Conductive particles, their manufacturing method and conductive material

Abstract

To provide a conductive particle which can reduce connection resistance between electrodes by improving adhesion of a nickel plating film to core particles, while having excellent connection reliability.SOLUTION: The conductive particle comprises a conductive layer formed on the surface of a core particle. The conductive particle has a withstand current value per particle of 1 mA or more at a compression rate of less than 5% and a withstand current value per particle of 10 mA or more at a compression rate of 5% or more. Such a conductive particle can be obtained by delaying film formation on the core particle surface at an early stage of plating treatment than at the late stage.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a conductive particle, a method for producing the same, and a conductive material. [Background technology]

[0002] Conductive particles used as conductive materials in anisotropic conductive materials such as anisotropic conductive films and anisotropic conductive pastes are generally known to have a conductive layer made of metal formed on the surface of a core particle, and this conductive layer provides electrical connection between electrodes and wiring.

[0003] Nickel plating films produced by electroless plating are often used as the conductive layer of these conductive particles, but various innovations have been made to achieve the desired properties. One example is a method proposed in which the phosphorus concentration in a conductive layer containing nickel and phosphorus is unevenly distributed, thereby effectively reducing connection resistance when electrodes are electrically connected (see, for example, Patent Documents 1 to 3). These patent documents describe, in their examples, a method for unevenly distributing the phosphorus concentration in the conductive layer, in which nickel plating films with different phosphorus concentrations are obtained by changing the pH of the nickel plating solution during electroless plating treatment. Patent Document 4 also describes that, in forming a metal film, the metal film may be composed of multiple layers by performing electroless plating in multiple stages. However, there is no mention of the technical significance of the conductive layer being composed of multiple metal films, and it is only mentioned as one of the common techniques. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-214511 [Patent Document 2] International Publication No. 2013 / 108842 Brochure [Patent Document 3] International Publication No. 2014 / 054572 Brochure [Patent Document 4] International Publication No. 2010 / 035708 Brochure Summary of the Invention [Problem to be solved by the invention]

[0005] In a method for forming a nickel plating film on the surface of core particles by electroless nickel plating, the plating process is generally performed by dropping a nickel plating solution into a slurry of core particles, but the method proposed in the above patent document, in which the nickel plating solution is added in multiple batches, leaves room for improvement in the adhesion of the nickel plating film to the core particles. That is, when the conductive particles obtained by the above conventional method are used to connect electrodes, the nickel plating film peels off due to compressive deformation of the conductive particles during connection, resulting in problems such as high connection resistance between electrodes and low connection reliability.

[0006] Therefore, the object of the present invention is to provide conductive particles that can reduce the connection resistance between electrodes while also providing excellent connection reliability by improving the adhesion of a nickel plating film to core particles. [Means for solving the problem]

[0007] As a result of intensive research aimed at solving the above-mentioned problems, the present inventors have found that by slowing the rate of formation of a plating film on the surface of core particles in the early stages of the plating process compared to the later stages, a denser nickel plating film is formed than in the conventional method, thereby improving the adhesion of the nickel plating film to the core particles. Furthermore, they have found that conductive particles having the nickel plating film formed in this way as a conductive layer have excellent resistance to large currents, and therefore have low connection resistance and excellent connection reliability, and have completed the present invention.

[0008] In other words, the present invention provides conductive particles having a conductive layer formed on the surface of a core particle, wherein the current resistance value per conductive particle is 1 mA or more when the compression ratio is less than 5%, and the current resistance value per conductive particle is 10 mA or more when the compression ratio is 5% or more.

[0009] The present invention also provides a method for producing conductive particles, characterized by comprising: a first step of mixing an aqueous slurry of core particles with an electroless nickel plating bath containing a dispersant, a nickel salt, a reducing agent, and a complexing agent, and performing an electroless nickel plating process; and a second step of continuously adding an aqueous solution containing a nickel salt, an aqueous solution containing a reducing agent, and an aqueous solution containing an alkali to the liquid obtained in the first step while controlling the amounts added so as to change the plating deposition rate at least once, thereby performing an electroless nickel plating process. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide conductive particles that have excellent adhesion to core particles, low connection resistance, and excellent connection reliability, and a method for producing the conductive particles. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a SEM photograph of the conductive particles obtained in Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0012] The conductive particles of the present invention have a current resistance value of 1 mA or more, preferably 1.5 mA or more, per conductive particle when the compression ratio is less than 5%, particularly when the compression ratio is 1% or more but less than 5%, and a current resistance value of 10 mA or more, preferably 15 mA or more, per conductive particle when the compression ratio is 5% or more, particularly when the compression ratio is 5% or more but less than 50%. Having a current resistance value per conductive particle within the above range provides excellent resistance to large currents, resulting in low connection resistance and excellent connection reliability.

[0013] The withstand current value in the present invention is the withstand current value per conductive particle at a target compression ratio measured using a conductive particle electrical property measuring device (hereinafter sometimes referred to as a VI device). The VI device may be any device that can measure the voltage-current characteristics and / or current capacity while maintaining the compression ratio of the conductive particles at a constant value, and for example, the device described in JP-A-10-221388 can be used. The withstand current value in the present invention is the value measured for one conductive particle.

[0014] The conductive particles of the present invention preferably have a withstand current value per conductive particle of 0.5 mA or more, particularly 1 mA or more, when the compression ratio is 1% or more and 4% or less. When the withstand current value per conductive particle is within the above range at the initial stage when the compression ratio is small during pressure connection of electrodes, the conductive particles have low connection resistance and excellent connection reliability.

[0015] The conductive particles of the present invention preferably have a withstand current value per conductive particle of 15 mA or more, particularly 20 mA or more, when the compression ratio is 10% or more and 50% or less. Furthermore, it is more preferable that the withstand current value per conductive particle is 20 mA or more when the compression ratio is 30%. By having a withstand current value per conductive particle within the above range in the middle and later stages of pressure connection of electrodes, the conductive particles have excellent resistance to large currents, resulting in low connection resistance and excellent connection reliability.

[0016] As described above, the conductive particles of the present invention have a higher withstand current value in the middle and later stages of compression when the compression ratio is 5% or more than in the early stages of compression when the compression ratio is less than 5%. The inventors believe that this is because the conductive layer of the conductive particles obtained by the method for producing conductive particles of the present invention described below is formed of a dense coating, which improves the adhesion of the coating to the core particles, making it less likely that the conductive layer will peel or break due to deformation of the conductive particles that occurs when electrodes are connected under pressure. This leads to excellent resistance to large currents, and the effects of the present invention, such as low connection resistance and excellent connection reliability, are achieved.

[0017] The conductive particles are formed by forming a conductive layer on the surface of a core particle. The core particles can be inorganic or organic, as long as they are particulate. Examples of inorganic core particles include metal particles such as gold, silver, copper, nickel, palladium, and solder; alloys; glass; ceramics; silica; metal or non-metal oxides (including hydrates); metal silicates including aluminosilicates; metal carbides; metal nitrides; metal carbonates; metal sulfates; metal phosphates; metal sulfides; metal acid salts; metal halides; and carbon. Examples of organic core particles include thermoplastic resins such as natural fibers, natural resins, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polybutene, polyamide, polyacrylate, polyacrylonitrile, polyacetal, ionomers, and polyester; and thermosetting resins such as alkyd resins, phenolic resins, urea resins, benzoguanamine resins, melamine resins, xylene resins, silicone resins, epoxy resins, and diallyl phthalate resins. These may be used alone or in combination.

[0018] The core particles may be composed of both inorganic and organic materials instead of the aforementioned inorganic and organic materials. When the core particles are composed of both inorganic and organic materials, the inorganic and organic materials may be present in the core particles in a core-shell configuration, such as a configuration having an inorganic core and an inorganic shell covering the surface of the core, or a core made of an organic material and an inorganic shell covering the surface of the core. Other examples include blend configurations in which inorganic and organic materials are mixed or randomly fused within a single core particle.

[0019] The core particles are preferably composed of an organic material or a material consisting of both inorganic and organic materials, and more preferably composed of a material consisting of both inorganic and organic materials. The inorganic material is preferably glass, ceramic, silica, metal or non-metal oxides (including hydrated oxides), metal silicates including aluminosilicates, metal carbides, metal nitrides, metal carbonates, metal sulfates, metal phosphates, metal sulfides, metal acid salts, metal halides, and carbon. The organic material is preferably natural fiber, natural resin, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polybutene, polyamide, polyacrylate, polyacrylonitrile, polyacetal, ionomer, polyester, or other thermoplastic resin. Using a core material consisting of such a material can improve the dispersion stability of the particles and also provide appropriate elasticity and improve conductivity during electrical connection of electronic circuits.

[0020] When an organic substance is used as the core particles, it is preferable that the organic substance does not have a glass transition temperature or that the glass transition temperature is higher than 100° C., because the shape of the core particles is easily maintained and the shape of the core particles is easily maintained in the process of forming a metal coating. The glass transition temperature can be determined, for example, as the intersection point of the tangent to the original baseline and the inflection point in the baseline shift portion of a DSC curve obtained by differential scanning calorimetry (DSC).

