Abstract:
A three dimensional vapor chamber is disclosed which has a horizontal vapor chamber portion and a vertical flat heat pipe portion. The interiors of the two portions are in fluid communication and can have a wick material saturated with a working fluid such as water. The vertical flat heat pipe portion can also have fins or other heat exchange structure connected to the exterior thereof to increase heat transfer away from the heat pipe portion. In operation, the vapor chamber portion is placed in contact with a heat source, thus causing the working fluid to evaporate and move into the vertical flat heat pipe portion, where it is condensed. The fluid is then transported back to the vapor chamber portion via capillary action through the wick. The interiors of the two portions may be constructed as a vacuum chamber, so that evaporation of the working fluid can occur at lower temperatures than would occur at atmospheric pressure.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation-in-part of application Ser. No. 10/924,586, filed on Aug. 24, 2004, which is a continuation of application Ser. No. 10/458,168, filed Jun. 10, 2003, now issued as U.S. Pat. No. 6,793,009, the entire contents of which are hereby incorporated by reference in their entirety. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The invention relates to the management of thermal energy generated by electronic systems, and more particularly to an improved thermal vapor chamber for efficiently and cost-effectively routing and controlling the thermal energy generated by various components of an electronic system.  
       BACKGROUND OF THE INVENTION  
       [0003]     The electronics industry, following Moore&#39;s Law, has seemed to be able to defy the laws of economics by providing ever increasing computing power at less cost. However, the industry has not been able to suspend the laws of physics inasmuch as high computing performance has been accompanied by increased heat generation. Board level heat dissipation has advanced to a point that several years ago was only seen at the system level. The trend toward ever increasing heat dissipation in microprocessor and amplifier based systems, such as are housed in telecommunication and server port cabinets, is becoming increasingly critical to the electronics industry. In the foreseeable future, finding effective thermal solutions will become a major constraint for the reduction of system cost and time-to-market, two governing factors between success and failure in commercial electronics sales.  
         [0004]     The problems caused by the increasing heat dissipation are further compounded by the industry trend toward system miniaturization—one of the main methodologies of the electronics industry to satisfy the increasing market demand for faster, smaller, lighter and cheaper electronic devices. The result of this miniaturization is increasing heat fluxes. For example, metal oxide semiconductor-controlled thyristors may generate heat fluxes from 100 to 200 W/cm 2 , some high voltage power electronics for military applications may generate heat fluxes of 300 W/cm 2 , while some laser diode applications require removal of 500 W/cm 2 . Also, non-uniform heat flux distribution in electronics may result in peak heat fluxes in excess of five times the average heat flux over the entire semiconductor chip surface (˜30 W/cm 2 ).  
         [0005]     Thus, as clock speeds for integrated circuits increase, package temperatures will be required to correspondingly decrease to achieve lower junction temperatures. However, increasing package temperatures will result from the increase in heat dissipation in the package from higher clock speed devices. This increase in temperature will cascade throughout the interior of the structure that encloses or houses such circuits, (e.g. a typical telecommunications or server port cabinets, or the like) as the number of high power semiconductor components positioned within the housing increases. The difference between these physical aspects (i.e., the difference between the interior cabinet temperature and the package temperature) of the electronic system defines a “thermal budget” that is available for the design of the cooling devices/systems needed to manage the heat fluxes generated by the various electronic devices in the system. As these two conflicting parameters converge, the available thermal budget shrinks. When the thermal budget approaches zero, refrigeration systems become necessary to provide the requisite cooling of the electronic system.  
         [0006]     It is well known to those skilled in the art that thermal resistances (often referred to as “delta-T”) for typical thermal systems at the semiconductor junction-to-package, package-to-sink and sink-to-air levels have been trending up over the past decade.  
         [0007]     Extensive efforts in the areas of heat sink optimization (including the use of heat pipes) and interface materials development in the past have resulted in the significant reduction of sink-to-air and package-to-sink thermal resistances. However, the reduction of these two thermal resistances has now begun to approach the physical and thermodynamic limitations of the materials. On the other hand, the junction-to-package thermal resistance (delta-T) has increased recently, due to the increasing magnitude and non-uniformity (localization) of the heat generation and dissipation from the semiconductor package.  
