The lower the thermal conductivity and the smaller thermal expansion coefficient the molding compound, the higher the amount of quartz powder. The performance of the electronic component produced is better if the thermal expansion coefficient of silicon monocrystalline is close to that of the molding compound.
It is made by purifying and ultra-finely grinding natural quartz stone, and then passing it through a high temperature field. This causes its phase, shape and crystal to change instantly, from solid to molten to solid, and from crystalline to amorphous. Its preparation methods are currently mainly high-temperature Plasma melting, high-temperature Melting Injection Method and Gas Combustion Flame Method.
High Temperature plasma Melting
The high temperature plasma melting method sprays quartz powder into the plasma flame using high-temperature gases generated by AC/DC arc plasma. The powder is heated to melt and vaporize, then instantly quenched. A cyclone and cloth bag are used to collect the powder. This produces a spherical silica powder. It is characterized as a high heating temperature which can achieve a temperature field more than five times higher than chemistry combustion (above 3000K). A high temperature, high heat, and a high active atmosphere cause the chemical reaction to proceed quickly. This leads to the rapid formation high temperature phase compounds, which are difficult for liquid phase chemistry to synthesize. Such as nitrides carbides and borides etc. After rapid cooling, particles that have left the plasma will not grow.
The technology of plasma is extremely difficult. First, magnetic and electric properties of plasma can affect the plasma temperature field. The temperature field has a small and concentrated size. Second, the generation of plasma energy by the current through the medium of ionized gases is achieved. A plasma that is too diluted will interfere with the current, and the effect will be lost. It is hard to control how fast the product spheriodizes.
High Temperature Melt Injection
The high-temperature injection method involves melting the material to a liquid by putting it in a hot field. When the melt comes out of the ejector it is sprayed high-pressured air, which breaks up the melt and disperses it into a mist. When the droplets cool down, they shrink back into smooth spheres. The method of high temperature melt atomization is the most effective way to achieve spheroidization. The key technologies of viscous quartz melting atomization in furnaces, high temperature materials for the quartz, and the prevention of secondary pollutants have yet to be developed. This makes it difficult to make high-purity spherical powder.
Gas Combustion Flame method
The gas combustion method produces a flame using acetylene and hydrogen. It also uses natural gas and other fuels as raw materials. Air or oxygen is used as a support gas. Angular quartz powder and air are transported simultaneously into the fire. As the angular particles pass through the high temperature flame field, they are first melted to amorphous powder. It shrinks immediately into spherical powder when it exits the high temperature field. The cyclone then collects the final product. Thermodynamics, gas dynamics and particle hydrodynamics are all involved in this method. The temperature field in plasma flames is much lower and there are also fewer factors that influence it. It does not involve electromagnetic theory or the flow ions in an electromagnetic field. The movement problem makes it easier to manage various conditions. Equipment manufacturing is simplified, industrialization is easy, and development prospects are better.
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