JPH06132167A - Manufacture of solid electrolytic capacitor - Google Patents

Abstract

PURPOSE:To provide a method of manufacturing a solid electrolytic capacitor which can simplify the process of forming a manganese dioxide layer, and can form it equally, and reduce a leak current. CONSTITUTION:An anode element is made by molding metallic powder and sintering it, and an oxide film is made around the metallic powder and the anode element, and then the anode element 1 is dipped in manganese nitrate aqueous solution of low concentration, and then it is dried at high temperature, and next, it is dipped in manganese nitrate aqueous solution (liquid temperature is 80-130 deg.C) 7 of high concentration, and then it is dried at high temperature so as to thermally decompose it, thus a manganese dioxide layer 5 is formed. Furthermore, a graphite layer and a silver layer are made around it.

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. More specifically, the present invention relates to a method for manufacturing a solid electrolytic capacitor that can simplify the process of forming a manganese dioxide layer and reduce the leakage current.

[0002]

2. Description of the Related Art A conventionally known solid electrolytic capacitor is manufactured as follows.

First, a metal powder of tantalum, aluminum, niobium or the like is molded and sintered to form an anode element. Then, an oxide film is formed around the metal powder by anodic oxidation or the like. Then, the anode element on which the oxide film is formed is immersed in an aqueous solution of manganese nitrate and pulled out to
Pyrolyzes at 0 to 400 ℃. This is repeated many times to form a manganese dioxide layer on the oxide film around the metal powder inside the anode element. After that, a metal layer composed of a graphite layer for electrodes and a silver layer is formed around the anode element to manufacture a solid electrolytic capacitor.

[0004]

However, in the manganese dioxide layer forming step, in order to form a manganese dioxide layer having a uniform and constant thickness around the sintered metal powder,
Immersion in a manganese nitrate aqueous solution and thermal decomposition after pulling must be repeated many times. Therefore, the anodic oxide film is thermally deteriorated and the leakage current increases. Further, there is a problem in that the cost is increased because the man-hour of the thermal decomposition increases.

Further, when a high-concentration manganese nitrate solution is used from the beginning, the manganese dioxide layer covers the outer surface of the anode element and prevents penetration into the anode element even if it is repeated many times. For this reason, the manganese dioxide layer formed on the surface of the oxide film cannot completely cover the oxide film, which causes problems such as a decrease in capacitance after capacitor formation or an increase in loss tangent loss. Bring about a decline.

The present invention solves such a problem, can reduce the number of thermal decomposition steps required for forming a uniform and constant-thickness manganese dioxide layer inside the anode element, and can reduce leakage current. An object of the present invention is to provide a method for producing a solid electrolytic capacitor that can be manufactured.

[0007]

The method for producing a solid electrolytic capacitor according to the present invention comprises: (a) a step of forming an anode element by molding and sintering a metal powder; (b) the metal powder and the anode element. Forming an oxide film around the
A method for producing a solid electrolytic capacitor, comprising the steps of (c) forming a manganese dioxide layer on the oxide film, and (d) forming a metal layer around the anode element, wherein the manganese dioxide layer is formed. (E) After immersing the anode element in water or a low-concentration aqueous solution of manganese nitrate, the temperature is raised from ambient temperature (for example, 0 to 60 ° C.) to dry the surface, and (f) after that, high-concentration nitric acid is added. After immersing the anode element in a manganese aqueous solution, the ambient temperature (for example, 0-60
(G) to cause the high-concentration manganese nitrate aqueous solution to permeate into the anode element, and (g) further raise the temperature to pyrolyze to form a manganese dioxide layer in the anode element. I am trying.

Further, in the step (e), the temperature of the water or the low-concentration manganese nitrate aqueous solution adhered to the surface of the anode element is raised to 80 to 130 ° C., and in the step (f), It is preferable to raise the temperature of the high-concentration aqueous solution of manganese nitrate attached to the surface of the anode element to 100 to 130 ° C.

