JP2847001B2 - 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 which makes it possible to improve the permeation of an electrolytic solution during re-chemical conversion treatment and to repair an oxide film satisfactorily in a short time.

[0002]

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

[0003]

In the above-mentioned production method, it is impossible to sufficiently infiltrate the electrolytic solution for anodic oxidation into the metal sintered body 1 at the time of re-chemical conversion treatment. However, the oxide film cannot be completely repaired, and sufficient electrical characteristics cannot be obtained. That is, if the deteriorated portion of the oxide film 2 is not repaired, the leak current (wet leak current when the element is put in 38% sulfuric acid and 18.3 V is applied, hereinafter referred to as LC) increases, and L
Variations in the C value and breakdown voltage increase, and the reliability of the solid electrolytic capacitor decreases. FIG. 7 shows a distribution of LC values of a solid electrolytic capacitor manufactured by a conventional manufacturing method.

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

SUMMARY OF THE INVENTION An object of the present invention is to solve such a problem and to allow an electrolytic solution to rapidly penetrate into a sintered body during re-chemical conversion treatment.
An object of the present invention is to provide a method for manufacturing a solid electrolytic capacitor that can repair a good oxide film in a short time.

[0006]

According to a first aspect of the present invention, there is provided a method for manufacturing a solid electrolytic capacitor, comprising: (a) forming a capacitor element by molding and sintering a metal powder;
(B) forming an oxide film by anodic oxidation around the metal powder and the capacitor element; (c) forming a manganese dioxide layer on the oxide film; and (d) forming a capacitor element having the manganese dioxide layer formed thereon. Boil in hot water,
(E) Re-chemical treatment for repairing the oxide film by anodic oxidation again, and (f) forming a metal layer around the capacitor element.

The method for manufacturing a solid electrolytic capacitor according to the second aspect of the present invention comprises the steps of: (a) forming a capacitor element by molding and sintering a metal powder; and (b) forming a capacitor element of the metal powder and the capacitor element. Forming an oxide film on the periphery thereof by anodic oxidation; (c) forming a manganese dioxide layer on the oxide film; and (e ′) an electrolytic solution containing a permeation aid added to the capacitor element having the manganese dioxide layer formed thereon. (F) forming a metal layer around the capacitor element.

In a third aspect of the present invention, a method for manufacturing a solid electrolytic capacitor includes the steps of (a) forming a capacitor element by molding and sintering a metal powder; (C) forming a manganese dioxide layer on the oxide film, and (e ″) immersing the capacitor element with the formed mankaman dioxide layer in an electrolytic solution under vacuum. And (f) forming a metal layer around the capacitor element.

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

[0010]

According to the first aspect of the present invention, the metal sintered body is immersed in hot water as a pretreatment of the re-chemical conversion treatment, so that moisture is allowed to penetrate into the pores inside the metal sintered body in advance. After that, since the re-chemical conversion treatment is performed by immersion in the electrolytic solution, the water and the electrolytic solution for anodic oxidation are replaced by a mixing action, and the electrolytic solution is introduced into the pores inside the sintered body in a short time. Penetrate. As a result, the oxide film can be repaired in a short time and in a good condition.

According to the second aspect of the present invention, the surface tension of the metal sintered body can be reduced by adding a penetration aid to the electrolyte for anodic oxidation. The penetration of the electrolyte into the internal pores can be promoted.

Further, according to the third aspect of the present invention, by immersing the metal sintered body in the electrolytic solution in a vacuum and performing anodic oxidation, bubbles in the pores and the anodic oxidation are generated. Hydrogen bubbles generated on the surface can be removed. As a result, permeation of the electrolyte is facilitated, a good energized state is obtained, and the oxide film can be satisfactorily repaired in a short time.

[0013]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. FIG. 1 is an explanatory view showing one embodiment of a manufacturing process of the tantalum electrolytic capacitor according to the first embodiment of the present invention, and FIG.
Is a flowchart 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 time of the chemical conversion treatment of the tantalum electrolytic capacitor in the middle of the step of FIG. 1, and FIG. 2 is a graph showing a distribution of LC values of the tantalum electrolytic capacitor obtained by the process of FIG.

