Abstract:
Embodiment related to a curved display including a curved panel, a printed circuit board separated from the curved panel, and a plurality of flexible films electrically connecting the curved panel and the printed circuit board. The lengths of the flexible films is increased as the flexible films approach an edge of the curved panel.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the priority under 35 U.S.C. §119(a) to Korean Patent Application No. 10-2013-0169311 filed on Dec. 31, 2013, which is incorporated herein by reference for all purposes as if fully set forth herein. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a curved display. 
     Discussion of the Related Art 
     In the field of display devices, a slim, lightweight, and large-scaled flat panel display (FPD) has been rapidly replaced a cathode ray tube (CRT) that tends to be heavy and bulky. Examples of the flat panel display include a liquid crystal display (LCD), a plasma display panel (PDP), an organic light emitting diode (OLED) display, and an electrophoretic display (EPD). 
     Generally, a flat panel display includes a module where a polarizer and an optical film are attached to a display panel, and a case top supporting and covering the module. The display panel or the polarizer shrinks or expands according to an external environment, and thus a shape of the panel may be changed. When the panel is deformed, an internal liquid crystal layer is deformed to twist an optical axis of the panel. Accordingly, a light leakage may occur. Particularly, a curved display using a curved panel formed by artificially bending the panel has a noticeable problem of the light leakage due to tension of a chip-on film bonding the curved panel and a printed circuit board. 
     SUMMARY 
     Embodiments relate to a curved display including a curved panel, a printed circuit board and a plurality of flexible films. The printed circuit board is separate from the curved panel. The plurality of flexible films electrically connect the curved panel and the printed circuit board. The distance between the curved panel and the printed circuit board increases toward an edge of the curved panel. 
     In one or more embodiments, a length of a flexible film closer to an edge of the curved panel is longer than a length of another flexible film further away from the edge. 
     In one or more embodiments, the printed circuit board includes a first printed circuit board disposed at one side of a surface of the curved panel, and a second printed circuit board disposed at another side of the surface of the curved panel. 
     In one or more embodiment, an angle between the first printed circuit board and the curved panel and an angle between the second printed circuit board and the curved panel correspond to a curvature angle of the curved panel. 
     In one or more embodiment, at least one of a horizontal slit, a vertical slit, and a diagonal slit is formed in each of the flexible films. 
     In one or more embodiment, each of the flexible films has at least one lateral side that is indented inwardly at a region not bonded to the curved panel or the printed circuit board. 
     Embodiments also relate to a display device including a curved display panel, a first printed circuit board, a first flexible film and a second flexible film. The curved display panel is formed with a pixel array and includes a curved first surface and a curved second surface opposed to the first curved surface. The first, the curved first surface defined by a first lateral edge, a second lateral edge, a first curved line connecting one end of the first lateral edge and one end of the second lateral edge, and a second curved line connecting another end of the first lateral edge and another end of the second lateral edge. The first printed circuit board is separate from the curved display panel. The first flexible film is secured to a first region of the first curved surface and the first printed circuit board to electrically connect the curved display panel to the first printed circuit board. The first region is closer to the first lateral edge than the second lateral edge. The first flexible film extends around the first curved line along a first curved path of a first length. The second flexible film is secured to a second region of the first curved surface and the first printed circuit board. The second region is closer to the first lateral edge than the first region. The second flexible film extends around the first curved line along a second curved path of a second length longer than the first length. 
     In one or more embodiments, an integrated circuit is mounted on each of the first and second flexible films. 
     In one or more embodiments, the first curved line is a first arc and the second curved line is a second arc, the first and the second arcs having a same radius of curvature. 
     In one or more embodiments, a ratio of the first length relative to a distance from a center of the first arc to the first region is same as a ratio of the second length relative to a distance from the center of the first arc to the second region. 
     In one or more embodiments, the ratio of the first length relative to the distance from the center of the first arc to the first region corresponds to tan(φ) where φ represents the radius of curvature. 
