Study On Light Aging And Preparation Of Epoxy Packaging Materials For LED Applications

RGB LED device uses red,green,and blue(RGB)three primary color LED lights or chips to achieve white and full-color light emission.And due to its high color rendering index,high reliability,and large color rendering range,it is widely used in the field of white light illumination and display.In terms of its packaging materials,bisphenol A epoxy resin has the advantages of low cost and excellent comprehensive properties,and is widely used in LED packaging.And the cycloaliphatic epoxy resin has excellent UV aging resistance and low curing shrinkage,which is often used in outdoor LED packaging.However,nowadays RGB LED device is facing the problems of color deviation and warpage caused by the aging of packaging materials and deformation during molding respectively,which severely limits the device's market promotion and application prospects.Therefore,this thesis mainly focuses on the problems of aging and warping of packaging materials,and conducts research on the light aging properties of epoxy resin packaging materials and the preparation of modified packaging materials,which contribute to solving the problems in the molding and use of RGB LED devices for practical significance and industrial application prospects.First of all,in order to solve the problems of color decay and color deviation after using RGB LED devices for a period of time,two epoxy systems,bisphenol A epoxy resin(DGEBA)and alicyclic epoxy resin(ECC),were studied.Combining device performance,structure characterization of its packaging material and quantum chemical theoretical calculations,the aging study was designed to reveal the aging mechanism of packaging materials.During the study,Array spectrometer,ATR-FTIR and XPS were used for characterization.The results showed that blue light induced degradation and aging reaction on the surface of LED packaging materials.The aging reactions involved post-curing reaction,active hydrogen oxidation reaction,chain scission and rearrangement reactions of C-C,C-O-?(?represents benzene ring or carbon)or ester groups.And several possible aging reaction processes were proposed.The results of quantum chemical theoretical calculations further showed that the C-O bond of C-O-?in the main chain of DGEBA epoxy system was most easily broken during aging.The possible aging reaction might involve the rearrangement reaction of the C-O-?structure to form the?-O-?structure after the C-O bond was broken,or of the H atoms on the second carbon to form a carbonyl or ester structure.In the ECC epoxy system,the C-O bond in the ester group was more easily broken.And the possible aging reaction might involve the rearrangement reaction to form the carbonyl structure and the C-O-C structure,or the oxidation reaction of the H atoms on the secondary carbon to form a carbonyl or ester structure.Then,according to the results of the aging mechanism of packaging materials,the C-O-?structure in the DGEBA epoxy system is susceptible to occur chain scission,rearrangement and oxidation reactions induced by blue light.We speculate that it is related to the absorption of blue light due to the benzene ring.Therefore,hydrogenated bisphenol A epoxy resin(HBADGE)without benzene rings was used to explore the effect of the benzene ring.The thermodynamic and optical properties performances of the resin blends contained DGEBA and HBADGE and their neat resins were characterized.The results showed that when the HBADGE content was 30 wt%,the toughening effect of the composite was significantly improved.The transmittance of the epoxy system also increased obviously.The results of blue light aging test and the characterization of the transmittance of two neat epoxy resins showed that the transmittance of the HBADGE system in the blue light region first decreased and then stabilized after 192 hours as the aging time increased,while the DGEBA system still decreased after 192 hours.It was indicated that the DGEBA epoxy system containing benzene rings absorbed blue light,which led to chain scission,rearrangement and oxidation reactions and led to the decrease of the blue-light transmittance of DGEBA epoxy system.It further verified the aging mechanism of epoxy packaging materials.In addition,in order to reduce the thermal expansion coefficient of the packaging material that is susceptible to thermal stress and warping during use,and a filler with a negative thermal expansion coefficient is added to the epoxy resin composite.Negative thermal expansion nano powder tungsten zirconium phosphate(ZWP)was prepared by microwave hydrothermal-sintering method,and ZWP/DGEBA composites were prepared.And the structure and properties of powders and composites were characterized by FTIR,XRD,FE-SEM,TMA,DMA and so on.The results showed that the ZWP powder prepared by microwave hydrothermal method was smaller and more uniform in size and had better negative thermal expansion performance compared to the ordinary hydrothermal method.The CTE in the temperature range of 30?70?was approximately-23.8 ppm/K,and the CTE in the temperature range of 120?180?was about-4.6 ppm/K.The results of TMA characterization showed that ZWP powder had a significant reduction on decreasing the CTE of the DGEBA system,and the CTE decreased more as the ZWP content increased.For example,the CTE in the glass state(30?90°C)of the epoxy composite with 40 wt%ZWP content decreased by about 42.7%(about 30.5 ppm/K).Moreover,the overall performance of the ZWP/DGEBA composite material with 10 wt%ZWP content was better.Finally,focus on the problem that PCB(printed circuit board)in the COB(chip-on-board)packaging of RGB LED device is prone to serious warping due to curing shrinkage stress,the optimized design of formulation components and processes are used to prepare COB packaging materials with low-stress warping.The COB packaging process includes molding and post-curing steps.The molding step requires the formula to be cured rapidly.Therefore,orthogonal experiment design was performed on the three components(diluent,accelerator and toughener)in the formula that affect the rapid curing performance of molding.Under the same molding conditions,the curing degree of the 3A-B system was used as a reference index.The DSC was used to characterize the exothermic curve of the formula system before and after molding to obtain the corresponding curing degree.Finally,the optimal ratio of diluent,accelerator and toughener was obtained.The post-curing step requires the formulation to have low curing shrinkage internal stress and thermal stress.Therefore,another orthogonal experiment design was performed on the R value of the curing ratio,silica powder filler,and toughener,which affect the curing stress.The stress value SI was used as a reference index.The modulus,the glass transition temperature T_g,the glassy CTE and the rubbery CTE of the cured product were obtained by using DMA and TMA respectively to calculate the corresponding SI values.Finally,the optimal ratio of R value,silica powder filler and toughener was obtained.In addition,through the sifting of the size of silica powder,it was found that the silica powder owning a size of 2.70?m had good processing performance and low stress,and the optimized condition of post-curing process was 90°C for 2 h,110°C for 2h and 130°C for 2 h.Finally,through the curing experiments of PCB boards,the results of characterization showed that compared to 3A-B system(about 0.346%),the warpage rates of PCB boards cured by the three optimized formulas were all less than 0.1%,which indicated that the warpage problem of PCB boards had improved.And other comprehensive performance was also improved compared to 3A-B system.