JP4947888B2 - Manufacturing method of solid electrolytic capacitor - Google Patents

Description

This invention relates to a method for producing a solid electrolytic capacitor.

  Niobium oxide has high insulation properties, and its dielectric constant is about 1.8 times that of tantalum oxide, which is the material of conventional solid electrolytic capacitors. Therefore, niobium oxide is a dielectric material for next-generation high-capacity solid electrolytic capacitors. Attention has been paid. Here, niobium oxide having a high insulating property can be easily formed on the anode by anodizing with a niobium substrate as the anode. Note that the niobium oxide formed at this time is amorphous.

In conventional solid electrolytic capacitors using niobium oxide, the niobium oxide formed by anodic oxidation is used as a dielectric layer. The dielectric layer made of niobium oxide is not affected by heat treatment such as a reflow process. It was easy to receive, and the stability of the capacitance was inferior to that of solid electrolytic capacitors using other dielectric materials such as tantalum oxide. Therefore, a solid electrolytic capacitor in which a niobium nitride region is formed in niobium oxide constituting the dielectric layer has been proposed in order to suppress a decrease in capacitance (see, for example, Patent Document 1).
JP 11-329902 A

  However, even in a solid electrolytic capacitor using niobium oxide having a niobium nitride region formed as described above, there is a problem that leakage current between the anode and the cathode increases after heat treatment such as a reflow process.

The present invention has been made to solve the above problems,
One object of the present invention is to provide a solid electrolytic capacitor with low leakage current.

  Another object of the present invention is to provide a method of manufacturing a solid electrolytic capacitor with a small leakage current.

In order to achieve the above object, a solid electrolytic capacitor formed by the method of manufacturing a solid electrolytic capacitor of the present invention includes an anode made of niobium, a dielectric layer made of niobium oxide containing magnesium formed on the anode, And a cathode formed on the dielectric layer.

In the solid electrolytic capacitor formed by this solid electrolytic capacitor manufacturing method , as described above, the dielectric layer made of niobium oxide contains magnesium. In the dielectric layer, magnesium can be strongly bonded to oxygen, so that diffusion of oxygen can be suppressed. As a result, even when a heat treatment such as a reflow process is performed, the diffusion of oxygen from the dielectric layer to the anode or the like can be suppressed, so that the thickness of the dielectric layer is difficult to decrease and the insulation of the dielectric layer is also reduced. Hard to do. Therefore, in the invention of the first aspect, a solid electrolytic capacitor with a small leakage current can be obtained.

  Further, by including magnesium in the dielectric layer made of niobium oxide, an increase in equivalent series resistance (ESR) of the solid electrolytic capacitor can be suppressed.

In the solid electrolytic capacitor formed by the method for manufacturing a solid electrolytic capacitor, the magnesium concentration in the dielectric layer is preferably in the range of 0.2 atomic% to 0.6 atomic%. By comprising in this way, the electrostatic capacitance of a solid electrolytic capacitor can be enlarged.

The manufacturing method of solid bodies electrolytic capacitor of the present invention, by anodizing the anode of niobium in an aqueous solution containing magnesium ions, forming a dielectric layer made of niobium oxide containing magnesium in said positive superb And a step of forming a cathode on the dielectric layer.

In the manufacturing method of the solid-body electrolytic capacitor this, as described above, by anodizing in an aqueous solution containing magnesium ions, can be contained magnesium in niobium oxide. This makes it difficult for oxygen in the dielectric layer to diffuse, so that it is difficult to reduce the thickness of the dielectric layer, and it is possible to suppress a decrease in the insulating properties of the dielectric layer. Therefore, in the invention of the second aspect, a solid electrolytic capacitor with a small leakage current can be easily manufactured.

  Furthermore, magnesium is contained substantially uniformly in the dielectric layer made of niobium oxide by the above process. Magnesium oxide is likely to occur in a region where the magnesium concentration is high. In particular, when the magnesium concentration at the interface between the anode and the dielectric layer is large, a layer made of magnesium oxide is likely to be formed at this interface, so that the series resistance component at the interface between the anode and the dielectric layer is likely to increase. . Therefore, increase in ESR of the solid electrolytic capacitor can be suppressed by containing magnesium substantially uniformly in the dielectric layer.

