Norm,
    I am not real clear on what you were saying here:
> On inner layers you don't want a large mass of copper working on the
> plated through holes.
     I believe the stresses related to the mismatched CTEs are not focused
entirely on the joint at the PTH barrel but rather are distributed throughout
the entire assembly due to the nature of laminated construction.  Any
movement of the plane at the PTH should be extreamly localized and thus small. a
     That said, I think you a probably correct on any board that will be
subjected to really high temperatures, but then, delamination will be an
issue there at the same time.  In this case materials with a better matched
CTE would be the answer.
     Of course, all of this is just supposition on my part.  If you have
any numbers or experimental data I, for one, would love to see them.  Up to
now the only hard data is inferential from places like Cisco who say they
have seen no ill effects from direct connections.  I am seriously considering
designing a test board.  I would welcome any input.

[log in to unmask]
Don Walker

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