Solid-state interfacial reaction of eutectic Sn3.5Ag and pure tin solders with polycrystalline Cu substrate

Abstract

Intermetallic compounds (IMCs) that form at eutectic Sn3.5Ag/Cu and pure Sn/Cu interfaces during solid-state aging are comparatively studied in terms of their respective morphological formations, orientation evolution behaviors, and growth kinetics. During solid-state aging, all the interfacial Cu6Sn5 grains evolve into a layer-type morphology, except for select grains that experience abnormal growth. This abnormal growth is caused by the preferential growth of the Cu6Sn5 at the grain boundary in solder matrix. Meanwhile, textured growth occurs in the Cu6Sn5 layer formed at the eutectic Sn3.5Ag/Cu interface. The morphology of each texture is determined by the initial joint preparation conditions and affects the growth of interfacial IMCs. The results reveal that Sn diffusion occurs faster along the [0001] direction of the Cu6Sn5 crystal than along angles from 25° to 50° relative to the [0001] direction. Additionally, the effects of solder composition on the interfacial IMC growth are evaluated. The results indicate that Ag addition retards IMC growth upon aging by inhibiting diffusion of Cu.