Abstract:
A bonding method of a flexible film is provided, which includes: positioning an anisotropic conductive film on a plurality of first signal lines formed on the flexible film to be bonded to a thin film transistor (TFT) panel; arranging the anisotropic conductive film on the TFT panel to align the first signal lines formed on the flexible film and a plurality of second signal lines formed on the TFT panel; positioning at least one portion of a protection film for protecting the second signal lines of the flexible film to be overlapped with the TFT panel; and pressing the flexible film and the TFT panel.

Description:
This application relies for priority upon Korean Patent Application No. 2004-0051151 filed on Jul. 1, 2004, the contents of which are herein incorporated by reference in its entirety. 
   BACKGROUND OF THE INVENTION 
   (a) Field of the Invention 
   The present invention relates to a bonding method for a flexible film and a display device having a flexible film bonded by the bonding method. 
   (b) Description of Related Art 
   A liquid crystal display (LCD) includes (a) a lower panel having gate lines, data lines, switching elements, such as thin film transistors (TFTs), and pixel electrodes; (b) an upper panel facing the lower panel and having color filters and a common electrode; and (c) a liquid crystal (LC) layer interposed between the upper panel and the lower panel. 
   The switching elements, which receive both gate signals and data signals on the gate lines and the data lines, are activated by gate signals transmitted through the gate lines. The switching elements supply data voltages transmitted through the data lines to the pixel electrodes. 
   The gate lines are supplied with gate signals from a gate driver, and the data lines are supplied with data voltages from a data driver. The gate and data drivers include a plurality of integrated circuit (IC) chips which may be provided according to various types of assembly. The assembly is connected to the lower panel. In one type of assembly, the IC chips are mounted on the lower panel, and in another type of assembly, the IC chips are mounted on at least one flexible film. The former is called a COG (chip on glass) or a FOG (film on glass) assembly, and the latter is called a TCP (tape carrier package) assembly. 
   In the COG or FOG type assembly, the IC chips and the flexible film are directly mounted on the lower panel. The flexible film is called an FPC (flexible printed circuit), and it includes a flexible body, a plurality of signal lines formed on the body, and a protection film formed on the signal lines. The protection film for the FPC is formed with a cover layer, but it may be formed with a solder resist. 
   In the TCP type assembly, the IC chips are mounted on at least one flexible film attached to the lower panel. Under TCP type assembly, the assembly may be further classified into a TAB (tape automated bonding) type assembly or a COF (chip on film) type assembly. The TCP type assembly includes a flexible body, a plurality of signal lines formed on the body, a protection film formed on the signal lines, and IC chips mounted on the protection film. In this assembly type, the protection film is formed with a solder resist. The primary difference between flexible films of the TCP type assembly and flexible films of the COG or FOG type assembly is the mounting position of the IC chips. 
   A plurality of signals are generated at a controller mounted on a separate PCB (printed circuit board) and transmitted to the IC chips through the flexible film. The flexible film is attached to the lower panel using an anisotropic conductive film (ACF), which contains conductive particles that electrically connect the signal lines formed on the flexible film and the signal lines formed on the lower panel to each other. 
   However, when the flexible film is attached to the lower panel, a disconnection of the signal lines caused by external stress can occur at the bonding portions of the signal lines, which are not covered with a protection film. 
   SUMMARY OF THE INVENTION 
   In an embodiment of the present invention, a bonding method for a flexible film is provided, which includes positioning an anisotropic conductive film on a plurality of first signal lines formed on the flexible film to be bonded to a thin film transistor (TFT) panel, aligning the anisotropic conductive film on the TFT panel, such that the first signal lines formed on the flexible film are aligned with a plurality of second signal lines formed on the TFT panel, positioning a portion of a protection film on the flexible film to overlap with a portion of the TFT panel, the protection film protecting the first signal lines of the flexible film, and pressing the flexible film and the TFT panel, such that the flexible film and the TFT panels are in contact along the overlapping portions of the protection film and the TFT panel. 
   The anisotropic conductive film may overlap at least one portion of a flexible body of the flexible film. 
   The method may further include forming a cover layer on a surface of the protection film which is not attached to the anisotropic conductive film. 
   The cover layer may be formed on a portion of the TFT panel. 
