Classifications

• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K7/00—Constructional details common to different types of electric apparatus
  • H05K7/20—Modifications to facilitate cooling, ventilating, or heating
  • H05K7/2039—Modifications to facilitate cooling, ventilating, or heating characterised by the heat transfer by conduction from the heat generating element to a dissipating body
  • H05K7/20409—Outer radiating structures on heat dissipating housings, e.g. fins integrated with the housing
  • H05K7/20418—Outer radiating structures on heat dissipating housings, e.g. fins integrated with the housing the radiating structures being additional and fastened onto the housing
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K7/00—Constructional details common to different types of electric apparatus
  • H05K7/14—Mounting supporting structure in casing or on frame or rack
  • H05K7/1422—Printed circuit boards receptacles, e.g. stacked structures, electronic circuit modules or box like frames
  • H05K7/1427—Housings
  • H05K7/1434—Housings for electronics exposed to high gravitational force; Cylindrical housings
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K7/00—Constructional details common to different types of electric apparatus
  • H05K7/20—Modifications to facilitate cooling, ventilating, or heating
  • H05K7/20218—Modifications to facilitate cooling, ventilating, or heating using a liquid coolant without phase change in electronic enclosures
  • H05K7/20254—Cold plates transferring heat from heat source to coolant
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K7/00—Constructional details common to different types of electric apparatus
  • H05K7/20—Modifications to facilitate cooling, ventilating, or heating
  • H05K7/2039—Modifications to facilitate cooling, ventilating, or heating characterised by the heat transfer by conduction from the heat generating element to a dissipating body
  • H05K7/20436—Inner thermal coupling elements in heat dissipating housings, e.g. protrusions or depressions integrally formed in the housing
  • H05K7/20445—Inner thermal coupling elements in heat dissipating housings, e.g. protrusions or depressions integrally formed in the housing the coupling element being an additional piece, e.g. thermal standoff
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K7/00—Constructional details common to different types of electric apparatus
  • H05K7/20—Modifications to facilitate cooling, ventilating, or heating
  • H05K7/2039—Modifications to facilitate cooling, ventilating, or heating characterised by the heat transfer by conduction from the heat generating element to a dissipating body
  • H05K7/20509—Multiple-component heat spreaders; Multi-component heat-conducting support plates; Multi-component non-closed heat-conducting structures