  Hereinafter, the present invention will be described in more detail based on the embodiments. However, the present invention is not limited to the following embodiments, and can be appropriately modified and implemented without departing from the scope of the present invention. It is a thing.

  FIG. 1 is a cross-sectional structure diagram of a rectangular parallelepiped solid electrolytic capacitor according to an embodiment of the present invention.

  As shown in FIG. 1, in the solid electrolytic capacitor 100, the anode 1 has an outer shape of about 3.3 mm × about 2.7 mm × about 1.7 mm made of a porous sintered body of niobium particles having a particle size of about 1 μm. It is composed of a rectangular parallelepiped base 1a and a linear anode lead 1b made of niobium partially embedded in the base 1a.

  A dielectric layer 2 made of niobium oxide containing magnesium is formed on the base 1a so as to cover the periphery of the base 1a. An electrolyte layer 3 made of polypyrrole or the like is formed on the dielectric layer 2 so as to cover the periphery of the dielectric layer 2, and a cathode 4 is formed on the electrolyte layer 3 so as to cover the periphery of the electrolyte layer 3. Is formed. The cathode 4 includes a first conductive layer 4a made of carbon paste formed so as to cover the periphery of the electrolyte layer 3, and a second conductive layer 4b made of silver paste formed so as to cover the periphery of the first conductive layer 4a. It consists of and.

  A conductive adhesive layer 5 is formed on the upper surface of the periphery of the cathode 4, and a cathode made of an iron foil having a thickness of about 0.1 mm whose surface is nickel-plated on the conductive adhesive layer 5. Terminal 6 is formed. On the anode lead 1c exposed from the substrate 1a, an anode terminal 7 made of an iron foil having a thickness of about 0.1 mm whose surface is nickel-plated is connected by welding. In addition, a mold exterior resin 8 is formed around the second conductive layer 4b, the cathode terminal 6, and the anode terminal 7 so that the end portions of the cathode terminal 6 and the anode terminal 7 are drawn to the outside. Thereby, the solid electrolytic capacitor 100 according to the embodiment of the present invention is configured.

  Next, a method for manufacturing a solid electrolytic capacitor according to an embodiment of the present invention shown in FIG. 1 will be described.

  First, a niobium particle powder having a particle size of about 1 μm is sintered to form a base body 1a made of a porous sintered body having an outer shape of about 3.3 mm × about 2.7 mm × about 1.7 mm. At this time, a part of the linear anode lead 1b made of niobium is embedded in the substrate 1a. Thereby, the anode 1 composed of the base body 1a and the anode lead 1b is manufactured.

  Next, the anode 1 is anodized at a constant voltage of about 10 V in an aqueous solution containing magnesium ions, such as an aqueous magnesium chloride solution maintained at about 60 ° C., so that the periphery of the base 1 a is covered. A dielectric layer 2 made of niobium oxide containing boron is formed.

  After the dielectric layer 2 is formed, an electrolyte layer 3 made of polypyrrole or the like is formed on the dielectric layer 2 by polymerization or the like so as to cover the periphery of the dielectric layer 2. Also, a carbon paste is applied on the electrolyte layer 3 so as to cover the periphery of the electrolyte layer 3, and dried at about 80 ° C. for about 30 minutes, thereby forming the first conductive layer 4a made of the carbon paste. Further, a silver paste is applied on the first conductive layer 4a and dried at about 170 ° C. for about 30 minutes to form the second conductive layer 4b made of the silver paste. Thereby, the cathode 4 in which the first conductive layer 4a made of carbon paste and the second conductive layer 4b made of silver paste are laminated is formed.

