Download Surface Finishes

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
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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…)
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The PCB Solution That's Right For Your Supply Chain
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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
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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
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The PCB Solution That's Right For Your Supply Chain
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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
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The PCB Solution That's Right For Your Supply Chain
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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
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The PCB Solution That's Right For Your Supply Chain
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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
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The PCB Solution That's Right For Your Supply Chain
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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
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The PCB Solution That's Right For Your Supply Chain
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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
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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
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The PCB Solution That's Right For Your Supply Chain
© 2009 PCB SOULTIONS. ALL RIGHTS RESERVED.