U.S. patent application number 15/543253 was filed with the patent office on 2018-02-01 for circuit board and production method therefor.
The applicant listed for this patent is NGK SPARK PLUG CO., LTD.. Invention is credited to Masanori ITO, Tatsuya KATOH, Masaki KUTSUNA.
Application Number | 20180035549 15/543253 |
Document ID | / |
Family ID | 56405670 |
Filed Date | 2018-02-01 |
United States Patent
Application |
20180035549 |
Kind Code |
A1 |
KATOH; Tatsuya ; et
al. |
February 1, 2018 |
CIRCUIT BOARD AND PRODUCTION METHOD THEREFOR
Abstract
A method of manufacturing a circuit substrate includes the steps
of preparing a conductor paste in which a powder of at least one of
a metal boride and a metal silicide is added to a powder of silver
(Ag), applying the conductor paste to a surface of a ceramic
substrate which has been fired, applying a glass paste to the
surface of the ceramic substrate after applying the conductor
paste, firing the conductor paste applied to the surface so as to
form a conductor trace, and firing the glass paste applied to the
surface so as to form a coating layer.
Inventors: |
KATOH; Tatsuya; (Nagoya-shi,
JP) ; ITO; Masanori; (Nagoya-shi, JP) ;
KUTSUNA; Masaki; (Ohbu-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NGK SPARK PLUG CO., LTD. |
Nagoya-shi, Aichi |
|
JP |
|
|
Family ID: |
56405670 |
Appl. No.: |
15/543253 |
Filed: |
January 8, 2016 |
PCT Filed: |
January 8, 2016 |
PCT NO: |
PCT/JP2016/000079 |
371 Date: |
July 13, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H05K 3/321 20130101;
C03C 10/0054 20130101; C04B 35/6303 20130101; C03C 2204/00
20130101; H05K 3/4629 20130101; C04B 2237/40 20130101; H05K 3/4664
20130101; C04B 2237/704 20130101; H05K 2201/0769 20130101; H05K
1/092 20130101; H05K 3/28 20130101; B32B 2307/202 20130101; H05K
3/12 20130101; B32B 9/005 20130101; H05K 1/0306 20130101; H05K
3/4061 20130101; H05K 3/40 20130101; H05K 1/0296 20130101; H05K
1/09 20130101; H05K 3/1291 20130101; H05K 2203/1126 20130101; C03C
4/14 20130101; H01L 23/15 20130101; Y10T 29/49163 20150115; H05K
2201/017 20130101; H05K 3/46 20130101; H05K 3/285 20130101; Y10T
428/12458 20150115 |
International
Class: |
H05K 3/40 20060101
H05K003/40; H05K 3/32 20060101 H05K003/32; H05K 1/02 20060101
H05K001/02; H05K 1/03 20060101 H05K001/03 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 13, 2015 |
JP |
2015-003819 |
Claims
1. A method of manufacturing a circuit substrate including a
ceramic substrate having a surface mainly formed of a ceramic, a
conductor trace formed on the surface of the ceramic substrate and
mainly formed of silver (Ag), and a coating layer which contains a
glass component and which is formed on the surface of the ceramic
substrate and covers the conductor trace, comprising: a step of
firing the ceramic substrate; a step of preparing a conductor paste
in which a powder of at least one of a metal boride and a metal
silicide is added to a powder of silver (Ag); a step of applying
the conductor paste to the surface of the fired ceramic substrate;
a step of applying a glass paste to the surface of the ceramic
substrate after applying the conductor paste; a step of firing the
conductor paste applied to the surface so as to form the conductor
trace; and a step of firing the glass paste applied to the surface
so as to form the coating layer.
2. The method of manufacturing a circuit substrate according to
claim 1, wherein the metal boride is at least one of lanthanum
hexaboride (LaB.sub.6), silicon hexaboride (SiB.sub.6), and
titanium diboride (TiB.sub.2).
3. The method of manufacturing a circuit substrate according to
claim 1, wherein the metal silicide is at least one of zirconium
disilicide (ZrSi.sub.2) and tantalum disilicide (TaSi.sub.2).
4. The method of manufacturing a circuit substrate according to
claim 1, wherein the total amount of the metal boride and the metal
silicide with respect to the amount of the inorganic component of
the conductor paste is 3 vol. % to 15 vol. %.
