KR20190129829A - Conductive paste - Google Patents

Abstract

The present invention provides a conductive paste having good electrical conductivity even in a conductive film layer formed on a small through hole.
The electrically conductive paste concerning one Embodiment of this invention is equipped with a copper powder, a phenol resin, a chelate formation substance, and a polyhydric alcohol.

Description

Conductive paste

TECHNICAL FIELD This invention relates to the electrically conductive paste which can be used suitably for the formation of the through-hole through-hole of a printed wiring board, for example.

As a means for conducting through-holes of a printed wiring board, there is a method of forming a conductive coating layer by applying a conductive paste to the through-holes using screen printing and heat curing.

For example, Patent Document 1 discloses a conductive paste containing a conductive filler such as copper powder, a chelate forming material, a phenol resin, a modified epoxy resin, and a printability improving agent.

Patent Document 1: International Publication No. WO 2016/121668

Recently, in accordance with the market expansion of high-performance electronic devices, miniaturization and thinning of printed wiring boards and electronic components are rapidly progressing. When the through hole is made small in size, the amount of the conductive paste filled in the through holes is reduced when screen printing is performed to form the conductive coating layer. When the amount of the conductive paste decreases, the conductive coating layer during heat curing becomes thin, so that the conductive filler is easily oxidized. Therefore, there existed a problem that the electrical resistance value of the resultant electroconductive film layer deteriorated (becomes high).

This invention is proposed in view of the said point, Comprising: In one side of the objective, it is providing the electrically conductive paste which has favorable electric conductivity also in the electroconductive film layer formed on the through-hole of a small diameter.

The electrically conductive paste concerning one Embodiment of this invention is equipped with a copper powder, a phenol resin, a chelate formation substance, and a polyhydric alcohol.

According to the embodiment of the present invention, on one side, a conductive paste having good electrical conductivity can be provided even in a conductive film layer formed on a small diameter through hole.

The electrically conductive paste which concerns on this embodiment can be used for the printed wiring board in which the conductor pattern for mounting an electronic component was formed, for example. In particular, as a means for conducting through-hole conduction of a printed wiring board, by conducting heat curing by applying a conductive paste to the through-hole using screen printing, a conductive coating layer can be formed to ensure conduction. In addition, since the electrically conductive paste which concerns on this embodiment can be applied also to uses other than the electrically conductive film layer for conduction of the through-hole of a printed wiring board, what heat-hardened the electrically conductive paste which concerns on this embodiment below is simply called paste hardened | cured material. There is a case.

The electrically conductive paste concerning this embodiment contains at least a copper powder, a phenol resin, a chelate forming substance, and a polyhydric alcohol. In addition, the electrically conductive paste which concerns on this embodiment may contain other components. As other components, a modified epoxy resin, a printability improving agent, etc. are mentioned, for example. Each component is explained in full detail below.

[Copper powder]

Since copper has low electrical resistivity and can obtain favorable electroconductivity with respect to the paste hardened | cured material obtained among metals, copper can be used suitably as a conductive filler for electrically conductive pastes. Moreover, copper is relatively inexpensive and can be procured stably.

Copper powder which is normally available has the surface covered with an oxide film. At this time, it may be difficult to obtain good conductivity only by bringing the particles of the copper powder into contact with each other.

However, in the electrically conductive paste which concerns on this embodiment, it prepares using polyhydric alcohol. In general, the primary alcohol is oxidized in the presence of an oxidizing agent to become an aldehyde (in a non-acidic atmosphere, for example in an aprotic organic solvent) or a carboxylic acid (in an acidic atmosphere, for example in an aqueous solvent). The secondary alcohol is also oxidized in the presence of an oxidizing agent to become a ketone. Since the oxide film on the surface of copper powder is reduced to copper by the oxidation reaction of alcohol, the paste hardened | cured material which has favorable electroconductivity can be obtained.

In addition, in the electrically conductive paste which concerns on this embodiment, it uses not polyhydric alcohol but to prepare polyhydric alcohol. Since the polyhydric alcohol has two or more hydroxyl groups in one molecule, it is inferred that by using the polyhydric alcohol, the reducing action of the surface of the copper powder due to the oxidation of the polyhydric alcohol is improved. In addition, the polyhydric alcohol or its oxide is considered to have the effect of stably forming copper ions and cyclic chelate compounds in one molecule, and suppressing deterioration of the resin due to diffusion of copper ions. In addition, since the polyhydric alcohol has a large number of hydrogen bonds between molecules, the vapor pressure is low, and the evaporation rate in the heat curing process of the conductive paste is slower than that of the monohydric alcohol. Therefore, it is thought that the oxidation of the copper powder which occurs in the heat curing process of the conductive paste is suppressed, and that a small reducing space is formed in the diameter of the through hole by the evaporated polyhydric alcohol. From the above reason, it is inferred that the electrically conductive paste which concerns on this embodiment prepared using polyhydric alcohol has favorable electroconductivity.

