US20070177348A1 - Ruggedized electronics enclosure - Google Patents

Abstract

The present invention relates to a ruggedized enclosure for housing and protecting electronic circuits. The enclosure utilizes a top compartment for housing the circuit and a cooling assembly rigidly coupled to the top compartment. The cooling assembly utilizes a passive radiator to form a rigid truss plate structure. The truss plate structure rigidifies the enclosure helping to protect the enclosure and circuit from destructive shock events and destructive vibration events. The cooling assembly further provides an efficient heat exchange for removing heat from the electronic circuit. A method for protecting an electronic circuit utilizing a rigid truss plate structure is also provided.

Description

RELATED APPLICATION
• This application is a continuation of U.S. patent application Ser. No. 10/850,523, entitled “Ruggedized Electronics Enclosure”, that was filed on May 19, 2004, which is a continuation of U.S. patent application Ser. No. 10/232,915, entitled “Ruggedized Electronics Enclosure,” that was filed on Aug. 30, 2002.
BACKGROUND OF THE INVENTION
• 1. Field of the Invention
• This invention is related to enclosures for electronic circuits and particularly to ruggedized enclosures for use in installations subjected to hostile environments including destructive shock events and destructive vibration events. In one embodiment, the invention may operate without requiring additional mechanical isolation.
• 2. Description of the Related Art
• Conventional ruggedized electronics enclosures are often employed in military applications. The environments in which military electronic circuits must be able to operate typically present conditions outside of a commercial electronic circuit's operational parameters. Examples of such conditions include excessive moisture, salt, heat, vibrations, and mechanical shock. Historically, military electronic equipment was custom made to provide the required survivability in the hostile environments. While effective in surviving the environment, custom equipment is often significantly more expensive than commercial systems, and is typically difficult if not impossible to upgrade to the latest technologies. Therefore, a current trend in conventional military hardware is to adapt commercially available electronics for use in military applications. These systems are typically known as Commercial Off The Shelf systems, or COTS.
• The COTS design philosophy has allowed the military to keep current with technological innovations in computers and electronics, without requiring specialized and dedicated electronic circuit board assemblies. The COTS design methodology is attractive because of the rapidly increasing computational power of commercially available, general-purpose computers. Since the components in a COTS system are commercially available, though usually modified to some extent, the military can maintain an upgrade path similar to that of a commercial PC user. Thus the COTS philosophy allows the military to integrate the most potent electronic components available into their current hardware systems.
• While COTS systems have allowed the military to reduce the cost of equipment and to make more frequent upgrades to existing equipment, there are inherent disadvantages to COTS systems. As noted above, military applications must be able to withstand various environmental extremes, including humidity, temperature, shock and vibration. These conditions are typically outside of the operating parameters of commercial electronics and, thus, added precautions and modifications to the physical structures of the equipment must be made to ensure reliability of operation in these environments. Conventional COTS systems typically use two specialized modifications to maintain reliability. These approaches may be used separately, or in combination.
• To deploy COTS equipment in hazardous environments, COTS components are housed in a complex ruggedized enclosure or case. One approach, 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 compatible with COTS equipment. Another approach, sometimes called Rugged, Off The Shelf (ROTS) seeks to “harden” the COTS equipment, in a manner such as to make it immune to the rigors of the extended environmental conditions to which it is exposed. This later approach strengthens the equipment's enclosure and provides added support for internal components. Both cocooning and ROTS design methodologies must also improve cooling efficiency to accommodate higher operating ambient temperatures. Both approaches suffer from added complexity, size, weight and cost.
• The size and complexity exacerbates heat-removal from the enclosure and often complex heat flow routes must be devised in order to maintain a desirable operating temperature. Taken together, these design considerations drastically increase the cost and complexity of such an enclosure.
• Commercial systems are typically designed around three main criteria, cost, time-to-market and easy expansion. To deliver on all three design goals, the assumption is that the environment for the system will not be exposed to extreme environmental conditions. Cost is the primary motivator to keeping the packaging simple and inexpensive. The package support structures may have a low cost to keep the system cost from escalating. Keeping costs down to a minimum is counter to the requirements of making a system robust enough to survive a military environment.
• To easily accommodate system expansion, computer manufacturers try to simplify the installation of peripheral cards, memory and storage. The idea of having a minimum number of fasteners (i.e., a snap-in-place design) allows the customer easy access and installation of peripherals. The design's modularity preserves the customer's investment. When you couple the commercial constraints with the requirements of the military environment, the design requires a different approach, typically moving the structural changes to the system enclosure and it's attachments. The usual cocooning approach is to design the enclosure to absorb as much of the shock as possible to allow the incumbent system to survive the environment. In practice, this is not easily achieved, especially when using larger, and heavier computer systems. Thus, the idea of completely isolating a commercial system from the rigors of the military environment is difficult to achieve and adds a large cost premium because the rack is the item being modified. The current solution to supporting COTS technology in a military environment described above, adds significant complexity to the system.
