Semiconductor lighting technology is one of the most promising high-tech fields in the 21st century, and Light Emitting Diode (LED) is its core technology. A light-emitting diode is a type of light-emitting element that can directly convert electrical energy into light energy, that is, a semiconductor light-emitting device capable of emitting visible light, infrared light, or ultraviolet light when a forward current is applied to a semiconductor pn junction. Because it has low working voltage, low power consumption, high luminous efficiency, short response time, pure light color, firm structure, impact resistance, vibration resistance, stable and reliable performance, light weight, small volume and low cost. The characteristics have thus been widely applied and developed by leaps and bounds. Since the 1990s, with the rise of third-generation semiconductors represented by gallium nitride, blue, green, and white LEDs have been mass-produced. China has a good technology and industrial base in the field of LED lighting, and has formed an industrial chain from epitaxial wafer production, chip fabrication, and device packaging integration applications. At present, there are more than 400 large-scale enterprises engaged in the production of semiconductor LED devices and lighting systems in China. The annual output of ultra-high brightness LED dies of red, orange and yellow has exceeded 1 billion, accounting for about 12% of the world total. It is estimated that by the end of 2010, the global LED market demand will be about 210 billion, and the sales will reach 85 billion US dollars, and the value of China's LED industry will exceed 150 billion yuan. At present, LED products have occupied a considerable share in the international market, and packaging materials have also been widely used in LEDs, and their performance plays a key role in LED product applications. The LED is composed of a chip, a wire, a bracket, a conductive adhesive, a packaging material, etc., and the package is filled, potted or molded to fill the liquid glue into the device containing the electronic component and the line, at room temperature or heating. Under conditions, it is cured into a thermosetting polymer insulation material with high light transmittance (transmission of a sample having a thickness of 1 mm at a wavelength of 450 nm at a wavelength of more than 99%), high refractive index, high weather resistance, and ultraviolet radiation resistance. It can enhance the integrity of electronic devices, improve the resistance to external shocks and vibrations, improve the insulation between internal components and circuits, avoid linear exposure of components and lines, and improve the waterproof and moisture-proof performance of devices. The packaging materials currently used are mainly high transparency materials such as epoxy resin, polycarbonate, polymethyl methacrylate, glass, silicone, etc., in which polycarbonate, polymethyl methacrylate and glass are used as outer lens. Materials, epoxy resins and silicones are mainly used as packaging materials and as lens materials. 1 epoxy resin packaging material Epoxy resin has excellent adhesion, electrical insulation, sealing and dielectric properties, low cost, flexible formulation, easy molding, high production efficiency, and is the mainstream of LED, electronic devices and integrated circuits. material. Epoxy resin refers to a polymer compound containing two or more epoxy groups in the molecule. The epoxy group is more active and can be cross-linked with amines, acid anhydrides, imidazoles, phenolic resins, etc. to form insoluble or not. A molten polymer having a three-dimensional network structure containing a large number of polar groups such as a hydroxyl group, an ether bond, or an amino group, thereby imparting many excellent properties to the material, such as: high adhesion, insulation, and resistance Corrosive and low shrinkage. There are many types of epoxy resins, which are mainly classified into glycidyl ether type, glycidyl ester type, aliphatic group, and alicyclic group according to the structure. Different structures of epoxy resin may affect the performance of the packaged products, such as: The bisphenol A diglycidyl ether epoxy resin has an ether bond, a benzene ring and an isopropyl group in the main chain, and a secondary hydroxyl group in the side chain, wherein the polar ether bond and the hydroxyl group provide better wettability and stickiness. Attachment, benzene ring and isopropyl group give it good heat resistance and rigidity, but due to the benzene ring in the main chain, it is prone to photodegradation and aging and discoloration and yellowing, affecting the service life of LED devices; alicyclic epoxy The epoxy group of the resin is directly attached to the alicyclic ring to form a tight rigid molecular structure, so that the cured material has a high heat distortion temperature, and the molecule does not contain a benzene ring, so it has good ultraviolet light resistance. Internal stress is generated during the curing process to make it poor in other properties. 2 modified epoxy resin packaging materials Although epoxy resin packaging materials have many advantages, they also have defects, such as: aging, discoloration, brittleness and the like, for which modified epoxy resin packaging materials have emerged. The modification of epoxy resin mainly includes: improving light stability, improving heat resistance, increasing toughness, and increasing refractive index. Improving light stability mainly refers to improving the ability of epoxy resin to resist ultraviolet light aging. 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 maintain high transparency in the visible light region while having a high absorption rate of ultraviolet rays to prevent ultraviolet rays from leaking. The method for improving the photostability is mainly to add a light stabilizer to the epoxy resin, and the light stabilizer is an inorganic or organic ultraviolet absorber. For example, Li Yuanqing and other use of o-hydroxybenzophenones, benzotriazoles and hindered amines as organic light stabilizers can significantly improve the absorption of ultraviolet light without affecting the light transmittance of the epoxy resin in the visible light region; Inorganic light stabilizers are mainly nano-fillers such as ZnO and TiO2. It is important to note that it is very important to select a suitable filler particle size. If the particle size is too large, light scattering is caused, and the light transmittance is reduced. Blue shift occurs, reducing the light shielding effect of the material. Increasing the heat resistance of the epoxy resin encapsulating material mainly means increasing the glass transition temperature (Tg) thereof, and the modification method used is usually a combination of a heat resistant resin such as a novolac epoxy resin or a polyfunctional epoxy resin; A suitable curing catalyst is also beneficial for increasing the Tg of the material; the use of silicone-modified epoxy resins also improves the heat resistance of the packaging material. Toughening of epoxy resin generally adopts general toughening method, such as introducing a polyether segment with better toughness on the epoxy resin skeleton; conventional rubber toughening method can also be used, such as adding 015% to epoxy resin. 