Patent Publication Number: US-2017374740-A1

Title: Display device

Description:
TECHNICAL FIELD 
     The present invention relates to a display device. 
     BACKGROUND ART 
     A mobile electrical device such as a mobile phone, a smart phone, and a tablet computer includes a display device having a display panel such as a liquid crystal panel. This type of display device includes a display panel having a display area displaying an image, a signal supply board connected to a signal supply source, and a flexible board connected to both the display panel and the signal supply board such that signals are sent to the display panel therethrough. One example of the display device of this type includes a known display device described in Patent Document 1 listed below. 
     In the display device described in Patent Document 1, a flexible printed board is used to connect a flexible liquid crystal display panel to a drive circuit board. Wiring patterns on the flexible printed board are connected to external connection electrode terminals of the liquid crystal display panel, and the flexible printed board is disconnected or cut in a connection direction at predetermined intervals to prevent thermal distortion at the connection portion caused by a difference between the thermal expansion of the liquid crystal display panel and that of the flexible printed board. 
     RELATED ART DOCUMENT 
     Patent Document 
     
         
         Patent Document 1: Japanese Unexamined Patent Application Publication No. H6-18914 
       
    
     Problem to be Solved by the Invention 
     A decrease in the thickness of a display device and a decrease in the width of the frame of the display device have been increasingly demanded. To meet the demand, a rigid signal supply board configured to supply signals to the display panel through a flexible board is located closer to the display panel having a smaller thickness. In such a display device having a smaller thickness and including a narrower frame, the signal supply board may be deformed by, for example, heat generated during thermocompression bonding of the flexible board to the display panel. In such a case, a force is applied to the display panel from the signal supply board through the flexible board, leading to deformation of the display panel. 
     DISCLOSURE OF THE PRESENT INVENTION 
     The present invention was made in view of the above-described circumstance. It is an object of the present invention to provide a display device in which a display panel is less likely to be deformed. 
     Means for Solving the Problem 
     A display device according to the present invention includes a display panel having a display area capable of displaying an image and a non-display area outside the display area, a flexible board having flexibility and connected to the non-display area at a first end thereof, and a signal supply board connected to a second end of the flexible board opposite from the first end and configured to supply signals to the display panel through the flexible board. The signal supply board at least includes a first rigid portion having a higher rigidity than the flexible board, a second rigid portion located next to the first rigid portion and having a higher rigidity than the flexible board, and a low rigidity portion located between the first rigid portion and the second rigid portion and having a lower rigidity than the first rigid portion and the second rigid portion. 
     According to the invention, the displacement between the first rigid portion and the second rigid portion is absorbed by the deformation of the low rigidity portion, reducing the deformation of the first rigid portion and the second rigid portion. This reduces the force applied from the signal supply board to the display panel through the flexible board, which is generated by the deformation of the first rigid portion and the second rigid portion, reducing the deformation of the display panel caused by the deformation of a rigid section of the signal supply board. 
     The following configurations are preferable as aspects of the display device of the present invention. 
     (1) The non-display area extends along an edge of the display panel and the first rigid portion and the second rigid portion of the signal supply board are located next to each other along the edge of the display panel. This configuration reduces the deformation of the signal supply board in a direction along the edge of the display panel and thus reliably reduces the deformation of the display panel. 
     (2) The flexible board at least includes a first flexible portion and a second flexible portion separately located next to each other along the edge of the display panel with having a space between the first flexible portion and the second flexible portion. The first rigid portion and the second rigid portion of the signal supply board are respectively connected to the first flexible portion and the second flexible portion. The low rigidity portion of the signal supply board faces the space. This configuration enables the signal supply board to be connected to the flexible board at the first rigid portion and the second rigid portion, where the deformation is less likely to occur, and reduces the influence of the deformation of the low rigidity portion on the display panel through the flexible board. 
     (3) The flexible board is connected to the non-display area by thermocompression bonding. The signal supply board is integrally formed with the flexible board by stacking a rigid base member on a flexible base member constituting the flexible board. The rigid base member has a higher rigidity than the flexible base member. The low rigidity portion is constituted of at least a portion of the flexible base member. This configuration enables a so-called rigid flexible board integrally including the flexible board and the signal supply board to reliably have the low rigidity portion without the need for a separate flexible base member, for example. The deformation of the signal supply board caused by the heat generated during the thermocompression bonding of the flexible board to the display panel is absorbed by the low rigidity portion. 
     (4) The signal supply board is a separate member from the flexible board and is connected to the flexible board by thermocompression bonding. The low rigidity portion is a separate member from a flexible base member constituting the flexible board and at least constituted of a signal supply board side flexible base member having flexibility. With this configuration, the deformation of the signal supply board caused by heat generated during the thermocompression bonding of the signal supply board to the flexible board is absorbed by the low rigidity portion of the signal supply board. 
     (5) The low rigidity portion extends from a first edge of the signal supply board adjacent to the display panel to a second edge thereof remote from the display panel. The low rigidity portion constituted of the flexible base member enables the first rigid portion and the second rigid portion to be connected to each other through the flexible base member. This enables the low rigidity portion to extend from the first edge of the signal supply board to the second edge thereof, which is difficult if the low rigidity portion is constituted of a slit or the like in the signal supply board, for example. Then, with this configuration, the displacement between the first rigid portion and the second rigid portion is uniformly absorbed by the low rigidity portion from the first edge of the signal supply board to the second edge thereof, which is preferable. 
     (6) The low rigidity portion includes a slit extending through the signal supply board in a thickness direction thereof. This configuration enables the low rigidity portion to be readily formed, which is preferable. 
     (7) The slit is a cutout at a first edge of the signal supply board adjacent to the display panel. This configuration enables the low rigidity portion to readily absorb the deformation at the first edge of the signal supply board, and thus the force applied from the signal supply board to the display panel through the flexible board is reliably reduced. 
     (8) The slit is a cutout at a second edge of the signal supply board remote from the display panel. This configuration eliminates the need of positioning the slit away from the connection portion between the signal supply board and the flexible board and the need of routing wiring lines so as to avoid the slit, making it easy to design the signal supply board. 
     (9) The slit includes a plurality of slits located close to each other and in parallel to each other. With this configuration, the displacement in the signal supply board in an arrangement direction in which the slits are arranged is reliably absorbed. In addition, compared with a configuration in which one cutout extends over the area including the plurality of slits, the signal supply board readily has a larger surface area in an extending direction of the slits, readily enhancing the rigidity thereof. 
     (10) The display panel is a liquid crystal panel having liquid crystals sealed between two substrates. Such a display device has various uses as the liquid crystal display device and is applicable to various electronic devices such as a mobile phone, a smart phone, and a tablet computer, for example. 
     Advantageous Effect of the Invention 
     The present invention provides a display device in which a display panel is less likely to be deformed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view illustrating a liquid crystal panel and a rigid flexible board according to a first embodiment of the present invention. 
         FIG. 2  is a schematic cross-sectional view illustrating a cross-sectional configuration taken in a long side direction of a liquid crystal display device. 
         FIG. 3  is a schematic cross-sectional view illustrating a cross-sectional configuration of a liquid crystal panel. 
         FIG. 4  is a cross-sectional view taken along line IV-IV in  FIG. 4 . 
         FIG. 5  is an exploded perspective view illustrating a configuration of the rigid flexible board. 
         FIG. 6  is a horizontal cross-sectional view illustrating the rigid flexible board to be connected to the liquid crystal panel. 
         FIG. 7  is a vertical cross-sectional view illustrating a step of mounting the rigid flexible board on the liquid crystal panel. 
         FIG. 8  is a horizontal cross-sectional view illustrating the rigid flexible board connected to the liquid crystal panel. 
         FIG. 9  is a magnified horizontal cross-sectional view illustrating a low rigidity portion in  FIG. 8  in a magnified state. 
         FIG. 10  is a horizontal cross-sectional view illustrating a rigid flexible board according to a second embodiment of the present invention. 
         FIG. 11  is a plan view illustrating a liquid crystal panel and a rigid flexible board according to a third embodiment of the present invention. 
         FIG. 12  is a plan view illustrating a liquid crystal panel and a rigid flexible board according to a fourth embodiment of the present invention. 
         FIG. 13  is a cross-sectional view taken along line XIII-XIII in  FIG. 12 . 
         FIG. 14  is a plan view illustrating a liquid crystal panel and a rigid flexible board according to a fifth embodiment of the present invention. 
         FIG. 15  is a cross-sectional view taken along line XV-XV in  FIG. 14 . 
         FIG. 16  is a plan view illustrating a liquid crystal panel and a rigid flexible board according to a sixth embodiment of the present invention. 