Moreover, since the electrically conductive paste which concerns on this embodiment is prepared using the phenol resin which has a high shrinkage rate at the time of hardening, it can crimp strongly the particle | grains of a copper powder. As a result, the paste hardened | cured material which has the outstanding electroconductivity can be obtained by using the electrically conductive paste which concerns on this embodiment.

It is preferable to carry out the average particle diameter of the copper powder which concerns on this embodiment in 1 micrometer-15 micrometers, and it is more preferable to set it as 3 micrometers-10 micrometers. In the case where the particle diameter of the copper powder to be used is less than 1 µm, the effect of oxidation due to the increase in the contact resistance between the copper powders and the increase in the specific surface area of the copper powder may be increased and the resistance value may deteriorate. Moreover, when an average particle diameter exceeds 15 micrometers, it may become difficult to form a uniform cured film layer in a through hole of a small diameter.

[Phenolic resin]

The electrically conductive paste concerning this embodiment contains a phenol resin at least as resin. In addition, although the electrically conductive paste which concerns on this embodiment may contain only phenol resin as a resin component, it may contain other resin other than a phenol resin.

Since phenolic resin has a high shrinkage rate at the time of curing, the particles of copper powder can be strongly pressed together, and as a result, the conductivity of the resulting paste cured product is also high. Phenolic resins also have high adhesion to substrate materials, copper foils, and the like of printed wiring boards.

As the phenol resin, it is preferable to use a resol type phenol resin. Since the resol type phenol resin has a self-reactive functional group, it can be cured only by heating.

Resol type phenol resins can be obtained by reacting a phenol or a phenol derivative with formaldehyde under an alkali catalyst.

As said phenol derivative, alkylphenols, such as cresol, xylenol, t-butylphenol, a phenylphenol, a resorcinol, etc. are mentioned.

As the phenol resin, for example, REGITOP PL-4348 (trade name) manufactured by Gun-Ei Chemical Industry Co., Ltd. can be used.

[Other resin: Modified epoxy resin]

As mentioned above, the electrically conductive paste which concerns on this embodiment may contain other resin other than a phenol resin as a resin component. As another resin which it is preferable to use, a modified epoxy resin is mentioned, for example. By using a modified epoxy resin in addition to the phenol resin described above, it is possible to adjust (particularly reduce) the elastic modulus of the cured conductive paste. Therefore, in the case where the conductive coating layer is formed in the through hole portion using the conductive paste, the conductive coating layer can absorb the thermal expansion difference (thermal expansion difference between the substrate and the coating layer), so that cracks or peeling due to temperature changes ( It is possible to suppress the occurrence of i).

In addition, in the electrically conductive paste which concerns on this embodiment, the modified epoxy resin refers to the epoxy resin which modified | denatured in order to have various performance in a bisphenol-A epoxy resin. The epoxy resin modified in order to have various performances means that the epoxy resin is polymerized with other components to partially change the structure of the main chain, or introduces a functional group. The modified epoxy resin which can be suitably used in the conductive paste according to the present embodiment is a modified epoxy resin having flexibility, specifically, a urethane modified epoxy resin, rubber modified epoxy resin, ethylene oxide modified epoxy resin, and propylene oxide modified Epoxy resin, fatty acid modified epoxy resin, urethane rubber modified epoxy resin, etc. are mentioned. Moreover, as a modified epoxy resin, it is preferable to use the modified epoxy resin whose epoxy equivalent exceeds 186.

In addition, the electrically conductive paste which concerns on this embodiment may contain the highly reactive epoxy resin. In addition, in this embodiment, the highly reactive epoxy resin refers to the polyfunctional epoxy resin whose epoxy equivalent is 186 or less and two or more epoxy groups in 1 molecule. By using a highly reactive epoxy resin in addition to the phenol resin and the modified epoxy resin, preferable adhesion strength between the conductive coating layer of the conductive paste and the substrate can be obtained.

