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Tin Whiskers Grown on PCBA Detail PresentationTerry Munson Foresite [email protected]
PCBA Capacitor area of Interest
Battery Battery voltage
Output from IC which supply to 3 capacitors (C683, C684 & C685)
203-0071-001 – Murata (MPN:GRM155R61A104KA01D) – C685203-0075-001 - Yageo (MPN:CC0402KRX7R7BB103) – C683,C684
C685
C684
C683
GND
GNDVCC_BAT
VCC_BAT
Tin Whisker only on the Power Input Side
Tin Whisker on capacitor #2
Tin Whiskers on Capacitor #5
Typical Electrochemical Migration
Long Tin Whisker 5.16 mm
Tin completely used up to make the Tin Whiskers on the capacitor #1
Tin Whiskers on Cap #2
Corrosion and Initial Whisker on Cap #8
PCBA with ESD Bag over caps
SEM of the Whisker Removed from Cap
SEM of Tin Whiskers
SEM of Tin Whiskers
Inside ESD Bag over area of Cap
Inside ESD Bag 1 inch from Cap Area
Foresite Tin Plated Electrode
Foresite Test Samples
C3 extraction /Ion Chromatography Results
all values in ug/in2Board # Location Chloride Sulfate WOA Sodium AmmoniumBrd #1 1. Cap with whiskers and ESD Bag 15.98 9.85 18.05 3.23 22.36Brd #1 2. Cap without whisker and ESD Bag 1.36 0.33 19.34 1.26 2.04Brd #1 3. Cap without whisker no ESD Bag 1.59 0.54 18.47 2.05 1.69Brd #1 4. ESD Bag above whiskered cap 44.84 17.95 0 0 36.96Brd #1 5. ESD Bag 1 inch away from cap 41.05 16.36 0 0 51.27
Brd #2 1. Cap with whiskers and ESD Bag 18.95 8.04 15.24 1.69 16.11Brd #2 2. Cap without whisker and ESD Bag 1.05 0.61 16.94 2.66 1.25Brd #2 3. Cap without whisker no ESD Bag 0.95 0.52 15.47 1.65 1.05Brd #2 4. ESD Bag above whiskered cap 29.44 12.33 0 0 22.96Brd #2 5. ESD Bag 1 inch away from cap 31.05 14.26 0 0 35.05
Brd #3 1. Cap with whiskers and ESD Bag 16.69 8.24 16.55 2.36 9.65Brd #3 2. Cap without whisker and ESD Bag 1.14 1.22 17.41 2.15 1.69Brd #3 3. Cap without whisker no ESD Bag 1.62 1.06 16.53 2.63 1.52Brd #3 4. ESD Bag above whiskered cap 35.98 15.36 0 0 16.96Brd #3 5. ESD Bag 1 inch away from cap 38.54 16.27 0 0 21.25
C3 localized Extraction and Ion Chromatography
Some Other Current Tin Whisker Work
Conclusions• The whiskers that formed on the powered side of the capacitor
were not the result electromigraiton but localized heating of the capacitor power side and this released contaminants from the ESD dissipative bag waxy surface. This contamination was the driving force of the formation of the tin whiskers. No other areas of the PCBA show any sign of tin whisker or creep corrosion or even dendrite corrosion. The surface of the capacitor that grew the whiskers shows high chloride, sulfate, and ammonium which also was present inside the ESD bag (this is the dissipative elements inside the bag). The residues area not transferable to the board surface unless there heating or steam extracting.
• Under similar conditions Foresite was able to get growth on the surface of the tin plated electrode of a tin whisker with the ESD bag and the 3.3 volt battery in a sealed bag in 5 days indicates that the mechanism is reproducible.
