Three major crimes of tantalum capacitors
1. The problem of "continuous breakdown" and "continuous self-healing" caused by Gulu. After a period of normal use, the solder of the solid sealing port often melts, or when it is blown up, the solder flies to the circuit board. The reason for analysis is its work
At the time of "breakdown" and "self-healing", it is repeated, resulting in an increase in leakage current. This short-term (ns ~ ms) partial short circuit, and then resumed work after "self-healing."
About "self-healing." Ta2O5
The dielectric oxide film is continuous and consistent. When working under voltage or high temperature, due to the presence of TA+ ion defects, the leakage current in the defect micro-region increases, and the temperature can reach 500 ° C ~ 1000 ° C.
the above. This high temperature reduces MnO2 to low-cost Mn3O4. It has been tested that the resistivity of Mn3O4 is 4 to 5 orders of magnitude higher than that of MnO2. In close contact with the oxide film of Ta2O5 dielectric
Mn3O4 acts as an electrical barrier to prevent further destruction of the oxide film of Ta2O5 dielectric, which is the local "self-healing" of the solid. However, it is likely that the voltage of "breakdown" will be more than once before.
The "breakdown" voltage is lower. The leakage current will increase after each breakdown, and this breakdown power source may generate an ampere-level current. At the same time, the energy stored in the capacitor itself is also large, resulting in a capacitor.
The device is permanently disabled.
2. There is a "thermal failure" problem in the solid state.
The solid tantalum oxide film of Ta2O5 has unidirectional conductivity, and when there is a charging current through the Ta2O5 dielectric oxide film, it will lead
Fever failure. When the charging current is not charged, the thinning of the medium is quite stable, and the microscopic arrangement of the ions is irregular and disordered, which is called an amorphous structure. Visually present the color
It is a multicolored interference color. When the amorphous structure is gradually transformed into the shaped structure, it gradually becomes an ordered arrangement, which is called micro "crystallization". The color visually presented is no longer a multicolored interference color, but a dull, darker color.
The "crystallized" evacuated structure of the Ta2O5 dielectric oxide film causes the performance of the tantalum capacitor to deteriorate until breakdown failure.
3. There is a “field failure” problem (dV/dT).
The solid state is combined with a high voltage, and a high electric field is formed inside, which is easy to be partially broken down.
The incidence of breakdown accidents decreases to a stable value over time. When the breakdown voltage is approached, the incidence of breakdown increases. As the voltage increases, the probability of the device failing due to thermal runaway at a certain point increases. The breakdown voltage is dependent on the duration of the pulse. In some experiments, it can be seen that the breakdown voltage decreases as the pulse length increases. This process is not well defined; breakdown occurs at indefinite locations at varying time intervals. In the anti-mode, electrical breakdown is the final state of thermal breakdown due to Joule heat.
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