U.S. patent application number 09/798897 was filed with the patent office on 2001-09-06 for high-frequency circuit board and method of producing the same.
Invention is credited to Kanechika, Masayuki, Kuriyama, Yoshio, Urabe, Hideki.
Application Number | 20010018985 09/798897 |
Document ID | / |
Family ID | 18585176 |
Filed Date | 2001-09-06 |
United States Patent
Application |
20010018985 |
Kind Code |
A1 |
Kanechika, Masayuki ; et
al. |
September 6, 2001 |
High-frequency circuit board and method of producing the same
Abstract
A high-frequency circuit board free from variations in
transmission impedance and having the desired characteristics is
produced. A surface of a resin substrate is activated to form a
roughened surface, and a thin-wall pattern of an electrically
conductive metal is formed directly on the roughened surface of the
resin substrate.
Inventors: |
Kanechika, Masayuki; (Tokyo,
JP) ; Urabe, Hideki; (Tokyo, JP) ; Kuriyama,
Yoshio; (Tokyo, JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
18585176 |
Appl. No.: |
09/798897 |
Filed: |
March 6, 2001 |
Current U.S.
Class: |
174/256 |
Current CPC
Class: |
H05K 2203/1152 20130101;
H05K 1/0242 20130101; H05K 3/381 20130101; H05K 2203/092 20130101;
H05K 3/143 20130101; H05K 3/429 20130101; Y10T 29/49155 20150115;
H05K 3/146 20130101; H05K 3/06 20130101; Y10T 29/4913 20150115;
H05K 2201/015 20130101 |
Class at
Publication: |
174/256 |
International
Class: |
H05K 001/03 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 6, 2000 |
JP |
2000-65692 |
Claims
What is claimed is:
1. A high-frequency circuit board comprising: a resin substrate
having a surface activated to form a roughened surface; and a
thin-wall pattern of an electrically conductive metal formed
directly on the roughened surface of said resin substrate.
2. A high-frequency circuit board according to claim 1, wherein
said resin substrate is made of a fluorocarbon resin material.
3. A method of producing a high-frequency circuit board, comprising
the steps of: activating a surface of a resin substrate to form a
roughened surface; and forming a thin-wall pattern of an
electrically conductive metal directly on the roughened surface of
said resin substrate.
4. A method of producing a high-frequency circuit board, comprising
the steps of: preparing a resin substrate having copper foil
provided on a surface thereof; removing the copper foil from said
resin substrate to expose said surface; and forming a thin-wall
pattern of an electrically conductive metal directly on the exposed
surface of said resin substrate.
5. A method of producing a high-frequency circuit board according
to claim 3 or 4, wherein said step of forming a thin-wall pattern
includes the steps of: evaporating an electrically conductive metal
onto a whole surface of said resin substrate; and etching said
electrically conductive metal to form said pattern.
6. A method of producing a high-frequency circuit board according
to claim 3 or 4, wherein said step of forming a thin-wall pattern
includes the steps of: covering the surface of said resin substrate
with a mask formed with a pattern to be transferred; and
selectively evaporating an electrically conductive metal onto the
surface of said resin substrate through said mask.
7. A method of producing a high-frequency circuit board according
to any one of claims 3 to 6, wherein said resin substrate is a
fluorocarbon resin substrate.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a high-frequency circuit
board and a method of producing the same.
[0003] 2. Discussion of Related Art
[0004] FIGS. 5 and 6 are flowcharts showing a conventional process
for producing a circuit board, e.g. a printed-wiring board. As a
blank board, a copper-clad laminate having copper foil bonded to
both sides of an insulating substrate of glass-reinforced epoxy
resin, fluorocarbon resin or the like is used. After the surf aces
(both sides) of the copper-clad laminate have been subjected to
exposure and development, etching is carried out to remove unwanted
portions of the copper foil, thereby forming copper foil patterns.
After a resist has been printed on the surfaces of the copper-clad
laminate, the resist on the copper foil patterns is removed, and an
electrically conductive metal, e.g. gold, is deposited on the
exposed copper foil patterns by plating or vacuum evaporation,
thereby forming the desired patterns.
