U.S. patent application number 16/658334 was filed with the patent office on 2020-04-30 for printed circuit board, electronic device and heat conduction sheet.
This patent application is currently assigned to SEIKO EPSON CORPORATION. The applicant listed for this patent is SEIKO EPSON CORPORATION KITAGAWA INDUSTRIES CO., LTD.. Invention is credited to Masaaki ITO, Yasuhiro KAWAGUCHI, Toru MATSUZAKI, Kensuke MITSUYA, Toshiyuki OMORI, Masahiro SAITO.
Application Number | 20200137870 16/658334 |
Document ID | / |
Family ID | 68296092 |
Filed Date | 2020-04-30 |
United States Patent
Application |
20200137870 |
Kind Code |
A1 |
ITO; Masaaki ; et
al. |
April 30, 2020 |
PRINTED CIRCUIT BOARD, ELECTRONIC DEVICE AND HEAT CONDUCTION
SHEET
Abstract
A printed circuit board includes a printed wiring board having a
mounting surface facing a first side, an electronic element
provided on the mounting surface, a heat dissipation member
disposed on the first side with respect to the electronic element,
and a heat conduction member disposed between the electronic
element and the heat dissipation member and having a first surface
facing the first side and a second surface facing a second side
opposite to the first side. The heat conduction member has a high
relative magnetic permeability portion and a low relative
dielectric constant portion. The high relative magnetic
permeability portion surrounds the low relative dielectric constant
portion on at least the second surface of the heat conduction
member. At least part of the low relative dielectric constant
portion overlaps the electronic element in a plan view seen in a
direction perpendicular to the mounting surface.
Inventors: |
ITO; Masaaki; (Ina-shi,
JP) ; OMORI; Toshiyuki; (Kamiina-gun, JP) ;
MATSUZAKI; Toru; (Kasugai-shi, JP) ; KAWAGUCHI;
Yasuhiro; (Kasugai-shi, JP) ; SAITO; Masahiro;
(Kasugai-shi, JP) ; MITSUYA; Kensuke;
(Kasugai-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SEIKO EPSON CORPORATION
KITAGAWA INDUSTRIES CO., LTD. |
Tokyo
Inazawa-shi |
|
JP
JP |
|
|
Assignee: |
SEIKO EPSON CORPORATION
Tokyo
JP
KITAGAWA INDUSTRIES CO., LTD.
Inazawa-shi
JP
|
Family ID: |
68296092 |
Appl. No.: |
16/658334 |
Filed: |
October 21, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H05K 7/20481 20130101;
H05K 9/0022 20130101; H05K 1/021 20130101 |
International
Class: |
H05K 1/02 20060101
H05K001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 25, 2018 |
JP |
2018-201227 |
Claims
1. A printed circuit board comprising: a printed wiring board
having a mounting surface facing a first side; an electronic
element provided on the mounting surface; a heat dissipation member
which is disposed on the first side with respect to the electronic
element and is thermally connected to the electronic element; and a
heat conduction member disposed between the electronic element and
the heat dissipation member, the heat conduction member having a
first surface facing the first side and a second surface facing a
second side opposite to the first side, wherein the heat conduction
member has a high relative magnetic permeability portion including
a magnetic body and a low relative dielectric constant portion
having a relative dielectric constant smaller than a relative
dielectric constant of the high relative magnetic permeability
portion, the high relative magnetic permeability portion surrounds
the low relative dielectric constant portion on at least the second
surface of the heat conduction member, and at least part of the low
relative dielectric constant portion overlaps the electronic
element in a plan view seen in a predetermined direction
perpendicular to the mounting surface.
2. The printed circuit board according to claim 1, wherein a
relative dielectric constant of the low relative dielectric
constant portion is equal to or less than 8.0.
3. A printed circuit board comprising: a printed wiring board
having a mounting surface facing a first side; an electronic
element provided on the mounting surface; a heat dissipation member
which is disposed on the first side with respect to the electronic
element and is thermally connected to the electronic element; and a
heat conduction member disposed between the electronic element and
the heat dissipation member, the heat conduction member having a
first surface facing the first side and a second surface facing a
second side opposite to the first side, wherein the heat conduction
member has a high relative magnetic permeability portion including
a magnetic body and a low relative dielectric constant portion
having a relative dielectric constant equal to or less than 8.0,
the high relative magnetic permeability portion surrounds the low
relative dielectric constant portion on at least the second surface
of the heat conduction member, and at least part of the low
relative dielectric constant portion overlaps the electronic
element in a plan view seen in a predetermined direction
perpendicular to the mounting surface.
4. The printed circuit board according to claim 1, wherein the high
relative magnetic permeability portion has a frame shape
surrounding the low relative dielectric constant portion, and
surrounds the low relative dielectric constant portion on both the
first surface of the heat conduction member and the second surface
of the heat conduction member.
5. The printed circuit board according to claim 3, wherein the high
relative magnetic permeability portion has a frame shape
surrounding the low relative dielectric constant portion, and
surrounds the low relative dielectric constant portion on both the
first surface of the heat conduction member and the second surface
of the heat conduction member.
6. The printed circuit board according to claim 1, wherein the high
relative magnetic permeability portion has a portion positioned
between the low relative dielectric constant portion and the heat
dissipation member in the predetermined direction.
7. The printed circuit board according to claim 3, wherein the high
relative magnetic permeability portion has a portion positioned
between the low relative dielectric constant portion and the heat
dissipation member in the predetermined direction.
8. The printed circuit board according to claim 1, wherein, in the
plan view seen in the predetermined direction, the heat conduction
member is larger than the electronic element and overlaps the
entire electronic element.
9. The printed circuit board according to claim 3, wherein, in the
plan view seen in the predetermined direction, the heat conduction
member is larger than the electronic element and overlaps the
entire electronic element.
10. The printed circuit board according to claim 8, wherein, in the
plan view seen in the predetermined direction, a region where the
low relative dielectric constant portion is provided on the second
surface of the heat conduction member is larger than the electronic
element and overlaps the entire electronic element.
11. The printed circuit board according to claim 9, wherein, in the
plan view seen in the predetermined direction, a region where the
low relative dielectric constant portion is provided on the second
surface of the heat conduction member is larger than the electronic
element and overlaps the entire electronic element.
12. The printed circuit board according to claim 1, wherein the
heat conduction member has a sheet shape.
13. The printed circuit board according to claim 3, wherein the
heat conduction member has a sheet shape.
14. An electronic device comprising the printed circuit board
according to claim 1.
15. An electronic device comprising the printed circuit board
according to claim 3.
16. A heat conduction sheet having a first surface and a second
surface opposite to the first surface, comprising: a high relative
magnetic permeability portion including a magnetic body; and a low
relative dielectric constant portion having a relative dielectric
constant smaller than a relative dielectric constant of the high
relative magnetic permeability portion, wherein the high relative
magnetic permeability portion surrounds the low relative dielectric
constant portion on at least the second surface of the heat
conduction sheet.
17. The heat conduction sheet according to claim 16, wherein a
relative dielectric constant of the low relative dielectric
constant portion is equal to or less than 8.0.
18. A heat conduction sheet having a first surface and a second
surface opposite to the first surface, comprising: a high relative
magnetic permeability portion including a magnetic body; and a low
relative dielectric constant portion having a relative dielectric
constant equal to or less than 8.0, wherein the high relative
magnetic permeability portion surrounds the low relative dielectric
constant portion on at least the second surface of the heat
conduction sheet.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority from Japanese Patent
Application No. 2018-201227 filed on Oct. 25, 2018, the contents of
which are incorporated herein by reference.
BACKGROUND
1. Technical Field
[0002] The present invention relates to a printed circuit board, an
electronic device, and a heat conduction sheet.
2. Related Art
[0003] For example, as shown in Patent Document 1, an electronic
device unit in which a metal plate for heat dissipation is attached
to an integrated circuit (IC) provided on a printed board is
known.
