Careful Selection of Raw Materials
Apart from the composition of the ceramic material itself, optimizing the manufacturing process and strictly controlling process parameters are crucial factors influencing the quality of high-voltage ceramic capacitors. Therefore, when selecting raw materials, one must consider both cost-effectiveness and purity; specifically, when choosing industrially pure raw materials, particular attention must be paid to their suitability for the intended application.
Preparation of Frit
The quality of the prepared frit significantly impacts the fineness of the ceramic powder after ball milling as well as the subsequent firing process. For instance, if the frit synthesis temperature is too low, the synthesis will be incomplete, which is detrimental to downstream processes. If residual Ca²⁺ ions remain in the synthesized material, they can hinder the tape-casting (film-forming) process. Conversely, if the synthesis temperature is too high, the resulting frit becomes excessively hard, thereby reducing ball-milling efficiency. Furthermore, the introduction of impurities from the grinding media can lower the reactivity of the powder, necessitating a higher firing temperature for the ceramic components.
Forming Process
During the forming stage, it is essential to prevent uneven pressure distribution across the thickness of the component and to avoid the formation of excessive closed-cell pores within the green body. The presence of large pores or internal laminations can compromise the dielectric strength (electrical breakdown resistance) of the finished ceramic body.
Firing Process
The firing schedule must be strictly controlled, utilizing high-performance temperature control equipment and kiln furniture with excellent thermal conductivity.
Encapsulation
The selection of encapsulation materials, the control of the encapsulation process, and the surface cleaning treatment of the ceramic components have a profound impact on the capacitor's characteristics. Consequently, it is imperative to select encapsulation materials that exhibit excellent moisture resistance, form a strong bond with the ceramic surface, and possess high dielectric strength. Currently, epoxy resin is the most widely chosen material, although a small number of products utilize phenolic resin for encapsulation. Some manufacturers also employ a two-step method involving an initial coating of insulating varnish followed by encapsulation with phenolic resin; this approach offers certain advantages in terms of cost reduction. In large-scale production lines, powder encapsulation technology is frequently employed.
To enhance the breakdown voltage of ceramic capacitors, a layer of glass glaze is often applied around the periphery of the interface between the electrodes and the dielectric surface. This technique effectively improves both the voltage withstand capability and the high-temperature load performance of ceramic capacitors used in high-voltage circuits, such as those found in television sets. For example, the application of a lead borosilicate glass glaze can increase the capacitor's breakdown voltage by a factor of 1.4 under a DC electric field and by a factor of 1.3 under an AC electric field.