The present invention is directed to provide novel composite copper components. For example, provided is a composite copper component including a copper oxide-containing layer formed on at least a portion of the surface of a copper component, in which when the surface of the composite copper component is bonded to a resin substrate by thermocompression, and the copper component is peeled off from the resin substrate after the thermocompression bonding, metal contained in the copper oxide-containing layer is transferred to the resin substrate.

A problem is to provide a copper etchant capable of stably maintaining smoothness after etching. As means for solving the problem, the etchant contains hydrogen peroxide, sulfuric acid, an aromatic compound, and a chlorine ion, in which the aromatic compound has a structure in which a hydroxyl group and/or a carboxy group is bonded to a benzene ring.