Abstract:
A heat removal system includes a heatsink assembly having a base and a plurality of heat conducting folded fin members projecting from a first surface of the base and arranged to leave an open space on the first surface of the base. At least one thermally conductive slug projects from the center of the folded fm members and the folded fin members are thermally coupled to the slug. A gas circulating system is disposed over the slug and fin members projecting from the first surface of the base. The sidewall of a fin may be provided with at least one aperture. The top surface of the fin is closed, thereby permitting the fin to operate as a plenum of sorts. The bottom of the troughs may also be closed. The fins/troughs act as a plenum. A method of producing the folded fin heatsink member is also described.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims priority under 35 U.S.C. §119(e) to provisional patent application serial No. 60/295,932 filed Jun. 5, 2001, to provisional patent application serial No. 60/305,007 filed Jul. 12, 2001, and to provisional patent application serial No. 60/369,726 filed Apr. 4, 2002; the disclosures of which are incorporated by reference herein. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    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.  
           [0003]    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.  
           [0004]    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 that 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.  
           [0005]    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.  
           [0006]    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.  
           [0007]    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.  
           [0008]    It would, therefore, be desirable to provide a heat removal system which requires a relatively small surface area for mounting and which is capable of removing an amount of heat which is greater than the amount of heat removed by conventional heatsinks requiring a like amount of surface area. It would be further desirable to provide a method and apparatus for producing a heatsink member as part of the heat removal system, and to provide such a member in a cost-effective and repeatable manner.  
         SUMMARY OF THE INVENTION  
         [0009]    In accordance with the present invention, a heat removal system includes a heatsink having a base and a plurality of heat conducting folded fin members projecting from a first surface of the base and arranged to leave an open space on the first surface of the base. At least one thermally conductive slug projects from the center of the fin members. A gas circulating system (e.g. a fan) is disposed over the slug and fin members. With his particular arrangement, a heat removal system (a fan-heat sink assembly) which rapidly removes heat from devices, circuits and modules including high power CPU chips and custom ASICS is provided. By disposing the gas circulating system above the base and the thermally conductive slug and fins, the gas circulating system increases the amount of gas flow through and around the heat conducting members and thermally conductive plate. In a preferred embodiment, the gas circulating system blows gas downward toward a PC board on which a heat generating device is disposed. The folded fin members and slug provide increased heat sinking capability. In one embodiment, the folded fin heat sink members are arranged in a circular shape and are attached to a surface of a central slug having a right circular cylinder shape and disposed in the center of the circle formed by the folded fin members. The gas circulating system may be provided as a fan or squirrel cage type blower. In some embodiments it may be preferable to position the gas circulating system below, rather than above the base plate. In such embodiments, the base plate should have one or more openings therein to allow the passage and flow of gas through and around the thermally conductive members and thermally conductive plate. The assembly will be self aligning and self jigging and the attachment means can be by soldering in a belt furnace.  
           [0010]    The heatsink assembly folded fin member may be arranged to provide a plurality of fins and troughs. The sidewall of a fin is provided with at least one aperture. The top surface of the fin is closed, thereby permitting the fin to operate as a plenum of sorts. Different aperture patterns, shapes, and sizes are provided to produce the desired cooling for a particular application. The apertures may be provided on only a single sidewall of the fin, or may be provided on both sidewalls of the fin. The bottom of the troughs may also be closed.  
           [0011]    A method of producing the folded fin heatsink member is also disclosed. A piece of material is provided having a plurality of holes disposed therein. The material is aligned between a stripper plate and an upper die. Next a fold is punched into the material with a die block and a fin forming punch. The folded piece is retracted from an upper die and the process repeated until the desired number of fins has been produced. Then the folded fins are separated from the unformed material, thereby providing the folded fin member. The apparatus for forming the folded fin member comprises an upper die having a recess formed therein, the upper die being movable between a first upper die position and a second upper die position. The apparatus further includes a pilot pin movably disposed within said upper die and a stripper plate disposed below said upper die and having an aperture disposed there through. The stripper plate is capable of supporting the piece of material being formed into the folded fin heatsink member. A die block is disposed beneath the stripper plate, with the die block movable between a first die block position and a second die block position. The apparatus further includes a forming punch extending from said die block and movable through the aperture in the stripper plate and into the recess of the upper die. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    The invention will be better understood by reference to the following more detailed description and accompanying drawings in which:  
         [0013]    [0013]FIG. 1 is a side view of a heat removal system;  
         [0014]    [0014]FIG. 2 is a top view of a heat removal system;  
         [0015]    [0015]FIG. 3 is a bottom view of a heat removal system;  
         [0016]    [0016]FIG. 4 is an end view of a folded fin members disposed on a base plate.  
