Abstract:
A thermo-electro sub-assembly comprises a gas supply, a first duct, a first heatsink adjacent a first device, a second duct, and a second heat sink adjacent a second device. The gas supply may be realized as a fan, a blower, or a compressed gas source. The first duct provides a passageway for delivering pressurized gas from the gas supply to the first heat sink. The duct may include a plurality of vanes for reducing the turbulence and air boundary separation within the duct. The first heatsink is in thermal communication with a first heat-producing device such as a microprocessor. In a preferred embodiment the heatsink comprises an axial shaped folded fin heatsink. The second duct is used to provide a pathway for the air leaving the first heatsink and delivers the air to the second heatsink. The second duct may also include a plurality of vanes for reducing turbulence and boundary flow separation within the second duct.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims priority under 35 U.S.C. §119(e) to provisional patent application serial No. 60/311,214 filed Aug. 9, 2001; the disclosure of which is incorporated by reference herein. 
     
    
     
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH  
         [0002]    Not Applicable  
         FIELD OF THE INVENTION  
         [0003]    The present invention relates generally to electronics cooling subassemblies and more particularly to electronics cooling subassemblies for use with integrated circuits (ICs) and printed circuit boards.  
         BACKGROUND OF THE INVENTION  
         [0004]    As is known in the art, there is a trend to reduce the size of semiconductor devices, integrated circuits and microcircuit modules while at the same time having the devices, circuits and modules perform more functions. To achieve this size reduction and increased functionality, it is necessary to include a greater number of active circuits, such as transistors for example, in a given unit area. As a consequence of this increased functionality and dense packaging of active devices, such devices, circuits and modules (hereinafter collectively referred to as “circuits”) use increasingly more power. Such power is typically dissipated as heat generated by the circuits.  
           [0005]    This increased heat generation coupled with the need for circuits to have increasingly smaller sizes has led to an increase in the amount of heat generated in a given unit area. To further exacerbate the problem, the circuits are often densely mounted on printed circuit boards.  
           [0006]    This increase in the amount of heat generated in a given unit area has led to a demand to increase the rate at which heat is transferred away from the circuits in order to prevent the circuits from becoming damaged or destroyed due to exposure to excessive heat. To increase the amount of heat which such circuits can withstand, the circuits can include internal heat pathways which channel or otherwise direct heat away from the most heat-sensitive regions of the circuits.  
           [0007]    Although this internal heat pathway technique increases the amount of heat which the circuits can withstand while still operating, one problem with this internal heat pathway technique is that the amount of heat generated by the circuits themselves often can exceed the amount of self-generated heat which the circuits can successfully expel as they are caused to operate at higher powers. Furthermore, other heat generating circuit components mounted on printed circuit boards proximate the circuits of interest further increase the difficulty with which heat can be removed from heat sensitive circuits. Thus, to increase the rate at which heat is transferred away from the circuits, a heatsink is typically attached to the circuits.  
           [0008]    Such heatsinks typically include a base from which project fins or pins. The fins or pins are typically provided by metal extrusion, stamping or other mechanical manufacturing techniques. The heatsinks conduct and radiate heat away from the heat generating and thermally vulnerable regions of circuits. To further promote the heat removal process, fans are typically disposed adjacent the heatsink to blow or otherwise force air or gas through the sides of the fins or pins of the heatsink.  
           [0009]    One problem with this approach, however, is that the amount of air or other gas which a fan or blower can force through the heatsink fins/pins is limited due to the significant blockage of gas flow pathways due to the fins/pins themselves. Furthermore, in a densely populated printed circuit board (PCB) or multi-circuit module (MCM), other circuit components and mechanical structures required to provide or mount the PCB or module present additional blockage to gas pathways and also limits the amount of gas flow through the heatsink thus limiting the effectiveness of the heatsink. Thus, the ability of such conventional heatsinks and heatsink fan assemblies is limited and is not sufficient to remove heat as rapidly as necessary to ensure reliable operation of state of the art devices, circuits and modules having increased thermal cooling requirements.  
           [0010]    It would, therefore, be desirable to provide a heat removal system which is capable of removing an amount of heat which is greater than the amount of heat removed by conventional heatsinks. Additionally, it would be desirable to provide Electro-Magnetic Interference (EMI) protection in conjunction with the removal of heat from semiconductor devices, integrated circuits and microcircuit modules.  
