阅读说明：本技术 固体电解电容器和制造固体电解电容器的方法 (Solid electrolytic capacitor and method of manufacturing solid electrolytic capacitor ) 是由 高桥雅典 岩井悟志 保科勇辅 于 2019-01-18 设计创作，主要内容包括：根据本公开的固体电解电容器包括由多孔阀金属制成的阳极体、形成在阳极体的表面上的介电层和形成在介电层上的固体电解质层。在固体电解质层内部的空腔的至少一部分中填充羧酸酯。通过根据本公开的固体电解电容器,可以提供能够抑制ESR的增加和漏电流的增加的固体电解电容器。(A solid electrolytic capacitor according to the present disclosure includes an anode body made of a porous valve metal, a dielectric layer formed on a surface of the anode body, and a solid electrolyte layer formed on the dielectric layer. The carboxylate is filled in at least a part of the cavity inside the solid electrolyte layer. By the solid electrolytic capacitor according to the present disclosure, a solid electrolytic capacitor capable of suppressing an increase in ESR and an increase in leakage current can be provided.)

1. A solid electrolytic capacitor comprising:

an anode body made of a porous valve metal;

a dielectric layer formed on a surface of the anode body; and

a solid electrolyte layer formed on the dielectric layer,

wherein a carboxylic acid ester is present in at least a part of the cavity inside the solid electrolyte layer.

2. The solid electrolytic capacitor according to claim 1,

the solid electrolyte layer is formed in contact with the dielectric layer, and

the carboxylic acid ester also fills at least a part of the cavity at the interface between the dielectric layer and the solid electrolyte layer.

3. The solid electrolytic capacitor as claimed in claim 1, wherein the carboxylic acid ester is a compound of polyglycerol and at least one selected from adipic acid and ammonium adipate.

4. The solid electrolytic capacitor as claimed in claim 3, wherein the polyglycerol has a molecular weight of 500 to 600.

5. The solid electrolytic capacitor as claimed in claim 1, wherein the mass of the carboxylic acid ester is equal to or more than 10% of the mass of the solid electrolyte layer.

6. The solid electrolytic capacitor according to claim 1,

the solid electrolyte layer includes:

a first solid electrolyte layer formed on the dielectric layer; and

a second solid electrolyte layer formed on the first solid electrolyte layer, and

the carboxylic acid ester is filled in at least a part of the cavity of the first solid electrolyte layer.

7. A method of manufacturing a solid electrolytic capacitor, comprising:

a step of forming a dielectric layer on a surface of an anode body made of a porous valve metal;

a step of forming a solid electrolyte layer on the dielectric layer; and

a step of forming a carboxylic acid ester in at least a part of the cavity inside the solid electrolyte layer.

8. The method of manufacturing a solid electrolytic capacitor according to claim 7,

the step of forming a solid electrolyte layer includes forming a solid electrolyte layer in contact with the dielectric layer, and

the step of forming a carboxylic acid ester includes further filling a carboxylic acid ester into at least a part of the cavity at the interface between the dielectric layer and the solid electrolyte layer.

9. The method of manufacturing a solid electrolytic capacitor according to claim 7, wherein the step of forming a carboxylic acid ester includes forming a carboxylic acid ester by dipping into a solution containing polyglycerol and at least one selected from adipic acid and ammonium adipate and drying.

10. The method of manufacturing a solid electrolytic capacitor as claimed in claim 7, comprising:

a step of forming a first solid electrolyte layer which is a solid electrolyte layer containing the carboxylic ester and also forming a second solid electrolyte layer on the first solid electrolyte layer.

11. The method of manufacturing a solid electrolytic capacitor as claimed in claim 7, wherein the solid electrolyte layer is formed using chemical oxidative polymerization.

Technical Field

The present invention relates to a solid electrolytic capacitor and a method of manufacturing the solid electrolytic capacitor.

