Abstract:
A method for manufacturing a lens for a light emitting diode (LED) package is disclosed. The method for manufacturing a lens for an LED package includes: forming a dome lens on each of a plurality of LED packages placed on a fixing plate, the dome lens made of silicon; forming a concave groove in the dome lens by using a jig for pressing the dome lens; curing the dome lens; and removing the LED packages from the fixing plate.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to and the benefit of Korean Patent Application No. 2007-35417, filed on Apr. 11, 2007, the disclosure of which is incorporated herein by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a light emitting diode (LED) package, and more particularly, to a method for manufacturing a lens for an LED package in which a manufacturing process is simplified. 
         [0004]    2. Description of the Related Art 
         [0005]    A liquid crystal display (LCD) device displays an image such that an electric power is applied to each pixel to change an alignment of liquid crystal molecules. An LCD device is a non-emissive display device and so needs a backlight unit which uniformly irradiates light to a display panel so that it can be used even in a dark place. 
         [0006]    The backlight unit comprises a light source like a fluorescent lamp or a light emitting diode (LED), a light guide plate, and a prism sheet. 
         [0007]    In case of an LED, an LED package in which an LED chip is mounted to a lead frame, a fluorescent material is inserted, and a special material is injected to mount and mold the LED chip is provided as a light source. 
         [0008]      FIG. 1A  shows an orientation angle of a conventional LED package having no lens. 
         [0009]    Referring to  FIG. 1A , light emitted from the LED package having no lens is condensed at a certain orientation angle. The LED package has low light efficiency because a total reflection of light occurs in an interface between a molded upper surface and an air and so lots of light go back to an inside of the LED package. 
         [0010]    In order for the LED package to have a better performance, light emitted from the LED package should have an orientation pattern of a fan shape. The orientation pattern of a fan shape can be achieved by an appropriate package design. Also, in order to increase light efficiency, a dome lens is mounted onto an LED package. 
         [0011]      FIG. 1B  shows an orientation angle of a conventional LED package having a dome lens. 
         [0012]    Referring to  FIG. 1B , an orientation pattern of emitted light is wider than that of  FIG. 1A . The dome lens condenses and then irradiates light totally reflected in the LED package, so that a wider orientation angle is obtained. The dome lens is typically made of a plastic material such as polycarbonate (PC) or Polymethylmethaclylate (PMMA). The dome lens is mounted onto the LED package by using an adhesive. An interface and a fine gape are formed between the dome lens and the LED package since a material of the dome lens and a molding material molded in the LED package are different and the dome lens and the LED package are mounted by using an adhesive. 
         [0013]    However, in such a conventional LED package having the dome lens, a process for manufacturing the dome lens and a process for attaching the dome lens to the LED package are very complicated. In addition, since an interface and a fine gape are formed between the dome lens and the LED package, light efficiency is low due to a refraction index difference. 
       SUMMARY OF THE INVENTION 
       [0014]    It is an object of the present invention to provide a method for manufacturing a lens for an LED package in which a manufacturing process is simple. It is another object of the present invention to provide a method for manufacturing a lens for an LED package in which the thickness and volume of a backlight unit employing the LED package are reduced and the brightness is increased. 
         [0015]    An exemplary embodiment of the present invention provides a method for manufacturing a lens for a light emitting diode (LED) package, comprising: forming a dome lens on each of a plurality of LED packages placed on a fixing plate, the dome lens made of silicon; forming a concave groove in the dome lens by using a jig for pressing the dome lens; curing the dome lens; and removing the LED packages from the fixing plate. 
         [0016]    The dome lens is formed by using a dispensing technique or a printing technique. 
         [0017]    The dome lens is made of transparent silicon having viscosity enough for the dome lens to have a dome shape and not to stream down to the LED package. 
         [0018]    The viscosity of the dome lens is 30 to 50 Pas. 
         [0019]    The dome lens is cured at a temperature of 140° C. to 160° C. for 25 to 35 minutes. 
         [0020]    A distance between an optical sheet and an LED chip is reduced in consideration of an orientation angle of light emitted from the dome lens. 
         [0021]    The concave groove has a shape which provides an orientation angle at which light emitted from the LED package is widely spread. 
         [0022]    The concave groove has a predetermined angle. 
         [0023]    The step for forming the concave groove in the dome lens comprises moving an upper plate jig having a plurality of projection formed on a bottom thereof with a corresponding shape at locations corresponding to the plurality of LED packages down to a lower plate jig which supports the fixing plate to press the dome lens. 
         [0024]    The upper plate jig moves down to the lower plate jig to press the dome lens, the concave groove is formed corresponding to the height of a press arm of the upper plate jig for restricting the pressing range. 
         [0025]    The projection has a corn shape. 
