One embodiment provides a vapor chamber having an outwardly protruding boss. A frame surrounds a perimeter of the vapor chamber. A plurality of heat sink fins extend from the frame. A cross-member spans the frame across the vapor chamber wall and defines an opening through which the boss protrudes at least slightly beyond the cross-member. The heat sink may be secured to a socket on a circuit board, with the boss engaging a processor positioned in the socket. In response to securing the heat sink, the boss compresses flush with the cross-member and the cross-member engages the processor to seat the processor in the socket. The opening in the cross-member reinforces the boss against outward deformation.