U.S. patent application number 16/144319 was filed with the patent office on 2019-01-24 for materials including thermally reversible gels.
The applicant listed for this patent is Laird Technologies, Inc.. Invention is credited to Karen J. BRUZDA, Jason L. STRADER.
Application Number | 20190023962 16/144319 |
Document ID | / |
Family ID | 61617889 |
Filed Date | 2019-01-24 |
United States Patent
Application |
20190023962 |
Kind Code |
A1 |
BRUZDA; Karen J. ; et
al. |
January 24, 2019 |
Materials Including Thermally Reversible Gels
Abstract
Materials are disclosed that include or are based on thermally
reversible gels, such as thermally reversible gelled fluids, oil
gels and solvent gel resins. In an exemplary embodiment, a material
includes at least one filler in a thermally reversible gel.
Inventors: |
BRUZDA; Karen J.;
(Cleveland, OH) ; STRADER; Jason L.; (Cleveland,
OH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Laird Technologies, Inc. |
Chesterfield |
MO |
US |
|
|
Family ID: |
61617889 |
Appl. No.: |
16/144319 |
Filed: |
September 27, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15714425 |
Sep 25, 2017 |
10087351 |
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16144319 |
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15043808 |
Feb 15, 2016 |
9771508 |
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15714425 |
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12710538 |
Feb 23, 2010 |
9260645 |
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15043808 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 23/4275 20130101;
C09K 5/14 20130101; H01L 2224/29386 20130101; C08L 2205/025
20130101; C08L 91/00 20130101; H01L 24/29 20130101; C08L 2205/03
20130101; H01L 23/00 20130101; C08L 2207/322 20130101; C08L
2203/206 20130101; H01L 2224/29324 20130101; H01L 2224/2919
20130101; H01L 2224/2929 20130101; H01L 23/42 20130101 |
International
Class: |
C09K 5/14 20060101
C09K005/14; C08L 91/00 20060101 C08L091/00; H01L 23/427 20060101
H01L023/427; H01L 23/42 20060101 H01L023/42 |
Claims
1. A material comprising at least one filler in a thermally
reversible gel including block copolymer and process oil, wherein
the material comprises a pad formulated to be compliant against a
surface of a device at room temperature and during operation of the
device.
2. The material of claim 1, wherein the block copolymer comprises
di-block copolymer.
3. The material of claim 1, wherein the block copolymer comprises
di-block styrenic copolymer.
4. The material of claim 1, wherein the block copolymer comprises
di-block and tri-block copolymers.
5. The material of claim 1, wherein the block copolymer comprises
di-block and tri-block styrenic copolymers.
6. The material of claim 1, wherein the block copolymer comprises
di-block copolymer or tri-block copolymer.
7. The material of claim 1, wherein the block copolymer comprises
tri-block copolymer.
8. The material of claim 1, wherein the block copolymer comprises
tri-block styrenic copolymer.
9. The material of claim 1, wherein the block copolymer comprises
styrenic copolymer.
10. The material of claim 1, wherein a ratio of the process oil to
the block copolymer is at least about 4 to 1 but not more than
about 12 to 1.
11. The material of claim 1, wherein a ratio of the process oil to
the block copolymer is not more than about 5 to 1.
12. The material of claim 1, wherein a ratio of the process oil to
the block copolymer is at least about 11 to 1.
13. The material of claim 1, wherein a ratio of the process oil to
the block copolymer is about 4.5 to 1.
14. The material of claim 1, wherein: the material includes the at
least one filler in a total amount that is about 40 percent to
about 99 percent of the material by weight; and/or the material has
a hardness that is at least about 60 Shore 00 but not more than 90
Shore 00; and/or the material is silicone free, such that the
material is usable with no occurrence of silicone migration or
volatility due to the absence of silicone in the formulation;
and/or the process oil is less than or equal to about 43.2 percent
of the material by weight.
15. The material of claim 1, wherein the at least one filler
comprises an electrically-conductive filler.
16. The material of claim 15, wherein the material comprises an
electrically-conductive thermal insulator.
17. The material of claim 1, wherein the at least one filler
comprises an electromagnetic interference (EMI) absorber.
18. The material of claim 17, wherein the material comprises an EMI
absorbing thermal insulator.
19. The material of claim 1, wherein the at least one filler
comprises a thermally-conductive filler.
20. The material of claim 19, wherein the material comprises a
thermal interface material.
21. The material of claim 1, wherein the at least one filler
comprises an electrically-conductive filler, an electromagnetic
interference (EMI) absorber, and/or a thermally-conductive
filler.
22. The material of claim 1, wherein the device includes an
electrical component, and wherein the pad is formulated to be
compliant against a surface of the electrical component at room
temperature and during operation of the electrical component.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 15/714,425 filed Sep. 25, 2017, which
published as US2018/0079946 on Mar. 22, 2018 and which issues as
U.S. Pat. No. 10,087,351 on Oct. 2, 2018.
[0002] U.S. patent application Ser. No. 15/714,425 is a
continuation-in-part of U.S. patent application Ser. No. 15/043,808
filed Feb. 15, 2016, which published as US2016/0160104 on Jun. 9,
2016 and issued as U.S. Pat. No. 9,771,508 on September 26,
2017.
[0003] U.S. Patent Application No. 15/043,808 is a
continuation-in-part of U.S. Patent Application No. 12/710,538
filed February 23, 2010, which published as US2011/0204280 on
August 25, 2011 and issued as U.S. Pat. No. 9,260,645 on Feb. 16,
2016.
[0004] The entire disclosures of the above applications are
incorporated herein by reference in its entirety.
FIELD
[0005] The present disclosure relates generally to materials
including or based on thermally reversible gels, such as thermally
reversible gelled fluid, oil gel and solvent gel resins.
BACKGROUND
[0006] This section provides background information related to the
present disclosure which is not necessarily prior art.
[0007] Electrical components, such as semiconductors, integrated
circuit packages, transistors, etc., typically have pre-designed
temperatures at which the electrical components optimally operate.
Ideally, the pre-designed temperatures approximate the temperature
of the surrounding air. But the operation of electrical components
generates heat. If the heat is not removed, the electrical
components may then operate at temperatures significantly higher
than their normal or desirable operating temperature. Such
excessive temperatures may adversely affect the operating
characteristics of the electrical components and the operation of
the associated device.
