U.S. patent application number 09/741441 was filed with the patent office on 2001-08-02 for multilayer ceramic capacitor.
This patent application is currently assigned to Taiyo Yuden Co., Ltd.. Invention is credited to Mizuno, Youichi.
Application Number | 20010010616 09/741441 |
Document ID | / |
Family ID | 18487948 |
Filed Date | 2001-08-02 |
United States Patent
Application |
20010010616 |
Kind Code |
A1 |
Mizuno, Youichi |
August 2, 2001 |
Multilayer ceramic capacitor
Abstract
In a multilayer ceramic capacitor comprising a multilayer body
alternately laminating a conductor layer and a ceramic dielectric
layer, the thickness of the above described ceramic dielectric
layer is not more than the thickness of the above described
conductor layer, and therefore, as a whole, the ratio of the
occupation of the conductor layer comparatively having a
flexibility to the thermal shock is increased. Consequently, the
thermal shock resistance is improved.
Inventors: |
Mizuno, Youichi; (Tokyo,
JP) |
Correspondence
Address: |
LOWE HAUPTMAN GOPSTEIN GILMAN & BERNER, LLP
Suite 310
1700 Diagonal Road
Alexandria
VA
22314
US
|
Assignee: |
Taiyo Yuden Co., Ltd.
|
Family ID: |
18487948 |
Appl. No.: |
09/741441 |
Filed: |
December 21, 2000 |
Current U.S.
Class: |
361/306.3 |
Current CPC
Class: |
H01G 4/30 20130101 |
Class at
Publication: |
361/306.3 |
International
Class: |
H01G 004/228 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 24, 1999 |
JP |
H11-366890 |
Claims
What is claimed is:
1. A multilayer ceramic capacitor comprising a multilayer body
alternately laminating a conductor layer and a ceramic dielectric
layer, wherein a thickness of said ceramic dielectric layer is not
more than a thickness of said conductor layer.
2. The multilayer ceramic capacitor according to claim 1, wherein
the thickness of said ceramic dielectric layer is 70% or more and
100% or less of the thickness of said conductor layer.
3. The multilayer ceramic capacitor according to claim 1, wherein
the thickness of said conductor layer is not uniform.
4. The multilayer ceramic capacitor according to claim 1, wherein
said ceramic dielectric layer comprises ceramic grains and a
secondary phase existing between said ceramic grains.
5. A multilayer ceramic capacitor comprising a multilayer body
alternately laminating a conductor layer and a ceramic dielectric
layer, wherein said ceramic dielectric layer comprises ceramic
grains and a secondary phase existing between said ceramic grains,
and includes a part in which said ceramic grains do not exist
between opposite conductor layers and which is made of only said
secondary phase.
6. The multilayer ceramic capacitor according to claim 5, wherein
10% or more and 90% or less of all said ceramic dielectric layers
have said part made of only said secondary phase.
7. The multilayer ceramic capacitor according to claim 5, wherein,
said secondary phase comprises Si.
8. The multilayer ceramic capacitor according to claim 5, wherein,
the thickness of said conductor layer is not uniform.
Description
BACKGROUND OF THE INVENTION
[0001] A conventional multilayer ceramic capacitor comprises a
multilayer body made by alternately laminating a ceramic dielectric
layer and a conductor layer, and an external electrode formed at
both ends of the multilayer body and connected to the above
described conductor layer. Here, the conductor layer is alternately
connected to the external electrodes at both ends. That is, one
external electrode is connected to the conductor layer every other
layer, and the other external electrode is connected to the
conductor layer that is not connected to the above described one
external electrode.
[0002] For example, in the case of a multilayer ceramic capacitor
with an external size of 2.1 mm.times.1.25 mm.times.1.25 mm and an
electrostatic capacity of 10 .mu.F, the number of the laminated
conductor layers is 330, the thickness of the ceramic dielectric
layer is 1.8 .mu.m, and the thickness of the conductor layer is 1.5
.mu.m. That is, the thickness of the ceramic dielectric layer is
about 1.2 times the thickness of the conductor layer.
