A baseboard having through-holes for a printed circuit board which baseboard is made from a metal as a substrate, comprising at least one resin coat layer formed on the overall surface of the metal substrate including the inner wall surfaces of the through-holes and having, at the circumferential angular portions of the through-holes, a thickness larger than that on said upper and said lower surface of the metal substrate, and featured by its increased insulation characteristics at the circumferential angular portions of the through-holes.