Three-dimensional (3D) microstructure visualization of LaSn3 intermetallics in a novel Sn-rich rare-earth-containing solder

Global concern over the environmental impact and healtheffects of Pb-based solders in consumer electronics has led tothedevelopmentofPb-freesolderalternatives.Sn-richsolderssuch as Sn–Ag and Sn–Ag–Cu are the most promising Pb-freealloysforreplacementofPb–Snsolder[1].Manyissuesrelatingto their mechanical properties and reliability still need to beaddressed. This includes, in particular, their higher meltingpoint andlower ductility[2,3]. Thelower ductilityofthe solderhas important implications because it is directly related tomechanical shock and drop resistance [4].Recently, small additions of rare-earth elements (RE), suchas Ce and La, have been shown to refine the microstructuresand improve the mechanical response of Sn-rich solders [5–8].Due to the complexity of these ternary and quaternarysystems, very little information is available on Sn–RE inter-metallics formed during solidification. Dudek et al. [7] showedthat small La additions (0.1 wt.% and 0.5 wt.%) to Sn–Ag–Curesults in the formation of a stable, homogeneously distrib-utedLaSn