Abstract:
A backlight unit and a liquid crystal display device having the same are disclosed. The backlight unit includes a light source, a light guide plate guiding light emitted from the light source, an optical sheet arranged on the light guide plate, a mold frame receiving the light guide plate and the optical sheet, a printed circuit board (“PCB”) outlet in the mold frame, a printed circuit board (“PCB”) received in the PCB outlet, and a PCB adhesive sheet for adhering the PCB to the mold frame.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims priority to and the benefit of Korean Patent Application No. 2006-82280, filed Aug. 29, 2006, the entire contents of which are incorporated by reference herein in their entirety. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a backlight unit and a liquid crystal display (“LCD”) device having the same 
   2. Description of the Related Art 
   The importance of LCD devices is significantly increasing with the advent of the information age. Although a cathode ray tube (“CRT”) display which has been widely used as an information display device may have some advantages in performance and price, CRT displays are inferior in terms of size and portability. LCD devices are an advantageous substitute for the CRT due to advantages of compact size, light weight, and low power consumption. 
   Recently, research on structures of LCD device components and the overall assembly structure of LCD devices is actively in progress in order to satisfy requirements of compact size, light weight and low power consumption. 
   The typical LCD device comprises an LC panel for receiving an image signal to display an image, a backlight unit for supplying light to the LC panel, a mold frame and a chassis for supporting and fixing the LC panel and the backlight unit, and a PCB having a driving circuit for driving the LC panel. 
   The typical LCD device is assembled such that the backlight unit is received in the mold frame and chassis and the LC panel is arranged on the backlight unit. In order to prevent the LC panel and the backlight unit from being shaken or dislodged, the LC panel and the backlight unit are fixed using a panel adhesive sheet. 
   The PCB is electrically connected to one side of the LC panel and extends out of the mold frame. The PCB is bent and folded to thereby contact a rear surface of the backlight unit. 
   However, the PCB may not fixedly adhere to the mold frame and may be partially separated from the mold frame due to the elasticity of the PCB itself. As a result, one side of the LC panel is separated, and the LC panel is detached from the mold frame. The problem of the LC panel being detached from the mold frame is more serious in devices where the distance from the active region of the LC panel to the edge of the glass substrate is short. 
   SUMMARY OF THE INVENTION 
   Described herein is a backlight unit in which an LC panel is prevented from being separated from a mold frame by firmly adhering the PCB to the mold frame by using a PCB adhesive sheet, and an LCD device having the backlight unit. 
   In one exemplary embodiment, a backlight unit includes a light source, a light guide plate guiding light emitted from the light source, an optical sheet arranged on the light guide plate, a mold frame receiving the light guide plate and the optical sheet, a PCB outlet in the mold frame, a printed circuit board (“PCB”) received in the PCB outlet, and a PCB adhesive sheet positioned between the PCB and the PCB outlet to adhere the PCB to the mold frame. 
   The backlight unit may further include a panel accommodating projection having a step portion and formed at an inner side wall of the mold frame to accommodate a display panel, and a panel adhesive sheet formed on the panel accommodating projection and adhering the display panel to the mold frame. 
   In some embodiments, the PCB adhesive sheet and the panel adhesive sheet are formed as a single unit. 
   In some embodiments, a plurality of part mounting holes is formed by penetrating the mold frame at an inner side of the PCB outlet. 
   The backlight unit may further include a connection portion connecting the panel adhesive sheet to the PCB adhesive sheet. 
   In some embodiments, the PCB outlet is higher than the panel accommodating projection in height in order to prevent separation of the display panel. 
   In some embodiments, the PCB outlet has a curved edge. 
   In another exemplary embodiment, an LCD device includes a backlight unit, an LC panel arranged on the backlight unit, and a PCB connected to the LC panel, wherein the backlight unit includes a light source, a light guide plate guiding light emitted from the light source to the LC panel, an optical sheet arranged on the light guide plate, a mold frame for receiving the light guide plate and the optical sheet, a printed circuit board (“PCB”) outlet in the mold frame, and an adhesive sheet positioned in the PCB outlet between the PCB and the mold frame to adhere the PCB to the mold frame. 
