U.S. patent application number 15/486721 was filed with the patent office on 2017-08-03 for flexible metallic heat connector.
The applicant listed for this patent is Abaco Systems, Inc.. Invention is credited to Stuart Connolly, Tao Deng, Zeshan Jabar Hussain, Graham Charles Kirk, Binoy Milan Shah.
Application Number | 20170219303 15/486721 |
Document ID | / |
Family ID | 48944642 |
Filed Date | 2017-08-03 |
United States Patent
Application |
20170219303 |
Kind Code |
A1 |
Kirk; Graham Charles ; et
al. |
August 3, 2017 |
FLEXIBLE METALLIC HEAT CONNECTOR
Abstract
A thermal connector configured to be placed within a recess of a
heat sink between the heat sink and a heat generating component and
transfer heat from the component to the heat sink, including a heat
spreader configured to fit within the recess of the heat sink, a
spring configured to sit between the heat spreader and with the
heat sink and bias the heat spreader towards and away from the heat
sink, a flexible membrane attached to the heat sink and the heat
spreader and seal off the recess, and a phase change material that
fills the recess, wherein the flexible membrane contains the phase
change material and allows it to contract or expand in response to
the movement of the heat spreader towards or away from the heat
sink.
Inventors: |
Kirk; Graham Charles;
(Towcester, GB) ; Connolly; Stuart; (Towcester,
GB) ; Deng; Tao; (Niskayuna, NY) ; Hussain;
Zeshan Jabar; (Towcester, GB) ; Shah; Binoy
Milan; (Niskayuna, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Abaco Systems, Inc. |
Huntsville |
AL |
US |
|
|
Family ID: |
48944642 |
Appl. No.: |
15/486721 |
Filed: |
April 13, 2017 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
13750078 |
Jan 25, 2013 |
9658000 |
|
|
15486721 |
|
|
|
|
61599191 |
Feb 15, 2012 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 23/4275 20130101;
H01L 2924/0002 20130101; F28F 27/00 20130101; F28F 2013/008
20130101; B23P 15/26 20130101; H01L 23/4338 20130101; F28F 2255/02
20130101; H01L 23/40 20130101; F28D 20/02 20130101; H01L 2924/00
20130101; Y10T 29/4935 20150115; H01L 2924/0002 20130101; F28F 7/00
20130101 |
International
Class: |
F28F 27/00 20060101
F28F027/00; H01L 23/427 20060101 H01L023/427; H01L 23/433 20060101
H01L023/433; H01L 23/40 20060101 H01L023/40 |
Claims
1. A thermal connector, comprising: a heat sink; a heat spreader;
and a spring, positioned between, and in contact with, the heat
spreader and the heat sink, wherein the spring is held compressed
to its smallest height by a phase change material so that when the
phase material is melted, the heat spreader is pushed by the spring
away from the heat sink and into contact with a heat generating
component positioned adjacent to the heat sink.
2. The thermal connector according to claim 1, wherein the spring
comprises a body portion that is connected flush with the heat
spreader and a plurality of legs angled away from the heat spreader
and towards the heat sink so that the plurality of legs contact the
heat sink.
3. The thermal connector according to claim 1, further comprising a
flexible membrane attached to the heat sink and the heat spreader
that contains the phase change material.
4. The thermal connector according to claim 1, wherein the flexible
membrane is a silicone or urethane polymer.
5. The thermal connector according to claim 1, wherein the phase
change material is a low melting alloy.
6. The thermal connector according to claim 5, wherein the low
melting alloy has a melting point of about 118.degree. C. and a
thermal conductivity of about 35 W/mK.
7. The thermal connector according to claim 1, wherein the phase
change material has a melting point between about 40.degree. C. to
250.degree. C. and a thermal conductivity between about 20 W/mK and
400 W/mK.
8. The thermal connector according to claim 1, wherein the phase
change material has a melting point between about 60.degree. C. to
160.degree. C. and a thermal conductivity between about 30 W/mK and
100 W /mK.
9. The thermal connector according to claim 1, wherein the heat
generating component is an electrical device component.
10. The thermal connector according to claim 1, wherein the spring
biases the heat spreader within a range of 0.1 mm to 3 mm.
