U.S. patent application number 10/649519 was filed with the patent office on 2005-03-03 for variable height thermal interface.
Invention is credited to Delano, Andrew D., White, Joseph M..
Application Number | 20050045307 10/649519 |
Document ID | / |
Family ID | 34216977 |
Filed Date | 2005-03-03 |
United States Patent
Application |
20050045307 |
Kind Code |
A1 |
White, Joseph M. ; et
al. |
March 3, 2005 |
VARIABLE HEIGHT THERMAL INTERFACE
Abstract
A variable-height thermal-interface device is provided for
transferring heat from a heat source to a heat sink. The device
comprises a first uniaxial rotary cylindrical joint comprising a
first cylindrically concave surface in slidable contact with a
first cylindrically convex surface. The first cylindrically concave
surface and the first cylindrically convex surface share a common
first radius of curvature relative to a common first cylinder axis.
The first cylindrically concave surface is operable to rotate about
the common first cylinder axis relative to the first cylindrically
convex surface to compensate for uniaxial angular misalignment
between the heat source and the heat sink.
Inventors: |
White, Joseph M.; (Windsor,
CO) ; Delano, Andrew D.; (Fort Collins, CO) |
Correspondence
Address: |
HEWLETT PACKARD COMPANY
P O BOX 272400, 3404 E. HARMONY ROAD
INTELLECTUAL PROPERTY ADMINISTRATION
FORT COLLINS
CO
80527-2400
US
|
Family ID: |
34216977 |
Appl. No.: |
10/649519 |
Filed: |
August 25, 2003 |
Current U.S.
Class: |
165/80.3 ;
257/E23.09; 257/E23.094 |
Current CPC
Class: |
H01L 23/433 20130101;
H01L 2924/0002 20130101; H01L 23/4338 20130101; H01L 2924/00
20130101; H01L 2924/0002 20130101; F28F 13/00 20130101 |
Class at
Publication: |
165/080.3 |
International
Class: |
F28F 007/00 |
Claims
What is claimed is:
1. A variable-height thermal-interface device for transferring heat
from a heat source to a heat sink, said device comprising: a first
uniaxial rotary cylindrical joint comprising a first cylindrically
concave surface in slidable contact with a first cylindrically
convex surface, said first cylindrically concave surface and said
first cylindrically convex surface having a common first radius of
curvature relative to a common first cylinder axis; said first
cylindrically concave surface operable to rotate about said common
first cylinder axis relative to said first cylindrically convex
surface to compensate for uniaxial angular misalignment between
said heat source and said heat sink.
2. The device of claim 1 wherein: said common first cylinder axis
is inclined diagonally relative to the z-axis parallel to the
shortest distance between said heat source and said heat sink; and
said first cylindrically concave surface is operable to slide
linearly relative to said first cylindrically convex surface in a
direction parallel to said common first cylinder axis to provide
z-axis expansion of said variable height thermal interface
device.
3. The device of claim 2 further comprising a spring clip
mechanically spring loading said first cylindrically concave
surface and said first cylindrically convex surface, said spring
clip operable to apply a shear force across said first uniaxial
rotary cylindrical joint, said shear force coupling to provide said
z-axis expansion.
4. The device of claim 3 wherein said spring clip is shaped
approximating a deformed rectangular frame, comprising: a first
side and a second side opposite said first side, wherein said first
and second sides are bent inward toward one another; said first
side operable to couple a compressive force substantially parallel
to said first cylindrically concave surface; and said second side
operable to couple an oppositely directed compressive force to said
first cylindrically convex surface.
5. The device of claim 1, further comprising: a second uniaxial
rotary cylindrical joint comprising a second cylindrically concave
surface in slidable contact with a second cylindrically convex
surface, said second cylindrically concave surface and said second
cylindrically convex surface having a common second radius of
curvature relative to a common second cylinder axis; said second
cylindrically concave surface operable to rotate about said common
second cylinder axis relative to said second cylindrically convex
surface to compensate for uniaxial angular misalignment between
said heat source and said heat sink.
