Patent Document

CLAIM OF PRIORITY 
     This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from an application for FLAT PANEL DISPLAY DEVICE AND PORTABLE DISPLAY APPARATUS USING THE SAME earlier filed in the Korean Intellectual Property Office on the 22 nd  of Sep. 2006 and there duly assigned Serial No. 10-2006-0092494. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a dual type flat panel display device, and more specifically, a dual type flat panel display device and a portable display apparatus using the same, which includes an integrated flexible printed circuit board transferring electrical signals to the flat panel display panel and a light source device mounted in the flat panel display as a backlight unit 
     2. Description of the Related Art 
     In the contemporary terminology, a dual type flat panel display device means a flat panel display device including two display panels that display images in opposite directions. The two display panels are usually configured of a main display panel and a sub-display panel. For example, a main display panel is configured of a liquid crystal display device and a sub-display panel is configured of a liquid crystal display device or an organic electro-luminescence display device. 
     A dual type flat panel display device includes a printed circuit board for driving a main display panel, a first flexible printed circuit board for transferring signals form the printed circuit board to the main display panel to drive the main display panel, and a second flexible printed circuit board transferring signals form the printed circuit board to a sub-display panel to drive the sub-display panel 
     A flexible printed circuit board (FPCB) is a type of a printed circuit board having flexibility. The flexible printed circuit board has a conductive thin film layer such as copper formed in a pattern on a base film of an insulated resin material, and has a protective film formed on the thin film layer.  FIG. 1  is a cross-sectional view of a flexible printed circuit board. The flexible printed circuit board is disclosed in Korean Patent Laid-Open Publication No. 10-2005-0064550. According to the disclosure, the flexible printed circuit board is formed with conductive wiring layer  12  and protective film  30  covering wiring layer  12 . A part of conductive wiring layer  12  is exposed without protective film  30  (portion a in  FIG. 1 ) for a connection to a terminal of an external device. Conductive wiring layer  12  with a circuit pattern is formed on base film  11 . 
     A dual type flat panel display device has an additional flexible printed circuit board in addition to the first and second flexible circuit board described above. The additional flexible printed circuit board is necessary to connect the printed circuit board to a light source device to provide necessary electrical energy to the light source device. The increased number of flexible printed circuit board, however, makes the structure of portable display apparatus complicated. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a dual type flexible flat panel display device and a portable display apparatus using the same. It is another object of the present invention to provide a flexible printed circuit board that is integrated to simultaneously transfer electric signals to both of a light source device and a main display panel. 
     According to one aspect of the present invention, there is provided a flat panel display device including a main display panel, a sub-display panel, a printed circuit board disposed between the main display panel and the sub-display panel, a backlight unit disposed between the printed circuit board and the main display panel, a first flexible printed circuit board coupled to the main display panel, backlight unit, and the printed circuit board, and a second flexible printed circuit board connecting the sub-display panel to the printed circuit board. The printed circuit board includes a main terminal portion and a sub-terminal portion. 
     The first flexible printed circuit board includes a first substrate portion, a second substrate portion, a third substrate portion, and a connection substrate portion. The first substrate portion is connected to the main display panel. The second substrate portion is disposed between the main display panel and the backlight unit, and is connected to the first substrate portion. The second substrate portion includes at least one light source device to transmit light into the backlight unit. The backlight unit transmits light produced from the light source device into the main display panel. The third substrate portion is disposed between the backlight unit and the printed circuit board, and is connected to the main terminal portion of the printed circuit board. The connection substrate portion connects the second substrate portion to the third substrate portion. 
     The dual type flat panel display device of the present invention has an advantage that electrical signals are applied to the main display panel and the light source at the same time through a flexible printed circuit board. Therefore an additional flexible printed circuit board for supplying electricity to the light source device is not necessary. 
     The flexible printed circuit board of the present invention prevents a dislocation of the light source device, which could be caused by heat generated during soldering process of printed circuit board and flexible printed circuit board. 
