Gary, it has been a while since I worked on capacitors, but here are my 
comments.

I have not heard of tantalum capacitors failing as a result of current 
surges.  An aluminized paper capacitor supplier once showed me films of 
plastic film capacitors coming apart during surges (of course, his paper 
components did not fail under such stress).  Tantalums do not self clear 
if an internal short develops.  The part is destroyed.  They can't 
toerate any reverse voltage, so have to be installed with proper polarity.

Are aluminum electrolytics less stable with temperature?  I have not 
heard anyone express such a concern before.  They do have a tendency to 
dry out and become open circuit under temperature stress.  Long-lived Al 
electrolytics have low-loss electrolytes and superior paper, as compared 
with the more pedestrian variety.  By less stable, do you mean their 
capacitance value changes with temperature over a short time, or that 
they dry out, over a relatively long time?

Lou Hart



.

On Tue, 16 Apr 1996, Gary Peterson wrote:

> Does anyone have an opinion, comments or data to support a rumor I heard?
> 
> I'm told that tantalum caps can fail shorted if required to supply a current
> surge.  To prevent this failure aluminum electrolytics are preferred on digital
> boards.
> 
> I thought Aluminum electrolytics weren't very stable in capacitance over temp
> and were not preferred to tantalum for that reason as well as size (more
> Capacitance per volume in Ta than Al).
> 
> Gary P.
> ---
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