Ceramic capacitors are an integral part of most electronic circuits. Using ceramic materials with high dielectric constant and low loss as the medium, spray silver layers on both sides of the ceramic substrate, burn the silver film at high temperature as the electrode and weld the leads, and coat the outer surface with protective enamel or encapsulate it with epoxy resin. Because of its small size, good heat resistance, low loss, high insulation resistance, and small capacity, it is widely used in high-frequency circuits.

Different application environments have different requirements for ceramic capacitors. For example, in some extreme high-temperature applications, it is necessary to select a capacitor with smaller capacitance loss under the same high-temperature environment. There are KEMET capacitors specially designed for high-temperature applications, such as KEMET X7R 175+℃ ceramic capacitors, and KEMET C0G 200+℃ ceramic capacitors.

Classification of Ceramic Capacitors

The capacity of ceramic capacitor is determined by the area and thickness of the ceramic sheet. Thickness also determines the withstand voltage of ceramic capacitors. According to the structural form, it can be divided into tubular capacitors, disc capacitors, chip capacitors, rectangular capacitors, feedthrough capacitors, etc. According to the withstand voltage, it can be divided into high-voltage ceramic capacitors (above 1KVDC) and low-voltage ceramic capacitors (below 500VDC). According to the medium, there are Class I ceramic capacitors and Class II ceramic capacitors.

What do the Dielectric Parameters in a Capacitor Mean?

The X7R capacitor is a temperature-stable ceramic capacitor, which means that it works at -55~+125 degrees, and the deviation is plus or minus 15% in the entire temperature range. The capacity of this type of capacitor will change with time under different voltage and frequency conditions. Under the same volume, its capacitance can be made relatively large. Mainly used in less demanding industrial applications.

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Unlike X7R capacitors, Y5V capacitors have a certain temperature limit and a high dielectric coefficient. It is usually easier to achieve small volume and large capacity. Working at -30~+85 degrees, the deviation in the entire temperature range is -82%~+22%, that is, with the change of temperature, its capacity will have a relatively obvious change, but the cost is low, so it is widely used in capacity, Occasions where the loss requirement is not high.

X5R means that it works at -55~+85 degrees and the deviation within the entire temperature range is plus or minus 15%.

Y5U has no compensation for temperature changes, and the capacitance value variation range in the full temperature range is +22%/-56%

Y5P has the best temperature compensation performance, and the capacitance value variation range is ±10% in the whole temperature range

High-frequency ceramic capacitors have good capacity stability, low dielectric loss, and high insulation resistance, but small capacity; they are mainly used in high-frequency circuits and high-frequency high-voltage circuits in electronic equipment, such as secondary output rectification of computer motherboards and switching power supplies.

Low-frequency ceramic capacitors refer to capacitors using ferroelectric ceramics as the medium. Class II ceramic capacitors are small in size and large in capacity, but poor in stability and large in the loss. Mainly used for low-frequency bypass, DC blocking, and filter circuits, such as filtering after AC rectification.

The application fields of ceramic capacitors cover aerospace, industrial, automotive and consumer electronics. There are ceramic capacitors and chip capacitors that widely be used in most circuits. Ceramic chip capacitors are usually used in high-stability oscillation circuits as loops, bypass capacitors and pad capacitors. Chip capacitors are pinless miniature capacitors made of special materials, which are used in various microelectronic circuits.

Processing Steps of Ceramic Capacitors

Step One: Material preparation and molding. After the raw materials are calcined, pulverized and mixed, they will reach a certain particle fineness, usually the finer the particles, the better. The ceramic dielectric blank is formed according to the structural shape of the capacitor.

Step Two: High-temperature treatment is performed on the porcelain body to make it a porcelain body with high mechanical strength and excellent electrical properties. The firing temperature is generally above 1300°C. It should be noted that if the high temperature holding time is too short, the solid phase reaction will not be complete, which will affect the structure of the whole green body and cause the deterioration of electrical properties, which is the so-called burning; if the high temperature holding time is too long, the air bubbles in the green body will be deformed. And the crystal grain becomes larger, which will also cause the deterioration of electrical performance, that is overburning.

Step Three: Electrode fabrication, wire bonding, coating, encapsulation.

Selection of Ceramic Capacitors

Different circuits and working environments have different requirements for capacitors. Even if the required capacitance and rated voltage are the same, the types and material characteristics of the required capacitors are also different.

Ceramic Capacitors

Impedance is an important metric for determining the effect of a capacitor on an input signal. Low ESR is critical for high efficiency, low heat loss and reliability during charge and discharge cycles. Capacitive and inductive reactance represent the energy storage capacity and the induced magnetic field generated by the capacitor. When the capacitive and inductive reactances are equal, the resonant frequency of the device is reached. This is important when selecting decoupling capacitors to remove AC component noise from DC signals. Because the capacitor whose resonant frequency is close to the frequency of the AC noise to be removed can effectively eliminate the AC signal component in the DC link.

Ceramic capacitors do not have to take voltage derating to ensure reliability, but the voltage coefficient of capacity must be considered. Capacitors can lose up to 40% of their capacity when operating at or near their rated voltage.

Selecting a capacitor is a multi-dimensional consideration process. Each capacitor has its own electrical characteristics, performance weaknesses, and mechanical and economic considerations. The importance of each of these depends on the application, environmental conditions, and actual circuit functionality. With so many capacitors to choose from, it is important to refer to each manufacturer's specifications to select the right capacitor.