Conductive particles, their manufacturing method and conductive material containing them

Abstract

To provide a conductive particle with lower connection resistance and higher connection reliability than ever before.SOLUTION: A conductive particle manufacturing method for forming a conductive layer on a surface of a core material particle by electroless plating, has a step of adding a sulfur compound to an electroless plating reaction solution during forming the conductive layer. It is preferable that the sulfur compound is at least one kind selected from a group consisting of 2-mercaptobenzothiazole, 2-mercaptobenzoxazole and 2-mercaptobenzimidazol.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to conductive particles and conductive materials containing the same. [Background technology]

[0002] Conductive particles used as conductive materials in anisotropic conductive materials such as anisotropic conductive films and anisotropic conductive pastes are generally known to have a conductive layer made of metal formed on the surface of a core particle, and this conductive layer provides electrical connection between electrodes and wiring.

[0003] When electrodes are connected under pressure using such conductive particles, the oxide film formed on the electrode surface must be removed to ensure electrical continuity, and the conductive particles must be hard enough to withstand the initial pressure. For example, Patent Document 1 discloses conductive particles that can reduce connection resistance and improve connection reliability by incorporating a cross-linkable monomer having multiple ethylenically unsaturated groups into the core resin particles, thereby controlling the ratio of the compression hardness at 10% compression to the compression hardness at 50% compression within a specific range. However, in the initial stage of pressure connection between electrodes, the characteristics of the conductive layer as well as the characteristics of the core particles are likely to have an impact.

[0004] From this perspective, Patent Document 2 describes that conductive particles having a conductive layer including a crystalline layer having a nickel-phosphorus crystal structure have a compression hardness of a specific value or more when compressed by 5%. Patent Document 3 also describes conductive particles having a conductive portion with a plurality of protrusions on the outer surface, the proportion of (111) planes in X-ray diffraction of these protrusions being 50% or more, and the average maximum diameter of the base being 1 nm or more and 500 nm or less. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] WO2014 / 007334 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-214511 [Patent Document 3] Japanese Patent Application Laid-Open No. 2016-119304 Summary of the Invention [Problem to be solved by the invention]

[0006] Both Patent Document 2 and Patent Document 3 aim to reduce connection resistance and increase connection reliability when electrodes are electrically connected by improving the properties of the conductive layer, thereby eliminating the oxide film formed on the electrode and conductive layer and obtaining conductive particles that increase the contact area between the electrode and conductive particles after connection, but there is room for further improvement.

[0007] Therefore, an object of the present invention is to provide conductive particles having lower connection resistance and higher connection reliability than ever before. [Means for solving the problem]

[0008] As a result of extensive research to solve the above-mentioned problems, the inventors have discovered that conductive particles in which the ratio of the hardness of a conductive layer that is hard enough to remove the oxide film formed on the electrode at the initial stage of pressure connection of the electrode and the hardness of the conductive particles after connection satisfies a specific range can reduce connection resistance and also have excellent connection reliability, and have thus completed the present invention.

[0009] That is, the present invention provides conductive particles having a conductive layer formed on the surface of a core particle, the conductive particles having a maximum compressive hardness of 14700 N / mm 2 The maximum compressive hardness is observed at a compression rate of less than 5%, and the average compressive hardness at a compression rate of 20% to 50% is 1300N / mm 2 More than 5000N / mm 2 and the ratio of the maximum value of compression hardness to the average value of compression hardness at a compression rate of 20% to 50% is 1.5 to 50.

[0010] The present invention also provides a method for producing conductive particles by forming a conductive layer on the surface of a core particle by electroless plating, which method includes a step of adding a sulfur compound to an electroless plating reaction solution during the formation of the conductive layer. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide conductive particles having low connection resistance and high connection reliability. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is an SEM image of the conductive particles obtained in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0013] The conductive particles of the present invention have a maximum compression hardness (hereinafter sometimes referred to as "K value") of 14700 N / mm 2 or more, preferably 16000N / mm 2 The maximum compressive hardness is 30,000 N / mm or more, and the compressibility is less than 5%, preferably at a compressibility of 1%, 2%, 3% or 4%. 2 It is preferable that: The compression hardness in the present invention is a value obtained by measuring the load value F (N) when a load is applied to a conductive particle of radius R (mm) at a loading rate of 2.23 mN / sec using a microcompression tester (e.g., MCTM-500 manufactured by Shimadzu Corporation) and calculating it using the following formula. Compression hardness (N / mm 2 )=(3 / √2)×F×S -3 / 2 ×R -1 / 2 Here, the radius R (mm) of the conductive particles is a value calculated from the average particle diameter described below, and the compression ratio is the rate of change in length in the particle diameter direction, and is the ratio of the compression displacement S (mm) to the average particle diameter (mm).