[0005] FIG. 3 shows a conventional circuit board 20 produced by the
above-described process. Copper foil patterns 22 are formed on both
sides of an insulating substrate 21, and coating layers 23 of an
electrically conductive metal are deposited on the copper foil
patterns 22. In this case, the thickness of each copper foil
pattern 22 is of the order of 18 .mu.m, and each coating layer 23
of electrically conductive metal is formed as a thin-wall layer
with a thickness of about 1 .mu.m or less than 1 .mu.m.
[0006] FIG. 4 is an enlarged view of part B in FIG. 3. Because the
copper-clad laminate is subjected to etching, the remaining copper
foil pattern 22 has sloped sidewalls. That is, the width of the
copper foil pattern 22 is the largest at the bottom, i.e. at the
insulating substrate side end thereof, and the width decreases
gradually with distance from the insulating substrate 21. On this
copper foil pattern 22, the coating layer 23 with the
above-described thickness is deposited.
[0007] Incidentally, in high-frequency regions, particularly in
millimeter wave or higher frequency regions, the pattern accuracy
of a microstrip line affects the impedance characteristics of the
transmission line to a considerable extent. Accordingly, efforts
are being made to increase the dimensional accuracy of a mask used
in the exposure process in order to improve the pattern accuracy of
the microstrip line.
[0008] However, in the conventional circuit board, copper foil with
a thickness of about 18 .mu.m is provided on the insulating
substrate 21. Because the copper foil is thick, there is a
difference in pattern width between the top and the bottom of the
microstrip line, as shown in FIG. 4. Consequently, the transmission
impedance of the microstrip line varies. Accordingly, it is
difficult to obtain the desired characteristics.
SUMMARY OF THE INVENTION
[0009] The present invention was made in view of the
above-described problems associated with the prior art.
Accordingly, an object of the present invention is to provide a
high-frequency circuit board free from variations in transmission
impedance of the microstrip line and hence capable of providing the
desired characteristics.
[0010] Another object of the present invention is to provide a
method of producing the above-described high-frequency circuit
board.
[0011] To attain the above-described objects, the present invention
provides a high-frequency circuit board including a resin substrate
having a surface activated to for a roughened surface. A thin-wall
pattern of an electrically conductive metal is formed directly on
the roughened surface of the resin substrate.
[0012] According to the present invention, a pattern of an
electrically conductive metal is formed directly on a surface of a
resin substrate. Consequently, no thick copper foil intervenes
between the electrically conductive metal pattern and the resin
substrate. Therefore, there is no variation in transmission
impedance due to copper foil. In addition, the electrically
conductive metal pattern is a thin-wall layer in which there is
substantially no difference in width between the top and the bottom
thereof. Therefore, there is substantially no variation in
transmission impedance, and the desired characteristics can be
obtained.
[0013] In the above-described high-frequency circuit board, the
resin substrate may be made of a fluorocarbon resin material.
[0014] Accordingly, it is possible to obtain the desired
characteristics even when a fluorocarbon resin material is used as
a resin substrate.
[0015] In addition, the present invention provides a method of
producing a high-frequency circuit board. According to this method,
a surface of a resin substrate is activated to form a roughened
surface, and a thin-wall pattern of an electrically conductive
metal is formed directly on the roughened surface of the resin
substrate.
[0016] Thus, according to the present invention, the surface of the
resin substrate is roughened. Therefore, a pattern of an
electrically conductive metal can be surely deposited on the
surface of the resin substrate. The pattern on the high-frequency
circuit board according to the present invention is unrelated to
copper foil and formed in the shape of a thin-wall layer having no
thick copper foil. Therefore, there is no variation in transmission
impedance due to copper foil, and the desired characteristics can
be obtained.
[0017] In addition, the present invention provides a method of
producing a high-frequency circuit board. According to this method,
a resin substrate having copper foil provided on a surface thereof
is prepared. The copper roil is removed from the resin substrate to
expose the surface thereof, and a thin-wall pattern of an
electrically conductive metal is formed directly on the exposed
surface of the resin substrate.
[0018] The surface of the resin substrate exposed by removing the
copper foil is in the form of a roughened surface and hence allows
a pattern to be formed thereon directly. Therefore, the activation
step can be omitted, advantageously. In addition, a pattern of an
electrically conductive metal can be surely deposited on the
surface of the resin substrate because the copper foil has been
removed therefrom. The pattern on the high-frequency circuit board
according to the present invention is unrelated to the copper foil
and formed in the shape of a thin-wall layer having no thick copper
foil. Therefore, there is no variation in transmission impedance
due to copper foil, and the desired characteristics can be
obtained.
