Effects of ZrO Nano-Particles' Incorporation into SnAgCu Solder Alloys: An Experimental and Theoretical Study.

This study investigates the mechanism and effects of incorporating different ZrO nano-particles into SAC0307 solder alloys. ZrO nano-powder and nano-fibers in 0.25-0.5 wt% were added to the SAC0307 alloy to prepare composite solder joints by surface mount technology. The solder joints were shear tested before and after a 4000 h long 85 °C/85% RH corrosive reliability test. The incorporation of ZrO nano-particles enhanced the initial shear force of the solder joint, but they decreased the corrosion resistance in the case of 0.5 wt%. SEM, EDS, and FIB analysis revealed intensive growth of SnO on the solder joint surfaces, leading to the formation of Sn whiskers. Density functional theory (DFT) simulations showed that, despite Sn being able to bond to the surface of ZrO, the binding energy was weak, and the whole system was therefore unstable. It was also found that ZrO nano-particles refined the microstructure of the solder joints. Decreased β-Sn grain size and more dispersed intermetallic compounds were observed. The microstructural refinement caused mechanical improvement of the ZrO composite solder joints by dispersion strengthening but could also decrease their corrosion resistance. While ZrO nano-particles improved the solder joint mechanical properties, their use is recommended only in non-corrosive environments, such as microelectronics for space applications.