JP2006196411A - Conductive fine particle and anisotropic conductive material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide conductive fine particles capable of securing excellent conduction when heating and crimping electrode terminals when trying to connect them, and an anisotropic conductive material using the conductive fine particles. <P>SOLUTION: A conductive metal layer is formed on the surface of a cross-linked resin particle to obtain this conductive fine particles. The average particle diameter of the conductive fine particles is 2.5-4.5 μm, and its compressive elasticity modulus (20% K value) measured under an environment heated at 150°C when the diameter of the conductive fine particles is compressively deformed by 20% is 882-4410 N/mm<SP>2</SP>. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a conductive fine particle and an anisotropic conductive material, and particularly relates to a conductive fine particle capable of ensuring good conduction during thermocompression bonding, and an anisotropic conductive material using the conductive fine particle.

  The conductive fine particles are mixed and kneaded with a binder resin or an adhesive, for example, an anisotropic conductive paste, an anisotropic conductive ink, an anisotropic conductive adhesive, an anisotropic conductive film, Widely used as anisotropic conductive materials such as anisotropic conductive sheets.

  These anisotropic conductive materials are, for example, for electrically connecting substrates in electronic devices such as liquid crystal displays, personal computers, and mobile phones, and electrically connecting small components such as semiconductor elements to the substrate. In order to do so, it is used by being sandwiched between opposing substrates and electrode terminals.

  Conventionally, as the conductive fine particles used in the anisotropic conductive material, metal plated particles in which resin particles and organic / inorganic composite particles are used as core particles in addition to metal particles and the surfaces thereof are subjected to gold plating by an electroless plating method. Is used. For example, Patent Document 1 discloses metal plating particles having resin particles as core particles.

  Among these conductive fine particles, metal particles are harder and harder to embed gold bumps than metal-plated resin particles and metal-plated organic-inorganic-inorganic composite particles. While the dispersion cannot be absorbed and the connection reliability is low, the metal-plated resin particles and metal-plated organic-inorganic inorganic composite particles are softer than metal particles and have a high restoring force, so the electrode terminals are connected with relatively high reliability. be able to.

Japanese Examined Patent Publication No. 3-44149

  However, the metal-plated conductive fine particles are mixed with a binder resin or the like and used, for example, as an anisotropic conductive film. The anisotropic conductive film is sandwiched between electrode terminals, and is heated and pressed. When the electrode terminals are to be connected with each other, the compression characteristics of the conductive fine particles change depending on the heating temperature at the time of pressure bonding, and conduction may become unstable.

  In view of the above situation, the present invention provides a conductive fine particle capable of ensuring good conduction during thermocompression bonding when connecting electrode terminals, and an anisotropic conductive material using the conductive fine particle. The purpose is to provide.

In order to achieve the above object, the invention according to claim 1 is a conductive fine particle in which a conductive metal layer is formed on the surface of a crosslinked resin particle, and the average particle size of the conductive fine particle is 2.5 to 4. Provided is a conductive fine particle that is 5 μm and has a compressive elastic modulus (20% K value) of 882 to 4410 N / mm ² when the conductive fine particle diameter measured in a 150 ° C. heating environment is 20% compression deformed.

  The invention according to claim 2 provides an anisotropic conductive material in which the conductive fine particles according to claim 1 are dispersed in a resin binder.

Details of the present invention will be described below.
The conductive fine particles of the present invention are those in which a conductive metal layer is formed on the surface of the crosslinked resin particles.

  The method for obtaining the cross-linked resin particles to be the core particles of the conductive fine particles of the present invention is not particularly limited, and examples thereof include methods by polymerization methods such as emulsion polymerization, suspension polymerization, seed polymerization, dispersion polymerization, and dispersion seed polymerization. It is done. Of these, the seed polymerization method is preferred because crosslinked resin particles having a uniform particle diameter can be obtained without classifying the crosslinked resin particles after polymerization. In addition, about seed polymerization method, Unexamined-Japanese-Patent No. 2000-230005 etc. are known, for example.

  As a specific method of the seed polymerization method, for example, an aqueous emulsion composed of an ethylenically unsaturated monomer and an aqueous emulsion of an oil-soluble polymerization initiator are added to water in which seed particles are dispersed, and the seed particles are added to the seed particles. A method of polymerizing the ethylenically unsaturated monomer after absorbing the ethylenically unsaturated monomer and the oil-soluble polymerization initiator is mentioned.

  The weight average molecular weight of the seed particles is preferably 20000 or less. Moreover, it is preferable that the said ethylenically unsaturated monomer shall be 10-500 weight part with respect to 1 weight part of seed particles.