     Further, the flexible printed circuit board of the present invention has an advantage that the third substrate portion of the first flexible printed circuit board can be made relatively short in length because other driving elements are not mounted on the third substrate portion. Therefore, formation of terminal portion is relatively simple, and it is not necessary to extend the third portion over the entire surface of the printed circuit board. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the invention and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein: 
         FIG. 1  is a cross-sectional view showing a flexible printed circuit board; 
         FIG. 2A  is a perspective view showing a flexible printed circuit board constructed as one embodiment of the present invention; 
         FIG. 2B  is a bottom perspective view of the flexible printed circuit board shown in  FIG. 2A ; 
         FIG. 2C  is a perspective view showing a flexible printed circuit board constructed as another embodiment of the present invention; 
         FIG. 3  is an exploded perspective view showing a dual type flat panel display device constructed according to the principles of one embodiment of the present invention; 
         FIG. 4  is a cross-sectional view showing a dual type flat panel display device constructed according to the principles of one embodiment of the present invention; and 
         FIG. 5A  to  FIG. 5E  are perspective views showing assembly processes to assemble the flexible printed circuit board of one embodiment of the present invention on a dual type flat panel display device. 
         FIG. 6  is a perspective view showing a cellular phone in which a flat panel display device of one embodiment of the present invention is installed. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, preferred embodiments of the present invention will be described in a more detailed manner with reference to the accompanying drawings. 
       FIG. 2A  is a perspective view showing a flexible printed circuit board applied to a dual type flat panel display device constructed as one embodiment of the present invention, and  FIG. 2B  is a bottom perspective view of the flexible printed circuit board shown in  FIG. 2A . Referring to  FIGS. 2A and 2B , first flexible printed circuit board  100  includes first substrate portion  110 , second substrate portion  120 , connection substrate portion  130 , and third substrate portion  140 . 
     First substrate portion  110  includes at least one terminal  111  which can be connected to an external device. Terminal  111  is formed by exposing a conductive wiring layer enclosed in first substrate portion  110  of first flexible printed circuit board  100 . First substrate portion  110  is connected to one part of second substrate portion  120  in a manner that the conductive wiring layer of first substrate portion  110  is connected to a conductive wiring layer of second substrate portion  120 . In the present invention, first substrate portion  110  is a considerably bent part of first flexible printed circuit board  100 , and therefore it is preferable that first substrate portion  110  has a single conductive wiring layer. In this case, the thickness of first substrate  110  is smaller than the thicknesses of second substrate portion  120  and third substrate portion  140 . 
     Herein, terminologies related to substrate portions are defined. Referring to  FIG. 2A , a width side and a length side of a substrate portion are defined as follows. A side of first substrate portion  110 , along which first substrate portion  110  is connected to second substrate portion  120 , is defined as a width side of first substrate portion. Therefore, as shown in  FIG. 2A , first substrate portion  110  has two width sides, and one of the width sides of first substrate portion  110  is connected to second substrate portion  120 . The size of the width side of first substrate portion  110  is defined as a width of first substrate portion  110 . Accordingly, a length side of first substrate portion  110  is defined as a side substantially perpendicular to the width side of first substrate portion  110 , and the size of the length side of first substrate portion  110  is defined as a length of first substrate portion  110 . If first substrate portion  110  has a shape other than a rectangle, the width and length of first substrate portion  110  are defined as average sizes over a width side and a length side of first substrate portion  110 , respectively. As the width sides and length sides of first substrate portion  110  form a surface or a plane, first substrate portion  110  has an upper surface and a lower surface. A thickness of first substrate portion  110  is defined as a distance between the upper surface and the lower surface of first substrate portion  110 . The same definitions are applied to second, third, and connection substrate portions to define a width, a length, and a thickness. 
     As shown in  FIG. 2A , a part of width side of second substrate portion  120  is connected to a width side of first substrate portion  110 , and a part of length side of second substrate portion  120  is connected to a part of length side of connection substrate portion  130 . A width side of connection substrate portion  130  is defined as a side that is substantially parallel to the width side of second substrate portion  120 , and accordingly a length side of connection substrate portion  130  is defined as a side substantially perpendicular to the width side of connection substrate portion  130 . The size of the width side of connection substrate portion  130  is defined as a width of connection substrate portion  110 , and the size of the length side of connection substrate portion  130  is defined as a length of connection substrate portion  130 . 