[0014] Furthermore, the conductive particles of the present invention have an average compression hardness of 1300 N / mm at a compression ratio of 20% or more and 50% or less. 2 More than 5000N / mm 2 Less than 2000 to 3500 N / mm 2 The ratio of the maximum compression hardness to the average compression hardness at a compression rate of 20% to 50% is 1.5 to 50, preferably 2 to 30, particularly preferably 3 to 15. Here, the average value of the compression hardness at a compression ratio of 20% or more and 50% or less is the average value of the K values ​​at compression ratios of 20%, 30%, 40% and 50%.

[0015] In the present invention, it is preferable that the ratio of the K value at a compression rate of 3% to the K value at a compression rate of 40% is 1.5 or more and 70 or less, particularly 3 or more and 50 or less, since this results in conductive particles with low connection resistance and high connection reliability.

[0016] As described above, the conductive particles of the present invention have the property of being hard at the beginning of compression and becoming flexible with further compression, which makes it possible to sufficiently remove the oxide film formed on the electrode at the early stage of pressure connection of the electrodes, thereby reducing the connection resistance. Furthermore, since the conductive particles remain flexible after pressure connection, the contact area with the electrode can be maintained, resulting in excellent connection reliability.

[0017] The conductive particles of the present invention are obtained by forming a conductive layer on the surface of a core particle. The core particles can be inorganic or organic, as long as they are particulate. Examples of inorganic core particles include metal particles such as gold, silver, copper, nickel, palladium, and solder; alloys; glass; ceramics; silica; metal or non-metal oxides (including hydrates); metal silicates including aluminosilicates; metal carbides; metal nitrides; metal carbonates; metal sulfates; metal phosphates; metal sulfides; metal acid salts; metal halides; and carbon. Examples of organic core particles include natural fibers, natural resins, thermoplastic resins such as polyethylene, polypropylene, polyvinyl chloride, polystyrene, polybutene, polyamide, polyacrylate, polyacrylonitrile, polyacetal, ionomers, and polyester; alkyd resins; phenolic resins; urea resins; benzoguanamine resins; melamine resins; xylene resins; silicone resins; epoxy resins; and diallyl phthalate resins. These may be used alone or in combination of two or more.

[0018] The core particles may be composed of both inorganic and organic materials instead of the aforementioned inorganic and organic materials. When the core particles are composed of both inorganic and organic materials, the inorganic and organic materials may be present in the core particles in a core-shell configuration, such as an inorganic core and an inorganic shell covering the core's surface, or an organic core and an inorganic shell covering the core's surface. Other examples include blend configurations in which inorganic and organic materials are mixed or randomly fused within a single core particle. Core particles composed of both inorganic and organic materials can use the materials constituting the inorganic or organic core particles described above. These core particles may be composed of either the inorganic or organic material alone, or two or more inorganic and organic materials combined together.

[0019] The core particles are preferably made of a resin, more preferably a thermoplastic resin, and the use of such a core material can improve the dispersion stability of the particles and also improve electrical conductivity by providing appropriate elasticity when electrically connecting electronic circuits.

[0020] When an organic substance is used as the core particles, it is preferable that the core particles have no glass transition temperature or that the glass transition temperature is greater than 100°C, because this facilitates the maintenance of the shape of the core particles in the anisotropic conductive connection step and the metal coating formation step. Furthermore, when the core particles have a glass transition temperature, it is preferable that the glass transition temperature is 200°C or less, because this facilitates the softening of the conductive particles in the anisotropic conductive connection, thereby increasing the contact area and facilitating electrical continuity. From this perspective, when the core particles have a glass transition temperature, the glass transition temperature is more preferably greater than 100°C and less than 180°C, and particularly preferably greater than 100°C and less than 160°C. The glass transition temperature can be determined, for example, by differential scanning calorimetry (DSC) as the intersection of the tangent to the original baseline and the inflection point in the baseline shift portion of the DSC curve.

[0021] When an organic substance is used as the core particle, if the organic substance is a highly crosslinked resin, the glass transition temperature is barely observed even when measurements are attempted up to 200°C using the above method. In this specification, such particles are also referred to as particles without a glass transition point, and such core particles may be used in the present invention. Specific examples of core particle materials without a glass transition temperature include those obtained by copolymerizing the monomers constituting the organic substance exemplified above with a crosslinkable monomer. Examples of crosslinkable monomers include tetramethylene di(meth)acrylate, ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, ethylene oxide di(meth)acrylate, tetraethylene oxide (meth)acrylate, 1,6-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 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. Core particles made of such hard organic materials are widely used, particularly in the field of COG (chip on glass).

