JP4944359B2 - 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 a conductive polymer as a solid electrolyte and a manufacturing method thereof.

  Conventionally, a solid electrolytic capacitor using a conductive polymer as a solid electrolyte for the purpose of lowering ESR is known. In general, these conductive polymers include polythiophene, polypyrrole, or polyaniline. Among them, polythiophene has attracted attention in recent years because it has higher electrical conductivity and thermal stability than polypyrrole or polyaniline. Some solid electrolytic capacitors using polythiophene as a solid electrolyte are disclosed in Patent Document 1 and the like.

  By the way, in recent years, electronic information devices have been digitized, and the driving voltage has been reduced and the driving current has been increased with the increase in driving frequency. In particular, the speed of the microprocessor, which is the heart of a personal computer, has been remarkably increased, and the driving voltage has been steadily decreasing. As a circuit for supplying high-precision power to such a microprocessor, a DC-DC converter called a voltage control module (VRM) is widely used.

  By the way, as the voltage of the microprocessor is lowered, the voltage range for guaranteeing the operation of the microprocessor is becoming narrower. The demand current of the microprocessor changes very fast depending on the situation imposed on the microprocessor. Therefore, the DC-DC converter alone cannot cope with the change, and a load capacitor is connected to the output side to cope with the load fluctuation of the microprocessor. is doing.

  The function required for such a load capacitor is that the equivalent series resistance (ESR) is small in order to reduce the loss. For this reason, even in a solid electrolytic capacitor used for such a load capacitor, further reduction in ESR is required. Examples of attempts to lower the ESR of such a solid electrolytic capacitor include those disclosed in Patent Document 2 and Patent Document 3.

  All of the solid electrolytic capacitors disclosed in the above-mentioned patent documents are obtained by improving the cathode layer formed on the solid electrolyte layer of the conventional solid electrolytic capacitor. That is, the conventional solid electrolytic capacitor has a structure in which a conductive carbon layer is formed on a solid electrolyte layer and a silver paste layer is further formed and connected to an external lead wire. In solid electrolytic capacitors disclosed in the literature, a silver paste layer is formed directly on the solid electrolyte layer without forming a conductive carbon layer.

In particular, in the solid electrolytic capacitor disclosed in Patent Document 2, by using silver having a small particle diameter, the contact area is reduced by increasing the contact area with respect to fine irregularities on the surface of the solid electrolyte layer, and the silver paste The electric resistance of the cathode layer is reduced by not using conductive carbon having a lower conductivity than that of.
JP-A-2-15611 JP-A-11-135377 JP 2001-68381 A

  The problems to be solved by the present invention are as follows. In other words, the solid electrolytic capacitor disclosed in the above-mentioned patent document can achieve a certain level of ESR reduction, but is not sufficient for further reduction in ESR. Moreover, it has become clear by the present inventors' research that there are the following problems.

  That is, as disclosed in Patent Document 2, in a solid electrolytic capacitor in which a conductive film layer in which some organic compounds are contained in metal fine particles having a particle size of 10 to 500 mm is formed, silver particles are fine on the surface of the solid electrolyte layer. Although the contact resistance can be reduced by expanding the contact area between the silver paste layer and the solid electrolyte layer as a whole, the binder component is removed when the silver paste is sintered. Then, microcracks are generated in the silver paste layer, and the contact frequency between silver particles is lowered. As a result, the resistivity of the silver paste layer was increased, and the ESR characteristics of the solid electrolytic capacitor could not be reduced as expected.

  The present invention has been proposed to solve the above-described problems of the prior art, and an object of the present invention is to provide a solid electrolytic capacitor capable of further reducing ESR and a method for manufacturing the same. .

In order to achieve the above object, the solid electrolytic capacitor according to claim 1 is made of a conductive material on a capacitor element in which an anodized film is formed on the surface of a sintered body obtained by sintering valve metal powder. A solid electrolyte layer made of a polymer is formed, and silver powder particles having an average particle size of 0.2 to 20 μm, silver nanoparticles having an average particle size of 1 to 100 nm, and a predetermined binder are formed on the conductive polymer layer. A silver layer having a three-dimensional matrix structure formed by sintering a silver paste formed by mixing is formed.

