U.S. patent application number 09/899992 was filed with the patent office on 2002-02-21 for solid electrolytic capacitor element and method for producing the same.
This patent application is currently assigned to SHOWA DENKO K.K.. Invention is credited to Furuta, Yuji, Ichimura, Takashi, Sakai, Atsushi, Yamazaki, Katsuhiko.
Application Number | 20020021547 09/899992 |
Document ID | / |
Family ID | 27343990 |
Filed Date | 2002-02-21 |
United States Patent
Application |
20020021547 |
Kind Code |
A1 |
Sakai, Atsushi ; et
al. |
February 21, 2002 |
Solid electrolytic capacitor element and method for producing the
same
Abstract
The present invention provides a solid electrolytic capacitor
having a structure that relieves thermal stress, prevents leakage
current, exhibits low impedance and ensures high reliability. The
solid electrolytic capacitor element has a valve-acting metal
substrate with a dielectric film and an edge part acting as an
anode, an insulating layer circumferentially provided on the
substrate, a solid electrolyte layer and an electrically conducting
layer having a carbon paste layer and a metal powder-containing
electrically conducting layer formed in this order on the entire
substrate surface opposite to the anode with respect to the
insulating layer and acting as a cathode. The electrically
conducting layer is provided within a region of the carbon paste
layer or with a spacing from the cathode side edge part of the
insulating layer. The present invention also provides a method for
producing the element, and a solid electrolytic capacitor using the
element.
Inventors: |
Sakai, Atsushi; (Nagano,
JP) ; Furuta, Yuji; (Nagano, JP) ; Yamazaki,
Katsuhiko; (Nagano, JP) ; Ichimura, Takashi;
(Nagano, JP) |
Correspondence
Address: |
SUGHRUE, MION, ZINN, MACPEAK & SEAS, PLLC
2100 Pennsylvania Avenue, N.W.
Washington
DC
20037-3213
US
|
Assignee: |
SHOWA DENKO K.K.
|
Family ID: |
27343990 |
Appl. No.: |
09/899992 |
Filed: |
July 9, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60245574 |
Nov 6, 2000 |
|
|
|
Current U.S.
Class: |
361/532 |
Current CPC
Class: |
H01G 9/028 20130101;
H01G 9/0425 20130101; H01G 9/15 20130101 |
Class at
Publication: |
361/532 |
International
Class: |
H01G 009/04; H01G
009/145 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 7, 2000 |
JP |
P2000-207172 |
Claims
What is claimed is:
1. A solid electrolytic capacitor element comprising (1) a
valve-acting metal substrate having on a surface thereof a
dielectric film with an edge part acting as an anode, (2) an
insulating layer circumferentially provided on said valve-acting
metal substrate, (3) a solid electrolyte layer and (4) an
electrically conducting layer comprising a carbon paste layer and a
metal powder-containing electrically conducting layer, said solid
electrolyte layer and said electrically conducting layer being
formed in this order on an entire surface of the substrate on a
side opposite said anode with respect to the insulating layer and
acting as a cathode part, wherein said metal powder-containing
electrically conducting layer is provided within a region of the
carbon paste layer, such that said metal powder-containing
electrically conducting layer does not contact the insulating
layer.
2. A solid electrolytic capacitor element comprising (1) a
valve-acting metal substrate having on a surface thereof a
dielectric film with an edge part acting as an anode, (2) an
insulating layer circumferentially provided on said valve-acting
metal substrate, (3) a solid electrolyte layer and (4) an
electrically conducting layer comprising a carbon paste layer and a
metal powder-containing electrically conducting layer, said solid
electrolyte layer and said electrically conducting layer being
formed in this order on an entire surface of the substrate on a
side opposite said anode with respect to the insulating layer and
acting as a cathode part, wherein said metal powder-containing
electrically conducting layer is provided with a spacing from a
cathode side edge part of said insulating layer.
3. The solid electrolytic capacitor element as claimed in claim 2,
wherein the spacing between said metal powder-containing
electrically conducting layer and the cathode side edge part of
said insulating layer is about {fraction (1/10)} or more but less
than 1/2 of the entire length of said cathode part.
4. The solid electrolytic capacitor element as claimed in claim 2,
wherein the spacing between said metal powder-containing
electrically conducting layer and the cathode side edge part of
said insulating layer is from about 0.1 to about 1.5 mm.
5. The solid electrolytic capacitor element as claimed in claim 1,
wherein said metal powder-containing electrically conducting layer
comprises an electrically conducting filler comprising metal
powder, and a fluororubber as a main component of a binder.
6. The solid electrolytic capacitor element as claimed in claim 5,
wherein about 80% by mass or more of the binder is
fluororubber.
7. The solid electrolytic capacitor element as claimed in claim 5,
wherein about 80% by mass or more of the electrically conducting
filler is silver powder.
8. The solid electrolytic capacitor element as claimed in claim 5,
wherein said metal powder-containing electrically conducting layer
comprises from about 80 to about 95% by mass of the electrically
conducting filler and from about 5 to about 50% by mass of the
binder.
