U.S. patent application number 13/430736 was filed with the patent office on 2012-07-19 for circuit substrate and method of manufacturing same.
This patent application is currently assigned to MURATA MANUFACTURING CO., LTD.. Invention is credited to Noboru KATO, Masahiro OZAWA.
Application Number | 20120181068 13/430736 |
Document ID | / |
Family ID | 43826208 |
Filed Date | 2012-07-19 |
United States Patent
Application |
20120181068 |
Kind Code |
A1 |
KATO; Noboru ; et
al. |
July 19, 2012 |
CIRCUIT SUBSTRATE AND METHOD OF MANUFACTURING SAME
Abstract
A circuit substrate capable of reducing and preventing
deviations of circuit characteristics includes a relatively hard
region and a relatively soft region. A main body of the circuit
substrate includes a stack of a plurality of flexible sheets made
of a flexible material and includes rigid regions and a flexible
region, the flexible region being more easily deformable than the
rigid regions. Wiring conductors are disposed in the main body and
define circuitry. Reinforcing insulative films are disposed so as
to cover the portions where the wiring conductors are not disposed
in the rigid regions on the flexible sheets when seen in plan view
from the z-axis direction.
Inventors: |
KATO; Noboru;
(Nagaokakyo-shi, JP) ; OZAWA; Masahiro;
(Nagaokakyo-shi, JP) |
Assignee: |
MURATA MANUFACTURING CO.,
LTD.
Nagaokakyo-shi
JP
|
Family ID: |
43826208 |
Appl. No.: |
13/430736 |
Filed: |
March 27, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2010/066788 |
Sep 28, 2010 |
|
|
|
13430736 |
|
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Current U.S.
Class: |
174/254 ;
156/60 |
Current CPC
Class: |
H05K 3/4614 20130101;
H05K 3/281 20130101; Y10T 156/10 20150115; H05K 3/4691 20130101;
H05K 1/0281 20130101; H05K 3/4632 20130101; H05K 1/028 20130101;
H05K 3/44 20130101 |
Class at
Publication: |
174/254 ;
156/60 |
International
Class: |
H05K 1/02 20060101
H05K001/02; H05K 3/00 20060101 H05K003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 30, 2009 |
JP |
2009-227556 |
Claims
1. A circuit substrate comprising: a main body including a stack of
a plurality of first insulator layers made of a flexible material,
the main body including a rigid region and a flexible region, the
flexible region being more easily deformable than the rigid region;
a conductive layer disposed in the main body and defining
circuitry; and a second insulator layer disposed so as to cover at
least a portion of an area where the conductive layer is not
disposed in the rigid region on at least one of the first insulator
layers when seen in plan view from a stacking direction.
2. The circuit substrate according to claim 1, wherein the second
insulator layer is made of a material that is harder than a
material of the first insulator layers.
3. The circuit substrate according to claim 1, wherein the second
insulator layer is disposed in the main body, and the second
insulator layer has a thickness equal to or less than a thickness
of the conductive layer in the stacking direction.
4. The circuit substrate according to claim 1, wherein the
conductive layer extends across a border between the rigid region
and the flexible region.
5. The circuit substrate according to claim 1, wherein the main
body further includes a semi-rigid region between the rigid region
and the flexible region, the rigid region is less deformable than
the semi-rigid region, the flexible region is more easily
deformable than the semi-rigid region, and the second insulator
layer is disposed so as to cover a portion where the conductive
layer is not disposed in the semi-rigid region on at least one of
the first insulator layers when seen in plan view from the stacking
direction.
6. A method of manufacturing a circuit substrate comprising: a step
of preparing a plurality of first insulator layers on which
circuitry made of a conductive layer is formed, the plurality of
first insulator layers being made of a flexible material; a step of
forming a second insulator layer so as to cover at least a portion
of an area where the conductive layer is not disposed on at least
one of the first insulator layers when seen in plan view from a
stacking direction of the first insulator layers; and a step of
stacking and press-bonding the plurality of first insulator layers.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a circuit substrate and a
method of manufacturing the same and, in particular, to a circuit
substrate including a rigid region and a flexible region and a
method of manufacturing the same.
[0003] 2. Description of the Related Art
[0004] One known example of a traditional circuit substrate is a
wiring substrate described in Japanese Unexamined Patent
Application Publication No. 2006-339186. The wiring substrate
described in Japanese Unexamined Patent Application Publication No.
2006-339186 includes a flexible section and a rigid section
disposed to be contiguous to the flexible section. The flexible
section includes a flexible substrate in which wiring patterns are
stacked such that an insulative resin layer is disposed
therebetween. The rigid section includes a flexible substrate
formed integrally with the flexible section. The wiring density of
the wiring patterns in the rigid section is higher than that in the
flexible section. Thus, the rigid section has a higher hardness
than that of the flexible section.
[0005] However, for the wiring substrate described in Japanese
Unexamined Patent Application Publication No. 2006-339186, the
stray capacitance may increase, and the circuit characteristics may
deviate from a desired value. More specifically, for the wiring
substrate described in Japanese Unexamined Patent Application
Publication No. 2006-339186, to have a higher wiring density of the
wiring patterns in the rigid section than that in the flexible
section, a redundant wiring pattern is disposed in the rigid
section. The redundant wiring pattern faces other wiring patterns
and forms unnecessary stray capacitance. As a result, the circuit
characteristics in the wiring substrate described in Japanese
Unexamined Patent Application Publication No. 2006-339186 deviate
from a desired value.
SUMMARY OF THE INVENTION
[0006] Preferred embodiments of the present invention provide a
circuit substrate and a method of manufacturing the circuit
substrate, the circuit substrate having circuit characteristics in
which the occurrence of deviations can be reduced and including a
relatively hard region and a relatively soft region.