Specific examples of the highly reactive epoxy resin include the Denacol series (trade names EX212L, EX214L, EX216L, EX321L, and EX850L) and Nakase ChemteX Corporation, which are manufactured by ADEKA Corporation. ED-503G and ED-523G, Mitsubishi Chemical Corporation, trade names jER630, jER604, and jER152, Mitsubishi Gas Chemical Corporation, Inc. tradename TETRAD-X and TETRAD -C, the Nippon Kayaku Co., Ltd. brand names EPPN-501H, EPPN-5010HY, EPPN502, etc. are mentioned.

[Other Resin]

The electrically conductive paste which concerns on this embodiment may contain other resin other than the said phenol resin, modified epoxy resin, and high reactive epoxy resin. As other resin, if it is resin used for well-known electrically conductive paste, especially resin used for well-known electrically conductive paste used for conduction of the through-hole of a printed wiring board, it can use suitably. Suitable examples of other resins include resins with curing shrinkage, that is, thermosetting resins, and specific examples thereof include epoxy resins and silicone resins other than modified epoxy resins and highly reactive epoxy resins.

[Poly alcohol]

In the present embodiment, the polyhydric alcohol serves to reduce the oxide film on the surface of the copper powder to copper by its oxidation reaction.

It is preferable to use the thing whose boiling point is 182 degreeC or more as the polyhydric alcohol to be used. When apply | coating an electrically conductive paste using screen printing to a through-hole part, the value of a preferable viscosity exists in an electrically conductive paste. When the boiling point of a polyhydric alcohol is less than 182 degreeC, the viscosity of an electrically conductive paste becomes low and application | coating using screen printing may become difficult.

Specific examples of the polyhydric alcohol include 1,2-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,5-pentanediol, 2-methyl-2, 4-pentanediol, 2-methyl-1,4-butanediol, 1,2-dimethyl-1,4-butanediol, 2-ethyl-1,4-butanediol, 1,5-pentanediol, 2-methyl-1, 5-pentanediol, 3-methyl-1,5-pentanediol, 2,2,4-trimethyl-1,3-pentanediol, 3-ethyl-1,5-pentanediol, 1,6-hexanediol, 2 -Methyl-1,6-hexanediol, 3-methyl-1,6-hexanediol, 2-ethyl-1,3-hexanediol, 1,7-heptanediol, 2-methyl-1,7-heptanediol, 3-methyl-1,7-heptanediol, 4-methyl-1,7-heptanediol, 1,8-octanediol, 2-methyl-1,8-octanediol, 2-ethyl-1,8-octanediol , 3-methyl-1,8-octanediol, 4-methyl-1,8-octanediol, 1,9-nonanediol, ethylene glycol, propylene glycol, neopentyl glycol, diethylene glycol, dipropylene glycol, triethylene Glycol, cyclohexanedimethanol, polyethylene glycol, polypropyl Ethylene glycol, polytetramethylene glycol, trimethylol propane, 1,1,1-trimethylol propane ethylene glycol, glycerin, erythritol, 1,2,6-hexanetriol, and the like.

It is preferable to use 2-ethyl-1,3-hexanediol among the said polyhydric alcohols. 2-Ethyl-1,3-hexanediol is a high boiling point diol solvent having a boiling point of 244 ° C and is compatible with the phenol resin and the modified epoxy resin, and thus is used for curing conductive pastes, especially small through-holes. It is suitable for the case.

[Chelate-forming substance]

The electrically conductive paste concerning this embodiment contains a chelate formation material. In addition, in this embodiment, a chelate formation material refers to the ligand compound which can chelate with respect to the copper powder which is an electrically conductive filler. It is preferable to use the thing which can melt | dissolve in an organic solvent in the process of making a chelate formation material act on a copper powder in the case of adjustment of an electrically conductive paste.

Specific examples of chelate forming materials include chelate forming materials of amines such as ethylenediamine, N- (2-hydroxyethyl) ethylenediamine, trimethylenediamine, 1,2-diaminocyclohexane, triethylenetetramine, di Ethylenetriamine, 1,2,3-triaminopropane, thiodiethylamine, triethanolamine, tetraethylenepentamine, pentaethylenehexamine, trishydroxymethylaminomethane, ethyldiethanolamine, triisopropanolamine, ethylenediamine 1-3-dione which produces | generates the bidentate ligand which uses aromatic ring nitrogen and amino nitrogen, such as tetraacetic acid, for example, 2-aminomethylpyridine, purine, adenine, histamine, etc., and also the acetylacetonate type | mold bidentate ligand And similar compounds thereof, for example acetylacetone, 4,4,4-trifluoro-1-phenyl-1,3-butanedione, hexafluoroacetylacetone , Benzoylacetone, dibenzoylmethane, 5,5-dimethyl-1,3-cyclohexanedione, auxin, 2-methyloxine, auxin-5-sulfonic acid, dimethylglyoxime, 1-nitroso-2-naphthol, 2- Nitroso-1-naphthol, salicyaldehyde, and the like. In addition, in the above-mentioned 1,3-diones and the like compounds that produce the acetylacetonate type bidentate ligands, the keto body itself is not a chelating agent, but keto-enol tautomerism. As a result, the enol functions as an acid, and as a result, the anion species produced by releasing protons can function as a acetylacetonate type bidentate ligand.