9. The solid electrolytic capacitor element as claimed in claim 1,
wherein the carbon paste layer comprises an electrically conducting
carbon material, a binder and a solvent as main components, about
80% by mass or more of said electrically conducting carbon material
is an artificial graphite, and said binder comprises a material
having rubber elasticity.
10. The solid electrolytic capacitor element as claimed in claim 1,
wherein the valve-acting metal has a plate or foil shape.
11. The solid electrolytic capacitor element as claimed in claim 1,
wherein the valve-acting metal is an elemental metal selected from
the group consisting of aluminum, tantalum, niobium and titanium,
or the valve-acting metal is an alloy of said elemental metal.
12. The solid electrolytic capacitor element as claimed in claim 1,
wherein the solid electrolyte layer comprises an electrically
conducting polymer layer.
13. The solid electrolytic capacitor element as claimed in claim
12, wherein the electrically conducting polymer layer comprises a
polymer of a 5-member heterocyclic ring-containing compound.
14. The solid electrolytic capacitor element as claimed in claim
13, wherein the 5-member heterocyclic ring-containing compound
comprises a structure of bivalent thiophene skeleton.
15. The solid electrolytic capacitor element as claimed in claim
12, wherein the electrically conducting polymer layer comprises
poly(3,4-ethylenedioxythiophene).
16. The solid electrolytic capacitor element as claimed in claim 3,
wherein the spacing between said metal powder-containing
electrically conducting layer and the cathode side edge part of
said insulating layer is from about 0.1 to about 1.5 mm.
17. A solid electrolytic capacitor obtainable by placing at least
one capacitor element as claimed in any one of claims 1 to 16 on a
lead frame and joining these.
18. A method for producing a solid electrolytic capacitor element,
comprising a valve-acting metal substrate having on a surface a
dielectric film; circumferentially providing an insulating layer on
a position defining an edge part acting as an anode of the
valve-acting metal substrate; and sequentially forming a solid
electrolyte layer and an electrically conducting layer comprising a
carbon paste layer and a metal powder-containing electrically
conducting layer on an entire surface of the substrate on a side
opposite said anode with respect to said insulating layer, wherein
said metal powder-containing electrically conducting layer is
provided within a region of the carbon paste layer, such that said
metal powder-containing electrically conducting layer does not
contact the insulating layer.
19. A method for producing a solid electrolytic capacitor element,
comprising a valve-acting metal substrate having on a surface a
dielectric film; circumferentially providing an insulating layer on
a position defining an edge part acting as an anode of the
valve-acting metal substrate; and sequentially forming a solid
electrolyte layer and an electrically conducting layer comprising a
carbon paste layer and a metal powder-containing electrically
conducting layer on an entire surface of the substrate on a side
opposite said anode with respect to said insulating layer, wherein
said metal powder-containing electrically conducting layer is
provided with a spacing from a cathode side edge part of said
insulating layer.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is an application filed under 35 U.S.C.
.sctn.111(a) claiming benefit pursuant to 35 U.S.C. .sctn.119(e)(1)
of the filing date of Provisional Application No. 60/245,574 filed
Nov. 6, 2000 pursuant to 35 U.S.C. .sctn.111(b).
FIELD OF THE INVENTION
[0002] The present invention relates to a solid electrolytic
capacitor element in which the edge part of a valve-acting metal
substrate having on the surface thereof a dielectric film acts as
the anode, and an insulating layer having a predetermined width is
circumferentially provided on the substrate to come into contact
with the anode part. On the entire surface of the substrate on the
side opposite the anode with respect to the insulating layer, a
solid electrolyte layer comprising an organic material such as
electrically conducting polymer or an inorganic material such as
metal oxide and further thereon an electrically conducting layer
are sequentially formed to work out to the cathode. The present
invention also relates to a method for producing the capacitor
element; and a solid electrolytic capacitor using the element.
BACKGROUND OF THE INVENTION
[0003] With the progress of digitization and high frequency
processing of electronic instruments for reducing the size, saving
electric power and the like, there is an increasing demand for a
solid electrolytic capacitor having low impedance at a high
frequency, high reliability and high capacitance.
[0004] As a capacitor satisfying these capabilities, a capacitor
using a tantalum sintered body or an aluminum foil for the anode
and a solid electrolyte formed of an electrically conducting
polymer having high electrical conductivity or an inorganic oxide
for the cathode is commercially available. Particularly, a
chip-type capacitor that is surface-mounted on an electronic
circuit board is designed to employ a highly heat-resistant
material capable of enduing the heat of reflow soldering or to have
a structure capable of relieving thermal stress. However, the
above-described solid electrolyte is poor in the capability of
repairing the dielectric film, although the resistance is low, and
in some cases, the dielectric film is macroscopically broken due to
thermal stress to increase the leakage current.
