TW202411468A - Conductive particles, production method therefor, and conductive member - Google Patents

Abstract

The present invention provides conductive particles which have a small connection resistance value and have excellent insulation performance, and with which short circuit is inhibited, and thus exhibit excellent connection reliability. The conductive particles each have a core material particle, and a conductive layer having a plurality of projection parts on the surface of the core material particle. The height variation of the projection parts is 0.01-0.25.

Description

Conductive particles, method for producing the same, and conductive material

The present invention relates to a conductive particle, a method for producing the conductive particle, and a conductive material containing the conductive particle.

As conductive particles used as conductive materials for anisotropic conductive materials such as anisotropic conductive films or anisotropic conductive pastes, there is generally known a conductive particle having a conductive layer containing metal formed on the surface of a core particle. With the miniaturization or refinement of electronic devices in recent years, in the connection between electrode terminals with a fine pitch, the conductive layer of the conductive particles is used to make electrical connections between electrodes or wirings.

As the conductive layer of the conductive particles, a film formed on the surface of the core particles by electroplating a metal such as nickel using an electroless plating method is often used, and various efforts have been made to show the target characteristics. As an example, in Patent Document 1, it is described that a plurality of multi-prismatic protrusions are formed on the conductive layer of the conductive particles, whereby when the conductive particles are used for electrical connection between electrodes, the conductive particles can be efficiently arranged on the electrodes, and damage to the electrodes by the conductive particles can be suppressed. In addition, Patent Document 2 proposes a conductive particle having a plurality of non-polygonal protrusions formed on the conductive layer of the conductive particle, thereby effectively reducing the connection resistance after the connection even when the electrodes are connected at a low voltage. Furthermore, Patent Document 3 describes a conductive particle having a plurality of protrusions on the conductive layer of the conductive particle, and forming at least a portion of the plurality of protrusions as plate-shaped protrusions, thereby preventing the conductive particle from excessively flowing when the electrodes are connected, thereby improving the conduction reliability and insulation reliability.

Patent Documents 1 to 3 attempt to solve the problem by designing the shape of the protrusion formed on the conductive layer according to the target effect. Conductive particles that are given desired properties by making the shape of the protrusion different in this way are being studied. [Prior Art Document] [Patent Document]

[Patent Document 1] Japanese Patent Publication No. 2015-149277 [Patent Document 2] Japanese Patent Publication No. 2016-119302 [Patent Document 3] Japanese Patent Publication No. 2017-212033

[Problems to be solved by the invention] By using conductive particles having a conductive layer with protrusions formed on the surface of core particles, the contact efficiency between conductive particles is improved, and the amount of conductive particles can be reduced. In addition, when there is an oxide film on the electrode surface, the oxide film can be destroyed by the protrusions to achieve conduction, thereby suppressing resistance. By providing protrusions on the conductive layer in this way, the connection resistance can be reduced or the conduction reliability can be improved when connecting between electrodes.

However, with the demand for further miniaturization and refinement of electronic devices, it is required not only to further reduce the connection resistance of conventional conductive particles having protrusions, but also to prevent short circuits at insulating portions.

Therefore, the object of the present invention is to provide a conductive particle with a small connection resistance value, excellent insulation, and excellent connection reliability with short circuit suppressed. In addition, the object of the present invention is to provide a method for manufacturing a conductive particle with a small connection resistance value, excellent insulation, and excellent connection reliability with short circuit suppressed. [Means for solving the problem]

In order to solve the above-mentioned problem, the inventors of the present invention have conducted intensive research on the protrusions of the conductive particles and found that by controlling the deviation of the height of the protrusions within a certain range, the connection resistance of the conductive particles is small and short circuits are suppressed, thereby completing the present invention.

That is, the present invention provides a conductive particle including a core particle and a conductive layer having a plurality of protrusions on a surface of the core particle, wherein a variation in height of the protrusions is 0.01 or more and 0.25 or less.

In addition, the present invention provides a method for producing conductive particles, the method comprising the following steps: forming a conductive layer on the surface of a core particle; forming a protrusion protruding from the surface of the conductive layer; and averaging the height of the protrusion. [Effect of the invention]

According to the present invention, a conductive particle having a small connection resistance and excellent insulation, thereby suppressing short circuits and having excellent connection reliability is provided. In addition, according to the present invention, a method for manufacturing a conductive particle having a small connection resistance and excellent insulation, thereby suppressing short circuits and having excellent connection reliability is provided.

The present invention is described below based on the preferred embodiment of the present invention. The conductive particles of the present invention (hereinafter also described as "the present conductive particles") include core particles and a conductive layer having a plurality of protrusions on the surface of the core particles, wherein the deviation of the height of the protrusions is greater than 0.01 and less than 0.25. It is believed that if the deviation of the height of the protrusions of the conductive particles is large, the contact between the conductive particles and the electrode will become uneven, and the connection resistance will be greater. In addition, if the deviation of the height of the protrusions is large, a short circuit may sometimes occur due to unexpected conduction. It is believed that the deviation of the height of the protrusions of the present conductive particles is controlled within a certain range, and as a result, the connection resistance is small, the short circuit is suppressed, and the connection reliability is improved.

The core particles of the conductive particles (hereinafter also referred to as "the core particles") may be inorganic or organic as long as they are in particle form. Examples of inorganic materials include metal particles such as gold, silver, copper, nickel, palladium, solder, alloys of these metals, glass, ceramics, silicon dioxide, metal or non-metal oxides or their hydrates, metal silicates such as aluminosilicate, metal carbides, metal nitrides, metal carbonates, metal sulfates, metal phosphates, metal sulfides, metal acids, metal halides, and carbon. On the other hand, examples of organic materials include natural fibers, natural resins, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polybutene, polyamide, polyacrylate, polyacrylonitrile, polyacetal, ionomer, polyester and other thermoplastic resins, alkyd resins, phenol resins, urea resins, benzoguanamine resins, melamine resins, xylene resins, silicone resins, epoxy resins, diallyl phthalate resins and other thermosetting resins. These may be used alone or in combination of two or more.

The material of the core particles may be any one of the inorganic and organic materials, or both. When the core particles include materials including both inorganic and organic materials, the inorganic and organic materials in the core particles may include, for example, a core-shell structure including a core including an inorganic material and a shell including an organic material covering the surface of the core, or a core including an organic material and a shell including an inorganic material covering the surface of the core. In addition to these, a structure in which inorganic and organic materials coexist in one core particle, or a mixed structure of random fusion, may also be included.

The core particles are preferably made of an organic material, and more preferably a material comprising both an inorganic material and an organic material. In the case of a material comprising both an inorganic material and an organic material, the inorganic material is preferably glass, ceramic, silicon dioxide, metal or non-metal oxides or their hydrates, metal silicates such as aluminum silicate, metal carbides, metal nitrides, metal carbonates, metal sulfates, metal phosphates, metal sulfides, metal acids, metal halides, and carbon. In addition, the organic material is preferably a thermoplastic resin such as natural fiber, natural resin, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polybutylene, polyamide, polyacrylate, polyacrylonitrile, polyacetal, ionomer, polyester, etc. By using a core material containing such a material, the dispersion stability of the particles can be improved. In addition, when the electronic circuit is electrically connected, appropriate elasticity can be exhibited to improve conduction.

When a material containing an organic substance is included as the core particle, the organic substance is preferably an organic substance that does not have a glass transition temperature or has a glass transition temperature exceeding 100° C., from the perspective of easily maintaining the shape of the core particle or easily maintaining the shape of the core particle in the step of forming a metal film. The glass transition temperature can be obtained, for example, as the intersection of the original baseline and the tangent line of the inflection point in the baseline shift portion of the DSC curve obtained by differential scanning calorimetry (hereinafter also described as "DSC (Differential Scanning Calorimetry)").

When the organic substance is a highly cross-linked resin, even if the glass transition temperature is measured up to 200°C using the above method, there is sometimes little baseline shift observed. In this specification, such an organic substance is also referred to as an organic substance without a glass transition temperature. The core particles of the present invention can also use an organic substance without such a glass transition temperature as a material for the core particles. The organic substance without a glass transition temperature can be obtained by copolymerizing the monomers and cross-linking monomers constituting the thermoplastic resin or the thermosetting resin exemplified above. Examples of the crosslinking monomer 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, trihydroxymethylpropane tri(meth)acrylate, tetrahydroxymethylmethane di(meth)acrylate, tetrahydroxymethylmethane tri(meth)acrylate, tetrahydroxymethyl Methane tetra(meth)acrylate, tetrahydroxymethylpropane tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, glycerol di(meth)acrylate, glycerol tri-di(meth)acrylate and other multifunctional (meth)acrylates, divinylbenzene, divinyltoluene and other multifunctional vinyl monomers, vinyl trimethoxysilane, trimethoxysilylstyrene, γ-(meth)acryloxypropyl trimethoxysilane and other silane-containing monomers, triallyl isocyanurate, diallyl phthalate, diallyl acrylamide, diallyl ether and other monomers. In particular, in the field of chip on glass (COG), such highly cross-linked resins are preferably used as materials for core particles from the viewpoint of being hard.

The shape of the core particles can be amorphous, spherical, fibrous, hollow, plate-like or needle-like, and is usually spherical. The core particles can have a plurality of protrusions on their surface. From the perspective of excellent filling properties and easy metal coating, the shape of the core particles is preferably spherical.

The conductive particles of the present invention have a conductive layer on the surface of the core particles, and the conductive layer has a plurality of protrusions. The conductive layer of the conductive particles of the present invention contains a conductive metal. 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, curium, ruthenium, potassium, cadmium, nirconium, lithium, bismuth, gallium, molybdenum, cesium, niobium, strontium, proton, zirconium, barium, and manganese, or alloys thereof, and metal compounds such as indium tin oxide (ITO) and solder. Among them, gold, silver, copper, nickel, palladium, rhodium or solder is preferred due to its low resistance, and nickel, gold, palladium, nickel alloy, gold alloy and palladium alloy are particularly preferred. The metal may be one or more types in combination.

