JP5302824B2 - Solid electrolytic capacitor and manufacturing method thereof - Google Patents

Description

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

  In a conventional solid electrolytic capacitor, a dielectric oxide film is formed by anodic oxidation on a valve action metal element such as tantalum, niobium, or aluminum, and then a cathode forming step for forming a solid electrolyte layer and a cathode lead layer, which is covered with a resin. Although manufactured through an exterior process, the dielectric oxide film is very thin and easily damaged by stress or mechanical stress in the cathode formation process or the exterior process, which may deteriorate the leakage current characteristics.

  Therefore, various methods have been proposed as countermeasures. A method of preventing a decrease in leakage current characteristics due to damage to an oxide film has been proposed by forming a thick dielectric oxide film even when stress or mechanical stress is applied in a cathode forming process or an exterior process (for example, Patent Document 1). However, when this method is used, there is a problem that the electrostatic capacity is reduced. Therefore, the formation of the dielectric oxide film is about several tens to several hundreds μm, which is not sufficient as a countermeasure against the deterioration of the leakage current.

  In addition, by controlling the reaction conditions of the manganese dioxide forming solution that forms the solid electrolyte layer and the polymerization solution for forming the conductive polymer from the past, the solid electrolyte layer is formed at the edge of the capacitor anode body, which is particularly vulnerable to mechanical stress. Although it has been studied to form a thicker film, it has not been sufficient yet and has been an ongoing problem. For example, it has been studied to realize the above by a method in which a solid electrolyte layer is made to contain fibers or a sticking agent. However, if a fiber or a sticking agent is contained to make the solid electrolyte thick, the conductivity of the solid electrolyte layer is lowered. However, there is a disadvantage that ESR deteriorates. Even if this method is used, since the solid electrolyte forming material is basically liquid, surface tension works during formation, and the edge of the capacitor anode body is always thinner than other parts, so the solid electrolyte layer is always thinner. Also, it was not sufficient for countermeasures against leakage current deterioration due to mechanical stress (see, for example, Patent Documents 2 and 3).

  In addition, after forming a dielectric oxide film on the solid electrolytic capacitor anode body, a protective resist layer is formed over the entire periphery of the edge portion to cope with stress and mechanical stress in the cathode forming process and the exterior process. Technology has also been proposed, but if a resist layer is simply formed over the entire circumference, the formation of a solid electrolyte layer on the dielectric oxide film layer covered with the resist layer becomes insufficient, so naturally the capacitance There was a problem that would be significantly reduced. Furthermore, insulation can be ensured by using a material such as an epoxy resin shown in the same patent document, but there is no effect of buffering stress and mechanical stress, and it is still not sufficient for measures against leakage current deterioration ( For example, see Patent Document 4).

  In recent years, with the digitization of electronic equipment, solid electrolytic capacitors have been required to have excellent high-frequency characteristics, and solid electrolytes used in solid electrolytic capacitors are more conductive than manganese dioxide for the purpose of lowering ESR. The shift to highly conductive polymers is progressing.

  In general, examples of the conductive polymer used in the solid electrolytic capacitor include polythiophene, polypyrrole, polyaniline, and derivatives thereof, and electrolytic polymerization and chemical oxidation polymerization are used as the formation method. However, the conductive polymer has the advantage that the conductivity is dramatically improved over manganese dioxide, but also has the disadvantage that the hardness and mechanical strength are low. Due to this disadvantage, the deterioration of leakage current characteristics due to the stress and mechanical stress in the cathode forming process and the exterior process described above becomes more remarkable, and further improvement has been required.

Japanese Patent Laid-Open No. 58-190016 JP 2001-126963 A JP 2001-250743 A JP-A-5-304058

  The present invention provides a method for improving the leakage current characteristics, which is the above-mentioned continuous problem, and in particular, a conductive polymer solid electrolyte having improved leakage current characteristics while reducing a decrease in capacitance. The object is to provide a capacitor.

In order to solve the above problems, the solid electrolytic capacitor according to the present invention is a sintered body obtained by sintering a molded body made of a valve action metal powder, or a roughened valve action metal foil on the surface. A capacitor anode body on which a dielectric oxide film is formed, and a solid electrolyte layer and a cathode lead layer are sequentially formed on the surface of the dielectric oxide film,
A convex portion made of an insulating resin extends over 5 to 30% of the length of each line of the capacitor anode body at one or more of the apexes (edge apex portions) where the ridges of the three sides of the capacitor anode body intersect. It is formed.
According to this structure, since the apex portion of the edge having the weakest strength is protected by the insulating resin in the element, external stress and mechanical stress are buffered, and the solid electrolyte layer is sufficiently provided at the edge portion. Since it is formed, it is possible to provide a solid electrolytic capacitor, in particular, a conductive polymer solid electrolytic capacitor, in which the leakage current is hardly deteriorated and the capacitance is hardly lowered. The convex portions in the solid electrolytic capacitor of the present invention are generally substantially spherical or small elliptical, but are not limited thereto.

