A Sn—Ag—Cu eutectic alloy is modified with one or more low level and low cost alloy additions to enhance high temperature microstructural stability and thermal-mechanical fatigue strength without decreasing solderability. Purposeful fourth or fifth element additions in the collective amount not exceeding about 1 weight % (wt. %) are added to Sn—Ag—Cu eutectic solder alloy based on the ternary eutectic Sn—4.7%Ag—1.7%Cu (wt. %) and are selected from the group consisting essentially of Ni, Fe, and like-acting elements as modifiers of the intermetallic interface between the solder and substrate to improve high temperature solder joint microstructural stability and solder joint thermal-mechanical fatigue strength.
US 6,231,691 B1
Iowa State University Research Foundation, Inc.
Anderson, Iver E. and Terpstra, Robert L., "Lead-free Solder" (2001). Iowa State University Patents. 81.