The current invention provides a method of attaching a plurality of cores wherein a core has a via with a conductive surface to be electrically connected to a conductive surface on another core. The method provides for applying a metallurgical paste to a conductive surface, removing a portion of the flux from the paste and joining the two cores. The current invention also provides a structure including a plurality of cores wherein a metallurgical paste electrically connects a via with a conductive surface on a core to a conductive surface on another core.