U.S. patent application number 10/265262 was filed with the patent office on 2003-07-31 for electroconductive paste, method of producing monolithic ceramic electronic part, and monolithic ceramic electronic part.
Invention is credited to Nakamura, Tomoyuki, Sano, Harunobu, Shimizu, Motohiro.
Application Number | 20030142463 10/265262 |
Document ID | / |
Family ID | 26623781 |
Filed Date | 2003-07-31 |
United States Patent
Application |
20030142463 |
Kind Code |
A1 |
Nakamura, Tomoyuki ; et
al. |
July 31, 2003 |
Electroconductive paste, method of producing monolithic ceramic
electronic part, and monolithic ceramic electronic part
Abstract
A conductive paste contains a ceramic powder in addition to a
conductive metal powder and an organic vehicle. The ceramic powder
is a powder produced by calcining an ABO.sub.3 system in which A
represents Ba or alternatively Ba partially substituted by at least
one of Ca and Sr, and B represents Ti or alternatively Ti partially
substituted by at least one of Zr and Hf, the system containing at
least one selected from the group of consisting of Re compounds (La
or the like), Mg compounds, and Mn compounds. The ceramic powder
has an average grain size smaller than that of the metal powder and
being incapable of sintering at the sintering temperature of the
substrate-use ceramic.
Inventors: |
Nakamura, Tomoyuki;
(Shiga-ken, JP) ; Shimizu, Motohiro; (Kusatsu-shi,
JP) ; Sano, Harunobu; (Kyoto-shi, JP) |
Correspondence
Address: |
DICKSTEIN SHAPIRO MORIN & OSHINSKY LLP
Edward A. Meilman
41st Floor
1177 Avenue of the Americas
New York
NY
10036-2714
US
|
Family ID: |
26623781 |
Appl. No.: |
10/265262 |
Filed: |
October 7, 2002 |
Current U.S.
Class: |
361/321.2 |
Current CPC
Class: |
C04B 2237/408 20130101;
C04B 2235/6582 20130101; C04B 2235/3213 20130101; C04B 35/6262
20130101; C04B 2235/9615 20130101; C04B 35/4682 20130101; C04B
2237/346 20130101; C04B 2237/704 20130101; B32B 18/00 20130101;
B32B 2311/22 20130101; C04B 2235/3215 20130101; C04B 2235/3236
20130101; C04B 2237/405 20130101; C04B 2235/77 20130101; C04B
2235/96 20130101; C04B 2235/6025 20130101; C04B 2235/3224 20130101;
C04B 35/63 20130101; C04B 2235/3208 20130101; C04B 2235/3225
20130101; C04B 2235/3262 20130101; C04B 2235/3418 20130101; B32B
2311/08 20130101; C04B 2235/3206 20130101; C04B 2235/6584 20130101;
C04B 2235/79 20130101; H01G 4/30 20130101; C04B 2235/5445 20130101;
C04B 35/49 20130101; H01G 4/008 20130101 |
Class at
Publication: |
361/321.2 |
International
Class: |
H01G 004/06 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 5, 2001 |
JP |
2001-310383 |
Aug 14, 2002 |
JP |
2002-236240 |
Claims
What is claimed is:
1. An electroconductive paste which is used to form inner conductor
films of a monolithic ceramic electronic part having a plurality of
ceramic layers made of a substrate ceramic and the inner conductor
films extending on specific boundaries between the ceramic layers,
comprising: an electroconductive metallic powder; a ceramic powder;
and an organic vehicle; wherein the ceramic powder is a calcined
powder of an ABO.sub.3 ceramic in which A represents Ba or Ba
partially substituted by at least one of Ca and Sr, and B
represents Ti or Ti partially substituted by at least one of Zr and
Hf: the ceramic powder containing at least one Re compound, Mg
compound or Mn compounds, in which Re is at least one member
selected from the group of consisting of La, Ce, Pr, Nd, Sm, Eu,
Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y, and wherein the ceramic
powder has an average grain size smaller than that of the metal
powder and is incapable of sintering at the sintering temperature
of the substrate ceramic.
2. An electroconductive paste according to claim 1, wherein the
metallic powder is at least one selected from the group consisting
of Ag, Ag-base alloys, Ni, Ni-base alloys, Cu, and Cu-base
alloys.
3. An electroconductive paste according to claim 1, wherein the
ceramic powder contains a Re compound, a Mn compound and a Mg
compound.
4. An electroconductive paste according to claim 3, wherein Re is
Dy, Ho or Y.
5. A method of producing a monolithic ceramic electronic part
having a plurality of ceramic layers of substrate ceramic and inner
conductor films extending along specific boundaries between the
ceramic layers, comprising the steps of: providing ceramic green
sheets comprising a substrate ceramic raw material powder having
the general formula A'B'O.sub.3 in which A' represents Ba or Ba
partially substituted by at least one of Ca and Sr, and B'
represents Ti or Ti partially substituted by at least one of Zr and
Hf, the ceramic green sheets having an electroconductive paste as
defined in claim 2 on at least a portion of a surface thereof;
laminating a plurality of the ceramic green sheets so as to form a
green laminate in which the electroconductive paste is provided on
specific boundaries between the ceramic green sheets to form inner
conductor films; and firing the green laminate.
6. A method of producing a monolithic ceramic electronic part
according to claim 5, further comprising the step of arranging the
inner conductor films to be formed by use of the conductive paste
via the ceramic layers in such a manner that a static capacitance
can be generated, and after the firing the green laminate, forming
outer electrodes on the outer surface of the sintered laminate in
such a manner that the outer electrodes are electrically connected
to specific ones of the inner conductor films to use the static
capacitance, whereby a monolithic ceramic capacitor is formed.
7. A method of producing a monolithic ceramic electronic part
according to claim 6, wherein the ceramic powder contains a Re
compound, a Mn compound and a Mg compound.
8. A method of producing a monolithic ceramic electronic part
according to claim 3, wherein Re is Dy, Ho or Y.
9. A method of producing a monolithic ceramic electronic part
having a plurality of ceramic layers made of a substrate ceramic
and inner conductor films extending specific boundaries between the
ceramic layers, comprising the steps of: providing ceramic green
sheets comprising a substrate ceramic raw material powder having
the general formula A'B'O.sub.3 in which A' represents Ba or Ba
partially substituted by at least one of Ca and Sr, and B'
represents Ti or Ti partially substituted by at least one of Zr and
Hf, the ceramic green sheets having an electroconductive paste as
defined in claim 1 on at least a portion of a surface thereof;
laminating a plurality of the ceramic green sheets so as to form a
green laminate in which the electroconductive paste is provided on
specific boundaries between the ceramic green sheets to form inner
conductor films; and firing the green laminate.
10. A method of producing a monolithic ceramic electronic part
according to claim 9, further comprising the step of arranging the
inner conductor films to be formed by use of the conductive paste
via the ceramic layers in such a manner that a static capacitance
can be generated, and after the firing the green laminate, forming
outer electrodes on the outer surface of the sintered laminate in
such a manner that the outer electrodes are electrically connected
to specific ones of the inner conductor films to use the static
capacitance, whereby a monolithic ceramic capacitor is formed.
11. A method of producing a monolithic ceramic electronic part
according to claim 9, wherein the ceramic powder contains a Re
compound, a Mn compound and a Mg compound.
12. A method of producing a monolithic ceramic electronic part
according to claim 11, wherein Re is Dy, Ho or Y.
13. A monolithic ceramic electronic part comprising a laminate of a
plurality of ceramic layers of a substrate ceramic and inner
conductor films disposed at specific boundaries between ceramic
layers, the substrate ceramic comprising a component expressed by
the general formula A'B'O.sub.3 in which A' represents Ba or Ba
partially substituted by at least one of Ca and Sr, and B'
represents Ti or Ti partially substituted by at least one of Zr and
Hf, and the inner conductor films being a fired conductive paste as
defined claim 1.
14. A monolithic ceramic electronic part according to claim 13,
wherein the inner conductor films are arranged via the ceramic
layers in such a manner that a static capacitance can be generated,
and the part further comprises outer electrodes on the outer
surface of the sintered laminate in such a manner that the outer
electrodes are electrically connected to specific ones of the inner
conductor films to use the static capacitance, whereby a monolithic
ceramic capacitor is formed.
15. A monolithic ceramic electronic part according to claim 13,
wherein the ceramic powder contains a Re compound, a Mn compound
and a Mg compound.