The conductive layer of the conductive particles may be a single-layer structure or a multi-layered structure. In the case of a multi-layered structure, the outermost layer preferably comprises at least one selected from the group consisting of nickel, gold, silver, copper, and palladium, preferably nickel, gold, silver, copper, palladium, and alloys thereof. In the case of alloys, nickel, gold, silver, copper, or an alloy of palladium and phosphorus, i.e., nickel alloy, gold alloy, silver alloy, copper alloy, and palladium alloy, are preferably used, and nickel-phosphorus alloy and palladium-phosphorus alloy are more preferably used. The outermost layer of the conductive layer is more preferably an electroless nickel-phosphorus layer formed by an electroless method in the manufacturing method described below.

The conductive layer of the conductive particles may cover the entire surface of the core particles or only a portion thereof. When only a portion of the surface of the core particles is covered, the covered portion may be continuous or may be discontinuous, for example, in the form of islands.

From the viewpoint of the electrical properties of the obtained conductive particles, the thickness of the conductive layer of the conductive particles 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. The height of the protrusions of the conductive layer is not included in the thickness of the conductive layer described herein. The thickness of the conductive layer can be measured by cutting the particle to be measured into two and observing the cross section of the cut using a scanning electron microscope (SEM). The thickness of the conductive layer is preferably within the above range.

The deviation of the height of the protrusions (hereinafter also referred to as "the protrusions") possessed by the conductive layer of the present conductive particles is greater than 0.01 and less than 0.25. Furthermore, the so-called height deviation is a value obtained by dividing the standard deviation of the height of the protrusions by the average value of the height of the protrusions, and is represented by the following formula (1). The standard deviation of the height can be calculated by the following formula (2), and the average value of the height is the arithmetic mean of the heights of the protrusions calculated using the following formula (3). By making the value of the deviation within the above range, the contact between the conductive particles and the electrode becomes more uniform, thereby improving the connection stability.

The deviation of the height of the protrusion is preferably greater than 0.05 and less than 0.20. The height of the protrusion refers to the shortest distance from the highest point of the top of the protrusion to the point where the base of the protrusion touches the center of the conductive particle when the cross section of the conductive particle is spherical when SEM observation is performed on the cross section of the conductive particle. For 20 different conductive particles observed by SEM observation, the height of all protrusions of each conductive particle can be measured and substituted into the above formulas to obtain the deviation of the height of the protrusion. Furthermore, when the protrusion has multiple vertices, the highest vertex is set as the height of the protrusion.

The average height of the protrusions of the conductive particles is preferably 20 nm or more and 1,000 nm or less, more preferably 50 nm or more and 800 nm or less. The number of protrusions also depends on the particle size of the conductive particles, but the number of protrusions per conductive particle is preferably 1 or more and 20,000 or less, and more preferably 5 or more and 5,000 or less. In addition, the length of the base of the protrusion is preferably 5 nm or more and 1,000 nm or less, and more preferably 10 nm or more and 800 nm or less.

The average value of the height of the protrusions is obtained by calculating the height of the protrusions in the same manner as described above and by using the above formula (3). The average length of the base of the protrusions refers to the length along the surface 6 of the lower layer of the conductive layer at the portion where the protrusions are formed in FIG. 1 (a) and FIG. 1 (b). The base length of the protrusions is the arithmetic average of the values obtained by measuring the length of the base of all protrusions of each conductive particle for 20 different conductive particles observed by SEM observation.

From the viewpoint of making the contact between the conductive particles and the electrode more uniform, the shape of the top portion of the protrusion is preferably roughly planar. Here, the so-called roughly planar includes a completely flat surface and a curved surface having a curvature radius described later. For example, with respect to the completely flat surface portion 5 shown in FIG. 1 (a), the flat surface portion 5 having a curved surface within the range of the curvature radius described later shown in FIG. 1 (b) is also included in the concept of roughly planar in this specification.

When the top portion of the protrusion is roughly planar, the length of the top portion is preferably 10 nm or more and 500 nm or less, and more preferably 20 nm or more and 400 nm or less. The length of the roughly planar top portion is the shortest distance connecting the two ends of the roughly planar top portion in the cross section of the protrusion when the cross section of the conductive particle is observed by SEM. For example, in FIG. 1 (a) and FIG. 1 (b), the length of the straight line connecting the end 5a and the end 5b of the planar portion 5 of the roughly planar top portion is the length of the top portion. The length of the top portion of the substantially planar protrusion is the arithmetic mean of the values obtained by measuring the length of the top portion of the cross section of all protrusions of each conductive particle in cross sections of 20 different conductive particles observed by SEM observation.

The number of protrusions also depends on the particle size of the conductive particles, but from the perspective of the conductivity of the conductive particles, the number of protrusions per conductive particle is preferably 2 or more and 20,000 or less, and more preferably 5 or more and 5,000 or less. The number of protrusions is the arithmetic mean of the values measured for 20 different conductive particles observed by SEM observation.

When the curvature radius of the top portion of the protrusion is set to Ra when the top portion is roughly planar, and the curvature radius of the surface 6 of the lower layer of the conductive layer where the protrusion is formed is set to Rb, the ratio of Ra to Rb (Ra/Rb) is preferably greater than 0.15 and less than 1.20, especially greater than 0.20 and less than 1.00. Since the top portion of the protrusion has a curvature radius that satisfies the above range, the contact between the conductive particles and the electrode becomes more uniform, thereby improving the connection stability. Furthermore, Ra can be set to, for example, the radius of a circumscribed circle circumscribing the top portion of the cross section of each protrusion in terms of the cross section of the conductive particles observed by SEM observation. Rb can be set to, for example, the radius of a circumscribed circle circumscribing the surface of the lower layer of the conductive layer in a cross section of the conductive particle observed by SEM observation, that is, substantially the radius of the core particle.

It is believed that by setting the height of the protrusion to the range, the contact between the conductive particle and the electrode becomes uniform, and when the top portion of the protrusion is roughly flat, the contact with other conductive particles present near the conductive particle is suppressed, thereby preventing short circuit. From this point of view, it is preferred that the area of the sum of the roughly planar portions of the top portion of the protrusion of each conductive particle is wide. That is, the ratio of the sum of the areas of the top portions of the protrusions S2 to the projected area S1 of one conductive particle, S2/S1, is preferably greater than 0.50, particularly greater than 0.55. Furthermore, S2/S1 is less than 1, and from the point of view of confirming that a roughly planar protrusion is formed, it is preferably less than 0.95, and more preferably less than 0.90. The projected area S1 of the conductive particles and the total area S2 of the top portion of the protrusions can be measured by inputting the SEM photograph image into an automatic image analyzer (manufactured by NIRECO Co., Ltd., Luzex (registered trademark) AP).

In addition, from the perspective of preventing short circuits, at least one shape of the protrusion is preferably amorphous. The so-called amorphous protrusion means that when the top part of the protrusion is observed from the side opposite to the base, the top part is surrounded by multiple curves with different curvatures. When the top part of the protrusion is observed from the side opposite to the base, the top part is preferably a shape other than a circular shape and a polygonal shape. The number of protrusions with amorphous shapes is preferably 10 or more, and more preferably 20 or more for each conductive particle. Or, when the total number of protrusions of one conductive particle is 100%, the number of protrusions with amorphous shapes is preferably 90% or more, and more preferably 95% or more.

The protrusion is preferably continuous with the conductive layer formed on the surface of the core particle. That is, the protrusion preferably contains the same metal or alloy as the conductive layer. The so-called continuous body mentioned here means that the conductive layer and the protrusion contain the same material, and there is no joint or other part that damages the overall feeling between the conductive layer and the protrusion. By forming a continuous body with the conductive layer and the protrusion, the strength of the protrusion is ensured, so even if pressure is applied when using the conductive particle, the base of the protrusion is not easily damaged. The protrusion is more preferably composed of the same metal or alloy as the metal or alloy constituting the conductive layer formed on the surface of the core particle.

The average particle size of the conductive particles is preferably greater than 0.1 μm and less than 50 μm, and more preferably greater than 1 μm and less than 30 μm. By having the average particle size of the conductive particles within the above range, short circuits in directions different from those between the opposing electrodes will not occur, and it is easier to ensure conduction between the opposing electrodes. Furthermore, in the present invention, the average particle size of the conductive particles is the arithmetic mean value obtained by randomly extracting 200 particles through SEM observation and measuring the particle size at a magnification of 10,000 times. When the conductive particles are spherical, the diameter of the conductive particles is the diameter of a circle obtained by projecting the conductive particles onto a plane, excluding the height of the protrusions. When the conductive particles are not spherical, the particle size is the longest length of a line segment that crosses an image obtained by projecting the conductive particles onto a plane.

The shape of the conductive particles can be appropriately selected according to the shape of the core particles. The shape of the conductive particles can be the same as or different from the shape of the core particles. From the perspective of manufacturing efficiency, the two are preferably the same shape. The shape of the conductive particles can be, for example, spherical, fibrous, hollow, plate-like, needle-like or amorphous. From the perspective of excellent filling and connectivity, the shape of the conductive particles is preferably spherical.

The conductive particles can be produced, for example, by a production method (hereinafter also referred to as "the production method") comprising the following steps. Step of forming a conductive layer on the surface of the core particle Step of forming a protrusion protruding from the surface of the conductive layer Step of averaging the height of the protrusion

In the step of forming a conductive layer on the surface of the core particle (hereinafter also described as "conductive layer forming step"), a conductive layer is formed on the surface of the core particle by any of dry methods such as evaporation, sputtering, mechanochemical method, hybrid method, or wet methods such as electrolytic plating and electroless plating. In addition, these methods can be combined to form a conductive layer on the surface of the core particle. The core particle used can be the present core particle, and the preferred material and shape are as described above.

From the viewpoint of easily obtaining conductive particles having desired particle properties, the conductive layer forming step is preferably to form the conductive layer on the surface of the core particle by electroless plating, and from the viewpoint of easily obtaining conductive particles having desired particle properties and easily forming the protrusions described later, electroless plating is more preferred. In particular, the conductive layer is preferably an electroless nickel alloy layer formed by an electroless method, and is more preferably an electroless nickel-phosphorus layer.