   The LCD device may further include a window arranged on the LCD panel to protect the LC panel. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other features of the present invention will be described in reference to certain exemplary embodiments thereof with reference to the attached drawings in which: 
       FIG. 1  is an exploded perspective view illustrating an LCD device according to an exemplary embodiment of the present invention; 
       FIG. 2  is a perspective view illustrating the LCD device according to the exemplary embodiment of the present invention; 
       FIGS. 3 and 4  are cross-sectional views taken along line I-I′ of  FIG. 2 ; and 
       FIGS. 5A to 5C  are plan views illustrating various forms of PCB adhesive sheets according to an exemplary embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures. 
     FIG. 1  is an exploded perspective view illustrating an LCD device according to an exemplary embodiment of the present invention.  FIG. 2  is a perspective view illustrating the LCD device according to the exemplary embodiment of the present invention.  FIGS. 3 and 4  are cross-sectional views taken along line I-I′ of  FIG. 2   
   The LCD device of  FIG. 1  comprises a backlight unit  100 , an LC panel  200 , and a PCB  300 . 
   The backlight unit  100  supplies light to the LC panel  200 . The backlight unit  100  comprises a light source  110 , a light guide plate  120 , an optical sheet  130 , a mold frame  140 , a panel adhesive sheet  150 , and a PCB adhesive sheet  160 . 
   The light source  110  generates light and emits light to the light guide plate  120 . The light source  110  may comprise, e.g., a cold cathode fluorescent lamp or a light emitting diode. 
   The light guide plate  120  is arranged on one side of the light source  110  to guide light emitted from the light source  110  to the LC panel  200 . The light guide plate  120  is made of an acrylic-based material. 
   The optical sheet  130  is a functional sheet which diffuses and condenses light coming from the light guide plate  120  to improve brightness. The optical sheet  130  may comprise two or more sheets, such as a diffuser sheet, a prism sheet, a protector sheet, and/or a brightness improving sheet. The diffuser sheet evenly diffuses light coming from the light guide plate  120 . The prism sheet refracts and condenses light coming from the diffuser sheet to improve brightness. The protector sheet protects the prism sheet which can be easily scratched and uses the Moire phenomenon to diffuse light and widen the viewing angle narrowed by the prism sheet. The brightness improving sheet serves to improve brightness. 
   On a rear surface of the light guide plate  120  opposite the LC panel  200 , as shown in  FIG. 1 , a reflector sheet  170  may be further arranged. The reflector sheet  170  reflects light emitted away from the LC panel back toward the light guide plate  120 , thereby improving light efficiency. 
   The mold frame  140  provides a space where the light source  110  is received and surrounds sides of the light guide plate  120  and the optical sheet  130 . The mold frame  140  has a rectangular frame shape. At least one of the four sides of the rectangular frame has a larger area size than the other sides in order to safely mount the PCB  300  on the mold frame  140 . The mold frame  140  also receives the LC panel  200 . In order to receive the LC panel  200 , the mold frame  140  may be provided with a panel accommodating projection for supporting and maintaining a position of the LC panel  200 . For example, as shown in  FIGS. 3-4 , a panel accommodating projection  144  is formed to have a projection or a step portion at an inner side wall of the mold frame  140 . Thus, the LC panel  200  is placed on the mold frame  140  such that the LC panel  200  is supported by the panel accommodating projection  144 . Preferably, the height H of the panel accommodating projection  144  is equal to the sum of thicknesses T 1  and T 2  of the light guide plate  120  and the optical sheet  130  as shown in  FIG. 3 . The mold frame  140  has a height equal to or greater than a color filter substrate  200  of the LC panel  200  in order to prevent the LC panel  200  placed in the mold frame  140  from being separated in a horizontal direction. 
