JPH04240710A - Manufacture of solid-state electrolytic capacitor - Google Patents

Abstract

PURPOSE:To obtain a solid-state electrolytic capacitor having a stable electrostatic capacity in various environments by forming a first solid-state electrolytic layer by one sol-gel method and by forming a second solid-state electrolytic layer which is a manganese dioxide layer generated by pyrolysis of a manganese nitrate aqueous solution on the first layer. CONSTITUTION:A dielectric film 3, solid-state electrolytic layer 4 and cathode conductor layer 5 are formed in order on an anode body 1 which is made of valve action metal, to fabricate a solid-state electrolytic capacitor. At that time, after the dielectric film 3 is formed, a first solid-state electrolytic layer 4a is formed by the sol-gel method and then a second solid-state electrolytic layer 4b, a manganese dioxide layer which is generated by pyrolysis of a manganese nitrate aqueous solution, is formed on the first layer 4a. For example, the anode body 1 made of Ta powder is transformed in an electrolyte to form the dielectric film 3 and then is dipped in a manganese alcoholate aqueous solution and is left alone in the air of 85 deg.C to be gelled and is dried in the air of 300 deg.C to form the MnO2 film.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a solid electrolytic capacitor, and more particularly to a method for forming a solid electrolyte adjacent to a dielectric film formed on a valve metal anode body.

0002

[Prior Art] A conventional method for forming a solid electrolyte for a solid electrolytic capacitor is to immerse an anode body made of a valve metal such as tantalum or aluminum in an aqueous solution of manganese nitrate to sufficiently impregnate the interior of the anode body. It was thermally decomposed in a high-temperature atmosphere of about 300°C to form a solid electrolyte made of manganese dioxide.

[0003] Normally, manganese dioxide produced by immersion in the above-mentioned manganese nitrate aqueous solution or thermal decomposition does not sufficiently cover the pre-formed dielectric film in one treatment, and the manganese dioxide itself Because it is porous, it is usually repeated several to ten times.

0004

In the step of forming a solid electrolyte for a solid electrolytic capacitor, it is necessary to cover the entire surface of a previously formed dielectric film with a solid electrolyte. This is because if there is a part of the dielectric film that is not covered by the solid electrolyte, moisture contained in the atmosphere will be desorbed from the dielectric film in the uncovered part, resulting in a change in the capacitance of the capacitor. It is from. On the other hand, the miniaturization of valve metals is progressing due to the need for smaller size, larger capacity, and cost reduction, but with conventional methods,
Since a thick and porous manganese dioxide layer is likely to be formed, it is difficult to completely cover even the very fine pores of the dielectric film with the solid electrolyte.

The object of the present invention is to eliminate the conventional drawbacks and to provide a solid material having a dense, thin and uniform thickness on a pre-formed dielectric film and completely covering even the minute pores of the dielectric film. An object of the present invention is to provide a method for manufacturing a solid electrolytic capacitor in which an electrolyte layer can be formed and the capacitance is stable even in various environments.

[0006]

[Means for Solving the Problems] The method for manufacturing a solid electrolytic capacitor of the present invention includes the steps of sequentially forming a dielectric film, a solid electrolyte, and a cathode conductor layer on an anode body made of a valve metal. The manufacturing method includes a step of forming a first solid electrolyte layer by a sol-gel method after forming a dielectric film, and a step of forming a manganese dioxide layer on the first solid electrolyte by a thermal decomposition method of an aqueous solution of manganese nitrate. The method is characterized in that it includes a step of forming a second solid electrolyte layer.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be explained with reference to the drawings. Embodiments of the present invention will be explained by taking a tantalum solid electrolytic capacitor as an example. FIG. 1 is a cross-sectional view of a tantalum solid electrolytic capacitor formed in accordance with one embodiment of the present invention.

In FIG. 1, an anode body made of tantalum metal powder with a diameter of 1 mm, a length of 1 mm, and a weight of 0.01 g, from which an anode lead is led out, is immersed in an electrolytic solution, and a dielectric film ( Ta2O5) is formed.

Next, the anode body was immersed in 3 wt% manganese alcoholate, and after the anode body was sufficiently penetrated into the inside of the anode body,
The mixture was left in an air atmosphere at a temperature of 85° C. for 10 minutes to gel. Next, it is dried for 30 minutes in an air atmosphere at a temperature of 300° C. to form a MnO2 film having a uniform thickness. 300℃
Leaving it in an air atmosphere at 85℃ before heating it to a high temperature is
This is to suppress a rapid reaction so as not to cause cracks in the MnO2 film. MnO2 by sol-gel method
The production reaction can be expressed by the following formula.

