U.S. patent application number 09/799095 was filed with the patent office on 2002-02-07 for solid-state electrolytic capacitor.
Invention is credited to Fukuyama, Sachiko, Hirakawa, Hirotoshi, Iwanabe, Shuetsu.
Application Number | 20020015278 09/799095 |
Document ID | / |
Family ID | 26586894 |
Filed Date | 2002-02-07 |
United States Patent
Application |
20020015278 |
Kind Code |
A1 |
Fukuyama, Sachiko ; et
al. |
February 7, 2002 |
Solid-state electrolytic capacitor
Abstract
In a solid-state electrolytic capacitor in which a capacitor
element having an anode member with a dielectric film formed
thereon is impregnated with conductive polymer serving as a cathode
electrolyte and housed/sealed within an outer case, the capacitor
element impregnated with conductive polymer is covered with epoxy
resin mixed with a silane coupling element. Otherwise, the
capacitor element impregnated with conductive polymer is covered
with a first resin layer and a second resin layer which are formed
successively on an outside thereof, and the first resin layer is
made of a material having higher flexibility than that of the
second resin layer.
Inventors: |
Fukuyama, Sachiko; (Saga,
JP) ; Hirakawa, Hirotoshi; (Saga, JP) ;
Iwanabe, Shuetsu; (Saga, JP) |
Correspondence
Address: |
ARMSTRONG,WESTERMAN, HATTORI,
MCLELAND & NAUGHTON, LLP
1725 K STREET, NW, SUITE 1000
WASHINGTON
DC
20006
US
|
Family ID: |
26586894 |
Appl. No.: |
09/799095 |
Filed: |
March 6, 2001 |
Current U.S.
Class: |
361/523 |
Current CPC
Class: |
H01G 9/08 20130101; H01G
9/15 20130101 |
Class at
Publication: |
361/523 |
International
Class: |
H01G 009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 7, 2000 |
JP |
P. 2000-061378 |
Mar 14, 2000 |
JP |
P. 2000-070200 |
Claims
What is claimed is:
1. A solid-state electrolytic capacitor comprising: a capacitor
element having an anode member; a dielectric film formed on said
anode member; an outer case in which said capacitor element is
sealed to be impregnated with conductive polymer serving as a
cathode electrolyte; and an epoxy resin mixed with a silane
coupling element, which covers said capacitor element impregnated
with conductive polymer.
2. A solid-state electrolytic capacitor according to claim 1,
wherein said capacitor element has an anode foil with a dielectric
film formed thereon and an opposite cathode foil which are wound
with a separator interposed therebetween.
3. A solid-state electrolytic capacitor according to claim 1,
wherein said conductive polymer is oxidized/polymerized polymer of
thiophene or its derivative.
4. A solid-state electrolytic capacitor comprising: a capacitor
element having an anode member; a dielectric film formed on said
anode member; an outer case in which said capacitor element is
sealed to be impregnated with conductive polymer serving as a
cathode electrolyte; and a first resin layer and a second resin
layer which are formed successively on an outside of said capacitor
element impregnated with conductive polymer, and the first resin
layer is made of a material having higher flexibility than that of
said second resin layer.
5. A solid-state electrolytic capacitor according to claim 4,
wherein said capacitor element has an anode foil with a dielectric
film formed thereon and an opposite cathode foil which are wound
with a separator interposed therebetween.
6. A solid-state electrolytic capacitor according to claim 4,
wherein said conductive polymer is oxidized/polymerized polymer of
thiophene or its derivative.
Description
BACKGROUND OF THE INVENTION 1. Field of the Invention
[0001] This invention relates to a solid-state electrolytic
capacitor in which a capacitor element having an anode member with
a dielectric film formed thereon is impregnated with conductive
polymer serving as a cathode electrolyte and housed/sealed within
an outer case.
[0002] 2. Description of the Related Art
[0003] A previously known structure of a solid-state electrolytic
capacitor is shown in FIG. 4, in which a capacitor element having
an anode member with a dielectric film formed thereon is
impregnated with conductive polymer serving as a cathode
electrolyte and housed/sealed within an outer case.
[0004] In this solid-state electrolytic capacitor, a capacitor
element 11 is manufactured in a manner that an anode foil with a
dielectric film formed thereon and an opposite cathode foil are
wound with a separator interposed therebetween. The capacitor
element 11 is impregnated with conductive polymer serving as a
cathode electrolyte. The capacitor element 11 is housed within a
cylindrical bottomed outer case 15 and sealed by sealing rubber 16.
A seat plate 18 for surface mounting is mounted on the sealed end
of the outer case 15. In FIG. 4, reference numerals 17a and 17b
denote terminals for extending the anode and the cathode,
respectively.
