Copper paste

Abstract

The present invention relates to a copper paste, which uses surface-modified copper particles. The copper paste uses, as a sintering promoter, a phosphite having a thermal decomposition residue of 5 wt% or more at 300°C or more. The present invention provides a composition for forming an electrical conductor, the composition being capable of forming, via a short-time heating and sintering treatment, an electrical conductor film having low volume resistivity.

Description

Copper paste

[0001] This application claims priority from Chinese Patent Application No. 202411026247.0 filed on July 29, 2024, the disclosure of which is incorporated herein in its entirety by reference as part of the present application. TECHNICAL FIELD

[0002] The present application relates to a copper paste composition containing copper particles with surface modification used in a short curing process. BACKGROUND

[0003] It is known that a silver paste containing silver particles having good electrical conductivity (1 x 10 -6 Ωcm) is coated on a substrate in a desired wiring pattern, and cured, thereby manufacturing a printed board or the like having a metal film with a desired wiring pattern. However, the metal film of silver is prone to ion migration. Therefore, in consideration of the reliability of electronic devices, the use of a copper paste instead of a silver paste has been studied. However, copper particles are easily oxidized, and therefore the volume resistivity of a metal film of copper obtained by firing the copper particles is increased under the influence of an oxidation film on the surface of the copper particles.

[0004] As a copper paste that can form a metal film with low volume resistivity, the following scheme is proposed. An electrically conductive paste containing copper particles, a thermosetting resin, and a flux activator compound containing a carboxyl group and a phenolic hydroxyl group (Patent Literature 1). However, since the highly active flux activator compound contained in the electrically conductive paste in order to remove the surface oxidation film of the copper particles remains in the metal film formed by the copper paste even after the thermal curing of the paste, there is a risk of adversely affecting the reliability of electronic devices utilizing the metal film. In addition, it is also proposed that a fired-type copper paste that can form a metal film with low volume resistivity is manufactured by heat-treating the copper particles under a reducing atmosphere (Patent Literature 2). However, in addition to the use of a reducing gas, heat treatment at high temperature is also required, and therefore has the problem that the cost is easily increased. In order to compensate for these disadvantages, a composition for forming an electrical conductor characterized by containing copper particles with surface modification and a thermosetting resin is proposed (Patent Literature 3). However, this composition requires a heating and curing process at 150°C for 1 hour in order to obtain the desired resistance value.

[0005] Therefore, in terms of productivity, it is extremely difficult to apply.

[0006] PRIOR ART DOCUMENTS

[0007] PATENT LITERATURE

[0008] [Patent Literature 1] International Publication No. 2008 / 078409 pamphlet

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-298902

[0010] [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-298903 SUMMARY

[0011] PROBLEMS TO BE SOLVED BY THE INVENTION

[0012] The present application provides a conductive body forming composition which can form a conductive body film having a low volume resistivity by a short-time heating sintering process.

[0013] MEANS OF SOLVING THE PROBLEM

[0014] The present application provides a conductive body forming composition used in a copper paste composition which has a residual weight of 5% or more of a phosphite at a temperature of 300°C or more in a thermal gravimetric analysis in air as a sintering promoter, and uses a copper particle surface-modified.

[0015] EFFECTS OF THE INVENTION

[0016] The conductive body forming composition containing a copper particle obtained by the production method of the present application can form a conductive body film having a low volume resistivity.

[0017] In the case of a copper paste using a copper hydride particle as a conductive phase, the contact conduction path between the pure metal copper particles generated by hydrogen elimination in the firing process is coated with the polymer component in the organic binder to prevent oxidation, thereby ensuring the conductivity. However, since it is a contact conduction, the reduction of the resistance value is limited.

[0018] Therefore, a method of achieving a low resistance by a sintering action between the metal copper particles by rapid sintering at a temperature of about 300°C for several seconds is known. However, there is a limit to the reduction of the resistance value due to the competition (antagonistic) reaction between oxidation and solid-phase sintering. Furthermore, the antioxidant of the organic substance does not function due to thermal decomposition in this temperature region, and sintering inhibition due to the residual carbon hinders the low resistance.

[0019] The sintering promotion effect of the phosphite having a residual weight of 5% or more at a temperature of 300°C or more determined by the present application is different from the antioxidant effect known heretofore.

[0020] The antioxidant effect of the phosphite known heretofore is that the phosphite is a Lewis base, can form a coordination complex with various metal ions, is effectively coordinated to the metal surface, and the phosphite having a phosphite structure is easily oxidized to exhibit a high reducing action and is oxidized to a phosphate OP(OR)3which obtains an oxygen atom.

[0021] These antioxidant effects are limited to a temperature range (150°C or less) in which the constitutional structure can be maintained as an organic substance, and in the sintering temperature region (around 300°C) of the metal that is the object of the present application, the constitutional structure cannot be maintained, and thus the formation of a coordination complex is not expected.

