Void formation at the interface in Sn/Cu solder joints

The effect of electroplated Cu (EPC), electroplated Sn (EPS) and Cu addition (0.7 wt.%) on the void formation at the reaction interface was investigated through the reaction of solders with Cu substrates. The voids were observed at the Cu3Sn/EPC interface in the Sn/EPC joints after aging at 150 °C, while not at the Cu3Sn/high purity Cu (HPC) interface in the Sn/HPC joints even after aging at 180 °C for 720 h. In the EPS/HPC joints, the voids appeared at both Cu6Sn5/Cu3Sn and Cu3Sn/HPC interfaces after long time aging at 150 °C. The formation of these voids may be induced by the impurities, which were introduced during the electroplating process. The addition of Cu could reduce the interdiffusion of Cu and Sn at the interface and retard the growth of Cu3Sn layer. Consequently, the formation of voids was suppressed.

► The voids were observed at the Cu3Sn/Cu and Cu6Sn5/Cu3Sn interfaces.
► These voids may caused by the impurities introduced during the electroplating process.
► The addition of Cu could retard the growth of Cu3Sn layer and suppress the formation of voids.