5. The method of manufacturing a circuit substrate according to
claim 1, wherein the step of preparing the conductor paste includes
a step of causing the powder of at least one of the metal boride
and the metal silicide to adhere to surfaces of powder particles of
the silver (Ag).
6. The method of manufacturing a circuit substrate according to
claim 1, wherein the conductor paste and the glass paste are fired
at the same time so as to form the conductor trace and the coating
layer at the same time.
7. The method of manufacturing a circuit substrate according to
claim 1, wherein the glass paste is applied to the surface of the
ceramic substrate after the conductor trace is formed by firing the
conductor paste.
8. A circuit substrate comprising: a ceramic substrate having a
surface mainly formed of a ceramic; a conductor trace which is
formed on the surface of the ceramic substrate and which is mainly
formed of silver (Ag); and a coating layer which contains a glass
component and which is formed on the surface of the ceramic
substrate and covers the conductor trace, wherein in a region
located adjacent to the conductor trace, the concentration of
either silicon atoms (Si) or boron atoms (B) contained in the
coating layer increases toward the conductor trace.
Description
TECHNICAL FIELD
[0001] The present invention relates to a circuit substrate and to
a method of manufacturing the same.
BACKGROUND ART
[0002] Some circuit substrates include a ceramic substrate mainly
formed of alumina, mullite, silicon nitride, aluminum nitride, a
glass ceramic, or the like.
[0003] There has been known a circuit substrate which includes a
ceramic substrate and in which a conductor trace mainly formed of
silver (Ag) and a coating layer are formed on a surface of the
ceramic substrate. The coating layer contains a glass component and
covers the conductor trace (refer to Patent Document 1). The
coating layer is also referred to as an overcoat glass layer. The
conductor trace and the coating layer are formed by applying a
conductor paste and a glass paste to a surface of the ceramic
substrate and firing them.
PRIOR ART DOCUMENTS
Patent Documents
[0004] Patent Document 1: Japanese Patent Application Laid-Open
(kokai) No. H7-135394
SUMMARY OF THE INVENTION
Problem to be Solved by the Invention
[0005] The technique disclosed in Patent Document 1 has the
following problem. When the conductor trace and the coating layer
are formed by firing, the silver component of the conductor trace
diffuses into the coating layer, which may deteriorate electrical
insulation performance of the coating layer and change the color of
the coating layer. It is considered that diffusion of the silver
component into the coating layer is accelerated by oxidation of the
silver component of the conductor trace.
Means for Solving the Problem
[0006] The present invention has been accomplished to solve the
above-described problem. The present invention can be realized as
follows.
[0007] (1) One mode of the present invention is a method of
manufacturing a circuit substrate including a ceramic substrate
having a surface mainly formed of a ceramic, a conductor trace
formed on the surface of the ceramic substrate and mainly formed of
silver (Ag), and a coating layer which contains a glass component
and which is formed on the surface of the ceramic substrate and
covers the conductor trace. The manufacturing method includes a
step of firing the ceramic substrate, a step of preparing a
conductor paste in which a powder of at least one of a metal boride
and a metal silicide is added to a powder of silver (Ag), a step of
applying the conductor paste to the surface of the fired ceramic
substrate, a step of applying a glass paste to the surface of the
ceramic substrate after applying the conductor paste, a step of
firing the conductor paste applied to the surface so as to form the
conductor trace, and a step of firing the glass paste applied to
the surface so as to form the coating layer. According to this
mode, at least one of the metal boride and the metal silicide added
to the conductor paste oxidizes during firing. Therefore, diffusion
of the silver component of the conductor trace into the coating
layer can be prevented. As a result, it is possible to prevent
deterioration of the electrical insulation performance of the
coating layer and change of the color of the coating layer. Thus,
the quality of the circuit substrate can be improved.
[0008] (2) In the manufacturing method of the above-mentioned mode,
the metal boride added to the conductor paste may be at least one
of lanthanum hexaboride (LaB.sub.6), silicon hexaboride
(SiB.sub.6), and titanium diboride (TiB.sub.2). This mode prevents
diffusion of the silver component from the conductor trace into the
coating layer.
