Hi Folks

In the dim and distant past we presented to the forum our theory/feeling/guess
(delete as you see fit) that the traditional relationship seen for tin-lead
between lifetime and service conditions, as derived from accelerated
thermomechanical tests, was different for lead-free.  This came out of work in
the IDEALS European project that finished 2 years ago.

Specifically, we had some evidence to suggest that for lead-free, the service
life under benign (e.g. domestic) conditions would be longer than predicted by
standard accelerated tests, but that as service conditions got more severe
(e.g. approaching new automotive under-hood requirements) that tin-lead may be
better and certainly would be no worse than lead-free.  In other words there
might be a 'crossover' in the 'lifetime vs. severity' graph, with lead-free
better at the low severity end and tin-lead better at the high severity end.
The point of the crossover looked to be at about the severity of -25 / +125 deg
C cycling, so many of our test results suggested that SnPb and Pb-free were
equivalent in reliability, hence the carefully constructed comments in the
IDEALS write-ups you may have read.  (I am also aware that 'severity' itself is
complicated to define, but that really is a point for another day!)

Our data to support this supposition was real enough, but was not good enough
to publish so we could never really push the point.  I wonder if anyone out
there has data that can confirm or disprove this theory.  I know there was an
exchange on this topic back in July/August so apologies for any duplication.  I
am trying to draw together what 'we' know about thermomechanical reliability
and would appreciate any input.

By all means reply to me directly on [log in to unmask] if you feel that
the rest of the forum is not likely to be interested.

Thanks and regards to all.

Jim Vincent
(Project Manager of IDEALS)

+++++++++
    From: James H Vincent
          Marconi Optical Components
          Caswell, Towcester NN12 8EQ, UK

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