[0019] In the above-described high-frequency circuit board
producing methods, the thin-wall pattern may be formed by
evaporating an electrically conductive metal onto the whole surface
of the resin substrate and then etching the electrically conductive
metal to form the desired pattern.
[0020] By doing so, an extremely thin microstrip line having a
thickness of the order of 1 .mu.m can be formed on the surface of
the resin substrate. Thus, the desired characteristics can be
obtained.
[0021] In the above-described high-frequency circuit board
producing methods, the thin-wall pattern may be formed by covering
the surface of the resin substrate with a mask formed with a
pattern to be transferred and then selectively evaporating an
electrically conductive metal onto the surface of the resin
substrate through the mask.
[0022] With the above-described method, an electrically conductive
metal can be selectively evaporated in the desired pattern on the
surface of the resin substrate by using, for example, a metal mask
with a pattern to be transferred that is provided as a hollow
pattern. Accordingly, the step of etching the electrically
conductive metal can be omitted.
[0023] In the above-described high-frequency circuit board
producing methods, the resin substrate may be a fluorocarbon resin
substrate.
[0024] The above and other objects, features and advantages of the
present invention will become more apparent from the following
description of the preferred embodiments thereof, taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is a sectional view of a high-frequency circuit board
according to the present invention.
[0026] FIG. 2 is an enlarged view of part A in FIG. 1.
[0027] FIG. 3 is a sectional view of a conventional high-frequency
circuit board.
[0028] FIG. 4 is an enlarged view of part B in FIG. 3.
[0029] FIG. 5 is a flowchart showing the first half of the process
for producing the conventional high-frequency circuit board.
[0030] FIG. 6 is a flowchart showing the second half of the process
for producing the conventional high-frequency circuit board.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0031] The present invention will be described below more
specifically by way of embodiments and with reference to the
accompanying drawings. It should be noted that in the embodiments
the same elements as those in the prior art are denoted by the same
reference numerals.
[0032] FIG. 1 is a sectional view of a high-frequency circuit board
10 according to an embodiment of the present invention. The
high-frequency circuit hoard 10 includes a resin substrate 21
having a surface 21a activated to form a roughened surface. A
thin-wall pattern 23 of an electrically conductive metal is formed
directly on the surface 21a of the resin substrate 21.
[0033] The resin substrate 21 is a substrate using a fluorocarbon
resin material, e.g. PTFE (polytetrafluoroethylene) or PEA
(perfluoroalkoxy). The use of such a fluorocarbon resin substrate
makes it possible to obtain even more stable characteristics than
with a glass or epoxy resin substrate.
[0034] The surface 21a of the resin substrate 21 has been activated
to form a roughened surface, as stated above. The roughened surface
is formed by ion irradiation using a conventional ion beam
irradiation device. Alternatively, microscopic asperities may be
formed on the surface 21a by sanding or other similar method.
[0035] The above-described pattern 23 is formed as a thin layer
with a thickness of about 1 .mu.m or less than 1 .mu.m by using an
electrically conductive metal, e.g. Au. The electrically conductive
metal may be Cu or other metal depending on the use
application.
[0036] A high-frequency current flowing along a microstrip line
formed by the pattern 23 is concentrated on the conductor surface
by the skin effect phenomenon. Therefore, even if the thickness of
the pattern 23 is 1 .mu.m, the conductor loss is so small that it
will not give rise to a problem.
[0037] FIG. 2 is an enlarged view of part A in FIG. 1. When the
pattern 23 is formed by etching after vacuum evaporation, the
bottom surface 23b of the pattern 23 is slightly larger in width
than the top surface 23a thereof. However, because the pattern 23
itself is thin in thickness, the top surface 23a and the bottom
surface 23b are approximately equal in size to each other.
Therefore, the pattern accuracy can be markedly improved in
comparison to the conventional high-frequency circuit board 20 clad
with copper foil having a thickness of 18 .mu.m to 35 .mu.m.
[0038] The improvement in the pattern accuracy allows the
high-frequency circuit board to become free from variations in
transmission impedance of the microstrip line and enables stable
characteristics to be obtained.
