WO2023013465A1

WO2023013465A1 - Conductive particle, production method thereof and conductive material

Info

Publication number: WO2023013465A1
Application number: PCT/JP2022/028716
Authority: WO
Inventors: 裕之稲葉; 哲高橋; 直也田杉; 圭代星野; 昭紘久持
Original assignee: 日本化学工業株式会社
Priority date: 2021-08-02
Filing date: 2022-07-26
Publication date: 2023-02-09
Also published as: CN117795626A; JP2023021663A; KR20240033287A

Abstract

Conductive particles are provided which, while having excellent connection reliability, enable reducing connection resistance between electrodes by improving adhesion of a nickel plating film to core particles. In these conductive particles, which comprise a conductive layer formed on the surface of core particles, the withstand current value per single conductive particle when the compression rate is less than 5% is at least 1mA, and the withstand current value per single conductive particle when the compression rate is greater than or equal 5% is at least 10mA. These conductive particles enable film formation on the surface of the core particle at a stage earlier than the late-stage plating treatment.

Description

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

The present invention relates to conductive particles, methods for producing the same, and conductive materials.

As a conductive particle used as a conductive material for an anisotropic conductive material such as an anisotropic conductive film or an anisotropic conductive paste, it is generally known that a conductive layer made of a metal is formed on the surface of a core particle. This conductive layer provides electrical connection between electrodes and wiring.

As the conductive layer of the conductive particles, a nickel plating film formed by an electroless plating method is often used. As an example, a method of effectively lowering the connection resistance when electrodes are electrically connected by unevenly distributing the concentration of phosphorus in a conductive layer containing nickel and phosphorus has been proposed ( For example, see Patent Documents 1 to 3). In these patent documents, as a method for unevenly distributing the concentration of phosphorus in the conductive layer, nickel plating films with different phosphorus concentrations are obtained by changing the pH of the nickel plating solution during electroless plating in the examples. is described. Further, Patent Document 4 describes that the metal film may be composed of multiple layers by performing electroless plating in multiple stages in the formation of the metal film. However, there is no description of the technical significance of the conductive layer being composed of multiple layers of metal films, and it is only mentioned as one of general techniques.

JP 2013-214511 A International Publication No. 2013/108842 pamphlet International Publication No. 2014/054572 Pamphlet WO 2010/035708 pamphlet

In the method of forming a nickel plating film on the surface of the core particles by electroless nickel plating, the plating is generally performed by dropping a nickel plating solution into the slurry of the core particles. In the conventional method of adding the nickel plating solution in multiple steps, there is room for improvement in the adhesion of the nickel plating film to the core particles. That is, when the conductive particles obtained by the above-described conventional method are used for connection between electrodes, the peeling of the nickel plating film caused by the compressive deformation of the conductive particles during connection causes the connection resistance between the electrodes. However, there were problems such as an increase in the connection reliability and a decrease in connection reliability.

Therefore, an object of the present invention is to provide conductive particles that can reduce the connection resistance between electrodes and have excellent connection reliability by improving the adhesion of the nickel plating film to the core particles. That's what it is.

As a result of intensive studies to solve the above problems, the present inventors have found that by slowing the formation rate of the plating film on the surface of the core material particles in the early stage of the plating process rather than the late stage, nickel plating can be performed more effectively than before. It was found that the adhesion of the nickel-plated film to the core particles is improved because the film is formed densely. In addition, it was found that the conductive particles having the nickel plating film formed in this way as a conductive layer have excellent resistance to large currents, so that connection resistance is low and connection reliability is also excellent. We have completed the present invention.

That is, in the present invention, in conductive particles in which a conductive layer is formed on the surface of core particles, the withstand current value per conductive particle is 1 mA or more when the compressibility is less than 5%, and the compression Provided is a conductive particle having a withstand current value of 10 mA or more per conductive particle when the ratio is 5% or more.

Further, the present invention includes a first step of mixing an aqueous slurry of core particles and an electroless nickel plating bath containing a dispersant, a nickel salt, a reducing agent and a complexing agent, and performing electroless nickel plating; An aqueous solution containing a nickel salt, an aqueous solution containing a reducing agent, and an aqueous solution containing an alkali are continuously added to the liquid obtained in one step while controlling the addition amount so as to change the plating deposition rate once or more. A second step of electroless nickel plating is provided.

According to the present invention, it is possible to provide conductive particles with excellent adhesion to core particles, low connection resistance, and excellent connection reliability, and a method for producing the conductive particles.

4 is an SEM photograph of the conductive particles obtained in Example 2. FIG.

The conductive particles of the present invention have a withstand current value of 1 mA or more, preferably 1.5 mA per conductive particle when the compressibility is less than 5%, particularly when the compressibility is 1% or more and less than 5%. As described above, when the compressibility is 5% or more, particularly when the compressibility is 5% or more and 50% or less, the withstand current value per conductive particle is 10 mA or more, preferably 15 mA or more. When the withstand current value per conductive particle is within the above range, the connection resistance is low and the connection reliability is excellent because the resistance to large current is excellent.

The withstand current value in the present invention means the withstand current value per conductive particle with the desired compressibility using a conductive fine particle electrical property measuring device (hereinafter sometimes referred to as a VI device). Measured. The VI device may be any device capable of measuring the voltage-current characteristics and/or current capacity while the compressibility of the conductive particles is kept constant. can be used. The withstand current value in the present invention is a value obtained by measuring one conductive particle.

The conductive particles of the present invention preferably have a withstand current value of 0.5 mA or more, particularly 1 mA or more per conductive particle when the compressibility is 1% or more and 4% or less. At the initial stage when the compressibility is small when the electrodes are pressure-connected, the withstand current value per conductive particle is within the above range, so that the connection resistance is low and the connection reliability is excellent. become particles.

The conductive particles of the present invention preferably have a withstand current value of 15 mA or more, particularly 20 mA or more per conductive particle when the compressibility is 10% or more and 50% or less. Further, it is more preferable that the withstand current value per conductive particle is 20 mA or more when the compressibility is 30%. In the middle and late stages of pressurizing and connecting the electrodes, the withstand current value per conductive particle is within the above range, so that the resistance to large currents is excellent, so the connection resistance is low and the connection reliability is improved. become excellent.

As described above, the conductive particles of the present invention have a higher withstand current value in the middle and late stages of compression when the compression rate is 5% or more than in the early stage of compression when the compression rate is less than 5%. It is believed that this is because the conductive layer of the conductive particles obtained by the method for producing the conductive particles of the present invention, which will be described later, is formed of a dense film, so that the adhesion of the film to the core particles increases. This makes it difficult for the conductive layer to peel off or break due to deformation of the conductive particles that occur when the electrodes are pressure-connected, leading to excellent resistance to large currents, low connection resistance, and high connection reliability. The inventors of the present invention believe that the effect of the present invention, which is also excellent, can be achieved.

The conductive particles are obtained by forming a conductive layer on the surface of core particles.
As the core material particles, as long as they are in the form of particles, inorganic substances or organic substances can be used without particular limitation. Inorganic core particles include metal particles such as gold, silver, copper, nickel, palladium, solder, alloys, glass, ceramics, silica, metal or non-metal oxides (including hydrous), and aluminosilicates. metal silicates, metal carbides, metal nitrides, metal carbonates, metal sulfates, metal phosphates, metal sulfides, metal acid salts, metal halides and carbon containing metals. On the other hand, organic core particles include, for example, thermoplastic materials such as natural fibers, natural resins, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polybutene, polyamide, polyacrylate, polyacrylonitrile, polyacetal, ionomer, and polyester. thermosetting resins such as resins, alkyd resins, phenol resins, urea resins, benzoguanamine resins, melamine resins, xylene resins, silicone resins, epoxy resins, and diallyl phthalate resins. These may be used alone or in combination of two or more.

