Causes of Poor Withstand Voltage of Ceramic Capacitors

Ceramic capacitors, because the dielectric material is made of ceramics, also called ceramic capacitors, coated with metallized film and fired at high temperature to make electrodes, and then melted and bonded the lead wires on the conductive medium, and coated with protective enamel on the appearance. In addition, it can be encapsulated by epoxy resin. The shape is mostly round and flat, the color is blue, a few ocher, and the voltage performance is different with different material specifications.

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 due to temperature changes in temperature and heat, for epoxy-encapsulated high-voltage ceramic capacitors, whether it is a marginal or full-silver capacitor, there is a comparison of the electric field concentration at the electrode edge and the ceramic-epoxy bonding interface. 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, perovskite-type strontium titanate-based ceramics (SPBT), which make up the high-voltage ceramic capacitor porcelain, will undergo electromechanical stress and cause 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.

The direct cause: There is a gap in the ceramic-epoxy interface, which results in a reduction in its pressure resistance 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, and the internal interface stress is not completely released, and there are micro-cracks at the ceramic-epoxy interface, resulting in a reduction in the pressure resistance level.