Electrochemical deposition of Sn-0.7Cu alloy modified with nano-WO₃ for high-density mini-LED packaging

In this work, Sn-0.7Cu-WO₃ nanomodified solders were electrodeposited from an aqueous acidic plating bath containing various fractions of WO₃ nanoparticles (0.1, 0.25, 0.5 wt%) NPs for mini-light emitting diodes (mini-LEDs) packaging. The produced nanomodified solders were characterized for their morphology, microhardness, melting point, and electrical resistivity. Further, the nanomodified solder bumps were used to mount a 1608 mini-LED chip/ENIG (Electroless Nickel Immersion Gold) pad by reflowing at 240 °C in the air. High-temperature aging was done at 125 °C for 144, 256, and 400 h and joint shear tests were performed to examine the interfacial properties and growth kinetics of the soldered mini-LED/Sn-0.7Cu-WO₃/ENIG joints. The results indicated the formation of (Ni,Cu)₃Sn₄ intermetallic compounds (IMCs) across the solder/ ENIG pad joint. The thickness of the IMC layer decreases showing the maximum rate of decrease when the composition is Sn-0.7Cu-0.25WO₃. It was concluded that the optimal set of microstructure, melting point, electrical resistivity, and joint shear reliability could be achieved when the nanomodified solder is reinforced with 0.25 wt.% WO₃ NPs into Sn-0.7Cu matrix and thus it can be a potential contestant for the upcoming applications in mini-LED packaging.