Since the 21st century, human energy has become increasingly serious, and China’s energy situation is also very serious. Saving energy is as important as developing new energy; while saving energy is more economical and environmentally friendly, it should be in the first place. At present, lighting accounts for about 20% of the world's total energy consumption. If the low-efficiency, high-energy-consumption traditional light source is replaced by a light source with low energy consumption, long life, safety and environmental protection, it will undoubtedly bring about a worldwide lighting revolution, which is more strategic for China's sustainable development. Ultra-high-brightness light-emitting diodes (LEDs) consume only 1/10 of the energy of traditional light sources. They have the advantages of not using heavily polluted mercury, small size, long life, etc., first entering industrial equipment, instrumentation, traffic lights, and automobiles. , special sources of lighting such as backlights. With the improvement of the performance of ultra-high brightness LEDs, power LEDs are expected to replace illumination sources such as incandescent lamps and become the fourth generation of illumination sources. The packaging materials used in power LED devices require a refractive index higher than 1.5 (25 ° C) and a light transmittance of not less than 98% (wavelength 400 800 nm, sample thickness 1 mm). At present, the packaging material of ordinary LED is mainly bisphenol A type transparent epoxy resin. With the development of white LEDs, especially the development of white LEDs based on ultraviolet light, it is required that the outer packaging material can have a high absorption rate of ultraviolet light while maintaining high transparency in the visible light region to prevent leakage of ultraviolet light; In addition, the packaging material also needs to have strong resistance to ultraviolet light aging. After long-term use of epoxy resin, yellowing will inevitably occur under the ultraviolet light emitted by the LED chip, resulting in a decrease in light transmittance and a decrease in brightness of the LED device. In addition, the thermal resistance of epoxy resin is as high as 250 ~ 300 ° C / w, poor heat dissipation will lead to a rapid rise in the junction temperature of the chip, thereby accelerating the light decay of the device, and even failing due to the open stress caused by the rapid thermal expansion. Therefore, with the rapid development of LED research and development, the requirements for packaging materials are getting higher and higher, and epoxy resin can not fully meet the packaging requirements of LED. This paper mainly introduces the application progress of organic silicon in LED packaging materials in recent years. 1 silicone modified epoxy resin LED packaging material The use of silicone modified epoxy resin as encapsulation material can improve the toughness and cold resistance of the packaging material, and reduce its shrinkage rate and thermal expansion coefficient. The most straightforward method is to prepare a silicone-modified epoxy resin and then vulcanize it to obtain an LED packaging material. DAHaitko et al. used 4-vinyl hexylene oxide catalyzed by barium sulfate with tris(dimethylsiloxy)phenylsilane, bis(dimethylsiloxy)diphenylsilane, 1,7-( Reaction of dimethylsilyloxy)-3,3,5,5-tetraphenyltetrasilane, etc., to obtain a silicone-modified epoxy resin, which is then vulcanized to obtain excellent cold and thermal shock resistance and radiation resistance. , LED package with high transmittance and thermal expansion coefficient similar to the chip. K. Kodama et al. hydrolyzed and condensed an epoxy group-containing siloxane with a basic catalyst to obtain a silicone/epoxy oligomer. The outstanding advantages of the material after vulcanization molding were Na+, K+, Cl-. The mass fraction of plasma is lower than 2×1O-6 and has excellent insulation performance. In addition, the Shore D hardness of the material is up to 35 degrees, and the bonding performance is good. It is also impacted by -20 °C/120 °C for 100 times. No cracking. In order to improve the heat resistance and thermal conductivity of such LED packaging materials, inorganic fillers having a particle diameter of less than 400 nm, such as quartz powder, single crystal silicon, aluminum powder, zinc powder, and glass fiber, are often added. H.Ito et al. added silica with a particle size of 5 to 40 nm and spherical glass powder with a particle size of 5 to 100 nm to the silicone-modified epoxy resin. The transmittance of the material after vulcanization molding can reach 95.7 %. (25 ° C), the refractive index is 1.53 ~ 1.56 (sample thickness 1 mm, wavelength 589.3 nm), the coefficient of linear expansion is about 40 × 10 K, after 200 times a 25 ° C / 125 ° C cold and thermal shock damage rate is only 4% ~ 12.5 %. In addition to directly using silicone-modified epoxy resin as a packaging