Patent Publication Number: US-2018031918-A1

Title: Backlight unit and liquid crystal display device comprising the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Applications No. 2016-149608, filed Jul. 29, 2016; and No. 2017-109484, filed Jun. 1, 2017, the entire contents of all of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to a backlight unit and a liquid crystal display device comprising the same. 
     BACKGROUND 
     In recent years, liquid crystal display devices are widely used as a display device of smartphones, personal assistant devices (personal digital assistants) (PADs), tablet computers, vehicle-navigation systems, etc. In general, a liquid crystal display device comprises a liquid crystal display panel and a backlight unit overlaid on the rear surface of the liquid crystal display panel and illuminates the liquid crystal panel. The backlight unit includes a reflective layer, a light guide, an optical sheet, a light source unit which irradiates light which enters the light guide, a case (bezel) in which these members are accommodated, etc. The light source unit includes a wiring board and a plurality of light sources, for example, light-emitting diodes (LEDs) mounted on the wiring board. 
     As light source units, a side-view type LED and top-view type LED are known. In the side-view type LED, the light-emitting surface is provided normal to a mounting surface of the wiring board, whereas in the top-view type LED, the light-emitting surface is provided to face a mounting surface of the wiring board to be parallel thereto. 
     When using a side-view type LED as the light source unit, the LED is arranged such that the light-emitting surface thereof faces with the incidence surface of the light guide and the wiring board is parallel to the emission surface of the light guide, that is, parallel to the display surface of the liquid crystal panel. Because of this structure, if the wiring board is widened to enable routing of a great number of wiring lines on the wiring board, the wiring board may easily interfere with the display area, thus making it difficult to narrow the frame of the liquid crystal panel. 
     On the other hand, when using the top-view type LED as the light source unit, the LED is arranged in such a state that the light-emitting surface thereof faces with the incidence surface of the light guide and the wiring board is parallel to the incidence surface of the light guide, that is, to extend in the thickness direction of the backlight unit. With this structure, the wiring board do not interfere with the display area of the liquid crystal panel, and therefore it is advantageous for reducing the size of the backlight device and the width of the frame of the liquid crystal panel. 
     However, LEDs have, in some cases, a drawback due to their structure, that light passes through and leak from side surfaces other than the light-emitting surface. If light passes through and leaks from the LED, the brightness near the light source unit becomes uneven, undesirably causing an adverse effect on the display quality. When adopting a top-view type LED, the wiring board cannot be utilized for the alignment and fixation of the LED with respect to the light guide, which may undesirably cause an alignment error between the LED and the light guide. 
     SUMMARY 
     The present disclosure generally relates to a backlight unit or device and a liquid crystal display device. 
     In an embodiment, a backlight device is provided. The backlight device includes a light guide comprising a first main surface forming a light emission surface, a second main surface opposing the first main surface and an incidence surface crossing the first and second main surfaces; a light source unit comprising a wiring board and a light-emitting device on the wiring board, the light-emitting device comprising a light-emitting surface opposing the incidence surface of the light guide and a mounting surface located on an opposite side to the light-emitting surface and mounted on the wiring board, the wiring board opposing the incidence surface while interposing the light-emitting device therebetween; and an optical sheet on the first main surface of the light guide, comprising a light source-side end portion extending over the incidence surface to a position opposing the light-emitting device. 
     In another embodiment, a liquid crystal display device is provided. The liquid crystal display device includes a liquid crystal panel comprising a first substrate, a second substrate opposed to the first substrate and a liquid crystal layer between the first substrate and the second substrate; and a backlight device opposed to the first substrate; the backlight device including a light guide comprising a first main surface forming a light-emitting surface, a second main surface opposing the first main surface and an incidence surface crossing the first and second main surfaces; a light source unit comprising a wiring board and a light-emitting device on the wiring board, the light-emitting device comprising a light-emitting surface opposing the incidence surface of the light guide and a mounting surface located on an opposite side to the light-emitting surface and mounted on the wiring board, the wiring board opposing the incidence surface while interposing the light-emitting device therebetween; and an optical sheet on the first main surface of the light guide and comprising a light source-side end portion extending over the incidence surface to a position opposing the light-emitting device. 
     Additional features and advantages are described herein, and will be apparent from the following Detailed Description and the figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing a liquid crystal display device of the first embodiment from a display surface side. 
         FIG. 2  is a perspective view showing the liquid crystal display device from a rear surface side. 
         FIG. 3  is a perspective view showing the back surface side of the liquid crystal display device in the state where a main FPC is folded back and fixed. 
         FIG. 4  is an exploded perspective view of the liquid crystal display device. 
         FIG. 5  is an exploded perspective view of a backlight unit of the liquid crystal display device. 
         FIG. 6A  is a perspective view showing a light source unit of the backlight unit. 
         FIG. 6B  is a perspective view showing a light source unit of the backlight unit according to a modification. 
         FIG. 7  is a perspective view showing a light source side of the liquid crystal display device exploded along line A-A of  FIG. 3 . 
