Patent Publication Number: US-2020296862-A1

Title: Cooling electronic devices in a data center

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of, and claims priority to, U.S. patent application Ser. No. 15/957,161, filed on Apr. 19, 2018. The entire disclosure of the previous application is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     This document relates to systems and methods for providing cooling to electronic equipment, such as computer server racks and related equipment in computer data centers, with a cold plate. 
     BACKGROUND 
     Computer users often focus on the speed of computer microprocessors (e.g., megahertz and gigahertz). Many forget that this speed often comes with a cost—higher power consumption. This power consumption also generates heat. That is because, by simple laws of physics, all the power has to go somewhere, and that somewhere is, in the end, conversion into heat. A pair of microprocessors mounted on a single motherboard can draw hundreds of watts or more of power. Multiply that figure by several thousand (or tens of thousands) to account for the many computers in a large data center, and one can readily appreciate the amount of heat that can be generated. The effects of power consumed by the critical load in the data center are often compounded when one incorporates all of the ancillary equipment required to support the critical load. 
     Many techniques may be used to cool electronic devices (e.g., processors, memories, networking devices, and other heat generating devices) that are located on a server or network rack tray. For instance, forced convection may be created by providing a cooling airflow over the devices. Fans located near the devices, fans located in computer server rooms, and/or fans located in ductwork in fluid communication with the air surrounding the electronic devices, may force the cooling airflow over the tray containing the devices. In some instances, one or more components or devices on a server tray may be located in a difficult-to-cool area of the tray; for example, an area where forced convection is not particularly effective or not available. 
     The consequence of inadequate and/or insufficient cooling may be the failure of one or more electronic devices on the tray due to a temperature of the device exceeding a maximum rated temperature. While certain redundancies may be built into a computer data center, a server rack, and even individual trays, the failure of devices due to overheating can come at a great cost in terms of speed, efficiency, and expense. 
     SUMMARY 
     This disclosure describes a cooling system, for example, for rack mounted electronic devices (e.g., servers, processors, memory, networking devices or otherwise) in a data center. In various disclosed implementations, the cooling system may be or include a liquid cold plate assembly that is part of or integrated with a server tray package. In some implementations, the liquid cold plate assembly includes a base portion and a top portion that, in combination, form a cooling liquid flow path through which a cooling liquid is circulated and a thermal interface between one or more heat generating devices and the cooling liquid. 
     In an example implementation, a server tray package includes a motherboard assembly that includes a plurality of data center electronic devices, the plurality of data center electronic devices including at least one heat generating processor device; and a liquid cold plate assembly. The liquid cold plate assembly includes a base portion mounted to the motherboard assembly, the base portion and motherboard assembly defining a volume that at least partially encloses the plurality of data center electronic devices; and a top portion mounted to the base portion and including a heat transfer member shaped to thermally contact the heat generating processor device, the heat transfer member including an inlet port and an outlet port that are in fluid communication with a cooling liquid flow path defined through the heat transfer member. 
     In an aspect combinable with the example implementation further includes a first thermal interface material positioned between a bottom surface of the top portion and a top surface of the base portion. 
     Another aspect combinable with any one of the previous aspects further includes a second thermal interface material positioned between the top surface of the base portion and at least a portion of the plurality of data center electronic devices. 
     In another aspect combinable with any one of the previous aspects, the liquid cold plate assembly further includes a plurality of heat transfer surfaces enclosed within the cooling liquid flow path. 
     Another aspect combinable with any one of the previous aspects further includes a thermal interface material positioned to directly contact a bottom surface of the top portion and a top surface of each of the plurality of data center electronic devices. 
     In another aspect combinable with any one of the previous aspects, the base portion includes a ring member that circumscribes the volume and is coupled to the top portion. 
     Another aspect combinable with any one of the previous aspects further includes a seal between the ring member and the top portion. 
     Another aspect combinable with any one of the previous aspects further includes at least one mechanical fastener that couples the ring member to the top portion. 
     In another aspect combinable with any one of the previous aspects, the ring member is coupled to a perimeter member of the top portion that is coupled to the heat transfer member and includes a thickness less than a thickness of the heat transfer member. 
     In another aspect combinable with any one of the previous aspects, the perimeter member is integrally formed with the heat transfer member and at least partially defines the cooling liquid flow path. 
     Another aspect combinable with any one of the previous aspects further includes a seal positioned between the heat transfer member and the plurality of data center electronic devices. 
     In another aspect combinable with any one of the previous aspects, the seal includes a metallization layer that at least partially defines the cooling liquid flow path. 
     In another aspect combinable with any one of the previous aspects, the metallization layer is positioned through a plurality of flow channels formed on a top surface of the heat generating processor device. 
     In another aspect combinable with any one of the previous aspects, the plurality of flow channels are in fluid communication with the cooling liquid flow path. 
     Another aspect combinable with any one of the previous aspects further includes a gasket mounted between a bottom surface of the heat transfer member and top surfaces of fins that define the plurality of flow channels formed on the top surface of the heat generating processor device. 
     In another example implementation, a method for cooling heat generating devices in a data center includes circulating a flow of a cooling liquid to a server tray package that includes a motherboard assembly that includes a plurality of data center electronic devices that include at least one heat generating processor device; and a liquid cold plate assembly that includes a base portion mounted to the motherboard assembly, the base portion and motherboard assembly defining a volume that at least partially encloses the plurality of data center electronic devices, and a top portion mounted to the base portion and including a heat transfer member shaped to thermally contact the heat generating processor device; circulating the flow of the cooling liquid into an inlet port of the heat transfer member; circulating the flow of the cooling liquid from the inlet port through a cooling liquid flow path defined through the heat transfer member to transfer heat from the at least one heat generating processor device; and circulating the heated flow of the cooling liquid from the cooling liquid flow path to an outlet port of the heat transfer member. 
     In an aspect combinable with the example implementation further includes transferring the heat from the at least one heat generating processor device through a first thermal interface material positioned between the processing device and a top surface of the base portion. 
     Another aspect combinable with any one of the previous aspects further includes transferring the heat from the top surface of the base portion through a second thermal interface material positioned between the base portion and a bottom surface of the top portion of the liquid cold plate assembly. 
     In another aspect combinable with any one of the previous aspects, circulating the flow of the cooling liquid through the cooling liquid flow path defined through the heat transfer member includes circulating the cooling liquid through a plurality of flow channels defined by a plurality of heat transfer surfaces enclosed within the cooling liquid flow path. 
