U.S. patent number 9,271,391 [Application Number 13/899,243] was granted by the patent office on 2016-02-23 for multilayer wiring board.
This patent grant is currently assigned to Waka Manufacturing Co., Ltd.. The grantee listed for this patent is WAKA MANUFACTURING CO., LTD.. Invention is credited to Hiroshi Okayama, Toru Takada.
United States Patent |
9,271,391 |
Okayama , et al. |
February 23, 2016 |
**Please see images for:
( Certificate of Correction ) ** |
Multilayer wiring board
Abstract
A multilayer wiring board includes a first dielectric layer, a
high-frequency signal line formed on a first surface of the first
dielectric layer, a ground layer formed on a second surface of the
first dielectric layer, and a second dielectric layer covering part
of the ground layer. The high-frequency signal line is electrically
connectable to a center conductor of a coaxial structure. The
second dielectric layer is spaced from an edge of the first
dielectric layer to which the coaxial structure is to be connected,
so that a ground exposure portion of the ground layer is exposed on
the edge of the first dielectric layer. The ground layer is
electrically connectable directly to an outer conductor of the
coaxial structure at the ground exposure portion.
Inventors: |
Okayama; Hiroshi (Tokyo,
JP), Takada; Toru (Kanagawa, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
WAKA MANUFACTURING CO., LTD. |
Tokyo |
N/A |
JP |
|
|
Assignee: |
Waka Manufacturing Co., Ltd.
(Tokyo, JP)
|
Family
ID: |
49620704 |
Appl.
No.: |
13/899,243 |
Filed: |
May 21, 2013 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20130313003 A1 |
Nov 28, 2013 |
|
Foreign Application Priority Data
|
|
|
|
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May 28, 2012 [JP] |
|
|
2012-121419 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H05K
3/32 (20130101); H05K 1/0237 (20130101); H05K
1/117 (20130101); H05K 1/025 (20130101); H01R
24/50 (20130101); H05K 2201/10356 (20130101); H05K
1/0219 (20130101); H05K 2201/0919 (20130101); H05K
2201/09618 (20130101); H01R 4/04 (20130101) |
Current International
Class: |
H05K
1/02 (20060101); H05K 3/32 (20060101); H05K
1/11 (20060101); H01R 24/50 (20110101); H01R
4/04 (20060101) |
Field of
Search: |
;361/785,795 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Thompson; Timothy
Assistant Examiner: McGee, III; Paul
Attorney, Agent or Firm: Marger Johnson
Claims
What is claimed is:
1. A multilayer wiring board to which a coaxial structure for
transmitting an electric signal with a center conductor and an
outer conductor is connected, the multilayer wiring board
comprising: a first dielectric layer; a high-frequency signal line
formed on a first surface of the first dielectric layer, the
high-frequency signal line having a connecting portion that is
electrically connectable to the center conductor of the coaxial
structure; a ground layer formed on a second surface of the first
dielectric layer; and a second dielectric layer covering part of
the ground layer, the second dielectric layer having an edge spaced
from an edge of the first dielectric layer that faces with the
coaxial structure when the coaxial structure is connected to the
multilayer wiring board, the edge of the second dielectric layer
being located at an inner side of the multilaver wiring board than
the edge of the first dielectric layer, thereby exposing a ground
exposure portion of the ground layer-en between the edge of the
first dielectric layer and the edge of the second dielectric layer,
the ground layer being electrically connectable directly to the
outer conductor of the coaxial structure at the ground exposure
portion, wherein the high-frequency signal line is exposed to an
outside of the multilayer wiring board near the connecting portion
thereof when the coaxial structure is connected to the multilayer
wiring board.
2. The multilayer wiring board as recited in claim 1, wherein the
ground exposure portion of the ground layer is electrically
connected directly to the outer conductor of the coaxial structure
by at least one of a solder material, silver paste, and a
conductive adhesive material applied to the ground exposure
portion.
3. The multilayer wiring board as recited in claim 1, wherein the
ground exposure portion of the ground layer is electrically
connected directly to the outer conductor of the coaxial structure
by a contact protrusion extending from the outer conductor of the
coaxial structure.
