Patent Publication Number: US-2007121036-A1

Title: Portable display device

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
      This application claims priority to and the benefit of Korean Patent Application No. 10-2005-115995, filed on Nov. 30, 2005, in the Korean Intellectual Property Office, the entire content of which is incorporated herein by reference.  
     BACKGROUND  
      Recently, various flat panel displays (FPDs) have been developed. The FPDs include liquid crystal displays (LCDs), field emission displays (FEDs), plasma display panels (PDPs), and light emitting displays (LEDs).  
      Among the FPDs, LCDs are small and light and have low power consumption. Currently, LCDs are used in monitors and TVs that are large products as well as in portable devices, such as mobile telephones and personal digital assistants (PDAs).  
       FIG. 1  is an exploded perspective view illustrating a conventional portable display device. In  FIG. 1 , a dual display device that is used for a mobile telephone, in which at least one LCD is mounted, is illustrated.  FIG. 2  is a perspective view illustrating the rear surface of the reflecting plate illustrated in  FIG. 1 .  
      Referring to  FIGS. 1 and 2 , the conventional portable display device  60  includes a liquid crystal display panel  4 , a back light assembly  50 , a bottom chassis  22 , first and second printed circuit boards  24  and  26 , and a light emitting display panel  30 .  
      The liquid crystal display panel  4  displays a predetermined image. The liquid crystal display panel  4  includes a first substrate  4   a,  a second substrate  4   b,  and liquid crystal (not shown) implanted between the first and second substrates  4   a  and  4   b.    
      The second substrate  4   b  includes a plurality of thin film transistors (TFTs) arranged in a matrix. Here, the source electrodes of the TFTs are connected to data lines and the gate electrodes of the TFTs are connected to scan lines. The drain electrodes of the TFTs are connected to pixel electrodes made of conductive and transparent indium tin oxide (ITO). The TFTs are turned on when scan signals are supplied to the scan lines to supply data signals supplied from the data lines to the pixel electrodes.  
      An integrated circuit  6  from which the data signals and the scan signals are supplied is inserted into one side of the second substrate  4   b.  A protective layer  8  is formed around the integrated circuit  6 .  
      The first substrate  4   a  is arranged to face the second substrate  4   b.  Common electrodes made of ITO are formed on the front surface of the first substrate  4   a.  A predetermined voltage is applied to the common electrodes so that a predetermined electric field is formed between the common electrodes and the pixel electrodes. The arrangement angle of the liquid crystal implanted between the first substrate  4   a  and the second substrate  4   b  is changed by the electric field and light transmittance is changed by the changed arrangement angle so that it is possible to display a desired image.  
      Upper and lower polarizers (not shown) are further included on and under the liquid crystal display panel  4 .  
      The back light assembly  50  includes a mold frame  16 , light emitting diodes  12 , a light emitting diode substrate  14 , a light guide plate  18 , a reflecting plate  20 , and optical sheets  10 .  
      The light emitting diodes  12  generate light of a predetermined brightness in response to driving signals from the light emitting diode substrate  14 .  
      The light guide plate  18  supplies the light supplied from the light emitting diodes  12  to the liquid crystal display panel  4 . That is, the light guide plate  18  supplies the light supplied from the sides thereof to the liquid crystal display panel  4  positioned thereon.  
      The reflecting plate  20  is positioned on the rear surface of the light guide plate  18  to re-supply the light incident from the light guide plate  18  back toward the light guide plate  18 . That is, the reflecting plate  20  re-supplies the light incident thereon to the light guide plate  18  to improve optical efficiency. In the context of this disclosure, the “rear” surface refers to the surface on an opposite side as the liquid crystal display panel  4 . The reflecting plate  20  is attached to the bottom chassis  22  by adhesive members  21 , such as double-sided tapes. The adhesive members  21  are attached to opposite edges on the rear surface of the reflecting plate  20 , as illustrated in  FIG. 2 .  
