Abstract:
An apparatus includes an integrated circuit (IC) package and a heat sink having a base and a plurality of fins extending from the base. The apparatus further includes a plurality of heat pipes. Each heat pipe has a first end and a second end. The first ends of the heat pipes are thermally coupled to the IC package, and the second ends of the heat pipes are thermally coupled to the base of the heat sink to transfer heat from the IC package to the heat sink

Description:
BACKGROUND  
       [0001]     As the technology of integrated circuits (ICs) and particularly microprocessors has advanced, there has been a tendency for the devices to dissipate increased power. Thus cooling requirements for ICs have increased. In a typical desktop personal computer, a fan is provided in the computer housing to blow air at a heat sink that is thermally coupled directly on the microprocessor package. One disadvantage of such a system is the acoustic noise that may be produced by the fan. Although fan noise may be acceptable in an office environment, or in a home office, fan noise from the computer housing may prove to be an impediment to proposals to introduce so-called “entertainment PCs” intended for the home theater, living room, family room, etc. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0002]      FIG. 1  is a somewhat schematic, partial isometric view of a computer system provided according to some embodiments.  
         [0003]      FIG. 2  is a somewhat schematic, partial plan view of the computer system of  FIG. 1 .  
         [0004]      FIG. 3  is a somewhat schematic, partial side view of the computer system of  FIGS. 1 and 2 .  
         [0005]      FIG. 4  is a block diagram that represents a fan control system that is part of the computer system of  FIGS. 1-3 .  
         [0006]      FIG. 5  is a flow chart that illustrates operation of a control circuit that is part of the fan control system of  FIG. 4 . 
     
    
     DETAILED DESCRIPTION  
       [0007]      FIG. 1  is a somewhat schematic, partial isometric view of a computer system  100  provided according to some embodiments.  FIG. 2  is a somewhat schematic, partial plan view of the computer system  100 , and  FIG. 3  is a somewhat schematic, partial side view of the computer system  100 .  
         [0008]     The computer system  100  includes a housing which is generally indicated in phantom (reference numeral  102 ) in  FIG. 2 , but which for the most part is not otherwise shown in the drawings. The computer system  100  also includes a motherboard  104  that is mounted inside the housing  102 .  
         [0009]     In addition, the computer system  100  includes a microprocessor package  106  which is mounted on the motherboard  104  and thus is contained within the housing  102 . It will be appreciated that the microprocessor package  106  is a particular type of IC package, i.e., an IC package that includes a microprocessor die (not separately shown).  
         [0010]     The computer system  100  further includes a cooling system  108  for dissipating heat generated by operation of the microprocessor. The cooling system  108  includes a heat sink  110 . The heat sink  110  is mounted as part of the housing  102  (see  FIG. 2 ). In some embodiments the heat sink may be formed as a unitary body such as an extruded copper or aluminum body. The heat sink  110  includes a base  112  and a plurality of fins  114  that extend perpendicularly (and thus parallel to each other) from the base  112 . The base  112  of the heat sink  110  may be substantially in the form of a rectangular prism. The fins  114  may be rectangular in profile and may taper so as to be reduced in thickness away from base  112 . The fins  114  extend exteriorly ( FIG. 2 ) from the housing  102  and thus are in the ambient air outside of the housing. The heat sink  110 , and particularly its base  112 , also has a surface  116  ( FIG. 1 ), which may be referred to as an “inner surface” in that the surface  116  of the heat sink  110  effectively forms part of the inner surface of the housing  102  and thus is at the interior of the housing  102 .  
         [0011]     The heat sink  110  may be dimensioned so that it is rather large and thus can dissipate a large amount of heat. For example, in some embodiments the base  112  of the heat sink  110  may have a length of about 15 inches, a height of 3.5 to 4 inches and a thickness of about 1.5 inches. The fins  114  may have the same height as the base  112 , i.e., 3.5 to 4 inches, and may extend out from the base  112  to a length of about 1.5 inches. The fins  114  may have a thickness at the base  112  of about 100 thousands of an inch and may taper to a thickness of about 50 thousands of an inch near their tips. Each fin  114  may be spaced at a center-to-center distance of about one inch from its neighboring fins. The fins  114  may be formed at regular intervals all along the length of the base  112 .  
         [0012]     In other embodiments, the heat sink  110  may have a different shape and/or different dimensions from those just described.  
         [0013]     The cooling system  108  also includes a number of heat pipes  118 . In the particular embodiment illustrated there are four heat pipes  118 , though the number may be more or fewer than four. Each heat pipe  118  has a proximal end  120  ( FIGS. 1 and 2 ) that is thermally coupled to the microprocessor package  106 . Each heat pipe  118  also has a distal end  122  that is thermally coupled to the surface  116  of the base  112  of the heat sink  110 .  