         [0017]    [0017]FIG. 5 is an isometric view of the heatsink assembly of the present invention;  
         [0018]    [0018]FIG. 6 is a sectional view of a fin showing apertures extending through both sidewalls of the fin;  
         [0019]    [0019]FIG. 7 is a sectional view of a fin showing apertures extending through a single sidewall of the fin;  
         [0020]    [0020]FIG. 8 is sectional view showing an aperture in which the material is displaced away from the sidewall of a fin.  
         [0021]    [0021]FIG. 9A is a top view of an oval folded fin member attached to a circular base;  
         [0022]    [0022]FIG. 9B is a side view of the folded fin member of FIG. 9A;  
         [0023]    [0023]FIG. 9C is a bottom view of the folded fin member of FIG. 9A;  
         [0024]    [0024]FIG. 10A is a top view of a folded fin member attached to a square base;  
         [0025]    [0025]FIG. 10B is a side view of the folded fin member of FIG. 10A;  
         [0026]    [0026]FIG. 10C is a bottom view of the folded fin member of FIG. 10A;  
         [0027]    [0027]FIG. 11 is a flow chart of the present method for providing a folded fin heatsink member;  
         [0028]    [0028]FIG. 12 is a block diagram of the apparatus used for performing a first part of the method;  
         [0029]    [0029]FIG. 13 is a block diagram of the apparatus used for performing a second part of the method;  
         [0030]    [0030]FIG. 14 is a block diagram of the apparatus used for performing a third part of the method; and  
         [0031]    [0031]FIG. 15 is a block diagram of the apparatus used for performing a fourth part of the method. 
     
    
     DETAILED DESCRIPTION  
       [0032]    Referring now to FIGS.  1 - 4  in which like elements are provided having like reference designations throughout the several views, a heat removal system  10  includes a heatsink assembly  12  and a gas flow system  20 . Gas flow system  20  may be provided as a fan, a squirrel cage blower, or any other device well known to those of ordinary skill in the art to be useful for generating or otherwise increasing gas flow.  
         [0033]    In this particular embodiment, the heatsink assembly  12  includes first and second opposing plates  13   a  and  13   b  which are each adapted for mounting to the gas flow system  20 . Thermally conductive plates  13  are preferably fabricated from a thermally conductive material such as copper or any other thermally conductive material having suitable thermal and mechanical characteristics including but not limited to aluminum, brass, a zinc-aluminum die cast, a zinc alloy material. In the case where the plates are provided from aluminum, the plates are preferably plated to make them solderable. In some applications, it may be desirable or necessary to provide each of the plates  13  as single unitary pieces or as more than one piece. The plates form an outer housing similar to the venturi section of an axial fan housing.  
         [0034]    The particular number of pieces from which plates  13  are 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 material from which plate  13  is provided, the particular manufacturing techniques used and the cost to manufacture the plate. Similarly, the particular number of plates is also selected in accordance with consideration of the above-listed factors. In some applications related to cooling of processors (e.g. computer central processing units, digital signal processing units or image processing units) and other integrated circuits, six to ten plates may be used.  
         [0035]    Disposed between and in thermal contact with the plates  13   a ,  13   b  is a folded fin heat sink member  14 . In this particular example, the folder fin member is disposed in a circular shape. Thos of ordinary skill in the art should appreciate that other shapes may also be used. The folded fin members are thermally coupled to a thermally conductive slug  16 . A first surface of the slug is adapted to be in contact with an active portion of a heat generating device (e.g. an integrated circuit). Thus the folded fin member  14  is wrapped around the central post or slug  16 . Typically, the folded fin member  14  and central post  16  are provided from tinned copper.  
         [0036]    Ideally, the portion of the slug  16  in contact with the heat generating device should be provided having a shape which covers as much as possible the active area of the heat generating device. In one embodiment, the central post  16  is machined flat and a thermal interface material is disposed on the surface of the post  16  which will be in contact with the heat generating device. The thermal interface material may be a thermoelectric material or a thermoionic material. Thus, for example, in the case where the heat generating device is an IC which itself includes an internal heat sink, the slug  16  should cover the internal heat sink of the IC.  
         [0037]    Also, it may be desirable or necessary to provide folded fin member  14  as a single unitary piece or as more than one piece. The particular number of pieces from which member  14  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 base  14  is provided, the particular manufacturing techniques used to fabricate member  14  and the cost of manufacturing the member  14 .  
         [0038]    As shown in FIGS.  1 - 3 , the fan  20  is mounted on the first or top most plate  13   a  and is spaced-apart from the folded fin member  14  and the heat generating device.  
         [0039]    In an exemplary embodiment, the base plate  13   b  is provided having a substantially square shape, but it should be noted that although plates  13  are here shown having a substantially square 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 plates  13  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.  