     As shown in  FIGS. 2A and 2B , first substrate portion  110  is connected to around middle of a width side of second substrate portion  120 , and connection substrate portion  130  is connected to a length side of second substrate portion  120 . First substrate portion  110  and connection substrate portion  130  are stretched from second substrate portion  120  in the same direction (a length direction). The width W 1  of first substrate portion  110  is larger than the width W 2  of connection substrate portion, and the length L 1  of first substrate portion  110  is smaller than the length L 2  of connection substrate portion. 
     Driving components, to which electrical signals are applied, are mounted on second substrate portion  120 . The driving components include light source device  310  and boosting circuit  370 , but there is no limitation on the types of driving components that can be mounted on second substrate portion  120 . In this embodiment, light source device  310  is preferably a light emitting diode. 
     Connection substrate portion  130  connects second substrate portion  120  to third substrate portion  140 . Because connection substrate portion  130  is a portion to be bent, it is preferable that connection substrate portion  130  has single conductive wiring layer structure. In this case, the thickness of connection substrate portion  130  is smaller than those of second substrate portion  120  and third substrate portion  140 . 
     First flexible printed circuit board  100  can have one or more connection substrate portion.  FIG. 2C  shows another embodiment where two connection substrate portions  130   a  and  130   b  are provided. First connection substrate portion  130   a  is formed at one end of second substrate portion  120 , and second connection substrate portion  130   b  is formed at the other end of second substrate portion  120 . At this time, the conductive wiring layer of second substrate portion  120  is divided into two to be connected to first connection substrate portion  130   a  and second connection substrate portion  130   b , respectively. 
     Third substrate portion  140  includes at least one terminal  141 , where the conductive wiring layer of third substrate portion  140  is exposed. The conductive wiring layer of third substrate portion  140  is connected to a conductive wiring layer of second substrate portion  120  through a conductive wiring layer of connection substrate portion  130 . Through-hole  142  is formed in terminal  141 . In the present invention, electricity that is necessary to drive light source device  310  is supplied through first flexible printed circuit board  100 . Therefore, the conductive wiring layer of third substrate portion  140  can include a sub-wiring for supplying electricity to light source device  310 . The sub-wiring is connected to light source device  310  through connection substrate portion  130  and second substrate portion  120 . 
     Referring to  FIG. 3 , one embodiment of a dual type flat panel display device, to which the foregoing flexible printed circuit board is applied, will be described.  FIG. 3  is an exploded perspective view showing a dual type flat panel display device constructed as an embodiment of the present invention. The dual type flat panel display device includes main display module M, sub-display module S, printed circuit board  500  for driving main display module M and sub-display module S, first flexible printed circuit substrate  100 , and second flexible printed circuit substrate  700 . Printed circuit board  500  is disposed between main display module M and sub-display module S. 
     Main display module M includes main display panel  200 , backlight unit  300 , bezel  400 , and all parts and components installed between bezel  400  and main display panel  200 . Backlight unit  300  is disposed between main display panel  200  and bezel  400 . 
     Main display panel  200  of main display module M can be a liquid crystal display. The liquid crystal display requires backlight unit  300 . The liquid crystal display includes first substrate  210 , second substrate  220 , and liquid crystal (not shown) injected between first substrate  210  and second substrate  220 . 
     First substrate  210  and second substrate  220  are arranged in a manner that inner surfaces of first substrate  210  and second substrate  220  faces each other. A common electrode made of indium tin oxide (ITO) is formed on an inner surface of first substrate  210 . A plurality of thin film transistors (TFT) are formed on an inner surface of second substrate  220  in a form of a two-dimensional array. A plurality of pixel electrodes is formed on the inner surface of second substrate  220 , and each of pixel electrode is connected to one of the thin film transistors. Integrated circuit  230  is mounted on a portion of the inner surface of second substrate  220 , and data signals and scan signals to drive main display panel  200  are supplied from integrated circuit  230 . The second substrate also includes pad portion  240  that receives electrical signals from an external circuit such as a flexible printed circuit board. A polarizing plate (not shown) is further provided on external surfaces of first substrate  210  and second substrate  220 . 