6. The device of claim 5 wherein: the orientation about said z-axis
of said common first cylinder axis is different relative to the
orientation of said common second cylinder axis about said z-axis;
and said first and said second uniaxial rotary cylindrical joints
are operable to rotate cooperatively to compensate for biaxial
angular misalignment between said heat source and said heat
sink.
7. The device of claim 5 wherein: said common first cylinder axis
and said common second cylinder axis are each inclined diagonally
relative to the z-axis parallel to the shortest distance between
said heat source and said heat sink; and said first and said second
uniaxial rotary cylindrical joints are each operable to slide
linearly to provide combined z-axis expansion of said variable
height thermal interface device equivalent to the sum of the z-axis
expansions of said individual first and second uniaxial rotary
cylindrical joints.
8. The device of claim 1 further comprising a wedge interface
having a first planar surface in slidable contact with a second
planar surface, said slidably contacting planar surfaces inclined
diagonally relative to the z-axis parallel to the shortest distance
between said heat source and said heat sink, said wedge interface
operable to provide z-axis expansion of said variable height
thermal interface device.
9. The device of claim 1 further comprising a multi-axis rotary
spherical joint operable to compensate for multi-axis angular
misalignment between said heat source and said heat sink.
10. The device of claim 1 further comprising a shim operable to
provide z-axis expansion of said variable height thermal interface
device.
11. The device of claim 1 further comprising a conformal
thermal-interface material applied to interface surfaces within
said uniaxial rotary cylindrical joint.
12. The device of claim 1 wherein said uniaxial rotary cylindrical
joint consists substantially of high thermal conductivity solid
materials.
13. The device of claim 12 wherein said solid high thermal
conductivity materials are selected from the group consisting of
metals, insulators, semiconductors, and composite materials.
14. The device of claim 12 operable to transfer heat from said heat
source through said uniaxial rotary cylindrical joint to said heat
sink.
15. The device of claim 14 further operable to transfer heat under
compressive loading applied between said heat sink and said heat
source.
16. The device of claim 15 coupled mechanically and thermally with
a heat sink hold-down device, wherein said heat sink hold-down
device is operable to apply said compressive loading.
17. The device of claim 1 wherein said heat source comprises an
integrated circuit chip.
18. A variable-height thermal-interface device for transferring
heat from a heat source to a heat sink, said device comprising: a
first wedge interface having a first planar surface in slidable
contact with a second planar surface, said slidably contacting
first and second planar surfaces inclined diagonally relative to
the z-axis parallel to the shortest distance between said heat
source and said heat sink, said first wedge interface operable to
provide z-axis expansion of said variable height thermal interface
device; and a second wedge interface having a third planar surface
in slidable contact with a fourth planar surface, said slidably
contacting third and fourth planar surfaces inclined diagonally
relative to the z-axis parallel to the shortest distance between
said heat source and said heat sink, said second wedge interface
operable to provide z-axis expansion of said variable height
thermal interface device.
19. The device of claim 18 wherein: the orientation direction about
said z-axis of said first wedge interface is different relative to
the orientation direction of said second wedge axis about said
z-axis; and said first and said second wedge interfaces are
operable to slide cooperatively to provide z-axis expansion of said
variable height thermal interface device between said heat source
and said heat sink equivalent to the sum of the individual z-axis
expansions of said first wedge interface and said second wedge
interface.
20. The device of claim 18 further comprising: a spring clip
mechanically spring loading said first wedge interface, said spring
clip operable to apply a shear force across said first wedge
interface, said shear force coupling to provide said z-axis
expansion.