SUMMARY OF THE INVENTION
[0005] An object of the present invention is to construct a solid
electrolytic capacitor element having a capability of relieving the
thermal stress generated in the reflow soldering or the like to
prevent an increase of leakage current and to provide a solid
electrolytic capacitor favored with low impedance and high
reliability.
[0006] The outline of the solid electrolytic capacitor element of
the present invention is described below by referring to FIG. 1
showing a cross section.
[0007] In FIG. 1, (1) is a valve-acting metal substrate (anode
substrate) having on the surface thereof a dielectric film (2), (3)
is an insulating layer having a predetermined width and
circumferentially provided on the valve-acting metal substrate, (4)
is a solid electrolyte layer, (5) is a carbon paste layer, and (6)
is a metal powder-containing electrically conducting layer.
[0008] The solid electrolytic capacitor of the present invention,
by which the described-above objects can be attained, has a
structure such that the metal powder-containing electrically
conducting layer (6) constituting the cathode part does not contact
with the insulating layer (3) which works out to the boundary with
the anode part, while preventing increase in the resistance of the
metal powder-containing electrically conducting layer (6). More
specifically, a spacing (t.sub.1) is provided between the cathode
side edge part (3a) of the insulating layer and the insulating
layer side edge part (6a) of the metal powder-containing
electrically conducting layer to prevent the metal
powder-containing electrically conducting layer (6) to run beyond
the region of the carbon paste layer (5), so that electrical
conduction can be reduced in the vicinity thereof and an increase
in leakage current can be prevented.
[0009] Furthermore, a structure for preventing the increase in ESR
(equivalent series resistance) is also employed, where the relative
ratio of the spacing (t.sub.1) between the cathode side edge part
(3a) of the insulating layer and the insulating layer side edge
part (6a) of the metal powder-containing electrically conducting
layer to the length (t.sub.0) of the cathode part (7) is
specified.
[0010] In the embodiment constructed as such, a substance having
high electrically conductivity (the metal powder-containing
electrically conducting layer) is not present in the vicinity of
the insulating layer and the metal powder-containing electrically
conducting layer is kept apart from the insulating layer.
Therefore, even when the insulating layer is partially broken under
mechanical or thermal stress, the electrical conduction hardly
occurs in the vicinity thereof and the leakage current does not
increase.
[0011] The term "circumferentially provided" as used in the present
specification means to encompass a certain site. The term "placed
on" is not limited only to the vertical relationship but includes
the state where two substances are disposed to contact each other.
The term "join" means to connect and bond two members.
[0012] That is, the present invention provides a solid electrolytic
capacitor element, a method for producing the capacitor element,
and a solid electrolytic capacitor, which are described below.
[0013] (1) A solid electrolytic capacitor element comprising (1) a
valve-acting metal substrate having on a surface thereof a
dielectric film with an edge part acting as an anode, (2) an
insulating layer circumferentially provided on said valve-acting
metal substrate, (3) a solid electrolyte layer and (4) an
electrically conducting layer comprising a carbon paste layer and a
metal powder-containing electrically conducting layer, said solid
electrolyte layer and said electrically conducting layer being
formed in this order on an entire surface of the substrate on a
side opposite said anode with respect to the insulating layer and
acting as a cathode part, wherein said metal powder-containing
electrically conducting layer is provided within a region of the
carbon paste layer, such that said metal powder-containing
electrically conducting layer does not contact the insulating
layer.
[0014] (2) A solid electrolytic capacitor element comprising (1) a
valve-acting metal substrate having on a surface thereof a
dielectric film with an edge part acting as an anode, (2) an
insulating layer circumferentially provided on said valve-acting
metal substrate, (3) a solid electrolyte layer and (4) an
electrically conducting layer comprising a carbon paste layer and a
metal powder-containing electrically conducting layer, said solid
electrolyte layer and said electrically conducting layer being
formed in this order on an entire surface of the substrate on a
side opposite said anode with respect to the insulating layer and
acting as a cathode part, wherein said metal powder-containing
electrically conducting layer is provided with a spacing from a
cathode side edge part of said insulating layer.
[0015] (3) The solid electrolytic capacitor element as described in
2 above, wherein the spacing between said metal powder-containing
electrically conducting layer and the cathode side edge part of
said insulating layer is about {fraction (1/10)} or more but less
than 1/2 of the entire length of said cathode part.
[0016] (4) The solid electrolytic capacitor element as described in
2 or 3 above, wherein the spacing between said metal
powder-containing electrically conducting layer and the cathode
side edge part of said insulating layer is from about 0.1 to about
1.5 mm.
[0017] (5) The solid electrolytic capacitor element as described in
1 above, wherein said metal powder-containing electrically
conducting layer comprises an electrically conducting filler
comprising metal powder, and a fluororubber as a main component of
a binder.
[0018] (6) The solid electrolytic capacitor element as described in
5 above, wherein about 80% by mass or more of the binder is
fluororubber.
