The Effect of Eutectic Structure on the Creep Properties of Sn-3.0Ag-0.5Cu and Sn-8.0Sb-3.0Ag Solders

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 (TH~0.91 for SAC305 and TH~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.