21. The device of claim 18 further comprising: a first uniaxial
rotary cylindrical joint comprising a first cylindrically concave
surface in slidable contact with a first cylindrically convex
surface, said first cylindrically concave surface and said first
cylindrically convex surface having a common first radius of
curvature relative to a common first cylinder axis; said first
cylindrically concave surface operable to rotate about said common
first cylinder axis relative to said first cylindrically convex
surface to compensate for uniaxial angular misalignment between
said heat source and said heat sink.
22. The device of claim 18 further comprising a multi-axis rotary
spherical joint operable to compensate for multi-axis angular
misalignment between said heat source and said heat sink.
23. The device of claim 18 further comprising a shim operable to
provide z-axis expansion of said variable height thermal interface
device.
24. A method of transferring heat from a heat source to a heat sink
using a variable-height thermal-interface device, said method
comprising: providing a first uniaxial rotary cylindrical joint
comprising a first cylindrically concave surface in slidable
contact with a first cylindrically convex surface, said first
cylindrically convex surface and said first cylindrically concave
surface having a common first radius of curvature relative to a
common first cylinder axis; sliding said first cylindrically
concave surface relative to said first cylindrically convex
surface, causing filling of gaps between said heat source and said
heat sink; applying compressive loading between said heat source
and said heat sink through said first uniaxial rotary cylindrical
joint; and transferring heat from said heat source through said
first uniaxial rotary cylindrical joint to said heat sink.
25. The method of claim 24 wherein said sliding comprises rotating
said first cylindrically concave surface relative to said first
cylindrically convex surface about said common first cylinder axis,
causing compensating of uniaxial angular misalignment between said
heat source and said heat sink.
26. The method of claim 24 wherein: said common first cylinder axis
is inclined diagonally relative to the z-axis parallel to the
shortest distance between said heat source and said heat sink; and
said sliding comprises said first cylindrically concave surface
sliding linearly relative to said first cylindrically convex
surface in a direction parallel to said common first cylinder axis
to provide z-axis expansion of said variable height thermal
interface device.
27. The method of claim 26 further comprising: coupling a spring
clip mechanically to said first uniaxial rotary cylindrical joint;
and applying a shear force across said first uniaxial rotary
cylindrical joint, causing a z-axis expansion of said first
uniaxial rotary cylindrical joint.
28. The method of claim 25 further comprising: providing a second
uniaxial rotary cylindrical joint comprising a second cylindrically
concave surface in slidable contact with a second cylindrically
convex surface, said second cylindrically concave surface and said
second cylindrically convex surface having a common second radius
of curvature relative to a common second cylinder axis; rotating
said second cylindrically concave surface about said common second
cylinder axis relative to said second cylindrically convex surface,
causing compensating of uniaxial angular misalignment between said
heat source and said heat sink; applying compressive loading
between said heat source and said heat sink through said second
uniaxial rotary cylindrical joint; and transferring heat from said
heat source through said second uniaxial rotary cylindrical joint
to said heat sink.
29. The method of claim 28 wherein: the orientation about said
z-axis of said common first cylinder axis is different relative to
the orientation of said common second cylinder axis about said
z-axis; and said rotating of said first and said second uniaxial
rotary cylindrical joints cooperatively compensate for biaxial
angular misalignment between said heat source and said heat
sink.
30. The method of claim 24 further comprising applying
thermal-interface material to interfaces within said uniaxial
rotary cylindrical joint.