The following is an explanation of the conductive layer formation step of forming a nickel-phosphorus alloy layer as a conductive layer. When an electroless plating method is used in the conductive layer formation step, the core particles preferably have a surface that has the ability to capture precious metal ions, or are surface-modified in a manner that has the ability to capture precious metal ions. The precious metal ions are preferably palladium or silver ions. The so-called ability to capture precious metal ions means that the precious metal ions can be captured in the form of a chelate or a salt. For example, when an amine group, an imine group, an amide group, an imide group, a cyano group, a hydroxyl group, a nitrile group, a carboxyl group, etc. are present on the surface of the core particles, the surface of the core particles has the ability to capture precious metal ions. When surface modification is performed in a manner that provides the ability to capture precious metal ions, for example, the method described in Japanese Patent Publication No. 61-64882 can be used.

Core particles having the ability to capture precious metal ions or having their surfaces modified in such a way as to have the ability to capture precious metal ions are used as the core particles, and precious metals are loaded 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. Precious metal ions are thereby captured on the surface of the core particles. The concentration of the precious metal salt is generally in the range of 1×10 ^-7 mol to 1×10 ^-2 mol per 1 m ² of the surface area of the core particles. The core particles in which the precious metal ions are captured are separated from the aqueous solution and washed with water. Subsequently, the core particles are suspended in water, and a reducing agent is added thereto to perform a reduction treatment of the precious metal ions. Thereby, the noble metal is loaded on the surface of the core particles. The reducing agent is, for example, sodium hypophosphite, sodium borohydride, potassium borohydride, dimethylamine borane, hydrazine, formalin, etc. It is preferably selected from these based on the constituent material of the target conductive layer.

Before the surface of the present core material particles captures the precious metal ions, a sensitization treatment may be performed for the purpose of adsorbing tin ions on the surface of the particles and improving the adhesion with the precious metal. In order to adsorb tin ions on the surface of the particles, for example, the present core material particles after the surface modification as described above can be placed in an aqueous solution of stannous chloride and stirred for a predetermined time.

The present core particles subjected to the pretreatment are subjected to the conductive layer forming step to form a conductive layer on the surface of the present core particles. After the conductive layer forming step, a step of forming protrusions protruding from the upper surface of the conductive layer (hereinafter also referred to as "protrusion forming step") is performed.

The protrusion forming step is preferably performed immediately after the following conductive layer forming step. The conductive layer forming step is preferably an electroless nickel plating method in which an aqueous slurry of the core material particles is mixed with an electroless nickel plating bath containing a dispersant, a nickel salt, a reducing agent, and a complexing agent. In the conductive layer forming step using the electroless nickel plating method, self-decomposition of the plating solution occurs while the conductive layer is formed on the core material particles. The self-decomposition occurs near the core material particles, so that the self-decomposition products are captured on the surface of the core material particles when the conductive layer is formed, thereby generating the core of the micro-protrusions and simultaneously forming the conductive layer. Based on the core of the generated micro-protrusion, the protrusion is grown by the protrusion forming step described later.

In the step of forming the conductive layer by the electroless nickel plating method, it is preferred to fully disperse the core material particles in water in a range of preferably 0.1 g/L to 500 g/L, and more preferably 1 g/L to 300 g/L, to prepare an aqueous slurry. The dispersion operation can be performed using conventional stirring, high-speed stirring, or a shearing dispersion device such as a colloid mill or a homogenizer. In addition, ultrasound can also be used in the dispersion operation. If necessary, a dispersant such as a surfactant is sometimes added to the dispersion operation. Then, the aqueous slurry of the core material particles that has been dispersed is added to an electroless nickel plating solution containing a nickel salt, a reducing agent, a complexing agent, and various additives, and the electroless plating method is performed.

As the dispersant, for example, nonionic surfactants, amphoteric surfactants and/or water-soluble polymers can be listed. As nonionic surfactants, polyoxyalkylene ether-based surfactants such as polyethylene glycol, polyoxyethylene alkyl ether, and polyoxyethylene alkylphenyl ether can be used. As amphoteric surfactants, betaine-based surfactants such as alkyl dimethyl acetate betaine, alkyl dimethyl carboxymethyl acetate betaine, and alkyl dimethyl aminoacetic acid betaine can be used. As water-soluble polymers, polyvinyl alcohol, polyvinyl pyrrolidone, hydroxyethyl cellulose, etc. can be used. These dispersants can be used alone or in combination of two or more. The amount of dispersant used also depends on its type, but is generally 0.5 g/L to 30 g/L relative to the volume of the electroless nickel plating solution. In particular, if the amount of dispersant used is in the range of 1 g/L to 10 g/L relative to the volume of the electroless nickel plating solution, it is better from the perspective of further improving the adhesion of the conductive layer.

As nickel salt, nickel chloride, nickel sulfate or nickel acetate is used, and its concentration is preferably set to a range of 0.1 g/L to 50 g/L. As a reducing agent, it is used for the reduction of precious metal ions and is selected based on the constituent material of the target conductive layer. As reducing agents, phosphorus compounds and boron compounds can be listed. When sodium hypophosphite is used as the phosphorus compound, its concentration is preferably set to a range of 0.1 g/L to 50 g/L.

As complexing agents, for example, carboxylic acids or carboxylic acid salts such as citric acid, hydroxyacetic acid, tartaric acid, apple acid, lactic acid, gluconic acid or their alkali metal salts or ammonium salts, amino acids such as glycine, ethylenediamine, alkylamines, other ammonium, EDTA or pyrophosphate (salt) and other compounds that have complexing effects on nickel ions can be used. These can be used alone or in combination of two or more. The concentration is preferably in the range of 1 g/L to 100 g/L, and more preferably in the range of 5 g/L to 50 g/L. The preferred pH value of the electroless nickel plating solution in this stage is in the range of 3 to 14. The electroless nickel plating reaction starts quickly after adding the aqueous slurry of the core particles, accompanied by the generation of hydrogen gas. When the generation of hydrogen gas is completely unconfirmed, the conductive layer formation step is completed. The thickness of the conductive layer can be controlled by adjusting the concentration of the nickel salt, the dispersant and the complexing agent as needed, the pH value, etc. in the conductive layer formation step, and can be set to a range of the preferred thickness of the conductive layer.

Next, a protrusion forming step is performed after the conductive layer forming step. In the protrusion forming step, it is preferred to form the protrusion by adding a nickel salt, a reducing agent, and an alkali to the electroless nickel plating solution of the conductive layer forming step using the electroless nickel plating method. The method of adding the nickel salt, the reducing agent, and the alkali is preferably, for example, (i) using a first aqueous solution containing one of the nickel salt, the reducing agent, and the alkali, and a second aqueous solution containing the remaining two, or (ii) using a first aqueous solution containing a nickel salt, a second aqueous solution containing a reducing agent, and a third aqueous solution containing an alkali. The aqueous solutions of (i) or (ii) are added to the electroless nickel plating solution at the same time, and the addition is continued to continue the electroless nickel plating. When the addition of each aqueous solution is interrupted, the electroplating reaction stops, and the electroplating reaction is restarted after the addition. By adjusting the amount of each aqueous solution added, the conductive layer formed can be controlled to a desired film thickness, and further, the protrusions are formed starting from the cores of the micro-protrusions generated on the surface of the conductive layer in the conductive layer formation step. After the addition of the aqueous solution to the electroless nickel plating solution is completed, after the generation of hydrogen gas is completely confirmed, the reaction is completed while the liquid temperature is temporarily maintained and stirring is continued.

In the case of (i) above, it is preferred to use a first aqueous solution containing a nickel salt and a second aqueous solution containing a reducing agent and an alkali, but the present invention is not limited to this combination. In this case, the first aqueous solution does not contain a reducing agent and an alkali, and the second aqueous solution does not contain a nickel salt. As the nickel salt and the reducing agent, the substances described above can be used. As the alkali, for example, a hydroxide of an alkaline metal such as sodium hydroxide or potassium hydroxide can be used.

In the case of (ii), the first to third aqueous solutions contain nickel salt, reducing agent and base, respectively, and each aqueous solution does not contain the other two components. The base used is the same as that in the case of (i).

In either case of (i) or (ii), the concentration of the nickel salt in the aqueous solution is preferably 10 g/L to 1,000 g/L, more preferably 50 g/L to 500 g/L. When a phosphorus compound is used as a reducing agent, the concentration of the reducing agent is preferably 100 g/L to 1,000 g/L, more preferably 100 g/L to 800 g/L. When a boron compound is used as a reducing agent, it is preferably 5 g/L to 200 g/L, more preferably 10 g/L to 100 g/L. When hydrazine or a derivative thereof is used as a reducing agent, it is preferably 5 g/L to 200 g/L, more preferably 10 g/L to 100 g/L. The concentration of the alkali is preferably 5 g/L to 500 g/L, more preferably 10 g/L to 200 g/L.

The protrusion forming step may be performed continuously after the conductive layer forming step is completed, or the protrusion forming step may be performed after the conductive layer forming step is completed and the core material particles formed with the conductive layer are temporarily separated from the electroless nickel plating solution. In the case of separating the core material particles formed with the conductive layer from the electroless nickel plating solution, after the conductive layer forming step is completed, the core material particles formed with the conductive layer can be separated from the electroplating solution by filtering or the like. After separation, the core particles with the conductive layer formed thereon are redispersed in water to prepare an aqueous slurry, and an aqueous solution obtained by dissolving the complexing agent in a concentration range of preferably 1 g/L to 100 g/L, more preferably 5 g/L to 50 g/L is added thereto, thereby preparing an aqueous slurry obtained by dissolving the dispersant in a concentration range of preferably 0.5 g/L to 30 g/L, more preferably 1 g/L to 10 g/L. The aqueous solution described in (i) or (ii) can also be added to the prepared aqueous slurry to perform the protrusion forming step. In this way, a conductive layer with protrusions can be formed.