Definitions

• 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.
• the invention may operate without requiring additional mechanical isolation.
• 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.
• 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.
• 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.
• 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.
• FIG. 1 illustrates a conventional mechanically isolated cocoon.
• a cocoon 100 is provided to house the various ruggedized enclosures 110.
• the cocoon 100 may be attached to a floor 130 and/or a wall 140 of its surroundings. Commonly this includes the fuselage or deck plate of a military vehicle.
• the cocoon 100 is attached to the surroundings 130, 140 via mechanical isolators 120.
• a particularly advanced mechanical isolator 120 is the polymer isolator illustrated in Figure 1, though conventional systems may use any spring-like apparatus to provide the isolation.
• the cocoon 100 In order to reduce the shock to the equipment, the cocoon 100 must be provided with a sway space 150 in which it may move unobstructed. Typically this sway space 150 is four to seven inches in each direction of movement. Thus the cocoon 100 consumes additional space 150 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. [0012] Additionally, while the cocoon 100 does isolate the equipment from some vibration and shock, it does not completely isolate the equipment.
• a conventional cocoon 100 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.
• 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
• the performance of the cocoon 100 is limited by sway space available, materials used, and equipment placement within the cocoon 100. Additionally, if the environment around the cocoon 100 moves more than the sway space 150 can accommodate, then the cocoon 100 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.
• the present invention overcomes the limitations and disadvantages of conventional electronics enclosures used in harsh operating environments.
• the invention provides protection from destructive shock events and destructive vibration events without need of external mechanical isolation.
• 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.
• 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.
• 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.
• 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.
• the passive radiator may be comprised of a corrugated fin.
• 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.
• the passive radiator is comprised of a pin- style heatsink.
• the pin-style heatsink is arranged according to a pin density pattern to create a turbulence gradient for the cooling assembly.
• the enclosure is rigidified by the truss plate structure in order to protect the electronic circuit against an anticipated destructive shock event.
• the enclosure and circuit can withstand and survive a 60G shock event.
• 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 20G to at least 60G depending upon these design criteria.
• the enclosure's resonant frequency is raised above an anticipated destructive vibration event.
• the enclosure and circuit have a resonant frequency in the range of 200 Hz to at least 1kHz. In another embodiment, of special interest for shipboard applications, the enclosure and circuit have a resonant frequency in the range of 20 to 40Hz.
• the listed ranges are merely exemplary, and alternate embodiments may have a resonant frequency selected to be higher than a known destructive vibration event.
• the cooling assembly further provides heat pipes for drawing away additional heat from the electronic circuit and delivering it to an external heat exchanger.
• the heat pipes cooperate with the passive radiator to provide an efficient heat exchanger.
• 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.
• Figure 1 illustrates a conventional mechanically isolated cocoon system.
• Figure 2 illustrates an exploded view of a ruggedized electronics enclosure according to one embodiment of the present invention.
• Figure 3 illustrates a cut-away structural detail of the assembled ruggedized electronics enclosure according to one embodiment of the present invention.
• Figure 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.
• Figure 5 illustrates a cooling assembly utilizing a triangular fin structure.
• Figure 6 illustrates a cooling assembly utilizing a pin-style heatsink.
• Figure 7 illustrates a cooling assembly utilizing a pin-style heatsink forming a turbulence gradient.
• 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.
• 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 a ruggedized electronics enclosure 200 according to the present invention.
• the enclosure 200 is configured to house and protect a compute element 210.
• the compute element 210 is chosen by way of example as illustrative of the primary features and operation of the enclosure 200, and one skilled in the art will recognize that the enclosure 200 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.
• the enclosure 200 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.
• the ruggedized electronics enclosure 200 includes a top compartment 220 for housing the electronic circuit 210 (illustrated as a compute element), and a cooling assembly 230 coupled to the bottom of the top compartment 220. As illustrated, the enclosure 200 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.
• the top compartment 220 includes a top cover 222, one or more thermal interposers 224, a pair of side walls 226, a front wall 227, a rear wall (not shown) and a heat spreader plate 240.
• the side walls 226, front wall 227 and rear wall as well as the top cover 222 are formed from aluminum.
• these portions of the top compartment 220 may be may be formed of any rigid material including, but not limited to steel, and plastics.
• side walls 226 are sized to extend the entire combined height of the top compartment 220 and cooling assembly 230.
• Front wall 227 and rear wall are preferably sized to extend the height of the top compartment 220.
• top compartment 220 for housing the electronic circuit 210.
• the top compartment 220 may not be sealed, but may instead be open to the environment.
• the various parts which form the top compartment 220 may be coupled together using screws or other fastener types that may require special tools for removal.
• the screw fasteners may be augmented by other self-aligning/locking mechanical components.
• the top compartment 220 may be opened as necessary to provide service to the electronics housed inside.
• 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 the top compartment 220 together to form a solid enclosure. However, while welding may increase structural stability, it decreases the enclosure's 200 serviceability.
• the cooling assembly 230 is coupled to the bottom of top compartment 220 and further includes a passive radiator 232 (here illustrated in one embodiment 232a) and a bottom plate 234.
• the passive radiator 232 and bottom plate 234 are coupled to the cooling assembly 230 in order to draw heat away from the highest dissipation components (the top compartment 220) to a high efficiency heat exchanger (the passive radiator 232).
• the passive radiator 232 may be formed from an aluminum corrugated fin 232a.