[0021] When an organic substance is used as the core particle, if the organic substance is a highly crosslinked resin, almost no baseline shift is observed even when the glass transition temperature is measured up to 200°C using the above method. In this specification, such particles are also referred to as particles that do not have a glass transition temperature, and such core particles may be used in the present invention. Specific examples of core particle materials that do not have a glass transition temperature can be obtained by copolymerizing the monomers that make up the organic substance exemplified above with a crosslinkable monomer. Examples of crosslinkable monomers include tetramethylene di(meth)acrylate, ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, ethylene oxide di(meth)acrylate, tetraethylene oxide (meth)acrylate, 1,6-hexane di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, trimeterolpropane tri(meth)acrylate, tetramethylolmethane di(meth)acrylate, tetramethylolmethane tri(meth)acrylate, Examples include polyfunctional (meth)acrylates such as tetramethylolmethane tetra(meth)acrylate, tetramethylolpropane tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, glycerol di(meth)acrylate, and glycerol tridi(meth)acrylate, polyfunctional vinyl monomers such as divinylbenzene and divinyltoluene, silane-containing monomers such as vinyltrimethoxysilane, trimethoxysilylstyrene, and γ-(meth)acryloxypropyltrimethoxysilane, and monomers such as triallyl isocyanurate, diallyl phthalate, diallyl acrylamide, and diallyl ether. Core particles made of such hard organic materials are widely used, particularly in the field of COG (chip on glass).

[0022] There are no particular limitations on the shape of the core particles. Generally, the core particles are spherical. However, the core particles may have shapes other than spherical, such as fibrous, hollow, plate-like, or needle-like, and may have a large number of protrusions on their surfaces or may be amorphous. In the present invention, spherical core particles are preferred because they have excellent filling properties and are easy to coat with metal.

[0023] The conductive layer formed on the surface of the core particle is made of a conductive metal. Examples of metals constituting the conductive layer include gold, platinum, silver, copper, iron, zinc, nickel, tin, lead, antimony, bismuth, cobalt, indium, titanium, germanium, aluminum, chromium, palladium, tungsten, molybdenum, calcium, magnesium, rhodium, sodium, iridium, beryllium, ruthenium, potassium, cadmium, osmium, lithium, rubidium, gallium, thallium, tantalum, cesium, thorium, strontium, polonium, zirconium, barium, and manganese, as well as metal compounds such as ITO and solder. Among these, gold, silver, copper, nickel, palladium, rhodium, and solder are preferred due to their low electrical resistance, and nickel, gold, nickel alloys, and gold alloys are particularly preferred. The metal may be used alone or in combination with two or more.

[0024] The conductive layer may have a single layer structure or a laminated structure consisting of multiple layers. In the case of a laminated structure consisting of multiple layers, the outermost layer is preferably at least one selected from nickel, gold, silver, copper, palladium, a nickel alloy, a gold alloy, a silver alloy, a copper alloy, and a palladium alloy.

[0025] The conductive layer does not have to cover the entire surface of the core particle, but may cover only a portion of it. When only a portion of the surface of the core particle is covered, the covered portion may be continuous, or may be discontinuous, for example, in the form of islands.

[0026] The thickness of the conductive layer is preferably 0.1 nm or more and 2000 nm or less, and more preferably 1 nm or more and 1500 nm or less. When the thickness of the conductive layer is within the above range, the conductive particles have excellent electrical properties. When the conductive particles have protrusions, as described below, the height of the protrusions is not included in the thickness of the conductive layer referred to here. In the present invention, the thickness of the conductive layer can be measured by cutting the particle to be measured in two and observing the cross section of the cut surface with a scanning electron microscope (SEM).

[0027] The average particle diameter of the conductive particles is preferably 0.1 μm or more and 50 μm or less, more preferably 1 μm or more and 30 μm or less. When the average particle diameter of the conductive particles is within the above range, it is easy to ensure conduction between the opposing electrodes without causing a short circuit in a direction different from that between the opposing electrodes. In the present invention, the average particle diameter of the conductive particles is a value measured by SEM observation. Specifically, the average particle diameter of the conductive particles is measured by the method described in the Examples. The particle diameter is the diameter of a circular conductive particle image. When the conductive particles are not spherical, the particle diameter refers to the longest length (maximum length) of the line segments crossing the conductive particle image.

[0028] When the conductive particles have protrusions on their surfaces, i.e., when the outer surface of the conductive layer has protrusions, the height of the protrusions is preferably 20 nm to 1,000 nm, more preferably 50 nm to 800 nm. The number of protrusions depends on the particle size of the conductive particles, but it is advantageous to have 1 to 20,000 protrusions per conductive particle, more preferably 5 to 5,000 protrusions per conductive particle, in order to further improve the conductivity of the conductive particles. Furthermore, the length of the base of the protrusions is preferably 5 nm to 1,000 nm, more preferably 10 nm to 800 nm. The length of the base of the protrusion refers to the length along the surface of the conductive particle at the location where the protrusion is formed when the cross section of the particle is observed with an SEM, and the height of the protrusion refers to the shortest distance from the base of the protrusion to the apex of the protrusion. If a single protrusion has multiple apexes, the highest apex is used as the height of that protrusion. The length of the base of the protrusion and the height of the protrusion are the arithmetic mean values ​​measured for 20 different particles observed with an electron microscope.

[0029] The shape of the conductive particles is not particularly limited, although it depends on the shape of the core particles. For example, the conductive particles may be fibrous, hollow, plate-like, or needle-like, and may have many protrusions on their surfaces or may be amorphous. In the present invention, spherical shapes or shapes having many protrusions on their outer surfaces are preferred in terms of excellent packing properties and connectivity.

[0030] Methods for forming a conductive layer on the surface of core particles include dry methods using vapor deposition, sputtering, mechanochemical methods, hybridization methods, etc., and wet methods using electrolytic plating, electroless plating, etc. Alternatively, a conductive layer may be formed on the surface of core particles by combining these methods.

[0031] In the present invention, forming a conductive layer on the surface of core particles by electroless plating is preferred because it is easy to obtain conductive particles with desired particle properties. In particular, it is preferred that the conductive particles have an electroless nickel-phosphorus plating layer formed on the surface of the core particles as the conductive layer.

[0032] A preferred embodiment of the method for producing conductive particles of the present invention will be described below. When a conductive layer is formed on the surface of a core particle by electroless plating, the surface of the core particle preferably has the ability to capture precious metal ions or is surface-modified to have the ability to capture precious metal ions. The precious metal ions are preferably palladium or silver ions. "Having the ability to capture precious metal ions" means being able to capture precious metal ions as chelates or salts. For example, when an amino group, imino group, amido group, imido group, cyano group, hydroxyl group, nitrile group, carboxyl group, or the like is present on the surface of the core particle, the surface of the core particle has the ability to capture precious metal ions. When the surface is modified to have the ability to capture precious metal ions, for example, the method described in JP-A-61-64882 can be used.

[0033] Such core particles are used to support precious metals on their surfaces. Specifically, the core particles are dispersed in a dilute acidic aqueous solution of a precious metal salt such as palladium chloride or silver nitrate. This allows precious metal ions to be captured on the particle surface. The concentration of the precious metal salt is 1 / m of the surface area of ​​the particle. 2 1x10 -7 ~1×10 -2 A molar range is sufficient. The core particles with the captured precious metal ions are separated from the system and washed with water. The core particles are then suspended in water, and a reducing agent is added to reduce the precious metal ions. This results in the precious metal being supported on the surface of the core particles. Examples of reducing agents that can be used include sodium hypophosphite, sodium borohydride, potassium borohydride, dimethylamine borane, hydrazine, and formalin, and it is preferable to select one of these based on the constituent materials of the desired conductive layer.

[0034] Before capturing the precious metal ions on the surface of the core particles, the particles may be subjected to a sensitization treatment to adsorb tin ions onto the particle surface. To adsorb tin ions onto the particle surface, for example, the surface-modified core particles may be placed in an aqueous solution of stannous chloride and stirred for a predetermined period of time.

[0035] The core particles thus pretreated are then subjected to a conductive layer forming process. There are two types of conductive layer forming processes: a process for forming a conductive layer having protrusions, and a process for forming a conductive layer with a smooth surface. First, the process for forming a conductive layer having protrusions will be described.

[0036] In the treatment for forming a conductive layer having protrusions according to the method for producing conductive particles of the present invention, the following first and second steps are carried out. The first step is an electroless nickel plating step in which an aqueous slurry of core particles is mixed with an electroless nickel plating bath containing a dispersant, nickel salt, a reducing agent, a complexing agent, etc. In this first step, the plating bath self-decomposes simultaneously with the formation of a conductive layer on the core particles. Because this self-decomposition occurs near the core particles, the self-decomposition products are captured on the surface of the core particles during the formation of the conductive layer, generating nuclei for microprojections, which simultaneously form the conductive layer. The microprojections then grow from the generated nuclei.

[0037] In the first step, the core particles described above are thoroughly dispersed in water, preferably in a range of 0.1 to 500 g / L, more preferably 1 to 300 g / L, to prepare an aqueous slurry. The dispersion can be carried out using normal stirring, high-speed stirring, or a shear dispersion device such as a colloid mill or homogenizer. Ultrasound may also be used in the dispersion. If necessary, a dispersant such as a surfactant may be added during the dispersion. Next, the aqueous slurry of the dispersed core particles is added to an electroless nickel plating bath containing a nickel salt, a reducing agent, a complexing agent, and various additives, to carry out the first electroless plating step.

