Experimental study of the kinetics of transient liquid phase solidification reaction in electroplated gold-tin layers on copper

The kinetics of transient liquid phase (TLP) solidification in Au-Sn layers electroplated on Cu foil was investigated using differential scanning calorimetry (DSC). The solidification reaction takes place between a eutectic liquid of melting point 280 °C, which is shown to form in preference to other compositions, and an excess gold-rich layer. The solidification kinetics and the amount of melt formed were measured as a function of foil aging time. It is shown that the well-documented rapid interdiffusion at low temperatures between gold and tin can account for a decrease in the amount of melt produced during heating with age time. An estimate of the effective diffusivity of tin into gold at 295 °C has been obtained from measured solidification rates. The effect of copper diffusing through the gold film on the solidification kinetics was also investigated.