Base material particles, base material particle production method, conductive particles, and conductive material

Abstract

Provided are base material particles for forming conductive particles having large protrusions that can effectively remove an oxide film or a binder resin from an electrode. The base material particles have protrusions on base particle surfaces, and the protrusions are aggregates of metal oxide or metal hydroxide having an average primary particle diameter of 1 to 100 nm. The base material particles can be produced by using a production method in which hydrophilically treated base particles are added to an aqueous solution containing a metal fluorocomplex compound and a fluoride ion scavenger, thereby forming aggregates of metal oxide or metal hydroxide on the base particle surfaces and obtaining base material particles having protrusions on the particle surfaces.

Description

Base particle, its manufacturing method, conductive particle, and conductive material

[0001] The present invention relates to a base particle and a method for producing the same, a conductive particle having a conductive layer formed on the surface of the base particle, and a conductive material containing the conductive particle.

[0002] Conductive particles used as the conductive material in anisotropic conductive materials such as anisotropic conductive films and anisotropic conductive pastes generally have a conductive layer made of metal formed on the surface of a core particle. In recent years, the miniaturization and refinement of electronic devices has led to the need for fine-pitch connections between electrode terminals, and electrical connections between electrodes and wiring are achieved through the conductive layer of the conductive particles.

[0003] When electrodes are connected under pressure using such conductive particles, it is necessary to remove the oxide film formed on the electrode surface to ensure conductivity. Having protrusions on the surface of the conductive particles can effectively remove this oxide film, and technologies related to the shape and method of forming the protrusions have been studied. As an example, Patent Document 1 discloses conductive particles having protrusions with a core material made of a metal such as zinc or titanium or its metal oxide, and describes how this can provide conductive particles with low connection resistance and low variation in the conductive performance of the particles, resulting in excellent conductive reliability. Patent Document 2 also describes how conductive particles having protrusions with a core material made of titanium oxide of a specific particle size can increase the adhesion between the core material and the conductive portion, thereby providing conductive particles that can reduce connection resistance when used to connect electrodes.

[0004] JP 2007-35573 A JP 2015-57768 A

[0005] The conductive particles described in the above patent documents have core materials in the protrusions, which result in high protrusion strength, lower connection resistance, and superior connection reliability compared to conventional ones. However, customer demands are increasing, and further improvements are required. Specifically, increasing the size of the protrusions can increase protrusion strength, thereby improving the ability to remove oxide films and binder resins from electrodes, leading to improved connection resistance and connection reliability. However, if the size of the base particle is kept the same while the resulting protrusions are enlarged, the protrusions tend to peel off. Furthermore, when attempting to increase the size of the protrusions by using a larger core material, the core material, which is larger and heavier than conventional core materials, is difficult to disperse, making it difficult to attach the core material to the base particle.

[0006] Therefore, an object of the present invention is to provide a base particle for forming a conductive particle having large protrusions that can effectively remove an oxide film and a binder resin from an electrode. Another object of the present invention is to provide a conductive particle using the base particle.

[0007] As a result of intensive research to solve the above-mentioned problems, the inventors have found that conductive particles obtained by electroless plating on base particles obtained by precipitating a metal oxide or metal hydroxide to a desired size on a mother particle as a core substance that forms the nucleus of the protrusions have large protrusions, and therefore have excellent binder resin removal performance, and at the same time, have the strength to break through the oxide film of the electrode, thereby achieving excellent connection resistance and connection reliability, and have completed the present invention.

[0008] That is, the present invention provides a base particle having convex portions on the surface of a mother particle, the convex portions being an aggregate of a metal oxide or metal hydroxide having an average primary particle diameter of 10 to 100 nm.

[0009] The present invention also provides a conductive particle in which a conductive layer is formed on the surface of the base particle.

[0010] The present invention also provides a method for producing base particles, in which hydrophilically treated base particles are added to an aqueous solution containing a metal fluorocomplex compound and a fluoride ion scavenger, thereby forming aggregates of metal oxide or metal hydroxide on the surfaces of the base particles and obtaining base particles having convex portions on the particle surfaces.

[0011] The base particle of the present invention can form large protrusions on the conductive layer, and therefore can provide conductive particles with low connection resistance and excellent connection reliability.

[0012] 1 is a scanning electron microscope (SEM) photograph of a base particle with protrusions obtained in Example 1. FIG. 2 is a scanning electron microscope (SEM) photograph of a conductive particle obtained in Example 1.

[0013] The base particle of the present invention is a base particle having protrusions on the surface of a mother particle, characterized in that the protrusions are aggregates of a metal oxide or metal hydroxide having an average primary particle diameter of 1 to 100 nm. The base particle of the present invention has protrusions formed by precipitating aggregates of primary particles of a metal oxide or metal hydroxide on the surface of the mother particle, so the size of the protrusions can be increased. Because the base particle of the present invention has large protrusions, conductive particles with large protrusions can be obtained by forming a conductive layer on the surface by electroless plating or the like.

[0014] The base particle of the present invention has protrusions on the surface of the base particle. The base particles used in the present invention may be inorganic or organic, as long as they are particulate, and can be used without any particular limitation. Examples of inorganic base 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 base particles include thermoplastic resins such as natural fibers, natural resins, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polybutene, polyamide, polyacrylate, polyacrylonitrile, polyacetal, ionomers, and polyesters, 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 of two or more.

[0015] The base particles may be composed of both inorganic and organic materials instead of the aforementioned inorganic and organic materials. When the base particles are composed of both inorganic and organic materials, the inorganic and organic materials may be present in the base particles in a core-shell configuration, such as a core made of an inorganic material and a shell made of an inorganic material that covers the surface of the core, or a core made of an organic material and a shell made of an inorganic material that covers the surface of the core. Other examples include blend configurations in which inorganic and organic materials are mixed or randomly fused within a single base particle.

[0016] The base particles are preferably composed of an organic material or a material composed of both inorganic and organic materials, and more preferably composed of a material composed 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 base particles composed of such materials can improve the dispersion stability of the particles and also provide appropriate elasticity and improve conductivity during electrical connection of electronic circuits.

[0017] When an organic substance is used as the base 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 base particles is easily maintained and the shape of the base 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).

[0018] When an organic material is used as the base particles and the organic material 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 base particles may be used in the present invention. Specific examples of base particle materials that do not have a glass transition temperature can be obtained by copolymerizing the monomers that make up the organic materials 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 of suitable hard organic materials 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. In particular, in the field of COG (chip on glass), base particles made of such hard organic materials are often used.

[0019] There are no particular limitations on the shape of the base particles. Generally, the base particles are spherical. However, the base particles may have a shape other than spherical, such as fibrous, hollow, plate-like, or needle-like, and may have many protrusions on their surfaces or may be amorphous. In the present invention, it is preferable to use spherical base particles because they have excellent packing properties and are easy to coat with metal.

