U.S. patent application number 09/751130 was filed with the patent office on 2001-06-28 for solid electrolytic capacitor and method of manufacturing the same.
Invention is credited to Kobatake, Yasuhiro, Nitta, Yukihiro, Saito, Kazuyo.
Application Number | 20010005305 09/751130 |
Document ID | / |
Family ID | 12476727 |
Filed Date | 2001-06-28 |
United States Patent
Application |
20010005305 |
Kind Code |
A1 |
Kobatake, Yasuhiro ; et
al. |
June 28, 2001 |
Solid electrolytic capacitor and method of manufacturing the
same
Abstract
A conductive high polymer layer as an electrolyte is formed on
the entire surface of fine pores of a dielectric oxide layer of an
anode electrode having an undulated surface of fine pores or the
like. As a result, a solid electrolytic capacitor having
characteristics such as capacitance, impedance, and leak current
exactly as designed will be obtained. It comprises a manganese
dioxide layer composed of a porous sinter of valve metal or
roughened meal foil, placed continuously on the entire surface of
the undulated surface of a dielectric oxide layer of an anode
electrode having an undulated surface, a conductive high polymer
layer formed by electrolytic polymerization, in contact with the
surface of the manganese dioxide layer, and a cathode electrode
placed on this conductive high polymer layer.
Inventors: |
Kobatake, Yasuhiro; (Osaka,
JP) ; Nitta, Yukihiro; (Kyoto, JP) ; Saito,
Kazuyo; (Osaka, JP) |
Correspondence
Address: |
Ratner & Prestia
PO Box 980
Valley Forge
PA
19482
US
|
Family ID: |
12476727 |
Appl. No.: |
09/751130 |
Filed: |
December 29, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09751130 |
Dec 29, 2000 |
|
|
|
09505602 |
Feb 16, 2000 |
|
|
|
Current U.S.
Class: |
361/502 ;
29/25.03 |
Current CPC
Class: |
H01G 11/48 20130101;
H01G 9/15 20130101; H01G 11/56 20130101; H01G 9/028 20130101; Y02E
60/13 20130101 |
Class at
Publication: |
361/502 ;
29/25.03 |
International
Class: |
H01G 009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 16, 1999 |
JP |
11-036686 |
Claims
What is claimed is:
1. A solid electrolytic capacitor comprising: (a) an anode
electrode having a first undulated surface, (b) a dielectric oxide
layer placed on a first undulated surface of said anode electrode,
said dielectric oxide layer having a second undulated surface
placed continuously coinciding with the shape of said first
undulated surface, (c) a manganese dioxide layer placed on said
second undulated surface of said dielectric oxide layer, said
manganese dioxide layer having a third undulated surface placed
continuously coinciding with the shape of said second undulated
surface, on said second undulated surface of said dielectric oxide
layer, (d) a conductive high polymer layer placed on said third
undulated surface of said manganese dioxide layer, said conductive
high polymer layer placed on said third undulated surface of said
manganese dioxide layer, and (e) a cathode layer placed above said
conductive high polymer layer.
2. The solid electrolytic capacitor of claim 1, wherein said first
undulated surface has a surface with a plurality of fine pores and
exposed portions.
3. The solid electrolytic capacitor of claim 1, wherein said anode
electrode having said first undulated surface has a porous sinter
of valve metal.
4. The solid electrolytic capacitor of claim 1, wherein said anode
electrode having said first undulated surface has a roughened metal
foil.
5. The solid electrolytic capacitor of claim 1, wherein said
conductive high polymer layer has a conductive high polymer layer
formed by electrolytic polymerization.
6. The solid electrolytic capacitor of claim 1, wherein said first
undulated surface has first fine pores and first exposed portions,
said second undulated surface has second fine pores and second
exposed portions, and said manganese dioxide layer is placed on an
entire surface of a surface of said second fine pores of said
dielectric oxide layer and a surface of said second exposed
portions thereof.
7. The solid electrolytic capacitor of claim 1, wherein said anode
electrode having said first undulated surface has at least one of
porous sinter of valve metal and roughened metal foil, said
conductive high polymer layer has a conductive high polymer layer
formed by electrolytic polymerization, and said manganese dioxide
layer is placed on the entire surface of said dielectric oxide
layer.
8. The solid electrolytic capacitor of claim 1, wherein said
manganese dioxide layer is placed in a range of about 5 ng to about
15 ng in 1 mm.sup.2 of said dielectric oxide layer.
9. The solid electrolytic capacitor of claim 1, wherein said
manganese dioxide layer is a layer formed by pyrolysis of aqueous
solution of manganese sulfate in a concentration range of about 6.5
wt. % to 26.5wt. %.