Further, it is preferable that the surface of the anode element is blown with hot air or the surface of the anode element is exposed to a high temperature heat source for a short time to raise the temperature.

[0010]

According to the method of the manganese dioxide forming step of the present invention, the anode element is first immersed in water or a low-concentration manganese nitrate aqueous solution, and then heated to dryness. It penetrates inside and only the surface of the anode element dries. Then, since the anode element is immersed in a high-concentration manganese nitrate aqueous solution and heated again, the water inside the anode element or the water vapor of the low-concentration aqueous solution evaporates and the inside of the anode element becomes a pressure lower than the outer wall. To a simple vacuum,
The manganese nitrate aqueous solution adhering to the surface is sucked inside. That is, water or a low-concentration aqueous solution has a lower boiling point than a high-concentration aqueous solution, evaporates earlier than the high-concentration aqueous solution adhering to the surroundings, and a high-concentration manganese nitrate aqueous solution evaporates from the upper surface etc. Voids are generated between the powders inside the element, and the high-concentration manganese nitrate aqueous solution attached to the periphery is sucked. After that, the manganese dioxide layer having a uniform and constant thickness can be formed by thermal decomposition.

[0011]

The method for producing the solid electrolytic capacitor of the present invention will be described below with reference to the drawings.

FIG. 1 is an explanatory view showing a manufacturing process of a tantalum electrolytic capacitor which is one embodiment of the present invention, and FIG. 2 is an explanatory view showing a manganese dioxide layer forming process in the manufacturing process of FIG.

First, the anode element 1 is formed by molding and sintering metal powder (see FIG. 1A). As a specific example, the anode element 1 is formed by molding tantalum powder into a rectangular parallelepiped shape having a side length of about 1 mm, embedding the wire 2 from the upper surface thereof, and then sintering the wire 2.

Next, an oxide film 3 is formed around the metal powder and the anode element 1 (see FIG. 1 (b)). As a specific example, the anode element 1 is dipped in a 0.1 wt% (hereinafter, simply referred to as%) phosphoric acid aqueous solution 4 and the voltage is set to 20 to 100 V for 2 seconds.
By performing anodic oxidation for about 3 hours, the oxide film 3, that is, tantalum pentoxide (Ta) is formed on the surface of the anode element, the surface of the metal powder inside the anode element, and a part of the surface of the wire 2.
₂ O ₅ ) film is formed.

Next, a manganese dioxide layer 5 is formed on the oxide film 3 (see FIGS. 1 (c) and 1 (d)). This manganese dioxide layer 5 is formed at an ambient temperature (for example, 0 to
The anode element 1 is immersed in water or a low-concentration manganese nitrate aqueous solution 6 at 60 ° C.) and then heated to dry the surface (see FIGS. 2 (a) and 2 (b)), and then at ambient temperature (for example, 0 ° C.).
The anode element 1 is immersed in a high-concentration manganese nitrate aqueous solution 7 at -60 ° C.) and then heated to permeate the high-concentration manganese nitrate aqueous solution into the anode element (FIG. 2C).
(See (d)). The manganese dioxide layer 5 is formed by further raising the temperature and thermally decomposing (see FIG. 2E). Here, the low-concentration manganese nitrate aqueous solution preferably has a concentration of about 30% or less, and the high-concentration manganese nitrate aqueous solution is 55-
It is preferably about 78%.