16. A monolithic ceramic electronic part according to claim 15,
wherein Re is Dy, Ho or Y.
17. A monolithic ceramic electronic part comprising a laminate of a
plurality of ceramic layers of a substrate ceramic and inner
conductor films disposed at specific boundaries between the ceramic
layers, the substrate ceramic comprising a component expressed by
the general formula A'B'O.sub.3 in which A' represents Ba or Ba
partially substituted by at least one of Ca and Sr, and B'
represents Ti or Ti partially substituted by at least one of Zr and
Hf, and the inner conductor films being a final conductive paste as
defined claim 2.
18. A monolithic ceramic electronic part according to claim 17,
wherein the inner conductor films are arranged via the ceramic
layers in such a manner that a static capacitance can be generated,
and the part further comprises outer electrodes on the outer
surface of the sintered laminate in such a manner that the outer
electrodes are electrically connected to specific ones of the inner
conductor films to use the static capacitance, whereby a monolithic
ceramic capacitor is formed.
19. A monolithic ceramic electronic part according to claim 17,
wherein the ceramic powder contains a Re compound, a Mn compound
and a Mg compound.
20. A method of producing a monolithic ceramic electronic part
according to claim 19, wherein Re is Dy, Ho or Y.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an electroconductive paste,
a method of producing a monolithic ceramic electronic part in which
the conductive paste is used to form inner conductor films, and a
monolithic ceramic electronic part made from the conductive paste
and in particular, to an improvement in that structural defects can
be suppressed even if layers contained in a monolithic ceramic
electronic part are thinned and the number of the layers is
increased.
[0003] 2. Description of the Related Art
[0004] Monolithic ceramic capacitors as examples of monolithic
ceramic electronic parts are generally produced by the following
method.
[0005] First, ceramic green sheets containing a dielectric ceramic
raw material and having inner conductor films formed in required
patterns on a surface of the sheets by use of a conductive paste
containing a conductive component are prepared. For example, a
material containing BaTiO.sub.3 as a major component is employed as
the dielectric ceramic raw material.
[0006] A plurality of ceramic green sheets including the
above-described ceramic green sheets having the inner conductor
films formed thereon are laminated and hot-press bonded. Thus, an
integrated green laminate is produced.
[0007] Subsequently, the green laminate is fired. Thereby, a
sintered laminate is obtained. The laminate has a lamination
structure containing a plurality of the ceramic layers which are
made form the above-described ceramic green sheets. The
above-described inner conductor films are arranged via the ceramic
layers inside the laminate so that an electrostatic capacitance can
be generated.
[0008] Then, outer electrodes are formed on the surface of the
laminate to be electrically connected to specific ones of the inner
conductor films for use of the static capacitance.
[0009] Thus, a monolithic ceramic capacitor is produced.
[0010] In recent years, the ceramic layers of such monolithic
ceramic capacitors have been further thinned and the number of the
layers has been increased for the purpose of reducing the size and
increasing the capacitance.
[0011] To thin the ceramic layers and increase the number of the
ceramic layers, it is important to sufficiently harmonize the
shrinkage behaviors during firing of the ceramic layers and the
inner conductor films with each other.
[0012] Ordinarily, the shrink-starting temperatures of conductive
metallic powders contained in inner conductor films are
considerably lower than those of the ceramic layers. In the case in
which there are differences between the shrink behaviors of the
conductive metallic powders and the ceramic layers, relatively
large stresses are generated inside the monolithic ceramic
capacitors, so that the thermal impact resistances are reduced, and
seriously, cracks and peeling may be caused between the ceramic
layers and the inner conductor films.
[0013] To solve the above-described problems, for example, Japanese
Unexamined Patent Application Publication No. 6-290985 has proposed
a method of causing the shrink behavior of the inner conductor
films to approach that of the ceramic layers as much as possible.
According to that method, different types of ceramic raw material
powders of which the compositions are the same as or different from
those of ceramic raw materials contained in the ceramic layers are
added to conductive pastes for forming the inner conductor
films.
[0014] According to the above-described Japanese Unexamined Patent
Application Publication No. 6-290985, oxides of Zr, rare earth
elements and the like are added to a conductive paste to suppress
the conductive metallic powder contained in the conductive paste
from sintering, so that the shrink behavior of the inner conductor
films can approach that of the ceramic layers. Thereby,
successfully, cracking and peeling between the ceramic layers and
the inner conductor films are suppressed.
[0015] In addition to Japanese Unexamined Patent Application
Publication No. 6-290985, for example, Japanese Examined Patent
Application Publication No. 5-63929, Japanese Unexamined Patent
Application Publication Nos. 2001-15375, 2000-269073, and 6-969998
and so forth, describe that ceramic raw material powders are added
to conductive pastes for forming inner conductor films. In these
Patent Specifications, it is described as advantages of the
inventions that the dielectric constants are increased, and the
coverage of inner conductor films is enhanced in addition to the
prevention of structural defects in monolithic ceramic
capacitors.
[0016] With the recent advancement of electronics, the size of
small electronic parts has been remarkably reduced. Also, for
monolithic ceramic capacitors, it has been required to further
reduce the size and increase the capacitance. For example,
monolithic ceramic capacitors having a ceramic layer thickness of
about 2 .mu.m are about to be provided for practical
applications.
[0017] Regarding the inner conductor films, film-thicknesses of
about 1 to 2 .mu.m are employed in most cases. Accordingly, the
thickness of each of the ceramic layers becomes nearly equal to
that of each of the inner conductor films. As a result, the
problems caused by the difference between the shrink behaviors at
firing of the ceramic layers and the inner conductor films become
more serious. Thus, structural defects are readily caused in the
monolithic ceramic capacitors.
[0018] From the standpoint of the principle of material diffusion,
it is supposed that some reaction occurs between ceramic raw
materials contained in a conductive paste for forming inner
conductor films and components present on the ceramic layer side.
For example, according to the method described in Japanese
Unexamined Patent Application Publication No. 6-290985, structural
defects in the monolithic ceramic capacitor can be suppressed.
However, a metal oxide, which is not a major component of the
ceramic layers, is added to the conductive paste, and therefore,
the metal oxide contained in the conductive paste and a component
contained in the ceramic layers react with each other. This may
change the electrical characteristic of the ceramic layers.
[0019] If the above-described reaction occurs uniformly, the
problems will not become serious. However, since the reaction
occurs unevenly as a practical matter, the electrical
characteristics of the ceramic layers are locally changed. This
causes the electrical characteristics of the monolithic ceramic
capacitor to disperse.
[0020] In particular, as described in Japanese Patent No. 2722457,
when an oxide of a rare earth element is added to a conductive
paste, the part of the ceramic layers in contact with the rare
earth element oxide powder becomes semi-conductive. Thus, the
thickness of the part of the ceramic layers which practically
function as a dielectric is smaller than the apparent thickness of
the ceramic layers. As a result, the reliability of the insulation
resistance and the other electrical characteristics of the
monolithic ceramic capacitor is deteriorated. Therefore, the method
in which the rare earth element oxide is added cannot correspond to
the thinning of the ceramic layers.
[0021] In the case in which a conductive paste having rare earth
element oxides added thereto is used, advantages such as increase
of the dielectric constant, enhancement of the reliability and so
forth, can be obtained by devising the application method, as
described in Japanese Examined Patent Application Publication No.
5-63929 and Japanese Unexamined Patent Application Publication No.
2001-15375. However, a major component of the ceramic layers and
this major component of the conductive paste, which are metal
oxides different from each other, react with each other at random.
Therefore, the electrical characteristics of the ceramic layers are
dispersed.
[0022] This causes the electrical characteristics of the monolithic
ceramic capacitor as a product to be disperse.
[0023] To cope with the above-described dispersion, products may be
selected for shipment so as to comply with the standards for the
respective characteristics. In this case, the yield in
mass-production is low. The defective proportion is high. The high
cost is also a problem.
[0024] It is estimated that a thickness of up to 1 .mu.m will be
employed in future. Thus, if further thinning of the ceramic layers
is realized, the effects of the dispersion will be more remarkable.
Thus, the above-described problems will become more serious.
[0025] In case in which a metal oxide such as a rare earth element
oxide, which is different from a major component of ceramic layers,
is added to a conductive paste for forming inner conductor films,
it may be more effective if the metal oxide is added not singly but
together with the major component of the ceramic layers or a
component analogues to the major component.