31. The method of claim 24 wherein said applying compressive
loading further comprises: providing a heat sink hold-down device
operable to apply a compressive load; coupling said heat sink, said
variable-height thermal-interface device, and said heat source
mechanically and thermally with said heat sink hold-down device;
and applying a compressive load between said heat sink and said
heat source using said heat sink hold-down device.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is related to concurrently filed,
co-pending, and commonly assigned U.S. Patent Application [Attorney
docket 200300041-1], titled "METHOD OF ASSEMBLY OF A WEDGE THERMAL
INTERFACE TO ALLOW EXPANSION AFTER ASSEMBLY"; co-pending and
commonly assigned U.S. patent application Ser. No. 10/419,386,
titled "HEAT SINK HOLD-DOWN WITH FAN-MODULE ATTACH LOCATION," filed
Apr. 21, 2003; co-pending and commonly assigned U.S. patent
application Ser. No. 10/419,373, titled "VARIABLE-GAP
THERMAL-INTERFACE DEVICE," filed Apr. 21, 2003; co-pending and
commonly assigned U.S. patent application Ser. No. 10/419,406,
titled "VARIABLE-WEDGE THERMAL-INTERFACE DEVICE," filed Apr. 21,
2003; and co-pending and commonly assigned U.S. patent application
Ser. No. 10/074,642, titled THERMAL TRANSFER INTERFACE SYSTEM AND
METHODS," filed Feb. 12, 2002; the disclosures of all of which are
hereby incorporated herein by reference.
FIELD OF THE INVENTION
[0002] This invention relates to heat transfer and more
particularly to a variable height thermal interface.
DESCRIPTION OF THE RELATED ART
[0003] There are circumstances in which a heat sink is fixed at a
set distance above a heat source, for example a processor or other
active electronic device. Due to variations in thickness of the
parts, primarily the active device, a gap of unknown height may
exist between the heat sink and the active device. There is then a
need for a thermal interface to fill the gap and concurrently
provide good heat transfer properties.
[0004] Traditionally, heat has been transferred between a heat
source and a heat sink across non-uniform width gaps through the
use of "gap pads," or silicone-based elastic pads. For example, The
Bergquist Company (see web page
http://www.bergquistcompany.com/tm_gap_list.cfm and related web
pages) offers a range of conformable, low-modulus filled silicone
elastomer pads of various thickness on rubber-coated fiberglass
carrier films. This material can be used as a thermal-interface,
where one side of the interface is in contact with an active
electronic device. Relative to metals, these pads have low thermal
conductivity. Furthermore, large forces are generally required to
compress these pads. Moreover, silicone-based gap pads cannot
withstand high temperatures.
BRIEF SUMMARY OF THE INVENTION
[0005] In accordance with an embodiment disclosed herein, a
variable-height thermal-interface device is provided for
transferring heat from a heat source to a heat sink. The device
comprises a first uniaxial rotary cylindrical joint comprising a
first cylindrically concave surface in slidable contact with a
first cylindrically convex surface. The first cylindrically concave
surface and the first cylindrically convex surface share a common
first radius of curvature relative to a common first cylinder axis.
The first cylindrically concave surface is operable to rotate about
the common first cylinder axis relative to the first cylindrically
convex surface to compensate for uniaxial angular misalignment
between the heat source and the heat sink.
[0006] In accordance with another embodiment disclosed herein, a
variable-height thermal-interface device is provided for
transferring heat from a heat source to a heat sink. The device
comprises a first wedge interface having a first planar surface in
slidable contact with a second planar surface. The slidably
contacting first and second planar surfaces are inclined diagonally
relative to the z-axis parallel to the shortest distance between
the heat source and the heat sink. The first wedge interface is
operable to provide z-axis expansion of the variable height thermal
interface device. The device further comprises a second wedge
interface having a third planar surface in slidable contact with a
fourth planar surface. The slidably contacting third and fourth
planar surfaces are inclined diagonally relative to the z-axis. The
second wedge interface is operable to provide z-axis expansion of
the variable height thermal interface device.