[0009] (3) In the manufacturing method of the above-mentioned mode,
the metal silicide added to the conductor paste may be at least one
of zirconium disilicide (ZrSi.sub.2) and tantalum disilicide
(TaSi.sub.2). This mode prevents diffusion of the silver component
from the conductor trace into the coating layer.
[0010] (4) In the manufacturing method of the above-mentioned mode,
the total amount of the metal boride and the metal silicide with
respect to the amount of the inorganic component of the conductor
paste may be 3 vol. % to 15 vol. %. This mode can sufficiently
prevent diffusion of the silver component from the conductor trace
into the coating layer.
[0011] (5) In the manufacturing method of the above-mentioned mode,
the step of preparing the conductor paste may include a step of
causing the powder of at least one of the metal boride and the
metal silicide to adhere to surfaces of powder particles of silver
(Ag). This mode prevents diffusion of the silver component from the
conductor trace into the coating layer to a greater degree.
[0012] (6) In the manufacturing method of the above-mentioned mode,
the conductor trace and the coating layer may be formed at the same
time by firing the conductor paste and the glass paste together.
This mode simplifies the production process compared with the case
where the conductor trace and the coating layer are formed
separately.
[0013] (7) In the manufacturing method of the above-mentioned mode,
the glass paste is applied to the surface of the ceramic substrate
after the conductor trace is formed by firing the conductor paste.
According to this mode, diffusion of the silver component from the
conductor trace into the coating layer is prevented to a greater
degree.
[0014] (8) One mode of the present invention provides a circuit
substrate including a ceramic substrate having a surface mainly
formed of a ceramic, a conductor trace which is formed on the
surface of the ceramic substrate and which is formed mainly of
silver (Ag), and a coating layer which contains a glass component
and which is formed on the surface of the ceramic substrate and
covers the conductor trace. In the circuit substrate, the
concentration of either silicon atoms (Si) or boron atoms (B)
contained in the coating layer increases toward the conductor trace
in a region located adjacent to conductor traces. According to this
mode, it is possible to prevent deterioration of the electrical
insulation performance of the coating layer and change of the color
of the coating layer. Thus, the quality of the circuit substrate
can be improved.
[0015] The present invention is not limited to a circuit substrate
and a method of manufacturing the same and can be realized in
various other forms. For example, the present invention can be
realized in the form of a device including a circuit substrate, a
manufacturing apparatus for manufacturing a circuit substrate,
etc.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 Explanatory view schematically showing a cross
section of a circuit substrate.
[0017] FIG. 2 Flowchart showing a method of manufacturing the
circuit substrate.
[0018] FIG. 3 Table showing the results of an evaluation test.
[0019] FIG. 4 Flowchart showing a method of manufacturing the
circuit substrate according to a second embodiment.
MODES FOR CARRYING OUT THE INVENTION
A. Embodiment
[0020] FIG. 1 is an explanatory view schematically showing a cross
section of a circuit substrate 100. At least a portion of a circuit
for realizing a predefined function is formed on the circuit
substrate 100. In the present embodiment, a circuit for
transmitting signals to electronic components is formed on the
circuit substrate 100. The circuit substrate 100 includes a ceramic
substrate 110, conductor traces 170, and a coating layer 180.
[0021] The ceramic substrate 110 of the circuit substrate 100 is a
plate-shaped ceramic member. In the present embodiment, the ceramic
substrate 110 is mainly formed of a glass ceramic. In this
description, "mainly formed of (a component)" means that the
component accounts for at least 50 mass % of the entirety. In
another embodiment, the main component of the ceramic substrate 110
may be any of other types of ceramic materials such as alumina,
mullite, silicon nitride, and aluminum nitride. In the present
embodiment, the ceramic substrate 110 is a low temperature fired
ceramic substrate. The ceramic substrate 110 has a structure in
which a plurality of insulating ceramic layers (unillustrated) are
laminated. In the present embodiment, the ceramic substrate 110 has
an unillustrated conductor layer, unillustrated vias, and
unillustrated through holes as conductors which form the
circuit.
[0022] The ceramic substrate 110 has surfaces 111 and 112. The
surface 112 is a backside surface opposite the surface 111.
