U.S. patent application number 13/588836 was filed with the patent office on 2013-08-15 for contact cooled electronic enclosure.
The applicant listed for this patent is JOHN PHILLIP NEVILLE HUGHES, ROBERT J. LIPP. Invention is credited to JOHN PHILLIP NEVILLE HUGHES, ROBERT J. LIPP.
Application Number | 20130208422 13/588836 |
Document ID | / |
Family ID | 41608134 |
Filed Date | 2013-08-15 |
United States Patent
Application |
20130208422 |
Kind Code |
A1 |
HUGHES; JOHN PHILLIP NEVILLE ;
et al. |
August 15, 2013 |
CONTACT COOLED ELECTRONIC ENCLOSURE
Abstract
Various embodiments disclose a system and an associated method
to provide cooling to a plurality of electronic components mounted
proximately to one another in an electronic enclosure is disclosed.
The system comprises a cold plate that is mounted on the electronic
enclosure to conduct heat thermally. The cold plate has a first
surface to mount proximate to the plurality of electronic
components and a second surface to mount distal from the plurality
of electronic components. One or more heat risers are configured to
be thermally coupled between the first surface of the cold plate
and at least one of the plurality of electronic components.
Inventors: |
HUGHES; JOHN PHILLIP NEVILLE;
(MENLO PARK, CA) ; LIPP; ROBERT J.; (LOS GATOS,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HUGHES; JOHN PHILLIP NEVILLE
LIPP; ROBERT J. |
MENLO PARK
LOS GATOS |
CA
CA |
US
US |
|
|
Family ID: |
41608134 |
Appl. No.: |
13/588836 |
Filed: |
August 17, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12535272 |
Aug 4, 2009 |
8270170 |
|
|
13588836 |
|
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|
|
61085931 |
Aug 4, 2008 |
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Current U.S.
Class: |
361/700 ;
361/704 |
Current CPC
Class: |
H01L 2924/0002 20130101;
H05K 7/20445 20130101; H05K 7/2049 20130101; H01L 2924/0002
20130101; H05K 7/20318 20130101; H01L 2924/00 20130101; H05K
7/20509 20130101 |
Class at
Publication: |
361/700 ;
361/704 |
International
Class: |
H05K 7/20 20060101
H05K007/20 |
Claims
1. A thermal interface that thermally couples an electronic
component to a heat-removal mechanism, the thermal interface
comprising: a first pliable strength layer that provides strength
to the thermal interface and substantially conforms to the profile
of the electronic component, the first strength layer comprising a
thin polymeric sheet; a second pliable strength layer that provides
strength to the thermal interface and substantially conforms to the
profile of the heat-removal mechanism, the second strength layer
comprising thin polymeric sheet; a first and a second pliable
conductive layer that facilitates heat transfer from the strength
layer, the first and second conductive layers comprising thin
metallic sheets, the first and second conductive layers coupled
along a broad face to a broad face of the first and second strength
layers, respectively, to form a first and second sheet; a thermally
conductive fluid, thermally coupled to the first and second
conductive layers, that facilitates heat transfer from the first
conductive layer to the heat-removal mechanism, wherein the
thermally conductive fluid is substantially self-leveling, inert,
and electrically insular; and an auxiliary layer, fluidly coupled
to the thermally conductive fluid, that facilitates diffusion of
heat from the first conductive layer throughout the thermally
conductive fluid, the auxiliary layer having a first and a second
broad face; wherein the first sheet encapsulates the thermally
conductive fluid against the first broad face of the auxiliary
layer.
2. The interface of claim 1, wherein the strength layer comprises
polyester.
3. The interface of claim 1, wherein the conductive layer includes
aluminum.
4. The interface of claim 1, wherein the thermally conductive layer
includes metal paste.
5. The interface of claim 1, wherein the heat-removal mechanism is
a prismatic cold plate.
6. The interface of claim 1, wherein an entire broad face of the
first and second conductive layers is substantially laminated to an
entire broad face of the first and second strength layers to form
the first and second sheets, respectively.
7. The interface of claim 1, wherein the edges of the first and
second sheets are joined together to form a pouch that encapsulates
the auxiliary layer, wherein the first and second conductive layers
are in fluid communication with the thermally conductive fluid.
8. The interface of claim 7, wherein the first and second
conductive layers comprise a single sheet, and the first and second
strength layers comprise a single sheet.
9. The interface of claim 1, wherein the first sheet is joined to
opposing edges of the first broad face of the auxiliary layer, and
the second sheet is joined to opposing edges of the second broad
face of the auxiliary layer.
10. The interface of claim 9, wherein the first sheet is joined to
the perimeter of the first broad face of the auxiliary layer, the
second sheet is joined to the perimeter of the second broad face of
the auxiliary layer, the first sheet encapsulating the thermally
conductive fluid against the first broad face of the auxiliary
layer, the thermal interface further including a second thermally
conductive fluid, wherein the second sheet encapsulates the second
thermally conductive fluid against the second broad face of the
auxiliary layer.
11. The interface of claim 10, wherein the first and second
thermally conductive fluid have substantially the same
composition.
12. The interface of claim 9, wherein the first and second sheets
are joined to the auxiliary layer by adhesive.
13. The interface of claim 1, wherein the auxiliary layer is
substantially metallic.
14. The interface of claim 13, wherein the auxiliary layer is a
flexible plate.
15. The interface of claim 13, wherein the auxiliary layer
electromagnetically shields the electronic component.
16. The interface of claim 13, wherein the interface is coupled to
a hole in an enclosure wall, wherein the interface is substantially
coplanar with the enclosure wall.
17. The interface of claim 1, wherein the auxiliary layer is
porous.
18. The interface of claim 1, further including a coupling
mechanism that couples the heat-removal mechanism and the thermal
interface to the electronic component, wherein the thermal
interface is disposed between the heat-removal mechanism and the
electronic component.
19. The interface of claim 18, wherein the coupling mechanism
includes metallicized adhesive.
20. The interface of claim 18, wherein the coupling mechanism
comprises a clip that couples to an edge of the heat-removal
mechanism and an edge of the electronic component and applies a
substantially normal compressive force against a broad face of the
heat-removal mechanism towards the electronic component.
21. The interface of claim 19, wherein the clip is a spring clip
comprising two compressive tines coupled by a spring element,
wherein the spring element applies a restorative reaction force to
the tines when the tines are displaced from a resting position.
22. The interface of claim 20, wherein the end of each tine curves
away from the opposing tine.
23. The interface of claim 21, wherein the coupling mechanism
comprises multiple clips joined along a rail.
24. The interface of claim 19, wherein coupling the thermal
interface to the heat-removal mechanism conforms the second sheet
to the profile of the heat-removal mechanism by inflating a contact
area of the second sheet, wherein the contact area is inflated by
forcing the thermally conductive fluid away from the coupled
area.
25. The interface of claim 18, further including a second coupling
mechanism substantially identical to the first that couples the
opposing edge of the heat-removal mechanism to the opposing edge of
the thermal interface.
26. A cooling system that cools an electronic component, the
cooling system comprising: a cold plate coupled to an enclosure; a
thermal interface coupled between the cold plate and the electronic
component, the thermal interface including: a first pliable
strength layer that provides strength to the thermal interface and
substantially conforms to the profile of the electronic component,
the first strength layer comprising a thin sheet, a second pliable
strength layer that provides strength to the thermal interface and
substantially conforms to the profile of the cold plate, the second
strength layer comprising thin sheet, a first and a second pliable
conductive layer that facilitates heat transfer from the strength
layer, the first and second conductive layers comprising thin
sheets, the first and second conductive layers joined along a broad
face to a broad face of the first and second strength layers,
respectively, to form a first and second sheet, a thermally
conductive fluid, fluidly coupled to the first and second
conductive layers, that facilitates heat transfer from a conductive
layer to the heat-removal mechanism, wherein the thermally
conductive fluid is substantially self-leveling, inert, and
electrically insular, and a planar auxiliary layer, fluidly coupled
to the thermally conductive fluid, that facilitates heat diffusion
throughout the thermally conductive fluid and structurally supports
the first and second sheets, the auxiliary layer having a first and
a second broad face, wherein the first and second sheets
encapsulate the thermally conductive fluid against the first and
second broad faces of the auxiliary layer, respectively; and a clip
that couples the thermal interface to the cold plate comprising two
tines with outwardly curved ends, the tines coupled by a spring
element, wherein the spring element applies a compressive normal
force through the tines to the opposing broad faces of the thermal
interface and the cold plate.
