Abstract:
A structure of a light emitting diode is provided. The light emitting diode comprises a light emitting diode die; two conductive frames electronically and respectively connecting to the cathode and anode of the light emitting diode die, and two substrates. Each conductive frame has a fixing hole and each substrate has a protrusive pillar. The upper opening of the fixing hole is broader than the bottom opening. The protrusive pillar is inserted into the fixing hole and the shape of the protrusive pillar is deformed for fitting and binding with the fixing hole.

Description:
RELATED APPLICATIONS 
     This application claims priority to Taiwan Application Serial Number 96106508, filed Feb. 26, 2007, which is herein incorporated by reference. 
     BACKGROUND 
     1. Field of Invention 
     The present invention relates to a light emitting diode structure. More particularly, the present invention relates to a fixing structure of a light emitting diode and a method to assemble thereof. 
     2. Description of Related Art 
     The manufacturing technology of light emitting diodes is getting advanced recently, so that the light emitting efficiency for light emitting diodes is accordingly improved. The application of light emitting diode is based on its good characters, such as low operating temperature and low power assumption, etc. Therefore, the light emitting diode is getting more used in the light emitting field. For example, the light emitting diode is introduced to manufacture flashlights or automobile headlights. 
     The normal LED (Light Emitting Diode) structure consists of the die that is attached to the leadframe with an electrically conductive glue. Gold wire is used to connect the metal contact on the top of the LED die to the adjacent pin. Finally, the epoxy package is molded around the leadframe. Pins set of the leadframe extends outside the LED package. The pins can be inserted into holes in a circuit board, and be fixed on the circuit board by welding. The temperature for welding can be up to hundreds of Celsius degrees, which may be conducted to LED die and make the die burn down. 
     A prior structure and method of fixing a LED package on a circuit board without welding is provided. Referring to  FIG. 1 , it illustrates a prior structure and method for fixing a LED package on a transferring board without welding. A LED package  10  includes a conductive leadframe  20 . The conductive leadframe  20  has fixing holes  30 . Corresponding to the locations of the fixing holes  30 , holes  50  are formed by protruding from the bottom surface to the upper surface of a transferring board  40 . After the holes  50  are formed, a fixing plate  60  is naturally formed from the protruding part of the holes  50 . Referring to  FIG. 2 , it illustrates a prior structure of a LED package fixed on a transferring board without welding according to  FIG. 1 . The fixing plate  60  passes through the fixing holes  30 , and the fixing plate  60  is bended inside out by using proper tools to fix the LED package  10  with the conductive leadframe  20  on the transferring board  40 . The transferring board  40  can be used as a circuit board to transmit current to LED die and a media for heat-dissipation at the same time. 
     The prior structure and method for fixing a LED package on a transferring board can prevent high temperature which is generated by welding from the assembly processes. However, it is not easy to form a uniform fixing plate  60  by protruding out from the holes  50 . Furthermore, the length of the fixing plate  60  is limited by the diameter of the holes  50 , which is generally equal to the radii of the fixing holes  30 . Referring to  FIG. 3 , it illustrates a prior structure and method for a fixing plate passing through a fixing hole. The included angle ⊖ between the fixing plate  60  and the transferring board  40  herein is larger than 90 degrees, so that the fixing plate  60  can pass through the fixing hole  30  easily. However, the included angle ⊖ would make it difficult to bend the fixing plate  60  inside out for the following bending process. On the contrary, the fixing plate  60  with the included angle ⊖ would be bended inwards, it accordingly reduce the efficiency for fixing the LED package  10  and the conductive leadframe  20  on the transferring board  40 . Thus, for normally fixing the LED package  10  and the conductive leadframe  20  on the transferring board  40 , the included angle ⊖ between the fixing plate  60  and the fixing holes  30  should be less than 90 degrees. That is, the fixing plate  60  should be bended inside out. However, it will make the fixing plate  60  passing through the fixing holes  30  difficulty. Therefore, after the fixing plate  60  passing through the fixing holes  30 , it needs another process to deal with the included angle ⊖ between the fixing plate  60  and the transferring board  400 . It&#39;s really a dilemma. 
