Abstract:
It is to provide a light source module capable of downsizing an edge-light type backlight in thickness and reducing the usage amount of resin. A method of manufacturing a light source module includes a process of preparing a substrate with a first reflector including a reflecting surface mounted thereon, a process of mounting a plurality of light emitting elements on the substrate, a process of mounting a wiring board having an electrode on the substrate, a process of connecting the electrode of the light emitting element and the electrode of the wiring board with metal wire, a process of mounting a second reflector having a reflecting surface on the wiring board, and a process of filling the space between the first reflector and the second reflector, with resin.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Technical Field 
         [0002]    The invention relates to a light source module using an LED and a manufacturing method thereof, and more particularly, to a preferred LED light source module for use in a backlight of a liquid crystal monitor. 
         [0003]    2. Background Art 
         [0004]    As a backlight of a liquid crystal monitor, an LED (light-emitting diode) has been used recently. A backlight using an LED includes a direct type in which LEDs are arranged on the rear side of a liquid crystal panel and an edge-light type in which LEDs are arranged at the lower edge of a liquid crystal panel. In the edge-light type backlight, LEDs are arranged in lines at the lower edge portion of a liquid crystal panel and a light from an LED is guided to the rear side of the liquid crystal panel by a light guide plate, to illuminate the whole surface of the liquid crystal panel equally. 
         [0005]    The edge-light type backlight can be adopted to make a liquid crystal television thinner but it enlarges the size of the liquid crystal television in the vertical direction. Therefore, in order to reduce the size of the liquid crystal television in the vertical direction, it is necessary to reduce the height of each LED. 
         [0006]    Recently, a thin liquid crystal display device has been developed. In the liquid crystal display device, the thickness of an edge-light type backlight has to be further reduced. 
       Patent Document 1 Japanese Patent Application Laid-Open (JP-A) No. 
     DISCLOSURE OF THE INVENTION 
     Problems to be solved by the Invention 
       [0007]    An LED used as an edge-light type backlight is sealed by resin having a high refractive index. A silicon resin is generally used as this type of resin. The price of a silicon resin, however, is high comparatively. JP-A No. 2006-93672 discloses a semiconductor light emitting device designed to house a light emitting device in a recess which is provided in a lead or a support. In the example of the publication, since each package is sealed by resin, the usage amount of resin can be reduced, but a work of filling the resin becomes complicated. 
         [0008]    On the other hand, there is a method for forming a line-shaped long light source module by mounting a plurality of LED chips on a base and sealing all the LEDs by single filling of resin. In this method, however, a work of filling the resin becomes easy, but the usage amount of silicon resin increases, hence to increase the cost. 
         [0009]    The light source module dissipates heat from the LEDs through the silicon resin sealing the LEDs. In other words, the resin sealing the LEDs has a function of dissipating the heat from the LEDs. Therefore, a light incident edge surface of a light guide plate is formed of thermal deformable methacrylate, which is protected from the heat of the LEDs. When the usage amount of silicon resin is reduced, however, the resin&#39;s function of dissipating heat is deteriorated and the light incident edge surface of the light guide plate can be affected by the heat. In addition, when the usage amount of silicon resin is reduced, a space between the surface of the silicon resin and the light incident surface of the light guide plate becomes wider and the light use efficiency is reduced. 
         [0010]    The purpose of the invention is to provide a light source module which can be downsized in depth with the reduced usage amount of resin. 
         [0011]    A method of manufacturing a light source module, according to the invention includes: a first process of preparing a substrate with a first reflector including a reflecting surface mounted thereon; a second process of mounting a plurality of light emitting elements on the substrate so that each of the light emitting elements is put near the reflecting surface of the first reflector to reflect light from the light emitting element; a third process of mounting a wiring board including an electrode on the substrate so that the electrode of the wiring board approaches to the light emitting element and that the light emitting element is sandwiched between the first reflector and the wiring board; a fourth process of connecting the electrode of the light emitting element and the electrode of the wiring board with metal wire; a fifth process of mounting a second reflector including a reflecting surface on the wiring board so that the light from the light emitting element is reflected on the reflecting surface of the second reflector and that the light emitting element is sandwiched between the first reflector and the second reflector; and a sixth process of filling a space between the first reflector and the second reflector with resin, to seal the light emitting element. 
