Why does the capacitance of film capacitors decrease

Film capacitors are a common type of capacitor, primarily used in power electronics, audio circuits, and high-frequency circuits; they consist of metallized film or metal foil electrodes and an insulating film dielectric.

Depending on the dielectric material used, film capacitors can be classified into various types, such as polyester capacitors, polypropylene capacitors, and polystyrene capacitors.

Film capacitors possess advantages such as high temperature resistance, low loss, good stability, and strong self-healing capabilities; consequently, they are widely utilized in numerous electronic devices.

After prolonged use, electronic devices inevitably encounter various issues—such as poor battery life, buzzing noises, or intermittent lagging—and film capacitors are susceptible to similar problems.

During long-term use, the capacitance of film capacitors gradually decreases; this gradual reduction in capacitance impacts the normal operation of electronic devices.

For instance, a decrease in capacitance may lead to issues such as degraded filtering performance, altered circuit frequency characteristics, and increased power loss. Therefore, it is essential to understand the underlying causes of capacitance reduction in film capacitors in order to take appropriate remedial measures.

Based on inspections and data analysis, the possible reasons for a decrease in film capacitor capacitance are as follows:

1. Aging Effect

During long-term operation, the dielectric material within a film capacitor may undergo physical or chemical changes, resulting in a decrease in the capacitor's capacitance value. This aging effect primarily manifests as the decomposition, oxidation, or moisture absorption of the dielectric material.

2. Impact of the Operating Environment

Film capacitors are relatively sensitive to environmental factors such as temperature, humidity, and external mechanical stress. In high-temperature environments, the dielectric material may undergo thermal decomposition or deformation, resulting in a reduction in the capacitor's capacitance.

Conversely, in high-humidity environments, moisture absorption by the dielectric material can lead to an increase in leakage current, which in turn affects the capacitor's capacitance.

3. Effects of Excessive Voltage

When operating under conditions of high voltage or high frequency, film capacitors experience accelerated degradation of their dielectric material, resulting in a decrease in capacitance. For instance, excessive voltage can lead to dielectric breakdown, creating microscopic breakdown points that cause the capacitor's capacitance to gradually diminish.

4. Manufacturing Process Issues

The manufacturing process of film capacitors also influences the stability of their capacitance. For instance, factors such as non-uniform film thickness or poor adhesion between the electrodes and the dielectric can lead to capacitance instability.

A decrease in film capacitor capacitance is a common and often unavoidable issue. It is therefore essential to identify the underlying factors contributing to this capacitance reduction and implement appropriate countermeasures to ensure the proper operation of electronic devices.