25. A cooling interface that thermally couples an electronic
component to a heat-removal mechanism, the cooling interface
comprising: a first thermally conductive strip, including a first
section and a short section substantially perpendicular to the long
section; a second thermally conductive strip, substantially
identical to the first; wherein the first sections of the first and
second strips couple to opposing broad surfaces of the electronic
component, and the second sections couple to a second surface
adjacent the broad surfaces, wherein the second section of the
first strip at least partially overlaps the second section of the
second strip on the second surface.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority benefit of U.S. Ser. No.
12/535,272 filed on 4 Aug. 2009, which claims priority to U.S. Ser.
No. 61/085,931 filed on 4 Aug. 2008, which are both hereby
incorporated in their entirety by reference.
TECHNICAL FIELD
[0002] The present application relates generally to the cooling of
compute and storage systems; and, in a specific exemplary
embodiment, to a system and method for cooling electronic equipment
in modularly deployed systems cooled by attachment to a cold
plate.
BACKGROUND
[0003] In a variety of contemporaneous applications, various types
of fluid-based cooling systems cool computers and other electronic
equipment. In the simplest case, fluid moves heat from a
hard-to-cool location to a different area. For example, a liquid
circulation system consisting of a heat absorber, a pump and a heat
dissipater could be employed to remove heat from hot electronic
components to finned sides of a computer case where convective
cooling with ambient air removes the heat without the use of forced
air.
[0004] Enterprise-based compute and storage systems are
increasingly deployed as modular systems with standardized form
factor electronic enclosure modules mounted in standardized support
structures. The standardized electronic enclosure modules can be
devoted to perform any of a number of different functions such as
computing, storage, or networking. The enclosure modules are
commonly mounted in standardized support structures such as 19 inch
(approximately 0.482 m) or 24 inch (approximately 0.610 m) wide
racks. Such enclosures are commonly industry standard 1 U (1.75
inch; approximately 4.45 cm), 2 U (3.5 inch; approximately 8.89
cm), 3 U (5.25 inch; approximately 13.3 cm), or 4 U (7 inch;
approximately 17.8 cm) high. Often, the reasons for the adoption of
the larger 2 U, 3 U, or 4 U modules are to increase reliability of
electronic components through improved airflow for cooling and to
provide space for more adapter cards.
[0005] Modular enclosures are frequently air-cooled. The enclosures
draw air in from the room in which they are housed by means of fans
that accelerate the air and force it over the enclosure's internal
components, thus cooling the components. The resulting heated air
is exhausted back into the room. The room air itself is cooled by
chillers or other means.
[0006] Other cooling methods have focused on fluid cooled systems
using a cold plate means. The cold plate means are typically
complex. For example, an individual spring-loaded cold plate is
used for each component. Each cold plate, in turn, is connected
with individual flexible pipes. Each cold plate includes, at least,
a temperature-controlled valve, temperature sensors, and
controllers.
[0007] Other cooling methods have employed a compressible
thermally-conductive-material heat sink assembly. To be
compressible, the heat sink assembly must conform to components to
be cooled. However, all conformable materials have a relatively low
thermal conductivity as compared to pure metals or heat pipes.
Thus, the conformable heat sink assemblies have a relatively high
thermal resistance. Consequently, very little heat spreading is
provided such that each thermal interface must have a very low
thermal resistance for the assembly to be effective. Further, the
assembly is not extensible to vertical daughter cards on a
motherboard such as, for example, dual in-line memory modules
(DIMMs) used in computer and other memory systems.
[0008] Importantly, no existing solution comprises a conventional,
modularly deployed system with a high thermal conductivity
connectable to all components. Further, no such system also
includes high heat dissipation on a conventional motherboard,
including removable daughter and memory cards, to a common cold
plate. Moreover, such a system should also be readily serviceable.
Additionally, no solution proposes thermally connecting all such
high heat dissipation devices to a common cooling plate by thermal
elevation and co-planarization to a side of the enclosure. None of
the existing systems further includes an easily serviceable system
accessible through a removable lid as part of the heat removal
system.
BRIEF DESCRIPTION OF DRAWINGS
[0009] FIGS. 1A and 1B are a cross-sectional drawing illustrating
an exemplary embodiment of an enclosure with heat risers and
thermal interfaces, and a schematic representation of the thermal
interface construction, respectively;
[0010] FIG. 2 is a bottom and side view of an exemplary embodiment
of a heat-riser/spreader made from a highly thermally-conductive
material such as a block of metal;
[0011] FIG. 3 is a bottom and side view of an exemplary embodiment
of a heat-riser/spreader using heat pipes mounted in, for example,
metal plates;
[0012] FIG. 4 is a bottom and side view of an exemplary embodiment
of a heat-riser/spreader made from a flat heat pipe;
[0013] FIG. 5 is a bottom and side view of an exemplary embodiment
of spring heat riser;
[0014] FIGS. 6A and 6B are a front and side view of an exemplary
embodiment of a heat riser usable with a DIMM, and a schematic
representation of an embodiment of a coupling mechanism;
[0015] FIG. 7 is a cross-sectional drawing illustrating an
exemplary embodiment of an enclosure with an auxiliary card and a
motherboard;
[0016] FIGS. 8A, 8B, 8C, and 8D are an isometric view of an
exemplary embodiment of a planarization thermal interface bag, a
cross sectional view of an embodiment of a thermal interface bag, a
cross sectional view of an embodiment of a thermal interface bag
including a joined third layer, and a cross sectional view of an
embodiment of the thermal interface bag encapsulating a third
layer, respectively; and
[0017] FIG. 9 illustrates an exemplary embodiment of a grooved
interface between a between heat riser and a lid.
[0018] FIG. 10 is a schematic representation of a grooved support
interface between a cold plate and a thermal interface.
DETAILED DESCRIPTION
[0019] The description that follows includes illustrative systems,
methods, and techniques that cover various exemplary embodiments
defined by various aspects of the present disclosure. In the
following description, for purposes of explanation, numerous
specific details are set forth in order to provide an understanding
of various embodiments of the inventive subject matter. It will be
evident, however, to those skilled in the art that embodiments of
the inventive subject matter may be practiced without these
specific details. Further, well-known instruction instances,
protocols, structures, and techniques have not been shown in
detail.
[0020] As used herein, the term "or" may be construed in an
inclusive or exclusive sense. Similarly, the term "exemplary" may
be construed merely to mean an example of something or an exemplar
and not necessarily a preferred means of accomplishing a goal.
Additionally, although various exemplary embodiments discussed
below focus on a thermal cooling system for electronic components,
the embodiments are merely given for clarity in disclosure. Thus,
any type of thermal cooling application is considered as being
within a scope of the present invention.
[0021] Disclosed herein is a comprehensive system for adapting
conventional electronic enclosures, components, motherboards,
subassemblies, and similar components to conductive cooling
systems. Also described herein are methods and structures to
calculate and thermally couple electronic components or
subassemblies housed in the conventional electronic enclosures
though a side of the enclosure to a proximate cold plate. In a
specific exemplary embodiment, the cold plate comprises a lid of
the enclosure. In another specific exemplary embodiment, the lid
contacts an external cold plate therein taking at least a portion
of the function of the cold plate itself.
[0022] The electronic components, subassemblies, or similar
components are thermally elevated, planarized, and coupled, by
means of heat risers and/or thermal interfaces, to a proximate cold
plate. The enclosures may be the common electronic enclosures
described above, other form-factor enclosures, or unenclosed
systems such as server blades or bare server motherboards. Each of
these components are known independently in the art.
[0023] The contact-cooled enclosure described herein can, among
other things, comprise an instantiation of the contact-cooled
enclosure referred to in a previously filed patent application by
Lipp and Hughes. The patent application describes a rack mounted
cold plate system is found in U.S. Provisional Patent Application
No. 61/008,136, entitled "A Cooling System for Contact Cooled
Electronic Modules," filed Dec. 19, 2007, and U.S. Pat. No.