     Another aspect combinable with any one of the previous aspects further includes transferring the heat from the at least one heat generating processor device through a thermal interface material positioned to directly contact a bottom surface of the top portion and a top surface of the at least one heat generating processor device. 
     Another aspect combinable with any one of the previous aspects further includes circulating the heated flow of the cooling liquid through a portion of the cooling liquid flow path defined by a perimeter member of the top portion is integrally formed with the heat transfer member and at least partially defines the cooling liquid flow path. 
     Another aspect combinable with any one of the previous aspects further includes circulating the flow of the cooling liquid between a seal positioned between the heat transfer member and the heat generating processing device. 
     In another aspect combinable with any one of the previous aspects, the seal includes a metallization layer that at least partially defines the cooling liquid flow path. 
     Another aspect combinable with any one of the previous aspects further includes circulating the flow of cooling liquid through a plurality of flow channels formed on a top surface of the heat generating processor device, at least a portion of each of the plurality of flow channels filled with the metallization layer. 
     In another example implementation, a method for forming a server tray package includes mounting a plurality of data center electronic devices to a motherboard assembly the plurality of data center electronic devices including at least one heat generating processor device; mounting a liquid cold plate assembly base to the motherboard assembly to at least partially define a volume that encloses the plurality of data center electronic devices; and mounting a liquid cold plate assembly top hat to the liquid cold plate assembly base, the liquid cold plate assembly top hat including a heat transfer member shaped to thermally contact the heat generating processor device when mounted to the liquid cold plate assembly base, the heat transfer member including an inlet port and an outlet port that are in fluid communication with a cooling liquid flow path defined through the heat transfer member. 
     In an aspect combinable with the example implementation further includes mounting the plurality of data center electronic devices to an interposer of the motherboard assembly. 
     Another aspect combinable with any one of the previous aspects further includes mounting the interposer to a substrate of the motherboard assembly. 
     Another aspect combinable with any one of the previous aspects further includes mounting the substrate to a motherboard of the motherboard assembly. 
     In another aspect combinable with any one of the previous aspects, mounting the liquid cold plate assembly base to the motherboard assembly includes mounting a stiffener ring member to the substrate with an adhesive. 
     In another aspect combinable with any one of the previous aspects, mounting the liquid cold plate assembly top hat to the liquid cold plate assembly base includes mounting the liquid cold plate assembly top hat to the stiffener ring member with one or more mechanical fasteners. 
     Another aspect combinable with any one of the previous aspects further includes inserting a gasket between the liquid cold plate assembly top hat and the stiffener ring member. 
     Another aspect combinable with any one of the previous aspects further includes applying a liquid sealant between the stiffener ring member and the motherboard assembly. 
     Another aspect combinable with any one of the previous aspects further includes positioning a first thermal interface material between a lid of the liquid cold plate assembly base and the heat transfer member to form a first heat transfer interface between the lid and the heat transfer member. 
     Another aspect combinable with any one of the previous aspects further includes positioning a second thermal interface material between the lid and the plurality of data center electronic devices to form a second thermal interface between the lid and the plurality of data center electronic devices. 
     Another aspect combinable with any one of the previous aspects further includes positioning a thermal interface material between the heat transfer member and the plurality of data center electronic devices to form a heat transfer interface between the heat transfer member and the plurality of data center electronic devices. 
     Another aspect combinable with any one of the previous aspects further includes applying a metallizing layer between the plurality of data center electronic devices and the heat transfer member. 
     In another aspect combinable with any one of the previous aspects, the metallizing layer is applied within a plurality of channels formed on a top surface of the at least one heat generating processor device. 
     Various implementations of a data center cooling system according to the present disclosure may include one, some, or all of the following features. For example, a server tray package according to the present disclosure may provide for direct liquid cooling to high heat generating electronic devices in a data center. As another example, a server tray package according to the present disclosure may provide for multiple functionality including cooling, mechanical rigidity, and liquid coolant sealing. As another example, a server tray package according to the present disclosure may provide for custom cooling liquid flow paths and flow geometries to cool both high and low heat generating electronic devices mounted on a single substrate. As yet another example, the server tray package according to the present disclosure may allow for the cooling of heat-generating devices mounted on a substrate that have different heights (and different power usages). 
     The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  illustrates a front view of a server rack and server rack sub-assemblies configured to mount within a rack used in a data center environment. 
         FIG. 2  illustrates a schematic side view of an example implementation of a server tray package that includes a liquid cold plate assembly. 
         FIG. 3  illustrates a schematic side view of another example implementation of a server tray package that includes a liquid cold plate assembly. 
         FIG. 4  illustrates a schematic side view of a portion of an example implementation of a server tray package that includes a liquid cold plate assembly. 
         FIG. 5  illustrates a schematic side view of a portion of an example implementation of a server tray package that includes a liquid cold plate assembly. 
         FIG. 6  illustrates a schematic side view of another example implementation of a server tray package that includes a liquid cold plate assembly. 
         FIG. 7  illustrates a schematic side view of an example implementation of a server tray package that includes a liquid cold plate assembly. 
     
    
    
     DETAILED DESCRIPTION 
     In some example implementations, a cooling system, for example, for rack mounted electronic devices (e.g., servers, processors, memory, networking devices or otherwise) in a data center is disclosed. In various disclosed implementations, the cooling system may be or include a liquid cold plate assembly that is part of or integrated with a server tray package. In some implementations, the liquid cold plate assembly includes a base portion and a top portion that, in combination, form a cooling liquid flow path through which a cooling liquid is circulated and a thermal interface between one or more heat generating devices and the cooling liquid. 
       FIG. 1  illustrates an example system  100  that includes a server rack  105 , e.g., a 13 inch or 19 inch server rack, and multiple server rack sub-assemblies  110  mounted within the rack  105 . Although a single server rack  105  is illustrated, server rack  105  may be one of a number of server racks within the system  100 , which may include a server farm or a co-location facility that contains various rack mounted computer systems. Also, although multiple server rack sub-assemblies  110  are illustrated as mounted within the rack  105 , there might be only a single server rack sub-assembly. Generally, the server rack  105  defines multiple slots  107  that are arranged in an orderly and repeating fashion within the server rack  105 , and each slot  107  is a space in the rack into which a corresponding server rack sub-assembly  110  can be placed and removed. For example, the server rack sub-assembly can be supported on rails  112  that project from opposite sides of the rack  105 , and which can define the position of the slots  107 . 