[0007] In accordance with yet another embodiment disclosed herein,
a method of transferring heat from a heat source to a heat sink
using a variable-height thermal-interface device is provided. The
method comprises providing a first uniaxial rotary cylindrical
joint comprising a first cylindrically concave surface in slidable
contact with a first cylindrically convex surface, the first
cylindrically convex surface and the first cylindrically concave
surface sharing a common first radius of curvature relative to a
common first cylinder axis. The method further comprises sliding
the first cylindrically concave surface relative to the first
cylindrically convex surface, causing filling of gaps between the
heat source and the heat sink. The method further comprises
applying compressive loading between the heat source and the heat
sink through the first uniaxial rotary cylindrical joint, and
transferring heat from the heat source through the first uniaxial
rotary cylindrical joint to the heat sink.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1A is a perspective view of an embodiment illustrating
a variable-wedge thermal-interface device
[0009] FIG. 1B is a perspective view of an embodiment illustrating
a spring-loaded variable-wedge thermal-interface device, in which a
spring clip is added to the thermal-interface device of FIG.
1A;
[0010] FIG. 2 is a perspective view of an embodiment illustrating a
cascaded variable-wedge thermal-interface device, in which two or
more wedge structures similar to variable-wedge thermal-interface
devices depicted in FIGS. 1A and 1B are stacked or cascaded in the
z-direction;
[0011] FIG. 3A is a perspective view of an embodiment illustrating
an assembled variable-height thermal-interface device, including at
least one single-axis rotary cylindrical joint;
[0012] FIG. 3B is an exploded perspective view of an embodiment
illustrating the variable-height thermal-interface device of FIG.
3A; and
[0013] FIG. 4 is a schematic diagram of an embodiment illustrating
a heat sink hold-down device, in accordance with a disclosure
incorporated herein.
DETAILED DESCRIPTION
[0014] The embodiments disclosed herein describe a system and
method for creating a thermal interface that will fill a variable
gap and concurrently provide efficient heat transfer
properties.
[0015] FIGS. 1A and 1B show a wedge-based variable gap thermal
interface, as disclosed in co-pending and commonly assigned U.S.
patent application Ser. No. 10/419,406, the disclosure of which has
been incorporated herein by reference.
[0016] FIG. 1A is a perspective view of an embodiment illustrating
variable-wedge thermal-interface device 110. Thermal-interface
device 110 comprises heat sink extension 106 with flat upper end
107 mechanically and thermally coupled to a heat sink base (not
shown in FIG. 1A). Alternatively, heat sink extension 106 may be
fabricated as an integral part of the heat sink or heat sink base.
For convenience, coordinate axes are shown in FIG. 1A, such that x,
y, and z are orthogonal rectangular axes fixed with respect to heat
sink extension 106 and rotating through angular coordinates .theta.
and .phi. about the respective z and y axes. Heat sink extension
106 has a lower flat face inclined at a wedge angle relative to the
x-axis in the example of FIG. 1A.
[0017] Lower wedge element 105 has an upper surface inclined at the
same wedge angle and making sliding contact with the lower inclined
flat face of heat sink extension 106. Although the lower flat face
of lower wedge element 105 can be inclined at any angle relative to
the xyz rotating coordinate system, for convenience in the example
of FIG. 1A it is oriented parallel to the rotating xy plane.
Likewise, although the lower flat face of lower wedge element 105
can be inclined at any angle relative to flat upper end 107 of heat
sink extension 106, for convenience in the example of FIG. 1A it is
oriented parallel to flat upper end 107. Lower wedge element 105 is
coupled thermally and mechanically to heat source 101 and thus
provides efficient heat transfer from heat source 101 through
solid, high thermal-conductivity material of lower wedge element
105 and heat sink extension 106 to the heat sink base. The
sliding-contact interface between lower wedge element 105 and heat
sink extension 106 may be filled with a conformal thermal-interface
material, typically thermal grease or paste, to reduce both thermal
resistance and friction. Heat source 101, as shown in the example
of FIG. 1A, includes processor chip 104, processor lid 102, and
circuit board 103.
[0018] FIG. 1B is a perspective view of an embodiment illustrating
spring-loaded variable-wedge thermal-interface device 120, in which
spring clip 141 is added to thermal-interface device 110 of FIG.
