JP5973257B2 - Conductive particles and conductive material containing the same - Google Patents

Description

  The present invention relates to conductive particles and a conductive material including the same.

  As conductive particles used as a material for an anisotropic conductive film or anisotropic conductive paste, those having a conductive film formed on the surface of core particles are generally known. A nickel plating film is often used as the conductive film. In order to further improve various performances of such conductive particles, a nickel plating film having a multilayer structure has been proposed.

  For example, Patent Document 1 discloses that a nickel film formed on the surface of core material particles includes a first layer formed on the surface of core material particles and a second layer formed adjacent to the first layer. In other words, conductive particles having different orientation directions of grain boundaries in the first layer and the second layer have been proposed. This conductive particle has the advantage that the adhesion between the nickel coating and the core particle is improved, the heat resistance of the conductive particle is improved, and the increase in electrical resistance is small even when stored at a high temperature for a long time. is there.

  Patent Document 2 discloses that a conductive layer made of a nickel coating has an amorphous structure nickel-phosphorous plating layer in contact with the surface of the core material particles, and a crystalline structure nickel-tungsten in contact with the surface of the amorphous structure nickel-phosphorus plating layer. Conductive particles having a phosphor plating layer have been proposed. This document describes that the conductive particles have high adhesion between the core particles and the conductive layer and are excellent in impact resistance and conductivity.

Japanese Patent Laid-Open No. 2004-197160 JP 2007-173075 A

  By the way, when a nickel film is formed on the surface of the core material particles, a method is generally employed in which a plating solution containing nickel is used and nickel is reduced and deposited on the surface of the core material particles by a reducing agent. Hypophosphite is often used as the reducing agent. When hypophosphite is used as the reducing agent, phosphorus is eventually contained in the nickel film formed by reduction deposition. The presence of phosphorus in the nickel film contributes to a decrease in the conductivity of the nickel film. From this point of view, it is desirable that the amount of phosphorus present is as small as possible. On the other hand, when there is a small amount of phosphorus, the conductive particles tend to be magnetically aggregated due to the inherent magnetism of nickel, and as a result, the dispersibility of the conductive particles tends to decrease. Become. When the conductive particles are used as, for example, an anisotropic conductive film or an anisotropic conductive paste, the decrease in dispersibility may cause a short circuit of the circuit. In Patent Document 2 described above, the contents of phosphorus in the nickel-phosphorus layer of the underlying layer and the nickel-tungsten-phosphorus layer of the upper layer in the nickel film of the conductive particles described in the same document are prescribed, With that content, it is not easy to satisfy both conductivity and dispersibility at the same time.

  Therefore, the subject of this invention is providing the electroconductive particle which various performances improved further compared with the electroconductive particle of the prior art mentioned above.

The present invention provides conductive particles in which a conductive film is formed on the surface of the core material particles.
The conductive film has a base film in contact with the surface of the core particles, and an upper film in contact with the surface of the base film,
The undercoat includes nickel and phosphorus,
The undercoat has a flat portion and a plurality of protrusions protruding from the flat portion and being a continuous body from the flat portion, and the flat portion and the protrusion are made of the same material. Has been
The upper film has a crystal structure, and includes nickel, phosphorus, and one or more kinds of metals M (excluding nickel),
The upper layer coating is a flat portion projects from the flat part, and a plurality of protrusions that is a continuum from the flat portion, and the flat portion and the protrusion portion from the same material The present invention provides conductive particles characterized by being configured.

Furthermore, the present invention is the above-described method for producing conductive particles, which uses an electroless plating bath containing a nickel source and a reducing agent comprising a phosphorus compound, and contains nickel and phosphorus on the surface of the core material particles by electroless plating. Form a base film with protrusions ,
Using an electroless plating bath containing a nickel source, a metal M (excluding nickel) source, a reducing agent composed of a phosphorus compound and a hydroxy acid, nickel, phosphorus and metal M ( Except for nickel.) And a plurality of protrusions protruding from the flat part and being a continuous body from the flat part, and the flat part and the protrusions are The present invention provides a method for producing conductive particles, which includes a step of forming an upper layer film made of the same material.

  According to the present invention, conductive particles having high conductivity are provided. In particular, conductive particles in which a decrease in conductivity is suppressed even after storage at high temperature and high humidity are provided. Therefore, when the conductive particles of the present invention are used, for example, as a material for an anisotropic conductive film or anisotropic conductive paste, the conductive film or conductive paste has high conductivity and is reliable in harsh environments. It becomes a thing with high property.

  Hereinafter, the present invention will be described based on preferred embodiments thereof. As described above, the conductive particles of the present invention include core material particles, and a conductive film having a base film that contacts the surface of the core material particles and an upper film that contacts the surface of the base film. The upper layer film has a crystal structure and contains nickel, phosphorus, and one or more kinds of metals M (excluding nickel). The upper film has a plurality of protrusions. In the present invention, by combining the upper layer film having such a configuration with a base film containing nickel and phosphorus, the conductivity of the particles, particularly the conductivity in a harsh environment of high temperature and high humidity is increased. .

  As described above, the base film contains phosphorus. The phosphorus content in the base film can be appropriately set according to the specific use of the conductive particles of the present invention. For example, by setting the phosphorus content of the base film 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 base film is preferably 8% by mass or less, more preferably 7% by mass or less, and particularly preferably 6% by mass or less. However, even if the phosphorus content of the base film is relatively high, such as 5% by mass or more, the presence of the upper film having the above-described structure can keep the conductivity high enough to satisfy. In the presence of the upper film, even if the phosphorus content of the base film is reduced to less than 10% by mass, magnetic aggregation can be effectively suppressed and good dispersibility of the conductive particles is maintained. be able to. Although the reason why such an effect of maintaining dispersibility is exerted is not clear, it is considered that one reason is that the metal M in the upper film prevents aggregation due to the magnetism of nickel.

  The phosphorus content in the undercoat can also be set to 10% by mass or more. For example, it is preferable to set it as 10-18 mass%, and it is still more preferable to set it as 10-15 mass%. Setting the phosphorus content in the undercoat to be high is advantageous from the viewpoint of making it difficult for the conductive particles of the present invention to cause magnetic aggregation. On the other hand, setting the phosphorus content in the undercoat to be high may have a negative effect from the viewpoint of improving the conductivity of the undercoat. However, in the present invention, the conductivity of the conductive particles as a whole is ensured by forming the upper layer film having the structure described above on the surface of the base film.