[0007] A circuit substrate according to a preferred embodiment of
the present invention includes a main body including a stack of a
plurality of first insulator layers made of a flexible material,
the main body including a rigid region and a flexible region, the
flexible region being more easily deformable than the rigid region,
a conductive layer disposed in the main body and forming circuitry,
and a second insulator layer disposed so as to cover at least a
portion of an area where the conductive layer is not disposed in
the rigid region on at least one of the first insulator layers when
seen in plan view from a stacking direction.
[0008] A method of manufacturing a circuit substrate according to
another preferred embodiment of the present invention includes a
step of preparing a plurality of first insulator layers on which
circuitry made of a conductive layer is formed, the plurality of
first insulator layers being made of a flexible material, a step of
forming a second insulator layer so as to cover at least a portion
of an area where the conductive layer is not disposed on at least
one of the first insulator layers when seen in plan view from a
stacking direction, and a step of stacking and press-bonding the
plurality of first insulator layers.
[0009] According to various preferred embodiments of the present
invention, a circuit substrate that has circuit characteristics in
which the occurrence of deviations can be reduced and that includes
a relatively hard region and a relatively soft region is
obtainable.
[0010] The above and other elements, features, steps,
characteristics and advantages of the present invention will become
more apparent from the following detailed description of the
preferred embodiments with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is an external perspective view of a circuit
substrate according to a preferred embodiment of the present
invention.
[0012] FIG. 2 is an exploded perspective view of the circuit
substrate illustrated in FIG. 1.
[0013] FIGS. 3A and 3B are perspective views of a flexible sheet in
the circuit substrate in its manufacturing process.
[0014] FIG. 4 is a cross-sectional configuration view of the
circuit substrate illustrated in FIG. 2 taken along the line
A-A.
[0015] FIG. 5 is an exploded perspective view of a circuit
substrate according to a first variation of a preferred embodiment
of the present invention.
[0016] FIG. 6 is an exploded perspective view of a circuit
substrate according to a second variation of a preferred embodiment
of the present invention.
[0017] FIG. 7 is a cross-sectional configuration view of a circuit
substrate according to a third variation of a preferred embodiment
of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] A circuit substrate and a method of manufacturing the same
according to preferred embodiments of the present invention are
described below with reference to the drawings.
[0019] A configuration of a circuit substrate according to a
preferred embodiment of the present invention is described below
with reference to the drawings. FIG. 1 is an external perspective
view of a circuit substrate 10 according to a preferred embodiment
of the present invention. FIG. 2 is an exploded perspective view of
the circuit substrate 10 illustrated in FIG. 1. FIGS. 3A and 3B are
perspective views of a flexible sheet 26a in the circuit substrate
10 in its manufacturing process. FIG. 3A illustrates the back side
of the flexible sheet 26a, and FIG. 3B illustrates the front side
of the flexible sheet 26a in a state where resist films 20a and 24a
are not formed. FIG. 4 is a cross-sectional configuration view of
the circuit substrate 10 illustrated in FIG. 2 taken along the line
A-A. In FIGS. 1 to 4, the stacking direction of the circuit
substrate 10 is defined as the z-axis direction, the longitudinal
direction of a line section 16 in the circuit substrate 10 is
defined as the x-axis direction, and the direction to which the
x-axis direction and the z-axis direction are orthogonal is defined
as the y-axis direction. The front side of each of the circuit
substrate 10 and the flexible sheets 26 indicates a surface
positioned on the positive-direction side in the z-axis direction,
and the back side of each of the circuit substrate 10 and the
flexible sheet 26 indicates a surface positioned on the
negative-direction side in the z-axis direction.
[0020] As illustrated in FIG. 1, the circuit substrate 10 includes
a main body 11 including substrate sections 12 and 14 and the line
section 16. As illustrated in FIG. 2, the main body 11 includes a
stack of a plurality of (for example, preferably four in FIG. 2)
flexible sheets (insulator layers) 26 (26a to 26d) made of a
flexible material (e.g., thermoplastic resin, such as liquid
crystal polymer or polyimide). Each of the flexible sheets 26
preferably has a Young's modulus of approximately 2 GPa to 20 GPa,
for example.
[0021] The substrate section 12 is substantially rectangular and
includes, on the front side, an implementation surface on which a
plurality of chip components 50 and an integrated circuit 52 are
implemented. The substrate section 14 has the shape of a
substantially rectangle smaller than the substrate section 12 and
includes, on the front side, an implementation surface on which a
connector 54 is implemented. The substrate sections 12 and 14 are
not prone to deforming (bending) to allow the chip components 50,
integrated circuit 52, and connector 54 to be stably implemented
therein. Hereinafter, the substrate sections 12 and 14 are also
referred to as rigid regions R1 and R2, respectively. The line
section 16 connects the substrate sections 12 and 14 together. The
circuit substrate 10 is used in a state where the line section 16
is curved in a substantially U shape. The line section 16 is easily
deformable (bendable). Hereinafter, the line section 16 is also
referred to as a flexible region F1.
[0022] First, the substrate section 12 (rigid region R1) is
described. As illustrated in FIG. 2, the substrate section 12
includes a stack of substrate-section sheets 27a to 27d of the
flexible sheets 26a to 26d. As illustrated in FIGS. 1 to 3, the
substrate section 12 includes the resist film 20a, reinforcing
insulative films 20b to 20d, lands 28, wiring conductors 30 (30b,
30c), a ground conductor 37, and via-hole conductors b1 to b3 and
b21 to b26. In FIGS. 1 to 3, reference numerals are provided to
only representative ones of the lands 28, the wiring conductors 30,
and the via-hole conductors b1 to b3 to prevent complication in the
drawings.
