Research On Phosphor Coating Technology And Color Uniformity For High-power White LED

High-power LEDs have been widely used in various lighting fields due to their high light efficiency,excellent energy-saving performance and long life.In the existing packaging process,the yellow circle phenomenon is caused by traditional dispensing coating,which seriously affects the optical performance of the LED and reduces the light extraction efficiency and color uniformity.In order to obtain high light quality and high color uniformity of white LEDs,this thesis studies the phosphor coating technology of highpower LED from the perspective of adjusting the distribution and morphology of phosphor layer,and propose a remote phosphor coating method based on the principle of layering and squeezing each other with two insoluble liquids and a wafer level phosphor coating method which utilizes the square hole mask to leash the flow of phosphor gel.The detailed contents and innovations are as follows:1)For typical high-power LED,based on the insolubility of alcohol-water droplet and pure silica gel and the distinct layered interface between alcohol-water droplet and pure silica gel,alcohol-water droplet can be used to fabracate the free-form surface structure,then,dispense phosphor gel on the free-form surface structure,which can improve the color uniformity of the LED module by adjusting the distribution of phosphor.The test results show that with the average correlated color temperature of 4500 K,5500 K,6500 K and 7500 K,the maximum correlated color temperature deviations of the white LED modules packaged by proposed remote coating method were 245 K,549 K,812 K and 1636 K,respectively,compared with the white LED module fabricated by dispensing coating,the maximum correlated color temperature deviation value of the white LED modules fabricated by proposed remote coating method were reduced by 64.1%,61.7%,57.7%,and 41.2%,respectively.2)For high-power flip LED chip,an optical model of the CSP-LED was established,and the effects of the width and thickness of the phosphor layer on the light extraction efficiency and color uniformity of the CSP-LED module were simulated and analyzed which provides a theoretical reference for the wafer-level phosphor layer coating process.The simulation shows that when the width of the phosphor layer is in the range of 1100 μm to 1600 μm and the thickness is in the range of 200 μm to 450 μm,with a similar average correlated color temperature,the width and thickness of the phosphor layer have little effect on the light output efficiency;the narrower width and the thinner thickness of the phosphor layer,the more effectively to improve the color uniformity of the LED.3)For high-power flip LED chip,a wafer-level phosphor coating process was realized with a square-hole mask,which was designed based on the simulation.The CSP-LED array was fabricated by the wafer-level phosphor coating method.then,the light quality of the CSP-LED modules was analyzed.For a CSP-LED module with a correlated color temperature near 5615 K,the color uniformity is as high as 89.4% in the viewing angle of-90° ～ 90°,and the color uniformity is as high as 96.1% in the viewing angle of-75° ～ 75°;when the driving current is increased from 300 m A to 400 m A,the correlated color temperature is only increased by 61 K,and the light extraction efficiency is only reduced by 2.63%.Therefore,with the rated driving current 350 m A,the light quality of CSP-LED is relatively stable.The color temperature values of all samples were in the range of 5000 K to 6000 K,the maximum correlated color temperature deviation between CSP-LED modules is 509 K,compared with the average color temperature of all samples,the maximum correlated color temperature deviation rate does not exceed 4.65%;the average lumen efficiency of all samples is 123.46 lm/W,the maximum deviation of lumen efficiency is 15.86 lm/W,the maximum deviation rate from the average lumen efficiency is 6.61%;the average light output efficiency of all samples is 33.98%,the maximum deviation of light output efficiency is 4.59%;Therefore,the wafer-level phosphor coating based on the squarehole mask can meet the consistency of LED products.