• an aluminum corrugated fin 232a provides specific advantages over other passive radiators, however, one skilled in the art will recognize that other passive radiators may be used in place of the corrugated fin 232a, as well as that the radiator 232 may be made from other material aside from aluminum.
• 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 a corrugated fin 232a may be used.
• Figure 5 illustrates a triangular fin, or A-frame, truss structure 232b preferably formed from aluminum or steel.
• FIG. 6 illustrates another embodiment of the passive radiator 232 utilizing pin-style heat-sinks 232c sandwiched between the heat spreader plate 240 and the bottom plate 234. This forms a rigid truss plate structure while allowing some measure of heat dissipation profiling based on the placement and density of the pins.
• heat spreader plate 240 a lower portion of side walls 226, and bottom plate 234 cooperate to "sandwich" the passive radiator 232 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.
• 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 the top compartment 220.
• the cooling assembly 230 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 the passive radiator 232.
• One way of doing this with a metallic passive radiator 232 is through welding. If a non-metallic passive radiator 232 is used, a thermally conductive adhesive may be used.
• electronic circuit 210 is a compute element and includes a PCB
• a thermal interposer 224a is positioned to contact the back of PCB 212 and the memory components 216 to provide a heat exchange between PCB 212 and memory components 216.
• the interposer 224 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.
• the interposer 224 may be formed from a gel or a foam.
• the top compartment 220 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 interposer 224 is preferred to aid in the keeping the electronics inside the top compartment 220 serviceable.
• processors 214 and PCB 212 are positioned within top compartment 220 such that processors 214 are placed in physical contact with heat spreader plate 240, allowing for heat to be conducted away from processors 214.
• a heat conducting material such as a thermal interposer similar to interposer 224, may be position between the processors 214 and the heat spreader plate 240.
• a second thermal interposer 224 is positioned between the memory components 216 and the top cover 222.
• Top compartment 220 is preferably sized to provide just enough vertical and horizontal room to fit electronic circuit 210 within its confines.
• thermal interposers 224 are created from a resilient material which is slightly compressed to ensure a "snug" fit for the electronic circuit 210 within top compartment 220. By ensuring that the thermal interposers 224 make tight contact with the top cover 222, additional thermal and structural benefits are realized.
• FIG. 3 illustrates a cut-away structural detail of the assembled ruggedized electronics enclosure 200.
• the electronic circuit 210 housed in the top compartment 220 is again a compute element.
• One of the objectives for the ruggedized electronics enclosure 200 is to provide protection to the electronic circuit 210 housed in the top compartment 220 from harsh operating environments.
• the top compartment 220 may be completely sealed by appropriately sizing the side walls 226, front wall 228 (not shown), back wall (not shown), top cover 222 and heat spreader plate 240 to ensure that no open spaces exist in the top compartment 220 surface.
• a destructive shock event is any shock event that may render the electronic circuit 210 or enclosure 200 inoperative due to a large change in force and momentum being applied to the circuit 210 and enclosure 200.
• the circuit 210 or enclosure 200 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.
• 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.
• a destructive vibration event is any vibration event that may cause the electronic circuit 210 or enclosure 200 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.
• destructive vibration events include engine vibrations, turbine vibrations, screw vibrations, prolonged shock events, travel along uneven surfaces etc.
• the electronic circuit 210 In typical military applications, the electronic circuit 210 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 , MIL 167 and ISO 10055 provide specific requirements for shock and vibration resistance depending on the desired application and are incorporated in their entireties herein.
• 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.
• PCB printed circuit board
• One design goal is to make the entire enclosure assembly one rigid structural element in order to protect against destructive shock and vibration events.
• the enclosure is rigidified by the truss plate structure in order to protect the electronic circuit against an anticipated destructive shock event.
• the enclosure and circuit can withstand and survive a 60G shock event.
• 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 20G to at least 60G depending upon these design criteria.
• One aspect of forming the enclosure 200 as a rigid structural element includes raising the enclosure's 200 resonant frequency to a frequency higher than the destructive vibration events to which the enclosure 200 will be subject.
• Two major factors that affect the resonant frequency of a given structure are the mass, and the material's inherent stiffness.
• the enclosure 200 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.
• the ruggedized enclosure 200 is composed primarily of aluminum.
• the enclosure 200 is designed to have a resonant frequency that is at least approximately twice the 12-25 Hz frequency of naval shock events.
• the enclosure 200 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 1kHz. 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 the enclosure 200.
• the overall vertical height of the enclosure 200 is 1 rack unit ("U") or 1.75 inches.
• the top compartment 220 is configured to house the electronic circuit 210 snugly, without allowing for significant horizontal or vertical movement within the compartment 220. Further cushioning and insulation from vibration is garnered by the use of the thermal interposers 224 which may be compressed slightly to ensure a snug fit while providing an efficient heat conduit to remove heat from the electronic circuit 210.
• Passive radiator 232 provides additional resistance to destructive shock and vibration events.
• a passive radiator and fluid channel structure such as the corrugated fin 232a, the triangular fin 232b, or the pin-style heatsink 232c
• a light-weight rigid truss plate structure may be formed from the cooling assembly 230. This structure is stiffened by cross coupling (via the passive radiator 232) between the top compartment 220 and bottom plate 234.
• the passive radiator 232 provides the cooling assembly 230 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 the enclosure 200, there is a tradeoff between plate thickness and overall mass.
• the resonant frequency of the enclosure 200 would be decreased by the increased mass of a solid plate.
• the enclosure 200 retains the benefit of a thick plate while avoiding the lower resonant frequency associated with a thick, heavy plate.
• the interposers act to absorb high frequency vibrations by acting as lossy dissipative elements.