         FIG. 17  is a plan view illustrating a liquid crystal panel and a rigid flexible board according to a seventh embodiment of the present invention. 
         FIG. 18  is a plan view illustrating a liquid crystal panel and a rigid flexible board according to an eighth embodiment of the present invention. 
         FIG. 19  is a plan view illustrating a liquid crystal panel and a rigid flexible board according to a ninth embodiment of the present invention. 
         FIG. 20  is a plan view illustrating a liquid crystal panel and a rigid flexible board according to a tenth embodiment of the present invention. 
         FIG. 21  is a plan view illustrating a liquid crystal panel and a rigid flexible board according to an eleventh embodiment of the present invention. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     First Embodiment 
     A first embodiment of the present invention is described with reference to  FIG. 1  to  FIG. 9 . In this embodiment, a liquid crystal display device (display device)  10  is described as an example. The X axis, Y axis, and Z axis are indicated in some of the drawings, and each of the axes indicates the same direction in the respective drawings. The up and down direction is based on that of  FIG. 2 , and the upper side in  FIG. 2  is a front side and the lower side in  FIG. 2  is a rear side. 
     As illustrated in  FIG. 1  and  FIG. 2 , the liquid crystal display device  10  includes a liquid crystal panel  11 , drivers (mounted component)  21 , which are mounted on the liquid crystal panel  11  and configured to drive the liquid crystal panel  11 , a rigid flexible board  20  integrally including a rigid board portion (signal supply board, control circuit board)  30 , which is configured to supply various input signals to the drivers  21 , and a flexible board portion (flexible board, external connection component)  40 , which electrically connects the liquid crystal panel  11  to a rigid board portion  30 , and a backlight apparatus (lighting apparatus)  14 , which is an external light source configured to provide light to the liquid crystal panel  11 . The liquid crystal display device  10  further includes front and rear exterior members  15  and  16  housing and holding the liquid crystal panel  11  and the backlight apparatus  14 , which are attached to each other. The front exterior member  15  has an opening  15   a  allowing an image displayed on the liquid crystal panel  11  to be seen from outside. The liquid crystal display device  10  according to this embodiment is used in various electronic devices (not illustrated) such as a mobile phone, a smart phone (including a phablet and the like), a tablet computer, a laptop computer, a mobile terminal device (including an electronic book, a PDA, and the like), a digital photo frame, a portable video game player, and an electronic ink paper. Thus, the liquid crystal panel  11  included in the liquid crystal display device  10  has a screen size of about a few inches to a dozen inches, which is categorized as a small size or a small to medium size in general. 
     The backlight apparatus  14  is briefly described first. As illustrated in  FIG. 2 , the backlight apparatus  14  includes a box-like shaped chassis  14   a  having an opening in the front (side adjacent to the liquid crystal panel  11 ), a light source (not illustrated) disposed in the chassis  14   a  (such as a cold-cathode tube, an LED, and an organic EL, for example), and an optical member (not illustrated) covering the opening of the chassis  14   a . The optical member has a function of converting light from the light source into planar light, for example. 
     Next, the liquid crystal panel  11  is described. As illustrated in  FIG. 1 , the liquid crystal panel  11  has a horizontally elongated quadrilateral overall shape (rectangular shape) and includes a display area (active area) AA, which is capable of displaying an image, at a position closer to a first edge in the long side direction and a first edge in the short side direction (right lower side in  FIG. 1 ) and a non-display area (non-active area) NAA, which does not display an image, at a position outside the display area AA. In other words, the non-display area NAA at least extends along a second edge LE extending in the long side direction of the liquid crystal panel  11  and a second edge SE extending in the short side direction. The non-display area NAA adjacent to the second edge LE extending in the long side direction of the liquid crystal panel  11  is a mounting area for the drivers  21  and the flexible board  13 . The non-display area NAA adjacent to the edge LE extending in the long side direction has a width of about 2 mm to 3 mm, for example, to meet the demand for the liquid crystal panel  11  to have a smaller frame. In  FIG. 1 , a one-dot chain line extending in a frame-like shape slightly smaller than a CF substrate  11   a  indicates an outer shape of the display area AA, and an area outside the one-dot chain line is the non-display area NAA. In the drawings, the width of the non-display area NAA is larger than the actual width for ease of description. The long side direction of the liquid crystal panel  11  matches the X axis direction in the drawings and the short side direction matches the Y axis direction in the drawings. 
     As illustrated in  FIG. 3 , the liquid crystal panel  11  includes two transparent (high light transmission) substrates  11   a  and  11   b  and a liquid crystal layer  11   c  sandwiched between the two substrates  11   a  and  11   b . The liquid crystal layer  11   c  includes liquid crystal molecules, which are substances whose optical properties are changed by application of an electrical field. The substrates  11   a  and  11   b  are bonded together by a sealant, which is not illustrated, with a cell gap corresponding to the thickness of the liquid crystal layer  11   c  therebetween. The substrates  11   a  and  11   b  each include a glass substrate including an alkali-free glass or a quartz glass, for example, and a plurality of films laminated by a known photolithography method on the glass substrate. The substrate  11   a  on the front side (front surface side) is a CF substrate (counter substrate)  11   a  and the substrate  11   b  on the rear side (rear surface side) is an array substrate (a mounting substrate, a device substrate, an active matrix substrate)  11   b . As illustrated in  FIG. 2 , the CF substrate  11   a  is slightly smaller than the array substrate  11   b  and bonded to the array substrate  11   b  with a first edge thereof extending in the long side direction and a first edge thereof extending in the short side direction (sides on the lower side and the right side in  FIG. 2 ) being aligned with those of the array substrate  11   b . Thus, the second edges LE and SE extending in the long side direction and the short side direction of the array substrate  11   b  do not overlap the CF substrate  11   a  over a predetermined area, and front and rear planar surface of the array substrate  11   b  are exposed to the outside. Alignment films  11   d  and  11   e  for orienting the liquid crystal molecules in the liquid crystal layer  11   c  are respectively formed on the inner surfaces of the substrates  11   a  and  11   b . Furthermore, polarizing plates  11   f  and  11   g  are respectively attached to outer surfaces of the substrates  11   a  and  11   b.    
     Subsequently, the configurations inside the display area AA of the array substrate  11   b  and the CF substrate  11   a  are briefly described. As illustrated in  FIG. 3 , many TFTs (Thin Film Transistor)  17 , which are switching elements, and many pixel electrodes  18  are disposed next to each other in a matrix on the inner side of the array substrate  11   b  (side adjacent to the liquid crystal layer  11   c , side facing the CF substrate  11   a ), and gate wiring lines and source wiring lines (both are not illustrated) are disposed in a grid shape so as to surround the TFTs  17  and the pixel electrodes  18 . In other words, the TFTs  17  and the pixel electrodes  18  are placed next to each other in rows and columns at intersections of the gate wiring lines and the source wiring lines in a grid shape. The gate wiring lines and the source wiring lines are respectively connected to the gate electrodes and the source electrodes of the TFTs  17 , and the pixel electrodes  18  are connected to drain electrodes of the TFTs  17 . The pixel electrode  18  has a vertically elongated quadrilateral (rectangular) shape in plan view and is formed of a transparent electrode material such as ITO (Indium Tin Oxide) or ZnO (Zinc Oxide). Capacitor wiring lines (not illustrated) extending parallel to the gate wiring lines and intersecting the pixel electrodes  18  may be disposed on the array substrate  11   b.    
     As illustrated in  FIG. 3 , color filters  11   h  each including a coloring portion of R (red), G (green), or B (blue), for example, arranged next to each other in a matrix is disposed on the CF substrate  11   a  so as to overlap the pixel electrodes  18  on the array substrate  11   b  in plan view. A light blocking layer (black matrix)  11   i  having a substantially grid shape is disposed between the respective coloring portions constituting the color filter  11   h  to prevent mixture of colors. The light blocking layer  11   i  overlaps the above-described gate wiring lines and the source wiring lines in plan view. A planar counter electrode  11   j  facing the pixel electrodes  18  on the array substrate  11   b  is disposed on surfaces of the color filters  11   h  and surfaces of the light blocking layers  11   i . In the liquid crystal panel  11 , three coloring portions of R (red), G (green), and B (blue) and three pixel electrodes  18  facing the respective coloring portions form one display pixel, which is a display unit. The display pixel includes a red pixel including R coloring portion, a green pixel including G coloring portion, and a blue pixel including B coloring portion. The pixels of each color are repeatedly arranged in the row direction (X axis direction) on a planar surface of the liquid crystal panel  11  to form a pixel group. Many pixel groups are arranged in the column direction (Y axis direction). 