[0004] [Patent Document 1] Japanese Unexamined Patent Application,
First Publication No. H09-17921
[0005] [Patent Document 2] Japanese Unexamined Patent Application,
First Publication No. H07-14950
[0006] [Patent Document 3] Japanese Unexamined Patent Application,
First Publication No. H11-307974
[0007] In the electronic device unit (printed circuit board) as
described above, for example, a heat conduction member such as a
heat dissipation sheet as shown in Patent Document 2 may be
disposed between the metal plate for heat dissipation (heat
dissipation member) and the IC (electronic element). However, when
such a heat conduction member is provided, there is a problem that
undesired radiation noises (electromagnetic noises) emitted from
the electronic device unit increase, with the IC serving as the
source of the undesired radiation. With respect to the above
problem, for example, as shown in Patent Document 3, it is
conceivable to shield the undesired radiation noises by surrounding
the entire IC with a shield case. However, in this case, there are
problems that the number of components in the electronic device
unit increases, a size of the electronic device unit is enlarged,
or the like.
SUMMARY
[0008] One aspect of a printed circuit board of the invention
includes a printed wiring board having a mounting surface facing a
first side, an electronic element provided on the mounting surface,
a heat dissipation member which is disposed on the first side with
respect to the electronic element and is thermally connected to the
electronic element, and a heat conduction member disposed between
the electronic element and the heat dissipation member, the heat
conduction member having a first surface facing the first side and
a second surface facing a second side opposite to the first side
and is characterized in that the heat conduction member has a high
relative magnetic permeability portion including a magnetic body
and a low relative dielectric constant portion having a relative
dielectric constant smaller than a relative dielectric constant of
the high relative magnetic permeability portion, the high relative
magnetic permeability portion surrounds the low relative dielectric
constant portion on at least the second surface of the heat
conduction member, and at least part of the low relative dielectric
constant portion overlaps the electronic element in a plan view
seen in a predetermined direction perpendicular to the mounting
surface.
[0009] A relative dielectric constant of the low relative
dielectric constant portion may be equal to or less than 8.0.
[0010] One aspect of a printed circuit board of the invention
includes a printed wiring board having a mounting surface facing a
first side, an electronic element provided on the mounting surface,
a heat dissipation member which is disposed on the first side with
respect to the electronic element and is thermally connected to the
electronic element, and a heat conduction member disposed between
the electronic element and the heat dissipation member, the heat
conduction member having a first surface facing the first side and
a second surface facing a second side opposite to the first side
and is characterized in that the heat conduction member has a high
relative magnetic permeability portion including a magnetic body
and a low relative dielectric constant portion having a relative
dielectric constant equal to or less than 8.0, the high relative
magnetic permeability portion surrounds the low relative dielectric
constant portion on at least the second surface of the heat
conduction member, and at least part of the low relative dielectric
constant portion overlaps the electronic element in a plan view
seen in a predetermined direction perpendicular to the mounting
surface.
[0011] The high relative magnetic permeability portion may have a
frame shape surrounding the low relative dielectric constant
portion, and may be configured to surround the low relative
dielectric constant portion on both the first surface of the heat
conduction member and the second surface of the heat conduction
member.
[0012] The high relative magnetic permeability portion may be
configured to have a portion positioned between the low relative
dielectric constant portion and the heat dissipation member in the
predetermined direction.
[0013] In the plan view seen in the predetermined direction, the
heat conduction member may be larger than the electronic element
and overlap the entire electronic element.
[0014] In the plan view seen in the predetermined direction, a
region where the low relative dielectric constant portion is
provided on the second surface of the heat conduction member may be
configured to be larger than the electronic element and overlap the
entire electronic element.
[0015] The heat conduction member may have a sheet shape.
[0016] One aspect of an electronic device of the invention is
characterized by including the printed circuit board mentioned
above.
[0017] One aspect of a heat conduction sheet of the invention is a
heat conduction sheet having a first surface and a second surface
opposite to the first surface, which includes a high relative
magnetic permeability portion including a magnetic body and a low
relative dielectric constant portion having a relative dielectric
constant smaller than a relative dielectric constant of the high
relative magnetic permeability portion, and which is characterized
in that the high relative magnetic permeability portion surrounds
the low relative dielectric constant portion on at least the second
surface of the heat conduction sheet.
[0018] One aspect of a heat conduction sheet of the invention is a
heat conduction sheet having a first surface and a second surface
opposite to the first surface, which includes a high relative
magnetic permeability portion including a magnetic body and a low
relative dielectric constant portion having a relative dielectric
constant equal to or less than 8.0, and which is characterized in
that the high relative magnetic permeability portion surrounds the
low relative dielectric constant portion on at least the second
surface of the heat conduction sheet.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a schematic configurational view showing a
projector of a first embodiment.
[0020] FIG. 2 is a cross-sectional view showing a printed circuit
board of the first embodiment.
[0021] FIG. 3 is a plan view showing a heat conduction member of
the first embodiment from below.
[0022] FIG. 4 is a cross-sectional view showing a printed circuit
board according to a second embodiment.
[0023] FIG. 5 is a graph showing measurement results of
horizontally polarized waves among undesired radiation noises in an
example and comparative examples 1 and 2.
[0024] FIG. 6 is a graph showing measurement results of vertically
polarized waves among undesired radiation noises in the example and
the comparative examples 1 and 2.
[0025] FIG. 7 is a graph showing measurement results of
horizontally polarized waves among undesired radiation noises in
each sample.
[0026] FIG. 8 is a graph showing measurement results of vertically
polarized waves among undesired radiation noises in each
sample.
[0027] FIG. 9 is a cross-sectional view showing a printed circuit
board of a comparative example.
DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0028] Hereinafter, a printed circuit board according to an
embodiment of the invention and an electronic device including the
printed circuit board will be described with reference to the
drawings. In the following embodiments, a projector is described as
an example of the electronic device.
[0029] Also, the scope of the invention is not limited to the
following embodiments and can be arbitrarily changed within the
scope of the technical idea of the invention. In addition, in the
following drawings, in order to make each structure intelligible,
the scale, the number, or the like in each structure may be
different from those in an actual structure.
First Embodiment
[0030] FIG. 1 is a schematic configurational view showing a
projector (an electronic device) 1 of the present embodiment.
[0031] The projector 1 of the present embodiment is a projection
type image display device that projects a color image on a screen
SCR. As shown in FIG. 1, the projector 1 includes a light source
device 2, a uniform illumination optical system 40, a color
separation optical system 3, a light modulation device 4R, a light
modulation device 4G, a light modulation device 4B, an optical
mixing system 5, a projection optical device 6, and a control
device 50. The light source device 2 emits illumination light WL
toward the uniform illumination optical system 40.
[0032] The uniform illumination optical system 40 includes an
integrator optical system 31, a polarization conversion element 32,
and a superposition optical system 33. The integrator optical
system 31 includes a first lens array 31a and a second lens array
31b. The uniform illumination optical system 40 equalizes an
intensity distribution of the illumination light WL emitted from
the light source device 2 in each of the light modulation device
4R, the light modulation device 4G, and the light modulation device
4B, which are regions to be illuminated. The illumination light WL
emitted from the uniform illumination optical system 40 enters the
color separation optical system 3.
[0033] The color separation optical system 3 separates the white
illumination light WL into red light LR, green light LG and blue
light LB. The color separation optical system 3 includes a first
dichroic mirror 7a, a second dichroic mirror 7b, a first reflection
mirror 8a, a second reflection mirror 8b, a third reflection mirror
8c, a first relay lens 9a, and a second relay lens 9b.
[0034] The first dichroic mirror 7a separates the illumination
light WL from the light source device 2 into red light LR and other
light (green light LG and blue light LB). The first dichroic mirror
7a transmits the separated red light LR and reflects other light
(green light LG and blue light LB). On the other hand, the second
dichroic mirror 7b separates other light into green light LG and
blue light LB. The second dichroic mirror 7b reflects the separated
green light LG and transmits the blue light LB.
[0035] The first reflection mirror 8a is disposed in an optical
path of the red light LR and reflects the red light LR transmitted
through the first dichroic mirror 7a toward the light modulation
device 4R. On the other hand, the second reflection mirror 8b and
the third reflection mirror 8c are disposed in an optical path of
the blue light LB and reflect the blue light LB transmitted through
the second dichroic mirror 7b toward the light modulation device
4B. Also, the green light LG is reflected by the second dichroic
mirror 7b toward the light modulation device 4G.
[0036] The first relay lens 9a and the second relay lens 9b are
disposed on a light emitting side of the second dichroic mirror 7b
in the optical path of the blue light LB. The first relay lens 9a
and the second relay lens 9b correct a difference in illumination
distribution of the blue light LB resulting from the fact that an
optical path length of the blue light LB is longer than an optical
path length of the red light LR and an optical path length of the
green light LG.
