Microstructure Evolution and Shear Strength Study of Sn–9Zn and Sn–8Zn–3Bi on Cu Substrate

• Published in: Transactions on Electrical and Electronic Materials
• Main Author: Mayappan R.; Ahmad Z.A.
• Format: Article
• Language: English
• Published: Korean Institute of Electrical and Electronic Material Engineers 2024
• Online Access: https://www.scopus.com/inward/record.uri?eid=2-s2.0-85174314222&doi=10.1007%2fs42341-023-00481-5&partnerID=40&md5=c08659b451499d6e60cb2ae2d8958599

In electronics assembly, solder joints not only serve as mechanical supporters-, but also as heat removers. Therefore, solder joint reliability is a major concern not only during production, but also during the life time of electronic products. It can be pointed out that reliability of solder joint determines the lifetime of electronics products. This issue becomes more important with the use of Pb-free soldering alloys. This study focuses on the reliability of Sn–9Zn and Sn–8Zn–3Bi lead-free solder joints with Cu substrates. This study deals with interface intermetallic morphology, solder joint strength and fracture surface analysis after isothermal aging at 50, 100, and 150 °C for 100, 250, and 500 h. For all aging conditions, a flat Cu5Zn8 intermetallic was formed, and as the aging conditions increased, Cu atoms diffused through the intermetallic to form isolated Cu5Zn8 intermetallics in the bulk solder. Furthermore, Sn atoms from bulk the solder diffused through the intermetallic to form Cu6Sn5 on the Cu side. The formation of a thick Cu5Zn8 intermetallic and the diffusion of Sn and Zn atoms created a depletion zone near the solder/intermetallic boundary, which weakened the joint strength. As the intermetallic layer thickness increased, the joint strength decreased as the aging increased. The fracture path generally occurred at the bulk solder/intermetallic boundary under all aging conditions. © 2023, The Korean Institute of Electrical and Electronic Material Engineers.