         [0014]     In some embodiments, the distal ends  122  of the heat pipes  118  may be thermally coupled to the surface  116  of the base  112  of the heat sink  110  by thermal grease which is not shown. The distal ends  122  of the heat pipes  118  may be mechanically secured to the surface  116  of the base  112  of the heat sink  110  by straps, which are not shown. In other embodiments, the distal ends  122  of the heat pipes  118  may be soldered to the surface  116  of the base  112  of the heat sink  110 . In some embodiments, some of the distal ends  122  may run along the surface  116  of the base  112  of the heat sink  110  from a central portion  124  ( FIG. 1 ) of the base  112  to an end  126  of the base  112 , while other of the distal ends  122  may run along the surface  116  from the central portion of the base  112  to the other end  128  of the base  112 .  
         [0015]     The courses of the heat pipes  118  may be generally parallel between the microprocessor package  106  and the heat sink  110 .  
         [0016]     The heat pipes  118  may be generally conventional in terms of their internal construction. In some embodiments the heat pipes  118  may be hollow but fully enclosed copper tubes partially filled with a fluid such as water. A suitable diameter for the heat pipes may be 6 millimeters, although other diameters such as 4 or 8 millimeters may be used. The heat pipes  118  may also include a wicking structure (not shown) inside the tubes to wick condensed fluid from the cool end (distal end) of the heat pipes to the hot end (proximal end) of the heat pipes. For example, the wicking structure may be formed of sintered metal, copper strands held against the inside wall of the heat pipe by a spiral spring or the like, a metal screen and/or grooves in the inside wall of the heat pipe.  
         [0017]     The cooling system  108  also includes a number of fins  130  mounted along the parallel courses of the heat pipes  118 . Each fin may be a square or otherwise rectangular metal (e.g., copper or aluminum) plate. Each fin  130  may be rather thin (e.g., with a thickness of 0.4 mm or 0.2 mm). The fins  130  may be oriented so as to be substantially parallel to each other and may be mounted at regular intervals such as every 1 to 2 mm on the heat pipes  118  along the parallel course of the heat pipes  118 . The fins  130  may be rather numerous, e.g., numbering in the dozens, and may be oriented transversely relative to the lengths of the heat pipes  118 . The fins  130  may largely fill the space between the microprocessor package  106  and the heat sink  110 .  
         [0018]     The cooling system  108  also includes one or more fans  132  (e.g., two fans as shown in the drawings). The fans may be positioned side-by-side relative to each other, and may be positioned so as to selectively (i.e., when actuated) blow air between the fins  130 .  
         [0019]     Certain other components of the computer system  100  will now be identified. For example, the computer system  100  also includes memory cards  134  mounted on the motherboard  104 . Also included in the computer system  100  and mounted on the motherboard  104  is a riser card  136 . Mounted to the motherboard  104  via the riser card  136  are PCI Express add-in cards  138 .  
         [0020]     The computer system  100  includes a memory controller hub (MCH) chipset, which is not visible in the drawings. However, a heat sink  140  for the MCH chipset is visible and is shown mounted on the motherboard  104 . In addition, the computer system  100  includes data connectors shown at  142  to allow data to be transferred to/from the motherboard  104 . The computer system  100  also may include low-profile PCI add-in cards  144  mounted on the motherboard  104 .  
         [0021]     The computer system  100  may include other components which either are not shown in the drawings or are not named above. Except for the cooling system  108  and a control system for the cooling system to be described below, the computer system  100  may be, in some embodiments, entirely conventional in its design and in its constituent components and in its operation.  
         [0022]      FIG. 4  is a block diagram that represents a fan control system  150  that is part of the computer system  100 . The fan control system  150  may also be considered to be part of the cooling system  108 . Except for the fans  132 , components of the fan control system  150  are not separately shown in  FIGS. 1-3 .  
         [0023]     Referring to  FIG. 4 , the fan control system  150  may include one or more temperature sensors  152 . For example, a thermal diode (not separately shown) may be included on-die as part of the microprocessor that is housed in the microprocessor package  106  ( FIG. 1 ). In addition, or alternatively, another temperature sensor or sensors may be mounted on the microprocessor package  106 , or on the motherboard  104  or elsewhere within the housing  102  of the computer system  100 .  
         [0024]     The fan control system  150  may also include a control circuit  154 . For example, the control circuit  154  may be constituted by a controller IC (not separately shown) that may be mounted on the motherboard  104 . The control circuit  154  may be coupled to the temperature sensor  152  to receive an output signal from the temperature sensor  152 . A fan drive circuit  156 , in turn, may be coupled to the control circuit  154 , and may be controlled by the control circuit  154  to selectively provide a drive signal to the fans  132  to selectively actuate the fans  132 .  