[0022] There are no particular limitations on the shape of the core particles. Generally, the core particles are spherical. However, the core particles may have shapes other than spherical, such as fibrous, hollow, plate-like, or needle-like, and may have a large number of protrusions on their surfaces or may be amorphous. In the present invention, spherical core particles are preferred because they have excellent filling properties and are easy to coat with metal.

[0023] The conductive layer formed on the surface of the core particle is made of a conductive metal. Examples of metals constituting the conductive layer include metals such as gold, platinum, silver, copper, iron, zinc, nickel, tin, lead, antimony, bismuth, cobalt, indium, titanium, antimony, bismuth, germanium, aluminum, chromium, palladium, tungsten, and molybdenum, as well as alloys thereof, and metal compounds such as ITO and solder. Among these, gold, silver, copper, nickel, palladium, and solder are preferred due to their low electrical resistance, and nickel, gold, nickel alloys, and gold alloys are particularly preferred. One type of metal may be used, or two or more types may be used in combination.

[0024] The conductive layer 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, it is preferable that the outermost layer is made of at least one material selected from nickel, gold, silver, copper, palladium, a nickel alloy, a gold alloy, a silver alloy, a copper alloy, and a palladium alloy. The conductive layer does not have to cover the entire surface of the core particle, but may cover only a portion of it. 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. The thickness of the conductive layer is preferably 0.1 nm or more and 2000 nm or less, and more preferably 1 nm or more and 1500 nm or less. When the conductive particle has protrusions described below, the height of the protrusions is not included in the thickness of the conductive layer referred to here. In the present invention, 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 using an SEM.

[0025] 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 metal-coated particles is within the above range, it is easy to ensure conduction between the opposing electrodes without causing a short circuit in a direction different from that between the opposing electrodes. In the present invention, the average particle diameter of the conductive particles is a value measured using a scanning electron microscope (SEM). Specifically, the average particle diameter of the conductive particles is measured by the method described in the Examples. The particle diameter is the diameter of a circular conductive particle image. When the conductive particles are not spherical, the particle diameter refers to the longest length (maximum length) of the line segments crossing the conductive particle image.

[0026] When conductive particles have protrusions on their surfaces, the height of the protrusions is preferably 20 nm to 1,000 nm, more preferably 50 nm to 800 nm. The number of protrusions varies depending on the particle size of the conductive particles. Preferably, the number of protrusions per conductive particle is 1 to 20,000, more preferably 5 to 5,000, which is advantageous in terms of further improving the conductivity of the conductive particles. Furthermore, the length of the base of the protrusions is preferably 5 nm to 1,000 nm, more preferably 10 nm to 800 nm. The length of the base of the protrusion refers to the length along the surface of the conductive particle at the location where the protrusion is formed, as measured using an electron microscope image of the cross-section of the particle, and the height of the protrusion refers to the shortest distance from the base of the protrusion to the apex of the protrusion. If a single protrusion has multiple apexes, the highest apex is used as the height of that protrusion. The length of the base of the protrusion and the height of the protrusion are arithmetic average values ​​measured for 20 different particles observed under an electron microscope.

[0027] The shape of the conductive particles is not particularly limited, although it depends on the shape of the core particles. For example, they may be fibrous, hollow, plate-like, or needle-like, and may have many protrusions on their surface or may be amorphous. In the present invention, a spherical shape or a shape having many protrusions on the outer surface is preferred in terms of excellent packing properties and connectivity. In particular, a shape having large protrusions on the outer surface tends to result in conductive particles with high compression hardness at the initial stage of compression.

[0028] Methods for forming a conductive layer on the surface of core particles include dry methods using vapor deposition, sputtering, mechanochemical methods, hybridization methods, etc., and wet methods using electrolytic plating, electroless plating, etc. Alternatively, a conductive layer may be formed on the surface of core particles by combining these methods.

[0029] In the present invention, it is preferable to form a conductive layer on the surface of the core particles by electroless plating, since this makes it easy to obtain conductive particles having the desired compression hardness.