  Regardless of the above-described range of phosphorus content, the undercoat is made of a nickel-phosphorus alloy. A nickel-phosphorus alloy is an alloy produced when a phosphorous compound such as hypophosphorous acid or a salt thereof is used as a nickel reducing agent during formation of a base coating in the conductive particle manufacturing process described later. It is preferable that the base film contains only nickel and phosphorus and does not substantially contain other elements. The phrase “substantially free of other elements” means that when the base film is subjected to elemental analysis, the ratio of elements other than nickel and phosphorus is 1% by mass or less. The nickel content in the undercoat is the remainder obtained by subtracting the above-described phosphorus content from the total undercoat.

  As described later, the nickel content and the phosphorus content in the base film are obtained by dissolving the core material particles formed up to the base film in an acid and conducting ICP or chemical analysis on the base film component in the obtained solution. Can be measured.

  The undercoat has a crystalline structure or an amorphous structure. The crystal structure here is a crystal structure of a nickel-phosphorus alloy. Moreover, having an amorphous structure means that the undercoat has no crystal structure. When the ground film has a crystal structure, the conductivity of the conductive particles is improved. On the other hand, when the undercoat has an amorphous structure, magnetic aggregation of the conductive particles is suppressed and dispersibility is improved.

  Whether the base film has a crystal structure or an amorphous structure can be determined by, for example, performing XRD measurement on the core material particles formed up to the base film. Whether the base film has a crystalline structure or an amorphous structure depends on, for example, the composition of the plating bath when the base film is formed by electroless plating in the method for producing conductive particles described later. Specifically, the lower the concentration of the phosphorus compound, which is a reducing agent used during electroless plating, in the plating bath, the easier it is to form a base film having a crystal structure. Conversely, the higher the concentration of the phosphorus compound in the plating bath, the easier it is to form a base film having an amorphous structure. For example, when a plating bath containing a phosphorus compound at a concentration such that the amount of phosphorus contained in the undercoat is less than 10% by mass is used, an undercoat having a crystal structure is easily formed. Conversely, when a plating bath containing a phosphorus compound at a concentration such that the amount of phosphorus contained in the undercoat is 10% by mass or more is used, an undercoat having an amorphous structure is likely to be formed.

  The undercoat can be formed on the surface of the core particle with a substantially uniform thickness. Instead, a plurality of protrusions can be formed to form the base film in a concavo-convex shape. In the latter case, the base film has a flat portion and a plurality of protrusions that protrude from the flat portion and are continuous from the flat portion, and the flat portion and the protrusion are the same. The material is preferably composed of a nickel-phosphorus alloy. A “continuum” is a portion in which the protrusion and flat portion of the base film are formed by a single process, and there is a portion that impairs the sense of unity such as a seam between the flat portion and the protrusion of the base film. It means not existing. When the ground film is formed in a concavo-convex shape, the concavo-convex shape is reflected on the surface of the conductive particles. Therefore, when conducting the electrode using the conductive particles of the present invention, the protrusion can break through the oxide film formed on the electrode surface, and the connection resistance can be reduced. Moreover, since the protrusions are made of the same material as the flat part of the base film and are continuous with the flat part of the base film, the strength of the protrusions of the conductive particles is ensured, so that pressure is applied to the conductive particles. Even if added, the protrusions are hard to break.

  In the conductive particles, it can be confirmed by observing the cross section of the conductive particles with a microscope that the base film has a substantially uniform thickness, or that the base film has flat portions and protrusions.

  As described above, the upper layer film that is in direct contact with the surface of the base film contains nickel, phosphorus, and one or more kinds of metals M (excluding nickel). The metal M is preferably a transition metal, and more preferably has a Mohs hardness higher than that of nickel. In particular, it is preferable to use a metal M having a Mohs hardness of 4 or more because an advantageous effect that the conductivity is further increased can be obtained. The reason for this is that the upper layer film becomes hard, so when using an anisotropic conductive film containing conductive particles to establish electrical continuity between the electrodes, the resin present at the interface between the conductive particles and the electrodes is eliminated. And the conductive particles easily break through the oxide film present on the electrode surface.

  Preferable examples of the metal M include transition metal elements of Groups 6, 8, 9, and 10 of the periodic table. Particularly preferred are palladium, cobalt, rhodium, iron, platinum, iridium, tungsten, molybdenum and chromium. Among them, the use of a metal having a Mohs hardness of 4 to 10, for example, one or more selected from tungsten, molybdenum, palladium, and platinum is preferable because the conductivity can be further enhanced. In particular, it is preferable to use one or more selected from tungsten and molybdenum. In addition, it is more preferable in terms of conductivity to use not only one type but also two or more types simultaneously.

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

  The upper film has a crystal structure. Thereby, the electroconductivity of electroconductive particle improves. In particular, in addition to the upper layer film having a crystal structure, it is preferable that the above-described undercoat film also has a crystal structure, since the conductive particles are further improved in conductivity. The crystal structure of the upper film can be either metallic nickel, nickel-phosphorus alloy or nickel-phosphorus-metal M alloy. Whether the upper film has a crystal structure is determined by measuring the film with a depth of several nanometers from the particle surface by X-ray diffraction after thinning the film with FIB, etc., and observing diffraction peaks such as nickel It is judged by whether or not it is done. Further, whether or not the upper layer film contains the metal M is determined by dissolving conductive particles with dilute nitric acid or the like, collecting a plurality of eluates over time, and analyzing elements contained in the eluate at each time point. This can be confirmed.

  In order for the upper layer film 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 film is formed by electroless plating may be appropriately adjusted. Specifically, when a phosphorus compound is used as the reducing agent used during electroless plating, the lower layer concentration of the phosphorus compound in the plating bath is more likely to form an upper film having a crystal structure. For example, when a plating bath containing a phosphorus compound at a concentration such that the amount of phosphorus contained in the upper layer film is less than 10% by mass is used, an upper layer film having a crystal structure is easily formed.

