U.S. patent application number 11/905813 was filed with the patent office on 2008-02-14 for structure for electromagnetically shielding a substrate.
This patent application is currently assigned to Mitsubishi Denki Kabushiki Kaisha. Invention is credited to Hiroyuki Kimata, Yasuhiro Yamanaka.
Application Number | 20080037238 11/905813 |
Document ID | / |
Family ID | 34985645 |
Filed Date | 2008-02-14 |
United States Patent
Application |
20080037238 |
Kind Code |
A1 |
Kimata; Hiroyuki ; et
al. |
February 14, 2008 |
Structure for electromagnetically shielding a substrate
Abstract
A circuit board that requires electromagnetic shielding is
enclosed in a cavity formed between a metal case and a base
substrate. A ground plane, which is electrically conductive, is
embedded in each of the base substrate and the circuit board. The
metal case is electrically connected to the ground planes in both
the base substrate and the circuit board.
Inventors: |
Kimata; Hiroyuki; (Tokyo,
JP) ; Yamanaka; Yasuhiro; (Tokyo, JP) |
Correspondence
Address: |
BUCHANAN, INGERSOLL & ROONEY PC
POST OFFICE BOX 1404
ALEXANDRIA
VA
22313-1404
US
|
Assignee: |
Mitsubishi Denki Kabushiki
Kaisha
Tokyo
JP
|
Family ID: |
34985645 |
Appl. No.: |
11/905813 |
Filed: |
October 4, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10894120 |
Jul 20, 2004 |
7295083 |
|
|
11905813 |
Oct 4, 2007 |
|
|
|
Current U.S.
Class: |
361/818 |
Current CPC
Class: |
H05K 9/0039 20130101;
H05K 1/141 20130101; H05K 9/0026 20130101 |
Class at
Publication: |
361/818 |
International
Class: |
H05K 9/00 20060101
H05K009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 17, 2004 |
JP |
2004-076659 |
Claims
1. An electromagnetic shield structure for electromagnetically
shielding a target substrate, the target substrate having a first
surface, a second surface opposite to the second surface, and a
plurality of side surfaces, comprising: a metal case that covers
the first surface and the side surfaces of the target substrate;
and a base substrate that includes a first ground plane and opposes
the second surface, wherein the metal case rests on the base
substrate and is electrically connected to the first ground
plane.
2. The electromagnetic shield structure according to claim 1,
wherein at least a part of the metal case and the first ground
plane are electrically connected via a through hole through the
base substrate.
3. The electromagnetic shield structure according to claim 1,
wherein the target substrate and the base substrate are connected
by connectors, the connectors being a means for input/output of
power and signals from the base substrate to the target
substrate.
4. The electromagnetic shield structure according to claim 1,
wherein the metal case is electrically connected to a second ground
plane provided within the target substrate.
5. The electromagnetic shield structure according to claim 4,
further comprising a selecting unit for selecting whether to
electrically connect the second ground plane and the metal
plate.
6. The electromagnetic shield structure according to claim 5,
wherein the selecting unit includes a first member that is
electrically connected to the second ground plane; and a second
member that is electrically connected to the metal case; and a
selecting member that electrically connects or disconnects the
first member and the second member.
7. An electromagnetic shield structure for electromagnetically
shielding a target substrate containing at least one circuit, the
target substrate having a first surface, a second surface opposite
to the second surface, and a plurality of side surfaces,
comprising: a metal case that covers the first surface and the side
surfaces of the target substrate; a base substrate that opposes the
second surface, wherein the metal case rests on the base substrate,
and base substrate includes a first ground plane; and connectors
that electrically connect the base substrate to the target
substrate to input power and signals from the base substrate to the
target substrate.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a Continuation Application of
Application No. 10/894,120, filed Jul. 20, 2004.
BACKGROUND OF THE INVENTION
[0002] 1) Field of the Invention
[0003] The present invention relates to an electromagnetic shield
structure for electromagnetically shielding a circuit board
substrate. More particularly, the present invention relates to an
electromagnetic shield structure that can block electromagnetic
noise radiating from a circuit board substrate.
[0004] 2) Description of the Related Art
[0005] Occurrence of electromagnetic noise when circuit elements
are powered up is a common phenomenon in a circuit board substrate
on which circuit elements such as transistors, IC, LSI, etc. are
mounted. If the electromagnetic noise is ignored and no appropriate
action is taken to shield it, it may lead to the malfunctioning of
the circuit board substrate, the electronic gadget in which the
circuit board substrate is used, and/or other electronic
gadgets.
