BACKGROUND 
     Field of the Invention 
     The present invention relates to a heat sink to remove heat from a heat-generating electronic component used in a computer. 
     Background of the Related Art 
     Computer systems require removal of heat from heat-generating electronic components such as processors. Heat-generating electronic components are often coupled to a generally planar circuit board having a series of electronic connectors along an edge of the circuit board to facilitate electronic engagement between the circuit board and a motherboard. Electrical current and data are routed to and from the heat-generating electronic component through the motherboard and the electronic connectors of the circuit board. Heat generated by the electronic component may be transferred by conduction to a heat sink having a plurality of fins coupled to the heat sink to dissipate heat to air flowing through a computer chassis housing the circuit board. One or more air movers, such as fans, may be used to move air through the computer chassis so that the air will flow across the fins to enhance dissipation of heat from the heat sink. Air movers are fixed relative to the computer chassis to draw air into one end of the chassis, across components disposed within the chassis and then through the air movers to exit the chassis. 
     Electronic components are generally coupled to a circuit board in an arrangement that saves space and promotes compactness of the computer. Furthermore, an expansion card may be disposed horizontally or vertically with respect to the motherboard within a chassis as needed to utilize available space given the form factor of the chassis. Similarly, an electronic component, such as a processor, may be disposed on the expansion card in an orientation that provides the most efficient layout of the components on the expansion card. A heat sink may be disposed on the electronic component to conduct heat generated by the electronic component through the heat sink to a plurality of air-cooled fins to remove heat from the electronic component by dissipation to surrounding air flow. For computers relying upon air flow to enhance heat dissipation from the fins, the fins on the heat sink must be favorably oriented with respect to the air flow through the chassis in order to optimize the operating temperature of the electronic component. 
     BRIEF SUMMARY 
     One embodiment of the present invention provides a heat sink comprising a first thermally conductive base having a first face securable to a heat-generating device and a second face opposite the first face, a second thermally conductive base having a first face with a plurality of fins and a second face selectively engaging the second face of the first base, a biasing member to bias the second face of the first base to engage the second face of the second base in a first orientation and in a second orientation that is about 90 degrees out of phase with the first orientation, and an alignment member extending from at least one of the first and second bases to prevent relative rotation between the first and second bases from the first orientation or the second orientation, wherein the second base is movable relative to the first base from the first orientation to the second orientation by overcoming the biasing member to remove the second face of the second base from engagement with the second face of the first base, rotating the second base relative to the first base 90 degrees from the first orientation to the second orientation, and releasing the heat sink to allow the biasing member to re-engage the second face of the second base with the second face of the first base. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1A  is a diagram of an expansion card having a heat sink disposed in a first orientation within a computer chassis. 
         FIG. 1B  is a diagram of the expansion card of  FIG. 1  having a second heat sink disposed in a second orientation within the computer chassis. 
         FIGS. 2A-2D  are a series of perspective views of a heat sink, in accordance with one embodiment of the present invention, having a second base being repositioned from a first orientation to a second orientation. 
         FIG. 3  is a plan view of a second face of a first thermally conductive base having a first portion of a spring clip thereon. 
         FIG. 4  is a plan view of a second face of a second thermally conductive base to engage the first base of  FIG. 3 , the second face of the second base having a second portion of the spring clip thereon. 
         FIG. 5  is a cross-sectional side view of the second base of  FIG. 4 . 
         FIG. 6  is elevation side view of the first portion of a spring clip of  FIG. 3 . 
         FIG. 7A-7C  are side views of the first portion of the spring clip of the first base of  FIG. 3  as it releasably engages the second portion of the spring clip of the second base of  FIG. 4 . 
         FIG. 8  is a plan view of an alternate embodiment of a first thermally conductive base of the heat sink of the present invention having a key. 
         FIG. 9  is a plan view of an alternative embodiment of a second thermally conductive base having a second portion of a spring clip comprising a bulbous member and illustrating positions at which the key of  FIG. 8  may be disposed. 
         FIG. 10  is a cross-sectional side view of the embodiment of the first base of  FIG. 8 . 
         FIG. 11  is a plan view of an alternative embodiment of a first thermally conductive base of the heat sink of the present invention having a key positioned within the periphery of the first base. 