[0020] The average particle diameter of the base particles is preferably 0.1 to 50 μm, and more preferably 1 to 30 μm, from the viewpoint of improving connection reliability by producing the conductive particles of the present invention described below. The average particle diameter of the base particles is the arithmetic mean value measured for 20 different particles observed using a scanning electron microscope (SEM). This particle diameter is the diameter of a circular base particle image. When the base particles are not spherical, the particle diameter refers to the longest length (maximum length) of the line segments crossing the base particle image.

[0021] The convex portions of the base particle of the present invention are aggregates of primary particles of a metal oxide or metal hydroxide formed on the surface of a base particle. The aggregates of primary particles of a metal oxide or metal hydroxide are formed by agglomeration of primary particles of a metal oxide or metal hydroxide. The average particle diameter of the primary particles of the metal oxide or metal hydroxide is 1 to 100 nm, preferably 5 to 90 nm, and particularly preferably 5 to 80 nm, from the viewpoint of easily forming aggregates that become convex portions on the base particle. Furthermore, the average height of the convex portions, i.e., the average height of the aggregates, is preferably 20 to 1,500 nm, more preferably 40 to 1,000 nm, from the viewpoint of improving connection resistance and connection reliability when producing the conductive particles of the present invention described below. The average width of the bases of the convex portions, i.e., the average width of the bases of the aggregates, is preferably 5 to 1,500 nm, more preferably 10 to 1,000 nm, from the viewpoint of improving connection resistance and connection reliability when producing the conductive particles of the present invention described below.

[0022] The metal oxide forming the convex portions is preferably one or more selected from the oxides of titanium, molybdenum, tin, silicon, tungsten, vanadium, and iron. The metal hydroxide forming the convex portions is preferably one or more selected from the hydroxides of titanium, molybdenum, tin, silicon, tungsten, vanadium, and iron. The hydroxide also includes oxyhydroxides, which are hydroxides having an independent oxygen atom bonded to the metal element. Among these, from the viewpoint of improving connection resistance and connection reliability by producing the conductive particles of the present invention described later, an oxide of titanium, i.e., titanium oxide (TiO ２ ) is more preferable.

[0023] The conductive layer formed on the surface of the base particle is made of a metal having electrical conductivity. Examples of the metal 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, manganese, and alloys thereof, 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 of 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, it is preferable that the outermost layer is made of at least one material 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 base particle, but may cover only a portion of it. When only a portion of the surface of the base 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 2,000 nm or less, and more preferably 1 nm or more and 1,500 nm or less. When the thickness of the conductive layer is within the above range, the conductive particles have excellent electrical properties. In the present invention, the thickness of the conductive layer can be measured by cutting the particle to be measured into two pieces 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, and 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] The height of the protrusions of the conductive particles is preferably 20 nm or more and 1,500 nm or less, and more preferably 50 nm or more and 800 nm or less. 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. The length of the base of the protrusions is preferably 5 nm or more and 1,500 nm or less, and more preferably 10 nm or more and 800 nm or less. The length of the base of the protrusions refers to the length along the surface of the conductive particle at the location where the protrusions are formed when the cross section of the particle is observed with a scanning electron microscope (SEM), and the height of the protrusions refers to the shortest distance from the base of the protrusions to the apex of the protrusions. 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 protrusions and the height of the protrusions are the arithmetic mean values ​​measured for 20 different particles observed with a scanning electron microscope (SEM).

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

[0030] Next, a preferred embodiment of the method for producing base particles of the present invention will be described. In the method for producing base particles of the present invention, hydrophilically treated base particles are added to an aqueous solution containing a metal-fluoro complex compound and a fluoride ion scavenger, thereby forming aggregates of metal oxide or metal hydroxide on the surfaces of the base particles, thereby obtaining base particles having protrusions.

[0031] In the present invention, the hydrophilization treatment is preferably carried out by contacting the base particles with a hydrophilization treatment agent in a liquid phase. Examples of the hydrophilization treatment agent include alkalis, acids, surfactants, and surface modifiers. The liquid phase may be either aqueous or non-aqueous, but from the viewpoint of ease of handling, an aqueous liquid phase is preferred.

[0032] Examples of the alkali include lithium hydroxide, sodium hydroxide, potassium hydroxide, magnesium hydroxide, calcium hydroxide, strontium hydroxide, barium hydroxide, and aqueous ammonia. Examples of the acid include sodium permanganate, potassium permanganate, chromic anhydride, dichromate, and chromium oxide. Examples of the surfactant include polyethylene glycol, polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, alkyldimethyl acetate betaine, and alkyldimethylamino acetate betaine.

[0033] Examples of aqueous liquid phases for dispersing the base particles include pure water, ion-exchanged water, etc. Examples of non-aqueous liquid phases include alcohols, ethers, etc.

[0034] The time for the hydrophilization treatment is not particularly limited, but from the viewpoint of uniformly hydrophilizing the surface of the base particle, it is preferably 20 minutes or more, particularly preferably 20 minutes or more and 300 minutes or less. The temperature for the hydrophilization treatment is not particularly limited, but from the viewpoint of uniformly hydrophilizing the surface of the base particle, it is preferably 25° C. or more and 90° C. or less, more preferably 40° C. or more and 80° C. or less.

[0035] In the present invention, primary particles of a metal oxide or metal hydroxide are precipitated on the surface of hydrophilically treated base particles to form aggregates of the metal oxide or metal hydroxide, thereby forming convex portions. One method for precipitating the primary particles of a metal oxide or metal hydroxide is to mix a fluoride ion scavenger with the base particles in an aqueous solution in the presence of a metal fluorocomplex compound, thereby shifting the hydrolysis equilibrium reaction of the metal fluorocomplex toward the production of the metal oxide or metal hydroxide, thereby precipitating the metal oxide or metal hydroxide on the surface of the base particles. By using the metal fluorocomplex compound as a metal oxide source or metal hydroxide source, fine primary particles of a metal oxide or metal hydroxide can be precipitated.

[0036] Examples of the metal oxides include the oxides of titanium, molybdenum, tin, silicon, tungsten, vanadium, and iron, and examples of the metal hydroxides include the hydroxides and oxyhydroxides of titanium, molybdenum, tin, silicon, tungsten, vanadium, and iron.

[0037] Examples of the metal fluorocomplex compound include ammonium hexafluorotitanate, potassium hexafluorotitanate, calcium hexafluorotitanate, ammonium hexafluorozirconate, potassium hexafluorozirconate, calcium hexafluorozirconate, ammonium hexafluorosilicate, potassium hexafluorosilicate, calcium hexafluorosilicate, ammonium zinc difluoro, potassium zinc difluoro, calcium zinc difluoro, etc. Among these, ammonium hexafluorotitanate is preferred from the viewpoint of precipitating fine metal oxide particles.

