Overview of Low-Temperature Sn-Bi and Sn-Zn Solder Systems and Cu Interfacial Reliability for Advanced Electronic Packaging

In this review, low-temperature Sn-Bi and Sn-Zn solders and the reliability of their Cu interfaces are summarized for advanced electronic packaging. Sn-58Bi can markedly reduce the soldering temperature because its eutectic temperature is approximately 139 °C; however, the brittle Bi-rich phase and the coarsening of the two-phase microstructure remain important problems. The addition of Zn or In has been used to reduce these problems. Bi addition to Sn-3.5Ag and Sn-9Zn also decreased the melting temperature and increased the joint strength under selected conditions. In addition, electrodeposited Sn/Bi bilayers and Sn-Sb/Sn-Bi mixed solders provide another route to form low-temperature joints during heating. The Cu interface was also considered because Cu6Sn5/Cu3Sn morphology, impurities in electroplated Cu, Cu grain size, and surface finish strongly affect IMC growth and void formation. The effects of thermomigration and electromigration are also discussed because they become important as the joint size decreases. This review will provide useful information for understanding low-temperature solder materials and for designing reliable Cu/solder interfaces for advanced electronic packaging.