[0008] To avoid or at least reduce the adverse operating
characteristics from the heat generation, the heat should be
removed, for example, by conducting the heat from the operating
electrical component to a heat sink. The heat sink may then be
cooled by conventional convection and/or radiation techniques.
During conduction, the heat may pass from the operating electrical
component to the heat sink either by direct surface contact between
the electrical component and heat sink and/or by contact of the
electrical component and heat sink surfaces through an intermediate
medium or thermal interface material. The thermal interface
material may be used to fill the gap between thermal transfer
surfaces, in order to increase thermal transfer efficiency as
compared to having the gap filled with air, which is a relatively
poor thermal conductor. Most especially in the cases of phase
changes and thermal greases, a significant gap is not required and
the purpose of the thermal interface material may be just to fill
in the surface irregularities between contacting surfaces. In some
devices, an electrical insulator may also be placed between the
electronic component and the heat sink, in many cases this is the
thermal interface material itself.
DETAILED DESCRIPTION
[0009] Example embodiments will now be described more fully.
[0010] Many thermal interface materials are based on silicone resin
systems. But in some applications, a silicone-free thermal
interface compliant gap filler is desired, such as for fiber optic
applications, automotive modules, disk drives, plasma display
panels, liquid crystal display panels, etc. Ideally, silicone free
thermal interface materials would not only be silicone free, but
they would also be extremely soft, elastomeric, of reasonable cost,
temperature and atmospherically stable, and free of significant
resin migration. But silicone free thermally-conductive gap fillers
are often based on acrylic, polyurethane, polyolefin, etc. resin
systems, which suffer from the fact that they produce a relatively
hard elastomer, resulting in a non-compliant gap filler. After
recognizing the above, the inventor hereof has developed and now
discloses various exemplary embodiments of silicone-free, compliant
thermal interface materials that include or are based on thermally
reversible gels, such as thermally reversible gelled fluids, oil
gels and solvent gel resins. In addition, the inventor hereof has
also developed and discloses herein other exemplary embodiments of
thermal interface materials that include or are based on thermally
reversible gels, some of which may be silicone-based gels.
Accordingly, while some exemplary embodiments disclosed herein are
entirely or substantially free of silicone, other exemplary
embodiments may include silicone. In the embodiments that are
substantially free of silicone, a thermal interface material may
include a de minimis or trivial amount of silicone, where that
amount of silicone is low enough so as to not adversely affect the
end use applications of the thermal interface material, which might
otherwise be adversely affected by the presence of a more than
trivial amount of silicone. Some embodiments of a thermal interface
material are based on an oil gel resin system and are silicone free
(e.g., entirely silicone free, substantially silicone free),
extremely soft, elastomeric, of reasonable cost, temperature and
atmospherically stable and free of significant resin migration.
[0011] By way of background, the term "gel" as used herein may
generally refer to semi-rigid colloidal dispersion of a solid with
a liquid or gas, as jelly, glue, etc. A "gel" may generally be a
solid, jelly-like material that can have properties ranging from
soft and weak to hard and tough. "Gel" as used herein may be
defined as a substantially dilute elastic or micelle network that
exhibits no flow when in the steady-state. By weight, a gel may be
mostly liquid, yet they behave like solids due to a
three-dimensional network within the liquid. It is the network
within the liquid that gives gel its structure (hardness). With a
gel, a solid three-dimensional network generally spans the volume
of a liquid medium. By way of further background, "a thermally
reversible gel" as used herein refers to a gel that may be heated
to a liquid and cooled to a gel over and over again, such that the
thermally reversible gel may thus be reused, reformed, recycled,
etc. by reheating the gel to a liquid and cooling back to a gel. In
some cases, this transition temperature at which the thermally
reversible gel changes from substantially liquid to a gel may be
below room temperature.
[0012] As recognized by the inventor hereof, thermally reversible
gels, such as thermally reversible gelled fluids, oil gels and
solvent gel resins, are well suited for use as a base for thermal
interface materials. Accordingly, the inventor has disclosed herein
example embodiments of novel thermal interface materials and
methods of making such novel thermal interface materials that
include or are based on thermally reversible gels, such as
thermally reversible gelled fluids, oil gels and solvent gel
resins. The thermal interface materials may also include at least
one thermally conductive filler in the thermally reversible
gel.
[0013] Also, the inventor has recognized that thermally reversible
gels, such as oil gels, may be specifically formulated to soften at
a given temperature. This, in turn, may allow for greater
customization for some of the inventor's exemplary embodiments of
thermal interface materials that are based on oil gel resin systems
as compared to some thermal interface materials based on a silicone
resin system. For example, some of the inventor's exemplary
embodiments provide thermal interface materials based on oil gel
resin systems in which the oil gel has been selected or formulated
such that the thermal interface material begins to soften at a
temperature of about 150 degrees Celsius. In other embodiments, a
thermal interface material may include an oil gel resin system in
which the oil gel is formulated to soften at a temperature higher
or less than 150 degrees Celsius, such as within a temperature from
about 5 degrees Celsius to about 200 degrees Celsius.
[0014] In various exemplary embodiments, thermally conductive
filler is added to oil (or other gellible fluid) and gelling agent
to produce a thermally conductive grease, phase change, putty,
and/or gap filler. By using an oil gel (or other suitable thermally
reversible gel) as the base for a thermal interface material, the
inventor hereof has discovered that it is possible to produce a gap
filler with physical properties comparable to that of traditional
silicone based gap filler yet with no occurrence of silicone
migration or volatility due to the absence of silicone in the
formulation.
[0015] A thermally reversible gel is generally a blend of one or
more oils and/or solvents and one or more gelling agents. The
majority of the blend typically comprises the oil(s) and/or
solvent(s). Suitable oils or other materials for a thermally
reversible gel that may be used in exemplary embodiments of the
present disclosure include naphthenic oils, paraffinic oils,
iso-paraffinic oils, hydrocarbon oils, aromatic oils, paraffinic
solvents, isoparaffinic solvents (e.g., Isopar), naphthenic
solvents, silicone oils, etc., mineral oils, natural oils (such as
soybean oils, coconut oils and ester oils) and synthetic products
(such as polybutene or polyisobutene). Suitable gelling agents that
may be used in exemplary embodiments of the present disclosure
include waxes, fumed silica, fatty acid soaps, thermoplastic
materials (e.g., thermoplastic elastomers, etc.) and polymers
(e.g., block copolymers, etc.). Oil gels are commonly used for air
fresheners, candles, cable fillers, sealants, lubricating greases,
strippable coatings, corrosion protectors, etc. But oil gels have
not been used as a base for thermal interface materials. Exemplary
embodiments of the present disclosure may vary the type and
quantities of the thermally reversible gels included in a thermal
interface material. By way of example, thermal interface materials
disclosed herein may include a wide range of different types and
quantities of thermally reversible gels with a di-block and/or
tri-block copolymer(s) (e.g., di-block styrenic copolymers,
tri-block styrenic copolymers, etc.), oils and/or solvents blended
with elastomers (e.g., thermoplastic elastomers, etc.), gelling
agents, etc. One or more of these above-listed materials may be
selected for various exemplary embodiments of the present
disclosure and then varied to produce particular gels (e.g.,
thermally reversible gelled fluids, oil gel and solvent gel resin,
etc.) with different characteristics for a given thermal interface
material.