[0038] Examples of the fluoride ion scavenger include boric acid, metallic aluminum, sodium hydroxide, ammonia, etc. Among these, boric acid and metallic aluminum are preferred from the viewpoint of generating stable fluoride complex ions.

[0039] The concentration of the base particles in the liquid phase is preferably 1 g / L to 200 g / L, particularly 5 g / L to 50 g / L, from the viewpoints of easily forming convex aggregates of the metal oxide or metal hydroxide and maintaining the stability of the reaction solution. The concentration of the metal-fluoro complex compound in the liquid phase is preferably 0.01 mol / L to 5 mol / L, particularly 0.02 mol / L to 1 mol / L, from the viewpoints of easily forming convex aggregates of the metal oxide or metal hydroxide and maintaining the stability of the reaction solution. The concentration of the fluoride ion scavenger is preferably 0.01 mol / L to 5 mol / L, particularly 0.02 mol / L to 1 mol / L, from the viewpoints of easily forming convex aggregates of the metal oxide or metal hydroxide and maintaining the stability of the reaction solution. By the above-described operations, convex portions composed of aggregates of the metal oxide or metal hydroxide are formed on the surface of the base particles, thereby providing the base particles of the present invention.

[0040] The surface of the base particle preferably has a noble metal ion trapping ability or is surface-modified to have noble metal ion trapping ability. The noble metal ions are preferably palladium or silver ions. "Having noble metal ion trapping ability" means being able to trap noble 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 base particle, the surface of the base particle has noble metal ion trapping ability. When the surface is modified to have noble metal ion trapping ability, for example, the method described in JP-A-61-64882 can be used.

[0041] Such base particles are used to support a noble metal on their surfaces. Specifically, the base particles are dispersed in a dilute acidic aqueous solution of a noble metal salt such as palladium chloride or silver nitrate. This allows noble metal ions to be captured on the particle surface. The concentration of the noble metal salt is adjusted to 1 / m of the surface area of ​​the particle. ２ 1x10 －７ ~1 x 10 －２ A molar range is sufficient. The base particles with the captured precious metal ions are separated from the system and washed with water. The base particles are then suspended in water, and a reducing agent is added to reduce the precious metal ions. Examples of reducing agents that can be used include sodium hypophosphite, sodium borohydride, potassium borohydride, dimethylamine borane, hydrazine, and formalin.

[0042] Before capturing the precious metal ions on the surface of the base particles, the base particles may be subjected to a sensitization treatment to adsorb tin ions onto the surface of the particles. To adsorb tin ions onto the surface of the particles, for example, the surface-modified base particles may be placed in an aqueous solution of stannous chloride and stirred for a predetermined period of time.

[0043] The substrate particles thus pretreated are then subjected to a conductive layer formation process. This conductive layer formation process involves the following first and second steps. In the first step, substrate particles are mixed with an electroless nickel plating bath containing a nickel salt, a reducing agent, and a complexing agent to prepare a slurry containing primary plated particles having an initial nickel thin film layer formed on the surface of the substrate particles. In this first step, depending on the composition and reaction conditions of the electroless nickel plating bath, autolysis of the plating bath occurs simultaneously with the formation of the initial nickel thin film layer on the substrate particles. This autolysis occurs near the base particles, and the autolysis products are captured on the surface of the substrate particles during the formation of the initial nickel thin film layer, thereby generating nuclei of microprojections, and simultaneously forming the initial nickel thin film layer. Therefore, protrusions may be formed from the generated microprojection nuclei by the operation in the second step described below. In the present invention, protrusions derived from the nuclei of the autolysis products may be formed within a range that does not impair the effects of the present invention.

[0044] In the first step, the above-described primary plated particles are thoroughly dispersed in water, preferably in the range of 0.1 to 500 g / L, more preferably 1 to 300 g / L, to prepare an aqueous slurry. The dispersion operation can be carried out by normal stirring, high-speed stirring, or using a shear dispersion device such as a colloid mill or homogenizer. Ultrasonic waves may also be used in the dispersion operation. If necessary, a dispersant such as a surfactant may be added during the dispersion operation.

[0045] Examples of the dispersant include nonionic surfactants, zwitterionic surfactants, and / or water-soluble polymers. Examples of nonionic surfactants include polyoxyalkylene ether surfactants such as polyethylene glycol, polyoxyethylene alkyl ether, and polyoxyethylene alkylphenyl ether. Examples of zwitterionic surfactants include betaine surfactants such as alkyldimethyl acetate betaine, alkyldimethylcarboxymethyl acetate betaine, and alkyldimethylamino acetate betaine. Examples of water-soluble polymers 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 preferably 0.5 to 30 g / L relative to the volume of the electroless nickel plating bath. In particular, a dispersant amount in the range of 1 to 10 g / L relative to the volume of the electroless nickel plating bath is preferred from the viewpoint of further improving the adhesion of the conductive layer.

[0046] 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 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.

[0047] Examples of the complexing agent include compounds that have a complexing effect on nickel ions, such as carboxylic acid salts (e.g., citric acid, hydroxyacetic acid, tartaric acid, malic acid, lactic acid, gluconic acid, or their alkali metal or ammonium salts), amino acids (e.g., glycine), amines (e.g., ethylenediamine, alkylamine), other ammonium salts, EDTA, pyrophosphate, or its salts. These can be used alone or in combination. The concentration is preferably in the range of 1 to 100 g / L, more preferably 5 to 50 g / L. The preferred pH of the electroless nickel plating bath at this stage is in the range of 3 to 14. The electroless nickel plating reaction begins rapidly upon addition of the aqueous slurry of base particles, accompanied by the evolution of hydrogen gas. The first step is terminated when the evolution of hydrogen gas is completely stopped. In this manner, a slurry containing primary plated particles having an initial thin nickel layer formed on the surface of the base particles can be obtained.

[0048] The second step is a subsequent step to the first step, in which electroless nickel plating is performed by using either (i) a first aqueous solution containing one of a nickel salt, a reducing agent, and an alkali, and a second aqueous solution containing the remaining two, or (ii) a first aqueous solution containing a nickel salt, a second aqueous solution containing a reducing agent, and a third aqueous solution containing an alkali, and adding these aqueous solutions simultaneously and sequentially to the solution from the first step. In this second step, the plating reaction is restarted by adding these solutions, and the conductive layer formed can be controlled to a desired film thickness by adjusting the amounts added. After the addition of these solutions is completed, stirring is continued while maintaining the solution temperature for a while after hydrogen gas generation has completely ceased to be observed, to complete the reaction.

