Tin Whiskers Theory and Mitigation Practices Guideline:
http://www.jedec.org/DOWNLOAD/search/JP002.pdf

"The amount of damage required for
a BGA to fail on an assembly was used to predict lifetimes for other BGAs,
at other locations, on the same board. They tested: Sn3.9Ag0.6 for reflow
soldering, Sn3.4Ag1.0Cu3.3Bi for reflow, Sn0.7Cu0.05Ni for wave, and
63Sn37Pb for reflow and wave. The surprising part is that BGAs using
tin/lead will outlast SAC BGAs by a factor of 20x. Thus, SAC BGAs in
high-reliability electronics could be problematic in high-vibration
environments.

I'm not sure that I would find this "surprising", having seen the general
performance of lead-free from a service angle, for several years now. At the
end of the day, like several other technologies we have been forced to ditch
as a result of dubious science and conclusions, lead-based soldering was a
mature, proven, and above all *reliable* way to construct electronic
equipment.

If Boeing Corporation are really leading research into the performance of
this hateful material, then I hope that it is with a view to reinforcing the
avionics industry's opinion that this stuff has no right to up be in the
sky, and responsible for getting 450 people safely to their destination. If
they are researching with the intention of determining the best compromise
alloy to use in place of conventional solder, then I believe that is indeed
a worrying development ...

It would be interesting to know from someone directly involved in avionics
or avionics service, how many in-service equipment failures are currently as
a result of bad joints, and what sorts of levels of failures are being
recorded in the vibration tests that must be being done on evaluation sample
pieces, constructed with lead-free.

Arfa