The conductive particles formed with protrusions in the protrusion forming step average the height of the protrusions by a step of averaging the height of the protrusions (hereinafter also referred to as an "averaging step"). By setting the deviation of the height of the protrusions to the above range by the averaging step, the conductive particles can be obtained. In the averaging step, the height of the protrusions formed in the protrusion forming step is reduced by grinding the top part of the protrusions obtained in the protrusion forming step, thereby setting the deviation of the height of the protrusions to a predetermined range.

As a method for grinding the top part of the protrusion, for example, there can be listed a method of mixing a mixing medium used in a ball mill, a bead mill, etc. with the conductive particles obtained in the protrusion forming step, a method of mixing an abrasive with the conductive particles obtained in the protrusion forming step, a method of mixing the conductive particles obtained in the protrusion forming step with each other, a method of rotating the conductive particles obtained in the protrusion forming step on a plane such as a belt, etc., etc.

When the mixed medium and the conductive particles are mixed, the material of the mixed medium is preferably a material having a hardness equal to or greater than that of the material of the protrusions of the conductive particles. As the mixing method, there can be cited a method of using a stirrer with stirring blades, a method of mixing in a container that rotates or revolves or both, a method of mixing in a vibrating container, etc. As the material of the mixed medium, there can be cited, for example, zirconia, zircon, agate, aluminum oxide, iron, stainless steel, glass, etc.

When the abrasive is mixed with the conductive particles obtained in the protrusion forming step, diamond, boron nitride, silicon carbide, aluminum oxide, etc. can be listed as the abrasive. As for the mixing method with the abrasive, the same method as the method of mixing the mixed medium with the conductive particles can be listed. As for the method of mixing the conductive particles with each other, the same method as the method of mixing the mixed medium with the conductive particles can also be listed.

When the conductive particles obtained in the protrusion forming step are rotated on a plane such as a belt, the material of the plane is preferably a material having a hardness equal to or greater than that of the material of the protrusion of the conductive particles. The conductive particles obtained in the protrusion forming step may be rotated and moved on the plane in a manner such that the conductive particles obtained in the protrusion forming step fall on a plane with an inclination. In addition, the conductive particles obtained in the protrusion forming step may be moved in the opposite direction on a plane moving in a certain direction.

In each method of performing the polishing, the relationship between the polishing conditions and the height of the protrusions can be measured in advance, and the polishing conditions can be determined in advance in such a way that the deviation of the height of the protrusions is within the range of the conductive particles. In addition, the deviation of the height of the protrusions can be measured over time while polishing, and based on the result, the polishing can be terminated when the deviation of the height of the protrusions is within the range of the conductive particles. In addition, the height of the protrusions can be set to the preferred range in the same manner.

In the process of lowering the height of the protrusion in the averaging step, the protrusion is polished so that the top portion of the protrusion becomes a plane, thereby making the top portion of the protrusion substantially planar. In addition, by lowering the height of the protrusion in accordance with the curvature of the surface of the core particle, the curvature radius Ra of the top portion of the protrusion and the curvature radius Rb of the outer surface of the conductive layer can be set to the above-mentioned preferred relationship.

The manufacturing method may further include the following step after the averaging step: heat treatment at a temperature of 200°C to 600°C, preferably 250°C to 500°C, and particularly 300°C to 450°C under a vacuum of less than 1,000 Pa, preferably 0.01 Pa to 900 Pa, and particularly preferably 0.1 Pa to 500 Pa. By heating the conductive particles while maintaining such a vacuum state, the metal of the conductive layer is less likely to undergo side reactions even at high temperatures, and crystallization progresses, so the resistance becomes low and the electrical conductivity is excellent. Furthermore, the vacuum degree in the present invention is the value when the absolute pressure, that is, the absolute vacuum, is set to 0.

The heat treatment time in the step of performing the heat treatment is preferably 0.1 to 10 hours, and more preferably 0.5 to 5 hours. By adopting this treatment time, the increase in manufacturing cost can be suppressed, and the modification of the core particles or the conductive layer caused by the thermal history can be suppressed, thereby reducing the impact on the quality. In addition, the heat treatment time is the time from reaching the target treatment temperature to the end of the heat treatment.

The step of performing the heat treatment may be performed while the conductive particles are left at rest or while being stirred. When the conductive particles are left at rest for the heat treatment, it is preferred that the conductive particles be left at a thickness of 0.1 mm to 100 mm. By leaving the conductive particles at this thickness, the heat treatment of the conductive layer can be smoothly performed, thereby suppressing the manufacturing cost.

The step of heat treatment is to reduce the pressure of the container containing the conductive particles to vacuum and then perform the heat treatment in a static state or while stirring. At this time, the gas phase of the container containing the conductive particles can be replaced with an inert gas such as nitrogen and then reduced to vacuum, or it can be directly reduced to vacuum. In addition, the heat treatment can be performed multiple times as needed.

In addition, it is preferred that the heat treatment step is performed by maintaining the vacuum degree at room temperature to 1,000 Pa or less, preferably 0.01 Pa to 900 Pa, and particularly preferably 0.1 Pa to 500 Pa, for 5 to 60 minutes, and further 10 to 50 minutes, and then raising the temperature to the treatment temperature. This operation can prevent oxidation of the conductive layer caused by the heated environment or oxygen or moisture in the conductive particles, thereby reducing the connection resistance.

It is preferred that after the step of performing the heat treatment, the temperature is lowered to 50°C or less while maintaining the vacuum degree, and then the vacuum is released after the temperature is lowered to 40°C or less. The reason is that when the vacuum is released at a temperature immediately after the heat treatment, the oxidation of the conductive layer is promoted in the presence of oxygen or moisture in the environment, so the connection resistance may become higher. In addition, from the perspective of manufacturing cost, the vacuum can be released in a normal atmosphere, and from the perspective of preventing oxidation of the conductive layer, it is more preferably released by blowing an inert gas such as nitrogen, argon, helium, or a non-oxidizing gas such as a hydrogen-nitrogen mixed gas.

As described below, the conductive particles can be preferably used as a conductive material such as a conductive filler of a conductive adhesive. The conductive material comprising the conductive particles and an insulating resin (hereinafter, also described as "the conductive material") is preferably further coated with an insulating resin to prevent short circuits between the 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 at least the protrusions on the surface of the conductive particles are exposed when the conductive adhesive is used to bond two electrodes. The thickness of the insulating resin can be set to about 0.1 μm to 0.5 μm. The insulating resin may cover the entire surface of the conductive particles or may cover only a portion of the surface of the conductive particles.

Examples of the insulating resin include phenol resins, urea resins, melamine resins, allyl resins, furan resins, polyester resins, epoxy resins, silicone resins, polyamide-imide resins, polyimide resins, polyurethane resins, fluororesins, polyolefin resins such as polyethylene, polypropylene, and polybutene; polyalkyl (meth)acrylate resins, poly Resins including organic polymers such as (meth)acrylic resins, polystyrene resins, acrylonitrile-styrene-butadiene resins, vinyl resins, polyamide resins, polycarbonate resins, polyacetal resins, ionomer resins, polyether sulfone resins, polyphenylene oxide resins, polysulfone resins, polyvinylidene fluoride resins, ethyl cellulose resins and cellulose acetate resins.

Methods for forming an insulating coating layer by coating the surface of conductive particles with an insulating resin include chemical methods such as coagulation, interfacial polymerization, in situ polymerization, and liquid curing coating; physical and mechanical methods such as spray drying, air suspension coating, vacuum evaporation coating, dry blending, mixing, electrostatic polymerization, solution dispersion cooling, and inorganic encapsulation; and physical and chemical methods such as interfacial precipitation.

Regarding the organic polymer constituting the insulating resin, from the viewpoint of improving the adhesion with the conductive particles under the condition of non-conductivity, a monomer component containing an ionic group may be included in the structure of the polymer. The monomer component containing an ionic group may be any one of a crosslinking monomer component and a non-crosslinking monomer component. It is preferred to use at least one monomer component having an ionic group among the crosslinking monomer component and the non-crosslinking monomer component to form the organic polymer. Furthermore, the so-called "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 containing an ionic group to polymerization, an organic polymer containing the monomer component containing an ionic group as a structural unit is formed.

The ionic group is preferably present in the organic polymer constituting the insulating resin. In addition, the ionic group is preferably chemically bonded to the monomer component constituting the organic polymer. Whether the ionic group is present at the interface of the organic polymer can be determined by observing with a scanning electron microscope whether the insulating resin is attached to the surface of the conductive particles when an insulating resin containing an organic polymer having an ionic group is formed on the surface of the conductive particles.

Examples of the ionic group include onium functional groups such as phosphonium, ammonium, and cobalt. Among these, ammonium or phosphonium groups are preferred, and phosphonium groups are more preferred, from the viewpoint of improving the adhesion between the conductive particles and the insulating resin and forming conductive particles having both high levels of insulation and conduction reliability.

As the onium functional group, preferably, there can be mentioned those represented by the following general formula (1).

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

As a counter ion to the ionic group, for example, a halide ion can be cited. Examples of the halide ion include Cl ^- , F ^- , Br ^- , and I ^- .

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

In the general formula (1), examples of the branched alkyl group represented by R include branched alkyl groups having 3 to 8 carbon atoms, and specifically include isopropyl, isobutyl, sec-butyl, t-butyl, isopentyl, sec-pentyl, t-pentyl, isohexyl, sec-hexyl, t-hexyl, ethylhexyl and the like.

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

In the general formula (1), examples of the aryl group represented by R include phenyl, benzyl, tolyl, and o-xylyl.

In the 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. In the general formula (1), R is also even more preferably a linear alkyl group. By forming the onium functional group into such a structure, the adhesion between the insulating resin and the conductive particles can be improved to ensure insulation, and the conduction reliability during heat pressing can be further improved.

From the viewpoint of facilitating the acquisition of monomers and the synthesis of polymers and improving the production efficiency of the insulating resin, the organic polymer having an ionic group constituting the insulating resin preferably has a structural unit represented by the following general formula (2) or (3).

[Chemistry 2] In the general formula (2), X, R and n have the same meanings as in the general formula (1). m is an integer of 0 or more and 5 or less. ^An- represents a monovalent anion. When m is 0, it means that X is directly bonded to the benzene ring.