[0026] However, when the methods described in Japanese Unexamined
Patent Application Publication No. 2001-1537 and Japanese
Unexamined Patent Application Publication No. 2000-269073 are used
while the above-described technique is applied, the rare earth
element oxide diffuses into the ceramic layers and reacts with
components of the ceramic layers. This causes the electrical
characteristics of the monolithic ceramic capacitor to disperse,
resulting in deterioration of the yield in mass production and an
increase of the proportion of defectives.
[0027] Under the above-described situations, it is desired to
develop a conductive paste for forming inner conductor films which
cause no structural defects in monolithic ceramic capacitors and
exerts substantially no undesired influences over the electrical
characteristics of the ceramic layers, even if the sizes of the
monolithic ceramic capacitors are reduced more, and the
capacitances are further increased.
[0028] The above-description is true of other monolithic ceramic
electronic parts in addition to the monolithic ceramic
capacitor.
SUMMARY OF THE INVENTION
[0029] Accordingly, it is an object of the present invention to
provide an electroconductive paste, a method of producing a
monolithic ceramic electronic part in which the conductive paste is
used to form inner conductor films, and a monolithic ceramic
electronic part formed by use of the conductive paste.
[0030] This invention has been devised by the inventors of the
invention, based on the following knowledge.
[0031] That is, to cause the shrink behavior of the inner conductor
films at firing to approach that of the ceramic layers, it is
effective that the grains of a ceramic powder finer than those of a
conductive metallic powder contained in a conductive paste for
forming the inner conductor films, and are uniformly distributed
between the grains of the conductive metallic powder contained in
the dried conductive paste before firing. Thereby, effects by the
addition of the ceramic powder can be realized. Thus, the required
amount of the ceramic powder to be added to the conductive paste
can be suppressed and minimized.
[0032] When a metal oxide, which is not a major component of the
ceramic layers, is added to the conductive paste for forming the
inner conductor films, the metal oxide is added not singly but
together with the major component of the ceramic layers or a
component analogous to the major component. However, the components
of the ceramic layers are not directly mixed and added to the
conductive paste. Preferably, they are previously heat-treated, so
that they become impossible to be sintered at the sintering
temperature of a ceramic used as the substrate, and thereafter, are
added to the conductive paste.
[0033] The conductive paste of the present invention devised based
on the above-described knowledge is used to form inner conductor
films of a monolithic ceramic electronic part, which contains a
plurality of ceramic layers composed of substrate ceramic layers
and the inner conductor films extending on specific boundaries
between the ceramic layers. Characteristically, the conductive
paste has the following constitution.
[0034] That is, the conductive paste contains a conductive metallic
powder, a ceramic powder and an organic vehicle.
[0035] The ceramic powder is a powder produced by calcining an
ABO.sub.3 system ceramic in which A represents Ba or alternatively
Ba partially substituted by at least one of Ca and Sr, and B
represents Ti or alternatively Ti partially substituted by at least
one of Zr and Hf, the system containing at least one selected from
the group of consisting of Re compounds in which Re represents at
least one of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu
and Y, Mg compounds and Mn compounds. The ceramic powder has an
average grain size smaller than that of the metal powder and is
incapable of sintering at the sintering temperature of the
substrate-use ceramic.
[0036] Preferably, the metallic powder is at least one selected
from the group of Ag, Ag-base alloys, Ni, Ni-base alloys, Cu, and
Cu-base alloys.
[0037] According to the present invention, there is provided a
method of producing a monolithic ceramic electronic part having a
plurality of ceramic layers made of a substrate ceramic and inner
conductor films extending specific boundaries between the ceramic
layers.
[0038] The method of producing a monolithic ceramic electronic part
comprises the steps of preparing a ceramic green sheet containing
as a major component a substrate ceramic raw material powder having
the general formula A'B'O.sub.3 in which A' represents Ba or
alternatively Ba partially substituted by at least one of Ca and
Sr, and B' represents Ti or alternatively Ti partially substituted
by at least one of Zr and Hf, and laminating a plurality of the
ceramic green sheets so as to form the ceramic layers to produced a
green laminate in which the above-described electroconductive paste
is provided on specific boundaries between the ceramic green sheets
to form the inner conductor films, and firing the green
laminate.
[0039] Preferably, this production method is applied to a method of
producing a monolithic ceramic capacitor. In this case, the method
further comprises the step of arranging the inner conductor films
to be formed by use of the conductive paste via the ceramic layers
in such a manner that a static capacitance can be generated, and
after the firing step for the green laminate, forming outer
electrodes on the outer surface of the sintered laminate in such a
manner that the outer electrodes are electrically connected to
specific ones of the inner conductor films to use the static
capacitance.
[0040] Further, according to the present invention, there is
provided a monolithic ceramic electronic part which comprises a
plurality of ceramic layers made of a substrate ceramic and inner
conductor films extending specific boundaries between the ceramic
layers.
[0041] In this monolithic ceramic electronic part, the substrate
ceramic contains a major component expressed by the general formula
A'B'O.sub.3 in which A' represents Ba or alternatively Ba partially
substituted by at least one of Ca and Sr, and B' represents Ti or
alternatively Ti partially substituted by at least one of Zr and
Hf, and the inner conductor films are made of a sintered material
produced by firing the above-described conductive paste.
[0042] Preferably, the monolithic ceramic electronic part is a
monolithic ceramic capacitor. In this case, the inner conductor
films are arranged via the ceramic layers in such a manner that a
static capacitance can be generated, and the part further comprises
outer electrodes formed on the outer surface of the sintered
laminate in such a manner that the outer electrodes are
electrically connected to specific ones of the inner conductor
films to use the static capacitance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0043] FIG. 1 is a schematic cross-sectional view of a monolithic
ceramic capacitor as an example of a monolithic ceramic electronic
part formed by use of a conductive paste according to an embodiment
of the present invention.
[0044] FIG. 2 is a graph showing the change of the shrink ratios
with increasing temperature of the ceramic powders and the
substrate ceramic of Example 1 and Comparative Examples 1 to 3 each
added to the conductive paste in Experiment 1 carried out according
the present invention.
[0045] FIG. 3 is a graph showing the change of the shrink ratios
with increasing temperature of the ceramic powders and the
substrate-use ceramic of Example 2 and Comparative Example 4 each
added to the conductive paste in Experimental Experiment 2 carried
out according the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0046] FIG. 1 is a schematic cross-sectional view of a monolithic
ceramic capacitor 1 which is an example of a monolithic ceramic
electronic part formed by a conductive paste according to an
embodiment of the present invention.
[0047] The monolithic ceramic capacitor 1 contains a laminate 2.
The laminate 2 comprises a plurality of dielectric ceramic layers 3
laminated to each other, and a plurality of inner conductor films 4
and 5 formed on specific boundaries between a plurality of the
dielectric ceramic layers 3.
[0048] The inner conductor films 4 and 5 are formed so as to reach
the outer surface of the laminate 2. The inner conductor films 4
extended to one end face 6 of the laminate 2 and the inner
conductor films 5 extended to the other end face 7 of the laminate
2 are alternately arranged via the dielectric ceramic layers 3
inside the laminate 2 in such a manner that electrostatic
capacities can be generated.
[0049] To use the above-described static capacities, outer
electrodes 8 and 9 are formed on the outer surface of the laminate
2, that is, on the end faces 6 and 7 thereof, so as to be connected
to specific ones of the inner conductor films 4 and 5. First
plating layers 10 and 11 made of nickel, copper or the like, are
formed on the outer electrodes 8 and 9, respectively. Second
plating layers 12 and 13 made of solder, tin or the like, are
formed thereon, respectively.
[0050] In the monolithic ceramic capacitor 1, a substrate ceramic
for forming the dielectric ceramic layers 3 contains a major
component expressed by the general formula A'B'O.sub.3 in which A'
represents at least one of Ba or alternatively Ba partially
substituted by at least one of Ca and Sr, and B' represents Ti or
alternatively Ti partially substituted by at least one of Zr and
Hf.
[0051] On the other hand, the inner conductor films 4 and 5 are
made of a sintered material obtained by firing a conductive paste
having the following composition: a conductive metallic powder, a
ceramic powder and an organic vehicle.
[0052] As the conductive metallic powder, for example, powders of
Ag, an Ag-base alloy, Ni, an Ni-base alloy, Cu, a Cu-base alloy,
and mixtures thereof are used.