[0016] For example, depending on the specific ingredients and
formulation, a resulting oil gel may vary from a cohesive highly
elastic continuous rubber network, to a weak gel, to a grease.
Accordingly, thermal interface materials of the present disclosure
may include any of a wide range of thermally reversible gels, so as
to be configured to provide one or more of thermally conductive gap
fillers, thermally conductive gels, thermally conductive putties,
thermally conductive dispensable materials, and thermally
conductive greases. In various exemplary embodiments, the thermal
interface material may have a hardness less than or equal to about
100 Shore A. Furthermore, some thermal interface materials based on
oil gel may also be formulated to soften at a given temperature
(e.g., at 150 degrees Celsius, etc.), function as phase change
materials, etc.
[0017] In example embodiments of the present disclosure in which
the thermal interface material includes oil gel, the oil gel may
comprise process oil and a gelling agent. Process oils are
typically oils for which one or more key properties are reported
and controlled. Process oils and/or solvents are typically used in
manufacturing to modify the properties of an article, improve the
properties of an article, and/or impart desired properties to a
finished article.
[0018] Example embodiments of thermal interface materials of the
present disclosure may include naphthenic oils and solvents and/or
paraffinic oils and solvents (e.g., isopars, etc.). Temperature
stability of the oil and/or solvent is one example characteristic
to be considered when selecting the oil/solvent for a thermal
interface material of the present disclosure. Because thermal
interface materials may be exposed to varying, and relatively high,
temperatures, in some embodiments a high temperature stable oil
and/or solvent may be desirable.
[0019] Thermal interface materials according to the present
disclosure may use thermoplastic materials (e.g., thermoplastic
elastomers, etc.) for the gelling agent of the oil gel. Suitable
thermoplastic materials include block copolymers, such as di-block
and tri-block polymers (e.g., di-block and tri-block styrenic
polymers, etc.). Some exemplary embodiments of a thermal interface
material include block polymers comprising polystyrene segments and
rubber segments. With di-block polymers, a polystyrene segment is
attached to a rubber segment, while tri-block polymers include
polystyrene segments on both ends of a rubber segment. In oil gels
made with tri-block styrenic polymers, the styrene segments act as
physical crosslinks with the rubber to form a highly elastic
continuous rubber network. Di-block polymers, however, do not form
such physical crosslinks and an oil gel made with di-block polymers
tends to resemble a grease rather than a solid rubber. Di-block and
tri-block polymers may be used alone or together in various
proportions according to the desired characteristics for the
thermal interface material that will include the same. The rubber
is the elastomeric portion of such polymers and may be, for
example, a saturated olefin rubber (such as polyethylene/butylene,
polyethylene/propylene, etc.).
[0020] One or more thermally conductive fillers are added during
processing to create a thermally conductive interface material in
which one or more thermally conductive fillers will be suspended
in, added to, mixed into, etc. the thermally reversible gel. For
example, at least one thermally conductive filler may be added to a
mixture including gellable fluid and gelling agent before the
gellable fluid and gelling agent have gelled or form the thermally
reversible gel. As another example, at least one thermally
conductive filler may be added to the gellable fluid and then
gelling agent may be added to the mixture containing gellable fluid
and thermally conductive filler. In yet another example, at least
one thermally conductive filler may be added to the gelling agent
and then gellable fluid may be added to the mixture containing
gelling agent and thermally conductive filler. By way of further
example, at least one thermally conductive filler may be added
after the gellable fluid and gelling agent have gelled. For
example, at least one thermally conductive filler may be added to
the gel when the gel may be cooled and be loosely networked such
that filler can be added. The amount of thermally conductive filler
in the thermally reversible gel may vary in different embodiments.
By way of example, some exemplary embodiments of a thermal
interface material may include not less than 5 percent but not more
than 98 percent by weight of at least one thermally conductive
filler.
[0021] A wide range of different thermally conductive fillers may
be used in exemplary embodiments of a thermal interface material
according to the present disclosure. In some preferred embodiments,
the thermally conductive fillers have a thermal conductivity of at
least 1 W/mK (Watts per meter-Kelvin) or more, such as a copper
filler having thermally conductivity up to several hundred W/mK,
etc. Suitable thermally conductive fillers include, for example,
zinc oxide, boron nitride, alumina, aluminum, graphite, ceramics,
combinations thereof (e.g., alumina and zinc oxide, etc.). In
addition, exemplary embodiments of a thermal interface material may
also include different grades (e.g., different sizes, different
purities, different shapes, etc.) of the same (or different)
thermally conductive fillers. For example, a thermal interface
material may include two different sizes of boron nitride. By
varying the types and grades of thermally conductive fillers, the
final characteristics of the thermal interface material (e.g.,
thermal conductivity, cost, hardness, etc.) may be varied as
desired.
[0022] Other suitable fillers and/or additives may also be added to
a thermal interface material to achieve various desired outcomes.
Examples of other fillers that may be added include pigments,
plasticizers, process aids, flame retardants, extenders,
electromagnetic interference (EMI) or microwave absorbers,
electrically-conductive fillers, magnetic particles, etc. For
example, tackifying agents, etc. may be added to increase the
tackiness of a thermal interface material, etc.
