Patent Publication Number: US-6661657-B1

Title: Circuit board assembly for use in a central inlet chassis configuration

Description:
BACKGROUND OF THE INVENTION 
     The invention pertains to digital data processing and, more particularly, to methods and apparatus for improving the processing power, ruggedness and/or longevity of digital data processing systems. The invention has application, by way of non-limiting example, in high-density embedded computer systems for image and signal processing applications such as radar, sonar, medical data acquisition and imaging, semiconductor device inspection and imaging, to name a few. 
     As processor speeds and circuit board densities increase, heat has become the limiting factor in computer design. Unless adequately dissipated, it can cause computers to run unpredictably or to crash. Excessive heat also substantially reduces component lifetimes. While this is merely annoying to the typical, home or business user, it can prove catastrophic in mission critical applications, such as medical imaging, surveillance, and so forth. 
     The power requirements of reasonably sized individual computer circuit boards appear to be reaching asymptotic limits. Not so of the computers that house them. Manufacturers of at least high-end computer systems are pressured to include ever more circuitry in ever smaller chassis in order to meet customer throughput, redundancy and space requirements. The latter presents a real conundrum, however, since higher density board stacking reduces throughput and reliability, necessitating still more boards. 
     While cooling computer systems—and, particularly, for example, high density systems which now consume up to 3000 watts per cubic foot—can be accomplished using low temperature fluids or special gasses, forced air-convection cooling remains the preferred mechanism. The dilemma of using this choice is compounded where inlet operating temperature requirements for some systems, for example, high-density embedded systems, is typically 50°-55° C., extending up to 70° C. in some cases. 
     Holding junction temperatures to acceptable levels for meeting the required reliability with these high inlet temperatures is at best difficult, and at worst impossible, using prior art techniques. This is likewise true of maintaining basic component operation temperatures of 85-100° C. Moreover, many of these systems are placed in close proximity to people, so the noise-levels must typically be at or below 65-68 dB(A) at 1 meter. 
     An object of this invention is to provide improved methods and apparatus for digital data processing. 
     A more particular object is to provide such methods and apparatus as improve the capacity, density, efficiency, ruggedness, and/or longevity of such digital data processing systems. 
     Another object of the invention is to provide such methods and apparatus as can be used with air-cooling and more particularly, for example, forced air-cooling—as well as with other heat dissipation techniques. 
     Still other objects of the invention are to provide such methods and apparatus as can be implemented at low cost using existing components, materials and/or fabrication techniques. 
     SUMMARY OF THE INVENTION 
     The foregoing objects are among those attained by the invention which provides, in one aspect, a circuit board assembly comprising a substrate with one or more circuit components mounted thereon. A cover or other member is disposed adjacent to the substrate and, for example, spaced therefrom so as to define a plenum. One or more heat sinks (or other heat dissipative elements) are spring-mounted (or otherwise resiliently mounted) to the cover and, thereby, placed in thermal contact with one or more of the circuit components. 
     The heat sinks are self-aligning, according to related aspects of the invention. Thus, they are disposed on the cover so that when it is coupled to the substrate (permanently, removably or otherwise) the heat sinks come into thermal contact with the respective circuit components. According to further related aspects of the invention, the cover is a substantially planar member, such as, for example, a cold plate or other thermal conductor, that is sized to match the footprint of the substrate. 
     Further aspects of the invention provide a circuit board or circuit board assembly of the type used, for example, with other circuit boards in a computer or other equipment chassis. A circuit board according to this aspect of the invention includes one or more flow-diverting elements that define, at least in part, the board&#39;s impedance to air flow in the chassis. The flow-diverting elements are adapted so that the overall impedance of the board substantially matches that of one or more of the other circuit boards. 
     According to related aspects of the invention, one or more of the flow-diverting elements are adapted to shape an air flow pattern within a plenum, for example, of the type established between the circuit board and its cover. Moreover, the flow-diverters can serve as heat sinks mounted, for example, to the substrate, the circuit components or (as discussed above) to the circuit board cover. 
     Still further aspects of the invention provide a circuit board assembly, e.g., of the types discussed above, in which cover is a substantially planar member with one or more structural elements that regulate shock and/or vibration in the cover and the circuit board. The structural elements may be rod-like or other elongate members, e.g., affixed to or incorporated into the planar member. Moreover, the structural members may be elongated heat sinks (or heat sinks of other shapes) that are coupled to the cover by spring-mounts, other resilient elements or otherwise. 
     In related aspects of the invention, the structural elements of the cover of a circuit board assembly as described above are adapted to control thermal and/or electromagnetic emission control, as well as shock and vibration. 
     The invention provides, in yet other aspects, a circuit board for use in a chassis that has a plurality of board insertion slots. The board includes an air inlet edge through which cooling air flow is received and an air outlet edge through which the air flow exits. The edges fall, for example, at the ends of a plenum defined, e.g., between the circuit board substrate and a cover as described above. A connector arrangement provides electrical, mechanical and/or other operational coupling between-the circuit board and the chassis regardless of whether the board is disposed in a slot on a first (e.g., upper) side of a source of cooling air for the chassis or on a second (e.g., lower) opposite side of that source. 
     According to related aspects of the invention, the connector arrangement includes first (e.g., upper) and second (e.g., lower) connectors. The first (e.g., upper) connector provides, for example, electrical coupling between the circuit board and the chassis when the circuit board is disposed in the slot on the first (e.g., upper) side of the source of cooling air. The second (e.g., lower ) connector provides such coupling when the board is disposed in the second (e.g., lower) slot on the opposite side of that source. 
     Related aspects of the invention provide a digital data processor in a cabinet having, for example, a central air inlet and a chassis with board insertion slots disposed on opposite sides of that inlet. Circuit boards, as described above, disposed in the chassis have connector arrangements that provide operational coupling regardless of which slots the boards are inserted into. 
     Other aspects of the invention provide a circuit board having two parts, each with an air flow inlet edge through which cooling air flow is received and an air flow outlet edge through which the air flow exits. Each of these parts is disposed on opposing sides of a central source of cooling air for the circuit board. That source, according to related aspects of the invention, is an air inlet incorporated into a panel that provides any of mechanical protection and electromagnetic interference (EMI) protection when the circuit board is operationally coupled in a slot in a chassis. The inlet can be disposed centrally on the panel (e.g., between the first (or upper) and second (or lower) board parts) and can be aligned with a corresponding air inlet on the chassis cover of a digital data processor into which the board is inserted. 
