U.S. patent application number 15/219555 was filed with the patent office on 2016-11-17 for combined electromagnetic shield and thermal management device.
The applicant listed for this patent is Baomin Liu, Todd W. Steigerwald. Invention is credited to Baomin Liu, Todd W. Steigerwald.
Application Number | 20160338232 15/219555 |
Document ID | / |
Family ID | 54192496 |
Filed Date | 2016-11-17 |
United States Patent
Application |
20160338232 |
Kind Code |
A1 |
Liu; Baomin ; et
al. |
November 17, 2016 |
COMBINED ELECTROMAGNETIC SHIELD AND THERMAL MANAGEMENT DEVICE
Abstract
Various EMI shields with thermal management capabilities are
disclosed. In one aspect, an EMI shield is provided that includes a
thermal spreader plate adapted to be seated on and convey heat from
an electromagnetic emissions generating component. The thermal
spreader plate has a first material composition and a shield
effectiveness that is absorption dominant to electromagnetic waves
at a given electromagnetic emissions frequency. The EMI shield also
includes a shell to cover and reflect electromagnetic emissions
from the electromagnetic emissions generating component. The shell
has a second material composition different than the first material
composition and a shield effectiveness that is reflection dominant
to electromagnetic waves at the given electromagnetic emissions
frequency.
Inventors: |
Liu; Baomin; (Austin,
TX) ; Steigerwald; Todd W.; (Austin, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Liu; Baomin
Steigerwald; Todd W. |
Austin
Austin |
TX
TX |
US
US |
|
|
Family ID: |
54192496 |
Appl. No.: |
15/219555 |
Filed: |
July 26, 2016 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
14231988 |
Apr 1, 2014 |
9420734 |
|
|
15219555 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H05K 1/0203 20130101;
G06F 1/203 20130101; H01L 2924/0002 20130101; H01L 2924/3025
20130101; H05K 9/0024 20130101; H05K 9/0026 20130101; H01L 23/552
20130101; G06F 1/1656 20130101; H05K 1/0243 20130101; H01L 21/4882
20130101; H05K 1/0209 20130101; H05K 2201/10371 20130101; H01L
2924/0002 20130101; H01L 2924/00 20130101; H01L 23/3675 20130101;
Y10T 29/4902 20150115; H01L 23/36 20130101 |
International
Class: |
H05K 9/00 20060101
H05K009/00; H01L 23/552 20060101 H01L023/552; H01L 21/48 20060101
H01L021/48; G06F 1/16 20060101 G06F001/16; G06F 1/20 20060101
G06F001/20; H01L 23/367 20060101 H01L023/367; H05K 1/02 20060101
H05K001/02 |
Claims
1. An EMI shield, comprising: a thermal spreader plate adapted to
be seated on and convey heat from an electromagnetic emissions
generating component positioned on a substrate having a ground
pathway, the thermal spreader plate having a first material
composition and a shield effectiveness that is absorption dominant
to electromagnetic waves at a given electromagnetic emissions
frequency; and a shell to cover and reflect electromagnetic
emissions from the electromagnetic emissions generating component,
the shell having a second material composition different than the
first material composition and a shield effectiveness that is
reflection dominant to electromagnetic waves at the given
electromagnetic emissions frequency, the shell having sidewalls
surrounding the electromagnetic emissions generating component
laterally and extending to the substrate when the EMI shield is
seated on the electromagnetic emissions generating component, the
shell being operable to connect to the ground pathway.
2. The EMI shield of claim 1, comprising a gap between the spreader
plate and the shell.
3. The EMI shield of claim 2, comprising plural posts positioned
between the spreader plate and the shell to transfer heat.
4. The EMI shield of claim 1, wherein the shell comprises a first
metal jacketed by a second metal.
5. The EMI shield of claim 1, comprising a first thermal interface
material between the thermal spreader plate and the shell.
6. An apparatus, comprising: a substrate having a ground pathway;
an electromagnetic emissions generating component on the substrate;
and an electromagnetic emissions shield coupled to the substrate
and having a thermal spreader plate seated on the electromagnetic
emissions generating component, the thermal spreader plate having a
first material composition and a shield effectiveness that is
absorption dominant to electromagnetic waves at a given
electromagnetic emissions frequency, and a shell to cover and
reflect electromagnetic emissions from the electromagnetic
emissions generating component, the shell having a second material
composition different than the first material composition and a
shield effectiveness that is reflection dominant to electromagnetic
waves at the given electromagnetic emissions frequency, the shell
being electrically connected to the ground pathway and having
sidewalls surrounding the electromagnetic emissions generating
component laterally and extending to the substrate.
7. The apparatus of claim 6, comprising a gap between the thermal
spreader plate and the shell.
8. The apparatus of claim 7, comprising plural posts positioned
between the thermal spreader plate and the shell to transfer
heat.
9. The apparatus of claim 6, wherein the shell comprises a first
metal jacketed by a second metal.
10. The apparatus of claim 6, comprising a first thermal interface
material between the thermal spreader plate and the shell and a
second thermal interface material between the thermal spreader
plate and the electromagnetic emissions generating component.
11. The apparatus of claim 6, comprising an electronic device, the
substrate being mounted in the electronic device.
