Interfacial reactions between Cu single crystals and lead-free solders during solid-state aging

The interfacial reactions between (111) Cu single crystals and lead-free solders (pure Sn, Sn-0.7Cu and Sn-0.7Cu-0.1Ni) during solid-state aging at 150 °C were investigated in this study. The morphological evolution and the growth behavior of interfacial IMCs during short-period (0 to 100 h) aging process were studied. For the solders without Ni, the interfacial Cu₆Sn₅ grains displayed prism shape in as-soldered state. But after a very short-period aging, their morphology quickly turned into a facet scallop type. It was considered that the morphological change was induced by the broken of the initial interfacial balance, i.e., the rapid formation and growth of a new Cu₃Sn layer at the Cu₆Sn₅/Cu interface broke the local equilibrium. Furthermore, a small amount addition of Ni into the solder resulted in a great variation in morphology and growth behavior of the interfacial IMCs.