Abstract: An array of electronic modules on the top of a circuit board is cooled by a heat sink secured to the bottom of the board. Vias transfer heat through the board to a compliant interface pad which permits heat to flow to the heat sink while maintaining electrical isolation between the vias. The heat sink is held on the board by push pin assemblies including springs that compress the interface pad between the circuit board and the heat sink. The body of each push pin assembly includes flexing legs supporting locking barbs, and flex of the legs is limited by a strut defining a closed end slot in the shank of the body.