     In one or more embodiments, the first and second flexible films have a same length but attached to the first printed circuit board at different longitudinal locations. 
     In one or more embodiments, the first and second flexible films have different lengths. 
     In one or more embodiments, the display device further includes a second printed circuit board, a third flexible film, and a fourth flexible film. The second printed circuit board is separate from the curved display panel and the first printed circuit board. The third flexible film is secured to a third region of the first curved surface and the second printed circuit board to electrically connect the curved display panel to the second printed circuit board, the third region closer to the second lateral edge than the first lateral edge. The third flexible film extends around the first curved line along a third curved path of a third length. The fourth flexible film is secured to a fourth region of the first curved surface and the second printed circuit board. The fourth region is closer to the second lateral edge than the third region. The fourth flexible film extends around the first curved line along a fourth curved path of a fourth length longer than the third length. 
     In one or more embodiments, each of the first and second flexible films is rectangular in shape with one or more slits to increase flexibility. 
     In one or more embodiments, each of the first and second flexible films is mounted with an integrated circuit and lateral sides of each of the first and second flexible films is indented towards the integrated circuits. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings: 
         FIG. 1  is a perspective view of a curved display panel according to one embodiment. 
         FIG. 2  is a front view of the curved display panel according to one embodiment. 
         FIG. 3  is a diagram illustrating chip-on films (COF) connecting the curved display panel and printed circuit boards mounted to a backlight unit, according to one embodiment. 
         FIGS. 4( a ) and 4( b )  are diagrams illustrating surfaces of COFs attached to a flat panel and curved panel, respectively. 
         FIG. 5  is a conceptual view illustrating geometric configuration of a curved display panel relative to a flat panel, according to one embodiment. 
         FIG. 6  is a front view showing varying lengths of the COFs connecting the curved display panel and a printed circuit board, according to one embodiment. 
         FIG. 7  is a front view showing securing of a printed circuit board to COFs at different locations, according to one embodiment. 
         FIGS. 8 through 13  are plan views illustrating COFs of various configurations, according to embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. Detailed description of well-known components is omitted herein to avoid obfuscation. 
     Although embodiments are described below with reference to curved liquid crystal display (LCD) panels, the same principle can be applied to display panels for use in devices such as an organic light emitting diode (OLED) display, a field emission display (FED), a plasma display panel (PDP), and an electrophoresis display (EPD). 
       FIG. 1  is a perspective view of a curved display panel  10 , according to one embodiment. The curved display panel  10  includes a front curved surface  16 , a rear curved surface  12 , left and right surfaces, and bottom and top surfaces. The front curved surface  16  includes a right edge  12 , a left edge  14 , a curved top edge  13  and a curved bottom edge  15 . 
     In the embodiments, the liquid crystal display may include, among other components, a curved panel  10 , printed circuit boards  20 - 1  and  20 - 2  (hereinafter collectively referred to as “the printed circuit boards  20 ”), and chip-on films  100 . 
     Different tension forces are applied to both sides of a chip-on film attached to a curved panel  10  and bent to surround curved panel  10 . The reason for the different tension forces is that the curved panel  10  is bent but the chip-on film  100  is flat and has both sides that are parallel to each other. In such configuration, the light leakage is noticeable due to local stress caused by tension in the chip-on films  100 . Particularly, since the chip-on films  100  are bent in an opposite direction to a bending direction of the curved panel  10 , tension is increased at both sides of the curved panel  10 . Accordingly, the light leakage is further noticeable in the chip-on film  100  positioned near the right or left edge of the curved panel  10 . Further, since the chip-on film  100  is bent while being bonded to the curved panel  10  and the printed circuit board, stress is present in the chip-on film  100 . The stress may affect the curved panel  10  or destroy a circuit pattern formed on the chip-on film  100 . 