  The upper layer film has an uneven surface. Specifically, the upper layer film has a flat portion and a plurality of protrusions protruding from the flat portion and being a continuous body from the flat portion, and the flat portion and the protrusion are the same. It is preferable that it is made of a material. Each protrusion may be in the form of a single continuous body made of a material constituting the upper layer film, or a particle connected body in which a plurality of particles made of the material constituting the upper layer film are connected in a row. The grain boundary may be observed between the grains. Since the surface of the upper layer film has an uneven shape, the uneven shape is reflected on the surface of the conductive particles. Therefore, when conducting the electrode using the conductive particles of the present invention, the protrusion can break through the oxide film formed on the electrode surface, and the connection resistance can be reduced. Moreover, since the protrusions are made of the same material as the flat part of the upper film and are continuous with the flat part of the upper film, the strength of the protrusions of the conductive particles is ensured, so that pressure is applied to the conductive particles. Even if added, the protrusions are hard to break. In particular, if the surface of the undercoat described above also has an uneven shape, the uneven shape obtained by superimposing the uneven shape and the concave shape of the surface of the upper layer film is reflected on the surface of the conductive particles. This makes it possible to break through the oxide film more easily. In addition, the damage to the protrusions is less likely to occur. In this case, the position of the protrusion formed on the base film and the position of the protrusion formed on the upper film may be the same or different.

  Regarding the protrusions of the upper film, the meaning of “continuum” in the “plurality of protrusions that are continuous from the flat portion” described above is a continuum of protrusions formed on the base film described above. It is synonymous with. Therefore, for example, a flat upper layer film is formed on the surface of the base film, and core particles for forming protrusions, for example, a non-metallic inorganic material such as metal, metal oxide, and graphite, a conductive polymer, etc. are attached to the core film. Protrusions formed using grains as starting points of growth are not included in the continuum referred to in the present invention because the flat portions and the protrusions are not formed by a single step. However, conductive particles having protrusions formed by attaching such core particles to the upper film and using the core particles as growth starting points, that is, conductive particles in which the flat portion and the protrusions are not continuous, It should be noted that it is within the scope of the present invention.

  In the conductive particles, it can be confirmed by observing the cross section of the conductive particles with a microscope that the upper film has a flat portion and a protrusion.

  As described above, in the conductive particles of the present invention, at least the protrusions reflecting the uneven shape of the protrusions formed on the upper layer film are formed on the surface. The protrusion H preferably has an average height H of 20 nm or more, particularly 50 nm or more. Although the number of protrusions depends on the particle size of the conductive particles, it is preferably 1 to 20000, particularly 5 to 5000 per particle, from the viewpoint of further improving the conductivity of the conductive particles. . The aspect ratio of the protrusion is preferably 0.5 or more, more preferably 1 or more. A large aspect ratio of the protrusions is advantageous because it can easily break through the oxide film described above. In addition, when an anisotropic conductive film is formed using conductive particles, if the aspect ratio of the protrusion is large, the resin exclusion property is increased, so that the conductivity is considered to be increased. The aspect ratio is a ratio defined by the ratio of 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 protrusion formed on the surface of the conductive particles is as described above, and the length D of the base of the protrusion is preferably 5 to 500 nm, particularly preferably 10 to 400 nm. The length H is preferably 5 to 500 nm, particularly 10 to 400 nm.

  The above aspect ratio measurement method is as follows. The conductive particles are enlarged and observed with an electron microscope. The length D and height H of the base are measured for at least one protrusion for each particle. In this case, it is important from the viewpoint of accurate measurement of dimensions that the projections present at the periphery of the particles are measured rather than the projections present at the center of the particles in the observed image. Such a measurement is performed on at least 20 different particles. The data of a plurality of aspect ratios thus obtained are arithmetically averaged, and the value is used as the aspect ratio. In addition, since the cross section of the protrusion has a shape with small anisotropy (for example, a substantially circular shape), there is little concern that the value of the length D of the protrusion base varies depending on the observation angle of the particles.

  With respect to the protrusions formed on the surface of the conductive particles, one having a height H of 50 nm or more may be 1 to 10,000, particularly 2 to 2000, especially 2 to 20 per particle. From the viewpoint of further improving the conductivity of the conductive particles. From the same viewpoint, the aspect ratio of the protrusion having a height H of 50 nm or more is preferably 0.3 to 3.0, particularly 0.5 to 2.0, and particularly preferably 0.5 to 1.0.

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

  The conductive particles of the present invention in which the conductive film has the above-described structure are preferably spherical in shape. The term “spherical” as used herein refers to a spherical shape when the appearance of the particles is observed except for the above-described protrusions.

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

  Next, the suitable manufacturing method of the electroconductive particle of this invention is demonstrated. This production method is greatly divided into two steps: (1) a first step of forming a base coating on the surface of the core particles, and (2) a second step of forming an upper coating on the particles obtained in the first step. Separated.

  In the first step, prior to that, pretreatment for supporting a noble metal on the surface of the core material particles is performed. There is no restriction | limiting in particular in the kind of core material particle, Both organic substance and an inorganic substance are used. In order to satisfactorily form an undercoat, the core particles are preferably dispersible in water. Accordingly, the core particles are preferably substantially insoluble in water, and more preferably not dissolved or denatured in acid or alkali. “Dispersible in water” means that a suspension substantially dispersed in water can be formed to such an extent that the base film can be formed on the surface of the core material particles by ordinary dispersing means such as stirring.

  The shape of the core particles greatly affects the shape of the target conductive particles. Since the thickness of the base coating and the upper coating covering the surface of the core particles is thin, the shape of the core particles is almost directly reflected in the shape of the conductive particles. Since it is preferable that the conductive particles have a spherical shape as described above, the shape of the core particles is also preferably a spherical shape.

  When the core material particles are spherical, the particle size of the core material particles greatly affects the particle size of the target conductive particles. Since the thickness of the base coating and the upper coating covering the surface of the core particle is thin, the particle size of the core particle is substantially reflected in the particle size of the conductive particles. From this viewpoint, the particle diameter of the core particles can be set to be approximately the same as the particle diameter of the target conductive particles. Specifically, it is preferably 0.5 to 1000 μm, particularly 1 to 500 μm, particularly 1 to 100 μm. The particle diameter of the core particles can be measured by the same method as that of the conductive particles.

There is a range in the particle size distribution of the powder composed of the core material particles measured by the method described above. In general, the width of the particle size distribution of the powder is represented by a coefficient of variation represented by the following formula (1).
Coefficient of variation (%) = (standard deviation / average particle diameter) × 100 (1)
A large coefficient of variation indicates that the distribution is wide, while a small coefficient of variation indicates that the particle size distribution is sharp. In the present invention, it is preferable to use the core particles having a coefficient of variation of 30% or less, particularly 20% or less, particularly 10% or less. 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 for connection is increased.

