components and the soldering process

When use is made of Through-Hole-

is used, PCBs can be equipped with SMD

There are still applications in which

Technology

the

components both on one side and on

SMDs and leaded components have

standard process in module production

both sides. They are assembled with

to be placed on the PCB. Up to now,

up to a few years ago, the wire terminals

machines, for example "Pick & Place" or

in the case of modules with such

of the components are inserted into

"Collect

systems, which

component mixes use has been made of

the holes on the printed circuit board.

process all components in the state in

two different soldering processes: firstly

Boards are assembled manually or

which they were delivered, dispensing

reflow soldering for the SMDs followed

with special placement machines. The

with special preparation of components.

by (mostly manual) placement of the

(THT),

which

employed. Thus, when the SMT process

was

&

Place"

so-called manual or wave soldering

leaded components with subsequent In the SMT process, use is made of

process is used.

SMT compatibility in the case of modules with component mixes

manual or wave soldering.

reflow soldering, for example infrared, Drawbacks of THT:

convection and vapour phase soldering.

• production is time-consuming and

Contrary to the wave soldering process, only a solder paste deposit applied to the

costly

PCB is melted on.

• low function density • increased susceptibility to faults

PCB double-sided mixed assembly with THT and SMD components

due to a lack of manual precision

Manual placement and the use of manual/wave

soldering

for

SMT

manufactured PCBs is a costly and critical process, which can lead to quality defects. There is a need for Single-side PCB assembly with THT components

achieving consistent SMT compatibility, i.e. making leaded components suitable for the SMT reflow soldering process in PCB double-sided assembly with SMD components

SMT – assembly with SMD components

order to reduce manufacturing costs and to eliminate the wave soldering process,

With the advent of Surface-Mount-

Advantages of SMT:

which is susceptible to faults.

Devices

• high quality

The special process developed for this

Technology has increasingly taken the

• lower processing cost

purpose is known by various names on

place of THT. And the trend towards

• smaller components

the market, namely Through-Hole-Reflow

producing electronic modules by surface

• high packing and integration density

(THR), Pin-in-Paste (PIP) or Pin-In-Hole-

mounting is continuing.

• optionally single-sided or double-

Intrusive-Reflow (PIHIR).

(SMD),

Surface-Mount-

As the current standard process in

sided assembly

electronic module production, SMT is defined by the method of processing 4

APPLICATION INFORMATION

2 THR

T H E R E V O L U T I O N I N P C B A S S E M B LY

Through-Hole-Reflow is a process for joining THT components using the SMT reflow soldering process. In addition to conventional SMD placement, when THR is employed the SMD components are placed onto the SMT board together with leaded components and are soldered in the reflow process.

Mechanically not stressable connection: e.g."Gull Wing" type

The THR process was the result of the awareness that stable soldered joints are still needed for heavy components such

Advantages of THR:

as coils or transformers and wherever

• stable connection to the PCB

mechanical forces act on the PCB

• only one soldering process

(e.g. in the case of connection terminals,

• manual/wave soldering is eliminated

connectors,

• automatic component placement

relay

sockets,

etc.).

Considering mechanical criteria, SMD

• lower production cost

soldered joints are not suitable for heavy components.

For THR components to be processed in the SMT process, certain demands have

A SMT compatible product is always

to be met. These are described in greater

a compromise between optimum SMT

detail in Chapter 3.

capability and maximum stability of the soldered joint. With push-through pins, THR ensures a stable joint between the THT

components

and

the

PCB.

100% SMT process compatibility is achieved at the same time.

Mechanically stressable connection: THT

APPLICATION INFORMATION

5

3 THE SMT PROCESS

FOR MODULES WITH THR COMPONENTS

3.1 The process steps at a glance

1

3.2 Design-in

The design of a printed circuit board

The SMT production process begins with

for SMD components is generally very

design of the PCB. It is as early as in

easy to produce. Once the design of the

this first step that the later smooth

soldered joints has been defined, to

sequence of the production process and

avoid process errors the hole layout of

thus the quality of the PCB a s s e m b l y

the stencils for paste printing is often

process are defined. In comparison

defined about 10% smaller.

