Patent Publication Number: US-7903411-B2

Title: Cold plate stability

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 11/741,852 filed Apr. 30, 2007, the contents of which are incorporated by reference herein in their entirety. 
    
    
     BACKGROUND 
     The present disclosure relates generally to integrated circuit heat dissipation devices, and, in particular, to methods and apparatuses for cold plate stability. 
     As high performance computers increase in performance, which may be measured in floating-point operations per second (FLOPS) or millions of instructions per second (MIPS), the associated microprocessors within the computers typically increase in both speed and required electrical power. As manufacturers have sought to integrate multiple microprocessors or other components within a single package, such as a multi-chip module (MCM) or other multi-core technologies, the associated number of electrical connections for such packages has grown. In order to reduce package size, many manufacturers have turned from pin grid array (PGA) and ball grid array (BGA) interfaces to land grid array (LGA) interfaces. An LGA interface may use pads instead of pins or balls to connect to a printed wire board (PWB) through a socket or similar interface. LGAs may be preferred over PGAs or BGAs due to larger contact points and higher connection densities, allowing for higher clock frequencies and more power contacts. However, since power consumed is dissipated as heat, LGAs may produce more heat than PGAs and BGAs of comparable size. With the combined challenges of more numerous and powerful microprocessors in a given package, limits of air-cooling may be exceeded as performance demands continue to increase. Moreover, traditional cold plate assemblies may not meet mechanical constraints of modern packages, particularly in a server environment where multiple packages may be installed in a physically confined space. 
     Since it is desirable for performance and reliability to maintain a module&#39;s active metallurgy at a specified temperature, advanced heat transfer structures and methods are needed to maintain both thermal and structural stability. 
     SUMMARY 
     Embodiments of the invention include a cold plate assembly. The cold plate assembly includes a cold plate with at least two plumbing ports. The cold plate assembly further includes a spring plate assembly, which applies an actuation load to the cold plate. The spring plate assembly includes a spring plate and a spring pin moveable in a slot of the spring plate assembly to maintain the actuation load. The actuation load is configured to mechanically actuate the cold plate to a module. 
     Additional embodiments include a cold plate assembly that includes a cold plate with at least two plumbing ports and a spring plate assembly, which applies an actuation load to the cold plate. The cold plate includes a top component coupled to a bottom component and cooling fins brazed to at least one of the top component and the bottom component. The cooling fins provide a cooling fluid circulation path between the plumbing ports. The spring plate assembly includes at least one spring plate, at least one spring pin, and an actuation screw, the actuation screw adjustable to set the actuation load. The cold plate assembly further includes at least one load arm, which locks the spring plate assembly onto the cold plate via the at least one spring pin of the spring plate assembly and maintains the actuation load. 
     Other apparatuses, and/or systems according to embodiments will be or become apparent to one with skill in the art upon review of the following drawings and detailed description. It is intended that all such additional apparatuses and/or systems be included within this description, be within the scope of the present invention, and be protected by the accompanying claims. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other objects, features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a perspective view of a node with multiple quadrants of cold plate assemblies that are plumbed together in accordance with exemplary embodiments; 
         FIG. 2  is a perspective view of a quadrant of cold plate assemblies that are plumbed together in accordance with exemplary embodiments; 
         FIG. 3   a  is a perspective view of a cold plate assembly with load arms and a module subject to cooling in accordance with exemplary embodiments; 
         FIG. 3   b  is an exploded view of a cold plate assembly with load arms and a module subject to cooling in accordance with exemplary embodiments; 
         FIG. 4 . includes a top view and side cross sectional views of the structure of a cold plate assembly in accordance with exemplary embodiments; 
         FIG. 5  is a top cross sectional view of the structure of a channel and manifold for a cold plate assembly in accordance with exemplary embodiments; and 
         FIG. 6  is a flow diagram describing a process for providing cold plate stability in accordance with exemplary embodiments. 