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

Next, an oxide film 3 is formed around the metal powder and the capacitor element 1 (see FIG. 1B). As a specific example, 0.1% by weight of the capacitor element 1 is used.
Immersed in an aqueous phosphoric acid solution 4 (hereinafter simply referred to as%),
By performing anodic oxidation at 50 to 100 V for 2 to 3 hours, the surface of the anode element and the surface of
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. 1C and 1D). The manganese dioxide layer 5 is formed by impregnating with a manganese nitrate aqueous solution and then thermally decomposing (interior manganese dioxide layer). In order to relieve external stress, the outer peripheral wall of the capacitor element 1 is also impregnated with an aqueous solution of manganese nitrate 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 element is impregnated with an aqueous solution of manganese nitrate having a specific gravity of 1.4, and then is held at 80 ° C for 15 minutes as thermal decomposition, and then at 230 ° C.
Perform the main decomposition for 10 minutes. The decomposition temperature is divided into two stages by lowering the surface tension at 80 ° C to allow the manganese nitrate aqueous solution to penetrate inside the sintered body, and then
This is for decomposing into MnO ₂ at 230 ° C., thereby improving the coating of MnO ₂ . However, it is not essential.

Next, after the capacitor element is boiled, re-formation is performed. As a specific example, the capacitor element is immersed in hot water at 90 to 100 ° C. and boiled for about 10 minutes. This boiling is performed for the purpose of infiltrating the liquid into the inside of the sintered body. Next, as a re-chemical 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-rechemical formation is repeated seven times to form a manganese dioxide layer and to repair the oxide film. After that, the capacitor element is immersed in a solution in which electrolytic manganese dioxide fine particles (average 0.2 μm) are mixed with manganese nitrate aqueous solution,
Decomposes at about 230 ° C to form an outer manganese dioxide layer.

Next, 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 or a paste thereof to such a depth that the upper surface is not immersed, and baked to form the graphite layer 9 as an electrode underlayer. Furthermore, after immersing the obtained capacitor element in a silver-containing liquid or its paste at a depth such that the upper surface is not immersed,
After drying, the silver layer 10 is formed as an outer electrode layer. The graphite layer 9 serving as the electrode underlayer and the silver layer serving as the electrode outer layer
The metal layer made of 10 is a portion to be 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.

Next, the external lead terminals of both the anode and the cathode are connected, and the package is made using an epoxy resin (not shown).

Next, using the graph of FIG. 3, the re-formation time according to the present embodiment is compared with the case of the conventional production method. FIG.
Shows the change of the LC value (the value when 2,000 elements are connected in parallel) with respect to the re-formation processing time, and A1 shows the LC value with respect to the first re-formation processing time by the method of this embodiment.
In the change of the value, A2 is 1 minute for 20 minutes according to the method of the present embodiment.
The graph shows the change in the LC value with respect to the time of the second re-chemical conversion treatment after the second re-chemical conversion treatment. B1,
B2 similarly shows the change of the LC value with respect to the time of the first and second re-chemical conversion treatments by the conventional production method.
The applied voltage is 25V. As a result, if the same chemical conversion treatment time is used, the LC value of the present 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 in a short time of the chemical conversion treatment. I understand.
Therefore, when a capacitor having a LC value equal to or less than a certain reference value is manufactured, in the present manufacturing method, a capacitor of the same quality can be manufactured by a short re-chemical conversion treatment.

Further, when the 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 re-chemical conversion treatment are the same) are compared, the respective figures are as follows. 4
Is obtained. In FIG. 4, the LC value after performing the re-chemical treatment seven times is adopted as an example. FIG.
Comparing the LC value distributions of this method, the average of the LC value is 206.5 nA and the distribution width is 24.5 nA in the case of this production method, whereas the average of the LC value is 270.6 nA and the distribution width is in the case of the conventional production method.
47.1 nA, which indicates that in the case of this production method, the absolute value of the LC value is small and the dispersion is very small.

Embodiment 2 This embodiment is an embodiment of the second aspect of the present invention, and a series of manufacturing steps are the same as those in Embodiment 1, except that the pretreatment in the re-chemical conversion step is not performed. Anodization is carried out using an electrolytic solution obtained 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 a re-chemical conversion treatment solution. The anodizing time was about 5 minutes, and the impregnation-pyrolysis-
Re-formation is repeated seven times to form a 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 reduced,
The penetration of the electrolyte can be promoted, and the oxide film can be surely repaired.