[0023] Each of the substrate-section sheets 27a to 27d of the
flexible sheets 26a to 26d corresponds to a first insulator layer
according to a preferred embodiment of the present invention, and
each of the reinforcing insulative films 20b to 20d corresponds to
a second insulator layer according to a preferred embodiment of the
present invention. The same applies to variations described
below.
[0024] The lands 28 are disposed in the main body 11 and,
preferably are defined by a conductive layer disposed on the front
side of the substrate-section sheet 27a, as illustrated in FIG. 2.
The chip components 50 and the integrated circuit 52 are
implemented on the lands 28 preferably by soldering, for example,
as illustrated in FIG. 1.
[0025] As illustrated in FIG. 3A, the via-hole conductors b1
penetrate through the substrate-section sheet 27a along the z-axis
direction. The via-hole conductors b1 are connected to the lands
28.
[0026] The wiring conductors 30b are disposed in the main body 11
and, preferably are a conductive layer disposed on the front side
of the substrate-section sheet 27b, as illustrated in FIG. 2. The
via-hole conductors b2 penetrate through the substrate-section
sheet 27b along the z-axis direction, as illustrated in FIG. 2. The
via-hole conductors b2 are connected to the via-hole conductors b1.
As illustrated in FIG. 2, the via-hole conductors b21 to b23
penetrate through the substrate-section sheet 27b along the z-axis
direction. The via-hole conductors b21 to b23 are connected to the
wiring conductors 30b.
[0027] The wiring conductors 30c are disposed in the main body 11
and, preferably are a conductive layer disposed on the front side
of the substrate-section sheet 27c, as illustrated in FIG. 2. The
via-hole conductors b3 penetrate through the substrate-section
sheet 27c along the z-axis direction, as illustrated in FIG. 2.
Each of the via-hole conductors b3 is connected to one of the
via-hole conductors b2. As illustrated in FIG. 2, the via-hole
conductors b24 to b26 penetrate through the substrate-section sheet
27c along the z-axis direction. The via-hole conductors b24 to b26
are connected to the via-hole conductors b21 to b23,
respectively.
[0028] The ground conductor 37 is disposed in the main body 11 and,
preferably is a single film electrode having the shape of a
substantially rectangle arranged to cover the front side of the
substrate-section sheet 27d. As illustrated in FIG. 2, not all of
the substrate-section sheet 27d is covered by the ground conductor
37; the ground conductor 37 is not disposed in the vicinity of the
outer regions of the substrate-section sheet 27d. The ground
conductor 37 is grounded and thus maintained at a ground potential.
The ground conductor 37 is connected to the via-hole conductors b3
and b24 to b26. As described above, the substrate-section sheets
27a to 27d are stacked, and thus the wiring conductors 30b and 30c,
the ground conductor 37, and the via-hole conductors b1 to b3 and
b21 to b26 are connected to each other and define circuitry.
[0029] The resist film 20a is disposed so as to cover the front
side of the substrate-section sheet 27a and is an insulative film
to protect the substrate-section sheet 27a. The resist film 20a is
not disposed on the lands 28. The resist film 20a is a solder
resist film to define an area in which solder is to be applied on
the lands 28.
[0030] The reinforcing insulative film 20b is disposed in the main
body 11 and, preferably is an insulative film that covers the
portion where the wiring conductors 30b and the via-hole conductors
b2 and b21 to b23 are not disposed on the front side of the
substrate-section sheet 27b (in the rigid region R1) when seen in
plan view from the z-axis direction, as illustrated in FIG. 2. The
thickness of the reinforcing insulative film 20b is equal to or
less than the thickness of each of the wiring conductors 30b. In
the present preferred embodiment, the thickness of the reinforcing
insulative film 20b is equal to the thickness of the wiring
conductor 30b. The reinforcing insulative film 20b is made of a
material that is harder than the material of the substrate-section
sheet 27b and can be produced by application of thermosetting resin
(e.g., epoxy resin), for example. The reinforcing insulative film
20b preferably has a Young's modulus of approximately 12 GPa to 30
GPa, for example.
[0031] The reinforcing insulative film 20c is disposed in the main
body 11 and, preferably is an insulative film that covers the
portion where the wiring conductors 30c and the via-hole conductors
b3 and b24 to b26 are not disposed on the front side of the
substrate-section sheet 27c (in the rigid region R1) when seen in
plan view from the z-axis direction, as illustrated in FIGS. 2 and
4. The thickness of the reinforcing insulative film 20c is equal to
or less than the thickness of each of the wiring conductors 30c, as
illustrated in FIG. 4. In the present preferred embodiment, the
thickness of the reinforcing insulative film 20c preferably is
equal to the thickness of the wiring conductor 30c. The reinforcing
insulative film 20c is made of a material harder than the material
of the substrate-section sheet 27c and can be produced by
application of thermosetting resin (e.g., epoxy resin), for
example. The reinforcing insulative film 20c preferably has a
Young's modulus of approximately 12 GPa to 30 GPa, for example.
[0032] The reinforcing insulative film 20d is disposed in the main
body 11 and, preferably is an insulative film that covers the
portion where the ground conductor 37 is not disposed on the front
side of the substrate-section sheet 27d (in the rigid region R1)
when seen in plan view from the z-axis direction, as illustrated in
FIG. 2. The thickness of the reinforcing insulative film 20d is
equal to or less than the thickness of the ground conductor 37. In
the present preferred embodiment, the thickness of the reinforcing
insulative film 20d is equal to the thickness of the ground
conductor 37. The reinforcing insulative film 20d preferably is
made of a material that is harder than the material of the
substrate-section sheet 27d and can be produced by application of
thermosetting resin (e.g., epoxy resin), for example. The
reinforcing insulative film 20d preferably has a Young's modulus of
approximately 12 GPa to 30 GPa, for example.
