Thermodynamic reassessment of Au-Cu-Sn ternary system

The Au-20 wt.%Sn|Cu diffusion couples were annealed at 320 °C for 100 s and 2500 s and at 150 °C for 6600 h. The microstructures of these samples were studied with SEM + EDS technique. It was found out that the interface between Cu and near eutectic AuSn alloy consisted of AuCu3/AuCu/Au5Sn layers after annealing at 150 °C. For having a better understanding on the formation and evolution of metal bonding interconnection microstructures, the Au-Cu-Sn ternary system was thermodynamically reassessed on the basis of the experimental results from this work as well as by using the data available in the literature and the thermodynamic descriptions of the binary systems. The thermodynamic parameters from all the three binary systems were directly cited in this work, except for those of Cu6Sn5_HT and Cu6Sn5_LT. In the present work, the compounds AuSn and Cu6Sn5_HT were described as a one phase due to the reported complete solid solubility at 200 °C and 360 °C. A set of self-consist thermodynamic parameters for Au-Cu-Sn system was obtained in the present work. This thermodynamic description can reproduce most of the experimentally determined values, i.e. both the thermochemical quantities and phase equilibria.