Research progress on silicone resin for LED packaging

1. Modified epoxy resin for LED packaging

Epoxy resin has a high refractive index and light transmittance, and the mechanical properties and bonding properties are quite good, so there are still certain products on the market. By introducing a silicone functional group-modified epoxy resin, the high-temperature use performance and impact resistance of the epoxy resin can be improved, the shrinkage rate and thermal expansion property of the product can be reduced, and the application range of the product can be improved. According to the reaction mechanism, silicone modified epoxy resin can be divided into physical blending and chemical copolymerization. If purely relying on pure physical blending, the solubility coefficient of silicone and epoxy resin is quite different, the microscopic phase structure is easy to be separated, and the modification effect is not good. Generally, it needs to be improved by adding a transition compatible group. Its compatibility. SS Hou et al. used a hydrosilylation reaction of a hydrogen-containing polysiloxane with allyl glycidyl ether to prepare an epoxy group-containing polysiloxane, which was then blended with a bisphenol A type epoxy resin. The experimental results show that the microstructure of the modified product is better and there is no phase separation.

The chemical copolymerization method utilizes reactive groups on the silicone polymer, such as a hydroxyl group, an alkoxy group, etc., to react with a reactive group such as an epoxy group on the epoxy resin to form a copolymer for modification. As early as 2007, some people in foreign countries have used this method to develop epoxy resin encapsulation materials for LED products. The experiment proves that the method can make the impact resistance and high and low temperature resistance of the package material obvious. The increase, shrinkage, and coefficient of thermal expansion are significantly reduced. Deborah et al. used a condensation reaction to mix 4-vinyl oxirane with various silanes such as bis(dimethylsilane)tetraphenylcyclotetrasiloxane and tris(dimethylsilane)phenylsiloxane. The reaction produces a modified epoxy resin product which is excellent in impact resistance, strong in UV aging resistance, high in light transmittance, and has a thermal expansion coefficient satisfying the requirements of the chip product. Li Xueming et al. used UV curing technology to crosslink the polyorganosilsesquioxane and epoxy resin in situ to obtain high light transmission, thermal stability, UV aging resistance, excellent impact resistance and high adhesion. The epoxy polysiloxane silsesquioxane hybrid membrane material can be used to replace the currently used high temperature curing epoxy materials for LED, electronic packaging and other industries. Seung Cheol Yang and other alicyclic epoxy resins react with diphenyldihydroxy and triphenylhydroxyl to produce a high refractive index (1.58), good thermal stability, and UV-resistant silicone epoxy modified materials. Huang Yunxin et al first synthesized oligomeric silsesquioxanes of different molecular weights and modified bisphenol A epoxy resins with synthetic polyorganosiloxanes. The results showed that all three polysiloxanes can improve epoxy resins. Product toughness and flexural strength. Yang Xin et al. prepared a polyfunctional silicone epoxy resin by hydrolysis condensation reaction of 2-(3,4-epoxycyclohexyl)ethylmethyldiethoxysilane, using methyl hexahydrophthalic anhydride as curing agent. The obtained products have great improvement in light transmittance and heat aging resistance, and are expected to be popularized and applied in the field of LED packaging materials. Crivello. J and the like use an epoxy monomer containing a double bond to have an allyl glycidyl ether and a 4-vinyl epoxy cyclohexane, and a hydrosilylation reaction with a hydrogen-containing polysiloxane to synthesize a silicone modification Epoxy resin with good transparency and heat resistance.

Silicone epoxy resin has recently been widely used due to its advantages in both epoxy resin and silicone resin. It exhibits mechanical properties, adhesion, aging resistance, UV resistance, and refractive index. Excellent performance is the research direction of LED packaging materials in the future, and significant progress will be made.