[0003] Herein, generally, in a multilayer ceramic capacitor, there
are some cases where a capacitor with a high resistance to the
thermal shock is required. Furthermore, recently, a small-sized
multilayer ceramic capacitor with a large capacity has been
required. However, in some cases, a conventional multilayer ceramic
capacitor has not reached to have a sufficient thermal shock
resistance. Especially, when attempting to make a small-sized
capacitor with a large capacity by increasing the number of
laminated layers, in some cases, a sufficient thermal shock
resistance has not been obtained.
SUMMARY OF THE INVENTION
[0004] It is an object of the present invention to provide a
multilayer ceramic capacitor with an excellent thermal shock
resistance.
[0005] In order to attain this object, the present invention
proposes a multiplayer ceramic capacitor comprising a multilayer
body alternately laminating a conductor layer and a ceramic
dielectric layer, wherein the thickness of said ceramic dielectric
layer is not more than the thickness of said conductor layer.
[0006] In a multilayer ceramic capacitor, generally, the conductor
layer has a comparatively higher flexibility to the thermal shock
than the ceramic grain making up the ceramic dielectric layer.
Therefore, according to the present invention, the thickness of the
ceramic dielectric layer is not more than the thickness of the
conductor layer, and consequently, as a whole, the ratio of the
occupation of the conductor layer becomes large, and as a result of
this, the resistance to the thermal shock is improved.
[0007] Furthermore, the present invention proposes a multilayer
ceramic capacitor comprising a multilayer body alternately
laminating a conductor layer and a ceramic dielectric layer,
wherein said ceramic dielectric layer comprises ceramic grains and
a secondary phase existing between said ceramic grains, and
includes a part in which said ceramic grains do not exist between
said opposite conductor layers and which is made of only said
secondary phase.
[0008] In a multilayer ceramic capacitor, generally, the secondary
phase existing between the above described ceramic grains has a
comparatively higher flexibility to the thermal shock than the
ceramic grain making up the ceramic dielectric layer. Therefore,
according to the present invention, the part made of only the above
described secondary phase relieves the thermal shock, and
therefore, the thermal shock resistance is improved.
[0009] The object, constitution, and effect of the present
invention other than those in the above description will be clear
by the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a partially cut perspective view of a multilayer
ceramic capacitor;
[0011] FIG. 2 is an enlarged cross sectional view of the multilayer
ceramic capacitor;
[0012] FIG. 3 is a table showing the test result of a heat
resistance test;
[0013] FIG. 4 is an enlarged cross sectional view of the multilayer
ceramic capacitor; and
[0014] FIG. 5 is a table showing the test result of a heat
resistance test.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] (First Embodiment)
[0016] A multilayer ceramic capacitor according to the first
embodiment of the present invention will be described by referring
to drawings. FIG. 1 is a partially cut illustration of a multilayer
ceramic capacitor, and FIG. 2 is an enlarged cross sectional view
of the multilayer ceramic capacitor.
[0017] As shown in FIG. 1, this multilayer ceramic capacitor 10
comprises an approximately rectangular multilayer body 13 made by
alternately laminating a ceramic dielectric layer 11 and a
conductor layer 12, and external electrodes 14 formed at both ends
of the multilayer body 13 and connected to the above described
conductor layer 12. Here, the conductor layers 12 are alternately
connected to the external electrodes 14 at both ends. That is, one
external electrode 14 is connected to the conductor layer 12 every
other layer, and the other external electrode 14 is connected to
the conductor layer 12 that is not connected to the above described
one external electrode 14.
[0018] The ceramic dielectric layer 11 is made of a ceramic
sintered body having a strong dielectric, for example, of the
BaTiO.sub.3 family. Furthermore, the conductor layer 12 is made of
a metal material, for example, a noble metal such as Pd, Ag, or Au,
or a base metal such as Ni or Cu. The multilayer body 13 is formed
in a way where a plurality of ceramic green sheets on which
conductive paste is printed are laminated and these are sintered.
