Hi All,
To really address a problem, one needs to understand its root cause(s).
Resin Ressession and Hole Wall Pullaway [Separation] are related phenomena.
Unlike a hole in a steel plate, a hole in a PCB gets smaller when heated, not
larger--this is the consequence of the constraining effect of the glass-fiber
reinforcements. Thus, on heating the epoxy will move towards the copper
plating, not away. The resin will 'recede' to its initial geometry on
cooling. This recession on cooling can leave voids when other materials do
not return to their original position.
What happens is that the resin on heating will compress the copper barrel.
For PTHs with thin plating, large diameters, low Tg resins, and absence of
internal lands this is more pronounced. This barrel compression can
plastically deform the copper barrel which thus will not return to its
original geometry--the resin will. The result is 'hole wall pullaway.'

Werner Engelmaier

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