Abstract:
A clamshell enclosure is disclosed for providing thermal and kinetic management for an enclosed electronic circuit. The clamshell enclosure comprises a sealed clamshell casing containing the circuit, and a cover that in combination with a wall of the clamshell casing forms a duct. A heat exchanger conducts heat from the electronic circuit inside the clamshell casing to a thermal interface element located within the duct, and a thermally conductive gas moving through the duct comes into contact with the interface element, dispelling the heat and thereby cooling the enclosed electronic circuit. A cellular topology of the clamshell casing and of the cover provides stiffness to the enclosure and reduces the effects of shock and vibration on the enclosed electronic circuit.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/886,057, filed Jan. 22, 2007, and is related to patent application Ser. No. 11/203,005, filed on Aug. 11, 2005, both of which are herein incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention is related to enclosures for electronic circuits and particularly to enclosures for providing thermal and kinetic (shock and vibration resilience) management as well as protection of the circuits from contamination and electromagnetic interference. 
       BACKGROUND OF THE INVENTION 
       [0003]    There are a number of problems inherent in housing electronic circuits. One major problem is that of kinetic management, i.e. protecting the electronic circuits against destructive forces, such as shock. One conventional approach to providing kinetic management, sometimes referred to as “cocooning,” places a smaller, isolated equipment rack within a larger, hard mounted enclosure. With this approach, shock, vibration and other environmental extremes are attenuated by the isolation system to a level that is not harmful to the electronic circuits. Another approach, sometimes called Rugged, Off the Shelf (ROTS) seeks to “harden” the equipment in which the electronic circuits are enclosed, in a manner such as to make the electronic circuits immune to the rigors of the extended environmental conditions to which they are is exposed. This later approach strengthens the equipment&#39;s enclosure and provides added support for internal components, such as the electronic circuits. Both approaches suffer from added complexity, size, weight and cost. 
         [0004]    A second major problem is that of providing adequate thermal management for the electronic circuits. Electronic circuits generate heat during use and must be properly cooled in order to continue to function properly. Various conventional systems addressing the need for cooling exist, including inducing an air flow (forced convection), natural convection and radiation. Other alternatives include circulating liquid, to carry thermal energy from heat exchangers coupled to the heat source to external radiators or coolers. 
         [0005]    Conventional systems that operate by inducing an air flow typically utilize fans or blowers to move air directly over the circuitry requiring cooling. In a system having multiple electronics enclosures, such as a rack-shelf system, there may be multiple fans/blowers, e.g., one or more per enclosure, which induce air flow across their own associated circuit boards. Alternatively, there might be one large fan for the entire rack-shelf system, inducing air flow across all circuit boards simultaneously. 
         [0006]    However, such conventional cooling systems suffer from a number of problems. First, high-density packaging usually compromises cooling airflow. In conventional “blade” shelf enclosure systems, blade assemblies and their circuit boards are built differently and each enclosure/circuit board combination tends to have a different amount of internal vacant space (air channels), and thus presents different pressure drops to an induced airflow. As a consequence, system designers and integrators are obliged to add dampers and air ducts to adjust the flow of air as needed for each individual circuit board, thus significantly complicating system design and maintenance. Second, the cooling methods of some systems introduce the problem of contamination of the circuitry. While this problem can be mitigated with air filters, these filters are subject to clogging and are themselves a significant maintenance problem. Contaminants that are not removed by filtration are a problem for conventional systems that blow air directly over the circuitry, since such a technique introduces contaminants as the cooling air comes in contact with the circuitry. Third, some systems have inadequate shielding, leading to the problem of electromagnetic interference, in which electromagnetic waves from other sources penetrate the enclosure, potentially disrupting the operations of the enclosed circuitry and leading to data corruption. Fourth, some systems lack proper stiffening and rigidity, as needed to protect against shock and vibration that can damage the enclosed circuitry. Fifth, some systems are incapable of being readily adapted to standard commercial, off-the-shelf (COTS) electronics assemblies, such as motherboards. Thus, the benefits of such systems cannot be easily extended to circuitry other than that for which they were originally designed. Sixth, some systems provide thermal management through equipment, such as air movers, external to the enclosure, not as an integral part of the enclosure itself. Thus, cooling airflow is dependent on the pressure drop for a specific field-replaceable unit (FRU). 
         [0007]    What is needed is an electronics enclosure providing thermal management. Such an enclosure will preferably have the additional beneficial properties of: (1) providing optimized air flow; (2) protecting the contained electronic circuits from contamination; (3) shielding the enclosed electronic circuits against emissions and electromagnetic waves; (4) providing mechanical strengthening and stiffening to protect against shock and vibration; (5) providing ready adaptability to COTS electronics assemblies; and (6) constituting a single field-replaceable unit. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention overcomes the limitations and disadvantages of conventional electronics enclosures that provide thermal and kinetic management. 
