"Glen Walpert" wrote in message
...
On Tue, 24 Jul 2007 23:42:47 +0100, Eeyore
wrote:

The debate about lead free solders seem to be nearly as politically
charged as
that about anthropogenic global warming and a casualty seems to be useful
data.

I've read plenty of comments to the effect that lead-free is less reliable
in
the long term (vibration seems to be a key weakness AIUI - maybe also
thermal
cycling) which presumably explains the exemptions for certain categories,
yet
I've also seen some studies that claim it can out-perform lead containing
solders.

Is there any real hard and fast information out there that one can rely on
?

Graham

Don't look to this newsgroup for factual info on lead free! Instead
look at actual test results in the trade publications such as SMT
magazine:
http://smt.pennnet.com/home.cfm
They have published numerous tests comparing various lead free
materials and processes with tin-lead. Some lead free materials and
processes are better than others (no surprise) and picking the best
one for your situation is non-trivial.

My nutshell summary of the published test results is that lead free is
significantly harder to do right than tin-lead, requiring tighter
process controls, but if done right it can be more reliable than
tin-lead for non-shock situations. Lead free is harder, stronger and
more brittle than tin-lead so tin-lead will deform plastically under
high shock when lead free will break, however lead free will withstand
more hot-cold cycles than before failure than tin-lead (better fatigue
resistance). So you need to know what the significant failure
mechanisms are in your design to pick the most reliable materials.

Glen

And in the meantime whilst smaller manufacturers who don't have the
resources of the big boys to research this crap in sufficient detail to find
the 'correct' process to replace the previously utterly reliable and simple
leaded soldering that they were using, cartloads of electronic equipment are
failing as a result of the bad joints that the experimentation or 'best fit'
replacement alloys are causing.

I wonder what qualifies you to make that remark at the beginning of your
post, telling people not to look to this group for 'factual' information on
lead-free ? When I tell you that I work day in day out with equipment from
major manufacturers that uses the stuff, and that since they have been using
it, I have seen the incidence of bad joints in places that would never
previously have suffered, skyrocket, do you consider that to not be
'factual' ? Am I lying perhaps ? There are many good engineers that
contribute to this group, and most have reported seeing an increase in such
bad joints. Are they all being less than 'factual' ?

When push comes to shove, this is an electronic repair group, frequented by,
amongst others, repair professionals who have to deal with the effects of
legislation such as RoHS, and its implications, at the sharp end, which is
more than the manufacturers and political activists / pseudo scientists
responsible for creating these situations, do. As such, I feel that it is
therefore rather presumptuous of you to suggest that opinions voiced on this
group, are not based in fact, and thus not valid.

Arfa