JP3070446B2 - Solid electrolytic capacitors - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid electrolytic capacitor having a conductive polymer layer as a semiconductor layer and, more particularly, to preventing an increase in equivalent series resistance due to oxidation of a conductive polymer at a high temperature. It is related to technology.

[0002]

2. Description of the Related Art In recent years, in response to higher frequencies in electronic circuits,
For example, a solid electrolytic capacitor using a conductive polymer layer as a semiconductor layer as disclosed in Japanese Patent Publication No. 4-56445 has been developed. In this type of capacitor, a conductive polymer layer is formed on an oxide film obtained by forming a valve action such as tantalum or aluminum having a roughened surface, and a graphite layer as a cathode conductor layer and an Ag layer are formed thereon. A paste layer is sequentially formed, an external cathode terminal is connected to the cathode conductor layer, and an external anode terminal is welded to an anode lead wire planted on a valve action metal, and then a sheath is applied. It is. The solid electrolytic capacitor thus obtained uses a conductive polymer layer having a conductivity of 10 S / cm, which is about 100 times higher than that of conventional manganese dioxide, as a semiconductor layer. Applicable to higher frequency circuits. As the above-mentioned conductive polymer, polypyrrole, polythiophene, polyaniline and the like have been proposed.

[0003]

As described above, a solid electrolytic capacitor using a conductive polymer layer as a semiconductor layer has excellent high-frequency characteristics. However, it is known that, when a conductive polymer is placed in a high-temperature environment, an oxidation reaction proceeds due to trace amounts of water and oxygen, and its resistance increases. As a result, as a capacitor,
Equivalent series resistance (ESR; Equivalent Serent)
ie Resistance) will increase.

[0004] The invention thus provides, in a solid electrolytic capacitor using a conductive polymer layer as a semiconductor layer is not particularly increased ESR due to oxidation of the conductive polymer in a high temperature environment, no degradation of the high frequency characteristics solid An object of the present invention is to provide an electrolytic capacitor.

[0005]

A solid electrolytic capacitor according to the present invention is a solid electrolytic capacitor having a conductive polymer layer as a semiconductor layer, wherein an anode lead is provided on one end surface of the column perpendicular to the axis of the column. A capacitor element in which an oxide film layer of the valve action metal, the conductive polymer layer, and the cathode conductor layer are sequentially formed on the surface of the valve action metal on which the wire is implanted, and an insulation covering the capacitor element In a solid electrolytic capacitor including a conductive resin body, a resin layer for oxygen blocking made of an insulating resin containing an insulating filler, the conductive polymer layer on the surface of the capacitor element is exposed from the cathode conductor layer. The solid electrolytic capacitor has a structure provided so as to cover at least a portion and a peripheral portion of the exposed portion.

In the above solid electrolytic capacitor, the oxygen-blocking resin layer is formed from the periphery of the exposed portion of the conductive polymer layer to the anode lead, and the anode lead is Is characterized in that a layer of a coupling agent such as a silane coupling agent or a titanium coupling agent is formed between the anode lead wire and the oxygen blocking resin layer covering the anode lead wire. And

In the above solid electrolytic capacitor, the insulating filler contained in the oxygen-blocking resin layer has a volume content of not less than 50% in the resin layer and a particle size of not more than 5 μm. If there is, the effect is particularly remarkable.

The present inventors have conducted studies to solve the problems that have conventionally been encountered in solid electrolytic capacitors using a conductive polymer layer as a semiconductor layer, and conducted the following experiments. The present inventors have found a route for specifying the oxygen intrusion route into the conductive polymer layer and a method for preventing the oxygen intrusion.

That is, a chip type solid electrolytic capacitor having the structure shown in FIG. 3 and using the conductive polymer layer as the semiconductor layer 2 was manufactured. The capacitor shown in this figure is an example of a capacitor having a general structure conventionally used in practical use. An epoxy resin layer 5 as an oxygen barrier layer is provided at three portions shown in FIG. 4 and described below with respect to the exterior resin layer 8 of this capacitor.
Was coated. Then, each capacitor was placed in a thermostat at 105 ° C., and the change over time in ESR was measured. The lead-out portion of the external anode terminal 9 from the exterior resin layer 8 (FIG. 4)
(A)). The lead-out portion of the external cathode terminal 10 from the exterior resin layer 8 (FIG. 4)
(B)). A portion including both a portion where the external anode terminal 9 extends from the exterior resin layer 8 and a portion where the external cathode terminal 10 extends from the exterior resin layer 8 (FIG. 4C).