The core particles may be composed of a material composed of both an inorganic substance and an organic substance instead of the material composed of either one of the inorganic substance and the organic substance described above. In the case where the core particles are composed of a material comprising both an inorganic substance and an organic substance, the mode of existence of the inorganic substance and the organic substance in the core particles includes, for example, a core made of an inorganic substance and an inorganic substance coating the surface of the core. Alternatively, a core-shell type configuration, such as an embodiment having a core made of an organic substance and a shell made of an inorganic substance covering the surface of the core, may be mentioned. In addition to these, a blend type configuration in which an inorganic substance and an organic substance are mixed or fused at random in one core particle can be used.

The core particles are preferably composed of an organic substance or a material composed of both an inorganic substance and an organic substance, and more preferably composed of a material composed of both an inorganic substance and an organic substance. The inorganic substances include glass, ceramics, silica, metal or non-metal oxides (including hydrates), metal silicates including aluminosilicates, metal carbides, metal nitrides, metal carbonates, metal sulfates, metal phosphorus. Acid salts, metal sulfides, metal acid salts, metal halides and carbon are preferred. The organic material is preferably thermoplastic resin such as natural fiber, natural resin, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polybutene, polyamide, polyacrylate, polyacrylonitrile, polyacetal, ionomer, and polyester. By using a core material made of such a material, it is possible to improve the dispersion stability of the particles, and to develop appropriate elasticity and enhance conduction when electrically connecting an electronic circuit. .

When an organic substance is used as the core particles, it is preferable that the core particles have no glass transition temperature or that the glass transition temperature is higher than 100° C., because the shape of the core particles can be easily maintained, and the core particles can be used in the step of forming the metal coating. This is preferable because the shape of the material particles can be easily maintained. The glass transition temperature can be determined, for example, as the intersection of the original baseline and the tangent of the inflection point in the baseline shift portion of the DSC curve obtained by differential scanning calorimetry (DSC).

When an organic substance is used as the core particles and the organic substance is a highly crosslinked resin, almost no baseline shift is observed even if the glass transition temperature is measured up to 200°C by the above method. In the present specification, such particles are also referred to as particles having no glass transition temperature, and such core particles may be used in the present invention. A specific example of the core particle material having no glass transition temperature can be obtained by copolymerizing the above-exemplified monomers constituting the organic matter with a crosslinkable monomer. Examples of crosslinkable monomers include tetramethylene di(meth)acrylate, ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, ethylene oxide di(meth)acrylate, tetraethylene oxide (meth)acrylate, 1,6-hexanedi(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethane di( meth) acrylate, tetramethylolmethane tri(meth)acrylate, tetramethylolmethane tetra(meth)acrylate, tetramethylolpropane tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, glycerol di(meth)acrylate, glycerol tridi( Polyfunctional (meth)acrylates such as meth)acrylates, polyfunctional vinyl monomers such as divinylbenzene and divinyltoluene, vinyltrimethoxysilane, trimethoxysilylstyrene, γ-(meth)acryloxypropyltrimethoxysilane, etc. Monomers such as silane-containing monomers, triallyl isocyanurate, diallyl phthalate, diallyl acrylamide, and diallyl ether can be used. Especially in the field of COG (Chip on Glass), core material particles made of such a hard organic material are often used.

There are no particular restrictions on the shape of the core particles. Generally, the core particles are spherical. However, the core particles may have a shape other than spherical, such as fibrous, hollow, plate-like or needle-like, and may have many protrusions on their surface or be amorphous. In the present invention, spherical core particles are preferred in terms of excellent filling properties and easy metal coating.

The conductive layer formed on the surface of the core particles is made of a conductive metal. Metals constituting the conductive layer include, for example, gold, platinum, silver, copper, iron, zinc, nickel, tin, lead, antimony, bismuth, cobalt, indium, titanium, germanium, aluminum, chromium, palladium, tungsten, molybdenum. , calcium, magnesium, rhodium, sodium, iridium, beryllium, ruthenium, potassium, cadmium, osmium, lithium, rubidium, gallium, thallium, tantalum, cesium, thorium, strontium, polonium, zirconium, barium, manganese and other metals or these In addition to alloys, metal compounds such as ITO and solder can be used. Among them, gold, silver, copper, nickel, palladium, rhodium, and solder are preferred because of their low electrical resistance, and nickel, gold, nickel alloys, and gold alloys are particularly preferred. One kind of metal may be used, or two or more kinds of metals may be used in combination.

The conductive layer may have a single-layer structure or a multilayer structure consisting of multiple layers. In the case of a laminated structure consisting of multiple layers, the outermost layer is at least one selected from nickel, gold, silver, copper, palladium, nickel alloys, gold alloys, silver alloys, copper alloys and palladium alloys. preferable.

Further, the conductive layer may not cover the entire surface of the core particles, and may cover only a part of them. When only a part of the surface of the core particles is coated, the coated portion may be continuous, or may be discontinuously coated, for example, like an island.

The thickness of the conductive layer is preferably 0.1 nm or more and 2000 nm or less, more preferably 1 nm or more and 1500 nm or less. When the thickness of the conductive layer is within the above range, the conductive particles have excellent electrical properties. When the conductive particles have protrusions, which will be described later, the height of the protrusions is not included in the thickness of the conductive layer. In the present invention, 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 end with a scanning electron microscope (SEM).

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

When the conductive particles have protrusions on their surfaces, that is, when the outer surface of the conductive layer has protrusions, the height of the protrusions is preferably 20 nm or more and 1000 nm or less, more preferably 50 nm or less and 800 nm or less. Although the number of protrusions depends on the particle size of the conductive particles, it is preferable that the number of protrusions per conductive particle is 1 to 20,000, more preferably 5 to 5,000. It is advantageous in terms of further improving conductivity. The length of the base of the projection is preferably 5 nm or more and 1000 nm or less, more preferably 10 nm or more and 800 nm or less. The length of the base of the protrusion refers to the length along the surface of the conductive particle at the site where the protrusion is formed when observing the cross section of the particle with an SEM. means the shortest distance to In addition, when one projection has a plurality of vertices, the highest apex is taken as the height of the projection. The length of the base of the protrusion and the height of the protrusion are taken as the arithmetic mean value of the values measured for 20 different particles observed by electron microscopy.

The shape of the conductive particles is not particularly limited, although it depends on the shape of the core particles. For example, it may be fibrous, hollow, plate-like, or needle-like, and may have many projections on its surface or be amorphous. In the present invention, a spherical shape or a shape having a large number of projections on the outer surface is preferable from the viewpoint of excellent filling properties and connectivity.

Methods for forming a conductive layer on the surface of the core particles include dry methods such as vapor deposition, sputtering, mechanochemical methods, and hybridization, and wet methods such as electroplating and electroless plating. mentioned. Alternatively, these methods may be combined to form a conductive layer on the surface of the core particles.

In the present invention, it is preferable to form a conductive layer on the surface of the core material particles by electroless plating because it is easy to obtain conductive particles having desired particle properties. In particular, it is preferable that the conductive particles are obtained by forming an electroless nickel-phosphorus plating layer as a conductive layer on the surface of the core particles.

Preferred embodiments of the method for producing conductive particles of the present invention are described below.
When the conductive layer is formed on the surface of the core particles by electroless plating, the surfaces of the core particles have the ability to capture noble metal ions, or are surface-modified so as to have the ability to capture noble metal ions. is preferred. The noble metal ions are preferably palladium or silver ions. Having the ability to capture noble metal ions means being able to capture noble metal ions as chelates or salts. For example, when an amino group, an imino group, an amide group, an imide group, a cyano group, a hydroxyl group, a nitrile group, a carboxyl group, or the like is present on the surface of the core material particle, the surface of the core material particle has an ability to trap noble metal ions. have In the case of modifying the surface so that it has the ability to capture noble metal ions, the method described in Japanese Patent Application Laid-Open No. 61-64882, for example, can be used.

