Effects of Minor Alloying Additions on the Properties and Reliability of Pb-free Solders and Joints

Since July, 2006, following the EU’s RoHS legislation, the consumer electronics industry has been offering “green” products by eliminating Pb-containing solders and other toxic materials. This transition has been relatively smooth, because the reliability requirements are less stringent. However, the Pb-free transition for high performance electronic systems (such as servers and telecommunication) is still on-going due to their rigorous reliability requirements. For example, the research and development efforts to implement Pb-free flip chip interconnections for high end applications are still very active. In this paper, the recent progress in Pb-free solder development, especially minor alloy additions to Sn-rich solders is reviewed in light of improving various physical, mechanical, metallurgical or electrical properties of solder joints. The topics to be discussed include such as control of undercooling, microstructure, interfacial reactions, or void formation, as well as enhancing impact resistance, electromigration, and other mechanical properties.