JP5091710B2 - Solid electrolytic capacitor and manufacturing method thereof - Google Patents

Description

  The present invention relates to a solid electrolytic capacitor and a manufacturing method thereof, and more particularly to a solid electrolytic capacitor using niobium or a niobium alloy as an anode material and a manufacturing method thereof.

  In general, in a solid electrolytic capacitor, an anode made of a valve metal such as niobium (Nb) or tantalum (Ta) is anodized to form a dielectric layer mainly made of oxide on the surface thereof. It is configured by forming a cathode thereon. In particular, niobium is attracting attention as a material for next-generation high-capacity solid electrolytic capacitors because its dielectric constant is about 1.8 times as large as that of tantalum, which is a material of conventional solid electrolytic capacitors.

  Usually, when surface mounting a solid electrolytic capacitor on a substrate, it may be exposed to a high temperature in a reflow process. In a solid electrolytic capacitor using niobium or a niobium alloy as an anode material, a phenomenon occurs in which part of amorphous niobium oxide that functions as a dielectric layer is crystallized due to such a thermal load. For this reason, there is a problem that the insulation property of the dielectric layer is lowered with the change of the state of niobium oxide from amorphous to crystalline, and the leakage current of the dielectric layer is increased.

In order to suppress such an increase in leakage current, a method has been proposed in which a dielectric layer is formed by anodizing an anode made of niobium or a niobium alloy in an aqueous solution containing fluorine ions (for example, Patent Documents). 1). By doing so, the dielectric layer made of niobium oxide contains fluorine, and the presence of such fluorine suppresses crystallization of the dielectric layer and suppresses increase in leakage current. become.
JP 2005-252224 A

  However, with the recent improvement in performance of solid electrolytic capacitors, niobium solid electrolytic capacitors are strongly desired not only to suppress an increase in leakage current but also to improve capacitance. As a result of repeated studies on niobium solid electrolytic capacitors in which the dielectric layer contains fluorine, the intermediate layer is formed so as to cover the entire surface of the dielectric layer at the interface between the dielectric layer and the conductive polymer layer. It was found that such an intermediate layer contributes to a decrease in capacitance due to heat load.

  This invention is made | formed in view of such a subject, The objective is to provide the solid electrolytic capacitor which can suppress the fall of the electrostatic capacitance by a heat load, and its manufacturing method.

To achieve the above object, a solid electrolytic capacitor according to the present invention includes an anode made of niobium or a niobium alloy, a dielectric layer containing niobium oxide formed on the surface of the anode, and the dielectric layer exposed. And a cathode formed on the intermediate layer and the exposed dielectric layer , the intermediate layer being a layer containing niobium and oxygen .
To achieve the above object, a solid electrolytic capacitor according to the present invention includes an anode made of niobium or a niobium alloy, a dielectric layer containing niobium oxide formed on the surface of the anode, and the dielectric layer exposed. It comprises a formed intermediate layer and a cathode formed on the intermediate layer and the exposed dielectric layer, and the region containing niobium oxide contains fluorine.

In order to achieve the above object, a method of manufacturing a solid electrolytic capacitor according to the present invention includes forming a dielectric layer containing niobium oxide doped with fluorine on the surface of an anode made of niobium or a niobium alloy, and Forming an intermediate layer thereon, then removing a portion of the intermediate layer to partially expose the dielectric layer from the intermediate layer, and forming a cathode on the intermediate layer and on the exposed dielectric layer; And a second step of forming.
In order to achieve the above object, a method of manufacturing a solid electrolytic capacitor according to the present invention includes forming a dielectric layer containing niobium oxide doped with fluorine on the surface of an anode made of niobium or a niobium alloy, and And a first step of forming an intermediate layer so that the dielectric layer is exposed, and a second step of forming a cathode on the intermediate layer and the exposed dielectric layer. Has a first step of anodizing the anode in an electrolytic solution containing fluorine ions, and a second step of washing the anode in an aqueous solution containing an acid after the anodization. .
In order to achieve the above object, a method of manufacturing a solid electrolytic capacitor according to the present invention includes forming a dielectric layer containing niobium oxide doped with fluorine on the surface of an anode made of niobium or a niobium alloy, and And a first step of forming an intermediate layer so that the dielectric layer is exposed, and a second step of forming a cathode on the intermediate layer and the exposed dielectric layer. Comprises anodizing the anode in an electrolyte containing fluorine ions,
And the step is repeated a plurality of times.

  ADVANTAGE OF THE INVENTION According to this invention, the solid electrolytic capacitor which can suppress the fall of the electrostatic capacitance by heat load, and its manufacturing method are provided.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, embodiments of the invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(First embodiment)
FIG. 1 is a schematic cross-sectional view showing the configuration of the solid electrolytic capacitor according to the first embodiment. 2 is a partially enlarged view of the solid electrolytic capacitor, FIG. 2 (A) is an enlarged sectional view of the vicinity of the anode body in the solid electrolytic capacitor of FIG. 1, and FIG. 2 (B) is one metal constituting the anode body. It is the schematic diagram which expanded the particle | grain vicinity.

