U.S. patent application number 11/967307 was filed with the patent office on 2009-07-02 for method of forming a thermo pyrolytic graphite-embedded heatsink.
Invention is credited to David L. McDonald, David S. Slaton.
Application Number | 20090169410 11/967307 |
Document ID | / |
Family ID | 40328462 |
Filed Date | 2009-07-02 |
United States Patent
Application |
20090169410 |
Kind Code |
A1 |
Slaton; David S. ; et
al. |
July 2, 2009 |
METHOD OF FORMING A THERMO PYROLYTIC GRAPHITE-EMBEDDED HEATSINK
Abstract
The present disclosure is related to creating blocks of aluminum
and/or copper material having embedded TPG elements for forming
heatsinks. The metal blocks have an improved thermal conductivity
in the X-Y plane. Furthermore, the TPG-embedded heatsinks can be
created using methods capable of being performed using various
machines and equipment in many various facilities.
Inventors: |
Slaton; David S.;
(Huntsville, AL) ; McDonald; David L.; (Lacey's
Spring, AL) |
Correspondence
Address: |
General Electric Company;GE Global Patent Operation
PO Box 861, 2 Corporate Drive, Suite 648
Shelton
CT
06484
US
|
Family ID: |
40328462 |
Appl. No.: |
11/967307 |
Filed: |
December 31, 2007 |
Current U.S.
Class: |
419/9 ; 164/100;
164/112; 164/76.1 |
Current CPC
Class: |
H01L 23/373 20130101;
H01L 2924/0002 20130101; B22D 19/00 20130101; H01L 21/4871
20130101; H01L 23/367 20130101; H01L 2924/0002 20130101; H01L
2924/00 20130101 |
Class at
Publication: |
419/9 ; 164/112;
164/100; 164/76.1 |
International
Class: |
B22F 7/06 20060101
B22F007/06; B22D 23/00 20060101 B22D023/00 |
Claims
1. A method for forming a thermo pyrolytic graphite (TPG) therein
according to a first embodiment of the present disclosure-embedded
heatsink, the method comprising: suspending at least one TPG
element in a form; filling the form with a metal material; heating
the form to bond the at least one TPG element within the metal
material to produce a TPG-embedded heatsink; and cooling the bonded
TPG-embedded heatsink.
2. A method in accordance with claim 1, comprising suspending at
least one planar TPG strip in the form.
3. A method in accordance with claim 1, comprising suspending the
at least one TPG element using a metal peg.
4. A method in accordance with claim 1, comprising filling the form
with a metal material selected from the group consisting of
aluminum, copper, and combinations thereof.
5. A method in accordance with claim 4, comprising filling the form
with a powdered metal material.
6. A method in accordance with claim 4, comprising filling the form
with a liquid metal material.
7. A method in accordance with claim 1, wherein filling the form
comprises metal injection molding.
8. A method in accordance with claim 1, wherein heating the form
comprises a sintering process.
9. A method in accordance with claim 1, further comprising plating
the at least one TPG element with a metal.
10. A method in accordance with claim 9, comprising plating the at
least one TPG element with the metal selected from the group
consisting of aluminum, copper, and combinations thereof.
11. A method in accordance with claim 1, wherein the form is
designed further contain at least one of fin features and complex
details to reduce machining of the TPG-embedded heatsink.
12. A method for forming an thermo pyrolytic graphite (TPG) therein
according to a second embodiment of the present disclosure-embedded
heatsink, the method comprising: obtaining a foam block; depositing
at least one TPG element into the foam block; depositing the foam
block with the at least one TPG element into a container; and
filling the container with molding sand; and filling the foam block
with a molten metal material.
13. A method in accordance with claim 12, comprising depositing at
least one planar TPG strip into the foam block.
14. A method in accordance with claim 12, comprising filling the
container with the molten metal material being selected from the
group consisting of aluminum, copper, and combinations thereof.
15. A method in accordance with claim 12, further comprising
removing the metal block with the at least one TPG element embedded
therein from the container.
16. A method in accordance with claim 15, further comprising
machining the metal block.
17. A method for forming a thermo pyrolytic graphite (TPG) therein
according to a third embodiment of the present disclosure-embedded
heatsink, the method comprising: separating a foam block into at
least two portions; depositing at least one TPG element between the
at least two portions of the foam block; coupling the at least two
portions of the foam block together to form a single block with the
at least one TPG element; depositing the single block with the at
least one TPG element into a container; and filling the container
molding sand; and filling the foam block with a molten metal
material.