[0053] The ceramic powder is a powder produced by calcining an
ABO.sub.3 system ceramic in which A represents Ba or alternatively
Ba partially substituted by at least one of Ca and Sr, and B
represents Ti or alternatively Ti partially substituted by at least
one of Zr and Hf, the system containing at least one selected from
the group of consisting of Re compounds in which Re represents at
least one of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb,
Lu, and Y, Mg compounds and Mn compounds. The ceramic powder has an
average grain size smaller than that of the metal powder and is
incapable of being sintered at the sintering temperature of the
substrate ceramic.
[0054] The above-described ceramic powder is a powder obtained
after the calcining. In this case, the calcined material of the
ABO.sub.3 system and, as an addition component, at least one of the
Re compounds, the Mg compounds and the Mn compounds may be mixed
and calcined. Alternatively, the above-described compound as an
addition component may be added to and mixed with ACO.sub.3 and
BO.sub.2 as starting materials of the ABO.sub.3 system, and then,
these materials are simultaneously calcined.
[0055] Referring to the ceramic powder contained in the conductive
paste for forming the inner conductor films 4 and 5, the average
grain size is smaller than that of the metallic powder contained in
the same conductive paste, and can not be sintered at the sintering
temperature of a substrate ceramic. Thereby, as apparent from the
experimental examples which will be described below, structural
defects in the monolithic ceramic capacitor 1 can be suppressed
from occurring. Moreover, the electrical characteristics can be
suppressed from dispersing. As a result, the dielectric ceramic
layers 3 can be advantageously thinned.
[0056] The monolithic ceramic capacitor 1 shown in FIG. 1 can be
produced as follows.
[0057] First, a slurry containing the above-described substrate
ceramic raw material powder having a major component expressed by
the above-described general formula A'B'O.sub.3 is prepared. The
slurry is formed into a sheet. Thus, a ceramic green sheet is
prepared.
[0058] Then, the inner conductor films 4 and 5 having required
patterns are formed on the ceramic green sheet by printing or the
like, using the above-described conductive paste having the
specific composition.
[0059] Then, a required number of the ceramic green sheets having
the inner conductor films 4 and 5 formed thereon, respectively, are
laminated, and moreover, ceramic green sheets having no inner
conductor films formed thereon are laminated to the upper and lower
sides of the laminate made of the green sheets, and hot-pressed to
be bonded to each other. Thus, the integrated laminate 2 in the
green state is obtained.
[0060] Subsequently, the green laminate 2 is fired in a reducing
atmosphere, and thereby, the laminate 2 is sintered. In the
sintered laminate 2, the above-described green sheets form the
dielectric ceramic layers 3, and the conductive paste applied so as
to form the inner conductor films 4 and 5, respectively, is a
sintered material.
[0061] Then, the outer electrodes 8 and 9 are formed on the end
faces 6 and 7 of the laminate 2 so as to be connected to specific
ones of the inner conductor films 4 and 5, respectively. The
materials for the outer electrodes 8 and 9 may be the same as those
for the inner conductor films 4 and 5. As conductive components of
the outer electrodes 8 and 9, Pd and Ag--Pd alloys may be used in
addition to Ag, Ag-base alloys, Ni, Ni-base alloys, Cu, and Cu-base
alloys described previously as an example. Moreover, glass frits of
the B.sub.2O.sub.3--Li.sub.2O--SiO.sub.2--BaO,
B.sub.2O.sub.3--SiO.sub.2--BaO type, or the like, added to a
metallic powder may be employed. An appropriate material should be
selected considering the uses and use environment of the monolithic
ceramic capacitor 1.
[0062] Ordinarily, the outer electrodes 8 and 9 are formed by
applying a paste containing a conductive metallic powder onto the
sintered laminate 2, and baking it. The paste may be applied on the
laminate 2 in the green state and baked together with the laminate
2 during the firing process for the laminate 2.
[0063] Thereafter, the outer electrodes 8 and 9 are plated with
nickel, copper or the like, to form the fist plating layers 10 and
11, and moreover, are plated with solder, tin, or the like to form
the second plating layers 12 and 13, respectively. Thus, the
monolithic ceramic capacitor 1 is produced.
[0064] Hereinbefore, the present invention has been described with
reference to the monolithic ceramic capacitor. The conductive paste
of the present invention can be advantageously applied to other
monolithic ceramic electronic parts to form inner conductor films,
in addition to the monolithic ceramic capacitor, provided that the
monolithic ceramic electronic part comprises a plurality of ceramic
layers made of a substrate ceramic and inner conductor films
extended on specific boundaries between the ceramic layers.
[0065] Hereinafter, preferred ranges of the composition of the
conductive paste of the present invention, the properties and
characteristics of a ceramic powder contained in the conductive
paste, and so forth will be described. Moreover, experimental
examples carried out to identify the advantages of the present
invention will be described.
EXPERIMENTAL EXAMPLES
Experiment 1
[0066] In Experiment 1, a substrate ceramic containing a major
component of BaTiO.sub.3 with a Ba/Ti ratio of 1.004 and
Dy.sub.2O.sub.3, MgO, MnO and SiO.sub.2 added thereto, was used. As
a conductive metallic powder to be contained in a conductive paste
for forming inner conductor films, a nickel powder was used.
[0067] In particular, as starting materials for the substrate-use
ceramic, TiCl.sub.4 and Ba(NO.sub.3).sub.2 each having a purity of
at least 99.9% were prepared. After weighing, they were
precipitated by use of oxalic acid to form titanyl barium oxalate
{BaTiO(C.sub.2O.sub.4).4H.sub.2O}. The precipitate was pyrolyzed at
a temperature of 1000.degree. C., so that BaTO.sub.3 as a major
component was formed. Thus, the BaTiO.sub.3 powder with an average
grain size of 0.3 .mu.m was obtained.
[0068] On the other hand, powders of Dy.sub.2O.sub.3, MgO, MnO and
SiO.sub.2 each having an average grain size of 0.1 .mu.m were
prepared.
[0069] Subsequently, 1 mol of Dy.sub.2O.sub.3, 1.5 mols of MgO, 0.2
mol of MnO, and 2 mols of SiO.sub.2 were compounded with 100 mols
of BaTiO.sub.3 to produce a mixed powder.
[0070] A polyvinylbutyral type binder, an organic solvent such as
ethanol or the like were added to the mixed powder, and wet-mixed
by means of a ball mill to produce a ceramic slurry.
[0071] The ceramic slurry was formed into a sheet by the doctor
blade method. Thus, a parallelepiped ceramic green sheet with a
thickness of 2.5 .mu.m was formed.
[0072] On the other hand, a conductive paste for forming inner
electrodes was prepared. In particular, 47.5% by weight of nickel
powder with an average grain size of 0.4 .mu.m, 2.5% by weight of a
ceramic powder described below, 35% by weight of an organic vehicle
prepared by dissolving 10% by weight of ethyl cellulose in 90% by
weight of terpineol, and 15% by weight of terpineol were mixed and
dispersed by means of a three-roll mill. Thus, a conductive paste
containing the nickel powder and the ceramic powder dispersed
sufficiently therein was produced.
[0073] Referring to the ceramic powder added to the conductive
paste, four types of ceramic powders for use in Example 1 and
Comparative Examples 1, 2, and 3 were prepared, and four types of
conductive pastes were produced by use of the respective ceramic
powders, as described below.
(1) Example 1
[0074] Dy.sub.2O.sub.3 and MgO powders each having an average grain
size of 0.2 .mu.m were added to a (Ba.sub.0.95Ca.sub.0.05)TiO.sub.3
powder having an average grain size of 0.1 .mu.m prepared by the
same procedures as those for the substrate ceramic, wet-mixed by
means of a ball mill, calcined at 800.degree. C. for 2 hours, and
ground. Thereby, a ceramic powder, which was a calcined material,
was obtained. In this case, (Ba.sub.0.95Ca.sub.0.05)TiO.sub.3,
Dy.sub.2O.sub.3, and MgO were compounded at a molar ratio of
100:2:1. The average grain size of the produced ceramic powder was
about 0.2 .mu.m, since the (Ba.sub.0.95Ca.sub.0.05)TiO.sub.3 powder
with an average grain size of 0.2 .mu.m was a major component.
(2) Comparative Example 1
[0075] A ceramic powder with an average grain size of about 0.5
.mu.m was obtained in the same manner as that employed in Example 1
excepting that the average grain size of the
(Ba.sub.0.95Ca.sub.0.05)TiO.sub.3 powder was 0.5 .mu.m. The ceramic
powder used in Comparative Example 1 was different from the ceramic
powder in Example 1 only with respect to the average grain
size.
