1. There are a lot of impurities in minerals

　　Mica sheets with different impurities can present different colors. According to different colors, the types of impurities can be determined. Black or green impurities are generally magnetite, which is more harmful; red brown and light brown impurities are hematite and limonite, which are less harmful. Among these impurities, the conductivity of magnetite is larger than that of Zui, so the insulation electric limit of Muscovite containing black magnetite impurity is reduced by 2-3 Zui levels.

　　2. There are a lot of bubbles on the surface

　　The air bubble in Yunwu sheet often contains moisture, which is difficult to be removed by general drying method, so the loss of mica sheet increases. Especially at high frequency, because the ionization effect of these bubbles is strengthened, the loss increases significantly, and even leads to dielectric breakdown. If mica chip with visible bubbles is used to make capacitor, it is likely to become the hidden danger of capacitor failure. In addition, due to the existence of bubbles, the temperature coefficient of the dielectric constant of mica sheet increases.

　　3. Unexpected factors

　　The corrugation on the surface of mica sheet mainly affects the temperature coefficient of capacitance and causes the instability of capacitance. The cracks and cracks in the drill lead to ionization, which affects the capacitance. Pinholes and sand holes affect the pressure resistance, which can lead to ionization and breakdown. The red green silk has little influence on the general situation, but when the area is too large, it may affect the pressure and capacity stability.