[0005] Conventionally, in such a solid-state electrolytic
capacitor, the following thing occurred. The conductive polymer
impregnated in the capacitor element absorbs moisture during a
manufacturing process after the conductive polymer has been formed.
As a result, in a solder heat resistant test or endurance test
executed for the completed product of the capacitor, the equivalent
series resistance and the lead current increase.
[0006] JP-A-11-204377 discloses a technique that in such a
solid-state electrolytic capacitor, in order to suppress gas
generation from conductive polymer due to a solder heat resistance
test, thereby preventing a case or sealing member from swelling,
the outside of the capacitor element impregnated with conductive
polymer is covered with epoxy resin.
[0007] However, the solid-state capacitor with an epoxy resin layer
formed outside the capacitor element impregnated with conductive
polymer according to the technique disclosed in JP-A-11-204377 has
the following defect. Specifically, in the solder heat resistance
test, as the case maybe, mechanical stress is applied to the
interior of the capacitor element owing to a difference in a
thermal expansion coefficient between the members of the capacitor
including conductive polymer and the epoxy resin layer so that the
dielectric film on the anode member is damaged. As a result, the
leakage current is increased very greatly.
SUMMARY OF THE INVENTION
[0008] An object of this invention is to provide a solid-state
electrolytic capacitor including conductive polymer as a cathode
electrolyte which is free from attenuation of the characteristic
such as an increase in a leakage current.
[0009] In order to attain the above object, in accordance with the
first aspect of this invention, there is provided a solid-state
electrolytic capacitor in which a capacitor element having an anode
member with a dielectric film formed thereon is impregnated with
conductive polymer serving as a cathode electrolyte and
housed/sealed within an outer case, wherein the capacitor element
impregnated with conductive polymer is covered with epoxy resin
mixed with a silane coupling element.
[0010] In accordance with this invention, after the conductive
polymer has been formed, moisture absorption by this polymer is
suppressed. Thus, during the solder heat resistant test and
endurance test executed the product of the capacitor, the
equivalent series resistance and leakage current are made difficult
to vary.
[0011] In accordance with the second aspect of this invention,
there is provided a solid-state electrolytic capacitor in which a
capacitor element having an anode member with a dielectric film
formed thereon is impregnated with conductive polymer serving as a
cathode electrolyte and housed/sealed within an outer case, wherein
the capacitor element impregnated with conductive polymer is
covered with a first resin layer and a second resin layer which are
formed successively on an outside thereof, and the first resin
layer is made of a material having higher flexibility than that of
the second resin layer.
[0012] In this configuration, since the capacitor element is
covered with the first resin layer made of higher flexibility in
intimate contact with the outside thereof, mechanical stress is
difficult to spread to the interior of the capacitor so that the
dielectric film within the capacitor element is difficult to be
damaged.
[0013] Since the first resin layer is made of such a material,
freedom of selecting the material of the second resin layer can be
enhanced.
[0014] In this configuration of the solid-state electrolytic
capacitor, it is possible to prevent the case or sealing member
from being swelled during a solder heat resistance test, and to
suppress an increase in the leakage current.
[0015] The above and other objects and features of this invention
will be more apparent from the following description taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a sectional view of a solid-state electrolytic
capacitor according to a first embodiment of this invention;
[0017] FIG. 2 is a graph showing the experimental result of the
hygroscopic property (moisture absorption property) according to
the embodiment of this invention and a comparative example;
[0018] FIG. 3 is a sectional view of a solid-state electrolytic
capacitor according to a second embodiment of this invention;
and
[0019] FIG. 4 is a sectional view of a solid-state electrolytic
capacitor according to a conventional art.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] Now referring to the drawings, an explanation will be given
of embodiments of this invention.
Embodiment 1
[0021] The solid-state electrolytic capacitor according to a first
embodiment of this invention is shown in FIG. 1. As seen from FIG.
1, a winding type capacitor element 11 with conductive polymer
formed therein is coated with epoxy resin 12 mixed with silane
coupling agent. Thereafter, the capacitor element is housed within
an outer case 15 of aluminum and sealed with sealing member 16 of
rubber. A seat plate 18 for surface mounting is mounted on the
sealed end of the outer case.
[0022] The winding type capacitor element is wounded in a
cylindrical shape with an anode of an aluminum foil subjected to an
etching treatment and anodic oxidation treatment and an opposite
cathode with a separator interposed therebetween.
[0023] In order to form a conductive polymer layer within the
winding type capacitor element, prepared are monomer of
3,4-ethylene dioxythiophene which becomes conductive polymer by
oxidation/polymerization, iron (III) para-toluene sulfonic acid
serving as an oxidizing agent and a chemical polymerizing liquid
containing n-butyl alcohol which is diluent. The capacitor element
is immersed in the chemical polymerizing liquid and thereafter
heat-treated for several minutes at about 200.degree. C. so that a
polymer layer of 3,4-ethylene dioxythiophene in intimate contact
with an anode-formed foil and an opposite cathode foil within the
capacitor is formed.