         FIG. 8  is a perspective view showing the liquid crystal display device, including the cross section corresponding to  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments will be described hereinafter with reference to the accompanying drawings. In general, according to one embodiment, a backlight device comprises a light guide comprising a first main surface forming an emission surface, a second main surface opposing the first main surface and an incidence surface crossing the first main surface and the second main surface; a light source unit comprising a wiring board and a light-emitting device on the wiring board, the light-emitting device comprising a light-emitting surface opposing the incidence surface of the light guide and a mounting surface on an opposite side to the light-emitting surface and mounted on the wiring board, the wiring board opposing the incidence surface while interposing the light-emitting device therebetween; and an optical sheet on the first main surface of the light guide, comprising a light source-side end portion extending over the incidence surface to a position opposing the light-emitting device. 
     Note that the disclosure is presented for the sake of exemplification, and any modification and variation conceived within the scope and spirit of the invention by a person having ordinary skill in the art are naturally encompassed in the scope of invention of the present application. Furthermore, a width, thickness, shape, and the like of each element are depicted schematically in the figures as compared to actual embodiments for the sake of simpler explanation, and they do not limit the interpretation of the invention of the present application. Furthermore, in the description and figures of the present application, structural elements having the same or similar functions will be referred to by the same reference numbers and detailed explanations of them that are considered redundant may be omitted. 
     Embodiment 
       FIGS. 1 and 2  are perspective views showing a liquid crystal display device according to an embodiment as seen from a display surface side and a rear side, respectively.  FIG. 3  is a perspective view showing the rear surface side of the liquid crystal display device in the state where a main FPC on which a driver IC is mounted is folded onto the rear surface side.  FIG. 4  is an exploded perspective view of the liquid crystal display device. 
     A liquid crystal display device  10  can be incorporated into, for example, various kinds of electronic devices, such as smartphones, tablet computers, mobile phones, notebook PCs, portable game consoles, electronic dictionaries, television sets and car-navigation systems, to be used. 
     As shown in  FIGS. 1, 2 and 4 , the liquid crystal display device  10  comprises an active-matrix liquid crystal panel  12 , a transparent cover panel  14  overlaid on a display surface  12   a , which is one flat surface of the liquid crystal panel  12  and configured to cover the entire display surface  12   a , and a backlight unit  20  as a backlight device, provided to face the rear surface, which is the other flat surface of the liquid crystal panel  12 . 
     The liquid crystal panel  12  comprises a rectangular plate shaped first substrate SUB, a rectangular plate shaped second substrate SUB 2  opposed to the first substrate SUB 1 , and a liquid crystal layer LQ held between the first substrate SUB 1  and the second substrate SUB 2 . A circumferential portion of the second substrate SUB 2  is attached to the first substrate SUB 1  with a sealing member SE. On the surface of the second substrate SUB 2 , a polarizer PL 2  is attached to form the display surface  12   a . A polarizer PL 1  is attached on a surface (a rear surface of the liquid crystal panel  12 ) of the first substrate SUB 1 . 
     In the liquid crystal panel  12 , a rectangular display area (active area) DA is provided in a region inner side of the sealing member SE as the liquid crystal panel  12  is seen in plan view (, which is a view of the liquid crystal panel from the normal direction of the display surface of the panel), to display images on the display area DA. A rectangular frame area ED is provided around the display area DA. The liquid crystal panel  12  is a transmissive liquid crystal panel having a transmissive display function of displaying imaging by selectively transmitting or modulating the light from the backlight unit  20  to the display area DA. The liquid crystal panel  12  may have a structure provided for the lateral electric field mode which mainly utilizes a lateral electric field substantially parallel to a surface of the substrate, or a structure provided for the vertical electric field mode which mainly utilizes a vertical electric field crossing the main surface of the substrate. 
     In the example illustrated, a flexible printed circuit board FPC (main FPC)  23  is joined to a shorter side end of the first substrate SUB 1  and extends from the liquid crystal panel  12  outward. On the main FPC  23 , semiconductor devices including a driver IC  24  are mounted as signal supply sources which supply signals necessary to drive the liquid crystal panel  12 . A sub-FPC  25  is joined to the extending edge of the main FPC  23 . On the sub-FPC  25 , a capacitor C 1 , a connector  26  and the like are mounted. As shown in  FIG. 3 , the main FPC  23  and the sub-FPC  25  are folded over along a shorter-side end edge of the first substrate SUB 1  and are overlaid on a bottom of the backlight unit  20 . As will be described later, the main FPC  23  and the sub-FPC  25  are adhered to the bottom of the backlight unit  20  with an adhesive member such as a double-stick tape. 
     As shown in  FIGS. 1 and 4 , the cover panel  14  is formed into a rectangular plate shape from glass or an acrylic transparent resin, for example. The cover panel  14  has dimensions (width and length) greater than those of the liquid crystal panel  12  and an area greater than that of the liquid crystal panel  12  in planar view. The lower surface (rear surface) of the cover panel  14  is adhered to the display surface  12   a  with an adhesive layer made from a transparent adhesives or adhesive, for example, and covers the entire display surface  12   a.    
     On the lower surface (rear surface, surface on a liquid crystal panel side) of the cover panel  14 , a frame-shaped light-shielding layer RS is formed. In the cover panel  14 , a region other than the region which opposes the display area DA of the liquid crystal panel  12  is shielded by the light-shielding layer RS. The light-shielding layer RS may be formed on the upper surface (outer surface) of the cover panel  14 . Note that the cover panel  14  may be omitted according to the use status of the liquid crystal display device  10 . 
