U.S. patent application number 10/850540 was filed with the patent office on 2004-11-18 for method of manufacturing an elastomeric heat sink with a pressure sensitive adhesive backing.
Invention is credited to McCullough, Kevin A., Panek, Jeffrey, Sagal, E. Mikhail.
Application Number | 20040226707 10/850540 |
Document ID | / |
Family ID | 33425001 |
Filed Date | 2004-11-18 |
United States Patent
Application |
20040226707 |
Kind Code |
A1 |
Sagal, E. Mikhail ; et
al. |
November 18, 2004 |
Method of manufacturing an elastomeric heat sink with a pressure
sensitive adhesive backing
Abstract
The present invention discloses method of manufacturing a
net-shape molded elastomeric heat-dissipating device that includes
an integrally formed conformable interface surface. A base
elastomeric matrix material is loaded with thermally conductive
filler and injected into a mold cavity to form the completed
device. Further, a layer of thermally conductive pressure sensitive
adhesive material is applied to the conformable interface surface
to allow the device to be securely fastened to a heat-generating
surface. The present invention provides superior sealing and
elimination of voids and air gaps that are typically found between
the thermal transfer surfaces thereby facilitating enhanced thermal
transfer properties.
Inventors: |
Sagal, E. Mikhail;
(Narragansett, RI) ; Panek, Jeffrey; (North
Kingstown, RI) ; McCullough, Kevin A.; (North
Kingstown, RI) |
Correspondence
Address: |
BARLOW, JOSEPHS & HOLMES, LTD.
101 DYER STREET
5TH FLOOR
PROVIDENCE
RI
02903
US
|
Family ID: |
33425001 |
Appl. No.: |
10/850540 |
Filed: |
May 20, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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|
10850540 |
May 20, 2004 |
|
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10222574 |
Aug 16, 2002 |
|
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60314433 |
Aug 23, 2001 |
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60314892 |
Aug 24, 2001 |
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Current U.S.
Class: |
165/185 ;
29/890.03 |
Current CPC
Class: |
F28F 3/022 20130101;
F28F 3/02 20130101; Y10T 29/4935 20150115 |
Class at
Publication: |
165/185 ;
029/890.03 |
International
Class: |
F28F 007/00; B21D
053/02 |
Claims
What is claimed is:
1. A method of manufacturing a heat dissipating assembly,
comprising: providing a base matrix of an elastomer polymer;
loading a thermally conductive filler material into said base
matrix to form a mixture; molding said mixture to form a heat sink
having a base element with a top surface, a bottom surface and
surface area enhancements adjacent to said top surface; and
applying a layer of pressure sensitive adhesive to said bottom
surface of said base element.
2. The method of manufacturing said heat-dissipating assembly of
claim 1, further comprising: installing said heat sink on a heat
generating surface, said heat generating surface having surface
irregularities, said bottom surface of said base member being
received on said heat generating surface wherein said bottom
surface of said base member conforms to said surface irregularities
and is retained in contact with said heat generating surface by
said layer of adhesive.
3. The method of manufacturing said heat dissipating assembly of
claim 1, wherein said surface area enhancements are integrally
molded with said base member from said elastomeric polymer base
matrix and said thermally conductive filler.
4. The method of manufacturing said heat dissipating assembly of
claim 1, wherein said surface are enhancements are an array of
metallic elements, said base member being insert molded around said
metallic elements.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 10/222,574, filed Aug. 16, 2002 and claims priority from
earlier filed provisional patent application No. 60/314,433 filed
Aug. 23, 2001 and 60/314,892 filed Aug. 24, 2001.
BACKGROUND OF THE INVENTION
[0002] The present invention relates generally to an elastomeric
material composition for use in connection with heat generating
electronic devices and a method for manufacturing the same. More
particularly, this invention relates to a new net-shape molded
thermally conductive elastomeric polymer heat sink device having an
integral interface and fastening means. The composition contains
thermally conductive filler material in a conformable elastomeric
matrix and an integral means for adhering the device to a
heat-generating surface to forming an improved heat sink device
with an integral, conformable thermally conductive interface layer.
Further, a method of manufacturing the device is also provided.
