Patent Publication Number: US-11665822-B2

Title: Electronic device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/898,942, filed on Jun. 11, 2020. Further, this application claims priority from Japanese Patent Application JP 2019-118324 filed on Jun. 26, 2019, the entire contents of which are hereby incorporated by reference into this application. 
    
    
     BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention relates to the electronic devices, like display devices, sensor substrates and so forth, which the substrates can be used in curved state. 
     (2) Description of the Related Art 
     Self-luminous type display devices like the organic EL display device and the micro-LED display device, and other display devices like the liquid crystal display device and the electrophoresis display device are sometimes required to be used in curved state because of their application and their design needs. In addition, not only display devices but touch panels or sensor substrates for e.g. photo sensors are also sometimes required to be used in curved state according the design of equipment that those devices are installed. The curving direction can be in lateral axis (may be expressed x axis) or in longitudinal axis (may be expressed as y axis). 
     The display device comprises a display panel, printed circuit board, in which several circuits are installed to supply powers and signals to the display device, and a flexible wiring substrate to connect the printed circuit board and the display panel. The flexible wiring substrate is folded so that the printed circuit board is set at the back of the display panel to make the outer dimension of the display device small in total. 
     The patent document 1 discloses to provide a hole in the printed circuit board to accommodate the IC driver so that the IC driver does not protrude outwardly from the surface of the printed circuit board. The patent document 1 also discloses to separate the printed circuit board into two parts; each of the separated printed circuit boards and the curved display panel are connected by plural flexible wiring substrates. 
     PRIOR TECHNICAL DOCUMENT 
     Patent Document 
     
         
         Patent document 1: Japanese patent application laid open No. 2018-97223 
       
    
     SUMMARY OF THE INVENTION 
     The structure, which one side of the flexible wiring substrate is connected to the curved side of the display panel and another side of the flexible wiring substrate is connected to the printed circuit board, produces a stress in the connection portions between the flexible wiring substrate and the display panel and between the flexible wiring substrate and the printed circuit board. The reason is that the printed circuit board, in which circuits are formed on the glass epoxy substrate and various electronic components are installed, is flat and comparatively rigid. 
     In addition, in order to make the outer dimension of the display device small, when the printed circuit board is folded to the back of the display panel, the stress in the connection portions between the flexible wiring substrate and the display panel and between the flexible wiring substrate and the printed circuit board becomes very big. Consequently, the reliability of the connections between the flexible wiring substrate and the display panel and between the flexible wiring substrate and the printed circuit board becomes a problem. Concretely, electrical connection at those connections or peeling off of the substrates at the connection portion becomes a problem. 
     The purpose of the present invention is to mitigate the stress at the connection terminal and keep high reliability of connection in the structure, in which one side of the flexible wiring substrate is connected to the curved side of the display panel and another side of the flexible wiring substrate is connected to the printed circuit board. 
     The present invention overcomes the above explained problem; the concrete structures are as follows. 
     (1) An electronic device comprising: a substrate having a curved surface, a printed circuit board, and plural flexible wiring substrates, 
     each of two of the plural flexible substrates has a terminal portion that is connected to the curved surface, 
     the printed circuit board has a cutout between the two flexible wiring substrates. 
     (2) The electronic device according to (1), wherein a major surface of the printed circuit board is flat. 
     (3) The electronic device according to (1), wherein the printed circuit board is folded to a back of the substrate through the plural flexible substrate, and the printed circuit board is flat. 