     The backlight unit  20  comprises a case  22 , and optical members and a light source unit installed or arranged in the case  22 . The backlight unit  20  is disposed to oppose the rear surface of the liquid crystal panel  12  and attached to the rear surface, that is, for example, the polarizer PL 1  with a frame-shaped adhesive member, for example, a double-stick tape TP 1 . 
     As shown in  FIG. 4 , in this embodiment, the widths of the edges of the rectangular frame-shaped non-display area ED corresponding to the respective sides of the rectangular display area DA are all the same or substantially the same. More specifically, widths WL 1  and WL 2  of the non-display area ED, which correspond to a pair of long sides of the display area DA are equal to each other (WL 1 =WL 2 ). Note here that the widths WL 1  and WL 2  are referred to as the size from the boundary between the display area DA and the non-display area ED to the outer edge of the first substrate SUB 1  (and the second substrate SUB 2 ) in the long sides of the display area. Moreover, of a pair of short sides of the display area DA, the width of the non-display area ED on a side where the flexible printed circuit substrate  23  is provided (, which may be referred to as the mounting side, hereafter) is defined as WS 1 , and the width of the non-display area ED on a short side edge opposite to thereto is defined as WS 2 . Here, WS 2 ≦WS 1  should be satisfied and WS 1 /WS 2 ≦2.0 is preferable. More preferably, WS 1 /WS 2 ≦1.5, and still more preferably, WS 1 /WS 2 ≦1.0 can be adopted. Here, the width WS 1  is defined as the size from the boundary between the display area DA and the non-display area ED to the outer edge of the second substrate SUB 2  in the short side on the mounting side of the display area. The width WS 2  is defined as the size from the boundary of the display area DA and the non-display area ED to the outer edge of first substrate SUB 1  (and second substrate SUB 2 ) in the short side opposite to the mounting side. 
     Moreover, the above-described structures should preferably satisfy: WL 1 =WL 2 &lt;1.5 mm and WS 2 &lt;1.5 mm, and more preferably, WL 1 =WL 2 &lt;1.0 mm and WS 2 &lt;1.0 mm. Furthermore, in any of these structures, WL 1 =WL 2 =WS 2  can be adopted. 
     With the above-described conditions, this embodiment can achieve such a structures that the width WS 1  of the mounting side of the liquid crystal panel  12  can be remarkably narrowed then the conventional technique, i.e., the width WS 1  of the non-display area on the mounting side can be made substantially equal to that of the other regions of the non-display area ED. Thus, such a liquid crystal panel  12  can be provided with a narrowed frame in which the widths of all the sides of the non-display area ED which surrounds the display area DA are all substantially the same. 
     Next, the backlight unit  20  will be described in more detail. As described above, in order to achieve a significantly narrowed frame in the non-display area of the mounting side as compared to the conventional techniques, a structure different from that of the conventional techniques is employed especially in the light-source side portion of the backlight unit. The structure of the light-source side portion of the backlight unit will be described in more detail. 
       FIG. 5  is an exploded perspective view of the backlight unit  20 .  FIG. 6A  includes perspective views of the light source unit, each including a partially expanded view thereof.  FIG. 7  is a cross section of the light-source side portion of the backlight unit taken along line A-A in  FIG. 3 .  FIG. 8  is an exploded perspective view showing the light-source side portion of the backlight unit  20 . 
     As shown in  FIG. 5 , the backlight unit  20  comprises case (bezel)  22 , a plurality of optical members arranged in the case  22 , and the light source unit  50  which supplies the light which enters into the optical members. 
     The case  22  is formed into a flat rectangular lid by, for example, bending or press-molding a stainless plate material having a thickness of 0.1 mm. The case  22  includes a rectangular bottom  16 , a pair of long-side walls  18   a  and a pair of short-side walls  18   b , formed to stand on side edges of the bottom  16  and integrated as one body. As shown in  FIGS. 5 and 7 , in this embodiment, the bottom  16  comprises an end located on a side of one short side and opposing the light source unit  50 , which is formed into a step portion (projection)  16   a  one step lower than the other portion, and to slightly protrude outwards, more specifically, to a direction away from the light-source unit  50  accommodated in the case  22 . In planar view, the bottom  16  is formed slightly larger in the dimensions of the first substrate SUB 1  of the liquid crystal panel  12 , and also smaller than the dimensions (length, width) of those of the cover panel  14 . 
     The long-side walls  18   a  are formed to stand substantially perpendicular to the bottom  16  and extend over the long sides of the bottom  16  in full length. The short-side walls  18   b  are formed to stand substantially perpendicular to the bottom  16  and extend over the short sides of the bottom  16  in full length. The height of these side walls  18   a  and  18   b  from the bottom  16  is, for example, about 1 mm. 
     As shown in  FIGS. 5 and 7 , the bottom  16  has a plurality of; for example, three openings  30 . The openings  30  are formed near one short side of the bottom  16  and arranged to be spaced from each other along the short side over substantially full length. In this embodiment, the openings  30  are provided in the step portion  16   a  of the bottom  16 . A width of the openings  30  is greater than a thickness of the wiring board of the light source unit  50 , which will be described later. 
