JPH06124854A - Manufacture of solid-state capacitor - Google Patents

Abstract

PURPOSE:To allow excellent oxide film recovery in a short re-chemical conversion treatment time by impregnating a metal sintered body with hot water as the pretreatment of the re-chemical conversion treatment and then performing the chemical conversion treatment by impregnating the metal sintered body with electrolyte. CONSTITUTION:A capacitor element 1 is formed by molding and sintering metal powder and an oxide film 3 is formed by anodic oxidation on the circumference of the metal powder and the capacitor element 1. Then, a manganese dioxide layer 5 is formed on the oxide film 3, the capacitor element 1 provided with the manganese dioxide film 5 is boiled in the water and re-chemical conversion treatment that recovers the oxide film 3 by re-anodic oxidation is performed. A graphite layer 9 is formed on the circumference of the capacitor element 1 as an electrode F base layer and a silver layer 10 is formed as the electrode outer layer. Thus, excellent oxide film recovery is performed in a short re- chemical conversion treatment time and the stable quality and highly reliable solid-state electrolytic capacitor is provided.

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 producing a solid electrolytic capacitor, which allows good penetration of an electrolytic solution during a re-chemical conversion treatment and repairs an oxide film in a short time.

[0002]

2. Description of the Related Art Conventionally, solid electrolytic capacitors are manufactured by the following procedure. First, an oxide film is formed around metal powder of a sintered metal such as tantalum, aluminum or niobium by anodic oxidation, and then a manganese dioxide (MnO ₂ ) layer is formed by thermal decomposition of an aqueous solution of manganese nitrate. As a result, as shown in FIG. 5, the oxide film 3 and the manganese dioxide layer 5 are formed around the individual metal powder or the lump 11 thereof inside the metal sintered body. Along with this, as shown in FIG. 6, the manganese dioxide layer 5 is also formed around the entire capacitor element 1 which is a sintered metal body.
Is formed. Next, re-formation treatment, that is, anodic oxidation is performed again to repair the deteriorated portion of the oxide film 3 during thermal decomposition, and then the outer periphery of the capacitor element 1 is composed of a graphite layer 9 and a silver layer 10 for electrode extraction. The metal layer is formed to complete the manufacturing.

[0003]

In the above-mentioned manufacturing method, since the electrolytic solution for anodizing cannot be sufficiently permeated into the inside of the metal sintered body 1 during the re-chemical conversion treatment, it takes time for a predetermined energizing treatment. In addition, the oxide film is not completely repaired and sufficient electrical characteristics cannot be obtained. That is, if the deteriorated portion of the oxide film 2 is not repaired, the leakage current (wet leakage current when the element is placed in 38% sulfuric acid and 18.3 V is applied, hereinafter referred to as LC) becomes large, and L
Variations in C value and breakdown voltage increase, and reliability of the solid electrolytic capacitor decreases. FIG. 7 shows the distribution of the LC value of the solid electrolytic capacitor manufactured by the conventional manufacturing method.

That is, as a result of measuring 50 samples, the average LC value was 270.6 nA, and the distribution was ± 23.6.
It was as wide as nA.

The object of the present invention is to solve the above problems and to rapidly permeate the electrolytic solution into the sintered body during the re-chemical conversion treatment.
An object of the present invention is to provide a method for producing a solid electrolytic capacitor that restores a favorable oxide film in a short time.

[0006]

The solid electrolytic capacitor manufacturing method according to the first aspect of the present invention comprises: (a) forming a capacitor element by molding and sintering a metal powder;
(B) An oxide film is formed around the metal powder and the capacitor element by anodic oxidation, (c) a manganese dioxide layer is formed on the oxide film, and (d) a capacitor element having the manganese dioxide layer is formed. Boil in boiling water,
(E) A re-formation treatment for repairing the oxide film by anodic oxidation is performed again, and (f) a metal layer is formed around the capacitor element.

In the method for producing a solid electrolytic capacitor according to the second aspect of the present invention, (a) a capacitor element is formed by molding and sintering metal powder, and (b) the metal powder and the capacitor element. An oxide film is formed around the oxide film by anodic oxidation, (c) a manganese dioxide layer is formed on the oxide film, and (e ') a capacitor element having the manganese dioxide layer is formed in an electrolytic solution containing a penetration aid. (F) A metal layer is formed around the capacitor element by performing a re-chemical conversion treatment for anodic oxidation to repair the oxide film.

