CN115667580A

CN115667580A - Conductive particle, conductive material using same, and connection structure

Info

Publication number: CN115667580A
Application number: CN202180036685.3A
Authority: CN
Inventors: 高桥哲; 田杉直也; 成桥智真
Original assignee: Nippon Chemical Industrial Co Ltd
Current assignee: Nippon Chemical Industrial Co Ltd
Priority date: 2020-05-20
Filing date: 2021-05-18
Publication date: 2023-01-31
Also published as: TW202219318A; KR20230011946A; WO2021235435A1

Abstract

The present invention provides a conductive particle having excellent storage stability, excellent corrosion resistance, and low connection resistance, wherein a nickel plating layer is formed as a conductive layer on the surface of a core particle, and the conductive particle has a molar ratio of carbon to the total of nickel and phosphorus (C/(Ni + P)) or a molar ratio of carbon to the total of nickel and boron (C/(Ni + B)) of 0.0002 to 1.65, a molar ratio of oxygen to the total of nickel and phosphorus (O/(Ni + P)) or a molar ratio of oxygen to the total of nickel and boron (O/(Ni + B)) of 0.0001 to 1.8, and a molar ratio of phosphorus to nickel (P/Ni), or a molar ratio of boron to nickel (B/Ni)) of 0.003 to 0.7, as measured by a scanning Auger electron spectrometer.

Description

Conductive particle, conductive material using same, and connection structure

Technical Field

The present invention relates to conductive particles, a conductive material containing the conductive particles, and a connection structure using the conductive material.

Background

As conductive particles used as a conductive material as an anisotropic conductive material such as an anisotropic conductive film or an anisotropic conductive paste, it is generally known that conductive particles in which a conductive layer made of a metal is formed on the surface of a core material particle and electrodes or wirings are electrically connected through the conductive layer.

As the conductive layer of the conductive particles, a nickel plating film obtained by an electroless plating method is generally used, and various attempts have been made to express target characteristics. As an example thereof, patent document 1 describes that in order to obtain conductive particles having excellent storage stability, the surfaces of the conductive particles are treated with a treatment liquid containing a radical polymerizable compound, an acidic compound, and water, and thereby a uniform resin coating is formed on the surfaces of the conductive particles, thereby suppressing the activity of the conductive layer. Patent document 2 describes that a coated conductive particle having excellent storage stability and the like is provided by a conductive particle having an organometallic complex that covers at least a part of the surface of the conductive particle.

In addition, in order to obtain conductive particles having excellent storage stability, the conductive layer is also required to have high corrosion resistance. As such a technique, for example, patent document 3 describes conductive particles in which a hydrophobic group containing phosphorus is introduced to the surface of a conductive layer. This can suppress oxidation of the conductive layer and improve corrosion resistance. Patent document 4 describes conductive particles containing nickel, phosphorus, and tungsten in a specific range of amounts in a conductive layer, the conductive layer containing phosphorus in an inner region and tungsten in an outer region of the conductive layer. It is reported that thus corrosion does not proceed easily even if exposed in the presence of an acid. In these patent documents, an attempt is made to impart corrosion resistance by modifying the conductive layer.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2003-77335

Patent document 2: japanese patent laid-open publication No. 2017-134902

Patent document 3: japanese laid-open patent publication No. 2010-278026

Patent document 4: japanese patent laid-open publication No. 2015-110834

Disclosure of Invention

Technical problem to be solved by the invention

In general, the storage stability of the conductive particles can be achieved by suppressing the deterioration of the surface of the conductive layer such as oxidation of the metal, and therefore, the surface of the conductive layer and the vicinity thereof are protected by the methods described in patent documents 1 to 4, but when an anisotropic conductive material such as an anisotropic conductive film or an anisotropic conductive paste is produced, the surface of the conductive layer is protected, and the connection resistance is increased, which has been a problem.

Accordingly, an object of the present invention is to provide conductive particles having excellent storage stability, excellent corrosion resistance, and low connection resistance.

Technical solution for solving technical problem

The present inventors have found that when a specific element present in a surface layer of a conductive layer made of a nickel plating layer is present at a certain ratio to the total amount of nickel and phosphorus or boron, the storage stability and corrosion resistance are excellent, and have completed the present invention.

That is, the present invention provides a conductive particle in which a nickel plating layer is formed as a conductive layer on a surface of a core material particle, wherein a molar ratio of carbon to a total of nickel and phosphorus (C/(Ni + P)) or a molar ratio of carbon to a total of nickel and boron (C/(Ni + B)) is 0.0002 to 1.65, a molar ratio of oxygen to a total of nickel and phosphorus (O/(Ni + P)) or a molar ratio of oxygen to a total of nickel and boron (O/(Ni + B)) is 0.0001 to 2.0, and a molar ratio of phosphorus to nickel (P/Ni) or a molar ratio of boron to nickel (B/Ni) is 0.003 to 0.7, as measured by a scanning auger electron spectroscopy apparatus.

The present invention also provides an electrically conductive particle having a nickel plating layer as a conductive layer formed on a surface of a core particle, wherein the conductive particle has CH within 1nm in a depth direction from the surface of the conductive layer as measured by a time of flight secondary ion mass spectrometer (TOF-SIMS) ₄ N ⁺ Intensity of positive ion count relative to Ni ⁺ Counting intensity of Positive ions (CH) ₄ N ⁺ /Ni ⁺ ) Is 0.1 or less, or C ₂ H ₃ O ₂ ^－ Intensity of negative ion count with respect to Ni ^－ Intensity of negative ion count (C) ₂ H ₃ O ₂ ^－ /Ni ^－ ) Is 10.0 or less, or PO ₂ ^－ Intensity of negative ion count relative to Ni ^－ Counting intensity of negative ions (PO) ₂ ^－ /Ni ^－ ) Is 10.0 or less, or B ₂ O ₄ H ₃ ^－ And B ₃ O ₆ H ₄ ^－ Intensity of negative ion count with respect to Ni ^－ Count intensity of negative ion ((B) ₂ O ₄ H ₃ ^－ +B ₃ O ₆ H ₄ ^－ )/Ni ^－ ) Is 10.0 or less.

The present invention also provides a method for producing conductive particles, which comprises a step of forming a conductive layer on the surface of a core material particle to obtain conductive particles, and a step of heating the obtained conductive particles at a temperature of 200 to 600 ℃ under a vacuum of 1000Pa or less.

Effects of the invention

The present invention can provide conductive particles having excellent storage stability, excellent corrosion resistance, and low connection resistance.

Drawings

Fig. 1 is an SEM image of the conductive particles obtained in example 1.

Fig. 2 is an SEM image of the conductive particles obtained in example 4.

Detailed Description

The conductive particle of the present invention is obtained by forming a nickel plating layer as a conductive layer on the surface of a core material particle, and has a molar ratio of carbon to the total of nickel and phosphorus (C/(Ni + P)) or a molar ratio of carbon to the total of nickel and boron (C/(Ni + B)) within 5nm from the surface of the conductive layer of 0.0002 to 1.65, preferably 0.0005 to 1.55, a molar ratio of oxygen to the total of nickel and phosphorus (O/(Ni + P)) or a molar ratio of oxygen to the total of nickel and boron (O/(Ni + B)) of 0.0001 to 2.0, preferably 0.0003 to 1.8, and a molar ratio of phosphorus to nickel (P/Ni) or a molar ratio of boron to nickel (P/Ni) of 0.003 to 0.7, preferably 0.005 to 0.5.

In the present invention, the molar ratio of each element is a value obtained by measuring the atomic% of carbon, oxygen, nickel, and phosphorus or boron within 5nm from the surface of the conductive layer using a scanning auger electron spectroscopy analyzer (hereinafter, also referred to as AES analyzer) and calculating the total of the measured values of each element of carbon and oxygen with respect to the measured values of nickel and phosphorus or nickel and boron and the measured value of phosphorus or boron with respect to the measured value of nickel. As an AES analyzer, PHI-710 manufactured by ULVAC-PHI, inc., for example, can be used.

If the molar ratio of each element of carbon and oxygen to the total of nickel and phosphorus or nickel and boron and the molar ratio of phosphorus or boron to nickel are less than the lower limit of the above range, the crystal structure portion becomes too much and becomes a starting point of corrosion, and therefore, the storage stability is deteriorated, and if the molar ratio exceeds the upper limit of the above range, the amorphous structure portion becomes too much and the connection resistance becomes high.

The conductive particle of the present invention is obtained by forming a nickel plating layer as a conductive layer on the surface of a core particle, and has a CH of not more than 1nm from the surface of the conductive layer as measured by a time-of-flight secondary ion mass spectrometer (hereinafter sometimes referred to as TOF-SIMS) ₄ N ⁺ Intensity of positive ion count relative to Ni ⁺ Intensity of positive ion Count (CH) ₄ N ⁺ /Ni ⁺ ) Is 0.1 or less, preferably 0.05 or less, or C ₂ H ₃ O ₂ ^－ Intensity of negative ion count relative to Ni ^－ Intensity of negative ion count (C) ₂ H ₃ O ₂ ^－ /Ni ^－ ) Is 10.0 or less, preferably 9.0 or less, or PO ₂ ^－ Intensity of negative ion count relative to Ni ^－ Counting intensity of negative ions (PO) ₂ ^－ /Ni ^－ ) Is 10.0 or less, preferably 9.0 or less, or B ₂ O ₄ H ₃ ^－ And B ₃ O ₆ H ₄ ^－ Intensity of negative ion count with respect to Ni ^－ Count intensity of negative ion ((B) ₂ O ₄ H ₃ ^－ +B ₃ O ₆ H ₄ ^－ )/Ni ^－ ) Is 10.0 or less, preferably 9.0 or less. As TOF-SIMS, for example, TOF-SIMS5 manufactured by ION-TOF corporation can be used.

CH ₄ N ⁺ Intensity of positive ion count relative to Ni ⁺ Intensity of positive ion Count (CH) ₄ N ⁺ /Ni ⁺ )、C ₂ H ₃ O ₂ ^－ Intensity of negative ion count relative to Ni ^－ Intensity of negative ion count (C) ₂ H ₃ O ₂ ^－ /Ni ^－ )、PO ₂ ^－ Intensity of negative ion count with respect to Ni ^－ Counting intensity of negative ions (PO) ₂ ^－ /Ni ^－ ) Or B ₂ O ₄ H ₃ ^－ And B ₃ O ₆ H ₄ ^－ Intensity of negative ion count relative to Ni ^－ Count intensity of negative ion ((B) ₂ O ₄ H ₃ ^－ +B ₃ O ₆ H ₄ ^－ )/Ni ^－ ) When the content is less than the above range, corrosion can be suppressed, and the connection resistance after pressure connection is low, which is preferable. On the other hand, if the amount exceeds the above range, the conductive layer is easily corroded, and the connection reliability after the pressure connection is affected.

