Abstract:
An exemplary method for making a backlight module, the method includes steps in following order: providing a transparent base sheet and at least one light emitting diode; punching the base sheet to form an aperture therein; fixing the at lease one light emitting diode in the aperture, the at least one light emitting diode and an inner side surface of the aperture cooperatively defining a space; injecting an adhesive into the space between the at least one light emitting diode and the inner side surface of the aperture; solidifying the adhesive; and trimming the base sheet with the at least one light emitting diode in the aperture to form the backlight module.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to backlight modules, particularly, to an edge-lighting type backlight module for use in, for example, a liquid crystal display (LCD), and methods for making the backlight modules. 
     2. Discussion of the Related Art 
     In a liquid crystal display device, a liquid crystal is a substance that does not itself radiate light. Instead, the liquid crystal relies on light received from a light source, thereby displaying data images. In the case of a typical liquid crystal display device, a backlight module powered by electricity supplies the needed light. Generally, backlight modules can be classified into an edge lighting type or a bottom lighting type based upon the location of lamps within the device. 
     Referring to  FIG. 6 , a typical edge lighting type backlight module  10  includes a frame  11 , a light reflective plate  12 , a plurality of light emitting diodes  13 , a light guide plate  14  and at least one optical plate  15 . The frame  11  includes four sidewalls  114  that connect with each other to form a receiving space  112 . The light reflective plate  12 , the light guide plate  14  and the optical plate  15  are stacked in that order, and are mounted in the receiving space  112  together. The light guide plate  14  includes a light input surface  141 , and a light output surface  142  adjoining the light input surface  141 . An inner side surface of the sidewalls  114  facing the light input surface  141  defines a plurality of grooves  111  therein. The light emitting diodes  13  are received in the corresponding grooves  111  of the sidewall  114 . 
     Referring to  FIG. 7 , each light emitting diode  13  includes a base  131 , a semiconductor chip  132  fixed on the base  131 , and a transparent resin member  133  sealed with the semiconductor chip  132  at one side of the base  131 . Also referring to  FIG. 6 , the light guide plate  14  includes a light input surface  141 , and a light output surface  142  adjoining the light input surface  141 . The transparent resin member  133  of each of the light emitting diodes  13  faces the light input surface  141 . In use, light from the light emitting diodes  13  passes through the light input surface  141  and enters the light guide plate  14 . The light is reflected and refracted in the light guide plate  14 , and finally surface light is outputted from the light output surface  142 . 
     Generally, it is difficult to assemble the light emitting diodes  13  to be in continuous contact with the light input surface  141  of the light guide plate  14 . A space still exists between the light input surface  141  and the transparent resin members  133  of the light emitting diodes  13 . Because a refractive index of the transparent resin members  133  of the light emitting diodes  13  is relatively larger than of the refractive index of air, when light from the semiconductor chip  132  passes through the space, the light undergoes total reflection at the space. As a result, the light energy utilization ratio of the backlight module  10  is reduced. 
     What is needed, therefore, is a backlight module that overcomes the above mentioned disadvantages. Methods for making the backlight module are also desired. 
     SUMMARY 
     A method for making a backlight module, the method includes: providing a transparent base sheet and at least one light emitting diode; punching the base sheet to form an aperture therein; fixing the at lease one light emitting diode in the aperture, the at least one light emitting diode and an inner side surface of the aperture cooperatively defining a space; injecting an adhesive into the space between the at least one light emitting diode and the inner side surface of the aperture; solidifying the adhesive; and trimming the base sheet with the at least one light emitting diode in the aperture to form the backlight module. 
     Other advantages and novel features will become more apparent from the following detailed description of the preferred embodiments, when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present backlight module and method for making the backlight module. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views, and all the views are schematic. 
         FIG. 1  is an assembled, isometric view of a backlight module according to a first preferred embodiment of the present invention. 
         FIG. 2  is a cross-sectional view of the backlight module of  FIG. 1 , taken along II-II line thereof. 
         FIG. 3  is a diagram of a process for making the backlight module of  FIG. 1  without a frame. 
         FIG. 4  is a cross-sectional view of a backlight module according to a second preferred embodiment of the present invention. 
         FIG. 5  is a cross-sectional view of a backlight module according to a third preferred embodiment of the present invention. 
         FIG. 6  is an exploded, isometric view of a conventional backlight module. 
         FIG. 7  is a cross-sectional view of the backlight module of  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made to the drawings to describe preferred embodiments of the present backlight module and methods for making the backlight module, in detail. 
     Referring to  FIGS. 1 and 2 , a backlight module  20  in accordance with a first preferred embodiment of the present invention is shown. The backlight module  20  includes a frame  21 , three light emitting diodes  23 , a light guide plate  24 , and an adhesive member  25 . The frame  21  includes four sidewalls  214  connected with each other defining a receiving space (not labeled). The light guide plate  24  includes a light input surface  241 , and a light output surface  242  adjoining the light input surface  241 . The light guide plate  24  is mounted in the receiving space. An inner side surface of the sidewall  214  facing the light input surface  241  defines a plurality of grooves  211 . 
