9. Mechanically Induced Tin Whiskers

This chapter discusses the pressure‐induced whisker at separable interfaces as a key reliability issue of lead‐free separable contacts and connectors. It shows theories of mechanically induced tin whiskers. Then, several case studies with pure tin and lead‐free finishes were performed to evaluate pressure‐induced tin whiskers. For electronics components, several factors affect the stress field of the finish: (i) thickness of the plating, (ii) structure of the ambient component material, and (iii) material microstructures. As a methodology for the assessment of pressure‐induced tin whisker formation, the creep‐based tin whisker formation model shows good results. Several connectors with tin or tin‐rich alloy finishes were assessed by means of the nanoindentation technique. For the flexible printed circuit (FPC), mechanical properties of adhesives are key factors influencing tin whisker formation. Each mechanical property can be obtained by the indentation technique, and stress distribution can be estimated by finite element analysis (FEA).