Thin-film reactions during diffusion soldering of Cu/Ti/Si and Au/Cu/Al2O3 with Sn interlayers

The multilayer thin-film systems of Cu/Ti/Si and Au/Cu/Al2O3 were diffusion-soldered at temperatures between 250°C and 400°C by inserting a Sn thin-film interlayer. Experimental results showed that a double layer of intermetallic compounds (IMCs) η-(Cu0.99Au0.01)6Sn5/δ-(Au0.87Cu0.13)Sn was formed at the interface. Kinetics analyses revealed that the growth of intermetallics was diffusion-controlled. The activation energies as calculated from Arrhenius plots of the growth rate constants for (Cu0.99Au0.01)6Sn5 and (Au0.87Cu0.13)Sn are 16.9 kJ/mol and 53.7 kJ/mol, respectively. Finally, a satisfactory tensile strength of 132 kg/cm2 could be attained under the bonding condition of 300°C for 20 min.