Patent Publication Number: US-2005128705-A1

Title: Composite cold plate assembly

Description:
FIELD OF THE INVENTION  
      The present invention relates in general to cooling of electronic systems. In particular, the present invention relates to a cooling fluid distribution apparatus for an electronic system having two or more fluid cooled electronic modules.  
     BACKGROUND OF THE INVENTION  
      As is known, operating electronic devices produce heat. This heat should be removed from the devices in order to maintain device junction temperatures within desirable limits: failure to remove the heat thus produced results in increased device temperatures, potentially leading to thermal runaway conditions. Several trends in the electronics industry have combined to increase the importance of thermal management, including heat removal for electronic devices, including technologies where thermal management has traditionally been less of a concern, such as CMOS. In particular, the need for faster and more densely packed circuits has had a direct impact on the importance of thermal management. First, power dissipation, and therefore heat production, increases as the device operating frequencies increase. Second, increased operating frequencies may be possible at lower device junction temperatures. Finally, as more and more devices are packed onto a single chip, power density (Watts/cm 2 ) increases, resulting in the need to remove more power from a given size chip or module. These trends have combined to create applications where it is no longer desirable to remove the heat from modern devices solely by traditional air cooling methods, such as by using traditional air cooled heat sinks.  
      As is also known, electronic devices are more effectively cooled through the use of a cooling fluid, such as chilled water or a refrigerant. For example, electronic devices may be cooled through the use of a cold plate in thermal contact with the electronic devices. Chilled water (or other cooling fluid) is circulated through the cold plate, where heat is transferred from the electronic devices to the cooling fluid. The cooling fluid then circulates through an external heat exchanger or chiller, where the accumulated heat is transferred from the cooling fluid. Fluid flow paths are provided connecting the cold plates to each other and to the external heat exchanger or chiller. These fluid flow paths are constructed of conduits such as, for example, copper tubing, which are typically joined to cold plates by one or more mechanical connections.  
      Modern electronic systems often include many electronic devices in need of the enhanced cooling provided by such a fluid based cooling system. In such systems, where two or more electronic devices are located in close physical proximity, it is frequently desirable to manifold or plumb together the cold plates associated with the electronic devices into a multi-cold plate fluid distribution assembly. Such an assembly may be constructed in a way that reduces or minimizes the number of cooling fluid inlets to the assembly, and the number of cooling fluid outlets from the assembly. Reducing or minimizing the number of cooling fluid inlets and outlets also minimizes the number of mechanical conduit connections required to provide cooling fluid to all cold plates within the assembly. For example, a group of four cold plates, plumbed individually, requires eight connections: one inlet and one outlet per cold plate. By plumbing the four cold plates into a single assembly, the eight connections may be reduced, or minimized to two connections (one assembly inlet, one assembly outlet). Since mechanical conduit connections are often a point of cooling system failure, it is desirable to reduce or minimize the number of mechanical conduit connections by manifolding multiple cold plates into a multi-cold plate fluid distribution assembly, thereby improving system reliability by reducing the number of system points of failure.  
      A multi-cold plate fluid distribution assembly constructed using known methods and materials, however, may not provide sufficient flexibility to maintain adequate thermal contact with all associated electronic devices. Manufacturing and assembly tolerances in electronic devices, boards, cold plates, etc., may result in variations in component dimensions and alignment, requiring some degree of flexibility in the multi-cold plate fluid distribution assembly in order to simultaneously maintain good thermal contact with all associated electronic devices. For example, manufacturing and process tolerances may cause similar types of modules, such as processor modules, to vary in height by several millimeters. Furthermore, it may be desirable to manifold cold plates associated with different types of electronic devices, where relative tolerances may result in greater height differences, alignment differences, etc. Constructing a multi-cold plate fluid distribution assembly using known materials and methods, such as using copper or other metal tubing soldered or brazed to several metal cold plates, results in an assembly that may lack sufficient flexibility to maintain good thermal contact in the presence of normal manufacturing and assembly process variations.  