         [0012]    The invention can provide a light source module which can be downsized in depth with the reduced usage amount of resin. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0013]      FIG. 1  is a diagram showing an example of a method of manufacturing the conventional light source module. 
           [0014]      FIG. 2  is a diagram showing an example of a method of manufacturing a light source module according to the invention. 
           [0015]      FIG. 3  is a diagram for explaining the size of an LED and a submount in the light source module according to the invention. 
           [0016]      FIG. 4  is a diagram for explaining the size between a wiring board and the submount in the light source module according to the invention. 
           [0017]      FIG. 5  is a diagram showing a second example of the light source module according to the invention. 
           [0018]      FIG. 6  is a diagram showing an example of a backlight module according to the invention. 
           [0019]      FIG. 7  is a diagram showing an example of a liquid crystal display device according to the invention. 
           [0020]      FIG. 8  is a diagram showing a second example of the liquid crystal display device according to the invention. 
           [0021]      FIGS. 9A ,  9 B and  9 C are diagrams showing a third example of the light source module according to the invention. 
       
    
    
     DESCRIPTION OF REFERENCE NUMERALS 
       [0022]      11  . . . substrate,  11   a  . . . recess,  12  . . . substrate,  12   a  . . . reflector unit,  12   b  . . . engagement portion,  13  . . . wiring board,  14  . . . multi-layer wiring board,  15  . . . adhesive sheet,  16 ,  17 ,  18 ,  19  . . . reflector,  21  . . . LED,  22  . . . submount,  23  . . . silver paste,  25  . . . metal wire,  26  . . . resin,  50  . . . light guide plate,  52  . . . radiation heat sink,  52   a  . . . fin, and  53  . . . liquid crystal panel module 
       DESCRIPTION OF PREFERRED EMBODIMENT 
       [0023]    Referring to  FIG. 1 , a process of assembling the conventional light source module will be described.  FIG. 1  shows a cross sectional structure of the light source module which is cut along a vertical plane orthogonal to the liquid crystal display surface. Therefore, The liquid crystal display surface is vertical to the plane of paper. In Step S 1 , a package board is prepared. The package board is generally provided from another process, another factory, or another company. The package board has a substrate  11 , a wiring board  13  disposed on the substrate, and a reflector  16  arranged on the wiring board. The wiring board  13  is attached on the substrate  11  through an adhesive sheet  15 , the reflector  16  is attached on the wiring board  13  through the adhesive sheet  15 . The wiring board  13  is a three-layer board comprising an insulating layer  131 , a metal layer  132  put thereon, and an insulating layer  133  put thereon. 
         [0024]    In Step S 2 , an LED  21  is mounted. In this specification, an LED chip will be referred to simply as an LED. A silver paste  23  is applied to the substrate  11  and the LED  21  is arranged thereon. In this way, the LED  21  is bonded to the substrate  11 . In Step S 3 , wire bonding is carried out. An electrode of the wiring board  13  is electrically connected to the LED  21  by a metal wire  25 . In Step S 4 , resin sealing is carried out. The resin  26  is filled to coat the LED  21 . The light source module is completed by hardening the resin  26 . 
         [0025]    The reflector  16  has a function of reflecting a light from the LED  21  to guide the light upward, also serving as a wall for protecting the resin  26  from flowing out. In other words, the resin  26  is retained in a region surrounded by the reflector  16 . In order to efficiently lead the light from the LED  21  forwardly, it is preferable that the reflector  16  is arranged near the LED  21 . However, in the case that the reflector  16  is arranged near the LED  21 , when the LED  21  is mounted, there is a fear that a tool used for it may interfere with the reflector  16 . Also in the wire bonding, there is a fear that a wire and a tool may interfere with the reflector  16 . The reflector  16  is generally arranged at a position far from the LED  21 . Therefore, the size of the reflector  16  becomes large from the viewpoint of an optical reason. Further, the usage amount of resin required for sealing is increased. 