     Yet still other aspects of the invention provide an improved chassis of the type having slots for slidable insertion of circuit boards. Each slot, according to this aspect of the invention, has a first air flow aperture disposed adjacent to a first edge of an inserted circuit board and a second aperture adjacent to a second edge of the board. The first air aperture is an air flow source; the second is an air flow exit. These apertures can be disposed, for example, on opposite ends of plenum in the circuit board, e.g., whether defined by a cold plate on which the board substrate is mounted or by a cover to which the board is coupled. 
     According to related aspects of the invention, the aforementioned chassis includes a cabinet with an air flow inlet. It provides to the first air flow aperture of the slots cooling air flow drawn from an environment outside the cabinet. Air flow exiting the slots&#39; second air flow apertures, conversely, can be directed to that outside environment or to another region within the covered chassis. 
     Still further related aspects of the invention provide a chassis as described above in which the first and second apertures are sized so that the impedance to air flow to the circuit board inserted in the slot substantially matches that to one or more other boards in the chassis. Yet still further related aspects provide a card cage having card insertion slots as described above that is vacuum or dip brazed, or by alternate process yielding a cage of sufficient structural stiffness and air-flow/interference sealing. 
     The invention provides, in still further aspects, circuit boards and chassis as described above in which an air and/or electromagnetic interference (EMI) seal is provided between each circuit board and the chassis slot into which it is inserted. 
     Further aspects of the invention provide digital data processors, e.g., in closed chassis or cabinets having centrally disposed air inlet grills, with card cages as described above and with circuit boards and circuit board assemblies, also as described above, in those chassis. Such digital data processors, as well as the assemblies of which they are made, provide for improved capacity, density, efficiency, ruggedness, and/or longevity of components that provide digital data processing functions. They can be used with air-cooling and more particularly, for example, forced air-cooling—as well as with other heat dissipation techniques. Moreover, they can be implemented at low cost using existing components, materials and/or fabrication techniques. 
    
    
     These and other aspects of the invention are evident in the description that follows and in the attached drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete understanding of the invention may be attained by reference to the drawings, in which: 
     FIGS. 1A-1B depicts a circuit board assembly according to one practice of the invention having multiple self-aligning heat dissipative elements (e.g., heat sinks) mounted by springs (or other resilient elements) on a cover; 
     FIGS. 1C-1D depict circuit board assemblies according to the invention with combination thermal, shock, vibration, and/or electromagnetic compatibility (EMC) cover; 
     FIG. 2A depicts a circuit board assembly according to the invention for use in a center inlet chassis; 
     FIG. 2B depicts a center inlet circuit board assembly according to the invention; 
     FIG. 3A depicts a card cage for use with circuit board assemblies according to the invention; 
     FIGS. 3B-3D depict a card-cage according to the invention with integrated control and shaping of air resistance curve for multiple plenum chambers; 
     FIG. 3E depicts a chassis according to the invention comprising a plurality of card cages of the type depicted in FIGS. 3A-3D. 
     FIGS. 4A-4C depicts a card cage support and circuit board assembly according to the invention with improved air flow sealing; and 
     FIGS. 5A-5B depicts an air-cooled digital data processor according to the invention capable of operating with high inlet temperatures and high levels of shock and vibration. 
    
    
     DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT 
     Circuit Board Assembly with Integrated Air Plenum Chamber using Self-Aligning Heat Sinks 
     FIG. 1A depicts a circuit board assembly  100  according to the invention with an integrated plenum and with self-aligning heat sinks or other thermal dissipative elements (collectively, “heat sinks”). Illustrated assembly has a substrate  102  with chips and/or other circuit components (collectively, “components”)  104  disposed thereon. Heat sinks  106 ,  122  are disposed on a cover  108  that is removably affixed to substrate  102  via mounts  110 . As illustrated, for example, with respect to heat sinks  106 ,  122 , these may. be disposed on springs  112  or other resilient elements such that, as the cover is placed on the circuit board, the sinks come into thermal contact with the components  104 —with controlled positive pressure applied by the springs (or other resilient elements) to maintain that contact. Illustrated assembly  100  also includes a connector or connector array  120  through which the assembly achieves operational coupling, e.g., electrical, optical and/or mechanical coupling with a chassis or other structure in which the assembly is installed. 
     In reading the discussion that follows, those skilled in the art will appreciate that the illustrated use of spring-mounted (or other resiliently-mounted) heat sinks differs from the prior art practice of permanently mounting heat sinks directly on the substrate  102  or components  104 , and of the prior art practice of fabricating a monolithic heat sink that covers the. entire board and that is machined to fit each component thereon. Of course, however, the illustrated assembly may utilize heat sinks in accord with these prior art techniques, as well. 
     Illustrated substrate  102  comprises a conventional printed circuit board substrate sized in accord with well known IEEE 1101.× or“Eurocard”3U, 6U, 9U standards, or other standard, or non-standard form factors known in the art. The substrate comprises plastic, resin, ceramic, metal and/or other material suitable for supporting components  104  and providing electrical coupling, through conductive vias or otherwise, therebetween. According to some practices of the invention, substrate  102  is formed of, or mounted on, a “cold plate”  114  or other thermally conductive material (such as, by way of example, copper, brass, aluminum, other metals, composites or compounds) suitable for drawing heat away from the underside (or “solder side”) of the substrate  102  or mounted components  104 . Illustrated cold plate  114  is of the variety having a plenum  116  (or plural plenums) through which cooling air (represented by arrows  118 ) can flow. Solid cold plates or those without plenums (whether or not solid), or those of still other configurations, may be used in addition or instead. 
     Components  104  are selected and operated in accord with the digital data processing function of the circuit board assembly  100 . This may be as a motherboard, coprocessor card, signal processing board, memory board, interconnect fabric, input/output board, and so forth. Selection, configuration and operation are per convention in the art, as modified in accord with the teachings hereof for thermal, shock, vibration, and/or electromagnetic compatibility (EMC) control. 
     In preferred embodiments, the components  104  are mated with the substrate  102  in the conventional manner. As noted above, that substrate is formed of and/or mounted to the cold plate  114 , thereby, providing a large path of heat dissipation and spreading. The internal thickness or structure of the substrate  102  and/or cold-plate  114  are machined or otherwise fabricated based on the mix of component densities and power levels in each region of the substrate  102 . Thus, for example, the plate thickness in regions beneath processors and other high-temperature components is adjusted to rapidly dissipate heat to the other regions. As discussed below, that heat is preferably removed via air flow through the cold plate plenum  116 , which can form part of a leak-free air channel-ensuring the heat will be removed even more quickly by making efficient use of the available air flow. 
