Patent Publication Number: US-2023156971-A1

Title: Heat sink assembly for electronic equipment

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. application Ser. No. 16/993,885, filed Aug. 14, 2020, the entirety of which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to high performance and/or high density computing solutions, such as line cards and computing blades, that can receive field replaceable computing modules, and in particular to a heat sink assembly for these computing solutions. 
     BACKGROUND 
     Over the past several years, the information technology field has seen a tremendous increase in the performance of electronic equipment coupled with a decrease in geometric floor space to house the equipment. For instance, due at least to recent advances in high throughput computing, field replaceable computing modules, such as optical transceivers, are dissipating more power (e.g., 25 Watts (W) or more) in smaller form factors (i.e., computing modules are being provided with increasingly higher power densities). However, permissible operating temperatures, which may be defined by temperature limits of internal components included in the field replaceable computing modules, have remained relatively stagnant. Moreover, as computing solutions become denser, less space is available for cooling solutions. Thus, cooling solutions for field replaceable computing modules that can provide improved cooling in smaller form factors are continuously desired. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1 A  is a schematic diagram illustrating a sectional view of an example embodiment of a heat sink assembly formed in accordance with the present application. 
         FIG.  1 B  is a diagram illustrating heat transfer between a field replaceable computing module and conventional heat sinks. 
         FIG.  2 A  illustrates a front perspective view of an example embodiment of a computing solution that includes an example embodiment of the heat sink assembly presented herein. 
         FIG.  2 B  illustrates a field replaceable computing module included in the computing solution of  FIG.  2 A . 
         FIG.  3 A  illustrates a front perspective view of a computing apparatus of the computing solution of  FIG.  2 A  with its top cover removed to show the heat sink assembly included therein. 
         FIG.  3 B  illustrates a front perspective view of a module cage included in the computing apparatus of  FIG.  3 A , according to an example embodiment. 
         FIG.  3 C  illustrates a bottom perspective view of an example embodiment of a heat sink that may be included in the heat sink assembly of  FIG.  3 A , according to an example embodiment. 
         FIG.  4    illustrates a top, front perspective view of the heat sink assembly and module cage included in the computing apparatus of  FIG.  3 A . 
         FIG.  5    illustrates an exploded view of the heat sink assembly included in the computing apparatus of  FIG.  3 A . 
         FIG.  6    is a diagram that schematically illustrates circuitry that may be included in the heat sink assembly of  FIG.  3 A , according to an example embodiment. 
         FIG.  7    is a side view of a shape memory alloy (SMA) element that may be included in the heat sink assembly of  FIG.  3 A , according to an example embodiment. 
         FIG.  8    illustrates a front perspective view of a portion of an exterior of the computing apparatus of  FIG.  3 A , according to an example embodiment. 
         FIG.  9    is a flow chart depicting a method for operating components of an example embodiment of a heat sink assembly of the present application. 
         FIG.  10 A  illustrates a side, sectional view of another example embodiment of a heat sink assembly, the heat sink assembly being in a lowered position. 
         FIG.  10 B  illustrates a side, sectional view of the heat sink assembly of  FIG.  10 A  while in a raised position, according to an example embodiment. 
         FIGS.  11 A and  11 B  illustrate perspective views of a heat sink and a field replaceable computing module, respectively, with which the heat sink assembly presented herein may be utilized, according to another example embodiment. 
         FIG.  12    illustrates a side, sectional view of another example embodiment of the heat sink assembly presented herein. 
         FIG.  13    illustrates a top perspective view of still another example embodiment of the heat sink assembly presented herein 
         FIGS.  14 A and  14 B  illustrate side, sectional views of yet another example embodiment of a heat sink assembly that may be included in the computing solution of  FIG.  2   , the heat sink assembly being illustrated in a lowered position in  FIG.  14 A  and a raised position in  FIG.  14 B . 
         FIGS.  15 A and  15 B  are side views of a shape memory alloy (SMA) element that may be included in the heat sink assembly of  FIGS.  14 A and  14 B , according to an example embodiment. 
         FIGS.  16  and  17    illustrate front perspective views of example embodiments of computing solutions and computing modules with which the heat sink assembly presented herein may be utilized. 
         FIG.  18    is a diagram illustrating thermal advantages provided by the heat sink assembly presented herein. 
     
    
    
     Like reference numerals have been used to identify like elements throughout this disclosure. 
     DESCRIPTION OF EXAMPLE EMBODIMENTS 
     Overview 
     A heat sink assembly for a cage for a field replaceable computing module, an apparatus including the cage, and a system including the apparatus and the field replaceable computing module are presented herein. In one embodiment, a heat sink assembly for a cage for a field replaceable computing module includes a heat sink, a thermal interface material, and an actuation assembly. The heat sink facilitates heat dissipation and includes a mating surface. The thermal interface material includes a first surface that is coupled to the mating surface of the heat sink and a second surface that is opposite the first surface. Thus, the second surface can engage a heat transfer surface of a field replaceable computing module installed adjacent to the heat sink. The actuation assembly includes a shape memory alloy (SMA) element. When the SMA element is in a first position, the second surface of the thermal interface material contacts the heat transfer surface of the field replaceable computing module, and when the SMA element is moved to a second position, the second surface of the thermal interface material is moved a distance away from the heat transfer surface of the field replaceable computing module. 
     Example Embodiments 
     The heat sink assembly presented herein enables high performance and/or high density computing solutions, such as line cards and computing blades, to effectively dissipate heat from field replaceable computing modules without inhibiting insertion or removal of the field replaceable computing modules (also referred to herein as “modules,” “pluggable modules,” “swappable modules,” and the like), such as during online insertion and removal (“OIR”) operations. Specifically, the heat sink assembly presented provides a movable or “floating” heat sink and an actuation assembly that can move the floating heat sink towards and/or away from a module cage included in a computing solution. 
     Notably, the heat sink assembly presented herein may be primarily actuated via an electrical actuation. Thus, the actuator may occupy a minimal amount of space on a front panel of a computing solution, which may be beneficial, if not required, for computing solutions with dense front panel layouts. In fact, in some instances, the heat sink assembly presented herein may be actuated via a purely electrical actuation (i.e., only an electrical actuation). In these instances, the heat sink assembly need not include a physical/mechanical actuator. That is, in at least some instances, the heat sink assembly may eliminate any need for a physical/mechanical actuator. Regardless, the heat sink assembly presented herein can also lock a heat sink in a raised position or a lowered position, which may simplify insertion and removal of a module. This locking may also allow that the heat sink assembly presented herein to compress a heat sink and a thermal interface material (“TIM”) included thereon against a module. 
     Moreover, in at least some embodiments, the actuation assembly moves the entire heat sink away from the module cage (and/or a module installed therein), thereby reducing, if not eliminating, the risk of a module scraping against the heat sink assembly during insertion or removal operations. In fact, the actuation assembly may move the heat sink so that the mating surface of the heat sink (e.g., a bottom surface) remains parallel to a heat transfer surface of a module (e.g., a top surface). Consequently, during insertion or removal of the module, the entire mating surface of the heat sink (e.g., the bottom surface) will be equally spaced apart from the heat transfer surface of the module (e.g., the top surface) by a gap and the module will not rub or slide against the mating surface of the heat sink. This gap, in turn, allows a TIM, which would be damaged by sliding or rubbing, to be included on the mating surface. The TIM increases thermal conductivity between the heat sink and a module and, thus, improves cooling for the module. Additionally, parallel motion of the heat sink with respect to the module cage may provide a substantially consistent gap between the heatsink and the module, which may allow the gap required for module removal to be minimized. 
