JP5358422B2 - Solid electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid electrolytic capacitor which is low in rise of ESR and high in reliability. <P>SOLUTION: After an oxide coating of valve action metal is formed, as a dielectric layer, on a surface of a porous body made of a sintered body of the valve action metal and a conductive polymer layer is formed, as a solid electrolyte layer 5, on an anode body 3 through chemical oxidation polymerization, a graphite paste layer 6 is formed as a cathode lead-out layer. Further, a first silver paste layer 7 and a second silver paste layer 8 are formed as a cathode layer. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a solid electrolytic capacitor.

  Conventionally, in a solid electrolytic capacitor, a molded body obtained by molding a valve action metal powder from which an anode lead made of a foil or wire of valve action metal such as tantalum is drawn out is an anode body. The anode body is porous, and after forming a dielectric layer on the surface of the anode body and further forming a conductive polymer layer as a solid electrolyte layer thereon, a graphite paste layer is formed as a cathode lead layer. Form. Furthermore, as a cathode layer, a silver paste layer made of a conductive paste containing silver or the like in a fluorine-based elastomer is formed on the surface of the graphite paste layer to obtain a capacitor element. Thereafter, the capacitor element is connected to a lead frame that forms an external terminal for connection to an external substrate. And it molds to a product shape with exterior resin, leaving a part of external terminal.

  In Patent Document 1, in order to provide a chip-type solid electrolytic capacitor having excellent thermal shock resistance and long-term reliability in a high temperature environment, a silver paste layer using a thermosetting resin and a thermoplastic resin are used for the cathode layer of the capacitor element. It proposes forming the used silver paste layer in order.

  Patent Document 2 discloses a solid electrolyte in which a solid electrolyte layer made of a conductive polymer and a cathode layer are laminated in order to provide a solid electrolytic capacitor made of a conductive polymer that can suppress an increase in equivalent series resistance (ESR) even when left at high temperature. In a capacitor, a carbon paste layer mainly composed of carbon particles and a resin, and metal particles or carbon particles laminated on the carbon paste layer and a fluorine-based plastomer (plastomer: a polymer having plasticity like plastic) It has been proposed to have a cathode layer comprising an intermediate layer as a main component and a silver paste layer mainly composed of silver particles and resin laminated on the intermediate layer.

  In Patent Document 3, as a silver paste layer of a solid electrolytic capacitor, the first silver using a thermoplastic resin such as an acrylic resin as a binder in order to suppress the initial ESR reduction of the solid electrolytic capacitor and the increase in ESR after soldering. It has been proposed that a second silver paste layer using a thermosetting resin such as a phenol resin is formed on the paste layer to form a two-layered silver paste layer.

JP 2007-142160 A JP 2005-86125 A JP 2005-294385 A

  However, in the conventional technology, in the solid electrolytic capacitor, the adhesive strength between the silver paste layer and the exterior resin made of an epoxy resin provided on the outside of the silver paste layer, and the graphite paste that is the base of the silver paste layer and the silver paste layer When the adhesive strength with the layer is compared, the adhesive strength to the underlying graphite paste layer is weaker, so the silver paste layer is pulled by the exterior resin, causing peeling at the interface between the silver paste layer and the graphite paste layer, and the ESR is There was concern that it would grow.

  As an improvement method, it is desired to further improve the adhesive strength of a silver paste using a fluorine-based elastomer, but there is a limit and a sufficient one is not obtained.

  Furthermore, a silver paste using a thermoplastic acrylic resin was studied as a silver paste layer that can further increase the adhesive strength to the graphite paste layer. As a result, it was found that the adhesion with the graphite paste layer was improved, and the degree of peeling at the interface between the silver paste layer and the graphite paste layer was less than that of the fluorine elastomer silver paste layer. However, since the adhesive strength due to the adhesive strength between the silver paste layer and the epoxy resin of the exterior resin is still strong, it is necessary to study the structure and silver paste material that incorporates relaxation of stress from the mold due to thermal stress such as reflow. It had been.

  Accordingly, the present invention reexamines the structure and constituent materials of the silver paste layer placed between the graphite paste layer that serves as a cathode lead and the epoxy resin layer that is used as the exterior resin, thereby providing a first silver paste layer. To improve the adhesive strength with the graphite paste layer as a base, and the second silver paste layer absorbs stress from the mold due to thermal stress such as reflow and provides a solid electrolytic capacitor that suppresses the increase in ESR With the goal.

