Abstract: An economical process for producing metal plated through holes in metal core circuit boards which permits the formation of small holes and fine conductor lines is disclosed. A metal sheet, which will become the core of a metal core circuit board, is provided with insulation layers on both sides, and through holes are provided through the insulation layers. The process involves incorporating fillers in a resinous coating solution which is electrophoretically applied to the hole walls to form an insulating layer of uniform thickness thereon. An increased diameter in the metal wall portion of each hole acts to restrict flow of the filled resinous coating solution during cure resulting in a straight hole wall. The coating is adhesion promoted and a metal layer is deposited thereon.