8,000,103, having the same title, filed Dec. 19, 2008 (issued Aug.
16, 2011), both of which are incorporated herein by reference in
their entirety.
[0024] In an exemplary embodiment, a system to provide cooling to a
plurality of electronic components mounted proximately to one
another in an electronic enclosure is disclosed. The system
comprises a cold plate to mount on the electronic enclosure and
thermally conduct heat. The cold plate has a first surface to mount
proximate to the plurality of electronic components and a second
surface to mount distal from the plurality of electronic
components. At least one of the plurality of electronic components
are thermally coupled by one or more heat risers and/or thermal
interfaces to the first surface of the cold plate.
[0025] In another exemplary embodiment, a system to provide cooling
to a plurality of electronic components mounted proximately to one
another in an electronic enclosure is disclosed. The system
comprises a cold plate to provide heat removal. The cold plate is
configured to be mounted external to the electronic enclosure. One
or more heat risers is configured to be thermally coupled on a
first end to at least one of the plurality of electronic
components. A lid, configured to be mounted on the electronic
enclosure, has a first surface to mount proximate to the plurality
of electronic components and a second surface to mount distal from
the plurality of electronic components. The lid has a plurality of
holes positioned to accommodate the one or more heat risers to poke
through the lid. A layer of thermal interface material thermally
couples a second end of the one or more heat risers to the cold
plate. In a variation, the thermal interface material may be
affixed in the same plane as the lid and held in place with a
series of clips placed around the periphery of the thermal
interface, as shown in FIG. 8. Alternatively, tape (e.g. metalized
tape) can be used for the same function. Another function of the
lid is to provide a barrier against electromagnetic interference
(EMI). By providing an electrical contact, either capacitively by
means of the clips, metalized tape or lid overlap of metal layer
804, or an additional electrical connection between 804 or 805 and
the surrounding lid 111 the interposed thermal interface material
can provide a barrier against EMI.
[0026] In another exemplary embodiment, a method for thermally
coupling a plurality of heat generating components in an electronic
enclosure to a cold plate is disclosed. The method comprises
calculating a power dissipation of each of the plurality of heat
generating components, determining an acceptable temperature rise
between the cold plate and the plurality of heat generating
components, and determining an acceptable thermal impedance to
maintain the acceptable temperature rise. A surface area of the
cold plate needed to conduct heat from each of the plurality of
heat generating components is calculated. A type of heat riser
selected for each of a plurality of heat risers is determined based
on the thermal impedance where at least one of the plurality of
heat risers is associated with each of the plurality of heat
generating components.
[0027] In another exemplary embodiment, a thermal interface to
provide cooling to a plurality of electronic components is
disclosed. The thermal interface comprises a first layer of a first
thermal interface material. The first thermal interface material
has a first thermal conductivity. A second layer of a second
compliant thermal interface material is joined to the first layer.
The second compliant thermal interface material has a second
thermal conductivity being lower the first thermal conductivity. In
a specific exemplary embodiment, the first thermal interface
material is laminated to the second complaint thermal interface
material, and the edges sealed to form a bag. A thermally
conductive fluid is encapsulated within the bag, as shown in FIG.
8A.
[0028] In a specific exemplary embodiment described herein, a
system for thermally coupling one or more heat generating
components in a 1 U enclosure to, for example, the removable lid of
the enclosure, is disclosed. The lid can be further coupled to an
external cold plate for additional heat removal. Although the
actual descriptions provided herein are limited to 1 U enclosures,
a skilled artisan will recognize that similar systems, methods, and
means may be applied to other styles of enclosures of various
styles and dimensions. In addition, upon reading the disclosure,
the skilled artisan will further recognize that the heat may be
coupled to a different side of the enclosure, other than the lid,
such as the bottom. Coupling to a different side of the enclosure
can be accomplished by rearranging various elements of the various
embodiments described.
Overview
[0029] In an exemplary embodiment, described in detail below, one
or more heat-generating components in an electronic enclosure are
maintained at acceptable temperatures primarily through conduction
cooling to a proximate cold plate. Heat is thermally coupled from
the heat generating components to thermal interfaces, heat-risers
or spreaders. The heat flux may be spread out over a larger area
and further coupled through the enclosure lid to a cold plate for
heat removal. Although heat and heat flux are the elements of
interest, for purposes herein, power and power dissipation are
sometimes used as a proxy for heat flux.
[0030] In an exemplary embodiment, a methodology to design a
cooling mechanism for a given electronic component or components
may start with calculating a design window. A physical
implementation of the design can use information derived from the
calculating steps.
[0031] In this exemplary embodiment, a design window can be
calculated by identifying and quantifying (e.g., calculating) a
power dissipation of all heat generating components that are not
maintained at a sufficiently low temperature by natural convection
and conduction cooling means. A maximum or acceptable temperature
rise from the cold plate interface to the heat generating
components is then determined. A maximum or acceptable allowable
heat flux (or power) per unit area at the cold plate/enclosure
interface is determined to maintain the maximum acceptable
temperature rise. The heat flux per unit area is commonly referred
to as the thermal impedance. A cold plate surface area required to
conduct the heat to the cold plate is calculated for each the heat
generating components. The cold plate surface area determines an
overall thermal resistance between each of the components and the
cold plate. Each of these calculations and associated governing
equations are known independently in the art.
Physical Implementation
[0032] Once preliminary calculations are determined, a distance
between each of the one or more components and the cold plate
interface is determined. An additional spatial allowance is made
for one or more thermal interfaces, generally between each of the
one or more components and the cold plate interface. However, in
certain applications, thermal interfaces may be placed between one
or more of the components and an adjacent component as well. The
one or more thermal interfaces can be placed in various locations,
such as between a component and a heat riser, between a heat riser
and a cold plate, or between a component and a cold plate, between
a heat riser and a lid, between a component and a lid or between a
cold plate and a lid, as aforementioned. A type and size of each of
the heat-risers or spreaders is determined based on the heat flux,
spreading information, and distances between each of the one or
more components and the cold plate. The heat-risers or spreaders
are produced and installed. The heat-risers or spreaders are
generally placed to be substantially coplanar with the cold plate
or lid interface with thermal coupling between the heat-risers or
spreaders and the cold plate or lid, achieved with the one or more
thermal interfaces. Similarly, the thermal coupling between lid and
cold plate is achieved with a thermal interface.
1 U Enclosure Embodiments
[0033] A conventional motherboard is deployed in a 1 U form factor
electronic enclosure. The 1 U electronic enclosure is nominally
1.75 inches (approximately 4.45 cm) high by 19 inches
(approximately 0.482 m) wide by 24 inches (approximately 0.610 m)
deep with a removable top lid in one embodiment. The enclosure may
contain one or more of a compute server, a storage device, a
network switch, a power supply, other electronic devices, or any
combination, singly or multiply, thereof.
[0034] With reference to FIG. 1A, an exemplary cross-sectional view
of an electronic enclosure 100 includes a lid 111 and has a
motherboard 110 mounted therein. The electronic enclosure 100 and
the lid 111 may each be fabricated from thermally conductive
materials, independently known in the art. The motherboard no
carries some or all of the VLSI components (e.g., integrated
circuits in addition to discrete electronic components) and most,
if not all, auxiliary circuits. The motherboard no is coupled to
the electronic enclosure 100 via a plurality of standoffs 105. The
motherboard 110 acts as a heat sink for components attached
thereon. Through convective and radiative heat transfer to the
electronic enclosure 100, the motherboard 110 has sufficient heat
dissipation to provide generally sufficient heat removal for
lower-powered circuits. Heat dissipation from the motherboard 110
may be further enhanced by one or more layers of thermal interface
material 113 arranged between the motherboard no and one or more
walls of the electronic enclosure 100. The thermal interface 113
functions to bring the motherboard no into thermal contact with the
cold plate (e.g. enclosure wall or any other suitable cooling
component.). Heat risers 102, 104 and 106 preferably conduct heat
from higher-powered components to the cold plate (preferably
through the lid). An exterior side of the lid 111 can be covered
with a thin layer of a compliant thermal interface 103 to optimize
contact with an external cold plate (not shown in FIG. 1A) while
the interior side can be covered in whole or in part with a second
layer of compliant thermal interface material 101 to optimize
thermal contact with the heat risers 102,104 and 106.
