Method of making laminate sheets for printed circuit boards

Abstract

In preparing an epoxy resin laminate sheet by impregnating a nonwoven fabric of glass fiber with an epoxy resin to form a prepreg, laminating a predetermined number of so formed prepregs and pressing, while heating, the laminate, when the nonwoven fabric of glass fiber to be used as a substrate is treated with a liquid mixture containing a water-soluble phenol resin and a silane coupler prior to the impregnation step, a laminate sheet suitable for formation of a printed circuit board can be obtained at a low manufacturing cost. The so formed laminate sheet not only has excellent heat resistance, drilling workability and punching workability at room temperature but also is characterized by such an excellent property that when it is subjected to the boiling water treatment, the degree of reduction of electric properties such as the insulation resistance is very small and whitening of the substrate is not caused to occur.

Dependencies are inferred from the claim text.