material, a silicone-modified epoxy resin can be blended with a silicone resin to form an LED packaging material. GE Corporation of the United States uses phenyltrichlorosilane, methyltrichlorosilane, and dimethyldichlorosilane to co-hydrolyze polycondensation to prepare a hydroxy silicone resin; then blending it with a silicone-modified epoxy resin, using hexa-hydroxy- 4～methyl-phthalic anhydride as a curing agent, stannous octoate as a curing accelerator, and heat vulcanization molding to obtain a packaging material with an adjustable refractive index (1.2-1.6). The material is irradiated by a light wave at a wavelength of 380 nm for 500 h or at 500 ° C for 500 h at a wavelength of 400-450 nm in an artificial aging machine, and the light transmittance is still as high as 80% or more (sample thickness 5 mm). If a phosphorus compound, a phenol derivative, a transparent metal oxide (such as an oxide of titanium, magnesium, lanthanum, zirconium, aluminum, etc.) is added to the mixture, the thermal conductivity of the encapsulating material can be improved and the moisture resistance can be improved. The addition of inorganic fillers also reduces the coefficient of thermal expansion of the LED package material. For example, TBGorczyca has a refractive index of 1.52 and a thermal expansion coefficient of a blend of an epoxy resin having a refractive index of 1.55 and a thermal expansion coefficient of 6×10 K and a silicone resin having a refractive index of 1.46 and a thermal expansion coefficient of 200×10 K. 0.65×10 K is called quartz glass powder, and a package material with a refractive index of not less than 1.50 and a thermal expansion coefficient of 5×10 K is obtained. The above LED packaging materials have poor solvent corrosion resistance. In order to overcome this shortcoming, YKSuehiro et al. blended and vulcanized hydroxy silicone resin with silicone epoxy resin and bisphenol A epoxy resin at 100-200 C to obtain a transparent encapsulating material with good solvent resistance. The material also has a high refractive index (refractive index of 1.49 at a source wavelength of 1 700 nm and a refractive index of 1.58 at a wavelength of 350 nm), and is excellent in heat resistance and moisture resistance. In order to improve the hardness, cold and thermal shock resistance of the material, and reduce its modulus and shrinkage, H. Shin-Etsu Chemical Co., Ltd. added silicone-containing vinyl silicone resin, hydrogen-containing silicone oil and a small amount of silicone elastomer to the epoxy resin. The platinum-based catalyst is used to catalyze the hydrosilylation reaction, and the alkoxy or acyl or silanol aluminide is used as an epoxy curing agent. After injection molding, the refractive index is up to 1.51, the Shore A hardness is 70 degrees, no dusting, and low mode. The amount of LED shrinkage material with low shrinkage; and the package material is not cracked by thermal shock at 1000 ° C / 12 ° C for 1 000 times. In addition, in order to save costs and simplify the process, DAHaitko directly cured the epoxy resin with silicone anhydride to produce a silicone-modified epoxy resin LED packaging material. The packaged material has a refractive index of 1.45 and a light transmittance of 88 at a wavelength of 400 nm. The transmittance is reduced by less than 10% after being irradiated with a 405 nm UV lamp for 40 h at 100 °C. 2 silicone LED packaging materials Although the performance of the epoxy resin encapsulant can be improved by the modification of the silicone; the molecular structure of the silicone-modified epoxy resin contains an epoxy group, and as the LED encapsulant, there are still disadvantages such as poor radiation resistance and yellowing. It is difficult to meet the technical requirements of power LED packages. To this end, people have successively developed high-refractive index, high transmittance, epoxy-free silicone LED packaging materials. The vinyl silicone resin and the hydrogen-containing silicone oil are vulcanized by a hydrosilylation reaction to form a silicone LED packaging material. In order to obtain a high refractive index, radiation resistant silicone encapsulant, the vinyl silicone resin and the hydrogen containing silicone oil generally need to contain a certain amount of diphenyl siloxane or methyl phenyl siloxane. K.Miyoshi_1 and T.Goto et al. r1 obtained a vinyl silicone resin by a chlorosilane co-hydrolysis condensation process, and then vulcanized with a phenyl silicone-containing hydrogen-containing silicone oil catalyzed by a platinum catalyst to obtain an LED package material. . The refractive index of the material can reach 1.51, the Shore D hardness is 75-85 degrees, the bending strength is 95-135 MPa, the tensile strength is 5.4 MPa, and the light transmittance is reduced from 95% to 92% after 500 hours of ultraviolet radiation. In order to reduce the shrinkage rate of such silicone materials and improve their resistance to