U.S. patent application number 11/101372 was filed with the patent office on 2006-01-19 for thermal management system and computer arrangement.
Invention is credited to Viktor Frul.
Application Number | 20060011336 11/101372 |
Document ID | / |
Family ID | 35463336 |
Filed Date | 2006-01-19 |
United States Patent
Application |
20060011336 |
Kind Code |
A1 |
Frul; Viktor |
January 19, 2006 |
Thermal management system and computer arrangement
Abstract
It is the object of the present invention to provide a low
weight, compact, low vertical profile thermal management system for
removing heat from electronic components. The thermal management
system comprises of a plurality of "flow-through" type cooling
devices, a source of filtered pressurized fluid suitable for use as
a coolant, and a fluid delivering device that supplies the cooling
devices with fluid. A preferred fluid is air, such as a filtered
pressurized air. The cooling device is comprised of a high
conductivity metal matrix composite heat spreader, a miniature heat
sink, preferably of the same material, a permeable heat exchanger
with high specific surface, and a closure that provides structural
integrity of the cooling device.
Inventors: |
Frul; Viktor; (N. Attleboro,
MA) |
Correspondence
Address: |
ELMORE PATENT LAW GROUP, PC
209 MAIN STREET
N. CHELMSFORD
MA
01863
US
|
Family ID: |
35463336 |
Appl. No.: |
11/101372 |
Filed: |
April 7, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60591254 |
Jul 26, 2004 |
|
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60560382 |
Apr 7, 2004 |
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Current U.S.
Class: |
165/185 ;
165/80.2; 257/E23.099; 257/E23.112; 75/247 |
Current CPC
Class: |
H01L 2224/32225
20130101; H01L 2924/3011 20130101; B22F 2998/00 20130101; F28F
21/02 20130101; F28F 3/12 20130101; H01L 23/467 20130101; B22F
7/006 20130101; F28F 13/003 20130101; C22C 2204/00 20130101; H01L
23/3733 20130101; B22F 2998/00 20130101 |
Class at
Publication: |
165/185 ;
075/247; 165/080.2 |
International
Class: |
F28F 7/00 20060101
F28F007/00; B22F 9/00 20060101 B22F009/00; C22C 5/00 20060101
C22C005/00 |
Claims
1. A thermal heat management system comprising flow-through cooling
device, a source of filtered pressurized air and a closure that
provides structural integrity of the cooling device.
2. The thermal heat management system of claim 1 further comprising
a heat spreader, a heat sink, a substrate and a permeable heat
exchanger.
3. A thermal heat management system for removing heat from
electronic components comprising: a) a plurality of flow-through
type cooling devices; b) a source of pressurized air; and c) an air
delivering device wherein the cooling device of (a) further
comprises a heat spreader, a heat sink, a substrate and a heat
exchanger.
4. The thermal heat management system of claim 3, wherein the
source of pressurized air of (b) is filtered.
5. The thermal heat management system of claim 3, wherein the heat
exchanger is permeable.
6. The thermal heat management system of claim 3, wherein the heat
spreader is metal matrix.
7. The thermal heat management system of claim 6, wherein the metal
matrix possesses high conductivity.
8. The thermal heat management system of claim 6, wherein the heat
spreader is a microcomposite heat spreader.
9. The heat spreader of claim 8, wherein the thermal conductivity
and the CTE are isotropic.
10. The thermal heat management system of claim 6, wherein the heat
spreader is a macrocomposite heat spreader.
11. The thermal heat management system of claim 3, wherein the heat
spreader is made of material selected from the group consisting of
graphite foams, metal foams, ceramic foams, graphic fabrics, porous
metals and nanotubes.
12. The thermal heat management system of claim 3, wherein the heat
sink is ceramic.
13. The thermal heat management system of claim 3, wherein the heat
sink is made of the same material as the heat spreader.
14. The thermal heat management system of claim 3, wherein the
substrate has a thermal expansion coefficient compatible with
semiconductor materials.
15. The thermal heat management system of claim 14, wherein the
substrate is ceramic.
16. The thermal heat management system of claim 3, wherein the
substrate is a metal matrix composite.
17. The thermal heat management system of claim 16, wherein the
metal matrix composite possess high thermal conductivity.
18. The thermal heat management system of claim 3, wherein the heat
exchanger is permeable.
19. The heat exchanger of claim 18 having a high specific surface
area.
20. The heat exchanger of claim 18 further comprising a high
thermal conductivity.
21. The heat exchanger of claim 18 further comprising porosity in
range of about 50 to about 60 percent.
22. The heat exchanger of claim 18 further comprising graphite
foams, metal foams, ceramic foams, graphic fabrics, and porous
metals.
23. The heat exchanger of claim 18 further comprising carbon
nanotubes.
24. The heat exchanger of claim 3, wherein the heat exchanger is a
labyrinth type heat exchanger.
25. The labyrinth type heat exchanger of claim 24, wherein the heat
exchange is branched.
26. A method of producing an integrated cooling system comprising
forming a silicon die integrated metallurgically into the
flow-through cooling structure to form a single whole thermally
uninterrupted body.
Description
RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/591,254, filed on Jul. 26, 2004 and U.S.
Provisional Application No. 60/560,382, filed on Apr. 7, 2004. The
entire teachings of the above applications are incorporated herein
by reference.
FIELD OF INVENTION
[0002] The present invention relates to a thermal management
system, especially electronics cooling and computer arrangement,
and more particularly, to high performance electronics thermal
management device that achieves high heat dissipation rates and
provides a compact arrangement in which the electronic components
are disposed with maximized space and weight efficiency.
BACKGROUND OF THE INVENTION
[0003] High power electronic components continue to have an
increasing demand for higher power dissipating waste heat generated
during computer operating within a relatively confined space. A
major thermal management challenge is to adjust the constantly
increasing heat emission from the electronic components to the
constantly reducing weight and size of the computer arrangement.
Conventionally used electronics cooling materials and technologies
often become beyond of demands of modern computer idea. The further
computer miniaturization requires the development of fundamentally
new thermal management technologies and materials able to meet a
combined requirement of high thermal conductivity, miniature
performance, high heat dissipating rate, and low cost.