         [0040]    Likewise, although slug  16  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 slug  16  will be selected in any particular application in accordance with a variety of factors including but not limited to the shape of the folded fin member  14  and the shape of the particular part being cooled and the amount of area available for mounting of the heat sink.  
         [0041]    The heatsink assembly 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.  
         [0042]    A heatsink as shown and described herein may be disposed over a first surface of an integrated circuit which is disposed on a printed circuit board. Disposed between a first surface of a circuit and a first surface of the heatsink is a sheet of a thermally conductive matrix material. The matrix material facilitates an extraction of heat from the circuit to the heatsink. The material may be either a thermoelectric material or a thermoionic material.  
         [0043]    It should also be noted that in some applications it may 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 may 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.  
         [0044]    Referring now to FIGS.  5 - 8  in which like elements are provided having like reference designations throughout the several views, a heatsink assembly  110  is shown. The heatsink assembly  110  includes a folded fin member  115 . In this particular example, the folded fin member  115  is disposed in a circular shape. Those of ordinary skill in the art should appreciate that other shapes may also be used. The folded fin member  115  has a plurality of ridges and troughs which define a plurality of spaced fins  130 . A sidewall of a fin includes at least one aperture  160  extending through the sidewall. A side edge of a fin  130  may also include an aperture  170 . In a preferred embodiment a plurality of apertures  160  are provided in a predetermined pattern, shape and size to provide the desired cooling. The top edges  140  of the fins  130  are closed, and the bottom edges  150  of the troughs are also closed, thereby allowing the fin/trough combination to act as a plenum.  
         [0045]    The apertures  160  can be of any size or shape. Referring to FIG. 6, a cross sectional view of a fin  130  shows apertures  160  present in both side walls of the fin. In FIG. 7, a cross-sectional view of a fin shows the apertures  160  disposed in only one sidewall of the fin. Additionally, the material  165  originally in the sidewall  130  where the aperture is provided may not be completely removed, but merely displaced from the sidewall as shown in FIG. 8. 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  165  displaced from the sidewall provides increased turbulence which breaks up boundary layers, thereby providing additional cooling. In addition, an aperture  170  may be disposed in a side edge of a fin.  
         [0046]    The heatsink assembly  110  may further include a thermally conductive member or slug (not shown), similar to thermally conductive slug  16  of FIGS.  1 - 3 . A first surface of the member is adapted to be in contact with an active portion of a heat-generating device  180  (e.g. an integrated circuit). Thus the folded fin stock  115  is wrapped around the slug and is in thermal communication with the slug. Typically, the folded fin stock and slug are provided from tinned copper or aluminum. The slug may be of any shape, and the folded fin material may follow the shape of the slug and have edges of the fins attached to the slug. While the slug is shown in a generally vertical alignment with respect to the device being cooled, the slug may be tilted such that the cylindrical slug is at an angle with respect to the device being cooled. The bottom surface of the slug is provided having an angled surface such that the bottom surface of the slug would be in contact with the device being cooled. Similarly, the folded fin member would also be attached to the slug such that the folded fins would be at an angle with respect to the device being cooled. Alternately, the slug is generally perpendicular to the device being cooled, and the fins are provided having different heights such that one section of the fins are lower than another section, thereby defining an air scoop section for receiving cooling gas provided in a generally non-vertical direction.  
         [0047]    Ideally, the portion of the slug in contact with the heat generating device  180  is provided having a shape which covers as much as possible the active area of the heat generating device. In one embodiment, the slug 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 heatsink, the member should cover the internal heatsink of the IC.  
         [0048]    In an exemplary embodiment, the thermally conductive slug 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 member will be selected in any particular application in accordance with a variety of factors including but not limited to the shape of the folded fin member and the shape of the particular part being cooled and the amount of area available for mounting of the heatsink.  
         [0049]    Referring now to FIGS.  9 A- 9 C, a folded fin member  115  is shown having a generally oval shape. The folded fin member is shown coupled to a generally circular base  118  in FIGS.  9 A- 9 C, and is shown couple dot a generally square base in FIGS.  10 A- 10 C. as shown in FIGS. 9B and 10C the folded fin member can be disposed such that a first portion of the folded fin member is at a different v\horizontal height than another portion of the fodled fin member. This orientation provides additional cooling as a gas source may be couples to provide gas in a generally horizontal direction to impinge on the fins.  
         [0050]    It may be desirable or necessary to provide folded fin member  115  as a single unitary piece or as more than one piece. The particular number of pieces from which the folded fin member  115  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, and the amount of space available for mounting of the heatsink and other components.  
         [0051]    As shown in FIG. 5 a gas supply source  190  is coupled to the folded fin member  115  and the heat-generating device  180 . The gas supply source  190  may be a fan, a blower or a compressed gas source and supplies gas to the folded fin member  115  and to the slug.  
         [0052]    The heatsink assembly  110  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.  