[0022] As a result of the present inventors' focusing on the effects that can be exhibited in phosphites and conducting intensive research, it was found that the amount of thermal decomposition residue under conditions of 300°C or more is related to the sintering promotion effect, and that the phosphorus compounds generated during thermal decomposition promote the reduction from copper hydride to copper and the sintering of copper particles.

[0023] In the case of phosphorus compounds, particularly phosphorus pentoxide, which is expected to be the main component, it is not practical to directly incorporate it into the copper paste. Phosphorus compounds are white solids that are not soluble in the copper paste, which is an organic solvent dispersion system, and even if forcibly mixed, they are highly reactive with moisture, and thus deteriorate during storage. Therefore, the basic properties of the copper paste cannot be maintained. DETAILED DESCRIPTION

[0024] (Copper particles)

[0025] As the copper particles subjected to reduction treatment, well-known metal copper particles that are generally used in the conductive body-forming composition called copper paste can be cited. The copper particles subjected to reduction treatment in the present application are primary particles unless otherwise specified, and the particle shape can be spherical or plate-like. Note that the conductive body-forming composition will also be referred to as copper paste hereinafter. The average particle diameter of the copper particles subjected to reduction treatment is 0.5 to 20 μm, and preferably 1 to 10 μm. When the average particle diameter of the copper particles is 0.5 μm or more, the flowability of the copper paste is good. When the average particle diameter of the copper particles is 20 μm or less, fine wiring is easily produced. In the case of the average particle diameter of the copper particles subjected to reduction treatment, the particle diameters of 100 metal copper particles randomly selected from a scanning electron microscope (hereinafter referred to as SEM) image are measured, and the average value is calculated.

[0026] In the case of the copper particles before reduction treatment, the surface is easily oxidized and easily combines with acids. Commercially available copper particles are usually surface-treated with long-chain carboxylic acids such as stearic acid, palmitic acid, and myristic acid in order to impart surface oxidation resistance. In the case of copper particles surface-treated with long-chain carboxylic acids, the surface is hydrophobic, and thus the copper particles easily aggregate in the highly polar dispersion medium used in the present application. In the production method of the present application, copper particles surface-treated with long-chain carboxylic acids can be used as the copper particles subjected to reduction treatment, or the long-chain carboxylic acids on the surface can be removed before reduction treatment, and furthermore, copper particles that have not been surface-treated with long-chain carboxylic acids can be used.

[0027] Further, in the present application, as the copper particles subjected to the reduction treatment, it is preferable to use copper particles subjected to surface treatment with a carboxylic acid having no hydrophobicity in place of a long-chain carboxylic acid. Further, a dispersant is preferably used in order to disperse the copper particles in a dispersion medium. Under the conditions of using such a carboxylic acid having no hydrophobicity and a dispersant, it is preferable to previously subject the copper particles to pretreatment with these compounds. By this pretreatment, the surface of the copper particles can be hydrophilized, and the dispersibility in a polar dispersant such as water can be improved.

[0028] As the carboxylic acid having no hydrophobicity, it is preferable to use a low-molecular-weight aliphatic carboxylic acid, and more preferable to use an aliphatic monocarboxylic acid having 6 or less carbon atoms, an aliphatic hydroxy monocarboxylic acid, an aliphatic amino acid, and the like, and an aliphatic polycarboxylic acid having 10 or less carbon atoms, an aliphatic hydroxy polycarboxylic acid, and the like. The most preferable carboxylic acid is an aliphatic polycarboxylic acid having 8 or less carbon atoms. Specifically, glycine, alanine, citric acid, citric anhydride, malic acid, maleic acid, malonic acid, and the like can be mentioned.

[0029] As the dispersant, various water-soluble compounds having adsorptivity to the copper particles can be used. As the water-soluble compound, water-soluble high-molecular compounds such as polyvinyl alcohol, polyacrylic acid, polyvinylpyrrolidone, hydroxypropyl cellulose, propyl cellulose, ethyl cellulose, chelate compounds such as ethylenediaminetetraacetic acid, iminodiacetic acid, and the like can be mentioned. In particular, for the pretreatment, it is preferable to use an aliphatic dicarboxylic acid such as citric acid, citric anhydride, malic acid, maleic acid, and the like. The amount of the carboxylic acid and the dispersant supported on the copper particles by the pretreatment is preferably 0.1 to 10 mass% with respect to the copper particles. For the pretreatment, the carboxylic acid and the dispersant can be dissolved in a solvent such as water, and the carboxylic acid and the dispersant can be supported on the surface of the copper particles by stirring the solution together with the copper particles. This treatment can be performed under heating, and the treatment speed can be improved by heating. The heating temperature is preferably 50°C or higher and the boiling point of the solvent such as water or lower (the boiling point of the carboxylic acid and the dispersant used or lower). The heating time is preferably 5 minutes or longer. Long heating is not economical, and thus is generally preferably 3 hours or shorter.