     The slots  107 , and the server rack sub-assemblies  110 , can be oriented with the illustrated horizontal arrangement (with respect to gravity). Alternatively, the slots  107 , and the server rack sub-assemblies  110 , can be oriented vertically (with respect to gravity). Where the slots are oriented horizontally, they may be stacked vertically in the rack  105 , and where the slots are oriented vertically, they may be stacked horizontally in the rack  105 . 
     Server rack  105 , as part of a larger data center for instance, may provide data processing and storage capacity. In operation, a data center may be connected to a network, and may receive and respond to various requests from the network to retrieve, process, and/or store data. In operation, for example, the server rack  105  typically facilitates the communication of information over a network with user interfaces generated by web browser applications of users who request services provided by applications running on computers in the datacenter. For example, the server rack  105  may provide or help provide a user who is using a web browser to access web sites on the Internet or the World Wide Web. 
     The server rack sub-assembly  110  may be one of a variety of structures that can be mounted in a server rack. For example, in some implementations, the server rack sub-assembly  110  may be a “tray” or tray assembly that can be slidably inserted into the server rack  105 . The term “tray” is not limited to any particular arrangement, but instead applies to the motherboard or other relatively flat structures appurtenant to a motherboard for supporting the motherboard in position in a rack structure. In some implementations, the server rack sub-assembly  110  may be a server tray package, server chassis, or server container (e.g., server box). In some implementations, the server rack sub-assembly  110  may be a hard drive cage. 
       FIG. 2  illustrates a schematic side view of an example implementation of a server tray package  200  that includes a liquid cold plate assembly  201 . In some implementations, the server tray package  200  may be used as one or more of the server rack sub-assemblies  110  shown in  FIG. 1 . Referring to  FIG. 2 , the server tray package  200  includes a printed circuit board  202 , e.g., motherboard  202 , that supports one or more data center electronic devices; in this example, two or more memory modules  214  and one or more processing devices  216  (e.g., one or more application-specific integrated circuits (ASIC)). In some aspects, the motherboard  202  may be mounted on a frame (not shown), which can include or simply be a flat structure that can be grasped by technicians for moving the motherboard  202  into place and holding it in position within the rack  105 . For example, the server tray package  200  may be mounted horizontally in the server rack  105  such as by sliding the frame into the slot  107  and over a pair of rails in the rack  105  on opposed sides of the server tray package  200 —much like sliding a lunch tray into a cafeteria rack. The frame can extend below the motherboard  202  or can have other forms (e.g., by implementing it as a peripheral frame around the motherboard  202 ) or may be eliminated so that the motherboard itself is located in, e.g., slidably engages, the rack  105 . The frame can be a flat plate or include one or more side walls that project upwardly from the edges of the flat plate, and the flat plate could be the floor of a closed-top or open-top box or cage. 
     In some examples, one motherboard  202  is mounted on a frame; alternatively, multiple motherboards  202  may be mounted on a frame, depending on the needs of the particular application. In some implementations, the one or more fans (not shown) can be placed on the motherboard  202  or a frame so that air enters at the front edge of the server tray package  200 , closer to the front of the rack  105  when the server tray package  200  is installed in the rack  105 , flows over the motherboard  202 , over some of the data center electronic components on the motherboard  202 , and is exhausted from the server tray package  200  at the back edge, closer to the back of the rack  105  when the server tray package  200  is installed in the rack  105 . The one or more fans can be secured to the motherboard  202  or a frame by brackets. 
     As illustrated, a substrate  204  and an interposer  212  (e.g., a silicon interposer) are positioned between the data center electronic devices  214  and  216  and the motherboard  202 . The substrate  204 , for example, provides an interface between one or more of the data center electronic devices (e.g., the processing device  216 ) and the motherboard  202 , such as through pins that provide electrical and communication interfaces. The substrate  204  also, in this example, may provide a mounting location for one or more components of the liquid cold plate assembly  201 . The interposer  212 , for example, provides a high bandwidth connection between the data center electronic devices, such as between the memory modules  214  and the processing device  216 . 
     As shown in  FIG. 2 , the liquid cold plate assembly  201  includes a top portion  222 , also referred to as a top hat  222 , and a base portion  206 . The base portion  206  includes a lid  208  that defines a top surface of the base portion  206  and sides  216  that couple the lid  208  to the substrate  204 . In combination, the lid  208  and the sides  210  define or enclose a volume  203  in which the interposer  212  and the data center electronic devices  214  and  216  (mounted thereon) are positioned in the server tray package  200 . As shown in this example, a thermal interface material  218  (e.g., a phase change material or otherwise thermally conductive material) is contactingly positioned between a bottom side of the lid  208  and the data center electronic devices  214  and  216  to provide a conductive heat transfer interface between these components. 
     In this example implementation, the top hat  222  is mounted to a top surface of the lid  208  through another thermal interface material  220  (e.g., a phase change material or otherwise thermally conductive material) that provides a conductive heat transfer interface between a bottom  228  of the top hat  222  and the lid  208  of the base portion  206 . The top hat  222 , as shown, includes a cap  224  that is connected to the bottom  228  through sides  226 . In combination, the cap  224 , sides  226 , and bottom  228  define a volume  234  through which a flow of a cooling liquid may be circulated. 
     As shown in this example, the cap  224  includes a cooling liquid inlet  230  through which a supply  240  of cooling liquid may enter. The cap  224  also includes a cooling liquid outlet  232  through which a return  242  of cooling liquid may exit. The volume  234  defines or includes a cooling liquid flow path between the inlet  230  and the outlet  232 . As shown in this example, one or more heat transfer surfaces  236  (e.g., fins, undulations, ridges, or other extended surfaces that increase a heat transfer area) are positioned in the volume  234 . The heat transfer surfaces  236  define channels  238 , for example, through which the cooling liquid may be circulated to increase an amount of heat transferred from the data center electronic devices  214  and  216  to the cooling liquid (e.g., relative to an amount transferred in an implementation of the server tray package  200  that does not include the heat transfer surfaces  236 ). Alternative implementations of the server tray package  200  may include multiple inlets  230 , multiple outlets  232 , or may not include the heat transfer surfaces  236 . 