In the solid electrolytic capacitor having the above characteristics, the present invention is characterized in that the convex portion has elasticity.
The present invention is also characterized in that, in the solid electrolytic capacitor having the above characteristics, the convex portions are formed at all the vertices.
The present invention is also a solid electrolytic capacitor having the above characteristics, wherein the solid electrolyte layer is made of a conductive polymer.

Furthermore, the present invention provides a capacitor anode by forming a dielectric oxide film on the surface of a sintered body obtained by sintering a molded body made of a valve action metal powder or a roughened valve action metal foil. A solid electrolytic capacitor manufacturing method for forming a solid electrolyte layer and a cathode lead layer on the surface of the dielectric oxide film after forming a body,
Before or after the formation of the dielectric oxide film, the convex portion is insulated over 5 to 30% of the length of each ridge line of the capacitor anode body at one or more points where the ridges of the three sides of the capacitor anode body intersect. It is characterized in that it is made of a functional resin.
The present invention is also characterized in that, in the method of manufacturing a solid electrolytic capacitor having the above characteristics, a material having elasticity is used as the insulating resin when the convex portions are formed.
Further, the present invention provides a method for producing a solid electrolytic capacitor having the above characteristics, wherein when forming the solid electrolyte layer, the capacitor anode body is immersed in a polymerization solution for forming a conductive polymer layer, and thereafter It is also characterized by raising.

According to the present invention, since the apex portion of the edge having the weakest strength is protected by the insulating resin having elasticity, the externally applied stress and mechanical stress are buffered, and the solid electrolyte layer is sufficiently formed at the edge portion. Therefore, it is possible to realize a solid electrolytic capacitor, particularly a conductive polymer type solid electrolytic capacitor, in which the decrease in capacitance is small and the leakage current characteristic is improved.
Furthermore, since the convex portion made of the insulating resin is formed only at the apex portion of the edge portion, the flow of the resin is not hindered when the exterior resin is formed by transfer molding or the like. Therefore, the assembly failure does not deteriorate.

It is a schematic diagram of the capacitor | condenser anode body which formed the convex part by insulating resin in all the vertices (a total of eight vertices) where the ridges of the three sides of the valve action metal element in an Example cross. It is a schematic diagram of the capacitor anode body in Conventional Examples 1, 2, and 3. It is a schematic diagram of the capacitor | condenser anode body which apply | coated the epoxy resin (insulating property) to all the ridge periphery parts of the valve action metal element in the prior art example 4. FIG. It is a schematic diagram which shows the liquid lifting state of the edge part at the time of pulling up after the capacitor | condenser anode body in an Example is immersed in the polymerization liquid for conductive polymer layer formation.

  Hereinafter, specific embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[Example 1]
Detailed contents according to the first embodiment will be described. First, an anode lead was embedded in tantalum powder, press-molded into a predetermined shape, and sintered to prepare a rectangular valve-shaped porous valve metal element of 4.7 mm × 3.6 mm × 1.8 mm.

  Next, fluororubber-based insulating resin with a viscosity of 3000 mPa · s is applied to all the vertices where the ridges of the three sides of the valve action metal element intersect (total of eight vertices) with a syringe with a discharge port of Φ0.2 mm. After applying so that the convex part of the magnitude | size corresponding to the length of about 5% of length was formed, it dried (FIG. 1). The viscosity measurement conditions were measured after rotating the rotor for 1 minute with a rotary viscometer at a liquid temperature of 20 ° C. Incidentally, the size of the small elliptical convex portion formed of the fluororubber-based insulating resin was about 240 μm × 180 μm × 90 μm.

  Next, anodization was performed for 120 minutes at an applied voltage of 8 V in a 0.1 wt% phosphoric acid aqueous solution, a dielectric oxide film was formed on the entire valve action metal element, and a capacitor anode body was obtained. The thickness of the dielectric oxide film formed by the above anodic oxidation was about 14 μm.