      Alternatively, known materials and methods may be used to create a multi-cold plate fluid distribution assembly having sufficient flexibility but which lacks the reliability improvements associated with a reduced number of mechanical conduit connections. For example, a number of metal cold plates may be plumbed together using flexible tubing, such as plastic tubing. Since plastic tubing cannot be soldered, brazed, or otherwise reliably and permanently joined to a metal cold plate, a mechanical connection is required between the plastic tubing and each inlet and outlet of each cold plate. As previously noted, increasing the number of mechanical conduit connections increases the potential points of failure in the cooling distribution assembly. Thus, known materials and methods may provide a multi-cold plate fluid distribution assembly that is sufficiently flexible to maintain good thermal contact with associated electronic devices in the presence of normal manufacturing and assembly process variations, however such flexibility is obtained at the expense of the reliability improvement that served as motivation for creating the multi-cold plate fluid distribution assembly.  
      For the foregoing reasons, therefore, there is a need in the art for a multi-cold plate fluid distribution assembly that is simultaneously capable of providing a reliability benefit by reducing mechanical conduit connections, while also providing sufficient assembly flexibility to maintain good thermal contact between assembly cold plates and their associated electronic devices in the presence of normal manufacturing and assembly process tolerances.  
     SUMMARY  
      The shortcomings of the prior art are overcome, and additional advantages realized, through the provision of a multi-cold plate fluid distribution assembly utilizing a composite cold plate structure.  
      In one aspect, the present invention involves a cooling fluid distribution assembly for a plurality (i.e., two or more) of electronic modules, the assembly including a plurality of cold plates and a plurality of flexible, nonmetallic fluid distribution conduits. Each of the plurality of cold plates is associated with one of the plurality of electronic modules, and each cold plate includes: a high thermal conductivity cold plate base; a nonmetallic cold plate cover having at least one cover fluid inlet and at least one cover fluid outlet, the cold plate cover being sealably affixed to the cold plate base; and a fluid circulation structure for directing fluid flow from the at least one cover fluid inlet to the at least one cover fluid outlet. The plurality of flexible, nonmetallic fluid distribution conduits are bonded to, and in fluid communication with, the cover fluid inlets and cover fluid outlets. The cold plates and conduits thus form an assembly for distributing a cooling fluid to the plurality of electronic modules, the assembly having at least one assembly fluid inlet and at least one assembly fluid outlet, the assembly further having connectors only at the assembly fluid inlet(s) and assembly fluid outlet(s).  
      In a further aspect, the present invention involves an electronic module assembly capable of being cooled by a fluid, the assembly including a plurality of electronic module substrate assemblies, a plurality of cold plates, and a plurality of flexible, nonmetallic fluid distribution conduits. Each of the plurality of electronic module substrate assemblies includes a substrate and at least one electronic device electrically connected to the substrate. Each of the plurality of cold plates is associated with one of the plurality of electronic modules, and each cold plate includes: a high thermal conductivity cold plate base, the cold plate base also providing a high thermal conductivity module cap; a nonmetallic cold plate cover having at least one cover fluid inlet and at least one cover fluid outlet, the cold plate cover being sealably affixed to the cold plate base; and a fluid circulation structure for directing fluid flow from the at least one cover fluid inlet to the at least one cover fluid outlet. The plurality of flexible, nonmetallic fluid distribution conduits are bonded to, and in fluid communication with, the cover fluid inlets and cover fluid outlets. The cold plates and conduits thus form an assembly for distributing a cooling fluid to the plurality of electronic modules, the assembly having at least one assembly fluid inlet and at least one assembly fluid outlet, the assembly further having connectors only at the assembly fluid inlet(s) and assembly fluid outlet(s).  
      It is therefore an object of the present invention to provide a a multi-cold plate fluid distribution assembly utilizing a composite cold plate structure.  
      It is a further object of the present invention to provide a multi-cold plate fluid distribution assembly that is simultaneously capable of providing a reliability benefit by reducing mechanical conduit connections, while also providing sufficient assembly flexibility to maintain good thermal contact between assembly cold plates and their associated electronic devices in the presence of normal manufacturing and assembly process tolerances.  
