Conductive particles, their manufacturing method and conductive material

Abstract

To provide conductive particles which have a small connection resistance value and excellent insulation performance, inhibit a short circuit, and exhibit excellent connection reliability.SOLUTION: The conductive particles each have a core material particle, and a conductive layer having a plurality of projection parts on the surface of the core material particle. The height variation of the projection parts is from 0.01 to 0.25 inclusive.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to conductive particles, a method for producing the same, and a conductive material containing the conductive particles. [Background technology]

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

[0003] The conductive layer of these conductive particles is often a coating formed on the surface of core particles by electroless plating with a metal such as nickel, and various innovations have been made to achieve the desired properties. Patent Document 1, for example, describes how forming multiple polygonal columnar protrusions on the conductive layer of a conductive particle allows the conductive particle to be efficiently positioned on the electrode when used for electrical connection between electrodes, thereby reducing damage to the electrode caused by the conductive particle. Patent Document 2 also proposes conductive particles that form multiple polyhedral protrusions, rather than polygonal columnar protrusions, on the conductive layer of the conductive particle, thereby efficiently reducing connection resistance after connection, even when electrodes are connected at low voltage. Patent Document 3 further describes conductive particles that have multiple protrusions on the conductive layer of the conductive particle, at least some of which are plate-shaped, making the conductive particles less likely to flow excessively when electrodes are connected, thereby improving conductivity and insulation reliability.

[0004] All of Patent Documents 1 to 3 attempt to solve the problem by designing the shape of the protrusions formed on the conductive layer to match the desired effect. By varying the shape of the protrusions in this way, conductive particles that are imparted with desired properties are being studied. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-149277 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-119302 [Patent Document 3] Japanese Patent Application Publication No. 2017-212033 Summary of the Invention [Problem to be solved by the invention]

[0006] By using conductive particles with a conductive layer having protrusions formed on the surface of core particles, the contact efficiency between the conductive particles is improved, making it possible to reduce the amount of conductive particles. Furthermore, if an oxide film exists on the electrode surface, the oxide film can be broken by the protrusions, allowing for conductivity and reducing electrical resistance. It is said that providing the protrusions on the conductive layer in this way makes it possible to lower the connection resistance when connecting electrodes and to increase the reliability of conduction.

[0007] However, with the demand for further miniaturization and precision in electronic devices, there is a demand for further reduction in connection resistance of conventional conductive particles having protrusions, as well as prevention of short circuits at insulating points.

[0008] Therefore, an object of the present invention is to provide conductive particles having low connection resistance, excellent insulation properties, and excellent connection reliability with short circuits suppressed. Another object of the present invention is to provide a method for producing conductive particles having low connection resistance, excellent insulation properties, and excellent connection reliability with short circuits suppressed. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems, the inventors conducted extensive research into the protrusions of conductive particles and discovered that conductive particles with protrusion height variation controlled within a certain range have low connection resistance and suppress short circuits, thereby completing the present invention.

[0010] That is, the present invention provides a conductive particle having a core particle and a conductive layer having a plurality of protrusions on the surface of the core particle, the protrusions having a height variation of 0.01 to 0.25, the core particle being made of a material containing an organic substance. wherein the ratio of Ra to Rb (Ra / Rb) is 0.15 or more and 1.20 or less, where Ra is the radius of curvature of the top of the protrusion and Rb is the radius of curvature of the surface of the lower layer of the conductive layer at the portion where the protrusion is formed. This provides:

[0011] The present invention also provides forming a conductive layer on the surface of the core particles; forming a protrusion on the conductive layer so as to protrude from the surface; and A step of leveling the height of the protrusions The core particles are made of a material containing an organic substance. wherein the radius of curvature of the top of the protrusion is Ra and the radius of curvature of the surface of the lower layer of the conductive layer at the portion where the protrusion is formed is Rb, the ratio of Ra to Rb (Ra / Rb) is 0.15 or more and 1.20 or less. A method for producing conductive particles is provided. [Effects of the Invention]

[0012] According to the present invention, there is provided a conductive particle having excellent connection reliability with reduced short circuiting due to its low connection resistance and excellent insulation properties. Also, according to the present invention, there is provided a method for producing a conductive particle having excellent connection reliability with reduced short circuiting due to its low connection resistance and excellent insulation properties. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a conceptual diagram of a conductive particle having protrusions. [Figure 2] 1 is a SEM photograph of the conductive particles obtained in Example 1. [Figure 3] 1 is a SEM photograph of the conductive particles obtained in Example 3. [Figure 4] 1 is an SEM photograph of the conductive particles obtained in Example 4. [Figure 5]1 is an SEM photograph of the conductive particles obtained in Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described below based on preferred embodiments thereof. The conductive particles of the present invention (hereinafter also referred to as "the present conductive particles") have a core particle and a conductive layer having a plurality of protrusions on the surface of the core particle, and the variation in height of the protrusions is 0.01 to 0.25. If the height of the protrusions on the conductive particles varies greatly, it is thought that the contact between the conductive particles and the electrode will be uneven, which will increase the connection resistance.Furthermore, if the height of the protrusions varies greatly, it may cause unexpected conduction and short circuits. The conductive particles have height variations in the protrusions controlled within a certain range, which is thought to result in low connection resistance, suppression of short circuits, and improved connection reliability.

[0015] The core particles of the conductive particles (hereinafter also referred to as "core particles") may be particulate and may be made of either inorganic or organic materials. Examples of inorganic materials include metal particles such as gold, silver, copper, nickel, palladium, and solder, alloys of these metals, glass, ceramic, silica, metal or non-metal oxides or hydrates thereof, metal silicates such as aluminosilicates, metal carbides, metal nitrides, metal carbonates, metal sulfates, metal phosphates, metal sulfides, metal acid salts, metal halides, and carbon. On the other hand, examples of organic materials include thermoplastic resins such as natural fibers, natural resins, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polybutene, polyamide, polyacrylic acid ester, polyacrylonitrile, polyacetal, ionomer, and polyester, and thermosetting resins such as alkyd resin, phenol resin, urea resin, benzoguanamine resin, melamine resin, xylene resin, silicone resin, epoxy resin, and diallyl phthalate resin. These may be used alone or in combination of two or more.

[0016] The material of the core particle may be either the inorganic or organic material described above, or both. When the core particle is composed of both inorganic and organic materials, the inorganic and organic materials may be present in the core particle, for example, in a core-shell structure having an inorganic core and an organic shell covering the surface of the core, or in a core-shell structure having an organic core and an inorganic shell covering the surface of the core. In addition, a core particle may contain a mixture of inorganic and organic materials, or a blend structure in which the inorganic and organic materials are randomly fused.

[0017] The core particles are preferably composed of a material containing an organic substance, and more preferably composed of both inorganic and organic substances. When composed of both inorganic and organic substances, the inorganic substances are preferably glass, ceramic, silica, metal or non-metal oxides or their hydrates, metal silicates such as aluminosilicates, metal carbides, metal nitrides, metal carbonates, metal sulfates, metal phosphates, metal sulfides, metal acid salts, metal halides, and carbon. Furthermore, the organic substances are preferably natural fibers, natural resins, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polybutene, polyamides, polyacrylates, polyacrylonitriles, polyacetals, ionomers, polyesters, and other thermoplastic resins. Using core particles made of such materials can improve the dispersion stability of the particles and also provide appropriate elasticity and improved conductivity during electrical connection of electronic circuits.

[0018] When the core particles are made of a material containing an organic substance, the organic substance preferably has no glass transition temperature or a glass transition temperature of more than 100° C., because the shape of the core particles is easily maintained during the process of forming a metal coating. The glass transition temperature can be determined, for example, by differential scanning calorimetry (hereinafter also referred to as “DSC”) as the intersection of the tangent to the original baseline and the inflection point in the baseline shift portion of a DSC curve.

[0019] When the organic substance is a highly crosslinked resin, even if the glass transition temperature is measured up to 200°C using the above method, almost no baseline shift may be observed. In this specification, such organic substances are also referred to as organic substances without a glass transition temperature. The core particles may be made of such organic substances without a glass transition temperature. The organic substance without a glass transition temperature can be obtained by copolymerizing a crosslinkable monomer with a monomer constituting the thermoplastic resin or thermosetting resin exemplified above. Examples of crosslinkable monomers include tetramethylene di(meth)acrylate, ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, ethylene oxide di(meth)acrylate, tetraethylene oxide (meth)acrylate, 1,6-hexane di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, trimeterolpropane tri(meth)acrylate, tetramethylolmethane di(meth)acrylate, tetramethylolmethane tri(meth)acrylate, Examples of suitable crosslinked resins include polyfunctional (meth)acrylates such as tetramethylolmethane tetra(meth)acrylate, tetramethylolpropane tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, glycerol di(meth)acrylate, and glycerol tridi(meth)acrylate, polyfunctional vinyl monomers such as divinylbenzene and divinyltoluene, silane-containing monomers such as vinyltrimethoxysilane, trimethoxysilylstyrene, and γ-(meth)acryloxypropyltrimethoxysilane, and monomers such as triallyl isocyanurate, diallyl phthalate, diallyl acrylamide, and diallyl ether. Particularly in the field of COG (chip on glass), such highly crosslinked resins are preferably used as the material for core particles because of their hardness.

[0020] The core particles may have an irregular shape, such as spherical, fibrous, hollow, plate-like, or needle-like, but are usually spherical. The core particles may have numerous protrusions on their surfaces. The core particles are preferably spherical in shape, as this provides excellent packing properties and allows for easy metal coating.

[0021] The conductive particles have a conductive layer on the surface of the core particle, and the conductive layer has a plurality of protrusions. The conductive layer of the conductive particles is made of a conductive metal. Examples of metals constituting the conductive layer include gold, platinum, silver, copper, iron, zinc, nickel, tin, lead, antimony, bismuth, cobalt, indium, titanium, germanium, aluminum, chromium, palladium, tungsten, molybdenum, calcium, magnesium, rhodium, sodium, iridium, beryllium, ruthenium, potassium, cadmium, osmium, lithium, rubidium, gallium, thallium, tantalum, cesium, thorium, strontium, polonium, zirconium, barium, and manganese, as well as metal compounds such as ITO and solder. Among these, gold, silver, copper, nickel, palladium, rhodium, and solder are preferred due to their low electrical resistance, and nickel, gold, palladium, nickel alloys, gold alloys, and palladium alloys are particularly preferred. A single metal may be used, or two or more metals may be used in combination.

