JP2006228475A - Conductive fine particles and anisotropic conductive material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide conductive fine particles having excellent resin rejection property and capable of improving connection reliability by increasing a connecting area with an electrode, and to provide an anisotropic conductive material using the conductive fine particles when they are subjected to thermocompression bonding to an electrode with an anisotropic conductive film etc. <P>SOLUTION: Surfaces of base material fine particles are covered with a metal plating coating film layer containing nickel and phosphor and multilayers of conductive membranes whose outermost surface is a gold layer. The conductive membranes are conductive fine particles having projections heaved on the surfaces. The metal plating coating contains phosphor ≥10 wt%. The projections heaved in the surface of the conductive membrane use a conductive material as a core material. The film thickness of the metal plating coating is preferably 40-150 nm. In the anisotropic conductive material, the conductive fine particles are dispersed in a resin binder. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention provides a conductive fine particle that is excellent in resin exclusion property and can increase the connection area with the electrode and improve connection reliability when thermally bonded to the electrode with an anisotropic conductive film or the like, and The present invention relates to an anisotropic conductive material using conductive fine particles.

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, for example, a metal plating layer is used as a conductive film on the surface of non-conductive fine particles such as resin fine particles having a uniform particle size and appropriate strength. The formed conductive fine particles have been used. However, with rapid progress and development of electronic devices in recent years, further improvement in connection reliability of conductive fine particles used as anisotropic conductive materials has been demanded.
In order to improve the connection reliability of the conductive fine particles, for example, conductive fine particles having protrusions on the surface have been reported (see, for example, Patent Document 1 and Patent Document 2).

Patent Document 1 describes conductive fine particles obtained by performing metal plating on the surface of non-conductive fine particles having protrusions formed on the surface. However, this is a protruding particle formed by a composite particle in which the mother particle and the child particle are combined, and the protruding portion is made of a non-conductive material such as plastic or silicate glass as the core material, and the connection resistance The reduction in value was not sufficient.
Further, Patent Document 2 discloses that a non-conductive fine particle is formed by simultaneously forming a micro-projection of nickel and a nickel coating by utilizing self-decomposition of a nickel plating solution in an electroless nickel plating method. Is described. However, in this manufacturing method, the protruding portion is a protrusion made of a nickel lump, and it is extremely difficult to control the size, shape, etc., and the resin exclusion property by this protrusion is not sufficient.

JP-A-4-36902 JP 2000-243132 A

  Furthermore, with recent developments in more diverse electronic devices, conductive fine particles used as anisotropic conductive materials under various usage conditions have been required to further improve connection reliability. For this reason, while resin exclusion property by a protrusion is calculated | required, the connection to the electrode by a protrusion part is calculated | required reliably. However, when the conductive film such as a nickel coating that covers the protruding portion is hard as in the prior art, the connection area between the electrodes does not increase sufficiently when thermocompression bonding is performed, and the connection between the electrodes is not reliable. Connection reliability was not enough.

  The object of the present invention is to improve the connection reliability by increasing the connection area with the electrode, and excellent in resin rejection when thermocompression bonded to the electrode with an anisotropic conductive film, etc. It is an object to provide conductive fine particles that can be produced, and an anisotropic conductive material using the conductive fine particles.

  In order to achieve the above object, according to the first aspect of the present invention, the surface of the substrate fine particles is coated with a multi-layer conductive film having a metal plating film layer containing nickel and phosphorus and a gold layer as the outermost surface, The conductive film is a conductive fine particle having protrusions protruding on the surface, the metal plating film contains 10% by weight or more of phosphorus, and the protrusions protruding on the surface of the conductive film are made of a conductive substance as a core. Provided is a conductive fine particle as a substance.

  The invention according to claim 2 provides the conductive fine particles according to claim 1, wherein the metal plating film has a thickness of 40 to 150 nm.

  Further, the invention according to claim 3 is characterized in that in the metal plating film, the metal plating composition contains 10 to 20% by weight of phosphorus in the region of 20% or less of the metal plating film thickness from the substrate fine particle side. The conductive fine particles according to claim 1 or 2, which contain 1 to 10% by weight of phosphorus in the metal plating composition in a region of 10% or less of the thickness of the metal plating film from the surface of the plating film.