(3) Comparative Example 2
[0076] The same ceramic raw material powder as that for the
substrate ceramic was prepared. In particular, a BaTiO.sub.3 powder
with an average grain size of 0.3 .mu.m, and powders of
Dy.sub.2O.sub.3, MgO, MnO and SiO.sub.2 each having an average
grain size of 0.1 .mu.m were prepared. Then 1 mol of
Dy.sub.2O.sub.3, 1.5 mols of MgO, 0.2 mol of MnO and 2 mols of
SiO.sub.2 were compounded with 100 mols of BaTiO.sub.3 to produce a
mixed powder with an average grain size of 0.3 .mu.m. This mixed
powder was not heat-treated (not calcined).
(4) Comparative Example 3
[0077] The same raw material powders as those in Example 1 were
mixed. Also, the compounding ratio was the same as that in Example
1. Thus, a mixed powder with an average grain size of about 0.2
.mu.m was obtained. The mixed powder was not heat-treated (not
calcined).
[0078] Regarding the conductive pastes of Example 1 and Comparative
Examples 1, 2, and 3 produced as described above, the average grain
sizes of the nickel powders contained in the conductive pastes, and
the composition ratios, the treatment, and the average grain sizes
of the ceramic powders contained therein were summarized in Table
1.
1TABLE 1 Average grain size Ceramic powder of nickel Average powder
grain size (.mu.m) Composition ratio and treatment (.mu.m) Example
1 0.4 Calcined material of 100 mol 0.2 (Ba.sub.0.95Ca.sub.0.05) - 2
mol TiO.sub.3 - Dy.sub.2O.sub.3 - 1 mol MgO Comparative 0.4
Calcined material of 100 mol 0.5 example 1 (Ba.sub.0.95Ca.sub.0.05)
- 2 mol TiO.sub.3 - Dy.sub.2O.sub.3 - 1 mol MgO Comparative 0.4
Mixture of 100 mol 0.3 examp1e 2 (BaTiO.sub.3 - 1 mol
Dy.sub.2O.sub.3 - 1.5 mol MgO - 0.2 mol MnO - 2 mol SiO.sub.2
Comparative 0.4 Mixture of 100 mol example 3
(Ba.sub.0.95Ca.sub.0.05)TiO.sub.3 - 2 0.2 mol Dy.sub.2O.sub.3 - 1
mol MgO
[0079] Subsequently, the conductive pastes of Example 1 and
Comparative Examples 1 to 3 were screen-printed on the
above-described ceramic green sheets. Thus, the conductive paste
films to be the inner conductor films were formed.
[0080] Subsequently, a plurality of ceramic green sheets which
include the ceramic green sheets having the conductive paste films
thereon as described above were laminated and hot-press bonded.
Thus, green laminates ware produced. In each of the green
laminates, the conductive paste films extended to one of the
end-faces thereof and those extended to the other end-face were
alternately arranged in the lamination direction.
[0081] Next, the green laminate was heated at a temperature of
350.degree. C. in a nitrogen-gas atmosphere to burn out the binder.
Thereafter, the laminate was fired at a temperature 1220.degree. C.
for 2 hours in a reducing atmosphere having an oxygen partial
pressure of 10.sup.-9 to 10.sup.-12 MPa and containing an
H.sub.2--N.sub.2--H.sub.2O gas. Thus, a sintered laminate was
obtained. The laminate was provided with the dielectric ceramic
layers and the inner conductor films. The dielectric ceramic layers
were formed by the sintering of the ceramic green sheets, and the
inner conductor films were formed by the sintering of the
conductive paste films.
[0082] Thereafter, a conductive paste containing a glass frit of
the B.sub.2O.sub.3--Li.sub.2O--SiO.sub.2--BaO system and copper as
a electroconductive component was coated onto both of the end-faces
of the laminate, and baked at a temperature of 800.degree. C. in a
nitrogen atmosphere. Thus, outer electrodes electrically connected
to the inner conductor films were formed.
[0083] Regarding the outer size of the monolithic ceramic capacitor
produced as described above, the width was 1.6 mm, the length was
3.2 mm and the thickness was 1.2 mm. The thickness of each of the
dielectric ceramic layers present between the inner conductor films
was 2 .mu.m. The number of the effective dielectric ceramic layers
was 100. The effective opposed-area per one layer of the inner
conductor film was 2.1 mm.sup.2.
[0084] Regarding the monolithic ceramic capacitors and the sintered
laminates as samples formed as described above, the crack
generation ratio, the electrostatic capacitance, the dispersion in
electrostatic capacitance, the insulation resistance log IR, the
dispersion in IR, and the number of products failing a high
temperature loading test were evaluated, respectively. Table 2
shows the results.
[0085] In particular, the appearance of the sintered laminates as
the samples was observed by means of an optical microscope to
evaluate the generation of cracks. Moreover, each sintered laminate
was coated with a resin to be strengthened and polished to a
mirror-finish. An exposed cross-section was observed to evaluate
the presence or absence of cracks generated inside the laminate.
Thus, the generation ratio of cracks, that is, the sum of cracks
present on the surface of the laminate and on the inner side
thereof was determined.
[0086] Moreover, monolithic ceramic capacitors having no defects in
the appearance and structure thereof were used as measurement
samples. The electrostatic capacitances of the samples were
measured under the condition of a temperature of 25.degree. C., 1
kHz and 1 V.sub.rms. The maximum, the minimum, and the standard
deviation were determined to evaluate the dispersion of the static
capacitances.
[0087] Similarly, monolithic ceramic capacitors having no defects
in the appearance and structure were used as measurement samples. A
6 V DC voltage was applied to the samples at a room temperature for
2 minutes, and the insulation resistance (log IRs) thereof were
measured. The maximum, the minimum, and the standard deviation were
determined to evaluate the dispersion of the IRs.
[0088] Similarly, seventy two monolithic ceramic capacitors having
no defects in the appearance and structure were used as measurement
samples. A 10 V voltage was applied to the samples at a temperature
of 150.degree. C., and a high temperature loading test was carried
for 250 hours. A sample of which the insulation resistance became
200 k.OMEGA. or lower was judged as an acceptable sample. Thus, the
number of defectives in the high temperature loading test was
determined.
2TABLE 2 Number of products unaccepted by high Dispersion in
temperature Crack Static static capacitance (.mu.F) Insulation
Dispersion in IR loading test generation capacitance Standard
resistance Standard (based on 72 ratio (%) (.mu.F) Maximum Minimum
deviation Log IR Maximum Minimum deviation pieces) Example 1 0 2.54
2.63 2.45 0.03 10.33 10.52 10.12 0.03 0 Comparative 3 2.42 2.53
2.31 0.04 10.26 10.43 10.1 0.02 0 example 1 Comparative 25 2.33
2.77 1.88 0.18 9.64 10.51 8.72 0.27 5 example 2 Comparative 0 2.36
2.87 1.84 0.21 9.58 10.52 8.62 0.29 6 example 3
[0089] Subsequently, the ceramic powders added to prepare the
conductive pastes of Example 1 and Comparative Examples 1, 2, and 3
as described above were formed into sheets in the same method as
the ceramic raw material powder for forming a substrate ceramic.
The produced sheets were punched and pressed to form disk-shaped
samples.
[0090] The disk-shaped samples were fired at a firing temperature
of 1220.degree. C. as well as the substrate-use ceramic. Then, the
bulk densities of the samples were measured. Moreover, the ratios
of the bulk densities to the true densities of the ceramic powders
as the samples were determined. The ratios were evaluated as
relative densities. Table 3 shows the relative densities determined
as described above.
3 TABLE 3 Relative density (%) Example 1 62 Comparative example 1
35 Comparative example 2 96 Comparative example 3 67, If the
relative density in Table 3 is 90% or higher, the ceramic power can
be securely determined to have been sintered.
[0091] Moreover, regarding the ceramic powders to be added to the
conductive pastes of Examples 1 and Comparative Examples 1 to 3,
the change of the shrink ratios, that is, the shrink behaviors,
caused by raising of the temperature during the above-described
firing process, were determined. FIG. 2 shows the results.
[0092] FIG. 2 also shows the shrink behavior of the substrate
ceramic for comparison with those of the ceramic powders of Example
1 and Comparative Examples 1 to 3. The ceramic powder used in
Comparative Example 2 was the same as the ceramic raw material
powder for the substrate ceramic. Therefore, in FIG. 2, the curve
of Comparative Example 2 overlaps that of the substrate
ceramic.
