Abstract:
An LED module includes: a package having electrodes provided on the outer surface of opposing sidewalls, and a light-emitting element connected to the electrodes and mounted on the package; a base member having a copper metal; an insulating layer stacked on the surface of the base member and having an insulating material; and a conductive wiring pattern connected to the electrodes by soldering and formed on the surface of the insulating layer. The insulating layer has a through-hole formed by removing a part of the section where the package is positioned, and a heat dissipation unit formed by soldering between the back surface of the package and the base member, which face one another with the through-hole interposed therebetween.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to an LED module in which an LED chip is mounted within a package. 
       BACKGROUND OF THE INVENTION 
       [0002]    Conventionally, there have been available light source devices in which a discharge lamp, a laser oscillator, or the like have been used as a light source. In recent years, a variety of light source devices employing an LED (Light Emitting Diode) module as a light source has been proposed in an effort to seek reduced power consumption and prolonged lifespan. For example, an LED module whose emission wavelength is set to fall within an ultraviolet region is used as an ultraviolet irradiation source in an ultraviolet irradiation device for irradiating ultraviolet rays on an ultraviolet curable resin such as paint, an adhesive agent, a pigment, or the like to thereby cure and dry the ultraviolet curable resin. 
         [0003]    In the LED module for use in this kind of light source device, an LED chip is mounted within a package. The LED module is manufactured by arranging a plurality of packages side by side so as to obtain a desired light quantity. An LED chip with high output power is used as the LED chip. The LED chip is set so as to obtain a desired light quantity. 
         [0004]    If the LED chip emits a light by supplying an electric current to the LED module, the LED chip generates heat. As stated above, the LED module of this kind makes use of a plurality of LED chips. Therefore, the LED module generates an increased amount of heat. The emission efficiency of the LED chip has a negative temperature coefficient. This poses a problem in that, if the amount of heat generated by the LED chip becomes larger, the emission efficiency of the LED module gets lower. 
         [0005]    Just like an LED mounting structure as disclosed in, e.g., JP2006-100687A, there are proposed an LED module with an enhanced heat dissipation effect and a mounting structure thereof. In the LED mounting structure disclosed in JP2006-100687A, a substrate is formed by stacking an insulating layer, wiring patterns, and a resist on the upper surface of a base member made of metal having high heat conductivity. A package equipped with an LED chip is mounted on the surface of the substrate. At this time, the insulating layer or the resist of the substrate positioned at the bottom surface side of the package is removed. A heat transfer member such as silicon rubber or the like is arranged between the package and the base member. As a result, the heat generated from the LED chip is dissipated via the heat transfer member and the base member, thereby enhancing the heat dissipation effect. 
         [0006]    In order to manufacture the LED module disclosed in JP2006-100687A, however, there is a need to first stack the insulating layer, the wiring patterns, and the resist on the base member and then secondly, to remove the insulating layer, the wiring patterns, and the resist from the region over which the package is to be mounted. The heat transfer member is arranged in the region from which the insulating layer, the wiring patterns, and the resist are removed. The package equipped with the LED chip is arranged on the heat transfer member. Electrodes arranged in the package are soldered to the wiring patterns. The manufacturing process of the LED module disclosed in JP2006-100687A is too complex. 
       SUMMARY OF THE INVENTION 
       [0007]    In view of the above, the present invention provides an LED module capable of reliably dissipating heat generated from an LED chip and simplifying a manufacturing process thereof. 
         [0008]    In accordance with an embodiment of the present invention, there is provided an LED module including: a package including electrodes formed on outer surfaces of opposite sidewalls of the package and a light emitting element mounted in the package and connected to the electrodes; a base member made of copper-based metal; an insulating layer made of an insulating material and stacked on a surface of the base member; and an electrically conductive wiring pattern formed on a surface of the insulating layer and soldered to the electrodes. 
         [0009]    The insulating layer includes a through portion formed by partially removing a region of the insulating layer in which the package is to be arranged, and a heat dissipation member made of a solder is arranged between a bottom surface of the package and the base member opposite to each other through the through portion. 
         [0010]    In the LED module, a metal-made heat dissipation layer may preferably be provided on the bottom surface of the package. 
         [0011]    With the LED module in accordance with the embodiment of the present invention, it becomes unnecessary to use a step for arranging a heat transfer member in a region from which an insulating layer or the like is removed. It is also possible to reliably dissipate the heat generated from the light emitting element and to simplify the manufacturing process. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The objects and features of the present invention will become apparent from the following description of a preferred embodiment given in conjunction with the accompanying drawings. 