When using a chelate-forming substance, a nitrogen-containing heteroaromatic compound composed of a pyridine derivative and 1,10-phenanthroline represented by the following formula I (wherein n represents a natural number of 2 to 8) It is preferable to use one or more types of multidentate ligand compounds selected from the group of 複 素 香 環 化合物). The pyridine derivatives and 1,10-phenanthroline shown in Formula I can chelate metal ions, such as copper ions efficiently, and the produced chelate complex is also relatively stable near room temperature.

An example of the synthesis | combining method of the polypyridine shown by Formula I is shown below. The heat-mixing of the starting raw material with sodium azide causes azides of the ortho position relative to the nitrogen of the pyridine skeleton. Subsequently, it is treated with sodium nitrite in brominated oxyacid to make diazonium bromide, followed by bromination to bromine. When this brominated pyridine is dehalogenated and condensation-polymerized by a divalent nickel complex, for example at 60 ° C. in DMF (N, N-dimethylformamide), yellow to yellowish orange precipitates are obtained. The desired polypyridine is obtained by washing and drying the precipitate in the order of hot toluene, water and hot toluene. The degree of polymerization (n) is adjusted by the selection of starting materials and the degree of bromination of the brominated pyridine contained. For the zero-valent nickel complex, an equimolar mixture of a nickel-1,5-octadiene complex with 1,5-octadiene and triallylphosphine is used. In addition, n is 2 or 3, and the single compound refine | purified as a reagent is marketed. About compounds in which n is 4 or more, it is also possible to synthesize | combine that this n is 2 or 3 as a starting raw material.

In general, in the polypyridine represented by the formula (I) synthesized by the above method, in the recrystallization level purification, the number of repeats (n) of the pyridine skeleton shows a slight distribution, and the value of n is an average value obtained from the molecular weight distribution. Indicates. However, in the usual synthesis method, since pyridine of n = 1 is rarely incorporated in the precipitate obtained, only polypyridine of n or more is contained. When n is 2 or more, sufficient chelate formation ability is exhibited, whereas as n increases, solubility in solvents decreases, and when n exceeds 8, solubility in solvents is insufficient, so that the preparation of a solution required for the desired chelate formation is performed. It tends to become increasingly difficult. Therefore, when using the polypyridine shown by Formula I as a chelate formation substance added to the electrically conductive paste concerning this embodiment, it is preferable to select the repeating number (n) of a pyridine skeleton in the range of 2-8, and more preferable. Preferably, n is used in the range of 2-3.

[Other Ingredients]

The electrically conductive paste which concerns on this embodiment may contain other components other than the component demonstrated above. As another component, a printability improving agent, a boron compound, a coupling agent, a solvent, etc. are mentioned, for example.

[Printability Enhancer]

The electrically conductive paste which concerns on this embodiment may contain the printability improving agent. Examples of the print improver include thickeners, leveling improvers, rheology control agents, and the like. The thickener is an additive that increases the viscosity of the conductive paste, the leveling improver is an additive that lowers the surface tension of the conductive paste, and the rheology control agent imparts thixotropy to the conductive paste and prevents sedimentation during storage. Additives.

By adding the above-described printability improving agent to the conductive paste according to the present embodiment, the printing amount of the conductive paste with respect to the through hole portion can be adjusted, particularly when the conductive paste is applied to the through hole portion of the printed wiring board. Therefore, in the case where the conductive coating layer is formed in the through hole portion using the conductive paste to which the printability improver is added, the shape of the conductive coating after curing becomes good, and in particular, the corner portion of the through hole (through hole is opened on the surface of the substrate). The thickness of the electroconductive film layer in () part) becomes favorable.