  Specific examples of the core particles include, as inorganic substances, metals (including alloys), glass, ceramics, silica, carbon, metal or non-metal oxides (including hydrates), metal silicates including aluminosilicates, Examples thereof include metal carbide, metal nitride, metal carbonate, metal sulfate, metal phosphate, metal sulfide, metal acid salt, metal halide, and carbon. Organic materials include natural fibers, natural resins, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polybutene, polyamide, polyacrylate, polyacrylonitrile, polyacetal, ionomer, polyester, and other thermoplastic resins, alkyd resins, phenol resins, urea Examples of the resin include melamine resin, benzoguanamine resin, xylene resin, silicone resin, epoxy resin, and diallyl phthalate resin. These may be used alone or in a mixture of two or more. A composite material of an organic substance and an inorganic substance can also be used. Examples include styrene silica composite resin and acrylic silica composite resin.

The other physical properties of the core particles are not particularly limited, but when the core particles are resin particles, the value of K defined by the following formula (2) is 10 kgf at 20 ° C. / Mm ^{2 to} 10000 kgf / mm ² , and the recovery rate after 10% compression deformation is preferably in the range of 1% to 100% at 20 ° C. This is because, by satisfying these physical property values, the electrodes can be sufficiently brought into contact with each other without being damaged when the electrodes are crimped together.

K value (kgf / mm ² ) = (3 / √2) × F × S ^−3/2 × R ^−1/2 (2)
F and S represented by the formula (2) are respectively a load value (kgf) and compression at 10% compression deformation of the microsphere when measured by a micro compression tester MCTM-500 (manufactured by Shimadzu Corporation). Displacement (mm), and R is the radius (mm) of the microsphere.

  It is preferable that the surface of the core particle is modified so that the surface thereof has a precious metal ion capturing ability or a precious metal ion capturing ability. The noble metal ions are preferably palladium or silver ions. Having a precious metal ion scavenging ability means that the precious metal ion can be captured as a chelate or salt. 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 particle, the surface of the core particle is capable of capturing noble metal ions. Have In the case of modifying the surface so as to have the ability to trap noble metal ions, for example, a method described in JP-A-61-64882 can be used.

Using such core material particles, a noble metal is supported 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 traps noble metal ions on the surface of the particles. The concentration of the noble metal salt is sufficiently in the range of 1 × 10 ⁻⁷ to 1 × 10 ⁻² mol per 1 m ² of the particle surface area. The core particles in which the 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 to the suspension so that noble metal ions are reduced. As a result, the noble metal is supported on the surface of the core particles. As the reducing agent, for example, sodium hypophosphite, sodium borohydride, potassium borohydride, dimethylamine borane, hydrazine, formalin and the like are used, and selected from these based on the constituent material of the desired undercoat It is preferred that

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

  The core film particles that have been pretreated in this way are subjected to a base film forming process in the first step. Hereinafter, as the undercoat film forming process, (a) a process for forming an undercoat film having a protrusion (hereinafter also referred to as a process), and (b) a process for forming a base film having a smooth surface (hereinafter referred to as b process). 2 types) are also described.

As a process, the following a1 process and a2 process are performed.
Step a1 is an electroless nickel plating step in which an aqueous slurry of core material 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 a1 step, self-decomposition of the plating bath occurs simultaneously with the formation of the base film on the core particles. Since this self-decomposition occurs in the vicinity of the core particle, the self-decomposition product is trapped on the surface of the core particle when the base film is formed, thereby generating nuclei of microprojections, and at the same time, the formation of the base film is performed. Made. A protrusion grows with the nucleus of the generated fine protrusion as a base point.

  In the step a1, the above-described core material particles are preferably sufficiently dispersed in water in a range of preferably 1 to 500 g / L, more preferably 5 to 300 g / L to prepare an aqueous slurry. The dispersing operation can be usually performed using stirring, high-speed stirring, or a shearing dispersion device such as a colloid mill or a homogenizer. Further, ultrasonic waves may be used in combination with the dispersion operation. If necessary, a dispersing agent such as a surfactant may be added in the dispersing operation. Next, the aqueous slurry of the core material particles subjected to the dispersion operation is added to an electroless nickel plating bath containing a nickel salt, a reducing agent, a complexing agent, various additives, and the like, and the electroless plating a1 step is performed.

  Examples of the dispersant described above include nonionic surfactants, zwitterionic surfactants, and / or water-soluble polymers. As the nonionic surfactant, polyoxyalkylene ether surfactants such as polyethylene glycol, polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, and the like can be used. As the zwitterionic surfactant, a betaine surfactant such as alkyldimethylacetic acid betaine, alkyldimethylcarboxymethylacetic acid 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 can be used alone 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) although it depends on the type. In particular, the amount of the dispersant used is preferably 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 base film.

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

  Examples of complexing agents include citric acid, hydroxyacetic acid, tartaric acid, malic acid, lactic acid, gluconic acid or carboxylic acids (salts) such as alkali metal salts and ammonium salts thereof, amino acids such as glycine, and amines such as ethylenediamine and alkylamine. Compounds having a complexing action on nickel ions, such as acid, other ammonium, EDTA or pyrophosphoric acid (salt) are used. These can be used individually by 1 type or in combination of 2 or more types. The concentration 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 rapidly when an aqueous slurry of core particles is added, and is accompanied by the generation of hydrogen gas. The electroless plating a1 process ends when the generation of the hydrogen gas is not completely recognized.

  Next, in step a2, whether (i) a first aqueous solution containing one of a nickel salt, a reducing agent and an alkali and a second aqueous solution containing the remaining two are used following the step a1. Or (ii) using a first aqueous solution containing a nickel salt, a second aqueous solution containing a reducing agent, and a third aqueous solution containing an alkali, and each of these aqueous solutions are simultaneously and over time, Add to the solution and perform electroless nickel plating. When these liquids are added, the plating reaction starts again. By adjusting the amount of addition, the base film to be formed can be controlled to a desired film thickness. After completion of the addition of the electroless nickel plating solution, the reaction is completed by continuing stirring while maintaining the solution temperature for a while after generation of hydrogen gas is not completely observed.

  In the case of (i), it is preferable to use a first aqueous solution containing a nickel salt and a second aqueous solution containing a reducing agent and an alkali, but the present invention is not limited to this combination. In this case, the first aqueous solution contains no reducing agent and alkali, and the second aqueous solution contains no nickel salt. As the nickel salt and the reducing agent, those described above can be used. As the alkali, for example, an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide can be used. The same applies to the case (ii).

