Spherical quartz powder, as a kind of quartz powder with special shape and amorphous structure, not only has the general characteristics of good insulation and chemical stability of quartz materials, but also has its special properties. Spherical quartz powder has a spherical shape and good fluidity. For EMC, the amount of quartz powder added can be increased without changing the fluidity, thereby increasing the filling rate of the quartz powder. At present, in the EMC industry, in order to meet the requirements of environmental protection and achieve the indicators of environmental certification, increasing the filling amount of quartz powder in EMC is one of the effective ways. Internationally, the highest filling rate of spherical quartz powder in EMC has reached more than 90%. At the same time, the thermal expansion coefficient of spherical quartz powder is close to that of single crystal silicon, so the higher the filling rate of spherical quartz powder, the better the performance of the electronic components produced. In the production process of molding compound, the grinding force of spherical quartz powder is smaller than that of crystalline quartz powder, and the wear and tear on the mold is slow, which can double the service life of the mold.
In order to ensure the quality of spherical quartz powder products so that they can be better used in epoxy molding compounds, the performance parameters such as particle size distribution, chemical composition, electrical conductivity, pH, spheroidization rate and whiteness of spherical quartz powder products are generally tested to determine control its quality.
1. Particle size distribution
Particle size distribution is the most basic performance of powder materials. The particle size distribution of spherical quartz powder is related to its filling rate in epoxy molding compound. Particle size testing generally uses a laser particle size analyzer to characterize the particle size distribution of the powder through the particle size distribution curve and particle size characteristic parameters such as D10, D50, and D90. According to the principle of closest packing, spheres are the most ideal particles to achieve the closest packing. Compared with angular quartz powder and fused silica powder, the filling amount of spherical quartz powder with the same particle size distribution in epoxy molding compound is higher, and the mass ratio is the highest. Up to 90%. Spherical silica powder with unimodal distribution cannot achieve the closest packing, so the filling rate is not high. The method to increase the filling rate is usually to mix spherical quartz powder products with different particle size distributions, and form spherical quartz powders with multimodal distribution through mixing and proportioning. Good particle size distribution can significantly increase the addition of spherical quartz powder, improve the thermal expansion performance and thermal stability of the molding compound, and reduce the production cost of the epoxy molding compound.
2 chemical composition
Purity is one of the most critical performance indicators of spherical quartz powder products, which directly determines the quality of the final spherical quartz powder product, which in turn affects the dielectric insulation properties of molding compounds, and is related to the stability and reliability of integrated circuits and electronic components. For spherical quartz powder products, the lower the content of impurity elements, the higher the content of SiO2, and the better the purity of the product. If the process of producing spherical quartz powder by flame method is appropriate, basically no impurities will be introduced in the production process. Therefore, the chemical composition of spherical quartz powder has a great relationship with the purity of raw materials. If the purity of raw materials is high, the purity of the product is also high.
3 Conductivity and pH
The determination of electrical conductivity is an important indicator for the detection of the purity of spherical quartz powder. The higher the electrical conductivity, the more it will affect the dielectric properties of epoxy molding products. Most of the impurities in spherical quartz powder are soluble. Since the amount of charged ions in the water extract is proportional to the conductivity of the solution, the higher the ion concentration in the water extract, the greater the conductivity, indicating that the purity of the quartz powder is poorer. The conductivity of electronic grade quartz powder is generally required to be less than 5μS/cm. The impurities that cause the increase in the conductivity of spherical quartz powder are mainly iron, sodium, potassium and other elements. The content of aluminum has little effect on the conductivity. The above-mentioned impurity elements are generally not introduced in the production process, so as long as the purity of the raw materials is controlled and a suitable process is adopted, the conductivity of the spherical quartz powder can be controlled within the acceptable range. Generally, the smaller the particle size of spherical quartz powder, the higher the conductivity and the lower the pH value, as shown in Table 2, mainly because the finer the particle size of the raw material, the longer the ball milling time, so that more impurities enter the raw material.
4 Spheroidization rate
Spheroidization rate indicates the proportion of spherical particles in the product. The higher the spheroidization rate, the better the filling performance of spherical quartz powder products in epoxy molding compounds. When using the flame method to produce spherical quartz powder, the factors that affect the spheroidization rate of the product are the flame temperature and the degree of dispersion of the particles. The flame temperature can be optimized by adjusting the flow of gas and oxygen. Dispersion of quartz particles is the key process for producing ultrafine spherical quartz powder products. Ultrafine powder particles are small and have a large specific surface area. Due to electrostatic attraction and van der Waals force, agglomeration is very easy to occur. If the problem of agglomeration of angular quartz powder is not solved before entering the spheroidizing furnace, multiple quartz particles will bond and eutectic in the flame, and after spheroidizing, particles with a large particle size will be formed, which will affect the quality and yield of the product. High-pressure air can be used to atomize the ultrafine powder, and then carry out ultrasonic dispersion to deagglomerate the agglomerated raw material particles and improve the spheroidization rate of spherical quartz powder products.
Epoxy molding compound can be made into various colors, generally black, red and green are used, among which black is the most common, so the whiteness of spherical quartz powder has little effect on its performance. However, the whiteness can reflect the purity of the product to a certain extent. There are usually two reasons for the low whiteness. It may be due to the wear of the iron inner wall of the production equipment pipeline, which is oxidized at high temperature to form Fe2O3 into the product, or it may be The incomplete combustion of the gas produces carbon attached to the quartz particles. Generally, the whiteness of angular quartz powder is greater than 90, and the whiteness of the produced product should be greater than 85. If the whiteness of the product is too low, it can be improved by magnetic separation and iron removal.