     In an example operation of the server tray package  200  to cool the data center electronic devices  214  and  216 , the server tray package  200  may be deployed, for example, in a data center server rack  105  in a data center. During operation of the server tray package  200 , the processing device  216  and memory modules  214  generate heat that may need to be dissipated or removed from the server tray package  200  (e.g., for proper operation of the server tray package  200 ). Heat generated by the processing device  216  and memory modules  214  is transferred through the thermal interface material  218  and to the lid  208  of the base portion  206  of the liquid cold plate assembly  201 . The transferred heat is further transferred from the lid  208 , through the thermal interface material  220 , and to the bottom  228  of the top hat  222 . In some examples, one or more components of the liquid cold plate assembly  201  may be formed or made from a thermally conductive material, such as copper, aluminum, a combination of copper and aluminum, or other thermally conductive materials. 
     The heat transferred to the bottom  228  of the top hat  222  is then transferred to the supply  240  of the cooling liquid that is circulated through the inlet  230  and into the volume  234  of the top hat  222 . In some examples, the cooling liquid may be a chilled water or glycol, such as from one or more chillers fluidly coupled to the server tray package  200 . In alternative examples, the cooling liquid may be a condenser water or other evaporatively-cooled liquid (e.g., without mechanical refrigeration). In other examples, the cooling liquid may be a dielectric single or two-phase fluid. In any event, the cooling liquid supply  240  may be at an appropriate temperature and flow rate to remove a desired amount of heat from the data center electronic devices  214  and  216 . 
     In some examples, heat is transferred directly from the bottom  228  to the cooling liquid supply  240 . Heat may also be transferred from the bottom  228 , through one or more heat transfer surfaces  236 , and then to the cooling liquid supply  240  that flows through channels  238 . The heated cooling liquid supply  240  is circulated to the outlet  232  and exits the top hat  222  as the cooling liquid return  242  (e.g., that is at a higher temperature than the cooling liquid supply  240 ). The cooling liquid return  242  is circulated back, e.g., to a source of the cooling liquid, to expel the heat (e.g., in a chiller, cooling tower, or other heat exchanger) from the return  242 . 
     In an example operation for making the server tray package  200 , the interposer  212 , substrate  204 , and motherboard  202  may be mounted together to form an assembly to which the data center electronic devices  214  and  216  may be mounted and connected (e.g., for power and communication). The thermal interface material  218  is then mounted or positioned on top of the data center electronic devices  214  and  216 . 
     Next, the base portion  206  is mounted on the substrate  204  (in this example) to enclose the interposer  212  and data center electronic devices  214  and  216  within the volume  203 . In some examples, the sides  210  are first mounted to the substrate  204  and the lid  208  is then mounted to the sides  210  to contact the thermal interface material  218 . In some examples, mechanical fasteners or adhesive may be used to connect the base portion  206  to the substrate  204 . 
     Next, the thermal interface material  220  is mounted to the top surface of the lid  208  of the base portion  206 . The top hat  222  is then mounted onto the base portion  206  (with the thermal interface material  220  in between) so that the bottom  228  is on top of the lid  208 . In some aspects, mechanical fasteners or an adhesive may be used to connect the top hat  222  to the base portion  206 . Further, in some aspects, the top hat  222  may be mounted to the base portion  206  on a component-by-component basis. For example, the bottom  228  may first be mounted to the lid  208  of the base portion  206 . Next, the sides  226  may be mounted to the bottom  228 . Next, the cap  224  may be mounted to the sides  226 . 
       FIG. 3  illustrates a schematic side view of another example implementation of a server tray package  300  that includes a liquid cold plate assembly  301 . In some implementations, the server tray package  300  may be used as one or more of the server rack sub-assemblies  110  shown in  FIG. 1 . Referring to  FIG. 3 , the server tray package  300  includes a printed circuit board  302 , e.g., motherboard  302 , that supports one or more data center electronic devices; in this example, two or more memory modules  314  and one or more processing devices  316  (e.g., one or more application-specific integrated circuits (ASIC)). In some aspects, the motherboard  302  may be mounted on a frame (not shown), which can include or simply be a flat structure that can be grasped by technicians for moving the motherboard  302  into place and holding it in position within the rack  105 . For example, the server tray package  300  may be mounted horizontally in the server rack  105  such as by sliding the frame into the slot  107  and over a pair of rails in the rack  105  on opposed sides of the server tray package  300 —much like sliding a lunch tray into a cafeteria rack. The frame can extend below the motherboard  302  or can have other forms (e.g., by implementing it as a peripheral frame around the motherboard  302 ) or may be eliminated so that the motherboard itself is located in, e.g., slidably engages, the rack  105 . The frame can be a flat plate or include one or more side walls that project upwardly from the edges of the flat plate, and the flat plate could be the floor of a closed-top or open-top box or cage. 
     In some examples, one motherboard  302  is mounted on a frame; alternatively, multiple motherboards  302  may be mounted on a frame, depending on the needs of the particular application. In some implementations, the one or more fans (not shown) can be placed on the motherboard  302  or a frame so that air enters at the front edge of the server tray package  300 , closer to the front of the rack  105  when the server tray package  300  is installed in the rack  105 , flows over the motherboard  302 , over some of the data center electronic components on the motherboard  302 , and is exhausted from the server tray package  300  at the back edge, closer to the back of the rack  105  when the server tray package  300  is installed in the rack  105 . The one or more fans can be secured to the motherboard  302  or a frame by brackets. 
     As illustrated, a substrate  304  and an interposer  312  (e.g., a silicon interposer) are positioned between the data center electronic devices  314  and  316  and the motherboard  302 . The substrate  304 , for example, provides an interface between one or more of the data center electronic devices (e.g., the processing device  316 ) and the motherboard  302 , such as through pins that provide electrical and communication interfaces. The substrate  304  also, in this example, may provide a mounting location for one or more components of the liquid cold plate assembly  301 . The interposer  312 , for example, provides a high bandwidth connection between the data center electronic devices, such as between the memory modules  314  and the processing device  316 . 
     As shown in  FIG. 3 , the liquid cold plate assembly  301  includes a top portion  322 , also referred to as a top hat  322 , and a base portion  306 . The base portion  306 , in this example, includes a stiffener ring  307  that is mounted and sealingly coupled to the substrate  304  with a sealant layer  308 . In combination, the stiffener ring  307  and the sealant layer  308  at least partially define or enclose a volume  303  in which the interposer  312  and the data center electronic devices  314  and  316  (mounted thereon) are positioned in the server tray package  300 . As shown in this example, an epoxy ring  318  fills in the volume  303  to form a fluid seal between the data center electronic devices  314  and  316  and the stiffener ring  307 . The stiffener ring  307 , in some aspects, may provide a rigid structure that, for instance, provides mechanical stiffness for the server tray package  300 . 