     (4) An electronic device comprising: a substrate having a curved surface, a printed circuit board, and plural flexible wiring substrates, 
     each of two of the plural flexible substrates has a terminal portion that is connected to the curved surface, 
     the printed circuit board has a thinner portion between the two flexible wiring substrates than other portion of the printed circuit board. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a perspective view that the curved display panel and the printed circuit board are connected by two flexible wiring substrates; 
         FIG.  2    is a perspective view that the printed circuit board is folded to the back of the curved display panel; 
         FIG.  3    is a perspective view that the printed circuit board is divided into two; 
         FIG.  4    is a perspective view that second flexible wiring substrates and the second printed circuit board are disposed; 
         FIG.  5    is a perspective view of the structure of embodiment 1; 
         FIG.  6    is a plan view of embodiment 1 before the display panel is curved; 
         FIG.  7    is an enlarged plan view of the portion of V shaped cutout of the printed circuit board; 
         FIG.  8    is a perspective view of the structure of embodiment 1 when the display panel is the liquid crystal display panel; 
         FIG.  9    is the structure A for simulation; 
         FIG.  10    is the structure B for simulation; 
         FIG.  11    is the structure C for simulation; 
         FIG.  12    is the structure D for simulation; 
         FIG.  13    is the structure E for simulation; 
         FIG.  14    is the structure F for simulation; 
         FIG.  15    is a perspective view that shows the result of simulation of the structure A; 
         FIG.  16    is a perspective view that shows the result of simulation of the structure B; 
         FIG.  17    is a perspective view that shows the result of simulation of the structure C; 
         FIG.  18    is a perspective view that shows the result of simulation of the structure D; 
         FIG.  19    is a perspective view that shows the result of simulation of the structure E; 
         FIG.  20    is a perspective view that shows the result of simulation of the structure F; 
         FIG.  21    is a table that summarizes the results of the simulation; 
         FIG.  22    is a plan view that the semicircle shaped cutout is formed in the printed circuit board, which is an example of embodiment 2; 
         FIG.  23    is an enlarged view of the printed circuit board at the semicircle shaped cutout; 
         FIG.  24    is a plan view that the rectangular cutout is formed in the printed circuit board; 
         FIG.  25    is a plan view that the slit shaped cutout is formed in the printed circuit board; 
         FIG.  26    is a plan view that the T shaped cutout is formed in the printed circuit board; 
         FIG.  27    is a plan view of an example of embodiment 3; 
         FIG.  28    is a cross sectional view along the A-A line of  FIG.  27   ; 
         FIG.  29    is another example of a cross sectional view along the A-A line of  FIG.  27   ; 
         FIG.  30    is another example of embodiment 3; 
         FIG.  31    is a plan view that the display panel and the printed circuit board are connected by four flexible wiring substrates; 
         FIG.  32    is a first example of embodiment 4; 
         FIG.  33    is a second example of embodiment 4; 
         FIG.  34    is a third example of embodiment 4; 
         FIG.  35    is a fourth example of embodiment 4; 
         FIG.  36    is a fifth example of embodiment 4; 
         FIG.  37    is a sixth example of embodiment 4; 
         FIG.  38    is a seventh example of embodiment 4; 
         FIG.  39    is an eighth example of embodiment 4; 
         FIG.  40    is a ninth example of embodiment 4; 
         FIG.  41    is a tenth example of embodiment 4; 
         FIG.  42    is an eleventh example of embodiment 4; 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will be described in detail referring to the following embodiments. The present invention can be applied to various display devices as display devices having photo-electrical layers like the liquid crystal display device or the electrophoresis display device, or self-luminous display devices as organic EL display device and the micro LED device. In addition to the display devices, the present invention is applicable to other electronic devices like sensor devices, e.g. the external touch sensor or the finger print sensor, etc. 
     Further, in addition to the display devices and the sensor devices, the present invention is applicable to other electronic devices that the flexible wiring substrates are used. In such cases, in the following explanations, the display panel can be substituted by sensor substrate of the sensor device or the substrate that the flexible wiring substrate is connected to in the electronic device. 
     Embodiment 1 
       FIG.  1    is a development plan view of a curved display device according to the present invention before it is folded. In  FIG.  1   , the display panel  10  is curved. Such a display device is used as e.g. various display apparatus in a dashboard of a car. The printed circuit board  30  is set opposing to the curved side of the display panel  10 ; the printed circuit board  30  and the curved side of the display panel  10  are connected by the two flexible wiring substrates  20 . As depicted in  FIG.  1   , the flexible wiring substrate  20  is connected to the curved side of the display panel  10 . 
     The display panel  10  is curved by radius of curvature R 1  of 800 mm, on the other hand, the printed circuit board  30  is approximately flat. Therefore the flexible wiring substrate  20 , which connects the display panel  10  and the printed circuit board  30 , has a stress at the connection portions; especially at the portions indicated by arrows in  FIG.  1   . Such stresses give bad influence to connections between the display panel  10  and the flexible wiring substrate  20  and between the printed circuit board  30  and the flexible wiring substrate  20 . 
     In  FIG.  1   , the substrate of the display panel  10  is made of e.g. glass and a thickness is e.g. 0.15 mm. A protecting plate or supporting plate having a predetermined curvature is adhered by adhesive to the front surface or the back surface of the display panel  10  to give predetermined curvature to the display panel  10 . 
     The printed circuit board  30 , which is made of laminated glass epoxy sheets, is flat, a thickness is approximately 0.5 mm to 2.5 mm, and is comparatively rigid. Several electronic components as the controller IC  41 , the power generation circuit  42 , and the interface  40 , which means e.g. connector and so forth, are installed in the printed circuit board  30 . 
