JP3233702B2 - Manufacturing method of solid electrolytic capacitor - Google Patents

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 capable of simplifying a step of forming a manganese dioxide layer and reducing a leakage current.

[0002]

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

First, an anode element is formed by molding and sintering a metal powder such as tantalum, aluminum, or niobium. Next, an oxide film is formed around the metal powder by anodic oxidation or the like. Then, the anode element on which the oxide film was formed was immersed in an aqueous solution of manganese nitrate, pulled out, and pulled out.
Thermally decomposes at 0-400 ° C. This is repeated many times to form a manganese dioxide layer on the oxide film around the metal powder inside the anode element. Thereafter, a metal layer including a graphite layer and a silver layer for an electrode is formed around the anode element, and a solid electrolytic capacitor is manufactured.

[0004]

However, in the manganese dioxide layer forming step, a uniform and constant thickness manganese dioxide layer is formed around the sintered metal powder.
Immersion in the aqueous solution of manganese nitrate and thermal decomposition after lifting must be repeated many times. Therefore, the anodic oxide film undergoes thermal deterioration, and the leakage current increases. Further, there is a problem that the cost is increased because the number of steps of the thermal decomposition is increased.

If a manganese nitrate solution having a high concentration is used from the beginning, the manganese dioxide layer covers the outer surface of the anode element, so that penetration into the inside of the anode element is prevented 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, causing problems such as a decrease in capacitance or an increase in dielectric loss tangent after formation of the capacitor, and an increase in yield or quality. Causes a decrease.

The present invention solves such a problem, and can reduce the number of thermal decomposition steps required to form a uniform and constant thickness manganese dioxide layer inside the anode element, thereby reducing leakage current. It is an object of the present invention to provide a method for manufacturing a solid electrolytic capacitor that can be used.

[0007]

The method of manufacturing a solid electrolytic capacitor according to the present invention comprises: (a) forming an anode element by molding and sintering a metal powder; and (b) forming the anode and the metal powder. Forming an oxide film around the oxide film; (c) forming a manganese dioxide layer on the oxide film; and (d) forming a metal layer around the anode element. And (e) immersing the anode element in water or a low-concentration manganese nitrate aqueous solution, and then reducing the temperature from an environmental temperature (for example, 0 to 60 ° C.).
The manganese nitrate was dried surface was heated to a temperature that does not thermally decompose, (f) After that, the temperature was raised from After immersing the anode element in a high concentration aqueous solution of manganese nitrate in the environmental temperature (e.g., 0 to 60 ° C.) (G) causing the high-concentration manganese nitrate aqueous solution to penetrate into the anode element, and (g) further heating and thermally decomposing to form a manganese dioxide layer in the anode element.

In the step (e), the temperature of the water or the low-concentration aqueous solution of manganese nitrate attached 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 manganese nitrate aqueous solution attached to the surface of the anode element to 100 to 130 ° C.

Further, in the step (e) or (f),
It is preferable to blow hot air on the surface of the anode element or to expose the surface of the anode element to a high-temperature heat source for a short time to raise the temperature.

[0010]

According to the method of the present invention, the anode element is first immersed in water or a low-concentration manganese nitrate aqueous solution and then heated and dried. It penetrates inside and only the surface of the anode element dries. Next, 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 lower pressure than the outer wall. Vacuum state,
The manganese nitrate aqueous solution adhering to the surface is sucked into the inside. That is, water or a low-concentration aqueous solution has a lower boiling point than a high-concentration aqueous solution, evaporates faster than a high-concentration aqueous solution attached to the surroundings, and evaporates from an upper surface where a high-concentration manganese nitrate aqueous solution does not adhere to the anode. Voids are formed between the powders inside the device, and a high-concentration manganese nitrate aqueous solution attached to the surroundings is sucked. Thereafter, by performing thermal decomposition, a manganese dioxide layer having a uniform and constant thickness can be formed.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for manufacturing a solid electrolytic capacitor according to the present invention will now be described with reference to the drawings.