[0004] A variety of thermal management techniques are known in the
prior art. In general, the thermal management cycle for electronics
comprises two phases: the heat removal phase and heat dissipation
phase. The heat removal stage can be performed by the following
heat transfer methods:
[0005] a conductive heat transfer in solids
[0006] a convection heat transfer in fluids
[0007] a mixed phase change--convection heat transfer
[0008] a heat transfer accompanied thermal electric effects
[0009] These heat removal methods are used in the prior art and
provided with the corresponding design embodiments such as
solid-state high conductivity heat spreaders (often coupled with
heat sink), close-loop circulation systems for fluids, phase change
heat pipes, and thermal electrical cooling devices. The purpose for
all of the above listed heat removal methods is the dislocation of
the heat energy from a heat emitting component to a heat
dissipating device, which mostly is an air cooled heat sink.
Functional and designing division onto the heat removal and heat
dissipating parts becomes typical for the modern computer
architecture because the currently used cooling material and
technologies can no longer manage the increased heat flux being
coupled in one thermal management device. Commonly used heat pipes
in notebooks, heat spreaders, and recently developed liquid cooling
system are examples of such a functional dividing.
[0010] Unfortunately, the currently used solutions are not free
from the drawbacks. The solid-state conductivity heat removal
devices are heavy and their thermal conductivity often is beyond of
what is required. Another disadvantage of the commonly used
aluminum and cooper heat spreaders is the CTE mismatch with CTEs of
semiconductor materials by the factor 2-3. The liquid cooling
close-loop systems are heavy, roomy, and expensive in
manufacturing. Heat pipes are often bulky and fragile.
Thermoelectric cooling devices are heavy and bulky; their energy
consumption is in a range that puts them outside of battery-driven
applications.
[0011] The finned heat sinks are the most usable heat dissipating
devices in computers. FIGS. 1, 2A and 2B illustrates a prior art
device. Typically, heat sink 10 includes a plurality of fins 12
that extend outward from the plate 11. Thus, air flow 14 from the
fan (not shown) flows over and between the fins 12 and cools the
individual components. An electronic device 15 disposed on the
ceramic substrate 16 are mounted on the plate 11 of heat sink 10
through an interface material 13. Distribution of air streams
within the finned structure is uneven due to turbulent nature of
air flow and formation of the flow stagnation areas. Areas
adjusting to plate 11 tend to form air trapped zones 17, which
prevent the air circulation and heat exchange. As air is a very low
thermal conductivity substance, the stagnation and trapping areas
prevent heat removal from the plate 11, which is the hottest part
of heat sink 10. Instead, the most intensive heat exchange takes
place in the remote part of fins 12 having a significantly lower
temperature relative to temperature of plate 11. As shown in FIG.
2B, the difference .DELTA.T between fin temperature and air
temperature is the driver for heat exchange. Since .DELTA.T.sub.1
is lower than .DELTA.T.sub.2, then general heat removal capacity of
heat sink is reduced.
[0012] Conventional heat sink-fan tandems produce a large amount of
high velocity air flow that is the main source of computer noise. A
large amount of air pumped through the computer causes deposition
of contaminations on the surface of electronic components that
reduces heat exchange additionally. Use of air filtration devices
for fan air movers is limited because of the air pressure developed
by air fans do not meet the pressure drop conditions in the air
filtration systems. A large volume air flows produced by fans are
used in inefficient way in computer systems. A simple calculation
made on the basis of energy balance shows that the same amount of
waste heat energy can be removed from a computer by an air flow
that constitutes only 4-6% of the flow produced by conventional
fans. Thus, the heat accumulating capacity of air flow is used only
on 4-6% in the thermal solutions of the prior art. To achieve such
energetic efficiency a condition of a quasi--total entropy heat
exchange must be provided. Under this condition temperature of
exhausting air should be close to temperature of heat sink. In
turn, this high efficiency condition requires use of high thermal
conductive materials and heat exchangers with extremely high
specific surface. Unfortunately, the prior art does not disclose
solutions able to meet these requirements. Still another
disadvantage of the common design heat sinks is that they occupy
too much physical volume to be practical in extremely confined
applications. In view of the foregoing, it would be highly
desirable to provide a compact electronics cooling device with high
heat dissipating capacity, low noise, low energy consumption, harsh
environment protected, and a low vertical profile to insure its
compatibility with compact electronic equipment.
[0013] It is a continuing need in the prior art to provide low
thermal impedance, stress avoiding heat spreaders and substrates
that are thermal-mechanical compatible with the semiconductor
materials. Commonly used ceramic substrates have thermal expansion
coefficients similar to that of the semiconductor chip. However,
recent remarkable progress in the semiconductor industry has
promoted larger heat emission. Under such conditions, ceramic
substrate becomes the most thermal resistive component in the heat
transmitting path "semiconductor-substrate-heat sink" because of
relative low thermal conductivity of ceramics. With the condition
of close thermal-mechanical properties, high thermal conductivity
metal matrix composite materials can be used in a beneficial method
of the direct chip attachment to the high conductivity heat
spreader becomes practicable.
[0014] In order to satisfy requirements of low thermal expansion
the variety of metal matrix composites have been developed. The
U.S. Pat. No. 5,167,697 discloses W--Cu, W--Ag, Mo--Cu and Mo--Ag
materials and substrates of these materials made by sintering
powders of tungsten or molybdenum with following infiltration of
sintered preforms with copper or silver alloys. The heterogeneous
microstructure of such composite materials combines the specific
properties of both its components--high thermal conductivity of
copper and silver and low thermal expansion of tungsten and
molybdenum. The substrates with relative low CTE are provided by
use of aluminum-silicon carbide composite materials. However, the
mentioned metal matrix composite materials do not provide exact
harmony with the CTE of such semiconductor materials as silicon or
gallium arsenide. Besides, the conventionally used sintering and
die casting manufacturing technologies do not provide production of
the net-shape, net-size components with fine details. Additional
machining is requires for theses difficult-to-machine materials
that adds to their cost. A manufacturing process is still in need
able to produce net-shape and net-size parts and micro-parts of
metal matrix composite with adjustable thermal-mechanical
properties.
[0015] Generally, computer systems are comprised of a cabinet or
housing, that contains a plurality of components or subsystems,
such as processors, memory, power supply, video cards, audio cards,
disk drivers, and the like. Each of these components generates some
heat, and collectively, the computer system can be considered as a
thermal device requiring a fine thermal management.
[0016] Further, individual components, such as a microprocessor,
may produce significant heat emission in very local areas. This
waste heat is typically dissipated by a heat sink mounted directly
on the individual component. As computer systems have become more
complex and powerful, the individual components generate more heat.