The solid electrolytic capacitor of the present invention includes an anode body having a porous surface made of a valve metal from which an anode lead is drawn, a dielectric layer formed on the surface of the anode body, and a surface of the dielectric layer. A solid electrolytic capacitor comprising a formed solid electrolyte layer made of a conductive polymer, a graphite paste layer and a silver paste layer sequentially formed on a surface of the solid electrolyte layer, wherein the silver paste layer is a first The first silver paste layer is made of a silver paste using a thermoplastic acrylic resin, and the second silver paste layer is a thermoplastic fluorine-based elastomer. made of silver paste using and adhesive strength to the graphite paste layer of silver paste constituting said first silver paste layer, constituting the second silver paste layer Being larger than the adhesive strength with respect to the graphite paste layer of a silver paste that.

  In the present invention, in the solid electrolytic capacitor, the silver paste layer constituting the cathode layer has a two-layer structure, and the first silver paste layer is a silver paste layer having a larger adhesive strength than the second silver paste layer, It becomes possible to suppress the interface peeling with the graphite paste layer due to the stress stress of the exterior resin at the time of reflow and to prevent the ESR from rising. Further, by using a silver paste using a binder having rubber-like properties for the second silver paste layer, it plays a role of absorbing stress stress of the exterior resin during reflow. The structure of the two silver paste layers prevents peeling of the interface of each layer of the capacitor element, and provides a low ESR solid electrolytic capacitor.

  Furthermore, in the solid electrolytic capacitor of the present invention, it has a sufficient adhesive strength to the graphite paste layer and an elastic state necessary to ensure the reliability of the product, and the structure of the two-layer silver paste layer It is preferable to use a silver paste using a thermoplastic acrylic resin as the first silver paste layer and a thermoplastic fluorine-based elastomer as the second silver paste layer because it has durability against heating during reflow.

Sectional drawing of the capacitor | condenser element used for the solid electrolytic capacitor of this invention. Sectional drawing of the solid electrolytic capacitor of this invention. Sectional drawing of the capacitor | condenser element used for the solid electrolytic capacitor of a prior art. Sectional drawing which shows the measuring method of the adhesive strength of a silver paste layer and a graphite paste layer.

  Embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 2 is a cross-sectional view of the solid electrolytic capacitor of the present invention.

  In the present invention, the formation process of the porous body 2 includes a process of preparing a valve action metal powder such as tantalum, pressing, and sintering. For powder preparation, a binder is added to and mixed with tantalum powder as a valve action metal in order to improve press formability. For pressing / sintering, the anode lead 2a is inserted into a mixed powder of tantalum and press-molded into a cylindrical shape or a rectangular parallelepiped shape. Next, the press-molded product is sintered in a high vacuum to form the porous body 2.

  The dielectric layer 4 is formed by immersing the porous body 2 made of tantalum as an anode in an electrolyte solution such as phosphoric acid together with the counter electrode, and applying a voltage to the dielectric layer 4 on the surface of the porous body 2. A tantalum oxide film is formed to form anode body 3.

  The solid electrolyte layer 5 is formed by chemical oxidative polymerization of polyaniline, polypyrrole, polythiophene, or the like on the inside of the anode body 3 formed in the previous step and on the dielectric layer 4 on the surface.

  As shown in FIG. 2, the cathode layer is formed by forming a graphite paste layer 6 on the solid electrolyte layer 5 as a cathode lead layer.

  Further, a first silver paste layer 7 is formed thereon. At this time, the first silver paste layer 7 has an adhesive strength higher than that of the second silver paste layer, and a thermoplastic resin that maintains a sufficient adhesive state with respect to the graphite paste layer 6 is used as a binder. The silver paste used as is used. Further, a second silver paste layer 8 is formed thereon. The second silver paste layer 8 uses a silver paste using a rubber-like thermoplastic resin as a binder.

Specifically, the first silver paste layer 7 is a silver paste using an acrylic thermoplastic resin, and the adhesive strength of the silver paste using the thermoplastic acrylic resin to the graphite paste layer is 19.6. It has been found that when it is in the range of × 10 ^{−6 to} 29.4 × 10 ⁻⁶ N / m ² , the adhesive state with the underlying graphite paste layer can be sufficiently maintained. The second silver paste layer 8 is a silver paste using a thermoplastic fluorine-based elastomer, and the adhesive strength of the silver paste using the thermoplastic fluorine-based lastmer is 14.7 × 10 ⁻⁶ to When it is within the range of 19.6 × 10 ⁻⁶ N / m ² , it can absorb the thermal stress generated during reflow.

  In addition, the measuring method of the adhesive strength of each silver paste layer described above is demonstrated with reference to FIG.

  FIG. 4 is a cross-sectional view showing a method for measuring the adhesive strength between the silver paste layer 15 and the graphite paste layer 16. This measurement method was performed with dimensions as close as possible to the product shape of the solid electrolytic capacitor in order to clarify the bond strength at the actual level.