Design-In: design of the PCB and

with the classical SMD or Through-Hole-

stencil layout for THR components

Technology, a few special features have

By contrast, in the case of THR

to be observed in the design of PCBs

components a drill hole must be filled

for THR components. Special design

with solder paste. In this case, the

recommendations contribute towards

quality of the soldering process depends

ensuring

on what degree of filling of the holes

an

optimum

production

process.

with solder paste can be achieved in the printing process.

2

To optimise the degree of filling,

Paste printing: solder paste applied

Weidm端ller recommends the following

into THR placement holes

steps:

3.2.1 define the diameters of placement holes and soldering eyelets

3.2.2 calculate the solder volume or

3

Placement: inserting the THR component pins in the solder paste

4

Reflow soldering: melting on the

solder paste

the necessary paste volume

3.2.3 determine the degree of solder paste filling

3.2.4 design the stencil layout

5

Quality control: assessment of the finished THR soldered joint

6

APPLICATION INFORMATION

3.2.1 Defining the diameters of placement holes and soldering eyelets

The

tolerances

of

the

PCBs,

the

Soldering eyelet diameter:

placement machine and the component

The volume of the soldering meniscuses

must be taken into account as further

should also be optimised so as to

To calculate the necessary paste volume,

factors in determining the placement

minimise the solder volume. This is

first define the volume of the soldered

hole

automatic

achieved by minimising the soldering

joint in accordance with the required

placement process. For example, in

eyelet diameter in comparison with

quality. For an adequate soldered joint,

the case of connectors the position of

diameters as are usual in classical

the internationally recognised quality

the pin end in the pitch is subject to

Through-Hole-Technology.

standard IPC A610B calls for a 75%

special tolerances, with the result that

filling height in the PCB (see also

it is the respective manufacturer's task

Recommended soldering eyelet diameter

Section 3.5 "Quality control").

to optimise the pin end position's circle

for through-hole soldered joints:

The designer first defines the relevant

of throwout.

diameter

for

the

diameter of the placement hole and of

placement hole diameter

the soldering eyelet. Both parameters

Weidm端ller recommends the following

+

determine

as suitable placement hole diameters

2 x residual ring width

the

necessary

soldering

volume for a given THR component.

=

for THR soldering processes:

soldering eyelet diameter Placement hole diameter:

For round pins:

For THR soldered joints (contrary to

pin diameter + at least 0.3 mm

The residual ring width usually amounts

wave

For rectangular pins:

to 0.3 mm. For THR components such

pin diameter + at least 0.25 mm

as connectors a slight increase in the

soldering),

a

slightly

larger

placement hole diameter is advisable because melting-on of the paste in the

residual ring width to about 0.4 mm is

hole needs sufficient space. Solder

advisable for reasons of higher soldered

pastes also consists of a mixture of

joint stability and reparability.

soldering globules and admixtures (flux), and are categorised according to grain sizes. To avoid jamming or friction of the pin in the hole with these soldering globules during the placement process,

Soldering eyelet diameter

the chosen grain size should be as small as possible.

Residual ring width Placement hole diameter Placement hole layout for THR pins

APPLICATION INFORMATION

7

3 THE SMT PROCESS

FOR MODULES WITH THR COMPONENTS

3.2.2 Calculating the solder volume or the necessary paste volume

3.2.3 Determining the degree of solder paste filling

The solder volume that is necessary for

For an optimum layout of the PCB, it

an optimum soldered joint is calculated

makes sense to check whether the

as follows:

previously calculated necessary paste volume can be achieved at all. Therefore,

placement hole volume

in a test the degree of solder paste filling

+

should be determined in a PCB hole.

meniscus volume

According to the test setting, a test PCB

–

with the defined hole diameters, for

terminal pin volume

example is entered in the paste printing

=

process. The filling height of the holes in

Degree of filling approx. 120 %

solder volume

Determining the degree of filling

3.2.4 Design of the stencil layout

the PCB can then be checked visually.