Table 1 shows the measurement results of the above-mentioned changes over time in ESR.
Shown in

[0011]

[Table 1]

From the results shown in Table 1, it was assumed that the main route of oxygen intrusion into the conductive polymer layer 2 was the portion of the external anode terminal 9 leading out from the exterior resin layer 8.

In order to further clarify this point, in the solid electrolytic capacitor having the structure shown in FIG. 3, the external resin layer 8 of each terminal is connected to the external anode terminal 9 or the external cathode terminal 10.
Etching pits 14 as shown in FIG. That is, a solid electrolytic capacitor in which an etching pit was formed only in the external anode terminal 9 and a solid electrolytic capacitor in which an etching pit was formed only in the external cathode terminal 10 were prepared and placed in a thermostat at 105 ° C. Was measured. The measurement result,
It is shown in Table 2.

[0014]

[Table 2]

From the results shown in Table 2, the deterioration with time of the ESR is clearly suppressed at the level where the etching pit is formed only on the external anode terminal 9 as compared with the level where the etching pit is formed only on the external cathode terminal 10. . From this, it became clear that external oxygen mainly transmitted through the external anode terminal 9 and penetrated into the exterior resin layer 8 to cause the oxidative deterioration of the conductive polymer layer 2.

That is, external oxygen penetrates through the interface between the exterior resin layer 8 and the external positive and negative electrode terminals 9 and 10 which are metal, reaches the internal capacitor element, The conductive polymer layer 2 at a portion not covered with the graphite layer 3 and the Ag paste layer 4 is oxidatively degraded,
This increases the ESR of the capacitor. It has also been found that oxidative degradation can be suppressed by increasing the distance of the oxygen intrusion path.

However, in the chip type solid electrolytic capacitor, the formation of the oxygen blocking resin layer at the lead-out portion of the external anode terminal 9 after the resin coating is performed because the portion of the external anode terminal 9 which is exposed to the outside from the external resin layer 8. It is easy to cause resin adhesion to the surface. In extreme cases, the exterior resin layer 8 of the external cathode terminal 10
In some cases, a resin layer for blocking oxygen may adhere to a portion protruding from the surface. Such adhesion of the resin to the external terminals 9 and 10 naturally affects the solder mounting performance. However, a decrease in the solder mounting performance is a fatal problem for surface mount components. In addition, since a resin layer is further formed outside the exterior resin layer 8, the outer dimensions are inevitably increased, which does not meet the market demand for miniaturization of components. On the other hand, although it has been confirmed that the method of forming the etching pits on the positive and negative external terminals 9 and 10 has the effect of increasing the distance of the oxygen entry path and improving the heat resistance of the capacitor, today's electronic components 105 ° C, 1000 generally required for
The heat resistance of about time is not sufficiently satisfied, and it can be said that this alone is still insufficient.

From the above, in order to improve the heat resistance of a solid electrolytic capacitor using a conductive polymer layer as a semiconductor layer to a level sufficient to meet the demands of the market, the anode lead wire of the capacitor element must be provided before the exterior is provided. On the side, the conductive polymer layer exposed from the cathode conductor layer (in this case, composed of the graphite layer 3 and the Ag paste layer 4) may be covered with a resin layer to block oxygen entering from the outside. I thought.

Further, in this case, in order to maximize the length of the oxygen invasion path with the minimum amount of resin, the oxygen reaching the oxygen-blocking resin layer should be retained in the resin layer for a sufficiently long time. That is, as shown in FIG. 6, the filler 17 is mixed into the resin 16 so that oxygen moves along the surface of the filler 17. That is, the oxygen entry path 15 is formed along the filler 17. For this reason, the higher the filler content in the resin layer 5, the more effective. Also, the smaller the filler particle size, the larger the surface area, that is, the moving distance of oxygen, even at the same filler content, so that the effect of preventing oxygen intrusion is greater.