By this baking, the ceramic green sheets are sintered and the
ceramic dielectric layer 11 is formed. Furthermore, by this baking,
the conductive paste is sintered and the conductor layer 12 is
formed. The external electrode 14 is made of a metal material such
as Ni or Ag.
[0019] As shown in FIG. 2, this multilayer ceramic capacitor 10 is
characterized in that the thickness Dd of the ceramic dielectric
layer 11 is not more than the thickness De of the conductor layer
12. Concretely, the thickness Dd of the ceramic dielectric layer 11
is preferably about 70% to 100% of the thickness De of the
conductor layer 12, and more preferably about 85% to 100%. Here,
when comparing the ceramic dielectric layer 11 and the conductor
layer 12, the conductor layer 12 has a higher flexibility to the
thermal shock.
[0020] Herein, FIG. 2 shows a state where the conductor layer 12 is
broken, and this is the state where the thickness of the conductor
layer 12 becomes non-uniform because of the aggregation of the
metal grains included in the conductive paste forming the conductor
layer 12 and as a result, a part having no conductor is created.
That is, the thickness of the conductor layer 12 is formed to be
non-uniform. The part where the conductor layer 12 is broken is
filled with the secondary phase 15 included in the ceramic
dielectric layer 11.
[0021] Next, one example of the manufacturing method of this
multilayer ceramic capacitor will be described. First, a given
amount of organic binder, organic solvent, or water is mixed and
stirred in a dielectric ceramic material made by mixing BaTiO.sub.2
or the like as a main material and SiO.sub.2, rare earth oxide,
Mn.sub.3O.sub.4 or the like as an additional matter to obtain a
ceramic slurry. Next, this ceramic slurry is subjected to the tape
molding method such as the doctor blade method to form a ceramic
green sheet.
[0022] Next, on this ceramic green sheet, the conductive paste with
a given shape is printed by the screen printing method, the
intaglio printing method, the letterpress printing method or the
like. Here, the conductive paste is coated so that the thickness of
the conductor layer after the sintering may be thicker than that of
the ceramic dielectric layer.
[0023] Next, the ceramic green sheets where the conductive paste is
printed are laminated and pressed by using a press device to obtain
the ceramic multilayer body. Next, the ceramic multilayer body is
cut to have a size for a part unit to obtain a multilayer chip.
Next, this multiplayer chip is baked under a given heat condition
and atmospheric condition to obtain a sintered body. Finally,
external electrodes are formed at both ends of the sintered body by
the dip method or the like to obtain a multilayer ceramic
capacitor.
[0024] In this embodiment, a multilayer ceramic capacitor shown
below was prepared. The size of the external shape is 2.1
mm.times.1.25 mm.times.1.25 mm, and the dielectric constant of the
ceramic dielectric layer is 3800, and the average thickness of the
ceramic dielectric layer is 1.7 .mu.m, and the average thickness of
the conductor layer is 2.0 .mu.m and the number of the laminated
conductor layers is 300, and the electrostatic capacitance is 10
.mu.F, and the material of the conductor layer is Ni. The test of
the thermal shock resistance was applied to this multilayer ceramic
capacitor. It was performed by such a concrete method where the
multilayer ceramic capacitor was dipped in a dissolved solder
vessel for five seconds at 350.degree. C. and the creation of a
crack was observed by the eye. The result of this test is shown in
FIG. 3. The table of FIG. 3 shows the number of created cracks in
100 samples. From this table, it is known that the multilayer
ceramic capacitor 10 according to this embodiment has a better
thermal shock resistance than the above described conventional
multilayer ceramic capacitor.
[0025] Thus, in the multilayer ceramic capacitor 10 according to
this embodiment, the conductor layer 12 having a comparatively
higher flexibility to the thermal shock is formed to be thicker
than the ceramic dielectric layer 11, and therefore, as a whole, it
becomes excellent in thermal shock resistance. Especially, in the
case where each layer is thinned and the number of laminated layers
is increased to attain miniaturization and a large capacity, this
multilayer ceramic capacitor 10 has an excellent thermal shock
resistance.
