Reactive Diffusion between Ag and Sn at Solid State Temperatures

Abstract

The reactive diffusion at solid-state temperatures was experimentally studied for the binary Ag–Sn system. Sn/Ag/Sn diffusion couples were prepared by a diffusion bonding technique and then annealed at temperatures between T=433 and 473 K for various periods in an oil bath with silicone oil. After annealing, layers of the ε (Ag₃Sn) and ζ compounds were observed to form at the Sn/Ag interface. Furthermore, a thin layer alloyed with Sn was produced into the Ag specimen from the ζ/Ag interface owing to diffusion induced recrystallization (DIR). The thickness is about one order of magnitude greater for the ε layer than for the ζ and DIR layers. The total thickness l of the ε and ζ layers is described as a function of the annealing time t by the equation l=k(t⁄t₀)ⁿ. Here, t₀ is unit time, 1 s. The exponent n is 0.40, 0.38 and 0.36 at T=433, 453 and 473 K, respectively. If the reactive diffusion is controlled by the volume diffusion, n is equal to 0.5. However, n is actually smaller than 0.5 at all the annealing temperatures. This indicates that the grain boundary diffusion contributes to the reactive diffusion and the grain growth occurs at certain rates. As the annealing temperature decreases, the contribution of the grain boundary diffusion should be more remarkable, but the grain growth will become sluggish. This is the reason why the value of n increases with decreasing annealing temperature.