In order to examine the influence of Ag upon 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 50at%Ag were prepared by a diffusion bonding technique, and then isothermally annealed at between 433 and 473K for various times up to 312h. During annealing, a PdSn4 compound layer dispersed with fine particles of Ag3Sn was formed at the (Pd–Ag)/Sn interface in the diffusion couple. The square of the mean thickness l of the compound layer was proportional to the annealing time t as: l2 = Kt, where K was the parabolic coefficient. Since the grain size of PdSn4 monotonically increased with increasing annealing time, the growth of the compound layer was controlled by volume diffusion in each phase. The value of K became less than half due to addition of Ag with 50at% into Pd. Hence, the addition of Ag to the Pd layer inhibited the deterioration of the electrical and mechanical properties at the interconnection between the Sn-base solder and the multilayer Pd/Ni/Cu conductor during heating.

Kinetics of Reactive Diffusion between Pd–Ag Alloys and Sn at Solid-State Temperatures. T.Sakama, M.Kajihara: Journal of Alloys and Compounds, 2009, 475[1-2], 608-13