hereinafter , preferred embodiments of the present invention are explained in detail in conjunction with drawings showing the embodiments . fig1 is a developed perspective view for explaining an essential part of the embodiment 1 which applies an image display device according to the present invention to a liquid crystal display device . in the liquid crystal display device , a liquid crystal display module is constituted of a liquid crystal panel 1 , a backlight 5 and a display control printed circuit board 22 . here , most of a center portion of a substrate constituting the liquid crystal panel 1 is a display region ar , and a plurality of single - layered cofs 30 each of which is formed by mounting a source driver 3 on a printed film 2 is mounted on one side ( an upper long side of the display panel shown in fig1 ) out of a periphery of the display region ar . further , a plurality of single - layered cofs 30 each of which is formed by mounting a gate driver 4 on a printed film 2 is mounted on other side ( a right short side of the display panel shown in fig1 ) out of the periphery of the display region ar . the backlight 5 is arranged on a back side of the liquid crystal panel 1 , and the display control printed circuit board 22 is arranged on a back surface of the backlight 5 . the single - layered cof 30 which mounts the source driver 3 thereon and has one end thereof mounted on the upper long side of the liquid crystal panel 1 has another end thereof connected to a printed circuit board 20 . the single - layered cof 30 which mounts the gate driver 4 thereon and has one end thereof mounted on the right short side of the liquid crystal panel 1 has another end thereof connected to a printed circuit board 23 . the printed circuit board 20 and the printed circuit board 23 are connected to the display control printed circuit board 22 via an fpc 21 . fig2 a to fig2 c are views for explaining the embodiment 1 of the image display device according to the present invention . in the embodiment 1 , the single - layered cof 30 is used for mounting the driver on the liquid crystal panel . fig2 a is a plan view of the single - layered cof 30 , fig2 b is a cross - sectional view taken along a line x - x ′ in fig2 a , and fig2 c is a cross - sectional view taken along a line y - y ′ in fig2 a . here , in fig1 , although a length of the single - layered cof 30 in the direction along the line y - y ′ is described larger than a length of the single - layered cof 30 in the direction along the y - y ′ line shown in fig2 a to fig2 c , the length and sizes of other parts can be arbitrarily changed corresponding to the specification of the liquid crystal panel . further , although fig2 a to fig2 c show the structure of the single - layered cof 30 for mounting the source driver on the liquid crystal panel of fig1 , the single - layered cof for mounting the gate driver on the liquid crystal panel has the substantially same basic structure as the single - layered cof 30 for mounting the source driver on the liquid crystal panel . in fig2 a to fig2 c , the single - layered cof 30 which mounts the source driver 3 thereon forms input - side signal lines 10 a and output - side signal lines 10 b on one surface ( an upper surface ) of the base film 12 by patterning . the input - side signal lines 10 a and the output - side signal lines 10 b are formed of a copper foil in this embodiment . the input - side signal lines 10 a are connected to the printed circuit board 20 in fig1 , and the output - side signal lines 10 b are connected to source - line lead lines extending to the periphery of the display region ar from the display region ar of the panel 1 . on a surface of the source driver 3 , bumps ( input - side bumps 6 a and output - side bumps 6 b ) preferably made of gold are mounted corresponding to the input - side signal line 10 a and the output - side signal line 10 b respectively , and the these bumps are connected to the input - side signal lines 10 a and the output - side signal lines 10 b . the constitutions of connection portions between the bumps and the signal lines are omitted from the drawings . further , a heat radiation metal foil 11 also formed of a copper foil is arranged on both sides of the source driver 3 in the direction along the x - x ′ line of the base film 12 on the same layer as the input - side signal lines 10 a and the output - side signal lines 10 b . on a surface of the source driver 3 , dummy bumps 7 are arranged in addition to the input - side bumps 6 a and the output - side bumps 6 b , and the dummy bumps 7 are connected to the heat radiation metal foil 11 . the input - side signal lines 10 a and the output - side signal lines 10 b have end portions thereof which are connected to the input - side bumps 6 a and the output - side bumps 6 b arranged on the surface of the