JP2004304063A - Solid electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid electrolytic capacitor which has a low ESR (equivalent series resistance) and a small loss, and also a method for manufacturing the capacitor. <P>SOLUTION: In the solid electrolytic capacitor, an anodic oxide film is formed on a sintered compact made of valve action metal powder, a solid electrolyte layer made of manganese dioxide or the like is formed thereon, and then a cathode layer is formed thereon. A first carbon layer 41 made of mainly carbon particles having small diameters as the cathode layer, a second carbon layer 42 made of mainly scale-like carbon particles having large diameters, a third carbon layer 43 having small diameters and a silver paste layer 5, are sequentially laminated. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a solid electrolytic capacitor and a method for manufacturing the same.
[0002]
[Prior art]
In recent years, there has been a demand for a highly reliable solid electrolytic capacitor having a small leakage current and excellent high-frequency characteristics. In order to meet this demand, JP-A-64-47016, JP-A-1-253226 and JP-A-2-130906 disclose a solid electrolytic capacitor using manganese dioxide or a conductive polymer as a solid electrolyte. is suggesting. Such a solid electrolytic capacitor is manufactured as follows.
[0003]
First, a chemical conversion film is grown on the surface of a porous body by anodizing a porous body made of a valve metal such as tantalum, aluminum, and niobium. A solid electrolyte layer made of manganese dioxide as a semiconductor or a functional polymer is formed on the chemical conversion film. Subsequently, a carbon layer is formed on the surface of the solid electrolyte layer, and a paint containing silver is applied on the carbon layer to provide a cathode extraction electrode made of a silver conductive resin layer. The carbon layer joins the solid electrolyte layer and the silver conductive resin layer to improve conduction in the capacitor.
[0004]
[Patent Document 1] JP-A-64-47016 [Patent Document 2] JP-A-1-253226 [Patent Document 3] JP-A-2-130906 [0005]
[Problems to be solved by the invention]
However, in the above-described solid electrolytic capacitor, even when manganese dioxide or a polymer solid electrolyte having higher conductivity is used as the solid electrolyte, the equivalent series resistance (Equivalent Series Resistance, hereinafter referred to as ESR) of the solid electrolytic capacitor is constant. There was a problem that it did not drop below the value. As a result of a detailed study, it was found that the ESR was much larger than the total value of the resistance of each member in the conductive path of the capacitor charging / discharging current. In addition, it has been found that the contact resistance depending on the contact between the carbon layer and the solid electrolyte layer is a main factor of the ESR, and this ESR affects the characteristics of the solid electrolytic capacitor.
[0006]
The present invention has been made to solve the above-described problems, and has as its object to provide a solid electrolytic capacitor having low ESR and low loss, and a method of manufacturing the same.
[0007]
[Means for Solving the Problems]
The present invention relates to a solid electrolytic capacitor in which an anodic oxide film is formed on a sintered body made of a valve metal powder, and a solid electrolyte layer and a cathode layer are sequentially laminated. A second carbon layer mainly composed of flaky carbon having a large particle diameter, a third carbon layer mainly composed of carbon having a small particle diameter, and a silver paste layer.
[0008]
The surface of the solid electrolyte layer is not flat, but has irregularities. For example, in the case of using manganese dioxide as a solid electrolyte, a sintered body obtained by sintering tantalum powder is dipped in an aqueous manganese nitrate solution, then withdrawn, and heated and fired at a temperature of about 200 ° C. a plurality of times (for example, (About 10 times) to form a solid electrolytic layer of manganese dioxide, but manganese dioxide is not densely formed due to volume shrinkage due to firing and evaporation of the solvent of the manganese nitrate aqueous solution, and the manganese dioxide layer is It has a gap.
[0009]
In addition, even when the conductive polymer is used as a solid electrolyte, when the conductive polymer layer is formed by chemical polymerization, it is difficult to control the polymerization direction by chemical polymerization, and the surface has irregularities. It will be formed.
[0010]
Therefore, when a carbon layer mainly composed of carbon having a small particle diameter is formed, carbon particles enter the unevenness on the surface of the solid electrolyte layer, and the contact area with the solid electrolyte layer can be reduced. However, carbon particles having a small particle diameter have a small cross-sectional area inside the carbon particles and a high contact frequency with the carbon particles, so that the contact resistance is large. Therefore, the conductivity of the carbon layer cannot be said to be good when the entire carbon layer is viewed.
[0011]
Therefore, by forming a second carbon layer mainly composed of flaky carbon having a large particle diameter on the first carbon layer mainly composed of a carbon particle having a small particle diameter, the carbon of the first carbon layer is formed. The contact area with the particles is increased, and the internal resistance of the flaky carbon itself having a large particle size is small (because the cross-sectional area of the conductive path is large due to the large particle size). , The resistance of the carbon layer is low.