[0022] The conductive layer of the conductive particles may have a single layer structure or a laminated structure consisting of multiple layers. In the case of a laminated structure consisting of multiple layers, the outermost layer preferably contains at least one selected from the group consisting of nickel, gold, silver, copper, and palladium, with nickel, gold, silver, copper, palladium, and alloys thereof being preferred. In the case of alloys, nickel alloys, gold alloys, silver alloys, copper alloys, and palladium alloys, which are alloys of nickel, gold, silver, copper, or palladium and phosphorus, are preferred, with nickel-phosphorus alloys and palladium-phosphorus alloys being more preferred. The outermost layer of the conductive layer is more preferably an electroless nickel-phosphorus plating layer formed by an electroless method in the manufacturing method described below.

[0023] The conductive layer of the conductive particle may cover the entire surface of the core particle or only a portion thereof. When only a portion of the surface of the core particle is covered, the covered portion may be continuous or may be discontinuous, for example, in the form of islands.

[0024] From the viewpoint of the electrical properties of the resulting conductive particles, the thickness of the conductive layer of the conductive particles is preferably 0.1 nm or more and 2,000 nm or less, and more preferably 1 nm or more and 1,500 nm or less. Note that the height of the protrusions on the conductive layer is not included in the thickness of the conductive layer. The thickness of the conductive layer can be measured by cutting the particle to be measured in two and observing the cross section of the cut surface with a scanning electron microscope (SEM). The thickness of the conductive layer is preferably within the above range.

[0025] The protrusions (hereinafter also referred to as "protrusions") of the conductive layer of the present conductive particles have a height variation of 0.01 to 0.25. The height variation is the value obtained by dividing the standard deviation of the protrusion heights by the average protrusion height, and is expressed by the following formula (1). The standard deviation of the heights can be calculated by the following formula (2), and the average height is the arithmetic mean value of the protrusion heights calculated by the following formula (3). When this variation value is within the above range, the contact between the conductive particles and the electrode becomes more uniform, leading to improved connection stability.

[0026] TIFF0007803820000001.tif24151

[0027] TIFF0007803820000002.tif33151

[0028] TIFF0007803820000003.tif31151

[0029] The variation in height of the projections is more preferably 0.05 to 0.20. When the cross section of a conductive particle is observed using an SEM, if the conductive particle is spherical, the height of the protrusion refers to the shortest distance from the highest point of the protrusion's apex toward the center of the conductive particle to the point where the base of the protrusion meets. The height of all protrusions on 20 different conductive particles observed using an SEM can be measured and substituted into the above formulas to determine the variation in protrusion height. If a protrusion has multiple vertices, the highest vertex is taken as the height of that protrusion.

[0030] The average height of the protrusions on the conductive particles is preferably 20 nm to 1,000 nm, more preferably 50 nm to 800 nm. The number of protrusions per conductive particle varies depending on the particle size of the conductive particles, but is preferably 1 to 20,000, more preferably 5 to 5,000. The length of the base of the protrusion is preferably 5 nm or more and 1,000 nm or less, and more preferably 10 nm or more and 800 nm or less.

[0031] The average height of the protrusions is determined by determining the height of the protrusions in the same manner as above and then using the formula (3) above. The average length of the base of the protrusion is shown in Fig. 1(a) and (b). 4 Conductive layer in the area where of The length of the base of the protrusions is the arithmetic mean value of the lengths of all the bases of the protrusions of 20 different conductive particles observed by SEM.

[0032] The shape of the top of the protrusion is preferably substantially planar, from the viewpoint of more uniform contact between the conductive particles and the electrode. Here, substantially planar includes both a completely flat surface and a surface having a curved surface with a radius of curvature, as described below. For example, in this specification, the concept of substantially planar includes the completely flat surface 5 shown in FIG. 1(a) and the flat surface 5 shown in FIG. 1(b) having a curved surface within the radius of curvature, as described below.

[0033] When the apex portion of the protrusion is substantially planar, the length of the apex portion is preferably 10 nm or more and 500 nm or less, more preferably 20 nm or more and 400 nm or less. The length of the substantially planar apex portion is determined by observing the cross section of the conductive particle using an SEM and measuring the shortest distance connecting both ends of the substantially planar apex portion in the cross section of the protrusion. For example, in Figures 1(a) and 1(b), the length of the apex portion is the length of the straight line connecting the ends 5a and 5b of the flat portion 5 having a substantially planar apex portion. The length of the substantially planar apex portion of the protrusion is determined by measuring the arithmetic mean value of the lengths of the apex portions of the cross sections of all protrusions of 20 different conductive particles observed by SEM.

[0034] The number of protrusions varies depending on the particle size of the conductive particles, but from the viewpoint of the conductivity of the conductive particles, the number of protrusions is preferably 2 or more and 20,000 or less, more preferably 5 or more and 5,000 or less on average per conductive particle. The number of protrusions is the arithmetic mean value of values ​​measured for 20 different conductive particles observed by SEM.

[0035] When the top portion of the protrusion is substantially flat, the curvature radius of the top portion is Ra, and the curvature radius of the surface 6 of the lower layer of the conductive layer at the portion where the protrusion is formed is Rb. The ratio of Ra to Rb (Ra / Rb) is preferably 0.15 or more and 1.20 or less, particularly 0.20 or more and 1.00 or less. When the top portion of the protrusion has a curvature radius that satisfies the above range, the contact between the conductive particle and the electrode becomes more uniform, leading to improved connection stability. Note that Ra can be the radius of a circumscribed circle that circumscribes the top portion of the cross section of each protrusion, for example, in the cross section of the conductive particle observed by SEM observation. Rb can be the radius of a circumscribed circle that circumscribes the top portion of the cross section of the conductive particle observed by SEM observation, for example. 1 The radius of the circumscribing circle that circumscribes the surface of the lower layer of the conductive layer, i.e., the radius of the core material particle, 2 The radius of the

[0036] By having the height of the protrusions within the above range, contact between the conductive particles and the electrode becomes uniform, and if the top portions of the protrusions are substantially planar, contact with other conductive particles nearby is suppressed, which is thought to lead to the prevention of short circuits. From this perspective, it is preferable that the total area of ​​the substantially planar top portions of the protrusions per conductive particle is large. That is, the ratio S2 / S1 of the total area of ​​the top portions of the protrusions (S2) to the projected area (S1) of a single conductive particle is preferably 0.50 or greater, particularly 0.55 or greater. Note that S2 / S1 is preferably less than 1, and from the viewpoint of confirming the formation of substantially planar protrusions, it is preferably 0.95 or less, more preferably 0.90 or less. The projected area (S1) of the conductive particles and the total area of ​​the top portions of the protrusions (S2) can be measured by importing SEM photographs into an automatic image analyzer (Luzex (registered trademark) AP, manufactured by Nireco Corporation).

[0037] Furthermore, from the viewpoint of preventing short circuits, it is preferable that the shape of at least one of the protrusions be irregular. An irregular protrusion means that, when the top of the protrusion is viewed from the opposite side of the base, the top is surrounded by multiple curves with different curvatures. When the top of the protrusion is viewed from the opposite side of the base, it is preferable that the top has a shape other than a circle or a polygon. The number of irregularly shaped protrusions per conductive particle is preferably 10 or more, and even more preferably 20 or more. Alternatively, the number of irregularly shaped protrusions is preferably 90% or more, and even more preferably 95% or more, of the total number of protrusions per conductive particle taken as 100%.

[0038] The protrusions are preferably continuous with the conductive layer formed on the surface of the core particle. That is, the protrusions are preferably made of a metal or alloy, just like the conductive layer. "Continuous" here means that the conductive layer and the protrusions are made of the same material, and there are no seams or other parts between the conductive layer and the protrusions that would impair the sense of unity. The strength of the protrusions is ensured by the conductive layer and the protrusions being continuous, making the bases of the protrusions less likely to break even when pressure is applied during use of the conductive particles. It is more preferable that the protrusions are made of the same metal or alloy as the metal or alloy that constitutes the conductive layer formed on the surface of the core particle.

[0039] The average particle diameter of the conductive particles is preferably 0.1 μm or more and 50 μm or less, more preferably 1 μm or more and 30 μm or less. When the average particle diameter of the conductive particles is within the above range, electrical continuity between the opposing electrodes can be more easily ensured without causing a short circuit in a direction different from that between the opposing electrodes. In the present invention, the average particle diameter of the conductive particles is the arithmetic mean value obtained by randomly selecting 200 particles and measuring their particle diameters at a magnification of 10,000 times using SEM observation. When the conductive particles are spherical, the diameter of the conductive particles is the diameter of a circle obtained by projecting the conductive particles onto a plane, excluding the height of protrusions. When the conductive particles are not spherical, the particle diameter is the longest length of the line segment intersecting the image of the conductive particles projected onto a plane.

[0040] The shape of the conductive particles is appropriately selected depending on the shape of the core particles. The shape of the conductive particles may be the same as or different from the shape of the core particles, but from the viewpoint of production efficiency, it is preferable that both have the same shape. The shape of the conductive particles may be, for example, spherical, fibrous, hollow, plate-like, needle-like, or amorphous. From the viewpoint of excellent packing property and connectivity, the shape of the conductive particles is preferably spherical.

[0041] The present conductive particles can be produced, for example, by a production method including the following steps (hereinafter also referred to as "the present production method"). A step of forming a conductive layer on the surface of the core particles forming a protrusion on the conductive layer that protrudes from the surface; A step of leveling the height of the protrusions

[0042] In the step of forming a conductive layer on the surface of the core particle (hereinafter also referred to as the "conductive layer forming step"), a conductive layer is formed on the surface of the core particle by either a dry method such as a vapor deposition method, a sputtering method, a mechanochemical method, or a hybridization method, or a wet method using an electrolytic plating method, an electroless plating method, etc. Alternatively, a conductive layer may be formed on the surface of the core particle by a combination of these methods. The core particles used may be the same as those of the present invention, and the preferred material and shape are as described above.

[0043] In the conductive layer forming step, forming a conductive layer on the surface of a core particle by an electroless plating method is preferred from the viewpoint of easily obtaining conductive particles having desired particle properties, and electroless plating is more preferred from the viewpoint of easily obtaining conductive particles having desired particle properties and easily forming protrusions described later. In particular, the conductive layer is preferably an electroless nickel alloy plating layer formed by an electroless method, and more preferably an electroless nickel-phosphorus plating layer.