  In the case of (ii) above, the first to third aqueous solutions each contain a nickel salt, a reducing agent, and an alkali, and each aqueous solution contains no other two components other than the components.

  In any case of (i) and (ii), the concentration of the nickel salt in the aqueous solution is preferably 10 to 1000 g / L, particularly 50 to 500 g / L. The concentration of 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 using a boron compound as a reducing agent, it is preferable that it is 5-200 g / L, especially 10-100 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 is preferably 5 to 500 g / L, more preferably 10 to 200 g / L.

  The step a2 is continuously performed after the end of the step a1, but instead of this, the step a1 and the step a2 may be intermittently performed. In this case, after completion of the step a1, the core material particles and the plating solution are separated by a method such as filtration, and the core material particles are newly dispersed in water to prepare an aqueous slurry, and the complexing agent is added thereto. Preferably, an aqueous solution dissolved in a concentration range of 1 to 100 g / L, more preferably 5 to 50 g / L is added, and the dispersant is preferably 0.5 to 30 g / L, more preferably 1 to 10 g / L. Alternatively, a method may be used in which an aqueous slurry is prepared by dissolution in step A2 and the aqueous solution is added to the aqueous slurry. In this way, a base film having a target protrusion is obtained.

Next, the case where the b process, which is a process for forming a smooth surface undercoat, is performed instead of the a process. The b process can be performed as follows. First, an aqueous slurry containing pretreated core material particles, a dispersant, and a complexing agent is prepared. Then, the first aqueous solution and the second aqueous solution (i) described in the step a2 are used, or the first to third aqueous solutions (ii) are used. Electroless nickel plating is performed by adding over time. The pH of the plating solution obtained by adding each aqueous solution to the aqueous slurry is preferably adjusted to a range of 3 to 11, for example. About the kind of dispersing agent and complexing agent, and those density | concentrations, what was mentioned in description of the a1 process can be used by the density | concentration demonstrated 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) are the same as those used for these aqueous solutions in step a2. Things can be used. The concentration of the nickel salt in the aqueous solution is preferably 10 to 1000 g / L, particularly 50 to 500 g / L. The concentration of 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. The alkali concentration is preferably 5 to 500 g / L, more preferably 10 to 200 g / L. In this way, the desired smooth surface undercoat is obtained.

  After the base film is formed as described above, the second step is then performed to form an upper film having protrusions on the surface of the base film. In the second step, the base coat-coated 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 features of the second step is that a hydroxy acid is blended in the electroless plating bath in order to form a protrusion on the upper layer film.

  The reducing agent used in the second step is preferably a phosphorus compound such as hypophosphorous acid or a salt thereof, and 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 nickel ions used in the second step, the same nickel salt 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.

  Examples of the metal source of the metal M ion include sulfates, nitrates, sodium salts, chlorides and hydroxides. When using a sodium salt, 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 types of metals M when the upper layer film contains two or more types 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 film. As the hydroxy acid, for example, monohydroxy monocarboxylic acid or dihydroxy monocarboxylic acid can be used. Further, as the hydroxy acid, for example, α-hydroxy acid, β-hydroxy acid, and α, β-hydroxy acid can be used. In particular, when glycolic acid and lactic acid, which are α-monohydroxymonocarboxylic acids, or glyceric acid, which is α, β-dihydroxymonocarboxylic acid, is used as a hydroxy acid, a protrusion having a desired shape can be easily formed. preferable. These hydroxy acids can be used alone or in combination of two or more. The hydroxy acid concentration 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 the same ones as mentioned in the description of the step a1. The concentration of the complexing agent can be the same as in step a1.

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

  There is no particular limitation on the method of mixing the undercoat-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 undercoat-coated particles can be put into the electroless plating bath under this condition. By this operation, nickel ions are reduced, and the nickel produced by the reduction forms an upper film having protrusions on the surface of the base particles.

  In this way, desired conductive particles are obtained. The conductive particles can be further subjected to post-treatment for forming an outermost layer film as necessary. Examples of the post-treatment include an electroless gold plating step or an electroless palladium plating step. By applying this step, a gold plating layer or a palladium plating layer is formed as the outermost layer film on the surface of the conductive particles. The gold plating layer can be formed according to a conventionally known electroless plating method. For example, by adding an electroless plating solution containing tetrasodium ethylenediaminetetraacetate, disodium citrate, and potassium gold cyanide and adjusted to pH with sodium hydroxide to an aqueous suspension of conductive particles, A plating layer can be formed.

  The palladium plating layer can also be formed according to a conventionally known electroless plating method. For example, reduction of water-soluble palladium compounds such as palladium chloride; hypophosphorous acid, phosphorous acid, formic acid, acetic acid, hydrazine, borohydride, amine borane compounds, or salts thereof into an aqueous suspension of conductive particles A conventional electroless palladium plating solution containing an agent; and a complexing agent, and a dispersant, a stabilizer, and a pH buffering agent are added as necessary. Then, while adjusting the pH with an acid such as hydrochloric acid or sulfuric acid or a base such as sodium hydroxide, reduction type electroless plating can be performed to form a palladium plating layer. Alternatively, a palladium ion source such as tetraamminepalladium salt, a complexing agent and, if necessary, a dispersing agent are added to an aqueous suspension of conductive particles, and substitution is performed using a substitution reaction between palladium ions and nickel ions. A palladium electroplating layer may be formed by performing mold electroless plating.

  As the dispersant used in the reduction type electroless plating or the displacement type electroless plating, the same dispersants as those exemplified in the aforementioned a1 step can be used. In addition, as a conventional electroless palladium plating solution, for example, a commercially available product available from Kojima Chemical Co., Ltd., Nippon Kanisen Co., Ltd., Chuo Chemical Industrial Co., Ltd. or the like may be used.

  As another post-treatment, the conductive particles can be subjected to a pulverization step using a media mill such as a ball mill. By attaching | subjecting to this grinding | pulverization process, the mass which the primary particle occupies with respect to the mass of the powder which consists of electroconductive particles can be further improved further easily.

  When the conductive particles of the present invention are used as a conductive filler of a conductive adhesive, as will be described later, the surface of the conductive particles may be further coated with an insulating resin in order to prevent short-circuiting between the conductive particles. it can. Insulating resin coating is destroyed by heat and pressure applied when two electrodes are bonded using a conductive adhesive so that the surface of the conductive particles is not exposed as much as possible without applying pressure. And at least the protrusions 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 part of the surface of the conductive particles.

