U.S. patent application number 09/761368 was filed with the patent office on 2001-10-04 for emi reduction device and assembly.
Invention is credited to Cheong Chan, Bertram Kim, Gardner, Susannah, Mellberg, Hans T..
Application Number | 20010026440 09/761368 |
Document ID | / |
Family ID | 23246312 |
Filed Date | 2001-10-04 |
United States Patent
Application |
20010026440 |
Kind Code |
A1 |
Mellberg, Hans T. ; et
al. |
October 4, 2001 |
EMI reduction device and assembly
Abstract
An EMI reduction device coupled between to a printed circuit
board (PCB) assembly and a heat sink is herein disclosed. The PCB
assembly includes a processor core that is the source of
unintentional electromagnetic interference (EMI). The EMI reduction
device is attached to a heat sink which is positioned over the
processor core such that it capacitively couples emissions from the
processor core to a grounding plane resident in the PCB assembly,
thereby reducing the unintentional EMI. Simultaneously, the EMI
reduction device is able to maintain thermal contact with the heat
sink.
Inventors: |
Mellberg, Hans T.; (Santa
Cruz, CA) ; Cheong Chan, Bertram Kim; (Sunnyvale,
CA) ; Gardner, Susannah; (San Carlos, CA) |
Correspondence
Address: |
HEWLETT-PACKARD COMPANY
Intellectual Property Administration
P. O. Box 272400
Fort Collins
CO
80527-2400
US
|
Family ID: |
23246312 |
Appl. No.: |
09/761368 |
Filed: |
January 16, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09761368 |
Jan 16, 2001 |
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09320412 |
May 26, 1999 |
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6219239 |
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Current U.S.
Class: |
361/704 |
Current CPC
Class: |
H05K 9/002 20130101;
H05K 7/1431 20130101 |
Class at
Publication: |
361/704 |
International
Class: |
H05K 007/20 |
Claims
In the claims:
1. An electronic assembly apparatus, comprising: a circuit board
having a top surface and a bottom surface, the circuit board
including an electronic device emanating electromagnetic emissions;
an EMI reduction device that is coupled to the circuit board, the
EMI reduction device is positioned around the outer periphery of
the electronic device, the EMI reduction device touches the circuit
board at contact points that surround the electronic device, the
EMI reduction device has no physical contact with the electronic
device; and a thermal dissipation device that is coupled to the EMI
reduction device and the circuit board, the thermal dissipation
device is positioned over the top surface of the circuit board;
wherein the thermal dissipation device dissipates heat generated
from the circuit board; wherein the EMI reduction device reduces
electromagnetic emissions generated from the electronic device.
2. The apparatus of claim 1, the EMI reduction device including at
least one mounting clip for attaching the EMI reduction device to
the thermal dissipation device.
3. The apparatus of claim 1, the EMI reduction device including a
plurality of spring fingers that surround the electronic device and
maintain physical contact with the circuit board.
4. The apparatus of claim 1, the EMI reduction device including an
aperture that is positioned over the electronic device; wherein the
aperture enables the electronic device to maintain thermal contact
with the thermal dissipation device.
5. The apparatus of claim 1, the thermal dissipation device having
a top surface and a bottom surface, the bottom surface including a
thermal compound; wherein the thermal compound is coupled to the
electronic device.
6. The apparatus of claim 1, the EMI reduction device having a top
surface and a bottom surface, the bottom surface having a
dielectric layer.
7. An EMI reduction device for use with an electronic device
mounted on a circuit board, comprising: a frame that is coupled to
the circuit board, the frame surrounds peripheral portions of the
electronic device, the frame is not in physical contact with the
electronic device, the frame having a top surface and a bottom
surface; and a plurality of spring fingers that are coupled to the
circuit board, the spring fingers are positioned onto the circuit
board at points that surround the electronic device.
8. The apparatus of claim 7, comprising: an aperture that surrounds
the electronic device; wherein the aperture enables the electronic
device to maintain thermal contact with a thermal dissipation
device.
9. The apparatus of claim 7, comprising: a fastener that is coupled
to a thermal dissipation device; wherein the fastener enables the
EMI reduction device to be detachably mounted to a thermal
dissipation device.
10. The apparatus of claim 7, wherein the electronic device is a
processor.