If the optimal degree of solder paste filling was achieved, the standard design Pin

rule can be used for the stencil hole design: stencil hole diameter about 10% smaller then soldering eyelet. Diverse process parameters contribute towards a situation in which the degree of hole filling is not achieved. In this case, several possibilities of optimising the

Solder meniscus

degree of filling are at the printed

Placement hole

circuit board designer's disposal:

Necessary solder volume for THR soldered joint

Once the solder volume has been

The following applies:

• optimising the printing parameters (see Section 3.3 "Paste printing")

determined, the necessary paste volume

• optimising the stencil layout: If there

can also be calculated. Due to the high

100% filling of the PCBs thickness

evaporation factor of the solder paste in

=

is not enough paste, printing over the

the soldering process (generally about

100% degree of filling

soldering eyelet is advisable. Various

50%), it amounts to approximately twice

forms of asymmetrical printing can

the volume:

also be applied. As an alternative, stepped and additive stencils or paste volume

= solder volume x 2

double printing by means of extremely thick stencils can also be applied. If there is too much paste, webs over the breakouts of the stencil may function as a paste brake.

8

APPLICATION INFORMATION

Stencil hole diameter

Additional design factors : For a smooth SMT production process, the following factors should also be observed when designing a module:

• shadow formation in the reflow oven, caused by high housings of the THR components, can be avoided by an adequate distance between the components

Stencil hole layout assuming adequate degree of paste filling

• the components' contact faces must be taken into account to ensure that the insulator does not come into contact with the paste • fixing by glueing may be necessary if, in the case of double-sided

Stencil hole diameter about 10% smaller than soldering eyelet diameter

modules, a THR component is placed on the first placement side

Solutions and recommendations from Weidmüller In a first draft of the printed circuit board and stencil layout, you can safely work with the known standard process parameters.

For their SL-SMT pin headers with short pins (1.5 mm), Weidmüller suggests the following PCB design: Placement hole diameter: 1.5 mm Soldering eyelet diameter: 2.3 mm Stencil hole diameter: 2.1 mm (assuming adequate degree of paste filling) Stencil hole diameter: 2.8 mm (if the degree of paste filling is not enough) Valid for: PCB thickness: 1.5 - 1.6 mm Stencil thickness: 0.12 - 0.18 mm

APPLICATION INFORMATION

9

3 THE SMT PROCESS

FOR MODULES WITH THR COMPONENTS

For an optimum degree of solder paste

3.3 Paste printings

filling, the following process parameters Preparation of the PCB, i.e. applying

must be taken into account in the paste

solder paste on the soldering pads, is

printing process:

one of the most important steps in the SMT production process. The quality

• stencil thickness:

achieved here has a crucial influence

generally 120 to 200 µm

on the quality of all further process

• optimum coordination of the solder paste grain size (20-40 µm) and

steps. The soldering result in the subsequent

placement

and

reflow

Open stencil printing process

volume percentage of the flux (mostly 50%)

process is determined by the necessary paste volume and thus the degree

In closed printing systems such as

• coordination of squeegee speed and

of solder paste filling during paste

"ProFlow", however, a paste deposit with

pressure: a higher degree of filling

application. For optimum filling of the

a variably adjustable pressure travels

with open paste systems is achieved

THR holes within the usual process

over the stencil. The advantage: better

by a lower speed or a flatter angle

tolerances, printing of the solder paste in

monitoring of the pressure and printing

(e.g. 45° instead of 60°)

two different stencil printing processes

speed permits paste printing by High-

has asserted itself, namely the open and

Speed Fine-Pitch Technology as well as

closed stencil printing processes.

controlled filling of the THR hole. Various stencil variants can be used depending

In the open stencil printing process,

on the chosen technology, namely the

a metal or plastic squeegee pushes the

low-cost standard metal stencils or even

roll of solder paste over the stencil.

expensive "exotic" variants such as

The drawback of this process is that both

stepped or double printing stencils.

the pressure and the printing speed can only be varied within a very limited range.