[0003] In the prior art, it is well known that the most critical
locations that effect the overall performance of a heat transfer
assembly are the interface points. These locations are where two
different materials mate to one another introducing two contact
surfaces and often an air gap across which the heat being
dissipated must be transferred. Generally, the contact surfaces are
not always perfectly flat due to milling or manufacturing
tolerances thus creating gaps between the heat generating surface
and the heat dissipating devices thereby increasing the overall
thermal resistance of the assembly. These imperfections and gaps
between the mating surfaces often contain small pockets of air and
thus reduce the heat transfer potential across the interface
between the heat generating surface and the heat-dissipating
device.
[0004] Various materials have been employed in the prior art in an
attempt to bridge this interface gap. In particular, organic base
materials such as polysiloxane oils or polysiloxane elastomeric
rubbers and thermoplastic materials such as PVC, polypropylene,
etc. loaded with thermally conducting ceramics or other fillers
such as aluminum nitride, boron nitride or zinc oxide have been
used to impart thermally conducting properties to the organic base
material. In the case of polysiloxane oils loaded with thermally
conducting materials, these materials are applied by smearing the
heat sink or other electronic component with the thermally
conducting paste and then securing the heat sink in place by
mechanical means using clips or screws. While the prior art,
thermal greases show superior film forming and gap filling
characteristics between uneven surfaces thus providing an intimate
contact between the surface of the heat sink and the surface of the
heat-generating source. However, it has been found that the use of
thermal greases exhibit poor adhesions to the surfaces of the heat
sink and heat generating surface, thus effectively seeping out from
between the heat sink and the heat generating surface, causing air
voids to form between the two surfaces leading to hot spots.
Moreover, excessive pressure placed upon the heat sink by the
mechanical fasteners accelerates this seepage from between the heat
sink and the surface of the heat-generating surface. It has been
reported that excessive squeeze out of polysiloxane oils can
evaporate and recondense on sensitive parts of the surrounding
microcircuits. The recondensed oils lead to the formation of
silicates thereby interfering with the function of the
microprocessor and eventually causing failure.
[0005] In the case of polysiloxane rubbers and thermoplastic
polymers, these materials are typically cast in sheet form and die
cut into shapes corresponding to the shape of the heat sink and
heat generating device. The resulting preformed sheet is then
applied to the surface of the heat-generating surface securing the
heat sink by means of clips or screws. The precut films solve the
problems associated with greases but do not provide adequate
intimate contact required for optimum heat transference between the
heat generating source and the heat sink. The added step of cutting
preforms and manually applying the pad adds cost to the assembly
process. Furthermore, these types of materials show variable
performance due to variation in the thickness of the pad and the
amount of pressure applied to the thermally conducting precut film,
based upon the mechanical device or action used to secure the heat
sink. Further, while these known interface materials, are suitable
for filling undesirable air gaps, they are generally are less
thermally conductive than the heat sink member thus detracting from
the overall thermal conductivity of the assembly.
[0006] An additional drawback to most of the above noted interface
materials is that they require a machined heat sink be secured to a
heat generating surface or device using mechanical clips or screws
adding to the complexity and assembly time for the overall
assembly.
[0007] In an attempt to overcome the requirement of mechanical
fastening some prior art thermal interface pads are formed of a
material that is soft and pliable, having an adhesive on both
sides. The pad is first applied under pressure to the mating
surface of the heat-dissipating device and the assembly is then
pressed onto the heat-generating surface. The pliability of the
interface material allows the pad to be compressed into the small
grooves and imperfections on the two mating surfaces thus improving
the overall performance of the heat transfer through the interface
area. The drawback in the prior art is that the use of an adhesive
interface pad requires an additional fabrication/assembly step and
introduces an additional layer of material along the heat
dissipation pathway. Further, as mentioned above, since all of the
materials within the assembly are different, optimum heat transfer
cannot be achieved.
[0008] Therefore, in view of the foregoing, heat transfer
assemblies that are formed of a monolithic material having an
integral interface contact surface that includes a means for
mounting the assembly to a heat-generating surface are highly
desired. There is also a demand for a heat dissipating assembly for
use in an electronic device that is lightweight, has an integral
interface surface and is net-shape moldable from a thermally
conductive material so that complex geometries for accurate mating
of the case surfaces can be achieved.