Thermal Interface
[0035] In a specific exemplary embodiment, the compliant thermal
interface 103 can comprise two layers laminated or otherwise joined
together to form a sheet, as shown in FIG. 1B. The first layer 103A
functions to resist wear and tear, and the second layer 103B
functions to facilitate heat flux from the first layer 103A to the
cold plate. The two layers can be laminated together, joined at or
near the edges, in a quilted pattern, or in various other fashions
as will be recognizable to a skilled artisan. Alternately, one
layer may be deposited onto the other by chemical deposition,
vacuum deposition, or any other suitable deposition method. In this
specific exemplary embodiment, the layers can be substantially
comprised of polyester and aluminum; the polyester layer being
roughly about 0.5 thousandths of an inch (approximately 13 microns)
in thickness and the aluminum, about 2 thousandths of an inch. A
skilled artisan will recognize that other thicknesses and materials
(such as PTFE, PET, LDPE or any other polymer or shear-resistant
material for the first layer, and copper, gold, or any other
conductive material for the second layer) can be readily employed.
The substantially polyester layer provides strength and toughness
to the compliant thermal interface 103 but the thermal conductivity
is still high due to the relative thinness of the polyester layer.
The substantially polyester layer surface also provides good
thermal coupling from an external cold plate (not shown) to itself
(i.e., the compliant thermal interface 103). The aluminum layer is
substantially hermetic, containing the thermally conductive fluid,
and spreads the heat flux coupled to the polyester layer from/to
the external heat source/cold plate, ensuring a more uniform heat
flux to a proximate thermally conductive fluid and reducing the
overall thermal impedance. In a specific embodiment, shown in FIG.
8A, the dual layer sheet can be formed into a dual layer bag 801 by
joining opposing edges of the sheet, by joining the corners of the
sheet, or by joining a second sheet of substantially similar or
dissimilar construction (e.g. materials, geometry, number of
layers, etc.) to the first sheet. The edges and/or corners are
preferably overlapped and laminated to seal the bag, but may
alternately be crimped or otherwise joined. In another specific
exemplary embodiment, shown in FIG. 8C, a dual-layer bag 801 could
be formed and be further reinforced with a third layer 805 for
strength or structure, such as a porous fiberglass though which a
thermally conductive fluid 802 could flow, thus providing
additional strength while maintaining good thermal conductivity.
The third layer 805 may also be heat-conductive, such that it
facilitates heat transfer within the thermal interface. For
example, the third layer 805 may be a thermally conductive plate,
coupled to the thermally conductive fluid 805, that facilitates
heat spreading throughout the bag 801 (e.g. through the thermally
conductive fluid 802). The conductive plate is preferably metallic
or prismatic, (e.g. graphite), and is preferably slightly flexible,
with a thickness of approximately 0.02 inches (0.5 mm). However,
the conductive plate may comprise other materials, properties, and
thicknesses. The conductive plate may additionally be porous or
include through holes to allow thermally conductive fluid flow. The
third layer 805 may be laminated along the edges to the bag 801,
with a first 802 and a second 802A thermally conductive fluid
encapsulated against each main face (shown in FIG. 8C). More
preferably, layers, approximately 0.02 inch (0.5 mm) thick, of
thermally conductive fluid 802 and 802A are encapsulated against
the first and second main faces by a first and second dual-layer
sheet, respectively, wherein the first and second main faces are
joined along the edges to the edges of the third layer. However,
the third layer 805 may be merely enclosed within the bag 801, such
that the thermally conductive fluid 802 has unrestricted flow over
every face (shown in FIG. 8D), or may be entirely laminated to the
bag interior. Thermal interface 101 can also be similarly
constructed. Where the thermal interface is to be used to provide
electromagnetic shielding, an electrically conductive path 806,
which can be a wire or a metal ribbon, may be attached to
conductive layer 804 and auxiliary layer 805. When installed, an
electrical connection is made to the lid. Clips or metal tape may
be used to install the thermal interface, providing additional
shielding by bridging the gap between lid and thermal
interface.
[0036] Another variant of this dual-layer bag is described with
reference to FIG. 8, below.
[0037] Higher power dissipation devices, in particular high-density
(e.g., LSI, VLSI, ULSI, etc.) integrated circuit devices such as a
CPU 108, a graphics chip 109, a memory 106, a power supply
transistor 114, and inductors (not shown) require heat risers to
provide a low thermal impedance path to a common plane as defined
by, for example, the lid 111. The heat risers conduct heat to the
lid 111 from a component that is, for example, from 0.9 inches
(approximately 2.3 cm) to 1.3 inches (approximately 3.3 cm) below
the lid 111. Consequently, in a specific exemplary embodiment, each
of a plurality of heat risers 102, 104, 112 have an overall length
of from about 0.9 inches (approximately 2.3 cm) to 1.3 inches
(approximately 3.3 cm). Tops of the plurality of heat risers 102,
104, 112 are effectively planarized through the use of a plurality
of riser thermal interfaces 101 so that at least one of the
plurality of heat risers 102, 104, 112 conforms to the lid 111.
Minimizing thermal impedances from a high power dissipation device
to the external cold plate (not shown) can be accomplished by
spreading the heat flux over a larger area. For example, one of the
plurality of heat risers 102, which is also a heat spreader, is
designed to spread the heat flux over an area about ten times
greater at its top thermal contact with one of the plurality of
riser thermal interfaces 101 to the lid 111 than at a bottom
thermal contact 107 to the CPU 108. The ten times greater area
thereby reduces the heat flux and thermal gradient across one of
the plurality of riser thermal interfaces 101, the lid 111, and the
compliant thermal interface 103 by a factor of about ten. The
reduction in heat flux due to the greater area is more fully
described under VLSI cooling below. As will be recognized by a
skilled artisan upon reading the disclosure, a heat riser may be
used to carry the heat away from more than one component. For
example, one of the plurality of heat risers 102 is also in thermal
contact with the power supply transistor 114, transporting heat
generated therein, along with heat from the CPU 108 to the lid
111.
[0038] Thermal paths for high dissipation, high heat flux
integrated circuit devices (e.g., devices fabricated according to
VLSI or ULSI design principles) are provided by combination
heat-risers/spreaders. Such heat-risers/spreaders have top surfaces
from about two to twenty times larger than their bottom surfaces.
For example, with reference now to FIG. 2, one of the plurality of
heat risers 102 that also has heat spreading characteristics, is
examined in further detail. In an exemplary embodiment, at least
one of the plurality of heat risers 102 is constructed from a
highly thermally conductive material, such as a metal block.
[0039] In a specific exemplary embodiment, the metal block is
fabricated from aluminum. In this specific exemplary embodiment,
the heat riser 102 is 3 inches (approximately 70.6 cm) wide by 6
inches (approximately 15.2 cm) long by 1 inch (approximately 2.5
cm) high. A pad area 202 is configured to mount to the CPU 108. The
heat riser 102 receives heat from a high heat flux area of the pad
area 202 and spreads the heat flux (illustrated by a plurality of
dashed arrows 204) over a larger area 203 to reduce the heat flux.
A surface area of the larger area 203 is about 10 times larger than
a surface area of the pad area 202, thus reducing heat flux
proportionately (i.e., by a factor of ten). Reducing the heat flux
allows use of thermal interfaces with lower thermal conductivity,
while still maintaining a thermal resistance from the electronic
component through the lid 111 (or another side of the electronic
enclosure 100) of less than about 0.25.degree. C./Watt.
[0040] The heat riser 102 is installed in contact with the VLSI
component, such as the CPU 108, using the same fixtures as are
normally used to hold down a conventional heat sink. In this
specific exemplary embodiment, two screws 205 secure the heat riser
102 to the VLSI component.
