Electricity: electrical systems and devices – Electrolytic systems or devices – Solid electrolytic capacitor
Reexamination Certificate
2003-05-20
2004-08-10
Reichard, Dean A. (Department: 2831)
Electricity: electrical systems and devices
Electrolytic systems or devices
Solid electrolytic capacitor
C361S532000
Reexamination Certificate
active
06775127
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention claims priority to prior Japanese patent application JP 2002-147505, the disclosure of which is incorporated herein by reference.
This invention relates to an anode member for a solid electrolytic capacitor, a method of producing the same, and a solid electrolytic capacitor using the same and, in particular, to a flat anode member including a thin plate of a valve metal as an anode lead and a sintered member laminated thereon, a method of producing the same, and a solid electrolytic capacitor using the same.
There is known a solid electrolytic capacitor including an anode including a sintered member formed by sintering a powder of a valve metal such as tantalum (Ta). Typically, the sintered member has a cylindrical shape such as a circular cylinder or a rectangular cylinder. For convenience of description, the capacitor of the type will be referred to as a cylindrical element capacitor. On the other hand, Japanese Unexamined Patent Publication No. S59-219923 (JP 59-219923 A) discloses a capacitor using a sintered member of a flat structure. The capacitor includes a thin plate (foil) of a valve metal and a layered sintered member laminated on the thin plate. For convenience of description, the capacitor of the type will be referred to as a foil element capacitor. This invention relates to the sintered member of the foil element capacitor. Hereinafter, the foil element capacitor will be described in conjunction with a tantalum solid electrolytic capacitor by way of example. It is well known that, in a solid electrolytic capacitor using a sintered member formed by sintering a powder of a valve metal, the sintered member electrically serves as an anode of the capacitor. In this connection, the thin plate of the valve metal and the sintered member formed thereon may collectively be called an anode member in the following description. Japanese Unexamined Patent Publication No. 2002-50550 (JP 2000-50550 A) discloses a method of producing an anode element for a tantalum electrolytic capacitor, in which a paste containing metal powder is applied or printed to form an anode element.
Referring to
FIG. 1A
, a related tantalum foil element solid electrolytic capacitor will be described. The related tantalum foil element solid electrolytic capacitor includes a tantalum foil
1
, i.e., a foil of a tantalum metal and a layered sintered member
2
obtained by sintering a tantalum powder as a material powder and laminated on the tantalum foil
1
. The layered sintered member
2
of the tantalum powder has small pores formed by sintering and interconnected in a complicated manner. Therefore, the layered sintered member
2
has a very large surfaced area. As described above, the sintered member
2
serves as an anode. On an outer surface of the sintered member
2
and on inner walls of the small pores, a tantalum oxide (Ta
2
O
5
) film (not shown) is formed. The tantalum oxide film serves as a dielectric member of the capacitor. On the tantalum oxide film, a solid electrolyte layer (not shown) is formed. The solid electrolyte layer serves as a cathode of the capacitor. A combination of the sintered member
2
as the anode, the tantalum oxide film as the dielectric member, and the solid electrolyte layer as the cathode forms a fundamental structure of the capacitor.
On the solid electrolyte layer, a conductive substance layer (cathode conductor layer) is formed although not shown in the figure. The cathode conductor layer includes a plurality of layers, for example, a graphite layer and a silver paste layer, successively laminated. To the outermost layer of the cathode conductor layer, a cathode-side terminal (external cathode terminal)
3
for electrical connection to an external circuit is fixedly attached. On the other hand, the tantalum foil
1
partially has an exposed surface on which the sintered member
2
is not formed, as shown at a left side in the figure. To the exposed surface, an anode-side terminal (external anode terminal)
4
for electrical connection to the external circuit is fixedly attached.
An outer resin member
5
, for example, made of epoxy resin covers the tantalum foil
1
, the layered sintered member
2
, and the external cathode and the external anode terminals
3
and
4
except a part of each of the external cathode and the external anode terminals
3
and
4
. The part of each of the external cathode and the external anode terminals
3
and
4
led out of the outer resin member
5
is shaped and bent to extend at first along a side wall and then along a bottom surface of the outer resin member
5
.
In the foil element solid electrolytic capacitor having the above-mentioned structure, the tantalum foil
1
serves to electrically connect the sintered member
2
as the anode of the capacitor and the external anode terminal
4
. Thus, the tantalum foil
1
corresponds to a tantalum wire well known as a so-called “anode lead” in the cylindrical element solid electrolytic capacitor and planted to the cylindrical sintered member.
The tantalum foil element solid electrolytic capacitor mentioned above is generally produced in the following manner. At first, a tantalum powder (a powder of a tantalum metal), a solvent, and a binder are mixed to form a tantalum powder paste. The solvent and the binder are appropriately selected with respect to each other. For example, a water soluble binder is selected for use with a water-based solvent.
Next, on the tantalum foil
1
separately prepared, the tantalum powder paste is printed to form a tantalum powder layer. As a printing mask, a screen mask or a metal mask may be used. In order to reduce a printing thickness, the screen mask is preferable. In order to increase the printing thickness, the metal mask is appropriate.
Then, the tantalum foil
1
with the tantalum powder layer formed thereon is sintered in a high vacuum of, for example, about 10
−6
Torr at a temperature lower than the melting point of the tantalum metal, for example, at a high temperature between about 1300° C. and about 1600° C. Thus, an anode member is obtained.
Thereafter, in the manner similar to the production of the cylindrical element solid electrolytic capacitor, the tantalum oxide film as a dielectric film, the solid electrolyte layer, and the cathode conductor layer are formed. Then, the external cathode and the external anode terminals
3
and
4
are fixedly attached and electrically connected. Furthermore, the outer resin member
5
is formed and the external cathode and the external anode terminals
3
and
4
are shaped.
Specifically, on the inner and the outer surfaces of the anode member obtained by the above-mentioned sintering, a tantalum oxide (Ta
2
O
5
) film, i.e., a thin film of oxide of the tantalum metal as a raw material of the sintered member
2
is formed by anodic oxidation well known in the art. Furthermore, on the tantalum oxide film, the solid electrolyte layer is formed. As a solid electrolyte, use may be made of manganese dioxide obtained by thermal decomposition of manganese nitrate or a conductive polymer such as polypyrrole. In recent years, the conductive polymer is increasingly used as the solid electrolyte because the conductive polymer is smaller in intrinsic resistance so that the capacitor is reduced in equivalent series resistance (ESR) and because a heat insulating reaction is quick so that the capacitor hardly emit smoke or catch fire.
Following the formation of the solid electrolyte layer, the cathode conductor layer is formed. Generally, the cathode conductor layer has a laminate structure including the graphite layer formed on the solid electrolyte layer and the silver paste layer formed on the graphite layer. The cathode conductor layer serves to electrically connect the solid electrolyte layer and the external cathode terminal
3
. Furthermore, the cathode conductor layer also serves to protect the dielectric film by relaxing the stress which would be produced during formation of the outer resin member
5
in the subsequent production process and upon mounting the
Frishauf Holtz Goodman & Chick P.C.
NEC Tokin Corporation
Reichard Dean A.
Thomas Eric
LandOfFree
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