     The backlight unit  20  includes, as optical members, a reflective sheet RE having a rectangular shape in planar view, a light guide LG, a plurality of, for example, two first optical sheets OS 1  and second optical sheets OS 2 . The number of optical sheets is not limited to two, but three or more sheets may be used. 
     The reflective sheet RE is formed to have outer dimensions substantially equal to the inner dimensions of the bottom  16  of the case  22 . The reflective sheet RE has a thickness of 200 μm or less, preferably, 50 to 90 μm and a reflectivity of 90% or higher, preferably, 95% or higher. The reflective sheet RE is provided on the bottom  16  to covers substantially the entire portion of the flat section of the bottom  16  and to oppose only the step portion  16   a . With this structure, the openings  30  are not covered by the reflective sheet RE. As shown in  FIG. 7 , the end REa on the light source side of the reflective sheet RE is extends over the display area DA of the liquid crystal panel  12  to the light source side, and is located on a front side to an incidence surface EF of the light guide LG. A portion of the reflective sheets RE including the end REa is attached to the bottom  16  by double-stick tape TP 6 . 
     As shown in  FIG. 5  and  FIG. 7 , the rectangular light guide LG comprises a first main surface S 1  functioning as an light-emission surface, a second main surface S 2  opposing the first main surface S 1  and a plurality of, for example, a pair of long-side side surfaces and a pair of short-side side surfaces, which connect side edges of the first main surface S 1  and the second main surface S 2  to each other. In this embodiment, one side surface on a short side of the light guide LG is the incidence surface EF. The light guide LG has, for example, a thickness of about 0.23 to 0.32 mm. Moreover, the light guide LG is formed from, for example, a resin such as polycarbonate, an acrylic or silicon resin. 
     The light guide LG is formed to have outer dimensions (length and width) slightly smaller than the inner dimensions of the case  22  and slightly larger than the display area DA of the liquid crystal panel  12  in planar view. The light guide LG is accommodated in the case  22  and placed on the reflective sheet RE while the second main surface S 2  opposes the reflective sheet RE. Thereby, the first main surface (emission surface) S 1  of the light guide LG is located substantially parallel to the bottom  16  and the incidence surface EF is located substantially perpendicular to the bottom  16 . As shown in  FIG. 7 , the incidence surface side end of the light guide LG extends over the display area DA to the light source side. Furthermore, the incidence surface side end of the light guide LG extends over the end REa of the reflective sheet RE to the light source side. Thereby, the incidence surface EF is placed to oppose the side wall  18   b  by the short side of the case  22  with a slight gap therebetween. The gap should preferably be 1.0 mm or less, more preferable 0.8 mm or less, and still more preferably, 0.5 mm or less. Conventionally, the gap is about 3.0 mm to 4.0 mm, and as compared to the conventional structure, the gap between the short side wall  18   b  and the light guide LG in this embodiment is remarkably narrow. Then, the light source unit  50  is provided in such a gap. 
     As shown in  FIGS. 5 and 6A , the light source unit  50  comprises, for example, a slender belt-shaped wiring board  52  and a plurality of light sources mounted in lines on the wiring board  52 . As light sources, light-emitting devices, for example, light-emitting diodes (LEDs)  54  are employed. 
     A flexible printed circuit board (FPC) is used for the wiring board  52 . That is, the wiring board  52  includes an insulating base formed from polyimide or the like and a conductive layer such as a copper foil, formed on the insulating base. The conductive layer is patterned to form a plurality of contact pads  55  and wiring lines  56 . 
     The wiring board  52  includes a belt-shaped mounting portion (mounting region)  52   a  extending along the side wall  18   b  of the case  22 , and a plurality of for example, three belt-shaped lead-out portions (wiring regions)  52   b  extending from one side edge of the mounting portion  52   a , all integrated as one body. A length L 1  of the mounting portion  52   a  is substantially equal to a length of the incidence surface EF. The three lead-out portions  52   b  are arranged to be spaced from each other in a longitudinal direction of the mounting portion  52   a.    
     The contact pads  55  are formed in the mounting portion  52   a  and are arranged in a longitudinal direction of the mounting portion  52   a . The wiring lines  56  extend respectively from the contact pads  55  to the lead-out portions  52   b  and are routed on the lead-out portions  52   b.    
     As shown in  FIG. 6A , the LEDs  54  used here are each a top-view type LED. Each LED  54  comprises a substantially rectangular parallelepiped case (package)  60  formed of a resin, for example. An upper surface of the case  60  forms a light-emitting surface  62  and a bottom surface of the case  60 , which is located on an opposite side to the light-emitting surface  62 , forms a mounting surface. Contact terminals  63  are provided on the bottom of the case  60 . 
     Note that each LED  54  is formed into a substantially rectangular parallelepiped, but the shape is not limited to this. For example, the LED  54  may comprise projections and recesses in side surfaces, or may be formed into a curvy shape. 
     As to each LED  54 , the bottom of the case  60  is mounted on the mounting portion  52   a , and thus the contact terminals  63  are electrically connected to the contact pads  55 . The light-emitting surface  62  is set substantially parallel to the wiring board  52 , and the LED  54  emits light from the light-emitting surface  62  in a direction substantially perpendicular to the wiring board  52 . 