[0039] Next, a method of producing the high-frequency circuit board
10 according to the present invention will be described. The
high-frequency circuit board producing method according to the
present invention includes the step of activating a surface of a
resin substrate 21 to form a roughened surface and the step of
forming a thin-wall pattern of an electrically conductive metal
directly on the roughened surface of the resin substrate 21.
[0040] The activation step is carried out to activate the surface
21a of the resin substrate 21 to form a roughened surface. A
conventional ion beam irradiation device is usable for the
activation step. When the surface of the resin material is
irradiated with an ion beam, the resin surface is etched by the
energy of ions at the time of collision with the surface.
Microscopic acicular asperities can be formed on the resin surface
by appropriately controlling ion beam irradiation conditions such
as ionic species, acceleration voltage and current density.
Alternatively, microscopic asperities may be formed on the resin
surface by sanding.
[0041] According to the present invention, the surface of the resin
substrate is roughened. Therefore, a pattern of an electrically
conductive metal can be surely deposited on the surface of the
resin substrate. Accordingly, the pattern on the high-frequency
circuit board is unrelated to copper foil and formed in the shape
of a thin-wall layer having no thick copper foil. Therefore, there
is no variation in transmission impedance due to copper foil, and
the desired characteristics can be obtained.
[0042] The step of forming a thin-wall pattern directly on the
surface of the resin substrate is carried out as follows. A deposit
layer of an electrically conductive metal is obtained by a publicly
known vacuum evaporation process. Thereafter, the electrically
conductive metal is etched to form a microstrip line, thereby
producing a high-frequency circuit board 10.
[0043] Accordingly to another embodiment of the present invention,
an electrically conductive metal is selectively evaporated onto the
surface of the resin substrate covered with a mask formed with a
pattern to be transferred.
[0044] According to this embodiment, an electrically conductive
metal is selectively evaporated in the desired pattern on the
surface of the resin substrate by using, for example, a metal mask
with a pattern to be transferred that is provided as a hollow
pattern, thereby forming a microstrip line. Thus, a high-frequency
circuit board 10 can be produced. Accordingly, the step of etching
the electrically conductive metal can be omitted.
[0045] A high-frequency circuit board producing method according to
still another embodiment of the present invention includes the step
of preparing a resin substrate 21 having copper foil 22 provided on
a surface thereof and the step of removing the copper foil 22 from
the resin substrate 21 to expose the surface thereof. The method
further includes the step of forming a thin-wall pattern of an
electrically conductive metal directly on the exposed surface of
the resin substrate 21.
[0046] The surface of the resin substrate 21 exposed by removing
the copper foil 22 is in the form of a roughened surface and hence
allows a pattern to be formed thereon directly. Therefore, the
activation step can be omitted, advantageously. In addition, a
pattern 23 of an electrically conductive metal can be surely
deposited on the surface 21a of the resin substrate 21 because the
copper foil 22 has been removed therefrom. The pattern 23 on the
high-frequency circuit board according to the present invention is
unrelated to the copper foil 22 and formed in the shape of a
thin-wall layer having no thick copper foil 22. Therefore, there is
no variation in transmission impedance due to the copper foil 22,
and the desired characteristics can be obtained.
[0047] According to the present invention, a pattern of an
electrically conductive metal is formed directly on a surface of a
resin substrate. Consequently, no thick copper foil intervenes
between the electrically conductive metal pattern and the resin
substrate. Therefore, there is no variation in transmission
impedance due to copper foil. In addition, the electrically
conductive metal pattern is a thin-wall layer in which there is
substantially no difference in width between the top and the bottom
thereof. Therefore, there is substantially no variation in
transmission impedance, and the desired characteristics can be
obtained.
[0048] The high-frequency circuit board producing method according
to the present invention enables an electrically conductive metal
pattern to be formed with a reduced thickness. Accordingly, it is
possible to improve the dimensional accuracy of the pattern width
of a microstrip line and hence possible to obtain a high-frequency
circuit board exhibiting superior transmission line impedance
characteristics.
[0049] It should be noted that the present invention is not
necessarily limited to the foregoing embodiments but can be
modified in a variety of ways without departing from the gist of
the present invention.
* * * * *