Hi Gary,
In a message dated 06/21/2001 13:45:20, [log in to unmask] writes:
>Werner:    I would argue your point, in that by having interfacial
connections in a MLB >composite, that you are mechanically re-inforcing the
hole wall barrel. This is important >on thicker boards, as the more
interstitial connections, the less prone you are to hole >wall pull-away.
Hence the reason for the stitched vias in DS products.
>Gary Erickson

Hole wall pull-away is not really a reliability threat, but PTV barrel
cracking definitely is. And the point I made is experimentally substantiated
in IPC-TR-579 "Round Robin Reliability Evaluation of Small Diameter Plated
Through Holes in Printed Wiring Boards." And of course, the connections of
the barrels to the innerlayer can get stressed enough to fail as well. A
study on innerlayer separation (ILS) or post separation has just been
finished and published, IPC-TR-486, "Report on Round Robin Study to Correlate
Interconnect Stress Test (IST) with Thermal Stress/Microsectioning Evaluation
for Detecting the Presence of Innerlayer Separations."

Werner Engelmaier

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