[0030] The copper particles subjected to the pretreatment are obtained by using commercially available copper particles treated with a long-chain carboxylic acid as the copper particles. In the pretreatment, the inside of the treatment vessel is preferably replaced with an inert gas in a manner such that the copper surface is not oxidized. As the inert gas, nitrogen, argon, or the like is used. After the pretreatment, the solvent is removed, and, as necessary, washing is performed with water or the like to obtain the copper particles subjected to the pretreatment. The concentration of the copper particles in the copper particle dispersion liquid supplied to the reduction treatment is preferably 0.1 to 50 mass%. When the concentration of the copper particles is 0.1 mass% or more, the amount of water is suppressed, and the production efficiency of the copper particles subjected to the surface modification is good. When the concentration of the copper particles is 50 mass% or less, a tendency can be seen in which the influence of aggregation is reduced and the yield of the copper particles subjected to the surface modification is high. As the dispersion medium of the copper particle dispersion liquid, there is no particular limitation as long as it is a dispersion medium that disperses the copper particles, and a high-polarity dispersion medium is preferred. As the high-polarity dispersion medium, for example, water, methanol, ethanol, 2-propanol, ethylene glycol, or the like can be given. Water is particularly preferred.

[0031] The pH of the copper particle dispersion liquid is adjusted to 3 or less. In the case where the pH of the dispersion liquid obtained by dispersing the copper particles obtained by the pretreatment or the like in a dispersion medium is 3 or less, the reduction treatment can be performed as it is. In the case where the pH of the copper particle dispersion liquid is not 3 or less, the pH is adjusted to 3 or less using a pH adjuster. An acid is generally used as the pH adjuster. As the acid for adjusting the pH, formic acid, citric acid, maleic acid, malonic acid, acetic acid, propionic acid, sulfuric acid, nitric acid, hydrochloric acid, or the like can be appropriately used. By adjusting the pH of the dispersion liquid subjected to the reduction treatment to 3 or less, the removal of the oxide film on the surface of the copper particles is smoothly performed. When the pH of the aqueous solution exceeds 3, there is a tendency in which the effect of removing the surface oxide film is reduced, and the surface modification becomes insufficient. Furthermore, the lower limit of the pH is preferably 0.5. When the pH is 0.5 or more, the elution of copper ions does not excessively proceed, and the surface modification is smoothly performed. In particular, the pH of the dispersion liquid is more preferably 0.5 to 2.0. Note that in the case where the pH is excessively low or the like, an alkali can be used as the pH adjuster to adjust the pH.

[0032] As the acid as the pH adjusting agent, a carboxylic acid having no hydrophobicity as exemplified in the description of the pretreatment is preferable. When a carboxylic acid is used as the pH adjusting agent, there is a case where the carboxylic acid remains on the surface of the copper particles after the reduction treatment. The remaining carboxylic acid is expected to have an effect of protecting the surface of the copper particles and suppressing oxidation of the surface of the copper particles. As the acid as the pH adjusting agent, formic acid is particularly preferable. Formic acid among the carboxylic acids is a compound having an aldehyde structure (-CHO), and thus has reducing property. Therefore, it is expected that even when formic acid remains on the surface of the surface-modified copper particles, oxidation of the surface of the copper particles is further suppressed, and an effect of suppressing an increase in volume resistivity of the conductor obtained using the copper particles is further enhanced. Note that the same effect is expected in the case where formic acid is used as the reducing agent as described below.

[0033] As the reducing agent as the compound for adjusting the oxidation-reduction potential, hypophosphorous acid, hypophosphite salts such as sodium hypophosphite, dimethylamine borane, formic acid, sodium borohydride, and the like can be used. In particular, hypophosphorous acid, sodium hypophosphite, and formic acid are preferable. Formic acid can be used as the pH adjusting agent as described above, and can also be used as the reducing agent. In the case where a reducing agent other than formic acid is not used as the reducing agent, formic acid functions as the pH adjusting agent and the reducing agent. In the case where a reducing agent other than formic acid and formic acid are used in combination, it is similarly considered that formic acid functions as the pH adjusting agent and the reducing agent.

[0034] The amount of the reducing agent used is preferably in excess with respect to copper on the surface of the copper particles. The amount of copper on the surface of the copper particles is difficult to specify, and thus the amount of the reducing agent is preferably expressed with respect to the entire copper particles, and is preferably equal to or more than the equivalent amount. More preferably, 1.2 to 10 times the molar amount of the reducing agent is used with respect to the molar amount of copper of the copper particles. When the amount of the reducing agent is too large, it is not economical, and in addition, the amount of the decomposition product of the reducing agent increases, and removal thereof becomes complicated. The reduction can be performed by adding the reducing agent to a dispersion liquid of the copper particles, and the reduction can also be performed by dispersing the copper particles after the reducing agent is added to the dispersion medium. The reduction reaction is preferably performed at 5 to 60°C, and more preferably at 35 to 50°C. When the temperature of the dispersion liquid is 60°C or lower, the influence of the change in the concentration of the reaction system due to evaporation of the dispersion medium is small.