[0038] Examples of the dispersant include nonionic surfactants, zwitterionic surfactants, and / or water-soluble polymers. Examples of the nonionic surfactant include polyoxyalkylene ether surfactants such as polyethylene glycol, polyoxyethylene alkyl ether, and polyoxyethylene alkylphenyl ether. Examples of the zwitterionic surfactant include betaine surfactants such as alkyldimethyl acetate betaine, alkyldimethylcarboxymethyl acetate betaine, and alkyldimethylamino acetate betaine. Examples of the water-soluble polymer include polyvinyl alcohol, polyvinylpyrrolidinone, and hydroxyethyl cellulose. These dispersants can be used alone or in combination. The amount of dispersant used varies depending on the type, but is generally 0.5 to 30 g / L relative to the volume of the liquid (electroless nickel plating bath). In particular, it is preferable for the amount of dispersant used to be in the range of 1 to 10 g / L relative to the volume of the liquid (electroless nickel plating bath), as this further improves the adhesion of the conductive layer.

[0039] The nickel salt may be, for example, nickel chloride, nickel sulfate, or nickel acetate, and its concentration is preferably in the range of 0.1 to 50 g / L. The reducing agent may be, for example, the same as those used for reducing the precious metal ions described above, and is selected based on the constituent material of the target base coating. When a phosphorus compound, such as sodium hypophosphite, is used as the reducing agent, its concentration is preferably in the range of 0.1 to 50 g / L.

[0040] Examples of complexing agents include compounds that have a complexing effect on nickel ions, such as carboxylic acids (salts) such as citric acid, hydroxyacetic acid, tartaric acid, malic acid, lactic acid, gluconic acid, or their alkali metal salts or ammonium salts; amino acids such as glycine; amine acids such as ethylenediamine and alkylamines; other ammonium compounds; EDTA; and pyrophosphate (salts). These can be used alone or in combination. The concentration is preferably 1 to 100 g / L, more preferably 5 to 50 g / L. The pH of the electroless nickel plating bath at this stage is preferably 3 to 14. The electroless nickel plating reaction begins immediately upon addition of the aqueous slurry of core particles and is accompanied by the generation of hydrogen gas. The first step is considered complete when the generation of hydrogen gas has completely ceased.

[0041] Next, in the second step, an electroless nickel plating process is performed by continuously adding an aqueous solution containing a nickel salt, an aqueous solution containing a reducing agent, and an aqueous solution containing an alkali to the solution obtained in the first step while controlling the amounts added so as to change the plating deposition rate one or more times, preferably two or more times. In the second step, these aqueous solutions are each added simultaneously and continuously to the solution obtained in the first step.

[0042] The addition of each aqueous solution to the solution obtained in the first step is preferably carried out while controlling the amount added so that the initial plating deposition rate is 0.05 nm / min to 1.5 nm / min, particularly 0.1 nm / min to 1.2 nm / min. By keeping the initial plating deposition rate within this range, the nickel plating film is deposited more densely on the surfaces of the core particles, thereby improving the adhesion of the resulting conductive layer.

[0043] In the second step of the method for producing conductive particles of the present invention, the plating deposition rate is changed at least once. The plating deposition rate after the change is preferably 0.3 nm / min to 3.0 nm / min, particularly 0.5 nm / min to 2.5 nm / min, and the amount of each aqueous solution added is preferably controlled so that the plating deposition rate falls within the above range. By setting the plating deposition rate after the change within this range, a conductive layer of the desired thickness can be quickly formed on the dense nickel plating film obtained initially, thereby ensuring excellent adhesion of the resulting conductive layer and reducing industrial production costs.

[0044] In the second step of the method for producing conductive particles of the present invention, the plating deposition rate may be changed two or more times. The plating deposition rate after the two changes is preferably 0.3 nm / min to 3.0 nm / min, particularly 0.5 nm / min to 2.5 nm / min. By setting the plating deposition rate within this range, a conductive layer of the desired thickness can be quickly formed on the dense nickel plating film obtained initially, thereby ensuring excellent adhesion of the resulting conductive layer and reducing industrial production costs.

[0045] In the second step, it is preferable to control the amount of each aqueous solution added so as to increase the plating deposition rate, i.e., it is preferable to increase the amount of each aqueous solution added per unit time to increase the plating deposition rate.

[0046] In the second step, after the addition of each of the aqueous solutions has been completed and the generation of hydrogen gas has completely ceased, stirring is continued while maintaining the liquid temperature for a while to complete the reaction.

[0047] In the second step, from the viewpoint of forming a dense film, it is preferable to add an aqueous solution containing a nickel salt and a mixed aqueous solution containing a reducing agent and an alkali to the liquid obtained in the first step.

[0048] The concentration of the nickel salt in the aqueous solution containing the nickel salt is preferably 10 to 1000 g / L, particularly 50 to 500 g / L. When a phosphorus compound is used as the reducing agent, the concentration of the reducing agent in the aqueous solution containing the reducing agent is preferably 100 to 1000 g / L, particularly 100 to 800 g / L. When a boron compound is used as the reducing agent, the concentration is preferably 5 to 200 g / L, particularly 10 to 100 g / L. When hydrazine or a derivative thereof is used as the reducing agent, the concentration is preferably 5 to 200 g / L, particularly 10 to 100 g / L. The concentration of the alkali in the aqueous solution containing the alkali is preferably 5 to 500 g / L, particularly 10 to 200 g / L.

[0049] The second step is carried out continuously after the first step is completed, but alternatively, the first and second steps may be carried out intermittently. In this case, after the first step is completed, the core particles and the plating solution are separated by a method such as filtration, the core particles are dispersed in water to prepare a new aqueous slurry, an aqueous solution containing a complexing agent dissolved in a concentration of preferably 1 to 100 g / L, more preferably 5 to 50 g / L, is added thereto, and a dispersant is dissolved in a concentration of preferably 0.5 to 30 g / L, more preferably 1 to 10 g / L, to prepare an aqueous slurry. The second step may then be carried out by adding the aqueous solutions described above to the aqueous slurry. In this manner, a conductive layer having protrusions can be formed.

[0050] The process for forming a conductive layer with a smooth surface according to the method for producing conductive particles of the present invention will be described below. A conductive layer with a smooth surface can be formed by reducing the concentration of nickel salt in the electroless nickel plating bath in the first step of the treatment for forming the conductive layer having protrusions. That is, the nickel salt may be, for example, nickel chloride, nickel sulfate, or nickel acetate, and its concentration is preferably in the range of 0.01 to 0.5 g / L. A conductive layer with a smooth surface can be formed by performing the first and second steps described above without reducing the concentration of nickel salt in the electroless nickel plating bath.

[0051] The conductive particles of the present invention are preferably obtained by heat-treating the conductive particles obtained by the above-mentioned method under a vacuum of 1000 Pa or less, preferably 0.01 to 900 Pa, and particularly 0.01 to 500 Pa, at a temperature of 200 to 600°C, preferably 250 to 500°C, and particularly 300 to 450°C. Heating the conductive particles while maintaining such a vacuum promotes crystallization of the metal in the conductive layer, thereby reducing electrical resistance and improving electrical conductivity. Note that the degree of vacuum in the present invention is an absolute pressure, i.e., a value when an absolute vacuum is defined as 0.

[0052] The heat treatment time is preferably 0.1 to 10 hours, and more preferably 0.5 to 5 hours. By adopting this treatment time, increases in production costs can be suppressed, and denaturation of the core particles and conductive layer due to thermal history can be suppressed, minimizing the impact on quality. This heat treatment time is the time from when the target treatment temperature is reached to when the heat treatment is completed.

[0053] The heat treatment may be carried out while the conductive particles are left standing, or while stirring. When the heat treatment is carried out while the conductive particles are left standing, it is preferable that the conductive particles are left standing at a thickness of 0.1 mm to 100 mm. By leaving the conductive particles standing at this thickness, the heat treatment of the conductive layer is carried out successfully, and the manufacturing cost can be reduced.

[0054] The heat treatment is carried out after evacuating the container containing the conductive particles, either in a stationary state or with stirring. At this time, the gas phase of the container containing the conductive particles may be replaced with an inert gas such as nitrogen before evacuating, or the container may be evacuated as is. The heat treatment may be carried out multiple times as necessary.

[0055] The heat treatment is preferably carried out by reaching a vacuum of 1000 Pa or less, preferably 0.01 to 900 Pa, and particularly preferably 0.01 to 500 Pa, at room temperature, maintaining the pressure for 5 to 60 minutes, and more preferably 10 to 50 minutes, and then raising the temperature to the treatment temperature. This operation can prevent oxidation of the conductive layer due to oxygen and moisture in the heated atmosphere or the conductive particles, thereby reducing the connection resistance.

