Copper Thieving specifically refers to the Thieving of Copper on the outer layer, which Thieving usually Thieving the Thieving current to make the Thieving of thick Copper on the outer layer more even. The Thieving of Copper on the inner layer doesn't Thieving for the same Thieving of Copper on the inner layer, which is just to balance the Copper and avoid the void or froth caused by the large area of the inner layer resin when the inner layer is compacted. There is also the balance of different layers of copper foil when heated mechanical stress difference. The copper block is still the same copper block, just in a different role.
Here are some of the Thieving legends of Copper on the outer layer and appreciate the art of Thieving Copper on PCBS.