[0037] The light modulation device 4R modulates the red light LR in
accordance with the image information to form image light
corresponding to the red light LR. The light modulation device 4G
modulates the green light LG in accordance with the image
information to form image light corresponding to the green light
LG. The light modulation device 4B modulates the blue light LB in
accordance with the image information to form image light
corresponding to the blue light LB.
[0038] For example, a transmissive type liquid crystal panel is
used for the light modulation device 4R, the light modulation
device 4G, and the light modulation device 4B. In addition,
polarizing plates (not shown) are disposed on each of a light
incident side and a light emitting side of the liquid crystal panel
and are configured to transmit only light that is linearly
polarized in a specific direction.
[0039] A field lens 10R, a field lens 10G, and a field lens 10B are
disposed respectively on light incident sides of the light
modulation device 4R, the light modulation device 4G, and the light
modulation device 4B. The field lens 10R, the field lens 10G, and
the field lens 10B collimate main light beams of red light LR,
green light LG, and blue light LB which are incident respectively
on the light modulation device 4R, the light modulation device 4G,
and the light modulation device 4B.
[0040] As the image light emitted from the light modulation device
4R, the light modulation device 4G, and the light modulation device
4B is incident on the optical mixing system 5, the optical mixing
system 5 mixes the image light corresponding to the red light LR,
the green light LG, and the blue light LB, and emits the mixed
image light toward the projection optical device 6. For example, a
cross dichroic prism is used for the optical mixing system 5.
[0041] The projection optical device 6 is configured of a plurality
of projection lenses. The projection optical device 6 enlarges and
projects the image light mixed by the optical mixing system 5
toward the screen SCR. Thus, an image is displayed on the screen
SCR.
[0042] Next, the control device 50 will be described.
[0043] In the following description, relative positional
relationships and the like between respective portions will be
described, assuming that a Z-axis direction shown in appropriate
figures is a vertical direction (a predetermined direction). A
positive side (+Z side) in the Z-axis direction is referred to as
an upper side (a first side), and a negative side (-Z side) in the
Z-axis direction is referred to as a lower side (a second side).
Also, a direction orthogonal to the vertical direction is referred
to as a horizontal direction.
[0044] In addition, the vertical direction, the horizontal
direction, the upper side and the lower side are names only for
describing the relative positional relationships and the like
between the respective portions, and actual dispositional
relationships and the like may be different from dispositional
relationships and the like indicated by these names.
[0045] FIG. 2 is a cross-sectional view showing a printed circuit
board 51 in the control device 50. FIG. 3 is a plan view of a heat
conduction member 54 in the control device 50 from below. In
addition, the cross-sectional view of the heat conduction member 54
in FIG. 2 is a cross-sectional view taken along line II-II in FIG.
3.
[0046] The control device 50 is a main board that controls each
portion of the projector 1 including the light source device 2. As
shown in FIG. 2, the control device 50 includes the printed circuit
board 51. The printed circuit board 51 includes a printed wiring
board 52, an electronic element 53, a heat dissipation member 57,
and a heat conduction member (heat conduction sheet) 54.
[0047] The printed wiring board 52 has a plate shape of which plate
surfaces are directed in the vertical direction. Although not shown
in the drawings, the printed wiring board 52 has a configuration in
which a wiring pattern made of copper foil is provided on at least
one surface of a substrate made of a material such as a paper
phenol laminate or a glass epoxy board laminate. Any one of a
single-sided printed wiring board, a double-sided printed wiring
board, and a multilayer printed wiring board may be used for the
printed wiring board 52. Also, for the printed wiring board 52, a
rigid printed wiring board without flexibility may be used, or a
flexible printed wiring board with flexibility may be used. In the
present embodiment, the printed wiring board 52 has a mounting
surface 52a provided with the wiring pattern. The mounting surface
52a is a surface of the printed wiring board 52 facing upward
between the plate surfaces. In the present embodiment, the mounting
surface 52a is orthogonal to the vertical direction. That is, the
vertical direction is the predetermined direction perpendicular to
the mounting surface 52a.
[0048] The electronic element 53 is provided on the mounting
surface 52a of the printed wiring board 52. The electronic element
53 is, for example, an integrated circuit (IC) such as a large
scale integration (LSI). Although not shown in the drawings, the
electronic element 53 includes a semiconductor chip made of
silicon, a package covering the semiconductor chip, and a plurality
of terminals provided on a lower surface of the package. The
electronic element 53 is electrically connected to the wiring
pattern provided on the mounting surface 52a of the printed wiring
board 52 via the plurality of terminals. Also, the electronic
element 53 is a heat source and a source of undesired radiation,
which will be described in detail later. In the present embodiment,
the electronic element 53 has, for example, a substantially
rectangular parallelepiped shape. As shown in FIG. 3, the
electronic element 53 has, for example, a square shape in a plan
view seen in the vertical direction.
[0049] The heat dissipation member 57 is disposed above the
electronic element 53 as shown in FIG. 2. The heat dissipation
member 57 is attached to the electronic element 53 via the heat
conduction member 54. In the present embodiment, the heat
dissipation member 57 has a plate shape of which plate surfaces are
directed in the vertical direction. The plate surfaces of the heat
dissipation member 57 are, for example, orthogonal to the vertical
direction. In a plan view seen in the vertical direction, the heat
dissipation member 57 is larger than the electronic element 53 and
the heat conduction member 54, and overlaps the entire electronic
element 53 and the entire heat conduction member 54.
[0050] The heat dissipation member 57 is configured of, for
example, a flat plate made of a metal having a relatively high
thermal conductivity, such as aluminum or copper. The heat
dissipation member 57 is thermally connected to the electronic
element 53.
[0051] Also, in the present specification, "some objects are
thermally connected" may mean a state in which some objects are
directly or indirectly connected to each other and heat is
transferred between the objects. In the present embodiment, the
heat dissipation member 57 is indirectly connected to the
electronic element 53 via the heat conduction member 54, and the
heat of the electronic element 53 is transferred to the heat
dissipation member 57 via the heat conduction member 54.
[0052] The heat conduction member 54 is a member that transfers
heat from the electronic element 53 to the heat dissipation member
57. The heat conduction member 54 is a dielectric. The heat
conduction member 54 is disposed between the electronic element 53
and the heat dissipation member 57 in the vertical direction. In
the present embodiment, the heat conduction member 54 has a sheet
shape extending in the horizontal direction orthogonal to the
vertical direction. That is, in the present embodiment, the heat
conduction member 54 is a heat conduction sheet. As sheet surfaces,
the heat conduction member 54 has an upper surface (a first
surface) 54b which faces upward, and a lower surface (a second
surface) 54a which is a surface opposite to the upper surface 54b
and faces downward. In the present embodiment, the lower surface
54a of the heat conduction member 54 and the upper surface 54b of
the heat conduction member 54 are perpendicular to the vertical
direction.
[0053] The lower surface 54a of the heat conduction member 54 is
bonded to an upper surface of the electronic element 53. The upper
surface 54b of the heat conduction member 54 is bonded to a lower
surface of the heat dissipation member 57. A method for bonding the
heat conduction member 54 and the electronic element 53 and a
method for bonding the heat conduction member 54 and the heat
dissipation member 57 are not particularly limited. The heat
conduction member 54 and the electronic element 53 are bonded, for
example, by an adhesive or the like. Similarly, the heat conduction
member 54 and the heat dissipation member 57 are bonded, for
example, by an adhesive or the like. Also, a base material of the
heat conduction member 54 may be a substance having adhesiveness,
and the heat conduction member 54 and the electronic element 53 may
be directly bonded together without an adhesive or the like. Also,
similarly, the heat conduction member 54 and the heat dissipation
member 57 may be directly bonded without an adhesive or the
like.
[0054] In a plan view seen in the vertical direction, the heat
conduction member 54 is larger than the electronic element 53 and
overlaps the entire electronic element 53. The heat conduction
member 54 has a low relative dielectric constant portion (a second
portion) 55 and a high relative magnetic permeability portion (a
first portion) 56.
[0055] The low relative dielectric constant portion 55 is a portion
where a relative dielectric constant .epsilon. is relatively small.
The relative dielectric constant .epsilon. of the low relative
dielectric constant portion 55 is smaller than the relative
dielectric constant .epsilon. of the high relative magnetic
permeability portion 56. The relative dielectric constant .epsilon.
of the low relative dielectric constant portion 55 is 8.0 or less.
