An enclosure is formed by coupling an outer cover to a back enclosure piece. The enclosure defines an interior volume for receiving components of an electronic device. The back enclosure piece is formed from a metal frame component and a non-metal outer cover. A metal layer overlaps the metal frame component and the outer cover within the interior volume. The metal layer has a thickness that provides support and shatter resistance to the non-metal outer cover. The metal layer can form an inductor of a wireless power transfer circuit.