Effect of alloying elements on properties and microstructures of SnAgCu solders

Recent years, the SnAgCu family of alloys has been found a widely application as a replacement for the conventional SnPb solders in electronic industry. In order to further enhance the properties of SnAgCu solder alloys, alloying elements such as rare earth, Bi, Sb, Fe, Co, Mn, Ti, In, Ni, Ge and nano-particles were selected by lots of researchers as alloys addition into these alloys. Rare earth (RE) elements have been called the ‘‘vitamin” of metals, which means that a small amount of RE elements can greatly enhance the properties of metals, such as microstructure refinement, alloying and purification of materials and metamorphosis of inclusions. In addition, a small amount of Zn addition has the ability to reduce undercooling efficiently and suppress the formation of massive primary Ag₃Sn plates, and Bi/Ga has the ability to enhance the wettability of SnAgCu alloys as well as Ni. Moreover, adding Co/Fe/Ge can effectively refine microstructure, modify interfacial Cu-Sn compounds and increase the shear strength of joints with Cu. This paper summarizes the effects of alloying elements on the wettability, mechanical properties, creep behavior and microstructures of SnAgCu lead-free solder alloys.