Interfacial reactions of high-temperature Zn–Sn solders with Ni substrate

The interfacial reactions of Ni substrate with various high-temperature Zn–xSn (x = 20, 30, 40, and 50 wt%) solders were studied through the microstructural observation and reaction kinetics analysis of interfacial products. Regarding liquid/solid reactions at temperatures of 380 °C to 420 °C, only one uniform intermetallic compound (IMC), γ-Ni5Zn21, was formed on the interface. In the Zn–20Sn/Ni reacted at 400 °C, the Ni5Zn21 layer demonstrated an unusually porous structure that grew rapidly; the average thickness reached ∼140 μm after a reaction time of 1 h. Specially, the layer exhibited a linear growth correlating to the reaction time. In contrast, the specimens with the Sn content above 30 wt% exhibited a considerably lower Ni5Zn21 growth rate, following a parabolic relationship. Additionally, the Ni5Zn21 microstructure was relatively denser. Microstructural variations could be responsible for the different growth kinetics among the Zn–Sn/Ni couples. The Zn–Sn/Ni solid/solid interfacial reactions were also examined at 150–170 °C. The Ni5Zn21 layer revealed a linear growth relationship for all the couples. This study determines the relevant growth kinetic parameters, and then discusses the possible growth mechanisms.