Mechanisms of γ-ray irradiation induced oxidation corrosion in SnBi eutectic solder joints: Insights from first-principles calculations

As deep space exploration and extraterrestrial missions increase, the long-term radiation-induced deterioration of solder joint performance has become a critical factor limiting their long-term operational stability. This study employs quasi-in-situ characterization and first-principles calculations to investigates the microstructural evolution and oxidation behavior of SnBi eutectic solder joints under γ-ray irradiation. Sn oxides preferentially form at the Sn/Bi interface, and with prolonged irradiation, Sn and Bi oxides accumulate. After 200 h, the solder joint surface becomes fully covered by Sn oxides. Atomic vacancies induced by γ-ray irradiation enhance the adsorption of O₂ molecules on the Sn and Bi surfaces and accelerates the oxidation process. Bi incorporation lowers the work function of the Sn-based solid solution than Bi-based solid solution, making Sn more susceptible to oxidation. Additionally, the low diffusion energy barrier of Sn atoms into SnO₂ facilitates their continuous migration across the Sn/SnO₂ interface and SnO₂, thereby promoting the sustained thickening of the SnO₂ oxide layer. The present results provide key insights into microstructural evolution and oxidation processes of the SnBi solder joints, supporting the development of more reliable solder materials for next-generation spaceborne electronic systems.