     When voltage is applied between the common electrode and a pixel electrode, electrical field is formed between the common electrode and the pixel electrode, and alignment of liquid crystal molecules, which is contained between first substrate  210  and second substrate  220 , is changed in response to the electric field formed between the common electrode and the pixel electrode. The change of alignment of liquid crystal molecules causes change of light transmission passing the liquid crystal. 
     Backlight unit  300  transmits light into main display panel  200  in order to provide light to main display panel  200 . Backlight unit  300  includes reflective sheet  320 , mold frame  330 , light guide plate  340 , optical sheets  350 , and rim frame  360 . Backlight unit  300  receives light from light source device  310 , which is mounted on second substrate portion  120  of first flexible printed circuit board  100 . Light source device  310  produces light of predetermined brightness in response to a driving signal transferred to second substrate portion  120  of first flexible printed circuit board  100 . 
     Light guide plate  340  transmits the light generated from light source device  310  to main display unit  200  through upper surface of light guide plate. As shown in  FIG. 3 , light source device  310  is placed on a side of light guide plate  340 . Therefore, light guide plate  340  supplies light, which is supplied from a side of light guide plate  340 , upwards to main display unit  200 . Herein, an upper or lower surface of light guide plate  340  is surfaces substantially parallel to surfaces of main display unit  200 , and side of light guide plate is a surface that is not the upper or lower surface of light guide plate  340 . 
     Reflective sheet  320  is arranged on a lower surface of light guide plate  340  to reflect light, which is leaked from light guide plate  340  or from other elements, back into light guide plate  340 . Therefore, reflective sheet  320  prevents waste of light, and improves light efficiency. Optical sheets  350  improves the brightness of light supplied from light guide plate  340 , and provides the light into main display panel  200 . Mold frame  330  encloses sides of light guide plate  340 , and includes mounting groove  320   a  in which light source device  310 , which is mounted on second substrate portion  120 , is placed. Bezel  400  supports main display panel  200  and backlight unit  300  from the bottom, and is generally manufactured with metal. 
     Sub-display module S includes sub-display panel  600  that displays images in an opposite direction from main display panel  200 . Sub-display panel  600  can be a liquid crystal display panel or an organic electro-luminescence display panel that includes an organic electro-luminescence element. 
     The organic electro-luminescence display panel is a display panel using a principle of electro-luminescence phenomenon of organic thin film layer. The electro-luminescence element of organic thin film layer emits light when electric field is applied to the organic thin film layer. The organic electro luminescence display panel includes a first substrate, which includes an organic thin film, and a second substrate, which prevents the organic thin film from being exposed to air. The organic electro-luminescence display panel can be driven by passive driving method or by active driving method. For the active driving method, active driving element such as thin film transistor can be included in the organic electro-luminescence display panel. Further detailed description of the organic-electro luminescence display will be omitted. 
     Printed circuit board  500  applies signals to main display panel  200 , sub-display panel  600 , and backlight unit  300  through first flexible printed circuit board  100  in response to the control signals supplied from an external device or a user. Printed circuit board  500  includes main terminal portion  510  to be connected to terminal  141  (shown in  FIG. 2B ) of third substrate portion  140  of first flexible circuit substrate  100 , and a sub-terminal portion (not shown) of printed circuit board  500  to be connected to terminal  710  of second flexible circuit board  700 . Sub-terminal  720  of second flexible circuit board  700  is connected to sub-display panel  600 . Printed circuit board  500  can have a groove in which sub-display panel  600  is positioned, but depending on the structures of printed circuit board  500  and sub-display panel  600 , printed circuit board  500  may not have the groove. 
