Abstract: The invention provides a flexible metal-foiled laminate of an insulating base film of a synthetic resin, e.g. polyimide, and a metal, e.g. copper, foil adhesively bonded together and suitable for use as a base plate for printed circuit boards by virtue of the high heat resistance and greatly increased adhesive bonding strength between the base film and the metal foil. The laminate is prepared by use of a silicone-based adhesive and the surface of the base film is, prior to adhesive bonding, subjected to a treatment of exposure to an atmosphere of low temperature plasma generated in a gaseous organosilicon compound such as trimethyl ethoxy silane, optionally, diluted with an inorganic gas such as oxygen.