[0049] In the case of (i) above, it is preferable to use a first aqueous solution containing a nickel salt and a second aqueous solution containing a reducing agent and an alkali, but this combination is not limiting. In this case, the first aqueous solution does not contain a reducing agent or an alkali, and the second aqueous solution does not contain a nickel salt. As the nickel salt and the reducing agent, those described above can be used. As the alkali, for example, an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide can be used. The same applies to the case of (ii) above.

[0050] In the case of (ii) above, the first to third aqueous solutions each contain a nickel salt, a reducing agent, and an alkali, and each aqueous solution does not contain the other two components other than the nickel salt, the reducing agent, and the alkali.

[0051] In either case (i) or (ii), the concentration of the nickel salt in the aqueous solution 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 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 is preferably 5 to 500 g / L, particularly 10 to 200 g / L.

[0052] The second step is carried out continuously after the completion of the first step, but alternatively, the first step and the second step may be carried out intermittently. In this case, after the completion of the first step, the base particles and the plating solution may be separated by a method such as filtration, the base particles may be dispersed in water to prepare a new aqueous slurry, an aqueous solution in which a complexing agent is dissolved in a concentration range of preferably 1 to 100 g / L, more preferably 5 to 50 g / L, and a dispersant is dissolved in a concentration range of preferably 0.5 to 30 g / L, more preferably 1 to 10 g / L to prepare an aqueous slurry, and the second step may be carried out by adding the aqueous solutions to the aqueous slurry.

[0053] The conductive particles obtained by the above-described method are preferably heat-treated 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. By heating the conductive particles while maintaining such a vacuum, crystallization of the metal in the conductive layer progresses, thereby lowering the electrical resistance and improving electrical conductivity. Note that the degree of vacuum in this invention is an absolute pressure, i.e., a value when an absolute vacuum is defined as 0.

[0054] 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 base particles and conductive layer due to thermal history can be suppressed, thereby 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.

[0055] The heat treatment may be carried out while the conductive particles are left stationary or while stirring. When the heat treatment is carried out while the conductive particles are left stationary, it is preferable that the conductive particles are left stationary at a thickness of 0.1 mm to 100 mm. By leaving the conductive particles stationary at this thickness, the heat treatment of the conductive layer can be carried out successfully and the manufacturing cost can be reduced.

[0056] 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.

[0057] The heat treatment is preferably carried out by reaching a vacuum of 1000 Pa or less, preferably 0.01 to 900 Pa, particularly preferably 0.01 to 500 Pa, at room temperature, maintaining the vacuum 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, moisture, etc. in the heated atmosphere or the conductive particles, thereby reducing the connection resistance.

[0058] After the heat treatment, it is preferable to lower the temperature to 50°C or less, or even 40°C or less, while maintaining the vacuum level, and then release the vacuum. 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 increasing the 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.

[0059] In this manner, the conductive layer is formed on the surface of the base particle by electroless plating, thereby obtaining the conductive particles of the present invention.

[0060] When the conductive particles obtained by 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.

[0061] 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.

[0062] 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.

[0063] The conductive particles of the present invention are suitable for use as conductive materials for, for example, anisotropic conductive films (ACFs), heat seal connectors (HSCs), and for connecting electrodes of liquid crystal display panels to the circuit board of a driving LSI chip. Examples of such conductive materials include the conductive particles of the present invention used as they are, or conductive materials obtained by dispersing the conductive particles of the present invention in a binder resin. The other forms of the conductive material are not particularly limited, and in addition to the above, examples include anisotropic conductive pastes, conductive adhesives, anisotropic conductive inks, and the like.

[0064] The binder resin may be a thermoplastic resin or a thermosetting resin, etc. Examples of the thermoplastic resin include an acrylic resin, a styrene resin, an ethylene-vinyl acetate resin, and a styrene-butadiene block copolymer, while examples of the thermosetting resin include an epoxy resin, a phenol resin, a urea resin, a polyester resin, a urethane resin, and a polyimide resin.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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, with those that exhibit adhesive properties upon heating being 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.

[0069] Specific examples of adhesive resins include those prepared using, as a base resin, one or a combination of two or more selected from 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. 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.

[0070] As the epoxy resin, any commonly used epoxy resin can be used as long as it is a 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 polyvalent carboxy 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 can be used alone or in combination.

[0071] The various adhesive resins mentioned above contain impurity ions (Na ＋ and Cl － From the viewpoint of preventing ion migration, it is preferable to use a high-purity product in which the content of fluorine, etc., and hydrolyzable chlorine, etc., is reduced.

[0072] 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.

[0073] 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.

[0074] 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 novolak resins such as phenol novolak and cresol novolak. These can be used alone or in combination of two or more. Furthermore, a latent curing agent may be used as needed. Usable latent curing agents include, for example, imidazoles, hydrazides, boron trifluoride-amine complexes, sulfonium salts, aminimides, polyamine salts, dicyandiamide, and modified products thereof. These can be used alone or in combination of two or more.

[0075] The anisotropic conductive adhesive is manufactured using manufacturing equipment 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 obtained in this manner may be applied as a coating or in the form of a film.

[0076] 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.

[0077] The present invention will be further explained below with reference to examples. However, 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 diameter: 200 particles were randomly selected from a scanning electron microscope (SEM) photograph of the object to be measured, and the particle diameters were measured at 10,000x magnification. 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 with a scanning electron microscope (SEM). (3) Qualitative analysis of the protrusions of the base particle: The base particle was measured using an X-ray diffractometer (Rigaku Corporation's "Ultima IV") under the following conditions: radiation source: Cu-Kα, tube voltage: 40 kV, tube current: 40 mA, and scanning speed: 4° / sec. If a diffraction peak of a metal oxide or metal hydroxide was confirmed during measurement, the base particle was deemed to contain a metal oxide or metal hydroxide. Furthermore, elemental mapping analysis was performed using SEM-EDX (Bruker's XFlash5060FlatQUAD energy dispersive X-ray analyzer) to confirm the distribution of metal and oxygen. If the metal and oxygen were mapped on the convex portions, the convex portions were determined to be made of metal oxide or metal hydroxide.