  As the insulating resin, those known in the technical field can be widely used. For example, phenol resin, urea resin, melamine resin, allyl resin, furan resin, polyester resin, epoxy resin, silicone resin, polyamide-imide resin, polyimide resin, polyurethane resin, fluorine resin, polyolefin resin (example: polyethylene) , Polypropylene, polybutylene), polyalkyl (meth) acrylate resin, poly (meth) acrylic acid resin, polystyrene resin, acrylonitrile-styrene-butadiene resin, vinyl resin, polyamide resin, polycarbonate resin, polyacetal resin, ionomer resin, polyethersulfone Mention may be made of resins, polyphenyl oxide resins, polysulfone resins, polyvinylidene fluoride resins, ethyl cellulose and cellulose acetate.

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

  The conductive particles of the present invention thus obtained are used for connecting, for example, an anisotropic conductive film (ACF), a heat seal connector (HSC), and an electrode of a liquid crystal display panel to a circuit board of a driving LSI chip. It is suitably used as a conductive material. In particular, the conductive particles of the present invention are suitably used as a conductive filler of a conductive adhesive.

  The conductive adhesive is preferably used as an anisotropic conductive adhesive that is disposed between two substrates on which a conductive base material is formed, and adheres and conducts the conductive base material by heating and pressing. . This anisotropic conductive adhesive contains the conductive particles of the present invention and an adhesive resin. Any adhesive resin can be used without particular limitation as long as it is insulative and used as an adhesive resin. Either a thermoplastic resin or a thermosetting resin may be used, and those that exhibit adhesive performance by heating are preferred. Examples of such an adhesive resin include a thermoplastic type, a thermosetting type, and an ultraviolet curing type. In addition, there are so-called semi-thermosetting types that exhibit intermediate properties between thermoplastic types and thermosetting types, combined types of thermosetting types and ultraviolet curing types, and the like. These adhesive resins can be appropriately selected according to the surface characteristics and usage pattern of the circuit board or the like to be attached. In particular, an adhesive resin including a thermosetting resin is preferable from the viewpoint of 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, 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- 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 or Those obtained by one or more combinations selected from such recone resins those prepared as main agent. Of these, as the thermoplastic resin, styrene-butadiene rubber, SEBS, and the like are preferable because of their excellent reworkability. As the thermosetting resin, an epoxy resin is preferable. Of these, epoxy resins are most preferred because of their advantages of high adhesive strength, excellent heat resistance and electrical insulation, low melt viscosity, and connection at low pressure.

  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, resorcin, and bishydroxydiphenyl ether, ethylene glycol, neopentyl glycol, glycerin, and trimethylolpropane. Obtained by reacting polychlorohydric alcohols such as polypropylene glycol, polyamino compounds such as ethylenediamine, triethylenetetramine, and aniline, polycarboxyl compounds such as adipic acid, phthalic acid, and isophthalic acid with epichlorohydrin or 2-methylepichlorohydrin. A glycidyl type epoxy resin is exemplified. Moreover, aliphatic and alicyclic epoxy resins such as dicyclopentadiene epoxide and butadiene dimer epoxide are listed. These can be used individually by 1 type or in mixture of 2 or more types.

  In addition, as various adhesive resin mentioned above, it is preferable from a viewpoint of prevention of ion migration to use the high purity goods in which impurity ions (Na, Cl, etc.), hydrolyzable chlorine, etc. were reduced.

  The amount of the conductive particles of the present invention used in the anisotropic conductive adhesive is usually 0.1 to 30 parts by weight, preferably 0.5 to 25 parts by weight, more preferably 1 to 100 parts by weight of the adhesive resin component. ˜20 parts by mass. When the amount of the conductive particles used is within this range, an increase in connection resistance and melt viscosity is suppressed, connection reliability is improved, and connection anisotropy can be sufficiently secured.

  In the anisotropic conductive adhesive, in addition to the conductive particles and the adhesive resin described above, additives known in the art can be blended. The blending amount can also be within a range known in the art. Other additives include, for example, tackifiers, reactive auxiliaries, epoxy resin curing agents, metal oxides, photoinitiators, sensitizers, curing agents, vulcanizing agents, deterioration inhibitors, heat resistant additives, heat Examples thereof include a conductivity improver, a softener, a colorant, various coupling agents, or a metal deactivator.

  Examples of the tackifier include rosin, rosin derivatives, terpene resins, terpene phenol resins, petroleum resins, coumarone-indene resins, styrene resins, isoprene resins, alkylphenol resins, xylene resins and the like. Examples of the reactive assistant, that is, the crosslinking agent include polyols, isocyanates, melamine resins, urea resins, utropines, amines, acid anhydrides and peroxides. As an epoxy resin hardening | curing agent, if it has two or more active hydrogens in 1 molecule, it can be especially used without a restriction | limiting. Specific examples include polyamino compounds such as diethylenetriamine, triethylenetetramine, metaphenylenediamine, dicyandiamide, and polyamideamine; organic acid anhydrides such as phthalic anhydride, methyl nadic anhydride, hexahydrophthalic anhydride, and pyromellitic anhydride. Products: novolak resins such as phenol novolac 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. Examples of latent curing agents that can be used include imidazole series, hydrazide series, boron trifluoride-amine complexes, sulfonium salts, amine imides, polyamine salts, dicyandiamide, and the like and modified products thereof. These can be used alone or as a mixture of two or more.

  The anisotropic conductive adhesive is manufactured using a manufacturing apparatus usually used in the technical field. For example, the conductive particles of the present invention, an adhesive resin, and a curing agent or various additives as necessary are blended. When the adhesive resin is a thermosetting resin, the thermoplastic resin is mixed in an organic solvent. In this case, it is produced by melt-kneading at a temperature equal to or higher than the softening point of the adhesive resin, specifically preferably about 50 to 130 ° C, more preferably about 60 to 110 ° C. The anisotropic conductive adhesive thus obtained may be applied or applied in the form of a film.

  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 such examples. Unless otherwise specified, “%” and “part” mean “% by mass” and “part by mass”, respectively.

