this invention relates to an insulating material for a wiring substrate and to a method of producing a multi - layered wiring substrate , and is directed to put into practical application a multi - layered wiring substrate suitable for processing high speed signals . the production method of the multi - layered wiring substrate of this invention uses an insulating material prepared by allowing voids of a porous perfluorocarbon polymer film to be impregnated with a thermosetting resin containing a benzocyclobutene ring , and thermally setting the resin , and comprises laminating alternately a wiring layer and an insulating layer made of the insulating material for the wiring substrate on a rigid support substrate .