         FIG. 12  is a plan view of an alternative embodiment of a second thermally conductive base of the heat sink of the present invention having two recesses positioned to selectively receive the key on the first base of  FIG. 11 . 
         FIG. 13  is a cross-sectional side view of the embodiment of the second base of  FIG. 12 . 
     
    
    
     DETAILED DESCRIPTION 
     One embodiment of the present invention provides a heat sink comprising a first thermally conductive base having a first face for conductively engaging a heat-generating electronic component and a second face. The heat sink further comprises a second thermally conductive base having a first face, supporting a plurality of fins, and a second face to conductively engage the second face of the first base to form a heat transfer interface across which heat generated by the heat-generating electronic component can be transferred for dissipation by the fins. The second base of the heat sink engages the first base of the heat sink in a plurality of permissible fin orientations to facilitate the alignment of the fins on the second base with a direction of cooling air movement through a computer chassis to maximize the dissipation of heat from the heat-generating electronic component. This structure permits the heat sink to be used on a heat-generating electronic component on a circuit board disposed within a computer chassis in either of two different orientations, and it prevents the need for stocking multiple heat sinks having different fin orientations. 
     In one embodiment of the heat sink of the present invention, a spring clip releasably engages the first base of the heat sink with the second base of the heat sink in two or more permitted fin orientations relative to the first base. A first portion of the spring clip is disposed on the first base and a second portion of the spring clip is disposed on the second base in a manner that determines the orientations in which the second base will releasably engage the first base. In a first permissible orientation, the second base, which has the heat sink fins, is 90 degrees out of phase a second permissible orientation of the second base. Having the first and second permissible orientations enables the heat sink to be easily adjusted for use where the heat-generating electronic component is aligned with the air flow through the computer chassis or where the air flow is transverse with the air flow through the computer chassis. Optionally, the spring clip may be designed to prevent releasable engagement of the second base with the first base in any orientation other than predetermined orientations. 
     For example, but not by limitation, the first portion of the spring clip on the first base may comprise, in one embodiment, a pair of opposed spring members having an interior therebetween, and the second portion of the spring clip provided on the second base may comprise an insertion member sized to be received within the interior of the first portion of the spring clip by elastic separation of the spring members of the first portion during insertion of the insertion member of the second portion. The first portion of the spring clip on the first base may comprise guide portions to facilitate centering and insertion of the insertion member on the second base, and/or the insertion member on the second portion of the spring clip may comprise tapered edges to facilitate elastic spreading of the spring members of the first portion during insertion of the insertion member into the first portion. The insertion member may have a cross-section that is generally round or a polygon, such as a square. Advantageously, an insertion member with a square cross-section may be used to limit the second base to the first and second orientations relative to the first base. 
     In an alternative embodiment of the spring clip, the second portion of the spring clip may comprise a first pair of generally parallel shaft portions and a second pair of generally parallel shaft portions disposed within an aperture in the second base. The first pair of shaft portions may be in an orientation generally perpendicular to the first pair of shaft portions to define the orientations in which the second base is able to releasably engage the first base. The first pair or the second pair of shaft portions of the second portion of the spring clip on the second base are spaced to elastically displace the spring members of the first portion of the spring clip on the first base during engagement of the second base with the first base in the first or the second permissible fin orientation, respectively, and the spring clip prevents engagement of the second base with the first base in fin orientations that do not provide for alignment of either the first or second pair of shaft portions of the second portion of the spring clip with the spring members of the first portion of the spring clip. 
     In an alternate embodiment, at least one of the first and second bases comprises a key that prevents relative rotation between the first and second bases while the bases are engaged. Accordingly, the orientation between the first and second bases can only occur when the first and second bases have been disengaged and separated by overcoming the biasing force of the biasing member. Preferably, the key will only permit engagement of the first base with the second base in predetermined orientations of the second base with the first base, and the key obstructs engagement of the first base with the second base in orientations other than the permitted fin orientations. For example, a key on the second face of the first base may protrude beyond the plane of the second face of the first base and in the direction away from the first face to prevent engagement of the first base with the second base in orientations other than a first fin orientation and a second fin orientation, which may be, for example, 90 degrees out of phase with the first fin orientation. The key may be formed along the periphery of the second face of the first base, and the key may thereby protrude beyond and adjacent to the second face of the second base where the second base is in a first fin orientation or in a second fin orientation. The key may be positioned on the first base to engage the second face of the second base and thereby prevent the second face of the second base from engaging the second face of the first base in all orientations therebetween other than the first fin orientation and the second fin orientation. 