[0035] The pH in the reaction system composed of the dispersion medium containing the copper particles and the reducing agent is 3 or lower at the start of the reaction, and is preferably maintained at 3 or lower from the start of the reaction to the end of the reaction (the time when the reducing agent has been substantially completely decomposed). Under the conditions of the reduction reaction in the present application, generally, the pH of the reaction system hardly changes from the start of the reaction to the end. Therefore, when the pH at the start of the reaction is 3 or lower, the pH of the reaction system is maintained at 3 or lower from the start of the reaction to the end. In addition, when the pH of the reaction system at the end of the reaction is 3 or lower, it is considered that the pH of the reaction system is maintained at 3 or lower from the start of the reaction to the end.

[0036] After the reducing agent has been substantially completely decomposed, the surface-modified copper particles are separated from the reaction system, washed with water or the like as necessary, and dried to obtain a powder of the surface-modified copper particles. Since the by-products such as the reducing agent decomposition product are generally soluble in the dispersion medium, the surface-modified copper particles can be separated by filtration, centrifugal separation, or the like.

[0037] By the surface modification in the present application, it is considered that the copper oxide present on the surface of the copper particles is reduced to copper. Therefore, it is presumed that the copper oxide that inhibits the conductivity on the surface of the surface-modified copper particles is very little. Further, it is considered that at least a part of the copper on the surface of the copper particles becomes copper hydride by the reduction based on the reducing agent. It is presumed that the copper hydride having been formed on the surface of the copper particles has an effect of delaying the formation of the copper oxide based on oxidation on the surface of the copper particles. Further, the copper hydride becomes copper at a relatively low temperature. For example, it is considered that the copper hydride becomes copper when heated to a temperature exceeding 60°C. Therefore, by the heating for the curing of the thermosetting resin hereinafter, the copper hydride on the surface becomes copper, which is useful for the formation of the conductive path of the joining of the copper particles to each other.

[0038] (Conductive body-forming composition)

[0039] As for the slurry-like conductive body-forming composition (copper paste) of the present application, a powder of the surface-modified copper particles obtained by the present application (which can be heated in a manner that the copper hydride becomes copper as described above), a sintering promoter, a resin binder, and a solvent are contained. As the resin binder, the known thermosetting resin binder used in metal pastes and the like can be cited, and a resin component capable of being sufficiently cured at the temperature at the time of curing is preferably used.

[0040] As the thermosetting resin, a phenol resin, a diallyl phthalate resin, an unsaturated alkyd resin, an epoxy resin, a polyurethane resin, a bismaleimide triazine resin, a polysiloxane resin, a thermosetting acrylic resin, and the like can be cited, and a phenol resin is particularly preferred. As for the amount of the thermosetting resin in the copper paste, the amount of the cured product thereof should not hinder the conductivity caused by the copper particles, and when the amount of the cured product is too much, the contact between the copper particles is hindered, and the volume resistivity of the conductive body is increased. The amount of the thermosetting resin can be appropriately selected depending on the ratio of the volume of the copper particles to the voids present between the copper particles, and generally, 5 to 50 parts by mass, more preferably 5 to 20 parts by mass, relative to 100 parts by mass of the copper particle powder is preferred. When the amount of the thermosetting resin is 5 parts by mass or more, the flow properties of the paste are good. When the amount of the thermosetting resin is 50 parts by mass or less, the volume resistivity of the conductive body film is suppressed to be low.

[0041] As the phosphite ester serving as a sintering promoter, one that can maintain 5% by weight or more of the phosphite ester under the condition of thermal decomposition residue in air at 300°C or higher can be used. For example, there are triethyl phosphite, trilauryl trithiophosphite, diphenyl phosphite, and the like. Those in which the thermal decomposition residue is 5% or less in the same phosphite ester, such as triphenyl phosphite, tris(2,4-di-t-butylphenyl) phosphite, and the like, are not suitable.

[0042] The optimum content varies depending on the reducing ability, and is preferably 20% by weight or less in the paste, and particularly preferably 0.1 to 10%.

[0043] As needed, the copper paste of the present application can contain a solvent, various additives (leveling agents, coupling agents, viscosity modifiers, antioxidants, and the like), and the like, within a range that does not impair the effects of the present application. In particular, a solvent that dissolves the thermosetting resin is preferably contained in order to make the composition a paste-like composition having an appropriate fluidity. As the solvent used in the copper paste, for example, cyclohexanone, cyclohexanol, terpineol, ethylene glycol, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, diethylene glycol, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, and the like can be given. The amount of the solvent used in the copper paste can be adjusted to a viscosity suitable as a printing paste, and thus is preferably 1 to 10% by mass with respect to the copper particles.

