Study of interfacial reactions between Sn–Ag–Cu alloys and Au substrate

Abstract

Abstract Interfacial reactions between Sn – Ag – Cu lead-free solders and Au were investigated by the use of SAC/Au solid/solid reaction couples which were annealed at 150, 180 and 200 °C for various reaction times. Five intermetallic compounds, AuSn, AuSn2, AuSn4, (Au, Cu)Sn, and (Cu, Au)5Sn6, were formed at a higher temperature and lower Cu content. As the reaction temperature was dropped and Cu content was increased, only three intermetallic layers, AuSn, (Au, Cu)Sn, and (Cu, Au)5Sn6, could be observed. Meanwhile, when the Cu content in SAC alloys increased, the thickness of total reaction layers decreased, but that of (Au, Cu)Sn/(Cu, Au)6Sn5 layers increased. It likely resulted from (Au, Cu)Sn/(Cu, Au)6Sn5 layers acting as a diffusion barrier to resist Sn diffusing to Au – Sn intermetallic compounds and decrease the growth rate of Au – Sn intermetallic compounds. The growth and formation of intermetallic compounds are sensitive to the reaction temperature and Cu content in the SAC/Au couple systems.