Abstract: A substrate assembly includes a number of printed circuit substrates (PCS'). Each PCS includes a first or top surface and a second or bottom surface spaced from each other and an edge that runs at least partially about a periphery of the PCS between the top surface and the bottom surface. The edge of each PCS includes or defines on a facet or edge surface of the edge a number of spaced projections or nodules that extend transverse or normal to the facet or edge surface. The spaced projections or nodules of each pair of the number of PCS' are connected in an interdigitated manner with adjacent or proximate edge surfaces of the pair of PCS' positioned at an angle between 30° and 135° to each other, for example, at an angle of 90° to each other.