12. A method of thermally managing and electromagnetically
shielding an electromagnetic emissions generating component
positioned on a substrate, comprising: seating a thermal spreader
plate on the electromagnetic emissions generating component, the
thermal spreader plate having a first material composition and a
shield effectiveness that is absorption dominant to electromagnetic
waves at a given electromagnetic emissions frequency; and covering
the thermal spreader plate and the electromagnetic emissions
generating component with a shell to reflect electromagnetic
emissions from the electromagnetic emissions generating component,
the shell having a second material composition different than the
first material composition and a shield effectiveness that is
reflection dominant to electromagnetic waves at the given
electromagnetic emissions frequency, the shell being electrically
grounded and having sidewalls surrounding the electromagnetic
emissions generating component laterally and extending to the
substrate.
13. The method of claim 12, comprising establishing a gap between
the thermal spreader plate and the shell.
14. The method of claim 13, comprising positioning plural posts
positioned between the thermal spreader plate and the shell to
transfer heat.
15. The method of claim 12, wherein the shell comprises a first
metal jacketed by a second metal.
16. The method of claim 12, comprising placing a first thermal
interface material between the thermal spreader plate and the shell
and a second thermal interface material between the thermal
spreader plate and the electromagnetic emissions generating
component.
17. The method of claim 12, wherein the substrate is positioned in
an electronic device.
18. A method of manufacturing, comprising: fabricating a thermal
spreader plate adapted to be seated on and convey heat from an
electromagnetic emissions generating component positioned on a
substrate having a ground pathway, the thermal spreader plate
having first material composition and a shield effectiveness that
is absorption dominant to electromagnetic waves at a given
electromagnetic emissions frequency; and fabricating a shell to
cover and reflect electromagnetic emissions from the
electromagnetic emissions generating component, the shell having a
second material composition different than the first material
composition and a shield effectiveness that is reflection dominant
to electromagnetic waves at the given electromagnetic emissions
frequency, the shell having sidewalls surrounding the
electromagnetic emissions generating component laterally and
extending to the substrate when the EMI shield is seated on the
electromagnetic emissions generating component, the shell being
operable to connect to the ground pathway.
19. The method of claim 18, comprising placing the thermal spreader
plate on the electromagnetic emissions generating component and the
shell over the thermal spreader plate and the electromagnetic
emissions generating component.
20. The method of claim 19, establishing a gap between the thermal
spreader plate and the shell.
21. The method of claim 20, comprising positioning plural posts
positioned between the thermal spreader plate and the shell to
transfer heat.
22. The method of claim 19, comprising placing a first thermal
interface material between the thermal spreader plate and the shell
and a second thermal interface material between the thermal
spreader plate and the electromagnetic emissions generating
component.
Description
[0001] This application is a continuation of prior application Ser.
No. 14/231,988, filed Apr. 1, 2014.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates generally to electronic devices, and
more particularly to thermal management and electromagnetic
interference shielding for electronic devices.
[0004] 2. Description of the Related Art
[0005] The form factors and thicknesses of handheld computing
devices, such as smart phones, tablet computers and e-book readers,
have been trending downward for some time. At the same time, the
complexity and power dissipation of these devices has been
increasing. There is ongoing user demand for devices that are not
only smaller form factor for greater portability but also powerful
enough to handle video and other computing intensive tasks. The
provision for significant computing power in a relatively small
form device often translates into the need for significant thermal
management of the heat dissipating devices. The inclusion of
electromagnetic interference (EMI) sensitive components, such as
radios, into these devices has introduced challenges in EMI
shielding in addition to thermal management. Onboard components,
such as processors, generate electromagnetic emissions with
electric field (E-field) and magnetic field (H-field components)
that interfere with the operations of the onboard radios. The near
field effects created by the tight spacing in small form electronic
devices present shielding challenges.
[0006] One common solution used to transfer heat from a processor
in a small form device includes the use of a thermal spreader that
is in thermal contact with the processor. The heat spreader is in
turn, in thermal contact with a heat exchanger via a heat pipe or
other structure. The heat exchanger often includes an air mover
such as a fan. One example of such a conventional device is the
model LE1700 manufactured by Motion Computing, Inc. The LE1700
includes a very thin fan that drives air flow through metal fins
that are connected thermally to a thermal spreader mounted to the
microprocessor and by way of a heat pipe. The hot air then goes to
the external ambient by way of a small vent. An Acer model Iconia
is another conventional example.
[0007] In many conventional designs, EMI shielding and thermal
management have been treated as discrete problems and addressed
with discrete solutions. One conventional EMI shield design
utilizes a shell that is placed over a processor on a system board.
The shell is connected to the system board ground plane, but is not
in thermal contact with the processor and thus does not provide
thermal management.
[0008] The present invention is directed to overcoming or reducing
the effects of one or more of the foregoing disadvantages.
SUMMARY OF THE INVENTION
[0009] In accordance with one aspect of the present invention, an
EMI shield is provided that includes a thermal spreader plate
adapted to be seated on and convey heat from an electromagnetic
emissions generating component. The thermal spreader plate has a
first material composition and a shield effectiveness that is
absorption dominant to electromagnetic waves at a given
electromagnetic emissions frequency. The EMI shield also includes a
shell to cover and reflect electromagnetic emissions from the
electromagnetic emissions generating component. The shell has a
second material composition different than the first material
composition and a shield effectiveness that is reflection dominant
to electromagnetic waves at the given electromagnetic emissions
frequency.