[Chemistry 3] In the general formula (3), X, R and n have the same meanings as in the general formula (1). ^An- represents a monovalent anion. ^m1 is an integer of 1 to 5. _R5 is a hydrogen atom or a methyl group.

As examples of R in the general formula (2) and the general formula (3), the description of the functional group of R in the general formula (1) is appropriately applied. The ionic group may be bonded to the CH group of the benzene ring of the general formula (2) at any of the para position, ortho position, or meta position, and preferably at the para position. In the general formula (2) and the general formula (3), as the monovalent An ^- , preferably a halide ion can be listed. Examples of the halide ion include Cl ^- , F ^- , Br ^- , and I ^- .

In general formula (2), m is preferably an integer of 0 to 2, more preferably 0 or 1, and particularly preferably 1. In general formula (3), m is preferably ¹ to 3, more preferably 1 or 2, and most preferably 2.

The organic polymer having an ionic group is preferably composed of a monomer component having an onium functional group and an ethylenically unsaturated bond. From the viewpoint of facilitating the acquisition of monomers and the synthesis of polymers and improving the production efficiency of insulating resins, the organic polymer having an ionic group is also preferably composed of a non-crosslinking monomer component.

Examples of non-crosslinking monomers having an onium functional group and an ethylenic unsaturated bond include: monomers containing an ammonium group such as N,N-dimethylaminoethyl methacrylate, N,N-dimethylaminopropyl acrylamide, and N,N,N-trimethyl-N-2-methacryloyloxyethyl ammonium chloride; monomers containing an ammonium group such as phenyldimethylcopperium methyl methacrylate; 4-(vinylbenzyl)triethylphosphonium chloride, 4-(vinylbenzyl)trimethylphosphonium chloride; , 4-(vinylbenzyl)tributylphosphonium 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, 2-(methacryloyloxyethyl)triphenylphosphonium chloride and the like. The organic polymer having an ionic group may contain two or more non-crosslinking monomer components.

The organic polymer constituting the insulating resin may be one in which all monomer components are bonded with ionic groups, or may be one in which a portion of all structural units of the organic polymer are bonded with ionic groups. When a portion of all structural units of the organic polymer are bonded with ionic groups, the ratio of the monomer components bonded with ionic groups is preferably 0.01 mol% to 99 mol%, more preferably 0.02 mol% to 95 mol%. Here, regarding the number of monomer components in the organic polymer, when the organic polymer has an ethylenically unsaturated bond, the structure derived from one ethylenically unsaturated bond is counted as a structural unit of one monomer. When the ionic group is contained in both the crosslinking monomer and the non-crosslinking monomer, the ratio of the monomer component is set to the total amount thereof.

Examples of the coating form using the insulating resin include a form in which a plurality of insulating fine particles containing the insulating resin are arranged in layers, or a form in which the insulating resin forms a continuous film.

When the insulating resin contains insulating particles, the conductive particles coated with the insulating particles are heat-pressed between the electrodes, whereby the insulating particles melt, deform, peel off, or move on the surface of the conductive particles, thereby exposing the metal surface of the conductive particles at the hot-pressed portion, thereby achieving conduction between the electrodes and obtaining connectivity. On the other hand, with respect to the surface portion of the conductive particles facing a direction other than the hot-pressing direction, the coating state of the conductive particle surface by the insulating particles is roughly maintained, thereby preventing conduction in a direction other than the hot-pressing direction.

The insulating particles contain the ionic groups on their surfaces, so that they can be easily in close contact with the conductive particles, thereby making the proportion of the conductive particles covered by the insulating particles sufficient, and effectively preventing the insulating particles from peeling off from the conductive particles. Therefore, the insulating particles can easily exert the effect of preventing short circuits in a direction different from the opposing electrodes, and the improvement of the insulation in that direction can be expected.

The shape of the insulating microparticles 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, or needle-like. In addition, the insulating microparticles may have a plurality of protrusions on their surface or may be amorphous. In terms of adhesion to conductive particles or ease of synthesis, spherical insulating microparticles are preferred.

The average particle size of the insulating microparticles is preferably greater than 10 nm and less than 3,000 nm, and more preferably greater than 15 nm and less than 2,000 nm. When the average particle size of the insulating microparticles is within the above range, the obtained coated particles will not produce a short circuit in a direction different from that between the opposing electrodes, and it is easy to ensure conduction between the opposing electrodes. The average particle size of the insulating microparticles is a value measured by observation using a scanning electron microscope, and is specifically measured by the method described in the embodiments described below.

The particle size distribution of the insulating microparticles measured by the above method usually has a width. In general, the width of the particle size distribution of a powder is represented by the coefficient of variation (hereinafter also referred to as "C.V.") represented by the following formula (4). C.V. (%) = (standard deviation/average particle size) × 100... (4) The larger the C.V., the wider the range of the particle size distribution. On the other hand, the smaller the C.V., the sharper the particle size distribution. The C.V. of the insulating microparticles used in the present conductive material is preferably 0.1% or more and 20% or less, more preferably 0.5% or more and 15% or less, and particularly preferably 1% or more and 10% or less. By setting the C.V. to this range, there is an advantage that the thickness of the coating layer formed by insulating fine particles can be made uniform.

In addition, the insulating resin may be in the form of a continuous film instead of the insulating particles being arranged in layers. When the continuous film is an insulating resin having an ionic group, the conductive particles are heat-pressed between electrodes to melt, deform or peel off the continuous film, thereby exposing the surface of the conductive particles, thereby achieving conduction between the electrodes and obtaining connectivity. In particular, by heat-pressing the conductive particles between electrodes, the continuous film is broken, and more conductive particles are exposed on the surface. On the other hand, in the surface portion of the conductive particles facing in a direction different from the hot pressing direction, the continuous film covering the conductive particles is roughly maintained, thereby preventing conduction in directions other than the hot pressing direction. When the insulating resin is a continuous film, it is preferably a continuous film having ionic groups on the surface.

In terms of improving the insulation in a direction different from the opposing electrodes, the thickness of the continuous film is preferably 10 nm or more, and in terms of the ease of conduction between the opposing electrodes, the thickness of the continuous film is preferably 3,000 nm or less. In this regard, 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.

Similar to the insulating fine particles, in the continuous film, the ionic group preferably forms a part of the chemical structure of the insulating resin as a part of the insulating resin constituting the continuous film. In the continuous film, the ionic group is preferably contained in at least one structure of the structural unit of the insulating resin constituting the continuous film. The ionic group is preferably chemically bonded to the insulating resin constituting the continuous film, and more preferably bonded to the side chain of the insulating resin.

In the case where the conductive material has a continuous film of an insulating resin, it is preferably a continuous film obtained by coating the conductive particles with insulating particles having ionic groups on their surfaces and then heating the insulating particles, or a continuous film obtained by dissolving the insulating particles with an organic solvent. As described above, the insulating particles having ionic groups are easily in close contact with the conductive particles, thereby making the proportion of the conductive particles on the surface covered by the insulating particles sufficient, and easily preventing the insulating particles from peeling off from the conductive particles. Therefore, the thickness of the continuous film obtained by heating or dissolving the insulating fine particles covering the conductive particles is uniform, and the coating ratio on the surface of the conductive particles can be increased.

From the viewpoint of improving affinity with the insulating resin and improving adhesion, the conductive particles can also be treated with a surface treatment agent. As the surface treatment agent, for example, benzotriazole compounds, titanium compounds, higher fatty acids or their derivatives, phosphates and phosphites can be listed. These can be used alone or in combination as needed.

The surface treatment agent may or may not chemically bond to the surface of the present conductive particle. The surface treatment agent only needs to be present on the surface of the present conductive particle, and in this case, it may be present on the entire surface of the present conductive particle or only on a portion of the surface.

Examples of the triazole compound include compounds having a nitrogen-containing heterocyclic structure including three nitrogen atoms in a five-membered ring.

Examples of triazole compounds include compounds having a triazole monocyclic structure that is not condensed with other rings, and compounds having a ring structure in which a triazole ring is condensed with other rings. Examples of other rings include a benzene ring and a naphthyl ring.

Among them, compounds having a ring structure formed by condensation of a triazole ring and other rings are preferred in terms of excellent adhesion to insulating resins, and compounds having a structure formed by condensation of a triazole ring and a benzene ring, i.e., benzotriazole compounds, are particularly preferred. As benzotriazole compounds, compounds represented by the following general formula (4) can be cited.

[Chemistry 4] In the general formula (4), R ¹¹ is a negative charge, a hydrogen atom, an alkali metal, an alkyl group which may be substituted, 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 independently a hydrogen atom, a halogen atom, an alkyl group which may be substituted, a carboxyl group, a hydroxyl group or a nitro group.

Examples of the alkali metal represented by R ¹¹ in the general formula (4) include lithium, sodium, potassium, and the like. The alkali metal represented by R ¹¹ is an alkali metal cation, and when R ¹¹ in the general formula (4) is an alkali metal, the bond between R ¹¹ and the nitrogen atom can be an ionic bond. Examples of the alkyl group represented by R ¹¹ , R ¹² , R ¹³ , R ¹⁴ , and R ¹⁵ in the general formula (4) include alkyl groups having 1 to 20 carbon atoms, and particularly preferably alkyl groups 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 proton group, a sulfonyl group, a phosphonium group, a cyano group, a fluoroalkyl group, an oxirane group, and a halogen atom. As the alkoxy group represented by R ¹¹ , an alkoxy group having a carbon number of 1 to 12 is preferably listed. In addition, the carbon number of the alkoxy group as a substituent of the alkyl group represented by R ¹² , R ¹³ , R ¹⁴ and R ¹⁵ is preferably 1 to 12. As the halogen atom represented by R ¹² , R ¹³ , R ¹⁴ and R ¹⁵ in the general formula (4), a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, etc. are listed.

