Abstract
The interfacial reaction and mechanical properties of Sn–Zn lead-free alloys/Cu joints were investigated under thermal exposure conditions. In the solder layer, Zn phases reacted with Cu and were transformed to Cu–Zn compounds with increasing exposure time. The microstructure change caused decreasing Vickers hardness of the solder layer. At the joint interface, although Cu–Zn compounds formed first, the formation of Cu–Sn compounds occurred with increasing exposure time. Simultaneously, the disappearance of Cu–Zn compounds and void formation occurred. The activation energy of the growth of Cu–Zn compounds at the joint interface was determined to be approximately 70 kJ/mol. That value is close to the activation energy of the diffusion of Zn in Sn crystal.