[0044] The conductive layer forming step of forming a nickel-phosphorus alloy plating layer as the conductive layer will be described below. When electroless plating is used in the conductive layer formation process, the core particles preferably have a surface capable of capturing precious metal ions or have been surface-modified to have such ability. The precious metal ions are preferably palladium or silver ions. Having the ability to capture precious metal ions means being able to capture precious metal ions as chelates or salts. For example, when amino groups, imino groups, amide groups, imide groups, cyano groups, hydroxyl groups, nitrile groups, carboxyl groups, etc. are present on the surface of the core particles, the surface of the core particles has the ability to capture precious metal ions. For example, the method described in JP-A-61-64882 can be used to modify the surface to have the ability to capture precious metal ions.

[0045] Core particles that have the ability to capture precious metal ions or have been surface-modified to have the ability to capture precious metal ions are used as the core particles, and the precious metal is supported on the surface. Specifically, the core particles are dispersed in a dilute acidic aqueous solution of a precious metal salt such as palladium chloride or silver nitrate. This allows the precious metal ions to be captured on the surface of the core particles. The concentration of the precious metal salt is usually 1 / m2 per m2 of the surface area of ​​the core particles. 2 1x10 -7 From 1×10 -2 The core particles with the captured precious metal ions are separated from the aqueous solution and washed with water. The core particles are then suspended in water, and a reducing agent is added to reduce the precious metal ions. This results in the precious metal being supported on the surface of the core particles. Examples of reducing agents that can be used include sodium hypophosphite, sodium borohydride, potassium borohydride, dimethylamine borane, hydrazine, and formalin, and it is preferable to select one of these based on the constituent materials of the desired conductive layer.

[0046] Before capturing precious metal ions on the surface of the core particles, the particles may be subjected to a sensitization treatment to adsorb tin ions onto the surface of the particles and enhance adhesion to the precious metal. To adsorb tin ions onto the surface of the particles, for example, the surface-modified core particles as described above may be placed in an aqueous solution of stannous chloride and stirred for a predetermined period of time.

[0047] The core particles thus pretreated are subjected to a conductive layer forming step, whereby a conductive layer is formed on the surface of the core particles. After the conductive layer forming step, a step of forming protrusions protruding from the upper surface of the conductive layer (hereinafter also referred to as a "protrusion forming step") is carried out.

[0048] The protrusion forming step is preferably carried out subsequent to the conductive layer forming step described below. The conductive layer formation step is preferably an electroless nickel plating method in which an aqueous slurry of the core particles is mixed with an electroless nickel plating bath containing a dispersant, nickel salt, a reducing agent, a complexing agent, etc. In the conductive layer formation step using the electroless nickel plating method, the plating solution self-decomposes simultaneously with the formation of the conductive layer on the core particles. This self-decomposition occurs near the core particles, and the self-decomposition products are captured on the surface of the core particles during the formation of the conductive layer, thereby generating nuclei of microprojections, and simultaneously forming the conductive layer. Using the generated nuclei of microprojections as base points, protrusions grow in the protrusion formation step described below.

[0049] In the electroless nickel plating process for forming a conductive layer, the core particles are preferably thoroughly dispersed in water at a concentration of preferably 0.1 to 500 g / L, more preferably 1 to 300 g / L, to prepare an aqueous slurry. The dispersion can be carried out using conventional stirring, high-speed stirring, or a shear dispersion device such as a colloid mill or homogenizer. Ultrasound may also be used in the dispersion process. If necessary, a dispersant such as a surfactant may be added during the dispersion process. The aqueous slurry of dispersed core particles is then added to an electroless nickel plating solution containing nickel salt, a reducing agent, a complexing agent, and various additives, and electroless plating is carried out.

[0050] Examples of the dispersant include a nonionic surfactant, a zwitterionic surfactant, and / or a water-soluble polymer. As the nonionic surfactant, polyoxyalkylene ether surfactants such as polyethylene glycol, polyoxyethylene alkyl ether, and polyoxyethylene alkylphenyl ether can be used. As the zwitterionic surfactant, betaine surfactants such as alkyldimethyl acetate betaine, alkyldimethylcarboxymethyl acetate betaine, and alkyldimethylamino acetate betaine can be used. Examples of the water-soluble polymer that can be used include polyvinyl alcohol, polyvinylpyrrolidinone, and hydroxyethyl cellulose. These dispersants can be used alone or in combination of two or more. The amount of dispersant used varies depending on the type, but is generally 0.5 to 30 g / L relative to the volume of the electroless nickel plating solution. In particular, it is preferable that the amount of dispersant used is in the range of 1 to 10 g / L relative to the volume of the electroless nickel plating solution, from the viewpoint of further improving the adhesion of the conductive layer.

[0051] 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. The reducing agent is used to reduce precious metal ions and is selected based on the constituent material of the intended conductive layer. Examples of reducing agents include phosphorus compounds and boron compounds. When sodium hypophosphite is used as the phosphorus compound, its concentration is preferably in the range of 0.1 to 50 g / L.

[0052] Examples of complexing agents include carboxylic acids or carboxylates such as citric acid, hydroxyacetic acid, tartaric acid, malic acid, lactic acid, gluconic acid, or their alkali metal salts or ammonium salts; amino acids such as glycine; amino acids such as ethylenediamine and alkylamines; other ammonium salts; EDTA; and pyrophosphate (salts). These can be used alone or in combination. The concentration of the complexing agent is preferably 1 to 100 g / L, more preferably 5 to 50 g / L. The preferred pH of the electroless nickel plating solution at this stage is in the range of 3 to 14. The electroless nickel plating reaction begins immediately upon addition of the aqueous slurry of core particles, and is accompanied by the generation of hydrogen gas. The conductive layer formation process is completed when the generation of hydrogen gas is no longer observed. The thickness of the conductive layer can be controlled in the conductive layer forming step by adjusting the concentration, pH, etc. of the nickel salt, and if necessary, the dispersant, complexing agent, etc., and the thickness can be set within a preferred range.

[0053] Next, after the conductive layer forming step, a protrusion forming step is carried out. In the protrusion forming step, it is preferable to form the protrusions by adding a nickel salt, a reducing agent, and an alkali to the electroless nickel plating solution used in the conductive layer forming step by electroless nickel plating. The nickel salt, the reducing agent, and the alkali can be added, for example, by the following method: (i) using a first aqueous solution containing one of a nickel salt, a reducing agent, and an alkali, and a second aqueous solution containing the remaining two, or (ii) 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; It is preferable that: The aqueous solutions (i) and (ii) are simultaneously added to the electroless nickel plating solution, and the addition is continued to continue the electroless nickel plating. If the addition of each aqueous solution is interrupted, the plating reaction stops, and if the solution is added, the plating reaction starts again. By adjusting the amount of each aqueous solution added, the conductive layer formed can be controlled to the desired film thickness, and further, protrusions are formed starting from the nuclei of the microprotrusions generated on the surface of the conductive layer in the conductive layer formation step. After the addition of the aqueous solution to the electroless nickel plating solution is completed and the generation of hydrogen gas is no longer observed, stirring is continued while maintaining the liquid temperature for a while to complete the reaction.

[0054] In the case of (i) above, it is preferable to use a first aqueous solution containing a nickel salt and a second aqueous solution containing a reducing agent and an alkali, but this combination is not limiting. In this case, the first aqueous solution does not contain a reducing agent or an alkali, and the second aqueous solution does not contain a nickel salt. The nickel salt and reducing agent may be those described above. The alkali may be, for example, an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide.

[0055] In the case of (ii) above, the first to third aqueous solutions each contain a nickel salt, a reducing agent, and an alkali, and each aqueous solution does not contain the other two components other than the components in question. The alkali used is the same as in the above case (i).

[0056] In either case (i) or (ii) above, the concentration of the nickel salt in the aqueous solution is preferably 10 to 1,000 g / L, more preferably 50 to 500 g / L. The concentration of the reducing agent is preferably 100 to 1,000 g / L, more preferably 100 to 800 g / L, when a phosphorus compound is used as the reducing agent. When a boron compound is used as the reducing agent, the concentration is preferably 5 to 200 g / L, more preferably 10 to 100 g / L. When hydrazine or its derivatives are used as the reducing agent, the concentration is preferably 5 to 200 g / L, more preferably 10 to 100 g / L. The alkali concentration is preferably 5 to 500 g / L, more preferably 10 to 200 g / L.

[0057] The protrusion-forming step may be performed immediately after the conductive layer-forming step, or after the conductive layer-forming step, the core particles with the conductive layer formed thereon may be separated from the electroless nickel plating solution and then the protrusion-forming step may be performed. When the core particles with the conductive layer formed thereon are separated from the electroless nickel plating solution after the conductive layer-forming step, the core particles with the conductive layer formed thereon may be separated from the plating solution by a method such as filtration. After separation, the core particles with the conductive layer formed thereon are newly dispersed in water to prepare an aqueous slurry, to which an aqueous solution containing a complexing agent dissolved in a concentration of preferably 1 to 100 g / L, more preferably 5 to 50 g / L, is added, and a dispersant dissolved in a concentration of preferably 0.5 to 30 g / L, more preferably 1 to 10 g / L, is prepared to prepare an aqueous slurry. The aqueous solution described in (i) or (ii) above may be added to the prepared aqueous slurry to perform the protrusion-forming step. In this manner, a conductive layer having protrusions can be formed.

[0058] The conductive particles having protrusions formed thereon in the protrusion-forming step are subjected to a step of leveling the height of the protrusions (hereinafter also referred to as a "leveling step"). The leveling step limits the variation in the height of the protrusions to the above range, thereby obtaining the present conductive particles. In the leveling process, the height of the protrusions formed in the protrusion forming process is lowered by polishing the top portions of the protrusions obtained in the protrusion forming process, thereby making it possible to keep the variation in the height of the protrusions within a predetermined range.

[0059] Methods for polishing the top portions of the protrusions include, for example, a method of mixing a mixed media used in a ball mill, a bead mill, etc. with the conductive particles obtained in the protrusion formation process, a method of mixing an abrasive with the conductive particles obtained in the protrusion formation process, a method of mixing the conductive particles obtained in the protrusion formation process with each other, and a method of rotating the conductive particles obtained in the protrusion formation process on a flat surface such as a belt.

[0060] When mixing a mixing medium with conductive particles, the material of the mixing medium is preferably a material having a hardness equal to or greater than that of the material of the protrusions of the conductive particles. Mixing methods include a method using a stirrer with stirring blades, a method of mixing in a container that rotates, revolves, or both, and a method of mixing in a vibrating container. Examples of materials for the mixed media include zirconia, zircon, agate, alumina, iron, stainless steel, and glass.