As specific triazole compounds, compounds having a triazole monocyclic structure include: 1,2,3-triazole, 1,2,4-triazole, 3-amino-1H-1,2,4-triazole, 5-ol-1H-1,2,3-triazole sodium, 4-amino-3-hydrazino-5-ol-1,2,4-triazole, 3-amino-5-ol-1,2,4-triazole, Other examples include: benzotriazole having a ring structure formed by condensation of a triazole ring and other rings, 1-methyl-1H-benzotriazole, 4-methyl-1H-benzotriazole, 5-methyl-1H-benzotriazole, 4-carboxyl-1H-benzotriazole, 5-carboxyl-1H-benzotriazole, 5-ethyl-1H-benzotriazole, 5-propyl-1H-benzotriazole, 5,6-dimethyl-1H-benzotriazole, 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)-1H-benzotriazole, 4-(2-ethylhexyl)aminomethyl)benzotriazole, benzotriazole butyl ester, 4-carboxy-1H-benzotriazole butyl ester, 4-carboxy-1H-benzotriazole octyl ester, 1-[N,N-bis(2-ethylhexyl)aminomethyl]methylbenzotriazole, 2,2'-[[(methyl-1H-benzotriazol-1-yl)methyl]imino]bisethanol, tetrabutylphosphonium benzotriazole salt, 1H-benzotriazol-1-yloxy 1-[bis(dimethylamino)methylene]-1H-benzotriazolium 3-oxide hexafluorophosphate, 1-[bis(dimethylamino)methylene]-1H-benzotriazolium 3-oxide tetrafluoroborate, (6-Chloro-1H-benzotriazol-1-yloxy)tripyrrolidonephosphonium 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 tetrafluoroborate 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, (trifluoroacetyl)benzotriazole , tris(1H-benzotriazol-1-yl)methane, 9-(1H-benzotriazol-1-ylmethyl)-9H-carbazole, [(1H-benzotriazol-1-yl)methyl]triphenylphosphonium chloride, 1-(isocyanatomethyl)-1H-benzotriazole, 1-[(9H-fluoren-9-ylmethoxy)carbonyloxy]benzotriazole, 1,2,3-benzotriazole sodium salt, naphthotriazole, etc.

The titanium compound is particularly preferably a compound having a structure represented by the following general formula (5), for example, in that when the titanium compound is present on the surface of the conductive particles, the affinity between the insulating resin and the conductive particles can be easily obtained or the surface of the conductive particles can be uniformly treated by being easily dispersed in a solvent.

[Chemistry 5] In the general formula (5), ^R21 is a divalent or trivalent group, ^R22 is an aliphatic alkyl group having 2 to 30 carbon atoms, an aryl group having 6 to 22 carbon atoms, or an arylalkyl group having 7 to 23 carbon atoms, p and r are integers of 1 to 3, respectively, satisfying p+r=4, q is an integer of 1 or 2, and when ^R21 is a divalent group, q is 1, and when ^R21 is a trivalent group, q is 2. When q is 2, multiple ^R22s may be the same or different. * represents a bond.

Examples of the aliphatic alkyl group having 4 to 28 carbon atoms represented by R ²² include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, eicosyl, heneicosyl, and docosyl. Examples of the unsaturated aliphatic alkyl group include alkenyl, dodecenyl, tridecenyl, tetradecenyl, pentadecyl, hexadecyl, heptadecyl, nonadecyl, icosenyl, eicosenyl, heneicosenyl, and docosenyl. Examples of the aryl group having 6 to 22 carbon atoms include phenyl, tolyl, naphthyl, anthracenyl, and the like. Examples of the arylalkyl group having 7 to 23 carbon atoms include benzyl, phenethyl, naphthylmethyl, and the like. As the hydrophobic group, a linear or branched aliphatic hydrocarbon group is particularly preferred, and a linear aliphatic hydrocarbon group is particularly preferred. In terms of improving the affinity between the insulating resin and the conductive particles, the aliphatic hydrocarbon group as the hydrophobic group is particularly preferably a group having 4 to 28 carbon atoms, and most preferably a group having 6 to 24 carbon atoms.

Examples of the divalent group represented by ^R21 include -O-, -COO-, -OCO-, and _-OSO2- . Examples of the trivalent group represented by ^R21 include -P(OH)(O-) ₂ , -OPO(OH)-OPO(O-) ₂ , and the like.

In the general formula (5), * is a bond, and the bond may be bonded to the metal film of the conductive particle or may be bonded to other groups. Examples of other groups in this case include alkyl groups, and specifically, alkyl groups having 1 to 12 carbon atoms.

As the titanium compound having a structure represented by the general formula (5), a compound having a structure in which R ²¹ in the general formula (5) is a divalent group is preferred in terms of ease of acquisition or handling without damaging the conductive properties of the conductive particles. In the general formula (5), a structure in which R ²¹ is a divalent group is represented by the following general formula (6).

[Chemistry 6] In the general formula (6), R ²¹ is a group selected from -O-, -COO-, -OCO-, and -OSO ₂ -, and p, r, and R ²² have the same meanings as in the general formula (II).

In general formula (5) and general formula (6), from the viewpoint of improving the adhesion between the insulating resin and the conductive layer, r is preferably 2 or 3, and most preferably r is 3.

Specific examples of titanium ester compounds used in the surface treatment include: isopropyl triisostearate titanium ester, isopropyl tri-dodecylbenzenesulfonyl titanium ester, isopropyl tri(dioctyl pyrophosphate) titanium ester, tetraisopropyl(dioctyl phosphite) titanium ester, tetraisopropyl bis(dioctyl phosphite) titanium ester, tetraoctyl bis(di-tridecyl phosphite) titanium ester, tetrakis(2,2-diallyloxymethyl-1-butyl)bis(di-tridecyl) titanium phosphite, bis(dioctyl pyrophosphate) oxyacetic titanium ester, bis(dioctyl pyrophosphate) ethylene titanium ester, etc. One or more of these can be used. Furthermore, these titanium ester compounds are commercially available, for example, from Ajinomoto Precision Technology Co., Ltd.

As the higher fatty acid, preferably, it is a saturated or unsaturated straight chain or branched monocarboxylic acid or polycarboxylic acid, more preferably, it is a saturated or unsaturated straight chain or branched monocarboxylic acid, more preferably, it is a saturated or unsaturated straight chain monocarboxylic acid. The carbon number of the fatty acid is preferably 7 or more. In addition, the so-called derivative refers to the salt or amide of the fatty acid.

In the higher fatty acid or its derivative used in the surface treatment, the carbon number of the higher fatty acid is preferably 7 to 23, and more preferably 10 to 20. As such higher fatty acid or its derivative, for example, saturated fatty acids such as capric acid, lauric acid, myristic acid, palmitic acid, and stearic acid, unsaturated fatty acids such as oleic acid, linolenic acid, linolenic acid, and arachidonic acid, or metal salts or amides thereof, etc. As metal salts of higher fatty acids, alkali metals, alkaline earth metals, transition metals such as Zr, Cr, Mn, Fe, Co, Ni, Cu, and Ag, and salts of other metals other than transition metals such as Al and Zn can be cited, preferably polyvalent metal salts such as Al, Zn, W, and V. The higher fatty acid metal salt may be a monomer, a dimer, a trimer, a tetramer, etc. according to the valence of the metal. The higher fatty acid metal salt may be any combination of these.

As phosphates and phosphites, those having an alkyl group with a carbon number of 6 to 22 can be preferably used. As phosphates, for example, hexyl phosphate, heptyl phosphate, monooctyl phosphate, monononyl phosphate, monodecyl phosphate, monoundecyl phosphate, monododecyl phosphate, monotridecyl phosphate, monotetradecyl phosphate, monopentadecyl phosphate, etc. can be listed. As phosphites, for example, hexyl phosphite, heptyl phosphite, monooctyl phosphite, monononyl phosphite, monodecyl phosphite, monoundecyl phosphite, monododecyl phosphite, monotridecyl phosphite, monotetradecyl phosphite, monopentadecyl phosphite, etc. can be listed.

From the viewpoint of excellent affinity with the insulating resin and the effect of improving the coverage of the insulating resin, the surface treatment agent used in the surface treatment is preferably a triazole compound or a titanium compound, and particularly preferably benzotriazole, 4-carboxybenzotriazole, isopropyl triisostearate titanium ester, and tetraisopropyl (dioctyl phosphite) titanium ester.

The method of treating the conductive particles with a surface treatment agent is to disperse the conductive particles in a solution of the surface treatment agent and then filter the solution. Before the surface treatment agent is used, the conductive particles may be treated with other treatment agents or may be untreated. The concentration of the surface treatment agent in the solution of the surface treatment agent in which the conductive particles are dispersed is, for example, 0.01 mass % or more and 10.0 mass % or less. In addition, the solvent of the surface treatment agent solution can be listed as follows: water, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, isoamyl alcohol, cyclohexanol and other alcohols, acetone, methyl isobutyl ketone, methyl ethyl ketone, methyl-n-butyl ketone and other ketones, methyl acetate, ethyl acetate and other esters, diethyl ether, ethylene glycol monoethyl ether and other ethers, n-hexane, cyclohexanone, toluene, 1,4-dioxane, N,N-dimethylformamide, tetrahydrofuran and the like. The conductive particles after the surface treatment of dispersion and filtration are preferably dispersed again in the solvent to remove excess surface treatment agent.

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

The conductive particles have low connection resistance and excellent connection reliability, so they are preferably used as conductive materials for connecting the electrodes of anisotropic conductive film (ACF) or heat seal connector (HSC) or liquid crystal display panel to a circuit substrate for driving LSI chips. As a conductive material, the conductive particles can be used directly, or the conductive particles can be dispersed in an adhesive resin to be used as a conductive material. In addition, as a conductive material, the conductive material can be used directly, or the conductive material can be dispersed in an adhesive resin for use. Other forms of the conductive material are not particularly limited. In addition to the above forms, for example, anisotropic conductive paste, conductive adhesive, anisotropic conductive ink and the like can be listed.

Examples of the adhesive resin include thermoplastic resins and thermosetting resins. Examples of the thermoplastic resins include acrylic resins, styrene resins, ethylene-vinyl acetate resins, and styrene-butadiene block copolymers, and examples of the thermosetting resins include epoxy resins, phenol resins, urea resins, polyester resins, urethane resins, and polyimide resins.