10. The solid electrolytic capacitor of claim 1, wherein said
manganese dioxide layer is placed in contact with the entire
surface of the concave and convex portions of said second undulated
surface.
11. The solid electrolytic capacitor of claim 1, wherein said
conductive high polymer layer is placed in contact with the entire
surface of the concave and convex portions of said third undulated
surface.
12. A manufacturing method of solid electrolytic capacitor
comprising the steps of: (a) supplying an anode electrode having a
first undulated surface, (b) forming a dielectric oxide layer on
said first undulated surface, said dielectric oxide layer having a
second undulated surface coinciding with said first undulated
surface, (c) forming a manganese dioxide layer on said second
undulated surface, said manganese dioxide layer having a third
undulated surface placed continuously coinciding with the shape of
said second undulated surface, on said second undulated surface,
(d) forming a conductive high polymer layer on said third undulated
surface, said conductive high polymer layer formed on said third
undulated surface of said manganese dioxide layer, and (e) forming
a cathode layer above said conductive high polymer layer.
13. The manufacturing method of solid electrolytic capacitor of
claim 12, wherein said first undulated surface has a plurality of
fine pores.
14. The manufacturing method of solid electrolytic capacitor of
claim 12, wherein said anode electrode having said first undulated
surface has a porous sinter of valve metal.
15. The manufacturing method of solid electrolytic capacitor of
claim 12, wherein said anode electrode having said first undulated
surface has a roughened metal foil.
16. The manufacturing method of solid electrolytic capacitor of
claim 12, wherein said step of forming the dielectric oxide layer
is a step of forming an oxide layer by forming treatment.
17. The manufacturing method of solid electrolytic capacitor of
claim 12, wherein said step of forming the manganese dioxide
includes a step of adhering an aqueous solution of manganese
nitrate on said second undulated surface of said dielectric oxide
layer, and a step of forming said manganese dioxide layer by
pyrolytic treatment of said aqueous solution of manganese
nitrate.
18. The manufacturing method of solid electrolytic capacitor of
claim 12, wherein said step of forming the manganese dioxide
includes a step of impregnating said anode electrode having said
dielectric oxide layer in an aqueous solution of manganese nitrate
in a concentration range of about 6.5 wt. % to 26.5 wt. %, a step
of taking out said anode electrode from said aqueous solution of
manganese nitrate, and a step of treating said aqueous solution of
manganese nitrate adhered to said anode electrode by pyrolysis.
19. The manufacturing method of solid electrolytic capacitor of
claim 12, wherein said step of forming the conductive high polymer
layer includes a step of forming said conductive high polymer on
said third undulated surface by passing current in said manganese
dioxide layer while placing said anode electrode having said
manganese dioxide layer in a solution containing monomer.
20. The manufacturing method of solid electrolytic capacitor of
claim 12, wherein said anode electrode having said first undulated
surface at least one of porous sinter of valve metal and roughened
metal foil, said step of forming the dielectric oxide layer
includes a step of forming an oxide film by forming treatment, said
step of forming the manganese dioxide includes a step of
impregnating said anode electrode having said dielectric oxide
layer in an aqueous solution of manganese nitrate in a
concentration range of about 6.5 wt. % to 26. 5 wt. %, and adhering
the aqueous solution of manganese nitrate to said second undulated
surface of said dialectic oxide layer, and a step of treating said
aqueous solution of manganese nitrate adhered to said anode
electrode by pyrolysis, and said step of forming said conductive
high polymer layer includes a step of forming said conductive high
polymer on said third undulated surface by passing current in said
manganese dioxide layer while placing said anode electrode having
said manganese dioxide layer in a solution containing monomer.
21. The manufacturing method of solid electrolytic capacitor of
claim 12, wherein said step of forming the manganese dioxide layer
includes a step of impregnating said anode electrode having said
dielectric oxide layer in an aqueous solution of manganese nitrate
in a temperature range of about 10.degree. C. to about 40.degree.
C.
22. The manufacturing method of solid electrolytic capacitor of
claim 12, wherein said first undulated surface of said anode
electrode has first fine pores, said second undulated surface of
said dielectric oxide layer has second fine pores coinciding with
the shape of said first fine pores, and said step of forming the
manganese dioxide layer includes a step of impregnating said anode
electrode in an aqueous solution of manganese nitrate until said
aqueous solution of manganese nitrate permeates into the inner
surface of said second fine pores.