     The LEDs  54  are mounted on the mounting portion  52   a  so that the longitudinal direction of the case  60  is aligned with the longitudinal direction of the mounting portion  52   a . The width W 1  of the mounting portion  52   a  is 1.1 to 1.5 times the width W of the LED  54 . In this embodiment, the light source unit  50  includes, for example, thirty to fifty LEDs  54 , the number of which may vary according to the width of the display area DA. The number of the LEDs installed is about 2.5 to 3 times that of the conventional structure of the same display area. The LEDs  54  are arranged in one row on the mounting portion  52   a  from one longitudinal end to the other of the mounting portion  52   a.    
     Note that in this embodiment, an arrangement pitch P of the LEDs  54  is set to about 1.1 to 1.5 times of the length L of each LED  54  in the aligning direction, and a gap D of each adjacent pair of LEDs  54  is set to about 10% to 50% of the length L. Conventionally, the arrangement pitch of LEDs is set to two times or more the length of the LEDs. In this embodiment, the gap D between the LEDs  54  is set narrower than conventional cases, and thus the region of uneven brightness, which may be generated between each adjacent pair of light sources, can be narrowed. 
     In this embodiment, a belt-shaped fixing tape TP 2  as a second adhesive member for fixing and positioning each LED  54  is adhered onto a side surface of each LED  54 . The fixing tape TP 2  is used such that about a half of the region in a width direction is adhered to each LED  54 , and a remaining half of the region is adhered to the light guide LG. The fixing tape TP 2  comprises a belt-shaped base material  55   a  formed of for example, polyethylene terephthalate (PET), and an adhesive layer  55   b  or sticker layer formed on at least one surface of the base material  55   a . Further, at least one of the base material  55   a  and the adhesive layer  55   b  is colored in black with, for example, fine black particles, black ink or the like. Thus, the fixing tape TP 2  forms a light-shielding member with light shielding property. The fixing tape TP 2  employed here is not limited to one continuous tape, but may be of a plurality of divided fixing tapes. 
     The number of LEDs  54  mounted is not limited to thirty to fifty, but may be increased or decreased as needed. When LEDs longer than the length L 1  are used, the number of LEDs to be mounted may be decreased. According to a modification shown in  FIG. 6B , the length L 1  of the LEDs  54  is set to about 4 to 5 times that of the LEDs  54  shown in  FIG. 6A . The width W 1  of the mounting portion  52   a  of the wiring board  52  is 1.1 to 1.5 times the width W 1  of the LEDs  54 . The arrangement pitch P of the LEDs  54  is set to about 1.1 to 1.5 times the length L 1  of the LEDs  54 , and the gap D between adjacent pairs of LEDs  54  is about 10% to 50% of the length L 1  of the LEDs  54 . 
     As shown in  FIGS. 7 and 8 , the light source unit  50  configured as described above is arranged in the case  22 . The mounting portion  52   a  of the wiring board  52  and the LEDs  54  are arranged between the incidence surface EF of the light guide LG and the side wall  18   b  of the case  22 . The light-emitting surfaces  62  of the LEDs  54  oppose or abut against the incidence surface EF. The mounting portion  52   a  is attached to the inner surface of the side wall  18   b  by an adhesive member, for example, a double-stick tape TP 3 . The mounting portion  52   a  opposes the incidence surface EF via the LEDs  54  interposed therebetween. Note that the adhesive material is not limited to the double-stick tape TP 3 , but, for example, a UV-curing adhesive can be used as well. The light emitted from the LEDs  54  contains light of an ultraviolet region, and therefore it can cure the UV-curing adhesive with this ultraviolet ray. 
     The fixing tape TP 2  is adhered to the side surfaces of all the LEDs  54  (the side surface of the case  22  on the bottom  16  side) and the second main surface S 2  of the light guide LG. The LEDs  54  are positioned with respect to the light guide LG and fixed there with the fixing tape TP 2 . 
     The LEDs  54  each comprises four side surfaces perpendicularly crossing the light-emitting surface  62 . Of the four side surfaces, a long-side surface  54   b  located on the bottom  16  side is arranged to be substantially flush with the second main surface S 2  of the light guide LG. The fixing tape TP 2 , more specifically, about a half of the region in its width direction, is adhered on the surface side  54   b  of the LED  54 , and the rest of the half is adhered onto an incidence surface-side end portion of the second main surface S 2 . Each LED  54  has a light emission center C at a location of an equal distance from both of the light-emitting surface  62  and the mounting surface. The fixing tape TP 2  covers at least a region of the side surface  54   b  of the LED  54 , which opposes the emission center C. Further, the fixing tape TP 2  is arranged along the reflective sheet RE in a surface direction of the light guide LG. That is, the fixing tape TP 2  extends to the vicinity of the light source-side end portion REa of the reflective sheet RE, and is arranged in a surface direction of the reflective sheet RE with a slight gap therebetween. Thus, the fixing tape TP 2  and the reflective sheet RE are not stacked on each other. 
