Abstract:
A system and method for cooling individual electronic components utilizes individual manifolds to create individual flows of a negatively pressurized cooling fluid. This permits components with significantly different cooling loads to be located immediately adjacent each other on a circuit board, but without loss of space and computation time efficiencies, because cooling the components individually avoids heat generated by each component from adversely affecting the performance of the cooling system for adjacent components. A heat sink can be coupled to the components for increased heat transfer, and a preferred design of heat sink both dissipates heat and directs the flow of the fluid in an optimum manner.

Description:
TECHNICAL FIELD 
     This invention is concerned with the cooling of electronic components, especially high performance components that generate significant amounts of heat. 
     BACKGROUND 
     Modern high performance computers, commonly known as supercomputers, rely on components that generate amounts of heat that would, absent a cooling system, degrade the performance of the components. Thus, it is common for supercomputers to have dedicated fluid (gas or liquid) cooling systems. 
     As the far less powerful personal computers increase in capability, they also are beginning to rely on components that generate amounts of heat that must be cooled with more than the simple convection air venting they have used in the past. Common approaches include the use of heat sinks to dissipate the generated heat more efficiently, and fans located immediately adjacent the hottest components (typically the microprocessors). 
     In any cooled computer system, cooling system design must take into account all the sources of heat under maximum load conditions, in accordance with accepted engineering principles. In simpler designs, all sources of heat are treated the same regardless of location, and their individual cooling needs are simply summed together to determine the total system need. 
     In some designs, the location of the components generating the greatest amounts of heat are modified to accommodate a more efficient cooling system. An example is shown in U.S. Pat. No. 5,926,367 (Gutierrez et al.). In this design, the power supply, typically a major source of heat, is physically located within a cooling air plenum (or the housing of the supply is modified in shape and size to become such a plenum). The microprocessors are mounted to the outside of the plenum and either the heat they generate is conducted directly into the plenum by the conductive material of the plenum wall, or heat sinks within the plenum at the locations of the microprocessors conduct the heat into the plenum. A fan blows or pulls air through the plenum. 
     DISCLOSURE OF INVENTION 
     The invention is a system and method for cooling a plurality of electronic components, comprising a supply of cooling fluid and a plurality of individual fluid supply manifolds. Each supply manifold directs a portion of the fluid, which flows under negative pressure, into thermal contact with its respective electronic component. 
     In the most preferred embodiment, a heat sink is thermally coupled to the electronic component and located within the flow of cooling fluid directed to that component. The heat sink is designed to both dissipate heat and direct the flow of the fluid in an optimum manner. 
     In general, the amount of heat generated by any particular electronic component is different from that generated by any other component. Thus, the use of individual sub-supplies and/or individually sized heat sinks can permit the system design to accommodate the different cooling loads placed on it. 
     Several variations on the configuration of the supply manifold are possible. For example, a common supply may branch into several sub-supplies of cooling fluid, each of which may be coupled to one of the plurality of individual fluid supply manifolds. 
     Similarly, because there typically is at least one exhaust manifold to collect cooling fluid after it flows over the electronic components, the exhaust manifold also may comprise a plurality of individual component exhaust ducts. This also contributes to the ability of the invention to accommodate different cooling loads. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a perspective view of an example of a supercomputer circuit board, including some components of one embodiment of the invention. 
     FIG. 2 is a perspective view of the supercomputer circuit board of FIG. 1, including additional elements of one embodiment of the invention. 
     FIG. 3 is a schematic side view of the cooling fluid flow path in one embodiment of the invention, taken along the line  3 — 3  of FIG.  2 . 
     FIG. 4 is a perspective view of a preferred design of a heat sink component of a preferred embodiment of the invention. 
     FIG. 5 is a side view taken along the line  5 — 5  of FIG.  4 . 
     FIG. 6 is a magnified view of the region so indicated in FIG.  5 . 
     FIG. 7 is a side view taken along the line  7 — 7  of FIG.  5 . 
     FIG. 8 is a schematic illustration of four possible combinations of supply and exhaust manifold configurations within the scope of the invention. 
     FIG. 9 is a bottom interior view of an embodiment of the exhaust manifold component of the invention. 
    
    
     DETAILED DESCRIPTION 
     The cooling designs of the prior art are not optimal solutions to the cooling needs of modem supercomputers. For example, the approach of Gutierrez et al. is like even simpler cooling systems in that it fails to fully address the fact that because individual components generate different amounts of heat depending on their composition, function, and the like, they are best served by individual amounts of cooling. Their approach simply moves these components physically together into a common plenum, but does not address their individual cooling needs with individual amounts of cooling. Also, moving components together for cooling purposes assumes that other factors, such as computational performance, are not compromised. Computational performance is critical in supercomputer design, and therefore it is necessary to use a more robust approach to supercomputer cooling design than is shown in Gutierrez et al. 