     Due to a recent demand for the liquid crystal panel  11  to have a smaller thickness and a smaller weight, the glass substrates of the CF substrate  11   a  and the array substrate  11   b  included in the liquid crystal panel  11  are also demanded to have a smaller thickness. To meet the demand, in the present embodiment, various films are formed on the glass substrate of each of the CF substrate  11   a  and the array substrate  11   b , and after patterning, etching (wet etching) is performed to a planar surface of the glass substrate opposite the planar surface having the various films thereon, i.e., an outer planar surface, to make the glass substrate thinner. The glass substrate in the present embodiment is made thinner to have a thickness of about 150 μm, for example, by the above-described thinning process. 
     Next, components connected to the liquid crystal panel  11  is described. As illustrated in  FIG. 2 , the driver  12  is constituted of an LSI chip having a drive circuit therein and operates on the basis of driving power and a reference potential supplied from a main board portion, which is a power source, through the rigid flexible board  20  to produce output signals by processing input signals relating to images supplied from the main board portion, which is a signal supply source, through the rigid flexible board  20 , and the driver  12  outputs the output signals to the display area AA of the liquid crystal panel  11 . The driver  12  has a horizontally elongated quadrilateral shape in plan view and is directly mounted on the non-display area NAA of the array substrate  11   b  of the liquid crystal panel  11 , i.e., mounted by using COG (Chip On Glass) technology. The long side direction of the drivers  12  that are disposed along the edge LE extending in the long side direction of the liquid crystal panel  11  matches the X axis direction and the short side direction thereof matches the Y axis direction. The long side direction of the drivers  12  that are disposed along the edge SE extending in the short side direction of the liquid crystal panel  11  matches the Y axis direction and the short side direction thereof matches the X axis direction. The drivers  12  are arranged next to each other in the extending direction of the mounting region in the non-display area NAA with a space therebetween. 
     As illustrated in  FIG. 7 , on the non-display area NAA of the array substrate  11   b  on which the drivers  12  are mounted, panel-side driver input-output terminals  19   a , which are connected to corresponding driver-side input-output terminals  12   a  included in the drivers  12 , are disposed, and a panel-side output wiring line (not illustrated) for connecting an output of the panel-side driver input-output terminals  19   a  to the display area AA and a panel-side input wiring line (not illustrated) for connecting an input of the panel-side driver input-output terminals  19   a  to the rigid flexible board  20  are also disposed. A panel-side flexible board terminal  19   b , which is connected to the rigid flexible board  20 , is disposed at the end of the panel-side input wiring line adjacent to the rigid flexible board  20  (remote from the driver  20 ). Many panel-side flexible board terminals  19   b  are arranged along the edge LE (in the X axis direction) extending in the long side direction of the non-display area NAA of the array board  11   b , which is connected to the rigid flexible board  20 , with a space therebetween. The panel-side driver output-input terminals  19   a  and the panel-side flexible board terminals  19   b  are exposed to outside for connection with the drivers  12  and the rigid flexible board  20 . The panel-side output wiring lines and the panel-side input wiring line portion are covered with an insulation film, which is not illustrated, over almost all area thereof. 
     The rigid flexible board  20  is directly connected to the non-display area NAA of the liquid crystal panel  11 , as illustrated in  FIG. 2 , so as to be electrically connected thereto and is electrically connected to the main board included in the liquid crystal display device  10  through a wiring member, which is not illustrated. Various signals relating to images are sent from the main board to the rigid flexible board  20 , and thus the signals are able to be supplied to the drivers  12  mounted on the liquid crystal panel  11 . The rigid flexible board  20  is disposed along the edge LE of the non-display area NAA of the liquid crystal panel  11  to which the rigid flexible board  20  is attached. The width direction of the rigid flexible board  20  matches the arrangement direction (Y axis direction) in which the liquid crystal panel  11  and the rigid flexible board  20  are arranged. The longitudinal direction of the rigid flexible board  20  matches a direction (X axis direction) perpendicular to the arrangement direction of the liquid crystal panel  11  and the rigid flexible board  20  along the planar surface of the liquid crystal panel  11 . 
     As illustrated in  FIG. 5 , the rigid flexible board  20  includes a flexible base member  21  having flexibility and rigid base members  22  having rigidity and almost no flexibility. The flexible base member  21  is a film formed of a synthetic resin material (polyimide-based resin, for example) having insulation properties and has a flexible-side wiring line routed on a surface of the film. The flexible base member  21  has an elongated comb-like overall shape. A portion  21   a  of the flexible base member  21  adjacent to the liquid crystal panel  11  in the short side direction (a portion constituting a flexible base portion  40 , which is described later) is separated into three portions in the long side direction. A portion  21   b  of the flexible base member  21  remote from the liquid crystal panel  11  (a portion constituting the rigid board portion  30 , which is described later) has a rectangular shape extending in the long side direction. A flexible-side terminal  43  connected to the liquid crystal panel  11  is disposed on one end of the flexible base member  21  adjacent to the liquid crystal panel  11  (remote from the rigid board portion  30 ) (see  FIG. 7 ). The flexible base member  21  is more flexible than the rigid base member  22  and is readily subjected to deflection deformation or bending deformation. 
     As illustrated in  FIG. 5 , the rigid base member  22  includes a power source component, which is configured to supply driving power and a reference potential to the drivers  12 , an electronic component (circuit component), which is configured to control transmission of input signals relating to images to the liquid crystal panel  11 , and a rigid-side wiring line routed on the main surface thereof (all are not illustrated) on a substrate having a predetermined thickness, which is formed of phenolic paper or glass epoxy resin, for example. The rigid base member  22  has many via holes, which are not illustrated. The rigid-side wiring lines of the rigid base member  22  are electrically connected to the flexible-side wiring lines of the flexible base member  21  through the via holes. In this embodiment, three pairs of rigid base members  22  each having the flexible base member  21  therebetween are arranged along the edge LE of the liquid crystal panel  11  (in the longitudinal direction of the flexible base member  21 ). The rigid base member  22  is rigid with almost no flexibility, compared with the flexible base member  21 , and is hardly subjected to deflection deformation or bending deformation. 
     As illustrated in  FIG. 4  and  FIG. 5 , the rigid flexible board  20  includes the rigid board portion  30  having a laminated structure, which includes the two rigid base members  22  and the portion  21   b  of the flexible base member  21  sandwiched between the rigid base members  22 , and the flexible board portion  40 . The flexible board portion  40  includes the portion  21   a  of the flexible base member  21 , which is not sandwiched between the rigid base members  22 . In other words, in the rigid flexible board  20 , the rigid board portion  30  is integrally formed with the flexible board portion  40  such that the rigid base members  22  are disposed on the flexible base member  21  constituting the flexible board portion  40 . In still other words, a portion of the rigid flexible board  20  adjacent to the liquid crystal panel  11  is the flexible board portion  40  and a portion thereof remote from the liquid crystal panel  11  is the rigid board portion  30 . The flexible board portion  40  is attached to the non-display area NAA of the liquid crystal panel  11  at a first end  40   a  in the Y axis direction (a lower side in  FIG. 1 ) and is connected to the rigid board portion  30  at a second end  40   b  (an upper side in  FIG. 1 ). The flexible board portion  40  and the rigid board portion  30  are electrically connected to each other by flexible-side wiring lines of the flexible base member  21 , which extend across the flexible board portion  40  and the rigid board portion  30 . A rigid-side terminal, which is not illustrated, is disposed on the rigid board portion  30  to electrically connect the rigid board portion  30  and the main board of the liquid crystal display device  10  to each other through the rigid-side terminal. This configuration enables the rigid board portion  30  to transmit the signals to the liquid crystal panel  11  through the flexible board portion  40 . In this embodiment, the rigid board portion  30  of the rigid flexible board  20  functions as the “signal supply board” and the flexible board portion  40  thereof functions as the “flexible board”. 
     As illustrated in  FIG. 1 , the flexible board portion  40  is separated along the edge LE of the liquid crystal panel  11 . Specifically, the flexible board portion  40  is separated into three flexible portions  41   a ,  41   b , and  41   c  along the edge LE of the liquid crystal panel  11  (in the longitudinal direction of the flexible base member  21 ). The flexible board portion  40  includes a space  42   a  between the flexible portion  41   a  and the flexible portion  41   b  and a space  42   c  between the flexible portion  41   b  and the flexible portion  41   c . In this embodiment, the flexible board portion  40  including separated portions are described as an example, but the flexible board portion may be one integral portion extending over the entire area. Alternatively, the flexible board portion may be separated into two portions or four or more portions. The configuration and the number of flexible board portions may be suitably determined depending on the size, resolution, or the number of mounted terminals of the liquid crystal panel  11 . 
