JPH1092700A - Method and device for manufacturing solid-state electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain the characteristic of a solid-state electrolytic capacitor at a high level by preventing leakage currents by performing a chemical conversion treatment process, while impurities contained in the electrolytic solution used in the process are removed by performing weak electrolytic treatment on the electrolytic solution. SOLUTION: A circulating pipe 11 and pump 12 constitute an electrolytic solution circulating means between a container 4 and a sub-tank. While an electrolytic solution 5, such as a phosphoric acid solution, ammonium carbonate solution, etc., is contained in the container 4 and maintained at about 60 deg.C, a capacitor element 1, the anode lead 2 of which is partially welded to a stainless steel plate 3, is dipped in the solution 5 and anodic oxidation is performed by means of an anodic oxidation treating device which applies a voltage across the element 1 and the container 4 so that the element 1 and the container 4 sides can respectively become (+) and (-). On the other hand, part of the electrolytic solution 5 is transferred to the sub-tank 7 of a weak electrolytic treatment device, and such impurities as Fe, Ni, Cu, C, etc., dissolved in the solution 5 are removed by applying a voltage across electrodes 8 and 9 in the solution 5, so that the impurities can adhere to the electrode 9. Therefore, the occurrence of leakage failures can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a solid electrolytic capacitor and a manufacturing apparatus used for the method. More specifically, in a chemical conversion process or a re-chemical conversion process in which a dielectric film is formed on the surface of metal powder by anodic oxidation, the process is performed while cleaning the electrolytic solution so that impurities such as iron and nickel do not enter the capacitor. The present invention relates to a method for manufacturing a solid electrolytic capacitor and an apparatus for manufacturing the same.

[0002]

2. Description of the Related Art A solid electrolytic capacitor such as a tantalum capacitor is manufactured by the following procedure. First, tantalum (Ta), aluminum (Al), niobium (Nb)
A capacitor element is produced by molding and sintering such metal powders, and a chemical conversion treatment for forming an oxide film on the surface of each metal powder by anodic oxidation is performed. Next, after immersion in an aqueous solution of manganese nitrate, an electrolyte of a manganese dioxide layer is formed on the oxide film by evaporating water in a furnace. This operation is repeated several times, and in order to repair the thermal damage of the chemical conversion film during this time, another chemical conversion treatment step is inserted to form a manganese dioxide layer while performing the chemical conversion treatment again, and the oxide film is physically and chemically Protect, and electrically. Thereafter, graphite is applied to the outer periphery of the capacitor element, and a conductive paint such as copper or silver is applied to form a metal layer on the outer peripheral surface. Then, it is manufactured by assembling into a lead frame and molding with a synthetic resin.

In this manufacturing process, a chemical conversion treatment step and a re-chemical conversion treatment step for forming an oxide film on the surface of a metal powder are performed as follows. First, as shown in FIG. 2, several tens of the anode leads 2 of the molded and sintered capacitor element 1 are arranged and welded to a stainless steel plate called a suspension bar 3, and then put in a container 4. The anode lead 2 side of the capacitor element 1 is + (positive) by a power source 6 by immersing several tens of them in a suspension bar unit in an electrolyte solution 5 such as a phosphoric acid aqueous solution or an ammonium carbonate aqueous solution.
Anodization is performed by setting the container 4 side connected to to-(negative).
This chemical conversion treatment is performed by immersing the electrolytic solution 5 at, for example, about 60 ° C. for a long time of about several hours.

[0004]

As described above, since the chemical conversion treatment is carried out for a long time, the electrolytic solution 5 soaks through the anode lead 2 and the suspension bar 3 gets wet, so that electrolysis may be performed. When the suspension bar 3 is electrolyzed, impurities such as Fe, Ni, Cr, and C mixed in the stainless steel become cations and dissolve in the electrolyte 5. When such impurities dissolve in the electrolytic solution, they adhere to the capacitor element 1 immersed in the electrolytic solution 5, and there is a problem that the characteristics of the capacitor, such as an increase in leak current, deteriorate.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem. A solid electrolytic solution capable of preventing leakage current of a capacitor and maintaining its characteristics at a high level by always keeping the electrolytic solution clean. An object of the present invention is to provide a method for manufacturing a capacitor.