[0093] Hereinafter, evaluation of the ceramic powders of Example 1
and Comparative Examples 1 to 3 with reference to Tables 1 to 3 and
FIG. 2 is made.
[0094] In Example 1 and Comparative Examples 1 to 3, the static
capacitances were about 2.5 .mu.F and the insulation resistance log
IRs were about 10, as shown in Table 2. Substantially no
differences are present between these measurements. However,
regarding the dispersion in the static capacitance, the dispersion
in the IR and the number of defectives determined by the high
temperature loading test, a relatively large difference is present
between Example 1 and Comparative Examples 1 to 3.
[0095] In Example 1, the average grain size of the ceramic powder
added to the conductive paste is smaller than that of the nickel
powder, as shown in Table 1. Moreover, the relative density was
62%, that is, the relative density is significantly smaller than
90%, as shown in Table 3. Furthermore, as seen in the shrink
behavior of FIG. 2, the ceramic powder was not sintered at the
sintering temperature (1220.degree. C.) of the substrate ceramic.
Accordingly, no cracks were generated as shown in Table 2, and the
ceramic power was suppressed from reacting with the substrate-use
ceramic, the dispersions in static capacitance and IR are small,
and the number of defectives determined by the high temperature
loading test was zero. Thus, the stable characteristics can be
obtained.
[0096] Comparative Example 1 and Example 1 are compared. It can be
seen that cracks were generated in Comparative Example 1, although
they are slight. The reason lies in that although the relative
density of the ceramic powder to be added to the conductive paste
in Comparative Example 1 and obtained by firing at the sintering
temperature (1220.degree. C.) of the substrate ceramic is low, as
shown in Table 3, the average grain size of the ceramic powder is
larger than that of the nickel powder as shown in Table 1, and
therefore, the ceramic powder cannot be uniformly distributed
between grains of the nickel powder in the dried conductive paste
film before firing. Regarding the dispersions in static capacitance
and IR, and the number of defectives determined by the high
temperature loading test, the ceramic powder of Comparative Example
1 gives test results substantially equal to those of Example 1,
since the ceramic was a calcined material, as was the ceramic
powder of Example 1, and was suppressed from reacting with the
substrate ceramic.
[0097] Comparative Example 2 and Example 1 are compared. It is seen
that the crack generation ratio in Comparative Example 2 is very
high, as shown in Table 2. This is supported by the shrink behavior
shown in FIG. 2 and the high relative density of 96% of the ceramic
powder fired at the sintering temperature (1220.degree. C.) of the
substrate ceramic shown in Table 3. The reason for the high crack
generation ratio lies in that the ceramic powder of Comparative
Example 2 was also sintered at the sintering temperature of the
substrate ceramic. The ceramic powder of Comparative Example 2 was
only a mixture of BaTiO.sub.3 with Dy.sub.2O.sub.3, MgO, MnO and
SiO.sub.2. Therefore, a part of Dy.sub.2O.sub.3, MgO, MnO and
SiO.sub.2 reacted with the substrate-use ceramic. This increases
the dispersions in static capacitance and IR and also the number of
defectives determined by the high temperature loading test.
[0098] Comparative Example 3 and Example 1 are compared. The
average grain size of the ceramic powder of Comparative Example 3
is smaller than that of the nickel powder as shown in Table 1.
Moreover, as seen in the shrink behavior of FIG. 2 and the relative
density in Table 3, the ceramic powder of Comparative Example 3 was
not sintered at the sintering temperature (1220.degree. C.) of the
substrate ceramic. Therefore, no cracks were generated as shown in
Table 2. However, since the ceramic powder of Comparative Example 3
was a mixture of BaTiO.sub.3 with Dy.sub.2O.sub.3 and MgO as shown
in Table 1, a part of Dy.sub.2O.sub.3 and MgO reacted with the
substrate ceramic, so that the dispersions in static capacitance
and IR become large. Moreover, the number of defectives determined
by the high temperature loading test is increased.
Experiment 2
[0099] In Experiment 2, a substrate ceramic containing as a major
component (Ba.sub.0.9Ca.sub.0.1)TiO.sub.3 having a molar ratio of
Ba to Ca of 90:10 (moles) and a ratio of (Ba, Ca)/Ti of 1.002, and
having Ho.sub.2O.sub.3, MgO, MnO, and SiO.sub.2 added thereto was
used. A copper powder with an average grain size of 0.5 .mu.m was
used as a conductive metallic powder to be contained in the
conductive paste for forming the inner conductor films.
[0100] First, the (Ba.sub.0.9Ca.sub.0.1)TiO.sub.3 powder having an
average grain size of 0.3 .mu.m was prepared by substantially the
same method as that used in Experiment 1. On the other hand, powers
of Ho.sub.2O.sub.3, MgO, MnO, and SiO.sub.2 each having an average
grain size of 0.1 .mu.m were prepared. Then, 0.5 mol of
Ho.sub.2O.sub.3, 0.5 mol of MgO, 0.5 mol of MnO, and 3 mols of
SiO.sub.2 were compounded with 100 mols of
(Ba.sub.0.9Ca.sub.0.1)TiO.sub.3 to produce a mixed powder, which is
a ceramic raw material powder for forming a substrate ceramic.
[0101] Subsequently, the mixed powder was processed to be slurry by
the same method as that in Experiment 1. Then, a ceramic green
sheet was formed by use of the obtained ceramic slurry.
[0102] On the other hand, a conductive paste for forming inner
conductor films was prepared by the same procedures as those in
Experiment 1.
[0103] Regarding the ceramic powders added to the conductive paste,
two types of ceramic powders were prepared in Example 2 and
Comparative Example 4 as follows. Two types of conductive pastes
were produced by use of the respective ceramic powders.
(1) Example 2
[0104] A Y.sub.2O.sub.3 powder having an average grain size of 0.1
.mu.m was added to a (Ba.sub.0.90Sr.sub.0.05Ca.sub.0.05)(Ti.sub.0
85Zr.sub.0.15)O.sub.3 powder having an average grain size of 0.1
.mu.m, we mixed by means of a ball mill, calcined at a temperature
of 800.degree. C. for 2 hours, and ground. Thereby, a ceramic
powder made of the calcined material was obtained. The compounding
ratio of
(Ba.sub.0.90Sr.sub.0.05Ca.sub.0.05)(Ti.sub.0.85Zr.sub.0.15))O.sub.3
and Y.sub.2O.sub.3 was 100:1 (mole). The average grain size of the
produced ceramic powder was about 0.1 .mu.m, since the
(Ba.sub.0.90Sr.sub.0.05Ca.s- ub.0.05)(Ti.sub.0
85Zr.sub.0.15)O.sub.3 with an average grain size of 0.1 .mu.m was a
major component.
(2) Comparative Example 4
[0105] Powders of Y.sub.2O.sub.3 and SiO.sub.2 each having an
average grain size of 0.1 .mu.m was added to a
(Ba.sub.0.90Sr.sub.0.05Ca.sub.0.05- )(Ti.sub.0
85Zr.sub.0.15)O.sub.3 powder having an average grain size of 0.3
.mu.m, and wet-mixed by means of a ball mill. Thus, a ceramic
powder was obtained as a mixture. Then,
(Ba.sub.0.90Sr.sub.0.05Ca.sub.0.05)(Ti.s- ub.0
85Zr.sub.0.15)O.sub.3, Y.sub.2O.sub.3, and SiO.sub.2 were
compounded at a mole ratio of 100:1:2. The average grain size of
the produced ceramic powder was about 0.3 .mu.m, since the
(Ba.sub.0.009Sr.sub.0.05Ca.-
sub.0.05)(Ti.sub.0.85Zr.sub.0.15)O.sub.3 powder with an average
grain size of 0.3 .mu.m was a major component.
[0106] Table 4 shows the outlines of the conductive pastes of
Example 2 and Comparative Example 4 produced as described above.
Table 4 corresponds to Table 1 in Experiment 1.
4TABLE 4 Average Ceramic powder grain size of Average Cu powder
grain size (.mu.m) Composition ratio and processing (.mu.m) Ex- 0.5
Calcined material of 100 mol 0.1 ample
(Ba.sub.0.90Sr.sub.0.05Ca.sub.0.05)(Ti.sub.0.85-
Zr.sub.0.15)O.sub.3 - 2 1 mol Y.sub.2O.sub.3 Com- 0.5 Mixture of
100 mol 0.3 parative (Ba.sub.0.90Sr.sub.0.05Ca.sub.0.0-
5)(Ti.sub.0.85Zr.sub.0.15)O.sub.3 - ex- 1 mol Y.sub.2O.sub.3 - 2
mol SiO.sub.2 ample 4
[0107] Subsequently, monolithic ceramic capacitors as samples were
produced by use of the above-described ceramic green sheet and the
conductive pastes of Example 2 and Comparative Example 4 by the
same method as that in Experiment 1.