CH as mentioned above ₄ N ⁺ Is a positive ion derived from an amine compound, C ₂ H ₃ O ₂ ^－ Is a negative ion derived from an organic acid, the above PO ₂ ^－ Is a negative ion derived from a phosphoric acid compound, the above B ₂ O ₄ H ₃ ^－ And B ₃ O ₆ H ₄ ^－ Is a negative ion derived from a boric acid compound.

The amine compound, the organic acid, the phosphoric acid compound, and the boric acid compound are derived from a complexing agent, a dispersing agent, a reducing agent, a pH buffer, a surfactant, and the like, which are contained in an electroless plating solution when the method for producing conductive particles of the present invention is carried out, as described later.

The complexing agent is an effective component because it forms a stable complex with nickel ions, prevents precipitation of a nickel compound such as nickel hydroxide, and further allows the precipitation reaction of nickel to proceed at an appropriate rate, and various complexing agents used in known electroless nickel plating solutions can be used. Specific examples of such complexing agents include monocarboxylic acids such as acetic acid, propionic acid and butyric acid and soluble salts thereof, dicarboxylic acids such as oxalic acid and adipic acid and soluble salts thereof, oxycarboxylic acids such as malic acid and tartaric acid and soluble salts thereof, aminocarboxylic acids such as glycine and alanine and soluble salts thereof, ethylenediamine tetraacetic acid, ethylenediamine derivatives such as dienol (versenol, N-hydroxyethylethylenediamine-N, N '-triacetic acid) and quadrol (N, N' -tetrahydroxyethylethylenediamine) and soluble salts thereof, phosphonic acids such as 1-hydroxyethane-1, 1-diphosphonic acid and ethylenediamine tetramethylene phosphonic acid and soluble salts thereof, pyrophosphoric acid and soluble salts thereof, and the like. These complexing agents may be used alone in 1 kind, or 2 or more kinds may be mixed and used.

Examples of the amine compound include aliphatic amines such as methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethylenediamine, triethanolamine, N-diisopropylethylamine, tetramethylethylenediamine, and hexamethylenediamine, aromatic amines such as aniline, benzylamine, and N-phenylhydroxylamine, hydroxylamines such as O-methylhydroxylamine and O-carboxyhydroxylamine, heterocyclic amines such as pyrrole, pyrazole, imidazole, pyridine, oxazole, thiazole, benzothiazole, triazole, and benzotriazole, alkali metal salts thereof, and amino acids such as alanine, arginine, glutamine, glutamic acid, glycine, leucine, phenylalanine, cysteine, histidine, glutathione, methionine, asparagine, and aspartic acid.

Examples of the organic acid include saturated aliphatic carboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, valeric acid, lauric acid, tridecanoic acid, palmitic acid and stearic acid and alkali metal salts thereof, unsaturated aliphatic carboxylic acids such as acrylic acid, methacrylic acid, oleic acid, linoleic acid and α -linolenic acid and alkali metal salts thereof, saturated dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid and adipic acid and alkali metal salts thereof, unsaturated dicarboxylic acids such as maleic acid and fumaric acid and alkali metal salts thereof, aconitic acid and alkali metal salts thereof, aromatic carboxylic acids such as benzoic acid, salicylic acid and phthalic acid and alkali metal salts thereof, hydroxycarboxylic acids such as lactic acid, glyceric acid, malic acid, tartaric acid, 2-hydroxybutyric acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, citric acid, leucine acid, pantoic acid, pantothenic acid and oxycephalic acid (cerebellonic acid) and alkali metal salts thereof, ethylenediaminetetraacetic acid and disodium ethylenediaminetetraacetate.

Examples of the phosphoric acid compound include oxyphosphoric acid and soluble salts thereof such as phosphorous acid, hypophosphorous acid and phosphoric acid, pyrophosphoric acid and soluble salts thereof, phosphoric acid esters and soluble salts thereof such as monododecyl phosphate, phosphorous acid esters and soluble salts thereof, and phosphonic acid and derivatives thereof. The phosphoric acid compound is derived from a phosphorus compound such as sodium hypophosphite or potassium hypophosphite, which is a reducing agent contained in the electroless plating solution.

Examples of the boric acid compound include boric anhydride, pyroboric acid, orthoboric acid, and derivatives thereof. The boric acid compound is derived from a boron compound such as methyl hexaborane, dimethylamine borane, diethylamine borane, morpholine borane, pyridylamine borane, piperidine borane, ethylenediamine diborane, tert-butylamine borane, imidazole borane, methoxyethylamine borane, sodium borohydride, potassium borohydride and the like which are reducing agents contained in an electroless plating solution.

The conductive particle of the present invention is a conductive particle in which a conductive layer is formed on the surface of a core particle.

The core material particles may be any particles, and any particles may be used without particular limitation, regardless of whether they are inorganic or organic. Examples of the inorganic core material particles include metal particles such as gold, silver, copper, nickel, palladium, and solder, alloys, glasses, ceramics, silica, metal or nonmetal 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. On the other hand, examples of the core material particles of the organic material include thermoplastic resins such as natural fibers, natural resins, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polybutene, polyamide, polyacrylate, polyacrylonitrile, polyacetal, ionomer, and polyester, and thermosetting resins such as alkyd resins, phenol resins, urea resins, benzoguanamine resins, melamine resins, xylene resins, silicone resins, epoxy resins, and diallyl phthalate resins. These may be used alone, or 2 or more of them may be used in combination.

The core material particles may be made of a material containing both an inorganic substance and an organic substance, instead of being made of a material containing either one of the inorganic substance and the organic substance. When the core material particles are made of a material containing both inorganic substances and organic substances, examples of the mode of existence of the inorganic substances and organic substances in the core material particles include: a mode in which the core is made of an inorganic material and the shell is made of an inorganic material covering the surface of the core; or a core-shell type structure such as a structure having a core made of an organic material and a shell made of an inorganic material covering the surface of the core. In addition to these, a blend type structure in which an inorganic material and an organic material are mixed in one core material particle, or randomly fused, or the like can be mentioned.

The core material particles are preferably made of a material containing an organic substance or both of an inorganic substance and an organic substance, and more preferably made of a material containing both of an inorganic substance and an organic substance. The inorganic substance is preferably glass, ceramic, silica, metal or nonmetal oxide (including hydrous matters), metal silicate including aluminosilicate, metal carbide, metal nitride, metal carbonate, metal sulfate, metal phosphate, metal sulfide, metal acid salt, metal halide and carbon. The organic material is preferably a thermoplastic resin such as natural fiber, natural resin, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polybutylene, polyamide, polyacrylate, polyacrylonitrile, polyacetal, ionomer, and polyester. By using the core material made of such a material, the dispersion stability of the particles can be improved, and at the time of electrical connection of the electronic circuit, appropriate elasticity can be expressed to improve conduction.

In the case of using an organic material as the core material particles, it is preferable that the glass transition temperature is not higher than 100 ℃ or the glass transition temperature is higher than 100 ℃ from the viewpoint of easily maintaining the shape of the core material particles and easily maintaining the shape of the core material particles in the step of forming the metal coating. The glass transition temperature can be determined, for example, as the intersection of the original base line of the base line shift portion of a DSC curve obtained by Differential Scanning Calorimetry (DSC) and the tangent to the inflection point.

In the case of using an organic material as the core material particles, when the organic material is a highly crosslinked resin, the baseline shift is hardly observed even when the measurement of the glass transition temperature is attempted to 200 ℃ by the above-mentioned method. In the present specification, such particles are also referred to as particles having no glass transition temperature, and such core material particles can be used in the present invention. As a specific example of the core particle material having no glass transition temperature, a core particle material can be obtained by copolymerizing a crosslinkable monomer in combination with a monomer constituting the organic material exemplified above. Examples of the crosslinkable monomer include a silane-containing monomer such as tetramethylene di (meth) acrylate, ethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, ethylene oxide di (meth) acrylate, tetracyclooxyethylene (meth) acrylate, 1, 6-hexane di (meth) acrylate, neopentyl glycol di (meth) acrylate, 1, 9-nonanediol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, tetramethylolmethane di (meth) acrylate, tetramethylolmethane tri (meth) acrylate, tetramethylolmethane tetra (meth) acrylate, tetramethylolpropane tetra (meth) acrylate, dipentaerythritol penta (meth) acrylate, glycerol di (meth) acrylate, a multifunctional (meth) acrylate such as glycerol tri-di (meth) acrylate, divinylbenzene, divinyltoluene and the like, a vinyltrimethoxysilane, a trimethoxysilylstyrene, a gamma- (meth) acryloxypropyltrimethoxysilane and the like, a triallyl isocyanurate, a phthalic acid ester, a diallylamide, a diallyl ether and the like. In particular, in the field of COG (Chip on Glass), core particles made of such a hard organic material are often used.

The shape of the core material particle is not particularly limited. The core particles are generally spherical. However, the core material particle may have a shape other than a spherical shape, for example, a fiber shape, a hollow shape, a plate shape, or a needle shape, may have a plurality of protrusions on the surface thereof, or may be amorphous. In the present invention, spherical core particles are preferable because they have excellent filling properties and are easily covered with metal.

The conductive layer formed on the surface of the core material particle is made of a metal having conductivity. Examples of the metal constituting the conductive layer include metals such as 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, alloys thereof, and metal compounds such as ITO and solder. Among them, gold, silver, copper, nickel, palladium, rhodium, or solder is preferable because of its low resistance, and nickel, gold, a nickel alloy, or a gold alloy is particularly preferably used. The number of the metal may be 1, or 2 or more kinds may be used in combination.

The conductive layer may have a single-layer structure or a multilayer structure. In the case of a laminated structure composed of a plurality of layers, the outermost surface layer is preferably at least 1 selected from the group consisting of nickel, gold, silver, copper, palladium, a nickel alloy, a gold alloy, a silver alloy, a copper alloy, and a palladium alloy.

The outermost surface layer of the conductive particle of the present invention is a nickel-phosphorus plating layer or a nickel-boron plating layer.

The conductive layer may not cover the entire surface of the core material particle, and may cover only a part thereof. When only a part of the surface of the core material particle is covered, the covered portion may be continuous or may be discontinuously covered in an island shape, for example.

The thickness of the conductive layer is preferably 5nm to 2,000nm, more preferably 10nm to 1,500nm. When the thickness of the conductive layer is within the above range, conductive particles having excellent electrical characteristics and excellent storage stability are produced. When the conductive particles have protrusions described later, the height of the protrusions is not included in the thickness of the conductive layer described here. In the present invention, the thickness of the conductive layer can be measured by cutting the particles to be measured into two halves and observing the cross section of the cut with a Scanning Electron Microscope (SEM).

The average particle diameter of the conductive particles is preferably 0.1 μm to 50 μm, and more preferably 1 μm to 30 μm. When the average particle diameter of the conductive particles is within the above range, short circuit does not occur in a direction different from that between the opposing electrodes, and it is easy to ensure conduction between the opposing electrodes. In the present invention, the average particle diameter of the conductive particles is a value measured by SEM observation. Specifically, the average particle diameter of the conductive particles can be measured by the method described in examples. Here, the particle diameter is the diameter of the circular conductive particle image. When the conductive particles are not spherical, the particle diameter refers to the maximum length (maximum length) of a line segment crossing the conductive particle image.

