Activation energies of intermetallic compound growth at interface between Sn–5Bi–3.5Ag solder and Cu substrate

The growth kinetics of intermetallic compound layers formed between Sn–5Bi–3.5Ag solder and Cu substrate were investigated at temperatures between 70°C and 200°C for 0 to 60 days. A quantitative analysis of the intermetallic compound layer thickness as a function of time and temperature was performed. Diffusion couples showed a composite intermetallic layer comprised of Cu6Sn5 and Cu3Sn. The growth of intermetallic compounds followed diffusion controlled kinetics and the layer thickness reached only 10 μm after 60 days of aging at 150°C. The apparent activation energies calculated for the growth of the total intermetallic compound (Cu6Sn5 + Cu3Sn), Cu6Sn5 and Cu3Sn intermetallic are 88.6, 84.3 and 70.28 kJ mol-1, respectively.