Interfacial transfer and phase evolution between Cu and Sn solder doped with minor Cu, Ag and Ni: experimental and theoretical investigations

The effects of minor Cu (0.7%), Ag (3.5%) and Ni (0.1%) additions in Sn solder on the interfacial transfer and phase evolution were clarified in Sn/Cu solder joints. (Cu,M)6Sn5 and (Cu,M)3Sn (M = Cu, Ni) layers were observed at the Sn/Cu interface during thermal aging at 150 °C. The additions of Cu, Ag and Ni alloy elements were found to change the growth of the Cn–Sn intermetallic compounds (IMCs). The results showed that Cu, Ag and Ni additions were able to suppress the growth of (Cu,M)3Sn (M = Cu, Ni) layers, but promoted the (Cu,M)6Sn5 growth. This was because the reactions on the (Cu,M)6Sn5 side were promoted by the refined IMCs grain size, whose growth was at the expense of (Cu,M)3Sn. In addition, the interfacial transfer rate (thickness ratio, y) of (Cu,M)3Sn/(Cu,M)6Sn5 versus the thermal aging time (t) was found to be close to parabola relationship, the y increased gradually with the alloy elements from Ni, Cu to Ag. The phase evolution (η′-Cu6Sn5, η-Cu6Sn5, e-Cu3Sn, Ag3Sn, η′-(Cu,Ni)6Sn5, η-(Cu,Ni)6Sn5 and e-(Cu,Ni)3Sn) at the interface between Cu and Sn solder doped with minor Cu, Ag and Ni was also elucidated.