KR20170012529A - Conductive particle, conductive material, and method for manufacturing the conductive particle - Google Patents

Abstract

Provided is a conductive particle with high conductivity. The conductive particle is formed by coating the surface of a core material particle with a conductive film. The conductive film includes an upper layer film and a bottom film in contact with the surface of the core material particle. The bottom film includes nickel and phosphorus. The upper layer film has a crystalline structure and includes nickel, phosphorus, and one or more kinds of metal M. The upper layer film includes a flat part and a plurality of protrusion parts which protrude from the flat part and also, become continuums from the flat part. The flat part and the protrusion parts are made of the same materials.

Description

TECHNICAL FIELD [0001] The present invention relates to a conductive particle, a conductive material, and a method for manufacturing the conductive particle. BACKGROUND OF THE INVENTION < RTI ID = 0.0 >

The present invention relates to a conductive particle and a conductive material containing it.

As the conductive particles used as the material of the anisotropic conductive film or the anisotropic conductive paste, it is generally known that a conductive film is formed on the surface of the core material particles. As the conductive film, a nickel plating film is frequently used. For the purpose of further enhancing various performances of such conductive particles, it has been proposed that a plating film of nickel has a multilayer structure.

For example, Patent Document 1 discloses that a nickel coating formed on the surface of core material particles includes a first layer formed on the surface of the core material particles and a second layer formed adjacent to the first layer, And the orientation directions of the grain boundaries in the first layer and the second layer are different from each other. These conductive particles have an advantage that the adhesion between the nickel coating and the core material particles is improved, the heat resistance of the conductive particles is improved, and the increase in electrical resistance is reduced even when the conductive particles are stored at a high temperature for a long time.

Patent Document 2 discloses that a conductive layer made of a nickel film has an amorphous structure nickel-phosphorus plating layer in contact with the surface of core material particles and a crystal structure nickel-tungsten phosphorus layer in contact with the surface of the amorphous nickel- Conductive particles have been proposed. These conductive particles are described in the same document as high adhesion between the core material particles and the conductive layer, and excellent impact resistance and conductivity.

Japanese Patent Application Laid-Open No. 2004-197160 Japanese Patent Laid-Open No. 2007-173075

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When a nickel film is formed on the surface of the core material particles, a method of reducing and depositing nickel on the surface of the core material particles with a reducing agent is generally used by using a plating solution containing nickel. As the reducing agent, hypophosphite is often used. When hypophosphite is used as the reducing agent, phosphorus is consequently contained in the nickel film formed by the reduction precipitation. The presence of phosphorus in the nickel film is a factor for lowering the conductivity of the nickel film. From this viewpoint, it is preferable that the amount of phosphorus present is as small as possible. On the other hand, when the amount of phosphorus present is small, the conductive particles tends to be magnetically aggregated due to the inherent magnetism of nickel, and as a result, the dispersibility of the conductive particles tends to be lowered. When the conductive particles are used as an anisotropic conductive film or an anisotropic conductive paste, for example, the degradation of the dispersibility may be a cause of short circuit of the circuit. In the above-described Patent Document 2, the content of phosphorus in each of the nickel-phosphorus layer of the bottom layer and the nickel-tungsten-phosphorus layer of the upper layer in the nickel coating of the conductive particles described in this document is specified. It is not easy to satisfy both of conductivity and dispersibility at the same time.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide conductive particles with improved performance in various properties than the conductive particles of the prior art described above.

The present invention provides a conductive particle in which a conductive film is formed on the surface of core material particles,

Wherein the conductive coating has a bottom coating in contact with the surface of the core material particles and an upper coating in contact with the surface of the bottom coating,

Wherein the bottom coating comprises nickel and phosphorus,

Wherein the upper coating film has a crystal structure and includes nickel, phosphorus, and at least one kind of metal M (except for nickel)

Wherein the upper layer coating has a flat portion and a plurality of protrusions protruding from the flat portion and continuing from the flat portion, wherein the flat portion and the protrusions are made of the same material. .

Further, the present invention provides a method for forming a bottom coating film comprising nickel and phosphorus on the surface of core material particles by electroless plating using an electroless plating bath containing a reducing agent comprising a nickel source and a phosphorus compound,

Nickel source, metal M (except nickel) Nickel, phosphorus, and phosphorus are added to the surface of the bottom coating by electroless plating using an electroless plating bath containing a reducing agent composed of a phosphorus compound and a hydroxy acid And a metal M (but excluding nickel), and has a flat portion and a plurality of protrusions protruding from the flat portion and being a continuum from the flat portion, wherein the flat portion and the protrusion are made of the same material And a step of forming an upper coating film formed on the upper layer coating film.

According to the present invention, conductive particles having high conductivity are provided. Particularly, conductive particles whose conductivity is suppressed from being lowered even after being stored under high temperature and high humidity are provided. Therefore, when the conductive particles of the present invention are used, for example, as an anisotropic conductive film or an anisotropic conductive paste material, such conductive films and conductive pastes have high conductivity and high reliability under harsh environments.

Hereinafter, the present invention will be described based on its preferred embodiments. As described above, the conductive particles of the present invention comprise a core material particle, a bottom coating in contact with the surface of the core material particle, and a conductive coating having an upper coat film in contact with the surface of the bottom coating film. The upper layer coating has a crystal structure and contains nickel, phosphorus and at least one kind of metal M (except nickel). The upper layer coating has a plurality of protrusions. With respect to the present invention, by combining the upper coating film having such a constitution and the bottom coating film containing nickel and phosphorus, the conductivity of particles, in particular, the conductivity under a harsh environment of high temperature and high humidity, is enhanced.

As described above, the bottom coating contains phosphorus. The content of phosphorus in the bottom film can be appropriately set in accordance with the specific use of the conductive particles of the present invention. For example, when the phosphorus content of the bottom film is set to 1% by mass or more and less than 10% by mass, the conductivity of the conductive particles is greatly improved. From the viewpoint of further improving the conductivity, the phosphorus content of the bottom film is preferably 8 mass% or less, more preferably 7 mass% or less, particularly preferably 6 mass% or less. However, even when the phosphorus content of the bottom film is relatively high, i.e., 5 mass% or more, the presence of the upper film of the above-described constitution makes it possible to keep the conductivity high enough to satisfy the conductivity. Even in the presence of the upper coating film, even when the phosphorus content of the bottom coating film is lowered to less than 10 mass%, the magnetic flocculation can be effectively suppressed and the good dispersibility of the conductive particles can be maintained. The reason why such dispersibility maintenance effect is exhibited is not clear, but for one reason, it is considered that the metal M in the upper layer coating may prevent aggregation due to nickel magnetism.

The content of phosphorus in the bottom film may be set to 10 mass% or more. For example, 10 to 18% by mass, and more preferably 10 to 15% by mass. It is advantageous in that the content of phosphorus in the bottom film is set to be high in view of making it difficult for the conductive particles of the present invention to cause self-agglomeration. On the other hand, setting the content of phosphorus in the bottom film to a high value can act as a negative point in terms of improving the conductivity of the bottom film. However, in the present invention, the upper layer coating having the above-described structure is formed on the surface of the bottom coating to ensure the conductivity of the whole conductive particles.