source driver 3 ( portions thereof corresponding to the surface of the driver ) covered with an exposed solder resist 8 . the source driver 3 is connected to the input - side signal lines 10 a , the output - side signal lines 10 b and the heat radiation metal foil 11 on the printed film 2 and , thereafter , a resin 9 is applied to a chip base portion of the source driver 3 for sealing . fig3 is a schematic view for explaining an arrangement example of the bumps formed on the surface of the source driver . fig3 corresponds to a view as viewed from a back side of a paper showing fig2 . the input - side bumps 6 a and the output - side bumps 6 b are formed along upper and lower long sides of the surface ( a surface facing the printed film 2 ) of the source driver 3 , and the dummy bumps 7 are formed along left and right short sides of the surface of the source driver 3 . in the drawing , although two dummy bumps 7 are arranged on each short side , the number of dummy bump 7 is not limited to two , and , one , three or more dummy bumps 7 may be arranged on each short side . further , the larger a contact area of the dummy bump 7 with the heat radiation metal foil 11 indicated by an imaginary line , it is possible to efficiently transmit the heat generated by the chip to the heat radiation metal foil 11 . according to the embodiment 1 , the heat generated by the source driver 3 is efficiently transmitted to the heat radiation metal foil 11 , and the heat is radiated from the heat radiation metal foil 11 and hence , it is possible to suppress the increase of a temperature of the source driver 3 per se . in this constitution , by using only the cof film which has been used conventionally , it is possible to obtain a high heat radiation effect without pushing up a cost . fig4 a to fig4 c are views for explaining an embodiment 2 of the image display device according to the present invention . in the embodiment 2 , a two - layered cof 40 is used for mounting a driver on a liquid crystal panel . fig4 a is a plan view of the two - layered cof 40 , fig4 b is a cross - sectional view taken along a line x - x ′ in fig4 a , and fig4 c is a cross - sectional view taken along a line y - y ′ in fig4 a . here , also in fig4 a to fig4 c , although a size of the two - layered cof 40 in a line y - y ′ differs from a size of the single - layered cof 30 shown in fig1 in the direction along the y - y ′ line , lengths and sizes of other parts can be arbitrarily changed corresponding to the specification of the liquid crystal panel in the same manner as the embodiment 1 . further , although fig4 a to fig4 c show the structure of the two - layered cof for mounting the source driver on the liquid crystal panel of fig1 , the two - layered cof having the substantially same constitution as the two - layered cof for mounting the source driver on the liquid crystal panel may be used for mounting a gate driver on the liquid crystal panel . however , the generation of heat of the gate driver is smaller than the generation of heat of the source driver and hence , a single - layered cof may be used for mounting the gate driver on the liquid crystal panel in the same manner as the embodiment 1 . in fig4 a to fig4 c , the two - layered cof 40 which mounts the source driver 3 thereon forms input - side signal lines 10 a and output - side signal lines 10 b on one surface ( an upper surface ) of a base film 12 by patterning . the input - side signal lines 10 a and the output - side signal lines 10 b are respectively formed of a copper foil in this embodiment . the input - side signal lines 10 a are connected to the printed circuit board 20 in fig1 , and the output - side signal lines 10 b are connected to source line lead lines which extend to a periphery of the display region ar from the display region ar of the panel 1 . on a surface of the source driver 3 , in the same manner as the above - mentioned constitution shown in fig3 , bumps ( input - side bumps 6 a and output - side bumps 6 b ) preferably made of gold are mounted corresponding to the input - side signal line 10 a and the output - side signal line 10 b respectively , and the these bumps are connected to the input - side signal lines 10 a and the output - side signal lines 10 b . the constitutions of connection portions between the bumps and the signal lines are omitted from the drawings . further , a heat radiation metal foil 11 also formed of a copper foil is arranged on both sides of the source driver 3 in the direction along the x - x ′ line of the base film 12 in the same layer as the input - side signal lines 10 a and the output - side signal lines 10 b . on a surface of the source driver 3 , dummy bumps 7 are arranged in addition to the input - side bumps 6 a and the output - side bumps 6 b , and the dummy bumps 7 are connected to the heat radiation metal