Internal structure of film capacitor

Calculated according to the capacitance formula, the size of the capacitance is not only related to the specification of the capacitor, but also related to the thermal conductivity of the dielectric.The performance of the dielectric affects the performance of the capacitor, and different media are suitable for different production processes.

For the performance comparison of common media, you can refer to a technical information of AVX.

AVXDielectricComparisonChart（tips：Apply Bing Search, the first one is)

The manufacturing process of capacitors can be mainly divided into three categories:

-Film Capacitor

- Electrolytic Capacitor

- Porcelain Capacitor

Film Capacitor

It is different from ThinFilm processing technology. In order to distinguish, I think it is better to directly translate it into film capacitor. Film capacitors are based on rewinding two pieces of plastic film containing metal electrodes into a cylindrical shape, and finally packaged into shape; because its medium is generally plastic material, it is also called plastic film capacitor; its internal structure is roughly shown in the figure below :

Film capacitors can be divided into two categories according to the processing technology of their electrodes:

Metal material foil film capacitor

For metal foil film capacitors, a thin layer of metal foil, usually aluminum platinum, is directly added to the plastic film as an electrode; this kind of process is relatively simple, and the electrodes are easily drawn out, and can be used in high current applications.

Metallized Film Capacitor

Metallized film capacitors, according to the vacuum deposition process, directly form a thin metal surface layer on the surface of the plastic film as an electrode;Because the electrode is too thin, it can be wound into a capacitor with a larger space; but because the electrode is thin and thick, it is only suitable for places with small currents.

Metallized film capacitors have the function of self-repair, that is, if there is a penetrating damage point inside the capacitor, it will cause an avalanche effect at the damage point,the vaporized metal material will produce a vaporized joint surface at the damaged place, the short circuit fault will disappear, and the damaged point will be repaired;Therefore, the reliability of the metallized film capacitor is very high, and there will be no short-circuit failure;There are two rewinding methods for film capacitors: the post-inductive winding method is used before the rewinding machine, and the wires are already connected to the internal electrodes; The internal electrodes of the inner hole are connected into one surface, so that a smaller ESL can be obtained, and the high frequency performance should be higher;In addition, there is also a stacked non-inductive capacitor, which is similar in structure to MLCC and has good performance, which is conducive to making SMD packaging.

The dielectric raw material of the first film capacitor was soaked in oil or paraffin with paper, which was invented by American D'Fitzvaldes in 1876; the working frequency is very high.Nowadays, plastic materials, that is, polymer materials and polymers, are used.According to the different media materials, there are mainly the following types:

The most widely used film capacitors are polyester film capacitors, which are more cost-effective because of their high thermal conductivity and smaller specifications;The second is polypropylene film capacitors.Other materials include polytetrafluoroethylene, polyethylene, polycarbonate and so on.