JP5395482B2 - Coated conductive fine particles, anisotropic conductive material, and conductive connection structure - Google Patents

Description

The present invention relates to a coated conductive fine particle, an anisotropic conductive material, and a conductive connection structure excellent in connection reliability.

Particles having a metal surface are mixed with a binder resin and used as an anisotropic conductive material. The anisotropic conductive material is used for electrically connecting a small electric component such as a semiconductor element to a substrate.

In recent years, electronic devices and electronic components have been miniaturized, and electrodes such as substrates have become finer. On the other hand, in order to ensure high connection reliability, it is necessary to increase the blending amount of the conductive fine particles in the anisotropic conductive material. However, a substrate or the like having such fine wiring has a problem in that conduction between adjacent conductive fine particles occurs in a lateral direction, and a short circuit occurs between adjacent electrodes. In order to solve this problem, coated conductive fine particles in which the surface of the conductive fine particles is coated with an insulator have been proposed.

As a method for coating the surface of the conductive fine particles with an insulator, for example, in Patent Document 1, interfacial polymerization, suspension polymerization, emulsion polymerization, etc. are performed in the presence of the conductive fine particles, and the conductive fine particles are microencapsulated with a resin. How to do is described. Patent Document 2 describes a method of encapsulating conductive fine particles by a dipping method in which conductive fine particles dispersed in a resin solution are dried. Patent Document 3 describes a method of forming an insulating coating layer on the surface of conductive fine particles by a spray drying method or a hybridization method.

However, with such a method, it has been difficult to keep the thickness of the insulating layer constant. In addition, a plurality of conductive fine particles may be coated at the same time. When the electrodes are connected using an anisotropic conductive material containing coated conductive fine particles whose insulating coating layer thickness is not uniform, the connection resistance value may be increased. For example, a method for forming an insulating coating by a hybridization method is a method in which insulating fine particles serving as a coating layer are attached to the surface of conductive fine particles by a physical force. In the hybridization method, a single insulating coating layer could not be formed on the surface of the conductive fine particles. In addition, it is difficult to control the thickness of the insulating coating layer. Since heat and impact such as heating and frictional heat are applied and the insulating fine particles are melted, it is difficult to form a uniform insulating coating layer on the surface of the conductive fine particles. Further, since the contact area where the insulating fine particles are in contact with the conductive fine particles is increased, there is a problem that the insulating coating layer is hardly removed and the connection resistance value is increased.

Patent Documents 4 and 5 describe coated conductive fine particles in which insulating fine particles are attached to the surface of the conductive fine particles by electrostatic interaction or a hybridization method. However, the coated conductive fine particles have a very weak bonding force between the insulating fine particles and the conductive fine particles. When the coated conductive fine particles are dispersed in the binder resin, there is a problem that the insulating fine particles are peeled off from the surface of the conductive fine particles and sufficient insulation cannot be secured.

The conductive fine particles are dispersed in an insulating binder resin and used as an anisotropic conductive material. When such an anisotropic conductive material is used for conductive connection, there is a problem that the connection resistance value is increased. This was considered because the binder resin between the electrode and the conductive fine particles could not be sufficiently eliminated, and the binder resin remained between the electrode and the conductive fine particles.

JP-A-4-362104 JP 62-40183 A JP-A-7-105716 JP-A-4-259766 Japanese Patent Laid-Open No. 3-112011

An object of the present invention is to provide a coated conductive fine particle, an anisotropic conductive material, and a conductive connection structure excellent in connection reliability.

The present invention is a coated conductive fine particle in which insulating fine particles are attached to the surface of a substrate fine particle having a conductive metal surface, wherein the substrate fine particle has a protrusion on the surface, and the diameter of the insulating fine particle 200 to 500 nm, and the height of the protrusion is 50 nm or more, and the coated conductive fine particles are 100 nm or more smaller than the diameter of the insulating fine particles.
The present invention is described in detail below.

In the coated conductive fine particles of the present invention, insulating fine particles are attached to the surface of the substrate fine particles having a conductive metal surface. Thus, when conductive connection of a substrate or the like is performed using coated conductive fine particles in which insulating fine particles are attached to the surface of the substrate fine particles having a conductive metal surface, the substrate or the like having fine wiring is obtained. However, it is difficult for the adjacent conductive fine particles to conduct in the lateral direction. Further, when the coated conductive fine particles are thermocompression bonded, the metal surface is exposed, so that the electrodes facing each other can be made conductive.

The substrate fine particles have a conductive metal surface on the outermost surface of the substrate fine particles, and protrusions are formed on the metal surface. The substrate fine particles are not particularly limited. For example, the substrate fine particles substantially formed of metal, the substrate fine particles in which a metal layer is formed on the surface of the core particles, and the metal fine particles adhere to the surface of the core particles. Base material fine particles and the like.
The core particles are not particularly limited, and examples thereof include organic fine particles, inorganic fine particles, and organic / inorganic hybrid fine particles.
In particular, when the substrate fine particles having a metal layer formed on the surface of the organic fine particles are sandwiched between the electrodes and pressed, the substrate fine particles are deformed to increase the contact area with the electrodes.

The organic fine particles are not particularly limited, and include, for example, polyolefin resin, acrylic resin, polyalkylene terephthalate resin, polysulfone resin, polycarbonate resin, polyamide resin, phenol formaldehyde resin, melamine formaldehyde resin, benzoguanamine formaldehyde resin, urea formaldehyde resin, and the like. Organic fine particles.
The polyolefin resin is not particularly limited, and examples thereof include polyethylene resin, polypropylene resin, polystyrene resin, polyisobutylene resin, polybutadiene resin, polyvinyl chloride resin, polyvinylidene chloride resin, and polytetrafluoroethylene resin. The acrylic resin is not particularly limited, and examples thereof include polymethyl methacrylate resin and polymethyl acrylate resin.