  In the invention according to claim 4, the hardness ratio of the hardness of the conductive film to the hardness of the core substance according to the Vickers hardness is 0.2 to 0.7. The conductive fine particles are provided.

  In the invention described in claim 5, the core material is made of at least one metal selected from nickel, copper, gold, silver, and zinc. The conductive fine particles according to any one of claims 1-4. I will provide a.

  The invention according to claim 6 provides the conductive fine particles according to any one of claims 1 to 5, wherein the substrate fine particles are resin fine particles.

  In the invention according to claim 7, the average height of the raised protrusions is 0.5% or more of the average particle diameter of the conductive fine particles. The conductivity according to any one of claims 1 to 6 Provide fine particles.

  The invention according to claim 8 provides an anisotropic conductive material in which the conductive fine particles according to any one of claims 1 to 7 are dispersed in a resin binder.

Details of the present invention will be described below.
In the conductive fine particles of the present invention, the surface of the substrate fine particles is coated with a multi-layered conductive film having a metal plating film layer containing nickel and phosphorus and the outermost surface being a gold layer, and the conductive film is formed on the surface. Conductive fine particles having raised protrusions, wherein the metal plating film contains 10% by weight or more of phosphorus, and the raised protrusions on the surface of the conductive film have a conductive substance as a core substance.
Therefore, the protrusion in the present invention is composed of a core material made of a conductive material and the conductive film, and appears as a protrusion raised on the surface of the conductive film. Due to the presence of this protrusion, when the electrodes are thermocompression bonded with an anisotropic conductive film or the like, the protrusion can obtain a conductive connection with a low connection resistance value and excellent connection reliability due to the effect of eliminating the insulating resin, etc. it can.

The conductive film is a multi-layered film having a metal plating film layer containing nickel and phosphorus and a gold layer as the outermost surface, and the metal plating film contains 10% by weight or more of phosphorus. is there.
Therefore, since the conductive film in the present invention includes nickel containing 10% by weight or more of phosphorus and a metal plating film containing phosphorus, for example, the conductive film becomes softer than when including a nickel plating film. When the protrusions protruding on the surface of the conductive film are thermocompression bonded to the electrode with an anisotropic conductive film or the like, a sufficient connection area with the electrode occurs, and the connection reliability can be improved.

The metal plating film needs to contain nickel, which is a metal component, and may contain other metal components. For example, copper etc. may be contained.
Further, the metal plating film needs to contain phosphorus, which is a nonmetallic component, and may contain other nonmetallic components. For example, boron or the like may be contained.
The phosphorus content in the metal plating film needs to be 10% by weight or more. When the phosphorus content is less than 10% by weight, the conductive film including the metal plating film may not be soft, and a sufficient connection area with the electrode may not increase when the electrode is thermocompression bonded.

  The content ratio of nickel, phosphorus, etc. in the metal plating film in the present invention can be determined by, for example, EDX (Energy Dispersing X-ray analyzer).

  The thickness of the metal plating film is preferably 40 to 150 nm. When the thickness is less than 40 nm, the sufficient connection area with the electrode does not increase when thermocompression bonding is performed, and the connection between the electrodes may not be reliable and the connection reliability may not be sufficient. The metal plating film may be easily peeled off due to the difference in coefficient of thermal expansion between the metal plating film and the metal plating film.

  The conductive fine particle of the present invention contains 10 to 20% by weight of phosphorus in the metal plating composition in a region of 20% or less of the metal plating film thickness from the substrate fine particle side in the metal plating film. It is preferable to contain 1 to 10% by weight of phosphorus in the metal plating composition in the region of 10% or less of the metal plating film thickness from the surface side.

  In the metal plating film, the metal plating composition contains 10 to 20% by weight of phosphorus in the region of 20% or less of the metal plating film thickness from the substrate fine particle side, and the metal plating film thickness from the metal plating film surface side. By containing 1 to 10% by weight of phosphorus in the metal plating composition in an area of 10% or less, the metal plating film maintains the flexibility as a whole, while the adhesion to the substrate fine particles is maintained on the substrate fine particle side. It can be improved and hardened on the surface of the metal plating film to improve the resin exclusion property at the time of thermocompression bonding.