Background

Nowadays, solid electrolytic capacitors are widely used in various fields such as electronic devices. Japanese unexamined patent application publication No. 2011-151205 discloses a technique relating to a solid electrolytic capacitor using a conductive polymer as a solid electrolyte.

Disclosure of Invention

As shown above, japanese unexamined patent application publication No. 2011-151205 discloses a technique relating to a solid electrolytic capacitor using a conductive polymer as a solid electrolyte. The conductive polymer has the characteristics of low density and multiple cavities. In particular, when a polymer film of a conductive polymer is formed by chemical oxidative polymerization, the density of the formed conductive polymer is low, and a large number of cavities are formed in the conductive polymer.

As described above, when a material having a low density and many cavities is used to form the solid electrolyte layer, the strength of the solid electrolyte layer is reduced. Therefore, when mechanical stress is applied to the solid electrolyte layer in a reflow soldering process when the solid electrolytic capacitor is externally formed or mounted, the solid electrolyte layer may be deformed and peeled off or cut, which may result in a decrease in the conductivity of the solid electrolyte layer. The decrease in the conductivity of the solid electrolyte layer causes a problem of an increase in the Equivalent Series Resistance (ESR) of the solid electrolytic capacitor.

Further, if a large number of cavities are present in the solid electrolyte layer, a cathode layer (graphite layer) formed on the solid electrolyte layer may penetrate into the solid electrolyte layer when the solid electrolyte layer is compressed, so that the cathode layer and the dielectric layer partially contact each other. This may cause problems such as an increase in leakage current and occurrence of short circuits in the solid electrolytic capacitor.

In view of the above circumstances, an object of the present disclosure is to provide a solid electrolytic capacitor and a method of manufacturing the solid electrolytic capacitor, which are capable of suppressing an increase in ESR and an increase in leakage current.

A solid electrolytic capacitor according to one aspect of the present disclosure includes an anode body made of a porous valve metal, a dielectric layer formed on a surface of the anode body, and a solid electrolyte layer formed on the dielectric layer, wherein a carboxylic ester is present in at least a part of a cavity inside the solid electrolyte layer.

A method of manufacturing a solid electrolytic capacitor according to one aspect of the present disclosure includes: a step of forming a dielectric layer on a surface of an anode body made of a porous valve metal; a step of forming a solid electrolyte layer on the dielectric layer; and a step of forming a carboxylic acid ester in at least a part of the cavity inside the solid electrolyte layer.

According to the present disclosure, a solid electrolytic capacitor and a method of manufacturing a solid electrolytic capacitor can be provided, which are capable of suppressing an increase in ESR and an increase in leakage current.

The above and other objects, features and advantages of the present disclosure will be more fully understood from the detailed description given hereinafter and the accompanying drawings, which are given by way of illustration only, and thus are not to be considered as limiting the present disclosure.

Drawings

Fig. 1 is a sectional view of a solid electrolytic capacitor according to an embodiment;

fig. 2 is an enlarged sectional view of a solid electrolytic capacitor according to an embodiment;

fig. 3 is a graph showing a change in ESR of the solid electrolytic capacitor;

fig. 4 is a graph showing the occurrence rate of short circuits in the solid electrolytic capacitor.

Detailed Description

Embodiments of the present disclosure are described below with reference to the drawings.

Fig. 1 is a sectional view of a solid electrolytic capacitor according to an embodiment. As shown in fig. 1, the solid electrolytic capacitor 1 according to the present embodiment includes an anode body 11, a dielectric layer 12, a solid electrolyte layer 13, a cathode layer 16, a conductive adhesive 17, an anode lead 18, an external resin 19, and lead frames 20 and 21.

