JP2005109247A - Solid electrolytic capacitor and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To further reduce the ESR characteristics of a solid electrolytic capacitor which uses a conductive polymer as a solid electrolyte. <P>SOLUTION: In a capacitor element, in which an oxidized dielectric coating film is formed on the surface of a sintered compact obtained by sintering the powder of a valve-action metal, a solid electrolyte layer composed of the conductive high polymer is formed. In addition, a cathode layer is formed, by applying a mixed paste of silver oxide nanoparticles and an organic silver compound to the electrolyte layer and successively subjecting it to first heat treatment within a temperature range of 150-160°C and second heat treatment within a temperature range of 170-190°C. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a solid electrolytic capacitor, and more particularly to a solid electrolytic capacitor using a conductive polymer as a solid electrolyte and a method for manufacturing the same.

  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, polyaniline, etc. Among them, polythiophene has attracted attention in recent years because it has higher electrical conductivity and thermal stability than polypyrrole or polyaniline. JP-A-2-15611 discloses a solid electrolytic capacitor using polythiophene as a solid electrolyte.

  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 the 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. A DC-DC converter called a voltage control module (VRM) is widely used as a circuit for supplying high-precision power to such a microprocessor.

  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. 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.

  One method for reducing the ESR of a solid electrolytic capacitor is to improve the cathode layer formed on the solid electrolyte layer. That is, there are cathode layers in which a carbon layer is formed on a solid electrolyte and a silver paste layer is formed thereon to form a cathode layer, and a silver paste layer is directly formed on the solid electrolyte layer. In any case, however, a silver paste layer is indispensable for a solid electrolytic capacitor. This is because the capacitor element is a porous body, and in order to increase the capacitance of the solid electrolytic capacitor, it is necessary to increase the contact area of the dielectric oxide film on the surface of the capacitor element with silver paste. .

  Thus, attempts have been made to reduce the ESR of the solid electrolytic capacitor by improving the conductivity of the cathode layer.

  In general, the silver paste used for the cathode layer of a solid electrolytic capacitor is obtained by dispersing silver particles as a conductive material in a resin or the like, and is roughly classified into a high-temperature fired type and a polymer type. In the high-temperature firing mold, the silver particles are fused to form a continuous conductive film by heating to about 500 to 900 ° C., and conductivity is obtained. On the other hand, the polymer type contains a resin for the purpose of improving the coating property, improving the dispersibility of the silver particles and improving the adhesion to the substrate, and is heated by a temperature of about 200 ° C. from room temperature. By curing, the metal particles come into contact with each other at the same time to form a conductive film, and the conductivity appears.

With regard to such a silver paste, there has heretofore been known an improved cathode layer for the purpose of reducing the ESR of a solid electrolytic capacitor. For example, Japanese Patent Application Laid-Open No. 11-135377 discloses a technique for forming a conductive film layer having a film thickness of 0.01 to 5 μm in which some organic compounds are contained in metal fine particles having a particle diameter of 10 to 500 mm on an electrolyte layer. Has been.
JP-A-11-135377

  In the technique disclosed in Japanese Patent Application Laid-Open No. 11-135377, a heat treatment at 150 to 300 ° C. is required to form a conductive film layer, and although the heat treatment temperature can be set low, it is classified as a high-temperature sintered silver paste. Is done. It is disclosed that since the conductive layer is made of metal except for some organic compounds, ESR does not deteriorate even when heated, so that it can be made excellent in heat resistance.

  However, the technique disclosed in Japanese Patent Application Laid-Open No. 11-135377 is considered effective when used in a solid electrolytic capacitor using, for example, manganese dioxide having high heat resistance as a solid electrolyte. In the solid electrolytic capacitor used as the solid electrolyte, the conductive polymer itself may be deteriorated by the heat treatment, and the conductivity of the conductive polymer may be lowered. Therefore, the technique disclosed in JP-A-11-135377 is disclosed. It was difficult to use as it was.

  Therefore, in a solid electrolytic capacitor using a conductive polymer as a solid electrolyte, it is conceivable to form a cathode layer using a polymer-type silver paste having a low heat treatment temperature, but the polymer-type silver paste contacts silver particles. Therefore, it has the disadvantage of poor electrical conductivity compared to the high-temperature firing type silver paste that fuses silver particles together, and does not fully meet the demand for low ESR of solid electrolytic capacitors. It was.

  In this invention, a solid electrolytic capacitor capable of reducing ESR by using a silver paste having a low heat treatment temperature and good conductivity so that a conductive polymer can be used for a solid electrolytic capacitor used as a solid electrolyte, And a method for manufacturing such a solid electrolytic capacitor.