     However, one more process will result in increasing cost and decreasing yield rate, even downgrading manufacture automation process. It is not the manufacturers wanted. Thus, it is very important to provide a simple and non-welding structure and method for fixing the LED package and the conductive leadframe on the transferring board. 
     SUMMARY 
     It is therefore, the present invention to provide a structure of a light emitting diode and a method to assemble thereof, such that the light emitting diode can be fixed on a substrate. The substrate includes a circuit board, a transferring board or any kind of carrying board which can be used for fixing the light emitting diode thereon. 
     The light emitting diode structure comprises conductive frames electronically and respectively connecting to a packaged die of the light emitting diode. Each conductive frame comprises fixing holes, which pass through the conductive frame. The top radius of the fixing hole (output opening) is broader than the bottom radius of the fixing hole (input opening). Therefore, the fixing hole may have an inclined sidewall from top to bottom, or the fixing hole may have a ladder-shaped sidewall. In addition, the design that top and bottom radii of the fixing hole are broader than the middle radius of the fixing hole is also within the scope of the present invention. Besides, the fixing hole also can be set on the substrate. The bottom radius of the fixing hole is broader than the top radius of the fixing hole on the substrate. Therefore, the fixing hole may have an inclined sidewall from bottom to top, or the fixing hole may have a reversed-ladder shaped sidewall. 
     In one of the embodiments, a protrusive pillar is set on the substrate. The material of the protrusive pillar is a kind of conductive and expandable material, such as metal. The protrusive pillar can be a cylinder or hollow pillar. Generally, the hollow pillar is more deformable than the cylinder pillar. The cross-sectional area of the protrusive pillar can be equal to or smaller than the area of the bottom of the fixing hole or the cross-sectional area with the smallest radius of the fixing hole. Of course, the cross-sectional area of the protrusive pillar is not limited in the above-mentioned requirement. Any one of the protrusive pillar can pass through the input opening and protrude out of the output opening of the fixing hole is within the scope of the present invention. In addition, in the other embodiment, the protrusive pillar can be set on the surface of the conductive frame corresponding to the substrate, rather than set on the substrate. 
     In accordance with the foregoing disclosed structures of the present invention, a method for assembling a light emitting diode is provided. When a protrusive pillar passes through the fixing hole, the light emitting diode is not fixed yet. The protrusive pillar is then pressed by tools, and is deformed to hook the fixing hole. That is, the protrusive pillar fills the fixing holes, or the outer sidewalls of the protrusive pillar adhere to the inner inclined sidewalls of the fixing holes closely, so that the light emitting diode can be fixed on the substrate. The present method for assembling a light emitting diode without welding is easy and efficient. Therefore, the present invention provides a light emitting diode and a method to assemble thereof with low cost, high production rate and high yield rate. 
     These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description, figures, and appended claims. 
     It is to be understood that both the foregoing general description and the following detailed description are by examples, and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings, 
         FIG. 1  is a prior structure and method for fixing a packaged light emitting diode on a transferring board without welding; 
         FIG. 2  is a prior structure of a light emitting diode fixed on a transferring board without welding according to  FIG. 1 ; 
         FIG. 3  is a prior structure and method for a fixing plate passing through a fixing hole; 
         FIG. 4  is a three-dimensional explosion diagram illustrating a structure of a light emitting diode according to first preferred embodiment of the present invention; 
         FIG. 5A  is a cross-sectional view illustrating a structure and method for fixing a light emitting diode on a substrate according to first preferred embodiment of the present invention; 
         FIG. 5B  is a cross-sectional view illustrating a structure of a light emitting diode fixed on a substrate according to first preferred embodiment of the present invention; 
         FIG. 6A  is a cross-sectional view illustrating a structure and method for fixing a light emitting diode on a substrate according to second preferred embodiment of the present invention; 
         FIG. 6B  is a cross-sectional view illustrating a structure of a light emitting diode fixed on a substrate according to second preferred embodiment of the present invention; 
         FIG. 7  is a cross-sectional view illustrating a structure of a light emitting diode fixed on a substrate according to third preferred embodiment of the present invention; and 
         FIG. 8  is a cross-sectional view illustrating a structure of a light emitting diode fixed on a substrate according to fourth preferred embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention provides a fixing structure of a light emitting diode, which uses riveting process rather than welding process for fixing the light emitting diode on a substrate to prevent the damage of the light emitting diode chip from high temperature of the welding process. Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
     Referring to  FIG. 4 , it is a three-dimensional explosion diagram illustrating a structure of a light emitting diode according to first preferred embodiment of the present invention. As shown in  FIG. 4 , a packaged light emitting diode  100  has a packaged die  102  and conductive frames  104  and  104 ′. The conductive frames  104  and  104 ′ electrically connect to the cathode and anode of the light emitting diode respectively (not shown). The conductive frames  104  and  104 ′ have fixing holes  106  and  106 ′ respectively. 