The relative dielectric constant .epsilon. of the low relative
dielectric constant portion 55 is preferably, for example, about
4.0 or less. This is so that undesired radiation noises emitted
from the printed circuit board 51 can be further reduced. The low
relative dielectric constant portion 55 is made of, for example, a
silicone resin, an acrylic resin, or the like. The low relative
dielectric constant portion 55 does not contain a magnetic body and
is a nonmagnetic portion. A relative magnetic permeability .mu. of
the nonmagnetic low relative dielectric constant portion 55 is
approximately 1.0.
[0056] In addition, the relative dielectric constant .epsilon. in
the present specification is a value at a frequency of 1 GHz
measured by using E4991A RF Impedance/Material Analyzer
manufactured by Keysight Technologies under conditions of a
temperature of 25.degree. C. and a relative humidity of 30%. Also,
the relative magnetic permeability .mu. in the present
specification is a value at a frequency of 1 GHz measured by using
E4991A RF Impedance/Material Analyzer manufactured by Keysight
Technologies under conditions of a temperature of 25.degree. C. and
a relative humidity of 30%.
[0057] A thermal conductivity of the low relative dielectric
constant portion 55 is large enough to appropriately transfer heat
from the electronic element 53 to the heat dissipation member 57,
and is, for example, about 0.5 or more and 20.0 or less. The
thermal conductivity of the low relative dielectric constant
portion 55 is, for example, larger than a thermal conductivity of
the high relative magnetic permeability portion 56. In the present
embodiment, the heat of the electronic element 53 is transferred to
the heat dissipation member 57 via the low relative dielectric
constant portion 55.
[0058] The low relative dielectric constant portion 55 is a central
portion of the heat conduction member 54. In the present
embodiment, the low relative dielectric constant portion 55 is
formed such that its surfaces on both sides in the vertical
direction are exposed to the outside of the heat conduction member
54 when the heat conduction member 54 is viewed alone. A lower
surface 55a of the low relative dielectric constant portion 55
constitutes a portion of the lower surface 54a of the heat
conduction member 54. An upper surface 55b of the low relative
dielectric constant portion 55 constitutes a portion of the upper
surface 54b of the heat conduction member 54. The low relative
dielectric constant portion 55 has, for example, a square shape in
a plan view seen in the vertical direction, as shown in FIG. 3.
[0059] In a plan view seen in the vertical direction, the low
relative dielectric constant portion 55 is larger than the
electronic element 53 and overlaps the entire electronic element
53. In the present embodiment, the lower surface 55a and the upper
surface 55b of the low relative dielectric constant portion 55 are
both larger than the electronic element 53 and overlap the entire
electronic element 53 in a plan view seen in the vertical
direction. That is, a region provided with the low relative
dielectric constant portion 55 in the lower surface 54a of the heat
conduction member 54 and a region provided with the low relative
dielectric constant portion 55 in the upper surface 54b of the heat
conduction member 54 are larger than the electronic element 53 and
overlap the entire electronic element 53 in a plan view seen in the
vertical direction. As shown in FIG. 3, an outer edge of the low
relative dielectric constant portion 55 is disposed at a position
spaced outward from an outer edge of the electronic element 53 and
surrounds the outer edge of the electronic element 53 in a plan
view seen in the vertical direction. As shown in FIG. 2, the lower
surface 55a of the low relative dielectric constant portion 55 is
bonded to the upper surface of the electronic element 53. The upper
surface 55b of the low relative dielectric constant portion 55 is
bonded to the lower surface of the heat dissipation member 57.
[0060] The high relative magnetic permeability portion 56 is a
portion including magnetic bodies. The relative magnetic
permeability .mu. of the high relative magnetic permeability
portion 56 is larger than 1.0. The relative magnetic permeability
.mu. of the high relative magnetic permeability portion 56 is, for
example, about 3.0 or more and 15.0 or less. Although not shown in
the drawings, the high relative magnetic permeability portion 56
has a configuration in which a plurality of magnetic bodies are
included in a base material. For the base material, for example, a
silicone resin, an acrylic resin, etc. may be used. Each of the
plurality of magnetic bodies is, for example, a small piece having
a needle shape, a rod shape, a plate shape or another shape, and
has a longer side direction. For the magnetic bodies, for example,
a soft magnetic material such as a ferrite containing an iron oxide
as a main component may be used. The relative magnetic permeability
.mu. of the high relative magnetic permeability portion 56
increases as an amount of the magnetic bodies contained in the base
material increases. The relative dielectric constant .epsilon. of
the high relative magnetic permeability portion 56 is larger than
the relative dielectric constant .epsilon. of the low relative
dielectric constant portion 55. A thermal conductivity of the high
relative magnetic permeability portion 56 is not particularly
limited.
[0061] In the present embodiment, the high relative magnetic
permeability portion 56 has a frame shape surrounding the low
relative dielectric constant portion 55, as shown in FIGS. 2 and 3,
and surrounds the low relative dielectric constant portion 55 over
a whole circumference thereof in the surfaces on both sides in the
vertical direction (the lower surface 54a and the upper surface
54b) among a plurality of surfaces of the heat conduction member
54. The high relative magnetic permeability portion 56 has, for
example, a square frame shape. The high relative magnetic
permeability portion 56 of the present embodiment is disposed
outside the electronic element 53 in a plan view seen in the
vertical direction. The low relative dielectric constant portion 55
is fitted inside the high relative magnetic permeability portion
56. An inner edge of the high relative magnetic permeability
portion 56 is disposed in contact with the outer edge of the low
relative dielectric constant portion 55. The low relative
dielectric constant portion 55 and the high relative magnetic
permeability portion 56 may be joined by using, for example, an
adhesive or the like. In the present embodiment, a dimension of the
high relative magnetic permeability portion 56 in the vertical
direction is, for example, the same as a dimension of the low
relative dielectric constant portion 55 in the vertical
direction.
[0062] As shown in FIG. 2, a lower surface 56a of the high relative
magnetic permeability portion 56 constitutes a portion of the lower
surface 54a of the heat conduction member 54. A lower surface 56a
of the high relative magnetic permeability portion 56 is smoothly
connected to the lower surface 55a of the low relative dielectric
constant portion 55. In the present embodiment, the lower surface
54a of the heat conduction member 54 is configured of the lower
surface 55a of the low relative dielectric constant portion 55 and
the lower surface 56a of the high relative magnetic permeability
portion 56. The lower surface 56a of the high relative magnetic
permeability portion 56 is positioned above the mounting surface
52a of the printed wiring board 52, and is disposed to be opposite
to the mounting surface 52a with a gap.
[0063] An upper surface 56b of the high relative magnetic
permeability portion 56 constitutes a portion of the upper surface
54b of the heat conduction member 54. The upper surface 56b of the
high relative magnetic permeability portion 56 is smoothly
connected to the upper surface 55b of the low relative dielectric
constant portion 55. In the present embodiment, the upper surface
54b of the heat conduction member 54 is configured of the upper
surface 55b of the low relative dielectric constant portion 55 and
the upper surface 56b of the high relative magnetic permeability
portion 56. The upper surface 56b of the high relative magnetic
permeability portion 56 is bonded to the lower surface of the heat
dissipation member 57.
[0064] Hereinafter, operations and effects of the printed circuit
board 51 of the present embodiment will be described.
[0065] FIG. 9 is a cross-sectional view showing a printed circuit
board 251 of a comparative example.
[0066] As shown in FIG. 9, the printed circuit board 251 of the
comparative example is different from the printed circuit board 51
of the above-described embodiment in that a heat conduction member
254 is provided instead of the heat conduction member 54. The heat
conduction member 254 has the same properties throughout the
member. A relative dielectric constant .epsilon. of the heat
conduction member 254 is larger than 8.0. The relative dielectric
constant .epsilon. of the heat conduction member 254 is, for
example, 10.0 or more. A thermal conductivity of the heat
conduction member 254 is, for example, substantially the same as
the thermal conductivity of the low relative dielectric constant
portion 55. The heat conduction member 254 is a nonmagnetic member
that does not contain a magnetic body. In a plan view seen in the
vertical direction, the heat conduction member 254 has the same
shape and size as the electronic element 53 and the entire heat
conduction member 254 overlaps the electronic element 53.
