WO2017159611A1 - Fine copper particle dispersion liquid, electroconductive film formation method, and circuit board - Google Patents

Abstract

A fine copper particle dispersion liquid is characterized by having: first fine copper particles having a median particle diameter of 1-100 nm; second fine copper particles having a median particle diameter that is greater than or equal to 0.3 µm and less than 2 µm; a resin in a concentration greater than or equal to 0.05 mass% and less than 8 mass% in relation to the first fine copper particles and the second fine copper particles; a solvent; and a dispersing agent for dispersing the first fine copper particles and the second fine copper particles in the solvent.

Description

Copper fine particle dispersion, conductive film forming method, and circuit board

This case relates to a copper fine particle dispersion, a conductive film forming method, and a circuit board.

Techniques have been disclosed in which a pattern is formed by printing using ink containing copper fine particles, and a conductive film is formed by light baking (see, for example, Patent Documents 1 and 2). On the other hand, a gravure offset printing method using ink containing conductive metal particles is disclosed (for example, see Patent Document 3).

JP 2013-105605 A JP 2013-104089 A JP2015-193722A

When it is attempted to perform gravure offset printing using ink containing copper fine particles, it is difficult to print patterns having different line widths at once. That is, good printing characteristics may not be obtained. Therefore, it is conceivable to add a resin to the ink, but even if the resin is added, good printing characteristics may not be obtained. Moreover, the resistance of the electrically conductive film obtained after photobaking may become large by adding resin.

The present invention has been made in view of the above problems, and an object thereof is to provide a copper fine particle dispersion, a method for forming a conductive film, and a circuit board that can achieve both good printing characteristics and low resistance.

The copper fine particle dispersion according to the present invention includes a first copper fine particle having a center particle diameter of 1 nm to 100 nm, a second copper fine particle having a center particle diameter of 0.3 μm to less than 2 μm, the first copper fine particle, and the first 2. A resin having a concentration with respect to 2 copper fine particles of 0.05 mass% or more and less than 8 mass%, a solvent, and a dispersant for dispersing the first copper fine particles and the second copper fine particles in the solvent. .

The resin may contain at least one of polyvinyl pyrrolidone, polyester resin, polyvinyl alcohol, terpene phenol resin, acrylic resin, urea-modified medium polarity polyamide, modified urea, and epoxy resin. The ratio of the first copper fine particles to the total mass of the first copper fine particles and the second copper fine particles may be not less than 30 mass% and not more than 70 mass%. The total concentration of the first copper fine particles and the second copper fine particles with respect to the copper fine particle dispersion may be 1 mass% or more and 85 mass% or less.

The method for forming a conductive film according to the present invention includes forming a film of the copper fine particle dispersion on the surface of the object, drying the film, and forming the conductive film by light firing that irradiates the dried film with light. Features. A film of the copper fine particle dispersion may be formed on the object surface using a gravure offset printing method.

The circuit board according to the present invention is characterized in that a circuit having a conductive film formed by the above conductive film forming method is provided on the substrate.

According to the copper fine particle dispersion, the conductive film forming method and the circuit board according to the present invention, both good printing characteristics and low resistance can be achieved.

It is a figure which illustrates a gravure offset printing machine.

First, the conductive film formation procedure using the gravure offset printing method which is suitable for the copper fine particle dispersion according to the embodiment will be described. FIG. 1 is a diagram illustrating a gravure offset printing machine 100. As illustrated in FIG. 1, the gravure offset printing machine 100 includes a first stage 20 on which an intaglio (gravure plate) 10 is placed, a second stage 40 on which a substrate 30 that is a printing object is placed, A transport device 50 that reciprocates the first stage 20 and the second stage 40 in a predetermined linear direction, a doctor blade 60 that can be pressed against the intaglio 10, and a blanket 70 that can be pressed against the intaglio 10 and the substrate 30. And including.

In the gravure offset printing method, a copper fine particle dispersion is applied to the intaglio 10. Next, the first stage 20 is transported to the doctor blade 60 side by the transport device 50, and the doctor blade 60 is pressed against the intaglio 10 to fill the concave portions of the intaglio 10 with the copper fine particle dispersion. The first stage 20 is further transported to the blanket 70 side by the transport device 50, and the blanket 70 is pressed against the intaglio 10, whereby the copper fine particle dispersion filled in the recesses of the intaglio 10 is sucked into the blanket 70. That is, the printing pattern corresponding to the concave portion of the intaglio 10 is transferred to the blanket 70. Next, the second stage 40 is transported to the blanket 70 side by the transport device 50, and the blanket 70 is pressed against the substrate 30 to form a printed pattern film on the substrate 30. Next, if necessary, the coating is dried. By drying the film, the resin, solvent and dispersant in the copper fine particle dispersion are evaporated, leaving copper fine particles. Next, the copper fine particles are fired by irradiating the dried film with light. Thereby, a conductive film is formed.

