JP4665866B2 - Manufacturing method of valve metal composite electrode foil - Google Patents

Description

  The present invention relates to a method for producing a valve metal composite electrode foil used as an anode foil or the like of a solid electrolytic capacitor.

  In recent years, along with miniaturization and high functionality of electronic devices, miniaturization, high integration, and high operating frequency of electronic circuits have been promoted. Similarly, passive components used in electronic circuits are also required to be smaller and have higher characteristics. For example, capacitors are also required to be as small, low profile, large capacity, and low impedance as possible. Yes.

As a capacitor having a large capacitance per volume, an electrolytic capacitor using a valve metal as an anode and an anodic oxide film as a dielectric is widely used. For example, an Al electrolytic capacitor in which Al foil roughened by electrochemical etching is anodized to form Al ₂ O ₃ , and a Ta electrolytic capacitor in which Ta ₂ O ₅ is formed by anodizing Ta porous pellets In addition, an Nb electrolytic capacitor in which Nb ₂ O ₅ is formed by anodizing a porous pellet of Nb is used. As a dielectric, Ta ₂ O ₅ (dielectric constant 24 to 27) and Nb ₂ O ₅ (dielectric constant 41) have a larger dielectric constant than Al ₂ O ₃ (dielectric constant 7 to 10). As a material for a small and large capacity electrolytic capacitor, Ta or Nb is more suitable than Al.

  As shown in FIG. 2, a general Ta electrolytic capacitor or Nb electrolytic capacitor is manufactured by compacting and sintering Ta powder or Nb powder with a wire (2) made of Ta or Nb inserted. The made porous pellet (1) is used as an anode body. Porous pellets with a very large surface area can be obtained by using submicron Ta powder or Nb powder, but there is a limit to reducing the size and thickness of porous pellets from the manufacturing method, so the obtained Ta electrolytic capacitor Or, there is a limit to the reduction in size and height of the Nb electrolytic capacitor.

  On the other hand, for example, as disclosed in Patent Document 1 (US Pat. No. 3,889,357), Ta powder capacitors or Nb electrolytic capacitors have Ta powder or It has been attempted for some time to obtain a foil-like anode body by making Nb powder into a paste, applying it to Ta foil or Nb foil, and baking it. However, in this method, cracks are likely to occur in the sintered body due to sintering shrinkage. In addition, since the sintering of the powder is more likely to proceed than between the powder and the foil, sufficient adhesion at the interface between the sintered body and the foil cannot be obtained. The occurrence of cracks or insufficient adhesion is not preferable because the sintered body is peeled off from the foil during handling in the capacitor manufacturing process, or the leakage current characteristics are deteriorated.

  In Patent Document 2 (Japanese Patent Application Laid-Open No. 2006-49816), Ta or Nb and a heterophasic component having no compatibility with them are mixed and deposited on a substrate of Ta or Nb, and in vacuum or It is disclosed that a foil-like anode body having a porous layer made of Ta or Nb is manufactured by a method in which only a heterogeneous component is selectively removed after heat treatment in an inert gas. A cross-sectional view of the foil-like anode body manufactured in this way is shown in FIG. The obtained foil-like anode body is effective for further downsizing and lowering the capacitor. However, these foil-like anode bodies use rare metals such as Ta foil and Nb foil as the substrate (3) in addition to the porous layer (4), so compared to conventional compacted pellets, There is a problem that the amount of Ta and Nb used increases and the cost of the foil-like anode body increases.

  On the other hand, from the viewpoint of lowering the impedance of the electrolytic capacitor, it is effective to stack a plurality of thin solid electrolytic capacitor elements and connect them electrically. For example, Patent Document 3 (Japanese Patent Laid-Open No. 11-135367) discloses such a multilayer solid electrolytic capacitor. Although this method is effective for lowering the impedance of the capacitor, since an etched Al foil is used as the foil-like anode body, as described above, compared to a solid electrolytic capacitor made of Ta or Nb, There is a problem that the capacitance density per volume becomes low.

Further, as in the above-mentioned Patent Document 2 (Japanese Patent Laid-Open No. 2006-49816), using a thin solid electrolytic capacitor element using a foil-like anode body made of Ta or Nb is a static per volume. Although it is considered effective for improving the capacitance density, as described above, the amount of rare metals Ta and Nb increases, leading to an increase in the cost of the foil-like anode body. In order to reduce the impedance of the electrolytic capacitor, it is important to reduce the equivalent series resistance (ESR) of the capacitor, and it is desirable that the resistance of the foil-like anode body is as low as possible. However, since Ta and Nb have relatively high volume resistivity (Ta volume resistivity: 13.5 μΩcm, Nb volume resistivity: 14.5 μΩcm), the resistance of the foil-like anode body made of Ta or Nb is: There is also a problem that it becomes larger than an etched Al foil (volume resistivity of Al: 2.7 μΩcm).
U.S. Pat. No. 3,889,357 JP 2006-49816 A JP-A-11-135367

  In view of these problems, the present inventors have studied, and in Japanese Patent Application No. 2006-191194, a volume resistivity is smaller than that of Ta and Nb, and a low cost Al foil is used as a substrate, Ta and Nb, A conventional etching Al is formed by mixing different phase components having no compatibility with them, forming a film, heat-treating in vacuum or inert gas, and adjusting the grains, and then selectively removing only the different phase components. It has been proposed that an electrode foil made of Ta alone or Nb alone can be obtained with a higher capacity density than the foil. A cross-sectional view of the electrode foil thus manufactured is shown in FIG. In this method, an inexpensive Al foil is used as a substrate (5), a dense layer (6) made of Ta or Nb is formed on one or both surfaces, and a porous layer (7) made of Ta or Nb is further formed thereon. The formed electrode foil is obtained.

