Abstract:
An LED display includes a substrate on which an LED device including an LED element is mounted. The display also includes a light exit surface through which light emitted from the LED device exits. The light exit surface is spaced from the LED device mounting surface of the substrate in the substrate&#39;s thickness direction. The LED device is provided at a position which does not overlap the position of the light exit surface in the in-plane direction of the substrate. The LED display further includes a reflection region for reflecting light traveling from the LED device between the light exit surface and the substrate toward the light exit surface.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an LED display and particularly to a 7-segment LED display used for displaying a numeral, for example.  
         [0003]     2. Description of the Related Art  
         [0004]      FIGS. 10 and 11  show a conventional LED display disclosed in JP-A-H09-97928. The illustrated LED display X includes a case  91 , a lead frame  92 , an LED element  93  and a transparent resin package  94 . The display includes seven light exit surfaces  94   a  constituting seven segments, whereby a numeral selected from 0 through 9 or an alphabetical letter can be displayed. The LED element  93  is mounted on the lead frame  92  and accommodated in a recess  91   a  of the case  91 . The transparent resin package  94  is so formed as to fill recess  91   a . The case  91  is made of e.g. white resin having a relatively high light reflectivity so that inclined surfaces  91   b  surrounding the recess  91   a  serve as light reflective surfaces. When current is caused to flow through the LED element  93  in accordance with the character to be displayed, light is emitted from the LED element  93  in an upward and a lateral directions in  FIG. 2 . The light traveled in a lateral direction is reflected by the inclined surfaces  91   b  and then travels upward in the figure. These rays of light exit through the light exit surface  94   a , whereby the intended character is displayed.  
         [0005]     To cause a large amount of light emitted from the LED element  93  to travel upward in the figure, the size of the inclined surfaces  91   b  needs to be increased. However, when the size of the inclined surfaces  91   b  is increased, the height of the case  91  increases correspondingly, which hinders reduction in size and thickness of e.g. an electronic device to which the LED display X is mounted.  
         [0006]     Further, generally, an LED display X is mounted in an electronic device to be seen from the outside. In the case where the LED display X is mounted on a circuit board, the dimension between the circuit board and the housing of the electronic device needs to be determined in view of the height of the LED display X, which limits the design options of the electronic device. Alternatively, the idea of arranging the LED display X at a location which can be seen constantly may need to be given up, and the LED display X cannot help being mounted at a location which can be seen by opening a lid of the housing, for example.  
       SUMMARY OF THE INVENTION  
       [0007]     An object of the present invention, which is conceived under the circumstances described above, is to provide an LED display which is capable of being reduced in thickness and mounted at various portions.  
         [0008]     According to the present invention, there is provided an LED display comprising a substrate, at least one light emitter mounted on a mounting-surface of the substrate and including an LED element, at least one light exit surface through which light emitted from the light emitter exits. The light exit surface is spaced from the mounting-surface of the substrate in the thickness direction of the substrate. The LED display further comprises at least one reflection region for reflecting light traveling from the light emitter between the light exit surface and the substrate toward the light exit surface. The light emitter is provided at a position which does not overlap the position of the light exit surface in the in-plane direction of the substrate.  
         [0009]     With this structure, it is not necessary to increase the distance between the substrate and the light exit surface in order to increase the amount of light reaching the light exit surface. Therefore, it is possible to reduce the thickness of the LED display while increasing the area of the light exit surface. Moreover, the light emitted from the light emitter hardly exit directly through the light exit surface, which is advantageous for making the distribution of light exiting through the light exit surface uniform.  
         [0010]     In a preferred embodiment of the present invention, the LED display further comprises at least one light guide portion positioned between the substrate and the light exit surface. The light guide portion includes a light incident surface facing the light emitter, and the reflection region is provided on a supported-surface of the light guide portion which is positioned adjacent to the mounting-surface of the substrate. With this structure, the light emitted from the light emitter can be properly guided to the light exit surface while keeping the distance between the substrate and the light exit surface small.  
         [0011]     In a preferred embodiment of the present invention, the LED display includes seven light exit surfaces arranged to form a  FIG. 8 , seven light guide portions each positioned between a respective one of the seven light exit surfaces and the substrate, and seven light emitters each facing the light incident surface of a respective one of the seven light guide portions. With this structure, a segment-type LED display having a small thickness and capable of displaying an intended numeral or alphabetical letter can be realized.  
         [0012]     In a preferred embodiment of the present invention, the LED display further comprises a light guide plate which provides the seven light guide portions and includes seven rooms each connected to the light incident surface of a respective one of the seven light guide portions and accommodating a respective one of the light emitters. With this structure, the light emitters can be arranged without increasing the thickness of the LED display. Moreover, the light emitted from the light emitters can be properly guided to the light guide portions.  