11. A method for thermally connecting a heat generating component
and a heat sink that are separated by a tolerance, the method
comprising: providing a thermal connector comprised of: a heat
spreader, and a spring connected to the heat spreader that is held
compressed at its smallest height by a phase change material;
placing the thermal connector in the tolerance between the heat
generating component and the heat sink; and heating the phase
change material to a melting temperature to allow the spring to
push the heat spreader away from the heat sink and into contact
with the heat generating component.
12. The method according to claim 11, wherein the spring comprises
a body portion that is connected flush with the heat spreader and a
plurality of legs angled away from the heat spreader and towards
the heat sink so that the plurality of legs contact the heat
sink.
13. The method according to claim 11, wherein the thermal connector
further comprises a flexible membrane attached to the heat sink and
the heat spreader that contains the phase change material.
14. The method connector according to claim 11 wherein the flexible
membrane is a silicone or urethane polymer.
15. The method according to claim 1, wherein the phase change
material is a low melting alloy.
16. The method according to claim 15, wherein the low melting alloy
has a melting point of about 118.degree. C. and a thermal
conductivity of about 35 W/mK.
17. The method according to claim 11, wherein the phase change
material has a melting point between about 40.degree. C. to
250.degree. C. and a thermal conductivity between about 20 W/mK and
400 W/mK.
18. The method according to claim 11, wherein the phase change
material has a melting point between about 60.degree. C. to
160.degree. C. and a thermal conductivity between about 30 W/mK and
100 W /mK.
19. The method according to claim 11, wherein the tolerance is
within a range of 0.1 mm to 3 mm.
20. A method for assembling a thermal connector, the method
comprising: providing the thermal connector comprised of: a heat
spreader and a spring, the spring comprising a body portion that is
connected flush with the heat spreader and a plurality of legs
angled away from the heat spreader; a low melting point alloy
surrounding the spring, wherein (i) when the alloy is in a melted
state, the spring may move the heat spreader, and (ii) when the
alloy is in a hardened state, the spring may not move the heat
spreader; a flexible membrane that contains the low melting point
alloy within the gap and allows the alloy to contract and expand in
response to the movement of the heat spreader towards and away from
the heat sink; melting the alloy to a melted state; compressing the
spring to its smallest height; cooling the alloy to a hardened
state to hold the spring in compression.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. Patent
Application Ser. No. 13/750,078 filed on Jan. 25, 2013, which
claims the benefit of U.S. Provisional Patent Application No.
61/559,191, filed on Feb. 15, 2012. The entire contents of each of
these applications is hereby incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The subject matter disclosed herein relates generally to a
system and method for heat dissipation. More particularly, the
subject matter disclosed herein relates to thermal connectors
between heat generating devices and heat sinks.
BACKGROUND
[0003] Electronic devices and other devices often produce heat
during operation that needs to be dissipated away from the device.
Heat sinks are often used for this purpose; a heat sink is a
passive component that cools a device by dissipating heat into the
surrounding environment. In order for the heat sink to operate
properly, the heat from the device must be transferred to the heat
sink over a thermal connection. While the term heat sink is used
herein it should be understood that the term refers to all types of
heat dissipating devices, including heat pipe modules and thermal
ground planes.
[0004] A common arrangement for electronic devices is a plurality
of electronic components attached to a printed circuit board (PCB).
Heat from these multiple components is transferred to one or more
heat sinks using thermal connections. Each component on the PCB is
a particular distance from the heat sink (tolerance) and the heat
must be effectively transferred across the tolerance from the
component to the heat sink. Accordingly, the tolerance is often
filled with a thermal connector, such as a heat spreader and/or
thermal interface material.
[0005] When a single heat sink serves multiple components, the
thermal connectors often must accommodate several different
tolerances. Some of the proposed solutions for this issue include
the use of thermal pastes, thermal greases, and thermally
conductive pads that are compressible and expandable. These thermal
connectors typically have fairly low thermal conductivities, in the
range of 3 watts per meter kelvin (W/mK). Some thermal pads have
conductivity as high as 17 W/mK but they can only be compressed to
10%-20% between the heat sink and the component or the component
will be damaged. This limits the size of the starting gap between
the component and the heat sink and makes it more difficult to
assemble the device.
[0006] Accordingly, there is a need for better thermal connectors
to transfer heat between heat generating components and heat sinks.