[0023] As another example, EMI or microwave absorbers,
electrically-conductive fillers, and/or magnetic particles may be
added such that the thermal interface material may be operable or
usable as an EMI and/or RFI shielding material. A wide range of
materials may be added to a thermal interface material according to
exemplary embodiments, such as carbonyl iron, iron silicide, iron
particles, iron-chrome compounds, metallic silver, carbonyl iron
powder, SENDUST (an alloy containing 85% iron, 9.5% silicon and
5.5% aluminum), permalloy (an alloy containing about 20% iron and
80% nickel), ferrites, magnetic alloys, magnetic powders, magnetic
flakes, magnetic particles, nickel-based alloys and powders, chrome
alloys, and any combinations thereof. Other embodiments may include
one or more EMI absorbers formed from one or more of the above
materials where the EMI absorbers comprise one or more of granules,
spheroids, microspheres, ellipsoids, irregular spheroids, strands,
flakes, powder, and/or a combination of any or all of these shapes.
Accordingly, some exemplary embodiments may thus include thermal
interface materials that include or are based on thermally
reversible gels, where the thermal interface materials are also
configured (e.g., include or are loaded with EMI or microwave
absorbers, electrically-conductive fillers, and/or magnetic
particles, etc.) to provide shielding.
[0024] By way of background, EMI absorbers convert electromagnetic
energy into another form of energy through a process commonly
referred to as a loss. Electrical loss mechanisms include
conductivity losses, dielectric losses, and magnetization losses.
Conductivity losses refer to a reduction in EMI resulting from the
conversion of electromagnetic energy into thermal energy. The
electromagnetic energy induces currents that flow within the EMI
absorbers having a finite conductivity. The finite conductivity
results in a portion of the induced current generating heat through
a resistance. Dielectric losses refer to a reduction in EMI
resulting from the conversion of electromagnetic energy into
mechanical displacement of molecules within the EMI absorbers
having a non-unitary relative dielectric constant. Magnetic losses
refer to a reduction in EMI resulting from the conversion of
electromagnetic energy into a realignment of magnetic moments
within the EMI absorbers.
[0025] In some exemplary embodiments, a thermal interface material
may include an adhesive layer. The adhesive layer may be a
thermally conductive adhesive to preserve the overall thermal
conductivity. The adhesive layer may be used to affix the thermal
interface material to an electronic component, heat sink, EMI
shield, etc. The adhesive layer may be formulated using a
pressure-sensitive, thermally-conducting adhesive. The
pressure-sensitive adhesive (PSA) may be generally based on
compounds including acrylic, silicone, rubber, and combinations
thereof. The thermal conductivity is enhanced, for example, by the
inclusion of ceramic powder.
[0026] In some exemplary embodiments, thermal interface materials
including thermally-reversible gel may be attached or affixed
(e.g., adhesively bonded, etc.) to one or more portions of an EMI
shield, such as to a single piece EMI shield and/or to a cover,
lid, frame, or other portion of a multi-piece shield, to a discrete
EMI shielding wall, etc. Alternative affixing methods can also be
used such as, for example, mechanical fasteners. In some
embodiments, a thermal interface material that includes
thermally-reversible gel may be attached to a removable lid or
cover of a multi-piece EMI shield. A thermal interface material
that includes thermally-reversible gel may be placed, for example,
on the inner surface of the cover or lid such that the thermal
interface material will be compressively sandwiched between the EMI
shield and an electronic component over which the EMI shield is
placed. Alternatively, a thermal interface material that includes
thermally-reversible gel may be placed, for example, on the outer
surface of the cover or lid such that the EMI shield is
compressively sandwiched between the EMI shield and a heat sink. A
thermal interface material that includes thermally-reversible gel
may be placed on an entire surface of the cover or lid or on less
than an entire surface. A thermal interface material that includes
thermally-reversible gel may be applied at virtually any location
at which it would be desirable to have an EMI absorber.
[0027] Aspects of the present disclosure will be further
illustrated by the following examples. The following examples are
merely illustrative, and do not limit this disclosure to the
particular formulations in any way.
EXAMPLES
Example 1
[0028] In this example, a thermal interface material (specifically
a thermally-conductive gap filler) including one or more aspects of
the present disclosure was generally formed from di-block and
tri-block styrenic copolymers, a paraffinic oil, and thermally
conductive fillers.
[0029] In this example thermal interface material, the oil is about
14.1 percent of the thermal interface material by weight, the
di-block styrenic copolymer is about 4.2 percent of the thermal
interface material by weight, the tri-block styrenic copolymer is
about 1.1 percent of the thermal interface material by weight, and
the thermally conductive fillers are about 80.2 percent of the
thermal interface material by weight. The thermal interface
material also includes an antioxidant that is about 0.1 percent of
the thermal interface material by weight and pigment that is about
0.4 percent of the thermal interface material by weight.
[0030] The tri-block styrenic copolymer used in this example
formulation includes polyethylene/butylene as the elastomeric (or
rubber) portion. The structure is predominantly tri-block and has a
styrene to rubber ratio of 29 to 71. The copolymer has a medium
molecular weight and a glass transition temperature of -55.degree.
C.
[0031] The di-block styrenic copolymer used in this example
formulation includes polyethylene/propylene as the elastomeric (or
rubber) portion. The structure is predominantly di-block and has a
styrene to rubber ratio of 37 to 63. The copolymer has a high
molecular weight and a glass transition temperature of -55.degree.
C.
[0032] For this example formulation, the thermally conductive
filler included two different grades of alumina. The first grade of
alumina is ground aluminum oxide with mean particle size of 2
microns and is about 15.6 percent of the thermal interface material
by weight. The second grade of alumina is a generally spherical
aluminum oxide with a mean particle size of 30 microns and is about
64.3 percent of the thermal interface material by weight.
[0033] This example thermal interface material exhibited a thermal
conductivity of 0.9 W/mK (as measured according to the Hot Disk
method). The thermal interface material exhibited a hardness of
about 48 Shore 00 (three seconds, as measured according to ASTM
standard D2240-00).
[0034] An exemplary process will now be described, which may be
used for preparing a thermal interface material consistent with
this Example 1. Alternative processes, however, may also be
employed for making a thermal interface material. In this example,
the oil, the di-block styrenic copolymer, the tri-block styrenic
copolymer, pigment and antioxidant may be mixed together to get a
homogenized mixture. The mixture may then be heated to soften the
polystyrene segments of the di-block styrenic copolymer and the
tri-block styrenic copolymer, freeing them to move with shear. The
mixture may then be maintained at about 150.degree. C. for two to
three hours with mixing until the mixture achieves a smooth
consistency. The thermally conductive fillers may then be added to
the mixture, resulting in a mixture having the consistency of wet
sand. The mixture may then be cooled to a rubber consistency.