     Illustrated cover  108  is a substantially planar (or otherwise-shaped) member removably (or otherwise) mounted on substrate  102  defining an integrated plenum  124  for cooling air  118  on the topside (or “component side”) of the substrate. In this illustrated embodiment this is a metal cover of solid, hollow or other construction having a substantially like footprint (i.e., size and shape) as substrate  102 —downsized, upsized or otherwise modified as necessary to accommodate use or placement of the assembly  100  in a chassis or otherwise. Though constructed of metal in the illustrated embodiment, in other embodiments it may comprise other materials, thermally conductive or otherwise. 
     Mounts  110  can be screw-mounts or other structures suitable for affixing cover  108  to substrate  102 , directly, via rotation or otherwise. Such affixation can be permanent, though, preferably provides for detachment or at least partial removal (e.g., via rotation) of the cover, e.g., for inspection and/or repair of the components. 
     Illustrated heat sinks  106 ,  122  are thermal conductive and/or dissipative elements of the type known in the art. These may be passive elements (e.g., such as cold plates or fins) fabricated of copper, brass, aluminum or other metals, composites or compounds or active elements (such as micro-fans). Though disk-shaped and stepped heat sinks are shown in the drawing, it will be appreciated that sinks of any other shape or configuration may be used in addition or instead. These heat-sinks may be of commodity or custom design. As in the case of elements  106 , a single heat sink may be provided for each component  104  expected to generate substantial heat during system operation or susceptible to failure or degradation on account of such heat. Alternatively, a single heat sink may be provided for multiple components, as in the case of heat sink  122 . 
     Regardless, the heat sinks  106 ,  122  are provided with a surface suitable for thermal coupling with its respective component(s)  104 . This may comprise a smooth, ridged or knobbly surface, or otherwise. The surfaces of sinks  106  may also be contoured, as desired, to insure more accurate registration between each sink  106  and its corresponding component  104 . A thermal interface material can also be combined with or applied to the sinks to facilitate registration and/or thermal coupling. 
     Though the illustrated embodiment contemplates thermal coupling via surface contact between the lower surfaces of heat sinks  106  and the upper surfaces of the respective components  104 , other contact/coupling may be provided instead or in addition. In the case of micro-fans, such an interface may not be necessary, though suitable means may be provided for directing the action (e.g., suction or blowing) of such element to the respective component  104 . 
     Illustrated heat sinks  106 ,  122  are disposed on springs  112  such that, as the cover is put into place the sinks come into thermal contact with their respective components  104 , thereby, facilitating manufacture of the assembly  100 . Heat sink  122  may, too, be spring-mounted, though this is not shown in the drawing. In the illustrated embodiment, the springs themselves are affixed to the cover (and, in turn, the sinks mounted on their respective springs) so as to insure that the sinks  106 ,  122  are self-aligning or will otherwise maintain alignment with their respective components  104  as the cover  108  is affixed into place on substrate  102  and, preferably, through repeated removals and reaffixations of the cover on the substrate. Affixation of the springs  112  to the cover  108  (and, in turn, affixation of the heat sinks  106  to the springs may be via screws, adhesives, friction fit, integral molding, or otherwise, although since the springs and mounts may be an EMI ground bonded to the cover, appropriate materials must be selected; 
     One or more springs can be provided for each heat sink, with the characteristics of each spring selected to meet operational constraints. These springs maintain a load on the heat sink and component interface without exceeding the maximum load of the component dies. Further stability and greater assurance of thermal contact between the sinks  106  and components  104  may be gained through use of more springs of greater spring constant k. Alternatively, or in addition, springs of larger cross-section surface area may be employed. Though springs are used in the preferred embodiment, those skilled in the art will appreciate that mechanisms and materials exhibiting spring-like qualities—e.g., of resilience and of applying a positive controlled pressure between the heat sinks and the components in which they are in thermal contact—may be used instead. Such mechanisms and materials are referred to throughout this document as “resilient elements,” and components mounted thereon are referred to as “resiliently-mounted.” 
     As discussed below, in addition to drawing heat away from the substrate  102 , cold plate  114  and/or circuit components  104 , the heat sinks may shape the air flow patterns within plenum  124 , e.g., so as to divert air flow to/from components  104  or regions of the board requiring greater/less air flow. Other features built directly into cover  108  can also shape the air flow patterns. 
     A further appreciation of the construction of circuit board assembly  100  may be had through reference to FIG. 1B, which shows the assembly in a partially disassembled form. As illustrated, attached to cover  108  are heat sinks  106 ,  122 , tile former via springs  112  (or other resilient elements). Conversely, mounted on substrate  102  are components  104 . Though shown as affixed to cover  108 , mounts  110  may be affixed to that to substrate  102 , or otherwise. Conversely, while circuit board connector or connector array  120  can be mounted on cover  108 , in the illustrated embodiment, they are affixed to the substrate  102 , the connector and substate attached via a cable, circuit card, or other means. 
     Circuit Board Assembly with Integrated Shaping and Control of Flow Resistance Curve 
     Circuit board assembly  100  is intended for insertion in a covered chassis or “cabinet” along with one or more other circuit board assemnblies, though, those skilled in the art will appreciate that the features discussed herein are applicable in other environments as well (e.g., those including no chassis and/or other assemblies). The assembly  100  can, according to one practice of the invention, include integrated features, as detailed below, for control of the assembly&#39;s air flow resistance curve and for shaping of air flow patterns within plenum  124 , e.g., so as to divert air flow to/from components  104  or regions of the board requiring greater/less air flow. 
     Referring, again, to FIG. 1A, in the illustrated embodiment, impedance presented by assembly  100  to air flows  118  in such a chassis—or otherwise in the environment surrounding the board (e.g., if not disposed in a chassis—is preferably matched with other circuit board assemblies in the cabinet. This assures, with a known overall air flow, that board  100  will receive a predictable air flow, regardless of what other boards are present at any given time and regardless of where (e.g., in which slots) those other boards are positioned. 
     In alternate embodiments, the impedance presented by assembly  100  to air flows  118  is sized in relation to those of the other boards, though, is not necessarily set to match them. Thus, by way of example, an assembly  100  may be configured with 10%-80% less (or greater) impedance than the other circuit board assemblies, depending on the power dissipation and number of components  104  carried it. For example, the mechanisms discussed below may be employed to increase the impedance of a board that has fewer components and that would otherwise have less impedance, say, than boards with more components. This can be useful in environments where a single cabinet is expected to house boards of two or more types, e.g., some requiring greater air flow. 