     The flexible wiring substrate  20  is made of polyimide, and a thickness is approximately 0.1 mm. The flexible wiring substrate  20  itself is rectangle; however, the flexible wiring substrate  20  in  FIG.  1    is deviated from the rectangle since it connects the display panel  10 , which is curved, and the printed circuit board  30 , which is flat. Since the flexible wiring substrate  20  is deformed, a stress is produced at the connection terminals. In the display device in  FIG.  1   , the printed circuit board  30  is folded to the back of the display panel  10  as depicted by the partly shaded broad arrow in  FIG.  1    to make the outer dimension of the display device small. 
       FIG.  2    is a perspective view that the printed circuit board  30  is folded back to the display panel  10 . In this case, in addition to the stress in the state of  FIG.  1   , the flexible wiring substrate  20  gets a big and complex stress including a twist stress caused by being folded to the back of the display panel  10 . As a result, a big peeling off stress is generated at the connection terminals between the flexible wiring substrate  20  and the display panel  10  or between the flexible wiring substrate  20  and the printed circuit board  30 ; consequently, a danger arises that an electrical connection fails in those connection terminals. 
     To countermeasure this problem, it is conceivable to divide the printed circuit board into two parts as depicted in  FIG.  3   . By the way, in general, one controller IC  41  and one power generation circuit  42  are installed in the printed circuit board  30 . The controller IC  41 , the power generation circuit  42 , and interface  40  etc. must commonly work in the two printed circuit board  30 . Consequently, a means to connect the two printed circuit boards  30  is necessary. It is conceivable to install the controller IC  41 , the power generation circuit  42 , and the interface  40  into each of the two printed circuit boards  30 ; however, that measure is not preferable from the view of the manufacturing cost. In addition, a synchronizing means for the two printed circuit boards is necessary; thus, connection means for the two printed circuit boards is still necessary. 
       FIG.  4    is an example that a second printed circuit board  60  and the second flexible wiring substrates  50  are disposed to connect two printed circuit boards  30 . The structure of  FIG.  4   , however, needs additional components, which arises additional cost; in addition, a space for the second printed circuit board  60  and the second flexible wiring substrates  50  is necessary. 
       FIG.  5    is a development plan view of embodiment 1 of the present invention that countermeasures the above explained problem.  FIG.  5    features that the V shaped cutout  31  is formed in the printed circuit board  30  between the two flexible wiring substrates  20 . Thus, the section modulus of the printed circuit board  30  at the V shaped cutout  31  is made smaller; consequently, the printed circuit board  30  becomes not completely rigid and is allowed to be bent at the V shaped cutout  31 . Therefore, the stress at the connections between the flexible wiring substrate  20  and the printed circuit board  30  and between the flexible wiring substrate  20  and the display panel  10  are mitigated. 
     In  FIG.  5   , the printed circuit board  30  remains as one piece, thus, the controller IC  41 , the power generation circuit  42  and interface  40  can work for entire printed circuit board  30 . Other structure of  FIG.  5    is the same as explained in  FIG.  1   . In  FIG.  5   , the printed circuit board  30  is folded to the back of the display panel  10  as depicted by the half shaded broad arrow, and then, is installed in the apparatus. A perspective view after the printed circuit board  30  is folded to the back of the display panel  10  is the same as  FIG.  2   . 
       FIG.  6    is a plan view of  FIG.  5    before the display panel  10  is curved. In  FIG.  6   , the plan view of the flexible wiring substrate  20 , which connects the display panel  10  and the printed circuit board  30 , remains rectangle since both of the display panel  10  and the printed circuit board  30  are flat. The V shaped cutout  31  is formed at approximately center of the side of the printed circuit board  30 , which opposes to the display panel  10 . 
       FIG.  7    is an enlarged view of the printed circuit board  30  at the V shaped cutout  31 . In  FIG.  7   , the tip of the V shaped cutout  31  is at approximately the center of the space between the two flexible wiring substrates  20 . Provided the distance between the two flexible wiring substrates  20  is W 1  and the opening width of the V shaped cutout  31  is W 2 , 0.4×W 1 ≤W 2 ≤1.0×W 1  is satisfied. In addition, provided the width of the printed circuit board  30  in y direction is L 1  and the depth of the V shaped cutout  31  in y direction is L 2 , 0.3×L 1 ≤L 2 ≤0.7×L 1  is satisfied. 
     In the above case, the width WF of the flexible wiring substrate  20  in x direction is 50 mm; the distance W 1  between the two flexible wiring substrates  20  in x direction is 25 mm. In the meantime, when the display panel  10  is curved, the stresses at the connections between the display panel  10  and the flexible wiring substrate  20  and between the flexible wiring substrate  20  and the printed circuit board  30  become bigger when the width WF of the flexible wiring substrate  20  is bigger and when the distance in y direction between the display panel  10  and the printed circuit board  30  is smaller. In any events, however, the V shaped cutout  31  in the printed circuit board  30  between the flexible wiring substrates  20  mitigates the stress at the connections. 