Conductor traces 170 and a coating layer 180 are formed on the
surface 111. In another embodiment, like the surface 111, a
conductor trace 170 and a coating layer 180 may be formed on the
surface 112.
[0023] The surfaces 111 and 112 are mainly formed of a ceramic. In
the present embodiment, the surfaces 111 and 112 are surfaces of
ceramic layers formed by firing powders of borosilicate glass and
alumina (Al.sub.2O.sub.3) . Borosilicate glass is mainly formed of
silicon dioxide (SiO.sub.2), alumina (Al.sub.2O.sub.3), and boron
oxide (B.sub.2O.sub.3).
[0024] The conductor trace 170 of the circuit substrate 100 is an
electrically conductive ceramic formed on the surface 111 of the
ceramic substrate 110. The conductor trace 170 is mainly formed of
silver (Ag). In the present embodiment, the conductor trace 170
contains powders of silver (Ag) and borosilicate glass, and has
electrical conductivity. In the present embodiment, each conductor
trace 170 is covered entirely by the coating layer 180. In another
embodiment, a portion of each conductor trace 170 may be exposed
out of the coating layer 180. In the present embodiment, each
conductor trace 170 has a thickness of about 10 .mu.m.
[0025] The coating layer 180 of the circuit substrate 100 is an
electrically insulating ceramic formed on the surface 111 of the
ceramic substrate 110. The coating layer 180 contains a glass
component. The coating layer 180 is also referred to as an overcoat
glass layer. In the present embodiment, the coating layer 180 is
mainly formed of a glass ceramic. In the present embodiment, the
coating layer 180 is an electrically insulating ceramic formed by
firing powders of borosilicate glass and alumina (Al.sub.2O.sub.3)
. The coating layer 180 covers at least a portion of each conductor
trace 170. In the present embodiment, the coating layer 180 has a
thickness of about 10 to 20 .mu.m.
[0026] The coating layer 180 includes regions 181 located adjacent
to the conductor traces 170. In the regions 181 located adjacent to
conductor traces 170, the concentration of silicon atoms (Si)
and/or boron atoms (B) contained in the coating layer 180 increases
toward the conductor traces 170.
[0027] FIG. 2 is a flowchart showing a method of manufacturing the
circuit substrate 100. First, the ceramic substrate 110 is formed
by firing (step P110).
[0028] As a preparation for forming the ceramic substrate 110, a
green sheet which is the material of the ceramic substrate 110 is
prepared. The green sheet is formed by mixing a binder, a
plasticizer, a solvent, etc., into powders of inorganic components
and forming the resultant mixture into the shape of a thin plate
(sheet). In the present embodiment, powders of borosilicate glass
and alumina which are inorganic component are weighed such that
their volume ratio becomes 60:40 and the total weight becomes 1 kg.
These powders are placed in a container (pot) formed of alumina.
Subsequently, 120 g of acrylic resin serving as a binder, a proper
amount of methyl ethyl ketone (MEK) serving as a solvent, and a
proper amount of dioctyl phthalate (DOP) serving as a plasticizer
are added to the materials (powders) in the pot. The materials in
the pot are mixed for five hours to thereby obtain a ceramic
slurry. Then, a green sheet is made from the ceramic slurry using
the doctor blade method. In the present embodiment, the green sheet
has a thickness of 0.15 mm. In the present embodiment, the green
sheet is formed into a desired shape by means of punching.
[0029] After preparing the green sheet, a conductor paste is
applied to the green sheet. In the present embodiment, the
conductor paste is prepared by mixing a binder, a plasticizer, a
solvent, etc. into powders of inorganic components; i.e., a powdery
mixture of silver (Ag) and borosilicate glass. In the present
embodiment, after ethyl cellulose serving as a binder and terpineol
serving as a solvent are added to the powder of inorganic
components, the resultant material is kneaded with a triple roll
mill, whereby the conductor paste is obtained. Subsequently, the
conductor paste is applied to the green sheet by means of screen
printing and hole-filling printing.
[0030] After applying the conductor paste to the green sheet, a
plurality of the green sheets are laminated to form a laminate. In
the present embodiment, by cutting operation, the laminate is
formed into a shape suitable for firing. In the present embodiment,
the laminate is exposed to an atmosphere of 250.degree. C. for 10
hours for debindering.