  However, in this production method, since the melting point of Al is as low as 660 ° C., there is a limit to the heat treatment temperature for grain adjustment, that is, the grain size of Ta and Nb forming the porous layer is limited. When the particle size of Ta or Nb is not sufficiently large, when the anodic oxidation voltage is increased, the entire Ta or Nb particle is oxidized, resulting in a rapid decrease in capacitance or an increase in leakage current. . In such an electrode foil, since the anodic oxidation voltage cannot be increased, only an electrolytic capacitor having a low withstand voltage can be produced.

  The present invention has been made in order to solve such problems, and is suitable for the production of a multilayer solid electrolytic capacitor, has a higher capacity density than an etched Al foil, and has an equivalent electrode resistance, Furthermore, it aims at providing the manufacturing method of the electrode foil for electrolytic capacitors of the low cost which reduced the usage-amount of expensive rare metals Ta and Nb.

  The manufacturing method of the valve metal composite electrode foil of the present invention forms an alloy thin film in which Ta or a Ta alloy and a heterophasic component incompatible with Ta are uniformly distributed in a particle diameter range of 1 nm to 1 μm on a copper foil. Then, a Ta or Ta alloy dense layer is formed on the obtained alloy thin film, and after heat treatment, the Ta or Ta alloy and the heterogeneous component are grain-adjusted, and then on the dense layer, An electrode comprising the current collector layer, the dense layer, and a porous layer of Ta or Ta alloy by forming a current collector layer made of Al or an Al alloy and removing the copper foil and the heterogeneous component. Get a foil.

  Alternatively, on the copper foil, an alloy thin film in which Nb or Nb alloy and a heterogeneous component incompatible with Nb are uniformly distributed in a particle size range of 1 nm to 1 μm is formed, and on the obtained alloy thin film, After the Nb or Nb alloy dense layer is formed and heat-treated, the Nb or Nb alloy and the heterogeneous phase component are grain-adjusted, and then the current collector layer made of Al or Al alloy is formed on the dense layer. By forming and removing the copper foil and the heterogeneous component, an electrode foil comprising the current collector layer, the dense layer, and a porous layer of Ta or Ta alloy is obtained.

  Furthermore, it is desirable to form the current collector layer by vapor deposition.

  Furthermore, the current collector layer is preferably formed by pressure bonding or heat bonding in which the dense layer and an Al foil or Al alloy foil having a thickness of 100 μm or less are opposed to each other and pressed.

  Furthermore, it is desirable to make an electrode foil composed of a porous layer, a dense layer, a current collector layer, a dense layer, and a porous layer by facing the dense layer on both sides of the Al foil or Al alloy.

  It is desirable to remove in advance the natural oxide film on the surface of the current collector layer and the surface of the dense layer.

  Furthermore, it is desirable that the heterogeneous component in the alloy thin film is 30 to 70% in volume fraction.

  Furthermore, it is desirable to form the dense layer and the alloy thin film using a sputtering method or a vacuum evaporation method.

  Furthermore, the heterogeneous component is preferably Cu or Ag.

  Furthermore, a step of providing a thermodynamically stable barrier layer for any of the Ta, Ta alloy, Nb, Nb alloy, Al, and Al alloy between the dense layer and the current collector layer is further provided. It is desirable to have.

  Furthermore, it is desirable that the barrier layer is formed of TiN, ZrN, or HfN.

  Since the manufacturing method of the valve metal composite electrode foil of the present invention uses Ta, Ta alloy, Nb or Nb alloy for the porous layer, the capacitance density per volume is larger than the etching Al foil. In addition, since an Al or Al alloy layer is formed as a current collector, the electrode resistance can be lowered compared to a Ta or Nb single electrode foil, which is advantageous in reducing the equivalent series resistance of the electrolytic capacitor. Furthermore, since the amount of rare metals Ta and Nb used can be reduced, the electrode foil can be manufactured at a lower cost.

  In addition, in order to form a current collector layer made of Al or Al alloy after heat treatment using copper foil as a substrate and adjusting the grain, heat treatment is performed after film formation of Al or Al alloy as a substrate and grain adjustment Compared to the above, the grain can be adjusted at a high temperature. As a result, Ta particles and Nb particles forming the porous layer can be further grown and can be anodized at a higher voltage, so that the withstand voltage of the electrolytic capacitor can be increased.

  From the above, the valve metal composite electrode foil of the present invention can be suitably used as an electrode foil of an electrolytic capacitor. In particular, it is suitable as an anode foil of a thin solid electrolytic capacitor or a multilayer solid electrolytic capacitor.

