U.S. patent application number 12/859591 was filed with the patent office on 2010-12-16 for heat spreader and method of making the same.
This patent application is currently assigned to Specialty Minerals (Michigan) Inc.. Invention is credited to Richard James LEMAK, V.N.P. Rao.
Application Number | 20100315783 12/859591 |
Document ID | / |
Family ID | 40410031 |
Filed Date | 2010-12-16 |
United States Patent
Application |
20100315783 |
Kind Code |
A1 |
LEMAK; Richard James ; et
al. |
December 16, 2010 |
HEAT SPREADER AND METHOD OF MAKING THE SAME
Abstract
A heat spreader having at least two adjoining strips of
pyrolytic graphite material is made by cutting a strip from a sheet
of pyrolytic graphite in the z direction. Thermal conductivity in
the xy plane of the graphite sheet is greater than in the z
direction. The z direction cut provides strips which are then each
individually oriented 90 degrees such that the thickness direction
of the original pyrolytic graphite sheet becomes the width or
length of the cut strip. A face on the side of a first strip
adjoins a face on the side of a second strip. Due to the greater
thermal conductivity in the xy plane of the strips as compared to
in the z direction heat transfers more rapidly in the length and
thickness direction of the strips than across adjoining sides of
the oriented strips.
Inventors: |
LEMAK; Richard James;
(Allentown, PA) ; Rao; V.N.P.; (Easton,
PA) |
Correspondence
Address: |
MINERALS TECHNOLOGIES, INC.
1 HIGHLAND AVENUE
BETHLEHEM
PA
18017-9482
US
|
Assignee: |
Specialty Minerals (Michigan)
Inc.
Bingham Farms
MI
|
Family ID: |
40410031 |
Appl. No.: |
12/859591 |
Filed: |
August 19, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11899712 |
Sep 7, 2007 |
7808787 |
|
|
12859591 |
|
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Current U.S.
Class: |
361/708 ;
165/185 |
Current CPC
Class: |
H01L 23/373 20130101;
Y10T 428/269 20150115; H01L 2924/00 20130101; H01L 2924/0002
20130101; H01L 2924/0002 20130101; H01L 23/3735 20130101; Y10T
29/49366 20150115 |
Class at
Publication: |
361/708 ;
165/185 |
International
Class: |
H05K 7/20 20060101
H05K007/20; F28F 7/00 20060101 F28F007/00 |
Claims
1. (canceled)
2. (canceled)
3. (canceled)
4. (canceled)
5. (canceled)
6. A heat spreader comprising: a) a first planar element of
pyrolytic graphite having a relatively high thermal conductivity in
a direction of a first lateral dimension of a first plane of the
first planar element and in the thickness direction of the first
planar element and having a relatively low thermal conductivity in
a direction of second lateral dimension of the first planar
element, wherein the direction of the first lateral dimension of
the first plane of the first planar element and the thickness
direction of the first planar element extend substantially in
directions of orientation of a axes of the pyrolytic graphite of
the first planar element and the direction of the second lateral
dimension of the first planar element extends substantially in the
direction of the c axis of the pyrolytic graphite of the first
planar element, b) a second planar element of pyrolytic graphite
having a relatively high thermal conductivity in a direction of a
first lateral dimension of a second plane of the second planar
element and in the thickness direction of the second planar element
and having a relatively low thermal conductivity in a direction of
a second lateral dimension of the second planar element, wherein
the direction of the first lateral dimension of the second plane of
the second planar element and the thickness direction of the second
planar element extend substantially in directions of orientation of
a axes of the pyrolytic graphite of the second planar element and
the direction of the second lateral dimension of the second planar
element extends substantially in the direction of the c axis of the
pyrolytic graphite of the second planar element, wherein each of
the first planar element and second planar element have a first
side and a second side, the first side and second side of each of
the first planar element and second planar element being
substantially parallel and being spaced apart in the direction of
the second lateral dimension at a first distance, the first side
and second side of each of the first planar element and second
planar element extending substantially normal to the direction of
the second lateral dimension of the first planar element and the
second planar element respectively wherein at least a portion of
the first side of the first planar element adjoins at least a
portion of the second side of the second planar element; and
wherein the first side of the first planar element substantially
coextensively adjoins at least a portion of the second side of the
second planar element.
