Effect of TiC addition on the isothermal aging performance of Sn–Bi/Sn–Ag–Cu hybrid solder joints

The demand for 3D packaging has grown with the drive toward high-performance, lightweight, and miniaturized electronics. However, issues such as warpage, interfacial delamination, and thermal stress accumulation intensify under repeated high-temperature bonding processes. The widely used Sn–3.0Ag–0.5Cu (SAC305) solder exacerbates these problems owing to its high melting point of 217 °C. Although Sn58Bi solder, with a low melting point of 139 °C, can mitigate thermal damage, its high Bi content induces brittleness and reduces long-term reliability owing to Bi segregation during isothermal aging. In this study, Sn58Bi–xTiC (x = 0, 0.1)/SAC305 hybrid solder joints were fabricated to investigate the effect of TiC nanoparticles on long-term reliability. Sn58Bi–xTiC (x = 0, 0.1) solder paste was printed onto Organic Solderability Preservative (OSP)-finished Cu pads, and reflowed with SAC305 solder balls at 185 °C. Subsequently, isothermal aging was conducted at 110 °C for up to 1000 h. With aging, the Cu 6 Sn 5 intermetallic compound (IMC) transformed from scallop-type to layer-type, with Cu 3 Sn growing underneath, and no Bi segregation was observed. TiC nanoparticles effectively suppressed IMC growth and grain coarsening, while delaying Bi-rich phase diffusion and agglomeration. Nanoindentation tests revealed that the hardness and elastic modulus decreased up to 100 h, followed by an increase, converging to ∼420 MPa and 53 GPa after 1000 h, respectively. TiC-containing joints exhibited higher values across all aging intervals. Shear tests confirmed that TiC-containing joints displayed higher shear strength and fracture energy after aging, with a persistent ductile fracture mode. These findings demonstrate that the addition of TiC nanoparticles is effective in enhancing the long-term reliability of Sn58Bi/SAC305 hybrid solder joints.