Microwave hybrid joining using SAC305-xNi@Sn solder paste to achieve superior performance and high-efficiency heating and unveiling cross-scale mechanisms

Microwave hybrid joining (MHJ) is an innovative, high-efficiency technique that uniformly heats materials, offering superior performance compared to traditional methods. This study developed a multi-physical MHJ model using silicon carbide (SiC) as the susceptor. SAC305-xNi@Sn solder paste was found to enable compound heating, significantly improving joining efficiency. The temperature field, electric field, and maximum electromagnetic power loss density distributions of the self-designed dual susceptors were analyzed. Ni/Sn-Ag-Cu-xNi@Sn/Ni joints were fabricated and compared with reflow soldering. The fracture mechanism and the optimal Ni@Sn content were analyzed. The multi-physics simulation examined the cross-scale mechanisms of MHJ. The results indicate that incorporating 3.6 g of SnCl₂·2H₂O uniformly covers Ni@Sn nanoparticles, meeting weldability standards. MHJ technology achieves a shear strength of 40.20 MPa at 2.45 GHz, 2 kW, a peak temperature of 400 °C, and a 5-min exposure time, which is 35.67 % higher than that of reflow soldering (29.63 MPa). Under identical process parameters, MHJ infused with 1 % Ni@Sn nanoparticles achieves a shear strength of 43.11 MPa, representing a 45.49 % increase over the shear strength of reflow soldering (29.63 MPa). SAC305 has a thickness of 3.1 mm, a minimum reflectance of −53.06 dB at 9.28 GHz, and an effective absorption bandwidth of 2.39 GHz. Ni@Sn exhibits a minimum reflectance of −2.71 dB and an optimal thickness of 3.04 mm at 4.32 GHz.