Isothermal aging effect on microstructure and mechanical properties of Ni/Sn3.0Ag0.5Cu/Ni interconnects with the decreasing height

Isothermal aging effect on the microstructure and mechanical properties of line-type Ni/Sn3.0Ag0.5Cu/Ni sandwich structure interconnects with small heights of 50 and 25 μm was investigated in this study. Microstructural analysis showed that interfacial (Ni, Cu)₃Sn₄ IMC layer grew thick after aging at 125 °C for 100 h with the formation of local voids and cracks due to volume shrinkage induced by the interfacial reaction; the interfacial IMC thicknesses of the aged joints with different heights were similar, while the volume fraction of IMC in the joints with a height of 25 μm was much higher than that of the joints with a height of 50 μm; the isothermal aging effect was much severer when the joints were undergone aging at 200 °C. In addition, β-Sn grains and Ag₃Sn precipitates would grow coarsened during aging. Results of the tensile test showed that the joints aged at 125 °C had a similar ultimate tensile strength (UTS) despite the different heights of them; while the UTS of the joints aged at 200 °C degraded to 67%. The fracture of the aged joints was more likely to occur in the bulk solder in a ductile mode. The influence of the coarsening β-Sn matrix and Ag₃Sn particles on the reliability of the aged joints was much stronger than that of the slow growth of the interfacial IMC. Ni/SAC/Ni joints with small heights showed better thermal reliability than that of the large ones.