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.

Automated summary

A survey on the reaction between Cu-18Ni-18Zn substrate and Sn-3.5Ag solder during different reflow times was conducted. The traditional scallop-type Cu6Sn5 in Cu/Sn/Cu system was replaced by layer-type (Cu,Ni)6(Sn,Zn)5, and Cu3Sn disappeared while granule-type Cu5(Sn,Zn)8 was revealed. The addition of zinc-rich layer distinctly suppressed the growth of IMCs, and the volume fraction of IMCs increased significantly after it collapsed due to prolonged reflow time. The Cu-18Ni-18Zn/Sn-3.5Ag/Cu-18Ni-18Zn system showed higher shear strength compared to Cu/Sn-3.5Ag/Cu system, with an increase of approximately 32% with 150 seconds reflow process and about 111% with 300 seconds reflow process. In conclusion, the Cu-18Ni-18Zn/Sn-3.5Ag/Cu-18Ni-18Zn system is a favorable option for advanced electronic packaging in the near future.