[Boatanchors] Questions about silver-mica capacitors

[mikea]

On Wed, Sep 09, 2015 at 03:14:54AM -0800, Jim Wiley wrote:
> 
> A question for the various group(s) :
> 
> 
> We have all heard reports of silver-mica capacitors failing due to
> "whiskers" forming on the metallic surfaces and subsequently causing shorts.
> Does anyone know if this problem is dependent on whether or not the
> capacitor is in use or not?
> 
> In other words, does the problem occur even it the part is simply stored in
> a box somewhere, or does it require the application of operating voltages
> (either DC or RF) for the problem to manifest itself?   Or it it a
> combination effect, with the rate of failure being faster (or slower) when
> in use, but the problem will still happen at a faster (or slower) rate than
> when the capacitor is simply sitting in dry storage?
> 
> Next, does this problem occur in all types of packages or just some, such as
> the common "epoxy dipped" vs. "postage stamp" (or other type)
> configurations?
> 
> Finally, is there a way to reverse the effect?
> 
> Inquiring minds want to know.

This is the best general explanation I've found: 

https://en.wikipedia.org/wiki/Whisker_%28metallurgy%29

and it's pretty scary. 

There are a lot more hits in a Google search for "metal whisker", and most of
them look interesting. 
-- 
Mike Andrews, W5EGO
mikea at mikea.ath.cx
Tired old sysadmin