The solid electrolytic capacitor manufacturing method according to the third aspect of the present invention includes (a) forming a capacitor element by molding and sintering metal powder, and (b) the metal powder and the capacitor element. To form an oxide film by anodic oxidation on the periphery of (a), (c) form a manganese dioxide layer on the oxide film, and (e ″) immerse the capacitor element on which the manganese dioxide layer is formed in an electrolytic solution under vacuum. A re-chemical treatment is carried out to restore the oxide film by anodic oxidation, and (f) a metal layer is formed around the capacitor element.

In each of the above methods, the steps from the formation of the manganese dioxide layer to the re-chemical conversion treatment are preferably repeated twice or more.

[0010]

According to the first aspect of the present invention, water is preliminarily permeated into pores inside the metal sintered body by immersing the metal sintered body in hot water as a pretreatment for the re-chemical conversion treatment, After that, since the re-chemical conversion treatment is performed by immersing in the electrolytic solution, the water content and the electrolytic solution for anodization are replaced by a mixing action, and the electrolytic solution within a pore inside the sintered body in a short time. Penetrate. As a result, the oxide film can be repaired in a short time and in good condition.

Further, according to the second aspect of the present invention, the surface tension of the metal sintered body can be lowered by adding the permeation aid to the electrolytic solution for anodic oxidation. It is possible to promote the permeation of the electrolytic solution into the internal pores.

According to the third aspect of the present invention, bubbles in pores and anodic oxidation are generated by immersing the metal sintered body in the electrolyte in a vacuum and performing anodic oxidation. The bubbles of hydrogen generated on the surface can be removed. As a result, the permeation of the electrolytic solution is facilitated, a favorable electric conduction state is obtained, and the oxide film can be favorably repaired in a short time.

[0013]

The present invention will be described below with reference to the drawings. FIG. 1 is an explanatory view showing one embodiment of a manufacturing process of the tantalum electrolytic capacitor according to the first aspect of the present invention, FIG.
1 is a flow chart showing steps from the chemical conversion treatment to the re-chemical conversion treatment in the step of FIG. 1, FIG. 3 is a graph showing a change in LC value with respect to the re-chemical conversion treatment time of the tantalum electrolytic capacitor in the middle of the step of FIG. 1, and FIG. 3 is a graph showing a distribution of LC values of the tantalum electrolytic capacitor obtained by the process of FIG. 1.

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

Next, an oxide film 3 is formed around the metal powder and the capacitor element 1 (see FIG. 1 (b)). As a specific example, the capacitor element 1 is 0.1% by weight.
(Hereinafter simply referred to as%) immersed in phosphoric acid aqueous solution 4,
By performing anodization at 50 to 100 V for 2 to 3 hours, the surface of the anode element and the surface of the metal powder therein,
Further, an oxide film 3, that is, a tantalum pentoxide (Ta ₂ O ₅ ) film is formed on a part of the surface of the wire 2.

Next, a manganese dioxide layer 5 is formed on the oxide film 3 (see FIGS. 1 (c) and 1 (d)). The manganese dioxide layer 5 is formed by impregnating a manganese nitrate aqueous solution and then thermally decomposing it (inner manganese dioxide layer). In order to relieve external stress also on the outer peripheral wall of the capacitor element 1, it is impregnated with a manganese nitrate aqueous solution in which fine particles of electrolytic MnO ₂ are dispersed and thermally decomposed to form a manganese dioxide layer (exterior manganese dioxide layer). As a specific example, after washing and drying the capacitor element, the inside of the element is impregnated with an aqueous solution of manganese nitrate with a specific gravity of 1.4, followed by thermal decomposition at 80 ° C for 15 minutes and then at 230 ° C.
Perform main decomposition for 10 minutes. This decomposition temperature is divided into two steps: the surface tension is lowered at 80 ° C to allow the manganese nitrate aqueous solution to penetrate into the interior of the sintered body, and then
This is because it decomposes into MnO ₂ at 230 ° C., and thereby improves the coating of MnO ₂ . However, it is not absolutely necessary.