cold and heat cycle impact, the mass fraction of phenyl groups in the encapsulating material can be improved; even excellent mechanical properties and bonding properties can be obtained, and can withstand 1 000 times. A 50 ° C / 150. C hot and cold cycle impact without cracking silicone packaging material. Because they are not reinforced, these silicone encapsulants have poor hardness and strength and still cannot meet certain technical requirements of LED packaging materials. K.Miyoshi adds fumed silica, heat conductive filler, light wave modifier, flame retardant, etc. to methylphenyl hydrogen silicone oil and vinyl silicone resin, and cures at 120-180 ° C for 30-180 min. The flexural strength of the material is 95-100 MPa, the tensile strength is 5.4 MPa, the Shore D hardness is 75-85 degrees, and the refractive index is as high as 1.51. After 100 h of radiation from a 400 nm wavelength source, the transmittance decreases from 95 to 92%. It was still 92% after 500 h of irradiation. Silicone LED packaging materials can also be made by adding liquid silicone rubber. T. Shiobara et al. used additive liquid silicone rubber at 165. Under C injection molding, a package material having a shrinkage ratio of 3.37, a shrinkage ratio of only 0.04, and a refractive index of 1.50 to 1.60 (wavelength of 400 nm) was obtained. E.Tabei et al. even obtained an LED package material l with a Shore D hardness of 50 degrees, an elastic modulus of 350 to 1 500 MPa, a light transmittance of 88% to 92% (wavelength of 400 nm, and a sample thickness of 4 mm). Adding an appropriate amount of inorganic filler (such as oxides of boron, silicon, titanium, aluminum, zinc, etc.) to the addition liquid silicone rubber can improve the heat resistance and radiation resistance of the material, and the obtained LED packaging material is used at 450 ° C for 450~ When the light is irradiated at 470 nm for 1 000 h, the light transmittance drops by less than 10%. Under normal circumstances, the LED packaging material needs to be vulcanized at a certain temperature for 2 to 5 hours, and the production cycle is long. L D. Boardman et al. used D4 and 1,3,2-divinyl-1,1,3,3,tetramethyldisiloxane (vinyl double head) to undergo ring-opening polymerization under concentrated sulfuric acid catalysis. Vinyl silicone oil; then, the hydrogen-containing silicone oil, the platinum catalyst and the sensitizer are added in proportion, and the mixture is uniformly mixed and then irradiated with visible light or ultraviolet light for 2.5 to 20 minutes to be completely cured, thereby obtaining a LED package material with better performance. The blend of vinyl silicone resin and vinyl silicone oil and hydrogen-containing silicone oil are cured by a hydrosilylation process, which can take advantage of the respective advantages of silicone resin and silicone rubber to obtain a high-performance LED packaging material. The LED package material obtained by this method by M.Yoshitsugu et al. has a refractive index of 1.54, a light transmittance of 85 to 100, a Shore A hardness of 45 to 95 degrees, a tensile strength of 1.8 MPa, and a heating of 100 hours at 150 ° C. Cracks appear. As mentioned above, the silicone LED packaging material generally needs to adopt a platinum catalyst in the preparation process, and the platinum catalyst often turns yellow after being left for a while, and the continued use will affect the light transmittance of the LED packaging material. In order to overcome this shortcoming, K. To~moko et al. developed a platinum catalyst which is difficult to change color and uses organosiloxane as a ligand, namely 1,3 dimethyl- 1,3-diphenyl- 1 , 3 - divinylsiloxane platinum complex, using this catalyst to catalyze the vulcanization molding of the addition of silicone rubber, to obtain an LED packaging material with a refractive index higher than 1.50 and a light transmittance of 92 to 100. 3 Conclusion Silicone materials have the advantages of resistance to thermal shock, ultraviolet radiation, colorless transparency, etc. They are ideal packaging materials for white light power LEDs and are widely concerned by researchers and lighting source manufacturers. In order to improve the refractive index and radiation resistance of the LED packaging material, it is necessary to introduce an appropriate amount of phenyl groups in the polysiloxane molecule, and to uniformly disperse the phenyl group; at the same time, it is necessary to comprehensively consider the optical properties, mechanical properties, and production of the material. Cost and other factors. With the deepening of research, it is certain to develop silicone packaging materials that meet the packaging requirements of white light power LEDs in different environments and different application fields. White light power LEDs are also expected to be used as ordinary lighting sources in the near future. . Edit: Cedar
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