Used to build MLB's with up to 60 mil thick copper, or al, thermal planes on
each side. Etching worked ok to that point. Additional thickness required
separate chem milling, then bonding sinks was required with no flow preg, or
whatever.

Those still building military/aerospace boards should still be doing this
almost routinely. Start with an IPC directory and work there first on West
Coast as someone like Details, McCurdy, or someone else MIL qualified.

If your design required thick internal planes, the practical thickness is up
to 5 oz. Cu but 10 oz achievable with high resin content prepreg. This is
another way to achieve thermal dissipation, with pipes and/or cutouts,
notwithstanding high current carrying capabilities.

Earl Moon

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