[0026] (Second Embodiment)
[0027] A multilayer ceramic capacitor according to the second
embodiment of the present invention will be described by referring
to drawings. FIG. 4 is an enlarged cross sectional view of the
multilayer ceramic capacitor.
[0028] Similarly to the above described first embodiment, this
multilayer ceramic capacitor comprises an approximately rectangular
multilayer body made by alternately laminating a ceramic dielectric
layer 21 and a conductor layer 22, and external electrodes formed
at both ends of the multilayer body and connected to the above
described conductor layer 22. Here, the conductor layers 22 are
alternately connected to the external electrodes at both ends. That
is, one external electrode is connected to the conductor layer 22
every other layer, and the other external electrode is connected to
the conductor layer 22 that is not connected to the above described
one external electrode.
[0029] The ceramic dielectric layer 21 is made of a ceramic
sintered body having a strong dielectric, for example, of the
BaTiO.sub.3 family. Furthermore, the conductor layer 22 is made of
a metal material, for example, a noble metal such as Pd, Ag, or Au,
or a base metal such as Ni or Cu. The multilayer body is formed in
a way where a plurality of ceramic green sheets on which conductive
paste is printed are laminated and these are sintered. By this
baking, the ceramic green sheet is sintered and the ceramic
dielectric layer 21 is formed. Furthermore, by this baking, the
conductive paste is sintered and the conductor layer 22 is formed.
The external electrode is made of a metal material such as Ni or
Ag.
[0030] This multilayer ceramic capacitor is characterized by the
structure of the ceramic dielectric layer 21. Generally, the
ceramic dielectric layer comprises a ceramic grain and a secondary
phase existing between the above described ceramic grains. Here,
the secondary phase is an additional matter added together with the
raw material when baking the ceramic, or a reaction product of this
additional matter and the ceramic grain. This secondary phase has a
higher flexibility to the thermal shock than the ceramic grain.
Herein, the ceramic dielectric layer is generally in the state
where each ceramic grain is closely connected through the whole
area.
[0031] As shown in FIG. 4, the multilayer ceramic capacitor
according to this embodiment is characterized in that the ceramic
dielectric layer 21 includes a part 21a in which no ceramic grain
31 exists through the space between the opposite conductor layers
22 and which is made of only the secondary phase 32. Here, the size
of the part 21a made of only the secondary phase 32, that is, the
distance between the opposite ceramic grains is not less than the
thickness of the ceramic dielectric layer. Furthermore, it is
preferable for one ceramic dielectric layer 21 to include the part
21a made of only the secondary phase 32 of about 0% to 15%, and it
is more preferable to include the part 21a of about 0% to 5%.
Furthermore, the percentage of the ceramic dielectric layer 21
having the part 21a made of only the secondary phase 32 to the
total ceramic dielectric layer 21 is preferably about 10% to 90%,
and more preferably about 15% to 30%.
[0032] Herein, FIG. 4 shows a state where the conductor layer 22 is
broken, and this is the state where the thickness of the conductor
layer 22 becomes non-uniform because of the aggregation of the
metal grains included in the conductive paste forming the conductor
layer 22 and as a result, a part where no conductor is formed is
created. That is, the thickness of the conductor layer 22 is formed
to be non-uniform. The part where the conductor layer 22 is broken
is filled with the secondary phase 32 included in the ceramic
dielectric layer 21.
[0033] Next, one example of the manufacturing method of this
multilayer ceramic capacitor will be described. First, a given
amount of organic binder, organic solvent, or water is mixed and
stirred in a dielectric ceramic material to obtain a ceramic
slurry. Here, the dielectric ceramic material is made by mixing the
main material of the balium titanate family such as BaTiO.sub.3 and
the additional matter such as SiO.sub.2, rare earth oxide, or
Mn.sub.3O.sub.4. Part of this additional matter forms the secondary
phase at the time of baking to be described later. The percentage
of this additional matter to be mixed to the main material is
preferably about 1% to 10%, and more preferably about 3% to 7%.