  The present inventors first examined the silver paste layer in the conventional solid electrolytic capacitor, and as a result, when nanoscale silver particles were used, the solid electrolyte layer adhered well to the fine irregularities on the surface of the solid electrolyte layer, and the contact resistance was reduced. However, it has been found that the contact frequency between silver particles in the silver paste increases and the contact resistance increases. As a result of further investigation, it was found that the above problem can be solved by mixing silver nanoparticles having an average particle diameter of 1 to 100 nm and silver powder particles having an average particle diameter of 0.2 to 20 μm. It is a thing.

  That is, by adhering silver powder particles having an average particle diameter of 0.2 to 20 μm in silver nanoparticles having an average particle diameter of 1 to 100 nm, the adhesion of the silver paste to the surface of the solid electrolyte layer is maintained. At the same time, when the silver paste is sintered, the silver nanoparticles and the silver powder particles are bonded in such a shape that they are cross-linked to form a three-dimensional matrix structure. Therefore, it has been found that the contact resistance between silver particles is reduced, and the ESR of the solid electrolytic capacitor can be further reduced.

The invention according to claim 1 is characterized in that the silver powder particles are mixed in a range of 150 to 10,000 parts by mass per 100 parts by mass of the silver nanoparticles.

As a result of studying various mixing ratios of silver nanoparticles and silver powder particles, the present inventors have found that the above ratio is the most effective for reducing the ESR of a solid electrolytic capacitor. It is. That is, if the addition amount of silver powder particles is less than 150 parts by mass per 100 parts by mass of silver nanoparticles, a three-dimensional matrix structure when the silver paste layer is sintered is not sufficiently formed, Electrical resistance increases. On the other hand, if the amount of silver powder particles exceeds 10000 parts by mass per 100 parts by mass of silver nanoparticles, the amount of silver nanoparticles in the silver paste becomes too small, and the contact area with respect to the surface of the solid electrolyte layer having a fine structure decreases. Contact resistance increases.

According to a second aspect of the present invention, in the solid electrolytic capacitor of the first aspect, the solid electrolyte layer is made of a conductive polymer formed by chemical polymerization.
When a conductive polymer formed by chemical polymerization is used as the solid electrolyte, the surface of the solid electrolyte layer has fine irregularities, so silver mixed with the silver powder particles and silver nanoparticles described above. When the paste is used, the effect of lowering the ESR becomes more remarkable.

According to a third aspect of the present invention, in the solid electrolytic capacitor of the second aspect , the conductive polymer is any one of polythiophene, polypyrrole, polyaniline, polyphenylene vinylene, and derivatives thereof.
The conductive polymer is a substance that can be polymerized by chemical polymerization and has high conductivity. Therefore, when a silver paste in which the above-described silver powder particles and silver nanoparticles are mixed is used for the cathode layer, a solid is obtained. A solid electrolytic capacitor that does not impair the good conductivity of the electrolyte can be realized.

The method for producing a solid electrolytic capacitor according to claim 4 includes: a solid electrolyte made of a conductive polymer on a capacitor element in which an anodized film is formed on the surface of a sintered body obtained by sintering valve metal powder. A layer is formed, and a silver paste obtained by mixing silver powder particles having an average particle diameter of 0.2 to 20 μm, silver nanoparticles having an average particle diameter of 1 to 100 nm, and a binder is applied on the conductive polymer layer. In addition, the conductive layer having a three-dimensional matrix structure is formed by sintering in a temperature range of 150 to 350 ° C.

  When silver paste particles having an average particle diameter of 0.2 to 20 μm, silver nanoparticles having an average particle diameter of 1 to 100 nm and a binder are applied, sintering is performed at a temperature range of 150 to 350 ° C. Therefore, microcracks are not generated in the sintered silver paste layer, and the resistivity of the silver paste layer is not increased. If the sintering temperature is lower than 150 ° C., the silver paste layer does not sinter. On the other hand, if the sintering temperature exceeds 350 ° C., polymer decomposition may occur in the conductive polymer. It causes deterioration of the properties of the polymer layer.