[0044] For the copper paste, the above-described components are mixed. At the time of mixing, heating to a degree that the thermosetting resin does not cure and the solvent does not volatilize and disappear can be performed. Furthermore, as needed, the mixing can be performed in a manner that the inside of the mixing vessel is replaced with an inert gas in a manner that the copper particles are not oxidized at the time of mixing. As described above, in the copper paste of the present application, since the copper particles obtained according to the manufacturing method are contained, oxidation in air is less likely to occur, and thus a conductor film having a lower volume resistivity can be formed compared to conventional copper pastes.

[0045] (Manufacture of conductor film)

[0046] The copper paste is used for the formation of a conductor film. The copper paste is applied to the surface of a substrate or the like to form a film of the copper paste, and after the volatile components such as the solvent are removed, the thermosetting resin is cured to manufacture a conductor film. The obtained conductor film contains the copper particles and the cured product of the thermosetting resin. As the substrate, a glass substrate, a plastic substrate (a film-like substrate such as a polyimide film, a polyester film, and the like), a fiber-reinforced composite material (a glass fiber-reinforced resin substrate, and the like), a ceramic substrate, a solar cell crystalline Si substrate, and the like can be given.

[0047] The solar cell crystalline Si substrate is subjected to various treatments and imparted with a conductive film layer according to the use.

[0048] As the coating method, there are known methods such as screen printing, roll coating, air doctor coating, blade coating, bar coating, gravure coating, die coating, and slide coating. As the curing method, there are methods such as hot air heating and heat radiation. The curing temperature and the curing time are appropriately determined according to the kind of the substrate required, and the characteristics of the conductive film. In particular, the curing temperature is preferably from 100 to 350°C. In the conditions for forming the conductive film, the surrounding atmosphere can be air or nitrogen having less oxygen. Since the manufacturing equipment is simple, it is preferable that the surrounding atmosphere is air.

[0049] The volume resistivity of the conductive film is preferably 1.0 x 10 -4 Ωcm or less, depending on the use. When the volume resistivity exceeds 1.0 x 10 -4 Ωcm, there are cases where the use as a conductive body for electronic devices is difficult. In particular, in the present application, from the aspect of achieving a level of conductivity equivalent to that of silver paste, 1.0 x 10 -5 Ωcm or less is preferable. In the conductive film of the present application as described above, the conductive film is formed from the copper paste of the present application, and therefore copper oxide is not easily generated, and the volume resistivity of the film is lower than that of the conductive film obtained from the conventional copper paste.

[0050] Example

[0051] Hereinafter, the present application will be described in more detail based on examples, and the present application is not limited to these examples.

[0052] (Average particle diameter)

[0053] In the case of the copper particles and the surface-modified copper particles, the particle diameters of 100 particles randomly selected from the SEM images obtained by SEM (JEOL-1000) were measured, and the average value was calculated.

[0054] (Measurement of pH)

[0055] The measurement of pH was performed by a pH meter (manufactured by Toa DKK Co., Ltd., HM-20P).

[0056] (Thickness of conductive film)

[0057] The thickness of the conductive film was measured using a contact type film thickness meter.

[0058] (Volume resistivity of conductive film)

[0059] The volume resistivity of the conductive film was measured using a four-probe volume resistivity meter (Keisly).

[0060] [Example 1]

[0061] An aqueous solution was prepared by dissolving 0.86 g of citric anhydride in 50 g of distilled water in a glass three-necked flask. To this was added 5.0 g of commercially available copper particles (manufactured by Kanto Chemical Co., Inc., GUC-P015, average particle diameter: 3 μm), and after replacing the flask with nitrogen, the mixture was heated to reflux at 100°C for 30 minutes. After cooling to room temperature, the copper particles were purified by repeating filtration and dispersion in distilled water three times to obtain pretreated copper particles. The pretreated copper particles were dispersed in 80 g of distilled water in a glass beaker, and 3.0 g of formic acid was added to the beaker which was placed in a water bath at 40°C. Then, 4.0 g of 50 wt% aqueous hypophosphorous acid was added while stirring, and the mixture was stirred for 30 minutes as it was. The pH immediately after the addition of the hypophosphorous acid was 1.3, and the redox potential was 206 mV. After the stirring was completed, the pH of the reaction solution was 1.3, and the redox potential was 205 mV. The precipitate was separated by centrifugal separation. The precipitate was redispersed in 30 g of distilled water, and the agglomerate was precipitated by centrifugal separation again to separate the precipitate. The precipitate was heated at 45°C under reduced pressure of -35 kPa for 60 minutes to volatilize and slowly remove the residual water to obtain surface-modified copper particles.

