Abstract:
A method of fabricating a light-guide plate includes preparing an upper mold frame having an inclined inner surface and a lower mold frame having a space therein, preparing a micro pattern plate having a surface including one of a plurality of grooves and a plurality of protrusions formed using photolithographic processes, inserting the micro pattern plate into the space of the lower mold frame, the surface of the micro pattern plate facing the inclined inner surface of the upper mold frame, positioning the upper and lower mold frames together, and injecting light-guide plate forming material into a space between the upper and lower mold frames.

Description:
[0001]    The present invention claims the benefit of Korean Patent Application No. P2003-11763 filed in Korea on Feb. 25, 2003, which is hereby incorporated by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a method of fabricating a light-guide plate, and more particularly, to a method of fabricating a light-guide plate for a liquid crystal display module.  
           [0004]    2. Description of the Related Art  
           [0005]    In general, liquid crystal display (LCD) devices display images using an external light source. FIG. 1 is a schematic cross sectional view of a liquid crystal display module according to the related art. In FIG. 1, a liquid crystal display module includes a main support  2 , a backlight unit and a liquid crystal display panel  10  stacked inside the main support  2 , a bottom cover  14  enclosing bottom and side surfaces of the main support  2 , and a case top  16  for enclosing edges of the liquid crystal display panel  10  and the bottom cover  14 .  
           [0006]    The main support  2  is a molded part and side surface of an inner wall of the main support  2  is formed to have a step portion. In addition, a backlight unit is installed on the inner bottom portion of the main support  2 , and the liquid crystal display panel  10  is mounted above the backlight unit.  
           [0007]    The liquid crystal display panel  10  includes a lower substrate  10   b  upon which switching devices, such as thin film transistors TFT are installed, an upper substrate  10   a  upon which color filters are installed, and a liquid crystal material injected into a space between the upper substrate  10   a  and the lower substrate  10   b . Polarizing plates  22  and  24  are installed above and below the liquid crystal display panel  10 , wherein the lower polarizing plate  22  polarizes light coming from the back light unit and guides the polarized light to the liquid crystal display panel  10 . The upper polarizing plate  24  polarizes the polarized light coming through the liquid crystal display panel  10  and transmits the doubly-polarized light.  
           [0008]    The bottom cover  14  is installed to enclose the bottom and side surfaces of the main support  2 . In addition, the case top  16  is installed to enclose the upper and side portions of the main support  2  to affix the main support  2  and the liquid crystal display panel  10  together.  
           [0009]    The backlight unit includes a lamp housing  18  accommodating a light source  20 , a light-guide plate  6  for transforming the incident light emitted from the light source  20  into planar light, optical sheets  12  attached onto the light-guide plate  6  for increasing efficiency of the light incident to the liquid crystal display panel  10 , and a reflection plate attached onto a rear surface of the light-guide plate  6  for reflecting the light transmitted from the back of the light-guide plate  6  to the liquid crystal display panel  10 .  
           [0010]    The light source  20  supplies amounts of light to the light-guide plate  6  in response to an extremely supplied power. Accordingly, the light radiated to the opposite direction of the light-guide plate  6  is reflected toward the light-guide plate  6  by the lamp housing  18 , and the reflection plate  4  reflects the light incident to the lower part of the light-guide plate  6 . Thus, the reflection plate  4  guides the incident light from the light-guide plate  6  toward the liquid crystal display panel  10 .  
           [0011]    The optical sheets  12  include upper and lower diffusion sheets and upper and lower prism sheets. The optical sheets scatter the light incident from the light-guide plate  6  to distribute the lights evenly over an entire surface of the light-guide plate  6 . In addition, the optical sheets  12  increase surface brightness by refracting and collecting the scattered light, thereby widen a viewing angle by diffusing the light.  
           [0012]    [0012]FIG. 2 is a cross sectional view of the light-guide plate of FIG. 1 according to the related art. In FIG. 2, a plurality of protrusions  30  are formed on a rear surface of the light-guide plate  6  to reflect the incident light and to uniformly distribute the light and guide the light toward the liquid crystal display panel  10 .  
           [0013]    [0013]FIG. 3 is a cross sectional view of a mold frame used to mold the light-guide plate of FIG. 2 according to the related art. In FIG. 3, a plurality of grooves  36  are formed within designated intervals on a lower mold frame  32  in order to create the plurality protrusions  30 . Then, an upper mold frame  34  is provided to have an inclined inner surface. Next, a light-guide plate forming material, such as polymethyl methacrylate (PMMA), is inserted between the upper and lower mold frames  34  and  32 , and the light-guide plate  6  is formed, as shown in FIG. 2.  