The average particle diameter of the core particles is not particularly limited, and a preferable lower limit is 0.5 μm and a preferable upper limit is 100 μm. If the average particle diameter of the core particles is less than 0.5 μm, the core particles are likely to aggregate, and therefore, the base particles in which a metal layer is formed on the surface of the aggregated core particles may short-circuit between adjacent electrodes. is there. When the average particle diameter of the core particles exceeds 100 μm, the metal layer of the coated conductive fine particles may be easily peeled off. The more preferable lower limit of the average particle diameter of the core particles is 1 μm, and the more preferable upper limit is 20 μm.
In addition, the average particle diameter of the said core particle means the average value of the diameter obtained by observing 50 core particles selected at random using an optical microscope or an electron microscope.

In addition, the upper limit of the CV value of the core particles is 15%. If the CV value exceeds 15%, the connection reliability of the coated conductive fine particles may be lowered. A more preferable upper limit of the CV value is 10%. The CV value is a numerical value obtained by dividing the standard deviation by the average particle diameter in percentage (%).

A preferred lower limit of the 10% K value of the core particles 1000 N / mm ^2, the upper limit is preferably 15000 N / mm ^2. If the 10% K value is less than 1000 N / mm ² , the core particles may be destroyed when the coated conductive fine particles are greatly compressed and deformed. When the 10% K value exceeds 15000 N / mm ² , the coated conductive fine particles may damage the electrode. A more preferred lower limit of the 10% K value 2000N / mm ^2, and more preferable upper limit is 10000 N / mm ^2.
The 10% K value is obtained by using a micro compression tester (for example, “PCT-200” manufactured by Shimadzu Corporation), the core particle is a smooth indenter end face of a diamond cylinder having a diameter of 50 μm, and the compression speed is 2.6 mN / The compression displacement (mm) when compressed under conditions of seconds and a maximum test load of 10 g can be measured and determined by the following equation.
K value ^{(N / mm 2) = (} 3 / √2) · F · S -3/2 · R -1/2
F: Load value at 10% compression deformation of core particles (N)
S: Compression displacement (mm) in 10% compression deformation of core particles
R: Core particle radius (mm)

The metal is not particularly limited as long as it has conductivity, for example, gold, silver, copper, platinum, zinc, iron, tin, lead, palladium, aluminum, cobalt, indium, nickel, chromium, Examples thereof include metals such as titanium, antimony, bismuth, germanium, cadmium, and silicon, and metal compounds such as ITO and solder.

The metal layer may have a single layer structure or a stacked structure in which a plurality of layers are stacked. When the metal layer has a laminated structure, the outermost layer of the laminated structure is preferably a gold layer, and more preferably a nickel layer or a palladium layer. When the outermost layer of the laminated structure is a gold layer, the connection resistance value between the electrodes is low, and when the outermost layer of the laminated structure is a nickel layer or a palladium layer, the metal layer becomes harder, and thus the conductivity is higher. improves.

Although the thickness of the said metal layer is not specifically limited, A preferable minimum is 0.005 micrometer and a preferable upper limit is 1 micrometer. When the thickness of the metal layer is less than 0.005 μm, the connection resistance value between the electrodes may increase. When the thickness of the metal layer exceeds 1 μm, the specific gravity of the coated conductive fine particles increases, and the coated conductive fine particles may not be uniformly dispersed in the binder resin. The more preferable lower limit of the thickness of the metal layer is 0.01 μm, and the more preferable upper limit is 0.3 μm.

The method for forming the metal layer is not particularly limited, and examples thereof include a metal vapor deposition method and an electroless plating method. An electroless plating method is preferred because the metal layer can be easily formed on the surface of the core particles.
Examples of the metal layer include metal layers containing gold, silver, copper, platinum, palladium, nickel, rhodium, ruthenium, cobalt, tin and the like.
When the metal layer has a laminated structure, a nickel layer and a gold layer may be sequentially formed on the surface of the core particle, and a nickel layer and a palladium layer are sequentially formed on the surface of the core particle. May be.

The protrusion on the surface of the substrate fine particle is not particularly limited as long as at least the surface of the protrusion is covered with a conductive metal.

The lower limit of the height of the protrusion is 50 nm. If the height of the protrusion is less than 50 nm, the protrusion cannot contact the electrode even if the electrodes are connected by sandwiching the coated conductive fine particles between the electrodes. A preferable lower limit of the height of the protrusion is 100 nm, and a more preferable lower limit is 150 nm.
Further, the height of the protrusion is preferably 40% or less of the diameter of the base particle. When the height of the protrusion exceeds 40% of the diameter of the base particle, the protrusion may damage the electrode. The height of the protrusion is more preferably 20% or less of the diameter of the substrate fine particles.

Further, the height of the protrusion is 100 nm or more smaller than the diameter of insulating fine particles described later. If the height of the protrusion is not smaller than 100 nm by the diameter of the insulating fine particle, the protrusion of the coated conductive fine particle may come into contact with the adjacent coated conductive fine particle. As a result, the adjacent electrodes are short-circuited. The height of the protrusion is preferably 150 nm or more smaller than the diameter of the insulating fine particles, more preferably 200 nm or more, and even more preferably 250 nm or more.

The height of the protrusion can be calculated by the following method. Fifty coated conductive fine particles of the present invention are observed with a scanning electron microscope, and the heights of all the protrusions at the peripheral edge of the observed coated conductive fine particles are measured. The height of the protrusion was calculated by measuring the height of the protrusion using the metal surface on which the protrusion was not formed as a reference surface, and arithmetically averaging the measured values.

The number of protrusions is not particularly limited, but the average number of protrusions per coated conductive fine particle is preferably 8 or more. If the average number of protrusions is less than 8, the connection resistance value between the electrodes may increase.

