Lead-free solders with rare earth additions

There have been significant research efforts to improve the properties of globally recognized lead-free solders, such as Sn-Ag-Cu, Sn-Cu, Sn-Bi, etc. Rare earth (RE) elements have been selected in the current research to be added into lead-free solders as alloying elements in an effort to improve the comprehensive properties, such as wettability, microstructural stability, creep resistance, and mechanical strength and integrity of the solders. This article overviews the background and rationale for the alloy development, the fabrication techniques for RE-containing solders, the roles of RE elements, as well as current status of RE-containing solder research. Examples of several representative RE-containing solders are introduced. The effects of RE element addition on the wetting behavior, microstructure, and mechanical properties of certain lead-free solder alloys are presented and analyzed.