[0010] In accordance with another aspect of the present invention,
an apparatus is provided that includes a substrate, an
electromagnetic emissions generating component on the substrate and
an electromagnetic emissions shield coupled to the substrate. The
shield has a thermal spreader plate seated on the electromagnetic
emissions generating component. The thermal spreader plate has a
first material composition and a shield effectiveness that is
absorption dominant to electromagnetic waves at a given
electromagnetic emissions frequency. The shield also includes a
shell to cover and reflect electromagnetic emissions from the
electromagnetic emissions generating component. The shell has a
second material composition different than the first material
composition and a shield effectiveness that is reflection dominant
to electromagnetic waves at the given electromagnetic emissions
frequency.
[0011] In accordance with another aspect of the present invention,
a method of thermally managing and electromagnetically shielding an
electromagnetic emissions generating component is provided. The
method includes seating a thermal spreader plate on the
electromagnetic emissions generating component. The thermal
spreader plate has a first material composition and a shield
effectiveness that is absorption dominant to electromagnetic waves
at a given electromagnetic emissions frequency. The method also
includes covering the thermal spreader plate and the
electromagnetic emissions generating component with a shell to
reflect electromagnetic emissions from the electromagnetic
emissions generating component. The shell has a second material
composition different than the first material composition and a
shield effectiveness that is reflection dominant to electromagnetic
waves at the given electromagnetic emissions frequency.
[0012] In accordance with another aspect of the present invention,
a method of manufacturing is provided that includes fabricating a
thermal spreader plate adapted to be seated on and convey heat from
an electromagnetic emissions generating component where the thermal
spreader plate has a first material composition and a shield
effectiveness that is absorption dominant to electromagnetic waves
at a given electromagnetic emissions frequency. A shell is
fabricated to cover and reflect electromagnetic emissions from the
electromagnetic emissions generating component. The shell has a
second material composition different than the first material
composition and a shield effectiveness that is reflection dominant
to electromagnetic waves at the given electromagnetic emissions
frequency.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The foregoing and other advantages of the invention will
become apparent upon reading the following detailed description and
upon reference to the drawings in which:
[0014] FIG. 1 is an exploded pictorial view of an exemplary
embodiment of a computing device with an EMI shield;
[0015] FIG. 2 is a sectional view of FIG. 1 taken at section
2-2;
[0016] FIG. 3 is a portion of FIG. 2 shown at greater
magnification;
[0017] FIG. 4 is a schematic view of a small portion of the
computing device depicted in FIGS. 1, 2 and 3 depicting
electromagnetic wave propagation;
[0018] FIG. 5 is a sectional view of an alternate exemplary EMI
shield;
[0019] FIG. 6 is a sectional view of another alternate exemplary
EMI shield;
[0020] FIG. 7 is a sectional view of another alternate exemplary
EMI shield;
[0021] FIG. 8 is a sectional view of another alternate exemplary
EMI shield;
[0022] FIG. 9 is a portion of FIG. 2 shown at greater
magnification;
[0023] FIG. 10 is a view like FIG. 9, but depicting an alternate
exemplary electromagnetic shield coupling process;
[0024] FIG. 11 is a view like FIG. 10, but depicting another
alternate exemplary shield coupling process;
[0025] FIG. 12 is a pictorial view of an alternate exemplary
circuit board and EMI shield configuration; and
[0026] FIG. 13 is a pictorial view of an alternate exemplary
circuit board and EMI shield configuration.
DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
[0027] Various embodiments of a computing device are disclosed. In
one arrangement, a computing device, such as a tablet computer,
includes a housing with an internal space holding a circuit board
and an electromagnetic emissions generating component, such as a
semiconductor chip. A combined EMI shield and thermal spreader is
mounted over the electromagnetic emissions generating component.
The shield and thermal spreader includes a spreader plate on the
chip and a shell over the spreader plate and chip. The spreader
plate is fabricated with a material composition that is absorption
dominant to electromagnetic waves to electromagnetic waves and the
shell is fabricated with a different material composition that is
reflection dominant to electromagnetic waves to electromagnetic
waves. This arrangement produces an electromagnetic intrinsic wave
impedance mismatch between the spreader plate and the shell, which
enhances signal attenuation due to multiple wave reflections at
layer interfaces. Additional details will now be described.
[0028] In the drawings described below, reference numerals are
generally repeated where identical elements appear in more than one
figure. Turning now to the drawings, and in particular to FIG. 1
which is an exploded pictorial view of an exemplary embodiment of a
computing device 100 that includes a housing 105 that includes an
internal volume 110 designed to hold a variety of components, such
as a substrate 115 configured as a circuit board or other type of
substrate and a battery 120. A display unit 125, which may or may
not be touch-enabled, may be seated on the housing 105. The housing
105 may be composed of well-known materials such as plastics,
carbon fibers, aluminum, stainless steel or others. The computing
device 100 may be any of a number of different types of computing
devices, such as hand held computers, smart phones, or virtually
any other portable computing device.