  The ethylenically unsaturated monomer used for forming the crosslinked resin particles in the present invention is not particularly limited as long as it contains a crosslinkable monomer. Therefore, although it may be formed only from a crosslinkable monomer, in addition to a crosslinkable monomer, a non-crosslinkable monomer may be used together.

  Examples of the crosslinkable monomer include divinylbenzene and its derivatives, conjugated dienes such as butadiene and isoprene, polytetramethylene glycol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, and the like. Examples include functional (meth) acrylates. Here, (meth) acrylate means methacrylate or acrylate. The said crosslinkable monomer may be used independently and may use 2 or more types together.

  Examples of the non-crosslinkable monomer include styrene derivatives such as styrene, α-methylstyrene, p-methylstyrene, p-chlorostyrene, and chloromethylstyrene; unsaturated nitriles such as vinyl chloride and acrylonitrile, isobutyl ( And monofunctional (meth) acrylates such as (meth) acrylate and isooctyl (meth) acrylate. The said non-crosslinkable monomer may be used independently and may use 2 or more types together.

  The oil-soluble polymerization initiator is not particularly limited. For example, benzoyl peroxide, lauroyl peroxide, orthochlorobenzoyl peroxide, orthomethoxybenzoyl peroxide, 3,5,5-trimethylhexanoyl peroxide, t-butyl peroxide Organic peroxides such as oxy-2-ethylhexanoate and di-t-butyl peroxide; azos such as azobisisobutyronitrile, azobiscyclohexacarbonitrile, azobis (2,4-dimethylvaleronitrile) System compounds and the like.

  The amount of the oil-soluble polymerization initiator used is preferably 0.1 to 3 parts by weight with respect to 100 parts by weight of the ethylenically unsaturated monomer.

  In the polymerization, a surfactant and a dispersion stabilizer may be used as necessary.

  The conductive fine particles of the present invention are particles in which a conductive metal layer is coated on the surface having crosslinked resin particles as core particles.

  The metal used for the said conductive metal layer is not specifically limited, For example, nickel, gold | metal | money, silver, copper, cobalt or the alloy etc. which have these as a main component are mentioned.

  The conductive metal layer can be formed by, for example, metal plating of core particles by electroless plating or the like. The metal plating may be a single metal layer or a multilayer composed of a plurality of metals.

  The thickness of the conductive metal layer in the conductive fine particles of the present invention is preferably 0.02 to 5 μm. When the thickness of the conductive metal layer is less than 0.02 μm, the metal layer is thin and it is difficult to obtain conductivity. On the other hand, if the thickness of the conductive metal layer exceeds 5 μm, the conductive fine particles become too hard, and the conductive fine particles are difficult to deform following the distance between the electrode terminals.

  The thickness of the conductive metal layer can be obtained, for example, by observing a cross section of the conductive fine particles with a transmission electron microscope (TEM). As the magnification, a magnification that is easy to observe may be selected. For example, 50,000 times is used.

  In the present invention, the average particle size of the conductive fine particles needs to be 2.5 to 4.5 μm. When the average particle diameter is less than 2.5 μm, aggregation is likely to occur when forming the conductive metal layer, and it may be difficult to form single particles. When the average particle diameter exceeds 4.5 μm, anisotropic conductive It may exceed the range used between electrode terminals such as a substrate having fine wiring as a material.

  The CV value of the conductive fine particles (value obtained by dividing the standard deviation of the particle size distribution by the average particle size as a percentage) is preferably 10% or less. When the CV value is 10% or less, variation in the contact area between the conductive fine particles and the electrode terminal is small, and a stable connection is easily obtained.

In the present invention, the compression elastic modulus (hereinafter also referred to as 20% K value) measured in a 150 ° C. heating environment when the conductive fine particle diameter is 20% compression deformed is 882 to 4410 N / mm ² . It is necessary.
It is important that the conductive fine particles of the present invention have a specific hardness in order to ensure good conduction during thermocompression bonding. For example, when used as an anisotropic conductive film, the measurement is performed in a 150 ° C. heating environment. In addition, when the 20% K value is 882 to 4410 N / mm ^2, it is not too hard and the contact area becomes narrow at the time of thermocompression bonding, and conduction is not unstable, and it is too soft and conductive. The conductive resin does not become unstable because the binder resin between the conductive fine particles and the electrode terminal is not excluded or the restoring force is low, so that variations in the height of the substrate and bumps cannot be absorbed. For example, when thermocompression bonding is performed on an anisotropic conductive film, it is usually heated to 150 ° C. or higher, and the conductive fine particles of the present invention have a heating temperature set to a relatively low temperature of about 150 ° C. However, good conduction can be ensured.