[0031] After preparing the laminate, the laminate is fired to
thereby form the ceramic substrate 110. In the present embodiment,
the laminate is fired by being exposed to an atmosphere of
900.degree. C. for 60 minutes. After these steps, the ceramic
substrate 110 is obtained.
[0032] After forming the ceramic substrate 110 (step P110), a
conductor paste which is the pre-firing form of the conductor
traces 170 is prepared (step P120). The conductor paste which is
the pre-firing form of the conductor traces 170 is prepared by
adding a powder of at least one of a metal boride and a metal
silicide to a powder of silver (Ag).
[0033] From the viewpoint of preventing diffusion of silver into
the coating layer 180, the metal boride to be added to the
conductor paste is preferably at least one of lanthanum hexaboride
(LaB.sub.6), silicon hexaboride (SiB.sub.6), and titanium diboride
(TiB.sub.2). From the viewpoint of preventing diffusion of silver
into the coating layer 180, the metal silicide to be added to the
conductor paste is preferably at least one of zirconium disilicide
(ZrSi.sub.2) and tantalum disilicide (TaSi.sub.2).
[0034] From the viewpoint of sufficiently preventing diffusion of
silver into the coating layer 180, the total amount of the metal
boride and the metal silicide with respect to the amount of the
inorganic component of the conductor paste is preferably 3 vol. %
to 15 vol. %.
[0035] In the present embodiment, for preparing the conductor paste
which is the pre-firing form of the conductor traces 170, a mixture
of silver (Ag) powder which is an electrically conductive material
and borosilicate glass powder which is common with the ceramic
substrate 110 is prepared as an inorganic component material of the
conductor paste. Subsequently, a powder of at least one of the
metal boride and the metal silicide, ethyl cellulose serving as a
binder, and terpineol serving as a solvent are added to the mixture
of inorganic components. The resultant material is kneaded with a
triple roll mill, whereby the conductor paste is obtained.
[0036] After preparation of the conductor paste (step P120), the
conductor paste is applied to the surface 111 of the ceramic
substrate 110 which has been fired (step P130). In the present
embodiment, the conductor paste is applied to the ceramic substrate
110 by means of screen printing.
[0037] After the conductor paste is applied to the ceramic
substrate (step P130), a glass paste which is the pre-firing form
of the coating layer 180 is applied to the surface 111 of the
ceramic substrate 110 carrying the conductor paste applied thereto
(step P150). In the present embodiment, a mixture of borosilicate
glass powder and alumina powder is prepared as an inorganic
component material of the glass paste. Subsequently, ethyl
cellulose serving as a binder and terpineol serving as a solvent
are added to the mixture of powders of inorganic components. The
resultant mixture is kneaded with a triple roll mill, whereby the
glass paste is obtained. In the present embodiment, the glass paste
is applied to the surface 111 of the ceramic substrate 110 by means
of screen printing.
[0038] After applying the glass paste to the ceramic substrate 110
(step P150), the conductor paste and the glass paste applied to the
surface 111 of the ceramic substrate 110 are fired to thereby form
the conductor traces 170 and the coating layer 180 (step P160). In
the present embodiment, the ceramic substrate 110 carrying the
conductor paste and the glass paste applied thereto is exposed to
an atmosphere of 850'C for 60 minutes to fire the conductor paste
and the glass paste. Thus, the conductor traces 170 and the coating
layer 180 are formed on the surface 111 of the ceramic substrate
110. After these steps, the circuit substrate 100 is completed.
[0039] When the conductor traces 170 and the coating layer 180 are
formed by firing, oxygen near the conductor paste is consumed by
oxidation of the additive component(s) (at least one of the metal
boride and the metal silicide) contained in the conductor paste. As
a result, oxidation of the silver component contained in the
conductor paste is prevented. Thus, diffusion of the silver
component into the coating layer 180 is prevented.
[0040] At least a portion of the additive component(s) oxidized
during firing diffuses into the regions 181, which are located
adjacent to the conductor traces 170, of the coating layer 180.
Therefore, in the regions 181 located adjacent to the coating layer
170, the concentration of silicon atoms (Si) and/or boron atoms (B)
contained in the coating layer 180 increases toward the conductor
traces 170.