  Next, about 2 mg of a conductive adhesive is applied on the cathode terminal 6 made of an iron foil having a thickness of about 0.1 mm whose surface is nickel-plated, and then the cathode 4 and the cathode terminal are passed through the conductive adhesive. 6 is brought into contact. Further, the conductive adhesive layer 5 that connects the cathode 4 and the cathode terminal 6 is formed by drying at a temperature of about 60 ° C. for about 30 minutes while pressing the conductive adhesive between the cathode 4 and the cathode terminal 6. Form. Further, an anode terminal 7 made of an iron foil having a thickness of about 0.1 mm whose surface is nickel-plated is welded onto the anode lead 1c. Further, a mold exterior resin 8 is formed around the second conductive layer 4b, the cathode terminal 6 and the anode terminal 7 so that the end portions of the cathode terminal 6 and the anode terminal 7 are drawn to the outside. Thus, the solid electrolytic capacitor 100 according to one embodiment of the present invention is manufactured.

  In the present embodiment, since the dielectric layer 2 made of niobium oxide contains magnesium, oxygen in the dielectric layer 2 is difficult to diffuse when heat treatment such as a reflow process is performed. It can suppress that the thickness of 2 reduces and the insulation of the dielectric material layer 2 falls. As a result, the leakage current between the anode 1 and the cathode 4 of the solid electrolytic capacitor can be reduced.

  In the present embodiment, since magnesium is contained in dielectric layer 2 made of niobium oxide, diffusion of oxygen in dielectric layer 2 can be suppressed. Thereby, even when heat treatment such as a reflow process is performed, oxygen can be prevented from diffusing from the dielectric layer 2 to the anode 1 or the electrolyte layer 3, so that the thickness of the dielectric layer 2 is not easily reduced, and the dielectric The insulation of the body layer 2 is also difficult to deteriorate. Therefore, the leakage current between the anode 1 and the cathode 4 of the solid electrolytic capacitor can be reduced.

  In the present embodiment, since anodization is performed in an aqueous solution containing magnesium ions such as an aqueous magnesium chloride solution, magnesium can be easily contained in the dielectric layer 2 made of niobium oxide. Thereby, even when a heat treatment such as a reflow process is performed, the dielectric layer 2 in which the oxygen in the dielectric layer 2 is difficult to diffuse and the insulating property is not easily lowered can be easily formed. As a result, a solid electrolytic capacitor having a small leakage current between the anode 1 and the cathode 4 can be easily manufactured.

  Furthermore, since the magnesium is contained substantially uniformly in the dielectric layer 2 made of niobium oxide by the above process, in particular, an increase in the magnesium concentration at the interface between the anode 1 and the dielectric layer 2 is suppressed, and the anode The formation of a layer made of magnesium oxide at the interface between 1 and the dielectric layer 2 can be suppressed. Thereby, since the increase in the series resistance component at the interface between the anode 1 and the dielectric layer 2 can be suppressed, the increase in ESR of the solid electrolytic capacitor can be suppressed.

  In this embodiment, a niobium porous sintered body is used as the substrate 1a. However, the present invention is not limited to this, and for example, a metal foil made of niobium may be used. In addition, the anode 1a may be composed of not only niobium alone but also a niobium alloy containing elements such as tungsten, vanadium, zinc, aluminum, molybdenum, hafnium, and zirconium.

  In the present embodiment, other conductive polymer such as polythiophene or other conductive material such as manganese dioxide can be used as the electrolyte layer 3 in addition to polypyrrole.

  In the present embodiment, the electrolyte layer 3 is formed between the dielectric layer 2 and the cathode 4. However, the present invention is not limited to this, and the cathode 4 is formed without forming the electrolyte layer 3. It may be formed directly on the dielectric layer 2.

  In the present embodiment, the stacked structure of the first conductive layer 4a and the second conductive layer 4b is used as the cathode 4, but the present invention is not limited to this, and for example, the first conductive layer 4a. Or the single layer structure which consists only of the 2nd conductive layer 4b may be sufficient.

  Next, in order to evaluate the anode and dielectric layer used in the solid electrolytic capacitor of the above embodiment, the following test electrolytic capacitors were produced.

  FIG. 2 is a cross-sectional structure diagram of a test electrolytic capacitor for evaluating an anode and a dielectric layer used in the solid electrolytic capacitor of the present invention.