   The protection film adjacent to the anisotropic conductive film may have an end with an uneven shape. 
   Dummy lines without signal transmission capabilities may be formed beside the first signal lines. 
   The dummy lines may be the outermost lines with respect to the first signal lines. 
   The dummy lines may have widths wider than widths of the first remaining signal lines. 
   The number of the dummy lines may be two or more. 
   In a further embodiment of the present invention, a bonding method of a flexible film is provided, which includes positioning an anisotropic conductive film on a plurality of first signal lines formed on a thin film transistor (TFT) panel, positioning the flexible film on the anisotropic conductive film to align the first signal lines formed on the TFT panel with a plurality of second signal lines formed on the flexible film, positioning at least one portion of a protection film for protecting the second signal lines of the flexible film to be overlapped with the TFT panel, and pressing the flexible film and the TFT panel such that the flexible film and TFT panel are in contact along the overlapping portion of the protection film and the TFT panel. 
   The anisotropic conductive film may overlap at least one portion of a flexible body of the flexible film. 
   The method may further include forming a cover layer on a surface of the protection film which is not attached to the anisotropic conductive film. 
   The cover layer may be formed on a portion of the TFT panel. 
   The protection film adjacent to the anisotropic conductive film may have an end with an uneven shape. 
   Dummy lines without signal transmission capabilities may be formed beside the second signal lines. 
   The dummy lines may be the outermost lines with respect to the second signal lines. 
   The dummy lines may have widths wider than widths of the second remaining signal lines. 
   The number of the dummy lines may be two or more. 
   In a still further embodiment of the present invention, a display device is provided, which includes a thin film transistor panel including a plurality of first signal lines, a flexible film including a second plurality of second signal lines and a protection film for protecting the second signal lines, and an anisotropic conductive film connecting the first signal lines with the second signal lines wherein the protection film exposes a portion of the first signal lines, the exposed first signal lines and the second signal lines are aligned to match each other, and a portion of the protection film is overlapped with the TFT panel. 
   The anisotropic conductive film may overlap at least one portion of a flexible body of the flexible film. 
   The method may further include forming a cover layer on a surface of the flexible film which is not attached to the anisotropic conductive film. 
   The cover layer may be formed on a portion of the TFT panel. 
   The protection film adjacent to the anisotropic conductive film may have an end with an uneven shape. 
   Dummy lines without signal transmission capabilities may be formed beside the second signal lines. 
   The dummy lines may be the outermost lines with respect to the second signal lines. 
   The dummy lines may have widths wider than widths of the second remaining signal lines. 
   The number of the dummy lines may be two or more. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more apparent by describing preferred embodiments thereof in detail with reference to the accompanying drawings, in which: 
       FIG. 1  is schematic diagram of an LCD with a flexible film attached thereto according to an embodiment of the present invention; 
       FIG. 2  illustrates an assembly process of the LCD shown in  FIG. 1 ; 
       FIG. 3  illustrates another assembly process of the LCD shown in  FIG. 1 ; 
       FIG. 4  is schematic diagram of an LCD with a flexible film attached thereto according to another embodiment of the present invention; 
       FIG. 5  is a plan diagram of an example of the flexible film according to the embodiments of the present invention; 
       FIG. 6  is a plan diagram of another example of the flexible film according to the embodiments of the present invention; and 
       FIG. 7  is a plan diagram of another example of the flexible film according to the embodiments of the present invention. 
   

   DETAILED DESCRIPTION OF EMBODIMENTS 
   The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the inventions invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. 
   In the drawings, the thickness of layers and regions are exaggerated for clarity. Like numerals refer to like elements throughout. It will be understood that when an element such as a layer, film, region, substrate, or panel is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present. 
   Bonding methods of a flexible film and display devices bonded with the bonding method according to embodiments of the present invention will be now described with reference to the drawings. 
     FIG. 1  is schematic diagram of an LCD with a flexible film attached thereto according to an embodiment of the present invention. 
   An LCD  10  according to the embodiment of the present invention includes a lower panel  200 , an upper panel  300 , a liquid crystal (LC) layer (not shown) interposed between lower panel  200  and upper panel  300 , a plurality of driving chips  400 , at least one flexible film  100 , and at least one anisotropic conductive film  150 . 