[0041] FIG. 3 is a table showing the results of an evaluation test.
In the evaluation test whose results are shown in FIG. 3, samples
S01 to S10 of the circuit substrate 100 were made through use of
different conductor pastes and different glass pastes. In the table
of FIG. 3, the amount of the additive(s) in the conductor paste
which is the pre-firing form of the conductor traces 170 is shown
as the amount (volume percent) of the additive(s) with respect to
the amount of the inorganic component of the conductor paste.
[0042] The method of preparing the samples S01 to S07 is the same
as that described with reference to FIG. 2. The method of preparing
the sample S08 is the same as that described with reference to FIG.
2 except that the borosilicate glass powder contained in the
material of each member of the circuit substrate 100 is substituted
with a powder of Na.sub.2--ZnO--B.sub.2O.sub.3 glass and that the
firing temperature for the conductor paste and the glass paste is
600.degree. C. The method of preparing the sample S09 is the same
as that described with reference to FIG. 2 except that the metal
boride and the metal silicide are not added to the conductor paste.
The method of preparing the sample S10 is the same as that for the
sample S08 except that the metal boride and the metal silicide are
not added to the conductor paste.
[0043] A cross section of each sample was observed using a scanning
electron microscope (SEM) and an electron probe micro analyzer
(EPMA) to measure the distance of diffusion of silver into the
coating layer 180. The concentration of silver (Ag) at the
interface between each conductor trace 170 and the coating layer
180 was used as a reference concentration, and the distance between
the interface and a position in the coating layer 180 at which the
concentration of silver (Ag) becomes half the reference
concentration was measured at 10 points. The average of the
measured distances was obtained as a silver diffusion distance.
[0044] Each sample was evaluated on the basis of the following
criteria.
[0045] AA (excellent): The silver diffusion distance is less than 5
.mu.m. [0046] XX (poor): The silver diffusion distance is equal to
or greater than 5 .mu.m.
[0047] The evaluation results of the samples S01 to S03 and S09
show that diffusion of silver into the coating layer 180 can be
prevented by adding one of lanthanum hexaboride (LaB.sub.6),
silicon hexaboride (SiB.sub.6), and titanium diboride (TiB.sub.2),
which are metal borides, to the conductor paste which is the
material of the conductor traces 170.
[0048] The evaluation results of the samples S04, S05, and S09 show
that diffusion of silver into the coating layer 180 can be
prevented by adding one of zirconium disilicide (ZrSi.sub.2) and
tantalum disilicide (TaSi.sub.2), which are metal silicides, to the
conductor paste which is the material of the conductor traces
170.
[0049] The evaluation results of the samples S01 to S07 show that
diffusion of silver into the coating layer 180 can be sufficiently
prevented when the total amount of the metal boride and the metal
silicide with respect to the amount of the inorganic component of
the conductor paste which is the material of the conductor traces
170 is 3 vol. % to 15 vol. %.
[0050] The evaluation results of the samples S01, S08, S09, and S10
show that, even if the material of the glass paste is a powder of
Na.sub.2--ZnO--B.sub.2O.sub.3 glass, diffusion of silver into the
coating layer 180 can be prevented as in the case where the
material of the glass paste is borosilicate glass.
[0051] According to the embodiment described above, at least one of
the metal boride and the metal silicide added to the conductor
paste oxidizes during firing. Therefore, diffusion of the silver
component of the conductor traces 170 into the coating layer 180
can be prevented. As a result, it is possible to prevent
deterioration of the electrical insulation performance of the
coating layer 180 and change of the color of the coating layer 180.
Thus, the quality of the circuit substrate 100 can be improved.
[0052] The metal boride added to the conductor paste may be at
least one of lanthanum hexaboride (LaB.sub.6), silicon hexaboride
(SiB.sub.6), and titanium diboride (TiB.sub.2). This prevents
diffusion of the silver component from the conductor traces into
the coating layer.
[0053] The metal silicide added to the conductor paste may be at
least one of zirconium disilicide (ZrSi.sub.2) and tantalum
disilicide (TaSi.sub.2). This prevents diffusion of the silver
component from the conductor traces into the coating layer.