     Additionally or alternatively, the actuation assembly may move the heat sink along one degree of freedom (e.g., vertically). Moving the heat sink along one degree of freedom (e.g., vertically) may ensure that the heat sink does not need to be positioned adjacent open space, which is necessary when a heat sink moves in a lateral or depth direction (e.g., a front-to-back direction). Instead, the surface area of the heat sink size may be maximized to span a perimeter of a module and/or module cage and the cage need not be positioned with open space surrounding its peripheral boundaries. That is, moving the heat sink along one degree of freedom may maximize a thermal contact area. Furthermore, moving the heat sink along one degree of freedom may allow the heat sink to generate compression forces on a TIM (e.g., if the one degree of freedom is linear, vertical movement) that are often necessary to maximize TIM performance with the assembly that moves the heat sink. This may reduce the number of components in the assembly, reducing costs of manufacture and servicing. The TIM also tends to reduce, if not eliminate, the effects of minor dimensional differences between different pluggable modules. 
     In order to describe the heat sink assembly, computing apparatus, and computing system presented herein, terms such as “left,” “right,” “top,” “bottom,” “front,” “rear,” “side,” “height,” “length,” “width,” “upper,” “lower,” “interior,” “exterior,” “inner,” “outer,” “depth,” and the like as may be used. However, it is to be understood that these terms merely describe points of reference and do not limit the embodiments to any particular orientation or configuration. For example, the terms “height,” “width,” and “depth” may be used to describe certain embodiments presented herein, but it is to be understood that these terms are not intended to limit the present application to specific implementations. Instead, in at least some embodiments, the heat sink assembly presented herein may be oriented horizontally (as shown) or vertically (i.e., a housing of a computing solution may be rotated 90 degrees about an axis extending through a front and back of the housing), or in any other manner during use (e.g., when installed into a blade chassis/enclosure). Consequently, even if a certain dimension is described herein as a “width,” it may be understood that this dimension may provide a height or depth when a computing solution in which it is included is moved to different orientations. 
     Now turning to  FIG.  1 A , this Figure schematically illustrates an example embodiment of a computing solution  10  that includes an example embodiment of the heat sink assembly  30  presented herein (for simplicity, at least some components of the heat sink assembly  30  are not shown in  FIG.  1 A ). The computing solution  10  may also be referred to as a computing system; however, it is to be understood that the term “system,” when used herein, does not imply that the solution/system  10  is a stand-alone system. Instead, a solution/system  10  may be a stand-alone system or a portion/subsystem of a larger system (e.g., solution  10  may be a blade of a server). That said, in  FIG.  1 A , the computing solution  10  includes an apparatus  12  and a removable computing module  20 . The apparatus  12  includes a housing  14  that houses a PCB  16  and a module cage  18  (e.g., an optical cage). Additionally, the housing  14  houses a heat sink assembly  30  with a heat sink  31  and a thermal interface material (TIM)  35 . The TIM  35  is included on a bottom or mating surface of the heat sink  31  and, as is depicted, during insertion or removal of the computing module  20  into the module cage  18 , the heat sink assembly  30  moves the heat sink  31  and TIM  35  away from the module cage  18  to provide a gap “G” between the computing module  20  and the TIM  35 . 
     In the depicted embodiment, the heat sink assembly  30  moves the heat sink  31  and the TIM  35  upwards. More specifically, the heat sink assembly  30  moves the entire heat sink  31  and entire TIM  35  upwards, away from the module cage  18 . In at least some embodiments, the heat sink assembly  30  moves the heat sink  31  and TIM  35  while keeping the TIM  35  parallel to a top of the module cage  18 . Alternatively, the heat sink  31  and TIM  35  might be moved upwards in any manner, but are moved into a raised position that is parallel to a top of the module cage  18 . Still further, in some embodiments, the TIM  35  is not parallel to the top of the module cage  18  when in a raised position, but is spaced apart from the top of the module cage  18  across its surface area (e.g., so that the gap G spans the whole TIM  35 ). Regardless of how the heat sink  31  and TIM  35  are moved to a raised position (and regardless of how the TIM  35  is oriented in its raised position), the gap G allows the computing module  20  to be inserted into or removed from module cage  18  without contacting and damaging TIM  35 . If, instead, only a portion of the TIM  35  was moved away from the module cage  18  (e.g., if the heat sink assembly  30  was tipped about a lateral axis, which would extend into the plane of the drawing sheet on which  FIG.  1 A  is included), the computing module  20  might contact and damage the TIM  35  (e.g., by scraping a portion of the TIM  35  off of the heat sink assembly  30 ). 
     Alternatively, and now turning to  FIG.  1 B , if the heat sink assembly  30  does not include a TIM  35 , a metal surface of a heat sink  31  included in the heat sink assembly  30  might not form an effective thermal connection with the computing module  20 . For example, since metal surfaces (e.g., a bottom of a heat sink and/or top of a module) can have surface irregularities, such as flatness irregularities, waviness irregularities, roughness irregularities, etc., air gaps may form between the metal surfaces of a heat sink  31  and a computing module  20 . In  FIG.  1 B , the left image illustrates air gaps AG 1  that form between metal surfaces with surface flatness irregularities while the right image illustrates air gaps AG 2  that form between metal surfaces with surface roughness irregularities. Notably, many riding heat sinks, which are often biased into contact with a module via spring clips that press the heat sink against a module during insertion or removal, provide inefficient heat transfer away from computing modules  20  due to air gap issues. These issues cannot be remedied by a TIM  35 , because the TIM would be scraped off or otherwise damaged as a heat sink “rides” on a sliding module. Regardless of how air gaps form between the module  20  and the heat sink assembly  30 , air gaps are detrimental to heat transfer because the low thermal conductivity of air provides significant contact resistance. A TIM can reduce or eliminate these air gaps and significantly reduce contact resistance, especially if the TIM is compressed to a specific compression to maximize heat transfer (which may differ for different materials). 
       FIG.  2 A  illustrates a top perspective view of a computing apparatus  12  and a replaceable computing module  20  that may be installed within the apparatus  12  to form a computing solution  10 . As is shown, the computing apparatus  12  includes a front surface or panel  100  with an opening  101  that provides access to the module cage  18  defined therein. In the depicted embodiment, the module cage  18  extends in a depth direction (e.g., front-to-back) within the housing  14  of the apparatus  12 . That is, the module cage  18  extends from the front panel  100  towards a back end  102  of the housing  14 . Additionally, in the depicted embodiment, the module cage  18  is arranged to be substantially flat within the housing  14 , such that the module cage  18  is parallel to a cover  104  that defines a top of the housing  14 . 
     Meanwhile, and now referring to  FIG.  2 A  in combination with  FIG.  2 B , the module  20  includes a top surface  22 , a back surface  24  with a connector  25 , a bottom surface  26 , and a front surface  28 . As is discussed in further detail below, in the depicted embodiment, the top surface  22  of the computing module  20  is a heat transfer surface for the computing module  20 . However, in other embodiments, any surface of the computing module  20  could serve as a heat transfer surface. During insertion of the computing module  20  into the module cage  18 , the perimeter of back surface  24  is aligned with the module cage  18  and then the computing module  20  is pushed into the module cage  18  to connect the connector  25  on the back surface  24  with a connector  124  included in the module cage  18  (see  FIG.  3 B ). During removal of the computing module  20  from the module cage  18 , the front surface  28  may be grasped, e.g., by handle  29 , and pulled out of the module cage  18 . However, handle  29  is merely representative of a feature that enables a user to easily grasp the front surface  28  and, in other embodiments, the module  20  could include any other features instead of or in addition to handle  29 . Alternatively, the computing module  20  can be ejected or removed from the module cage  18  in any manner now known or developed hereafter (including mechanical ejections). Before or after the computing module  20  is installed in the module cage  18 , the housing  14  may be installed into another computing solution (e.g., a rack) and secured thereto with installation member  112  (see  FIGS.  2 A and  3 A ). 
