The Effect of Tiny Voids on the Performance of LED Solder Joints
Using SnCu0.7 solder paste for reflow soldering process to prepare flip-chip LEDs,addressing welding defects caused by the miniaturization of solder joints.The study utilized X-ray Inspection to categorizes solder joints with different void rates.It systematically investigated the influence of void rate on the bonding strength of joints and the fracture characteristics of joints after reflow soldering,through finite element simulation.Furthermore,it explored the impact of void rate on chip heat dissipation capability.Additionally,the paper designed a junction temperature measurement experiment to validate the accuracy of the simulation results.Finally,through high-temperature aging experiments,the study delved into the variation trends of luminous flux and photoelectric conversion efficiency of LED samples with different void rates.The results indicate that the bonding strength of solder joints is not solely determined by the quantity of voids;the size and location of voids also have a certain impact on the bonding strength.Furthermore,as the void rate increases,the fracture mode of solder joints gradually shifts from ductile fracture to brittle-ductile mixed fracture.With the increase in void rate,the chip junction temperature of LEDs under normal operation shows a generally linear growth trend.Moreover,as the void rate increases,the chip's heat dissipation capability deteriorates.When the void rate is approximately 5%,the chip's junction temperature is 41.472℃,whereas when the void rate is 30%,the chip's junction temperature reaches 45.969℃.As the void rate increases,the luminous flux and photoelectric conversion efficiency show an initial upward trend during the early stage of high-temperature aging.After 500 h,the luminous flux gradually begins to decline.At the 1 500 h mark,the maintenance rate of luminous flux for samples with a 5%void rate is 93.22%,which is 10.85%higher than that of samples with a 30%void rate,which is 82.37%.Similarly,the luminous efficacy of samples with a 5%void rate is 42.5%,which is 12%higher than that of samples with a 30%void rate,which is 30.5%.
万方数据
维普
