Ionic contamination, moisture, and electrical bias can combine to create electro-chemical migration (ECM) shorts under an IC device as shown in this example.

ECM short 1

This is an optical image showing residue on the bottom surface of the FPGA package.

ECM short 2

This is a BSE SEM image of the same corner location. The residue bridges several signals at this corner.

ECM short 3

An EDS spectrum of the residue suggest that it contains chlorine and bromine. Part of the bromine signal likely originates from the brominated epoxy molding compound. The chlorine & perhaps some of the bromine is most likely residual solder flux activator.

The analysis results suggest that the most likely cause of failure was external corrosion and ECM due to halide contamination. The corrosion and ECM was likely exacerbated by elevated temperature and humidity conditions.

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A client provided a flex cable sample to SEM Lab, Inc. for SEM/EDS analysis of the crimp contact plating.

tin whiskers 1

EDS of the contact plating revealed that the plating was pure tin, which explains in part the many tin whiskers associated with the crimped region of the flex cable.

tin whiskers 2

The longest whisker in this image is very close to shorting two adjacent signals.

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