23. The manufacturing method of solid electrolytic capacitor of
claim 12, wherein said step of forming the manganese dioxide layer
includes a step of adhering an aqueous solution of manganese
nitrate on said second undulated surface of said dielectric oxide
layer, a step of removing excess portion of said aqueous solution
of manganese nitrate adhered on said anode electrode, and a step of
treating said aqueous solution of manganese nitrate by
pyrolysis.
24. The manufacturing method of solid electrolytic capacitor of
claim 12, wherein said step of forming the manganese dioxide layer
includes a step of adhering an aqueous solution of manganese
nitrate on said second undulated surface of said dielectric oxide
layer, and a step of treating said aqueous solution of manganese
nitrate adhered on said second undulated surface by pyrolysis in a
moist atmosphere.
25. The manufacturing method of solid electrolytic capacitor of
claim 12, wherein said step of forming the manganese dioxide layer
includes a step of adhering an aqueous solution of manganese
nitrate on said second undulated surface of said dielectric oxide
layer, and a step of treating said aqueous solution of manganese
nitrate adhered on said second undulated surface by pyrolysis in an
atmosphere containing steam by 85.+-.10 vol. %.
26. The manufacturing method of solid electrolytic capacitor of
claim 12, wherein said step of forming the manganese dioxide layer
includes a step of immersing said anode electrode having said
dielectric oxide layer in an aqueous solution of manganese nitrate,
a step of taking out said anode electrode from said aqueous
solution of manganese nitrate, and adhering said aqueous solution
of manganese nitrate to said second undulated surface of said
dielectric oxide layer, and a step of heating said anode electrode
having said aqueous solution of manganese nitrate up to pyrolysis
treatment temperature within a minute, and holding said pyrolysis
treatment temperature for three minutes or more.
27. The manufacturing method of solid electrolytic capacitor of
claim 26, wherein said pyrolysis treatment temperature is
300.+-.10.degree. C.
28. The manufacturing method of solid electrolytic capacitor of
claim 12, wherein said step (c) includes a step of forming a
manganese dioxide layer in contact with the entire surface of
concave and convex portions of said second undulated surface.
29. The manufacturing method of solid electrolytic capacitor of
claim 12, wherein said step (d) includes a step of forming a
conductive high polymer layer in contact with the entire surface of
concave and convex portions of said second undulated surface.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention relates to a solid electrolytic
capacitor using a conductive high polymer in the electrolyte used
in various electronic appliances, and a method of manufacturing the
same.
BACKGROUND OF THE INVENTION
[0002] Owing to the advancement in digital appliances, recently,
capacitors having a low impedance and an excellent high frequency
characteristic even in a high frequency region are strongly
demanded. To meet such market needs, capacitors using conductive
high polymers obtained by polymerizing pyrrole, thiophene or
aniline as the electrolyte are being developed and commercially
produced.
[0003] Hitherto, a solid electrolytic capacitor of this kind
comprises, as disclosed in Japanese Laid-open Patent No. 63-158829,
an anode electrode made of a valve metal having a dielectric oxide
layer, the dielectric oxide layer formed on this anode electrode, a
conductive high polymer layer formed by pyrolysis of manganese
dioxide layer on this dielectric oxide layer, and a cathode
electrode placed on this conductive high polymer layer. The
conductive high polymer layer is formed by electrolytic process in
an electrolytic polymerization solution using manganese dioxide
layer as the anode.
[0004] Formation of conductive high polymer layer by this
electrolytic polymerization is quick in forming a conductive high
polymer layer as compared with chemical polymerization or vapor
phase polymerization, and it requires a relatively simple
equipment, and hence it is said to be beneficial for industrial
production.
[0005] In the prior art, however, the forming condition of
manganese dioxide layer has great effects on the principal
characteristics of the solid electrolytic capacitor such as
capacitance, tan .delta. and impedance.
[0006] That is, when the anode electrode is formed by a method of
bonding particles of valve metal into a porous substance by
sintering, or a method of multiple etching pits by etching process,
such anode electrode has an undulated surface of an expanded
surface area of fine pores or the like. The dielectric oxide layer
formed on the surface of the anode electrode having fine pores has
multiple fine pores and exposed portions reaching the inner depth.
In the prior art, the manganese dioxide layer formed on this
dielectric oxide layer is formed only on the exposed portions, and
not formed in the inner parts of the fine pores. The conductive
high polymer layer is formed only on this manganese dioxide layer.
That is, in such conventional solid electrolytic capacitor, it was
possible to have a cavity in the inside. In such conventional
constitution, when the anode electrode has an expanded undulated
surface, sufficient capacitance and sufficient impedance
corresponding to the expanded undulated surface could not be
obtained. Thus, there were serious problems also in the
constitution of using conductive high polymer as the
electrolyte.
