DIELECTRIC SUBSTRATE AND ITS PRODUCTION

PURPOSE:To reduce the dielectric constant and the dielectric loss tangent by joining electrolytic copper foils to both faces of a dielectric base material through crosslinked super molecular weight polyethylene layers so that surfaces opposite to specular surfaces of copper foils are brought into contact with super molecular weight polyethylene layers. CONSTITUTION:With respect to a dielectric substrate, two dielectric base materials each of which consists of a glass cloth 1 and a crosslinked polyethylene layer which is impregnated in the cloth 1 and covers surfaces of the cloth 1, and crosslinked UHPE layers 3 are arranged on both faces of these laminated base materials, and electrolytic copper foils 4 are arranged on UHPE layers 3 so that rough surfaces 5 of foils 4 face crosslinked UHPE layers 3, and they are joined into one body. A crosslinked polyethylene layer 6 is provided as desired for the purpose of adhering base materials to each other more firmly. UHPE films are crosslinked by irradiation of an electron beam or the like, and it is preferably from the aspect of adhesion that UHPE films are crosslinked in such degree that the gel rate is 30-100%, and it is obtained if the exposure of the electron beam is 0.1-10M rad normally. Thus, the dielectric constant and the dielectric loss tangent are reduced.