Interfacial reaction of gas-atomized Sn–Zn solder containing Ni and Cu additives

Sn–Zn-based alloy is expected as an alternative low-temperature lead-free solder because of its melting temperature being close to that of Sn–Pb eutectic solder. The Sn–Zn solder is, however, inferior in terms of interfacial reaction with Cu substrate; that is, a hard and brittle Cu–Zn intermetallic compound (IMC) layer is formed at the joint interface, which leads to degradation of adhesion strength. In order to prevent the formation of Cu–Zn IMCs, we have investigated the effects of atomizing treatment on the Sn–Zn solders with additives Ni and Cu. In the solder containing Cu and Ni additives, the Cu–Zn IMC layer commonly observed is formed for the non-atomized solder, whereas the Cu–Sn IMC layer is formed for the atomized solder as well as Sn–Pb solder alloy. This is significant improvement for practical use of Sn–Zn based solder alloy.