[0024] A coating layer of epoxy resin mixed with silane coupling
agent is created in such a manner that the capacitor element with
the conductive polymer layer formed is immersed in a solution
consisting of silane coupling agent and epoxy resin mixed at a
ratio of about 1:1 by weight, and taken out and dried. The silane
coupling agent maybe 3-glysidoxypropyltrimethoxy silane (chemical
fomula:CH.sub.2 (O) CH.sub.2C.sub.3O.sub.3H.sub.6Si
(OCH.sub.3).sub.3. The mixing ratio of silane coupling agent and
epoxy resin should not be limited to about 1:1, but may be suitably
selected within a range of e.g. about 0.001.about.1000:1.
[0025] The capacitor element with the coating layer thus formed is
housed within a cylindrical bottomed outer case 15 made of aluminum
in a state where a sealing rubber 16 is mounted on the root of the
terminals 17a and 18a for extending the anode and cathode,
respectively. The capacitor element is subjected in its opening
portion to lateral reduction and curling and thereafter to the
aging for several tens or several hours while a rated voltage is
applied. Thus, a product of the capacitor can be completed.
[0026] In comparison between the capacitor element with the
conductive polymer and coating layer formed in accordance with the
embodiment of this invention (embodiment 1) and the capacitor
element with no coating layer (comparative example 1), FIG. 2 shows
the changes in the moisture per one element when these elements are
left in an air at a temperature of 25.degree. C. and moisture of
70%.
[0027] Further, in comparison between the solid-state electrolytic
capacitor including the capacitor element with the conductive
polymer and coating layer formed according to the embodiment of
this invention (embodiment 1) and the solid-state electrolytic
capacitor including the capacitor element with no coating layer
(comparative example 1), Table 1 shows the results when they have
been subjected to the solder heat resistance test according to VPS
(Vaper Phase Soldering) method (240.degree. C..times.40
sec.times.twice) and the subsequent endurance test (105.degree.
C..times.500 hours under the application of a rated voltage).
1 TABLE 1 Before Test After VPS Test After Endurance Test ESR LC
.DELTA.C/C ESR LC .DELTA.C/C ESR LC (m.OMEGA.) (.mu.A) (%)
(m.OMEGA.) (.mu.A) (%) (m.OMEGA.) (.mu.A) Embodiment 46.1 63.3
-0.53 46.5 42.1 -1.04 46.9 0.95 1 Comp. Exa. 46.1 60.6 -0.64 58.3
1125 -1.34 73.6 263 1
[0028] The capacitor elements according to this embodiment 1 and
comparative example 1 have ratings of 16V-27 .mu.F and outer
dimensions of .phi.6.3 mm.times.L5.8 mm. In Table 1, .DELTA.C/C
denotes a changing rate of the electrostatic capacitance at 120 Hz;
ESR denotes an equivalent series resistance at 100 kHz; and LC
denote a leakage current after 60 sec from when a rated voltage has
been applied. Incidentally, each of these characteristics is an
average value of 20 samples.
[0029] As apparent from FIG. 2, the capacitor element according to
the embodiment of this invention is more difficult to absorb
moisture than the capacitor element according to the comparative
example is. Further, as apparent from Table 1, the capacitor
element according to the embodiment of this invention has less
change in the characteristics by the VPS test and endurance test
than the capacitor element according to the comparative example
has.
[0030] In this embodiment, although the polymer of 3, 4-ethylene
dioxythiophene was used as the material of the cathode electrolyte,
other conductive polymers (e.g. oxidized/polymerized polymer of
pyrrole, thiophene, aniline or their derivative) may be used.
[0031] Further, in this embodiment, a winding type capacitor
element was used, a capacitor element with an anode member made of
a sintered tantalum body coated with a dielectric film may be
used.
Embodiment 2
[0032] The solid-state electrolytic capacitor according to a second
embodiment of this invention is shown in FIG. 3.
[0033] As seen from FIG. 3, a winding type capacitor element 11
with conductive polymer formed therein is coated, in its outside,
with a first resin layer 21 having high flexibility and further
with a second resin layer 22 having high hermeticity. Thereafter,
the capacitor element is housed within an outer case 15 of aluminum
and sealed with sealing member 16 of rubber. A seat plate 18 for
surface mounting is mounted on the sealed end of the outer
case.
[0034] The winding type capacitor element is wounded in a
cylindrical shape with an anode of an aluminum foil subjected to an
etching treatment and anodic oxidation treatment and an opposite
cathode with a separator interposed therebetween.