         [0009]    In one embodiment, the clamshell electronics enclosure comprises a clamshell casing enclosing electronic circuitry, sealed so as to substantially prevent external air (or other gases) from entering the clamshell casing and coming into contact with the enclosed circuitry, thus substantially reducing the problem of contaminants. Additionally, the clamshell enclosure comprises a cover, which is attached to the clamshell casing and which, in conjunction with the clamshell casing, forms a duct external to the clamshell casing. In one embodiment, the duct contains, at one end, an impeller device and, at a second end, at least one opening. The impeller induces a flow of air (or other thermally conductive gaseous substance) through the duct by creating a pressure differential. In one embodiment the air enters the duct through the impeller and travels through the channels formed by the duct and exits through the opening at the second end of the duct; in another embodiment, the flow may be in the opposite direction. 
         [0010]    In order to provide cooling, a heat exchanger is thermally coupled to the circuitry contained within the sealed clamshell casing. The heat exchanger conducts heat away from the circuitry by conducting the heat energy to an interface element and in turn, to the ducted air stream. More specifically, the heat exchanger further comprises interface elements, which extend through a wall of the clamshell casing into the duct such that the clamshell casing remains sealed. The heat exchanger&#39;s interface elements are within the path of the cooling air flowing through the duct, which serves to transfer the heat conducted by the heat exchanger to the air channel, thus cooling the electronic circuits contained within, while simultaneously allowing the clamshell casing to remain sealed against the external environment. 
         [0011]    Such a clamshell enclosure beneficially provides an effective cooling mechanism, only causing the air stream to travel to locations corresponding to circuitry in need of cooling, rather than forcing the air across the entire surface of the circuit board or boards housing the circuitry. Second, as noted, the sealed nature of the clamshell casing with respect to the duct substantially prevents contaminants, such as dust and moisture, from coming into contact with the internal circuitry. Third, in one embodiment the impeller, duct, heat exchanger, and other elements of the thermal management system are a part of the clamshell enclosure, rather than external to it, and thus the clamshell enclosure can operate as a closed system. Hence, the clamshell enclosure&#39;s cooling characteristics are independent of other such assemblies that may be combined in a rack shelf. In particular, there is no need to connect heat pipes or any other heat transfer mechanism to external cooling components. 
         [0012]    In one embodiment, the clamshell casing is composed of a material, such as aluminum, having conductive properties or a conductive surface. This conductivity has the benefit of providing shielding against emissions and substantially reducing the intrusion of electromagnetic waves. 
         [0013]    In one embodiment, the clamshell casing and cover of the clamshell enclosure are designed to capture the internal circuits and arrange their accompanying heat exchangers in a cellular topology. Such a topology is inherently strong and so beneficially provides additional stiffness, further strengthening the clamshell enclosure and providing protection against vibration and shock to the enclosed circuitry. 
         [0014]    In one embodiment, the combination of the clamshell casing and the cover forms a clamshell enclosure that is essentially a rectangular solid in shape. This beneficially allows the user to easily and compactly store individual clamshell enclosures within larger units, such as a rack-shelf system. 
         [0015]    The features and advantages described in the specification are not all inclusive, and particularly, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings, specification and claims herein. Moreover, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and may not have been selected to delineate or circumscribe the inventive subject matter, resort to the claims being necessary to determine such inventive subject matter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is an overhead view of the exterior of a clamshell enclosure, according to one embodiment of the present invention. 
           [0017]      FIG. 2  is a rear view of the exterior of a clamshell enclosure, according to the embodiment of  FIG. 1 . 
           [0018]      FIG. 3  is a cutaway view of a clamshell enclosure illustrating its internal components, according to one embodiment of the present invention. 
           [0019]      FIG. 4  illustrates the aggregation of a plurality of clamshell enclosures within a single rack-shelf unit, according to one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    A preferred embodiment of the present invention is now described with reference to the figures where like reference numbers indicate identical or functionally similar elements. Also in the figures, the left most digit of each reference number corresponds to the figure in which the reference number is first used. 
         [0021]    The present invention relates to a clamshell electronics enclosure for providing thermal and kinetic management for electronic circuits while simultaneously providing additional beneficial properties, such as protection for the circuits against contaminants and electromagnetic interference. 
