We have a few PCB's that we use a SM IC power amp with a heat slug that is
reflow soldered to the board.  We have a via hole pattern under the device,
and the opp side of the board is exposed HASL finish gnd plane that is
mounted against a metal heatsink.  As has been discussed on this forum, a
problem with this design idea is during reflow, solder will tend to drain
away from the slug through the vias, but we have generally had acceptable
via fill, except for a recent batch of boards.
The bare boards had less consistent HASL finish leaving more solder on the
gnd plane side in places, and the QA person is wondering if that may be the
cause for increased solder drain?  Or alternatively if it is just related to
reflow temp profile?  Or some combination of both?

Genny

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