Detailed explanation of dielectric aging and anti-aging of ceramic capacitors

Date：2022-04-22 16:40:11Views：1217

Ceramic capacitor takes electronic ceramics as the dielectric material. It has the advantages of high service temperature, large specific capacity, good moisture resistance, small dielectric loss and wide selection of capacitance temperature coefficient. It is widely used in electronic circuits. However, with the extension of time, the dielectric aging phenomenon of ceramic capacitors will appear, which should be paid attention to in use.

Dielectric aging

In circuit applications, we mostly use class 2 ceramic capacitors, and the aging is mainly caused by dielectric characteristics (np0, X7R, z5u, Y5V). Dielectric aging is an effect of ferroelectric dielectric materials (mainly barium titanate). It is mainly manifested in the slow decrease of dielectric constant with time. The aging rate is the change rate of dielectric constant decreasing with time, which is logarithmic with time.

The relationship between aging rate and volume value after t hours can be expressed by formula:

Ct=C10 × (1-A/100lgt)

Of which:

CT: capacity after t hours;

C10: the capacity value at t0 time. Generally, the capacity value 24 hours after the completion of production and processing is selected as the capacity value at t0 time, the starting point of the aging time axis;

A: Medium aging constant (aging rate);

t: The aging time experienced by the capacitor starts from the end of the last heating in the production process, and the unit is hour.

Therefore, when designing low drift lines, low aging rate or non aging capacitors should be selected. And the designer should select the minimum capacitance of the capacitor according to the aging rate and temperature characteristic (TCC).

Capacitor anti-aging

If the capacitor is stored for more than 1000h or tested after aging screening test, and the capacitance value exceeds the specification requirements, anti-aging treatment shall be carried out: that is, heating the capacitor to a temperature higher than Curie temperature will play an anti-aging role and the aging phenomenon of the capacitor will disappear; When the capacitor cools down again, the aging will start again.

The common method of anti-aging is: place it at the upper limit temperature (or higher than the limit temperature, the maximum temperature can be up to 150 ℃) for 1h, and then keep it at room temperature for 24h before testing.

After the capacitor is installed in the equipment, if it is not powered on for a long time, the capacitor will also have aging phenomenon, that is, the electrical capacity will be reduced slowly. At the moment when the equipment is powered on, under the action of the power supply electric field, the part where the polarity of the dielectric electric coupling pole deflects due to the extension of the storage time will be immediately twisted, that is, the polarity arrangement state will be close to the factory state of the capacitor, and the capacitance will be restored to a certain extent.

Capacitor storage

In order to slow down aging, ceramic capacitors should be stored at a temperature of (5 ~ 40) ℃ and a relative humidity of less than 70%. Only open the moisture-proof packaging bag when using, and avoid storing the capacitor in a corrosive environment containing sulfur dioxide and acid gas.

If the capacitor is used more than one year after delivery, the electrical performance of the capacitor must be retested and the weldability must be tested. It can be used only after it is qualified.

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