           [0014]    However, during the process for forming the light-guide plate  6 , since a plurality of grooves  36  are directly formed on the lower plate, it is difficult for the intervals between the protrusions  30  to be less than or equal to 10 μm. Similarly, the interval between the protrusions  30  is formed to be greater than or equal to 10 μm. Accordingly, the protrusions  30 , where the interval between the protrusions is greater than or equal to 10 μm, are limited in the amount of light reflected therefrom, and result in lowering the uniformity of light and making it be difficult to implement high light brightness.  
         SUMMARY OF THE INVENTION  
         [0015]    Accordingly, the present invention is directed to a method of fabricating a light-guide plate that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.  
           [0016]    An object of the present invention is to provide a method of fabricating a light-guide plate having micro-sized patterns to improve brightness of a liquid crystal display.  
           [0017]    Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.  
           [0018]    To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a method of fabricating a light-guide plate includes preparing an upper mold frame having an inclined inner surface and a lower mold frame having a space therein, preparing a micro pattern plate having a surface including one of a plurality of grooves and a plurality of protrusions formed using photolithographic processes, inserting the micro pattern plate into the space of the lower mold frame, the surface of the micro pattern plate facing the inclined inner surface of the upper mold frame, positioning the upper and lower mold frames together, and injecting light-guide plate forming material into a space between the upper and lower mold frames.  
           [0019]    It is to be understood that both the foregoing general description and the follow detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings:  
         [0021]    [0021]FIG. 1 is a schematic cross sectional view of a liquid crystal display module according to the related art;  
         [0022]    [0022]FIG. 2 is a cross sectional view of the light-guide plate of FIG. 1 according to the related art;  
         [0023]    [0023]FIG. 3 is a cross sectional view of a mold frame used to mold the light-guide plate of FIG. 2 according to the related art;  
         [0024]    [0024]FIGS. 4A to  4 J are cross sectional views of exemplary process steps of a method of fabricating a micro pattern plate according to the present invention;  
         [0025]    [0025]FIGS. 5A and 5B are cross sectional views of an exemplary method of fabricating a light-guide plate according to the present invention;  
         [0026]    [0026]FIGS. 6A and 6B are cross sectional views of another exemplary method of fabricating a light-guide plate according to the present invention; and  
         [0027]    [0027]FIG. 7 is a cross sectional view of an exemplary photoresist of FIG. 4D according to the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]    Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.  
         [0029]    [0029]FIGS. 4A to  4 J are cross sectional views of exemplary process steps of a method of fabricating a micro pattern plate according to the present invention. In FIG. 4A, a plate  40 , such as copper (Cu), for micro-sized patterns may be prepared.  
         [0030]    In FIG. 4B, an organic insulating material  42  may be deposited onto the plate  40 . The organic insulating material may be one of benzocyclobutene (BCB), perfluorocyclobutane (PFCB), and the like.  
         [0031]    In FIG. 4C, a photoresist (PR)  44  may be applied onto the organic insulating material  42 .  
         [0032]    In FIG. 4D, the PR  44  may be exposed using a plurality of masks  46 . A cross-section of the mask  46  may resemble a trapezoid, wherein two sides are of equal length and the side facing the PR is shorter than the opposite side. In addition, an interval between the masks  46  may be regulated to set an interval between protrusions or grooves to be formed less than or equal to about 9 μm.  
         [0033]    After the masks  46  are aligned onto the PR  44 , irradiation of ultraviolet (UV) light may divide the PR  44  into two different types of regions, i.e., irradiated region  50  and non-irradiated region  48 .  
         [0034]    In FIG. 4E, the PR  44  may be developed to remove the irradiated region  50 . Accordingly, only the non-irradiated regions  48  may remain on the organic insulating material  42 . The non-irradiated regions  48  may have two sides of equal length and an upper surface that may be wider than a lower surface.  
         [0035]    In FIG. 4F, the organic insulating material  42  may be anisotropically etched so that triangular protrusions  52  remain on the plate  40 . Thus, producing a micro patterned plate  80 .  
         [0036]    Alternatively, the PR  44  may be formed by removing the non-irradiated regions  48 , as shown in FIG. 7. Accordingly, only the irradiated regions  48  may remain on the organic insulating material  42 . The irradiated regions  48  may have two sides of equal length and an upper surface may be narrower than a lower surface. Then, as shown in FIG. 4F, the organic insulating material  42  may be anisotropically etched so that the triangular protrusions  52  remain on the plate  40 .  
