Analysis of appearance problems of metal film capacitors

When using metal film capacitors, I believe you will encounter many problems, such as color changes, unclear printing, poor performance and so on. It is inevitable that a product will have problems. The important thing is to deal with the problem attitude and speed of processing, to find out the problem in time, analyze the cause of the problem, and improve it to serve the customer.

1) Appearance color changes

The metal film capacitor is encapsulated by epoxy resin, and the color of the epoxy resin encapsulating component A is prepared by a certain ratio of iron red, iron yellow and red dan, sometimes cured by epoxy resin encapsulating material. After the phenomenon of darkening of the color, it is mainly caused by changes in the pigment. Iron oxide red is relatively stable and difficult to change. Red Dan is decomposed into lead oxide and oxygen when heated to 500 ° C, but the oven will not reach such a high temperature and can be eliminated. The iron oxide yellow is a crystalline iron oxide hydrate which easily dissociates from the crystal water upon heating and discolors. When the metal film capacitor is heated and solidified in the oven, the part close to the heating wire may have a high temperature. The heating wire can directly heat the capacitor, and the temperature of the portion is relatively high, so that the iron oxide yellow pigment is easily caused. Decomposes to discolor the capacitor. After discovering this situation, we raised the distance between the capacitor and the bottom plate and did not make the local temperature too high, which solved the problem.

2) Printing is not dry

The metal film capacitor is produced by using the encapsulant mixed with the diluent. There has been a problem that the ink does not dry. In addition to the ink quality problem, it is very likely that the manufacturer adds the defoaming agent in the process of preparing the diluent. The materials of the defoaming agent are all low-boiling, high-boiling organic compounds which lower the surface tension of the liquid, prevent the formation of foam or reduce or destroy the original foam. At the same time, they can also function as a plasticizer for the polymer, which is uniformly mixed in the polymer, weakening the force between the polymer molecules, thereby reducing the viscosity, increasing the fluidity and the like. When the metal film capacitor is cured by heating, it is easy to precipitate to the surface of the capacitor, so that the marked ink is not adhered to the product. Therefore, we have reduced the amount of defoamer used and solved this problem.