      The optical sheets  10  improve the brightness of the light supplied from the light guide plate  18  to supply the light to the liquid crystal display panel  4 .  
      The light emitting diode substrate  14  is connected to the first printed circuit board  24  to supply the driving signals to the light emitting diodes  12  in response to control signals supplied from the first printed circuit board  24 .  
      The light emitting diode substrate  14  in which the light emitting diodes  12  are mounted is accommodated in and fixed to the mold frame  16  and the liquid crystal display panel  4  and the back light assembly  50  are fixedly supported by the mold frame  16 .  
      The bottom chassis  22  is fixed to the mold frame  16  in the lower part of the mold frame  16 . An aperture is formed in a part of the bottom chassis  22  so that the light emitting display panel  30  can be inserted into the bottom chassis  22 .  
      The second printed circuit board  26  receives the driving signals from a driving circuit of a mobile telephone (not shown). The second printed circuit board  26  includes a mobile telephone connector  28 . The mobile telephone connector  28  is fixed to another connector attached to the driving circuit of the mobile telephone to receive the driving signals from the driving circuit of the mobile telephone. The second printed circuit board  26  that receives the driving signals generates various control signals corresponding to the driving signals supplied thereto.  
      The first printed circuit board  24  is connected to the second printed circuit board  26  through a first pad unit  38  formed in the second printed circuit board  26 . The first printed circuit board  24  is connected to the integrated circuit  6  of the liquid crystal display panel  4  and the light emitting diode substrate  14  by a flexible printed circuit board (not shown). The first printed circuit board  24  connected to the integrated circuit  6  and the light emitting diode substrate  14  drives the integrated circuit  6  and the light emitting diode substrate  14  in response to the control signals supplied from the second printed circuit board  26 .  
      The light emitting display panel  30  includes a first substrate  30   a  and a second substrate  30   b.  Organic light emitting diodes (not shown) are arranged on the second substrate  30   a  in 3 matrix. The organic light emitting diodes generate light of predetermined brightness in response to the amount of current supplied thereto. The light emitting display panel  30  is connected to the second printed circuit board  26  by the second pad unit  36  of a flexible printed circuit board  32 . An integrated circuit  34  is mounted on the flexible printed circuit board  32 . The integrated circuit  34  allows the light emitting display panel  30  to display a predetermined image in response to the control signals supplied from the second printed circuit board  26 .  
      However, since the reflecting plate  20  is attached to the bottom chassis  22  only by the adhesive members  21  attached to the two edges of the reflecting plate  20  in the above-described conventional portable display device  60 , the adhesive force between the reflecting plate  20  and the bottom chassis  22  is weak. Also, foreign substances such as air, moisture, and minute dust may enter the gap between the reflecting plate  20  and the bottom chassis  22  where the adhesive members  21  are not applied.  
     SUMMARY OF THE INVENTION  
      Accordingly, in some embodiments of the present invention, a portable display device is provided in which the adhesive strength of a reflecting plate is improved so that the reliability of the portable display device is improved.  
      One embodiment of a portable display device includes a liquid crystal layer; a back light assembly including a light source for supplying light to the liquid crystal layer; a reflecting plate included in the back light assembly to supply light from the light source to the liquid crystal layer; and at least one adhesive member attached to at least three edges of a rear surface of the reflecting plate and arranged such that if the at least one adhesive member were to abut a surface, an air hole would be provided between the rear surface of the reflecting plate, the at least one adhesive member, and said surface.  
      A bottom chassis may also be provided on the rear surface of the reflecting plate for accommodating and supporting the back light assembly, wherein the bottom chassis is attached to the reflecting plate by the at least one adhesive member. The at least one adhesive member may be attached to the at least three edges in the form of an opened square, and may include double-sided tape. The air hole may have a width between 1 mm and 2 mm. Alternatively, a printed circuit board may be positioned on the rear surface of the reflecting plate and attached by the at least one adhesive member.  
