[AR] Re: Tin whiskers
- From: Norman Yarvin <yarvin@xxxxxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Tue, 2 Aug 2016 21:30:57 -0400
On Mon, Aug 01, 2016 at 03:40:58PM -0400, Henry Spencer wrote:
On Sun, 31 Jul 2016, Norman Yarvin wrote:
...it only takes one or two percent of lead to suppress whiskering.
(And that in an already-thin tin plating; in a world where lead-acid car
batteries are made by the millions, banning lead in tin platings seems
pretty silly.)
It is pretty silly. The ill-advised attempt to eliminate lead from
electronics has caused grief out of all proportion to any likely benefit.
I'm not sure about lead in solder itself; traditional leaded solder
has about 40% lead and is used in larger quantities than go into
platings. And there doesn't seem to be much wrong with lead-free
solders, though they do need a bit higher temperature. So that part
of the ban might be reasonable enough, but not the platings part.
They also help against whiskers that are floating around in the
environment (say, zinc whiskers from a nearby piece of galvanized
steel).
Generally better addressed by excluding such conductive debris, i.e. by
being more careful about materials choices and cleaning.
With all the little parts that come galvanized, that isn't a small
task. (The presentation I linked to shows a D-sub connector with a
zinc-plated shell with whiskers growing. "What additives quench zinc
and cadmium whiskers? We don't know, but certainly NOT chromate
conversion finishes!")
Not that I'm going to argue for conformal coatings, which are indeed a
pain.
An interesting thing here is that metal whiskers can explain a lot of
things that might be put down to software glitches or radiation
events: you get a short and it quickly fries the whisker, clearing the
short but not before producing some anomalous behavior. But even if
you _aren't_ sending your system into orbit, the anomaly is then
almost impossible to debug since the whisker is now gone.
--
Norman Yarvin
http://yarchive.net/blog
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