In the gravure offset printing method as described above, an effect that a high-definition line of, for example, 50 μm or less can be printed is obtained. However, since the amount of the copper fine particle dispersion sucked into the blanket 70 differs depending on the line width, if the print pattern includes different line widths, the line width patterns are printed at once (batch printing). Is difficult). That is, good printing characteristics cannot be obtained. For example, in any line width pattern, the copper fine particle dispersion may remain on the blanket 70 and cannot be transferred to the substrate 30.

Therefore, it is conceivable to print patterns with different line widths at once by adding a resin to the copper fine particle dispersion. This is because the amount of the copper fine particle dispersion sucked into the blanket 70 can be suppressed by controlling the rheological characteristics of the copper fine particle dispersion with the resin. Furthermore, the use of a resin that is difficult to wet for the blanket 70 makes it difficult for the copper fine particle dispersion to remain on the blanket 70. However, it has been found that even if a resin is added, good printing characteristics may not be obtained. Moreover, it has been found that by adding a resin, the resistance of the conductive film obtained by photo-baking the copper fine particle dispersion may be increased. Therefore, in the following embodiments, a copper fine particle dispersion, a conductive film forming method, and a circuit board that can achieve both good printing characteristics and low resistance will be described.

(Embodiment)
The copper fine particle dispersion according to one embodiment includes a first copper fine particle having a center particle diameter of 1 nm to 100 nm, a second copper fine particle having a center particle diameter of 0.3 μm to less than 2 μm, a first copper fine particle, and a second copper fine particle. A resin having a concentration with respect to the copper fine particles of 0.05 mass% or more and less than 8 mass%, a solvent, and a dispersant for dispersing the first copper fine particles and the second copper fine particles in the solvent.

By adding a resin to the copper fine particle dispersion, each line width can be printed at once (collective printing) in the gravure offset printing method. That is, good printing characteristics can be obtained. In order to obtain good printing characteristics, a higher resin concentration is preferable. This is because the amount of the copper fine particle dispersion sucked by the blanket can be suppressed by controlling the rheological characteristics of the copper fine particle dispersion with the resin. Furthermore, it is because the copper fine particle dispersion liquid is less likely to remain on the blanket by using a resin that is difficult to wet the blanket. Therefore, the concentration with respect to the first copper fine particles and the second copper fine particles is set to 0.05 mass% or more. The resin concentration is preferably not excessively high in order to reduce the evaporation amount during the light baking and to lower the resistivity of the conductive film. Therefore, the concentration with respect to the first copper fine particles and the second copper fine particles is set to less than 8 mass%. In order to obtain good printing characteristics, it is preferable to use copper fine particles having a small particle diameter and copper fine particles having a large particle diameter. In order to obtain good dispersion stability of the copper fine particles in the copper fine particle dispersion, the first copper fine particles preferably have a small particle size. Furthermore, it is preferable that the particle diameter of the first copper fine particles is small in order to make a conductor by photo-firing. Therefore, the center particle diameter of the first copper fine particles is set to 1 nm or more and less than 100 nm. By adding the second copper fine particles having a large particle diameter to the first copper fine particles, the amount of the copper fine particle dispersion sucked by the blanket can be suppressed. In order to obtain good printing characteristics, the center particle diameter of the second copper fine particles is preferably sufficiently larger than that of the first copper fine particles. Therefore, the center particle diameter of the second copper fine particles is set to 0.3 μm or more. If the center particle diameter of the second copper fine particles is too large, good dispersion stability cannot be obtained. Therefore, the center particle diameter of the second copper fine particles is set to less than 2 μm.

Hereinafter, other aspects of the copper fine particle dispersion will be described. As the first copper fine particles, those having the same center particle diameter may be used alone, or those having two or more kinds of center particle diameters may be mixed and used. As the second copper fine particles, those having the same center particle diameter may be used alone, or those having two or more kinds of center particle diameters may be mixed and used.