  Thereafter, as a step of forming a solid electrolyte layer made of a conductive polymer, a monomer solution containing 3,4-ethylenedioxythiophene and an oxidizing agent solution containing ferric dodecylbenzenesulfonate are mixed, and the temperature is -5 ° C. The capacitor anode body was immersed in a mixed solution held in 1 second for 1 second, then pulled up and chemically oxidized and polymerized at 25 ° C. to form a conductive polymer layer. Thereafter, the polymerization residue of the formed conductive polymer was removed by washing in an organic solvent, and then dried at 105 ° C. for 30 minutes.

  The solid electrolyte layer made of the conductive polymer was formed by repeating the process of forming the solid electrolyte layer made of the conductive polymer 10 times in total.

  A carbon paste and a silver paste are applied on the conductive polymer layer, and then dried to sequentially form a carbon layer and a silver layer. A cathode lead terminal is drawn from the anode body on the silver layer. After connecting the anode terminal to each anode lead, an exterior resin was applied by transfer molding to produce a solid electrolytic capacitor rated at 2.5V-680 μF.

[Example 2]
In Example 2, fluororubber-based insulating resin having a viscosity of 3000 mPa · s is applied to all of the vertices (three vertices in total) where the ridges of the three sides of the valve-acting metal element manufactured in the same manner as in Example 1 intersect with the discharge ports Φ0. After applying an amount of 10% of the length of the ridge line of the element with a 2 mm syringe, it is dried to form a convex part, and then anodized in a 0.1 wt% phosphoric acid aqueous solution at an applied voltage of 8 V for 120 minutes. Then, a dielectric oxide film was formed on the entire valve metal element to obtain a capacitor anode body. Otherwise, a solid electrolytic capacitor was produced in the same manner as in Example 1.

[Example 3]
In Example 3, fluororubber-based insulating resin having a viscosity of 3000 mPa · s is applied to all the vertices (three vertices in total) at which the ridges of the three sides of the valve-acting metal element manufactured in the same manner as in Example 1 intersect with the discharge ports Φ0. After applying an amount of 20% of the length of the ridge line of the element with a 2 mm syringe, it was dried to form a convex part, and then anodized in a 0.1 wt% phosphoric acid aqueous solution at an applied voltage of 8 V for 120 minutes. Then, a dielectric oxide film was formed on the entire valve metal element to obtain a capacitor anode body. Otherwise, a solid electrolytic capacitor was produced in the same manner as in Example 1.

[Example 4]
In Example 4, fluororubber-based insulating resin having a viscosity of 3000 mPa · s is applied to all of the vertices (three vertices in total) where the ridges of the three sides of the valve-acting metal element manufactured in the same manner as in Example 1 intersect with the discharge ports Φ0. After applying an amount of 30% of the length of the ridge line of the element with a 2 mm syringe, it was dried to form a convex part, and then anodized in a 0.1 wt% phosphoric acid aqueous solution at an applied voltage of 8 V for 120 minutes. Then, a dielectric oxide film was formed on the entire valve metal element to obtain a capacitor anode body. Otherwise, a solid electrolytic capacitor was produced in the same manner as in Example 1.

[Comparative Example 1]
In Comparative Example 1, fluororubber-based insulating resin having a viscosity of 3000 mPa · s was discharged at the outlets Φ0... At all vertices (total of 8 vertices) where the ridges of the three sides of the valve metal element manufactured in the same manner as in Example 1 intersect. After applying an amount of 3% of the length of the ridge line of the element with a 2 mm syringe, it was dried to form a convex part, and then anodized in a 0.1 wt% phosphoric acid aqueous solution at an applied voltage of 8 V for 120 minutes. Then, a dielectric oxide film was formed on the entire valve metal element to obtain a capacitor anode body. Otherwise, a solid electrolytic capacitor was produced in the same manner as in Example 1.

[Comparative Example 2]
In Comparative Example 2, a fluororubber-based insulating resin having a viscosity of 3000 mPa · s is applied to all the vertices (three vertices in total) where the ridges of the three sides of the valve metal element manufactured in the same manner as in Example 1 intersect with the discharge ports Φ0. After applying an amount of 35% of the length of the ridge line of the element with a 2 mm syringe, it is dried to form a convex part, and then anodized in a 0.1 wt% phosphoric acid aqueous solution at an applied voltage of 8 V for 120 minutes. Then, a dielectric oxide film was formed on the entire valve metal element to obtain a capacitor anode body. Otherwise, a solid electrolytic capacitor was produced in the same manner as in Example 1.