In the solid electrolytic capacitor 1 according to the present embodiment, the dielectric layer 12, the solid electrolyte layer 13, and the cathode layer 16 are stacked in this order on top of the anode body 11, as shown in fig. 1. The anode body 11 has an anode lead 18, and the anode lead 18 is connected to a lead frame 20. The anode lead 18 is connected to the lead frame 20 by soldering, for example. Further, the cathode layer 16 is connected to a lead frame 21 by a conductive adhesive 17. For example, the cathode layer 16 can be formed by stacking graphite layers and silver layers. The solid electrolytic capacitor 1 according to the present embodiment is covered with the external resin 19 in which a part of the two lead frames 20 and 21 is exposed to the outside.

Fig. 2 is an enlarged sectional view of the solid electrolytic capacitor according to the present embodiment, and it shows a cross section of a portion surrounded by a broken line in fig. 1 and the vicinity thereof on an enlarged scale. As shown in fig. 2, the anode body 11 is formed using a porous valve metal. For the anode body 11, for example, at least one selected from tantalum (Ta), aluminum (Al), niobium (Nb), titanium (Ti), zirconium (Zr), hafnium (Hf), and tungsten (W), or an alloy of these metals can be used. In particular, it is preferable to use at least one selected from tantalum (Ta), aluminum (Al), and niobium (Nb), or an alloy of these metals for anode body 11. Anode element 11 is formed using, for example: the valve metal in the form of a plate, foil or wire includes a sintered body of valve metal particles, a porous valve metal expanded by etching, and the like.

A dielectric layer 12 is formed on the surface of the anode body 11. For example, dielectric layer 12 can be formed by anodizing the surface of anode element 11. As shown in fig. 2, the surface of the anode body 11 is porous, and the dielectric layer 12 is also formed in the porous pores. For example, when anode body 11 is formed using tantalum, an oxidized tantalum film (dielectric layer 12) is formed on the surface of anode body 11 by anodizing anode body 11. For example, the thickness of the dielectric layer 12 can be appropriately adjusted by the anodization voltage.

The solid electrolyte layer 13 is formed on the dielectric layer 12. As shown in fig. 2, a solid electrolyte layer 13 is also formed inside the hole of the anode body 11 in which the dielectric layer 12 is formed. Thus, the solid electrolyte layer 13 is formed in contact with the entire surface of the dielectric layer 12. Further, a cavity is present inside the solid electrolyte layer 13, and a carboxylic ester 14 is formed (filled) in at least a part of the internal cavity. Further, a cavity is also present at the interface between the dielectric layer 12 and the solid electrolyte layer 13, and a carboxylic ester 15 is formed (filled) in at least a part of the cavity at the interface.

Note that, in fig. 2, although the carboxylic ester filled in the cavity inside the solid electrolyte layer 13 is denoted by reference numeral 14 and the carboxylic ester filled in the cavity at the interface between the dielectric layer 12 and the solid electrolyte layer 13 is denoted by reference numeral 15, the carboxylic esters 14 and 15 are the same material.

For example, the solid electrolyte layer 13 can be formed using a conductive polymer. For example, chemical oxidative polymerization, electropolymerization, or the like can be used in forming the solid electrolyte layer 13. Further, the solid electrolyte layer 13 may be formed by applying (impregnating) a conductive polymer solution and drying it.

In particular, when the conductive polymer (the solid electrolyte layer 13) is formed by chemical oxidative polymerization, the density of the formed conductive polymer is low, and a large number of cavities are formed inside the conductive polymer. Therefore, the present disclosure is suitably used when the conductive polymer is formed by chemical oxidative polymerization (i.e., when a conductive polymer having a low density and many cavities is used as the solid electrolyte layer 13).

The solid electrolyte layer 13 preferably contains a polymer composed of a monomer containing, for example, at least one of pyrrole, thiophene, aniline, and derivatives thereof. In addition, it preferably contains a sulfonic acid compound as a dopant.

In addition to the above-described conductive polymer, the solid electrolyte layer 13 may contain an oxide material such as manganese dioxide or ruthenium oxide, an organic semiconductor such as TCNQ (7,7,8,8, -tetracyanoterephthalquinodimethane complex salt), or the like.