Next, the capacitor element is boiled and then reformed. As a specific example, the capacitor element is immersed in hot water of 90 to 100 ° C., and it is boiled for about 10 minutes. This boiling is performed for the purpose of permeating the liquid into the inside of the sintered body. Then, as a re-chemical conversion treatment, the capacitor element is immersed in a 0.1% phosphoric acid aqueous solution and anodized at 25 to 50 V for about 5 minutes. This series of treatments of impregnation-pyrolysis-boiling-reformation is repeated 7 times to form a manganese dioxide layer and repair the oxide film. After that, the capacitor element is dipped in a liquid obtained by mixing fine particles of electrolytic manganese dioxide (average 0.2 μm) in an aqueous solution of manganese nitrate,
Decomposes at about 230 ° C to form an exterior manganese dioxide layer.

Then, a metal layer is formed around the content element 1 (see FIG. 1E). As a specific example,
The capacitor element 1 is immersed in a graphite dispersion liquid or a paste thereof at a depth such that the upper surface is not soaked, and fired to form the graphite layer 9 as an electrode underlayer. Further, after immersing the obtained capacitor element in a silver-containing liquid or its paste at a depth such that the upper surface is not soaked,
It is dried to form the silver layer 10 as an electrode outer layer. Graphite layer 9 serving as the electrode underlayer and silver layer serving as the electrode outer layer
The metal layer made of 10 is a portion which becomes 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.

Then, the external lead terminals of both the anode and the cathode are connected, and an epoxy resin is used for packaging (not shown).

Next, the re-formation time according to this embodiment will be compared with the case of the conventional manufacturing method using the graph of FIG. Figure 3
Shows the change of the LC value (value when 2000 elements are connected in parallel) with respect to the re-formation treatment time, and A1 is the LC with respect to the first re-formation treatment time by the method of the present embodiment.
By the change of the value, A2 is 1 for 20 minutes by the method of this embodiment.
The graph shows the change in the LC value with respect to the time of the second re-formation treatment after the second re-formation treatment. Also B1,
B2 similarly shows the change in the LC value with respect to the time of the first and second re-chemical conversion treatments by the conventional manufacturing method.
The applied voltage is 25V. As a result, if the same re-formation treatment time is used, the LC value of this production method can be suppressed lower than that of the conventional production method, and in order to obtain the same LC value, it can be achieved with a short re-formation treatment time. I understand.
Therefore, when a capacitor having a certain standard LC value or less is manufactured, this manufacturing method can manufacture a capacitor of the same quality by a short-time re-formation treatment.

Further, when comparing the respective LC values of 50 samples of the capacitor manufactured by the present manufacturing method and the capacitor manufactured by the conventional manufacturing method (the time and the number of times of the re-chemical conversion treatment are the same), the respective figures are shown. Four
The distribution is shown in. Note that, in FIG. 4, as an example, the LC value after performing the re-chemical conversion treatment seven times is adopted. Figure 4
Comparing the LC value distributions of the above, the average LC value of this production method is 206.5 nA and the distribution width is 24.5 nA, while the average LC value of the conventional production method is 270.6 nA and the distribution width is
It is 47.1 nA, and it can be seen that in the case of this manufacturing method, the absolute value of the LC value is small and the variation is very small.

Example 2 This example is an example of the second aspect of the present invention. The series of manufacturing steps is the same as that of Example 1, but the pretreatment in the re-chemical conversion treatment step is not performed. Then, anodization is carried out by using an electrolytic solution prepared by adding a small amount of ethyl alcohol, ethylene glycol, methyl alcohol, polyoxyethylene sorbitan ester or the like as a penetration aid to a 0.1% phosphoric acid aqueous solution as the re-chemical conversion treatment solution. The time for anodic oxidation is about 5 minutes, and impregnation-pyrolysis-as in Example 1
The re-formation is repeated 7 times to form the manganese dioxide layer and repair the oxide film. By adding the penetration aid in this way, the surface tension of the metal sintered body can be lowered,
Permeation of the electrolytic solution can be promoted, and the oxide film can be reliably repaired.

The capacitors obtained by this manufacturing method were 50 samples, and the average LC value was 218.5 nA and the distribution width was 26.3 nA.

In this example, the boiling of Example 1 was not carried out, but a synergistic effect can be obtained by using the pretreatment of the boiling together with the addition of the penetration aid of this example.

