Research Progress of Organic Silicone for electronics
This article reviews the research progress in the preparation and application of organic silicon materials at home and abroad, introduces the applications of organic silicone for electronics in potting and LED packaging, and looks forward to the research progress and development trends of organic silicon materials.
1. Application of Organic Silicone for electronics in Potting and Sealing
From the perspective of cross-linking mechanism, organic silicon sealing materials can be divided into two types: condensation type and addition type. The condensation type organic silicon sealing material is based on hydroxyl terminated polydiorganosiloxanes as the basic polymer, and multifunctional silanes or siloxanes as crosslinking agents. Under the action of a catalyst, condensation reactions can occur at room temperature when exposed to moisture or mixed evenly, forming a network like elastomer. During the curing process, small molecule compounds such as water, carbon dioxide, methanol, and ethanol are released.
The addition of organic silicon sealant is an important development and application of the Sibel hydrogen silicification reaction in the vulcanization of silicone rubber. The principle is to perform silicification addition reaction between siloxane containing vinyl group and siloxane containing Si-H bond under the catalysis of Group VIII transition metal compounds such as (P), forming new Si – ℃ bonds to crosslink the linear siloxane into a network structure.
The addition molding of organic silicon sealing materials does not produce small molecules during the curing process, has a low shrinkage rate, good process adaptability, and high production efficiency. Since its emergence, addition type organic silicon sealing materials have developed rapidly, with a trend towards replacing condensation type organic silicon sealing materials – organic silicone for electronics.
1.1 Addition type liquid filled silicone rubber – organic Silicone for electronics
Addition type silicone rubber potting material is based on ethylene-based polydimethylsiloxane as the base polymer, low molecular weight hydrogen containing silicone oil as the crosslinking agent, and crosslinked into a network structure under the action of platinum based catalysts. Compared with traditional condensation type potting silicone rubber, it does not produce small molecule by-products during the vulcanization process, the crosslinking structure is easy to control, and the shrinkage rate of vulcanized products is small.
The product has superior process performance, which can be vulcanized at room temperature or under heating conditions, and can be deeply and rapidly vulcanized. The product has good processing performance, low viscosity, good flowability, and can be poured. It can be pumped and statically mixed, and has the advantages of simplified process, fast, efficient and energy-saving. Therefore, it is recognized as a highly promising electronic industry. Use new packaging materials – organic silicone for electronics.
The chemical industry uses low viscosity ethylene based silicone oil and low hydrogen containing silicone oil, with high-purity quartz powder as the filler and platinum complex as the catalyst, to prepare two-component addition liquid encapsulated silicone rubber. By changing the amount of quartz powder, the hydrogen content of the hydrogen containing silicone oil, and the molar ratio of silicon hydrogen to ethylene, silicone rubber with different crosslinking densities can be obtained. By designing the crosslinking structure, the performance of the addition liquid encapsulated silicone rubber can be optimized, resulting in excellent mechanical and electrical properties.
The tensile strength of XHG8310 liquid filled silicone rubber is 2.44MPa, with a Shore A hardness of 47 degrees and a fracture elongation of 136%. The tear strength is 3.88kN/m, the volume resistivity is 9.4X10 “Ω. cm, the relative dielectric constant is 3.1, the loss factor is 0.0011, the electrical strength is 21.5MV/m, the thermal conductivity is 0.4W/(m. k), the thermal expansion coefficient is 2.4×10’K, and the flame retardant grade is 94 V0. Its mechanical, electrical, thermal, and process properties are close to similar foreign products.
1.2 Thermal conductive silicone potting silicone rubber – Organic Silicone for electronics
Traditional thermal conductive materials are mostly metals, metal oxides, and other non-metallic materials such as graphite, carbon black, ALN, SiC, etc. With the advancement of science and technology and the development of industrial production, many special occasions such as aviation, aerospace, and electronic and electrical fields have put forward new requirements for thermal conductive materials, hoping that the materials have excellent comprehensive performance, can provide a safe and reliable heat dissipation path for electronic components, and can also play an insulating and vibration reducing role. Thermal conductive adhesive precisely meets this requirement, and thermal conductive silicone rubber is a typical representative of it. organic silicone for electronics.