[0061] When mixing an abrasive with the conductive particles obtained in the protrusion forming step, examples of the abrasive include diamond, boron nitride, silicon carbide, aluminum oxide, etc. The method of mixing with the abrasive can be the same as the method of mixing the mixing media with the conductive particles. The conductive particles may be mixed together by the same method as that for mixing the mixing medium and the conductive particles.

[0062] When the conductive particles obtained in the protrusion-forming step are rotated on a flat surface such as a belt, the material of the flat surface is preferably a material having a hardness equal to or greater than that of the material of the protrusions of the conductive particles. The conductive particles obtained in the protrusion-forming step may be rotated and moved on a flat surface by falling on an inclined flat surface. Alternatively, the conductive particles obtained in the protrusion-forming step may be moved in the opposite direction on a flat surface moving in a fixed direction.

[0063] In each of the polishing methods, the relationship between the polishing conditions and the height of the protrusions may be measured in advance, and the polishing conditions may be determined in advance so that the variation in the height of the protrusions falls within the range of the present conductive particles. Alternatively, the variation in the height of the protrusions may be measured over time during polishing, and the polishing may be terminated when the variation in the height of the protrusions falls within the range of the present conductive particles based on the results. In a similar manner, the height of the protrusions can be set within the preferred range.

[0064] In the process of lowering the height of the protrusions in the leveling step, the tops of the protrusions can be polished to have a flat surface, thereby making the tops of the protrusions approximately flat. Furthermore, by lowering the height of the protrusions to match the curvature of the surface of the core material particle, the radius of curvature of the tops of the protrusions, Ra, and the radius of curvature of the outer surface of the conductive layer, Rb, can be made to have the above-mentioned preferred relationship.

[0065] After the leveling step, the present production method may further include a step of heat-treating the mixture under a vacuum of 1,000 Pa or less, preferably 0.01 Pa to 900 Pa, and particularly preferably 0.1 Pa to 500 Pa, at a temperature of 200°C to 600°C, preferably 250°C to 500°C, and particularly preferably 300°C to 450°C. By heating the conductive particles while maintaining such a vacuum state, the metal in the conductive layer is less likely to undergo side reactions even at high temperatures, and crystallization progresses, resulting in lower electrical resistance and excellent electrical conductivity. Note that the degree of vacuum in this invention is an absolute pressure, i.e., a value when an absolute vacuum is set to 0.

[0066] The heat treatment time in the heat treatment step is preferably 0.1 to 10 hours, more preferably 0.5 to 5 hours. By adopting this treatment time, increases in manufacturing costs can be suppressed, and denaturation of the core particles and conductive layer due to thermal history can be suppressed, minimizing the impact on quality. The heat treatment time is the time from when the target treatment temperature is reached to when the heat treatment is completed.

[0067] The heat treatment step may be performed while the conductive particles are left stationary or while stirring. When the heat treatment is performed while the conductive particles are left stationary, it is preferable that the conductive particles are left stationary at a thickness of 0.1 mm to 100 mm. By leaving the conductive particles stationary at this thickness, the heat treatment of the conductive layer can be successfully performed and manufacturing costs can be reduced.

[0068] The heat treatment step is carried out after the container containing the conductive particles is depressurized to a vacuum, either in a stationary state or with stirring. At this time, the gas phase of the container containing the conductive particles may be replaced with an inert gas such as nitrogen before depressurizing to a vacuum, or the container may be depressurized to a vacuum directly. The heat treatment may also be carried out multiple times as necessary.

[0069] The heat treatment step preferably involves reaching a vacuum of 1,000 Pa or less, preferably 0.01 to 900 Pa, and particularly preferably 0.1 to 500 Pa, at room temperature, maintaining the pressure for 5 to 60 minutes, and even 10 to 50 minutes, and then raising the temperature to the treatment temperature. This operation can prevent oxidation of the conductive layer due to oxygen and moisture in the heated atmosphere or the conductive particles, thereby reducing the connection resistance.

[0070] After the heat treatment step, it is preferable to lower the temperature to 50°C or less, or even 40°C or less, while maintaining the vacuum level, and then release the vacuum. The reason for this is that if the vacuum is released at the temperature immediately after the heat treatment, the presence of oxygen or moisture in the atmosphere may promote oxidation of the conductive layer, resulting in a risk of increased connection resistance. Furthermore, from the perspective of production costs, the vacuum may be released in normal air, but from the perspective of preventing oxidation of the conductive layer, it is more preferable to release the vacuum by purging with an inert gas such as nitrogen, argon, or helium, or a non-oxidizing gas such as a hydrogen-nitrogen mixed gas.

[0071] The conductive particles can be suitably used as a conductive material such as a conductive filler in a conductive adhesive, as will be described later. sex The surface of the resin-containing conductive material (hereinafter also referred to as "the conductive material") is preferably further coated with an insulating resin to prevent short circuits between conductive particles. The insulating resin coating is formed so that the surface of the conductive particles is not exposed as much as possible when no pressure is applied, and so that it is broken by the heat and pressure applied when bonding two electrodes with a conductive adhesive, exposing at least the protrusions on the surface of the conductive particles. The thickness of the insulating resin can be approximately 0.1 to 0.5 μm. The insulating resin may cover the entire surface of the conductive particles, or only a portion of the surface of the conductive particles.

[0072] Examples of insulating resins include resins made of organic polymers such as phenol resin, urea resin, melamine resin, allyl resin, furan resin, polyester resin, epoxy resin, silicone resin, polyamide-imide resin, polyimide resin, polyurethane resin, fluororesin, polyolefin resins such as polyethylene, polypropylene, and polybutylene, polyalkyl(meth)acrylate resin, poly(meth)acrylic acid resin, polystyrene resin, acrylonitrile-styrene-butadiene resin, vinyl resin, polyamide resin, polycarbonate resin, polyacetal resin, ionomer resin, polyethersulfone resin, polyphenyloxide resin, polysulfone resin, polyvinylidene fluoride resin, ethyl cellulose resin, and cellulose acetate resin.

[0073] Methods for coating the surfaces of conductive particles with an insulating resin to form an insulating coating layer include chemical methods such as coacervation, interfacial polymerization, in situ polymerization, and liquid curing coating; physico-mechanical methods such as spray drying, air suspension coating, vacuum deposition coating, dry blending, hybridization, electrostatic coalescence, melting dispersion cooling, and inorganic encapsulation; and physico-chemical methods such as interfacial precipitation.

[0074] The organic polymer constituting the insulating resin may contain a monomer component containing an ionic group in the polymer structure, provided that the organic polymer is non-conductive, in order to improve adhesion with conductive particles. The monomer component containing an ionic group may be either a crosslinkable monomer component or a non-crosslinkable monomer component. It is preferable that the organic polymer is formed using a monomer component in which at least one of the crosslinkable monomer component and the non-crosslinkable monomer component has an ionic group. Note that the "monomer component" refers to a structure derived from a monomer in the organic polymer, and is a component derived from the monomer. By subjecting a monomer containing an ionic group to polymerization, an organic polymer containing the monomer component containing an ionic group as a constituent unit is formed.

[0075] The ionic group is preferably present in the organic polymer constituting the insulating resin. Furthermore, the ionic group is preferably chemically bonded to a monomer component constituting the organic polymer. Whether or not the ionic group is present at the interface of the organic polymer can be determined by determining whether or not the insulating resin is attached to the surface of the conductive particle by scanning electron microscope observation when an insulating resin containing an organic polymer having an ionic group is formed on the surface of the conductive particle.

[0076] Examples of the ionic group include onium-based functional groups such as a phosphonium group, an ammonium group, a sulfonium group, etc. Among these, from the viewpoint of increasing the adhesion between the conductive particle and the insulating resin and forming conductive particles that combine high levels of insulation and conduction reliability, an ammonium group or a phosphonium group is preferred, and a phosphonium group is more preferred.

[0077] The onium functional group is preferably one represented by the following general formula (1).

[0078] [ka] In the general formula (1), X represents a phosphorus atom, a nitrogen atom, or a sulfur atom, and R may be the same or different and represents a hydrogen atom, a linear, branched, or cyclic alkyl group, or an aryl group. n is 1 when X represents a nitrogen atom or a phosphorus atom, and 0 when X represents a sulfur atom. * represents a bond.

[0079] Counterions for the ionic groups include, for example, halide ions. Examples of halide ions include Cl. - , F - , Br - , I - Examples include:

[0080] In the general formula (1), examples of the linear alkyl group represented by R include linear alkyl groups having 1 to 20 carbon atoms, and specific examples thereof include a methyl group, an ethyl group, an n-propyl group, an n-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, an n-nonyl group, an n-decyl group, an n-undecyl group, an n-dodecyl group, an n-tridecyl group, an n-tetradecyl group, an n-pentadecyl group, an n-hexadecyl group, an n-heptadecyl group, an n-octadecyl group, an n-nonadecyl group, and an n-icosyl group.

[0081] In the general formula (1), examples of the branched alkyl group represented by R include branched alkyl groups having 3 to 8 carbon atoms, and specific examples include an isopropyl group, an isobutyl group, a s-butyl group, a t-butyl group, an isopentyl group, a s-pentyl group, a t-pentyl group, an isohexyl group, a s-hexyl group, a t-hexyl group, and an ethylhexyl group.

[0082] In the general formula (1), examples of the cyclic alkyl group represented by R include cycloalkyl groups such as a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, and a cyclooctadecyl group.

[0083] In the general formula (1), examples of the aryl group represented by R include a phenyl group, a benzyl group, a tolyl group, and an o-xylyl group.

[0084] In the general formula (1), R is preferably an alkyl group having 1 to 12 carbon atoms, more preferably an alkyl group having 1 to 10 carbon atoms, and even more preferably an alkyl group having 1 to 8 carbon atoms. Furthermore, in the general formula (1), R is more preferably a linear alkyl group. Such a configuration of the onium functional group improves the adhesion between the insulating resin and the conductive particles, ensuring insulation, and further improving the reliability of conduction during thermocompression bonding.

[0085] From the viewpoint of facilitating the acquisition of monomers and the synthesis of polymers, as well as increasing the production efficiency of insulating resins, it is preferable that the organic polymer having an ionic group that constitutes the insulating resin has a constituent unit represented by the following general formula (2) or general formula (3).

[0086] [ka] In the general formula (2), X, R, and n have the same meanings as in the general formula (1). m is an integer of 0 to 5. - indicates a monovalent anion. When m is 0, X is directly bonded to the benzene ring.

