You did not say when (after what processing step) this hole wall pullaway
occurred.
Assuming this was after assembly, the cause is excessive heating during the
soldering process, which likely was a manual process. In this case, you do
NOT have a 'hole wall pullaway', but a 'resin pullaway.'  This can be easily
ascertained with the cross-sections; if the hole wall looks bent inwards
between innerlayer lands, you have 'resin pullaway.' During excessive heating
of the MLB, the resin expands, particularly above Tg, normally in the
z-direction. If the hole wall is relatively thin (less than 1 mil) and/or the
distance between innerlayer lands is large, the resin also expnds into the
PTV plastically deforming the copper wall. On cooling, the resins shrinks
back to its original volume, but the plasyically deformed PTV wall resists
the movement and if the adhesion is not very strong, you get 'hole wall
pullaway'.

Werner Engelmaier
Engelmaier Associates, Inc.
Electronic Packaging, Interconnection and Reliability Consulting
23 Gunther Street
Mendham, NJ  07945  USA
Phone & Fax: 973-543-2747
E-mail: [log in to unmask]