[0067] The printed circuit board 251 emits undesired radiation
noises (electromagnetic noises) from the electronic element 53
serving as the source of the undesired radiation. The undesired
radiation noises are electromagnetic waves. The undesired radiation
noises emitted from the printed circuit board 251 are increased
because the heat conduction member 254 is provided. The principle
is as follows.
[0068] Since the heat conduction member 254 is a dielectric,
dielectric polarization occurs in the heat conduction member 254
due to an electric field of undesired radiation noises emitted from
the electronic element 53. When the dielectric polarization occurs,
the heat conduction member 254 functions as a capacitor CS as
virtually shown in FIG. 9, and a voltage is induced between the
electronic element 53 and the heat dissipation member 57. Such a
phenomenon is called electrostatic coupling. The electrostatic
coupling causes a displacement current to flow between the
electronic element 53 and the heat dissipation member 57. Also, in
the following description, generation of electrostatic coupling due
to undesired radiation noises is referred to as "coupling of
undesired radiation noises."
[0069] By coupling the undesired radiation noises emitted from the
electronic element 53 to the heat dissipation member 57, the heat
dissipation member 57 resonates and functions as an antenna that
amplifies and emits the undesired radiation noises. By the heat
conduction member 254 being provided according to the principle as
described above, undesired radiation noises emitted from the
printed circuit board 251 increase. The undesired radiation noises
emitted from the heat dissipation member 57 functioning as an
antenna are undesired radiation noises NV emitted upward from the
heat dissipation member 57.
[0070] Here, as the relative dielectric constant .epsilon. of the
heat conduction member 254 becomes larger, an electrostatic
capacitance of the virtual capacitor CS increases, and the voltage
induced by the electrostatic coupling increases. That is, the
undesired radiation noises emitted from the electronic element 53
are easily coupled to the heat dissipation member 57. As a result,
the displacement current flowing between the electronic element 53
and the heat dissipation member 57 increases, and the undesired
radiation noises NV emitted from the heat dissipation member 57
further increase. Therefore, as the relative dielectric constant
.epsilon. of the heat conduction member 254 becomes larger, the
undesired radiation noises emitted from the printed circuit board
251 increase.
[0071] In addition, although the phenomenon itself in which the
undesired radiation noises emitted from the printed circuit board
251 increase when the heat conduction member 254 is provided is
known conventionally, the inventors newly found the principle
described above.
[0072] The undesired radiation noises emitted from the printed
circuit board 251 also include undesired radiation noises other
than the undesired radiation noises NV emitted from the heat
dissipation member 57 described above. Specifically, the undesired
radiation noises emitted from the printed circuit board 251 include
undesired radiation noises NH emitted in the horizontal direction
orthogonal to the vertical direction from between the printed
wiring board 52 and the heat dissipation member 57. The principle
on which the undesired radiation noises NH are emitted is as
follows.
[0073] Since air between the printed wiring board 52 and the heat
dissipation member 57 is also a dielectric, it is dielectrically
polarized by an electric field of undesired radiation noises from
the electronic element 53, and functions as a capacitor CA
virtually shown in FIG. 9. In addition, an electrostatic
capacitance of the capacitor CA is smaller than the electrostatic
capacitance of the capacitor CS. A circuit configured of the air
capacitor CA, the capacitor CS of the heat conduction member 254,
the printed wiring board 52, the electronic element 53, and the
heat dissipation member 57 generates a displacement current flowing
between the heat dissipation member 57 and the printed wiring board
52. Due to this displacement current, dielectric resonance occurs,
and undesired radiation noises NH are emitted in the horizontal
direction from between the printed wiring board 52 and the heat
dissipation member 57.
[0074] As described above, the undesired radiation noises emitted
from the printed circuit board 251 include the undesired radiation
noises NV emitted upward and the undesired radiation noises NH
emitted in the horizontal direction.
[0075] According to the present embodiment, the heat conduction
member 54 has the low relative dielectric constant portion 55 whose
relative dielectric constant .epsilon. is smaller than that of the
high relative magnetic permeability portion 56. For this reason,
the relative dielectric constant .epsilon. of the low relative
dielectric constant portion 55 can be easily made relatively small,
and when the low relative dielectric constant portion 55 functions
as the capacitor CS, the capacitance of the capacitor CS can be
made small. As a result, undesired radiation noises emitted from
the electronic element 53 are less likely to be coupled to the heat
dissipation member 57 via the heat conduction member 54. Therefore,
the undesired radiation noises emitted from the electronic element
53 can be inhibited from being amplified by the heat dissipation
member 57, and the undesired radiation noises NV emitted from the
heat dissipation member 57 can be reduced. As a result, the total
undesired radiation noises emitted from the printed circuit board
51 can be reduced.
[0076] Here, as described above, it is a finding newly obtained by
the present inventors that the relative dielectric constant
.epsilon. of the heat conduction member 54 is related to an
increase of the undesired radiation noises. The printed circuit
board 51 of the present embodiment is a printed circuit board that
can realize reduction of the undesired radiation noises to be
emitted based on this new finding.
[0077] Further, according to the present embodiment, the heat
conduction member 54 has the high relative magnetic permeability
portion 56 including the magnetic bodies. By including the magnetic
bodies, the relative magnetic permeability .mu. of the high
relative magnetic permeability portion 56 becomes larger than 1.0.
Magnetic flux easily passes through a member having the relative
magnetic permeability .mu. of more than 1.0, so that a magnetic
field is easily generated inside. For this reason, the magnetic
field of the undesired radiation noises emitted from the electronic
element 53 is attracted, and the undesired radiation noises easily
pass through the high relative magnetic permeability portion 56.
When the undesired radiation noises pass through the high relative
magnetic permeability portion 56, magnetic flux and current are
generated in the high relative magnetic permeability portion 56 to
become heat, resulting in a magnetic loss. As a result, the energy
of the undesired radiation noises emitted from the electronic
element 53 is reduced, and the undesired radiation noises emitted
from the printed circuit board 51 can be further reduced. As
described above, the energy of the undesired radiation noises
emitted from the electronic element 53 can be reduced, so that the
undesired radiation noises NH emitted in the horizontal direction
from the printed circuit board 51 can also be reduced.
[0078] As described above, according to the present embodiment, by
providing the low relative dielectric constant portion 55 and the
high relative magnetic permeability portion 56, the undesired
radiation noises emitted from the printed circuit board 51 due to
the heat conduction member 54 are appropriately reduced. For this
reason, even when heat dissipating properties of the electronic
element 53 are improved by providing the heat dissipation member 57
and the heat conduction member 54, the undesired radiation noises
emitted from the printed circuit board 51 can be inhibited without
providing a shielding member such as a shield case. Thus, an
increase in size of the printed circuit board 51 can be inhibited
while the undesired radiation noises can be inhibited. Therefore,
it is possible to inhibit enlargement of the projector 1 while
improving reliability of the projector 1 on which the printed
circuit board 51 is mounted.
[0079] Moreover, since it is not necessary to additionally provide
a shielding member such as a shield case, it is possible to inhibit
an increase in the number of components of the printed circuit
board 51. Thus, the number of steps and cost for assembling the
printed circuit board 51 can be reduced. Therefore, the
manufacturing cost of the projector 1 can be reduced. Further, it
is possible to inhibit deterioration of the heat dissipating
properties of the electronic element 53 resulting from the
shielding member such as the shield case.
[0080] Also, in particular, the low relative dielectric constant
portion 55 easily inhibits the coupling between the undesired
radiation noises having a relatively low frequency and the heat
dissipation member 57. On the other hand, the low relative
dielectric constant portion 55 more easily causes the coupling with
heat dissipation member 57 with respect to undesired radiation
noises having a relatively high frequency as compared with
undesired radiation noises having a relatively low frequency. That
is, the low relative dielectric constant portion 55 is less likely
to reduce the undesired radiation noises having a relatively high
frequency as compared with the undesired radiation noises having a
relatively low frequency.
[0081] On the other hand, the high relative magnetic permeability
portion 56 easily causes a loss of the energy of the undesired
radiation noises having a high frequency, in particular. For this
reason, the undesired radiation noises having a relatively high
frequency can be particularly reduced. Therefore, by combining the
low relative dielectric constant portion 55 and the high relative
magnetic permeability portion 56, both of the undesired radiation
noises having a relatively low frequency and the undesired
radiation noises having a relatively high frequency can be
reduced.
