JP4507750B2 - Conductive paste - Google Patents

Description

  The present invention relates to a heat-curable conductive paste that contains a conductive metal powder and a binder resin as main components and can form a conductive film or a conductive bond by heat-curing the binder resin.

  The heat-curable conductive paste is prepared by mixing the conductive powder with a binder resin and a curing agent, a catalyst, a solvent, and other additives blended as necessary, and uniformly dispersing the paste into a paste or paint. In general, the binder resin is cured by applying it to the substrate by means such as screen printing, brush coating, application by a dispenser, etc., and heat-treating at a low temperature of about 100 to 300 ° C., usually 200 ° C. or less. A conductive resin film is formed.

  Examples of the conductive powder include metal powders such as silver, gold, palladium, platinum, copper, and nickel, alloy powders containing these metals, powders obtained by coating these metals on inorganic or organic particles, carbon, or ITO. Conductive metal oxide powder or the like is used. Further, as the binder resin, a thermosetting resin or a thermoplastic resin such as an epoxy resin, a phenol resin, a melamine resin, an alkyd resin, an unsaturated polyester resin, or an acrylic resin is usually used.

  Such a heat-curable conductive paste does not require a baking process at a high temperature, so that a conductive film can be formed on a substrate having poor heat resistance such as plastic or amorphous silicon. For this reason, conventionally, as a conductive adhesive for mounting a semiconductor element or electronic component on a substrate, forming a conductor circuit including a jumper circuit or a through-hole conductor of a printed circuit board, forming a conductor circuit of a touch panel, a resistor It is used for forming electrodes of various electronic parts such as capacitors and capacitors, forming electrodes of various display elements, and forming conductive films for electromagnetic wave shielding. In particular, recently, there is an increasing demand for conductive adhesives as a joining material with a low environmental load, which replaces solder containing a large amount of lead that causes environmental pollution. Furthermore, it has been attracting attention as an electrode material for solar cells, particularly as an electrode material for solar cells using an amorphous silicon semiconductor having low heat resistance. In addition, since the resin coating is highly flexible, the external electrodes of chip-type ceramic electronic components such as multilayer ceramic capacitors, multilayer ceramic inductors, multilayer ceramic actuators, etc., which have conventionally used high-temperature firing type conductive pastes, are also cured at low temperatures. There is a movement to replace with type conductive paste.

  In recent years, due to demands for miniaturization and high density of circuit boards and electronic components, conductivity that exhibits extremely high conductivity so that good conduction can be maintained even when a fine conductor circuit with a thinner film thickness is formed. A paste is sought. However, when the amount of the conductive powder is increased for the purpose of improving the conductivity of the conventional low-temperature curable conductive paste, the ratio of the resin is decreased, so that the adhesiveness and the film strength are greatly decreased. Moreover, since the electroconductivity after hardening is implement | achieved by the contact of electroconductive particles, even if the quantity of electroconductive powder is increased, unless the contact between electroconductive particles is optimal, it will not lead to an improvement in electroconductivity.

  In heat-curable conductive pastes, conductive metal powders are usually used for higher dispersibility and leafing properties, and in the case of base metal powders, for the purpose of oxidation prevention, higher fatty acids such as stearic acid and these metals. In many cases, it is surface-treated with salt or the like and blended into a paste (Patent Documents 1 and 2). In these conductive pastes, the fatty acids adhering to the powder surface improve the paste coatability and dispersibility, and further heat cure to form a cured film showing high conductivity, adhesion, and film strength. be able to. Further, Patent Document 3 includes, for the purpose of oxidation resistance, high conductivity, and long-term stability, a copper powder whose surface is coated with silver, a thermosetting resin, a fatty acid or a metal salt thereof, and an amine compound. A conductive paste is disclosed.

However, there is a limit to further improve the conductivity in the conventional conductive paste. For example, even when a highly conductive silver powder is used as the conductive powder, the specific resistance is lower than 2 × 10 ⁻⁵ Ω · cm. It was extremely difficult to produce a conductive paste having a value.
JP 47-16989 A JP 2002-332502 A JP-A-3-67402

  An object of the present invention is to provide a thermosetting conductive paste capable of forming a conductive film having extremely high conductivity without reducing adhesiveness or film strength. In particular, a highly conductive thermosetting conductive paste that sufficiently satisfies the mechanical and electrical properties required for conductors of electronic circuits and electronic components without causing a decrease in adhesive strength due to a decrease in the resin ratio. The purpose is to provide.