Pin header (open and closed ended):

2 to 8 poles

Pin header (flanged LF): recommended inside diameter

9 to 24 poles 2 to 24 poles

d I = 1.4

+0.1

mm

d I = 1.5 +0.1 mm

finished hole *1): paste volume VP [mm 3] / filling level fp [%] after print minimum solder joint shape

2.4 mm 3 / 70 %

3.1 mm 3 / 85 %

optimum solder joint shape

2.9 mm 3 / 90 %

3.5 mm 3 / 100 %

Example of a recommended paste volume or degree of filling for SL-SMT pin headers accord. to data sheet

10

APPLICATION INFORMATION

Various requirements for the leaded components can now be derived from these parameters:

• as the housing of the leaded component must not touch the solder paste, its stand-off height should be at least 0.3 mm • the pin cross-section geometry, the pin tip and its length must be optimised to minimise the paste volume needed

If the degree of solder paste filling is too low, then it is advisable to overprint to achieve the necessary paste volume.

Overprinting means that the stencil hole diameter is designed to be larger than the soldering eyelet diameter and the paste is printed over an area larger than the soldering eyelet, and out onto the PCB. This can, of course, cause soiling of the underside of the stencil, which can be removed by a shorter cleaning

Overprinting can lead to soiling of the underside of the stencil

cycle of the stencil.

Solutions and recommendations from Weidmüller To realise the lowest possible paste volume in stencil printing, the SL-SMT pin headers from Weidmüller feature short octagonal pins with chamfered pin ends.

Above all thanks to the pin length of only 1.5 mm for standard pc boards with a thickness of 1.6 mm, a filling degree of 90 % only is adequate for an optimal solder joint shape. Therefore in most cases normal single-layer stencils for fine-pitch technology and the standard process parameters for the squeegee speed and pressure can be used during paste printing.

Further advantage: in the placement process, the paste is forced out of the placement hole to a lesser extent.

APPLICATION INFORMATION

11

3 THE SMT PROCESS

FOR MODULES WITH THR COMPONENTS

The following parameters must be

This

observed with regard to the optimum

requirements

Automatic sequential placement is one of

placement suitability of leaded terminal

elements:

the placement processes that is used

elements and thus easy integration

most frequently in the SMT process. Use

into the placement process with usual

is made of both pick & place systems

standard placement systems:

3.4 The placement process

results

in for

the

following

leaded

terminal

• minimised weight for an placement speed that is as high as possible • minimised component length for a

and of collect & place systems (chip shooter). In the pick & place station, only

high rotation and transport speed

one components is taken from the

and thus maximum placement

component feeder by means of a vacuum

performance • minimised height to avoid a

pipette, and is placed on the pcb.

Tray packaging accord. to IEC 286-5

restriction of the travel height over the PCB and thus to prevent

• packaging in line with standards:

collisions

fully automatic feeding of the terminal elements with tape-on-reel or tray is possible • dimensional stability of the component: lowest possible water absorption during storage under Pick & Place head transports SL-SMT 3.5

normal climatic conditions ensuring

By contrast, a chip shooter transports

pitch fidelity of the component

several components to the corresponding

• suction surface of the component:

placement position and deposits them

determined in relation to the weight

there.

or size for the use of standardised

Packaging of the components is the

vacuum nozzles

basis for the use of both processes.

• precision of the pin end position:

A distinction is made between tape-on-

smallest possible tolerances

reel, tray, tube and bulk. The pick & place

(in addition to hole position and

process with tape-on-reel or tray has

machine placement tolerance)

established itself for leaded terminal

prevent problems caused by collision

elements.

of the component with the PCB

12

Tape-on-reel packaging accord. to IEC 286-3

• minimised tooling effort by using components in high packed numbers to achieve lower product and tooling costs

APPLICATION INFORMATION

Changes in length because of water absorption

% PA 4.6: 1 % => 0.5 mm / 50 mm => „50.5“ mm (total length for a 10 pole pin header)

1.0

50.5 Pin header SL-SMT with pick & place pad

LCP: 0.03 % => 0.015 mm / 50 mm => „50.015“ mm (total length for a 10 pole pin header)

50.015

0.03

mm Total length for a 10 pole pin header with pitch 5.00 mm Dimension changes because of water absorption for different materials.