Using such a core material particle, a noble metal is supported on the surface thereof. Specifically, the core particles are dispersed in a dilute acidic aqueous solution of a noble metal salt such as palladium chloride or silver nitrate. This traps the noble metal ions on the surface of the particles. A noble metal salt concentration in the range of 1×10 ⁻⁷ to 1×10 ⁻² mol/m ² of particle surface area is sufficient. The core particles with trapped noble metal ions are separated from the system and washed with water. Subsequently, the core particles are suspended in water, and a reducing agent is added to reduce the noble metal ions. This allows the noble metal to be carried on the surfaces of the core particles. As the reducing agent, for example, sodium hypophosphite, sodium borohydride, potassium borohydride, dimethylamine borane, hydrazine, formalin, etc. are used, and selected from these based on the constituent material of the target conductive layer. preferably.

Before allowing precious metal ions to be trapped on the surface of the core particles, a sensitization treatment may be performed to adsorb tin ions to the surface of the particles. In order to adsorb tin ions on the surface of the particles, for example, the surface-modified core particles may be put into an aqueous solution of stannous chloride and stirred for a predetermined time.

The core particles that have been pretreated in this manner are subjected to a process for forming a conductive layer. There are two types of conductive layer forming processes: a process for forming a conductive layer having projections and a process for forming a conductive layer with a smooth surface. First, the process for forming a conductive layer having projections will be described.

In the process of forming a conductive layer having protrusions according to the method for producing conductive particles of the present invention, the following first step and second step are performed.
The first step is an electroless nickel plating step in which an aqueous slurry of core particles is mixed with an electroless nickel plating bath containing a dispersant, a nickel salt, a reducing agent, a complexing agent, and the like. In the first step, self-decomposition of the plating bath occurs simultaneously with the formation of the conductive layer on the core particles. Since this self-decomposition occurs in the vicinity of the core particles, the self-decomposition product is captured on the surface of the core particles during the formation of the conductive layer, thereby generating the nucleus of the microprojections and simultaneously forming the conductive layer. done. The projection grows from the nucleus of the generated minute projection as a base point.

In the first step, the aforementioned core particles are sufficiently dispersed in water preferably in the range of 0.1 to 500 g/L, more preferably 1 to 300 g/L, to prepare an aqueous slurry. The dispersing operation can be carried out using ordinary stirring, high-speed stirring, or a shear dispersing device such as a colloid mill or homogenizer. Also, ultrasonic waves may be used in combination with the dispersing operation. If necessary, a dispersing agent such as a surfactant may be added in the dispersing operation. Next, an aqueous slurry of the dispersed core particles is added to an electroless nickel plating bath containing a nickel salt, a reducing agent, a complexing agent, various additives, and the like, to carry out the first step of electroless plating.

Examples of the aforementioned dispersant include nonionic surfactants, zwitterionic surfactants and/or water-soluble polymers. As the nonionic surfactant, polyoxyalkylene ether-based surfactants such as polyethylene glycol, polyoxyethylene alkyl ether, and polyoxyethylene alkylphenyl ether can be used. As the amphoteric surfactant, betaine-based surfactants such as betaine alkyldimethylacetate, betaine alkyldimethylcarboxymethylacetate, and betaine alkyldimethylaminoacetate can be used. Polyvinyl alcohol, polyvinylpyrrolidinone, hydroxyethyl cellulose and the like can be used as the water-soluble polymer. These dispersants can be used singly or in combination of two or more. The amount of the dispersant used is generally 0.5 to 30 g/L with respect to the volume of the liquid (electroless nickel plating bath), depending on the type. In particular, it is preferable that the amount of the dispersant used is in the range of 1 to 10 g/L with respect to the volume of the liquid (electroless nickel plating bath), from the viewpoint of further improving the adhesion of the conductive layer.

As the nickel salt, for example, nickel chloride, nickel sulfate, nickel acetate, or the like is used, and its concentration is preferably in the range of 0.1 to 50 g/L. As the reducing agent, for example, one similar to that used for reducing the noble metal ions described above can be used, and the reducing agent is selected based on the constituent material of the intended underlying film. When a phosphorus compound such as sodium hypophosphite is used as the reducing agent, its concentration is preferably in the range of 0.1 to 50 g/L.

Complexing agents include, for example, citric acid, hydroxyacetic acid, tartaric acid, malic acid, lactic acid, carboxylic acids (salts) such as gluconic acid or its alkali metal salts and ammonium salts, amino acids such as glycine, amines such as ethylenediamine and alkylamines. Compounds with a complexing effect on nickel ions are used, such as acids, other ammonium, EDTA or pyrophosphate (salts). These can be used individually by 1 type or in combination of 2 or more types. Its concentration preferably ranges from 1 to 100 g/L, more preferably from 5 to 50 g/L. The preferred pH of the electroless nickel plating bath at this stage is in the range of 3-14. The electroless nickel plating reaction begins immediately upon addition of the aqueous slurry of core particles and is accompanied by the evolution of hydrogen gas. The first step is terminated when the generation of hydrogen gas is completely stopped.

Next, in the second step, an aqueous solution containing a nickel salt, an aqueous solution containing a reducing agent, and an aqueous solution containing an alkali are added to the liquid obtained in the first step, and the plating deposition rate is increased once or more, preferably twice or more. The electroless nickel plating treatment is performed by continuously adding while controlling the addition amount so as to change. In the second step, these aqueous solutions are added simultaneously and continuously to the liquid obtained in the first step.

Addition of each of the aqueous solutions to the liquid obtained in the first step is performed so that the initial plating deposition rate is 0.05 nm / min or more and 1.5 nm / min or less, particularly 0.1 nm / min or more and 1.2 nm / min or less. It is preferable to carry out while controlling the addition amount so that By setting the initial plating deposition rate within this range, the nickel plating film is deposited more densely on the surface of the core material particles, and the adhesion of the obtained conductive layer is improved.

In the second step of the method for producing conductive particles of the present invention, the plating deposition rate is changed once or more. The plating deposition rate after the change is preferably 0.3 nm / min or more and 3.0 nm / min or less, particularly 0.5 nm / min or more and 2.5 nm / min or less. It is preferable to control the amount of each aqueous solution added. By setting the plating deposition rate after the change within this range, it is possible to quickly form a conductive layer with a desired thickness on the dense nickel plating film obtained at the beginning. It is possible to reduce the industrial production cost while having excellent properties.

In the second step of the method for producing conductive particles of the present invention, the plating deposition speed may be changed two or more times. The plating deposition rate after the two-time change is preferably 0.3 nm/min or more and 3.0 nm/min or less, particularly 0.5 nm/min or more and 2.5 nm/min or less. By setting the plating deposition rate within this range, it is possible to quickly form a conductive layer of the desired thickness on the first dense nickel plating film, so that the resulting conductive layer has excellent adhesion. It is possible to hold down the industrial manufacturing cost while maintaining the low cost.

In the second step, it is preferable to control the amount of each of the aqueous solutions added so as to increase the plating deposition rate. That is, it is preferable to increase the plating deposition rate by increasing the amount of each aqueous solution added per unit time.

In the second step, after the completion of the addition of each of the aqueous solutions, the reaction is completed by continuing stirring while maintaining the liquid temperature for a while after the generation of hydrogen gas is completely stopped.

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

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

The second step is performed continuously after the first step is completed, but instead of this, the first step and the second step may be performed intermittently. In this case, after the completion of the first step, the core particles and the plating solution are separated by a method such as filtration, and the core particles are newly dispersed in water to prepare an aqueous slurry, in which a complexing agent is added. is preferably dissolved in a concentration range of 1 to 100 g/L, more preferably 5 to 50 g/L. A second step of dissolving within the above range to prepare an aqueous slurry and adding each of the above aqueous solutions to the aqueous slurry may be performed. Thus, a conductive layer having projections can be formed.

The process for forming a conductive layer having a smooth surface according to the method for producing conductive particles of the present invention will be described below.
A conductive layer having a smooth surface can be formed by reducing the concentration of nickel salt in the electroless nickel plating bath in the first step of forming the conductive layer having protrusions. For example, nickel chloride, nickel sulfate, nickel acetate, or the like is used as the nickel salt, and the concentration thereof is preferably in the range of 0.01 to 0.5 g/L. A conductive layer having a smooth surface can be formed by a method of performing the first step and the second step other than reducing the concentration of the nickel salt in the electroless nickel plating bath.

