Electrical components such as integrated circuits and other components may be mounted on a substrate such as a printed circuit substrate. A molded plastic cap may cover the components and a portion of the printed circuit substrate to form a packaged electrical device. Metal structures such as springs, posts, and other metal members may be insert molded within the plastic cap. A metal layer on the surface of the cap may be patterned to from electromagnetic shielding, signal paths, contact pads, sensor electrodes, antennas, and other structures. Multiple substrates each with a respective set of mounted electrical components may be joined using a flexible printed circuit. The flexible printed circuit may be covered with a rigid cap portion or an elastomeric material or may be left uncovered.