   The lower panel  200  includes a plurality of signal lines such as gate lines and data lines, a plurality of thin film transistors (TFTs), and a plurality of pixel electrodes. Lower panel  200 , including the signal lines, TFTs and panel electrodes, is referred to herein as a TFT panel. The upper panel  300  includes a plurality of color filters and a common electrode. 
   Lower and upper polarizers  250  and  350  are attached to the outer surfaces of the lower and upper panels  200  and  300 , respectively. 
   The flexible film  100  includes a flexible body  110 , a plurality of metallic signal lines  120  formed on flexible body  110 , and a protection film  130 . 
   As shown in  FIG. 1 , the signal lines  120  are formed to the ends of the flexible body  110 , and the protection film  130  is formed adjacent to the signal lines  120 , except near one end of signal lines  120 , to enable the signal lines  120  to be connected to a plurality of signal lines formed on the lower panel  200  through exposed portions of the signal lines  120 . The protection film  130  is formed with a cover layer, but it may be formed with a solder resist. 
   As shown in  FIG. 1 , the lower panel  200  is electrically and mechanically connected to the flexible film  100  through the anisotropic conductive film  150 . In addition, a portion of the protection film  130  overlaps the lower panel  200 . The conductive film  150  is formed adjacent to the end of the overlapping portion of the protection film  130  without a gap between conductive film  150  and protective film  130 , to protect lower panel  200  from contamination, such as from dust. 
   Next, an assembly processes of the above-described LCD will be described with reference to  FIGS. 2 and 3 . 
     FIG. 2  illustrates an assembly process of the LCD shown in  FIG. 1 , and  FIG. 3  illustrates another assembly process of the LCD shown in  FIG. 1 . 
   First, referring to  FIG. 2 , an assembly process of the LCD will be described in detail. 
   The conductive film  150  is applied to a connection portion of the signal lines  120  which are exposed, ready to be connected to the lower panel  200 . 
   Next, the conductive film  150  is arranged such that the signal lines  120  of the flexible film  100  overlap signal lines (not shown) of the lower panel  200 . At this time, a predetermined portion of the protection film  130  overlaps the lower panel  200 , but is apart from the lower panel  200  by a distance D. 
   By pressing, the flexible film  100  is mechanically connected to the lower panel  200 ,—i.e., eliminating the distance D—through the anisotropic conductive film  150  having a plasticity. Signal lines  120  are electrically connected to the lower panel  200  by conductive particles which are contained in the conductive film  150 . 
   When the flexible film  100  is connected to the lower panel  200  through the conductive film  150  by the process shown in  FIG. 2  and as described above, alignment errors due to the conductive film  150  plastically flowing down along one side wall of the lower panel  200  while attaching the flexible film  100  to the lower panel  200  decreases; so that the exposure of the signal lines formed on the lower panel  200  is reduced. Since a predetermined portion of the protective film  130  overlaps the lower panel  200 , crack generation at a point of connection between the lower panel  200  and the protective film  130  is prevented. 
   In addition, by overlapping the protection film  130  on the lower panel  200 , cracks in the signal lines which can be generated at an edge of the lower panel  200  due to stress generated by the bending of the flexible film  100  are reduced. 
   Next, referring to  FIG. 3 , another assembly process of the above-described LCD will be described in detail. In this process, unlike in  FIG. 2 , an anisotropic conductive film  150  is directly mounted on a lower panel  200 , to allow connecting signal lines  120  of a flexible film  100  to the lower panel  200 . 
   The above-described connection will now be described in detail. 
   First, the anisotropic conductive film  150  is applied to an upper portion of the lower panel  200 , which is to be connected to the flexible film  100 . 
   Next, the flexible film  100  is aligned on the conductive film  150  such that the signal lines  120  of the flexible film  100  overlap signal lines (not shown) of the lower panel  200 . At this time, a predetermined portion of the protection film  130  overlaps the lower panel  200 , but is apart from the lower panel  200  by a distance D. 
   By pressing, the flexible film  100  is mechanically connected to the lower panel  200 —i.e., elimininating the distance D—through the anisotropic conductive film  150  having a plasticity. The signal lines  120  are electrically connected to the lower panel  200  by conductive particles which are contained in the conductive film  150 . 
