JPS6336134B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a solid electrolytic capacitor using a valve metal such as tantalum or aluminum as an anode substrate. BACKGROUND ART In general, a conventional solid electrolytic capacitor uses a sintered body, plate, foil, rod, thin film, etc. of a valve metal such as tantalum or aluminum as an anode substrate 1, as shown in FIG. A dielectric oxide film 2 such as tantalum oxide is formed on the surface of 1 by an anodizing method, and manganese dioxide etc. are formed on this dielectric oxide film 2 by thermal decomposition of a pyrolyzable metal salt such as manganese nitrate A solid electrolyte layer 3 was formed, and a carbon layer 4, a silver paint layer 5, and a solder layer 6 were sequentially laminated thereon for cathode current collection. In addition, in FIG. 4, 7 is an anode lead wire drawn out from the anode base 1. In this way, in conventional solid electrolytic capacitors, the cathode current collector is formed as a carbon layer 4 by impregnating and drying a conductive substance such as colloidal graphite on a solid electrolyte layer 3 formed by thermal decomposition. Furthermore, a silver paint layer 5 was formed on this carbon layer 4. Problems to be Solved by the Invention However, as shown in FIG. The carbon layer 4 formed on the solid electrolyte layer 3 by coating and drying graphite does not contact the porous solid electrolyte layer 3 with sufficient adhesive force, and therefore becomes a series resistance component of the capacitor. tanδ and its frequency characteristics,
There is a problem of poor impedance characteristics, and a solution to this problem has been desired. Furthermore, the silver paint layer 5 formed on the carbon layer 4 serves as a conductor, but this silver paint layer 5 has a large amount of silver dispersed in an organic binder and is quite expensive. The price is around 40,000 to 50,000 yen/kg. Therefore, in terms of material costs for small capacitor elements such as solid electrolytic capacitors, the material cost of silver paint accounts for about 6 to 10% of the total material cost of valve metal powder, etc. Even for large capacitors, the amount of silver paint used per element has increased considerably, and there is a need for inexpensive conductive materials to replace silver paint. In addition, when using this silver paint, as mentioned above, silver paint has fine silver powder dispersed in an organic binder.
When the capacitor is left in an atmosphere of 90 to 100% humidity, as shown in FIG. The leakage current then reaches the dielectric oxide film 2, resulting in leakage current deterioration and short-circuit breakdown. For this reason, capacitors that require volumetric efficiency, such as chip capacitors, are currently moving toward unpacked types, which require high humidity resistance. At present, moisture resistance is maintained by coating with a synthetic resin. In this way, the reason why the cathode current is collected by the carbon layer 4 and the silver paint layer 5 as in the conventional solid electrolytic capacitor is that there is incomplete electrical contact between the carbon layer 4 and the solid electrolyte layer 3, and expensive silver is used. High material costs due to the use of paint There are various problems such as poor moisture resistance of silver paint, which leads to problems in electrical characteristics such as tan δ, frequency characteristics, impedance characteristics, etc., and price problems, and improvements are desired. was. The present invention solves these conventional problems and aims to improve the electrical characteristics and reduce the cost of solid electrolytic capacitors. Means for Solving the Problems In the method for manufacturing a solid electrolytic capacitor of the present invention, the cathode layer formed on the solid electrolyte layer for cathode current collection is configured as a layer containing ruthenium oxide,
And the cathode conductor layer formed on this cathode layer is made of copper,
It is constructed by forming a single metal such as tin, nickel, aluminum, lead, silver, or an alloy thereof by plasma spraying or arc spraying. Effects Compared to conventional carbon layers, the adhesion of ruthenium oxide to the solid electrolyte layer is stronger and can withstand the formation of a cathode conductor layer by thermal spraying, fully utilizing the advantages of forming a cathode conductor layer by thermal spraying. You can take advantage of it. Embodiment FIG. 1 shows an embodiment of the solid electrolytic capacitor of the present invention. In FIG. 1, the same parts as those of the conventional solid electrolytic capacitor shown in FIG. 4 are given the same numbers. In FIG. 1, 12 is a cathode layer made of ruthenium oxide for cathode current collection. Reference numeral 13 denotes a cathode conductor layer formed on this cathode layer 12. This cathode conductor layer 13 is formed by thermal spraying a conductive material such as a single metal such as copper, tin, nickel, aluminum, lead, or silver or an alloy thereof. It is formed by depositing on the cathode layer 12. First, the superiority of ruthenium oxide as the cathode layer 12 will be described. Ruthenium oxide has a low resistivity of ρ = 10 ^-5 to ^{10 -2} Ωcm, and is easily decomposed by thermal decomposition of chlorides, nitrates, carbonates, oxalates, etc. of these metals. can get.