  Another object of the present invention is to form a highly conductive film by heat treatment at a low temperature of about 100 to 300 ° C., particularly at a temperature of 200 ° C. or less, and therefore a resin substrate such as polyethylene terephthalate having poor heat resistance. It is an object to provide a heat-curable conductive paste that can be applied to a substrate such as silicon or amorphous silicon.

The present invention includes a conductive metal powder surface-treated with fatty acids and / or fatty acid anhydrides, alkali metal ion includes a down, a binder resin containing a thermosetting resin, wherein the alkali metal ion is an alkali metal carbonate , Bicarbonate, oxalate, β-diketone complex, and alkoxide, and the amount of the alkali metal ions is 10 to 3000 ppm based on the weight of the conductive metal powder. The gist of the present invention is a conductive paste characterized by the above.

The conductive paste of the present invention comprises a conductive metal powder surface-treated with a fatty acid and / or a fatty acid anhydride (hereinafter sometimes referred to as “fatty acids”) and a thermosetting binder resin. By blending a specific amount of alkali metal ions,
・ After curing, a highly conductive film can be obtained.
-The conductivity can be improved without reducing the amount of binder resin, and thus without lowering the adhesive strength and film strength to the substrate.
Since a highly conductive film can be formed by heat treatment at a low temperature of about 100 to 300 ° C., particularly 200 ° C. or less, it can be applied to a substrate having low heat resistance such as a resin substrate or amorphous silicon.

    Conventionally, in heat-curable conductive pastes, alkali metal ions have been evaded as adversely affecting the electrical properties and reliability of printed circuit boards, electronic components, semiconductor elements, etc. Although it was desired to reduce as much as possible, the present inventors blended a specific amount of a controlled amount of alkali metal ions in combination with a specific component, thereby preventing electric conductivity and reliability from deteriorating. It has been found that the improvement of property can be achieved.

  The mechanism by which the conductivity is improved by blending alkali metal ions is not necessarily clear, but the present inventors have considered as follows.

  When the conductive metal powder is surface treated with fatty acids, the fatty acids adhering to the powder surface act as a dispersant, lubricant, antioxidant, anti-migration agent, stabilizer, or leafing agent in the paste. Although the conductivity is improved, fatty acids remain on the surface of the conductive metal particles, thereby inhibiting the contact between the conductive metal particles.

  Alkali metal ions have the effect of removing fatty acids from the surface of the conductive metal particles during the paste curing process. At this time, the alkali metal ions lose their charge, and the conductive metal is ionized to maintain the charge balance in the field. It is considered that it has an effect of promoting elution. The eluted metal ions cause a so-called ion migration phenomenon, and are reduced between the conductive metal particles to precipitate active metal fine particles, which fill gaps between the conductive particles or fuse the conductive particles together. Thereby, the electroconductivity of a cured film improves markedly.

  In particular, when alkali metal ions are blended in an amount of 30 to 1000 ppm with respect to the weight of the conductive metal powder, the most excellent effect of improving the conductivity is exhibited and the electronic component or the semiconductor element is not adversely affected.

  Further, when a metal powder containing silver is used as the conductive metal powder, the effect is particularly high, and an extremely low resistance conductive film can be obtained.

(Conductive metal powder surface-treated with fatty acid and / or fatty acid anhydride)
The conductive metal powder is not particularly limited as long as it contains a conductive metal. For example, a noble metal or base metal powder, or an alloy powder containing these metal components is used. The conductive metal powder of the present invention includes a composite powder obtained by coating a surface of an inorganic powder such as a metal, a metal compound, glass, ceramic, or carbon or an organic powder such as a resin with a noble metal, a base metal, or an alloy thereof. . These conductive metal powders may be used alone or in combination of two or more.

  In particular, silver, gold, palladium, platinum, copper, nickel, or an alloy powder or composite powder containing these metals is preferable. Among them, a silver-based conductive metal powder having a low specific resistance, that is, a silver or silver-copper alloy. It is desirable to use silver-palladium-copper alloy, silver-copper-nickel alloy powder, silver-coated powder, or the like.