The method for producing the substrate fine particles having the protrusions is not particularly limited. For example, the following method is mentioned.
1) A method of forming the metal layer on the surface of the core particle while incorporating particles composed of an inorganic material or an organic material into the metal layer.
2) A substance having a high affinity for the metal constituting the metal layer is attached to the surface of the core particle, and a conductive protrusion is grown at a location where a substance having a high affinity for the metal is attached. However, the method of forming the said metal layer on the surface of the said core particle.
3) A method of forming the metal layer on the surface of the protruding particles in which particles composed of an inorganic material or an organic material are attached to the core particles.

The method 1) is not particularly limited, and examples include the following method.
The suspension in which the core particles are dispersed in ion-exchanged water is added to an electroless plating bath containing a nickel salt, a reducing agent, a complexing agent, etc., and electroless nickel plating is performed. A nickel layer is formed on the surface of the core particles, and at the same time, self-decomposition of the electroless plating bath occurs. Since the self-decomposed product becomes the nucleus of the protrusion, a nickel layer and a protrusion are simultaneously formed on the surface of the core particle.

The method 2) is not particularly limited, and examples include the following method.
A palladium salt is attached to the surface of the core particle. The palladium salt adhering to the surface of the core particle is extremely gently reduced, and a palladium catalyst serving as a starting point for electroless nickel plating is supported on the surface of the core particle. The core particles carrying the palladium catalyst are added to an electroless plating bath containing a nickel salt, a reducing agent, a complexing agent, etc., and electroless nickel plating is performed.
In this method, the nickel deposition rate is higher at the places where a large amount of palladium is supported than at the places where the palladium is less supported, so that a nickel layer and protrusions are simultaneously formed on the surface of the core particles. The

The method 3) is not particularly limited, and examples include the following method.
Protrusion particles in which particles composed of an inorganic material or an organic material are attached to the surface of the core particles by a hybridization method or the like are produced. The protruding particles are plated with electroless nickel, and a nickel layer and protrusions are formed simultaneously.
In addition, protruding particles in which metal particles such as nickel particles are attached to the surface of the core particles may be prepared, and the protruding particles may be electroless nickel-plated to form the nickel layer and the protrusions simultaneously.
Further, an inorganic material or an organic material is formed on the surface of a polymerizable droplet containing a polymerizable unsaturated monomer and a medium, or a polymerizable droplet obtained by swelling seed particles with a polymerizable monomer in a medium. The particles composed of etc. are adhered. Polymerizable droplets with particles attached are polymerized to produce protruding particles. The protruding particles are plated with electroless nickel, and a nickel layer and protrusions are formed simultaneously.

The method for forming the metal layer on the surface of the core particle to which particles composed of an inorganic material or an organic material are attached is not particularly limited. For example, a step of preparing a dispersion liquid in which polymerizable droplets containing a polymerizable unsaturated monomer and a medium are dispersed in the medium; and the particles are added to the dispersion liquid, and the particles are converted into the polymerizable liquid droplets. A method comprising a step of adhering to the surface of the material, a step of polymerizing the polymerizable droplets to which the particles adhere, producing a protruding particle, and a step of metal plating the protruding particle.

As another method, for example, a step of mixing a seed particle and a medium containing a polymerizable unsaturated monomer to prepare a dispersion in which the seed particle is dispersed in the medium, and polymerization onto the seed particle. A step of preparing polymerizable droplets by absorbing the polymerizable unsaturated monomer, a step of adding the particles to the dispersion and attaching the particles to the surface of the polymerizable droplets, and a polymerization property of the particles attached Examples thereof include a method of polymerizing droplets to produce protruding particles and a step of metal plating the protruding particles.

The insulating fine particles are not particularly limited as long as they are insulating particles, and examples thereof include insulating fine particles composed of an insulating resin, and insulating fine particles such as silica. Among these, insulating fine particles composed of an insulating resin are preferable. The insulating resin is not particularly limited, and examples thereof include resins used for the organic fine particles. These resins may be used alone or in combination of two or more.

The lower limit of the diameter of the insulating fine particles is 200 nm, and the upper limit is 500 nm. When the diameter of the insulating fine particles is in the range of 200 to 500 nm, the short circuit between the adjacent electrodes is prevented, and the effect of reducing the connection resistance value between the opposing electrodes is excellent. A preferable lower limit of the diameter of the insulating fine particles is 240 nm, and a more preferable lower limit is 250 nm. A preferable upper limit of the diameter of the insulating fine particles is 450 nm, and a more preferable upper limit is 420 nm.
The diameter of the insulating fine particles means an average value of diameters obtained by observing 50 insulating fine particles selected at random using an electron microscope.

The insulating fine particles preferably have a CV value of a particle diameter of 20% or less. When the CV value exceeds 20%, the connection reliability of the coated conductive fine particles may be lowered.

The insulating fine particles are preferably insulating fine particles having a positive charge. When the insulating fine particles have a positive charge, the insulating fine particles adhere to the base particle using a heteroaggregation method described later. Further, since the insulating fine particles repel each other, aggregation of the insulating fine particles is suppressed. As a result, a single coating layer is formed on the surface of the substrate fine particles.
Further, when the insulating fine particles have an ammonium group or a sulfonium group, the insulating fine particles have a positive charge. The ammonium group or sulfonium group also acts as a functional group (A) having a binding property to the metal described later. As a result, the insulating fine particles easily form a chemical bond with the metal on the surface of the base fine particles. Therefore, the insulating fine particles are preferably composed of a resin having an ammonium group or a sulfonium group. Among these, the insulating fine particles are more preferably made of a resin having a sulfonium group.