As a means for raising the temperature of the anode element, for example, a hot air of about 100 to 195 ° C. is blown to improve the heat conversion to raise the temperature in a short time, or a near infrared lamp,
Means for raising the temperature by exposing it to a high-temperature heat irradiation source such as a far-infrared heater or a laser for a short time can be used. By placing in such hot air or high temperature atmosphere, the temperature of water or aqueous solution adhering to the surface of the anode element is 80 to 130 ° C.
The temperature can be raised in a short time, and after the water or the low-concentration manganese nitrate aqueous solution is deposited, the water or the low-concentration manganese nitrate aqueous solution permeates into the gaps between the powders inside the anode element 1 and the anode element The surface of 1 is dried. Further, when the high-concentration manganese nitrate aqueous solution is attached to the periphery of the side wall of the anode element 1, the water permeated into the inside of the anode element 1 or the low-concentration manganese nitrate aqueous solution is deposited around the side wall of the anode element 1. Since the boiling point is lower than that of the adhered high-concentration manganese nitrate aqueous solution and it is likely to evaporate, the vapor evaporates first, and the vapor escapes from a portion of the upper surface of the anode element 1 to which the high-concentration manganese nitrate aqueous solution is not adhered, so Becomes a pseudo-vacuum state, and the high-concentration manganese nitrate aqueous solution adhering to the periphery of the side wall is sucked into the anode element 1. At this time, when the manganese nitrate aqueous solution is heated to 135 ° C. or higher, the solidified substance adheres to the surface of the anode element 1 to prevent the subsequent manganese nitrate aqueous solution from penetrating into the anode element 1. Especially, when exposed to a high temperature atmosphere, it is necessary to sufficiently control the time so that the temperature does not rise excessively.

When the above-mentioned hot air is blown to raise the temperature, the higher the wind speed is, the shorter the temperature can be raised, and by blowing out the hot air from the slit width of about 1 mm, a relatively small compression force is applied. You can get the wind speed. There is a mutual relationship between the wind speed, the air temperature, and the temperature rise time of the deposit on the surface of the anode element. For example, by blowing air at 100 ° C at a wind speed of 30 m / sec, the temperature of the deposits on the surface of the anode element becomes 100 at 100 ° C in an atmosphere of 25 ° C.
It takes about 5 seconds to raise the temperature to ~ 130 ℃, and even if you blow air at 195 ℃ at a wind speed of 10 m / s, it will take about 10 seconds in about 5 seconds.
The temperature can be raised to 0 to 130 ° C.

When the temperature is raised from, for example, 25 ° C. by a high-temperature heat irradiation source, the temperature is reduced to 0.
The temperature of the aqueous solution adhering to the outer peripheral wall of the anode element 1 becomes 100 to 130 ° C. by exposing it for 5 (900 ° C.) to 5 (300 ° C.) seconds. In addition, 1 to 600-800 ℃
Exposure for 2 seconds is particularly preferred. In the shortest possible time
Increasing the temperature to around 100 ° C is effective in permeating the aqueous solution into the anode element. Conversely, if the temperature is too high, manganese nitrate is thermally decomposed and the product adheres to the element surface, This is because it blocks penetration.

As a specific example, the anode element 1 having the oxide film 3 is immersed in water for about 1 second under an atmosphere of 25 ° C., and this is irradiated with a near infrared ray lamp for about 1 second under an atmosphere of about 800 ° C. After drying, it is about 1 in a 75% strength manganese nitrate aqueous solution.
After being soaked for 2 seconds, pulled up, and again heated in an atmosphere of about 800 ° C. for about 1 second. Further, it was decomposed in a decomposition furnace at 230 ° C. for 5 minutes. After repeating this process three times, the anode element 1 is immersed in a dispersion liquid prepared by mixing fine particles of electrolytic manganese dioxide (average 0.2 μm) with a 64% concentration aqueous solution of manganese nitrate, and decomposed at 230 ° C. A manganese dioxide layer 5 is formed on the outer peripheral wall of the anode element. The above conditions are conditions when the decomposition step is repeated three times, and the conditions also change when the number of repetitions is different.

Next, a metal layer is formed around the anode element 1 (see FIG. 1 (e)).

As a specific example, the anode element 1 was immersed in a graphite dispersion liquid or a paste thereof at a depth such that the upper surface was not soaked, and fired to form a graphite layer 9 as an electrode underlayer. Further, the obtained anode element 1 was immersed in a silver-containing liquid or its paste to a depth such that the upper surface was not soaked, and then dried to form a silver layer 10 as an electrode outer layer. The graphite layer 9 serving as the electrode underlayer and the silver layer 10 serving as the electrode outer layer are portions that serve as one electrode of the capacitor. In this case, instead of the silver layer 10, a Ni plating layer can be used as the electrode outer layer. The other electrode is the wire 2. Next, external lead terminals of both the anode and the cathode were connected, and an epoxy resin was used for exterior packaging (not shown).