[0041] In other specific exemplary embodiments, the heat riser 102
can be constructed using a simple block of a conducting material
such as aluminum or graphite. Each of these, and related materials,
may be machined or cast into more complex shapes to optimize
performance per unit weight, to fit into limited areas, or to
contact multiple heat generating components. Alternately, the heat
riser 102 may be fabricated from more complex constructs using, for
example, heat pipes.
[0042] Referring to FIG. 3, another exemplary embodiment of a heat
riser 102a uses a plurality of heat pipes 301. The plurality of
heat pipes 301 are preferably tubular and may have a cross section
that is round, square, or other shapes, and can be fabricated from
highly thermally conductive material such as, for example, copper.
They typically contain a small amount of fluid, generally water
under a partial vacuum. The plurality of heat pipes 301 are
thermally coupled with two or more parallel plates (only two plates
are shown for clarity) including a small plate 302 and a large
plate 303. The small plate 302 and the large plate 303 can be
fabricated from any highly thermally conductive material, such as
copper. The small plate 302 is intended for placement on top of the
device to be cooled, such as the CPU 108, and the large plate 303
can be placed against the lid 111 of the electronic enclosure 100
(see FIG. 1).
[0043] The plurality of heat pipes 301 is arranged so that their
center sections are in good thermal contact with the small plate
302 and each of the ends of the plurality of heat pipes 301 are
arranged in good thermal contact with the large plate 303. In a
specific exemplary embodiment, thermal contact with both the small
plate 302 and the large plate 303 is augmented by placing each of
the plurality of heat pipes in grooves (not shown explicitly but
understandable to a skilled artisan) milled into the small plate
302 and the large plate 303. The grooves are roughly equal in
diameter to each of the plurality of heat pipes 301. In another
specific exemplary embodiment, each of the plurality of heat pipes
301 is affixed by soldering. Using the design and fabrication
techniques described herein, the heat riser 102a preferably has a
thermal resistance of less than about 0.03.degree. C./Watt, but may
have a thermal resistance of less than about 0.07.degree.
C./Watt.
[0044] A total number of the plurality of heat pipes 301 and
dimensions of the small plate 302 and the large plate 303 can be
adapted to fit various applications. The larger the large plate 303
in relation to the small plate 302, the greater the reduction in
heat flux across the large plate 303. In a specific exemplary
embodiment, the small plate 302 has dimensions of about 2 inches by
2 inches (approximately 5.1 cm square) and the large plate has
dimensions of about 6 inches by 3 inches (approximately 15.2 cm by
7.6 cm). As the device to be cooled, such as the CPU 108 (see FIG.
1) has a top surface of about 1.3 inches by 1.3 inches
(approximately 3.3 cm square), the generated heat flux is
effectively spread over an area about ten times greater at the
large plate 303 as compared to the small plate 302.
[0045] The plurality of heat pipes 301 could be replaced by a
single wide flat heat pipe (not shown, but understandable to a
skilled artisan). Taking it a step further as illustrated in an
exemplary embodiment of FIG. 4, the small 302 and the large 303
plates of FIG. 3 can be eliminated and substituted by a flat, wide
heat pipe 401. The flat, wide heat pipe 401 may be used as a
heat-riser/spreader all by itself. The flat, wide heat pipe 401 is
fabricated from a highly thermally conductive material such as
metal (e.g., copper). In a specific exemplary embodiment, the flat,
wide heat pipe 401 is 3 inches (approximately 7.6 cm) wide and
placed so that its center portion lies directly on top of the
device to be cooled, such as the CPU 108, and a large portion of
the ends of the flat, wide heat pipe is in contact with the lid 111
of the electronic enclosure 100 (see FIG. 1). Compared to the heat
pipe/riser/spreader described above with reference to FIG. 3,
thermal performance is slightly better with the flat, wide heat
pipe 401 and a lack of coplanarity between the component (e.g., the
CPU 108) and the lid 111 can be compensated for by the flexibility
of the heat pipe. In other exemplary embodiments (not shown), the
flat, wide heat pipe 401 can be used in conjunction with the
plurality of heat pipes 301 of FIG. 3.
[0046] The block 203 shown in FIG. 2 may also be hollow and
partially filled with a fluid, such as water, and may be partially
evacuated. The hot component 202 causes the fluid to boil and
subsequently condense on the opposite surface where it is in
contact with lid 111.
Heat Risers
[0047] In the various exemplary embodiments disclosed above, each
of the risers also spreads the heat over a larger area. For
components that dissipate less heat than various ones of the
high-density integrated circuits discussed above, simpler risers
can sufficiently be effective for cooling the components. For
example, a simple block heat riser having dimensions of 1 inch by 1
inch by 1 inch (approximately 2.5 cm on a side) can be fabricated
from aluminum. Since any face in contact with a component has an
opposing face, to be thermally coupled to the lid 111, has as
identical surface area, no heat spreading occurs.
[0048] With reference to FIG. 5, an exemplary embodiment of one
type of effective heat riser is a spring riser 500 as illustrated.
The spring riser 500 is similar to one of the plurality of heat
risers 104 of FIG. 1 and the flat, wide heat pipe 401 of FIG. 4.
The spring riser 500 can be constructed out of a highly thermally
conductive flexible material such as, for example, copper. The
spring riser benefits from being fabricated from an at least
slightly resilient material, such as hard (e.g. cold rolled)
copper, to provide a spring-like characteristic to the spring riser
500.
[0049] In a specific exemplary embodiment, the spring riser 500 can
be a round or elliptical spring having a width 506 of about 1 inch
(approximately 2.5 cm) wide and a thickness 505 of about 5 mils
(0.005 inches or approximately 127 microns). However, various
shapes other than round can readily be employed as well as other
dimensions.
[0050] The spring riser 500 removes heat from a component, such as
the graphics chip 109 of FIG. 1, by a combination of conduction to
the lid 111, and natural convective and radiative heat transfer to
a local environment of the component. The spring riser 500 can be
affixed to the component by gluing or other means, and has at least
one of a plurality of riser thermal interfaces 101 thermally
coupling the spring riser 500 to the lid in. The spring-like nature
of the spring riser 500 assures a good mechanical and thermal
contact to the lid 111, while automatically compensating for
variations in height and coplanarity. The spring riser 500 is light
in weight and low in cost. Thermal resistance for an exemplary
embodiment of the spring riser 500 described above ranges from
about 0.5.degree. C./Watt to 2.degree. C./Watt.
[0051] Referring now to FIG. 6, various types of volatile and
non-volatile memory subassemblies, such as VRAM or DRAM dual
in-line memory modules (DIMMs), can be cooled by conductive heat
transfer. In an exemplary embodiment, a DIMM 606, is encased with
one or more thermally conductive strips 612 on its sides that act
as heat risers. The one or more thermally conductive strips 612
make thermal contact to memory components 613 within the DIMM 606
at a thermal interface 607. The thermal interface 607 is preferably
a dual-layer thermal interface as described above, but alternately
can be a thermally conductive grease known independently in the
art. Thus, the thermal interface 607 can be a thermal-grease-based
thermal interface.
[0052] Vertical sides of the one or more thermally conductive
strips 612 provide a low thermal impedance path from the DIMM 606
to an uppermost portion 614 of the one or more thermally conductive
strips 612. In a specific exemplary embodiment, a 1 mm thick
aluminum block is used for the one or more thermally conductive
strips 612. The one or more thermally conductive strips 612 can be
held in place by, for example, a plurality of spring clips 611,
such that the thermal interface is sandwiched between the thermally
conductive strip 612 and the electronic component. The spring clips
611 each preferably comprise two tines joined by a spring element,
wherein spring element applies a restorative reaction force to the
tines when the tines are displaced from a resting position. The end
of each tine is preferably curved away from the end of the opposing
tine. The clips preferably apply a substantially normal,
compressive force to the coupling surfaces, and are preferably
stamped, machined, or otherwise formed as a single piece from a
metallic sheet or block. However, other manufacturing methods may
be used. The plurality of spring clips 611 is preferably coupled
together on a rail.
[0053] In an alternative exemplary embodiment, the one or more
thermally conductive strips 612 can be glued to components of the
memory components 613 without requiring the plurality of spring
clips 611. The glue thus provides both a mechanical and thermal
attachment.