7. A heat spreader comprising: a) a first planar element of
pyrolytic graphite having a relatively high thermal conductivity in
a direction of a first lateral dimension of a first plane of the
first planar element and in the thickness direction of the first
planar element and having a relatively low thermal conductivity in
a direction of second lateral dimension of the first planar
element, wherein the direction of the first lateral dimension of
the first plane of the first planar element and the thickness
direction of the first planar element extend substantially in
directions of orientation of a axes of the pyrolytic graphite of
the first planar element and the direction of the second lateral
dimension of the first planar element extends substantially in the
direction of the c axis of the pyrolytic graphite of the first
planar element, b) a second planar element of pyrolytic graphite
having a relatively high thermal conductivity in a direction of a
first lateral dimension of a second plane of the second planar
element and in the thickness direction of the second planar element
and having a relatively low thermal conductivity in a direction of
a second lateral dimension of the second planar element, wherein
the direction of the first lateral dimension of the second plane of
the second planar element and the thickness direction of the second
planar element extend substantially in directions of orientation of
a axes of the pyrolytic graphite of the second planar element and
the direction of the second lateral dimension of the second planar
element extends substantially in the direction of the c axis of the
pyrolytic graphite of the second planar element, wherein at least a
portion of a first side of the first planar element which extends
in a direction out of the first plane of the first planar element
adjoins at least a portion of a second side of the second planar
element which extends in a direction out of the second plane of the
second planar element, and a third planar element of pyrolytic
graphite having a relatively high thermal conductivity in a
direction of a first lateral dimension of a third plane of the
third planar element and in the thickness direction of the third
planar element and having a relatively low thermal conductivity in
a direction of a second lateral dimension of the third planar
element, wherein the direction of the first lateral dimension of
the third plane of the third planar element and the thickness
direction of the third planar element extend substantially in
directions of orientation of a axes of the pyrolytic graphite of
the third planar element and the direction of the second lateral
dimension of the third planar element extends substantially in the
direction of the c axis of the pyrolytic graphite of the third
planar element, wherein at least a portion of a third side of the
third planar element which extends in a direction out of the third
plane of the third planar element adjoins at least a portion of a
fourth side of the second planar element which extends in a
direction out of the second plane of the second planar element.
8. A heat spreader in combination with an electronic device,
wherein the electronic device is provided on the heat spreader and
the heat spreader conducts heat from the electronic device wherein
the heat spreader comprises: a) a first planar element of pyrolytic
graphite having a relatively high thermal conductivity in a
direction of a first lateral dimension of a first plane of the
first planar element and in a thickness direction of the first
planar element and having a relatively low thermal conductivity in
a direction of second lateral dimension of the first planar
element, and b) a second planar element of pyrolytic graphite
having a relatively high thermal conductivity in a direction of a
first lateral dimension of a second plane of the second planar
element and in a thickness direction of the second planar element
and having a relatively low thermal conductivity in a direction of
a second lateral dimension of the second planar element, wherein at
least a portion of a first side of the first planar element which
extends in a direction out of the first plane of the first planar
element adjoins at least a portion of a second side of the second
planar element which extends in a direction out of the second plane
of the second planar element.
9. A heat spreader in combination with an electrical device and a
heat sink, wherein the electronic device is provided on the heat
spreader and the heat spreader conducts heat from the electrical
device to the heat sink wherein the heat spreader comprises: a) a
first planar element of pyrolytic graphite having a relatively high
thermal conductivity in a direction of a first lateral dimension of
a first plane of the first planar element and in a thickness
direction of the first planar element and having a relatively low
thermal conductivity in a direction of second lateral dimension of
the first planar element, and b) a second planar element of
pyrolytic graphite having a relatively high thermal conductivity in
a direction of a first lateral dimension of a second plane of the
second planar element and in a thickness direction of the second
planar element and having a relatively low thermal conductivity in
a direction of a second lateral dimension of the second planar
element, wherein at least a portion of a first side of the first
planar element which extends in a direction out of the first plane
of the first planar element adjoins at least a portion of a second
side of the second planar element which extends in a direction out
of the second plane of the second planar element.
