Abstract:
Disclosed is a system for cooling an electronics package. The system includes a fluid pump and a microcooler assembly. The system utilizes one or more cooling layers interspersed with layers of electronics in the electronics package. Each cooling layer has an array of cooling channels formed in a substrate, an input manifold through which cooling fluid is provided for distribution through the array of cooling channels, and an output manifold which collects fluid from the array of cooling channels. The elements of the cooling system are integrated by conduits including a package conduit for passage of fluid from the fluid pump to the electronics package, a cooler conduit for passage of fluid from the electronics package to the microcooler assembly, and a pump conduit for passage of fluid from the microcooler assembly to the fluid pump. Also disclosed is a method for cooling the electronics package.

Description:
BACKGROUND 
     The subject invention relates to a cooling system for high performance electronic devices. More particularly, the invention relates to an improved fluid cooling system for high performance electronic devices that includes an improved pump and improved heat rejection component. 
     Many high performance electronic devices require a cooling system to prevent components, such as microprocessors, from overheating, and to improve reliability and efficiency of such components. One method for cooling such components is by utilizing a heatsink and fan combination. The heatsink is disposed in contact with the component to be cooled and conducts heat away from the component. The fan moves a volume of air across the heatsink removing heat from the heatsink and into the air by convection. As microprocessors become faster and more densely packed, more heat is generated by the microprocessors and the size of the heatsink and fan combination must be increased in order to provide the necessary cooling. 
     An alternative to the heatsink and fan combination is a fluid cooling system. A fluid cooling system may include fluid-cooled heat sink plates that can increase heat flux performance of the system by an order of magnitude compared with air-cooled designs, thus reducing the size of heat sink required to achieve a required heat flux. The addition of heat pipes, impinging sprays, and two-phase cooling can further improve performance of the fluid cooling system. The fluid cooling system may include a substrate with channels formed into it that is disposed at the microprocessor. Cooling fluid is pumped through the channels and conducts heat from the microprocessor. The heated fluid then proceeds away from the microprocessor to a remotely located heat dissipater, for example a heatsink and fan combination. There the heat is dissipated into the atmosphere by the fan moving a volume of air over the heatsink, and the fluid is cooled. The cooled fluid is then pumped back to the microprocessor channels. As heat generated by microprocessors increases, fluid pressure provided by the pump and air volume moved by the fan must be increased to provide adequate cooling. Conventional pumps and fans that meet these requirements can be undesirably noisy as well as too large to meet the size requirements for the overall electronics device. 
     What is needed is a fluid cooling system for high performance electronics components capable of removing an adequate amount of heat in order to maintain the functionality of the electronics, and that can be packaged into a smaller volume than a comparable conventional fluid cooling system. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The present invention solves the aforementioned problems by providing an improved system for cooling an electronics package. The system utilizes one or more cooling layers interspersed with layers of electronics in the electronics package. Each cooling layer comprises an array of cooling channels formed in a substrate, an input manifold having a plurality of input manifold arms through which cooling fluid is provided for distribution through the array of cooling channels, and an output manifold having a plurality of output manifold arms which collect fluid from the array of cooling channels. The system includes a fluid pump and a microcooler assembly including a turbomachine which forces a volume of air across a heatsink. The elements of the cooling system are integrated by conduits including a package conduit for passage of fluid from the fluid pump to the electronics package, a cooler conduit for passage of fluid from the electronics package to the microcooler assembly, and a pump conduit for passage of fluid from the microcooler assembly to the fluid pump. 
     The system cools the electronics in the electronics package by pumping fluid from the fluid pump through the package conduit to the input manifold disposed at the electronics package. The fluid is distributed to one or more cooling layers interspersed with one or more electronics layers in the electronics package and through the input manifold arms into the array of cooling channels. The fluid absorbs heat in the electronics package as the fluid is forced through the array of cooling channels. The fluid is collected in the output manifold arms and continues through the output manifold and further through the cooler conduit to the heatsink of the microcooler assembly. The heatsink absorbs heat from the fluid, and the heat is radiated from the heatsink to ambient air by utilizing the turbomachine to force a volume of air across the heat sink. The fluid then continues back to the fluid pump through the pump conduit. 
