JP2003082194A - Electroconductive paste and solid electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid electrolytic capacitor excellent in electric characteristics after moisture-absorption, mass productivity and migration- preventing effects, and to obtain an electroconductive paste for the solid electro lytic capacitor. SOLUTION: The thermosetting electroconductive paste comprises as essential ingredients (A) an epoxy resin, (B) a polyamideimide resin of the formula (wherein R<1> is a diamine residue; R<2> is a tetracarboxylic dianhydride residue; and (m) and (n) are each a positive integer), (C) an electroconductive powder and (D) a dilution solvent, where the compounded amount of the polyamideimide resin (B) is at least 10 pts.wt. based on 1 pt.wt. of the epoxy resin. The solid electrolytic capacitor has a cathode layer formed by using the electroconductive paste.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid electrolytic capacitor which is excellent in electric characteristics after moisture absorption and migration resistance and has a thin and uniform cathode layer, and a thermosetting conductive paste suitable for use in the cathode layer.

[0002]

2. Description of the Related Art A solid electrolytic capacitor to which the present invention relates is formed by subjecting an anode body made of a metal having a valve action, such as tantalum, aluminum or niobium, to a chemical conversion treatment, forming a dielectric layer on the surface thereof, and then further forming the surface thereof. A semiconductor layer, a carbon layer, and a cathode layer are formed in sequence, and the cathode layer is bonded and fixed to the cathode lead frame using a conductive adhesive, and the anode lead that is connected to the anode body is connected to the anode lead frame by welding. In addition, the outer peripheral surface is further covered with a covering resin.

[0003]

However, the conventional cathode layer is composed of ordinary epoxy resin, phenol resin, etc.,
It is formed of a conductive paste mainly composed of silver particles, and the performance of the silver conductive paste of the cathode layer deteriorates the electrical characteristics of the solid electrolytic capacitor after moisture absorption,
There are drawbacks such as an increase in leakage current and tan δ, and a short circuit failure. That is, when the solid electrolytic capacitor is exposed to a high-temperature and high-humidity environment, water enters through the substance of the exterior resin and the interface between the terminal and the exterior resin, and the silver of the silver-based conductive paste is dissolved and ionized, which The electrical characteristics deteriorate due to the occurrence of so-called "silver migration" that precipitates again.

As a method for preventing the deterioration of the electrical characteristics due to the migration, a method in which a chrome powder, a manganese powder, an indium powder or the like is mixed with a silver-based conductive paste used for a cathode layer or a conductive adhesive, or a porous filler is used. Although a mixed product has been proposed, it is still not sufficiently satisfactory in terms of high reliability.

Further, when a cathode layer of a solid electrolytic capacitor is formed, if a conductive paste mainly composed of silver-based particles made of usual epoxy resin, phenol resin or the like is used,
There is a drawback that the corners of the element cannot be covered, and if it is attempted to eliminate this, the thickness of the film is not uniform and becomes thick.

More recently, as electronic devices process large amounts of digital information at high clock frequencies,
Solid electrolytic capacitors are required to have high frequency and low impedance, and the conductive paste used for them has been required to have stable high conductivity and improved electrical joint reliability.

The object of the present invention is to eliminate the above-mentioned drawbacks, and to provide a silver-based conductive paste excellent in electric characteristics after moisture absorption, mass productivity and migration prevention effect. An object of the present invention is to provide a solid electrolytic capacitor having high humidity resistance reliability by using a conductive paste.

[0008]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventor has found that the above object can be achieved by using a conductive paste having a composition described later. The invention has been completed.

That is, the present invention is (A) Epoxy resin, (B) a polyamide-imide resin represented by the following formula,

[Chemical 2] (However, in the formula, R ¹ represents a diamine residue, R ² represents a tetracarboxylic acid dianhydride residue, and m and n each represent a positive integer.) (C) Conductive powder and (D) diluting solvent Is a necessary component, and the blending amount of the polyamideimide resin of (B) is 10 parts by weight or more with respect to 1 part by weight of the epoxy resin of (A). The solid electrolytic capacitor is characterized in that a cathode layer is formed by using the conductive paste.

The present invention will be described in detail below.

The epoxy resin (A) used in the present invention can be used without particular limitation as long as it has two or more epoxy groups in one molecule. For example, bisphenol A glycidyl ether, bisphenol F glycidyl ether, phenol novolac type epoxy resin, alicyclic epoxy resin, glycidyl ester type epoxy resin,
Examples thereof include glycidyl amine type epoxy resins, and these may be used alone or in admixture of two or more.

The polyamideimide resin (B) used in the present invention is a polymer having the following skeleton.

[0013]

[Chemical 3] (However, in the formula, R ¹ represents a diamine residue, R ² represents a tetracarboxylic acid dianhydride residue, and m and n each represent a positive integer.) Specific examples include, for example, NA-100. (Manufactured by Toyobo Co., Ltd., trade name). The blending ratio of the polyamideimide resin of (B) is the epoxy resin 1 of (A).
It is desirable to mix such that the content is 10 parts by weight or more with respect to parts by weight. When the blending ratio is less than 10 parts by weight, there is no effect in improving the moisture resistance and the coating property.