4. The multilayer wiring board as recited in claim 1, wherein the
ground exposure portion is located right below the center conductor
of the coaxial structure when the coaxial structure is connected to
the multilayer wiring board.
5. The multilayer wiring board as recited in claim 1, further
comprising a control signal layer formed on a surface of the second
dielectric layer for forming a control signal circuit.
6. The multilayer wiring board as recited in claim 1, wherein the
coaxial structure comprises a connector to be mounted on the
multilayer wiring board.
7. The multilayer wiring board as recited in claim 1, wherein the
edge of the first dielectric layer is brought into contact with the
coaxial structure when the coaxial structure is connected to the
multilayer wiring board.
8. The multilayer wiring board as recited in claim 1, wherein the
high-frequency signal line is electrically connectable to the
center conductor of the coaxial structure at the shortest distance.
Description
This application claims priority from Japanese patent application
No. 2012-121419, filed on May 28, 2012, of which the specification,
drawings, and claims are incorporated herein by reference in its
entirety.
BACKGROUND
1. Field of the Invention
The present invention relates to a multilayer wiring board used for
a high-frequency signal interface or the like, and more
particularly to a multilayer wiring board to which a coaxial
structure such as a connector is connected.
2. Description of the Related Art
In recent years, demands for reduction in device scale have
increasingly grown in applications for various communication
devices used in wireless or optical communication systems. Size
reduction is also necessarily required for circuit boards for
communication devices and high-frequency device modules. Therefore,
the dimension of high-frequency connectors used as internal or
external interfaces of communication devices is desired to be
reduced. As one of connectors that meet such market demands, a
small-sized connector such as a push-on SMP connector or a push-on
SMPM connector has been put into practice. Furthermore, such a
small-sized connector has heretofore been mounted directly on a
circuit board. See, e.g., JP-A 2004-363593.
When a small-sized connector is mounted directly on a circuit
board, a center conductor of the small-sized connector is brought
into close contact with a high-frequency signal line of the circuit
board. An outer conductor of the small-sized connector is brought
into close contact with a ground electrode of the circuit board,
which is formed on the same plane as the high-frequency signal
line. When a ground layer is formed on a rear face of a circuit
board as in the case of a microstrip line, a ground electrode
formed on a front face of the circuit board is electrically
connected to the ground layer formed on the rear face of the
circuit board via through holes. In this manner, connection of
high-frequency signals is established between the small-sized
connector and the circuit board.
Meanwhile, what is called a multilayer wiring board is used in
order to enhance the functionality of communication devices within
a limited space. A multilayer wiring board is formed of a
multilayered substrate, and a control signal line is also
incorporated in the same substrate while the transmission
characteristics of high-frequency signals are maintained. FIGS. 1A
and 1B show a conventional example of a multilayer wiring board. As
shown in FIGS. 1A and 1B, a multilayer wiring board 200 has a
dielectric layer 500, a high-frequency signal line 400 formed on a
surface of the dielectric layer 500 for transmitting high-frequency
signals, and a ground layer 600. Additionally, the multilayer
wiring board 200 has a control signal layer 900 for forming a
control signal circuit that controls devices mounted on the
multilayer wiring board 200. Thus, in view of size reduction and
space saving of a communication device, it is important to
effectively combine the multilayer wiring board 200 with a
small-sized connector for a high-frequency device module.
In a high-frequency region, the characteristic impedance is likely
to be discontinuous at a connection portion between a small-sized
connector and a multilayer wiring board. Particularly, in a case
where high-speed data signals over 10 Gb/s are transmitted, the
signal band is so wide as to arise a serious problem of quality
degradation of signal waveforms that is caused by discontinuous
characteristic impedance. For example, in the conventional device
illustrated in FIG. 5 of JP-A 2004-363593, the amount of signal
reflection increases at a discontinuous point of the characteristic
impedance, thus deteriorating the flatness of the
transmission-frequency characteristics. As a result, the waveform
quality of high-speed data signals is degraded.
