Research On The Preparation Of Phosphor Layer And Optical-thermal Performances Optimization For LED Packaging

Light-emitting diode（LED）has been widely used in many fields of modern life as the new generation of light source due to its advantages of high efficiency,long life,small size,energy saving and environmental protection.The packaging technology can determine the optical and thermal performances as well as reliability of LED products.There are still many problems about the existing packaging technology such as poor angular color uniformity（ACU）,low light efficiency（LE）,low color rendering index（CRI）and poor heat dissipation ability,which seriously influence the further promotion of LED.In this dissertation,the phosphor coating process of LED packaging was studied in order to improve the optical and thermal performances of LED module through improving the structure and heat dissipation solution for phosphor layer.The manufacturing process of the improved phosphor layer structures and heat management technologies for phosphor layer were realized by existing LED packaging technology and technologies in other field which were simple,low cost and feasible.The detailed contents and their innovations are shown as follows:（1）In order to improve the ACU of LED module,a method to manipulate phosphor particles spatial distributions in phosphor layer by silicone gel selective laser curing was proposed.The selective curing process of silicone gel doped with phosphor particles by laser local heating and its influences on spatial distributions of phosphor particles were analyzed by simulation and the prepared phosphor layer by selective curing process was proved to be able to realize good ACU.The experimental results show that the maximum correlated color temperature（CCT）deviation of LED module encapsulated with the selective cured phosphor layer is only 184K,268K and 1315K at average CCT of 5500K,8000K and 16000K,respectively.Compared with LED module with phosphor layer where phosphor particles were uniformly distributed or totally settling on the surfaces of the substrate and the chip,the ACU is improved by more than 70%.Besides,the spatial distribution of light intensity of the LED module with selectively cured phosphor layer is not changed when compared with the LED module with the phosphor prepared only by free coating.（2）In order to enhance the light extraction efficiency（LEE）of LED module,a patterned phosphor layer structure formed by a red phosphor layer with microstructure patterned on the surface stacked on Y₃Al₅O₁₂:Ce³⁺(YAG:Ce³⁺)phosphor-in-glass（Pi G）was proposed.The process of water droplet imprinting to produce microstructure on polymer surface was simulated by air-water-polymer three phase flow model based on phase field method.The influence of surface tension between water and polymer on the aspect ratio of microstructure was studied.The parameters such as operation current and operation time of thermo electric cooler（TEC）which can form uniform microstructure on surface of polymer were obtained by experiments.The polymer film doped with red phosphor particles was spin-coated on the YAG:Ce³⁺Pi G which was prepared by screen-printing and sintering processes.The concave microstructures on the surface of the polymer film with average ratio of 1.02,0.75 and 0.40were prepared by changing the ultraviolet（UV）pre-exposure time,and the experimental results show that the LEE of the LED module with the three patterned phosphor layer is increased by 8.49%,14.01%and 7.86%when compared with LED module packaged with unpatterned phosphor layer,respcectively.The CRI of all three LED modules with patterned phosphor layer are higher than 79.（3）In order to enhance the optical and thermal performances stability of quantum dot（QD）based LED module,a composite phosphor layer structure formed by stacking QD,sapphire with high thermal conductivity and Pi G together（QD-PSC）was proposed.The Pi G was prepared on sapphire substrate with high thermal conductivity by screen-printing and sintering processes while the red QD film was prepared by molding and UV-curing processes.The experimental results show that the surface temperature of LED based on QD-PSC is lower than that of LED based on QD stacked on Pi G（QD-Pi G）and LED based on phosphor in silicone gel（QD-Pi S）.The value deviations of CCT and LE of the LED based on QD-PSC caused by the variations of working current are also smaller.The LE of LED based on QD-PSC is reduced by 5%after working at 350 m A for 100h which is better than the reduction of 10.2%and 31.4%for LED based on QD-Pi G and QD-Pi S,respectively.（4）In order to lower the junction temperature and improve the LE of LED filament lamp,an approach to enhancing the heat convection effect on the surface of the phosphor layer of LED filament by producing ionic wind through corona discharge was proposed.The operation parameters such as the number of needle electrodes,the gap between the needle electrode and ring electrode and their influences on the flow rate of ionic wind were studied by theoretical analysis and experiments.The ionic wind generator made up of three-needle electrodes and ring electrode was embedded in the bulb to test the cooling ability of ionic wind on LED filaments.Compared with situation that there is no ionic wind generated within the bulb,the maximum temperature drop is 17.6°C and 30°C when the gap between the ring and the needle is 10mm and 15mm,respectively.Owing to the cooling effect of ionic wind,the LE of the LED filament bulb is increased by 3.2%and 5.8%at best when the gap between the ring and the needle is 10mm and 15mm,respectively.