     First flexible printed circuit board  100  transfers electrical signals supplied from printed circuit board  500  to backlight unit  300  and main display panel  200 . In other words, first flexible printed circuit board  100  transfers the electrical signals, which are transferred to printed circuit board  500  from an external device, to main display panel  200  as well as the components installed on first flexible printed circuit board  100 , which includes light source device  310 . 
       FIG. 4  shows how first flexible printed circuit board  100  is connected to main display panel  200 , to backlight unit  300 , and to printed circuit board  500 . As described referring to  FIGS. 2A and 2B , first flexible printed circuit board  100  includes first substrate portion  110 , second substrate portion  120 , connection substrate portion  130 , and third substrate portion  140 .  FIG. 4  shows only an edge portion of main display unit  200  and backlight unit  300 , where first flexible printed circuit board  100  is connected to these elements.  FIG. 4  also shows how first flexible printed circuit board  100  can be bent to be connected to each of main display panel  200 , backlight unit  300 , and printed circuit board  500 . 
     As shown in  FIG. 4 , backlight unit  300  is placed between printed circuit board  500  and main display unit  200 . First flexible circuit board  100  is arranged to be coupled to each of printed circuit board  500 , backlight unit  300 , and main display unit  200 . 
     First substrate portion  110 , which is connected to main display panel  200 , includes terminal  111  (shown in  FIG. 2B ). Terminal  111  includes a conductive wiring layer, and the conductive wiring layer of terminal  111  contacts pad portion  240  (shown in  FIG. 3 ) of main display panel  200 . Therefore, main display panel  200  is connected to first flexible printed circuit board  100  through first substrate portion  110 . One width side of first substrate portion  110  is connected to a width side of second substrate portion  120 , and the opposite width side of first substrate portion  110  is connected to pad portion  240  of main display panel  200 . As shown in  FIG. 4 , because second substrate portion  120  is disposed between backlight unit  300  and main display panel  200 , first substrate portion  110  is considerably bent to be connected to both of second substrate portion  120  and main display panel  200 . It is preferable that the thickness of first substrate portion  110  is smaller than the thicknesses of second substrate portion  120  and third substrate portion  140 . Thinner first substrate portion  110  has more flexibility than thicker second substrate portion  120  and third substrate portion  140 , which are not necessarily to be bent. 
     Second substrate portion  120  is positioned between main display panel  200  and backlight unit  300 . Second substrate portion  120  is placed around an edge regions of main display panel  200  (non-display area), and therefore does not interrupt light transmission between backlight unit  300  and main display panel  200 . Light source device  310 , which is installed on second substrate portion  120 , is positioned between main display panel  200  and printed circuit board  500 . Light source device  310  is also placed within mold frame  330  on a side of light guide place  340 . The position of light source device  310  is secured by mounting groove  320   a  (shown in  FIG. 3 ) of mold frame  330 . 
     Backlight unit  300  is placed on the bottom surface of main display panel  200 . Backlight unit  300  includes reflective sheet  320 , light guide plate  340 , optical sheet  350 , and rim frame  360  (shown in  FIG. 3 ). Light guide plate  340 , optical sheet  350 , and rim frame  360  are placed within a display area of main display panel  200  where pixel electrodes are formed and images are displayed. Light guide plate  340 , optical sheet  350 , and rim frame  360  are also placed within mold frame  330 . Mounting groove  320   a  of mold frame  330  is placed in a non-display area, and holds light source device  310 . 
     As second substrate portion  120  is placed between main display panel  200  and backlight unit  300 , light source device  310  is positioned inside backlight unit  300  in a manner that light source device  310  fits into mounting groove  320   a . Therefore, light source device  310  is securely positioned on a side of light guide plate  340 , and transmits light into light guide plate  340 . Second substrate portion  120  can further includes other driving elements such as boosting circuit  370 , which boosts voltage before applying the voltage to main display panel  200 . Mold frame  330  includes groove  370   a  to securely place the other driving elements such as boosting circuit  370  within mode frame  330 . 