0010

[0011] Furthermore, the same construction method may be repeated. In addition to drawing out the cathode, the solid electrolyte also has the function of protecting the capacitor element from external mechanical stress, and therefore needs to have a sufficient thickness around the anode body. However, the solid electrolyte layer formed by the sol-gel method tends to crack easily if it becomes too thick;
An extremely dense and solid product can be obtained at a thickness of 0 micron, ideally about 1 micron. Therefore, after forming the first solid electrolyte layer by the above-mentioned sol-gel method, a second solid electrolyte layer made of manganese dioxide and having a sufficient thickness is formed by thermal decomposition of manganese nitrate using known means, and then a graphite layer, A cathode conductor layer consisting of a silver paste layer is formed to obtain a tantalum solid electrolytic capacitor element.

[0012] The history of capacitance values of the capacitor element formed in this manner after a humidity test (85°C, 90-95% R.H., after 24 hours) and after being left at high temperature (125°C, after 25 hours) was investigated. As a result of the measurement, the results shown in Table 1 were obtained. For comparison, the results of a conventional product obtained by thermal decomposition of manganese nitrate are also shown.

[0013]

Next, another embodiment will be explained. After forming the dielectric film in the same manner as in Example 1, the anode body was dip-coated using, for example, a zinc ethylate {Zn(OC2H5)2} solution, and then left in an air atmosphere at a temperature of 85°C for 10 minutes to gel. let Next, Zn was dried for 30 minutes in an air atmosphere at a temperature of 300°C to obtain a uniform thickness.
Form an O film. Subsequently, a second solid electrolyte layer made of manganese dioxide is formed by thermal decomposition of manganese nitrate using a known method, and a cathode conductor layer made of a graphite layer and a silver paste layer is formed, thereby forming a tantalum solid electrolytic capacitor element. .

[0015] The above method also provides the same effects as in Example 1, and also uses Zn, which has a lower resistivity than MnO2.
Since the first solid electrolyte layer made of O is formed, there is an advantage that a solid electrolytic capacitor element with a small loss coefficient can be obtained. Table 2 shows the loss coefficient of the product of this example as well as the conventional example product and the example 1 product.

[0016]

[0017]

As explained above, in the method for manufacturing a solid electrolytic capacitor according to the present invention, after forming a dielectric film, a first solid electrolyte layer having a very dense, thin, and uniform thickness is formed by a sol-gel method. After that, a second solid electrolyte layer made of manganese dioxide is formed by thermal decomposition of manganese nitrate using a known method, so that the following effects are obtained.

(1) Since the first solid electrolyte layer is very dense and has a uniform thickness, a capacitor element with stable capacitance in various environments can be obtained.

(2) Since the first solid electrolyte layer is dense and thin, it can completely cover even the very fine pores of the dielectric film.

The present invention is characterized in that a dense electrolyte is formed by a sol-gel method, and Table 3 shows materials that have high conductivity and can be used as solid electrolytes for solid electrolytic capacitors. Not only the simple substances shown in these tables but also complex compounds thereof can be used.

[0021]

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a solid electrolytic capacitor element obtained according to an example of the present invention.

[Explanation of symbols]

1 Anode body 2 Anode lead 3 Dielectric film 4a First solid electrolyte layer 4b Second solid electrolyte layer 5 made of manganese dioxide Cathode conductor layer

Claims (3)

[Claims] Claim 1. A method for manufacturing a solid electrolytic capacitor, which comprises the steps of sequentially forming a dielectric film, a solid electrolyte, and a cathode conductor layer on an anode body made of a valve metal, after forming the dielectric film, a first step is performed using a sol-gel method. and forming a second solid electrolyte layer made of a manganese dioxide layer produced by a thermal decomposition method of an aqueous manganese nitrate solution on the first solid electrolyte. A method for manufacturing a solid electrolytic capacitor. [Claim 2] A first film formed by a sol-gel method.
The solid electrolytes of CuO, ZnO, PbO2, V2O
5. The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein the solid electrolytic capacitor is a single substance or a composite compound of SnO2. [Claim 3] A first film formed by a sol-gel method.
2. The method of manufacturing a solid electrolytic capacitor according to claim 1, wherein the solid electrolyte layer has a thickness of 0.1 to 10 microns.