Abstract:
The apparatus is a heat transferring clamp with a heat pipe connecting the clamp&#39;s stationary base part to each moveable clamping part. A connecting heat pipe section between the heat pipe sections in the base part and each clamping part is flexible enough to permit both the required clamping and unclamping movements of the clamping part. The heat pipes thereby provide a superior heat transfer path between a clamped circuit board or other device and an available heat sink.

Description:
BACKGROUND OF THE INVENTION 
     This invention deals generally with mechanical clamping devices for mounting electronic circuit boards within a chassis, but it is suitable in any other situation which requires a clamping device with excellent heat transfer capability. It is common to use a chassis that has parallel guide channels so that individual circuit boards can slide into the channels and be connected to the appropriate electric connectors when located in the channels. It is therefore necessary to clamp the circuit boards in place to prevent disturbing the electrical connections, and the almost universal device for mechanical clamping is known as the wedgelock clamp. 
     The main benefit of a wedgelock clamp is that it provides a consistent clamp force along its entire length while only requiring physical access from one end. The clamp is typically loosened and tightened by means of a hex head machine screw. A typical chassis receptacle for a circuit board has channels at the top and bottom of the receptacle. The circuit card assembly is comprised of a circuit board (often mounted to a heat spreader) with wedge lock clamps attached to its face near the top and bottom edges. The assembly is then slid into the chassis channels, and the clamps are tightened. The benefits of the wedgelock style clamp that make it appealing to designers is that it is lightweight, simple and easy to manufacture and assemble. 
     Another requirement for any circuit board clamp is to transfer the heat generated by the circuit board components to a heat sink for disposal. However, a problem with most of the conventional clamps is that the moveable mating parts provide poor heat transfer pathways for heat to move to the receptacle to which the circuit board is mated. Since the clamps are typically used to mount circuit boards which carry sensitive heat generating components, there is almost always a need to improve heat transfer from the circuit board to the device into which it is mounted. This is the only point of physical contact with the circuit board assembly, and it is therefore the logical source of heat transfer. Often the clamps are connected to heat spreaders which collect heat from the electronic components and are used to help with thermal management of the system. As the heat is conducted from the component to the heat sink, large temperature gradients occur at the circuit board clamp location, because the conductive surface contact area is dramatically reduced due to the separation of the moveable parts which interconnect the circuit board and the receptacle into which it is being installed. As electronic assemblies in general progress and the heat transfer requirements of edge cooled circuit boards increase, this restriction in heat transfer at the clamp will become more signficant as a weakness in the system. 
     The present invention overcomes the heat transfer limitation in the clamp, which is the weakest link in the heat transfer path. 
     SUMMARY OF THE INVENTION 
     The present invention is a superior heat transferring circuit board clamp which clamps the circuit board into a receptacle from which it is interconnected with the system electronics, and through which the heat generated by the circuit board components is transferred to a heat sink. 
     It is common to use a chassis that has receptacles that are parallel guide channels so that individual circuit boards can slide into the channels and be connected to the appropriate electric connectors when located in the channels. It is therefore necessary to clamp the circuit boards in place to prevent disturbing the electrical connections. The clamp typically has at least one base part that applies force to the heat source and at least one moveable clamping part that applies force to the receptacle. A typical chassis receptacle for a circuit board has channels at the top and bottom of the circuit board assembly, and there are clamps attached to the top and bottom of the circuit board. The circuit board then slides into the chassis channels, and the clamps are tightened. However, in some cases the clamps are installed in the circuit board receptacle and the same clamping action takes place when the circuit board is slid in. 
     Another requirement for any circuit board clamp is to transfer the heat generated by the circuit board components to the chassis, from which the heat is transferred to a heat sink for disposal. Regardless of the specific design of the clamp, it has at least one base part that is attached to or applies force to the circuit board and at least one moveable clamping part that applies force to a connection to a heat path to the heat sink. The base part is usually in contact with the heat source through the circuit board, and the clamping part moves away from the base part to press against the receptacle and clamp the board in place. This action means that there is at least some space created between the two parts of the clamp when the circuit board is clamped in place. That space and the limited heat conductivity of the base part and clamping part make the circuit board clamp a poor heat transfer path. 
     To overcome this limitation, in the present invention at least one connecting heat pipe is attached to the base part and to each moveable clamping part, and the connecting heat pipes are flexible enough to permit both the required clamping and releasing movements of the clamping part. Furthermore, additional heat pipes can also be installed within the clamp&#39;s base part and within each clamping part. The heat pipes thereby provide a superior heat transfer path between the clamped circuit board and an available heat sink because they surpass the mere conductivity of the clamp&#39;s parts and furnish heat pipes to transfer heat across the insulating separations between the parts. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a cross section view of a clamp which includes the preferred embodiment of the invention, the clamp is shown in a relaxed state. 
         FIG. 1B  is a cross section view of a clamp which includes the preferred embodiment of the invention, the clamp is shown in a clamped state. 
         FIG. 2A  is a cross section view of a clamp which includes an alternate embodiment of the invention, the clamp is shown in the relaxed state. 
