Solder joints are the main weak points of power modules used in harsh environments. For the power module of electric vehicles, the maximum operating temperature of a chip can reach 175 °C under driving conditions. Therefore, it is necessary to study the high-temperature reliability of solder joints. This study investigated the creep properties of Sn-3.0Ag-0.5Cu (SAC305) and Sn-8.0Sb-3.0Ag (SSA8030) solder joints. The creep test was conducted at 175 and 190 °C with the application of 2.45 MPa. The SAC305 solder had superior creep properties to those of SSA8030 solder at 175 °C and at largely the same homologous temperature ( $T_H$ ~0.91 for SAC305 and $T_H$ ~0.92 for SSA8030). Both solders had primary β-Sn and a eutectic mixture of β-Sn and Ag₃Sn. Compared to SSA8030, the SAC305 solder contained ~10% more eutectic structure and contained Ag₃Sn that was 3 times smaller and more round in shape. Furthermore, the SSA8030 solder precipitated SnSb in an elongated fiber shape (1–50 μm in size) after the creep test. Coarse and elongated Ag₃Sn and SnSb of the SSA8030 solder negatively affected crack propagation in the dislocation creep region and decreased the creep resistance.

To preserve the structural integrity of power semiconductor devices, ensuring a reliable connection between wide-bandgap (WBG) chips and their substrates at temperatures above 200 °C is crucial. Therefore, easily processable chip-attach materials with high bonding strengths at high temperatures should be developed. Herein, we determined the optimal pre-heating conditions of chip-attach materials to achieve highly reliable WBG semiconductor devices. Sintering with silver-coated copper (Cu@Ag) particle paste was investigated as a model system for chip attachment in electric power devices. After printing the paste onto a direct-bonded ceramic substrate and placing the Si chip on the paste, the pre-heating process was conducted at 50 and 70 °C for different periods of time. Finally, the samples were sintered at a pressure of 9 MPa at 250 °C in an N₂ atmosphere for 1 h. The quality of the obtained Cu@Ag joints significantly varied depending on the pre-heating temperature and time. When Cu@Ag joints were pre-heated at 50 °C, more reliable and reproducible bonding was achieved than at 70 °C. In particular, high-quality sintered joints were obtained with a pre-heating time of 4 min. However, after excessive pre-heating time, cracks and voids were generated impacting negatively the performance of the sintered joints.