[0035] In order to form a conductive polymer layer within the
winding type capacitor element, prepared are monomer of
3,4-ethylene dioxythiophene which becomes by
oxidation/polymerization, iron (III) para-toluene sulfonic acid
serving as an oxidizing agent and a chemical polymerizing liquid
containing n-butyl alcohol which is diluent. The capacitor element
is immersed in the chemical polymerizing liquid and thereafter
heat-treated for several minutes at about 200.degree. C. so that a
polymer layer of 3,4-ethylene dioxythiophene in intimate contact
with an anode formed foil and an opposite cathode foil within the
capacitor is formed.
[0036] The first resin layer is preferably made of thermosetting
resin (e.g. epoxy resin) which has higher flexibility than that of
the second resin layer. On the other hand, the second resin layer
is preferably made of thermosetting resin (e.g. acid anhydride
epoxy resin) which has higher hermeticity than that of the first
resin layer. The flexibility of the resin can be quantified in
terms of numeric values of Rockwell hardness, tensile strength,
elongation coefficient after fracture, etc. The first resin layer
preferably has the Rockwell hardness of 100 or less in M scale,
tensile strength of 5 kg weight/mm.sup.2 or more, and tension
extension coefficient of 4% or more.
[0037] Further, the first resin layer preferably has adherence to
the outer surface of the capacitor element covered with conductive
polymer, and surface resistivity of 10.sup.13 .OMEGA. or more. The
capacitor element thus coated with the first and the second resin
layer is housed within a cylindrical bottomed outer case 15 made of
aluminum in a state where a sealing rubber 16 is mounted on the
root of the terminals 17a and 18a for extending the anode and
cathode, respectively. The capacitor element is subjected in its
opening portion to barring and curling and thereafter to the aging
for several tens or several hours while a rated voltage is applied.
Thus, a product of the capacitor can be completed.
[0038] The inventors of this invention manufactured the solid-state
electrolytic capacitor having the first and the second resin layer
according to the embodiment of this invention (embodiment 2) and
the solid-state electrolytic capacitor having a single layer of the
same material as that of the above second resin layer (comparative
example 2). These solid-state electrolytic capacitors were
subjected to the solder heat-resisting test (240.degree.
C..times.90 sec.times.twice) by the VPS technique.
[0039] Table 2 shows the characteristics of these solid-state
electrolytic capacitors before the solder heat-resisting test.
Table 3 shows changes in the leakage current of these solid-state
electrolytic capacitors before and after the solder heat-resisting
test.
2 TABLE 2 C (.mu.F) tan .delta. (%) ESR (m.OMEGA.) LC yield (%)
Embodiment 2 221 10 49 92 Comp. Exa. 2 222 10 50 84
[0040]
3 TABLE 3 LC before Solder LC after Solder Heat-Resisting Test
(.mu.A) Heat-Resisting Test (.mu.A) Minimum Maximum Minimum Maximum
Embodiment 2 1 39 10 100 Comp. Ex. 2 6 26 410 1310
[0041] The capacitor elements according to this embodiment and
comparative example have ratings of 20V-22 .mu.F and outer
dimensions of .phi. 6.3 mm.times.L6.0 mm. In Table 2, C denotes an
electrostatic capacitance at 120 Hz; tan .delta. denotes tangent of
the loss angle at 120 Hz; and ESR denotes an equivalent series
resistance at 100 kHz. Incidentally, each of these characteristics
is an average value of 50 samples.
[0042] The LC yield in Table 2 shows the ratio of the number of
good products to that of samples (50 pieces for each) where the
good product means that the leakage current after 60 sec from when
a rate voltage has been applied is not larger than 88 .mu.A.
[0043] Table 3 shows a minimum value and a maximum value of the
leakage current (LC) before and after 60 sec from when a rate
voltage has been applied for the 50 samples according to this
embodiment and the comparative example.
[0044] As apparent from Table 2, the capacitor element according to
the embodiment of this invention has approximately equal initial
characteristics to those of the capacitor element according to the
comparative example. Further, as apparent from Table 3, in the
capacitor element according to the embodiment of this invention, an
increase in the leakage current by the solder heat-resisting test
is suppressed more greatly than in the capacitor element according
to the comparative example.
[0045] In this embodiment, although the polymer of 3,4-ethylene
dioxythiophene was used as the material of the cathode electrolyte,
other conductive polymers (e.g. oxidized/polymerized polymer of
pyrrole, thiophene, aniline or their derivative) may be used.
[0046] Further, in this embodiment, a winding type capacitor
element was used, a capacitor element with an anode member made of
a sintered tantalum body coated with a dielectric film may be
used.
* * * * *