  As shown in FIGS. 1 and 2A, the solid electrolytic capacitor of the first embodiment includes an anode body 1 made of a niobium porous sintered body from which an anode lead wire 1a is derived, and the surface of the anode body 1. A dielectric layer 2 containing niobium oxide formed on the conductive layer; a conductive polymer layer 4 formed on the dielectric layer 2; a cathode layer 5 formed on the conductive polymer layer 4; The capacitor element 10 is provided. As shown in FIG. 2B, an intermediate layer 3 is formed between the dielectric layer 2 and the conductive polymer layer 4 so that the dielectric layer 2 is exposed. The polymer layer 4 is formed on the intermediate layer 3 and the exposed dielectric layer 2. Then, as shown in FIG. 1, a flat cathode terminal 8 is joined to the cathode layer 5 of the capacitor element 10 via a conductive adhesive 6, and a flat anode terminal 7 is joined to the anode lead wire 1a. Has been. And the mold exterior body 9 is shape | molded in the form from which the anode terminal 7 and a part of cathode terminal 8 are pulled out outside.

  The specific configuration of the solid electrolytic capacitor is as follows.

  As shown in FIG. 2A, the anode body 1 is mainly composed of a porous sintered body of niobium metal particles, and a part of the anode lead wire 1a made of niobium metal is embedded therein. A niobium alloy may be adopted as the niobium metal constituting the anode body 1 and the anode lead wire 1a.

  The dielectric layer 2 is mainly composed of a dielectric made of niobium oxide, which is an oxide of niobium metal, and is provided on the surfaces of the anode body 1 and the anode lead wire 1a. In the present embodiment, the dielectric layer 2 is doped with fluorine (F), and the fluorine is unevenly distributed on the anode side of the dielectric layer 2. Specifically, the fluorine has a concentration distribution in the thickness direction of the dielectric layer 2 (the direction from the cathode side to the anode side of the dielectric layer 2), and the fluorine concentration varies between the dielectric layer 2 and the anode body 1 and It is the largest at the interface.

  The intermediate layer 3 is composed of a layer containing niobium oxide oxidized by reattaching the niobium metal eluted from the anode body 1 during the anodic oxidation. As shown in FIG. It is formed in an island-like state that partially covers (or a state in which the dielectric layer 2 is partially exposed). Such island-shaped portions (or exposed portions) are formed distributed over the entire surface of the dielectric layer 2.

  The conductive polymer layer 4 functions as an electrolyte layer, and is formed on the intermediate layer 3 and the dielectric layer 2 exposed from the intermediate layer 3 as shown in FIG. . The material of the conductive polymer layer 4 is not particularly limited as long as it is a polymer material having conductivity, but materials such as polypyrrole, polythiophene, polyaniline, and derivatives thereof having excellent conductivity are employed.

  The cathode layer 5 is composed of a laminated film of a conductive carbon layer 5 a made of a layer containing carbon particles and a silver paste layer 5 b made of a layer containing silver particles, and is provided on the conductive polymer layer 4. Yes. The cathode layer 5 and the conductive polymer layer 4 constitute a cathode.

  The capacitor element 10 includes an anode body 1 from which the above-described anode lead wire 1a is derived, a dielectric layer 2, an intermediate layer 3, a conductive polymer layer 4, and a cathode layer 5.

  The anode terminal 7 and the cathode terminal 8 are made of flat terminals made of a conductive material such as copper (Cu) and nickel (Ni), and function as external lead terminals of the solid electrolytic capacitor. The anode terminal 7 is joined to the anode lead wire 1 a by spot welding, and the cathode terminal 8 is joined to the cathode layer 5 via the conductive adhesive 6.

  And the mold exterior body 9 which consists of an epoxy resin etc. is shape | molded in the form where a part of anode terminal 7 and the cathode terminal 8 is pulled out to the exterior of the opposite direction. Further, the ends of the anode terminal 7 and the cathode terminal 8 exposed from the mold exterior body 9 are bent along the side surface and the lower surface of the mold exterior body 9, and the solid electrolytic capacitor is mounted (soldered) on the mounting substrate. Function as a terminal.

  The anode body 1 is the “anode” of the present invention, the dielectric layer 2 is the “dielectric layer” of the present invention, the intermediate layer 3 is the “intermediate layer” of the present invention, and the conductive polymer layer 4 and the cathode layer 5. The cathode made of is an example of the “cathode” of the present invention.

(Production method)
Next, a method for manufacturing the solid electrolytic capacitor according to the first embodiment shown in FIGS. 1 and 2 will be described.

  Process 1: A niobium porous sintered body is formed by sintering a molded body made of niobium metal particles formed so as to embed a part of the anode lead wire 1a around the anode lead wire 1a in a vacuum. An anode body 1 is formed. At this time, the niobium metal particles are fused.

  Step 2: The anode body 1 is anodized in an electrolytic solution containing fluorine ions to form a dielectric layer 2 mainly made of niobium oxide so as to cover the periphery of the anode body 1 and the dielectric layer 2 An intermediate layer (an intermediate layer containing niobium oxide oxidized by reattaching niobium metal eluted from anode body 1 during anodic oxidation) is uniformly formed so as to cover the entire surface. At this time, fluorine is taken into the dielectric layer 2, and the fluorine is unevenly distributed on the anode side of the dielectric layer 2 (interface between the dielectric layer 2 and the anode body 1).