The conductive particles of the present invention are obtained by heating the conductive particles obtained by the above-described method under a vacuum of 1000 Pa or less, further 0.01 to 900 Pa, particularly 0.01 to 500 Pa, at 200 to 600 ° C., further 250 to 500 ° C. , particularly preferably by heat treatment at a temperature of 300 to 450°C. By heating the conductive particles while maintaining such a vacuum state, the crystallization of the metal of the conductive layer proceeds, so that the electrical resistance is lowered and the electrical conductivity is excellent. The degree of vacuum in the present invention is a value when the absolute pressure, that is, the absolute vacuum is 0.

The heat treatment time is preferably 0.1 to 10 hours, more preferably 0.5 to 5 hours. By adopting this treatment time, it is possible to suppress an increase in manufacturing cost, and to suppress the denaturation of the core material particles and the conductive layer due to heat history, thereby reducing the influence on quality. This heat treatment time is the time from reaching the target treatment temperature to the end of the heat treatment.

The heat treatment may be performed while the conductive particles are left standing, or may be performed while stirring. When the heat treatment is performed while the conductive particles are left standing, it is preferable to leave them standing at a thickness of 0.1 mm to 100 mm. By allowing the conductive layer to stand still at this thickness, the heat treatment of the conductive layer can be performed successfully, and the manufacturing cost can be suppressed.

After the container containing the conductive particles is evacuated, the heat treatment is performed while standing still or while stirring. At this time, the gas phase portion of the container containing the conductive particles may be replaced with an inert gas such as nitrogen and then evacuated, or the container may be evacuated as it is. Further, the heat treatment may be performed multiple times, if necessary.

In addition, the heat treatment is performed for 5 to 60 minutes, further 10 to 50 minutes after reaching a vacuum degree of 1000 Pa or less, preferably 0.01 to 900 Pa, particularly preferably 0.01 to 500 Pa at room temperature. After holding, it is preferable to raise the temperature to the treatment temperature. This operation can prevent the conductive layer from being oxidized due to oxygen, moisture, etc. in the heating atmosphere and the conductive particles, so that the connection resistance can be reduced.

After the heat treatment, it is preferable to release the vacuum after the temperature is lowered to 50° C. or lower, further to 40° C. or lower while maintaining the degree of vacuum. The reason for this is that if the vacuum is released at the temperature immediately after the heat treatment, the oxidation of the conductive layer is accelerated in the presence of oxygen or moisture in the atmosphere, which may increase the connection resistance. From the viewpoint of manufacturing costs, the vacuum may be released in the normal atmosphere. It is more preferable to carry out by purging the gas.
Thus, the conductive particles of the present invention are obtained.

When the conductive particles of the present invention are used as a conductive filler of a conductive adhesive as described later, the surface thereof can be further coated with an insulating resin in order to prevent short circuits between the conductive particles. . The insulating resin coating is designed so that the surfaces of the conductive particles are not exposed as much as possible when no pressure is applied, and the coating is destroyed by the heat and pressure applied when the two electrodes are adhered using a conductive adhesive. , are formed such that at least the projections of the surface of the conductive particles are exposed. The thickness of the insulating resin can be about 0.1 to 0.5 μm. The insulating resin may cover the entire surface of the conductive particles, or may cover only a portion of the surfaces of the conductive particles.

As the insulating resin, one widely known in the technical field can be used. Examples include phenolic resins, urea resins, melamine resins, allyl resins, furan resins, polyester resins, epoxy resins, silicone resins, polyamide-imide resins, polyimide resins, polyurethane resins, fluorine resins, polyolefin resins (e.g. polyethylene). , polypropylene, polybutylene), polyalkyl(meth)acrylate resin, poly(meth)acrylic acid resin, polystyrene resin, acrylonitrile-styrene-butadiene resin, vinyl resin, polyamide resin, polycarbonate resin, polyacetal resin, ionomer resin, polyether sulfone Resins, resins made of organic polymers such as polyphenyl oxide resins, polysulfone resins, polyvinylidene fluoride resins, ethyl cellulose resins and cellulose acetate resins can be mentioned.

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

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

The ionic group is preferably present at the interface of the organic polymer that constitutes the insulating resin. Moreover, it is preferable that the ionic group is chemically bonded to the monomer component constituting the organic polymer. Whether or not the ionic group exists at the interface of the organic polymer can be determined by observing the insulating resin with a scanning electron microscope when the insulating resin containing the organic polymer having the ionic group is formed on the surface of the conductive particles. It can be determined by whether it adheres to the surface of the particles.

Examples of ionic groups include onium-based functional groups such as phosphonium groups, ammonium groups, and sulfonium groups. Among these, an ammonium group or a phosphonium group is preferable from the viewpoint of increasing the adhesion between the conductive particles and the insulating resin and forming conductive particles having both insulation and conduction reliability at a high level. A phosphonium group is more preferred.

The onium-based functional group is preferably represented by the following general formula (1).

(Wherein, X is a phosphorus atom, a nitrogen atom, or a sulfur atom, R may be the same or different, 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 0 when X is a sulfur atom.* is a bond.)

Counter ions for ionic groups include, for example, halide ions. Examples of halide ions include Cl ⁻ , F ⁻ , Br ⁻ , I ⁻ .

In formula (1), the straight-chain alkyl group represented by R includes, for example, a straight-chain alkyl group having 1 to 20 carbon atoms, specifically, a methyl group, an ethyl group, n- Propyl group, n-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, n-nonyl group, n-decyl group, n-undecyl group, n-dodecyl group, n- tridecyl group, n-tetradecyl group, n-pentadecyl group, n-hexadecyl group, n-heptadecyl group, n-octadecyl group, n-nonadecyl group, n-icosyl group and the like.

In formula (1), the branched-chain alkyl group represented by R includes, for example, a branched-chain alkyl group having 3 to 8 carbon atoms, specifically isopropyl group, isobutyl group, s- butyl group, t-butyl group, isopentyl group, s-pentyl group, t-pentyl group, isohexyl group, s-hexyl group, t-hexyl group, ethylhexyl group and the like.

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

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

In general formula (1), R is preferably an alkyl group having 1 to 12 carbon atoms, more preferably an alkyl group having 1 to 10 carbon atoms, and an alkyl group having 1 to 8 carbon atoms. is more preferable. Further, in general formula (1), it is more preferable that R is a linear alkyl group. Such a configuration of the onium-based functional group can enhance the adhesion between the insulating resin and the conductive particles to ensure insulation, and can further enhance reliability of conduction during thermocompression bonding.

From the viewpoint of facilitating the availability of monomers and the synthesis of polymers and improving the production efficiency of insulating resins, the organic polymer having an ionic group that constitutes the insulating resin is represented by the following general formula (2) or general formula (3). It is preferable to have the represented structural unit.

(Wherein, X, R and n have the same definitions as in the general formula (1) above. m is an integer of 0 to 5. An ⁻ represents a monovalent anion.)

(Wherein, X, R and n have the same definitions as in the above general formula (1). An ^- represents a monovalent anion. ^{m 1} is an integer of 1 or more and 5 or less. R ₅ is a hydrogen atom or is a methyl group.)

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

In general formula (2), m is preferably an integer of 0 or more and 2 or less, more preferably 0 or 1, and particularly preferably 1. In general formula (3), ^m1 is preferably 1 or more and 3 or less, more preferably 1 or 2, and most preferably 2.

The organic polymer having an ionic group preferably contains, for example, a monomer component having an onium-based functional group and an ethylenically unsaturated bond. The organic polymer having an ionic group preferably contains a non-crosslinkable monomer component from the viewpoint of facilitating the availability of monomers, facilitating the synthesis of polymers, and increasing the efficiency of manufacturing insulating resins.

