The film capacitor is formed by winding two plastic films with metal electrodes into a cylindrical shape and finally molding. Since the medium is usually a plastic material, it is also called a plastic film capacitor. Its internal structure is roughly as shownbelow:
Film capacitors can be divided into two categories according to the manufacturing process of their electrodes:
Metal foil film capacitor
The metal foil film capacitor is directly applied to the plastic film with a thin metal foil, usually aluminum foil, as an electrode. This process is relatively simple, the electrode is easy to lead out, and can be applied to large current applications.
Metallized film capacitor
The metallized film capacitor is a thin metal surface formed directly on the surface of the plastic film by a vacuum deposition process as an electrode. Due to the thin thickness of the electrode,it can be wound into a larger capacity capacitor. However, due to the thin thickness of the electrode, it is only suitable for small current applications.
Metallized film capacitors have a self-healing function. If there is a breakdown damage point inside the capacitor, an avalanche effect will occur at the damage. The vaporized metal will form a vaporized collecting surface at the damaged place, the short circuit disappears, and the damaged point is repaired. Therefore, the reliability of the metallized film capacitor is very high, and there is no short circuit failure.
There are two winding methods for film capacitors: the susceptor winding method is connected to the internal electrodes before winding. After the non-inductive winding method is used, gold plating and other processes are used to connect the internal electrodes of the two end faces into one surface. This results in a smaller ESL with higher frequency performance. In addition, there is a laminated non-inductive capacitor, which has a similar structure to MLCC and has better performance and is easy to be made into an SMD package.
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