Furthermore, in the case of the multilayer wiring board illustrated
in FIGS. 1A and 1B, when a small-sized connector 100 is mounted
onto the multilayer wiring board 200, a center conductor 300 of the
small-sized connector 100 is connected to the high-frequency signal
line 400 formed on the surface of the dielectric layer 500.
Projecting portions 1000A of an outer conductor 1000 of the
small-sized connector 100, which serves as a ground, are connected
to ground electrodes 1200 formed on the surface of the dielectric
layer 500. In order to exert a function of the high-frequency
signal line 400, the ground electrodes 1200 on the dielectric layer
500, which also has the high-frequency signal line 400 formed
thereon, are electrically connected to the ground layer 600 via a
plurality of through holes 130.
However, each of those through holes 130 has a thickness
corresponding to the thickness of the dielectric layer 500 and thus
has a finite inductance. Therefore, provision of many through holes
cannot sufficiently reduce a ground inductance at a connection
portion between the coaxial structure (connector) and the circuit
board. Accordingly, impedance discontinuity thus caused results in
deterioration of frequency characteristics in transmission of
high-frequency signals. Furthermore, for wide-band and
high-frequency signals, such as high-speed data signals, variations
in location and dimension of the through holes 130 being formed
exert additional influences, make it difficult to obtain good
frequency characteristics.
SUMMARY
The present invention has been made in view of the above drawbacks.
It is, therefore, an object of the present invention to provide a
multilayer wiring board capable of ensuring good frequency
characteristics at a connection portion between a coaxial structure
such as a connector and the multilayer wiring board so as to solve
a problem of an increased ground inductance at the connection
portion.
In order to attain the above object, according to an aspect of the
present invention, there is provided a multilayer wiring board to
which a coaxial structure for transmitting an electric signal with
a center conductor and an outer conductor is connected. The
multilayer wiring board includes a first dielectric layer, a
high-frequency signal line formed on a first surface of the first
dielectric layer, a ground layer formed on a second surface of the
first dielectric layer, and a second dielectric layer covering part
of the ground layer. The high-frequency signal line is electrically
connectable to the center conductor of the coaxial structure. The
second dielectric layer is spaced from an edge of the first
dielectric layer to which the coaxial structure is to be connected,
so that a ground exposure portion of the ground layer is exposed on
the edge of the first dielectric layer. The ground layer is
electrically connectable directly to the outer conductor of the
coaxial structure at the ground exposure portion.
In other words, the multilayer wiring board has a multilayer
structure including a dielectric layer having a high-frequency
line, a ground layer, and a control signal layer for forming a
control signal circuit. A coaxial structure capable of transmitting
an electric signal with a center conductor and an outer conductor
is connected to the multilayer wiring board. A ground exposure
portion of the ground layer is exposed at a connection portion at
which the coaxial structure is connected to the multilayer wiring
board. A connection structure is provided at the connection portion
to connect the ground exposure portion of the ground layer directly
to the outer conductor of the coaxial structure for electrical
conduction between the ground exposure portion of the ground layer
and the outer conductor of the coaxial structure.
The ground exposure portion of the ground layer may electrically be
connected to the outer conductor of the coaxial structure by a
solder material, silver paste, or a conductive adhesive material
applied to the ground exposure portion. Alternatively, the ground
exposure portion of the ground layer may electrically be connected
to the outer conductor of the coaxial structure by a contact
protrusion extending from the outer conductor of the coaxial
structure. Furthermore, it is preferable to locate the ground
exposure portion right below the center conductor of the coaxial
structure when the coaxial structure is connected to the multilayer
wiring board. Moreover, the multilayer wiring board may further
include a control signal layer formed on a surface of the second
dielectric layer for forming a control signal circuit.
The coaxial structure may be a connector to be mounted on the
multilayer wiring board.
The above and other objects, features, and advantages of the
present invention will be apparent from the following description
when taken in conjunction with the accompanying drawings which
illustrate preferred embodiments of the present invention by way of
example.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is a side view showing an example of a conventional
multilayer wiring board with a small-sized connector;
FIG. 1B is a cross-sectional view taken along line A-A of FIG.