         [0037]    In FIG. 4G, a copper film  54  may be plated onto the micro patterned plate  80  including the triangular protrusions  52  and the plate  40 . The copper plating contributes to increasing a strength of the protrusions  52  and maintains a uniform surface roughness of the triangular protrusions  52 . In addition, intervals between the triangular protrusions  52  may be set to be less than or equal to about 9 μm, for example, about 0.5 μm. Thus, since the triangular protrusions  52  may be formed using photolithographic processes capable of regulating a gap between the masks  52 , the intervals between the triangular protrusions  52  may be set to be small. The micro pattern plate  80  resulting from the processes of FIGS. 4A to  4 G may be used to form a depressed engraving pattern.  
         [0038]    [0038]FIGS. 5A and 5B are cross sectional views of an exemplary method of fabricating a light-guide plate according to the present invention. In FIG. 5A, the micro pattern plate  80  having densely formed protrusions  52  may be inserted into a lower mold frame  62 . Then, an upper mold frame  64  may be provided have an inclined inner surface so as to form a light-guide plate having a designated slope. After the micro pattern plate  80  is inserted into the lower mold frame  62 , light-guide plate forming material, such as polymethyl methacrylate (PMMA), may be injected into a space between the lower and upper mold frames  62  and  64 . Accordingly, a light-guide plate  66  having a depressed engraving pattern, i.e. grooves  68  with designated intervals, may formed, as shown FIG. 5B. Here, the intervals between the grooves  68  on the light-guide plate  66  may be set to correspond to the intervals between the protrusions  52  on the micro pattern plate  80 . Consequently, since the intervals between the grooves  68  on the light-guide plate may be set to be less than or equal to about 9 μm, i.e., about 0.5 μm, the light-guide plate may contribute to increase the uniformity of light and achieve high ligth brightness.  
         [0039]    On the other hand, additional processes in FIGS. 4H to  4 J may be used to fabricate a light-guide plate having a raised carving pattern. After the protrusions  52  on the plate  40  are formed, as shown in FIG. 4F, micro pattern forming material  56  may be deposited on the plate  40 . For example, copper, nickel, or the like may be used for the micro pattern forming material  56 .  
         [0040]    In FIG. 4I, a micro pattern plate  82  may be formed by removing the micro pattern forming material  56  from the plate  40 . Accordingly, the intervals between the grooves  58  on the micro pattern plate  82  may be set to be less than or equal to about 9 μm, for example about 0.5 μm.  
         [0041]    [0041]FIGS. 6A and 6B are cross sectional views of another exemplary method of fabricating a light-guide plate according to the present invention. In FIG. 6A, the micro pattern plate  82  having protrusions  70  with the intervals may be inserted into a lower mold frame  62 . In addition, a upper mold frame  64  may be provided having an inclined inner surface so as to form a light-guide plate having a designated slope. After the micro pattern plate  82  is inserted into the lower mold frame  62 , light-guide plate forming material, such as polymethyl methacrylate (PMMA), may be injected into a space between the lower and upper mold frames  62  and  64 . Accordingly, a light-guide plate  72  having raised carving pattern, i.e. protrusions  74  with designated intervals, may be formed, as shown FIG. 6B. In addition, the intervals between the protrusions  74  on the light-guide plate  72  may be set to correspond to the intervals between the grooves  70  on the micro pattern plate  82 . Consequently, since the intervals between the protrusions  74  on the light-guide plate  72  may be set to be less than or equal to about 9 μm, for example about 0.5 μm, the light-guide plate  72  may contribute to increase the uniformity of light and achieve high light brightness. For example, the densely formed protrusions  74  may reflect large amounts of light, thereby increasing the uniformity of  
         [0042]    In FIG. 4J, thin copper film  60  may be applied over an entire surface of the micro pattern plate  82 . The copper film  60  may contribute to increase the strength of the micro pattern plate  82  and maintain a uniform surface roughness of the grooves  58 .  
         [0043]    According to the present invention, a micro pattern plate having a plurality of densely formed grooves or protrusions may be formed using photolithographic processes. Thus, a light-guide plate having a raised carving or depressed engraving pattern may be formed using the micro pattern plate. Since the grooves or protrusions of the micro pattern plate may be formed using photolithographic processes, a raised carving or depressed engraving pattern on the light-guide plate may have a micro pattern, thereby enhancing brightness of a liquid crystal display.  
         [0044]    It will be apparent to those skilled in the art that various modifications and variations can be made in the method of fabricating a light guide plate of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.