Mechanism of Low level failure of High Frequency Precision Capacitors

Mica is an ideal dielectric material for capacitors with high insulation, high temperature resistance, low dielectric loss and thickness of up to 25 microns. The main advantages of mica capacitor are low loss, good frequency stability, small distributed inductance and large insulation resistance, so it is especially suitable for high frequency communication circuits as precision capacitors.However, mica resources are limited and difficult to be popularized. In recent decades, organic film capacitors have been rapidly developed, among which polystyrene film capacitors have the advantages of low loss, large insulation resistance, good stability, high dielectric strength and so on. Precision polystyrene capacitors can be used in high-frequency circuits instead of mica capacitors. It is important to note that the metal foil plate is generally used in the precision polystyrene capacitors applied in high frequency circuits to increase insulation resistance and reduce loss.Low level failure of capacitors is a new problem since 1960s. Low level failure refers to the failure of capacitors under low voltage operating conditions, such as open circuit of capacitors or drop of capacity. Since 60s, semiconductor devices have been widely used. The voltage of semiconductor circuit is much lower than that of electronic tube circuit. The actual working voltage of capacitor is only a few millivolts in some circuits, which results in the low level failure of capacitor. The concrete performance is that the capacitors lose their capacity completely or partially. For the low level impulse, the capacitance of the capacitor is restored to normal.

The main reason for the low level failure is the poor contact between the capacitor outlet line and the capacitor plate, and the increase of the contact resistance, which leads to the complete open circuit of the capacitor or the decrease of the capacitance amplitude.