     
    
    
     The detailed description explains the preferred embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Disclosed herein are apparatuses and methods for cold plate stability. While there are a wide variety of electronic packaging and interface options, such as pin grid array (PGA), ball grid array (BGA), land grid array (LGA), and hybrid LGA, a common issue exists in removing heat dissipated from modules utilizing these technologies. Greater module size, module density, and clock frequencies typically result in a greater production of heat. As a single module can contain multiple components, such as a multi-chip module (MCM) or multi-core module of microprocessors, memory, and the like, the heat dissipated from such a module can be substantial. Moreover, an LGA module (interfacing via pad connections) or a hybrid LGA module (interfacing via pad and solder connections) may require a large actuation load (e.g., about 60 grams per electrical connection point) to maintain electrical continuity between the module and a printed wire board (PWB) through which the module interfaces to other system components. In exemplary embodiments, the cold plate assembly disclosed herein provides both cooling and an actuation load for a variety of module designs, such as an LGA or hybrid LGA module, through an enhanced stability structure that supports fluid cooling and interconnections to additional cold plate assemblies. 
     Turning now to  FIG. 1 , a perspective view of a node  100  with multiple quadrants of cold plate assemblies  200  that are plumbed together is depicted in accordance with exemplary embodiments. In exemplary embodiments, the node  100  is a processing assembly including processing system components such as memory modules, busses, and microprocessor modules affixed to a printed wire board (PWB)  102 . The node  100  may be a subsystem of a larger system such as a mainframe computer. In exemplary embodiments, the PWB  102  supports coupling modules, such as hybrid LGA modules, to the PWB  102 . The PWB  102  may support multiple or mixed packaging and interfacing technologies. The node  100  may include multiple quadrants of cold plate assemblies  200  for cooling multiple modules. In exemplary embodiments, plumbing lines  104  route a cooling fluid, such as water, through each of the quadrants of cold plate assemblies  200 , providing a cooling fluid circulation path though the node  100 . While the configuration of cold plate assemblies depicted in  FIG. 1  includes four quadrants of cold plate assemblies  200 , the scope of the invention is not so limited. To the contrary, there may be any number of quadrants of cold plate assemblies  200 , or alternate plumbing schemes between cold plate assemblies. Moreover, any number of cold plate assemblies may be used, including a single cold plate assembly. 
     Turning now to  FIG. 2 , a perspective view of a quadrant of cold plate assemblies  200  that are plumbed together in accordance with exemplary embodiments is depicted. The quadrant of cold plate assemblies  200  includes four cold plates  202  interconnected via plumbing lines  104 . A spring plate assembly  204  is depicted atop each of the cold plates  202 . It will be understood by one skilled in the art that while one plumbing configuration is depicted in  FIG. 2 , many other configurations are possible to source and return a cooling fluid to each of the cold plates  202 . In exemplary embodiments, the plumbing lines  104  are made primarily of noncompliant (e.g., low flexibility) tubing to create a robust structure that can be brazed together between the cold plates  202  to reduce the possibility of leaks. Plumbing the cold plates  202  together may facilitate cooling of multiple modules in a substantially planar fashion. Further details of the cold plates  202  and the spring plate assemblies  204  are provided herein. 
     Turning now to  FIG. 3   a , a perspective view of a cold plate assembly  300  is depicted in accordance with exemplary embodiments. In exemplary embodiments, the cold plate assembly  300  includes a cold plate  202  and a spring plate assembly  204 . The cold plate  202  includes a top component  302  and a bottom component  304 . A cooling fluid circulation path, described in greater detail herein, may run internally through the cold plate  202  between plumbing ports  306 . In exemplary embodiments, the two plumbing ports  306  are located at diagonally opposing corners of the top component  302  of the cold plate  202 , providing inlet and outlet points for a cooling fluid to circulated through the cold plate  202 . While two plumbing ports  306  are depicted on the cold plate  202 , multiple plumbing ports  306  may be included in the cold plate  202  (e.g., multiple zones), providing inlet and outlet points on any surface of the cold plate  202 . Moreover, the plumbing ports  306  may be located at any position relative to each other, e.g., adjacent. To assist in alignment and placement of the components of the cold plate  202 , a guide marker may be placed at one or more location on the cold plate  202 , such as guide marker  308  on the bottom component  304 . In exemplary embodiments, the guide marker  308  is located near a plumbing port  306  to aid in orienting the top component relative  302  to the bottom component  304  when mating the top and bottom components  302  and  304 . The guide marker  308  may be, for example, a hole, a raised element, or a printed indicator. 
