Characteristic classification and precautions for use of ceramic capacitors

Ceramic dielectric capacitor is a capacitor made of dielectric materials for ceramics. According to different ceramic materials, capacitors can be divided into low-frequency ceramic dielectric capacitors with a capacity of 1~300pF and high-frequency ceramic dielectric capacitors with a capacity of 300~22000pF. It can be divided into image capacitor, tubular capacitor, rectangular capacitor, chip capacitor, perforated capacitor, etc. This article has collected and collated some materials, hoping to be of great reference value to all readers.

1、 Classification and characteristics of ceramic capacitors

1. Semiconductor ceramic capacitor

The miniaturization of capacitor means that the capacitor can obtain the largest capacity in the smallest volume, which is one of the trends of capacitor development. For the separation capacitor module, there are two basic ways to miniaturize, even if the dielectric constant of the dielectric material is as high as possible and the thickness of the dielectric layer is as thin as possible.

In ceramic materials, the dielectric constant of ferroelectric ceramics is very high, but when using ferroelectric ceramics to make ordinary ferroelectric ceramic capacitors, it is difficult to make the ceramic medium very thin. First of all, ferroelectric ceramics have low strength and are easy to break when they are thin, which makes it difficult to carry out actual production operations. Second, when the ceramic medium is very thin, it is easy to cause various structural defects, and the production process is very difficult.

The surface layer ceramic capacitor uses the thin insulating layer formed on the surface of semiconductor ceramics such as BaTiO3 as the dielectric layer, and the semiconductor ceramic itself can be regarded as the series circuit of the dielectric. The thickness of insulating surface layer of ceramic capacitor varies from 0.01 to 100 depending on the formation mode and conditions μ M. This not only makes use of the very high dielectric constant of ferroelectric ceramics, but also effectively reduces the thickness of the dielectric layer. It is an effective plan to prepare miniature ceramic capacitors.

2. Grain boundary layer ceramic capacitor

On the surface of BaTiO3 semiconductor ceramics with fully developed grains, appropriate metal oxides (such as CuO or Cu2O, MnO2, Bi2O3, Tl2O3, etc.) are coated, and heat treatment is carried out under oxidation conditions at appropriate temperature. The coated oxides will form a low-eutectic solution phase with BaTiO3, and rapidly diffuse into the ceramics along the open pores and grain boundaries, forming a thin solid solution insulation layer on the grain boundary. The resistivity of this thin solid solution insulating layer is very high (up to 1012~1013 Ω · cm). Although the ceramic grains are still semiconductors, the entire ceramic body shows an apparent dielectric constant of up to 2 × 104 to 8 × 104. The capacitor made of this kind of porcelain is called the boundary layer ceramic capacitor, or BL capacitor for short.

3. High voltage ceramic capacitor

With the rapid development of electronic industry, it is urgent to develop high-voltage ceramic capacitors with high breakdown voltage, small loss, small size and high reliability. Over the past 20 years, high-voltage ceramic capacitors successfully developed at home and abroad have been widely used in power systems, laser power supplies, tape recorders, color televisions, electronic microscopes, photocopiers, office automation equipment, aerospace, missiles, navigation and other aspects.

Barium titanate based ceramic materials have the advantages of high dielectric coefficient and good AC withstand voltage characteristics, but also have the disadvantages of capacitance change rate increasing with the dielectric temperature and insulation resistance decreasing. The Curie temperature of strontium titanate crystal is - 250 ℃, and it is a cubic perovskite structure at room temperature. It is a paraelectric, and there is no spontaneous polarization phenomenon. At high voltage, the dielectric coefficient of strontium titanate based ceramic material changes little, tg δ And the capacitance change rate is small. These advantages make it very advantageous as a medium for high-voltage capacitors.

4. Multilayer ceramic capacitor

Multilayer ceramic capacitor (MLCC) is the most widely used type of chip components. It is the combination of internal electrode material and ceramic body in multiple layers in parallel, and fired into a whole. It is also called chip monolithic capacitor. It has the characteristics of small size, high specific capacitance and high precision, and can be mounted on printed circuit board (PCB) and hybrid integrated circuit (HIC) substrates, Effectively reduce the volume and weight of electronic information terminal products (especially portable products) and improve product reliability. It conforms to the development direction of miniaturization, lightweight, high-performance and multi-function of IT industry.

Characteristic classification and precautions for use of ceramic capacitors

2、 Precautions for use of ceramic capacitors

1. The ceramic capacitor housing is damaged

The damaged ceramic capacitor of the shell is prone to leakage current. When the leakage current is large, a large amount of heat will be emitted to raise the temperature. The temperature will rise to a certain extent, burning the circuit and causing fire.

When using ceramic capacitor, we will check the ceramic capacitor first. If there are cracks and impurities on the ceramic capacitor, do not use the ceramic capacitor, and replace it with a new ceramic capacitor without damage.

2. Operating ambient temperature

Generally, the working temperature range of ceramic capacitor is - 25 ℃~+85 ℃. Before using ceramic capacitor, confirm the working ambient temperature. The working environment temperature is too low, which has little impact on the ceramic capacitor. However, attention should be paid to avoid the condensation of the ceramic capacitor and the deterioration of the working performance.

If the temperature is too high, the current surge is too large, the capacity of the ceramic capacitor will drop, and the working time of the ceramic capacitor will be shortened, which will also lead to the breakdown failure of the ceramic capacitor, and in serious cases, the circuit will be burned, causing losses to the company. Change the working environment with proper temperature and ventilation, or add a radiator or electric fan when the ceramic capacitor works to reduce the temperature to ensure the normal operation of the ceramic capacitor.

3. Working voltage

Before using ceramic capacitors, pay attention that the working voltage in the circuit cannot exceed the rated voltage of ceramic capacitors. If the rated voltage exceeds the rated voltage, it will easily lead to the short circuit failure of the ceramic capacitor, and the electronic product cannot work normally. It is necessary to replace the ceramic capacitor with the rated voltage greater than the working voltage to ensure the normal operation of the circuit.