[0056] After the heat treatment, it is preferable to release the vacuum after lowering the temperature to 50°C or less, or even 40°C or less, while maintaining the vacuum level. The reason for this is that if the vacuum is released at the temperature immediately after the heat treatment, the presence of oxygen or moisture in the atmosphere may promote oxidation of the conductive layer, resulting in a risk of increased connection resistance. Furthermore, from the perspective of production costs, the vacuum may be released in normal air, but from the perspective of preventing oxidation of the conductive layer, it is more preferable to release the vacuum by purging with an inert gas such as nitrogen, argon, or helium, or a non-oxidizing gas such as a hydrogen-nitrogen mixed gas. In this way, the conductive particles of the present invention are obtained.

[0057] When the conductive particles of the present invention are used as a conductive filler in a conductive adhesive as described below, their surfaces can be further coated with an insulating resin to prevent short circuits between conductive particles. The insulating resin coating is formed so that the surface of the conductive particles is not exposed as much as possible when no pressure is applied, and so that it is broken by the heat and pressure applied when bonding two electrodes with the conductive adhesive, exposing at least the protrusions on the surface of the conductive particles. The thickness of the insulating resin can be approximately 0.1 to 0.5 μm. The insulating resin may cover the entire surface of the conductive particles, or only a portion of the surface of the conductive particles.

[0058] A wide variety of insulating resins known in the art can be used, including, for example, resins made of organic polymers such as phenolic resin, urea resin, melamine resin, allyl resin, furan resin, polyester resin, epoxy resin, silicone resin, polyamide-imide resin, polyimide resin, polyurethane resin, fluororesin, polyolefin resin (e.g., polyethylene, polypropylene, polybutylene), polyalkyl(meth)acrylate resin, poly(meth)acrylic acid resin, polystyrene resin, acrylonitrile-styrene-butadiene resin, vinyl resin, polyamide resin, polycarbonate resin, polyacetal resin, ionomer resin, polyethersulfone resin, polyphenyloxide resin, polysulfone resin, polyvinylidene fluoride resin, ethyl cellulose resin, and cellulose acetate resin.

[0059] Methods for forming an insulating coating layer on the surface of conductive particles include chemical methods such as coacervation, interfacial polymerization, in situ polymerization, and liquid curing coating; physico-mechanical methods such as spray drying, air suspension coating, vacuum deposition coating, dry blending, hybridization, electrostatic coalescence, melting dispersion cooling, and inorganic encapsulation; and physico-chemical methods such as interfacial precipitation.

[0060] The organic polymer constituting the insulating resin may contain a compound containing an ionic group in the polymer structure as a monomer component, provided that the organic polymer is non-conductive. The compound containing an ionic group may be a crosslinkable monomer or a non-crosslinkable monomer. In other words, it is preferable that the organic polymer is formed using a compound in which at least one of the crosslinkable monomer and the non-crosslinkable monomer has an ionic group. The "monomer component" refers to a structure derived from a monomer in the organic polymer, and is a component derived from the monomer. By subjecting the monomer to polymerization, an organic polymer containing the monomer component as a constituent unit is formed.

[0061] The ionic group is preferably present at the interface of the organic polymer that constitutes the insulating resin. Furthermore, the ionic group is preferably chemically bonded to a monomer component that constitutes the organic polymer. Whether or not the ionic group is present at the interface of the organic polymer can be determined by determining whether or not the insulating resin is attached to the surface of the conductive particle by scanning electron microscope observation when an insulating resin containing an organic polymer having an ionic group is formed on the surface of the conductive particle.

[0062] Examples of the ionic group include onium-based functional groups such as a phosphonium group, an ammonium group, a sulfonium group, etc. Among these, from the viewpoint of increasing the adhesion between the conductive particle and the insulating resin and forming conductive particles that combine high levels of insulation and conduction reliability, an ammonium group or a phosphonium group is preferred, and a phosphonium group is more preferred.

[0063] The onium functional group is preferably one represented by the following general formula (1).

[0064] [ka] (In the formula, X represents a phosphorus atom, a nitrogen atom, or a sulfur atom; R may be the same or different and represents a hydrogen atom, a linear, branched, or cyclic alkyl group, or an aryl group; n is 1 when X represents a nitrogen atom or a phosphorus atom, and is 0 when X represents a sulfur atom; * represents a bond.)

[0065] Counterions for the ionic groups include, for example, halide ions. Examples of halide ions include Cl. - , F - , Br - , I - Examples include:

[0066] In formula (1), examples of the linear alkyl group represented by R include linear alkyl groups having 1 to 20 carbon atoms, and specific examples thereof include a methyl group, an ethyl group, an n-propyl group, an n-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, an n-nonyl group, an n-decyl group, an n-undecyl group, an n-dodecyl group, an n-tridecyl group, an n-tetradecyl group, an n-pentadecyl group, an n-hexadecyl group, an n-heptadecyl group, an n-octadecyl group, an n-nonadecyl group, and an n-icosyl group.

[0067] In formula (1), examples of the branched alkyl group represented by R include branched alkyl groups having 3 to 8 carbon atoms, and specific examples include an isopropyl group, an isobutyl group, an s-butyl group, a t-butyl group, an isopentyl group, an s-pentyl group, a t-pentyl group, an isohexyl group, an s-hexyl group, a t-hexyl group, and an ethylhexyl group.

[0068] In formula (1), examples of the cyclic alkyl group represented by R include cycloalkyl groups such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, and cyclooctadecyl.

[0069] In formula (1), examples of the aryl group represented by R include a phenyl group, a benzyl group, a tolyl group, and an o-xylyl group.

[0070] In general formula (1), R is preferably an alkyl group having 1 to 12 carbon atoms, more preferably an alkyl group having 1 to 10 carbon atoms, and even more preferably an alkyl group having 1 to 8 carbon atoms. Furthermore, in general formula (1), R is more preferably a linear alkyl group. Such a configuration of the onium functional group improves the adhesion between the insulating resin and the conductive particles, ensuring insulation, and further improving the reliability of conduction during thermocompression bonding.

[0071] From the viewpoint of facilitating the acquisition of monomers and the synthesis of polymers, as well as increasing the production efficiency of insulating resins, it is preferable that the organic polymer having an ionic group that constitutes the insulating resin has a constituent unit represented by the following general formula (2) or general formula (3).

[0072] [ka] (In the formula, X, R, and n are defined as in the general formula (1). m is an integer of 0 to 5. An - indicates a monovalent anion.)

[0073] [ka] (In the formula, X, R, and n are the same as those in the general formula (1). - indicates a monovalent anion. m 1 is an integer of 1 or more and 5 or less. R5 is a hydrogen atom or a methyl group.

[0074] As examples of R in formula (2) and formula (3), the explanation of the functional group of R in general formula (1) above is applied as appropriate. The ionic group may be bonded to the para-position, ortho-position, or meta-position relative to the CH group of the benzene ring in formula (2), and is preferably bonded to the para-position. In formula (2) and formula (3), monovalent An - Suitable examples of the halide ions include Cl. - , F - , Br - , I - Examples include:

[0075] In the general formula (2), m is preferably an integer of 0 or more and 2 or less, more preferably 0 or 1, and particularly preferably 1. In the general formula (3), m 1 is preferably 1 or more and 3 or less, more preferably 1 or 2, and most preferably 2.

[0076] The organic polymer having an ionic group preferably contains a monomer component having, for example, an onium-based functional group and an ethylenically unsaturated bond. From the viewpoint of facilitating the availability of the monomer and the synthesis of the polymer and improving the production efficiency of the insulating resin, the organic polymer having an ionic group also preferably contains a non-crosslinkable monomer component.

[0077] Examples of non-crosslinkable monomers having an onium functional group and an ethylenically unsaturated bond include ammonium group-containing monomers such as N,N-dimethylaminoethyl methacrylate, N,N-dimethylaminopropylacrylamide, and N,N,N-trimethyl-N-2-methacryloyloxyethyl ammonium chloride; sulfonium group-containing monomers such as phenyl methacrylate dimethylsulfonium methyl sulfate; 4-(vinylbenzyl)triethylphosphonium chloride, 4-(vinylbenzyl)trimethylphosphonium chloride, and 4-(vinylbenzyl)tributyl Examples of suitable monomers include phosphonium chloride, 4-(vinylbenzyl)trioctylphosphonium chloride, 4-(vinylbenzyl)triphenylphosphonium chloride, 2-(methacryloyloxyethyl)trimethylphosphonium chloride, 2-(methacryloyloxyethyl)triethylphosphonium chloride, 2-(methacryloyloxyethyl)tributylphosphonium chloride, 2-(methacryloyloxyethyl)trioctylphosphonium chloride, and 2-(methacryloyloxyethyl)triphenylphosphonium chloride. The organic polymer having an ionic group may contain two or more non-crosslinkable monomer components.

[0078] In the organic polymer constituting the insulating resin, ionic groups may be bonded to all of the monomer components, or ionic groups may be bonded to a portion of all the structural units of the organic polymer. When ionic groups are bonded to a portion of all the structural units of the organic polymer, the proportion of the monomer components to which ionic groups are bonded is preferably 0.01 mol% to 99 mol%, more preferably 0.02 mol% to 95 mol%. Here, the number of monomer components in the organic polymer is calculated by counting a structure derived from one ethylenically unsaturated bond as one structural unit of the monomer. When ionic groups are contained in both crosslinkable and non-crosslinkable monomers, the proportion of the monomer components is the total amount.

[0079] The insulating resin coating may be in the form of a layer of insulating fine particles or a continuous insulating film.