     The curved panel  10  includes a pixel array having pixels arranged in a matrix form to display input image data. The pixel array includes a thin film transistor (TFT) array formed on a lower substrate, a color filter array formed on an upper substrate, and liquid crystal cells formed between the lower substrate and the upper substrate. Each pixel may include, for example, a data line DL, a gate line (or scan lines) GL intersecting the data line DL, a TFTs formed at the intersection of the data line DL and the gate line GL, a pixel electrode  1  and a storage capacitor Cst connected to the TFT. 
     The printed circuit boards  20  may be mounted, for example, with timing controllers (not shown) and power modules (not shown). The timing controller receives signals such as digital video data, and timing signals such as a vertical synchronizing signal Vsync, a horizontal synchronizing signal Hsync, a data enable signal DE, and a main clock CLK from an external host system. The timing controller transfers the digital video data to a source drive IC  110 . The timing controller also generates a source timing control signal for controlling operation timing of source drive ICs, and gate timing control signals ST, GCLK, and MCLK for controlling operation timing of a level shifter and a shift register of a gate driving circuit (not shown) by using the timing signals Vsync, Hsync, DE, and CLK. 
     The power module is operated when an input voltage supplied from the host system is a UVLO level or more, and generates an output after a predetermined time is delayed. The output of the power module includes VGH, VGL, VCC, VDD, HVDD, RST, and the like. 
     The source drive IC  110  receives the source timing control signal to generate analog signals transmitted over the data line (DL) to control the TFTs in the pixels P of the pixel array. 
     COFs  100  connect the curved panel  10  and the first printed circuit boards  20 . The source drive IC  110  is mounted on each of COFs  100 . The gate driving circuit may be mounted in the form of gate driver integrated circuits (ICs) on COFs  100 , or may be provided as separate components. Alternatively, the gate driving circuit is a gate in panel (GIP) type, and may include the level shifter (not shown) formed on the printed circuit board  20  and the shift register (not shown) formed on the curved panel  10 . 
       FIG. 2  is a front view of the curved display panel according to one embodiment. In the embodiment of  FIG. 3 , COFs  100 - 1 ,  100 - 2 , and  100 - 3  have different lengths h1, h2, h3. Length h1 is longest followed by length h2 and length h3 is the shortest. That is, the lengths of COFs increase as they are located further away from the center of the curved panel  10 . Lengths of COFs  100 - 4 ,  100 - 5  and  100 - 5  are set in a similar manner. The lengths of COFs may be in proportion to a curvature angle of the curved panel  10 , as described below with reference to  FIGS. 4 and 5 . 
       FIGS. 3( a ) and 3( b )  are diagrams illustrating chip-on films (COF)  100  connecting the curved display panel  10  and printed circuit boards  20  mounted to a backlight unit, according to one embodiment. Referring to  FIGS. 3( a ) and 3( b ) , a backlight unit  50  is coupled to a rear surface  12  of the display panel  10 . The COFs  100  are attached to a rear surface of the backlight unit  50  through an upper portion of the backlight unit  50 . In a first embodiment, the COF  100 - 1 , COF  100 - 2 , and COF  100 - 3  have different lengths, and thus, variations of distortion of the COF  100 - 1 , COF  100 - 2 , and COF  100 - 3  in a coupled state may be reduced. Thus, the occurrence of light leakage in a gap between the COFs  100  and the upper portion of the backlight unit  50  may be enhanced. This will be described in more detail as follows. 
     In order to manufacture the curved panel  10 , a flat panel  10 - 1  as illustrated in  FIG. 4( a )  is manufactured and subsequently bent through an aging process, or the like. The COFs  100  are attached to the manufactured flat panel  10 - 1  as illustrated in  FIG. 4( a ) . 