More particularly, there is a need for thermal connectors that
accommodate a variety of tolerances between multiple components of
a heat generating device and a heat sink.
SUMMARY
[0007] In at least one aspect, the present disclosure provides a
thermal connector configured to be placed within a recess of a heat
sink between the heat sink and a heat generating component and
transfer heat from the component to the heat sink. The thermal
connector includes a heat spreader configured to fit within the
recess of the heat sink, a spring configured to sit between the
heat spreader and with the heat sink and bias the heat spreader
towards and away from the heat sink, a flexible membrane attached
to the heat sink and the heat spreader and seal off the recess, and
a phase change material that fills the recess, wherein the flexible
membrane contains the phase change material and allows it to
contract or expand in response to the movement of the heat spreader
towards or away from the heat sink.
[0008] In at least another aspect, the present disclosure provides
a cartridge for placing between a heat generating component and a
heat sink for facilitating transfer of heat from the component to
the heat sink. The cartridge includes a heat spreader and a spring
attached to the heat spreader. The heat spreader and spring are
circumferentially enclosed by a frame and a flexible membrane is
attached to the frame and the heat spreader to define an open
topped void filled by a phase change material. The spring, flexible
membrane, and phase change material expand or contract to
accommodate the tolerance between the heat sink and component.
[0009] In yet another aspect, the present disclosure provides a
method for transferring heat from a heat generating component to a
heat sink. The method includes the steps of providing the thermal
connector or cartridge as described above and positioning the
thermal connector or cartridge between a heat sink and a heat
generating component. The thermal connector or cartridge can
accommodate several different components.
[0010] Further features and advantages of the invention, as well as
the structure and operation of various embodiments of the
invention, are described in detail below with reference to the
accompanying drawings. It is noted that the invention is not
limited to the specific embodiments described herein. Such
embodiments are presented herein for illustrative purposes only.
Additional embodiments will be apparent to persons skilled in the
relevant art(s) based on the teachings contained herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 illustrates a cross-sectional schematic view of a
thermal connector in accordance with at least one embodiment of the
present disclosure.
[0012] FIG. 2 illustrates a top plan view of the spring in
accordance with at least one embodiment of the present
disclosure.
[0013] FIG. 3 illustrates a cross-sectional schematic view of a
thermal connector cartridge in accordance with at least one
embodiment of the present disclosure in exploded view with a heat
sink and heat generating component.
[0014] FIG. 4 is a perspective view of the thermal connector
cartridge of FIG. 3.
DETAILED DESCRIPTION
[0015] The following detailed description is merely exemplary in
nature and is not intended to limit the applications and uses
disclosed herein. Further, there is no intention to be bound by any
theory presented in the preceding background or summary or the
following detailed description. While embodiments of the present
technology are described herein primarily in connection with
dissipation of heat from an electrical circuit board to a heat
sink, the concepts are also applicable to other types of systems
where it is desirable to transfer thermal energy from a heat
generating component to a heat dissipation device.
[0016] In at least one aspect, the present disclosure provides a
device and method for the transfer of thermal energy from
components on an electrical circuit board to a heat sink.
[0017] Thermal conductor 10 as applied in an electrical device is
shown in FIG. 1. A portion of an electrical device includes a
printed circuit board (PCB) 12 having an electrical device
component 14 attached thereto via a ball grid array (BGA) 16.
Silicon die 15 is a part of component 14 and a thermal interface
material (TIM) 24 is connected to silicon die 15 to provide for
thermal conductivity between silicon die 15 and the thermal
conductor 10.
[0018] Heat sink 18 is displaced away from the PCB 12 and component
14 and there is a tolerance or gap (not numbered) there between
that is filled here with the thermal conductor 10.
[0019] The thermal conductor 10 includes heat spreader 22 and
spring 26. Desirably spring 26 includes body portion 27 and legs 28
extending away from the body portion 27 (shown more clearly in FIG.
2). Desirably, spring 26 is attached to heat spreader 22 at its
body portion 27, leaving leg portions 28 free (as further
illustrated by FIG. 2 and described below).
[0020] Heat sink 18 has a recess (not numbered) into which the
assembly of the spring 26 and heat spreader 22 fits. A flexible
membrane 32 is fixed to the edges of heat spreader 22 and heat sink
18 and seals off the void 29 between the heat sink 18 and heat
spreader 22. The flexible membrane 32 can extend across the heat
spreader 22 or simply to the edges thereof in order to adequately
retain the phase change material.
