I wasn't going to comment on this thread...but I think it's
now in order... here's a concise snip of the previous (without
attribution), followed by my comments:
-0-
Whiskers are an issue in reliability of (usually space)
components and
> circuits. The culprits are Tin >97% pure, 100% pure
cadmium and 100% pure
> zinc. If these metals are NOT pure, there is little
problem.
-0-
Unless we send our solder joints deep into space or
otherwise place them in a vacuum for many years whiskers are
not an issue.
They only form in a high vacuum and it takes a long time, so
why worry about it?
-0-
Not so Tom. Although much progress has been made with "no-clean" solders,
dendrite growth is still an issue when pc board assemblies are exposed to
humidity. To remove flux residues after waveline or smt reflow soldering
processes,
it was common to use either chemical or deionized water board washers
followed by dryers. Eventually, the EPA banned the CFC emissions and the
deionized
washers were expensive and a mess to maintain, so "no-clean" solders took
the
lead. Believe me, we wouldn't have gone to all this trouble in the industry
if
whiskers only formed in a high vacuum.
-0-
MY COMMENTS:
First, appologies for removing attribution, but I didn't have
the ability to properly cite the first post. So I deleted all.
Secondly, I am aware of significant problems with semiconductor
test systems, where something other than pure zinc was used to plate
the guide rails for board sets. Dendrites were scrubbed off whenever
a board was changed out...and the fallout caused leakage currents on
circuitry beneath the removed card. For NDA reasons, I can't be more
specific, nor comment on the scope of the problem, other than to say
that it is not trivial.
Thirdly, there have been recent publications on dendrite growth with
zinc, tin, and other metals. For those interested, I recommend googling
the subject. I think Discover and Scientific American had pieces, along
with Electronic News and Semiconductor International.
And Finally, I have not seen any reports of problems with amateur radio
equipment in regard to this problem. If anyone has anything specific,
a citation would be a good thing to post.
Best regards(and slow growing whiskers)
N2EA
jimjarvis@ieee.org
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