[0007] It is hence an object of the invention to present a solid
electrolytic capacitor exhibiting a desired effect sufficiently, in
the solid electrolytic capacitor using an anode electrode having an
undulated surface and a conductive high polymer as electrolyte, and
a method of manufacturing the same.
SUMMARY OF THE INVENTION
[0008] The solid electrolytic capacitor of the invention
comprises:
[0009] (a) an anode electrode having a first undulated surface,
[0010] (b) a dielectric oxide layer placed on a first undulated
surface of the anode electrode, in which the dielectric oxide layer
includes a second undulated surface placed continuously coinciding
with the shape of the first undulated surface,
[0011] (c) a manganese dioxide layer placed on the second undulated
surface of the dielectric oxide layer, in which the manganese
dioxide layer includes a continuous third undulated surface, placed
coinciding with the shape of the second undulated surface, on the
second undulated surface of the dielectric oxide layer,
[0012] (d) a conductive high polymer layer placed on the third
undulated surface of the manganese dioxide layer, in which the
conductive high polymer layer is placed on the third undulated
surface of the manganese dioxide layer, and
[0013] (e) a cathode layer placed above the conductive high polymer
layer.
[0014] The manufacturing method of solid electrolytic capacitor of
the invention comprises:
[0015] (a) a step of supplying an anode electrode having a first
undulated surface,
[0016] (b) a step of forming a dielectric oxide layer on the first
undulated surface, in which the dielectric oxide layer includes a
second undulated surface coinciding with the first undulated
surface,
[0017] (c) a step of forming a manganese dioxide layer on the
second undulated surface, in which the manganese dioxide layer
includes a continuous third undulated surface, placed coinciding
with the shape of the second undulated surface, on the second
undulated surface,
[0018] (d) a step of forming a conductive high polymer layer on the
third undulated surface, in which the conductive high polymer layer
is formed on the third undulated surface of the manganese dioxide
layer, and
[0019] (e) a step of forming a cathode layer above the conductive
high polymer layer.
[0020] Preferably, the manganese dioxide layer is placed in contact
with the entire surface of concave and convex portions of the
second undulated surface.
[0021] Preferably, the conductive high polymer layer is placed in
contact with the entire surface of concave and convex portions of
the third undulated surface.
[0022] Preferably, the first undulated surface has a surface with a
plurality of fine pores and exposed portions.
[0023] Preferably, the anode electrode having the first undulated
surface has a porous sinter of valve metal or a roughened metal
foil.
[0024] Preferably, the conductive high polymer layer has a
conductive high polymer layer formed by electrolytic
polymerization.
[0025] Preferably, it also includes a step of impregnating the
manganese dioxide layer sufficiently in a 6.5 wt. % to 26.5 wt. %
aqueous solution of manganese nitrate at 10.degree. C. to
40.degree. C. sufficiently, and lifting, and a subsequent step of
removing the excess portion of aqueous solution of manganese
nitrate adhered to the surface and a step of heating to more than
80% of pyrolysis temperature within a minute and performing
pyrolysis for three minutes or more at 300.+-.10.degree. C.
[0026] In this constitution and manufacturing method, a manganese
dioxide layer can be formed on the entire surface of the undulated
surface of the oxide film without damaging the dielectric oxide
film of the anode electrode having fine pores or undulated surface.
Accordingly, the conductive high polymer layer by electrolytic
polymerization is formed securely from the inner surface of fine
pores to the outer surface. As a result, a capacitor having the
capacitance, impedance, leak current and other characteristics
exactly as designed is obtained.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a sectional view showing principal parts of a
solid electrolytic capacitor in an embodiment of the invention.
[0028] FIG. 2 is a sectional view showing principal parts of a
solid electrolytic capacitor in a comparative example of the
invention.
[0029] FIG. 3 is a sectional view showing principal parts of a
solid electrolytic capacitor in other comparative example of the
invention.
[0030] FIG. 4 shows the process of manufacturing method of solid
electrolytic capacitor in the embodiment of the invention.