[0006] There are two approaches to counter this problem. One is to
see to it that no major electromagnetic noise occurs in the first
place. The other is to suppress the electromagnetic noise, if there
is any, so that there is no widespread diffusion outside.
[0007] The former approach is a question of selection of the
circuit. There are technologies those make it possible to
drastically reduce the electromagnetic noise, for instance, see
Japanese Patent Laid-Open Publication No. H10-270862. In the
technology disclose in this literature, a multi-layer printed
circuit board substrate is fabricated by employing the method of
assembling on the printed circuit board substrate the circuit
elements such as the IC, LSI, etc. and wiring of the power source
layer (pattern design).
[0008] In the latter approach, a method involving shielding, that
is, using an appropriate material to enclose the circuit board
substrate so as to block the radiating electromagnetic noise, may
be used. Conventional shielding method involves sealing both the
surfaces of the circuit board substrate by a metal frame in order
to block the electromagnetic noise.
[0009] However, the conventional method of sealing both surfaces of
the circuit board substrate with a metal frame requires more area
because the frame needs to be accommodated. In addition, the cost
is higher since the metal frame adds to the product cost.
SUMMARY OF THE INVENTION
[0010] It is an object of the present invention to at least solve
the problems in the conventional technology.
[0011] An electromagnetic shield structure according to an aspect
of the present invention is for electromagnetically shielding a
target substrate. The target substrate has a first surface, a
second surface opposite to the second surface, and a plurality of
side surfaces. The electromagnetic shield structure includes a
metal case that covers the first surface and the side surfaces of
the target substrate; and a base substrate that opposes the second
surface. The metal case rests on the base substrate. The base
substrate holds a first ground plane that is electrically connected
to the metal case.
[0012] The other objects, features, and advantages of the present
invention are specifically set forth in or will become apparent
from the following detailed description of the invention when read
in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a cross-section of an electromagnetic shield
structure according to an embodiment of the present invention;
[0014] FIG. 2 is a perspective view from above of the metal frame
shown in FIG. 1;
[0015] FIG. 3 is a perspective view from below of the metal
frame;
[0016] FIG. 4 is a magnified cross-section of a region of
connection between the metal frame and an electromagnetic
shield-requiring substrate;
[0017] FIG. 5 is a magnified cross-section of a region of
connection between the metal frame and a base substrate;
[0018] FIG. 6 is a cross-section along the line C-C shown in FIG.
5;
[0019] FIG. 7 is a cross-section of a conventional electromagnetic
shield structure;
[0020] FIG. 8 is a magnified cross-section of an electromagnetic
shield structure according to another embodiment of the present
invention; and
[0021] FIG. 9 is a magnified cross-section of an electromagnetic
shield structure according to still another embodiment of the
present invention.
DETAILED DESCRIPTION
[0022] Exemplary embodiments of an electromagnetic shield structure
according to an embodiment of the present invention are explained
next with reference to the accompanying drawings. Although the
invention has been described with respect to specific embodiments
for a complete and clear disclosure, the appended claims are not to
be thus limited but are to be construed as embodying all
modifications and alternative constructions that may occur to one
skilled in the art which fairly fall within the basic teaching
herein set forth.
[0023] FIG. 1 is a cross-section of an electromagnetic shield
structure according to an embodiment of the present invention. An
electromagnetic shield-requiring substrate 2 in FIG. 1 is the
circuit board substrate that is shielded by the electromagnetic
shield structure. Various kinds of circuit elements such as
transistors, integrated circuits (ICs), large-scale integrations
(LSIs), etc. are mounted on the electromagnetic shield-requiring
substrate 2. When these circuit elements are powered up, they
produce an electromagnetic noise. If the electromagnetic noise is
ignored and no appropriate action is taken to check it, it may lead
to malfunctioning of the electromagnetic shield-requiring substrate
2 and the electronic gadget of which the electromagnetic
shield-requiring substrate 2 is a part, and in addition, may cause
other electronic gadgets to malfunction as well. The present
embodiment aims to block the electromagnetic noise. A metal frame 1
encloses a top surface 2a and sides of the electromagnetic
shield-requiring substrate 2. As shown in FIG. 2 and FIG. 3, the
metal frame 1 is a one-side-open, rectangular, metal case. FIG. 2
is a perspective view of the metal frame 1 viewed from above and
FIG. 3 is a perspective view of the metal frame 1 viewed from
below.