Another object of the present invention is to remove impurities in the electrolytic solution, thereby continuously using the electrolytic solution, eliminating waste of the electrolytic solution, and reducing the cost of the solid electrolytic capacitor. And

Still another object of the present invention is to automatically remove impurities from an electrolytic solution to save the trouble of controlling the impurity concentration, and to cause impurities to enter the capacitor element due to delay in purification of the electrolytic solution. It is an object of the present invention to provide a method of manufacturing a solid electrolytic capacitor without deteriorating the characteristics of the capacitor and an apparatus for manufacturing the same.

[0008]

Means for Solving the Problems As a result of intensive studies for improving characteristics such as improvement of leakage current of a solid electrolytic capacitor, the present inventor has found that Fe, Fe, It has been found that impurities such as Ni, Cr, and C are dissolved as cations and adhere to the capacitor element, leading to an increase in leak current. In order to solve this problem, a method of periodically replacing the electrolyte may be considered, but the dissolution of impurities into the electrolyte is irregular, and it is difficult to accurately grasp the limit of the impurity concentration of the electrolyte. In some cases, impurities may enter the capacitor element and deteriorate the characteristics of the capacitor. further,
Since the electrolytic solution must be discarded and replaced with a new electrolytic solution every time a certain amount of work is performed, the electrolytic solution is wasted and causes an increase in cost. However, it has been found that by subjecting this electrolytic solution to weak electrolytic treatment, the dissolved impurities can be effectively removed, and a high-performance solid electrolytic capacitor can be obtained without wasting the electrolytic solution.

A method for manufacturing a solid electrolytic capacitor according to the present invention is a method for manufacturing a solid electrolytic capacitor having a chemical conversion treatment step of forming a dielectric film on the surface of a metal powder by anodic oxidation. The method is characterized in that the treatment is performed while removing impurities in the electrolytic solution by performing a weak electrolytic treatment. By doing so, the electrolytic solution can be cleaned and the characteristics of the solid electrolytic capacitor can be prevented from deteriorating, and the electrolytic solution can be used repeatedly without discarding.

[0010] While the electrolytic solution is refluxed in a sub-tank communicating with the vessel for performing the anodization, the weak electrolytic treatment is performed in the sub-tank to automatically remove impurities in the electrolytic solution, thereby always removing the electrolytic solution. The impurity concentration in the electrolyte can be kept low, the performance of the solid electrolytic capacitor can be kept high, and the purification process of the electrolyte does not need to be performed periodically, so that the process can be automated. .

[0011] The production apparatus of the present invention comprises an anodizing apparatus capable of filling a container with an electrolytic solution and anodizing a capacitor element immersed in the electrolytic solution, and two electrodes provided in a sub-tank so as to face each other. A weak electrolysis treatment device for weakly electrolyzing the electrolyte solution that can be filled therein; and a circulating means for mutually circulating the electrolyte solution in the container and the sub tank. As a result, it is possible to continuously purify the electrolytic solution while performing the chemical conversion treatment of the capacitor, and it is possible to perform the chemical conversion treatment and the re-chemical conversion treatment in a clean state at all times. An electrolytic capacitor can be obtained.

[0012]

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

FIG. 1 is an explanatory view of a chemical conversion treatment step in the method for producing a solid electrolytic capacitor of the present invention. As described above, a solid electrolytic capacitor is formed by molding and sintering a metal powder such as tantalum (Ta), aluminum (Al), or niobium (Nb), and forms an anode lead of the capacitor element 1. 2 are welded to the suspension bar 3 by dozens, and a chemical conversion treatment is performed to form an oxide film on the surface of each powder by anodic oxidation. Then, a manganese dioxide layer is formed on the oxide film, In order to repair damage, a chemical conversion treatment (re-chemical conversion treatment) step is inserted again, and a conductive paint such as copper or silver is applied to form a metal layer on the outer peripheral surface. In the present invention, the method of the chemical conversion treatment step and the re-chemical conversion treatment step are different, and are assembled into other steps and subsequent lead frames,
The process of molding with a synthetic resin is the same as the conventional method.