[0029] The substrate 115 may be populated by a variety of
components, a few of which are depicted in FIG. 1. For example, the
substrate 115 may include one or more electromagnetic emissions
generating components, such as a packaged semiconductor device 130
that includes a semiconductor chip 135 mounted on a package
substrate 140, as well as other devices such as the memory devices
145 and 150. In addition, the substrate 115 may include one or more
radios 155 and 160. The radios 155 and 160 may be near field
communications devices, local area network devices, wide area
network devices, global positioning devices, radio frequency
identification devices, combinations of these or other types of
communications devices. To shield the radios 155 and 160 from
potentially interfering electromagnetic (E-field and H-field)
emissions from the semiconductor chip 135 and/or the chips 145 and
150, an EMI shield/thermal spreader 165 (hereinafter STS 165) may
be placed over the semiconductor chip device 130 and the chips 145
and 150 as well as any other components that might produce
potentially interfering emissions. The STS 165 is designed to
provide both thermal management and electromagnetic emission
shielding. In this illustrative embodiment, the STS 165 and the
substrate 115 may have rectangular footprints. However, various
other types of footprints are possible as will be illustrated in
subsequent figures. It should be understood that the STS 165 and
any disclosed alternatives may be used to provide thermal
management and E-field/H-field shielding in virtually any
circumstance where a given device may be sensitive to
E-field/H-field interference from another nearly located device
that is emitting such potentially interfering emissions. Examples
of such devices are legion and include microprocessors, graphics
processors, optical chips, systems-on-chip, combined
microprocessors/graphics processors or virtually any other type of
integrated circuit.
[0030] Additional details of the substrate 115 and the STS 165 may
be understood by referring now also to FIG. 2, which is a sectional
view of a portion of FIG. 1 taken at section 2-2. It should be
understood that FIG. 2 shows the substrate 115 and the STS 165 but
only portions of the housing 105 and the display unit 125 depicted
in FIG. 1 are shown for simplicity of illustration. The mounting
substrate 140 may be electrically interfaced with the substrate 115
in a variety of ways. For example, ball grid arrays, pin grid
arrays or other types of interconnect schemes may be used. As noted
above, two functions of the STS 165 are to providing thermal
management for components, such as the semiconductor chip 135, and
to shield the radios 155 and 160 from potentially interfering
E-field and H-field emissions from the semiconductor chip 135
and/or the semiconductor chips 145 and 150 (only 150 is visible in
the sectional view of FIG. 2). In this regard, the STS 165 may
include a thermal spreader plate 170 and an external shell 175. The
thermal spreader plate 170 is designed to provide thermal
management for the semiconductor chip 135. A thermal interface
material 180 may be positioned between the spreader plate 170 and
the semiconductor chip 135. Another thermal interface material 185
may be positioned between the spreader plate 170 and the shell 175.
Thermal interface materials 180 and 185 may play a part in
attenuating E-field and H-field emissions as described below.
Accordingly, exemplary materials for the thermal interface
materials 180 and 185 will also be described in more detail below.
The types of materials suitable for the shell 175 and the spreader
plate 170 will influence the shielding and thermal management
characteristics of the STS 165 and will be discussed in more detail
below.
[0031] The shield shell 175 also plays a part in thermal management
in a few ways. The shell 175 reduces the width z of the gap 186
between the display 125 and the STS 165 below what a typical
conventional EMI shield in a portable device would yield. A typical
value of z for a conventional design might be around 1.0 mm. In an
exemplary embodiment the value of z may be much less than 1.0 mm. A
smaller value of z translates into less thermal resistance of the
fluid (e.g., air) in the gap 186. In addition, the shell 175
provides a relatively larger surface area and thus improved thermal
spreading functionality. Finally, the shell 175 provides a
conductive heat transfer pathway from the chip 135 to the substrate
115.
[0032] The portion of FIG. 2 circumscribed by the dashed rectangle
190 will be shown at greater magnification in FIG. 3 and used to
illustrate additional features of the STS 165. The portion of FIG.
2 circumscribed by the dashed rectangle 195 will be shown at
greater magnification in the subsequent figure to illustrate an
exemplary technique of securing the shield shell 175 to the
substrate 115. Attention is now turned to FIG. 3, which as just
noted, is the portion of FIG. 2 circumscribed by the dashed
rectangle 190. Because of the location of the dashed rectangle 190,
portions of the semiconductor chip 135, the thermal interface
material 180, the spreader plate 170, the thermal interface
material 185, and the shell 175 are visible. The thermal interface
material 180 may have some thickness d.sub.180, the spreader plate
170 may have some thickness d.sub.170, the thermal interface
material 185 may have some thickness d.sub.185, and the shell 175
may have some thickness d.sub.175 where d.sub.170 and d.sub.175 are
selected based on the anticipated E-field and H-field emissions
from the semiconductor chip 135 and any other adjacent devices, the
anticipated sensitivity to near field interference of other devices
on the substrate 115 shown in FIG. 2, as well as a variety of other
physical parameters such as material composition, thermal
conductivity, electrical conductivity, permeability and the
strength of the E-field and H-field emissions from the chip 135.
The desired thicknesses of the thermal interface material layers
180 and 185 will be dictated largely, though not exclusively, by
thermal management considerations.
