Electricity: electrical systems and devices – Electrolytic systems or devices – Solid electrolytic capacitor
Reexamination Certificate
2003-03-18
2004-04-27
Reichard, Dean A. (Department: 2831)
Electricity: electrical systems and devices
Electrolytic systems or devices
Solid electrolytic capacitor
C029S025030, C361S538000, C361S528000
Reexamination Certificate
active
06728097
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a solid electrolytic capacitor in which an electroconductive polymer is used as a solid electrolyte and a method for manufacturing the solid electrolytic capacitor.
BACKGROUND OF THE INVENTION
In recent years, with the development of electronic devices smaller in size and capable of operating at higher frequencies, solid electrolytic capacitors using an electroconductive polymer as a solid electrolyte capable of realizing a high-frequency and low-impedance characteristics have been introduced to the market as a capacitor for use in such electronic devices. Because of use of an electroconductive polymer of a high conductivity as a solid electrolyte, this kind of solid electrolytic capacitor has an equivalent series resistance (ESR) component smaller than that of conventional dry electrolytic capacitors using an electrolytic solution or solid electrolytic capacitors using manganese dioxide, and can therefore be realized as a solid electrolytic capacitor large in capacity, small in size and close to an ideal. Therefore this kind of solid electrolytic capacitor has undergone many improvements and a number of its variations have become available on the market.
FIG. 9
is a cross-sectional view of the structure of a conventional solid electrolytic capacitor of this kind,
FIG. 10
is a partially cut-away perspective view of a capacitor element constituting the electrolytic capacitor, and
FIG. 11
is a perspective view of the capacitor element in a single state connected to lead frames.
The capacitor element indicated by
1
in the figures is constituted by an anode member
2
and a cathode member
3
. The anode member
2
is made of aluminum and has an insulating dielectric oxide film layer
1
b
formed on its external surface, and an insulating layer formed of polyimide adhesive tape
4
in a predetermined position on its electrode body
1
a
. The cathode member
3
is constituted by cathode layers: a solid electrolyte layer
1
c
formed of an electroconductive polymer, a carbon paint layer
1
d
, an electroconductive silver paint layer
1
e
, formed one on another.
The anode member
2
of the capacitor element
1
is joined to an anode lead frame
11
by a certain means, e.g., welding. The cathode member
3
of the capacitor element
1
is joined to a cathode lead frame
12
by a certain means, e.g., an electroconductive adhesive. The anode lead frame
11
has a joint member
11
a
provided at its end and bent so as to wrap round the anode member
2
at the joint end, thereby clamping the end of the anode member
2
. By welded portions
11
b
in the joint member
11
a
, the end of the anode member
2
is fixed to the joint member
11
a
. Guide members
12
a
are provided on the cathode lead frame
12
to guide the cathode member
3
. An insulating casing resin
13
covers the above-described capacitor element
1
with the anode lead frame
11
and the cathode lead frame
12
partially exposed.
Various electroconductive polymers have been developed which can be used as the solid electrolyte
1
c
in the conventional solid electrolytic capacitor constructed as described above. The development of applications of such polymers to solid electrolytic capacitors is being promoted.
However, it is known that any of electroconductive polymers usable as the solid electrolyte
1
c
degrades in an oxidizing atmosphere since it is an organic material. The casing resin
13
has a role to prevent oxidation of such solid electrolyte
1
c
. However, air enters through a small gap between contact surfaces of the cathode lead frame
12
and the casing resin
13
to cause a reduction in conductivity, a deterioration of adhesion to the dielectric oxide film, and a reduction in stability. It is known that, from this cause, deteriorations in capacitor characteristics (a reduction in capacity and an increase in equivalent series resistance in particular) are caused particularly under a high-humidity condition.
For the purpose of solving the above-described problem in conventional solid electrolytic capacitors of this kind, the surface of the cathode lead frame
12
in contact with the casing resin
13
in which the capacitor element
1
and a part of the cathode lead frame
12
are molded is roughened to improve the adhesion between the casing resin
13
molding a part of the cathode lead frame
12
and the cathode lead frame
12
. Further, a trial has been made to prevent oxidation under an oxidizing atmosphere in such a manner that, as shown in
FIG. 9
, the distance B between the outer end of the casing resin
13
and the end of the capacitor element
1
on the cathode side is increased by increasing the thickness of the casing resin
13
on the cathode lead frame
12
side to maximize the distance through which the cathode lead frame
12
and the casing resin
13
contact each other.
The above-described conventional solid electrolytic capacitor, however, has an increased external size because of use of a method for increasing a distance through which the cathode lead frame
12
and the casing resin
13
contact each other by increasing the thickness of the casing resin
13
so that the distance B between the outer end of the casing resin
13
and the end of the capacitor element
1
increases. Therefore there is a problem that it is extremely difficult for the conventional solid electrolytic capacitor to be reduced in size. Because of this problem, it is not possible to meet the recent strict size reduction requirement on electronic devices such as portable telephones.
In a type of solid electrolytic capacitor in which a plurality of capacitor elements
1
are stacked on anode lead frame
11
and cathode lead frame, a positioning error occurs between the stacked capacitor elements and it is necessary to determine the size of casing resin
13
by factoring in such a positioning error. This means a further increase in the degree of difficulty in the size of the solid electrolytic capacitor.
DISCLOSURE OF THE INVENTION
In view of the above-described problem, an object of the present invention is to provide a solid electrolytic capacitor capable of limiting oxidation deterioration of a solid electrolyte under an oxidizing condition by reducing the probability of external oxygen reaching the capacitor element and also capable of being reduced in size by reducing the thickness of the casing resin, and a method for manufacturing the solid electrolytic capacitor.
To achieve the above-described object, according to the present invention, there is provided a solid electrolytic capacitor in which an anode member and a cathode member provided in a capacitor element are respectively connected to an anode lead frame and a cathode lead frame, and in which the capacitor element including parts of the anode lead frame and the cathode lead frame are covered with a casing resin, the capacitor having a stepped portion formed in the portion of the cathode lead frame covered with the casing resin, and a gap provided between a vertical part of the stepped portion and the end of the capacitor element on the cathode member side.
In the above-described construction, the distance through which external oxygen (oxygen in atmospheric air) entering the capacitor through the gap between the cathode lead frame and the casing resin moves to reach the capacitor element can be increased to reduce the probability of external oxygen reaching the capacitor element to an extremely small value. That is, intrusion of external oxygen can be limited to ensure that oxidation deterioration does not occur easily even in an oxidizing atmosphere or at a high temperature, and that stable capacitor characteristics can be obtained under such a condition.
Therefore there is no need to maximize the distance between the outer end of the casing resin and the end of the capacitor element on the cathode member side by increasing the thickness of the casing resin as in the conventional art. Consequently, the capacitor can easily be reduced in size.
In the solid electrolytic capacitor of the present in
Nakamura Katsuyuki
Wada Tomohide
Matsushita Electric - Industrial Co., Ltd.
Parkhurst & Wendel L.L.P.
Thomas Eric
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