In any of the above ranges of phosphorus content, the bottom coating is composed of a nickel-phosphorus alloy. The nickel-phosphorus alloy is an alloy that is formed when a phosphorus compound such as hypophosphorous acid or its salt is used as a reducing agent of nickel at the time of forming a bottom coating film in a manufacturing process of a conductive particle to be described later. It is preferable that the bottom film contains only nickel and phosphorus, and substantially does not contain any other element. The fact that substantially no other element is included means that the ratio of elements other than nickel and phosphorus is 1% by mass or less when the bottom film is subjected to elemental analysis. The content of nickel in the bottom film is the remainder obtained by subtracting the above-mentioned content of phosphorus from the total amount of the bottom film.

The nickel content and phosphorus content in the bottom film can be measured by dissolving the core material particles formed up to the bottom film into an acid and subjecting the bottom film component in the obtained solution to ICP or chemical analysis as described later.

The bottom coating has a crystalline structure or an amorphous structure. The crystal structure referred to herein is a crystal structure of a nickel-phosphorus alloy. In addition, having an amorphous structure means that the bottom film has no crystal structure. When the bottom coating has a crystal structure, the conductivity of the conductive particles is improved. On the other hand, when the bottom coating has an amorphous structure, magnetic aggregation of the conductive particles is suppressed and the dispersibility is improved.

Whether the bottom coating has a crystal structure or not has an amorphous structure can be determined, for example, by carrying out XRD measurement on the core material particles formed up to the bottom coating. Whether the bottom coating has a crystal structure or not has an amorphous structure depends on the composition of the plating bath when the bottom coating is formed by electroless plating, for example, in the method for producing conductive particles described below. Specifically, the lower the concentration of the phosphorus compound in the plating bath used for electroless plating, the more easily a bottom film having a crystal structure is formed. Conversely, the higher the concentration of the phosphorus compound in the plating bath is, the more easily the bottom film having an amorphous structure is likely to be formed. For example, when a plating bath containing a phosphorus compound at a concentration such that the amount of phosphorus contained in the bottom coating is less than 10% by mass is used, a bottom coating having a crystal structure tends to be formed. On the contrary, when a plating bath containing phosphorus compound having a concentration such that the amount of phosphorus contained in the bottom coating is 10 mass% or more is used, a bottom coating film having an amorphous structure is likely to be formed.

The bottom coating can be formed on the surface of the core material particles with a substantially uniform thickness. Instead, a plurality of protrusions may be formed to form the bottom film in a concavo-convex shape. In the latter case, the bottom film has a flat portion and a plurality of protrusions which protrude from the flat portion and form a continuum from the flat portion, and the flat portion and the protrusion portion are made of the same material, that is, a nickel- . "Continuum" means that the projections and flat portions of the bottom coating are formed by a single process, and that there is no portion that interferes with the sense of identity such as joints between the flat portion and the projection portion of the bottom coating. If the bottom coating is formed in a concave-convex shape, the concave-convex shape is reflected on the surface of the conductive particle. Therefore, when the conductive particles of the present invention are used to conduct the electrode, the protrusions can penetrate the oxide film formed on the electrode surface, and the connection resistance can be reduced. In addition, since the protrusions are made of the same material as the flat portion of the bottom coating and are continuous with the flat portion of the bottom coating, the protrusions of the conductive particles are secured in strength, so that the protrusions are not easily broken even when pressure is applied to the conductive particles.

In the conductive particle, it is possible to confirm that the bottom coating has a substantially uniform thickness or that the bottom coating has a flat portion and a protruding portion by observing a cross section of the conductive particle with a microscope.

The top coat directly contacting the surface of the bottom coat contains nickel, phosphorus and one or more metals M (except nickel), as previously mentioned. The metal M is preferably a transition metal, and more preferably has a higher Mohs hardness than nickel. Especially when a metal M having a Mohs hardness of 4 or more is used, an advantageous effect that the conductivity is further increased is obtained, which is preferable. The reason for this is that when the anisotropic conductive film containing conductive particles is used to conduct electrical conduction between the electrodes, the resin present at the interface between the conductive particles and the electrode is easily removed, and the conductive particles The oxide film existing on the electrode surface tends to be torn easily.

Preferable examples of the metal M include transition metals of Group 6, Group 8, Group 9 and Group 10 of the Periodic Table. Particularly preferable examples include palladium, cobalt, rhodium, iron, platinum, iridium, tungsten, molybdenum and chromium. Among them, it is preferable to use at least one selected from metals having a Mohs hardness of 4 to 10, for example, tungsten, molybdenum, palladium and platinum, because the conductivity can be further increased. Particularly, it is preferable to use at least one selected from tungsten and molybdenum. In addition, it is more preferable to use two or more types at the same time in view of conductivity.

The content of the metal M in the upper layer coating film is preferably 1 to 20% by mass, more preferably 2 to 15% by mass, still more preferably 3 to 13% by mass from the viewpoint of improving the conductivity of the conductive particles. Mass%. This content is the total content of two or more kinds of metals M when the upper layer coating contains two or more kinds of metals M. The content of phosphorus in the upper layer coating film is preferably 1 to 7% by mass, more preferably 1 to 5% by mass, still more preferably 1 to 3% by mass from the viewpoint of improving the conductivity of the conductive particles. Mass%. The nickel content is preferably 75 mass% or more, particularly 80 mass% or more from the viewpoint of further improving the conductivity of the conductive particles. The content of phosphorus and the content of metal M in the upper coating film can be measured by a method described later. The nickel content in the upper layer coating can also be measured by the same method as the phosphorus content and the content of the metal M. [

The upper coating has a crystal structure. This improves the conductivity of the conductive particles. In particular, in addition to the fact that the upper layer coating has a crystal structure, if the above-mentioned bottom coating has a crystal structure, it is preferable that the conductive particles have improved conductivity. The crystal structure of the upper layer coating may be any of metal nickel, nickel-phosphorus alloy or nickel-phosphorus-metal M alloy. Whether or not the upper layer coating has a crystal structure can be determined by thinning the coating with FIB or the like and then measuring the coating with a depth of several nm from the surface of the particle by X-ray diffraction or the like to see whether a diffraction peak of nickel or the like is observed . Whether or not the upper layer coating contains the metal M can be confirmed by dissolving the conductive particles with dilute acid or the like and collecting a plurality of elution solutions over time and analyzing the elements contained in the elution solution at each time point.

In order for the upper layer coating to have a crystal structure, for example, in the method for producing conductive particles described later, the composition of the plating bath when the upper layer coating is formed by electroless plating may be suitably adjusted. Specifically, when a phosphorus compound is used as a reducing agent used in electroless plating, the lower the concentration of the phosphorus compound in the plating bath is, the more easily an upper layer coating having a crystal structure is likely to be formed. For example, if a plating bath containing a phosphorus compound having a concentration such that the amount of phosphorus contained in the upper layer coating is less than 10% by mass is used, the upper layer coating having a crystal structure tends to be formed.