[0024] The metal frame 1 may be made of any material as long as it
effectively blocks the electromagnetic noise.
[0025] Further, although it is mentioned above that the metal frame
1 is one-side-open, rectangular, metal case, it may have any other
shapes. For instance, the metal frame 1 may be of a shape that is
same as that of the electromagnetic shield-requiring substrate 2,
or of a shape that is same as that of the electronic gadget in
which the electromagnetic shield-requiring substrate 2 is mounted.
The metal frame 1 may be of any shape as long as it effectively
encloses the top surface and the sides of the electromagnetic
shield-requiring substrate 2.
[0026] The metal frame 1 may also be of any size, such as to suit
the size of the electromagnetic shield-requiring substrate 2 or the
space inside the electronic gadget in which the-electromagnetic
shield-requiring substrate 2 is mounted, etc. as long as the metal
frame 1 effectively encloses the top surface and the sides of the
electromagnetic shield-requiring substrate 2.
[0027] The metal frame 1 is electrically connected to the
electromagnetic shield-requiring substrate 2 via connecting members
la provided inside the metal frame 1. To be more specific, the
metal frame 1 is connected to a connector pad 5 (see FIG. 4)
provided on the surface (the top surface 2a in FIG. 1), in other
words, the side that is opposite to a base substrate 11, of the
electromagnetic shield-requiring substrate 2 which is facing the
metal frame 1. The connector pad 5 is connected to an embedded
ground (GND) plane 2c provided within the electromagnetic
shield-requiring substrate 2. FIG. 4 is a magnified view of the
region A shown in FIG. 1, which is the point of connection between
the metal frame 1 and the electromagnetic shield-requiring
substrate 2.
[0028] The connector pad 5 and the embedded GND plane 2c are
electrically connected by a through hole 2d that traverses
widthwise from the top surface 2a of the electromagnetic
shield-requiring substrate 2 to the embedded GND plane 2c. This
connector pad 5 may be etched to match the surface pattern that is
pre-etched on the top surface 2a of the electromagnetic
shield-requiring substrate 2. If the electromagnetic
shield-requiring substrate 2 is a printed circuit board and the
like, the connector pad 5 can be etched together with the wiring
print, thus making the etching process simple.
[0029] The through hole 2d may have any shape or size as long as it
enables the embedded GND plane 2c and the top surface 2a of the
electromagnetic shield-requiring substrate 2 to be effectively
electrically connected. Further, there are no limitations on the
number of through holes 2d, and any number of through holes 2d may
be provided.
[0030] Further, the connector pad 5 used in the electromagnetic
shield according to the present invention may be of any material as
long as it enables the metal frame 1 and the electromagnetic
shield-requiring substrate 2 to be effectively electrically
connected.
[0031] The connector pad 5 again may be of any shape as long as it
enables the metal frame 1 and the electromagnetic shield-requiring
substrate 2 to be effectively electrically connected, and may have
a shape that matches the shape of the connecting member 1a, and the
like.
[0032] The connector pad 5 may be of any size as long as it enables
the metal frame 1 and the electromagnetic shield-requiring
substrate 2 to be effectively electrically connected, and may be of
a size that matches the size of the connecting member 1a, and the
like.
[0033] The other surface (the bottom surface 2b) of the
electromagnetic shield-requiring substrate 2 is covered by the base
substrate 11 provided on the side of the bottom surface 2b of the
electromagnetic shield-requiring substrate 2. The base substrate 11
functions as a foundation for the electromagnetic shield-requiring
substrate 2. The base substrate 11 is disposed substantially
parallel to and at a predetermined distance from the
electromagnetic shield-requiring substrate 2.
[0034] An embedded GND plane 4 is disposed in the base substrate 11
running roughly parallel to the main surfaces (a top surface 11a
and a bottom surface 11b) of the base substrate 11. The width of
the embedded GND plane 4 is broader than the width of the
electromagnetic shield-requiring substrate 2 in all directions.
Consequently, the bottom surface 2b of the electromagnetic
shield-requiring substrate 2 is covered by the embedded GND plane 4
provided within the base substrate 11.
[0035] The base substrate 11 having such a structure is connected
to the electromagnetic shield-requiring substrate 2 via connectors
3 provided on the top surface 11a of the base substrate 11. An
input/output 9 of power and signals from the base substrate 11 to
the electromagnetic shield-requiring substrate 2 takes place via
the connectors 3. Consequently, no opening is required in the metal
frame 1 for connection to the outside.