[0087] [ka] In the general formula (3), X, R, and n have the same meanings as in the general formula (1). - indicates a monovalent anion. m 1 is an integer of 1 to 5. R5 is a hydrogen atom or a methyl group.

[0088] As examples of R in the general formula (2) and the general formula (3), the explanation of the functional group of R in the general formula (1) above is applied as appropriate. The ionic group may be bonded to the para-position, ortho-position, or meta-position relative to the CH group of the benzene ring in the general formula (2), and is preferably bonded to the para-position. In the general formula (2) and the general formula (3), monovalent An - Suitable examples of the halide ions include Cl. - , F - , Br - , I - Examples include:

[0089] In the general formula (2), m is preferably an integer of 0 or more and 2 or less, more preferably 0 or 1, and particularly preferably 1. In the general formula (3), m 1 is preferably 1 or more and 3 or less, more preferably 1 or 2, and most preferably 2.

[0090] The organic polymer having an ionic group preferably contains a monomer component having, for example, an onium-based functional group and an ethylenically unsaturated bond. From the viewpoint of facilitating the availability of the monomer and the synthesis of the polymer and improving the production efficiency of the insulating resin, the organic polymer having an ionic group also preferably contains a non-crosslinkable monomer component.

[0091] Examples of non-crosslinkable monomers having an onium functional group and an ethylenically unsaturated bond include ammonium group-containing monomers such as N,N-dimethylaminoethyl methacrylate, N,N-dimethylaminopropylacrylamide, and N,N,N-trimethyl-N-2-methacryloyloxyethyl ammonium chloride; sulfonium group-containing monomers such as phenyl methacrylate dimethylsulfonium methyl sulfate; 4-(vinylbenzyl)triethylphosphonium chloride, 4-(vinylbenzyl)trimethylphosphonium chloride, and 4-(vinylbenzyl)tributyl Examples of suitable monomers include phosphonium chloride, 4-(vinylbenzyl)trioctylphosphonium chloride, 4-(vinylbenzyl)triphenylphosphonium chloride, 2-(methacryloyloxyethyl)trimethylphosphonium chloride, 2-(methacryloyloxyethyl)triethylphosphonium chloride, 2-(methacryloyloxyethyl)tributylphosphonium chloride, 2-(methacryloyloxyethyl)trioctylphosphonium chloride, and 2-(methacryloyloxyethyl)triphenylphosphonium chloride. The organic polymer having an ionic group may contain two or more non-crosslinkable monomer components.

[0092] The organic polymer constituting the insulating resin may have ionic groups bonded to all of its monomer components, or may have ionic groups bonded to only a portion of all of the organic polymer's structural units. When ionic groups are bonded to only a portion of all of the organic polymer's structural units, the proportion of the monomer components to which ionic groups are bonded is preferably 0.01 mol% to 99 mol%, and more preferably 0.02 mol% to 95 mol%. Here, when the organic polymer contains an ethylenically unsaturated bond, the number of monomer components in the organic polymer is determined by counting a structure derived from one ethylenically unsaturated bond as one structural unit of the monomer. When an ionic group is contained in both a crosslinkable monomer and a non-crosslinkable monomer, the proportion of the monomer components is the total amount.

[0093] The insulating resin coating may be in the form of a layer of insulating fine particles made of insulating resin, or in the form of a continuous insulating resin film.

[0094] When the insulating resin is made of insulating fine particles, by thermocompression bonding conductive particles coated with the insulating fine particles between electrodes, the insulating fine particles melt, deform, peel off, or move on the conductive particle surface, exposing the metal surface of the conductive particle in the thermocompression bonded portion, thereby enabling conduction between the electrodes and obtaining connectivity. On the other hand, the surface portion of the conductive particle facing in a direction other than the thermocompression bonding direction is generally maintained in a state where the conductive particle surface is covered with the insulating fine particles, so that conduction in a direction other than the thermocompression bonding direction is prevented.

[0095] The insulating fine particles, containing the ionic groups on their surfaces, easily adhere to the conductive particles, thereby ensuring a sufficient proportion of the conductive particle surfaces covered with the insulating fine particles and effectively preventing the insulating fine particles from peeling off from the conductive particles, etc. Therefore, the insulating fine particles are more likely to exhibit a short-circuit prevention effect in a direction different from that between the opposing electrodes, and improved insulation in that direction can be expected.

[0096] The shape of the insulating fine particles is not particularly limited and may be spherical or may be a shape other than spherical. Examples of shapes other than spherical include fibrous, hollow, plate-like, and needle-like. The insulating fine particles may also have a large number of protrusions on their surface or may be amorphous. Spherical insulating fine particles are preferred in terms of adhesion to conductive particles and ease of synthesis.

[0097] The average particle diameter of the insulating fine particles is preferably 10 nm or more and 3,000 nm or less, more preferably 15 nm or more and 2,000 nm or less. When the average particle diameter of the insulating fine particles is within this range, the resulting coated particles do not cause short circuits in a direction different from that between the opposing electrodes, and electrical continuity between the opposing electrodes is easily ensured. The average particle diameter of the insulating fine particles is a value measured by observation using a scanning electron microscope, and specifically, is measured by the method described in the Examples below.

[0098] The particle size distribution of insulating fine particles measured by the above method usually has a width. In general, the width of the particle size distribution of a powder is expressed by the coefficient of variation (hereinafter also referred to as "CV") shown in the following formula (4). CV(%)=(standard deviation / average particle diameter)×100...(4) A larger CV indicates a wider particle size distribution, whereas a smaller CV indicates a sharper particle size distribution. The CV of the insulating fine particles used in this conductive material is preferably 0.1% to 20%, more preferably 0.5% to 15%, and particularly preferably 1% to 10%. A CV within this range has the advantage of allowing the thickness of the insulating fine particle coating layer to be uniform.

[0099] Alternatively, instead of the insulating fine particles arranged in layers, the insulating resin may be a continuous film. When the continuous film is an insulating resin having ionic groups, the conductive particles are thermocompressed between electrodes, whereby the continuous film melts, deforms, or peels off, exposing the surfaces of the conductive particles, thereby enabling electrical continuity between the electrodes and providing connectivity. In particular, the continuous film breaks when the conductive particles are thermocompressed between electrodes, resulting in an increase in the number of conductive particles with their surfaces exposed. On the other hand, in the surface portions of the conductive particles facing in a direction different from the thermocompression bonding direction, the state of coating of the conductive particles with the continuous film is generally maintained, preventing conduction in directions other than the thermocompression bonding direction. When the insulating resin is a continuous film, it is preferable that the continuous film has ionic groups on its surface.

[0100] The thickness of the continuous film is preferably 10 nm or more from the viewpoint of improving insulation in a direction different from that between the opposing electrodes, and is preferably 3,000 nm or less from the viewpoint of facilitating electrical conduction between the opposing electrodes. From this viewpoint, the thickness of the continuous film is preferably 10 nm or more and 3,000 nm or less, and more preferably 15 nm or more and 2,000 nm or less.

[0101] As with the insulating fine particles, the ionic group in the continuous film preferably forms part of the chemical structure of the insulating resin as part of the insulating resin that constitutes the continuous film. The ionic group in the continuous film is preferably contained in at least one structure of the structural unit of the insulating resin that constitutes the continuous film. The ionic group is preferably chemically bonded to the insulating resin that constitutes the continuous film, more preferably bonded to a side chain of the insulating resin.

[0102] When the conductive material has a continuous coating of insulating resin, it is preferable that the conductive particles are coated with insulating fine particles having ionic groups on their surfaces, and then the insulating fine particles are heated to form a continuous coating, or that the insulating fine particles are dissolved in an organic solvent to form a continuous coating. As described above, insulating fine particles having ionic groups are easily adhered to the conductive particles, which makes it possible to sufficiently coat the insulating fine particles on the conductive particle surface and to prevent the insulating fine particles from peeling off from the conductive particles. Therefore, the continuous coating obtained by heating or dissolving the insulating fine particles that coat the conductive particles can have a uniform thickness and a high coating rate on the conductive particle surface.

[0103] The conductive particles may be treated with a surface treatment agent in order to increase the affinity with the insulating resin and improve adhesion. Examples of the surface treatment agent include benzotriazole compounds, titanium compounds, higher fatty acids or derivatives thereof, phosphate esters, phosphites, etc. These may be used alone or in combination as needed.

[0104] The surface treatment agent may or may not be chemically bonded to the surface of the conductive particle. The surface treatment agent is sufficient as long as it is present on the surface of the conductive particle. In this case, the surface treatment agent may be present on the entire surface of the conductive particle, or only on a portion of the surface.

[0105] Examples of the triazole-based compounds include compounds having a nitrogen-containing heterocyclic structure having three nitrogen atoms in a five-membered ring.

[0106] Examples of triazole compounds include compounds having a triazole monocyclic structure that is not condensed with other rings, as well as compounds having a ring structure in which a triazole ring is condensed with other rings, such as a benzene ring or a naphthalene ring.

[0107] Among these, compounds having a ring structure in which a triazole ring is fused with another ring are preferred because of their excellent adhesion to insulating resins, and benzotriazole-based compounds, which are compounds having a structure in which a triazole ring is fused with a benzene ring, are particularly preferred. Benzotriazole compounds include those represented by the following general formula (4).

[0108] [ka] In the general formula (4), R 11 is a negative charge, a hydrogen atom, an alkali metal, an optionally substituted alkyl group, an amino group, a formyl group, a hydroxyl group, an alkoxy group, a sulfonic acid group, or a silyl group, and R 12 , R 13 , R 14 and R 15 are each independently a hydrogen atom, a halogen atom, an optionally substituted alkyl group, a carboxyl group, a hydroxyl group, or a nitro group.