The thermal conductivity of ordinary silicone rubber is poor, usually only about 0.2Wmk; Adding thermal conductive fillers can improve the thermal conductivity of silicone rubber. Common thermal conductive fillers include metal powders (such as A1, Ag, Cu, etc.), metal oxides (such as AlO;, MgO, BeO, etc.), metal nitrides (such as SiN, AIN, BN, etc.), and non-metallic materials (such as SiC, graphite black, etc.). Compared with metal powders, although the thermal conductivity of metal oxides and metal nitrides is poor, they can ensure that silicone rubber has good electrical insulation performance. Metal oxides contain AO; Among the most commonly used thermal conductive fillers, metal ammonia compounds are the most commonly used thermal conductive fillers.
These thermal conductive fillers have their own advantages and disadvantages, with metal and non-metal fillers having good thermal and electrical conductivity, while their compounds have high electrical insulation properties. The thermal conductivity of fillers is not only related to the material itself, but also closely related to the particle size distribution, morphology, interface contact, and degree of binding within the molecules of the thermal conductive fillers. Generally speaking, fibrous or foil shaped thermal conductive fillers have better thermal conductivity.
2. Organic silicon material for LED packaging – organic silicone for electronics
Since entering the 21st century, energy issues have become increasingly severe, and the energy situation in China is also very serious. Saving energy and developing new energy are equally important; Energy conservation is more economical and environmentally friendly, and should be given top priority. Currently, lighting accounts for about 20% of the world’s total energy consumption.
If low-energy, long-life, safe, and environmentally friendly light sources are used to replace traditional light sources with low efficiency and high power consumption, it will undoubtedly bring about a global lighting revolution and have strategic significance for China’s sustainable development. Ultra high brightness light-emitting diodes (LEDs) consume only 1/10 of the electrical energy of traditional light sources, and have advantages such as not using mercury that seriously pollutes the environment, small size, and long lifespan.
They first entered the field of special lighting such as industrial equipment, instruments and meters, traffic signals, automobiles, and backlights. With the improvement of ultra-high brightness LED performance, power LED is expected to replace incandescent lamps and other lighting sources as the fourth-generation lighting source. organic silicone for electronics.
The packaging material used for power type LED devices requires a refractive index higher than 115 (25 ℃) and a light transmittance of not less than 98% (wavelength 400~800nm, sample thickness 1mm). At present, the packaging material for ordinary LEDs is mainly bisphenol A-type transparent epoxy resin. With the development of white LEDs, especially those based on ultraviolet light, it is necessary for the outer packaging material to maintain high transparency in the visible light region while having a high absorption rate for ultraviolet light to prevent leakage.
In addition, the packaging material also needs to have strong resistance to ultraviolet aging. After long-term use, epoxy resin will inevitably undergo yellowing under the ultraviolet light emitted by LED chips, resulting in a decrease in its transmittance and a reduction in the brightness of LED devices. In addition, the thermal resistance of epoxy resin is as high as 250-300 ℃/W. Poor heat dissipation can lead to a rapid increase in the temperature of chip nodes, resulting in light attenuation of accelerator components, and even failure due to open circuits caused by stress generated by rapid thermal expansion.
Therefore, with the rapid development of LED research and development, the requirements for packaging materials are also increasing, and epoxy resin can no longer fully meet the packaging requirements of LEDs. This article mainly introduces the application progress of organosilicon in LED packaging materials in recent years.