     In this example, a thermal interface material  310  (e.g., a metallizing layer or otherwise thermally conductive material) is contactingly positioned on a top side of the data center electronic devices  314  and  316  and the epoxy ring  318 . The thermal interface material  310 , as a metallizing layer, may be comprised of nickel, gold, stainless steel, or other thermally conductive material, and provides a conductive heat transfer interface between these components and the top hat  322 . The thermal interface material  310  also provides, in this example, a fluid seal between the data center electronic devices  314  and  316 , and the volume  303 , generally, and a cooling liquid supplied to the top hot  322 . 
     In this example implementation, the top hat  322  is mounted to the thermal interface material  320  and a top surface of the stiffener ring  307 . As shown in this example, a gasket  320  is positioned in grooves formed in the stiffener ring  307  and the top hat  322  and, once secured together with one or more mechanical fasteners  336 , there is a fluid seal between the top hat  322  and the base portion  306  of the liquid cold plate assembly  301 . 
     Further, once secured together, a fluid channel  338  is defined by the top hat  322 , the thermal interface material  310 , and the stiffener ring  307 . The fluid channel  338  extends laterally from a middle centerline of the top hat  322  (coincident with a cooling liquid inlet  330 ) toward the stiffener ring  307  and under a middle portion  323  of the top hot  322 . As shown, as the fluid channel  338  reaches a portion of its volume that is vertically above the epoxy ring  318  (separated by the thermal interface material  310 ), a height of the fluid channel  338  increases as the middle portion  323  transitions to a perimeter portion  325  of the top hat  322  that is thinner (as shown in this perspective) than the middle portion  323 . 
     As shown in this example, the top hat  322  includes the cooling liquid inlet  330  through which a supply  340  of cooling liquid may enter. The top hat  322  also includes a cooling liquid outlet  332  through which a return  342  of cooling liquid may exit, after passing through the cooling liquid flow path  338 . In some aspects, one or more heat transfer surfaces, such as fins, undulations, ridges, or other extended surfaces that increase a heat transfer area, may be positioned in the cooling liquid flow path  338 . Alternative implementations of the server tray package  300  may include multiple inlets  330  and/or multiple outlets  332 . 
     In an example operation of the server tray package  300  to cool the data center electronic devices  314  and  316 , the server tray package  300  may be deployed, for example, in a data center server rack  105  in a data center. During operation of the server tray package  300 , the processing device  316  and memory modules  314  generate heat that may need to be dissipated or removed from the server tray package  300  (e.g., for proper operation of the server tray package  300 ). Heat generated by the processing device  316  and memory modules  314  is transferred through the thermal interface material  310 . 
     The heat transferred to the thermal interface material  310  is then transferred to the supply  340  of the cooling liquid that is circulated through the inlet  330  and into the cooling liquid flow path  338  of the top hat  322 . In some examples, the cooling liquid may be a chilled water or glycol, such as from one or more chillers fluidly coupled to the server tray package  300 . In alternative examples, the cooling liquid may be a condenser water or other evaporatively-cooled liquid (e.g., without mechanical refrigeration). In other examples, the cooling liquid may be a dielectric single or two-phase fluid. In any event, the cooling liquid supply  340  may be at an appropriate temperature and flow rate to remove a desired amount of heat from the data center electronic devices  314  and  316 . 
     The heated cooling liquid supply  340  is circulated to the outlet  332  and exits the top hat  322  as the cooling liquid return  342  (e.g., that is at a higher temperature than the cooling liquid supply  340 ). The cooling liquid return  342  is circulated back, e.g., to a source of the cooling liquid, to expel the heat (e.g., in a chiller, cooling tower, or other heat exchanger) from the return  342 . 
     In an example operation for making the server tray package  300 , the interposer  312 , substrate  304 , and motherboard  302  may be mounted together to form an assembly to which the data center electronic devices  314  and  316  may be mounted and connected (e.g., for power and communication). The stiffener ring  307  of the base portion  306  may be secured to the substrate  304  with the sealant layer  308  to at least partially define the volume  303 . The epoxy ring  318  may then be positioned or circulated to fill in the volume  303  between the stiffener ring  307  and the data center electronic devices. The thermal interface material  310  may then be mounted or positioned on top of the data center electronic devices  314  and  316 . 
     Next, the gasket  320  may be fitted within a groove formed on a top surface of the stiffener ring  307 . The top hat  322  is then mounted onto the base portion  306  (onto the stiffener ring  307 ) and the thermal interface material  310  so that the gasket  320  fits into a groove formed in a bottom surface of the perimeter portion  325  of the top hot  322 . As shown, one or more mechanical fasteners  336  are used to connect the top hat  322  to the stiffener ring  307 . 
       FIG. 4  illustrates a schematic side view of a portion of an example implementation of a server tray package that includes a liquid cold plate assembly. More specifically,  FIG. 4  shows a processing device  402  that is positioned between memory modules  410  (separated by air gaps or heat transfer material  412 ). The processing device  402  may be used, for example, in the server tray package  300  (or other server tray packages according to the present disclosure). For example, as shown, the processing device  402  includes grooves  406  formed in a top portion  403  of the processing device package. The grooves  406  are formed or defined by heat transfer surfaces  404  (e.g., fins, ridges, or otherwise) formed in the top portion  403  of the processing device package. 
     As shown, a thermal interface material  408 , such as a metallizing layer, is positioned or spread within the grooves  406 . As shown, in some aspects, the material  408  may only fill a portion of each of the grooves  406  (e.g., not up to a height of the heat transfer surfaces  404 ). The thermal interface material  408 , as a metallizing layer, may be comprised of nickel, gold, stainless steel, or other thermally conductive materials, and provides a conductive heat transfer interface between these components and, for example, a portion of a liquid cold plate assembly. The thermal interface material  408  also provides, in this example, a fluid seal between the processing device  402  and a cooling liquid supplied to a liquid cold plate assembly. 
     In an alternative aspect, the top portion  403  of the processing device  402  may be separate from the device  402 , itself. For example, a housing of the processing device  402  may be substantially planar on a top surface, and the top portion  403  (which includes the heat transfer surfaces  406  and grooves  408 ) may be coupled (e.g., attached by an indium thermal interface material) to the processing device  402 . Thus, the housing of the processing device  402  may stay relatively identical across a multitude of the devices  402 . 