     As illustrated in  FIG. 1 , the flexible board portion  40  is attached to the liquid crystal panel  11  at the end portions adjacent to the first end  40   a  over the substantially entire length of the edge LE with a space between the end portions. As illustrated in  FIG. 7 , the flexible-side terminal  43  on the first end  40   a  is thermocompression bonded to the panel-side flexible board terminal  19   b  on the liquid crystal panel  11  such that the flexible board portion  40  is electrically and mechanically connected to the liquid crystal panel  11 . Specifically, an anisotropic conductive film (ACF)  24  including a plurality of conductive particles  27   a  made of a metal material and a thermosetting resin  27   b  having the conductive particles  27   a  therein in a dispersed state is disposed on the panel-side flexible board terminal  19   b . The flexible-side terminal  43  is electrically connected to the panel-side flexible board terminal  19   b  through the conductive particles  24   a . The thermosetting resin  24   b  in the cured state allows the flexible board portion  40  (the rigid flexible board  20 ) to be fixed to the liquid crystal panel  11 . The flexible-side terminal  43  and the panel-side flexible board terminal  19   b  are connected to each other through the anisotropic conductive film  24  by mounting the flexible board portion  40  on the array substrate  11   b  by using a flexible board mounting apparatus  26 . The step of mounting by using the flexible board mounting apparatus  26  is described later. 
     As illustrated in  FIG. 5  and  FIG. 6 , the rigid board portion  30  includes three rigid portions  31   a ,  31   b , and  31   c , which are constituted of the two rigid base members  22  and the flexible base member  21  sandwiched between the rigid base members  22 , and a low rigidity portion  32   a  and a low rigidity portion  32   c , which are respectively located between the rigid portion  31   a  and the rigid portion  31   b  positioned next to each other and between the rigid portion  31   b  and the rigid portion  31   c  positioned next to each other and are constituted of the flexible base member  21 . In other words, the rigid board portion  30  at least includes the rigid portion  31   a  (the rigid portion  31   b ), which has a higher rigidity than the flexible board portion  40 , the rigid portion  31   b  (the rigid portion  31   c ), which is located next to the rigid portion  31   a  and has a higher rigidity than the flexible board portion  40 , the low rigidity portion  32   a  (the low rigidity portion  32   c ), which is located between the rigid portion  31   a  and the rigid portion  31   b  (the rigid portion  31   b  and the rigid portion  31   c ) and has a lower rigidity than the rigid portion  31   a  and the rigid portion  31   b.    
     As illustrated in  FIG. 5  and  FIG. 6 , the rigid board portion  30  includes the three rigid portions  31   a ,  31   b , and  31   c , which are arranged along the edge LE of the liquid crystal panel  11 , and the low rigidity portions  32   a  and  32   c  extending from the first edge  30   a  adjacent to the liquid crystal panel  11  to the second edge  30   b  remote from the liquid crystal panel  11  at positions between the rigid portions  31   a ,  31   b , and  31   c . In the rigid board portion  30 , the rigid portion  31   a  (the rigid portion  31   b ) is connected to the flexible portion  41   a  (the flexible portion  41   b ) and the rigid portion  31   b  (the rigid portion  31   c ) is connected to the flexible portion  41   b  (the flexible portion  41   c ), and the low rigidity portion  32   a  (the low rigidity portion  32   c ) faces the space  42   a  (the space  42   c ). The rigid portions  31   a ,  31   b , and  31   c  are electrically connected to each other through the respective low rigidity portions  32   a  and  32   c  (the flexible base member  21 ) located therebetween. 
     The liquid crystal display device  10  has recently increasingly demanded to have a smaller thickness and to have a frame with a smaller width. To meet the demand, the rigid flexible board  20  is disposed closer to the liquid crystal panel  11  such that the display area AA constitutes a high proportion of the overall size of the liquid crystal display device  10 . Thus, as illustrated in  FIG. 1  and  FIG. 4 , in the liquid crystal display device  10 , the dimension L 1  from the edge LE of the liquid crystal panel  11  to the rigid board portion  30  is small. The dimension L 1  may only be about 2 mm when the frame is demanded to have a further smaller width for smartphones, for example. In this configuration, it is recognized that the rigid board portion  30  is heated to about 150 to 200° C., for example, by the heat generated during thermocompression bonding of the flexible board portion  40  to the liquid crystal panel  11 , and the rigid board portion  40  of the small to medium sized liquid crystal display device  10  is thermally expanded by about a few millimeters. The flexible base member  21  and the rigid base member  22 , which are included in the rigid flexible board  20 , have different thermal expansion coefficients. In a rigid board portion of a conventional rigid flexible board having no low rigidity portion, a displacement due to thermal expansion occurring at two separate positions is absorbed by a displacement in a direction perpendicular to the planar surface thereof, leading to warping deformation (upward warping or downward warping) or corrugated deformation of the planer surface of the rigid board portion. In such a case, the deformed rigid board portion may deform the liquid crystal panel through the flexible board portion. If the liquid crystal panel  11  is deformed, the deformation may lead to display unevenness in the display area AA. Such a problem readily occurs particularly in the liquid crystal panel  11  having a smaller thickness and in the liquid crystal panel  11  having a smaller dimension L 1 , which is measured from the edge LE of the liquid crystal panel  11  to the rigid board portion  30 . 
     Meanwhile, regarding this embodiment, i.e., the rigid board portion  30  of the rigid flexible board  20  having the low rigidity portions  32   a  and  32   b , a flexible board mounting step of mounting the flexible board portion  40  on the liquid crystal panel  11  and an operation of the rigid flexible board  20  during the step are described. First, in the flexible board mounting step, the positions of the flexible-side terminal  43  and the panel-side flexible board terminal  19   b  are adjusted, and as illustrated in  FIG. 6 , the rigid flexible board  20  is mounted on the liquid crystal panel  11  (the array substrate  11   b ). At this time, the rigid board portion  30  of the rigid flexible board  20  is not subjected to deformation or the like and is substantially flat in the X axis direction. Then, as illustrated in  FIG. 7 , the liquid crystal panel  11  is disposed on a board retainer  27  and a board receiver  28 , which are components of the flexible board mounting apparatus  26 . This allows a portion of the array substrate  11   b  having the panel side flexible board terminal  19   b  thereon to be supported by the board receiver  28  at the rear surface thereof and the other portion than the above-described portion is strongly held by the board retainer  27  due to vacuum contact over a large area. A pressure portion  29  is moved down toward the rigid flexible board  20  and a pressing pressure and heat are applied to the flexible board portion  40  by the pressure portion  29  when the pressure portion  29  contacts with the flexible board portion  40 . After the application of pressure and heat for a predetermined time by the pressure portion  29 , the thermocompression bonding of the rigid flexible board  20  (the flexible board portion  40 ) to the liquid crystal panel  11  is completed. 
     In the flexible board mounting step, the heat from the pressure portion  29  is transferred to the rigid board portion  30  through the flexible base member  21  or as radiant heat. Then, the flexible base member  21  and the rigid base member  22  included in the rigid board portion  30  are subjected to the thermal expansion depending on the respective thermal expansion coefficient. The rigid board portion  30  deforms due to the difference in the thermal expansion coefficient between the flexible base member  21  and the rigid base member  22 . The rigid flexible board  20  has an elongated shape extending along the edge LE of the liquid crystal panel  11  for its function, and the rigid board portion  30  particularly readily deforms (warping deformation or wave deformation) in the longitudinal direction thereof. Furthermore, the rigid flexible board  20  is connected to the liquid crystal panel  11  along the edge LE of the liquid crystal panel  11 , and thus force acting on the liquid crystal panel  11  due to the deformation of the rigid flexible board  20  in the longitudinal direction may cause a problem. Here, since the low rigidity portions  32   a  and  32   c  have a lower rigidity than the rigid portions  31   a ,  31   b , and  31   c , i.e., the low rigidity portions  32   a  and  32   c  are configured to be relatively readily deformed, the low rigidity portion  32  deforms to absorb the displacement between the rigid portion  31   a  and the rigid portion  31   b  and the displacement between the rigid portion  31   b  and the rigid portion  31   c  ( FIG. 9 ). As illustrated in  FIG. 8 , this reduces the displacement in the direction perpendicular to the planar surface at a position between the rigid portion  31   a  and the rigid portion  31   b  and at a position between the rigid portion  31   b  and the rigid portion  31   c . Furthermore, the low rigidity portions  32   a  and  32   b  allow the rigid portions  31   a ,  31   b , and  31   c  themselves to be expanded in the longitudinal direction (direction along the edge LE of the liquid crystal panel  11 ), and thus the deformation in the direction perpendicular to the planar surface is unlikely to occur. In other words, in the rigid board portion  30 , since the deformation of the portions other than the low rigidity portions  32   a  and  32   b  is reduced, the rigid board portion  30  has a flat outer shape as a whole. 