   In order to firmly hold the LC panel  200  positioned on the mold frame  140 , the panel adhesive sheet  150  is arranged on the panel accommodating projection  144 . The panel adhesive sheet  150  is formed such that the two opposing faces of the panel adhesive sheet  150  are coated with an adhesive material. The top surface of the panel adhesive sheet  150  adheres to the LC panel  200  and the bottom surface of the panel adhesive sheet  150  adheres to the optical sheet  130  and to the panel accommodating projection  144 . Thus, the panel adhesive sheet  150  adheres and fixes the LC panel  200  to the optical sheet  130  and the panel accommodating projection  144  of the mold frame  140 . 
   The mold frame  140  further has a PCB outlet  142  for providing a passage through which the PCB  300  connected to the LC panel  200  may pass. The PCB outlet  142  is formed such that at least a part of one of the four sides of the mold frame  140  has an opening or a lower height than the other three sides. The PCB outlet  142  may have a higher height than the panel accommodating projection  144  as shown in  FIG. 3  or equal height to the panel accommodating projection  144  as shown in  FIG. 4 . In the former case, there is an advantage in that the PCB outlet  144  is high enough to prevent horizontal movement of the LC panel  200 . In the latter case, however, the LC panel  200  may be displaced horizontally. For the foregoing reason, the mold frame  140  may have a panel restricting projection  146  (shown in  FIG. 5A ) for preventing the LC panel  200  from slipping and moving horizontally. The panel restricting projection  146  is preferably on both ends of the PCB outlet  142  at a higher height than the panel accommodating projection  144 . That is, two panel restricting projections  146  are formed at both corners of one side of the mold frame  140  where the PCB outlet  144  is formed. 
   The PCB adhesive sheet  160  is arranged on the PCB outlet  142  between the PCB  300  to the mold frame  140  to adhere and fix the PCB  300  to the mold frame  140 . That is, when the PCB  300  is bent to envelop one side of the mold frame  140 , the PCB adhesive sheet  160  attached to the PCB outlet  142  adheres and fixes the PCB  300  to the PCB outlet  142  to thereby prevent the PCB  300  from being separated from the mold frame  140 . In a conventional LCD device, the PCB is not coupled to the mold frame, which leads to separation of the LC panel connected to the PCB from the mold frame. However, according to the illustrated embodiments, the PCB adhesive sheet  160  firmly fixes the PCB  300  to the mold frame  140  to thereby prevent the LC panel  200  from being separated from the mold frame  140 . 
     FIGS. 5A to 5C  are plan views illustrating various forms of the PCB adhesive sheets  160  according to exemplary embodiments of the present invention. 
   The PCB adhesive sheet  160  may be integrated with the panel adhesive sheet  150  as shown in  FIG. 5A . That is, the PCB adhesive sheet  160  extends from the panel adhesive sheet  150 . In this embodiment, a process for making the adhesive sheet and a process for adhering the adhesive sheet to the mold frame  140  are simplified because only a single application of a sheet to the mold frame  140  is performed. The single unit or integral adhesive sheet is suitable for a case where the PCB outlet  142  is equal in height to the panel accommodating projection  144 . 
   As shown in  FIG. 5B , the mold frame  140  may further comprise a part mounting hole  148  which provides a space where a part (e.g., driving circuit  310  in  FIG. 1 ) mounted on the PCB  300  is placed. The part mounting hole  148  is formed to penetrate a portion of the mold frame  140  corresponding to the PCB outlet  142 . Depending on where the part mounting hole  148  is formed, it may be difficult to fabricate the panel adhesive sheet  150  and the PCB adhesive sheet  160  as a single unit, i.e., the integral adhesive sheet described above. Thus the PCB adhesive sheet  160  may be formed separate from the panel adhesive sheet  150 , as shown in  FIG. 5B . 
   Alternatively, an integral adhesive sheet may be formed such that the panel adhesive sheet  150  and the PCB adhesive sheet  160  are connected by a connection portion  162  as shown in  FIG. 5C . That is, the integral adhesive sheet of  FIG. 5C  comprises the panel adhesive sheet  150 , the PCB adhesive sheet  160  and the connecting portion  162  for connecting the panel adhesive sheet  150  and the PCB adhesive sheet  160 . The integral adhesive sheet of  FIG. 5C  has an advantage in that it can be adhered to the mold frame  140  by a single adhering process. 