      In another embodiment, the liquid crystal layer is a first display panel, and the portable display device further includes a second display panel positioned on the rear surface of the reflecting plate. The second display panel may be attached to the reflecting plate by the at least one adhesive member, and may be a light emitting display panel including a first substrate, light emitting diodes arranged on the first substrate, and a second substrate facing the first substrate. In one embodiment, the second display panel is a liquid crystal display panel.  
      Another embodiment of a portable display device includes a liquid crystal layer; a back light assembly including a light source for supplying light to the liquid crystal layer; a reflecting plate included in the back light assembly to supply light from the light source to the liquid crystal layer; and at least one adhesive member attached to at least three edges of a rear surface of the reflecting plate. The at least one adhesive member may surround a central portion of the rear surface of the reflecting plate and define at least one opening to the central portion. The at least one opening may be between 1 mm and 2 mm.  
      One embodiment also includes a bottom chassis provided on the rear surface of the reflecting plate for accommodating and supporting the back light assembly, wherein the bottom chassis is attached to the reflecting plate by the at least one adhesive member such that an air hole is formed between the bottom chassis, the at least one adhesive member, and the rear surface of the reflecting plate.  
      Alternatively, a printed circuit board may be positioned on the rear surface of the reflecting plate, such as attached to the reflecting plate by the at least one adhesive member such that an air hole is formed between the printed circuit board, the at least one adhesive member, and the rear surface of the reflecting plate.  
      In one embodiment, the liquid crystal layer is a first display panel, and the portable display device further includes a second display panel positioned on the rear surface of the reflecting plate. The second display panel may be attached to the reflecting plate by the at least one adhesive member such that an air hole is formed between the second display panel, the at least one adhesive member, and the rear surface of the reflecting plate. The second display panel may be a light emitting display panel including a first substrate, light emitting diodes arranged on the first substrate, and a second substrate facing the first substrate.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      These and/or other features and aspects of the invention will become apparent and more readily appreciated from the following description of examples of embodiments, taken in conjunction with the accompanying drawings of which:  
       FIG. 1  is an exploded perspective view illustrating a conventional portable display device;  
       FIG. 2  is a perspective view illustrating the rear surface of the reflecting plate illustrated in  FIG. 1 ;  
       FIG. 3  is an exploded perspective view illustrating a portable display device according to an embodiment of the present invention; and  
       FIG. 4  is a perspective view illustrating the rear surface of the reflecting plate illustrated in  FIG. 3 . 
    
    
     DETAILED DESCRIPTION  
      Hereinafter, examples of embodiments according to the present invention will be described with reference to  FIGS. 3 and 4 .  
       FIG. 3  is an exploded perspective view illustrating a portable display device according to an embodiment of the present invention. In  FIG. 3 , a dual display device that is used for a mobile telephone, in which at least one liquid crystal display (LCD) is mounted, is illustrated. The present invention, however, is not limited to the above.  FIG. 4  is a perspective view illustrating the rear surface of the reflecting plate illustrated in  FIG. 3 .  
      Referring to  FIGS. 3 and 4 , the portable display device  160  according to this embodiment of the present invention includes a liquid crystal display panel  104 , a back light assembly  150 , a bottom chassis  122 , first and second printed circuit boards  124  and  126 , and a light emitting display panel  130 .  
      The liquid crystal display panel  104  displays a predetermined image. The liquid crystal display panel  104  includes a first substrate  104   a,  a second substrate  104   b,  and liquid crystal (not shown) implanted between the first substrate  104   a  and the second substrate  104   b.    
      The second substrate  104   b  includes a plurality of transistors (TFTs) arranged in a matrix. Here, the source electrodes of the TFTs are connected to data lines, and the gate electrodes of the TFTs are connected to scan lines. The drain electrodes of the TFTs are connected to pixel electrodes made of conductive and transparent indium tin oxide (ITO). The TFTs are turned on when scan signals are supplied to the scan lines to supply data signals, supplied from the data lines, to the pixel electrodes.  
      An integrated circuit  106  from which the data signals and the scan signals are supplied is inserted into one side of the second substrate  104   b.  A protective layer  8  is formed around the integrated circuit  106 .  