         [0022]      FIG. 1  is an overhead view of a clamshell enclosure  100 , according to one embodiment of the invention. The clamshell enclosure  100  comprises a clamshell casing  102  and a cover  104 , which together form a duct  105  in the space enclosed between them. In one embodiment, both the clamshell casing  102  and the cover  104  are composed primarily of aluminum, a metal offering a good compromise between high strength and low mass and having favorable conductive properties. In other embodiments, the clamshell casing  102  can be composed of other materials that provide stiffness and reduce electromagnetic interference, e.g., thermally conductive composite materials, which can have substantially all of the benefits of aluminum, but with lower mass. In one embodiment, the duct  105  is coplanar and occupies a lateral space with respect to the clamshell casing  102 . 
         [0023]    Within the interior of the clamshell casing  102  is a plurality of electronic circuits in need of cooling. Each of these circuits is thermally coupled with a heat exchanger which conducts heat away from the circuit. Each heat exchanger comprises a thermal connector located within the interior of the sealed clamshell casing  102  that provides thermal coupling with a circuit, and each extends through the wall of the clamshell casing  102  adjacent to the duct  105 , entering the duct  105  and forming a thermal interface element  106  but leaving no gap in the clamshell casing  102  through which contaminants may enter the interior of the clamshell casing  102 . Thus, there is a thermal path from the circuits on the interior of the clamshell casing  102 , through the thermal connectors, to the thermal interface elements  106  within the duct  105  on the exterior of the clamshell casing  102 , yet the clamshell casing  102  remains sealed. 
         [0024]    The thermal interface elements  106  are designed to maximize heat transfer away from the internal circuitry to which they are thermally coupled, and may be formed in a variety of ways. In the embodiment of  FIG. 1  and related figures, the thermal interface elements  106  are implemented as conventional fin-style heatsinks. The fins may be of various types, such as pin-fins or contoured fins. 
         [0025]    Thermal management is achieved by inducing a flow of a thermally conductive gaseous substance through the duct  105 . In the embodiment of  FIG. 1 , in which the thermally conductive gaseous substance employed is air, a plurality of thermal interface elements  106 , each corresponding to an internal circuit, are located within the duct  105 . Further, the duct  105  contains an impeller  110 , which draws air into the impeller and in turn into the duct  105 , and the air exiting at an opening  108  located near each thermal interface element  106 . This design causes the air introduced into the duct  105  by the impeller  110  to flow over the thermal interface elements  106  and out their nearby opening  108 , cooling the thermal interface elements  106  and in turn causing the internal circuits to which they are attached to be cooled. In other embodiments, the air flow is in the opposite direction, with the impeller  110  forcing air to exit the duct through the impeller, thus producing a pressure drop, drawing air inward through the opening  108 . One of skill in the art would realize that an impeller  110 , such as a fan, is merely one means of accomplishing the more general technique of inducing a pressure differential through the duct  105 , thereby causing a flow of air or other thermally conductive substance across the thermal interface elements  106 . 
         [0026]    Note that by locating the impeller  110  within the duct  105 , the clamshell enclosure  100  becomes a single field-replaceable unit (FRU), with no dependency on external cooling equipment. 
         [0027]    Optionally, the surface of the duct  105  may additionally include surface area enhancing features, such as fins, connected to heat sources internal to the clamshell casing  102 , using thermal shunts or heat pipes, thus providing cooling for any additional circuitry not cooled by the thermal interface element  106 . 
         [0028]    In some embodiments, the individual clamshell enclosures  100  may be aggregated into a larger enclosure such as a rack-shelf system. 
         [0029]    Note that the duct system provides more efficient airflow than conventional systems, in which the air must be forced across the entire surface of the system in question. Using the duct system, the air stream is directed over the regions corresponding to circuitry in need of cooling. As a beneficial consequence, less power is required for the impellers  110 . 
         [0030]    Conventional thermal management systems that cause a cooling air stream to come into direct contact with circuitry suffer from the problem of the introduction of external contaminants, such as moisture and dust. The clamshell enclosure addresses and eliminates this problem by preventing the air stream from coming into contact with the circuitry. Rather, the duct  105  formed by the clamshell casing  102  and the cover  104  is external to the clamshell casing  102  itself, with the cooling mechanism being provided by an air stream contacting only the external thermal interface elements, and not their internal circuits, which are safely sealed within the clamshell casing  102 . 
         [0031]    The embodiment of  FIG. 1  also illustrates a cellular topology, in which the clamshell casing  102  and the cover  104  are divided into a set of blocks, or cells, each corresponding to a particular electronic circuit housed within. This cellular topology is inherently stiff, and along with the stiffness of the materials composing the clamshell casing  102  and the cover  104  provides a rigid enclosure. This prevents damaging flexure of the electronic circuit board assemblies contained within the enclosure and thereby mitigates the deleterious effects of shock and vibration experienced by the clamshell enclosure  100 . 