[0019] (7) The solid electrolytic capacitor element as described in
5 above, wherein about 80% by mass or more of the electrically
conducting filler is silver powder.
[0020] (8) The solid electrolytic capacitor element as described in
5 above, wherein said metal powder-containing electrically
conducting layer comprises from about 50 to about 95% by mass of
the electrically conducting filler and from about 5 to about 50% by
mass of the binder.
[0021] (9) The solid electrolytic capacitor element as described in
1 above, wherein the carbon paste layer comprises an electrically
conducting carbon material, a binder and a solvent as main
components, about 80% by mass or more of said electrically
conducting carbon material is an artificial graphite, and said
binder comprises a material having rubber elasticity.
[0022] (10) The solid electrolytic capacitor element as described
in 1 above, wherein the valve-acting metal has a plate or foil
shape.
[0023] (11) The solid electrolytic capacitor element as described
in 1 above, wherein the valve-acting metal is an elemental metal
selected from the group consisting of aluminum, tantalum, niobium
and titanium, or the valve-acting metal is an alloy of said
elemental metal.
[0024] (12) The solid electrolytic capacitor element as described
in 1 above, wherein the solid electrolyte layer comprises an
electrically conducting polymer layer.
[0025] (13) The solid electrolytic capacitor element as described
in 12 above, wherein the electrically conducting polymer layer
comprises a polymer of a 5-member heterocyclic ring-containing
compound.
[0026] (14) The solid electrolytic capacitor element as described
in 13 above, wherein the 5-member heterocyclic ring-containing
compound comprises a structure of bivalent thiophene skeleton.
[0027] (15) The solid electrolytic capacitor element as described
in 12 above, wherein the electrically conducting polymer layer
comprises poly(3,4-ethylenedioxythiophene).
[0028] (16) A solid electrolytic capacitor obtainable by placing at
least one capacitor element as described in any one of 1 to 15 on a
lead frame and joining these.
[0029] (17) A method for producing a solid electrolytic capacitor
element, comprising a valve-acting metal substrate having on a
surface a dielectric film; circumferentially providing an
insulating layer on a position defining an edge part acting as an
anode of the valve-acting metal substrate; and sequentially forming
a solid electrolyte layer and an electrically conducting layer
comprising a carbon paste layer and a metal powder-containing
electrically conducting layer on an entire surface of the substrate
on a side opposite said anode with respect to said insulating
layer, wherein said metal powder-containing electrically conducting
layer is provided within a region of the carbon paste layer, such
that said metal powder-containing electrically conducting layer
does not contact the insulating layer.
[0030] (18) A method for producing a solid electrolytic capacitor
element, comprising a valve-acting metal substrate having on a
surface a dielectric film; circumferentially providing an
insulating layer on a position defining an edge part acting as an
anode of the valve-acting metal substrate; and sequentially forming
a solid electrolyte layer and an electrically conducting layer
comprising a carbon paste layer and a metal powder-containing
electrically conducting layer on an entire surface of the substrate
on a side opposite said anode with respect to said insulating
layer, wherein said metal powder-containing electrically conducting
layer is provided with a spacing from a cathode side edge part of
said insulating layer
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] FIG. 1 is a cross-sectional view showing the structure of a
solid electrolytic capacitor element according to the present
invention.
[0032] FIG. 2 is a cross-sectional view of a solid electrolytic
multilayer capacitor element according to the present
invention.
[0033] FIG. 3 is a cross-section view of a comparative solid
electrolytic capacitor element where the metal powder-containing
electrically conducting layer (silver paste layer) runs over the
carbon paste layer.
DESCRIPTION OF THE PRESENT INVENTION
[0034] The present invention is described in detail below.
[0035] The present invention provides a capacitor element where a
metal powder-containing electrically conducting layer is kept apart
from the insulating layer and a positional relationship between the
metal powder-containing electrically conducting layer and the
carbon paste layer is specified. The present invention also
provides a method for producing the capacitor element and a solid
electrolytic capacitor using the element.
[0036] According to the present invention, the spacing (t.sub.1)
between the cathode side edge part (3a) of the insulating layer and
the cathode side edge part (6a) of the metal powder-containing
electrically conducing layer is about {fraction (1/10)} or more of
the length of the cathode part (7) with the maximum being less than
1/2 of the length of the cathode part (7) of the element. The
spacing (t.sub.1) between the cathode side edge part (3a) of the
insulating layer and the insulating layer side edge part (6a) of
the metal powder-containing electrically conducing layer is
preferably about 1/8 or more of the length of the cathode part (7)
with the maximum being about 3/8 or less of the length of the
cathode part (7) of the element. With the spacing in this range, a
high yield can be attained while preventing an increase in ESR and
in leakage current, even when the dielectric film is
microscopically broken due to thermal or mechanical stress
generated in the reflow soldering or the like.