  As shown in FIG. 2, in the test electrolytic capacitor 200, a dielectric layer 12 made of niobium oxide is formed on the anode 11 made of niobium foil so as to cover the periphery of the anode 11. Here, the niobium foil is an example of a substrate constituting the anode of the above embodiment. The anode 11 and the dielectric layer 12 are made of a metal such as stainless steel, and are immersed in an electrolyte solution 14 such as an adipic acid aqueous solution in a beaker 13 used as a cathode. At this time, the anode 11 is held so as not to contact the beaker 13 and the electrolytic solution 14. Thus, the test electrolytic capacitor 200 is configured.

  The dielectric layer 12 is formed as follows. First, the anode 11 made of niobium foil is anodized in a magnesium chloride aqueous solution (first step). Thereby, the dielectric layer 12 made of niobium oxide containing magnesium is formed on the anode 11 so as to cover the periphery of the anode 11. Here, the magnesium chloride aqueous solution is an example of the “aqueous solution containing magnesium ions” of the present invention.

  Next, the anode 11 and the dielectric layer 12 formed as described above are anodized in a phosphoric acid aqueous solution (second step). Thereby, phosphorus can be further contained in the surface of the dielectric layer 12 made of niobium oxide. By including phosphorus in the dielectric layer 12 made of niobium oxide, crystallization of niobium oxide can be suppressed, so that crystallization of the surface of the dielectric layer 12 and occurrence of cracks can be suppressed. As a result, when the anode 11 and the dielectric layer 12 are immersed in the electrolyte solution 14, it is possible to suppress a short circuit between the anode 12 and the electrolyte solution 14.

  Further, in order to evaluate the influence of the dielectric layer 12 by the heat treatment, the anode 11 and the dielectric layer 12 produced as described above are subjected to a heat treatment for about 10 minutes in a drying furnace at about 250 ° C.

  Thereafter, the anode 11 is immersed in the electrolytic solution 14 in the beaker 13, and the anode 11 is held so as not to contact the beaker 13 and the electrolytic solution 14, whereby the test electrolytic capacitor 200 used in Experiment 1 is manufactured.

(Experiment 1)
In Experiment 1, for the formation of the dielectric layer 12, as a first step, anodization is performed at a constant voltage of about 10 V in various concentrations of magnesium chloride aqueous solution maintained at about 60 ° C., and then the second step. Then, anodization was performed for about 6 hours at a constant voltage of about 10 V in a phosphoric acid aqueous solution having a concentration of about 0.05 wt% maintained at about 60 ° C. Using the dielectric layer 12 thus formed, test electrolytic capacitors A1 to A5 were produced. Table 1 shows the conditions for forming the dielectric layer 12 in the first step of the test electrolytic capacitors A1 to A5.

(Experiment 2)
In Experiment 2, a test electrolytic capacitor X1 was produced in the same manner as in Experiment 1 except that the dielectric layer was formed only in the second step. That is, in Experiment 2, the anode was anodized only in the second step to form a dielectric layer made of niobium oxide not containing magnesium on the anode so as to cover the periphery of the anode.

(Experiment 3)
In Experiment 3, a dielectric layer was formed on the anode as follows.

First, a thin film made of magnesium having a thickness of about 50 nm was formed on the surface of an anode made of niobium foil by vacuum sputtering. Next, this anode was heat-treated at about 600 ° C. for about 60 minutes in a vacuum of 10 ⁻⁵ Torr or less to diffuse magnesium inside the anode. Thereafter, in the same manner as in Experiment 2, only the second step was performed on the anode.

  Using the anode and the dielectric layer thus formed, a test electrolytic capacitor X2 was produced.

(Experiment 4)
In Experiment 4, a dielectric layer was formed on the anode as follows.

First, an anode made of niobium foil is heat-treated at about 600 ° C. for about 5 minutes in a nitrogen atmosphere of about 300 Torr (about 4 × 10 ⁻⁴ Pa), so that niobium nitriding is performed on the anode so as to cover the periphery of the anode. A physical layer was formed.

  Next, as in Experiment 2, the anode was anodized only in the second step. Thus, a dielectric layer made of niobium oxide having a niobium nitride region was formed on the anode so as to cover the periphery of the anode. The dielectric layer thus formed corresponds to a dielectric layer in which a niobium nitride region is formed in niobium oxide in the solid electrolytic capacitor described in Patent Document 1.