Solutions and recommendations from Weidmüller To avoid quality-reducing dimensional changes, the SL-SMT pin headers from Weidmüller are made of LCP (Liquid Crystal Polymer). LCP is particularly distinguished by very low water absorption.

The SL-SMT pin headers have a low height thanks to the use of short pins (1.5 mm).

This is why the height of the tape-on-reel or tray packaging can also be very low.

The result: a large number of packaged units in each reel. The antistatic packaging in line with standards also permits fully automatic placement using commercially available pick & place systems.

Further advantages of the short pins of the SL-SMT are optimised travel height and the precision of the pin end position, thus avoiding collisions between the components and the PCB. And, as the SMT-optimised pin headers from Weidmüller are very light, they also maximise placement performance.

APPLICATION INFORMATION

13

3 THE SMT PROCESS

FOR MODULES WITH THR COMPONENTS

Each of the three processes calls for a

Soldering heat resistance is tested for

special process temperature curve,

the highest category A, by dipping the

The most important step in the SMT

which also applies to THR components.

component in a soldering bath:

production

As increased use will be made of

The insulator floats on the surface of

printing is the reflow soldering process.

unleaded

the solder and all soldering contacts

This process is characterised by melting

increased temperatures in the future,

are immersed. The minimum

of an existing solder deposit. During the

the demands on the temperature load

requirement is 260 °C/10 sec.

process about 50% of the paste volume

carrying capacity of components will

evaporates. The aim of reflow soldering

continue to rise.

3.5 Reflow soldering

process

besides

paste

soldering

processes

with

is to enable soldering of all THR joints in all soldering processes.

For use in the reflow soldering process, the following factors or requirements are

Currently three different reflow soldering

crucial in regards to THR components:

processes are needed in industrial applications:

• Soldering heat resistance:

Melted isolation body due to inadequat thermal resistance of the plastic

the shape and the functionality of the

Moreover, the component's suitability

component must not be damaged by

for passing through the soldering

exploits heat radiation with natural

the soldering process. In this respect,

process twice (double-sided

convection, as generated by quartz

all components can be checked with

assembly) must be guaranteed.

or area radiators, for example, to heat

a test method that is described in

the module.

EN 61760-1. This process permits the

• Infrared soldering:

measurement of THR component’s • Convection soldering: heats up the module by force

thermal resistance by means of a simulation.

convection by means of the

process gas such as air or nitrogen.

• Vapour phase soldering:

Temperature (°C)

circulation of large volumes of a

Melting 240° C 230° C 215° C

uses a condensating saturated vapour phase as the transmission

180° C 160° C 150° C

medium which dissipates its

Approx. 60sec > 180° C

130° C

condensation heat directly to the surface of the medium.

Pre-heating

Usual

Time (sec)

Infrared soldering, convection soldering – temperature/time diagram (temperature on connection)

14

APPLICATION INFORMATION

• Thermal coefficient of expansion:

• Solution:

The most frequent sources of faults are:

very long components such as

make components out of highly

multiple-pin connectors, which

temperature-resistant plastics with

exhibit a significantly different

low water absorption.

• Errors in component design: accessibility of the soldered joints for

thermal response to that of the PCB

the thermal transmission medium

material may lead to sagging of the

Even if apparently all factors and

(e.g. air) is restricted by neighbouring

module after soldering or in the

requirements

components. This can, however, be

cooling phase. To avoid this problem,

participating in the reflow soldering

defined in advance by means of an

the temperature response of the

process have been met, though, in some

appropriate component design.

components and PCB materials

cases the desired production quality

• Errors in PCB design:

should be as similar as possible.

cannot be achieved.

for

the

components

copper terminal faces that are too

Usual materials such as PBT or

large lead to heat sinks on the

PA 6.6, which are used in connectors

soldering eyelets.

designed for wave soldering

• Faults of the soldering machine:

processes are therefore not suitable

the melting temperature that is

for reflow processes.

necessary for the solder paste at the soldered joint is not reached due to inadequate efficiency of the reflow soldering machine or of the programmed process profile.