     In exemplary embodiments, the cold plate  202  is placed atop a module  310 , providing a heat transfer path to cool the module  310  for thermal stability of the module  310 . The module  310  may include a variety of electronic components such as one or more microprocessors, memory, busses, and the like. In exemplary embodiments, the module  310  is a multi-chip module (MCM) with multiple chip subcomponents encapsulated in a single package. While the module  310  is depicted as a single package, it will be understood that the module  310  may also include multiple mechanical subcomponents which may be separable from the module  310 , such as a lid, lateral supports, substrate material, and the like. The module  310  may utilize any packaging and interfacing technology known in the art, such as a PGA, BGA, LGA, or hybrid LGA module. The module  310  may make electrical contact with the PWB  102  via a socket  312 . Although the socket  312  obstructs a direct view of the module  310  in  FIG. 3   a , the distinction between the socket  312  and the module  310  is apparent in  FIG. 3   b . In exemplary embodiments, the socket  312  acts as an interface between the module  310  and the PWB  102 , and can vary in design based on the module technology. For example, the socket  312  may include two-sided spring or pad interfaces when the module  310  in an LGA, or one side of the socket  312  may include solder connections when the module  310  is a hybrid LGA. As the module  310  may require an actuation load to maintain electrical connections, the cold plate assembly  300  may further include one or more load arm  314  to hold the spring plate assembly  204  in place above the cold plate  202 . 
     While the cold plate assembly  300  is depicted with two load arms  314 , it will be understood that any number of load arms  314  with a variety of designs may be used within the scope of the invention (e.g., 1, 2, 4). For example, one or more of the load arms  314  could be designed as a post, a clip, or a hinge member. In exemplary embodiments, each load arm  314  is coupled to a hinge plate  316 . Each hinge plate  316  may be attached to the PWB  102  using any fastening method known in the art (e.g., through-hole fasteners). In exemplary embodiments, the coupling of the load arm  314  to the hinge plate  316  provides a pivot point such that the load arm  314  can pivot outwardly, thus simplifying placement and removal of the cold plate  202  and the spring plate assembly  204  above the module  310 . 
     In exemplary embodiments, the spring plate assembly  204  includes two spring plates  318  and an actuation screw  320 . Actuation may be provided by fixed travel of the actuation screw  320  though the spring plates  318 . While the exemplary spring plate assembly  204  includes a single actuation screw  320  and two spring plates  318 , it will be understood that the scope of the invention is not so limited. To the contrary, there may be multiple screws, or similar coupling means, and any number of spring plates, laminated or otherwise, within embodiments of the present invention. For example, in applications that require an increased actuation load, additional spring plates  318  can be added to the spring plate assembly  204 , while applications with a lower actuation load requirement may use a single spring plate  318 . The spring plate assembly  204  may have vertical slots  322  at either end of the spring plate assembly  204 . The vertical slots  322  allow for adjustment and travel of spring pins  324 . The spring pins  324  may apply a force at each end of the spring plates  318 . In exemplary embodiments, each spring pin  324  is located above an end of the spring plates  318 , providing an attachment point for each load arm  314 . 