     FIG. 1 shows a supercomputer circuit board  10  which has been adapted for use with the invention. The electronic components on circuit board  10  include two rows  11  of eight single chip modules (SCM)  14 , each SCM  14  has an individual cooling fluid supply manifold  38  located above the SCM, two rows  12  of dual in-line memory modules (DIMM)  15 , and a single row  13  of  4  multichip modules (MCM)  16  (one of which has its cover removed to indicate the multichip nature of the module). (The identity, number, and arrangement of the components shown in this and all the other Figures are only examples and do not limit the scope of the invention in any manner.) However, because the electronic components have different functions and therefore different internal designs, they will generally produce different amounts of heat during normal operation. And, as indicated in FIG. 1, the components are located very close to each other on circuit board  10 , as is common in the design of supercomputers. Together these factors present the design challenge of providing different amounts of cooling, to different types of components, in a very limited volume. 
     FIG. 2 is a perspective view of circuit board  10 , but now including various cooling fluid manifolds for each of the major types of electronic components (SCM, DIMM, and MCM). In particular, SCM exhaust manifold  21  over the individual cooling fluid supply manifolds  38 , and DIMM cooling manifold  22  are shown; they represent two different approaches to distributing cooling fluid to electronic components. DIMM cooling manifold  22  is a traditional common manifold approach in which a supply of cooling fluid enters at one end of the common manifold (as indicated by entry arrow  23 ) and cools all components within the manifold, in the order that the cooling fluid encounters the components, before leaving the common manifold at the other end (as indicated by exit arrow  24 ). To ensure that the cooling fluid moves through the manifold at a rate consistent with the design of the cooling system, the fluid is typically introduced under positive pressure (as produced by a conventional blower fan, pump, or any other suitable means) relative to the ambient, i.e., relative to the pressure outside the manifold. 
     By contrast, the SCM cooling system according to one embodiment of the invention operates differently from the conventional cooling design. That is, individual streams from the supply of cooling fluid are employed for each SCM through each individual cooling fluid supply manifold  38 , as indicated schematically by the collection of eight inlet arrows indicated as  25  and the collection of eight outlet arrows indicated as  26 . These collections are symbolic of either individual supply streams for each SCM, as could be accomplished by use of a plurality of sub-supplies of cooling fluid (not shown in FIG.  2 ), each sub-supply coupled to individual cooling fluid supply manifolds  38 ; or, as is employed in the preferred embodiment shown in the Figures and discussed below, use of a common supply of cooling fluid that is divided into a plurality of sub-supplies of cooling fluid and directed to each individual cooling fluid supply manifold  38  and SCM by controlling the flow area and/or pressure drop in the fluid path cooling each SCM; or, by any other convenient means. All such approaches are within the scope of the invention. The cooling fluid is delivered to each SCM at a negative pressure (relative to the ambient) and into thermal contact with the SCM. 
     To illustrate this, FIG. 3 is a schematic representation of the flow of cooling fluid through an individual cooling supply manifold  38  in the vicinity of a single electronic component, for example, SCM  14 . The arrows indicate the direction of cooling fluid flow as the fluid is pulled from its source (not shown) by the negative pressure within exhaust manifold  21 . As shown, the region  35  above SCM  14  is open to fluid flow from at least one horizontal direction (the left side as shown), and that is the preferred embodiment when, as illustrated in FIG. 2, access from the other horizontal side of the component is restricted (in this case, by the DIMMs and their cooling manifold  22 ). It is within the scope of the invention, however, to draw cooling fluid over or around a component from any convenient direction and/or from multiple directions. In doing so, there may be tradeoffs between thermal performance and manufacturing considerations related to the configuration of the manifolds, other components, required component cooling surface area available, and the like, but any particular embodiments produced by making such tradeoffs are considered to be within the scope of this invention. In particular, the configuration of the opening into region  35  and the outlet from region  35  can be modified in accordance with known thermodynamic principles to optimize the cooling of SCM  14 . It is also possible, in accordance with the same thermodynamic principles, to vary the configuration of exhaust manifold  21  so that desirable total flow, pressure drop, and the like are achieved at the final outlet  27  (FIG.  2 ). 
