Tin Whiskers Grown on PCBA Detail Presentation Terry Munson Foresite Inc [email protected].

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.