     In exemplary embodiments, the module  310  is seated on the socket  312 , the cold plate  202  is placed on top of the module  310 , and the spring plate assembly  204  is placed on top of the cold plate  202 . An actuation load may be applied to the cold plate  202  via the spring plate assembly  204 . In exemplary embodiments, the actuation load is configured to mechanically actuate the cold plate  202  to the module  310 . The load arms  314  can be locked down onto the spring pins  324  of the spring plate assembly  204 , thus maintaining the actuation load on the cold plate  202 . The actuation screw  320  may be adjusted to increase or decrease the actuation load. Although a range of actuation load forces may be applied, the actuation load force achieved through locking the spring plate assembly  204  on the cold plate  202  may be about 200 to about 300 lbs. The actuation load may be adjusted depending on the number of connections required between the module  310  and the socket  312 . For example, if the module  310  is a hybrid LGA module, the required actuation load may be about 60 grams per electrical connection point. In exemplary embodiments, the actuation load maintains a thermal interface material gap thickness  326  of about 30 to about 50 microns between the bottom of the cold plate  202  and the top of the module  310 . Moreover, the actuation load may be adjusted to account for varying height differences between modules  310 , as different modules  310  are manufactured within a tolerance range, and the modules  310  may include chips or cores of varying heights. The actuation load may also be adjusted to account for additional forces imparted by plumbing lines, such as the plumbing lines  104  of  FIG. 2 , connected to the plumbing ports  306  when multiple cold plate assemblies are plumbed together, as depicted in the quadrant of cold plate assemblies  200  of  FIG. 2 . 
     Turning now to  FIG. 3   b , an exploded view of the cold plate assembly  300  is depicted in accordance with exemplary embodiments.  FIG. 3   b  provides an enhanced view of the cold plate  202  and the spring plate assembly  204  separated and raised above the module  310 , making the thermal interface material gap thickness  326  more apparent. In exemplary embodiments, a thermal interface material, such as thermal grease, is placed or applied in the thermal interface material gap thickness  326 , thus enhancing heat transfer between the cold plate  202  and the module  310 .  FIG. 3   b  further depicts the pivoting motion of the load arms  314  relative to the hinge plates  316 , as the load arms  314  are pivoted outwardly to ease placement and removal of the cold plate  202  and the spring plate assembly  204  on the module  310 . 
     Turning now to  FIG. 4 , a top view and side cross sectional views of the structure of the cold plate  202  and the spring plate assembly  204  are depicted in accordance with exemplary embodiments. Sections A-A and B-B provide side cross-sectional views of the cold plate  202  and the spring plate assembly  204 . In section A-A of  FIG. 4 , a cooling fluid reservoir  402  can be seen as gap between the top and bottom components  302  and  304  of the cooling plate  202 . In exemplary embodiments, the plumbing ports  306  depicted in section A-A, are brazed to the bottom component  304  of the cold plate  202 , providing structural stability while reducing the risk of leaks. The plumbing ports  306  may also be brazed or otherwise coupled to the top component  302  of the cold plate  202 . Section A-A further depicts other details previously described, such as the structural relationship between components of the spring plate assembly  204 . 
     Section B-B of  FIG. 4  depicts cooling fins  404  that run through the cooling fluid reservoir  402 . In exemplary embodiments, the cooling fins  404  are integral with the bottom component  304  of the cold plate  202 , as depicted in detail C. The dimensioning depicted on various views in  FIG. 4  is provided merely for purposes of example, and should not be viewed as limiting in scope, as the various components depicted can be scaled based upon a particular application (e.g., various module sizes, actuation load requirements, cooling fluid flow requirements, and the like). In exemplary embodiments, structural stability of the cold plate  202  is achieved through brazing the cooling fins  404  to the top component  302  of the cold plate  202 . Brazing the cooling fins  404  may enable the cold plate  202  to withstand a high actuation load associated with various module designs, such as a hybrid LGA (e.g., actuation load of about 200 to about 300 lbs.), and thus providing cold plate stability. Brazing the cooling fins  404  to the top component  302  of the cold plate  202  may further enable center point actuation, providing a substantially uniform a thermal interface material gap thickness  326 . Brazing the cooling fins  404  to the top component  302  of the cold plate  202  may further contribute to a low deformation rate of the cold plate  202  and the cold plate assembly  300 , providing substantially uniform deformation, and thus making coupling of multiple assemblies possible, such as the quadrant of cold plate assemblies  200  of  FIGS. 1 and 2 . Moreover, brazing may also provide enhance durability and resistance to corrosive effects associated with long-term contact with a cooling fluid, such as water. 