[0062] To a resin solution in which 0.5 g of phenol-formaldehyde resin (manufactured by Kanto Chemical Co., Inc., RESITOP PL6220) was dissolved in 0.3 g of diethylene glycol monoethyl ether (ECA (CAS 111-90-0), manufactured by Tokyo Chemical Industry Co., Ltd., Grade 1), were added 4.3 g of the surface-modified copper particles and 0.2 g of diphenyl phosphite as a sintering promoter. The mixture was mixed at room temperature with a rotation and revolution mixer, and further kneaded with a three-roll mill to obtain a copper paste. The copper paste was applied to a Si crystal solar cell substrate, dried on a hot plate at 110°C for 1 minute, and a dried conductor film having a width of 2 mm and a thickness of 20 μm was formed. The Si crystal solar cell substrate was heated in a hot laminator set at 300°C for 5 seconds to sinter the conductor film on the Si crystal solar cell substrate, and the volume resistivity of the conductor film was measured. The results are shown in Table 1.

[0063] [Comparative Example 1]

[0064] Surface-modified copper particles were obtained by the same method as in Example 1, and 4.3 g of the surface-modified copper particles were added to a resin solution in which 0.5 g of a phenol resin (manufactured by Group Rika Chemical Industry Co., Ltd., RESITOP PL6220) was dissolved in 0.3 g of diethylene glycol monoethyl ether (ECA (CAS 111-90-0), manufactured by Tokyo Chemical Industry Co., Ltd., Grade 1). The mixture was mixed at room temperature using a rotation and revolution mixer, and further kneaded using a three-roll mill, to obtain a copper paste. The copper paste was applied to a Si crystal solar cell substrate, dried by heating at 110°C for 1 minute on a hot plate, and a dried conductor film having a width of 2 mm and a thickness of 20 μm was formed. The Si crystal solar cell substrate was heated at 300°C for 5 seconds using a heat seal machine, sintered, and the volume resistivity of the conductor film on the Si crystal solar cell substrate was measured. The results are shown in Table 1. The composition was the same as that disclosed in Japanese Patent No. 5439995, and it was confirmed that a resistance value of only 2.5 x 10 -3 Ωcm could be achieved in a high-speed heating process.

[0065] [Example 2]

[0066] Surface-modified copper particles were obtained by the same method as in Example 1, except that commercially available copper particles were changed to GUC-P035 (manufactured by Kanto Chemical Co., Inc., average particle diameter: 5 μm).

[0067] 4.3 g of the surface-modified copper particles were mixed with 0.5 g of a phenoxy resin solution (PKHB 25% butyl carbitol solution, manufactured by Huntsman), 0.08 g of a blocked isocyanate, 0.2 g of diethylene glycol monoethyl ether (ECA (CAS 111-90-0), manufactured by Tokyo Chemical Industry Co., Ltd., Grade 1), and 0.2 g of diphenyl phosphite as a sintering promoter. The mixture was mixed at room temperature using a rotation and revolution mixer, and further kneaded using a three-roll mill, to obtain a copper paste. The copper paste was applied to a Si crystal solar cell substrate, dried by heating at 110°C for 1 minute on a hot plate, and a dried conductor film having a width of 2 mm and a thickness of 20 μm was formed. The Si crystal solar cell substrate was heated at 300°C for 5 seconds using a heat seal machine, sintered, and the volume resistivity of the conductor film on the Si crystal solar cell substrate was measured. The results are shown in Table 2.

[0068] [Comparative Example 2]

[0069] As described above, the surface-modified copper particles were obtained in the same manner as in Example 2, except that the sintering accelerator was not used. The copper paste was obtained in the same manner as above, except that the copper paste was not sintered. The copper paste was applied to the Si crystal solar cell substrate, and dried to form a dried conductor film having a width of 2 mm and a thickness of 20 μm. The Si crystal solar cell substrate was heated for 5 seconds at 300°C in a heat press machine, and the volume resistivity of the conductor film on the Si crystal solar cell substrate was measured. The results are shown in Table 2.

[0070] [Comparative Example 3]

[0071] A mixture of 4.3 g of commercially available copper particles (GUC-P015, manufactured by Hasen Powder New Materials Co., Ltd., average particle diameter: 3 μm) and a resin solution in which 0.5 g of phenol aldehyde resin (RESITOP PL6220, manufactured by Grouping Chemical Co., Ltd.) was dissolved in 0.3 g of diethylene glycol monoethyl ether (ECA (CAS 111-90-0), manufactured by Tokyo Chemical Industry Co., Ltd., Grade 1) was mixed. The mixture was mixed at room temperature using a self-rotation and revolution mixer, and further kneaded using a three-roll mill, to obtain a copper paste. The copper paste was applied to the Si crystal solar cell substrate, and dried on a hot plate at 110°C for 1 minute to form a dried conductor film having a width of 2 mm and a thickness of 20 μm. The Si crystal solar cell substrate was heated for 5 seconds at 300°C in a heat press machine, and the volume resistivity of the conductor film on the Si crystal solar cell substrate was measured. The results are shown in Table 1.

