A novel antioxidant and low-temperature Sn-Zn solder paste based on Zn@Sn core-shell structure

With the advancement of lead-free solder, Sn-Zn solder was once considered the best choice. However, the high activity of Zn limited its application. To solve the problems of serious oxidation of zinc in Sn-Zn solder, a novel Sn-Zn solder paste based on Zn@Sn core-shell structure was developed. The Zn particles with a diameter of 3.5 µm are coated with a Sn layer with a thickness of 1.5 µm, which improves the oxidation resistance of Zn particles. The effect of the weight ratio of Zn@Sn to the Sn particles on the type and thickness of the intermetallic compounds (IMCs) layer was investigated. The shear strengths of solder joints based on the Zn@Sn core-shell particles were increased by 44% compared with that of the commercial Sn-Zn preforms, after reflowing at 230 °C for 10 min. The fracture microstructure showed a mixed fracture mode with both ductile and brittle characteristics. The results demonstrate that composite solder paste based on Zn@Sn core-shell structure is a promising die attach material for power device packaging.