Electricity: electrical systems and devices – Electrolytic systems or devices – Solid electrolytic capacitor
Reexamination Certificate
2001-10-11
2003-01-07
Dinkins, Anthony (Department: 2831)
Electricity: electrical systems and devices
Electrolytic systems or devices
Solid electrolytic capacitor
C361S523000, C361S529000, C029S025030
Reexamination Certificate
active
06504705
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an electrolytic capacitor that can be built in a board, for use in a high-speed power source circuit, to a circuit board containing an electrolytic capacitor, and to a method for producing the same.
2. Related Background Art
Conventionally, an electrolytic capacitor in which a valve metal such as aluminum or tantalum is used, and a multilayered ceramic capacitor in which Ag/Pd or Ni is used for electrodes and barium titanate is used as a dielectric, have been known as capacitors. These capacitors are used in many power source circuits. Recently, since CPU driving circuits and switching power source circuits particularly are required to be driven with a lower driving voltage, to consume less power, and to be fitted for high frequencies, a capacitor also is required to have a large capacitance, a low equivalent series resistance (hereinafter referred to as ESR), and a low equivalent series inductance (hereinafter referred to as ESL). To meet with these requirements, particularly for a capacitor to have a low ESR, a technique in which a specialty polymer having a high electroconductivity (conductive polymer) is used as a solid electrolyte for a cathode has been examined and developed.
A configuration of a conventional specialty polymer electrolytic capacitor is described below, with reference to FIG.
11
.
FIG. 11
is a cross-sectional view of a conventional specialty polymer electrolytic capacitor. In
FIG. 10
,
101
denotes an aluminum foil for an anode (hereinafter referred to as anode-use aluminum foil).
102
denotes a dielectric layer.
103
denotes a conductive polymer layer.
104
denotes a carbon layer.
105
denotes an Ag paste layer.
106
denotes a lead frame.
107
denotes a lead frame.
108
denotes a molding resin.
The anode-use aluminum foil
101
has been treated so as to have rough surfaces, and is provided with the dielectric layer
102
on the surfaces. On the surfaces of the anode-use aluminum foil
101
provided with the dielectric layer
102
, the conductive polymer layer
103
made of polypyrrole, polythiophene, polyaniline, etc. is formed. Furthermore, on the conductive polymer layer
103
, the carbon layer
104
and the Ag paste layer
105
are formed in the stated order, so that a conventional capacitor unit is provided. Further, the lead frame
106
and the lead frame
107
that function as an anode terminal and as a cathode terminal, respectively, are bonded with the foregoing conventional capacitor unit, and the capacitor unit is sealed with the molding resin
108
. Thus, the conventional specialty polymer electrolytic capacitor is formed.
Such a conventional specialty polymer electrolytic capacitor has a lower ESR than that of an electrolytic capacitor using an electrolytic solution as the electrolyte (hereinafter referred to as an electrolytic solution-type electrolytic capacitor). To further increase the capacitance and decrease the ESR, however, a configuration in which a plurality of conventional capacitor units are laminated with an Ag adhesive (Ag adhesive paste) has been developed. Furthermore, as to the foregoing conventional capacitor unit, to decrease the ESR thereof further, materials for the conductive polymer layer
103
, the carbon layer
104
, and the Ag paste layer
105
have been developed.
Furthermore, recently, the development of capacitors arranged so that not only the ESRs but also the ESLs of the same are reduced for suppression of voltage falling due to inductance components has been needed, for use in high-frequency driving circuits such as MPU power source circuits. Therefore, small-size multilayered ceramic capacitors with small ESLs and electrolytic capacitors with three terminals or four terminals have been developed. Furthermore, circuit boards provided with such capacitors are required to allow LSIs to be driven with high frequencies, in addition to meeting requests for reduction in size and thickness. To obtain such a circuit board, it is necessary to shorten wirings and connections. Therefore, a technique of, for instance, burying a capacitor in a circuit board so as to dispose the capacitor closer to an LSI and thereby reducing inductance components of wirings has been developed.
In the case of the conventional specialty polymer electrolytic capacitor having the aforementioned configuration, however, lead frames are provided as an anode terminal and a cathode terminal, and further, the capacitor unit is larger in size. Therefore, a product of the same has a relatively large size. This makes it difficult to obtain an ESL value lower than 1 nH in the conventional specialty polymer electrolytic capacitor. For this reason, the conventional specialty polymer electrolytic capacitor, whose ESL hardly is reduced despite having a reduced ESR, is inferior to a multilayered ceramic capacitor, which is small in size as a capacitor used in a high-frequency-driven circuit.
On the other hand, as described above, in the case of a high-frequency-driving circuit, which requires the shortening of wirings and connections, a technique of burying a capacitor unit in a circuit board has been developed. However, if the conventional specialty polymer electrolytic capacitor is embedded in the circuit board as it is, serious problems have arisen. Namely, an anode-use valve metal foil having rough surfaces (an etching layer of the anode-use aluminum foil
101
in
FIG. 11
) and a dielectric (the dielectric layer
102
in
FIG. 11
) are broken due to stress and the like during a burying operation, thereby causing short circuits to occur and causing leak current to increase. Thus, it has been difficult to obtain sufficient characteristics and reliability by burying the conventional specialty polymer electrolytic capacitor in a circuit board. On the other hand, in the case where a multilayered ceramic capacitor is embedded in a circuit board as well, a drawback is that the multilayered ceramic capacitor is broken due to stress and the like upon a burying operation.
Furthermore, in the case where the conventional specialty polymer electrolytic capacitor is embedded in a circuit board, problems to be solved are present also in the connection of the capacitor with circuit wiring. When a specialty polymer electrolytic capacitor of a conventional lead frame structure is connected with circuit wiring, the lead frame and the circuit wiring are connected by soldering. In this case, the shortening of the connections cannot be achieved, and it is difficult to drive a circuit with a high frequency.
SUMMARY OF THE INVENTION
Therefore, with the foregoing in mind, it is an object of the present invention to provide an electrolytic capacitor with a reduced ESL such that the occurrence of short circuits and an increase in leak current can be suppressed when the electrolytic capacitor is embedded in a circuit board, and a method for producing the same, as well as an electrolytic-capacitor-containing circuit board that ensures high-frequency response and large-current driving, and a method for producing the same.
To achieve the foregoing object, an electrolytic capacitor of the present invention includes a valve metal element for an anode including a capacitor forming part and an electrode lead part, a dielectric layer provided on a surface of the valve metal element for an anode, a solid electrolyte layer provided on the dielectric layer, and a charge collecting element for a cathode provided on the solid electrolyte layer. In the electrolytic capacitor, in the valve metal element for an anode, the capacitor forming part and the electrode lead part have a rough surface layer on surfaces thereof, and is compressed in a thickness direction of the rough surface layer.
The electrolytic capacitor is formed using a valve metal element for an anode in a state of being compressed in the thickness direction of the rough surface layer after the surface roughening treatment. Since the valve metal element for an anode is compressed beforehand, it is possible to avoid damage to
Handa Hiroyuki
Ishikawa Akihiro
Nakada Yasuhiko
Nakatani Seiichi
Shimada Mikinari
Dinkins Anthony
Matsushita Electric - Industrial Co., Ltd.
Merchant & Gould P.C.
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