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Date: | Wed, 16 Nov 2005 13:35:32 EST |
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Hi Ingemar,
We have been aware for some time that the lead-content is higher near the IMC
layers, because some of the Sn has been used to form the IMCs. However, any
Pb-nonuniformity that might otherwise be present in solder joints would have
its impact felt [but not directly recognized] in the results of any accelerated
testing.
Now if there is a difference between the Pb-uniformity between the short-term
ACT samples and the long-term product solder joints, that is a different
matter--and I do not know how to currently address it.
We do, however, know of a difference between the short-term ACT samples and
the long-term product solder joints. that is the coarseness of the solder grain
structure which changes over time with temperature and loads. The difference
can be as high as a factor of 2 to 3. that is why IPC-SM 785 and IPC-9701
recommend artificially aging [meaning grain coarsening] solder joints prior to
ACT.
Werner
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