Abstract:
A light source module for a light emitting diode (LED) is provided. In the present invention, a common printed circuit board (PCB) is utilized to provide electric current and isolated from the heat dissipation mechanism, and the thermal conductive element, protruding from the LED package structure, is connected to another thermal conductive element to dissipate out the internal heat.

Description:
[0001]     This application claims the benefit of Taiwan application Serial No. 94104800, filed Feb. 18, 2005, the subject matter of which is incorporated herein by reference.  
       FIELD OF THE INVENTION  
       [0002]     The present invention relates to a light source module, and more particularly relates to a light source module of the light emitting diode (LED).  
       DESCRIPTION OF THE RELATED ART  
       [0003]     Light emitting diode (LED) is a common lighting element. It can be used as an instructor light in the electrical products, or the high power LED can be used for lighting, for example, the high power LED is often used as the backlight for the display devices. However, the lighting efficiency and the life of the LED are affected by the design of the heat dissipation of the light source module. When the LED is in high temperature of the working environment, the light output efficiency will be reduced. By increasing the input current of the power merely products more heat but the temperature of the LED increases, and eventually results in permanent damage.  
         [0004]     A light source module, having LEDs as lighting elements, usually contains an LED package structure and a printed circuit board (PCB) for transmitting input power. In order to provide a good heat dissipation efficiency, the PCB with good heat conductive efficiency, such as a metal-base PCB and so on, can be chosen to applied in the LED package structure. Referring to  FIG. 1A  and  FIG. 1B , showing cross-sectional view of an LED package structure disposed in a metal-base PCB  16  and a top plan view showing an LED package structure before being encapsulated on a metal-base PCB  16 . The LED package structure includes a base  11 , an LED chip  12 , a first thermal conductive element  13  applied in the LED chip  12 , a lead  14  electrically connected to the LED chip  12  and metal-base PCB  16 , and a package colloid  15  encapsulated the LED chip  12 . Metal-base PCB  16  includes a conductive layer  16 A, a dielectric layer  16 B, and a substrate  16 C, which may be made of metal or other materials for heat dissipation.  
         [0005]     Still referring to  FIG. 1A , in order to dissipate out the heat in the LED package structure, the first thermal conductive element  13  applied in with LED chip  12  is become the path of the thermal conductivity, which is inserted through the bottom  11 A of the base  11  and contacted directly with the metal-base PCB  16 . Therefore, the heat can be conducted in sequence of the conductive layer  16 A, the dielectric layer  16 B, and the substrate  16 C and finally dissipate out through the external heat sink attached on the metal-base PCB  16 .  
         [0006]     By considering the heat dissipation problem, the light source module of the related art has a metal-base PCB  16 , with good thermal conductivity, applied in the LED package structure. However, the cost of this kind of PCBs is very expensive, and it is not guaranteed that the heat can be conducted efficiently in the process of the multi-layers conduction. For example, the conductive layer  16 A connected with the first thermal conductive element  13  is usually in high temperature but cannot conduct the heat as soon as possible to the dielectric layer  16 B which is in the lower place and increase the temperature of the LED package structure. It should be noted, referring to  FIG. 1A  and  FIG. 1B , in the light source module of the related art, the LED chip  12  must be cooperated with the first thermal conductive element  13  and the metal-base PCB  16  that has bigger volume than the LED chip  12  in order to dissipate the heat out. Therefore on the one hand, the volume of the LED package structure is too hard to be reduced and cannot be fit in with the trend of the development to smallize the electrical products and on the other hand it would increase the cost of production of the whole light source module and would have to use expensive metal-base PCB  16 .  
       SUMMARY OF THE INVENTION  
       [0007]     It should be noted that the electrical products are become smaller and smaller, the light emitting diode (LED) is chosen to be the light source module of the lighting device. However, the size cannot be decreased because the heat dissipation problem and the expensive metal-base printed circuit board (PCB) must be applied in the LED package structure. The light source module design of the lighting device has an LED provided herein, one of the purposes is to provide an efficient heat dissipation structure and is not necessary to use expensive or heavy PCB applied in the LED package structure. And the volume of the light source module also may be reduced to fit in the trend of the development of the smallization.  
         [0008]     According to the goal of above description, LEDs are applied in a light source module of the lighting device in the present invention. Wherein the PCB transmitting the input power is isolated at the outside of the heat dissipation of the LED package structure. And the first thermal conductive element is connected thermally to the second thermal conductive element in the LED package structure. Therefore, the light source module only has to apply a conventional PCB to execute the operation of the input power and the heat dissipation structure can be simplified in the LED package structure and then reduce the size of the whole light source module. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1A  is a cross-sectional view illustrating a light emitting diode package structure of the related art, which is disposed in the metal-based printed circuit board.  
         [0010]      FIG. 1B  is a top plan view illustrating a light emitting diode package structure of the related art, which is disposed in a metal-based printed circuit board before encapsulating.  
         [0011]      FIG. 2A  is a cross-sectional view illustrating an LED light source module in accordance with a preferred embodiment of the present invention, wherein the light emitting diode package structure is disposed in a printed circuit board.  
