Abstract:
There is disclosed a system and method for increasing heat dissipation of LED displays by using the current PCB packaging mounted to a LCD panel support structure thereby eliminating the need for a metal core PCB. In one embodiment, reverse mounted LEDs having heat dissipation pads are used to optimize heat transfer to a metal layer which is then placed in contact with the LCD support structure.

Description:
BACKGROUND OF THE INVENTION 
     The need for LEDs having high power (increased brightness) is increasing. As power increases, so does the need for heat dissipation since if the heat generated by the LED junction is not dissipated effectively the brightness of the LED is diminished. 
     Currently LEDs are produced in surface-mounted LED packages which are mounted to aluminum metal core PCBs. The metal core PCBs act as direct heat-sinks drawing the heat away from the LEDs. Using metal core PCBs is relatively expensive since the cost of the material for a metal core PCB is high. 
     BRIEF SUMMARY OF THE INVENTION 
     There is disclosed a system and method for increasing heat dissipation of LED displays by using the current PCB packaging mounted to a LCD panel support structure thereby eliminating the need for a metal core PCB. In one embodiment, reverse mounted LEDs having heat dissipation pads are used to optimize heat transfer to a metal layer which is then placed in contact with the LCD support structure. 
    
    
     
       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 drawing, in which: 
         FIG. 1  shows a perspective view of one embodiment of a single LED and dome package; 
         FIG. 2  shows one embodiment of the LED package of  FIG. 1  with the LED removed; 
         FIGS. 3A and 3B  show embodiments of side views of the single LED package of  FIG. 1  taken along section line  3 A- 3 A of  FIG. 2 ; 
         FIGS. 4 and 5  show top and side views, respectively, of a multiple LED package; and 
         FIGS. 6 and 7  show a display using LED strips constructed in accordance with the teachings of this disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a perspective view of one embodiment of single LED package  10  consisting of PCB substrate  22  mated to heat-sink pad  25 . Optical dome  12  is constructed, by molding or otherwise, above surface  11  which in turn is mated to substrate  22 . Contact strips  23  and  24  are constructed on the surface of substrate  22  and are used as discussed in more detail hereinafter. 
       FIG. 2  shows package  10  with the LED and optical dome  12  removed. An LED chip (or other light emitting source) would be physically attached to heat-sink pad  25  inside reflector cup  21  by a terminally conductive bonding agent, or by other fastener means. The LED would then be wire bond connected to pads  23 - 1  and  24 - 1  of contact strips  23  and  24 , respectively, for subsequent connection to an external electrical path. The heat path from the LED is through heat-sink pad  25  which can be, for example, copper. Note that the heat path from the LED is pad  25  and is separate from the electrical path to optimize the heat dissipation from the die to the back structure. The LED is mounted to pad  25  using a thermally conductive (but non-electrically conductive) adhesive dielectric. The heat dissipation is better than in prior art metal core PCBs because the pad has a wider surface area. 
     Reflector cup  21  is constructed having an optimum angle for reflecting LED side light to the top of the package. The reflector cup is formed, for example, using bright color opaque material. Once the LED is mated with pad  25 , transparent material is poured around the LED to encapsulate the LED and wire bond to form complete LED package  10 . 
     Optical dome  12  ( FIG. 1 ) is constructed to direct the light from the LED source in a desired direction. The light output of the LED can be changed, as desired, to applications simply by redesigning the dome shape. 
       FIG. 3A  shows a sectional cut-away side view of LED package  10  taken along section line  3 A- 3 A of  FIG. 2  having light source, such as LED  31 , physically bonded to heat dissipation pad  25  by bonding material  302 . Bond wire  32  connects one terminal of LED  31  to contact pad  24 - 1  of contact strip  24  ( FIG. 1 ). The second electrical terminal of LED  31  is connected to contact pad  23 - 1  by path  33 . Any electrical contact system can be used to connect LED  31  to respective contacts external to dome  12 . In the embodiment shown, there are two such leads but there could be three or more, if desired. 
       FIG. 3B  shows in a cut-away view how external power is connected via contacts  52  and  53  to contact area  23 - 2  and  24 - 2 . The position of contact areas  23 - 1 ,  23 - 2 ,  24 - 1 , and  24 - 2  is shown in  FIG. 2 . Note that these contacts can be any place along contact strip  23 ,  24  so long as they do not interfere with the wire bonds to the LED.  FIG. 4  shows display  40  having a plurality of LED packages  10 - 1  through  10 -N, each with an LED  12 - 1  to  12 -N. Surrounding each LED package is a opening, such as opening  42 - 1  through  42 -N formed in structure  42  to allow light from the respective LED to pass through. 
       FIG. 5  is a cross-section of display  40  taken a long line  5 - 5  of  FIG. 4  showing three LEDs  12 - 1 ,  12 - 2 ,  12 - 3  mounted to mounting plate  61 . (Mounting plate  61  will be described more fully with respect to  FIG. 6 .) Shown in  FIG. 5  are contacts  52  and  53  which are formed beneath the surface of structure  41  for the purpose of providing control and power to the respective LEDs. This then allows for the contact surface to be on the top side of the LED device and away from heat pad  25  for better electrical and heat separation. 
       FIG. 6  shows system  60  which has a plurality of LED strips  40  mounted to heat dissipation bar  63  which in turn is connected to back mounting plate  61 . If desired, cover  62  can be added. Cover  62  could have opaque areas for allowing the LED light to be seen externally. 
       FIG. 7  shows a cross-section of structure  60  taken along section line  7 - 7  of  FIG. 6 . In  FIG. 7  light diffusers and other elements  72 ,  73  are shown for diffusing, or otherwise controlling the light. Such control can be on an individual basis, if desired. 
       FIG. 8  shows one alternate embodiment  80  of a device using light source  92  having both bond wires on the top of the light source. This is possible because of the horizontal structure of light source  92  as shown in  FIG. 9B . In this embodiment adhesive (or other bonding agent)  802  can be both heat conductive as well as electrically conductive. This then allows for the use of solder as the bonding agent which could, in some situations, be more effective than simply being heat conductive. 
       FIG. 9A  shows a diagram of vertical structure light source  91  having its electrical connections at the top and at the bottom of the device. 
       FIG. 9B  shows a diagram of horizontal structure light source  92  having both its electrical connections at the top of the device. Note that while only two electrical connections are shown, any number can be used and the concepts discussed herein could work with conductors coming from the sides of the device if desired. 
     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.