      The recitation herein of a list of desirable objects which are met by various embodiments of the present invention is not meant to imply or suggest that any or all of these objects are present as essential features, either individually or collectively, in the most general embodiment of the present invention or in any of its more specific embodiments.  
      Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention. For a better understanding of the invention with advantages and features, refer to the description and to the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of practice, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings in which:  
       FIG. 1  illustrates an isometric view of a cooling fluid distribution assembly per an embodiment of the present invention;  
       FIG. 2  illustrates an exploded view of a cold plate assembly per an embodiment of the present invention;  
       FIG. 3A  illustrates a plan view of a cold plate cover and fluid circulation structure per an embodiment of the present invention;  
       FIG. 3B  illustrates a plan view of a cold plate cover and fluid circulation structure per an embodiment of the present invention;  
       FIG. 4A  illustrates a plan view of a series fluid distribution assembly per an embodiment of the present invention;  
       FIG. 4B  illustrates a plan view of a parallel fluid distribution assembly per an embodiment of the present invention;  
       FIG. 5A  illustrates a sectional view of a module assembly plus cold plate assembly per an embodiment of the present invention;  
       FIG. 5B  illustrates a sectional view of a module assembly plus cold plate assembly per an embodiment of the present invention; and  
       FIG. 6  illustrates a sectional view of an integrated module and cold plate assembly per an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      In accordance with preferred embodiments of the present invention, a multi-cold plate fluid distribution assembly utilizing a composite cold plate structure is disclosed herein.  
       FIG. 1  illustrates a multi-cold plate fluid distribution assembly, per an embodiment of the present invention. The assembly of  FIG. 1  is exemplary only; other assembly configurations are envisioned within the spirit and scope of the present invention. As illustrated in  FIG. 1 , a fluid distribution assembly of the present invention includes a plurality of cold plates  110 : in the exemplary embodiment of  FIG. 1 , assembly  100  includes four cold plates  110 . The teachings of the present invention are applicable to any system having two or more electronic modules: as used herein, therefore, the term plurality equates to a quantity of two or more. Assembly  100  also includes a plurality of flexible, nonmetallic conduits  140 . Conduits  140  are sealably affixed to cold plates  110 , thereby creating fluid distribution assembly  100 . In the embodiment illustrated in  FIG. 1 , assembly  100  includes one assembly fluid inlet  145 A, and one assembly fluid outlet  145 B. Each cold plate  110  is assembled using a plurality of mechanical fasteners  111 , such as threaded bolts, screws, or the like. At least four fasteners  111  are required, one per cold plate comer. Additional fasteners  111  may be used in larger cold plate designs, such as the 8 fasteners  111  per cold plate illustrated in  FIG. 1 .  
       FIG. 2  illustrates further details of a cold plate  110 , such as cold plates  110  illustrated in assembly  100  of  FIG. 1 . Cold plate  110  includes two primary components: base  130 , and cover  112 . Base  130  provides a high thermal conductivity connection to an electronic module. In preferred embodiments of the present invention, base  130  is composed of a high thermal conductivity metal, such as, for example, copper, aluminum, etc. Cover  112  includes two fluid connections  114 ; one connection  114  providing a fluid inlet, the other connection  114  providing a fluid outlet. In preferred embodiments of the present invention, cover  112  is composed of a material that is capable of being sealably and permanently bonded to flexible, nonmetallic conduits  140 . In preferred embodiments of the present invention, conduits  140  and cover  112  are composed of plastic, and are bonded by any of several methods known in the art such as: chemical bonding, glue, epoxy, etc. Cover  112  is formed using processes known in the art, such as a molding process or the like. Unlike conduits  140 , cover  112  is preferably rigid. Cover  112  includes a plurality of through holes  122 : the embodiment illustrated in  FIG. 2  depicts four holes  122 , one per comer. Base  130  includes a plurality of holes  120 , matching holes  122  in number and location. Holes  120  may be either through holes or threaded holes. In preferred embodiments of the present invention, cover  112  and base  130  are mechanically joined using connectors as known in the art, such as threaded bolts; a fluid tight seal is obtained using methods known in the art, such as a gasket, O-ring, or the like (see  FIG. 5  and associated description).  