     Continue to  FIG. 4 . Protrusive pillars  110  and  110 ′ are set on two substrates  108  and  108 ′ respectively. According to the first preferred embodiment of the present invention, the protrusive pillars  110  and  110 ′ can be hollow cylinders. The protrusive pillars  110  and  110 ′ are drawn to cylinders by pressing mold technic. Of course, the above-mentioned example is one of the embodiments of the present invention, the protrusive pillars  110  and  110 ′ are not limited to cylinders or hollow pillars, and are not limited to be formed in one piece (in an integral) with substrates  108  and  108 ′. A hollow or non-hollow pillar can be pressed into or screwed into the holes of the substrate. 
     Referring to  FIG. 5A , it is a cross-sectional view illustrating a structure and method for fixing a light emitting diode on a substrate according to first preferred embodiment of the present invention. A light emitting diode  100  has a packaged die  102  and conductive frames  104  and  104 ′. The conductive frames  104  and  104 ′ electrically connect to the cathode and anode of packaged die  102  of the light emitting diode respectively (not shown). The conductive frames  104  and  104 ′ have fixing holes  106  and  106 ′ respectively. Protrusive pillars  110  and  110 ′ are set on the two substrates  108  and  108 ′ respectively. The protrusive pillars  110  and  110 ′ can be hollow pillars. As shown in  FIG. 5A , the protrusive pillar  110  passes through the fixing hole  106  and combines with the fixing hole  106 , and the protrusive pillar  110 ′ passes through the fixing hole  106 ′ and combines with the fixing hole  106 ′. 
     Referring to  FIG. 5B , it is a cross-sectional view illustrating a structure of a light emitting diode fixed on a substrate according to first preferred embodiment of the present invention. As shown in  FIG. 5B , the protrusive pillars  110  and  110 ′ in  FIG. 5A  pass through the fixing hole  106  and combine with the fixing holes  106  and  106 ′ respectively. The protrusive pillars  110  and  110 ′ protrude out from the top surface of the substrates  108  and  108 ′ respectively. A pressing process then performs on the protrusive pillars  110  and  110 ′ by using proper tools, so that the protrusive pillars  110  and  110 ′ in  FIG. 5A  are deformed to become protrusive pillars  110   a  and  110   a ′ in  FIG. 5B  and fill the fixing holes  106  and  106 ′. According to other embodiments of the present invention, the outer sidewalls of the protrusive pillars  110   a  and  110   a ′ can adhere to the inner sidewalls of the fixing holes  106  and  106 ′ closely and not fill the fixing holes  106  and  106 ′. Generally, the height of the top surfaces of the protrusive pillars  110   a  and  110   a ′ can be equal to, slightly higher than or slightly lower than the height of the top surfaces of the fixing holes  106  and  106 ′. 
     Please refer to  FIG. 6A . It is a cross-sectional view illustrating a structure and method for fixing a light emitting diode on a substrate according to second preferred embodiment of the present invention. And referring to  FIG. 6B , it is a cross-sectional view illustrating a structure of a light emitting diode fixed on a substrate according to second preferred embodiment of the present invention. The differences between the embodiment of  FIGS. 6A and 6B  and the embodiment of  FIGS. 5A and 5B  are that the shapes of fixing holes  206  and  206 ′ differ from the fixing holes  106  and  106 ′. As shown in  FIG. 6A , the cross-sectional view of the fixing hole  206  is in a ladder shape. When protrusive pillars  210  and  210 ′ are inserted into the fixing holes  206  and  206 ′, a pressing process then performs on the protrusive pillars  210  and  210 ′ by using proper tools. The protrusive pillars  210  and  210 ′ in  FIG. 6A  are deformed into protrusive pillars  210   a  and  210   a ′ in  FIG. 6B  and fill the fixing holes  206  and  206 ′. Of course, the outer sidewalls of the protrusive pillars  210   a  and  210   a ′ may adhere to the inner sidewalls of the fixing holes  206  and  206 ′ closely and not fill the fixing holes  206  and  206 ′. 
