is assembled completely the top portion 353 of the second engaging member 35 protrudes up beyond the operating member 37 a bore diameter of the through hole 3531 is larger than a diameter of the bolt 38 a width of each of the slot 371 and the slit 3141 is larger than a thickness of the top portion 353 of the second engaging member 35 thus the second engaging member 53 may be slidable along the bolt 38 when the top portion 353 is operated the fan 50 includes a frame 51 and an impeller 53 received in the frame 51 an aperture is defined in each corner of the frame 51 for assembling the fan 50 to the heat sink 10 when assembled the fan 50 is arranged on the heat sink 10 such that the apertures are aligned with the elongated grooves 133 of the heat sink 10 respectively then bolts 55 are extended through the apertures to engage in the elongated grooves 133 and thereby fix the fan 50 on the heat sink 10 when the heat dissipation 100 is assembled the heat sink 10 is arranged on the chassis 300 and contacts the electronic component 211 the body 31 of the clip 30 spans over the heat sink 10 with the first and second connecting plates 313 314 being located at an outside of the heat sink 10 the middle portions of the arms 312 of the body 31 are received in the grooves 113 of the heat absorbing portion 11 of the heat sink 10 the operating member 37.