[0080] When the insulating resin is made of insulating fine particles, by thermocompression bonding conductive particles coated with the insulating fine particles between electrodes, the insulating fine particles melt, deform, peel off, or move on the conductive particle surface, exposing the metal surface of the conductive particle in the thermocompression-bonded portion, thereby enabling conduction between the electrodes and obtaining connectivity. Meanwhile, the surface portion of the conductive particle facing in a direction other than the thermocompression bonding direction is generally maintained in a state where the conductive particle surface is covered with the insulating fine particles, so that conduction in a direction other than the thermocompression bonding direction is prevented.

[0081] The insulating fine particles, containing the ionic groups on their surfaces, easily adhere to the conductive particles, thereby ensuring a sufficient proportion of the conductive particle surfaces covered with the insulating fine particles and effectively preventing the insulating fine particles from peeling off from the conductive particles, etc. Therefore, the insulating fine particles are more likely to exhibit a short-circuit prevention effect in a direction different from that between the opposing electrodes, and improved insulation in that direction can be expected.

[0082] The shape of the insulating fine particles is not particularly limited and may be spherical or may be a shape other than spherical. Examples of shapes other than spherical include fibrous, hollow, plate-like, and needle-like. The insulating fine particles may also have a large number of protrusions on their surface or may be amorphous. Spherical insulating fine particles are preferred in terms of adhesion to conductive particles and ease of synthesis.

[0083] The average particle diameter (D) of the insulating fine particles is preferably 10 nm or more and 3,000 nm or less, more preferably 15 nm or more and 2,000 nm or less. When the average particle diameter of the insulating fine particles is within the above range, the obtained coated particles do not cause a short circuit in a direction different from that between the opposing electrodes, and it is easy to ensure conductivity between the opposing electrodes. In the present invention, the average particle diameter of the insulating fine particles is a value measured by observation using a scanning electron microscope, and specifically, it is measured by the method described in the examples below.

[0084] The particle size distribution of insulating fine particles measured by the above-mentioned method has a certain range. Generally, the range of the particle size distribution of a powder is expressed by the coefficient of variation (hereinafter also referred to as "CV") shown in the following calculation formula (1). CV(%)=(standard deviation / average particle diameter)×100...(1) A large CV indicates a wide particle size distribution, while a small CV indicates a sharp particle size distribution. The coated particles of this embodiment preferably use insulating fine particles with a CV of 0.1% or more and 20% or less, more preferably 0.5% or more and 15% or less, and most preferably 1% or more and 10% or less. A CV within this range has the advantage of allowing the thickness of the coating layer of insulating fine particles to be uniform.

[0085] Furthermore, the insulating resin may be a continuous film made of a polymer and having ionic groups, instead of the insulating fine particles. When the insulating resin is a continuous film having ionic groups, thermocompression bonding of the conductive particles between electrodes melts, deforms, or peels the continuous film, exposing the metal surface of the conductive particles, thereby enabling conduction between the electrodes and achieving connectivity. In particular, thermocompression bonding of the conductive particles between electrodes often results in the continuous film being torn, exposing the metal surface. Meanwhile, the surface portions of the conductive particles facing in a direction different from the thermocompression bonding direction generally maintain the state of coating the conductive particles with the continuous film, preventing conduction in directions other than the thermocompression bonding direction. It is preferable that the continuous film also has ionic groups on its surface.

[0086] The thickness of the continuous film is preferably 10 nm or more from the viewpoint of improving insulation in a direction different from that between the opposing electrodes, and is preferably 3,000 nm or less from the viewpoint of facilitating electrical conduction between the opposing electrodes. From this viewpoint, the thickness of the continuous film is preferably 10 nm or more and 3,000 nm or less, and more preferably 15 nm or more and 2,000 nm or less.

[0087] As with insulating fine particles, in the continuous coating, the ionic group is preferably part of the chemical structure of the substance that constitutes the continuous coating. In the continuous coating, the ionic group is preferably contained in at least one structure of the structural unit of the polymer that constitutes the continuous coating. The ionic group is preferably chemically bonded to the polymer that constitutes the continuous coating, more preferably bonded to a side chain of the polymer.

[0088] When the insulating resin is a continuous film, it is preferable that the continuous film be obtained by coating conductive particles with insulating fine particles having ionic groups on their surfaces and then heating the insulating fine particles. Alternatively, it is preferable that the continuous film be obtained by dissolving the insulating fine particles in an organic solvent. As described above, insulating fine particles having ionic groups tend to adhere to conductive particles, which ensures a sufficient proportion of the insulating fine particles on the conductive particle surface and makes it easier to prevent the insulating fine particles from peeling off from the conductive particles. Therefore, the continuous film obtained by heating or dissolving the insulating fine particles that coat the conductive particles can have a uniform thickness and a high proportion of the insulating fine particles on the conductive particle surface.

[0089] The conductive particles according to the manufacturing method of the present invention may be treated with a surface treatment agent in order to enhance the affinity with the insulating resin and improve adhesion. Examples of the surface treatment agent include benzotriazole compounds, titanium compounds, higher fatty acids or derivatives thereof, phosphate esters, phosphites, etc. These may be used alone or in combination as needed.

[0090] The surface treatment agent may or may not be chemically bonded to the metal on the surface of the conductive particle. The surface treatment agent is sufficient as long as it is present on the surface of the conductive particle, and in this case, it may be present on the entire surface of the conductive particle or only on a part of the surface.

[0091] The triazole-based compounds include compounds having a nitrogen-containing heterocyclic structure having three nitrogen atoms in a five-membered ring.

[0092] The triazole compounds include compounds having a triazole monocyclic structure that is not condensed with other rings, as well as compounds having a ring structure in which a triazole ring is condensed with other rings, such as a benzene ring or a naphthalene ring.

[0093] Among these, compounds having a ring structure in which a triazole ring is fused with another ring are preferred because of their excellent adhesion to insulating resins, and benzotriazole-based compounds, which are compounds having a structure in which a triazole ring is fused with a benzene ring, are particularly preferred. Benzotriazole compounds include those represented by the following general formula (I).

[0094] [ka] (In the formula, R 11 is a negative charge, a hydrogen atom, an alkali metal, an optionally substituted alkyl group, an amino group, a formyl group, a hydroxyl group, an alkoxy group, a sulfonic acid group, or a silyl group, and R 12 , R 13 , R 14 and R 15 are each independently a hydrogen atom, a halogen atom, an optionally substituted alkyl group, a carboxyl group, a hydroxyl group, or a nitro group.

[0095] R in formula (I) 11 Examples of the alkali metal represented by R include lithium, sodium, and potassium. 11 The alkali metal represented by R in formula (I) is an alkali metal cation. 11 is an alkali metal, R 11 The bond between the nitrogen atom and the alkyl group may be an ionic bond. R in formula (I) 11 , R 12 , R 13 , R 14 and R 15 Examples of the alkyl group represented by the formula (I) include those having 1 to 20 carbon atoms, and particularly preferably those having 1 to 12 carbon atoms. The alkyl group may be substituted, and examples of the substituent include an amino group, an alkoxy group, a carboxyl group, a hydroxyl group, an aldehyde group, a nitro group, a sulfonic acid group, a quaternary ammonium group, a sulfonium group, a sulfonyl group, a phosphonium group, a cyano group, a fluoroalkyl group, a mercapto group, and a halogen atom. R 11The alkoxy group represented by the following formula is preferably an alkoxy group having 1 to 12 carbon atoms. Also, R 12 , R 13 , R 14 and R 15 The number of carbon atoms in the alkoxy group as a substituent of the alkyl group represented by formula (I) is preferably 1 to 12. 12 , R 13 , R 14 and R 15 Examples of the halogen atom represented by the formula (I) include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

