A magnetic core is situated in a cavity routed into an insulating substrate. The cavity and magnetic core are coved with a first insulating layer. Through holes are then formed through the first insulating layer and the insulating substrate, and plated to form conductive vias. Metallic traces are added to the exterior surfaces of the first insulating layer and the insulating substrate to form upper and lower winding layers. The metallic traces and conductive vias define the respective primary and secondary side windings for an embedded transformer. At least a second set of the outer conductive vias, are spaced farther from the cavity than a first set, and have greater via hole diameter than the vias in the first set. This reduces the resistance of the windings for a given substrate size and improves the performance of the device.