Surprisingly, after almost 60 years of research into the causes of tin whisker formation, very little experimental evidence exists to verify some of the basic mechanisms believed to be involved in whisker growth. Long range diffusion of tin is thought to occur in order to supply the amount of tin required to form a whisker, however, no direct experimental data to support the long range diffusion hypothesis has been generated. The objective of this study was to use tin isotopes and secondary ion mass spectroscopy (SIMS) to evaluate the room temperature self-diffusion of tin within whisker-prone tin platings (bright and matte tin). Tin diffusion was monitored through the plating thickness and also parallel to the substrate by using SIMS surface analysis and depth profiling techniques. The amount of each isotope that was incorporated into the whiskers that formed and variations in the isotopic percentages along the length of each whisker were quantified (before and after sputtering of the whiskers).
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