For example, ruthenium oxide can be produced by thermally decomposing ruthenium chloride. For this reason, if a capacitor element having a porous solid electrolyte layer such as manganese dioxide on the outer shell is immersed in an aqueous ruthenium chloride solution and the ruthenium chloride impregnated in the porous solid electrolyte layer is thermally decomposed, the ruthenium chloride will be released onto the solid electrolyte layer. A ruthenium oxide layer can be formed. The ruthenium oxide layer produced in this way is thermally decomposed while the starting material, ruthenium chloride, is impregnated as an aqueous solution into the pores of the porous solid electrolyte layer, and the particle size of this ruthenium oxide is extremely small. The ruthenium oxide layer has a fineness of about 0.1μ or less, and can form a ruthenium oxide layer even in pores that are difficult for carbon to penetrate, as shown in Figure 2. Becomes good. Furthermore, when carbon is conventionally used as the cathode layer, although carbon has conductivity, it is different from the solid electrolyte layer made of metal oxides such as manganese dioxide. In the invention, ruthenium oxide is an oxide that has conductivity, and therefore, it can be assumed that the contact with the solid electrolyte layer such as manganese dioxide will be stronger as the same oxide, and from this point of view, the contact state between the two is Very strong and good quality. Next, the advantages of the cathode conductor layer 13 formed by thermal spraying on the cathode layer 12 as described above will be described. Metals to be sprayed to form the cathode conductor layer 13 include copper, tin, nickel, aluminum,
Although single metals such as lead and silver and alloys thereof can be used, copper, aluminum, and alloys thereof are optimal in terms of economy and workability. Additionally, metal spraying methods include plasma spraying,
Although arc spraying can be used, plasma spraying is more preferred due to its properties. Note that the cathode conductor layer 13 formed by this thermal spraying is effective only when the cathode layer is basically composed of ruthenium oxide.
This is clear from the experimental results of the present inventors, and when the cathode conductor layer 13 is formed by thermal spraying on the conventional carbon layer 4, tan δ and impedance due to poor adhesion between the carbon layer 4 and the solid electrolyte layer 3. Not only is the characteristic deterioration observed, but also the carbon layer 4 may peel off from the solid electrolyte layer 3 depending on the thickness of the cathode conductor layer 13 due to thermal spraying. In contrast, in the case of the present invention, since the adhesion between the cathode layer 12 and the solid electrolyte layer 3 is strong, the above-mentioned problem does not occur. By configuring the cathode layer to include ruthenium oxide in this way, the contact with the porous solid electrolyte layer such as manganese dioxide is very strong and good, resulting in good electrical properties such as tanδ and impedance properties. Become. Note that to form the cathode layer, ruthenium oxide may not be used alone as described above, but may be dispersed and mixed in carbon, or a ruthenium oxide layer may be formed on the solid electrolyte layer 3 and ruthenium oxide may be formed on the solid electrolyte layer 3. A similar effect can be obtained by forming a carbon layer. Furthermore, a cathode current collector layer 1 formed by thermal spraying
3 is a structure in which individual metal particles are strongly bonded to each other, and even in high humidity, as in the case of silver paint, metal fine particles diffuse and reach the dielectric oxide film 2, increasing leakage current. Never.