1A. A wedge-based thermal-interface device including a spring clip
is disclosed in co-pending and commonly assigned U.S. patent
application Ser. No. 10/419,406, the disclosure of which has been
incorporated herein by reference. In the example of FIG. 1B, wedge
element 105 and heat sink extension 106 are spring-loaded together
in the x-direction by spring clip 141. In one variation, spring
clip 141 is shaped approximating a deformed rectangular frame. Two
opposing sides 142a, 142b may be but need not necessarily be
straight and parallel as shown in FIG. 1B. Two alternating opposing
sides 143a, 143b are typically bent inward toward one another and
are pre-stressed to exert a compressive force toward one
another.
[0019] In spring-loaded variable-wedge thermal-interface device
120, spring clip 141 is aligned, so that a first inwardly bent
side, for example side 143a, presses against the largest area
vertical surface (aligned normal to the x-axis) of wedge element
105, and a second inwardly bent side, for example side 143b,
presses against the largest area vertical surface (also aligned
normal to the x-axis) of heat sink extension 106. The combined
compressive forces applied by spring clip 141 to wedge element 105
and heat sink extension 106 generate shear force components across
the inclined interface between wedge element 105 and heat sink
extension 106, urging the contacting inclined interface surfaces of
wedge element 105 and heat sink extension 106 to slide relative to
one another, thereby driving wedge element 105 to expand the z-axis
length of spring-loaded variable-wedge thermal-interface device 120
to fill the available gap between heat sink extension 106 and heat
source 101. This simultaneously drives wedge element 105 along the
x-axis to become offset relative to heat sink extension 106,
thereby somewhat reducing the inclined surface contact area. When
the z-axis gap is filled, z-axis compressive forces prevent further
offset between wedge element 105 and heat sink extension 106.
Spring clip 141 may be used similarly to apply shear forces to
sliding wedge elements in other applications, including both heat
transfer and non-heat transfer applications. Optionally, spring
clip 141 may be attached to one of the wedge elements using a
screw, bolt, or other traditional fastener.
[0020] FIG. 2 is a perspective view of an embodiment illustrating
cascaded variable-wedge thermal-interface device 200, in which two
or more wedge structures similar to variable-wedge
thermal-interface devices 110 and 120 depicted in FIGS. 1A and 1B
are stacked or cascaded in the z-direction. For purposes of
illustration, in the example of FIG. 2 are depicted two such wedge
structures having inclined wedge interfaces 215 and 216 oriented at
a 90-degree rotation angle about the z-axis relative to one
another. In other implementations, arbitrary numbers of wedge
structures may be stacked at arbitrary orientations relative to one
another. For most applications, however, there is little or no
advantage achieved by increasing the number of cascaded wedge
structures beyond two.
[0021] In the example depicted in FIG. 2, wedge interface 215,
formed between lower wedge element 205 and second wedge element
206, is inclined to provide offset motion along the x-direction,
whereas wedge interface 216, formed between second wedge element
206 and heat sink extension 207, is inclined to provide offset
motion along the y-direction. Lower surface 204 of lower wedge
element 205 is typically flat and is coupled thermally and
mechanically with a heat source, for example heat source 101 in
FIGS. 1A and 1B, whereas heat sink extension 207 typically has a
flat upper surface, but is typically coupled thermally and
mechanically with a heat sink (not pictured). The upper surface of
heat sink extension 207 is typically but not necessarily parallel
to lower surface 204. Alternatively, heat sink extension 207 may be
fabricated as an integral part of a heat sink or heat sink base.
Multiply-cascaded wedge thermal interfaces, for example wedge
interfaces 215 and/or 216, may be spring-loaded under shear force,
for example using spring clips, as represented by spring clip 141
in FIG. 1B.