The total concentration of the first copper fine particles and the second copper fine particles is preferably 1 mass% or more and 85 mass% or less with respect to the copper fine particle dispersion. By setting the total concentration to 1 mass% or more, a sufficient amount of copper fine particles for forming the conductive film can be obtained. By setting the total concentration to 85 mass% or less, good dispersion stability and printing characteristics of the first copper fine particles and the second copper fine particles can be obtained.

The ratio of the first copper fine particles to the total mass of the first copper fine particles and the second copper fine particles is preferably 30 mass% or more and 70 mass% or less. In other words, the ratio of the second copper fine particles to the total mass of the first copper fine particles and the second copper fine particles is preferably 30 mass% or more and 70 mass% or less. If the ratio of the first copper fine particles to the total mass of the first copper fine particles and the second copper fine particles is less than 30 mass%, the copper fine particle dispersion may not have sufficient viscosity, and may not be used as a gravure offset ink. Because there is. In addition, if the ratio of the first copper fine particles to the total mass of the first copper fine particles and the second copper fine particles is larger than 70 mass%, the amount of the copper fine particle dispersion sucked into the blanket varies greatly depending on the line width. It is because there is a possibility that it cannot be done. That is, good printing characteristics may not be obtained.

The resin is not particularly limited, and a thermoplastic resin, a thermosetting resin, a thermally decomposable resin, and the like can be used. Examples of the thermoplastic resin include vinyl-based polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, vinyl chloride / vinyl acetate copolymer, polystyrene-based polystyrene, styrene / acrylonitrile copolymer, styrene / butadiene / acrylonitrile copolymer. Polymer, polyethylene, ethylene / vinyl acetate copolymer, polyphenol, polypropylene, polyacetal, polyester, terpene resin, cyclized rubber, alkyd resin, acrylic polymethyl acrylate, polymethyl methacrylate, modified acrylic, Methacryl / styrene copolymer, cellulose acetate, polycarbonate, polyethylene terephthalate, polyamide polyamide, polyimide, polyamideimide, nylon, polyurethane, fluorine Such as butter, and the like, but not limited thereto. Examples of the thermosetting resin include, but are not limited to, phenol resin, melamine resin, epoxy resin, unsaturated polyester, and silicone. Further, they may be cured by photoreaction with ultraviolet rays instead of heat. Examples of the degradable resin include polyperoxide, but are not limited thereto. These resins may be used alone or in combination of two or more.

As the resin, it is preferable to use polyvinyl pyrrolidone, polyester resin, epoxy resin, polyvinyl alcohol, terpene phenol resin, acrylic resin, urea-modified medium polar polyamide, modified urea, or the like. Since these resins are relatively high in polarity, they are easily compatible with copper fine particles and a polar dispersion medium, and are not easily compatible with a non-polar blanket. Because the resin is easily compatible with copper fine particles and polar dispersion media, the rheological properties of the copper fine particle dispersion can be changed, and by controlling the rheological properties, the amount of copper fine particle dispersion absorbed by the blanket can be suppressed. . Further, since the resin is not easily adapted to the blanket, the copper fine particle dispersion is less likely to remain on the blanket. For these reasons, these resins are considered to exhibit good printing characteristics.

Solvent (dispersion medium) is not particularly limited. As the solvent, for example, a polar dispersion medium can be used. As the polar dispersion medium, a protic dispersion medium or an aprotic dispersion medium can be used. The protic dispersion medium is a linear or branched alkyl compound or alkenyl compound having one hydroxyl group and having 5 to 30 carbon atoms. This protic dispersion medium may have 1 to 10 ether bonds and may have 1 to 5 carbonyl groups. By setting the carbon number to 5 or more, elution (corrosion) of copper fine particles into the dispersion medium is suppressed, and good dispersion stability is obtained. By setting the number of carbon atoms to 30 or less, a decrease in the polarity of the dispersion medium is suppressed, and the dispersant is easily dissolved.

Examples of such a protic dispersion medium include 3-methoxy-3-methylbutanol, triethylene glycol monomethyl ether, triethylene glycol monobutyl ether, diethylene glycol monobutyl ether, diethylene glycol monomethyl ether, propylene glycol monobutyl ether, and dipropylene. Glycol monomethyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol mono-tert-butyl ether, 2-octanol, etc. It is not a thing.

The protonic dispersion medium may be a linear or branched alkyl compound or alkenyl compound having 2 to 30 hydroxyl groups and 2 to 30 carbon atoms. This protic dispersion medium may have 1 to 10 ether bonds and may have 1 to 5 carbonyl groups.