     In  FIG.  2 A  (as well as many other Figures), the computing solution  10  is a line card; however, it is to be understood that a line card is simply one example of a computing solution in which the heat sink assembly presented herein may be included. For example, the computing solution  10  could also be a rack server, a storage drawer, a stand-alone computing solution, or any other computing solution that accepts modular computing components (e.g., “field replaceable computing modules”). Likewise, in  FIGS.  2 A and  2 B  (as well as many other Figures), the module  20  is an optical transceiver, but it is to be understood that an optical transceiver is simply one example of a module with which the heat sink assembly presented herein may be used. That said, it may be beneficial to utilize the heat sink presented herein with optical transceivers because technical advancements in optical transceivers have generated high power dissipation (e.g., 25 W or more) in a small form factor (e.g., C form-factor pluggable 2 (“CFP2”) form factor, which has dimensions of 41.5 millimeters (“mm”)×12.4 mm×107.5 mm (w×h×d)). These characteristics make it difficult to satisfy Network Equipment-Building System (NEBS) thermal standards for these modules. 
     Now turning to  FIGS.  3 A,  3 B, and  3 C , these Figures illustrate portions of the apparatus  12  in further detail. In  FIG.  3 A , the apparatus  12  is shown with its top cover  104  removed. With the top cover  104  removed, the heat sink assembly  30  can be seen disposed above the module cage  18 . Meanwhile,  FIG.  3 B  illustrates the module cage  18  removed from the housing  14  and  FIG.  3 C  illustrates a heat sink  31  of heat sink assembly  30  removed from the apparatus  12 . As can be seen in  FIG.  3 B , the module cage  18  extends from an open front end  120  to a back end  122 . The back end  122  includes a connector  124  that may connect a computing module  20  to an apparatus  12  in which the module cage  18  is included (e.g., via PCB  16 ). That is, the connector  124  may be configured to provide a Small Computer System Interface (SCSI) connection, Serial Attached SCSI (SAS) connection, an advanced technology attachment (ATA) connection, a Serial ATA (SATA) connection, and/or or any other type of connection for field replaceable computing modules. 
     Additionally, the module cage  18  extends from a first side  126  to a second side  128  and includes an open top  130 . Collectively, the open front end  120 , the back end  122 , the first side  126 , the second side  128 , and the open top  130  define an internal chamber  132 . That is, the open front end  120 , the back end  122 , the first side  126 , the second side  128 , and the open top  130  define a perimeter or periphery of chamber  132  (with sides  126  and  128  defining a lateral periphery while front end  120  and back end  122  defining a longitudinal periphery). The chamber  132  is sized to house/receive computing module  20  and the open top  130  allows the heat sink assembly  30  to access and engage the top surface  22  (i.e., the heat transfer surface) of a computing module  20  installed within a chamber  132 . 
     In different embodiments, the open top  130  may provide access to the chamber  132  in any desirable manner, such as via one or more windows, cut-outs, segments, etc. However, in the depicted embodiment, the open top  130  spans the entire surface area of the chamber  132 , extending a length L 1  from the open front end  120  to the back end  122  (e.g., in a front-to-back or depth dimension) and a width W 1  from the first side  126  to the second side  128  (e.g., in a lateral or width dimension). Thus, the depicted embodiment may maximize the area within which heat may transfer from the computing module  20  to the heat sink assembly  30 . 
     In  FIG.  3 C , the heat sink  31  is shown from a bottom perspective view, which illustrates the TIM  35  that is included on a mating surface  133  of the heat sink  31 . The TIM  35  includes a first surface  135  and a second surface  136 . The second surface  136  is fixedly coupled to the mating surface  133  of the heat sink  31  (e.g., via adhesive, ultrasonic welding, etc.) and the first surface  135  is disposed opposite the second surface  136 . Thus, the first surface  135  faces the open top  130  of the module cage  18  when the heat sink  31  is installed above the module cage  18 . In at least some embodiments, the first surface  135  may include or be coated with a protective film that prevents the first surface  135  from sticking to a module  20 . In the depicted embodiment, the first surface  135  and second surface  136  converge towards both a front  144  and a back  146  (see  FIG.  5   ) of the heat sink  31  so that the second surface  135  includes convergent sections  137  and a flat section  138 . However, in other embodiments, the first surface  135  and the second surface  136  need not converge and, for example, may be parallel to each other across the dimensions of the TIM  35 . 
     Regardless of the shape of the TIM  35 , the mating surface  133  of the heat sink  31  may have dimensions L 2  (e.g., a front-to-back dimension) and W 2  (e.g., a width) that are at least as large as the corresponding top dimensions (L 1  and W 1 , respectively) of the chamber  132  (defined by the open top  130 ) and a heat receiving portion of the TIM  35  (e.g., the flat section  138 ) may span or cover a majority of the mating surface  133 . More specifically, the TIM  35  may span (e.g., cover) at least a depth or front-to-back dimension L 1  of the open top  130  (which defines a depth of a top of the chamber  132 ). Additionally or alternatively, the TIM  35  may span a lateral dimension L 2  of the open top  130  (which defines a lateral dimension of a top of the chamber  132 ). For example, the flat section  138  of the TIM  35  may have a lateral dimension W 3  (e.g., width W 3 ) that is equal to or greater than W 1  and/or the flat section  138  of the TIM  35  may have a front-to-back dimension L 3  (e.g., depth L 3 ) that is equal to or greater than L 1 . Consequently, the flat section  138  of the TIM  35  may cover as much of the computing module  20  as possible and maximize heat transfer between a computing module  20  and the heat sink  31 . 
     Notably, with the heat sink assembly presented herein, the TIM  35  can span the entire surface area (e.g., L 1  by W 1 ) of the chamber  132  because, in at least some embodiments, the heat sink assembly  30  only moves the heat sink  31  vertically with respect to the module cage  18  (and a computing module  20  installed therein). If, instead, the heat sink  31  moved laterally or in a front-to-back direction, open space would need to be available to allow movement of heat sink  31 . In some instances, this issue might be addressed by moving the heat sink  31  outside the peripheral boundaries of the module cage  18  (e.g., laterally beyond side  126  or  128 ). However, such movement would increase the dimensional footprint of the heat sink assembly  30 , which is often undesirable, if not impossible, in high-density computing solutions. 
     Still referring to  FIG.  3 C , the mating surface  133  of the heat sink  31  forms a bottom of the heat sink  31  and fins  140  extend upwards therefrom. Specifically, the fins  140  and/or the mating surface  133  may include/define a base  142  and the fins  140  may extend from the base  142  to a top  143  of the heat sink  31 . In the depicted embodiment, the fins  140  cover a majority of the base  142  between a front  144  and a back  146  of the heat sink  31  to maximize cooling and each of the fins  140  extends in a side-to-side direction across the heat sink  31 . However, in other embodiments, the fins  140  may be arranged in any orientation or configuration. For example, the fin geometry, profile, and dimensions can be customized for different types of applications and airflow directions (e.g., front-to-back and/or side-to-side airflow). Still further, in yet other embodiments, heat sink  31  might be finless and may, for example, dissipate heat via heat pipes, fluid thermal management, or other mechanisms/arrangements that dissipate heat. 