Further, the above-mentioned oxygen blocking resin layer 5 is considered to exhibit a sufficient effect if it covers at least a portion where the conductive polymer is exposed from the cathode conductor layer. For this purpose, it is preferable to form the resin layer 5 from the exposed portion 13 of the conductive polymer layer to the anode lead wire 1. In this case, the better the adhesion between the anode lead wire 1 made of metal and the oxygen blocking resin layer 5 made of resin, the higher the effect of preventing oxygen intrusion. In the present invention, a layer of a coupling agent such as a silane coupling agent or a titanium coupling agent is interposed between the resin layer 5 and the anode lead wire 1 in order to enhance the adhesion between the two.

[0021]

Next, several embodiments of the present invention will be described in comparison with comparative examples. Beginning
In order to facilitate understanding of the present invention, some references
Examples will be described.

(First Reference Example ) In this reference example , a tantalum solid electrolytic capacitor element having the structure shown in FIG.
The relationship between the content of the filler 17 contained in the oxygen-blocking resin layer 5 and the heat resistance was investigated. First, diameter 3mm,
The 4 mm long tantalum sintered body 6 is anodized at 35 V in a 0.01 wt% phosphoric acid aqueous solution to form a tantalum oxide film 1
1 (see FIG. 3). Then, pyrrole 50wt
% Ethanol solution and ferric nitrate Fe (NO ₃ ) ₃
A polypyrrole layer, which is a conductive polymer, was formed on the tantalum oxide film 11 by successive immersion in a 30 wt% aqueous solution. This dipping operation was repeated four times to form a conductive polypyrrole layer 2 as a semiconductor layer on the surface of the tantalum sintered body. Next, a graphite layer 3 and a silver paste layer 4 were sequentially formed as a cathode conductor layer, and a tantalum solid electrolytic capacitor element 7 was obtained.

An epoxy resin layer 5 as an oxygen barrier layer is applied to the capacitor element 7 obtained as described above by a syringe so that the polypyrrole layer 2 covers the portion 13 exposed from the graphite layer 3. 150 ° C
For 60 minutes. This curing was performed in a nitrogen atmosphere in order to prevent the polypyrrole from being oxidized and degraded at the curing temperature. The oxygen blocking epoxy resin layer 5 contains silica as a filler 17. In this reference example , the filler content was 10, 30, 50, 70 vol.
%, And four samples were prepared for each level.

Next, these samples were left in a thermostat at 105 ° C., and the time-dependent changes in ESR at 100 kHz were measured. Table 3 shows the measurement results.

COMPARATIVE EXAMPLE 1 This comparative example is the same as the first example except that the oxygen-blocking epoxy resin layer 5 was not formed.
This is the same capacitor element as the tantalum solid electrolytic capacitor element according to the reference example . In Comparative Example 1, the change over time of the ESR was measured using this capacitor element as an evaluation sample. Table 3 shows the measurement results.

[0026]

[Table 3]

Referring to Table 3, it can be seen that the ESR of the sample according to the first reference example is clearly smaller than that of the sample of the comparative example. Also, from the measurement results in the first reference example, it can be said that the content of the filler 17 is desirably 50 vol% or more.

The correlation between the filler content and the heat resistance in the first reference example is explained as follows. In general, oxygen enters the epoxy resin layer 5 at the interface between the filler 17 and the resin 16 as an oxygen entry path 15 as shown in FIG. Therefore, the filler 1 in the resin 16
It is considered that the sample having the larger amount of 7 has a longer distance of the oxygen intrusion path 15 per unit volume of the epoxy resin layer 5 and exhibits a higher oxygen intrusion inhibiting ability.

(Second Reference Example ) In this reference example , the relationship between the particle size of the filler 17 contained in the oxygen blocking resin layer 5 and the heat resistance was investigated. A tantalum capacitor element having the same structure as the capacitor element according to the first reference example was manufactured.
A silica-containing epoxy resin is quantitatively applied to the same portion as in the reference example , that is, the portion 13 where the polypyrrole layer 2 is exposed from the graphite layer 3 with a syringe, and cured at 150 ° C. for 30 minutes in a nitrogen atmosphere to prevent oxygen. The epoxy resin layer 5 for use was formed. The filler (silica) 17 contained in the epoxy resin layer 5 has a content of 50 vol%,
Filler particle size of 1.0, 5.0, 8.0, 10.0 μm
m of four levels. In the present reference example , ten samples were prepared for each level, and the changes over time in the ESR were investigated in a thermostat at 105 ° C. as in the first reference example . Table 4 shows the results.

