Cooling fan and heat dissipation device having the same

A heat dissipation device, comprising:

• a heat sink comprising a substrate and a plurality of fins being located on the substrate;
• a cooling fan being attached to the heat sink, comprising:
• a fan housing defining an air inlet and an air outlet at two opposite sides along an axial direction of the fan housing, respectively, the air outlet being located adjacent to the heat sink and the air inlet being located distant from the heat sink;
• an impeller being received in the fan housing and mounted to a supporting base provided at the air inlet, the impeller comprising:
• a hub including a top wall being located at the air outlet and a sidewall extending downwardly from the top wall towards the air inlet;
• a plurality of main blades extending radially and outwardly from the sidewall;
• and
• a plurality of auxiliary blades being located on the top wall extending from a center of the top wall to an outer periphery of the top wall.