Abstract:
A heat sink is provided. The heat sink contains a first vapor chamber section having a top surface and a bottom surface that is in thermal contact with a heat source, a second vapor chamber section that extends vertically from the top surface of the first vapor chamber section, and heat-dissipating fins that are attached to the second vapor chamber section. The first and second vapor sections are connected to each other forming a continuous vapor chamber space.

Description:
TECHNICAL FIELD 
       [0001]    The technical field relates generally to cooling systems for electronics, and more particularly to a heat sink with vapor chambers and thermal dissipating fins. 
       BACKGROUND 
       [0002]    Increasing levels of component power and power density from electronic devices such as integrated circuits and memory are creating an increased demand for thermal management solutions. For example, hid blade servers have been in great demand in recent years due to their outstanding performance. This high density computing power, however, comes with very limited space in the server enclosure. Accordingly, high performance heat sinks are necessary for efficient cooling. The heat sinks in use today have reached their limit in dissipating the heat generated by power chips. A need for more efficient cooling exists to expand the thermal dissipation performance envelope. 
       SUMMARY 
       [0003]    A heat sink is disclosed. The heat sink comprises a first vapor chamber section having an upper surface and a lower surface, a second vapor chamber section extending vertically from said upper surface of said first vapor chamber section, and heat dissipating fins extending horizontally from said second vapor chamber section, wherein said lower surface is in thermal contact with a heat source and wherein said first and second vapor sections are connected to each other, forming a continuous vapor chamber space. 
         [0004]    Also disclosed is a heat site comprising: a hollow-centered base having a top surface and a bottom surface, wherein said bottom surface is in thermal contact with a heat source; two hollow-centered sidewalls located on two opposite sides of the base and extending upwardly from the top surface of the base; and one or more hollow-centered center columns located between the two sidewalls and extending upwardly from the top surface of the base, wherein the hollow centers of said base, said sidewalls and said one or more center columns are connected to each other forming a continuous vapor chamber space, and wherein said sidewalls and said center columns comprise fins for heat dissipation. 
         [0005]    Also disclosed is a heat sink comprising: a planar-shaped first vapor chamber having a first surface and a second surface, wherein said first surface is opposite to said second surface and is in contact with a heat source; a second vapor chamber formed on said second surface, said second vapor chamber is connected to said first vapor chamber thus forming a continuous vapor chamber space; and a plurality of planar-shaped heat dissipating fins extending from said second vapor chamber. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    Embodiments of the invention will be readily understood by the following detailed description in conjunction with the accompanying drawings. To facilitate this description, like reference numerals designate like structural elements. Embodiments of the invention are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings. 
           [0007]      FIG. 1  is a cross-sectional view of a prior art heat sink. 
           [0008]      FIGS. 2A and 2B  are schematic representations of two embodiments of a heat sink with innovative vapor chamber configuration; 
           [0009]      FIG. 3  is a composite of schematic representations of a heat sink with free-standing center column configuration with (upper panel) or without (lower panel) fins; 
           [0010]      FIGS. 4A-4C  are results of computational fluid dynamics (CFD) analysis of the heat sink configuration shown in  FIG. 3 ; 
           [0011]      FIGS. 5A and 5B  are results of CFD analysis of the airflow in the heat sink configuration shown in  FIG. 3 ; 
           [0012]      FIG. 6  is a schematic representation of a heat sink with wall-like center column configuration; 
           [0013]      FIGS. 7A and 7B  are results of CFD analysis of the heat sink configuration shown in  FIG. 6 ; 
           [0014]      FIGS. 8A and 8B  are results of CFD analysis of the airflow in the heat sink configuration shown in  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    In the following detailed description, reference is made to the accompanying drawings which form a part hereof wherein like numerals designate like parts throughout, and in which is shown by way of illustration embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural or logical changes may be made in alternate embodiments. Therefore, the following detailed description is not to be taken in a limiting sense, and the scope of embodiments in accordance with the present invention is defined by the appended claims and their equivalents. 
         [0016]    This description is intended to be read in connection with the accompanying drawings, which are to be considered pan 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,” “&#39;down,” “top” and “bottom” as well as derivatives thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as been 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,” “upwardly” versus “downwardly,” “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. 
