Abstract:
A method for fabricating a thermal cap for cooling an electronic device includes steps of: machining a main housing of the thermal cap from a single element of a thermally conducting material; and fabricating a top plate including a centered intact area within the main housing by machining orifices around a perimeter of the main housing. The orifices represent a gap between the top plate and the main housing to allow movement of the top plate in the x, y, and z directions. Additionally, moveable connectors are fabricated along an edge of the top plate by cutting connector orifices in the main housing to allow movement of the top plate in the x direction; and moveable bars coupled with the moveable connectors are fabricated by cutting slot orifices in the main housing to allow movement of the top plate in the y and z directions.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application is a divisional of co-pending U.S. patent application Ser. No. 10/944,979. The aforementioned U.S. patent application is hereby incorporated by reference in its entirety. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED-RESEARCH OR DEVELOPMENT  
       [0002]     None.  
       INCORPORATION BY REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC  
       [0003]     None.  
       FIELD OF THE INVENTION  
       [0004]     The invention disclosed broadly relates to the field of electronic devices and more particularly relates to the field of multi-dimensional compliant thermal caps for electronic devices.  
       BACKGROUND OF THE INVENTION  
       [0005]     During the normal operation of a computer, integrated circuit devices generate significant amounts of heat. This heat must be continuously removed, or the integrated circuit device may overheat, resulting in damage to the device and/or a reduction in operating performance. Cooling devices, such as heat sinks, have been used in conjunction with integrated circuit devices in order to avoid such overheating. Generally, a passive heat sink in combination with a system fan has provided a relatively cost-effective cooling solution. In recent years, however, the power of integrated circuit devices has increased exponentially, resulting in a significant increase in the amount of heat generated by these devices, thereby making it extremely difficult to extract heat from these devices.  
         [0006]     Heat is typically extracted by coupling a heat spreader and a thermal cap to the electronic device as a heat sink. Heat sinks operate by conducting heat from a processor to the heat sink and then radiating it into the air. The better the transfer of heat between the two surfaces (the processor and the heat sink metal) the better the cooling. Some processors come with heat sinks glued to them directly, or are interfaced through a thin and soft layer of thermal grease, ensuring a good transfer of heat between the processor and the heat sink. The thermal paste serves not only to transfer heat but to provide some degree of mechanical compliance to compensate for dimensional changes driven by the high operating temperatures of the devices. However, the paste is a weak link in the thermal path. Attempts to thin this layer have resulted in failure of the layer when it is exposed to dimensional changes.  
         [0007]     There are some known mechanically complaint solutions but these solutions still rely on paste film somewhere in the path. Thus there is a need for a solution that addresses these shortcomings.  
       SUMMARY OF THE INVENTION  
       [0008]     Briefly, according to an embodiment of the invention, a method for manufacturing a cooling structure for an electronic device includes steps or acts of: placing an electronic device on a substrate and producing a cooling structure disposed over the electronic device. The cooling structure includes a plate comprising a thermally conducting material, a first support connected to the plate and a second support connected to the first support, wherein one of the first support and the second support provides compliance in the x-y directions, and the other provides compliance in the z direction.  
         [0009]     In yet another embodiment of the present invention, a cooling structure for a plurality of electronic devices comprises a plate for each of the plurality of electronic devices, each plate comprising a thermally conducting material disposed over the corresponding electronic device. The cooling structure further comprises a first support connected to each of the plates and a second support connected to each of the first supports. One of the first supports and the second supports provide compliance in the x-y directions, and the other provides compliance in the z direction.  
         [0010]     Further, in another embodiment of the present invention, a method for fabricating a thermal cap for cooling an electronic device includes steps of: machining a main housing of the thermal cap from a single element of a thermally conducting material; and fabricating a top plate including a large intact area within the main housing by machining orifices around a perimeter of the main housing. The orifices represent a gap between the top plate and the main housing to allow movement of the top plate in the x, y, and z directions. Additionally, moveable connectors are fabricated along an edge of the top plate by cutting connector orifices in the main housing to allow movement of the top plate in the x direction; and moveable bars coupled with the moveable connectors are fabricated by cutting slot orifices in the main housing to allow movement of the top plate in the y and z directions. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features and also the advantages of the invention will be apparent from the following detailed description taken in conjunction with the accompanying drawings. Additionally, the left-most digit of a reference number identifies the drawing in which the reference number first appears.  
