Solid electrolytic capacitor and method of fabricating the same

Details Solid electrolytic capacitor and method of fabricating the same Solid electrolytic capacitor and method of fabricating the same

2000-09-08

2002-06-04

Reichard, Dean A. (Department: 2831)

Electricity: electrical systems and devices

Electrolytic systems or devices

Solid electrolytic capacitor

C361S437000, C361S311000, C361S509000, C361S511000, C361S323000

Reexamination Certificate

active

06400556

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a solid electrolytic capacitor for use in an electronic apparatus, and a method of fabricating the same.
BACKGROUND OF THE INVENTION
In general, electrolytic capacitors for use in the secondary side of a power supply circuit, or with the CPU of a personal computer have been desired for decreased dimensions and increased capacitance, as well as minimizing both the equivalent serial resistance (ESR) and the equivalent serial inductance(ESL).
FIG. 10
illustrates the typical structure of a conventional chip solid electrolytic capacitor. More specifically, capacitor element
26
has a positive electrode
20
made of a valve metal in which positive electrode lead
21
is embedded and connected at its proximal end with dielectric oxide film
23
, electrolyte layer
24
, and negative electrode layer
25
in a sequence. Positive electrode lead
21
of capacitor element
26
is welded to external positive electrode terminal
27
, while negative electrode layer
25
is connected by conductive adhesive
28
to external negative electrode terminal
29
. Capacitor element
26
and its joints are protected with resin coating
30
shaped by mold forming. External positive electrode terminal
27
and external negative electrode terminal
29
, projecting outwardly from opposite ends of resin coating
30
, are folded down to extend vertically along the surface of resin coating
30
and then horizontally along the bottom side of resin coating
30
, whereby the shape of a chip solid electrolytic capacitor can be determined.
To improve the productivity of such capacitors, a method of modifying a solid of the chip into a wafer form is disclosed in Japanese Patent (Publication No. 8-31696).
Recently, for minimizing ESR, a solid electrolytic capacitor employing, as the solid electrolyte, a functional polymer which is remarkably higher in electric conductivity than a conventional material or manganese dioxide has been proposed.
The above mentioned conventional chip solid electrolytic capacitor however has a considerable size of dead space created by the feed-out region and the folded leads at the joints between positive electrode lead
21
and external positive electrode terminal
27
and between negative electrode lead
25
and external negative electrode terminal
29
in capacitor element
26
. Accordingly, the installation of capacitor element
26
will hardly be efficient, hence making the chip capacitor of favorably minimized dimensions much difficult. The feed-out of positive electrode
20
is connected by a point to positive electrode lead
21
. This may increase the resistance to the positive electrode output, hence increasing ESR of the conventional chip solid electrolytic capacitor.
Alternatively, a small-sized, large-capacitance chip solid electrolytic capacitor employs traditionally a high capacitance/voltage (CV) powder of valve metal. The high CV powder is increased in the actual surface area by reducing the diameter of each primary particle. This increases the electrostatic capacitance per unit volume, but decreases mass of bubbles in the particles after shaping and sintering. Accordingly, when the electrostatic capacitance is fed out from a solid electrolyte layer after the development of an oxide film, the resistance of the solid electrolyte layer increases and ESR thus increases in theory. Also, as its impregnation of the solid electrolyte solution is relatively low, a capacitance achievement rate, which is expressed by a ratio of the electrostatic capacitance of a liquid electrolyte to the electrostatic capacitance of a solid electrolyte, may possibly be declined.
Moreover, as the positive electrode of such a conventional capacitor is a solid material, its productivity will remain low. Even the high CV powder may fail to demonstrate its advantage in increasing a capacitance and thus hardly minimize ESR.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a solid electrolytic capacitor in which the capacitor element has improved volumetric installation efficiency, hence minimizing the overall thickness and lowering the equivalent serial resistance (ESR).
The solid electrolytic capacitor according to the present invention includes a capacitor element which comprises:
(a) a positive electrode lead made of a valve metal in any form selected from a net, a sheet, a foil, and their modification with rough surface;
(b) a positive electrode body which is fabricated by forming and sintering a desired shape of the valve metal and which is arranged for the positive electrode lead to be embedded with one end exposed to the outside; and
(c) a dielectric oxide film and a negative electrode layer provided on the surface of the positive electrode body.
The solid electrolytic capacitor further comprises a positive electrode terminal connected to the exposed end of the positive electrode lead extending from the capacitor element, a negative electrode terminal connected to the negative electrode layer, and an insulating housing resin covering entirely the capacitor element with the positive electrode terminal and the negative electrode terminal partially exposed to the outside.
The capacitor is consequently decreased in thickness while eliminating redundant of the space created by the feed-out for external connection. As the charge feed-out distance between the positive electrode and the negative electrode is minimized, the equivalent serial resistance pertinent to the chip solid electrolytic capacitor can be lowered.


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patent: 4017773 (1977-04-01), Cheseldine
patent: 4105513 (1978-08-01), Nishino et al.
patent: 5036434 (1991-07-01), Kobayashi
patent: 5140502 (1992-08-01), Kudoh et al.
patent: 5223120 (1993-06-01), Kojima et al.
patent: 5329421 (1994-07-01), Kuriyama
patent: 5583740 (1996-12-01), Fujino
patent: 5608602 (1997-03-01), Kuriyama
patent: 5729424 (1998-03-01), Sharp et al.
patent: 6188566 (2001-02-01), Aoyama
patent: 405159988 (1993-06-01), None

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