[0096] Specific triazole compounds include compounds having a triazole monocyclic structure such as 1,2,3-triazole, 1,2,4-triazole, 3-amino-1H-1,2,4-triazole, 5-mercapto-1H-1,2,3-triazole sodium, 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole, and 3-amino-5-mercapto-1,2,4-triazole, as well as compounds having a ring structure in which a triazole ring is condensed with another ring, such as benzotriazole, 1-methyl-1H-benzotriazole, 4-methyl-1H-benzotriazole, 5-methyl-1H-benzotriazole, 4-carboxy-1H-benzotriazole, 5-carboxy-1H-benzotriazole, 5-ethyl-1H-benzotriazole, and 5-propyl-1H-benzotriazo benzotriazole, 5,6-dimethyl-1H-benzotriazole, 1-aminobenzotriazole, 5-nitrobenzotriazole, 5-chlorobenzotriazole, 4,5,6,7-tetrabromobenzotriazole, 1-hydroxybenzotriazole, 1-(methoxymethyl)-1H-benzotriazole, 1H-benzotriazole-1-methanol, 1H-benzotriazole-1-carboxaldehyde, 1-(chloromethyl)-1H-benzotriazole, 1-hydroxy-6-(trifluoromethyl)benzotriazole, benzotriazole butyl ester, 4-carboxyl-1H-benzotriazole butyl ester, 4-carboxyl-1H-benzotriazole octyl ester, 1-[N,N-bis(2-ethylhexyl)aminomethyl]methylbenzotriazole, 2,2'-[[(methyl-1H-benzotriazol-1-yl)methyl]imino]bisethanol, tetrabutylphosphonium benzotriazolate, 1H-benzotriazol-1-yloxytris(dimethylamino)phosphonium hexafluorophosphate, 1H-benzotriazol-1-yloxytripyrrolidinophosphonium hexafluorophosphate, 1-(formamidomethyl)-1H-benzotriazole, 1-[bis(dimethylamino)methylene]-1H-benzotriazolium 3- Oxide hexafluorophosphate, 1-[bis(dimethylamino)methylene]-1H-benzotriazolium 3-oxide tetrafluoroborate, (6-chloro-1H-benzotriazol-1-yloxy)tripyrrolidinophosphonium hexafluorophosphate, O-(benzotriazol-1-yl)-N,N,N',N'-bis(tetramethylene)uronium hexafluorophosphate, O-(6-chlorobenzotriazol-1-yl)-N,N,N',N'-tetramethyluronium Tetrafluoroborate, O-(6-chlorobenzotriazol-1-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate, O-(benzotriazol-1-yl)-N,N,N',N'-bis(pentamethylene)uronium hexafluorophosphate, 1-(trimethylsilyl)-1H-benzotriazole, 1-[2-(trimethylsilyl)ethoxycarbonyloxy]benzotriazole, 1-(trifluoromethanesulfonyl)-1H-benzotriazole, (trimethylsilyl)-1H-benzotriazole, trifluoroacetyl)benzotriazole, tris(1H-benzotriazol-1-yl)methane, 9-(1H-benzotriazol-1-ylmethyl)-9H-carbazole, [(1H-benzotriazol-1-yl)methyl]triphenylphosphonium chloride, 1-(isocyanomethyl)-1H-benzotriazole, 1-[(9H-fluoren-9-ylmethoxy)carbonyloxy]benzotriazole, 1,2,3-benzotriazole sodium salt, naphthotriazole, and the like.

[0097] As the titanium-based compound, for example, a compound having a structure represented by general formula (II) is particularly preferred because when present on the surface of a conductive particle, affinity between the insulating resin and the conductive particle can be easily obtained, and the compound is easily dispersed in a solvent, allowing the surface of the conductive particle to be uniformly treated.

[0098] [ka] (R 21 is a divalent or trivalent group, and R 22 is an aliphatic hydrocarbon group having from 2 to 30 carbon atoms, an aryl group having from 6 to 22 carbon atoms, or an arylalkyl group having from 7 to 23 carbon atoms, p and r are each an integer of from 1 to 3, satisfying p+r=4, q is an integer of 1 or 2, and R 21 is a divalent group, q is 1, and R 21 When R is a trivalent group, q is 2. When q is 2, multiple R 22 may be the same or different. * represents a bond.)

[0099] R 22 Examples of the aliphatic hydrocarbon group having 4 to 28 carbon atoms represented by the formula (I) include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, icosyl, henicosenyl, docosyl, etc. Examples of unsaturated aliphatic hydrocarbon groups include alkenyl groups such as dodecenyl, tridecenyl, tetradecenyl, pentadecenyl, hexadecenyl, heptadecenyl, nonadecenyl, icosenyl, eicosenyl, henicosenyl, and docosenyl. Examples of the aryl group having 6 to 22 carbon atoms include a phenyl group, a tolyl group, a naphthyl group, and an anthryl group. Examples of the arylalkyl group having 7 to 23 carbon atoms include a benzyl group, a phenethyl group, and a naphthylmethyl group. As the hydrophobic group, a straight-chain or branched-chain aliphatic hydrocarbon group is particularly preferred, and a straight-chain aliphatic hydrocarbon group is particularly preferred. In order to enhance the affinity between the insulating resin and the conductive particles, the aliphatic hydrocarbon group as the hydrophobic group is more preferably one having 4 to 28 carbon atoms, and most preferably one having 6 to 24 carbon atoms.

[0100] R 21 Examples of the divalent group represented by the formula include -O-, -COO-, -OCO-, and -OSO2-. 21 Examples of the trivalent group represented by the formula include -P(OH)(O-)2, -OPO(OH)-OPO(O-)2, and the like.

[0101] In general formula (II), * represents a bond, which may be bonded to the metal coating of the conductive particle or to another group, etc. In this case, examples of the other group include hydrocarbon groups, and specific examples include alkyl groups having 1 to 12 carbon atoms.

[0102] The titanium-based compound having the structure represented by general formula (II) includes the titanium-based compound having the structure represented by general formula (II) 21 A compound having a structure in which R is a divalent group is preferred in terms of availability and the ability to process the conductive particles without impairing their conductive properties. 21 The structure in which is a divalent group is represented by the following general formula (III).

[0103] [ka] (R 21 is a group selected from -O-, -COO-, -OCO-, and -OSO2-; p, r, and R 22 has the same meaning as general formula (II).

[0104] In general formulas (II) and (III), r is preferably 2 or 3 from the viewpoint of improving the adhesion between the insulating resin and the conductive layer, and r is most preferably 3.

[0105] Specific examples of titanate-based coupling agents used in the present invention include isopropyl triisostearoyl titanate, isopropyl tridodecylbenzenesulfonyl titanate, isopropyl tris(dioctyl pyrophosphate) titanate, tetraisopropyl(dioctyl phosphite) titanate, tetraisopropyl bis(dioctyl phosphite) titanate, tetraoctyl bis(ditridecyl phosphite) titanate, tetra(2,2-diallyloxymethyl-1-butyl)bis(ditridecyl)phosphite titanate, bis(dioctyl pyrophosphate)oxyacetate titanate, bis(dioctyl pyrophosphate)ethylene titanate, and the like, and these can be used alone or in combination of two or more. These titanate coupling agents are commercially available from, for example, Ajinomoto Fine-Techno Co., Ltd.

[0106] The higher fatty acid is preferably a saturated or unsaturated, straight-chain or branched-chain mono- or polycarboxylic acid, more preferably a saturated or unsaturated, straight-chain or branched-chain monocarboxylic acid, and even more preferably a saturated or unsaturated, straight-chain monocarboxylic acid. The fatty acid preferably has 7 or more carbon atoms. Furthermore, the derivative refers to a salt or amide of the fatty acid.

[0107] The higher fatty acid or derivative thereof used in the present invention preferably has 7 to 23 carbon atoms, more preferably 10 to 20 carbon atoms. Examples of such higher fatty acids or derivatives thereof include saturated fatty acids such as capric acid, lauric acid, myristic acid, palmitic acid, and stearic acid; unsaturated fatty acids such as oleic acid, linoleic acid, linolenic acid, and arachidonic acid; and metal salts or amides thereof. Metal salts of higher fatty acids include salts of alkali metals, alkaline earth metals, transition metals such as Zr, Cr, Mn, Fe, Co, Ni, Cu, and Ag, and metals other than transition metals such as Al and Zn. Polyvalent metal salts such as Al, Zn, W, and V are preferred. Higher fatty acid metal salts may be mono-, di-, tri-, or tetra-forms depending on the valence of the metal. The higher fatty acid metal salt may also be any combination of these.

[0108] As the phosphate ester and phosphite ester, those having an alkyl group having 6 to 22 carbon atoms are preferably used. Examples of phosphate esters include hexyl phosphate, heptyl phosphate, monooctyl phosphate, monononyl phosphate, monodecyl phosphate, monoundecyl phosphate, monododecyl phosphate, monotridecyl phosphate, monotetradecyl phosphate, and monopentadecyl phosphate. Examples of phosphite esters include hexyl phosphite, heptyl phosphite, monooctyl phosphite, monononyl phosphite, monodecyl phosphite, monoundecyl phosphite, monododecyl phosphite, monotridecyl phosphite, monotetradecyl phosphite, and monopentadecyl phosphite.

[0109] In the present invention, the surface treatment agent is preferably a triazole-based compound or a titanium-based compound, in that it has excellent affinity with the insulating resin and is highly effective in increasing the coverage rate of the insulating resin, and in particular, benzotriazole, 4-carboxybenzotriazole, isopropyl triisostearoyl titanate, and tetraisopropyl (dioctyl phosphite) titanate are particularly preferred.

[0110] The conductive particles can be treated with a surface treatment agent by dispersing the conductive particles in a solution of the surface treatment agent and then filtering the dispersion. Before the treatment with the surface treatment agent, the conductive particles may have been treated with another treatment agent or may be untreated. The concentration of the surface treatment agent in the solution of the surface treatment agent (solution containing conductive particles) in which the conductive particles are dispersed can be 0.01% by mass or more and 10.0% by mass or less. Examples of solvents for the solution of the surface treatment agent include water, alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, isopentyl alcohol, and cyclohexanol, ketones such as acetone, methyl isobutyl ketone, methyl ethyl ketone, and methyl-n-butyl ketone, esters such as methyl acetate and ethyl acetate, ethers such as diethyl ether and ethylene glycol monoethyl ether, normal hexane, cyclohexanone, toluene, 1,4-dioxane, N,N-dimethylformamide, and tetrahydrofuran. The dispersed and filtered surface-treated conductive particles are preferably dispersed again in a solvent to remove excess surface treatment agent.