  For production of a small, thin, and large capacity electrolytic capacitor, it is advantageous to use an electrode foil made of Ta or Nb rather than an etched Al foil because of the difference in dielectric constant. However, in order to reduce the equivalent series resistance of the capacitor, it is advantageous to use a metal having a volume resistivity lower than that of Ta or Nb as the substrate of the electrode foil. Since the amount of Ta and Nb used can be reduced, the electrode foil can be manufactured at a lower cost.

  The inventors of the present invention have made extensive studies based on such knowledge, and used Al, which has a volume resistivity several times smaller than Ta and Nb, and has a low cost. On top of this, a method of forming a porous layer made of Ta or Nb that can be anodized at a high voltage has a higher capacity density than the conventional etching Al foil, and has a higher electrode density than the electrode foil made of Ta or Nb alone. The inventors have found a method for producing an electrode foil that has low resistance, is low in cost, and can be anodized at a practical voltage, and has completed the present invention.

  Hereinafter, the manufacturing method of the valve metal composite electrode foil of this invention is demonstrated in detail for every process using FIG. FIG. 1 is a series of flowcharts showing a plurality of embodiments of the method for producing a valve metal composite electrode foil of the present invention.

  The method for producing a valve metal composite electrode foil of the present invention is as follows: [1] An alloy in which Ta or a Ta alloy and a different phase component incompatible with Ta are uniformly distributed on a copper foil within a particle size range of 1 nm to 1 μm A first step of forming a thin film, [2] a second step of forming a dense layer of Ta or Ta alloy on the obtained alloy thin film, [3] Ta or Ta alloy by heat treatment, and A third step of adjusting the grains of the different phase component, [4] a fourth step of forming a current collector layer made of Al or an Al alloy on the dense layer, and [5] removing the copper foil and the different phase component. It consists of a fifth step.

  Alternatively, Nb or Nb alloy can be used instead of Ta or Ta alloy.

Note that Ta alloys and Nb alloys include valve metals such as Zr, Ti, Hf, and Al that improve the leakage current and thermal stability of Ta ₂ O ₅ and Nb ₂ O ₅ films that serve as dielectrics for electrolytic capacitors. And a material containing a trace amount of a dopant such as P, N or B.

  In the present invention, a substrate (8) made of copper foil is used as the substrate. Such a substrate (8) is used for forming a composite electrode foil, and is required to have low reactivity with Ta, Ta alloy, Nb, and Nb alloy, and needs to be removed in a subsequent process. Therefore, by using the copper foil as the substrate (8), it is possible to dissolve and remove simultaneously with the heterogeneous component.

  The substrate (8) made of copper foil uses smooth rolled copper foil or electrolytic copper foil. The reason is that the surface properties of the finally obtained electrode foil reflect the surface roughness of the substrate (8) made of copper foil. However, the type of copper foil used and the surface roughness are not limited. Therefore, when a special electrode foil having an uneven surface is required, a copper foil having an uneven surface may be used. Moreover, when there are many impurities in copper foil, it may diffuse into Ta and Nb and may deteriorate the leakage current characteristics of the electrode foil. Therefore, it is preferable to use a copper foil with as few impurities as possible.

[1] On a copper foil, an alloy thin film in which Ta or Ta alloy (Nb or Nb alloy) and a different phase component incompatible with Ta (Nb) are uniformly distributed in a particle diameter range of 1 nm to 1 μm is formed. First step:
Porous layer finally obtained when Ta or Ta alloy (Nb or Nb alloy) and a different phase component incompatible with Ta (Nb) are not 1 nm to 1 μm in particle size or non-uniform in distribution The particle size and pore distribution of (14) become non-uniform, leading to deterioration of the characteristics of the electrolytic capacitor. The uniformity of the particle size range and distribution can be easily confirmed with a scanning electron microscope or the like when the particle size is 100 nm or more. Even when the particle diameter is as fine as less than 100 nm, it can be confirmed with a transmission electron microscope.

  The amount of the heterophasic component added is determined by the volume fraction and is preferably in the range of 30 to 70%. The porous layer (14) is finally obtained by removing the heterogeneous component. In order to completely remove the heterogeneous component, it is necessary that the heterophasic component is completely connected. However, if the added amount of the heterophasic component is less than 30% as a volume fraction, the heterophasic component is completely removed. Without being connected, it becomes difficult to remove, and it remains in the porous layer (14) to reduce the surface area per apparent area, or it becomes difficult to impregnate the cathode when forming an electrolytic capacitor. If the added amount of the different phase component exceeds 70% as a volume fraction, after removing the different phase component, the bonding strength of the particles made of Ta or Ta alloy (Nb or Nb alloy) is weak, or the particles are completely The porous structure cannot be maintained without being completely connected. However, the range of the added amount of the heterophasic component is a guide and does not absolutely limit the added amount of the heterophasic component. Depending on the degree of orientation of the film and the purpose of use, an additive amount outside the above range may be employed.

