For a three-layer flexible board, there is provided a copper alloy foil that requires no roughening processing, that has good adhesion with an adhesive containing an epoxy resin, that can be laminated to form a copper-clad laminate, that has a low surface roughness, and that has high conductivity and strength. The copper alloy of the foil contains at least one of 0.01-2.0 weight percent Cr and 0.01-1.0 weight percent Zr or contains 1.0-4.8 weight percent Ni and 0.2-1.4 weight percent Si. Good adhesion of the copper alloy foil to a resin substrate with an adhesive containing an epoxy resin is obtained by setting the thickness of the anticorrosive coating to less than 3 nm; the surface roughness of the copper alloy foil is below 2 m expressed as ten-point average surface roughness (Rz); and, without roughening processing, the 180 C. peel strength, after adhesion of the copper alloy foil to the board film by means of an adhesive containing an epoxy resin, is greater than 8.0 N/cm.