     Now turning to  FIGS.  4  and  5   , the fins  140  may also define a number of openings, cavities, channels, mounting features, etc. to accommodate and secure portions of the heat sink assembly  30 , such as an actuation assembly  150  of the heat sink assembly  30 . In the depicted embodiment, the fins  140  define a passageway  152  that extends in a front-to-back direction through the heat sink  31  and also define three mounting points  154  spaced along top edges of the passageway  152  (i.e., at a top of sides of the passageway  152 ). The passageway  152  is an open-top passageway that is centered with respect to the fins  140 , but in other embodiments, the passageway  152  could be a through hole, a partially covered passageway, or any other opening/passageway/cavity. Additionally or alternatively, in other embodiments, the passageway  152  need not be centered with respect to the fins  140  and/or could be one of a plurality of passageways. Moreover, although not shown, in some embodiments the fins  140  may define additional channels configured to accommodate other features or elements, such as longitudinal channels for guide pins that extend fully or partially through the fins  140 . Still further, in some embodiments the fins  140  need not define any openings, cavities, channels, etc. For example, the actuation assembly  150  might extend along one or more sides of heat sink  31  (such an actuation assembly  150  might have a height that is low enough not to impair airflow through the heat sink  31 ). 
     Generally, and still referring to  FIGS.  4  and  5   , the heat sink  31  is positioned atop the cage  18 , but is not directly connected to the module cage  18 . Instead, the heat sink  31  is “floating” with respect to the module cage  18  and the actuation assembly  150  movably couples the heat sink  31  to the module cage  18 . That is, the actuation assembly  150  included in the heat sink assembly  30  presented herein is configured to lift and lower the heat sink  31 . In the embodiment of  FIGS.  2 A- 5   , the actuation assembly  150  includes a biasing member  160 , a shape memory alloy (SMA) element  172 , and closure brackets  180 . Additionally, in the depicted embodiment, the heat sink assembly  30  includes a support frame  190  that helps couple the actuation assembly  150  to the module cage  18 . 
     In the depicted embodiment, the biasing member  160  is connected the module cage  18  via connectors  166  and includes spring members  164  that are positioned above the base  142  of the heat sink  31 . Specifically, the spring members  164  engage corners  145  of a top surface of the base  142  of the fins  140 , which are left open by shortened fins  140  disposed at a front  144  and back  146  of the heat sink  31 . The spring members  164  are connected together by support members  162  and, since the biasing member  160  is anchored to (i.e., fixedly coupled to) the module cage via connectors  166 , the spring members  164  resist upwards movement of the heat sink  31 . Thus, the spring members  164  exert a restorative force on the heat sink  31  in response to upwards movement of the heat sink  31 . That is, due to the aforementioned features and connections, the biasing member  160  will consistently urge the heat sink  31  towards the module cage  18 . However, biasing member  160  is only one example of an element, structure, and/or feature that may return the SMA element  172  to a rest or engaged position on or adjacent to the module cage  18  and, in other embodiments, SMA element  172  may be returned to its rest or engaged position in any desirable manner. In fact, other example techniques or elements are discussed in further detail below. 
     Meanwhile, the SMA element  172  includes a proximal end  174 , a distal end  176 , and an elongate section  178  extending between the proximal end  174  and the distal end  176 . The elongate section  178  is positioned in the passageway  152  of the heat sink  31  and secured therein by closure brackets  180 . To be clear, in this embodiment, the closure brackets  180  are not coupled to the SMA element  172 ; instead, the closure brackets  180  close the passageway  152  to capture the elongate section  178  therein. By contrast, the proximal end  174  and the distal end  176  of the SMA element  172  are fixed or anchored with respect to the module cage  18 . Thus, elongate section  178  can flex or deform with respect to the proximal end  174  and the distal end  176  and act on (e.g., push) the closure brackets  180  and/or the heat sink  31  to move the heat sink  31  (which moves with the closure brackets  180 ) with respect to the module cage  18 . In at least some embodiments, the elongate section  178  may be coated or covered with insulation, such as with a hot shrink tube, over molding, or any other technique, so that electric current does not leak between the SMA element  172  and the heat sink  31  (and/or closure brackets  180 ). 
     In the depicted embodiment, the closure brackets  180  are secured to the mounting points  154  of the heat sink  31  with fasteners, but in other embodiments, the closure brackets  180  can be secured to the fins  140  in any manner (e.g., welding, soldering, etc.). Additionally, in the depicted embodiment, the proximal end  174  and the distal end  176  of the SMA element  172  are secured to the module cage  18  via support frame  190 , but in other embodiments the proximal end  174  and the distal end  176  of the SMA element  172  could be secured directly to the module cage  18  (e.g., the module cage  18  could include upwardly extending brackets that provide connection points). 
     That said, in the depicted embodiment, the support frame  190  includes a first frame portion  192  and a second frame portion  194  that are coupled together around the module cage  18 . Additionally, the first frame portion  192  and the second frame portion  194  can be coupled to the PCB  16  and/or the module cage  18 . Regardless, the first frame portion  192  includes or defines a first mounting portion  196  above the module cage  18  and the second frame portion  194  defines a second mounting portion  198  above the module cage  18 . Mounting portions  196  and  198  are or include insulated or non-conductive portions that can insulate SMA element  172  from the module cage  18  and/or the remainder of heat sink assembly  30 . Alternatively, the entire support frame  190  can be insulated or non-conductive. Either way, due to this insulation, current delivered to the SMA element  172  will not run into the heat sink  31 , the module cage  18 , and/or a module  20  installed in the module cage  18 . 
     Now referring to  FIGS.  4  and  6   , generally, SMA actuates (e.g., deforms and/or contracts) in response to heating. Consequently, the SMA element  172  is included in or connected to circuitry  200  that can provide current to the SMA element  172  and cause resistive heating of the SMA element  172 . For example, in  FIG.  4   , the proximal end  174  and the distal end  176  of SMA element  172  are coupled to positive and negative poles of a power source  202  via wires  204 A and  204 B (represented as wires  204  in  FIG.  6   ) to form a circuitry  200  including the SMA element  172 . The power source  202  can be a dedicated battery or any power source included in or connected to a computing solution in which the heat sink assembly  30  is installed.  FIG.  6    illustrates this circuity schematically in combination with additional electrical elements. 
     Specifically, in  FIG.  6   , the circuitry  200  includes a switch  206  that can be closed to deliver current to the SMA element  172 . The switch  206  may be a mechanical switch actuated by a mechanical/physical actuator (e.g., a push button actuator) and/or an electrical/digital switch that is actuatable by a processor. Either way, closing the switch  206  may deliver current to the SMA element  172  that effectuates resistive heating of the SMA element  172  to cause an actuation of the SMA element  172  (e.g., a contraction or deformation). Additionally, in some embodiment, the circuitry  200  may include an indicator  210 , such as a light, arranged in parallel with the SMA element  172 . With such an arrangement, closing the switch  206  actuates the SMA element  172  and the indicator  210 , for example, to provide an illuminated indication. However, this is just one example arrangement for an indicator and indicators could be arranged and operated in any manner now known or developed hereafter. For example, circuitry  200  could have any other configuration that allows indicator  210  to be activated in one or more colors. Additionally or alternatively, circuitry  200 , or portions thereof, could be duplicated, to provide two or more indications (e.g., raised and lowered). Circuitry  200  may also include a constant-current feature that helps enable protracted actuation of SMA element  172  without exceeding thermal limits for the SMA material. 