       FIG. 5  illustrates a schematic side view of a portion of an example implementation of a server tray package  500  that includes a liquid cold plate assembly  501 . In the illustrated example, the processing device  402  is used in the server tray package  500  in combination, for example, with at least portions of a liquid cold plate assembly similar to liquid cold plate assembly  301  shown in  FIG. 3 . For example, as shown, the processing device  402  and memory modules  410  are mounted to an interposer  511  (e.g., a silicon interposer) that is in turn, mounted to a substrate  504  (which is mounted to a motherboard, not shown). An epoxy ring  520  surrounds the memory modules  410  and provides a fluid seal between a volume  503  and a base portion of the liquid cold plate assembly  501  (not shown in this example, but similar, for instance, to base portion  306 ). 
     As shown in this example, a top hat  502  is mounted at least partially to the processing device  401 , such as to top surfaces of the heat transfer surfaces  404 . As shown, a seal  512  (e.g., a gasket or otherwise) is positioned between a bottom surface of the top hat  502  and the heat transfer surfaces  404  in order to, e.g., fluidly seal some channels  406  from other channels  406  at tops of the channels  406 . Further, as shown, a heat transfer material  513  (e.g., a metallizing layer) is also positioned or mounted on tops of the memory modules  410  and epoxy ring  520  to fluidly seal these components from a liquid flow through flow path  510 . 
     In this example, the top hat  502  includes a middle portion  506  and a perimeter portion  508  that is thinner (as shown in this perspective) than the middle portion  506 . A flow path  510  is shown in this example, and includes the channels  406  and extends laterally from a cooling liquid inlet  504  that, in this example, is centered in the top hat  502 . 
     In an example operation of the server tray package  500  to cool the processing device  402  and the memory modules  410 , the server tray package  500  may be deployed, for example, in a data center server rack  105  in a data center. During operation of the server tray package  500 , the processing device  402  and memory modules  410  generate heat that may need to be dissipated or removed from the server tray package  500  (e.g., for proper operation of the server tray package  500 ). 
     Heat generated by the processing device  402  is transferred to the thermal interface material  408 . The heat transferred to the thermal interface material  408  is then transferred to the supply  514  of the cooling liquid that is circulated through the inlet  504  and into the cooling liquid flow path  510  (including channels  406 ) of the top hat  502 . In some examples, the cooling liquid may be a chilled water or glycol, such as from one or more chillers fluidly coupled to the server tray package  500 . In alternative examples, the cooling liquid may be a condenser water or other evaporatively-cooled liquid (e.g., without mechanical refrigeration). In other examples, the cooling liquid may be a dielectric single or two-phase fluid. In any event, the cooling liquid supply  514  may be at an appropriate temperature and flow rate to remove a desired amount of heat from the processing device  402  and memory modules  410 . 
     The heated cooling liquid supply  514  is circulated to an outlet of the top hat  502  (not shown) and exits the top hat  502  as a cooling liquid return (e.g., that is at a higher temperature than the cooling liquid supply  514 ). The cooling liquid return is circulated back, e.g., to a source of the cooling liquid, to expel the heat (e.g., in a chiller, cooling tower, or other heat exchanger) from the return. 
       FIG. 6  illustrates a schematic side view of another example implementation of a server tray package  600  that includes a liquid cold plate assembly  601 . In some implementations, the server tray package  600  may be used as one or more of the server rack sub-assemblies  110  shown in  FIG. 1 . Referring to  FIG. 6 , the server tray package  600  includes a printed circuit board  602 , e.g., motherboard  602 , that supports one or more data center electronic devices; in this example, two or more memory modules  614  and one or more processing devices  616  (e.g., one or more application-specific integrated circuits (ASIC)). In some aspects, the motherboard  602  may be mounted on a frame (not shown), which can include or simply be a flat structure that can be grasped by technicians for moving the motherboard  602  into place and holding it in position within the rack  105 . For example, the server tray package  600  may be mounted horizontally in the server rack  105  such as by sliding the frame into the slot  107  and over a pair of rails in the rack  105  on opposed sides of the server tray package  600 —much like sliding a lunch tray into a cafeteria rack. The frame can extend below the motherboard  602  or can have other forms (e.g., by implementing it as a peripheral frame around the motherboard  602 ) or may be eliminated so that the motherboard itself is located in, e.g., slidably engages, the rack  105 . The frame can be a flat plate or include one or more side walls that project upwardly from the edges of the flat plate, and the flat plate could be the floor of a closed-top or open-top box or cage. 
     In some examples, one motherboard  602  is mounted on a frame; alternatively, multiple motherboards  602  may be mounted on a frame, depending on the needs of the particular application. In some implementations, the one or more fans (not shown) can be placed on the motherboard  602  or a frame so that air enters at the front edge of the server tray package  600 , closer to the front of the rack  105  when the server tray package  600  is installed in the rack  105 , flows over the motherboard  602 , over some of the data center electronic components on the motherboard  602 , and is exhausted from the server tray package  600  at the back edge, closer to the back of the rack  105  when the server tray package  600  is installed in the rack  105 . The one or more fans can be secured to the motherboard  602  or a frame by brackets. 
     As illustrated, a substrate  604  and an interposer  612  (e.g., a silicon interposer) are positioned between the data center electronic devices  614  and  616  and the motherboard  602 . The substrate  604 , for example, provides an interface between one or more of the data center electronic devices (e.g., the processing device  616 ) and the motherboard  602 , such as through pins that provide electrical and communication interfaces. The substrate  604  also, in this example, may provide a mounting location for one or more components of the liquid cold plate assembly  601 . The interposer  612 , for example, provides a high bandwidth connection between the data center electronic devices, such as between the memory modules  614  and the processing device  616 . 
     As shown in  FIG. 6 , the liquid cold plate assembly  601  includes a top portion  622 , also referred to as a top hat  622 , and a base portion  606 . The base portion  606 , in this example, includes a stiffener ring  607  that is mounted and sealingly coupled to the substrate  604  with a sealant layer  608 . In combination, the stiffener ring  607  and the sealant layer  608  at least partially define or enclose a volume  603  in which the interposer  612  and the data center electronic devices  614  and  616  (mounted thereon) are positioned in the server tray package  600 . As shown in this example, an epoxy ring  618  fills in the volume  603  to form a fluid seal between the data center electronic devices  614  and  616  and the stiffener ring  607 . The stiffener ring  607 , in some aspects, may provide a rigid structure that, for instance, provides mechanical stiffness for the server tray package  600 . 