The method for forming the metal plating film is not particularly limited, and examples thereof include electroless plating and electroplating. Among these, when the substrate fine particles are non-conductive such as resin fine particles, a method of forming by electroless plating is preferably used.
In addition, in the case of forming by electroless plating, a method of including a phosphorus component in a nickel plating solution can be used, and in order to control the phosphorus content in the thickness direction in the metal plating film, the first period of nickel plating A method of controlling the pH, temperature, reducing agent concentration, etc. of the nickel plating solution can be used in the process and the later process. The electroless plating will be further described later.

In addition to the metal plating film, a metal film may be further formed on the conductive film as long as the softening of the conductive film is not hindered. That is, a plurality of films including a metal plating film may be formed on the conductive film.
The metal constituting the metal coating is not particularly limited. For example, nickel, gold, copper, silver, platinum, zinc, iron, lead, tin, aluminum, cobalt, indium, chromium, titanium, antimony, bismuth, germanium. And metals such as cadmium; alloys composed of two or more kinds of metals such as tin-lead alloys, tin-copper alloys, tin-silver alloys, tin-lead-silver alloys, and the like.

  The method for forming the metal coating is not particularly limited, and examples thereof include electroless plating, electroplating, and sputtering.

The conductive film in the present invention needs to have a gold layer on the outermost surface. By making the outermost surface a gold layer, the connection resistance value can be reduced and the surface can be stabilized.
Therefore, the raised protrusion in the present invention causes the outermost gold layer of the conductive fine particles to protrude. That is, the protrusion raised on the surface of the conductive film appears as a protrusion raised on the outermost gold layer of the conductive fine particles.

  The gold layer can be formed by a known method such as electroless plating, displacement plating, electroplating, or sputtering.

  Although the film thickness of the said gold layer is not specifically limited, 1-100 nm is preferable, More preferably, it is 1-50 nm. If the thickness is less than 1 nm, for example, it may be difficult to prevent oxidation of the metal plating film containing nickel and phosphorus as the underlying layer, and the connection resistance value may increase. When the thickness exceeds 100 nm, for example, in the case of displacement plating, the base layer may be eroded and adhesion between the substrate fine particles and the base layer may be deteriorated.

  The film thickness of the conductive film is preferably 40 to 500 nm. When the thickness is less than 40 nm, the sufficient connection area with the electrode does not increase when thermocompression bonding is performed, and the connection between the electrodes may not be reliable and the connection reliability may not be sufficient. Due to the difference in thermal expansion coefficient between the conductive film and the conductive film, the conductive film may be easily peeled off or it may be difficult to obtain a raised protrusion on the surface of the conductive film.

  In the conductive fine particles of the present invention, the hardness ratio of the hardness of the conductive film to the hardness of the core substance by Vickers hardness is preferably 0.2 to 0.7. Since the hardness of the conductive film is softer than the hardness of the core material and the hardness ratio is 0.2 to 0.7, the protrusions raised on the surface of the conductive film are formed on the electrode by an anisotropic conductive film or the like. When the thermocompression bonding is performed, the conductive film is easily crushed and a sufficient connection area with the electrode is increased, so that the connection reliability can be improved.

  The Vickers hardness is a kind of indentation hardness. A static indentation is applied to a diamond pyramid shaped indenter with a face angle of 136 degrees to make a permanent indentation on the specimen, and the length of the diagonal line of the indentation is measured to determine the hardness. This is the value (index). The feature of Vickers hardness is that the indentation always has a similar shape regardless of the load size, so the similarity law is that the measured value of hardness is the same regardless of the test load, and therefore the value due to different loads It is a point that can be compared as it is.

  Examples of the conductive material constituting the core material include conductive non-metals such as metals, metal oxides, graphite, and conductive polymers such as polyacetylene. Of these, metals are preferred. The metal may be an alloy, and therefore it is preferable that the metal is at least one metal.

  The metal is not particularly limited. For example, nickel (Vickers hardness of about 500), copper (Vickers hardness of about 100), gold, silver, platinum, zinc, iron, lead, tin, aluminum, cobalt, indium, chromium, Metals such as titanium, antimony, bismuth, germanium, cadmium; alloys composed of two or more metals such as tin-lead alloy, tin-copper alloy, tin-silver alloy, tin-lead-silver alloy, etc. . Especially, since moderate hardness and electroconductivity are obtained, nickel, copper, gold | metal | money, silver, and zinc are preferable. These may be used alone or in combination of two or more. Therefore, the core material is preferably made of at least one metal selected from nickel, copper, gold, silver, and zinc.

