Effects of impurities on void formation at the interface between Sn-3.0Ag-0.5Cu and Cu electroplated films

Void formation is a critical reliability concern for solder joints in electronic packaging. The control of microstructures and the quantity of impurities in Cu electroplated films significantly affect void formation at the joint interface, but studies investigating these factors are rare. In this study, three Cu films (denoted as A, B, and C) are fabricated using an electroplating process. The Cu A film has a faceted grain texture embedded with twin boundaries, while Cu B and C films have similar columnar textures. After thermal aging at 200 °C for 1000 h, the SAC 305 (Sn-3.0Ag-0.5Cu) solder joints with Cu A and B films exhibit robust interfacial structures without voids. However, microstructural collapse is observed in the solder joint of SAC 305/Cu C, where many crevices are formed parallel to the interface. Based on the microanalysis, the concentration of impurities is higher in Cu C than in Cu A and B. Moreover, discrete voids rather than continuous crevices are present in the SAC305/Cu C system when the impurity concentration in Cu C is reduced. The findings demonstrate that impurity control in Cu electroplated film is critical for the control of void/crevice formation in electronic solder joints.