     The bigger values of the opening W 2  and the depth L 2  can decrease the stresses at the connections between the display panel  10  and the flexible wiring substrate  20  and between the flexible wiring substrate  20  and the printed circuit board  30 ; however, a design liberty of wring in the printed circuit board  30  is restricted when the values of W 2  and L 2  are too big. Therefore, there is a tradeoff between the stress at the connection terminals and the design liberty of wiring in the printed circuit board  30 . In the meantime, the tip of the V shaped cutout  31  can be a sharp angle or round r. 
       FIGS.  8 - 21    show how the V shaped cutout  31  disclosed in  FIGS.  5  and  6    in the printed circuit board  30  gives an effect to mitigation in stress at the connection terminals by taking an example when the display panel  10  is the liquid crystal display panel. 
       FIG.  8    is a perspective view for simulation of the stress at the connection terminal.  FIG.  8    is the same as  FIG.  5   ; however, the liquid crystal display panel is used as the display panel  10 . The liquid crystal display panel  10  comprises: the TFT substrate  100 , in which the signal wirings, TFTs, and so on are formed, the counter substrate  200 , in which color filters and so forth are formed, opposing to the TFT substrate  100 , and the liquid crystal layer, sandwiched between the TFT substrate  100  and the counter substrate  200 . A thickness of each of the TFT substrate  100  and the counter substrate  200  is 0.15 mm. 
     The area that the TFT substrate  100  and the counter substrate  200  do not overlap is the terminal area  150 , namely, this area is on the TFT substrate  100  only. Other structures of  FIG.  8    is the same as  FIG.  5   . In the simulation, the area, where the TFT substrate  100  and the counter substrate  200  overlap, curves by predetermined radius of curvature; the terminal area  150 , where only the TFT substrate exists, to which the flexible wiring substrate  20  is connected to, constitutes a free end. 
     When the display panel  10  is bent from the state of  FIG.  6    to the state of  FIG.  8   , stresses arises at the connections between the printed circuit board  30  and the flexible wiring substrate  20  and between the display panel  10  and the flexible wiring substrate  20 . The bigger the stress, the bigger the problem of reliability in the connection terminals.  FIGS.  9 - 14    are plan views of printed circuit boards  30  in the structures that the simulation is conducted. Among them,  FIG.  14    does not have the cutout in the printed circuit board  30 . 
       FIG.  9    shows a structure A, which is a representative form of embodiment 1; the V shaped cutout  31  is formed in the printed circuit board  30  between the two flexible wiring substrates  20 .  FIG.  9    is the same as  FIG.  6   , however, sizes of the components for the simulation are written. In  FIG.  9   , the width W 3  of the printed circuit board  30  in x direction is 272 mm, the length L 1  in y direction is 72 mm, the width W 2  of the V shaped cutout  31  is 98 mm, the depth L 2  of the V shaped cutout  31  is 36 mm; the width W 4  of the display panel  10  in x direction is 302 mm, length L 4  in y direction is 120 mm; the width WF of the flexible wiring substrate  20  in x direction is 48 mm, the distance W 1  between the two flexible wiring substrates in x direction is 100 mm. The distance L 3  between the display panel  10  and the printed circuit board  30  in y direction is 18 mm. The corresponding dimensions in  FIGS.  10  to  14    are the same except specifically noted. 
       FIG.  10    shows structure B, which has the side cutouts  33 , where the two sides of the printed circuit boards  30  are obliquely cut out. The width W 6  of the side cutout  33  in x direction is 72 mm.  FIG.  11    shows structure C, in which side cutouts  33  are added to the structure A of  FIG.  9   . 
       FIG.  12    shows structure D, in which slits  32  are formed in the printed circuit board  30 . The width W 5  of the slit in x direction is 5 mm, the length L 5  in y direction is 54 mm; the shape of the slit  32  at the end is a half circle of radius of (W 5 )/2. The slits  32  in the printed circuit board  30  are set at the end of the flexible wiring substrates. 
       FIG.  13    shows structure E, in which slits  32  are formed in oblique to the sides of the printed circuit board  30 . In  FIG.  13   , the angle θ is approximately 60 degrees.  FIG.  14    shows structure F, in which the printed circuit board  30  is rectangle, namely, the same as the prior art. 
       FIGS.  15 - 20    show the deformation values at the various places in the display panel  10 , the flexible wiring substrate  20  and printed circuit board  30 , and the maximum load value in each of the structures A to F shown in  FIGS.  9 - 14    when the terminal area of the display panel  10  is curved so that a height of the end of the terminal area becomes 12 mm. 
