Study on the properties of low silver Sn1.0Ag0.5Cu composite solder reinforced with nickel-plated zinc oxide and its soldering joint

Based on the preparation of nickel-plated zinc oxide (Ni-ZnO) by pyrolysis-reduction method, low silver Sn1.0Ag0.5Cu lead-free composite solders reinforced with Ni-ZnO were prepared by the powder metallurgy method, and the microstructure and properties of the soldering joints were investigated accordingly. The results showed that the particle size of ZnO was reduced after ball milling. The Ni-ZnO reinforcement phase was successfully prepared by pyrolysis-reduction method, in which Ni particles with an average particle size of 9.7 nm were uniformly and densely deposited on the surface of ZnO particles, and the interface between ZnO (002) and Ni (111) showed a semi-coherent relationship with a mismatch of 0.203. The moderate addition of Ni-ZnO had little effect on the electrical conductivity of the Sn1.0Ag0.5Cu composite solders reinforced with Ni-ZnO. But it refined the primary β-Sn grains in the composite solders and improved the wettability and tensile strength of the composite solders. At an addition of 1.0 wt% Ni-ZnO reinforcement phase, the tensile strength and shear strength of the composite solder and its soldering joint reached a maximum value of 41.8 MPa and 28.9 MPa, with an increase of 39.3 % and 41.7 % respectively compared to the base solder material. The fracture position of composite solder/Cu soldering joint occurred in the transition zone of the soldering seam and IMC (Intermetallic Compound) layers. With the increase of Ni-ZnO reinforcement phase addition, the shear fracture location of the soldering joint moved from the near copper substrate side to the near soldering seam side in the transition zone, and the fracture mode gradually changed from a mixed ductile-brittle fracture to a typical ductile fracture dominated by parabolic toughness dimples.