10. A heat spreader in combination with a heat sink wherein the
heat spreader is provided on the heat sink and wherein the heat
spreader comprises: a) a first planar element of pyrolytic graphite
having a relatively high thermal conductivity in a direction of a
first lateral dimension of a first plane of the first planar
element and in a thickness direction of the first planar element
and having a relatively low thermal conductivity in a direction of
second lateral dimension of the first planar element, and b) a
second planar element of pyrolytic graphite having a relatively
high thermal conductivity in a direction of a first lateral
dimension of a second plane of the second planar element and in a
thickness direction of the second planar element and having a
relatively low thermal conductivity in a direction of a second
lateral dimension of the second planar element, wherein at least a
portion of a first side of the first planar element which extends
in a direction out of the first plane of the first planar element
adjoins at least a portion of a second side of the second planar
element which extends in a direction out of the second plane of the
second planar element.
11. The combination of claim 10 wherein the heat sink is a copper
plate.
12-22. (canceled)
23. A heat spreader comprising: a) a first planar element of
pyrolytic graphite having a relatively high thermal conductivity in
a direction of a first lateral dimension of a first plane of the
first planar element and in a thickness direction of the first
planar element and having a relatively low thermal conductivity in
a direction of second lateral dimension of the first planar
element, and b) a second planar element of pyrolytic graphite
having a relatively high thermal conductivity in a direction of a
first lateral dimension of a second plane of the second planar
element and in a thickness direction of the second planar element
and having a relatively low thermal conductivity in a direction of
a second lateral dimension of the second planar element, wherein at
least a portion of a first side of the first planar element which
extends in a direction out of the first plane of the first planar
element adjoins at least a portion of a second side of the second
planar element which extends in a direction out of the second plane
of the second planar element, wherein at least one of the first
planar element and second planar element has a throughhole at least
partially therethrough and the heat spreader further comprises a
core received in the throughhole the core being of a material such
that heat from a heat source can be conducted via the core into the
thickness of the at least one of the first planar element and
second planar element.
24. A heat spreader comprising: a) a first planar element of
pyrolytic graphite having a relatively high thermal conductivity in
a direction of a first lateral dimension of a first plane of the
first planar element and in a thickness direction of the first
planar element and having a relatively low thermal conductivity in
a direction of second lateral dimension of the first planar
element, and b) a second planar element of pyrolytic graphite
having a relatively high thermal conductivity in a direction of a
first lateral dimension of a second plane of the second planar
element and in a thickness direction of the second planar element
and having a relatively low thermal conductivity in a direction of
a second lateral dimension of the second planar element, wherein at
least a portion of a first side of the first planar element which
extends in a direction out of the first plane of the first planar
element adjoins at least a portion of a second side of the second
planar element which extends in a direction out of the second plane
of the second planar element, wherein at least one of the first
planar element and second planar element has a hole at least
partially therethrough and the heat spreader further comprises a
core received in the throughhole the core being of an anisotropic
material such that heat from a heat source can be conducted via the
core into the thickness of the at least one of the first planar
element and second planar element.
25. The heat spreader of claim 24 wherein the core comprises
pyrolytic graphite.
26. (canceled)
27. A method of dissipating heat from a heat source, comprising: a)
providing a heat spreader comprising: i) a first planar element of
pyrolytic graphite having a relatively high thermal conductivity in
a direction of a first lateral dimension of a first plane of the
first planar element and in a thickness direction of the first
planar element and having a relatively low thermal conductivity in
a direction of second lateral dimension of the first planar
element, and ii) a second planar element of pyrolytic graphite
having a relatively high thermal conductivity in a direction of a
first lateral dimension of a second plane of the second planar
element and in a thickness direction of the second planar element
and having a relatively low thermal conductivity in a direction of
a second lateral dimension of the second planar element, wherein at
least a portion of a first side of the first planar element which
extends in a direction out of the first plane of the first planar
element adjoins at least a portion of a second side of the second
planar element which extends in a direction out of the second plane
of the second planar element; b) placing the heat spreader in heat
conducting relationship with a heat source; c) conducting heat from
the heat source into the first strip and second strip; and d)
conducting heat through the heat spreader in the direction of
relatively high thermal conductivity.
Description
BACKGROUND
[0001] The present invention relates to a heat spreader for
conducting heat from a device and a method of making the heat
spreader. Electronic components are becoming smaller while heat
dissipation requirements are becoming greater. In order to
dissipate heat generated by these electronic components, heat
spreaders are utilized between the electronic component and a heat
sink. Heat spreaders can be made of a solid thermally conductive
metal. The solid conductive metal has a limited ability to spread
heat and has limited thermal conductivity characteristics.