  Step 3: The anode body 1 on which the intermediate layer 3 is formed is washed in an aqueous solution containing an acid, thereby removing a part of the intermediate layer 3 and exposing the dielectric layer 2 partially. Thereby, the intermediate layer 3 is processed into a plurality of island shapes that partially cover the dielectric layer 2. The intermediate layer 3 is oxidized with the niobium metal eluted from the anode body 1 reattached during anodic oxidation as a nucleus and grows to form a uniform layer by connecting a plurality of islands together. Therefore, the intermediate layer 3 is separated into a plurality of islands so as to partially cover the dielectric layer 2 by such acid cleaning.

Step 4: A conductive polymer layer 4 made of a conductive polymer is formed on the intermediate layer 3 and on the surface of the dielectric layer 2 exposed from the intermediate layer 3 by using a chemical polymerization method, an electrolytic polymerization method, or the like. Specifically, as a first step, a first conductive polymer layer is formed by oxidative polymerization of a monomer with an oxidizing agent using a chemical polymerization method. Subsequently, as the second step, by using the electropolymerization method, the first electroconductive polymer layer is used as the anode, and the second electroconductive polymer layer is electropolymerized with the external cathode in the electrolytic solution containing the monomer and the electrolyte. A molecular layer is formed. Thus, the conductive polymer layer comprising the laminated film of the first conductive polymer layer and the second conductive polymer layer on the intermediate layer 3 and on the dielectric layer 2 exposed from the intermediate layer 3 4 is formed.

  Step 5: A conductive carbon layer 5a is formed by applying a carbon paste on the conductive polymer layer 4 and drying. Furthermore, a silver paste layer 5b is formed by applying and drying a silver paste on the conductive carbon layer 5a. In this way, the cathode layer 5 made of a laminated film of the conductive carbon layer 5a and the silver paste layer 5b is formed on the conductive polymer layer 4.

  Step 6: After applying the conductive adhesive 6 on the flat cathode terminal 8, the cathode layer 5 and the cathode terminal 8 are dried through contact with the conductive adhesive 6, whereby the cathode The layer 5 and the cathode terminal 8 are connected. A flat anode terminal 7 is connected to the anode lead wire 1a by spot welding.

  Step 7: Molding is performed by a transfer method, and a mold exterior body 9 made of an epoxy resin is formed around the periphery. At this time, the capacitor element 10 (the anode lead wire 1a, the anode body 1, the dielectric layer 2, the intermediate layer 3, the conductive polymer layer 4, and the cathode layer 5) is accommodated therein, and the anode terminal 7 and the cathode terminal. It forms so that the edge part of 8 may be pulled out outside (reciprocal direction).

  Step 8: The anode terminal 7 and the cathode terminal 8 exposed from the mold exterior body 9 are cut to a predetermined length. And the front-end | tip part of the anode terminal 7 and the cathode terminal 8 is bend | folded below, and it arrange | positions along the lower surface of the mold exterior body 9. FIG. The tips of both terminals function as terminals of the solid electrolytic capacitor, and are used to electrically connect the solid electrolytic capacitor to the mounting substrate.

  Step 9: Finally, an aging process is performed in which a predetermined voltage is applied via both terminals of the solid electrolytic capacitor. This stabilizes the characteristics of the solid electrolytic capacitor.

  Through the above steps, the solid electrolytic capacitor according to the first embodiment of the present invention is manufactured.

(Second Embodiment)
The solid electrolytic capacitor according to the second embodiment of the present invention has the same configuration as that of the first embodiment. The difference from the first embodiment is the manufacturing method, and the specific difference is that in step 2 of the first embodiment, the electrolyte containing fluorine ions is replaced with a new electrolyte every predetermined time. It is to perform oxidation and to perform step 4 (formation of a conductive polymer layer) without performing step 3 (acid cleaning after anodization) after such step 2. The rest is the same as each step of the first embodiment.

  Next, Examples 1 to 9 (solid electrolytic capacitors A1 to A9) produced for evaluating the characteristics of the solid electrolytic capacitor according to the first embodiment will be described.

Example 1
In Example 1, the solid electrolytic capacitor A1 was manufactured through the following steps.

  Step 1A: Using niobium metal powder having an average particle diameter of about 2 μm, a portion of the anode lead wire 1a is embedded and molded into a substantially plate shape (size: length 4 mm × width 3 mm × thickness 1 mm), and vacuum Sinter in. Thereby, the anode body 1 made of a niobium porous sintered body is formed. At this time, the niobium metal particles are fused.

Step 2A: The anode body 1 is anodized for 1 hour at a constant voltage of 50 V in a 0.05 wt% aqueous ammonium fluoride solution maintained at about 45 ° C. Thereby, the dielectric layer 2 (thickness: about 125 nm) made of niobium oxide containing fluorine is formed so as to cover the periphery of the anode body 1, and the intermediate layer 3 ( Thickness: about 10 nm). At this time, fluorine has a concentration distribution in the thickness direction of the dielectric layer 2, and the concentration of fluorine becomes maximum at the interface between the dielectric layer 2 and the anode body 1.