         [0008]     Successful cooling technologies must deal with thermal issues at the device, device cluster, printed wiring board, subassembly, and cabinet or rack levels, all of which are within the original equipment manufacturer&#39;s (OEM&#39;s) products. Many times, the problem is further complicated by the fact that the thermal solution is many times an “after thought” for the OEM. A new equipment design may utilize the latest software or implement the fastest new semiconductor technology, but the thermal management architecture is generally relegated to the “later phases” of the new product design. The thermal management issues associated with a given electronic system are often solved by the expedient of a secondary cooling or refrigeration system that is arranged in tandem with the electronics system.  
         [0009]     There are several negatives associated with the use of tandem cooling or refrigeration systems. The additional electrical power required by such systems not only increases the cost to operate the electronic equipment, but also causes an adverse environmental impact in the form of pollution (from power generation processes) and noise. Reliability issues are also of considerable concern with refrigeration systems.  
         [0010]     Thus, there is a compound challenge in the art to provide a thermal management architecture that satisfactorily accumulates and transfers variable amounts of thermal energy, generated by a wide variety of electronic components arranged together in an enclosed space, while avoiding or minimizing the use of non-passive, tandem cooling or refrigeration systems for cooling.  
       SUMMARY OF THE INVENTION  
       [0011]     A vapor chamber is disclosed, comprising a vapor chamber portion and a heat pipe portion. Each portion can have a length measured in a first direction, a width measured in a second direction, and a height measured in a third direction. Each portion further can comprise an inner cavity having a wick structure disposed on a surface of the cavity, the inner cavities being in fluid communication with each other. The heat pipe portion can be disposed on the vapor chamber portion such that the width of the heat pipe portion is substantially smaller than the width of the vapor chamber portion and the length of the heat pipe portion is substantially equal to the length of the vapor chamber portion.  
         [0012]     A three-dimensional vapor chamber comprising a vapor chamber portion and a heat pipe portion. The portions each can have a respective major surface comprising a substantially rectangular shape. The portions further each can have an inner cavity comprising a wick, and the inner cavities can be in fluid communication with each other. The heat pipe portion can be connected to the vapor chamber portion such that the major surfaces are oriented substantially perpendicular to each other. Further, the lengths of the respective portions can be substantially equal as measured in a first direction, and the heights of the respective portions can be substantially different when measured in a second direction substantially orthogonal to the first direction.  
         [0013]     A three dimensional vapor chamber is disclosed, comprising first and second heat exchange chambers having inner cavities with wick structures disposed on respective inner surfaces thereof. The chambers can be connected together so that the inner cavities are in fluid communication with each other. The first heat exchange chamber can have a length, a width and a height as measured in first, second and third mutually orthogonal directions, respectively. The second heat exchange chamber can have a length, a width and a height as measured in the first, second and third directions. The lengths of the first and second heat exchange chambers can be substantially equal, and the widths of the first and second heat exchange chambers can be substantially unequal. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     The accompanying drawings illustrate preferred embodiments of the invention so far devised for the practical application of the principles thereof, and in which:  
         [0015]      FIG. 1  is a perspective view of the inventive vapor chamber assembly;  
         [0016]      FIG. 2  is a side view of the vapor chamber assembly of  FIG. 1 ;  
         [0017]      FIG. 3  is a cross-sectional view of a portion of the vapor chamber assembly of  FIG. 1 , taken along line  3 - 3 ;  
         [0018]      FIG. 4  is an end view of an alternative embodiment of the vapor chamber of  FIG. 1 , incorporating multiple vertical condenser portions with cooling fins mounted thereto. 
     
    
     DETAILED DESCRIPTION  
       [0019]     This description of preferred embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description of this invention. The drawing figures are not necessarily to scale and certain features of the invention may be shown exaggerated in scale or in somewhat schematic form in the interest of clarity and conciseness. In the description, relative terms such as “horizontal,” “vertical,” “up,” “down,” “top” and “bottom” as well as derivatives thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing figure under discussion. These relative terms are for convenience of description and normally are not intended to require a particular orientation. Terms including “inwardly” versus “outwardly,” “longitudinal” versus “lateral” and the like are to be interpreted relative to one another or relative to an axis of elongation, or an axis or center of rotation, as appropriate. Terms concerning attachments, coupling and the like, such as “connected” and “interconnected,” refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise. The term “operatively connected” is such an attachment, coupling or connection that allows the pertinent structures to operate as intended by virtue of that relationship. In the claims, means-plus-function clauses are intended to cover the structures described, suggested, or rendered obvious by the written description or drawings for performing the recited function, including not only structural equivalents but also equivalent structures.  
