JP2005082636A - Electrically conductive coating and solid electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrically conductive coating for solid electrolytic capacitors, excellent in leveling tendency and electrical conductivity and high in coating film strength, and to provide a solid electrolytic capacitor whose cathode is formed using this coating. <P>SOLUTION: The electrically conductive coating essentially comprises (A) an electrically conductive filler, (B) an alicyclic epoxy resin, (C) an organic solvent or monomer and (D) sulfonium salts of the respective general formulas(1) and (2)( in the formula(1), X is CH<SB>3</SB>, H, a halogen atom or NO<SB>2</SB>; and M is Sb, As or P; in the formula(2), R<SP>1</SP>and R<SP>2</SP>are each an alkyl, halogen atom or H; R<SP>3</SP>is an ether or ester group; and A<SP>-</SP>is SbF<SB>6</SB><SP>-</SP>, AsF<SB>6</SB><SP>-</SP>, PF<SB>6</SB><SP>-</SP>or CH<SB>3</SB>SO<SB>4</SB><SP>-</SP>). In this coating, the amount of the electrically conductive filler(A) is 60-85 wt.% in terms of the weight ratio[ the electrically conductive filler/(resin solids+electrically conductive filler) ] and the amount of the sulfonium salts(D) is 0.1-10 pt(s). wt. based on 100 pts. wt. of the alicyclic epoxy resin(B). The solid electrolytic capacitor whose cathode layer is formed using this coating is also provided. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a conductive paint for forming a cathode of a solid electrolytic capacitor and a solid electrolytic capacitor formed using the paint.

    The solid electrolytic capacitor to which the present invention relates is conventionally a chemical conversion treatment of an anode body made of a metal having a valve action such as tantalum, aluminum, niobium, etc., a dielectric layer is formed on the surface, and a semiconductor is further formed on the surface Forming a layer, a carbon layer, and a cathode layer sequentially, and bonding and fixing the cathode layer to the cathode lead frame using a conductive adhesive, and connecting the anode body lead leading to the anode body to the anode lead frame by welding; Furthermore, the outer peripheral surface is constituted by an exterior resin.

  However, the conventional cathode layer is formed of a conductive paste mainly composed of a normal silver-based conductive paint, and has a drawback that the surface portion of the cathode layer is thick and the corner portion is thin because of its low leveling property. It was. That is, when the solid electrolytic capacitor is entirely rounded and the outer peripheral surface is covered with the exterior resin, the exterior resin layer is formed into a rectangular parallelepiped, resulting in a large variation in the thickness of the exterior resin layer. The variation in the thickness of the outer resin layer is considered to cause unevenness in volume change of the outer resin layer when the solid electrolytic capacitor is subjected to a thermal load, causing stress on each layer inside the capacitor, leading to capacitor failure. It is done. Furthermore, since the thickness of the exterior resin layer should not have an extremely thin portion, it must be formed with reference to the thickest portion of the cathode layer. It was an obstacle to reducing the size of itself.

  Until now, in order to solve the variation in thickness of the cathode layer, a method of using a conductive paint using a polyimide resin or a polyamideimide resin has been studied. However, a cathode layer formed of a conductive paint using these resins is uniform in thickness but very fragile. If the cathode layer is brittle, the cathode lead frame may be peeled off in the capacitor manufacturing process after the cathode lead frame is bonded.

  As described above, it has been difficult to develop a conductive paint that makes the coating film uniform and strong. Furthermore, in recent years, as electronic devices have processed a large amount of digital information at a high clock frequency, there has been a strong demand for high frequency impedance for solid electrolytic capacitors, and the conductive paint used therefor has a stable and high conductivity. Improvement of electrical joint reliability has been demanded.

  An object of the present invention is to solve the above-mentioned drawbacks, and has a leveling property for forming a uniform coating film at the time of forming a capacitor cathode layer, and has a strong coating film after curing. An object of the present invention is to provide a conductive paint having high adhesion reliability at the time of bonding a lead frame and having higher conductivity, and further to provide a solid electrolytic capacitor having high reliability using the conductive paint.

  As a result of earnest research to achieve the above-mentioned object, the present inventor has achieved solid level electrolysis with excellent leveling properties, high coating strength, and excellent electrical bonding reliability by using the composition described later. It has been found that a conductive paint for forming a capacitor cathode can be obtained, and the present invention has been completed.