[0012]
Further, a silver paste layer is formed on the carbon layer. In many cases, silver particles in the silver paste layer have a size of 3 to 10 μm, which is larger than the carbon particles. Therefore, when the silver paste layer is applied directly on the second carbon layer mainly composed of flaky carbon, the surface of the flaky carbon layer is rough. In some cases, it is not possible to enter the gap, and as a result, a sufficient contact area between the carbon layer and the silver paste cannot be secured, resulting in an increase in contact resistance. Therefore, in the present invention, a third carbon layer mainly composed of carbon having a small particle diameter is formed on a second carbon layer mainly composed of flaky carbon, the surface irregularities of the carbon layer are reduced, and a silver paste is formed. To reduce the contact resistance.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, an embodiment of the present invention will be described.
[0014]
FIG. 1 is a sectional view showing the structure of the solid electrolytic capacitor, and FIG. 2 is an enlarged view showing the structure of the cathode layer of the solid electrolytic capacitor.
[0015]
Reference numeral 1 denotes an anode body formed by elongating an anode lead wire 2 by sintering, for example, a powder of tantalum, which is a metal having a valve action, under pressure molding. A dielectric oxide film is formed on the surface of the anode body 1, and then the anode body 1 is impregnated with a manganese nitrate solution and baked to form a manganese dioxide layer 3 on the surface of the anode body 1 to form a solid electrolyte layer. .
[0016]
Further, a carbon layer 4 is formed on the manganese dioxide layer 3. As the carbon layer 4, first, a first carbon layer 41 mainly containing carbon particles having an average particle diameter of 0.1 to 1 μm is formed. The carbon layer can be formed by immersing the anode body 1 in a dispersion in which carbon particles and a binder are dispersed in a dispersion medium, and then pulling up and drying.
[0017]
After forming the first carbon layer, a second carbon layer 42 having carbon particles having an average particle diameter of 1 to 10 μm as a main component is formed on the surface thereof. Further, after forming the second carbon layer, a third carbon layer 43 mainly containing carbon particles having an average particle diameter of 0.1 to 1 μm is formed on the surface thereof. The formation method of the second carbon layer 42 and the third carbon layer 43 is similar to the formation of the first carbon layer 41. The anode body 1 is formed into a dispersion liquid in which predetermined carbon particles and a binder are dispersed in a dispersion medium. It can be formed by a method of drying after dipping.
[0018]
Then, a silver paste layer 5 mainly composed of flaky silver having an average particle size of 1 to 10 μm is formed on the carbon layer to form a cathode layer.
[0019]
Subsequently, a conductive adhesive 7 such as a silver adhesive is applied to a connection portion of the silver paste layer 5 where the cathode lead terminal 6 is connected, and the cathode lead terminal 6 is connected. Thereafter, the anode lead wire 2 is connected to the anode lead terminal 8 by, for example, spot welding, and then the entire device body including the anode body 1 and the cathode layer is epoxy-based including the bases of the anode lead terminal 8 and the cathode lead terminal 6. To complete the solid electrolytic capacitor.
[0020]
In the solid electrolytic capacitor having the above configuration, the cathode layer has a first carbon layer mainly composed of carbon having a small particle diameter, a second carbon layer mainly composed of flaky carbon having a large particle diameter, and a carbon layer having a small particle diameter. Since it is composed of a third carbon layer and a silver paste layer mainly composed of, the contact resistance between the solid electrolyte layer and the cathode layer and the contact resistance between the carbon layer and the silver paste layer of the cathode layer can be reduced. ESR of the entire solid electrolytic capacitor can be reduced.
[0021]
【The invention's effect】
As described above, the present invention can reduce the ESR of the solid electrolytic capacitor.
[Brief description of the drawings]
FIG. 1 is a sectional view showing a structure of a solid electrolytic capacitor of the present invention.
FIG. 2 is a sectional view showing a structure of a cathode layer of the solid electrolytic capacitor of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Sintered body 2 Anode lead wire 3 Manganese dioxide layer (solid electrolyte layer)
Reference Signs List 4 carbon layer 41 first carbon layer 42 second carbon layer 43 third carbon layer 5 silver paste layer 6 cathode lead terminal 7 conductive adhesive 8 anode lead terminal 9 insulating resin

Claims (1)

An anodic oxide film is formed on a sintered body made of powder of valve action metal, and in a solid electrolytic capacitor obtained by sequentially laminating a solid electrolyte layer and a cathode layer,
The cathode layer includes a first carbon layer mainly composed of carbon having a small particle diameter, a second carbon layer mainly composed of flaky carbon having a large particle diameter, a third carbon layer mainly composed of carbon having a small particle diameter, silver A solid electrolytic capacitor comprising a paste layer.

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