[0109] R in the general paper formula (4) 11 Examples of the alkali metal represented by R include lithium, sodium, and potassium. 11 The alkali metal represented by R in general formula (4) is an alkali metal cation. 11 is an alkali metal, R 11 The bond between the nitrogen atom and the alkyl group may be an ionic bond. R in general formula (4) 11 , R 12 , R 13 , R 14 and R 15 Examples of the alkyl group represented by the formula (I) include those having 1 to 20 carbon atoms, and particularly preferably those having 1 to 12 carbon atoms. The alkyl group may be substituted, and examples of the substituent include an amino group, an alkoxy group, a carboxyl group, a hydroxyl group, an aldehyde group, a nitro group, a sulfonic acid group, a quaternary ammonium group, a sulfonium group, a sulfonyl group, a phosphonium group, a cyano group, a fluoroalkyl group, a mercapto group, and a halogen atom. R 11 The alkoxy group represented by the formula (I) preferably includes an alkoxy group having 1 to 12 carbon atoms. do. Also, R 12 , R 13 , R 14 and R 15 The number of carbon atoms of the alkoxy group as a substituent of the alkyl group represented by the general formula (4) is preferably 1 to 12. 12 , R 13 , R 14 and R 15 Examples of the halogen atom represented by the formula (I) include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

[0110] Specific triazole compounds include compounds having a triazole monocyclic structure such as 1,2,3-triazole, 1,2,4-triazole, 3-amino-1H-1,2,4-triazole, 5-mercapto-1H-1,2,3-triazole sodium, 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole, and 3-amino-5-mercapto-1,2,4-triazole, as well as compounds having a ring structure in which a triazole ring is condensed with another ring, such as benzotriazole, 1-methyl-1H-benzotriazole, 4-methyl-1H-benzotriazole, 5-methyl-1H-benzotriazole, 4-carboxy-1H-benzotriazole, 5-carboxy-1H-benzotriazole, 5-ethyl-1H-benzotriazole, and 5-propyl-1H-benzotriazo benzotriazole, 5,6-dimethyl-1H-benzotriazole, 1-aminobenzotriazole, 5-nitrobenzotriazole, 5-chlorobenzotriazole, 4,5,6,7-tetrabromobenzotriazole, 1-hydroxybenzotriazole, 1-(methoxymethyl)-1H-benzotriazole, 1H-benzotriazole-1-methanol, 1H-benzotriazole-1-carboxaldehyde, 1-(chloromethyl)-1H-benzotriazole, 1-hydroxy-6-(trifluoromethyl)benzotriazole, benzotriazole butyl ester, 4-carboxyl-1H-benzotriazole butyl ester, 4-carboxyl-1H-benzotriazole octyl ester, 1-[N,N-bis(2-ethylhexyl)aminomethyl]methylbenzotriazole, 2,2'-[[(methyl-1H-benzotriazol-1-yl)methyl]imino]bisethanol, tetrabutylphosphonium benzotriazolate, 1H-benzotriazol-1-yloxytris(dimethylamino)phosphonium hexafluorophosphate, 1H-benzotriazol-1-yloxytripyrrolidinophosphonium hexafluorophosphate, 1-(formamidomethyl)-1H-benzotriazole, 1-[bis(dimethylamino)methylene]-1H-benzotriazolium 3- Oxide hexafluorophosphate, 1-[bis(dimethylamino)methylene]-1H-benzotriazolium 3-oxide tetrafluoroborate, (6-chloro-1H-benzotriazol-1-yloxy)tripyrrolidinophosphonium hexafluorophosphate, O-(benzotriazol-1-yl)-N,N,N',N'-bis(tetramethylene)uronium hexafluorophosphate, O-(6-chlorobenzotriazol-1-yl)-N,N,N',N'-tetramethyluronium Tetrafluoroborate, O-(6-chlorobenzotriazol-1-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate, O-(benzotriazol-1-yl)-N,N,N',N'-bis(pentamethylene)uronium hexafluorophosphate, 1-(trimethylsilyl)-1H-benzotriazole, 1-[2-(trimethylsilyl)ethoxycarbonyloxy]benzotriazole, 1-(trifluoromethanesulfonyl)-1H-benzotriazole, (trimethylsilyl)-1H-benzotriazole, trifluoroacetyl)benzotriazole, tris(1H-benzotriazol-1-yl)methane, 9-(1H-benzotriazol-1-ylmethyl)-9H-carbazole, [(1H-benzotriazol-1-yl)methyl]triphenylphosphonium chloride, 1-(isocyanomethyl)-1H-benzotriazole, 1-[(9H-fluoren-9-ylmethoxy)carbonyloxy]benzotriazole, 1,2,3-benzotriazole sodium salt, naphthotriazole, and the like.

[0111] As the titanium-based compound, for example, a compound having a structure represented by the following general formula (5) is particularly preferred because, when present on the surface of a conductive particle, affinity between the insulating resin and the conductive particle can be easily obtained, and the compound is easily dispersed in a solvent, allowing the surface of the conductive particle to be uniformly treated.

[0112] [ka] In the general formula (5), R 21 is a divalent or trivalent group, and R 22 is an aliphatic hydrocarbon group having from 2 to 30 carbon atoms, an aryl group having from 6 to 22 carbon atoms, or an arylalkyl group having from 7 to 23 carbon atoms, p and r are each an integer of from 1 to 3, satisfying p+r=4, q is an integer of 1 or 2, and R 21 is a divalent group, q is 1, and R 21 When R is a trivalent group, q is 2. When q is 2, multiple R 22 may be the same or different. * represents a bond.

[0113] R 22 Examples of the aliphatic hydrocarbon group having 4 to 28 carbon atoms represented by the formula (I) include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, icosyl, henicosenyl, docosyl, etc. Examples of unsaturated aliphatic hydrocarbon groups include alkenyl groups such as dodecenyl, tridecenyl, tetradecenyl, pentadecenyl, hexadecenyl, heptadecenyl, nonadecenyl, icosenyl, eicosenyl, henicosenyl, and docosenyl. Examples of the aryl group having 6 to 22 carbon atoms include a phenyl group, a tolyl group, a naphthyl group, and an anthryl group. Examples of the arylalkyl group having 7 to 23 carbon atoms include a benzyl group, a phenethyl group, and a naphthylmethyl group. As the hydrophobic group, a straight-chain or branched-chain aliphatic hydrocarbon group is particularly preferred, and a straight-chain aliphatic hydrocarbon group is particularly preferred. In order to enhance the affinity between the insulating resin and the conductive particles, the aliphatic hydrocarbon group as the hydrophobic group is more preferably one having 4 to 28 carbon atoms, and most preferably one having 6 to 24 carbon atoms.

[0114] R 21 Examples of the divalent group represented by the formula include -O-, -COO-, -OCO-, and -OSO2-. 21 Examples of the trivalent group represented by the formula include -P(OH)(O-)2, -OPO(OH)-OPO(O-)2, and the like.

[0115] In the general formula (5), * represents a bond, which may be bonded to the metal coating of the conductive particle or to another group, etc. In this case, examples of the other group include hydrocarbon groups, and specific examples include alkyl groups having 1 to 12 carbon atoms.

[0116] The titanium-based compound having a structure represented by general formula (5) includes R 21 A compound having a structure in which R is a divalent group is preferred in terms of availability and the ability to process the conductive particles without impairing their conductive properties. 21 The structure in which is a divalent group is represented by the following general formula (6).

[0117] [ka] In the general formula (6), R 21 is a group selected from -O-, -COO-, -OCO-, and -OSO2-; p, r, and R 22 has the same meaning as general formula (II).

[0118] In the general formulas (5) and (6), r is preferably 2 or 3 from the viewpoint of improving the adhesion between the insulating resin and the conductive layer, and r is most preferably 3.

[0119] Specific examples of titanate compounds used in the surface treatment include isopropyl triisostearoyl titanate, isopropyl tridodecylbenzenesulfonyl titanate, isopropyl tris(dioctyl pyrophosphate) titanate, tetraisopropyl(dioctyl phosphite) titanate, tetraisopropyl bis(dioctyl phosphite) titanate, tetraoctyl bis(ditridecyl phosphite) titanate, tetra(2,2-diallyloxymethyl-1-butyl)bis(ditridecyl)phosphite titanate, bis(dioctyl pyrophosphate)oxyacetate titanate, and bis(dioctyl pyrophosphate)ethylene titanate, and these can be used alone or in combination of two or more. These titanate compounds are commercially available from, for example, Ajinomoto Fine-Techno Co., Ltd.

[0120] As the higher fatty acid, saturated or unsaturated, straight-chain or branched-chain mono- or polycarboxylic acids are preferred, saturated or unsaturated, straight-chain or branched-chain monocarboxylic acids are more preferred, and saturated or unsaturated, straight-chain monocarboxylic acids are even more preferred. The fatty acid preferably has 7 or more carbon atoms. Furthermore, the derivative refers to a salt or amide of the fatty acid.

[0121] The higher fatty acid or its derivative used in the surface treatment preferably has 7 to 23 carbon atoms, more preferably 10 to 20 carbon atoms. Examples of such higher fatty acids or their derivatives include saturated fatty acids such as capric acid, lauric acid, myristic acid, palmitic acid, and stearic acid, unsaturated fatty acids such as oleic acid, linoleic acid, linolenic acid, and arachidonic acid, and metal salts or amides thereof. Metal salts of higher fatty acids include salts of alkali metals, alkaline earth metals, transition metals such as Zr, Cr, Mn, Fe, Co, Ni, Cu, and Ag, and metals other than transition metals such as Al and Zn, with polyvalent metal salts such as Al, Zn, W, and V being preferred. Higher fatty acid metal salts may be mono-, di-, tri-, or tetra-forms depending on the valence of the metal. The higher fatty acid metal salt may also be any combination of these.

[0122] As the phosphate ester and phosphite ester, those having an alkyl group having 6 to 22 carbon atoms are preferably used. Examples of phosphate esters include hexyl phosphate, heptyl phosphate, monooctyl phosphate, monononyl phosphate, monodecyl phosphate, monoundecyl phosphate, monododecyl phosphate, monotridecyl phosphate, monotetradecyl phosphate, and monopentadecyl phosphate. Examples of phosphite esters include hexyl phosphite, heptyl phosphite, monooctyl phosphite, monononyl phosphite, monodecyl phosphite, monoundecyl phosphite, monododecyl phosphite, monotridecyl phosphite, monotetradecyl phosphite, and monopentadecyl phosphite.

[0123] The surface treatment agent used in the surface treatment has excellent affinity with the insulating resin and is preferably a triazole-based compound or a titanium-based compound from the viewpoint of increasing the coverage rate of the insulating resin, and particularly preferably benzotriazole, 4-carboxybenzotriazole, isopropyl triisostearoyl titanate, or tetraisopropyl (dioctyl phosphite) titanate.

[0124] The conductive particles can be treated with a surface treatment agent by dispersing the conductive particles in a solution of the surface treatment agent and then filtering the dispersed particles. Before the treatment with the surface treatment agent, the conductive particles may have been treated with another treatment agent or may be untreated. The concentration of the surface treatment agent in the solution of the surface treatment agent in which the conductive particles are dispersed is, for example, 0.01% by mass or more and 10.0% by mass or less. Examples of solvents for the solution of the surface treatment agent include water, alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, isopentyl alcohol, and cyclohexanol, ketones such as acetone, methyl isobutyl ketone, methyl ethyl ketone, and methyl-n-butyl ketone, esters such as methyl acetate and ethyl acetate, ethers such as diethyl ether and ethylene glycol monoethyl ether, normal hexane, cyclohexanone, toluene, 1,4-dioxane, N,N-dimethylformamide, and tetrahydrofuran. The conductive particles after dispersion and filtration and surface treatment are preferably dispersed again in a solvent to remove excess surface treatment agent.