18. A method in accordance with claim 17, comprising depositing at
least one planar TPG strip.
19. A method in accordance with claim 17, coupling the at least two
portions using an adhesive composition.
20. A method in accordance with claim 17, comprising filling the
container with the molten metal material being selected from the
group consisting of aluminum, copper, and combinations thereof.
21. A method in accordance with claim 17, further comprising
removing the metal block with the at least one TPG element embedded
therein from the container.
22. The method as set forth in claim 21, further comprising
machining the metal block.
Description
BACKGROUND OF THE INVENTION
[0001] This disclosure relates generally to methods of forming
thermo pyrolytic graphite (TPG)-embedded metal blocks to serve as
heatsinks and, more particularly, to forming metal blocks of
aluminum and/or copper material having TPG elements embedded
therein to serve as heatsinks.
[0002] Modern embedded computer systems contain very high thermal
power electrical components in a volumetrically constrained
environment. The volumes typically do not change as the power
dissipation of the components increase, presenting significant
challenges in the management of component temperatures. In the
past, a variety of direct cooling techniques such as active or
passive heatsinks composed of high thermally conductive materials,
such as aluminum and/or copper, have been used to manage rising
temperatures. These materials, however, are only sufficient if a
relatively large amount of surface area is presented to the
airstream, necessitating a physically larger heatsink structure
that occupies a large amount of the total available volume. As the
physical size of the heatsink increases, the ability of the
material to rapidly carry heat to the extremities of the heatsink,
thereby exposing the heat to the airstream, is diminished.
[0003] Thermo Pyrolytic Graphite (TPG) materials have been found to
have the ability to conduct heat in a single (X-Y) plane as
compared to conventional metal materials. Furthermore, TPG has been
found to have an improved overall conductivity as compared to
copper. Recently, a method has been developed to embed TPG material
into an aluminum structure using a diffusion bonding process. The
diffusion bonding process, while resulting in a suitable thermal
contact between the TPG material and the aluminum structure, has
limitations in that specialized equipment is needed to create the
TPG-embedded structures in a time-consuming process, resulting in
an expensive product.
[0004] As such, there is a need for a method to create a
cost-effective product having TPG embedded into a metal structure,
such as an aluminum structure, to provide effective thermal
conductivity in the X-Y plane. Additionally, it would be
advantageous if the method were easily reproducible and could be
performed in many various facilities using many various types of
equipment.
BRIEF DESCRIPTION OF THE INVENTION
[0005] In one aspect, a method for forming a thermo pyrolytic
graphite (TPG)-embedded heatsink is provided. The method includes
suspending at least one TPG element in a form. The form is filled
with a metal material and heated to bond the TPG element within the
metal material. The bonded TPG-embedded metal material is
cooled.
[0006] In another aspect, a method for forming a thermo pyrolytic
graphite (TPG)-embedded heatsink is provided. The method includes
obtaining a foam block. At least one TPG element is deposited into
the foam block. The foam block with the at least one TPG element is
deposited into a container, and the container is filled with
molding sand. The foam block is filled with a molten metal
material.
[0007] In another aspect, a method for forming a thermo pyrolytic
graphite (TPG)-embedded heatsink is provided. The method includes
separating a foam block into at least two portions. At least one
TPG element is deposited between the at least two portions of the
foam block. The at least two portions of the foam block are coupled
together to form a single block with the TPG element. The single
block with the TPG element is deposited into a container, and the
container is filled with molding sand. The foam block is filled
with a molten metal material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a schematic view of a method for forming a thermo
pyrolytic graphite (TPG)-embedded heatsink according to a first
embodiment of the present disclosure.
[0009] FIG. 2 is a schematic view of a foam block for depositing a
thermo pyrolytic graphite (TPG) therein according to a second
embodiment of the present disclosure.
[0010] FIG. 3 is a schematic view of the foam block of FIG. 2
having a TPG element deposited therein.
[0011] FIG. 4 is a schematic view of the foam block with the TPG
element of FIG. 3 deposited within a container.
[0012] FIG. 5 depicts two portions of a foam block for depositing a
thermo pyrolytic graphite (TPG) therein according to a third
embodiment of the present disclosure.