• Two of the most difficult conditions to design for are vibration and mechanical shock. Mechanical shock and vibration may over time destroy electronic equipment by deforming or fracturing enclosures and internal support structures and by causing electrical connectors, circuit card assemblies and other components to fail. In military applications, as well as in commercial avionics and the automotive industry, electronics must be able to operate while being subjected to constant vibrational forces generated by the vehicle engines, or waves, as well as being subjected to sudden, and often drastic, shocks. Examples of such shocks are those generated by bombs, missiles, depth charges, air pockets, potholes, and other impacts typically encountered by military or commercial vessels. Furthermore, these conditions may also be seen in the operating conditions of a network or telephone server during an earthquake. While providing some protection from shock and vibration, the conventional ruggedized enclosure operating alone cannot provide adequate protection for mission-critical electrical components and circuits.
• In order to provide additional protection against shock and vibration, conventional COTS systems mount the ruggedized enclosures described above in a mechanically isolated cocoon.FIG. 1 illustrates a conventional mechanically isolated cocoon. As illustrated inFIG. 1, acocoon100 is provided to house the variousruggedized enclosures110. Thecocoon100 may be attached to a floor130 and/or awall140 of its surroundings. Commonly this includes the fuselage or deck plate of a military vehicle. Thecocoon100 is attached to thesurroundings130,140 viamechanical isolators120. A particularly advancedmechanical isolator120 is the polymer isolator illustrated inFIG. 1, though conventional systems may use any spring-like apparatus to provide the isolation. By attaching thecocoon100 to itssurroundings130,140 viamechanical isolators120, thecocoon100 is allowed limited movement with five degrees of freedom. This limited movement helps to dampen the effects of shock and vibration.
• There are several drawbacks to using the mechanicallyisolated cocoon100. In order to reduce the shock to the equipment, thecocoon100 must be provided with asway space150 in which it may move unobstructed. Typically thissway space150 is four to seven inches in each direction of movement. Thus thecocoon100 consumesadditional space150 which might otherwise be utilized for other activities or equipment. In military applications, commercial aircraft, as well as automotive applications, space is often at a premium.
• Additionally, while thecocoon100 does isolate the equipment from some vibration and shock, it does not completely isolate the equipment. For example, aconventional cocoon100 can receive a 60-80 G shock (a “G” is a unit of force equal to the force exerted by Earth's gravity on a body at rest and is used to indicate the force the equipment is subjected to when accelerated by a shock event) and reduce the shock felt by the equipment to 10-15 G's. Typically the performance of thecocoon100 is limited by sway space available, materials used, and equipment placement within thecocoon100. Additionally, if the environment around thecocoon100 moves more than thesway space150 can accommodate, then thecocoon100 and its equipment will feel the entire shock event. While a significant reduction in the shock may be experienced, it is important to note that commercial equipment is frequently rated for 5 G's or less. Thus, there is still a significant chance for failure within the system.
• To provide the additional shock protection, conventional COTS systems pair thecocoon100 with theruggedized enclosures110, or cocoon. However, while more effective in protecting the equipment from mechanical shock, theseruggedized enclosures110 work only when the shock isolation system is carefully integrated with the included systems. Since the enclosure is allowed to move, issues such as weight, position, center of gravity and heat removal all have to be balanced. Thus, the cost and complexity of such a system are significantly higher when compared to a commercial system using similar electrical components.
• What is needed is a ruggedized enclosure for use in hostile environments which: 1) provides a simplified and effective heat flow design; 2) may utilize COTS components; 3) does not require the use of a mechanical isolator or sway space; 4) provides a high level of shock and vibration protection without need for augmentation; and 5) may be manufactured at low cost.
SUMMARY OF THE INVENTION
• The present invention overcomes the limitations and disadvantages of conventional electronics enclosures used in harsh operating environments. In one embodiment, the invention provides protection from destructive shock events and destructive vibration events without need of external mechanical isolation.
• In one embodiment, the electronics enclosure includes a top compartment for housing the electronic circuit, and a cooling assembly attached thereto. The top compartment may be sealed to further protect the electronic circuit from moisture and unwanted particles in the air. The cooling assembly includes a rigid truss plate structure which forms a structural member for rigidifying the enclosure, and also forms an efficient heat radiator for removing heat from the electronic circuit. The truss plate structure achieves it's high strength to weight ratio in a manner similar to conventional “honey-comb” or sandwich structures. The truss plate structure converts bending mode forces, applied to opposing plates, into compression and extension mode forces. However, unlike conventional “honey-comb” or sandwich constructions, the present invention provides ducts or passage ways through which cooling air (or other cooling fluid) is allowed to flow to aid in the efficient removal of heat from the top compartment. In an alternate embodiment, the truss plate structure is a honey-comb truss structure that provides passages through which cooling air (or other cooling fluid) is allowed to flow.