  The solid electrolytic capacitor of the present invention includes a capacitor element in which a dielectric oxide film is formed on the surface of a sintered body obtained by sintering valve metal powder, a solid electrolyte layer made of a conductive polymer, a carbon layer, and a silver paste layer. In the solid electrolytic capacitor formed by sequentially forming, a solid electrolyte layer is formed, a mixed paste of silver oxide nanoparticles and an organic silver salt compound is applied, and a cathode layer is further heat-treated in a temperature range of 150 to 200 ° C. It is characterized by that.

  Further, the present invention provides a solid electrolytic layer comprising a conductive polymer on a capacitor element in which a dielectric oxide film is formed on the surface of a sintered body obtained by sintering valve metal powder as a method for producing a solid electrolytic capacitor, In the method for producing a solid electrolytic capacitor in which the cathode layer is formed in sequence, the cathode layer is formed by applying a mixed paste of silver oxide nanoparticles and an organic silver compound and further performing a heat treatment at a temperature range of 150 to 200 ° C. It is characterized by that.

  Silver oxide nanoparticles contained in the mixed paste are reduced from silver oxide to silver when heated to 150 ° C. or higher. At this time, the reduced nano-sized silver particles are fused with each other to form a porous silver coating film having a three-dimensionally fused structure. Moreover, an organic silver compound decomposes | disassembles in the temperature range of 150-200 degreeC, and becomes an organic substance component and silver. The decomposed organic component is volatilized by being heated, and only the silver component remains. This remaining silver component becomes very active silver fine particles. In a mixture of these silver oxide particles and an organic silver compound, silver particles obtained by reduction of silver oxide are fused, but as described above, the particles are porous and have gaps. Thus, the gap is filled with silver decomposed from the organic silver compound, and a dense silver paint film is formed. As described above, since the silver is fused and the gap is further filled, the conductive path is sufficiently formed, and the conductivity of the cathode layer is improved.

  Further, since the heat treatment is performed in a relatively low temperature region of 150 to 200 ° C., even when the conductive polymer is used for the solid electrolyte, the conductive polymer is not deteriorated.

  It is preferable that after the first heat treatment is performed in the temperature range of 150 to 160 ° C., the second heat treatment is performed in the temperature range of 170 to 190 ° C.

  When heat treatment is performed at a temperature of 170 to 190 ° C., rapid sintering and gas volatilization proceed inside the cathode layer, and the surface irregularity of the cathode layer increases, causing an increase in contact resistance with the lead frame. And in some cases, microcracks are generated in the cathode layer, and the conductive path of the cathode layer is interrupted, thereby deteriorating the conductivity of the cathode layer itself. As a result, the ESR of the solid electrolytic capacitor is increased. I might let you. On the other hand, when heat treatment at 150 to 160 ° C. is performed, some organic components remain without being volatilized, and thus remain as black spots on the surface of the silver paste layer. The remaining organic component increases the contact resistance with the lead frame to which the cathode layer is connected, resulting in an increase in ESR of the solid electrolytic capacitor.

  Therefore, the first heat treatment is performed in a temperature range of 150 to 160 ° C., and sintering is performed so that unevenness and microcracks are not formed on the surface of the cathode layer. Furthermore, the organic component remaining on the surface of the cathode layer is volatilized by a heat treatment at 170 to 190 ° C., so that the appearance shape of the cathode layer is good, and there are no microcracks inside. A cathode layer with good adhesion can be obtained.

  In the present invention, even a solid electrolytic capacitor using a conductive polymer as a solid electrolyte can form a highly conductive cathode layer without impairing the conductivity of the conductive polymer. Can be achieved.

  Next, an embodiment of the present invention will be described with reference to FIG.

  Capacitor element 1 is formed by molding tantalum fine powder into a rectangular parallelepiped shape and sintering. An anode lead wire 8 made of tantalum is implanted in the capacitor element 1 and led out to the outside. A dielectric oxide film is formed on the surface of tantalum of the capacitor element 1 by dipping in an aqueous phosphoric acid solution and anodizing.

  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.

  The polymerizable monomer in such a polymerizable monomer solution is preferably thiophene or a derivative thereof. Examples of thiophene derivatives include the following structures. Such a thiophene or a derivative thereof has a high electrical conductivity and a particularly excellent thermal stability as compared with polypyrrole or polyaniline, so that a solid electrolytic capacitor having a low ESR and excellent heat resistance can be obtained.

X is O or S
When X is O, A is alkylene or polyoxyalkylene When at least one of X is S,
A is alkylene, polyoxyalkylene, substituted alkylene, substituted polyoxyalkylene: wherein the substituent is an alkyl group, alkenyl group, alkoxy group

  Among the thiophene derivatives, 3,4-ethylenedioxythiophene is preferably used. 3,4-Ethylenedioxythiophene produces poly- (3,4-ethylenedioxythiophene) (PEDT) by a gentle polymerization reaction when in contact with an oxidizing agent. 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 above polymerizable monomer 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. Although various organic solvents can be used as the solvent, isopropyl alcohol is suitable when 3,4-ethylenedioxythiophene is used as the polymerizable monomer.