[0030]

[Table 4]

Referring to Table 4, the filler particle size was 5.0.
It can be said that it is desirable to be not more than μm. The correlation between the filler particle size and the oxygen intrusion inhibiting ability is also explained by the same mechanism as in the first reference example . That is, it is considered that the smaller the filler particle diameter, the longer the oxygen intrusion path length in the unit volume of the oxygen barrier layer 5, and as a result, the oxygen intrusion prevention ability is improved.

(Third Reference Example ) In this reference example , the relationship between the application site of the oxygen blocking resin layer 5 and the heat resistance was investigated. Using a capacitor element having the same structure as that of the first reference example , three-level samples having different application sites of the resin layer 5 for oxygen barrier layer were produced. That is, the application site of each level is as follows. As in the first reference example , a portion 13 of the polypyrrole layer 2 on the side of the anode lead wire 1 and exposed from the graphite layer 3 (see FIG. 1). The entire capacitor element (FIG. 2A). The cathode conductor layer side of the capacitor element (FIG. 2B).

For the oxygen-blocking resin layer 5, an epoxy resin containing silica was used. The silica content and particle size are all 50 vol%, 1.0 μm. After the epoxy resin layer 5 was formed, the change over time of the ESR was measured in a thermostat at 105 ° C. as in the first reference example . Table 5 shows the measurement results.

[0034]

[Table 5]

Referring to Table 5, at least a portion on the anode lead wire 1 side is required as a portion on which the oxygen-blocking epoxy resin layer 5 is formed, and covering the cathode conductor layer of the capacitor element has little effect. I understand.

[0036] (First Embodiment) In this embodiment, intended to enhance the oxygen ingress blocking capability, the anode lead wire 1, the external anode terminal 9 or the external cathode terminal 10
The effect of improving the airtightness between the metal terminal member such as the above and the oxygen blocking resin layer 5 on the heat resistance of the capacitor was investigated. That is, in order to examine the effect of performing the silane coupling treatment on the metal terminal member in advance,
After manufacturing the same capacitor element as in the first reference example , the entire capacitor element was immersed in a 2 wt% citric acid aqueous solution containing 3 wt% of a silane coupling agent, left at room temperature for 30 minutes, and then at 125 ° C. for 10 minutes. The water was evaporated. Thereafter, silica having a particle size of 1 μm is contained (content 5
As in the first reference example , a fixed amount of an epoxy resin was applied by a syringe so as to cover the exposed portion 13 of the polypyrrole layer 2 and cured at 150 ° C. for 30 minutes. The changes over time in the ESR of these samples were measured in a thermostat at 105 ° C. in the same manner as in the first reference example . Table 6 shows the results.

[0037]

[Table 6]

Comparison between Table 6 and Table 3 shows that when the filling conditions of the epoxy resin layer 5 for blocking oxygen are the same (content: 50 vol%, particle size: 1 μm), 1000 hours after the initial ESR ESR increase rate of
In this embodiment, about 1.14 times (299 mΩ / 263 m
Ω), whereas the first reference example is about 1.71.
Double (437 mΩ / 256 mΩ). From this,
It is apparent that the oxidative degradation of polypyrrole is clearly suppressed by applying the silane coupling agent.
This is because, due to the action of the silane coupling agent, the adhesion between the oxygen-blocking epoxy resin layer 5 and the metal terminal member such as the anode lead wire 1 is improved, and the ability to prevent external oxygen from entering is improved. It is thought that it was.

In the reference examples and embodiments described above, polypyrrole was used as the conductive polymer as the semiconductor layer, but the present invention is not limited to this. For example, it is apparent that the same operation and effect as those of the embodiments described above can be obtained even with a solid electrolytic capacitor using another conductive polymer that causes oxidative deterioration such as polythiophene and polyaniline.

Also, an example in which silica is used as a filler contained in the oxygen-blocking epoxy resin layer 5 has been described. However, if it is an insulating substance that does not itself have oxygen permeability,
Not limited to silica. Such filler materials include:
Examples include calcium carbonate and alumina.

Furthermore, an example in which a silane coupling agent is used to enhance the adhesion between the metal terminal member such as the anode lead wire 1 and the oxygen blocking resin layer 5 has been described. The material is not limited to the silane coupling agent as long as it enhances the adhesiveness, and other materials may be used. For example, the same effect can be obtained by using a titanium coupling agent or the like.

