A physical model and analysis for whisker growth caused by chemical intermetallic reaction

Abstract The formation of intermetallic compound Cu 6 Sn 5 gives rise to the internal stress in the lead-free coating, which causes the growth of Sn whiskers. This phenomenon is characterized with the expansion of inclusion in a plate perfectly bonded between two infinite solids. Based on the grain boundary diffusion mechanism, a model is established to evaluate the growth rate of Sn whiskers. The results show that the growth rate of whisker varies with the relative site between whisker and inclusion. When the distance between the whisker and inclusion exceeds a critical value, negative growth rate will appear, and it approaches zero as the distance increases. They explain some phenomena observed in experiments.

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