Solutions and recommendations from Weidmüller Weidmüller manufactures long components such as multiple-pin pin headers out of fibre-glass reinforced LCP (Liquid Crystal Polymer). This high temperature-resistant, Melted isolation body due to inadequat thermal resistance of the plastic

halogen-free insulator has a melting point of 335 °C and therefore exhibits high stability of shape and very good soldering heat resistance. Weidmüller surpasses

• Water content:

EN 61760-1 and subjects its terminal elements to 2 x 260 °C/10 sec. for a double

only components made of insulators

passage through the process. The SL-SMT pin headers made of LCP even withstand

with minimum water absorption

2 x 290 °C/30 sec. and are therefore oriented to the future and can also be used in

prevent bubble formation during the

every lead-free soldering process.

soldering process and thus modification of the insulator's

One further advantage of LCP is its extremely low thermal coefficient of expansion.

surface.

Measured on the SL-SMT pin header from Weidmüller, it amounts to 0.16% at 260 °C = 0.08 mm for a length of 50 mm, for example.

It therefore exhibits a thermal response that is similar to that of common PCB base material, for example FR4, with the result that sagging of a pcb after the soldering process is avoided in any case.

APPLICATION INFORMATION

15

3 THE SMT PROCESS

FOR MODULES WITH THR COMPONENTS

In the case of X-ray inspection, a

Standards:

so-called radiographic evaluation is

Various standards have come into force

Quality control concludes the SMT

run by means of an automated X-ray

in the past years to enable objective

production process. The aim of this

microscope. In addition the inspection

quality control. Besides other acceptance

process step is to enable swift and

processes during the production process,

test criteria for the production quality

simple assessment, by suitable means,

an important inspection step consists

of electronic modules, the assessment

of the quality of the soldered joints of

of destruction tests. Carried out on

criteria based on the IPC-A-610B have

THR components with short or long pins.

samples, they serve to check measurable

been acknowledged the world over.

The same rules apply to quality control of

quantities:

According to IPC-A-610B, the quality

3.6 Quality control

the THR technology as to reflow or wave-

requirements for THR soldered joints are

soldered THT components.

subdivided

into

three

categories.

Generally the requirements of category 3 Inspection method:

are decisive for high-power electronics

Quality control in parallel with the

in industrial applications. The following

process can be realised by means of

values have been defined for the total

different processes. At the moment,

number of five assessment criteria:

mostly optical or X-ray inspection is used. The optical test evaluates the shape, reflection and colour of soldered joints.

Cross-section of the THR-solder joint with short pin

• analysis of the degree of filling by

• circumferential wetting of the primary side (i.e. the component

means of a cross-section through the

side from the component's point of

soldered joint

view), the terminal and the sleeve

• mechanical inspection of the force needed to pull the pins out of the

must not fall below 270° • vertical solder filling must be at least 75%

through plated holes

Optical test of soldered joints below the housing body.

When done manually, a magnifying glass or a microscope is used and, in the automated process, a computercontrolled camera performs computerassisted image evaluation.

75 %

Dimensioning the filling height for through-hole soldered joints in accordance with IPC-A-610B

16

APPLICATION INFORMATION

• circumferential wetting of the

These requirements apply to long pins:

in the case of surface connections with

secondary side (i.e. underside from the point of view of the component) must not fall below 330° • solder wetting of the original land face (i.e. residual ring in the case of

For comparison:

• the soldered joints on the secondary side must be visible

SMD components, the required pull-out force amounts only to about 15 – 20 N.

• by comparison, soldered joints on the primary side are not necessary

THR soldered joints) on the primary side is defined as 0% • solder wetting of the original land

In the case of destructive inspections in conjunction with THR components,

face on the secondary side must be

demands are also placed on the PCB.

at least 75%

The force needed to pull the pins out of the soldered joint is checked to ensure

With regard to quality control, these

the quality of PCB production:

standards result in several requirements for leaded components. It is necessary

Required pull-out force:

to take into account the fact the two

- for short pins: approx. > 150 N

different designs are normally used for

- for long pins with solder meniscus on

the THR process:

Short pin pulled out with pull-out force of >150N

the primary and secondary sides: approx. > 220 N

• shorter pins in comparison with the PCBs thickness • longer pins in comparison with

Solutions and recommendations from Weidmüller

the PCBs thickness (approx.

