U.S. patent application number 11/203005 was filed with the patent office on 2007-08-02 for ruggedized electronics enclosure.
Invention is credited to William E. Kehret, Dennis H. Smith.
Application Number | 20070177348 11/203005 |
Document ID | / |
Family ID | 31977104 |
Filed Date | 2007-08-02 |
United States Patent
Application |
20070177348 |
Kind Code |
A1 |
Kehret; William E. ; et
al. |
August 2, 2007 |
Ruggedized electronics enclosure
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.
Inventors: |
Kehret; William E.;
(Oakland, CA) ; Smith; Dennis H.; (Fremont,
CA) |
Correspondence
Address: |
FENWICK & WEST LLP
SILICON VALLEY CENTER
801 CALIFORNIA STREET
MOUNTAIN VIEW
CA
94041
US
|
Family ID: |
31977104 |
Appl. No.: |
11/203005 |
Filed: |
August 11, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10850523 |
May 19, 2004 |
6944022 |
|
|
11203005 |
Aug 11, 2005 |
|
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10232915 |
Aug 30, 2002 |
6765793 |
|
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10850523 |
May 19, 2004 |
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Current U.S.
Class: |
361/690 ;
361/688 |
Current CPC
Class: |
H05K 7/20509 20130101;
H05K 7/20254 20130101; H05K 7/20445 20130101; H05K 7/20418
20130101; H05K 7/1434 20130101 |
Class at
Publication: |
361/690 ;
361/688 |
International
Class: |
H05K 7/20 20060101
H05K007/20 |
Claims
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 of claim 1, wherein said
first direction is substantially vertical.
3. The ruggedized electronics enclosure of claim 1, wherein said
first direction is substantially horizontal.
4. The ruggedized electronics enclosure of claim 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 of claim 5, wherein said first direction is
substantially vertical.
7. The system of claim 5, wherein said first direction is
substantially horizontal.
8. The system of claim 5, wherein said first direction is
substantially in any direction.
Description
RELATED APPLICATION
[0001] 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
[0002] 1. Field of the Invention
[0003] 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.
[0004] 2. Description of the Related Art
[0005] 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.
[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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.
[0010] 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.
[0011] 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.
[0012] 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.
[0013] 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 in FIG. 1, 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 FIG. 1, though conventional
systems may use any spring-like apparatus to provide the isolation.
By attaching the cocoon 100 to its surroundings 130, 140 via
mechanical isolators 120, the cocoon 100 is allowed limited
movement with five degrees of freedom. This limited movement helps
to dampen the effects of shock and vibration.
[0014] There are several drawbacks to using the mechanically
isolated 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.
[0015] Additionally, while the cocoon 100 does isolate the
equipment from some vibration and shock, it does not completely
isolate the equipment. For example, 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. Typically 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.
[0016] To provide the additional shock protection, conventional
COTS systems pair the cocoon 100 with the ruggedized enclosures
110, or cocoon. However, while more effective in protecting the
equipment from mechanical shock, these ruggedized enclosures 110
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.
[0017] 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
[0018] 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.
[0019] 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.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] A method for protecting and cooling an electronic circuit
via a rigid truss plate structure is also provided.
[0025] 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
[0026] FIG. 1 illustrates a conventional mechanically isolated
cocoon system.
[0027] FIG. 2 illustrates an exploded view of a ruggedized
electronics enclosure according to one embodiment of the present
invention.
[0028] FIG. 3 illustrates a cut-away structural detail of the
assembled ruggedized electronics enclosure according to one
embodiment of the present invention.
[0029] 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.
[0030] FIG. 5 illustrates a cooling assembly utilizing a triangular
fin structure.
[0031] FIG. 6 illustrates a cooling assembly utilizing a pin-style
heatsink.
[0032] FIG. 7 illustrates a cooling assembly utilizing a pin-style
heatsink forming a turbulence gradient.
DETAILED DESCRIPTION
[0033] 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.
[0034] 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.
[0035] FIG. 2 illustrates an exploded view of a ruggedized
electronics enclosure 200 according to the present invention. As
illustrated in FIG. 2, 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.
As will be discussed below, 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.
[0036] 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.
[0037] 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. In
one embodiment, the side walls 226, front wall 227 and rear wall as
well as the top cover 222 are formed from aluminum. Alternatively,
these portions of the top compartment 220 may be may be formed of
any rigid material including, but not limited to steel, and
plastics. Preferably, 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. An upper portion of side
walls 226, front wall 227, the back wall, top cover 22 and heat
spreader plate 240 cooperate to form the sealed top compartment 220
for housing the electronic circuit 210. In another embodiment, 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. Additionally, the screw
fasteners may be augmented by other self-aligning/locking
mechanical components. By utilizing screw fasteners or other
removable fasteners, the top compartment 220 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 the top compartment 220
together to form a solid enclosure. However, while welding may
increase structural stability, it decreases the enclosure's 200
serviceability.
[0038] 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).
[0039] As illustrated, the passive radiator 232 may be formed from
an aluminum corrugated fin 232a. As will be discussed below, the
use of 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. 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 a corrugated fin 232a may
be used. FIG. 5 illustrates a triangular fin, or A-frame, truss
structure 232b preferably formed from aluminum or steel. As will be
discussed below, this embodiment of the passive radiator 232 is
more difficult and more expensive to manufacture, but provides
additional structural integrity to the enclosure 200. 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.