      Cold plate structures of the present invention further include an internal fluid circulation structure to direct the flow of cooling fluid from the cover inlet, over a region of base  130  nearest the electronic device or devices from which heat is to be removed, and finally to the cover outlet. The internal fluid circulation structure may be formed entirely within cover  112 , or entirely within base  130 , or partially within cover  112  and partially within base  130 . In preferred embodiments of the present invention, an internal fluid circulation structure is formed partially within cover  112  and partially within base  130 .  
       FIGS. 2 and 3  illustrate preferred embodiments of the base and cover circulation components, respectively.  FIG. 2  illustrates a set of high thermal conductivity fins  132 , which form a plurality of fluid channels disposed between fins  132 . Fins  132  are mechanically and thermally connected to base  130 , and are ideally formed of a high thermal conductivity metal such as, for example, copper or aluminum. A variety of methods may be used to form base  130  with fins  132 . For example, a solid block of copper may be bonded to base  130 , fins  132  may then be formed using an operation as known in the art, such as sawing or milling, for example.  
      FIGS.  3  illustrate two embodiments of cover circulation components in relation to fluid channels formed by fins  132 .  FIG. 3A  illustrates a plenum arrangement creating parallel flow through channels formed by fins  132 , and  FIG. 3B  illustrates an end manifold subsection arrangement creating serial, serpentine flow through channels formed by fins  132 . Both  FIGS. 3A and 3B  depict a top view of a cold plate assembly such as assembly  110  of  FIG. 1 , without fasteners  111 . Fluid circulation components are therefore illustrated as hidden features: cover fluid circulation components are located on the underside of cover  112 , and base fluid circulation components (i.e., fins  132 ) are located on the upper portion of base  130 .  
      Cover  112  of the embodiment illustrated in  FIG. 3A  includes a cover fluid inlet  114 A, and a cover fluid outlet  114 B. Cover  112  further includes an inlet plenum or manifold  116 A and an outlet plenum or manifold  116 B, both located on the underside of cover  112 . Each plenum  116  consists of a vertical wall (when assembly  110  is viewed from the side), extending from cover  112  to the upper surface of base  130 , preferably formed during the same molding process used to form cover  112 . Inlet plenum  116 A provides a fluid flow path from inlet  114 A to channels formed by fins  132 : fluid is directed in parallel to all channels formed by fins  132  from inlet  114 A. In similar fashion, outlet plenum  116 B provides a fluid flow path from channels formed by fins  132  to cover outlet  114 B: fluid is collected in parallel from all channels formed by fins  132  and directed to outlet  114 B. During assembly of cold plate  100 , inlet plenum  116 A and outlet plenum  116 B sealably mate with fins  132  located on base  130 , thereby forming a closed fluid path from inlet  114 A to outlet  114 B. In alternative embodiments of the present invention, cover  112  may further include gasket material in the region located directly above fins  132 , and at the base of plenum walls  116  (not illustrated).  