     Please refer to both  FIGS. 7 and 8 .  FIG. 7  is a cross-sectional view illustrating a structure of a light emitting diode fixed on a substrate according to third preferred embodiment of the present invention.  FIG. 8  is a cross-sectional view illustrating a structure of a light emitting diode fixed on a substrate according to fourth preferred embodiment of the present invention. As shown in  FIG. 7 , the structure of the third preferred embodiment of the present invention in  FIG. 7  is like the structure of the first preferred embodiment of the present invention in  FIG. 5B . The only difference between  FIG. 7  and  FIG. 5B  is that the locations of the protrusive pillars  310   a  and  310   a ′ in  FIG. 7  and the locations of the protrusive pillars  110   a  and  110   a ′ in  FIG. 5B  are different. The protrusive pillars  110   a  and  110   a ′ in  FIG. 5B  are set on the substrates  108  and  108 ′ respectively, while the protrusive pillars  310   a  and  310   a ′ in  FIG. 7  are set on the conductive frames  304  and  304 ′ respectively. In detail, the protrusive pillars  310   a  and  310   a ′ in  FIG. 7  are set on the surfaces of the conductive frames  304  and  304 ′ in correspondence with to the substrates  308  and  308 ′ respectively. Other characters of the third preferred embodiment of the present invention are the same with the first preferred embodiment of the present invention and can refer to the above description for the first preferred embodiment of the present invention. 
     Referring to  FIG. 8 , the structure of the fourth preferred embodiment of the present invention in  FIG. 8  is like the structure of the second preferred embodiment of the present invention in  FIG. 6B . The only difference between  FIG. 8  and  FIG. 6B  is that the locations of the protrusive pillars  410   a  and  410   a ′ in  FIG. 8  differ from the locations of the protrusive pillars  210   a  and  210   a ′ in  FIG. 6B . The protrusive pillars  210   a  and  210   a ′ in  FIG. 6B  are set on the substrates  208  and  208 ′ respectively, while the protrusive pillars  410   a  and  410   a ′ in  FIG. 8  are set on the conductive frames  404  and  404 ′ respectively. In detail, the protrusive pillars  410   a  and  410   a ′ in  FIG. 8  are set on the surfaces of the conductive frames  404  and  404 ′ corresponding to the substrates  408  and  408 ′ respectively. Other characters of the fourth preferred embodiment of the present invention are the same with the second preferred embodiment of the present invention and can refer to the above description for the second preferred embodiment of the present invention. 
     In the above-mentioned embodiments of the present invention, the substrates can be used as circuit boards to transmit current to light emitting diode package. The protrusive pillars are added on the circuit board herein. The materials of the substrates can be metal, such as gold, silver, copper, aluminum, nickel, chromium, iron, or an alloy composed of the above-mentioned metals. The metal substrates not only can form a transmissible route for working current, but also can provide a heat-dissipation surface for the light emitting diode, so that the heat-dissipation efficiency is improved to prolong the lifetime of the light emitting diode. 
     According to the above-mentioned embodiments of the present invention, there are some advantages described as follows. The present structure of a light emitting diode and a method to assemble thereof is very easy and efficient, and does not need any welding process at all. Therefore, the present structure and method for fixing a LED package on a transferring board can reduce cost, and provide high production rate and high yield rate. 
     Although there are some embodiments have been disclosed above, they are not used to limit the scope of the present invention. It will be apparent to those skilled in the art that various modifications and variations can be made to the structure and method of the present invention without departing from the scope or spirit of the invention. For example, the protrusive pillar can be pressed and deformed to fix on the top surface of the conductive frame or on the bottom surface of the substrate. A fixing hole with straight inner sidewall can be used at this time. In view of the foregoing, it is intended that the present invention covers modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.