Non-crosslinkable monomers having an onium-based functional group and an ethylenically unsaturated bond include, for example, N,N-dimethylaminoethyl methacrylate, N,N-dimethylaminopropylacrylamide, N,N,N-trimethyl -Ammonium group-containing monomers such as N-2-methacryloyloxyethylammonium chloride; monomers having a sulfonium group such as phenyldimethylsulfonium methyl methacrylate sulfate; 4-(vinylbenzyl)triethylphosphonium chloride, 4-(vinylbenzyl)trimethyl Phosphonium chloride, 4-(vinylbenzyl) tributylphosphonium chloride, 4-(vinylbenzyl)trioctylphosphonium chloride, 4-(vinylbenzyl)triphenylphosphonium chloride, 2-(methacryloyloxyethyl)trimethylphosphonium chloride, 2-( Phosphonium groups such as methacryloyloxyethyl)triethylphosphonium chloride, 2-(methacryloyloxyethyl)tributylphosphonium chloride, 2-(methacryloyloxyethyl)trioctylphosphonium chloride, and 2-(methacryloyloxyethyl)triphenylphosphonium chloride Examples include monomers having The organic polymer having ionic groups may contain two or more non-crosslinking monomer components.

In the organic polymer constituting the insulating resin, the ionic group may be bonded to all of the monomer components, or the ionic group may be bonded to a part of all structural units of the organic polymer. good. When an ionic group is bonded to a portion of all structural units of the organic polymer, the ratio of the monomer component to which the ionic group is bonded is preferably 0.01 mol% or more and 99 mol% or less. It is more preferably 0.02 mol % or more and 95 mol % or less. Here, for the number of monomer components in the organic polymer, the structure derived from one ethylenically unsaturated bond is counted as one constituent unit of the monomer. When the ionic group is contained in both the crosslinkable monomer and the non-crosslinkable monomer, the ratio of the monomer components is the total amount.

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

When the insulating resin is composed of insulating fine particles, the insulating fine particles are melted, deformed, peeled off, or moved on the conductive particle surface by thermocompression bonding the conductive particles coated with the insulating fine particles between the electrodes. The metal surface of the conductive particles is exposed in the crimped portion, thereby enabling conduction between the electrodes and providing connectivity. On the other hand, the surface portion of the conductive particles facing in a direction other than the direction of the thermocompression bonding is generally kept covered with the insulating fine particles, so that the conduction in the direction other than the direction of the thermocompression bonding is prevented. .

By including the ionic group on the surface of the insulating fine particles, the insulating fine particles easily adhere to the conductive particles. Peeling of the insulating fine particles from the particles is effectively prevented. For this reason, the short-circuit prevention effect by the insulating fine particles is likely to be exhibited in a direction different from that between the opposed electrodes, and an improvement in insulation in this direction can be expected.

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

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

There is a wide range in the particle size distribution of the insulating fine particles measured by the method described above. In general, the width of the particle size distribution of powder is represented by the coefficient of variation (hereinafter also referred to as "C.V.") shown by the following formula (1).
C. V. (%) = (standard deviation/average particle size) x 100 (1)
This C.I. V. A large C.I. indicates a broad particle size distribution, while a C.I. V. A small value indicates a sharp particle size distribution. The coated particles of this embodiment are made of C.I. V. is preferably from 0.1% to 20%, more preferably from 0.5% to 15%, and most preferably from 1% to 10%. C. V. is within this range, there is an advantage that the thickness of the coating layer of the insulating fine particles can be made uniform.

In addition, the insulating resin may be a continuous film made of a polymer and having an ionic group instead of the one made of the insulating fine particles. When the insulating resin is a continuous film having an ionic group, the continuous film is melted, deformed, or peeled off by thermocompression bonding the conductive particles between the electrodes, thereby exposing the metal surface of the conductive particles. It enables conduction between the electrodes and obtains connectivity. In particular, there are many cases where the metal surface is exposed due to breakage of the continuous film due to thermocompression bonding of the conductive particles between the electrodes. On the other hand, in the surface portion of the conductive particles facing in a direction different from the direction of the thermocompression bonding, the conductive particles are generally covered with the continuous film, so that conduction in directions other than the direction of the thermocompression bonding is prevented. The continuous film also preferably has ionic groups on its surface.

The thickness of the continuous film is preferably 10 nm or more from the viewpoint of improving insulation in a direction different from that between the opposing electrodes, and is preferably 3,000 nm or less in terms of ease of conduction between the opposing electrodes. is preferred. From this point of view, the thickness of the continuous film is preferably 10 nm or more and 3,000 nm or less, more preferably 15 nm or more and 2,000 nm or less.

As with the insulating fine particles, in the continuous film, the ionic group preferably forms part of the chemical structure of the substance as part of the substance that constitutes the continuous film. In the continuous film, the ionic group is preferably contained in the structure of at least one structural unit of the polymer constituting the continuous film. The ionic groups are preferably chemically bonded to the polymer forming the continuous film, more preferably to side chains of the polymer.

When the insulating resin is a continuous film, it is preferably a continuous film obtained by coating conductive particles with insulating fine particles having ionic groups on their surfaces and then heating the insulating fine particles. Alternatively, it is preferably a continuous film obtained by dissolving the insulating fine particles in an organic solvent. As described above, the insulating fine particles having an ionic group easily adhere to the conductive particles. It becomes easy to prevent the insulating fine particles from peeling off. Therefore, the continuous film obtained by heating or dissolving the insulating fine particles covering the conductive particles can have a uniform thickness and a high coating ratio on the surfaces of the conductive particles.

Further, the conductive particles according to the production method of the present invention may be treated with a surface treatment agent for the purpose of enhancing affinity with the insulating resin and improving adhesion.
Examples of the surface treatment agent include benzotriazole-based compounds, titanium-based compounds, higher fatty acids or their derivatives, phosphates and phosphites. These may be used alone, or may be used in combination as necessary.

The surface treatment agent may or may not be chemically bonded to the metal on the surface of the conductive particles. The surface-treating agent may be present on the surface of the conductive particles, in which case it may be present on the entire surface of the conductive particles, or may be present only on a part of the surface.

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

Examples of triazole-based compounds include compounds having a triazole monocyclic structure that is not condensed with other rings, as well as compounds having a ring structure in which a triazole ring and another ring are condensed. Other rings include a benzene ring and a naphthalene ring.

Among them, a compound having a ring structure in which a triazole ring and another ring are condensed is preferable because it has excellent adhesion to an insulating resin, and in particular, a benzotriazole-based compound, which is a compound having a structure in which a triazole ring and a benzene ring are condensed. is preferred.
Benzotriazole compounds include those represented by the following general formula (I).

(wherein R ¹¹ is a negative charge, hydrogen atom, alkali metal, optionally substituted alkyl group, amino group, formyl group, hydroxyl group, alkoxy group, sulfonic acid group or silyl group; R ¹² , R ¹³ , R ¹⁴ and R ¹⁵ are each independently a hydrogen atom, a halogen atom, an optionally substituted alkyl group, a carboxyl group, a hydroxyl group or a nitro group.)

Alkali metals represented by R ¹¹ in formula (I) include lithium, sodium, potassium and the like. The alkali metal represented by R ¹¹ is an alkali metal cation, and when R ¹¹ in formula (I) is an alkali metal, the bond between R ¹¹ and the nitrogen atom may be an ionic bond.
The alkyl groups represented by R ¹¹ , R ¹² , R ¹³ , R ¹⁴ and R ¹⁵ in formula (I) include those having 1 to 20 carbon atoms, with 1 to 12 carbon atoms being particularly preferred. The alkyl group may be substituted, and examples of substituents include an amino group, an alkoxy group, a carboxyl group, a hydroxyl group, an aldehyde group, a nitro group, a sulfonic acid group, a quaternary ammonium group, a sulfonium group, a sulfonyl group, Phosphonium groups, cyano groups, fluoroalkyl groups, mercapto groups, and halogen atoms are included.
The alkoxy group represented by R ¹¹ preferably has 1 to 12 carbon atoms.
The alkoxy group as a substituent of the alkyl group represented by R ¹² , R ¹³ , R ¹⁴ and R ¹⁵ preferably has 1 to 12 carbon atoms. Halogen atoms represented by R ¹² , R ¹³ , R ¹⁴ and R ¹⁵ in formula (I) include fluorine, chlorine, bromine and iodine atoms.

