Bertrand -

If I understand your problem correctly, it would seem that you are dealing
with a situation where the three internal layers of copper are heat sinking
the plated thru hole and preventing complete solder flow thru during the wave
soldering process.

We use an attachment configuration for internal planes and heavy conductors
which we call an "isotherm".  This is simply a thermal break which surrounds
the internal circuit pad forming a structure somewhat like a wagon wheel.  We
have several configurations of this form which allow connection of ~30 to 60%
of the internal pad to the surrounding circuit or plane area.

Hope this helps - regards - Kelly

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