         [0053]    The heatsink assembly  110  as shown and described herein may be disposed over a first surface of an integrated circuit which is disposed on a printed circuit board. Disposed between a first surface of a circuit and a first surface of a heatsink is a sheet of a thermally conductive matrix material. The matrix material facilitates an extraction of heat from the circuit to the heatsink.  
         [0054]    It should also be noted that in some applications it may 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 may 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.  
         [0055]    The above-described heatsink assembly rapidly and efficiently removes heat from devices, circuits and modules. The heatsink assembly of the present invention is relatively inexpensive to manufacture, assemble and install.  
         [0056]    The present invention further comprises an apparatus and a method for providing the folded fin heat sink member  115 . The method utilizes an apparatus to perform a variety of functions which results in the formation of a folded fin heat sink member  115  having certain desirable characteristics.  
         [0057]    The apparatus for performing the method includes two stamping machines coupled together with an air feeder mechanism. The first stamping machine is conventional in design, and is used to place a plurality of holes or apertures in predetermined areas of the material. The second stamping machine is used to provide the folding of the material into the desired shape.  
         [0058]    Referring now to FIG. 11, a flow chart of the method  200  is shown. The rectangular elements, are herein denoted “processing blocks” and represent computer software instructions or groups of instructions. The diamond shaped elements, are herein denoted “decision blocks,” represent computer software instructions, or groups of instructions which affect the execution of the computer software instructions represented by the processing blocks.  
         [0059]    Alternatively, the processing and decision blocks represent steps performed by functionally equivalent circuits such as a digital signal processor circuit or an application specific integrated circuit (ASIC). The flow diagrams do not depict the syntax of any particular programming language. Rather, the flow diagrams illustrate the functional information one of ordinary skill in the art requires to fabricate circuits or to generate computer software to perform the processing required in accordance with the present invention. It should be noted that many routine program elements, such as initialization of loops and variables and the use of temporary variables are not shown. It will be appreciated by those of ordinary skill in the art that unless otherwise indicated herein, the particular sequence of steps described is illustrative only and can be varied without departing from the spirit of the invention. Thus, unless otherwise stated the steps described below are unordered meaning that, when possible, the steps can be performed in any convenient or desirable order.  
         [0060]    The first step is step  205  and recites that a plurality of holes are provided in the material. One of the holes may function as an index hole and provide a reference point for the second stamping machine. The holes may be of any design or shape and any number of holes may be provided in the material. The holes may be punched clear through such that the material which formerly occupied the hole is completely removed from the rest of the material, or the holes may be provided such that the material which formerly occupied the hole is displaced such that it is only partially removed, and remains attached to the remaining material while still providing an aperture through the material.  
         [0061]    Referring now also to FIG. 12, step  210  of the method is shown. In this stamping machine  300 , and as recited in step  210 , a reference hole is located within the material. The upper die  330  of the stamping machine includes a pilot pin  320 . The pilot pin  320  guides the material to its desired position for the folding as recited in step  215 .  
         [0062]    During step  220 , and as shown in FIG. 13, the upper die  330  is lowered until it is adjacent the material. The material is now secured in position between the stripper plate  340  and the upper die  330 . During this time the pilot pin  320  retracts into the upper die  330  as recited in step  225 .  
         [0063]    Referring now to FIG. 14, the apparatus is shown during step  230 . The die block  350  and fin forming punch  360  are raised up to the stripper plate  340 . During step  235 , the fin forming punch  360  draws the material into the cavity of the upper die  330 . At the end of this step the fold is complete in the upper die  330 .  
         [0064]    Step  240  is depicted in FIG. 15. At this step the die block  350  and the forming punch  360  are lowered back to their starting position. The upper die  330  is also raised away from stripper plate  340 . Upper die  330  further includes a knock back device (not shown) that aids in removing the just-formed folded fin from the cavity as the upper die is raised as recited in step  245 .  
         [0065]    At step  250 , a determination is made whether the desired number of fins has been formed. If not, then steps  215  et seq. are performed again. When the desired number of fins have been formed operation proceeds to step  255  wherein the material is cut thereby providing the folded fin member. In a particular application, the fin folding process is performed a total of 63 times to form the folded fin member. There is a counting device which counts up to 63 and then a cutting tool cuts off the string of folded fins. Following step  255 , the process is finished, as shown at step  260 .  
         [0066]    By way of the presently disclosed method and apparatus it is very simple to change fin heights and pitch by simply changing the front edge of the upper die and the forming punch. A variety of materials can be used to form the folded fin member, in the preferred embodiment copper is the material of choice. The number of fins, the height of the fins, and the spacing of the fins can be of any size, dependent on the application the folded fin member will be utilized in.  
         [0067]    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.  
         [0068]    All publications and references cited herein are expressly incorporated herein by reference in their entirety.