     A feature of the invention in its preferred embodiment is that each electronic component, such as each of the eight SCM  14  shown in FIGS. 1 and 2, may be cooled individually by using individual cooling fluid flow paths. This is advantageous for two reasons. First, it avoids the problem of caloric temperature rise in the cooling fluid due to the progressive cooling of components in sequence. That is, if a series of components is cooled in a common flow path (for example, the series of DIMM  15  are cooled within the common flow path provided by DIMM manifold  22 ), the heat transfer into the fluid from the first component raises the temperature of the fluid before the next component is cooled, and so on for each successive component. In the case of components that give off large amounts of heat, it is possible that the ability of the fluid to cool components near the end of the series will be compromised, if not entirely eliminated. For example, it is not unusual for the major semiconductor components of a supercomputer to generate  40  watts of heat. In a design having reasonable air volumes and velocities, this would require a stream of air to absorb an increase of approximately 10° C. for each component. If a series of such components were cooled with a system capable of re-cooling 40° C. return air down to 20° C. for supply to the components, only two components could be accommodated in a single common flow path. This would place a serious constraint on the design of the supercomputer. 
     Second, a cooling system having individual cooling fluid flows for individual components is a more robust design that easily accommodates variations in the cooling needs of the individual components due to the different amounts they may generate. The problem of caloric temperature rise is present whether the heatproducing electronic components are identical or not. But, if the components are not identical, a cooling system design that treats all components the same is not desired, because it tends to overcool less demanding components in order to have the capacity to adequately cool the more demanding components. The result is a less than optimal design in terms of fluid capacity and cost. The approach of individual cooling fluid flows allows for a more efficient design that will operate at a lower cost. 
     FIGS. 4-7 show a preferred embodiment of a heat sink  17  that may be used in preferred embodiments of the invention when increased heat transfer between an electronic component and the cooling fluid is needed. Heat sink  17  is thermally coupled to an electronic component and located within the flow of cooling fluid directed to that electronic component. Heat sink  17  is designed to both dissipate heat and direct the flow of the cooling fluid in an optimum manner. 
     In general terms, heat sink  17  comprises an enclosure defining an interior, an inlet, and an outlet, and a series of fins within the interior and in thermal contact with the enclosure. Cooling fluid flows in a first direction through the inlet into thermal contact with the fins, then in a second direction substantially perpendicular to the first direction, then out the outlet. 
     In the preferred embodiment shown, the enclosure is formed by base  18 , top plate  20  that surrounds a series of folded fins  19  on two sides and the top of heat sink  17 , and back plate  28 . The folded fins  19  are in thermal contact with base plate  18 . Base plate  18  is placed in thermal contact with the electronic component to be cooled. The preferred material for base plate  18  is type  6061  aluminum; for folded fins  19 , type  1100  aluminum; and for top plate  20  and back plate  28 , type  6061  aluminum is preferred . Other possible materials include aluminum oxides, ceramics, and copper. However, the invention is not limited to such materials and other suitable substitutes may be used. 
     Folded fins  19  are produced by repeatedly folding a flat, flexible length of material into the configuration shown, and attaching the folded fins to the base plate by known techniques that produce a thermal bond, such as brazing or the preferred embodiment of thermally conductive (preferably at least 90 W/mK) filler material. The filler material is also the preferred means to attach back plate  28  to the other components of heat sink  17 . 
     Heat sink  17  is preferably sized and shaped to serve the role for region  35  as described above and illustrated in FIG.  3 . In particular, this means that heat sink  17  is open to fluid flow in the substantially perpendicular directions indicated by inlet arrow  25  and outlet arrow  26 . This is accomplished by omitting any face plate that might be opposite back plate  28 , and also cutting away both top plate  20  and the upper region of folded fins  19  at outlet  29 . Cutting away the upper region of folded fins  19  is required to permit fluid that flows on alternate sides of any given fin to exit heat sink  17  and therefore exploit as much fin surface area as possible. There is a tradeoff between the amount of area removed and the pressure drop of fluid passing through the opening. The preferred technique of cutting away the upper region is electrodischarge machining, but any convenient method that exposes both sides of folded fins  19  may be used. 
     Preferred dimensions for base  18  are sixty millimeters length, forty-three millimeters width, three millimeters thickness. For folded fins  19 , length as required, forty-three millimeters sheet width, 0.41 millimeter sheet thickness,  19  cycles of two folds (one upper, one lower) at nineteen millimeters height and 1.56 millimeters center-to-center distance. For top plate  20 , length as required, thirty-one millimeters width, 0.81 millimeter thickness. For back plate  28 , sixty millimeters length, forty-three millimeters width, 0.81 millimeter thickness. Outlet  29  preferably begins two millimeters from back plate  28 , is ten millimeters in width, and cuts into folded fins  19  a depth of two millimeters. These dimensions are suitable for a cooling system in which a rectangular exhaust manifold serving eight heat sinks has a capacity of 37 cfm of air (4.6 cfm per heat sink) at 1400 fpm air velocity, the heat sinks are in thermal contact with eight identical SCMs each generating heat at a rate of forty watts, and the temperature of each SCM must be maintained below 85° C. Of course, these dimensions are exemplary only, and other dimensions may be substituted. 