[0031] Reference Numerals
[0032] 1 Aluminum metal foil
[0033] 2 Undulated surface
[0034] 2a Fine pore
[0035] 2b Exposed portion
[0036] 3 Dielectric oxide film
[0037] 4 Manganese dioxide layer
[0038] 5 Conductive high polymer layer
[0039] 6 Cathode layer
DETAILED DESCRIPTION OF THE INVENTION
[0040] A solid electrolytic capacitor in an embodiment of the
invention comprises
[0041] an anode electrode having a first undulated surface of
porous sinter of valve metal or roughened metal foil,
[0042] a dielectric oxide layer having a second undulated surface
placed on the first undulated surface of the anode electrode,
[0043] a manganese dioxide layer having a third undulated surface
placed on the second undulated surface of the dielectric oxide
layer,
[0044] a conductive high polymer layer formed by electrolytic
polymerization in contact with the third undulated surface of the
manganese dioxide layer, and
[0045] a cathode electrode placed on this conductive high polymer
layer. The conductive high polymer layer has a function as an
electrolyte.
[0046] The first undulated surface of the anode electrode has a
widened surface having fine pores and exposed portions. The
dielectric oxide film also has the second undulated surface placed
on the first undulated surface without gap. The manganese dioxide
layer further has the third undulated surface placed on the second
undulated surface without gap. Moreover, the conductive high
polymer layer is placed on the third undulated surface without gap.
In this constitution, the all surface region including the fine
pores of the expanded first undulated surface of the anode
electrode acts effectively for the capacitor characteristics, and,
as a result, the solid electrolytic capacitor having the
characteristics exactly as designed, such as the capacitance,
impedance and leak current, will be obtained.
[0047] Preferably, the manganese dioxide layer is contained by 5 to
15 ng per unit surface area 1 mm.sup.2 of the dielectric layer.
Herein, "ng" stands for nanogram, and 1 ng is equal to 10.sup.-9 g.
If the content of the manganese dioxide layer is small than this
range, the manganese dioxide layer may not be formed in the entire
surface. If the content of the manganese dioxide layer is more than
this range, the manganese dioxide layer may be formed excessively
so as to plug the openings of fine pores. Therefore, by containing
the manganese dioxide layer in a range of 5 to 15 ng per unit
surface area 1 mm.sup.2 of the dielectric layer, the capacitor
having the characteristics exactly as designed will be
realized.
[0048] Preferably, the manganese dioxide layer is formed by
pyrolysis of aqueous solution of manganese nitrate at concentration
of 6.5 to 26.5 wt. %. In this range of concentration, the aqueous
solution of manganese nitrate permeates deeply into the fine pores,
and the manganese dioxide layer is formed on the entire surface of
the dielectric oxide layer.
[0049] A manufacturing method of solid electrolytic capacitor in
the embodiment of the invention includes:
[0050] a step of supplying an anode electrode having a first
undulated surface of a porous sinter of valve metal or roughened
metal foil,
[0051] a step of forming a dielectric oxide layer having a second
undulated surface of a continuous shape coinciding with the shape
of the first undulated surface, on the first undulated surface, by
forming treatment of the anode electrode having the first undulated
surface,
[0052] a step of forming a manganese dioxide layer having a third
undulated surface of a continuous shape on the second undulated
surface of the dielectric oxide layer by pyrolysis treatment, by
impregnating the formed dielectric oxide layer in an aqueous
solution of manganese nitrate at concentration of 6.5 to 26.5 wt.
%.
[0053] a step of forming a conductive high polymer layer on the
third undulated surface of the manganese dioxide layer by passing
current in the manganese dioxide layer in an electrolytic
polymerization solution, and
[0054] a step of forming a cathode electrode on the conductive high
polymer layer.
[0055] In this method, too, all the surface region including fine
pores of the expanded first undulated surface of the anode
electrode acts effectively for the capacitor characteristics, and,
as a result, the solid electrolytic capacitor having the
characteristics exactly as designed, such as the capacitance,
impedance and leak current, will be obtained. Moreover, the
conductive high polymer layer corresponding to the entire surface
including the fine pores of the anode electrode can be formed. As a
result, the solid electrolytic capacitor having excellent
characteristics will be obtained.
[0056] Preferably, the aqueous solution of manganese nitrate
permeates into the anode electrode in a temperature range of 10 to
40.degree. C. In this range, the aqueous solution of manganese
nitrate permeates in a short time, and breakage of the dielectric
oxide layer is prevented.
[0057] Preferably, impregnation of the aqueous solution of
manganese nitrate continues until sufficiently permeating into the
fine pores of the anode electrode. By this method, the manganese
dioxide layer is formed on the entire surface of the anode
electrode.
[0058] Preferably, after impregnation of the aqueous solution of
manganese nitrate into the anode electrode, the excess portion of
the aqueous solution of manganese nitrate adhered to the surface of
the anode electrode is removed. By this method, plugging of the
openings of the fine pores is prevented when forming the manganese
dioxide layer.