[0033] As noted above, the selection of the materials for the
spreader plate 170 and the shield shell 175 as well as the
respective thicknesses thereof may be selected in concert to
provide a synergistic shielding effect due to a deliberately
selected intrinsic wave impedance mismatch between the spreader
plate 170 and the shield shell 175. To illustrate the various
physical phenomena associated with E-field and H-field propagation
from the semiconductor chip 135, attention will be directed to FIG.
4, which is a view like FIG. 3 but with the cross-hatching removed
so that various vectors and labels may be more easily seen.
Incident waves of electromagnetic energy are generated by the chip
135. The incident waves have an electric field component E.sub.inc
and a magnetic field component H.sub.inc, where the subscript "inc"
denotes incident. The traditional technique of using the symbol
.circleincircle. to graphically representing a magnetic field
component of an electromagnetic wave coming out of the page and the
symbol to represent the magnetic field component going into the
page is followed here. Some of the incident waves reflect off of
the interface 200 between the chip and the thermal interface
material 180 and those result in reflected waves which similarly
have E-field and H-field components. For simplicity of
illustration, the remainder of the various types of waves that
propagate through the layers 180, 170, 185 and 175 are shown
without E-field and H-field terminology or symbols. Some of the
incident waves pass through the interface 200 and into the thermal
interface material 180, resulting in plural forward waves, plural
reverse waves and plural multiple reflective waves. As described in
more detail below, some of the forward waves will produce multiple
reflective waves upon encountering the interfaces 210 and 205 on
either side of the thermal interface material 180, while others
will produce reflected waves. Some of the energy propagating
through the layer 180 will be absorbed and some propagated into the
spreader plate 170 as forward waves where again reverse waves will
exist as well as multiple reflective waves. This process continues
through the thermal interface material 185 and the external shell
175 where some portion of the incident waves generated by the chip
135 will emerge from the shield shell 175 as transmitted (sometimes
alternatively termed "retransmitted") waves that have both an
E-field and H-field component. The total attenuation of the signal
from the chip 135 due to the combined mechanisms of reflection,
absorption and multiple reflection through the various layers 180,
170, 185 and 175 is such that the magnitude or strength of
transmitted waves is less than the magnitude or strength incident
waves. The presence of the various interfaces 200, 205, 210, 215,
220, 225, 230, 235 and 240 provide structure to facilitate the
attenuation by way of reflection and multiple reflection as
described in more detail below. It should be understood that the
attenuation due to absorption, reflection and multiple reflection
will be dependent on, among other things, the thicknesses
d.sub.180, d.sub.170, d.sub.185 and d.sub.175 of the various layers
180, 170, 185 and 175.
[0034] The shield effectiveness SE(f) as a function of frequency f
for a hypothetical single layer shield with an air to metal
interface is usually denoted in units of dB and given by:
SE(f)=R(f)+A(f)+M(f) (1)
where R(f) is the signal attenuation due to reflection at air-metal
interface, AO is the signal attenuation due to absorption in the
metal layer and M(f) is signal attenuation due to multiple
reflections in the metal layer. Depending on the properties of the
shield layer, one component of the right hand side of Equation (1)
may be dominant or larger than the others. For the example of a
copper layer, the A(f) component will be dominant, while for a
stainless layer, the R(f) will be dominant.
[0035] The situation is more complex with additional layers of
metals and/or dielectrics, including air. The shield effectiveness
SE.sub.nlayers(f) as a function of f for a shield of any number of
n layers is denoted and given generally by:
SE nlayers ( f ) = 1 n R x ( f ) + 1 n A x ( f ) + 1 n M x ( f ) (
2 ) ##EQU00001##
In the illustrative embodiment depicted in FIGS. 1-4, the STS 165
has four layers: the thermal interface material layer 180, the
metal layer 170, a thermal interface material layer 185 and the
metal shell layer 175, thus n is equal to 4 for Equation (2). Since
the effect of adding additional layers is cumulative, the first two
layers, namely the thermal interface material layer 180 and the
metal layer 170, will be used to provide a simplified illustration
of the calculation of shield effectiveness. The shield
effectiveness SE.sub.180&170 for the combination of the thermal
interface material layer 180 and the metal layer 170 is given
by:
SE.sub.180&170(f)R.sub.180(f)+R.sub.170(f)+A.sub.180(f)+A.sub.170(f)+M.s-
ub.180(f)+M.sub.170(f) (3)
where the subscripts "180" and "170" denote the values for the
layers 180 or 170. The behavior the two layers 180 and 170 may be
modeled by using an analogous arrangement of two cascaded
transmission lines. Under this assumption, the total signal
attenuation due to reflection R.sub.180(f)+R.sub.170(f) is given
by:
R 180 ( f ) + R 170 ( f ) = 20 log ( 1 2 1 + .eta. 180 ( f ) .eta.