     Now turning to  FIG.  7   , this Figure illustrates an actuation of SMA element  172 . The initial or rest state or position P 1  of the SMA element  172  is shown in dashed lines and the actuated state or position P 2  is shown in solid lines. In this embodiment, SMA element  172  is a one-way SMA formed from any material that deforms when heated, including but not limited to copper-aluminum-nickel (Cu—Al—Ni), nickel-titanium (Ni—Ti), iron-manganese-silicon (Fe—Mn—Si), copper-zinc-aluminum (Cu—Zn—Al), and other alloys of zinc, copper, gold, and iron. Generally, the deformation behavior of a specific alloy can be modeled using hysteresis curves, which map material states of SMA as a function of temperature. Thus, specific alloy materials may be selected for SMA element  172  based on environmental characteristics of a computing solution in which the SMA element  172  is to be included and/or the current that will be delivered to the SMA element  172 . For example, the SMA element  172  may be designed to actuate at a temperature that is significantly higher than a temperature of heat sink  31  during cooling operations to prevent heating of the heat sink  31  from causing an actuation of the SMA element  172 . 
     Moreover, regardless of the specific composition of the SMA element  172 , the SMA element  172  can be trained with thermomechanical treatments now known or developed hereafter so that the SMA element  172  deforms to specific shape when heated to a specific temperature (e.g., with resistive heating). For example, the SMA element  172  may be trained to move vertically between positions P 1  and P 2 . Additionally or alternatively, the SMA element  172  may be trained to move along one degree of freedom (e.g., vertical, linear movement) and, thus, may restrict the heat sink assembly  30  to movement along one degree of freedom. Still further, the SMA element  172  can be trained to move in any direction and the heat sink assembly  30  might include additional features (e.g., guide pins) to control or restrict movement of the heat sink  31  (e.g., to one degree of freedom). 
     Still referring to  FIG.  7   , but now in combination with  FIGS.  3 A- 6   , regardless of how the SMA element  172  is trained or tuned, actuating the SMA element  172  presented herein may move the heat sink  31  vertically with respect to a module cage  18  (and, if installed, a computing module  20 ). For example, in the embodiment of  FIGS.  2 A- 7   , actuating the SMA element  172  may contract the SMA element  172  and cause the elongated section  178  to move upwards along vertical axis A 1 . Upwards movement of the elongated section  178  along vertical axis A 1  pushes the closure brackets  180  upwards (see  FIGS.  4  and  5   ) which may move the heat sink  31  upwards (along vertical axis A 1 ) with respect to the module cage  18  (since the closure brackets  180  are fixedly secured to the heat sink  31 ). More specifically, upwards movement of the elongated section  178  along vertical axis A 1  may move the heat sink  31  upwards a distance D 1  upwards along axis A 1 , creating a gap G (see  FIG.  1 A ) of, for example, 2-3 millimeters between the computing module  20  and the TIM  35 . Notably, the proximal end  174  and the distal end  176  of the SMA element  172  remain fixed or anchored during deformation of the SMA element  172  and, thus, the elongate section  178  can drive vertical movement of the heat sink  31 , which is essentially floating on the SMA element  172  (or at least on the elongate section  178  of the SMA element  172 ). 
     In the specific embodiment depicted in  FIGS.  3 A- 7   , the SMA element  172  is a one-way SMA and, thus, provides movement in one direction (when it&#39;s crystalline structure changes), but must be restored to its original or rest position (position P 1 ) before it can provide another actuation. Thus, the biasing member  160  works in combination with the circuitry  200  to control movement of the heat sink  31 . In particular, the circuitry  200  delivers a current to the SMA element  172  to cause a change to the crystalline structure of SMA element  172  that contracts the SMA element  172  to lift the heat sink  31  to its actuated position P 2  (e.g., to provide a gap Gas shown in  FIG.  1 A ). Then, since the biasing member  160  is constantly exerting a restorative force on the heat sink  31 , the biasing member  160  will return the SMA element  172  to its rest position P 1  when current is no longer to the SMA element  172 . This lowers the heat sink  31  into engagement with the module cage  18  and/or a module  20  installed within the module cage  18 . Thus, to maintain the heat sink  31  in a raised position, current must be continually delivered to the SMA element  172 . In fact, in at least some embodiment, the voltage is continuously adjusted (in any manner now known or developed hereafter) to maintain a constant current across the SMA element  172  when the heat sink  31  should be in a raised position (e.g., based on a user actuation and/or processor generated instructions). 
     Further, in at least some embodiments, the SMA element  172  may be trained, tuned, or controlled (e.g., controlled with current delivery) to provide non-constant vertical motion of the heat sink  31 . This may be advantageous, for example, to provide an initially rapid downward motion of the heat sink, followed by a more gradual “seating” of TIM  35  onto the module  20 . Alternatively, the tuning/training/controlling could provide a slow initial raising of the TIM  35  away from the module  20  to prevent the TIM  35  from being damaged when the TIM  35  is disconnected from the module  20 . Additionally or alternatively, the configuration shown in  FIGS.  3 A- 7    could be reversed and actuation of the SMA element  172  could compress the TIM  35  against a module  20 . In such embodiments, the SMA element  172  can be trained to provide a specific compression of the TIM  35  to maximize heat transfer (e.g., tuned for a specific TIM material), either in combination with or independent of additional components (e.g., spring clips) that create compression. Example embodiments including such an arrangement are discussed in further detail below. 
     Overall, when the SMA element  172  is in its actuated position P 2  (such that gap G is provided between the TIM  35  and the module cage  18 ), a computing module  20  can be installed or removed from the module cage  18 . In at least some embodiments, the gap G may be consistent across the surface area of the TIM  35  (e.g., an area defined by W 3  and L 3 ), such that the TIM  35  (or at least a portion thereof) is parallel to the module cage  18  and/or the computing module  20  (i.e., the heat sink assembly  30  may provide uniform lifting). In any case, after a computing module  20  is installed in module cage  18  (which may be detected, for example, in the manner discussed below in connection with  FIG.  9   ), the SMA element  172  may be moved to its rest position P 1  (e.g., by opening switch  206  or otherwise stopping the flow of current to SMA element  172 ), which may move the TIM  35  into engagement with a heat transfer surface of the computing module  20  (e.g., top surface  22 ). In fact, in some embodiments, moving the SMA element  172  to its rest position P 1  may compress the TIM  35  against the heat transfer surface of the computing module  20  (e.g., top surface  22 ), further encouraging heat transfer. 
     Now turning to  FIG.  8 - 15 B , these Figures depict additional embodiments of the heat sink assembly presented herein, or at least of portions thereof. In these Figures, components that are similar to components shown in  FIGS.  2 A- 7    are labeled with like reference numerals and, any description of like reference numerals included above should be understood to apply to like components included in  FIGS.  8 - 15 B . Thus, for brevity, the foregoing description focuses on differences between the embodiments. Additionally, if components of  FIGS.  2 A- 7    are not shown in embodiments depicted in  FIGS.  8 - 15 B , these embodiments may nevertheless be described with reference to components of  FIGS.  2 A- 7    to provide clarity and/or context. 
