Investigation of interfacial reactions between Sn–5Bi solder and Cu substrate

The growth kinetics of intermetallic compound layers formed between Sn–5Bi solder and Cu substrate by solid state isothermal aging were examined at temperatures between 343 and 473 K for 0–30 days. In the solder joints between the Sn–5Bi solder and Cu substrate, the intermetallic compound layer was composed of two phases: Cu 6 Sn 5 (η-phase) adjacent to the solder and Cu 3 Sn (e-phase) adjacent to the copper. As a whole, because the values of the time exponent ( n ) are approximately 0.5, the layer growth of the intermetallic compound was mainly controlled by a diffusion-controlled mechanism over the temperature range studied. The intermetallic compound layer thickness reached 2.16 μm after 30 days of aging at 393 K. The apparent activation energies for growth of total Cu–Sn (Cu 6 Sn 5 +Cu 3 Sn), Cu 6 Sn 5 and Cu 3 Sn intermetallic compound layers were 107.1, 98.35 and 90.5 kJ/mol, respectively.