1A;
FIG. 2A is a plan view schematically showing a configuration of a
multilayer wiring board with a small-sized connector according to a
first embodiment of the present invention;
FIG. 2B is a cross-sectional view taken along line B-B of FIG.
2A;
FIG. 2C is a cross-sectional view taken along line C-C of FIG.
2B;
FIG. 3A is a plan view schematically showing a configuration of the
multilayer wiring board according to the first embodiment of the
present invention;
FIG. 3B is a cross-sectional view taken along line D-D of FIG.
3A;
FIG. 3C is a plan view showing that a connector is to be mounted
onto the multilayer wiring board of FIG. 3A.
FIG. 4 is a diagram schematically showing a configuration of a
multilayer wiring board with a small-sized connector according to a
second embodiment of the present invention;
FIG. 5A is a graph showing results of measuring frequency
characteristics of transmission and reflection of high-frequency
signals for a multilayer wiring board according to the present
invention, for the purposes of comparison.
FIG. 5B is a graph showing results of measuring frequency
characteristics of transmission and reflection of high-frequency
signals for a conventional multilayer wiring board, for the
purposes of comparison.
FIG. 6A is a diagram schematically showing a configuration of a
multilayer wiring board with a small-sized connector according to a
third embodiment of the present invention; and
FIG. 6B is a cross-sectional view taken along line E-E of FIG.
6A.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A multilayer wiring board according to embodiments of the present
invention will be described below with reference to FIGS. 2A to 6B.
Like or corresponding parts are denoted by like or corresponding
reference numerals throughout drawings, and will not be described
below repetitively.
FIGS. 2A to 2C are diagrams schematically showing a configuration
of a multilayer wiring board 2 according to a first embodiment of
the present invention. A small-sized connector 1, which corresponds
to a coaxial structure according to the present invention, is
mounted on the multilayer wiring board 2. FIG. 2A is a plan view of
the multilayer wiring board 2, FIG. 2B is a cross-sectional view
taken along line B-B of FIG. 2A, and FIG. 2C is a cross-sectional
view taken along line C-C of FIG. 2B. Specifically, the multilayer
wiring board 2 has a multilayered structure including a first
dielectric layer 5 having a high-frequency signal line 4 formed on
an upper surface thereof, a ground layer 6 formed on a lower
surface of the first dielectric layer 5, a second dielectric layer
20 covering part of the ground layer 6, and at least one control
signal layer 9 for forming a control signal circuit, and a third
dielectric layer 22. At least one small-sized connector 1 is
mounted onto the multilayer wiring board 2.
In this case, the line formation of the high-frequency signal line
4 is of a grounded coplanar type, which has ground electrode
portions 12 formed on both sides of the central signal line 4 as
shown in FIG. 3A. Each of the ground electrode portions 12 has a
plurality of through holes 13 formed therein. The small-sized
connector 1 has a center conductor 3 and a cylindrical outer
conductor 10 with two projecting portions 10A (see FIG. 2A). The
through holes 13 are used to electrically connect the projecting
portions 10A of the outer conductor 10 of the small-sized connector
1 to the ground layer 6. From a state shown in FIG. 3C where the
small-sized connector 1 has not been mounted on the multilayer
wiring board 2, the small-sized connector 1 is mounted onto the
multilayer wiring board 2 as shown in FIG. 2A. Upon mounting the
small-sized connector 1 on the multilayer wiring board 2, the
center conductor 3 of the small-sized connector 1 is brought into
electrical contact with the high-frequency signal line 4 of the
multilayer wiring board 2 at the shortest distance (for example, by
joint, bonding, or adhesion). For example, the center conductor 3
of the small-sized connector 1 may be joined to the high-frequency
signal line 4 of the multilayer wiring board 2 by a solder
material, silver paste, or the like, or may be bonded to the
high-frequency signal line 4 of the multilayer wiring board 2 by a
conductive adhesive material.