[0036] The base substrate 11 is electrically connected to the metal
frame 1 via a connector pad 10 provided on the surface (the top
surface 11a in FIG. 1, FIG. 5, and FIG. 6) of the base substrate 11
that faces the electromagnetic shield-requiring substrate 2. To be
more specific, as shown in FIG. 5, the base substrate 11 is
connected via the connector pad 10 to a mounting member 1c provided
at an end of a side surface 1b of the metal frame 1. The connector
pad 10 and the mounting member 1c may for instance be connected by
a solder 12. The connector pad 10 is connected to the embedded GND
plane 4 provided within the base substrate 11. FIG. 5 is a
magnified view of the region B shown in FIG. 1, which is the point
of connection between the metal frame 1 and the base substrate 11.
FIG. 6 is a view of the region B shown in FIG. 5 cut along the line
C-C.
[0037] The connector pad 10 and the embedded GND plane 4 are
electrically connected by a through hole 6 that traverses widthwise
from the top surface 11a of the base substrate 11 to the embedded
GND plane 4.
[0038] The through hole 6 may have any shape or size as long as it
enables the embedded GND plane 4 and the connector pad 10 to be
effectively electrically connected. Further, there are no
limitations on the number of through holes 6, and any number of
through holes 6 may be provided.
[0039] Further, the connector pad 10 used in the electromagnetic
shield may be of any material as long as it enables the metal frame
1 and the embedded GND plane 4 to be effectively electrically
connected, and effectively blocks the electromagnetic noise issuing
from the electromagnetic shield-requiring substrate 2.
[0040] The connector pad 10 again may be of any shape as long as it
enables the metal frame 1 and the embedded GND plane 4 to be
effectively electrically connected, and effectively blocks the
electromagnetic noise issuing from the electromagnetic
shield-requiring substrate 2. The connector pad 10 may have a shape
that matches the shape of the through hole 6 and that of the
mounting member 1c.
[0041] The connector pad 10 may be of any size as long as it
enables the metal frame 1 and the electromagnetic shield-requiring
substrate 2 to be effectively electrically connected, and
effectively blocks the electromagnetic noise issuing from the
electromagnetic shield-requiring substrate 2. The connector pad 10
may be of a size that matches the size of the through hole 6 or
that of the mounting member 1c.
[0042] In this manner, according to the present invention, the
electromagnetic shield-requiring substrate 2 is covered by a metal
frame 1 and the embedded GND plane 4 of the base substrate 11. In
other words, in this structure, the electromagnetic
shield-requiring substrate 2 is electromagnetically sealed by the
metal frame 1 and the embedded GND plane 4 of the base substrate
11. This structure effectively blocks the electromagnetic noise
that is issued when the circuit elements such as the transistor,
IC, LSI, etc. mounted on the electromagnetic shield-requiring
substrate 2 are powered up. Thus, the electromagnetic
shield-requiring substrate is effectively shielded by the metal
frame 1 and the embedded GND plane 4 of the base substrate 11. As a
result, malfunctioning of the electromagnetic shield-requiring
substrate 2 or the electronic gadget in which the electromagnetic
shield-requiring substrate 2 is mounted, and other electronic
gadgets caused by the electromagnetic noise issuing from the
electromagnetic shield-requiring substrate 2 can be prevented.
[0043] In this electromagnetic shield structure, the top surface 2a
and the sides of the electromagnetic shield-requiring substrate 2
are covered by the metal frame 1, and the bottom surface 2a of the
electromagnetic shield-requiring substrate 2 is covered by the
embedded GND plane 4 of the base substrate 11 disposed facing the
bottom surface 2b of the electromagnetic shield-requiring substrate
2.
[0044] In a conventional electromagnetic shield structure, as shown
in FIG. 7, an electromagnetic shield-requiring substrate 102 is
fixed to a base substrate 111 by connectors 103. The base substrate
111 functions as a foundation for the electromagnetic
shield-requiring substrate 102. Both surfaces (a top surface 102a
and a bottom surface 102b) of the electromagnetic shield-requiring
substrate 102 are sealed by covering them with metal frames 101 and
107. Thus, this structure enables blockade of the electromagnetic
noise. However, in this structure, more area is required for
accommodating the two metal frames 101 and 107. Besides, this
structure leads to higher components cost since two metal frames
101 and 107 are required.