0 ) + 20 log ( 1 2 1 + .eta. 170 ( f ) .eta. 180 ( f ) ) + 20 log (
1 2 1 + .eta. 0 .eta. 170 ( f ) ) ( 4 ) ##EQU00002##
where the intrinsic wave impedance .eta..sub.180(f) of the layer
180 is given by:
.eta. 180 ( f ) = 2 .pi. f .mu. 180 .mu. 0 2 .sigma. 180 .sigma. 0
( 1 + j ) ( 5 ) ##EQU00003##
where .mu..sub.180 is the permeability in teslam/ampere of the
layer 180, .mu..sub.0 is the permeability constant 4.pi.10.sup.-7
teslam/ampere, .sigma..sub.0 is the conductivity of air or
3.times.10.sup.-15 to 8.times.10.sup.-15 mhos/m, .sigma..sub.180 is
the conductivity in mhos/m of the layer 180 and given by:
.delta. 180 ( f ) = 1 .pi. f .mu. 180 .sigma. 180 .sigma. 0 and ( 6
) j = - 1 ( 7 ) ##EQU00004##
In Equation (4), the intrinsic wave impedance .eta..sub.170(f) of
the layer 170 is given by:
.eta. 170 ( f ) = 2 .pi. f .mu. 170 .mu. 0 2 .sigma. 170 .sigma. 0
( 1 + j ) ( 8 ) ##EQU00005##
where .mu..sub.170 is the permeability in tesla of the layer 170
and .sigma..sub.170 is the conductivity in mhos/m of the layer 170
and given by:
.delta. 170 ( f ) = 1 .pi. f .mu. 170 .sigma. 170 .sigma. 0 ( 9 )
##EQU00006##
Finally, the intrinsic wave impedance .eta..sub.0 of air is given
by:
.eta. 0 = .mu. 0 0 ( 10 ) ##EQU00007##
where .di-elect cons..sub.0 is the permittivity constant
8.854.times.10.sup.-12 C.sup.2/Nm.sup.2.
[0036] Referring again to Equation (4), the total signal
attenuation A.sub.180(f)+A.sub.170(f) due to absorption is given
by:
A 180 ( f ) + A 170 ( f ) = 20 log 10 1 ( d 180 .delta. 180 ( f ) +
d 170 .delta. 170 ( f ) ) ( 11 ) ##EQU00008##
where d.sub.180 and d.sub.170 are the thicknesses of the layers 180
and 170 and .sigma..sub.180 and .sigma..sub.170 are given by
Equations (6) and (9).
[0037] The calculations for signal attenuation due to multiple
reflections under a cascade transmission lines model is more
complicated than for either reflection or absorption. Here, the
attenuation M.sub.180(f) due to multiple reflections in the layer
180 is given by:
M 180 ( f ) = 20 log [ 1 - ( .eta. 180 ( f ) - .eta. 0 .eta. 180 (
f ) + .eta. 0 ) ( .eta. 180 ( f ) - .eta. in 170 ( f ) .eta. 180 (
f ) + .eta. in 170 ( f ) ) - 2 ( 1 .delta. 180 ( f ) + j 1 .delta.
180 ( f ) ) d 180 ] ( 12 ) ##EQU00009##
where the intrinsic wave impedance .eta..sub.in170(f) of the layer
170 is given by:
.eta. in 170 ( f ) = n 170 ( f ) .eta. 0 cos h [ ( 1 .delta. 170 (
f ) + j 1 .delta. 170 ( f ) ) d 170 ] + n 170 ( f ) sin h [ ( 1
.delta. 170 ( f ) + j 1 .delta. 170 ( f ) ) d 170 ] .eta. 2 cos h [
( 1 .delta. 170 ( f ) + j 1 .delta. 170 ( f ) ) d 170 ] + n 170 ( f
) sin h [ ( 1 .delta. 170 ( f ) + j 1 .delta. 170 ( f ) ) d 170 ] (
13 ) ##EQU00010##
and the attenuation M.sub.170(f) due to multiple reflections in the
layer 170 is given by:
M 170 ( f ) = 20 log [ 1 - ( .eta. 170 ( f ) - .eta. 180 ( f )
.eta. 170 ( f ) + .eta. 180 ( f ) ) ( .eta. 170 ( f ) - .eta. 0
.eta. 170 ( f ) + .eta. 0 ) - 2 ( 1 .delta. 170 ( f ) + j 1 .delta.
170 ( f ) ) d 170 ] ( 14 ) ##EQU00011##
The calculations of attenuation due to reflection, absorption and
multiple reflections for each succeeding layer, such as the layers
185 and 175, may be performed by plugging additional terms for the
layers 185 and 175 into Equations (3)-(6), (8)-(9) and (11)-(14)
above to yield to total attenuation. It is anticipated that
attenuation may be enhanced by deliberately mismatching the
intrinsic wave impedance of adjacent layers. For example, the
thermal spreader plate 170 and the shell 175 may be constructed of
materials and/or thicknesses that yield mismatched intrinsic wave
impedances. The same is true of interposed dielectrics, such as the
thermal interface material layers 180 and 185. The interfaces
between such intrinsic wave impedance mismatched layers can enhance
signal attenuation.