SUMMARY OF THE INVENTION
[0009] The present invention is generally directed to a highly
thermally conductive elastomeric heat-dissipating device that is
net shape molded and includes an adhesive on the interface surface
thereof. The elastomeric device of the present invention enables
complex shapes to be injection molded cost-effectively while
providing passive cooling and an improved thermal interface having
a reduced thermal resistivity as compared to analogous devices in
the prior art. The thermally conductive elastomer is molded into an
engineered shape having surface area enhancements and is employed
for dissipating heat from a heat-generating source, such as a
semiconductor device. Further, the device of the present invention
includes an integrally molded conformable thermal interface
surface. The thermal composite material is preferably an
elastomeric polymer base loaded with thermally conductive filler
material. The molded shape may be of any type suited for efficient
transfer and dissipation of heat. In addition, the device may be
insert molded to include arrays of pins or fins, other heat
dissipation geometries or to incorporate heat tubes for increased
heat transfer.
[0010] An elastomeric base polymer is included in the present
invention in order to allow the heat dissipation element to have a
resilient and flexible structure that provides a base or interface
that can be conformed to intimately contact the heat-generating
surface. As can be seen, using an elastomer having a relatively
high modulus of elasticity allows the base material to bridge and
fill the gaps present in the prior art without requiring an
additional interface pad.
[0011] Further, the present invention provides for a layer of
pressure sensitive adhesive to be applied on the contact surface
where it meets the heat-generating surface. This adhesive may be of
the release type where a layer of release paper is removed to
expose the adhesive for use. In general, the use of an adhesive on
the elastomeric material facilitates use of the material and
obviates the need for separate clamps or clips. In addition, final
assembly is simplified by eliminating an element and a required
assembly step. Also, the adhesive is preferably thermally
conductive in nature. In this configuration, the present can be
firmly mounted to the heat-generating device to effectively provide
continuous contact and hold the conformable elastomeric material in
conformance to the surface of the heat-generating surface to
eliminate the air gaps found in the prior art.
[0012] Various adhesive materials are known in the prior art that
can be applied either during manufacture or at the time of assembly
to adhere the heat dissipating assembly of the present invention to
the heat-generating surface. Alternately, the adhesive material may
be incorporated into a matrix of the base elastomeric material and
molded over the base interface surface of the present device to
provide an integral adhesive bonding material while maintaining the
continuity of the thermal transfer properties of the present
invention.
[0013] It is therefore an object of the present invention to
provide an elastomeric heat sink for use in an electronic device
that enhances the dissipation of heat from a heat generating
electronic component upon which the device is mounted.
[0014] It is also an object of the present invention to provide an
elastomeric heat sink for use in an electronic device that has an
integrally formed conformable thermal interface surface that
directly provides heat dissipation for a heat generating electronic
component upon which the device is mounted.
[0015] It is a further object of the present invention to provide
an elastomeric heat sink having an integrally formed conformable
thermal interface surface that includes a means for adhesively
fastening the device to a heat generating surface, eliminating the
need for additional fastening means
[0016] It is yet another object of the present invention to provide
a heat sink as described above that passively provides heat
transfer between the heat generating surface and the heat sink
while having an integrally formed conformable interface that fills
any gaps or voids therebetween.
[0017] It is a further object of the present invention to provide
an elastomeric heat sink having an integrally formed conformable
interface surface for an electronic device that is injection
moldable from a thermal composite material into complex geometries
to accommodate a variety of device case shapes.
