Kinetics of Ni solid-state dissolution in Sn and Sn3.5Ag alloys

This study investigates the kinetics of solid-state dissolution of Ni into Sn and Sn3.5Ag solders. At annealing temperatures of 150, 180, and 200 °C for 100–400 h, more amount of Ni was dissolved in Sn3.5Ag solder than in pure solder. The activation energies of Ni dissolution into pure Sn solder and Sn3.5Ag solder were 0.84 and 0.71 eV, respectively, indicating that the Ag content in the Sn3.5Ag solder can lower the activation energy of Ni dissolution into the Sn3.5Ag solder matrix. This study also proposes a potential enhancement mechanism for Ni dissolution using Ag solutes. Ag solutes in Sn3.5Ag solder promote a higher density of grain boundaries and a higher Sn vacancy concentration in β-Sn grains in Sn3.5Ag solder, resulting in more Ni dissolution into Sn3.5Ag solder compared to pure Sn solder. Based on the Ni dissolution results, a radial growth equation for a Ni₃Sn₄ interfacial layer surrounding a Ni wire was established. Further, the parameters of the radial growth of this Ni₃Sn₄ interfacial layer were deduced.