Partial Segregation of Bi and Microvoid Formation on a Pure Cu Substrate After Solid-Solid Reactions

With the trend of technology development and carbon reduction, reducing the process temperature to prevent greenhouse effects is of great urgency. The back-end process of semiconductors is increasingly important because of the limitation of Moore's Law. High-temperature bonding is serious for semiconductor packages, which induces high cost and device damage. One of the critical ways to reduce the process temperature is to adopt low-temperature solders. In this study, we utilize the low-temperature solder Sn58Bi to achieve energy savings and device protection. The interfacial reactions between Sn58Bi and Cu after reflow and aging reactions were investigated. The solubility of Bi in Sn influences the Bi segregation at the interface. Partial Bi segregation, microvoids, and uneven Cu₃Sn were observed at the interface after aging. There is no doubt that the aforementioned structures are unfavorable for solder joint strength.