[0033] It is preferable that each of these reinforcing insulative
films may be disposed in the entire portion where the ground
conductor is not disposed on the substrate-section sheet in the
substrate section 12 (rigid region R1), as described above.
Alternatively, they may be disposed in a portion of the portion
where the ground conductor is not disposed. Alternatively, only one
of the plurality of substrate-section sheets being stacked may be
overlaid with the reinforcing insulative film.
[0034] In the case where the reinforcing insulative film is
disposed in a portion of an area where the ground conductor is not
disposed on the substrate-section sheet, the reinforcing insulative
film may preferably be disposed on the substrate-section sheet in
the vicinity of the border between the substrate section 12 (rigid
region R1) and the line section (flexible region F1). The
reinforcing insulative film may preferably be disposed on the
substrate-section sheet in a fixation portion fixed on a casing or
mother board in the rigid region R1. In addition, in the case where
a component is mounted on or incorporated in the rigid region R1,
the reinforcing insulative film may preferably be disposed on the
substrate-section sheet adjacent to the mounting side, or on each
of the substrate-section sheets above and below the component
incorporated, in the region that overlaps the component when the
circuit substrate 10 is seen in plan view from the stacking
direction.
[0035] Next, the substrate section 14 (rigid region R2) is
described. As illustrated in FIG. 2, the substrate section 14
includes a stack of substrate-section sheets 29a to 29d of the
flexible sheets 26a to 26d. As illustrated in FIGS. 1 to 3, the
substrate section 14 includes the resist film 24a, reinforcing
insulative films 24b to 24d, lands 35, wiring conductors 36 (36b,
36c), a ground conductor 40, and via-hole conductors b11, b12, and
b31 to b36. In FIGS. 1 to 3, reference numerals are provided to
only representative ones of the lands 35, the wiring conductors 36,
and the via-hole conductors b11 and b12 to prevent complication in
the drawings.
[0036] The lands 35 are disposed in the main body 11 and,
preferably are conductive layers disposed on the front side of the
substrate-section sheet 29a, as illustrated in FIG. 2. The
connector 54 is implemented on the lands 35 preferably by
soldering, as illustrated in FIG. 1, for example.
[0037] As illustrated in FIG. 3A, the via-hole conductors b11
penetrate through the substrate-section sheet 29a along the z-axis
direction. The via-hole conductors b11 are connected to the lands
35.
[0038] The wiring conductors 36b are disposed in the main body 11
and, preferably are a conductive layer disposed on the front side
of the substrate-section sheet 29b, as illustrated in FIG. 2. The
via-hole conductors b12 penetrate through the substrate-section
sheet 29b along the z-axis direction, as illustrated in FIG. 2. The
via-hole conductors b12 are connected to the via-hole conductors
b11. As illustrated in FIG. 2, the via-hole conductors b31 to b33
penetrate through the substrate-section sheet 29b along the z-axis
direction. The via-hole conductors b31 to b33 are connected to the
wiring conductors 36b.
[0039] The wiring conductors 36c are disposed in the main body 11
and, preferably are a conductive layer disposed on the front side
of the substrate-section sheet 29c, as illustrated in FIG. 2. The
wiring conductors 36c are connected to the via-hole conductors b12.
As illustrated in FIG. 2, the via-hole conductors b34 to b36
penetrate through the substrate-section sheet 29c along the z-axis
direction. The via-hole conductors b34 to b36 are connected to the
via-hole conductors b31 to b33, respectively.
[0040] The ground conductor 40 is disposed in the main body 11 and,
preferably is a single film electrode having the shape of a
substantially rectangle arranged so as to cover the front side of
the substrate-section sheet 29d. As illustrated in FIG. 2, not all
of the substrate-section sheet 29d is covered by the ground
conductor 40; the ground conductor 40 is not disposed in the
vicinity of the outer regions of the substrate-section sheet 29d.
The ground conductor 40 is grounded and thus maintained at a ground
potential. The ground conductor 40 is connected to the via-hole
conductors b34 to b36. As described above, the substrate-section
sheets 29a to 29d are stacked, and thus the wiring conductors 36b
and 36c, the ground conductor 40, and the via-hole conductors b11,
b12, and b31 to b36 are connected to each other and define
circuitry.
[0041] The resist film 24a is disposed so as to cover the front
side of the substrate-section sheet 29a and is an insulative film
to protect the substrate-section sheet 29a. The resist film 24a is
not disposed on the lands 35. The resist film 24a is a solder
resist to define an area in which solder is to be applied on the
lands 35.
[0042] The reinforcing insulative film 24b is disposed in the main
body 11 and, preferably is an insulative film that covers the
portion where the wiring conductors 36b and the via-hole conductors
b12 and b31 to b33 are not disposed on the front side of the
substrate-section sheet 29b (in the rigid region R2) when seen in
plan view from the z-axis direction, as illustrated in FIG. 2. The
thickness of the reinforcing insulative film 24b is equal to or
less than the thickness of each of the wiring conductors 36b. In
the present preferred embodiment, the thickness of the reinforcing
insulative film 24b is equal to the thickness of the wiring
conductor 36b. The reinforcing insulative film 24b is preferably
made of a material that is harder than the material of the
substrate-section sheet 29b and can be produced by application of
thermosetting resin (e.g., epoxy resin), for example. The
reinforcing insulative film 24b has a Young's modulus of
approximately 12 GPa to 30 GPa, for example.