SUMMARY
[0002] According to the present invention, a heat spreader and a
method for making the heat spreader is provided, and a method of
dissipating from a heat source are disclosed.
[0003] In some embodiments, a heat spreader is provided which has
at least two adjoining planar elements or strips of pyrolytic
graphite material. The strips are made by cutting strips from a
sheet of pyrolytic graphite such that the sheet has a cut there
through in the z direction. Thermal conductivity in the xy plane of
the pyrolytic graphite sheet is greater than in the z direction.
The z direction cut provides strips which are then each
individually oriented about 90 degrees such that the thickness
direction of the original pyrolytic graphite sheet becomes the
width or length of the cut strip. A portion of a lateral side of a
first strip which has been formed by cutting the sheet of graphite
and oriented about 90 degrees adjoins a face on the side of a
second strip. Due to the greater thermal conductivity in the xy
plane of the strips as compared to in the z direction heat
transfers more rapidly along the length of the strip and in the
thickness direction of the oriented strips than across a side of a
strip which adjoins an adjoining strip.
[0004] In some embodiments of the invention the side of a first
strip which adjoins the side of a second strip is coextensive with
the second side.
[0005] In some embodiments of the invention three or more strips of
substantially equal length are placed side by side.
[0006] Another embodiment of the invention is a method of making a
heat spreader by providing at least two pyrolytic graphite strips
or planar elements from a sheet of pyrolytic graphite, A cut is
made in the thickness direction of the sheet which is known as the
z direction. The thermal conductivity of the sheet in the z
direction or as is commonly referred to as the c direction is
relatively low as compared to the thermal conductivity in the xy
plane or as is commonly referred to as the a directions or axes.
The side of a first strip is then placed such that the side adjoins
the side of a second strip. In this configuration heat transfers
more rapidly along the length of the strip and in the thickness
direction of the oriented strips than across a side of the strip
which adjoins an adjacent strip.
[0007] Another embodiment of the invention is a method of placing
the heat spreader in a heat conducting relationship with a heat
source by providing adjoining pyrolytic graphite strips. The side
of a first strip is placed such that the side adjoins the side of a
second strip. Heat transfers more rapidly along the length of the
strip and in the thickness direction of the oriented strips than
across a side of the strip which adjoins an adjacent strip. Heat is
conducted from the heat source into the first strip and second
strip. Heat is conducted through the heat spreader in the direction
of the a directions or axes of the pyrolytic graphite strips.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a parallel perspective view of a sheet of
pyrolytic graphite for use in the present invention showing the
direction of the a and c axes of the layers of pyrolytic graphite
of the sheet;
[0009] FIG. 2 is a parallel perspective view of the sheet of
pyrolytic graphite of FIG. 1 showing a first planar element which
has been diced from the sheet and separated therefrom;
[0010] FIG. 3a shows the first planar element of FIG. 2 after
orientation of about 90 degrees;
[0011] FIG. 3b shows the first planar element and the second planar
element prior to adjoining;
[0012] FIG. 4 shows an embodiment of the heat spreader of the
present invention and the direction of the a and c axes of the
pyrolytic graphite in the first planar element and second planar
element;
[0013] FIG. 5 shows another embodiment of the heat spreader of the
present invention and the direction of the a and c axes of the
pyrolytic graphite in the first planar element and second planar
element;
[0014] FIG. 6 shows another embodiment of the heat spreader of the
present invention and the direction of the a and c axes of the
pyrolytic graphite in the first planar element, second planar
element and third planar element;
[0015] FIG. 6A shows a third planar element of the heat spreader of
FIG. 6;
[0016] FIG. 7 shows the heat spreader of the present invention in
combination with an electronic device and a heat sink; and
[0017] FIG. 8 shows another embodiment of the heat spreader of the
present invention having a throughhole in the thickness direction
of the planar elements of the heat spreader.
DETAILED DESCRIPTION OF THE INVENTION
[0018] The invention will now be described in detail by reference
to the following specification and non-limiting examples.