         [0020]     Referring to  FIGS. 1-3 , the present invention comprises a three-dimensional vapor chamber  1  that is sized and shaped to transfer thermal heat energy generated by at least one thermal energy source, e.g., a semiconductor device that is thermally engaged with a bottom surface of the vapor chamber  1 . The vapor chamber  1  has a horizontal evaporator portion  2  and a vertical condenser portion  4 . The horizontal evaporator portion  2  comprises an inner cavity  3  defined between top and bottom walls  7 ,  11 , and has a generally flat rectangular shape with a height “h,” a width “w,” and a length “I.” The vertical condenser portion  4  can comprise an inner cavity  5  defined between opposing side walls  9 ,  13 , and has a generally flat rectangular shape with a height “h 1 ,” a width “w 1 ,” and a length “l 1 .” The horizontal evaporator portion  2  and the vertical condenser portion  4  are connected and hermetically sealed so that their respective inner cavities  3 ,  5  form a single vapor space.  
         [0021]     The inner cavities  3 ,  5  of the evaporator and condenser portions  2 ,  4  can have inner surfaces  22 ,  42  with a wick  50  disposed thereon. The wick  50  can be saturated with a working fluid, and the inner cavities  3 ,  5  can be maintained at a partial vacuum. Thus, as heat is applied to the bottom wall  11  of the evaporator portion  2 , the working fluid (which may be saturated in the wick  50 ) vaporizes, and the vapor rushes to fill the vacuum in the inner cavities  3 ,  5 . Wherever the vapor comes into contact with a cooler wall surface  42 , it condenses, releasing its latent heat of vaporization. The condensed fluid then returns to the horizontal evaporator portion  2  via capillary action in the wick  50 . Advantageously, employing capillary action as a fluid return mechanism allows the vapor chamber  1  to be used in any physical orientation, without respect to gravity, since capillary action can act to drive or draw the working fluid “up hill.” Thus, the device will operate effectively even if the installed upside down. It is noted that providing a wick is not critical, and thus the interior surfaces  22 ,  42  of the vapor chamber  1  may be provided without a wick  50 , particularly in gravity-aided embodiments of the invention.  
         [0022]     Thusly configured, the three dimensional vapor chamber  1  provides a highly efficient means of spreading the heat from a concentrated source (through the bottom wall  11  of the evaporator portion  2 ) to a large surface (the interior surfaces  22 ,  42  of the interior spaces  3 ,  5 ). Furthermore, the thermal resistance associated with the aforementioned vapor spreading is negligible as compared to traditional heat sinks. Further, the present design will provide increased cooling performance as compared to typical vapor chamber designs which use multiple discrete cylindrical “tower-type” condenser portions. This is because the present design maximizes the cooling area (i.e. the wick-wall area), and also the volume, of the condenser portion by extending it all the way across the length l of the evaporator portion  2 . The “T-shape” of the present invention is also expected to perform better than vapor chambers incorporating multiple cylindrical “tower-type” condenser portions because the condenser portion  4  of the present design retains a substantial vertical dimension even if placed on its side. Vapor chambers utilizing multiple cylindrical “tower-type” condenser portions typically are of limited to use in the vertical orientation, and also are limited in the amount of wick-wall area available for cooling. The present design provides substantially more wick-wall area and vapor space than prior devices, thus providing increased device efficiency.  
         [0023]     The present invention is also expected to be less expensive and easier to manufacture than the prior designs, since the assembly process will require the attachment of a single condenser portion  4  (by welding, brazing or soldering) to the evaporator portion  2 , rather than having to attach a multiplicity of individual small towers.  