The high-frequency signal line 4 is formed on the upper surface
(first surface) of the dielectric layer 5, and the ground layer 6
is formed on the lower surface (second surface) of the dielectric
layer 5. The width of the high-frequency signal line 4 and the
thickness of the dielectric layer 5 are determined such that the
characteristic impedance of the high-frequency signals is made
equal to a predetermined value by the high-frequency signal line 4
and the ground layer 6.
According to the present embodiment, the ground layer 6 is exposed
so as to form a ground exposure portion 6A at a connection portion
7 of the multilayer wiring board 2 at which the small-sized
connector 1 is mounted on the multilayer wiring board 2. The
control signal layer 9 in which a control signal circuit is
provided is formed in an area 8 other than the connection portion 7
of the multilayer wiring board 2. More specifically, as shown in
FIG. 2B, the second dielectric layer 20 is spaced from an edge of
the first dielectric layer 5, so that a portion of the ground layer
6 is exposed on the edge of the first dielectric layer 5
(connection portion 7) to thus form a ground exposure portion 6A. A
connection structure 11 is provided in the connection portion 7 for
electrically connecting the ground exposure portion 6A of the
ground layer 6 to the outer conductor 10 of the small-sized
connector 1. For example, the connection structure 11 may be formed
of a solder material, silver paste, or a conductive adhesive
material applied to the ground exposure portion 6A.
With the above configuration of the multilayer wiring board 2, the
outer conductor 10 and the ground layer 6 are connected directly to
each other and are thus brought into satisfactory conduction with
each other. Therefore, a high-frequency signal line for the ground
can be formed by the shortest distance of connection. Thus, the
ground inductance of the small-sized connector 1 and the multilayer
wiring board 2 is prevented from increasing, thereby ensuring the
waveform quality of high-speed data signals.
FIG. 4 is a diagram schematically showing a configuration of a
multilayer wiring board with a small-sized connector according to a
second embodiment of the present invention. FIG. 4 corresponds to
FIG. 2C. As with the first embodiment, a portion of the ground
layer 6 is exposed at the connection portion 7 at which the
small-sized connector 1 is mounted on the multilayer wiring board
2, and the control signal layer 9 in which a control signal circuit
is provided is formed in an area 8 other than the connection
portion 7 of the multilayer wiring board 2 (see FIG. 2B).
In the second embodiment, only a portion of the ground exposure
portion 6A of the ground layer 6 that is located near a portion
opposed to the center conductor 3 of the small-sized connector 1 is
electrically connected to the outer conductor 10 of the small-sized
connector 1 in order to prevent the ground inductance from
increasing at the connection portion 7 when the outer conductor 10
of the small-sized connector 1 and the ground exposure portion 6A
of the ground layer 6 are brought into conduction with each other.
In the second embodiment, a joining member 15 such as a solder
material or silver paste is filled between the ground exposure
portion 6A of the ground layer 6 and the outer conductor 10 of the
small-sized connector 1 such that a portion of the ground exposure
portion 6A of the ground layer 6 that is located near a portion
opposed to the center conductor 3, for example, a portion 14 of the
ground exposure portion 6A located right below the center conductor
3 (see FIG. 3B) is brought into conduction with the outer conductor
10 of the small-sized connector 1. Thus, the ground exposure
portion 6A of the ground layer 6 and the outer conductor 10 of the
small-sized connector 1 are electrically connected to each
other.
The density of electric lines of force between the center conductor
3 of the small-sized connector 1 and the ground surface is the
highest near the portion opposed to the center conductor 3. For
example, the density of electric lines of force is the highest at
the portion 14 located right below the center conductor 3, i.e., a
portion located at the shortest distance from the ground surface.
Under those circumstances, in the present embodiment, the ground
exposure portion 6A of the ground layer 6 is connected to the outer
conductor 10 with the shortest distance by the joining member 15 on
the portion 14 located right below the center conductor 3.
Therefore, disturbance of the electric lines of force between the
high-frequency signal line 4 and the ground layer 6 are minimized
at the connection portion 7 (see FIG. 2B) between the small-sized
connector 1 and the multilayer wiring board 2. As a result, the
ground inductance is prevented from increasing at the connection
portion 7. Thus, satisfactory high-frequency transmission
characteristics can be achieved.