[0082] Here, in a video device such as the projector 1 of the
present embodiment, both of the undesired radiation noises having a
relatively low frequency and the undesired radiation noises having
a relatively high frequency are easily emitted from the printed
circuit board 51. For this reason, the effect capable of reducing
both of the undesired radiation noises having a relatively low
frequency and the undesired radiation noises having a relatively
high frequency can be obtained more usefully when the printed
circuit board 51 is mounted in a video device.
[0083] In addition, the relatively low frequency is, for example, a
frequency smaller than 1 GHz. The relatively high frequency is, for
example, a frequency of 1 GHz or more.
[0084] In FIG. 2, the inhibition effect of the undesired radiation
noises mentioned above is visually shown using arrows. White arrows
EF indicate a behavior of the undesired radiation noises as an
electric field. Black arrows MF indicate a behavior of the
undesired radiation noises as a magnetic field. Also, the arrows EF
and MF are shown virtually for the purpose of visually explaining
the inhibition effect of the undesired radiation noises.
[0085] As indicated by the arrows EF in FIG. 2, the low relative
dielectric constant portion 55 inhibits the undesired radiation
noises from the electronic element 53 from being coupled to the
heat dissipation member 57. In addition, although FIG. 2 shows, for
the purpose of clearly showing the inhibition effect of the
undesired radiation noises, that the undesired radiation noises
emitted from the electronic element 53 to the heat dissipation
member 57 side (upper side) are blocked by the low relative
dielectric constant portion 55, in fact, the undesired radiation
noises themselves which are emitted from the electronic element 53
to the heat dissipation member 57 side (upper side) are reduced
because of the presence of the low relative dielectric constant
portion 55.
[0086] Further, the undesired radiation noises emitted from the
electronic element 53 in the horizontal direction show a behavior
of avoiding the high relative magnetic permeability portion 56 as
an electric field, as indicated by the arrows EF, but show a
behavior of being attracted to the high relative magnetic
permeability portion 56 as a magnetic field, as indicated by the
arrows MF. As a result, the undesired radiation noises emitted from
the electronic element 53 in the horizontal direction are attracted
to the high relative magnetic permeability portion 56 and show a
behavior of passing through the high relative magnetic permeability
portion 56. Thus, a magnetic loss occurs in the high relative
magnetic permeability portion 56.
[0087] According to the present embodiment, the low relative
dielectric constant portion 55 at least partially overlaps the
electronic element 53 in a plan view seen in the vertical
direction. For this reason, the low relative dielectric constant
portion 55 is position immediately above at least a portion of the
electronic element 53, and the low relative dielectric constant
portion 55 is connected to the electronic element 53. Here, the
undesired radiation noises coupled from the electronic element 53
to the heat dissipation member 57 has many undesired radiation
noises coupled to the heat dissipation member 57 through a
connection portion between the electronic element 53 and the heat
conduction member 54. For this reason, by configuring at least some
of the portion connected to the electronic element 53 in the heat
conduction member 54 as the low relative dielectric constant
portion 55, the low relative dielectric constant portion 55 can
more appropriately inhibit the undesired radiation noises from
being coupled to the heat dissipation member 57, so that the
undesired radiation noises emitted from the printed circuit board
51 can be more appropriately reduced.
[0088] Also, according to the present embodiment, the high relative
magnetic permeability portion 56 surrounds the low relative
dielectric constant portion 55 over a whole circumference thereof
at least on the lower surface 54a of the heat conduction member 54.
For this reason, as shown by the arrows MF in FIG. 2, the undesired
radiation noises emitted from the entire circumference of side
surfaces of the electronic element 53 in the horizontal direction
can be attracted toward the high relative magnetic permeability
portion 56, thereby appropriately passing through the high relative
magnetic permeability portion 56. In addition, since the magnetic
flux and the current can flow to rotate around the low relative
dielectric constant portion 55 in the high relative magnetic
permeability portion 56, a path through which the magnetic flux and
the current flow can be made longer. Thus, the magnetic loss can be
appropriately generated to appropriately reduce the energy of the
undesired radiation noises, and the undesired radiation noises
emitted from the printed circuit board 51 can be more appropriately
reduced.
[0089] Also, the undesired radiation noises that tends to pass
through the low relative dielectric constant portion 55 in the
vertical direction can be attracted to the high relative magnetic
permeability portion 56 around the low relative dielectric constant
portion 55. Thus, the energy of the undesired radiation noises can
be more appropriately reduced, and the undesired radiation noises
emitted from the printed circuit board 51 can be more appropriately
reduced.
[0090] Also, according to the present embodiment, the relative
dielectric constant .epsilon. of the low relative dielectric
constant portion 55 is 8.0 or less. For this reason, the relative
dielectric constant .epsilon. of the low relative dielectric
constant portion 55 can be appropriately reduced. Thus, the
undesired radiation noises can be more appropriately inhibited from
being coupled to the heat dissipation member 57. Therefore, the
undesired radiation noises emitted from the printed circuit board
51 can be reduced more appropriately.
[0091] Also, according to the present embodiment, the high relative
magnetic permeability portion 56 has a frame shape surrounding the
low relative dielectric constant portion 55, and surrounds the low
relative dielectric constant portion 55 over a whole circumference
thereof on the upper surface 54b and the lower surface 54a of the
heat conduction member 54. For this reason, the heat conduction
member 54 can be manufactured by fitting the low relative
dielectric constant portion 55 to the inside of the high relative
magnetic permeability portion 56 after separately manufacturing the
low relative dielectric constant portion 55 and the frame-shaped
high relative magnetic permeability portion 56 with the same
thickness. Therefore, the heat conduction member 54 can be easily
manufactured.
[0092] Also, according to the present embodiment, the heat
conduction member 54 is larger than the electronic element 53 and
overlaps the entire electronic element 53 in a plan view seen in
the vertical direction. For this reason, most of the undesired
radiation noises emitted from the electronic element 53 can be
easily inhibited by the heat conduction member 54.
[0093] Also, according to the present embodiment, the region
provided with the low relative dielectric constant portion 55 in
the lower surface 54a of the heat conduction member 54 is larger
than the electronic element 53 and overlaps the entire electronic
element 53 in a plan view seen in the vertical direction. Thus, the
low relative dielectric constant portion 55 is positioned
immediately above the entire electronic element 53, and the portion
of the heat conduction member 54 connected to the electronic
element 53 becomes the low relative dielectric constant portion 55.
Therefore, the low relative dielectric constant portion 55 can more
appropriately inhibit the undesired radiation noises from being
coupled to the heat dissipation member 57 and can more
appropriately reduce the undesired radiation noises emitted from
the printed circuit board 51.
[0094] Also, according to the present embodiment, the heat
conduction member 54 is a sheet-shaped heat conduction sheet. For
this reason, the heat conduction member 54 can be easily attached
to the upper surface of the electronic element 53 in accordance
with the shape of the electronic element 53. In addition, the heat
conduction member 54 can be easily attached to the lower surface of
the heat dissipation member 57 in accordance with the shape of the
heat dissipation member 57. As a result, the electronic element 53
and the heat dissipation member 57 can be brought into close
contact with each other via the heat conduction member 54, and the
heat dissipating properties of the electronic element 53 can be
appropriately improved.
Second Embodiment
[0095] The present embodiment is different from the first
embodiment in terms of the heat conduction member. Also, the same
configurations as those of the above-described embodiment may be
denoted by the same reference signs and the description may be
omitted.
[0096] FIG. 4 is a cross-sectional view showing a printed circuit
board 151 of the present embodiment.
[0097] As shown in FIG. 4, the printed circuit board 151 of the
present embodiment includes a printed wiring board 52, an
electronic element 53, a heat dissipation member 57, and a heat
conduction member (heat conduction sheet) 154.
[0098] The heat conduction member 154 has a low relative dielectric
constant portion (a second portion) 55 and a high relative magnetic
permeability portion (a first portion) 156.
[0099] A recessed portion 156e that is recessed upward is formed at
a central portion of a lower surface 156a of the high relative
magnetic permeability portion 156. Although not shown in the
drawings, the recessed portion 156e has a square shape in a plan
view seen in the vertical direction. The low relative dielectric
constant portion 55 is fitted into the recessed portion 156e. An
outer edge of the low relative dielectric constant portion 55 is
disposed in contact with an inner edge of the recessed portion
156e. The low relative dielectric constant portion 55 and the high
relative magnetic permeability portion 156 may be joined, for
example, by an adhesive or the like. By forming the recessed
portion 156e, a frame portion 156c surrounding the low relative
dielectric constant portion 55 and an intervening portion 156d
positioned between the low relative dielectric constant portion 55
and the heat dissipation member 57 in the vertical direction are
formed in the high relative magnetic permeability portion 156.