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

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

Next, an oxide film 3 is formed around the metal powder and the anode element 1 (see FIG. 1B). As a specific example, the anode element 1 is immersed in a 0.1% by weight (hereinafter simply referred to as%) phosphoric acid aqueous solution 4,
By performing anodic oxidation for up to 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 element, and a part of the surface of the wire 2.
₂ O ₅ ) A film is formed.

Next, a manganese dioxide layer 5 is formed on the oxide film 3 (see FIGS. 1C and 1D). The method of forming the manganese dioxide layer 5 is based on the environmental 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. 2A and 2B).
The anode element 1 is immersed in a high-concentration manganese nitrate aqueous solution 7 at 6060 ° C., and then heated to allow the high-concentration manganese nitrate aqueous solution to penetrate into the anode element (FIG. 2C).
(D)). The manganese dioxide layer 5 is formed by further increasing 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 has a concentration of 55 to 50%.
It is preferably about 78%.

As 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, and the temperature can be raised in a short time.
Means for raising the temperature by exposing to a high-temperature heat irradiation source such as a far-infrared heater or a laser for a short time can be given. The temperature of the water or aqueous solution adhering to the surface of the anode element is set to 80 to 130 ° C by placing it under such hot air or high temperature atmosphere.
The temperature can be raised in a short time to the extent that the water or the low-concentration manganese nitrate aqueous solution adheres to the gap between the powders inside the anode element 1 while the temperature rises after the water or the low-concentration manganese nitrate aqueous solution is attached. The surface of 1 dries. In addition, when the temperature is raised after the high-concentration manganese nitrate aqueous solution is attached around the side wall of the anode element 1, the water that has penetrated into the inside of the anode element 1 or the low-concentration manganese nitrate aqueous solution is closer to the periphery of the side wall of the anode element 1. Since the boiling point is lower than that of the attached high-concentration manganese nitrate aqueous solution and it is easy to evaporate, it evaporates first, and vapor escapes from a portion of the upper surface of the anode element 1 where the high-concentration manganese nitrate aqueous solution does not adhere and the inside of the anode element 1 Is brought into a simulated vacuum state, and the high-concentration manganese nitrate aqueous solution attached to the periphery of the side wall is sucked into the anode element 1. At this time, if the temperature of the aqueous manganese nitrate solution is raised to 135 ° C. or higher, solidified substances adhere to the surface of the anode element 1 and prevent the subsequent aqueous manganese nitrate solution from penetrating into the inside of 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 too much.

When the temperature is increased by blowing the above-mentioned hot air, the temperature can be raised in a shorter time as the wind speed is higher, and the hot air is blown out from a slit width of about 1 mm, thereby increasing the temperature with a relatively small compression force. Wind speed can be obtained. There is a correlation between the wind speed, the air temperature, and the temperature rise time of the deposit on the anode element surface. For example, by blowing air at 100 ° C. at a wind speed of 30 m / sec, the temperature of the deposit on the anode element surface can be reduced to 100 ° C. in an atmosphere of 25 ° C., for example.
It takes about 5 seconds to raise the temperature to ~ 130 ° C. Even if air at 195 ° C is blown at a wind speed of 10 m / s, it takes about 10 seconds in about 5 seconds.
The temperature is raised to 0-130 ° C.

When the temperature is raised from, for example, 25.degree. C. by a high-temperature heat irradiation source, the temperature is raised to 0.3 to 900.degree.
By exposing for about 5 (at 900 ° C.) to 5 (at 300 ° C.) seconds, the temperature of the aqueous solution adhering to the outer peripheral wall of the anode element 1 becomes 100 to 130 ° C. Note that at 600 to 800 ° C,
Exposure for 2 seconds is particularly preferred. In as short a time as possible
Increasing the temperature to around 100 ° C is effective in penetrating the aqueous solution inside the anode element. Conversely, if the temperature is too high, manganese nitrate thermally decomposes and the product adheres to the element surface, and This is because it prevents penetration.

