Capacitor element for solid electrolytic capacitor, process...

Details Capacitor element for solid electrolytic capacitor, process... Capacitor element for solid electrolytic capacitor, process...

2003-05-13

2004-08-31

Reichard, Dean A. (Department: 2831)

Electricity: electrical systems and devices

Electrolytic systems or devices

Solid electrolytic capacitor

C361S540000

Reexamination Certificate

active

06785124

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
Typical solid electrolytic capacitors are generally divided into such a solid electrolytic capacitor
100
as disclosed in JP-A-60-220922 and shown in
FIG. 1
, and such a solid electrolytic capacitor
200
with a safety fuse as disclosed in JP-A-2-105513 and shown in FIG.
2
.
2. Description of the Related Art
The former solid electrolytic capacitor
100
includes a capacitor element
1
arranged between a pair of lead terminals
5
and
6
. The capacitor element comprises a porous anode chip body
2
formed by compacting and sintering valve (valve action) metal powder, an anode wire
3
made of valve metal powder and fixedly connected to one end surface
2
a
of the anode chip body
2
, and a cathode electrode film
4
formed on the anode chip body
2
via a dielectric film and a solid electrolyte layer. In setting the capacitor element
1
, the anode wire
3
of the capacitor element
1
is connected to the anode lead terminal
5
by welding for example, whereas the cathode lead terminal
6
is electrically connected directly to the cathode electrode film
4
of the capacitor element
1
. These components are sealed in a package
7
made of synthetic resin.
Similarly, the latter solid electrolytic capacitor
200
with a safety fuse includes a capacitor element
1
arranged between a pair of lead terminals
5
and
6
. The capacitor element comprises a porous anode chip body
2
formed by compacting and sintering valve metal powder, an anode wire
3
made of valve metal powder and fixedly connected to one end surface
2
a
of the anode chip body
2
, and a cathode electrode film
4
formed on the anode chip body
2
via a dielectric film and a solid electrolyte layer. In setting the capacitor element
1
, the anode wire
3
of the capacitor element
1
is connected to the anode lead terminal
5
by welding for example. The cathode electrode film
4
of the capacitor element
1
is electrically connected to the cathode lead terminal
6
via a safety fuse wire M which melts and breaks due to overcurrent or temperature increase. These components are sealed in a package
9
made of synthetic resin.
Conventionally, a capacitor element for such solid electrolytic capacitors is manufactured by the following method.
Firstly, as shown in
FIG. 3
, valve metal powder such as tantalum is compacted into a porous anode chip body
2
so that an anode wire
3
made of valve metal such as tantalum projects from one end surface of the anode chip body
2
and then sintered. Subsequently, as shown in
FIG. 4
, the porous anode chip body
2
is immersed in a chemical solution A such as an aqueous solution of phosphoric acid with one end surface
2
a
of the anode chip body
2
oriented upward. In this state, anodization is performed by applying direct current across an electrode B in the chemical liquid A and the anode wire
3
. As a result, a dielectric film
2
b
of tantalum pentoxide, for example, is formed on the surfaces of metal particles of the anode chip body
2
. At that time, a dielectric film of tantalum pentoxide, for example, is formed also on a root portion of the anode wire
3
connected to the anode chip body
2
.
Then, as shown in
FIG. 5
, the anode chip body
2
is immersed in an aqueous solution C of manganese nitrate with the end surface
2
a
of the anode chip body
2
oriented upward. After the aqueous solution of manganese nitrate C infiltrates into the anode chip body
2
, the anode chip body is pulled out of the solution of manganese nitrate C and baked. These process steps are repeated a plurality of times. As a result, a solid electrolyte layer
4
a
of metal oxide such as manganese dioxide is formed on the dielectric film
2
b
of the anode chip body
2
.
Subsequently, the cathode electrode film
4
comprising a graphite layer as a base layer and a metal layer of e.g. silver or nickel as an upper layer is formed over the solid electrolyte layer
4
a
on the surface of the anode chip body
2
except for the end surface
2
a.
When the solid electrolyte layer
4
a
of metal oxide such as manganese dioxide is formed in the above-described manufacturing process of a capacitor element, the solution of manganese nitrate C rises onto the surface of the root portion of the anode wire
3
connected to the anode chip body
2
. Therefore, the solid electrolyte layer of manganese dioxide or the like is formed also at the root portion as connected to the solid electrolyte layer
4
a
of the anode chip body
2
. Therefore, in assembling the capacitor element
1
into a complete solid electrolytic capacitor
100
,
200
, when the anode wire
3
is connected to an anode lead terminal
5
made of a metal plate by e.g. welding, the solid electrolyte layer formed on the root portion of the metal wire
3
may come into contact with the anode lead terminal
5
, which may cause electrical short and often result in product failure.
Conventionally, therefore, before or after forming the dielectric film
2
b
of tantalum pentoxide by anodization, a ring member
8
made of a water-repellent synthetic resin such as fluoroplastic is attached around the root portion of the anode wire
3
, as disclosed in JP-A-2000-348975 and shown in FIG.
6
(
a
), or a coating
8
′ as shown in FIG.
6
(
b
) is formed by applying water-repellent synthetic resin dissolved in a solvent to the root portion followed by drying. Then, in such a state as shown in FIG.
6
(
a
) or
6
(
b
), the above-described formation of the solid electrolyte layer
4
a
by immersing in the aqueous solution of manganese nitrate, pulling out from the solution and baking is performed. In this method, the ring member
8
made of water-repellent synthetic resin or the coating
8
′ prevents the aqueous solution of manganese nitrate from rising up to the root portion of the anode wire, and hence prevents a solid electrolyte layer from being continuously formed on the root portion of the anode wire
3
. Thus, it is possible to reduce the possibility of product failure in assembling in to a completed solid electrolytic capacitor.
However, when the ring member
8
is attached around the root portion of the anode wire
3
as is in the former case (See FIG.
6
(
a
)), a gap is inevitably defined between the lower surface of the ring member
8
and the end surface
2
a
of the anode chip body
2
due to the irregularity of the end surface
2
a
. Further, a gap is also defined between the outer circumferential surface of the anode wire
3
and the inner circumferential surface of the ring member
8
.
The gap between the outer circumferential surface of the anode wire
3
and the inner circumferential surface of the ring member
8
is formed because the inner diameter of a through-hole of the ring member
8
is made larger than the diameter of the anode wire
3
for easily fitting the ring member
8
around the anode wire
3
. Further, fin or the like formed in punching the ring member
8
from a plate material also inevitably causes the formation of the gap.
Therefore, as shown in
FIG. 5
, when the anode chip body
2
is immersed in a solid electrolyte forming solution such as an aqueous solution of manganese nitrate C or the like for forming the solid electrolyte layer
4
a
, the solid electrolyte forming solution such as manganese nitrate solution flows into the gap between the lower surface of the ring member
8
and the end surface
2
a
of the anode chip body
2
by capillary action. Then, the solid electrolyte forming solution passes through the gap between the inner circumferential surface of the ring member
8
and the outer circumferential surface of the anode wire
3
to reach the upper surface side of the ring member
8
. Thus, the ring member
8
cannot prevent the rising of manganese nitrate solution perfectly. Since a solid electrolyte layer is formed also on the upper surface side of the ring member
8
of the anode wire
3
as connected to the solid electrolyte layer
4
a
on the anode chip body
2
, the possibility of product failure in assembling into a complete

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