     In an alternate embodiment, a key may be formed within the periphery of the second face of the first base to be received in a one of two or more notches or recesses within the second face of the second base. The first notch or recess may receive the key in a first permitted fin orientation, and the second notch or recess may receive the key in a second permitted fin orientation. Alternately, the key may be formed within the periphery of the second face of the first base to be received within one of two or more bays or channels in the periphery of the second face of the second base. The first bay or channel may receive the key in the first permitted fin orientation and the second bay or channel may receive the key in the second permitted fin orientation. The key may be formed within the periphery of the second face of the first base to engage the second face of the second base at a location outside any notch, recess, channel or bay to thereby prevent the second face of the second base from conductively engaging the second face of the first base in orientations therebetween other than those corresponding to the first fin orientation or the second fin orientation which may be 90 degrees out of phase with the first fin orientation. 
     In another alternate embodiment, the first base may comprise two keys and the second base may comprise three or more notches, recesses, channels or bays to permit both of the keys to be received into notches, recesses, channels or bays in either of a first fin orientation and a second fin orientation that is 90 degrees out of phase with the first fin orientation. In fin orientations other than the permitted first and second fin orientations, the two keys will engage the second face of the second base to prevent the second face of the second base from conductively engaging the second face of the first base. 
     In another embodiment of the heat sink of the present invention, the heat sink comprises a spring clip having a first portion on the first base, where the first portion has a pair of opposed spring members defining an interior, and a second portion on the second base, where the second portion comprises a rounded member sized to be received within an interior of the first portion. The rounded member of the second portion of the spring clip facilitates the elastic displacement of the spring members one from the other as the second base is forced into conductive engagement with the first base to releasably engage the first and second portions of the spring clip. The rounded member permits rotation of the second base relative to the first base from a first fin orientation to a second fin orientation. 
     An alignment structure may impair full engagement between the second face of the second base and the second face of the first base in orientations therebetween other than a first orientation and a second orientation 90 degrees out of phase with the first orientation. In one embodiment of the heat sink, a key may be disposed on one of the first base and the second base to be received in a receiving element, such as a notch, recess, channel or bay, disposed on the other of the first base and the second base to determine the permitted fin orientations. 
       FIG. 1A  is a diagram of an expansion card  11  connected by connectors  17  in a first orientation within a computer chassis  10 . The expansion card  11  has a first heat sink  13  in thermal communication with a heat generating device  12  (disposed under the heat sink), such as a processor, on the circuit board  11  to transfer heat from the heat generating device  12  to a plurality of air-cooled fins  18  on the first heat sink  13 . In order to achieve efficient heat transfer, the fins  18  are aligned with the direction of air flow  15  through the computer chassis  10 . The heat sink  13  is secured in face-to-face thermally conductive engagement with the heat generating device to facilitate the transfer of heat from the heat generating device  12  to the first heat sink  13  for dissipation into air flow  15  around the fins  18 . The air flow  15  through the computer chassis  10  is provided by air movers  14 , such as fans that draw cooling air flow through the computer chassis  10 . Rack or computer room air conditioner (CRAC) air movers may also be used to provide the air flow. 
       FIG. 1B  is a schematic illustrating a circuit board  11  connected by connectors  17  in a second orientation within the computer chassis  10  and having a second heat sink  19  in conductive engagement with the heat generating device  12  to transfer heat generated by the device  12  to the plurality of fins  18  aligned with the direction of air flow  15  through the computer chassis  10 . The air flow  15  is again provided by a plurality of air movers  14 . Similar to the arrangement of  FIG. 1A , the second heat sink  19  is secured to the heat generating device  12  to dispose a face (not shown) on the heat generating device  12  to facilitate the transfer of heat generated by the device  12  through the second heat sink  19  for dissipation to air flow  15  through the fins  18 . The connectors  17  on the circuit board  11  in  FIG. 2  are generally transverse to the direction of the air flow  15 , and are about 90 degrees out of phase with the position of the connectors  17  on the circuit board  11  in  FIG. 1A , those being generally aligned with the direction of air flow  15 . The orientation of the first heat sink  13  of  FIG. 1A  would not effectively dissipate heat generated by the device  12  and conductively transferred to the fins  18  in the second orientation illustrated in  FIG. 2  because the fins  18  of the first heat sink  13  would not be aligned with the direction of the air flow  15  through the computer chassis  14 . It is necessary, therefore, to stock two different models of a heat sink, a first heat sink  13  having fins  18  in a first orientation for circuit boards connected in the orientation of the circuit board  11  in  FIG. 1A  and a second heat sink  19  having fins  18  for circuit boards connected in the orientation of the circuit board  11  in  FIG. 1B . 
