Reasons for failure of ceramic capacitor withstand voltage

Ceramic capacitors, because the dielectric material is made of ceramics, also called ceramic capacitors, coated metallized films are fired into electrodes by high temperature, and then the bonding leads are melted on the conductive medium, and the outer shape is coated with protective enamel. It can also be encapsulated with epoxy resin. The appearance is mostly round and flat, the color is blue, a few earthy yellow, and the material specifications are different, and the voltage performance is also different.

Under the action of electric field, the breakdown failure of ceramic capacitors follows the weak click-through theory, and partial discharge is the source of weak point damage. In addition to cracking due to thermal stress caused by thermal and thermal changes, for epoxy-encapsulated high-voltage ceramic capacitors, both edge-type and full-silver capacitors have electrode edge electric field concentration and ceramic-epoxy bonding interface. Weak link. The epoxy-encapsulated ceramic capacitor retains the internal stress in the form of residual stress in the encapsulation layer due to the volume shrinkage of the epoxy resin during the ice-cooling process, and acts on the ceramic-epoxy interface to deteriorate the bonding of the interface.

Under the action of an electric field, the perovskite-type barium titanate-based ceramics (SPBT) constituting the high-voltage ceramic capacitor ceramic body undergoes electro-mechanical stress and generates electrical strain. When the residual stress of the epoxy encapsulation layer is large, the combined action of the two may extremely cause shelling between the encapsulation and the ceramic body, resulting in an air gap, thereby lowering the voltage level.

The direct cause is that there is a gap at the ceramic-epoxy interface, resulting in a decrease in the withstand voltage level. Indirect causes: 1. The stress of the epoxy material is generated during the curing process of the secondary encapsulation module, which causes the ceramic-epoxy interface to deteriorate and form a path of weak point discharge. 2. After the secondary encapsulation module is cured, the sample placement time is too short, the internal interface stress is not completely released, and micro-cracks exist at the ceramic-epoxy interface, resulting in a decrease in the withstand voltage level.