[0059] Preferably, the pyrolysis treatment is performed at high
humidity. By this method, a dense manganese dioxide layer is
formed. As a result, the capacitor characteristics are
enhanced.
[0060] Preferably, the pyrolysis treatment is performed in a state
of high humidity with the steam content of 85.+-.10 vol. %. By this
method, a dense manganese dioxide layer is formed. As a result, the
capacitor characteristics are enhanced.
[0061] Preferably, in the pyrolysis treatment, by heating up to 80%
of the pyrolysis temperature in a minute, the pyrolysis temperature
is held for at least three minutes. By this method, the dense
manganese dioxide layer is formed securely into the inner parts of
the fine pores.
[0062] Preferably, the pyrolysis temperature of the pyrolysis
treatment is 300.+-.10.degree. C. By this method, a dense manganese
dioxide layer is formed securely.
[0063] A specific embodiment of the invention is described below
while referring to the drawings.
[0064] The constitution of the solid electrolytic capacitor in the
embodiment of the invention is described while referring to FIG. 1
to FIG. 4. As an embodiment of the anode electrode, a solid
electrolytic capacitor using an aluminum metal foil roughened by
etching is explained below.
[0065] FIG. 1 is a magnified sectional view of principal parts of
the solid electrolytic capacitor in the embodiment of the
invention. In FIG. 1, an aluminum metal foil 1 as an anode
electrode includes a first undulated surface 2 having multiple fine
pores 2a and exposed portions 2b formed by etching. A dielectric
oxide layer 3 formed by forming treatment is placed on the entire
surface of the first undulated surface 2 of the aluminum metal foil
1. This dielectric oxide layer 3 has a second undulated surface
coinciding with the shape of the first undulated surface. A thin
manganese dioxide layer 4 is formed on the entire surface of the
second undulated surface of the dielectric oxide layer 3 (that is,
the entire surface including the dielectric oxide layer 3 formed in
the fine pores 2a). The manganese dioxide layer has a third
undulated surface coinciding with the shape of the second undulated
surface. The manganese dioxide layer has a manganese dioxide layer
of a continuous shape, formed on the second undulated surface. A
conductive high polymer layer 5 of polypyrrole, polythiophene, or
polyaniline is formed on the third undulated surface of the
manganese dioxide layer 4 by electrolytic polymerization method or
the like. Further, a cathode electrode 6 of carbon paste layer or
silver paste layer is placed on this conductive high polymer layer
5.
[0066] Preferably, the manganese dioxide layer is uniformly placed
on the entire surface of concave and convex portions of the second
undulated surface, and more preferably placed in contact without
gap.
[0067] The conductive high polymer layer is uniformly placed on the
entire surface of concave and convex portions of the third
undulated surface, and more preferably placed in contact without
gap.
[0068] The manganese dioxide layer 4 of the embodiment is formed by
a weight of 5 to 15 ng per unit surface area 1 mm.sup.2 of the
dielectric oxide layer 3. If the weight of the manganese dioxide
layer 4 is less than 5 ng/1 mm.sup.2, as shown in FIG. 2, the
manganese dioxide layer 4 may not be formed uniformly on the entire
surface of the second undulated surface of the dielectric oxide
layer 3, and, for example, the manganese dioxide layer 4 may be
formed in an insular shape 4a. Accordingly, there is a portion 5a
not forming the conductive high polymer layer 5, and the desired
capacitance or impedance may not be obtained.
[0069] Or if the weight of the manganese dioxide layer 4 is more
than 15 ng/1 mm.sup.2, as shown in FIG. 3, plugging portions 4b may
be formed in the manganese dioxide layer 4 to plug the openings of
the fine pores 2. As a result, there are gaps 5c not forming the
conductive high polymer layer 5, and the desired characteristics
may not be obtained.
[0070] Therefore, as the condition of forming the manganese dioxide
layer 4 completely also on the surface of the dielectric oxide
layer 3 positioned inside of the fine pores 2a, what is important
is the concentration of aqueous solution of manganese nitrate for
forming the manganese dioxide layer 4. The concentration of aqueous
solution of manganese nitrate is preferred to be in a range of
about 6.5 to about 26.5 wt. %. When the concentration of aqueous
solution of manganese nitrate is less than about 6.5 wt. %, the
manganese dioxide layer 4 cannot be formed on the surface of the
dielectric oxide layer 3 uniformly by a small number of times of
pyrolysis treatment. When the concentration of aqueous solution of
manganese nitrate is more than about 26.5 wt. %, the viscosity of
the aqueous solution of manganese nitrate is too high, and the
aqueous solution of manganese nitrate cannot permeate sufficiently
into the fine pores 2. As a result, the manganese dioxide layer 4
is not formed uniformly on the surface of the dielectric oxide
layer 3. That is, in order to form the manganese dioxide layer 4
uniformly on the surface of the dielectric oxide layer 3, it is
preferred to use the aqueous solution of manganese nitrate at a
concentration in a range of about 6.5 wt. % to 26.5 wt. %.