When the conductive particles have protrusions on the surface thereof, that is, when the outer surface of the conductive layer has a shape having protrusions, the height of the protrusions is preferably 20nm or more and 1,000nm or less, and more preferably 50nm or less and 800nm or less. The number of protrusions varies depending on the particle diameter of the conductive particles, and is preferably 1 to 20,000, more preferably 5 to 5,000 per conductive particle, which is advantageous in view of further improving the conductivity of the conductive particles. The length of the base of the protrusion is preferably 5nm to 1,000nm, more preferably 10nm to 800 nm. The length of the base of the protrusion is the length along the surface of the conductive particle of the portion where the protrusion is formed when the cross section of the particle is observed by SEM, and the height of the protrusion is the shortest distance from the base of the protrusion to the apex of the protrusion. In the case where one protrusion has a plurality of apexes, the highest apex is defined as the height of the protrusion. The length of the base of the protrusion and the height of the protrusion are arithmetic averages of values measured for 20 different particles observed by an electron microscope.

The shape of the conductive particles is also different depending on the shape of the core material particles, and is not particularly limited. For example, the polymer may be in the form of a fiber, a hollow, a plate, or a needle, may have a plurality of protrusions on the surface thereof, or may be amorphous. In the present invention, a spherical shape or a shape having a plurality of protrusions on the outer surface is preferable in terms of excellent filling properties and connectivity.

Examples of a method for forming the conductive layer on the surface of the core material particle include a dry method such as a vapor deposition method, a sputtering method, a mechanochemical method, or a hybrid method, and a wet method such as an electrolytic plating method or an electroless plating method. In addition, these methods may be combined to form a conductive layer on the surface of the core material particle.

In the present invention, in order to easily obtain conductive particles having desired particle characteristics, it is preferable to form a nickel-phosphorus plating layer or a nickel-boron plating layer as a conductive layer on the surface of the core material particles by an electroless plating method.

A method of forming a nickel plating layer as the conductive layer will be described below.

When the conductive layer is formed on the surface of the core material particle by the electroless plating method, the surface of the core material particle preferably has a noble metal ion capturing ability, or is modified so as to have a noble metal ion capturing ability. The noble metal ion is preferably an ion of palladium or silver. The ability to capture noble metal ions means that noble metal ions can be captured in the form of a chelate or a salt. For example, when amino groups, imino groups, amide groups, imide groups, cyano groups, hydroxyl groups, nitrile groups, carboxyl groups, or the like are present on the surface of the core material particles, the surface of the core material particles has the ability to capture noble metal ions. In the case of modifying the surface so as to have the ability to trap noble metal ions, for example, the method described in Japanese patent application laid-open No. Sho 61-64882 can be used.

Such core particles are used to support a noble metal on the surface thereof. Specifically, the core material particles are dispersed in a dilute acidic aqueous solution of a noble metal salt such as palladium chloride or silver nitrate. Thereby, the surface of the particle is made to capture the noble metal ion. The concentration of the noble metal salt is 1m per particle ² Surface area 1X 10 ^-7 ～1×10 ^-2 The molar range is sufficient. The core material particles with the noble metal ions captured are separated from the system and washed with water. Next, the core material particles are suspended in water, and a reducing agent is added thereto to perform reduction treatment of the noble metal ions. Thereby, the noble metal is carried on the surface of the core material particle. As the reducing agent, for example, sodium hypophosphite, sodium boron hydroxide, potassium borohydride, dimethylamine borane, hydrazine, formalin, or the like can be used, and it is preferable to select the reducing agent from these based on the constituent material of the target conductive layer.

Before the precious metal ions are captured on the surface of the core material particles, sensitization treatment may be performed to adsorb tin ions on the surface of the particles. For example, the core material particles subjected to surface modification treatment may be put into an aqueous solution of stannous chloride and stirred for a predetermined time to adsorb tin ions on the surface of the particles.

The core material particles thus pretreated are subjected to a conductive layer formation treatment. As the formation process of the conductive layer, there are two types of processes of forming a conductive layer having projections and forming a conductive layer having a smooth surface, and first, the process of forming a conductive layer having projections will be described.

In the process of forming the conductive layer having the projections, the following first and second steps are performed.

The first step is an electroless nickel plating step in which an aqueous slurry of core material particles is mixed with an electroless nickel plating bath containing a dispersant, a nickel salt, a reducing agent, a complexing agent, and the like. In such a first step, self-decomposition of the plating bath occurs while the conductive layer is formed on the core material particles. Since the self-decomposition occurs in the vicinity of the core material particle, when the conductive layer is formed, the self-decomposed substance is captured on the surface of the core material particle, thereby generating a core of the fine protrusion and simultaneously forming the conductive layer. The growth of the projections proceeds with the nuclei of the generated minute projections as base points.

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

Examples of the dispersant include a nonionic surfactant, a zwitterionic surfactant, and/or a water-soluble polymer. As the nonionic surfactant, a polyoxyalkylene ether-based surfactant such as polyethylene glycol, polyoxyethylene alkyl ether, or polyoxyethylene alkylphenyl ether can be used. As the zwitterionic surfactant, a betaine-type surfactant such as alkyldimethylacetobetaine, alkyldimethylcarboxymethylacetobetaine, alkyldimethylaminoacetobetaine, or the like can be used. As the water-soluble polymer, polyvinyl alcohol, polyvinyl pyrrolidone, hydroxyethyl cellulose, or the like can be used. These dispersants may be used alone in 1 kind, or in combination of 2 or more kinds. The amount of the dispersant used varies depending on the kind thereof, and is generally 0.5 to 30g/L based on the volume of the liquid (electroless nickel plating bath). In particular, from the viewpoint of further improving the adhesion of the conductive layer, the amount of the dispersant used is preferably in the range of 1 to 10g/L with respect to the volume of the liquid (electroless nickel plating bath).

As the nickel salt, for example, nickel chloride, nickel sulfate, nickel acetate or the like can be used, and the concentration thereof is preferably in the range of 0.1 to 50 g/L. As the reducing agent, for example, the same reducing agent as that for reducing the noble metal ion as described above can be used, and the reducing agent is selected based on the constituent material of the target base coating film. When a phosphorus compound, for example, sodium hypophosphite is used as a reducing agent, the concentration thereof is preferably in the range of 0.1 to 50 g/L. When a boron compound, for example, dimethylamine borane, is used as the reducing agent, the concentration thereof is preferably in the range of 0.01 to 100g/L.

Examples of the complexing agent include carboxylic acids (salts) such as citric acid, glycolic acid, tartaric acid, malic acid, lactic acid, gluconic acid, alkali metal salts thereof, and ammonium salts thereof, amino acids such as glycine, amino acids such as ethylenediamine and alkylamine, and other ammonium salts, and compounds having a complexing action with nickel ions such as EDTA and pyrophosphoric acid (salts). These may be used alone in 1 kind, or more than 2 kinds may be used in combination. The concentration thereof is preferably in the range of 1 to 100g/L, more preferably 5 to 50 g/L. The preferred electroless nickel plating bath at this stage has a pH in the range of 3 to 14. The electroless nickel plating reaction starts rapidly upon addition of the aqueous slurry of the core material particles, accompanied by the generation of hydrogen gas. The first step is completed when the hydrogen generation is not observed at all.

Next, in the second step, the first step is followed by (i) using a first aqueous solution containing 1 of a nickel salt, a reducing agent and an alkali and a second aqueous solution containing the remaining 2 or (ii) using a first aqueous solution containing a nickel salt, a second aqueous solution containing a reducing agent and a third aqueous solution containing an alkali, and these aqueous solutions are added to the liquid in the first step simultaneously and with time, respectively, to carry out electroless nickel plating. When these liquids are added, the plating reaction is restarted, and the amount of addition is adjusted to control the thickness of the conductive layer to be formed to a desired thickness. After the addition of the electroless nickel plating solution was completed and hydrogen gas was not generated at all, the solution temperature was temporarily maintained and the stirring was continued to complete the reaction.

In the case of the above (i), a first aqueous solution containing a nickel salt and a second aqueous solution containing a reducing agent and a base are preferably used, but not limited to the combination. In this case, the first aqueous solution does not contain a reducing agent and a base, and the second aqueous solution does not contain a nickel salt. As the nickel salt and the reducing agent, the above-mentioned can be used. As the base, for example, a hydroxide of an alkali metal such as sodium hydroxide or potassium hydroxide can be used. The same applies to the case (ii) above.

In the case of (ii) above, the first to third aqueous solutions contain a nickel salt, a reducing agent and an alkali, respectively, and each aqueous solution does not contain 2 components other than the above components.

In both cases (i) and (ii), the concentration of the nickel salt in the aqueous solution is preferably 10 to 1,000g/L, particularly preferably 50 to 500g/L. When a phosphorus compound is used as the reducing agent, the concentration of the reducing agent is preferably 100 to 1,000g/L, and particularly preferably 100 to 800g/L. When a boron compound is used as the reducing agent, it is preferably 5 to 200g/L, particularly preferably 10 to 100g/L. When hydrazine or a derivative thereof is used as the reducing agent, the amount is preferably 5 to 200g/L, and particularly preferably 10 to 100g/L. The concentration of the alkali is preferably 5 to 500g/L, and particularly preferably 10 to 200g/L.

The second step is continuously performed after the first step is completed, but instead of this, the first step and the second step may be intermittently performed. In this case, a method may be adopted in which after the first step is completed, a second step is performed in which the core material particles and the plating solution are separated by a method such as filtration, the core material particles are redispersed in water to prepare an aqueous slurry, an aqueous solution in which the complexing agent is dissolved at a concentration in the range of preferably 1 to 100g/L, more preferably 5 to 50g/L is added thereto, the dispersant is dissolved at a concentration in the range of preferably 0.5 to 30g/L, more preferably 1 to 10g/L to prepare an aqueous slurry, and the aqueous solutions are added to the aqueous slurry. In this manner, a conductive layer having a protrusion can be formed.

Next, a process of forming a conductive layer having a smooth surface will be described below.

The formation of the conductive layer having a smooth surface can be performed by reducing the concentration of the nickel salt in the electroless nickel plating bath in the first step of the process of forming the conductive layer having the protrusions. That is, as the nickel salt, for example, nickel chloride, nickel sulfate, nickel acetate, or the like can be used, and the concentration thereof is preferably in the range of 0.01 to 0.5 g/L. By performing the first step and the second step in addition to the reduction of the concentration of the nickel salt in the electroless nickel plating bath, a conductive layer having a smooth surface can be formed.