  The shape of the core substance in the present invention is not particularly limited, and examples thereof include a spherical shape, a disk shape, a column shape, a plate shape, a needle shape, a cube shape, a rectangular parallelepiped shape, and the like. Of these, spherical is preferable.

  The shape of the protrusion in the present invention is not particularly limited, but the conductive film wraps around and coats the core material, and therefore depends on the shape of the core material.

  The method for producing the conductive fine particles of the present invention is not particularly limited, and for example, a method of coating a conductive film such as a metal plating film by electroless plating described later; A method in which the surface of the substrate fine particles is coated with a conductive film by electroless plating, and then a core substance is attached, and further the conductive film is coated by electroless plating; in the above method, electroplating instead of electroless plating And the like, and the like.

  The method for attaching the core substance to the surface of the substrate fine particles is not particularly limited. For example, the core substance is added to the dispersion of the substrate fine particles, and the core substance is added onto the surface of the substrate fine particles, for example. A method of collecting and adhering by van der Waals force; a method of adding a core substance to a container containing base material fine particles, and attaching a core substance on the surface of the base material fine particles by mechanical action such as rotation of the container Can be mentioned.

In the present invention, the presence of the core substance in the conductive film is not particularly limited. For example, the core substance may be present on the surface of the base particle, or may be separated from the surface of the base particle. You may do it. Especially, it is preferable that the core substance is in contact with the base particle or is present at a distance within 5 nm from the base particle. Moreover, although 2 or 3 core materials in the conductive film may be aggregated, it is preferable that the aggregate number is small.
When the core substance is in contact with the substrate fine particles or exists at a distance of 5 nm or less from the substrate fine particles, the core substance is surely covered with the conductive film, and the raised protrusions with respect to the substrate fine particles Conductive fine particles having excellent adhesion can be obtained, and conductive fine particles having raised protrusions of uniform height can be obtained. Therefore, at the time of connection between the electrodes using the conductive fine particles as an anisotropic conductive material, the variation in conductive performance of the conductive fine particles is reduced, and the effect of excellent connection reliability can be obtained.

  The substrate fine particles in the present invention are not particularly limited as long as they have an appropriate elastic modulus, elastic deformability, and resilience, and may be inorganic materials or organic materials. It is preferable that

The resin fine particles are not particularly limited. For example, polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyvinylidene chloride, polytetrafluoroethylene, polyisobutylene, polybutadiene, polyalkylene terephthalate, polysulfone, polycarbonate, polyamide, phenol formaldehyde resin, Divinylbenzene such as melamine formaldehyde resin, benzoguanamine formaldehyde resin, urea formaldehyde resin; (meth) acrylic acid ester polymer; divinylbenzene polymer; divinylbenzene-styrene copolymer, divinylbenzene- (meth) acrylic acid ester copolymer The thing which consists of a system polymer etc. is mentioned. The (meth) acrylic acid ester may be either a crosslinked type or a non-crosslinked type, if necessary, and a mixture thereof may be used. Of these, fine particles comprising a (meth) acrylic acid ester polymer, a divinylbenzene polymer, and a divinylbenzene polymer are preferably used. Here, (meth) acrylic acid ester means methacrylic acid ester or acrylic acid ester.
These resin fine particles may be used independently and 2 or more types may be used together.

  The average particle size of the substrate fine particles is preferably 1 to 20 μm, more preferably 1 to 10 μm. When the average particle diameter is less than 1 μm, for example, it is easy to aggregate when performing electroless plating, and it may be difficult to form single particles. When it exceeds 20 μm, it is used as an anisotropic conductive material between substrate electrodes and the like. May be exceeded.

In the present invention, the average height of the raised protrusions is preferably 0.5% or more and more preferably 25% or less of the average particle diameter (diameter) of the conductive fine particles.
The average height of the protrusions depends on the particle diameter of the core substance and the conductive film, but if it is less than 0.5% of the average particle diameter of the conductive fine particles, it is difficult to obtain the effect of protrusions. If it exceeds 50%, the electrode may be deeply cut and the electrode may be damaged.
A more preferable range of the average height of the protrusions is 1 to 20% of the average particle diameter of the conductive fine particles.
In addition, the average height of the protruding portion is obtained by a measurement method using an electron microscope described later.

