An apparatus includes a main substrate, a device, and a heat spreader. The main substrate is configured for mounting the device in a mounting location thereon and having a cavity located below the mounting location. The device is mounted in the mounting location, and the heat spreader is fitted into the cavity and coupled to the device and to a heat sink. The heat spreader is configured to conduct heat from the device to the heat sink and to provide electrical insulation between the device and the heat sink.