Specific triazole compounds include 1,2,3-triazole, 1,2,4-triazole, 3-amino-1H-1,2,4-triazole, 5 - mercapto-1H-1,2,3-triazole sodium, 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole, 3-amino-5-mercapto-1,2,4-triazole, In addition, benzotriazole having a ring structure in which a triazole ring and another ring are condensed, 1-methyl-1H-benzotriazole, 4-methyl-1H-benzotriazole, 5-methyl-1H-benzotriazole, 4 -carboxy-1H-benzotriazole, 5-carboxy-1H-benzotriazole, 5-ethyl-1H-benzotriazole, 5-propyl-1H-benzotriazole, 5,6-dimethyl-1H-benzotriazole, 1-aminobenzo triazole, 5-nitrobenzotriazole, 5-chlorobenzotriazole, 4,5,6,7-tetrabromobenzotriazole, 1-hydroxybenzotriazole, 1-(methoxymethyl)-1H-benzotriazole, 1H-benzotriazole- 1-methanol, 1H-benzotriazole-1-carboxaldehyde, 1-(chloromethyl)-1H-benzotriazole, 1-hydroxy-6-(trifluoromethyl)benzotriazole, benzotriazole butyl ester, 4-carboxyl-1H -benzotriazole butyl ester, 4-carboxyl-1H-benzotriazole octyl ester, 1-[N,N-bis(2-ethylhexyl)aminomethyl]methylbenzotriazole, 2,2'-[[(methyl-1H-benzo triazol-1-yl)methyl]imino]bisethanol, tetrabutylphosphonium benzotriazolate, 1H-benzotriazol-1-yloxy tris(dimethylamino)phosphonium hexafluorophosphate, 1H-benzotriazol-1-yloxy tripyrrolidinophosphonium hexafluorophosphate, 1-(formamidomethyl)-1H-benzotriazole, 1-[bis(dimethylamino)methylene]-1H-benzotriazolium 3-oxide hexafluorophosphate, 1-[bis (dimethylamino)methylene]-1H-benzotriazolium 3-oxide tet Lafluoroborate, (6-chloro-1H-benzotriazol-1-yloxy)tripyrrolidinophosphonium hexafluorophosphate, O-(benzotriazol-1-yl)-N,N,N',N'-bis (Tetramethylene)uronium hexafluorophosphate, O-(6-chlorobenzotriazol-1-yl)-N,N,N',N'-tetramethyluronium tetrafluoroborate, O-(6-chloro benzotriazol-1-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate, O-(benzotriazol-1-yl)-N,N,N',N'-bis( pentamethylene)uronium hexafluorophosphate, 1-(trimethylsilyl)-1H-benzotriazole, 1-[2-(trimethylsilyl)ethoxycarbonyloxy]benzotriazole, 1-(trifluoromethanesulfonyl)-1H-benzotriazole, ( trifluoroacetyl)benzotriazole, tris(1H-benzotriazol-1-yl)methane, 9-(1H-benzotriazol-1-ylmethyl)-9H-carbazole, [(1H-benzotriazol-1-yl)methyl] triphenylphosphonium chloride, 1-(isocyanomethyl)-1H-benzotriazole, 1-[(9H-fluoren-9-ylmethoxy)carbonyloxy]benzotriazole, 1,2,3-benzotriazole sodium salt, naphthotriazole, etc. is mentioned.

As the titanium-based compound, for example, when a compound having a structure represented by general formula (II) is present on the surface of the conductive particles, affinity between the insulating resin and the conductive particles can be easily obtained, and solvent It is particularly preferable in that it can be easily dispersed in a liquid and the surfaces of the conductive particles can be treated uniformly.

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

Examples of aliphatic hydrocarbon groups having 4 to 28 carbon atoms represented by R ²² include methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group and nonyl group. , decyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group, octadecyl group, nonadecyl group, icosyl group, henicosyl group, docosyl group and the like. Examples of unsaturated aliphatic hydrocarbon groups include alkenyl groups such as dodecenyl, tridecenyl, tetradecenyl, pentadecenyl, hexadecenyl, heptadecenyl, nonadecenyl, icosenyl, eicosenyl, henicosenyl, and docosenyl. be done.
Examples of the aryl group having 6 to 22 carbon atoms include a phenyl group, a tolyl group, a naphthyl group, an anthryl group and the like.
Examples of the arylalkyl group having 7 or more and 23 or less carbon atoms include a benzyl group, a phenethyl group and a naphthylmethyl group.
As the hydrophobic group, a linear or branched aliphatic hydrocarbon group is particularly preferable, and a linear aliphatic hydrocarbon group is particularly preferable.
From the viewpoint of increasing the affinity between the insulating resin and the conductive particles, the aliphatic hydrocarbon group as the hydrophobic group preferably has 4 to 28 carbon atoms, most preferably 6 to 24 carbon atoms. preferable.

The divalent group represented by R ²¹ includes -O-, -COO-, -OCO-, -OSO ₂ - and the like. Examples of the trivalent group represented by R ²¹ include -P(OH)(O-) ₂ and -OPO(OH)-OPO(O-) ₂ .

In general formula (II), * is a bond, and the bond may be bonded to the metal film of the conductive particles, or may be bonded to other groups. Other groups in that case include, for example, hydrocarbon groups, specifically alkyl groups having 1 to 12 carbon atoms.

As the titanium-based compound having the structure represented by the general formula (II), a compound having a structure in which R ²¹ in the general formula (II) is a divalent group has excellent availability and conductive properties of the conductive particles. It is preferable in that it can be processed without damaging it. A structure in which R ²¹ is a divalent group in general formula (II) is represented by general formula (III) below.

(R ²¹ is a group selected from —O—, —COO—, —OCO— and —OSO ₂ —, and p, r and R ²² are the same as defined in general formula (II).)

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

Specific examples of titanate-based coupling agents used in the present invention include isopropyltriisostearoyl titanate, isopropyltridodecylbenzenesulfonyltitanate, isopropyltris(dioctylpyrophosphate)titanate, tetraisopropyl(dioctylphosphite)titanate, tetraisopropylbis (dioctylphosphite) titanate, tetraoctylbis(ditridecylphosphite) titanate, tetra(2,2-diallyloxymethyl-1-butyl)bis(ditridecyl)phosphite titanate, bis(dioctylpyrophosphate)oxyacetate titanate, Bis(dioctyl pyrophosphate) ethylene titanate and the like can be mentioned, and these can be used alone or in combination of two or more.
These titanate-based coupling agents are commercially available from Ajinomoto Fine-Techno Co., Ltd., for example.

The higher fatty acid is preferably a saturated or unsaturated linear or branched mono- or polycarboxylic acid, more preferably a saturated or unsaturated linear or branched monocarboxylic acid, A saturated or unsaturated linear monocarboxylic acid is more preferred. The fatty acid preferably has 7 or more carbon atoms. Moreover, a derivative refers to a salt or an amide of the fatty acid.

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

As the phosphate and phosphite, those having an alkyl group of 6 to 22 carbon atoms are preferably used.
Phosphate esters include, for example, hexyl phosphate, heptyl phosphate, monooctyl phosphate, monononyl phosphate, monodecyl phosphate, monoundecyl phosphate, monododecyl phosphate, acid monotridecyl ester, phosphate monotetradecyl ester, phosphate monopentadecyl ester, and the like.
Examples of phosphites include hexyl phosphite, heptyl phosphite, monooctyl phosphite, monononyl phosphite, monodecyl phosphite, monoundecyl phosphite, monododecyl phosphite, monotridecyl phosphite, monotetradecyl phosphite, monopentadecyl phosphite and the like.