  After immersing the capacitor element in the polymerizable monomer solution for a predetermined time, the capacitor element is pulled up from the polymerizable monomer solution and left in the air. By leaving in the air, the isopropyl alcohol of the polymerizable monomer solution is volatilized and 3,4-ethylenedioxythiophene is attached to the capacitor element.

  Further, the capacitor element is immersed in an oxidant solution. As the oxidizing agent solution, a solution obtained by dissolving a persulfate such as ammonium persulfate or a sulfonate 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 up to the inside of 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 to obtain a solid electrolyte layer.

  Since the capacitor element is a porous body, the inside of the capacitor element may not be completely filled even after the solid electrolyte layer is formed, and has a structure having a gap. Moreover, since it is difficult to control the direction in which chemical polymerization proceeds in a conductive polymer layer formed by chemical polymerization, the conductive polymer layer has a structure with fine irregularities on the surface.

  Furthermore, after performing pure water washing and drying, a silver paste is applied on the solid electrolyte layer 2. This silver paste is a mixed paste in which silver oxide nanoparticles are added at a ratio of 4.0 and silver neodecanoate which is an organic silver compound is added at a ratio of 3.0 and mixed in a predetermined organic solvent.

  In addition, as an organic silver compound used for a silver paste, the silver salt of tertiary fatty acids, such as pivalic acid, neoheptanoic acid, neononanoic acid other than silver neodecanoate, can be used.

  Since the silver oxide of this silver paste is nano-sized fine particles, the gap between the capacitor elements described above enters the surface irregularities, and a sufficient contact area with the solid electrolyte layer can be secured.

  Then, the silver paste layer is first sintered at a temperature range of 150 to 160 ° C. for 30 minutes to cure the silver paste layer. And the residual organic component on the surface of a silver paste layer is volatilized by heat-processing for 30 minutes in the temperature range of 170-190 degreeC.

  By this heat treatment, the silver particles are fused to each other, a conductive path is secured inside the silver paste layer, and the conductivity of the entire silver paste layer 3 is improved. 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 wire 5 is joined to the silver paste layer 3 with a conductive adhesive, and the anode lead wire 4 is attached to the anode wire drawn from the anode body. Join by means such as welding. Further, the resin sheath 6 was applied by transfer molding, and the cathode lead wire and the anode lead wire were bent at predetermined positions to complete a chip-shaped solid electrolytic capacitor.

  In the above embodiment, an example in which a silver paste layer is directly applied to a solid electrolyte layer made of a conductive polymer layer to form a cathode layer is shown. However, as shown in FIG. A cathode layer may be formed by forming a carbon layer thereon and further forming a silver paste layer thereon.

  The carbon layer can be formed by applying and drying a carbon paste in which carbon powder and a resin binder are mixed. When the carbon layer is formed, the resin binder of the carbon layer acts to improve the adhesion strength between the solid electrolyte layer and the carbon layer, and between the carbon layer and the silver paste layer, and the solid electrolyte layer, carbon layer, silver The paste layer adheres firmly. As a result, even if a solid electrolytic capacitor is subjected to a thermal load or used for a long time, the contact resistance at the interface of each layer does not increase, and the ESR characteristics are deteriorated when the solid electrolytic capacitor is used as a whole. Can be reduced.

Next, a description will be given based on a more specific embodiment of the present invention.
A tantalum sintered body having a size of 1.0 × 3.5 × 4.9 mm ³ was used as a capacitor element, and a sintered body using a tantalum wire as an anode wire was heated to 90 ° C. with 0.4% phosphorous. Anodization was performed by applying a DC voltage of 15 V in an acid aqueous solution for 240 minutes, and after completion, washing was performed with running deionized water, followed by drying to obtain a capacitor element.

  Next, this capacitor element is immersed for 7 minutes in a monomer solution obtained by mixing 50 g of isopropyl alcohol and 50 g of 3,4-ethylenedioxythiophene, and then p-toluenesulfonic acid 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 ferric 40 g of butanol in an oxidant solution obtained for 15 minutes, followed by 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 is re-formed in a 0.4% phosphoric acid aqueous solution heated to 60 ° C. by applying a DC voltage of 13 V for 30 minutes to repair defects in the film, and then deionized. It was washed with running water and dried. Thereafter, the number of polymerizations until dipping and drying in the monomer solution was repeated 4 times until the polymer layer had a desired thickness.

  Next, a silver paste was applied on the conductive polymer layer of the capacitor element. As this silver paste, Dotite (trade name) XA-9501 manufactured by Fujikura Kasei Co., Ltd. was used as it was.

