Dissolution and reaction between Au and molten eutectic PbSn solder

Dissolution and reaction both play important roles in the interaction between Au studs and PbSn solders. The kinetics of interfacial reaction in this system has been studied by measuring the rate of Au consumption and growth rate of the AuSn intermetallic compound (IMC) layer at temperatures from 190 °C through 260 °C. Different AuSn compounds are identified at different isothermal bonding temperatures in accordance with the Au/Pb/Sn ternary phase diagram. The rates of Au consumption and AuSn layer growth can be shown to obey a time-based power-law relationship. The rate of Au consumption into molten eutectic PbSn solder is non-parabolic with a time exponent varying from 0.276 to 0.575. The Au consumption is faster than the growth of the AuSn layers because Au dissolves rapidly into molten solder even with the formation of intermetallic layers.