The conductive particles of the present invention can be obtained by subjecting the conductive particles obtained by the above-described method to a heat treatment at a temperature of 200 to 600 ℃, preferably 250 to 500 ℃, and particularly preferably 300 to 450 ℃ under a vacuum of 1,000pa or less, preferably 0.01 to 900Pa, and particularly preferably 0.01 to 500 Pa. By heating the conductive particles while maintaining such a vacuum state, the ratio of carbon to oxygen present on the surface of the conductive layer can be reduced, and the molar ratio of phosphorus to carbon, oxygen, and nickel becomes appropriate. The vacuum degree in the present invention is an absolute pressure, that is, a value obtained when the absolute vacuum is 0.

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

The heat treatment may be performed in a state where the conductive particles are left to stand, or may be performed while stirring. When the heat treatment is performed in a state where the conductive particles are left to stand, the conductive particles are preferably left to stand in a thickness of 0.1mm to 100 mm. By leaving the conductive layer at rest with this thickness, the conductive layer can be smoothly heated, and the manufacturing cost can be reduced.

The heating treatment is performed in a state where the container containing the conductive particles is left standing after vacuum-pumping, or while stirring. In this case, the gas phase portion of the container containing the conductive particles may be replaced with an inert gas such as nitrogen gas and then evacuated, or the evacuation may be performed as it is. Further, the heat treatment may be performed a plurality of times as necessary.

In this way, the conductive particles of the present invention can be obtained.

When the conductive particles of the present invention are used as a conductive filler of a conductive adhesive as described later, the surfaces of the conductive particles may be further covered with an insulating resin in order to prevent short-circuiting between the conductive particles. The insulating resin coating is formed so that the surface of the conductive particles is not exposed as much as possible without applying pressure or the like, and so that at least the protrusions are exposed on the surface of the conductive particles by breaking due to heat and pressure applied when the 2 electrodes are bonded using the conductive adhesive. The thickness of the insulating resin may be about 0.1 to 0.5 μm. The insulating resin may cover the entire surface of the conductive particles, or may cover only a part of the surface of the conductive particles.

As the insulating resin, a resin known in the art can be widely used. Examples of the resin include resins composed of organic polymers such as phenol resins, urea resins, melamine resins, allyl resins, furan resins, polyester resins, epoxy resins, silicone resins, polyamide-imide resins, polyimide resins, polyurethane resins, fluorine resins, polyolefin resins (e.g., polyethylene, polypropylene, polybutylene), polyalkyl (meth) acrylate resins, poly (meth) acrylic resins, polystyrene resins, acrylonitrile-styrene-butadiene resins, vinyl resins, polyamide resins, polycarbonate resins, polyacetal resins, ionomer resins, polyethersulfone resins, polyphenylene ether resins, polysulfone resins, polyvinylidene fluoride resins, ethyl cellulose resins, and cellulose acetate resins.

Examples of the method for forming the insulating coating layer on the surface of the conductive particle include chemical methods such as coagulation, interfacial polymerization, in-situ (in situ) polymerization, and in-liquid solidification coating, physical-mechanical methods such as spray drying, in-gas suspension coating, vacuum vapor deposition coating, dry mixing, mixing (hybridization), electrostatic fusion, melt dispersion cooling, and inorganic encapsulation, and physicochemical methods such as interfacial precipitation.

The organic polymer constituting the insulating resin may contain an ionic group-containing compound as a monomer component in the structure of the polymer, provided that the polymer is nonconductive. The compound containing an ionic group may be a crosslinkable monomer or a non-crosslinkable monomer. That is, it is preferable that the organic polymer is formed using a compound having an ionic group for at least 1 of the crosslinkable monomer and the non-crosslinkable monomer. The "monomer component" refers to a structure derived from a monomer in an organic polymer, and is a component derived from a monomer. By subjecting the monomer to polymerization, an organic polymer containing the monomer component as a constituent unit can be formed.

The ionic group is preferably present at the interface of the organic polymer constituting the insulating resin. Further, the ionic group is preferably chemically bonded to a monomer component constituting the organic polymer. When an insulating resin containing an organic polymer having an ionic group is formed on the surface of a conductive particle, whether the insulating resin is attached to the surface of the conductive particle can be observed by a scanning electron microscope, and whether the ionic group is present at the interface of the organic polymer can be determined.

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

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

( Wherein X is a phosphorus atom, a nitrogen atom or a sulfur atom, and R may be the same or different and is a hydrogen atom, a linear, branched or cyclic alkyl group or an aryl group. n is 1 when X is a nitrogen atom or a phosphorus atom, and 0 when X is a sulfur atom. * Is a bond. )

Examples of the counter ion corresponding to the ionic group include halide ions. Examples of the halide ion include Cl ^－、F ^－、Br ^－、I ^－。

In the 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-eicosyl group.

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

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

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

In 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 still more preferably an alkyl group having 1 to 8 carbon atoms. In the general formula (1), R is also more preferably a linear alkyl group. By configuring the onium functional group in this manner, the adhesion between the insulating resin and the conductive particles can be improved, the insulating property can be ensured, and the conduction reliability at the time of thermocompression bonding can be further improved.

The organic polymer having an ionic group constituting the insulating resin preferably has a constituent unit represented by the following general formula (2) or (3) from the viewpoint of easy availability of monomers and synthetic polymers and improvement of production efficiency of the insulating resin.

(wherein X, R and n have the same meanings as in the above general formula (1) and m is An integer of 0 to 5, an ^－ Represents a monovalent anion. )

(wherein X, R and n have the same meanings as in the above general formula (1). An ^－ Represents a monovalent anion. m is a unit of ¹ Is an integer of 1 to 5 inclusive. R ₅ Is a hydrogen atom or a methyl group. )

As examples of R in the formula (2) and the formula (3), the description of the functional group of R in the above general formula (1) can be appropriately applied. The ionic group may be bonded to any of the para, ortho, and meta positions with respect to the CH group of the benzene ring of formula (2), and is preferably bonded to the para position. In the formulae (2) and (3), an is monovalent ^－ Preferably, a halide ion is mentioned. Examples of halide ions include Cl ^－、F ^－、Br ^－、I ^－。

In general formula (2), m is preferably an integer of 0 to 2, more preferably 0 or 1, and particularly preferably 1. In the general formula (3), m ¹ Preferably 1 to 3, more preferably 1 or 2, and most preferably 2.

The organic polymer having an ionic group is preferably composed of a monomer component having an onium functional group and an ethylenically unsaturated bond, for example. The organic polymer having an ionic group preferably contains a non-crosslinkable monomer component from the viewpoint of easy availability of monomers and synthetic polymers and improvement of production efficiency of the insulating resin.

Examples of the non-crosslinkable monomer having an onium functional group and an ethylenically unsaturated bond include: ammonium group-containing monomers such as N, N-dimethylaminoethyl methacrylate, N, N-dimethylaminopropyl acrylamide, N, N, N-trimethyl-N-2-methacryloyloxyethyl ammonium chloride and the like; monomers having a sulfonium group such as phenyldimethylsulfonium methylsulfate methacrylate; monomers having a phosphonium group such as 4- (vinylbenzyl) triethylphosphonium chloride, 4- (vinylbenzyl) trimethylphosphonium chloride, 4- (vinylbenzyl) tributylphosphonium 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, 2- (methacryloyloxyethyl) triphenylphosphonium chloride, and the like. The organic polymer having an ionic group may contain 2 or more types of non-crosslinkable monomer components.

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

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

In the case where the insulating resin is composed of insulating fine particles, the conductive particles covered with the insulating fine particles are thermocompression bonded between the electrodes, whereby the insulating fine particles are melted, deformed, peeled off, or moved on the surfaces of the conductive particles, and the metal surfaces of the conductive particles in the thermocompression bonded portions are exposed, whereby conduction between the electrodes can be achieved, and connectivity can be obtained. On the other hand, the surface portions of the conductive particles facing in directions other than the thermocompression bonding direction are approximately maintained in a state where the insulating fine particles cover the surfaces of the conductive particles, and therefore conduction in directions other than the thermocompression bonding direction can be prevented.

The insulating fine particles contain the ionic group on the surface thereof, and therefore, the insulating fine particles can be easily adhered to the conductive particles, and thus, the ratio of the conductive particle surface to be covered with the insulating fine particles can be made sufficient, and the insulating fine particles can be effectively prevented from peeling off from the conductive particles. Therefore, the short-circuit prevention effect in a direction different from that between the opposing electrodes is easily exhibited by the insulating fine particles, and improvement in the insulating property in that direction can be expected.

The shape of the insulating fine particles is not particularly limited, and may be spherical or other shapes. Examples of the shape other than spherical include a fiber shape, a hollow shape, a plate shape, and a needle shape. The insulating fine particles may be fine particles having a plurality of protrusions on the surface thereof, or amorphous fine particles. From the viewpoint of adhesion to the conductive particles and ease of synthesis, spherical insulating fine particles are preferable.

The average particle diameter (D) of the insulating fine particles is preferably 10nm to 3,000nm, more preferably 15nm to 2,000nm. When the average particle diameter of the insulating fine particles is within the above range, the obtained coated particles are not short-circuited in a direction different from the direction between the opposed electrodes, and the conduction between the opposed electrodes is easily ensured. In the present invention, the average particle diameter of the insulating fine particles is a value measured by observation with a scanning electron microscope, and is specifically measured by the method described in the examples described later.

The particle size distribution of the insulating fine particles measured by the aforementioned method has a width. Generally, the width of the particle size distribution of the powder is represented by a Coefficient of Variation (hereinafter also referred to as "c.v.") shown in the following equation (1).

C.V. (%) = (standard deviation/average particle diameter) × 100 \8230; (1)

The large c.v. indicates a wide particle size distribution, while the small c.v. indicates a narrow particle size distribution. The coating particles of the present embodiment preferably use insulating fine particles having a c.v. of preferably 0.1% to 20%, more preferably 0.5% to 15%, and most preferably 1% to 10%. When the c.v. is in this range, there is an advantage that the thickness of the coating layer formed of the insulating fine particles can be made uniform.

Instead of the insulating resin composed of the insulating fine particles, a continuous coating film composed of a polymer and having an ionic group may be used as the insulating resin. When the insulating resin is a continuous coating film having an ionic group, the conductive particles are thermally pressed between the electrodes, and the continuous coating film is melted, deformed, or peeled off, whereby the metal surfaces of the conductive particles are exposed, whereby conduction between the electrodes can be achieved, and connectivity can be obtained. In particular, by thermocompression bonding conductive particles between electrodes, the coating film is broken continuously in many cases, and the metal surface is exposed. On the other hand, at the surface portion of the conductive particles facing in a direction different from the thermocompression bonding direction, the state in which the continuous coating covers the conductive particles is approximately maintained, and therefore conduction in a direction other than the thermocompression bonding direction can be prevented. The continuous coating film preferably has an ionic group on the surface.

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

In the continuous coating, the ionic group is preferably a part of the chemical structure of a substance constituting the continuous coating so as to constitute the same part of the substance, as in the insulating fine particles. In the continuous coating film, it is preferable that at least 1 structure of the constituent unit of the polymer constituting the continuous coating film contains an ionic group. The ionic group is preferably chemically bonded to the polymer constituting the continuous film, and more preferably bonded to a side chain of the polymer.

