Abnormal grain growth in Cu6Sn5 Grains formed at SN-based solder/Cu interfaces

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. 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. Additionally, the effects of solder composition on the interfacial IMC growth are evaluated. The results indicate that the Ag addition retards IMC growth upon aging by inhibiting the diffusion of Cu.