• In one embodiment, the rigid truss plate structure is formed from a passive radiator coupled between a heat spreader plate and a bottom plate. The heat spreader plate also forms the bottom of the top enclosure and provides both mechanical and thermal coupling between the top compartment and the cooling assembly. In one embodiment, the passive radiator may be comprised of a corrugated fin. In another embodiment, the passive radiator is comprised of triangularly shaped fins (an A-frame structure). Both the corrugated fin and the triangular fin structure may provide additional protection against destructive shear and twisting of the enclosure. In another embodiment, the passive radiator is comprised of a pin-style heatsink. In one embodiment the pin-style heatsink is arranged according to a pin density pattern to create a turbulence gradient for the cooling assembly.
• In one embodiment, the enclosure is rigidified by the truss plate structure in order to protect the electronic circuit against an anticipated destructive shock event. In one embodiment, the enclosure and circuit can withstand and survive a 60 G shock event. In alternate embodiments the enclosure is designed based upon various criteria such that a particular enclosure and enclosed device (e.g., circuit) is designed to withstand and survive shock events in the range of 20 G to at least 60 G depending upon these design criteria. In another embodiment, the enclosure's resonant frequency is raised above an anticipated destructive vibration event. In one embodiment, of special interest for land vehicle or aircraft applications, the enclosure and circuit have a resonant frequency in the range of 200 Hz to at least 1 kHz. In another embodiment, of special interest for shipboard applications, the enclosure and circuit have a resonant frequency in the range of 20 to 40 Hz. The listed ranges are merely exemplary, and alternate embodiments may have a resonant frequency selected to be higher than a known destructive vibration event.
• In one embodiment, the cooling assembly further provides heat pipes for drawing away additional heat from the electronic circuit and delivering it to an external heat exchanger. In one embodiment, the heat pipes cooperate with the passive radiator to provide an efficient heat exchanger.
• In one embodiment, the electronic enclosure includes the use of microchips. These chips may be placed top-down on the heat spreader plate in order to provide a more efficient heat transfer from the chip to the cooling assembly.
• A method for protecting and cooling an electronic circuit via a rigid truss plate structure is also provided.
• 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
• FIG. 1 illustrates a conventional mechanically isolated cocoon system.
• FIG. 2 illustrates an exploded view of a ruggedized electronics enclosure according to one embodiment of the present invention.
• FIG. 3 illustrates a cut-away structural detail of the assembled ruggedized electronics enclosure according to one embodiment of the present invention.
• FIG. 4 illustrates a cut-away diagram of the ruggedized electronics enclosure showing heat and airflow related to the enclosure according to one embodiment of the present invention.
• FIG. 5 illustrates a cooling assembly utilizing a triangular fin structure.
• FIG. 6 illustrates a cooling assembly utilizing a pin-style heatsink.
• FIG. 7 illustrates a cooling assembly utilizing a pin-style heatsink forming a turbulence gradient.
DETAILED DESCRIPTION
• 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(s) of each reference number correspond(s) to the figure in which the reference number is first used.
• The present invention relates to a ruggedized electronics enclosure for protecting electronic circuits that must be able to survive and operate under harsh conditions such as those in military and automotive environments. The enclosure must be able to protect the electronic circuits from severe vibration and shock, heat, moisture, dust particulate, and various other adverse conditions. Throughout this description, the word “destructive” will be used to indicate a force or event which may cause the enclosure or the electronic circuit to fail after a single occurrence of the event, or after repeated occurrences of the event between maintenance intervals. Specific destructive events will be discussed in more detail below.
• FIG. 2 illustrates an exploded view of aruggedized electronics enclosure200 according to the present invention. As illustrated inFIG. 2, theenclosure200 is configured to house and protect acompute element210. Thecompute element210 is chosen by way of example as illustrative of the primary features and operation of theenclosure200, and one skilled in the art will recognize that theenclosure200 may be configured to house and protect any electronic circuit. Examples of alternate electronic circuits include various other components used in a computer, ordinance guidance and communication boards, vehicle control modules, radio and communications equipment, radar equipment, etc. As will be discussed below, theenclosure200 may most advantageously be used for any electronic circuit which may be formed having a low vertical profile, but may be used to add increased protection to any dimensioned electronic circuit.
• Theruggedized electronics enclosure200 includes atop compartment220 for housing the electronic circuit210 (illustrated as a compute element), and acooling assembly230 coupled to the bottom of thetop compartment220. As illustrated, theenclosure200 is shaped as a rectangle, however any footprint shape may be used. Non-rectangular shapes may be preferred in applications where space is at a premium, such as in aircraft, or military ordinance.
