Abstract:
A cooling arrangement has a circuit board and a plurality of electronic components in operable communication with the circuit board. An enclosure is attached to the circuit board being configured to retain a fluid around at least one of the plurality of electronic components. The circuit board with the enclosure is attached thereto being removably connectable to a motherboard.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This application relates to immersion cooling of power electronic circuits. 
         [0002]    Modern systems are becoming more and more complex and, as a result, complex electrical controls are provided for many such systems. One example system would be aerospace equipment, such as an aircraft. 
         [0003]    Control modules for such system often include a motherboard and a plurality of line removable modules (“LRMs”) or other circuit boards. One particular type of LRM carries a number of power transistors forming solid state power controllers (“SSPC”). Power transistors have unique cooling challenges. 
         [0004]    One known type of power transistors is a metal oxide field effect transistor (“MOSFET”). Although MOSFETs are mentioned, other types of solid state power controllers also raise similar challenges. 
         [0005]    Modern control modules may include a very high number of such transistors and electronic controls. The heat generated by these transistors raises challenges with cooling. 
         [0006]    Solid state power controllers are subject to transient heat loss due to a number of reasons, including load in-rush currents, fly back when inductive load currents are braked, lightning strikes, overcurrent faults that must be carried for a short period of time prior to turning the SSPC off, etc. 
         [0007]    In general, fluid immersion cooling for control circuits have surrounded the entire control module. This raises challenges, as a designer of modern control modules would like to be able to tailor a particular combination of motherboard and circuit boards. Further, when the entire control module is surrounded by cooling fluid, it is difficult to replace any one LRM. Fluid cooling circuits typically include a hermetic seal and, thus, are not prone to easy repair. 
       SUMMARY OF THE INVENTION 
       [0008]    A cooling arrangement has a circuit board and a plurality of electronic components in operable communication with the circuit board. An enclosure is attached to the circuit board being configured to retain a fluid around at least one of the plurality of electronic components. The circuit board with the enclosure is attached thereto being removably connectable to a motherboard. 
         [0009]    These and other features may be best understood from the following drawings and specification. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  shows an example control module. 
           [0011]      FIG. 2  shows a circuit board within the  FIG. 1  control module. 
           [0012]      FIG. 3A  shows a first embodiment of an optional feature. 
           [0013]      FIG. 3B  shows a second embodiment. 
           [0014]      FIG. 3C  shows a third embodiment. 
           [0015]      FIG. 4  shows an alternative circuit board. 
           [0016]      FIG. 5  shows a control module utilizing the  FIG. 4  embodiment. 
           [0017]      FIG. 6A  shows an optional feature. 
           [0018]      FIG. 6B  shows another embodiment. 
           [0019]      FIG. 6C  shows yet another embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]      FIG. 1  shows a control module  20  including a motherboard  22  and a plurality of removable circuit boards  24 . The module  20  communicates control signals to and from a use, such as a system on an aircraft. Boards  24  may be LRMs, but other board types may be used. As known, the boards are electrically connected to the motherboard. An outer housing  26  surrounds the boards  22  and  24 . Of course, this view is highly schematic. 
         [0021]    As mentioned above, it would be desirable to be able to freely replace the circuit boards  24  on the motherboard  22  to achieve tailored control features for a particular system. Also, some replacement may be required for maintenance purposes. In addition, it is desirable to provide cooling for elements on the circuit boards  24 . This becomes particularly valuable if the circuit boards are power distribution circuits carrying power transistors. 
         [0022]      FIG. 2  shows a circuit board embodiment  24 . As shown, control circuits or switches  28  communicate with transistors in an enclosure  30 . The enclosures  30  each surround an individual power transistor or group of power transistors and/or other components that can benefit from additional cooling. In an embodiment the board  24  has connections to be secured to motherboard  22 . 
         [0023]      FIG. 3A  shows a first embodiment wherein a power transistor  32  is mounted within the enclosure  30 . Internal chamber  34  is filled with a dielectric cooling fluid. As shown by the curved line, fluid flowing adjacent to the power transistor  32  is heated and flows away, towards the enclosure wall, where it may dissipate heat to the outer environment. 
         [0024]    As mentioned above, much of the heat generated by the transistor  32  may be transient. As the fluid absorbs this heat, the fluid expands such that the pressure within the chamber  34  rises. Pressure relief valve  36  may allow fluid to then flow outward of the enclosure. A holding container  38  is shown schematically along with a return inlet  40 . Once the fluid within chamber  34  cools, the fluid may return from holding chamber  38  into inlet  40 . In this manner, the enclosure  30  facilitates handling an expanding fluid. In some embodiments the fluid may boil as result of absorbing the heat, increasing the pressure and assisting heat transfer. 