     That said,  FIGS.  8  and  9    depict a heat sink assembly  30  that can be actuated in response to a physical/mechanical actuator.  FIG.  8    illustrates an example actuator  220  that may be included on a front panel  100  of computing apparatus  12  in combination with example indicators  210 A and  210 B. Notably, since  FIG.  8    depicts two indicators  210 A and  210 B, the circuitry of this embodiment may be modified as compared to the circuitry  200  shown in  FIG.  6   .  FIG.  9    illustrates a method  250  of operating indicators  210 A and  210 B. As is described in detail below, indicators  210 A and  210 B may be operated based on actuations of actuator  220  and/or electrical actuations (e.g., based on commands generated by a processor). That is, with this arrangement, processing logic may control operations of indicator  210 A, indicator  210 B, and/or SMA element  172 , either in combination with actuations of actuator  220  or independent of actuations of actuator  220 . In fact, in some embodiments, the computing solution need not include an actuator and a processor  248  could execute instructions stored in memory  249  to control indicator  210 A, indicator  210 B, and/or SMA element  172  (or any other arrangement of indicators and SMA elements) with purely electrical operations. 
     In  FIG.  9   , method  250  illustrates operations that processor  248 , which may comprise any processor included in the computing solution of  FIG.  8    may execute to control indicator  210 A, indicator  210 B, and/or SMA element  172  (or any other arrangement of indicators and SMA elements). Generally, the processor  248  may comprise one or more processing cores and the memory  249  may comprise at least one non-transitory computer readable medium or memory for holding instructions programmed according to the embodiments presented, for containing data structures, tables, records, etc. Instructions stores in memory  249  may include software code scripts, etc. for controlling indicators and/or the SMA element  172 . In any case, initially, at  252 , the processor  248  determines if an unlock command has been received. In some instances, the unlock command can be the actuation of actuator  220 . Alternatively, an unlock command could be a command input or generated via a graphical user interface or other computing interface connected to processor  248 . In response to such a command, electrical circuitry of the SMA element  172  is enabled. That is, current is delivered to SMA element  172  (e.g., by power source  202 ). This actuates (e.g., deforms/contracts) the SMA element  172  and lifts the heat sink  31  in the manner described above. 
     Then, at  256 , the processor monitors the current and maintains a constant current across the SMA element  172  by adjusting the voltage, as was discussed above. During operations  254  and/or  256 , the processor  248  can activate indicator  210 B, for example, to provide a green light indication that the module cage  18  is “OPEN,” as is shown at  258 . Additionally or alternatively, as mentioned above, an actuation of actuator  220  might close a switch that activates indicator  210 B or allows processor  248  to activate indicator  210 B. 
     Once the module cage is “OPEN,” the processor  248  may, at  260 , monitor for presence of a module  20  in the module cage  18 . That is, once the heat sink  31  is in a raised position, the processor  248  may monitor for presence of a module  20  in the module cage  18  at  260 . For example, the module cage  18  may include an interrupt at or adjacent its back end  122  that provides a signal when a module  20  is fully installed in the module cage  18 . Additionally or alternatively, the processor  248  can monitor connector  124  to sense when the connector  25  of the module  20  has been fully inserted into the module cage  18  and connected with connector  124 . Still further, in some embodiments, a user might be able to actuate the actuator  220  a second time to indicate that a module  20  has been fully installed in the module cage  18 . Regardless, the processor  248  may ensure that the SMA element  172  stays activated (maintaining the heat sink  31  in a raised position) until the module  20  is detected as being installed in the module cage  18 . That is, the processor  248  may cause the power source  202  to continue delivering power to SMA element  172  (with continued instructions or by withholding a command to cut off power) until a module  20  is determined to be fully installed in module cage  18 . 
     When processor  248  determines that a module  20  is fully installed in the module cage  18 , the processor  248  may, at  262 , disable electrical circuitry of the SMA element  172 . That is, the processor  248  may disconnect power from the SMA element  172  to discontinue the delivery of current to SMA element  172  (e.g., by providing instructions to power source  202 ). This may deactivate the SMA element  172  and allow biasing member  160  to move the heat sink  31  into contact with the module  20  and/or the module cage  18 . Additionally, indicator  210 A can be activated (while indicator  210 B is deactivated), for example, to provide a red light indication that the module cage  18  is “LOCKED,” as is shown at  264 . The heat sink assembly  30  may then remain in a locked position until a new unlock command is received at  252 . 
     Next,  FIGS.  10 A and  10 B  illustrate another example embodiment of a heat sink assembly  30 ′ presented herein. Heat sink assembly  30 ′ is substantially similar to the heat sink assembly  30  shown in at least  FIG.  3 A . Thus, to reiterate, like reference numerals are used to denote similar parts and, for brevity, the foregoing description focuses on differences between the embodiments. Most notably, in this embodiment, the heat sink assembly  30 ′ does not include a support frame. Instead, the proximal end  174  of the SMA element is connected to the front panel  100  of the apparatus  12  and the distal end  176  is connected to a bracket  276  extending from the module cage  18 . Moreover, the SMA element  172  is not secured within the heat sink  31  by covers, such as closure brackets  180  and, instead, is directly connected to heat sink  31  via one or more insulated couplings  279 . Still further, heat sink assembly  30 ′ does not include a biasing member  160  in the form of a spring clip, but instead, includes compression springs  160 ′ that exert a constant restorative or biasing force BF (see  FIG.  10 B ) on the heat sink  31  and SMA element  172  (like biasing member  160 ). 
     Despite the differences between heat sink assembly  30  and heat sink assembly  30 ′, heat sink assembly  30 ′ still operates in a substantially similar manner to heat sink assembly  30 . That is, SMA element  172  is still a one-way SMA that contracts to an actuated position P 2  and lifts the heat sink along axis Al a distance D 1  to a raised position P 4  (see  FIG.  10 B ) in response to resistive heating. This creates a gap G that allows a module  20  to be inserted or removed from cage  20  without damaging TIM  35 . Then, when power to the SMA element  172  is turned off, the biasing force BF of compression springs  160 ′ returns the SMA element  172  to its rest position P 1  while lowering the heat sink  31  into a lowered position P 3  where it can compress TIM  35  against a module  20  (see  FIG.  10 A ). Additionally, like previously described embodiments, heat sink assembly  30 ′ includes an actuator  220  and indicator  210  that can actuate the heat sink assembly  30 ′ and provide indications of how the heat sink  31  is positioned, respectively. 
     Still referring to  FIGS.  10 A and  10 B , but now with reference to  FIGS.  11 A and  11 B  as well, in this embodiment, the heat sink assembly  30 ′ also includes a locking feature that can prevent insertion or removal of the module  20  when the heat sink assembly  30 ′ is in its lowered position P 3 . Specifically, in this embodiment, the heat sink assembly  30 ′ includes a protrusion  282  positioned forwardly of the TIM  35  on the mating surface  133  of the heat sink  31  (e.g., closer to the open front end  120  of the module cage  18 ), as is shown clearly in  FIG.  11 A . With this embodiment, and as is shown in  FIG.  11 B , the computing module  20  includes a corresponding receptacle  284  configured to mate with the protrusion  282  when the computing module  20  is fully installed into a module cage  18 . Thus, when the heat sink assembly  30 ′ moves the TIM  35  into engagement with the top surface  22  of the computing module  20 , the protrusion  282  will engage the receptacle  284  and resist movement in the front-to-back direction. Then, if the computing module  20  is pulled outwardly prior to the heat sink assembly  30  moving the TIM  35  out of engagement with the top surface  22  of the computing module  20 , the protrusion  282  and the receptacle  284  may resist this movement and prevent damage to the TIM  35  that can occur when the module  20  slides along the TIM  35 . This arrangement will also ensure that module  20  is not forcefully inserted or extracted which could cause an unintentional damage for the TIM  35  (insertion prevention is illustrated in  FIG.  10 A ). 
