SMD tantalum capacitors explosion causes (A)
"The explosion of chip tantalum capacitors has been the most troublesome problem for the R & D personnel. Especially in the switching power supply industry, so that a part of R & D personnel reluctant to use the chip tantalum capacitors in the circuit design. In fact, as long as our understanding of the characteristics of chip tantalum capacitors, will be able to analyze the cause of the explosion of chip tantalum capacitors, some conclusions have the following:
A low-impedance, high voltage lead SMD tantalum capacitors explosion
When the power part of the design of electronic machinery, some of our R & D staff will capacitors in parallel in such a circuit, chip tantalum capacitorson the one hand to the input signal is filtered, the other is to a certain frequency and power to discharge. Such an electrical circuit impedance is very low in order to ensure the power supply output power. In each switch machine of the moment, the circuit will produce a sustained peak of high intensity is less than 1 microsecond pulse, the pulse voltage value of at least three times more than the input value of the stability of chip tantalum capacitors, the current can reach Post -chip tantalum capacitors more than 10 times the steady-state value. In this very short duration, high energy density, the chip tantalum capacitors will be far more than the tantalum capacitor voltage values of the pulse voltage to breakdown, even if you are using KEMET, AVX tantalum capacitors is the same.
Therefore, selected in such circuit chip tantalum capacitor voltage rating of the value of the circuit stable voltage value of 3 times. Non-electrical circuit impedance type any derating 50%, the minimum loop impedance of the DC-DC circuit, must take into account the value of the AC ripple in the impedance of the circuit level and the size of the input and output power and circuit high and low. Because the circuit impedance, the level can determine the size of the surge amplitude of switching transients. The internal resistance of the lower circuit derating rate should be more. Derating margin size. Must not be generalized. Must be accurate reliability calculation to determine the derating margin.
In the case of the use of a suitable voltage circuit peak output current is too large to chip tantalum capacitors explosion
The maximum DC current of chip tantalum capacitors can safely withstand the impact of I with the product itself equivalent series resistance ESR and rated voltage UR can use this formula: I = the UR / 1 + the ESR.
If tantalum capacitors with a low capacity in the peak output current of the circuit, the only product is likely due to current overload and burned. This is very easy to understand.
3, SMD tantalum capacitor equivalent series resistance ESR is too high and the circuit in the AC ripple is too high to cause the explosion
Derating margin, even if the voltage is much lower than the application of excessive ESR SMD tantalum capacitors when used in excessive AC ripple filter circuit, and sometimes, at boot the moment will still be an abrupt breakdown phenomenon; The main reason for such problems is the size of the AC ripple in the ESR of the capacitor and circuit serious mismatch. Tantalum capacitor is polarity strength, will ripple through the exchange of heat, while the size of the shell number of products able to maintain thermal equilibrium allows the heat. ESR values of the different capacity difference between the higher value of the different specifications of chip tantalum capacitors can safely withstand the AC ripple also vary widely, so if the AC ripple in a circuit exceeds the posted chip tantalum capacitors can safely withstand the AC ripple value, the product will be the phenomenon of thermally induced breakdown. Similarly, if the AC ripple in the circuit must, while the choice of chip tantalum capacitor ESR value is too high, the product will be the same phenomenon.
In general, filtering and power charge and discharge circuit, you must use the ESR values as low as possible, SMD tantalum capacitors. The failure of the capacitor for AC ripple in the circuit is too high, many circuit designers to ignore the dangers or lack of awareness. Simply identified the problem of the quality of chip tantalum capacitors. This phenomenon is very common in the industry.
This article editor domestic manufacturer of tantalum capacitors - loose fill (new.sont.cc) Department