[0108] Referring to the above-described production of the
monolithic ceramic capacitors, the firing process was carried out
at a temperature of 1000.degree. C. for 2 hours in a reducing
atmosphere having an oxygen partial pressure of 10.sup.-75 to
10.sup.-10 MPa and containing an H.sub.2--N.sub.2--H.sub.2O gas.
Regarding the outer size of the obtained monolithic ceramic
capacitors, the width was 1.6 mm, the length was 3.2 mm, and the
thickness was 1.2 mm, as was those in Experiment 1. However, the
thickness of each of the dielectric ceramic layers present between
inner conductor films was 2.3 .mu.m.
[0109] Subsequently, the various characteristics and properties
thereof were evaluated in the same manners as those in Experiment
1. Tables 5 and 6 and FIG. 3 show the evaluation results. Table 5,
Table 6, and FIG. 3 correspond to Table 2, Table 3, and FIG. 2 in
Experiment 1, respectively.
5TABLE 5 Number of products unaccepted by high Dispersion in
temperature Crack Static static capacitance (.mu.F) Insulation
Dispersion in IR loading test generation capacitance Standard
resistance Standard (based on 72 ratio (%) (.mu.F) Maximum Minimum
deviation Log IR Maximum Minimum deviation pieces) Example 2 0 2.21
2.37 2.08 0.04 10.53 10.64 10.2 0.02 0 Comparative 15 2.1 2.38 1.81
0.11 10.31 10.65 9.91 0.11 7 example 4
[0110]
6 TABLE 6 Relative density (%) Example 2 66 Comparative Example 4
94
[0111] In Example 2, the average grain size of the ceramic powder
is smaller than that of the copper powder as shown in Table 4.
Also, as shown in Table 6, the relative density is low, that is,
66%. Further, as seen in the shrink behavior of FIG. 3, the ceramic
powder was not sintered at the sintering temperature (1000.degree.
C.) of the substrate ceramic. Accordingly, as shown in Table 5,
cracks were not generated, and moreover, the ceramic power was
suppressed from reacting with the substrate ceramic. Thus, the
dispersions in static capacitance and IR are small, and the number
of defectives determined by the high temperature loading test was
zero, as shown in Table 5. That is, characteristics can be obtained
with high stability.
[0112] On the other hand, a relatively large number of cracks were
generated in Comparative Example 4, as shown in Table 5. The reason
lies in that the ceramic powder was sintered at the sintering
temperature (1000.degree. C.) of the substrate-use ceramic, which
can be seen in the shrink behavior in FIG. 3 and the high relative
density of 94% in Table 6. Moreover, the ceramic powder of
Comparative Example 4 was only a mixture of
(Ba.sub.0.90Sr.sub.0.05Ca.sub.0.05)(Ti.sub.0.85Zr.sub.0.15)O.s-
ub.3, Y.sub.2O.sub.3, and SiO.sub.2. Therefore, a part of
Y.sub.2O.sub.3 and SiO.sub.2 reacted with the substrate ceramic, so
that the dispersions in static capacitance and IR become large, and
the number of defectives determined by the high temperature loading
test increases.
Experiment 3
[0113] In Experiment 3, a substrate-use ceramic containing as a
major component (Ba.sub.0.90Ca.sub.0.05Sr.sub.0.05)(Ti.sub.0
85Zr.sub.0.15)O.sub.3 having a molar ratio of Ba to Ca to Sr of
90:5:5 (mole), a ratio of Ti:Zr of 85:15 (mole), and a ratio of
(Ba, Ca, Sr)/(Ti, Zr) of 1.001, and having Y.sub.2O.sub.3, MnO and
SiO.sub.2 added thereto was used. An Ag--Pd alloy powder having an
average grain size of 0.4 .mu.m was used as a conductive metallic
powder to be contained in a conductive paste for forming inner
conductor films.
[0114] First, a ceramic raw material powder for forming the
substrate-use ceramic was prepared. That is, a
(Ba.sub.0.90Ca.sub.0.05Sr.sub.0.05)(Ti.s-
ub.0.85Zr.sub.0.15)O.sub.3 powder having an average grain size of
0.3 .mu.m was prepared by using substantially the same method as
that in Experiment 1. 0.2 mol of Y.sub.2O.sub.3 powder, 0.5 mol of
MgO powder, 0.2 mol of MnO powder and 2 mols of SiO2 powder each
having an average grain size of 0.1 .mu.m were added to and mixed
with 100 mols of the
(Ba.sub.0.9Ca.sub.0.05Sr.sub.0.05)(Ti.sub.0.85Zr.sub.0.15)O.sub.3
power. Thus, a mixed powder was prepared as a substrate-use ceramic
raw material powder.
[0115] Subsequently, the mixed powder was processed to become
slurry by using the same manner as that in Experiment 1. Then, a
ceramic green sheet was formed by use of the obtained ceramic
slurry.
[0116] On the other hand, the conductive paste for forming the
inner conductor films were prepared by the same procedures as those
in Experiment 1. With respect to the ceramic powders to be added to
the conductive paste, the following two types of conductive pastes
were prepared in Example 3 and Comparative Example 5. Two types of
conductive pastes were prepared by use of the respective ceramic
powders.
(1) Example 3
[0117] Powders of Ho.sub.2O.sub.3 and MnO each having an average
grain size of 0.1 .mu.m were added to a BaTiO.sub.3 powder with an
average grain size of 0.1 .mu.m, wet-mixed by means of a ball mill,
calcined at 800.degree. C. for 2 hours, and grounded. Thus, the
ceramic powder was obtained as the calcined material. In this case,
the compounding mole ratios of BaTiO.sub.3, Ho.sub.2O.sub.3, and
MnO were 100:1.5:0.5 (mole). The average grain size of the produced
ceramic powder was about 0.1 .mu.m, since the BaTiO.sub.3 powder
with an average grain size of 0.1 .mu.m was a major component.
(2) Comparative Example 5
[0118] A ceramic powder with an average grain size of about 0.6
.mu.m was produced by the same method as that in Example 3
excepting that the average grain size of the BaTiO.sub.3 powder as
the major component was 0.6 .mu.m.
[0119] Table 7 shows the outlines of the conductive pastes of
Example 3 and Comparative Example 5 produced as described above.
Table 7 corresponds to Table 1 in Experiment 1 or Table 4 in
Experiment 2.
7TABLE 7 Ceramic powder Average Average grain grain size of Ag--Pd
Composition ratio and size powder(.mu.m) processing (.mu.m) Example
3 0.4 Calcined material of 100 mol 0.1 BaTiO.sub.3 - 1.5 mole
Ho.sub.2O.sub.3 - 0.5 mole MnO Comparative 0.4 Calcined material of
100 mol 0.6 Example 5 BaTiO.sub.3 - 1.5 mole Ho.sub.2O.sub.3 - 0.5
mole MnO
[0120] Monolithic ceramic capacitors as samples were produced by
use of the above-described ceramic green sheet and the conductive
pastes of Example 3 and Comparative Example 5 by substantially the
same method as that in Experiment 1.
[0121] The firing process for producing the above-described
monolithic ceramic capacitors was carried out at a temperature of
1100.degree. C. for 2 hours in the atmosphere, which is different
from that employed in Experiment 1. Regarding the outer sizes of
the produced monolithic ceramic capacitors, the width was 1.6 mm,
the length was 3.2 mm, and the thickness was 1.2 mm, similarly to
those of the monolithic ceramic capacitors of Experiment 1.
However, the thickness of each of the dielectric ceramic layers
present between the inner conductor films was 2.1 .mu.m.
[0122] Subsequently, of the various evaluation items with respect
to Experiments 1 and 2, only the crack generation ratio and the
relative density of the ceramic powders to be added to the
conductive pastes and sintered at the sintering temperature
(1100.degree. C.) of the substrate ceramic regarding Example 3 and
Comparative Example 5 were evaluated. Table 8 shows the evaluation
results.