2.1 Organic silicon modified epoxy resin LED packaging material – organic Silicone for electronics
The use of organosilicon modified epoxy resin as packaging material can improve the toughness and heat resistance of the packaging material, reduce its shrinkage rate and thermal expansion coefficient. The most direct method is to first prepare organosilicon modified epoxy resin, and then cure it to obtain LED packaging material. D1A1 Haitko et al. reacted 4-vinylepoxyhexane with tris (dimethylsiloxy) phenylsilane, di (dimethylsiloxy) diphenylsilane, 1,7- (dimethylsiloxy) -3,3,5,5-tetraphenyltetrasilane under rhodium sulfate catalysis to obtain organosilicon modified epoxy resin, which was then vulcanized and molded to obtain LED packaging materials with excellent thermal shock resistance, radiation resistance, high transmittance, and thermal expansion coefficient similar to chips. organic silicone for electronics.
K1Kodama et al. synthesized organosilicon/epoxy resin oligomers by hydrolysis and condensation of siloxane with epoxy groups catalyzed by alkaline catalysts. The outstanding advantage of this material after vulcanization is that the mass fraction of Na+, K+, C1- ions is less than 2×10-6, and it has excellent insulation properties.
In addition, the Shore D hardness of this material reaches 35 degrees, and it has good adhesion performance. It does not crack even after 100 cycles of cold and hot impact at -20 ℃/120 ℃. In order to improve the heat resistance and thermal conductivity of such LED packaging materials, inorganic fillers with particle sizes less than 400nm, such as quartz powder, monocrystalline silicon, aluminum powder, zinc powder, glass fiber, etc., are often added. organic silicone for electronics.
H1to et al. added silica with a particle size of 5-40nm and spherical glass powder with a particle size of 5-100nm to organosilicon modified epoxy resin. After vulcanization molding, the material’s transmittance reached 9517% (25 ℃), refractive index was 1153-1156 (sample thickness 1mm, wavelength 58913nm), and linear expansion coefficient was about 40X10-6K-1. After 200 cycles of -25 ℃/125 ℃ thermal shock, the damage rate was only 4% -1215%.
In addition to directly using organic silicon modified epoxy resin as the packaging material, organic silicon modified epoxy resin can also be blended with silicone resin to make LED packaging materials. GE Corporation in the United States uses phenyltrichlorosilane, methyltrichlorosilane, and dimethylchlorosilane for co hydrolysis and condensation to produce hydroxysilane resin; Then it is blended with organic silicon modified epoxy resin, using hexahydroxy-4-methyl-phthalic anhydride as a curing agent and stannous octoate as a curing accelerator, and heated and vulcanized to obtain an encapsulation material with adjustable refractive index (112-116).
After being irradiated with 380nm wavelength light waves in an artificial aging machine for 500 hours or with 400-450nm wavelength ultraviolet light at 150 ℃ for 500 hours, the transmittance of the material still reaches over 80% (with a sample thickness of 5mm). If phosphorus compounds, phenol derivatives, transparent metal oxides (such as titanium, magnesium, yttrium, zirconium, aluminum, etc.) nanoparticles are added to the mixture, the thermal conductivity of the packaging material can be improved and its moisture resistance can be enhanced. organic silicone for electronics.
Adding inorganic fillers can also reduce the thermal expansion coefficient of LED packaging materials. For example, T1B1Gorczyca blends epoxy resin with a refractive index of 1155 and a thermal expansion coefficient of 6X10-6K-1 with silicone resin with a refractive index of 1146 and a thermal expansion coefficient of 200X10-6K-1, and adds quartz glass powder with a refractive index of 1152 and a thermal expansion coefficient of 0165×10-6K-1 to produce an encapsulation material with a refractive index of not less than 1150 and a thermal expansion coefficient of 5X10-6K-1. The solvent corrosion resistance of LED packaging materials is poor.
To overcome this drawback, Y1K1 Suehiro et al. blended and vulcanized hydroxysilicone resin with organosilicon epoxy resin and bisphenol A epoxy resin at 100-200 ℃ to obtain a transparent packaging material with excellent solvent resistance. The material also has high refractive index (about 1149 under 1700nm wavelength light source irradiation and 1158 under 350nm wavelength light source irradiation), excellent heat resistance, moisture resistance and other properties – organic silicone for electronics.