         [0012]      FIG. 1  shows a top view of a multi-dimensional compliant thermal cap disposed over an electronic device, according to an embodiment of the invention;  
         [0013]      FIG. 2A  shows a side cross-section of a portion of the multi-dimensional compliant thermal cap  100  of  FIG. 1 ;  
         [0014]      FIG. 2B  shows another side cross-section of a portion of the multi-dimensional compliant thermal cap of  FIG. 1 , as it adapts to dimensional changes of the electronic device and surrounding structures;  
         [0015]      FIG. 3  shows a top view of an alternative multi-dimensional compliant thermal cap, in one embodiment of the present invention; and  
         [0016]      FIG. 4  shows a top view of an alternative multi-processor multi-dimensional compliant thermal cap, in one embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0017]     We describe an apparatus for cooling an electronic device and a method for fabricating the apparatus.  FIG. 1  shows a top view of a multi-dimensional compliant thermal cap  100  disposed over an electronic device  104 , according to an embodiment of the invention. A compliant thermal cap  100  comprises a moveable top plate  102  for providing the resilience required to overcome the problems of the prior art. The top plate  102  comprises a flat rectangular plate that covers the top surface area of the electronic device (e.g., a semiconductor chip) that is not shown. Note that while a flat plate is preferred, the plate may include a structure, such as heat sink fins, on the side opposing the electronic device. A main housing  110  encircles and is coupled with the top plate  102 . The main housing  110  extends downward and is placed on a substrate or an electronic circuit board.  
         [0018]     The top plate  102  is attached to at least one movable connector  106  that allows movement of the top plate  102  in the z-directions, or upwards and downwards. In an embodiment of the present invention, the top plate  102  can be connected to additional movable connectors, such as connectors  107 ,  108  and  109 , located in each corner of the top plate  102 . The movable connector  106  is further connected to a movable bar  126  that allows movement in the x-y direction, or sideways. Thus, one end of the movable connector  106  is coupled with the top plate  102  and the other end of the movable connector  106  is coupled with the movable bar  126 . Note that the movable bar  126  is integrated with the main housing  110  and the movable bar  126  is formed from the establishment of a slot orifice  136 . That is, the fabrication of the slot orifice  136  creates the movable bar  126  as an integrated element of main housing  110 . In an embodiment of the present invention, additional movable connectors  107 ,  108  and  109  are connected to additional movable bars  127 ,  128  and  129 , respectively, also allowing movement in the x-y direction. Note that movable connectors  127 ,  128  and  129  are integrated with the main housing  110  and each movable connector is formed from the establishment of slot orifices  137 ,  138  and  139 , respectively.  
         [0019]     Each movable bar  126 - 129  comprises a thin bar-like structure that can bend or otherwise change shape so as to allow the body of the movable bar to move towards and away from the top plate  102 . This bending or morphing action is a result of the spring-like structure of the movable bars. This allows movement of the top plate  102  in the x-y direction, since the top plate  102  is connected to the movable bar  126  or movable bars  126 - 129 .  
         [0020]      FIG. 1  also shows orifices  146 ,  147 ,  148  and  149 . These orifices represent a gap between the top plate  102  and the main housing  110 . The orifices  146 - 149  allow for the movement of the top plate  102  in any direction, including the x-direction and the x-y direction. In an embodiment of the present invention, the orifices  146 - 149 , as well as orifices  136 - 139 , are filled with low-modulus seal material such as silicone. The seal material fills each orifice and allows for stretch and movement in multiple directions such that the thermal compliant cap  100  is compliant with thermal expansion and compression of the electronic device. The seal material can be used to seal the electronic device such that it is environmentally separated from the outside. This can be beneficial in situations where the electronic device can react adversely to air, certain gases, liquids or other environmental hazards.  
