Manufacturing process for manufacturing printed circuit boards from an extruded polymer, comprising the steps:-preparing an electro-conductive plate (10) and form embossments (11) by means of selective engraving on a first side (10a), corresponding to future tracks and depressions (12) corresponding to future inter-track areas;-applying a dielectric substrate material, in a pasty or semi-pasty state, according to a first sheet (20a) obtained by extrusion of a thermal-plastic material, arranging it on said first side (10a), covering said embossments (11) and filling said depressions (12), and subjecting the first sheet (20a) and plate (10) assembly to a predetermined pressure so that the dielectric substrate material completely fills said depressions and encloses said embossments (11), and-on the hardened dielectric substrate, carrying out a second selective engraving on a side opposite the first side (10a), removing the material corresponding to said future inter-track areas.