     In the illustrated embodiment, the impedance presented by assembly  100  to air flows  118  can be managed by adjusting the thickness, the features on the inside surface, and the size of cover  108 , substrate  102  and/or cold plate  114  (if any) on which the substrate is mounted or of which it is formed, as well as by the relative spacing of these structures, the placement and sizing of components  104 , heat sinks  106 , and mounts  110 . This is likewise true of the air flow patterns within the plenum  116  and in the  124  plenum defined between cover  108  and substrate  102  of circuit board assembly  100 . 
     According to one practice of the invention, cover  108  is preferably dimensioned and spaced-apart from substrate  102  such that assembly  100  presents an impedance to air flows  118  somewhat below a target value that is selected to substantially match (e.g., to fall within 0%-2%, 0%-5%, 0%-10% or 0%-20% or other ranges, depending on operation requirements) or be sized in relation to that of other boards in the cabinet. That impedance is then “finely tuned” to the target and air flow patterns within plenum  124  adjusted by inclusion of air-flow diverting structures mounted on substrate  102 , cover  108 , or otherwise within (or adjacent to) the plenum  124  and  116 . 
     Heat sink  122  (which otherwise serves to draw heat from components  104 ) serves this purpose in the illustrated embodiment, though in other embodiments other structures (heat dissipative or otherwise) may be used, in addition or instead. To this end, the sink  122  or other flow-diverting structures are placed at or near an air flow inlet of plenum  124 . Other embodiments may, instead or in addition, incorporate such sinks or other structures at or near an outlet of the plenum (e.g., to create more pressure drop within the plenum  124 ) and/or at other locations within the plenum. Examples of the latter include heat sinks  106 . A cover that utilizes other structures—particularly, apertured endpieces  108   d ,  108   e —at the inlet and outlet for purposes of tuning impedance and/or diverting airflow within the plenum is shown in FIG.  1 D. These tuned apertured end-pieces can form part of and stay with the circuit board assembly  100  and, thus, for example, the assembly  100  can be removed from a chassis and replaced with a different such assembly (e.g., having a different tuned impedance) without substantial changes to the card cage or chassis. 
     Regardless, the heat sinks or other the flow diverting structures are positioned, sized and shaped to tune the overall air-flow impedance of the assembly  100  to the target value, as well as to effect a desired flow pattern within plenum  124  (e.g., so as to divert air flow to/from components  104  or regions of the board requiring greater/less air flow). By one practice of the invention, this is done empirically, with measurements of air-flow impedance and air-flow being determined using an air-flow chamber and an air-flow meter. Alternatively, or in addition, positioning, sizing and shaping of the sinks or other flow-diverting structures can be performed with a computer aided design modeling program, or otherwise. 
     Circuit Board Assembly with a Combination Thermal, Shock, Vibration. and/or Electromagnietic Compatibility Cover 
     As evident in the discussion above and, further, in that which follows, circuit board assembly cover  108  is configured to provide thermal, shock, vibration, and/or electromagnetic compatibility (EMC). control through use of mounts  110 , heat sinks  106 ,  122  and/or further structural members that are incorporated into cover  108 . 
     Referring to FIG. 1C, supports  110  are fabricated into cover  108  or affixed thereto by adhesives, rivets, screws or other affixation means known in the art. The number, dimensions, and structure of the supports  110 , as well as the materials out of which they are fabricated, are selected to regulate shock and/or vibration in the assembly  100  in accord with the layout, rigidity and other characteristics of the board (e.g., substrate  102  and cold plate  114 , if any) with which the cover  108  is used and of the expected operational environment of the assembly  100 . By one practice of the invention. such selection is performed empirically, while in other embodiments it is performed using computer aided design modeling program, or otherwise, of the type known in the art. 
     In the illustrated embodiment, the supports  110  are annular metal peg-like structures formed integrally with the cover  108  and suitable for screw-mounting cover  108  to the sub-strate  102  and/or cold plate. Two rows of those supports  110  are provided, as shown, consistent with the layout of the components  104  on the substrate  102 . Again, other embodiments may use supports of other shapes and configurations, e.g., consistent with the discussion herein, chosen either for mounting air-flow shaping and/or EMI considerations. Likewise, support materials other than metal may be used, such as, plastics, elastomers, and/or compound structures (such as air-filled plastic “balloons” although a metallic material would typically be chosen for grounding and EMI reasons. 
     In addition to controlling shock and/or vibration, supports  110  can be arranged to control electromagnetic emission from the assembly  100 , e.g., by spacing them appropriately in selected regions of the board. Thus, for example, the supports can be formed into supportive endpieces  18   a ,  108   b  of the cover  108 , blocking emissions from the respective regions of the board and providing further shock and/or vibration control. If placed in thermal communication with substrate  102  and/or cold plate  114 , metal and other thermally conductive supports  108   a ,  108   b ,  110  (collectively,  110 ) can, moreover, draw heat away from the board and its components  104 . Likewise, the tuned apertured end-pieces  108   d  and  108   e  can also serve to control electromagnetic emission from the respective regions of the board and/or to provide further shock and/or vibration control. In addition, localized EMI containment “boxes” can be formed in cover  108  to surround components on substrate  102 . 
     Incorporation and/or affixation of heat sinks  106 ,  122  to cover  108  provides further control of shock, vibration, temperature and electromagnetic emission. For example, when the cover  108  is mounted on substrate  102 , the heat sinks flush with the cover  108 , as well as with the component in which they are in thermal contact, thus, providing reinforcement against shock and/or vibration. 
     In addition to airflow diversion, as discussed above, the sinks  106 ,  122  are placed to optimize drawing excess heat from the substrate  102  and /or directly from components  104 . Consistent with the principles above, the dimensions and configuration of heat sinks  106 ,  122 , as well as the materials out of they are fabricated, are selected to regulate shock, vibration, temperature and electromagnetic emission in accord with the characteristics of the cover, the board (e.g., substrate  102  and/or cold plate  114 ) and the expected operation environment of the assembly  100 . In the illustrate embodiment, such selection is performed empirically, while in other embodiments it is performed using computer aided design modelling programs, or otherwise. 
