Packaging and dimension description of Ceramic capacitor
Ceramic capacitor is a kind of capacitor with small positive capacitance temperature coefficient, which is used in high stability oscillation circuit as circuit capacitor and padding capacitor. Low frequency ceramic capacitors are limited to being used as bypass or DC isolation in circuits with lower operating frequencies, or in situations where stability and loss requirements are not high. These capacitors are not suitable for use in pulse circuits because they are prone to breakdown by pulse voltage.
Although ceramic capacitors have many of the advantages mentioned above, due to the low mechanical strength and easy fragmentation of ceramic materials, the geometric size of their discs is limited, which is also the main reason why different temperature characteristics have different capacity ranges. Generally, the allowable diameter D for low-voltage circular capacitors is ≤ 12mm, and the allowable diameter D for high-voltage capacitors is ≤ 16mm. If this size is exceeded, the production and processing difficulty and scrap rate will greatly increase, and the small cracks generated on the ceramic body will pose a great risk to the reliability of the capacitor. Due to the varying levels of material development and manufacturing processes among different manufacturers, their external dimension standards also vary, resulting in some differences in their nominal capacity range. Therefore, the above capacity division table is just a summary of the average level of the industry. In the future, with the further improvement of material technology, the size of Ceramic capacitor will be further reduced, and its capacity range will be further expanded.
The encapsulation form of circular ceramic capacitors is usually distinguished by voltage. Low voltage products below 500VDC, CC1 and CT1 series, are all encapsulated with phenolic resin, which has poor insulation strength and moisture resistance, but has lower cost. To improve moisture resistance, a thin layer of wax is applied to the outer layer of this type of encapsulation. Both the 1KVDC and AC capacitor series are encapsulated with flame retardant epoxy resin with excellent insulation strength and moisture resistance.
In addition to the wafer type ceramic capacitor, the axial lead color ring Ceramic capacitor and patch type Ceramic capacitor are also widely used. Their internal structure is laminated, so the volume is very small, but the capacity can reach 1 μ F or above is very conducive to assembly, but due to its structural limitations, the insulation resistance and withstand voltage cannot be very high. Therefore, it is currently limited to low-voltage (within 50V) products, and its loss and temperature characteristics are the same as those of circular capacitors.