Increasing the number and size of the fins located on the heat
sinks has generally provided increased cooling. Unfortunately, as
the number of fins has increased, airflow provided by the fans has
been inadequate to penetrate the now relatively dense fin
structure, limiting the ability to cool the component. Increasing
air flow to a sufficiently high level has proven problematic
because fans tend to be noisy, consume substantial electrical power
and increase their size consuming valuable real estate in the
computer housing. As consequence, modern computer systems have
added a small auxiliary fan adjacent to the overheating component.
Quantity of auxiliary fans in modern computers reaches 9 pieces at
the time of composing this patent application. These auxiliary fans
have provided some relief but they have created additional
problems. For example, increase of the number of auxiliary fans
adds to the cost and complicity of the computer system. Further,
with the growing complexity of modern computer systems, more and
more individual components require additional cooling capacity. As
the number of components grows, the problem associated with
installing additional auxiliary fans is compounded. A plurality of
auxiliary fans create a plurality of separate air flows within
compressed space of a computer case. This creates an additional
problem of air flows matching, which often becomes an obstacle for
further miniaturization of computer systems.
[0017] Conventionally, computer components, such as those of
"desktop" computers, are disposed within an exterior housing such
that various computer components are stacked one over the other in
a generally horizontal manner within the housing. Depending on the
system requirements, heat dissipation is controlled using typically
air fan--heat sink thermal management structures. The fans take up
valuable space within the housing, increase costs and noise, and
are particularly susceptible to failure due to their mechanical
nature. The fans and heat sinks also complicate the general layout
of the components within the housing, hampering overall size of the
computer. To resolve this problem, conventional arrangements have
relied on a less compact layout, such the components, while taking
up less space, still provide sufficient heat removal.
SUMMARY OF THE INVENTION
[0018] It is the object of the present invention to provide a low
weight, compact, low vertical profile thermal management system for
removing heat from electronic components. The thermal management
system comprises of a plurality of "flow-through" type cooling
devices, a source of filtered pressurized fluid suitable for use as
a coolant, and a fluid delivering device that supplies the cooling
devices with fluid. A preferred fluid is air, such as a filtered
pressurized air. The cooling device is comprised of a high
conductivity metal matrix composite heat spreader, a miniature heat
sink, preferably of the same material, a permeable heat exchanger
with high specific surface, and a closure that provides structural
integrity of the cooling device.
[0019] It is the further object of the present invention to provide
a source of pressurized filtered air for use in the flow-through
cooling devices. The source of pressurized air (air port) is
comprised of a miniature air mover, an air filter, an air
distribution device, and a plurality of flexible hoses that connect
the air port with a plurality of the flow-through cooling
devices.
[0020] It is the further object of the present invention to provide
a self-cleaning air filtering system in which the self-cleaning
effect is provided by use of two air filters and a cyclical air
flow directivity change. Within this system the filters are
self-cleaning by turn by means of expulsion of the filter by
exhausted air.
[0021] It is the further object of the present invention to provide
a miniature air mover capable of overcoming the hydraulic
resistance of the air filtration device and a plurality of the
flow-through cooling devices.
[0022] It is the further object of the present invention to provide
a Coefficient of Thermal Expansion (CTE) controlled heat spreader
applicable for direct and non-direct chip attachment. More
particularly, an improved thermal conductivity heat spreader with
an adjustable CTE within 4.0-6.5 PPM is provided.
[0023] It is the further object of the present invention to provide
a high conductivity, CTE controlled heat spreader that is
integrated metallurgically with a ceramic substrate, on which an
electronic device can be placed using conventional technique. Thus,
an ideal thermal contact between the ceramic substrate and a heat
removal structure is created, and use of the low thermal
conductivity interface materials is avoided.
[0024] It is the further object of the present invention to provide
an electronic device with an integrated cooling system within which
a silicon die integrated metallurgically into the flow-through
cooling structure to form a single whole thermally uninterrupted
body.
[0025] It is the further object of the present invention to provide
a flow-by type electronics cooling device that unites a CTE
controlled high thermal conductivity heat spreader and a miniature
metal matrix composite heat sink in one thermally interrupted
item.
[0026] It is the further object of the present invention to provide
a computer arrangement in which one or more electronic components
can be arranged in any desirable order and orientation without
concern of air flow directivity, components proximity, gravitation,
and electro magnetic influence. New computer arrangement comprises
the encapsulated modules with electronic components and the thermal
management system on the basis the flow-through cooling devices and
a supply of filtered pressurized air. New computer arrangement
provides freedom in layout for electronic devices and protection
from exterior contamination factors.
[0027] It is the further object of the present invention to provide
micro composite and macro composite high thermal conductivity
materials applicable for the electronics cooling devices.
[0028] It is the further object of the present invention to provide
a method for manufacturing the components of "flow-through" cooling
devices in high volume and low cost.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] FIG. 1 is a cross-sectional view of a prior art device.
[0030] FIG. 2A is a more detailed cross-sectional view of a single
set of fins of the prior art device of FIG. 1.
[0031] FIG. 2B is a graph demonstrating the difference .DELTA.T
between the fin temperature and the air temperature at the location
joined by the dotted lines with FIG. 2A.
[0032] FIGS. 3A and 3B depict of cross-sectional and top views,
respectively, of one embodiment of a micro heat spreader of the
invention.
[0033] FIGS. 4A and 4B depict of cross-sectional and top views,
respectively, of one embodiment of a macro heat spreader of the
invention.
[0034] FIGS. 5A and 5B depict of cross-sectional and top views,
respectively, of an alternative embodiment of a macro heat spreader
of the invention.
[0035] FIGS. 6A and 6B depict of cross-sectional and top views,
respectively, of another alternative embodiment of a macro heat
spreader of the invention.
[0036] FIG. 6C is a graphic depicting the thermal conductivity
range of embodiment of the invention in FIGS. 6A and 6B.
[0037] FIG. 7 depicts an alternative arrangement of a macro
composite heat spreader of the invention with a single flexible
heat connector.
[0038] FIG. 8 depicts another alternative arrangements of a macro
composite heat spreader of the invention with a dual flexible heat
connectors.
[0039] FIG. 9 depicts one embodiment of a flow-through cooling
device which unites a heat spreader, a heat sink and a heat
exchanger.
[0040] FIG. 10A depicts a cross-section across the air flow of one
embodiment of the invention.