The insulating fine particles having a positive charge are not particularly limited, but the insulating fine particles obtained by polymerizing a polymerizable monomer having a positive charge, the insulating fine particles polymerized using a radical initiator having a positive charge, the dispersion stability having a positive charge. Insulating fine particles produced using an agent or an emulsifier.
Examples of the positively charged polymerizable monomer include N, N-dimethylaminoethyl methacrylate, N, N-dimethylaminopropylacrylamide, N, N, N-trimethyl-N-2-methacryloyloxyethylammonium chloride, and the like. And monomers having a sulfonium group such as phenyldimethylsulfonium methylsulfate methacrylate. Examples of the radical initiator having a positive charge include 2,2′-azobis {2-methyl-N- [2- (1-hydroxy-butyl)]-propionamide}, 2,2′-azobis [2- (2-imidazolin-2-yl) propane], 2,2′-azobis (2-aminodipropane) and salts thereof.

It is preferable that the substrate fine particles having the conductive metal surface are chemically bonded to the insulating fine particles via the functional group (A) having a binding property to the conductive metal.
Since the insulating fine particles are chemically bonded to the substrate fine particles, the bonding strength is stronger than the bonding by van der Waals force or electrostatic force. Therefore, even if the coated conductive fine particles of the present invention are mixed with a binder resin or the like, the insulating fine particles are difficult to peel off. Therefore, when the coated conductive fine particles of the present invention are used as an anisotropic conductive material, the insulating fine particles are not easily peeled off, so that a short circuit between adjacent coated conductive fine particles can be prevented.
Since the substrate fine particles have protrusions on the surface, even if the insulating fine particles are strongly chemically bonded to the substrate fine particles, the protrusions push away the insulating fine particles by thermocompression bonding. As a result, the electrodes can be reliably conductively connected. Further, since this chemical bond is formed only between the base material fine particles and the insulating fine particles, the insulating fine particles do not chemically bond with each other. Therefore, the coating layer made of insulating fine particles is a single layer. From this, the particle diameter of the coated conductive fine particles of the present invention can be controlled by aligning the particle diameters of the substrate fine particles and the insulating fine particles.

The functional group (A) is not particularly limited as long as it is a functional group capable of ionic bond, covalent bond, and coordinate bond with the conductive metal. For example, silane group, silanol group, carboxyl group, amino group, ammonium group Nitro group, hydroxyl group, carbonyl group, thiol group, sulfonic acid group, sulfonium group, boric acid group, oxazoline group, pyrrolidone group, phosphoric acid group, nitrile group and the like. Especially, the functional group which can be coordinate-bonded is preferable, and the functional group which has S, N, and P atom is more preferable. For example, when the metal is gold, the functional group (A) is preferably a functional group having an S atom that forms a coordinate bond with gold, and particularly a thiol group or a sulfide group. More preferred.

A method for chemically bonding the base material fine particles and the insulating fine particles using such a functional group (A) is not particularly limited. For example, 1) a method of introducing insulating fine particles having a functional group (A) on the surface thereof to the surface of the substrate fine particles, 2) a compound having a functional group (A) and a reactive functional group (B) Examples thereof include a method of introducing into a metal surface and reacting and bonding the reactive functional group (B) and insulating fine particles by a one-step or multi-step reaction.
In the method 1), the method for producing the insulating fine particles having the functional group (A) on the surface is not particularly limited. For example, a method in which a monomer having the functional group (A) is mixed during the polymerization of the insulating fine particles, insulating fine particles A method of introducing a functional group (A) into the surface of the substrate by chemical bonding, a method of chemically treating the surface of the insulating fine particles to modify the surface to the functional group (A), and modifying the surface of the insulating fine particles into a functional group (A) with plasma or the like. The method of quality is mentioned.

In the above method 2), for example, a functional group (A) and a reactive functional group (B) such as hydroxyl group, carboxyl group, amino group, epoxy group, silyl group, silanol group, and isocyanate group in the same molecule A compound having a reaction with the substrate fine particles. Next, a method of reacting insulating fine particles having a functional group that can be covalently bonded to the reactive functional group (B) on the surface can be mentioned. Examples of such a compound having a functional group (A) and a reactive functional group (B) in the same molecule include 2-aminoethanethiol and p-aminothiophenol. For example, by bonding 2-aminoethanethiol to the surface of the substrate fine particle via a thiol group, and reacting an insulating fine particle having, for example, an epoxy group or a carboxyl group on the surface with one amino group, the group The material fine particles can be bonded to the insulating fine particles.

When joining between electrodes using the coated conductive fine particles of the present invention, heat and pressure are applied to apply heat and pressure to expose the metal surface of the substrate fine particles, thereby conducting. Here, the metal surface is exposed is a state in which at least a part of the metal surface of the substrate fine particles can be in direct contact with the electrode without being blocked by the insulating fine particles. The thermocompression bonding conditions are not necessarily limited by the density of the coated conductive fine particles in the anisotropic conductive material, the type of electronic component to be connected, and the like. However, the thermocompression bonding is performed at a temperature of 120 to 220 ° C., 9 The pressure is from 8 × 10 ^{4 to} 4.9 × 10 ⁶ Pa.

The following three aspects are mentioned as the aspect which the metal surface of the said base material microparticles | fine-particles exposes.
In the first aspect, the insulating fine particles are melted by thermocompression bonding, and the metal surface of the substrate fine particles is exposed. In the second aspect, the insulating fine particles are deformed by thermocompression bonding, and the metal surfaces of the base material fine particles are exposed. The third aspect is an aspect in which the base material fine particles and the insulating fine particles are dissociated by thermocompression bonding, and the metal surface of the base material fine particles is exposed.
In particular, it is preferable that the metal surface of the base particle is exposed and conductively connected according to the second aspect.
In the case of the first aspect, the molten insulating fine particles may bleed out and contaminate the binder resin or the substrate. In addition, the coating layer that insulates adjacent coated conductive fine particles may melt, and sufficient insulation may not be obtained.
In the case of the third aspect, the connection reliability may be lowered if the base particle and the insulating particle are arranged between the facing electrodes during thermocompression bonding. In addition, when the substrate fine particles have protrusions on the surface, the metal surface of the substrate fine particles is easily exposed even in the second aspect and the third aspect.