[0125] The surface treatment of the conductive particles with the surface treatment agent can be carried out by mixing the conductive particles, the surface treatment agent, and a solvent at room temperature. Alternatively, the conductive particles and the surface treatment agent may be mixed in a solvent and then heated to promote the reaction. The heating temperature is, for example, 30°C or higher and 50°C or lower.

[0126] The present conductive particles have low connection resistance and excellent connection reliability, and are therefore suitable for use as a conductive material for, for example, anisotropic conductive films (ACFs), heat seal connectors (HSCs), and for connecting electrodes of liquid crystal display panels to the circuit board of a driving LSI chip. The present conductive particles may be used as is, or the present conductive particles may be dispersed in a binder resin to form a conductive material. The present conductive material may be used as is, or the present conductive material may be dispersed in a binder resin. The other forms of the conductive material are not particularly limited, and in addition to the above, examples include anisotropic conductive paste, conductive adhesive, anisotropic conductive ink, and the like.

[0127] Examples of the binder resin include thermoplastic resins and thermosetting resins. Examples of the thermoplastic resin include acrylic resin, styrene resin, ethylene-vinyl acetate resin, and styrene-butadiene block copolymer, while examples of the thermosetting resin include epoxy resin, phenol resin, urea resin, polyester resin, urethane resin, and polyimide resin.

[0128] In addition to the conductive particles and binder resin of the present invention, the conductive material may contain, as necessary, a tackifier, a reactivity aid, an epoxy resin curing agent, a metal oxide, a photoinitiator, a sensitizer, a curing agent, a vulcanizing agent, an anti-degradation agent, a heat-resistant additive, a thermal conductivity improver, a softener, a colorant, various coupling agents, or a metal deactivator.

[0129] In the conductive material, the amount of conductive particles used may be determined appropriately depending on the application. From the viewpoint of easily achieving electrical conduction without the conductive particles coming into contact with each other, the amount of conductive particles used is preferably, for example, 0.01 parts by mass or more and 50 parts by mass or less, particularly 0.03 parts by mass or more and 40 parts by mass or less, per 100 parts by mass of the conductive material.

[0130] The conductive particles of the present invention are particularly suitable for use as a conductive filler for a conductive adhesive, among the above-mentioned forms of conductive materials.

[0131] The conductive adhesive is preferably used as an anisotropic conductive adhesive that is placed between two substrates each having a conductive base material and adheres the conductive base material to establish electrical conductivity by heating and pressurization. This anisotropic conductive adhesive contains the conductive particles of the present invention and an adhesive resin. Any adhesive resin can be used without particular limitations as long as it is insulating and suitable for use as an adhesive resin. Either a thermoplastic or thermosetting resin may be used, and those that exhibit adhesive properties upon heating are preferred. Examples of such adhesive resins include thermoplastic, thermosetting, and UV-curable types. Other examples include semi-thermosetting types that exhibit intermediate properties between thermoplastic and thermosetting types, and hybrid types that combine thermosetting and UV-curable types. These adhesive resins can be selected appropriately depending on the surface characteristics and usage of the circuit board or other substrate to be adhered. In particular, adhesive resins containing a thermosetting resin are preferred due to their excellent material strength after adhesion.

[0132] Specific examples of adhesive resins include those prepared using one or a combination of two or more resins selected from the group consisting of ethylene-vinyl acetate copolymer, carboxyl-modified ethylene-vinyl acetate copolymer, ethylene-isobutyl acrylate copolymer, polyamide, polyimide, polyester, polyvinyl ether, polyvinyl butyral, polyurethane, SBS block copolymer, carboxyl-modified SBS copolymer, SIS copolymer, SEBS copolymer, maleic acid-modified SEBS copolymer, polybutadiene rubber, chloroprene rubber, carboxyl-modified chloroprene rubber, styrene-butadiene rubber, isobutylene-isoprene copolymer, acrylonitrile-butadiene rubber (hereinafter referred to as NBR), carboxyl-modified NBR, amine-modified NBR, epoxy resin, epoxy ester resin, acrylic resin, phenolic resin, and silicone resin as the main component. Among these, thermoplastic resins such as styrene-butadiene rubber and SEBS are preferred due to their excellent reworkability. As a thermosetting resin, epoxy resin is preferred. Of these, epoxy resin is most preferred because it has the advantages of high adhesive strength, excellent heat resistance and electrical insulation, and also low melt viscosity, allowing connection at low pressure.

[0133] The epoxy resin may be any commonly used polyhydric epoxy resin containing two or more epoxy groups per molecule. Specific examples include novolak resins such as phenol novolak and cresol novolak; polyhydric phenols such as bisphenol A, bisphenol F, bisphenol AD, resorcinol, and bishydroxydiphenyl ether; polyhydric alcohols such as ethylene glycol, neopentyl glycol, glycerin, trimethylolpropane, and polypropylene glycol; polyamino compounds such as ethylenediamine, triethylenetetramine, and aniline; and polycarboxylic compounds such as adipic acid, phthalic acid, and isophthalic acid, reacted with epichlorohydrin or 2-methylepichlorohydrin. Other examples include aliphatic and alicyclic epoxy resins such as dicyclopentadiene epoxide and butadiene dimer diepoxide. These may be used alone or in combination.

[0134] The various adhesive resins mentioned above include Na + and Cl - From the viewpoint of preventing ion migration, it is preferable to use a high-purity product in which impurity ions such as those mentioned above and hydrolyzable chlorine are reduced.

[0135] The amount of conductive particles used in the anisotropic conductive adhesive is usually 0.1 to 30 parts by mass, preferably 0.5 to 25 parts by mass, and more preferably 1 to 20 parts by mass, per 100 parts by mass of the adhesive resin component. By keeping the amount of conductive particles within this range, increases in connection resistance and melt viscosity are suppressed, connection reliability is improved, and sufficient anisotropy of the connection can be ensured.

[0136] In addition to the conductive particles and adhesive resin described above, the anisotropic conductive adhesive may contain additives known in the art. The amounts of these additives may be within the ranges known in the art. Examples of other additives include tackifiers, reactivity aids, epoxy resin curing agents, metal oxides, photoinitiators, sensitizers, curing agents, vulcanizing agents, anti-degradants, heat-resistant additives, thermal conductivity improvers, softeners, colorants, various coupling agents, and metal deactivators.

[0137] Examples of tackifiers include rosin, rosin derivatives, terpene resins, terpene phenol resins, petroleum resins, coumarone-indene resins, styrene resins, isoprene resins, alkylphenol resins, and xylene resins. Examples of reactive auxiliaries, i.e., crosslinking agents, include polyols, isocyanates, melamine resins, urea resins, utropines, amines, acid anhydrides, and peroxides. Examples of epoxy resin curing agents include 1-minute curing agents, ... child Anything having two or more active hydrogen atoms can be used without particular limitations. Specific examples include polyamino compounds such as diethylenetriamine, triethylenetetramine, metaphenylenediamine, dicyandiamide, and polyamidoamine; organic acid anhydrides such as phthalic anhydride, methylnadic anhydride, hexahydrophthalic anhydride, and pyromellitic anhydride; and novolak resins such as phenol novolak and cresol novolak. These can be used alone or in combination of two or more. A latent curing agent may also be used if necessary. Examples of usable latent curing agents include imidazoles, hydrazides, boron trifluoride-amine complexes, sulfonium salts, amine imides, polyamine salts, dicyandiamide, and modified products thereof. These can be used alone or in combination of two or more.

[0138] The anisotropic conductive adhesive is manufactured using a manufacturing device commonly used in the art. For example, conductive particles, an adhesive resin, and optionally a curing agent and various additives are blended and mixed in an organic solvent if the adhesive resin is a thermosetting resin. If the adhesive resin is a thermoplastic resin, the adhesive resin is melt-kneaded at a temperature above the softening point of the adhesive resin, specifically, preferably about 50 to 130°C, more preferably about 60 to 110°C. The anisotropic conductive adhesive thus obtained can be applied as a coating or in the form of a film.

[0139] The connection structure according to the present invention is obtained by connecting two circuit boards together using the conductive particles according to the present invention or the conductive material according to the present invention. Examples of the form of the connection structure include a connection structure between a flexible printed circuit board and a glass substrate, a connection structure between a semiconductor chip and a flexible printed circuit board, and a connection structure between a semiconductor chip and a glass substrate. [Example]

[0140] The present invention will be further described below with reference to examples, but the scope of the present invention is not limited to these examples.

[0141] The properties in the examples were measured by the following methods. (1) Average particle diameter 200 particles were randomly selected from a scanning electron microscope (SEM) photograph of the object to be measured, and the particle diameters were measured at a magnification of 10,000 times, and the arithmetic mean value was taken as the average particle diameter. (2) Thickness of the conductive layer The conductive particle was cut into two pieces, and the cross section of the cut surface was observed and measured using a scanning electron microscope (SEM). (3) Variation in the height of the protrusions The height of the protrusions was measured for the cross section of the conductive particle observed by SEM, and calculated using the following formula (1). TIFF0007803820000010.tif24151(4) Radius of curvature For the cross-section of the conductive particles observed by SEM, the radius of the circumscribed circle circumscribing the top part of the cross-section of each protrusion was measured as Ra, and the radius of the circumscribing circle circumscribing the surface of the lower layer of the conductive layer was measured as Rb. (5) Projected area of ​​conductive particles and area of ​​the top of the protrusions Measurement was performed by capturing SEM photographic images of the conductive particles into an automatic image analyzer (Luzex (registered trademark) AP, manufactured by Nireco Corporation).

