Interfacial reaction and morphology between molten Sn base solders and Cu substrate

The morphologies and growth of ε(Cu₃Sn) and η(Cu ₆Sn₅) intermetallic compounds (IMCs) between a molten Sn base solder and a Cu substrate were experimentally investigated. It is shown that the thickness of the ε(Cu₃Sn) and η(Cu ₆Sn₅) compounds decreases with deceasing Sn content and that the order of the growth rate of the compounds on the Cu substrate are as follows: Sn-57(mass%)Bi < Sn-37Pb < Sn-3.5Ag < Sn < Sn-6.7Sb. The growth of these phases basically obeys the parabolic law, but the growth behavior is divided into two stages, the growth rate and morphology of the η(Cu₆Sn₅) compound are differing from each other in the two-stage. It is suggested that the grooving effect is at least one of the origins of the formation of the scallop morphology of the η(Cu ₆Sn₅) compound.