     The light guide plate  24  has a thin body, and a thickness of the light guide plate  24  is preferably in a range from 0.075 millimeters to about 0.8 millimeters. A material of the light guide plate  24  is selected from polymethyl methacrylate (PMMA), polycarbonate (PC), and any other suitable transparent resin materials. Preferably, the light guide plate  24  is made of transparent resin materials with relatively high heat-resistant capabilities, such as PC that can endure 150° C. temperatures, or modified PMMA with a heat-resistant agent uniformly dispersed in the PMMA. 
     The light emitting diodes  23  are correspondingly received in the grooves  211 . Each light emitting diode  23  includes a base  231 , a semiconductor chip  232  fixed on the base  231 , and a transparent resin member  233  sealing the semiconductor chip  232  on a side of the base  231 . The transparent resin member  233  of each of the light emitting diodes  23  includes a light-emitting surface  2331  facing the light input surface  241 . In alternative embodiments, the three light emitting diodes  23  are welded on a flexible printed circuit board (not shown) in an array along a direction parallel to the light input surface  241 , and the flexible printed circuit board are fixed to a bottom surface of the light guide plate  24  with a double-coated adhesive tape (not shown). Accordingly, the three light emitting diodes  23  are positioned adjacent to the light guide plate  24  securely. 
     The light emitting surface  2331  of the light emitting diodes  23  and the light input surface  241  of the light guide plate  24  cooperatively define a plurality of spaces between them. The adhesive member  25  fills the spaces between the light-emitting surface  2331  of the light emitting diodes  23  and the light input surface  241  of the light guide plate  24 . The adhesive member  25  is transparent, and is solidified by solidifying either an UV-curable adhesive or a thermal curable adhesive. Preferably, a refractive index of the adhesive member  25  equals to or closely matches a refractive index of the transparent resin members  233  of the light emitting diodes  23 . 
     In use, the light from the light emitting diodes  23  passes through the adhesive member  25  and enters the light guide plate  24  via the light input surface  241 . The light is reflected and refracted in the light guide plate  24 , and finally surface light is outputted from the light output surface  242 . Because the refractive index of the adhesive member  25  almost equals to that of the transparent resin members  233  of the light emitting diodes  23 , a critical angle of total reflection at the light-emitting surface  2331  is reduced. Therefore, a frequency of light from the semiconductor chip  232  being reflected back is decreased. A light energy utilization efficiency of the backlight module  20  is improved. Furthermore, the light emitting diodes  23  can be positioned and fixed tightly to the light guide plate  24  by the adhesive member  25 . 
     It is to be understood that, if fluorescent particles are dispersed in the adhesive member  25 , the backlight module  20  can provide colored light according to characteristics of the fluorescent particles. For example, if the light emitting diode  23  is a blue colored light emitting diode, and yttrium aluminum garnet fluorescent particles are uniformly dispersed in the adhesive member  25 , white light can be outputted from the light output surface  242 . Therefore, either colored light or white light outputted from the backlight module  20  can obtained efficiently by employing the adhesive member  25  with different fluorescent particles. 
       FIG. 3  is a diagram of a process for making the backlight module  20  of  FIG. 1  without the frame  21 . The process mainly includes the following six steps. 
     Step one: a transparent base sheet  201  is provided. A thickness of the light guide plate  24  is preferably in the range from 0.075 millimeters to about 0.8 millimeters. A material of the base sheet  201  is preferably selected from a group consisting of polymethyl methacrylate (PMMA), polycarbonate (PC), and other suitable transparent resin materials. In this embodiment, the base sheet  201  is a rolled-up sheet. The base sheet  201  can be continuously fed to a punching machine (not shown) by a number of rolling devices (not shown). 
     Step two: the transparent base sheet  201  is punched by the punching machine to form an elongated aperture  202  in the transparent base sheet  201 . A light input surface  241  is defined at an inner side surface of the aperture  202 . A shape of the aperture  202  can be configured according to a shape and/or an amount of the light emitting diodes  23 . 
     Step three: the Three light emitting diodes  23  are provided, and are regularly arranged in the aperture  202  with the transparent resin members  233  of each of the light emitting diodes  23  facing the light input surface  241 . In this embodiment, the light emitting diodes  23  are welded on a flexible printed circuit board (FPCB hereafter)  203  in an array along a direction parallel to the light input surface  241 . The FPCB  203  includes a plurality of electrical components (not shown) formed on a surface to control actuations of the three light emitting diodes  23  or other components. The light emitting diodes  23  are electrically connected with electrical components of the FPCB  203 . A part of the FPCB  203  may be fixed to a bottom surface of the transparent base sheet  201  with a double-coated adhesive tape (not shown), thus the light emitting diodes  23  is securely positioned in the aperture  202 . Generally, a space  204  would exist between the light input surface  241  and the transparent resin members  233 . 