           [0013]      FIG. 1  is a schematic section view showing certain major portions of an LED module in accordance with the present embodiment. 
           [0014]      FIGS. 2A through 2D  show a substrate configuring the LED module in accordance with the present embodiment,  FIG. 2A  showing a plane view for explaining a substrate as a whole,  FIG. 2B  showing a plane view for explaining wiring patterns,  FIG. 2C  showing a plane view for explaining a resist layer, and  FIG. 2D  showing a plane view for explaining a through-hole. 
           [0015]      FIGS. 3A through 3D  show a package configuring the LED module in accordance with the present embodiment,  FIG. 3A  showing a plane view of the package,  FIG. 3B  showing a bottom view of the package,  FIG. 3C  showing a side view of the package, and  FIG. 3D  showing a cross-sectional view taken along line  3 D- 3 D in  FIG. 3A . 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0016]    An embodiment of the present invention will now be described in detail with reference to the accompanying drawings which form a part of the subject specification. Throughout the drawings, identical or similar portions will be designated by like reference symbols without redundant description thereof. 
         [0017]    An LED module in accordance with the embodiment of the present invention is described with reference to the drawings. 
         [0018]    The LED module  1  in accordance with the present embodiment is used as an ultraviolet irradiation source in an ultraviolet irradiation device for irradiating ultraviolet rays on an ultraviolet curable resin such as paint, an adhesive agent, or a pigment to thereby cure and dry the ultraviolet curable resin. In the following description, unless otherwise stated, the up-down direction in  FIG. 2A  will be defined as the front-back direction of the LED module  1 . The left-right direction in  FIG. 2A  will be defined as the left-right direction of the LED module  1 . The up-down direction in  FIG. 1  will be defined as the up-down direction of the LED module  1 . 
         [0019]    As shown in  FIGS. 1 and 2A , the LED module  1  includes a substrate  10  of a rectangular flat plate whose left-right direction extends in the longitudinal direction and a plurality of packages  2  arranged side by side along the left-right direction on the upper surface of the substrate  10 . In an ultraviolet irradiation device, a plurality of LED modules  1  is arranged side by side along the left-right direction and the front-back direction so as to irradiate a specified region with a desired quantity of light. 
         [0020]    As shown in  FIGS. 3A through 3D , each of the packages  2  includes an LED chip  3 , an over-voltage-preventing zener diode chip  6  for limiting a voltage applied to the LED chip  3 , and a package body  20  having a recess portion  21  formed on the surface thereof, the LED chip  3  and the zener diode chip  6  being arranged within the recess portion  21  of the package body  20 . 
         [0021]    The package body  20  is made of a ceramic material with high heat-dissipating property, e.g., alumina, aluminum nitride or the like, and is formed of an injection-molded product of a substantially rectangular parallelepiped shape whose longitudinal direction extends in the front-back direction. Conductive patterns  26  and  27  and electrode pads  4   a  and  4   b  are patterned on the surface of the package body  20  through the use of, e.g., a MID (Molded Interconnect Device: three-dimensional injection-molded circuit part) technique. 
         [0022]    An elongated recess portion  21  whose long side extends in the front-back direction when seen from a top view is formed on the surface (the upper surface in  FIG. 3D ) of the package body  20 . The LED chip  3  is arranged on the bottom of the recess portion  21  in the left-right and front-back central position of the package body  20 . The zener diode chip  6  is arranged on the bottom of the recess portion  21  at one front-back-direction side (e.g., the front side) of the LED chip  3 . A through-hole  22  to be later described is formed at the other front-back-direction side (the back side) of the LED chip  3 . 
         [0023]    On the bottom of the recess portion  21 , there are provided ribs  23   a  and  23   b  that protrude toward the opening side (upper side) of the recess portion  21  from the region between the LED chip  3  and the zener diode chip  6  and the region between the LED chip  3  and the through-hole  22 . 
         [0024]    Within the recess portion  21  of the package body  20 , the LED chip  3 , the zener diode chip  6 , and the through-hole  22  are arranged side by side along the front-back direction where they are isolated by the ribs  23   a  and  23   b . The top surfaces of the ribs  23   a  and  23   b  are positioned above the top surface of the LED chip  3  mounted in a recess portion  21   a.    