It is preferable to add a rheology control agent especially in said printability improvement agent. Suitable rheology control agents include polyethylene oxide rheology control agents, silica rheology control agents, surfactant rheology control agents, metal soap rheology control agents, carbon black rheology control agents, and fine particle calcium carbonates. Rheology control agents, organic bentonite-based rheology control agents, and the like. As a specific example of the rheology control agent, for example, HDK ("HDK" is a registered trademark and is the same in the following), for example, is manufactured by Wacker Asahikasei Silicone Co., Ltd., HDK H15. , HDK H18, HDK H20, HDK H30), TOKABLACK (TOKAI CARBON CO., LTD.), TOKABLACK # 8500 / F, # 8300 / F, # 7550SB / F, # 7400, # 7360SB, # 7350 / F) etc. are mentioned.

Boron Compound

The electrically conductive paste concerning this embodiment may contain the boron compound. By adding a boron compound to the said component with respect to an electrically conductive paste, it is possible to improve the storage stability of an electrically conductive paste, without adding a latent hardening | curing agent. Therefore, when a boron compound is added to the electrically conductive paste which concerns on this embodiment, the electrically conductive paste is not a latent hardening | curing agent, for example, a pyridine derivative (for example, a compound shown by Formula I), or 1,10- Even if it contains amines, such as phenanthroline, it has the characteristic that it is excellent in storage stability. However, the electrically conductive paste which concerns on this embodiment does not need to contain the boron compound.

It is preferable that the boron compound added when adding a boron compound is a boric acid ester compound or a boric acid triester compound. The carbon number of the boric acid triester compound is preferably 3 to 54, more preferably 6 to 30, further preferably 6 to 12 from the viewpoint of availability and / or ease of production.

Examples of the boric acid ester compound include alkyl or aryl esters of boric acid, and specific examples thereof include trimethyl borate, triethyl borate, tributyl borate, tridecyl borate, trioctadecyl borate, and triphenyl borate.

Specific examples of the boric acid triester compound having 6 to 12 carbon atoms include triethyl borate, 2-methoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane and 2-isopropoxy. -4,4,5,5-tetramethyl-1,3,2-dioxaborolane, 2-isopropoxy-4,4,6-trimethyl-1,3,2-dioxaborinane, boric acid Tripropyl, isopropyl borate, tris (trimethylsilyl) borate, tributyl borate and the like.

[Coupling Agent]

The electrically conductive paste concerning this embodiment may contain the coupling agent. By adding a coupling agent with respect to an electrically conductive paste, preferable adhesive strength (fixed strength between the cured coating layer of a conductive paste and a board | substrate) can be obtained easily.

As a preferable coupling agent, the coupling agent effective with respect to the electrically conductive filler which is copper powder, for example, a silane coupling agent, a titanium coupling agent, and / or an aluminum coupling agent, etc. are mentioned.

As a specific example of a preferable coupling agent, for example, (gamma)-glycidoxy propyl trimethoxysilane, (gamma)-glycidoxy propylmethyl diethoxysilane, N-((beta) -aminoethyl)-(gamma) -aminopropyl trimethoxysilane, N- (β-aminoethyl) -γ-aminopropylmethyldimethoxysilane, β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-phenyl-γ- Aminopropyl trimethoxysilane, isopropyl triisostearoyl titanate, titanium tetra-n-butoxide, titanium tetra-2-ethylhexoxide, etc. are mentioned. The coupling agent described above has low volatility and low reactivity with a resin (especially a thermosetting resin).

[menstruum]

The electrically conductive paste which concerns on this embodiment may contain the solvent for adjusting a viscosity.

The solvent is not particularly limited as long as the solvent does not react with the resin (especially the thermosetting resin) and can dissolve the chelate forming material when the chelate forming material is used. Specific examples of the solvent include ethyl cellosolve, methyl cellosolve, butyl cellosolve, ethyl cellosolve acetate, methyl cellosolve acetate, butyl cellosolve acetate, ethyl carbitol, methyl carbitol, butyl carbitol, Ethyl carbitol acetate, methyl carbitol acetate, butyl carbitol acetate and the like.

Moreover, the electrically conductive paste which concerns on this embodiment may contain the antifoamer, the sedimentation inhibitor, the dispersing agent, the zinc powder as antioxidant, the hardening | curing agent of resin, etc. as needed in addition to said component.

[Preferable Content of Each Component]

Next, preferable content of each component with respect to the quantity of the copper powder at the time of preparing the electrically conductive paste which concerns on this embodiment is demonstrated.