         [0025]     Operation of the cooling system  108  will now be described, in part by reference to  FIG. 5 , which is a flow chart that represents a process performed by the control circuit  154 .  
         [0026]     At  160  in  FIG. 5 , a determination is made (based at least in part, e.g., on the output of the temperature sensor  152 ) as to whether the temperature of the microprocessor package  106  (and/or the temperature of another component of the computer system  106 ) is sufficiently low that active cooling by driving the fans  132  is not required. If a positive determination is made at  160  (i.e., if it is determined that the temperature is low enough to operate only with passive cooling), then the fans  132  are not driven, as is indicated at  162  in  FIG. 5 . As a result, the microprocessor package is cooled only by passive cooling.  
         [0027]     During passive cooling, heat is generated in the microprocessor package  106  and causes heating of the fluid in the proximal ends  120  of the heat pipes  118 . The heating of the fluid may cause the fluid to undergo a phase change from a liquid state to a vapor. This phase change may serve to absorb a relatively large amount of the heat generated in the microprocessor package  106 . The fluid in its vapor state may travel through the heat pipes  118  to the distal ends  122  of the heat pipes  118 . The distal ends  122  of the heat pipes  118  are thermally coupled to the heat sink  110  and may be relatively cool. The fluid may condense from its vapor state to a liquid state at the distal ends  122  of the heat pipes  118 , thereby releasing heat to the heat sink  110 . This heat, in turn, may be radiated outside of the housing  102  by the fins  114  of the heat sink  110 . The condensed fluid may be wicked back from the distal ends  122  of the heat pipes  118  to the proximal ends  120  of the heat pipes by the above-mentioned wicking structures (not separately shown) within the heat pipes.  
         [0028]     In addition to heat transport from the microprocessor package  106  to the heat sink  110  by phase changes in the heat pipe fluid, other heat transport mechanisms may occur in the heat pipes  118 , including conduction of heat by metal structures (e.g., the outer tubes) of the heat pipes  118 .  
         [0029]     Referring again to decision block  160 , if a negative determination is made at that decision (i.e., if it is found that passive cooling alone was not sufficient to keep the microprocessor package temperature below a certain threshold temperature), then the control circuit  154  and the fan drive circuit  156  operate (as indicated at  164  in  FIG. 5 ) to drive (actuate) the fans  132  to blow air between the fins  130  mounted along the parallel courses of the heat pipes  118  between the microprocessor package  106  and the heat sink  110 . This may increase the amount of heat dissipated by fins  130 , thereby increasing the amount of cooling provided via the heat pipes  118  to the microprocessor package  106 . Moreover, in some embodiments, the fans  132  may be operable at variable speeds, and the control circuit  154  and the fan drive circuit  156  may operate to increase the fan speeds at higher microprocessor package temperatures above the minimum temperature which requires operation of the fans, and to operate the fans at relatively low speeds when the microprocessor package temperature is not much above the minimum temperature which requires operation of the fans. Thus the control circuit  154  may operate to adjust the fan speed according to the temperature of the microprocessor package, as indicated at  166 . That is, the speed of rotation of the fans may be varied in dependence on an output received by the control circuit  154  from the temperature sensor  152 .  
         [0030]     It may be the case that a degree of passive cooling via transport of heat from the microprocessor package  106  to the heat sink  110  via the heat pipes  118  continues during operation of the fans  132 . In addition, essentially passive cooling by radiation of heat from the fins  130  on the heat pipes  118  may occur when the fans  132  are not operating.  
         [0031]     In any case, with the provision of the large heat sink  110 , with fins extending outside of the system housing  102 , and thermally coupled to the microprocessor package  106  via the heat pipes  118 , it may be possible to minimize the time of operation and/or the speed of operation of the fans  132 , thereby minimizing the amount of acoustic noise generated during operation of the computer system  100 . Consequently, the computer system  100  may be quiet enough to serve satisfactorily as a so-called “entertainment PC”.  
         [0032]     In some embodiments there may be provided more or fewer than the two fans shown. For example, in some embodiments only one fan may be provided. In other embodiments, the fans may be eliminated entirely, and cooling of the microprocessor package  106  may be entirely passive. In some embodiments, the fins  130  may also be dispensed with.  
         [0033]     In some embodiments, during manufacture of the cooling system  108 , the fins  130  may be strung along the heat pipes  118  and the heat pipes may be bent thereafter to provide the bent shapes of the heat pipes shown in  FIG. 1 . In other embodiments, the heat pipes may be formed as a composite of two heat pipes spliced at their ends to form, e.g., side-by-side splices.  
         [0034]     The several embodiments described herein are solely for the purpose of illustration. The various features described herein need not all be used together, and any one or more of those features may be incorporated in a single embodiment. Therefore, persons skilled in the art will recognize from this description that other embodiments may be practiced with various modifications and alterations.