         [0026]    Each of the plurality of LED packages is formed such that an LED chip is mounted to a lead frame, a fluorescent material is inserted, and one of synthetic resin, transparent epoxy or silicon is injected to mount and mold the LED chip. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0027]    The above and other features of the present invention will be described in reference to certain exemplary embodiments thereof with reference to the attached drawings in which: 
           [0028]      FIG. 1A  shows an orientation angle of a conventional LED package having no lens; 
           [0029]      FIG. 1B  shows an orientation angle of a conventional LED package having a dome lens; 
           [0030]      FIG. 2A  is a side view illustrating a dome lens according to an exemplary embodiment of the present invention; 
           [0031]      FIG. 2B  is a side view illustrating a modified dome lens according to the exemplary embodiment of the present invention. 
           [0032]      FIG. 3  shows an orientation angle of light emitted from a backlight unit having the LED package in which one of the dome lenses of  FIGS. 2   a  and  2   b  is employed; 
           [0033]      FIG. 4  is a perspective view illustrating a jig for forming a concave groove in the dome lens according to the exemplary embodiment of the present invention; 
           [0034]      FIG. 5  is a flowchart illustrating a method for manufacturing the lens for the LED package according to the exemplary embodiment of the present invention; 
           [0035]      FIGS. 6A to 6F  are perspective views illustrating the method for manufacturing the lens for the LED package according to the exemplary embodiment of the present invention; 
           [0036]      FIG. 7  is a flowchart illustrating a process for forming the concave groove in the dome lens according to the exemplary embodiment of the present invention; and 
           [0037]      FIG. 8  is a flowchart illustrating a curing process according to the exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0038]    Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures. 
         [0039]    According to the present invention, an LED chip is mounted to a lead frame through a die bonding (D/B) and wire boding (W/B), and the LED chip is molded by silicon. A dome lens of a dome shape is manufactured on the LED package by silicon. The dome lens is manufactured by a dispensing technique or a printing technique. The LED package having the dome lens is located between upper and lower plate jigs, and the upper plate jig moves down toward the lower plate jig to thereby forming a concave groove in the dome lens. In this pressed state, the concave grove is cured. 
         [0040]      FIG. 2A  is a side view illustrating a dome lens according to an exemplary embodiment of the present invention, and  FIG. 2B  is a side view illustrating a modified dome lens according to the exemplary embodiment of the present invention. 
         [0041]    Referring to  FIGS. 2A and 2B , a dome lens is manufactured on an LED package by using silicon with predetermined viscosity. Here, silicon has viscosity enough for the dome lens to have a dome shape and not to stream down to the LED package. Preferably, silicon has viscosity of about 30 to 50 Pas. The dome lenses  10  and  20  may be manufactured by using a dispensing technique or a printing technique. The dispensing and printing techniques are well known to a person having ordinary skill in the art. 
         [0042]    A concave groove of a predetermined shape is formed in the dome lens by a projection attached to a bottom of an upper plate jig, which will be described in detail later. 
         [0043]    For example, if a concave groove of a corn shape having a predetermined angle is formed in the dome lens  10  as shown in  FIG. 2   a , light emitted from the LED package has a wide orientation angle. Thus, a color mixing between light sources of a backlight unit BLU having the dome lens for the LED package is increased, and light uniformity is increased, so that the thickness of the backlight unit can be reduced. That is, the thickness of the backlight unit can be reduced since an orientation angle of light emitted from the LED package is widened by the dome lens having the concave groove and so a distance between an optical sheet (not shown) and the LED package can be minimized. 
         [0044]    A concave groove formed in the dome lens  20  of  FIG. 2B  has an angle which depends on the height or depth of the dome lens  20 . 
         [0045]    For example, the concave groove has an angle of 60° at the low height and an angle of 76° at the high height. The concave groove having different angles according to the height of the dome lens  20  can be formed by a projection of the upper plate jig corresponding to the concave groove. 
         [0046]    If the dome lenses  10  and  20  for the LED package of  FIGS. 2   a  and  2   b  are employed to the backlight unit, an orientation angle of light emitted from the LED package is widened. It can be understood in  FIG. 3  that a curve of an orientation angle is wider spread compared to the conventional LED package having the dome lens.  FIG. 3  shows an orientation angle of light emitted from the backlight unit having the LED package in which one of the dome lenses  10  and  20  of  FIGS. 2   a  and  2   b  is employed. The dome lenses  10  and  20  of  FIGS. 2A and 2B  may have different orientation angles. 
         [0047]      FIG. 4  is a perspective view illustrating the jig for forming the concave groove in the dome lens according to the exemplary embodiment of the present invention. 
         [0048]    Referring to  FIG. 4 , the jig comprises an upper plate jig  41  and a lower plate jig  42 . 
         [0049]    The upper plate jig  41  comprises a plurality of projections  41   a  formed on a bottom thereof. A plurality of projections  41   a  are formed with a corresponding shape at locations corresponding to a plurality of LED packages. The upper plate jig  41  further comprises a press arm  41   b  which restricts a range for pressing the dome lenses  10  and  20  in a direction of the lower plate jig  42 . Here, the length of the press arm  41   b  is determined in consideration of the concave groove to be formed in the dome lenses  10  and  20 . 