The mode in which the metal surface of the substrate fine particles is exposed and conductive connection is made may be affected by the thermocompression bonding conditions and the like. Usually, this aspect can be controlled by the relative relationship between the hardness of the substrate fine particles and the hardness of the insulating fine particles. Here, the hardness of the particles refers to the relative hardness under thermocompression bonding conditions. For example, if the softening temperature of the insulating fine particles is lower than that of the base fine particles and only the insulating fine particles soften under the thermocompression bonding condition, it can be said that the insulating fine particles are soft.

In order to expose the metal surface of the substrate fine particles, the insulating fine particle coverage is preferably 5 to 50%. The coverage of insulating fine particles means the ratio of the area of the portion covered with the insulating fine particles to the entire surface area of the substrate fine particles. If the coverage of insulating fine particles is less than 5%, insulation between adjacent coated conductive fine particles may not be sufficient. When the coverage of the insulating fine particles exceeds 50%, in the case of the first aspect, the coating layer that insulates the adjacent coated conductive fine particles may melt and may not exhibit sufficient insulation. In the case of the second aspect, even if the insulating fine particles are deformed, the metal surface of the substrate fine particles may not be sufficiently exposed. In the case of the third aspect, it is necessary to push away the insulating fine particles existing between the coated conductive fine particles and the electrode.

As a method for producing the coated conductive fine particles of the present invention, a method in which the insulating fine particles are brought into contact with and chemically bonded to the surface of the substrate fine particles having the protrusions is preferable. For example, step 1 of aggregating insulating fine particles to base fine particles having a conductive metal surface in an organic solvent or water by van der Waals force or electrostatic interaction, and insulating the base fine particles having a conductive metal surface. A method including the step 2 of chemically bonding the fine particles is preferable. The aggregation method in Step 1 is a method called a heteroaggregation method. If the hetero-aggregation method is used, a chemical reaction between the substrate fine particles and the insulating fine particles occurs quickly and reliably due to the solvent effect. When insulating fine particles are introduced onto the surface of the base material fine particles by a conventional dry method such as a high-speed stirrer or a hybridizer, a load such as pressure or frictional heat is easily applied to the base material fine particles. If the insulating fine particles are harder than the substrate fine particles, the substrate fine particles may be damaged or the metal layer may be peeled off. If the insulating fine particles are softer than the base fine particles, the insulating fine particles may be deformed by collision with the base fine particles or frictional heat.
The organic solvent is not particularly limited as long as it does not dissolve the insulating fine particles.

Since the coated conductive fine particles of the present invention have insulating fine particles attached to the surface of the substrate fine particles, even when used as an anisotropic conductive material, short-circuiting between adjacent coated conductive fine particles is unlikely to occur. Furthermore, since there are protrusions on the surface of the substrate fine particles, the metal surface of the substrate fine particles is exposed at the time of connection, and conduction can be reliably obtained. Further, when the base particles and the insulating particles are chemically bonded, the insulating particles are not easily peeled off even when mixed with the binder resin.

The coated conductive fine particles of the present invention can be used for applications such as anisotropic conductive materials, heat ray reflective materials, and electromagnetic shielding materials. Among these, the coated conductive fine particles of the present invention can be suitably used as an anisotropic conductive material by being dispersed in an insulating binder resin.
An anisotropic conductive material in which the coated conductive fine particles of the present invention are dispersed in an insulating binder resin is also one aspect of the present invention.
Note that in this specification, the anisotropic conductive material includes an anisotropic conductive film, an anisotropic conductive paste, an anisotropic conductive adhesive, an anisotropic conductive ink, and the like.

The insulating binder resin is not particularly limited as long as it is insulative. For example, acrylic ester, ethylene-vinyl acetate resin, styrene-butadiene block copolymer, hydrogenated product of styrene-butadiene block copolymer, Examples thereof include styrene-isoprene block copolymers, hydrogenated products of styrene-isoprene block copolymers, epoxy resins, melamine resins, urea resins, and phenol resins.

The anisotropic conductive material of the present invention, in addition to the binder resin as an essential component and the coated conductive fine particles of the present invention, as necessary, for example, in a range that does not hinder the achievement of the present invention, Various additives such as a softener, a plasticizer, a polymerization catalyst, a curing catalyst, a colorant, an antioxidant, a heat stabilizer, a light stabilizer, an ultraviolet absorber, a lubricant, an antistatic agent, and a flame retardant may be added. .

In the anisotropic conductive material of the present invention, the functional group contained in the insulating fine particles and the functional group in the binder resin are preferably chemically bonded. By chemically bonding the insulating fine particles and the binder resin, the stability of the coated conductive fine particles of the present invention dispersed in the binder resin is excellent. In addition, the thermally melted insulating fine particles do not bleed out and contaminate the electrodes and the liquid crystal. As a result, an anisotropic conductive material having excellent long-term connection stability and reliability can be obtained.

The method for dispersing the coated conductive fine particles of the present invention in the binder resin is not particularly limited, and a conventionally known dispersion method can be used. For example, after adding the coated conductive fine particles in the binder resin, kneading and dispersing with a planetary mixer or the like, after uniformly dispersing the coated conductive fine particles in water or an organic solvent using a homogenizer or the like, Add into binder resin, knead and disperse with planetary mixer, etc., dilute binder resin with water or organic solvent, add coated conductive fine particles, knead and disperse with planetary mixer etc. Examples thereof include a dispersion method for applying a mechanical shearing force such as a method. These dispersion methods may be used alone or in combination.

A method for producing the anisotropic conductive film is not particularly limited. For example, a solvent is added to the binder resin, and the coated conductive fine particles of the present invention are suspended to prepare a suspension. Examples include a method in which this suspension is applied onto a release film to form a film, and a solvent is volatilized from the film to prepare an anisotropic conductive film.

