[time-nuts] The Smell of Tantalum in the Morning

[Chuck Harris]

The history of tantalum failures is wide and varied, but
there are some common characteristics:

1) The tantalum is in a power supply circuit and receives
    a rapid ramp from 0V to operating voltage.
2) The tantalum is spec'd close to its operating voltage,
    very close.... 5V on a 6.3V part, 12.5V on a 15V part...
3) The tantalum is dry slug, and is sealed with epoxy.
4) The instrument has been powered down for an extended
    period.

HP equipment from the 1980's is pretty immune to the problem
because they typically use hermetically sealed mil spec
tantalum capacitors.  Tektronix equipment from the 1980's
is infested with tantalum problems because they used the
cheap epoxy dipped parts.

Tantalum failures are pretty rare in equipment that is
run continuously.  Tantalum has a self healing feature that
corrects any small problems while in operating... Large problems
result in detonation.

Dipped tantalum capacitors of any age are prone to failure.
The tendency can be mitigated largely by never allowing a
tantalum capacitor to see voltage above 50% of its rating.

And finally, powering a tantalum in reverse, will cause instant
and irreparable damage.

-Chuck Harris



Tom Van Baak wrote:
> I powered up a 5071A to watch the end of Loran-C today
> and was greeted by the special smell that only a mother
> board could love.
> 
> Does anyone know the history of tantalum capacitor
> failures in ten-year old [HP/Agilent] test equipment?
> This is not my first. Last one was more like July 4th.
> 
> Thanks,
> /tvb
> 
> 
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