Abstract:
Adjustable threaded cores for LED thermal management. The cores provide a direct thermal path between a LED and a heat sink while minimizing gaps and stresses between materials. The system includes a heat generating object, a first substrate housing containing a threaded hole beginning adjacent to the heat generating object, a second substrate having compatible threading with the threaded hole, and a third substrate including a heat sink. The second substrate has a higher thermal conductivity in comparison to the first substrate. The threaded hole and threaded core may terminate adjactent to the heat sink or may extent into the heat sink.

Description:
BACKGROUND OF THE INVENTION 
     A number of attempts have been made to replace incandescent and halogen bulbs with Light Emitting Diodes (LEDs) in various lighting applications because of their relatively small power consumption and long life. LEDs are more efficient than bulbs at converting electricity into light. LEDs are also durable and immune to filament breakage due to shock or vibration. When heat from the LEDs is properly managed, LEDs can last several times longer than incandescent or halogen bulbs. Accordingly, LEDs require less frequent maintenance and/or replacement compared to bulbs. 
     However, LED products are not without design challenges. LED systems require significant design efforts to keep component junction temperatures at acceptable levels. A high-power LED can generate a substantial amount of heat. Overheating could cause the LED system to fail prematurely and possibly damage other objects located nearby. 
     LEDs are frequently attached to circuit board materials that are poorly suited to dissipate heat. Also, most current LED mounting designs require heat to travel through multiple materials (LED, circuit board, heat sink) to reach the ambient environment. Thermal resistances occur through each material and at each junction between materials in the system. Any air gaps between materials add thermal resistance. The gaps can be eliminated, but not without expensive precision fabrication and mounting techniques. If materials are forced together, the resulting configuration could strain the LEDs or other circuit components, leading to system failure. In designs containing multiple LEDs, these challenges not only become increasingly difficult, but also contain LED position and assembly tolerance concerns. Solutions to these challenges are often costly and difficult to replicate. 
     SUMMARY OF THE INVENTION 
     The present invention provides an adjustable threaded core providing a direct thermal path between a heat generating object and a heat sink. 
     The present invention includes a system for facilitating a thermal path between a heat generating object and an ambient environment. The system includes a heat generating object, a first substrate housing containing a threaded hole beginning adjacent to the heat generating object, a second substrate having compatible threading with the threaded hole, and a third substrate including a heat sink. The second substrate has a higher thermal conductivity in comparison to the first substrate. In accordance with other aspects of the invention, the threaded hole extends into the third substrate and possibly the heat sink and fins. The second substrate is adjustable to be in contact with the heat generating object and the third substrate. 
     In accordance with still further aspects of the invention, the heat generating object is mounted on and/or powered by a circuit board. 
     In accordance with yet other aspects of the invention, the heat generating object comprises a semiconductor device or an LED. 
     As will be readily appreciated from the foregoing summary, the invention provides an adjustable direct thermal path between a heat generating object and a heat sink. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred and alternative embodiments of the present invention are described in detail below with reference to the following drawings: 
         FIG. 1  is cross-sectional view showing LED mount formed in accordance with the present invention; 
         FIG. 2  is a partial cross-sectional view showing a circuit board, LED, and threaded cores formed in accordance with embodiments of the present invention; and 
         FIG. 3  is a cross-sectional view showing an alternate configuration of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a Light Emitting Diode (LED) threaded core assembly  8  including a circuit board  12 , a plurality of LEDs  10 , a plurality of threaded holes  24 , and a plurality of threaded cores  16  included within a housing  14 . The circuit board  12  is configured to receive the plurality of LEDs  10 . Adjustable threaded cores for LED thermal management provide a direct thermal path between the LED  10  and the heat sink  18  while minimizing both gaps and stresses between materials. 
     In an exemplary embodiment, the circuit board  12  is a printed circuit board (PCB). The circuit board  12  can be attached to a housing  14  with screws, adhesive, or clamps. The housing  14  can be attached to a heat sink  18  with screws, adhesive, or clamps. 
     The threaded hole  24  extends within the housing  14  from a first junction  20  to a second junction  28 . The threaded hole  24  is formed with conventional machining techniques. The threaded hole  24  includes a tapered thread pattern. Correspondingly, the outer surface of the threaded core  16  includes threading compatible with the threads of the threaded hole  24 . The threading has been applied to the threaded hole  24  and threaded core  16  using standard machining and fabrication techniques. 
