Mike and Jack,
My apologies for posting based on my lack of knowledge.
Thanks for the educational updates. I certainly am not prone to argue
with the NASA research folks.
I do recall that it was a big concern inside ICs back in the 1980s and
90s when I was closely associated with the industry and more and more
density was being crammed inside those multi-legged critters.
I am surprised at the magnitude of inconsistencies and uncertainties
still present in the research data.
It is very interesting to find that dipping with tin-lead solder appears
to inhibit the growth, so those of us using tin-lead solders are
actually helping a bit to inhibit the growth - but then we don't re-tin
the full length of all the leads on all components either, so there is
remaining exposure.
So based on reading those articles - my conclusion is that we should
continue using the tin-lead solder and discourage the use of lead-free
solder for as long as we are able to do that. Since the tin-whisker
induced failures seem to take about a year or more to develop, I might
consider extended warranty coverage for any expensive electronic devices
as more and more of them move to RoHS compliance. This is really a
two-edged sword.
73,
Don W3FPR
Mike S wrote:
At 12:28 AM 10/19/2007, Don Wilhelm wrote...
The 'tin-whiskers' problem is one that exists mainly at the chip level.
The migration of conductive paths between pins that can be soldered
by hand techniques is *not* a problem because the 'whiskers'
typically do not extend that far. It is a problem inside the chips
where distances are measured in angstroms rather than in fractional
inches or millimeters.
Not according to NASA studies. They state "Whiskers as long as a few
millimeters are not uncommon..." -
http://nepp.nasa.gov/whisker/background/index.htm
Common through hole IC packages (DIP) have 2.54mm center to center,
which means ~1 mm air gap between pins, and that is also a _very_
common hole spacing pattern for discrete components. Here's an example
of non-"chip level" failure caused by tin whiskers:
http://nepp.nasa.gov/whisker/photos/pom/2004april.htm
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