JPH05144678A - Solid electrolytic capacitor and its manufacture - Google Patents

Abstract

PURPOSE:To improve frequency characteristics by forming a solid electrolytic layer composed of mixture of manganese dioxide and lead dioxide. CONSTITUTION:Fine powder of tantalum is molded in a rectangular form and sintered. A sintered body is formed and dipped in a phosphoric acid solution. An anodic oxidation coating film is formed by performing formation. After the sintered body is dipped in manganese nitrate solution, thermal decomposition is performed. After the thermal decompostion, formation is again performed. After the formation is again performed, the sintered body is dipped in manganese nitrate suspension acqueous solution mixed with lead dioxide. Thermal decomposition is performed and formation is again performed. After the formation is performed, the sintered body is dipped in manganse nitrate aqueous solution mixed with lead dioxide, thermal decomposition is performed, and formation is again performed to form a solid electrolytic layer. Thereby conductivity of the electrolytic layer can be lowered, frequency characteristics of equivalent series resistance or the like can be improved, and characteristics of tandelta and leak current are enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid electrolytic capacitor and a method for manufacturing the same.

[0002]

2. Description of the Related Art Modern electronic circuits are designed to operate at high frequencies. Therefore, a capacitor incorporated in this electronic circuit is also required to have excellent performance in frequency characteristics, particularly in the rate of change in capacitance and the special series resistance (hereinafter referred to as ESR).

A solid electrolytic capacitor, which is one of the capacitors, uses a sintered body obtained by sintering fine powder of a valve metal such as tantalum or aluminum. Then, an oxide film is electrochemically provided on this sintered body, and then a solid electrolyte layer made of manganese dioxide is provided. This solid electrolyte layer is formed by a thermal decomposition method by impregnating it with a manganese dioxide aqueous solution. After forming the solid electrolyte layer, carbon and silver paste are sequentially applied to the surface to form a cathode layer.

In the solid electrolytic capacitor, the frequency characteristic can be improved as the electric conductivity of the solid electrolyte layer increases.

[0005]

However, the conductivity of manganese dioxide forming the conventional solid electrolyte layer is about 0.01 to 0.05 S / cm, which is a relatively low value. Therefore, it is difficult to improve the frequency characteristics of the solid electrolytic capacitor.

In particular, ESR has a drawback that it is larger than other capacitors such as ceramic capacitors, film capacitors, and aluminum electrolytic capacitors using an organic semiconductor as a solid electrolyte.

An object of the present invention is to provide a solid electrolytic capacitor which can improve the above-mentioned drawbacks and can improve frequency characteristics, and a manufacturing method thereof.

[0008]

In order to achieve the above object, the invention of claim 1 is such that a anodic oxide film, a solid electrolyte and a cathode layer are sequentially provided on a sintered body made of fine powder of valve metal. A solid electrolytic capacitor having a solid electrolyte layer made of a mixture of manganese dioxide and lead dioxide.

Further, the invention of claim 2 is a method for manufacturing a solid electrolytic capacitor, in which a anodic oxide film, a solid electrolyte and a cathode layer are sequentially formed on a sintered body made of fine powder of valve metal, and the anodic oxide film is formed. A method for producing a solid electrolytic capacitor, characterized in that the latter sintered body is immersed in a manganese nitrate solution in which lead dioxide is suspended to impregnate the solution and thermally decompose to form a solid electrolyte layer. Is.

The manganese nitrate solution in which lead dioxide is suspended has a relatively high viscosity and is difficult to impregnate.
Therefore, at first, it is preferable to impregnate a manganese nitrate solution in which lead dioxide is not suspended and perform a thermal decomposition treatment to precipitate only manganese dioxide. When manganese dioxide is deposited in the pores inside the sintered body to a certain extent, a manganese nitrate solution in which lead dioxide is suspended is impregnated and subjected to thermal decomposition treatment to precipitate a mixture of manganese dioxide and lead dioxide.

[0011]

[Function] The conductivity of the solid electrolyte layer when the content ratio of manganese dioxide MnO ₂ and lead dioxide PbO ₂ is changed is shown in FIG.
It becomes the street. That is, as is clear from FIG.
The higher the content of lead dioxide, the higher the electrical conductivity and the better the frequency characteristics.

However, if only lead dioxide is used, it is chemically deposited, so that the adhesion strength is weak and peeling easily occurs. Therefore, always lead dioxide should be used as a mixture with manganese dioxide. And the preferable ratio is PbO ₂ / MnO ₂ = 8
About 0 to 90/20 to 10 is preferable.

[0013]

EXAMPLES The present invention will be described below based on examples.
First, fine powder of tantalum is formed into a square shape and sintered,
A sintered body having a size of 1.8 mm × 0.9 mm × 1.80 mm and a weight of 20 mg is formed.

Next, this sintered body is dipped in a phosphoric acid solution at a temperature of 50 ° C. and formed at 75 V to form an anodized film.