     Thus, the LEDs  54  are fixed to the light guide LG via the fixing tape P 2 , and the light-emitting surface  62  is positioned to abut against the incidence surfaces EF of the light guide LG. Further, the fixing tape TP 2  shields the side surface  54   b  side of each LED  54  to inhibit light from leaking from the LEDs  54 . 
     According to this embodiment, the fixing tape TP 2  is formed to be thicker than the reflective sheet RE, and is placed in the step portion  16   a  of the bottom  16 . The fixing tape TP 2  is provided to abut against the inner surface of the bottom  16  and cover at least partially each of the openings  30 . 
     Further, as shown in  FIG. 7 , the end portion of the fixing tape TP 2  on the light guide LG opposes the end REa of the reflective sheet RE in the non-display area ED. Furthermore, the end portion of the fixing tape TP 2  on the light guide LG opposes end portions of both the polarizing plates PL 1  and PL 2  via the light guide LG (they are stacked on each other in planar view). In the end portion of the light guide LG, the region thus adhered to the fixing tape TP 2  is located to be extremely close to the LEDs  54  as the light source and to oppose the fixing tape TP 2  with light-shielding property without opposing the reflective sheet RE. Therefore, at the end portion of the light guide LG, the light from the light source is not reflected on the second main surface S 2 , and therefore no substantial light is irradiated onto the light emission surface (the first main surface S 1 ) from that region. However, by covering the region by polarizer PL 1  and PL 2 , it is possible to suppress the emitted light from unexpectedly leaking to the display area DA, which may cause the degradation in display quality. 
     As shown in  FIGS. 2 and 5 , on the rear surface side of the bottom  16 , a belt-shaped connection FPC  72  is fixed by a double-stick tape TP 5 . The connection FPC  72  extends along a light-source side short edge of the bottom  16 . The connection FPC  72  includes a connection portion  73  and a connector  74  is provided at the extending end of the connection portion  73 . 
     As shown in  FIGS. 2, 7 and 8 , three lead-out portion  52   b  of the wiring board  52  penetrate the openings  30 , respectively, to lead out from the rear side of the bottom  16 , and further bent towards a bottom  16  side so as to oppose the rear surface thereof. The lead-out end of each lead-out portion  52   b  is joined to the connection FPC  72  by solder, for example. Thereby, the wiring lines  56  of the wiring board  52  are electrically connected to the wiring lines of the connection FPC  72 . As described above, the width of the openings  30  to which the lead-out portions  52   b  penetrates is greater than the thickness of the wiring board  52 . Therefore, when bending the lead-out portions  52   b , they can be bent at a comparatively great curvature without interfering with the bottom  16 . 
     On the rear surface of the bottom  16 , a belt-shaped reinforcing double-stick tape TP 7  is adhered. The reinforcing double-stick tape TP 7  extends along the light source-side short edge of the bottom  16  so as to partially cover each of the openings  30 . The lead-out portions  52   b  led out from the rear surface side via the openings  30  are bent, and the reinforcing double-stick tape T 7  is applied thereon. Thus, the lead-out portions  52   b  are held in the bent state. 
     Furthermore, in this embodiment, a part of the reinforcing double-stick tape TP 7  extends while blocking each of the openings  30 , and abuts to the fixing tape TP 2  via a spacer  61 . 
     According to this embodiment, as the first optical sheet OS 1  and the second optical sheet OS 2 , a light-transmissive diffusion sheet and a light-transmissive prism sheet, formed from, for example, a synthetic resin such as polyethylene terephthalate, are used. As shown in  FIG. 5 , the first optical sheet OS 1  is formed into a rectangular shape having slightly larger (longer) outer dimensions than those of the light guide LG. The first optical sheet OS 1  is overlaid on the first main surface S 1  of the light guide LG, to cover the entire first main surface S 1 . Similarly, the second optical sheet OS 2  is formed into a rectangular shape having slightly larger (longer) outer dimensions than those of the light guide LG. The second optical sheet OS 2  is overlaid on the first optical sheet OS 1 , to cover substantially the entire first optical sheet OS 1 . 
     As shown in  FIGS. 7 and 8 , a short-side end portion OS 1   a  of the first optical sheet OS 1  extends over the incidence surface EF to a position opposing the LED  54 . The end portion OS 1   a  extends to the region opposing the light emission center C of the LED  54 . 
     The first optical sheet OS 1  can adopt such a structure that a light-shielding portion RS 2  (for example, black printing or a black film) is provided on an edge portion of the first optical sheet OSA, overlapping the light source LED and the incidence surface EF, as indicated by an alternate long and two short dashes line shown in  FIG. 7 . By adopting such a structure, the light leaking from the light source can be absorbed by the light-shielding portion RS 2 , and the deterioration in display quality, resulting from the light thus leaking entering the display area DA side can be inhibited more effectively. 
     The light-shielding portion RS 2  should preferably be provided in a predetermined region which covers from the end edge of the first optical sheet (diffusion sheet) OS 1  to at least the LED  54  and the incidence surface EF, or more preferably from the incidence surface EF towards the inner side of the light guide LG to such a degree to cover the area approximately equivalent to the thickness of the light guide LG. Moreover, the light-shielding portion RS 2  can also adopt such a structure that, for example, a black light-shielding sheet is adhered on either one of the surfaces of the first optical sheet OS 1 , or the corresponding region of the light-shielding sheet is painted in black. 