The invention according to claim 4 is characterized in that the amount of the silver powder particles added is in the range of 150 to 10,000 parts by mass per 100 parts by mass of the silver nanoparticles.
When the present inventors have had experimentally confirmed, the sintering temperature range, per 100 parts by weight of silver nanoparticles, it is effective when a range of the addition amount of 150 to 10,000 parts by weight of the silver particles.

  According to the present invention, it is possible to improve the ESR characteristics of a solid electrolytic capacitor. Moreover, the solid electrolytic capacitor which improved the ESR characteristic more can be obtained with the manufacturing method of the solid electrolytic capacitor which concerns on this invention.

Next, an embodiment of the present invention will be specifically described with reference to FIG.
In FIG. 1, a capacitor element 1 is formed by molding tantalum fine powder into a rectangular parallelepiped shape and sintering it. The capacitor element 1 is provided with an anode lead wire 8 made of tantalum and led to the outside. A dielectric oxide film is formed on the tantalum surface of the capacitor element 1 by a known method. In order to form such a capacitor element 1, a powder of valve action metal such as aluminum, niobium, titanium, etc. can be used in addition to tantalum.

In order to form the conductive polymer layer 2 on the capacitor element 1, the capacitor element 1 is first immersed in a polymerizable monomer solution. As this polymerizable monomer, thiophene or a derivative thereof is suitable. This is because thiophene or a derivative thereof has high conductivity and particularly excellent thermal stability as compared with polypyrrole or polyaniline, so that a solid electrolytic capacitor having low ESR and excellent heat resistance can be obtained. Examples of thiophene derivatives include the following structures.

  Among thiophene derivatives, 3,4-ethylenedioxythiophene is more preferable. Since 3,4-ethylenedioxythiophene produces poly- (3,4-ethylenedioxythiophene) (PEDT) by a gentle polymerization reaction when in contact with an oxidizing agent, 3,4-ethylenedioxy Polymerization can be performed in a state where the monomer solution of thiophene penetrates into the capacitor element having a fine structure. As a result, the conductive polymer layer can be formed even inside the capacitor element, and the capacitance of the solid electrolytic capacitor can be increased.

  The polymerizable monomer solution is obtained by diluting the polymerizable monomer as described above with a predetermined solvent. By diluting, the viscosity of the polymerizable monomer solution becomes low, and the polymerizable monomer easily penetrates into the capacitor element. Various organic solvents can be used as the solvent, but isopropyl alcohol is suitable when 3,4-ethylenedioxythiophene is used as the polymerizable monomer.

  After the capacitor element is immersed in the polymerizable monomer solution for a predetermined time, the capacitor element is pulled up and left in the air. By being left in the atmosphere, isopropyl alcohol, which is a solvent for the polymerizable monomer solution, is volatilized, and 3,4-ethylenedioxytheophene is attached to the capacitor element.

  Further, the capacitor element is immersed in an oxidant solution. As this oxidizing agent solution, a solution in which a persulfate such as ammonium persulfate or a sulfonate is dissolved in a predetermined solvent such as pure water can be used. By soaking in the oxidant solution, the polymerization of the polymerizable monomer proceeds and becomes a polymer.

  The conductive polymer is formed even inside the capacitor element by the process as described above. And the capacitor | condenser element which complete | finished superposition | polymerization of the conductive polymer is wash | cleaned with the flowing water by a pure water. Thereafter, the capacitor element is dried, and one polymerization is completed.

  The steps from the immersion in the polymerizable monomer solution to the drying as described above are repeated a plurality of times to obtain a conductive polymer layer having a desired thickness. When the conductive polymer layer is prepared by chemical polymerization in this way, it is difficult to control the direction in which the polymerization of the polymerizable monomer proceeds, so the surface of the prepared conductive polymer layer is fine. It will be uneven.