The anisotropic conductive paste can be produced, for example, by making an anisotropic conductive adhesive into a paste. An anisotropic conductive paste is applied on the electrode to be connected to a desired thickness, the counter electrode is overlaid thereon, and the resin is cured by thermocompression bonding.

The anisotropic conductive ink can be produced, for example, by adding a solvent to the anisotropic conductive adhesive to adjust the viscosity to be suitable for printing. Connection can be made by screen-printing anisotropic conductive ink on the electrodes, then volatilizing the solvent, and overlapping the opposing electrodes and thermocompression bonding.

A conductive connection structure in which an electronic component such as an IC chip or a substrate is conductively connected by the coated conductive fine particles of the present invention or the anisotropic conductive material of the present invention is also one aspect of the present invention.

According to the present invention, it is possible to provide coated conductive fine particles, an anisotropic conductive material, and a conductive connection structure excellent in connection reliability.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

Example 1
(Electroless plating pretreatment process)
50 parts by weight of tetramethylol methane tetraacrylate and 50 parts by weight of divinylbenzene were copolymerized to prepare resin fine particles (average particle size 3 μm). A palladium catalyst was applied to the surface of 10 g of resin fine particles.

(Core material compounding process)
10 g of resin fine particles provided with a palladium catalyst were dispersed in 300 mL of ion-exchanged water to prepare an aqueous solution. 1 g of metallic nickel particles (average particle diameter 50 nm) was added to the aqueous solution over 3 minutes to prepare resin fine particles to which the metallic nickel particles adhered.

(Electroless nickel plating process)
The resin fine particles to which the metallic nickel particles were adhered were dispersed in 1200 mL of ion exchange water, and 4 mL of a plating stabilizer was added to prepare a suspension. To the suspension, 120 mL of a mixed solution of 450 g / L nickel sulfate, 150 g / L sodium hypophosphite, 116 g / L sodium citrate, and 6 mL plating stabilizer was added through a metering pump at an addition rate of 81 mL / min. Thereafter, the plating solution was stirred until the pH of the plating solution was stabilized, and the electroless plating first stage step was performed until hydrogen bubbling stopped.

Next, 650 mL of a mixed solution of nickel sulfate 450 g / L, sodium hypophosphite 150 g / L, sodium citrate 116 g / L, and plating stabilizer 35 mL was added to the plating solution through a metering pump at an addition rate of 27 mL / min. Then, it stirred until the pH of plating solution was stabilized, and the electroless-plating late process was performed until hydrogen foaming stopped.
Next, the plating solution was filtered, and the resulting particles were washed with water and then dried with a vacuum dryer to produce conductive fine particles on which a 0.1 μm nickel layer was formed.

(Gold plating process)
The conductive fine particles on which the nickel layer was formed were subjected to substitution gold plating to produce conductive fine particles in which a gold layer of 0.03 μm was formed on the surface of the nickel layer. In addition, the thickness of the nickel layer after substitution gold plating was 0.07 micrometer.

(Preparation of insulating fine particles)
A 1000 mL separable flask equipped with a four-neck separable cover, stirring blade, three-way cock, condenser, temperature probe, glycidyl methacrylate 20 mmol, methyl methacrylate 180 mmol, dimethacrylic acid ethylene glycol 6 mmol, phenyldimethylsulfonium methacrylate A monomer composition containing 1 mmol of methyl sulfate and 1 mmol of 2,2′-azobis {2- [N- (2-carboxyethyl) amino] dipropane} was prepared. After being dispersed in ion-exchanged water so that the solid content of the monomer composition was 5% by weight, the mixture was stirred at 200 rpm and polymerized at 70 ° C. for 24 hours in a nitrogen atmosphere. After completion of the reaction, the mixture was freeze-dried to produce insulating fine particles having a sulfonium group and an epoxy group on the surface, an average diameter of 240 nm, and a CV value of 7%.

(Manufacture of coated conductive fine particles)
Insulating fine particles were dispersed in ion-exchanged water under ultrasonic irradiation to prepare a 10 wt% insulating fine particle dispersion.
10 g of conductive fine particles having a gold layer formed on the surface of the nickel layer were dispersed in 500 mL of ion-exchanged water, 4 g of 10 wt% insulating fine particle dispersion was added, and the mixture was stirred at room temperature for 6 hours. The dispersion was filtered through a 3 μm mesh filter, and the resulting particles were washed with water and then dried in a vacuum dryer to produce coated conductive fine particles.

When observed with a scanning electron microscope (SEM), the coated conductive fine particles had only one insulating fine particle coating layer formed on the surface of the substrate fine particles having protrusions. When the coated area of the insulating fine particles (that is, the projected area of the particle diameter of the insulating fine particles) with respect to the area of 2.5 μm from the center of the coated conductive fine particles was calculated by image analysis, the coverage was 30%.

Further, the height of the protrusion formed on the surface of the obtained coated conductive fine particle was 55 nm.
The height of the protrusion can be calculated by the following method. Fifty coated conductive fine particles are observed with a scanning electron microscope, and the heights of all the protrusions at the peripheral edge of the observed coated conductive fine particles are measured. The height of the protrusion was calculated by measuring the height of the protrusion using the metal surface on which the protrusion was not formed as a reference surface, and arithmetically averaging the measured values.

The obtained coated conductive fine particles were dispersed in t-butyl alcohol and coated on a 10 mm × 10 mm silicon wafer so that the weight of the coated conductive fine particles after drying was 0.00004 g (about 240,000 particles). After volatilizing t-butyl alcohol, a silicon wafer of 10 mm × 10 mm was covered and heated at 200 ° C. for 30 seconds under a pressure of 100 N. Thereafter, the silicon wafer was peeled off, and the insulating fine particles on the surface of the coated conductive fine particles were observed with a scanning electron microscope (SEM). It was confirmed that protrusions of the substrate fine particles were exposed by pushing away the molten insulating fine particles.