[Example 5]
In Example 5, a valve action metal element produced in the same manner as in Example 1 was anodized in a 0.1 wt% phosphoric acid aqueous solution at an applied voltage of 8 V for 120 minutes, and a dielectric oxide film was formed on the entire valve action metal element. After forming, the fluororubber-based insulating resin with a viscosity of 3000 mPa · s is applied to all the vertices where the ridges of the three sides of the valve action metal element intersect (total of eight vertices) with a syringe with a discharge port of Φ0.2 mm, After applying an amount of 20% of the length, it was dried to form a convex portion to obtain a capacitor anode body. Otherwise, a solid electrolytic capacitor was produced in the same manner as in Example 1.

[Conventional example 1]
In Conventional Example 1, a solid electrolytic capacitor was produced in the same manner as in Example 1 except that the fluororubber insulating resin was not applied to the apex of the valve metal element (FIG. 2).

[Conventional example 2]
In the conventional example 2, the fluororubber insulating resin is not applied to the apex of the valve action metal element, and the capacitor is anodized in a 1.0 wt% ammonium borate aqueous solution before anodizing in the phosphoric acid aqueous solution. A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the dielectric oxide film around the outer periphery of the anode body was formed thick. The thickness of the dielectric oxide film formed by the above anodic oxidation was about 90 μm.

[Conventional example 3]
In Conventional Example 3, no fluororubber insulating resin is applied to the apex of the valve metal element, and the capacitor anode body is suspended by 2 wt% pulp and 0.05 wt% synthetic glue during the process of forming the conductive polymer layer. A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the pulp fiber was adhered by being immersed in the turbid liquid.

[Conventional example 4]
In Conventional Example 4, the valve action metal element is anodized in a 0.1 wt% phosphoric acid aqueous solution at an applied voltage of 8 V for 120 minutes to form a dielectric oxide film on the entire valve action metal element. An epoxy resin (insulating property) having a viscosity of 300 mPa · s was applied to all the peripheral portions of the ridge with a syringe having a discharge port of Φ0.2 mm and dried to obtain a capacitor anode body as shown in FIG. Otherwise, a solid electrolytic capacitor was produced in the same manner as in Example 1.

  Capacitance (120 Hz), ESR (100 kHz), leakage current (1 at the time of applying the rated voltage) in each of 100 solid electrolytic capacitors produced in Examples 1 to 5, Comparative Examples 1 and 2 and Conventional Examples 1 to 4 Table 1 shows the average value of the measured (min) values. Moreover, about the thickness (center part of a plane, and center part of a ridge) of the formed conductive polymer layer, the average value of 20 places measured with the electron microscope is shown.

  As can be seen from Table 1, the example showed a lower value of the capacitance and a good leakage current as compared with the conventional example 1.

  This is because, in Conventional Example 1, the thickness of the conductive polymer layer at the edge of the capacitor element that is vulnerable to external stress is not sufficient, so that the dielectric oxide film is damaged by external mechanical stress in the subsequent process such as transfer molding. In contrast to the deterioration of the leakage current, the working example can protect against external mechanical stress by forming a convex portion with an insulating resin having elasticity at the apex where the ridges of the three sides that are most susceptible to external mechanical stress intersect, This prevents the leakage current from deteriorating. In addition, since the insulating resin portion formed on the edge portion is convex, the polymer solution lifted after being immersed in the polymer solution for forming the conductive polymer layer is held thick at the ridge portion by the surface tension (FIG. 4). Since the conductive polymer layer is formed thick, it can be protected from external mechanical stress, and deterioration of leakage current can be further prevented.

Here, the convex portion formed of the insulating resin at one or more vertexes where the ridges of the three sides of the capacitor element intersect is formed over 5 to 30% of the length of each of the three ridge lines constituting the vertex. In particular, more preferably 5 to 20%.
Further, as is apparent from Table 1, it can be seen that the example has better leakage current and higher capacitance than the conventional example 2.

  This is because the edge portion does not sufficiently cope with external stress only by increasing the thickness of the dielectric oxide film according to Conventional Example 2, and the leakage current is better in the embodiment. Further, since the dielectric oxide film around the outer peripheral portion is formed thick, there is a demerit that the capacitance is greatly reduced.

  Further, as is clear from Table 1, it can be seen that the example has better leakage current and lower ESR than the conventional example 3.

  In the case of Conventional Example 3, the addition of fibers or adhesives decreases the conductivity of the solid electrolyte layer and deteriorates the ESR. Even if this method is used, since the solid electrolyte forming material is basically liquid, the edge portion of the capacitor anode body is always thinner than other parts due to the effect of surface tension at the time of formation. After all, it was not sufficient as a countermeasure for the deterioration of leakage current due to mechanical stress.

  Further, as is clear from Table 1, it can be seen that the example had better leakage current, higher capacitance, and reduced ESR, as compared with the conventional example 4.

