Effect of nano-SAC0307 content on performance of Cu/Al joints in dual-ultrasonic assisted low-temperature soldering

The influence of SAC0307 content on Cu/Al joint performance was systematically investigated via dual-ultrasonic assisted soldering technology with solder formulated with x SAC0307 + (1-x) Zn hybrid powders, (x=10 wt.% ~ 50 wt.%). Experimental results demonstrated that the consistent formation of a about 2 μm thick Cu-Zn diffusion layer at the Cu interface, containing indistinct Cu5Zn8 and CuZn4 IMCs, while a thin irregular Al-Zn solid solution layer was developed on the Al interface. Impressively, the shear strength exceeding 30 MPa was preserved across all SAC concentrations. A characteristic trend of initial improvement followed by gradual decline in the shear strength with increasing SAC content, peaking at 39.21 MPa with 20 wt.% SAC content. Fractographic analysis revealed exclusive fracture propagation within the solder matrix, displaying ductile-brittle hybrid fracture characteristics. Spherical Zn particles progressively disappeared with SAC content elevation, accompanied by fracture location progressively shifting from Cu substrate to A substrate.