Examples of such a protic dispersion medium include 2-methylpentane-2,4-diol, ethylene glycol, propylene glycol, 1,5-pentanediol, polyethylene glycol, triethylene glycol, glycerin, sorbitol and the like. However, it is not limited to these.

Examples of the aprotic polar dispersion medium having a relative dielectric constant of 30 or more include propylene carbonate, 1,3-dimethyl-2-imidazolidinone, hexamethylphosphoramide, N-methylpyrrolidone, N-ethylpyrrolidone, and nitrobenzene. , N, N-diethylformamide, N, N-dimethylacetamide, furfural, γ-butyrolactone, ethylene sulfite, sulfolane, dimethyl sulfoxide, succinonitrile, ethylene carbonate and the like, but are not limited thereto. .

These polar dispersion media may be used alone or in combination of two or more.

The dispersant is not particularly limited. As the dispersant, for example, a compound having at least one acidic functional group and a molecular weight of 200 or more and 100,000 or less or a salt thereof can be used. The acidic functional group of the dispersant is a functional group having acidity, that is, a proton donating property, such as a phosphoric acid group, a phosphonic acid group, a sulfonic acid group, a sulfuric acid group, and a carboxyl group.

When these dispersants are used, one kind may be used alone, or two or more kinds may be appropriately mixed and used. The concentration of the dispersant is, for example, 0.5 mass% or more and 50 mass% or less with respect to the copper fine particle dispersion. A sufficient dispersion effect can be obtained by setting the concentration of the dispersant to 0.5 mass% or more. By setting the concentration of the dispersant to 50 mass% or less, good printing characteristics can be obtained when the copper fine particle dispersion is used in the printing method.

In these copper fine particle dispersions, a leveling agent, a surface conditioner, an antifoaming agent, an anticorrosive, a light baking conditioner, and the like can be appropriately added within a range not impairing the dispersion stability.

In the copper fine particle dispersion liquid formulated as described above, if the dispersant has an acidic functional group and the dispersion medium is a polar dispersion medium, the dispersant has compatibility with the dispersion medium. Furthermore, when the dispersion medium is a protic dispersion medium, it has a proton donating property, so that a hydrogen bond is formed between the dispersion medium molecules and interacts with the acidic functional group of the dispersant. When the dispersion medium is an aprotic polar dispersion medium, it has no proton donating property, but has a high relative dielectric constant of 30 or more, so that the acidic functional group of the dispersant can dissociate protons (H ⁺ ).

Since the surface of the copper fine particles is covered with the dispersant molecule, it is dispersed in the dispersion medium by the electrostatic interaction between the dispersant and the dispersion medium. Since the copper fine particles have a small particle size, aggregation is prevented if the electrostatic interaction between the dispersant and the dispersion medium is large, and if the particles do not aggregate, they do not settle and the dispersion stability of the copper fine particle dispersion becomes high. .

When the protic dispersion medium has an ether bond or a carbonyl group, the polarity is increased, so that the compatibility with the dispersant is increased and the dispersion stability of the copper fine particle dispersion is increased.

Subsequently, the conductive film forming method according to the present embodiment will be described with reference to FIG. 1 again. As the intaglio 10, for example, an intaglio in which a photosensitive resin on a glass plate is formed by exposure, development and washing, an intaglio in which a glass plate, a metal plate, a metal roll or the like is formed by chemical etching and laser etching, or the like can be used. In addition, a known and commonly used intaglio can be used as the intaglio 10. As the blanket 70, for example, a sheet having a layer structure such as a silicone rubber layer, a PET layer, or a sponge layer can be used. These sheets are used, for example, in a state of being wound around a rigid cylinder called a blanket cylinder. As the substrate 30, polyimide, glass, polycarbonate, PET, PEN, cycloolefin polymer, metal plate, or the like can be used.

First, a printed pattern film is formed on the substrate 30 in accordance with the description of FIG. Next, the film is dried. By drying the film, the resin, solvent and dispersant in the copper fine particle dispersion are evaporated, leaving copper fine particles. The drying time of the film is completed in about 30 minutes in an air atmosphere at 100 ° C., for example. In order to shorten the drying time of the film, an air flow or a nitrogen flow may be applied to the film.

