Abstract: Methods for the production of insulated, conductive through-features in conductive core materials for electronics packaging are disclosed. Invention methods employ protective mask technology in order to facilitate the selective removal of material from planar conductive core material that has been encapsulated in electrically insulated materials. By filling the cavity in the conductive core material with an electrically insulated material, the through-feature is electrically isolated from the remainder of the core material. In this manner, a conductive through-feature that completely transverses the core of the substrate board is created. Also provided are planar substrates for multilayer printed circuit boards, or chip carriers, comprising the conductive through-features produced by invention methods.