In order to examine microstructure evolution at the interconnection between the Sn-base solder and Au/Ni/Cu multilayer conductor alloys during energization heating, the kinetics of the reactive diffusion between a binary Sn-5 at% Au alloy and pure Ni was experimentally observed at solid-state temperatures. Sandwich (Sn-Au)/Ni/(Sn-Au) diffusion couples were prepared by a diffusion bonding technique, and then isothermally annealed at temperatures of T = 433, 453 and 473 K for various periods up to 1057 h. During annealing, AuNiSn 8 and Ni 3 Sn 4 compound layers are formed along the (Sn-Au)/Ni interface in the diffusion couple. The total thickness of the compound layers is expressed as a power function of the annealing time. The exponent of the power function is close to 0.5 at T = 453-473 K, and equal to 0.7 at T = 433 K. Therefore, volume diffusion is the rate-controlling process for the growth of the compound layers at T = 453-473 K, but interface reaction contributes to the rate-controlling process at T = 433 K. The growth of the compound layers occurs slower for the reactive diffusion between the Sn-5Au alloy and Ni than for that between Sn and Au, but faster for that between the Sn-5Au alloy and Ni than for that between Sn and Ni.