         FIG. 2B  is a cross section view of a clamp which includes an alternate embodiment of the invention, the clamp is shown in the clamped state. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a cross section view of clamp  10  which is the preferred embodiment of the invention and is mounted in space A. Clamp  10  is constructed from three parts. 
     The first parts are moveable clamping parts  16 ,  30 ,  32 , the parts that apply force to lock clamp  10  in the fixed position. Base part  12  is shown in contact with chassis part  14  or some other structure that can act as a heat sink or a heat pathway to a heat sink. Clamping part  16  travels in path B from its clamping position shown in  FIG. 1B  in contact with chassis part  13  or circuit board  15  in which it locks clamp  10  and clamping part  16  to prevent them from moving, and then clamping part  16  moves into any location in which clamping part  16  is no longer in contact with any part such as chassis part  13  or circuit board  15  so that entire clamp  10  and circuit board or other clamped item  15  can move freely ( FIG. 1A ). 
     Clamping part  16  is the part that applies force to circuit board or other clamped item  15  or another heat generating component. In  FIG. 1  clamping part  16  is shown in contact with or attached to circuit board or other clamped item  15  and thus shows clamp  10  in its expanded condition clamping circuit board or other clamped item  15  tightly against chassis part  13  and preventing movement of clamp  10  and circuit board or other clamped item  15 . 
     It should be understood that the parts which base  12  and moveable clamping part  16  are contacting or attached to can be interchanged and it has no effect on the operation or benefit of the invention as long as one clamp part can be withdrawn from contact to permit withdrawal or circuit board or other clamped part  15 . Under such circumstances, if clamping part  16  is permanently attached to circuit board or clamped item  15 , clamp  10  and circuit board or clamped item  15  will move out of space A together. 
     The structure to impart motion to moveable clamping part  16  is not shown in any of the figures, but can be accomplished by various conventional means. For instance, in a wedgelock clamp, the clamping part is typically tightened and loosened by means of a machine screw that is turned to push one or more wedge shaped clamping parts  16  up a slope to separate it from the base  12 , and the screw is reversed to bring the clamping part back toward the base and release the clamping force. 
     It is the third part of the invention, heat pipe  18 , which gives clamp  10  its superior heat transfer qualities. Heat pipe  18  is attached to or integrated into both base  12  and clamping part  16 , thus transferring heat between base  12  and clamping part  16  with virtually no heat resistance. In the typical application heat enters into clamping part  16  and is transferred to base  12  from which it moves into chassis part  14  and then to a heat sink for disposal. 
     Section  20  of heat pipe  18  is a key factor in the satisfactory operation of the present invention, because section  20  of heat pipe  18  tolerates flexing due to the movement of clamping part  16  away from and toward base  12  without problems. Section  20  can survive such flexing because the clamping movement B is quite small and because of its design geometry and material properties. 
     Heat pipe  18  is able to be connected to base  12  and clamping part  16  while still allowing relative movement between the two parts because heat pipe  18  functions as a spring. Heat pipe  18  can be flexed over a small distance without undue force or mechanical damage due to its design and ductility. This behavior is made possible by the material properties, heat treatment, and geometry. Standard cantilever beam design of heat pipe  18  allows it to meet the required overall deflection without exceeding stress and fatigue requirements. Ultimately heat pipe  18  must be designed to accommodate the necessary movements of clamp  10  from a relaxed state ( FIG. 1A ) to clamped state ( FIG. 1B ) without damaging the integrity of the envelope of heat pipe  18 . 
     During manufacture heat pipe  18  can be annealed to a relatively soft state. Heat pipe  18  can also be constructed as a relatively flat structure rather than the more conventional cylindrical heat pipe, and that shape makes it even more suitable for the required flexing. Another example of a flexible design is a bellows used in the midsection of heat pipe  18  to provide the required flexibility. 
       FIGS. 2A and 2B  are a cross section view of clamp  22  which includes an alternate embodiment of the invention. Essentially, clamp  22  includes the same component parts as clamp  10  of  FIGS. 1A and 1B , but also has additional heat pipes  24  and  26  to aid in the distribution of heat throughout base  12  and clamping part  16 . The use of such multiple heat pipes helps change the clamp from the poorest heat transfer component in the system to the very best. 
     It is to be understood that the form of this invention as shown are merely preferred embodiments. Various changes may be made in the function and arrangement of parts; equivalent means may be substituted for those illustrated and described; and certain features may be used independently from others without departing from the spirit and scope of the invention as defined in the following claims. 
     For example, Additional heat pipes may be added at any location on the base of the clamp or along any of the moving clamping parts. The heat pipes are held in thermal contact (solder, epoxy or mechanically) with the different clamp components. There is no limit to the number of heat pipes or their orientation between the moving components of the clamp. Typically the heat pipes will be nested together to maximize the amount of evaporator and condenser area of each heat pipe. The pipes may be bent, twisted or flattened in any orientation that is advantageous, and heat pipe variations such as thereto siphons or vapor chambers may be used in place of conventional heat pipes to accomplish the same results. 
     Furthermore, it should be understood that multiple installations such as those shown in  FIG. 1  and  FIG. 2  can be used on any clamp to accommodate to the clamp&#39;s size.