11. The apparatus of claim 7, wherein the bottom surface of the
frame is non-electrically conductive.
12. The apparatus of claim 7, wherein the top surface of the frame
is electrically conductive.
13. A method for reducing EMI emissions emanating from an
electronic device having a ground plane, said method comprising the
steps of: surrounding the outer periphery of the electronic device
with a frame that has no direct physical contact with the
electronic device; contacting the frame to the ground plane at
contact points that surround the electronic device; and
capacitively coupling the EMI emissions from the electronic device
to the ground plane.
14. The method of claim 13, comprising the steps of: placing a
thermal dissipation device over the electronic device; and
dissipating heat generated from the electronic device through the
thermal dissipation device.
15. The method of claim 14, comprising the step of: attaching the
frame to the thermal dissipation device.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to electronic
systems. More particularly, the invention relates to an
electromagnetic interference (EMI) reduction device.
BACKGROUND OF THE INVENTION
[0002] A trend in the electronics industry is to generate smaller
and faster electronic devices. As a result, these devices consume
more power and hence, produce more heat. Excessive heat can cause
significant damage to an electronic device thereby reducing its
life. For this reason, various techniques are employed to eliminate
or dissipate the heat generated from the electronic device. A heat
sink is one such technique. A heat sink is thermally coupled to the
electronic device and as such, allows the heat to flow from the
electronic device through the heat sink to the surrounding open
space.
[0003] In addition, the operation of these electronic devices is
accompanied by the generation of electromagnetic radiation or
energy. The emissions of the electromagnetic radiation can cause
significant electronic interference or noise with other surrounding
electronic circuitry. To reduce such disturbances, the source of
these emissions is usually suppressed. However, the EMI suppression
problem is further complicated when the electronic device is
coupled to a heat sink. The heat sink acts as an antenna for the
EMI energy thereby amplifying the EMI energy.
[0004] A common solution for suppressing EMI energy is to ground
the heat sink. FIG. 1 illustrates an exemplary grounded heat sink.
There is shown a heat sink 100 coupled to a grounded electronic
device 102 that is mounted onto a printed circuit board (PCB) 104.
In this example, the grounded electronic device 102 is a processor
core having a silicon logic die 106. A thermal compound 108, such
as a dielectric material, is placed between the heat sink 100 and
the grounded electronic device 102 so that thermal contact is
maintained and the heat generated by the device 102 is transferred
to the heat sink 100.
[0005] Mounting fences 110 are positioned on four opposite sides of
the PCB 104 in order to ground the heat sink 100. The mounting
fences 110 are attached to the heat sink 100 and the PCB 104, which
acts in this case as a ground plane. The mounting fences 110
provide a Faraday shield around the device 102 in order to shield
the EMI energy generated from the clock circuitry internal to the
processor 102 from damaging adjacent components and from releasing
EMI energy outside of the heat sink 100.
[0006] Additional EMI suppression is provided by four sets of
grounding pads 112a-112d on the PCB 104 that surround the processor
102, as shown in FIG. 2. The grounding pads 112 minimize or ground
EMI noise generated by the switching of all the component pins
under maximum capacitive load. Thus, the combination of the
grounding pads and the grounded heat sink dissipates the heat from
the processor core and grounds the EMI energy generated by the
processor core.
[0007] As the internal clock speed of processors increase, these
processors will require more extensive EMI reduction or grounding.
In some cases, the grounded heat sink approach may not be suitable
to effectively eliminate the EMI emissions since this approach has
a longer grounding path. As such, grounding may need to be
performed closer to the silicon logic die in order to create a
shorter grounding path that effectively shields the EMI energy
emanating from the processor core.
[0008] Accordingly, there is a need for an EMI reduction technique
that can minimize or eliminate EMI energy generated from a
processor core closer to the source of the emissions and in such a
manner that is cost efficient and easy to manufacture.
SUMMARY OF THE INVENTION
[0009] The present invention pertains to an EMI reduction device
that is coupled between a printed circuit board (PCB) assembly and
a heat sink. The PCB assembly includes a processor core that is the
source of a large amount of electromagnetic interference. In a
first embodiment, the EMI reduction device is fastened to a heat
sink which is positioned over the processor core such that it
capacitively couples the emissions from the processor while
maintaining thermal contact with the heat sink.