[0100] The frame portion 156c has the same shape as the high
relative magnetic permeability portion 56 of the first
embodiment.
[0101] The intervening portion 156d is a bottom portion of the
recessed portion 156e. A lower surface of the intervening portion
156d is in contact with an upper surface of the low relative
dielectric constant portion 55. An upper surface of the intervening
portion 156d is bonded to a lower surface of the heat dissipation
member 57. The intervening portion 156d has a plate shape which
extends in the horizontal direction.
[0102] In the present embodiment, the high relative magnetic
permeability portion 156 surrounds the low relative dielectric
constant portion 55 over a whole circumference thereof in a lower
surface (second surface) 154a of the heat conduction member 154.
The lower surface 154a of the heat conduction member 154 is
configured of a lower surface 55a of the low relative dielectric
constant portion 55 and a lower surface 156a of the high relative
magnetic permeability portion 156. A distribution of the low
relative dielectric constant portion 55 and the high relative
magnetic permeability portion 156 in the lower surface 154a of the
heat conduction member 154 is the same as that of the low relative
dielectric constant portion 55 and the high relative magnetic
permeability portion 56 in the lower surface 54a of the heat
conduction member 54 of the first embodiment. On the other hand, in
the present embodiment, an upper surface (a first surface) 154b of
the heat conduction member 154 is configured by only the upper
surface 156b of the high relative magnetic permeability portion
156. In the present embodiment, a dimension of the high relative
magnetic permeability portion 156 in the vertical direction is
larger than a dimension of the low relative dielectric constant
portion 55 in the vertical direction.
[0103] In the present embodiment, a thermal conductivity of the
high relative magnetic permeability portion 156 is large enough to
appropriately transfer heat from the electronic element 53 to the
heat dissipation member 57, and is, for example, about 0.5 or more
and 20.0 or less. In the present embodiment, the heat of the
electronic element 53 is transferred to the heat dissipation member
57 through the low relative dielectric constant portion 55 and the
high relative magnetic permeability portion 156.
[0104] The other configuration of the high relative magnetic
permeability portion 156 is the same as the other configuration of
the high relative magnetic permeability portion 56 of the first
embodiment. The other configuration of the printed circuit board
151 is the same as the other configuration of the printed circuit
board 51 of the first embodiment.
[0105] According to the present embodiment, the high relative
magnetic permeability portion 156 includes the intervening portion
156d as a portion positioned between the low relative dielectric
constant portion 55 and the heat dissipation member 57 in the
vertical direction. For this reason, when the undesired radiation
noises that pass through the low relative dielectric constant
portion 55 in the vertical direction from the electronic element 53
and are coupled to the heat dissipation member 57 are generated,
the undesired radiation noises pass through the intervening portion
156d. Thus, the energy of undesired radiation noises coupled to the
heat dissipation member 57 through the low relative dielectric
constant portion 55 and the intervening portion 156d can be reduced
due to a magnetic loss in the intervening portion 156d. Therefore,
the energy of the undesired radiation noises emitted from the
electronic element 53 can be further reduced, and the undesired
radiation noises emitted from the printed circuit board 151 can be
more appropriately reduced.
[0106] In each embodiment mentioned above, the following
configurations can also be adopted.
[0107] The relative dielectric constant .epsilon. of the low
relative dielectric constant portion (second portion) may be
smaller than the relative dielectric constant .epsilon. of the high
relative magnetic permeability portion (first portion) or equal to
or smaller than 8.0. That is, the relative dielectric constant
.epsilon. of the low relative dielectric constant portion may be
larger than 8.0 as long as it is smaller than the relative
dielectric constant .epsilon. of the high relative magnetic
permeability portion. Further, the relative dielectric constant
.epsilon. of the low relative dielectric constant portion may be
equal to or larger than the relative dielectric constant .epsilon.
of the high relative magnetic permeability portion as long as it is
equal to or smaller than 8.0. Materials of the low relative
dielectric constant portion is not particularly limited as long as
the material satisfies relationships of the relative dielectric
constant .epsilon. described above and has thermal conductivity.
The low relative dielectric constant portion may include a magnetic
body. The relative magnetic permeability .mu. of the low relative
dielectric constant portion is not particularly limited.
[0108] The low relative dielectric constant portion may at least
partially overlap the electronic element in a plan view seen in the
vertical direction. The low relative dielectric constant portion
may entirely overlap the electronic element in a plan view seen in
the vertical direction. The region provided with the low relative
dielectric constant portion in the lower surface of the heat
conduction member may be the same size as the electronic element or
smaller than the electronic element.
[0109] The shape of the high relative magnetic permeability portion
is not particularly limited as long as it surrounds the low
relative dielectric constant portion at least on the lower surface
of the heat conduction member. The high relative magnetic
permeability portion may at least partially overlap the electronic
element in a plan view seen in the vertical direction. The material
of the high relative magnetic permeability portion is not
particularly limited as long as it contains a magnetic body.
[0110] The heat conduction member may have a portion other than the
low relative dielectric constant portion and the high relative
magnetic permeability portion. The heat conduction member may have,
for example, a portion having a property different from any one of
the low relative dielectric constant portion and the high relative
magnetic permeability portion, between the low relative dielectric
constant portion and the high relative magnetic permeability
portion. The heat conduction member may be smaller than the
electronic element in a plan view seen in the vertical direction,
or may overlap only a portion of the electronic element in a plan
view seen in the vertical direction. The heat conduction member may
not have a sheet shape.
[0111] The electronic element is not particularly limited as long
as it is an element provided on the mounting surface of the printed
wiring board. The electronic element may be, for example, a
transistor such as a field effect transistor (FET). The heat
dissipation member is not particularly limited as long as it is
thermally connected to the electronic element and can dissipate
heat from the electronic element. The heat dissipation member may
be, for example, a heat sink provided with fins for heat
dissipation.
[0112] Also, in the first embodiment described above, an example in
which the invention is applied to a transmissive type projector has
been described, but the invention can also be applied to a
reflective type projector. Here, the "transmissive type" indicates
that a liquid crystal light valve including a liquid crystal panel
or the like is a type that transmits light. The "reflective type"
indicates that the liquid crystal light valve is a type that
reflects light. In addition, the light modulation device is not
limited to a liquid crystal panel or the like, and may be, for
example, a light modulation device using a micro mirror.
[0113] Also, in the first embodiment described above, an example of
the projector 1 using the three light modulation devices 4R, 4G and
4B has been described, but the invention is also applicable to a
projector using only one light modulation device and a projector
using four or more light modulation devices.
[0114] In addition, the electronic device on which the printed
circuit board is mounted is not limited to the projector, and may
be another electronic device.
[0115] Further, each structure described in the present
specification can be appropriately combined in a range in which
they do not contradict mutually.
EXAMPLES
[0116] Usefulness of the invention was confirmed by comparing an
example and comparative examples 1 and 2. The example was a printed
circuit board provided with a heat conduction member similar to the
first embodiment described above. The material of the low relative
dielectric constant portion in the example was acrylic resin, and
the relative dielectric constant .epsilon. of the low relative
dielectric constant portion in the example was 6.1. The low
relative dielectric constant portion in the example is a
nonmagnetic portion containing no magnetic body. That is, the
relative magnetic permeability .mu. of the low relative dielectric
constant portion in the example is approximately 1.0. The high
relative magnetic permeability portion in the example had a
configuration in which ferrite was mixed with an acrylic resin as a
base material. The relative magnetic permeability .mu. of the high
relative magnetic permeability portion in the example was 13.0. The
relative dielectric constant .epsilon. of the high relative
magnetic permeability portion in the example was 10.8. In the heat
conduction member of the example, the thickness of the low relative
dielectric constant portion and the thickness of the high relative
magnetic permeability portion were the same as each other, and were
3.5 mm. In addition, when the heat conduction member is
incorporated into the printed circuit board, the heat conduction
member is pressed and crushed by the heat dissipation member and
the electronic element, and the thickness of the low relative
dielectric constant portion and the thickness of the high relative
magnetic permeability portion are approximately 3.0 mm.