Although the solid electrolytic capacitor made of tantalum powder has been described in the above-described embodiments, the same effect can be obtained when the solid electrolytic capacitor is made of a material other than tantalum, for example, aluminum or niobium.

Next, characteristics of two types of solid electrolytic capacitors (No. 1 and No. 2) manufactured by the manufacturing method of the above-mentioned embodiment and a conventional solid electrolytic capacitor (No. 3) will be compared and examined. .

No. 1: Tantalum electrolytic capacitor manufactured by the manufacturing method of the above embodiment, No. 2: Tantalum electrolysis manufactured by using a manganese nitrate aqueous solution having a concentration of 20% instead of water in the manufacturing method of the above embodiment. Capacitor, and No. 3: Compare the characteristics of tantalum electrolytic capacitors manufactured by the conventional manufacturing method. The results are shown in Table 1. The specifications of the capacitor are 4V and 4.7 μF.

[0025]

[Table 1]

As can be seen from Table 1, the capacitors of Example No. 1 and Example No. 2 produced by the production method of the present invention have the number of thermal decompositions of N produced by the conventional production method.
It can be seen that the number of capacitors is less than that of the o.3 capacitor and the leakage current is also greatly reduced. Similarly, the dielectric loss tangent (loss coefficient) tan δ is also reduced. on the other hand,
It can be seen that the withstand voltage is improved as compared with the conventional example.

[0027]

According to the present invention, since the number of times of immersion in an aqueous solution of manganese nitrate and thermal decomposition can be reduced,
The man-hours can be reduced, the cost can be reduced, and the manganese nitrate aqueous solution can be sufficiently impregnated inside. Furthermore, along with this, the thermal deterioration of the oxide film can be prevented, the leakage current can be greatly reduced, and a manganese dioxide layer is sufficiently formed inside, so that a high-performance solid electrolytic capacitor can be obtained. You can get it.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a manufacturing process of a tantalum electrolytic capacitor which is an embodiment of the present invention.

FIG. 2 is an explanatory view showing a manganese dioxide layer forming step in the manufacturing step of FIG.

[Explanation of symbols]

 1 Anode element 3 Oxide film 5 Manganese dioxide layer 6 Low concentration manganese nitrate aqueous solution 7 High concentration manganese nitrate aqueous solution 9 Graphite layer 10 Silver layer

Claims (4)

[Claims] 1. A step of forming an anode element by molding and sintering metal powder, and a step of forming an oxide film around the metal powder and the anode element. A method for manufacturing a solid electrolytic capacitor, comprising: a step of forming a manganese dioxide layer on an oxide film; and (d) a step of forming a metal layer around the anode element. ) Immersing the anode element in water or a low-concentration manganese nitrate aqueous solution and then raising the temperature to dry the surface. (F) After that, immersing the positive electrode element in a high-concentration manganese nitrate aqueous solution and then raising the temperature. Solid electrolyte, wherein a manganese dioxide layer is formed in the anode element by infiltrating the anode element with the high-concentration aqueous solution of manganese nitrate, and (g) further heating to thermally decompose the anode element. Preparation of the capacitor. 2. The step (e) according to claim 1, wherein the temperature of the water or the low concentration manganese nitrate aqueous solution adhered to the surface of the anode element is raised to 80 to 130 ° C., In step (f), the temperature of the high-concentration manganese nitrate aqueous solution attached to the surface of the anode element is 100 to
The temperature is raised to 130 ° C. 3.
A method for producing the solid electrolytic capacitor described. 3. The method for producing a solid electrolytic capacitor according to claim 1, wherein hot air is blown onto the surface of the anode element to raise the temperature. 4. The method for producing a solid electrolytic capacitor according to claim 1, wherein the surface of the anode element is exposed to a high temperature heat source for a short time to raise the temperature.