310% of nitrile rubber can improve its crack resistance; using polyamic acid in phenolic epoxy resin can reduce internal stress and improve crack resistance; add silane couple to epoxy resin/anhydride component The co-processed silicon micropowder is also beneficial for reducing the internal stress of the cured resin. The refractive index is increased by introducing sulfur into the epoxy resin, and the introduction form is mostly a thioether bond, a thioester bond, a thiourethane, etc., and the sulfur element is introduced into the polymer monomer in the form of an epoxide. The polymerization of an episulfide group as a reactive group is a relatively new method. The epoxy resin silsesquioxane and epoxy resin hybrid encapsulation material can not only improve the defects of epoxy resin, such as heat resistance and yellowing, but also keep the material high transmittance; The addition of nano-MgO filler to the material can improve the thermal conductivity of the cured product. Adding a mass fraction of 012% MgO filler will enhance the light transmittance and thermal conductivity of the cured product. 3 silicone packaging materials The main chain of silicone is Si-O-Si, the side group is methyl, and the whole molecular chain is spiral. This special hetero-chain molecular structure gives it many excellent properties, such as: Si-O bond length and bond angle are relative Larger, the bond has less steric hindrance to the side group rotation, the chain segment is very compliant, and thus has better low temperature resistance, and the Si-O bond energy is relatively high, so that it has good thermal stability and weather resistance. It can work in a wide temperature range ( - 50~ 250°); low surface energy (21~22mN /m) makes it have good hydrophobicity; low surface tension and flexibility can increase the permeability of polymer system . The above characteristics make the silicone have high light transmittance, good thermal stability, strong ultraviolet light resistance, low internal stress, low hygroscopicity, and superior performance to epoxy resin, making it an ideal choice for LED packaging materials. With the emergence and development of high-brightness long-life white LEDs and lead-free reflow soldering processes, silicone LED packaging materials have attracted the attention of researchers at home and abroad, and have become a new development trend and research hotspot of current LED packaging materials. The silicone material for LED encapsulation is generally prepared by a hydrosilylation reaction of a siloxane monomer or polymer containing an active hydrogen with a silicone polymer having an unsaturated bond under the action of a catalyst. Shiobara et al. firstly synthesized vinyl-terminated silicone oils with different degrees of polymerization by hydrosilylation, and then solidified with hydrogen-containing silicone resin cross-linking agents. The obtained encapsulants remained 94% after aging for 200°. Light transmittance; Kashiwagi uses three different functional groups of siloxane for hydrosilylation, the prepared encapsulant has excellent impact resistance and is well casted; Kesong will be a silicone monomer, a fatty alcohol, an organic solvent and The organometallic compound hydrolysis catalyst is polymerized together to obtain a vinyl silicon high polymer, and a curing catalyst and an inhibitor are separately added to form A and B components, and then a packaging material is prepared according to 1:1 to 1:20, and the material has High refractive index and excellent heat aging resistance. 4 modified silicone packaging materials Silicone materials have lower refractive index, and have defects such as poor corrosion resistance, low bond strength, poor mechanical properties and high production cost. With the diversification of LED applications, higher requirements are placed on LED packaging materials. Organosiloxanes do not fully meet the requirements and require further modification to ensure the reliability of packaged devices. At present, modified silicone packaging materials mainly improve the performance of silicone materials by selecting base polymers with certain active links or adding high-performance fillers. For improving the refractive index and radiation resistance of the material, a silicone resin containing a certain amount of diphenyl siloxane or methyl phenyl siloxane can be selected to prepare a silicone encapsulating material. Such materials have low shrinkage and good thermal shock resistance. In order to improve the hardness and strength of silicone materials, K. Miyoshi adds gas phase white carbon to methylphenyl hydrogen silicone oil and vinyl silicone resin. Black, thermal conductive filler, light wave modifier, flame retardant, etc. After curing at 120 ~ 180 ° for 30 ~ 180min, the bending strength of the packaging material is 95 ~ 100MPa, tensile strength is 514 MPa, Shore D hardness is 75 ~ 85 Degree, refractive index up to 1.51; the use of nano-inorganic oxide sol and silicone polymer system composite packaging materials can not only improve the refractive index and UV radiation resistance, but also improve the overall performance of the material, which is due to silicone resin and The components of the machine are combined at the molecular level to form a nano-inorganic oxide-modified silicone polymer without phase separation. 5 Conclusion With the continuous improvement of LED brightness and power and the development of white LEDs, the defects of traditional epoxy resin packaging materials such as aging, discoloration and internal stress have greatly affected the performance of LED devices. Compared with epoxy resin, silicone material has the advantages of thermal shock resistance, ultraviolet radiation resistance, low moisture absorption and good insulation. It is an ideal packaging material for white light power LEDs, and is supported by researchers and lighting source manufacturers. Widely concerned, and the silicone packaging materials with excellent comprehensive performance through modification are the research direction of high-end LED packaging in the future, which has broad application prospects and huge economic benefits. Edit: Cedar Rectifier bridge is to seal the rectifier tube in a shell. Points full bridge and half bridge. The full bridge connects the four diodes of the connected bridge rectifier circuit together. The half bridge is half of four diode bridge rectifiers, and two half bridges can be used to form a bridge rectifier circuit. One half bridge can also be used to form a full-wave rectifier circuit with a center-tapped transformer. Select a rectifier bridge to consider. Rectifier circuit and operating voltage. Bridge Rectifier,Original Bridge Rectifier,Full Bridge Rectifier ,Diodes Bridge Rectifier,Single Phase Rectifier Bridge, Three Phase Bridge Rectifier YANGZHOU POSITIONING TECH CO., LTD. , https://www.cnchipmicro.com