         [0013]     In a preferred embodiment of the present invention, the light guide plate further includes a light shielding portion partitioning the seven light guide portions. With this structure, light is prevented from leaking from one light guide portion to an adjacent light guide portion. Therefore, when any light guide portion is in a light emission state, improper light emission through other light guide portions can be prevented.  
         [0014]     In a preferred embodiment of the present invention, the light guide plate is formed with a groove or a slit for partitioning the seven light guide portions. With this structure again, light is prevented from leaking from one light guide portion to an adjacent light guide portion.  
         [0015]     Other features and advantages of the present invention will become more apparent from detailed description given below with reference to the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  is a perspective view showing, partially in section, an LED display according to a first embodiment of the present invention;  
         [0017]      FIG. 2  is an overall plan view showing the LED display according to the first embodiment of the present invention;  
         [0018]      FIG. 3  is a sectional view taken along lines III-III in  FIG. 2 ;  
         [0019]      FIG. 4  is a perspective view showing a light guide plate of the LED display according to the first embodiment of the present invention;  
         [0020]      FIG. 5  is a sectional view showing a principal portion of an LED device according to a second embodiment of the present invention;  
         [0021]      FIG. 6  is a plan view showing a principal portion of an LED device according to a third embodiment of the present invention;  
         [0022]      FIG. 7  is a sectional view taken along lines VII-VII in  FIG. 6 ;  
         [0023]      FIG. 8  is a perspective view showing a principal portion of an LED device according to a fourth embodiment of the present invention;  
         [0024]      FIG. 9  is an overall plan view showing an LED device according to a fifth embodiment of the present invention;  
         [0025]      FIG. 10  is an overall plan view showing an example of conventional LED display; and  
         [0026]      FIG. 11  is a sectional view taken along lines XI-XI in  FIG. 10 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]     Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.  
         [0028]      FIGS. 1-3  show an LED display according to a first embodiment of the present invention. The LED display A 1  of this embodiment includes a substrate  1 , seven LED devices  2 , a light guide plate  3 , a cover  4  and a light shielding sheet  5 . The LED display A 1  includes seven light exit surfaces  4   a  and is structured as a 7-segment LED display capable of displaying a numeral or alphabetical letter. The LED display A 1  has a thickness of about 0.6 mm and the dimension in plan view is adaptable for about 3×5 mm to 45×63 mm.  
         [0029]     The substrate  1  is rectangular in plan view and utilized for mounting the LED devices  2  and bonding the light guide plate  3 . For instance, the substrate  1  is a printed wiring board including a resin layer and a wiring layer laminated thereon and has a thickness of about 0.1 mm. Instead of the printed wiring board, a so-called rigid board made of glass fiber reinforced epoxy resin may be used. As shown in  FIG. 3 , lands  11  and terminals  12  are formed on the substrate  1 . The lands  11  are utilized for mounting the LED devices  2 . The terminals  12  are utilized for connecting e.g. a connector C, and signals corresponding to the character to be displayed are inputted from an external controller through the terminals  12 . The land  11  and the terminals  12  are electrically connected to each other.  
         [0030]     Each of the LED devices  2  includes an LED element and is an example of light emitter according to the present invention. The LED device  2  can emit light by supplying electrical power to the LED device  2  through the connector C shown in  FIG. 3 . As shown in  FIG. 3 , the light is emitted from the LED device  2  laterally (to left in  FIG. 3 ), i.e., in the in-plane direction of the substrate  1 . This type of LED device  2  is called a side-emitting LED device. Unlike this embodiment, a lamp-type LED including a resin lens portion may be used as oriented laterally.  
         [0031]     The light guide plate  3  is bonded to the substrate  1  and serves to guide the light emitted from the LED devices  2  toward the light exit surfaces  4   a . As shown in  FIG. 4 , the light guide plate  3  includes seven light guide portions  31  and a light shielding portion  32 . In this embodiment, the light guide plate  3  has a thickness of about 0.4 mm.  
         [0032]     Each of the light guide portions  31  is made of acrylic resin or polycarbonate resin capable of transmitting light emitted from the LED device  2  and generally in the form of a sector in plan view. The light guide portion  31  includes a recess positioned adjacent to an end thereof. The portion surrounded by the recess and the light shielding portion  32  is a room  33 . The room  33  is utilized for accommodating the LED device  2  and penetrates through the light guide plate  3  in the thickness direction. The surface of the light guide portion  31  which faces the room  33  is a light incident surface  31   a . The light incident surface  31   a  faces the LED device  2 , and the light emitted from the LED device  2  impinges on the light incident surface  31   a.    