(Examples 2 to 6)
Coated conductive fine particles were produced in the same manner as in Example 1 except that the height of the protrusions and the diameter of the insulating fine particles were adjusted to the values shown in Table 1.

(Example 7)
(Manufacture of coated conductive fine particles)
The insulating fine particles obtained in the same manner as in Example 1 were dispersed in ion-exchanged water under ultrasonic irradiation to prepare a 10% by weight insulating fine particle dispersion.
Conductive fine particles 10 g formed with a 0.1 μm nickel layer formed in the same manner as in Example 1 were dispersed in 500 mL of ion-exchanged water, 4 g of 10 wt% insulating fine particle dispersion was added, and the mixture was heated at room temperature for 6 hours. Stir. The dispersion was filtered through a 3 μm mesh filter, and the resulting particles were washed with water and then dried in a vacuum dryer to produce coated conductive fine particles.
The obtained coated conductive fine particles were measured in the same manner as in Example 1. As a result, the coverage was 30%, and the height of the protrusion formed on the surface was 55 nm.

The obtained coated conductive fine particles were dispersed in t-butyl alcohol and coated on a 10 mm × 10 mm silicon wafer so that the weight of the coated conductive fine particles after drying was 0.00004 g (about 240,000 particles). After volatilizing t-butyl alcohol, a silicon wafer of 10 mm × 10 mm was covered and heated at 200 ° C. for 30 seconds under a pressure of 100 N. Thereafter, the silicon wafer was peeled off, and the insulating fine particles on the surface of the coated conductive fine particles were observed with a scanning electron microscope (SEM). It was confirmed that protrusions of the substrate fine particles were exposed by pushing away the molten insulating fine particles.

(Examples 8 to 12)
Coated conductive fine particles were produced in the same manner as in Example 7 except that the height of the protrusions and the diameter of the insulating fine particles were adjusted to the values shown in Table 1.

(Example 13)
(Electroless palladium plating process)
10 g of conductive fine particles formed with a nickel layer of 0.07 μm obtained in the same manner as in Example 1 were dispersed in 500 mL of ion-exchanged water using an ultrasonic processor to obtain a particle suspension. While stirring the suspension at 50 ° C., 0.02 mol / L of palladium sulfate, 0.04 mol / L of ethylenediamine as a complexing agent, 0.06 mol / L of sodium formate as a reducing agent, and pH 10.0 containing a crystal modifier. The electroless plating solution was gradually added to perform electroless palladium plating. When the thickness of the palladium layer reached 0.03 μm, the electroless palladium plating was finished. Next, by washing and vacuum drying, conductive fine particles having a palladium layer formed on the surface of the nickel layer were obtained.

(Manufacture of coated conductive fine particles)
The insulating fine particles obtained in the same manner as in Example 1 were dispersed in ion-exchanged water under ultrasonic irradiation to prepare a 10% by weight insulating fine particle dispersion.
10 g of conductive fine particles having a palladium layer formed on the surface of the nickel layer were dispersed in 500 mL of ion-exchanged water, 4 g of 10 wt% insulating fine particle dispersion was added, and the mixture was stirred at room temperature for 6 hours. The dispersion was filtered through a 3 μm mesh filter, and the resulting particles were washed with water and then dried in a vacuum dryer to produce coated conductive fine particles.

The obtained coated conductive fine particles were measured in the same manner as in Example 1. As a result, the coverage was 30%, and the height of the protrusion formed on the surface was 55 nm.

The obtained coated conductive fine particles were dispersed in t-butyl alcohol and coated on a 10 mm × 10 mm silicon wafer so that the weight of the coated conductive fine particles after drying was 0.00004 g (about 240,000 particles). After volatilizing t-butyl alcohol, a silicon wafer of 10 mm × 10 mm was covered and heated at 200 ° C. for 30 seconds under a pressure of 100 N. Thereafter, the silicon wafer was peeled off, and the insulating fine particles on the surface of the coated conductive fine particles were observed with a scanning electron microscope (SEM). It was confirmed that protrusions of the substrate fine particles were exposed by pushing away the molten insulating fine particles.

(Examples 14 to 18)
Coated conductive fine particles were produced in the same manner as in Example 13 except that the height of the protrusions and the diameter of the insulating fine particles were adjusted to the values shown in Table 1.

(Comparative Examples 1-7, 11)
Coated conductive fine particles were produced in the same manner as in Example 1 except that the height of the protrusions and the diameter of the insulating fine particles were adjusted to the values shown in Table 2.

(Comparative Example 8)
(Electroless plating pretreatment process)
50 parts by weight of tetramethylol methane tetraacrylate and 50 parts by weight of divinylbenzene were copolymerized to prepare resin fine particles (average particle size 3 μm).

(Electroless nickel plating process)
The obtained resin fine particles were dispersed in 1200 mL of ion exchange water, and 4 mL of a plating stabilizer was added to prepare a suspension. To the suspension, 120 mL of a mixed solution of 450 g / L nickel sulfate, 150 g / L sodium hypophosphite, 116 g / L sodium citrate, and 6 mL plating stabilizer was added through a metering pump at an addition rate of 81 mL / min. Thereafter, the plating solution was stirred until the pH of the plating solution was stabilized, and the electroless plating first stage step was performed until hydrogen bubbling stopped.

Next, 650 mL of a mixed solution of nickel sulfate 450 g / L, sodium hypophosphite 150 g / L, sodium citrate 116 g / L, and plating stabilizer 35 mL was added to the plating solution through a metering pump at an addition rate of 27 mL / min. Then, it stirred until the pH of plating solution was stabilized, and the electroless-plating late process was performed until hydrogen foaming stopped.
Next, the plating solution was filtered, and the resulting particles were washed with water and then dried with a vacuum dryer to produce conductive fine particles (no protrusions) on which a 0.1 μm nickel layer was formed.