Rather than immediately adding the thermally conductive fillers,
the thermally conductive fillers may be added later. For example,
the homogenized mixture or resin may be cooled and stored before
any thermally conductive fillers are added. After a time, the
homogenized mixture or resin may be re-heated and then the
thermally conductive fillers may be added. After which, the mixture
including the thermally conductive fillers is cooled to a rubber
consistency.
[0035] After the mixture with the thermally conductive fillers
therein is cooled to a rubber consistency and while warm, the
mixture may then be processed for use as a thermal interface
material. In this Example 1, the warm mixture may be formed, etc.
into sheets of material with release liners (e.g., for protection
of the formed thermal interface material during cutting, shipping,
etc.) added to both sides of the sheets for final distribution.
Alternatively, it should be appreciated that the warm mixture could
be allowed to cool (by suitable cooling operations) after the
fillers are added, stored for later use, and then subsequently
re-warmed to be processed into thermal interface materials. The
mixture may be formed into a thermal interface material sheet by
calendaring the mixture between two liner sheets. The nip (or gap)
between a series of heated rollers may be set to the desired
thickness of the final thermal interface material. The mixture may
then be run through the rollers to form a pad with a thickness as
determined by the gap between the rollers. Simultaneously, liner
sheets may be run through the rollers on either side of the
mixture/thermal interface material resulting in a finished thermal
interface material that includes release liners on both sides of
the thermal interface material. The release liners may be any
suitable release liner, for example, Mylar liners. Alternatively,
the release liner may only be located on one side of the thermal
interface material, or there may be no release liner applied to the
thermal interface material.
[0036] In some other exemplary embodiments such as those in which
the thermally-reversible gel is of very low hardness or grease-like
at room temperature (or a cooled state), the gel might not have to
be heated to add the filler. Instead, the room-temperature or cool
gel may be of low enough viscosity that the gel does not need to be
liquefied by heat to add filler. The gel may be substantially
liquid enough at room temperature or even in a cooled state to
allow for the addition of one or more fillers to the gel.
[0037] A thermal interface material may also be molded, such as by
injection molding, instead of being calendared. Injection molding
may permit three dimensionally shaped thermal interface materials
to be created.
[0038] After the thermal interface material sheet has been
calendared, it is ready for use or further processing. The
completed thermal interface material sheet may be further processed
in a manner similar to other thermal interface materials. For
example, the thermal interface material sheet may be cut into
smaller sheets, die-cut into specific shapes, laser cut, etc.
[0039] Thermal interface materials according to the present
disclosure may be reused/reformed/recycled/etc. by reheating the
material, which is unlike for example, various known thermal
interface materials that are not based on thermally reversible
gels. Accordingly, a thermal interface material based on a
thermally reversible gel may be reheated and reprocessed (e.g.,
reshaped, re-sized, etc.) in the manner described above.
Example 2
[0040] In this example, a thermal interface material including one
or more aspects of the present disclosure was generally formed from
a di-block styrenic copolymer, a tri-block and di-block styrenic
copolymer blend, paraffinic oil, and thermally conductive
fillers.
[0041] In this example thermal interface material, the oil is about
13.5 percent of the thermal interface material by weight, the
di-block styrenic copolymer is about 1.7 percent of the thermal
interface material by weight, the di-block/tri-block copolymer
blend is about 3.4 percent of the thermal interface material by
weight, and the thermally conductive fillers are about 81 percent
of the thermal interface material by weight. The thermal interface
material also includes an antioxidant that is about 0.1 percent of
the thermal interface material by weight and pigment that is about
0.3 percent of the thermal interface material by weight.
[0042] The di-block styrenic copolymer used in this example
formulation includes polyethylene/propylene as the elastomeric (or
rubber) portion. The structure is predominantly di-block and has a
styrene to rubber ratio of 37 to 63. The copolymer has a high
molecular weight and a glass transition temperature of -55.degree.
C.
[0043] The di-block/tri-block styrenic copolymer blend used in this
example formulation includes polyethylene/butylene as the
elastomeric (or rubber) portion. The blend is 30 percent tri-block
and 70 percent di-block and has a styrene to rubber ratio of 30 to
70. The copolymer blend has a low molecular weight and a glass
transition temperature of -55.degree. C.
[0044] For this example formulation, the thermally conductive
filler included two different thermally conductive fillers. The
first thermally conductive filler is a ground alumina tri-hydrate
(ATH) with mean particle size of 20 microns and is about 72.5
percent of the thermal interface material by weight. The second
thermally conductive filler is a fine zinc oxide (ZnO) with a mean
particle size of 0.3 microns and is about 8.5 percent of the
thermal interface material by weight.
[0045] The thermal interface material of this example may be
prepared and processed as described above in regard to Example
1.
[0046] This example thermal interface material exhibited a thermal
conductivity of 1.53 W/mK (as measured according to the Hot Disk
method). The thermal interface material exhibited a hardness of
about 75 Shore 00 (three seconds, as measured according to ASTM
standard D2240-00).
Example 3
[0047] In this example, a thermal interface material including one
or more aspects of the present disclosure was generally formed from
a di-block styrenic copolymer, a tri-block styrenic copolymer,
paraffinic oil, and boron nitride fillers.
[0048] In this example thermal interface material, the oil is about
43.2 percent of the thermal interface material by weight, the
di-block styrenic copolymer is about 2.9 percent of the thermal
interface material by weight, the tri-block copolymer is about 6.7
percent of the thermal interface material by weight, and the
thermally conductive filler is about 46.1 percent of the thermal
interface material by weight. The thermal interface material also
includes an antioxidant that is about 0.2 percent of the thermal
interface material by weight and pigment that is about 1 percent of
the thermal interface material by weight.
[0049] The tri-block styrenic copolymer used in this example
formulation includes polyethylene/butylene as the elastomeric (or
rubber) portion. The structure is predominantly tri-block and has a
styrene to rubber ratio of 29 to 71. The copolymer has a medium
molecular weight and a glass transition temperature of -55.degree.
C.
[0050] The di-block styrenic copolymer used in this example
formulation includes polyethylene/propylene as the elastomeric (or
rubber) portion. The structure is predominantly di-block and has a
styrene to rubber ratio of 37 to 63. The copolymer has a high
molecular weight and a glass transition temperature of -55.degree.
C.
[0051] For this example formulation, the thermally conductive
filler included boron nitride with a mean particle size of 125
microns.