     In the rigid board portion  30 , the rigid portions  31   a ,  31   b , and  31   c  are rigid and force the array substrate  11   b  included in the liquid crystal panel  11  to deform in conformity with the rigid board portion  30  (the rigid portions  31   a ,  31   b , and  31   c ) through the flexible portions  41   a ,  41   b , and  41   c  of the flexible board portion  40 . This force causes a problem particularly in the array substrate  11   b  constituting of a thin glass substrate as in the present embodiment. In the present embodiment, since the amounts of displacement in the direction perpendicular to the planar surface at the positions between the rigid portion  31   a  and the rigid portion  31   b  and between the rigid portion  31   b  and the rigid portion  31   c  are reduced, the portions of the array substrate  11   b  to which the flexible portion  41   a , the flexible portion  41   b , and the flexible portion  41   c  are connected are unlikely to be deformed. In addition, since the rigid portions  31   a ,  31   b , and  31   c  are configured to be less deformed, the portions to which the flexible portions  41   a ,  41   b , and  41   c  are connected are unlikely to be locally deformed in conformity with the rigid portions  31   a ,  31   b , and  31   c . This enables the planar surface of the array substrate  11   b  to have high flatness. 
     As described above, the liquid crystal display device  10  in this embodiment includes the liquid crystal panel  11  having the display area AA capable of displaying an image and the non-display area NAA outside the display area AA, the flexible board portion  40  having flexibility and connected to the non-display area NAA at the first end  40   a  thereof, and the rigid board portion  30  connected to the second end  40   b  of the flexible board portion  40  opposite the first end  40   a  and configured to supply signals to the liquid crystal panel  11  through the flexible board portion  40 . The rigid board portion  30  at least includes the rigid portion  31   a  (the rigid portion  31   b ) having a higher rigidity than the flexible board portion  40 , the rigid portion  31   b  (the rigid portion  31   c ) located next to the rigid portion  31   a  (the rigid portion  31   b ) and having a higher rigidity than the flexible board portion  40 , and the low rigidity portion  32   a  (the low rigidity portion  32   c ) located between the rigid portion  31   a  and the rigid portion  31   b  (the rigid portion  31   b  and the rigid portion  31   c ) and having a lower rigidity than the rigid portion  31   a  and the rigid portion  31   b  (the low rigidity portion  31   b  and the low rigidity portion  31   c ). 
     In this embodiment, the displacement between the rigid portion  31   a  and the rigid portion  31   b  (the rigid portion  31   b  and the rigid portion  31   c ) is absorbed by the deformation of the low rigidity portion  32   a  (the low rigidity portion  32   c ), reducing the deformation of the rigid portion  31   a  and the rigid portion  31   b  (the rigid portion  31   b  and the rigid portion  31   c ). This reduces the force applied from the rigid board portion  30  to the liquid crystal panel  11  through the flexible board portion  40 , which is generated by the deformation of the rigid portion  31   a  and the rigid portion  31   b  (the rigid portion  31   b  and the rigid portion  31   c ), reducing the deformation of the liquid crystal panel  11  caused by the deformation of a rigid section of the rigid board portion  30 . 
     In this embodiment, the non-display area NAA extends along the edge LE of the liquid crystal panel  11  and the rigid portion  31   a  and the rigid portion  31   b  (the rigid portion  31   b  and the rigid portion  31   c ) of the rigid board portion  30  are located next to each other along the edge LE of the liquid crystal panel  11 . This configuration reduces the deformation of the rigid board portion  30  in a direction along the edge LE of the liquid crystal panel  11  and thus reliably reduces the deformation of the liquid crystal panel  11 . 
     Furthermore, in this embodiment, the flexible board portion  40  at least includes the flexible portions  41   a , the flexible portion  41   b , and the flexible portion  41   c , which are separately located next to each other along the edge LE of the liquid crystal panel  11 , and further includes the spaces  42   a  and  42   c  between the flexible portion  41   a  and the flexible portion  41   b  (the flexible portion  41   b  and the flexible portion  41   c ). The rigid portion  31   a  (the rigid portion  31   b ) and the rigid portion  31   b  (the rigid portion  31   c ) of the rigid board portion  30  are respectively connected to the flexible portion  41   a  (the flexible portion  41   b ) and the flexible portion  41   b  (the flexible portion  41   c ). The low rigidity portion  32   a  (the low rigidity portion  32   c ) faces the space  42   a  (the space  42   c ). This configuration enables the rigid board portion  30  to be connected to the flexible board portion  40  at the rigid portion  31   a  (the rigid portion  31   b ) and the rigid portion  31   b  (the rigid portion  31   c ) of the rigid board portion  30 , where the deformation is less likely to occur, and reduces the influence of the deformation of the low rigidity portion  32   a  (the low rigidity portion  32   c ) on the liquid crystal panel  11  through the flexible board portion  40 . 
     Furthermore, in this embodiment, the flexible board portion  40  is connected to the non-display area NAA by the thermocompression bonding. The rigid board portion  30  is integrally formed with the flexible board portion  40  by stacking the rigid base member  22  on the flexible base member  21  constituting the flexible board portion  40 . The rigid base member  22  has a higher rigidity than the flexible base member  21 . The low rigidity portions  32   a  and  32   c  are at least constituted of a portion of the flexible base member  21 . This configuration enables the rigid flexible board  20  integrally including the flexible board portion  40  and the rigid board portion  30  to reliably have the low rigidity portions  32   a  and  32   c  without the need for a separate flexible base member, for example. The deformation of the rigid board portion  30  caused by the heat generated during the thermocompression bonding of the flexible board portion  40  to the liquid crystal panel  11  is absorbed by the low rigidity portions  32   a  and  32   c.    
     In particular, when the configuration relating to the rigid flexible board  20  is employed, the connection between the terminals on the signal supply board (the rigid board portion  30 ) and the terminals on the flexible board (the flexible board portion  40 ) may be eliminated, leading to an improvement in the reliability of the connection and the downsize (merit). However, since the connection area between the flexible base member  21  and the rigid base member  22  is large, this configuration may readily cause a problem of deformation of the rigid board portion  30  (demerit). In this embodiment, the low rigidity portions  32   a  and  32   c  reduce the demerit of the rigid flexible board  20  and enjoy the merit of the employment of the rigid flexible board  20 . 
     Furthermore, in this embodiment, the low rigidity portions  32   a  and  32   c  extend from the first edge  30   a  of the rigid board portion  30  to the second edge  30   b  thereof. The low rigidity portions  32   a  and  32   c  constituted of the flexible base member  21  enable the rigid portion  31   a  and the rigid portion  31   b  (the rigid portion  31   b  and the rigid portion  31   c ) to be connected to each other through the flexible base member  21 . This enables the low rigidity portions  32   a  and  32   c  to extend from the first edge  30   a  of the rigid board  30  to the second edge  30   b  thereof, which is difficult if the low rigidity portion is constituted of a slit or the like in the signal supply board, for example. Then, with this configuration, the displacement between the rigid portion  31   a  and the rigid portion  31   b  (the rigid portion  31   b  and the rigid portion  31   c ) is uniformly absorbed by the low rigidity portions  32   a  and  32   c  from the first edge  30   a  of the rigid board  30  to the second edge  30   b , which is preferable. 
     Furthermore, in this embodiment, the liquid crystal panel  11  includes the liquid crystal layer  11   c  sealed between the two substrates  11   a  and  11   b . Such a display device has various uses as the liquid crystal display device  10  and is applicable to various electronic devices such as a mobile phone, a smart phone, and a tablet computer, for example. 
     Second Embodiment 
     A second embodiment of the present invention is described with reference to  FIG. 10 . In the second embodiment, the configuration of a rigid board portion  130  of a rigid flexible board  120  is different from the rigid flexible board  20  in the above-described first embodiment. The configurations, operations, and effects similar to those in the first embodiment are not described. 
     In this embodiment, the rigid base members  22  sandwich the flexible base member  21 . One of the rigid base members  22  on a first film surface of the flexible base member  21  (a lower side in  FIG. 10 ) has an oblong shape extending along the edge LE of the liquid crystal panel  11  (in the longitudinal direction of the flexible base member  21 ). Three of the rigid base members  22  on a second film surface of the flexible base member  21  (an upper side in  FIG. 10 ) are disposed next to each other along the edge LE of the liquid crystal panel  11  (in the longitudinal direction of the flexible base member  21 ). 