[0045] However, in the electromagnetic shield structure according
to the present invention, the need to enclose all the surfaces of
the electromagnetic shield-requiring substrate 2 with a metal frame
is obviated. In other words, as against two metal frames 101 and
107 required in the conventional electromagnetic shield structure,
only one metal frame 1 is required in the present invention.
Consequently, the area required for accommodating the metal frame
can be drastically reduced. Thus, the electromagnetic shield
structure 20 of the electromagnetic shield-requiring substrate 2 is
space-efficient. As a result, the electronic gadget using this
space-efficient electromagnetic shield-requiring substrate 2 can be
made really compact.
[0046] In the electromagnetic shield structure of the present
invention, the need to enclose all the surfaces of the
electromagnetic shield-requiring substrate 2 with a metal frame is
obviated. In other words, as against two metal frames 101 and 107
required in the conventional electromagnetic shield structure, only
one metal frame 1 is required in the present invention.
Consequently, the weight of the metal frame can be drastically
reduced. Thus, a light electromagnetic shield structure 20 is
realized. As a result, the electronic gadget using this light
electromagnetic shield-requiring substrate 2 can be made
lightweight.
[0047] In the electromagnetic shield structure of the present
invention, the need to enclose all the surfaces of the
electromagnetic shield-requiring substrate 2 with a metal frame is
obviated. In other words, as against two metal frames 101 and 107
required in the conventional electromagnetic shield structure, only
one metal frame 1 is required in the present invention.
Consequently, the cost of the metal frame can be drastically
reduced. Thus, a cost-effective electromagnetic shield structure 20
is realized. As a result, the cost of the electronic gadget using
this cost-effective electromagnetic shield-requiring substrate 2
can be effectively reduced.
[0048] Thus, according to the present invention, a space-efficient
and cost-effective electromagnetic shield structure is realized
that enables electromagnetic shielding of the electromagnetic
shield-requiring substrate 2.
[0049] In the above description, a structure is explained in which
the metal frame 1 and the electromagnetic shield-requiring
substrate 2 are uniquely connected through the connection between
the connecting members la of the metal frame 1 and the connector
pads 5 of the electromagnetic shield-requiring substrate 2.
However, in the present invention, a structure can be obtained in
which the connection can be selected. In other words, as shown in
FIG. 8, a connector pad 13 is provided on the top surface 2a of the
electromagnetic shield-requiring substrate 2 corresponding to the
connecting member 1a of the metal frame 1. A chip part 14 that
connects with the embedded GND plane 2c of the electromagnetic
shield-requiring substrate 2 is provided on the top surface 2a of
the electromagnetic shield-requiring substrate 2. Thus a structure
is obtained in which the metal frame 1 and the electromagnetic
shield-requiring substrate 2 can be electrically connected by
connecting the connector pad 13 and the chip part 14 by a solder
15, as shown in FIG. 9. This structure enables the selection of
whether or not the metal frame 1 and the embedded GND plane 2 of
the electromagnetic shield-requiring substrate 2 are to be
connected, at the step in which electromagnetic noise radiation is
evaluated.
[0050] The chip part may be a condenser, resistor, inductor,
ferrite beats, and the like. The electromagnetic shielding effect
of the electromagnetic shield structure according to the present
invention can be controlled in according to the selection of the
chip part.
[0051] It is preferable to mount faster circuits on the
electromagnetic shield-requiring substrate 2 and slower circuits on
the base substrate 11. In this way, more circuits can be mounted,
and in spite of more circuits, the electromagnetic waves issuing
from the electromagnetic shield-requiring substrate 2 and the base
substrate 11 can be effectively blocked.
[0052] The electromagnetic shield structure according the present
invention can be adapted as an electromagnetic shield of any
circuit board substrate that issues electromagnetic noise, though
it is most suitable for electronic gadgets in which very low
electromagnetic radiation, if at all, from the circuit board
substrate is desirable. The electromagnetic shield structure
according to the present invention may be used in electronic
gadgets in which space-efficiency is desirable. The usefulness of
the electromagnetic shield structure can be more effectively
demonstrated by using it in electronic gadgets in which very low
electromagnetic radiation from the circuit board substrate as well
as space efficiency is desirable.
[0053] Although the invention has been described with respect to a
specific embodiment for a complete and clear disclosure, the
appended claims are not to be thus limited but are to be construed
as embodying all modifications and alternative constructions that
may occur to one skilled in the art which fairly fall within the
basic teaching herein set forth.
* * * * *