When the insulating resin is a continuous coating, it is preferable that the surface of the conductive particles is coated with insulating fine particles having an ionic group, and then the insulating fine particles are heated to obtain a continuous coating. Alternatively, a continuous coating film obtained by dissolving the insulating fine particles in an organic solvent is preferable. As described above, the insulating fine particles having an ionic group easily adhere to the conductive particles, so that the ratio of the insulating fine particles covering the surface of the conductive particles becomes sufficient, and the insulating fine particles are easily prevented from peeling from the conductive particles. Therefore, a continuous coating obtained by heating or dissolving the insulating fine particles covering the conductive particles can be formed into a product having a uniform thickness and a high coverage ratio of the conductive particle surface.

In addition, in order to improve affinity with the insulating resin and to improve adhesion, the conductive particles according to the production method of the present invention may be treated with a surface treatment agent.

Examples of the surface treatment agent include benzotriazole compounds, titanium compounds, higher fatty acids or derivatives thereof, phosphoric acid esters, and phosphorous acid esters. These may be used alone, or a plurality of them may be used in combination as required.

The surface treatment agent may be chemically bonded to the metal on the surface of the conductive particle, or may not be bonded thereto. The surface treatment agent may be present on the surface of the conductive particles, and in this case, may be present on the entire surface of the conductive particles or may be present only on a part of the surface.

Examples of the triazole-based compound include compounds having a nitrogen-containing heterocyclic structure in which 3 nitrogen atoms are contained in a 5-membered ring.

Examples of the triazole-based compound include a compound having a triazole monocyclic structure not condensed with another ring, and a compound having a ring structure in which a triazole ring is condensed with another ring. Examples of the other rings include benzene ring and naphthalene ring.

Among them, from the viewpoint of excellent adhesion to the insulating resin, a compound having a ring structure obtained by condensing a triazole ring with another ring is preferable, and a benzotriazole-based compound which is a compound having a structure obtained by condensing a triazole ring with a benzene ring is particularly preferable.

Examples of the benzotriazole-based compound include compounds represented by the following general formula (I).

(wherein R is ¹¹ Is a negative charge, a hydrogen atom, an alkali metal, an alkyl group which may be substituted, an amino group, a formyl group, a hydroxyl group, an alkoxy group, a sulfonic acid group or a silyl group, R ¹² 、R ¹³ 、R ¹⁴ And R ¹⁵ Each independently a hydrogen atom, a halogen atom, an alkyl group which may be substituted, a carboxyl group, a hydroxyl group or a nitro group. )

As R in formula (I) ¹¹ Examples of the alkali metal include lithium, sodium, and potassium. R is ¹¹ The alkali metal is an alkali metal cation, R in the formula (I) ¹¹ In the case of alkali metals, R ¹¹ The bond to the nitrogen atom may be an ionic bond.

As R in formula (I) ¹¹ 、R ¹² 、R ¹³ 、R ¹⁴ And R ¹⁵ Examples of the alkyl group include alkyl groups having 1 to 20 carbon atoms, and particularly preferably having 1 to 12 carbon atoms. The alkyl group may be substituted, and as the substituent, there may be mentioned amino group, alkoxy group, carboxyl group, hydroxyl group, aldehyde group, nitro group, sulfonic acid group, quaternary ammonium group, sulfonium group, sulfonyl group, phosphonium group, cyano group, fluoroalkyl group, mercapto group and halogen atom.

As R ¹¹ The alkoxy group preferably includes alkoxy groups having 1 to 12 carbon atoms.

In addition, as R ¹² 、R ¹³ 、R ¹⁴ And R ¹⁵ The alkoxy group as a substituent of the alkyl group preferably has 1 to 12 carbon atoms. As R in formula (I) ¹² 、R ¹³ 、R ¹⁴ And R ¹⁵ Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

Specific examples of the triazole-based compound include 1,2, 3-triazole, 1,2, 4-triazole, 3-amino-1H-1, 2, 4-triazole, sodium 5-mercapto-1H-1, 2, 3-triazole, 4-amino-3-hydrazino-5-mercapto-1, 2, 4-triazole, and 3-amino-5-mercapto-1, 2, 4-triazole, further, benzotriazole having a ring structure obtained by condensing a triazole ring with another ring, 1-methyl-1H-benzotriazole, 4-methyl-1H-benzotriazole, 5-methyl-1H-benzotriazole, 4-carboxy-1H-benzotriazole, 5-ethyl-1H-benzotriazole, 5-propyl-1H-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-formaldehyde, 1- (chloromethyl) -1H-benzotriazole, 1-hydroxy-6- (trifluoromethyl) benzotriazole, benzotriazole butyl ester, 4-carboxy-1H-benzotriazole octyl ester, 1- [ N ], N-bis (2-ethylhexyl) aminomethyl ] methylbenzotriazole, 2' - [ [ (methyl-1H-benzotriazol-1-yl) methyl ] imino ] bisethanol, tetrabutylphosphonium benzotriazolate 1H-benzotriazol-1-yloxytris (dimethylamino) phosphonium hexafluorophosphate, 1H-benzotriazol-1-yloxytripyrrolidinylphosphonium hexafluorophosphate, 1- (formamidomethyl) -1H-benzotriazole, 1- [ bis (dimethylamino) methylene ] -1H-benzotriazolium-3-oxohexafluorophosphate, 1- [ bis (dimethylamino) methylene ] -1H-benzotriazolium-3-oxotetrafluoroborate, (6-chloro-1H-benzotriazol-1-yloxy) trispyrrolidinylphosphonium 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) ethoxy ] benzotriazole, 1H-triphenyltriazole, (1H-triphenyltriazolyl) tris (trifluoromethyl) triazol-1H-benzotriazolyl) phosphonium, 9-trifluoromethyl (1H-benzotriazol-1H-yl) triazolyl [ (1H-trifluoromethyl) benzotriazol-1H-yl ] triazole, 9H-benzotriazol-1H-yl ] fluorene, and (trifluoromethyl) benzotriazol-1H-yl) phosphonium chloride, 1,2, 3-benzotriazole sodium salt, naphthotriazole and the like.

The titanium-based compound is preferably a compound having a structure represented by the general formula (II) in particular, in the case where the titanium-based compound is present on the surface of the conductive particles, from the viewpoint of easily obtaining affinity between the insulating resin and the conductive particles and from the viewpoint of being easily dispersed in a solvent and enabling uniform treatment of the surface of the conductive particles.

(R ²¹ Is a 2-or 3-valent radical, R ²² Is an aliphatic hydrocarbon group having 2 to 30 carbon atoms, an aryl group having 6 to 22 carbon atoms or an arylalkyl group having 7 to 23 carbon atoms, p and R are each an integer of 1 to 3 inclusive and satisfy p + R =4, q is an integer of 1 or 2, and R is an alkyl group ²¹ Q is 1 in the case of a 2-valent radical, in which R ²¹ And q is 2 in the case of a 3-valent group. In the case where q is 2, a plurality of R ²² May be the same or different. * Represents a bond. )

As R ²² Examples of the aliphatic hydrocarbon group having 4 to 28 carbon atoms include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl and dodecyl groupsTridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, eicosyl, heneicosyl, docosyl and the like. Examples of the unsaturated aliphatic hydrocarbon group include an alkenyl group such as a dodecenyl group, a tridecenyl group, a tetradecenyl group, a pentadecenyl group, a hexadecenyl group, a heptadecenyl group, a nonadecenyl group, an eicosenyl group (icosenyl group), a heneicosenyl group and a docosenyl group. Examples of the aryl group having 6 to 22 carbon atoms include a phenyl group, a tolyl group, a naphthyl group, an anthryl group and the like.

Examples of the arylalkyl group having 7 to 23 carbon atoms include benzyl, phenethyl and naphthylmethyl.

The hydrophobic group is particularly preferably a linear or branched aliphatic hydrocarbon group, and particularly preferably a linear aliphatic hydrocarbon group.

From the viewpoint of improving the affinity between the insulating resin and the conductive particles, the aliphatic hydrocarbon group as the hydrophobic group is more preferably a group having 4 to 28 carbon atoms, and most preferably a group having 6 to 24 carbon atoms.

As R ²¹ The group having a valence of 2 as shown, mention may be made of-O-, -COO-, -OCO-, -OSO ₂ -and the like. As R ²¹ As the 3-valent group, there may be mentioned-P (OH) (O-) ₂ 、－OPO(OH)－OPO(O－) ₂ And the like.

In the general formula (II), a is a bond, and the bond may be bonded to the metal coating of the conductive particle, or may be bonded to another group or the like. Examples of the other groups include hydrocarbon groups, and specifically, alkyl groups having 1 to 12 carbon atoms are mentioned.

The titanium compound having a structure represented by the general formula (II) is preferably R in the general formula (II) in view of availability and ability to be treated without impairing the conductive properties of the conductive particles ²¹ A compound having the structure of a 2-valent group. R in the general formula (II) ²¹ The structure of the group having a valence of 2 is represented by the following general formula (III).

(R ²¹ Is selected from-O-, -COO-, -OCO-, -OSO ₂ The group of (A), p, R and R ²² The meaning of (A) is the same as in the general formula (II). )

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

Specific examples of the titanate-based coupling agent used in the present invention include isopropyl triisostearoyl titanate, isopropyl tris (dodecylbenzenesulfonyl) titanate, isopropyl tris (dioctylpyrophosphate) titanate, tetraisopropyl (dioctylphosphite) titanate, tetraisopropyl bis (dioctylphosphite) titanate, tetraoctyl bis (ditridecylphosphite) titanate, tetrakis (2, 2-diallyloxymethyl-1-butyl) bis (ditridecylphosphite) titanate, bis (dioctylpyrophosphate) oxyacetate titanate, bis (dioctylpyrophosphate) ethylene titanate, and 1 or 2 or more of these may be used.

Further, these titanate-based coupling agents are sold by, for example, K.K. K.K.K.of Weitonine-Techno.

The higher fatty acid is preferably a saturated or unsaturated, linear or branched monocarboxylic acid or polycarboxylic acid, more preferably a saturated or unsaturated, linear or branched monocarboxylic acid, and still more preferably a saturated or unsaturated, linear monocarboxylic acid. The number of carbon atoms of the fatty acid is preferably 7 or more. The derivative refers to a salt or amide of the fatty acid.

The higher fatty acid or a derivative thereof used in the present invention preferably has 7 to 23 carbon atoms, more preferably 10 to 20 carbon atoms. Examples of the higher fatty acid or a derivative thereof include saturated fatty acids such as capric acid, lauric acid, myristic acid, palmitic acid, and stearic acid, unsaturated fatty acids such as oleic acid, linoleic acid, linolenic acid, and arachidonic acid, and metal salts and amides thereof. The metal salt of the higher fatty acid includes salts of transition metals such as alkali metals, alkaline earth metals, zr, cr, mn, fe, co, ni, cu, and Ag, and other metals than transition metals such as Al and Zn, and preferably polyvalent metal salts such as Al, zn, W, and V. The higher fatty acid metal salt may be a dimer, a trimer, a tetramer, or the like, depending on the valence number of the metal. The higher fatty acid metal salt may be any combination thereof.

