Experimental Observation on Solid-State Reactive Diffusion between Sn–Ag Alloys and Ni

Abstract

The kinetics of the solid-state reactive diffusion between Sn–Ag alloys and pure Ni was experimentally observed to examine effects of addition of Ag into Sn on the growth behavior of compound at the interconnection between the Sn-base solder and the multilayer Au/Ni/Cu conductor during energization heating. In this experiment, sandwich (Sn–Ag)/Ni/(Sn–Ag) diffusion couples with Ag concentrations of y = 0.011–0.033 were prepared by a diffusion bonding technique, and then isothermally annealed at temperatures of T = 453–473 K for various periods up to 3169 h, where y is the mol fraction of Ag. After annealing, an intermetallic layer consisting of Ni₃Sn₄ was recognized between the Sn–Ag and Ni specimens in the diffusion couple. Here, the concentration of Ag in Ni₃Sn₄ is negligible. The mean thickness of the intermetallic layer is proportional to a power function of the annealing time, and the exponent of the power function takes values of 0.33–0.43 at T = 453 K and those of 0.54–0.62 at T = 473 K. Thus, the growth of the intermetallic layer is controlled by boundary and volume diffusion at T = 453 K. In contrast, at T = 473 K, interface reaction and interdiffusion contribute to the rate-controlling process of the intermetallic growth. The addition of Ag into Sn accelerates the intermetallic growth within the experimental annealing times.