[0054] The uppermost portion 614 of the one or more thermally
conductive strips 612 is substantially orthogonal to the sides and
made as wide as a pitch of the DIMM 606 allows (e.g., 0.4 inches or
approximately 10 mm), thus minimizing the thermal resistance of the
DIMM 606 to an interface of the lid 111 of the electronic enclosure
100 (see FIG. 1). A typical thermal resistance of the interface
between the DIMM 606 and the lid 111 is 1.6.degree. C./Watt with
0.2 mm thick thermal interface. Generally, a worst case thermal
resistance is 2.degree. C./Watt for the exemplary embodiment shown,
resulting in a temperature rise of approximately 20.degree. C. for
a 10 Watt DIMM.
[0055] Thermally conductive strips 612 on opposite sides of the
DIMM module can be overlapped at the top of the module and
thermally coupled by a thermal interface such as thermal grease of
a thermal pad. The top strip 614 then extends across the entire
DIMM top surface (or more) providing a larger planarized surface to
the cold plate interface for a lowered thermal resistance.
Furthermore, a flexible circuit populated with DIMMs may be wrapped
around a thermally conductive metal strip to improve thermal
performance. The DIMM substrate may additionally be formed into a
"T" shape to improve heat transfer to ambient air (e.g.
air-cooling). The substrate is more preferably formed as a wide "T"
shape and coupled to a cold plate through a thermal interface to
conduct heat to the cold plate. However, the substrate may be
formed as an "L" shape or any other suitable form.
[0056] Note that although the one or more thermally conductive
strips 612 are shown on both sides of the memory subassembly, in
many cases components are mounted on one only side. Thus, in such
an application only the single mounted side requires only one of
the one or more thermally conductive strips 612.
[0057] In a specific application of various embodiments of
thermally cooling electronic components described herein, a voltage
regulator module (VRM, not shown) converts an internal 12 V power
supply to voltages required by the individual components, such as
the CPU 108 and the memory 106 (see FIG. 1). The VRM often supplies
over 100 amps of current at just over 1 VDC and dissipates up to 30
Watts. In contemporaneous designs, the power is commonly dissipated
among six transistors and inductors.
[0058] Most server designs have the VRMs built onto the motherboard
with the inductors and switching transistors laid out in a row up
to 4 inches (approximately 10 cm) long. Consequently, a generated
heat flux is relatively low. A piece of metal such as 4 inch long
by 1/8 inch thick (approximately 10 cm long by 3.2 mm thick)
aluminum strip (not shown) is placed over the transistors and
inductors with a thin thermal interface coating there-between. The
piece of metal can, in turn, be coupled to the lid 111 of FIG. 1 by
one of the plurality of heat risers 102 as shown for the power
supply transistor 114, or a solid metal, such as the heat riser
iota of FIG. 3, or one of the spring risers, such as flat, wide
heat pipe 401 or the spring riser 500, of FIGS. 4 and 5
respectively, can be employed to thermally rise and couple the
aluminum strip to the lid 111.
[0059] In another specific application of various embodiments of
thermally cooling electronic components described herein, an input
power converter converts input power to a lower intermediate
voltage, nominally 12 VDC. Power is delivered to a motherboard
through one or more electrical connectors. Input power converter
subassemblies are mounted (not shown), typically by screws,
directly to the lid 111 of the electronic enclosure 100. A layer of
thermal interface material between the cover and the device ensures
good thermal contact.
[0060] In another specific application of various embodiments of
thermally cooling electronic components described herein, disk
drives (not shown) consume about 10 Watts so adequate cooling is
typically achieved by conductive and natural convective heat
transfer within an enclosure. Cooling of the disk drives can be
enhanced by inserting, for example, a thermal interface 113 such as
was done for the motherboard no of FIG. 1 between the disk drive
and the electronic enclosure 100.
[0061] In another specific application of various embodiments of
thermally cooling electronic components described herein, auxiliary
circuit board subassemblies generally have low dissipation (e.g.,
below 30 Watts) and just a few integrated circuit components. With
reference to FIG. 7, in a 1 U-sized system, an auxiliary circuit
board 701 is commonly inserted into the motherboard no so that the
auxiliary circuit board 701 is coplanar with and slightly above the
motherboard 110 as illustrated. Components mounted to the auxiliary
circuit board 701 can be cooled via an aluminum block or a spring
riser 704 glued, coupled, or otherwise adhered on top of the
components and coupled to the lid 111 of the electronic enclosure
100 in a fashion similar to that described for other devices,
above.
[0062] Further, a plurality of auxiliary circuit boards (not shown
explicitly) can be placed in an area previously occupied by fans
and associated control mechanisms normally used for forced-air
convective cooling. The plurality of auxiliary circuit boards can
be connected to the motherboard with high speed interfaces such as
HyperTransport.RTM., PCI Express.RTM., or any other similar widely
accepted protocol. Mounting the plurality of auxiliary circuit
boards in an area previously occupied by fans and associated
control mechanisms enables a 1 U enclosure to offer the same
functionality as a 2 U, 3 U, or 4 U enclosure.
[0063] Other objects, such as the auxiliary circuit board
subassemblies described immediately above, may obstruct a direct
thermal path between the motherboard no component and the lid 111.
In such a case, heat generated by the component is directed around
the obstruction. For example and with continuing reference to FIG.
7, a component, such as the graphics chip 109, no longer has a
direct unobstructed path to the lid 111. The auxiliary circuit
board 701 (plugged into a socket 702) lies directly above the
graphics chip 109. In this case, an exemplary half spring riser 703
has one end in thermal contact with the graphics chip 109, wraps
around the auxiliary circuit board 701, and thermally contacts at
least one of the plurality of riser thermal interfaces 101 under
the lid 111. For medium and lower power devices, the half spring
riser 703 can be a simple strip of copper as described above for
one of the spring risers, such as the spring riser 500 of FIG. 5.
If a lower thermal resistance is required, the half spring riser
703 can be constructed much like the flat, wide heat pipe 401
described with reference to FIG. 4.
[0064] Alternatively, the half spring riser 703 can be fabricated
from a heavier gauge thermally-conductive material or even a block
of metal cut in such a fashion as to extend out from under the
obstruction and rise to the lid 111. In another exemplary
embodiment, a thermal interface (not shown) may be inserted under
the obstructed component in order to conduct heat to the enclosure
bottom as referred to above. The variations described are not all
not shown as they are too numerous to itemize and are readily
apparent to one skilled in the art using the disclosure and
embodiments provided herein.
Heat Riser Planarization
[0065] After thermal risers are attached to many or all components
within the electronic enclosure 100, thus bringing the thermal
risers nominally up to a level of a lower portion on the underside
of the lid 111, a planarization step can be included further
enhancing thermal coupling to the lid 111 with a low thermal
resistance.
[0066] Assembly of the motherboard 110 may result in the top
portions of the components not being coplanar either with one
another or an uppermost portion of heat risers attached thereto not
being coplanar with the lower portion of the underside of the lid
111. Consequently, the upper portions of the attached heat risers
may not be at an exact distance below the lid 111. For example, an
integrated circuit may have dimensions of 33 mm.times.33 mm with an
installed height variance of roughly 0.2 mm, and a surface
coplanarity variance of about 0.3 mm between either of the two sets
of parallel faces. A top face or surface of, for example, the
larger area 203 of one of the plurality of heat risers 102 (see
FIG. 2), multiplies an effect of the variation simply due to the
increased surface area. Moreover, both the motherboard 110 and the
electronic enclosure 100 are flexible and can sag away from their
respective support structures. In this example, coplanarity
variance can be up to roughly 1.4 mm or more.
[0067] While any of the various spring risers described herein are
flexible, and will therefore adjust to variations in height and
planarity automatically, the tops of larger risers/spreaders (e.g.,
one of the plurality of heat risers 102) can benefit from
planarization and a resulting height adjustment thus assuring good,
low-thermal resistance coupling to the lid 111. Ordinary
rubber-like thermal interface sheet materials of the prior art do
not have sufficient compliance to overcome large coplanarity
differences.