         [0026]    Referring to  FIG. 2 , the process of assembling the light source module according to the invention will be described.  FIG. 2  shows a cross sectional structure of the light source module which is cut along a vertical plane orthogonal to the liquid crystal display surface. In Step S 101 , a package board is prepared. The package board according to the example has a substrate  11  and a first reflector  17  attached to it. The substrate  11  may be formed of a metal plate with high heat conductivity, for example, like an aluminum plate or may be formed of a ceramic substrate with high heat radiation. The first reflector  17  may be formed of a material with high heat conductivity, for example, a metal such as aluminum or copper. When the aluminum is used, the reflector may be manufactured at a low cost by extrusion processing. The first reflector  17  may be formed separately from the substrate  11 , or it may be formed integrally with the substrate  11 . 
         [0027]    The first reflector  17  has a reflecting surface. When the LED  21  is mounted, the light from the LED  21  is reflected on the reflecting surface and the surface is vertical to the substrate  11  in the example. The whole reflecting surface or outer surface of the first reflector  17  is coated with a white reflective film in order to improve surface reflectance. The white reflective film may be formed by anodizing treatment or it may be formed by applying a white solder resist. 
         [0028]    In Step S 102 , the LED  21  is mounted on the substrate  11 . As shown in the figure, the LED  21  is mounted on the submount  22 . The LED  21  is previously attached to the submount  22  with the silver paste  23 . The silver paste  23  is applied to the substrate  11  and the LED  21  is mounted thereon together with the submount  22 .  FIG. 2  shows the cross sectional structure of the light source module which is cut along a vertical plane orthogonal to the liquid crystal display surface and a plurality of LEDs  21  are arranged along the direction vertical to the plane of paper. 
         [0029]    The submount  22  is designed to have an electrode formed on an insulating board. The board may be formed of insulating ceramics comprising aluminum nitride, alumina or the like, or it may be a silicon board with its surface processed by thermal oxidation process to secure insulation properties. 
         [0030]    The light emitting property of the LED  21  is not uniform. Then, before the LED  21  is mounted on the substrate  11 , a property test is carried out for checking the light emitting property of the LED  21 . At this time, the test becomes easier when the LED  21  is mounted on the submount  22  than when it&#39;s not. This is because an extraction electrode for making contact with the rear surface electrode of the LED  21  is formed on the top surface of the submount  22 . When the property test of the LED  21  is carried out, a probe may be made contact with the extraction electrode of the submount  22 , instead of making the probe contact with the rear surface electrode of the LED  21 . 
         [0031]    In the example, after the test for checking the light emitting property of the LED  21  is performed, a combination of the LEDs  21  to be mounted on the light source module is selected based on the light emitting property of the LED  21 . As the result, a light source module satisfying a predetermined standard can be obtained. 
         [0032]    In Step S 103 , a wiring board  13  is mounted. Namely, the wiring board  13  is attached to the substrate  11  with the adhesive sheet  15 . The wiring board  13  is mounted near the LED  21  and the submount  22 . The wiring board  13  is a three-layer board comprising an insulating layer  131 , a metal layer  132  put thereon, and an insulating layer  133  put thereon. The wiring board  13  may be a glass epoxy board or it may be a flexible board such as a polyimide wiring board. As the glass epoxy board, there is the FR4 board. 
