Tantalum - "fastest crow-bar known to man" - capacitors  fail
short-circuit if subject to overvoltage even moderately above their
rated value. Even a small low energy spike will achieve the initial
breakdown and then the full available supply current is shunted into
the short circuit. This is excellent for entertainment (some or all
of bad smells, smoke, explosion, fire and screaming acoustic affects
(I have experienced all these in a single failure)) but doesn't do
much good to customer confidence in your product.

The biggest single gain would be to use something else - eg SOLID
aluminium capacitors (which many people don't seem to have heard of).
If you MUST use tantalums then ENSURE that the applied voltage never
exceeds their rating. Using 25 volt parts as suggested here is one
way to try to do this but this is just fudging  - why won't the
spikes sometimes exceed even 25 volts in your application? - if at
all possible try to design the system rather than just getting
further away from the problem - or best of all, don't use tantalums.


regards

            Russell McMahon

From: Stuart Meier <smeier@PAVILION.CO.UK>

>Following a topic here a while back, I have several 1 and 10u
tantalum
>capicitors on boards where the PIC switches a couple of relays. The
5v
>relays are switching 12v,and a cap on the 12volt line has just
fried. It was
>rated at 16 volts.
>
>I thought this was a defective component, but another one has just
gone...
>
>I'll be uprating them in future, but surely a 16v cap should be
satisfactory
>on a 12v line?
>