A display device having two opposite long sides and two opposite short sides, the display device comprising: a display panel; a flat frame at the rear of the display panel; a backlight unit positioned between the display panel and the flat frame and providing light for the display panel, wherein the backlight unit includes a plurality of substrates and a plurality of light sources (124, 203) mounted on each of the substrates, each of the substrates forming a strap elongated in a longitudinal direction of the substrate, the straps extending in a first direction parallel to the long sides of the display device and being separated from one another by a predetermined distance in a second direction parallel to the short sides of the display device and perpendicular to the first direction; and a plurality of heat dissipation protrusions each formed on the flat frame at a respective location corresponding to one of the light sources (124, 203), wherein the heat dissipation protrusion contacts the substrate, wherein the frame and the heat dissipation protrusions are formed as one body, and the display device further comprises: a plurality of coupling protrusions formed on the flat frame, wherein each of the coupling protrusions fixes the backlight unit to the frame, and wherein each of the coupling protrusions is positioned adjacent to at least one of the heat dissipation protrusions while being separated from said at least one of the heat dissipation protrusions, wherein each of the substrates has a coupling groove, into which one of the coupling protrusions is inserted, wherein the coupling groove elongates on the substrate along the longitudinal direction of the substrate and has a circular insertion groove at one end, wherein each of the coupling protrusions has a head smaller than a diameter of the insertion groove and larger than a width of the coupling groove. a display panel; a flat frame at the rear of the display panel; a backlight unit positioned between the display panel and the flat frame and providing light for the display panel, wherein the backlight unit includes a plurality of substrates and a plurality of light sources (124, 203) mounted on each of the substrates, each of the substrates forming a strap elongated in a longitudinal direction of the substrate, the straps extending in a first direction parallel to the long sides of the display device and being separated from one another by a predetermined distance in a second direction parallel to the short sides of the display device and perpendicular to the first direction; and a plurality of heat dissipation protrusions each formed on the flat frame at a respective location corresponding to one of the light sources (124, 203), wherein the heat dissipation protrusion contacts the substrate, wherein the frame and the heat dissipation protrusions are formed as one body, and the display device further comprises: a plurality of coupling protrusions formed on the flat frame, wherein each of the coupling protrusions fixes the backlight unit to the frame, and wherein each of the coupling protrusions is positioned adjacent to at least one of the heat dissipation protrusions while being separated from said at least one of the heat dissipation protrusions, wherein each of the substrates has a coupling groove, into which one of the coupling protrusions is inserted, wherein the coupling groove elongates on the substrate along the longitudinal direction of the substrate and has a circular insertion groove at one end, wherein each of the coupling protrusions has a head smaller than a diameter of the insertion groove and larger than a width of the coupling groove. a plurality of coupling protrusions formed on the flat frame, wherein each of the coupling protrusions fixes the backlight unit to the frame, and wherein each of the coupling protrusions is positioned adjacent to at least one of the heat dissipation protrusions while being separated from said at least one of the heat dissipation protrusions, wherein each of the substrates has a coupling groove, into which one of the coupling protrusions is inserted, wherein the coupling groove elongates on the substrate along the longitudinal direction of the substrate and has a circular insertion groove at one end, wherein each of the coupling protrusions has a head smaller than a diameter of the insertion groove and larger than a width of the coupling groove.