         [0033]     As shown in  FIG. 3 , the lower surface of each of the light guide portions  31  is formed with a plurality of light diffusion portions  31   b . The light guide portions  31  may be portions of the lower surface which are made rougher than neighboring portions. As shown in  FIG. 2 , the light diffusion portions  31   b  are distributed in a region under the light exit surface  4   a  so that the distribution density increases as proceeding away from the LED device  2 . For instance, the light diffusion portions  31   b  have a diameter of about 0.05 to 0.4 mm and the distribution density is about 0.1 to 0.5 mm. As shown in  FIG. 3 , the light emitted from the LED device  2  is reflected by the light diffusion portions  31   b  to travel upward. Each of the light diffusion portions  31   b  is an example of reflection region according to the present invention.  
         [0034]     The light shielding portion  32  serves to prevent the light traveling within the light guide portions  31  from unduly leaking to the outside of the light guide portions  31 . The light shielding portion  32  surrounds each of the seven light guide portions  31 . For instance, the light shielding portion  32  is made of white polycarbonate resin or ABS resin. To enhance the reflectivity for the light emitted from the LED devices  2 , it is preferable that the light shielding portion  32  contains titanium.  
         [0035]     The cover  4  covers the light guide plate  3 . The seven light exit surfaces  4   a  as the characteristic of the 7-segment LED display are provided by the cover  4 . Specifically, the cover  4  includes a light transmitting layer  41  and a light shielding layer  42 . For instance, the light transmitting layer  41  is made of polyethylene terephthalate resin or polycarbonate resin and has a thickness of about 0.1 mm. The light shielding layer  42  covers the light transmitting layer  41  while exposing portions of the light transmitting layer  4  to provide the light exit surfaces  4   a . For instance, the light shielding layer  42  may be formed by performing printing on the obverse surface of the light transmitting layer  41  using black paint. The cover may be so designed as to diffuse the light from the light guide portion  31  to realize uniform light distribution. For this purpose, the light transmitting layer  41  may be made of milk-white resin, or a light-transmitting milk-white paint may be applied to the surface.  
         [0036]     The seven light exit surfaces  4   a  comprise the portions of the light transmitting layer  41  which are not covered by the light shielding layer  42 . As shown in  FIG. 2 , the light exit surfaces  4   a  are so arranged as to form a  FIG. 8 . As shown in this figure, the size in plan view of each of the light exit surfaces  4   a  is smaller than that of the light guide portion  31 . In the light guide portion  31 , the light incident surface  31   a  is provided at a position which is farthest from the light exit surface  4   a  in plan view. Thus, the LED device  2  is disposed at a position retreated inward from the light exit surface  4   a  in the in-plane direction of the substrate  1 .  
         [0037]     As shown in  FIGS. 1 and 3 , the light shielding sheet  5  is bonded to the lower surface of the substrate  1 . The light shielding sheet  5  is provided to make the light shielding perfect on the lower surface side of the substrate  1 .  
         [0038]     The operation and advantages of the LED display A 1  will be described below.  
         [0039]     According to this embodiment, the light emitted from the LED device  2  enters the light guide portion  31  through the light incident surface  31   a . The light is then guided toward the light exit surface  4   a  by the light diffusion portions  31   b  provided on the bottom surface side of the light guide portion  31 . The dimension of the light diffusion portions  31   b  in the thickness direction of the light guide plate  3  is extremely small. Therefore, unlike the structure shown in  FIG. 11  which includes inclined surfaces  91   b , the thickness of the light guide plate  3  does not need to be increased even when the area of the light exit surface  4   a  is increased. Therefore, the thickness of the LED display A 1  can be reduced, which is suitable for reducing the size and thickness of an electronic device in which the LED display A 1  is mounted.  
         [0040]     The light emitted from the LED device  2  reaches the light exit surface  4   a  after it is reflected by the light diffusion portions  31   b . Therefore, almost all of the light rays exiting through the light exit surface  4   a  are indirect light rays and do not include light rays traveling directly from the LED device  2 . Therefore, noticeable nonuniformity in light distribution can be prevented, which prevents such a situation that a certain portion of the light exit surface  4   a  is extremely bright as compared with other portions. Particularly, the arrangement of the light diffusion portions  31   b  in which the distribution density increases as proceeding away from the LED device  2  is advantageous for realizing the uniform light distribution at the light exit surface  4   a . When the light transmitting layer  41  is milk-white, the uniformity of the light distribution at the light exit surface  4   a  can be further enhanced. Moreover, since the light incident surface  31   a  is dented, the light traveling from the LED device  2  can be spread in the in-plane direction of the light guide portion  31 , which is also advantageous for the uniform light distribution at the light exit surface  4   a.    
