Sn–Bi–Ag Solder Enriched with Ta2O5 Nanoparticles for Flexible Mini-LED Microelectronic Packaging

Mini light-emitting diodes (mini-LEDs) with high contrast and brightness have the potential to compete with modern organic light-emitting diodes in consumer appliances and flexible displays. In this study, a nanodispersed Sn-58 wt %Bi-0.4 wt %Ag (Sn-58 Bi-0.4Ag) solder alloy with Ta2O5 nanoparticles (NPs, ranging from 0 to 0.6 wt %) was added by an ultrasonic-assisted casting process. The melting point, microstructure, wetting property, and tensile test were examined to investigate the metallurgical and bonding reliability of the nanodispersed solder. The results demonstrated that the produced Sn–Bi–Ag/Ta2O5 solder had slightly lowered from the pristine Sn-58 Bi-0.4Ag alloy by 2.3 °C. The microstructural observations indicated that the β-Sn-grain area got finer with the addition of 0.6 wt %Ta2O5 NPs and eutectic lamellar spacing also decreased as a result. The wetting properties of the nanodispersed solder were also enhanced (wetting force = 5.34 mN, spreading ratio = 83.4%, wetting angle = 10.4°, and zero cross time = 1.93 s) in comparison to the pristine Sn–Bi–Ag alloy. The tensile strength and ductility both tended to improve by 34.24 and 114.6% over the pristine Sn–Bi–Ag solder. The solder joint reliability study was carried out by mounting the nanodispersed solder onto a mini-LED chip of a flexible printed circuit board and measuring the joint shear strength. The results showed that a reduced void fraction of 3.03% (pores, shrinkage, solidified cracks) boosted the shear strength of the composite matrix by 15.6%, confirming that the addition of Ta2O5 NPs can be a potential strategy to develop high-reliability Sn–Bi–Ag alloy used for wearable mini-LED electronic packaging.