Investigation of diffusion behavior in Cu–Sn solid state diffusion couples

Abstract

The diffusion behaviors and diffusion parameters of intermetallic compounds (IMCs) formed in Cu–Sn diffusion couples were investigated at the temperature range of 130 °C–200 °C. Interdiffusion coefficients of IMCs were calculated based on the measured composition profiles of the diffusion zones. Considering the wavy type of the diffusion layers and the narrow homogeneity range of the IMCs (Cu3Sn and Cu6Sn5), the integrated method was performed to evaluate the integrated interdiffusion coefficients based on the measured thicknesses of the IMCs layers. The transient initial growth stage was excluded by considering two diffusion times where the growths of both IMCs are in the diffusion control stage. The activation energies for diffusion of the IMCs were evaluated from the integrated diffusion coefficients. The growth behavior of Cu3Sn suggested the existence of a transient growth regime for Cu3Sn at the initial stage in cold-bonded Cu–Sn diffusion couple. The intrinsic diffusion coefficients of Cu and Sn in Cu6Sn5 were estimated based on the integrated diffusion coefficients. Sn was found to be the faster diffusion component in the Cu6Sn5 phase. Phase-field simulations combined with the experimentally measured diffusion coefficients and steady-state growth-rate coefficients were performed to estimate the homogeneity range of IMCs. The estimated results are consistent with the experimental results from this study as well as those from literature experimental values and showed that the homogeneity ranges of Cu3Sn and Cu6Sn5 phases in the Cu–Sn system are almost temperature independent.