Furthermore, the average grain diameter of the main material is
preferably 0.2 to 1.5 .mu.m, and more preferably 0.2 to 1.0
.mu.m.
[0034] Next, this ceramic slurry is subjected to the tape molding
method such as the doctor blade method and the ceramic green sheet
is formed. Next, on this ceramic green sheet, the conductive paste
with a given shape is printed by the screen printing method, the
intaglio printing method, the letterpress printing method or the
like. Next, the ceramic green sheets where the conductive paste is
printed are laminated and pressed by using the press device to
obtain the ceramic multilayer body.
[0035] Next, the ceramic multilayer body is cut to have a size for
a part unit to obtain a multilayer chip. Next, this multilayer chip
is baked under the given heat condition and atmospheric condition
to obtain a sintered body. Finally, external electrodes are formed
at both ends of the sintered body by the dip method or the like to
obtain a multilayer ceramic capacitor.
[0036] In this embodiment, a multilayer ceramic capacitor shown
below was prepared. The size of the external shape is 2.1
mm.times.1.25 mm.times.1.25 mm, and the dielectric constant of the
ceramic dielectric layer is 3800, and the average grain diameter of
the ceramic grain is 0.35 .mu.m, and the average thickness of the
ceramic dielectric layer is 1.7 .mu.m, and the average thickness of
the conductor layer is 1.7 .mu.m, and the number of the laminated
conductor layers is 320, and the electrostatic capacitance is 10.5
.mu.F, and the material of the conductor layer is Ni. The test of
the thermal shock resistance was applied to this multilayer ceramic
capacitor. The test was performed by such a concrete method where
the multilayer ceramic capacitor was dipped in a dissolved solder
vessel for five seconds at 350.degree. C., and the creation of a
crack was observed by the eye. The result of this test is shown in
FIG. 5. The table of FIG. 5 shows the number of created cracks in
100 samples. From this table, it is known that the multilayer
ceramic capacitor according to this embodiment has a better thermal
shock resistance than that of the above described conventional
multilayer ceramic capacitor.
[0037] In the multilayer ceramic capacitor according to this
embodiment, the ceramic dielectric body 21 includes a part 21a made
of only the secondary phase comparatively flexible to the thermal
shock, and therefore, as a whole, it is excellent in the thermal
shock resistance. That is, this part 21a made of only the secondary
phase works for relieving the stress. Especially, in the case where
each layer is thinned and the number of laminated layers is
increased to attain miniaturization and a large capacity, this
multilayer ceramic capacitor has an excellent thermal shock
resistance. Especially, when using a material including Si as an
additional matter, the secondary phase becomes glassy, and
therefore, it is preferable in view of the relief of the thermal
shock.
[0038] Herein, the embodiments according to the present invention
are illustrative and not limited. The scope of the present
invention is shown by the accompanying claims, and all the deformed
examples included in the meanings of those claims are included in
the present invention.
[0039] For example, in the above described respective embodiments,
as a material of the ceramic dielectric layer, a ceramic material
powder whose main material is BaTiO.sub.3 and whose additional
matter is SiO.sub.2, rare earth oxide, or Mn.sub.3O.sub.4 is shown
as an example, but the present invention is not limited to this. As
a main material, for example, it is also possible to use
BaTiO.sub.3, Bi.sub.4Ti.sub.3O.sub.12- , (Ba, Sr, Ca)TiO.sub.3,
(Ba, CA)(Zr, Ti) O.sub.3, (Ba, Sr, Ca)(Zr, Ti)0.sub.3, Ba(Ti,
Sn)O.sub.3. Furthermore, as an additional matter, for example, it
is also possible to use MgO, glass of the Li family, or glass of
the B family.
* * * * *