Interfacial reactions of Pb-free solders with Au/Pd/Ni/brass multilayer substrates

► The interfacial reactions of Sn, Sn–3.0wt% Ag–0.5wt% Cu (SAC), Sn–0.7wt% Cu (SC), Sn–58wt% Bi (SB) and Sn–9wt% Zn (SZ) lead-free solders with the Au/Pd/Ni/brass multilayer substrate were first systematically investigated in this study. ► The Cu–Zn phase was formed at the interface, and it can act a diffusion barrier to prevent the interfacial reaction between the solder and brass. ► This information is very interesting and valuable for soldering community. The interfacial reactions of Sn, Sn–3.0wt% Ag–0.5wt% Cu (SAC), Sn–0.7wt% Cu (SC), Sn–58wt% Bi (SB) and Sn–9wt% Zn (SZ) lead-free solders with an Au/Pd/Ni/brass multilayer substrate were systematically investigated in this study. The results revealed that (Cu, Ni)6Sn5 and CuZn phases were formed at the interface in the Sn, SAC, and SC solders reacting with Au/Pd/Ni/brass systems. In the SB/Au/Pd/Ni/brass system, (Ni, Cu)3Sn4, (Cu, Ni)6Sn5 and CuZn phases were formed at the interface. The CuZn5, Pd2Zn9, Ni5Zn21 and Cu5Zn8 phases were formed in the SZ/Au/Pd/Ni/brass system.