• Thetop compartment220 includes atop cover222, one or more thermal interposers224, a pair ofside walls226, a front wall227, a rear wall (not shown) and aheat spreader plate240. In one embodiment, theside walls226, front wall227 and rear wall as well as thetop cover222 are formed from aluminum. Alternatively, these portions of thetop compartment220 may be may be formed of any rigid material including, but not limited to steel, and plastics. Preferably,side walls226 are sized to extend the entire combined height of thetop compartment220 and coolingassembly230. Front wall227 and rear wall are preferably sized to extend the height of thetop compartment220. An upper portion ofside walls226, front wall227, the back wall,top cover22 andheat spreader plate240 cooperate to form the sealedtop compartment220 for housing theelectronic circuit210. In another embodiment, thetop compartment220 may not be sealed, but may instead be open to the environment. The various parts which form thetop compartment220 may be coupled together using screws or other fastener types that may require special tools for removal. Additionally, the screw fasteners may be augmented by other self-aligning/locking mechanical components. By utilizing screw fasteners or other removable fasteners, thetop compartment220 may be opened as necessary to provide service to the electronics housed inside. Alternatively, the compartment structures, or a substructure therein, may be formed by milling or casting a single piece of material such as aluminum, steel or plastic. Another alternative includes welding the elements comprising thetop compartment220 together to form a solid enclosure. However, while welding may increase structural stability, it decreases the enclosure's200 serviceability.
• The coolingassembly230 is coupled to the bottom oftop compartment220 and further includes a passive radiator232 (here illustrated in oneembodiment232a) and abottom plate234. Thepassive radiator232 andbottom plate234 are coupled to thecooling assembly230 in order to draw heat away from the highest dissipation components (the top compartment220) to a high efficiency heat exchanger (the passive radiator232).
• As illustrated, thepassive radiator232 may be formed from an aluminum corrugatedfin232a.As will be discussed below, the use of an aluminum corrugatedfin232aprovides specific advantages over other passive radiators, however, one skilled in the art will recognize that other passive radiators may be used in place of thecorrugated fin232a,as well as that theradiator232 may be made from other material aside from aluminum. For example, the passive radiator may be formed from copper, carbon fiber, composite structures of aluminum and copper or plastic, and may additionally be used in conjunction with heat-pipes and cold plates. Additionally, other structures aside from acorrugated fin232amay be used.FIG. 5 illustrates a triangular fin, or A-frame, truss structure232bpreferably formed from aluminum or steel. As will be discussed below, this embodiment of thepassive radiator232 is more difficult and more expensive to manufacture, but provides additional structural integrity to theenclosure200.FIG. 6 illustrates another embodiment of thepassive radiator232 utilizing pin-style heat-sinks232csandwiched between theheat spreader plate240 and thebottom plate234. This forms a rigid truss plate structure while allowing some measure of heat dissipation profiling based on the placement and density of the pins.
• In general,heat spreader plate240, a lower portion ofside walls226, andbottom plate234 cooperate to “sandwich” thepassive radiator232 into a solid rigid truss plate structure. The truss plate structure achieves a high strength to weight ratio by converting bending mode forces, applied to opposing plates, into compression and extension mode forces. This is similar to plates formed from conventional honey-comb or sandwich construction. However, unlike conventional “honey-comb” or sandwich construction, the present invention provides ducts or passageways through which cooling air (or other cooling fluid) is allowed to flow to aid in the efficient removal of heat from thetop compartment220.
• The coolingassembly230 may be assembled in a number of ways, with one goal being to keep the assembly process simple, while preserving structural rigidity and allowing the effective transfer of heat from the base-plate to thepassive radiator232. One way of doing this with a metallicpassive radiator232 is through welding. If a non-metallicpassive radiator232 is used, a thermally conductive adhesive may be used.
• As illustrated,electronic circuit210 is a compute element and includes aPCB212, a plurality ofprocessors214 coupled to a front of thePCB212, and a plurality ofmemory components216 electrically coupled to a back ofPCB212. Athermal interposer224ais positioned to contact the back ofPCB212 and thememory components216 to provide a heat exchange betweenPCB212 andmemory components216. Typically, the interposer224 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 interposer224 may be formed from a gel or a foam. Alternatively, thetop compartment220 may be filled with thermally conductive foam. While this alternative provides structure and heat removal, it is not preferred due to the permanent nature of the installation. A removable interposer224 is preferred to aid in the keeping the electronics inside thetop compartment220 serviceable.
• As will be discussed in greater detail below,processors214 andPCB212 are positioned withintop compartment220 such thatprocessors214 are placed in physical contact withheat spreader plate240, allowing for heat to be conducted away fromprocessors214. Alternatively, a heat conducting material, such as a thermal interposer similar to interposer224, may be position between theprocessors214 and theheat spreader plate240. A second thermal interposer224 is positioned between thememory components216 and thetop cover222.Top compartment220 is preferably sized to provide just enough vertical and horizontal room to fitelectronic circuit210 within its confines. In a preferred embodiment, thermal interposers224 are created from a resilient material which is slightly compressed to ensure a “snug” fit for theelectronic circuit210 withintop compartment220. By ensuring that the thermal interposers224 make tight contact with thetop cover222, additional thermal and structural benefits are realized.
• FIG. 3 illustrates a cut-away structural detail of the assembledruggedized electronics enclosure200. As introduced inFIG. 2, in one embodiment, theelectronic circuit210 housed in thetop compartment220 is again a compute element. One of the objectives for theruggedized electronics enclosure200 is to provide protection to theelectronic circuit210 housed in thetop compartment220 from harsh operating environments. As noted above, thetop compartment220 may be completely sealed by appropriately sizing theside walls226, front wall228 (not shown), back wall (not shown),top cover222 andheat spreader plate240 to ensure that no open spaces exist in thetop compartment220 surface.
