Abstract:
An electronic assembly incorporates a sealed chamber that is filled with a first cooling fluid. A second cooling fluid that does not contact the first cooling fluid is circulated so as to remove heat from the first cooling fluid. The second cooling fluid is transported to an external heat removal system. Fluid circulation apparatus circulates the first cooling fluid within the chamber and facilitates heat transfer from components in the chamber. Optionally, the second cooling fluid may provide power to circulate the first cooling fluid.

Description:
BACKGROUND 
       [0001]    The present invention relates to electronic component cooling systems and methods. 
         [0002]    Electronic devices often require cooling. If such devices are to operate within an enclosure, such as an electromagnetic interference (EMI) enclosure, for example, heat must be removed in some way that does not compromise the enclosure. Multiple devices may also be packaged in an electronic assembly at high density which inhibits heat removal directly to ambient air. 
         [0003]    Conventional conductive cooling elements are typically attached to one surface of each component that is to be cooled. Using only one surface results in a high heat flux in the heat removal path that can create large temperature gradients. These gradients can result in high temperatures within components, and/or a lower temperature requirement for heat rejection, and/or thermal stresses in components. 
         [0004]    To ensure adequate thermal contact, the location of each attachment surface must be well controlled, the heat removal path must mechanically accommodate variable surface locations, a conductive contact/bridging material must be used, or some combination of the above must be used. These can be expensive to fabricate and/or difficult to assemble. 
         [0005]    Other approaches may spray a liquid coolant onto each device requiring cooling. These are specific to the arrangement of devices to be cooled and typically remove heat through only one surface of each device. 
         [0006]    Existing cooling solutions developed by the assignee of the present invention are disclosed in U.S. Pat. Nos. 6,867,976, 6,819,562, 6,695,042, 6,625,026, and 6,580,610. 
         [0007]    It would be desirable to have improved cooling systems and methods for use in cooling electronic assemblies, and the like. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The various features and advantages of disclosed embodiments may be more readily understood with reference to the following detailed description taken in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and in which: 
           [0009]      FIG. 1  illustrates a first embodiment of electronic apparatus comprising an exemplary active cooling system; and 
           [0010]      FIG. 2  illustrates a second embodiment of electronic apparatus comprising another exemplary active cooling system; and 
           [0011]      FIG. 3  is a flow diagram that illustrates an exemplary cooling method. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    Referring to the drawing figures,  FIG. 1  illustrates a first embodiment of electronic apparatus  10  comprising an exemplary active cooling system  20 . The electronic apparatus  10  comprises a printed circuit board  12  having a sealed enclosure  11  or sealed chamber  11  disposed thereon in which one or more electronic components  13  are housed. 
         [0013]    A first coolant  17  or first cooling fluid  17  is disposed within the sealed chamber  11 . The first cooling fluid  17  contacts exposed surfaces of, or bathes, each of the electronic components  13  disposed within the sealed chamber  11 . The first cooling fluid  17  is adapted to remove heat generated within the sealed chamber  11  by the one or more electronic components  13 . 
         [0014]    The exemplary active cooling system comprises one or more fluid circulators  15 , such as pumps  15  or fans  15 , for example, that circulate the first cooling fluid  17  within the sealed chamber  11 . An exemplary fluid circulator  15  may comprise a drive motor  15   a  disposed exterior to the sealed chamber  11  that is coupled to a fan  15   b  or impeller  15   b  disposed within the sealed chamber  11 . In other applications the drive motor  15   a  may be disposed internal to the sealed chamber. In either case the drive motor  15   a  may be coupled to the fan or impeller  15   b  mechanically or magnetically. 
         [0015]    The exemplary active cooling system comprises a heat exchanger  14  disposed within the sealed chamber  11 . The heat exchanger  14  is illustrated as a tube or coil that may be located inside the sealed chamber  11  or may be embedded within the walls of the sealed chamber  11 . The heat exchanger  14  is coupled to a heat removal system  16  that is external to the sealed chamber  11 . A second cooling fluid  18  flows through the heat exchanger  14  that is used to remove heat from the first coolant fluid  17  and couple it to the external heat removal system  16 . 
         [0016]    Thus, the exemplary cooling system  20  comprises a sealed chamber  11  filled with a first cooling fluid  17 , which bathes all components  13  within the chamber  12 . The first cooling fluid  17  is circulated using the one or more pumps  15  or fans  15 , as appropriate to enhance removal of heat from the components  13  within the sealed chamber  11 . Multiple pumps or fans  15  may be used for redundancy. The heat exchanger  14  is provided to transfer heat from the first cooling fluid  17  to the second coolant fluid  18  which is supplied from and coupled to the external heat removal system  16 . 
         [0017]    The first and second cooling fluids  17 ,  18  thus have different functions, and they are not allowed to mix with each other. The first and second cooling fluids  17 ,  18  may be the same substances, or may be different substances each optimized for its function in the application. For example the first cooling fluid may be selected for such properties as chemical compatibility with the devices to be cooled and low vapor pressure in the intended operating temperature range, whereas the second cooling fluid may be selected for such properties as low cost and low toxicity. Exemplary first cooling fluids include Fluorinert™, available from Minnesota Mining and Manufacturing Co. (3M), for example. Exemplary second fluids include deionized water, for example. 
         [0018]      FIG. 2  illustrates a second embodiment of electronic apparatus comprising another exemplary active cooling system. As is illustrated in  FIG. 2 , optionally, each pump/fan  15  may be driven by a fluid motor  15   a  (that rotates the turbine  15   b  or impeller  15   b , for example) that is driven by the second coolant fluid  18 .  FIG. 2  shows an application in which the chamber  11  comprises a package  13  comprising an integrated circuit chip  13  or die  13 . As is shown in  FIG. 2 , the die  13  is the only device that is cooled. In this application the pump drive motor  15   a  is disposed internal to the sealed chamber  11  and coupled to the turbine or fan  15   b  mechanically via a drive shaft. In other applications the drive motor  15   a  may be disposed external to the sealed chamber. In some applications the drive motor  15   a  and turbine or fan  15   b  may be coupled magnetically. 
         [0019]      FIG. 3  is a flow diagram that illustrates an exemplary cooling method  30 . The exemplary cooling method  30  may be used with an electronic assembly  13  comprising an electronic component  13  disposed within a sealed housing  11  or enclosure  11 . 
         [0020]    In implementing the exemplary cooling method  30  a first cooling fluid is disposed  31  within the sealed housing  11 . A heat exchanger  14  is configured to contact  32  the first cooling fluid. The heat exchanger  14  is coupled to an external heat removal system  16 . The first cooling fluid  17  is circulated within the sealed housing  11  to remove heat generated by the electronic component  13 . A second cooling fluid  18  is circulated between the heat exchanger  14  and the heat removal system  16  to remove heat contained in the first cooling fluid  17 . 
         [0021]    Advantages of the disclosed cooling systems  20  and methods  30  are that heat is removed from all available surfaces of each component  13 , thus removing more heat for a given temperature differential and reducing thermal gradients in the components  13 . Furthermore, the use of fluid motors  15   a  to drive the internal pumps/fans  15  eliminates a local source of electromagnetic interference (EMI) and additional waste heat, as would exist with electric motors. 
         [0022]    Thus, cooling systems have been disclosed. It is to be understood that the above-described embodiments are merely illustrative of some of the many specific embodiments that represent applications of the principles described herein. Clearly, numerous and other arrangements can be readily devised by those skilled in the art without departing from the scope of the invention.