[0037] The capacitor element of the present invention is
manufactured by allowing the edge part of a valve-acting metal
substrate (1) having on the surface thereof a dielectric film layer
(2) to act as an anode, circumferentially providing an insulating
layer (3) having a predetermined width on the substrate to come
into contact with the anode part, and on the dielectric film layer
exclusive of the anode part and the insulating layer part,
sequentially forming a solid electrolyte layer (4) and further
thereon an electrically conducting layer comprising a carbon paste
layer (5) and a metal powder-containing electrically conducting
layer (6).
[0038] The valve-acting metal substrate may be sufficient if it is
an elemental metal selected from aluminum, tantalum, niobium and
titanium, or an alloy thereof. The shape thereof may be any of
plate, foil, sintered body and the like. For example, in the case
of a metal foil, the thickness varies depending on the use end but
is generally on the order of 40 to 150 .mu.m. The size and the form
also vary depending on the use; however, the plate-like element
unit is preferably in a rectangular form having a width of
approximately from 1 to 15 mm and a length of approximately from 1
to 15 mm, more preferably having a width of approximately from 2 to
10 mm and a length of approximately from 2 to 7 mm.
[0039] The insulating layer circumferentially provided may be
formed by coating a composition comprising an insulating resin, an
inorganic fine powder and a cellulose-based resin (see,
JP-A-11-80596 (the term "JP-A" as used herein means an "unexamined
published Japanese patent application")) or by attaching an
insulating tape.
[0040] The insulating material is not particularly limited.
Specific examples thereof include polyphenylsulfone,
polyethersulfone, cyanic ester resin, fluororesin (e.g.,
tetrafluoroethylene, tetrafluoroethylene/perfluoroalkyl vinyl ether
copolymer), low molecular weight polyimide and derivatives thereof,
and a composition comprising soluble polyimidesiloxane and epoxy
resin (see, JP-A-8-253677). The method for providing the insulating
layer is also not particularly limited and the method may be
sufficient if an insulating layer can be formed to a predetermined
width on a substrate.
[0041] The solid electrolyte layer may be formed using any one of
an electrically conducting polymer, an electrically conducing
organic material and an electrically conducting inorganic oxide. A
plurality of materials may be sequentially coated or a composite
material may be coated. A known electrically conducing polymer is
preferably used, such as an electrically conducting polymer
containing as a repeating unit any one divalent group selected from
pyrrole, thiophene, furan and aniline structures, or at least one
substitution derivative thereof. For example, a method where a
3,4-ethylenedioxythiophene monomer and an oxidizing agent, each
preferably in the solution form, are coated separately one after
another or simultaneously on the dielectric film of a metal foil
(see, JP-A-2-15611 and JP-A-10-32145), may be used.
[0042] In the electrically conducting polymer, a dopant is
generally used. The dopant may be any compound as long as it has a
doping ability and examples of the dopant which can be used include
an organic sulfonic acid, an inorganic sulfonic acid, an organic
carboxylic acid, and salts thereof. In general, an aryl
sulfonate-based dopant is used. Examples of the salt which can be
used include salts of benzenesulfonic acid, toluenesulfonic acid,
naphthalenesulfonic acid, anthracene sulfonic acid,
anthraquinonesulfonic acid, and a substitution derivative thereof.
Also, a compound, which can bring out particularly excellent
capacitor performance, can be used, and examples thereof include a
compound containing one or more sulfonic acid group and a quinone
structure, a heterocyclic sulfonic acid, an anthracenemonosulfonic
acid, and salts thereof. These dopants may be used individually or
in combination of two or more thereof.
[0043] The electrically conducting layer is generally formed by
coating a carbon paste and a paste containing electrically
conducting metal powder, but may also be formed by a method other
than the coating.
[0044] In the present invention, metal powder other than silver
powder, such as gold and copper, may also be used as the
electrically conducing filler used in the paste for forming the
metal powder-containing electrically conducting layer, but silver
powder is most preferred. The silver powder is preferably contained
to occupy 80% by mass or more of the filler as a whole. The
particle size is preferably from about 1 to about 10 .mu.m in terms
of the average particle size. If the average particle size is less
than about 1 .mu.m, the bulk density is small, the paste volume
increases and this is disadvantageous for the formation of the
electrically conducting layer. If the average particle size exceeds
about 10 .mu.m, the metal powder is excessively coarse and
connection failure readily occurs with the cathode lead
terminal.
[0045] Although the electrically conducting layer may be formed
using only the above-described paste for the metal
powder-containing electrically conducting layer of the present
invention, usually, a layer (5) formed by a carbon paste is
provided on the electrically conducting polymer layer (4) and a
layer (6) formed by the metal powder-containing electrically
conducting paste of the present invention is provided thereon. In
particular, the silver powder migrates, and therefore, it is
preferred to first coat a carbon paste and then coat thereon a
silver powder-containing electrically conducting paste.