  The particle size of the conductive metal powder is not particularly limited, but it is desirable that the average particle size is 0.1 to 30 μm from the viewpoint of dispersibility in the paste, applicability, and conductivity. However, the presence of a small amount of ultrafine powder having a particle size of less than 100 nm is preferable because the conductivity tends to be further improved.

  There is no restriction | limiting also in the shape of electroconductive metal powder, The thing of various shapes, such as spherical shape, flake shape, dendritic shape, and fiber shape, is used according to the objective, the coating method, and a required characteristic.

  The conductive metal powder is surface-treated with a fatty acid and / or a fatty acid anhydride by a usual method. As the fatty acid and fatty acid anhydride, for example, fatty acids having 6 to 24 carbon atoms and acid anhydrides thereof are used. Specific examples include saturated fatty acids such as octylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, etc., tertiary fatty acids such as oleic acid, linoleic acid, linolenic acid, tertiary grades such as neononanoic acid, neodecanoic acid, etc. Fatty acids, adipic acid, pimelic acid, polyvalent carboxylic acids such as alkyl-substituted succinic acid and hydrogenated phthalic acid, and acid anhydrides thereof are preferable from the viewpoints of adhesion to metal powder and dispersibility improvement effect. Of these, those having a total carbon number of 8 to 20 are particularly preferred.

  The amount of these fatty acids varies depending on the particle size and shape of the conductive metal powder and the type of fatty acid, and is not particularly limited, but is usually 0.05 to 2 weights with respect to the weight of the conductive metal powder. %.

(Alkali metal ions)
The alkali metal ions blended in the paste of the present invention are not particularly limited, and one or more of lithium ions, sodium ions, potassium ions, rubidium ions, and cesium ions are used. In particular, those having high chemical activity and stable presence in the conductive film after curing and being difficult to elute are preferred. In this respect, sodium ion and potassium ion are particularly preferable. Among these, potassium ions are considered suitable for electronics because of their low ion mobility in the cured coating.

Alkali metal ions are added to and mixed with the paste in the form of at least one of alkali metal carbonates, bicarbonates, oxalates, β-diketone complexes, and alkoxides . Wherein the alkali metal compound is an alkali metal tends to ionize in the paste, and is used in free of elements that adversely affect the electronic components and semiconductor devices.

  Alkali metal ions are blended in a total amount of 10 to 3000 ppm based on the weight of the conductive metal powder. By blending a controlled amount of metal ions in this manner, extremely high conductivity can be obtained without reducing reliability. If the blending ratio is lower than the above range, the above effect is not sufficient. Further, when the blending ratio is higher than such a range, the adhesive strength is lowered and the conductivity is further lowered. Moreover, there is a risk of adversely affecting electronic components and semiconductor elements. The range of 30-1000 ppm is particularly preferable. Furthermore, it is most preferable to mix | blend in 30-500 ppm.

(Binder resin)
The binder resin of the present invention is not particularly limited as long as it contains at least one thermosetting resin. Examples of thermosetting resins include epoxy resins, phenol resins, alkyd resins, unsaturated polyester resins, urea resins, amino resins, xylene resins, polyimide resins, silicone resins, urethane resins, polyester / polyol resins, acrylic resins, and the like. A modified resin or the like is appropriately selected and used depending on the application and required characteristics. In particular, an epoxy resin, a modified epoxy resin, and a phenol resin are preferable in terms of adhesiveness, curability, and conductivity. The phthalic acid glycidyl ester type epoxy resin described in Japanese Patent Application No. 2004-166761 filed earlier by the present inventors is also preferably used.

  These thermosetting resins may be used alone or in admixture of two or more. Further, a thermoplastic resin may be used in combination. Examples of the thermoplastic resin include butyral resin, acrylic resin, methacrylic resin, novolac type phenol resin, acrylic styrene resin, saturated polyester resin, polyurethane resin, polyamide resin, thermoplastic xylene resin, hydroxystyrene polymer, cellulose derivative. Etc.