• In addition to being able to make thetop compartment220 airtight, additional steps may be made to “ruggedize” theenclosure200 to help reduce the effects of destructive shock events and destructive vibration events on theelectronic circuit210 housed within. A destructive shock event is any shock event that may render theelectronic circuit210 orenclosure200 inoperative due to a large change in force and momentum being applied to thecircuit210 andenclosure200. Thecircuit210 orenclosure200 may be rendered inoperative after a single destructive shock event or after a series of destructive shock events occurring between maintenance intervals. Examples of destructive shock events include impacts and explosions from bombs, missiles, other military ordinance, water craft hitting depth charges, aircraft hitting air pockets, wheeled vehicles hitting potholes as well as other impacts typically encountered by military or commercial vessels. One skilled in the art will recognize that other destructive shock events exist and that the above list provides only a general context for the nature of a destructive shock event.
• Similarly, a destructive vibration event is any vibration event that may cause theelectronic circuit210 orenclosure200 to fail due to a weakened structural integrity. Destructive vibration events may be isolated and short-lived in duration or may always be present in the operating environment. Examples of destructive vibration events include engine vibrations, turbine vibrations, screw vibrations, prolonged shock events, travel along uneven surfaces etc. One skilled in the art will recognize that other destructive vibration events exist and that the above list provides only a basic context for the nature of a destructive vibration event.
• In typical military applications, theelectronic circuit210 must be able to survive and continue to operate efficiently after being subjected to an 60 G shock or constant vibration from engines and other movement. Military specifications MIL810, MIL901, MIL167 and ISO10055 provide specific requirements for shock and vibration resistance depending on the desired application and are incorporated in their entireties herein. Typically, the individual chip-level components used in a standard commercial environment will withstand up to an 60 G shock load. This is due in part to the fact that the interconnects and silicon are packaged such that there is high structural rigidity in the component. However, one concern is with the printed circuit board (PCB) and its assembly. To minimize the shock impact to the PCB and the solder connections, it is beneficial to have structural ties between the board and its components and coolingassembly230.
• One design goal is to make the entire enclosure assembly one rigid structural element in order to protect against destructive shock and vibration events. In one embodiment, the enclosure is rigidified by the truss plate structure in order to protect the electronic circuit against an anticipated destructive shock event. In one embodiment, the enclosure and circuit can withstand and survive a 60 G shock event. In alternate embodiments the enclosure is designed based upon various criteria (e.g., materials, mass, truss plate, dimensions, assembly methods, etc.) such that a particular enclosure and enclosed device (e.g., circuit) is designed to withstand and survive shock events in the range of 20 G to at least 60 G depending upon these design criteria.
• One aspect of forming theenclosure200 as a rigid structural element includes raising the enclosure's200 resonant frequency to a frequency higher than the destructive vibration events to which theenclosure200, will be subject. Two major factors that affect the resonant frequency of a given structure are the mass, and the material's inherent stiffness. Typically, the lower the mass, the higher the resonant frequency. Thus, the overall mass of theenclosure200 helps determine the resonant frequency of theenclosure200 as well as its susceptibility to vibrational damage. Also, the higher the material stiffness, the higher the resonant frequency. As noted above, from a vibration standpoint, it is desirable to have the resonant frequency above the frequencies of any anticipated destructive vibration events to keep the mechanical structure from adding to the vibration energy.
• Thus, theenclosure200 is formed from a material that balances stiffness and mass to provide an overall high resonant frequency which is higher than the anticipated destructive vibration event frequencies. In the preferred embodiment, theruggedized enclosure200 is composed primarily of aluminum. The use of aluminum offers a good compromise between strength needed to protect theelectronic circuit210, while providing a lower total mass for the enclosure. As will be discussed below, the use of aluminum also provides an efficient way of removing heat generated by theelectronic circuit210. In one embodiment, theenclosure200 is designed to have a resonant frequency that is at least approximately twice the 12-25 Hz frequency of naval shock events. In an alternate embodiment, theenclosure200 has a resonant frequency in the range of hundreds of Hz, to protect the enclosure against an aircraft's prop or turbine vibrations. The specific resonant frequency chosen will be dictated by the specific vibrational frequency of the prop or turbine engine used, e.g., between 200 Hz and 1 kHz. These frequencies are merely examples of the resonant frequencies supported by the present invention. Alternate embodiments will have a resonant frequency selected to be greater than the vibrational frequency of an anticipated shock event that is to be dissipated by theenclosure200.
• Another aspect of theruggedized enclosure200 is its overall profile. In a preferred embodiment, the overall vertical height of theenclosure200 is 1 rack unit (“U”) or 1.75 inches. Additionally, in one embodiment, thetop compartment220 is configured to house theelectronic circuit210 snugly, without allowing for significant horizontal or vertical movement within thecompartment220. Further cushioning and insulation from vibration is garnered by the use of the thermal interposers224 which may be compressed slightly to ensure a snug fit while providing an efficient heat conduit to remove heat from theelectronic circuit210.