      The first substrate  104   a  is arranged to face the second substrate  104   b.  Common electrodes made of ITO are formed on the front surface of the first substrate  104   a.  A predetermined voltage is applied to the common electrodes so that a predetermined electric field is formed between the common electrodes and the pixel electrodes. The arrangement angle of the liquid crystal implanted between the first substrate  104   a  and the second substrate  104   b  is changed by the electric field and light transmittance is changed by the changed arrangement angle so that it is possible to display a desired image.  
      Upper and lower polarizers (not shown) may also be included on and under the liquid crystal display panel  104 .  
      The back light assembly  150  includes a mold frame  116 , light emitting diodes  112 , a light emitting diode substrate  114 , a light guide plate  118 , a reflecting plate  120 , and optical sheets  110 .  
      The light emitting diodes  112  act as a light source for supplying light to the liquid crystal layer of the liquid crystal display panel  104 , and generate light of a predetermined brightness in response to driving signals from the light emitting diode substrate  114 .  
      The light guide plate  118  supplies the light supplied from the light emitting diodes  112  to the liquid crystal display panel  104 . That is, the light guide plate  118  supplies the light supplied from the sides thereof to the liquid crystal display panel  104  positioned thereon.  
      The reflecting plate  120  is positioned on the rear surface of the light guide plate  118  to re-supply the light incident from the light guide plate  118  back toward the light guide plate  118 . That is, the reflecting plate  120  supplies the light incident. thereon to the liquid crystal layer of the liquid crystal display panel  104  via the light guide plate  118  to improve optical efficiency. The reflecting plate  120  is attached to the rear surface of the bottom chassis  122  positioned by adhesive members  121 , such as double-sided tapes. The adhesive members  121  are attached to at least three edges of the rear surface of the reflecting plate  120  so that the adhesive strength of the reflecting plate  120  is improved and that inflow of foreign substances is reduced. For example, the adhesive members  121  may be attached to the four edges of the rear surface of the reflecting plate  120  in the form of a square, as illustrated in  FIG. 4 . Although multiple adhesive members  121  are shown in  FIGS. 3 and 4 , a single adhesive member may also be used.  
      If the adhesive members  121  are attached to the four edges of the reflecting plate  120  in the form of a closed square, foreign substances such as air and moisture may flow to the between the adhesive members  121 . Thus, when thermal shock is applied from the outside, the foreign substances expand to swell so that the adhesive strength between the reflecting plate  120  and the bottom chassis  122  deteriorates, and the reliability of the portable display device  160  deteriorates as a result.  
      In the embodiment of the present invention shown in  FIGS. 3 and 4 , the adhesive members  121  are attached to the four edges of the rear surface of the reflecting plate  120  to surround a central area of the reflecting plate  120  and to define an opening to the central area. Thus, when the reflecting plate  120  is attached to the bottom chassis  122  by the adhesive members  121 , an air hole  121   a  having width W of about 1 mm to 2 mm is formed. That is, the adhesive members  121  are attached to the reflecting plate  120  in the form of an opened square having the air hole  121   a.  In this embodiment, although the foreign substances such as air and moisture flow to the area between the adhesive members  121  when the reflecting plate  120  and the bottom chassis  122  are attached to each other, the foreign substances that expand when thermal shock is applied are discharged through the air hole  121   a  so that the foreign substances do not swell. Therefore, it is possible to improve the adhesive strength between the reflecting plate  120  and the bottom chassis  122  and to improve the reliability of the portable display device  160  compared with the conventional art.  
      Further, since double-sided tapes are provided at the four edges of the reflecting plate  120 , excluding the part of the air hole  121   a,  it is possible to reduce the inflow of the foreign substances after the reflecting plate  120  and the bottom chassis  122  are attached to each other.  