  The blending ratio of the binder resin is a design matter that is appropriately determined depending on the type of resin, required characteristics, and the like, but the optimum range is 5 to 30 parts by weight with respect to 100 parts by weight of the conductive metal powder. If it exceeds 30 parts by weight, the resistance value tends to increase. On the other hand, when the amount is less than 5 parts by weight, the strength and adhesiveness of the film become insufficient, and the resistance value tends to increase due to this.

(Other additive components)
In addition to the above components, the conductive paste of the present invention can be appropriately mixed with a solvent, a curing agent, and the like that are usually added as necessary.

  When the binder resin is in a liquid state at room temperature, it is not essential to use a solvent, but a solvent is blended as necessary in order to adjust the viscosity, coating properties, and the like. As the solvent, for example, known solvents such as alcohol solvents, ester solvents, ether solvents, ketone solvents, hydrocarbon solvents, fatty acid solvents, reactive diluents and the like are used. Specifically, for example, benzene, toluene, hexanone, methyl ethyl ketone, methyl isobutyl ketone, ethyl carbitol acetate, butyl carbitol acetate, butyl carbitol, butyl cellosolve, butyl cellosolve acetate, propylene glycol monomethyl ether acetate, triethylene glycol monobutyl ether, Examples include, but are not limited to, organic solvents such as isophorone and terpineol.

  The curing agent may be any one that is normally used as a curing agent for the thermosetting resin, and is appropriately selected according to the curing time and the curing temperature. For example, as an epoxy resin curing agent, an acid anhydride curing agent, an imidazole curing agent, an amine curing agent, a phenol resin, and the like can be given. A compounding quantity is about 1-100 weight part with respect to 100 weight part of binder resin. A curing accelerator and a curing catalyst can be used in combination.

  In addition, surfactants, antifoaming agents, plasticizers, thixotropic agents, dispersants, reducing agents, ultraviolet absorbers, chelating agents, coupling agents, inorganic fillers, and the like may be added as appropriate. With these, it is possible to appropriately adjust properties such as paste coating properties, heat resistance, water resistance, environmental resistance, flexibility, solderability, solder heat resistance, etc. of the conductive film to be formed. It becomes possible to apply to a use.

(Manufacture of conductive paste)
The electrically conductive paste of this invention is manufactured by mixing the said component according to a conventional method, and making it disperse | distribute uniformly using a roll mill etc. into a paste form.

(Formation of conductive film)
The conductive paste of the present invention is applied to the substrate by various means such as screen printing, transfer printing, dipping, brush coating, and application using a dispenser. The substrate can be applied to various substrates such as a resin substrate, a ceramic substrate, a glass substrate, a ceramic electronic component, a silicon semiconductor, and a compound semiconductor. The conductive paste applied on the substrate is heat-treated by a known method to cure the resin, thereby obtaining a conductive film. Optimum curing conditions vary depending on the resin and curing agent, but the curing treatment is usually performed at a temperature of about 100 to 300 ° C., preferably 200 ° C. or less, for several tens of seconds to 2 hours.

(Use)
The conductive paste of the present invention can be used for various applications. Typical application examples include jumper circuits and through-hole conductors for printed circuit boards, additive circuits, conductor circuits for touch panels, tantalum capacitor electrodes, film capacitor electrodes, resistance terminals, solar cell electrodes, chip-type ceramic electronic components Formation of external electrodes and internal electrodes, and use as an electromagnetic wave shield. Moreover, as an alternative to solder, in addition to the use as a conductive adhesive for mounting semiconductor elements and electronic components on a substrate, a grid electrode of a type that covers the surface of a high-temperature-baked silver electrode of a solar cell with solder, It can also be used as an alternative to the solder part.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited thereto.

Example 1
100 parts by weight of flaky silver powder surface-treated with neodecanoic acid and having an average particle diameter of 2 μm, 0.03 parts by weight of potassium carbonate (170 ppm in terms of potassium ions with respect to flaky silver powder), binder resin, curing agent, and solvent They were mixed and kneaded by a three roll mill to obtain a conductive paste. The adhesion amount of the surface treatment agent was about 0.4% by weight with respect to the silver powder. As binder resin, 9.4 parts by weight of dimethyl glycidyl phthalate epoxy resin (Epiclon 200 manufactured by Dainippon Ink & Chemicals, Inc.) and butyral resin (Sekisui Chemical Co., Ltd., ESREC BL3) with respect to 100 parts by weight of silver powder. ) Was used in a mixture of 2.6 parts by weight of a 28% ethyl carbitol acetate solution. As the curing agent, 0.5 part by weight of an acid anhydride curing agent and 3.1 parts by weight of a phenol resin curing agent were used in combination. As a solvent, ethyl carbitol acetate was appropriately blended to adjust the viscosity.

