Silicon micro powder is a type of silica powder made from crystalline quartz, fused silica, and other raw materials. The process is through grinding, precision classification, impurity removal, and other processes. It is widely used in various fields, including copper-clad laminates, epoxy plastic packaging, electrical insulation materials, rubber, plastics, coatings, adhesives, artificial stones, honeycomb ceramics, cosmetics, and more.
1. Copper-Clad Laminates
Currently, silicon micro powder used in copper-clad laminates can be categorized into crystalline silicon micro powder, molten silicon micro powder, spherical silicon micro powder, and composite silicon micro powder. The resin content in copper-clad laminates is about 50%, and the typical filling rate of silicon micro powder in the resin is around 30%. This means the filling weight ratio of silicon micro powder in copper-clad laminates is approximately 15%.
As an inorganic filler, silicon micro powder enhances the thermal stability, stiffness, thermal expansion coefficient, and thermal conductivity of copper-clad laminates, improving the reliability and heat dissipation of electronic products. It also has good dielectric properties, which can enhance signal transmission speed and quality in electronic products. Crystalline silicon micro powder, being more cost-effective, is used in industries with lower production requirements, such as air conditioners, refrigerators, washing machines, and desktop computers. Copper-clad laminates for smartphones, tablets, automobiles, network communication, and industrial equipment generally use molten silica micro powder due to specific requirements for dielectric constant and linear expansion coefficient. For high-frequency and high-speed applications, such as supercomputers and 5G communications, low-dielectric and low-loss spherical silicon micro powder is required as the key functional filler, with low impurity content and a high filling rate.
2. Epoxy Plastic Sealing Material
Silicon micro powder is a crucial filler in epoxy sealants (EMC), accounting for about 60%–90% of the composition. Improving the performance of epoxy sealants depends on enhancing the quality of silicon micro powder, thus imposing higher requirements on its particle size, purity, and sphericity. Middle and low-end epoxy plastic sealants often use angular silicon micro powder, while high-end sealants mainly utilize spherical silicon micro powder. Plastic sealing materials for discrete devices and small integrated electrical appliances typically contain crystalline and molten silicon micro powders. High thermal conductivity packaging for power devices mainly uses crystalline silicon micro powder along with other high thermal conductivity materials. For low expansion and low warpage packaging of large-scale integrated circuits, spherical silicon micro powder is preferred. Finally, low modulus packaged memory devices commonly use low-radiation spherical silicon micro powder as the filler.
It is estimated that China’s demand for spherical silicon powder for semiconductor packaging in 2022 will be 71,000 tons. As the proportion of advanced packaging continues to increase, it is expected to reach 93,000 tons in 2025, with a CAGR of 9.25%. Based on the price of spherical silicon powder of 15,000 yuan/ton, the market size in 2025 will be nearly 1.5 billion yuan.
3. Electrical Insulation Materials
Silicon micro powder is used as an epoxy resin insulation filler for electrical insulation products, effectively reducing the linear expansion coefficient of the cured material and the shrinkage rate during the curing process. This reduces internal stress and improves the mechanical strength of the insulation material, thereby enhancing the mechanical and electrical properties of the insulation material.
Therefore, customers in this field have specific functional requirements for silicon micro powder, such as a low linear expansion coefficient, high insulation, and high mechanical strength, while their demand for dielectric and thermal conductivity properties is relatively lower. In the field of electrical insulation materials, single-specification silicon micro powder products with an average particle size between 5 microns and 25 microns are typically selected based on the characteristics of electrical insulation products and the requirements of their production processes. There are also high standards for product whiteness and particle size distribution.
4. Rubber
Silicon micro powder offers advantages such as a small particle size, large specific surface area, good heat resistance, and wear resistance, which can improve the wear resistance, tensile strength, modulus, and high tear resistance of rubber composite materials. However, the surface of silicon micro powder contains many acidic silanol groups. If not modified, these groups can cause uneven dispersion of the silicon micro powder in rubber and may react with alkaline accelerators, prolonging the vulcanization time of rubber composite materials.
Currently, modification of silicon micro powder is mainly applied in rubber research, with silane coupling agent modification being the primary method. Examples include phenyltrimethoxysilane, ethylenetrimethoxysilane, hexamethyldisilazane, 3-mercaptopropyl triethoxysilane, and (3-aminopropyl) trimethoxysilane.
5. Plastics
Silicon micro powder can be used as a filler in the production of plastics, including polyethylene (PE), polyvinyl chloride (PVC), polypropylene (PP), polyphenylene oxide (PPO), and other materials. It is widely used in various fields such as construction, automotive, electronic communication, insulation materials, agriculture, daily necessities, and national defense and military industries.
Powdered quartz is modified with KH-550, and the modified powdered quartz is uniformly mixed with PE to prepare PE plastic film, which can be used in agricultural greenhouse film. The results showed that when the filling mass fraction of powdered quartz was 8%–12%, the mechanical properties of the agricultural film exceeded those of pure resin film and met national standard requirements. Using a silane coupling agent to modify silicon micro powder and mixed the modified silicon micro powder with polyphenylene ether to prepare polyphenylene ether automotive plastic material. The results indicated that the prepared material had properties such as high hardness, wear resistance, high-temperature resistance, and corrosion resistance, making it suitable for automotive plastic products.
6. Paint
Silicon micro powder can be used as a filler in the coating industry, which not only reduces the cost of preparing coatings but also enhances properties such as high-temperature resistance, acid and alkali resistance, wear resistance, and weather resistance. It is widely used in building materials, automobiles, pipelines, hardware, household appliances, and other fields.