As shown in fig. 2, in the solid electrolytic capacitor 1 according to the present embodiment, the carboxylic acid ester 14 is filled in at least a part of the cavity formed inside the solid electrolyte layer 13. Further, the carboxylic acid ester 15 is filled in at least a part of the cavity formed at the interface between the dielectric layer 12 and the solid electrolyte layer 13. For the carboxylic acid esters 14 and 15, a combination of carboxylic acid esters obtained by reacting a carboxylic acid with a material containing a hydroxyl group can be used. The carboxylic acid may be a carboxylate.

For example, as for the carboxylic acid esters 14 and 15, polyglycerol and a compound selected from at least one of adipic acid and ammonium adipate can be used. Specifically, the carboxylic acid esters 14 and 15 can be obtained by reacting at least one selected from adipic acid and ammonium adipate, which serves as a carboxylic acid, with polyglycerol, which serves as a hydroxyl group-containing material.

For example, after the solid electrolyte layer 13 is formed, when the carboxylic acid esters 14 and 15 are filled into the cavity of the solid electrolyte layer 13, the anode body 11 on which the dielectric layer 12 and the solid electrolyte layer 13 are formed is immersed in a mixed solution of adipic acid (ammonium adipate) and polyglycerol to impregnate the cavity of the solid electrolyte layer 13 with the mixed solution, and then dried at a high temperature, thereby generating ester bonds between the adipic acid (ammonium adipate) and the polyglycerol and forming the carboxylic acid ester. Since the esterification temperature is 130 ℃ or higher, the drying temperature is preferably 130 ℃ or higher.

Further, the molecular weight of the polyglycerin is preferably 500 or more. When the molecular weight of the polyglycerin is 500 or more, the decomposition temperature of the polyglycerin is 250 ℃ or more, and the heat resistance of the formed carboxylic acid esters 14 and 15 is improved.

As the molecular weight is greater, the viscosity of the polyglycerol increases. Further, as the molecular weight of the polyglycerol is larger, the number of OH groups per unit weight of the polyglycerol is smaller. Therefore, the molecular weight of the polyglycerol is preferably 500 to 600 in consideration of the viscosity of the polyglycerol and the tendency of ester bond (number of OH groups).

Further, the mass of the carboxylic acid esters 14 and 15 is preferably 10% or more of the mass of the solid electrolyte layer 13. By setting the mass of the carboxylic acid esters 14 and 15 to 10% or more of the mass of the solid electrolyte layer 13, the cavity of the solid electrolyte layer 13 can be filled.

Further, in the solid electrolytic capacitor 1 according to the present embodiment, the solid electrolyte layer 13 may have a double-layer structure. For example, the solid electrolyte layer 13 may have a double-layer structure including a first solid electrolyte layer formed on the dielectric layer 12 and a second solid electrolyte layer formed on the first solid electrolyte layer. In this case, the carboxylic acid ester is filled in at least a part of the cavity of the first solid electrolyte layer (i.e., the first solid electrolyte layer in contact with the dielectric layer 12). Specifically, to form the solid electrolyte layer 13 of the two-layer structure, the first solid electrolyte layer containing a carboxylic ester is first formed, and then the second solid electrolyte layer is formed on the first solid electrolyte layer.

Further, in the solid electrolytic capacitor 1 according to the present embodiment, the solid electrolyte layer 13 may have a structure of three or more layers. In this case, the carboxylic acid ester is filled in the cavity of at least the first solid electrolyte layer (i.e., the solid electrolyte layer in contact with the dielectric layer 12).

After the solid electrolyte layer 13 is formed in the above manner, the cathode layer 16 is formed on the solid electrolyte layer 13. Cathode layer 16 can be formed by stacking graphite layers and silver layers. Note that the graphite layer and the silver layer are merely examples, and the material of the cathode layer 16 is not particularly limited as long as it is a material having conductivity.