  First, a rectangular parallelepiped plate made of copper having a length of 25 mm, a width of 10 mm, and a thickness of 0.5 mm (dimensional tolerance ± 0.02 mm) is prepared as a set, and the surface of one plate 13 (referred to as plate A) is prepared. A graphite paste layer 16 and a silver paste layer 15 were sequentially formed, and an epoxy resin corresponding to an exterior resin was further applied and sandwiched between the remaining one plate 14 (referred to as plate B), and the adhesive strength after thermosetting was quantified. .

  A specific configuration of the adhesive strength measurement sample will be described. The graphite paste layer 16 was formed in the range of 10 mm inward and 10 mm in width from the end of the length method of the plate A13. The graphite paste layer 16 was formed by liquid immersion so as to have a thickness of 10 μm to 15 μm. Thereafter, the silver paste layer 15 was immersed in the same area of the surface of the graphite paste layer 16 so as to have a thickness of 10 to 20 μm, and the temperature was set to 120 ° C. to 140 ° C. and cured for 1 hour. Further, an epoxy resin was applied to a range of the area where the silver paste layer 15 was formed with a thickness of 1.0 to 2.0 mm, and the plate B14 was adhered and cured at a temperature of 140 ° C. to 150 ° C. for 1 hour. In addition, the measurement sample of adhesive strength was produced for each five pieces by several levels.

  An end portion (length 10 mm) of the measurement sample plate A13 on which the graphite paste layer 16 and the silver paste layer 15 are not formed is fixed to a table having a gripping structure, and a plate B14 (10 ± 2 mm from the end portion) is fixed. Range) was pushed in with a push-pull gauge, and the adhesive strength was measured. The indentation speed was 10 mm / min. Furthermore, the measurement sample after measuring the adhesive strength was observed, and it was confirmed that peeling occurred at the interface between the graphite paste layer 16 and the silver paste layer 15. Therefore, the range of the adhesive strength described above was found by this measuring method.

  In addition, the range of the adhesive strength with respect to the graphite paste layer 16 of the obtained silver paste layer 15 is based on producing and evaluating several levels of silver paste. A plurality of silver paste levels were prepared by examining the content of each of the thermoplastic acrylic resin and the thermoplastic fluoroelastomer in a range where the silver paste can be used as an adhesive and can function.

  Thus, the contents of the embodiment are returned again.

  As shown in FIG. 2, the lead frame 10 on the anode side of the solid electrolytic capacitor is joined to the tip of the anode lead 2 a by spot welding, and the lead frame 10 on the cathode side is conductively connected to the second silver paste layer 8. Bonding is performed using an adhesive 9. Finally, the entirety is molded with the exterior resin 11 and the lead frame 10 is bent to complete a tantalum solid electrolytic capacitor having a structure as shown in FIG.

  Next, a more specific embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 is a sectional view of a capacitor element used in the solid electrolytic capacitor of the present invention, and FIG. 2 is a sectional view of the solid electrolytic capacitor of the present invention. As an example of the present invention, a solid electrolytic capacitor having a rated voltage of 2.5 V and a rated capacity of 220 μF was manufactured by the following process. Examples of the present invention are described in detail below.

Using tantalum powder (about 80 kCV / g: CV is the product of capacitance and rated voltage), the press density was adjusted to 6.0, dimensions 2.20 × 1.20 × 1.72 mm ³ A cuboid pressed body was produced. There, a tantalum wire (diameter 0.34 mm) is embedded. The pressed body was sintered at about 1250 ° C. to produce a porous body 2.

  The porous body 2 made of tantalum is used as an anode, immersed in an electrolyte such as phosphoric acid at 0.6 mass% and 85 ° C. together with the counter electrode, and a voltage of 6.5 V is applied to the surface of the porous body 2. A tantalum oxide film to be the dielectric layer 4 was formed, and this was used as the anode body 3.

  Next, the anode body 3 was immersed in an oxidant solution. As the oxidizing agent solution, a solution in which 20 mass% of a sulfonate was dissolved in a predetermined solvent such as pure water was used.

  After being immersed in an oxidizing agent aqueous solution for 5 minutes, the anode body 3 was pulled up from the oxidizing agent solution and further allowed to stand at room temperature for 30 minutes. Then, after immersing in 3,4-ethylenedioxythiophene as a polymerizable monomer solution for 1 second, the anode body 3 was pulled up from the polymerizable monomer solution and allowed to stand at room temperature for 60 minutes for chemical oxidative polymerization. .

  In order to obtain the capacitor element in this way, after forming a conductive polymer layer on the anodized film constituting the inside of the anode body 3, the polythiophene and acrylic resin mixed in a weight ratio of 1: 1 are dispersed in diethylene glycol. The solid electrolyte layer 5 inside the capacitor element was formed by immersing in a conductive polymer solution having a solid content of 5 mass% and a viscosity adjusted to 100 mPa · s for 1 minute and then drying at 150 ° C. for 30 minutes.