     Illustrated, cover utilizes further structural members  108   c  for additional shock and vibration regulation. These add structural rigidity to the cover  108  and may be formed integrally with or affixed to it. A cross-shaped member  108   c  is shown in FIG. 1C, those skilled in the art will appreciate that any manner of structures may be formed with or affixed to cover  108  in order to enhance shock and vibration regulation. Examples include individual rod-like members (e.g., of the type that make up the cross-shaped member  108   c ) and/or elongate members (e.g., endpieces  108   a ,  108   b ,  108 d,  108   e ) attached to or formed integrally with an upper or lower surface of the planar cover  108 . Alternate examples include the use of such or other members within the cover  108  itself. These internal members can also be used to control air flow in  124 . 
     As above, the dimensions and configuration of further structural members  108   c , as well as the materials out of they are fabricated and integrated into cover  108 , are selected to regulate shock and vibration in accord with the characteristics of the cover, the board (e.g., substrate  102  and/or cold plate  114 ) and the expected operation environment of the assembly  100 . In the illustrated embodiment, such selection is performed empirically, while in other embodiments it is performed using computer aided design modelling programs, or otherwise. 
     Circuit Board Assembly for use in a Central Inlet Chassis Configuration 
     A circuit board assembly of the type discussed above can be mounted in a cabinet along with one or more other circuit board assemblies, in the manner shown in FIG.  2 A. That drawing shows six such assemblies: three  202 ,  204 ,  206  in upper chassis slots and three  203 ,  205 ,  207  in lower chassis slots. Each of the assemblies  202 - 207  is constructed in the manner of assembly  100 —though they do not all necessarily include the same circuit components  104  nor carry out the same digital data processing functions. Thus, for example, the assemblies include circuit boards (e.g., substrates and cold plates, if any) with integrated plenums  116  and/or  124  on which components are mounted. Examples of these are denoted as  203   a  (board and components) and  203   b  (cover forming plenum  124 ), the latter of which is shown in partial transparency for convenience. In addition, each assembly includes a panel for mechanical and electromagnetic interference (EMI) protection post-insertion. An example of this is denoted as  203   c.    
     The assemblies are mounted in a cabinet, only air inlet grill  208  and electrical connector arrays  210 ,  212 ,  214  of which are shown. A more complete illustration of a preferred cabinet is provided in FIG. 5, et seq. and described below in the accompanying text. Referring back to FIG.  2 A. in a preferred embodiment, the grill  208  forms part of the front cover of the cabinet and is generally disposed centrally between the upper assemblies  202 ,  204 ,  206  and the lower assemblies  203 ,  205 ,  207 , in the manner indicated in the drawing. This central location, e.g., between assemblies  202  and  203 , allows flow  216  to enter plenums  124  (and  116 ) of both assemblies  202 ,  203 , concurrently in the common chassis in which they are disposed. Though such a configuration facilitates drawing air from the ambient environment for distribution to, and cooling of, the assemblies, the grill  208  can be positioned elsewhere—preferably, so long as cooling air is available to be drawn over the air flow impedance-matched (or -relationally sized) assemblies, e.g., as illustrated with respect to assemblies  202 ,  203  by flow arrows  216 . And, though a regular aperture pattern is shown for grill  208 , an irregular pattern may be used as well, e.g., in order to achieve desired air flow shaping or impedances, as can be determined empirically, through use of a computer aided design modelling programs or otherwise. 
     According to a preferred practice of the invention, the assemblies  202 - 207  are each fabricated for insertion and operational coupling (e.g., electrical, optical and/or mechanical coupling such as alignment pins) in either the upper or lower chassis slots of a chassis having centrally disposed air inlet grill  208 . Thus, though shown in an upper slot, assembly  202  can be rotated 180° and inserted for operation in a lower slot, as well. Conversely, though shown in a lower slot, assembly  203  can be rotated 180° and inserted for operation in an upper slot. 
     This is achieved in some embodiments, by sizing and/or arranging each assembly&#39;s respective parts (e.g., cover, substrate, componentry, flow-diverting elements, etc.) so that the assembly presents substantially like impedances and air flow patterns (e.g., within plenum  124 ) regardless of which edge of the assembly (e.g., top edge or bottom edge shown in FIG. 2A) serves as an inlet or outlet for cooling air within the chassis, and so that the assembly achieves the necessary electrical and mechanical coupling regardless of whether it is inserted in an upper or lower slot. 
     The assemblies of the illustrated embodiment do not present such symmetry of impedances and air flow patterns (e.g., on account of asymmetry of flow-diverting element or other part placement within each assembly). These assemblies  202 - 207  require that cooling air flow be received along one edge (e.g., bottom edge of assemblies  202 ,  204 ,  206  and top edge of assemblies  203 ,  205 ,  207 ). In such an embodiment, the flexibility to insert any given assembly, e.g.,  202 , in either an upper or lower chassis slot is achieved by inverting the connector sockets (not shown) in the chassis connector array  210 . Thus, for example, if the connectors sockets  202   d ,  202   e  for circuit board assemblies in the upper slots are oriented with specific pins on the bottom, the corresponding sockets  203   d ,  203   e  for assemblies in the lower slots are oriented with those same pins on top. Thus, regardless of which slot an assembly, e.g.,  202 , is inserted, its connectors can necessarily be oriented to mate with the socket(s) for that slot. Other embodiments could, for example, use pairs of connectors on each assembly, with one member of each pair going active depending on which slot (upper or lower) the assembly is inserted into. 
     Central Inlet Circuit Board Assembly 
     FIG. 2B depicts an alternate configuration of a circuit board-assembly of the type discussed above. That drawing shows four such assemblies, here, identified as  202 ′,  203 ′,  204 ′  205 ′. These are constructed and operated to like-numbered (sans primes) elements  202 - 205  of FIG. 2A, except as noted below. Thus, for example, as above each of the assemblies  202 ′- 205 ′ is constructed in the manner of assembly  100 —though they do not all necessarily include the same circuit components  104  nor carry out the same digital data processing functions. And, as above, the assemblies include circuit boards (e.g., substrates and/or cold plates) on which components are mounted and covers. 
     Unlike the configuration of FIG. 2A, the assemblies are mounted or otherwise formed in pairs  202 ′,  203 ′ and  204 ′,  205 ′—or larger groupings—on boards  218 ,  220 , respectively, as shown. These boards  218 ,  220  are well suited for large format factors such as the IEEE 1101 or Eurocard 9U standards, or other standard or non-standard large-form form factors, and, accordingly, labelled below as “large format” assemblies. Those skilled in the art will, of course, appreciate that the teachings with respect thereto can be equally applied to smaller format factors, such as IEEE or Eurocard 6U standards, or other standard or non-standard smaller-form form factors, and below and, hence, that the label selected is merely for convenience and not to be treated as limiting. 