       FIGS. 2A-2D  are a series of perspective views of a heat sink, in accordance with one embodiment of the present invention, having a second base being repositioned from a first orientation to a second orientation. In  FIG. 2A , the first base  30  is shown in face-to-face engagement with the second base  20 , which has fins  18  extending therefrom. As shown, the second base  20  has a key  70  received within a first notch  72  on the first base  30 , which also has a second notch  74  on an adjacent side. Accordingly, the heat sink fins  18  are aligned with the airflow (shown generally from left to right on the page). 
     In  FIG. 2B , the expansion card, on which the heat sink  13  is installed, has been installed in a computer chassis such that the air flow (shown generally from right to left on the page) is generally perpendicular to the heat sink fins  18 . Since this will not produce good heat transfer, the second base  20  and heat sink fins  18  should be reoriented. Specifically,  FIG. 2B  shows the second base  20  having been disengaged and separated from the first base  30 , such that the key  70  is no longer secured in the first notch  72 . Although the biasing member is not shown, it is necessary to overcome the biasing force to get the second base  20  into this separated position. 
     In  FIG. 2C , the second base  20  is rotated 90 degrees about a central axis  76  while the second base  20  is still in the separated position. At this orientation, the heat sink fins  18  are now in alignment with the air flow. 
     In  FIG. 2D , the second base  20  is allowed to re-engage the first base  30 . Accordingly, the heat sink  13  is again in an operative condition, but is now in a second orientation ( FIG. 2D ) as compared with the first orientation ( FIG. 2A ). As shown, the key  70  is now received in the second notch  74  to prevent accidental rotation of the second base  20  relative to the first base  30 . 
       FIG. 3  is a plan view of the first thermally conductive base  30  having a first face (not shown) to thermally engage a heat generating device, such as a processor (not shown), a second face  32  to engage a second thermally conductive base, and a first portion  33  of a spring clip having a pair of opposed spring members  52 ,  53  to releasably engage a second portion of the spring clip to secure the second base to the first base  30  to bias a face of the second base against the face  32  of the first base  30 . The first portion  33  of the spring clip is illustrated in  FIG. 3  as being disposed generally central to the second face  32 , but may be located at other positions. The second face  32  of the first base  30  is illustrated in  FIG. 3  as being square, but may have other shapes. Also note the presence of the notches  72 ,  74  that serve as alignment features. 
       FIG. 4  is an elevation view of the second thermally conductive base  20  having a first face (not shown) to support a plurality of air-cooled fins (not shown), a second face  22  to engage the first base, and a second portion  24  of the spring clip. The second portion  24  comprises an aperture  21  containing a first pair of parallel shaft portions  61 ,  62  and a second pair of parallel shaft portions  26 ,  28  therein. The shaft portions  61 ,  62  of the first pair are spaced apart within the aperture  21  to facilitate releasable engagement between the second portion  24  of the spring clip and the first portion of the spring clip on the first base. The shaft portion  61  is adjacent to spring member passage  63  and the opposed shaft portion  62  is adjacent to spring member passage  64 . Similarly, the second pair of parallel shaft portions  26 ,  28  are spaced apart within the aperture  21  to facilitate releasable engagement between the second portion  24  of the spring clip and the first portion of the spring clip. The shaft portion  26  is adjacent to spring member passage  25  and opposed shaft portion  28  is adjacent to spring member passage  27 . Also note the presence of the key  70  that serves as an alignment feature, as discussed in relation to  FIGS. 2A-2D . 
       FIG. 5  is a cross-sectional side view of the second base  20  of  FIG. 4  to illustrate the position of a fin  18  on the first face  23  of the second base  20 . It will be understood that additional, parallel fins are hidden by the single fin  18  shown in  FIG. 5 . The cross-sectional view of  FIG. 5  is taken through the spring member passage  27  of the second base  20  at the second portion  24  of the spring clip. The shaft portions  61 ,  62  are positioned within the aperture  21  in parallel positions generally above and below the second pair of shaft portions  26 ,  28  (shaft portion  26  not shown in  FIG. 5 ). 