DETAILED DESCRIPTION OF THE INVENTION
[0013] The present disclosure is related to forming thermo pyrolic
graphite (TPG)-embedded heatsinks and heatframes. As used herein,
"TPG" refers to any graphite-based material in which the graphite
is aligned in one direction for optimal heat transfer. The
materials are typically referred to as "aligned graphite", "TPG",
and "Highly Oriented Pyrolytic Graphite (HOPG)". The TPG elements
provide improved thermal conductivity in the X-Y plane of the metal
blocks. Specifically, it has been found that by using the methods
of embedding TPG elements into metal blocks as provided in the
present disclosure, temperatures created during the use of
electrical systems, such as computer systems, can be lowered by
about 10.degree. C. or more as compared to conventional thermal
solutions. This improved temperature release allows for almost a
doubling of the electrical systems' power capacity in the same
volume environment. Furthermore, the increase in power may result
in systems being supported that could not have otherwise been
supported, or may allow existing systems to be used in environments
having higher ambient temperatures.
[0014] In one embodiment, as depicted in FIGS. 1-3, at least one
TPG element 10, 12 is held in form 20, to embed elements 10, 12
into a metal block (not shown) for use in a heatsink or a
heatframe. The TPG elements 10, 12 are suspended in a form 20. The
form 20 is filled at least partially with a metal material (not
shown) and heated to bond TPG elements 10, 12 within the metal
material. The bonded TPG-embedded metal material is then cooled to
form a metal block including embedded TPG elements 10, 12 (i.e., a
TPG-embedded heatsink).
[0015] TPG elements 10, 12 can be obtained using any suitable
method and/or equipment known in the art for fabricating TPG
elements and guided by the teachings herein provided.
Alternatively, TPG elements 10, 12 can be obtained commercially
from suppliers, such as Momentive Performance Material located in
Wilton, Conn.
[0016] In one embodiment, as shown in FIG. 1, TPG elements 10, 12
are configured in a planar TPG strip. In a particular embodiment,
TPG elements 10, 12 are planar TPG strips having 90 degree edges.
Furthermore, while one or more dimensions of TPG elements 10, 12
may vary, TPG elements 10, 12 of one embodiment have a thickness of
about 0.06 inches. While shown in FIG. 1 as in a planar strip, it
should be understood by one skilled in the art that TPG elements
10, 12 may have any suitable configuration known in the art without
departing from the present disclosure. For example, TPG elements
10, 12 can be configured in any suitable shape including, without
limitation, an oblong or a triangular shape, and including, without
limitation, intermediate holes to be filled with metal.
[0017] In one embodiment, TPG elements 10, 12 are plated with a
metal-based coating material (not shown). More specifically, a
layer of metal, such as aluminum, copper, iron, silver, gold,
nickel, zinc, tin, or a combination thereof, is applied to an outer
surface of TPG elements 10, 12. In a particular embodiment, the
metal-based coating material is a copper coating material with a
nickel overcoat.
[0018] The metal-based coating material suitably provides
mechanical strength. The metal-based coating material is typically
at least about 0.001 inches thick. More suitably, the metal-based
coating material is applied to TPG elements 10, 12 in an amount of
from about 0.0005 inches to about 0.002 inches and, even more
suitably, the metal-based coating material has a thickness of from
about 0.006 inches to about 0.025 inches.
[0019] The metal-based coating material can be applied to the outer
surface of TPG elements 10, 12 in any pattern known in the art. For
example, in one embodiment, the metal-based coating material is
applied in a cross-hatched pattern. In an alternative embodiment,
the metal-based coating material is applied in a striped
pattern.
[0020] At least one TPG element 10, 12 is suspended in form 20.
Form 20 can be any suitable form known in the art. Dimensions of
form 20 depend at least partially upon the desired dimensions of
the metal block (i.e., heatsink) to be formed.
[0021] As TPG elements 10, 12 are suspended, and as such, are
"floating" within form 20, stresses experienced during high
temperature heating processes, such as a soldering process as
described below, can be avoided. Suitably, one or more TPG elements
10, 12 are suspended in form 20. More specifically, as shown in
FIG. 1, two TPG elements 10, 12 are suspended in form 20. While
shown in FIG. 1 as including two TPG elements 10, 12 suspended in
form 20, it should be understood by one skilled in the art and
guided by the teachings herein provided that less than two or more
than two TPG elements 10, 12 may be suspended without departing
from the scope of the present disclosure. For example, three TPG
elements may be suspended in the form and, even more suitably, four
or more TPG elements may be suspended in the form. Also, while
shown in FIG. 1 as being in a particular orientation in the form,
it should be understood by one skilled in the art and guided by the
teachings herein provided that any orientation known in the art may
be used.
