Patent Publication Number: US-2007096133-A1

Title: System and method for LED manufacturing

Description:
TECHNICAL FIELD  
      This invention relates to LED manufacturing systems and methods and more particularly to LEDs manufactured with using roller formed terminals having increased heat dissipation.  
     BACKGROUND OF THE INVENTION  
      Digital still cameras have come into widespread usage around the world. As their popularity grows, so does the need to make the cameras smaller, more versatile and, of course, less expensive. One vital function of all cameras is the need for a “flash” of light to illuminate subjects, particularly when the subject is in shadows or darkness.  
      Another function of a camera light source is to illuminate the subject to allow the camera to auto-focus its lens. This auto-focus light is less intense than the actual “flash” of light, but still must encompass the subject at varying focal lengths. Often, a single light source is called upon to perform multiple tasks, such as auto-focus, red-eye protection, timer alert and subject illumination (flash). Light emitting diodes (LEDs) having high brightness (usually greater than 10 cd), a narrow viewing angle and relatively inexpensive manufacturing are often used in such situations. The LED must have a long life and low current drain while maintaining an acceptable brightness level.  
      Typical prior art LED camera light sources use tie-bars to hold the pad to the LED chip while electrical leads are attached to each chip. These tie-bars then must be cut away during the singulation process. In addition, the electrical leads are formed using die sets which are expensive to make and maintain. These die-formed leads increase the physical size of the entire resulting structure.  
      A further problem is that existing LED electrical lead structures have high heat resistance and thus do not pass heat away from the junction as fast as desired if higher power is desired for increased brightness.  
     BRIEF SUMMARY OF THE INVENTION  
      An LED is formed using terminals that are folded using roller techniques instead of die-set formed terminals and the LED is formed by molding a cover over the LED chip and the flat terminals. Using this process, the LED can have several heat conduction paths thereby allowing higher heat dissipation which in turn results in the ability to apply higher power levels to the LED if desired. The LED can be produced using a LED chip that has light coming only from the top or light coming from the sides as well. In one embodiment, the side emitting LED can have reflectors constructed within the device to reflect light to the top. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:  
       FIG. 1A  shows one embodiment of a molded LED device having flat multi-ends electrical terminals;  
       FIG. 1B  shows one embodiment of the LED of  FIG. 1A  having internal side reflectors;  
       FIGS. 2A, 2B  and  2 C show one embodiment of the top, front and side views, respectively, of the molded structure of the LED of  FIG. 1A ;  
       FIG. 3  shows one embodiment of a flow chart of a manufacturing process for the LED of  FIG. 1A ;  
       FIG. 4  shows one embodiment of a device using the LED of  FIG. 1A ;  
       FIGS. 5A, 5B ,  5 C,  5 D,  5 E and  5 F show one embodiment of LED terminal construction; and  
       FIGS. 6A, 6B ,  7 A,  7 B,  7 C,  7 D,  7 E,  7 F,  7 G,  7 H,  7 I and  7 J show prior art LED construction.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Prior to beginning a detailed description of the inventive concepts, it might be helpful to review prior art construction techniques with respect to  FIGS. 6A and 6B .  FIG. 6A  shows device  60  having tie-bars  62 ,  63  and  64  surrounding the device to hold pad  65  in place during construction. LED dice  601  is held on pad  65 . Device  60  has terminals  63 - 1 ,  63 - 2 ,  63 - 3 ,  63 - 4 ,  63 - 5  and  63 - 6  which are folded around the bottom of the device as shown and as discussed with respect to  FIGS. 7A through 7J . While six terminals are shown, only two terminals, namely  63 - 2  and  63 - 5 , make electrical contact with the die within the device. Terminal  63 - 2  is the only terminal available for heat dissipation when power is applied to the device since terminal  63 - 5  is connected to the LED chip by a wire trace. Tie-bars  62 ,  63 ,  64  are cut away during the singulation process, but certain portions of the tie-bar remain as part of the finished product. The extra four terminals ( 63 - 1 ,  63 - 3 ,  63 - 4  and  63 - 6 ) are used for mechanical stability during the manufacturing process, but are not electrically connected to the chip.  
       FIG. 6B  shows a side view of device  60  with housing  64  and shows terminals  63 - 2  and  63 - 5  which were trimmed and formed using a die-set. Note gap  66  between body  61 ,  67  of the device and the terminal where the die tool ( 705 ,  FIGS. 7D and 7E ) was located for forming the terminal. The die wears easily and is expensive to manufacture and replace. In addition, its use increases the size of the entire package, primarily due to gap  66  needed for the die tool to sit when forming the terminal.  
       FIGS. 7A through 7J  show a prior art method for forming terminals on LED devices.  FIG. 7A  shows terminal  63 - 5  extending from device portions  61  to  67  (as shown in  FIG. 6B ). Supports  701  and  702  are used to stabilize the LED device in the terminal and to support terminal  63 - 5  so that knife  71  can shear off the terminal at a desired length as shown.  
       FIG. 7B  shows supports  703  and  704  put in place around the LED device to support the device and terminal  63 - 5 , so that the end of the terminal can be bent upward, as shown in  FIG. 7C , under control of die  72 .  
       FIG. 7D  shows that the LED device is now being supported by supports  705  and  706 , with  705  having an end  705 A used to support the bending, as shown in FIG.  7 E, of terminal  63 - 5  under control of die  73 . Note that end  705 A forms gap  66  (as can be seen in  FIG. 7F ).  
