Reliability Evaluations of Bonding Characteristics of Combined Pb-free Solder Joints with Sn-Bi-Ag and Sn-Ag-Cu

Recently, the electronic devices have tended to be miniaturized and intergrated. Accordingly, the size of the solder balls is getting smaller and the reliability of the solder joints is becoming important. Meanwhile, the bonding temperature is a significant factor which affects to reliabilities because thermal damages can be occurred by warpages during the bonding process. In this study, we formed combined Pb-free solder joints using two Pb-free solders: Sn-3.0Ag-O.5Cu (SAC305) and Sn-57Bi-lAg to lower the bonding temperature. The solder joints for reflow and laser soldering were compared by analyzing the effect of Bi diffusion on the combined Pb-free solder joints. It was confirmed that Bi diffused evenly for the reflow soldering. However, Bi did not diffused well in solder joints used the laser soldering. The bonding process time could be reduced and the bonding temperature also be lowered when using the laser bonding compared to the reflow bonding.