[0041] FIG. 10B depicts a cross-section along the air flow of one
embodiment of the invention.
[0042] FIG. 11 depicts one embodiment of the invention having a
single body with uninterrupted heat flux.
[0043] FIG. 12 is a bar graph representing different performance of
commonly used air fans and sources of pressurized air.
[0044] FIG. 13 is a graph comparing the air supply requirements for
different cooling solutions.
[0045] FIG. 14 depicts Heat dissipation versus air flow of a finned
heat sink versus a Flow-through heat sink of the invention.
[0046] FIG. 15 is a graphic which compares pressure and device size
versus specific heat exchange surface for three different device
combinations (i) fan plus heat sink, (ii) vacuum pump plus
flow-through heat sink and (iii) compressor and flow-through heat
sink.
[0047] FIG. 16 is an illustration of a flow-by heat sink of a micro
composite material according to one embodiment of the
invention.
[0048] FIG. 17 is an illustration of a flow-by micro composite heat
sink of the invention having a spreader and a plurality of primary
fins.
[0049] FIG. 18 is an illustration of a flow-by brush-type heat sink
of the invention.
[0050] FIG. 19 is a nested and cut away views of a macro composite
article of the invention.
[0051] FIGS. 20A and 20B are a front view and a cross-section of
the CTE controlling core shown in FIG. 19.
[0052] FIG. 20C is a graphic depicting the relative magnitude and
directivity of compressive and tensile stresses of an embodiment of
the invention.
[0053] FIG. 21 is a cross-section of an integrated substrate of one
embodiment of the invention.
[0054] FIG. 22 illustrates an arrangement of an integrated
substrate such as in FIG. 21 couple with a flow-through cooling
device of the invention.
[0055] FIG. 23 shows a schematic of an exemplary general-purpose
computer arrangement in which the flow-through cooling device
embodiment of the invention is employed (vertically oriented).
[0056] FIG. 24 shows a schematic of another exemplary
general-purpose computer arrangement in which the flow-through
cooling device embodiment of the invention is employed
(horizontally oriented).
[0057] FIG. 25 shows a schematic of an exemplary general-purpose
computer arrangement of the invention in which the vacuum pump acts
as an air mover (vertically oriented).
[0058] FIG. 26 shows a schematic of another exemplary
general-purpose computer arrangement of the invention in which the
vacuum pump acts as an air mover (horizontally oriented).
[0059] FIG. 27 is a graph which depicts a typical surface area and
heat load distribution in a cooler of the present device.
[0060] FIG. 28A-D depict additional embodiments of the device.
FIGS. 28A and B show cut away views of devices where the CTE is
present or absent and where the CTE has the same dimensions. FIGS.
28C and D illustrate an embodiment where the heat spreader and
pedestal are used.
[0061] FIG. 29 depicts an CTE controlled substrate according to one
embodiment of the invention.
[0062] FIG. 30 illustrates an arrangement of an CTE controlled
internally cooled substrate in which the functions of CTE
controlling and heat removal are provided by the same
component.
[0063] FIG. 31 illustrates an arrangement of an CTE controlled
internally cooled substrate in which the functions of CTE
controlling and heat removal are provided by separate
components.
DETAILED DESCRIPTION OF THE INVENTION
[0064] A description of preferred embodiments of the invention
follows.
[0065] Illustrative embodiments of the thermal management system
for electronics and computer arrangement according to the present
invention are shown in FIGS. 3-15. As will be readily apparent to
those skilled in the upon a complete reading of the present
application, the present cooling device and electronic system
arrangement are applicable to a variety of computer systems (such
as servers, personal computers, notebooks, and the like) other than
the embodiment illustrated herein, and moreover to electronic and
electrical devices other than computer systems, including, but not
limited to, power supply, plasma TV, automotive electronics,
airborne electronics, and the like. Several non-limiting
embodiments are provided and described in more detail herein.
Embodiments include, but are not limited to, (a) high conductivity
micro composite heat sinks, (b) graphite fiber brush-type heat
sinks, (c) CTE controlled substrates and heat spreaders, (d) heat
spreaders with flexible heat cable(s), (e) micro composite
impingement cooling device, (f) macro composite flow-through heat
sink, (g) macro composite super conductivity CTE controlled cooling
device, (h) air station enabling computer architecture and
combinations thereof.
[0066] The present invention provides a high thermal conductivity
micro composite and macro composite heat spreaders that absorb
waste heat generated by an electronic component distribute heat
onto larger surface area, and transfers heat to a heat dissipating
structure. According to the present invention, the heat spreader
can be provided as a separate item or in a combination with a heat
dissipating unit. Turning to FIGS. 3A and 3B, a heat spreader 20,
preferably a micro composite heat spreader, is shown. A heat
emitting electronic component 21 is mounted on the surface of a
heat spreader 20 through a conventionally used interface material.
A macro composite material 19 used in a heat spreader 20 is another
embodiment of the present invention and disclosed in more detail in
the following corresponding example in this description. In a
preferred embodiment, the thermal conductivity of micro composite
substrate constitutes 450-550 w/mK that provide rapid and uniform
heat distribution within heat spreader 20. CTE in micro composite
heat spreader is close to that of typically used silicon
semiconductor material typically in the range of 5-9 PPM,
preferably about 6 to about 8 PPM. Both thermal conductivity and
CTE in micro composite heat spreader are isotropic.
[0067] A heat spreader, preferably macro composite super thermal
conductivity heat spreader, is shown on FIGS. 4A and 4B. In the
embodiment shown in FIG. 4, a macro composite heat spreader
comprising a micro composite material 19 and inserts 23, preferably
pyrolitic graphite inserts, having thermal conductivity in the
range 1,400-1,700 w/mK at that micro composite material 19 which
serves a matrix phase in the macro composite heat spreader. Micro
composite material 19 envelops inserts 23 and provides structural
integrity of macro composite spreader. Inserts 23 are oriented
within heat spreader in such a way that their most heat conducting
axis's coincide with directions of heat flow 25 from electronic
component (Z direction) and direction of heat flow within heat
spreader (X direction). Volume of inserts 23 can reach 85% in the
most thermally loaded areas, which coincide with the projecting
area of electronic component 21. Thus, bulk thermal conductivity in
these areas can reach 1,200 w/mK. Other areas of macro composite
heat spreader are less saturated with pyrolitic graphite inserts
23, and the most remote areas consist of micro composite material
19 only and provide local thermal conductivity within 450-550 w/mK.
In this embodiment, CTE within macro composite heat spreader is
non-uniform and depends on the volume of pyrolitic graphite inserts
23. The most CTE-sensitive area within location of electronic
component 21 has CTE that is very close to that of electronic
component, for example around about 3 to about 5 PPM, preferably 4
PPM. Thus, this macro composite heat spreader unites two important
advantages in one product: the highest known thermal conductivity
and CTE matched with semiconductor materials.
[0068] Another arrangement for macro composite heat spreader
according to the present invention is shown on FIGS. 5A and 5B.
Macro composite heat spreader comprises of a graphite fabric insert
26 of a pitch-based fiber and a micro composite material 19. Micro
composite material 19 envelops the graphite fabric insert 26 and
provides structural integrity for macro composite spreader. In a
preferred embodiment, the graphite fabrics used in the present
invention have thermal conductivity in the range of about 600 to
about 1,100 w/mK that provides a good bulk thermal conductivity for
macro composite heat spreader. Highest thermal conductivity in
macro composite heat spreader coincides with direction of tows and
rows in graphite fabric insert 26. Heat transfer in the transverse
direction in macro composite heat spreader is provided by the micro
composite material 19 having thermal conductivity of about 450 to
about 550 w/mK.
[0069] Still another arrangement for macro composite heat spreader
according to the present invention is shown on FIGS. 6A and 6B.
Macro composite heat spreader comprises of a net of pitch-based
graphite fiber 27 and a micro composite material 19. Micro
composite material 19 envelops graphite fibers 27 and provides
structural integrity of macro composite heat spreader. Graphite
fibers used in this embodiment of the present invention have
thermal conductivity in the range of about 600 to about 1,100 w/mK
and CTE that is close to negative value. The bulk CTE and thermal
conductivity depends on volumetric ratio between micro composite
material 19 and graphite fiber 27. In this embodiment, the volume
of graphite fiber is different in different areas of heat spreader.
Maximal fiber saturation takes place in the heat collecting zone
that coincides with the projecting area of electronic component 21.
Volumetric content of fibers in this zone constitutes approximately
80% of that which provides bulk thermal conductivity approximately
900 w/mK. In the heat spreading area beyond of the heat collecting
area the bulk thermal conductivity gradually falls to about 450
w/mK (FIG. 6C).
[0070] Further another arrangement for macro composite heat
spreader 22 combined with a flexible heat connector 28 is shown on
FIGS. 7 and 8. The flexible heat connector 28 is made of a high
conductivity graphite fiber or fabric, which combines good heat
transferring capacity with flexibility. Macro composite heat
spreader 22 comprises a graphite fabric insert 26 enveloped by a
micro composite material 19. Graphite fabric insert 26 is exposed
to sides and continued to form a heat connector 28, preferably
flexible heat connector. In one embodiment, waste heat 29a is
transferred to a desirable destination by the high conductivity
heat connectors 28 and attached to a heat dissipating device using
fasteners 29 made of a micro composite material 19.
[0071] Suitable materials for manufacturing the coolers of the
invention include graphite foam (about 70 w/mK), pitch graphite
fabric (up to about 1,100 w/mK), and pyrographite (1,400 w/mK). The
conduits for controlling fluid flow can be made of, for example,
steel, PVC or other material. The device can be encapsulated in a
shell made of, for example, a macrocomposite material.
[0072] Turning to FIG. 9 a flow-through cooling device 30 of the
present invention is shown. The flow-through cooling device 30
unites a heat spreader 32, a heat sink 33, and a heat exchanger 34,
preferably a permeable heat exchanger, into one, low vertical
profile and thermally uninterrupted body (an exploded view is shown
on FIG. 9 for clarity). A component to be cooled 31, preferably an
electronic component, is mounted onto heat spreader 32 using
conventional technique and interface materials. High density heat
load emitted (shown by arrows) by the electronic component 31 comes
to the heat spreader 32 that is made of a high thermal conductivity
metal matrix composite material according to the present invention.
The heat spreader 32 is significantly larger than electronic
component 31. Therefore the specific heat load in heat spreader 32
is reduced by several times comparing to the heat load in
electronic component 31. Heat spreader 32 is made of high thermal
conductivity composite materials according to the present
invention; due to high thermal conductivity heat rapidly stretches
within heat spreader 32.
[0073] While the relative sizes of the components can vary
substantially depending upon the materials and fluids selected and
the volume of air flow employed, in one example, the electronic
component can have a surface area of about 50 mm.sup.2; the heat
spreader can have a surface area of about 5 cm.sup.2; the micro
heat sink can have a surface area of about 120 cm.sup.2; and the
permeable heat exchange of up to about 50 m.sup.2 or more.
[0074] Further heat comes to heat sinks 33, for example a net of
miniature heat sinks, which are metallurgically connected to the
heat spreader 32 forming a single body with uninterrupted heat flux
(FIGS. 10A, 10B and 11). Heat sinks 33 have extended thermal
contacts with permeable heat exchanger 34. Heat transfer path
continues further within permeable heat exchanger 34. A cooling
fluid 37 enters through an inlet channel (see arrow on FIG. 11) is
forced through permeable heat exchanger 34 using inlet channel 38
and outlet channel 39. The cooling fluid 37 can be in form of
either gas or liquid. Cooling fluid 37 provides intensive heat
removal from the permeable material of heat exchanger 34 and
transfer of heat outside of the flow-through cooling device.
Further the cooling fluid 37 now hot fluid as it exits the outlet
channel (see exiting arrow on FIG. 11) can be collected and
transferred either to an exhausted point (typically used in air
embodiments), or to be returned for next cooling cycle (typically
used in liquid embodiments). A heat exchanger 34 is lodged into a
closure 40, preferably a hermetically sealed closure, which
provides structural integrity of cooling device 30 and prevents
leakage of cooling fluid 37. Additionally cooling device 30 is
provided with a fluid delivering and fluid exhausting systems
through inlet 44, outlet 45, and connecting hoses (not shown).
[0075] In one embodiment, the present invention provides a source
of filtered and pressurized air for the flow-through cooling
devices. The principal advantage of the pressurized air supply is
that it enables miniaturized heat exchangers with extremely high
heat dissipating capacity, but having a significant hydraulic
resistance and pressure drop. By this, use of pressurized air
enables basically new electronics cooling concept, one core
principle of which is the use of miniature permeable heat
exchangers with extremely large heat exchanging surface. Another
advantage is that pressurized air has enough power to overcome
hydraulic resistance of air filtering devices that produce clean
contamination--free air flow and prevents contaminating impurity of
the permeable heat exchanging media. FIG. 12 illustrates a
principal difference in performance of commonly used air fan and
sources of pressurized air according to one embodiment of the
present invention. Computer air fans produce high air flow at
several hundred liters per minute. However, air pressure developed
by fans is very low, typically in the range from about 0.005 to
about 0.01 atm. Air pressure at this level is not enough to
overcome a hydraulic resistance of heat exchanging structures with
well developed heat exchanging surface. Low pressure made by fans
prevent the use of reliable air filtering devices in computers as
the pressure drop in these devices are beyond of what can be
produces by fans. Still another inevitable consequence of low air
pressure made by fans is the large size of commonly used heat
sinks. Main heat sink designing parameters such as fins size and
distance between fins are selected as a compromise between a
possible largest heat exchanging surface and admissible pressure
drop. Since air pressure developed by fans is limited, the further
improvement of heat sinks is limited too. Therefore the further
increase of heat dissipating capacity on basis of fans is available
in an extensive, but not in an intensive way. The last development
in modern computer technology confirms this conclusion by the fact
that number of fans in computers constantly grows.
[0076] In contrast to fans, compressors and vacuum pumps produce
high air pressure sufficient to overcome hydraulic resistance in
both, flow-through cooling devices and air filtering devices (See
FIG. 13 which shows a graph of Air Supply Requirements for
different cooling solutions). A moderate amount of air flow
developed by air compressors and vacuum pumps is sufficient for
removal heat from the heat generating electronic components with
calculation of sharply increased heat removal efficiency in the
flow-through cooling devices. These circumstances create a basis
for new thermal management concept in the computer cooling area. A
core idea of this concept is that commonly used "heat sink-fan"
cooling structures can be replaced by the space saving and more
energetically effective "flow-through cooling device--source of
pressurized air" structures.
[0077] The flow-through cooling device in a combination with the
source of filtered pressurized air represents a number of
advantages before the commonly used finned heat sink-fan
structures. This new electronics cooling solution provides a
significantly greater heat dissipating capacity than solutions of
the prior art. See FIG. 14 for a comparison. It is known that the
heat dissipating limit for the heat sink-fan structures lies in the
range of about 25 to about 35 w/ cm.sup.2 It also known that heat
emitted by modern microprocessors approaches about 50 to about 75
w/cm.sup.2, and will reach about 150 to about 250 w/cm.sup.2 in
near future. The heat removal capacity for flow-through cooling
devices of the invention constitutes from at least about 100 to at
least about 150 w/cm.sup.2 for air cooling media, and at least
about 250 to about 300 w/cm.sup.2 for liquid cooling media.
[0078] Expected air requirements for different computer
applications include an air flow between about 3-6 l/min at about
0.01-0.015 atm for a mobile personal computer; between about 5-10
l/min at about 0.015-0.03 atm for a desktop personal computer; and
between about 10-20 l/min at about 0.025-0.05 atm for a performance
computer;
[0079] An especially important advantage is low weight and
miniature arrangement for cooling devices. Comparing to
conventional solutions based on finned heat sinks, the flow-through
cooling devices of the invention are lighter by 4-8 times and
smaller by 3-5 times (FIG. 15). The size reduction in flow-through
cooling devices is directed in vertical direction that makes the
cooling devices thinner and better adapted to the smaller
electronic devices, such as but not limited to a computer notebook
layout. According to the present invention, the permeable heat
exchanger 34 (FIGS. 10A, 10B and 11) is made of a material having
high specific surface area and a relative high thermal
conductivity. It is preferable that the materials have porosity in
the range from at least about 30 to at least about 70%, more
particularly from about 50 to about 60%. In one embodiment, the
greater part of the porous portion of the exchanger should be
interconnected to provide a through pass, for example for a cooling
fluid. A number of commercially available materials can be used for
making permeable heat exchangers according to the present
invention. Suitable material include but are not limited to
graphite foams, metal foams, ceramic foams, graphite fabrics,
porous metals, carbon nanotubes and the like. In an alternative
embodiment, a labyrinth type heat exchanger can made as an integral
micro structure of a high thermal conductive micro composite
material according to the present invention and by a micro
manufacturing process according to the present invention. Such a
labyrinth type heat exchanger comprises a highly branched, high
specific surface and specific volume micro composite ribs which
manage air flow and produce high heat transfer in a relative small
volume.
[0080] FIGS. 16 and 17 illustrate still more embodiments of the
invention. In these embodiments, a flow-by heat sink 70 comprises a
micro composite material 79. The heat sink 70 comprises a heat
spreader 72 and a system of primary fins 74. Primary fins 74 might
be preformed as straight or wavy ribs, broken or continues ribs, or
other shapes. Primary fins 74 manage air flow within heat sink 70
and provide the macro level heat exchange. A secondary micro-fin
structure is formed on the surface of primary fins 74. The second
micro-fin structure (not shown) turbulizes airflow, prevents
formation of air stagnation zones and provides the micro level heat
exchange. A flow-by micro composite heat sink 70 with a side fins
location is shown on FIG. 17.
[0081] A flow-by brush-type heat sink 77 is shown on FIG. 18.
Brush-type heat sink 77 comprises a heat spreader 72 of a micro
composite material 79 and a plurality of fibers 78, preferably
graphite fibers. One end of fibers 78 is embedded into micro
composite material of heat spreader 72 (not shown in FIG. 18) and
is located significantly close to the heat receiving surface of
heat spreader 72. The non-embedded end of the fibers 78, in this
example graphite fibers, exit and are exposed to air flow. The
embedded portions of graphite fibers 78 collect heat and transfer
it to the exposed part of graphite fibers 78, where heat exchange
with surrounding air takes place. Brush-type heat sink 77 provides
a beneficial combination of an extremely high heat removal
capacity, low weight, and small overall size.
[0082] The present invention provides a CTE controlled heat
spreaders and substrates that can be made as a separate item or as
a joint item that comprises a heat spreader, a heat sink, a ceramic
substrate, and a permeable heat exchanger. The CTE controlled heat
spreader and substrate 50 is a macro composite article comprising a
CTE controlling core 51, which has CTE close that of the electronic
component, and a shell 57 that three-dimensionally envelopes the
core 51 (FIG. 19). In a preferred embodiment the shell is a metal,
a metal alloy or metal matrix composite (further metal shell). The
shell 57 provides structural integrity for the macro composite heat
spreader 50 and high thermal conductivity due to specifically
selected components of the metal matrix composite material. Core 51
has a number of through holes 55 placed in a predetermined manner
onto its footprint. The manner in which the holes are configured
depends upon the device to be cooled, the materials selected and
other factors as described herein. All mating surfaces 54 on the
core 51 are rounded to reduce stress concentration in shell 57,
particularly the metal matrix composite shell of the embodiment
shown.
[0083] Due to different properties of the core 51 and shell 57, a
thermal mechanical conflict takes place within the CTE controlling
substrate 50 during manufacturing process and over time following
service in an electronic device. During fabrication a residual
tensile stress 59 and a residual compressive stress 58 are
purposely created in the shell 57 by braking shrinkage according to
the manufacturing process of the present invention. Magnitude and
directivity of residual tensile stress 58 and residual compression
stress 59 in shell 57 can be specified and managed by a proper
disposition of through holes 55 in core 51 (FIG. 20). According to
the present invention, arrangement of and distances between holes
55 are configured in a such way that residual stresses 58 and 59
developed in the local fields between holes 55 do not reach the
limiting tensile stress 61 and compressive stress 62, inherent to a
particular metal matrix composite material (or combination of
materials) employed in shell 57. One skilled in the are will
appreciate that this approach provides formation of residual
stresses with controlled magnitude and prevents from cracking and
integrity failure in the shell 57, for example a metal matrix
composite shell, during the manufacturing process according to the
present invention. The residual stresses have opposite directivity
relative to thermal stresses generated by operation of the
semiconductor device. The interaction between differently oriented
stresses produces absorption and mutual cancellation of thermal
stresses. The result of such interaction is that the source for
substrate expansion disappears and no substrate expansion is
produced, except an expansion, which is inherent for the TBS core
material. Residual stresses 58 and 58 disappear with time due to
the stress self-relaxation process, which can be accelerated by
corresponding heat treatment.
[0084] Generally, the core 51 is subjected mostly to compressive
stress 59, while metal matrix composite shell 57 is subjected to
tensile stress 58. Generally, materials better withstand against
compressive loads than against tensile load. Therefore the shell 57
is not able to compress the core 51 when temperature comes down.
Further, the shell 57 cannot withstand against expansion of core 51
when temperature rises. Being a weaker structure, shell 57 follows
to thermal mechanical behaving of the core 51. Since the CTE of the
core material 51 is selected similar to the CTE of electronic
component, the CTE controlled substrate 50 becomes
thermal-mechanically matched with the electronic component 52. The
thermal-mechanical matching method according to the present
invention provides the electronic supporting and cooling components
with useful properties as it shown in the following embodiment
examples.
[0085] Turning to FIG. 21 an integrated substrate 70 for electronic
component 71 is shown. Integrated substrate 70 comprises a CTE
controlled heat spreader 73 in which a ceramic substrate 74 is
integrated metallurgically. A heat spreader 73 is comprised of a
CTE controlled core 75 and a metal matrix composite shell 77.
Arrangement of core 75 and shell 77, as well as the character of
interactions between them are similar to that described in the
embodiment for CTE controlled heat spreader. Heat spreader 73
contains an alighting deepening 76 that matches to the
configuration of ceramic substrate 74. CTEs for core 75 and ceramic
substrate 74 are selected to be the same or substantially close.
Thermal-mechanical interaction within integrated substrate 70 takes
place between core 75 and shell 77. The relative thin ceramic
substrate 74 is protected from creation of stresses by the larger
and stronger core 75. By this, ceramic substrate obtains a gentle
support from the CTE controlled heat spreader 73 that prevents
deformation or cracking. Detention of ceramic substrate in the CTE
controlled heat spreader is provided by a combination of mechanical
and metallurgical action. The integrated substrate 70 provides an
ideal thermal contact between ceramic substrate 74 and heat
spreader 73 and eliminates a need for use of interface materials.
FIG. 22 shows an arrangement of an integrated substrate 70 that is
coupled with a flow-through cooling device 79, which is described
in more details in the following embodiments of the present
invention.
[0086] Turning now to FIGS. 23 and 24, the views of two embodiments
of a general-purpose computer arrangement 100, such as a personal
computer or server that may advantageously employ one or more
aspects of the present invention are shown. FIGS. 23 and 24 show
the vertical and horizontal components layout, accordingly.
Generally, the computer arrangement 100 is comprised of a case 115,
a plurality of electronic devices, such as a microprocessor 101, a
power supply 102, a hard disk drive 103, a video card 104, and the
like. These components (e.g., power supply, CPU, video card, and
hard drive) are coupled together via an architecture, which allows
the components to communicate with one another and potentially with
external devices (not shown), such as other computer systems,
scanners, etc. The architecture may take on any of a variety of
forms without departing from the scope of the instant
invention.
[0087] The electronic components 101, 102, 103, and 104 lie on the
flow-through cooling device 107 which is connected with the air
port 106 by mean of flexible hoses 105. Although only four cooled
electronic devices shown on FIG. 1, any of a wide variety of
electronic devices may be readily employed without departing from
the scope of the instant invention. The air port 106 comprises of a
micro compressor 110, an electro motor 109, an air filter 111, and
an air distributor 114.
[0088] The air compressor 110 sucks cold air 116 through the air
filter 111 entrapping contamination particles and preventing the
pollution deposition within the flow-through cooling devices 107
and clogging the porous heat exchange media. The flow path of
slightly pressurized cold air starts in the air filter 111 and the
micro compressor 110 is powered by an electrical motor 109. Further
purified air passes the air distributor 114, in which air flow is
divided on a plurality of flows destined to cool electronic
components 111, 112, 113, and 115 by flowing through cooling
devices 107, on which the electronic devices are mounted. Within
the permeable media of the cooling devices 107 the heat exchange
between cold air and a heat exchanging structure takes place as it
explained in more details below. Cold air removes heat from the
heat exchanging structure and passes out of the cooling devices
107. Further hot air 117 exiting different cooling devices 107 is
collected in the air collector 121, transferred to a definite
location beyond the bounds of the computer case 115 and then
exhausted to atmosphere. Alternatively, exiting hot air 117 can be
exhausted into atmosphere in the destined points within the
computer case 115 by connecting the air outlets of the flow-through
cooling devices 107 and desirable exhausting points with the
flexible hoses 105 (not shown).
[0089] FIGS. 25 and 26 show the schematic views of a compact
computer arrangement 100 according to the present invention, in
which a micro vacuum pump is used as an air mover. Vacuum pump
creates an overpressure on the sucking side that is lower than 1
atmosphere. This pressure is sufficient for use in the flow-through
cooling devices according to the present invention. An additional
advantage of vacuum pumps before the micro compressors is that this
air mover does not increase temperature of air as it takes place in
the compressors. Therefore heat removal in the flow-through cooling
devices is better when a vacuum pump is used. It is noted that,
while FIG. 25 depicts the use of hoses 105 to move air from the air
intake filter 116 to the components 107, the use of such hoses can
be, preferably, be omitted. Further, while the hoses to move the
air from the components 107 to the vacuum pump 110 can also be
omitted, efficiency can be expected with their use.
[0090] In both such embodiments, while the figures may suggest that
a single cooling device is matched with an electronic component.
While this configuration may be convenient, other configurations
are also possible. For example, a single cooling device may service
two or more electronic components or all of the electronic
components. Indeed, even the units of the cooling devices can be
combined. For example, a single micro heat sink can service two or
more heat spreaders.
[0091] In one embodiment, the air mover is a vane machine,
preferably a toroidal vane machine. Suitable vane machines include
but are not limited to those embraced by U.S. Pat. No. 5,233,954,
U.S. Published application 2003/0111040 and U.S. applications
entitled "Improvements in Intersecting Vane Machines" U.S. Ser. No.
10/744,230 filed Dec. 22, 2003 as Atty. Docket number 4004-3001;
"Improvements in Sealing Intersecting Vane Machines" U.S. Ser. No.
10/744,229 filed Dec. 22, 2003 as Atty. Docket No. 4004-3004; and
"The Use of Intersecting Vane Machines in Combination with Wind
Turbines" U.S. Ser. No. 10/744,232 filed Dec. 22, 2003. The entire
teachings of the aforementioned patents and patent applications are
incorporated herein by reference. The toroidal vane machine is
capable of serving as a micro compressor or vacuum pump which can
be scaled to meet a variety of dimensional requirements. In one
embodiment the toroidal intersecting machine is a micro air mover
capable of being used in small computer applications, such as but
not limited to, in computer "notebooks", desktop computers or
servers. Other suitable air movers are known to those skilled in
the art.
[0092] Turning to the following drawings, a vertical (FIG. 25), and
a horizontal (FIG. 26) layout of electronic components within the
computer arrangement 100 are shown. A micro vacuum pump powered by
an electro motor is connected with a plurality of cooling devices
107, an air distributor 114, and air filter 111 by flexible hoses
105. When operating, the vacuum pump sucks cold air 116 through the
air filter 111 and the cooling devices 107. As cold air 116
advances within the heat exchanging structure of the flow-through
cooling devices 107, an intensive heat exchange takes place between
the heat exchanging structure and air. Air removes heat from the
cooling device 107 and transfers it to the vacuum pump and further
hot air 117 exhausts outside of the computer case 115.
[0093] A thermal-mechanical matching method according to the
present invention provides the electronic supporting and cooling
components with useful properties as it shown in the following
embodiment examples. Turning to FIG. 29, a CTE controlled substrate
70 for electronic component 71 is shown. Material for the
perforated core 74 is selected with consideration to be close to
CTE of the semiconductor material. Different types of solid and
porous graphite and ceramic can comply with these requirements.
Material for the metal shell 77 is selected with consideration of
high thermal conductivity and manufacturability. A plurality of
copper and aluminum alloys can fulfill these requirements.
Manufacturing process for the CTE controlled substrate 70 can be
provided by different metal forming technologies such as the insert
die casting, the insert investment casting, powder sintering,
infiltration, etc. In general the manufacturing process includes
preparation of the perforated core of graphite or ceramic, and
following encapsulation of the core by the metal shell using one of
the above listed methods.
[0094] Turning to FIG. 29 a simple CTE controlled solution is
shown. An CTE controlled substrate 70 is comprised of a perforated
core 75 and a metal shell 77, which envelops the perforated core 75
and fills the perforation openings. Materials for the perforated
core 75 and metal shell 77 are selected according to the above
explained considerations. One of described above manufacturing
methods can be used for fabrications of the CTE controlled
substrate 70.
[0095] Turning to FIG. 30 a CTE controlled, internally cooled
substrate 80 is shown. Arrangement of core 75 and shell 77, as well
as the character of interactions between them are similar to that
described in the embodiment for CTE controlled heat spreader. The
perforated core 75 is made of a porous permeable material 81 such
as graphite foam, porous graphite, porous ceramic, metal foam, etc.
Beside of the CTE controlling function, the perforated core 75
provides the heat removal function by flowing the cooling media
through the permeable media 81. Configuration of the perforated
core 75 is designed in a way that provides a desirable path of the
flowing through cooling media within the CTE controlled substrate
80. The CTE controlled internally cooled substrate comprises an
inlet and outlet for the cooling media similarly to the above
explained cooling device on FIG. 10 (not shown on FIG. 30).
[0096] Turning to FIG. 31, a CTE controlled, internally cooled
substrate 90 is shown. Arrangement of core 75 and shell 77, as well
as the character of interactions between them are similar to that
described in the embodiment for CTE controlled heat spreader shown
on FIG. 29. Internal cooling in the substrate 90 is provided by a
separate permeable insert 91. Inlet 92 and outlet 94 provide a
managed flow 93 of the cooling media within the substrate 90. Such
a dividing of the heat removal and CTE controlling functions in the
substrate 90 allowing use of the permeable materials having CTE
different than the semiconductor material. A CTE mismatch between
the semiconductor material 71 and the permeable core 91 is smoothed
by the perforated core 75, which has CTE equal or close to what of
the semiconductor material 71. One of described above manufacturing
methods can be used for fabrications of the CTE controlled
internally cooled substrate 90.
[0097] While this invention has been particularly shown and
described with references to preferred embodiments thereof, it will
be understood by those skilled in the art that various changes in
form and details may be made therein without departing from the
scope of the invention encompassed by the appended claims.
* * * * *