[0030] Hereinafter, a case where a nickel-phosphorus plating layer is formed as the conductive layer will be described. When a conductive layer is formed on the surface of a core particle by electroless plating, the surface of the core particle preferably has the ability to capture precious metal ions or is surface-modified to have the ability to capture precious metal ions. 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 an amino group, imino group, amido group, imido group, cyano group, hydroxyl group, nitrile group, carboxyl group, or the like is present on the surface of the core particle, the surface of the core particle has the ability to capture precious metal ions. When the surface is modified to have the ability to capture precious metal ions, for example, the method described in JP-A-61-64882 can be used.

[0031] Such core particles are used to support precious metals on their surfaces. Specifically, the core particles are dispersed in a dilute acidic aqueous solution of a precious metal salt such as palladium chloride or silver nitrate. This allows precious metal ions to be captured on the particle surface. The concentration of the precious metal salt is 1 / m of the surface area of ​​the particle. 2 1x10 -7 ~1×10 -2 A molar range is sufficient. The core particles with the captured precious metal ions are separated from the system 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.

[0032] 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. To adsorb tin ions onto the surface of the particles, for example, the surface-modified core particles may be placed in an aqueous solution of stannous chloride and stirred for a predetermined period of time.

[0033] The core particles thus pretreated are then subjected to a conductive layer forming process. There are two types of conductive layer forming processes: a process for forming a conductive layer having protrusions, and a process for forming a conductive layer with a smooth surface. First, the process for forming a conductive layer having protrusions will be described.

[0034] In the process of forming the conductive layer having the protrusions, the following first and second steps are carried out. The first step is an electroless nickel plating step in which an aqueous slurry of core particles is mixed with an electroless nickel plating bath containing a dispersant, nickel salt, a reducing agent, a complexing agent, etc. In this first step, the plating bath self-decomposes simultaneously with the formation of a conductive layer on the core particles. Because this self-decomposition occurs near the core particles, the self-decomposition products are captured on the surface of the core particles during the formation of the conductive layer, generating nuclei for microprojections, which simultaneously form the conductive layer. The generated microprojection nuclei serve as base points for the growth of protrusions.

[0035] In the first step, the core particles described above are thoroughly dispersed in water, preferably in a range of 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 normal stirring, high-speed stirring, or a shear dispersion device such as a colloid mill or homogenizer. Ultrasound may also be used in the dispersion. If necessary, a dispersant such as a surfactant may be added during the dispersion. Next, the aqueous slurry of the dispersed core particles is added to an electroless nickel plating bath containing a nickel salt, a reducing agent, a complexing agent, and various additives, to carry out the first electroless plating step.

[0036] Examples of the dispersant include nonionic surfactants, zwitterionic surfactants, and / or water-soluble polymers. Examples of nonionic surfactants include polyoxyalkylene ether surfactants such as polyethylene glycol, polyoxyethylene alkyl ether, and polyoxyethylene alkylphenyl ether. Examples of zwitterionic surfactants include betaine surfactants such as alkyldimethyl acetate betaine, alkyldimethylcarboxymethyl acetate betaine, and alkyldimethylamino acetate betaine. Examples of water-soluble polymers include polyvinyl alcohol, polyvinylpyrrolidinone, and hydroxyethyl cellulose. These dispersants can be used alone or in combination. 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 liquid (electroless nickel plating bath). In particular, it is preferable for the amount of dispersant used to be in the range of 1 to 10 g / L relative to the volume of the liquid (electroless nickel plating bath), as this further improves the adhesion of the conductive layer.

[0037] The nickel salt may be, for example, nickel chloride, nickel sulfate, or nickel acetate, and its concentration is preferably in the range of 0.1 to 50 g / L. The reducing agent may be, for example, the same as those used for reducing the precious metal ions described above, and is selected based on the constituent material of the target base coating. When a phosphorus compound, such as sodium hypophosphite, is used as the reducing agent, its concentration is preferably in the range of 0.1 to 50 g / L.

[0038] Examples of complexing agents include compounds that have a complexing effect on nickel ions, such as carboxylic acids (salts) 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; amine acids such as ethylenediamine and alkylamines; other ammonium compounds; EDTA; and pyrophosphate (salts). These can be used alone or in combination. The concentration is preferably 1 to 100 g / L, more preferably 5 to 50 g / L. The pH of the electroless nickel plating bath at this stage is preferably 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 first step is considered complete when the generation of hydrogen gas has completely ceased.