     As above, in the illustrated embodiment, the large format assemblies  218 ,  220  are mounted in a covered chassis or cabinet (not shown), only air flow inlet grill  208  and electrical connector arrays  210 ′,  212 ′ of which are shown. Grill  208  is positioned and functions identically as discussed above and is labelled the same accordingly. Connectors arrays  210 ′,  212 ′ are likewise constructed and operated identically to arrays  210 ,  212  discussed, albeit in the illustrated embodiment arrays  210  need not (but can) accommodate assemblies (or boards) that can be “flipped over” in the manner of assemblies  202 - 207 , discussed above. A more complete illustration of a preferred chassis is provided in FIGS. 3, et seq. and  5 , et seq. and described below in the accompanying text. 
     Rather than providing a panel, e.g.,  203   c , for mechanical and electromagnetic interference (EMI) protection on each sub-assembly  202 ′- 205 ′, a single such panel is provided for the each entire large format assembly  218 ,  220 . An example of this is denoted as  218   c . Such a panel  218   c  can include an integral grill portion  218   g  mounted adjacent to, for example, any grill  208  provided for the cabinet as a whole and serving the same purpose as that grill  208 . Thus, the integral grill portion  218   g  is generally disposed centrally between the sub-assemblies pairs  202 ′,  203 ′ and  204 ′,  205 ′ that make up each large format assembly and is generally aligned with the chassis air flow inlet grill  208  through which airflow  216  enters. As above, though such a configuration facilitates drawing air from the ambient environment for distribution to, and cooling of, the sub-assemblies, the grill portion  218   g  can be positioned elsewhere. 
     In some embodiments, the sub-assembly pairs  202 ′,  203 ′ and  204 ′,  205 ′ are formed independently of—and, thereafter, mounted to—the respective large format assemblies  218 ,  220 , respectively. Preferably, however, the pairs are at least, in part, integral to the respective large format assemblies. Thus, for example, sub-assemblies  202 ′,  203 ′ share a common substrate and/or cold plate with the large format assembly  218 . Regardless, the larger format assembly can include circuit components, e.g.,  222 , and other elements separate from those provided on the respective assembly pairs. 
     Although in some embodiments, each sub-assembly  202 ′- 205 ′ includes a connector for attachment to the respective connector array  210 ′ (sub-assemblies  202 ′- 203 ′) and  212 ′ (sub-assemblies  204 ′- 205 ′), in the illustrated embodiment, a single set of connectors are provided for each large format assembly. One such set is denoted as  218 d. Though that illustrated set has two elements, greater or fewer elements set may be provided-which elements may (but need not) correspond to the assemblies that make up the respective large format assembly  218 . 
     Card-Cage with Integrated Control and Shaping of Flow Resistance Curve for Multiple Plenum Chambers 
     A “card cage” or other portion of a chassis for mounting circuit board assemblies  202 - 207  can be fabricated in any manner or configuration known in the art. One such cage  302 , of the type fashioned from sheet metal members, extrusions, mill products, or other elongate members  304 , brazed, screwed or otherwise fixed into a frame-like structure, is shown in FIG.  3 A. Cages of this type are characterized by open spaces  306  between inserted assemblies, e.g.,  202 ,  204 , through which air may flow—as indicated by flow arrows  308   a ,  308   b . Other card cage assemblies or chassis arrangements of this or other types known in the art may be used as well or instead. These cages can be used in an open rack configuration or, preferably, as part of a covered chassis or cabinet, for example, as shown in FIGS. 5A-5B, with one (or more) cage(s) positioned in an upper portion of the chassis (i.e. forming upper board slots) and one (or more) other cage(s) positioned in a lower portion (i.e., forming lower board slots). Those skilled in the art will appreciate that the cages can be fabricated integral to such chassis or fabricated separately. 
     In a preferred embodiment, a card cage  310  as shown in FIG. 3B is used. Unlike the cage  302 , cage  310  has integrated features, such as the surfaces and apertures discussed below, that permit air flow only through inserted circuit board assemblies  202 - 207  and, more particularly, through any plenum (e.g.,  124 ) defined between the cover and board of each respective assembly and any plenum (e.g.,  116 ) in a cold plate on which the board is disposed or formed. More generally, those features provide for control and shaping of flow resistance of the assemblies  202 - 207  mounted therein. This is likewise true if used with prior art circuit boards insofar as the  310  cage limits air flows entering and exiting at the edges of those boards and, more generally, within the cage as a whole; though a more full benefit of the card cage  310  is attained when used with assemblies such as  202 - 207 . 
     Referring to FIGS. 3B and 3C, cage  310  has surfaces  312 ,  314  with guides  316  for the circuit board assemblies and/or circuit boards. The guides  316  comprise channels of U-shaped cross-section (though other shapes may be used instead) in which the assemblies  202 - 207 ,  218 ,  220  are slidably received. Apertures  318  are disposed in surface  312  of the channels above the locations where the upper edges of the respective assemblies and/or boards will reside upon insertion in the slots. Such apertures  318  are likewise disposed in surface  314  of the channels and below the locations of the lower edges of the inserted assemblies and/or boards. FIG. 3C is a plan view of the underside of surface  314 . Apertures  318  are visible from this perspective, though (of course) guides  316  are not. Also visible are the bottom edges of the cage sides  320  (if any) in the vicinity of surface  314  and the plenum  322  (if any) formed thereby beneath that surface. 
     In the illustrated embodiment, the apertures  318  are sized to present equal impedances to air flow entering and exiting the card cage  310  and to pass like volumes of air to each inserted assembly or board. In alternate embodiments, the impedances of the respective slots are adjusted in accord with requirements of the assemblies/boards that will reside in the slots, e.g., in accord with principles discussed above in connection with varying the impedances presented by the assemblies  100  themselves to air flows. Apertures that are or will be occupied by no assembly or board are covered. Apertures could be of different physical size without impacting the ability to adjust their impedance. 
     Illustrated cage  310  includes a left-side structural member  323  providing spacing and support for surfaces  312  and the sides  320  that support them. A corresponding right-side structural member (not shown) can be provided as well, e.g., in configurations where the cage  310  is fabricated as a module separate from any chassis in which it may be embodied. In some embodiments of the invention, structural members  323  and/or sides  320  are not used. Instead, the surfaces  312 ,  314  are fabricated integral to the chassis and/or fabricated separately, and affixed thereto. 