を必須成分とし且つ、（Ａ）導電性充填剤を（導電性充填剤／（樹脂の固形分＋導電性充填剤））の比率で６０〜８５重量％、（Ｄ）スルホニウム塩を（Ｂ）脂環式エポキシ樹脂１００重量部に対し０．１〜１０重量部含有することを特徴とする導電性塗料であり、またその導電性塗料を用いて陰極層が形成されてなることを特徴とする固体電解コンデンサである。 That is, the present invention
A dielectric layer, a semiconducting electrolyte layer, a carbon layer, and a cathode layer are sequentially formed on an anode body made of a metal having a valve action, and the cathode layer and the cathode frame (terminal) are connected with a conductive adhesive, and the resin is It is a conductive paint for forming a cathode in a solid electrolytic capacitor to be used and is (A) a conductive filler, (B) an alicyclic epoxy resin, (C) an organic solvent or monomer, (D) the following general formula 1 Sulfonium salts and

And (A) a conductive filler in a ratio of (conductive filler / (resin solid content + conductive filler)) of 60 to 85% by weight, (D) a sulfonium salt (B) It is a conductive paint characterized by containing 0.1 to 10 parts by weight with respect to 100 parts by weight of an alicyclic epoxy resin, and a cathode layer is formed using the conductive paint. It is a solid electrolytic capacitor.

  The conductive paint used in the present invention is excellent in leveling and conductivity, and has high adhesive strength. By using this conductive paint for forming the cathode of the solid electrolytic capacitor, it is possible to improve the electrical and physical bonding reliability.

  Hereinafter, the present invention will be described in detail.

  Examples of the conductive filler (A) used in the present invention include silver powder, silver-coated copper powder having a silver layer on the surface, copper powder, nickel powder, and the like. They can be used in combination. Here, the conductive filler needs to contain at least a conductive filler having a silver layer on the surface, such as silver powder and silver-coated copper powder. The particle shape of the conductive filler is not particularly limited, but the average particle diameter is 20 μm or less, and preferably the average particle diameter is 5 to 15 μm. When the average particle size exceeds 20 μm, dispersion in the paint is deteriorated, resulting in a problem in workability when the paint is applied.

  The blending amount of the conductive filler is desirably in the range of 60 to 85% by weight in terms of the ratio of [conductive filler / (solid content of resin + conductive filler)] of the conductive filler. When the blending ratio is out of this range, the electrical conductivity is low, and electrical connection reliability cannot be obtained. Examples of the (B) alicyclic epoxy resin used in the present invention include compounds having a cyclohexene oxide group, a tricyclodecene oxide group, a cyclopentene oxide group, or the like.

  The (C) organic solvent or monomer used in the present invention is for diluting the conductive paint according to the present invention, and can adjust and improve the coating work viscosity. Specific examples of the solvent include dioxane, hexane, toluene, methyl cellosolve, cyclohexanone, cyclopentanone, butyl cellosolve, butyl cellosolve acetate, butyl carbitol acetate, diethylene glycol diethyl ether, N-methylpyrrolidone, dimethylformamide, dimethylacetamide and the like. These may be used alone or in combination of two or more. As monomers, N-butyl glycidyl ether, allyl glycidyl ether, 2-ethylhexyl glycidyl ether, styrene oxide, phenyl glycidyl ether, cresyl glycidyl ether, p-sec-butylphenyl glycidyl ether, glycidyl methacrylate, t-butylphenyl Glycidyl ether, diglycidyl ether, (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, butanediol diglycidyl ether, trimethylolpropane triglycidyl ether, 1,6-hexanediol diglycidyl ether, etc. These can be used alone or in admixture of two or more. Moreover, a solvent and a monomer can be mixed and used. When a solvent is used, it is necessary to select a solvent having an appropriate boiling point in accordance with the curing temperature, curing time, and application work conditions.

  As the (D) sulfonium salt used in the present invention, a cation or a Lewis acid is generated by heating, and the epoxy groups are ring-opened by cation polymerization (cation polymerization). The blending ratio of the sulfonium salt is desirably 0.1 to 10 parts by weight with respect to 100 parts by weight of the alicyclic epoxy resin. When the sulfonium salt is less than 0.1 part by weight relative to 100 parts by weight of the alicyclic epoxy resin, curing does not proceed and a strong coating film cannot be formed. In addition, when the sulfonium salt exceeds 10 parts by weight with respect to 100 parts by weight of the alicyclic epoxy resin, Lewis acid remains in the coating film purified by curing of the conductive paint. There is a tendency for the electrical characteristics of the metal to deteriorate or to corrode the cathode lead frame made of a thin metal plate or aluminum.

  In the conductive paint according to the present invention, the above-mentioned (A) conductive filler, (B) alicyclic epoxy resin, (C) organic solvent or monomer, and (D) sulfonium salt were sufficiently mixed according to a conventional method. Thereafter, it can be easily obtained by further kneading with a disperser, a kneader, a three-roll mill or the like and then degassing under reduced pressure. Moreover, when hardening the electroconductive coating material concerning this invention, it is easily implemented by heating for 5 minutes-45 minutes by 100 degreeC-200 degreeC normally with a high temperature tank.

