A low-profile printed circuit board has discrete components mounted within openings provided in a rigid substrate forming art of the board. The components are mounted with leads soldered to mounting pads on the surface of the board, and arranged around the periphery of the openings. The stand-off design of discrete components for mounting to the surfaces of boards allows such components to be mounted within openings simply by reversing the orientation of the components relative to the board. In a preferred embodiment a DRAM card is a four-level board with circuitry on each side of a thin, flexible substrate and each side of a rigid substrate, the two substrates spaced apart by a thin, insulating layer. The rigid substrate has openings with DRAM modules mounted within the openings, and further modules are mounted on the opposite surface in the conventional manner.