     In an alternative embodiment of heat sink  17 , folded fins  19  are replaced with well-known solid fins, such as those produced by milling a block of material into a unified base/fin structure. In this embodiment, to expose both sides of each fin it is only necessary to size top plate  20  to produce outlet  29 , and not necessary to cut into the fins to any depth. 
     At least one exhaust manifold to collect cooling fluid after thermal contact of the fluid with the electronic components is preferred. When the cooling fluid is air, it is possible to omit the exhaust manifold and either let the heated air dissipate or use whatever enclosure may surround the equipment serve as a return air plenum. Neither of these approaches is preferred because they are inefficient compared to the use of an exhaust manifold, which permits the re-use of only moderately heated air (as opposed to cooling ambient air) by returning the exhausted air to the cooling source, as is well-known in the art. 
     In the other direction of cost and complexity, it is possible for the exhaust manifold to be coupled to the plurality of electronic components by at least one individual component exhaust duct. For example, a component generating a significantly larger amount of heat than other components could have a dedicated exhaust manifold, directed to a separate (larger capacity) cooling system than is used to re-cool the exhausted fluid from the other components. 
     FIG. 8 is a schematic illustration of four possible combinations of supply and exhaust manifold configurations within the scope of the invention. In each configuration, electronic components (indicated as shaded boxes) are coupled to supply (S) and return (R) manifolds, and the direction of flow of cooling fluid is indicated by arrows. For convenience, actual cooling mechanisms (e.g., coils) and pumps/fans are not shown. The number of electronic components is arbitrary, as is whether their cooling needs are identical or different, except as noted below. 
     FIG. 8 a  illustrates the simplest configuration, in which each component is coupled to a common supply manifold S and a common return manifold R. FIG. 8 b  shows the situation described immediately above, in which individual component exhaust ducts R 1  and R 2  are used to serve the two lower and upper components, respectively. This configuration could be used when the two sets of components have different cooling loads and it is desired to treat their (different temperature) exhaust streams differently for any reason (such as the separate cooling system described above). FIG. 8 c  illustrates this principle as applied to the supply side, i.e., separate supply manifolds S 1  and S 2  are directed to the two sets of components, and a common return manifold is employed. FIG. 8 d  is the combination of the two approaches, but it should be clear that each of the S 1 -R 1  and S 2 -R 2  systems is simply a smaller version of the S-R system of FIG. 8 a.    
     FIG. 9 is an interior bottom view of a preferred embodiment of a portion of exhaust manifold  21 . This view emphasizes the importance of balancing cooling fluid flow among the individual flow paths from each electronic component. Even in the case in which the individual components are identical in their cooling demand, the cumulative amount of fluid in exhaust manifold  21  increases from the closed end (the left end as shown in FIG. 2) to the open end where outlet  27  (see FIG. 2) is located. Thus, optimal performance is achieved by adjusting each individual exhaust manifold inlet  30  so that it presents a total open area that balances considerations of cooling fluid volume, temperature gradient, pressure drop, cumulative flow volume, etc. 
     In gross detail, each individual exhaust manifold inlet  30  is sized, shaped and located to correspond to the full extent of each corresponding outlet  29 . In fine detail, the preferred technique for adjusting the total flow area uses intermediate plates  31 , each of which includes is a series of holes  32 . (Although it is not required, the design is simplified when each hole  32  in a given plate  31  is the same size, and similarly if the collection of holes  32  in each plate  31  is distributed in some uniform or symmetric pattern.) The number and size of the holes will vary among the set of intermediate plates  31  to account for the different cooling fluid volume, pressure drop, cumulative flow volume, etc. to be handled by exhaust manifold  21  at each location. 
     In a preferred embodiment, in which air was the cooling fluid, the best balance of air flow through a series of eight outlets  29  was achieved when the total open area was approximately 85% at the outlet  29  farthest from the final outlet  27 , decreasing progressively to a final value of approximately 45% at the final outlet  27 . Air flows through each outlet  29  were within the approximate range of 275-375 feet/minute, and varied (one standard deviation) by less than 10% from the mean value of approximately 330 feet/minute. The total air flow at final outlet  27  was approximately 1400 feet/minute. The temperatures of eight identical components varied (one standard deviation) by less than 2% of the mean of the eight temperature values. 
     Of course, the art of cooling electronic components includes the use of both liquid and gaseous fluids for cooling, and both are within the scope of the invention. 
     And, as is very well-known, electronics equipment can be oriented in virtually any direction. Thus, as used in the entire disclosure above, the terms “horizontal,” “vertical,” “upward,” “lateral,” etc. identify only relative directions with respect to the circuit board regardless of its absolute orientation.