US Patent 7222421 Circuit substrate manufacturing method

A circuit substrate manufacturing method including the steps of preparing a substrate on which a metallic foil is formed in a releasable state, forming a build-up wiring on the metallic foil, obtaining a circuit member having a structure that the build-up wiring is formed on the metallic foil by releasing the metallic foil from the substrate, and exposing a lowest wiring layer of the build-up wiring by removing the metallic foil of the circuit member.