  As a method for producing an alloy thin film in which different phase components are finely and uniformly distributed, Ta or Ta alloy (Nb or Nb alloy) having a particle size in the range of 1 nm to 1 μm and particles of different phase components are dispersed in a volatile binder. Various methods such as a printing method, CVD (chemical vapor deposition method), thermal spraying, sputtering, and vapor deposition are conceivable.

  Various methods are conceivable as described above. In the present invention, it is preferable to use a co-sputtering method or a co-evaporation method. In these methods, the flying material adheres to the substrate at the atomic or cluster level to form a thin film. Therefore, a thin film having a fine particle size and uniformly dispersed can be easily obtained with good reproducibility. Further, the alloy composition can be easily changed by changing the electric power supplied to the target or the evaporation source. That is, the porosity of the finally obtained porous layer (14) can be easily adjusted.

  As the heterogeneous component, a component that does not dissolve in Ta and Ta alloy, or Nb and Nb alloy, is easily sputtered, and is easy to adjust grains is preferable. Cu or Ag hardly dissolves in Ta, Ta alloy, Nb and Nb alloy, and sputtering is easy. Furthermore, since the melting point is relatively high (Cu: 1083 ° C., Ag: 960 ° C.) and it is easy to adjust grains, it is suitable as a heterogeneous component.

  Moreover, Mg, Ca, or these oxides are also preferable. Mg and Ca hardly dissolve in Ta, Ta alloy, Nb, and Nb alloy, and these oxides are more thermodynamically stable than Ta oxide and Nb oxide.

[2] Second step of forming a dense layer of Ta or Ta alloy on the obtained alloy thin film:
The dense layer (10) serves as a bonding layer between the porous layer (14) and the current collector layer (12, 13), and also provides alloying between the heterogeneous component and the current collector layer (12, 13) described later. It has a role to prevent. When the current collector layers (12, 13) are formed directly without using the dense layer (10), for example, by using Cu or Ag as a heterogeneous component, the current collector layer in which Cu or Ag is directly made of Al. In contact with (12, 13), a reaction product is formed with Al, which is difficult to remove, and the porous layer (14) cannot be obtained, or a lot of heterogeneous components remain in the porous layer (14), This is not preferable because it affects the capacitor characteristics.

  Even if the dense layer (10) is formed, depending on the film quality and film thickness of the dense layer (10), the deposition conditions of Al, and the conditions of diffusion bonding with the Al foil, mutual diffusion of Al and different phase components may occur. May occur and form a compound. A thermodynamically stable barrier layer can be formed on the dense layer (10). By such a barrier layer, mutual diffusion of Al and a different phase component can be prevented more reliably. When the barrier layer is formed, the barrier layer and Al do not react with each other, and it is difficult to perform diffusion bonding with each other. Therefore, when the Al foil is diffusion bonded, a dense layer is further formed on the barrier layer, and the obtained dense layer is used as a bonding layer.

  As the barrier layer, TiN, ZrN, or HfN is preferable because it is thermodynamically stable and exhibits relatively high conductivity. From the viewpoint of barrier properties, the film quality of the barrier layer is preferably as dense as possible, and from the viewpoint of suppressing an increase in electrode resistance as much as possible, the film thickness of the barrier layer is preferably as thin as possible. Such a dense and thin barrier layer is preferably formed by reactive sputtering in which nitrogen gas is introduced or reactive vapor deposition.

[3] Third step of adjusting grains of Ta or Ta alloy and the heterogeneous component by heat treatment:
Without grain growth of Ta or Ta alloy (Nb or Nb alloy), the integrity of the porous layer cannot be ensured, and it is possible to dissolve and remove foreign phase components by growing the different phase components and making them continuous. become.

  Grain growth can be performed in an inert atmosphere such as argon as the heat treatment atmosphere, but the oxidation of Ta or Ta alloy (Nb or Nb alloy) is prevented as much as possible, and the leakage current of the electrode foil is reduced. From the viewpoint, an atmosphere in a high vacuum is preferable.

  In general, as the heat treatment is performed at a higher temperature, grain growth proceeds and the structure of the finally obtained porous layer becomes rougher. The heat treatment temperature for grain growth can be arbitrarily determined at 200 ° C. or higher and below the melting point of the heterogeneous component or the substrate, but is preferably 700 ° C. or higher. When the heat treatment temperature is less than 200 ° C., the integrity of the structure of the porous layer is lost, and the continuum may not be obtained. On the other hand, if the heat treatment temperature is 200 ° C. or higher, the lower the heat treatment temperature, the less likely grain growth occurs and the larger the surface area of the resulting porous layer. However, when the temperature is lower than 700 ° C., the obtained composite electrode foil has a very large area capacitance at an anodic oxidation voltage of 10 V, but the CV per area rapidly decreases when the anodic oxidation voltage is increased. This phenomenon indicates that all the Nb particles are oxides when the anodic oxidation voltage is increased because the Nb particles forming the porous layer are too fine. Such a phenomenon not only reduces the effective surface area that contributes to the capacitance, but also causes problems such as an increase in leakage current and difficulty in impregnating the electrolyte with the cathode due to collapse of the pores. When such an electrode foil is used, the anodic oxidation voltage is limited. For example, the rated voltage of a solid electrolytic capacitor is said to be about 1/3 of an anodic oxidation voltage, and when such an electrode foil is used as an anode, only a solid electrolytic capacitor with a low withstand voltage can be produced. It will be. Accordingly, when anodizing is performed at a more practical voltage when forming a capacitor, for example, in the case of an anodic oxidation voltage of 15 V or higher, it is preferable that the heat treatment temperature is set to 700 ° C. or higher.