       FIG. 3B  illustrates fluid flow components of an assembly  110  per another embodiment of the present invention. Cover conduits  317  and manifold subsections  318  are located on the underside of cover  112 . When cover  112  is assembled onto base  130 , cover components  317  and  318  sealably mate with base fins  132  to form a closed fluid flow path from inlet  114 A to outlet  114 B. Each cover component  317  and  318  consists of a vertical wall (when assembly  110  is viewed from the side), extending from cover  112  to the upper surface of base  130 , preferably formed during the same molding process used to form cover  112 . Conduits  317  include two sections: a curved conduit section surrounding a portion of inlets/outlets  114 , and a substantially straight conduit section connecting the curved conduit section and one of more channels formed by fins  132 . In the embodiment illustrated in  FIG. 3B , cover conduits  317  and manifold subsections  318  direct fluid flow from inlet  114 A, through channels formed by fins  132 , to outlet  114 B. As illustrated in  FIG. 3B , one end of inlet conduit  317 A is in fluid flow communication with inlet  114 A, and the opposing end of conduit  317 A is in fluid flow communication with one or more of channels formed by fins  132 . Conduit  317 A thus directs fluid flow from inlet  114 A to one or more (but not all) channels formed by fins  132 . Manifold subsections  318  place one end of one or more channels formed by fins  132  in fluid communication with an adjacent end of an equal number of channels, thereby causing fluid flow in the second set of channels in a direction opposed to the flow of fluid through the first set of channels. Subsequent manifold subsections  318  provide a similar function, creating a serial serpentine flow through channels formed by fins  132 . As illustrated in  FIG. 3B , one end of outlet conduit  317 B is in fluid flow communication with outlet  114 B, and the opposing end of conduit  317 B is in fluid flow communication with one or more of channels formed by fins  132 . When the cooling fluid reaches the last set of channels formed by fins  132 , the fluid flows into outlet conduit  317 B, then to cover outlet  114 B. In alternative embodiments of the present invention, cover  112  may further include gasket material in the region located directly above fins  132 , and at the base of cover components  317  and  318  (not illustrated).  
       FIGS. 1 and 4  illustrate a variety of embodiments, each depicting an alternative structure for connecting the cold plates and flexible conduits. For example,  FIG. 4A  illustrates an embodiment of the present invention providing serial fluid flow among cold plates  110 . In the embodiment of  FIG. 4A , one cooling assembly inlet  445 A is provided by one of a plurality of conduits  440 : this conduit  440  is in fluid flow communication with a cover inlet of a first cold plate  110 . Another conduit  440  provides a fluid flow connection from the outlet of the first cold plate  110  to the inlet of a second cold plate  110 , etc. In this manner, fluid flows from assembly inlet  445 A, serially from one cold plate to another, then to assembly fluid outlet  445 B. Also for example,  FIG. 4B  illustrates an embodiment of the present invention providing parallel fluid flow among cold plates  110 . In the embodiment of  FIG. 4B , one cooling assembly inlet  446 A is provided by one of two conduits  441 : this inlet conduit is in fluid flow communication with a cover inlet of each cold plate  110  within assembly  401 .  FIG. 4B  also illustrates a single assembly outlet  446 B provided by the other conduit  441 : this outlet conduit is in fluid flow communication with a cover outlet of each cold plate  110  within assembly  401 . In assembly  401 , therefore, fluid flows into the assembly through assembly inlet  446 A, then in parallel to the cover inlet of all cold plates  110  within the assembly, through each cold plate  110  to its corresponding cover outlet, through outlet conduit  441  and finally to assembly outlet  446 B.  
      A further alternative is illustrated in  FIG. 1 , where a combination series and parallel flow is achieved by connecting assembly inlet  145 A to cover inlets of two cold plates  110 . Flexible conduits  140  then connect the cover outlets of the first two cold plates with cover inlets of the remaining two cold plates. A final conduit  140  connects the cover outlets of the last two cold plates to assembly outlet  145 B. In embodiments of the present invention having a different number of cold plates  110 , a variety of configurations may be achievable in a combination series and parallel flow arrangement. In general, combination series and parallel flow is achieved by first dividing the cold plates into a plurality of groups, each group having a plurality of cold plates. Conduits are arranged to provide parallel fluid flow to and from all cold plates within a group, and serial flow between groups.  
      While the conduit embodiments of  FIGS. 1 and 4  are illustrated in connection with the cold plate embodiments of  FIGS. 1 through 3 , each of the conduit embodiments are also combinable with alternative embodiments of cold plates and cold plate/module assemblies, such as the embodiments illustrated in  FIGS. 5A, 5B , and  6 .  
       FIGS. 5A, 5B , and  6  illustrate various embodiments of electronic module plus cold plate assemblies of the present invention.  FIGS. 5A, 5B , and  6  each depict a sectional view of a module plus cold plate assembly, viewed along line A-A of the cold plate assembly depicted in  FIG. 3A . These views are exemplary only: the assembly embodiments of  FIGS. 5A, 5B , and  6  are also combinable with other cover embodiments, such as the serial flow embodiment depicted in  FIG. 3B .  