       FIGS. 4( a ) and 4( b )  are top views of the flat panel  10 - 1  and the curved panel  10  with the COFs  100  attached thereto, respectively. As illustrated in  FIG. 4( a ) , the attached surfaces  121 ,  122 , and  123  of the COFs  100  attached to the flat panel  10 - 1  are positioned on the same plane. In contrast, referring to  FIG. 4( b ) , attached surfaces  131 ,  132 , and  133  of the COFs attached to the curved panel  10  are not positioned on the same plane. In a state in which the curved panel  10  is formed, the PCB  20 - 1  is maintained flat, and thus, the COFs  100  connecting the PCB  20 - 1  and the curved panel  10  are twisted. As a result, a gap is formed between the COFs  100  attached to the rear surface of the curved panel  10  after passing through the upper portion of the curved panel  10  and the upper portion of the curved panel  10 , and light leakage occurs from the gap. 
     When the PCB  20 - 1  is attached to the curved panel at the inner side, a gap between the PCB  20 - 1  and the curved panel  10  is largest in the edge of the curved panel  10 . Thus, a greater amount of stress is exerted on the COF  100 - 1 , relative to the COF  100 - 2  and COF  100 - 3 , and light leakage is salient in the region where the COF  100 - 1  is positioned. 
     In the first embodiment, the COF  100 - 1  is formed to be longer than the COF  100 - 2  and COF  100 - 3 , and thus, less tensile force is exerted on the COF  100 - 1 , relative to the COF  100 - 2  and the COF  100 - 3 . Therefore, the occurrence of salient light leakage in the region where the COF  100 - 1  is positioned can be improved. 
       FIG. 5  is a conceptual view illustrating geometric configuration of a curved display panel  10  relative to a flat panel, according to one embodiment. A virtual horizontal length x refers to a length of curved panel  10  when flattened to have a flat surface. A panel horizontal length y refers to a distance between both end points a and b of the curved panel  10 . When the curved panel  10  has a circular arc shape, the radius of curvature R is a distance between center O of a circle (fit to the circular arc shape) and the curved panel  10 . A deflection length D refers to a distance between a straight line connecting both ends a and b of the curved panel  10  and the center c of the curved panel. Curvature angle φ is defined as an angle between line b-c and a center plane of flattened version of the display panel. 
       FIG. 6  is a front view showing varying lengths h1, h2, h3 of the COFs  100 - 1  through  100 - 3  connecting the curved display panel  10  and printed circuit board  20 - 1 , according to one embodiment. In  FIG. 5 , extension line l of printed circuit board  20 - 1  indicates a line segment extended from a bottom edge of printed circuit board  20 - 1 . A horizontal line L indicates the upper edge of the curved panel  10 . COFs  100 - 1 ,  100 - 2 , and  100 - 3  are attached to the display surface of the curved panel  10  below the horizontal line L. 
     An angle between extension line l and the horizontal line L of the curved panel  10  corresponds to the curvature angle φ. Accordingly, the distance between the curved panel  10  and the printed circuit board  20 - 1  in proportion to the distance from center c. The extension line l of the printed circuit board  20 - 1  meets the panel center c of the curve panel  10 . Since the angle between the extension line l and the horizontal line of the curved panel  10  is the curvature angle φ, the length h1 of the COF  100 - 1  and a distance d between a region of the curved panel  10  bonding to the COF  100 - 1  and the panel center c the following relationship:
 
 h 1 /d =tan(φ)  (1)
 
     Therefore, the length h1 of the COF  100 - 1  may be defined as d×tan(φ). 
     The lengths of COFs  100 - 2  and  100 - 3  may be obtained by using Equation (1) but replacing distance d with distances from the center c to regions of the curved panel  10  bonding to the COF  100 - 2  and COF  100 - 3 , respectively. The lengths of COFs  100 - 4 ,  100 - 5 , and  100 - 6  may also be obtained by using Equation (1) but replacing distance d with distances from the center c to regions of the curved panel  10  bonding to the COF  100 - 4 , COF  100 - 5  and COF  100 - 6 , respectively. 
