Reactive Diffusion between Ag–5Pt Alloy and Sn at Solid-State Temperatures

Abstract

The kinetics of the reactive diffusion between a binary Ag–5 at% Pt alloy and Sn was experimentally studied at solid-state temperatures using sandwich Sn/Ag_0.95Pt_0.05/Sn diffusion couples. The diffusion couple was prepared by a diffusion bonding technique and then isothermally annealed at temperatures of T=433, 453 and 473 K for various times up to 408 h in an oil bath with silicone oil. During annealing, an intermetallic layer of Ag₃Sn dispersed with fine particles of PtSn₄ is formed at each interface in the diffusion couple. The mean thickness of the intermetallic layer is expressed as a power function of the annealing time. The exponent of the power function takes values around 0.35 at T=433–473 K. Thus, the growth of the intermetallic layer is controlled by grain boundary diffusion as well as volume diffusion. The growth rate of the intermetallic layer is greater for the Sn/Ag_0.95Pt_0.05/Sn diffusion couple than for the Sn/Ag/Sn diffusion couple at T=433–473 K. However, the temperature dependence of the growth rate shows that the growth rate may be smaller for the Sn/Ag_0.95Pt_0.05/Sn diffusion couple than for the Sn/Ag/Sn diffusion couple at T=393 K. Thus, addition of 5 at% Pt into Ag accelerates the kinetics of the reactive diffusion between Ag and Sn at T>400 K but decelerates the kinetics at T<400 K.