8TABLE 8 Crack generation Relative density ratio (%) (%) Example 3
0 68 Comparative Example 5 8 29
[0123] In Example 3, the average grain size of the ceramic powder
added to the conductive paste was smaller than that of the Ag--Pd
powder as shown in Table 7. The relative density shown in Table 8
of the ceramic powder is lower than 90%, that is, 68%. Therefore,
the ceramic powder was not sintered at the sintering temperature
(1100.degree. C.) of the substrate ceramic. For this reason, no
cracks were generated as shown in Table 8.
[0124] In Comparative Example 5, a relatively large number of
cracks were formed as shown in Table 8. The reason is as follows.
Although the relative density of the ceramic powder to be added to
the conductive paste and sintered at the sintering temperature
(1100.degree. C.) of the substrate ceramic is very small as shown
in FIG. 8, the average grain size of the ceramic powder is larger
than that of the Ag--Pd powder as shown in FIG. 7. Therefore, the
ceramic powder could not be evenly distributed between grains of
the Ag--Pd powder in the dried conductive paste film before
firing.
Experiment 4
[0125] In Experiment 4, a substrate ceramic containing as a major
component (Ba.sub.0.95Ca.sub.0.05)TiO.sub.3 having a molar ratio of
Ba to Ca of 95:5 and a ratio of (Ba, Ca)/Ti of 1.003, and having
Dy.sub.2O.sub.3, MgO, MnO, and SiO.sub.2 added thereto was used. A
nickel powder having an average grain size of 0.3 .mu.m was used as
a conductive metallic powder to be contained in a conductive paste
for forming inner conductor films.
[0126] First, the (Ba.sub.0.95Ca.sub.0.05)TiO.sub.3 powder having
an average grain size of 0.3 .mu.m was prepared by using
substantially the same method as that used in Experiment 1. Powders
of Dy.sub.2O.sub.3, MgO, MnO and SiO.sub.2 each having an average
grain size of 0.1 .mu.m were prepared, and 0.3 mol of
Dy.sub.2O.sub.3, 0.5 mol of MgO, 0.5 mol of MnO, and 2.0 mol of
SiO.sub.2 were compounded with 100 mols of
(Ba.sub.0.95Ca.sub.0.05)TiO.sub.3 to produce a mixed powder, which
is a ceramic raw material powder for forming a substrate
ceramic.
[0127] Subsequently, the mixed powder was processed into slurry by
using the same method as that in Experiment 1. Then, a ceramic
green sheet was formed by use of the obtained ceramic slurry.
[0128] On the other hand, a conductive paste of Example 4 for
forming inner conductor films was prepared by the following
method.
[0129] That is, BaCO.sub.3, CaCO.sub.3, TiO.sub.2, ZrO.sub.2 and
Y.sub.2O.sub.3 each having an average grain size of 0.1 .mu.m were
mixed. In particular, 90 mols of BaCO.sub.3, 5 mols of CaCO.sub.3,
90 mols of TiO.sub.2, 10 mols of ZrO.sub.2 and 2.5 mols of
Y.sub.2O.sub.3 were weighed out, compounded, wet-mixed by means of
a ball mill, calcined at a temperature of 1100.degree. C. for 2
hours, and grounded. Thus, a ceramic powder as a calcined material
was formed. The average grain size of the ceramic powder was 0.15
.mu.m.
[0130] Subsequently, 47.5% by weight of nickel powder with an
average grain size of 0.3 .mu.m, 2.5% by weight of the
above-described ceramic powder, 35% by weight of an organic vehicle
prepared by dissolving 10% by weight of ethyl cellulose in 90% by
weight of terpineol, and 15% by weight of terpineol were mixed and
dispersed by means of a three-roll mill. Thus, the conductive paste
of Example 4 containing the nickel powder and the ceramic powder
sufficiently dispersed therein was produced.
[0131] Table 9 shows the outlines of the conductive paste of
Example 4 produced as described above. Table 9 corresponds to Table
1 in Experiment 1.
9TABLE 9 Ceramic powder Average grain Average size of nickel
Composition ratio grain powder (.mu.m) and processing size (.mu.m)
Example 4 0.3 Calcined material of 90 mol 0.15 BaCO.sub.3 - 5 mol
CaCO.sub.3 - 2.5 mol Y.sub.2O.sub.3 - 90 mol- TiO.sub.2 - 10 mol
ZrO.sub.2
[0132] Subsequently, monolithic ceramic capacitors as samples were
produced by the same method as that in Experiment 1 using the
above-described ceramic green sheet and the conductive pastes of
Example 4.
[0133] Regarding the produced monolithic ceramic capacitors, the
thickness of each of the dielectric ceramic layer between inner
conductor films was 2.3 .mu.m.
[0134] Then, the various characteristics and the properties were
evaluated by the same method as that employed in Experiment 1.
Tables 10 and 11 show the evaluation results. Table 10 corresponds
to Table 2 in Experiment 1, and Table 11 corresponds to Table 3
therein.
10TABLE 10 Dispersion in static capacitance Number of products
Crack Static (.mu.F) Insulation Dispersion in IR unaccepted by high
generation capacitance Standard resistance Standard temperature
loading test ratio (%) (.mu.F) Maximum Minimum deviation Log IR
Maximum Minimum deviation (based on 72 pieces) Example 4 0 2.33
2.47 2.19 0.04 10.60 10.7 10.2 0.02 0
[0135]
11 TABLE 11 Relative density (%) Example 4 57
[0136] In Example 4, the average grain size of the ceramic powder
is smaller than that of the nickel powder as shown in Table 9. As
shown in Table 11, the relative density is low, that is, 57%. Thus,
the ceramic powder was not sintered at the sintering temperature
(1220.degree. C.) of the substrate ceramic. Accordingly, as shown
in Table 10, no cracks were generated, and moreover, the ceramic
power is suppressed from reacting with the substrate ceramic. Thus,
the dispersions in static capacitance and IR are small, and the
number of defectives determined by the high temperature loading
test was zero, as shown in Table 5. Therefore, it is seen that the
stable characteristics were obtained.
[0137] As described above, the conductive paste of the present
invention contains ceramic powder in addition to conductive
metallic powder.
[0138] The ceramic powder is a powder produced by calcining an
ABO.sub.3 system in which A represents Ba or alternatively Ba
partially substituted by at least one of Ca and Sr, and B
represents Ti or alternatively Ti partially substituted by at least
one of Zr and Hf, the system containing at least one selected from
the group of consisting of Re compounds in which Re represents at
least one of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu
and Y, Mg compounds and Mn compounds. Therefore, the shrink
behavior of the inner conductor films can be made to approach that
of the ceramic layers in the firing process by using the conductive
paste to form the inner conductor films of a monolithic ceramic
electronic part.
[0139] Moreover, the ceramic powder has a smaller average grain
size than the metallic powder. Therefore, the ceramic powder can be
evenly distributed between the metallic powder in the conductive
paste or the dried conductive past film.
[0140] Accordingly, structural defects such as cracks or the like
can be suppressed in the sintered laminate contained in the
produced monolithic ceramic electronic part.
[0141] The ceramic powder contained in the conductive paste is
processed so as to be incapable of sintering at the sintering
temperature of a substrate ceramic for forming ceramic layers of
the monolithic ceramic electronic part. Therefore, the ceramic
powder and the substrate ceramic can be prevented from partially
reacting with each other during the firing process. Thus, the
contained ceramic powder is prevented from substantially exerting
an influence over the electrical characteristics of the ceramic
layers. As a result, the dispersion in electrical characteristics
of the produced monolithic ceramic electronic part can be
reduced.
[0142] Accordingly, monolithic ceramic electronic parts having
stable characteristics can be mass produced at a high yield.
[0143] When the present invention is applied to the monolithic
ceramic capacitor, advantageously, the size of monolithic ceramic
capacitors can be reduced, and the capacities thereof can be
further increased.
[0144] In the monolithic ceramic electronic part of the present
invention, the substrate-use ceramic having a major component
expressed by the general formula A'B'O.sub.3 in which A' represents
Ba or alternatively Ba partially substituted by at least one of Ca
and Sr, and B' represents Ti or alternatively Ti partially
substituted by at least one of Zr and Hf, so that the ceramic
powder contained in the conductive paste for forming the inner
conductor films may have a composition which is the same as or
similar to that of the substrate ceramic for forming the ceramic
layers. Thereby, even if the components of the ceramic powder
contained in the conductive paste diffuse into the ceramic layers,
the effects of the diffusion can be prevented and minimized.
* * * * *