     In this example, a thermal interface material  610  (e.g., a metallizing layer or otherwise thermally conductive material) is contactingly positioned on a top side of the data center electronic devices  614  and  616  and the epoxy ring  618 . The thermal interface material  610 , as a metallizing layer, may be comprised of nickel, gold, stainless steel, or other thermally conductive material, and provides a conductive heat transfer interface between these components and the top hat  622 . The thermal interface material  610  also provides, in this example, a fluid seal between the data center electronic devices  614  and  616 , and the volume  603 , generally, and a cooling liquid supplied to the top hot  622 . 
     In this example implementation, the top hat  622  is mounted to the thermal interface material  620  and a top surface of the stiffener ring  607 . As shown in this example, an adhesive  621  (e.g., a metallurgical and/or epoxy sealant) is formed or positioned on top of the stiffener ring  607 . The top hat  623  is connected to the base portion  606  (and the stiffener ring  607 ) with the adhesive  619 . 
     Further, once secured together, a fluid channel  638  is defined by the top hat  622 , the thermal interface material  610 , and the stiffener ring  607 . The fluid channel  638  extends laterally from a middle centerline of the top hat  622  (coincident with a cooling liquid inlet  630 ) toward the stiffener ring  607  and under a middle portion  623  of the top hot  622 . As shown, as the fluid channel  638  reaches a portion of its volume that is vertically above the epoxy ring  618  (separated by the thermal interface material  610 ), a height of the fluid channel  638  increases as the middle portion  623  transitions to a perimeter portion  625  of the top hat  622  that is thinner (as shown in this perspective) than the middle portion  623 . 
     As shown in this example, the top hat  622  includes the cooling liquid inlet  630  through which a supply  640  of cooling liquid may enter. The top hat  622  also includes a cooling liquid outlet  632  through which a return  642  of cooling liquid may exit, after passing through the cooling liquid flow path  638 . In some aspects, one or more heat transfer surfaces, such as fins, undulations, ridges, or other extended surfaces that increase a heat transfer area, may be positioned in the cooling liquid flow path  638 . Alternative implementations of the server tray package  600  may include multiple inlets  630  and/or multiple outlets  632 . 
     In an example operation of the server tray package  600  to cool the data center electronic devices  614  and  616 , the server tray package  600  may be deployed, for example, in a data center server rack  105  in a data center. During operation of the server tray package  600 , the processing device  616  and memory modules  614  generate heat that may need to be dissipated or removed from the server tray package  600  (e.g., for proper operation of the server tray package  600 ). Heat generated by the processing device  616  and memory modules  614  is transferred through the thermal interface material  610 . 
     The heat transferred to the thermal interface material  610  is then transferred to the supply  640  of the cooling liquid that is circulated through the inlet  630  and into the cooling liquid flow path  638  of the top hat  622 . In some examples, the cooling liquid may be a chilled water or glycol, such as from one or more chillers fluidly coupled to the server tray package  600 . In alternative examples, the cooling liquid may be a condenser water or other evaporatively-cooled liquid (e.g., without mechanical refrigeration). In other examples, the cooling liquid may be a dielectric single or two-phase fluid. In any event, the cooling liquid supply  640  may be at an appropriate temperature and flow rate to remove a desired amount of heat from the data center electronic devices  614  and  616 . 
     The heated cooling liquid supply  640  is circulated to the outlet  632  and exits the top hat  622  as the cooling liquid return  642  (e.g., that is at a higher temperature than the cooling liquid supply  640 ). The cooling liquid return  642  is circulated back, e.g., to a source of the cooling liquid, to expel the heat (e.g., in a chiller, cooling tower, or other heat exchanger) from the return  642 . 
     In an example operation for making the server tray package  600 , the interposer  612 , substrate  604 , and motherboard  602  may be mounted together to form an assembly to which the data center electronic devices  614  and  616  may be mounted and connected (e.g., for power and communication). The stiffener ring  607  of the base portion  606  may be secured to the substrate  604  with the sealant layer  608  to at least partially define the volume  603 . The epoxy ring  618  may then be positioned or circulated to fill in the volume  603  between the stiffener ring  607  and the data center electronic devices. The thermal interface material  610  may then be mounted or positioned on top of the data center electronic devices  614  and  616 . 
     Next, the adhesive  621  is mounted or formed on the stiffener ring  607  as shown. The top hat  622  is then mounted onto the base portion  606  (onto the stiffener ring  607 ) and attached with the adhesive  621 . 
       FIG. 7  illustrates a schematic side view of an example implementation of a server tray package  700  that includes a liquid cold plate assembly  701 . In some implementations, the server tray package  700  may be used as one or more of the server rack sub-assemblies  110  shown in  FIG. 1 . Referring to  FIG. 7 , the server tray package  700  includes a printed circuit board  702 , e.g., motherboard  702 , that supports one or more data center electronic devices; in this example, two or more memory modules  714  and one or more processing devices  716  (e.g., one or more application-specific integrated circuits (ASIC)). In some aspects, the motherboard  702  may be mounted on a frame (not shown), which can include or simply be a flat structure that can be grasped by technicians for moving the motherboard  702  into place and holding it in position within the rack  105 . For example, the server tray package  700  may be mounted horizontally in the server rack  105  such as by sliding the frame into the slot  107  and over a pair of rails in the rack  105  on opposed sides of the server tray package  700 —much like sliding a lunch tray into a cafeteria rack. The frame can extend below the motherboard  702  or can have other forms (e.g., by implementing it as a peripheral frame around the motherboard  702 ) or may be eliminated so that the motherboard itself is located in, e.g., slidably engages, the rack  105 . The frame can be a flat plate or include one or more side walls that project upwardly from the edges of the flat plate, and the flat plate could be the floor of a closed-top or open-top box or cage. 
     In some examples, one motherboard  702  is mounted on a frame; alternatively, multiple motherboards  702  may be mounted on a frame, depending on the needs of the particular application. In some implementations, the one or more fans (not shown) can be placed on the motherboard  702  or a frame so that air enters at the front edge of the server tray package  700 , closer to the front of the rack  105  when the server tray package  700  is installed in the rack  105 , flows over the motherboard  702 , over some of the data center electronic components on the motherboard  702 , and is exhausted from the server tray package  700  at the back edge, closer to the back of the rack  105  when the server tray package  700  is installed in the rack  105 . The one or more fans can be secured to the motherboard  702  or a frame by brackets. 