In addition, it is possible to use inexpensive metals, and the cost can be reduced. Next, a specific example of the solid electrolytic capacitor of the present invention will be described, and its characteristics will be compared with that of a conventional solid electrolytic capacitor. A 60V anodic chemical conversion film is formed on the surface of a sintered body made of tantalum powder weighing 3g by cathodic oxidation. After this, manganese nitrate (specific gravity
1.5) Formation of manganese dioxide layer by thermal decomposition of aqueous solution. This operation is repeated 3 to 5 times. Next, divide this element into groups A, B, C, and D.
Four types of cathode current collectors described below were formed. Note that prototype evaluation was performed with n=10 elements in each group. (A) Ruthenium chloride aqueous solution (ruthenium chloride:water = 1g:1) in the generated manganese dioxide layer
Impregnated with ruthenium and pyrolyzed for 10 minutes at a temperature of 250 to 300°C to form a ruthenium oxide layer, and on top of this, a copper layer is formed by plasma spraying of copper by supplying copper powder into plasma using argon gas. . (B) Impregnation of colloidal graphite into the manganese dioxide layer and drying to form a carbon layer,
A copper layer is formed on this using the same method as in (A). (C) Form a copper layer directly on the manganese dioxide layer using the same method as in (A). (D) Form a carbon layer on the manganese dioxide layer in the same manner as in (B), form a silver paint layer on top of this, form a solder layer, and draw out the cathode lead wire. Note that in the methods (A) to (C) above, the cathode lead wire is drawn out directly from the copper layer. The following table shows the characteristics of the cathode current collector constructed by the methods (A) to (D) above. Furthermore, the frequency characteristics of the capacitance are shown in FIG.

[Table] From the above table and FIG. 3, it is clear that the solid electrolytic capacitor of the present invention can obtain very excellent effects in terms of tan δ, moisture resistance, frequency characteristics, and cost. In addition, the humidity resistance in the table is at a temperature of 85℃ and a relative humidity of 90℃.
%, and the LC value after 1000 hours was 5 times or less than the initial value and was considered good. In this example, the copper layer was formed using plasma spraying.
Similar effects can be obtained with the above-mentioned metals other than copper. Similar results were also obtained using arc spraying, which uses an arc to melt and spray metal without using plasma. Effects of the Invention As described above, the solid electrolytic capacitor according to the present invention has excellent electrical properties important for a capacitor, has good moisture resistance, and is very inexpensive. In addition, volumetric efficiency was required for chip capacitors, leading to a shift to smaller capacitors.
To provide a chip capacitor with no external packaging, low tan δ, high humidity resistance, and low price, such as the solid electrolytic capacitor of the present invention, in a situation where high temperature and high humidity are becoming harsher environments in which the capacitor is used. What we can do is of extremely high industrial value, as it can meet current demands and enhance our corporate image.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the main structure of a solid electrolytic capacitor according to an embodiment of the present invention, FIG. 2 is an enlarged cross-sectional view showing the main structure of the same capacitor, and FIG. 3 is an illustration of the effects of the present invention. FIG. 4 is a sectional view showing the main structure of a conventional solid electrolytic capacitor, and FIGS. 5 and 6 are enlarged sectional views showing the main structure of the same capacitor. 1... Anode substrate, 2... Dielectric oxide film, 3...
... solid electrolyte, 12 ... cathode layer, 13 ... cathode conductor layer.

Claims (1)

[Claims] 1. A solid electrolyte layer is formed on a dielectric oxide film of an anode substrate made of a valve metal, a cathode layer containing ruthenium oxide is formed on this solid electrolyte layer, and a cathode layer is formed on this cathode layer. A method for manufacturing a solid electrolytic capacitor, characterized in that a conductive layer is formed by plasma spraying or arc spraying. 2. The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein the cathode layer is composed of a mixture of ruthenium oxide and carbon. 3. The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein the cathode layer is formed by forming ruthenium oxide on a solid electrolyte layer and further forming a carbon layer thereon. 4. The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein at least one of copper, tin, nickel, aluminum, lead, and silver is used as the cathode conductor layer.