The surface of the upper layer coating has a concavo-convex shape. Specifically, it is preferable that the upper layer coating has a flat portion and a plurality of protrusions protruding from the flat portion and continuing from the flat portion, wherein the flat portion and the protrusion are made of the same material . Each projecting portion may be in the form of a single continuous body made of the material constituting the upper layer coating or may be composed of a particle connecting body in which a plurality of particles constituting the upper layer coating are connected in a row, . The surface of the upper layer coating is in the form of irregularities, and the irregularities are reflected on the surface of the conductive particles. Therefore, when conducting the electrode using the conductive particles of the present invention, the protrusions can penetrate the oxide film formed on the electrode surface, and the connection resistance can be reduced. In addition, since the protrusions are made of the same material as the flat portion of the upper layer coating and are continuous with the flat portion of the upper layer coating, the protrusions of the conductive particles are secured in strength, so that the protrusions are not easily broken even when pressure is applied to the conductive particles. Particularly, when the surface of the bottom film has a concave-convex shape, the concave-convex shape of the concave-convex shape and the concave-convex shape of the concave-convex shape of the surface of the upper-layer film are reflected on the surface of the conductive particle. As a result, the oxide film can be torn more easily. In addition, breakage of the protruding portions becomes more difficult to occur. In this case, the position of the protrusion formed on the bottom coating and the position of the protrusion formed on the upper coating may be the same or different.

With respect to the protrusions of the upper layer coating, the term " continuum " in the above-mentioned " plurality of protrusions constituting a continuum from the flat portion " means the same as the continuity of the protrusions formed in the above- Therefore, for example, a flat upper coat film is formed on the surface of the bottom film, core particles for forming projections, such as a metal, a metal oxide, a nonmetal inorganic material such as graphite, a conductive polymer, Is not included in the continuum of the present invention because the flat portion and the protruding portion are not formed by a single process. However, it is also noted that the conductive particles having protrusions formed as the starting points of growth of the core particles, that is, the conductive particles having no flat portion and no protrusions as a continuum are adhered to the upper layer coating, Should be.

In the conductive particles, the upper layer coating has flat portions and protrusions can be confirmed by observing a cross section of the conductive particles under a microscope.

As described above, in the conductive particle of the present invention, protrusions are formed on the surface of the conductive particles, at least reflecting the concavo-convex shape of the protrusions formed in the upper layer coating. It is preferable that the height H of the projections is 20 nm or more on average, particularly 50 nm or more. The number of protrusions is preferably from 1 to 20,000, particularly from 5 to 5000 per one particle, from the viewpoint of further improving the conductivity of the conductive particles, depending on the particle diameter of the conductive particles. The aspect ratio of the protrusions is preferably 0.5 or more, more preferably 1 or more. If the aspect ratio of the protrusions is large, it is advantageous because the above-mentioned oxide film can be easily torn. In addition, when the anisotropic conductive film is formed using the conductive particles, it is considered that when the aspect ratio of the protruding portion is large, the resin exclusion property is high, and thus the conductivity is high. The ratio between the height H of the protrusion and the length D of the base of the protrusion, that is, H / D,

The aspect ratio of the protrusions formed on the surface of the conductive particles is as described above. It is preferable that the length D itself of the protrusions is 5 to 500 nm, particularly 10 to 400 nm. As for the height H of the protrusions, It is preferably 5 to 500 nm, particularly preferably 10 to 400 nm.

The measurement method of the aspect ratio is as follows. The conductive particles are magnified and observed by an electron microscope. The length D and the height H of the base are measured for at least one protrusion with respect to one particle. In this case, it is important from the viewpoint of accurate measurement of the dimension that the protruding portion existing on the periphery of the particle rather than the protruding portion existing in the center of the particle on the observation. Perform these measurements on at least 20 different particles. The data of the plurality of aspect ratios thus obtained are arithmetically averaged, and the values are referred to as horizontal and vertical ratios. In addition, since the cross section of the projection has a small anisotropic shape (for example, almost circular), there is little possibility that the value of the length D of the base of the projection varies depending on the observation angle of the particle.

Concerning the protrusions formed on the surfaces of the conductive particles, the number of protrusions having a height H of 50 nm or more per 1 particle, preferably 1 to 10,000, particularly 2 to 2000, particularly 2 to 20, It is preferable in terms of further improvement. From the same viewpoint, the aspect ratio of the protrusions having a height H of 50 nm or more is preferably 0.3 to 3.0, particularly 0.5 to 2.0, particularly 0.5 to 1.0.

The conductive particles may further have an outermost layer coating contacting the surface of the upper layer coating. The outermost layer coating is preferably made of a noble metal. As the noble metal, it is preferable to use gold or palladium which is a metal having high conductivity, and it is particularly preferable to use gold. This coating makes it possible to further increase the conductivity of the conductive particles.

It is preferable that the conductive particles of the present invention having the above-described conductive film have a spherical shape. The sphere referred to here is a spherical shape when the appearance of the particles is observed except for the protrusions described above.

The size of the conductive particles can be appropriately set according to the specific use of the conductive material. Specifically, the conductive particles preferably have a particle diameter of 0.5 to 1000 μm, more preferably 1 to 500 μm, and still more preferably 1 to 100 μm. The particle diameter of the conductive particles can be measured by an electron microscope observation.

Next, a manufacturing method suitable for the conductive particles of the present invention will be described. This manufacturing method is largely divided into two steps: (1) a first step of forming a bottom coating on the surface of the core material particles, and (2) a second step of forming an upper coating on the particles obtained in the first step.

In the first step, a pre-treatment for supporting a noble metal is carried out on the surface of the core material particles. There is no particular limitation on the kind of the core material particles, and both organic materials and inorganic materials can be used. In order to form the bottom coating well, the core material particles are preferably dispersible in water. Therefore, the core material particles are preferably substantially insoluble in water, and more preferably they do not dissolve or deteriorate against acids or alkalis. The term "dispersible in water" means that a suspension which is substantially dispersed in water can be formed to such an extent that the bottom coating can form on the surface of the core material particles by a usual dispersing means such as stirring.

The shape of the core material particle greatly influences the shape of the intended conductive particle. Since the thicknesses of the bottom coating film and the upper layer coating film covering the surface of the core material particles are thin, the shape of the core material particles is almost reflected in the shape of the conductive particles. Since the conductive particles are preferably spherical as described above, the shape of the core material particles is also preferably spherical.

When the core material particles are spherical, the particle diameter of the core material particles greatly affects the particle diameter of the intended conductive particles. Since the thicknesses of the bottom coating film and the upper layer coating film covering the surface of the core material particles are thin, the particle diameter of the core material particles is almost reflected in the particle diameter of the conductive particles. From this point of view, the particle diameter of the core material particles can be made to be about the same as the particle diameter of the intended conductive particles. Specifically, it is preferably 0.5 to 1000 μm, particularly 1 to 500 μm, particularly preferably 1 to 100 μm. The particle diameter of the core material particles can be measured by the same method as the particle diameter of the conductive particles.

The particle size distribution of the powder made of the core material particles measured according to the above-mentioned method is wide. Generally, the width of the particle size distribution of the powder is expressed by the coefficient of variation shown in the following formula (1).