As the phosphate and the phosphite, esters having an alkyl group having 6 to 22 carbon atoms are preferably used.

Examples of the phosphate ester include hexyl phosphate, heptyl phosphate, monooctyl phosphate, monononyl phosphate, monodecyl phosphate, monoundecyl phosphate, monododecyl phosphate, monotridecyl phosphate, monotetradecyl phosphate, and monopentadecyl phosphate.

Examples of the phosphite include hexyl phosphite, heptyl phosphite, monooctyl phosphite, monononyl phosphite, monodecanyl phosphite, monoundecyl phosphite, monododecyl phosphite, monotridecyl phosphite, monotetradecyl phosphite, and monopentadecyl phosphite.

In the present invention, the surface treatment agent is preferably a triazole-based compound or a titanium-based compound, and particularly preferably benzotriazole, 4-carboxybenzotriazole, isopropyltriisostearoyltitanate, or tetraisopropyl (dioctyl phosphite) titanate, from the viewpoints of excellent affinity for the insulating resin and high effect of improving the coverage of the insulating resin.

The method of treating the conductive particles with the surface treatment agent is obtained by dispersing the conductive particles in a solution of the surface treatment agent and then filtering the solution. The conductive particles may be treated with another treatment agent or may not be treated before the treatment with the surface treatment agent.

The concentration of the surface treatment agent in the solution of the surface treatment agent for dispersing the conductive particles (solution containing the conductive particles) is, for example, 0.01 mass% to 10.0 mass%. Examples of the solvent in the solution of the surface treatment agent include water, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, isoamyl alcohol, cyclohexanol and other alcohols, acetone, methyl isobutyl ketone, methyl ethyl ketone, methyl-N-butyl ketone and other ketones, methyl acetate, ethyl acetate and other esters, diethyl ether, ethylene glycol monoethyl ether and other ethers, N-hexane, cyclohexanone, toluene, 1, 4-dioxane, N-dimethylformamide, tetrahydrofuran and the like. The conductive particles after the surface treatment, which have been subjected to the dispersion and filtration, are preferably dispersed again in a solvent to remove the excess surface treatment agent.

The surface treatment of the conductive particles with the surface treatment agent may be performed 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 ℃ to 50 ℃.

The conductive particles of the present invention have low connection resistance, and therefore are suitable for use as, for example, an Anisotropic Conductive Film (ACF), a Heat Sealing Contactor (HSC), or a conductive material for connecting electrodes of a liquid crystal display panel to a circuit board of a driving LSI chip. The conductive material may be the conductive particles of the present invention used as they are or a material obtained by dispersing the conductive particles of the present invention in a binder resin. Other forms of the conductive material are not particularly limited, and examples thereof include an anisotropic conductive paste, a conductive adhesive, and an anisotropic conductive ink, in addition to the above forms.

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

The conductive material may further contain, in addition to the conductive particles and the binder resin of the present invention, an adhesion promoter, a reactive auxiliary, an epoxy resin curing agent, a metal oxide, a photoinitiator, a sensitizer, a curing agent, a vulcanizing agent, a deterioration preventing agent, a heat-resistant additive, a heat conductivity enhancer, a softener, a colorant, various coupling agents, a metal deactivator, and the like, as required.

In the above-mentioned conductive material, the amount of the conductive particles to be used may be appropriately determined depending on the application, and is, for example, preferably 0.01 to 50 parts by mass, and particularly preferably 0.03 to 40 parts by mass, based on 100 parts by mass of the conductive material, from the viewpoint of facilitating electrical conduction without bringing the conductive particles into contact with each other.

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

The conductive adhesive is preferably used as an anisotropic conductive adhesive which is disposed between 2 substrates on which conductive substrates are formed, and bonds the conductive substrates by heating and pressing to conduct electricity. The anisotropic conductive adhesive comprises the conductive particles of the present invention and an adhesive resin. The adhesive resin is not particularly limited as long as it is an insulating resin that can be used as an adhesive resin. Both thermoplastic resins and thermosetting resins can be used, and resins exhibiting adhesive properties by heating are preferred. Examples of such adhesive resins include thermoplastic type, thermosetting type, and ultraviolet curing type. There are also so-called semi-thermosetting type, thermosetting type and ultraviolet curing type, which exhibit intermediate properties between thermoplastic type and thermosetting type. These adhesive resins can be appropriately selected depending on the surface properties and the use form of the circuit board or the like to be bonded. In particular, an adhesive resin containing a thermosetting resin is preferable in terms of excellent strength of the material after bonding.

Specific examples of the adhesive resin include those obtained using, as a main component, a resin obtained by combining 1 or 2 or more selected from 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, phenol resin, silicone resin, and the like. Among these, styrene-butadiene rubber, SEBS and the like are preferable as the thermoplastic resin because of excellent reworkability. As the thermosetting resin, an epoxy resin is preferable. Among these, the epoxy resin is most preferable because of its advantages of high adhesive force, excellent heat resistance and electrical insulation, low melt viscosity, and capability of connection at low pressure.

As the epoxy resin, any one may be used as long as it is a multi-component epoxy resin having 2 or more epoxy groups in 1 molecule, and a commonly used epoxy resin can be used. Specific examples thereof include novolak resins such as phenol novolak and cresol novolak, glycidyl-type epoxy resins obtained by reacting epichlorohydrin or 2-methyl epichlorohydrin with polyhydric phenols such as bisphenol a, bisphenol F, bisphenol AD, resorcinol, and bishydroxydiphenyl ether, polyhydric alcohols such as ethylene glycol, neopentyl glycol, glycerol, trimethylolpropane, and polypropylene glycol, polyamino compounds such as ethylenediamine, triethylenetetramine, and aniline, and polycarboxylic compounds such as adipic acid, phthalic acid, and isophthalic acid. Aliphatic and alicyclic epoxy resins such as epoxidized dicyclopentadiene and diepoxydipolybutadiene are also included. These may be used alone in 1 kind, or in combination of 2 or more kinds.

In addition, as the various adhesive resins described above, high-purity products in which impurity ions (Na, cl, or the like), hydrolyzable chlorine, and the like are reduced are preferably used from the viewpoint of preventing ion migration.

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

In the anisotropic conductive adhesive, additives known in the art may be added in addition to the conductive particles and the adhesive resin. The compounding amount thereof may be within a range known in the art. Examples of the other additives include an adhesion promoter, a reactive auxiliary, an epoxy resin curing agent, a metal oxide, a photoinitiator, a sensitizer, a curing agent, a vulcanizing agent, a deterioration preventing agent, a heat resistant additive, a heat conductivity enhancer, a softening agent, a coloring agent, various coupling agents, and a metal deactivator.

Examples of the tackifier include rosin, rosin derivatives, terpene resins, terpene phenol resins, petroleum resins, coumarone-indene resins, styrene resins, isoprene resins, alkylphenol resins, xylene resins, and the like. Examples of the crosslinking agent as the reactive auxiliary agent include polyols, isocyanates, melamine resins, urea resins, urotropines (utrapins), amines, acid anhydrides, peroxides, and the like. The epoxy resin curing agent is not particularly limited, and any epoxy resin curing agent may be used as long as it has 2 or more active hydrogens in 1 molecule. Specific examples include: polyamino compounds such as diethylenetriamine, triethylenetetramine, m-phenylenediamine, dicyandiamide, and polyamidoamine; organic acid anhydrides such as phthalic anhydride, nadic methyl anhydride, hexahydrophthalic anhydride and pyromellitic anhydride; and novolak resins such as phenol novolak and cresol novolak. These can be used alone in 1, or more than 2 mixed use. If necessary, a latent curing agent may also be used. Examples of the latent curing agent that can be used include imidazole type, hydrazide type, boron trifluoride-amine complex, sulfonium salt, aminimide, polyamine salt, dicyandiamide, and modified products thereof. These may be used alone in 1 kind, or in a mixture of 2 or more kinds.

The anisotropic conductive adhesive can be produced by a production apparatus commonly used in the art. For example, the conductive particles are mixed with a binder resin and, if necessary, a curing agent and various additives, and the mixture is mixed in an organic solvent when the binder resin is a thermosetting resin, or the mixture is melt-kneaded at a temperature equal to or higher than the softening point of the binder resin, specifically, preferably, approximately 50 to 130 ℃, and more preferably approximately 60 to 110 ℃ when the binder resin is a thermoplastic resin. The anisotropic conductive adhesive obtained in this way may be applied or may be used after being formed into a film.

The connection structure according to the present invention is obtained by connecting two circuit boards to each other by 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 of a flexible printed circuit board and a glass substrate, a connection structure of a semiconductor chip and a flexible printed circuit board, and a connection structure of a semiconductor chip and a glass substrate.

Examples

The present invention will be further described with reference to examples. However, the scope of the present invention is not limited to these examples.

The properties in the examples were measured by the following methods.

(1) Elemental analysis of conductive layer surface

The atomic% of carbon, oxygen, phosphorus, boron, and nickel within 5nm in the depth direction from the surface of the conductive particles was calculated using a scanning auger electron spectrometer (PHI 710, manufactured by ULVAC-PHI co.).

(2) Ion analysis of conductive layer surface

Using a time-of-flight type secondary ION mass spectrometer (TOF-SIMS 5 type, manufactured by ION-TOF Co., ltd.), conductive particles were uniformly and flatly spread over a substrate, and Bi was used as a primary ION source in the vicinity of the center of the conductive particles in the 200 μm square range ³ ⁺ And measuring positive ions (CH) derived from the amine compound within 1nm in the depth direction from the surface of the conductive particles under the condition that the acceleration voltage is 30kV ₄ N ⁺ : mass number of30.03 Positive ion (Ni) relative to Ni ⁺ : mass number 57.94), negative ion (C) from organic acid ₂ H ₃ O ₂ ^－ : mass number 59.01) relative to the counting intensity of negative ions (mass number 57.94) of Ni, negative ions (PO) derived from a phosphate compound ₂ ^－ : mass number 62.96) relative to negative ion of Ni (Ni) ^－ : mass number 57.94) and negative ions (B) derived from a boric acid compound ₂ O ₄ H ₃ ^－ : mass number 89.02 and B ₃ O ₆ H ₄ ^－ : mass number 133.03) relative to Ni ^－ The counting intensity of the negative ions.

(3) Average particle diameter

200 particles were arbitrarily extracted from a Scanning Electron Microscope (SEM) photograph of the measurement object, and the particle diameter was measured at a magnification of 10,000 times, and the arithmetic average thereof was taken as the average particle diameter.

(4) Thickness of the conductive layer

The conductive particles were cut into two halves, and the cross section of the cut was observed by a Scanning Electron Microscope (SEM) to measure the conductive particles.