  In the present invention, the 20% K value is a smooth end surface of a square column with a side of 50 μm using a micro compression tester (Fischer H-100, manufactured by Fischer), and the conductive fine particles are compressed at a rate of 0.33 mN / sec. Compressed with a maximum test load of 40 mN. The measurement is performed in a 150 ° C. heating environment. The measurement in a 150 ° C. heating environment is performed by using a hot plate set at 150 ° C. and placing conductive fine particles on the hot plate.

The 20% K value can be obtained from the following equation.
K = (3 / √2) ・ F ・ S ^-3/2・ R ^-1/2
F: Load value at 20% compression deformation of conductive fine particles (N)
S: Compression displacement (mm) in 20% compression deformation of conductive fine particles
R: Radius of conductive fine particles (mm)

  With respect to the conductive fine particles of the present invention, the above-described method for obtaining a specific hardness can be achieved by adjusting the crosslinking density of the crosslinked resin particles as the core particles. That is, it can be controlled by selecting the type of ethylenically unsaturated monomer that forms the core particles.

  The anisotropic conductive material of the present invention is obtained by dispersing the above-described conductive fine particles of the present invention in a resin binder.

  The anisotropic conductive material is not particularly limited as long as the conductive fine particles of the present invention are dispersed in a resin binder. For example, anisotropic conductive paste, anisotropic conductive ink, anisotropic conductive An adhesive, an anisotropic conductive film, an anisotropic conductive sheet, etc. are mentioned.

  The method for producing the anisotropic conductive material of the present invention is not particularly limited. For example, the conductive fine particles of the present invention are added to an insulating resin binder, and mixed and dispersed uniformly. For example, a method of using an anisotropic conductive paste, anisotropic conductive ink, anisotropic conductive adhesive, etc., or adding the conductive fine particles of the present invention to an insulating resin binder and mixing them uniformly. After preparing the conductive composition, the conductive composition is uniformly dissolved (dispersed) in an organic solvent as necessary, or heated and melted to release a release material such as release paper or release film. Applying to the mold processing surface so as to have a predetermined film thickness, and performing drying or cooling as necessary, for example, an anisotropic conductive film, an anisotropic conductive sheet, etc. Depending on the type of anisotropic conductive material to be produced, Manufacturing methods may Taking. Further, the insulating resin binder and the conductive fine particles of the present invention may be used separately without being mixed to form an anisotropic conductive material.

  The resin of the insulating resin binder is not particularly limited. For example, vinyl resins such as vinyl acetate resins, vinyl chloride resins, acrylic resins, styrene resins; polyolefin resins, ethylene -Thermoplastic resins such as vinyl acetate copolymers and polyamide resins; Epoxy resins, urethane resins, polyimide resins, unsaturated polyester resins, and curable resins composed of these curing agents; styrene-butadiene-styrene blocks Thermoplastic block copolymers such as copolymers, styrene-isoprene-styrene block copolymers, and hydrogenated products thereof; elastomers such as styrene-butadiene copolymer rubber, chloroprene rubber, acrylonitrile-styrene block copolymer rubber ( Rubbers). These resins may be used alone or in combination of two or more. The curable resin may be in any curing form such as a room temperature curing type, a thermosetting type, a photocuring type, and a moisture curing type.

  In addition to the insulating resin binder and the conductive fine particles of the present invention, the anisotropic conductive material of the present invention includes, for example, a bulking agent, a softening agent, etc. 1 type of various additives such as additives (plasticizers), tackifiers, antioxidants (anti-aging agents), heat stabilizers, light stabilizers, UV absorbers, colorants, flame retardants, organic solvents, etc. Or 2 or more types may be used together.

Since the conductive fine particles of the present invention have the above-described configuration, it is possible to obtain one that can ensure good conduction during thermocompression bonding when trying to connect the electrode terminals. In particular, even when the heating temperature at the time of pressure bonding is set to a relatively low temperature of about 150 ° C., good conduction can be ensured.
In addition, the anisotropic conductive material using the conductive fine particles can ensure good conduction during thermocompression bonding when attempting to connect the electrode terminals.

  Hereinafter, the present invention will be described in more detail with reference to examples. In addition, this invention is not limited to a following example.