[0117] The comparative examples 1 and 2 were printed circuit boards
provided with a heat conduction member having uniform properties
throughout the member. External shapes and dimensions of the heat
conduction member in the comparative examples 1 and 2 were the same
as the external shape and dimension of the heat conduction member
in the example. The comparative example 1 had a heat conduction
member the entire of which has the same material and physical
properties as the low relative dielectric constant portion of the
example. The comparative example 2 has a heat conduction member the
entire of which has the same material and physical properties as in
the high relative magnetic permeability portion of the example.
[0118] In each of the example and the comparative examples 1 and 2,
the printed wiring board was a multilayer printed wiring board, and
the electronic element was an LSI. The heat dissipation member was
a heat dissipating plate made of aluminum.
[0119] In each of the example and the comparative examples 1 and 2,
the LSI was operated to measure the undesired radiation noises
having the respective frequencies of 800 MHz, 1600 MHz and 2400
MHz. The measurement of the undesired radiation noises was
performed for each of the horizontally polarized waves and the
vertically polarized waves for each frequency.
[0120] The measurement of the undesired radiation noises was
performed in an anechoic chamber equipped with an electric field
strength measurement system based on the international standard set
by the International Special Committee on Radio Interference
(CISPR). The measurement results are shown in FIGS. 5 and 6. FIG. 5
is a graph showing the measurement results of horizontally
polarized waves in the undesired radiation noises. FIG. 6 is a
graph showing the measurement results of vertically polarized waves
in the undesired radiation noises. In FIGS. 5 and 6, the horizontal
axis is a noise frequency [MHz] of the undesired radiation noises,
and the vertical axis is a noise level [dB] of the undesired
radiation noises.
[0121] As shown in FIGS. 5 and 6, it was confirmed that the noise
level in the example is smaller than the noise levels in the
comparative examples 1 and 2 at 800 MHz, 1600 MHz and 2400 MHz in
the horizontally polarized waves and the vertically polarized
waves.
[0122] Also, it was confirmed that the noise level can be made
smaller in the comparative example 1 than in the comparative
example 2 at 800 MHz, while the noise level can be made smaller in
the comparative example 2 than in the comparative example 1 at 1600
MHz and 2400 MHz. As a result, it was confirmed that reducing the
relative dielectric constant .epsilon. is useful to inhibit the
undesired radiation noises having a frequency lower than 1 GHz,
while the contribution of including a magnetic body to make the
relative magnetic permeability .mu. greater than 1.0 is relatively
small to the inhibition of the undesired radiation noises having a
frequency lower than 1 GHz. Also, it was confirmed that including a
magnetic body to make the relative magnetic permeability .mu.
larger than 1.0 is useful to inhibit the undesired radiation noises
having a frequency of 1 GHz or more, while the contribution of
reducing the relative dielectric constant .epsilon. is relatively
small to the inhibition of the undesired radiation noises having a
frequency of 1 GHz or more. Therefore, it was confirmed that
reducing the relative dielectric constant .epsilon. and increasing
the relative magnetic permeability .mu. are insufficient for the
inhibition of the undesired radiation noises when only one of them
is used.
[0123] From the above, the usefulness of the example having both
the low relative dielectric constant portion and the high relative
magnetic permeability portion was confirmed.
[0124] Next, using the plurality of samples having different
relative dielectric constants .epsilon. as heat conduction members,
the same measurements as in the above-described example and
comparative examples 1 and 2 were performed. Eight samples SA to SH
were prepared. Each of the samples SA to SH was a heat conduction
member having uniform properties throughout the member. The base
material of the samples SA and SE was acrylic resin. Samples SB,
SC, SD, SF, SG, and SH were configured of ferrite mixed with
acrylic resin as a base material.
[0125] The relative dielectric constant .epsilon. of the sample SA
was 2.1. The relative dielectric constant .epsilon. of the sample
SB was 4.8. The relative dielectric constant .epsilon. of the
sample SC was 5.4. The relative dielectric constant .epsilon. of
the sample SD was 5.9. The relative dielectric constant .epsilon.
of the sample SE was 6.1. The relative dielectric constant
.epsilon. of the sample SF was 6.4. The relative dielectric
constant .epsilon. of the sample SG was 8.0. The relative
dielectric constant .epsilon. of the sample SH was 10.8. The
samples SA and SE were nonmagnetic, and the relative magnetic
permeability .mu. was approximately 1.0. The relative magnetic
permeability .mu. of the samples SB and SC was 2.3. The relative
magnetic permeability .mu. of the sample SD was 2.4. The relative
magnetic permeability .mu. of the sample SF was 2.8. The relative
magnetic permeability .mu. of the sample SG was 15.0. The relative
magnetic permeability .mu. of the sample SH was 4.9.
[0126] The configuration other than the heat conduction member of
the printed circuit board on which each of the samples SA to SH is
provided is the same as that of the example and the comparative
examples 1 and 2 described above.
[0127] The measurement was performed for each of the samples SA to
SH in the same measurement environment as the measurement of the
undesired radiation noises described above for each of the
horizontally polarized waves and the vertically polarized waves in
the undesired radiation noises at 800 MHz. The measurement results
are shown in FIGS. 7 and 8. FIG. 7 is a graph showing the
measurement results of horizontally polarized waves in the
undesired radiation noises. FIG. 8 is a graph showing the
measurement results of vertically polarized waves in the undesired
radiation noises. In FIGS. 7 and 8, the horizontal axis is relative
dielectric constant .epsilon., and the vertical axis is relative
noise level [dB] of the undesired radiation noises. The relative
noise level [dB] is a relative noise level with reference to the
noise level of the sample SH.
[0128] As shown in FIGS. 7 and 8, it was confirmed that, in the
samples SA to SG in which the relative dielectric constant
.epsilon. is 8.0 or less, the noise level can be largely reduced as
compared with the sample SH in which the relative dielectric
constant .epsilon. is larger than 8.0. The noise level in the
samples SA to SG is 3.0 dB or more smaller than the noise level of
the sample SH. In view of the fact that the width of the
distribution range of the noise level in the samples SA to SG in
which the relative dielectric constant .epsilon. is in the range of
2.1 to 8.0 is approximately 1.0 dB, it can be said that the noise
level reduction effect is remarkably large in that the noise level
is reduced by 3.0 dB or more when the relative dielectric constant
.epsilon. becomes from 10.8 to 8.0.
[0129] Also, in the "Technical Conditions of Radio Frequency
Interference Wave and Immunity Measurement Equipment Part 1--Volume
1: Radio Frequency Interference Wave and Immunity Measurement
Equipment-Measurement Receiver--" included in the "On all standards
of International Special Committee on Radio Interference (CISPR)"
in the standards of International Special Committee on Radio
Interference (CISPR), the antenna used for radiation interference
wave measurements is defined to have a measurement accuracy better
than .+-.3 dB. For this reason, the fact that the noise level can
be reduced by 3.0 dB or more means that the noise level can be
reduced beyond the tolerance of the measurement error, and an
effective noise level reduction effect can be obtained.
[0130] From the above, it was confirmed that the noise inhibition
effect can be more appropriately obtained by setting the relative
dielectric constant .epsilon. to be 8.0 or less.
[0131] Also, as described above, with respect to the inhibition of
the undesired radiation noises lower than 1 GHz, increasing the
relative magnetic permeability .mu. has a relatively small
contribution. In addition, the frequency of the undesired radiation
noises measured in the above samples SA to SH is 800 MHz. For this
reason, in the above comparison of the samples SA to SH, if the
relative magnetic permeability .mu. of the samples SA to SH is
within the numerical range, the influence of the difference in
relative magnetic permeability .mu. of the samples SA to SH is
sufficiently negligible. That is, even if the relative magnetic
permeability .mu. is made to be the same value without changing the
relative dielectric constant .epsilon. of the samples SA to SH, it
is possible to obtain a result showing the same tendency as the
above-mentioned result.
[0132] While preferred embodiments and modified example of the
invention have been described and illustrated above, it should be
understood that these are exemplary of the invention and are not to
be considered as limiting. Additions, omissions, substitutions, and
other modifications can be made without departing from the scope of
the invention. Accordingly, the invention is not to be considered
as being limited by the foregoing description, and is only limited
by the scope of the appended claims.
* * * * *