In FIG. 1, 1 to 6 indicate the same parts as in FIG. 2, 7 is a sub-tank for weak electrolysis treatment, 8 and 9 are electrodes for weak electrolysis treatment, 10 is a power supply for weak electrolysis treatment, and 11 is an electrolytic solution. 5
Is a pump for circulating the electrolyte 5. The circulation pipe 11 and the pump 12 constitute a means for circulating the electrolyte between the container 4 and the sub-tank 7. In this chemical conversion method, as in the prior art, the container 4 is filled with an electrolytic solution 5 such as a phosphoric acid aqueous solution or an ammonium carbonate aqueous solution and maintained at about 60 ° C. Is immersed, and anodic oxidation is performed by an anodic oxidation treatment apparatus which applies a voltage so that the capacitor element 1 side becomes + and the electrolytic solution 4 side becomes-by the power source 6.

On the other hand, a part of the electrolytic solution 5 is transferred to the sub-tank 7 of the weak electrolytic processing apparatus, and a voltage is applied to the electrodes 8 and 9 in the electrolytic solution 5 in the sub-tank 7 to remove impurities dissolved in the electrolytic solution 5. Fe, Ni, Cu, C and the like are attached to the negative electrode 9 and removed. The time for removing the impurities by the weak electrolyzer varies depending on the area of the electrodes 8 and 9 and the magnitude of the voltage applied to the electrodes 8 and 9, and these parameters can be freely adjusted according to the amount of the impurities mixed. Can be selected. However, generally, impurities dissolved in the electrolytic solution are mixed by being electrolyzed by the electrolytic solution 5 soaked into the sassbar 3, and are very small. Since the electrodes 8 and 9 are inserted into the electrodes and electrolytic treatment is performed to attach an impurity metal to the electrodes, the amount of the metal to be removed is much larger than the amount to be dissolved in the same time. Therefore, if a circulating means for automatically circulating the electrolytic solution 5 as shown in FIG. 1 is used, impurities dissolved during the anodic oxidation time can be sufficiently removed even by a weak voltage weak electrolytic treatment method, The clean electrolytic solution 5 can always be maintained, and the impurity concentration can be reduced to sub-ppm or less.

As a specific example, the concentration of Fe is 1.7 ppm.
At a solution temperature of about 60 ° C., for example, at 30 V and 1 A
For 4 hours, the Fe concentration became 0.2.
ppm. At this time, the electrode 8 on the + side used was a Ti plate plated with Pt to a thickness of about 5 μm, and the electrode 9 on the − side was a stainless steel plate. −
The electrode 9 on the side has no problem as a material because the metal of the electrode does not dissolve by electrolysis. However, the electrode 8 on the + side has a possibility that the electrode metal can be dissolved in the electrolytic solution even by weak electrolysis. Is preferably plated with platinum which is less likely to be electrolyzed than directly exposed. In this case, it is preferable to use a titanium plate as the base metal in view of familiarity with platinum plating.

The concentration of Fe in the electrolytic solution to be subjected to the chemical conversion treatment;
As a result of examining the relationship between the defect rate of the leak failure of the tantalum electrolytic capacitor manufactured by performing the chemical conversion treatment with the electrolytic solution,
The results in Table 1 were obtained. In Table 1, the voltage indicates the average value of the voltage when the voltage reaches 20 μA when the voltage is applied to both electrodes of the capacitor, and the variation (σ) indicates the difference between the maximum value and the minimum value of the voltage. When the voltage is equal to or lower than a certain value, the defect rate is calculated as a ratio to the number of samples as a defect. From Table 1, it can be seen that the defect rate is 1% or less when the concentration of Fe in the electrolytic solution is 1 ppm or less, whereas the defect rate is greatly increased to 45% when the concentration of Fe is 10 ppm or more, By reducing the concentration, the yield of the capacitor can be greatly improved. It should be noted that most of the other impurities are metal ions such as Cu and Ni, which have been similarly removed by the weak electrolysis treatment, and are considered to have contributed to a reduction in the defective rate.