     Step four: an adhesive  25 ′ is injected into the space  204  between the light input surface  241  and the transparent resin members  233  by a dispenser (not shown). The adhesive  25 ′ can be either an UV-curable adhesive or a thermal curable adhesive. Alternatively, the adhesive  25 ′ may further be modified UV-curable adhesive and modified thermal curable adhesive. In this embodiment, the adhesive  25  is an UV-curable adhesive that can be efficiently solidified. 
     Step five: the adhesive  25 ′ between the light input surface  241  and the light emitting diodes  23  is solidified to yield the adhesive member  25  by UV-light (ultraviolet-light) solidifying method. 
     Step six: the base sheet  201  with the light emitting diodes  23  positioned in the aperture  202  is trimmed by a die cut machine (not shown) according to a predetermined design to form the backlight module  20 . Each backlight module  20  includes the light guide plate  24 , three light emitting diodes  23 , and the adhesive member  25 . The light emitting diodes  23  are disposed adjacent to the light input surface  241  of the light guide plate  24 . The adhesive member  25  is located between the light emitting diodes  23  and the light guide plate  24 . In this embodiment, the backlight modules  20  are continuously punched out of the base sheet  201  during a punching procedure applied by the die cut machine. 
     In an exemplary embodiment, a method for making the backlight module  20  of  FIG. 1  includes following steps. Firstly, the light guide plate  24  and three light emitting diodes  23  are provided. Secondly, the three light emitting diodes  23  are positioned adjacent to the light guide plate  24 , the light-emitting surface  2331  of the light emitting diode  23  facing the light input surface  241  of the light guide plate  24 . Thirdly, a dispenser (not shown) injects an adhesive  25 ′ to fill a space cooperatively defined by the light-emitting surface  2331  and the light input surface  241 . Finally, the adhesive  25 ′ is solidified to form the backlight module  20 . 
     In other exemplary embodiments, a method for making the backlight module  20  of  FIG. 1  includes following steps. Firstly, the frame  21 , three light emitting diodes  23  and the light guide plate  24  are provided. Secondly, the light guide plate  24  and the three light emitting diodes  23  are assembled into the frame  21  with the light-emitting surface  2331  of the light-emitting diode  23  facing the light input surface  241  of the light guide plate  24 . The light-emitting surface  2331  and the light input surface  241  cooperatively defines a space. Thirdly, an adhesive  25 ′ is injected into the space. Finally, the adhesive  25 ′ is solidified to form the adhesive member  25 . Accordingly, the backlight module  20  is manufactured. 
     Referring to  FIG. 4 , a backlight module  30 , in accordance with a second preferred embodiment of the present invention, is similar in principle to the backlight module  20 . However, the backlight module  30  includes a light guide plate  34  and three light emitting diodes  33 . The three light emitting diodes  33  are regularly arranged adjacent to a light input surface  341  of the light guide plate  34 . A plurality of V-shaped depressions  343  are defined in parts of the light input surface  341  corresponding to the light emitting diodes  33 . The backlight module  30  further includes a plurality of adhesive members  35  to fill spaces defined between the light emitting diodes  33  and the light input surface  341 , and to connect the light emitting diodes with the light guide plate  34 . The V-shaped depressions  343  can eliminate shadows that may otherwise form adjacent to the light input surface  341 , such that a uniformity of light output from the backlight module  30  is increased. 
     Referring to  FIG. 5 , a backlight module  40 , in accordance with a third preferred embodiment of the present invention, is similar in principle to the backlight module  20 . However, the backlight module  40  includes a light guide plate  44  and three light emitting diodes  43 . The three light emitting diodes  43  are regularly arranged adjacent to a light input surface  341  of the light guide plate  44 . A plurality of arcuate depressions  443  are defined in parts of the light input surface  441  corresponding to the light emitting diodes  43 . The backlight module  40  further includes a plurality of adhesive members  45  to fill spaces defined between the light emitting diodes  43  and the light input surface  441 , and to connect the light emitting diodes with the light guide plate  44 . The arcuate depressions  443  can eliminate shadows that may otherwise form adjacent to the light input surface  441 , such that a uniformity of light output from the backlight module  40  is increased. 
     It is noted that the scope of the present backlight module is not limited to those described in the embodiments even though the numbers and shapes of the V-shaped depressions  343 , and the arcuate depressions  443  are illustrated specifically. Furthermore, the backlight module can further include other microstructures that are not described in the embodiments, such as V-shaped protrusions, arcuate protrusions and so on. 
     Finally, while the present invention has been described with reference to particular embodiments, the description is illustrative of the invention and is not to be construed as limiting the invention. Therefore, various modifications can be made to the embodiments by those skilled in the art without departing from the true spirit and scope of the invention as defined by the appended claims.