     As described above, in this embodiment, the LEDs  54  are attached and fixed to the light guide LG by the fixing tape TP 2 . As a result, each of the light-emitting surface  62  of the LEDs  54  abuts to or oppose with a slight gap, the incidence surface EF of the light guide LG, and this state is firmly maintained. Thus, it is possible to inhibit the LEDs  54  from changing their direction with respect to the incidence surface EF in case of an external shock and the like. Moreover, the sites of the double-stick tape TP 2  and the light-shielding portion RS 2 , which oppose the LEDs  54  and the incidence surface EF, are formed in black, and thus a black light-shielding region is provided in each of the spaces above and below the light-emitting surface  62  of each LED  54 . In the vicinity of each LED  54  as a light source, the light is emitted radially from the light-emitting surface  62 . Of the radially emitted light, incident light entering the incidence surface EF of the light guide LG at a steep angle, for example, 45° or higher, to the normal direction of the incidence surface EF is absorbed by the tape TP 2  and the light-shielding portion RS 2 . On the other hand, incident light entering at a moderate angle, for example, less than 45° to the normal direction travels straight inside the light guide LG or proceeds all the way through to the light guide LG while repeating reflection. As a result, the leakage of light at least towards the up-and-down directions from the light-emitting surface  62  can be restricted remarkably. Here, naturally, the light originally needed is effectively used, and further the light unexpectedly emitted towards the shielding region is absorbed, thereby making it possible to suppress the unexpected light emission towards the display area DA at an angle which is not originally needed. 
     Note that in the above-provided description, an angle made with respect to the normal direction of the incidence surface EF, which is less than 45° is defined as a moderate angle, whereas an angle which is 45° or more is defined as steep. But the definition of angle may be changed as needed according to the refraction characteristics of the light guide LG, and can be also defined with reference to a larger angle, for example, 50° or 60°, as moderate or steep. 
     As shown in  FIG. 7 , a light source-side end portion OS 2   a  of the second optical sheet OS 2  projects from the display area DA towards the non-display area ED to overlap the end edge of the first optical sheet OS 1 , and also extend slightly over the incidence surface EF. The end portion OS 2   a  is located to overlap the end portion OS 1   a  of the first optical sheet OS 1  and the light-shielding portion RS 2 . 
     As described above, in the non-display area ED as well, the first optical sheet OS 1  and the second optical sheet OS 2  formed from a prism sheet are stacked on each other and arranged to oppose the end portion of the light guide LG, the incidence surface EF, the light-emitting surface  62  of the LED  54  and the light-shielding portion RS 2 . With this structure, unexpected leaking light, which is easily generated in a space close to such a kind of a light-emitting site and directed towards the liquid crystal panel  12 , is guided to pass the first optical sheet OS 1  and the second optical sheet OS 2  as so in the display area AD. Therefore, disturbance of the emission light from the backlight device, especially in the edge portion of the display area (end edge of a light-emitting side) can be suppressed. 
     As shown in  FIG. 7 , a width WT from the boundary between the display area DA and the non-display area ED to the mounting side end of the first substrate SUB 1  should preferably be 1.5 mm or less, and more preferably, 1.3 mm or less. 
     In this embodiment, each LED  54  of the light source unit  50  is provided in the position overlapping the end edge of the first substrate SUB 1  in planar view. As a result, the distance from the boundary between the display area DA and the non-display area ED to the light-emitting surface  62  of the LED  54  is reduced to 1.3 mm or less, or more preferably, 0.8 mm or less, which is remarkably narrower than those of the conventional structures. 
     According to the conventional structures, the arrangement pitch of the LEDs serving as the point source lights is set about 2 times or more the length of the LEDs, and the gap between the light-emitting surface  62  and the boundary of the display area is about 2.0 mm to 3.0 mm. Thus, according to the conventional structures, the arrangement pitch of the point source lights is widened and the interval from each point source light to the outermost edge of the display area DA is set to be large to some degree, so as to prevent non-uniformity in luminance between adjacent pairs of the point sources lights (LEDs) from appearing in the display area DA. Furthermore, the light entering the incidence surface of the light guide from the light-emitting surface of the LED at an unexpected angle is repeatedly reflected between the light guide and the reflective sheet within the gap, thereby converting the light to be emitted towards the display. Thus, the gap functions as a buffer in a sense. 
     In this embodiment, the gap as the buffer is remarkably narrow, and it is difficult to solve the problem of the non-uniformity in luminance between the light sources described above with merely such a gap. According to this embodiment, a great number of LEDs  54  are arranged to solve the drawback of the non-uniformity in luminance and further the light-emitting surface and the surrounding of the incidence surface are shielded. Thus, unexpected light from the light-emitting surface  62  is absorbed to achieve stable emission of the light to the display area DA. 
     The backlight unit  20  configured as above is adhered to the rear surface of the liquid crystal panel  12  by the frame-shaped double-stick tape TP 1 . As shown in  FIGS. 4 and 7 , the double-stick tape TP 1  is adhered to the end edges of the side walls  18   a  and  18   b  and the outer circumferential portion of the second optical sheet OS 2 . A part of the double-stick tape TP 1  is bent to extend toward the bottom  16  and adhered to an outer surface of the side wall  18   b  on the light source side. 