[0052] The thermal interface material of this example may be
prepared and processed as described above in Example 1.
[0053] This example thermal interface material exhibited a thermal
conductivity of 2.7 W/mK (as measured according to the Hot Disk
method). The thermal interface material exhibited a hardness of
about 80 Shore 00 (three seconds, as measured according to ASTM
standard D2240-00).
Example 4
[0054] In this example, a thermal interface material (specifically
thermal grease) including one or more aspects of the present
disclosure was generally formed from a di-block styrenic copolymer,
paraffinic oil, and a boron nitride filler.
[0055] In this example thermal interface material, the oil is about
51.3 percent of the thermal grease by weight, the di-block styrenic
copolymer is about 33.3 percent of the thermal grease by weight,
and the thermally conductive filler is about 15.4 percent of the
thermal grease by weight.
[0056] The di-block styrenic copolymer used in this example
formulation includes polyethylene/propylene as the elastomeric (or
rubber) portion. The structure is predominantly di-block and has a
styrene to rubber ratio of 37 to 63. The copolymer has a high
molecular weight and a glass transition temperature of -55.degree.
C.
[0057] For this example formulation, the thermally conductive
filler included boron nitride with a mean particle size of 210
microns.
[0058] This example thermal grease exhibited a thermal conductivity
of 0.8 W/mK (as measured according to the Hot Disk method). As this
example thermal interface material is a grease, it has no
measureable hardness.
Example 5
[0059] In this example, a thermal interface material including one
or more aspects of the present disclosure was generally formed from
a di-block styrenic copolymer, a tri-block styrenic copolymer,
paraffinic oil, and a boron nitride filler.
[0060] In this example thermal interface material, the oil is about
42.4 percent of the thermal interface material by weight, the
di-block styrenic copolymer is about 2.8 percent of the thermal
interface material by weight, the tri-block copolymer is about 6.6
percent of the thermal interface material by weight, and the
thermally conductive filler is about 47.1 percent of the thermal
interface material by weight. The thermal interface material also
includes an antioxidant that is about 0.2 percent of the thermal
interface material by weight and pigment that is about 0.9 percent
of the thermal interface material by weight.
[0061] The tri-block styrenic copolymer used in this example
formulation includes polyethylene/butylene as the elastomeric (or
rubber) portion. The structure is predominantly tri-block and has a
styrene to rubber ratio of 29 to 71. The copolymer has a medium
molecular weight and a glass transition temperature of -55.degree.
C.
[0062] The di-block styrenic copolymer used in this example
formulation includes polyethylene/propylene as the elastomeric (or
rubber) portion. The structure is predominantly di-block and has a
styrene to rubber ratio of 37 to 63. The copolymer has a high
molecular weight and a glass transition temperature of -55.degree.
C.
[0063] For this example formulation, the thermally conductive
filler included boron nitride with a mean particle size of 125
microns.
[0064] The thermal interface material of this example may be
prepared and processed as described above in Example 1.
[0065] This example thermal interface material exhibited a thermal
conductivity of 3.37 W/mK (as measured according to the Hot Disk
method). The thermal interface material exhibited a hardness of
about 88 Shore 00 (three seconds, as measured according to ASTM
standard D2240-00).
Example 6
[0066] In this example, a thermal interface material including one
or more aspects of the present disclosure was generally formed from
a di-block styrenic copolymer, a tri-block/di-block styrenic
copolymer blend, paraffinic oil, and thermally conductive
fillers.
[0067] In this example thermal interface material, the oil is about
42.5 percent of the thermal interface material by weight, the
di-block styrenic copolymer is about 5.3 percent of the thermal
interface material by weight, the di-block/tri-block copolymer
blend is about 10.6 percent of the thermal interface material by
weight, and the thermally conductive fillers are about 40.3 percent
of the thermal interface material by weight. The thermal interface
material also includes an antioxidant that is about 0.2 percent of
the thermal interface material by weight and pigment that is about
1.1 percent of the thermal interface material by weight.
[0068] The di-block styrenic copolymer used in this example
formulation includes polyethylene/propylene as the elastomeric (or
rubber) portion. The structure is predominantly di-block and has a
styrene to rubber ratio of 37 to 63. The copolymer has a high
molecular weight and a glass transition temperature of -55.degree.
C.
[0069] The di-block/tri-block styrenic copolymer blend used in this
example formulation includes polyethylene/butylene as the
elastomeric (or rubber) portion. The blend is 30 percent tri-block
and 70 percent di-block and has a styrene to rubber ratio of 30 to
70. The copolymer blend has a low molecular weight and a glass
transition temperature of -55.degree. C.
[0070] For this example formulation, the thermally conductive
fillers include two different thermally conductive fillers. The
first thermally conductive filler is aluminum (Al) with a mean
particle size of 5 microns and is about 27.6 percent of the thermal
interface material by weight. The second thermally conductive
filler is zinc oxide (ZnO) with a mean particle size of 0.3 microns
and is about 12.7 percent of the thermal interface material by
weight.
[0071] The thermal interface material of this example may be
prepared and processed as described above in Example 1.
[0072] This example thermal interface material exhibited a thermal
conductivity of 0.3 W/mK (as measured according to the Hot Disk
method). The thermal interface material exhibited a hardness of
about 28 Shore 00 (three seconds, as measured according to ASTM
standard D2240-00).
[0073] In exemplary embodiments, a material (e.g., a thermal
interface material, an electrically-conductive thermal insulator,
an EMI absorbing thermal insulator, etc.) includes at least one
filler (e.g., a thermally-conductive filler, an
electrically-conductive filler, an electromagnetic interference
(EMI) absorber, etc.) in a thermally reversible gel including
di-block and tri-block styrenic copolymers and process oil. A ratio
of the process oil to the di-block and tri-block styrenic
copolymers may be within a range from 4 to 1 (4:1) to 12 to 1
(12:1). Stated differently, the ratio of the process oil to the
di-block and tri-block styrenic copolymers is at least 4 to 1 but
not more than 12 to 1. For example, the ratio of process oil to the
di-block and tri-block styrenic copolymers may be about 4:1, 4.3:1,
4.4:1, 4.5:1, 4.6:1, 11:1, 11.1:1, 12:1, or other ratio between 4:1
to 12:1. In some exemplary embodiments, the ratio of the process
oil to the di-block and tri-block styrenic copolymers may be at
least 4:1 but not more than 5:1 or at least 11:1 but not more
12:1.