         SUMMARY OF THE INVENTION  
         [0011]    In accordance with the present invention, an electronics cooling sub-assembly comprises a gas supply, a first duct, a first heatsink adjacent a first device, a second duct, and a second heat sink adjacent a second device. The gas supply may be realized as a fan, a blower, a compressed gas supply or other gas source. The first duct provides a passageway for delivering high velocity gas from the gas supply to the first heat sink. The first duct may include a plurality of vanes for reducing the turbulence and air boundary separation within the duct. The first heatsink is in thermal communication with a first heat-producing device such as a microprocessor. In a preferred embodiment the heatsink comprises an axial shaped folded fin heatsink. The second duct is used to provide a pathway for the air leaving the first heatsink and delivers the air to the second heatsink. The second duct may also include a plurality of vanes for reducing turbulence and boundary flow separation within the second duct. The second heatsink is disposed adjacent a second device such as a circuit which provides power to the first device. The second heatsink may be realized as a folded fin linear heatsink, and the gas delivered by the second duct is directed over the linear arrangement of fins. The ducts, in a preferred embodiment are used to provide EMI protection. The ducts are made of a conductive material or of a non-conductive material which has a conductive coating. By electrically connecting the ducts to ground, the ducts perform as an EMI shield. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    The invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which:  
         [0013]    [0013]FIG. 1 is a side view of a prior art heat removal assembly;  
         [0014]    [0014]FIG. 2 is a partially cut-away isometric view of the thermo-electro sub-assembly of the present invention;  
         [0015]    [0015]FIG. 3A is a partially cut-away top view of the thermo-electro sub-assembly of the present invention; and  
         [0016]    [0016]FIG. 3B is a side view of the thermo-electro sub-assembly of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]    Referring now to FIGS.  1 - 3 B in which like elements are provided having like reference designations throughout the several views, a prior art heat removal system is shown in FIG. 1, and the electronics cooling sub-assembly of the present invention is shown in FIGS.  2 - 3 B.  
         [0018]    As shown in FIG. 1, a prior art heat removal assembly  5  comprises a heatsink  60  coupled to a first heat producing device  50  and a second heat-producing device  40 . A frame  20  is used to mount the first and second device to a module  10 . In order to cool the devices  40  and  50  a pair of fans  70  and  80  are used. Fan  70  is disposed to direct an air stream to fan  80 , which directs its air stream across heat sink  60 . Heat sink  60  is a linear heatsink. This embodiment requires a significant amount of height, and is therefore not usable in many enclosures. Also, the heatsink  60  is a large, heavy component which has high costs associated with it. Further there is no EMI protection afforded the two devices by this configuration.  
         [0019]    Referring now to FIGS.  2 - 3 B, the present invention is shown. The presently disclosed electronics cooling sub-assembly utilizes a gas supply  75 , which is located remotely from the devices being cooled. The gas supply may be realized as a fan, a blower or a compressed air source. In a preferred embodiment, the gas supply comprises a “squirrel cage” type blower. A first duct  100  is coupled to the portion of the blower exhaust port which has the high velocity airflow exiting. First duct  100  provides a passageway for the gas flow from the blower to the first heatsink  120 . A second duct provides a passageway for gas flow from the first heatsink  120  to second heatsink  65 .  
         [0020]    Duct  100  includes a plurality of vanes  105  disposed therein. The vanes  105  are designed to reduce the turbulence within the first duct  100 , prevent or reduce air boundary separation within the duct, and to maintain the velocity head pressure. The vanes minimize the discontinuities in the airflow through the duct. As a result, a high pressure, generally uniform stream of gas is provided by the first duct  100  to a first heatsink  120 . The vanes are preferably solid pieces having a smooth finish in order to minimize turbulence. Transition vanes (not shown) may also be incorporated at the end of the duct  100 .  
         [0021]    As shown in FIGS.  2 - 3 B duct  100  is coupled to gas mover  75 . The gas velocity coming out of the gas mover  75  is non-uniform across the output of the gas mover. Accordingly, the duct  100  should be carefully matched to the fan to prevent large pressure drops from occurring. The incorporation of vanes  60  within the duct  20  keep the gas flow attached, thus the separation and turbulence are minimized as is the loss of velocity head pressure. The duct  20  and vanes  60  allow the gas flow from gas mover  10  to become evenly distributed, therefore making the useable output of the gas mover as large as possible.  
         [0022]    Duct  100  may be provided in any desired shape as long as the duct provides a passageway for the gas exiting the gas mover  75  to the first heatsink. The vanes  105  may be provided having any shape which prevents or reduces flow separation of the gas within the duct. The particular shape of the duct and the vanes will be selected in any particular application in accordance with a variety of factors including but not limited to the amount of gas flow being utilized, the size of the device being cooled and the amount of cooling required to cool the particular device. The vanes may also be configured to reduce the spin of the gas flow discharged from a propeller fan.  
