Fundamental studies on whisker growth in Sn-based Solders

Sn whisker growth is considered as a crucial reliability issue in the electronic packaging industry, especially with the massive application of Pb-free solder alloys. In this paper, we report our fundamental studies on Sn whisker growth through accelerated tests. Excessive rare earth element addition is one way we employed to investigate the kinetics of whisker growth. Several aspects of the morphological features were characterized and modelled. The growth mechanism was clarified through observing the diffusion path of oxygen atoms to form rare earth oxides. Our attempt to clarify the growth mechanism of the whiskers observed during electromigration test was be presented based on the experimental efforts on the one-dimensional joint specimens. Such mechanism was investigated from a series of comparative experiments to understand whether mass movement from electrical current or internal stresses from Joule heating induced diffusion plays the crucial role to form such whiskers.