     Referring to FIG. 3D, in operation of a digital data processing or other apparatus utilizing cage  310 , cooling air drawn in from the ambient environment (e.g., via grill  208 ) or otherwise, passes through slots in surface  314 , through the assemblies&#39; plenums (or around the boards, in case of boards without plenums), and exits through slots in surface  312 . That exit may be to the environment outside the chassis or, for example, merely to another region within the cabinet—e.g., a plenum leading to fans or other air movers for the cabinet. Those skilled in the art will, of course, appreciate that the flow of cooling air could be reversed without deviation from the spirit of the illustrated embodiment or of the invention. 
     According to a preferred practice of the invention, cage  310  is manufactured by dip brazing or vacuum brazing of aluminum, or other metals or composites (with corresponding manufacturing techniques being applied to such other metals or composites), so as to ensure an air tight junction between the surfaces  312 ,  314 , guides  316  and any sides  320  so the majority of available air flows through apertures  318 . More generally, it insures that available air flow into the card cage is evenly or otherwise predictably distributed through the circuit board assemblies in accord with their respective air-flow impedances. Dip or vacuum brazing also contributes to the structural integrity of the cages, e.g., for protection against damage from shock or vibration, and facilitates EMC control. 
     Those skilled in the art will appreciate that the air- and electromagnetic interference-tight seal of dip or vacuum brazing can be achieved by other techniques, as well. Thus, for example, surfaces  312 ,  314 , guides  316  and any sides  320  may be affixed to one another via welding, soldering, epoxies, or other adhesives. They may, as well, be bolted or otherwise affixed together, e.g., so long as a sealed plenum chamber is achieved. Moreover, the cage  310  can be milled from block. Plastics or other materials (composites, laminates or otherwise) may be used instead of metals, e.g., to the extent that their fabrication insures air-tightness and/or even or otherwise predictable air flow distribution and to the extent that they provide the requisite structural integrity and EMC control. 
     As above, card cage  310  can be used in an open rack configuration or, preferably, as part of a covered chassis, for example, as shown in FIGS. 5A-5B, with one (or more) cage(s) positioned in an upper portion of the chassis (i.e., forming upper board slots) and another positioned in a lower portion (i.e., forming lower board slots). Though in the embodiments of FIGS. 3B-3D cage  310  is fabricated separately from a covered chassis in which it is used, it can be fabricated integral to the chassis, as well. 
     Such a configuration is shown in FIG. 3E, where cages  310   a - 310   d  are formed integral to a chassis  324 , as shown. Each cage includes portions that correspond to surfaces  312  and  314  and that are labelled according, to wit, as  312   a ,  314   a ,  312   b ,  314   b , and so forth. The cages are positioned so that upper and lower cages  310   a ,  310   b  are separated by a region  326  corresponding to the position of grill  208  on doors, covers or panels (not shown) placed on the front of the chassis  324 . Upper and lower cages  310   c ,  310   d  are separated by a like region  328 . Moreover, the pairs of cages  310   a ,  310   b  and  310   c ,  310   d —which will hold assemblies  202 ,  203  and  204 ,  205 , respectively, are separated by a region that will hold large format assemblies, such as  218 ,  220 . 
     The chassis  324  is fabricated from elongate members and panels of aluminum or other metal, positioned and tacked in a configuration as shown. Per a conventional vacuum brazing process, a braze alloy is applied to the members, which are then treated in a vacuum furnace. Alternatively, the elongate members and panels are joined and brazed in accord with a conventional dip brazing process. Of course, where metals, composites or other materials are used that are not amenable to brazing, appropriate corresponding manufacturing techniques are employed. 
     Circuit Board Assembly Installation and Sealing Into the Air Plenum Chamber of a Card-Cage 
     Assemblies  202 - 207  and large format assemblies  218 ,  220  can be sealed and maintained within the card cage  310 , chassis  324  or other card cage or chassis structures using rubber, elastomers, nylon, wedge-locks and other conventional means known in the art. In a preferred embodiment, a seal is established to provide improved thermal, shock, vibration, and/or electromagnetic compatibility (EMC) control. 
     To this end, referring to FIG. 4A, as noted above guides  316  comprise channels of U-shaped cross-section (though other shapes may be used instead) in which the assemblies  202 - 207 ,  218 ,  220  are slidably received. The inner dimensions of those channels are preferably sized in accord with the dimensions of the edges of circuit board assembly, e.g.,  202 , which they contact upon sliding insertion of the assembly into the cage  310 . Of course, such sizing must take into account manufacturing tolerances, desired ease of insertion, expected thermal expansion, and so forth. 
     The assembly-contacting surfaces  402 ,  404  of guides  316  are metal, e.g., aluminum, brass, copper, or other metals, composites or compounds. At some points in the contact surface EMI gasketing may be used. In this regard, the guides can be fabricated entirely from such metal or they can be fabricated from a combination of other materials and provided with a coating or laminate (e.g., Teflon, nylon, etc.) on surfaces  402  or  404 . Likewise, illustrated circuit board assembly  202  includes metal on surfaces  406 ,  408  that contact surfaces  402 ,  404 , respectively. The surfaces  406 ,  408  can be formed integral with any metal cold plate  114  included in the assembly  202  or they can comprise a metalized layer or laminate added to an edge of the cold plate  114  and/or cover  108  and/or substrate  102  making up the assembly  202 . 
     While the surfaces  402 - 408  can be fabricated at right angles to their neighboring edges (or, put another way, so that surfaces  402 ,  404  are parallel to one another and surfaces  406 ,  408  are parallel to one another), preferably, one or more of them is angled in pairs (i.e.,  402  and  404  or  406  and  408 ) so as to ease at least initial sliding insertion of the assembly  202  into guide  316  and to insure tightness of fit upon final insertion. This is represented in the drawing by a slight canting of illustrated upper guide  316 . This can be at any angle θ that achieves the foregoing, e.g., for example, between 0.5° and 10° and, more typically, between 2° and 4° for a conventional circuit board, as determined empirically and/or through use of a computer aided design modelling program. 
     In addition to, or instead of, canting guide  316 , the spacing between the sides of its U-shaped (or other-shaped) channel can be varied and/or wedges, bumps or other perturbation incorporated therein, so as to provide the desired friction fit. Such canting, other dimensional variations or perturbations can be incorporated into surfaces  406 ,  408 , instead or in addition. Regardless, according to one practice of the invention, the goal is to achieve an air-tight and/or EMC-tight seal effective from 50%-100% and, preferably, between 90%-100%. 