• Passive radiator232 provides additional resistance to destructive shock and vibration events. By using a passive radiator and fluid channel structure such as thecorrugated fin232a,the triangular fin232b,or the pin-style heatsink232c,a light-weight rigid truss plate structure may be formed from the coolingassembly230. This structure is stiffened by cross coupling (via the passive radiator232) between thetop compartment220 andbottom plate234. By forming the truss plate structure, thepassive radiator232 provides the coolingassembly230 with structural properties similar to a solid thick plate from a rigidity standpoint for resisting destructive shock and vibration events. While a solid thick plate generally provides additional structural integrity to theenclosure200, there is a tradeoff between plate thickness and overall mass. As noted above, the resonant frequency of theenclosure200 would be decreased by the increased mass of a solid plate. By instead using a truss plate structure for thecooling assembly230, theenclosure200 retains the benefit of a thick plate while avoiding the lower resonant frequency associated with a thick, heavy plate.
• In addition to thepassive radiator232, the interposers act to absorb high frequency vibrations by acting as lossy dissipative elements. The combination oftop cover222, thermal interposers224,electronic circuit210, and coolingassembly230 in a small vertical space helps makes thetotal enclosure200 very stiff. Furthermore, the interposers reduce the transfer of energy between thebottom plate234 and thetop cover222, essentially dissipating the conducted- vibrational energy. Additionally, materials used inbottom plate234,heat spreader plate240 andtop cover222 may be selected to dissipate mechanical (vibrational) energy. In particular, composite materials can offer a combination of high strength (stiffness) and damping (mechanical energy dissipation).
• As noted above, the truss plate structure helps rigidify theenclosure200 by cross coupling thetop compartment220 and thebottom plate234. For example, the use of the triangular fin structure232borcorrugated fin232aas thepassive radiator232 may also help reduce the effects of destructive shear events and destructive vibration events in the horizontal direction indicated byarrow310 and in a vertical direction indicated by arrow320. Using acorrugated fin232afor thepassive radiator232 provides a good structure to transfer energy in both horizontal and vertical direction. The corrugation directs forces along the axes of the structure. The corrugations may also act to reduce the vibrational energy by acting as a dissipative spring. Tying the corrugations to the top andbottom plate240,234 at the peaks stiffens the structure in the “vertical” direction, effectively raising the structure's vertical (or bending mode) resonant frequency.
• FIG. 4 illustrates a cut-away diagram of the ruggedized electronics enclosure showing heat and airflow related to theruggedized electronics enclosure200. InFIG. 4, to more clearly illustrate the heatflow and airflow, thetop compartment220 is not fully shown, but it is understood that the coolingassembly230 is coupled to atop compartment220 which houses and protectselectronic circuit210 as illustrated inFIG. 2.
• FIG. 4 illustrates two directions for heat flow fromelectronic circuit210, here illustrated asPCB212 andprocessor214. A primary direction for heat flow is illustrated by anarrow410. This heat flow is accomplished by putting theprocessor214 in thermally conductive contact withheat spreader plate240. In one embodiment contact may be made by placing theprocessor214 in direct contact with theheat spreader plate240. Alternatively contact may be made by placing a heat conductive medium between theprocessor214 and theheat spreader plate240. Preferably,heat spreader plate240 has a high thermal conductivity. In a preferred embodiment,processor214 is oriented to be upside down so that its “top” is pressed againstheat spreader plate240. This arrangement allows for direct heat conduction betweenprocessor214 andheat spreader plate240. In conventional microchips, the main direction for heat to escape the chip is through its “top”. By positioning the top of theprocessor214 against theheat spreader plate240, heat is efficiently conducted from theprocessor214 to theheat spreader plate240. Alternatively, the microchips may face with their “tops” away from theheat spreader plate240 and a thermal interposer224 or other thermally conductive medium may be placed between the microchip and theheat spreader plate240.
• Heat spreader plate240 conducts heat away from theelectronic circuit210 in the direction indicated byarrow410, and into thepassive radiator232.Passive radiator232 is designed to radiate the heat conducted from theelectronic circuit210 into the environment. Preferably,passive radiator232 is exposed to an air flow across its surface area. This air flow is indicated byarrow430 inFIG. 4. By inducing anair flow430 through the spaces formed frompassive radiator232 and top andbottom plates240,234, heat may be efficiently removed from theelectronic circuit210 and from the ruggedizedelectronic enclosure200 in general. Alternatively, the coolingassembly230 can be mounted vertically to allow the heated air to rise, cooling the assembly through thermally induced convection currents. The specific proportions ofpassive radiator232 directly affect its efficiency in removing heat from theenclosure200. For instance, the overall height and width of a single “segment” directly affects the amount of surface area present for radiating heat, as well as changing the profile of the air channels. The profile of the air channels affects the channel's impedance to airflow and thus, the rate of airflow (for a given pressure differential) through the air channels of thepassive radiator232 and consequently theenclosure200.
• Additionally, for low airflow situations, the coolingassembly230 is designed to radiate the maximum amount of heat to the ambient air. Increasing the surface area increases the heat transfer between the processor and the air. This may result in a “tighter” corrugation or more transitions between theheat spreader plate240 and thebottom plate234. If, however, an externally generated pressure differential is used to induce air movement past thepassive radiator232, then the design may optimize the passageways through thepassive radiator232 for optimum heat transfer at a given pressure differential. The size of the passageways directly affects the impedance of air that may flow across thepassive radiator232. As the passageways decrease in size, the air flow for a given pressure differential, and therefore, the heat transfer efficiency of the coolingassembly230, will also decrease. Thus, one design goal is to balance the surface area of thepassive radiator232 against the size of the passageways and resultant air flow and heat transfer efficiency. In this way, different operating conditions may be met by adjusting the proportions of thepassive radiator232 to the requirements of the specific application and environment.