[0010] In a first embodiment, the EMI reduction device has a
electrically-conductive rectangular frame that includes a die
aperture positioned in the center of the device, four mounting clip
tabs, and four spring contact fingers. The die aperture allows the
processor logic die to be in direct physical contact with the
bottom surface of the heat sink thereby maintaining thermal contact
between the processor logic die and the heat sink. The four
mounting clip tabs are positioned on the outer periphery of the
reduction device and are used to clip the EMI reduction device to
the heat sink.
[0011] The spring contact fingers are located on each of the four
sides of the processor. The spring contact fingers are the only
portion of the EMI reduction device that maintains physical contact
with the PCB assembly. This is to ensure that the EMI reduction
device does not protrude directly onto the PCB assembly yet remains
in close proximity to the processor. As such, the EMI reduction
device is not in direct electrical contact with the PCB assembly.
The EMI reduction device grounds the processor emissions by
capacitively coupling them to the ground plane present in the PCB
assembly.
[0012] A pair of heat sink retention clips is used to secure the
heat sink to the PCB assembly. The heat sink retention clips are
inserted through mounting holes on the heat sink in a downward
direction through the mounting holes of the EMI clip and on the PCB
assembly.
[0013] The placement of the EMI clip in close proximity with the
processor is beneficial since it creates a shorter grounding path
thereby effectively reducing the EMI energy emanating from the
processor directly at the source. In addition, the EMI clip is able
to accomplish this while maintaining thermal contact with the heat
sink. Furthermore, performing the EMI reduction at the processor is
more economical than incorporating an EMI reduction technique into
a chassis assembly that houses the PCB assembly.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] For a better understanding of the nature and objects of the
invention, reference should be made to the following detailed
description taken in conjunction with the accompanying drawings, in
which:
[0015] FIG. 1 is a schematic view of a prior art grounded heat sink
assembly for a printed circuit board;
[0016] FIG. 2 is a top plan view of the printed circuit board used
in the grounded heat sink assembly shown in FIG. 1;
[0017] FIG. 3 is a perspective view of a processor module in
accordance with a first embodiment of the present invention;
[0018] FIG. 4 is an exploded view of the components of the
processor module shown in FIG. 3;
[0019] FIG. 5 illustrates the processor module positioned on a
printed circuit board as part of computer system in accordance with
the embodiments of the present invention;
[0020] FIG. 6 is a front perspective view of the printed circuit
board assembly shown in FIGS. 3 and 4;
[0021] FIG. 7 is a top plan view of the printed circuit board shown
in FIG. 6;
[0022] FIG. 8 is a perspective view of the bottom side of the EMI
clip shown in FIGS. 3 and 4;
[0023] FIG. 9 is a top plan view of the EMI clip positioned onto
the printed circuit board assembly in accordance with a first
embodiment of the present invention;
[0024] FIG. 10 is a perspective view of the heat sink shown in
FIGS. 3 and 4 in accordance with the embodiments of the present
invention;
[0025] FIG. 11 is cross-sectional view of the processor module
taken along plane AA shown in FIG. 3;
[0026] FIG. 12 is a rear perspective view of the heat sink with the
EMI clip attached thereto in accordance with the first embodiment
of the present invention;
[0027] FIG. 13 is an isometric view of a printed circuit board
having spring fingers mounted onto the PCB assembly in accordance
with a second embodiment of the present invention; and
[0028] FIG. 14 is an isometric view of a printed circuit board
having spring washers in accordance with a third embodiment of the
present invention.
[0029] Like reference numerals refer to corresponding parts
throughout the several views of the drawings.
DETAILED DESCRIPTION OF THE INVENTION
[0030] FIGS. 3 and 4 depict a processor module 120 having a PCB
assembly 122, an EMI clip or reduction device 124, a heat sink 126,
and a pair of heat sink retention clips 128a-128b. The PCB assembly
122 includes a processor core 130. The EMI clip 124 is positioned
onto the PCB assembly 122 surrounding the processor core 130 and is
used to efficiently shield the EMI emissions generated from the
processor core 130. The EMI clip 124 is removably mounted to the
heat sink 126. The heat sink 126 is thermally coupled to the PCB
assembly 122 and is used to transfer the heat from the electronic
components to the heat sink 126. A pair of heat sink retention
clips 128 is used to fasten the heat sink 126 to the PCB assembly
122.