Example 3 This example is an example of the third aspect of the present invention, and the series of manufacturing steps is the same as that of Example 1, but the pretreatment in the re-chemical conversion treatment step is performed by boiling. In this case, the anodic oxidation for re-chemical conversion treatment is carried out by immersing it in a 0.1% phosphoric acid aqueous solution under vacuum for about 5 minutes. By making the vacuum state in this way, hydrogen generated during anodic oxidation is positively removed, so that the electrolytic solution easily permeates into the interior, and anodic oxidation can be surely and quickly performed. The vacuum degree is particularly preferably 100 Torr or less.

The capacitor manufactured by this manufacturing method is LC
The average of the values was 198.5 nA and the width of the distribution was 21.4 nA.

In this example, the example in which the boiling and the addition of the penetration aid of Example 1 and Example 2 were not used together was shown, but the synergistic effect can be obtained by using these 1 or 2 together. To be

In the above Examples 1 to 3, a tantalum solid electrolytic capacitor made of sintered tantalum powder was shown as a capacitor element, but a solid electrolytic capacitor using another metal material such as aluminum or niobium. It goes without saying that it can also be applied to. Furthermore, in each of the above-mentioned embodiments, the re-formation treatment is repeated seven times, but the number of repetitions is not limited in consideration of the re-formation treatment time.

[0029]

According to the present invention, since the permeation of the electrolytic solution for anodic oxidation is promoted, the oxide film can be satisfactorily repaired in a short re-chemical conversion treatment time. As a result, it is possible to obtain a solid electrolytic capacitor having high performance, stable quality, and high reliability, because the decrease in LC value and the variation in LC value and withstand voltage can be reduced.

[Brief description of drawings]

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

FIG. 2 is a flowchart showing steps from a chemical conversion treatment step to a re-chemical conversion treatment step in the step of FIG.

FIG. 3 is a graph showing changes in the LC value with respect to the re-chemical conversion treatment time of the tantalum electrolytic capacitor during the process of FIG.

FIG. 4 is a graph showing a distribution of LC values of the tantalum electrolytic capacitor obtained by the process of FIG.

FIG. 5 is an explanatory cross-sectional view of metal powder of a capacitor element of a tantalum electrolytic capacitor.

FIG. 6 is a cross-sectional explanatory diagram of a capacitor element of a tantalum electrolytic capacitor.

FIG. 7 is a graph showing an LC value distribution of a solid electrolytic capacitor manufactured by a conventional method.

[Explanation of symbols]

 1 Capacitor element 3 Oxide film 5 Manganese dioxide layer 9 Graphite layer 10 Silver layer

Claims (6)

[Claims] 1. A capacitor element is formed by (a) molding and sintering a metal powder, (b) an oxide film is formed around the metal powder and the capacitor element by anodization, and (c) A manganese dioxide layer is formed on the oxide film, (d) the capacitor element on which the manganese dioxide layer is formed is boiled with hot water, and (e) re-formation treatment is performed to restore the oxide film by anodic oxidation, and (f) ) A method for producing a solid electrolytic capacitor, characterized in that a metal layer is formed around the capacitor element. 2. The method according to claim 1, wherein the steps (c) to (e) are repeated twice or more. 3. (a) A capacitor element is formed by molding and sintering metal powder, (b) An oxide film is formed around the metal powder and the capacitor element by anodic oxidation, and (c) A manganese dioxide layer is formed on the oxide film, and (e ′) the capacitor element on which the manganese dioxide layer is formed is anodized with an electrolyte solution containing a penetration aid to perform a re-chemical conversion treatment for repairing the oxide film. (F) A method for producing a solid electrolytic capacitor, characterized in that a metal layer is formed around the capacitor element. 4. The method according to claim 3, wherein the steps (c) and (e ′) are repeated twice or more. 5. A capacitor element is formed by molding (a) metal powder and sintering, (b) an oxide film is formed around the metal powder and the capacitor element by anodic oxidation, and (c) A manganese dioxide layer is formed on the oxide film, and (e ″) the capacitor element on which the manganese dioxide layer is formed is immersed in an electrolytic solution under vacuum, and anodized to perform re-chemical conversion treatment to repair the oxide film, (F) A method for producing a solid electrolytic capacitor, which comprises forming a metal layer around the capacitor element. 6. The method according to claim 5, wherein the steps (c) and (e ″) are repeated twice or more.