[Formula 1] Coefficient of Variation (%) = (Standard Deviation / Average Particle Size) x 100

The larger the coefficient of variation indicates that the distribution has a width, and the smaller the coefficient of variation indicates that the particle size distribution is sharp. In the present invention, as the core material particles, those having a coefficient of variation of 30% or less, particularly 20% or less, and particularly 10% or less are preferably used. This is because, when the conductive particles of the present invention are used as the conductive particles in the anisotropic conductive film, there is an advantage that the effective contribution ratio is increased.

Specific examples of the core material particles include inorganic materials such as metal (including alloys), glass, ceramics, silica, carbon, oxides of metals or nonmetals (including hydrous), metal silicates including aluminosilicates, metal carbides, Nitrides, metal carbonates, metal sulfates, metal phosphates, metal sulfides, metal halides, metal halides and carbon. Examples of the organic material include natural fibers, natural resins, thermoplastic resins such as polyethylene, polypropylene, polyvinyl chloride, polystyrene, polybutene, polyamide, polyacrylic acid ester, polyacrylonitrile, polyacetal, ionomer and polyester, , Phenol resin, urea resin, melamine resin, benzoguanamine resin, xylene resin, silicone resin, epoxy resin or diallyl phthalate resin. These may be used alone or as a mixture of two or more. Further, a composite material of an organic material and an inorganic material may be used. Examples thereof include a styrene-silica composite resin, an acrylic silica composite resin, and the like.

Further, the physical properties of the core material particles are not particularly limited. When the core material particles are resin particles, the K value defined by the following formula 2 is preferably 10 kgf / mm ² to 10,000 kgf / mm < ^{2 &} gt ;, while the recovery rate after 10% compression deformation is preferably in the range of 1% to 100% at 20 deg. By satisfying these physical properties, it is possible to sufficiently contact the electrodes without damaging the electrodes when the electrodes are pressed together.

K value (kgf / mm ² ) = (3 / √2) × F × S ^-3/2 × R ^-1/2

F and S in Equation 2 are the load value (kgf) at 10% compression deformation of the corresponding microspheres and the compressive displacement (kgf) when measured with a micro compression tester MCTM-500 (manufactured by Shimadzu Corporation) (mm), and R is the radius (mm) of the microsphere.

It is preferable that the surface of the core material particles is surface-modified so as to have a trapping ability of noble metal ions or a trapping ability of noble metal ions. The noble metal ions are preferably palladium or silver ions. The ability to capture noble metal ions means that noble metal ions can be captured 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 a capping ability I have. When the surface is modified to have a trapping ability of noble metal ions, for example, the method described in Japanese Patent Application Laid-Open No. 61-64882 can be used.

These core material particles are used to carry noble metal on the surface. Specifically, the core material particles are dispersed in a dilute acidic aqueous solution of a noble metal salt such as palladium chloride or silver nitrate. This allows noble metal ions to be trapped on the surface of the particles. The concentration of the noble metal salt is preferably in the range of 1 x 10 ^-7 to 1 x 10 ^-2 moles per m ² of the surface area of the particles. The core material particles in which noble metal ions are captured are separated from the system and washed with water. Subsequently, the core material particles are suspended in water, and a reducing agent is added thereto to perform reduction treatment of noble metal ions. Thereby supporting the noble metal on the surface of the core material particles. As the reducing agent, for example, sodium hypophosphite, sodium borohydride, potassium borohydride, dimethylamine borane, hydrazine, formalin and the like are used, and it is preferable to select them based on the constituent material of the desired bottom film.

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

In this manner, the bottom film forming process of the first step is performed on the core material particles subjected to the pre-treatment. Hereinafter, as the bottom film forming process, a process (a) for forming a bottom film having a protrusion (hereinafter also referred to as a process) and a process for forming a bottom film having a smooth surface ) Are described.

As a processing, the following a1 step and a2 step are carried out.

Step a1 is an electroless nickel plating process in which an aqueous electroless 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 this a1 step, self-decomposition of the plating bath occurs simultaneously with the formation of the bottom coat on the core material particles. Since the self-decomposition occurs in the vicinity of the core material particles, nuclei of the microprojections are generated by the self-decomposition substance being trapped on the surface of the core material particles at the time of forming the bottom coating film, and at the same time, . The projecting portion grows from the nucleus of the generated fine protrusion as a starting point.

In the step a1, an aqueous slurry is prepared by sufficiently dispersing the above-mentioned core material particles in water preferably in the range of 1 to 500 g / L, more preferably 5 to 300 g / L. The dispersion operation can be carried out using a shear dispersion apparatus such as a usual stirring, high-speed stirring, or a colloid mill or a homogenizer. Ultrasonic waves may also be used in combination for the dispersion operation. If necessary, a dispersant such as a surfactant may be added in the dispersing operation. Subsequently, an electroless plating a1 step is carried out by adding an aqueous slurry of core material particles subjected to a dispersion operation to an electroless nickel plating bath containing a nickel salt, a reducing agent, a complexing agent and various additives.

Examples of the dispersant include nonionic surfactants, amphoteric surfactants and / or water-soluble polymers. As the nonionic surfactant, polyoxyalkylene ether surfactants such as polyethylene glycol, polyoxyethylene alkyl ether, and polyoxyethylene alkyl phenyl ether can be used. As the amphoteric surfactant, a betaine surfactant such as alkyldimethyl acetate betaine, alkyldimethylcarboxymethylacetate betaine, and alkyldimethylaminoacetic acid betaine can be used. As the water-soluble polymer, polyvinyl alcohol, polyvinyl pyrrolidinone, hydroxyethyl cellulose and the like can be used. These dispersants may be used alone or in combination of two or more. The amount of the dispersing agent to be used varies depending on the kind thereof, but it is generally 0.5 to 30 g / L with respect to the volume of the liquid (electroless nickel plating bath). Particularly, when the amount of the dispersing agent used is in the range of 1 to 10 g / L with respect to the volume of the liquid (electroless nickel plating bath), it is preferable from the viewpoint of further improving the adhesion of the bottom film.

As the nickel salt, for example, nickel chloride, nickel sulfate or nickel acetate is used, and the concentration thereof is preferably in the range of 0.1 to 50 g / L. As the reducing agent, for example, the same materials as those used for the reduction of the noble metal ions mentioned above may be used, and they are selected on the basis of the intended constituent material of the bottom coating film. When a phosphorus compound such as sodium hypophosphite is used as the reducing agent, the concentration thereof is preferably in the range of 0.1 to 50 g / L.

Examples of the complexing agent include carboxylic acids (salts) such as citric acid, hydroxyacetic acid, tartaric acid, malic acid, lactic acid, gluconic acid or its alkali metal salts or ammonium salts, amino acids such as glycine, amine acids such as ethylenediamine, Other compounds having a complexing action with respect to nickel ions, such as ammonium, EDTA or pyrophosphoric acid (salt), are used. These may be used singly or in combination of two or more. The concentration thereof is preferably in the range of 1 to 100 g / L, more preferably 5 to 50 g / L. The pH of the preferred electroless nickel plating bath at this stage is in the range of 4-14. The electroless nickel plating reaction starts quickly upon addition of the aqueous slurry of the core material particles and involves generation of hydrogen gas. The electroless plating a1 process is terminated when the generation of the hydrogen gas is not completely confirmed.