[0022] In one embodiment, TPG elements 10, 12 are suspended in form
20 using at least one peg, such as respective pegs 30, 32.
Suitably, pegs 30, 32 for suspending TPG elements 10, 12,
respectfully, are metal pegs, such as pegs including steel.
[0023] Once TPG elements 10, 12 have been suspended within form 20,
form 20 is at least partially filled with a metal material (not
shown). In one embodiment, the metal material includes at least one
of aluminum and copper. Both aluminum and copper have been shown to
provide high conductivity when used in heatsinks. More
specifically, as shown in FIG. 3, aluminum provides good thermal
conductivity in a "Z" plane when used in heatsinks. However, as
noted above, aluminum and copper alone fail to provide sufficient
heat transfer in the X-Y plane and, as such, the present disclosure
has combined TPG with at least one of aluminum and copper.
[0024] In a particular embodiment, the metal material is a powdered
metal material. For example, the metal material may include
powdered aluminum and/or powdered copper. In an alternative
embodiment, the metal material includes a liquid or molten metal
material, such as liquid aluminum and/or liquid copper.
[0025] In a particular embodiment in which a molten metal material
is used, the molten metal material is introduced into form 20 using
a suitable metal injection molding (MIM) process. Specifically, the
metal material to be injected is heated above its liquidus
temperature and then forced into form 20 (i.e., mold) by the
extension of a piston in an injection chamber of the MIM equipment.
In an alternative embodiment using a MIM process, the molten metal
material is introduced into form 20 using a suitable thixotropic
injection molding method. In this method, the metal is first heated
to a thixotropic state rather than to a completely liquid state,
and then injected into form 20 from an injection chamber. In this
method, a screw rather than a piston is often used to inject the
metal material into form 20. The piston and the screw contain a
shaft portion, which is attached to a drive mechanism. The drive
mechanism is typically a motor, however, hydraulic mechanisms have
also been used.
[0026] When a powdered metal material is used to fill form 20,
filled form 20 is then heated to bond TPG elements 10, 12 within
the metal material. In a particular embodiment, TPG elements 10, 12
are heated using a sintering process. Generally, sintering
strengthens the powdered metal material and normally produces
densification and, in powdered metal materials,
recrystallization.
[0027] Once bonded, form 20 containing the bonded TPG-embedded
metal material is cooled to form metal block embedded with TPG
(i.e., TPG-embedded heatsink). Generally, form 20 and the
TPG-embedded metal material is stored in a suitable location until
it reaches room temperature (approximately 24.degree. C.).
[0028] In an alternative embodiment, as depicted in FIGS. 2-4, a
metal block is impregnated with TPG using a lost form casting
process. In this embodiment, a foam block 100 (shown in FIG. 2) is
obtained. At least one TPG element 110 is deposited into foam block
100 (shown in FIG. 3). Foam block 100 with TPG element 110 is
deposited into a container 200 (shown in FIG. 4), and container 200
is at least partially filled with molding sand (not shown) with
sprues 130, 132 exposed. Molten metal material (not shown) is
poured into the sprues, replacing the foam and forming the
TPG-embedded block.
[0029] As described above, to begin the lost form casting process,
foam block 100 is obtained. Suitably, with reference to FIG. 2,
foam block 100 is made from a medium to high density foam.
Typically, dimensions of foam block 100 will vary depending upon
the desired heatsink.
[0030] In one embodiment, as shown in FIG. 3, at least one TPG
element 110 is deposited in pre-cut slots 120 formed or defined
within foam block 100. Typically, slots 120 are sized according to
the TPG element 1 10. For example, in one embodiment, slots 120 are
6''.times.0.375''.times.0.60''. Slots 120 may have any shape known
in the art suitable for use with TPG elements 1 10. In one
embodiment, TPG elements 110 are similar to TPG elements 10, 12
described above. In one embodiment, TPG elements 110 are planar TPG
strips such as described above and, as such, pre-cut slots 120 are
rectangular openings sized to allow TPG element 110 to slide within
foam block 100. While shown in FIG. 3 as being rectangular pre-cut
slots 120 and planar TPG elements 110, it should be understood by
one skilled in the art that TPG elements 110 can be any suitable
shape known in the art (as described more fully above) and pre-cut
slots 120 can be any complementary shape for allowing TPG elements
110 to be deposited therein without departing from the scope of the
present disclosure. Furthermore, it should be understood by one
skilled in the art that slots 120 may not be pre-cut, but may be
formed by placing pre-heated TPG elements in the foam, allowing
them to melt the foam, thereby, forming slot 120, or that TPG
elements 110 may simply be wedged between two pieces of foam
without departing from the scope of the present disclosure.