[ example 1]

(1) Pretreatment

Spherical styrene-acrylate-silica composite resin particles having an average particle diameter of 3.0 μm were used as core material particles. 9g of this was put into 200mL of an aqueous conditioning agent solution ("Cleaner Conditioner 231" manufactured by ROHM AND HAAS ELECTRONIC MATERIALS K.K.) with stirring. The concentration of the regulator aqueous solution was 40mL/L. Subsequently, ultrasonic waves were applied at a liquid temperature of 60 ℃ and stirred for 30 minutes to perform surface modification and dispersion treatment of the core material particles. After the aqueous solution was filtered, the core material particles washed once again with water were made into 200mL of slurry. To this slurry was charged 0.1g of stannous chloride. The mixture was stirred at room temperature for 5 minutes to perform sensitization treatment for adsorbing tin ions on the surface of the core material particles. Subsequently, the aqueous solution was filtered, and the core material particles after once repulping and washing were made into 200mL of slurry and maintained at 60 ℃. To this slurry was added 1.5mL of a 0.11mol/L aqueous solution of palladium chloride. The mixture was stirred at 60 ℃ for 5 minutes to carry out an activation treatment for capturing palladium ions on the surface of the core material particles. Subsequently, the aqueous solution was filtered, and after the core material particles subjected to primary repulping and hot water washing were made into 100mL of slurry, 10mL of 0.5g/L dimethylamine borane aqueous solution was added, and the mixture was stirred for 2 minutes by applying ultrasonic waves, thereby obtaining a slurry of pretreated core material particles.

(2) Preparation of the plating bath

3L of an electroless nickel-phosphorus plating bath formed of an aqueous solution in which 5g/L of sodium tartrate, 2g/L of nickel sulfate hexahydrate, 10g/L of trisodium citrate, 0.1g/L of sodium hypophosphite, and 2g/L of polyethylene glycol were dissolved was prepared, and the temperature was raised to 70 ℃.

(3) Electroless plating treatment

The slurry of the pretreated core material particles was put into the electroless plating bath, and after stirring for 5 minutes, it was confirmed that the hydrogen gas bubbling was stopped.

To the slurry, 420mL of 224g/L aqueous nickel sulfate solution and 420mL of a mixed aqueous solution containing 210g/L sodium hypophosphite and 80g/L sodium hydroxide were continuously added by a metering pump at a rate of 2.5 mL/min, respectively, to initiate electroless plating.

After the total amount of the nickel sulfate aqueous solution and the mixed aqueous solution of sodium hypophosphite and sodium hydroxide were added, respectively, the temperature of 70 ℃ was maintained and stirring was continued for 5 minutes. Then, the liquid was filtered, and the filtrate was washed 3 times and dried by a vacuum drier at 110 ℃ to obtain conductive particles having a nickel-phosphorus alloy coating. The obtained conductive particles had an average particle diameter of 3.22 μm, a thickness of the conductive layer of 110nm, and had protrusions.

(4) Vacuum heat treatment

The obtained conductive particles were put into a square container to have a thickness of 5 mm. The resultant was placed in a vacuum heating furnace (KDF-75, manufactured by DENKEN HIGHDENTAL Co., ltd.) and subjected to a heating treatment at 390 ℃ for 2 hours under a vacuum of 10 Pa. After the heat treatment, the mixture was cooled to room temperature to obtain heat-treated conductive particles. The obtained conductive particles had an average particle diameter of 3.22 μm, a thickness of the conductive layer of 110nm, and had protrusions. The results of the elemental analysis of the surface of the conductive layer are shown in table 1, and the results of the ion analysis are shown in table 2.

[ example 2]

The vacuum heat treatment (4) of example 1 was performed in the following manner. The conductive particles obtained by the electroless plating treatment (3) of example 1 were charged into a square container to have a thickness of 5 mm. The resultant was placed in a heating furnace (KDF-75, manufactured by DENKEN HIGHDENTAL Co., ltd.) and subjected to a heating treatment at 390 ℃ for 2 hours under a vacuum of 100 Pa. After the heat treatment, the mixture was cooled to room temperature to obtain heat-treated conductive particles. The obtained conductive particles had an average particle diameter of 3.22 μm, a thickness of the conductive layer of 110nm, and had protrusions. The results of elemental analysis of the surface of the conductive layer are shown in table 1, and the results of ion analysis are shown in table 2.

[ example 3]

The vacuum heat treatment (4) of example 1 was performed in the following manner. The conductive particles obtained by the electroless plating treatment (3) of example 1 were charged into a square container to have a thickness of 5 mm. The resultant was placed in a heating furnace (KDF-75, manufactured by DENKEN HIGHDENTAL Co., ltd.) and subjected to a heating treatment at 320 ℃ for 2 hours under a vacuum of 10 Pa. After the heat treatment, the mixture was cooled to room temperature to obtain heat-treated conductive particles. The obtained conductive particles had an average particle diameter of 3.22 μm, a thickness of the conductive layer of 110nm, and had protrusions. The results of the elemental analysis of the surface of the conductive layer are shown in table 1, and the results of the ion analysis are shown in table 2.

[ comparative example 1]

The conductive particles obtained by the electroless plating treatment (3) of example 1 were used as the conductive particles of comparative example 1. The results of the elemental analysis of the surface of the conductive layer are shown in table 1, and the results of the ion analysis are shown in table 2.

[ comparative example 2]

The following procedure was performed instead of the vacuum heating treatment of (4) in example 1. The conductive particles obtained by the electroless plating treatment (3) of example 1 were put into a square container to have a thickness of 5 mm. The resultant was placed in a heating furnace (KDF-75, manufactured by DENKEN HIGHDENTAL Co., ltd.) and subjected to a heating treatment at 260 ℃ for 2 hours under a nitrogen atmosphere at normal pressure. After the heat treatment, the mixture was cooled to room temperature to obtain heat-treated conductive particles. The obtained conductive particles had an average particle diameter of 3.22 μm, a thickness of the conductive layer of 110nm, and had protrusions. The results of the elemental analysis of the surface of the conductive layer are shown in table 1, and the results of the ion analysis are shown in table 2.

[ comparative example 3]

The following procedure was carried out in place of the vacuum heat treatment of example 1 (4). The conductive particles obtained by the electroless plating treatment (3) of example 1 were put into a square container to have a thickness of 5 mm. The resultant was placed in a heating furnace (KDF-75, manufactured by DENKEN HIGHDENTAL Co., ltd.) and subjected to a heating treatment at 390 ℃ for 2 hours under a nitrogen atmosphere at normal pressure. After the heat treatment, the mixture was cooled to room temperature to obtain heat-treated conductive particles. The obtained conductive particles had an average particle diameter of 3.22 μm, a thickness of the conductive layer of 110nm, and had protrusions. The results of elemental analysis of the surface of the conductive layer are shown in table 1, and the results of ion analysis are shown in table 2.

[ Table 1]

[ Table 2]

	CH ₄ N ⁺ /Ni ⁺	C ₂ H ₃ O ₂ ^- /Ni ^-	PO ₂ ^- /Ni ^-
				Example 1	0.01	6.00	5.21
Example 2	0.01	7.20	7.86
				Example 3	0.01	8.10	7.99
Comparative example 1	0.35	15.5	25.3
				Comparative example 2	0.20	15.1	24.8
Comparative example 3	0.15	12.7	20.7

[ example 4]

(1) Pretreatment

Spherical styrene-acrylate-silica composite resin particles having an average particle diameter of 3.0 μm were used as core particles. 9g of this was put into 200mL of an aqueous conditioning agent solution ("Cleaner Conditioner 231" manufactured by ROHM AND HAAS ELECTRONIC MATERIALS K.K.) with stirring. The concentration of the regulator aqueous solution was 40mL/L. Next, ultrasonic waves were applied at a liquid temperature of 60 ℃ and stirred for 30 minutes, and surface modification and dispersion treatment of the core material particles were performed. After the aqueous solution was filtered, the core material particles washed once again with water were made into 200mL of slurry. To this slurry was charged 0.1g of stannous chloride. The mixture was stirred at room temperature for 5 minutes to perform sensitization treatment for adsorbing tin ions on the surface of the core material particles. Subsequently, the aqueous solution was filtered, and the core material particles after once repulping and washing were made into 200mL of slurry and maintained at 60 ℃. To this slurry was added 1.5mL of a 0.11mol/L aqueous solution of palladium chloride. The mixture was stirred at 60 ℃ for 5 minutes to carry out an activation treatment for capturing palladium ions on the surface of the core material particles. Subsequently, the aqueous solution was filtered, and the core material particles subjected to primary repulping and hot water washing were made into 100mL of slurry, and then 10mL of 0.5g/L dimethylamine borane aqueous solution was added thereto, and the mixture was stirred for 2 minutes by applying ultrasonic waves to obtain a slurry of pretreated core material particles.

(2) Preparation of the plating bath

An electroless nickel-boron plating bath of 3L formed from an aqueous solution in which 5g/L of sodium tartrate, 2g/L of nickel sulfate hexahydrate, 10g/L of trisodium citrate, 0.1g/L of dimethylamine borane, and 2g/L of polyethylene glycol were dissolved was prepared and heated to 70 ℃.

(3) Electroless plating treatment

To the slurry, 420mL of 224g/L nickel sulfate aqueous solution and 420mL of a mixed aqueous solution containing 120g/L dimethylamine borane and 80g/L sodium hydroxide were continuously added by a metering pump at 2.5 mL/min, respectively, and electroless plating was started.

After the total amount of the nickel sulfate aqueous solution and the mixed aqueous solution of dimethylamine borane and sodium hydroxide were added, respectively, the temperature of 70 ℃ was maintained and stirring was continued for 5 minutes. Then, the liquid was filtered, and the filtrate was washed 3 times and dried by a vacuum drier at 110 ℃ to obtain conductive particles having a nickel-boron alloy coating film. The obtained conductive particles had an average particle diameter of 3.22 μm, a thickness of the conductive layer of 110nm, and had protrusions.

(4) Vacuum heat treatment

The obtained conductive particles were put into a square container to have a thickness of 5 mm. The resultant was placed in a vacuum oven (KDF-75, manufactured by DENKEN HIGHDENTAL Co., ltd.) and subjected to a heat treatment at 390 ℃ for 2 hours under a vacuum of 10 Pa. After the heat treatment, the mixture was cooled to room temperature to obtain heat-treated conductive particles. The obtained conductive particles had an average particle diameter of 3.22 μm, a thickness of the conductive layer of 110nm, and had protrusions. The results of the elemental analysis of the surface of the conductive layer are shown in table 1, and the results of the ion analysis are shown in table 2.