     As illustrated, a substrate  704  and an interposer  712  (e.g., a silicon interposer) are positioned between the data center electronic devices  714  and  716  and the motherboard  702 . The substrate  704 , for example, provides an interface between one or more of the data center electronic devices (e.g., the processing device  716 ) and the motherboard  702 , such as through pins that provide electrical and communication interfaces. The substrate  704  also, in this example, may provide a mounting location for one or more components of the liquid cold plate assembly  701 . The interposer  712 , for example, provides a high bandwidth connection between the data center electronic devices, such as between the memory modules  714  and the processing device  716 . 
     As shown in  FIG. 7 , the liquid cold plate assembly  701  includes a top portion  722 , also referred to as a top hat  722 , and a base portion  706 . The base portion  706  includes a stiffener ring  710  that defines sides of the base portion  706  and is coupled (e.g., mechanically or adhesively) to the substrate  704 . The stiffener ring  710  at least partially defines a volume  703  in which the interposer  712  and the data center electronic devices  714  and  716  (mounted thereon) are positioned in the server tray package  700 . As shown in this example, a thermal interface material  718  (e.g., a phase change material or otherwise thermally conductive material) is contactingly positioned on top of the data center electronic devices  714  and  716  to provide a conductive heat transfer interface between these components and the top hot  722 . The stiffener ring  710 , in some aspects, may provide a rigid structure that, for instance, provides mechanical stiffness for the server tray package  700 . 
     In this example implementation, the top hat  722  is mounted to a top surface of the stiffener ring  710  (e.g., mechanically or adhesively) and to the thermal interface material  718  that provides a conductive heat transfer interface between a bottom  728  of the top hat  722  and the data center electronic devices  714  and  716 . The top hat  722 , as shown, includes a cap  724  that is connected to the bottom  728  (which, in this example, also serves as a lid to the base portion  706 ) through sides  726 . In combination, the cap  724 , sides  726 , and bottom  728  define a volume  734  through which a flow of a cooling liquid may be circulated. 
     As shown in this example, the cap  724  includes a cooling liquid inlet  730  through which a supply  740  of cooling liquid may enter. The cap  724  also includes a cooling liquid outlet  732  through which a return  742  of cooling liquid may exit. The volume  734  defines or includes a cooling liquid flow path between the inlet  730  and the outlet  732 . As shown in this example, one or more heat transfer surfaces  736  (e.g., fins, undulations, ridges, or other extended surface that increases a heat transfer area) are positioned in the volume  734 . The heat transfer surfaces  736  define channels  738 , for example, through which the cooling liquid may be circulated to increase an amount of heat transferred from the data center electronic devices  714  and  716  to the cooling liquid (e.g., relative to an amount transferred in an implementation of the server tray package  700  that does not include the heat transfer surfaces  736 ). Alternative implementations of the server tray package  700  may include multiple inlets  730 , multiple outlets  732 , or may not include the heat transfer surfaces  736 . 
     In an example operation of the server tray package  700  to cool the data center electronic devices  714  and  716 , the server tray package  700  may be deployed, for example, in a data center server rack  105  in a data center. During operation of the server tray package  700 , the processing device  716  and memory modules  714  generate heat that may need to be dissipated or removed from the server tray package  700  (e.g., for proper operation of the server tray package  700 ). Heat generated by the processing device  716  and memory modules  714  is transferred through the thermal interface material  718  and to the bottom  728  of the top hat  722 . In some examples, one or more components of the liquid cold plate assembly  701  may be formed or made from a thermally conductive material, such as copper, aluminum, a combination of copper and aluminum, or other thermally conductive materials. 
     The heat transferred to the bottom  728  of the top hat  722  is then transferred to the supply  740  of the cooling liquid that is circulated through the inlet  730  and into the volume  734  of the top hat  722 . In some examples, the cooling liquid may be a chilled water or glycol, such as from one or more chillers fluidly coupled to the server tray package  700 . In alternative examples, the cooling liquid may be a condenser water or other evaporatively-cooled liquid (e.g., without mechanical refrigeration). In other examples, the cooling liquid may be a dielectric single or two-phase fluid. In any event, the cooling liquid supply  740  may be at an appropriate temperature and flow rate to remove a desired amount of heat from the data center electronic devices  714  and  716 . 
     In some examples, heat is transferred directly from the bottom  728  to the cooling liquid supply  740 . Heat may also be transferred from the bottom  728 , through one or more heat transfer surfaces  736 , and then to the cooling liquid supply  740  that flows through channels  738 . The heated cooling liquid supply  740  is circulated to the outlet  732  and exits the top hat  722  as the cooling liquid return  742  (e.g., that is at a higher temperature than the cooling liquid supply  740 ). The cooling liquid return  742  is circulated back, e.g., to a source of the cooling liquid, to expel the heat (e.g., in a chiller, cooling tower, or other heat exchanger) from the return  742 . 
     In an example operation for making the server tray package  700 , the interposer  712 , substrate  704 , and motherboard  702  may be mounted together to form an assembly to which the data center electronic devices  714  and  716  may be mounted and connected (e.g., for power and communication). The thermal interface material  718  is then mounted or positioned on top of the data center electronic devices  714  and  716 . 
     Next, the base portion  706  (the stiffener ring  710 ) is mounted on the substrate  704  (in this example) to at least partially enclose the interposer  712  and data center electronic devices  714  and  716  within the volume  703 . In some examples, mechanical fasteners or adhesive may be used to connect the stiffener ring  710  to the substrate  704 . 
     Next, the top hat  722  is then mounted onto the stiffener ring  710  (and the thermal interface material  718 ) so that the bottom  728  is on top of the stiffener ring  710  and material  718 . In some aspects, mechanical fasteners or adhesive may be used to connect the top hat  722  to the stiffener ring  710 . Further, in some aspects, the top hat  722  may be mounted to the stiffener ring  710  on a component-by-component basis. For example, the bottom  728  may first be mounted to the stiffener ring  710  of the base portion  706 . Next, the sides  726  may be mounted to the bottom  728 . Next, the cap  724  may be mounted to the sides  726 . 
     A number of embodiments have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of what is described. For example, the steps of example operations of example methods and processes described herein may be performed in other orders, some steps may be removed, and other steps may be added. Accordingly, other embodiments are within the scope of the following claims.