[Example 1]
(1) First Step (1-1) Pretreatment A spherical styrene resin having an average particle size of 3.0 μm was used as the core material particles. 9 g of the solution was added to 400 mL of an aqueous conditioner solution (“Cleaner Conditioner 231” manufactured by Rohm and Haas Electronic Materials) with stirring. The concentration of the aqueous conditioner solution was 40 mL / L. Subsequently, the core material particles were surface-modified and dispersed by stirring for 30 minutes while applying ultrasonic waves at a liquid temperature of 60 ° C. The aqueous solution was filtered and the core particles washed once with repulp water were made into 200 mL slurry. 200 mL of stannous chloride aqueous solution was thrown into this slurry. The concentration of this aqueous solution was 5 × 10 ⁻³ mol / L. The mixture was stirred at room temperature for 5 minutes to carry out a sensitization treatment for adsorbing tin ions on the surface of the core material particles. Subsequently, the aqueous solution was filtered and washed once with repulp water. The core particles were then made into 400 mL slurry and maintained at 60 ° C. While stirring the slurry using ultrasonic waves, 2 mL of a 0.11 mol / L palladium chloride aqueous solution was added. The state of stirring as it was was maintained for 5 minutes, and an activation treatment for capturing palladium ions on the surface of the core particles was performed.

(1-2) Base film forming treatment having protrusions (1-2-1) a1 step 20 g / L sodium tartrate, 4.5 g / L nickel sulfate hexahydrate, 5.4 g / L hypochlorous acid 3 L of an electroless nickel-phosphorous plating bath made of an aqueous solution in which sodium phosphate and 5 g / L polyethylene glycol are dissolved is heated to 70 ° C., and 9 g of core material particles supporting palladium are put into this electroless plating bath. Then, step a1 was started. After stirring for 5 minutes, it was confirmed that hydrogen bubbling stopped, and step a1 was completed.

(1-2-2) Step a2 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 ) And 300 mL of each of these was continuously added to the slurry of the core material particles obtained in the a1 step by a metering pump, and the electroless plating a2 step was started. The addition rate was 2.5 mL / min. After all the liquid was added, stirring was continued for 5 minutes while maintaining the temperature at 70 ° C. Next, the liquid was filtered, and the filtrate was washed three times, and then dried with a vacuum dryer at 100 ° C. to obtain base coat coated particles on which a base coat made of a nickel-phosphorus alloy was formed. As a result of obtaining the film thickness of the undercoat film by the following method, it was 100 nm.

[Measurement method of thickness of undercoat]
The base coat particles before coating the top coat are immersed in aqua regia to dissolve the base coat, and the base coat components are analyzed by ICP or chemical analysis. From the following formulas (3) and (4), the thickness of the base coat (μm ) Was calculated. The value obtained by this method is a calculated value, and when a protrusion is formed on the base film, it means the thickness when the protrusion is virtually flattened.
J = [(r + t) ³ −r ³ ] d ₁ / r ³ d ₂ (3)
J = W / (100-W) (4)
In the formula, r is the radius of the core particle (μm), t is the thickness of the undercoat (μm), d ₁ is the density of the undercoat (g / μm ³ ), and d ₂ is the density of the core particles (g / μm ³ ), W is the total content (% by mass) of nickel and phosphorus in the undercoat-coated particles, and J is the mass ratio of the undercoat to the core particles.

(2) Second step (upper layer film forming process having protrusions)
Consists of 20 g / L sodium citrate, 2.5 g / L nickel sulfate, 0.5 g / L sodium tungstate, 5.0 g / L glycolic acid, and 2.7 g / L sodium hypophosphite An electroless nickel-tungsten-phosphorous plating bath was prepared. After heating 1 L of this plating bath to 80 ° C., the pH was adjusted to 9, 6 g of the undercoat-coated particles obtained in the first step were added while stirring this, and electroless plating was performed. The plating time was 30 minutes. As a result, the surface of the base film was subjected to electroless plating. After the treatment is completed, the liquid is filtered off, washed three times, and then vacuum-dried at 110 ° C. Conductive particles in which an upper layer film made of a nickel-tungsten-phosphorus alloy is coated on a base film made of a nickel-phosphorus alloy film Obtained. It was 25 nm as a result of measuring the film thickness of an upper film by the following method.

[Measurement method of upper layer thickness]
The conductive particles were immersed in aqua regia to dissolve the entire coating, and all coating components were analyzed by ICP or chemical analysis, 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 (5)
J ′ = W ′ / (100−W ′) (6)
In the formula, r is the radius of the core particles (μm), t ′ is the thickness of the entire coating (μm), d ₁ is the density of the total coating (g / μm ³ ), and d ₂ is the density of the core particles (g / Μm ³ ), W ′ is the total content (% by mass) of nickel, tungsten, molybdenum and phosphorus in the conductive particles, and J ′ is the mass ratio of the entire coating to the core particles.
The thickness T (μm) of the upper film was calculated by the following equation (7) using the thickness t ′ (μm) of the entire film and the thickness t (μm) of the base film. The value obtained by this method is a calculated value, and when a protrusion is formed on the upper layer film, it means the thickness when the protrusion is virtually flattened.
T = t′−t (7)

[Examples 2 to 14]
Conductive particles were obtained in the same manner as in Example 1 except that the conditions shown in Table 1 below were adopted. The obtained conductive particles had protrusions on both the base film and the upper film similarly to the conductive particles of Example 1.

Example 15
(1) 1st process (1-1) Pre-processing It carried out similarly to Example 1. FIG.

(1-2) Base film forming treatment having a substantially uniform thickness Mixing 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 300 mL each of the aqueous solution (second aqueous solution) was used. These were continuously added separately to the slurry of the pretreated core material particles by a metering pump, and the electroless plating process was started. The addition rate was 2.5 mL / min. After all the liquid was added, stirring was continued for 5 minutes while maintaining the temperature at 70 ° C. Next, the liquid was filtered, and the filtrate was washed three times, and then dried with a vacuum dryer at 100 ° C. to obtain base coat coated particles on which a base coat made of a nickel-phosphorus alloy was formed. As a result of obtaining the film thickness of the undercoat film by the above-described method, it was 100 nm.

(2) Second step (upper layer film forming process having protrusions)
The same operation as in Example 1 was performed. It was 25 nm as a result of measuring the film thickness of the formed upper film by the above-mentioned method.

[Examples 16 to 24]
Conductive particles were obtained in the same manner as in Example 15 except that the conditions shown in Table 2 below were adopted. The obtained conductive particles, like the conductive particles of Example 15, were provided with a flat base film having a substantially uniform thickness and an upper film having protrusions.