     Third substrate portion  140  is disposed between backlight unit  300  and printed circuit board  500 . Therefore, connection substrate portion  130  bends to connect second substrate portion  120  to third substrate portion  130 . A conductive wiring layer of connection substrate portion  130  is formed in a single layer as in first substrate portion  110 . In this case, the thickness of connection substrate portion  130  is smaller than the thicknesses of second substrate portion  120  and third substrate portion  130 , in which the conductive wiring layer is generally formed in multiple layers and is not to be easily bent. 
     Third substrate portion  140  is a portion of first flexible printed circuit board  100  that is connected to printed circuit board  500 . Third substrate portion  140  includes at least one terminal  141  (shown in  FIG. 2B ) to be connected to main terminal portion  510  of printed circuit board  500 . At this time, main terminal portion  510  of printed circuit board  500  and terminal  141  of first flexible printed circuit board  100  are connected by soldering. Third substrate portion  140  does not include a driving element, and therefore, length of third substrate portion  140  is normally short. 
     In the case that main display panel  200  is a liquid crystal display, the liquid crystal display has polarizing plates  270   a  and  270   b , which are placed on the top of first substrate  210  and on the bottom of second substrate  220 , respectively. Detailed description of polarizing plates  270   a  and  270   b  will be omitted. 
     Second flexible printed circuit board  700  (shown in  FIG. 3 ) transfers electrical signals from printed circuit board  500  to sub-display panel  600  to drive sub-display unit  600 . Sub-terminal portion  720  of second flexible circuit board  700  is connected to sub-display unit  600 , and terminal portion  710  of second flexible circuit board  700  is connected to sub-terminal portion of printed circuit board  500  (not shown). 
     Referring to  FIG. 5A  to  FIG. 5E , an assembly process of first flexible printed circuit board  100  constructed as the embodiment of the present invention will be described. The assembly process shown in  FIGS. 5A-5E  is to describe how first flexible printed circuit board  100  is connected to other elements, and the actual assembly process of a flat panel display device is not limited to the steps described hereafter. 
     For the first step, terminal  111  of first substrate portion  110  of first flexible printed circuit board  100  is connected to pad portion  240  of main display panel  200  as shown in  FIG. 5A . Then, second substrate portion  120  is positioned on the bottom surface of main display panel  200  by bending first substrate portion  110  as shown in  FIG. 5B . Backlight unit  300  is placed on the bottom surface of main display panel  200 , and second substrate portion  120  is inserted between backlight unit  300  and main display panel  200 . Light source device  310  installed on second substrate portion  120  is positioned in mounting groove  320   a  formed on mold frame  330  of backlight unit  300  as shown in  FIG. 5C . Terminal  141  of third substrate portion  140  and main terminal portion  510  of printed circuit board  500  are soldered. Connection substrate portion  130  is bent so that third substrate portion  140  and printed circuit board  500  are positioned on the bottom surface of backlight unit  300  as shown in  FIG. 5D . During the process of soldering of printed circuit board  500  and third substrate portion  140 , heat is not transferred to second substrate portion on which light source device  310  is mounted. Therefore, second substrate portion  120  is not affected by the heat, and light source device  310  mounted on second substrate portion  120  can maintain a predetermined position and can maintain uniform brightness. 
     Terminal portion  710  and sub-terminal portion of printed circuit substrate  500  are soldered, and sub-terminal portion  720  and a pad portion of sub-display panel  600  are soldered. Sub-display panel  600  is placed on the bottom surface of printed circuit board  500  as shown in  FIG. 5E . 
       FIG. 6  shows a cellular phone with a dual type flat panel display device constructed according to the principles of the present invention. In the case of a flip type cellular phone  800 , the dual type flat panel display provides images in both surfaces of the flip part of cellular phone  800 . 
     Although a few embodiments of the present invention have been shown and described, a skilled person can devise further embodiments, modifications and variations of the invention on the basis of the teachings disclosed herein. For example, the change in a display panel structure of a liquid crystal display device, the change in a structure of a backlight unit structure and the change in a structure of a printed circuit board and the combination relations thereof, etc., can be made without departing from the scope of the invention. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

Technology Category: 3