  Step 3A: The anode body 1 on which the intermediate layer 3 is formed is immersed in a 1.0 wt% hydrofluoric acid aqueous solution for 20 minutes and then washed with water. Thereby, the intermediate layer 3 is separated and processed into a plurality of island shapes (a state where the dielectric layer 2 is partially exposed) so as to partially cover the dielectric layer 2.

  Step 4A: The anode body 1 having the intermediate layer 3 and the dielectric layer 2 formed on the surface thereof is immersed in an oxidant solution and then reacted with pyrrole monomer vapor, so that the pyrrole monomer is formed on the intermediate layer 3 and the dielectric layer 2. Is polymerized. As a result, a first conductive polymer layer made of polypyrrole is formed on the intermediate layer 3 and the dielectric layer 2 as a precoat layer. Subsequently, by using the first conductive polymer layer as an anode and electrolytic polymerization in an electrolytic solution containing a pyrrole monomer and an electrolyte, a second conductive polymer layer is further formed on the first conductive polymer layer to a predetermined thickness. It will be formed. As a result, a second conductive polymer layer made of polypyrrole is formed on the first conductive polymer layer. In this manner, the first conductive polymer layer and the second conductive polymer layer are laminated on the intermediate layer 3 and the dielectric layer 2 (on the surface of the dielectric layer 2 exposed from the intermediate layer 3). A conductive polymer layer 4 made of a film is formed.

  Step 5A: A carbon paste is applied on the conductive polymer layer 4 and dried to form a conductive carbon layer 5a composed of a layer containing carbon particles, and a silver paste is applied onto the conductive carbon layer 5a and dried. By doing so, the silver paste layer 5b which consists of a layer containing a silver particle is formed. Thus, the cathode layer 5 made of a laminated film of the conductive carbon layer 5a and the silver paste layer 5b is formed on the conductive polymer layer 4.

  The capacitor element 10 is formed through the above steps, and the solid electrolytic capacitor A1 according to the first embodiment is manufactured through the steps 6 to 9 described above.

(Comparative Example 1)
FIG. 3 is an enlarged schematic view of the vicinity of one metal particle constituting the anode body of the solid electrolytic capacitor according to Comparative Example 1. The difference from the first embodiment is that the intermediate layer 3a is uniformly formed over the entire surface of the dielectric layer 2, and the dielectric layer 2 is not exposed from the intermediate layer 3a. The rest is the same as the configuration of the first embodiment.

  The solid electrolytic capacitor of Comparative Example 1 is the same as the first embodiment (see FIG. 1), and a dielectric containing niobium oxide on the surface of the anode body 1 made of a niobium porous sintered body from which the anode lead wire 1a is derived. A capacitor element 10 in which a layer 2, a conductive polymer layer 4, and a cathode layer 5 are sequentially formed is provided. As shown in FIG. 3, an intermediate layer 3 a is uniformly formed between the dielectric layer 2 and the conductive polymer layer 4 so as to cover the entire surface of the dielectric layer 2. The molecular layer 4 is formed on the intermediate layer 3 a without contacting the dielectric layer 2. Then, a flat cathode terminal 8 is joined to the cathode layer 5 of the capacitor element 10 via a conductive adhesive 6, and a flat anode terminal 7 is joined to the anode lead wire 1 a. The mold exterior body 9 is formed such that a part of the anode terminal 7 and the cathode terminal 8 is drawn out to the outside. Such a solid electrolytic capacitor can be easily manufactured by not performing step 3 (acid cleaning after anodization) in the first embodiment.

  Specifically, in order to perform a comparative evaluation with the characteristics of the example, in Comparative Example 1, the solid electrolytic capacitor X was subjected to the same steps as in Example 1 except that Step 3A of Example 1 was not performed. Produced.

(Examples 2 and 3)
Examples 2 and 3 are the same as Example 1 except that in Step 3A of Example 1, acid cleaning is performed with the immersion time in a 1.0 wt% hydrofluoric acid aqueous solution being 10 minutes and 30 minutes. Thus, solid electrolytic capacitors A2 and A3 were produced.

(Examples 4 to 6)
In Examples 4 to 6, in Step 3A of Example 1, the concentration of the hydrofluoric acid aqueous solution was 0.5% by weight, and the immersion time in the aqueous hydrofluoric acid solution was 10 minutes, 20 minutes, and 30 minutes. Solid electrolytic capacitors A4 to A6 were produced in the same manner as in Example 1 except that acid cleaning was performed.

(Examples 7 to 9)
In Examples 7 to 9, in Step 3A of Example 1, the concentration of the hydrofluoric acid aqueous solution was set to 2.0 wt%, and the immersion time in the hydrofluoric acid aqueous solution was set to 10 minutes, 20 minutes, and 30 minutes. Solid electrolytic capacitors A7 to A9 were produced in the same manner as in Example 1 except that acid cleaning was performed.

(Comparative Example 2)
In Comparative Example 2, Step 2A of Example 1 is changed to the following Step 2B to form a dielectric layer 2 that is not doped with fluorine, and Step 3A (acid cleaning after anodization) is performed. A solid electrolytic capacitor Y was produced in the same manner as in Example 1 except that it was not.