[4] Fourth step of forming a current collector layer made of Al or an Al alloy on the dense layer:
The current collector layer is formed by any one of [Al vapor deposition], [Al foil single-sided bonding], and [Al foil double-sided bonding].

[Al deposition]
In the previous step, after grain adjustment, a current collector layer (12) made of Al is formed on the surface of the dense layer (10) of Ta or Ta alloy (Nb or Nb alloy).

  Al can be deposited by various deposition methods, but vacuum deposition is particularly advantageous because the deposition rate of Al is high. The thickness of the current collector layer (12) made of Al can be arbitrarily adjusted depending on the film formation time, but is preferably 1 to 50 μm. As the thickness increases, the resistance of the electrode foil can be reduced, which is advantageous from the viewpoint of ESR of the electrolytic capacitor. However, the film formation takes a long time. ESR may be reduced by the element structure of the electrolytic capacitor. For example, when the current collector layer (12) made of Al is directly bonded to the external electrode with a conductive resin or the like, the current collector layer (12) made of Al may be thin.

[Single-sided bonding of Al foil] and [Double-sided bonding of Al foil]
In the previous step, after the grain adjustment, a current collector layer (13) made of Al foil or Al alloy foil is formed on the surface of the dense layer (10) of Ta or Ta alloy (Nb or Nb alloy).

  Diffusion bonding can be performed while applying pressure in a state where one surface or both surfaces of the Al foil or Al alloy foil and the dense layer (10) face each other (pressure bonding). Alternatively, diffusion bonding can be performed by heating while applying pressure (heating bonding). However, at the time of thermocompression bonding, due to the influence of the surface natural oxide film of the Al foil or Al alloy foil, sufficient adhesion may not be obtained by low-temperature pressure bonding. For this reason, it is preferable to perform diffusion bonding after physically removing the surface natural oxide film by plasma or the like. By doing so, diffusion bonding can be performed at a relatively low temperature and low pressure.

[5] Fifth step of removing the copper foil and the heterogeneous component:
The substrate (8) made of copper foil and the foreign phase component are removed. Various methods can be used as the removal method. From the simplicity of operation, the corrosion resistance of the constituent elements of the electrode foil, such as Ta, Ta alloy, Nb, Nb alloy, Al or Al alloy, can be used with an acid. It is preferable to dissolve and remove. As the acid, an acid that selectively dissolves the heterogeneous component and the copper foil is selected. For example, sulfuric acid or hydrochloric acid to which nitric acid or hydrogen peroxide is added can be used. After removing the heterogeneous component, it is washed with water and dried to obtain a valve metal composite electrode foil.

  The valve metal composite electrode foil thus obtained has a uniform distribution of voids and a large surface area. Further, since the porous layer (14) on which the dielectric film is formed by anodic oxidation is formed of Ta, Ta alloy, Nb, or Nb alloy particles, it is more electrostatic than the conventional etching Al foil. Capacity density increases. Moreover, since Al with a small volume resistivity is used, electrode resistance can be made smaller than electrode foil formed only with Ta, Ta alloy, Nb, or Nb alloy. In addition, since the amount of rare metals Ta and Nb used is small, it is possible to produce an electrode foil at a lower cost.

  Furthermore, using a copper foil as a substrate, and after adjusting the grain by heat treatment, to form a current collector layer made of Al, to adjust the grain by heat treatment after forming a film of Al or Al alloy as a substrate Compared to the case, the grain can be adjusted at a high temperature. As a result, grain growth of Ta particles and Nb particles forming the porous layer can be achieved. Since the electrode foil thus obtained can be anodized at a high voltage, the withstand voltage of the electrolytic capacitor can be increased.

  From the above, the valve metal composite electrode foil of the present invention can be suitably used as an electrode foil of an electrolytic capacitor. In particular, it is suitable as an electrode foil of a thin solid electrolytic capacitor or a multilayer solid electrolytic capacitor.

  Hereinafter, the present invention will be described by way of examples.

Example 1
A 20 mm × 20 mm × 18 μm thick rolled copper foil (oxygen-free copper, purity 99.9% or more) is used as the substrate, and a 99.99% purity Ta target and Cu target (both are φ152.4 mm, Using a multi-source sputtering apparatus (manufactured by ULVAC, Inc., SH-450), a film having a composition of Ta-60 vol% Cu is formed in a thickness of 20 μm in an argon atmosphere of 10 mtorr. A dense layer of about 1 μm was formed. Thereafter, heat treatment was performed at 950 ° C. × 1 hr in a vacuum of 3.0 × 10 ⁻³ Pa or less using a high-temperature vacuum furnace (turbo-vac, manufactured by Tokyo Vacuum Co., Ltd.). Then, about 10 micrometers of Al was formed into a film on the dense layer which consists of Ta with a vacuum evaporation machine (A1F-850SB by Shinko Seiki Co., Ltd.). Thereafter, Cu was completely dissolved by immersing in a 6.7 mol / l nitric acid aqueous solution for 1 hour, then washed with water and dried to obtain a Ta / Al composite electrode foil.