foil 11 . in the embodiment 2 , the so - called two - layered cof is constituted by also arranging a second heat radiation metal foil 25 on a back surface of the base film 12 ( a surface of the base film 12 on a side opposite to a chip - mounting surface ) the second heat radiation metal foil 25 is connected to the heat radiation metal foil 11 via a plurality of through holes 24 which goes through the base film 12 . a pattern of the second heat radiation metal foil 25 is not limited to a pattern shown in the drawing , and is arbitrarily adopted provided that the pattern does not interfere with the mounting of the source driver and a wiring pattern . other constitutions are substantially equal to the corresponding constitutions shown in fig2 . the embodiment 2 is effectively applicable when the heat radiation can not be performed sufficiently with the use of the single - layered cofs explained in conjunction with the embodiment 1 . heat generated by the source driver 3 is transmitted to the heat radiation metal foil 11 , and is also transmitted to the second heat radiation metal foil 25 by way of the through holes 24 . the transmitted heat is radiated from both of the heat radiation metal foil 11 and the second heat radiation metal foil 25 and hence , it is possible to suppress the elevation of temperature of the driver source 3 per se . also in the embodiment 2 , by using only the two - layered cof film which has been used conventionally , it is possible to obtain a high heat radiation effect without pushing up a cost . in the embodiments 1 , 2 , the explanation has been made with respect to the constitution in which the drivers are mounted on the display panel by a cof method . however , a tcp ( tape carrier package ) method may be adopted in place of the cof method . in the tcp method , a film thickness of a copper foil for wiring is larger than a film thickness of the copper foil for wiring used in the cof method by approximately 50 % or more even at minimum . when a profile size of the display panel does not depend on a wiring pitch , for example , when a size of long sides of the chip is large so that a length of lines falls within the size of the long sides of the chip , it is possible to provide the same constitution as the embodiment 1 or the embodiment 2 using the tcp method . fig5 is a circuit diagram of a circuit mounted on the back substrate which constitutes the display device according to the present invention . a plurality of scanning lines gl ( also referred to as gate lines ) which extends in the first direction ( x direction ) and is arranged in parallel to each other in the second direction ( y direction ) intersecting the first direction and a plurality of image data lines dl ( also referred to as drain lines or source lines ) which extends in the second direction ( y direction ) and is arranged in parallel to each other in the first direction ( x direction ) intersecting the second direction are formed on a main surface of a printed circuit board . the gate lines gl are connected to a gate driver gd , and the drain lines dl are connected to a drain driver dd . a timing control circuit tcon supplies timing signals to the gate driver gd and the drain driver dd . thin film transistors tft are formed in regions surrounded by these lines which are arranged in a matrix array for respective pixels . the thin film transistor tft has a gate electrode thereof connected to the gate line , a drain electrode thereof connected to the drain line and a source electrode thereof connected to the pixel electrode respectively . a region in which the pixel electrodes are formed constitutes an image display region . further , on the main surface of the printed circuit board , common lines cl are arranged in parallel to the gate lines . a capacitance is generated between the common line and the pixel electrode . in the above - mentioned two embodiments , the drain driver or the gate driver is arranged on the printed film on which the heat radiation metal film is formed , and the printed film on which the driver is mounted is connected to the terminals of the printed circuit board . due to such a constitution , it is possible to radiate the heat of the driver by way of the heat radiation metal foil . the explanation has been made with respect to the image display device of the present invention by taking the active - matrix - type liquid crystal display device as an example heretofore . however , the present invention is not limited to such a liquid crystal display device , and is applicable in the same manner to a simple - matrix - type liquid crystal display device , an image display device such as a plasma display device or an organic el display device , or an electronic apparatus which requires the substantially same heat radiation as the above - mentioned display devices .