Intermetallic compound layer formation between Au and In-48Sn solder

The growth of intermetallic compounds in Au and In-48Sn diffusion couples was investigated at 70 deg C, 90 deg C, and 110 deg C. The AuIn sub 2 layer is firstly formed at the boundary between the Au and In-48Sn solder. That AuIn sub 2 layer grows toward the In-48Sn solder. At 90 deg C and 110 deg C, a gamma -phase layer is also formed between the AuIn sub 2 layer and the original solder layer while the AuIn sub 2 layer is growing. The thickness of the AuIn sub 2 layer is almost the same as that of the gamma -phase layer. At 70 deg C, the temperature is so low that the diffusion reaction is insufficient to form a gamma -phase layer in 600 h. However, the formation of a gamma -phase layer was observed in samples annealed for > 700 h. From the experimental results, the activation energy for the formation of AuIn sub 2 is calculated as 42.8 kJ /mol, and seems to be equal to the activation energy for the diffusion of Au atoms in AuIn sub 2 .