In architectural coatings, Bai Wenkui et al. used silica powder as a filler to prepare exterior wall paints, which demonstrated good decorative effects, strong stability, and low cost. Yuan Rui et al. used ultrafine silica powder as a filler in phenylpropanoid coatings. The results showed that when the mass fraction of silicon micro powder reached 35% or more, the coating’s alkali resistance, washability, water absorption, and reflectivity were significantly improved.
For latex coatings, titanium dioxide is commonly used as the main pigment and filler, but it is expensive and its preparation process is complex. Therefore, using fillers like calcium carbonate, anhydrous calcium sulfate, and silicon micro powder in combination with titanium dioxide has become a research focus. Wang Pengzhu and colleagues used modified silica micro powder as a filler to partially replace titanium dioxide in latex coatings. Their results showed that when the mass ratio of titanium dioxide to silicon micro powder was 1:3, the hardness, impact strength, and flexibility of the latex coating were greatly improved.
In epoxy floor coatings, silicon micro powder as a filler enhances wear resistance, acid and alkali resistance, high-temperature resistance, and mechanical strength. Hu Gaoping et al. mixed silicon micro powder of different particle sizes with epoxy resin, curing agents, and other raw materials to prepare strong acid-resistant epoxy floor coatings. These coatings were used in acetic acid distillation workshops to prevent local powdering caused by acetic acid corrosion.
In flame retardant insulation coatings, Liu Tongwang et al. added activated silica micro powder to unsaturated polyester resin to prepare polyester insulation paint. The results showed that when the mass fraction of activated silica micro powder was 35%, the volume conductivity, water absorption, and mechanical strength of the insulation paint were significantly improved.
7. Adhesives
Silicon micro powder, as an inorganic functional filler, effectively reduces the linear expansion coefficient and shrinkage rate of cured adhesive resin. It improves the mechanical strength, heat resistance, permeability resistance, and heat dissipation performance of adhesives, thereby enhancing bonding and sealing effectiveness.
The particle size distribution of silica powder will affect the viscosity and sedimentation of the adhesive, thereby affecting the processability of the adhesive and the linear expansion coefficient after curing. Therefore, the adhesive field pays attention to the function of silica powder in reducing the linear expansion coefficient and improving the mechanical strength. It has high requirements for the appearance and particle size distribution of silica powder, and usually uses different particle size products with an average particle size of 0.1 micron-30 microns for compound use.
The silica powder is modified and then applied to vinyl silicone. With the extension of storage time, the viscosity of vinyl silicone is stable, the product has good stability and high strength, and can be used in thermal conductive silicone, thermal conductive gaskets, dental impression materials and other fields.
8. Artificial Quartz Stone
Silicon micro powder used as a filler in artificial quartz boards can reduce unsaturated resin consumption and improve wear resistance, acid and alkali resistance, and mechanical strength. The filling ratio of silicon micro powder in artificial marble is generally around 30%. For example, Liu Huichen et al. proposed using silicon micro powder modified with a silane coupling agent in artificial quartz boards. This approach can reduce unsaturated resin usage and lower the processing cost of artificial quartz boards.
9. Automotive Honeycomb Ceramics
The Diesel Particulate Filter (DPF), made from honeycomb ceramic carriers for automobile exhaust purification and cordierite material for diesel engine exhaust purification, involves mixing, extruding, drying, and sintering materials such as alumina and silica micro powder. The main component of molten silicon micro powder is SiO2, which has an amorphous structure, ultrafine particles, and a large specific surface area. It acts as a mineralizer for solid-state reactions and sintering of silicate materials. Silicon micro powder enhances the strength of honeycomb ceramic carriers, reduces the thermal expansion coefficient of cordierite, and improves its service life. Spherical silicon micro powder can enhance the forming rate and stability of honeycomb ceramic products, with a weight ratio of about 13% in the honeycomb ceramic carrier.
10. Cosmetics
Spherical silica micro powder is used in cosmetics such as lipstick, powder, and foundation cream due to its good fluidity and large specific surface area. Its characteristics include:
- Improved fluidity and storage stability in powder products, preventing caking.
- Smaller average particle size providing good smoothness and fluidity.
- Larger specific surface area for better adsorption of sweat, fragrances, and nutrients, making formulations more economical.
- Spherical shape offering good skin affinity and tactile sensation.
In addition, spherical silica micro powder is easy to mix with other cosmetic components, is non-toxic, odorless, and naturally white. Its notable features include a strong ability to reflect ultraviolet rays, good stability, and no decomposition or discoloration when exposed to UV radiation. Furthermore, it does not react with other components in the formula, making it an excellent choice for sunscreen cosmetic ingredients.
The specification requirements for spherical silica micro powder used in cosmetics generally include:
- Silicon content of 99.9%
- Controllable particle size ranging from 0.2 to 2 microns
- Sphericity above 95%
Low radiation (uranium content < 0.5 ppb)
Conclusion
Different application fields have varying quality requirements for silicon micro powder. Therefore, when selecting silicon micro powder for a particular application, it is essential to consider the needs of downstream industries, as well as factors such as cost, efficiency, and performance. Choosing the appropriate type of silicon micro powder, along with the correct modification process and formula, is crucial.
With the continuous advancement of China’s economy and society, research on the application of silicon micro powder will increasingly focus on high-tech fields such as high-end copper-clad laminates, high-end coatings, high-performance adhesives, and insulation materials made from spherical silicon micro powder. Refinement and functional specialization are expected to be the main trends in the future application of silicon micro powder.
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