[0078] Example 1 (1) Preparation of Base Particles Spherical styrene-acrylate-silica composite resin particles with an average particle size of 3.0 μm were used as base particles. 9 g of the base particles were added to 100 mL of pure water at 25°C and stirred for 30 minutes to obtain a base particle dispersion. This dispersion was then added to 600 mL of a 50% by weight aqueous solution of chromic anhydride (manufactured by Nippon Chemical Industry Co., Ltd.), heated to 50°C, and maintained for 60 minutes. After cooling to room temperature, the aqueous solution was filtered, and the base particles were repulped and washed once to obtain a 200 mL slurry. Separately from this slurry, a reaction solution was prepared by dissolving 7 g of boric acid and 25 g of ammonium hexafluorotitanate in 600 g of pure water and maintaining the temperature at 60°C. The slurry was then added to this reaction solution and stirred for 3 hours while maintaining the temperature at 60°C to precipitate metal oxides on the surface of the base particles, forming protrusions. The resulting slurry was filtered and repulped and washed three times to obtain base particles. The protrusions of this base particle were analyzed by the above-mentioned (3) qualitative method for the protrusions of the base particle, and it was found that the protrusions were titanium oxide (TiO ２) aggregates. The average height of the convex portions was 250 nm, and the average width of the base of the convex portions was 340 nm. (2) Pretreatment: 0.1 g of stannous chloride was added to the resulting slurry of base particles. The mixture was stirred at room temperature for 5 minutes, and a sensitization treatment was performed to adsorb tin ions onto the surface of the base particles. Subsequently, this aqueous solution was filtered, and the base particles were repulped and washed with water once to form a 200 mL slurry, which was maintained at 60°C. 1.5 mL of a 0.11 mol / L aqueous palladium chloride solution was added to this slurry. The mixture was stirred at 60°C for 5 minutes, and an activation treatment was performed to capture palladium ions onto the surface of the base particles. Subsequently, this aqueous solution was filtered, and the base particles were repulped and washed with hot water once to form a 100 mL slurry, to which 10 mL of a 0.5 g / L aqueous dimethylamine borane solution was added. The mixture was stirred for 2 minutes while applying ultrasound to obtain a slurry of pretreated base particles. (3) Preparation of Plating Bath: 3 L of electroless nickel-phosphorus plating bath was prepared from an aqueous solution containing 5 g / L sodium tartrate, 2 g / L nickel sulfate hexahydrate, 10 g / L trisodium citrate, 0.1 g / L sodium hypophosphite, and 2 g / L polyethylene glycol, and the temperature was raised to 70°C. (4) Electroless Plating: The pretreated base particle slurry was added to this electroless plating bath and stirred for 5 minutes, after which it was confirmed that hydrogen bubbling had ceased. To this slurry, 420 mL of a 224 g / L nickel sulfate aqueous solution and a mixed aqueous solution containing 210 g / L sodium hypophosphite and 80 g / L sodium hydroxide were continuously added at an addition rate of 2.5 mL / min using a metering pump, and electroless plating was initiated. After the entire amounts of the nickel sulfate aqueous solution and the mixed aqueous solution of sodium hypophosphite and sodium hydroxide were added, stirring was continued for 5 minutes while maintaining the temperature at 70°C. The liquid 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 a nickel-phosphorus alloy coating. The obtained conductive particles had an average particle size of 3.22 µm, a conductive layer thickness of 110 nm, and protrusions.

[0079] Example 2 (1) Preparation of Base Particles The same operations as in Example 1 were carried out until 200 mL of a slurry of base particles was obtained. Separately from this slurry, 7 g of boric acid and an aqueous solution of a molybdenum fluorocomplex compound obtained by dissolving 30 g of molybdic acid in 600 g of 2.8% hydrofluoric acid were mixed and maintained at 40°C to prepare a reaction solution. The slurry was added to this reaction solution and stirred for 3 hours while maintaining the temperature at 40°C, thereby precipitating a metal oxide on the surface of the base particles and forming convex portions. The obtained slurry was filtered and repulped and washed with water three times to obtain base particles. The convex portions of these base particles were analyzed by the above-mentioned (3) qualitative method for convex portions of base particles, and it was found that the convex portions were molybdenum oxide (MoO ２ ) aggregates. The average height of the protrusions was 210 nm, and the average width of the base of the protrusions was 310 nm. (2) The same operation as in Pretreatment Example 1 was carried out to obtain a slurry of pretreated base particles. (3) Preparation of Plating Bath 3 L of the same electroless nickel-phosphorus plating bath as in Example 1 was prepared and heated to 70°C. (4) The same operation as in Electroless Plating Treatment Example 1 was carried out to obtain conductive particles having a nickel-phosphorus alloy coating. The obtained conductive particles had an average particle diameter of 3.22 μm, a conductive layer thickness of 110 nm, and had protrusions.

[0080] Example 3 (1) Preparation of Base Particles The same operations as in Example 1 were carried out until 200 mL of a slurry of base particles was obtained. Separately from this slurry, 17 g of boric acid was mixed with an aqueous solution of a tin fluorocomplex compound obtained by dissolving 2.8 g of tin (II) fluoride, 1.2 g of hydrogen peroxide, and 1.4 g of a 50% aqueous solution of hydrofluoric acid in 600 g of pure water, and the mixture was maintained at 50°C to prepare a reaction solution. The slurry was added to this reaction solution and stirred for 5 hours while maintaining the temperature at 50°C, thereby depositing a metal oxide on the surface of the base particles and forming convex portions. The obtained slurry was filtered and repulped and washed with water three times to obtain base particles. The convex portions of this base particle were analyzed by the above-mentioned (3) qualitative method for convex portions of base particles, and it was found that the convex portions were composed of tin oxide (SnO) having an average primary particle diameter of 30 nm. ２) aggregates. The average height of the protrusions was 220 nm, and the average width of the base of the protrusions was 320 nm. The particles were washed with water. (2) The same operation as in Pretreatment Example 1 was carried out to obtain a slurry of pretreated base particles. (3) Preparation of Plating Bath 3 L of the same electroless nickel-phosphorus plating bath as in Example 1 was prepared and heated to 70°C. (4) The same operation as in Electroless Plating Treatment Example 1 was carried out to obtain conductive particles having a nickel-phosphorus alloy coating. The obtained conductive particles had an average particle diameter of 3.22 μm, a conductive layer thickness of 110 nm, and had protrusions.

[0081] Example 4 (1) Preparation of Base Particles The same operations as in Example 1 were carried out until 200 mL of base particle slurry was obtained. Separately from this slurry, a reaction solution was prepared by dissolving 7 g of boric acid and 27 g of hexafluorosilicic acid in 600 g of pure water and maintaining the temperature at 60°C. The slurry was added to this reaction solution and stirred for 3 hours while maintaining the temperature at 60°C, thereby precipitating a metal oxide on the surface of the base particles and forming convex portions. The obtained slurry was filtered and repulped and washed with water three times to obtain base particles. When the convex portions of these base particles were analyzed by the above-mentioned (3) qualitative method for convex portions of base particles, it was found that the average particle diameter of the primary particles was 25 nm and the silica (SiO ２ ) aggregates. The average height of the protrusions was 210 nm, and the average width of the base of the protrusions was 310 nm. (2) The same operation as in Pretreatment Example 1 was carried out to obtain a slurry of pretreated base particles. (3) Preparation of Plating Bath 3 L of the same electroless nickel-phosphorus plating bath as in Example 1 was prepared and heated to 70°C. (4) The same operation as in Electroless Plating Treatment Example 1 was carried out to obtain conductive particles having a nickel-phosphorus alloy coating. The obtained conductive particles had an average particle diameter of 3.22 μm, a conductive layer thickness of 110 nm, and had protrusions.