As described above, japanese unexamined patent application publication No. 2011-151205 discloses a technique relating to a solid electrolytic capacitor using a conductive polymer as a solid electrolyte. The conductive polymer has the characteristics of low density and multiple cavities. In particular, when a polymer film of a conductive polymer is formed by chemical oxidative polymerization, the density of the formed conductive polymer is low, and a large number of cavities are formed in the conductive polymer.

As described above, when a material having a low density and many cavities is used to form the solid electrolyte layer, the strength of the solid electrolyte layer is reduced. Therefore, when a mechanical stress is applied to the solid electrolyte layer in the reflow soldering process when forming the exterior of the solid electrolytic capacitor or mounting the solid electrolytic capacitor, the solid electrolyte layer may be deformed and peeled off or cut, which may result in a decrease in the conductivity of the solid electrolyte layer. The decrease in the conductivity of the solid electrolyte layer causes a problem of an increase in ESR of the solid electrolytic capacitor.

Further, if a large number of cavities are present in the solid electrolyte layer, a cathode layer (graphite layer) formed on the solid electrolyte layer may penetrate into the solid electrolyte layer when the solid electrolyte layer is compressed, so that the cathode layer and the dielectric layer partially contact each other. This may cause problems such as an increase in leakage current and occurrence of short circuits in the solid electrolytic capacitor.

In order to solve these problems, in the solid electrolytic capacitor 1 according to the present embodiment, the carboxylic acid ester 14 is filled in at least a part of the cavity inside the solid electrolyte layer 13. When the carboxylic ester 14 is filled in the cavity inside the solid electrolyte layer 13 in this way, the cavity of the solid electrolyte layer 13 may be filled with the carboxylic ester 14, thereby increasing the density of the solid electrolyte layer 13. This enhances the strength of the solid electrolyte layer 13, and therefore, even when mechanical stress is applied to the solid electrolyte layer 13 during the manufacture of the solid electrolytic capacitor 1, deformation of the solid electrolyte layer 13 can be suppressed. Therefore, a decrease in the electrical conductivity of the solid electrolyte layer 13 can be suppressed, thereby suppressing an increase in ESR of the solid electrolytic capacitor.

Further, the cathode layer 16 (graphite layer) formed on the solid electrolyte layer 13 can be prevented from infiltrating into the solid electrolyte layer 13 when the solid electrolyte layer 13 is compressed. Thereby, the cathode layer 16 and the dielectric layer 12 can be prevented from partially contacting each other, thereby suppressing an increase in leakage current and the occurrence of short circuits in the solid electrolytic capacitor 1.

In addition, since the carboxyl group is partially retained, the carboxylic acid ester exhibits conductivity. Therefore, when the carboxylic acid ester 14 is filled in the cavity inside the solid electrolyte layer 13, an increase in the resistance of the solid electrolyte layer 13 can be suppressed. This can suppress an increase in ESR of the solid electrolytic capacitor 1.

Further, in the solid electrolytic capacitor 1 according to the present embodiment, the solid electrolyte layer 13 is formed in contact with the dielectric layer 12, and the carboxylic ester 15 is filled in at least a part of the cavity at the interface between the dielectric layer 12 and the solid electrolyte layer 13. Since the carboxylic acid ester enables anodization (i.e., chemical conversion capability) of the valve metal, the dielectric layer 12 can be repaired when a defect occurs in the dielectric layer 12, thereby stabilizing the leakage current.

Further, when a material having low heat resistance is used as a material to be filled into the cavity inside the solid electrolyte layer, it is possible to release gas from the filled material due to heat in a reflow process or the like for mounting. The release of gas may lead to an increase in ESR and the appearance of cracks in the outer resin.

In order to solve the above problem, carboxylic acid esters 14 and 15 having high heat resistance are used as materials to be filled into the cavity inside the solid electrolyte layer 13 in the solid electrolytic capacitor 1 according to the present embodiment. Specifically, in forming the carboxylic acid ester, polyglycerol (polyglycerol having a molecular weight of 500 to 600) having a decomposition temperature of 250 ℃ or more is used, and further, polyglycerol is esterified using adipic acid (ammonium adipate), thereby improving heat resistance. Thereby, it is possible to suppress the release of gas from the filler material due to heat in the reflow process of mounting or the like. It is therefore possible to suppress an increase in ESR and the occurrence of cracks in the external resin.