[0039] In the second step, following the first step, electroless nickel plating is performed by using either (i) a first aqueous solution containing one of a nickel salt, a reducing agent, and an alkali, and a second aqueous solution containing the remaining two, or (ii) a first aqueous solution containing a nickel salt, a second aqueous solution containing a reducing agent, and a third aqueous solution containing an alkali, and adding these aqueous solutions simultaneously and sequentially to the solution from the first step. Adding these solutions restarts the plating reaction, and by adjusting the amounts added, the resulting conductive layer can be controlled to the desired film thickness. After the addition of the electroless nickel plating solution is complete, stirring is continued while maintaining the solution temperature for a while after hydrogen gas generation has completely ceased to be observed, to complete the reaction.

[0040] 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. The same applies to the case of (ii) above.

[0041] 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.

[0042] In either case (i) or (ii), the concentration of the nickel salt in the aqueous solution is preferably 10 to 1000 g / L, particularly 50 to 500 g / L. When a phosphorus compound is used as the reducing agent, the concentration of the reducing agent is preferably 100 to 1000 g / L, particularly 100 to 800 g / L. When a boron compound is used as the reducing agent, the concentration is preferably 5 to 200 g / L, particularly 10 to 100 g / L. When hydrazine or a derivative thereof is used as the reducing agent, the concentration is preferably 5 to 200 g / L, particularly 10 to 100 g / L. The concentration of the alkali is preferably 5 to 500 g / L, particularly 10 to 200 g / L.

[0043] The second step is carried out continuously after the first step is completed, but alternatively, the first and second steps may be carried out intermittently. In this case, after the first step is completed, the core particles and the plating solution are separated by a method such as filtration, the core particles are dispersed in water to prepare a new aqueous slurry, 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 thereto, and a dispersant is dissolved in a concentration of preferably 0.5 to 30 g / L, more preferably 1 to 10 g / L, to prepare an aqueous slurry. The second step may then be carried out by adding the aqueous solutions described above to the aqueous slurry. In this manner, a conductive layer having protrusions can be formed.

[0044] Next, a process for forming a conductive layer with a smooth surface will be described below. A conductive layer with a smooth surface can be formed by reducing the concentration of nickel salt in the electroless nickel plating bath in the first step of the treatment for forming the conductive layer having protrusions. That is, the nickel salt may be, for example, nickel chloride, nickel sulfate, or nickel acetate, and its concentration is preferably in the range of 0.01 to 0.5 g / L. A conductive layer with a smooth surface can be formed by performing the first and second steps described above without reducing the concentration of nickel salt in the electroless nickel plating bath.

[0045] In the present invention, it is preferable to add a sulfur compound during the formation of the conductive layer, since this tends to result in conductive particles with a large compression hardness in the initial stage of compression. Sulfur compounds include 2-mercaptobenzothiazole, 2-mercaptobenzoxazole, 2-mercaptobenzimidazole, 2-mercapto-1-methylimidazole, thioglycolic acid, thiodiglycolic acid, cysteine, saccharin, thiamine nitrate, sodium N,N-diethyl-dithiocarbamate, 1,3-diethyl-2-thiourea, dipyridine, N-thiazole-2-sulfamylamide, 1,2,3-benzotriazole-2-thiazoline-2- Examples of sulfur compounds include thiol, thiazole, thiourea, ethylenethiourea, thiozole, sodium thioindoxylate, o-sulfonamidobenzoic acid, sulfanilic acid, acid orange, methyl orange, naphthionic acid, naphthalene-α-sulfonic acid, 1-naphthol-4-sulfonic acid, Scheffer's acid, sulfadiazine, ammonium thiocyanate, potassium thiocyanate, sodium thiocyanate, rhodanine, ammonium sulfide, sodium sulfide, and ammonium sulfate. These sulfur compounds can be used alone or in combination of two or more. The amount of sulfur compound used is preferably such that the total sulfur compound concentration in the electroless plating reaction solution is 0.01 ppm by mass or more but 100 ppm by mass or less, more preferably 0.1 ppm by mass or more but 50 ppm by mass or less. If the amount of sulfur compound used is too small, the effect of increasing the compression hardness at the initial stage of compression is difficult to achieve, while if the amount is too large, the compression hardness increases from the middle to late stages of compression, which is undesirable.

