Sn-3.0Ag-0.5Cu Solder Enriched with Tb₄O₇ Nanoparticles for Mini-Light Emitting Diode Packaging

In this study, we perform innovative addition of Tb₄O₇ nanoparticles (NPs) into the Sn-3.0 wt % Ag-0.5 wt % Cu (SAC305) alloy for attaching a 1608 mini-LED chip to a Cu pad of a printed circuit board (PCB). The Tb₄O₇ NP-reinforced SAC305 solder alloy was prepared by a melting and casting route. The spreading ratio (SR) of the Tb₄O₇ NP-reinforced SAC305 solder was assessed using the JIS-Z-3197 standard. The melting and tensile properties of the nanomodified solders were also evaluated. The microstructural observations showed that as Tb₄O₇ NPs were gradually added to the Sn-rich matrix, the β-Sn-grain area became finer due to the adsorption of high surface active Tb₄O₇ NPs on the β-Sn grain and intermetallic compounds (IMCs). The findings showed that the produced Tb₄O₇ NP-reinforced SAC305 solder had a 6 °C depression in melting temperature over the pristine SAC305 alloy. The SR of the nanomodified solders was increased up to 90.5% at the optimal concentration of Tb₄O₇ NPs in the SAC305 matrix. A delayed microstructural coarsening and the inhibited Cu-Sn atomic interdiffusion at the joint interface were observed, which resulted in an enhancement of tensile and shear strength by 8.18 and 9.24%, respectively. The results indicate that addition of 0.3 wt % Tb₄O₇ NPs is needed to realize the optimum set of microstructural and thermodynamic reliability of a mini-LED/Cu chip joint.