      Although only the case in which the bottom chassis  122  is included has been described above, the present invention is not limited to the above. For example, when the bottom chassis  122  is not included, the reflecting plate  120  may be attached to the first printed circuit board  124  or the first substrate  130   a  of the light emitting display panel  130 . In this case, the adhesive members  121  are attached to the rear surface of the reflecting plate  120  so that the air hole  121   a  is formed to attach the reflecting plate  120  and the first printed circuit board  124  or the light emitting display panel  130  to each other.  
      The optical sheets  110  improve the brightness of the light supplied from the light guide plate  118  to supply the light to the liquid crystal display panel  104 .  
      The light emitting diode substrate  114  is connected to the first printed circuit board  124  to supply the driving signals to the light emitting diodes  112  in response to control signals supplied from the first printed circuit board  124 .  
      The light emitting diode substrate  114  in which the light emitting diodes  112  are mounted is accommodated in and fixed to the mold frame  116  and the liquid crystal display panel  104  and the back light assembly  150  are fixedly supported to the mold frame  116 .  
      The bottom chassis  122  is fixed to the mold frame  116  in the lower part of the mold frame  116  to accommodate and support the back light assembly  150 . An aperture is formed in a part of the bottom chassis  122  so that the light emitting display panel  130  can be inserted into the bottom chassis  122 .  
      The second printed circuit board  126  receives the driving signals from a driving circuit of a mobile telephone (not shown). The second printed circuit board  126  includes a mobile telephone connector  128 . The mobile telephone connector  128  is fixed to another connector attached to the driving circuit of the mobile telephone to receive the driving signals from the driving circuit of the mobile telephone. The second printed circuit board  126  that receives the driving signals generates various control signals corresponding to the driving signals supplied thereto.  
      The first printed circuit board  124  is connected to the second printed circuit board  126  through a first pad unit  138  formed in the second printed circuit board  126 . The first printed circuit board  124  is connected to the integrated circuit  106  of the liquid crystal display panel  104  and the light emitting diode substrate  114  by a flexible printed circuit board (not shown). The first printed circuit board  124  connected to the integrated circuit  106  and the light emitting diode substrate  114  drives the integrated circuit  106  and the light emitting diode substrate  114  in response to the control signals supplied from the second printed circuit board  126 .  
      The light emitting display panel  130  includes a first substrate  130   a  and a second substrate  130   b.  Organic light emitting diodes (not shown) are arranged on the first substrate  130   a  in a matrix. The organic light emitting diodes generate light of predetermined brightness in response to the amount of current supplied thereto. The light emitting display panel  130  is connected to the second printed circuit board  126  by the second pad unit  136  of a flexible printed circuit board  132 . An integrated circuit  134  is mounted on the flexible printed circuit board  132 . The integrated circuit  134  allows the light emitting display panel  130  to display a predetermined image in response to the control signals supplied from the second printed circuit board  126 . The light emitting display panel  130  may also be substituted for a liquid crystal display panel or any other suitable display panel.  
      As described above, according to the portable display device  160  of this embodiment of the present invention, the adhesive members  121  are attached to at least three edges of the reflecting plate  120  to attach the reflecting plate  120  and the bottom chassis  122  to each other so that it is possible to improve the adhesive strength between the reflecting plate  120  and the bottom chassis  122  and to reduce the amount of the foreign substances flowing between the reflecting plate  120  and the bottom chassis  122 . In one embodiment of the invention, the adhesive members  121  are attached to the four edges of the reflecting plate  120  not in the form of a closed square, but having an air hole  121   a  formed on at least one edge of the square so that it is possible to prevent the foreign substances from swelling when thermal shock is applied from the outside, thereby improving the reliability of the portable display device  160 .  
      As described above, the adhesive members in this embodiment are attached to at least three edges of the rear surface of the reflecting plate to attach the reflecting plate and the bottom chassis to each other so that it is possible to improve the adhesive strength of the reflecting plate and to reduce the inflow of foreign substances. Also, the air hole is formed when the adhesive members are attached so that it is possible to improve the reliability of the portable display device.  
      Although examples of embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes might be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.