The capacitors obtained by this method had an average LC value of 218.5 nA and a distribution width of 26.3 nA in 50 samples.

In this embodiment, the boiling in the first embodiment is not performed, but a synergistic effect can be obtained by using the pre-treatment of the boiling together with the addition of the penetration aid of the present embodiment.

Embodiment 3 This embodiment is an embodiment of the third aspect of the present invention, and a series of manufacturing steps is the same as that of Embodiment 1, but the pre-processing boiling in the re-chemical conversion step is performed. Instead, the anodization of the re-chemical conversion treatment is performed by immersing in a 0.1% phosphoric acid aqueous solution under vacuum for about 5 minutes. By setting the vacuum state as described above, hydrogen generated at the time of anodic oxidation is positively removed, so that the electrolyte easily permeates into the inside, and anodic oxidation can be performed reliably and quickly. The degree of vacuum is particularly preferably 100 Torr or less.

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

In this embodiment, an example is shown in which the boiling and the addition of the penetration aid of the above-mentioned Embodiments 1 and 2 are not used together. However, by using these 1 or 2 together, a synergistic effect can be obtained. Can be

In the first to third embodiments, a tantalum solid electrolytic capacitor obtained by sintering tantalum powder is shown as an example of a capacitor element. However, a solid electrolytic capacitor using another metal material such as aluminum or niobium is shown. Needless to say, it can be applied to Furthermore, in each of the above embodiments, the repetition of the re-formation treatment was described as an example of 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 penetration of the electrolytic solution for anodic oxidation is promoted, the oxide film can be satisfactorily repaired in a short re-chemical conversion time. As a result, a decrease in LC value and a variation in LC value and breakdown voltage can be reduced, and a high-performance, stable-quality, high-reliability solid electrolytic capacitor can be obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing one embodiment of a manufacturing process of a tantalum electrolytic capacitor according to a first embodiment 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 a change in LC value with respect to a re-chemical conversion treatment time of a 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 sectional view of a metal powder of a capacitor element of a tantalum electrolytic capacitor.

FIG. 6 is an explanatory sectional view of a capacitor element of a tantalum electrolytic capacitor.

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

[Explanation of symbols]

 Reference Signs List 1 capacitor element 3 oxide film 5 manganese dioxide layer 9 graphite layer 10 silver layer

Claims (6)

(57) [Claims] (A) forming a capacitor element by molding and sintering a metal powder; (b) forming an oxide film by anodic oxidation around the metal powder and the capacitor element; Forming a manganese dioxide layer on the oxide film; (d) boiling the capacitor element with the manganese dioxide layer formed thereon with hot water; A) a method of manufacturing a solid electrolytic capacitor, wherein a metal layer is formed around the capacitor element; 2. The method according to claim 1, wherein the steps (c) to (e) are repeated two or more times. (A) forming a capacitor element by molding and sintering the metal powder; (b) forming an oxide film by anodic oxidation around the metal powder and the capacitor element; A manganese dioxide layer is formed on the oxide film, and (e ') the capacitor element on which the manganese dioxide layer is formed is subjected to anodizing with an electrolytic solution to which a penetration aid has been added to perform a re-chemical conversion treatment to repair the oxide film. (F) A method of manufacturing a solid electrolytic capacitor, comprising forming a metal layer around the capacitor element. 4. The method according to claim 3, wherein the steps (c) and (e ′) are repeated at least twice. 5. A capacitor element is formed by molding and sintering a metal powder, and (b) forming an oxide film by anodic oxidation around the metal powder and the capacitor element. Forming a manganese dioxide layer on the oxide film, (e ″) immersing the capacitor element with the manganese dioxide layer formed in an electrolytic solution under vacuum, performing anodizing, and performing a re-chemical treatment to repair the oxide film; (F) A method for manufacturing a solid electrolytic capacitor, comprising forming a metal layer around the capacitor element. 6. The method according to claim 5, wherein the steps (c) and (e ″) are repeated at least twice.