         [0012]      FIG. 2B  is a top plan view illustrating an LED light source module in the preferred embodiment of the present invention, wherein the light emitting diode package structure is disposed in a printed circuit board before encapsulating.  
         [0013]      FIG. 2C  is a cross-sectional view illustrating an LED light source module of the present invention, wherein a plurality of light emitting diodes are disposed in the package structure.  
         [0014]      FIG. 2D  is a top plan view illustrating the heat conductive structure and the electrical conductive structure are separated, in accordance with a preferred embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0015]     The following is the detail description of the present invention. It should be noted and appreciated that the process steps and structures described below does not cover a complete process flow and structure. The present invention can be practiced in conjunction with various fabrication techniques that are used in the art, and only so much of the commonly practiced process steps are included herein as are necessary to provide an understanding of the present invention.  
         [0016]     The present invention will be described in detail with reference to the accompanying drawings. It should be noted that the drawings are in greatly simplified form and they are not drawn to scale. Moreover, dimensions have been exaggerated in order to provide a clear illustration and understanding of the present invention.  
         [0017]     In a preferred embodiment of the present invention, a light source module of the light emitting diode (LED)  2  is provided which includes an LED package structure and a printed circuit board  26  (PCB) for transmitting the input power to LED chip  22 . Referring to  FIG. 2A  and  FIG. 2B , there is a cross-sectional view showing an LED package structure of the light source module of the LED  2  disposed in a metal-base PCB  26  and a top plan view showing an LED package structure disposed in a PCB  26  before encapsulated. An LED package structure is composed of a base  21 , an LED chip  22 , a first thermal conductive element  23 , a lead  24  electrically connected to the LED chip  22  and the PCB  26 , and a package colloid  25  encapsulating the LED chip  22 . Conductive layer  26 A is disposed at side of the PCB  26 , which is electrically connected to the LED package structure to provide enough power for what the LED package structure needs.  
         [0018]     Still referring to  FIG. 2A , base  21  may be cup-shape. A bottom  21 A and a sidewall  21  B, with a slide surface or a reflective surface connected to the surrounding of the bottom  21 A, define a contained space. The heat conductive structure of the LED package is that the first thermal conductive element  23  inserted through the bottom  21 A is extended to the outside of the base  21  in order to contact with a second thermal conductive element  27 . Material of the first thermal conductive element and the second thermal conductive element may have good heat conduction such as metal. Power input to the LED package structure may be via lead  24 , which is inserted in the sidewall  21 B being a media to electrically connect with the electricity in the LED chip  22 , such as an anode, and the internal lead  24 B disposed in the volume space by the method of wire bonding. The external lead  24 A extending to the outside of the base  21  is electrically connected to the conductive layer  26 A on the PCB  26 . The first thermal conductive element  23  may be cathode.  
         [0019]     The light source module  2  of the LED in the present invention, the PCB  26  is used only to provide the power input for the LED package structure. PCE  26  may be normal fiberglass PCB or flexible PCB (FPC). The heat within the LED package structure may be conducted from the first thermal conductive element  23  to the second thermal conductive element  27  and then dissipates out. The heat dissipation structure of the LED package is simpler, more efficiency and cheaper than the related art using the metal-based PCB and also reduced the size of the LED package structure at the same time. In order to have the flexibility in size of the application in the light source module  2  of the light emitting diode of the present invention, and in the embodiment, the lead  24  including external lead  24 A and internal lead  24 B, referring to the  FIG. 2A , may be bended in 90 degree and inserted in the sidewall  21 B. Therefore, lead  24  may be mount on conductive layer  26 A by using Surface Mount Technology (SMT) and the arrangement of the PCB  26  can be changed to reduce the wide of the whole light source module  2  of the LED by the design of the parallel direction of the light output.  
         [0020]     In the other embodiments of the present invention, there may be a plurality of LED chips put in one LED package structure, for example in the  FIG. 2C , a plurality of the LED chips  22  in the same package structure are stick on the first thermal conductive element  23  and sharing same plane of the first thermal conductive element  23 , but the current input is entered by the different internal leads  24 B and is activated independently and controlled. This kind of bar like light source module of the LED is good to be used as a backlight source with sidelight emitting style in the small size display.  
         [0021]     Referring to  FIG. 2B , in the embodiment, the anode of the LED chip  22  is wire bonding to the internal lead  24 B and conducts the current from the PCB  26 . Cathode of the LED chip  22  may be stuck directly on the thermal conductive element  23  and may be considered ground. However, in other embodiments of the present invention, the heat and electricity conduction structure in the LED package structure may be separated and the PCB  26  is for the input and output of the current and isolated from the first thermal conductive element  23  that is for heat conduction. Therefore, the LED chip  22  is corresponding to two leads inserted into the sidewall  21 B, referring to  FIG. 2D , the anode of the LED chip  22  is corresponding to the first lead  241  and the cathode of the LED chip  22  is corresponding to the second lead  242 . After wire bonding the first internal lead  241 B and the second internal lead  242 B, the first external lead  241 A and the second external lead  242 A can be electrically connected to the PCB  26 .  
         [0022]     The foregoing description is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obvious modifications or variations are possible in light of the above teachings. In this regards, the embodiment or embodiments discussed were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly and legally entitled.