     In  FIGS.  15  to  20   , the deformations of the display panel  10  and the printed circuit board  30  at the center in x direction is zero. In  FIGS.  15  to  20   , the dotted lines indicate contours in the components; the numerals corresponding to the dotted lines indicate the heights, namely, values of deformation. By the way, in  FIGS.  15  to  20   , the numerals for the dotted lines are smaller than the numerals that indicate the components. In  FIGS.  15  to  20   , the connection portion between the flexible wiring substrate  20  and the printed circuit board  30  is framed; the numeral corresponding to the framed portion indicates a total load value in the framed connection portion. For example, the maximum load value in the connection portion in  FIG.  15    is 1.322 N (Newton). 
     In comparing  FIG.  15    (structure A) to  FIG.  20    (structure F), there is not a big difference in the deformation values in the display panel  10 , the flexible wiring substrate  20  and the printed circuit board  30  among those specifications. On the other hand, the load values at the connection portion between the flexible wiring substrate  20  and the printed circuit board  30  is much smaller in the cases of  FIG.  15    (structure A) and  FIG.  17    (structure C), in which V shaped cutout  31  is formed in the printed circuit board  30  between the two flexible wiring substrates  20  compared with the cases of  FIG.  16    (structure B),  FIG.  18    (structure D) and  FIG.  20    (structure F). Therefore, the effect of V shaped cutout  31  is very big for decreasing the load value at the connection portion. 
       FIG.  21    is a table that shows comparison of maximum load values among the structures A to F. In  FIG.  21   , the structure F, which no measure is added and is considered as a base for comparison, is listed at the upper most row. In  FIG.  21   , the maximum load value of the structure F is 2.257 N, while the maximum load value of the structure A, which has the V shaped cutout  31 , is 1.322 N, which is 40% less compared with the value of the structure F. 
     In  FIG.  21   , the structure C has an oblique cutout at the sides of the printed circuit board in addition to the V shaped cutout  31 ; the maximum load value of the structure C is 1.333 N, which is substantially the same as the value of the structure A. Therefore, the V shaped cutout  31  in the printed circuit board  30  has an essential role to decrease the load value in the connection portion. 
       FIGS.  15 - 20  and  21    are figures that evaluate the load value at the connection portion between the flexible wiring substrate  20  and the printed circuit board  30 ; evaluation of the load values at the connection portion between the flexible wiring substrate  20  and the display panel  10  is the same. Namely, since the load value at the connection portion is caused by curving the display panel  10 , the load value between the flexible wiring substrate  20  and the display panel  10  is generated as a reaction of the load value between the flexible wiring substrate  20  and the printed circuit board  30 . 
     By the way, when the display device is installed, the printed circuit board  30  is folded to the back of the display panel  10 . Further, bigger load values are generated, by folding the printed circuit board  30  to the back of the display panel  10 , between the printed circuit board  30  and the flexible wiring substrate  20 , and between the display panel  10  and the flexible wiring substrate  20 . The relative relations of the load values are the same as shown in  FIG.  21   . Therefore, there is no change that the v shaped cutout  31  greatly decreases the load values at the connection portions. 
     Embodiment 2 
     Embodiment 1 discloses examples to form the V shaped cutout  31  in the printed circuit board  30  between the two flexible wiring substrates  20 . The load values between the printed circuit board  30  and the flexible wiring substrate  20  and between the display panel  10  and the flexible wiring substrate  20  when the display panel  10  is curved can also be decreased by other shaped cutout  31  as well as the V shaped cutout  31 . Embodiment 2 discloses several examples of cutouts  33 .  FIG.  22    shows an example that the semicircle shaped cutout  31  is formed instead of the V shaped cutout  31 . 
       FIG.  23    is an enlarged plan view to show the semicircle shaped cutout  31  and its vicinity of the printed circuit board  30 . In  FIG.  23   , the center of the semicircle shaped cutout  31  is at the center of the space between the two flexible wiring substrates  20 . Provided the distance between the two flexible substrates is W 1  and the opening width of the semicircle shaped cutout  31  is W 2 , 0.4×W 1 ≤W 2 ≤1.0×W 1  is satisfied. In addition, provided the width of the printed circuit board  30  in y direction is L 1  and the depth of the semicircle shaped cutout  31  in y direction is L 2 , 0.3×L 1 ≤L 2 ≤0.7×L 1  is preferable. In this case, the width WF of the flexible wiring substrate in x direction is e.g. 50 mm; the distance W 1  between the two flexible wiring substrates  20  in x direction is 25 mm. 