[0019] Without further elaboration, it is believed that one skilled
in the art can, using the preceding description, utilize the
present invention to its fullest extent. The following embodiments
are, therefore, to be construed as merely illustrative, and not
limitative of the remainder of the disclosure in any way
whatsoever.
[0020] Graphite is made up of layer planes of hexagonal arrays or
networks of carbon atoms. These layer planes of hexagonal arranged
carbon atoms are substantially flat and are oriented so as to be
substantially parallel and equidistant to one another. The
substantially flat parallel layers of carbon atoms are referred to
as basal planes and are linked or bonded together in groups
arranged in crystallites. Conventional or electrolytic graphite has
a random order to the crystallites. Highly ordered graphite has a
high degree of preferred crystallite orientation. Accordingly,
graphite may be characterized as laminated structures of carbon
having two principal axes, the "c" axis or direction which is
generally identified as the axis or direction perpendicular to the
carbon layers and the "a" axes or directions parallel to the carbon
layers and transverse to the c axes.
[0021] Referring now to the drawings in detail, wherein like
reference numerals indicate like elements through the several
views, there is shown in FIG. 1 a sheet 10 for making the heat
spreader of the present invention having axes a which are in the
direction of the hexagonal array of carbon atoms. The c axis as
shown is perpendicular to the carbon layers.
[0022] Graphite materials that exhibit a high degree of orientation
include natural graphite and synthetic or pyrolytic graphite.
Natural graphite is commercially available in the form of flakes
(platelets) or as a powder. Pyrolytic graphite is produced by the
pyrolysis of a carbonaceous gas on a suitable substrate at elevated
temperature. Briefly, the pyrolytic deposition process may be
carried out in a heated furnace and at a suitable pressure, wherein
a hydrocarbon gas such as methane, natural gas, acetylene etc. is
introduced into the heated furnace and is thermally decomposed at
the surface of a substrate of suitable composition such as graphite
having any desirable shape. The substrate may be removed or
separated from the pyrolytic graphite. The pyrolytic graphite may
then be further subjected to thermal annealing at high temperatures
to form a highly oriented pyrolytic graphite commonly referred to
as HOPG.
[0023] In FIG. 2 is shown a sheet 10 of pyrolytic graphite having
the direction of the a axes and the c axis as shown. A first planar
element 12 or strip is cut or diced from the sheet 10 of pyrolytic
graphite and after the first planar element 12 is cut from the
sheet the direction of the a axes and c axis within the first
planar element 12 remain in the same direction as when the first
planar element 12 formed part of the sheet 10.
[0024] Planar element 12 after being cut from sheet 10 is oriented
about 90 degrees or about 270 degrees such that the direction of
the c axis of the first planar element 12 changes from the
direction shown in FIG. 2 to the direction shown in FIG. 3a.
Accordingly, it can be seen that after orientation of the first
planar element 12 the relative location of first side 14 of first
planar element 12 has changed from that shown in FIG. 2 to that
shown in FIG. 3a. A second planar element 16 as shown in FIG. 3b is
cut from sheet 10 and orientated 90 or 270 degrees in a manner
similar to that described above for the first planar element
12.
[0025] According to an embodiment of the present invention, a first
side 14 of first planar element 12 which is out of the plane of the
plane of the planar element 12 is adjoined with second side 18 of
second planar element 16 which is out of the plane of the second
planar element 16 such that at least a portion the first side 14
adjoins at least a portion of the second side 18 as seen in FIG.
5.
[0026] In another embodiment of the invention, the first side 14 of
the first planar element 12 can extend substantially coextensively
with the second side 18 of the second planar element 16.
[0027] As can be seen in FIGS. 4 and 5, the portion of the first
side 14 of the first planar element 12 which adjoins the portion of
the second planar element 16 extends substantially normal to the
first plane of the first planar element 12. The first plane of the
first planar element 12 is defined by the direction in which the
major dimension h and minor dimension g extend as shown in FIG. 4.
The major dimension h and minor dimension g can be of equal
magnitude, however the major dimension h and minor dimension g are
not the thickness dimension of the planar element.
[0028] The major dimension h and minor dimension g can be the first
lateral dimension and second lateral dimensions of the first planar
element 12.