Total amount of resin

The amount of the resin component (total amount of the entire resin contained in the conductive paste) relative to 100 parts by mass of the copper powder is preferably in the range of 11 parts by mass to 43 parts by mass, and more preferably in the range of 15 parts by mass to 30 parts by mass. desirable. When the resin component is 11 parts by mass or more and 43 parts by mass or less, the shrinkage of the resin component with respect to the whole paste becomes good, and a good contact ratio between the copper powders can be obtained. Therefore, the paste hardened | cured material obtained using an electrically conductive paste will have favorable electrical conductivity.

In addition, when the resin component is 15 parts by mass or more, more excellent conductivity can be obtained by hardening shrinkage force by the resin. When the resin component is 15 parts by mass or more, when it is 30 parts by mass or less, it is easier to secure the contact area between the copper particles, and more excellent conductivity can be obtained from the paste cured product.

Ratio of phenolic resin in resin component

The content of the phenol resin in the resin component greatly affects the conductivity of the cured paste. Specifically, the preferable range of the amount of the phenol resin relative to 100 parts by mass of the copper powder is in the range of 18% by mass to 20.5% by mass. As described above, the phenolic resin has a higher shrinkage rate at the time of curing than other resins, and the conductivity of the paste cured product obtained when the amount of the phenolic resin is in the range of 18% by mass to 20.5% by mass with respect to 100 parts by mass of copper powder It is optimal.

More generally, it is preferable to make the ratio of the phenol resin in all resin component into the range of 66.0 mass%-99.9 mass%, and when the ratio of the phenol resin in all resin component is 66.0 mass% or more, The more excellent electroconductivity can be obtained by hardening shrinkage force by the hardened | cured paste. When the ratio of the phenol resin in all the resin components is 99.0 mass% or less, since it is easy to ensure the contact area between copper particles, the electroconductivity more excellent in a paste hardened | cured material can be obtained.

Ratio of modified epoxy resin in resin component

It is preferable to make the ratio of the modified epoxy resin in all the resin components into the range of 1.0 mass%-34.0 mass%. When the quantity of the modified epoxy resin in all the resin components exists in the range of 1.0 mass%-34.0 mass%, the elasticity modulus of hardened | cured paste can be reduced and resistance to the temperature change of paste hardened | cured material can be made favorable. In addition, preferable adhesion strength (adhesion strength between the conductive coating layer of the conductive paste and the substrate) can be obtained.

Ratio of highly reactive epoxy resin in resin component

When using highly reactive epoxy resin, it is preferable to make the ratio of the high reactive epoxy resin in all the resin components into the range of 0.2 mass%-5.2 mass%. When the amount of the highly reactive epoxy resin in all the resin components is in the range of 0.2% by mass to 5.2% by mass, more preferable adhesion strength (adhesion strength between the conductive coating layer of the conductive paste and the substrate) can be obtained.

· Amount of alcohol

It is preferable to make the quantity of the polyhydric alcohol with respect to 100 mass parts of copper powders into the range of 0.05 mass part-20 mass parts. When the amount of the polyhydric alcohol is less than 0.05 parts by mass, the reducing effect of the oxide film on the surface of the copper powder by the polyhydric alcohol may not be expressed, and when the amount of the polyhydric alcohol exceeds 20 parts by mass, the dispersibility of the conductive filler In some cases, the polyhydric alcohol may remain in the paste cured product after heat curing, and the resistance value and the shape of the through hole may deteriorate.

The amount of chelate-forming substance

When using a chelate forming material, the amount of the chelate forming material with respect to 100 parts by mass of copper powder is preferably in the range of 0.1 parts by mass to 2.0 parts by mass. When the amount of the chelate forming material is 0.1 parts by mass or more, good through hole resistance can be obtained when the paste cured product is applied to the through hole. Moreover, when the quantity of a chelate formation material is 2.0 mass parts or less, the storage stability of an electrically conductive paste improves.

Amount of printability enhancer

When using a printability improving agent, it is preferable to make the quantity of the printability improvement agent with respect to 100 mass parts of copper powders into the range of 0.5 mass part-4.0 mass parts. In the case where the amount of the printability improving agent is in the range of 0.5 parts by mass to 4.0 parts by mass, the printability of the conductive paste (printing amount of the conductive paste to the through-hole portion at the time of screen printing) is improved, and the shape of the cured coating layer, In particular, the thickness of the cured coating layer in the corner portion of the through hole can be improved. As a result, a good through hole resistance value can be obtained. Moreover, in order to make contact between copper particle mutually favorable and to acquire favorable electroconductivity, it is preferable that the quantity of a printability improving agent is 4.0 mass parts or less.