Next, for the a2 step, following the step a1, (i) a first aqueous solution containing a nickel salt, a reducing agent and one kind of alkali, and a second aqueous solution containing the remaining two species are used, or ii) adding a first aqueous solution containing a nickel salt, a second aqueous solution containing a reducing agent and a third aqueous solution containing an alkali to these aqueous solutions at the same time, Electroless nickel plating is performed. When such a solution is added, the plating reaction starts again, but by adjusting the addition amount, the formed bottom film can be controlled to a desired film thickness. After the completion of the addition of the electroless nickel plating solution, generation of hydrogen gas is not completely confirmed, and stirring is continued while maintaining the temperature of the liquid for a while to complete the reaction.

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

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

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

The a2 step is carried out continuously after the end of the a1 step, but instead of this, the a1 step and the a2 step may be interrupted. In this case, after the end of the step a1, the core material particles and the plating liquid are separated by filtration or the like, the core material particles are dispersed in water to prepare an aqueous slurry, and a complexing agent is added thereto, The dispersant is preferably added in the range of 0.5 to 30 g / L, more preferably 1 to 10 g / L by adding the aqueous solution dissolved in the concentration range of 100 g / L, more preferably 5 to 50 g / L To prepare an aqueous slurry, and then carrying out the a2 step of adding the respective aqueous solutions to the aqueous slurry. In this way, a bottom film having a desired protrusion can be obtained.

Next, the case of performing the b process, which is the process of forming the surface smooth film, instead of the a process will be described. Process b can be carried out as follows. First, an aqueous slurry containing the pre-treated core material particles, a dispersant, and a complexing agent is prepared. Then, using the first aqueous solution and the second aqueous solution of (i) described in the a2 step, or using the first through third aqueous solutions of (ii), this aqueous solution is added to the aqueous slurry simultaneously and simultaneously And electroless nickel plating is performed. The pH of the plating solution formed by adding the respective aqueous solutions to the aqueous slurry is preferably adjusted to a range of, for example, 3 to 11. The kind of the dispersant and the complexing agent and the concentration thereof may be those described in the explanation of the a1 process as the concentrations described in the a1 process.

The nickel salt, reducing agent and alkali contained in the first and second aqueous solutions of (i) and the first to third aqueous solutions of (ii) may be the same as those used for such aqueous solutions in the a2 step. The concentration of the nickel salt in the aqueous solution is preferably 10 to 1000 g / L, particularly preferably 50 to 500 g / L. The concentration of the reducing agent is preferably 100 to 1000 g / L, more preferably 100 to 800 g / L when a phosphorus compound is used as a reducing agent. The concentration of alkali is preferably 5 to 500 g / L, particularly preferably 10 to 200 g / L. In this way, a desired surface smooth film can be obtained.

After the bottom film is formed as described above, the second process is then performed to form an upper layer film having projections on the surface of the bottom film. For the second step, the bottom coat covering particles formed in the first step are mixed with an electroless plating bath containing a nickel source, a metal M source, a reducing agent and a hydroxy acid. One of the characteristics of the second step is that a hydroxy acid is compounded in the electroless plating bath in order to form the projections on the upper coat.

The reducing agent used in the second step is preferably a phosphorus compound such as hypophosphorous acid or a salt thereof, particularly preferably sodium hypophosphite. The concentration of the reducing agent in the electroless plating bath is preferably 0.1 to 50 g / L, more preferably 0.5 to 20 g / L.

As the nickel source of the nickel ion used in the second step, a nickel salt such as the nickel source used in the first step can be used. The concentration of the nickel salt in the electroless plating bath is preferably 0.1 to 100 g / L, more preferably 1 to 50 g / L.

As the metal source of the metal M ions, for example, sulfate, nitrate, sodium salt, chloride, hydroxide and the like are used. When a sodium salt is used, the concentration in the electroless plating bath is preferably 0.01 to 100 g / L, more preferably 0.1 to 50 g / L. This concentration is the total concentration of two or more kinds of metals M when the upper layer coating contains two or more kinds of metals M.

The hydroxy acid compounded in the electroless plating bath used in the second step is used for the purpose of forming protrusions on the upper layer coating. As the hydroxy acid, for example, monohydroxymonocarboxylic acid, dihydroxymonocarboxylic acid and the like can be used. As the hydroxy acid, for example,? -Hydroxy acid,? -Hydroxy acid,?,? -Hydroxy acid can be used. Particularly, when glycolic acid and lactic acid, which is? -Monohydroxymonocarboxylic acid, or glyceric acid,?,? - dihydroxymonocarboxylic acid, are used as the hydroxy acid, protrusions having a desired shape can be easily formed, Do. These hydroxy acids may be used alone or in combination of two or more. The concentration of the hydroxy acid in the electroless plating bath is preferably 0.5 to 20 g / L, more preferably 1 to 15 g / L.

The electroless plating bath used in the second step may further contain a complexing agent. Examples of the complexing agent include those mentioned in the description of the a1 process. The concentration of the complexing agent may be the same as in the step a1.

The pH of the electroless plating bath used in the second step is preferably maintained at 3 to 11, more preferably 4 to 10.

There is no particular limitation on the method of mixing the bottom coat-coated particles and the electroless plating bath. For example, the electroless plating bath can be heated to a temperature at which nickel ions can be reduced, and the bottom coat-coated particles can be charged into the electroless plating bath under this condition. By this operation, the nickel ions are reduced, and the nickel formed by the reduction forms the upper layer coating having the protrusions on the surface of the bottom particles.

In this way, desired conductive particles can be obtained. The conductive particles may be added to a post-treatment for further forming an outermost layer coating as necessary. Examples of the post-treatment include an electroless gold plating process or an electroless palladium plating process. By adding to this step, a gold plating layer or a palladium plating layer is formed as an outermost layer coating on the surface of the conductive particles. The gold plating layer can be formed by a conventionally known electroless plating method. For example, an electroless plating solution whose pH is adjusted with sodium hydroxide, including tetraethylenediaminetetraacetate, disodium citrate and potassium cyanide, is added to an aqueous suspension of conductive particles to form a gold plating layer There is a number.

The palladium plating layer can also be formed by a conventionally known electroless plating method. For example, a water-soluble palladium compound such as palladium chloride, a reducing agent such as hypophosphorous acid, phosphorous acid, formic acid, acetic acid, hydrazine, boron hydride, an amine borane compound or a salt thereof, and a complexing agent are added to an aqueous suspension of the conductive particles A commercially available electroless palladium plating solution is added, and further, a dispersant, a stabilizer, and a pH buffer are added as necessary. The palladium plating layer can be formed by carrying out reduction electroless plating while adjusting the pH with an acid such as hydrochloric acid or sulfuric acid or a base such as sodium hydroxide. Alternatively, a palladium ion source such as tetraaminepalladium salt, a complexing agent and, if necessary, a dispersant are added to an aqueous suspension of the conductive particles to carry out substitutional electroless plating using substitution reaction between palladium ions and nickel ions And a palladium plating layer may be formed.

