Effect of bonding and aging temperatures on bond strengths of Cu with 75Sn25In solders

In the present study, the interaction between thin film Cu and non-eutectic Sn-In is studied. The effects of the bonding and aging temperature on microstructure, IMC formation and also shear strength are investigated by SEM/EDX, XRD and shear testing. The bonding mechanism is proposed based on the obtained results. The bonding mechanism is proposed to occur over 2 stages: (1) An increase in bonding temperatures leads to an increase in the true contact area, and (2) The aging temperature leads to interdiffusion and assists formation of the IMC. The type of IMC that forms is ¿ phase (Cu₆(Sn, In)₅) which is similar to the interaction between Cu and eutectic Sn-In. The shear strength increases with increasing the bonding temperature. On the other hand, the aging temperature does not have a significant impact on the shear strength. This indicates that the shear strength is mostly affected by the true contact area rather than the IMC formation.