Abstract: The present invention is directed to improving the peel strength of copper foil laminated to polyetherimide substrates which optionally are reinforced. The improvement in process comprises coating one side of the copper foil with an adhesive composition, placing the coated side of the copper foil in contact with pre-formed polyetherimide substrate, and heat-pressing the resulting build-up to form a cured laminate of improved peel strength. The adhesive composition utilized comprises a blend of a polyvinyl butyral resin; one or more resole resins, and an organic solvent. Heat-pressing conditions comprise a temperature ranging from about 450.degree. to 550.degree. F. and pressing conditions ranging from about 100 to 700 psi. Within this temperature/pressure range, the adhesive-coated copper foil mated with the pre-formed polyetherimide substrate yields desired peel strengths without inducing excessive flow of the polyetherimide substrate, i.e. maintaining a pre-desired thickness .+-.7.5%.

Abstract: A method of making close tolerance laminates comprises the steps of positioning in an open stack a plurality of B-staged epoxy resin saturated fibrous sheets and providing the top and bottom of each stack with a contour pad, the stack-facing side of which is adapted to provide a horizontal pressure gradient ranging from higher at the center to lower at the edges, and consolidating the stack under heat and pressure. In contrast to conventional processes which produce laminates which are eliptical in shape (thicker in the center), the new process produces laminates having little or no center-to-edge variation.