[sdiy] Tin Whiskers

[Paul Perry]

----- Original Message -----
From: "RMC" > Not directly related to what you were saying, but interesting
I think : my
> employer had a problem with silver whiskers forming in a silver-loaded
epoxy
> potting compound.
Something that used to cause problems with tube gear in the Old Days, was
"silver migration",
where silver plated components (especially valve pins or bases) somehow
formed
conductive paths. Whether you needed a potential differenc efor this to
happen, I don't know.

As to an earlier post about solder joints that look dull or cloudy (as
opposed to shiny) this
isn't a whisker problem, it is a result of the components beign soldered
havign moved before
the solder solidified, this gives a different crystalline structure. (you
lose some strength, but that is all).

Metallic tin itself changes to an amorphous allotrope at low temperatures
(which used to be a
serious problem for organ pipes made of tin, in unheated churches).
Personaly, I expect potting
would stop the problem, but it often arises in places where you can't pot!
like inside switches
and relays.

Having said all that, I havn't struck the problem myself.

paul perry Melbourne Australia