         [0025]    As an alternative, the pressure relief valve may simply vent the fluid to the environment. 
         [0026]      FIG. 3B  shows an embodiment  130  wherein a power transistor  132  is placed within a chamber  134 . The outer housing is shown to be flexible at  136 . A nominal position is shown in phantom at  138 . As the fluid with chamber  134  expands, it can force the enclosure to the expanded position  136 . Again, this will allow the enclosure  130  to facilitate expansion of the fluid as it heats. 
         [0027]    Another embodiment  230  is shown in  FIG. 3C . A power transistor  232  is placed within a chamber  234 . Within chamber  234 , there is a liquid cooling fluid level  236  and a compressible gas level  238 . As the fluid  236  expands, it can compress the gas  238  allowing expansion of the fluid. 
         [0028]    Notably, the  FIG. 3C  embodiment may be used in conjunction with a flexible housing such as shown in  FIG. 3B . This is shown schematically, as the housing moves from a nominal position  240  to an expanded position  242 . 
         [0029]    As shown in each of  FIGS. 3A-3C , switches work with the transistors  32 / 132 / 232  to communicate signals to a use, typically through the motherboard. 
         [0030]    With these embodiments, individual line removable modules  24  may be removed from a control module  20  without the complexity of removing the cooling liquid from the enclosure. Also, with these embodiments, individual transistors or groups of transistors, and the associated enclosures, may be removed from the circuit board  24  for replacement or repair. 
         [0031]      FIG. 4  shows another embodiment  300  wherein an entire circuit board  24  is placed within an enclosed immersion cooling housing or enclosure  302 . Housing  302  may be provided with heat transfer surfaces on its outer periphery, such as roughened surface or provided with other heat transfer enhancing features such as fins, etc. The enclosure is filled with dielectric cooling fluid and the expansion features of  FIGS. 3A, 3B, and 3C  may be applied to the entire housing. Of course, appropriate electrical connection shown at  303  extends outwardly of the enclosure. 
         [0032]      FIG. 5  shows a control module  310  having a motherboard  22 , a plurality of removable circuit boards  124 , which are not provided with immersion cooling, and an enclosed circuit board  300  as shown in  FIG. 4 . Again, the module  310  communicates with a use. 
         [0033]    The enclosed circuit board  300  is illustrated in  FIG. 6A , wherein the board  513  is received within a fluid  515 , with a pressure relief valve  312  leading to a holding container  314 , and an inlet  316 . This embodiment will operate to allow expansion of the fluid, and movement of the fluid outwardly of the enclosure should it exceed a predetermined pressure. As such, it operates similar to the  FIG. 3A  embodiment. 
         [0034]      FIG. 6B  shows an enclosed circuit board  410 , which may replace the enclosed board  300  of  FIG. 5 , wherein the board  517  is received within a fluid  519 , in which an enclosure has a nominal wall location  412 , but is flexible such that it can expand as shown at  414  to accommodate expansion of the liquid within the enclosure. As such, it functions like the  FIG. 3B  embodiment. 
         [0035]      FIG. 6C  shows an enclosure  510 , wherein the board  512  itself is received within a fluid  514 . The fluid is a liquid. A layer of compressible gas  516  is also included. As the liquid  514  expands, it can compress the gas layer  516 . In addition, the enclosure  518  may optionally have a flexible wall such that it can expand as shown at  520 . As such, this is similar to the  FIG. 3C  embodiment. 
         [0036]    In sum, a control module  20 ,  310  has a motherboard  22  and a plurality of removable circuit boards  24 / 124 / 300 . At least one of the circuit boards is provided with immersion cooling of an electronic component surrounded by an enclosure that does not enclose others of the plurality of circuit boards. 
         [0037]    In embodiments, a circuit board  24 / 300  has a plurality of electronic components, with an immersion cooling fluid within an enclosure  30 / 302 , such that the circuit board and enclosure can be removed or inserted as a unit into a motherboard without releasing the fluid from the enclosure. 
         [0038]    Providing the enclosed cooling facilitates the specific tailoring of the circuit boards  24  or  300 . Further, this arrangement facilitates the replacement or repair of individual line removable modules or circuits. 
         [0039]    The assembly can facilitate the tailoring of a combination of boards. Typically, a system would have a number of different module/board types such as a power supply, microprocessor, discrete I/O communications, and SSPC modules. As different customers have different numbers and types of loads to be controlled, a mix of modules can be tailored to particular needs. For example, one customer may need several low current DC SSPCs while another might need a mix of AC and DC of various load currents. 
         [0040]    It is desirable to be able to have high loss boards (high current especially AC) be specially cooled while the rest of the system be traditional boards. This disclosure achieves such a goal. 
         [0041]    Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.