In the present invention, the surface treatment agent is preferably a triazole-based compound or a titanium-based compound, particularly benzotriazole and 4-carboxylate, because they have excellent affinity with the insulating resin and are highly effective in increasing the coverage of the insulating resin. Benzotriazole, isopropyltriisostearoyl titanate, tetraisopropyl(dioctylphosphite) titanate are particularly preferred.

A method of treating the conductive particles with the surface treatment agent is obtained by dispersing the conductive particles in a solution of the surface treatment agent and then filtering. Before the treatment with the surface treatment agent, the conductive particles may be treated with another treatment agent 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 (solution containing the conductive particles) is 0.01% by mass or more and 10.0% by mass or less. Solvents in the surface treatment agent solution include alcohols such as water, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, isopentyl alcohol, cyclohexanol, acetone, methyl Ketones such as isobutyl ketone, methyl ethyl ketone, methyl-n-butyl ketone, esters such as methyl acetate, ethyl acetate, ethers such as diethyl ether, ethylene glycol monoethyl ether, normal hexane, cyclohexanone, toluene, 1,4 -dioxane, N,N-dimethylformamide, tetrahydrofuran and the like. It is preferable to re-disperse the dispersed and filtered conductive particles after the surface treatment in a solvent to remove the excess surface treatment agent.

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

The conductive particles of the present invention have low connection resistance and excellent connection reliability. It is suitably used as a conductive material for connection to a circuit board. Examples of the conductive material include the use of the conductive particles of the present invention as they are, and the use of the conductive particles of the present invention dispersed in a binder resin. Other forms of the conductive material are not particularly limited, and examples thereof include forms such as anisotropic conductive paste, conductive adhesive, and anisotropic conductive ink.

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

In addition to the conductive particles and the binder resin of the present invention, the conductive material may include, if necessary, a tackifier, a reactive aid, an epoxy resin curing agent, a metal oxide, a photoinitiator, a sensitizer, and a curing agent. agents, vulcanizing agents, antidegradants, heat resistant additives, thermal conductivity improvers, softeners, coloring agents, various coupling agents, metal deactivators, and the like.

In the conductive material, the amount of the conductive particles used may be appropriately determined according to the application. 0.01 to 50 parts by mass, particularly preferably 0.03 to 40 parts by mass.

Among the forms of the conductive material described above, the conductive particles of the present invention are particularly suitable for use as a conductive filler for a conductive adhesive.

The conductive adhesive is preferably used as an anisotropic conductive adhesive that is placed between two substrates on which conductive substrates are formed, and adheres and conducts the conductive substrates by heating and pressurizing. . This anisotropic conductive adhesive contains the conductive particles of the present invention and an adhesive resin. As the adhesive resin, any resin that is insulative and is used as an adhesive resin can be used without particular limitation. Either a thermoplastic resin or a thermosetting resin may be used, and a material exhibiting adhesion performance upon heating is preferable. Such adhesive resins include, for example, thermoplastic types, thermosetting types, ultraviolet curing types, and the like. In addition, there are so-called semi-thermosetting type, composite type of thermosetting type and ultraviolet curing type, etc., which exhibit intermediate properties between thermoplastic type and thermosetting type. These adhesive resins can be appropriately selected according to the surface characteristics of the circuit board or the like to be adhered and the mode of use. In particular, an adhesive resin containing a thermosetting resin is preferable from the viewpoint of excellent material strength after bonding.

Specific examples of adhesive resins include ethylene-vinyl acetate copolymer, carboxyl-modified ethylene-vinyl acetate copolymer, ethylene-isobutyl acrylate copolymer, polyamide, polyimide, polyester, polyvinyl ether, polyvinyl butyral, and polyurethane. , SBS block copolymer, carboxyl-modified SBS copolymer, SIS copolymer, SEBS copolymer, maleic acid-modified SEBS copolymer, polybutadiene rubber, chloroprene rubber, carboxyl-modified chloroprene rubber, styrene-butadiene rubber, isobutylene- One or two selected from isoprene copolymer, acrylonitrile-butadiene rubber (hereinafter referred to as NBR), carboxyl-modified NBR, amine-modified NBR, epoxy resin, epoxy ester resin, acrylic resin, phenol resin, silicone resin, etc. Examples include those prepared using the above combination as the main ingredient. Among these, styrene-butadiene rubber, SEBS, and the like are preferable as the thermoplastic resin because they are excellent in reworkability. Epoxy resin is preferable as the thermosetting resin. Among these resins, epoxy resins are most preferable because of their advantages of high adhesion, excellent heat resistance and electrical insulation, low melt viscosity, and low pressure connection.

As the epoxy resin, a generally 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 novolak resins such as phenol novolak and cresol novolak, polyhydric phenols such as bisphenol A, bisphenol F, bisphenol AD, resorcinol, and bishydroxydiphenyl ether, ethylene glycol, neopentyl glycol, glycerin, and trimethylolpropane. , polyhydric alcohols such as polypropylene glycol, polyamino compounds such as ethylenediamine, triethylenetetramine, and aniline, polyvalent carboxy compounds such as adipic acid, phthalic acid, and isophthalic acid, and epichlorohydrin or 2-methylepichlorohydrin. A glycidyl type epoxy resin is exemplified. Also included are aliphatic and alicyclic epoxy resins such as dicyclopentadiene epoxide and butadiene dimer diepoxide. These can be used individually by 1 type or in mixture of 2 or more types.

From the viewpoint of preventing ion migration, it is preferable to use high-purity products in which impurity ions (Na, Cl, etc.) and hydrolyzable chlorine are reduced as the various adhesive resins described above.

The amount of the conductive particles used in the anisotropic conductive adhesive is usually 0.1 to 30 parts by mass, preferably 0.5 to 25 parts by mass, more preferably 1 to 20 parts by mass with respect to 100 parts by mass of the resin component of the adhesive. Department. When the amount of the conductive particles used is within this range, it is possible to suppress increases in connection resistance and melt viscosity, improve connection reliability, and sufficiently ensure anisotropy in connection.

In addition to the conductive particles and adhesive resin described above, the anisotropically conductive adhesive may contain additives known in the art. The blending amount thereof can also be within the range known in the technical field. Other additives include, for example, tackifiers, reactive aids, epoxy resin curing agents, metal oxides, photoinitiators, sensitizers, curing agents, vulcanizing agents, antidegradants, heat resistant additives, heat Conductivity improvers, softeners, colorants, various coupling agents, metal deactivators, and the like can be exemplified.

Examples of tackifiers include rosin, rosin derivatives, terpene resins, terpene phenol resins, petroleum resins, coumarone-indene resins, styrene resins, isoprene resins, alkylphenol resins, and xylene resins. Examples of reactive aids, ie, cross-linking agents, include polyols, isocyanates, melamine resins, urea resins, utropines, amines, acid anhydrides, peroxides and the like. Any epoxy resin curing agent having two or more active hydrogens per minute can be used without particular limitation. Specific examples include polyamino compounds such as diethylenetriamine, triethylenetetramine, metaphenylenediamine, dicyandiamide, and polyamidoamine; organic acid anhydrides such as phthalic anhydride, methylnadic anhydride, hexahydrophthalic anhydride, and pyromellitic anhydride; substances; novolak resins such as phenol novolak and cresol novolak. These can be used individually by 1 type or in mixture of 2 or more types. Moreover, you may use a latent hardening|curing agent as needed. Usable latent curing agents include, for example, imidazole-based, hydrazide-based, boron trifluoride-amine complexes, sulfonium salts, amine imides, polyamine salts, dicyandiamide, and modified products thereof. These can be used individually by 1 type or as a mixture of 2 or more types.

