A heat dissipating assembly includes a heat sink (10) having a chassis (12), a back plate (30) and a plurality of fasteners (40). Each fastener includes a screw cap (42), a spring (44) and a sleeve (46). The screw cap and the sleeve are movably connected together. The screw cap includes a head (420) and a tube (422) extending from the head. The tube includes a first cavity (424) and a second cavity (426). The back plate forms a plurality of posts (34) passing through the chassis and threadedly engaging in the first cavities of the tubes. A spring (44) is compressed between the first cavity of the tube and a bottom wall of the sleeve, for providing appropriate downwardly pressing force on the chassis of the heat sink against a CPU (22) mounted on a PCB (20).