As a specific example, the anode element 1 having the oxide film 3 is immersed in water at about 25 ° C. for about 1 second, and irradiated with a near-infrared lamp for about 1 second at about 800 ° C. After drying, about 1% in 75% manganese nitrate aqueous solution
After dipping for 2 seconds and lifting, it was heated again in an atmosphere of about 800 ° C. for about 1 second. Furthermore, it was decomposed in a decomposition furnace at 230 ° C. for 5 minutes. After repeating this step three times, the anode element 1 is immersed in a dispersion obtained by mixing electrolytic manganese dioxide fine particles (average 0.2 μm) with a 64% manganese nitrate aqueous solution, and decomposed at 230 ° C. Then, a manganese dioxide layer 5 is formed on the outer peripheral wall of the anode element. The above condition is a condition when the decomposition step is repeated three times, and the condition changes when the number of repetitions is different.

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

As a specific example, the anode element 1 was immersed in a graphite dispersion or its paste at a depth such that the upper surface was not immersed, and baked to form the graphite layer 9 as an electrode underlayer. Further, the obtained anode element 1 was immersed in a silver-containing liquid or its paste at a depth such that the upper surface was not immersed, and then dried to form a silver layer 10 as an electrode outer layer. The graphite layer 9 serving as the electrode base layer 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 may be employed as the outer electrode layer. The other electrode is a wire 2. Then, the external lead terminals of both the anode and the cathode were connected, and the package was formed using an epoxy resin (not shown).

In the embodiment described above, the solid electrolytic capacitor made of tantalum powder has been described. However, 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, the characteristics of two types of solid electrolytic capacitors (No. 1 and No. 2) and the conventional solid electrolytic capacitor (No. 3) manufactured by the manufacturing method of the above-described embodiment will be compared and studied. .

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

[0025]

[Table 1]

As can be seen from Table 1, the capacitors of Examples No. 1 and No. 2 manufactured by the manufacturing method of the present invention have the number of thermal decompositions of N
It can be seen that it requires less than the capacitor of o.3, and the leakage current is greatly reduced. 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 number of steps can be reduced, the cost can be reduced, and the manganese nitrate aqueous solution can be sufficiently impregnated inside. In addition, the thermal degradation of the oxide film can be prevented, the leakage current can be greatly reduced, and the manganese dioxide layer is sufficiently formed inside, so that a high-performance solid electrolytic capacitor can be used. You can get.

[Brief description of the drawings]

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

FIG. 2 is an explanatory view showing a manganese dioxide layer forming step in the manufacturing step of FIG. 1;

[Explanation of symbols]

 DESCRIPTION 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

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01G 9/02

Claims (4)

(57) [Claims] (A) forming an anode element by molding and sintering a metal powder; (b) forming an oxide film around the metal powder and the anode element; A method for producing 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. ) The anode element is immersed in water or a low-concentration manganese nitrate aqueous solution, and then heated to a temperature at which manganese nitrate is not thermally decomposed. The surface is dried. (F) Then, a high-concentration manganese nitrate aqueous solution is used. After the anode element is immersed in the anode element, the temperature is raised to allow the high-concentration manganese nitrate aqueous solution to penetrate into the anode element, and (g) the temperature is further increased to thermally decompose the manganese dioxide layer in the anode element. Forming a solid electrolytic capacitor. 2. The method according to claim 1, wherein the temperature of the water or the low-concentration manganese nitrate aqueous solution attached to the surface of the anode element is raised to 80 to 130 ° C. in the step (e). The temperature of the high-concentration manganese nitrate aqueous solution adhered to the surface of the anode element in the step (f) described above is 100 to
2. The method according to claim 1, wherein the temperature is raised to 130.degree.
The method for producing the solid electrolytic capacitor described in the above. 3. The method for producing a solid electrolytic capacitor according to claim 1 , wherein in the step (e) or (f), the temperature of the anode element is increased by blowing hot air onto the surface of the anode element. 4. The method according to claim 1 , wherein in step (e) or (f), the surface of the anode element is exposed to a high-temperature heat source for a short time to raise the temperature.