[0068] Several methods may be employed to offset a lack of
coplanarity. In an exemplary embodiment, a compliant thermally
conductive substance, such as a thermal grease, known independently
in the art, can improve conductive heat transfer between contacting
surfaces. Additionally, a self-leveling thermally conductive
potting compound may be poured in a mask over the riser and allowed
to set. In another exemplary embodiment, a thermal grease or
thermally conducting potting compound may be encapsulated in a bag
and laid over one or a plurality of risers, functioning as at least
one of the plurality of riser thermal interfaces 101, 103. The bag
of this exemplary embodiment is described in detail with reference
to FIG. 8, below. Self-leveling thermally conductive potting
compounds are known independently in the art, as are ceramic or
metal based thermal greases.
[0069] In a specific exemplary embodiment, an uppermost top portion
of the heat riser 102 is covered with a moderately high
conductivity (e.g., 3 Watts/m-.degree.K) potting compound prior to
replacing the lid 111 on the electronic enclosure 100. The potting
compound is cured in place between the heat riser 102 and the lid
111. The cured potting compound then functions as at least one of
the plurality of riser thermal interfaces 101 described above with
a thermal impedance of less than about 0.1.degree. C./Watt/in.sup.2
(approximately 0.016.degree. C./W/cm.sup.2).
[0070] Further, since contacting surfaces between the top of
risers/spreaders and the underside of the lid 111 are never
perfectly flat or coplanar, and may even be non-rigid and flexible,
a thermal interface, such as a thermal grease or an elastomeric pad
(known separately and independently in the art), may be inserted
between the contacting surfaces. Alternatively or in addition, the
riser may be physically clamped to the lid by a screw or clamping
fixture, or otherwise adhered (e.g., by an epoxy or chemical
bonding agent), using a generally inherent flexibility of the
motherboard 110 and the lid 111 to compensate for non-coplanarity
and height variations. The flexibility of the motherboard 110 can
compensate for some or all the height and coplanarity issues. After
mounting the heat riser 102 on the component to be cooled and
replacing the lid 111, the lid 111 is pressed down on the heat
riser 102 (e.g. by clamps or any suitable coupling mechanism).
Thermal resistance is minimized by flattening the lid 111 against
the heat riser 102 and minimizing a thickness of one or more of the
plurality of riser thermal interfaces 101. Screwing or locking
sliders (not shown but readily understood by a skilled artisan) are
one form of attachment but other attachment methods will work. The
pressing down process can benefit from a semi flexible enclosure
lid capable of bending with the rest of the enclosure when force is
applied thereto. The lid is pressed into contact with heat riser
102 and the motherboard 110 is flexed to compensate for any
mechanical height differences due to, for example, dimensional
tolerances of the various components such as the enclosure,
motherboard, heat riser, etc.).
[0071] In another exemplary embodiment, any of the risers or
spreaders are patterned (not shown but readily understandable to a
skilled artisan) on an uppermost portion (i.e., that portion
configured to contact the lid 111). A portion of the lid 111,
corresponding to a contact point of the patterned riser or
spreader, is similarly patterned to engage with the riser or
spreader pattern. The patterned surface increases an overall
surface area of the contacting surfaces, thus increasing the
thermal contact area. Patterning of opposing surfaces brought into
contact with one another is discussed in more detail with reference
to FIG. 9, below.
[0072] In another exemplary embodiment, a compliant
thermally-conducting foam (not shown) can function as at least one
of the plurality of riser thermal interfaces 101. The compliant
thermally conducting foam is compressed by the lid 111 providing
coplanarity between the heat riser 102 and the lid 111. The
compliant thermally conducting foam is useful in situations where
planarity divergence is small or relatively high pressures can be
applied to press down the lid 111.
[0073] In yet another exemplary embodiment, a flexible vapor
chamber (not shown) fabricated from a resilient and thermally
conductive material can be clamped to the riser or device to be
cooled. A pressure-cooker-effect is then utilized to expand a top
of the vapor chamber top into planarity with the lid 111, thus
providing enhanced conductive heat transfer. A skilled artisan will
recognize that any or all of the methods and means described above
can be combined for various applications.
[0074] With reference now to FIG. 8, a bag 801, discussed briefly
above, is filled with a thermally conductive fluid 802 (note that
the thermally conductive fluid 802 is contained within the bag
801). The fluid can be, for example, a thermal grease. Various
types of thermal grease are known independently in the art. For a
single riser, the bag 801 can be fabricated to be slightly larger
than a top surface of the riser, for example, from about 5% to 20%
larger on a side. For example, for the 3 inch by 6 inch
(approximately 70.6 cm by 15.2 cm) dimension of the larger area 203
of the heat riser 102 (see FIG. 2) discussed above, the bag can be
3.3 inches by 6.6 inches (approximately 8.4 cm by 16.8 cm). The bag
801 can be sized large enough to allow an excess amount of the
thermally conductive fluid 802 a place to escape when the fit is
tight, but not so large that much of the thermally conductive fluid
802 will flow away beyond one or more edges of the heat riser 102
or cold plate, thus leaving a void above the heat riser 102 or cold
plate. The bag 801 can also be sized such that coupling the bag 801
to a heat riser 102 or cold plate causes the coupling surfaces of
the bag 801 to distend as thermally conductive fluid 801 is forced
away from the coupling site. An amount of the thermally conductive
fluid 802 used in the bag 801 is dependent upon a worst-case
coplanarity variation, as described above. The bag 801 could also
be large enough to cover a multiplicity of components, simply
covering over many or all of the components. In another exemplary
embodiment, the bag 801 can act as the lid 111 of the electronic
enclosure 100.
[0075] In a specific exemplary embodiment, the bag 801 can be
fabricated using a dual-layer polyester and aluminum construction.
This embodiment is described with reference to the specific
exemplary embodiment of constructing the compliant thermal
interface 103 discussed above. For the bag 801, the dual-layers can
be filled with various types of fluid such as the thermally
conductive fluid 802. In a related specific exemplary embodiment,
one of the layers of the bag can be the lid 111 of the electronic
enclosure 100. The second of the dual-layers is coupled to the lid
111 so as to form a cavity between the lid 111 and the second of
the dual-layers. The second of the dual-layers can be comprised
substantially of either, for example, aluminum or polyester. In
this case, the bag 801 can be in contact with one surface of the
entire lid 111 or, alternatively, in contact with only certain
portions. Of course, multiple instantiations of the bag 801 can be
in contact with different areas of the lid 111 as well.
Additionally either of the dual-layers can be comprised of any
other material that is generally non-reactive when in contact with
the thermally conductive fluid 802 or thermal greases and has a
relatively good thermal conductivity. Additionally, the materials
for the dual-layers should be relatively impervious to leaks when
used to encapsulate various types of fluid such as the thermally
conductive fluid 802. In other exemplary embodiments where the bag
801 comes into contact with the lid 111, there should be a good
thermal contact between the bag 801 and the lid 111.
[0076] In another exemplary embodiment, the bag 801 can be
fabricated using a dual-layer polyester and aluminum construction
on one side with the other side comprising the lid 111 of the
electronic enclosure 100 (see FIG. 1A). The dual-layer polyester
and aluminum construction side is affixed to the lid 111 by gluing
or other means. This embodiment is described with reference to the
specific exemplary embodiment of constructing the compliant thermal
interface 103 discussed above. For the bag 801, the space between
the dual-layers and the lid 111 can be filled with various types of
fluid as the thermally conductive fluid 802.
[0077] In another exemplary embodiment, the bag 801 with the
auxiliary spreader 805 can be located in a hole in the lid cut to
the dimensions of the bag and secured with clips or metallic tape
so that it is coplanar with the lid. FIG. 6B shows an exemplary
implementation. The clip 601 is fabricated from a thin, springy
material such as steel or beryllium copper. Typical thickness is
approximately 0.005 inches. The clip 611 may be a continuous spring
that spans the whole length of a single side of the bag 801, or may
be deployed in small sections with multiple instances along each
side of the bag. The clips are attached to the bag 801 by sliding
the jaw 602 over the edge of the bag. The bag is preferably
inserted from the top into an appropriately sized hole in the lid.
