A heat dissipation device (40) includes at least a heat pipe (45) and a plurality of metal fins (43) thermally connected to the heat pipe. Each of the metal fins defines therein an aperture (431). An extension flange (433) extends outwardly from the metal fin and surrounds the aperture. The extension flange defines therein a plurality of slits (435). The apertures and extension flanges of the metal fins are aligned together. The heat pipe is received in the aligned apertures and soldered by a thermal medium material to the metal fins via the aligned extension flanges. During the soldering process, rosin content contained in the thermal medium material can be discharged away via the slits formed in the extension flange.