     Next,  FIGS.  12 ,  13 ,  14 A, and  14 B  illustrate yet further example embodiments of the heat sink assembly presented herein that can operate without a biasing member exerting a constant restorative force on the heat sink  31 . First,  FIG.  12    provides a heat sink assembly  30 ( 2 ) with a bi-stable toggle element  300  disposed between two one-way SMA elements: SMA element  172 A and SMA element  172 B. When current is delivered to one of SMA element  172 A and SMA element  172 B, that SMA element may deform (e.g., contract) and move the bi-stable toggle element  300  to a first position. Then, when current is delivered to the other of SMA element  172 A and SMA element  172 B, that SMA element may deform (e.g., contract) and move the bi-stable toggle element  300  to a second position. Alternatively, SMA element  172 A and SMA element  172 B may have different compositions and/or characteristics (e.g., different “training” or “tuning”) that cause the different SMA elements to respond (e.g., deform or actuate) to different magnitudes of currents (and, thus, might be actuated by precisely controlling the current delivered to both SMA elements). Regardless, with this arrangement, actuation of one of SMA element  172 A and SMA element  172 B drives the bi-stable toggle element  300  to a specific position and then the bi-stable toggle element  300  holds or locks the heat sink  31  in that position. Consequently, current need not be constantly delivered to SMA element  172 A or SMA element  172 B to hold (e.g., lock) the heat sink assembly  30 ( 2 ) in a specific position (e.g., a raised or lowered position). 
     More specifically, in the depicted embodiment, delivering current to SMA element  172 B may contract SMA element  172 B, pivoting a bottom end of pivot points  302  inwards and moving (e.g., snapping) the bi-stable toggle element  300  to position P 5  (shown in solid lines). Pivoting pivot points  302  will also stretch or elongate SMA element  172 A (i.e., return SMA element  172 A to its rest position) so that SMA element  172 A is ready to actuate (e.g., contract) in response to receiving current. In the depicted embodiment, bi-stable toggle element  300  is coupled to heat sink  31  at pivot point  302 . Thus, moving the bi-stable toggle element  300  to position P 5  moves the heat sink upwards a distance D 1 . However, in other embodiments, the bi-stable toggle element  300  may be directly coupled to and/or enclosed within the heat sink  31  in any manner. Regardless, once the bi-stable toggle element  300  is in position P 5 , current need not be delivered to SMA element  172 B, as the bi-stable toggle element  300  will maintain (e.g., lock) the heat sink  31  in a raised position. 
     Then, to lower the heat sink  31 , current is delivered to SMA element  172 A to actuate (e.g., contract) SMA element  172 A and pivot top ends of pivot points  302  inwards. This moves (e.g., snaps) the bi-stable toggle element  300  to position P 6  (shown in dashed lines) and moves the heat sink downwards a distance D 1 . Again, once the bi-stable toggle element  300  is in position P 6 , current need not be delivered to SMA element  172 A, as the bi-stable toggle element  300  will maintain (e.g., lock) the heat sink  31  in a lowered position. 
       FIG.  13    illustrates another example embodiment of a heat sink assembly that can operate without a biasing member exerting a constant restorative force on the heat sink  31 . Heat sink assembly  30 ( 3 ) includes two SMA elements, like heat sink assembly  30 ( 2 ) of  FIG.  12   , but provides a first SMA element  172 C trained to deform to a shape that raises the heat sink  31  and a second SMA element  172 D trained to deform to a shape that lowers the heat sink  31 . For example, SMA element  172 C may be trained and/or arranged so that actuation of SMA element  172 C arcs or bends SMA element  172 C upwards. SMA element  172 C is connected to heat sink  31  at connection points  179 C and, thus, upward bending or arcing of SMA element  172 C moves heat sink  31  upwards. Meanwhile, SMA element  172 D may be trained and/or arranged so that actuation of SMA element  172 D arcs or bends SMA element  172 D downwards. SMA element  172 D is connected to heat sink  31  at connection points  179 D and, thus, downward bending or arcing of SMA element  172 D moves heat sink  31  downwards. However, SMA elements  172 C and  172 D are only shown directly attached to heat sink  31  as an example and SMA elements  172 C and  172 D could be coupled to heat sink  31  in any manner provided that actuation (e.g., contraction) of SMA element  172 C or  172 D moves the heat sink  31  up or down. 
     Now turning to  FIGS.  14 A and  14 B , these Figures depict yet another example embodiment of a heat sink assembly that can operate without a biasing member exerting a constant restorative force on the heat sink  31 . Heat sink assembly  30 ( 4 ) is substantially similar to the heat sink assembly  30 ′ shown in  FIGS.  10 A and  10 B ; however, now the heat sink assembly  30 ( 4 ) does not include compression springs  160 ′ or any kind of biasing member  160 . Instead, SMA element  172 E is a two-way SMA element. Thus, in response to a first current being delivered to a first portion of the SMA element  172 E, the SMA element  172 E may lift heat sink  31  a distance D 1  along a vertical axis A 1  to a raised position P 4  (see  FIG.  14 B ). Then, in response to a current being delivered to a second portion of the SMA element  172 E, the SMA element  172 E may lower heat sink  31  a distance D 2  (which may be equal to distance D 1 ) along a vertical axis A 1  to a lowered position P 3  (see  FIG.  14 A ). Alternatively, different magnitudes of current might cause SMA  172 E to raise and lower. Regardless, the arrangement shown in  FIGS.  14 A and  14 B  is similar to the arrangement of heat sink assembly  30 ( 3 ) of  FIG.  13   , but now the functionality of SMA elements  172 C and  172 D from  FIG.  13    is achieved by a single SMA element  172 E. 
     Notably, with this embodiment, the currents that actuate SMA element  172 E may move the SMA element  172 E between a first actuated position P 7  (corresponding to lowered position P 3  of heat sink  31 ) and a second actuated position P 8  (corresponding to raised position P 4  of heat sink  31 ). However, since a restorative force (e.g., a biasing force) is not constantly acting on the heat sink  31  of heat sink assembly  30 ( 4 ), SMA element  172 E need not receive a constant current to stay in positions P 7  and P 8 . Instead, current can be delivered to SMA element  172 E to move the SMA element  172 E between positions P 7  and P 8  and can be turned off after an actuation (like the embodiments shown and described in connection with  FIGS.  12  and  13   ). 