         [0023]    In an exemplary embodiment, the first heatsink  120  is provided having a substantially circular shape, other shapes, including, but not limited to, rectangular, circular, oval, square, triangular, rhomboidal and irregular shapes, may also be used. The particular shape of the heatsink will be selected in any particular application in accordance with a variety of factors including but not limited to the shape of the particular part being cooled and the amount of area available for mounting of the heat sink. The first heatsink  120  may further be realized as a folded fin heatsink. First heatsink  120  is thermally coupled to a first device, and provides for removal of heat from the first device. In a preferred embodiment, the first device comprises a microprocessor. In a preferred embodiment the first heatsink is provided having a plurality of ridges and troughs which define a plurality of spaced fins. A sidewall of the fin includes at least one aperture extending through the sidewall. The plurality of apertures are provided in a predetermined pattern, shape and size to provide the desired cooling. The top edges of the fins are closed, and the bottom edges of the troughs are also closed, thereby allowing the fin/trough combination to act as a plenum.  
         [0024]    The apertures can be of any size or shape. Additionally, the material originally in the side wall where the aperture is may not be completely removed, but merely bent displaced from the sidewall. This arrangement provides additional material for cooling as opposed to the embodiment wherein the original material in the sidewall is completely removed to form the aperture. Additionally, the portion displaced from the sidewall provides increased turbulence which breaks up boundary layers, thereby providing additional cooling.  
         [0025]    The heat sink may further include a thermally conductive member. A first surface of the member is adapted to be in contact with an active portion of a heat generating device (e.g. an integrated circuit). Thus the folded fin stock is wrapped around the member and is in thermal communication with the member. Typically, the folded fin stock and member are provided from tinned copper or aluminum.  
         [0026]    Ideally, the portion of the member in contact with the heat generating device is provided having a shape which covers as much as possible the active area of the heat generating device. In one embodiment, the member is machined flat and a thermal interface material is disposed on the surface of the member which will be in contact with the heat generating device. Thus, for example, in the case where the heat generating device is an IC which itself includes an internal heat sink, the member should cover the internal heat sink of the IC.  
         [0027]    Also, it may be desirable or necessary to provide folded fin members of the heatsink as a single unitary piece or as more than one piece. The particular number of pieces from which the first heatsink is provided may be selected in accordance with a variety of factors including but not limited to the particular application, the amount of heat which must be transferred away from heat generating devices, the amount of space available for mounting of the heat sink and other components, the particular material from which the heatsink pieces is provided, the particular manufacturing techniques used to fabricate heatsink and the cost of manufacturing the heatsink.  
         [0028]    A second duct  110  is coupled adjacent first duct  100  and is utilized to provide gas exiting first heatsink  120  to second heatsink  65 . Second duct  110  may also include a plurality of vanes disposed therein to reduce or eliminate turbulence and boundary flow separation. In a preferred embodiment there are two ducts, though the ducts could be combined into a single unitary duct.  
         [0029]    Second duct  110  may be provided in any desired shape as long as the duct provides a passageway for the gas exiting the first heatsink to the second heatsink. The particular shape of the duct will be selected in any particular application in accordance with a variety of factors including but not limited to the amount of gas flow being utilized, the size of the device being cooled and the amount of cooling required to cool the particular device.  
         [0030]    Second heatsink  65  in a preferred embodiment is linear heatsink and is coupled to a second device  40 . While the second heatsink is shown having a generally rectangular shape, other shapes could also be used. Second heatsink may also be realized as a folded fin heatsink. Second device  40  may be a device which provides power to first device  50 .  
         [0031]    The heatsinks may be coupled to any type of integrated circuit package including, but not limited to, dual-in-line packages (DIP) leadless chip carriers, leaded chip carriers, flat packs, pin-grid arrays as well as other surface mount packages and small outline integrated circuit packages for surface-mounting.  
         [0032]    One or both of the heatsinks as shown and described herein may be disposed over a first surface of one or more integrated circuits which are disposed on a printed circuit board. Disposed between a first surface of a circuit and a first surface of a particular heatsink is a sheet of a thermally conductive matrix material. The matrix material facilitates an extraction of heat from the circuit to the heatsink.  
         [0033]    It should also be noted that in some applications it might be desirable to mount the circuit on the printed circuit board prior to placing the heatsink/thermally conductive matrix material assembly on to the circuit. It should also be noted that in some applications it might be desirable to apply the thermally conductive matrix material first to the surface of the circuit and then to mount the heatsink to the circuit/thermally conductive matrix assembly and then mount the assembly on the PCB.  
         [0034]    The present invention solves the problem of providing heat removal for a device that must be fit into a small space, unlike the prior art solutions. The typical size of a box that fits into a rack is known as a “U” which is equal to about 1.75 inches in height. Presently, there exist needs for cooling solutions which fit within a 1U, 2U, 3U and 4U box. The present invention fits within a 1U box and can be implemented on a top side of a module and on a bottom side of a module within a 2U or bigger box.  
         [0035]    Having described the preferred embodiments of the invention, it will now become apparent to one of ordinary skill in the art that other embodiments incorporating their concepts may be used. It is felt therefore that these embodiments should not be limited to disclosed embodiments but rather should be limited only by the spirit and scope of the appended claims. All publications and references cited herein are expressly incorporated herein by reference in their entirety.