     The rigid board portion  130  includes three rigid portions  131   a ,  131   b , and  131   c  each constituted of the rigid base members  22  in two layers with the flexible base member  21  therebetween and the flexible base member  21  sandwiched by the rigid base members  22 , and low rigidity portions  132   a  and  132   c  each constituted of the rigid base member  22  in one layer and the flexible base member  21 . The low rigidity portions  132   a  and  132   c  are respectively located between the rigid portion  131   a  and the rigid portion  131   b , which are positioned next to each other, and the rigid portion  131   b  and the rigid portion  131   c , which are positioned next to each other. In other words, in the first embodiment, the low rigidity portion  32   a  and the low rigidity portion  32   c  are constituted of the flexible base member  21  alone, but the low rigidity portion  132   a  and the low rigidity portion  132   c  are constituted of the flexible base member  21  and the rigid base member  22  in one layer on the first film surface (a lower side in  FIG. 10 ) of the flexible base member  21  in this embodiment. Thus, the low rigidity portions  132   a  and  132   c  in this embodiment have a lower rigidity than the rigid portions  131   a ,  131   b , and  131   c , but have a higher rigidity than the low rigidity portions  32   a  and  32   c  in the first embodiment. This configuration makes the rigid flexible board  120  to be readily handled during mounting of various electronic components on the rigid board portion  130 , for example, compared with the rigid flexible board portion  20  in the first embodiment. 
     The inventor of this application conducted a comprehensive study and found that the low rigidity portions  132   a  and  132   c  having a rigidity not so low (not so deformable) as that of the flexible base member  21  included in the flexible board portion  40  but lower than that of the other portions of the rigid board portion  130  (the rigid portion  131   a , the rigid portion  131   b , and the rigid portion  131   c ) even by a small amount reduce the deformation of the rigid board portion  130 . The operations and effects of the rigid board portion  130  are similar to those in the first embodiment and are not described. 
     Third Embodiment 
     A third embodiment of the present invention is described with reference to  FIG. 11 . In the third embodiment, the configuration of a rigid board portion  230  of a rigid flexible board  220  is different from the rigid flexible board  20  in the above-described first embodiment. The configurations, operations, and effects similar to those in the first embodiment are not described. 
     In this embodiment, the two rigid base members  22  sandwich the flexible base member  21 . Each of the rigid base members  22  has an oblong overall shape extending along the edge LE of the liquid crystal panel  11  (in the longitudinal direction of the flexible base member  21 ) and the oblong shape has two cutouts at the first edge  30   a  of the rigid board portion  230  to be in a comb-like shape. 
     The rigid board portion  230  includes three rigid portions  231   a ,  231   b , and  231   c , which are constituted of the teeth-shaped portions of the two rigid base members  22  and the portions of the flexible base member  21  sandwiched therebetween, and low rigidity portions  232   a  and  232   c , which are constituted of the flexible base member  21 . The low rigidity portions  232   a  and  232   c  are respectively located between the rigid portion  231   a  and the rigid portion  231   b  positioned next to each other and between the rigid portion  231   b  and the rigid portion  231   c  positioned next to each other. 
     The inventor of the present application conducted a comprehensive study and found that, like the low rigidity portion  232   a  and  232   c , the low rigidity portion not extending from one edge to the other edge of the rigid board portion and extending along only a portion of the rigid board portion is capable of reducing the deformation of the rigid board portion  230 . The operations and effects of the rigid board portion  240  are similar to those in the first embodiment and are not described. 
     Fourth Embodiment 
     A fourth embodiment of the present invention is described with reference to  FIG. 12  and  FIG. 13 . In the fourth embodiment, the configuration of a rigid board portion  330  of a rigid flexible board  320  is different from the rigid flexible board  20  in the above-described first embodiment. The configurations, operations, and effects similar to those in the above-described first embodiment are not described. 
     In this embodiment, two pairs of the two rigid base members  22 , each of which sandwich the flexible base member  21 , are disposed in an arrangement direction in which the rigid flexible board  320  and the liquid crystal panel  11  are arranged (the short side direction of the flexible base member  21 , Y axis direction). 
     The rigid board portion  330  includes two rigid portions  331   a  and  331   b , which are constituted of the two rigid base members  22  and the flexible base member  21  sandwiched therebetween, and a low rigidity portion  332   a , which is located between the rigid portion  331   a  and the rigid portion  331   b  positioned next to each other and is constituted of the flexible base member  21 . In other words, the low rigidity portion  332   a  extends in parallel to the edge LE of the liquid crystal panel  11  (to which the flexible board portion  40  is connected) from one end to the other end in the longitudinal direction of the rigid board portion  330 . The rigid board portion  330  is connected to the flexible board portion  40  (the flexible portion  41   a , the flexible portion  41   b , and the flexible portion  41   c ) at the first edge  30   a  of the rigid portion  331   a . The rigid portion  331   a  and the rigid portion  331   b  are electrically connected to each other through the low rigidity portion  332   a  located therebetween. 
     In this embodiment, a portion of the rigid board portion  330  which applies force to the liquid crystal panel  11 , i.e., the dimension of the rigid portion  331   a  in the Y axis direction, is small compared with a configuration, for example, in which a rigid base member extends over the entire area of the rigid board portion and force is applied to the liquid crystal panel  11  by the entire portion thereof. Thus, the rigidity of the portion is reduced. This reduces the force itself to be applied from the rigid board portion  330  to the liquid crystal panel  11 . A component that may readily cause local deformation (for example, high-voltage densely arranged electrically conducting paths or amounting component generating a large amount of heat) may be disposed on the rigid board portion  330 . In such a case, the component is disposed on the rigid board portion  331   b  such that the low rigidity portion  332   a  absorbs the deformation of the rigid board portion  331   b . This reduces that the deformation of the rigid board portion  331   b  affects the rigid portion  331   a  (see  FIG. 13 ). 
     Fifth Embodiment 
     A fifth embodiment of the present invention is described with reference to  FIG. 14  and  FIG. 15 . In the fifth embodiment, instead of the rigid flexible board described in the first embodiment, a rigid board (signal supply board)  430  and a flexible board  440 , which are separate components, are included. The configurations, operations, and effects similar to those in the above-described first embodiment are not described. 
     The flexible board  440  is formed of a flexible base member having flexibility. The flexible base member is a film formed of a synthetic resin material having insulation properties (such as a polyimide-based resin) and has a flexible-side wiring pattern routed on a film surface thereof. The flexible board  440  includes separated three flexible portions  441   a ,  441   b , and  441   c  each having a rectangular shape. The flexible side panel terminal  43 , which is connected to the liquid crystal panel  11 , is disposed on the first end  40   a  of the flexible board  440  adjacent to the liquid crystal panel  11  (remote from the rigid board  430 ). 
     The rigid board  430  includes three rigid portions  431   a ,  431   b , and  431   c  and low rigidity portions  432   a  and  432   c  constituted of a rigid board side flexible base member (signal supply board side flexible base member)  37 . The low rigidity portions  432   a  and  432   c  are respectively located between the rigid portion  431   a  and the rigid portion  431   b  positioned next to each other and between the rigid portion  431   b  and the rigid portion  431   c  positioned next to each other. In each of the rigid portion  431   a , the rigid portion  431   b , and the rigid portion  431   c , a power component, which is configured to supply driving power and a reference potential to the drivers  12 , and an electronic component (circuit component), which is configured to control the transmission of input signals relating to images to the liquid crystal panel  11 , are mounted on a rigid base board having a predetermined thickness and formed of phenolic paper or glass epoxy resin, for example, and a rigid side wiring pattern (all are not illustrated) is routed on a main surface thereof. In other words, the rigid portion  431   a , the rigid portion  431   b , and the rigid portion  431   c  each have a configuration of a so-called printed wiring board. The rigid board side flexible base member  37  of the low rigidity portion  432   a  (the low rigidity portion  432   c ) is a film formed of a synthetic resin material having insulation properties (such as a polyimide-based resin) and has a low rigidity portion side wiring line routed on the film surface such that the rigid portions  431   a  and  431   b  (the rigid portions  431   b  and  431   c ) are electrically connected to each other. Ends of the low rigidity portion wiring line have low rigidity portion side terminals (not illustrated) configured to be connected to the rigid portion  431   a  and the rigid portion  431   b  (the rigid portion  431   b  and the rigid portion  431   c ), and are connected to rigid portion side terminals (not illustrated) of the rigid portion  431   a  and the rigid portion  431   b  (the rigid portion  431   b  and the rigid portion  431   c ) through an anisotropic conductive film. In this embodiment, the low rigidity portion  432   a  and the low rigidity portion  432   c  are separate components, but the low rigidity portion  432   a  and the low rigidity portion  432   c  may be an integral component. 