[0082] Example 5 (1) Preparation of Base Particles The same operations as in Example 1 were carried out until 200 mL of base particle slurry was obtained. Separately from this slurry, 7 g of boric acid and an aqueous solution of a tungsten fluorocomplex compound obtained by dissolving tungstic acid in 600 g of 2.8% hydrofluoric acid were mixed and maintained at 60°C to prepare a reaction solution. The slurry was added to this reaction solution and stirred for 3 hours while maintaining the temperature at 60°C, causing metal oxide to precipitate on the surface of the base particles and forming convex portions. The obtained slurry was filtered and repulped and washed with water three times to obtain base particles. When the convex portions of this base particle were analyzed using the above-mentioned (3) qualitative method for convex portions of base particles, tungsten oxide (WO) with an average primary particle diameter of 28 nm was found. ２ ) aggregates. The average height of the protrusions was 160 nm, and the average width of the base of the protrusions was 250 nm. (2) The same operation as in Pretreatment Example 1 was carried out to obtain a slurry of pretreated base particles. (3) Preparation of Plating Bath 3 L of the same electroless nickel-phosphorus plating bath as in Example 1 was prepared and heated to 70°C. (4) The same operation as in Electroless Plating Treatment Example 1 was carried out to obtain conductive particles having a nickel-phosphorus alloy coating. The obtained conductive particles had an average particle diameter of 3.22 μm, a conductive layer thickness of 110 nm, and had protrusions.

[0083] Example 6 (1) Preparation of Base Particles The same operations as in Example 1 were carried out until 200 mL of base particle slurry was obtained. Separately from this slurry, 7 g of boric acid and a vanadium fluorocomplex compound obtained by dissolving 20 g of vanadium (V) oxide in 600 g of 5% hydrofluoric acid were mixed and maintained at 60°C to prepare a reaction solution. The slurry was added to this reaction solution and stirred for 3 hours while maintaining the temperature at 60°C, thereby precipitating a metal oxide on the surface of the base particles and forming convex portions. The obtained slurry was filtered and repulped and washed with water three times to obtain base particles. When the convex portions of this base particle were analyzed by the above-mentioned (3) qualitative method for convex portions of base particles, vanadium oxide (VO) with an average primary particle diameter of 20 nm was found. ２) aggregates. The average height of the protrusions was 180 nm, and the average width of the base of the protrusions was 280 nm. (2) The same operation as in Pretreatment Example 1 was carried out to obtain a slurry of pretreated base particles. (3) Preparation of Plating Bath 3 L of the same electroless nickel-phosphorus plating bath as in Example 1 was prepared and heated to 70°C. (4) The same operation as in Electroless Plating Treatment Example 1 was carried out to obtain conductive particles having a nickel-phosphorus alloy coating. The obtained conductive particles had an average particle diameter of 3.22 μm, a conductive layer thickness of 110 nm, and had protrusions.

[0084] Example 7 (1) Preparation of Base Particles The same procedures as in Example 1 were carried out until 200 mL of a slurry of base particles was obtained. Separately from this slurry, 7 g of boric acid and an iron-fluoro complex compound obtained by dissolving 11 g of β-iron oxyhydroxide (β-FeOOH) in 600 g of a 5% aqueous solution of ammonium hydrogen fluoride were mixed and maintained at 60°C to prepare a reaction solution. The slurry was added to this reaction solution and stirred for 1 hour while maintaining the temperature at 60°C, causing metal hydroxide to precipitate on the surface of the base particles and forming convex portions. The resulting slurry was filtered and repulped and washed with water three times to obtain base particles. The convex portions of these base particles were analyzed using the above-mentioned (3) Qualitative Method for Convex Portions of Base Particles. They were found to be aggregates of β-iron oxyhydroxide with an average primary particle diameter of 15 nm. The average height of the convex portions was 150 nm, and the average base width of the convex portions was 280 nm. (2) Pretreatment The same procedures as in Example 1 were carried out to obtain a slurry of pretreated base particles. (3) Preparation of Plating Bath Three liters of the same electroless nickel-phosphorus plating bath as in Example 1 was prepared and heated to 70°C. (4) Electroless Plating Treatment The same operation as in Example 1 was carried out to obtain conductive particles having a nickel-phosphorus alloy coating. The obtained conductive particles had an average particle diameter of 3.22 µm, a conductive layer thickness of 110 nm, and protrusions.

[0085] Example 8 (1) Preparation of Base Particles with Protrusions The same operations as in Example 1 were carried out until 200 mL of a slurry of base particles was obtained. Separately from this slurry, a reaction solution was prepared by dissolving 80 g of metallic aluminum powder and 25 g of ammonium hexafluorotitanate in 600 g of pure water and maintaining the temperature at 60°C. The slurry was added to this reaction solution and stirred for 3 hours while maintaining the temperature at 60°C, causing metal oxide to precipitate on the surfaces of the base particles and forming protrusions. After removing the metallic aluminum powder from the obtained slurry, the slurry was filtered and repulped and washed with water three times to obtain base particles. When the protrusions of this base particle were analyzed by the above-mentioned (3) qualitative method for protrusions of base particles, titanium oxide (TiO ) having an average primary particle diameter of 28 nm was found to be present. ２ ) aggregates. The average height of the protrusions was 240 nm, and the average width of the base of the protrusions was 340 nm. (2) The same operation as in Pretreatment Example 1 was carried out to obtain a slurry of pretreated base particles. (3) Preparation of Plating Bath 3 L of the same electroless nickel-phosphorus plating bath as in Example 1 was prepared and heated to 70°C. (4) The same operation as in Electroless Plating Treatment Example 1 was carried out to obtain conductive particles having a nickel-phosphorus alloy coating. The obtained conductive particles had an average particle diameter of 3.22 μm, a conductive layer thickness of 110 nm, and had protrusions.

[0086] Example 9 (1) Preparation of Base Particles The same operations as in Example 1 were carried out until 200 mL of a slurry of base particles was obtained. Separately from this slurry, 80 g of metallic aluminum powder and an aqueous solution of a molybdenum fluorocomplex compound obtained by dissolving molybdic acid in 600 g of 2.8% hydrofluoric acid were mixed and maintained at 40°C to prepare a reaction solution. The slurry was added to this reaction solution and stirred for 3 hours while maintaining the temperature at 40°C, thereby precipitating a metal oxide on the surface of the base particles and forming convex portions. After removing the metallic aluminum powder from the obtained slurry, the slurry was filtered and repulped and washed three times with water to obtain base particles. The convex portions of these base particles were analyzed by the above-mentioned (3) qualitative method for convex portions of base particles, and it was found that the convex portions were composed of molybdenum oxide (MoO) having an average primary particle diameter of 30 nm. ２) aggregates. The average height of the protrusions was 200 nm, and the average width of the base of the protrusions was 300 nm. (2) The same operation as in Pretreatment Example 1 was carried out to obtain a slurry of pretreated base particles. (3) Preparation of Plating Bath 3 L of the same electroless nickel-phosphorus plating bath as in Example 1 was prepared and heated to 70°C. (4) The same operation as in Electroless Plating Treatment Example 1 was carried out to obtain conductive particles having a nickel-phosphorus alloy coating. The obtained conductive particles had an average particle diameter of 3.22 μm, a conductive layer thickness of 110 nm, and had protrusions.