Short pins with a solder meniscus only on the primary side attains a comparably

1.0 – 1.5 mm overhang)

high stability which is otherwise only possible when using the conventional THT. Hence THR components - like Weidmüllers SL-SMT - fitted with short THR pins have

The following requirements apply in the

a considerable advantage over real surface-mount connections.

case of short pins: The special design of the SL-SMT pin headers from Weidmüller permits visual • the soldered joints on the primary

inspection of a PCBs primary side, even in the case of variants with an 180°

side of the PCB must be visible

outgoing direction, thus creating the prerequisite for quality control in parallel

• in the case of components with pins

with the process.

under the insulator, the height of the stand-off or the product design must

However it is important that the control side of the components is not concealed by

be adequately dimensioned for visual

other high elements. Weidmüller recommends therefore, during the layout of the

inspection

PCB, to take into consideration the placement possibilities of the components on the primary or quality inspection side.

APPLICATION INFORMATION

17

4 S L - S M T – W E I D M Ü L L E R ' S I N N O VAT I V E

THR COMPONENTS FOR THE SMT PROCESS

The new standard in the SMT process

SL-SMT are consistent!

SL-SMT are extraordinary!

SL-SMT are made of high-grade LCP

SL-SMT use short pins with a length

(Liquid Crystal Polymer).

of only 1.5 mm.

of experience in the SMT production

Your advantages:

Your advantages:

process and the concentrated know-

• maximum pitch fidelity and

• double-sided SMT placement with

how about what demands it places

dimensional stability in the

on THR components. This is why

placement process

of printed circuit board assembly comes from

Weidmüller:

the

SL-SMT

pin

headers. Every SL-SMT pin header incorporates Weidmüller's many years

SL-SMT pin headers not only fulfill

• required paste volume minimised

• thermal response similar to that

these requirements, they also offer

of common PCB materials

you the optimum workflow in automatic

• temperature-resistant for all

two-sided PCB assembly, thus reducing

common soldering processes

your production costs by up to 30%.

a PCB thickness >= 1.5 mm

• simplified paste printing process • no-problem outgassing of the flux in the soldering process

• maximum orientation to the future: halogen-free and capable of recycling • maximum design flexibility: available in versions from 2 to 24 pins

1.5 mm

• guaranteed assumption of the necessary temperature in the soldering process thanks to a reduced metal mass • lower component height avoids collisions in the placement process • reduced packaging height permits the use of standard feeders • optimised quantity in each packaged reel 2 to 24 poles

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APPLICATION INFORMATION

SL-SMT are innovative!

• optimised stability in the soldered

SL-SMT are intelligent!

joint in comparison with round pins SL-SMT feature an integrated paste

• minimisation of the placement force

SL-SMT are obtainable in the intelligent

space with stand-off height of at

needed, for setting the pins

packaging design – suitable for several

least 0.3 mm.

into the paste by the placement

pin number variants.

machines Your advantages: • only one feeder width is necessary for several pole numbers • compatible with all common pick & place placement systems • lowest possible packaging heigth

0.3 mm

for a higher quantity per reel • antistatic ESD materials for problem-free placement Your advantages: • very simple stencil design for standard layout or for printing over

Optimised pin tip

• design-compatible with standard pin headers because there is no additional stand-off Pin header with 180° outgoing direction and open ends: SL-SMT 5.08/8/180

SL-SMT are application-optimised!

SL-SMT feature octagonal pins which are specially designed at the ends.

Your advantages: • minimisation of the necessary through hole diameter and thus of the necessary paste volume • better recognition in vision systems thanks to enlarged reflection faces

Product specific packaging design

APPLICATION INFORMATION

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PCB-kompendium EL-nr. 79 00 011 163