[0071] In the step of forming the manganese dioxide layer, it is
preferred to treat the aqueous solution of manganese nitrate
adhered to the surface of the dielectric oxide layer by pyrolysis
in an atmosphere of high humidity, or an atmosphere containing
85.+-.10 vol. % of steam. If having the manganese dioxide layer
formed at humidity out of this humidity range, the characteristics
of the solid electrolytic capacitor are slightly inferior.
[0072] Typical embodiments are described below, but it must be
noted that the invention is not limited to these embodiments
alone.
[0073] Embodiment 1
[0074] The process of manufacturing method of the solid
electrolytic capacitor in the embodiment of the invention is shown
in FIG. 4. A roughened aluminum metal foil is prepared. The
aluminum metal foil has an undulated surface 2 having multiple fine
pores 2a and exposed portions 2b formed by etching process so that
the surface area may be about 125 times. That is, the aluminum
metal foil has a roughened surface. In part of the surface of the
aluminum metal foil, an electric insulating resist tape was glued,
and the cathode electrode and anode electrode were separated. Thus,
an anode electrode 1 having an effective area of 3.2 mm.times.3.9
mm was fabricated. This anode electrode 1 was immersed in an
aqueous solution of ammonium dihydrogenphosphate at concentration
of 0.3 wt. % at liquid temperature of 70.degree. C., and a
direct-current voltage of 12 V was applied for 20 minutes. Thus, a
dielectric oxide layer 3 was formed on the surface of the aluminum
metal foil.
[0075] In succession, the anode electrode 1 having the dielectric
oxide layer 3 was immersed in an aqueous solution of manganese
nitrate at concentration of 20 wt. % at liquid temperature of
25.degree. C. for 3 seconds, and was lifted from the aqueous
solution. Then, the excess portion of the aqueous solution of
manganese nitrate adhered to the surface of the dielectric oxide
layer 3 of the anode electrode 1 was removed by blowing out with
air. Then, within one minute after lifting the anode electrode 1
adhered with the aqueous solution of manganese nitrate on the
surface of the dielectric oxide layer 3 from the aqueous solution,
it was heated to over 250.degree. C., and treated by pyrolysis at
300.degree. C. for five minutes. Thus, the manganese dioxide layer
4 was formed on the surface of the dielectric oxide layer 3 of the
anode electrode 1. The pyrolysis was treated in the atmosphere
containing about 85.+-.10 vol. % of steam.
[0076] Then, the anode electrode 1 having the manganese dioxide
layer 4 was immersed in an aqueous solution of ammonium
dihydrogenphosphate at concentration of 0.3 wt. % at liquid
temperature of 70.degree. C., and a direct-current voltage of 10 V
was applied for 10 minutes. Thus, the anode electrode having the
manganese dioxide layer 4 was re-formed. On the manganese dioxide
layer, a conductive high polymer layer 5 made of polypyrrole film
was formed by electrolytic polymerization method. On the conductive
high polymer layer 5, further, carbon paste and silver paste were
applied sequentially, and a cathode electrode 6 was formed.
Terminals were placed in the device having thus formed anode
electrode 1, dielectric oxide layer 3, manganese dioxide layer 4,
and conductive high polymer layer 5. By resin molding of the outer
surface of the device, the casing was formed. Thus, the solid
electrolytic capacitor was manufactured.
[0077] Embodiment 2
[0078] In the foregoing embodiment 1, an aqueous solution of
manganese nitrate having a concentration of 25 wt. % was used. A
solid electrolytic capacitor was prepared in the same manner as in
embodiment 1 except for this method.
[0079] Embodiment 3
[0080] In the foregoing embodiment 1, an aqueous solution of
manganese nitrate having a concentration of 35 wt. % was used. A
solid electrolytic capacitor was prepared in the same manner as in
embodiment 1 except for this method.
[0081] Embodiment 4
[0082] The temperature of the aqueous solution of manganese nitrate
is 50.degree. C. A solid electrolytic capacitor was prepared in the
same manner as in embodiment 1 except for this method.
[0083] Embodiment 5
[0084] In the foregoing embodiment 1, the time of immersing the
anode electrode in the aqueous solution of manganese nitrate was
0.5 sec. A solid electrolytic capacitor was prepared in the same
manner as in embodiment 1 except for this method.