       FIG. 6  is an elevation view of the first portion  33  of the spring clip of  FIG. 3  to bias the second face of the second base against the second face of the first base to conductively engage the fins on the second base with the heat-generating device. Spring members  52 ,  53  comprise angled guides  54 ,  55  which cooperate to guide the first pair of shaft portions or the second pair of shaft portions of the second portion of the spring clip on the second base to the interior  37  of the first portion  33  of the spring clip on the first base to releasably engage the first base  30  with the second base. A foot  36  of the first portion  33  of the spring clip is connected to the first base  30  and recessed therein below second face  32 . 
       FIGS. 7A-7C  are elevation views of the first portion  33  of the spring clip during releasable engagement of the first base  30  with the second portion  24  of the spring clip on the second base  20  to engage the fins  29  on the second base  20  in conductive engagement with the heat-generating device (not shown). 
       FIG. 7A  illustrates initial engagement between the first portion  33  and the second portion  24  as the second pair of shaft portions  26 ,  28  engage the angled guides  54 ,  55  on spring members  52 ,  53 , respectively. The application of a downward force on the second portion  24  will elastically displace the spring members  52 ,  53  to pivot in the direction of arrows  56 ,  57 , respectively. The spring members  52 ,  53  spread apart to receive the shaft portions  26 ,  28  to the intermediate position illustrated in  FIG. 7B . The second face  22  of the second base  20  is illustrated in  FIG. 7A  as spaced apart from the second face  32  of the first base  30 . 
       FIG. 7B  illustrates the second pair of shaft portions  26 ,  28  of the second portion  24  of the spring clip disposed in an intermediate position generally between the elastically displaced spring members  52 ,  53  and above and adjacent to the interior  37  of the first portion  33  of the spring clip. The second face  22  of the second base  20  is illustrated as adjacent to, but still spaced apart from, the second face  32  of the first base  30 . Spring members  52 ,  53  are biased to return to the original positions illustrated in  FIG. 7A  by movement in the direction of arrows  58 ,  59 . 
       FIG. 7C  illustrates the made-up spring clip  51  comprising the second pair of shaft portions  26 ,  28  disposed within the interior  37  of the first portion  33  of the spring clip and between the spring members  52 ,  53  that are restored towards their original positions to capture the shaft portions  26 ,  28  within the interior  37  of the first portion  33  of the spring clip. A residual restoring force within the spring members  52 ,  53  acting on the shaft portions  26 ,  28  serves to bias the second face  22  of the second thermally conductive base  20  against the second face  32  of the first thermally conductive base  30 . A thermally conductive material  50  may be disposed intermediate the second face  22  of the second base  20  and the second face  32  of the first base  30  to enhance thermal communication between the second base  20  and the first base  30 . The thermally conductive material  50  may be, for example, a thermal grease. 
       FIG. 8  is a plan view of an alternate embodiment of a first base  30  of the heat sink of the present invention having a key  41  to limit the orientations in which a second base may conductively engage the first base  30 . In other words, the key  41  prevents rotation between the first and second bases while the first and second bases are engaged. The key  41  is disposed on a tab  40  that protrudes laterally from the side of the first base  30  and the key  41  extends beyond the second surface  32  of the first base  30  towards the viewer of  FIG. 8 . 
       FIG. 9  is a plan view of an alternative embodiment of a second base  20  of the heat sink of the present invention having a second surface  22  and a second portion  24  of a spring clip comprising a rounded member  49 .  FIG. 9  illustrates positions  42 ,  43 ,  44 ,  45  at which the key of  FIG. 8  may be disposed in orientations in which the second face  22  of the second base  20  may conductively engage the second face of the first base of  FIG. 8  without the key preventing conductive engagement between the second base  20  and the first base  8 . It should be noted that the first portion  33  of the spring clip in  FIG. 8  and the second portion  24  of the spring clip are axially centered on the first and second bases  30 ,  20 , respectively, such that the square first and second bases will have full face-to-face engagement in either the first orientation or the second orientation. 