[0087] Example 10 (1) Preparation of Base Particles The same operations as in Example 1 were carried out until 200 mL of base particle slurry was obtained. Separately from this slurry, a reaction solution was prepared by dissolving 120 g of metallic aluminum powder, 2.8 g of tin (II) fluoride, 1.2 g of hydrogen peroxide, and 1.4 g of a 50% aqueous solution of hydrofluoric acid in 600 g of pure water and maintaining the temperature at 50°C. The slurry was added to this reaction solution and stirred for 5 hours while maintaining the temperature at 50°C, thereby precipitating a metal oxide on the surface of the base particles and forming convex portions. After removing the metallic aluminum powder from the obtained slurry, the slurry was filtered and repulped and washed with water three times to obtain base particles. When the convex portions of these base particles were analyzed using the above-mentioned (3) qualitative method for convex portions of base particles, it was found that the convex portions were composed of tin oxide (SnO) having an average primary particle diameter of 29 nm. ２ ) aggregates. The average height of the protrusions was 230 nm, and the average width of the base of the protrusions was 310 nm. (2) The same operation as in Pretreatment Example 1 was carried out to obtain a slurry of pretreated base particles. (3) Preparation of Plating Bath 3 L of the same electroless nickel-phosphorus plating bath as in Example 1 was prepared and heated to 70°C. (4) The same operation as in Electroless Plating Treatment Example 1 was carried out to obtain conductive particles having a nickel-phosphorus alloy coating. The obtained conductive particles had an average particle diameter of 3.22 μm, a conductive layer thickness of 110 nm, and had protrusions.

[0088] Example 11 (1) Preparation of Base Particles The same operations as in Example 1 were carried out until 200 mL of a slurry of base particles was obtained. Separately from this slurry, 50 g of metallic aluminum powder and 27 g of hexafluorosilicic acid were dissolved in 600 g of pure water, and the mixture was maintained at 60°C to prepare a reaction solution. The slurry was added to this reaction solution, and the mixture was stirred for 3 hours while maintaining the temperature at 60°C, causing a metal oxide to precipitate on the surface of the base particles, forming convex portions. After removing the metallic aluminum powder from the obtained slurry, the mixture was filtered and repulped and washed with water three times to obtain base particles. When the convex portions of these base particles were analyzed using the above-mentioned (3) qualitative method for convex portions of base particles, it was found that the average height of the primary particles was 23 nm, and the silica (SiO ２ ) aggregates. The average height of the protrusions was 220 nm, and the average width of the base of the protrusions was 320 nm. (2) The same operation as in Pretreatment Example 1 was carried out to obtain a slurry of pretreated base particles. (3) Preparation of Plating Bath 3 L of the same electroless nickel-phosphorus plating bath as in Example 1 was prepared and heated to 70°C. (4) The same operation as in Electroless Plating Treatment Example 1 was carried out to obtain conductive particles having a nickel-phosphorus alloy coating. The obtained conductive particles had an average particle diameter of 3.22 μm, a conductive layer thickness of 110 nm, and had protrusions.

[0089] [Example 12] (1) Preparation of Base Particles Separately from this slurry, 50 g of metallic aluminum powder was mixed with an aqueous solution of a tungsten fluorocomplex compound obtained by dissolving tungstic acid in 600 g of 2.8% hydrofluoric acid, and the mixture was maintained at 60°C to prepare a reaction solution. The slurry was added to this reaction solution and stirred for 3 hours while maintaining the temperature at 60°C, causing metal oxide to precipitate on the surface of the base particles and forming convex portions. After removing the metallic aluminum powder from the obtained slurry, the slurry was filtered and repulped and washed with water three times to obtain base particles. When the convex portions of these base particles were analyzed by the above-mentioned (3) qualitative method for convex portions of base particles, it was found that the average particle diameter of the primary particles was 30 nm and the resulting tungsten oxide (WO ２) aggregates. The average height of the protrusions was 170 nm, and the average width of the base of the protrusions was 240 nm. (2) The same operation as in Pretreatment Example 1 was carried out to obtain a slurry of pretreated base particles. (3) Preparation of Plating Bath 3 L of the same electroless nickel-phosphorus plating bath as in Example 1 was prepared and heated to 70°C. (4) The same operation as in Electroless Plating Treatment Example 1 was carried out to obtain conductive particles having a nickel-phosphorus alloy coating. The obtained conductive particles had an average particle diameter of 3.22 μm, a conductive layer thickness of 110 nm, and had protrusions.

[0090] Example 13 (1) Preparation of Base Particles The same operations as in Example 1 were carried out until 200 mL of a base particle slurry was obtained. Separately from this slurry, 50 g of metallic aluminum powder and a vanadium fluorocomplex compound obtained by dissolving 20 g of vanadium (V) oxide in 600 g of 5% hydrofluoric acid were mixed and maintained at 60°C to prepare a reaction solution. The slurry was added to this reaction solution and stirred for 3 hours while maintaining the temperature at 60°C, thereby precipitating a metal oxide on the surface of the base particles and forming convex portions. After removing the metallic aluminum powder from the obtained slurry, the slurry was filtered and repulped and washed with water three times to obtain base particles. When the convex portions of these base particles were analyzed by the above-mentioned (3) qualitative method for convex portions of base particles, vanadium oxide (VO) with an average primary particle diameter of 22 nm was found. ２ ) aggregates. The average height of the protrusions was 170 nm, and the average width of the base of the protrusions was 270 nm. (2) The same operation as in Pretreatment Example 1 was carried out to obtain a slurry of pretreated base particles. (3) Preparation of Plating Bath 3 L of the same electroless nickel-phosphorus plating bath as in Example 1 was prepared and heated to 70°C. (4) The same operation as in Electroless Plating Treatment Example 1 was carried out to obtain conductive particles having a nickel-phosphorus alloy coating. The obtained conductive particles had an average particle diameter of 3.22 μm, a conductive layer thickness of 110 nm, and had protrusions.