• As noted above with respect toFIG. 3, thepassive radiator232 also provides shock and vibration protection. These shock and vibration aspects of thepassive radiator232 are also dependent on the proportions of each “segment”. It may be necessary to balance the application's need for shock and vibration protection against the operating temperature requirements. Typically, it is required that systems operate at ambient temperature extremes above 50 degrees Celsius. Maximum chip case temperatures measured at the package are commonly specified not to exceed 75 C. For low power devices, this is easily achieved. For higher power devices, the thermal resistance from the electronics to air becomes a significant factor. In the case of higher power devices, a different material may be used for thepassive radiator232 in order to improve the heat transfer to thecooling assembly230, such as copper or carbon composite materials.
• As noted above,heat spreader plate240 is preferably formed from a material with a high thermal conductivity, such as aluminum. Alternatively, theheat spreader plate240 may be formed from copper or a carbon composite in order to provide a higher thermal conductivity and improved cooling efficiency at higher rates of airflow. Any type of material may be used for thepassive radiator232 in this alternate embodiment.
• In one embodiment,heat spreader plate240 or thepassive radiator232 may be configured to conduct heat from a “hotter”exhaust side715 of the air channels to a “cooler”inlet side710, to allow the energy flux into the air channel to stay constant, along an axis of theheat spreader plate240. This can be accomplished by making the heat spreader plate relatively thicker at theinlet side710 and thinner at theexhaust side715. In another embodiment, a turbulence gradient may be achieved by varying thecooling assembly230 channel capacity, or by varying the pin density of thepassive radiator232, (if a pin-style heat sink similar to pin-style heat sink232cis used,) by changing the profile of pins, or by any other means.FIG. 7 illustrates acooling assembly230 with a turbulence gradient. The coolingassembly230 has anintake710 represented by the air-flow arrow710aand anexhaust715, represented by arrow715a.Near theintake710 of the coolingassembly230 thepassive radiator232 is comprised of elliptical pin fins232d.As air moves along thepassive radiator232 fromintake710 toexhaust715, along a direction indicated byarrow720, the pressure drop along thedirection720 of airflow is increased. At theexhaust715 end of the coolingassembly230, the pin fins232eare shaped to be more cylindrical, which may be similar to the pinstyle heat sink232c.These cylindrical pin-fins232einduce more turbulence and thus create a higher pressure drop. The varying turbulence caused by changing the pin profile alongarrow720, tends to keep the rate of energy transfer constant, even though the temperature of the air increases from theintake710 to theexhaust715 of the coolingassembly230. This turbulence profiling makes it easier for the heat spreader to maintain an isotherm. The thermal conductivity of the heat spreader can be increased, usually meaning the mass can be reduced, thus allowing the structure's resonant frequency (for flexure modes) to be increased, with no reduction in heat transfer efficiency.
• The turbulence profiling described above helps maintain several chips in contact with theheat spreader plate240 at a similar temperature. This may be especially helpful in the situation where high rates ofairflow430 are induced by an externally generated pressure differential from inlet to exhaust. Referring back toFIG. 4, as the air flows in the direction ofarrow430, it will be heated bypassive radiator232, thereby reducing its effectiveness in cooling the remainder of thepassive radiator232. By designing the turbulence profile to match the changes in airflow temperature, the temperature of theelectronic circuit210 may be maintained. By maintaining a substantially uniform temperature across all components inelectronic circuit210, timing variances due to temperature variations between components may be reduced. This may be especially important if several processors are operating in parallel.
• While the above discussion focused primarily on an embodiment of theenclosure200 which utilizes an air cooled corrugated finpassive radiator232a,one skilled in the art will recognize that liquids such as sea water or a commercial refrigerant, other gasses such as gaseous nitrogen, may be used to conduct heat away from thepassive radiator232. Alternatively, there may be no liquid or gas present in the system and thermal transfer is achieved by radiation or convection from the external surfaces of the enclosure. One embodiment utilizes a liquid heat exchanger, substituting fluid channels for thepassive radiator232. All the mechanical benefits of the truss plate structure would be retained, and the modest increase in mass would be more than compensated for in heat transfer efficiency. Another embodiment puts the passive radiator in physical contact with a cold wall in an aircraft. Additionally, heat pipes may be embedded in theheat spreader plate240 to help remove heat to an external heat exchanger. Additionally, while acorrugated fin232aand a triangular fin truss232bhave proven to be advantageous from a production and structure standpoint, one skilled in the art will recognize that other passive radiators are also contemplated by this disclosure. Examples of other possible passive radiators include punched corrugated fins, conventional fin-style heat sinks that may be coupled to the top andbottom plates240,234, honey-comb truss structures oriented to allow air to pass through them, or a solid metal plate with longitudinal channels or holes placed therein.
• 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.