[0046] The sulfur compound may be added during the formation of the conductive layer, but is preferably added during the second step. Starting the addition 5 to 20 minutes after the start of the second step is particularly preferred, as this facilitates increasing the compression hardness at the initial stage of compression. The sulfur compound may be added all at once, in multiple portions, or continuously, but adding the entire amount at once is preferred, as this facilitates increasing the compression hardness at the initial stage of compression. In the case of adding the sulfur compound all at once, the addition time is preferably 30 seconds or less, more preferably 15 seconds or less, depending on the scale of the reaction system, for example, when a 1 L reactor is used. There is no lower limit to the addition time, but it is usually 0.1 seconds or more, or 0.5 seconds or more. Adding the sulfur compound within this range makes it easier to increase the compression hardness at the initial stage of compression. In the present invention, by adding a sulfur compound in this manner in the process of forming the conductive layer having the above-mentioned protrusions, the protrusions tend to become larger, thereby obtaining the effect of further increasing the compression hardness at the initial stage of compression. In this way, the conductive particles of the present invention are obtained.

[0047] When the conductive particles of the present invention are used as a conductive filler in a conductive adhesive as described below, their surfaces can be 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 or the like is applied, and so that it is broken by the heat and pressure applied when bonding two electrodes using the 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 may only cover a portion of the surface of the conductive particles.

[0048] A wide variety of insulating resins known in the art can be used, including, for example, phenolic resin, urea resin, melamine resin, allyl resin, furan resin, polyester resin, epoxy resin, silicone resin, polyamide-imide resin, polyimide resin, polyurethane resin, fluororesin, polyolefin resin (e.g., polyethylene, polypropylene, polybutylene), polyalkyl(meth)acrylate resin, poly(meth)acrylic acid resin, polystyrene resin, acrylonitrile-styrene-butadiene resin, vinyl resin, polyamide resin, polycarbonate resin, polyacetal resin, ionomer resin, polyethersulfone resin, polyphenyloxide resin, polysulfone resin, polyvinylidene fluoride resin, ethyl cellulose, and cellulose acetate.

[0049] Methods for forming an insulating coating layer on the surface of conductive particles 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.

[0050] The conductive particles of the present invention thus obtained are suitably used, for example, as an anisotropic conductive film (ACF), a heat seal connector (HSC), a conductive material for connecting electrodes of a liquid crystal display panel to a circuit board of a driving LSI chip, etc. In particular, the conductive particles of the present invention are suitably used as a conductive filler for a conductive adhesive.

[0051] 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 pressurizing. 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.

[0052] 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 thermosetting resins, 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.

[0053] The epoxy resin may be any commonly used polyhydric epoxy resin having 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.

[0054] It is preferable to use high-purity adhesive resins with reduced impurity ions (Na, Cl, etc.) and hydrolyzable chlorine as the various adhesive resins mentioned above, from the viewpoint of preventing ion migration.

[0055] The amount of the conductive particles of the present invention 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 using conductive particles in this range, increases in connection resistance and melt viscosity are suppressed, connection reliability is improved, and connection anisotropy can be sufficiently ensured.

[0056] 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.

[0057] Examples of tackifiers include rosin, rosin derivatives, terpene resins, terpene phenol resins, petroleum resins, coumarone-indene resins, styrene-based resins, isoprene-based 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. Any epoxy resin curing agent having two or more active hydrogen atoms per minute 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 novolac resins such as phenol novolac and cresol novolac. These can be used alone or in combination. A latent curing agent may also be used if necessary. Usable latent curing agents include, for example, 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.

[0058] The anisotropic conductive adhesive is manufactured using a manufacturing apparatus commonly used in the art. For example, the conductive particles of the present invention and an adhesive resin, as well as a curing agent and various additives as needed, are blended together, and if the adhesive resin is a thermosetting resin, they are mixed in an organic solvent. If the adhesive resin is a thermoplastic resin, they are 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 may be applied as a coating or in the form of a film. [Example]

[0059] 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. The properties in the examples were measured by the following methods. (1) Compression hardness of conductive particles (K value) The K value was determined by the above-mentioned method using a microcompression tester (MCTM-500, manufactured by Shimadzu Corporation). In addition, the K value when the compression rate is X% may be expressed as "X% K value." (2) Average particle size 200 particles were randomly extracted from a scanning electron microscope (SEM) photograph of the measurement target, 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.

[0060] Example 1 (1) Pretreatment Spherical benzoguanamine-based soft resin particles with an average particle size of 3.0 μm were used as core particles. 9 g of these particles were added to 200 mL of an aqueous conditioner solution (Rohm and Haas Electronic Materials' "Cleaner Conditioner 231") while stirring. The concentration of the aqueous conditioner solution was 40 mL / L. The solution was then stirred at 60°C for 30 minutes with ultrasonic waves to modify the surface of the core particles and disperse them. This 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 this slurry. The mixture was stirred at room temperature for 5 minutes to perform a sensitization treatment, in which tin ions were adsorbed onto the surface of the core particles. 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 aqueous 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.

