Abstract: An improved circuit board having electrically conductive traces connected to respective terminals of a number of electrically current components mounted on a substrate. The substrate has cavities for mounting the components, and a plurality of grooves extend into one or both of a pair of opposed surfaces of the substrate. The grooves are filled by plating with an electrically conductive material to form the traces. Thus, the traces not only extend in the plane of a surface of the substrate but also extend perpendicular to such plane and into the substrate itself whereby a high packing density of traces can be achieved while maintaining essentially electrical paths between the components. The depth of each trace is a number of times greater than the width of the trace, a typical ratio being 10:1. The substrate can be molded from a plateable plastic or ceramic material and the grooves can be machined by a laser beam.