Next, the copper fine particles are fired by irradiating the dried film with light. In firing by light irradiation (photo-firing), reduction of the surface oxide film of the copper fine particles and sintering of the copper fine particles occur. The copper fine particles are melted together in the sintering and welded to the substrate 30. The light baking is performed, for example, in the atmosphere and at room temperature. The light source used for light baking is, for example, a xenon lamp. A laser device may be used as the light source. Energy range of the light irradiated from the light source, for example, 0.1 J / cm ² or more and 100 J / cm ² or less. The irradiation time is, for example, 0.1 ms or more and 100 ms or less. The number of times of irradiation may be one time or multiple times of multistage irradiation. The photo-fired film has conductivity. Thereby, a conductive film having a printed pattern is formed. The form of the formed conductive film is a continuous film. The resistivity of the conductive film is, for example, 2 μΩ · cm to 9 μΩ · cm.

Subsequently, a circuit board manufactured using this conductive film forming method will be described. The circuit board has a circuit on the board. A board | substrate shape | molds insulators, such as a polyimide and glass, in plate shape, for example, is a flexible substrate or a rigid board | substrate. The substrate may be made of a semiconductor such as a silicon wafer. The substrate may be one coated with a hard coat layer or primer layer for improving heat resistance, preventing scratches and improving optical properties. The circuit has a conductive film formed by this conductive film forming method. The conductive film constitutes, for example, a conductive wire that electrically connects circuit elements. The conductive film may constitute a circuit element or a part thereof, for example, a coil, a capacitor electrode, or the like.

(Example)
In the following, experiments were conducted on printing characteristics of the copper fine particle dispersions according to the above-described embodiments (Samples 1 to 16 and Comparative Samples 1 to 6). Specifically, batch printing 1 and 2 were performed for a plurality of different line widths using the gravure offset printing method. Then, the electrically conductive film was formed by drying and light baking. In batch printing 1, a line width of 10 μm between 10 μm and 50 μm was used. In batch printing 2, a line width of 7 μm and a line width of about 10 μm between 10 μm and 100 μm were used.

Table 1 and Table 2 show the particle size range of the first copper fine particles. Tables 1 and 2 show the center particle diameters of the second copper fine particles. Tables 1 and 2 show the ratios of the second copper fine particles of the first copper fine particles to the total mass of the first copper fine particles and the second copper fine particles. Tables 1 and 2 show the types of resins contained in the copper fine particle dispersion and the resin concentration (mass%) relative to the total mass of the first copper fine particles and the second copper fine particles. The results of batch printing 1 and 2 are shown in Tables 1 and 2. Tables 1 and 2 show the results of resistance tests of the conductive films formed by drying and light baking.

PVP 2500 is a reagent polyvinyl pyrrolidone having a weight average molecular weight of about 2500. VYLON220 is an amorphous polyester resin (100%) manufactured by Toyobo, and has a number average molecular weight of about 3000. PVP K90 is a reagent polyvinylpyrrolidone having a weight average molecular weight of about 360000. PVA is a reagent polyvinyl alcohol and has a molecular weight of about 2000. PSK125 is a terpene phenol resin having a weight average molecular weight of about 650, which is YS Polystar K125 manufactured by Yasuhara Chemical. XZ # 7157 is Toei Kasei Acrynal, which is an acrylic resin. BYK-430 is a urea-modified medium polar polyamide manufactured by Big Chemie. BYK-410 is a modified urea manufactured by Big Chemie. YX8100BH30 is an epoxy resin having a weight average molecular weight of about 38000 manufactured by Mitsubishi Chemical.

In samples other than Samples 10 and 11, the total concentration of the first copper fine particles and the second copper fine particles in the copper fine particle dispersion is about 80 mass%. In Samples 10 and 11, the total concentration of the first copper fine particles and the second copper fine particles in the copper fine particle dispersion is about 85 mass%. The other composition of the copper fine particle dispersion is as follows.
Solvent: 20% by mass of γ-butyrolactone and 80% by mass of tripropylene glycol monomethyl ether in the balance of the total weight of the copper fine particles and the dispersant.
Dispersant: 4 mass% with respect to the total concentration of DISPERBYK-111 manufactured by Big Chemie, the first copper fine particles and the second copper fine particles.

(analysis)
A blank in the batch printing 2 column of Tables 1 and 2 indicates that only batch printing 1 is performed and batch printing 2 is not performed. The numerical range in the column of batch printing 1 and 2 indicates the range of the line width at which good printing was obtained. Good printing means that the copper fine particle dispersion did not remain in the blanket 70. For example, 10-50 indicates that good printing was obtained for each line width of 10 μm to 50 μm. “X” indicates that good printing could not be obtained at any line width. The wider the line width range, the better the printing characteristics. “◯” in the resistance column of Tables 1 and 2 means that resistance on the order of μΩ · cm was obtained by photo-baking on a polyimide Kapton 150ENA substrate manufactured by Toray DuPont.