[0031] The processor module 120 can be removably mounted onto a
motherboard or other type of circuit board. For example, as shown
in FIG. 5, the processor module 120 is positioned onto a
motherboard 127 through a processor retention assembly 129. The
motherboard 127 can be part of a computer system, subsystem, or the
like.
[0032] Preferably, the PCB assembly 122 is a Single Edge Contact
Cartridge 2 (SECC2) manufactured by the Intel Corporation. The
SECC2 supports "slot" type processors. A slot is a connector that
is resident on a motherboard and which supports the Intel P6
microprocessor bus. Previously, microprocessors were mounted onto a
motherboard through a socket. In a slot-type processor, the
processor is placed on a PCB known as a single edge contact (SEC).
The SEC has pins on an edge of the card which is inserted into a
242-pin slot on the motherboard . This pin construction is
otherwise known as an edge finger connection.
[0033] A more detailed discussion of the SECC2 can be found in
Intel Corporation, Single Edge Contact Connector 2 (S.E.C.C.2)
Thermal Interface Material Functional Requirements, Order No:
244458-001, November 1998; Intel Corporation, Single Edge Contact
Cartridge 2 (S.E.C.C.2) Heat Sink Attachment and Heat Sink
Functional Requirements Order Number: 244456-001, Nov. 23, 1998;
and Intel Corporation, S.E.C.C.2 Heat Sink Installation and Removal
Process, Order Number 244454-001, December 1998 which are hereby
incorporated by reference as background information.
[0034] FIG. 6 illustrates the SECC2 122. There is shown a printed
circuit board 132 and a cover 134. The PCB 132 is preferably a
substrate constructed of a multilayer plastic laminate, such as a
plastic land grid array or organic land grid array processor core
substrates. The substrate 132 has an edge finger connection. In
addition, the substrate 132 includes a ground plane. The cover 134
is used to protect the PCB 132 and is removably mounted to the
cover 134 through a set of snaps 136. However, it should be noted
that the technology of the present invention is not constrained to
the SECC2, to any particular circuit board, or to any particular
circuit board layout.
[0035] FIG. 7 illustrates the PCB 132 in further detail. There is a
processor core 130 that includes a silicon logic die 138. The PCB
132 includes four attachment holes 140a-140d through which the heat
sink retention clips 128 are fit so that the heat sink can be
attached to the PCB assembly 122. In addition, surrounding the
logic die 138, there are other electronic components, such as but
not limited to cache memory, resistors, capacitors, and the like.
However, in this embodiment of the PCB 132, there are no grounding
pads.
[0036] FIG. 8 illustrates the EMI clip 124. The EMI clip 124 has
rectangular-shaped frame including a die aperture 150, four
mounting clip tabs 152a-152d, four attachment holes 154a-154d, and
four spring contact fingers 156a-156d. The die aperture 150 is of a
rectangular shape and is located in the center of the EMI clip 124.
The EMI clip 124 is positioned over the logic die 138 so that the
die aperture 150 allows the logic die 138 to be in direct physical
contact with the surface of the heat sink 126.
[0037] The four mounting clip tabs 152a-152d are used to attach the
EMI clip 124 to the heat sink 126. The mounting clip tabs 152a-152d
are located on the outer periphery of the EMI clip 124 and are
situated in each corner of the top side of the EMI clip 124.
[0038] The mounting holes 154a-154d are located on the surface of
the top side of the EMI clip 124 and each mounting hole 154 is
located at a particular corner of the EMI clip 124. Each of the
four mounting holes 154a-154d are aligned with a respective
mounting hole 140 on the PCB 132 and with a respective mounting
hole on the heat sink. The retention clips 128 are inserted through
the mounting holes 166 on the heat sink 126 in a downward direction
through the mounting holes 154 on the EMI clip 124 through the
mounting holes 140 on the PCB 132.
[0039] The four spring contact fingers 156a-156d are situated on
the bottom side of the EMI clip 124 and allow the EMI clip 124 to
maintain physical contact on four sides of the processor core 130.