     The resulting increasing force necessary to slide the assembly  202  into the guides  316 —and corresponding increasing tightness of fit—is represented by the enlargened force arrow  410  shown in FIG. 4B and, then again, in FIG.  4 C. To facilitate insertion or extraction, camed leavers or other board insertion/extraction mechanisms (not shown) can be employed. 
     Digital Data Processor Chassis With Flow Balanced Air Intake Into Multiple Circuit Board Assemblies 
     FIG. 5A is an exploded view of digital data processor  500  according to the invention utilizing a central flow-balanced air intake. The digital data processor includes circuit board assemblies  502  constructed in the manner of assembly  100  (though all not necessarily include the same circuit components  104  nor carrying out the same digital data processing functions), as well as center inlet circuit board assemblies  504  constructed in the manner of larger format assemblies  218  (again, all not necessarily including the same circuit components  104  nor carrying out the same digital data processing functions). The digital data processor may also include prior art circuit boards. 
     According to one practice of the invention, digital data processor is configured as a digital signal processor, with one or more assemblies  502 ,  504  or boards configured as mother-boards, coprocessors and/or for performing signal processing boards (e.g., for fast Fourier transforms or other signal processing functions). Those assemblies/boards may include on-board memory, though, one or more other assemblies/boards may be solely dedicated to memory or other storage functions. Still further assemblies/boards may be dedicated to input/output, fabric interconnects, or other desired functions. 
     The assemblies are disposed in a chassis (not shown) that holds them in position, e.g., during operation of the digital data processor  500 . The chassis may include one or more card cages of any of the types described above or otherwise known in the art. Thus, for example, it may comprise a rack or open design of the type shown in FIG. 2A described in connection therewith. According to a preferred practice of the inventions, the chassis comprises one or more cages of the type described in connection with FIGS. 3B-3D. FIG. 5A assumes a chassis of the illustrated embodiment is of the type identified above as chassis  324 , though it will be appreciated that chassis of other configurations and types may be used instead. 
     The components are surrounded by cabinet sides  510 , here arranged in a cubic configuration of typically 4-5 cubic feet, though configurations of other shapes and volumes may be used as well. One of the sides,  510   a , includes or comprises a removable, rotatable or other panel facilitating access to the assemblies/boards  502 ,  504 , e.g., for purposes of insertion and removal (e.g., via guides  316 ) and connection to (or disconnection from) electrical connector arrays  512  at the “back” of the chassis. Those arrays  512  are constructed and operated in the manner of electrical connector arrays  210 ,  212 ,  214 , discussed above. 
     Air inlet grill  511  positioned and functioning in the manner of grill  208  is provided on side  510   a , providing cooling air-typically of temperatures ranging up to 50°-55° C., though, extending up to 70° C.—from outside the cabinet to assemblies  502  and boards  504 . In the illustrated embodiment, the grill is positioned substantially at the center of the side  510   a , as illustrated. More generally, the grill disposed centrally between the assemblies  502  in upper card cage or chassis slots and those in lower card cage or chassis and/or assemblies that make up the. respective large format assemblies  504 , in the manner indicated in the drawing. Though such a configuration facilitates drawing air from the ambient environment for distribution to, and cooling of, the assemblies, the grill  208  can be positioned elsewhere—preferably, so long as cooling air is available to be drawn over the flow impedance-matched (or -relationally sized) assemblies. Note that reversing the flow is possible while retaining the described benefits. 
     In addition to chassis and assemblies/boards  502 ,  504 , the digital data processor includes power subsystem  506  of the conventional type known and sized in accord with the power requirements of the other components. Illustrated subsystem  506  can accommodate 3000-6000W (e.g., with up to 1500 watts/foot 3  for enclosed digital data processor  500  as a whole, and with up to 3000 watts/foot 3  per card cage or sub-chassis), though other embodiments may accommodate lesser and greater wattages. The subsystem is positioned “behind” the assemblies/boards and chassis, as shown, so as to leave a plenum  514   a  above (and a similar plenum  514   b  below) and plenum  516  behind for air flow exiting the assemblies/boards. Those skilled in the art will appreciate that the subsystem  506  can be disposed elsewhere, even outside the enclosure, so long as there is a pathway for the exiting air flow. 
     Also included in digital data processor  500  are fans  508 . Referring to FIG. 5B, these are conventional fans of the type known in the art sized to pull the requisite volume of cooling air flow  518  through grill  511 , assemblies/boards  502 ,  504 , and plenums  514 ,  516  and back out of the cabinet. Illustrated fans move a combined total of up to 1,000 cubic feet of air per minute (figures that represent an upper end of present air mover technology), though fans of lesser and greater capacity may be used as well. Though illustrated fans  508  are shown at the back of the cabinet, they can be positioned elsewhere (e.g., on racks external to the digital data processor  500 , with ducts leading to/from its enclosed chassis) that defines a pathway for cooling airflow through the assemblies/boards  502 ,  504 . Moreover, while illustrated fans are positioned to pull air through the digital data processor, in alternate embodiments, they may be positioned to push air flow instead, or in addition. In alternate embodiments, the fans could be placed in the front of the chassis rather than the rear. 
     Described above are circuit board assemblies, card cages, chassis, cabinets, digital data processors and methods of fabrication and operation thereof meeting the aforementioned objects. These provide for improved capacity, density, efficiency, ruggedness, and/or longevity of components that provide digital data processing functions. They can be used with air-cooling and more particularly, for example, forced air-cooling—as well as with other heat dissipation techniques. Moreover, they can be implemented at low cost using existing components, materials and/or fabrication techniques. 
     It will be appreciated that the embodiments shown and described here are merely examples of the invention and that other embodiments incorporating changes therein fall within the scope of the invention. By way of non-limiting example, it will be appreciated that the spring-mounted (or other resiliently-mounted) heat sinks shown, for example, in FIG. 1 may be disposed for contact with the substrate and/or a cold plate to which the substrate is mounted (or of which it is formed) instead of, or in addition to, circuit components. By way of further non-limiting example, it will be appreciated that, although the circuit board and circuit board assemblies described above are shown (and described) with circuit components (e.g.,  104 ) and covers (e.g.,  108 ) on only one side of the substrate, such components and/or covers may be provided on both sides of the substrate consistent with the teachings herein. In view of the foregoing,