         [0033]    In Step S 104 , the wire bonding is carried out. The electrode on the wiring board  13  and the electrode on the upper surface of the LED  21  are electrically connected by a metal wire  25 . The electrode on the wiring board  13  and the electrode on the submount  22  are also connected by the metal wire  25 . For example, the metal wire may be a gold wire. In Step S 105 , a second reflector  18  is mounted. Specifically, the second reflector  18  is attached to the wiring board  13  with the adhesive sheet  15 . The second reflector  18  has an inclined reflecting surface. The whole reflecting surface or the outer surface of the second reflector  18  is coated with the white reflective film in order to improve the surface reflectance. In Step S 106 , resin sealing is carried out. The resin  26  is filled to cover the LED  21 . As described above, the resin  26  may be the silicon resin. The resin  26  is retained between the two reflectors  17  and  18 . By hardening the resin  26 , the light source module is completed. 
         [0034]    In the light source module in the example, the first reflector  17  has the reflecting surface vertical to the substrate  11  and the second reflector  18  has the inclined reflecting surface with respect to the substrate  11 . However, the two reflectors may have the reflecting surfaces vertical to the substrate  11  or the two reflectors may have the inclined reflecting surfaces. 
         [0035]    Referring to  FIG. 3 , the sizes of the LED  21  and the submount  22  will be described. As shown in the figure, the submount  22  is attached to the substrate  11  with the silver paste  23 . Further, the LED  21  is attached to the submount  22  with the silver paste  23 . The size in plan view of the LED  21  is defined as L 1 , the thickness of the LED chip  21  is defined as t 1 , and the size in plan view of the submount  22  is defined as L 2 . From the reason of the characteristic of dielectric strength voltage, these sizes are preferably in the following relationship. 
         [0000]        L 2 ≧L 1 +t 1×2  formula 1 
         [0036]    Transformation of this formula leads to the following formula. 
         [0000]      ( L 2− L 1)/2 ≧t 1  formula 2 
         [0037]    As shown in the figure, when the submount  22  is arranged so as to come into contact with the first reflector  17 , the left side of the formula 2 shows a space δ between the first reflector  17  and the LED  21 . Therefore, the formula 2 means that the space δ between the first reflector  17  and the LED  21  is larger than the thickness t 1  of the LED chip  21 . 
         [0038]    Therefore in the example, when the thickness t 1  of the LED chip  21  becomes larger, the space δ between the first reflector  17  and the LED  21  has to be enlarged. 
         [0039]    Referring to  FIG. 4 , the distance between the wiring board  13  and the LED  21  will be described. The distance between the edge surface of the submount  22  and the edge surface of the wiring board  13  is defined as L 3 . An outer diameter of the metal wire  25  is defined as d. From the reason of the characteristic of dielectric strength voltage, these sizes are preferably in the following relationship. 
         [0000]      L3≧50 micron  formula 3 
         [0000]      or 
         [0000]        L 3 ≧d× 2  formula 4 
         [0040]    The size of the electrode on the wiring board  13  is defined as L 4 . The size L 4  of the electrode is set based on the shape of the bonding tool such that the bonding tool does not suffer interference from the wiring board  13 . The size, however, has to be at least four or five times larger than the outside diameter of the metal wire  25 . 
         [0000]        L 4 ≧d ×(4˜5)  formula 5 
         [0041]      FIG. 5  shows a second example of the light source module according to the invention. In the example, a multi-layer wiring board  14  is used as the wiring board. Since the thickness of the multi-layer wiring board  14  is large, the distance between the reflecting surface of the second reflector  18  mounted on the multi-layer wiring board  14  and the LED  21  becomes large. Therefore, of all the light emitted from the side surface of the LED chip  21 , the amount of the light incident to the reflecting surface of the second reflector  18  becomes smaller. Then, in the example, a recess  11   a  for arranging the multi-layer wiring board  14  is formed in the substrate  11 . Hence, the position of the second reflector  18  mounted on the multi-layer wiring board  14  moves downwardly. Therefore, of the light emitted from the side surface of the LED chip  21 , the amount of the light incident to the reflecting surface of the second reflector  18  can be increased. Also, in the example, the first reflector  17  may have the inclined reflecting surface. 
