A heat sink assembly includes a heat sink (30), a retention frame (10), a rectangular fastener (50), four pins (20), and four springs (40). The heat sink includes a base (32) defining four bores (38) therein. The frame is secured to a printed circuit board (60) around an electronic package (70), and defines a pair of screw holes (16). The pins are received through the bores of the base and in the fastener. The springs surround the pins respectively between the base and the fastener. A pair of posts (90) is extended through positioning holes defined in the fastener and the through holes of the heat sink, and engaged in the screw holes of the frame, thereby securing the fastener to the retention frame with the spring members pressing toward the base. The heat sink is thus easily, firmly and evenly secured to the electronic package.