FIGS. 5A and 5B show measurement results of frequency
characteristics of transmission and reflection of high-frequency
signals in an example using a multilayer wiring board with a
small-sized connector according to the present invention and a
comparative example using a conventional multilayer wiring board
with a small-sized connector. In those examples, through lines were
formed with a length of 10 mm. FIG. 5A shows the results for the
multilayer wiring board according to the present invention, and
FIG. 5B shows the results for the conventional multilayer wiring
board. Comparison of those results reveals that the through line
according to the present invention exhibited less reflection and
demonstrated more flatness of the transmission-frequency
characteristic.
According to the present embodiment, the ground exposure portion 6A
of the ground layer 6 is electrically connected to the outer
conductor 10 at the shortest distance by the joining member 15 on
the portion 14 located right below the center conductor 3.
Accordingly, the discontinuity of the characteristic impedance is
mitigated as compared to the conventional technology as shown in
FIGS. 1A and 1B. Therefore, according to the present embodiment,
the discontinuity of the characteristic impedance can be reduced so
as to prevent quality degradation of waveforms of high-speed data
signals.
FIGS. 6A and 6B are diagrams schematically showing a configuration
of a multilayer wiring board with a small-sized connector according
to a third embodiment of the present invention. In the second
embodiment illustrated in FIG. 4, the joining member 15 is filled
between the portion 14 located right below the center conductor 3
and the outer conductor 10 of the small-sized connector 1.
Nevertheless, as shown in FIGS. 6A and 6B, the shape of the
small-sized connector 1 may be changed so as to have a contact
protrusion 17 extending from the outer conductor 10 of the
small-sized connector 1. This contact protrusion 17 may be adhered
to and brought into direct contact with the ground exposure portion
6A of the ground layer 6 right below the center conductor 3.
The line formation of the high-frequency signal line 4 may not be
of a grounded coplanar type and may be of a microstrip type, which
has no ground patterns on the top side of a multilayer wiring
board. The present invention is applicable to such a line
formation, and the same advantageous effects can also be obtained
in such a case.
The above embodiments illustrate examples in which the outer
conductor 10 of the small-sized connector 1 is connected to the
ground layer 6 via the through holes 13. Nevertheless, no through
holes 13 may be formed in the multilayer wiring board 2 as long as
the outer 10 of the small-sized connector 1 is electrically
connected directly to the ground exposure portion 6A of the ground
layer 6.
While a multilayer wiring board with a small-sized connector has
been described in the above embodiments of the present invention,
the present invention is not limited to the aforementioned
embodiments. It should be understood that those skilled in the art
would make any modifications to the above embodiments within the
scope of the present invention. For example, instead of a
small-sized connector, a high-frequency coaxial cable may be used
as a coaxial structure to be mounted on and connected to a
multilayer wiring board. The present invention is also effective in
such a case. Specifically, when an outer conductor of a
high-frequency coaxial cable is connected to a ground layer of a
multilayer wiring board, the outer conductor of the high-frequency
coaxial cable is connected directly to a ground exposure portion of
the ground layer formed in the multilayer wiring board. With such
an arrangement, the ground inductance is prevented from increasing,
so that influence on the waveform quality of high-frequency data
signals can be reduced.
As described above, according to the present invention, the ground
layer of the multilayer wiring board is connected directly to the
outer conductor of the coaxial structure. Therefore, the ground
inductance is prevented from increasing, so that high-frequency
connection having flat transmission-frequency characteristics and
less reflection can be achieved between the coaxial structure and
the multilayer wiring board. Accordingly, quality degradation of
waveforms of high-speed data signals is suppressed. Thus, the
present invention is advantageous to a multilayer wiring board on
which a small-sized connector is to be mounted. For example, the
present invention is advantageous to a multilayer wiring board with
a small-sized connector that has increasingly been desired to be
reduced in size.
Although certain preferred embodiments of the present invention
have been shown and described in detail, it should be understood
that various changes and modifications may be made therein without
departing from the scope of the appended claims.
* * * * *