Surface Finishes S f Surface Finishes Fi i h Overview: O i The PCB surface finish forms a critical interface between the component to be assembled and the bare printed circuit board. The surface finish has two essential functions: - To protect the exposed copper circuitry. g ((soldering) g) - To provide a solderable surface when assembling the components to the board. Most surface finishes are considered SMOBC (Solder Mask Over Bare Copper). Copper) Solder Mask Surface Finish
Laminate
Traces
Surface Mount Pad
http://www.pcb‐solutions.com 1
The PCB Solution That's Right For Your Supply Chain © 2009 PCB SOULTIONS. ALL RIGHTS RESERVED.
Surface Finishes
Factors when choosing surface finish: • Cost C t • Reliability • RoHS \ ELV \ WEEE • Assembly method (Reflow, IR, Wave, etc…) • Components C t used d (BGA (BGA, QFP, QFP DIP, DIP SOIC, SOIC etc…) t ) • Durability • Environment • Shelf life • Testability Testabilit • Productivity • Failures (Black Pad, Tin Whiskers, etc…)
http://www.pcb‐solutions.com 2
The PCB Solution That's Right For Your Supply Chain © 2009 PCB SOULTIONS. ALL RIGHTS RESERVED.
Surface Finishes
Surface Finishes available from PCB Solutions:
• HASL • Lead Free HASL • Immersion Tin • Immersion Silver • OSP / Entek E t k • Gold • ENIG • Full Body Flash Gold • Hard Gold (Tabs) • Hard Gold (Selective) • Wire Bondable Gold
http://www.pcb‐solutions.com 3
The PCB Solution That's Right For Your Supply Chain © 2009 PCB SOULTIONS. ALL RIGHTS RESERVED.
Surface Finishes Typical Process Flow: P Fl Clean
HASL / Lead Free HASL Micro‐etch
Flux Apply
S ld Solder Dip i
Air Knife Leveling
Typical thickness: 70 micro inch – 200 micro inch. IPC spec calls for only complete coverage of copper pads. Advantages: • Low cost Low cost • Widely available • Re‐workable
Disadvantages: • Uneven surfaces Uneven surfaces • Not good for fine pitch • Pb (With non‐lead free HASL) • Thermal shock • Solder Bridging • Plugged or reduced PTH’s
Rinsing http://www.pcb‐solutions.com 4
The PCB Solution That's Right For Your Supply Chain © 2009 PCB SOULTIONS. ALL RIGHTS RESERVED.
Surface Finishes Typical Process Flow: P Fl Clean
Immersion Tin
Micro‐etch
Pre‐Dip
Apply Tin l i
Post‐Dip
Typical thickness: 20 micro inch – l h k h 50 micro inch. h Advantages: • Flat surface Flat surface • No Pb • Will not tarnish • Re‐workable
Disadvantages: • Easy to cause handling damage Easy to cause handling damage • Process uses a carcinogen (Thiourea) • Exposed tin on final assembly can corrode • Tin Whiskers • Not good for multiple reflow/assembly processes • Difficult to measure thickness http://www.pcb‐solutions.com
5
The PCB Solution That's Right For Your Supply Chain © 2009 PCB SOULTIONS. ALL RIGHTS RESERVED.
Surface Finishes Typical Process Flow: P Fl Clean
Immersion Silver
Micro‐etch
Pre‐Dip
Apply Silver l Sil
Post‐Dip
Typical thickness: 4 micro inch – l h k h 12 micro inch h Advantages: • Flat surface Flat surface • Simple process • No Pb • Re‐workable • Easy to measure
Disadvantages: • Handling sensitive Handling sensitive • Exposed silver on final assembly may corrode • Tarnishing
http://www.pcb‐solutions.com 6
The PCB Solution That's Right For Your Supply Chain © 2009 PCB SOULTIONS. ALL RIGHTS RESERVED.
Surface Finishes Typical Process Flow: P Fl Apply Resist/Tape
Hard Gold (Tabs and Selective)
Clean
Typical thickness: Nickel: 125 micro inch – 150 micro inch Gold: 25 micro inch – 40 micro inch Gold: 25 micro inch 40 micro inch Micro‐etch
Electrolytic Electrolytic Nickel
Advantages: • Hard, durable surface • No Pb N Pb • Long shelf life
Electrolytic Gold
Rinse
Strip Resist/Tape
Disadvantages: • Very Expensive • Extra processing / Labor intensive E t i /L b i t i • Use of resist/tape • Plating/bus bars • Demarcation • Difficulty with other surface finishes
Clean http://www.pcb‐solutions.com
7
The PCB Solution That's Right For Your Supply Chain © 2009 PCB SOULTIONS. ALL RIGHTS RESERVED.
Surface Finishes Typical Process Flow: P Fl
Gold (ENIG)
Clean
Micro‐etch
Typical thickness: Nickel: 100 micro inch – 200 micro inch Gold: 2 micro inch – 4 micro inch Gold: 2 micro inch 4 micro inch Catalyst
Electrolytic Electrolytic Nickel
Advantages: • Flat surface • No Pb N Pb • Also good for PTH • Long shelf life
Disadvantages: • Expensive • Not re‐workable N t k bl • Black Pad/ Black Nickel • Damage from ET g ( ) • Signal loss (RF) • Complicated process
Rinse
Immersion Gold
Rinse
Clean http://www.pcb‐solutions.com
8
The PCB Solution That's Right For Your Supply Chain © 2009 PCB SOULTIONS. ALL RIGHTS RESERVED.
Surface Finishes Typical Process Flow: P Fl
OSP/Entek
Clean
Micro‐etch
Pre‐Dip
Flood OSP l d OS
Rinse /Clean
Typical thickness: 4 micro inch – l h k h 24 micro inch. Not usually specified. h ll f d Advantages: • Flat surface Flat surface • No Pb • Simple process • Re‐workable
Disadvantages: • No way to measure thickness No way to measure thickness • Not good for PTH • Very short shelf life • Can cause ICT issues • Exposed Cu on final assembly • Handling sensitive
http://www.pcb‐solutions.com 9
The PCB Solution That's Right For Your Supply Chain © 2009 PCB SOULTIONS. ALL RIGHTS RESERVED.
Surface Finishes Summary: Cost
RoHS
HASL
$
No
Lead Free HASL
$
Yes
Immersion Tin
$
Yes
Immersion Silver
$$
Yes
OSP/Entek
$$
Y Yes
Immersion Gold
$$$
Yes
Hard (Tab/Selective) Gold
$$$$
Yes
http://www.pcb‐solutions.com 10
The PCB Solution That's Right For Your Supply Chain © 2009 PCB SOULTIONS. ALL RIGHTS RESERVED.