Alloying regulation mechanism toward microstructure evolution of Sn-bi-based solder joint under current stress

Sn–Bi-based solder alloys have triggered substantial concern in development of low-temperature interconnecting materials of multi-level packaging electronic devices. However, with the high-density current treatment, dramatic atom migration occurs in Sn–Bi-based solder joint, which accelerates the evolution of solder joint microstructure, including the aggregation of Bi phase and the excessive growth of interfacial intermetallic compound (IMC). In this work, Sb element shows a unique influence mechanism on the electromigration (EM) resistance of Sn-Bi-based solder joint. Doped Sb in Sn58Bi-1Sb (SB-Sb) solder massive precipitate as Sn-Sb and Bi-Sb nano precipitations under current stress. These nano precipitates show the ability to capture the migrating atoms, inhibit the migration of Bi atoms and Sn atoms, and enhance the EM resistance of solder joint. Importantly, Bi twin crystal structure is observed in Sn-Bi-Sb solder for the first time. The variation of twins' phase orientations in different positions of solder joint is associated with atomic migration paths induced by the current stress and would eliminate the overgrowth of the Bi rich phase and IMCs. The presented study provides the valuable insights into the regulates mechanism of alloy elements on atom migration in Sn-Bi-based solder joint.