2. Silicone resin for LED packaging

2. 1 Characteristics of silicone materials

The silicone polymer has a Si—O bond as the main chain and an organic group on the silicon atom, and may have R 3 SiO 1 /2 ( M) , R 3 SiO 2 /2 ( D) , R 3 SiO 3 /2 ( T ) , R 3 SiO 2 ( Q) The chain links are combined according to a certain ratio; the Si-O bond can be high, so that it has better high temperature resistance or radiation performance, and the Si-O bond angle is large, which makes the molecular chain of the material soft. . Silicone materials have excellent properties in terms of heat resistance and yellowing resistance. The silicone material is easily modified, and functional groups having an increased refractive index such as sulfur, benzene, phenol, and epoxy groups can be introduced into the side chain to increase the refractive index of the packaging material and improve the luminous efficiency of the LED.

2. 2 Synthesis of silicone resin

According to its refractive index, it can be divided into low refractive index (1.4) and high refractive index (1.5). The refractive index of 1.4 is mainly methyl type silicone material, and the refractive index of 1.53 is mainly phenyl type silicone material. Since the refractive index of the silicone material is larger, the light extraction efficiency is higher, so the refractive index of the silicone material should be increased as much as possible.

The silicone resin is generally obtained by using an organosilane as a raw material and hydrolyzing and polycondensing in the presence of a solvent. The raw materials synthesized are generally chlorosilanes or alkoxysilanes. The specific process is as follows: first, the silane is hydrolyzed to silanol under certain conditions, second, the silanol itself undergoes polycondensation reaction, and the third is washed and neutralized by water, and concentrated to remove small molecules to obtain a silicone resin. For example, Xu Xiaoqiu first hydrolyzed methylphenyldiethoxysilane, pyrolyzed it into a methylphenyl ring, and then synthesized it by anionic ring-opening polymerization to synthesize a phenyl vinyl silicone oil with a colorless transparency of 1.5 or more. Wu Tao et al. Preparation of vinyl-terminated methylbenzene under the action of a basic catalyst from an anionic ring-opening polymerization method using a cyclic methylphenylsiloxane containing a dimethylsiloxane chain and a vinyl double head. Base silicone oil. Wu Chuan et al. used acid catalysis, octamethylcyclotetrasiloxane (D4), or a mixture of 1,3,5,7-tetramethylcyclotetrasiloxane (D4H) and methylphenyl in toluene Polymerization in a solvent to prepare a cross-linking silicone hydrosilylation oil. The ratio of the amount of Ph to Si is 0.30 to 0.60, the mass fraction of active hydrogen is 0 to 0.5%, the refractive index is 1.39 to 1.51 (25 ° C), and the dynamic viscosity is 100 to 550 mPa·s. Wang Xiaotong et al. synthesized phenylvinyl transparent silicone resin by solventless method; vinyl trimethoxysilane, hydroxyl terminated polydimethylsiloxane, diphenyldimethoxysilane and phenyltrimethoxysilane were selected. The raw material and the aqueous hydrochloric acid solution are used as a catalyst to carry out a hydrolysis condensation reaction to synthesize a high refractive index transparent silicone resin having fluidity at room temperature. In order to reduce the surface tension of the LED encapsulant, Yang Xiongfa and others made it easy to vacuum defoaming, and prepared a transparent vinyl silicone oil containing a methyl trifluoropropyl silicon oxy-chain and a methylphenyl siloxane. Huang Ronghua et al. used methyl vinyl chlorosilane phenyl chlorosilane, methyl chlorosilane and phenyl chlorosilane as raw materials, and blocked with methyl heading agent and vinyl heading agent to synthesize phenyl vinyl silicone resin. Then, filtration with a pore size of 0.55 μm can effectively remove residual small particles of hydrochloric acid, improve product transparency, and obtain a colorless transparent vinyl phenyl silicone resin.