[0043] The reinforcing insulative film 24c is disposed in the main
body 11 and, preferably is an insulative film that covers the
portion where the wiring conductors 36c and the via-hole conductors
b34 to b36 are not disposed on the front side of the
substrate-section sheet 29c (in the rigid region R2) when seen in
plan view from the z-axis direction, as illustrated in FIG. 2. The
thickness of the reinforcing insulative film 24c is equal to or
less than the thickness of each of the wiring conductors 36c. In
the present preferred embodiment, the thickness of the reinforcing
insulative film 24c is preferably equal to the thickness of the
wiring conductor 36c. The reinforcing insulative film 24c is
preferably made of a material that is harder than the material of
the substrate-section sheet 29c and can be produced by application
of thermosetting resin (e.g., epoxy resin), for example. The
reinforcing insulative film 24c has a Young's modulus of
approximately 12 GPa to 30 GPa, for example.
[0044] The reinforcing insulative film 24d is disposed in the main
body 11 and, preferably is an insulative film that covers the
portion where the ground conductor 40 is not disposed on the front
side of the substrate-section sheet 29d (in the rigid region R2)
when seen in plan view from the z-axis direction, as illustrated in
FIG. 2. The thickness of the reinforcing insulative film 24d is
equal to or less than the thickness of the ground conductor 40. In
the present preferred embodiment, the thickness of the reinforcing
insulative film 24d is preferably equal or substantially equal to
the thickness of the ground conductor 40. The reinforcing
insulative film 24d preferably is made of a material that is harder
than the material of the substrate-section sheet 29d and can be
produced by application of thermosetting resin (e.g., epoxy resin),
for example. The reinforcing insulative film 24d preferably has a
Young's modulus of approximately 12 GPa to 30 GPa, for example.
[0045] Next, the line section 16 (flexible region F1) is described.
As illustrated in FIG. 2, the line section 16 includes a stack of
line-section sheets 31a to 31d of the flexible sheets 26a to 26d.
As illustrated in FIGS. 1 and 2, the line section 16 includes
ground lines 32 (32b, 32d), 33 (33b, 33d), and 34 (34b, 34d) and
signal lines 42c, 43c, and 44c.
[0046] Each of the signal lines 42c, 43c, and 44c is disposed in
the main body 11 and, preferably is disposed in the line section 16
and extends between the substrate sections 12 and 14. As
illustrated in FIG. 2, each of the signal lines 42c, 43c, and 44c
preferably is a linear conductive layer disposed on the front side
of the line-section sheet 31c. A signal of a high frequency (e.g.,
800 MHz to 900 MHz) is transmitted to the signal lines 42c, 43c,
and 44c. As illustrated in FIG. 2, the signal lines 42c, 43c, and
44c connect the wiring conductors 30c and the wiring conductors
36c. That is, the conductive layer including the wiring conductors
30c and 36c and the signal lines 42c, 43c, and 44c extends across
the border between the flexible region F1 and each of the rigid
regions R1 and R2.
[0047] Each of the ground lines 32b, 33b, and 34b is disposed in
the main body 11 and, preferably is disposed in the line section 16
and positioned on the positive-direction side in the z-axis
direction with respect to the signal lines 42c, 43c, and 44c. As
illustrated in FIG. 2, each of the ground lines 32b, 33b, and 34b
is disposed on the front side of the line-section sheet 31b and
connects the wiring conductor 30b and the wiring conductor 36b.
That is, the conductive layer including the wiring conductors 30b
and 36b and the ground lines 32b, 33b, and 34b extends across the
border between the flexible region F1 and each of the rigid regions
R1 and R2. In addition, the wiring conductors 30b are connected to
the ground conductor 37 through the via-hole conductors b21 to b26.
The wiring conductors 36b are connected to the ground conductor 40
through the via-hole conductors b31 to b36. Accordingly, each of
the ground lines 32b, 33b, and 34b is electrically connected to the
ground conductor 37. Each of the ground lines 32b, 33b, and 34b is
electrically connected to the ground conductor 40.
[0048] As illustrated in FIG. 2, the ground lines 32b, 33b, and 34b
preferably have line widths that are wider than those of the signal
lines 42c, 43c, and 44c, respectively. Therefore when seen in plan
view from the z-axis direction, the signal lines 42c, 43c, and 44c
do not protrude from the ground lines 32b, 33b, and 34b,
respectively, and overlap the ground lines 32b, 33b, and 34b,
respectively.
[0049] The ground lines 32d, 33d, and 34d are disposed in the line
section 16 and positioned on the negative-direction side in the
z-axis direction with respect to the signal lines 42c, 43c, and
44c. Specifically, as illustrated in FIG. 2, each of the ground
lines 32d, 33d, and 34d is disposed on the front side of the
line-section sheet 31d and connects the ground conductor 37 and the
ground conductor 40. That is, the conductive layer including the
ground conductors 37 and 40 and the ground lines 32d, 33d, and 34d
extends across the border between the flexible region F1 and each
of the rigid regions R1 and R2.
[0050] As illustrated in FIG. 2, the ground lines 32d, 33d, and 34d
preferably have line widths that are wider than those of the signal
lines 42c, 43c, and 44c, respectively. Therefore, when seen in plan
view from the z-axis direction, the signal lines 42c, 43c, and 44c
do not protrude from the ground lines 32d, 33d, and 34d,
respectively, and overlap the ground lines 32d, 33d, and 34d,
respectively.
[0051] As described above, the ground lines 32b, 33b, and 34b, the
signal lines 42c, 43c, and 44c, and the ground lines 32d, 33d, and
34d overlap each other. Therefore, the ground line 32b, the signal
line 42c, and the ground line 32d define a strip line structure.
Similarly, the ground line 33b, the signal line 43c, and the ground
line 33d define a strip line structure. The ground line 34b, the
signal line 44c, and the ground line 34d define a strip line
structure. As a result, the impedance between the circuitry in the
substrate section 12 and the circuitry in the substrate section 14
is matched. Thus, in the main body 11, the circuitry in the
substrate section 12, the circuitry in the substrate section 14,
and the strip lines in the line section 16 define a single circuit
having matched impedance.