• the combination of top cover 222, thermal interposers 224, electronic circuit 210, and cooling assembly 230 in a small vertical space helps makes the total enclosure 200 very stiff.
• the interposers reduce the transfer of energy between the bottom plate 234 and the top cover 222, essentially dissipating the conducted vibrational energy.
• materials used in bottom plate 234, heat spreader plate 240 and top cover 222 may be selected to dissipate mechanical (vibrational) energy.
• composite materials can offer a combination of high strength (stiffness) and damping (mechanical energy dissipation).
• the truss plate structure helps rigidify the enclosure 200 by cross coupling the top compartment 220 and the bottom plate 234.
• the use of the triangular fin structure 232b or corrugated fin 232a as the passive radiator 232 may also help reduce the effects of destructive shear events and destructive vibration events in the horizontal direction indicated by arrow 310 and in a vertical direction indicated by arrow 320.
• Using a corrugated fin 232a for the passive radiator 232 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 and bottom plate 240, 234 at the peaks stiffens the structure in the "vertical" direction, effectively raising the structure's vertical (or bending mode) resonant frequency.
• Figure 4 illustrates a cut-away diagram of the ruggedized electronics enclosure showing heat and airflow related to the ruggedized electronics enclosure 200.
• the top compartment 220 is not fully shown, but it is understood that the cooling assembly 230 is coupled to a top compartment 220 which houses and protects electronic circuit 210 as illustrated in Figure 2.
• FIG. 4 illustrates two directions for heat flow from electronic circuit 210, here illustrated as PCB 212 and processor 214.
• a primary direction for heat flow is illustrated by an arrow 410.
• This heat flow is accomplished by putting the processor 214 in thermally conductive contact with heat spreader plate 240.
• contact may be made by placing the processor 214 in direct contact with the heat spreader plate 240.
• contact may be made by placing a heat conductive medium between the processor 214 and the heat spreader plate 240.
• heat spreader plate 240 has a high thermal conductivity.
• processor 214 is oriented to be upside down so that its "top" is pressed against heat spreader plate 240.
• This arrangement allows for direct heat conduction between processor 214 and heat spreader plate 240.
• the main direction for heat to escape the chip is through its "top”.
• heat is efficiently conducted from the processor 214 to the heat spreader plate 240.
• the microchips may face with their "tops" away from the heat spreader plate 240 and a thermal interposer 224 or other thermally conductive medium may be placed between the microchip and the heat spreader plate 240.
• Heat spreader plate 240 conducts heat away from the electronic circuit 210 in the direction indicated by arrow 410, and into the passive radiator 232.
• Passive radiator 232 is designed to radiate the heat conducted from the electronic circuit 210 into the environment.
• passive radiator 232 is exposed to an air flow across its surface area. This air flow is indicated by arrow 430 in Figure 4.
• the cooling assembly 230 can be mounted vertically to allow the heated air to rise, cooling the assembly through thermally induced convection currents.
• the specific proportions of passive radiator 232 directly affect its efficiency in removing heat from the enclosure 200.
• 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 the passive radiator 232 and consequently the enclosure 200.
• the cooling assembly 230 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 the heat spreader plate 240 and the bottom plate 234. If, however, an externally generated pressure differential is used to induce air movement past the passive radiator 232, then the design may optimize the passageways through the passive radiator 232 for optimum heat transfer at a given pressure differential. The size of the passageways directly affects the impedance of air that may flow across the passive radiator 232. As the passageways decrease in size, the air flow for a given pressure differential, and therefore, the heat transfer efficiency of the cooling assembly 230, will also decrease.
• one design goal is to balance the surface area of the passive radiator 232 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 the passive radiator 232 to the requirements of the specific application and environment.
• the passive radiator 232 also provides shock and vibration protection. These shock and vibration aspects of the passive radiator 232 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 the passive radiator 232 in order to improve the heat transfer to the cooling assembly 230, such as copper or carbon composite materials.
• heat spreader plate 240 is preferably formed from a material with a high thermal conductivity, such as aluminum.
• the heat spreader plate 240 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 the passive radiator 232 in this alternate embodiment.
• heat spreader plate 240 or the passive radiator 232 may be configured to conduct heat from a "hotter" exhaust side 715 of the air channels to a "cooler" inlet side 710, to allow the energy flux into the air channel to stay constant, along an axis of the heat spreader plate 240. This can be accomplished by making the heat spreader plate relatively thicker at the inlet side 710 and thinner at the exhaust side 715.
• a turbulence gradient may be achieved by varying the cooling assembly 230 channel capacity, or by varying the pin density of the passive radiator 232, (if a pin-style heat sink similar to pin-style heat sink 232c is used,) by changing the profile of pins, or by any other means.
• FIG. 7 illustrates a cooling assembly 230 with a turbulence gradient.
• the cooling assembly 230 has an intake 710 represented by the air-flow arrow 710a and an exhaust 715, represented by arrow 715a.
• the passive radiator 232 is comprised of elliptical pin fins 232d.
• the pin fins 232e are shaped to be more cylindrical, which may be similar to the pin style heat sink 232c.
• the turbulence profiling described above helps maintain several chips in contact with the heat spreader plate 240 at a similar temperature.. This may be especially helpful in the situation where high rates of airflow 430 are induced by an externally generated pressure differential from inlet to exhaust. Referring back to Figure 4, as the air flows in the direction of arrow 430, it will be heated by passive radiator 232, thereby reducing its effectiveness in cooling the remainder of the passive radiator 232.
• the turbulence profile By designing the turbulence profile to match the changes in airflow temperature, the temperature of the electronic circuit 210 may be maintained. By maintaining a substantially uniform temperature across all components in electronic circuit 210, timing variances due to temperature variations between components may be reduced. This may be especially important if several processors are operating in parallel.
• heat pipes may be embedded in the heat spreader plate 240 to help remove heat to an external heat exchanger.
• a corrugated fin 232a and a triangular fin truss 232b have 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 and bottom plates 240, 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.