     The threaded core  16  is adjustable within the threaded hole  24 . If the threaded core  16  is rotated angularly, the threaded core  16  translates up or down in the threaded hole  24 . The threaded core  16  may be rotated using a screw driver or Allen wrench from the end opposite the LED  10 . 
     The threaded core  16  is adjusted to a position adjacent to and/or in thermal communication with the LED  10  at the first junction  20 . Similarly, the threaded core  16  is adjustable to be adjacent to the heat sink  18  at the second junction  28 . This forms a thermal path from the LED  10  to the ambient environment around a plurality of fins  22  of the heat sink  18 . More specifically, heat generated by the LED  10  is transferred through the threaded core  16  into the heat sink  18  and then to the ambient environment. The heat sink  18  is made of a material with high thermal transfer properties, such as aluminum. 
     The material used in the threaded core  16  also has relatively high thermal transfer properties, especially relative to the material of the housing  14 . Possible materials of the threaded core  16  include, but are not limited to, aluminum, copper, carbon foam, graphite, or comparable materials. Additionally, the threaded core  16  could include a heat pipe or other self-contained heat transfer system. 
     An adhesive, grease, or phase change material (PCM) may be added to the threads to provide lubrication to the threaded core  16  and threaded hole  24 . Once the thermal core  16  has been adjusted to the desired position, e.g. adjacent to the LED  10 , any applied adhesive may be cured to prevent the threaded core  16  from translating. Also, a thermal grease, thermal adhesive, or PCM may be applied to the threaded core  16 , the LED  10 , or the heat sink  18  to maximize conductive heat transfer at the first junction  20  and/or the second junction  28 . 
       FIG. 2  shows a more detailed view of the plurality of LEDs  10  attached to the circuit board  12 . A plurality of leads  32  electrically couples the LEDs  10  to the circuit board  12 . The circuit board  12  provides power to the LEDs  10  through the leads  32 . The circuit board  12  has an opening  34  to allow thermal communication between the LED  10  and the threaded core  16 . The circuit board  12  has a surface  36 . The leads  32  are located above the surface  36 . The LED  10  has a slug  38 , which is positioned to be adjacent to and/or in thermal communication with the threaded core  16 . The threaded core  16  and the threaded hole  24  have a radius  40 . It should be understood that the radius  40  of the threaded hole  24  and the threaded core  16  may be modified to achieve a desired heat transfer with a variety of LED types and configurations. It should be understood that radius  40  of the threaded core  16  and the threaded hole  24  may differ. 
       FIG. 3  shows an alternative embodiment where a threaded hole  24 - 3  extends into at least a portion of a heat sink  18 - 3 . In this embodiment, the threaded hole  24 - 3  extends from the LED  10 - 3  through the housing  14 , the heat sink  18 - 3 , and a plurality of fins  22 - 3 . Alternatively, the threaded core  16 - 3  could extend through a portion of the heat sink  18 - 3  and bypass the fins  22 - 3 . In an exemplary embodiment, the heat sink  18 - 3  may contain an unthreaded hole. In the exemplary embodiment, the threaded core  16 - 3  has portion that is unthreaded corresponding to the hole within the heat sink  18 - 3 . In the exemplary embodiment the threaded core  16 - 3  would be adjusted and then the heat sink  18 - 3  would be attached to the housing  14 . 
     The threaded core assembly  8 ,  8 - 3  could be configured to have a lower weight than the prior art. More specifically, the density of the heat sink  18 ,  18 - 3  may be much lower than the prior art, because the threaded core  16 ,  16 - 3  carries much more of the heat load, leaving the threaded core assembly  8 ,  8 - 3  with a weight advantage. Moreover, the increased efficiency of heat transfer made possible by the threaded core  16 ,  16 - 3  could allow for different designs of the heat sink  18 ,  18 - 3  utilizing lighter and/or less expensive materials. 
     The LEDs  10  may be arranged in various configurations. In an alternative embodiment, the invention could include just one LED  10 . The leads  32  could be located below the surface  36  of the circuit board  12 . In other embodiments, the threaded core assembly  8 ,  8 - 3  could comprise a heat generating object other than just an LED. As an example, the heat generating object could include an LED and LED mounting components that could include materials that facilitate heat transfer such as a thermal interface material or similar device. 
     While the preferred embodiment of the invention has been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is not limited by the disclosure of the preferred embodiment. Instead, the invention should be determined entirely by reference to the claims that follow.