       FIG. 10  is a cross-sectional side view of the first base  30  of  FIG. 8 . The key  41  is disposed on the tab  40  extending from the first base  30  and extends beyond the second surface  32  of the first base  30 . The key  41  is disposed in a position to be received in positions indicated on  FIG. 9  to permit the second portion  24  of the spring clip on the second base to releasably engage the first portion  33  of the spring clip of the first base  30 , and to permit the second face of the second base to conductively engage the second face  32  of the first base  30 . The first portion  33  of the spring clip on the first base  30  will receive the rounded member of the second portion of  FIG. 9  in four orientations in which the key  41  on the first base  30  will be received in the positions indicated on  FIG. 9 . 
       FIG. 11  is a plan view of an alternative embodiment of a first base  30  of the heat sink of the present invention having a key  47  positioned within the periphery of the first base  30  to engage a receiving structure disposed on a second base (not shown). 
       FIG. 12  is a plan view of an alternative embodiment of a second base  20  of the heat sink of the present invention having two recesses  76 ,  77  positioned to selectively receive the key on the first base of  FIG. 11  to orient the fins (not shown) supported on a first face (not shown) of the second base. The key  47  (of  FIG. 11 ) may be received into a first recess  76  in a first fin orientation and the key  47  may be received into recess  77  in a second fin orientation that is 90 degrees out of phase with the first fin orientation. 
     A heat sink comprising the second base  20  of  FIG. 12  and the first base  30  of  FIG. 11  may be converted from a first fin orientation to a second fin orientation without complete detachment of the first base from the second base. For example, the recess  77  may initially receive the key  47  of the first base  30  of  FIG. 11  to conductively engage the second face  32  of the first base  30  of  FIG. 11  with the second face  22  of the second base  20  of  FIG. 12  and to dispose the fins (not shown) on the first face of the second base  20  in a first fin orientation. Subsequently, the second face  22  of the second base  12  may be separated from the second face  32  of the first base  20  enough to withdraw the key  47  from the recess  77  without fully detaching the first portion  33  of the spring clip on the first base  30  from the second portion  24  of the spring clip on the second base  20 . While the second base  30  separated apart from the first base  20 , the second base may be rotated 90 degrees in the direction of arrow  48  to align the key  47  on the first base  30  with the recess  76  on the second base  20 . The second face  22  of the second base  20  can then conductively re-engage the second face  32  of the first base  30  to dispose the fins (not shown) on the first face of the second base  20  in a second fin orientation 90 degrees out of phase with the first fin orientation. 
       FIG. 13  is a side section view of the second base  20  of  FIG. 12  illustrating the recess  46  disposed in the second base  20  to receive the key  47  of the first base to orient the fins in the first fin orientation. 
     It will be understood that while the embodiments illustrated in  FIGS. 3-13  may illustrate one or more keys disposed on the first base  30  and one or more notches, recesses, channels or bays disposed on the second base  20  to limit the orientations in which the first base may conductively engage the second base and thereby orient the fins on the second base, it is within the scope of the invention to provide one or more keys on the second base to engage one or more notches, recesses, channels or bays on the first base. Similarly, while, in certain embodiments, a first portion  33  of a spring clip is disposed on a first base  30  and a second portion  24  of a spring clip is disposed on a second base  20  to limit the orientations in which the first base  30  may conductively engage the second base and thereby orient the fins on the second base  20 , it is within the scope of the invention to provide a first portion of a spring clip on the second base to releasably engage a second portion of a spring clip on a first base with equal function. The present invention includes these variations and is limited only by the claims that follow. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, components and/or groups, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The terms “preferably,” “preferred,” “prefer,” “optionally,” “may,” and similar terms are used to indicate that an item, condition or step being referred to is an optional (not required) feature of the invention. 
     The corresponding structures, materials, acts, and equivalents of all means or steps plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but it is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.
A heat sink comprises a first thermally conductive base having a first face to thermally engage a heat-generating electronic component and a second thermally conductive base with a plurality of fins on a first face and a second face to engage the first base. The fins on the second base are positionable in either of two orientations relative to the heat-generating electronic component to which the heat sink is coupled. The fins are selectively placed in the orientation that best utilizes the direction of air flow available to the heat sink. The orientable fins of the heat sink afford flexibility in arranging the heat-generating electronic component on a circuit board or in arranging a circuit board within a computer chassis.