     Now turning to  FIGS.  15 A and  15 B , but with continued reference to  FIGS.  14 A and  14 B , generally, two-way SMA toggles between two different shapes or “conformations.” To achieve this, SMA element  172 E includes two opposing SMA layers or SMA wires  172 E( 1 ) and  172 E( 2 ) that are joined and separated by a flexible and heat resistant material  172 E( 3 ). The SMA wires  172 E( 1 ) and  172 E( 2 ) and the heat resistant material  172 E( 3 ) extend longitudinally along a length of SMA element  172 E and may be contained within an outer casing (giving SMA element  172 E the appearance of a single wire). The first SMA layer/wire  172 E( 1 ) and the second SMA layer/wire  172 E( 2 ) are each trained or programmed to attain a specific shape when heated. That is, SMA layers/wires  172 E( 1 ) and  172 E( 2 ) may each be or function like one-way SMAs and, thus, any description of one-way SMAs included herein (e.g., relating to composition or training) should be understood to apply to SMA layers/wires  172 E( 1 ) and  172 E( 2 ). Consequently, to actuate SMA element  172 E, current may be applied independently and sequentially to SMA layer/wire  172 E( 1 ) and  172 E( 2 ) to toggle the configuration of SMA element  172 E between two configurations or states. Additionally or alternatively, first SMA layer/wire  172 E( 1 ) and the second SMA layer/wire  172 E( 2 ) may have different compositions that respond to different currents.  FIG.  15 A  illustrates (in an exaggerated fashion) contraction of first SMA layer/wire  172 E( 1 ) driving SMA element  172 E to its first actuated position P 7  and  FIG.  15 B  illustrates (in an exaggerated fashion) contraction of second SMA layer/wire  172 E( 2 ) driving SMA element  172 E to its second actuated position P 8 . 
     Now turning to  FIGS.  16  and  17   , these Figures illustrate example solutions that can utilize the heat sink assembly  30  presented herein. First, in  FIG.  16   , system  400  is a server or switch assembled in an apparatus  12  that is a pizza-box style chassis. The apparatus  12  includes a cage to receive a module  20  in the form of a modular port adapter (MPA). This provides flexibility for customer-based specializations and the heat sink assembly  30  presented herein can provide cooling for any MPA. Second,  FIG.  17    illustrates a solution  500  with an apparatus  12  in the form of an MPA that can support computing modules  20  in the form of CFP 2  optical transceivers. In this instance, the heat sink assembly  30  can be installed in the MPA to provide cooling for the CFP 2  optical transceivers. Then, if the MPA was installed in, for example, a line card, the line card might also include a heat sink assembly  30  formed accordance with the embodiments presented herein to cool the MPA within the line card. 
     Among other advantages, the heat sink assembly presented herein may improve cooling of computing modules while minimizing a footprint of cooling components (at least because a heat sink may cover an entire computing module without moving beyond a lateral periphery of a computing module). In fact, in at least some embodiments, the heat sink assembly presented herein may completely eliminate the need for an actuator and leave the front panel unobstructed with any actuators. These embodiments may utilize a purely electrical actuation of the heat sink assembly. Alternatively, the heat sink assembly may provide a small button that requires only a push actuation and, thus a computing solution need not be installed or manufactured in a manner that provides space to accommodate linear or rotational movement of a user&#39;s hand at the front panel. 
     In  FIG.  18   , diagram  600  illustrates the temperature improvements provided by the heat sink assembly  30  as compared to a heat sink  31  that is not modified to support the actuation assembly  170  of heat sink assembly  30  (e.g., a heat sink  31  of the same size, but without the features (including the TIM  35 ) of heat sink assembly  30  described herein). Notably, the heat sink assembly  30  presented herein achieves lower temperatures under the same airflow conditions. For example, the heat sink assembly  30  may cool a module case to 70 degree Celsius with approximately 9 cubic feet per minute (CFM) of airflow while the unmodified heat sink requires approximately 12 CFM to achieve the same temperature. Thus, the heat sink assembly  30  may provide approximately 25% improvement. 
     Moreover, the thermal data from diagram  600  indicates that the heat sink assembly  30  does not induce thermal spreading that mitigates improvements in contact resistance provided by the TIM  35  engaging the computing module  20 . That is, forming passageway  152  and/or corners  145  in/on heat sink  31  will not generate thermal spreading that counteracts the thermal effectiveness of the heat sink  31 . Thus, the heat sink assembly presented herein may support higher operational temperatures while still meeting regulatory standards. Additionally or alternatively, the heat sink assembly presented herein may reduce operating temperatures which may lower power consumption (e.g., due to reduced fan speeds) and/or reduce acoustic noise (e.g., from fans). The heat sink assembly presented herein may also achieve these advantages with an inexpensive solution that, for example, does not require expensive and maintenance intensive spring clips. 
     In summary, an apparatus is provided comprising: a cage defining a chamber; a heat sink to facilitate heat dissipation, the heat sink including a mating surface; a thermal interface material including a first surface and a second surface, the first surface being coupled to the mating surface of the heat sink and the second surface being opposite the first surface so that the second surface can be positioned against a perimeter of the chamber; and an actuation assembly including a shape memory alloy (SMA) element, wherein when the SMA element is in a first position, the second surface of the thermal interface material is disposed within or adjacent the perimeter of the chamber, and when the SMA element is moved to a second position, the second surface of the thermal interface material is moved a distance away from the perimeter of the chamber. 
     In another form, a heat sink assembly for a cage for a field replaceable computing module is provided, comprising: a heat sink to facilitate heat dissipation, the heat sink including a mating surface; a thermal interface material including a first surface and a second surface, the first surface being coupled to the mating surface of the heat sink and the second surface being opposite the first surface so that the second surface can engage a heat transfer surface of the field replaceable computing module installed adjacent the heat sink; and an actuation assembly including a shape memory alloy (SMA) element, wherein when the SMA element is in a first position, the second surface of the thermal interface material contacts the heat transfer surface of the field replaceable computing module, and when the SMA element moves to a second position, the second surface of the thermal interface material is moved a distance away from the heat transfer surface of the field replaceable computing module. 
     In yet another form, a system is provided, comprising: a cage defining a chamber sized to receive the field replaceable computing module with a heat transfer surface; a heat sink to facilitate heat dissipation, the heat sink including a mating surface; a thermal interface material including a first surface and a second surface, the first surface being coupled to the mating surface of the heat sink and the second surface being opposite the first surface so that the second surface can selectively engage the heat transfer surface of the field replaceable computing module when the field replaceable computing module is installed in the chamber of the cage; and an actuation assembly including a shape memory alloy (SMA) element, wherein when the field replaceable computing module is installed in the chamber of the cage and the SMA element is in a first position, the second surface of the thermal interface material contacts the heat transfer surface of the field replaceable computing module, and when the SMA element moves to a second position, the second surface of the thermal interface material is moved a distance away from the heat transfer surface of the field replaceable computing module. 
     The above description is intended by way of example only. Although the techniques are illustrated and described herein as embodied in one or more specific examples, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made within the scope and range of equivalents of the claims. In addition, various features from one of the embodiments may be incorporated into another of the embodiments. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the disclosure as set forth in the following claims. 
     It is also to be understood that the heat sink assembly, apparatus, and system presented herein described herein, or portions thereof, may be fabricated from any suitable material or combination of materials, such as plastic, metal, foamed plastic, wood, cardboard, pressed paper, supple natural or synthetic materials including, but not limited to, cotton, elastomers, polyester, plastic, rubber, derivatives thereof, and combinations thereof. Suitable plastics may include high-density polyethylene (HDPE), low-density polyethylene (LDPE), polystyrene, acrylonitrile butadiene styrene (ABS), polycarbonate, polyethylene terephthalate (PET), polypropylene, ethylene-vinyl acetate (EVA), or the like. 
     Finally, when used herein, the term “approximately” and terms of its family (such as “approximate,” etc.) should be understood as indicating values very near to those that accompany the aforementioned term. That is to say, a deviation within reasonable limits from an exact value should be accepted, because a skilled person in the art will understand that such a deviation from the values indicated is inevitable due to measurement inaccuracies, etc. The same applies to the terms “about” and “around” and “substantially.”