PURPOSE: To improve the peel strength of the copper foil laminated to a polyetherimide substrate reinforced according to circumstances to keep the flat surface characteristics of an obtained copper-clad substrate.

CONSTITUTION: An adhesive compsn. is applied to the single surface of a copper foil and the coated surface of the copper foil is brought into contact with a preformed polyetherimide substrate and the obtained laminate is heated and pressed to form a cured laminate improved in peel strength. The adhesive compsn. to be used comprises a blend of a polyvinyl butyral resin, one or more kind of a resole resin and an org. solvent. A heating and pressure condition is set so that temp. is within a range of about 450-550° F and pressure is within a range of about 100-700 psi. Desired peel strength is obtained without bringing about the flow of the polyetherimide substrate, that is, a preset desired thickness is held to ±7.5%.