     A step of mounting the flexible board  440  on the liquid crystal panel  11  (a flexible board mounting step) and a step of mounting the rigid board  430  on the flexible board  440  (a rigid board mounting step) in this embodiment are described. First, in the flexible board mounting step, a first end  40   a  of each of the three flexile portions  441   a ,  441   b , and  441   c  is positioned on the non-display area NAA of the liquid crystal panel  11  and is thermally bonded thereto by using a flexible board mounting apparatus in a similar way to the first embodiment. Next, in the rigid board mounting step, the rigid board  430  is positioned on the same side as the liquid crystal panel  11  (the lower side) in relation to the second end  40   b  of the flexible board  440 , and a rigid board side flexible terminal on the first edge  30   a  of the rigid board  430  is connected to the flexible board side rigid terminal on the flexible board  440  through an anisotropic conductive film. At this time, a rigid board mounting apparatus having a similar configuration to the flexible board mounting apparatus is used to thermally bond the rigid board  430  to the flexible board  440  in a similar way to the flexible board mounting apparatus. The flexible board mounting step and the rigid board mounting step may be sequentially performed in this order or may be sequentially performed in a reverse order. 
     In this embodiment, since the rigid board  430  includes the low rigidity portions  432   a  and  432   c , the deformation of the rigid board  430  caused by the heat during the thermocompression bonding of the rigid board  430  to the flexible board  440  is absorbed by the low rigidity portions  432   a  and  432   c  of the rigid board  430 . Furthermore, since the rigid board  430  and the flexible board  440  are separate members, the connection area between the flexible base member and the rigid base member is limited to the first edge  30   a  of the rigid board  430 . This reduces the deformation of the rigid board  430  itself compared with the rigid board portion of the rigid flexible board, for example, in which the connection area between the flexible base member and the rigid base member extends substantially over the entire area of the surface of the rigid board portion. 
     In this embodiment, the low rigidity portions  432   a  and  432   c  extend from the first edge  30   a  of the rigid board  430  adjacent to the liquid crystal panel  11  to the second edge  30   b  remote from the liquid crystal panel  11 . The low rigidity portion  432   a  (the low rigidity portion  432   c ) formed of the rigid board side flexible base member  37  allows the connection between the rigid portion  431   a  and the rigid portion  431   b  (the rigid portion  431   b  and the rigid portion  431   c ) through the rigid board side flexible base member  37 , enabling the low rigidity portions  432   a  and  432   c  to extend from the first edge  30   a  to the second edge  30   b  of the rigid board, which is difficult in the low rigidity portion constituted of a slit in the rigid board, for example. This configuration enables the low rigidity portion  432   a  (the low rigidity portion  432   c ) to uniformly absorb the displacement between the rigid portion  431   a  and the rigid portion  431   b  (the rigid portion  431   b  and the rigid portion  431   c ) from the first edge  30   a  of the rigid board portion  430  to the second edge  30   b , which is preferable. 
     Sixth Embodiment 
     A sixth embodiment of the present invention is described with reference to  FIG. 16 . In the sixth embodiment, the configuration of a rigid board portion  530  of a rigid flexible board  520  is different from the rigid flexible board  20  in the above-described first embodiment. The configurations, operations, and effects similar to those in the above-described first embodiment are not described. 
     In this embodiment, as in the third embodiment, two rigid base members  22  sandwich the flexible base member  21 . Each of the two rigid base members  22  has an oblong overall shape extending along the edge LE of the liquid crystal panel  11  (in the longitudinal direction of the flexible base member  21 ) and the oblong shape has two cutouts at the first edge  30   a  of the rigid board portion  530  to be in a comb-like shape. Furthermore, in this embodiment, unlike the third embodiment, the portion  21   b  of the flexible base member  21  remote from the liquid crystal panel  11  is configured to have the same shape as the rigid base member  22 . In other words, the rigid board portion  530  includes slits  535   a  and  535   c  extending therethrough in the thickness direction. The rigid board portion  530  has a rectangular overall shape and has the slits  535   a  and  535   c , which are cutouts, at the first edge  30   a . In the rigid board portion  530 , the slit  535   a  and the slit  535   c  are respectively located at positions close to the space  42   a  and the space  42   c.    
     Low rigidity portions  532   a  and  532   c  are obtained by forming the slits  535   a  and  535   c  in the rigid board portion  530 . Specifically, the low rigidity portion  532   a  and the low rigidity portion  532   c  each have a smaller width in the Y axis direction (about a half in this embodiment) than portions of the rigid board portion  530  not having the slits  535   a  and  535   c  (the rigid portion  531   a , the rigid portion  531   b , and the rigid portion  531   c ), and thus have lower rigidity. The rigidity of the low rigidity portions  532   a  and  532   c  are suitably adjusted by changing the size of the slits  535   a  and  535   c.    
     Thermal expansion of the rigid board portion  530  may occur during mounting of the rigid board portion  520  on the liquid crystal panel  11 . In such a case, the low rigidity portions  532   a  and  532   c  deform to absorb the displacement and deformation of the rigid portion  531   a , the rigid portion  531   b , and the rigid portion  531   c . At this time, stress concentrates on connection portions between the low rigidity portions  532   a  and  532   c  and the corresponding rigid portion  531   a ,  531   b , and  531   c , accelerating the deformation of the low rigidity portions  532   a  and  532   c  and reducing the displacement and deformation between the rigid portion  531   a , the rigid portion  531   b , and the rigid portion  531   c . The other operations of the low rigidity portions  532   a  and  532   c  for reducing the deformation of the rigid board portion  530  are similar to those in the first embodiment and are not described. 
     In this embodiment, since the low rigidity portions  532   a  and  532   c  are obtained by forming the slits  535   a  and  535   c  in the rigid board portion  530 , the low rigidity portions  532   a  and  532   c  are readily formed, which is preferable. In addition, since the connections between the rigid portion  531   a , the rigid portion  531   b , and the rigid portion  531   c  are made by using the same wiring lines on the rigid base member  22  of the low rigidity portions  532   a  and  532   c , for example, a configuration for connection between the rigid base member  22  and the flexible base member  21  is not required. 
     Furthermore, in this embodiment, since the slits  535   a  and  535   c  are cutouts at the first edge  30   a  of the rigid board portion  530 , the low rigidity portions  532   a  and  532   c  readily absorb the deformation at the first edge  30   a  of the rigid board portion  530 , and thus the force applied from the rigid board portion  530  to the liquid crystal panel  11  through the flexible board portion  40  is reliably reduced. 
     Seventh Embodiment 
     A seventh embodiment of the present invention is described with reference to  FIG. 17 . In the seventh embodiment, instead of the rigid flexible board described in the sixth embodiment, a rigid board (a signal supply board)  630  and a flexible board  440 , which are separate components, are included. The configurations, operations, and effects similar to those in the above-described sixth embodiment are not described. 
     The rigid board  630  has a configuration of a so-called printed wiring board and has a rectangular overall shape and has slits  635   a  and  635   c , which are cutouts, at the first edge  30   a  to provide low rigidity portions  635   a  and  635   c . The rigid portion  631   a , the rigid portion  631   b , and the rigid portion  631   c  have the configuration similar to those of the rigid portions  431   a , the rigid portion  431   b , and the rigid portion  431   c  in the fifth embodiment and are not described. In addition, the operations of the low rigidity portions  635   a  and  635   c  are similar to those of the low rigidity portions  532   a  and  532   c  in the sixth embodiment and are not described. 
     Eighth Embodiment 
     An eighth embodiment of the present invention is described with reference to  FIG. 18 . In the eighth embodiment, the configuration of a rigid board portion  730  of a rigid flexible board  720  is different from the rigid flexible board  520  in the above-described sixth embodiment. The configurations, operations, and effects similar to those in the above-described sixth embodiment are not described. 
     The rigid board portion  730  in this embodiment includes a plurality (two in this embodiment) of slits  735   a  and  735   b  (slits  735   c  and  735   d ) located close to each other and in parallel to each other, unlike the slit  535   a  (the slit  535   c ) in the sixth embodiment. With this configuration, the displacement in the rigid board portion  730  in an arrangement direction (X axis direction) in which the slit  735   a  and the slit  735   b  (the slit  735   c  and the slit  735   d ) are arranged is reliably absorbed. In addition, compared with a configuration in which one cutout extends over the area including the plurality of slits, the rigid board portion  730  readily has a larger surface area in an extending direction of the slits  735   a  and  735   b  (the slits  735   c  and  735   d ), readily enhancing the rigidity thereof. The number of slits located in parallel to each other is not limited to two and may be three or more. 