         [0021]     The compliant thermal cap  100  serves the function of dissipating heat generated by the electronic device and conforms to thermal expansion of the device caused by the difference in the coefficients of thermal expansions of the materials of the device and the top plate  102  of the thermal compliant cap  100  as well as thermally induced dimensional changes in the substrate structure underlying the electronic device. Due to the movable nature of the connectors  106 - 109  and the bars  126 - 129 , the complaint thermal cap  100  exhibits compliance in multiple directions, specifically, the “z” direction, as well as the “x-y’ directions, i.e., the up, down and sideways directions. Line  150  indicates the plane through which the cross section view of  FIG. 2  is taken.  
         [0022]      FIG. 2A  shows a side cross-section of a portion of the multi-dimensional compliant thermal cap  100  of  FIG. 1 .  FIG. 2A  shows the thermal compliant cap  100  and the device  104  in a rest state exhibiting no stress or thermal expansion. The top plate  102  comprises a flat rectangular plate that covers the top surface area of the electronic device  104  (e.g., a semiconductor chip). A main housing  110  encompasses the device  104  and extends downward and is placed on a substrate  120  or an electronic circuit board.  FIG. 2A  shows the top plate  102  attached to the movable bar  126  via the connector  106 . Orifice  136  separates the movable bar  126  from the remaining portions of the main housing  110 . In an embodiment of the present invention, a low modulus seal material fills the orifice  136  to provide a seal over the gap.  
         [0023]      FIG. 2B  shows another side cross-section of a portion of the multi-dimensional compliant thermal cap of  FIG. 1 , as it adapts to dimensional changes of the electronic device.  FIG. 2B  shows that the top plate  102  at a greater elevation than the top plate of  FIG. 2A .  FIG. 2B  shows that the electronic device  104  has also increased in vertical size. The increase in vertical size of the electronic device  104  is due to the thermal expansion of the electronic device  104 , resulting in the increase in elevation of the top plate  102 , which rests on the electronic device  104 .  
         [0024]     Note that the movable connector  106  has bent to allow the top plate  102  to elevate itself to accommodate the increased size of the electronic device  104 . The movable connector  106  allows for the first end of the movable connector  106  to maintain its connection with the top plate  102  and the second end to maintain its connection with the main housing  110  while allowing for movement in the z-direction of the top plate  102 . This allows the thermal compliant cap  100  to be compliant with thermal expansion and compression of the electronic device  104 .  
         [0025]     Also note that the gap  136  has grown in size to accommodate the shift in the x-y direction of the electronic device  104 . As a result, movable bar  126  has bent or otherwise morphed to accommodate the increase in the size of the orifice  136 . The orifice  136  and the movable bar  126  allow for movement in the x-y direction of the top plate  102 . This allows the thermal compliant cap  100  to be compliant with thermal expansion and compression of the electronic device  104  in an additional direction.  
         [0026]     In an embodiment where the orifice  136  includes a low modulus seal material, the material would stretch to cover the elongated gap  136  to accommodate the increase in the size of the orifice  136 . This would serve to further the purpose of the seal material, which is to seal the electronic device such that it is environmentally separated from the outside. Further, the seal material allows for stretch and movement in multiple directions such that the thermal compliant cap  100  is compliant with thermal expansion and compression of the electronic device.  
         [0027]     In an embodiment of the present invention, the electronic device  104  is attached to the top plate  102  via a coupling element comprising a thermal paste or other adhesive (not shown). The coupling element may also include a heat spreader that allows the heat emanating form the electronic device  104  to spread and be transferred to the top plate  102  for dissipation.  
         [0028]      FIG. 3  shows a top view of an alternative multi-dimensional compliant thermal cap  310 , in one embodiment of the present invention. The thermal compliant cap  310  includes the equivalent structures of the thermal compliant cap  110 , with the addition of supplementary movable connectors, movable bars and orifices in the main housing.  