  In the case of Conventional Example 4, it is possible to cope with mechanical stress to some extent by forming a protective resist layer with an epoxy resin or the like over the entire periphery of the edge portion of the capacitor anode body, but simply over the entire periphery. When the resist layer is formed, the formation of the solid electrolyte layer on the dielectric oxide film layer coated with the resist layer becomes insufficient, so that the electrostatic capacity is naturally greatly reduced and the ESR is also deteriorated. It is shown that. It can also be seen that the use of a material such as an epoxy resin can ensure insulation, but there is no effect of buffering stress and mechanical stress, and it is not sufficient for countermeasures against deterioration of leakage current.

  In addition, this invention is not limited to the said Example.

  (1) In the above embodiment, a fluoro rubber insulating resin having a viscosity of 3000 mPa · s is applied to all the vertices (total of 8 vertices) where the ridges of the three sides of the working metal element intersect with a syringe, and then dried and protruded. However, all of the vertices are not necessarily required, and the improvement effect is small, but the effect can be obtained by forming convex portions made of an insulating resin in at least one place. In addition, the viscosity is not limited to this, and the same effect can be obtained if a convex portion can be formed after drying. The size of the convex portion is not particularly limited, and the size of the capacitor anode body and the added machine Depending on the magnitude of the mechanical stress, it can be appropriately selected, but in general, a small spherical or small elliptical convex part having a volume of about 1/1000 to 1/50 of the anode body volume is preferable. Further, the insulating resin is not limited to the fluororubber system, and the same effect can be obtained if it is a material having elasticity. Also, the application method is not limited to a syringe, and any method that can apply a material with high viscosity may be used. Even if it is a method other than coating, the same effect can be obtained if a convex portion made of an insulating resin can be formed at the apex where the ridges of the three sides of the working metal element intersect.

  (2) In the above embodiment, the conductive polymer layer was formed by a method in which the capacitor anode body was immersed in a solution in which a monomer and an oxidant were mixed and subjected to chemical oxidative polymerization. However, the present invention is not limited to this, and the same effect can be obtained by any known conductive polymer layer forming method. In the above embodiment, 3,4-ethylenedioxythiophene is used as the conductive polymer for forming the solid electrolyte layer. However, the conductive polymer is not limited to this and is used for the solid electrolytic capacitor. Any of polythiophene, polypyrrole, polyaniline or their derivatives generally known as conductive polymers can be used.

  (3) Although a tantalum sintered body is used as the capacitor anode material, the same effect can be obtained by using a valve action metal sintered body such as niobium or aluminum or a roughened foil-like valve action metal. In the case of using a roughened foil-like valve action metal, it is more preferable to electrochemically etch the surface of an aluminum foil having a thickness of 0.1 mm.

  In addition, it is of course possible to make various design changes and modifications within the scope of the claims attached to this specification.

1 Anode lead 2 Valve metal element (capacitor anode)
3 Convex insulation resin formed at the apex where the ridges of the three sides intersect 4 Epoxy resin formed on the entire edge area (insulation)
5 Polymerization liquid for forming conductive polymer layer

Claims (4)

Dielectric oxidation of a sintered body obtained by sintering a molded body made of a valve action metal powder or a capacitor anode body in which a dielectric oxide film is formed on the surface of a roughened valve action metal foil. A solid electrolytic capacitor in which a solid electrolyte layer and a cathode lead layer are sequentially formed on the surface of the film,
The convex part which has the elasticity which consists of insulating resin is formed over 5-30% of the length of each ridgeline of the said capacitor anode body in all the vertices where the ridge of three sides in the said capacitor anode body crosses. A solid electrolytic capacitor.   The solid electrolytic capacitor according to claim 1, wherein the solid electrolyte layer is made of a conductive polymer. After forming a capacitor anode body by forming a dielectric oxide film on the surface of a sintered body obtained by sintering a molded body made of valve-acting metal powder or a roughened valve-acting metal foil, In the method of manufacturing a solid electrolytic capacitor in which a solid electrolyte layer and a cathode lead layer are formed on the surface of the dielectric oxide film,
Insulating resin covering all vertices where the ridges of the three sides of the capacitor anode body intersect before or after the formation of the dielectric oxide film over 5-30% of the length of each ridge line of the capacitor anode body The method for manufacturing a solid electrolytic capacitor is characterized in that an elastic material is used as the insulating resin when the protrusion is formed .   4. The method for producing a solid electrolytic capacitor according to claim 3, wherein when the solid electrolyte layer is formed, the capacitor anode body is immersed in a polymerization solution for forming a conductive polymer layer and then pulled up.

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