Electricity: electrical systems and devices – Electrolytic systems or devices – Solid electrolytic capacitor
Reexamination Certificate
1999-08-13
2001-02-13
Dinkins, Anthony (Department: 2831)
Electricity: electrical systems and devices
Electrolytic systems or devices
Solid electrolytic capacitor
C361S537000, C361S540000, C361S275400
Reexamination Certificate
active
06188566
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a solid electrolytic capacitor of the type containing within itself a circuit-opening mechanism such as a fuse. More particularly, the invention relates to such a solid electrolytic capacitor which can be designed to make its casing smaller or its capacitor element larger for the same size of its casing.
FIG. 4
shows an example of prior art solid electrolytic capacitor with a capacitor element
21
formed by subjecting a sintered body of valve action metallic powder such as tantalum powder to various treatment processes including chemical conversion process. A lead
22
is inserted into one of side surfaces of this capacitor element
21
to serve as its positive electrode, while its outer surface serves as its negative electrode. A first lead line
23
and a second lead line
24
are respectively connected electrically to the positive electrode
22
and the negative electrode. These electrodes are encapsulated inside a casing
26
of a resin material. The solid electrolytic capacitor thus structured has a definite polarity such that it will be short-circuited if it is connected in a wrong direction. In such a situation, not only may the capacitor heat up or become ignited but other electronic components of the circuit in which this solid electrolytic capacitor is incorporated may also be damaged. In view of such possibilities, a circuit-opening mechanism such as a fuse is frequently provided on the side of either the positive electrode or the negative electrode such that the circuit will open between the lead lines
23
and
24
in an abnormal situation. In order to make its connection easier, it has been known to provide a fuse
25
in the shape of a wire or a ribbon on the side of the negative electrode, as shown in FIG.
4
. connecting between the negative electrode on the outer surface of the capacitor element
21
and the second lead line
24
, being attached to them, say, be compression.
With the recent trend to miniaturize electronic components, it is becoming necessary to provide miniaturized tantalum capacitors. It is not desirable, however, to reduce the size of the casing
26
merely by making the capacitor element
21
smaller because this would adversely affect the electrical characteristic of the capacitor such as its capacitance. Instead, what is desirable is to reduce the size of the casing
26
while maintaining the electrical characteristic of the capacitor high by not making the capacitor element
21
smaller, or keeping the capacitor element
21
as large as possible.
For connecting the fuse
25
between the outer wall of the capacitor element
21
and the second lead line
24
, however, the fuse
25
is usually formed in a smoothly arcuate shape, as shown in
FIG. 4
, because a fuse having a sharply bent portion would more easily come off the capacitor element
21
or the second lead line
24
to which it is attached by compression. If the fuse
25
is to have a slowly curving shape between the outer surface of the capacitor element
21
and the second lead line
24
, however, the distance between the capacitor element
21
and the second lead line
24
as well as the distance between the capacitor element
21
and the upper surface of the casing
26
must be made sufficiently large, and this results in many wasteful spaces. Thus, there was a limit to how large the capacitor element could be made in order to improve the electrical characteristics of the capacitor while the size of the casing was kept fixed, or how small the capacitor could be made for a capacitor element of the same size with the same electrical characteristic. In other words, prior art solid electrolytic capacitors as shown in
FIG. 4
could not satisfy the current demand for miniaturized high-quality electronic components.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide a solid electrolytic capacitor with an improved design such that the size of its casing can be reduced although a circuit-opening mechanism such as a fuse is included or that its capacitor element can be made larger without also increasing the size of its casing.
A solid electrolytic capacitor embodying this invention, with which the above and other objects can be accomplished, may be characterized not only as comprising a capacitor element having a positive electrode and a negative electrode which are respectively connected electrically to a first lead and a second lead and a casing of a resin material surrounding the capacitor element but also wherein a low melting-point metal layer is inserted between and electrically connects the capacitor element and the second lead and an arc-extinguishing material capable of absorbing the melted metal of the low melting-point metallic material is provided inside a throughhole through the second lead where the latter contacts the low melting-point metal layer.
For a solid electrolytic capacitor thus characterized, the aforementioned low melting-point metal layer can be in the form of a flat ribbon such that the second lead and the contacting surface of the capacitor element can be overlapped with respect to each other. In other words, the distance between the second lead and the capacitor element and the distance between the capacitor element and the upper surface of the casing can be both reduced. As a result, the size of the casing can be reduced accordingly or the volume of the capacitor element can be increased without increasing the size of the casing. Thus, compact solid electrolytic capacitors with high capability can be provided according to this invention.
REFERENCES:
patent: 5329421 (1994-07-01), Kuriyama
patent: 5402307 (1995-03-01), Kuriyama
patent: 5502614 (1996-03-01), Kuriyama
patent: 5583740 (1996-12-01), Fujino
patent: 5608602 (1997-03-01), Kuriyama
Coudert Brothers
Dinkins Anthony
Rohm & Co., Ltd.
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