[0046] Examples of the carbon paste that can be used include
natural graphite, carbon black and artificial graphite. Among
these, preferred is artificial graphite. The artificial graphite
powder preferably has an average particle size of approximately 1
to 13 .mu.m and an aspect ratio of approximately 10 or less. Also,
in the artificial graphite, the ratio of particles having a
particle size of about 32 .mu.m or more is approximately 12% by
mass or less. The binder resin used in the carbon paste is
preferably fluororubber which is used as the binder resin of the
paste for the metal powder-containing electrically conducting layer
described below. The thickness of the carbon paste layer (5) may be
approximately from 1 to 5 .mu.m.
[0047] The binder of the electrically conducing metal
powder-containing paste is a material having rubber elasticity
(hereinafter sometimes referred to as a "rubber elastic body") and
having properties of, when distorted, repelling the distortion and
recovering the original shape, preferably a material further having
capability of swelling or suspending in a solvent in the practical
embodiment. A rubber elastic body having excellent heat resistance
in a reflow soldering treatment at the production of a capacitor is
used. Specific examples thereof include isoprene rubber, butadiene
rubber, styrene/butadiene rubber, nitrile/butadiene rubber,
isoputylene/isoprene rubber, ethylene/propylene copolymer (e.g.,
EPM, EPDM), polysulfide rubber, fluororubber (e.g., VDF/HFP,
VDF/HFP/TFE), silicone rubber and other thermoplastic elastomers.
Compared with epoxy resin, which is generally used as the binder,
these materials are high in modulus of elasticity and low in water
absorptivity and provide an effect of relieving the stress in the
bonded portion. Among these, fluororubber is preferred.
[0048] In particular, a binder mainly comprising fluororubber is
preferred and a binder containing from approximately 80 to 100% by
mass of fluororubber is more preferred. The remaining component of
the binder may be a resin or the like conventionally used.
[0049] The fluororubber used in the present invention has rubber
elasticity of, when distorted, repelling the distortion and
recovering the original shape and differs from fluororesin which
cannot repel the distortion and recover the original shape.
[0050] Examples of the fluororubber which can be used include
vinylidene fluoride-based copolymer rubber,
hexafluoro-propylene-based copolymer rubber,
tetrafluoroethylene-based copolymer rubber, fluorine-containing
acrylate rubber and fluorine-containing silicone rubber. These
rubbers are also distinguished from fluororesin in that, in the
unvulcanized state, the glass transition point (Tg) is lower than
room temperature.
[0051] The electrically conducting filler and the binder are
preferably mixed in such a ratio that the electrically conducting
filler is approximately from 50 to 95% by mass and the binder resin
is approximately from 5 to 50% by mass. If the electrically
conducting filler is less than about 50% by mass, the electrically
conductivity decreases, whereas if it exceeds 95% by mass, the
bonding strength of the binder (less than 5% by mass) lowers and
the formation of electrically conducting layer becomes
difficult.
[0052] In order to impart a suitable viscosity as a paste to the
mixture (solid contents) of the electrically conducting filler and
the binder, an organic solvent is usually added. In general, the
amount of the organic solvent is suitably from about 40 to about
100 parts by mass per 100 parts by mass of the solid contents.
Examples of the organic solvent which can be used include butyl
acetate, amyl acetate and propyl acetate. Depending on the solvent,
the fluororubber swells or dissolves, and fluororubber which
dissolves in a solvent is preferred.
[0053] For forming the electrically conducting polymer, a known
method may be used, such as chemical polymerization of a monomer
for forming the polymer by an oxidizing agent (polymerization
initiator), electrolytic polymerization or a combination thereof.
For example, an operation of dipping a valve-acting metal having an
oxide film layer in a monomer solution and then in an oxidizing
agent solution and heating it to undergo chemical polymerization is
repeated several times. By virtue of this repeated polymerization,
the electrically conducting polymer layer can form a multilayer
stacked structure (e.g., chimera structure, fibril structure), and
excellent resistance against thermal stress can be exhibited during
molding with an armoring resin.
[0054] The advantages of the electrically conducting metal
powder-containing layer using a fluororubber binder which is
preferably used in the present invention, is described below.
[0055] The electrically conducting polymer layer has a multilayer
stacked structure and excellent resistance against thermal stress,
but if an electrically conducting paste using a binder having a
large heat shrinkage, such as epoxy resin, is coated thereon, the
paste infiltrates into the surface layer of the electrically
conducting polymer. This paste generates a large stress during
heating, and affects the multilayer shape of the electrically
conducing polymer. On the other hand, when a binder containing a
rubber elastic body, such as fluororubber binder, is used, the
thermal stress generated in the paste infiltrated into the surface
layer of the electrically conducting polymer is small, and the
shape of the electrically conducting polymer layer provided is
maintained, whereby the capacitor can have good heat
resistance.
[0056] Examples of the oxidizing agent used for the chemical
polymerization include ammonium persulfate, organic ferric
sulfonate, inorganic acid iron such as ferric chloride,
Fe(ClO.sub.4).sub.3, organic acid iron(III), persulfate, alkyl
persulfate, hydrogen peroxide and K.sub.2Cr.sub.2O.sub.7.
