Growth of whiskers from Sn surfaces: Driving forces and growth mechanisms

► We simultaneously measure intermetallic volume, stress and whisker density leading to Sn whiskers. ► Stress from the growth of Sn-Cu intermetallic is the main driving force for whiskers. ► Rapid grain boundary diffusion spreads the stress across the Sn layer. ► Electron microscopy and backscattering reveal which sites are most prone to whiskering. ► Whiskers nucleate at “weak” sites on the surface such as horizontal grain boundaries.