[ example 5]

The vacuum heat treatment of (4) in example 4 was performed in accordance with the following procedure. The conductive particles obtained by the electroless plating treatment (3) of example 4 were charged into a square container to have a thickness of 5 mm. The resultant was placed in a heating furnace (KDF-75, manufactured by DENKEN HIGHDENTAL Co., ltd.) and subjected to a heating treatment at 390 ℃ for 2 hours under a vacuum of 100 Pa. After the heat treatment, the mixture was cooled to room temperature to obtain heat-treated conductive particles. The obtained conductive particles had an average particle diameter of 3.22 μm, a thickness of the conductive layer of 110nm, and had protrusions. The results of the elemental analysis of the surface of the conductive layer are shown in table 3, and the results of the ion analysis are shown in table 4.

[ example 6]

The vacuum heat treatment (4) of example 4 was performed in the following manner. The conductive particles obtained by the electroless plating treatment (3) of example 4 were put into a square container to have a thickness of 5 mm. The resultant was placed in a heating furnace (KDF-75, manufactured by DENKEN HIGHDENTAL Co., ltd.) and subjected to a heating treatment at 320 ℃ for 2 hours under a vacuum of 10 Pa. After the heat treatment, the mixture was cooled to room temperature to obtain heat-treated conductive particles. The obtained conductive particles had an average particle diameter of 3.22 μm, a thickness of the conductive layer of 110nm, and had protrusions. The results of elemental analysis of the surface of the conductive layer are shown in table 3, and the results of ion analysis are shown in table 4.

[ comparative example 4]

The conductive particles obtained by the electroless plating treatment (3) of example 4 were used as the conductive particles of comparative example 4. The results of the elemental analysis of the surface of the conductive layer are shown in table 3, and the results of the ion analysis are shown in table 4.

[ comparative example 5]

The following procedure was carried out in place of the vacuum heat treatment of example 4 (4). The conductive particles obtained by the electroless plating treatment (3) of example 4 were charged into a square container to have a thickness of 5 mm. The resultant was placed in a heating furnace (KDF-75, manufactured by DENKEN HIGHDENTAL Co., ltd.) and subjected to a heating treatment at 260 ℃ for 2 hours under a nitrogen atmosphere at normal pressure. After the heat treatment, the mixture was cooled to room temperature to obtain heat-treated conductive particles. The obtained conductive particles had an average particle diameter of 3.22 μm, a thickness of the conductive layer of 110nm, and had protrusions. The results of the elemental analysis of the surface of the conductive layer are shown in table 3, and the results of the ion analysis are shown in table 4.

[ comparative example 6]

The following procedure was carried out in place of the vacuum heat treatment of example 4 (4). The conductive particles obtained by the electroless plating treatment (3) of example 4 were charged into a square container to have a thickness of 5 mm. The resultant was placed in a heating furnace (KDF-75, manufactured by DENKEN HIGHDENTAL Co., ltd.) and subjected to a heating treatment at 390 ℃ for 2 hours under a nitrogen atmosphere at normal pressure. After the heat treatment, the mixture was cooled to room temperature to obtain heat-treated conductive particles. The obtained conductive particles had an average particle diameter of 3.22 μm, a thickness of the conductive layer of 110nm, and had protrusions. The results of the elemental analysis of the surface of the conductive layer are shown in table 3, and the results of the ion analysis are shown in table 4.

[ Table 3]

[ Table 4]

	CH ₄ N ⁺ /Ni ⁺	C ₂ H ₃ O ₂ ^- /Ni ^-	(B ₂ O ₄ H ₃ ^- +B ₃ O ₆ H ₄ ^- )/Ni ^-
				Example 4	0.02	5.98	2.27
Example 5	0.01	7.15	4.38
				Example 6	0.02	8.02	5.41
Comparative example 4	0.34	16.5	17.1
				Comparative example 5	0.22	14.9	16.9
Comparative example 6	0.13	12.9	16.6

[ evaluation of storage stability and Corrosion resistance ]

(1) Storage stability and corrosion resistance of conductive particles

Using the conductive particles of examples and comparative examples, the storage stability and corrosion resistance of the conductive particles were evaluated by the following methods.

After the conductive particles obtained in examples and comparative examples were stored at room temperature (25 ℃ C. 50% RH) for the time shown in Table 2, 1.0g of the conductive particles were charged into a vertically erected resin cylinder having an inner diameter of 10mm, and the volume resistance value between the upper and lower electrodes was determined at room temperature (25 ℃ C. 50% RH) in a state in which a load of 2kN was applied. The results are shown in Table 5.

[ Table 5]

From the results, it was judged that the conductive particles obtained in the examples had a smaller increase in volume resistance value than the conductive particles obtained in the comparative examples, and were excellent in storage stability and corrosion resistance.

(2) Storage stability of conductive material

Using the conductive particles of examples and comparative examples, a conductive material was produced by the following method, and the storage stability of the conductive material was evaluated by a pressure cooker test.

An insulating adhesive containing 100 parts by mass of an epoxy resin, 150 parts by mass of a curing agent, and 70 parts by mass of toluene was mixed with 15 parts by mass of the conductive particles obtained in examples and comparative examples to obtain a paste. This paste was coated on a silicone-treated polyester film by a bar coater, and then the paste was dried to form a thin film on the film. The obtained thin film-forming film was disposed between a glass substrate having an aluminum deposited on the entire surface thereof and a polyimide film substrate having a copper pattern formed at a pitch of 50 μm, to prepare a connection structure, and then electrically connected, and the connection resistance value of the connection structure was measured at room temperature (25 ℃. 50% rh). Thereafter, the connection structure was placed in a closed vessel, and a pressure cooking test was performed for 10 hours at a temperature of 121 ℃ and a relative humidity of 100% under 2 atmospheres. After the pressure cooking test, the connection resistance value of the connection structure was measured at room temperature (25 ℃. 50% RH). The smaller the difference in the connection resistance values before and after the retort test, the higher the storage stability of the conductive material can be evaluated. The results are shown in Table 6.

[ Table 6]

From the results, it was confirmed that the conductive material obtained in the example had a smaller difference in connection resistance values before and after the retort test and was superior in storage stability to the conductive material obtained in the comparative example.

[ evaluation of connection resistance and connection reliability ]

Using the conductive particles of examples and comparative examples, the connection resistance and connection reliability were evaluated by the following methods.

1.0g of the conductive particles obtained in examples and comparative examples were charged into a vertically standing resin cylinder having an inner diameter of 10mm, and the resistance between the upper and lower electrodes was measured at room temperature (25 ℃ C. 50% RH) under a load of 2kN to determine the initial volume resistance value. As the initial volume resistance value was lower, it was evaluated that the oxide film formed on the electrode could be effectively eliminated, and the connection resistance of the conductive particles was lower.

The resistance value after 24-hour retention was also measured under the conditions of 85 ℃ 85% RH. The smaller the difference in connection resistance value from room temperature, the more excellent the connection reliability of the conductive particles can be evaluated. The results are shown in Table 7.

[ Table 7]

	Initial volume resistance value (m omega cm)	85 ℃ RH, the electric resistance value after 24 hours (m.OMEGA.. Cm)
			Example 1	4.92	18.06
Example 2	5.05	22.82
			Example 3	5.59	24.69
Example 4	3.75	19.91
			Example 5	4.34	24.51
Example 6	5.22	29.88
			Comparative example 1	11.22	44.68
Comparative example 2	8.52	33.23
			Comparative example 3	5.35	25.64
Comparative example 4	9.55	59.66
			Comparative example 5	7.89	36.51
Comparative example 6	5.05	35.83

From the results, it was determined that the conductive particles obtained in the examples had a lower initial volume resistance value and a lower connection resistance than the conductive particles obtained in the comparative examples. It was also found that the conductive particles obtained in the examples had a smaller difference in initial volume resistance value from the resistance value after 24-hour retention at 85 ℃ · 85 rh, and had higher connection reliability than the conductive particles obtained in the comparative examples. In particular, when the conductive particles obtained in examples 1 and 2 on which the nickel-phosphorus plating layer was formed were compared with the conductive particles obtained in comparative example 3, it was determined that conductive particles having low connection resistance and excellent connection reliability could be obtained by heating under vacuum. When the conductive particles obtained in examples 4 and 5 on which the nickel-boron plating layer was formed were compared with the conductive particles obtained in comparative example 6, it was determined that conductive particles having low connection resistance and excellent connection reliability could be obtained by heating under vacuum.

Claims

1. An electrically conductive particle, characterized in that:

a nickel plating layer as a conductive layer is formed on the surface of the core material particle,

in the conductive particles, a molar ratio C/(Ni + P) of carbon to a total of nickel and phosphorus or a molar ratio C/(Ni + B) of carbon to a total of nickel and boron is 0.0002 to 1.65, a molar ratio O/(Ni + P) of oxygen to a total of nickel and phosphorus or a molar ratio O/(Ni + B) of oxygen to a total of nickel and boron is 0.0001 to 2.0, and a molar ratio P/Ni of phosphorus to nickel or a molar ratio B/Ni of boron to nickel is 0.003 to 0.7, as measured by a scanning auger electron spectroscopy apparatus, within 5nm in a depth direction from a surface of the conductive layer.

2. An electrically conductive particle, characterized in that:

in the conductive particles, CH within 1nm in the depth direction from the surface of the conductive layer measured by TOF-SIMS ₄ N ⁺ Intensity of positive ion count relative to Ni ⁺ Counting intensity of positive ions CH ₄ N ⁺ /Ni ⁺ Is 0.1 or less, or C ₂ H ₃ O ₂ ^－ Intensity of negative ion count with respect to Ni ^－ Counting intensity of negative ions C ₂ H ₃ O ₂ ^－ /Ni ^－ Is 10.0 or less, or PO ₂ ^－ Intensity of negative ion count with respect to Ni ^－ Counting intensity of negative ions PO ₂ ^－ /Ni ^－ Is 10.0 or less, or B ₂ O ₄ H ₃ ^－ And B ₃ O ₆ H ₄ ^－ Intensity of negative ion count relative to Ni ^－ Intensity of negative ion count (B) ₂ O ₄ H ₃ ^－ +B ₃ O ₆ H ₄ ^－ )/Ni ^－ Is 10.0 or less.

3. The conductive particle according to claim 1 or 2, wherein:

the thickness of the conductive layer is 5nm to 2000 nm.

4. The conductive particle according to any one of claims 1 to 3, wherein:

the average particle diameter is 0.1 to 50 μm.

5. The conductive particle according to any one of claims 1 to 4, wherein:

the outer surface of the conductive layer has protrusions.

6. The conductive particle according to any one of claims 1 to 4, wherein:

the outer surface of the conductive layer is smooth.

7. An electrically conductive material, characterized by:

comprising the conductive particles according to any one of claims 1 to 6 and a binder resin.

8. A connection structure, characterized in that:

the members to be connected are connected to each other via the conductive material according to claim 7.

9. A method for producing the conductive particles according to any one of claims 1 to 6, characterized in that:

comprises a step of heating conductive particles having a conductive layer on the surface of a core particle at a temperature of 200 to 600 ℃ in a vacuum of 1000Pa or less.

10. The method for producing conductive particles according to claim 9, wherein:

the conductive layer is formed on the surface of the core material particle by electroless plating, and the obtained conductive particle is heated.