[0021] Void 29 is filled by phase change material 30. Phase change
material 30 is a material, most preferably a low melting point
alloy, which melts at a particular temperature.
[0022] To assemble the thermal connector, the heat spreader 22 and
spring 26 assembly is placed in the heat sink recess. The spring 26
is compressed to its smallest height while the phase change
material 30 is in a melted state, and then the phase change
material 30 is hardened by lowering the temperature.
[0023] The thermal connector is deployed by raising the temperature
to the melting point of the phase change material 30. The melting
of the phase change material 30 allows the spring 26 to expand and
the spring 26 will push heat spreader 22 into thermal contact with
component 14 (via TIM 24).
[0024] The tolerance between a heat sink and heat generating
component in an electrical device ranges from about 0.1 mm to about
3 mm, more specifically about 0.3 to 1 mm, and is typically about
0.8 mm. Accordingly, the thermal conductor should be able to expand
to fit this range.
[0025] FIG. 2 illustrates one embodiment of the spring 34, having a
main body 36 and legs 38. Here, spring 34 is shown having three
legs 38 but it could have more or less legs. Spring main body 36 is
fixed to a heat spreader 39 such as by spot welding or soldering.
The spring 34 is preferably made out of an alloy such as beryllium
copper (BeCu). It can be from about 0.10 mm to 0.40 mm in
thickness, or more preferably from about 0.20 mm to 0.30 mm in
thickness. The spring thickness and dimensions are chosen to
achieve the correct loading for the device when compressed. In
other words, and referring to FIG. 1, the spring 26 should exert
sufficient pressure on the heat spreader 22 to hold it against TIM
24 and achieve good thermal contact. However, spring 26 should not
cause heat spreader 22 to exert an amount of pressure that damages
TIM 24 or the component 14. In one embodiment, the spring 34 is
nickel plated, to increase its wettability with the phase change
material, as described below.
[0026] Phase change material 30 is desirably a material that is
solid at near room temperature and melts at a temperature to deploy
the spring. As one example, for many electronic devices, a phase
change material having a melting point between about 40.degree. C.
to 250.degree. C. is appropriate, more preferably from about
60.degree. C. to 160.degree. C. One preferred metal alloy is 52 In
48 Sn which has a melting point of 118.degree. C. and a thermal
conductivity of 35 W/mK. This alloy is available from Indium
Corporation under the trademark INDALLOY.RTM. 1E. Eutectic alloys
are preferred but are not required. Mixtures or pastes could also
be used.
[0027] Other metals and metal alloys that might be useful for
certain applications include In, InBi, variations of InSn, BiSn,
PbSn, SnAg, InPbAg, InAg, InSnBi, InGa, SnBiZn, SnInAg, SnAgCu,
SnAgBi, and InPb.
[0028] In general, phase change materials having a thermal
conductivity between about 20 W/mK and 400 W/mK are preferred, most
desirably about 30 W/mK to 100 W/mK.
[0029] The flexible membrane 32 functions to retain the phase
change material 30 within the void defined by the heat spreader 22
and the heat sink 18. Flexible membrane 32 is preferably a plastic
film that can withstand the highest temperature reached by the
operating device. For many electronic devices, a flexible membrane
stable up to at least between about 150 to 200.degree. C. is
desirable, preferably up to at least 160.degree. C. Options for the
flexible membrane include polymers, silicon, urethane, rubbers, and
metal foil. One specific example is DUREFLEX.RTM. U073 125 .mu.m
which is a polyether-based thermoplastic polyurethane film.
Flexible membrane 32 can be attached to heat sink 18 and heat
spreader 22 with an appropriate adhesive.
[0030] Heat sink 18 can be a typical heat sink as used in the art,
such as an aluminum alloy plate. As discussed above, other heat
dissipating devices such as heat pipe modules and thermal ground
planes can be used with the thermal conductors as described herein.
As an example, the recess in the heat sink 18 can be about 2.25
mm.
[0031] Heat spreader 22 can be a typical heat spreader as used in
the art, such as a copper plate. Other materials can be used as
well, such as aluminum nitride (AlN) plates. Copper offers a higher
thermal conductivity but aluminum nitride offers electrical
isolation of the heat generating component from the heat sink. The
heat spreader can be of a variety of sizes, such as those presently
used in the art.