       FIG. 5A  illustrates further details of a cold plate assembly in relation to a module assembly, per an embodiment of the present invention. Assembly  500  includes cold plate assembly  110  and module assembly  550 . Module assembly  550  includes substrate  552 , to which electronic devices such as one or more semiconductor chips  554 , and one or more passive devices such as capacitor  555  are electrically connected. In preferred embodiments of the present invention, semiconductor chips  554  are connected using controlled collapse chip connections (C 4   s ) or similar flip-chip mounting technology, thereby enabling module cap  557  to be in thermal contact with most of the chip backside area via thermal material  556 . A thermal path between chips  554  and cold plate  110  is thus provided by thermal material  556  and module cap  557 : cap  557  is therefore formed of a material having high thermal conductivity. Thermal material  556  is a thermal grease, paste, or oil, as known in the art. In preferred embodiments of the present invention, cap  557  is formed of copper, however other materials as known in the art may be used, such as aluminum, alumina, aluminum nitride, ceramic, etc. Cap  557  is connected to substrate  552  by any of a variety of methods as known in the art, such as epoxy, mechanical fasteners (not shown), etc.  
      As previously discussed, cold plate  110  is comprised of a high thermal conductivity base  130  and a cover  112 . In the embodiment of  FIG. 5A , module cap  557  is substantially the same size and shape as base  130  and cover  112  (when viewed from the top, as in  FIG. 3A ). In this embodiment, fasteners  111  (not shown in  FIG. 5A ) are used to fasten cover  112 , base  130 , and cap  557  together. As illustrated in  FIG. 5A , base  130  and cover  112  include a plurality of holes  120  and  122 , respectively, through which a threaded bolt or other fastening device is used to mechanically fasten cover  112  and base  130  to module cap  557 . In the embodiment of  FIG. 5A , cap  557  includes a plurality of holes  523 , one hole  523  associated with and located below each hole  120 . In preferred embodiments, hole  523  is threaded. A gasket or O-ring  126  is provided to prevent cooling fluid leakage. In the embodiment illustrated in  FIG. 5A , O-ring  126  is seated in a recessed area such as groove  124  of cover  112 . An internal fluid circulation structure is provided by inlet  114 A, inlet plenum  116 A, channels formed by high thermal conductivity fins  132 , outlet plenum  116 B, and outlet  114 B.  
       FIG. 5B  depicts an alternative embodiment of the present invention, in which a cold plate is attached to a module having a module cap that does not extend to the edges of the cold plate. Assembly  501  includes cold plate  110  and module  551 . Cold plate  110  is similar to cold plate  110  illustrated in  FIG. 5A , except with respect to holes  120 . As in the embodiment of  FIG. 5A , module  551  includes substrate  552 , one or more semiconductor chips  554 , one or more passive devices such as capacitor  555 , and thermal material  556  between chips  554  and a module cap. Materials and assembly methods are also as described with respect to the embodiment of  FIG. 5A . Unlike the embodiment of  FIG. 5A , however, module  551  includes a module cap  560  that does not extend to the edges of cold plate  110 . In the embodiment of  FIG. 5B , therefore, holes  120  in base  130  are preferably threaded, and are used in conjunction with fasteners  111  (not shown) to mechanically fasten cover  112  to base  130 . In the embodiment depicted in  FIG. 5B , base  130  is substantially the same thickness throughout. In alternative embodiments, base  130  is thicker in the edge regions around holes  120 , thereby increasing the thread count within holes  120 . The thickness of base  130  is increased in the edge regions either by maintaining a flat upper surface of base  130  and extending a lower surface of base  130  in the edge regions, by maintaining a flat lower surface of base  130  and extending an upper surface of base  130  in the edge regions, or by extending both upper and lower surfaces of base  130  in the edge regions. In embodiments where an upper surface of base  130  is extended in the edge regions, cover  112  is reduced in thickness by a corresponding amount in the edge region above the extended upper surface of base  130 . As in the embodiment of  FIG. 5A , a gasket or O-ring  126  is provided to prevent cooling fluid leakage. In the embodiment illustrated in  FIG. 5B , O-ring  126  is seated in a recessed area such as groove  124  of cover  112 . An internal fluid circulation structure is provided by inlet  114 A, inlet plenum  116 A, channels formed by high thermal conductivity fins  132 , outlet plenum  116 B, and outlet  114 B.  