[0091] Example 14 (1) Preparation of Base Particles The same procedures as in Example 1 were carried out until 200 mL of base particle slurry was obtained. Separately from this slurry, 50 g of metallic aluminum powder and an aqueous solution of an iron-fluorocomplex compound obtained by dissolving 11 g of β-iron oxyhydroxide (β-FeOOH) in 600 g of a 5% aqueous solution of ammonium hydrogen fluoride were mixed and maintained at 60°C to prepare a reaction solution. The slurry was added to this reaction solution and stirred for 1 hour while maintaining the temperature at 60°C, causing metal hydroxide to precipitate on the surface of the base particles and forming convex portions. After removing the metallic aluminum powder from the resulting slurry, the mixture was filtered and repulped and washed three times with water to obtain base particles. When the convex portions of these base particles were analyzed using the above-mentioned (3) Qualitative Method for Convex Portions of Base Particles, they were found to be aggregates of β-iron oxyhydroxide with an average primary particle diameter of 18 nm. The average height of the convex portions was 160 nm, and the average base width of the convex portions was 290 nm. (2) The same operation as in Pretreatment Example 1 was carried out to obtain a slurry of pretreated base particles. (3) Preparation of Plating Bath 3 L of the same electroless nickel-phosphorus plating bath as in Example 1 was prepared and heated to 70°C. (4) The same operation as in Electroless Plating Treatment Example 1 was carried out to obtain conductive particles having a nickel-phosphorus alloy coating. The obtained conductive particles had an average particle size of 3.22 μm, a conductive layer thickness of 110 nm, and protrusions.

[0092] Comparative Example 1 In the (1) preparation of base particles in Example 1, a reaction solution was not prepared, and 200 mL of mother particle slurry was obtained, followed by the (2) pretreatment operation to obtain a pretreated base particle slurry. Thereafter, the same operations as in Example 1 were performed. The obtained conductive particles had an average particle diameter of 3.2 μm, a conductive layer thickness of 100 nm, and protrusions were present.

[0093] Comparative Example 2: In Example 1 (1) Preparation of Base Particles, a reaction solution was not prepared, but instead 200 mL of base particle slurry was obtained, followed by the pretreatment procedure (2) to obtain a pretreated base particle slurry. (3) Preparation of Plating Bath: 3 L of electroless nickel-phosphorus plating bath was prepared from an aqueous solution containing 5 g / L sodium tartrate, 0.1 g / L nickel sulfate hexahydrate, 10 g / L trisodium citrate, 0.25 g / L tetramethylethylenediamine, 0.15 g / L sodium pyrophosphate, 0.1 g / L sodium hypophosphite, and 2 g / L polyethylene glycol, and the temperature was raised to 70°C. (4) Electroless Plating: The pretreated base particle slurry was added to this electroless plating bath, stirred for 5 minutes, and the hydrogen bubbling was confirmed to have stopped. To this slurry, 420 mL of a 224 g / L nickel sulfate aqueous solution 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 an addition rate of 2.5 mL / min, respectively, to initiate electroless plating. After the entire amounts of the nickel sulfate aqueous solution and the mixed aqueous solution of sodium hypophosphite and sodium hydroxide were added, stirring was continued for 5 minutes while maintaining a temperature of 70°C. The liquid 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 a nickel-phosphorus alloy coating. The resulting conductive particles had an average particle size of 3.22 μm, and the conductive layer had a thickness of 110 nm and was smooth.

[0094] (Evaluation of Connection Resistance and Connection Reliability) Using the conductive particles of the Examples and Comparative Examples, the connection resistance and connection reliability were evaluated using the following method. An insulating adhesive containing 100 parts by weight of epoxy resin, 150 parts by weight of curing agent, and 70 parts by weight of toluene was mixed with 15 parts by weight of the conductive particles obtained in the Examples and Comparative Examples to obtain a paste. This paste was applied to a silicone-treated polyester film using a bar coater, and then the paste was dried to form a thin film on the film. The obtained thin-film-forming film was placed between a glass substrate entirely coated with aluminum and a polyimide film substrate with a copper pattern formed at a 50 μm pitch to prepare a connection structure and establish electrical connection. The connection resistance of this connection structure was measured at room temperature (25°C, 50% RH). Furthermore, the resistance value after 24 hours at 85°C and 85% RH was also measured. The smaller the difference from the connection resistance value at room temperature, the better the connection reliability of the conductive particles.

[0095]

[0096] These results demonstrate that the conductive particles of the present invention have low connection resistance. Furthermore, the difference between the connection resistance and the resistance after 24 hours at 85°C and 85% RH is small, demonstrating excellent connection reliability.

Claims

1. A base particle having protrusions on the surface of a base particle, the protrusions being an aggregate of metal oxide or metal hydroxide having an average primary particle diameter of 1 to 100 nm.

2. The base particle according to claim 1, wherein the metal oxide is at least one selected from the group consisting of oxides of titanium, molybdenum, tin, silicon, tungsten, vanadium and iron.

3. The base particle according to claim 1, wherein the metal hydroxide is at least one selected from the group consisting of hydroxides of titanium, molybdenum, tin, silicon, tungsten, vanadium and iron.

4. The base particle according to claim 1, wherein the average height of the convex portions is 20 to 1,500 nm.

5. The base particle according to claim 1, wherein the average width of the base of the protrusions is 5 to 1,500 nm.

6. The base particle according to claim 1, wherein the base particle is made of a material containing an organic substance.

7. The base particle according to claim 1, wherein the base particle is made of both inorganic and organic materials.

8. Conductive particles comprising a base particle according to any one of claims 1 to 7 and a conductive layer formed on the surface thereof.

9. The conductive particle according to claim 8, wherein said conductive layer is nickel or a nickel alloy.

10. A conductive material comprising the conductive particles according to claim 8 and an insulating resin.

11. A method for producing base particles, in which hydrophilically treated base particles are added to an aqueous solution containing a metal fluorocomplex compound and a fluoride ion scavenger, thereby forming aggregates of metal oxide or metal hydroxide on the surfaces of the base particles, thereby obtaining base particles having convex portions on the particle surfaces.

12. The method for producing base particles according to claim 11, wherein the hydrophilization treatment is carried out using one or more compounds selected from the group consisting of chromic anhydride, dichromic acid, and chromium oxide.

13. The method for producing base particles according to claim 11, wherein the metal fluorocomplex compound is at least one selected from the group consisting of fluorocomplex compounds of titanium, molybdenum, tin, silicon, tungsten, vanadium and iron.

14. The method for producing base particles according to claim 11, wherein the fluoride ion scavenger is at least one selected from the group consisting of boric acid and metallic aluminum.

15. The method for producing base particles according to claim 11, wherein the base particles are made of a material containing an organic substance.

16. The method for producing base particles according to claim 11, wherein the base particles are made of a material containing inorganic and organic substances.

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