   The PCB outlet  142  may have a curved edge R as shown in  FIGS. 3 and 4 , so that the PCB  300  and the mold frame  140  can more closely contact each other. Due to the curved edge R of the PCB outlet  142 , the PCB  300  is firmly adhered to the mold frame  140  because the PCB  300  may be bent to follow the curved contour of the curved edge R of the PCB outlet  142 . If the edge of the PCB outlet  142  is sharp, then it may not be possible for the PCB  300  to be bent to match such a sharp edge. 
   The backlight unit  100  may further comprise a bottom chassis  180  which receives the light source  110 , the light guide plate  120 , and the optical sheet  130  as shown in  FIG. 1 . 
   The LC panel  200  comprises a thin film transistor (“TFT”) substrate  210  and a color filter substrate  220  with a liquid crystal layer interposed therebetween as shown in  FIGS. 1 and 2 . The LC panel  200  further comprises a lower polarizer  230  arranged beneath the TFT substrate  210  and an upper polarizer  240  arranged on the color filter substrate  220  as shown in  FIGS. 3 and 4 . 
   The TFT substrate  210  may comprise a conventional TFT substrate typically used for LCD devices. Although these details are not shown, the TFT substrate  210  may comprise a gate line arranged in a transverse direction, a data line in a perpendicular direction to the gate line, a TFT arranged at a crossing point of the gate line and the data line, and a pixel electrode. The TFT comprises a gate electrode extended from the gate line, a source electrode extended from the data line, and a drain electrode electrically connected to the pixel electrode. The pixel electrode is made of a transparent conductive material and applies a data voltage supplied via the drain electrode to a LC layer when the TFT is turned ON by a gate signal. 
   The color filter substrate  220  may be a conventional color filter substrate typically used for LCD devices and may comprise red (R), green (G) and blue (B) color filters and a common electrode. The common electrode is made of a transparent conductive material and applies a common voltage to the LC layer. The LCD device varies the transmissivity of light emitted from the backlight unit by using the difference between the data voltage and the common voltage. 
   From the light emitted by the backlight unit, the lower polarizer  230  transmits and polarizes only light vibrating in a certain direction. From the light passing through the LC layer, the upper polarizer  240  polarizes and transmits only light vibrating in a certain direction. The lower polarizer  230  and the upper polarizer  240  are arranged to have perpendicular polarization directions. 
   The PCB  300  is connected to one side of the LC panel  200 , i.e., the TFT substrate  210 . The PCB  300  has a driving circuit  310  for driving the LC panel mounted thereon. The driving circuit  310  may comprise a data driver, a gate driver, a timing controller, and a power source. The PCB  300  is bent to contact the rear surface of the backlight unit  100  while surrounding one side of the mold frame  140  as described above, and thus the PCB  300  is made of a flexible material. As described above, the PCB  300  is firmly adhered to the mold frame  140  by the PCB adhesive sheet  160 . 
   In addition to the above described components of the LCD device, a window  400  may be further arranged on the LC panel  200  to protect the LC panel  200  as shown in  FIG. 1 . In case the LCD device is employed in a portable communication device such as a cellular phone or a personal digital assistant, the LC panel  200  may be easily broken by an external shock or impact. For the foregoing reason, the window  400  is arranged to protect the LC panel  200 . The window  400  is usually made of a transparent plastic material and is adhered to the LC panel  200  by an adhesive means. 
   As described above, the bent PCB is firmly adhered to the mold frame by the adhesive sheet, and thus the separation of the LC panel from the mold frame is prevented. Further, since the adhesive sheet can be fabricated in various forms, it can be widely employed in various LCD devices. 
   Although the present invention has been described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that a variety of modifications and variations may be made to the present invention without departing from the spirit or scope of the present invention defined in the appended claims, and their equivalents.