  When a cross section of the obtained Ta / Al composite electrode foil was observed with a scanning electron microscope, a Ta dense layer of 1 μm and a particle size of about 0.3 μm were formed on a current collector layer made of 10 μm thick Al. A laminated structure of 20 μm porous layer made of Ta particles was formed, and the total thickness of the Ta / Al composite electrode foil was about 31 μm.

The obtained Ta / Al composite electrode foil was cut into 10 mm square, and an Nb wire having a diameter of 0.2 mm was attached as a lead with a spot welder. Furthermore, after protecting the surface of the current collector layer by coating an insulating resin, in an aqueous phosphoric acid solution having an electric conductivity of 10 mS / cm and 80 ° C., an initial current density of 0.01 mA / cm ² , a voltage of 10 V, A Ta ₂ O ₅ film serving as a dielectric was formed on the surface by performing constant voltage formation for 6 hours at 20V and 30V.

Thereafter, the capacitance was measured in 40% by mass of sulfuric acid using an LCR meter (manufactured by Agilent, 4263B) at an applied bias of 1.5 V, a frequency of 120 Hz, and an effective value of 1.0 Vrms. It was calculated (μF / cm ²⁾ and per area CV (μFV / cm ^2). The measurement results are shown in Table 1.

(Example 2)
A Ta / Al composite electrode foil was obtained in the same manner as in Example 1 except that the heat treatment temperature was 800 ° C.

  When a cross section of the obtained Ta / Al composite electrode foil was observed with a scanning electron microscope, a Ta dense layer of 1 μm and a particle size of about 0.15 μm were formed on a current collector layer made of Al having a thickness of 10 μm. A laminated structure of 20 μm porous layer made of Ta particles was formed, and the total thickness of the Ta / Al composite electrode foil was about 31 μm.

  Thereafter, evaluation was performed in the same manner as in Example 1. The measurement results are shown in Table 1.

(Example 3)
A 20 mm × 20 mm × 18 μm-thick rolled copper foil (oxygen-free copper, purity 99.9% or more) is used as a substrate, and a Nb target and a Cu target (both φ152.4 mm, purity 99.99%) are used as sputtering targets. Using a high-purity chemical research laboratory), a multi-sputter apparatus (manufactured by ULVAC, Inc., SH-450) was used to deposit a 10 μm film of Nb-60 vol% Cu in an argon atmosphere of 10 mtorr. A dense layer made of about 0.4 μm was formed. Thereafter, reactive sputtering was performed by introducing nitrogen gas, and a TiN film having a thickness of about 0.2 μm was formed as a barrier layer, and a dense layer made of Nb was further formed thereon by a thickness of about 0.4 μm. The obtained sample was heat-treated at 800 ° C. for 1 hour in a vacuum of 3.0 × 10 ⁻³ Pa or less using a high-temperature vacuum furnace (turbo-vac, manufactured by Tokyo Vacuum Co., Ltd.). Two samples as described above were produced.

  Thereafter, these samples and a 50 μm thick Al foil (purity: 99.9%) were placed in the multi-source sputtering apparatus and subjected to reverse sputtering treatment, and the dense layer made of Nb and the surface native oxide film of the Al foil Was removed. Thereafter, a dense layer made of Nb was opposed to both surfaces of the Al foil, and heat-treated at 500 ° C. for 1 hour in vacuum while being subjected to diffusion bonding while being pressurized at 1 MPa. Then, it was immersed in a 6.7 mol / l nitric acid aqueous solution for 1 hr to completely dissolve Cu, and then washed with water and dried to obtain an Nb / Al composite electrode foil. When the cross section of the obtained electrode foil was observed with a scanning electron microscope, a dense layer made of Nb, a barrier layer made of TiN, and a dense layer made of Nb were about 1 μm on both sides of an Al foil having a thickness of 50 μm. A laminated structure with a 10 μm porous layer made of Nb particles having a diameter of about 0.2 μm was formed, and the total thickness of the Nb / Al composite electrode foil was 72 μm.

The obtained Nb / Al composite electrode foil was cut into 10 mm square, and a Nb wire having a diameter of 0.2 mm was attached as a lead with a spot welder. Furthermore, in a phosphoric acid aqueous solution with an electrical conductivity of 10 mS / cm and 80 ° C., by performing constant voltage formation for 6 hours with an initial current density of 0.01 mA / cm ² , three voltages of 10 V, 20 V, and 30 V, surface An Nb ₂ O ₅ film serving as a dielectric was formed.

  Thereafter, evaluation was performed in the same manner as in Example 1. The measurement results are shown in Table 1.