[0052] A non-limiting method of manufacturing the circuit substrate
10 according to another preferred embodiment of the present
invention is described below with reference to the drawings. In the
following description, the case where one circuit substrate 10 is
produced is described as an example. In actuality, however, a
plurality of circuit substrates 10 preferably are produced at one
time by cutting a stack of large flexible sheets.
[0053] First, flexible sheets 26 made of thermoplastic resin, such
as a liquid crystal polymer or polyimide, and having copper foil
with a thickness of 5 .mu.m to 50 .mu.m formed over the front side
thereof are prepared. The thickness of each of the flexible sheets
26 is approximately 10 .mu.m to 150 .mu.m. Next, each of the
locations where the via-hole conductors b1 to b3, b11, b12, b21 to
b26, and b31 to b36 are to be formed in the flexible sheets 26a to
26c (see FIGS. 2 and 3A) is radiated with a laser beam from the
back side thereof, thus forming via holes therein.
[0054] Next, the lands 28 and 35 illustrated in FIG. 3B are formed
on the front side of the flexible sheet 26a by a photolithography
step. Specifically, a resist having the same shape as that of each
of the lands 28 and 35 illustrated in FIG. 3B is printed on the
copper foil of the flexible sheet 26a. The copper foil in the
portion that is not covered by the resists is removed by etching
performed on the copper foil. After that, the resists are removed.
In this way, the lands 28 and 35 illustrated in FIG. 3B are formed
on the front side of the flexible sheet 26a. Then the resist films
20a and 24a illustrated in FIGS. 1 and 2 are formed by application
of resin on the front side of the flexible sheet 26a.
[0055] Next, the wiring conductors 30b and 36b and the ground lines
32b, 33b, and 34b illustrated in FIG. 2 are formed on the front
side of the flexible sheet 26b by a photolithography step. The
wiring conductors 30c and 36c and the signal lines 42c, 43c, and
44c illustrated in FIG. 2 are formed on the front side of the
flexible sheet 26c by a photolithography step. The ground lines
32d, 33d, and 34d and the ground conductors 37 and 40 illustrated
in FIG. 2 are formed on the front side of the flexible sheet 26d by
a photolithography step. These photolithography steps are
substantially the same as the photolithography step used in the
formation of the lands 28 and 35, so the description thereof is
omitted.
[0056] Next, the via holes in the flexible sheets 26a to 26c are
filled with conductive paste including an alloy of tin and silver
as the principal component, thus forming the via-hole conductors b1
to b3, b11, b12, b21 to b26, and b31 to b36 illustrated in FIGS. 2
and 3A. Through the above-described steps, the flexible sheets, 26a
to 26d being made of a flexible material, and on which the
circuitry is made are prepared. The circuitry is made up of the
wiring conductors 30b, 30c, 36b, and 36c, the ground conductors 37
and 40, the via-hole conductors b1 to b3, b11, b12, b21 to b26, b31
to b36, the ground lines 32b, 33b, 34b, 32d, 33d, and 34d, and the
signal lines 42c, 43c, and 44c.
[0057] Next, the reinforcing insulative film 20b is formed on the
substrate-section sheet 27b by application of resin so as to cover
the portion in which the wiring conductors 30b and the via-hole
conductors b2 and b21 to b23 are not disposed when seen in plan
view from the z-axis direction. The reinforcing insulative film 24b
is formed on the substrate-section sheet 29b by application of
resin so as to cover the portion in which the wiring conductors 36b
and the via-hole conductors b12 and b31 to b33 are not disposed
when seen in plan view from the z-axis direction. The reinforcing
insulative film 20c is formed on the substrate-section sheet 27c by
application of resin so as to cover the portion in which the wiring
conductors 30c and the via-hole conductors b3 and b24 to b26 are
not disposed when seen in plan view from the z-axis direction. The
reinforcing insulative film 24c is formed on the substrate-section
sheet 29c by application of resin so as to cover the portion in
which the wiring conductors 36c and the via-hole conductors b34 to
b36 are not disposed when seen in plan view from the z-axis
direction. The reinforcing insulative film 20d is formed on the
substrate-section sheet 27d by application of resin so as to cover
the portion in which the ground conductor 37 is not disposed when
seen in plan view from the z-axis direction. The reinforcing
insulative film 24d is formed on the substrate-section sheet 29d by
application of resin so as to cover the portion in which the ground
conductor 40 is not disposed when seen in plan view from the z-axis
direction. The application of resin is made by printing of liquid
thermosetting epoxy resin by screen printing, gravure printing, or
other process. The thickness of each of the reinforcing insulative
films 20b to 20d and 24b to 24d may preferably be about 5 .mu.m to
about 50 .mu.m, for example.
[0058] Lastly, the flexible sheets 26a to 26d are stacked in this
order. The flexible sheets 26a to 26d are press-bonded by the
application of force from both sides in the z-axis direction and
the application of heat. This causes the unhardened reinforcing
insulative films 20b to 20d and 24b to 24d to be hardened and also
join the flexible sheets 26 on both sides of the reinforcing
insulative films 20b to 20d and 24b to 24d in the z-axis direction
such that the reinforcing insulative films 20b to 20d and 24b to
24d are disposed therebetween. In the portion where the flexible
sheets 26 are adjacent to each other without the reinforcing
insulative films 20b to 20d and 24b to 24d, the surfaces of the
flexible sheets 26 flow and the flexible sheets 26 are coupled
together. The via-hole conductors b1 to b3, b11, b12, b21 to b26,
and b31 to b36, the wiring conductors 30b, 30c, 36b, and 36c, and
the ground conductors 37 and 40 are electrically coupled to each
other. In this way, the circuit substrate 10 illustrated in FIG. 1
is obtained.
