Microstructure and mechanical strength of Cu/Sn/Cu microbump via Ni and Zn doping into Cu substrate

Survey on Cu-18Ni-18Zn substrate reacting with Sn-3.5Ag solder during different reflow times is carried out in this study. In microstructural observation, scallop-type Cu6Sn5 in traditional Cu/Sn/Cu system was replaced by layer-type (Cu,Ni)6(Sn,Zn)5 and Cu3Sn disappeared. Besides, granule-type Cu5(Sn,Zn)8 was revealed. Moreover, Zinc-rich layer could distinctively suppress the growth of IMCs and volume fraction of IMCs dramatically increased after it collapsed owing to prolonged reflow time. Nonetheless, with Ni and Zn addition, grain orientation was much diversified and average grain sizes in Cu-18Ni-18Zn samples was only about 300 nm, which was considerably reduced as compared to Cu samples. After shear testing, Cu-18Ni-18Zn/Sn-3.5Ag/ Cu-18Ni-18Zn samples are generally stronger than Cu/Sn-3.5Ag/Cu samples. An increase around 32% in shear strength with 150 seconds reflow process and an increase about 111% with 300 seconds reflow process were demonstrated. In short, Cu-18Ni-18Zn/Sn-3.5Ag/Cu-18Ni-18Zn system is a favorable option for advanced electronic packaging in near future.