(Conventional example 1)
An AC-etched Al foil consisting of a substrate having a thickness of about 30 μm and an etching layer having a thickness of about 40 μm on both sides and having a total thickness of 110 μm was cut into 10 cm squares, and the diameter was measured by a spot welder. After attaching a 0.2 mm Nb wire as a lead, constant voltage formation was performed for 6 hr at a voltage of 10 V in an aqueous solution of ammonium adipate at 60 ° C. to form Al ₂ O _{3 serving} as a dielectric.

  Thereafter, evaluation was performed in the same manner as in Example 1. The measurement results are shown in Table 1.

(Conventional example 2)
Nb foil (purity of 99.9% or more) of 20 mm × 20 mm × 50 μmt is used as the substrate, and Nb target and Cu target of 99.99% purity (both are φ152.4 mm, high purity chemical research institute, Inc.) A film having a composition of Nb-60 vol% Cu was formed in a thickness of 10 μm using a multi-source sputtering apparatus (manufactured by ULVAC, Inc., SH-450) in an argon atmosphere of 10 mtorr. Thereafter, the sample was turned upside down, and a film of Nb-60 vol% Cu was similarly formed on the other surface by 10 μm. Thereafter, heat treatment was performed at 800 ° C. for 1 hour in a vacuum of 3.0 × 10 ⁻³ Pa or less using a high-temperature vacuum furnace (turbo-vac, manufactured by Tokyo Vacuum Co., Ltd.). Then, Cu was completely dissolved by immersing in a 6.7 mol / l nitric acid aqueous solution for 1 hour, then washed with water and dried to obtain an Nb electrode foil.

  When the cross section of the obtained Nb electrode foil was observed with a scanning electron microscope, a laminated structure with a porous layer of 10 μm composed of Nb particles having a particle size of about 0.2 μm was formed on both sides of the 50 μm thick Nb foil. The total thickness of the Nb electrode foil was 70 μm.

  Thereafter, evaluation was performed in the same manner as in Example 1. The measurement results are shown in Table 1.

(Comparative Example 1)
Using a Ti target with a purity of 99.99% on one side of a 20 mm × 20 mm × 50 μm thick Al foil (purity 99.9%) as a substrate, a multi-source sputtering apparatus (manufactured by ULVAC, Inc., SH-450) Then, reactive sputtering was performed in an Ar + 2.5% N ₂ atmosphere to form a TiN film of about 0.5 μm as a barrier layer. After that, using a Nb target and a Cu target (both φ152.4 mm, manufactured by Kojundo Chemical Laboratory Co., Ltd.), a dense layer made of Nb was formed to a thickness of about 1 μm in an argon atmosphere of 10 mtorr. Subsequently, Nb-60 vol% A film having a Cu composition was formed to a thickness of about 10 μm. Thereafter, the upper and lower sides of the sample are turned upside down, and on the other side, a barrier layer made of TiN is formed in a thickness of about 0.5 μm and a dense layer made of Nb is formed in a thickness of about 1 μm. About 10 μm was formed. Thereafter, heat treatment was performed at 600 ° C. for 1 hr in a vacuum of 3.0 × 10 ⁻³ Pa or less using a high-temperature vacuum furnace (turbo-vac, manufactured by Tokyo Vacuum Co., Ltd.). Then, Cu was completely dissolved by immersing in a 6.7 mol / l nitric acid aqueous solution for 1 hour, then washed with water and dried to obtain an Nb / Al composite electrode foil.

  When a cross section of the obtained Nb / Al composite electrode foil was observed with a scanning electron microscope, a barrier layer of 0.5 μm made of TiN, a dense layer of 1 μm made of Nb, and a particle diameter were formed on both sides of the 50 μm thick Nb foil. A laminated structure with a porous layer of 10 μm made of Nb particles of about 0.05 to 0.1 μm was formed, and the total thickness of the Nb / Al composite electrode foil was 73 μm.

  Thereafter, evaluation was performed in the same manner as in Example 1. The measurement results are shown in Table 1.

(Comparative Example 2)
Film formation was performed in the same manner as in Comparative Example 1, and the obtained sample was 800 ° C. in a vacuum of 3.0 × 10 ⁻³ Pa or less using a high-temperature vacuum furnace (turbo-vac, manufactured by Tokyo Vacuum Co., Ltd.). A heat treatment of × 1 hr was performed. In the sample after removal, the Al foil of the substrate was dissolved, and no electrode foil was obtained.

  In the valve metal composite electrode foils of Examples 1 to 3 and the etched Al foil of Conventional Example 1, when attention is paid to the area capacitance density when the anodic oxidation voltage is 10 V, both are thinner than the etched Al foil. It has an area capacitance density equal to or greater than that, which is advantageous for downsizing and increasing the capacity of the capacitor.

  Further, the Nb / Al composite electrode foil of Example 3 and the Nb electrode foil of Conventional Example 2 have an anodic oxidation voltage of 10V, 20V, and 30V and substantially the same area capacitance density. Therefore, it can be seen that the manufacturing method of the present invention can provide an Nb / Al composite electrode foil having almost the same characteristics as the Nb electrode foil even though inexpensive Al is used instead of the Nb foil.