Claims (8)

1. A ruggedized electronics enclosure for housing an electronic circuit comprising:

a first area configured to house the electronic circuit;

a cooling assembly comprising a rigid truss plate structure, rigidly coupled to first area and thermally coupled to the electronic circuit, the first area, cooling assembly, and electronic circuit providing a rigid structure that does not substantially deform in response to one or more destructive shock events, to protect the electronic circuit against said one or more destructive shock events; and

wherein a first axis aligned with the length of the ruggedized enclosure is in a first direction.

2. The ruggedized electronics enclosure ofclaim 1, wherein said first direction is substantially vertical.

3. The ruggedized electronics enclosure ofclaim 1, wherein said first direction is substantially horizontal.

4. The ruggedized electronics enclosure ofclaim 1, wherein said first direction is substantially in any direction.

5. A system for housing and protecting an electronic circuit in a ruggedized electronics enclosure comprising:

means for enclosing the electronic circuit in a first area;

means for externally cooling the electronic circuit with a rigid cooling assembly; and

means for rigidifying the electronics enclosure by rigidly coupling the cooling assembly comprising a rigid truss plate structure, to the first area, wherein said rigidified electronics enclosure does not substantially deform in response to one or more destructive shock events and a first axis aligned with the length of the ruggedized enclosure is in a first direction.

6. The system ofclaim 5, wherein said first direction is substantially vertical.

7. The system ofclaim 5, wherein said first direction is substantially horizontal.

8. The system ofclaim 5, wherein said first direction is substantially in any direction.

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