  It was immersed again in the oxidizing agent solution. As the oxidizing agent solution, a solution in which 35 mass% of sulfonate was dissolved in a predetermined solvent such as ethyl alcohol was used.

  After being immersed in the oxidant solution for 1 minute, the anode body 3 was pulled up from the oxidant solution and further allowed to stand at room temperature for 60 minutes. Then, after being immersed in 3,4-ethylenedioxythiophene as a polymerizable monomer solution for 1 second, it is pulled out from the polymerizable monomer solution and left at room temperature for 60 minutes to perform chemical oxidative polymerization. The solid electrolyte layer 5 was formed.

  Next, a graphite paste layer 6 was formed on the solid electrolyte layer 5 of the capacitor element so as to be 10 to 15 μm by liquid immersion.

  Furthermore, in order to form the 1st silver paste layer 7 on it, liquid immersion was carried out so that the thickness of the silver paste using a thermoplastic acrylic resin might be 10-20 micrometers, and it dried at 140 degreeC for 60 minutes. Then, in order to form the 2nd silver paste layer 8, it immersed in the liquid so that the thickness of the silver paste using a thermoplastic fluorine-type elastomer might be 10-20 micrometers, and dried at 130 degreeC for 30 minutes.

In addition, the adhesive strength of the silver paste using the thermoplastic acrylic resin which comprises the 1st silver paste layer 7 used for this sample preparation is a thing of 24.5 * 10 < ^-6 > N / m < ² >, 2nd The adhesive strength of the silver paste using the thermoplastic fluorine-based elastomer constituting the silver paste layer 8 was 17.6 × 10 ⁻⁶ N / m ² .

  Next, the anode side lead frame 10 was joined to the tip of the anode lead 2 a by spot welding, and the cathode side lead frame 10 was joined to the second silver paste layer 8 by the conductive adhesive 9. Finally, the whole was molded with the exterior resin 11 and the lead frame 10 was bent along the exterior resin to complete 50 solid electrolytic capacitors 1.

(Comparative example)
As a comparative example, 50 solid electrolytic capacitors, which are conventional techniques, were also produced. As described above, the sample of the comparative example is a one-layer structure of the silver paste layer using the silver paste using the thermoplastic fluorine-based elastomer, and the other manufacturing steps are the same as the steps of the embodiment of the present invention. Same as above.

  The solid electrolytic capacitor of the present invention manufactured as described above and the conventional solid electrolytic capacitor were mounted in a reflow bath, and the ESR before and after the reflow was measured by a known method. The results are shown in Table 1. As the reflow conditions, the temperature was set at a peak of 260 ° C., and a keep temperature of 240 ° C. for 20 seconds.

測定周波数：１００ｋＨｚ

Measurement frequency: 100 kHz

  From Table 1, it can be seen that the solid electrolytic capacitors manufactured in the examples of the present invention have lower ESR and a lower rate of increase than the solid electrolytic capacitors of the prior art. Further, as a result of observation with a magnifying glass, no peeling of the interface between the graphite paste layer 6 and the first silver paste layer 7 due to the stress of thermal history, which was a concern, was not observed, and the bonding of the first silver paste layer 7 was not observed. The effect of the present invention using a thermoplastic acrylic resin having high adhesive strength as the agent can be seen.

  The embodiments of the present invention have been described above using the embodiments. However, the present invention is not limited to these embodiments, and the present invention is not limited to the scope of the present invention. Included in the invention. That is, various changes and modifications that can be naturally made by those skilled in the art are also included in the present invention.

DESCRIPTION OF SYMBOLS 1 Solid electrolytic capacitor 2 Porous body 2a Anode lead 3 Anode body 4 Dielectric layer 5 Solid electrolyte layer 6, 16 Graphite paste layer 7 First silver paste layer 8 Second silver paste layer 9 Conductive adhesive 10 Lead frame 11 Epoxy exterior resin 12 Push-pull gauge 13 Plate A
14 Board B
15 Silver paste layer

Claims (1)

An anode body having a porous surface made of a valve metal from which an anode lead is drawn, a dielectric layer formed on the surface of the anode body, and a conductive polymer formed on the surface of the dielectric layer A solid electrolytic capacitor comprising a solid electrolyte layer, a graphite paste layer and a silver paste layer sequentially formed on the surface of the solid electrolyte layer, wherein the silver paste layer includes a first silver paste layer and a second silver paste layer; The first silver paste layer is made of a silver paste using a thermoplastic acrylic resin, and the second silver paste layer is made of a silver paste using a thermoplastic fluorine-based elastomer, And the adhesive strength of the silver paste constituting the first silver paste layer to the graphite paste layer is such that the graphite of the silver paste constituting the second silver paste layer The solid electrolytic capacitor being greater than the adhesive strength of the paste layer.

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