[ARC5] Questions about silver-mica capacitors

[Bruce Long via ARC5]

I know the dreaded tin whiskers grow with the component out of circuit.  i suspect at least potentially the same is true for silver migration although I think I remember reading, and it makes heretical sense to me as well that silver migration is also accelerated by applied voltage.


      From: Jim Wiley <jwiley at gci.net>
 To: DrakeRadio at yahoogroups.com; glowbugs <tetrode at googlegroups.com>; "boatanchors at mailman.qth.net" <boatanchors at mailman.qth.net>; ARC-5 List <arc5 at mailman.qth.net>; regenrx at yahoogroups.com 
 Sent: Wednesday, September 9, 2015 7:14 AM
 Subject: [ARC5] Questions about silver-mica capacitors
   

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.

- Jim, KL7CC


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