  Step 2B: Anodization is performed on the anode body 1 at a constant voltage of 50 V in a 0.5 wt% aqueous phosphoric acid solution maintained at about 60 ° C. for 1 hour. Thereby, the dielectric layer 2 (thickness: about 125 nm) made of niobium oxide is formed so as to cover the periphery of the anode body 1. At this time, the dielectric layer 2 is formed without introducing fluorine.

  Next, Example 10 (solid electrolytic capacitor B1) produced in order to evaluate the characteristics of the solid electrolytic capacitor according to the second embodiment will be described.

(Example 10)
In Example 10, in Step 2 of Example 1, the ammonium fluoride aqueous solution as the electrolytic solution was replaced with a new solution a total of three times every 20 minutes to perform anodization, and Step 3A (acid after anodization) A solid electrolytic capacitor B1 was produced in the same manner as in Example 1 except that the cleaning was not performed.

(Evaluation)
First, a cross-sectional observation in the vicinity of the anode body in each solid electrolytic capacitor was performed.

  In cross-sectional observation, one metal particle (particularly metal particle) constituting a niobium porous sintered body of an anode body using a transmission electron microscope (TEM) or a scanning electron microscope (SEM). The portion where the entire circumference of the can be observed was evaluated. As a result, in Examples 1 to 10 (solid electrolytic capacitors A1 to A9, B1) and conventional Comparative Example 1 (solid electrolytic capacitor X) that were anodized in an electrolytic solution containing fluorine ions, the dielectric layer and the high conductivity were obtained. It was confirmed that an intermediate layer was formed between the molecular layer. Further, in the conventional comparative example 1 (solid electrolytic capacitor X), as shown in FIG. 3, the intermediate layer is uniformly coated with the dielectric layer, and Examples 1 to 10 (solid electrolytic capacitors A1 to A1). In A9, B1), as shown in FIG. 2B, a plurality of intermediate layers are distributed in an island shape on the surface of the dielectric layer, and the intermediate layer partially covers the dielectric layer (dielectric material). It was found to be present (with the layer exposed). On the other hand, in Comparative Example 2 (solid electrolytic capacitor Y) that employs an aqueous phosphoric acid solution as an electrolytic solution, an intermediate layer is not formed between the dielectric layer and the conductive polymer layer. It was confirmed. From this, it is surmised that the intermediate layer is formed during the anodic oxidation in the electrolytic solution containing fluorine ions.

  Next, composition analysis of the intermediate layer in each solid electrolytic capacitor was performed.

  In the composition analysis, the intermediate layer was evaluated using an energy dispersive X-ray analysis method. As a result, it was found that the intermediate layer mainly contains niobium (Nb) and oxygen (O). This suggests that the intermediate layer is mainly composed of niobium oxide. On the other hand, since a boundary portion (interface) is observed between the dielectric layer and the intermediate layer in cross-sectional observation, it is presumed that the intermediate layer is a layer different from the dielectric layer. From these facts, it is presumed that the intermediate layer was formed by re-attaching niobium metal eluted from the anode body during anodic oxidation in an electrolytic solution containing fluorine ions, and oxidizing it with this as a nucleus.

  Next, the coverage of the intermediate layer, the leakage current, and the capacitance maintenance ratio in each solid electrolytic capacitor were evaluated.

  In the evaluation of the coverage of the intermediate layer, the portion where the entire circumference of the metal particles can be observed is expanded from the cross-sectional TEM image (or cross-sectional SEM image), and the existence ratio of the intermediate layer on the dielectric layer formed on the metal particles is measured And the average of these 10 metal particles was made into the coverage of an intermediate | middle layer. Specifically, the coverage of the intermediate layer is determined by using the peripheral length L1 of the dielectric layer formed on the surface of the metal particle and the integrated length L2 of the length of the intermediate layer in contact with the dielectric layer, as follows: It was calculated by the formula (1).

Coverage (%) = (L2 / L1) × 100 (1)
The leakage current is 5 V (to the rated voltage) for each solid electrolytic capacitor using a DC current source and a current monitor after heat treatment at 250 ° C. for 10 minutes (before the high temperature standing test). The current was measured 20 seconds after application of the corresponding voltage.

  The capacitance retention rate was calculated by the following equation (2) using the capacitance C1 before the high temperature storage test and the capacitance C2 after the high temperature storage test. Note that the closer this value is to 100, the smaller the decrease (degradation) in capacitance due to the thermal load.

Capacitance maintenance ratio (%) = (C2 / C1) × 100 (2)
The measurement conditions for the capacitance are as follows.

  The capacitance (capacitance of the solid electrolytic capacitor at a frequency of 120 Hz) is 2000 for each solid electrolytic capacitor before the high-temperature standing test and in a constant temperature bath holding the solid electrolytic capacitor at 105 ° C. as the high-temperature standing test. Measurements were made using an LCR meter after the passage of time.

<Evaluation 1>
First, the influence of the acid cleaning performed after anodization was evaluated. Table 1 shows the evaluation results of the intermediate layer coverage, leakage current, capacitance, and capacitance retention rate in the solid electrolytic capacitors of Example 1 and Comparative Example 1. Each value is an average of 10 samples.