As the dispersant used in the reduction type electroless plating or the substitutional electroless plating, the same dispersant as the one exemplified in the above a1 step can be used. As a commercially available electroless palladium plating solution, commercially available products such as those available from Kojima Chemical Co., Ltd., Nippon Kanzen Co., Ltd., and Chuo Chemical Industries Co., Ltd. may be used.

As another post-treatment, the conductive particles may be added to a milling step using a media mill such as a ball mill. By adding the powder to the pulverizing step, the mass occupied by the primary particles with respect to the mass of the powder made of the conductive particles can be easily further improved.

When the conductive particle of the present invention is used as an electrically conductive filler of a conductive adhesive agent as described later, the surface of the electrically conductive particle can further be covered with an insulating resin so as to prevent the occurrence of a short between the conductive particles. The coating of the insulating resin prevents the surface of the conductive particles from being exposed to the maximum in the state where the pressure or the like is not added and is destroyed by the heat and pressure added when the two electrodes are bonded using the conductive adhesive, At least the projections are exposed. The thickness of the insulating resin may be about 0.1 to 0.5 mu m. The insulating resin may cover the whole surface of the conductive particles and may be only partially covering the surface of the conductive particles.

As the insulating resin, those widely known in the technical field can be widely used. Examples of such resins include phenol resins, urea resins, melamine resins, aryl resins, furan resins, polyester resins, epoxy resins, silicone resins, polyamide-imide resins, polyimide resins, polyurethane resins, (Meth) acrylate resin, a polystyrene resin, an acrylonitrile-styrene-butadiene resin, a vinyl resin, a polyamide resin, a polycarbonate resin, A resin, a polyacetal resin, an ionomer resin, a polyether sulfone resin, a polyphenyl oxide resin, a polysulfone resin, a polyvinylidene fluoride resin, ethylcellulose, and cellulose acetate.

Examples of the method for forming the insulating coating layer on the surface of the conductive particles include chemical methods such as core sintering method, interfacial polymerization method, in situ polymerization method and liquid curing coating method, spray drying method, suspension coating method, vacuum evaporation coating method, dry Physical and mechanical methods such as blending, hybridization, electrostatic coalescence, fusion-dispersion cooling and inorganic encapsulation, and physicochemical methods such as interfacial precipitation.

The conductive particles of the present invention thus obtained can be used as an anisotropic conductive film (ACF), a heat seal connector (HSC), a conductive material for connecting electrodes of a liquid crystal display panel to a circuit board of a driving LSI chip . In particular, the conductive particles of the present invention are suitably used as conductive fillers for conductive adhesives.

The above-mentioned conductive adhesive is preferably used as an anisotropic conductive adhesive which is disposed between two substrates on which an electroconductive substrate is formed and which conducts the electroconductive substrate by heating and pressing. The anisotropic conductive adhesive includes the conductive particles of the present invention and an adhesive resin. The adhesive resin is not particularly limited as long as it is insulating and used as an adhesive resin. Thermoplastic resin, and thermosetting property, and it is preferable that the adhesive property is exhibited by heating. Such adhesive resins include, for example, a thermoplastic type, a thermosetting type, and an ultraviolet curing type. There are also so-called semi-thermosetting type, thermosetting type, and ultraviolet curing type, which exhibit an intermediate property between the thermoplastic type and the thermosetting type. Such an adhesive resin can be appropriately selected in accordance with the surface characteristics of the circuit board or the like to be adhered or the use form thereof. Particularly, an adhesive resin comprising a thermosetting resin is preferable in that it has excellent material strength after bonding.

Specific examples of the adhesive resin include ethylene-vinyl acetate copolymer, carboxyl-modified ethylene-vinyl acetate copolymer, ethylene isobutyl acrylate copolymer, polyamide, polyimide, polyester, polyvinyl ether, polyvinyl butyral , Polyurethane, SBS block copolymer, carboxyl modified SBS copolymer, SIS copolymer, SEBS copolymer, maleic acid modified SEBS copolymer, polybutadiene rubber, chloroprene rubber, carboxyl modified chloroprene rubber, styrene-butadiene rubber, isobutyl (1) selected from the group consisting of acrylonitrile-butadiene rubber (hereinafter referred to as NBR), carboxyl-modified NBR, amine-modified NBR, epoxy resin, epoxy ester resin, acrylic resin, phenol resin, Or a combination of two or more of them. Of these, styrene-butadiene rubber, SEBS and the like are preferable as the thermoplastic resin since they have excellent reworkability. As the thermosetting resin, an epoxy resin is preferable. Among them, an epoxy resin is most preferable from the viewpoint of high adhesive strength, excellent heat resistance, excellent electrical insulation, low melting viscosity, and connection at low pressure.

As the epoxy resin, a commonly used epoxy resin can be used as long as it is a polyvalent epoxy resin having two or more epoxy groups in a molecule. Specific examples thereof include novolac resins such as phenol novolak and cresol novolac; polyhydric phenols such as bisphenol A, bisphenol F, bisphenol AD, resorcin and bishydroxy diphenyl ether; ethylene glycol, neopentyl glycol, glycerin, Polyhydric alcohols such as methylol propane and polypropylene glycol, polyamino compounds such as ethylenediamine, triethylenetetramine and aniline, polyhydric carboxy compounds such as adipic acid, phthalic acid and isophthalic acid, and epichlorohydrin or 2- There can be exemplified the glycidyl-type epoxy resin obtainable by reacting chlorohydrin. Aliphatic and alicyclic epoxy resins such as dicyclopentadiene epoxide and butadiene dimer diepoxide; and the like. These may be used singly or in combination of two or more.

Furthermore, as the above-mentioned various kinds of adhesive resins, it is preferable to use a high-purity product in which impurity ions (such as Na and Cl) and hydrolyzable chlorine are reduced, from the viewpoint of prevention of ion migration.

The amount of the conductive particles of the present invention 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 based on 100 parts by mass of the adhesive resin component. When the amount of the conductive particles used is within this range, the connection resistance and the melt viscosity are prevented from increasing, so that the connection reliability is improved and the anisotropy of connection can be sufficiently secured.

The above-mentioned anisotropic conductive adhesive may be blended with known additives in the technical field besides the above-mentioned conductive particles and adhesive resin. And the amount thereof may be within the range known in the art. Examples of other additives include additives such as a tackifier, a reactive additive, an epoxy resin curing agent, a metal oxide, a photoinitiator, a sensitizer, a curing agent, a vulcanizing agent, a deterioration inhibitor, a heat resistant additive, a thermal conductivity improving agent, a softening agent, And the like can be exemplified.

Examples of the tackifier 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 the reactive preparation, that is, the crosslinking agent include polyols, isocyanates, melamine resins, urea resins, urotropins, amines, acid anhydrides, peroxides and the like. As the epoxy resin curing agent, any one having two or more active hydrogens in one molecule can be used without particular limitation. Specific examples thereof include polyamino compounds such as diethylenetriamine, triethylenetetramine, metaphenylenediamine, dicyandiamide, and polyamidoamine; acid anhydrides such as phthalic anhydride, methylnadic acid anhydride, hexahydrophthalic anhydride, And novolak resins such as phenol novolak and cresol novolak. These may be used singly or in combination of two or more. If necessary, a latent curing agent may be used. Examples of the latent curing agent that can be used include imidazole-based, hydrazide-based, boron trifluoride-amine complexes, sulfonium salts, amine imides, salts of polyamines, dicyandiamides, . These may be used singly or as a mixture of two or more kinds.