[0061] (2) Preparation of plating bath Three liters of an electroless nickel-phosphorus plating bath was prepared from an aqueous solution containing 5 g / L of sodium tartrate, 2 g / L of nickel sulfate hexahydrate, 10 g / L of trisodium citrate, 0.1 g / L of sodium hypophosphite, and 2 g / L of polyethylene glycol, and the temperature was raised to 70°C.

[0062] (3) Electroless plating The slurry of the pretreated core particles was added to this electroless plating bath and stirred for 5 minutes, after which it was confirmed that the hydrogen bubbling had stopped. To this slurry, 420 mL of a 224 g / L nickel sulfate solution and 420 mL of a mixed aqueous solution containing 210 g / L sodium hypophosphite and 80 g / L sodium hydroxide were continuously added in portions at a rate of 2.5 mL / min using a metering pump, and electroless plating was initiated. Ten minutes after the start of plating, 2-mercaptobenzothiazole was added over 1 second to achieve a final concentration of 7.5 ppm by mass in the resulting solution. Forty minutes after the start of plating, the addition rate of both solutions was increased to 4.7 mL / min. After the entire nickel sulfate solution and the mixed aqueous solution of sodium hypophosphite and sodium hydroxide were added, the mixture was stirred for 5 minutes while maintaining the temperature at 70°C. The solution was then filtered, and the filtrate was washed three times and dried in a vacuum dryer at 110°C to obtain conductive particles with a conductive layer made of a nickel-phosphorus alloy. The resulting conductive particles had an average particle size of 3.22 μm, a conductive layer thickness of 110 nm, and large protrusions. An SEM image is shown in Figure 1. The obtained conductive particles showed the highest compression hardness at a compression ratio of 3%. Table 1 shows the compression hardness at each compression ratio.

[0063] Example 2 Conductive particles were produced in the same manner as in Example 1, except that 2-mercaptobenzoxazole was added instead of 2-mercaptobenzothiazole in (3) the electroless plating treatment. The resulting conductive particles had an average particle size of 3.22 μm, a conductive layer thickness of 110 nm, and large protrusions. The resulting conductive particles showed the highest compression hardness at a compression ratio of 4%. The compression hardness at each compression ratio is shown in Table 1.

[0064] Example 3 Conductive particles were produced in the same manner as in Example 1, except that the concentration of nickel sulfate hexahydrate in (2) Preparation of Plating Bath was changed from 2 g / L to 0.1 g / L. The obtained conductive particles had an average particle size of 3.22 μm, a conductive layer thickness of 110 nm, and a smooth shape without protrusions. The obtained conductive particles showed the highest compression hardness at a compression ratio of 3%. The compression hardness at each compression ratio is shown in Table 1.

[0065] Comparative Example 1 (1) Pretreatment Spherical benzoguanamine-based soft resin particles with an average particle size of 3.0 μm were used as core particles. 9 g of these particles were added to 200 mL of an aqueous conditioner solution (Rohm and Haas Electronic Materials' "Cleaner Conditioner 231") while stirring. The concentration of the aqueous 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. This 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 this slurry. The mixture was stirred at room temperature for 5 minutes to perform a sensitization treatment, in which tin ions were adsorbed onto the surface of the core particles. 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 aqueous 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.

[0066] (2) Preparation of plating bath Three liters of an electroless nickel-phosphorus plating bath was prepared from an aqueous solution containing 5 g / L of sodium tartrate, 2 g / L of nickel sulfate hexahydrate, 10 g / L of trisodium citrate, 0.1 g / L of sodium hypophosphite, and 2 g / L of polyethylene glycol, and the temperature was raised to 70°C.

[0067] (3) Electroless plating The slurry of the pretreated core particles was added to this electroless plating bath and stirred for 5 minutes, after which it was confirmed that the hydrogen bubbling had stopped. To this slurry, 420 mL of a 224 g / L nickel sulfate solution and 420 mL of a mixed aqueous solution containing 210 g / L sodium hypophosphite and 80 g / L sodium hydroxide were continuously added in portions at a rate of 2.5 mL / min using a metering pump, and electroless plating was initiated. After the entire nickel sulfate 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 dried in a vacuum dryer at 110 °C to obtain conductive particles with a conductive layer made of a nickel-phosphorus alloy. The resulting conductive particles had an average particle size of 3.22 μm, a conductive layer thickness of 110 nm, and protrusions. The resulting conductive particles also exhibited the highest compression hardness at a compression ratio of 2%. Table 1 shows the compression hardness at each compression ratio.

