Performance and Reliability of Nanoparticles Reinforced Lead-Free Solder Joints – A Study

Abstract

The present study involved the development of Sn-3.6Ag, 99Sn-0.3Ag-0.7Cu (SAC0307), 96.5Sn-3Ag-0.5Cu (SAC305), and 96.5Sn-3Ag-0.5Cu-0.06Ni-0.01Ge (SAC305-NiGe) lead-free solders with the addition of Al2O3 nanoparticles and multi-walled carbon nanotubes (MWCNT). The effects of multiple reflow cycles and the addition of Al2O3 nanoparticles and MWCNT in 0.01, 0.05, 0.1, 0.3, and 0.5 weight percent concentration on microstructure development and mechanical strength of the solder joint were first investigated. The addition of nanoparticles in low weight percent concentration improved the wettability and solder joint shear strength. Based on superior shear strength and improved ductility compared to the original solder, nanocomposites containing 0.01 and 0.05 wt. pct. Al2O3 nanoparticles were selected and tested for the performance and reliability of the joint. The surface mount 2220 capacitor joint and single-lap-shear joint assemblies reflowed on bare copper and electroless Ni-coated Cu substrates were used in this study. The reliability of the solder joint was assessed in terms of the joint shear strength under varying thermal environments like thermal shock, multiple heating cycles, and aging. The nanocomposite with 0.05 wt.% nanoparticles addition yielded the most significant increase in the joint strength compared to the unreinforced solder. The Ni-substrate coating significantly suppressed the IMC growth under different thermal conditions. The joint reliability of nanocomposites improved for samples reflowed on Ni-coated substrate compared to that on bare Cu substrate. The Weibull analysis showed that the performance and reliability of the solder joint can be greatly improved by the addition of Al2O3 nanoparticles in small weight percent concentrations and Ni-coating on the substrate. The ANOVA study suggests that the solder joint performance was majorly influenced by the operating environments, solder composition, and the substrate coating. SAC305-NiGe and SAC0307 based nanocomposites were found to be better than all solder compositions studied in the present study. The low-silver content SAC0307+0.05Al2O3 nanocomposite will be an effective alternate solder composition in place of high silver content Sn-Ag-Cu solders.