[0111] The surface treatment of conductive particles with a surface treatment agent can be carried out by mixing the conductive particles, the surface treatment agent, and a solvent at room temperature. Alternatively, the conductive particles and the surface treatment agent may be mixed in a solvent and then heated to promote the reaction. The heating temperature can be, for example, 30°C or higher and 50°C or lower.

[0112] The conductive particles of the present invention have low connection resistance and excellent connection reliability, and are therefore suitable for use, for example, in anisotropic conductive films (ACFs), heat seal connectors (HSCs), and as conductive materials for connecting electrodes of liquid crystal display panels to circuit boards of driving LSI chips. Examples of such conductive materials include the conductive particles of the present invention used as they are, or materials prepared by dispersing the conductive particles of the present invention in a binder resin. Other forms of the conductive material are not particularly limited, and in addition to the above, examples include anisotropic conductive pastes, conductive adhesives, and anisotropic conductive inks.

[0113] Examples of the binder resin include thermoplastic resins and thermosetting resins, etc. Examples of the thermoplastic resin include acrylic resin, styrene resin, ethylene-vinyl acetate resin, and styrene-butadiene block copolymer, and examples of the thermosetting resin include epoxy resin, phenol resin, urea resin, polyester resin, urethane resin, and polyimide resin.

[0114] In addition to the conductive particles and binder resin of the present invention, the conductive material may contain, as necessary, a tackifier, a reactivity aid, an epoxy resin curing agent, a metal oxide, a photoinitiator, a sensitizer, a curing agent, a vulcanizing agent, an anti-degradation agent, a heat-resistant additive, a thermal conductivity improver, a softener, a colorant, various coupling agents, or a metal deactivator.

[0115] In the conductive material, the amount of conductive particles used may be determined appropriately depending on the application. From the viewpoint of easily achieving electrical conduction without the conductive particles coming into contact with each other, the amount of conductive particles used is preferably, for example, 0.01 parts by mass or more and 50 parts by mass or less, particularly 0.03 parts by mass or more and 40 parts by mass or less, per 100 parts by mass of the conductive material.

[0116] The conductive particles of the present invention are particularly suitable for use as a conductive filler for a conductive adhesive, among the above-mentioned forms of conductive materials.

[0117] The conductive adhesive is preferably used as an anisotropic conductive adhesive that is placed between two substrates each having a conductive base material and adheres the conductive base material to establish electrical conductivity by heating and pressurizing. This anisotropic conductive adhesive contains the conductive particles of the present invention and an adhesive resin. Any adhesive resin can be used without particular limitations as long as it is insulating and suitable for use as an adhesive resin. Either a thermoplastic or thermosetting resin may be used, and those that exhibit adhesive properties upon heating are preferred. Examples of such adhesive resins include thermoplastic, thermosetting, and UV-curable types. Other examples include semi-thermosetting types that exhibit intermediate properties between thermoplastic and thermosetting types, and hybrid types that combine thermosetting and UV-curable types. These adhesive resins can be selected appropriately depending on the surface characteristics and usage of the circuit board or other substrate to be adhered. In particular, adhesive resins containing a thermosetting resin are preferred due to their excellent material strength after adhesion.

[0118] Specific examples of adhesive resins include those prepared using one or a combination of two or more resins selected from the group consisting of ethylene-vinyl acetate copolymer, carboxyl-modified ethylene-vinyl acetate copolymer, ethylene-isobutyl acrylate copolymer, polyamide, polyimide, polyester, polyvinyl ether, polyvinyl butyral, polyurethane, SBS block copolymer, carboxyl-modified SBS copolymer, SIS copolymer, SEBS copolymer, maleic acid-modified SEBS copolymer, polybutadiene rubber, chloroprene rubber, carboxyl-modified chloroprene rubber, styrene-butadiene rubber, isobutylene-isoprene copolymer, acrylonitrile-butadiene rubber (hereinafter referred to as NBR), carboxyl-modified NBR, amine-modified NBR, epoxy resin, epoxy ester resin, acrylic resin, phenolic resin, and silicone resin as the main component. Among these, thermoplastic resins such as styrene-butadiene rubber and SEBS are preferred due to their excellent reworkability. As a thermosetting resin, epoxy resin is preferred. Of these, epoxy resin is most preferred because it has the advantages of high adhesive strength, excellent heat resistance and electrical insulation, and also low melt viscosity, allowing connection at low pressure.

[0119] The epoxy resin may be any commonly used polyhydric epoxy resin having two or more epoxy groups per molecule. Specific examples include novolak resins such as phenol novolak and cresol novolak; polyhydric phenols such as bisphenol A, bisphenol F, bisphenol AD, resorcinol, and bishydroxydiphenyl ether; polyhydric alcohols such as ethylene glycol, neopentyl glycol, glycerin, trimethylolpropane, and polypropylene glycol; polyamino compounds such as ethylenediamine, triethylenetetramine, and aniline; and polycarboxylic compounds such as adipic acid, phthalic acid, and isophthalic acid, reacted with epichlorohydrin or 2-methylepichlorohydrin. Other examples include aliphatic and alicyclic epoxy resins such as dicyclopentadiene epoxide and butadiene dimer diepoxide. These may be used alone or in combination.

[0120] It is preferable to use high-purity adhesive resins with reduced impurity ions (Na, Cl, etc.) and hydrolyzable chlorine as the various adhesive resins mentioned above, from the viewpoint of preventing ion migration.

[0121] The amount of conductive particles used in the anisotropic conductive adhesive is usually 0.1 to 30 parts by mass, preferably 0.5 to 25 parts by mass, and more preferably 1 to 20 parts by mass, per 100 parts by mass of the adhesive resin component. By keeping the amount of conductive particles within this range, increases in connection resistance and melt viscosity are suppressed, connection reliability is improved, and sufficient anisotropy of the connection can be ensured.

[0122] In addition to the conductive particles and adhesive resin described above, the anisotropic conductive adhesive may contain additives known in the art. The amounts of these additives may be within the ranges known in the art. Examples of other additives include tackifiers, reactivity aids, epoxy resin curing agents, metal oxides, photoinitiators, sensitizers, curing agents, vulcanizing agents, anti-degradants, heat-resistant additives, thermal conductivity improvers, softeners, colorants, various coupling agents, and metal deactivators.

[0123] Examples of tackifiers include rosin, rosin derivatives, terpene resins, terpene phenol resins, petroleum resins, coumarone-indene resins, styrene-based resins, isoprene-based resins, alkylphenol resins, and xylene resins. Examples of reactive auxiliaries, i.e., crosslinking agents, include polyols, isocyanates, melamine resins, urea resins, utropines, amines, acid anhydrides, and peroxides. Any epoxy resin curing agent having two or more active hydrogen atoms per minute can be used without particular limitations. Specific examples include polyamino compounds such as diethylenetriamine, triethylenetetramine, metaphenylenediamine, dicyandiamide, and polyamidoamine; organic acid anhydrides such as phthalic anhydride, methylnadic anhydride, hexahydrophthalic anhydride, and pyromellitic anhydride; and novolac resins such as phenol novolac and cresol novolac. These can be used alone or in combination. A latent curing agent may also be used if necessary. Usable latent curing agents include, for example, imidazoles, hydrazides, boron trifluoride-amine complexes, sulfonium salts, amine imides, polyamine salts, dicyandiamide, and modified products thereof. These can be used alone or in combination of two or more.

[0124] The anisotropic conductive adhesive is manufactured using a manufacturing device commonly used in the art. For example, it is manufactured by blending conductive particles, an adhesive resin, and optionally a curing agent and various additives, and mixing them in an organic solvent if the adhesive resin is a thermosetting resin, or by melt-kneading them at a temperature above the softening point of the adhesive resin, specifically preferably about 50 to 130°C, more preferably about 60 to 110°C, if the adhesive resin is a thermoplastic resin. The anisotropic conductive adhesive thus obtained may be applied as a coating or in the form of a film.

[0125] The connection structure according to the present invention is obtained by connecting two circuit boards together using the conductive particles according to the present invention or the conductive material according to the present invention. Examples of the form of the connection structure include a connection structure between a flexible printed circuit board and a glass substrate, a connection structure between a semiconductor chip and a flexible printed circuit board, and a connection structure between a semiconductor chip and a glass substrate. [Example]

[0126] The present invention will be further described below with reference to examples, but the scope of the present invention is not limited to these examples. The properties in the examples were measured by the following methods. (1) Average particle size 200 particles were randomly extracted from a scanning electron microscope (SEM) photograph of the object to be measured, and the particle diameters were measured at a magnification of 10,000 times, and the arithmetic mean value was taken as the average particle diameter. (2) Thickness of the conductive layer The conductive particle was cut into two pieces, and the cross section of the cut surface was observed and measured using a scanning electron microscope (SEM).