       FIG.  24    discloses the cutout  31  is rectangle. The examples of dimensions of the rectangular shaped cutout  31  is the same as those of the V shaped cutout  31  and the semicircle shaped cutout  31 . Namely, provided the distance between the two flexible wiring substrate  20  is W 1  and the opening width of the rectangular shaped cutout  31  is W 2 , 0.4×W 1 ≤W 2 ≤1.0×W 1  is satisfied. In addition, provided the width of the printed circuit board  30  in y direction is L 1  and the depth of the rectangular shaped cutout  31  in y direction is L 2 , 0.3×L 1 ≤L 2 ≤0.7×L 1  is preferable. 
       FIG.  25    shows a variation of the cutout  31 , in which the opening width of the rectangular cutout is very narrow and the tip is semicircle. This is called slit shaped cutout  31 . In this case, provided the distance between the two flexible wiring substrate is W 1  and the opening width of the slit shaped cutout  31  is W 2 , 0.1×W 1 ≤W 2 ≤0.4×W 1  is preferable. In addition, provided the width of the printed circuit board  30  in y direction is L 1  and the depth of the slit shaped cutout  31  in y direction is L 2 , 0.3×L 1 ≤L 2 ≤0.7×L 1  is satisfied. 
       FIG.  26    is another example of the cutout  31 , in which the tip of the cutout is widened so that the slit becomes T shaped. This is called T shaped cutout  31 . In this case, provided the distance between the two flexible wiring substrate  20  is W 1  and the opening width of the slit shaped cutout  31  is W 2 , 0.1×W 1 ≤W 2 ≤0.4×W 1  is preferable. In addition, provided the width of the printed circuit board  30  in y direction is L 1  and the depth of the T shaped cutout  31  in y direction is L 2 , 0.3×L 1 ≤L 2 ≤0.7×L 1  is preferable. Wherein W 1 &gt;W 2  and L 1 &gt;L 2 . The width W 7  of the laterally extended portion of the T shaped cutout  31  in x direction is e.g. 0.4×W 1 ≤W 7 ≤1.0×W 1 . In addition, provided the width L 6  in y direction of the laterally extended portion of the T shaped cutout  31 , 0.1×L 1 ≤L 6 ≤0.3×L 1  is satisfied. 
     Other examples for the cutout  31  can be ellipse, parabola or other shapes. The cutout  31  can be a combination of the above explained shapes. The cutout  31  preferably exists between the two flexible wiring substrates  20 , and at the side, opposing to the display panel  10 , of the printed circuit board  30 . 
     Embodiment 3 
       FIG.  27    is a plan view of embodiment 3. The structure of  FIG.  27    is to form the thin area  35  in the printed circuit board  30  between the two flexible wiring substrates to decrease bending strength in this area of the printed circuit board  30 , and thus, to decrease the stress at the connection portions between the display panel  10  and the flexible wiring substrate  20  and between the printed circuit board  30  and the flexible wiring substrate  20 . In  FIG.  27   , provided the distance between the two flexible wiring substrates  20  is W 1  and the width of the thin area in x direction is W 2 , the relation is W 2 ≤W 1 . 
       FIG.  28    is a cross sectional view along the line A-A of  FIG.  27   . In many cases, printed circuit board  30  is formed by laminating plural layers. Namely, the thin films, which wirings  36  are formed on the resin layer  37 , are laminated by adhesive.  FIG.  28    shows that such five films are laminated, and the wirings  36  on the upper most film is covered by protective layer  38 . 
     The thin portion  35  in  FIG.  27    corresponds to the structure in  FIG.  28    that upper three layers are eliminated. In  FIG.  28   , the wrings formed on one side of the printed circuit board  30  is connected to another side of the printed circuit board  30  through wrings formed on the two film layers. 
       FIG.  29    is a cross sectional view along A-A line of  FIG.  22    where the printed circuit board is formed by one resin layer. In  FIG.  29   , the thin portion  35  is formed in the resin layer  37 . The recess is formed on the back side of the resin layer  37 , thus, disconnection caused by step can be avoided. The protective layer  38  covers the wirings  36  in  FIG.  29   . 
       FIG.  30    discloses that the thin portion  35  is formed at the area nearer to the display panel  10  in the printed circuit board  30  not entire width of the printed circuit board  30  in y direction. In  FIG.  30   , provided the distance between the two flexible wiring substrates  20  is W 1  and the width of the thin portion in x direction is W 2 , then W 2 ≤W 1 . In addition, provided the width in y direction of the printed circuit board  30  is L 1  and the width in y direction of the thin portion is L 2 , then, e.g. 0.3×L 1 ≤L 2 ≤0.7×L 1  is satisfied. The structure of  FIG.  30    gives more liberty in designing wirings in the printed circuit board  30  as well as decreases the stress at the connection portion. 
