Packaging Structure Design And Process Optimization Of Ultraviolet LED COB Module

Ultraviolet(UV)LED has the advantages of energy saving and environmental protection,long life,high efficiency,single and adjustable wavelength,etc.It has become an ideal substitute for UV mercury lamp which containing harmful mercury elements.However,it is difficult for a single UV LED chip or lamp bead to meet the requirements of UV high light energy density in the field of UV application.Therefore,it must be packaged in the form of multi-chip or multi-lamp module to improve the packaging density to provide higher light energy output.Chip on Board(COB)is a mature packaging technology that can directly attach multiple chips to the substrate.However,with the increase of chips,the packaging density also increases.Among them,heat management and optical design-based heat dissipation problems,reliability problems,light spots,irradiance uniformity and other problems are more prominent.In addition,the electric power of single UV LED is often larger,the quantum efficiency is often much lower than that of visible LED and many materials also absorb ultraviolet light,which makes these problems more prominent.Therefore,it is urgent to conduct systematic research on them.The academia has made great progress in packaging technology in the visible light LED field,while there is relatively little research on packaging technology in the UV LED field,and some tend to focus on epitaxial chip research,which restricts the development of the UV LED industry to a certain extent.So,it is necessary to conduct comprehensive and systematic research on UV LED packaging technology.In this paper,the thermal properties of three common COB packaging substrates were studied by using the method of finite element simulation,and the packaging density of the devices could be improved as far as possible under the premise of ensuring reliability.The results show that based on the size of the substrate is 13×13×1 mm and the reliability of the substrate is guaranteed,the aluminum substrate is not suitable for the packaging density greater than 0.38 W/mm~2.According to the trend,the alumina ceramic substrate can't meet the packaging density above 0.94 W/mm~2.Aluminum nitride ceramic substrate can meet the packaging requirements of higher packaging density,but its high price is an important factor to be considered in its large-scale application.These conclusions provide a reference for further research.Then,in the case of comprehensive consideration of cost,process and other factors and based on the metal substrate,through finite element simulation and combining the optical design analysis and experiment,the different factors such as the chip spacing,packaging structure,substrate and adhesive materials,adhesive packaging area and void rate influence on the thermal performance of UV LED COB module were comprehensively and systematically studied.We obtained the high performance,high reliability,low thermal resistance packaging structure of the UV LED COB module.The results show that,in the packaging structure,the optimal chip spacing about 2.5 mm can achieve lower junction temperature and higher irradiance.And the introduction of high thermal conductivity aluminum block plate to optimize the packaging structure is an effective way to improve the cooling effect.In the selection of packaging materials,although the material with higher thermal conductivity can promote heat dissipation,when the thermal conductivity of substrate and adhesive is greater than 240 W/(m K)and 60 W/(m K)respectively,the increasing of thermal conductivity of substrate and adhesive has almost negligible effect on the heat dissipation of UV LED COB module.In addition,in the packaging process,when the area ratio between the adhesive area(Sa)and the chip area(Sc)(Sa/Sc)=0.9,both excellent heat dissipation can be achieved,and the adhesive material can be minimized,at the same time,the adhesive material is avoided to block the light output and cause electricity leakage.Dispersed voids have better heat dissipation performance,because they have a larger contact surface area and increase the heat dissipation path along all directions.Through many experiments,the optimal parameters of reflow welding were obtained,that is,when the temperature of the eight temperature zones of reflow welding process were 100,130,160,190,230,255,255,215?,and the reflow speed was 0.65 m/min,better bonding welding quality could be obtained.It is worth mentioning that,by comparing the preparation sample test with the simulation results,the error is found to be about 3.2%,which confirms the reliability and effectiveness of the research method and research idea used in this paper.In this paper,we have made some achievements in the research of UV LED packaging technology with high performance,high reliability and low thermal resistance,which is of positive significance to promote the development of UV LED packaging technology.