[0032] Thermal interface material 24 can also be a material
typically used in the art, such as a paste or thermal grease.
[0033] The metal parts that are in contact with the phase change
material (heat sink, heat spreader, spring) may be treated to
increase their wettability by the phase change material 30. One
treatment is a nickel plating with gold flash which increases the
wettability of the parts with the metal alloy 52 In 48 Sn. This
treatment is known in the art.
[0034] FIG. 3 illustrates another embodiment of a thermal conductor
in accordance with the disclosure. In this embodiment, the thermal
conductor is assembled as a cartridge 40 including the heat
spreader 44 and spring 46. As in the prior embodiment, spring 46 is
desirably connected to heat spreader 44 at its body portion 48,
leaving legs 50 free.
[0035] A frame 42 circumferentially surrounds the heat spreader
44/spring 46 assembly and a flexible membrane 52 extends from the
frame to the heat spreader. Phase change material 56 fills the void
created by frame 42, flexible membrane 52, and heat spreader 44.
The cartridge 40 is open on the top, so that the phase change
material 56 is exposed.
[0036] In one embodiment of assembling the heat connector cartridge
40, the spring 46 is attached to heat spreader 44 and flexible
membrane 52 is attached to the frame 42 and heat spreader 44. The
phase change material 56 is melted and placed in the void created
by frame 42, flexible membrane 52, and heat spreader 44. The spring
46 is flattened to its lowest height and the temperature lowered to
harden the phase change material 56. The cartridge 40 can then be
attached to the heat sink 58 using a sealant or adhesive.
[0037] As shown in exploded form in FIG. 3, the cartridge 40 is
installed between a heat sink 58 and electrical device. The
electrical device includes PCB 60 having an electrical device
component 62 attached thereto via a ball grid array (BGA) 64.
Silicon die 66 is a part of component 62 and a thermal interface
material (TIM) 68 is connected to silicon die 66 to provide for
thermal conductivity between silicon die 66 and the thermal
conductor 40.
[0038] In use, the thermal connector cartridge 40 is placed between
the heat sink 58 and the device component 62 (or multiple
components). Desirably the cartridge is attached to the heat sink
58 such as by adhesive or other mechanical means such as fasteners.
The assembly is deployed by heating to the melting point of the
phase change material 56, which allows the spring 46 to expand or
contract and engage the heat spreader 44 with the TIM 68 or
component 62 on the other side. The flexible membrane 52 will
expand or contract as needed to accommodate this expansion or
contraction of the phase change material 56.
[0039] As discussed above, the tolerance between a heat sink and
heat generating component in an electrical device ranges from about
0.1 mm to about 3 mm and is typically 0.8 mm. Accordingly, the
cartridge should be an appropriate thickness to fit within the gap
and the spring should be able to expand to fill the gap.
[0040] The elements in this embodiment can have essentially the
same properties as in the embodiment discussed above. Frame 42 can
be made out of a number of materials. One option is aluminum and
another option is a high melting point plastic. The frame can be a
variety of sizes and is at least partially dependent on the size of
the heat spreader. For an example, a frame that is about 35 mm
square and having 3 mm thick walls works well with a heat spreader
that is 20 mm square.
[0041] FIG. 4 further illustrates the cartridge 40 of the
embodiment shown in FIG. 3. Frame 42 circumferentially surrounds
the heat spreader 44 which has spring 46 attached thereto. Flexible
membrane 52 encloses the void between the heat spreader 44 and
frame 42 on one side thereof. The cartridge 40 as shown here has
not yet been filed with phase change material.
[0042] Alternative embodiments, examples, and modifications which
would still be encompassed by the disclosure may be made by those
skilled in the art, particularly in light of the foregoing
teachings. Further, it should be understood that the terminology
used to describe the disclosure is intended to be in the nature of
words of description rather than of limitation.
[0043] Those skilled in the art will also appreciate that various
adaptations and modifications of the preferred and alternative
embodiments described above can be configured without departing
from the scope and spirit of the disclosure. Therefore, it is to be
understood that, within the scope of the appended claims, the
disclosure may be practiced other than as specifically described
herein.
* * * * *