[0072] [Comparative Example 4]

[0073] A mixture of 4.3 g of commercially available copper particles (GUC-P015, manufactured by Hasen Powder New Materials Co., Ltd., average particle diameter: 3 μm) and a resin solution in which 0.5 g of phenol aldehyde resin (RESITOP PL6220, manufactured by Grouping Chemical Co., Ltd.) was dissolved in 0.3 g of diethylene glycol monoethyl ether (ECA (CAS 111-90-0), manufactured by Tokyo Chemical Industry Co., Ltd., Grade 1) was mixed. The mixture was mixed at room temperature using a self-rotation and revolution mixer, and further kneaded using a three-roll mill, to obtain a copper paste. The copper paste was applied to the Si crystal solar cell substrate, and dried on a hot plate at 110°C for 1 minute to form a dried conductor film having a width of 2 mm and a thickness of 20 μm. The Si crystal solar cell substrate was heated for 5 seconds at 300°C in a heat press machine, and the volume resistivity of the conductor film on the Si crystal solar cell substrate was measured. The results are shown in Table 1.

[0074] [Comparative Example 5]

[0075] An aqueous solution was prepared by dissolving 0.86 g of citric anhydride in 50 g of distilled water in a glass three-necked flask. To this was added 5.0 g of commercially available copper particles (manufactured by Kanto Chemical Co., Inc., GUC-P035, average particle diameter: 5 μm), and after replacing the flask with nitrogen, heating under reflux at 100°C was performed for 30 minutes. After cooling to room temperature, purification was performed by repeating filtration and dispersion into distilled water three times to obtain pretreated copper particles. The pretreated copper particles were dispersed into 80 g of distilled water in a glass beaker, and after adding 3.0 g of formic acid, the beaker was placed in a water bath at 40°C. Then, while stirring, 4.0 g of a 50 wt% aqueous hypophosphorous acid solution was added and stirring was performed as is for 30 minutes. Immediately after the addition of the hypophosphorous acid, the pH was 1.3 and the oxidation-reduction potential was 206 mV, and after the completion of stirring, the pH of the reaction solution was 1.3 and the oxidation-reduction potential was 205 mV. The precipitate was separated by centrifugal separation. After redispersion of the precipitate in 30 g of distilled water, the agglomerate was precipitated by centrifugal separation again, and the precipitate was separated. The precipitate was heated at 45°C under reduced pressure of -35 kPa for 60 minutes to volatilize and slowly remove the residual water, and surface-modified copper particles were obtained.

[0076] To a resin solution in which 0.5 g of phenol-formaldehyde resin (manufactured by Kukdo Chemical Co., Ltd., RESITOP PL6220) was dissolved in 0.2 g of diethylene glycol monoethyl ether (ECA (CAS 111-90-0), manufactured by Tokyo Chemical Industry Co., Ltd., Grade 1), 4.3 g of the surface-modified copper particles were added. The mixture was mixed with a self-rotating and revolving mixer at room temperature, and further kneaded with a three-roll mill to obtain a copper paste. The copper paste was applied to a Si crystal solar cell substrate, dried on a hot plate at 110°C for 1 minute, and a dried conductor film having a width of 2 mm and a thickness of 20 μm was formed. The Si crystal solar cell substrate was heated for 5 seconds in a heat sealer set at 300°C, sintered, and the volume resistivity of the conductor film on the Si crystal solar cell substrate was measured. The results are shown in Table 1.

[0077] [Comparative Example 6]

[0078] To the copper paste obtained in the same manner as in Comparative Example 5, 0.2 g of triphenyl phosphite as a sintering accelerator was added, the mixture was mixed with a self-rotating and revolving mixer at room temperature, and further kneaded with a three-roll mill to obtain a copper paste. The copper paste was applied to a Si crystal solar cell substrate, dried on a hot plate at 110°C for 1 minute, and a dried conductor film having a width of 2 mm and a thickness of 20 μm was formed. The Si crystal solar cell substrate was heated for 5 seconds in a heat sealer set at 300°C, sintered, and the volume resistivity of the conductor film on the Si crystal solar cell substrate was measured. The results are shown in Table 1.

[0079] [Example 3]

[0080] To the copper paste obtained in the same manner as in Comparative Example 5, triethyl phosphite 0.2 g as a sintering accelerator was added, and the mixture was mixed with a self-rotation revolution mixer at room temperature and further kneaded with a three-roll mill to obtain a copper paste. The copper paste was applied to a Si crystal solar cell substrate, dried by heating at 110°C for 1 minute on a hot plate, and a dried conductor film having a width of 2 mm and a thickness of 20 μm was formed. The Si crystal solar cell substrate was heated at 300°C for 5 seconds in a heat seal machine, sintered, and the volume resistivity of the conductor film on the Si crystal solar cell substrate was measured. The results are shown in Table 1.