The obtained conductive paste was applied on a glass substrate by a screen printing method, heat-treated at 200 ° C. for 60 minutes, and the resin was cured to form a conductive silver film. The specific resistance value of the obtained silver coating was measured by the four probe method. Moreover, the crosscut test was done according to JIS-K5400 8.5.2 cross cut test, and adhesiveness was evaluated, and the result was combined with Table 1 and shown.
Examples 2 to 5, Comparative Examples 1 and 2
A conductive paste was produced in the same manner as in Example 1 except that the compounding amount of potassium ions was as shown in Table 1. Similarly, the curing treatment was performed, and the characteristics of the obtained conductive silver coating were examined. The results are also shown in Table 1.

Example 6-1 6, Reference Examples 1-2, Comparative Example 3
The amount of potassium carbonate, sodium carbonate, sodium t-butoxide, sodium oleate or carbonic acid in the amount shown in Table 2 in terms of alkali metal ions, per 100 parts by weight of flaky silver powder surface-treated with neodecanoic acid and having an average particle diameter of 2 μm Lithium, a binder resin, and a solvent were mixed, kneaded by a three-roll mill, and then a curing agent was mixed to obtain a conductive paste. The adhesion amount of the surface treatment agent was about 0.4% by weight with respect to the silver powder. As a binder resin, 15 parts by weight of bisphenol A type epoxy resin (Epicoat 1001 manufactured by Japan Epoxy Resin Co., Ltd.) was blended with respect to 100 parts by weight of silver powder. As a curing agent, 1.5 parts by weight of an imidazole-based curing agent was used, and as a solvent, ethyl carbitol acetate was used.

  The obtained conductive paste was applied on a glass substrate by a screen printing method, heat-treated at 150 ° C. for 30 minutes, and the resin was cured to form a conductive silver film. The specific resistance value of the silver coating film obtained in the same manner as in Example 1 was measured, and a cross-cut test was performed to evaluate the adhesiveness. The results are also shown in Table 2.

Examples 17-22 , Comparative Examples 4-9
For 100 parts by weight of flaky silver powder surface-treated with the surface treatment agent shown in Table 3, an amount of potassium carbonate, binder resin and solvent shown in Table 3 in terms of alkali metal ions are mixed. The mixture was kneaded with a three-roll mill and then mixed with a curing agent to obtain a conductive paste. In Table 3, “unsaturated fatty acid (C = 18)” is a product name “No. 20 fatty acid” manufactured by NOF Corporation. The adhesion amount of the surface treatment agent was approximately 0.3 to 0.5% by weight with respect to the silver powder. As the binder resin, 15 parts by weight of silicone-modified bisphenol A type epoxy resin was blended with respect to 100 parts by weight of silver powder. As a curing agent, 1.5 parts by weight of an imidazole-based curing agent was used, and as a solvent, ethyl carbitol acetate was used.

  As in Example 6, a conductive paste was applied on a glass substrate and cured at 150 ° C. for 30 minutes to form a conductive silver film. The specific resistance value and adhesiveness of the obtained silver coating are shown together in Table 3. In Table 3, except the comparative example 10, after the test result of each Example of this invention which mix | blended the alkali metal ion, the test result of the comparative example similar to each Example was arranged except not mix | blending an alkali metal ion. . Comparative Example 10 uses phthalic anhydride, which is an aromatic carboxylic acid, as a surface treatment agent.

Claims (1)

A conductive metal powder surface-treated with fatty acids and / or fatty acid anhydride, an alkali metal ion, and a binder resin containing a thermosetting resin, wherein the alkali metal ions are alkali metal carbonates, bicarbonates , An oxalate, a β-diketone complex, and an alkoxide, and the amount of the alkali metal ions is 10 to 3000 ppm based on the weight of the conductive metal powder. Conductive paste.