     Further, on a liquid crystal panel  12  side, the double-stick tape TP 1  is adhered to the circumferential portion of the polarizer PL 1  and the circumferential portion of the first substrate SUB 1 , which interpose a spacer  82  therebetween. 
     As shown by two dots and dashed lines in  FIG. 4 , the double-stick tape TP 1  may be adhered also to the outer surfaces of the side walls  18   a  and the other side wall  18   b.    
     As shown in  FIGS. 3 and 7 , the main FPC 23  and the sub FPC 25  extending from the liquid crystal panel  12  are folded back to the rear surface side of the bottom  16  along the side wall  18   b  of the case  22 . The main FPC 23  and the sub FPC 25  are adhered to the bottom  16  with an adhesive member not shown. Moreover, the connector  74  of the connection FPC 72  is connected to the connector on the sub FPC 25 . 
     In the liquid crystal display device  10  configured as above, the light source unit  50  employs top-view type LEDs  54 , and therefore the wiring board  52  of the light source unit  50  can be disposed to oppose the incidence surface EF of the light guide LG while interposing the LEDs  54  therebetween. With this structure, the wiring board  52  does not interfere optical members such as an optical sheet and a light guide and the display area DA of the liquid crystal panel  12 , and therefore the light source-side frame area ED can be greatly reduced. 
     By arranging the light source-side end portion OS 1   a  of the first optical sheet OS 1  to oppose the LEDs  54 , the light leaking from the case-side surface of each LED  54  to the optical sheet side can be diffused by the first optical sheet OS 1 . In this embodiment, the light-shielding portion RS 2  is provided to shield the light leaking from the case-side surface of each LED  54  to the optical sheet side. Thus, it becomes possible to suppress the light leaking in unnecessary directions and to prevent non-uniformity in luminance and the occurrence of a hot spot. As a result, the display quality of the display device can be improved. 
     Moreover, the light-shielding portion RS 2  is formed by, for example, printing on the optical sheet OS 1  and it is remarkably thin as compared to the optical sheet OS 1 . Therefore, the light source-side end portion of the optical sheet OS 1  and the light source-side end portion of the optical sheet OS 2  are arranged while they are set along the first main surface S 1  of the light guide LG. Thus, the end portion is not warped or bent. As a result, an unexpected light path is not formed in this portion, and therefore it becomes easy to manage the light path from the light source of the LEDs  54 . Further, the light-shielding portion RS 2  exists in the portion, and therefore, in cooperation with the light-shielding effect by the light-shielding portion RS 2 , the generation of unexpected leaking light near the light source can be remarkably suppressed. 
     Moreover, according to this embodiment, the fixing tape (second adhesive member) TP 2  is adhered on the side surface of each LED  54  and the second main surface S 2  of the light guide LG, and thus the LEDs  54  are positioned and fixed to the light guide LG. With this structure, the LEDs  54  can be held in the state that the light-emitting surfaces thereof abut against the incidence surface EF of the light guide LG, and the optical axis of each LED  54  can be accurately aligned with the incidence surface EF. Further, the fixing tape TP 2  has a light-shielding effect, and therefore the light leaking out from the case-side surface of each LED  54  and the light leaking out from the boundary between the light-emitting surface of each LED  54  and the light guide LG can be shielded by the fixing tape TP 2 . Thereby, the unnecessary leakage of light can be prevented more reliably, making it possible to further improve the display quality of the display device. 
     According to this embodiment, the wiring board  52  of the light source unit  50  comprises the lead-out portion  52   b  drawn out to the rear surface side of the bottom  16 , and the lead-out portion  52   b  abuts against the bottom  16 . With this structure, the heat generated from the LEDs  54  is transferred to the case  22  of high heat capacity via the wiring board  52 , and further the heat is radiated outside from the case  22 . Thus, an excessive increase in temperature in the light source portion of the light source unit  50  can be suppressed, and regional increase in temperature in the back light unit  20  can be prevented. 
     As described above, according to this embodiment, a backlight device which can reduce the width of the frame and improve the display quality, and a liquid crystal display device comprising the backlight device can be provided. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions. 
     Note that all the structures and production steps which can be carried out by any modification and variation conceived within the scope and spirit of the invention by a person having ordinary skill in the art based on each structural elements described in the embodiments are naturally encompassed in the scope of invention of the present application. Further, regarding the present embodiments, any advantage and effect which would be obvious from the description of the specification or arbitrarily conceived by a skilled person are naturally considered achievable by the present invention. 
     For example, the light-shielding portion provided in the light source-side end portion of the first optical sheet may be formed from, not only, the black printing or light-shielding film described above, but also some other light-shielding layer. Further, since only the light source-side end portion of the diffusion sheet as the optical sheet can diffuse the leaking light and attenuate it, the light-shielding layer can be omitted. 
     The outer and inner shapes of the structural members of the display panel and backlight unit are not limited to rectangular, but one or both of the outer and inner shapes may be polygonal, circular, elliptical or combination of any of these in planar view. The materials of the structural members of the display device are not limited to those described in the example provided above, but may be selected from various types.