In order to improve the hardness and resistance to cold and hot impacts of materials, and reduce their modulus and shrinkage rate, Shin Etsu Chemical Company in Japan added vinyl silicone resin containing silicon hydroxyl groups, silicone oil containing silicone oil, and a small amount of organic silicone elastomer to epoxy resin. Platinum based catalysts were used to catalyze the hydrosilylation reaction, and alkoxyl or acyl or silicon hydroxyl aluminum compounds were used as epoxy curing agents.
After injection molding, LED packaging materials with a refractive index of up to 1151, Shore A hardness of 70 degrees, no dust collection, low modulus, and low shrinkage rate were obtained. Moreover, the packaging material did not crack after 1000 cold and hot impacts at -40 ℃/120 ℃. In addition, in order to save costs and simplify the process flow, D1A1Haitko directly cured epoxy resin with organosilicon anhydride to produce organosilicon modified epoxy resin LED packaging material. This packaging material has a refractive index of 1145 and a transmittance of 88% under a 400nm wavelength light source. After being irradiated with a 405nm wavelength ultraviolet lamp for 40 hours at 100 ℃, the transmittance decreases by less than 10%.
2.2 Organic silicon LED packaging material – organic Silicone for electronics
Although the performance of epoxy resin packaging materials can be improved through organic silicon modification, the molecular structure of organic silicon modified ring resin contains epoxy groups, and using it as LED packaging materials still has disadvantages such as poor radiation resistance and susceptibility to yellowing, making it difficult to meet the technical requirements of power type LED packaging. Therefore, people have successively developed high refractive index, high transmittance, and epoxy free organic silicone for electronics LED packaging materials.
Ethylene based silicone resin and hydrogen containing silicone oil can be vulcanized through silicon hydrogen addition reaction to form organic silicon LED packaging materials. In order to obtain high refractive index and radiation resistant organic silicon sealing materials, vinyl silicone resin and hydrogen containing silicone oil generally need to contain a certain amount of diphenylsiloxane or methylphenylsiloxane units.
K1 Miyoshi and T1 Goto used the gas silane co hydrolysis condensation process to produce vinyl silicone resin, which was then vulcanized with hydrogen containing silicone oil containing phenyl siloxane chains under platinum catalyst to obtain LED packaging materials. The refractive index of this material can reach 1151, the Shore D hardness is 75-85 degrees, the bending strength is 95-135MPa, the tensile strength is 514MPa, and the transmittance decreases from 95% to 92% after 500 hours of ultraviolet radiation.
In order to reduce the shrinkage rate of such organic silicon materials and improve their resistance to cold and hot cycle impact, the mass fraction of phenyl groups in the packaging material can be increased, and even organic silicon sealing materials with excellent mechanical and adhesive properties can be obtained, which can withstand 1000 cycles of -50 ℃/150 ℃ cold and hot cycle impact without cracking. Due to the lack of reinforcement, the hardness and strength of these organic silicone for electronics packaging materials are still poor and cannot meet certain technical requirements for LED packaging materials – organic silicone for electronics.
K1 Miyoshi added gas-phase white carbon black, thermal conductive fillers, light wave adjusters, flame retardants, etc. to methylphenyl hydrogenated silicone oil and vinyl silicone resin. After curing at 120-180 ℃ for 30-180 minutes, the bending strength of the packaging material was 95-100MPa, the tensile strength was 514MPa, the Shore D hardness was 75-85 degrees, and the refractive index was as high as 1151; After being irradiated by a 400nm wavelength light source for 100 hours, the transmittance decreased from 95% to 92%. After being irradiated for 500 hours, it remained at 92%.
Organic silicone for electronics LED packaging materials can also be made using additive liquid silicone rubber. T1 Shiobara et al. used additive liquid silicone rubber for injection molding at 165 ℃ to obtain a packaging material with a shrinkage rate of 3137%, a shrinkage ratio of only 0104, and a refractive index of 1150~1160 (wavelength 400nm). E1 Tabei et al. even obtained LED packaging materials with a Shore D hardness of up to 50 degrees, an elastic modulus of 350~1500 MPa, and a light transmittance of 88%~92% (wavelength of 400nm, sample thickness of 4mm).
