Electronic devices may be provided that include mechanical and electronic components. Connectors may be used to interconnect printed circuits and devices mounted to printed circuits. Printed circuits may include rigid printed circuit boards and flexible printed circuit boards. Heat sinks and other thermally conductive structures may be used to remove excess component heat. Structures may also be provided in an electronic device to detect moisture. Integrated circuits and other circuitry may be mounted on a printed circuit board under a radio-frequency shielding can.