[0029] The direction of the first lateral dimension or major
direction h of the planar element 12 and the thickness direction i
of the first planar element can be the direction of the a axes of
the sheet 10 of pyrolytic graphite from which the first planar
element 12 is formed. The direction of the second lateral dimension
can be the direction of the c axis of the sheet 10 of pyrolytic
graphite from which the first planar element 12 is formed as seen
in FIG. 1. Therefore, as seen in FIG. 4, the first planar element
has a relatively high thermal conductivity in the first lateral
dimension, here, major dimension h of the planar element and in the
thickness direction i of the first planar element but a relatively
low thermal conductivity in the second lateral dimension or minor
dimension g. Therefore, heat is conducted more readily along major
dimension h and in the thickness direction i than in minor
dimension g than across first side 14 of first planar element 12 to
second side 18 of second planar element 16.
[0030] The heat spreader of the present invention can be made such
that the planar elements each have three sets of parallel sides.
Each side can be orthogonal to two other sides of the planar
element. The two opposite sides of a planar element can be spaced
apart at substantially the same distance along each side.
[0031] The sheets of pyrolytic graphite from which the planar
elements are cut or diced by any means for cutting the sheets such
as wirecutting machines, dicing machines, or slicing machines are
available in sizes having a thickness in the f dimension shown in
FIG. 1 of from 0.2 millimeters up to 5 centimeters. A typical
thickness is 1.3 centimeters. Commercially available pyrolytic
graphite sheets are available having a length or d dimension of
about 3 meters and the width dimension e can be as large as 40
centimeters. Pyrolytic graphite sheets suitable for use in the
present invention are available from the Pyrogenies Group of Minteq
International Inc. of New York, N.Y. An example is PYROID.RTM. HT
pyrolytic graphite.
[0032] In one embodiment the distance in which the first side and
the second side of the first planar element are spaced apart is at
least about 1.5 millimeters.
[0033] In another embodiment the distance at which the first side
and the second side of the first planar element are spaced apart is
from about 1.5 millimeters to about 1.3 centimeters.
[0034] In another embodiment the distance at which the first side
and the second side of the first planar element are spaced apart is
from about 1.3 centimeters to about 2.5 centimeters.
[0035] In another embodiment the distance at which the first side
and the second side of the first planar element are spaced apart is
at least about 1.3 centimeters.
[0036] In another embodiment the distance at which the first side
and the second side of the first planar element are spaced apart is
at least about 4.0 centimeters.
[0037] In another embodiment the distance at which the first side
and the second side of the first planar element are spaced apart is
from about 1.3 centimeters to about 5.0 centimeters.
[0038] In another embodiment the distance at which the third side
and the fourth side of the first planar element are spaced apart is
at least about 1.0 centimeter.
[0039] In another embodiment the distance at which the third side
and the fourth side of the first planar element are spaced apart is
from about 1.0 centimeters to about 40 centimeters.
[0040] The thermal conductivity of the sheets in the a axes of the
sheets can be from about 450 to about 2000 Watts/m.degree. K and
the particular thermal conductivity for a particular application
can be tailored. The thermal conductivity in the z direction or
along the c axis can be as low as about 2.0 Watts/m.degree. K or in
the case of PYROID.RTM. HT pyrolytic graphite 7 Watts/m.degree. K.
By comparison the thermal conductivity of copper is 400
Watts/m.degree. K. As copper has a density of 8.9 g/cc as compared
to values for pyrolytic graphite of as high as 2.25 g/cc, greater
efficiencies and weight savings can be achieved using the heat
spreader of the present invention.
[0041] Thermal grease can be used at the interface between the
first planar element 12 and second planar element 16. The heat
spreader 22 of FIG. 4 can be adjoined to a substrate such as a heat
sink, here a copper plate 20 as seen in FIG. 7 by any suitable
means for adjoining the first planar element 12 and second planar
element 16 to a substrate. In the event that the heat spreader 22
is adjoined to a heat sink the means for adjoining the heat
spreader 22 to the substrate permits the transfer of heat from the
heat spreader 22 to the substrate. A mechanical means such as a
clamping means can be a means to adjoin the heat spreader to a
substrate which in turn transfers heat from the heat spreader to a
heat sink. Also, the heat spreader can be adjoined directly to a
heat sink. Additional means for adjoining the heat spreader to a
substrate or heat sink can be a bonding means. The bonding means
can be a layer of metal or a layer which comprises metal on a
planar element of the heat spreader which is bonded to the
substrate such as by soldering at least a portion of the metal
containing layer to the substrate or heat sink. The layer is
applied to a planar element on at least a portion of the planar
element which is to adjoin the substrate. After application of the
metal containing layer on at least a portion of the planar element,
the planar element can be adjoined to the substrate or heat sink by
techniques used in the semiconductor industry such as soldering or
even by a mechanical means such as a mechanical fastener.