[Comparative Examples 1 to 6]
Conductive particles were obtained in the same manner as in Example 15 except that the conditions shown in Table 2 below were adopted. The obtained conductive particles were provided with a flat base film having a substantially uniform thickness and a flat upper film having a substantially uniform thickness.

[Evaluation]
About the conductive particles obtained in the examples and comparative examples, the phosphorus content of the base film, the phosphorus content of the upper film, the tungsten content of the upper film, the molybdenum content of the upper film, the base film and the upper film, respectively. The presence / absence of a crystal structure, and conductivity at room temperature and high temperature and high humidity were measured and evaluated, respectively. Measurement and evaluation were performed by the following methods. The results are shown in Table 3 below.

[Phosphorus content of undercoat]
The undercoat film-coated particles before coating the upper film were immersed in aqua regia to dissolve the undercoat film, and the film components were subjected to ICP or chemical analysis to determine the phosphorus content (%).

[Phosphorus content, tungsten content, molybdenum content of the upper film]
After coating the upper layer, it is immersed in aqua regia to dissolve the entire film, and all film components are analyzed by ICP or chemical analysis. Nickel content A (%), phosphorus content B (%), tungsten content C (% ) And molybdenum content D (%). Furthermore, the nickel content A ′ (%) and the phosphorus content B ′ (%) were calculated from the ICP analysis when the base coating treatment was performed. Using these, the phosphorus content E (%) in the upper film is calculated by the following formula (8), the tungsten content F (% by mass) is calculated by the following formula (9), and the following formula (10 ) To calculate the molybdenum content G (mass%).
E = (BB ′) / (AA ′ + BB ′ + C + D) × 100 (8)
F = C / (AA ′ + BB ′ + C + D) × 100 (9)
G = D / (AA ′ + BB ′ + C + D) × 100 (10)

[Crystal structure of undercoat and overcoat]
The crystal structure of the undercoat was obtained by performing X-ray diffraction measurement on the undercoat-coated particles before the upper coat was coated. For X-ray diffraction measurement, “X-ray diffraction Ultimate IV” manufactured by Rigaku Corporation was used, and the measurement conditions were tube voltage: 40 kV, tube current: 40 mA, and X-ray: CuKα (wavelength λ = 1.541). When the diffraction peak of the nickel-phosphorus alloy was confirmed by X-ray diffraction measurement, it was judged that there was a crystal structure. In addition, the crystal structure of the upper film is the same as that of the X-ray diffraction measurement of the base film after the film is thinned with FIB or the like, and the film with a depth of about several nm from the outermost layer of the upper film is measured. X-ray diffraction measurement was performed, and when a diffraction peak of nickel or a nickel alloy was confirmed, it was judged that there was a crystal structure.

[Evaluation of conductivity at room temperature and high temperature and high humidity]
100 parts of epoxy resin, 150 parts of curing agent, and 70 parts of toluene were mixed to prepare an insulating adhesive. The insulating adhesive was mixed with 15 parts of conductive particles to obtain a paste. This paste was applied onto a silicone-treated polyester film and dried using a bar coater. Using the obtained coated film, electrical connection was made between a glass whose entire surface was vapor-deposited with aluminum and a polyimide film substrate having a copper pattern formed on a 20 μm pitch. And the electrical conductivity of electroconductive particle was evaluated by measuring the conduction | electrical_connection resistance value between both. The conduction resistance was measured at room temperature (25 ° C./50% RH) and high temperature and high humidity (85 ° C./85% RH, after storage for 500 hours).

  As is clear from the results shown in Table 3, the conductive particles obtained in each example (the product of the present invention) have a lower resistance value and higher conductivity than the conductive particles obtained in the comparative examples. I understand. In addition, it can be seen that the conductive particles obtained in each example have a smaller increase in resistance value after storage under high temperature and high humidity than the conductive particles obtained in the comparative example. In particular, as is clear from the comparison between Examples 1 to 14 and Examples 15 to 24, the conductive particles of Examples 1 to 14 in which protrusions are formed on both the base film and the upper film are formed on the upper film. It can be seen that the resistance value is lower and the conductivity is higher than that of the conductive particles of Examples 15 to 24 in which only the protrusions are formed.

Claims (9)

In the conductive particles formed by forming a conductive film on the surface of the core material particles,
The conductive film has a base film in contact with the surface of the core particles, and an upper film in contact with the surface of the base film,
The undercoat includes nickel and phosphorus,
The undercoat has a flat portion and a plurality of protrusions protruding from the flat portion and being a continuous body from the flat portion, and the flat portion and the protrusion are made of the same material. Has been
The upper film has a crystal structure, and includes nickel, phosphorus, and one or more kinds of metals M (excluding nickel),
The upper layer coating is a flat portion projects from the flat part, and a plurality of protrusions that is a continuum from the flat portion, and the flat portion and the protrusion portion from the same material An electrically conductive particle characterized by comprising. The conductive particle according to claim 1 , wherein the undercoat has a crystal structure and a phosphorus content is 1% by mass or more and less than 10. The conductive particles according to claim 1 , wherein the undercoat has an amorphous structure and a phosphorus content is 10 to 18% by mass. Said conductive film is further in contact with the surface of the upper layer coating, the conductive particles according to any one of claims 1 to 3 having an outermost coating of a noble metal. The conductive particle according to any one of claims 1 to 4 , wherein the metal M has a Mohs hardness of 4 or more. The electroconductive particle according to claim 5 , wherein the metal M is at least one selected from tungsten, palladium, platinum, and molybdenum. The electroconductive material containing the electroconductive particle and insulating resin as described in any one of Claims 1 thru | or 6 . It is a manufacturing method of the electroconductive particle of Claim 1, Comprising:
Using an electroless plating bath containing a reducing agent comprising a nickel source and a phosphorus compound , an undercoat film having protrusions containing nickel and phosphorus is formed on the surface of the core material particles by electroless plating,
Using an electroless plating bath containing a nickel source, a metal M (excluding nickel) source, a reducing agent composed of a phosphorus compound and a hydroxy acid, nickel, phosphorus and metal M ( Except for nickel.) And a plurality of protrusions protruding from the flat part and being a continuous body from the flat part, and the flat part and the protrusions are The manufacturing method of the electroconductive particle characterized by having the process of forming the upper film | membrane comprised from the same material. The method for producing conductive particles according to claim 8 , wherein the hydroxy acid is glycolic acid, lactic acid, or glyceric acid.