[0057] On the surface of the solid electrolyte layer (4), the
carbon paste layer (5) and the metal powder-containing electrically
conducting layer (6) are formed. The metal powder-containing
electrically conducting layer (6) is contacted and joined with the
solid electrolyte layer to act as the cathode and at the same time,
works out to an adhesive layer for connect-bonding a cathode lead
terminal (9) of the final capacitor product (see, FIG. 2). The
thickness of the metal powder-containing electrically conducting
layer (6) is generally from about 10 to 50 .mu.m.
[0058] The capacitor element of the present invention can provide
the same effect also when two or more elements are stacked to
fabricate a multilayer capacitor element. In the case of a solid
electrolytic multilayer capacitor, the element is preferably
processed by chamfering the lead frame, more specifically, shaving,
thereby slightly flattening or rounding the corner parts so that
the concentration of stress in the vicinity of corners of the
element can be relieved.
[0059] The material of the lead frame is not particularly limited
and may be a material generally used but the lead frame is
preferably constructed by a copper-based material (for example,
Cu--Ni, Cu--Sn, Cu--Fe, Cu--Ni--Sn, Cu--Co--P, Cu--Zn--Mg or
Cu--Sn--Ni--P alloy) or a material obtained by plating the surface
of a copper-based material. If such is the case, an effect such as
reduction in the resistance by the design of the lead frame shape
or good workability in chamfering of the lead frame can be
obtained.
EXAMPLES
[0060] The present invention is described in greater detail below
by referring to the Examples and Comparative Examples, however, the
present invention should not be construed as being limited thereto.
Unless indicated otherwise herein, all parts, percents, ratios and
the like are by mass.
Example 1
[0061] A single plate capacitor element having a structure shown in
FIG. 1 was manufactured as follows. An area of 1 mm
(length).times.3 mm (width) in the edge part of an aluminum etched
foil (anode substrate (1)) having on the surface thereof a
dielectric film and cut (slit) into a predetermined size of 100
.mu.m (thickness), 6 mm (length) and 3 mm (width) was used as the
anode part. In contact with the anode part, an insulating layer (3)
was circumferentially provided to a width of 1 mm. The area, except
for the anode part and the insulating layer part (4 mm in length
and 3 mm in width), was subjected to chemical forming at 13 V in
10% by mass of an aqueous ammonium adipate solution to form a
dielectric film (2) on the cut end part (cut surface). This
substrate was dipped in an aqueous solution prepared to have 20% by
mass of ammonium persulfate and 0.1% by mass of sodium
anthraquinone-2-sulfonate, and subsequently dipped in 1.2 mol/l of
an isopropanol solution having dissolved therein 5 g of
3,4-ethylenedioxythiophene (Baytron M (trademark), produced by
Bayer AG). Thereafter, the substrate was taken out and left
standing in an environment at 60.degree. C. for 10 minutes, thereby
completing the oxidative polymerization. After repeating this
polymerization reaction treatment 25 times, the substrate was
washed with water. Thus, a solid electrolyte layer (4) of
electrically conducting polymer was formed.
[0062] Subsequently, the area having the electrically conducting
polymer layer was dipped in a carbon paste (prepared by mixing as
the paste solid contents 50% by mass of artificial graphite powder
and 50% by mass of Viton SVX (trademark, produced by Du Pont Dow
elastomers, a vinylidene
fluoride/tetrafluoroethylene/hexafluoropropylene copolymer), adding
thereto butyl acetate as a solvent and kneading the mixture to a
solid content of 20% by mass), and the carbon paste was solidified
to form a carbon paste layer (5) to the cathode side edge part of
the insulating layer. Furthermore, this area was dipped in a silver
paste (prepared by mixing as paste solid contents 85% by mass of
silver powder and 15% by mass of Viton, adding butyl acetate as a
solvent, and kneading the mixture to a solid content of 60% by
mass), and the silver paste was solidified to form a silver
powder-containing electrically conducting layer (6). As a result, a
single plate capacitor element shown in FIG. 1 was obtained, where
the spacing t.sub.1 between the cathode side edge part (3a) of the
insulating layer and the insulating layer side edge part (6a) of
the silver powder-containing electrically conducting layer was 0.5
mm, and the length (to) of the cathode part 7 was 4 mm.
[0063] Four sheets of the thus-obtained single plate capacitor
elements (8) were stacked and bonded using the same silver paste.
The stacked elements were placed on a lead frame (copper alloy) (9)
and bonded thereto using the silver paste to obtain a multilayer
capacitor element (10) shown at FIG. 2. The anodes were joined and
thereafter, the multilayer element as a whole was molded with an
epoxy resin (EME-7320A, produced by Sumitomo Bakelite) and aged at
120.degree. C. for 2 hours by applying thereto a rated voltage. In
this way, 30 units in total of solid electrolytic multilayer
capacitors were manufactured. Each capacitor element was measured
with respect to the initial characteristics, capacitance and loss
factor (tan .delta..times.100%) at 120 Hz, and also the equivalent
series resistance (ESR) at 100 kHz as an index for impedance
showing the resistance against the alternating current of the
capacitor and the leakage current (LC) were measured. The leakage
current was measured 1 minute after the rated voltage was applied.