(Gold plating process)
Conductive fine particles (with no protrusions) on which the nickel layer was formed were plated by substitution gold to produce conductive fine particles (with no protrusions) on which a 0.03 μm gold layer was formed on the surface of the nickel layer. In addition, the thickness of the nickel layer after substitution gold plating was 0.07 micrometer.

(Manufacture of coated conductive fine particles)
The insulating fine particles obtained in the same manner as in Example 1 were dispersed in ion-exchanged water under ultrasonic irradiation to prepare a 10% by weight insulating fine particle dispersion.
10 g of conductive fine particles (no protrusions) having a gold layer formed on the surface of the nickel layer were dispersed in 500 mL of ion-exchanged water, 4 g of 10 wt% insulating fine particle dispersion was added, and stirred at room temperature for 6 hours. The dispersion was filtered through a 3 μm mesh filter, and the resulting particles were washed with water and then dried in a vacuum dryer to produce coated conductive fine particles (no protrusions).

(Comparative Examples 9 and 10)
Coated conductive fine particles (no protrusions) were produced in the same manner as in Comparative Example 8 except that the diameter of the insulating fine particles was adjusted to the values shown in Table 2.

(Comparative Examples 12-15)
Coated conductive fine particles were produced in the same manner as in Example 7 except that the height of the protrusions and the diameter of the insulating fine particles were adjusted to the values shown in Table 2.

(Comparative Examples 16-18)
Coated conductive fine particles were produced in the same manner as in Example 13 except that the height of the protrusions and the diameter of the insulating fine particles were adjusted to the values shown in Table 2.

<Evaluation>
The following evaluation was performed about the covering electroconductive fine particles obtained by the Example and the comparative example. The results are shown in Tables 1 and 2.

(1) Production of anisotropic conductive film 100 parts by weight of an epoxy resin (“Epicoat 828” manufactured by Yuka Shell Epoxy Co., Ltd.), 2 parts by weight of trisdimethylaminoethylphenol, and 100 parts by weight of toluene as a binder resin The mixture was sufficiently mixed using a stirrer to obtain a mixture. The obtained mixture was applied onto a release film so that the thickness after drying was 10 μm, and toluene was volatilized to obtain an adhesive film 1.
Next, coated conductive fine particles are added to 100 parts by weight of an epoxy resin (“Epicoat 828” manufactured by Yuka Shell Epoxy Co., Ltd.), 2 parts by weight of trisdimethylaminoethylphenol, and 100 parts by weight of toluene as a binder resin, and planetary type The mixture was sufficiently mixed using a stirrer to obtain a mixture. The obtained mixture was applied onto a release film so that the thickness after drying was 7 μm, and toluene was volatilized to obtain adhesive films 2 containing conductive fine particles. The content of conductive fine particles in the adhesive film 2 was adjusted to 200,000 particles / cm ² .
The obtained adhesive film 1 and adhesive film 2 were laminated at room temperature to obtain a 17 μm thick anisotropic conductive film having a two-layer structure.
A part of the mixture containing the coated conductive fine particles was washed with toluene, and the coated conductive fine particles were taken out. Next, when the coated conductive fine particles were observed by SEM, the insulating fine particles were not peeled off from the coated conductive fine particles.

(2) Conductivity evaluation The obtained anisotropic conductive film was cut into a size of 3 cm × 4 cm. The cut anisotropic conductive film is formed on a glass substrate (width 3 cm, length 4 cm) having an aluminum electrode (height 0.2 μm, L / S = 20 μm / 20 μm) having a resistance measurement lead wire on one side. Affixed almost at the center on the aluminum electrode side. Next, a glass substrate (width 3 cm, length 4 cm) having the same aluminum electrode was aligned and aligned so that the electrodes overlap each other. This laminated body of glass substrates was thermocompression bonded under pressure bonding conditions of 10N and 100 ° C. to obtain a conductive connection structure. The connection resistance value between the opposing electrodes of the obtained conductive connection structure was measured by a four-terminal method. Conductivity evaluation was performed according to the following criteria.
◎: Connection resistance value was less than 5Ω ○: Connection resistance value was less than 10Ω and 5Ω or more ×: Connection resistance value was 10Ω or more

(3) Evaluation of insulation The insulation between adjacent electrodes of the obtained conductive connection structure was evaluated. The insulation evaluation was performed according to the following criteria.
○: Short circuit was not confirmed between adjacent electrodes ×: Short circuit was confirmed between adjacent electrodes

According to the present invention, it is possible to provide coated conductive fine particles, an anisotropic conductive material, and a conductive connection structure excellent in connection reliability.

Claims (5)

Coated conductive fine particles, in which insulating fine particles are attached to the surface of the substrate fine particles having a conductive metal surface,
The substrate fine particles have protrusions on the surface, the diameter of the insulating fine particles is 200 to 500 nm, the height of the protrusions is 50 nm or more, and 100 nm or more smaller than the diameter of the insulating fine particles. Yes,
The insulating fine particles through a functional group (A) capable of binding to the metal surface, the Kutsugaeshirube conductive fine particles you characterized by forming a coating layer of a single layer by a chemical bond to the metal surface . 2. The coated conductive fine particle according to claim 1 , wherein the conductive metal surface of the substrate fine particle is formed of a nickel layer or a palladium layer. An anisotropic conductive material comprising the coated conductive fine particles according to claim 1 or 2 dispersed in a binder resin. A conductive connection structure, wherein the conductive connection structure is conductively connected using the coated conductive fine particles according to claim 1 . A conductive connection structure, wherein the conductive connection structure is conductively connected using the anisotropic conductive material according to claim 3 .