  EXAMPLES Next, although an Example demonstrates this invention concretely, this invention is not limited by these Examples. In the following examples and comparative examples, “parts” means “parts by weight” unless otherwise specified.

  110 parts of alicyclic epoxy resin ceroxide 2021P (trade name, manufactured by Daicel Chemical Industries, Ltd.), 370 parts of cyclohexanone as an organic solvent, 2 parts of Sun-Aid SI-80L (trade name, manufactured by Sanshin Chemical Industry Co., Ltd.) as a sulfonium salt, and silver powder After thoroughly mixing 640 parts, the mixture was further kneaded with disperse and degassed under reduced pressure to produce a conductive paint.

  110 parts of alicyclic epoxy resin ceroxide 2083 (trade name, manufactured by Daicel Chemical Industries, Ltd.), 370 parts of cyclopentanone as an organic solvent, 1 part of Sun-Aid SI-60L (trade name, manufactured by Sanshin Chemical Industries, Ltd.) as a sulfonium salt, and After thoroughly mixing 640 parts of silver powder, the mixture was further kneaded with a disperse and degassed under reduced pressure to produce a conductive paint.

Comparative Example 1

  Epoxy resin Epicoat 1004 (Japan Epoxy Resin Co., Ltd., trade name) 24 parts, phenol resin Marcalinker M6 parts, organic solvent 120 parts butyl cellosolve acetate and silver powder 170 parts in a heated flask, A kneading process was performed with a disperse, and degassed under reduced pressure to produce a conductive paint.

Comparative Example 2

  After thoroughly mixing 100 parts of polyamideimide resin HR-13NX (trade name, manufactured by Toyobo Co., Ltd.), 150 parts of N-methylpyrrolidone and 180 parts of silver powder, the mixture is further kneaded with a disperse and degassed under reduced pressure. Thus, a conductive paint was produced. Various performances of the conductive paints obtained in Examples 1 and 2 and Comparative Examples 1 and 2 were evaluated by the following methods.

Film thickness: A conductive paint was dip coated on a 5 mm square cube. After curing, the cross section was observed with an electron microscope, and the film thickness at the face and corners was measured.

Volume resistivity: A paint was applied on a slide glass to a width of 4 mm and a thickness of 10 μm, and the volume resistivity was measured after curing.

Adhesive strength: A conductive paint was applied to a silver-plated copper frame, a 2 mm square silicon chip was mounted, and the strength in the shear direction was measured after curing.

＊1：測定周波数は1.0ｋＨｚ、
＊2：測定信号レベルは1.0Ｖ、
表１、２から明らかなように比較例１では、バインダー樹脂として従来のエポキシ−フェノール硬化系を用いているため、塗膜の厚さに大きなバラツキがある。比較例２では、バインダー樹脂としてポリアミドイミド樹脂を用いているため、体積抵抗率が高く、接着強度が低い。これに対し、本発明の導電性塗料は、レベリング性、導電性に優れており、塗膜強度が高い。この導電性塗料を固体電解コンデンサの陰極形成に使用することにより、電気的、物理的な接合信頼性の向上が望める。 The above evaluation results are shown in Table 1. The present invention is excellent in all cases, and the effect of the present invention was confirmed.

* 1: Measurement frequency is 1.0 kHz.
* 2: Measurement signal level is 1.0V.
As is clear from Tables 1 and 2, in Comparative Example 1, since the conventional epoxy-phenol curing system is used as the binder resin, the thickness of the coating film varies greatly. In Comparative Example 2, since a polyamideimide resin is used as the binder resin, the volume resistivity is high and the adhesive strength is low. On the other hand, the conductive paint of the present invention is excellent in leveling properties and conductivity, and has high coating strength. By using this conductive paint for forming the cathode of the solid electrolytic capacitor, it is possible to improve the electrical and physical bonding reliability.

Claims (2)

(A) a conductive filler, (B) an alicyclic epoxy resin, (C) an organic solvent or monomer, and (D) a sulfonium salt represented by the following general formula 1

And (A) conductive filler in a ratio of (conductive filler / (resin solid content + conductive filler)) of 60 to 85% by weight, (D) sulfonium salt (B) A conductive paint containing 0.1 to 10 parts by weight with respect to 100 parts by weight of an alicyclic epoxy resin. A solid electrolytic capacitor formed by using the conductive paint according to claim 1 on a cathode layer, a conductive adhesive layer, or both.