We report roll-to-roll fabrication of conductive copper circuits on flexible polyimide substrates, followed by integration of ultrathin, bare silicon chips and surface mount device components via flip chip bonding and pick-and-place assembly, respectively. R2R fabrication of the circuits involved a combination of either optical lithographic patterning or screen-printing of metallic seed layers, followed by electrolytic or electroless plating. Fabricated copper circuits had strong adhesion to the substrate, low resistivity, and were easily bonded with silicon chips and device components. Materials characterization, reliability assessment and demonstration of an ECG monitor integrated onto the circuits will be presented.