  Furthermore, after performing pure water washing and drying, a silver paste is applied on the conductive polymer layer 2. This silver paste is composed of silver powder particles having an average particle diameter of 0.2 to 20 μm, silver nanoparticles having an average particle diameter of 1 to 100 nm and a binder, and 150 to 10,000 parts by mass of the silver powder particles per 100 parts by mass of the silver nanoparticles. The silver paste mixed in the range is used. Since silver nanoparticles having an average particle diameter of 1 to 100 nm as described above are contained in the silver paste, they enter fine irregularities on the surface of the conductive polymer layer, and the contact area between the conductive polymer layer and the silver paste layer Will increase. In addition, as a binder, the organic binder etc. which have a resol type phenol resin as a main component are used.

  And a silver paste layer is sintered in the temperature range of 150-350 degreeC, and a conductive layer is formed. By this sintering, the adhesion of the silver paste to the surface of the solid electrolyte layer is maintained, and when the silver paste is sintered, the silver nanoparticles and the silver powder particles are bonded in a shape that crosslinks, and the three-dimensional A typical matrix structure is formed. For this reason, the contact resistance between the silver nanoparticles and the silver powder particles is reduced, and a conductive path formed only of silver is secured in the silver powder particles, and the resistivity of the entire silver paste layer 3 is reduced. . In addition, microcracks are not generated in the silver paste layer 3 in the above temperature range. Therefore, the conductive path is not blocked by the microcracks, and the resistivity of the silver paste layer 3 can be reduced also from this point.

  As described above, after the silver paste layer 3 is formed, the cathode lead terminal 5 is joined to the silver paste layer 3 with a conductive adhesive, and the anode lead terminal 4 is welded to the anode lead wire 8. Join by means. Further, a resin exterior is provided by transfer molding, and the cathode lead terminal 5 and the anode lead terminal 4 are bent at predetermined positions to complete a chip-shaped solid electrolytic capacitor.

Next, the present invention will be described based on more detailed examples.
(Example)
As a capacitor element, a tantalum sintered body having a size of 3.5 × 4.6 × 1.7 mm ³ was used, and an anode body using a tantalum wire as an anode wire was heated at 90 ° C. in a 0.05% phosphoric acid aqueous solution. The capacitor element was anodized at 20 V for 180 minutes, washed with running deionized water and dried.

  Next, this capacitor element is immersed in a monomer solution obtained by mixing 50 g of butanol and 50 g of 3,4-ethylenedioxythiophene for 7 minutes, and then ferric paratoluenesulfonate as an oxidizing agent containing transition metal ions. A conductive polymer layer was formed on the anodic oxide film constituting the capacitor element by immersing in 40 g of oxidant solution obtained by dissolving in 60 g of butanol for 15 minutes and performing chemical oxidative polymerization. And in order to remove the excess monomer and oxidant adhering to the capacitor element, it was washed with butanol for 5 minutes and then dried at 105 ° C. for 5 minutes. Next, the capacitor element was re-formed in a 0.4% phosphoric acid aqueous solution at 60 ° C. and 20 V for 30 minutes, washed with running deionized water and dried. Thereafter, the polymerization process from immersion in the monomer solution to drying was repeated four times until the polymer layer had a desired thickness.

  Next, a silver paste was applied on the conductive polymer layer of the capacitor element. This silver paste is obtained by adding 400 parts by mass of silver powder particles having an average particle diameter of 3.9 μm and silver nanoparticles having an average particle diameter of 5.0 nm to 100 parts by mass of silver nanoparticles. The silver paste which mixed 90 mass parts of organic binders which have a type phenol resin as a main component, and also added 100 mass parts of diethylene glycol dibutyl ether was used. And this silver paste was apply | coated directly on the conductive polymer layer.

  Thereafter, the anode wire is welded to the anode lead frame, the cathode lead frame is bonded to the silver paste layer, and the capacitor element coated with the silver paste is left at room temperature for 30 minutes, and then left at 180 ° C. for 1 hour. The silver paste layer was sintered. Further, the whole was molded with a resin, the anode external terminal and the cathode external terminal were cut from the lead frame, and bent along the resin sheath to obtain a chip-type solid electrolytic capacitor.