As shown in Table 2, in Comparative Sample 1, although good resistivity was obtained, good printing characteristics were not obtained. This is presumably because the copper fine particle dispersion did not contain a resin. Next, in Comparative Sample 2, although good resistivity was obtained, good printing characteristics were not obtained. This is presumably because the copper fine particle dispersion did not contain the second copper fine particles. Next, in Comparative Sample 3, although good resistivity was obtained, good printing characteristics were not obtained. This is presumably because the first copper fine particles were not included in the copper fine particle dispersion. Next, in Comparative Sample 4, although good printing characteristics were obtained, the resistivity was not measured because it was blown off during light firing. This is presumably because a large amount of resin decomposed and vaporized when heat was instantaneously applied during photo-baking. Next, in Comparative Sample 5, the copper fine particles could not be dispersed in the copper fine particle dispersion. This is presumably because the amount of the second copper fine particles having a large particle size has increased. Next, in the copper fine particle dispersion of Comparative Sample 6, although good printing characteristics were obtained, the resistance was not lowered by light baking, and a resistance of μΩ · cm order was not obtained. This is thought to be due to the large amount of resin that could not be decomposed by light baking and remained.

In contrast, good printing characteristics and good resistivity were obtained in any of the samples. First, it is considered that good printing characteristics were obtained by including the second copper fine particles having a center particle size of 0.3 μm or more and less than 2 μm and the resin in the copper fine particle dispersion. Furthermore, it is considered that a favorable resistivity was obtained by setting the resin concentration with respect to the first copper fine particles and the second copper fine particles to 0.05 mass% or more and less than 8 mass%.

Furthermore, resistance was evaluated with a mesh pattern in each sample. Particularly good results were obtained for samples 2, 4, 9-12. Table 3 shows the results. As the base material, a hard coat PET (polyethylene terephthalate) base material (MKZ-GPMP manufactured by Higashiyama Film Co., Ltd.) is used, and the mesh pattern is formed by gravure offset printing so that a line having a width of 7 μm and a thickness of about 1 μm has a space interval of 300 μm. Formed. The 7 μm mesh resistance in Table 3 is a value obtained by pressing a copper plate against a printed and light-fired mesh pattern so that the distance is 1 cm ² and measuring the resistance between them with a tester. As shown in Table 3, when PVP2500 and PSK125 were used as the resin, particularly good results were obtained as compared with the case where other resins were used. These resins are considered to be easily decomposed at the time of light baking as compared with the resins of other samples.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

Claims (7)

A first copper fine particle having a center particle diameter of 1 nm or more and 100 nm or less;
Cupric fine particles having a center particle diameter of 0.3 μm or more and less than 2 μm;
A resin having a concentration with respect to the first copper fine particles and the second copper fine particles of 0.05 mass% or more and less than 8 mass%;
Solvent,
A copper fine particle dispersion comprising: a dispersant for dispersing the first copper fine particles and the second copper fine particles in the solvent. 2. The copper fine particle dispersion according to claim 1, wherein the resin contains at least one of polyvinyl pyrrolidone, polyester resin, polyvinyl alcohol, terpene phenol resin, acrylic resin, urea-modified medium polarity polyamide, modified urea, and epoxy resin. liquid. The copper fine particle dispersion according to claim 1 or 2, wherein a ratio of the first copper fine particles to a total mass of the first copper fine particles and the second copper fine particles is 30 mass% or more and 70 mass% or less. The total concentration of the first copper fine particles and the second copper fine particles with respect to the copper fine particle dispersion is 1 mass% or more and 85 mass% or less, according to any one of claims 1 to 3. Copper fine particle dispersion. A film of the copper fine particle dispersion according to any one of claims 1 to 4 is formed on an object surface,
Drying the coating,
A method of forming a conductive film, comprising forming a conductive film by light baking that irradiates the dried film with light. 6. The method of forming a conductive film according to claim 5, wherein a film of the copper fine particle dispersion is formed on the surface of the object using a gravure offset printing method. A circuit board comprising a circuit having a conductive film formed by the conductive film forming method according to claim 5 or 6 on a substrate.

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