In addition to the conductive particles and adhesive resin of the present invention, the conductive material can also be formulated with adhesive agents, reactive additives, epoxy resin hardeners, metal oxides, photoinitiators, sensitizers, hardeners, vulcanizers, anti-deterioration agents, heat-resistant additives, thermal conductivity enhancers, softeners, colorants, various coupling agents or metal deactivators, etc. as needed.

In the conductive material, the amount of conductive particles used can be appropriately determined according to the intended use. From the viewpoint of easily obtaining electrical conduction without the conductive particles contacting each other, the amount is preferably 0.01 parts by mass to 50 parts by mass, and particularly preferably 0.03 parts by mass to 40 parts by mass, relative to 100 parts by mass of the conductive material.

The conductive particles of the present invention in the form of the conductive material are also particularly preferably used as conductive fillers in conductive adhesives.

The conductive adhesive is preferably used as an anisotropic conductive adhesive that is arranged between two substrates formed with a conductive base material, and the conductive base materials are bonded and conducted by heating and pressurizing. The anisotropic conductive adhesive contains the conductive particles of the present invention and an adhesive resin. As the adhesive resin, any one that is insulating and can be used as an adhesive resin can be used without particular limitation. It can be any one of a thermoplastic resin and a thermosetting resin, and preferably one that exhibits adhesive properties by heating. Such adhesive resins include, for example, thermoplastic type, thermosetting type, ultraviolet curing type, and the like. In addition, there are so-called semi-thermosetting types that show intermediate properties between thermoplastic types and thermosetting types, and composite types of thermosetting types and ultraviolet curing types. These adhesive resins can be appropriately selected according to the surface characteristics of the circuit board or the form of use as the object to be bonded. In terms of excellent material strength after bonding, an adhesive resin composed of a thermosetting resin is particularly preferred.

As the adhesive resin, specifically, there can be mentioned a resin selected from ethylene-vinyl acetate copolymer, carboxyl modified ethylene-vinyl acetate copolymer, ethylene-isobutyl acrylate copolymer, polyamide, polyimide, polyester, polyvinyl ether, polyvinyl butyral, polyurethane, styrene-butadiene-styrene (SBS) block copolymer, carboxyl modified SBS copolymer, styrene-isoprene-styrene (Styrene-Isoprene) A material prepared by using as a main agent one or a combination of two or more of the following: acrylonitrile-butadiene rubber (hereinafter referred to as NBR), carboxyl-modified nitrile rubber (Nitrile Butadiene Rubber, NBR), amine-modified NBR, epoxy resin, epoxy ester resin, acrylic resin, phenolic resin or silicone resin. Among these, styrene-butadiene rubber or SEBS are preferred as thermoplastic resins due to their excellent secondary processability. Epoxy resin is preferred as thermosetting resin. Among these, epoxy resin is the best in terms of its high adhesiveness, heat resistance, excellent electrical insulation, low melt viscosity, and ability to connect at low pressure.

As the epoxy resin, any commonly used epoxy resin can be used as long as it is a polyvalent epoxy resin having two or more epoxy groups in one molecule. Specific examples include: phenol novolac resins such as cresol novolac, polyphenols such as bisphenol A, bisphenol F, bisphenol AD, resorcinol, dihydroxydiphenyl ether, polyols such as ethylene glycol, neopentyl glycol, glycerol, trihydroxymethylpropane, polypropylene glycol, polyamino compounds such as ethylenediamine, triethylenetetramine, aniline, polycarboxyl compounds such as adipic acid, phthalic acid, isophthalic acid, etc., and glycidyl epoxy resins obtained by reacting epichlorohydrin or 2-methylepichlorohydrin. In addition, there can be mentioned aliphatic and alicyclic epoxy resins such as dicyclopentadiene epoxide and butadiene dimer diepoxide, etc. These can be used alone or in combination of two or more.

Furthermore, as the various adhesive resins mentioned above, from the viewpoint of preventing ion migration, it is preferable to use high-purity varieties in which impurity ions such as Na ⁺ or Cl ^- or hydrolyzable chlorine are reduced.

The amount of the conductive particles in the anisotropic conductive adhesive is generally 0.1 to 30 parts by mass, preferably 0.5 to 25 parts by mass, and more preferably 1 to 20 parts by mass, relative to 100 parts by mass of the adhesive resin component. When the amount of the conductive particles is within this range, the connection resistance or melt viscosity can be suppressed from increasing, the connection reliability can be improved, and the anisotropy of the connection can be fully ensured.

In the anisotropic conductive adhesive, in addition to the conductive particles and adhesive resin described above, additives known in the art may also be formulated. The formulation amount may also be set within a range known in the art. Examples of other additives include: adhesion agents, reactive additives, epoxy resin hardeners, metal oxides, photoinitiators, sensitizers, hardeners, vulcanizers, anti-degradation agents, heat-resistant additives, thermal conductivity enhancers, softeners, colorants, various coupling agents or metal deactivators, etc.

Examples of adhesive agents include rosin, rosin derivatives, terpene resins, terpene phenol resins, petroleum resins, coumarone-indene resins, styrene resins, isoprene resins, alkylphenol resins, xylene resins, etc. Examples of reactive auxiliary agents, i.e., crosslinking agents, include polyols, isocyanates, melamine resins, urea resins, hexamethylenetetramine (urotropine), amines, acid anhydrides, peroxides, etc. As epoxy resin hardeners, any substance having two or more active hydrogen atoms per molecule can be used without particular limitation. Specific examples of the substance include polyamine compounds such as diethylenetriamine, triethylenetetramine, metaphenylenediamine, dicyandiamide, and polyamide; organic anhydrides such as phthalic anhydride, methylnadic anhydride, hexahydrophthalic anhydride, and pyromellitic anhydride; and phenolic novolac resins such as phenol novolac and cresol novolac. These can be used alone or in combination of two or more. In addition, a latent curing agent can be used as needed. Examples of the latent curing agent that can be used include imidazole series, hydrazide series, boron trifluoride-amine complex, coronium salt, amine imide, salt of polyamine, dicyandiamide, and modified products of these. These can be used alone or in combination of two or more.

The anisotropic conductive adhesive is manufactured using a manufacturing device commonly used in the art. For example, conductive particles and adhesive resin and a hardener or various additives as needed are mixed in an organic solvent when the adhesive resin is a thermosetting resin, and then melt-kneaded at a temperature above the softening point of the adhesive resin, preferably about 50°C to 130°C, and more preferably about 60°C to 110°C, in the case of a thermoplastic resin, to manufacture the anisotropic conductive adhesive. The anisotropic conductive adhesive obtained in this way can be applied or made into a film for application.

The connection structure of the present invention is obtained by connecting two circuit substrates to each other using the conductive particles of the present invention or the conductive material of the present invention. Examples of the connection structure include a connection structure of a flexible printed circuit board and a glass substrate, a connection structure of a semiconductor chip and a flexible printed circuit board, and a connection structure of a semiconductor chip and a glass substrate. [Example]

The present invention is further described below by way of embodiments. However, the scope of the present invention is not limited to these embodiments.

The properties in the examples were measured by the following methods. (1) Average particle size 200 particles were randomly selected from a scanning electron microscope (SEM) photograph of the measured object, and the particle size was measured at a magnification of 10,000 times. The arithmetic mean value was set as the average particle size. (2) Thickness of the conductive layer The conductive particles were cut into two pieces, and the cross section of the cut was observed and measured using a scanning electron microscope (SEM). (3) Deviation in the height of the protrusion The height of the protrusion was measured for the cross section of the conductive particles observed by SEM observation, and was calculated using the following formula (1). (4) Curvature radius For the cross section of the conductive particles observed by SEM observation, the radius of the circumscribed circle circumscribing the top portion of the cross section of each protrusion was set as Ra, and the radius of the circumscribed circle circumscribing the surface of the lower layer of the conductive layer was set as Rb. (5) The projected area of the conductive particles and the area of the top portion of the protrusion were measured by taking the SEM photograph image of the conductive particles into an automatic image analyzer (manufactured by NIRECO Co., Ltd., Luzex (registered trademark) AP).

[Example 1] (1) Pretreatment of core particles Spherical styrene-acrylate-silica composite resin particles with an average particle size of 2.0 μm were used as core particles. 9 g of the particles were added to 200 mL of a pore-forming agent aqueous solution ("Clean Pore-Forming Agent 231" manufactured by Roam & Haas Electronic Materials) while being stirred. The concentration of the pore-forming agent aqueous solution was 40 mL/L. Subsequently, the surface of the core particles was modified and dispersed by applying ultrasonic waves at a liquid temperature of 60°C while being stirred for 30 minutes. The aqueous solution was filtered, and the core particles were washed with water once to prepare a slurry of 200 mL. 0.1 g of stannous chloride was added to the slurry. Stir for 5 minutes at room temperature to perform a sensitization treatment to adsorb tin ions on the surface of the core particles. Next, filter the aqueous solution, make 200 mL of slurry from the core particles after re-slurrying and water washing and maintain it at 60°C. Add 1.5 mL of 0.11 mol/L aqueous solution of palladium chloride to the slurry. Stir for 5 minutes at 60°C to perform an activation treatment to capture palladium ions on the surface of the core particles. Next, filter the aqueous solution, make 100 mL of slurry from the core particles after re-slurrying and hot water washing, add 10 mL of 0.5 g/L dimethylamine borane aqueous solution, and stir for 2 minutes while applying ultrasound to obtain a slurry of core particles that have been pre-treated.

(2) Preparation of electroplating solution Prepare 3 L of electroless nickel-phosphorus plating solution containing an aqueous solution of 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 heat to 70°C.

(3) Electroless plating treatment The slurry of the core particles that had been pre-treated was added to the electroless plating bath and stirred for 5 minutes until the bubbling of hydrogen stopped. 420 mL of a 224 g/L nickel sulfate aqueous solution and 420 mL of a mixed aqueous solution containing 210 g/L sodium hypophosphite and 80 g/L sodium hydroxide were added to the slurry at a rate of 2.5 mL/min by a metering pump, and electroless plating was started. After the total amount of the nickel sulfate aqueous solution, sodium hypophosphite, and the mixed aqueous solution of sodium hydroxide were added, stirring was continued for 5 minutes while maintaining a temperature of 70°C. The liquid is then filtered, the filtrate is washed three times, and then dried in a vacuum dryer at 110°C to obtain conductive particles with protrusions.

