Abstract: During deep space exploration, electronic assemblies without thermal protection have to be subjected to extreme temperature environments and electric field coupling. In this work, the coupled load of extreme temperature thermal shock test -196-150℃ and 1.5×10⁴ A/cm² current density was conducted to investigate the microstructure evolution and current crowding of the solder joints, as well as the relationship between the microstructure evolution and the resistance change. The results show that the anodic intermetallic compound (IMC) increased parabolically and the composition of IMC was Cu₆Sn₅. Meanwhile, the thickness of cathodic IMC increased, and its composition was Cu₆Sn₅ at the pre-thermal shock stage. When the direction of electron wind and stress gradient of solder joints were identical, the anodic interfacial IMC was found to increase and the cathodic interfacial IMC was about to be fused as the thermal shock increased. However, when the direction was reversed, the thickness of the anodic IMC reduced obviously, the thickness of the interface IMC of the anodic and cathode reduced obviously and thicken respectively. The resistance of the solder joint increased and the phenomenon of current concentration was observed at the current input. In addition, a straight crack was formed at the IMC layer, which led to the failure of the solder joint and the resistance value of the solder joint reached infinity.

Key words: Sn-3.0Ag-0.5Cu solder joints, extreme temperature, thermal shock, current stress, intermetallic compounds