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

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 PdSn4 compound layer dispersed with fine particles of Ag3Sn is formed at the (Pd-Ag)/Sn interface in the diffusion couple. The square of the mean thickness I 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 PdSn4 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. (C) 2008 Elsevier B.V. All rights reserved.