Microstructural stability of Sn–1Ag–0.5Cu–xAl (x=1, 1.5, and 2wt.%) solder alloys and the effects of high-temperature aging on their mechanical properties

Abstract

Abstract The effects of Al addition on the microstructural stability and mechanical properties of Sn–1Ag–0.5Cu (wt.%) solder alloy under high-temperature aging were investigated. The addition of Al refines the primary β-Sn dendrites and enlarges the interdendritic regions. The addition of Al also suppresses the formation of Ag 3 Sn and Cu 6 Sn 5 intermetallic compounds and leads to the formation of Ag 3 Al and Al 2 Cu intermetallic compounds. Moreover, the addition of Al leads to the segregation of an Al-rich phase. Tensile test results indicated that the addition of Al significantly increased the yield strength and ultimate tensile strength, whereas the elastic modulus increased only slightly and the total elongation decreased. Similar to the Sn–1Ag–0.5Cu solder alloy, the microstructures of Al-modified Sn–1Ag–0.5Cu solder alloys become notably coarsened after aging, which in turn significantly degrades their mechanical properties. Fracture surface analysis indicated that the addition of Al to the Sn–1Ag–0.5Cu solder alloy leads to a brittle fracture instead of a ductile fracture.