[0031] In an alternative embodiment, as shown in FIG. 5, foam block
100 includes at least two portions 300, 302. Foam block 100 may be
separated into any suitable number of portions 300, 302 using any
suitable equipment known in the art for separating foam material.
First portion 300 and second portion 302 may be equal or may not be
equal. For example, in one embodiment (not shown), foam block 100
is separated into first portion 300 and second portion 302, wherein
second portion 302 is twice the volume of first portion 300.
Moreover, foam block 100 may be separate into more than two
portions 300, 302, for example, foam block 100 may be divided into
three portions, four portions, or even five or more portions
without departing from the scope of the present disclosure.
[0032] When foam block 100 is separated into portions 300, 302, TPG
element 110 is deposited between portions 300, 302 and then
portions 300, 302 are coupled to form a single foam block including
TPG element 1 10. Portions 300, 302 may be coupled using any means
known in the art for coupling foam materials. For example, in one
embodiment, foam portions 300, 302 are coupled using any adhesive
composition known in the adhesive art. In an alternative
embodiment, portions 300, 302 are coupled using mechanical means,
such as screws or rivets.
[0033] Referring back to FIG. 3, once TPG element 110 has been
deposited within foam block 100, sprues 130, 132 are added to foam
block 100. In one embodiment, foam block 100 with the sprues 130,
132 is dipped into a plaster (not shown) to form a hard shell
around foam block 100. Typically, the plaster provides a smoother
finish to an exterior surface of finished metal block that is
formed out of foam block 100.
[0034] Now referring to FIG. 4, foam block 100, with or without a
plaster shell, is deposited into a container 200 with spues 130,
132 located at a top 202 of the container 200. Sprues 130, 132 are
used to provide entry for molten metal and to form exhaust vents
for gasses that may form during the lost foam casting process.
[0035] In one embodiment, container 200 is a sand-filled container.
Sand-filled container 200 facilitates retaining the form of the
molten metal until the metal cools and solidifies.
[0036] Once foam block 100 has been deposited within container 200,
molten metal material, such as the molten metal material described
above, is poured into sprues 130, 132, vaporizing the foam and
forming the TPG-embedded block. Generally, the molten metal
material remains in container 200 until all of the foam of foam
block 100 is depleted. This results in a metal block embedded with
TPG elements 110 (i.e., TPG-embedded heatsink).
[0037] In one embodiment, metal block is further removed from
container 200 and machined down in size for use as a heatsink.
[0038] In one embodiment, wherein metal block embedded with the TPG
element 110 is created using sintering, metal injection molding, or
lost foam casting, metal block is machine-configured to have heat
fins (generally shown in FIG. 2 at 2, 4, 6, and 8). By including
heat fins 2, 4, 6, 8, the surface area of the material that is
thermally exposed to the surrounding environment is increased to
facilitate heat dissipation. Typically, the thickness of heat fins
2, 4, 6, 8 are substantially identical, and distances between two
adjacent heat fins 2, 4, 6, 8 are also suitably identical. However,
it should be understood by one skilled in the art that while FIG. 2
shows heat fins 2, 4, 6, 8 having substantially identical thickness
and substantially identical spacing, heat fins 2, 4, 6, 8 may have
different thicknesses and/or vary spacing between heat fins 2, 4,
6, 8 without departing from the scope of the present disclosure.
Heat fins 2, 4, 6, 8 in one embodiment are approximately 0.24
inches in height and approximately 0.024 inches thick, and the
spacing between adjacent heat fins is approximately 0.096
inches.
[0039] In one embodiment, wherein the metal block embedded with TPG
elements 110 is created using sintering, metal injection molding,
or lost foam casting, the mold or foam block may be created to
incorporate fins or other features prior to injection of molten
metal in order to reduce or eliminate machining steps.
[0040] In another embodiment, wherein the metal block embedded with
TPG elements 110 is created using sintering, metal injection
molding, or lost foam casting, the mold or foam block may be
created to incorporate more complex features prior to injection of
molten metal to create conduction-cooled heatframes.
[0041] While the invention has been described in terms of various
specific embodiments, those skilled in the art will recognize that
the invention can be practiced with modification within the spirit
and scope of the claims.
* * * * *