The anisotropic conductive adhesive described above is manufactured using manufacturing equipment commonly used in the technical field. For example, by blending conductive particles and adhesive resin, and if necessary, a curing agent and various additives, and mixing in an organic solvent when the adhesive resin is a thermosetting resin, adhesion is achieved in the case of a thermoplastic resin. It is produced by melt-kneading at a temperature higher than the softening point of the agent resin, specifically preferably about 50 to 130°C, more preferably about 60 to 110°C. The anisotropically conductive adhesive thus obtained may be applied or applied in the form of a film.

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

The present invention will be further described with reference to the following examples. However, the scope of the invention is not limited to these examples. Properties in the examples were measured by the following methods.
(1) Average particle size From the scanning electron microscope (SEM) photograph of the measurement object, 200 particles are arbitrarily extracted, the particle size is measured at a magnification of 10,000 times, and the arithmetic average value is the average particle diameter.
(2) Thickness of Conductive Layer The conductive particles were cut in two, and the cross section of the cut end was observed and measured with a scanning electron microscope (SEM).

[Example 1]
(1) Pretreatment Spherical styrene-acrylate-silica composite resin particles having an average particle size of 3.0 μm were used as core particles. 9 g of the solution was added to 200 mL of an aqueous conditioner solution (“Cleaner Conditioner 231” manufactured by Rohm and Haas Electronic Materials Co., Ltd.) with stirring. The concentration of the aqueous conditioner solution was 40 mL/L. Subsequently, the core material particles were subjected to surface modification and dispersion treatment by stirring for 30 minutes while applying ultrasonic waves at a liquid temperature of 60°C. This aqueous solution was filtered, and the core particles that had been repulp washed once were made into 200 mL of slurry. 0.1 g of stannous chloride was added to the slurry. The mixture was stirred at room temperature for 5 minutes to carry out a sensitization treatment in which tin ions were adsorbed on the surfaces of the core particles. Subsequently, this aqueous solution was filtered, and the once repulped water-washed core particles were made into a slurry of 200 mL and maintained at 60°C. 1.5 mL of a 0.11 mol/L palladium chloride aqueous solution was added to this slurry. The mixture was stirred at 60° C. for 5 minutes to perform an activation treatment to trap palladium ions on the surfaces of the core particles. Subsequently, this aqueous solution is filtered, and the core particles that have been repulp hot water washed once are made into a slurry of 100 mL, 10 mL of a 0.5 g/L dimethylamine borane aqueous solution is added, and the pretreated core material is stirred for 2 minutes while applying ultrasonic waves. A slurry of particles was obtained.
(2) Preparation of plating bath 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 3 L of an electroless nickel-phosphorus plating bath consisting of an aqueous solution in which polyethylene glycol was dissolved was prepared and heated to 70°C.
(3) Electroless Plating Treatment The slurry of the pretreated core particles was added to the electroless plating bath and stirred for 5 minutes to confirm that hydrogen bubbling stopped.
To this slurry, a mixed aqueous solution containing 224 g / L nickel sulfate aqueous solution, 210 g / L sodium hypophosphite and 80 g / L sodium hydroxide was added at an addition rate of 2.0 mL / min for 60 minutes. It was continuously added fractionally by a metering pump. The plating deposition rate in this operation was 0.55 nm/min, and the thickness of the resulting conductive layer was 33 nm.
Next, an aqueous nickel sulfate solution and a mixed aqueous solution of sodium hypophosphite and sodium hydroxide were added continuously and fractionally for 60 minutes at an addition rate of 4.1 mL/min using a metering pump. The plating deposition rate in this operation was 1.12 nm/min, and the thickness of the conductive layer obtained was 67 nm.
The obtained electroless plating treatment solution was continuously stirred for 5 minutes while maintaining the temperature of 70°C. Next, the liquid was filtered, and the filtrate was washed three times and then dried in a vacuum dryer at 110°C to obtain conductive particles having an electroless nickel-phosphorus plating layer formed on the surface of the core particles as a conductive layer. rice field. The obtained conductive particles had an average particle size of 3.2 μm, and the conductive layer had a thickness of 100 nm and had projections.

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

[Example 3]
The conductive particles obtained in Example 2 were placed in a rectangular container so as to have a thickness of 5 mm. This is placed in a vacuum heating furnace (KDF-75 manufactured by Denken-High Dental Co., Ltd.), heated from room temperature to 390° C. at a heating rate of 5° C./min under a vacuum of 10 Pa, and then heat-treated at this temperature for 2 hours. did After the heat treatment, the pressure was brought to atmospheric pressure by purging with nitrogen, and then cooled to room temperature at a cooling rate of 3° C./min by blowing in nitrogen gas to obtain heat-treated conductive particles. The obtained conductive particles had an average particle diameter of 3.19 μm, a thickness of the conductive layer of 94.5 nm, and had projections.

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

(Evaluation of current resistance and adhesion)
[Evaluation of current resistance]
Using a conductive particle electrical property device (VI device, self-made device with reference to the device described in JP-A-10-221388), flow per conductive particle at the compressibility to be measured A current value (mA) was measured.

[Evaluation of Adhesion]
0.5 g of conductive particles, 20 g of zirconia balls with a diameter of 1.0 mm, and 20 g of ethanol were placed in a polyethylene container and rotated at 200 rpm for 10 minutes using a ball mill processor. Then, it was filtered and dried to obtain conductive particles. 200 of the obtained conductive particles were observed with a scanning electron microscope, and the adhesion of the conductive layer was evaluated as follows.
○: 0 pieces of peeling of the conductive layer △: 1 to 5 pieces of peeling of the conductive layer ×: more than 5 pieces of peeling of the conductive layer

From the results in Table 1, it can be seen that the conductive particles obtained in Examples are superior to the conductive particles obtained in Comparative Examples in current resistance characteristics and adhesion of the conductive layer.

Claims

In the conductive particles in which a conductive layer is formed on the surface of the core particles, the withstand current value per conductive particle is 1 mA or more when the compressibility is less than 5%, and the compressibility is 5% or more. A conductive particle having a withstand current value of 10 mA or more per conductive particle at the time of
The conductive particles according to claim 1, wherein the withstand current value per conductive particle is 0.5 mA or more when the compressibility is 1% or more and 4% or less.
The conductive particles according to claim 1 or 2, wherein the withstand current value per conductive particle is 15 mA or more when the compressibility is 10% or more and 50% or less.
The conductive particles according to any one of claims 1 to 3, wherein the withstand current value per conductive particle is 20 mA or more when the compressibility is 30%.
The conductive particles according to any one of claims 1 to 4, wherein the conductive layer has projections on the outer surface.
The conductive particles according to any one of claims 1 to 5, wherein the conductive layer is at least one selected from nickel, gold, nickel alloys and gold alloys.
A conductive material containing the conductive particles according to any one of claims 1 to 6 and an insulating resin.
A first step of mixing an aqueous slurry of core material particles with an electroless nickel plating bath containing a dispersant, a nickel salt, a reducing agent and a complexing agent, and performing electroless nickel plating;
An aqueous solution containing a nickel salt, an aqueous solution containing a reducing agent, and an aqueous solution containing an alkali are continuously added to the liquid obtained in the first step while controlling the addition amount so as to change the plating deposition rate once or more. A second step of electroless nickel plating treatment,
A method for producing conductive particles having
The method for producing conductive particles according to claim 8, wherein the addition amount is controlled so that the initial plating deposition rate in the second step is 0.05 nm/min or more and 1.5 nm/min or less.
The method for producing conductive particles according to claim 8 or 9, wherein the addition amount is controlled so that the plating deposition rate after the change in the second step is 0.3 nm/min or more and 3.0 nm/min or less.
The method for producing conductive particles according to any one of claims 8 to 10, wherein the addition amount is controlled so as to change the plating deposition rate twice or more.
The method for producing conductive particles according to any one of claims 8 to 11, wherein the amount added is controlled so as to change the plating deposition rate to a high level.
The conductive particles according to any one of claims 8 to 12, wherein in the second step, an aqueous solution containing a nickel salt and a mixed aqueous solution containing a reducing agent and an alkali are added to the liquid in the first step. Production method.