As described above, according to the embodiments of the present disclosure, it is possible to provide a solid electrolytic capacitor and a method of manufacturing the solid electrolytic capacitor, which are capable of suppressing an increase in ESR and an increase in leakage current.

Examples of the invention

The present disclosure is described more specifically based on the following several examples; however, the present disclosure is not limited to these examples.

< example 1>

The following method was used to produce samples according to example 1.

First, tantalum powder is used for production to produce a tantalum sintered body. Specifically, tantalum powder in which an anode lead (tantalum wire) is embedded is press-molded. The molded body thus formed was a rectangular solid body 1.7mm long, 2.2mm wide and 1.2mm deep. Thereafter, the molded body was sintered at 1500 ℃, thereby producing a tantalum sintered body.

Next, the produced tantalum sintered body was anodized in a phosphoric acid solution to form a dielectric layer on the surface of the tantalum sintered body. The anodizing conditions were 40V.

Thereafter, the tantalum sintered body having the dielectric layer formed on the surface thereof is immersed in a solution including a monomer solution containing 3, 4-ethylenedioxythiophene as a dopant, 1,3, 6-naphthalenetrisulfonic acid, and an oxidizing solution containing ammonium persulfate as an oxidizing agent. This immersion was repeated several times, and a solid electrolyte layer (conductive polymer layer) containing poly (3, 4-ethylenedioxythiophene) was formed using chemical oxidative polymerization.

Then, 40 wt% of polyglycerin #500 (manufactured by Sakamoto Yakuhin Kogyo Co.; polyglycerin having an average molecular weight of 500), 5 wt% of ammonium adipate and 55 wt% of water (H) were mixed by using a stirrer₂O) to produce a solution. Then, a sample in which layers up to the solid electrolyte layer are formed is immersed in the produced solution. Thereafter, the sample was taken out of the solution and dried at 150 ℃ for 60 minutes to form a carboxylic ester. In this way, the carboxylate is filled into the cavity of the solid electrolyte layer.

Then, a cathode layer is formed by stacking a graphite layer and a silver layer on the solid electrolyte layer. The graphite layer is formed using graphite paste, and the silver layer is formed using silver paste. Then, the anode lead on the anode side and the lead frame were connected by welding. Further, the cathode layer on the cathode side and the lead frame are connected using a conductive adhesive. After that, the sample was covered with an external resin, and a part of the two lead frames was exposed to the outside, thereby forming a solid electrolytic capacitor.

< example 2>

Samples according to example 2 were produced using the following method.

First, a tantalum sintered body was produced by the same method as in example 1. Thereafter, anodic oxidation was performed by the same method as in example 1 to form a dielectric layer on the surface of the tantalum sintered body. Further, a solid electrolyte layer (conductive polymer layer) was formed on the dielectric layer by the same method as in example 1.

Then, 40 wt% of polyglycerin #500 (manufactured by Sakamoto Yakuhin Kogyo Co.; polyglycerin having an average molecular weight of 500), 5 wt% of ammonium adipate and 55 wt% of water (H) were mixed by using a stirrer₂O) to produce a solution. Then, a sample in which layers up to the solid electrolyte layer are formed is immersed in the produced solution. Thereafter, the sample was taken out of the solution and dried at 150 ℃ for 60 minutes to form a carboxylic ester. In this way, the carboxylate is filled into the cavity of the solid electrolyte layer.

Then, a solid electrolyte layer made of a conductive polymer solution is formed on the solid electrolyte layer. Specifically, the second solid electrolyte layer is formed by immersing the sample after forming carboxylate in a conductive polymer solution and drying it.