     Embodiment 4 
     Embodiments 1 to 3 explain the display panel  10  and the printed circuit board  30  are connected by two flexible wiring substrates  20 . When the display panel  10  becomes bigger, or the radius of curvature of the curved display panel  10  becomes small, there arises a case that three or more flexible wiring substrates  20  are necessary to connect the display panel  10  and the printed circuit board  30 . 
       FIG.  31    is an example that the display panel  10  and the printed circuit board  30  are connected by four flexible wiring substrates  20 . In  FIG.  31   , the printed circuit board  30  is one piece; consequently, when the display panel  10  is curved and when the printed circuit board  30  is folded to the back of the display panel  10 , the stress arises at the connection portions between the display panel  10  and the flexible wiring substrate  20  and between the printed circuit board  30  and the flexible wiring substrate  20  as explained in embodiment 1. 
       FIG.  32    is an example that the V shaped cutout  31  is formed in the printed circuit board  30  between the flexible wiring substrates  20  to decrease the stress at the connection portions between the display panel  10  and the flexible wiring substrate  20  and between the printed circuit board  30  and the flexible wiring substrate  20 . The dimensions of the V shaped cutout  31  and its function are the same as explained in embodiment 1. The stress generated in the flexible wiring substrate  20  according to curving of the display panel  10  is bigger at the sides than at the center of the printed circuit board  30 ; therefore, the shape or the dimensions of the V shaped cutout  31  in the printed circuit board  30  can be changed between at the center and at the sides of the printed circuit board  30 . 
       FIG.  33    is an example that the slit  32  is formed at the connection portion between the flexible wiring substrate  20  and the printed circuit board  30  in addition to the V shaped cutout  31  explained in  FIG.  32   . According to the structure, the printed circuit board  30  can be easily deformed; thus, stress at the connection terminals between the display panel  10  and the flexible wiring substrates  20  and between the printed circuit board  30  and the flexible wiring substrates  20  can be mitigated. In addition, the shape or dimensions of the V shaped cutout can be changed between at the center and at the sides of the printed circuit board  30  as explained above; further, the number of the slits at the sides can be different from the number of the slits at the center of the printed circuit board  30 . 
       FIG.  34    is an example that the V shaped cutouts  34  are formed at the opposite side of the printed circuit board  30  in addition to the V shaped cutouts  31  of  FIG.  32   . According to this structure, the printed circuit board  30  can be further easily deformed; thus, stress at the connection terminals between the display panel  10  and the flexible wiring substrates  20  and between the printed circuit board  30  and the flexible wiring substrates  20  can be mitigated. In addition, as described above, the shape or dimensions of the V shaped cutouts  31 ,  34  can be changed between at the center and at the sides of the printed circuit board  30  as explained above. 
       FIG.  35    is an example that the semicircle shaped cutout  31  is formed in the printed circuit board  30  between the flexible wiring substrates  20  to decrease the stress at the connection portions between the display panel  10  and the flexible wiring substrate  20  and between the printed circuit board  30  and the flexible wiring substrate  20 . The dimensions of the semicircle shaped cutout  31  and its function are the same as explained in embodiment 2. In addition, the shape or the dimensions of the semicircle shaped cutout  31  in the printed circuit board  30  can be changed between at the center and at the sides of the printed circuit board  30 . 
       FIG.  36    is an example that the rectangular shaped cutout  31  is formed in the printed circuit board  30  between the flexible wiring substrates  20  to decrease the stress at the connection portions between the display panel  10  and the flexible wiring substrate  20  and between the printed circuit board  30  and the flexible wiring substrate  20 . The dimensions of the rectangular shaped cutout  31  and its function are the same as explained in embodiment 2. In addition, the shape or the dimensions of the rectangular shaped cutout  31  in the printed circuit board  30  can be changed between at the center and at the sides of the printed circuit board  30 . 
       FIG.  37    is an example that the T shaped cutout  31  is formed in the printed circuit board  30  between the flexible wiring substrates  20  to decrease the stress at the connection portions between the display panel  10  and the flexible wiring substrate  20  and between the printed circuit board  30  and the flexible wiring substrate  20 . The dimensions of the T shaped cutout  31  and its function are the same as explained in embodiment 2. In addition, the shape or the dimensions of the T shaped cutout  31  in the printed circuit board  30  can be changed between at the center and at the sides of the printed circuit board  30 . 
       FIG.  38    is an example that the slit shaped cutout  31  is formed in the printed circuit board  30  between the flexible wiring substrates  20 , in addition, the slit shaped cutouts  34  are formed at the opposite side of the printed circuit board  30  to decrease the stress at the connection portions between the display panel  10  and the flexible wiring substrate  20  and between the printed circuit board  30  and the flexible wiring substrate  20 . The dimensions of the slit shaped cutouts  31  and  34  are the same as explained in embodiment 2. In  FIG.  38   , the upper slit shaped cutouts  31  and the lower slit shaped cutouts  34  are formed alternatively in x direction. In addition, the shape or the dimensions of the slit shaped cutouts  31  and  34  in the printed circuit board  30  can be changed between at the center and at the sides of the printed circuit board  30 . 