   Since a predetermined portion of the protective film  130  overlaps the lower panel  200 , crack generation at a point of connection between the lower panel  200  and the protective film  130  is prevented. In addition, by overlapping the protection film  130  on the lower panel  200 , cracks of signal lines, which can be generated at an edge of the lower panel  200  due to stress generated by the bending of the flexible film  100  are also reduced. 
   Next, an LCD according to another embodiment of the present invention will be described with reference to  FIG. 4 . 
     FIG. 4  is schematic diagram of an LCD with a flexible film attached, according to another embodiment of the present invention. 
   An LCD  20  according to another embodiment of the present invention has the same construction as that of  FIG. 1 , except it further includes a cover layer  160  over the anisotropic conductive film  150 . Thus, the elements performing the same operations are indicated in  FIG. 4  with the same reference numerals, and a repetitive detailed description of elements already described is omitted. 
   As shown in  FIG. 4 , the cover layer  160  is formed on upper surfaces of the flexible film  100  and the anisotropic conductive film  150 . Thus, stress due to bending of the flexible film  100  is dispersed toward an end of the cover layer  160 , and thereby dispersing the stress applied to the signal lines  120  at the edge of the lower panel  200 . As a result, the signal lines  120  are protected from cracks. 
   The flexible film  100  described above with reference to  FIGS. 1 and 4  can be applied to both the TCP type as well as the COG/FOG type. 
   Next, flexible films according to further embodiments of the present invention will be described with reference to  FIGS. 5 to 7 , which are plan diagrams of examples of the flexible film according to further embodiments of the present invention. The flexible films shown in  FIGS. 5 to 7  are for the TCP type assembly, but they may also be applied to the COG or FOG type assembly. 
   First, referring to  FIG. 5 , a plurality of signal lines  120  are formed on a flexible body  110  of a flexible film  100 . The signal lines  120  are formed with conductive materials such as a metal, and are formed from an upper end of the body  110  to a lower end thereof. The upper part of the body  110  is a portion for connecting to a lower panel (not shown). When connecting the flexible film  100  and the lower panel to each other, an upper surface of the flexible film  100  is connected to an upper surface of the lower panel. 
   A protection film  130  is formed on a predetermined portion of the signal lines  120  at the middle of the flexible body  110 . In this embodiment, the flexible film  100  is for a TCP type assembly and the protection film  130  is a solder resist. In addition, a driving chip  500  is mounted on the protection film  130 . 
   Align marks are formed at the signal lines which are positioned at both outermost portions thereof, such that a connection position when connecting the flexible film  100  to a lower panel (not shown) is clear. 
     FIG. 6  is another example of the flexible film modified with respect to the flexible film  100  of  FIG. 5 . As shown in  FIG. 6 , a protection film  130  of solder resist has a connection portion of an uneven shape, which is connected to a lower panel (not shown). Because of the connection portion of an uneven shape, stress applied toward the connection portion is effectively dispersed. 
     FIG. 7  is another example of the flexile film. As shown in  FIG. 7 , a flexible film  100  includes dummy lines  125  as well as a plurality of signal lines  120 . The dummy lines  125  are formed with conductive materials such as a metal and do not transmit signals, unlike the signal lines  120 . 
   When the flexible film  100  is connected to the lower panel and bent downward, the two outermost positioned signal lines bear the most stress. However, by forming the dummy lines  125  at both outermost positions, the stress is dispersed to the dummy lines  125  and even if the dummy lines  125  are disconnected by the stress, signal transmission is normal through the signal lines  120 . There may be one or more dummy lines  125 , depending on the desired design. As the number of dummy lines  125  becomes larger, the efficiency of dispersion of the stress applied from outside increases. In addition, rather than increasing the number of dummy lines  125 , the dummy lines  125  may have widths wider than those of the signal lines  120  to increase the efficiency of stress dispersion. In  FIG. 7 , for example, the dummy lines  125  have widths wider than those of the signal lines  120 . 
   The present invention decreases a probability of signal line disconnection, and protect against dust 
   Additionally, alignmnet error due to the conductive film flowing down along one side wall of the lower panel while attaching the flexible film to the lower panel is reduced. 
   While the present invention has been described in detail with reference to the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the sprit and scope of the appended claims.