Interfacial reactions on Pb-free solders with Au/Pd/Ni/Cu multilayer substrates

In this study, the interfacial reactions on Sn, Sn–3.0Ag–0.5Cu, Sn–0.7Cu, Sn–58Bi and Sn–9Zn lead-free solders with the Au/Pd/Ni/Cu multilayer substrate at 240–270 °C for 20 min to 20 h were investigated. The experimental results showed that the (Ni, Cu)3Sn4 phase is converted to the (Cu, Ni)6Sn5 and Cu3Sn phases in the Sn/Au/Pd/Ni/Cu system when the reaction time is longer than 4 h. In Sn–3.0Ag–0.5Cu/Au/Pd/Ni/Cu and Sn–0.7Cu/Au/Pd/Ni/Cu systems, the (Cu, Ni)6Sn5 and Cu3Sn phase were observed, and only the Ni3Sn4 phase was formed at the Sn–58Bi/Au/Pd/Ni/Cu interface. Furthermore, the Pd2Zn9 and NiZn phases were formed in the Sn–9Zn/Au/Pd/Ni/Cu system. When the reaction time was longer than 4 h, the Pd2Zn9, NiZn, and Ni5Zn21 phases were formed at the interface. The reaction mechanism for all the reaction systems was diffusion-controlled. The Sn–58Bi/Au/Pd/Ni/Cu system was found to have the lowest activation energy when compared with other systems, and its value was 17.43 kJ/mol.