[0022] Co-pending and commonly assigned U.S. patent application
Ser. No. 10/419,406, the disclosure of which has been incorporated
herein by reference, discloses a variable-wedge thermal-interface
device that includes a multi-axis rotary spherical joint. This
implementation is particularly advantageous for multi-axis angular
adjustment in a situation in which the heat source and the heat
sink may lie in non-parallel planes and/or where the distance
between heat source and heat sink is non-uniform. This situation
arises frequently when attempting to conduct heat from multiple
heat sources to a single heat sink.
[0023] FIG. 3A is a perspective view of an embodiment illustrating
assembled variable-height thermal-interface device 300, including
at least one single-axis rotary cylindrical joint 315a-315b,
316a-316b. FIG. 3B is an exploded perspective view of an embodiment
illustrating variable-height thermal-interface device 300. FIGS.
3A-3B depict a variable-height thermal-interface device 300
including two cascaded cylindrical joints 315a-315b and 316a-316b
oriented orthogonally relative to one another about the z-axis and
having respective cylinder axes 325 and 326 each inclined relative
to the x-y plane. In general, variable-height thermal-interface
devices, in accordance with the disclosed embodiments, may contain
from one cylindrical joint to any number of cascaded cylindrical
joints, each of which may be oriented at any angle(s) about the
z-axis relative to any other cylindrical joint, and each of which
may have a cylinder axis oriented parallel with the x-y plane or
inclined at any angle relative to the x-y plane.
[0024] In the example embodiment depicted in FIG. 3A and/or 3B,
cylindrical joint 315a-315b is formed at the sliding interface
between concave upper surface 321 of lower element 305 and convex
lower surface 322 (hidden in FIG. 3B) of second element 306.
Concave surface 321 and convex surface 322 have radii of curvature
matched to one another, represented by broken-line arrow 335,
centered at cylinder axis 325. Concave surface 321 is rotatably
slidable relative to convex surface 322 about cylinder axis 325, as
represented by curved arrows .alpha..sub.1, providing single-axis
bending capability in variable-height thermal-interface device 300.
Orthogonally, concave surface 321 is linearly slidable parallel to
cylinder axis 325 relative to convex surface 322, as represented by
linear arrows .+-..DELTA..sub.1, providing single-axis translation
capability in variable-height thermal-interface device 300.
[0025] Cylindrical joint 316a-316b is similarly formed at the
sliding interface between concave upper surface 323 of second
element 306 and the convex lower surface 324 (hidden in FIG. 3B) of
heat sink extension 307. Concave surface 323 and convex surface 324
have radii of curvature matched to one another, represented by
broken-line arrow 336, centered at cylinder axis 326. Concave
surface 323 is rotatably slidable relative to convex surface 324
about cylinder axis 326, as represented by curved arrows
.alpha..sub.2, providing single-axis bending capability in
variable-height thermal-interface device 300. Orthogonally, concave
surface 323 is linearly slidable, parallel to cylinder axis 326
relative to convex surface 324, as represented by linear arrows
.+-..DELTA..sub.2, providing single-axis translation capability in
variable-height thermal-interface device 300.
[0026] Radii of curvature 335 and 336 may be but need not
necessarily be matched between different joints of the same
variable height thermal interface device. Cylinder axes 325, 326
may be parallel to the x-y plane or may be oriented or inclined at
any angle relative to the x-y plane and/or relative to one another.
Cylindrical joints having cylinder axes so inclined may interface
wedged elements, such that relative translation between interfacing
elements provides z-axis expansion of the variable height thermal
interface device. Interfacing elements of a cylindrical joint may
optionally be spring-loaded for shear force across the interface,
facilitating z-axis expansion in a manner similar to spring-loaded
variable-wedge thermal-interface device 120 depicted in FIG. 1B. As
in the case of variable height thermal interface devices previously
described herein, the interfaces between contacting cylindrical
surfaces may be filled with a thermal-interface material, typically
thermal grease or paste, to reduce both thermal resistance and
sliding friction.
