This study deals with thermal oxidation behaviour in the liquid state of a commonly-used die-attach solder, Pb–Sn, and its potential Pb-free alternatives (Bi–Ag and Zn–Sn) from viewpoints of thermodynamics and kinetics. The characteristics of the oxidation reaction layers were investigated using XPS, XRD and AES. The superior performance in oxidation prevention of the Zn based alloys can be ascribed to their stable oxidative product, ZnO, which exhibits low free energy of formation, as well as slow growth rate.