The anisotropically conductive adhesive is manufactured using a manufacturing apparatus commonly used in the technical field. For example, by mixing the conductive particles and the adhesive resin of the present invention and, if necessary, a curing agent and various additives, and by mixing the adhesive resin in an organic solvent in the case of a thermosetting resin, in the case of a thermoplastic resin, , Specifically about 50 to 130 캜, and more preferably about 60 to 110 캜. The anisotropic conductive adhesive thus obtained may be applied or may be applied in the form of a film.

Example

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the scope of the present invention is not limited to these embodiments. "%" And "part" refer to "% by mass" and "part by mass", respectively, unless otherwise specified.

[Example 1]

(1) First step

(1-1) Pretreatment

A spherical styrene resin having an average particle diameter of 3.0 mu m was used as the core material particle. 9 g thereof was added to 400 ml of a conditioner aqueous solution ("Cleaner Conditioner 231" made by Rohm and Haas Electronic Materials) while stirring. The concentration of the conditioner aqueous solution was 40 mL / L. Subsequently, the mixture was stirred for 30 minutes while applying ultrasonic waves at a liquid temperature of 60 캜 to carry out surface modification and dispersion treatment of the core material particles. The aqueous solution was filtered, and the core material particles washed once with repulping to make 200 mL of the slurry. 200 mL of an aqueous solution of tin chloride was added to this slurry. The concentration of the aqueous solution is 5 × 10 ^- was a ³ mol / L. And the mixture was stirred at room temperature for 5 minutes to carry out a sensitization treatment in which tin ions were adsorbed on the surface of the core material particles. Subsequently, the aqueous solution was filtered and rinsed with water once. Subsequently, the core material particles were made into 400 mL of a slurry and maintained at 60 캜. 2 mL of 0.11 mol / L palladium chloride aqueous solution was added while stirring the slurry using ultrasonic waves in combination. The same stirring state was maintained for 5 minutes to carry out an activation treatment for trapping palladium ions on the surface of the core material particles.

(1-2) Bottom film formation treatment with protrusions

(1-2-1) a1 Process

3 L of an electroless nickel-phosphorus plating bath consisting of an aqueous solution of 20 g / L of sodium tartrate, 4.5 g / L of nickel sulfate hexahydrate, 5.4 g / L of sodium hypophosphite and 5 g / L of polyethylene glycol The temperature was raised to 70 占 폚, and 9 g of the core material particles carrying palladium was charged into this electroless plating bath to start the a1 step. The mixture was stirred for 5 minutes to confirm that the foaming of hydrogen stopped, and the a1 step was completed.

(1-2-2) a2 Process

300 mL of a mixed aqueous solution (second aqueous solution) containing 224 g / L of nickel sulfate aqueous solution (first aqueous solution), 210 g / L of sodium hypophosphite and 80 g / L of sodium hydroxide was used, Was added to the slurry of the core material particles obtained in the above-mentioned manner by a metering pump to initiate the electroless plating a2 step. All the addition rates were 2.5 mL / min. And the stirring was continued for 5 minutes while maintaining the temperature at 70 캜. Subsequently, the solution was filtered, and the filtrate was washed three times, and then dried with a vacuum dryer at 100 ° C to obtain a bottom coat coated particle having a bottom coat made of a nickel-phosphorus alloy. The film thickness of the bottom film was measured by the following method, and it was found to be 100 nm.

[Measurement method of thickness of bottom film]

The bottom coat-coated particles before top coat coating was immersed in aqua regia to dissolve the bottom coat, and the bottom coat component was subjected to ICP or chemical analysis, and the thickness (μm) of the bottom coat was calculated from the following formulas 3 and 4. The value obtained by this method is a calculated value, and when the protrusion is formed on the bottom coating, it means the thickness when the protrusion is virtually flattened.

J = [(r + t) ^{3 -} r ³ ] d ₁ / r ³ d ₂

J = W / (100-W)

Wherein, r is the radius of the core material particles (μm), t is (μm) The thickness of the bottom film, d ₁ is the density of the bottom film ^{(g / μm 3), d} 2 is the density (g / μm of the core material particles ³ ), W is the total content (% by mass) of the content of nickel and phosphorus in the bottom coat covering particles, and J is the mass ratio of the bottom coating to the core material particles.

(2) Second Step (Upper Layer Film Forming Process Having Projections)

An electroless nickel-tungsten-zinc alloy consisting of 20 g / L of sodium citrate, 2.5 g / L of nickel sulfate, 0.5 g / L of sodium tungstate, 5.0 g / L of glycolic acid and 2.7 g / L of sodium hypophosphite, Was prepared. 1 L of this plating bath was heated to 80 캜 and adjusted to pH 9, and 6 g of the bottom coat covering particles obtained in the first step was charged with stirring to perform electroless plating. The plating time was 30 minutes. Thus, the surface of the bottom coating was subjected to electroless plating treatment. After the completion of the treatment, the liquid was separated, washed three times, and then vacuum-dried at 110 캜 to obtain conductive particles coated with a nickel-tungsten-phosphorus alloy film on the bottom film made of nickel-phosphorus alloy film. The film thickness of the upper layer coating film was measured by the following method and found to be 25 nm.

[Method of Measuring Thickness of Upper Layer Film]

The conductive particles were immersed in aqua regia to dissolve the entire coating, and ICP or chemical analysis of the total coating component was carried out, and the thickness (μm) of the entire coating was calculated from the following formulas 5 and 6.

J '= [(r + t') ^{3 -} r ³ ] d ₁ / r ³ d ₂

J '= W' / (100-W ') <

Wherein, r is the core material a radius (μm), t 'is the density of the entire film thickness (μm), d ₁ is around the film density (g / μm ^3), d ₂ is the core material particles of the particles (g / ³ μm), W 'is the sum (% by weight of nickel, tungsten, molybdenum and phosphorus content of the conductive particles), J' is a mass ratio of the former coating on the core material particles.

The thickness T (μm) of the upper coating film was calculated by the following formula (7) using the thickness t '(μm) of the total coating and the thickness t (μm) of the bottom coating. The value obtained by this method is a calculated value, and in the case where a protrusion is formed on the upper layer coating, it means the thickness when the protrusion is virtually evenly formed.

[Equation 7] T = t'-t

[Examples 2 to 14]

Conductive particles were obtained in the same manner as in Example 1, except that the conditions shown in the following Table 1 were used. The conductive particles thus obtained had projections on both the bottom coating and the upper coating, as in the case of the conductive particles of Example 1.

[Table 1]

[Example 15]

(1) First step

(1-1) Pretreatment

Was carried out in the same manner as in Example 1.