[0074] In some exemplary embodiments, the at least one filler
comprises an electrically-conductive filler. And, the material
comprises an electrically-conductive thermal insulator.
[0075] In some exemplary embodiments, the at least one filler
comprises an electromagnetic interference (EMI) absorber. And, the
material comprises an EMI absorbing thermal insulator.
[0076] In some exemplary embodiments, the at least one filler
comprises a thermally-conductive filler. And, the material
comprises a thermal interface material.
[0077] In some exemplary embodiments, the at least one filler
comprises an electrically-conductive filler, an electromagnetic
interference (EMI) absorber, and/or a thermally-conductive filler.
For example, the filler may comprise an electrically-conductive
filler, an electromagnetic interference (EMI) absorber, and a
thermally-conductive filler. Alternatively, the filler may comprise
only one an electrically-conductive filler, an electromagnetic
interference (EMI) absorber, or a thermally-conductive filler. As
yet another example, the filler may comprise any combination of an
electrically-conductive filler, an electromagnetic interference
(EMI) absorber, and/or a thermally-conductive filler.
[0078] The ratio of di-block styrenic copolymer to tri-block
styrenic copolymer may be at least about 0.85 to 1 (0.85:1) but not
more than 1.6 to 1 (1.6:1). For example, the ratio of di-block
styrenic copolymer to tri-block styrenic copolymer may be about
0.85:1, 1:1, 1.2:1, 1:5.1, 1.6:1, or other ratio between 0.85:1 and
1.6:1. In some exemplary embodiments, the ratio of di-block
styrenic copolymer to tri-block styrenic copolymer may be at least
1:1 but not more than 1.6:1.
[0079] The material may include at least one or more fillers and/or
additives (e.g., an electrically-conductive filler, an
electromagnetic interference (EMI) absorber, a thermally-conductive
filler, etc.) in a total amount less than or equal to about 99
percent of the material by weight. For example, the material may
include at least one or more fillers and/or additives in a total
amount that is about 40 percent to about 99 percent of the material
by weight (e.g., 47%, 48%, 94%, 95%, 96% by weight, etc.).
[0080] The material may have a hardness less than or equal to about
90 Shore 00 (three seconds, as measured according to ASTM standard
D2240-00). For example, the material may have a hardness within a
range from about 60 to about 90 Shore 00 (three seconds, as
measured according to ASTM standard D2240-00), such as a hardness
of 72, 80, 81, 85, etc.
[0081] In an exemplary embodiment, the ratio of the process oil to
the di-block and tri-block styrenic copolymers may be about 4.5 to
1. The ratio of the di-block styrenic copolymer to the tri-block
styrenic copolymer may be about 1.5 to 1. The material (e.g., a
thermal interface material, an electrically-conductive thermal
insulator, an EMI absorbing thermal insulator, etc.) may include at
least one or more fillers and/or additives (e.g., a
thermally-conductive filler, an electrically-conductive filler, an
EMI absorber, etc.) in a total amount of about 94 or 95 percent of
the material by weight. The material may have a hardness of about
85 Shore 00 (three seconds, as measured according to ASTM standard
D2240-00).
[0082] In another exemplary embodiment, the ratio of the process
oil to the di-block and tri-block styrenic copolymers may be about
11 or 11.1 to 1. The ratio of the di-block styrenic copolymer to
the tri-block styrenic copolymer may be about 1.5 or 1.6 to 1. The
material (e.g., a thermal interface material, an
electrically-conductive thermal insulator, an EMI absorbing thermal
insulator, etc.) may include at least one or more fillers and/or
additives (e.g., a thermally-conductive filler, an
electrically-conductive filler, an EMI absorber, etc.) in a total
amount of about 94 or 95 percent of the material by weight. The
material may have a hardness of about 72 Shore 00 (three seconds,
as measured according to ASTM standard D2240-00).
[0083] In a further exemplary embodiment, the ratio of the process
oil to the di-block and tri-block styrenic copolymers may be about
4.5 to 1. The ratio of the di-block styrenic copolymer to the
tri-block styrenic copolymer may be about 1.2 to 1. The material
(e.g., a thermal interface material, an electrically-conductive
thermal insulator, an EMI absorbing thermal insulator, etc.) may
include at least one or more fillers and/or additives (e.g., a
thermally-conductive filler, an electrically-conductive filler, an
EMI absorber, etc.) in a total amount of about 47 or 48 percent of
the material by weight. The material may have a hardness of about
80 Shore 00 (three seconds, as measured according to ASTM standard
D2240-00).
[0084] In yet another exemplary embodiment, the ratio of the
process oil to the di-block and tri-block styrenic copolymers may
be about 4.3 or 4.4 to 1. The ratio of the di-block styrenic
copolymer to the tri-block styrenic copolymer may be about 1 to 1.
The material (e.g., a thermal interface material, an
electrically-conductive thermal insulator, an EMI absorbing thermal
insulator, etc.) may include at least one or more fillers and/or
additives (e.g., a thermally-conductive filler, an
electrically-conductive filler, an EMI absorber, etc.) in a total
amount of about 95 or 96 percent of the material by weight. The
material may have a hardness of about 81 Shore 00 (three seconds,
as measured according to ASTM standard D2240-00).
[0085] In exemplary embodiments, a material (e.g., a thermal
interface material, an electrically-conductive thermal insulator,
an EMI absorbing thermal insulator, etc.) includes at least one
filler (e.g., a thermally-conductive filler, an
electrically-conductive filler, an EMI absorber, etc.) in a
thermally reversible gel including di-block and tri-block styrenic
copolymers and process oil. The material may have a hardness less
than or equal to about 88 Shore 00 (three seconds, as measured
according to ASTM standard D2240-00). The process oil may be less
than or equal to about 43.2 percent of the material by weight. The
di-block styrenic copolymer may be less than or equal to about 5.3
percent of the material by weight. The material may further include
at least one filler that is less than or equal to about 98 percent
of the material by weight. The material may also include a di-block
and tri-block styrenic copolymer blend that is less than or equal
to about 10.6 percent of the material by weight. Or, the material
may include tri-block styrenic copolymer that is less than or equal
to about 6.7 percent of the material by weight.