(4) Treatment of protrusions The obtained conductive particles and alumina balls were placed in a ball mill container at a weight of 20 g, ethanol was added, and the mixture was crushed at 80 rpm for 6 hours. The balls and slurry were separated and dried in a vacuum dryer at 110°C to obtain conductive particles with low protrusion height. The protrusion height of the obtained conductive particles was 100.8 nm.

(5) Vacuum heat treatment The obtained conductive particles were placed in a square container in a manner to have a thickness of 5 mm. They were placed in a vacuum heating furnace (KDF-75, manufactured by DENKEN-HIGHDENTAL), and the vacuum was set to 10 Pa and maintained for 10 minutes. Then, the temperature was raised and heat-treated at 390°C for 2 hours. After the heat treatment, the particles were cooled to room temperature (25°C), and the vacuum was released by blowing nitrogen gas to obtain conductive particles that had been heat-treated. The SEM photograph of the obtained conductive particles is shown in FIG2. The average particle size of the obtained conductive particles was 2.2 μm, the thickness of the conductive layer was 110 nm, and the height of the protrusions was 100.8 nm. The physical properties of the obtained conductive particles are shown in Table 1.

[Example 2] (1) Pretreatment of core particles A slurry of core particles pretreated with the same procedures as in Example 1 was obtained except that resin particles having an average particle size of 2.0 μm (Opt Bead, manufactured by Nissan Chemical Co., Ltd.) were used as core particles. (2) Preparation of plating solution An electroless plating solution was prepared in the same manner as in (2) of Example 1. (3) Electroless plating treatment The same procedures as in (3) of Example 1 were performed to obtain conductive particles having protrusions. (4) Treatment of protrusions The same procedures as in (4) of Example 1 were performed to obtain conductive particles having protrusions with a height of 101 nm. (5) Vacuum heat treatment The same operation as in Example 1 was performed to obtain conductive particles that had been heat treated. The average particle size of the conductive particles obtained was 2.2 μm, the thickness of the conductive layer was 94.8 nm, and the height of the protrusions was 101 nm. The physical properties of the conductive particles obtained are shown in Table 1.

[Example 3] The same operation as in Example 1 was performed until (3) electroless plating treatment in Example 1, thereby obtaining conductive particles having protrusions. (4) Protrusion treatment The obtained conductive particles were crushed for 3 hours, and the same operation as in Example 1 was performed, thereby obtaining conductive particles having a protrusion height of 145.3 nm. (5) Vacuum heat treatment The same operation as in Example 1 was performed, thereby obtaining conductive particles after heat treatment. A SEM photograph of the obtained conductive particles is shown in FIG. 3 . The average particle size of the obtained conductive particles was 2.2 μm, the thickness of the conductive layer was 97.8 nm, and the protrusion height was 145.3 nm. The physical properties of the obtained conductive particles are shown in Table 1.

[Example 4] The same operation as in Example 1 was performed until (3) electroless plating treatment in Example 1, thereby obtaining conductive particles having protrusions. (4) Protrusion treatment The obtained conductive particles were crushed using zirconia balls at 80 rpm for 4 hours, and the same operation as in Example 1 was performed, thereby obtaining conductive particles having a protrusion height of 115.6 nm. (5) Vacuum heat treatment The same operation as in Example 1 was performed, thereby obtaining conductive particles after heat treatment. A SEM photograph of the obtained conductive particles is shown in FIG. 4 . The average particle size of the obtained conductive particles was 2.2 μm, the thickness of the conductive layer was 95.8 nm, and the protrusion height was 115.6 nm. The physical properties of the obtained conductive particles are shown in Table 1.

[Comparative Example 1] In Example 1, except that (4) the planar protrusion treatment was not performed, the same operation as in Example 1 was performed to obtain conductive particles. The physical property values of the obtained conductive particles are shown in Table 1.

[Comparative Example 2] The same operation as in Example 1 was performed until (3) electroless plating treatment in Example 1, thereby obtaining conductive particles having protrusions. (4) Protrusion treatment The obtained conductive particles were crushed for 1 hour, and the same operation as in Example 1 was performed, thereby obtaining conductive particles having a protrusion height of 174.9 nm. (5) Vacuum heat treatment The same operation as in Example 1 was performed, thereby obtaining conductive particles after heat treatment. The SEM photograph of the obtained conductive particles is shown in FIG. 5 . The average particle size of the obtained conductive particles was 2.2 μm, the thickness of the conductive layer was 99.9 nm, and the protrusion height was 174.9 nm. The physical properties of the obtained conductive particles are shown in Table 1.

[Table 1] s _ x Protrusion height deviation Ra R Ra/Rb Area ratio Embodiment 1 10.5 100.8 0.104 0.33 1.0 0.33 0.73 Embodiment 2 10.0 101.0 0.100 0.31 1.0 0.31 0.71 Embodiment 3 25.8 145.3 0.177 0.22 1.0 0.22 0.57 Embodiment 4 13.0 115.6 0.112 0.29 1.0 0.29 0.71 Comparison Example 1 63.5 189.7 0.335 0.11 1.0 0.11 0.47 Comparison Example 2 50.0 174.9 0.286 0.14 1.0 0.14 0.48 s: Standard deviation of protrusions _ x: Average height of protrusions Ra: Radius of curvature of the top part of the protrusions Rb: Radius of curvature of the surface of the lower layer of the conductive layer Area ratio: Total area of the top part of the protrusions / Projected area of the conductive particles

[Evaluation of connection resistance and insulation] Using the conductive particles of the examples and comparative examples, the connection resistance and insulation were evaluated by the following method. An insulating adhesive prepared by mixing 100 parts by mass of epoxy resin, 150 parts by mass of hardener, and 70 parts by mass of toluene was mixed with 15 parts by mass of the conductive particles obtained in the examples or comparative examples to obtain an insulating paste. The 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 is arranged and pressed between a glass substrate on which an aluminum electrode is vapor-deposited on the entire surface and a polyimide film substrate on which a copper electrode pattern is formed at a pitch of 50 μm, thereby preparing a sample for on-resistance measurement. The obtained sample for on-resistance measurement is electrically connected, and the connection resistance value of the sample is measured at room temperature (25°C, 50%RH), and the connection resistance is evaluated. In addition, the connection resistance is evaluated using a multimeter R6552 (manufactured by ADVANTEST Co., Ltd.) according to the following criteria. The results are shown in Table 2. 0: Resistance value is less than 2 Ω △: Resistance value is 2 Ω or more and less than 5Ω ×: Resistance value is 5 Ω or more

In addition, among the 100 samples used for the on-resistance measurement, the insulation was evaluated based on the proportion of short circuits. The insulation was evaluated using the following method. The results are shown in Table 2. ○: Short circuit occurrence rate is less than 5% △: Short circuit occurrence rate is 5% or more and less than 30% ×: Short circuit occurrence rate is 30% or more

[Table 2] Connection resistance (Ω) Insulation Embodiment 1 ○ ○ Embodiment 2 ○ ○ Embodiment 3 ○ ○ Embodiment 4 ○ ○ Comparison Example 1 ○ × Comparison Example 2 ○ △

From these results, it is found that the conductive particles obtained in the embodiment have lower connection resistance and better insulation properties than the conductive particles obtained in the comparative example.

1: Conductive particles 2: Core particles 3: Conductive layer 4: Protrusion 5: Planar portion of protrusion 5a and 5b: Ends of planar portion 6: Surface of lower layer of conductive layer

FIG1 is a conceptual diagram of a conductive particle having a protrusion. FIG2 is a SEM photograph of the conductive particle obtained in Example 1. FIG3 is a SEM photograph of the conductive particle obtained in Example 3. FIG4 is a SEM photograph of the conductive particle obtained in Example 4. FIG5 is a SEM photograph of the conductive particle obtained in Comparative Example 2.

1: Conductive particles

2: Core material particles

3: Conductive layer

4: Protrusion

5: Flat surface of protrusion

5a and 5b: Ends of the flat surface

6: The surface of the lower layer of the conductive layer

Claims (13)

A conductive particle includes a core particle and a conductive layer having a plurality of protrusions on a surface of the core particle, wherein a variation in height of the protrusions is 0.01 or more and 0.25 or less. The conductive particle as described in claim 1, wherein the top portion of the protrusion is substantially planar. The conductive particle as described in claim 1, wherein, when the curvature radius of the top portion of the protrusion is set to Ra and the curvature radius of the surface of the lower layer of the conductive layer where the protrusion is formed is set to Rb, the ratio of Ra to Rb, i.e., Ra/Rb, is greater than 0.15 and less than 1.20. The conductive particle according to claim 1, wherein a ratio of a total area of the top portion of the protrusion to a projected area of the conductive particle is 0.50 or more. The conductive particle according to claim 1, wherein the conductive layer comprises at least one selected from the group consisting of nickel, gold, and palladium. The conductive particles according to claim 1, wherein the average particle size is 0.1 μm or more and 50 μm or less. The conductive particle according to claim 1, wherein the conductive layer has a thickness of 0.1 nm to 2,000 nm. The conductive particle according to claim 1, wherein the height of the protrusion is greater than or equal to 20 nm and less than or equal to 1,000 nm. The conductive particle according to claim 1, wherein at least one of the protrusions has an amorphous shape. A conductive material comprises the conductive particles according to any one of claims 1 to 9 and an insulating resin. A method for producing conductive particles comprises the following steps: forming a conductive layer on the surface of a core particle; forming a protrusion protruding from the surface of the conductive layer; and averaging the height of the protrusion. The method for producing conductive particles according to claim 11, wherein in the step of forming the protrusions, the protrusions are formed on the conductive layer using self-decomposed products of an electroless nickel plating bath as cores. A method for producing conductive particles as described in claim 11 or 12, wherein in the step of averaging the height of the protrusions, the top portion of the protrusions obtained in the step of forming the protrusions is polished to average the height of the protrusions.