Reaction diffusions of Cu6Sn5 and Cu3Sn intermetallic compound in the couple of Sn-3.5Ag eutectic solder and copper substrate

The growth kinetics of intermetallic compound layers formed between Sn-3.5Ag solder and Cu substrate were investigated as a consequence of solid-state isothermal aging. Isothermal aging was carried out in a temperature range between 70degreesC and 200degreesC for 0 to 60 days. A quantitative analysis of the intermetallic compound layer thickness as a function of time and temperature was performed. The 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 9 mum after 60 day of aging at 150degreesC. The apparent activation energies were calculated for the growth of the total intermetallic compound (Cu6Sn5 + Cu3Sn); Cu6Sn5 and Cu3Sn intermetallic are 65.4, 55.4 and 75.7 kJ/mol, respectively.