[0081] [Comparative Example 7]

[0082] To the copper paste obtained in the same manner as in Comparative Example 5, triisodecyl phosphite 0.2 g as a sintering accelerator was added, and the mixture was mixed with a self-rotation revolution mixer at room temperature and further kneaded with a three-roll mill to obtain a copper paste. The copper paste was applied to a Si crystal solar cell substrate, dried by heating at 110°C for 1 minute on a hot plate, and a dried conductor film having a width of 2 mm and a thickness of 20 μm was formed. The Si crystal solar cell substrate was heated at 300°C for 5 seconds in a heat seal machine, sintered, and the volume resistivity of the conductor film on the Si crystal solar cell substrate was measured. The results are shown in Table 1.

[0083] [Comparative Example 8]

[0084] To the copper paste obtained in the same manner as in Comparative Example 5, diphenyl isodecyl phosphite 0.2 g as a sintering accelerator was added, and the mixture was mixed with a self-rotation revolution mixer at room temperature and further kneaded with a three-roll mill to obtain a copper paste. The copper paste was applied to a Si crystal solar cell substrate, dried by heating at 110°C for 1 minute on a hot plate, and a dried conductor film having a width of 2 mm and a thickness of 20 μm was formed. The Si crystal solar cell substrate was heated at 300°C for 5 seconds in a heat seal machine, sintered, and the volume resistivity of the conductor film on the Si crystal solar cell substrate was measured. The results are shown in Table 1.

[0085] [Example 4]

[0086] To the copper paste obtained in the same manner as in Comparative Example 5, tri- laurylthiophosphite 0.2 g as a sintering promoter was added, and the mixture was mixed at room temperature with a self-rotating and revolving mixer and further kneaded with a three-roll mill to obtain a copper paste. The copper paste was applied to a Si crystal solar cell substrate, heated at 110°C for 1 minute on a hot plate and dried to form a dried conductor film 2 mm in width and 20 μm in thickness. The Si crystal solar cell substrate was heated at 300°C for 5 seconds in a heat seal machine to perform sintering, and the volume resistivity of the conductor film on the Si crystal solar cell substrate was measured. The results are shown in Table 1.

[0087] [Example 5]

[0088] To the copper paste obtained in the same manner as in Comparative Example 5, tri- laurylthiophosphite 0.2 g as a sintering promoter was added, and the mixture was mixed at room temperature with a self-rotating and revolving mixer and further kneaded with a three-roll mill to obtain a copper paste. The copper paste was applied to a Si crystal solar cell substrate, heated at 110°C for 1 minute on a hot plate and dried to form a dried conductor film 2 mm in width and 20 μm in thickness. The Si crystal solar cell substrate was heated at 300°C for 5 seconds in a heat seal machine to perform sintering, and the volume resistivity of the conductor film on the Si crystal solar cell substrate was measured. The results are shown in Table 1.

[0089] [Comparative Example 9]

[0090] To the copper paste obtained in the same manner as in Comparative Example 5, tri- laurylthiophosphite 0.2 g as a sintering promoter was added, and the mixture was mixed at room temperature with a self-rotating and revolving mixer and further kneaded with a three-roll mill to obtain a copper paste. The copper paste was applied to a Si crystal solar cell substrate, heated at 110°C for 1 minute on a hot plate and dried to form a dried conductor film 2 mm in width and 20 μm in thickness. The Si crystal solar cell substrate was heated at 300°C for 5 seconds in a heat seal machine to perform sintering, and the volume resistivity of the conductor film on the Si crystal solar cell substrate was measured. The results are shown in Table 1.

[0091] [Table 1]

[0092] [Table 2]

[0093] [Table 3] Effect of the amount of sintering promoter added

[0094] [Table 4] Residual amount of sintering promoter at 300°C by thermal decomposition Industrial applicability

[0095] As for the copper paste obtained by the present application, a resistance value of 2 orders of magnitude is achieved compared with a copper paste using only the conventional surface-modified copper powder in a short-time curing process of 10 seconds or less, and is valuable as a method for achieving a low-resistance circuit without using silver, which is relatively expensive, in various applications.

[0096] The above-described exemplary embodiments of the present disclosure are merely for the purpose of illustration, not for the purpose of limiting the scope of protection of the present disclosure, and the scope of protection of the present disclosure is determined by the appended claims.

Claims

1. A copper paste which is a copper paste using a copper particle subjected to surface modification, wherein the copper paste uses a thermal decomposition residue under conditions of 300°C or higher of 5% by weight or more of a phosphite as a sintering promoter.

2. The copper paste according to claim 1, comprising: the copper particle subjected to surface modification 70-90% by weight, a binder resin solution 5-20% by weight, a sintering promoter 0.5-15% by weight, and a solvent 4.5-24.5% by weight.

3. The copper paste according to claim 1, using diphenyl phosphite as the sintering promoter.

4. The copper paste according to claim 1, using triethyl phosphite as the sintering promoter.

5. The copper paste according to claim 1, using trilauryl trithiophosphite as the sintering promoter.

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