     These and other objects of the present invention will become more apparent from the following description taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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 objects, features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is an illustration of a compact cooling system for high flux electronics. 
         FIG. 2  is an exploded view of an electronics circuit cooled by the system of  FIG. 1 . 
         FIG. 3  is a partial view of cooling channels of the system on  FIG. 1 . 
         FIG. 4  is an example of a surface treatment of a cooling channel of  FIG. 3 . 
         FIG. 5  is another example of a surface treatment of a cooling channel of  FIG. 3 . 
         FIG. 6  is yet another example of a surface treatment of a cooling channel of  FIG. 3 . 
         FIG. 7  is a perspective view of a viscous shear pump utilized in one embodiment of the system of  FIG. 1 . 
         FIG. 8  is a detail end-view of the interior of an example of a viscous shear pump of  FIG. 7 . 
         FIG. 9  is a perspective view of a synthetic jet pump utilized in one embodiment of the system of  FIG. 1 . 
         FIG. 10  is a cross-sectional view of the synthetic jet pump of  FIG. 9 . 
         FIG. 11  is a cross-sectional view of another example of a synthetic jet pump used in one embodiment of the system of  FIG. 1 . 
     
    
    
     The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , enhanced fluid cooling system  10  comprises a fluid pump  12  and a microcooler  14  to cool an electronics package  16 . As shown in  FIG. 2 , the electronics package  16  includes one or more electronics layers  18  which may contain a variety of components, for example a processor can be combined at chip level with DRAM, flash memory and resistors/capacitors. One or more cooling layers  20  are interspersed with the one or more electronics layers  18 . Each cooling layer  20  includes an array of channels  22 . Arrangement of the array of channels  22  may vary with the application and the cooling requirements of a particular component. As an example, the channels  22  in  FIG. 2  are substantially parallel to one another. As shown in  FIG. 3 , the channels  22  are formed in a substrate  24 . The substrate may be formed from a variety of materials, including silicon, ceramic materials, metallic materials, glass, or combinations thereof. The channels  22  may be formed in the substrate  24  by etching or by some other means. The channels  22  may have various diameters. For example, the channels  22  may have diameters of less than 3 mm, or the channels  22  may have diameters of less than 300 microns. Returning again to  FIG. 2 , the one or more cooling layers  20  also include an input manifold  26  for providing low temperature fluid to each of the cooling layers  20 , and an output manifold  28  for outputting high temperature fluid from each of the cooling layers  20 . Although the specific dimensions of the input manifold  26  and output manifold  28  may vary based on cooling requirements and the application, in one example the input manifold  26  and output manifold  28  have a diameter of about 2 millimeters. 
     In each cooling layer  20 , the fluid flows from the input manifold  26  and, referring now to  FIG. 3 , into a plurality of input manifold arms  30  which are disposed in the cooling layer  20  to provide fluid to the channels  22 . In the example shown in  FIG. 3 , the input manifold arms  30  are disposed perpendicular to and substantially coplanar with the channels  22 . The fluid flows from the input manifold arms  30  into the array of channels  22  where it conducts heat from the electronics layer  18  and is heated. The heated fluid then enters a plurality of output manifold arms  32  which are disposed in the cooling layer  20  to collect fluid from the channels  22 . In he example shown in  FIG. 3 , the output manifold arms  32  are disposed perpendicular to and coplanar with the channels  22  and are interspersed with the input manifold arms  30 . In one example, the input manifold arms  30  and output manifold arms  32  have substantially rectangular cross sectional shapes, but other cross sectional shapes, such as circular, are contemplated. In some embodiments, the cross section of each input manifold arm  30  and output manifold arm  32  may be constant along its length, or the cross section may taper or otherwise vary. The heated fluid is carried through the output manifold arms  32  and into the output manifold  28 . The interspersed arrangement of the input manifold arms  30  and the output manifold arms  32  greatly shortens a heatsink link  34  (the distance fluid travels in a channel  22 ) to, in one example, less than about 1 centimeter, and therefore improves thermal performance of the cooling system  10 . Furthermore, the perpendicular arrangement of the input manifold arms  30  and output manifold arms  32  relative to the channels  22  simplifies manufacture and assembly of the cooling layers  20 . 