[0059] The circuit substrate 10 can have circuit characteristics in
which the occurrence of deviations can be reduced and can include
relatively hard rigid regions R1 and R2 and relatively soft
flexible region F1, as described below. More specifically, in the
circuit substrate described in Japanese Unexamined Patent
Application Publication No. 2006-339186, a redundant wiring pattern
is disposed in the rigid portion. The redundant wiring pattern
faces other wiring patterns and generates unnecessary stray
capacitance. As a result, the circuit characteristics in the wiring
substrate described in Japanese Unexamined Patent Application
Publication No. 2006-339186 deviate from a desired value.
[0060] In contrast, in the circuit substrate 10, the reinforcing
insulative films 20b to 20d and 24b to 24d are disposed in the
rigid regions R1 and R2. Specifically, the reinforcing insulative
film 20b is disposed on the substrate-section sheet 27b (in rigid
region R1) so as to cover the portion where the wiring conductors
30b and the via-hole conductors b2 and b21 to b23 are not disposed.
The reinforcing insulative film 24b is disposed on the
substrate-section sheet 29b (in the rigid region R2) so as to cover
the portion where the wiring conductors 36b and the via-hole
conductors b12 and b31 to b33 are not disposed. The reinforcing
insulative film 20c is disposed on the substrate-section sheet 27b
(in the rigid region R1) so as to cover the portion where the
wiring conductors 30c and the via-hole conductors b3 and b24 to b26
are not disposed. The reinforcing insulative film 24c is disposed
on the substrate-section sheet 29c (in the rigid region R2) so as
to cover the portion where the wiring conductors 36c and the
via-hole conductors b34 to b36 are not disposed. The reinforcing
insulative film 20d is disposed on the substrate-section sheet 27d
(in the rigid region R1) so as to cover the portion where the
ground conductor 37 is not disposed. The reinforcing insulative
film 24d is disposed on the substrate-section sheet 29d (in the
rigid region R2) so as to cover the portion where the ground
conductor 40 is not disposed.
[0061] As described above, for the circuit substrate 10, the
reinforcing insulative films 20b to 20d and 24b to 24d are added in
the rigid regions R1 and R2. Therefore, the rigid regions R1 and R2
are harder than the flexible region F1 by the hardness
corresponding to the reinforcing insulative films 20b to 20d and
24b to 24d. Thus, the existence of the reinforcing insulative films
20b to 20d and 24b to 24d makes the rigid regions R1 and R2 hard
and eliminates the necessity to have an unnecessary conductive
layer. Because each of the reinforcing insulative films 20b to 20d
and 24b to 24d is not a conductive layer but an insulator layer, no
stray capacitance occurs between the reinforcing insulative film
and other wiring patterns. Accordingly, the circuit substrate 10
can have circuit characteristics in which the occurrence of
deviations can be reduced, and in particular, when it is used in
high-frequency ranges, a high-frequency characteristic, such as
impedance characteristic, is not prone to change. In addition, the
circuit substrate 10 can include the relatively hard rigid regions
R1 and R2 and the relatively soft flexible region F1.
[0062] In the circuit substrate 10, because the material of each of
the reinforcing insulative films 20b to 20d and 24b to 24d is
preferably harder than that of each of the flexible sheets 26 (that
is, has a larger Young's modulus), the rigid regions R1 and R2 are
less prone to deformation.
[0063] In the circuit substrate 10, the reinforcing insulative
films 20b to 20d and 24b to 24d, which are preferably made of
thermosetting resin, are disposed in the rigid regions R1 and R2.
Therefore the occurrence of plastic deformation caused by large
warping of the rigid regions R1 and R2 in the circuit substrate 10
can be more reduced than that in the case where the rigidity is
increased by the use of a metal material.
[0064] The circuit substrate 10 can also reduce separation of the
flexible sheets 26, as described below. More specifically, the
thickness of the reinforcing insulative film 20b is not larger than
and substantially the same as that of the wiring conductor 30b. The
thickness of the reinforcing insulative film 20c is not larger than
and substantially the same as that of the wiring conductor 30c. The
thickness of the reinforcing insulative film 20d is not larger than
and substantially the same as that of the ground conductor 37. The
thickness of the reinforcing insulative film 24b is not larger than
and substantially the same as that of the wiring conductor 36b. The
thickness of the reinforcing insulative film 24c is not larger than
and substantially the same as that of the wiring conductor 36c. The
thickness of the reinforcing insulative film 24d is not larger than
and substantially the same as that of the ground conductor 40.
Accordingly, the existence of the reinforcing insulative films 20b
to 20d and 24b to 24d can reduce differences in height occurring on
the front sides of the flexible sheets 26 caused by the wiring
conductors 30b, 30c, 36b, and 36c and the ground conductors 37 and
40. Therefore, gaps are prevented from being formed between the
flexible sheets 26 when the flexible sheets 26 are press-bonded. As
a result, the flexible sheets 26 are firmly attached together and
are not prone to being separated. Because the reinforcing
insulative films 20b to 20d and 24b to 24d accommodate differences
in height caused by the thicknesses of the wiring conductors 30b,
30c, 36b, and 36c and the ground conductors 37 and 40, the surface
flatness in the circuit substrate 10, which is a lamination of the
flexible sheets 26, can be improved.
[0065] A circuit substrate 10a according to a first variation of a
preferred embodiment of the present invention is described below
with reference to the drawing. FIG. 5 is an exploded perspective
view of the circuit substrate 10a according to the first
variation.