[0042]

As described above, the solid electrolytic capacitor of the present invention is different from the solid electrolytic capacitor using the conductive polymer layer as the semiconductor layer in that the conductive polymer layer on the capacitor element surface is separated from the cathode conductor layer. An oxygen barrier layer made of an insulating resin containing an insulating filler is provided so as to cover at least the exposed portion and a peripheral portion of the exposed portion.
Thus, according to the present invention, the intrusion of oxygen from the outside into the conductive polymer can be prevented, and the oxidative deterioration of the conductive polymer due to the oxygen can be suppressed. It is possible to provide a solid electrolytic capacitor excellent in high-frequency characteristics without an increase in ESR due to oxidative deterioration.

The solid electrolytic capacitor of the present invention is different from the above-described solid electrolytic capacitor in that an oxygen barrier layer is formed from the periphery of the exposed portion of the conductive polymer layer to the anode lead wire. In the wire portion, a layer of a coupling agent such as a silane coupling agent or a titanium coupling agent is formed between the anode lead wire and the oxygen barrier layer covering the anode lead wire. As a result, according to the present invention, the adhesion between the resin oxygen barrier layer and the metal anode lead wire can be increased, so that the ability to prevent oxygen intrusion can be further enhanced.

The insulating filler contained in the above-mentioned oxygen barrier layer is set so that its content in the oxygen barrier layer is 50% or more by volume and the particle size is 5 μm or less. The effect of improving the ability to prevent oxygen intrusion is particularly remarkable.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a section of a tantalum solid electrolytic capacitor element according to a first reference example of the present invention.

FIG. 2 is a sectional view showing a section of a tantalum solid electrolytic capacitor element according to a third reference example of the present invention.

FIG. 3 is a sectional view showing a cross section of a general chip type tantalum solid electrolytic capacitor and a schematic enlarged cross section thereof.

FIG. 4 is a cross-sectional view of the solid electrolytic capacitor for explaining the operation of the present invention.

FIG. 5 is a cross-sectional view of an external anode terminal and an external cathode terminal with an etching pit.

FIG. 6 is a schematic sectional view of a filler-containing oxygen blocking resin layer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Anode lead wire 2 Polypyrrole layer 3 Graphite layer 4 Silver paste layer 5 Oxygen blocking epoxy layer 6 Tantalum sintered body 7 Tantalum solid electrolytic capacitor element 8 Exterior resin layer 9 External anode terminal 10 External cathode terminal 11 Tantalum oxide film 12 Tantalum 13 Exposed portion of conductive polymer layer 14 Etching pit 15 Oxygen intrusion path 16 Resin 17 Filler

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-6-204099 (JP, A) JP-A-3-292716 (JP, A) JP-A-62-142310 (JP, A) 128932 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01G 9/08 H01G 9/012 H01G 9/028

Claims (3)

(57) [Claims] 1. A solid electrolytic capacitor using a conductive polymer layer as a semiconductor layer, comprising a column and a valve action metal having an anode lead wire on one end surface perpendicular to the axis of the column. An oxide film layer of the valve metal, and the conductive polymer layer,
Including a capacitor element formed by sequentially forming a cathode conductor layer and an insulating resin body covering the capacitor element,
At least a portion of the surface of the capacitor element where the conductive polymer layer is exposed from the cathode conductor layer and a peripheral portion of the exposed portion are covered with an oxygen blocking resin layer made of an insulating resin containing a filler. Solid electrolytic capacitor
In the sensor, the oxygen blocking resin layer is formed from the peripheral portion of the exposed portion of the conductive polymer layer to the anode lead wire, and the anode lead wire portion includes an anode lead. Between the wire and the oxygen blocking resin layer covering it, such as a silane coupling agent or a titanium coupling agent,
A solid electrolytic capacitor having a coupling agent layer formed thereon. 2. The solid electrolytic capacitor according to claim 1 , wherein the insulating filler contained in the oxygen-blocking resin layer comprises:
A solid electrolytic capacitor characterized in that its content in the resin layer is at least 50% by volume and its particle size is at most 5 μm. 3. The solid electrolytic capacitor according to claim 1 , wherein the oxygen-blocking resin layer is made of a silica-containing epoxy resin, and the coupling agent layer is made of a silane coupling agent. Solid electrolytic capacitor.