(1-2) Bottom film formation treatment having almost uniform thickness

300 mL each of a mixed aqueous solution (second aqueous solution) containing 224 g / L nickel sulfate aqueous solution (first aqueous solution), 210 g / L sodium hypophosphite and 80 g / L sodium hydroxide was used. These were added to the slurry of the pretreated core material particles continuously by fractionation pump to start the electroless plating step. All the addition rates were 2.5 mL / min. And the stirring was continued for 5 minutes while maintaining the temperature at 70 캜. Subsequently, the solution was filtered, the filtrate was washed three times, and then dried with a vacuum dryer at 100 ° C to obtain a bottom coat-coated particle having a bottom coat made of a nickel-phosphorus alloy. The film thickness of the bottom coating film was found to be 100 nm by the above-mentioned method.

(2) Second Step (Upper Layer Film Forming Process Having Projections)

Was carried out in the same manner as in Example 1. The film thickness of the formed upper coating film was measured by the above-mentioned method and found to be 25 nm.

[Examples 16 to 24]

Conductive particles were obtained in the same manner as in Example 15, except that the conditions shown in the following Table 2 were used. The obtained conductive particles had a flat bottom coating having a substantially uniform thickness and an upper coating having a projection as in the case of the conductive particles of Example 15.

[Comparative Examples 1 to 6]

Conductive particles were obtained in the same manner as in Example 15 except that the conditions shown in the following Table 2 were used. The obtained conductive particles had a flat bottom coating having a substantially uniform thickness and a flat upper coating having a substantially uniform thickness.

[Table 2]

[evaluation]

The phosphorus content of the bottom coating film, the phosphorus content of the upper coating film, the tungsten content of the upper coating film, the molybdenum content of the upper coating film, the presence or absence of the crystal structure of each of the bottom coating film and the upper coating film, And the conductivity at room temperature and under high temperature and high humidity were respectively measured and evaluated. Measurement and evaluation were carried out by the following methods. The results are shown in Table 3 below.

[Phosphorus content of bottom coating]

The bottom coat-coated particles before top coat coating was immersed in aqua regia to dissolve the bottom coat, and the content of the film component was determined by ICP or chemical analysis to determine the phosphorus content (%).

[Phosphorus content, tungsten content, molybdenum content in the upper layer film]

The coating film was subjected to ICP or chemical analysis to obtain a nickel content A (%), a phosphorus content B (%), a tungsten content C (%) and a molybdenum content D (%) Was calculated. Further, the nickel content A '(%) and the phosphorus content B' (%) were calculated from the ICP analysis when the bottom coating treatment was carried out. Using these, the phosphorus content E (%) in the upper coating film is calculated by the following Expression 8, and the tungsten content F (mass%) is calculated by the following Expression 9 and the molybdenum content G Mass%) was calculated.

E = (B-B ') / (A-A' + B-B '+ C + D) 100

F = C / (A-A '+ B-B' + C + D) x 100

G = D / (A-A '+ B-B' + C + D) 100

[Crystal structure of bottom coating and upper coating]

The crystal structure of the bottom coating was obtained by performing X-ray diffraction measurement on the bottom coating-coated particles before covering the upper coating. X-ray diffraction measurement was carried out under the conditions of a tube voltage of 40 kV, a tube current of 40 mA and an X-ray: CuK? (Wavelength? = 1. 541 ANGSTROM) using X-ray diffraction UltimaIV manufactured by Rigaku. When the diffraction peak of the nickel-phosphorus alloy was confirmed by X-ray diffraction measurement, it was judged that a crystal structure was present. The crystal structure of the upper layer coating is obtained by thinning the coating with FIB or the like and then coating a film having a depth of several nm at the uppermost layer of the upper layer coating film using a measuring instrument such as X- When the diffraction peaks of the nickel or nickel alloy were confirmed, it was judged that there was a crystal structure.

[Evaluation of conductivity under room temperature and high temperature and high humidity]

100 parts of an epoxy resin, 150 parts of a curing agent and 70 parts of toluene were mixed to prepare an insulating adhesive. 15 parts of conductive particles were blended with the insulating adhesive to obtain a paste. This paste was applied on a silicone-treated polyester film using a bar coater and dried. Using the obtained coated film, electrical connection was made between the glass having the entire surface thereof deposited with aluminum and the polyimide film substrate having a copper pattern having a pitch of 20 mu m. The conductivity of the conductive particles was evaluated by measuring the conduction resistance between them. The conduction resistance was measured at room temperature (25 캜, 50% RH) and at high temperature and high humidity (85 캜, 85% RH, after 500 hours of storage).

[Table 3]

As is clear from the results shown in Table 3, it can be seen that the conductive particles (the present invention) obtained in each example had a lower resistance value and higher conductivity than the conductive particles obtained in the comparative examples. It can also be seen that the conductive particles obtained in each of the Examples had a smaller increase in resistance value after storage under high temperature and high humidity than the conductive particles obtained in Comparative Example. Particularly, as apparent from the comparison between Examples 1 to 14 and Examples 15 to 24, the conductive particles of Examples 1 to 14 in which protrusions were formed in both the bottom coating and the upper coating were formed only in the upper layer coating It is understood that the resistance value is further lower and the conductivity is further higher than that of the conductive particles of Examples 15 to 24,

Claims (9)

In the conductive particle in which the conductive film is formed on the surface of the core material particles,
Wherein the conductive coating has a bottom coating contacting the surface of the core material particles and an upper coating contacting the surface of the bottom coating,
Wherein the bottom coating comprises nickel and phosphorus,
Wherein the bottom film is a smooth film having no concavo-convex shape,
Wherein the upper layer coating has a crystal structure and includes nickel, phosphorus, and at least one kind of metal M (except nickel)
Wherein the upper coating film has a flat portion and a plurality of protrusions projecting from the flat portion and continuing from the flat portion, wherein the flat portion and the protrusions are made of the same material, . The method according to claim 1,
Wherein the bottom film has a crystal structure and the content of phosphorus is 1% by mass or more and less than 10% by mass. The method according to claim 1,
Wherein the bottom film has an amorphous structure and a phosphorus content of 10 to 18 mass%. The method according to any one of claims 1 to 3,
Wherein the conductive coating further has an outermost layer coating that is in contact with the surface of the upper coating layer and is made of a noble metal. The method according to any one of claims 1 to 3,
And the metal M has a Mohs hardness of 4 or more. The method of claim 5,
And the metal M is one or more kinds selected from tungsten, palladium, platinum and molybdenum. A conductive material comprising the conductive particles according to any one of claims 1 to 3 and an insulating resin. In the method for producing conductive particles according to claim 1,
An electroless plating bath containing a reducing agent comprising a nickel source and a phosphorus compound is used to form a smooth bottom coating free of irregularities including nickel and phosphorus on the surface of the core material particles by electroless plating,
Nickel, phosphorus, and phosphorus were deposited on the surface of the bottom film by electroless plating using an electroless plating bath containing a nickel source, a metal M (except nickel) source and a phosphorus compound, and a hydroxy acid, And a plurality of protrusions protruding from the flat portion and continuing from the flat portion, wherein the flat portion and the protrusion are made of the same material And a step of forming an upper coat film constituting the conductive particles. The method of claim 8,
Wherein the hydroxy acid is glycolic acid, lactic acid or glyceric acid.