After forming the anodic oxide film, the sintered body is immersed in a 20% strength aqueous solution of manganese nitrate, impregnated with the solution, and then left in a furnace at a temperature of 260 ° C. for thermal decomposition. And it reforms after thermal decomposition.

After the re-formation, the sintered body is immersed in an aqueous solution of manganese nitrate in which 10 wt% of lead dioxide is mixed and suspended, and is thermally decomposed and re-formulated under the same conditions as above.

After this re-formation, the mixture amount of lead dioxide was sequentially increased to 3
The solid electrolyte layer is formed by immersing in an aqueous solution of manganese nitrate changed to 0 wt%, 50 wt%, 70 wt% and 80 wt%, thermally decomposing under the same conditions as above, and reforming.

After forming the solid electrolyte layer, colloidal carbon and silver paste are applied to form a cathode layer. After the cathode layer is formed, it is connected to a lead frame and is molded with epoxy resin to form an exterior.

In the above embodiment, the solid electrolyte layer was formed by first impregnating only the manganese dioxide aqueous solution containing no lead dioxide, but this treatment may be omitted. That is, you may impregnate the manganese dioxide aqueous solution which mixed and suspended lead dioxide from the beginning.

Next, with respect to the above-mentioned examples, comparative examples and conventional examples, the ESR value was obtained by changing the frequency and shown in FIG.

In the example, it is assumed that when the solid electrolyte layer is formed in the above example, a step of impregnating a manganese nitrate aqueous solution in which lead dioxide is not suspended and thermally decomposing is first performed.

Further, in the comparative example, after treating with an aqueous solution of manganese nitrate in which lead dioxide is not suspended in the example, an aqueous solution of ammonium acetate (2 mol) is added to an aqueous solution of lead acetate (1 mol / l).
(l / l) is immersed in an aqueous solution and then dried, which is repeated 6 times to form a solid electrolyte layer by precipitating lead dioxide to produce a solid electrolyte layer.

The conditions of the conventional example are the same as those of the example 1 except that the solid electrolyte layer is produced only by using an aqueous solution of manganese nitrate in which lead dioxide is not suspended. The manganese nitrate aqueous solution has five concentrations of 30%, 40%, 60%, 70%, and 80%, and is impregnated with a high-concentration liquid sequentially from a low concentration, and each is thermally decomposed.

As is apparent from FIG. 1, it is clear that the ESR of the embodiment is significantly lower than that of the conventional example. For example, at a frequency of 10 ⁶ Hz, the example is 0.15Ω and the conventional example is 0.7Ω, and the former is 3/14 of the latter. The comparative example is 0.11, which is a lower value than that of the example.

Further, with respect to the above Examples, Comparative Examples and Conventional Example, initial characteristics, characteristics after heat cycle, and characteristics after pressure cooker test (hereinafter referred to as PCT) were determined and shown in Table 1.

Heat cycle temperature -55 ° C to 125 ° C,
It is performed under the condition of 100 cycles. The PCT has a temperature of 12
It is left for 32 hours in an atmosphere of 1 ° C. and 2 atm. The number of each sample is 20. The margin below.

[0027]

[Table 1]

As is clear from Table 1, the examples are superior in tan δ and leakage current characteristics after heat cycle and PCT as compared with the conventional examples. In addition, the initial characteristics, heat cycle, and tan δ after PCT are superior to those of the comparative example.

For example, regarding tan δ, the example is 6/23 of the conventional example after the heat cycle, 3/10 of the comparative example, and 8/35 of the conventional example after PCT, and the comparative example 4/11. Also, regarding the leakage current, the example is 1/2 after the heat cycle and 2/3 after the PCT as compared with the conventional example.
Becomes The initial tan δ of the example is as low as 5/21 as compared with the comparative example.

[0030]

As described above, according to the present invention, the solid electrolyte layer is made of a manganese nitrate solution in which lead dioxide is suspended,
Since it is made of a mixture of manganese dioxide and lead dioxide, the solid electrolyte layer can have a low electric conductivity, can improve frequency characteristics such as ESR, and can improve tan δ and leakage current characteristics, and the production thereof. A method is obtained.

[Brief description of drawings]

FIG. 1 shows a frequency characteristic of an equivalent series resistance.

FIG. 2 is a graph showing the electrical conductivity of the solid electrolyte layer with respect to the content ratio of MnO ₂ and PbO ₂ .

Claims (2)

[Claims] 1. A solid electrolytic capacitor in which a anodic oxide film, a solid electrolyte layer and a cathode layer are sequentially provided on a sintered body made of a fine powder of a valve metal, and a solid electrolyte layer made of a mixture of manganese dioxide and lead dioxide. A solid electrolytic capacitor having. 2. A method for manufacturing a solid electrolytic capacitor in which an anodized film, a solid electrolyte layer and a cathode layer are sequentially formed on a sintered body made of fine powder of valve metal, and the sintered body after the anodized film is formed is used. A method for producing a solid electrolytic capacitor, which comprises immersing in a manganese nitrate solution in which lead dioxide is suspended, impregnating the solution, and thermally decomposing it to form a solid electrolyte layer.