Spherical silicon micropowder

Properties of spherical silicon micropowders

Spherical silicon micropowder is white powder with high purity and fine particles. It has good dielectric properties and thermal conductivity, and has the advantages of low expansion coefficient, high heat resistance, high moisture resistance, high filling amount, low expansion, low stress, low impurity and low friction coefficient.  Compared with angular silicon micropowders, spherical silicon micropowders have the following advantages.  

1. The surface of the liquid, and the resin to form a uniform film, makes the resin to add a little and silicon powder filling quantity highest, so the ball will mean a growing number of silicon powder filling rate, and the filling rate of micro silicon powder is higher, the smaller its thermal expansion coefficient, thermal conductivity and the lower, and the more close to the thermal expansion coefficient of single crystal silicon,  The performance of the electronic components produced by this is also better.  

2. Compared with the molding material made of angular silicon powder, the spherical molding material has the lowest stress concentration and the highest strength. When the stress concentration of the molding material made of angular powder is 1, the stress of spherical molding powder is only 0.6.  The resulting microelectronic devices have high yield, are easy to transport and install, and are not easy to cause mechanical damage during use.  

3. Compared with the angular silicon powder, the spherical powder has small friction coefficient and small wear on the mold, so that the service life of the mold can be doubled.

Preparation method of spherical silicon micropowder

At present, physical and chemical methods are used to prepare spherical silica powders.  Physical methods mainly include flame pelletization, high temperature melt injection, self-propagating low temperature combustion, plasma, and high temperature calcination spherification, etc.  Chemical methods mainly include gas phase method, hydrothermal synthesis method, sol-gel method, precipitation method, microemulsion method and so on.  

1. Flame pelletization method  

The technological process of flame pelletization method is as follows: firstly, the high-purity quartz sand is pre-treated by crushing, screening and purification, and then the quartz micropowder is sent into the high temperature field generated by gas and oxygen for high temperature melting and cooling into balls, and finally the high-purity spherical silicon micropowder is formed.  

The production technology of flame pelletization is simpler, which is beneficial to large-scale industrial production and has a good development prospect.  Spherical silicon powders prepared by flame pelletization can meet the requirements of integrated circuit packaging.  

2. High temperature melt injection method  

High temperature melt injection method is to melt high purity quartz into quartz liquid at 2100-2500℃. After spraying and cooling, the spherical silicon powder is obtained. Its surface is smooth, and the spherification rate and amorphous rate can reach 100%.  High temperature melt injection method is easy to ensure the spheroidization rate and amorphous rate, but the difficulty of this technology is the atomization system of high temperature materials, viscous quartz melt liquid, and solve the problem of preventing contamination and further purification.

3. Gas phase method  

Ultrafine spherical silica micropowder was prepared by hydrolyzing siloxane at high temperature by gas phase method.  The hydrolyzed silica molecules agglutinate each other to form spherical particles. These particles collide and fuse to form aggregates, which then condense to form spherical powders.  

The product prepared by this method has high content of impurities such as HCl and low pH, so it cannot be used as the main material in electronic products. It can only be added in a small amount to adjust viscosity and increase strength. In addition, the raw material is expensive, the equipment requires higher requirements, and the technology is more complex.  

4. Chemical precipitation method  

The preparation of silicon micropowder by precipitation method is based on sodium silicate and acidifier as raw materials, adding surfactants at the right time, controlling the reaction temperature, adding stabilizer when the pH value of precipitation solution is 8, the precipitation obtained is washed, dried and calcined to form silicon micropowder.  The silicon powder produced by precipitation method has uniform particle size and low cost, and the process is easy to control, which is conducive to industrial production, but there is a certain agglomeration phenomenon.  

5. Hydrothermal synthesis method  

Hydrothermal synthesis is a common method for preparing nanoparticles in liquid phase. Generally, inorganic and organic compounds are combined with water at 100-350℃ and high atmospheric pressure.  These ions, molecules or ion groups are transported to the growth region (i.e. the low temperature region) with seed crystals by strong convection (temperature difference between the upper and lower parts of the kettle and the solution in the kettle) to form supersaturated solution and then crystallize.  The resulting inorganic material is filtered, washed and dried to obtain high purity and ultrafine particles.  

The hydrothermal method can directly generate oxides, avoiding the step of forging and burning to convert oxides in general liquid phase synthesis method, thus reducing the probability of forming hard agglomeration.

3. Application field of spherical silicon micropowder

3.1 Electronic and electrical industry  

Electronic devices are usually packaged with epoxy resin (EMC), and silicon powder is an excellent filling material for conventional use, which can make epoxy resin obtain high cost performance.  Spherical silicon powder is widely used in high-end semiconductor device packaging because of its characteristics of high filling, high flow, low wear and low stress.  In particular, spherical silica particles with precise control of coarse particles can also be used as epoxy plasticisers for narrow gap packaging, Underfiller, Globetop and other liquid packaging resin fillers and filler for various resin substrates.

The power supply and other components in electronic and electrical products are usually sealed with epoxy or silicone electronic potting adhesive.  Crystalline silicon powder, molten silicon powder, spherical silicon powder can be selected as potting sealant filler according to the thermal expansion coefficient, thermal conductivity, viscosity, cost and other considerations.

3.2 Honeycomb Ceramics  

The DieselParticulateFilter DPF(DieselParticulateFilter), which is used for automobile exhaust purification with honeycomb ceramic carrier and cordierite material for diesel engine exhaust purification, is made of alumina, silicon powder and other materials by mixing, extruding, drying and sintering.  Spherical silicon powder can improve the forming rate and stability of honeycomb ceramic products.

3.3 Paint and coatings  

Spherical silicon powder can bring excellent performance in scratch resistance, leveling, transparency, weather resistance and other aspects of coatings, including decorative paint, wood paint, powder paint, anti-corrosion paint, floor paint and so on.  

3.4 Glue adhesion agent  

Spherical silicon micropowder can be used for wind turbine blades and similar large composite structural parts of adhesives, building structural adhesives and other adhesives, so that the adhesives have appropriate viscosity, excellent thixotropy and flow resistance, high bonding strength, fatigue resistance.  

3.5 Cutting-edge application fields  

Submicron spherical silicon powder is very suitable for reducing the viscosity of various resins and paints, as well as improving fluidity, reducing burrs and other applications.  It is widely used in semiconductor packaging as additives, carbon powder additives, silicone rubber fillers, sintering materials and additives, liquid packaging materials, various resin fillers, resin substrates, narrow gap applications.