     In some embodiments, each channel  22  may have one or more surface treatments applied to it to enhance the performance of the cooling system  10 . Examples of surface treatments are shown in  FIGS. 4-6 . As shown in  FIG. 4 , turbulators  36  are small protrusions extending from the inner walls  38  of the channel  22  into the fluid flow. As shown in  FIG. 5 , micro pin fins  40  are cylindrically shaped protrusions arrayed across the channel  22  and extending completely between the inner walls  38  creating periodic flow obstructions across the fluid flow. Another example of surface treatments, shown in  FIG. 6  is dimples  42 . Dimples  42  are concave features in the inner walls  38  and are disposed periodically along the inner walls  38 . The treatments described above, as well as others including vortex cooling, controlled roughness, and local jets, may be used alone or in combination to introduce turbulence to the fluid flow in the channels  22  thereby increasing the cooling performance of the channels  22 . 
     Returning to  FIG. 1 , increased pressure losses in the channels  22  require greater pumping pressures which would result in a substantial pump size increase with conventional pumping techniques. An example of a fluid pump  12  capable of pumping at a flow rate and a pressure necessary for performance of the cooling system  10  is a viscous shear pump  44 , shown in  FIG. 7 . As shown in  FIG. 7 , the viscous shear pump  44  includes herringbone-spiral grooves  46  disposed on a rotating element  48  of the viscous shear pump  44 . In addition to actively pumping the fluid, the grooves  46  increase the stability of the viscous shear pump  44  compared to non-grooved, hydrodynamically lubricated journal and thrust bearings. The viscous shear pump  44  provides the higher flow pressures needed to adequately remove the heated fluid from the channels  22 , and is able to do so with a pump ⅕ th  the size of a comparable conventional fluid pump. 
     In some embodiments of the cooling system  10 , the fluid pump  12  may comprise a synthetic jet pump  50 , an example of which is shown in  FIG. 9 . The synthetic jet pump  50  is a piezo-based pump which, as shown in  FIG. 10 , includes a plurality of pump chambers  52 ,  54 ,  56 ,  58  extending from an input chamber  60  to an output chamber  62 , with adjacent pump chambers separated by a deformable membrane  64 . An input valve  66  is disposed at each pump chamber  52 ,  54 ,  56 ,  58 , between the pump chamber  52 ,  54 ,  56 ,  58  and the input chamber  60 . An output valve  68  is disposed at each pump chamber  52 ,  54 ,  56 ,  58  between the pump chamber  52 ,  54 ,  56 ,  58  and the output chamber  62 . An actuator (not shown), for example a piezo or magnetic actuator, is mechanically coupled to at least a portion of each deformable membrane  64 . When an electrical signal is transmitted to each actuator, the actuator causes each deformable membrane  64  to deform, either expanding or contracting each pump chamber  52 ,  54 ,  56 ,  58 . For example, the actuators in synthetic jet pump  50  are disposed such that when activated, pump chamber  52  contracts and expels fluid through output valve  68  into output chamber  62 , pump chamber  54  expands and draws fluid into pump chamber  54  from the input chamber  60  through input valve  66 , pump chamber  56  contracts and expels fluid through output valve  68  into output chamber  62 , and pump chamber  58  expands and draws fluid into pump chamber  58  from the input chamber  60  through input valve  66 . When the actuators are de-activated, each pump chamber  52 ,  54 ,  56 ,  58  returns to its pre-actuated state. Pump chamber  52  expands and draws fluid into pump chamber  52  from the input chamber  60  through input valve  66 , pump chamber  54  contracts and expels fluid through output valve  68  into output chamber  62 , pump chamber  56  expands and draws fluid into pump chamber  56  from the input chamber  60  through input valve  66 , and pump chamber  58  contracts and expels fluid through output valve  68  into output chamber  62 . 
