The influence of Fe2O3 nano-reinforced SAC lead-free solder in the ultra-fine electronics assembly

This paper presents the influence of Fe2O3 nanoparticles on the microstructure and fillet height for the ultra-fine electronics assembly in the reflow soldering process. Lead-free SAC solder paste was reinforced with different weighted percentages of Fe2O3 nanoparticles (i.e., 0.01, 0.05, and 0.15 wt.%) using a mechanical solder paste mixer. A new form of nano-reinforced lead-free solder paste was applied to assemble the ultra-fine capacitor (i.e., 01005 size) onto the printed circuit board by applying the reflow soldering method. Focused ion beam (FIB), high-resolution transmission electron microscope (HRTEM) system equipped with energy-dispersive X-ray spectroscopy (EDS), field emission scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (EDS), and nanoindentation tester, were all used to examine the microstructure, hardness, and the fillet height of the solder joints. The experimental results revealed that nano-reinforced solder with the content of 0.01, 0.05, and 0.05 wt% yielded small changes in the intermetallic layers. Furthermore, applying an increment of Fe2O3 to 0.05 wt% also improved the fillet height. The mechanism of the agglomeration of Fe2O3 in the bulk solder is discussed in this study. Moreover, simulation analysis using the volume of fluid (VOF) and discrete phase method (DPM) was both employed to describe the mechanism of nanoparticle distribution in the solder and the reflow soldering process. The findings are expected to provide profound knowledge and further reference towards the reflow soldering process of the miniaturised electronic package.