         [0025]    A frame-shaped conductive pattern  26  extends over the entire periphery of the recess portion  21  on the surface of the package body  20 . The conductive pattern  26  is provided in a continuous relationship with die pad portions  50  and  52  formed in the recess portions  21   a  and  21   c  and is electrically connected to lower electrodes (not shown) of the LED chip  3  and the zener diode chip  6 . An electrode pad  4   b  extending from the conductive pattern  26  toward the bottom surface of the package body  20  is formed on one end surface in the longitudinal direction (e.g., the front end surface) of the package body  20 . 
         [0026]    A depressed portion  24  extending from the back end of the package body  20  beyond the through-hole  22  is provided on the bottom surface (the lower surface in  FIG. 3D ) of the package body  20 . On the bottom surface of the package body  20 , a step portion is provided between the depressed portion  24  and the remaining region of the bottom surface of the package body  20 . The bottom surface of the depressed portion  24  is positioned above the bottom surface of the package body  20  other than the depressed portion  24 . The inner circumferential surface of the through-hole  22  opened into the depressed portion  24  is plated with metal and is electrically connected to an electrode pad  4   a  formed on the opposite end surface (e.g., on the bottom end surface of the package body  20 ) of the package body  20  from the end surface on which the electrode pad  4   b  is formed. 
         [0027]    A conductive pattern  27  electrically connected to the through-hole  22  is formed in the substantially entire region of the recess portion  21   b  of the package body  20 . Bonding pads  28   a  and  28   b  formed on the ribs  23   a  and  23   b  are provided in a continuous relationship with the conductive pattern  27 . The bonding pad  28   a  is connected via bonding wires (thin metallic wires)  25   a  and  25   b  to an upper electrode (e.g., a cathode electrode) of the LED chip  3  and an upper electrode of the zener diode chip  6 . Similarly, the bonding pad  28   b  is connected via a bonding wire (a thin metallic wire)  25   c  to the upper electrode of the LED chip  3 . 
         [0028]    A junction pad  5  plated into a rectangular plate shape is provided in the left-right central region of the bottom surface of the package body  20 . 
         [0029]    As set forth above, in each of the packages  2 , the electrode pads  4   a  and  4   b  provided at the front and back side walls of the package body  20 , the LED chip  3  and the zener diode chip  6  are electrically connected to one another. Therefore, if an electric current is supplied to between the electrode pads  4   a  and  4   b , the LED chip  3  emits and irradiates ultraviolet rays. 
         [0030]    The substrate  10  is formed by stacking an insulating layer  12 , wiring patterns  13 , and a resist layer  14  on the upper surface of a base member  11  made of copper-based metal with high conductivity. Screw holes  10   a  for use in attaching the substrate  10  to the ultraviolet irradiation device are formed in four corners of the substrate  10 . 
         [0031]    Current reinforcing bars  18 , which is formed into a rectangular plate shape with its longitudinal direction extending in the left-right direction and made of highly conductive metal such as copper or the like, are attached to the upper surface of the substrate  10  at the front and back edge portions of the substrate  10 . The current reinforcing bars  18  and the packages  2  are attached to the substrate  10  by virtue of a reflow process to be described later. The current reinforcing bars  18  are electrically connected to the wiring patterns  13  of the substrate  10  so as to supply the electric power fed from the ultraviolet irradiation device to the respective packages  2  via the wiring patterns  13 . At this time, the electric power having a large current value is fed from the ultraviolet irradiation device. By attaching the current reinforcing bars  18  to the substrate  10 , it is possible to reduce the resistance against the electric current thus supplied. This makes it possible to supply the electric power having a large current value to the respective packages  2  with a reduced loss of electric power. 
         [0032]    The insulating layer  12  of the substrate  10  is formed into a thin film shape (with a thickness of, e.g., about 14 μm) by a polyimide having heat resistance and an insulation property. The insulating layer  12  is attached to the surface of the base member  11  by an adhesive agent or the like so as to cover the entire region of the surface of the base member  11 . 
         [0033]    Each of the wiring patterns  13  of the substrate  10  is formed into a thin film shape (with a thickness of, e.g., about 18 μm) by a metal having increased electric conductivity. Each of the wiring patterns  13  is formed of, e.g., a copper foil. As indicated by the hatching in  FIG. 2B , the wiring patterns  13  are provided in the regions of the top surface of the insulating layer  12 , excluding the front-back-direction central region and the regions around the screw holes  10   a . The wiring patterns  13  and the electrode pads  4   a  and  4   b  of each of the packages  2  arranged on the upper surface of the substrate  10  are connected to each other by solders  17  (see  FIG. 1 ). 