       FIG. 7F  shows the LED device now being held between stationary portion  708  and  709  while die  75  presses downward on terminal  63 - 5  as shown in  FIG. 7G . Tool  74  is shown pushing inward to support terminal  63 - 5  as it is being positioned by tool  75 . Note that gap  66  remains.  
       FIGS. 7H and 7I  show the spanking process which finishes off the folding of terminal  63 - 5  pressing it into position under control of stationary portions  709 ,  710  and tool  76 .  
       FIG. 7G  shows the singulation process where the die is removed and the device separated from other devices.  
      Turning now to  FIG. 1A , there is shown a bottom view of LED device  10  utilizing the concepts taught herein. Housing  22  (shown in  FIGS. 2A, 2B  and  2 C) has been removed for clarity. Note that there are two terminals,  14  and  15 , each terminal having several ends such that terminal  14  has ends  1 ,  2  and  4  and terminal  15  has ends  3 ,  5  and  6 . Terminal  14  contacts LED chip  12  directly, while terminal  15  is connected to LED chip  12  via wire (or trace)  13 . Because terminal  14  (ends  1 ,  2  and  4 ) are electrically connected pad  65  upon which LED dice  12  sits and thus these terminals are available for the dissipation of heat thereby spreading the heat dissipation capability so as to increase the heat dissipation from the LED junction. Also note that no tie-bar exists in the package and that the dice is attached and held by terminal  14 . Therefore there is no extra process needed to remove the tie-bar.  
      Ends  1 ,  2 ,  3 ,  4 ,  5  and  6  of terminals  14  and  15  are bent into position in one embodiment by roller forming rather than die-set forming as will be discussed with respect to  FIGS. 5A through 5F . This effectively minimizes the package size and reduces the manufacturing costs. Having multiple terminal ends increases the flexibility since there are more terminals that can be utilized to apply power to different segments of the LED, if desired.  
       FIG. 1B  is essentially the same as  FIG. 1A  except that reflector  16  is positioned around LED  12 . Reflector  16  is helpful in situations where an LED dice is used in which light is emitted from the sides (and not just from the top) of the dice. When side light emitting LEDs are used the side reflector reflects the light to the top of the device. If light is desired to be emitted from one or more sides of the device, the reflector would only be on the sides where light is not desired so as to concentrate the light where it is most effective to perform the function desired. The light can be designed to come out of the top or the sides or both, if desired.  
       FIGS. 2A, 2B  and  2 C show the top, front and side views, respectively, of one embodiment of a molded structure  20  which has housing  22  surrounding the LED chip (not shown in  FIGS. 2A, 2B  or  2 C). As discussed, one or more of these surfaces can be transparent to light while others can be opaque to light thereby allowing the diode to be constructed so that either all the light or some of the light comes out of any surface desired. In the embodiment of  FIGS. 1A and 1B , terminal ends  1 ,  2  and  4  are connected to the anode while terminal ends  3 ,  5  and  6  are connected to the cathode. The dimensions shown in  FIGS. 2A and 2B  are for illustrative purposes only and the concepts discussed herein can be used with any dimensions desired.  
       FIG. 3  shows one embodiment  30  of a flow chart of a manufacturing process for manufacturing LED  20 . Process  310  shows the selection of an LED dice, such as dice  12  ( FIG. 1A ). Process  311  shows the lead frame being positioned. Process  31  bonds the selected LED dice to the pad (such as pad  65 ,  FIG. 1A ) using, for example, Ag epoxy (process  312 ).  
      Process  32  bonds LED wire  13  to terminal  15  ( FIG. 1A ). Process  330  prepares the molding compound (which, in one embodiment, can be molding epoxy formed using pellets of epoxy used for transfer molding). Process  33  forms the mold material around the LED which is attached to pad  65 . The shape of the mold can be as desired for the function to be performed by the LED. Process  34  tin-plates the terminals. Process  35  trims and forms the terminals, (as will be discussed with respect to  FIGS. 5A through 5F ) while process  36  tests the device.  
       FIG. 4  shows one embodiment of electrical device  40  which in this case is a digital camera having lens  41  with diode  20  positioned near the lens. Diode  20  emits a beam of light  42  when activated. This light can be used to illuminate a subject (not shown) so that the camera can auto-focus itself prior to taking a picture.  
       FIG. 5A  shows LED device portions  11  and  21  holding terminal  6  which has been sheared as discussed above with respect to  FIG. 7A .  
       FIG. 5B  shows supports  52  and  53  coming into position and in  FIG. 5C  roller  51  is shown slowly bending terminal  6  into a 90° bend. Since a rolling motion has been substituted for the quick shear force shown with respect to  FIGS. 7A through 7J  in the prior art the LED device does not need to have as much support for the bending process. This is shown with respect to  FIG. 5D  where support  54  holds the device in position while roller  51  slowly bends pre-bent terminal  6  into position as is shown in  FIG. 5E  where terminal end  6 - 1  is flat against the bottom surface of the substrate and terminal area  6 - 2  is flat against the side of the substrate thereby eliminating gap  66  ( FIG. 6B ).  
       FIG. 5F  shows support  55  finishing the process by squaring terminal  6  so that it is flush against the side and bottom of portion  21  of the LED device.  
      Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.