Influence of Soldering Temperature on Microstructure and Thermal Properties of FC-LED Filaments Soldered with SAC0307

The influence of the soldering temperature on the performance of flip-chip light-emitting diodes (FC-LED) filaments soldered with SAC0307 has been investigated. Scanning electron microscopy (SEM) images, void rates, shearing force, junction temperature, steady-state voltage, blue light luminous flux, and luminous efficiency were measured to characterize the filament performance. The microstructure of the fracture surface after shear failure of the FC-LED filament joints soldered at 250°C and 270°C showed the lowest percentage of voids and was smoother than for the other groups. The shearing force of the FC-LED filament solder joints formed at 250°C and 270°C was higher than that for the other three groups, but the shearing force of all five groups of solder joints exceeded 200 gf. The steady-state voltage and junction temperature of the 250°C and 270°C FC-LED filaments were lower than those of the other three groups, and the blue light luminous flux of the 250°C and 270°C FC-LED filaments was higher than for the other three groups. In conclusion, the FC-LED filaments exhibited good photoelectric performance and thermal reliability when using soldering temperatures between 250°C and 270°C.