Example 1
After mixing 5 g of 0.8 μm styrene particles as seed particles, 500 g of ion-exchanged water and 100 g of a 5 wt% polyvinyl alcohol aqueous solution and applying ultrasonic waves to disperse, the mixture was placed in a separable flask and stirred uniformly.
Next, 128 g of polytetramethylene glycol diacrylate and 32 g of divinylbenzene, 1035 g of ion-exchanged water to which 12 g of an oil-soluble polymerization initiator (manufactured by NOF Corporation, “NIPER BW”), 9 g of triethanolamine lauryl sulfate, and 118 g of ethanol were added. The prepared emulsion was added to a separable flask and stirred for 12 hours to allow the seed particles to absorb the monomer.
Thereafter, 500 g of a 5% by weight aqueous polyvinyl alcohol solution was added, nitrogen gas was introduced, and the mixture was reacted in an autoclave at 85 ° C. for 9 hours to obtain crosslinked resin particles having an average particle size of 4 μm.
Electroless nickel plating was performed on the surface of the obtained crosslinked resin particles to form a nickel plating layer of about 0.08 μm. Further, substitution gold plating was performed, and a gold plating layer of about 0.03 μm was formed on the nickel plating layer to obtain conductive fine particles.
About the obtained electroconductive fine particles, 20% K value measured in 150 degreeC heating environment was calculated | required. The measurement results are shown in Table 1.

(Comparative Example 1)
After mixing 5 g of 0.8 μm styrene particles as seed particles, 500 g of ion-exchanged water, and 100 g of 5 wt% polyvinyl alcohol aqueous solution and applying ultrasonic waves to disperse, the mixture was placed in a separable flask and stirred uniformly.
Next, an emulsion prepared by using 1035 g of ion-exchanged water to which 150 g of divinylbenzene was added 12 g of an oil-soluble polymerization initiator (“Perbutyl Z” manufactured by NOF Corporation), 9 g of triethanolamine lauryl sulfate and 118 g of ethanol was separable. In addition to the flask, the mixture was stirred for 12 hours to allow the seed particles to absorb the monomer.
Thereafter, 500 g of a 5% by weight aqueous polyvinyl alcohol solution was added, nitrogen gas was introduced, and the mixture was reacted in an autoclave at 130 ° C. for 9 hours to obtain crosslinked resin particles having an average particle size of 4 μm.
Electroless nickel plating was performed on the surface of the obtained crosslinked resin particles to form a nickel plating layer of about 0.08 μm. Further, substitution gold plating was performed, and a gold plating layer of about 0.03 μm was formed on the nickel plating layer to obtain conductive fine particles.
About the obtained electroconductive fine particles, 20% K value measured in 150 degreeC heating environment was calculated | required. The measurement results are shown in Table 1.

(Evaluation of conductivity of anisotropic conductive materials)
As a resin binder resin, 100 parts by weight of an epoxy resin (manufactured by Yuka Shell Epoxy, “Epicoat 828”), 2 parts by weight of trisdimethylaminoethylphenol, and 100 parts by weight of toluene are obtained in Example 1 or Comparative Example 1. The conductive fine particles are added and mixed thoroughly using a planetary stirrer, and then coated on the release film so that the thickness after drying becomes 7 μm, and toluene is evaporated to contain the conductive fine particles. An adhesive film was obtained. In addition, the compounding quantity of electroconductive fine particles made content in a film 50,000 piece / cm < ² >.
Thereafter, an adhesive film containing conductive fine particles was bonded to an adhesive film obtained without containing conductive fine particles at room temperature to obtain a two-layer anisotropic conductive film having a thickness of 17 μm.

The obtained anisotropic conductive film was cut into a size of 5 × 5 mm. In addition, two glass substrates having a lead wire for resistance measurement on which an aluminum electrode having a width of 200 μm, a length of 1 mm, a height of 0.2 μm, and an L / S of 20 μm was formed were prepared. After attaching the anisotropic conductive film to the center of one glass substrate, align the other glass substrate so that it overlaps the electrode pattern of the glass substrate to which the anisotropic conductive film is attached. It was.
Two glass substrates were thermocompression bonded under the conditions of a pressure of 10 N and a temperature of 150 ° C., and then the resistance value between the electrodes was measured. The measurement was performed for each anisotropic conductive film using the conductive fine particles obtained in Example 1 or Comparative Example 1. The evaluation results are shown in Table 1.

  From Table 1, the anisotropic conductive film using the conductive fine particles obtained in Examples has a specific hardness with a 20% K value measured in a heating environment at 150 ° C. in a specific range, and a resistance value. Is low and good conduction.

  ADVANTAGE OF THE INVENTION According to this invention, when trying to connect between electrode terminals, the electroconductive fine particle which can ensure favorable conduction | electrical_connection at the time of thermocompression bonding, and the anisotropic conductive material using this electroconductive fine particle can be provided.

Claims (2)

Conductive fine particles in which a conductive metal layer is formed on the surface of the crosslinked resin particles, and the conductive fine particles have an average particle diameter of 2.5 to 4.5 μm and measured under a 150 ° C. heating environment. Conductive fine particles characterized by having a compression modulus (20% K value) of 882 to 4410 N / mm ² when the diameter is 20% compression deformed. An anisotropic conductive material comprising the conductive fine particles according to claim 1 dispersed in a resin binder.