Patent ID: 7282255

Claim:
A flexible printed circuit board having a copper thin film made of copper or an alloy containing primarily copper and directly formed on at least one side of a plastic film substrate, wherein said copper thin film has a two-layer structure comprising a surface layer having a crystalline structure and a bottom layer having a polycrystalline structure formed between said surface layer and said plastic film substrate, said copper thin film has an x-ray diffraction pattern in which an x-ray relative intensity ratio (200)/(111), that is a value obtained by dividing a peak intensity of the crystal lattice plane index (200) by a peak intensity of the crystal lattice plane index (111), is 0.1 or less, and said bottom layer is configured such that functional groups are generated on said plastic film substrate through plasma processing by glow discharge using a mixture gas containing nitrogen followed by evaporation to form copper metal or an alloy containing primarily copper on said plastic film substrate, wherein the metal or alloy bonds covalently to the functional groups of said plastic film substrate.