Double-sided flexible copper-clad laminated substrate and method of producing double-sided flexible copper-clad laminated substrate with carrier

A manufacturing method for a both-side flexible-copper-laminated board is disclosed, which is a manufacturing method for a both-side flexible-copper-laminated board that has extremely thin copper foil on both sides thereof, the extremely thin copper foil is formed by peeling of a carrier on the carrier-bearing extremely thin copper foil that is formed via a peeling-off layer on the carrier. The method comprises the steps of: forming a polyimide resin layer on the surface of the carrier-bearing extremely thin copper foil to attain a carrier-bearing single-side flexible-copper-laminated board; implementing annealing treatment to the carrier-bearing extremely thin copper foil; laminating the carrier-bearing extremely thin copper foil subjected to the annealing treatment, on the surface of the polyimide resin layer of the carrier-bearing single-side flexible-copper-laminated board with the carrier being as outer side, so as to acquire the carrier-bearing both-side flexible-copper-laminated board; peeling off the