     Another example of a synthetic jet pump  50  is shown in  FIG. 11 . In this example, pump chambers  52 ,  54 ,  56  are separated by two deformable membranes  64  with a spacer  70  therebetween. When the actuators are activated, pump chambers  52 ,  54 ,  56  expand and draw fluid into pump chambers  52 ,  54 ,  56  from input chamber  60  through input valves  66 . When the actuators are deactivated, pump chambers  52 ,  54 ,  56  contract to their pre-actuated state and expel fluid through output valves  68  into output chamber  62 . Inclusion of the spacers  70  allows the pump chambers  52 ,  54 ,  56  to expand and contract in unison further improving performance of the synthetic jet pump  50 . 
     Returning to  FIG. 1 , the microcooler  14  is used to reduce the temperature of fluid heated by the electronics package  16  and to dissipate the heat into the atmosphere. The microcooler  14  comprises a heatsink  72  and a high powered turbomachine  74 . The turbomachine  74  includes a compressor  76  which, in this example, includes a rotor  78  and a stator  80 . The compressor  76  is mechanically connected to a motor  82 , and the turbomachine  74  is contained in a housing  84 . Power is provided to the motor  82  from a power source (not shown), and the motor  82  drives the compressor  76 . The compressor  76  draws air from around the heatsink  72  through a transition duct  86  disposed between the heatsink  72  and the turbomachine  74 , compresses the air, drives the air along a length of the housing  84 , and exhausts the air to the atmosphere. The aerodynamic configuration of the compressor  76  makes the turbomachine  74  capable of high flow rates up to about 35 liters per second and high pressures in excess of conventional fans of similar size. The turbomachine  74  provides air cooling as much as 15 times more effective than conventional fans while occupying about ¼ th  the space of a conventional fan with similar capabilities. 
     The various components of the cooling system  10  are connected by conduits through which the cooling fluid is circulated through the cooling system  10 . A variety of fluids may be utilized as the cooling fluid including dielectric fluids, water based fluids and mixtures, or combinations thereof. The fluid pump  12  pumps cooling fluid through a package conduit  88  and to the electronics package  16 . Returning to  FIG. 2 , the cooling fluid enters the input manifold  26  from the package conduit  88 , and it is distributed through the input manifold  26  to channels  22  in the one or more cooling layers  20 . As the cooling fluid passes through the channels  22 , it absorbs heat from the surfaces of the channels  22 . The heated cooling fluid flows from the channels  22  through the output manifold  28 . Returning now to  FIG. 1 , the fluid flows from the output manifold  28  to the microcooler  14  through a cooler conduit  90 . Optionally, the package conduit  88  may be split into a plurality of package conduits  88  and carry cooling fluid from the fluid pump  12  to a plurality of electronics packages  16  within an electronic device. The fluid is utilized to cool the plurality of electronics packages  16  as described above, and the heated cooling fluid flows through a plurality of cooler conduits  90 , which may be joined into a single cooler conduit  90  before reaching the microcooler  14 . 
     Heat from the cooling fluid is absorbed by the heatsink  72 , and the heat migrates into the heatsink fins  92 . The turbomachine  74  moves a volume of air across the surfaces of the heatsink fins  92 , and through the turbomachine  74  as described above, thus rejecting the heat into the atmosphere. The cooling fluid then returns to the fluid pump  12  via a pump conduit  94 . This process continues as a closed loop, maintaining an operating temperature of the electronics package  16 , and thus preserving its functionality. 
     Examples of the cooling system  10  described above provide higher flow rates and pressures resulting in the capability to cool heat fluxes of greater than about 750 W/cm 2  and to achieve heat transfer rates of over about 30,000 W/m 2 /° K. Additionally, the cooling system  10  is smaller and lighter in weight allowing space within an electronic device to be utilized for other functions. 
     While embodiments of the invention have been described above, it will be understood that those skilled in the art, both now and in the future, may make various improvements and enhancements which fall within the scope of the claims which follow. These claims should be construed to maintain the proper protection for the invention first described.