         [0041]     The provision of the light shielding portion  32  prevents light from leaking from one light guide portion  31  to an adjacent light guide portion  31 . Therefore, when any selected light exit surface  4   a  is in a light emission state, light emission from other light exit surfaces  4   a  which are not selected can be prevented.  
         [0042]     As shown in  FIG. 3 , the LED display A 1  can be mounted to an electronic device by using a connector C. Therefore, the LED display A 1  does not need to be bonded to e.g. a circuit board accommodated in the housing of the electronic device. Instead, the LED display A 1  can be bonded to a surface of the housing. Further, it is also possible to bond the LED display A 1  to a surface of a panel which is already installed so that the panel can additionally display numerical information which can be changed as desired.  
         [0043]      FIGS. 5-9  show other embodiments of the present invention. In these figures, the elements which are identical or similar to those of the foregoing embodiment are designated by the same reference signs as those used for the foregoing embodiment.  
         [0044]      FIG. 5  shows an LED display according to a second embodiment of the present invention. The LED display A 2  of this embodiment differs from that of the foregoing embodiment in that the LED display A 2  utilizes an LED element  21  as the light emitter. The LED element  21  is a light emitting element of a so-called bare chip type and emits light in an upward and a lateral directions in the figure. A reflector  34  is provided in an upper left portion of the room  33  in the figure. The reflector  34  may be made of aluminum, for example, and serves to reflect light emitted from the LED element  21  and traveling upward or rightward in the figure toward the light incident surface  31   a  positioned on the left in the figure. In this embodiment again, the thickness of the LED display A 2  can be reduced.  
         [0045]      FIGS. 6 and 7  show an LED display according to a third embodiment of the present invention. The LED display A 3  of this embodiment differs from the foregoing embodiments in structure of the light guide plate  3 . For easier understanding, the illustration of the cover  4  is omitted in  FIG. 6 .  
         [0046]     The light guide plate  3  of the LED display A 3  is formed with a plurality of slits  34 . The slits  34  penetrate the light guide plate  3  in the thickness direction and serve to block light emitted from the LED devices  2  by utilizing difference in refractive index between air and the material of the light guide plate  3  such as acrylic resin. The slits  34  include those which surround the seven light guide portions  31  from outside, those which partition the adjacent light guide portions  31  and those positioned inward of the light guide portions  31 . The slits  34  surrounding the light guide portions  31  from outside serve to prevent light from leaking to the outside of the LED display A 3 . The slits  34  partitioning the adjacent light guide portions  31  serve to prevent light from leaking from a light guide portion  31  in the light emission state to a light guide portion  31  in a non-light-emission state. Light shielding walls  14  are fitted in the slits  34  partitioning the adjacent light guide portions  31 . As shown in  FIG. 7 , each of the light shielding walls  14  comprises a metal piece disposed on a pad  11  of the substrate  1 , for example. As the material of the light shielding wall  14 , any material can be used as long as it can block light, and resin may be used, for example. The slits  34  positioned inward of the light guide portions  31  serve to block light between mutually facing light guide portions  31 . In this embodiment, though not shown in  FIG. 6 , a plurality of light diffusion portions are provided in each of the light guide portions  31  at a region corresponding to the light exit surface  4   a , similarly to the first embodiment.  
         [0047]     The light guide plate  3  according to this embodiment can be easily formed by molding such as injection molding or transfer molding, which is advantageous for enhancing the manufacturing efficiency and reducing the manufacturing cost of the LED display and also for reducing the size of the LED display. As means for blocking light between adjacent light guide portions  31 , a groove which does not penetrate through the light guide plate  3  may be formed instead of the slit  34  which penetrates through the light guide plate  3 . In this case, it is preferable to make the depth of the groove as large as possible to reliably prevent the light leakage.  
         [0048]      FIG. 8  shows an LED display according to a fourth embodiment of the present invention. The LED display A 4  of this embodiment differs from the foregoing embodiment in that the LED display A 4  includes through-hole terminals  13 . By the provision of the through-hole terminals  13 , the LED display A 3  can be surface-mounted to a printed circuit board, for example. In this way, the LED display according to the present invention is adaptable to various modes of mounding such as connector connection, surface-mount connection and pin connection.  
         [0049]      FIG. 9  shows an LED display according to a fifth embodiment of the present invention. In addition to the seven light exit surfaces  4   a  as the characteristic of the 7-segment LED display, the LED display A 5  includes a pair of display surfaces  4   a  in the form of an arrow and two light exit surfaces  4   a  including letter regions made of a light shielding material. As will be understood from this embodiment, the LED display according to this embodiment is not limited to 7-segment LED display, and the shape of the light exit surfaces  4   a  can be changed in various ways to display the intended contents.  
         [0050]     The LED display according to the present invention is not limited to the foregoing embodiments. The specific structure of each part of the LED display according to the present invention can be changed in various ways.