[0054] When the total amount of the metal boride and the metal
silicide with respect to the amount of the inorganic component of
the conductor paste is 3 vol. % to 15 vol. %, diffusion of the
silver component from the conductor traces 170 into the coating
layer 180 can be sufficiently prevented.
[0055] Since the conductor traces 170 and the coating layer 180 are
formed at the same time by firing the conductor paste and the glass
paste together (step P160), the production process can be
simplified compared with the case where the conductor traces 170
and the coating layer 180 are formed separately.
B. Second Embodiment
[0056] FIG. 4 is a flowchart showing a method of manufacturing the
circuit substrate 100 according to a second embodiment. The
manufacturing method of the second embodiment is the same as that
of the first embodiment except that the steps after applying the
conductor paste (step P130) are different.
[0057] In the second embodiment, after the conductor paste is
applied (step P130), the conductor paste is fired to form the
conductor traces 170 (step P240). In the present embodiment, the
conductor paste having been applied to the ceramic substrate 110 is
fired by being exposed to an atmosphere of 850.degree. C. for 60
minutes. Thus, the conductor traces 170 are formed on the surface
111 of the ceramic substrate 110.
[0058] After the conductor traces 170 are formed (step P240), the
glass paste which is the material of the coating layer 180 is
applied to the surface 111 of the ceramic substrate 110 (step
P250). The methods of preparing and applying the glass paste in the
second embodiment are the same as those of the first
embodiment.
[0059] After the glass paste is applied (step P250), the glass
paste applied to the surface 111 of the ceramic substrate 110 is
fired to form the coating layer 180 (step P260). In the present
embodiment, the glass paste applied to the ceramic substrate 110 is
fired by being exposed to an atmosphere of 600.degree. C. for 60
minutes. Thus, the coating layer 180 is formed on the surface 111
of the ceramic substrate 110. After these steps, the circuit
substrate 100 is completed.
[0060] According to the second embodiment, as in the first
embodiment, diffusion of the silver component of the conductor
traces 170 into the coating layer 180 can be prevented. As a
result, it is possible to prevent deterioration of the electrical
insulation performance of the coating layer 180 and change of the
color of the coating layer 180. Thus, the quality of the circuit
substrate 100 can be improved.
[0061] After the conductor traces are formed by firing the
conductor paste (step P240), the glass paste is applied to the
surface 111 of the ceramic substrate 110. As a result, diffusion of
the silver component from the conductor traces 170 into the coating
layer 180 is prevented to a greater degree.
C. OTHER EMBODIMENTS
[0062] The present invention is not limited to the above-described
embodiment, examples, and modifications, but may be embodied in
various other forms without departing from the spirit of the
invention. For example, in order to solve, partially or entirely,
the above-mentioned problem or yield, partially or entirely, the
above-mentioned effects, technical features of the embodiments,
examples, and modifications corresponding to technical features of
the modes described in the section "SUMMARY OF THE INVENTION" can
be replaced or combined as appropriate. Also, the technical
feature(s) may be eliminated as appropriate unless the present
specification mentions that the technical feature(s) is
mandatory.
[0063] In another embodiment, when the conductor paste which is the
material of the conductor traces 170 is prepared (step P120),
before adding a binder and a solvent to a powder of silver (Ag), a
powder of at least one of the metal boride and the metal silicide
may be caused to adhere to the surfaces of powder particles of
silver (Ag) by adding a powder of at least one of the metal boride
and the metal silicide to the silver (Ag) powder. This prevents
diffusion of the silver component from the conductor traces 170
into the coating layer 180 to a greater degree.
[0064] In still another embodiment, after the conductor paste is
applied (step P130), a paste which is the material of resistors may
be applied to the ceramic substrate 110 before the glass paste is
applied (step P150). The paste which is the material of the
resistors may be prepared by kneading the mixture of ruthenium
oxide powder, borosilicate glass powder, a binder, and a
solvent.
DESCRIPTION OF REFERENCE NUMERALS
[0065] 100 . . . circuit substrate
[0066] 110 . . . ceramic substrate
[0067] 111 . . . surface
[0068] 112 . . . surface
[0069] 170 . . . conductor trace
[0070] 180 . . . coating layer
[0071] 181 . . . region
* * * * *