Investigation on microstructure evolution and mechanical reliability of Sn-Ni high-temperature resistant solder joints fabricated through microwave hybrid heating

In this study, microwave hybrid heating (MHH) technique was used to prepare full intermetallic compound (IMC) joints. The microstructure evolution, mechanical properties, and fracture mechanisms of the Sn-xNi(x = 10, 20, 30 wt.%) reaction were investigated under different temperatures and holding times. By varying the mass fraction of Ni particles, the optimal ratio for fabricating full IMC joints was determined. The morphology, mechanical properties at room and elevated temperatures, and the effects of high-temperature aging on microstructure, mechanical property, and reliability were also evaluated. The results show that when the Ni mass fraction is 20%, with process parameters of 2 kW microwave power and a 30 min holding time, a full IMC joint was formed, achieving a shear strength of 38.42 MPa. At 350 °C, the shear strength was 32.52 MPa, attributed to the formation of high-melting-point IMCs. Both joints exhibited intergranular fracture, and the fracture surfaces were composed entirely of Ni₃Sn₄. Reliability tests showed that the shear strength of the full IMC joint decreased slightly with aging time. After 360 h of aging, the joint strength had decreased by only 8.59%. These indicate that the Ni/Sn-20%Ni/Ni joint maintains good reliability after high-temperature aging.