[0142] Example 1 (1) Pretreatment of core particles Spherical styrene-acrylate-silica composite resin particles with an average particle size of 2.0 μm were used as core particles. 9 g of these particles were added to 200 mL of a conditioner solution (Rohm and Haas Electronic Materials' "Cleaner Conditioner 231") while stirring. The concentration of the conditioner solution was 40 mL / L. The solution was then stirred at 60°C for 30 minutes with ultrasonic waves to modify the surface and disperse the core particles. The solution was filtered, and the core particles were repulped and washed once to form a 200 mL slurry. 0.1 g of stannous chloride was added to the slurry. The mixture was stirred at room temperature for 5 minutes to sensitize the core particles, adsorbing tin ions onto their surfaces. The solution was then filtered, and the core particles were repulped and washed once to form a 200 mL slurry, which was then maintained at 60°C. 1.5 mL of a 0.11 mol / L palladium chloride solution was then added to the slurry. The core particles were activated by stirring at 60°C for 5 minutes, and the palladium ions were captured on their surfaces. The aqueous solution was then filtered, and the core particles were repulped and washed with hot water once to form a 100 mL slurry. 10 mL of a 0.5 g / L dimethylamine borane solution was added, and the mixture was stirred for 2 minutes while applying ultrasound to obtain a slurry of pretreated core particles.

[0143] (2) Preparation of plating solution 3 L of electroless nickel-phosphorus plating solution was prepared from an aqueous solution of 5 g / L sodium tartrate, 2 g / L nickel sulfate hexahydrate, 10 g / L trisodium citrate, 0.1 g / L sodium hypophosphite, and 2 g / L polyethylene glycol, and heated to 70°C.

[0144] (3) Electroless plating The pretreated core particle slurry was added to this electroless plating bath and stirred for 5 minutes until hydrogen bubbling ceased. 420 mL of a 224 g / L nickel sulfate aqueous solution and 420 mL of a mixed aqueous solution containing 210 g / L sodium hypophosphite and 80 g / L sodium hydroxide were continuously added to the slurry at a rate of 2.5 mL / min using a metering pump, and electroless plating was initiated. After the entire amounts of the nickel sulfate aqueous solution and the mixed aqueous solution of sodium hypophosphite and sodium hydroxide were added, stirring was continued for 5 minutes while maintaining the temperature at 70°C. The solution was then filtered, and the filtrate was washed three times and then dried in a vacuum dryer at 110°C to obtain conductive particles with protrusions.

[0145] (4) Processing of protrusions 20 g of the obtained conductive particles were placed in a ball mill container together with alumina balls, ethanol was added, and the particles were crushed at 80 rpm for 6 hours. The balls and slurry were then separated and dried in a vacuum dryer at 110°C to obtain conductive particles with low protrusion height. The protrusion height of the obtained conductive particles was 100.8 nm.

[0146] (5) Vacuum heat treatment The resulting conductive particles were placed in a rectangular container to a thickness of 5 mm. This was then placed in a vacuum heating furnace (Denken Hydental, KDF-75) and held at a vacuum of 10 Pa for 10 minutes. The temperature was then increased to 390°C for 2 hours for heat treatment. After heat treatment, the container was allowed to cool to room temperature (25°C) and then purged with nitrogen gas to release the vacuum and obtain heat-treated conductive particles. An SEM image of the resulting conductive particles is shown in Figure 2. The average particle diameter of the resulting conductive particles was 2.2 μm, the conductive layer thickness was 110 nm, and the protrusion height was 100.8 nm. The physical properties of the resulting conductive particles are shown in Table 1.

[0147] Example 2 (1) Pretreatment of core particles The same procedure as in Example 1 was carried out, except that resin particles having an average particle size of 2.0 μm (Optobeads, manufactured by Nissan Chemical Industries, Ltd.) were used as the core particles, to obtain a slurry of pretreated core particles. (2) Preparation of plating solution An electroless plating solution was prepared in the same manner as in Example 1(2). (3) Electroless plating The same procedure as in Example 1(3) was carried out to obtain conductive particles having protrusions. (4) Processing of protrusions The same procedure as in Example 1(4) was carried out to obtain conductive particles with a protrusion height of 101 nm. (5) Vacuum heat treatment Heat-treated conductive particles were obtained by the same procedure as in Example 1. The average particle diameter of the obtained conductive particles was 2.2 μm, the thickness of the conductive layer was 94.8 nm, and the height of the protrusions was 101 nm. The physical properties of the obtained conductive particles are shown in Table 1.

[0148] Example 3 The same operations as in Example 1 were carried out up to (3) electroless plating treatment in Example 1 to obtain conductive particles having protrusions. (4) Processing of protrusions The same procedure as in Example 1 was carried out except that the obtained conductive particles were crushed for 3 hours, to obtain conductive particles with a protrusion height of 145.3 nm. (5) Vacuum heat treatment The same operation as in Example 1 was carried out to obtain heat-treated conductive particles. An SEM photograph of the obtained conductive particles is shown in Figure 3. The obtained conductive particles had an average particle diameter of 2.2 μm, a conductive layer thickness of 97.8 nm, and a protrusion height of 145.3 nm. The physical properties of the obtained conductive particles are shown in Table 1.

[0149] Example 4 The same operations as in Example 1 were carried out up to (3) electroless plating treatment in Example 1 to obtain conductive particles having protrusions. (4) Processing of protrusions The same procedure as in Example 1 was carried out except that the obtained conductive particles were crushed using zirconia balls at 80 rpm for 4 hours, to obtain conductive particles with a protrusion height of 115.6 nm. (5) Vacuum heat treatment The same operation as in Example 1 was carried out to obtain heat-treated conductive particles. An SEM photograph of the obtained conductive particles is shown in Figure 4. The obtained conductive particles had an average particle diameter of 2.2 μm, a conductive layer thickness of 95.8 nm, and a protrusion height of 115.6 nm. The physical properties of the obtained conductive particles are shown in Table 1.

[0150] Comparative Example 1 In Example 1, (4) Processing of protrusions Conductive particles were obtained by the same procedure as in Example 1, except that step 1 was not carried out. The physical properties of the obtained conductive particles are shown in Table 1.

[0151] Comparative Example 2 The same operations as in Example 1 were carried out up to (3) electroless plating treatment in Example 1 to obtain conductive particles having protrusions. (4) Processing of protrusions The same procedure as in Example 1 was carried out except that the obtained conductive particles were crushed for 1 hour, to obtain conductive particles with a protrusion height of 174.9 nm. (5) Vacuum heat treatment Heat-treated conductive particles were obtained by the same procedure as in Example 1. An SEM photograph of the obtained conductive particles is shown in Figure 5. The obtained conductive particles had an average particle diameter of 2.2 µm, a conductive layer thickness of 99.9 nm, and a protrusion height of 174.9 nm. The physical properties of the obtained conductive particles are shown in Table 1.

[0152] [Table 1]

[0153] [Evaluation of connection resistance and insulation properties] Using the conductive particles of the examples and comparative examples, the connection resistance and insulating properties were evaluated by the following methods. An insulating paste was prepared by mixing 15 parts by weight of the conductive particles obtained in the examples or comparative examples with an insulating adhesive containing 100 parts by weight of epoxy resin, 150 parts by weight of curing agent, and 70 parts by weight of toluene. This paste was applied to a silicone-treated polyester film using a bar coater, and then dried to form a thin film on the film. The resulting thin-film-formed film was placed between a glass substrate with aluminum electrodes vapor-deposited on the entire surface and a polyimide film substrate with copper electrode patterns formed at a 50 μm pitch, and then pressed together to prepare a sample for conducting resistance measurement. Electrical connections were made to the resulting sample for conducting resistance measurement, and the connection resistance of the sample was measured at room temperature (25°C, 50% RH) to evaluate the connection resistance. The connection resistance was evaluated using a multimeter R6552 (manufactured by Advantest Corporation) according to the following criteria. The results are shown in Table 2. ○: Resistance is less than 2Ω △: Resistance is 2Ω or more and less than 5Ω ×: Resistance is 5Ω or more

[0154] Furthermore, the insulation property was evaluated based on the rate at which short circuits occurred in 100 samples for measuring the electrical resistance. The insulation property was evaluated by the following method. The results are shown in Table 2. ○: Short circuit occurrence rate is less than 5% △: Short circuit occurrence rate is 5% or more but less than 30% ×: Short circuit occurrence rate is 30% or more

[0155] [Table 2]

[0156] From these results, it can be seen that the conductive particles obtained in the examples have lower connection resistance values ​​and are superior in insulating properties compared to the conductive particles obtained in the comparative examples. [Explanation of symbols]

[0157] 1. Conductive particles 2. Core particles 3. Conductive layer 4...Protrusion 5...Plant part of protrusion 5a and 5b: End of flat surface 6. Surface of the lower layer of the conductive layer

Claims

1. Conductive particles having a core particle and a conductive layer having a plurality of protrusions on the surface of the core particle, wherein when the cross sections of 20 of the conductive particles are observed under an SEM and the heights of all of the protrusions of each conductive particle are measured, the variation in height of the protrusions calculated from the following calculation formula (1) is 0.01 or more and 0.25 or less, the core particle is a conductive particle composed of a material containing an organic substance, and when the radius of curvature of the top part of the protrusions is Ra and the radius of curvature of the surface of the lower layer of the conductive layer at the part where the protrusions are formed is Rb, the ratio of Ra to Rb (Ra / Rb) is 0.15 or more and 1.20 or less. [Equation 1] 【number】 【number】

2. The conductive particle according to claim 1 , wherein the top portions of the protrusions are substantially flat.

3. 2. The conductive particle according to claim 1, wherein the ratio of the total area of ​​the top portions of the protrusions to the projected area of ​​the conductive particle is 0.50 or more.

4. 2. The conductive particle according to claim 1, wherein the conductive layer contains at least one selected from the group consisting of nickel, gold, and palladium.

5. 2. The conductive particles according to claim 1, having an average particle size of 0.1 μm or more and 50 μm or less.

6. The conductive particle according to claim 1 , wherein the thickness of the conductive layer is 0.1 nm or more and 2,000 nm or less.

7. 2. The conductive particle according to claim 1, wherein the height of the protrusions is 20 nm or more and 1,000 nm or less.

8. The conductive particle according to claim 1 , wherein at least one of the protrusions has an irregular shape.

9. A conductive material comprising the conductive particles according to claim 1 and an insulating resin.

10. A step of forming a conductive layer on the surface of the core particles; forming a protrusion on the conductive layer so as to protrude from the surface; A step of leveling the height of the protrusions The method for producing conductive particles according to claim 1 , wherein the core particles are made of a material containing an organic substance.

11. The method for producing conductive particles according to claim 10, wherein the step of forming the protrusions comprises forming the protrusions on the conductive layer using autolysis products of the electroless nickel plating bath as nuclei.

12. 12. The method for producing conductive particles according to claim 10 or 11, wherein the step of leveling the height of the protrusions comprises polishing the top portions of the protrusions obtained in the step of forming the protrusions to level the height of the protrusions.

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