[0027] Two stacked or cascaded orthogonally oriented cylindrical
joints provide the same degrees of bending motion as those provided
by a single rotary spherical joint. Advantages of a
cylindrical-joint variable thermal interface implementation
include:
[0028] First, a cylindrical surface is much easier to fabricate
than a sphere. A cylindrical surface can be machined using many
methods, including any of the following methods:
[0029] Horizontal form milling;
[0030] Crush-form grinding;
[0031] Diamond dress grinding (traditional method of grinding
bearing raceways);
[0032] Fly-cutting, where the path of the part is at an oblique
angle to the axis of the fly-cutter. This will in reality create a
surface that is not quite cylindrical, but rather elliptical.
Modeling has shown that the deviation between the surfaces can be
less than 1.5 nanometers (nm), when the rotation range required for
heat source tilt is considered.
[0033] The cost of machining a bearing raceway is $0.05 to $0.10
per cut. If all three elements of a variable height thermal
interface device were made of copper, about 32 grams of copper
would be required, at a total material cost of about $0.22. The
cost of machining each of the six required cuts is .about.$0.60. An
assembly could then cost less than a dollar.
[0034] Second, with two stacked inclined cylindrical joints, the
vertical travel can be taken up by both of the effective wedges.
This doubles the vertical travel range of the variable height
thermal interface. In accordance with the embodiments disclosed
herein, a variable height thermal interface device may include from
one to any larger number of stacked cylindrical joints, spherical
joints, wedge interfaces, or any combination of these three
structures. A cylindrical or spherical joint provides respectively
uniaxial or multi-axial compensation for misalignment between a
heat source and a heat sink, whereas a wedge interface provides
variable height z-axis gap compensation between the heat source and
heat sink. An inclined-axis cylindrical joint provides hybrid
capabilities of a cylindrical joint combined with a wedge
interface.
[0035] Wedge-based variable thermal-interface devices, for example
variable thermal interface devices 200 and 300 are potentially
scalable dimensionally over a range from nanometers (nm) to
meters.
[0036] In practice, the compressive load between the heat sink base
and bolster plate in any of the embodiments disclosed herein can be
provided by any of a variety of heat sink hold-down devices. An
advantageous configuration of such a hold-down device is disclosed
in co-pending and commonly assigned U.S. patent application Ser.
No. 10/419,386, the disclosure of which has been incorporated
herein by reference. FIG. 4 is a schematic diagram of an embodiment
illustrating heat sink hold-down device 40, in accordance with the
above-incorporated disclosure. Bolster plate 49 supports heat
source 101. Heat sink 43 includes heat sink base 401 attached to
central post 44, and finned structure 42. Cage 45 is attached with
clips to bolster plate 49 and supports lever spring 46 through
clearance slots. Cap 47 rigidly attached to cage 45 using screws or
other fasteners 48 presses downward on the ends of lever spring 46,
which transfer the load through a bending moment to central post
44. Central post 44 is disposed to distribute the load
symmetrically across the area of heat sink base 401.
[0037] In some embodiments, heat sink extension 41 transfers the
compressive loading between heat sink base 401 and heat source 101.
Alternatively, a variable-height thermal-interface device in
accordance with the present embodiments, for example
variable-height thermal-interface device 110, 120, 200 or
cylindrical joint variable-height thermal-interface device 300, is
coupled thermally and mechanically with heat sink hold-down device
40, replacing at least in part heat sink extension 41. In this
configuration, heat sink hold-down device 40 applies the loading
that holds variable-height thermal-interface device 110, 120, 200
or cylindrical joint variable-height thermal-interface device 300
under compression against heat source 101.
[0038] Embodiments disclosed herein address the problem of
minimizing the thermal resistance between a heat source and a heat
sink for a situation in which the heat source and the heat sink may
lie in non-parallel planes and/or where the distance between heat
source and heat sink is non-uniform. This is a problem that arises
especially when attempting to conduct heat from more than one heat
source to a single heat sink.
* * * * *
References