Re: gEDA-user: Lead Free at home?

["Joel N. Weber II" <jwgeda@xxxxxxxxxxxxx>]

One concern I've seen expressed with Pb free parts is the possibility
of tin whiskers forming.  Tin whiskers simply don't form if there's
enough Pb mixed in with everything, but these days often the pins on
many modern parts don't contain any Pb even if you're using lead in
your solder.  As far as I can tell, the industry is generally moving
towards a matte tin finish for most parts.

http://nepp.nasa.gov/whisker/ has some basic background.

http://www.circuitsassembly.com/pdf/0408/0408nemi.pdf seems to suggest
that if you want good long term reliability wrt avoiding problems with
tin whiskers, it's best to avoid parts whose lead centers are spaced
less than 1mm apart.  I'm not at all clear how reliable the
information in this article is, though, or how often you're likely to
run into problems if you choose a less conservative approach.

One manufacturer's website I looked at indicated that they'd tested
for tin whisker formation by keeping samples of a part in an oven at a
constant temperature for some reasonably large number of hours (I
think it was a bit above 1000), and tried to imply that this was a
meaningful indication of whisker formation.  But I thought I'd read
elsewhere that thermal cycling and mechanical stresses may contribute
to tin whisker growth, which makes me very uncomfortable about putting
much faith into the usefulness of that manufacturer's data.