[0086] In an exemplary embodiment, the material has a hardness
within a range from 28 Shore 00 to 88 Shore 00 (three seconds, as
measured according to ASTM standard D2240-00). The process oil
(e.g., paraffinic oil, etc.) is about 13.5 percent to about 43.2
percent of the material by weight. The di-block styrenic copolymer
is about 1.7 percent to about 5.3 percent of the material by
weight. The at least one filler is about 40.3 percent to about 81
percent of the material by weight. The material also includes the
di-block and tri-block styrenic copolymer blend that is about 3.4
percent to about 10.6 percent of the material by weight, or the
tri-block styrenic copolymer that is about 1.1 percent to about 6.7
percent of the material by weight.
[0087] In some exemplary embodiments, the material may comprise a
thermally-conductive gap filler that is soft at room temperature
and that is operable for allowing heat generated by an operating
electrical component to pass through the gap filler. The material
may be free of silicone. The material may be compliant, soft at
room temperature, and operable for filling a gap between thermal
transfer surfaces to thereby allow heat generated by an operating
electrical component to pass from one of the thermal transfer
surfaces through the material to the other one of the thermal
transfer surfaces. The material may be formulated to soften at a
temperature of about 150 degrees Celsius. The at least one filler
may comprise one or more of boron nitride, alumina, aluminum,
graphite, copper, and combinations thereof. The material may
include not less than 5 percent but not more than 98 percent by
weight of the at least one thermally conductive filler.
[0088] The above described example formulations illustrate the
variability and adaptability of materials based on thermally
reversible gels. The example formulations described above
illustrate that those example materials exhibit a wide range of
characteristics. For example, the hardness of the final material
may range from a grease (Example 4) to a hardness of 88 shore 00
(Example 5). The thermal conductivity may range from 0.3 W/mK
(Example 6) to 3.37 W/mK (Example 5) in exemplary embodiments in
which the material comprises a thermal interface material. It can
be seen that by varying the type and percentages of the oil,
gelling agent, and/or fillers, various materials having different
characteristics (e.g., higher or lower thermal conductivities,
higher or lower hardness ratings, etc.) may be created. It should
be appreciated that numerical values and particular formulations
are provided in these examples, and in this disclosure, for
illustrative purposes only. The particular values and formulations
provided are not intended to limit the scope of the present
disclosure.
[0089] Example embodiments are provided so that this disclosure
will be thorough, and will fully convey the scope to those who are
skilled in the art. Numerous specific details are set forth such as
examples of specific components, devices, and methods, to provide a
thorough understanding of embodiments of the present disclosure. It
will be apparent to those skilled in the art that specific details
need not be employed, that example embodiments may be embodied in
many different forms and that neither should be construed to limit
the scope of the disclosure. In some example embodiments,
well-known processes, well-known device structures, and well-known
technologies are not described in detail.
[0090] The terminology used herein is for the purpose of describing
particular example embodiments only and is not intended to be
limiting. As used herein, the term "and/or" includes any and all
combinations of one or more of the associated listed items. Also as
used herein, the singular forms "a", "an" and "the" may be intended
to include the plural forms as well, unless the context clearly
indicates otherwise. The terms "comprises," "comprising,"
"including," and "having," are inclusive and therefore specify the
presence of stated features, integers, steps, operations, elements,
and/or components, but do not preclude the presence or addition of
one or more other features, integers, steps, operations, elements,
components, and/or groups thereof. The method steps, processes, and
operations described herein are not to be construed as necessarily
requiring their performance in the particular order discussed or
illustrated, unless specifically identified as an order of
performance. It is also to be understood that additional or
alternative steps may be employed.
[0091] When an element or layer is referred to as being "on",
"engaged to", "connected to" or "coupled to" another element or
layer, it may be directly on, engaged, connected or coupled to the
other element or layer, or intervening elements or layers may be
present. In contrast, when an element is referred to as being
"directly on," "directly engaged to", "directly connected to" or
"directly coupled to" another element or layer, there may be no
intervening elements or layers present. Other words used to
describe the relationship between elements should be interpreted in
a like fashion (e.g., "between" versus "directly between,"
"adjacent" versus "directly adjacent," etc.). As used herein, the
term "and/or" includes any and all combinations of one or more of
the associated listed items.
[0092] Although the terms first, second, third, etc. may be used
herein to describe various elements, components, regions, layers
and/or sections, these elements, components, regions, layers and/or
sections should not be limited by these terms. These terms may be
only used to distinguish one element, component, region, layer or
section from another region, layer or section. Terms such as
"first," "second," and other numerical terms, "next," etc., when
used herein, do not imply a sequence or order unless clearly
indicated by the context. Thus, a first element, component, region,
layer or section discussed below could be termed a second element,
component, region, layer or section without departing from the
teachings of the example embodiments.
[0093] Spatially relative terms, such as "inner," "outer,"
"beneath", "below", "lower", "above", "upper" and the like, may be
used herein for ease of description to describe one element or
feature's relationship to another element(s) or feature(s) as
illustrated in the figures. Spatially relative terms may be
intended to encompass different orientations of the device in use
or operation in addition to the orientation depicted in the
figures. For example, if the device in the figures is turned over,
elements described as "below" or "beneath" other elements or
features would then be oriented "above" the other elements or
features. Thus, the example term "below" can encompass both an
orientation of above and below. The device may be otherwise
oriented (rotated 90 degrees or at other orientations) and the
spatially relative descriptors used herein interpreted
accordingly.
[0094] The disclosure herein of particular values and particular
ranges of values for given parameters are not exclusive of other
values and ranges of values that may be useful in one or more of
the examples disclosed herein. Moreover, it is envisioned that any
two particular values for a specific parameter stated herein may
define the endpoints of a range of values that may be suitable for
the given parameter (i.e., the disclosure of a first value and a
second value for a given parameter can be interpreted as disclosing
that any value between the first and second values could also be
employed for the given parameter). Similarly, it is envisioned that
disclosure of two or more ranges of values for a parameter (whether
such ranges are nested, overlapping or distinct) subsume all
possible combination of ranges for the value that might be claimed
using endpoints of the disclosed ranges.
[0095] The foregoing description of the embodiments has been
provided for purposes of illustration and description. It is not
intended to be exhaustive or to limit the invention. Individual
elements or features of a particular embodiment are generally not
limited to that particular embodiment, but, where applicable, are
interchangeable and can be used in a selected embodiment, even if
not specifically shown or described. The same may also be varied in
many ways. Such variations are not to be regarded as a departure
from the invention, and all such modifications are intended to be
included within the scope of the invention.
* * * * *