         [0034]    The resist layer  14  of the substrate  10  is a solder resist serving to deter adherence of solders. As indicated by the hatching in  FIG. 2C , the resist layer  14  is formed in the necessary regions of central and peripheral portions in the front-back-direction of the substrate  10 . The resist layer  14  includes groove portions  14   a  and  14   b  depressed toward the front-back-direction center. The groove portions  14   a  and  14   b  are arranged along the left-right direction, i.e., the arranging direction of the packages  2 , in a specified interval equal to the arranging interval of the packages  2 . The width of each of the groove portions  14   a  and  14   b  is set pursuant to the arrangement position and size of the electrode pads  4   a  and  4   b  of each of the packages  2 . 
         [0035]    In the present embodiment, the groove portion  14   a  where the electrode pad  4   b  is arranged is formed in the left-right-direction central position of each of the packages  2  so as to have a width smaller than the width of the groove portion  14   b . The groove portion  14   b  where the electrode pad  4   a  is arranged is formed to have a dimension substantially equal to the left-right-direction dimension of each of the packages  2 . This prevents the solders from being attached to between the electrode pads  4   a  and between the electrode pads  4   b  of the adjacent packages  2 . 
         [0036]    As shown in  FIG. 2D , the regions of the insulating layer  12  and the resist layer  14  of the substrate  10  where the packages  2  are arranged (the substantially central regions of the substrate  10  in the front-back direction) are removed to form through portions  15 . The through portions  15  are formed into such a shape that at least the front-back-direction size thereof becomes smaller than the external dimension of the packages  2  (see  FIG. 1 ). 
         [0037]    A solder (heat dissipation member)  16  for dissipating the heat generated from each of the packages  2  is provided in the central region of each of the through potions  15 . The junction pad (heat dissipation layer)  5  arranged on the bottom surface of each of the packages  2  is thermally connected to the base member  11  through the solder  16  (see  FIG. 1 ). 
         [0038]    Description will now be made on a method of manufacturing the LED module  1  of the present embodiment. First of all, the insulating layer  12  is formed on the entire region of the top surface of the base member  11  made of copper-based metal. The through portions  15  are formed to penetrate the insulating layer  12 . Next, the wiring patterns  13  are formed on the top surface of the insulating layer  12 . The resist layer  14  is formed so as to cover the insulating layer  12  and the wiring patterns  13 . Then, cream solders are formed, by screen printing or other methods, on the edges of the surfaces of the wiring patterns  13  facing the front-back-direction center of the substrate  10 , on the regions of the surfaces of the wiring patterns  13  making contact with the current reinforcing bars  18  and on the surface of the base member  11  corresponding to the substantially central region of each of the through portions  15 . 
         [0039]    Thereafter, the current reinforcing bars  18  and the packages  2  are arranged on the substrate  10 . The cream solders are melted by a reflow process. As a result, the packages  2  are mounted on the substrate  10 . The electrode pads  4   a  and  4   b  of the packages  2  and the wiring patterns  13  of the substrate  10  are electrically connected to each other. The junction pads  5  of the packages  2  and the base member  11  of the substrate  10  are thermally connected to each other. At the same time, the current reinforcing bars  18  are mounted to the substrate  10 , so that the current reinforcing bars  18  and the wiring patterns  13  are electrically connected to each other. 
         [0040]    With the LED module  1  described above, the heat generated from the LED chip  3  of each of the packages  2  is dissipated via the solder  16  and the base member  11 . This makes it possible to reliably dissipate the heat generated from the LED chip  3 . The solder  16  for thermally interconnecting the junction pad  5  and the base member  11  can be simultaneously formed when electrically connecting the electrode pads  4   a  and  4   b  of the packages  2  to the wiring patterns  13 . For this reason, a step for arranging a heat transfer member becomes unnecessary. This makes it possible to reduce the number of manufacturing steps. 
         [0041]    The junction pad  5  is provided on the bottom surface of each of the packages  2 . It is therefore possible to reliably dissipate the heat generated from the LED chip  3  of each of the packages  2 . 
         [0042]    The groove portions  14   a  and  14   b  whose widths are set in conformity with the arranging positions of the electrode pads  4   b  and  4   a  of the packages  2  are provided in the resist layer  14 . This makes it possible to prevent the solders from being attached to between the electrode pads  4   a  and  4   b  of the adjacent packages  2 . 
         [0043]    While the invention has been shown and described with respect to the embodiments, the present invention is not limited thereto. It will be understood by those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.