The influence of Ni on the kinetics of the reactive diffusion between Au and Sn was studied experimentally at solid-state temperatures. Binary Sn–Ni alloys with Ni concentrations of 1, 3 or 5wt% were used to prepare sandwich (Sn–Ni)/Au/(Sn–Ni) diffusion couples by using a diffusion bonding technique. The diffusion couples were isothermally annealed at 433, 453 and 473K for various times in a silicone-oil bath. After annealing, AuNiSn8, AuSn4, AuSn2 and AuSn compound layers were observed to form at the (Sn–Ni)/Au interface in the diffusion couple. The total thickness, l, of the compound layers increased monotonically with increasing annealing time, t, according to: l = k(t/t0)n, where t0 was the unit time, 1s. The exponent took values of between n = 0.29 and 0.37 under the present annealing conditions. Such values (n < 0.5) indicated that grain boundary diffusion contributed to the rate-controlling process and that grain growth occurred at certain rates. The higher the Ni concentration of the Sn–Ni alloy, the faster was the overall growth of the compound layers. This implied that Ni was an accelerator for reactive diffusion between Au and Sn at solid-state temperatures. The accelerating effect of Ni became more marked at higher annealing temperatures. Such an influence of Ni upon the kinetics was attributed mainly to the dependences of the growth rate of the AuNiSn8 layer upon the composition of the Sn–Ni alloy and the annealing temperature.

Effect of Ni on Reactive Diffusion between Au and Sn at Solid-State Temperatures. M.Mita, K.Miura, T.Takenaka, M.Kajihara, N.Kurokawa, K.Sakamoto: Materials Science and Engineering: B, 2006, 126[1], 37-43