  After the silver paste was applied to the capacitor element, heat treatment was performed at 150 ° C. for 30 minutes, and then heat treatment was performed at 180 ° C. for 30 minutes to cure the silver paste layer.

  Further, the anode wire is welded to the anode lead frame, and the cathode lead frame is joined to the silver paste layer with a conductive adhesive. Then, the entire capacitor element is molded with resin, the lead frame is cut at a predetermined position to form an anode external terminal and a cathode external terminal, and the external terminal is bent along the resin sheath to obtain a chip-type solid electrolytic capacitor. .

  In the same manner as in Example 1, a capacitor element was formed up to a solid electrolyte layer made of a conductive polymer, and a carbon layer was further formed on the solid electrolyte layer.

  Next, a silver paste was applied on the carbon layer of the capacitor element. As this silver paste, Dotite (trade name) XA-9501 manufactured by Fujikura Kasei Co., Ltd. was used as it was.

  After the silver paste was applied to the capacitor element, heat treatment was performed at 150 ° C. for 30 minutes, and then heat treatment was performed at 180 ° C. for 30 minutes to cure the silver paste layer.

  Further, the anode wire is welded to the anode lead frame, and the cathode lead frame is joined to the silver paste layer with a conductive adhesive. Then, the entire capacitor element is molded with resin, the lead frame is cut at a predetermined position to form an anode external terminal and a cathode external terminal, and the external terminal is bent along the resin sheath to obtain a chip-type solid electrolytic capacitor. .

(Conventional example)
As a conventional example, a conductive polymer layer was formed in the same manner as in Example 2, and after further forming a carbon layer on the capacitor element, silver powder having an average particle size of 5 μm was further mixed with a binder on the carbon layer. A cathode paste was formed by applying a silver paste, further heat-treating and curing at 200 ° C., and a chip-type solid electrolytic capacitor in which the subsequent steps were formed in the same manner as in the examples was prepared.

(Test results)
The initial electrical measurement of the solid electrolytic capacitor produced as described above and the electrical characteristics after applying thermal stress under the solder reflow conditions (250 ° C., 5 seconds) were performed. The results are shown in the following table.

  As can be seen from the results shown in Table 1, it can be seen that the solid electrolytic capacitors of Examples 1 and 2 manufactured by the manufacturing method of the present invention have lower ESR than the solid electrolytic capacitors of the conventional examples. . In addition, compared to Example 2 in which a carbon layer was formed on a solid electrolyte layer, Example 1 in which a silver paste layer was formed directly on a solid electrolyte layer without forming a carbon layer was more effective for a solid electrolytic capacitor. It can be seen that ESR is reduced. However, in Example 2, the ESR value is not significantly different between before and after reflow, but in Example 1, the increase in ESR after reflow is larger than that in Example 2. Therefore, it can be evaluated that Example 2 is superior in terms of thermal stability.

It is sectional drawing which shows the internal structure of a solid electrolytic capacitor, and shows the solid electrolytic capacitor of the structure comprised only by the silver paste layer, without forming a carbon layer as a cathode layer. It is sectional drawing which shows the internal structure of a solid electrolytic capacitor, and shows the solid electrolytic capacitor of the structure comprised from the carbon layer and the silver paste layer as a cathode layer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Capacitor element 2 Conductive polymer layer 3 Carbon layer 4 Silver paste layer 5 Anode lead wire 6 Cathode lead wire 7 Exterior resin

Claims (3)

Solid electrolysis by sequentially forming a solid electrolyte layer composed of a conductive polymer, a carbon layer and a silver paste layer on a capacitor element in which a dielectric oxide film is formed on the surface of a sintered body obtained by sintering valve metal powder. In the capacitor
A solid electrolytic capacitor, wherein after forming a solid electrolyte layer, a mixed paste of silver oxide nanoparticles and an organic silver compound is applied, and a cathode layer is further heat-treated in a temperature range of 150 to 200 ° C. Solid electrolysis by sequentially forming a solid electrolyte layer composed of a conductive polymer, a carbon layer and a silver paste layer on a capacitor element in which a dielectric oxide film is formed on the surface of a sintered body obtained by sintering valve metal powder. In the method of manufacturing a capacitor,
A solid electrolytic capacitor characterized in that after forming a solid electrolyte layer, a mixed paste of silver oxide nanoparticles and an organic silver compound is applied, and further a heat treatment is performed in a temperature range of 150 to 200 ° C. to form a cathode layer. Manufacturing method. 3. The solid electrolysis according to claim 2, wherein after the first heat treatment is performed in a temperature range of 150 to 160 ° C., the second heat treatment is performed in a temperature range of 170 ° C. to 190 ° C. 4. Capacitor manufacturing method.