[0085] Embodiment 6
[0086] In the foregoing embodiment 1, the excess aqueous solution
of manganese nitrate was pyrolyzed without blowing away. A solid
electrolytic capacitor was prepared in the same manner as in
embodiment 1 except for this method.
[0087] Embodiment 7
[0088] In the foregoing embodiment 1, the pyrolysis was performed
without applying humidity in the process of pyrolysis. A solid
electrolytic capacitor was prepared in the same manner as in
embodiment 1 except for this method.
[0089] Embodiment 8
[0090] In the foregoing embodiment 1, the humidity in pyrolysis
process was adjusted to 50% RH. A solid electrolytic capacitor was
prepared in the same manner as in embodiment 1 except for this
method.
[0091] Embodiment 9
[0092] In the foregoing embodiment 1, the time required for heating
up to 250.degree. C. was more than three minutes after lifting the
anode electrode from the aqueous solution, and the holding time at
300.degree. C. was one minute. A solid electrolytic capacitor was
prepared in the same manner as in embodiment 1 except for this
method.
[0093] Embodiment 10
[0094] In the foregoing embodiment 1, the pyrolysis temperature was
250.degree. C. A solid electrolytic capacitor was prepared in the
same manner as in embodiment 1 except for this method.
[0095] Using various solid electrolytic capacitors fabricated in
these manners, initial characteristics were measured. Results are
summarized in Table 1. The measuring temperature was 25 to
30.degree. C. The capacitance and tan .delta. was measured at 120
Hz, and the impedance was measured at 400 kHz. To measure the leak
current, after applying direct-current voltage of 6.3 V, the
current was measured 30 seconds later. In each one of these samples
of the embodiments, 30 capacitors were used, and the average of 30
pieces is shown in Table 1. In the samples of embodiments 1 to 3,
the solid electrolytic capacitors were completely dissolved, and
the deposit amount of manganese dioxide was measured by atomic
absorption method.
1 TABLE 1 Deposit amount Capaci- Leak of manganese tance tan
.delta. Impedance current dioxide (.mu.F) (%) (m.OMEGA.) (nA)
(ng/mm.sup.2) Embodiment 1 10.35 0.9 48 25 11.7 Embodiment 2 11.05
0.8 45 28 14.1 Embodiment 3 8.63 1.7 102 30 21.5 Embodiment 4 10.42
0.9 53 236 -- Embodiment 5 7.54 2.3 113 60 -- Embodiment 6 9.20 1.8
107 32 -- Embodiment 7 9.21 1.2 80 354 -- Embodiment 8 9.59 1.1 74
267 -- Embodiment 9 8.59 1.1 95 53 -- Embodiment 10 8.27 0.8 88 42
--
[0096] As clear from Table 1, in the solid electrolytic capacitors
manufactured by the manufacturing methods of embodiments 1 and 2,
without damaging the dielectric oxide layer of the anode electrode
having fine pores, the manganese dioxide layer was formed uniformly
on the entire surface off the second undulated surface including
the fine pores and exposed portions of the dielectric oxide layer.
Accordingly, the conductive high polymer layer in the subsequent
step of electrolytic polymerization was securely formed on the
entire surface of the inner surfaces of fine pores and exposed
portion surfaces of the third undulated surface. All
characteristics of capacitance, tan .delta., impedance and leak
current satisfied the desired values. By contrast, as shown in
embodiments 3 to 10, the capacitors manufactured in the methods of
high concentration condition of aqueous solution of manganese
nitrate, high temperature condition, short immersion time
condition, condition without removal of excessive adhered portion,
insufficient condition of humidity in pyrolysis process, long
heating time condition to pyrolysis temperature, or low pyrolysis
temperature condition were inferior in some of the characteristics
of capacitance, tan .delta., impedance and leak current as compared
with the capacitors manufactured in the conditions of embodiments 1
and 2.
[0097] Thus, according to the method of the invention, without
damaging the dielectric oxide layer of the anode electrode having
the undulated surface of fine pores and the like, a manganese
dioxide layer continuous to the undulated surface can be formed on
the entire surface of undulated surface including the inner surface
of fine pores and exposed portion surfaces. Gaps in the undulated
surface are decreased significantly. Accordingly, the conductive
high polymer layer by electrolytic polymerization can be formed
securely on the entire surface from the inner surfaces of fine
pores to the outer surfaces. Therefore, the solid electrolytic
capacitor having excellent characteristics in all characteristics
including capacitance, impedance and leak current can be
obtained.
* * * * *