         [0042]      FIG. 6  shows an example of a backlight module according to the invention. The backlight module of the example has the light source module and a light guide plate  50 . In the light source module of the example, the first reflector is integrally formed with the substrate. In the example, the substrate  12  has a reflector unit  12   a . The reflector unit  12   a  has a shape similar to that of the second reflector  18 . Further, the light source module of the example has the light guide plate  50 . The light guide plate  50  is arranged on both the reflector unit  12   a  of the substrate  12  and the second reflector  18 . The method of manufacturing the light source module in the example is similar to the method shown in  FIG. 2 . 
         [0043]      FIG. 7  shows an example of a liquid crystal display device according to the invention. The liquid crystal display device of the example has the backlight module shown in  FIG. 6 , a liquid crystal panel module  53 , and a radiation heat sink  52 . The radiation heat sink  52  has a plurality of fins  52   a.    
         [0044]    The radiation heat sink  52  is connected to the reflector unit  12   a  of the substrate  12 . The heat from the LED  21  is transferred to the radiation heat sink  52  through the reflector unit  12   a  of the substrate  12 . Therefore this can prevent the temperature of the resin  26  from rising. Of the heat generated from the LED  21 , the amount of the heat directly transferred to the light guide plate  50  through the resin  26  can be reduced. As the result, such a possibility is decreased that the light guide plate  50  may be affected by the heat from the LED  21 . In the example, a necessity for dissipating the heat from the LED  21  by the resin is reduced. Therefore, it is possible to reduce the usage amount of resin. 
         [0045]    In the example, since the usage amount of resin can be reduced, the light guide plate  50  can be arranged near the LED  21 , hence to improve the light use efficiency. 
         [0046]    Referring to  FIG. 8 , another example of the liquid crystal display device will be described. In the liquid crystal display device of the example, an engagement portion  12   b  to be engaged with the lower edge of the rear side of the light guide plate  50  is formed in the reflector unit  12   a  of the substrate  21 . The engagement portion  12   b  is formed as a groove or a recess. In this way, by providing the engagement portion  12   b  in the reflector unit  12   a  of the substrate, positioning of the light guide plate  50  becomes easier with higher precision. 
         [0047]    The light guide plate  50  and the liquid crystal panel module  53  are arranged on the upper surface of the second reflector  18 . Specifically, the lower edge of the front surface of the light guide plate  50  is put on the rear side portion in the upper surface of the first reflector  18  and the liquid crystal panel module  53  is put on the front side portion in the upper surface of the first reflector  18 . In the upper surface of the first reflector  18 , the front side portion forms a liquid crystal panel supporting unit  18   a . Therefore, the liquid crystal panel module  53  can be mounted easily. 
         [0048]    When the thickness of the liquid crystal panel module  53  is defined as P and the size of the liquid crystal panel supporting unit  18   a  on the upper surface of the first reflector  18  is defined as P 2 , they shall be set so that the expression P 2 &lt;P is satisfied. As the result, the front surface of the liquid crystal panel module  53  is protruded frontward from the front surface of the light source module. As shown in the figure, a space may be provided between the light guide plate  50  and the liquid crystal panel module  53 . 
         [0049]    In the example, since the engagement portion  12   b  is provided in the reflector unit  12   a  of the substrate  12  and the liquid crystal panel supporting unit  18   a  is formed on the upper surface of the second reflector  18 , the process of positioning both the light guide plate and the liquid crystal panel becomes simple and the assembling work of the liquid crystal display device becomes easy. 
         [0050]    Further, it can realize a exceedingly compact light source module at a low cost, with high reliability and high optical performance, without too many optical parts. Furthermore, it can realize a thin and compact liquid crystal display. 
