Kinetics of reactive diffusion between Pd–Ag alloys and Sn at solid-state temperatures

Abstract

Abstract In order to examine the influence of Ag on the growth behavior of compounds at the interconnection between the Sn-base solder and the multilayer Pd/Ni/Cu conductor during energization heating, the kinetics of the reactive diffusion in the (Pd–Ag)/Sn system was experimentally studied at solid-state temperatures. Diffusion couples consisting of pure Sn and binary Pd–Ag alloys with concentrations of 25 and 50 at.% Ag were prepared by a diffusion bonding technique, and then isothermally annealed in the temperature range between T = 433 and 473 K for various times up to 312 h. During annealing, a PdSn 4 compound layer dispersed with fine particles of Ag 3 Sn is formed at the (Pd–Ag)/Sn interface in the diffusion couple. The square of the mean thickness l of the compound layer is proportional to the annealing time t as follows: l 2 = Kt , where K is the parabolic coefficient. Since the grain size of PdSn 4 monotonically increases with increasing annealing time, the growth of the compound layer is controlled by volume diffusion in each phase. The value of K becomes less than half due to addition of Ag with 50 at.% into Pd. Hence, the addition of Ag into the Pd layer inhibits the deterioration of the electrical and mechanical properties at the interconnection between the Sn-base solder and the multilayer Pd/Ni/Cu conductor during energization heating.