Average values of respective measured values, the defective ratio
when a leakage current of 6 .mu.A or more was considered defective,
and the results in the reflow soldering test are shown in Table 1.
The average of the leakage current values is a value calculated
exclusive of the defective units. The reflow soldering test was
performed by passing the element through a temperature zone of
230.degree. C. over 30 seconds and in the evaluation, an element
showing a leakage current of 12 .mu.A or more was considered
defective, and an element showing 300 .mu.A or more was considered
short circuit.
Example 2
[0064] Capacitors were manufactured and evaluated in the same
manner as in Example 1, except that the spacing t.sub.1 between the
cathode side edge part (3a) of the insulating layer and the
insulating layer side edge part (6a) of the silver paste layer was
1 mm. The results obtained are shown in Table 1.
Example 3
[0065] Capacitors were manufactured and evaluated in the same
manner as in Example 1, except that the spacing t.sub.1 between the
cathode side edge part of the insulating layer and the insulating
layer side edge part of the silver paste layer was about 1.4 mm.
The results obtained are shown in Table 1.
Example 4
[0066] Capacitors of Example 4 were manufactured and evaluated in
the same manner as in Example 2, except for using sodium
4-morpholinepropanesulfon- ate in place of sodium
anthraquinone-2-sulfonate in Example 2. The results obtained are
shown in Table 1.
Example 5
[0067] Capacitors of Example 5 were manufactured and evaluated in
the same manner as in Example 2, except for using sodium
anthracene-1-sulfonate in place of sodium anthraquinone-2-sulfonate
in Example 2. The results obtained are shown in Table 1.
Example 6
[0068] Capacitors of Example 6 were manufactured and evaluated in
the same manner as in Example 2, except for using sodium
1-naphthalenesulfonate in place of sodium anthraquinone-2-sulfonate
and using N-methylpyrrole in place of 3,4-ethylenedioxythiophene in
Example 2. The results obtained are shown in Table 1.
Comparative Example 1
[0069] Capacitors were manufactured and evaluated in the same
manner as in Example 1, except that the spacing t.sub.1 between the
cathode side edge part of the insulating layer and the insulating
layer side edge part of the metal powder-containing electrically
conducting layer (silver paste layer) was 0 mm. The results
obtained are shown in Table 1.
Comparative Example 2
[0070] Capacitors were manufactured and evaluated in the same
manner as in Example 1, except that the spacing t.sub.1 between the
cathode side edge part of the insulating layer and the insulating
layer side edge part of the silver paste layer was 2 mm. The
results obtained are shown in Table 1.
Comparative Example 3
[0071] Capacitors were manufactured and evaluated in the same
manner as in Example 1, except that the silver paste layer provided
on the carbon paste layer was formed to run over and cover the
insulating layer in the portion of t2=0.5 mm from the cathode side
edge part of the insulating layer as shown in FIG. 3. The results
obtained are shown in Table 1.
1 TABLE 1 Characteristics of Capacitor Reflow Soldering Test
Capacitance Loss Defective Defective Number (.mu.F) Factor (%) ESR
(m.OMEGA.) LC (.mu.A) Ratio* Ratio* of Short Circuit Example 1 51.8
0.68 9 0.12 0/30 0/30 0 Example 2 51.7 0.68 13 0.11 0/30 0/30 0
Example 3 51.8 0.67 21 0.12 0/30 0/30 0 Example 4 50.3 0.69 10 0.28
0/30 0/30 0 Example 5 49.2 0.68 12 0.25 0/30 0/30 0 Example 6 50.8
0.69 15 0.29 0/30 0/30 0 Comparative 51.8 0.70 8 0.41 2/30 2/28 2
Example 1 Comparative 51.7 0.68 38 0.10 0/30 0/30 0 Example 2
Comparative 51.9 0.71 7 0.89 5/30 6/25 5 Example 3 *Defective
Ratio: number of defectives/number of tested elements
[0072] According to the present invention, an electrically
conducting layer comprising a carbon paste and a metal
powder-containing electrically conducting layer is provided by
forming the metal powder-containing electrically conducting layer
within the region of the carbon paste layer. The metal
powder-containing electrically conducting layer is also formed with
a spacing from the cathode side edge part of the insulating layer,
so that the solid electrolytic capacitor manufactured can be
favored with low impedance, and an increase in leakage current can
be prevented, even when subject to the thermal or mechanical stress
generated in the reflow soldering or the like.
[0073] While the invention has been described in detail and with
reference to specific embodiments thereof, it will be apparent to
one skilled in the art that various changes and modifications can
be made therein without departing from the spirit and scope
thereof.
* * * * *