The contact fingers 156 are the only portion of the EMI clip 124
that is in physical contact with the PCB 132. The spring fingers
156 ensure that the frame of the EMI clip 124 does not protrude
directly onto any of the components of the PCB 132. Direct contact
with the processor substrate 132 would damage the electronic
components positioned under the EMI clip 124. As such, each of the
spring contact fingers 156 is positioned on the PCB 132 in an area
where there are no electronic components.
[0040] The shape, size and dimension of the EMI clip 124 is
tailored for the particular processor substrate 132 to which the
clip 124 is coupled. FIG. 9 illustrates the placement of the EMI
clip 124 onto a SECC2 122. For this embodiment, the EMI clip 124 is
approximately 48.97 mm by 54.35 mm. The die aperture 150 is 19 mm
by 18 mm and is constructed such that there is a 6 mm distance
between the outer edge of the processor aperture to the outer edge
of the processor logic die. It should be noted that the present
invention is not constrained to an EMI clip 124 having the
particular shape, size and dimensions described herein and one
skilled in the art can easily modify the design of the EMI clip 124
to suit other PCBs or the like.
[0041] The electromagnetic bandwidth of the processor core can
extend to include multiple times the advertised processor clock
speed. In the case of an Intel Pentium II processor with an
internal clock speed of 500 MHz, the EMI bandwidth can extend to
2500 MHz or more. The EMI clip 124 reduces portions of that
bandwidth with varying shielding effectiveness and can vary
depending on the mechanical dimensions of the EMI clip 124. Another
modifier to EMI reduction is the mechanical pressure that exits
both on the heat sink 126 and on the processor core 130. The higher
the pressure the more effective the capacitive coupling becomes and
hence the EMI reduction.
[0042] Preferably, the EMI clip 124 is constructed of thin steel
sheet metal. However, the present invention is not constrained to
any particular type of metal and can be constructed of any
material, such as but not limited to stainless steel, beryllium
copper, phospher bronze, hardened steel, spring steel, and the
like.
[0043] Referring to FIG. 12, the bottom side of the heat sink 126,
that side which touches the PCB 132, is coated with a dielectric
layer that ensures that the EMI clip 124 does not short the
electronic components mounted on the surface of the PCB 132. An
example of such a dielectric coating is powder paint, in
particular, the epoxy power coatings based on epoxy resins.
[0044] The placement of the EMI clip 124 over the processor core
130 and in the manner described above is effective in reducing the
EMI emissions from the processor core 130. Although, the EMI clip
124 is not in direct electrical contact with the processor core
130, its close proximity to the processor core 130 capacitively
couples these emissions to the ground plane of the substrate 132
and through a shorter grounding path. As a result, the emissions
are minimized or eliminated directly at the processor core 130.
[0045] FIGS. 10 and 11 illustrates the heat sink 126. The heat sink
126 has a number of fins 160, a base portion 162, and two skirts
164a-164b. The fins 160 project outwardly and upwardly from the
base portion 162. The base portion 162 extends over and covers the
processor core 130 thereby providing the maximum amount of thermal
contact area between the processor core 130 and the heat sink 126.
The two skirts 164a-164b extend laterally and downwardly from the
base portion 162 and extends over and covers opposite sides of the
PCB assembly 122.
[0046] The fins 160 are eliminated where the heat sink retention
clips 128 are positioned (see FIGS. 3 and 4) into two groves
situated on the top surface of the base portion of the heat sink
126. The groves include mounting holes 166 that enable the heat
sink retention clips 128 to fit through the top surface of the base
portion 162. The retention clips 128 are inserted through the
mounting holes 166 on the heat sink 126 in a downward direction
through the mounting holes 154 on the EMI clip 124 through the
mounting holes 140 on the PCB 132.
[0047] The heat sink retention clips 128 are made from a flexible
material that is non-electrically conductive, such as plastic. The
heat sink retention clips 128 are secured at one end in any
appropriate manner, and in the present example by barbed ties.
Preferably, the heat sink retention clips 128 are those heat sink
retention clips designed for the SECC2 and which are manufactured
by ITW Fastex.