         [0017]      FIG. 1  is a conceptual illustration of a prior art heat sink with a vapor chamber. The vapor chamber is confined in a base plate having a lower surface and an upper surface. The lower surface is in thermal contact with a heat source and the upper surface comprises planar fins extending vertically from the upper surface for heat dissipation. 
         [0018]      FIG. 2A  illustrates an embodiment of a heat sink with innovative vapor chamber configuration. Heat sink  10  comprises a vapor chamber base  20 , vapor chamber sidewalls  30  and optionally one or more vapor chamber center columns  40 . Each of the vapor chamber base  20 , vapor chamber sidewalls  30  and vapor chamber center columns  40  is a hollow-centered structure that comprises a vapor chamber space enclosed by surrounding walls. In one embodiment, the vapor chamber base  20 , the sidewalls  30  and the center columns  40  are operatively connected to each other to form a continuous vapor chamber space. 
         [0019]    The base  20  contains a bottom surface  22  that is in thermal contact with a heat source, and a top surface  24  on which the sidewalls  30  and/or center columns  40  are formed. The base  20  is made of a material having a high thermal conductivity, such as a metal or alloy. In one embodiment, the base  20  is made of copper or aluminum. The base  20  is filled or partially filled with an evaporable working fluid, such as water. 
         [0020]    The sidewalls  30  are formed only on selected sides of the base  20  so as to maintain an unobstructed airflow between the sidewalk  30 . In the embodiment shown in  FIG. 2A , two sidewalk  30  are formed on the opposite sides of the base  20 . It should be noted that the sidewalk  30  do not need to be formed on the edges of the base  20 . As shown in  FIG. 2B , the two sidewalls  30  are formed at locations near the edges of the base  20 . 
         [0021]    The center column  40  is formed between the sidewalls  30  to further facilitate heat dissipation from the base  20 . In one embodiment, the center column  40  is in the form of a free-standing column that serves as a heat pipe, Multiple free-standing center columns  40  may be used to facilitate heat transfer from the base  20  to fins  60 . In another embodiment, the center column  40  is in the form of a center will that is parallel to the sidewalls  30  and extends from one side of the base  20  to the other side of the base  20 . Multiple center walls may be formed between the sidewalk  30  to facilitate heat transfer from the base  20  to fins  60 . A person skilled in the art would also understand that efficient heat dissipation may be achieved with the sidewalls  30  alone, the center columns  40  alone, or a combination of the sidewalk  30  and the center columns  40 . The sidewalls  30  and center columns  40  are made of a material having a high thermal conductivity, such as a metal or alloy. In one embodiment, the sidewalk  30  and center columns  40  made of copper or aluminum. 
         [0022]    In one embodiment, the vapor chamber base  20 , sidewalls  30  and center columns  40  are filled with a porous material  50 . The porous material  50  has a porosity that allows vapor transport from the base  20 , where evaporation takes place, to sidewalk  30  and center columns  40 , where condensation of the vapor takes place. The capillary forces created by the porous material also facilitate the return of condensed working fluid to the base  20 . Examples of the porous material  50  include, but are not limited to, sintered powder wick which can be attached to the vapor chamber base  20 , sidewalls  30  and/or center columns  40  by solder. 
         [0023]    The sintered powder may be selected from any of the materials having high thermal conductivity and that are suitable for fabrication into porous structures, e.g., carbon, tungsten, copper, aluminum, magnesium, nickel, gold, silver, aluminum oxide, beryllium oxide, or the like, and may comprise either substantially spherical, arbitrary or regular polygonal, or filament-shaped particles of varying cross-sectional shape. In one embodiment, the porous material  50  comprises sintered copper wick. Other wick materials, such as aluminum-silicon-carbide or copper-silicon-carbide may be used with equal effect. 
         [0024]    The sidewalls  30  and/or center columns  40  thriller comprise a plurality of stacked fins  60  for efficient heat dissipation. The fins  60  are attached in horizontal arrangement to the sidewalls  30  and center columns  40 . Each fin  60  has a planar-shaped main body having a top surface  62  and a bottom surface  64  opposite to the top surface  62 . The top surface  62  of one fin and the bottom surface  64  of the neighboring fin are parallel to each other. The distance (d) between the two neighboring fins  60  may be determined experimentally to allow for efficient cooling of the fins  60  by airflow. In one embodiment, the distance (d) is in the range of 0.5-5 mm. The fins  60  are typically made of a material having high thermal conductivity, such as a metal or an alloy. In one embodiment, the fins  60  are made of aluminum. 