[0040] In general, 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.
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 the top compartment 220.
[0041] 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.
[0042] As illustrated, electronic circuit 210 is a compute element
and includes a PCB 212, a plurality of processors 214 coupled to a
front of the PCB 212, and a plurality of memory components 216
electrically coupled to a back of PCB 212. 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. Typically, 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. Alternatively, the interposer 224 may be formed from a
gel or a foam. Alternatively, 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.
[0043] As will be discussed in greater detail below, 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. Alternatively, 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. In a preferred embodiment, 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.
[0044] FIG. 3 illustrates a cut-away structural detail of the
assembled ruggedized electronics enclosure 200. As introduced in
FIG. 2, in one embodiment, 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. As noted above,
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.
[0045] In addition to being able to make the top compartment 220
airtight, additional steps may be made to "ruggedize" the enclosure
200 to help reduce the effects of destructive shock events and
destructive vibration events on the electronic circuit 210 housed
within. 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. 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.
[0046] Similarly, 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. 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.
[0047] 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, 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 cooling assembly 230.
[0048] 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.
[0049] 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. Typically, the
lower the mass, the higher the resonant frequency. Thus, the
overall mass of the enclosure 200 helps determine the resonant
frequency of the enclosure 200 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.
[0050] Thus, 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. In the preferred embodiment, the
ruggedized enclosure 200 is composed primarily of aluminum. The use
of aluminum offers a good compromise between strength needed to
protect the electronic circuit 210, 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 the electronic circuit 210. In one embodiment, 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.
In an alternate embodiment, 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 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 the enclosure 200.
[0051] Another aspect of the ruggedized enclosure 200 is its
overall profile. In a preferred embodiment, the overall vertical
height of the enclosure 200 is 1 rack unit ("U") or 1.75 inches.
Additionally, in one embodiment, 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.
[0052] Passive radiator 232 provides additional resistance to
destructive shock and vibration events. By using 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.
By forming the truss plate structure, 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. As noted above, the resonant frequency of the
enclosure 200 would be decreased by the increased mass of a solid
plate. By instead using a truss plate structure for the cooling
assembly 230, the enclosure 200 retains the benefit of a thick
plate while avoiding the lower resonant frequency associated with a
thick, heavy plate.
[0053] In addition to the passive radiator 232, 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.
Furthermore, the interposers reduce the transfer of energy between
the bottom plate 234 and the top cover 222, essentially dissipating
the conducted- vibrational energy. Additionally, materials used in
bottom plate 234, heat spreader plate 240 and top cover 222 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).
[0054] As noted above, the truss plate structure helps rigidify the
enclosure 200 by cross coupling the top compartment 220 and the
bottom plate 234. For example, 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.
[0055] FIG. 4 illustrates a cut-away diagram of the ruggedized
electronics enclosure showing heat and airflow related to the
ruggedized electronics enclosure 200. In FIG. 4, to more clearly
illustrate the heatflow and airflow, 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 FIG. 2.
[0056] 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. In one
embodiment contact may be made by placing the processor 214 in
direct contact with the heat spreader plate 240. Alternatively
contact may be made by placing a heat conductive medium between the
processor 214 and the heat spreader plate 240. Preferably, heat
spreader plate 240 has a high thermal conductivity. In a preferred
embodiment, 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. In conventional microchips, the main direction
for heat to escape the chip is through its "top". By positioning
the top of the processor 214 against the heat spreader plate 240,
heat is efficiently conducted from the processor 214 to the heat
spreader plate 240. Alternatively, 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.
[0057] 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. Preferably, passive radiator 232 is exposed to an air
flow across its surface area. This air flow is indicated by arrow
430 in FIG. 4. By inducing an air flow 430 through the spaces
formed from passive radiator 232 and top and bottom plates 240,
234, heat may be efficiently removed from the electronic circuit
210 and from the ruggedized electronic enclosure 200 in general.
Alternatively, 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. 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 the
passive radiator 232 and consequently the enclosure 200.
[0058] Additionally, for low airflow situations, 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. Thus, 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.
[0059] As noted above with respect to FIG. 3, 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.
[0060] As noted above, heat spreader plate 240 is preferably formed
from a material with a high thermal conductivity, such as aluminum.
Alternatively, 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.
[0061] In one 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. In
another embodiment, 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. Near the intake
710 of the cooling assembly 230 the passive radiator 232 is
comprised of elliptical pin fins 232d. As air moves along the
passive radiator 232 from intake 710 to exhaust 715, along a
direction indicated by arrow 720, the pressure drop along the
direction 720 of airflow is increased. At the exhaust 715 end of
the cooling assembly 230, the pin fins 232e are shaped to be more
cylindrical, which may be similar to the pin style heat sink 232c.
These cylindrical pin-fins 232e induce more turbulence and thus
create a higher pressure drop. The varying turbulence caused by
changing the pin profile along arrow 720, tends to keep the rate of
energy transfer constant, even though the temperature of the air
increases from the intake 710 to the exhaust 715 of the cooling
assembly 230. 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.
[0062] 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 FIG. 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. 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.
[0063] While the above discussion focused primarily on an
embodiment of the enclosure 200 which utilizes an air cooled
corrugated fin passive radiator 232a, 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 the passive radiator 232. 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 the passive radiator
232. 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 the heat
spreader plate 240 to help remove heat to an external heat
exchanger. Additionally, while 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.
[0064] 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.
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