  As shown in Table 1, the intermediate layer coverage in conventional Comparative Example 1 (solid electrolytic capacitor X) is 100%, whereas the intermediate layer coverage in Example 1 (solid electrolytic capacitor A1) is 50%. %Met. This has shown that the coverage of an intermediate | middle layer can be reduced by performing an acid cleaning after anodization.

  In addition, it can be seen that in Example 1 (solid electrolytic capacitor A1), the leakage current is about the same (0.1 mA or less) compared to the conventional comparative example 1 (solid electrolytic capacitor X). From this, it is presumed that almost no damage (etching damage due to acid) is caused to the dielectric layer by the acid cleaning.

  Furthermore, as shown in Table 1, in the conventional comparative example 1 (solid electrolytic capacitor X), the capacitance is reduced by the thermal load (high temperature standing test), and the capacitance maintenance ratio is 36%. I understand. This is presumed to be a layer of niobium oxide formed by reattaching the niobium metal eluted from the anode body during the anodic oxidation of the intermediate layer, and delamination between the dielectric layer and the intermediate layer due to the thermal load. This is likely to occur, and the effective contact area between the conductive polymer layer and the dielectric layer that contributes to the increase and decrease in capacitance is reduced, and it is assumed that the capacitance retention rate (decrease in capacitance) is low. .

  On the other hand, in Example 1 (solid electrolytic capacitor A1), the capacitance retention rate is 80%, and compared to the conventional comparative example 1 (solid electrolytic capacitor X), a decrease in capacitance due to thermal load is suppressed. I understand that This is because the intermediate layer is formed so that the dielectric layer is exposed (the conductive polymer layer is formed on the exposed dielectric layer), and peeling due to the intermediate layer due to thermal load is reduced, This is presumably because the reduction of the effective contact area between the conductive polymer layer and the dielectric layer was suppressed.

  From the above, in order to provide a solid electrolytic capacitor capable of suppressing a decrease in capacitance due to a thermal load, it is formed on a dielectric layer during anodization in an electrolytic solution containing fluorine ions. It is effective that the intermediate layer is in a state in which the dielectric layer is partially exposed, and that the conductive polymer layer is formed on the intermediate layer and on the dielectric layer exposed from the intermediate layer. I understand. And it turns out that such a state can be easily realized by performing acid cleaning after anodic oxidation in an electrolytic solution containing fluorine ions.

<Evaluation 2>
Next, the effects of acid concentration and treatment time were evaluated for acid cleaning performed after anodization. Table 2 shows the evaluation results of the leakage current and the capacitance maintenance ratio in the solid electrolytic capacitors of Examples 1 to 9, Comparative Example 1 and Comparative Example 2. Each value is an average of 10 samples. FIG. 4 shows the evaluation result of the capacitance maintenance ratio in each solid electrolytic capacitor (depending on the coverage of the intermediate layer), and FIG. 5 shows the evaluation result of the leakage current in each solid electrolytic capacitor (depending on the coverage of the intermediate layer). Indicates.

  As shown in Table 2, in Examples 1 to 9 (solid electrolytic capacitors A1 to A9), by adjusting the acid concentration and treatment time in the acid cleaning, the coverage of the intermediate layer is in the range of 80% to 10%. You can see that it is changing. In particular, it can be seen that the higher the acid concentration or the longer the treatment time, the lower the coverage of the intermediate layer. Here, the intermediate layer before the acid cleaning (state of Comparative Example 1) is oxidized and grown by using the portion where the niobium metal eluted from the anode body is reattached at the time of anodic oxidation as a core, and has a plurality of island shapes. Are connected to each other to form a uniform layer, and the intermediate layer after the acid cleaning (states of Examples 1 to 9) partially covers the dielectric layer by the acid cleaning. It is inferred that they were separated into a plurality of islands. Therefore, the reason why the coverage of the intermediate layer varies depending on the acid cleaning conditions is presumed that the size (dimension) of the island-shaped portion increases or decreases depending on the acid cleaning conditions.

  Further, as shown in Table 2 and FIG. 4, in Examples 1 to 9 (solid electrolytic capacitors A1 to A9), the leakage current is about the same (0.1 mA) compared to the conventional comparative example 1 (solid electrolytic capacitor X). It can be seen that From this, it is presumed that almost no damage (etching damage due to acid) is caused to the dielectric layer by the acid cleaning.

  On the other hand, as shown in Table 2, in Examples 1 to 9 (solid electrolytic capacitors A1 to A9) and conventional comparative example 1 (solid electrolytic capacitor X), a comparison in which an aqueous phosphoric acid solution was used as the electrolytic solution was anodized. It can be seen that the leakage current is reduced to less than half compared with Example 2 (solid electrolytic capacitor Y). This is presumably because the presence of fluorine in the dielectric layer made of niobium oxide suppressed the crystallization of the dielectric layer and the increase in leakage current.

  Moreover, as shown in FIG. 5, it turns out that the electrostatic capacitance maintenance factor is increasing by the reduction | decrease of the coverage of an intermediate | middle layer. This is because the rate of contact of the intermediate layer with the dielectric layer decreases (the rate of contact of the conductive polymer layer with the dielectric layer increases) as the coverage of the intermediate layer decreases. This is presumed to be due to a reduction in the resulting peeling.

