Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device
Reexamination Certificate
2000-12-01
2003-09-02
Nelms, David (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
C361S523000, C361S524000, C361S528000, C075S010330
Reexamination Certificate
active
06614063
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates a solid electrolytic capacitor and a method of making the same and, in particular to the solid electrolytic capacitor of a kind having a solid electrolytic layer made of an electroconductive polymer, and the method of making the same.
2. Description of the Prior Art
With the advent of electronic appliances that are high-frequency oriented, large capacitance electrolytic capacitors that are an electronic component part are desired to have an excellent impedance characteristic (hereinafter referred to as ESR characteristic) in a high frequency region.
A solid electrolytic capacitor is not an exception and, in order to realize this, a surface condition of an anode, a method of forming a dielectric oxide film, improvement of electrolyte, a surface condition of a cathode and the structure of a capacitor element have been studied and examined.
FIG. 12
illustrates a sectional representation of a standard solid electrolytic capacitor
50
. The solid electrolytic capacitor
50
includes a capacitor element
25
embedded in a package
29
generally made of an epoxy resin and reinforcing resin
30
with respective portions of anode and cathode terminals
26
and
27
exposed to the outside.
The capacitor element
25
is made up of a porous anode element
20
, a dielectric oxide film
22
formed on a surface of the anode element
20
, a solid electrolytic layer
23
formed over the dielectric oxide film
22
and a cathode layer
24
formed over the solid electrolytic layer
23
.
The porous anode element
20
is obtained by press-shaping a metal powder of tantalum which is a valve action metal to a desired shape and then sintering it, and the anode element
20
has embedded therein an anode lead line
21
made of a tantalum wire. The anode lead line
21
is connected with the anode terminal
26
.
On the other hand, the cathode layer
24
is formed by laminating a carbon and a silver paint and is connected with the cathode terminal
27
through an electroconductive bonding agent
28
.
A method of making the standard solid electrolytic capacitor
50
will be discussed with reference to
FIG. 13
in which there is shown a flowchart showing the sequence of making the solid electrolytic capacitor
50
according to the prior art. As shown therein the tantalum metal powder with the anode lead line
21
in the form of the tantalum wire embedded therein is press-shaped to a desired shape and is then sintered to provide the porous anode element
20
.
Subsequently, using phosphoric acid, the anode element
20
is anodized to form the dielectric oxide film
22
on an outer surface of the anode element
20
(Anodizing Step).
Thereafter, after the anode element
20
has been impregnated with a pyrrole monomer solution, the anode element
20
is dipped into an oxidizer solution containing iron(l) p-toluenesulfonic acid, iron dodecylbenzenesulfonic acid and so on so that the solid electrolytic layer
23
can be formed over the dielectric oxide film
22
by means of a chemical oxidation polymerization. See, the Japanese Laid-open Patent Publications No. 60-244017 and No. 63-181308.
The porous anode element
20
is repeatedly dipped into the monomer solution and then into the oxidizer solution as disclosed in, for example, U.S. Pat. No. 4,697,001 to form the solid electrolytic layer
23
on the outer surface of the anode element
20
and also within micropores of the anode element
20
.
For the solid electrolytic layer
23
, other than pyrrole, an electroconductive polymer formed by polymerization of thiophene, which is a heterocyclic compound, or furan is employed. Since the above described electroconductive polymer has a very low solid resistance, development has been made with the electroconductive polymer regarded as an effective compound to reduce the impedance of the solid electrolytic capacitor and is put into practical use.
Thus, by means of the chemical oxidation polymerization, the solid electrolytic layer
23
made of polypyrrole is formed on the dielectric oxide film
22
on the anode element
20
(Polymerizing Step).
Thereafter, carbon is coated, a silver paint is coated and drying is performed to complete formation of the cathode layer
24
, thereby completing the capacitor element
25
(Cathode Layer Forming Step).
Then, the anode lead line
21
extending from the capacitor element
25
is soldered to the anode terminal
26
of a COM terminal and the cathode layer
24
is connected with the cathode terminal
27
through an electroconductive bonding agent
28
(Fabricating Step). The capacitor element
25
is thereafter resin-molded in an epoxy covering resin
29
with respective portions of the anode and cathode terminals
26
and
27
exposed to the outside of the covering resin
29
(Resin-encasing Step). In general, by the sequence discussed above, a batch of capacitors
50
are manufactured at a time with the anode and cathode terminals
26
and
27
of one capacitor
50
continued to those of the next adjacent capacitor
50
. Accordingly, as a final step, the capacitors
50
connected together are separated into the individual capacitors
50
which are subsequently tested to provide the individual solid electrolytic capacitors
50
(Finishing Step).
However, the prior art capacitor making method discussed above has the following problems which occur during the polymerizing step in which the solid electrolytic layer
23
is formed.
In the first place, since the chemical oxidation polymerization is repeated a number of times to form the solid electrolytic layer
23
on the outer surface of the anode element
20
and within the micropores of the anode element
20
, residues
31
of solid electrolyte tend to be formed on the outer surface of the anode element
20
as shown in FIG.
14
and within the micropores
20
P of the anode element
20
as shown in FIG.
15
.
It is to be noted that
FIGS. 14 and 15
illustrate the anode element
20
obtained after the polymerization step discussed above. Although not shown in
FIG. 14
, the surface of the anode element
20
is formed with the oxide film
22
and the solid electrolytic layer
23
. The plural anode elements
20
are connected to a support bar
3
by means of the respective anode lead lines
21
connected therewith.
FIG. 14
makes it clear that the residues
31
are formed on the outer surface of the anode element
20
having the solid electrolytic layer
23
. Also,
FIG. 15
is a fragmentary enlarged diagram of a portion of the anode element
20
, and it makes clear that the residues
31
are formed within the micropores
20
P of the anode element
20
formed with the solid electrolytic layer
23
. It is to be noted that although not shown in
FIG. 15
, the dielectric oxide film
22
is formed on the surface of the anode element
20
.
The residues
31
of the electrolyte referred to above are made up of lees left during the chemical oxidation polymerization, unpolymerized electroconductive polymer and/or oxidizing agent and they do not only deteriorate an outer appearance of the capacitor element
25
to reduce the volumetric capacity and, hence, to reduce the capacitor characteristic, but may often leak out of the covering resin
29
in the worst case it may occur. It is noted that the term “volumetric capacity” means the degree of ease of encasing the capacitor element within, for example, an epoxy covering resin. Hence, when it comes to a high volumetric capacity, it means that the capacitor element is completely encased easily. Accordingly, in order to remove the residues
31
, the use has been made of a brush or the like to remove the residues
31
prior to the cathode layer forming step to render the surface of the solid electrolytic layer
23
to be flat and to repair the outer shape, resulting in reduction in productivity. Also, depending on the condition under which the residues
31
are removed, the solid electrolytic layer
23
may be damaged, resulting in deterioration of the capacitor characteristic.
Secondly, since during the step of form
Hashimoto Yoshiki
Hayashi Chiharu
Igaki Emiko
Kato Hisataka
Kawahito Kazuo
Matsushita Electric - Industrial Co., Ltd.
Tran Mai-Huong
LandOfFree
Solid electrolytic capacitor does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Solid electrolytic capacitor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Solid electrolytic capacitor will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3092787