The kinetics of the reactive diffusion between Pd and Sn at solid-state temperatures was experimentally examined using Sn/Pd/Sn diffusion couples prepared by a diffusion bonding technique. The diffusion couples were isothermally annealed at 433, 453 and 473K for various times up to 300h in an oil bath with silicone oil. After annealing, PdSn4, PdSn3 and PdSn2 compound layers were observed at 433K, but only PdSn4 and PdSn3 layers were recognized at 453 and 473K. The total thickness l of the Pd–Sn compound layers was mathematically described as a power function of the annealing time t as follows: l = k(t/t0)n, where t0 was unit time, 1s. The diameter d of the columnar grain in the compound layers was also expressed as a power function of the annealing time t: d = kd(t/t0)p. At T = 433–473K, n was close to 0.5, and p takes values of 0.14–0.17. Such values of p indicate that the grain growth occurred at certain rates in the compound layers. Nevertheless, the total thickness l was almost proportional to the square root of the annealing time t. Thus, it was concluded that the volume diffusion was the rate-controlling process of the reactive diffusion between Pd and Sn.

Reactive Diffusion between Pd and Sn at Solid-State Temperatures. T.Takenaka, M.Kajihara, N.Kurokawa, K.Sakamoto: Materials Science and Engineering A, 2005, 406[1-2], 134-41