       FIG.  39    is an example that, in addition to the semicircle shaped cutouts  31  explained at  FIG.  35   , the slit shaped cutouts  43  are formed at the opposite side in y direction of the printed circuit board  30  to decrease the stress at the connection portions between the display panel  10  and the flexible wiring substrate  20  and between the printed circuit board  30  and the flexible wiring substrate  20 . The dimensions of each of the slit shaped cutouts  34  are the same as explained in embodiment 2. In  FIG.  39   , the semicircle shaped cutout  31  and the slit shaped cutout  34  are formed alternatively in x direction. In addition, the shape and dimensions of the semicircle shaped cutout  31  can be changed between at the center and at the sides of the printed circuit board  30 . Further, the shape and dimensions of the slit shaped cutout can be changed between at the center and at the sides of the printed circuit board  30 . 
       FIG.  40    is an example that, in addition to the rectangular shaped cutouts  31  explained at  FIG.  36   , the slit shaped cutouts  43  are formed at the opposite side in y direction of the printed circuit board  30  to decrease the stress at the connection portions between the display panel  10  and the flexible wiring substrate  20  and between the printed circuit board  30  and the flexible wiring substrate  20 . The dimensions of each of the slit shaped cutouts  34  are the same as explained in embodiment 2. In  FIG.  40   , the rectangular cutout  31  and the slit shaped cutout  34  are formed alternatively in x direction. In addition, the shape and dimensions of the rectangular cutout  31  can be changed between at the center and at the sides of the printed circuit board  30 . Further, the shape and dimensions of the slit shaped cutout can be changed between at the center and at the sides of the printed circuit board  30 . 
       FIG.  41    is an example that the thin portion  35 , explained in embodiment 3, is formed in the printed circuit board  30  between the flexible wiring substrates  20  to decrease the stress at the connection portions between the display panel  10  and the flexible wiring substrate  20  and between the printed circuit board  30  and the flexible wiring substrate  20 . The structure and function of the thin portion  35  are the same as explained in embodiment 3. The shape and dimensions of the thin portion  35  are the same as explained in  FIG.  27   . In addition, as described above, the shape and the thickness of the thin portion  35  can be changed at the center and at the sides of the printed circuit board  30 . 
       FIG.  42    is an example that, in addition to the structure of  FIG.  41   , the slit shaped cutouts  43  are formed at the opposite side in y direction of the printed circuit board  30  to decrease the stress at the connection portions between the display panel  10  and the flexible wiring substrate  20  and between the printed circuit board  30  and the flexible wiring substrate  20 . The dimensions of each of the slit shaped cutouts  34  are the same as explained in  FIG.  25    of embodiment 2. In  FIG.  42   , the thin portion  35  and the slit shaped cutout  34  are formed alternatively in x direction. In addition, the shape and dimensions of the thin portion  35  can be changed between at the center and at the sides of the printed circuit board  30 . Further, the shape and dimensions of the slit shaped cutouts  43  can be changed between at the center and at the sides of the printed circuit board  30 . 
     The thin portions  35  in the printed circuit board  30  in  FIGS.  41  and  42    are formed through entire width in y direction of the printed circuit board  30 ; however, as explained by  FIG.  30    of embodiment 3, the thin portion  35  can be formed in part of the width in y direction of the printed circuit  30 . The dimensions in this case are the same as explained in  FIG.  30   . 
     In the above explanation, the invention is explained with respect to the display devices as the liquid crystal display device, the organic EL display device, the micro LED display device; however, the present invention can be applied to the devices comprising: curved substrate, the flat circuit board, and they are connected by two or more flexible wiring substrates, and wherein the two or more flexible wiring substrates are connected to the curved surface. 
     In the above example, the invention is explained when the surface of the display panel is curved and the print circuit board is flat. The present invention is, however, applicable to the case that both of the display panel and the printed circuit board are curved. Namely, for example, if the radiuses of curvature are different between the display panel and the printed circuit board  30 , a stress is generated at the connection portion when those are connected by two or more flexible wiring substrates. 
     In addition, even the radius of curvature is the same between the display panel and the printed circuit board, a stress is generated when the printed circuit board is folded to the back of the display panel. Even in that case, the structure of the present invention, explained in embodiments 1-4 can mitigate the stress at the connection portions between the display panel  10  and the flexible wiring substrate  20  and between the printed circuit board  30  and the flexible wiring substrate  20 .