[0038] Shielding is not the only design consideration envisioned by
the disclosed embodiments. In addition to serving as an
electromagnetic shield, the STS 165 also functions as a thermal
management device, such as a thermal spreader. In this regard,
material selection for components of a given STS embodiment can
take into account beneficial thermal conductivity to provide
desirable thermal management. For example, the spreader plate 170
may be composed of a variety of well-known materials that exhibit
good thermal conductivity, such as copper, aluminum, silver,
platinum, gold, nickel, laminates or combinations of these or the
like. Indeed some exemplary materials for the various components of
the shields may be as follows:
TABLE-US-00001 TABLE 1 Spreader Plate 170 and Shell 175 Electrical
Relative Thermal Conductivity .sigma. Permeability* Conductivity*
Material (mho/m) at 20.degree. C. .mu./.mu..sub.0 W/cm K Silver
6.30 .times. 10.sup.7 -- 4.29 Copper 5.96 .times. 10.sup.7 1 3.9
Gold 4.10 .times. 10.sup.7 -- 3.17 Aluminum 3.5 .times. 10.sup.7 1
2.37 Tungsten 1.79 .times. 10.sup.7 -- 1.74 Zinc 1.69 .times.
10.sup.7 -- 1.1 Nickel 1.43 .times. 10.sup.7 100 to 600 0.9 Iron
1.00 .times. 10.sup.7 25,000 0.802 Platinum 9.43 .times. 10.sup.6 1
0.716 Tin 9.17 .times. 10.sup.6 -- 0.66 Carbon steel .sup. 1.43
.times. 10.sup.-7 100 0.52 (1020) Lead 4.55 .times. 10.sup.6 --
0.35 Titanium 2.38 .times. 10.sup.6 -- 1.8 Constantan 2.04 .times.
10.sup.6 -- 0.2 (cupronickel 55-45) Stainless 1.45 .times. 10.sup.6
-- 0.15 steel (304) Indium 1.25 .times. 10.sup.7 -- 1.47 Carbon
1.25 to 2 .times. 10.sup.3 -- -- (amorphous) Carbon (graphite) 2 to
3 .times. 10.sup.5 -- -- 2.5 .times. 10.sup.-6 to //basal plane 5.0
.times. 10.sup.-6 3.3 .times. 10.sup.2 //basal plane .perp.basal
plane 3.0 .times. 10.sup.-3 .perp. basal plane Carbon (diamond) ~1
.times. 10.sup.-13 -- 8 to 35 1 .times. 10.sup.12 *Note that a dash
-- indicates that the physical constant in question was not
available to the inventors at the time of filing.
TABLE-US-00002 TABLE 2 Thermal Interface Materials 180 and 185
Material Properties* Greases, or thermal compounds, such thermal
conductivity from 0.8 as silicone or hydrocarbon oils based to 7.0
W/mK interface with various fillers, with bond line resistance from
1 K cm.sup.2/W to thickness from 50 to 100 .mu.m about 0.2 K
cm.sup.2/W Phase change materials, such as a melting range of about
45 low temperature thermoplastic to 80.degree. C. and thermal
adhesives resistance in the range 0.3- 0.7 K cm.sup.2/W Gels
thermal resistance in the range 0.4 to 0.8 K cm.sup.2/W. Thermal
adhesives, such as epoxy or thermal resistance in the silicone base
with fillers range of about 1 to 0.15 K cm.sup.2/W *note that
conductivity .sigma. will be dependent on particular
compositions
As discussed above, it is anticipated that attenuation may be
enhanced by deliberately mismatching the intrinsic wave impedance
of adjacent layers, and this may be accomplished by constructing
the spreader plate 170 with a material composition and the shell
175 with a different material composition. Furthermore, it is
desirable for the thermal spreader 170 to have a shield
effectiveness that is absorption dominant to electromagnetic waves
and the shell 175 to have a shield effectiveness that is reflection
dominant to electromagnetic waves at a given frequency of
electromagnetic emissions. In an exemplary embodiment, the thermal
spreader plate 170 may be fabricated from copper and with a
thickness of about 0.2-0.5 mm and the shell 175 from 301 stainless
steel with a thickness of about 0.050 to 0.15 mm. A thin coating of
a solderable material, such as tin in a thickness range of about 20
to 100 .mu.m may be added to the shell 175. These selections will
yield mismatched intrinsic wave impedances.
[0039] The number and types of layers used in the STS 165 and any
disclosed alternatives may be varied to provide different types of
characteristics. For example, FIG. 5 shows a sectional view of an
alternate exemplary STS 265 that includes a spreader plate 270 and
a shield shell 175 that may be configured like the spreader plate
170 and shell 175 discussed elsewhere herein. However, in lieu of a
material that physically contacts both the plate 270 and the shell
275, a gap 277 is provided between the spreader plate 270 and the
shell 275. The gap 277, in this embodiment an air gap, serves as an
additional layer to provide signal attenuation by way of reflection
and multiple reflections. It may be possible to establish the air
gap by first mounting the spreader plate 270 on an underlying
structure, such as a chip (not shown) and thereafter placing the
shell 275 over but not on the spreader plate 270. Optionally, the
spreader plate could be coupled to the shell 275 so as to create
the gap 277.
[0040] Another alternate exemplary STS 365 is depicted in section
in FIG. 6. In this illustrative embodiment, the STS 365 may include
a spreader plate 370 like the other plate 170 and 270. However, a
shell 375 may consist of a metallic core 379 jacketed by a plating
layer 381. The layers 370, 379 and 381 may be composed of the types
of metallic materials described elsewhere herein. The combination
of the plate 370, the core 379 and the plating layer 381 provide a
triple layer shield that not only provides thermal management but
also multiple interfaces between the layers 370, 379 and 381, which
provide the multiple reflection absorption and single reflection
signal attenuation as described elsewhere herein.
