Wettability and interfacial reactions of Sn–Ag–Cu/Cu and Sn–Ag–Ni/Cu solder joints

The effects of Cu and Ni additions on the wettability and interfacial reaction of Sn–Ag solder with Cu substrate were investigated. The wettability of the Sn–3.0Ag–0.5Cu (or Ni) solder alloy was firstly measured by a wetting balance test. The formation and growth of intermetallic compounds (IMCs) between the Sn–Ag–Ni solder and Cu substrate were evaluated, and compared the results to the Sn–Ag–Cu/Cu system. In the wetting test, the Cu and Ni additions exerted positive and negative effects, respectively, on the wettability of the Sn–Ag solder. In the solid-state reaction of the Sn–Ag–Cu/Cu solder joint, two IMC layers, Cu 6Sn 5 and Cu 3Sn, grew with increasing aging temperature and time. The growth rate of the Cu 3Sn IMC was higher than that of the Cu 6Sn 5 IMC at the high aging temperatures of 150 and 170 °C. On the other hand, in the case of the Sn–Ag–Ni/Cu solder joint, thick (Cu,Ni) 6Sn 5 and thin Cu 3Sn IMCs formed and grew at the interface during isothermal aging. The addition of Ni to the Sn–Ag solder effectively suppressed the growth of the Cu 3Sn IMC but increased the amount of the (Cu,Ni) 6Sn 5 IMC at the interface.