Effect of 1 wt% ZnO nanoparticles addition on the microstructure, IMC development, and mechanical properties of high Bi content Sn–57.6Bi–0.4Ag solder on Ni metalized Cu pads

In the present study, we investigate the performance of 1 wt% ZnO nanoparticles addition to Sn–57.6Bi–0.4Ag lead-free solder and thereby study the effect of nanoparticle addition on the hardness and the inter-metallic compound (IMC) growth, under different reflow conditions. The interfacial morphology of both the plain Sn–57.6Bi–0.4Ag solder and the composite Sn–57.6Bi–0.4Ag/1 % ZnO solder containing nanoparticles on Ni metalized Cu pads ball grid array substrates and the distribution of nanoparticles on the composite solder were characterized metallographically by using scanning electron microscope (SEM). Prior research efforts by others has found strong evidence that the thickness of the IMC layer increases substantially with the increase in the number of reflow cycles. At the interfaces between solder ball and substrate, scallop-shaped Sn–Ni–Cu IMC layer was found in both the plain solder and the composite solder. Meanwhile the SEM results indicated that the growth of IMC of the composite solder joint was different compared to the plain solder with same number of reflow cycles and reflow time. During the shear test, the shear strength of the composite solder samples containing nanoparticle reinforcement were consistently higher than the plain solder joints due to the fact that the IMC growth has been retarded substantially by the nanoparticle addition. The fracture surface of plain solder exhibited a brittle fracture mode with a relatively smooth surface while doped solder joints showed typical ductile failures with very rough dimpled surfaces.