Examples of the (C) conductive powder used in the present invention include metal powders such as silver powder, gold powder, aluminum powder, and copper powder, coating powders having these metals on the surface, plating powders, or composite powders. Powder and the like can be preferably used, and these can be used alone or in combination of two or more kinds. The particle shape of the conductive powder is not particularly limited, but the particle size is preferably 10 μm or less. If the particle size of the conductive powder exceeds 10 μm, the composition does not become a paste and the effect of improving the coating property is not achieved.

The blending amount of the conductive powder is the weight content ratio [(A) of the resin component (A) + (B) and the conductive powder (C).
+ B) / (C)] is preferably in the range of [40/60] to [5/95]. When the weight content ratio of the conductive powder (C) to the resin component is less than [40/60], it becomes difficult to obtain sufficient conduction, and when it exceeds [5/95], workability and coating property are obtained. There is no effect on the improvement of.

Examples of the (D) diluting solvent used in the present invention include:
For example, dioxane, toluene, methyl cellosolve, cyclohexanone, butyl cellosolve, butyl cellosolve acetate, butyl carbitol acetate, butyl acetate, diethylene glycol diethyl ether, diacetone alcohol, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, γ-butyrolactone,
Diethylene glycol diethyl ether, xylene, tetrahydrofuran, ethyl alcohol, etc. may be mentioned, and these may be used alone or in admixture of two or more. The mixing ratio of these diluting solvents is preferably in the range of 5 to 60 parts by weight with respect to 100 parts by weight of the conductive paint before dilution.

The conductive paste used in the present invention is the above-mentioned (A) epoxy resin, (B) polyamide-imide resin,
(C) The conductive powder and (D) the diluting solvent are essential components, but a defoaming agent, a leveling agent, a coupling agent, and other additives may be added as far as the object of the present invention is not impaired. It can be added and compounded. According to a conventional method, after thoroughly mixing the above-mentioned components, kneading is further performed with a disperser, a kneader, a three-roll mill, or the like,
Then, it can be degassed under reduced pressure to be manufactured.

The conductive paste thus obtained is further subjected to viscosity adjustment, and the solid electrolytic capacitor element is subjected to dipping and thermosetting to form a cathode layer. Next, the anode lead of the capacitor element is connected to the anode lead frame of the anode terminal by welding, and then the cathode layer and the cathode lead frame are connected by the conductive paste obtained by the above method.

After that, resin coating is performed by a transfer molding method or a dipping method, and an external lead frame is bent to complete a solid electrolytic capacitor.

[0020]

Incorporation of a polyamide-imide resin into the conductive paste used in the present invention makes it difficult to use a conventional conductive paste mainly composed of silver particles composed of an epoxy resin, a phenol resin or the like. It has been,
A high glass transition temperature, low water absorption, low dielectric constant, and low dielectric loss tangent can be imparted to the cured product in a well-balanced manner. By using a conductive paste with such a resin as a binder,
It is possible to obtain a solid electrolytic capacitor having excellent impedance characteristics, heat resistance, migration resistance after humidity resistance, and electrical junction reliability.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Next, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples. In the following examples and comparative examples, "parts" means "parts by weight" unless otherwise specified.

EXAMPLE Polyamide-imide resin NA-100 (manufactured by Toyobo Co., Ltd., trade name) 100 parts, Bisphenol F type epoxy resin YL-983U (manufactured by Japan Epoxy Resin Co., trade name) 5 parts, average grain Scale-like silver powder with a diameter of 4 μm 3
00 parts, silver-coated copper powder 26 parts, ion adsorbent 3 parts, N
-Methylpyrrolidone (30 parts) was mixed, further kneaded by disperse, and degassed under reduced pressure to produce a conductive paste.

Comparative Example Commercially available epoxy resin-based solvent-type conductive paste for solid electrolytic capacitors TC-3600G (trade name, manufactured by Hitachi Chemical Co., Ltd.) was obtained.

The conductive pastes obtained in Examples and Comparative Examples were diluted with N-methylpyrrolidone and butyl acetate to several poises.
The solid electrolytic capacitor element is subjected to dipping treatment, and the conductive paste is cured under predetermined curing conditions to form a cathode layer. Further, after the anode body lead and the anode lead frame are welded and joined, the cathode layer and the cathode lead frame are joined with a commercially available adhesive conductive paste. Then, a 16V, 15 μF solid electrolytic capacitor was manufactured by externally coating with a resin by a molding method. The results of the pressure cooker test of the solid electrolytic capacitor thus obtained after 100 hours are shown in Table 1. The present invention was excellent in all cases, and the effects of the present invention were confirmed.

[0025]

[Table 1]

[0026]

As is apparent from the above description and Table 1, the solid electrolytic capacitor of the present invention is excellent in migration resistance and electrical junction reliability even under high temperature and high humidity conditions, and has high frequency impedance. It can also be adapted to.

Claims (2)

[Claims] 1. (A) Epoxy resin, (B) Polyamide-imide resin represented by the following formula, and (However, in the formula, R ¹ represents a diamine residue, R ² represents a tetracarboxylic acid dianhydride residue, and m and n each represent a positive integer.) (C) Conductive powder and (D) diluting solvent Is a necessary component, and the blending amount of the polyamideimide resin of (B) is 10 parts by weight or more with respect to 1 part by weight of the epoxy resin of (A), a thermosetting conductive paste. 2. A solid electrolytic capacitor using a cured product of the thermosetting conductive paste according to claim 1 for a cathode layer.