The reason of ceramic capacitor failure

The dielectric material of ceramic capacitors is ceramic. The coated metallized film is used to make the electrode through high-temperature firing, and then the lead wires are melted and bonded on the conductive medium. The appearance is mostly round and flat, blue, and a few are ocher. Different material specifications have different voltage performance.

Under the action of an electric field, the breakdown of ceramic capacitors follows the theory of weak click breakdown, and partial discharge is the source of weak point damage. In addition to cracks caused by thermal stress caused by temperature changes, the epoxy-encapsulated high voltage ceramic capacitors have both the edge-field electric field concentration and the ceramic-epoxy bonding interface. The weak link. Due to the volume shrinkage of epoxy-encapsulated ceramic capacitors due to the cold curing process of epoxy resin curing, the internal stress generated in the form of residual stress remains in the encapsulation layer and acts on the ceramic-epoxy interface, which deteriorates the interface adhesion.

Under the action of an electric field, the SPBT constituting the high-voltage ceramic capacitors porcelain body undergoes electromechanical stress and generates electro-induced strain. When the residual stress of the epoxy encapsulation layer is large, the combined effect of the two is likely to cause shelling between the encapsulation and the ceramic body, creating an air gap, thereby reducing the voltage level.

Direct cause:

There is a gap in the ceramic-epoxy interface, which results in a reduction in its withstand voltage level.

Indirect causes:

1. Stress shrinkage of the epoxy material occurred during the curing process of the secondary encapsulation module, which caused the ceramic-epoxy interface to deteriorate and formed a path of weak point discharge.

2. After the secondary encapsulation module is cured, the sample is left for too short a time, the internal interface stress is not completely released, and there are micro-cracks at the ceramic-epoxy interface, resulting in a reduction in the withstand voltage level.