(Conventional example)
As a conventional example, a carbon layer is formed on a capacitor element that has been subjected to the formation of a conductive polymer layer in the same manner as in the examples, and further a silver paste layer in which silver powder having an average particle size of 5 μm is mixed with a binder is formed. A chip-type solid electrolytic capacitor formed in the same manner as in the example was prepared.

(Comparative Example 1)
As Comparative Example 1, a silver paste layer in which silver powder having an average particle size of 5 μm was directly mixed with a binder on the conductive polymer layer of the capacitor element which was formed up to the formation of the conductive polymer layer in the same manner as in the example. A chip-type solid electrolytic capacitor was prepared, and the subsequent steps were formed in the same manner as in the example.

(Comparative Example 2)
As Comparative Example 2, a silver paste in which silver nanoparticles having an average particle diameter of 5 nm were directly mixed with a binder on a conductive polymer layer of a capacitor element which was formed in the same manner as in the Examples until the formation of the conductive polymer layer A chip-type solid electrolytic capacitor in which a layer was formed and the subsequent steps were formed in the same manner as in the example was prepared.

(Test results)
Each solid electrolytic capacitor produced as described above was electrically measured. The results are shown in Table 1.

  As is apparent from Table 1, the conventional solid electrolytic capacitor is 15.4 mΩ, while the solid electrolytic capacitor of the embodiment of the present invention has an ESR of 11.4 mΩ, and the ESR characteristics are improved. I understood.

  On the other hand, Comparative Example 1 using only silver powder particles having an average particle diameter of 5 μm as a silver paste and Comparative Example 2 using only silver nanoparticles having an average particle diameter of 5 nm as a silver paste form a carbon layer on the solid electrolyte layer. Despite not doing so, the ESR characteristics deteriorated. This is considered to be due to the decrease in the contact area between the silver paste and the solid electrolyte layer in Comparative Example 1. Moreover, in the comparative example 2, it is thought that the electrical conductivity of the silver paste layer deteriorated due to microcracks generated in the silver paste layer.

  From the above results, it was confirmed that the solid electrolytic capacitor according to the present invention has improved ESR characteristics.

It is sectional drawing which shows the internal structure of a solid electrolytic capacitor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Capacitor element 2 ... Conductive polymer layer 3 ... Silver paste layer 4 ... Anode extraction terminal 5 ... Cathode extraction terminal 6 ... Resin exterior

Claims (4)

A solid electrolyte layer made of a conductive polymer is formed on the capacitor element on which the anodized film is formed on the surface of the sintered body formed by sintering the valve metal powder. In addition, silver powder particles having an average particle diameter of 0.2 to 20 μm and silver nanoparticles having an average particle diameter of 1 to 100 nm are mixed within a range of 150 to 10,000 parts by mass of silver powder particles per 100 parts by mass of silver nanoparticles. A solid electrolytic capacitor characterized in that a silver layer having a three-dimensional matrix structure is formed by sintering a silver paste formed by mixing a predetermined binder.   The solid electrolytic capacitor according to claim 1, wherein the solid electrolyte layer is made of a conductive polymer formed by chemical polymerization.   The solid electrolytic capacitor according to claim 2, wherein the conductive polymer is any one of polythiophene, polypyrrole, polyaniline, and polyphenylene vinylene. A solid electrolyte layer made of a conductive polymer is formed on a capacitor element in which an anodized film is formed on the surface of a sintered body obtained by sintering valve metal powder, and the conductive polymer layer is formed on the conductive polymer layer. In addition, silver powder particles having an average particle diameter of 0.2 to 20 μm and silver nanoparticles having an average particle diameter of 1 to 100 nm are mixed in a range of 150 to 10,000 parts by mass of silver powder particles per 100 parts by mass of silver nanoparticles. A method for producing a solid electrolytic capacitor, wherein a silver paste formed by mixing a predetermined binder is applied and sintered in a temperature range of 150 to 350 ° C. to form a conductive layer having a three-dimensional matrix structure .

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