         [0025]    The heat sink  10  may be used to cool a heat-generating device which may be an electronic component such as, but not limited to, an integrated circuit, as memory module, Micro-Electro-Mechanical System (MEMS), a sensor, a resister, or a capacitor. The heat sink  10  may be positioned directly on the electronic component, or on a thermal solution including, but not limited to, a heat pipe, a heat spreader, a heater block, and a thermal transfer plate. A fan may be complementarily positioned to accelerate airflow between fins  60  and increase the rate of heat dissipation. The exact complementary positioning is application dependent, and may be affected by a number of factors, including but not limited to, the amount of heat to be removed, the volume and velocity of the airflow, and so forth. The optimal complementary positioning for a particular application of flow provider and flow modifier may be determined empirically. 
         [0026]    During operation, the base  20  of the heat sink  10  absorbs heat generated by the heat-generating device. The working fluid that is contained in the inner side of the base  20  absorbs the heat and evaporates substantially and moves to the sidewalls  30  and/or center columns  40 . Evaporated working fluid is cooled and condensed in the sidewalls  30  and center columns  40 . The heat is released through fins  60 . Finally, the condensed working fluid flows back to the base  20  to begin another cycle. In this way, the working fluid can absorb/release amounts of heat. The heat generated by the heat-generating electronic device is thus transferred from the base  20  to the fins  60  almost immediately. 
       EXAMPLES 
     Example 1  
     CFD Analysis of Heat Sink with Free-Standing Center Column Configuration 
       [0027]      FIGS. 3-5B  show results of a CFD analysis of a heat sink with free-standing center column configuration. As shown in  FIG. 3 , the heat sink device contains six free-standing center columns  40  that are attached to the vapor chamber base  20 . The free-standing center columns  40  serve as heat pipes to transfer heat from the base  20  to fins  60 . Heat dissipation was achieved by eighteen aluminum plate fins  60  attached to the center columns  40 . In this embodiment, the fins have a thickness of 0.5 mm, a surface area of 80×85 mm, and a fin-to-fin gap of 1.1 mm.  FIGS. 4A-4C  show heat distribution on the center columns  40  ( FIG. 4A ) and fins  60  ( FIG. 4B ) and the base plate  20  ( FIG. 4C ).  FIGS. 5A and 5B  show the airflow generated by fins  60 . 
       Example 2 
       [0028]    CFD Analysis of Heat Sink with Wall-Like Center Column Configuration 
         [0029]      FIGS. 6A-8B  show results of a CFD analysis of a heat sink with wall-like center column configuration. As shown in  FIGS. 6A-6C , the heat sink device contains a base vapor chamber, two sidewalls and a wall-like center column. The sidewalls  30  and the center column  40  are operatively connected to base  20  and form a continuous vapor chamber space. Heat dissipation was achieved by eighteen aluminum plate fins attached to the center columns. The fins have a thickness of 0.5 mm, a surface area of 80×85 mm, and a fin-to-fin gap of 1.1 mm.  FIGS. 7A-7B  show heat distribution on the base plate  20  ( FIG. 7A ) and fins  60  ( FIG. 7B ).  FIGS. 8A and 8B  show the airflow generated by fins  60 . 
         [0030]    Under the same heat generation and air flow rate settings, the heat sink with wall-like center column configuration was able to achieve a 11° C. improvement over the heat sink with five-standing center column configuration, i.e., having a source temperature of 45° C. ( FIG. 7B ) vs. 56° C. ( FIG. 4C ). 
         [0031]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to accommodate various modifications and equivalent arrangements. It will be appreciated by those of ordinary skill in the art that a wide variety of alternate and/or equivalent embodiments or implementations calculated to achieve the same purposes may be substituted for the embodiments shown and described. This application is intended to cover any adaptations or variations of the embodiments discussed herein. Therefore, it is manifestly intended that embodiments in accordance with the present invention be limited only by the claims and the equivalents thereof.