[0018] Other objects, features and advantages of the invention
shall become apparent as the description thereof proceeds when
considered in connection with the accompanying illustrative
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The novel features which are characteristic of the present
invention are set forth in the appended claims. However, the
invention's preferred embodiments, together with further objects
and attendant advantages, will be best understood by reference to
the following detailed description taken in connection with the
accompanying drawings in which:
[0020] FIG. 1 is a cross-sectional view of the heat dissipation
assembly of the present invention;
[0021] FIG. 2 is a magnified view of the interface portion of the
heat dissipation assembly of FIG. 1;
[0022] FIG. 3 is a magnified view of the interface portion of an
alternate embodiment of the heat dissipation assembly of the
present invention;
[0023] FIG. 4 is a perspective view of a second alternate
embodiment of the heat dissipation assembly of the present
invention;
[0024] FIG. 5 is a cross-sectional view through the line 5-5 of
FIG. 4; and
[0025] FIG. 6 is perspective view of a third alternate embodiment
of the heat dissipation assembly of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0026] Referring now to the drawings, the heat dissipation assembly
of the present invention is shown and illustrated generally as 10.
The present invention is a heat dissipation assembly 10 and a
method by which that assembly, formed by combining an elastomeric
polymer base matrix and a thermally conductive filler, is molded
into a finished component for final installation onto a heat
generating electronic device.
[0027] The assembly 10 of the present invention is shown here, by
way of example, as a heat sink device 12 having a base element 14,
integrally formed surface area enhancements 16 and an interface
surface 18 to which an adhesive layer 20 is applied. The heat sink
device 12 is applied to a heat generating electronic device 22 that
has a heat generating surface 24 and is typically installed onto an
electronic circuit board 26 via wire leads 28. While specific
structure is used here to illustrate the present invention, it
would be understood by one skilled in the relevant art that the
disclosure provided herein could be modified to provide any
geometry or be applied in any application where heat must be
dissipated from a heat-generating device.
[0028] Turning now to FIGS. 1 and 2 the preferred embodiment of the
heat dissipating assembly 10 is shown. Specifically, the heat
dissipating assembly 10 is shown to include a heat sink 12 that is
formed from a thermally conductive material such as an elastomeric
base polymer matrix. Further, the heat sink 12 includes a base
member 14 and integrally formed fins 16 that are integrally formed
with and protrude upwardly from the base member 14. This geometry
allows heat to be transferred efficiently through the base member
14 for dissipation through the increased surface area found in the
fins 16. The base member further includes an interface surface 18
opposite the fins 16 for mounting the heat sink 12 in mated
relationship to the heat generating surface 24 of a heat generating
electronic component 22. In the preferred embodiment, a layer of
thermally conductive adhesive material 20 is applied onto the
interface surface 18 of the heat sink 12 for facilitating the
mounting of the heat sink 12 to the heat-generating surface 24.
[0029] The layer of adhesive material 20 is applied to the
interface surface 18 of the heat sink 12 at the time of
manufacture. This adhesive 20 is preferable of the pressure
sensitive type where in the heat sink 12 can be placed onto the
heat generating surface 24 during final assembly of the components
and repositioned if required before pressure is applied, affixing
the heat sink 12 into permanent contact with the heat generating
surface 24. If the heat sink 12 will be handled or shipped before
it is placed onto the heat-generating surface 24, a layer of
removable release paper (not shown) may be provided over the
adhesive layer 20 to protect the adhesive 20 from damage or
contamination during the intermediate handling or shipping steps.
Before final assembly of the heat sink 12 onto the heat-generating
surface 24, the release paper is removed, exposing the adhesive
layer 20.
[0030] As can be best seen in FIG. 2, the use of elastomeric
material is an important feature of the present invention. FIG. 2
is a magnified view of the interface between the interface surface
18 of the base element 14 of the heat sink 12 and the
heat-generating surface 24 of the electronic device 22. It can be
seen that the layer of adhesive material 20 is disposed there
between. While the heat generating surface 24 appears to be smooth,
in reality, in this magnified view, the heat generating surface 24
can be seen to include many surface imperfections that are the
result of milling, polishing or molding of the electronic device
22. In the prior art, a rigid heat sink would be applied over this
heat generating surface 24 resulting in numerous small air gaps
that would interfere with the efficiency of the heat transfer
across the interface. Since the base member 14 of the heat sink 12
in the present invention is formed using an elastomeric polymer, it
is conformable. Therefore, when the heat sink 12 is pressed into
contact with the heat-generating surface 24, the interface surface
18 on the base element 14 conforms to receive the raised ridges and
fills the depressed areas eliminating the voids and air gaps. The
layer of pressure sensitive adhesive 20 cooperates with the
conformable interface surface 18 to maintain the interface surface
18 in intimate contact with the heat-generating surface 24 and
retaining the interface surface 18 in its conformed state. In this
manner, the present invention represents an improvement over the
prior art by eliminating the air gaps typically found between a
heat generating surface and an interface surface of a heat sink,
while eliminating the need for providing an additional
interface/gap pad.
