Kinetics of Solid-State Reactive Diffusion in the (SnNi)/Cu System

The kinetics of the solid-state reactive diffusion between Sn­Ni alloys and pure Cu was experimentally observed to examine effects of addition of Ni into Sn on the growth behavior of compounds at the interconnection between the Sn-base solder and the multilayer Au/Ni/Cu conductor during energization heating. In this experiment, sandwich (Sn­Ni)/Cu/(Sn­Ni) diffusion couples with Ni concentrations of y = 0.01 and 0.03 were isothermally annealed in the temperature range of 433­473K for various periods up to 1152 h, where y is the mol fraction of Ni. After annealing, a compound layer consisting of Cu6Sn5 and Cu3Sn was recognized between the Sn­Ni alloy and the Cu specimen in the diffusion couple. Here, the thickness of the Cu3Sn layer is smaller than that of the Cu6Sn5 layer. The (Cu,Ni)6Sn5 grains were transformed from the Ni3Sn4 grains in the Sn­Ni alloy in the neighborhood of the Cu6Sn5 layer, and then adhered to the Cu6Sn5 layer. The overall growth of the compound layer including the (Cu,Ni)6Sn5 grains is remarkably accelerated by the adhesion, but that of the compound layer excluding the (Cu,Ni)6Sn5 grains is slightly decelerated by the adhesion. The mean thickness of each layer increases in proportion to a power function of the annealing time. For annealing at 433­473K, the ratio between the thicknesses of the Cu6Sn5 and Cu3Sn layers is hardly affected by the addition of Ni into Sn up to y = 0.03. [doi:10.2320/matertrans.M2014038]