Amount of boron compound

In the case of using a boron compound, the amount of the boron compound with respect to 100 parts by mass of the copper powder is preferably 0.02 parts by mass or more, and more preferably 0.05 parts by mass or more from the viewpoint of storage stability of the conductive paste. In addition, from the viewpoint of the through-hole resistance value when used for conducting through-holes, the amount of the boron compound is preferably 10.0 parts by mass or less, more preferably 3.0 parts by mass or less.

Quantity of coupling agent

When using a coupling agent, it is preferable to make a coupling agent into the range of 0.1-10.0 mass parts with respect to 100 mass parts of copper powders. When the amount of the coupling agent is in the range of 0.1 to 10.0 parts by mass, preferable adhesion strength (adhesion strength between the conductive coating layer of the conductive paste and the substrate) can be obtained.

[Use of conductive paste]

The hardened | cured material of the electrically conductive paste which concerns on this embodiment is equipped with the favorable electrical conductivity, and the printed wiring board through which the through hole was conducted by this hardened | cured material can be used suitably for various electronic devices. In particular, with the miniaturization of printed wiring boards in recent years, the diameter of through-holes has also been miniaturized to 300 µm or less. When the through hole is made small in size, the amount of the conductive paste filled in the through hole decreases and the conductive coating layer is thinned, so that the conductive filler is easily oxidized. Therefore, although the electric resistance value of the resultant electroconductive film layer deteriorates, the electrically conductive paste which concerns on this embodiment is equipped with a sufficiently low electric resistance value even in such a case.

In addition, in order to obtain the above-described printed wiring board, a known method of conducting through-holes of the printed wiring board using conductive paste, in particular, a known method of curing the conductive paste after printing the conductive paste on the substrate by the screen printing method It is available. By such a method, the hardened | cured material of an electrically conductive paste is filled in a through hole, and the board | substrate which electrically connected between the surface and the back surface is obtained.

EXAMPLE

Although this invention is demonstrated further in detail based on an Example below, this invention is not limited by this. Table 1 shows the evaluation results of the compounding amounts of the components in the Examples and Comparative Examples 1 and the through-hole resistance values. In addition, the unit of the compounding quantity of each component in a table is a mass part. In addition, in the table, for example, "room 1" means Example 1, and "ratio 1" means Comparative Example 1.

The material used by each Example and the comparative example 1 is as follows.

Copper powder

Copper powder (MITSUUI MINING & SMELTING CO., LTD. Product, brand name: T-22),

Phenolic resin

Resol type phenolic resin (product of Gunei Kagaku Kogyo Co., Ltd., brand name: Rejittop PL-4348) having a weight average molecular weight of about 20000 obtained by reacting phenol and formaldehyde under an alkali catalyst.

Modified epoxy resin

Urethane-modified epoxy resin (manufactured by Adeka Co., Ltd., product name: EPU-78-13S, epoxy equivalent weight: 210, epoxy groups in the molecule: two),

Rubber modified epoxy resin (manufactured by Adeka Co., Ltd., product name: EPR-21, epoxy equivalent weight: 200, epoxy groups in a molecule: two),

· Polyhydric alcohol

1,2-butanediol (Wako Pure Chemical Industries, Ltd. product: Examples 2-4, 7-8)

1,3-butanediol (Tokyo Chemical Industry Co., Ltd. Product: Examples 1 and 5)

2-ethyl-1,3-hexanediol (Kyowa Hakko Kogyo Co., Ltd. product: Example 6)

2,3-butanediol (manufactured by Tokyo Kasei Kogyo Co., Ltd .: Example 9)

1,2,6-hexanetriol (Tokyo Kasei Kogyo Co., Ltd. product: Example 10)

Printability Enhancer

Silica rheology control agent (Asahi Kasei Wacker Silicone Co., Ltd. make, brand name: HDK H15),

Chelate-forming substance

2,2'-bipyridyl (compound of formula I wherein n = 2),

·menstruum

Butyl Cellosolve

Butylcellosolve is a monohydric alcohol.

