Growth of phases in the solid-state from room temperature to an elevated temperature in the Pd–Sn and the Pt–Sn systems

Abstract

The solid-state growth of the product phases in bulk and electroplated diffusion couples of the Pd–Sn and the Pt–Sn systems is reported at various temperatures, ranging from room temperature to 215 °C. The growth rate of the product phase in the Pt–Sn system is found to be much lower compared to the Pd–Sn system and the Au–Sn system also, which is currently used in the microelectronics industry. The time dependent experiments indicate that the growth rate in the Pd–Sn system is parabolic in nature, i.e., it is controlled by the diffusion rates of components through the product phases. However, the growth rate is linear and hence reaction-controlled in the Pt–Sn system, which indicates that the formation of the compound is the rate-limiting step rather than the diffusion rates of components. The PdSn4 phase covers almost whole interdiffusion zone in the Pd/Sn couple, while PtSn4 is the only phase found in the Pt/Sn couple. The marker experiments indicate that both PdSn4 and PtSn4 grow mainly by the diffusion of Sn, with negligible diffusion of Pd and Pt, respectively. Furthermore, the analysis considering the same crystal structure (i.e., oC20) of these phases along with the concept of sublattice diffusion mechanism indicates that the diffusion rates of both Pd and Pt are negligible via both the lattice and the grain boundaries.