The edge 603 preferably gives during insertion and springs back to
hold the bag in place. The clips can also form a capacitive
coupling to the lid for EMI suppression, and can be augmented by a
direct electrical connection to the auxiliary spreader and
conduction layers of the bag. Removal of a small amount of the
protective layer under one or more clips may also provide an
adequate connection. The auxiliary layer can similarly be connected
to the conductive layer by a small leaf spring. This bag deployment
method reduces the number of variants required for various server
lid types as a single design may be used, thus benefiting more from
the economics of higher volume manufacturing.
[0078] The thermally conductive fluid 802 can either be a setting
or non-setting compound depending upon a specific application. For
example, if components within the electronic enclosure 100 are
changed over the life of the equipment, a non-setting compound is
adaptable to the new dimensions of one or more new components.
However, a setting compound is less likely to leak or otherwise
fail than a non-setting compound. Thus, the setting compound can be
better suited for applications that are not modified.
[0079] In certain applications, such as in blade servers, the
enclosure may be mounted on edge, (e.g. with the bag 801 positioned
vertically). In such a situation, a thixotropic grease in a tightly
contained bag 801 is preferred in order to ensure that the grease
does not puddle at the bottom of the bag to the detriment of its
thermal conductivity.
[0080] In a specific exemplary embodiment, the bag 801 is utilized
to achieve the pressure-cooker effect, describe above. This
specific exemplary embodiment is similar to the aforementioned
technique of encapsulating thermal grease or thermally conducting
potting compound in a bag. However, with the pressure-cooker
effect, the bag 801 is fabricated from a flexible and thermally
conductive material. The bag 801 is evacuated, except for a small
amount of volatile fluid 802 that boils just above the cold plate
operating temperature. The bag 801, acting as a vapor chamber, is
affixed to the heat riser 102. When the bag 801 cools, it is
compressed flat by the lack of vapor-counteracting air pressure.
When the heat riser 102 starts to conduct heat, the bag 801 warms
up until the fluid 802 boils, expanding the bag 801 and forcing it
tightly against the lid 111. At that point, the fluid 802 at the
top of the bag 801 that is in thermal contact with the lid 111
cools and condenses, thus releasing heat into the lid 111. In this
manner, heat is transferred from the heat riser 102 to the lid
111.
[0081] Referring now to FIG. 9, an exemplary embodiment of a
grooved interface between the heat riser 102 and the lid 111
exemplifies one of the techniques described above to compensate for
a lack of coplanarity. In this exemplary embodiment, the heat riser
102 is patterned with a plurality of grooves 901. The plurality of
grooves 901 engages a plurality of corresponding grooves 902 formed
into a lower portion of the lid 111.
[0082] In a specific exemplary embodiment, each of the plurality of
grooves 901 and the plurality of corresponding grooves 902 are
formed to a depth of 3 mm with a groove pitch 903 of 1 mm, along
the z-axis (the z-axis being defined as being orthogonal to the
drawing), such that a width of each "tooth" is slightly less than
one half the groove pitch 903. This ratio assures some skew
tolerance in the x-axis as well as the y- and z-axes. However, the
width of the teeth can vary between the plurality of grooves 901
and the plurality of corresponding grooves 902 or even from
tooth-to-tooth. The only requirement is that the two components
properly mate such that a surface area, and a resulting convective
heat transfer, increases. When the lid 111 is replaced, the two
sets of grooves mesh and, because of the skew tolerance,
compensation is made between a lack of coplanarity between the heat
riser 102 and the lid 111.
[0083] The grooved surfaces thus assure a larger interface area for
a lower thermal resistance between the heat riser 102 and the lid
111. The grooved surfaces may be manufactured as part of the heat
riser 102 and the lid 111, or they may be separate pieces of
thermally conductive material applied to either or both surfaces.
To further increase convective heat transfer between the mating
surfaces, either thermal grease is applied between the surfaces to
effect a low thermal resistance or one or both surfaces can include
a compliant and thermally conductive thermal interface. Using the
teachings herein, one skilled in the art will realize other depths,
pitches, and interlocking patterns other than grooves, (e.g., a
checkerboard pattern), may also be used in different
applications.
[0084] In another exemplary embodiment, the thermal interface
directly couples to the cold plate. The thermal interface comprises
the embodiment with a substantially rigid third layer 805, such
that it is self-supporting. As shown in FIG. 10, the cold plate
1001 includes an attached groove for mounting the thermal
interface. The thermal interface may be slid into place adjacent to
the cold plate along said grooves that guide and retain the thermal
interface 1002 along a broad surface. Alternately, the thermal
interface 1002 may be attached to the cold plate 1001 by adhesive
(e.g. metal tape) or by the spring clips described above.
Lid Modifications and Lidless Enclosures
[0085] In the various embodiments described herein, heat risers are
used as a thermal path between one or more of the various
components to be cooled and an enclosure lid. In an exemplary
embodiment, to properly couple heat from the top of the heat riser
to the cold plate through the lid utilizes, for example, at least
two of the plurality of riser thermal interfaces 101 or the
compliant thermal interface 103 as shown in FIG. 1A. In high power
applications, such as a 200-Watt CPU, or when it is desirous to
have the temperature difference between the component and the cold
plate lower, the two layers of thermal interface may add too much
thermal resistance. In such a case, the lid may be modified or
eliminated.
[0086] In the first case where the lid is modified, holes are cut
through the lid to match sizes of one or more of the heat-risers or
spreaders. The heat-risers/spreaders are made slightly taller than
described in other embodiments, above, so the heat-riser/spreaders
poke through the lid and are level with an outside portion of the
top of the lid. A thermal interface is then added to the top of the
riser that is then directly coupled to an external cold plate
through the thermal interface. A spring clip, as described above,
preferably couples the thermal interface to the lid to retain the
thermal interface position as well as to ground the thermal
interface. However, the thermal interface may also be adhered to
the lid with metal tape to achieve the same effects.
[0087] In the second case where the lid is completely eliminated,
the bag 801 of FIG. 8 above is designed to fit over the top of all
the heat riser components, thereby replacing and eliminating the
lid. In applications where the lid is used for other purposes, such
as Faraday shielding for EMI, the bag 801 can be metalized and
electrically coupled to the enclosure to provide for electrical
isolation. This technique is also applicable to blade servers.
Moreover, to spread heat better across the lid, the lid itself, or
a portion thereof, may be constructed as a flat heat pipe or vapor
chamber using techniques described above.
[0088] Although various embodiments have been described herein, it
will be evident that various modifications and changes may be made
to these embodiments without departing from the broader spirit and
scope of various forms of the present invention. Accordingly, the
specification and drawings are to be regarded in an illustrative
rather than a restrictive sense. The accompanying drawings that
form a part hereof show by way of illustration, and not of
limitation, specific embodiments in which the subject matter may be
practiced. The embodiments illustrated are described in sufficient
detail to enable those skilled in the art to practice the teachings
disclosed herein. Other embodiments may be utilized and derived
therefrom, such that structural and logical substitutions and
changes may be made without departing from the scope of this
disclosure. The Detailed Description, therefore, is not to be taken
in a limiting sense, and the scope of various embodiments is
defined only by the appended claims, along with the full range of
equivalents to which such claims are entitled.
[0089] Such embodiments of the inventive subject matter may be
referred to herein, individually or collectively, by the term
"invention" merely for convenience and without intending to
voluntarily limit the scope of this application to any single
invention or inventive concept if more than one is, in fact,
disclosed. Thus, although specific embodiments have been
illustrated and described herein, it should be appreciated that any
arrangement calculated to achieve the same or similar purposes may
be substituted for the specific embodiments shown. This disclosure
is intended to cover any and all adaptations or variations of the
various embodiments. Combinations of the above embodiments, and
other embodiments not specifically described herein, will be
apparent to those of skill in the art upon reviewing the above
description.
[0090] For example, particular embodiments describe various
arrangements, dimensions, materials, and topologies of systems.
Such arrangements, dimensions, materials, and topologies are
provided to enable a skilled artisan to comprehend principles of
the present disclosure. Thus, for example, numerous other materials
and arrangements may be readily utilized and still fall within the
scope of the present disclosure. Additionally, a skilled artisan
will recognize, however, that additional embodiments may be
determined based upon a reading of the disclosure given herein.
* * * * *