         [0050]    The lower plate jig  42  supports a fixing plate (not shown) on which a plurality of LED packages are placed. The lower plate jig  42  comprises a coupling portion  43  to be coupled to the press arm  41  b when pressed. 
         [0051]    An operation of the jig for forming the concave groove in the dome lens according to the exemplary embodiment of the present invention is described with reference to  FIG. 4 . 
         [0052]    The fixing plate on which a plurality of LED packages are placed is located between the upper plate jig  41  and the lower plate jig  42 . The upper plate jig  41  moves down toward the lower plate jig  42  to press the dome lens  10  mounted on the LED package  100  in a concave groove form until it is stopped by the press arm  41   b . As a result, the concave groove is formed in the dome lens  10  by the projection  41  of the upper jig  41 . In the pressed state, the dome lens  10  is subjected to a curing process. The curing process is preferably performed at a temperature of 140˜160° C. for 25 to 35 minutes. 
         [0053]    Hereinafter, a method for manufacturing the lens for the LED package according to the exemplary embodiment of the present invention is described in more detail with reference to  FIGS. 5 to 8 . 
         [0054]      FIG. 5  is a flowchart illustrating a method for manufacturing the lens for the LED package according to the exemplary embodiment of the present invention, and  FIGS. 6   a  to  6   f  are perspective views illustrating the method for manufacturing the lens for the LED package according to the exemplary embodiment of the present invention. 
         [0055]    First, as shown in  FIG. 6A , a plurality of LED packages  100  to be placed on the fixing plate  30  are manufactured (step  501 ). 
         [0056]    As shown in  FIG. 6B , dome lenses  10  are formed on a plurality of LED packages  100  by using silicon (step  503 ). The silicon is transparent silicon and has viscosity enough for the dome lens  10  to have a dome shape and not to stream down to the LED package. Preferably, the silicon has viscosity of 30 to 50 Pas. 
         [0057]    The dome lens  10  is located between the upper and lower plate jigs  41  and  42  as shown in  FIG. 6C , and the concave groove is formed in the dome lens  10  by the projection  41   a  of the upper plate jig  41  as shown in  FIG. 6D  (step  505 ). 
         [0058]    The process for forming the concave groove in the dome lens is described with reference to  FIG. 7 .  FIG. 7  is a flowchart illustrating a process for forming the concave groove in the dome lens according to the exemplary embodiment of the present invention. 
         [0059]    When the dome lens  10  is located between the upper and lower plate jigs  41  and  42 , the upper plate jig  41  moves down toward the lower plate jig  42  to press the dome lens  10  (step  701 ), and the press arm  41   b  of the upper plate jig  41  penetrates the fixing plate  30  to be coupled to the coupling portion  43  of the lower plate jig  42 . At this time, the projection  41   a  of the upper plate jig  41  forms the concave groove in the dome lens  10  (step  703 ). 
         [0060]    Returning now to  FIG. 5 , the dome lens  10  having the concave groove formed by the upper and lower plate jigs  41  and  42  is subject to a curing process (step  507 ). 
         [0061]    The process for curing the dome lens  10  is described with reference to  FIG. 8 .  FIG. 8  is a flowchart illustrating the curing process according to the exemplary embodiment of the present invention. 
         [0062]    In a state that the dome lens  10  is pressed by the projection  41   a  of the upper plate jig  41  (step  801 ), it is determined whether it is more than a predetermined temperature or not (step  803 ). 
         [0063]    If not, a temperature is increased until it is more than a predetermined temperature (step  805 ). 
         [0064]    However, if it is more than a predetermined temperature, a curing of the dome lens  10  begins (step  807 ). 
         [0065]    It is determined whether a predetermined time lapses or not (step  809 ). If so, a curing of the dome lens  10  stops (step  811 ). However, if not, a curing of the dome lens  10  is continuously performed until a predetermined time lapses. 
         [0066]    If the dome lens  10  is completely cured, the upper plate jig  41  which is pressing the dome lens  10  is detached from the lower plate jig  42  as shown in  FIG. 6E . Then, as shown in  FIG. 6F , a plurality of LED packages  100  having the dome lens  10  are removed from the fixing plate  30  (step  509 ). 
         [0067]    As described above, according to the present invention, since the concave groove is formed in the dome lens by the jig, the dome lens having excellent light efficiency and brightness can be manufactured, and the manufacturing process of the dome lens can be simplified. 
         [0068]    In addition, the thickness of the backlight unit which employs the LED package having the dome lens can be reduced. 
         [0069]    Although the present invention has been described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that a variety of modifications and variations may be made to the present invention without departing from the spirit or scope of the present invention defined in the appended claims, and their equivalents.