         [0029]     The compliant thermal cap  310  comprises a top plate  301  similar to top plate  102 , comprising a flat rectangular plate that covers the top surface area of the electronic device that is not shown. A main housing  310  encircles and is coupled with the top plate  301 . The main housing  110  extends downward and is placed on a substrate or an electronic circuit board.  
         [0030]     The top plate  301  is attached to at least one of the movable connectors  302 ,  303 ,  304 ,  305 ,  306 ,  307 ,  308  and  309  that allow movement of the top plate  301  in the z-directions, or upwards and downwards. The movable connectors  302 - 309  are further connected to movable bars  322 ,  323 ,  324 ,  325 ,  326 ,  327 ,  328  and  329 , respectively, that allow movement in the x-y direction, or sideways. Note that the movable bars  322 - 329  are integrated with the main housing  310  and the movable bars are formed from the establishment of slot orifices  332 ,  333 ,  334 ,  335 ,  336 ,  337 ,  338  and  339 , respectively. That is, the fabrication of the slot orifices  332 - 339  create the movable bars  322 - 329  as an integrated element of main housing  310 .  
         [0031]      FIG. 3  also shows orifices  351 - 358 . These orifices represent a gap between the top plate  301  and the main housing  310 . The orifices  351 - 358  allow for the movement of the top plate  301  in any direction, including the x-direction and the x-y direction. In an embodiment of the present invention, the orifices  351 - 358 , as well as slot orifices  332 - 339 , are filled with low-modulus seal material such as silicone. The seal material fills each orifice and allows for stretch and movement in multiple directions such that the thermal compliant cap  300  is compliant with thermal expansion and compression of the electronic device.  
         [0032]     The compliant thermal cap  300  serves the function of dissipating heat generated by the electronic device and conforms to thermal expansion of the device caused by the difference in the coefficients of thermal expansions of the materials of the device and the top plate  301  of the thermal compliant cap  300 . Due to the movable nature of the connectors  302 - 309  and the bars  322 - 329 , the complaint thermal cap  300  exhibits compliance in multiple directions, specifically, the “z” direction, as well as the “x-y’ directions, i.e., the up, down and sideways directions.  
         [0033]     In an embodiment of the present invention, the thermal cap  300  (or thermal cap  100 ) is machined from a single element of a thermally conducting material, such as copper. The single element of thermally conducting material initially is machined, or drilled or cut, to include the features of present invention. In this embodiment, the top plate  301 , as well as movable connectors  302 ,  303 ,  304 ,  305 ,  306 ,  307 ,  308  and  309  are created through the machining, or cutting, of orifices  351 - 358 . Further, the movable bars  322 ,  323 ,  324 ,  325 ,  326 ,  327 ,  328  and  329 , are created through the machining, or cutting, of slot orifices  332 ,  333 ,  334 ,  335 ,  336 ,  337 ,  338  and  339 , respectively. That is, the fabrication of the slot orifices  332 - 339  create the movable bars  322 - 329  as an integrated element of main housing  310 .  
         [0034]      FIG. 4  shows a top view of an alternative multi-processor multi-dimensional compliant thermal cap  410 , in one embodiment of the present invention. The thermal compliant cap  410  includes the equivalent of four cooling structures, as described in  FIG. 3 , aggregated to form one cooling structure that offers cooling and compliant functionalities to four separate electronic devices (not shown). Each quadrant of  FIG. 4  ( 402 ,  404 ,  406  and  408 ) includes a cooling structure  100  and its corresponding components, as described with reference to  FIG. 3 .  
         [0035]     The present invention can be utilized for cooling any of a variety of electronic devices. In one embodiment of the present invention, the present invention is used to cool a microprocessor of an information processing system such as a computer.  
         [0036]     Therefore, while there has been described what is presently considered to be the preferred embodiments, it will be understood by those skilled in the art that other modifications can be made within the spirit of the invention.