     Turning now to  FIG. 5 , a top cross sectional view of the structure of a channel and manifold for a cold plate  202  is depicted in accordance with exemplary embodiments. Section D-D of  FIG. 5  illustrates an exemplary cooling fluid circulation path  502  through the cooling fluid reservoir  402  and the cooling fins  404 . The cooling fluid reservoir  402  may include all gap space in the bottom component  304  of the cooling plate  202 , not otherwise occupied by the cooling fins  404  or the plumbing ports  306 . In exemplary embodiments, the direction of flow and flow rate through the cooling fluid circulation path  502  can be adjusted by varying the inlet and outlet pressure at the plumbing ports  306 . As previously described, the approximate location of the plumbing ports  306  may be identified as the corner nearest to the guide markers  308 . 
     Turing now to  FIG. 6 , a flow diagram describing a process  600  for providing cold plate stability is depicted in accordance with exemplary embodiments. For ease of explanation, the process  600  is described in reference to the cold plate assembly  300 , with the cold plate  202  and spring plate assembly  204  as depicted in  FIGS. 2-5 ; however, the process  600  is not so limited to the depicted embodiments. In exemplary embodiments, the cold plate  202  includes at least two plumbing ports  306 , providing an inlet and an outlet for a cooling fluid. The cold plate  202  may further include the top component  302  and the bottom component  304 . At block  602 , the cold plate  202  includes cooling fins  404  internal to the cold plate  202 , the cooling fins  404  brazed for providing internal stability for the cold plate  202 . The cooling fins  404  may be integral to the top or bottom component  302  and  304  of the cold plate  202 , with brazing applied between the cooling fins  404  and the non-integral component, e.g., the cooling fins  404  may be cast as features of the bottom component  304  and brazed to the top component  302  for enhanced internal structural stability of the cold plate  202 . In exemplary embodiments, the cooling fins  404  provide a cooling fluid circulation path  502  between the at least two plumbing ports  306 . The cooling fluid reservoir  402  may also be part of the cooling fluid circulation path through the bottom component  304  of the cold plate  202 . 
     At block  604 , the cold plate  202  is placed in contact with the module  310 . As previously described, the module  310  may utilize any packaging and interfacing technology known in the art, such as a PGA, BGA, LGA or hybrid LGA module. In exemplary embodiments, the module  310  interfaces with the socket  312 , which is positioned on the PWB  102 . A thermal interface material, such as thermal grease, may be applied to the top of the module  310  or the bottom of the cold plate  202  to enhance heat transfer through the thermal interface material gap thickness  326 . 
     At block  606 , an actuation load is applied to the cold plate  202  via the spring plate assembly  204 . In exemplary embodiments, the spring plate assembly  204  includes at least one spring plate  318  and actuation screw  320 , the actuation screw  320  adjustable to set the actuation load. The actuation load may also be influenced by the spring pins  324  and the movement of the spring pins  324  within the vertical slots  322 . In exemplary embodiments, the actuation load is centrally applied relative to the cold plate  202  with internally brazed cooling fins, establishing a substantially uniform thermal interface material gap thickness  326 . 
     At block  608 , the spring plate assembly  204  is secured with at least one load arm  314 . In exemplary embodiments, the at least one load arm  314  is secured to the PWB  102  via a hinge plate  316 . The secured spring plate assembly  204  translates the actuation load to the module  310  via the cold plate  202 , providing external stability for the cold plate  202 . The process  600  may further include connecting a plumbing line  104  between one of the at least two plumbing ports  306  and a plumbing port  306  of a second cold plate  202 , forming an interconnected assembly, such as that depicted in the quadrant of cold plate assemblies  200  of  FIG. 2 . 
     Technical effects of exemplary embodiments of the invention may include applying an actuation load to maintain electrically connectivity to a module, such as a hybrid LGA module, while providing fluid cooling. Further technical effects include support for multiple assemblies plumbed together, providing a scaleable solution for varying application scope. The use of brazing on internal cooling fins within a cold plate may provide substantially low and uniform deformation through enhanced structural stability, while enabling the cold plate to withstand high actuation loads. 
     While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. Moreover, the use of the terms first, second, etc. do not denote any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another. Furthermore, the use of the terms a, an, etc. do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item