2. 3 Silicone resin in LED packaging materials

At present, there are many patents on LED packaging materials, and phenyl encapsulating materials are the most studied. Zhang Wei et al. used tetraphenylcyclotetrasiloxane and vinyl double head as raw materials, and polymerized at 80-100 ° C for 6-8 hours in the presence of a base catalyst to synthesize vinyl phenyl silicone oil; Silane and hydrogen-containing double head are used as raw materials, reacted at 70-80 ° C for 3 h in the presence of hydrochloric acid, and then washed with water to obtain hydrogen-containing phenyl resin. Vinyl phenyl silicone oil and hydrogen-containing resin are cured for LED packaging materials. It has high refractive index (>1.54), high light transmittance, good heat resistance and thermal shock stability. Yang Huan, Yang Gang, Gao Qun use hydrolytic condensation to obtain phenyl silicone resin: phenyltrimethoxysilane, diphenyldimethoxysilane, vinyltrimethoxysilane as raw material, aqueous hydrochloric acid as catalyst, temperature rise The hydrolysis condensation reaction was carried out for 6 hours, and finally distilled under reduced pressure at 120 ° C for 3 hours. After obtaining a transparent silicone resin at room temperature, a certain amount of hydrogen-containing silicone oil and a Pt catalyst were added to carry out a hydrosilylation curing reaction. Ding Xiaowei et al. obtained a phenyl-containing hydrogen-based silicone resin by first hydrolyzing an alkoxysilane into a prepolymer and then polycondensing it with a hydrogen-containing alkoxysilane. The process is simple, controllable and environmentally friendly, with a refractive index of up to 1.531. The inorganic ultrafine particle composite type silicone LED encapsulant prepared by introducing the modification of the inorganic oxide fine particles having a high refractive index has the advantages of high refractive index and strong anti-ultraviolet radiation. Zhang Wenfei et al. modified nano zinc oxide with N-(trimethoxysilylpropyl)-4-azido-2,3,5,6-tetrafluorobenzamide and grafted it onto the silicone polymer chain. The grafting reaction changes the refractive index of the nanocomposite and makes the refractive index of the ZnO nanoparticle and the silicone matrix more matching, which improves the refractive index of the silicone polymer, and has great prospects for LED packaging materials. Zhan Xibing and others used a non-hydrolyzed sol-gel to prepare a series of transparent titanium hybrid silicone resin. The refractive index of the resin is as high as 1.62, and the obtained product has good light transmittance and thermal stability. We use phenyltrimethoxysilane, methylphenyldiethoxysilane, methylvinyldimethoxysilane as raw materials, organic acid as catalyst, synthetic vinyl phenyl silicone resin, vinyl obtained. The phenyl silicone resin and the hydrogen-containing silicone resin are cured, the Shore D hardness is 55-75 D, the refractive index is > 1. 53. The light transmittance is more than 99%, and is preferably used for the LED packaging material.

At present, the main brands of high-refractive-index LED packaging products in foreign countries are: SR7010, OE26336, OE6550, JCR6175 and so on. Japan's Shin-Etsu company's products have excellent aging resistance. The main brands are: SCR-1012, KER-2500, LPS-5547, etc., Momentive's silicone has outstanding operability, and its main IVS series products are 5332, 5862, 4542. 4622 and so on. The high-fold LED package adhesive developed by Commet has good performance. The main models are KMT-1266, KMT-1269, KMT-1272 and so on.

3. Conclusion

GaN-based power type white LED is the focus of current development. It has the characteristics of large heat and short wavelength of light, and the requirements for the performance of packaging materials are also stricter. At the same time, the use of high refractive index, UV resistance, heat aging and low stress packaging materials can significantly improve the LED light output power, and can extend the life of the product. At the same time, the development of high power LED devices requires silicone packaging materials as early as possible. Developed products with high transparency, refractive index, UV aging resistance and heat aging. For the problems of silicone materials such as low refractive index, poor adhesion, low mechanical strength, etc., the advantages of the two are combined by epoxy modification, or hybridization with inorganic materials to improve the silicone material. Refractive index.