If you mean that you will place copper plate between the heatsink and the bottom of the chip, while you use proper insulation pads and/or heatsink grease without air pockets between, then all should be fine. Just little less heat transfer than direct contact.
There is L-bracket in Vfet amp, similar situation.
There is L-bracket in Vfet amp, similar situation.
But if you mean top part of the chip, where the lettering is, forget it. That surface is not flat for proper heat transfer. It will not hurt, but it likely will not help either. Just do the right heat transfer in the first place.
The copper plate may not be a good radiator. An actual heat sink with fins would be better.
That said, as @adason points out, the thermal resistance from the IC die to the top of the package is pretty high so a heat sink won't help much. Surface mounted packages are better in this respect as they're thinner.
Tom
That said, as @adason points out, the thermal resistance from the IC die to the top of the package is pretty high so a heat sink won't help much. Surface mounted packages are better in this respect as they're thinner.
Tom