Microstructural and mechanical properties of Sn58Bi/Sn3.0Ag0.5Cu hybrid solder joints containing TiC nanoparticle additions

Sn-Bi-based solders have attracted considerable attention as promising materials for use in low-temperature soldering processes due to their low melting point of 139 °C and their excellent wettability. However, their long-term reliability is limited by the inherent brittleness of the Bi-rich phase. To address this issue, various approaches have been explored, including the incorporation of ceramic nanoparticles and the formation of hybrid solder joints with Sn-Bi and Sn-Ag-Cu alloys. In this study, a Sn58Bi-0.1TiC solder paste was prepared by adding 0.1 wt% TiC nanoparticles to Sn58Bi solder paste. Subsequently, SAC305 solder balls were mounted to form Sn58Bi-xTiC (x = 0,0.1)/SAC305 hybrid solder joints. The microstructures and mechanical properties of the resulting joints were comparatively analyzed under varying reflow temperatures and belt speeds. It was found that an increase in the reflow temperature and a reduction in the belt speed led to an increase in the Bismuth Mixing Ratio (BMR). The addition of TiC nanoparticles hindered the diffusion of Bi atoms, resulting in lower BMR values. The shear strength of Sn58Bi/SAC305 hybrid solder joints increased from ∼45 MPa at 170 °C to nearly 60 MPa at 200 °C, while Sn58Bi-0.1TiC/SAC305 hybrid solder joints showed slightly lower values. Nevertheless, the Sn58Bi-0.1TiC/SAC305 hybrid solder joints achieved a fracture energy of up to 670 μJ with a higher proportion of ductile fracture compared with the Sn58Bi/SAC305 hybrid solder joints. These findings confirm that the addition of TiC nanoparticles effectively regulates the behavior of Bi-rich phase under varying reflow conditions, thereby contributing to the improvement of the mechanical performances of the solder joints.