[0031] The heat sink 12 of the present invention is made from a
composition that employs a base matrix of elastomeric polymer with
different types of thermally conductive filler material loaded
therein. The composition is achieved through the steps of combining
the base matrix material with a thermally conductive filler
material and molding the composition. The base matrix is loaded
with thermally conductive filler. The mix may include, for example,
by volume, 40 percent base matrix and 60 percent filler material.
Depending on the base matrix and filler, loading can be even
higher. The filler material is introduced to the base elastomeric
polymer matrix. The two components are mixed and loaded into the
desired molding machine and associated mold in a fashion known in
the art which need not be discussed in detail here. Once removed
from the mold, the final composition is in its final shape and
ready for its end use. This process, referred to a net shape
molding, is known to result in producing polymer compositions with
high thermal conductivities as compared to the base matrix alone.
Fillers that are suitable for incorporation into the composition
used in the present invention include boron nitride, carbon fibers,
carbon flakes, carbon powders, metallic grains or flakes and
crushed glass. One of the primary reasons for employing a thermally
conductive elastomeric composition is that it is moldable into more
complex geometries to achieve better heat sink geometries. Because
of the versatility of the material, applications that would clearly
indicate its use are extremely widespread. Further, because the
material is conformable, the need for gap pads and thermal
interface pads is eliminated.
[0032] Turning now to FIG. 3 a magnified view of the interface area
between the heat generating surface 24 and an alternate embodiment
of a heat sink 100 interface surface 102 is shown. In this
configuration, the adhesive material 104 is incorporated within the
elastomeric polymer matrix of heat sink 100 near the interface
surface 102. The incorporation of the adhesive material 104 is done
during the manufacturing process where before injecting the last
shot of elastomeric polymer into the mold, the adhesive material is
mixed into the molten polymer resulting in the final layer of
elastomer injected near the interface surface 102 having integral
adhesive properties. In all other aspects, this embodiment of the
present invention incorporates all of the features described
above.
[0033] FIGS. 4, 5 and 6 illustrate alternate embodiments of the
heat sink 12 of the present invention. The heat sinks shown in
these Figs. are formed using an insert molding process. FIGS. 4 and
5 show a pin type, insert molded heat sink 200 where an array of
pins 202 are placed into a mold cavity and the base member 204 is
molded around the base of the pins. As can be seen in FIG. 5, the
end of the pins 202 are embedded into the base member 204 and
retained therein when the molten elastomer cures. As described
above adhesive layer 206 is provided on the bottom surface 208 of
the heat sink 200. Since the base element 204 is formed from an
elastomer, it is conformable in accordance with the description of
the preferred embodiment provided above.
[0034] Finally, FIG. 6 provides an alternate embodiment heat sink
300 where fins 302 are insert molded into a base element 304 and
further includes an adhesive layer 306. Again, since the base
element 304 is formed from an elastomer it is conformable in
accordance with the description of the preferred embodiment
provided above.
[0035] In view of the foregoing, a superior moldable heat
dissipating assembly that eliminates the requirement of additional
gap pads or thermal interfaces can be realized. The conformable
base element 14 of the present invention, greatly improves over
prior art attempts by integrally providing the heat sink 12 with
the ability to bridge and fill the gaps found in typical heat
generating surfaces 24. In particular, the present invention
provides an integrated thermal interface with a unitary thermal
dissipation assembly that is vastly improved over known assemblies
and was until now unavailable in the prior art.
[0036] While there is shown and described herein certain specific
structure embodying the invention, it will be manifest to those
skilled in the art that various modifications and rearrangements of
the parts may be made without departing from the spirit and scope
of the underlying inventive concept and that the same is not
limited to the particular forms herein shown and described except
insofar as indicated by the scope of the appended claims.
* * * * *