[Method of Preparing Conductive Paste]

In each Example and the comparative example 1, the electrically conductive paste was prepared based on the compounding (mass part) shown in Table 1. Specifically, materials other than a copper powder and a printability improving agent are first put into a container, and it stirred by using a rotating-rotating stirrer (KURABO INDUSTRIES LTD. Product), and it is a uniform liquid liquid. The resin composition of (iii) was prepared. Next, copper powder was added to the prepared resin composition, and the mixture was stirred using a rotating-rotating stirrer (manufactured by Kurashiki Boseki Co., Ltd.). Then, the printability improving agent was added to the prepared copper powder dispersion, and it stirred using the rotating-rotating stirrer (made by Kurashiki Boseki Co., Ltd.), and obtained the electrically conductive paste.

In Examples 1 and 5, 1,3-butanediol is used as the polyhydric alcohol, and 1,2-butanediol is used as the polyhydric alcohol in Examples 2 to 4 and 7 to 8, and in Example 6 2- as the polyhydric alcohol. Ethyl-1,3-hexanediol was used. In Example 9, 2,3-butanediol was used as the polyhydric alcohol, and in Example 10, 1,2,6-hexanetriol was used as the polyhydric alcohol.

In Comparative Example 1, no polyhydric alcohol is used. However, since the electrically conductive paste of the comparative example 1 uses butyl cellosolve as a solvent, it is an electrically conductive paste prepared using monohydric alcohol.

The evaluation test regarding the through-hole resistance value was done about the electrically conductive paste of each said Example and the comparative example 1. The results are also shown in Table 1.

[Through Hole Resistance Evaluation]

100 holes of 0.2 mm diameter (diameter) were formed in a 1.6 mm-thick through-hole-substrate base material by drill processing, and a conductive paste was filled by screen printing. After preheating at 50 ° C. for 2 hours, curing was performed at 150 ° C. for 1 hour. Moreover, in this board | substrate, 100 through-holes are connected in series by the circuit of the front and back of a board | substrate, and the measurement of the conduction resistance of 100 series through-holes is measured by measuring the conduction resistance between the through-holes of the terminal. It is possible. Table 1 shows the through-hole resistance values obtained by converting the resistance values of the 100 through-holes into one.

As can be seen from Table 1, the conductive paste obtained in each of the Examples was compared with the conductive paste obtained in Comparative Example 1 in which components other than the alcohol component were blended in the same amount, regardless of the type of the polyhydric alcohol. It can be seen that the hall resistance value is low and has good electrical conductivity.

Specifically, the through-hole resistance values of the conductive pastes obtained in Examples 1 to 10 were varied depending on the type of polyhydric alcohol and the compounding amount of each component, but any conductive pastes were compared to the conductive pastes obtained in Comparative Example 1, respectively. The resistance value is low. The electrically conductive paste obtained by each Example is prepared using polyhydric alcohol, and the electrically conductive paste obtained by the comparative example is prepared using monohydric alcohol. Compared with polyhydric alcohols, monohydric alcohols are inferior to the reducing action of the oxide film on the surface of the copper powder, and also evaporate and dissipate out of the system early in the heat curing process. Therefore, the electrically conductive paste obtained by the comparative example is considered to cause reoxidation of the copper powder surface, and as a result, the through-hole resistance value is considered to be high.

Moreover, in comparison of each Example, 2-ethyl-1,3-hexanediol compared with the electrically conductive paste prepared using 1, 2- butanediol, 1, 3- butanediol, and 2, 3- butanediol as a polyhydric alcohol. The conductive paste prepared by using 1,2,6-hexanetriol has a low through-hole resistance value. Compared with 1,2-butanediol, 1,3-butanediol, and 2,3-butanediol, 2-ethyl-1,3-hexanediol and 1,2,6-hexanetriol have low volatility, and thus, It is considered that this is because the reducing action of the copper powder occurs over a long time.

As mentioned above, the electrically conductive paste which concerns on this embodiment is equipped with copper powder, a phenol resin, a chelate formation material, and a polyhydric alcohol, and has favorable electrical conductivity also in the electroconductive film layer formed on the small diameter through-hole.

Claims (4)

A conductive paste containing copper powder, a phenol resin, a chelate-forming substance, and a polyhydric alcohol.
The method of claim 1,
The quantity of the said polyhydric alcohol with respect to 100 mass parts of said copper powders exists in the range of 0.05 mass part-20 mass parts.
The method according to claim 1 or 2,
The average particle diameter of the said copper powder is an electrically conductive paste in the range of 1 micrometer-15 micrometers.
The method according to any one of claims 1 to 3,
The quantity of the said phenol resin with respect to 100 mass parts of said copper powders exists in the range of 11 mass parts-43 mass parts.