  Then, using the anode and the dielectric layer thus formed, a test electrolytic capacitor X3 was produced.

(Evaluation)
By applying a constant voltage of about 3V to the anode 1 and the beaker 13 to the test capacitors A1 to A5 and X1 to X3, and measuring the leakage current after about 10 seconds, The leakage current between the anode and the cathode (beaker 13) was evaluated. Further, by using an LCR meter to apply an AC voltage of about 120 Hz between the anode and cathode (beaker 13) of each test electrolytic capacitor, the capacitance at a frequency of about 120 Hz is measured, and the anode The equivalent series resistance (ESR) at a frequency of about 100 kHz was measured by applying a high frequency voltage of about 100 kHz between the cathode and the cathode (beaker 13). Further, the magnesium concentration in the dielectric layer of each test electrolytic capacitor was measured by an X-ray photoelectron spectroscopy (XPS) method.

  These results are shown in Table 2. In addition, the measured values of leakage current, ESR, and capacitance were displayed as indices with each measured value in the test electrolytic capacitor X1 being 100, respectively.

  Magnesium was not detected from the dielectric layers of the test electrolytic capacitors X1 and X2.

  From Table 2, the leakage current and ESR of the test electrolytic capacitor X2 are both larger than those of the test electrolytic capacitor X1. The cause of this increase in ESR is thought to be that the series resistance component between the anode and the dielectric layer increased due to oxidation of a part of the magnesium layer formed between the anode and the dielectric layer. It is done. That is, it was found that when the magnesium content at the interface between the anode and the dielectric layer increases, the series resistance component between the anode and the dielectric layer increases and ESR tends to increase.

  Further, in the test electric field capacitor X3, the leakage current is small as compared with the test electrolytic capacitor X1, but the ESR is increased and the capacitance is also decreased. The cause of the increase in ESR of the test electric field capacitor X3 is also considered that the series resistance component between the anode and the dielectric layer is increased due to the formation of the niobium nitride region in the dielectric layer.

  In contrast to these results, it can be seen that the leakage current and ESR are reduced in the test electrolytic capacitors A1 to A5 having the dielectric layer 12 made of niobium oxide containing magnesium, compared to the test electrolytic capacitors X1 to X3. It was. Further, it was found that the leakage current was particularly small when the magnesium concentration in the dielectric layer 12 was in the range of about 0.2 atomic% to about 0.4 atomic%. Thus, it was found that the inclusion of magnesium in the dielectric layer 12 made of niobium oxide can suppress an increase in leakage current and ESR due to heat treatment.

  Further, the test electrolytic capacitors A2 to A4 in which the magnesium concentration in the dielectric layer 12 is in the range of about 0.2 atomic% to about 0.6 atomic% have a capacitance higher than that of the test electrolytic capacitors X1 to X3. It turned out to increase.

1 is a cross-sectional structure diagram of a cuboid solid electrolytic capacitor according to an embodiment of the present invention. It is a cross-section figure of the test electrolytic capacitor for evaluating the anode and dielectric layer which are used for the solid electrolytic capacitor of this invention.

DESCRIPTION OF SYMBOLS 1 Anode 1a Base | substrate 1b Anode lead 2 Dielectric layer 3 Electrolyte layer 4 Cathode 4a 1st conductive layer 4b 2nd conductive layer 5 Conductive adhesive layer 6 Cathode terminal 7 Anode terminal 8 Mold exterior resin 100 Solid electrolytic capacitor

Claims (2)

An anode made of niobium,
A dielectric layer made of niobium oxide containing magnesium formed on the anode;
A method for producing a solid electrolytic capacitor comprising a cathode formed on the dielectric layer,
A first step of forming a dielectric layer made of niobium oxide containing magnesium on the anode by anodizing the anode in an aqueous solution containing magnesium ions;
A solid electrolytic capacitor comprising: a second step of adding phosphorus to the surface of the dielectric layer by anodizing the anode formed in the first step and the dielectric layer in a phosphoric acid aqueous solution. Method. The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein a magnesium concentration in the dielectric layer is in a range of 0.2 atomic% to 0.6 atomic%.

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