         [0051]    Referring to  FIGS. 9A ,  9 B and  9 C, a third example of the light source module according to the invention will be described.  FIG. 9A  shows the cross sectional structure of the light source module in the example which is cut along a vertical plane parallel to the liquid crystal display surface.  FIG. 9B  shows the cross sectional structure of the light source module in the example which is cut along the vertical plane AA orthogonal to the liquid crystal display surface.  FIG. 9C  shows the cross sectional structure of the light source module in the example which is cut along the vertical plane BB orthogonal to the liquid crystal display surface. As shown in  FIG. 9A , in the example, third reflectors  19  are provided in the both sides of the LED  21  on the substrate  11 . Each of the third reflectors  19  is extended in the direction orthogonal to the liquid crystal display surface. The third reflector  19  has an inclined reflecting surface. The whole reflecting surface or the outer surface of the third reflector  19  is coated with the white reflective film. 
         [0052]    In the example, all the LEDs  21  are sealed with the single resin  26 . Therefore, the usage amount of resin increases more than that in the case of sealing the respective LEDs  21  with the resin one by one. However, by providing the third reflectors  19 , the usage amount of the sealing resin can be reduced by the amount corresponding to the volume occupied by the third reflectors  19 . 
         [0053]    As shown in the figure, by making the height of a liquid surface  26   a  of the resin  26  higher than that of the third reflectors  19 , the resin  26  can be formed into a shape having a uniform liquid surface. When the height of the liquid surface  26   a  of the resin  26  is lower than that of the third reflectors  19 , the resin  26  is divided by the third reflectors  19  and a plurality of liquid surfaces are formed. The heights of the liquid surfaces of the resin for sealing the LEDs  21  are preferably uniform. Then, as shown in  FIG. 9C , a space is formed between the third reflectors  19  and the first and second reflectors  17  and  18 . In the other words, the third reflector  19  is formed in smaller size than the space between the two reflectors  17  and  18 . In this way, the resins for sealing the respective LEDs  21  are connected to each other through the space between the third reflectors  19  and the first and second reflectors  17  and  18 . Therefore, the heights of the liquid surfaces  26   a  of the resins  26  for sealing the respective LEDs  21  becomes uniform. 
         [0054]    As shown in  FIG. 9C , when the width of the LED  21  is defined as L 5  and the width of the third reflector  19  is defined as L 6 , they shall be set so as to satisfy the expression L 6 &gt;L 5 . The width of the third reflector  19  is larger than that of the LED  21 . 
         [0055]    Part of the lights emitted from the side surface of the LED  21  goes out from the space between the third reflectors  19  and the first and second reflectors  17  and  18 . However, the sizes of the first reflector  17  and the second reflector  18  are set relatively longer. Therefore, the light going out from the space between the third reflectors  19  and the first and second reflectors  17  and  18  is securely isotropically-scattered by the inclined reflecting surfaces of the first and the second reflectors. Therefore, the light from the LED may be led to the light guide plate effectively. 
         [0056]    The third reflector  19  may be formed integrally with the first reflector  17  and the second reflector  18 . In this case, the space is provided only in one side of the third reflector  19 . For example, the third reflector  19  may be formed integrally with the first reflector  17  and a space may be provided between the third reflector  19  and the second reflector  18 . Alternatively, the third reflector  19  may be formed integrally with the second reflector  18  and a space may be provided between the third reflector  19  and the first reflector  17 . 
         [0057]    In the light source module according to the invention, since the distance between the first reflector and the second reflector can be decreased, the edge-light type backlight can be thinned and the usage amount of resin can be reduced, hence to cut down the cost. 
         [0058]    Further, by providing the third reflectors, the usage amount of resin can be reduced by the amount corresponding to the space occupied by the third reflectors. By providing a space in one side or both sides of the third reflector, the resin can be moved freely and the liquid surface of the resin can be uniform. Therefore, while convenience of single operation of resin sealing is kept, the usage amount of resin can be reduced, hence to reduce the material cost and the number of man-hour. 
         [0059]    The light source module of the invention can realize a short light source module with high reliability for a long time at a low cost. Therefore, the height of the backlight of the liquid crystal display device can be reduced. 
         [0060]    As mentioned above, although some examples of the invention have been described, the invention is not restricted to the examples but those skilled in the art will understand easily that various modifications can be made in the range of the invention described in Claims.