         [0024]     The top and bottom walls  7 ,  11  of the horizontal evaporator portion  2  can comprise substantially uniform thickness sheets of a thermally conductive material, and can be spaced-apart by about 2.0 (mm) to about 4.0 (mm) so as to form the interior space  3  that defines the evaporator portion  2 . The top and bottom walls  7 ,  11  preferably comprises substantially planar inner surfaces  22 , either or both of which can have an integrally formed wick  50  as previously noted. In one embodiment, sintered copper powder or felt metal wick structure, having an average thickness of about 0.5 mm to 2.0 mm is positioned over substantially all of the inner surface of bottom wall  11  so as to form wick  50 . Of course, other wick materials, such as, aluminum-silicon-carbide or copper-silicon-carbide may also be used.  
         [0025]     As previously described, to increase the thermal performance of the horizontal evaporator portion  2 , a vertical condenser portion  4  is connected to the evaporator portion  2 . More particularly, the vertical condenser portion  4  comprises a flat rectangular structure similar to that of the evaporator portion  2 . Specifically, first and second side walls  9 ,  13  can comprise substantially uniform thickness sheets of a thermally conductive material, and are spaced-apart by about 2.0 (mm) to about 4.0 (mm) so as to form the inner space  5  that defines the condenser portion  4 . The side walls  9 ,  13  preferably comprise substantially planar inner surfaces  42 , while the top wall  15  is also substantially planar. The condenser portion  4  is open at its bottom extremity  17  where it connects to a correspondingly sized opening  19  in the top wall  7  of the horizontal evaporator portion  2 .  
         [0026]     The walls of the evaporator and condenser portions  2 ,  4  can be hermetically sealed at their respective joining interfaces to prevent leakage of the working fluid, and to maintain partial vacuum conditions where appropriate.  
         [0027]     The interior surfaces  42  of the top and side walls  9 ,  13 ,  15  can comprise an integrally formed wick  52 , similar to that described in relation to wick  50  of the evaporator portion  2 . Alternatively, the interior surfaces  42  of the condenser portion  4  can have no wick, or only portions of the interior surfaces may be provided with a wick  52 . For example, where the vapor chamber  1  is oriented such that the condenser portion  4  is located above the evaporator portion  2 , it may not be required to provide wick material to the inner surfaces of the condenser portion  4  because gravity may provide the necessary force to return condensed liquid to the evaporator portion  2 . On the other hand, if the evaporator portion  2  is located at or above the level of the condenser portion  4 , it will likely be appropriate to provide wick material over at least a portion of the inner surfaces  42  of the condenser portion  4 . For applications in which the orientation of the vapor chamber may be variable, such as in aircraft or spacecraft applications, it may be appropriate to provide wick material to most or all of the interior surfaces  42  of the condenser portion  4 . It should be noted that in the preferred embodiment of the present invention, no wick structure is present in the top wall  15  of the condenser portion  4 .  
         [0028]     Where a wick is provided for both the evaporator and condenser portions  2 ,  4 , it can be the same material, thickness, etc. for both portions. Alternatively, different wick designs and/or materials can be used for each of the condenser and evaporator portions (or for limited areas on each), depending on the use and installed orientation of the vapor chamber  1 .  
         [0029]     In addition to the wick materials and configurations previously discussed, the wicks  50 ,  52  may also comprise screens or grooves integral with any of the interior surfaces  22 ,  52  of the evaporator portion  2  or condenser portion  4 . Further, a plastic-bonded wick can be applied simultaneously and as a contiguous structure after the structural elements of the evaporator portion  2  and condenser portion  4  are connected together. This could provide a contiguous fluid conduit between the evaporator and condenser regions of the device, which may be advantageous when the evaporator is elevated.  
         [0030]     In a further embodiment, a brazed wick may be formed on any of the inner surfaces of evaporator or condenser portions  2 ,  4 , as desired. Depending on the heat load and particular power density, other wick structures may also be appropriate. Examples of such structures include screen bonded to the input surface by spot-welding or brazing a monolayer of powder metal, grooves cut in the surface  22 ,  42  of either portion  2 ,  4 , or an array of posts, either of the all-powder variety or solid copper which is powder covered, or brazed to the wall, which in a preferred embodiment would be copper material.  