     Ninth Embodiment 
     A ninth embodiment of the present invention is described with reference to  FIG. 19 . In the ninth embodiment, the configuration of a rigid board portion  830  of a rigid flexible board  820  is different from the rigid flexible board  520  in the above-described sixth embodiment. The configurations, operations, and effects similar to those in the above-described sixth embodiment are not described. 
     In the rigid board portion  830  in this embodiment, a slit  835   a  (a slit  835   c ) is a cutout at the second edge  30   b  of the rigid board  830  remote from the liquid crystal panel  11 , unlike the slit  535   a  (the slit  535   c ) in the sixth embodiment. This configuration eliminates the need of routing wiring lines so as to avoid the slit  535   a  (the slit  535   c ) at the side of the rigid board portion  830  connected to the flexible board portion  40 , making it easy to design the rigid board portion  830 . 
     Tenth Embodiment 
     A tenth embodiment of the present invention is described with reference to  FIG. 20 . In the tenth embodiment, the configuration of a rigid board portion  930  of a rigid flexible board  920  is different from the rigid flexible board  820  in the above-described ninth embodiment. The configurations, operations, and effects similar to those in the above-described ninth embodiment are not described. 
     The rigid board portion  930  in this embodiment further includes slits at the second edge  30   b  of the rigid board portion  930  so as to face the connection portions between the rigid board portion  930  and the flexible board portion  40 , unlike the ninth embodiment. In other words, at the second edge  30   b  of the rigid board portion  930 , slits  935   b  and  935   d  face the spaces  42   a  and  42   c , and slits  935   a ,  935   c , and  935   e  face the flexible portions  41   a ,  41   b , and  41   c . If the first edge  30   a  of a rigid board portion includes a slit, the slit needs to be positioned away from the connection portion between the rigid board portion  930  and the flexible board portion  40 . However, since the slits are positioned at the second edge  30   b  of the rigid board portion  930  in the present embodiment, the formation positions of the slit  935   a  to  935   e , i.e., the positions of the low rigidity portions  932   a  to  932   e , are determined with a high degree of freedom. The displacement and deformation of the rigid portions  932   a  to  932   f  of the rigid board portion  930  is sufficiently absorbed by properly positioning the low rigidity portions  932   a  to  932   e.    
     Eleventh Embodiment 
     An eleventh embodiment of the present invention is described with reference to  FIG. 21 . In the eleventh embodiment, the configuration of a rigid board portion  1030  of a rigid flexible board  1020  is different from the rigid flexible board  920  in the above-described eighth embodiment. The configurations, operations, and effects similar to those in the above-described tenth embodiment are not described. 
     In the rigid board portion  1030  in this embodiment, the second edge  30   b  of the rigid board portion  1030  includes many slits  1035   a , unlike the tenth embodiment. In the rigid board portion  1030 , portions constituting rigid portions  1031   a  and portions constituting low rigidity portions  1032   a  are repeatedly arranged along the second edge  30   b . This configuration reliably enables the rigid board portion  1030  to have high flatness. 
     Other Embodiments 
     The present invention is not limited to the embodiments described above with reference to the drawings. For example, the following embodiments are included in the technical scope of the present invention. 
     (1) In the above-described embodiments except for the fourth embodiment, the configuration including three or more rigid portions is described as an example, but the number of rigid portions may be at least two. The size of each rigid portion and the number of rigid portions may be suitably changed depending on the material, size, or shape of the signal supply board, or connection configuration of the signal supply board to the flexible board, for example. 
     (2) In the above-described first embodiment, for example, the configuration in which the flexible board portion is separated such that the number of flexible portions is the same as the number of rigid portions is described as an example, but the configuration of the flexible board portion is not limited to this. For example, the flexible board portion may be unseparated or the number of flexible portions may be larger or smaller than the number of rigid portions. 
     (3) In the above-described embodiments, the configuration in which the rigid flexible boards in two layers are stacked is described as an example, but a configuration in which rigid members in three or more layers are stacked is included in the present invention. 
     (4) The configurations of the above-described embodiments may be suitably combined without departing from the spirit of the invention. For example, the slits described in the sixth to eleventh embodiments may be formed in the rigid board described in the seventh embodiment to provide the low rigidity portion. 
     (5) In the above-described embodiments, the low rigidity portion constituted of a flexible base member or a slit is described as an example, but the configuration of the low rigidity portion is not limited thereto. The low rigidity portion may be formed by thinning a portion of the rigid board portion or a portion of the rigid board. 
     (6) In the above-described sixth to eleventh embodiments, a configuration in which the slits are cutouts in the rigid board portion is described as an example, but the slit may be a through hole having an opening in a planar surface of the rigid board portion. In such a case, the low rigidity portion is able to be located at each side (for example, a first end and a second end of the rigid board portion) in the longitudinal direction of the slit. 
     (7) Other than the above-described embodiments, the positions, number, shape, or material of the low rigidity portion may be suitably determined. The rigidity of the low rigidity portion may be suitably changed as long as the rigidity thereof is lower than the rigidity of the rigid portion. 
     (8) In the above-described embodiments, the liquid crystal panel having a horizontally elongated quadrilateral shape is described as an example, but the present invention is applicable to a liquid crystal panel having a vertically elongated quadrilateral shape or a liquid crystal panel having a square shape. In addition, the present invention is applicable to a liquid crystal panel having another shape such as a semicircular shape and a doughnut shape. 
     (9) In the above-described embodiments, a transmissive liquid crystal display device including a backlight device, which is an external light source, is described as an example, but the present invention is applicable to a reflective liquid crystal display device configured to provide a display by using external light. In such a case, a backlight device may be eliminated. 
     (10) In the above-described embodiments, the TFT is used as the switching element in the liquid crystal display device, but the present invention is applicable to a liquid crystal display device that uses a switching element other than a TFT (a thin film diode (TFD), for example). The present invention is also applicable to a black-and-white liquid crystal display device other than a color liquid crystal display device. 
     (11) In the above-described embodiments, a liquid crystal display device using a liquid crystal panel as a display panel is described as an example, but the present invention is applicable to a display device that uses another type of display panel (such as a PDP (plasma display panel) and an organic EL panel). In such a case, a backlight device may be eliminated. 
     (12) In the above-described embodiments, the display area located closer to one edge of the liquid crystal panel in the long side direction and one edge in the short side direction is described as an example. However, a display area located at the middle of the liquid crystal panel in the long side direction and closer to one edge in the short side direction and a display area located at the middle of the liquid crystal panel in the short side direction and closer to one edge in the long side direction may be included in the present invention. Meanwhile, a configuration in which the display area is located at the middle of the liquid crystal panel in the long side direction and the short side direction is included in the present invention. 
     (13) In the above-described embodiments, the rigid flexible board or the rigid board having a length substantially equal to the dimension of the liquid crystal panel in the long side direction is described as an example, but the specific length of the rigid flexible board or the rigid board is suitably changed and may be about half of the dimension of the liquid crystal panel in the long side direction, for example. 
     EXPLANATION OF SYMBOLS 
     
         
         
           
               11  liquid crystal panel 
               21  flexible base member 
               22  rigid base member 
               30 ,  130 ,  230 ,  330 ,  530 ,  730 ,  830 ,  930 ,  1030  rigid board portion 
               30   a  first edge 
               30   b  second edge 
               31   a ,  131   a ,  231   a ,  331   a ,  431   a ,  531   a ,  731   a ,  831   a ,  931   a ,  1031   a  rigid portion 
               31   b ,  131   b ,  231   b ,  331   b ,  431   b ,  531   b ,  731   b ,  831   b ,  931   b  rigid portion 
               31   c ,  131   c ,  231   c ,  431   c ,  531   c ,  731   c ,  831   c ,  931   c  rigid portion 
               32   a ,  132   a ,  232   a ,  332   a ,  432   a ,  532   a ,  732   a ,  832   a ,  932   a ,  1032   a  low rigidity portion 
               32   c ,  132   c ,  232   c ,  432   c ,  532   c ,  732   c ,  832   c ,  932   c  low rigidity portion 
               37  rigid board side flexible base member (signal supply board side flexible base member) 
               40  flexible board portion (signal supply board) 
               40   a  first end 
               40   b  second end 
               41   a  flexible portion 
               41   b  flexible portion 
               41   c  flexible portion 
               42   a  space 
               42   c  space 
               430 ,  630  rigid board (signal supply board) 
               440  flexible board 
             LE edge