  On the other hand, in Comparative Example 2 (solid electrolytic capacitor Y), although the intermediate layer is not formed (coverage 0%), it can be seen that the capacitance maintenance ratio is 65%. This is because in anodization in an electrolytic solution containing fluorine ions, fluorine elutes from the anode body during anodization, and minute irregularities are formed on the surface of the dielectric layer. In contrast, the anodization in an aqueous phosphoric acid solution does not elute niobium metal from the anode body, and such irregularities are not formed on the surface of the dielectric layer. Therefore, it is guessed that the effect of improving adhesion cannot be obtained.

  From the above, in order to provide a solid electrolytic capacitor capable of suppressing a decrease in capacitance due to heat load, it is effective to perform acid cleaning after anodization in an electrolytic solution containing fluorine ions. Further, it can be seen that the coverage of the intermediate layer can be easily controlled by further adjusting the acid cleaning conditions.

<Evaluation 3>
Next, the influence of liquid exchange during anodic oxidation was evaluated on the electrolytic solution during anodic oxidation. Table 3 shows the evaluation results of the leakage current and the capacitance retention rate in the solid electrolytic capacitors of Example 10 and Comparative Example 1. Each value is an average of 10 samples.

  As shown in Table 3, the coverage of the intermediate layer in the conventional Comparative Example 1 (solid electrolytic capacitor X) is 100%, whereas the coverage of the intermediate layer in Example 10 (solid electrolytic capacitor B1) is 75. It can be seen that the coverage of the intermediate layer is reduced without acid cleaning. Thereby, the fall of the electrostatic capacitance by a heat load (high temperature leaving test) is suppressed, and the electrostatic capacitance maintenance factor is improving. This is because the concentration of niobium metal eluted from the anode body in the electrolyte is reduced by replacing the electrolyte during anodization, and the dissolved niobium metal is prevented from reattaching to the surface of the dielectric layer. It is inferred that

  Moreover, Example 10 (solid electrolytic capacitor B1) and conventional comparative example 1 (solid electrolytic capacitor X) had leakage currents of the same level (0.1 mA or less), and the electrolyte was replaced during anodization. The effect of is not seen.

  From the above, in order to provide a solid electrolytic capacitor capable of suppressing a decrease in capacitance due to a thermal load, an electrolytic solution is obtained in a predetermined time during anodization in an electrolytic solution containing fluorine ions. It can be seen that it is effective to perform anodic oxidation by exchanging.

From the above results, according to the solid electrolytic capacitor and the manufacturing method thereof according to the present embodiment (the first embodiment and the second embodiment), the following effects can be obtained.

  (1) By providing the intermediate layer 3 so that the dielectric layer 2 is exposed, and further providing the conductive polymer layer 4 on the intermediate layer 3 and on the exposed surface of the dielectric layer 2, conventional solid electrolysis is provided. Compared with a capacitor (a solid electrolytic capacitor in which the intermediate layer 3 is uniformly formed so as to cover the entire surface of the dielectric layer 2), a decrease in capacitance due to a thermal load can be suppressed.

  (2) The intermediate layer 3 is composed of a plurality of island-shaped portions (a state where the dielectric layer 2 is exposed) that partially covers the dielectric layer 2, and these island-shaped portions are formed on the dielectric layer 2. By providing it so as to be distributed over the entire surface, the conductive polymer layer 4 comes into contact with the dielectric layer 2 around the island-shaped portion, and the intermediate layer 3 is peeled over the entire surface of the dielectric layer 2. Since it is suppressed, the fall of an electrostatic capacitance can be suppressed more reliably.

  (3) Since the intermediate layer 3 is composed of a layer containing niobium (Nb) and oxygen (O), the intermediate layer 3 can function as a dielectric, so that the capacity performance of the solid electrolytic capacitor itself (initial static capacity) The coverage of the intermediate layer can be changed without reducing the electric capacity.

  (4) The inclusion of fluorine in the dielectric layer 2 mainly containing niobium oxide suppresses crystallization of amorphous niobium oxide when a thermal load is applied. Compared with a solid electrolytic capacitor that employs a dielectric layer that does not contain, an increase in leakage current can be suppressed.

  (5) In the method of manufacturing a solid electrolytic capacitor, the dielectric layer 2 containing niobium oxide doped with fluorine is formed on the surface of the anode body 1 made of niobium metal, and the dielectric layer 2 is formed on the dielectric layer 2. (1) to (4) including the step of forming the intermediate layer 3 exposing the conductive layer and the step of forming the conductive polymer layer 4 on the intermediate layer 3 and the exposed dielectric layer 2. A suitable solid electrolytic capacitor as described in 1) can be produced.

  (6) A suitable solid electrolytic capacitor as described in the above (1) to (4) can be easily manufactured by performing acid cleaning after anodization in an electrolytic solution containing fluorine ions. it can.

  (7) A suitable solid as described in the above (1) to (4) by performing the anodic oxidation by exchanging the electrolytic solution during the anodic oxidation in the electrolytic solution containing fluorine ions. An electrolytic capacitor can be easily manufactured.