[0048] FIG. 12 illustrates the bottom side of the base portion 162
of the heat sink 126. There is shown the EMI clip 124 mounted to
the base portion 162 of the heat sink 126. Each mounting clip 152
is fitted over onto a corresponding groove 170 on the base portion
of the heat sink 126.
[0049] The heat sink 126 is made of aluminum that is chromate
conversion coated and is electrically conductive. A thermal
compound 168, such as a dielectric layer, is placed on the bottom
side of the base portion 162 of the heat sink 126. This dielectric
layer is used to provide high dielectric capacity and to provide a
high thermal conductivity between the processor logic die 138 and
the heat sink 126. An example of such a compound is MCM-STRATE.RTM.
manufactured by Power Devices, Inc. However, the present invention
is not constrained to any particular type of material and other
materials having the same properties can also be used.
[0050] The foregoing description, for purposes of explanation, used
specific nomenclature to provide a thorough understanding of the
invention. However, it will be apparent to one skilled in the art
that the specific details are not required in order to practice the
invention. In other instances, well known circuits and devices are
shown in order to avoid unnecessary distraction from the underlying
invention. Thus, the foregoing descriptions of specific embodiments
of the present invention are presented for purposes of illustration
and description. They are not intended to be exhaustive or to limit
the invention to the precise forms disclosed, obviously many
modifications and variations are possible in view of the above
teachings. The embodiments were chosen and described in order to
best explain the principles of the invention and its practical
applications, to thereby enable others skilled in the art to best
utilize the invention and various embodiments with various
modifications as are suited to the particular use contemplated. It
is intended that the scope of the invention be defined by the
following claims and their equivalents.
[0051] In particular, one skilled in the art can alter the EMI clip
described above to include additional spring fingers in order to
provide more capacitive contacts between the EMI clip and the
substrate. In another alternate embodiment, the EMI clip can be
used in conjunction with grounding pads that are positioned on the
substrate. In yet another embodiment, the EMI clip can be made an
integral part of the heat sink and not a separate device.
Furthermore, the EMI clip can be made without the dielectric
coating on the bottom surface thereby making electrical contact
with the PCB. Alternatively, the EMI clip can be applied to a
processor that is mounted directly onto a motherboard and is not
constrained to edge finger connection devices.
[0052] FIG. 13 illustrates a second embodiment of the present
invention. In this embodiment, there is no EMI clip 124 rather
spring fingers 180a-180d mounted directly onto the printed circuit
board 132'. Preferably, a spring finger 180 is mounted on each side
surrounding the processor core 130'. As shown in FIG. 13, there are
four spring fingers 180a-180d mounted directly onto the circuit
board 132'. However, the number of spring fingers 180 and their
position of the circuit board 132 is not a limitation of this
embodiment.
[0053] A heat sink is mounted directly over the circuit board 132'
and coupled with retention clips in the manner described above. The
bottom surface of the heat sink will be in direct physical contact
with the processor die 138' and the top surface of the spring
fingers 180. As such, the emissions from the processor die 138' are
capacitively coupled to the ground plane in the circuit board 132'
and suppressed directly at the source of the emissions.
[0054] FIG. 14 illustrates a third embodiment of the present
invention. In this embodiment, the ground plane of the circuit
board 132" is extended to and through the mounting holes
140a"-140d" on the circuit board 132". A spring washer 182a-182d is
mounted in each mounting hole 140a"-140d". A heat sink is mounted
over the top surface of the circuit board 132".
[0055] The spring washers 182 are formed of an electrically
conductive material, such as but not limited to thin sheet steel
metal and are shaped as a compression coil. The spring washers 182
serve to ground the emissions from the processor core 130" while
ensuring that the placement of the heat sink on top of the circuit
board 132" does not damage the processor core 130" and the
electronic components mounted thereon.
[0056] Each spring washer 182 has a hollow core that is wide enough
to allow a retention clip to fit through it thereby allowing the
heat sink to be fastened to the circuit board 132" in the manner
described above. When the heat sink is fastened to the circuit
board 132", the spring washers 182 are compressed by the weight of
the heat sink and the bottom surface of the heat sink is in direct
physical contact with the processor die 138" and the top surface of
the spring washers 182. As such, the emissions from the processor
die 138" are grounded to the ground plane in the circuit board 132"
and suppressed directly at the source of the emissions.
* * * * *