Barrier effect of Sn-Bi-In multi-principal element solder on thermomigration

The design of multi-principal element alloying has shown potential for fabricating solder with low melting points, with ternary Sn-Bi-In solder being a promising candidate. During the application of solder joints, there are some flux-driven reliability issues such as electromigration or thermomigration. To investigate potential failure risks of the Sn-Bi-In solder, this paper compares thermomigration behaviors among SnCu0.7, Sn58Bi, and Sn-Bi-In solder in liquid states systematically. Sandwich structures of Cu/solder/Cu were fabricated and put on hot plates with temperatures of 250 °C, 270 °C, and 290 °C, respectively, to perform thermomigration. In each case, Cu is the dominant diffusion element, moving across the solder matrix from the hot end to the cold end, leading to thicker intermetallic compound (IMC) formation at the cold end. The activation energy of the IMC growth at the cold end determines the resistance of the solder to thermomigration, and low activation energy facilitates the diffusion progress. We calculated that the activation energy of diffusivity in Sn-Bi-In solder is 158.40 kJ/mol, which is significantly larger than that in Sn58Bi or SnCu0.7 solder. Besides, the atomic flux of thermomigration in Sn-Bi-In matrix is the lowest among the three solder alloys under each temperature condition. These results indicate that the multi-principal element Sn-Bi-In solder has a strong barrier effect on Cu diffusion across the solder matrix, showing its excellent resistance to flux-driven failures, such as thermomigration. © 2026 Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.