         [0032]    In one embodiment, clamshell casing  102  is formed of a conductive material, such as aluminum. Alternatively, the clamshell casing  102  may merely have a conductive surface. The conductive nature of the clamshell casing  102  has the desirable property of providing shielding against emissions and substantially reducing the intrusion of electromagnetic waves. This allows a clamshell enclosure  100  to be located in close proximity to another electromagnetic device without the internal circuitry of either one being adversely affected. This is particularly useful in, for example, the rack-shelf configuration discussed below, in which individual enclosures are aggregated in close proximity to one another. 
         [0033]    It is appreciated that the particular embodiment of the enclosure depicted in  FIG. 1  represents but one choice of implementation. For example, there need not be exactly four thermal interface elements, nor need there be exactly one cover opening per thermal interface element, nor need the thermal interface elements be implemented as fin-style heatsinks. Other choices would be clear and equally feasible to those of skill in the art. 
         [0034]      FIG. 2  is a rear-view image of the embodiment of  FIG. 1 . Shown more fully than in  FIG. 1  is the impeller  110 , which causes air to flow through the duct  105 . In the illustrated embodiment, the impellers  110  are blowers. Note that such blowers, being primarily mechanical rather than electronic, tend to require replacement more frequently than the circuitry within the clamshell casing  102 . Although, in one embodiment noted above, the blowers are located within the duct  105 , the cover  104  is easily removed for maintenance access to the impeller (blower assembly)  110 , and thus the blowers may be easily removed and replaced without replacing the entire clamshell enclosure  100 . 
         [0035]    Also illustrated in  FIG. 2  is system connector  202 , which provides the interface needed for aggregating the clamshell enclosure  100  into a larger unit, such as the rack-shelf system discussed below in conjunction with  FIG. 4 . The system connector  202  provides power to the individual enclosures, and also provides data transfer capabilities. 
         [0036]      FIG. 3  is a cutaway view illustrating the contents of the clamshell enclosure  100  according to one embodiment. Duct  105  is the space between one wall of clamshell casing  102  and cover  104 . Clamshell casing  102  securely encloses a variety of electronic circuits, including processors  308 , I/O board  310 , and memory  312 . Processor thermal interface elements  314  and I/O thermal interface elements  316  are located within the duct  105 , where they come into contact with cooling air, leading in turn to the cooling of the processors  308  and the I/O board  310 , respectively. The heat spreader plates  322  serve as thermal connectors, helping to spread the heat generated by processors  308  so as to improve heat transfer to the processor thermal interface elements  314 . Thermal conductive strap  318  is used to conduct heat from the hot spot integrated circuit (e.g. processors  308 , I/O board  310 , or integrated circuits (not shown)) to the I/O thermal interface element  316 , thus providing a conduction cooling path from hot spots internal to the clamshell enclosure  100  to the ducted external air stream. Additionally, thermal interposer  320  is used both to ensure a low thermal impedance path for the I/O board  310  and to facilitate heat transfer from the I/O board  310  to the I/O thermal interface element  316 . In one embodiment, the thermal interposer  320  is made up of a resilient plastic material, doped with a thermally conductive and insulating compound such as aluminum oxide, boron nitride or other materials. Alternatively, the thermal interposer  320  may be formed from a gel or a foam. 
         [0037]      FIG. 4  illustrates multiple clamshell enclosures  100  aggregated within a single rack-shelf system  400 . Individual clamshell enclosures  100  are plugged into to the rack-shelf system via their system connectors  202 . In a preferred embodiment, the clamshell enclosure  100  is designed to have a regular shape, such as the rectangular or “blade” shape of the embodiment of  FIG. 1 . Such blade-shaped enclosures may easily and compactly be housed within an enclosure storage unit such as rack-shelf system  400 . Note that due to the self-contained nature of each individual clamshell enclosure  100 , the close proximity of the clamshell enclosures  100  within the rack-shelf system  400  does not introduce complications, nor is there a need for external connections to provide features such as thermal management, although such additional features can be used with the present invention. In one embodiment, the clamshell enclosures  100  are independent of each other and may be inserted and removed in a modular manner. For example, since each clamshell enclosure  100  has its own built-in thermal management system, such as that comprised by impeller  110 , duct  105 , thermal interface elements  106 , and openings  108 , each maintains a proper temperature, independent of the presence of the others. Likewise, since in a preferred embodiment the clamshell casing  102  provides protection from electromagnetic interference, the internal circuitry of one clamshell enclosure  100  does not substantially interfere with that of another, nor is there a need for the rack-shelf system  400  to provide a shield that would otherwise be needed to prevent circuit-generated noise from escaping into the environment outside rack-shelf system  400 . 
         [0038]    While the invention has been particularly shown and described with reference to a preferred embodiment and various alternate embodiments, it will be understood by persons skilled in the relevant art that various changes in form and details can be made therein without departing from the spirit and scope of the invention.