Jerry gave you some good Tantalum articles to study. If it's not a
defective lot or bad cap manufacturer and you're having a 20% failure
rate with a 20V rated Tantalum on a 12V circuit then either the
capacitor is mounted backwards as Gene mentioned, or there is a peak
voltage higher than you expect at power-on. For the reversed voltage
check the capacitor markings to find the positive end and check with a
voltmeter to see if the voltage is reversed compared to what the
capacitor is expecting. It's also possible the assembler accidentally
inserted them the wrong way even if you designed them correctly. For
the peak voltage at startup look at the voltage on the capacitor at
power-up using a scope to see how high the voltage spike is at power-up.
I studied failure causes and failure rates as part of designing for high
reliability for building Telecom systems that sometimes stay in service
for 20-25 years. As a result of the research we designed out standard
Tantalum caps whenever possible in favor of ceramic or other more
reliable types when the available capacitance values would allow it. In
addition to the higher failure rate for Tantalums they tend to fail
shorted and will take out the board while ceramics usually fail open and
often allow the circuit to continue operating if there are other
parallel capacitors on the supply.
I should mention the type of circuit matters too, the characteristics of
each type of capacitor will also determine which types will work for
your particular circuit requirements.
Hope this helps.
Chuck Corley
On 2016-02-04 07:50, Bni I wrote:
Hi experts------------------------------------------------------------------
I am having issues with my 100uF 20V 1206 tantalum capacitor for 12V
input.
The ripple is lower, but close to the limit (said in the DS) [~150mA]
I am facing 20% failure.Most of the time, it explodes on the first
power on.
Sadly I have a lot of PCB without any hope to change the PCB.
I haven't found much on the application of the tantalum.
I found that there is some condensation/crystallization time on the
first
power up.
The article suggest to use 3xVin [Ohm] serial resistor.
I am not satisfied with this solution. I think it does not help on the
problem.
It only mitigates the problem and it will blow up in my customer hands.
Any experience or artical/book are welcome.
Thanks
Steve
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