Adding an appropriate amount of inorganic fillers (such as oxides of boron, silicon, titanium, aluminum, zinc, etc.) to the additive liquid silicone rubber can improve the material’s heat resistance and radiation resistance. The resulting LED packaging material has a transmittance decrease of less than 10% when irradiated with 450-470nm wavelength light for 1000 hours at 140 ℃.
In general, LED packaging materials need to be vulcanized at a certain temperature for 2-5 hours, resulting in a longer production cycle. L1D1Boardman et al. obtained vinyl silicone oil through ring opening polymerization of D4 and 1,3-divinyl-1,1,3,3-tetramethyldisiloxane (vinyl double capped) catalyzed by concentrated sulfuric acid; Then add hydrogen containing silicone oil, platinum catalyst, and photosensitive agent in proportion, mix evenly, and irradiate with visible light or ultraviolet light for 215-20 minutes to cure completely, obtaining LED packaging materials with good performance – organic silicone for electronics.
Organic silicone for electronics LED packaging materials can also be made using additive liquid silicone rubber. T1 Shiobara et al. used additive liquid silicone rubber for injection molding at 165 ℃ to obtain a packaging material with a shrinkage rate of 3137%, a shrinkage ratio of only 0104, and a refractive index of 1150~1160 (wavelength 400nm). E1 Tabei et al. even obtained LED packaging materials with a Shore D hardness of up to 50 degrees, an elastic modulus of 350~1500 MPa, and a light transmittance of 88%~92% (wavelength of 400nm, sample thickness of 4mm).
Adding an appropriate amount of inorganic fillers (such as oxides of boron, silicon, titanium, aluminum, zinc, etc.) to the additive liquid silicone rubber can improve the material’s heat resistance and radiation resistance. The resulting LED packaging material has a transmittance decrease of less than 10% when irradiated with 450-470nm wavelength light for 1000 hours at 140 ℃. In general, ED packaging materials need to be vulcanized at a certain temperature for 2-5 hours, resulting in a longer production cycle.
L1D1Boardman et al. obtained vinyl silicone oil through ring opening polymerization of D4 and 1,3-divinyl-1,1,3,3-tetramethyldisiloxane (vinyl double capped) catalyzed by concentrated sulfuric acid; Then add hydrogen containing silicone oil, platinum catalyst, and photosensitive agent in proportion, mix evenly, and irradiate with visible light or ultraviolet light for 215-20 minutes to cure completely, obtaining LED packaging materials with good performance. organic silicone for electronics.
By using a blend of vinyl silicone resin and vinyl silicone oil and hydrogen containing silicone oil through silicon hydrogen addition process vulcanization, the advantages of silicone resin and silicone rubber can be fully utilized to obtain high-performance LED packaging materials. The refractive index of the LED packaging material obtained by M1 Yoshitsugu et al. using this method is 1154, the transmittance is 85%~100%, the Shore A hardness is 45~95 degrees, and the tensile strength is 118MPa. Surface cracks only appear after heating at 150 ℃ for 100 hours.
As mentioned above, the preparation process of organic silicone for electronics LED packaging materials generally requires the use of platinum catalysts, and commonly used platinum catalysts will turn yellow after being left for a period of time, which will affect the light transmittance of LED packaging materials if continued to be used. To overcome this drawback, K1To2moko et al. developed a platinum catalyst using organosiloxanes as ligands that is not easily discolored, namely 1,3-dimethyl1,3-phenyl-1.3-divinylsiloxane platinum complex. Using this catalyst to catalyze the vulcanization molding of addition molded silicone rubber, LED packaging materials with refractive index higher than 1150 and transmittance of 92% to 100% can be obtained.
3. Conclusion – organic silicone for electronics
Organic silicone for electronics have the advantages of resistance to thermal shock, UV radiation, and colorless transparency, making them an ideal packaging material for white power LEDs and receiving widespread attention from researchers. With the deepening of research, the use of organosilicon will definitely be sought in different fields.