Landscapes

• Engineering & Computer Science (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Cooling Or The Like Of Electrical Apparatus (AREA)
• Cooling Or The Like Of Semiconductors Or Solid State Devices (AREA)
• Casings For Electric Apparatus (AREA)

Priority Applications (3)

Applications Claiming Priority (2)

Publications (2)

Family

ID=31977104

Family Applications (1)

Country Status (5)

Cited By (1)

Families Citing this family (84)

Family Cites Families (41)

• 2002
  • 2002-08-30 US US10/232,915 patent/US6765793B2/en not_active Expired - Lifetime
• 2003
  • 2003-08-20 JP JP2004532931A patent/JP2005537667A/ja not_active Abandoned
  • 2003-08-20 AU AU2003265552A patent/AU2003265552A1/en not_active Abandoned
  • 2003-08-20 EP EP03791711A patent/EP1552736A4/en not_active Withdrawn
  • 2003-08-20 WO PCT/US2003/026134 patent/WO2004021401A2/en not_active Ceased
• 2004
  • 2004-05-19 US US10/850,523 patent/US6944022B1/en not_active Expired - Lifetime
• 2005
  • 2005-08-11 US US11/203,005 patent/US20070177348A1/en not_active Abandoned
• 2008
  • 2008-01-25 US US12/020,487 patent/US20080218970A1/en not_active Abandoned

Also Published As

Similar Documents

Legal Events