  Further, the Nb / Al composite electrode foil of Comparative Example 1 has a very large area capacitance density at an anodic oxidation voltage of 10 V, but when the anodic oxidation voltage is increased, the CV per area rapidly decreases. I understand. This indicates that since the Nb particles forming the porous layer are too fine, when the anodic oxidation voltage is increased, all Nb particles become oxides. In such an electrode foil, since the anodic oxidation voltage is limited, only an electrolytic capacitor having a low rated voltage can be produced. Further, since grain growth is performed as in Comparative Example 2, if heat treatment is performed at a temperature equal to or higher than the melting point of Al, the Al foil of the substrate is completely dissolved, and an electrode foil cannot be obtained.

  On the other hand, the electrode foils of Examples 1 to 3 according to the present invention have very little decrease in CV per area when the anodizing voltage is increased, and can be anodized at a high voltage. An electrolytic capacitor having a high voltage can be produced.

  As described above, the manufacturing method of the valve metal composite electrode foil of the present invention has an area capacitance density higher than that of the conventional etching Al foil, and compared with the electrode foil of Ta alone and Nb alone, A valve metal composite electrode foil with low electrode resistance is obtained. Further, Al is used as the current collector layer, and it is possible to produce a valve metal composite electrode foil at a lower cost compared to an electrode foil using rare metals such as Ta alone and Nb alone.

  Furthermore, since grain growth is performed at a high temperature, a valve metal composite electrode foil that can be anodized to a higher voltage can be obtained, and an electrolytic capacitor having a high withstand voltage can be produced, which is useful.

It is a series of flowcharts which showed together the several embodiment of the manufacturing method of the valve metal composite electrode foil of this invention. It is sectional drawing which shows the anode body which consists of a porous pellet used for the conventional Ta electrolytic capacitor or Nb electrolytic capacitor. It is sectional drawing which shows the conventional foil-shaped anode body. It is sectional drawing which shows a valve metal composite electrode foil.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Porous pellet 2 Wire 3, 5 Substrate 4, 7 Porous layer 6 Dense layer 8 Substrate 9, 11 Alloy thin film 10 Dense layer 12, 13 Current collector layer 14 Porous layer

Claims (11)

  On the copper foil, an alloy thin film in which Ta or a Ta alloy and a heterogeneous component incompatible with Ta are uniformly distributed in a particle diameter range of 1 nm to 1 μm is formed. On the obtained alloy thin film, Ta or By forming a dense layer of Ta alloy and performing heat treatment, after adjusting the grain of Ta or Ta alloy and the heterogeneous component, a current collector layer made of Al or Al alloy is formed on the dense layer. A valve metal composite electrode foil obtained by removing the copper foil and the heterogeneous phase component to obtain an electrode foil comprising the current collector layer, the dense layer, and a porous layer of Ta or Ta alloy Manufacturing method.   On the copper foil, Nb or Nb alloy and a heterogeneous phase component incompatible with Nb are uniformly distributed in a particle size range of 1 nm to 1 μm, and Nb or Nb or Nb or Nb alloy is formed on the obtained alloy thin film. After forming a dense layer of Nb alloy and performing heat treatment, Nb or Nb alloy and the heterogeneous phase component are adjusted to form a current collector layer made of Al or Al alloy on the dense layer. A valve metal composite electrode foil obtained by removing the copper foil and the heterogeneous phase component to obtain an electrode foil comprising the current collector layer, the dense layer, and a porous layer of Ta or Ta alloy Manufacturing method.   The method for producing a valve metal composite electrode foil according to claim 1, wherein the current collector layer is formed by vapor deposition.   3. The current collector layer according to claim 1, wherein the current collector layer is formed by pressure bonding or heat bonding in which the dense layer and an Al foil or Al alloy foil having a thickness of 100 μm or less are pressed against each other. The manufacturing method of the valve metal composite electrode foil of description.   5. The electrode foil comprising a porous layer, a dense layer, a current collector layer, a dense layer, and a porous layer by opposing the dense layer to both sides of the Al foil or Al alloy. The manufacturing method of the valve metal composite electrode foil as described in 2.   The method for producing a valve metal composite electrode foil according to claim 4 or 5, wherein a natural oxide film on the surface of the current collector layer and the surface of the dense layer is removed in advance.   The method for producing a valve metal composite electrode foil according to any one of claims 1 to 6, wherein the heterogeneous component in the alloy thin film is 30 to 70% in terms of volume fraction.   The method for producing a valve metal composite electrode foil according to any one of claims 1 to 7, wherein the dense layer and the alloy thin film are formed by a sputtering method or a vacuum deposition method.   The method for producing a valve metal composite electrode foil according to any one of claims 1 to 8, wherein the heterogeneous component is Cu or Ag.   Further comprising a step of providing a thermodynamically stable barrier layer for any of the Ta, Ta alloy, Nb, Nb alloy, Al, and Al alloy between the dense layer and the current collector layer. Item 10. A method for producing a valve metal composite electrode foil according to any one of Items 1 to 9.   The method for producing a valve metal composite electrode foil according to claim 10, wherein the barrier layer is formed of TiN, ZrN, or HfN.

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