[0018]

[Table 1]

The kind of metal that easily adheres to the negative electrode differs depending on the distance between the electrodes of the weak electrolysis treatment apparatus, and the distance between the electrodes is changed during the weak electrolysis treatment. It is effective to arrange them obliquely so that the intervals are different. It is also effective to make the electrode plate waved to increase the area.

Further, in the above-described example, the weak electrolytic treatment was performed by automatically circulating the electrolytic solution while performing the anodic oxidation of the chemical conversion treatment. However, as described above, the impurities dissolved in the electrolytic solution were removed. Since the ability to remove impurities by the weak electrolysis treatment is larger than the amount, the weak electrolysis treatment may be periodically performed in a batch manner instead of continuously. In this case, unlike the conventional case, since the electrolytic solution is not discarded, it is possible to perform the weak electrolytic treatment as early as possible in a state where impurities are not so much dissolved, so that the chemical conversion treatment is not performed with the excessively dirty electrolytic solution. Can be performed periodically at regular intervals. As a result, there is no possibility that a chemical conversion treatment is performed by mistake with an electrolytic solution containing many impurities, and a high-performance solid electrolytic capacitor is obtained, and the impurity concentration of the electrolytic solution can be easily controlled.

[0021]

According to the present invention, in a chemical conversion treatment or a re-chemical conversion treatment in a manufacturing process of a solid electrolytic capacitor,
Since the electrolyte is periodically or continuously cleaned by weak electrolysis, even if impurities are mixed into the electrolyte by electrolysis such as a stainless steel plate holding the capacitor element, the impurities can be easily removed. As a result, the impurity concentration in the electrolytic solution can be maintained at sub-ppm or less. As a result, impurities such as Fe do not enter the capacitor, the leakage failure of the capacitor can be greatly reduced, and the yield is greatly improved.

Further, there is no need to strictly control the impurity concentration of the electrolytic solution, and it is not necessary to discard and replace the electrolytic solution every time the impurity concentration becomes high. This eliminates waste of liquid and greatly contributes to cost reduction of the capacitor.

[Brief description of the drawings]

FIG. 1 is a diagram showing an outline of an apparatus for performing a chemical conversion treatment in a method for producing a solid electrolytic capacitor of the present invention.

FIG. 2 is a diagram showing an outline of a conventional apparatus for performing a chemical conversion treatment.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 capacitor element 3 suspension bar 5 electrolyte solution 7 sub tank 8, 9 electrode for weak electrolysis 11 circulation pipe

Claims (3)

[Claims] 1. A method for producing a solid electrolytic capacitor having a chemical conversion treatment step of forming a dielectric film on the surface of a metal powder by anodic oxidation, wherein the chemical conversion treatment step is performed by subjecting an electrolytic solution to a weak electrolytic treatment. A method for producing a solid electrolytic capacitor, wherein the method is performed while removing impurities in an electrolytic solution. 2. The method according to claim 1, wherein the weak electrolytic treatment is performed in the sub-tank while refluxing the electrolytic solution in a sub-tank communicating with the container for performing the anodic oxidation, thereby automatically removing impurities in the electrolytic solution. Manufacturing method of solid electrolytic capacitor. 3. An anodizing apparatus capable of filling a container with an electrolytic solution and anodizing a capacitor element immersed in the electrolytic solution, and both electrodes provided in a sub-tank so as to face each other;
An apparatus for manufacturing a solid electrolytic capacitor, comprising: a weak electrolytic treatment device for weakly electrolyzing an electrolyte solution that can be filled therein; and a circulating means for mutually circulating the electrolyte solution in the container and the sub tank.