[0068] Comparative Example 2 (1) Pretreatment Spherical benzoguanamine-based soft resin particles with an average particle size of 3.0 μm were used as core particles. 9 g of these particles were added to 200 mL of an aqueous conditioner solution (Rohm and Haas Electronic Materials' "Cleaner Conditioner 231") while stirring. The concentration of the aqueous 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. This 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 this slurry. The mixture was stirred at room temperature for 5 minutes to perform a sensitization treatment, in which tin ions were adsorbed onto the surface of the core particles. 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 aqueous 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.

[0069] (2) Preparation of plating bath 3 L of an electroless nickel-phosphorus plating bath was prepared from an aqueous solution containing 5 g / L of sodium tartrate, 2 g / L of nickel sulfate hexahydrate, 10 g / L of trisodium citrate, 0.1 g / L of sodium hypophosphite, and 2 g / L of polyethylene glycol. 2-Mercaptobenzothiazole was added to the solution so that the final concentration in the solution was 7.5 ppm by mass, and the solution was heated to 70°C.

[0070] (3) Electroless plating The slurry of the pretreated core particles was added to this electroless plating bath and stirred for 5 minutes, after which it was confirmed that the hydrogen bubbling had stopped. To this slurry, 420 mL of a 224 g / L nickel sulfate solution and 420 mL of a mixed aqueous solution containing 210 g / L sodium hypophosphite and 80 g / L sodium hydroxide were continuously added in portions at a rate of 2.5 mL / min using a metering pump, and electroless plating was initiated. After the entire nickel sulfate 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 dried in a vacuum dryer at 110 °C to obtain conductive particles with a nickel-phosphorus alloy coating. The resulting conductive particles had an average particle size of 3.05 μm, a conductive layer thickness of 25 nm, and protrusions. The resulting conductive particles also exhibited the highest compression hardness at a compression ratio of 2%. Table 1 shows the compression hardness at each compression ratio.

[0071] [Table 1]

[0072] [Evaluation of connection resistance and connection reliability] Using the conductive particles of the examples and comparative examples, the connection resistance and connection reliability were evaluated by the following methods. An insulating paste was prepared by mixing 15 parts by weight of the coated particles obtained in the Examples and 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 entirely coated with aluminum and a polyimide film substrate with a 50 μm-pitch copper pattern to prepare a sample for conducting resistance measurement. Electrical connections were made, and the connection resistance of this sample was measured at room temperature (25°C, 50% RH). The lower the connection resistance, the better the conductive particle's connection resistance. The results are shown in Table 2. In addition, the samples for measuring the electrical resistance were placed in a sealed container and subjected to a pressure cooker test in which they were subjected to an environment of 121°C, 100% relative humidity, and 2 atmospheres for 10 hours. After the pressure cooker test, the connection resistance of the samples was measured at room temperature (25°C, 50% RH). The smaller the difference in connection resistance before and after the pressure cooker test, the higher the connection reliability of the conductive particles can be evaluated. The results are shown in Table 2.

[0073] [Table 2]

[0074] These results show that the conductive particles obtained in Examples 1 to 3 have lower resistance values ​​than the conductive particles obtained in Comparative Examples 1 and 2. Furthermore, it can be seen that the conductive particles obtained in Examples 1 to 3 maintain good conductivity without an increase in connection resistance value even after the pressure cooker test.

Claims

1. A method for producing conductive particles, comprising forming a conductive layer on the surface of a core particle by electroless plating, The maximum compressive hardness of the conductive particles is 14700 N / mm ２ or more, and the compressive hardness is at its highest when the compressibility is less than 5%; The average compression hardness at a compression rate of 20% to 50% is 1300 N / mm ２ More than 5000N / mm ２ is less than The ratio of the maximum value of compression hardness to the average value of compression hardness at a compression rate of 20% or more and 50% or less is 3 or more and 15 or less, A method for producing conductive particles, comprising the step of adding a sulfur compound to the electroless plating reaction solution during the formation of the conductive layer.

2. 2. The method for producing conductive particles according to claim 1, wherein the sulfur compound is at least one selected from the group consisting of 2-mercaptobenzothiazole, 2-mercaptobenzoxazole, and 2-mercaptobenzimidazole.

3. 3. The method for producing conductive particles according to claim 1, wherein the sulfur compound is added within 30 seconds.

4. 4. The method for producing conductive particles according to claim 1, wherein the amount of the sulfur compound added is an amount such that the total sulfide concentration in the electroless plating reaction solution is 0.01 ppm or more and 500 ppm or less.

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