[0066] In the circuit substrate 10a, the main body 11 includes
semi-rigid regions SR1 and SR2, in addition to the rigid regions R1
and R2 and the flexible region F1. The semi-rigid region SR1 is
disposed between the rigid region R1 and the flexible region F1.
The semi-rigid region SR2 is disposed between the rigid region R2
and the flexible region F1. The rigid regions R1 and R2 are less
deformable than the semi-rigid regions SR1 and SR2. The flexible
region F1 is more easily deformable than the semi-rigid regions SR1
and SR2. The semi-rigid regions SR1 and SR2 are configured such
that both ends of the flexible region F1 in the x-axis direction
are hard. Specifically, to form the semi-rigid regions SR1 and SR2,
reinforcing insulative films 55 (55b, 55d) and 57 (57b, 57d) are
disposed.
[0067] More specifically, the reinforcing insulative films 55b and
57b are disposed so as to cover the portions where the ground lines
32b, 33b, and 34b are not disposed in the semi-rigid regions SR1
and SR2, respectively, on the line-section sheet 31b when seen in
plan view from the z-axis direction. The reinforcing insulative
films 55d and 57d are disposed so as to cover the portions where
the ground lines 32d, 33d, and 34d are not disposed in the
semi-rigid regions SR1 and SR2, respectively, on the line-section
sheet 31d when seen in plan view from the z-axis direction.
[0068] The above-described circuit substrate 10a can reduce the
occurrence of breakage in the main body 11 at the border between
the flexible region F1 and each of the rigid regions R1 and R2.
More specifically, when the semi-rigid regions SR1 and SR2 are not
disposed between the rigid regions R1 and R2 and the flexible
region F1, the hardness of the main body 11 significantly varies at
the border between the flexible region F1 and each of the rigid
regions R1 and R2. If the line section (flexible region F1) is
bent, stress concentrates on the border between the flexible region
F1 and each of the rigid regions R1 and R2. As a result, the main
body 11 may be curved and broken at the border between the flexible
region F1 and each of the rigid regions R1 and R2.
[0069] In contrast, the circuit substrate 10a includes the
semi-rigid regions SR1 and SR2 between the rigid regions R1 and R2
and the flexible region F1. Therefore, the hardness of the main
body 11 varies in stages at the border between the flexible region
F1 and each of the rigid regions R1 and R2. Therefore, if the line
section 16 (flexible region F1) is bent, stress is distributed to
the semi-rigid regions SR1 and SR2. As a result, the occurrence of
breakage in the main body 11 at the border between the flexible
region F1 and each of the rigid regions R1 and R2 can be
reduced.
[0070] A circuit substrate 10b according to a second variation of a
preferred embodiment of the present invention is described below
with reference to the drawing. FIG. 6 is an exploded perspective
view of the circuit substrate 10b according to the second
variation.
[0071] In the circuit substrate 10b, a coil L is incorporated in
the substrate section 12 (rigid region R1). The coil L includes
spiral coil conductors 60b and 60c. Both ends of the coil L are
connected to signal lines 64b and 64c. The signal lines 64b and 64c
extend in the line section 16 along the x-axis direction. The
signal lines 64b and 64c are connected to wiring conductors 62b and
62c electrically coupled to the lands 35. The circuit substrate 10b
functions as a transmit/receive circuit for high-frequency signals
by using the coil L as an antenna.
[0072] In the above-described circuit substrate 10b, if the
substrate section 12, in which the coil L is disposed, is easily
deformed, the inductance value of the coil L changes and the
frequency characteristic of the coil L changes. Accordingly, the
circuit substrate 10b can reduce changes in the frequency
characteristic of the coil L by providing the substrate section 12
with the reinforcing insulative films 20b and 20c and thereby
making the substrate section 12 be the rigid region R1, which is
not easily deformable.
[0073] A circuit substrate 10c according to a third variation of a
preferred embodiment of the present invention is described below
with reference to the drawing. FIG. 7 is a cross-sectional
configuration view of the circuit substrate 10c according to the
third variation.
[0074] In the circuit substrates 10, 10a, and 10b, the flexible
sheets 26 have the same shape when seen in plan view from the
z-axis direction. That is, for the circuit substrates 10, 10a, and
10b, the number of the flexible sheets 26 is the same at any
location.
[0075] In contrast, for the circuit substrate 10c, the number of
the flexible sheets 26 in the flexible region F1 is smaller than
the number of the flexible sheets 26 in the rigid regions R1 and
R2. Thus, the thickness in the flexible region F1 is smaller and
the flexible region F1 is softer.
[0076] In manufacturing the circuit substrate 10c, after the
flexible sheets 26a to 26d are press-bonded, the flexible sheets
26a and 26d in the flexible region F1 may be removed.
Alternatively, the flexible sheets 26a and 26d from which the
portion in the flexible region F1 has been removed may be
press-bonded.
[0077] In the circuit substrates 10 and 10a to 10c, each of the
rigid regions R1 and R2 indicates a region where electronic
components, such as the chip components 50, are implemented, a
region where the coil L is disposed, and similar regions. The
flexible region F1 indicates a region where, even if it is
deformed, circuit characteristics are not easily changed and where
the signal lines 42c, 43c, and 44c and other elements are
disposed.
[0078] As described above, preferred embodiments of the present
invention are useful in a circuit substrate and a method of
manufacturing the same. In particular, it is advantageous in that a
circuit substrate that has circuit characteristics in which the
occurrence of deviations can be reduced and that includes a
relatively hard region and a relatively soft region is
obtainable.
[0079] While preferred embodiments of the present invention have
been described above, it is to be understood that variations and
modifications will be apparent to those skilled in the art without
departing from the scope and spirit of the present invention. The
scope of the present invention, therefore, is to be determined
solely by the following claims.
* * * * *