[0127] Example 1 (1) Pretreatment Spherical styrene-acrylate-silica composite resin particles with an average particle size of 3.0 μm were used as core particles. 9 g of these particles were added to 200 mL of an aqueous conditioner solution (Rohm and Haas Electronic Materials' "Cleaner Conditioner 231") while stirring. The concentration of the aqueous conditioner solution was 40 mL / L. The solution was then stirred at 60°C for 30 minutes with ultrasonic waves to modify the surface and disperse the core particles. This solution was filtered, and the core particles were repulped and washed once to form a 200 mL slurry. 0.1 g of stannous chloride was added to this slurry. The mixture was stirred at room temperature for 5 minutes to sensitize the core particles, adsorbing tin ions onto their surfaces. The solution was then filtered, and the core particles were repulped and washed once to form a 200 mL slurry, which was then maintained at 60°C. 1.5 mL of a 0.11 mol / L aqueous palladium chloride solution was then added to the slurry. The core particles were activated by stirring at 60°C for 5 minutes, and the palladium ions were captured on their surfaces. The aqueous solution was then filtered, and the core particles were repulped and washed with hot water once to form a 100 mL slurry. 10 mL of a 0.5 g / L dimethylamine borane solution was added, and the mixture was stirred for 2 minutes while applying ultrasound to obtain a slurry of pretreated core particles. (2) Preparation of plating bath Three liters of an electroless nickel-phosphorus plating bath was prepared from an aqueous solution containing 5 g / L of sodium tartrate, 2 g / L of nickel sulfate hexahydrate, 10 g / L of trisodium citrate, 0.1 g / L of sodium hypophosphite, and 2 g / L of polyethylene glycol, and the temperature was raised to 70°C. (3) Electroless plating The slurry of the pretreated core particles was added to this electroless plating bath and stirred for 5 minutes, after which it was confirmed that the hydrogen bubbling had stopped. To this slurry, a 224 g / L aqueous solution of nickel sulfate and a mixed aqueous solution containing 210 g / L sodium hypophosphite and 80 g / L sodium hydroxide were added continuously in portions using a metering pump at a rate of 2.0 mL / min for 60 minutes. The plating deposition rate during this operation was 0.55 nm / min, and the thickness of the resulting conductive layer was 33 nm. Next, an aqueous solution of nickel sulfate and a mixed aqueous solution of sodium hypophosphite and sodium hydroxide were added continuously and fractionally using a metering pump at a rate of 4.1 mL / min for 60 minutes. The plating deposition rate during this operation was 1.12 nm / min, and the thickness of the resulting conductive layer was 67 nm. The resulting electroless plating solution was stirred for 5 minutes while maintaining the temperature at 70°C. The solution was then filtered, and the filtrate was washed three times and then dried in a vacuum dryer at 110°C to obtain conductive particles having an electroless nickel-phosphorus plating layer formed as a conductive layer on the surface of the core particles. The resulting conductive particles had an average particle size of 3.2 μm, a conductive layer thickness of 100 nm, and protrusions.

[0128] Example 2 (3) Electroless plating treatment in Example 1 was carried out in the following manner. The slurry of the pretreated core particles was added to the electroless plating bath, and the mixture was stirred for 5 minutes, after which it was confirmed that the hydrogen bubbling had stopped. To this slurry, a 224 g / L aqueous solution of nickel sulfate and a mixed aqueous solution containing 210 g / L sodium hypophosphite and 80 g / L sodium hydroxide were added continuously in portions using a metering pump at a rate of 1.0 mL / min for 45 minutes. The plating deposition rate during this operation was 0.3 nm / min, and the thickness of the resulting conductive layer was 13.5 nm. Next, an aqueous solution of nickel sulfate and a mixed aqueous solution of sodium hypophosphite and sodium hydroxide were added continuously and fractionally using a metering pump at a rate of 2.25 mL / min for 60 minutes. The plating deposition rate during this operation was 0.6 nm / min, and the thickness of the resulting conductive layer was 36 nm. Then, an aqueous solution of nickel sulfate and an aqueous solution of sodium hypophosphite and sodium hydroxide were added continuously and fractionally using a metering pump at a rate of 3.25 mL / min for 45 minutes. The plating deposition rate during this operation was 1.0 nm / min, and the thickness of the resulting conductive layer was 45 nm. The resulting electroless plating solution was stirred for 5 minutes while maintaining the temperature at 70°C. The solution was then filtered, and the filtrate was washed three times and then dried in a vacuum dryer at 110°C to obtain conductive particles having an electroless nickel-phosphorus plating layer formed as a conductive layer on the surface of the core particles. The resulting conductive particles had an average particle size of 3.19 μm, a conductive layer thickness of 94.5 nm, and protrusions.

[0129] Example 3 The conductive particles obtained in Example 2 were placed in a rectangular container to a thickness of 5 mm. They were placed in a vacuum heating furnace (Denken Hydental, KDF-75) and heated from room temperature to 390°C at a heating rate of 5°C / min under a vacuum of 10 Pa. They were then heat-treated at this temperature for 2 hours. After the heat treatment, the pressure was returned to atmospheric pressure by nitrogen purging, and then cooled to room temperature at a heating rate of 3°C / min by blowing in nitrogen gas, yielding heat-treated conductive particles. The resulting conductive particles had an average particle diameter of 3.19 μm, a conductive layer thickness of 94.5 nm, and protrusions.

[0130] Comparative Example 1 Conductive particles were obtained in the same manner as in Example 1, except that the following procedure was carried out instead of (3) electroless plating treatment in Example 1. The slurry of the pretreated core particles was added to the electroless plating bath, and the mixture was stirred for 5 minutes, after which it was confirmed that the hydrogen bubbling had stopped. To this slurry, a 224 g / L aqueous solution of nickel sulfate and a mixed aqueous solution containing 210 g / L sodium hypophosphite and 80 g / L sodium hydroxide were continuously added in portions using a metering pump at a rate of 12.2 mL / min for 30 minutes, and electroless plating was performed. The plating deposition rate during this operation was 3.3 nm / min. The resulting electroless plating solution was stirred for 5 minutes while maintaining the temperature at 70°C. The solution was then filtered, and the filtrate was washed three times and then dried in a vacuum dryer at 110°C to obtain conductive particles having an electroless nickel-phosphorus plating layer formed as a conductive layer on the surface of the core particles. The resulting conductive particles had an average particle size of 3.2 μm, a conductive layer thickness of 100 nm, and protrusions.

[0131] (Evaluation of current resistance and adhesion) [Evaluation of current resistance] Using a conductive particle electrical property measurement device (VI device, a device made by ourselves based on the device described in JP-A-10-221388), the current value (mA) flowing per conductive particle at the compression ratio to be measured was measured.

[0132] [Evaluation of Adhesion] 0.5 g of conductive particles, 20 g of 1.0 mm diameter zirconia balls, and 20 g of ethanol were placed in a plastic container and milled at 200 rpm for 10 minutes using a ball mill. The mixture was then filtered and dried to obtain conductive particles. 200 of the obtained conductive particles were observed under a scanning electron microscope, and the adhesion of the conductive layer was evaluated as follows. ○: No peeling of conductive layer △: 1 to 5 pieces of conductive layer peeled off ×: More than 5 conductive layers peeled off

[0133] [Table 1]

[0134] The results in Table 1 show that the conductive particles obtained in the examples are superior in current resistance characteristics and conductive layer adhesion compared to the conductive particles obtained in the comparative examples.

Claims

1. Conductive particles having a conductive layer formed on the surface of a core particle, wherein the withstand current value per conductive particle is 1 mA or more when the compression ratio is less than 5%, and the withstand current value per conductive particle is 10 mA or more when the compression ratio is 5% or more.

2. 2. The conductive particles according to claim 1, wherein the withstand current value per conductive particle is 0.5 mA or more when the compressibility is 1% or more and 4% or less.

3. 3. The conductive particles according to claim 1, wherein the withstand current value per conductive particle is 15 mA or more when the compressibility is 10% or more and 50% or less.

4. 4. The conductive particles according to claim 1, wherein the withstand current value per conductive particle is 20 mA or more when the compression ratio is 30%.

5. 5. The conductive particle according to claim 1, wherein the conductive layer has protrusions on the outer surface.

6. 6. The conductive particle according to claim 1, wherein the conductive layer is made of at least one material selected from the group consisting of nickel, gold, nickel alloys, and gold alloys.

7. A conductive material comprising the conductive particles according to any one of claims 1 to 6 and an insulating resin.

8. a first step of mixing an aqueous slurry of core particles with an electroless nickel plating bath containing a dispersant, a nickel salt, a reducing agent, and a complexing agent to perform electroless nickel plating; and a second step of electroless nickel plating by continuously adding an aqueous solution containing a nickel salt, an aqueous solution containing a reducing agent, and an aqueous solution containing an alkali to the solution obtained in the first step while controlling the amounts of addition so as to change the plating deposition rate two or more times; A method for producing conductive particles having the above structure.

9. 9. The method for producing conductive particles according to claim 8, wherein the amount of addition is controlled so that the initial plating deposition rate in the second step is 0.05 nm / min or more and 1.5 nm / min or less.

10. The method for producing conductive particles according to claim 8 or 9, wherein the amount of addition is controlled so that the plating deposition rate after the change in the second step is 0.3 nm / min or more and 3.0 nm / min or less.

11. The method for producing conductive particles according to any one of claims 8 to 10, wherein the amount of addition is controlled so as to increase the plating deposition rate.

12. A method for producing conductive particles according to any one of claims 8 to 11, wherein in the second step, an aqueous solution containing a nickel salt and a mixed aqueous solution containing a reducing agent and an alkali are added to the liquid in the first step.

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