      As illustrated in  FIG. 5B , assembly  501  includes cold plate assembly  110  in thermal contact with module assembly  551 , using bonding material  558 . In particular, a lower surface of cold plate base  130  is bonded to an upper surface of cap  560 . In preferred embodiments of the present invention, bonding material  558  provides a mechanical bond and introduces minimal thermal resistance into the thermal path from chips  554  to a cooling fluid within cold plate  110 . In preferred embodiments of the present invention, bonding material  558  is a thermally enhanced epoxy as known in the art.  
      The embodiments depicted in  FIGS. 5A and 5B  are advantageous in circumstances where cold plates  110  are used in connection with existing modules, such as modules  550  or  551 . In particular, the embodiment of  FIG. 5B  provides the ability to attach cold plate assembly  110  to an upper surface of any module having an area that is smaller than the area of cold plate  110 , without requiring a matching module cap such as cap  557  of  FIG. 5A . In some circumstances, however, it may be desirable to reduce the thermal path between semiconductor chips, such as chips  554 , and a cooling fluid. In applications where a lower resistance thermal path is desirable, and where sufficient design flexibility exists to accommodate alternative module designs, a lower resistance thermal path is achievable by integrating cold plate  110  and module  550 . One example of a lower resistance thermal path embodiment is illustrated in  FIG. 6 .  
       FIG. 6  illustrates an exemplary embodiment of an assembly  600  having a lower resistance thermal path from chips  654  to a cooling fluid, per one or more embodiments of the present invention. Assembly  600  includes cold plate cover  112 , as previously discussed. Cold plate cover  112  includes inlet  114 A, inlet plenum  116 A, outlet plenum  116 B, outlet  114 B, O-ring  126  seated in recess  124 , and mounting holes  122 . Two components of assembly  500  are integrated into a single component in assembly  600 : module cap  557  and cold plate base  130  are replaced in assembly  600  by integrated cold plate base and module cap  630  (hereinafter, integrated base-cap). Integrated base-cap  630  is constructed of a high thermal conductivity material, such as, for example, copper or aluminum. Integrating cap  557  and base  130  eliminates bonding material  558  of  FIG. 5B  and its associated thermal resistance, as well as the thermal resistance associated with the thermal interfaces between base  130  and module cap  557  or cap  560 . Thus, the embodiment of  FIG. 6  provides a thermal path from chip to cooling fluid having lower thermal resistance than the embodiments of  FIG. 5 , assuming that integrated base-cap  630  is constructed of a material having similar thermal properties to those of caps  557  or  560 , and base  130  used in the embodiments of  FIG. 5 . As illustrated in  FIG. 6 , integrated base-cap includes holes  620  aligned with cover holes  122 : in preferred embodiments of the present invention, cover  112  is mechanically fastened to integrated base-cap  630  using threaded bolts or other fasteners as known in the art, through aligned holes  122  and  620 . In preferred embodiments of the present invention, base holes  620  are threaded. As discussed with respect to the embodiment of  FIG. 5B , base  630  may be increased in thickness in the edge regions around holes  620 , increasing the thread count within holes  620 . Integrated base-cap also provides channels formed by high conductivity fins  632 , similar in function, materials, and construction techniques to channels formed by fins  132  of the embodiments illustrated in  FIGS. 1 through 5 .  
      While the invention has been described in detail herein in accord with certain preferred embodiments thereof, many modifications and changes therein may be effected by those skilled in the art. Accordingly, it is intended by the appended claims to cover all such modifications and changes as fall within the true spirit and scope of the invention.