[0042] Application of the metal containing layer on a portion of
the planar element which adjoins the substrate can be achieved by
metallization techniques, sputtering or by applying a layer of
solder to the portion of the planar element which is to be joined
to the substrate. The planar elements can be provided with a
surface treatment prior to the application of the metal containing
layer using techniques suitable for use on semiconductors.
[0043] Any means for joining the first planar element 12 and the
second planar element 16 can be used. For example, a mechanical
clamping means such as a mechanical fastener can be used to join
the first planar element 12 and the second planar element 16
together or the first planar element 12 and the second planar
element 16 can be soldered together using techniques which are
capable of joining carbon-based surfaces together. Upon adjoining
of the first planar element 12 and the second planar element 16
heat can transfer from the first planar element 12 and the second
planar element 16 along the portion wherein the first planar
element 12 and the second planar element 16 are adjoined.
[0044] In another embodiment of the present invention, a heat
spreader has a first planar element 12, a second planar element 16
and a third planar element 24 as seen in FIGS. 6 and 6A. The third
planar element 24 is cut or diced from the sheet 10 of pyrolytic
graphite and oriented in a manner similar to that in which the
first planar element 12 and the second planar element 16 are cut. A
third side 26 of second planar element 16 is arranged such that the
third side 26 adjoins a fourth side 28 of third planar element 24.
In a similar way, heat spreaders of the present invention can be
made with a fourth, fifth or sixth etc. planar element. Each
additional planar element has a side which adjoins an adjacent side
of a planar element of the heat spreader such that heat transfers
more rapidly in the two dimensions of the heat spreader which do
not have a side which adjoins an adjacent planar element.
[0045] Because the a and c axes of the pyrolytic graphite of all
three of the strips which make up this embodiment of the invention
are arranged in the direction shown in FIG. 6, heat is transferred
more readily in the j and k dimensions as compared to the l
dimension.
[0046] In FIG. 7 a heat spreader of the present invention is shown
in combination with an electronic device 30 and a heat sink 20
which is a copper plate. Heat from the electronic device 30 is
transferred to the heat spreader 22. From the heat spreader 22,
heat is transferred most rapidly in the direction of the thickness
dimension i and in the direction of lateral dimension h which are
oriented in the a axes of the pyrolytic graphite from which the
heat spreader 22 is made. Heat is transferred less rapidly across
the interface between the first planar element 12 and the second
planar element 16.
[0047] The electronic device can be a microprocessor, an integrated
circuit, high power devices such as laser diodes, LEDs, wide band
gap, RF and microwave devices, power amplifiers, insulated gate
bipolar transistors (IGBTs), application specific integrated
circuits (ASICs), liquid crystal display (LCDs) and other types of
video displays.
[0048] In yet another embodiment of the present invention, at least
one of the first planar element 12 and the second planar element 16
has a throughhole 32 at least partially therethrough. A core 34 of
material which can be isotropic or anisotropic such as pyrolytic
graphite can be inserted into the throughhole 32. The core can be
or can comprise a metal having a relatively high thermal
conductivity or even diamond. The core 34 in the throughhole
permits the transfer of more heat in the thickness direction i of
the first planar element 12 or the second planar element 16.
[0049] The invention also includes another embodiment disclosing a
method of dissipating heat from a heat source comprising providing
a heat spreader having a first planar element and second planar
element arranged as described above. The heat spreader is placed in
a heat conducting relationship with a heat source such that the
heat spreader conducts heat from the heat source into the first
strip and second strip. Heat is conducted through the heat spreader
in the direction of relatively high thermal conductivity.
[0050] Accordingly, it is understood that the above description of
the present invention is susceptible to considerable modifications,
changes and adaptations by those skilled in the art, and that such
modifications, changes and adaptations are intended to be
considered within the scope of the present invention, which is set
forth by the appended claims.
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