     Tensile stress occurs within COFs as they are bent to bond to the curved panel  10  and the first printed circuit boards  20 . The COF  100 - 1  positioned at the furthest point from the panel center c experiences tensile stress smaller than those of COFs  100 - 2  and  100 - 3  because tensile stress applied to the chip-on film is in inverse proportion to an area. Accordingly, the COF  100 - 1  at the edge of the curved panel  10  is experiences lower tensile stress, preventing light leakage caused by local stress. 
       FIG. 7  shows a curved display panel  10  according to another exemplary embodiment. The curved display of  FIG. 6  includes the curved panel  10 , printed circuit boards  20 - 1  and  20 - 2 , and COFs  600 - 1  to  600 - 6 . All lengths h of the COFs  600 - 1  to  600 - 3  are the same. However, distances z1, z2, and z3 between the curved panel  10  and the printed circuit board  20 - 1  are set differently. That is, COFs  600 - 1  through  600 - 6  are have their end portions bonded to the curved panel  10  but different portions of the COFs  100 - 1  through  100 - 6  are bonded to the first printed circuit board  20 - 1  so that distance z1 is longer than distance z2 and distance z2 is longer than distance z3. Similarly, distance z6 is larger than distance z5 and distance z5 is longer than distance z4. Accordingly, the COFs  100 - 1 ,  100 - 6  experience lower tensile stress than those of the COFs  100 - 2  through  100 - 5 , and thus local stress occurring on the COFs  100 - 1  and  100 - 6  may be reduced. 
     The local stress on the curved panel  10  may be caused by stress in the COFs. The stress in the COF  100  may be transferred to the curved panel  10 , and also cause damage to a wiring pattern formed in the chip-on film  100 .  FIGS. 8 through 13  show exemplary embodiments where flexibility of the COFs  100  is increased to reduce damage to the COFs.  FIGS. 8 through 11  show exemplary embodiments of COFs having slits. A slit herein refers to opening formed in the chip-on film along a predetermined direction. 
       FIG. 8  is a plan view of COF  101  including vertical slits  121 , according to one embodiment. The vertical slits  121  are formed in a region of COF  101  not bonded to the curved panel  10  or the printed circuit board  20 . That is, the vertical slits  121  are formed in a region that is bent, and thus flexibility of the chip-on film  101  may be increased. 
       FIG. 9  is a plan view of COF  102  including horizontal slit  122 , according to one embodiment. The horizontal slit  122  may be formed in a region way from the source drive IC  110  where COF  102  is bent. 
       FIG. 10  is a plan view of COF  103  formed with horizontal slits  123  at both sides of the source drive IC  110  in a region where a chip-on film  103  is bent, according to one embodiment. 
       FIG. 11  is a plan view of COF  104  formed with diagonal slits  124 , according to one embodiment. The diagonal slits  124  may be formed to slant inward towards the center of the COF  104  from corners of the COF  104 . The diagonal slits  124  may be formed to pass through at least a region where the chip-on film  104  is bent. 
       FIGS. 12 and 13  are plan view of COFs  105 ,  106  having edges indented towards the source drive IC  110 , according to embodiments. Specifically, in  FIG. 11 , both sides of a chip-on film  105  have indents  505  formed perpendicularly towards the source drive IC  110 . In  FIG. 13 , sides of the COF  106  are formed with indents  506  to have slanted lines. In the embodiments of  FIGS. 11 and 12 , sides of the chip-on film are indented and hence, the widths of the COFs  105 ,  106  across the center the COFs  105 ,  106  are smaller than widths at top or bottom ends of the COFs  105 ,  106 . 
     As described in  FIGS. 8 through 13 , the flexibility of the COFs is enhanced by forming slits or indents at the sides. Since stress may be effectively dispersed in the COFs, light leakage in the curved panel due to local stress may be prevented or reduced. 
     Above embodiments are described primarily using COFs. However, the same principle may be applied to a tape carrier package (TCP) or other flexible films. 
     Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure.