U.S. patent application number 10/855046 was filed with the patent office on 2005-12-15 for method and apparatus for reducing thermal resistance in a vertical heat sink assembly.
This patent application is currently assigned to INTERNATIONAL BUSINESS MACHINES CORPORATION. Invention is credited to Goth, Gary F..
Application Number | 20050274487 10/855046 |
Document ID | / |
Family ID | 35459282 |
Filed Date | 2005-12-15 |
United States Patent
Application |
20050274487 |
Kind Code |
A1 |
Goth, Gary F. |
December 15, 2005 |
Method and apparatus for reducing thermal resistance in a vertical
heat sink assembly
Abstract
A method and apparatus for an electronic package includes a
substrate; a heat source component operably coupled to the
substrate, and in direct contact with and electrically connected to
a top surface of the substrate; a heat sink assembly in thermal
communication with the substrate. The heat sink assembly includes a
plurality of distinct vapor chambers, each containing a heat
transfer fluid configured to evaporate on a wall in thermal contact
with a back surface of the heat source component and condense on an
opposing wall defining an exterior wall defining the vapor
chambers. Each of the plurality of distinct vapor chambers are
serially aligned having facing sidewalls defining each relative to
contiguous vapor chambers and at least one of the plurality of
distinct vapor chambers includes a lower sidewall defining one
distinct vapor chamber substantially aligned with a bottom defining
the heat source component such that a bottom portion defining the
one distinct vapor chamber is substantially aligned with a bottom
portion of the heat source component.
Inventors: |
Goth, Gary F.; (Pleasant
Valley, NY) |
Correspondence
Address: |
CANTOR COLBURN LLP
55 GRIFFIN ROAD SOUTH
BLOOMFIELD
CT
06002
US
|
Assignee: |
INTERNATIONAL BUSINESS MACHINES
CORPORATION
ARMONK
NY
|
Family ID: |
35459282 |
Appl. No.: |
10/855046 |
Filed: |
May 27, 2004 |
Current U.S.
Class: |
165/80.2 ;
257/E23.088 |
Current CPC
Class: |
F28D 15/02 20130101;
F28F 9/001 20130101; H01L 2924/15311 20130101; H01L 2224/32245
20130101; H01L 23/427 20130101 |
Class at
Publication: |
165/080.2 |
International
Class: |
F28F 007/00; F28B
003/00 |
Claims
1. An electronic package comprising: a substrate; a heat source
component operably coupled to said substrate, said component in
direct contact with and electrically connected to a first surface
of said substrate; a heat sink assembly in thermal communication
with an opposite second surface of said substrate, said heat sink
assembly including a plurality of discrete vapor chambers
vertically aligned with respect to each other, each of said
plurality of discrete vapor chambers containing a heat transfer
fluid in thermal contact with a back surface of said heat source
component, said heat transfer fluid configured to evaporate from a
bottom portion defining each of said plurality of discrete vapor
chambers and condense on an upper surface defining an top portion
of each of said vapor chambers of said heat sink assembly; and
wherein said each of said plurality of discrete vapor chambers are
serially aligned having facing lower and upper surfaces defined by
at least one wall therebetween corresponding to contiguous vapor
chambers, a lower surface defining one of said plurality of
discrete vapor chambers being substantially aligned with a bottom
defining said heat source component such that the lower surface
defining said one of said plurality of discrete vapor chambers is
substantially aligned with a bottom portion of said heat source
component.
2. The electronic package of claim 1, wherein said heat sink
assembly includes a heat sink in thermal communication with an
outer surface defining a lid attached to said substrate.
3. The electronic package of claim 2, wherein said heat sink is
integrally formed with said lid.
4. The electronic package of claim 2, wherein said plurality of
discrete vapor champers are separated by a horizontal barrier
extending from said lower surface to said upper surface and
defining contiguous vapor chambers.
5. The electronic package of claim 1, wherein said plurality of
vapor chambers includes an upper vapor chamber and a lower vapor
chamber.
6. The electronic package of claim 5, wherein when said heat source
component is substantially centrally located relative to a length
defining said heat sink assembly, said upper vapor chamber is
longer than said lower vapor chamber.
7. The electronic package of claim 5, wherein when said heat source
component is located substantially above a central location
relative to a length defining said heat sink assembly, said lower
vapor chamber is longer than said upper vapor chamber.
8. The electronic package of claim 1, wherein said package is
selected from the group consisting of ball grid array modules, pin
grid array modules, land grid array modules and HyperBGA.RTM.
modules.
9. The electronic package of claim 2, wherein said lid is formed
from material selected from the group consisting of aluminum,
copper, Invar, gold, silver, nickel, aluminum-silicon carbide,
plastics, ceramics and composites.
10. The electronic package of claim 1, wherein said substrate
includes material selected from the group consisting of ceramics,
fiberglass, polytetraflouroethylene, and polymers.
11. The electronic package of claim 1, wherein a solid thermal
transfer medium is in direct contact with a back surface of each
heat source component and an outer surface of a lower wall of said
heat sink assembly.
12. The electronic package of claim 1, wherein said heat source
component is one of a DCM and a MCM.
13. A method for lowering a thermal resistance of a vertically
oriented heat sink assembly to dissipate heat from a heat source
component, the method comprising: configuring a heat sink assembly
with a plurality of discrete vapor chambers, each of said plurality
of discrete vapor chambers containing a heat transfer fluid in
thermal contact with a back surface of the heat source-component,
said heat transfer fluid configured to evaporate from a bottom
portion defining, each of said plurality of discrete vapor chambers
and condense on an upper surface a top portion of each of said
vapor chambers of said heat sink assembly; and configuring said
each of said plurality of discrete vapor chambers to be serially,
vertically aligned having facing lower and upper surfaces defined
by at least one wall therebetween corresponding to contiguous vapor
chambers, a lower surface defining one of said plurality of
discrete vapor chambers being substantially aligned with a bottom
defining the heat source component such that the lower surface
defining said one discrete vapor chamber is substantially aligned
with a bottom portion of the heat source component.
14. The method of claim 13, further comprising: disposing a heat
sink in thermal communication with an outer surface defining lid
attached to said substrate.
15. The method of claim 14, further comprising: integrally forming
said heat sink with said lid.
16. The method of claim 14, further comprising: separating said
plurality of discrete vapor champers with a horizontal barrier
extending from said lower surface to said upper surface defining
contiguous vapor chambers.
17. The method of claim 13, wherein said plurality of vapor
chambers includes an upper vapor chamber and a lower vapor
chamber.
18. The method of claim 17, further comprising: locating the heat
source component in a central location relative to a length
defining said heat sink assembly, wherein said upper vapor chamber
is longer than said lower vapor chamber.
19. The method of claim 17, further comprising: locating the heat
source component substantially above a central location relative to
a length defining said heat sink assembly, wherein said lower vapor
chamber is longer than said upper vapor chamber.
20. The method of claim 13, further comprising: disposing a solid
thermal transfer medium in direct contact with a back surface of
each heat source component and an outer surface defining said heat
sink assembly.
21. The method of claim 13, wherein the heat source component is
one of a DCM and a MCM.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to dissipating heat generated
by integrated circuit (IC) modules, and a method of constructing
such devices. In particular, the present disclosure relates to a
method and apparatus for eliminating a dry out condition of a heat
transfer or cooling fluid in a vertical heat sink assembly
configured to dissipate heat generated by integrated circuit
modules.
[0002] As is known, operating electronic devices produce heat. This
heat should be removed from the devices in order to maintain device
junction temperatures within desirable limits: failure to remove
the heat thus produced results in increased device temperatures,
potentially leading to thermal runaway conditions. Several trends
in the electronics industry have combined to increase the
importance of thermal management, including heat removal for
electronic devices, including technologies where thermal management
has traditionally been less of a concern, such as CMOS. In
particular, the need for faster and more densely packed circuits
has had a direct impact on the importance of thermal management.
First, power dissipation, and therefore heat production, increases
as the device operating frequencies increase. Second, increased
operating frequencies may be possible at lower device junction
temperatures. Finally, as more and more devices are packed onto a
single chip, power density (Watts/cm.sup.2) increases, resulting in
the need to remove more power from a given size chip or module.
These trends have combined to create applications where it is no
longer desirable to remove the heat from modern devices solely by
traditional air cooling methods, such as by using traditional air
cooled heat sinks.
[0003] For example, with the advent of multichip modules (MCMs),
containing multiple integrated circuit (IC) chips each having many
thousands of circuit elements, it has become possible to pack great
numbers of electronic components together within a very small
volume. As is well known, ICs generate significant amounts of heat
during the course of their normal operation. Since most
semiconductor or other solid state devices are sensitive to
excessive temperatures, a solution to the problem of the generation
of heat by IC chips in close proximity to one another in MCMs is of
continuing concern to the industry.
[0004] A conventional approach to cooling components in electronic
systems in which devices contained in MCMs are placed on printed
circuit/wire boards or cards is to direct a stream of cooling air
across the modules with the addition of heat sinks attached to the
module to enhance the effectiveness of the airflow.
[0005] Limitation in the cooling capacity of the simple
airflow/heat sink approach to cooling has led to the use of another
technique, which is a more advanced approach to cooling of
card-mounted MCMs. This technique utilizes heat pipe technology.
Heat pipes per se are of course, well known and heat pipes in the
form of vapor chambers are becoming common. In the related art,
there are also teachings of heat pipes/vapor chambers for
dissipating the heat generated by electronic components mounted on
cards.
[0006] One approach includes using a cooling fluid or heat transfer
fluid in a vapor chamber heat sink. A vapor chamber base enables
heat sinks to perform better as the thermal resistance to spreading
the heat in the base is reduced. The heat is removed from one side
of the base in thermal communication with a heat source by
evaporation of the heat transfer fluid and travels rapidly in a
gaseous state until it condenses on a fin side of the base. In this
manner, the heat is transferred from the base to the fins for
subsequent conduction to convectively cooled fins extending from
the base.
[0007] However, vapor chamber technology has several limitations
when applied to MCMs. One limitation is that the above described
heat transfer mechanism can fail if inadequate heat transfer fluid
or cooling fluid is present on the evaporator surface of the base
near the heat source. This is often the case when the vapor chamber
is positioned vertically such that gravity causes the returning or
condensed cooling fluid to accumulate at a lower area of the
vertically oriented vapor chamber. For applications where the heat
source is centrally located with respect to the vertically oriented
heat sink, dry out conditions are often created near the heat
source.
[0008] For the foregoing reasons, therefore, for an efficiently
cooled electronic module or MCM that employs vapor chamber cooling.
In particular, there is a need in the art for a method and
apparatus of providing a vertically oriented vapor chamber and
corresponding heat source to be cooled with a fluid coolant, while
simultaneously eliminating dry out conditions near the heat
source.
SUMMARY OF THE INVENTION
[0009] One embodiment is an electronic package includes a
substrate; a heat source component operably coupled to the
substrate, and in direct contact with and electrically connected to
a top surface of the substrate; a heat sink assembly in thermal
communication with the substrate. The heat sink assembly includes a
plurality of distinct vapor chambers, each containing a heat
transfer fluid configured to evaporate on a wall in thermal contact
with a back surface of the heat source component and condense on an
opposing wall defining an exterior wall defining the vapor
chambers. Each of the plurality of distinct vapor chambers are
serially aligned having facing sidewalls defining each relative to
contiguous vapor chambers and at least one of the plurality of
distinct vapor chambers includes a lower sidewall defining one
distinct vapor chamber substantially aligned with a bottom defining
the heat source component such that a bottom portion defining the
one distinct vapor chamber is substantially aligned with a bottom
portion of the heat source component.
[0010] Another embodiment is a method for lowering a thermal
resistance of a vertically oriented heat sink assembly to dissipate
heat from a heat source component. The method includes configuring
a heat sink assembly with a plurality of distinct vapor chambers,
each of the distinct vapor chambers containing a heat transfer
fluid configured to evaporate on a wall in thermal contact with a
back surface of the heat source component and condense on an
opposing wall defining an exterior wall of the heat sink assembly;
and configuring each of the plurality of distinct vapor chambers to
be serially aligned having facing sidewalls defining each relative
to contiguous vapor chambers and at least one of the plurality of
distinct vapor chambers includes a lower sidewall defining one
distinct vapor chamber substantially aligned with a bottom defining
the heat source component such that a bottom portion defining the
one distinct vapor chamber is substantially aligned with a bottom
portion of the heat source component.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Referring to the exemplary drawings wherein like elements
are numbered alike in the accompanying Figures:
[0012] FIG. 1 depicts a perspective view of a partially populated
central electronics complex (CEC) illustrating an exposed
vertically oriented MCM and a vertically oriented heat sink
assembly disposed over another MCM;
[0013] FIG. 2 depicts a partial exploded cross section view of the
vertically oriented heat sink assembly disposed over a MCM of FIG.
1;
[0014] FIG. 3 depicts a partial exploded cross section view of an
exemplary embodiment of a vertically oriented heat sink assembly
having vapor chambers integrated into a base of a heat sink
disposed over a MCM of FIG. 1;
[0015] FIG. 4 depicts a schematic side view of a prior art
vertically oriented heat sink assembly having a single vapor
chamber in thermal communication with a centrally located heat
source;
[0016] FIG. 5 depicts a schematic side view of a vertically
oriented heat sink assembly having two distinct vapor chambers in
thermal communication with the heat source of FIG. 4 in accordance
with an exemplary embodiment of the present disclosure; and
[0017] FIG. 6 depicts a schematic side view of a vertically
oriented heat sink assembly having two distinct vapor chambers in
thermal communication with the heat source of FIG. 5 in accordance
with an alternative exemplary embodiment of the present
disclosure.
DETAILED DESCRIPTION OF THE INVENTION
[0018] The present disclosure will now be described in more detail
by way of example with reference to the embodiments shown in the
accompanying figures. It should be kept in mind that the following
described embodiments are only presented by way of example and
should not be construed as limiting the inventive concept to any
particular physical configuration.
[0019] Further, if used and unless otherwise stated, the terms
"upper", "lower", "front", "back", "over", "under", and similar
such terms are not to be construed as limiting the invention to a
particular orientation. Instead, these terms are used only on a
relative basis.
[0020] For the purposes of the present disclosure, the terms
printed circuit board (PCB) and printed wire board (PWB) are
equivalent terms. The terms "in contact" and "contacting" indicate
mechanical and thermal contact
[0021] FIG. 1 illustrates a so-called central electronics complex
10 (CEC) of a computer system. The CEC 10 is comprised of an
enclosure (such as a cage 12), a backplane or midplane 14 as
illustrated, and a circuit board or daughter card, such as a blade
or node 16 having two processor multi-chip modules (MCM) 17, and a
corresponding vapor chamber heat sink assembly 20 disposed over
each MCM 17 (only one shown of each for sake of clarity), 256 GB
memory on 16 cards (not shown), an input/output (I/O) card 18, and
a control multiplexer card (not shown), for example, attachable to
the backplane 14. Air inlets 22 are shown at a back of CEC 10 and
air flow across fins of heat sink assembly 20 and out air exhausts
24 is generally shown with arrows 26.
[0022] FIG. 2 is a partial cross-sectional view of an exemplary
embodiment of a multichip module (MCM) mounted on a PCB having a
lid in accordance with the present disclosure. It will be
recognized by one skilled in the pertinent art that a dual chip
module (DCM) is also contemplated for use in the present
disclosure. In FIG. 2, MCM 100 includes a substrate 102 having a
multiplicity of components 105 mounted thereto, each component
having a front surface 110 and a back surface 115. MCM 100 is
mounted to a PCB 120 by a multiplicity of solder balls 125.
Substrate 102 may be a single or multi-level substrate and may be
ceramic, fiberglass or polymer based. MCM 100 also includes a lid
130. Lid 130 is mounted to substrate 102 by lid support 132
connecting the periphery of lid 130 to the periphery of substrate
102. Lid support 132 may be fabricated from the same material as
lid 130 and may be integral with the lid. Alternatively, lid
support 132 may be fabricated from a material different from that
of lid 130. Lid support 132 may provide a hermetic seal between lid
130 and substrate 102.
[0023] Lid 130 includes a lower wall 135 having an outer surface
140, an upper wall 145 having an outer surface 150 and sidewalls
155 defining a vapor chamber 160. It will be noted that opposing
sidewalls 155 defining vapor chamber 160 are shown closer together
than with respect to FIG. 5 for sake of clarity in describing
chamber 160. Moreover, FIG. 2 is shown with a single vapor chamber
160, wherein two or more vapor chambers 160 are included in an
exemplary embodiment depicted in FIG. 5 in accordance with the
present disclosure.
[0024] Vapor chamber 160 contains a heat transfer fluid such as,
inter alia, water, freon or glycol. Front sides 110 of components
105 are electrically connected to a top surface 165 of substrate
102. Components 105 may be flip chip, wire-bonded or soldered to
substrate 102. A thermal transfer medium 170 is in contact with
back surfaces 115 of components 105 and outer surface 140 of lower
wall 135 of lid 130 to enable thermal contact, mechanical restraint
and pressure support over the contacting region. Thermal transfer
medium 170 enables heat generated by the operation of components
105 to be efficiently transferred to lid 130.
[0025] Because of the excellent heat transfer capability afforded
to lid 130 by vapor chamber 160, the lid may be fabricated from
many different materials including but not limited to metals such
as aluminum, copper, nickel, gold or Invar and other materials such
as plastics, ceramics and composites. Because of the wide range of
materials available, lid 130 may fabricated from a material having
a CTE matched to (between about 25% to 700% of the coefficient of
thermal expansion) substrate 102 or from the same material as the
substrate. For example, if MCM 100 is a HyperBGA.RTM. International
Business Machine Corp., Armonk, N.Y., in which substrate 102 is a
polytetraflouroethylene (PTFE) based material having a CTE of about
10-12 ppm/.degree. C., then lid 130 may be fabricated from an
aluminum-silicon carbide composite having a CTE of about 10
ppm/.degree. C.
[0026] Thermal transfer medium 170 may include a thermal adhesive,
thermal grease, thermal-conductive pads, phase change or other
materials known in the art.
[0027] A heat sink 180 having a plurality of horizontal fins 182
(see also FIG. 1) is in thermal communication with outer surface
150 of lid 130. Heat sink 180 is shown remove from outer surface
150 for sake of clarity. Heat sink 180 may be formed from aluminum,
copper, beryllium, white metal or any other suitable material with
high heat conductivity. Furthermore, it will be recognized by one
skilled in the pertinent art that heat sink 180 may be fabricated
from a material having a CTE matched to (between about 25% to 700%)
the CTE of lid 130. Moreover, it will be recognized that although
heat sink 180 and lid 130 are shown as separable parts, heat sink
180 may be integrated with lid 130 in a single integral part.
[0028] In an exemplary embodiment referring to FIG. 3, vapor
chamber 160 is integrated in a base defining heat sink 180 while
lid 130 is a solid substrate. It will be recognized by one skilled
in the pertinent art that having vapor chamber 160 integrated in a
base of the heat sink versus lid 130, enables the vapor chambers to
spread the heat well beyond the confines of the cap of a module
(e.g., lid 130). In an exemplary embodiment depicted in FIG. 3, a
width of the heat sink vapor chambers are about twice the width of
lid 130. In either case, it is noted that the vapor chamber heat
sink assembly 20 of FIG. 2 includes a combination of heat sink 180
and lid 130 or a base of heat sink 180 having vapor chamber 160
integrated therewith, as in FIG. 3.
[0029] While MCM 100 has been illustrated in FIGS. 1 and 2 and
described above as a ball grid array (BGA) module, MCM 100 may be
pin grid array (PGA) module. Instead of solder balls 125 (see FIG.
2), Land Grid Array (LGA) connections between substrate 102 and PCB
120 are also contemplated. Since LGA connections are asperity
contact connections, generally some degree of pressure must be
maintained on the connection to ensure good electrical
conductivity. Therefore, flanges 184 defining ends of heat sink 180
may be used accept a mechanical fastener and engage substrate 120
to provide the necessary pressure to ensure suitable electrical
conductivity.
[0030] Referring now to FIG. 4, a vertically oriented heat sink 180
is in thermal communication with a prior art evaporator 200 having
a corresponding vertically oriented single vapor chamber 260, which
is in turn in thermal communication with a heat source 210. Heat
source 210 is centrally located with respect to a bottom surface
240 defining a length of evaporator 200. It will be recognized that
heat source 210 may be MCM 100 as described above. In many such
evaporators, a heat transfer fluid generally indicated at 220 such
as, inter alia, water, has a tendency to accumulate at a bottom of
vapor chamber 260 generally indicated at 224 because of gravity
acting on transfer fluid 220. The result is inadequate liquid to
evaporate heat load proximate heat source 210 and evaporator 200
proximate the heat source 240 dries out as the heat therefrom is
conducted further towards the water accumulation at 224, reducing
thermal performance of the assembly. The thermal performance is
reduced by the increase in thermal resistance due to an increase in
path length for the heat to travel to heat sink 180 because of the
dried out section local to the centrally located heat source
210.
[0031] Referring now to FIG. 5, vertically oriented heat sink 180
is illustrated in thermal communication with an exemplary
embodiment of an evaporator 300 defining at least two distinct
vapor chambers 360, which is in turn in thermal communication with
heat source 210. Heat source 210 is substantially centrally located
with respect to a bottom surface 340 defining a length of
evaporator 300 as described with respect to heat source 210 in FIG.
3, however, heat source 210 may be aligned anywhere along a length
defining bottom surface 340. It will be recognized that heat source
210 may be MCM 100 as described above. Since heat transfer fluid
220 has the tendency to accumulate at a bottom of vertically
oriented vapor chamber 260 in FIG. 4, vapor chamber 360 in FIG. 5
includes an upper vapor chamber 361 and a lower vapor chamber 362
separated from upper chamber 361 via a horizontal barrier 370
therebetween. Barrier 370 is configured to prevent condensed heat
transfer fluid 220 from being pulled by gravity past heat source
210 into vapor chamber 362. Barrier 370 extends from bottom surface
340 to upper surface 350, substantially normal to both.
[0032] In an exemplary embodiment as illustrated, barrier 370 is a
horizontal solid section separating vapor chamber 360 into two
distinct chambers, 361, 362. The larger upper vapor chamber 361
will have an ample supply of heat transfer fluid available near
heat source 210 in spite of gravity acting thereon in vertical
mount applications. Even though the lower vapor chamber 362 still
works against gravity, lower vapor chamber 362 still provides some
added cooling. Vapor chambers 361 and 362 together outperform a
single vapor chamber in most vertical applications because adequate
liquid is available and local to heat source 210 to evaporate heat
load proximate heat source 210. Heat from heat source 210 is less
prone to dry out vapor chamber 361 since a bottom of vapor chamber
361 is substantially aligned with heat source 210. In particular, a
bottom of heat source 210 substantially coincides with a bottom of
vapor chamber 361 where heat transfer fluid 220 would tend to
accumulate due to gravity. Thus, the heat transfer path is less
likely to increase because vapor chamber 361 insures that the local
evaporator area is wet, thus lowering thermal resistance of heat
transfer to heat sink 180.
[0033] The thermal performance is increased by lowering thermal
resistance due to a decreased path length for the heat to travel to
heat sink 180 because of eliminating a dried out section local to
the centrally located heat source 210.
[0034] In an exemplary embodiment, upper vapor chamber 361 is
configured having a bottom portion thereof substantially aligned or
alternatively, not extending much past heat source 210 insuring
that the evaporator area local to the heat source 210 is wet with
condensed heat transfer fluid 220. The lower vapor chamber 362
works against gravity over a region similar to that described with
respect to the single vapor chamber 260 in FIG. 3, but still
provides some added cooling. The mean path for the heat to travel
from heat source 210 to find condensed heat transfer fluid is
reduced by two or more separate vapor chambers defining evaporator
300, thus lowering the thermal resistance to heat sink 180.
Although, upper vapor chamber 361 has been described as being
larger, e.g., longer relative to vertical, than lower vapor chamber
362, vapor chambers may be configured having substantially the same
length or lower chamber 362 may be longer than upper vapor chamber
361.
[0035] For example, FIG. 6 depicts lower vapor chamber 362
configured longer than upper chamber 361. In this case, it will be
noted that heat source 210 is then more efficiently disposed
towards an upper portion defining a length of bottom surface
340.
[0036] Thus, an efficiently cooled IC, such as a MCM, that employs
vapor chamber cooling with a plurality of separate vapor chambers
in thermal communication with a vertically oriented heat sink
assembly while minimizing dry out conditions and reducing thermal
resistance has been described.
[0037] While the invention has been described with reference to
exemplary embodiments, it will be understood by those skilled in
the art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the invention. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
invention without departing from the essential scope thereof.
Therefore, it is intended that the invention is not to be limited
to the particular embodiment disclosed as the best or only mode
contemplated for carrying out this invention, but that the
invention will include all embodiments falling within the scope of
the appended claims. Moreover, the use of the terms first, second,
etc. do not denote any order or importance, but rather the terms
first, second, etc. are used to distinguish one element from
another. Furthermore, the use of the terms a, an, etc. do not
denote a limitation of quantity, but rather denote the presence of
at least one of the referenced item.
* * * * *