[0041] Another alternate exemplary embodiment of a STS 465 is
depicted in section in FIG. 7. The STS 465 may be substantially
identical to the STS 365 depicted in FIG. 6 and thus may include a
spreader plate 470, a shell 475 that includes a core 479 and a
plating layer 481 jacketing the core 479. Here, however, a
dielectric layer 483 may be interposed between the spreader plate
470 and the shell 475. The dielectric layer 483 may be composed of
any of the types of dielectric materials described elsewhere
herein. The provision of the dielectric layer introduces yet
another set of interfaces and a layer that may enhance the signal
attenuation of the shield 465.
[0042] Another alternate exemplary embodiment of a STS 565 is
depicted in section in FIG. 8. The STS 565 may be substantially
similar to the STS embodiment 265 depicted in FIG. 5. Here,
however, in lieu of a pure air gap 277 as is the case for the
embodiment depicted in FIG. 5, a spreader plate 570 may be
separated from a shell 575 by a gap 577, but also connected to the
shell 575 by plural posts 586. The posts 586 provide thermal
pathways between the spreader plate 570 and the shell 575. In this
way, the gap 577 provides less thermal resistance than a pure air
gap. The posts 586 may be composed of a variety of thermally
conductive materials such as copper, silver, diamond, platinum,
gold, laminates of these or the like. The number, size and spacing
of the posts 586 may be subject to a great variety. There may be
some reduction in the attenuation capacity of the shield 565 due to
the posts 586 and the connection that they make between the shell
575 and the plate 570. However, this reduction in attenuation
should be weighed against the benefit of providing better capacity
for heat transfer from the plate 570 to the shell 575.
[0043] A variety of mounting schemes may be used to connect the STS
165, and disclosed alternatives, to the substrate 115. In this
regard, attention is now turned to FIG. 9, which is the portion of
FIG. 2 circumscribed by the dashed rectangle 195 shown at greater
magnification. Note that due to the location of the dashed
rectangle 195, a portion of the shield shell 175 of the STS 165, as
well as a portion of the substrate 115 are shown. It is desirable
to electrically connect the shield shell 175 to a ground pathway
associated with the substrate 115. This may be accomplished in a
variety of ways. For example, the shield shell 175 may be both
physically and electrically connected to the substrate 115 by way
of one or more solder beads or fillets 686 that may be spaced
around the perimeter of the shield shell 175, on the outside and
optionally on the inside as well. The solder fillets 686 may be
connected electrically to a bond pad 687 that is tied to a ground
pathway 688 associated with the substrate 115. Optionally, the pad
687 may be constructed as a single contiguous trace that goes
around the perimeter of the shell 175. In like fashion, the solder
fillet 686 may be disposed around some or all of the perimeter of
the shell 175. In this illustrative embodiment, the shell 175 and
in particular a lower peripheral wall 689 thereof may seat directly
on an upper surface 691 of the substrate 115. The ground pathway
688, schematically illustrated, may be by through-hole via, buried
via, blind via or other conductor.
[0044] Another alternate exemplary embodiment of a substrate 715
and a STS 765 is depicted in section in FIG. 10. Like the
embodiment depicted in FIG. 9, the STS 765 may include a shield
shell 775 that is mounted on the substrate 715 and connected to a
bond pad 787 and ground pathway 788. The ground pathway 788,
schematically illustrated, may be by through-hole via, buried via,
blind via or other conductor. Instead of being seated on the upper
surface 791 of the substrate 715, the shell 775 is depressed into a
groove 792 formed in the upper surface 791 of the substrate 715 and
placed in direct ohmic contact with the bond pad 787. If desired,
an adhesive 793 may be placed at the interface of the upper surface
791 and the shell 775 (inside and outside if desired) to hold the
shell 775 in place.
[0045] Another alternate exemplary embodiment of a substrate 815
and a STS 865 is depicted in section in FIG. 11. Like the
embodiment depicted in FIG. 9, the STS 865 may include a shield
shell 875 that is mounted on the substrate 815 and connected by a
solder fillet 886 to a bond pad 887 and ground pathway 888. Instead
in this illustrative embodiment, the shield shell 875 may be
configured as a multi-piece structure that includes a bottom shell
894 that may be mounted on the substrate 815 and a top shell 896
that is designed to be placed over the bottom shell 894 and held in
place. The top shell 896 may be held in place relative to the
bottom shell 894 in a variety of ways. For example, the top shell
896 may be provided with plural bumps 897 that may depress into
corresponding dimples 899 in the lower shell 894. Other types of
fastening mechanisms include screws, flexible brads, or virtually
any other fastening technique.
[0046] As noted above, the footprints of the shields and substrates
may be other than rectangular. In this regard, attention is now
turned to FIG. 12, which is a pictorial view of an alternate
exemplary substrate 1015 and a STS 1065 with other than rectangular
footprints. Similarly, FIG. 13 is a pictorial view of another
alternate exemplary embodiment in which a substrate 1115 and a STS
1165 may have other than rectangular footprints.
[0047] While the invention may be susceptible to various
modifications and alternative forms, specific embodiments have been
shown by way of example in the drawings and have been described in
detail herein. However, it should be understood that the invention
is not intended to be limited to the particular forms disclosed.
Rather, the invention is to cover all modifications, equivalents
and alternatives falling within the spirit and scope of the
invention as defined by the following appended claims.
* * * * *