         [0031]     The working fluid may comprise any of the well known two-phase vaporizable liquids, e.g., water, alcohol, freon, methanol, acetone, fluorocarbons or other hydrocarbons, etc.  
         [0032]     The vapor chamber  1  is formed according to the invention by drawing a partial vacuum within the interior spaces  3 ,  5  and then back-filling with a small quantity of working fluid, e.g., just enough to saturate wick  50  just prior to final sealing of the spaces  3 ,  5  by pinching, brazing, welding or otherwise hermetically sealing, once the condenser portion  4  is mounted to the evaporator portion  2  such that their openings  17 ,  19  align. The atmosphere inside the vapor chamber  1  is set by an equilibrium of liquid and vapor.  
         [0033]     In practice, a heat source (not shown) is mounted to the bottom wall  11  of the evaporator portion  2 . Heat from the heat source is conducted through the wall  11  causing the working fluid in wick  50  to evaporate. The vapor travels through the inner space  5  in the condenser portion  4 , where it contacts the wick  52  and/or inner surfaces  42  of walls  9 , 13 , 15 . The vapor condenses on the walls, giving up its latent heat through condensation. The condensate then returns to the evaporator portion  2  by gravity, or through capillary action of the condenser portion wick  52  (if provided) and/or the evaporator portion wick  50 .  
         [0034]     An alternative embodiment of a vapor chamber  10  is shown in  FIG. 4 , in which the vapor chamber  10  has an evaporator portion  20  and a pair of parallel-oriented condenser portions  40 . The condenser portions  40  can be configured similarly to the condenser portion  40  described in relation to the vapor chamber  1  of  FIGS. 1-3 , including wick materials and arrangements, etc.  
         [0035]     Referring again to  FIG. 1 , a pair of folded fin assemblies  100 ,  102  can be provided on opposite sides of the condenser portion  4  of vapor chamber  1 . The folded fin assemblies  100 ,  102  each can comprise a plurality of substantially parallel, thin fin walls  112  separated from one another by alternating flat ridges  114  and troughs  120 . Each pair of thin fin walls  112  are spaced apart by a flat ridge  118  so as to form each trough  120  between them. Thus folded fin assemblies  100 ,  102  comprises a continuous sheet of thermally conductive material folded into alternating flat ridges  114  and troughs  120  defining spaced thin fin walls  112  having peripheral end edges  122 . A spacer  60  can be positioned between the top wall  7  of the evaporator portion  2  and the bottom-most fin wall  112  to support the folded fin assembly at each corner of the evaporator portion  2 . Advantageously, fin walls  112  have a thickness that is no more than about 0.020″, and in a preferred embodiment have a thickness in the range from about 0.002 to 0.020 inches. In this way, the thermal impedance of fin walls  112  to the conduction of thermal energy is in a range of no more than about 2.5×10 −3 ÿ c/w/cm 2  to about 2.54×10 −2 ÿ c/w/cm 2  for aluminum material. Materials other than aluminum can also be used, such as metals, polymers, etc.  
         [0036]     The monolithic extended geometry of the condenser portion  4  makes the folded fin assemblies  100 ,  102  efficient and easy to manufacture and assemble to the vapor chamber  1 , allowing the assemblies to cool the condenser portion all along the flat length of the condenser and evaporator portions  2 ,  4 . Again, this is in contrast to prior designs having multiple cylindrical “tower-type” condenser portions, which are not configured for use with simple rectangular folded fin assemblies, or which if used with such assemblies would not allow contact along the entire outer surface of the condenser portion.  
         [0037]     Alternatively as shown in  FIG. 4 , an array of plate fins  130  can be mounted to the condenser portion  4  to convey the heat to the ambient environment, similar to the folded fin arrangement.  
         [0038]     A forced air system can also be provided to move air through the troughs of the folded fin assemblies. For example, a fan could be mounted adjacent to one end of each of the folded fin assemblies to blow air through the troughs at a desired rate. Other similar forced cooling arrangements could also be provided.  
         [0039]     Accordingly, it should be understood that the embodiments disclosed herein are merely illustrative of the principles of the invention. Various other modifications may be made by those skilled in the art which will embody the principles of the invention and fall within the spirit and the scope thereof.