  (8) According to the manufacturing method of the present embodiment, the above-described change can be made by simply adding an acid cleaning after anodizing in an electrolytic solution containing fluorine ions, or by simply replacing the electrolytic solution during anodizing. Since a suitable solid electrolytic capacitor as described in 1) to (4) can be produced, a solid electrolytic capacitor in which a decrease in capacitance due to a thermal load is suppressed can be produced at low cost.

  The present invention is not limited to the above-described embodiment, and various modifications such as design changes can be added based on the knowledge of those skilled in the art, and the embodiment to which such a modification is added. Can also be included in the scope of the present invention.

In the said embodiment, although the example which employ | adopted ammonium fluoride aqueous solution as an electrolyte solution containing a fluorine was shown, this invention is not limited to this. For example, an aqueous potassium fluoride solution, an aqueous sodium fluoride solution, an aqueous hydrofluoric acid solution, ammonium hexafluoride, ammonium hexafluorozirconate, or ammonium hexafluorogermanate may be employed as the electrolytic solution. Moreover, you may combine these electrolyte solutions. In such a case, the same effect can be enjoyed.

  In the above-described embodiment, an example in which hydrofluoric acid is employed as the acid in the acid cleaning is shown, but the present invention is not limited to this. For example, hydrochloric acid, sulfuric acid, or nitric acid may be employed as the acid. In such a case, the same effect can be enjoyed.

  In the embodiment described above, an example in which the electrolyte solution is replaced three times within a predetermined anodic oxidation time range is shown, but the present invention is not limited to this. For example, the exchange of the electrolytic solution may be performed twice or four times or more. In such a case, the above effects can be enjoyed more significantly as the number of times of replacement of the electrolytic solution increases.

  In the said embodiment, although the example of the solid electrolytic capacitor which employ | adopted the anode body which consists of a porous sintered compact of a niobium metal particle was shown, this invention is not limited to this. For example, a solid electrolytic capacitor employing an anode body made of a niobium metal plate (or niobium metal foil) may be used. In this case, the same effect can be enjoyed.

1 is a schematic cross-sectional view showing a configuration of a solid electrolytic capacitor according to an embodiment. (A) The cross-sectional view which expanded the anode body vicinity in the solid electrolytic capacitor of FIG. 1, (B) The schematic diagram which expanded the one metal particle vicinity which comprises an anode body. The schematic diagram which expanded the one metal particle vicinity which comprises the anode body of the conventional solid electrolytic capacitor. The figure which shows the evaluation result (coverage rate dependence) of the electrostatic capacitance maintenance factor of each solid electrolytic capacitor. The figure which shows the evaluation result (coverage ratio dependence) of the leakage current of each solid electrolytic capacitor.

Explanation of symbols

  1a anode lead wire, 1 anode body, 2 dielectric layer, 3 intermediate layer, 4 conductive polymer layer, 5 cathode layer, 5a carbon layer, 5b silver paste layer, 6 conductive adhesive, 7 anode terminal, 8 cathode Terminal, 9 Mold exterior, 10 Capacitor element.

Claims (6)

An anode made of niobium or a niobium alloy;
A dielectric layer comprising niobium oxide formed on the surface of the anode;
An intermediate layer formed to expose the dielectric layer;
A cathode formed on the intermediate layer and on the exposed dielectric layer;
With
The said intermediate | middle layer is a solid electrolytic capacitor which is a layer containing niobium and oxygen. An anode made of niobium or a niobium alloy;
A dielectric layer comprising niobium oxide formed on the surface of the anode;
An intermediate layer formed to expose the dielectric layer;
A cathode formed on the intermediate layer and on the exposed dielectric layer;
With
A solid electrolytic capacitor , wherein the region containing niobium oxide contains fluorine. The intermediate layer is composed of a plurality of island-shaped portions, said island portion solid electrolytic capacitor according to claim 1 or 2, characterized in that distributed over the entire surface of the dielectric layer. A dielectric layer containing niobium oxide doped with fluorine is formed on the surface of the anode made of niobium or a niobium alloy, an intermediate layer is formed on the dielectric layer , and then a part of the intermediate layer is removed. A first step of partially exposing the dielectric layer from the intermediate layer ;
A second step of forming a cathode on the intermediate layer and the exposed dielectric layer;
A method for manufacturing a solid electrolytic capacitor. Forming a dielectric layer containing niobium oxide doped with fluorine on the surface of an anode made of niobium or a niobium alloy, and forming an intermediate layer on the dielectric layer so as to expose the dielectric layer; And the process of
A second step of forming a cathode on the intermediate layer and the exposed dielectric layer;
With
The first step includes a first step of anodizing the anode in an electrolyte containing fluorine ions, and a second step of washing in an aqueous solution containing an acid after the anodization. A method for producing a solid electrolytic capacitor. Forming a dielectric layer containing niobium oxide doped with fluorine on the surface of an anode made of niobium or a niobium alloy, and forming an intermediate layer on the dielectric layer so as to expose the dielectric layer; And the process of
A second step of forming a cathode on the intermediate layer and the exposed dielectric layer;
With
The first step includes a step of anodizing the anode in an electrolytic solution containing fluorine ions, replacing the electrolytic solution, and repeating the step a plurality of times.

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