Thereafter, a cathode layer is formed by stacking a graphite layer and a silver layer on the solid electrolyte layer. The graphite layer is formed using graphite paste, and the silver layer is formed using silver paste. Then, the anode lead on the anode side and the lead frame are connected by welding. Further, the cathode layer on the cathode side and the lead frame are connected using a conductive adhesive. After that, the sample was covered with an external resin, and a part of the two lead frames was exposed to the outside, thereby forming a solid electrolytic capacitor.

Example 2 differs from example 1 in that the solid electrolyte layer has a double-layer structure. The carboxylic acid ester filled into the solid electrolyte layer is not all solid, and the carboxylic acid ester filled into the first solid electrolyte layer can be limited by the second solid electrolyte layer in the solid electrolyte layer having a double-layer structure, as in example 2.

< comparative example 1>

A sample in which the cavity of the solid electrolyte layer was not filled with carboxylate was produced as a sample according to comparative example 1. Except for this, the sample according to comparative example 1 was the same as the sample according to example 1.

< comparative example 2>

A sample in which the cavity of the first solid electrolyte layer was not filled with carboxylic ester was produced as a sample according to comparative example 2. Except for this, the sample according to comparative example 2 was the same as the sample according to example 2.

< evaluation of sample >

A specific number of samples according to the above examples 1 and 2 and comparative examples 1 and 2 were produced, and those samples were evaluated by the following method.

For the samples according to examples 1 and 2 and comparative examples 1 and 2, variations in ESR before and after the reflow process of mounting were examined. Fig. 3 is a graph showing the change in ESR of each sample. In fig. 3, σ represents a standard deviation.

As shown in fig. 3, in the samples according to examples 1 and 2, the variations in ESR tended to be smaller than those of the samples according to comparative examples 1 and 2. Therefore, an increase in ESR of the solid electrolytic capacitor can be suppressed by filling the carboxylic ester into the cavity of the solid electrolyte layer.

Further, comparing the sample according to example 1 and the sample according to example 2, the ESR variation in the sample according to example 2 as a whole tends to be smaller than that in the sample according to example 1. Therefore, when the solid electrolyte layer has a two-layer structure as in example 2, the carboxylic acid ester filled into the first solid electrolyte layer can be confined by the second solid electrolyte layer, and thus variations in ESR of the solid electrolytic capacitor can be reduced.

Further, the occurrence rate of short circuits was examined for the samples according to examples 1 and 2 and comparative examples 1 and 2. Fig. 4 is a graph showing the incidence of short circuits in each sample.

The occurrence of short circuits was calculated by the following method. Specifically, with respect to the samples according to examples 1 and 2 and comparative examples 1 and 2, after the external resin was formed (molded), the reflow process, the aging process, the short circuit inspection process, and the inspection process were performed. Fig. 4 shows the occurrence of short circuits in the short circuit inspection process. Note that in the short circuit inspection, a rated voltage is applied between the electrodes of the solid electrolytic capacitor, and when the amount of current flowing between the electrodes is equal to or larger than a certain current value, it is determined that a short circuit occurs. The number of samples used was 10 kp.

As shown in fig. 4, the occurrence rate of short circuits was 12.0% in the sample according to comparative example 1, and the occurrence rate of short circuits was 1.6% in the sample according to comparative example 2. On the other hand, the occurrence rate of short circuits was 1.4% in the sample according to example 1, and the occurrence rate of short circuits was 0.3% in the sample according to example 2. According to these results, the incidence of short circuits in the samples according to examples 1 and 2 was lower than that in the samples according to comparative examples 1 and 2. In particular, the incidence of short circuits in the sample according to example 2 was 0.3%, which is lower than that in the other samples.

The results of fig. 4 show that by filling a carboxylic ester into the cavity of the solid electrolyte layer, an increase in the leakage current of the solid electrolytic capacitor can be suppressed.

It will be obvious from the described disclosure that the embodiments of the disclosure may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.