There are customers in the use of AVX tantalum capacitor during the tantalum capacitor explosion situation, especially in the switching power supply, LED power supply and controller industries, tantalum capacitor burned or exploded is the R & D technical staff the most headaches, so many technical staff feel Can not understand it. Because of the risk of tantalum capacitor failure mode, so many R & D technicians are afraid to use tantalum capacitors, in fact, if we can fully understand the characteristics of tantalum capacitors to find tantalum capacitor failure (manifested as burned or exploded) , Tantalum capacitors are not so terrible. After all, the benefits of tantalum capacitors are obvious. Tantalum capacitor failure reasons can be divided into tantalum capacitor itself, the quality of the problem and circuit design issues two categories:
Working circuit design and product selection
The performance parameters of tantalum capacitors can meet the characteristics of circuit signals, but often we can not guarantee that the two tasks are done in place, therefore, in the course of the use of such a failure will inevitably occur; now simply summarized as follows;
1. Low impedance circuit caused by the use of high voltage failure;
There are only two kinds of circuits used for tantalum capacitors; circuit with resistive protection and low impedance circuit without resistance protection.For circuits with resistance protection, because the resistance will play a step-down and suppress the effect of high current through, The voltage can reach 60% of the rated voltage of the tantalum capacitor.There are two kinds of circuit without resistance protection; one; the preamplifier has been rectified and filtered to output a stable charge and discharge circuit. In such circuit, the capacitor is used as the discharge power source Use, because the input parameters are stable without surge, therefore, despite the low impedance circuit, can safely use the voltage can still reach 50% of the rated voltage can guarantee a very high reliability. Second; the electronic part of the power supply; Parallel use in such a circuit, in addition to the requirements of the input signal filtering, often also at the same time in accordance with a certain frequency and power discharge requirements. Because it is the power circuit, so the loop impedance of such circuits is very low to ensure that The output power density of the power supply is sufficient. In this type of switching power supply circuit [also called DC-DC circuit], each time the power is turned on and off, the circuit will produce a duration of less than 1 microsecond high-intensity spike, The pulse voltage value can reach at least three times the stable input value, the current can reach more than 10 times the steady-state value, because the duration is extremely short, so the energy density per unit time is very high, if the capacitor voltage High, then the actual voltage applied to the product will be far more than the product rating of the breakdown.Therefore, the use of such circuits in the tantalum electrolytic capacitor allows the use of voltage can not exceed the rated value of 1/3 . If there is no circuit impedance type, a derating 50% of the circuit impedance in the lowest DC-DC circuit, a boot may be instantaneous breakdown short circuit or explosion phenomenon in such a circuit should be used in the capacitor down The amount of the circuit impedance value must be taken into account the level of the input and output power and the existence of the circuit in the exchange of ripple value because the circuit impedance level can determine the size of the instantaneous surge surge. The lower the internal resistance of the circuit should be the greater the amount of derating. For the size of the derating, it is not necessary to determine the derating rate by accurate reliability calculations.
2. The circuit peak output current is too large (use voltage is appropriate)
Tantalum capacitors in the work can safely bear the maximum DC current impact I, and the product itself equivalent series resistance ESR and rated voltage UR there are the following mathematical relationship; I = UR / 1 + ESR
If a low-capacity tantalum capacitor is used in a circuit with a large peak output current, the product is likely to be burned due to current overload, which is very easy to understand.
3. Tantalum capacitor equivalent series resistance ESR is too high and the circuit is too high AC ripple caused by failure
When an ESR is too high in the use of tantalum capacitors in the presence of high AC ripple filter circuit, even if the use of the voltage is much lower than the derating should be, sometimes, in the moment of power will still be a sudden breakdown of the phenomenon; The main reason for this problem is that the ESR of the capacitor and the frequency of the AC ripple in the circuit are not mismatched, and the capacitor is a polar element that generates heat when passing through the ripple while the product of the shell size is hot And the ESR values of different products are different. Therefore, different kinds of tantalum capacitors can be tolerant of the exchange of ripple values are also very different, so if there is a circuit in the exchange of ripple The use of capacitors can be safely tolerated by the exchange of ripple value, the product will appear hot breakdown phenomenon.Also, if the circuit in the exchange of ripple, and the choice of tantalum capacitor ESR value is too high, the product will appear The same phenomenon.
In general, in the filter and high-power charge-discharge circuit, you must use the ESR value as low as possible tantalum capacitors.For the existence of the circuit in the exchange of high ripple caused by capacitor failure, many circuit designers ignore its harm Or not enough. Just a simple identification of the quality of the capacitor there are many problems.
Tantalum capacitor leakage current is too large lead to the actual pressure is not enough
The occurrence of this problem is generally due to the actual withstand voltage of the tantalum capacitor is not enough.When the capacitor for a long time to exert a certain field strength, if the dielectric layer insulation resistance is low, then the product of the actual leakage current will be too large. Current large product, the actual pressure will drop.

Another reason for this problem is that the leakage current standard for tantalum capacitors is too loose, resulting in some companies that do not have tantalum electrolytic capacitor production capacity in the production of poor quality tantalum capacitors. Ordinary room temperature leakage current is too large Product, if the work at a higher temperature, the leakage current will exponentially increased, so its actual temperature at high temperatures will be significantly reduced in the use of high temperature will be very prone to breakdown phenomenon.
A small change in leakage current at high temperatures is one of the most important goals of all capacitor manufacturers' efforts, so the decisive impact of this indicator on reliability is beyond words.
If you choose to use the tantalum capacitor leakage current is too large, in fact it is already waste, the problem is therefore inevitable.
5. Tantalum capacitors used when the production process factors lead to failure
Many users often only pay attention to the choice of tantalum capacitor performance and design, and patch tantalum capacitor installation is easy to use when the problem turned a blind eye;
A, do not use the automatic placement and the use of manual welding, the product without preheating, direct use of temperature higher than 300 degrees of soldering iron for a long time heating capacitors, resulting in capacitor performance is too high temperature impact and failure.
B, the manual welding does not use the preheating table heating, welding a cold welding and Weld on the repeated use of iron heating products. C, the use of the tip temperature even up to 500 degrees. This can be welded quickly, but very easy to lead to tablets The reliability of the actual use of tantalum capacitors can actually be calculated by the calculation, and many of our users use the design margin is not enough, poor robustness, small batch of experiments by purely lucky, in the batch The quality of the problem occurs often at the moment, the cause of the problem is often simply pushed to the capacitor manufacturer who ignore the design reliability of the search tantalum capacitor when using the trouble-free interval MTBF for many users is still a strange Concept.Many users understand the superficial knowledge of reliability engineering, pay too much attention to the experiment and ignore the mathematical calculation.As a result of sub-circuit design reliability is lower than the whole machine reliability, therefore, the continuous production of bulk problems do not know how to failure is a probability problem, Non-simple individual problems. In fact, tantalum capacitors are prone to use when the causes and phenomena are still a lot, can not be discussed in this one.