Hi Rick,
You are still not clear. When you say "sink" do you mean the resin between
the PTHs relative to thr PTHs? If yes, the explanation is that on heating the
resin expands--primarily in the z-direction--causing palstic deformation by
stretching of the copper barrels as well dishing of the PTH pads. On cooling
the resin contracts to its initial volume, but the PYHs are plastically
deformed, thus giving the appearance of the PCB "sinking" around the P:THs.
I hope this helps.

Werner Engelmaier

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