(Characteristic measurement method)
Various characteristics of the conductive fine particles in the present invention, for example, the thickness of the metal plating film, the thickness of the gold layer, the average particle diameter of the substrate fine particles, the average particle diameter of the conductive fine particles, the shape of the core substance, the shape of the protrusions, The average height of the protrusions can be obtained by observing particles or cross sections of the conductive fine particles with an electron microscope.

  As a method of preparing a sample for performing the cross-sectional observation, conductive fine particles are embedded in a thermosetting resin and cured by heating, and the sample is polished to a specular state that can be observed using a predetermined abrasive paper or abrasive. Methods and the like.

  The observation of the conductive fine particles is performed with a scanning electron microscope (SEM). As the magnification, an easily observable magnification may be selected. For example, observation is performed at 4000 times. Further, the cross-sectional observation of the conductive fine particles is performed with a transmission electron microscope (TEM), and as the magnification, an easily observable magnification may be selected.

  The average film thickness of the conductive film such as a metal plating film or a gold layer of the conductive fine particles is a film thickness obtained by measuring 10 randomly selected particles and arithmetically averaging them. In addition, when the film thickness of each electroconductive fine particle has nonuniformity, the maximum film thickness and the minimum film thickness are measured, and let the film thickness be the arithmetic average value.

The average particle size of the above-mentioned substrate fine particles is obtained by measuring the particle size of 20 randomly selected substrate fine particles and arithmetically averaging them.
The average particle size of the conductive fine particles is obtained by measuring the particle size of 20 randomly selected conductive fine particles and arithmetically averaging them.

  The average height of the above-mentioned protrusions was measured from the reference surface forming the outermost surface as the protrusions of 20 protrusions that were almost entirely observed among the many protrusions confirmed. Then, it is arithmetically averaged to obtain the average height of the protrusions. At this time, assuming that the effect of providing the projection is obtained, a projection having a size of 0.5% or more with respect to the average particle diameter of the conductive fine particles is selected.

(Electroless plating)
The metal plating film in the present invention can be formed, for example, by an electroless nickel plating method. As a method for performing the electroless nickel plating, for example, an electroless nickel plating solution composed of sodium hypophosphite as a reducing agent is erected and heated according to a predetermined method. For example, a method of immersing metal fine particles and depositing a metal plating film containing nickel and phosphorus by a reduction reaction of Ni ²⁺ + H ₂ PO ₂ ⁻ + H ₂ O → Ni + H ₂ PO ₃ ⁻ + 2H ⁺ can be mentioned.

  At this time, as described above, for example, as a method of reducing the phosphorus content in the thickness direction in the metal plating film, the pH of the nickel plating solution is sequentially increased in the first and second stages of nickel plating. A method of increasing the speed of the nickel plating reaction, a method of increasing the temperature of the nickel plating solution and sequentially increasing the plating temperature, a method of sequentially increasing the concentration of the phosphorus reducing agent in the nickel plating solution, and the like can be used. These methods may be used alone or in combination of two or more.

  In the first step of nickel plating, for example, if the reaction rate is slowed by controlling the pH in the nickel plating solution, the deposition rate of nickel is slow and the by-product phosphorus is generated quickly, so there is a lot of phosphorus in the plating film. A metal plating film having a high phosphorus content is formed by being taken in. Such a metal plating film is not only flexible because of its high phosphorus content, but also has a uniform and dense metal plating film without irregularities, and therefore has excellent adhesion to the substrate fine particles.

Examples of the method for applying the catalyst include, for example, alkali degreasing, acid neutralization, sensitizing in a tin dichloride (SnCl ₂ ) solution, and activator in a palladium dichloride (PdCl ₂ ) solution. For example, a method of performing an electroless plating pretreatment step consisting of ching. Sensitizing is a process of adsorbing Sn ²⁺ ions on the surface of the insulating material, and activating causes a reaction of Sn ²⁺ + Pd ²⁺ → Sn ⁴⁺ + Pd ^{0 on the} surface of the insulating material. In this process, palladium is used as a catalyst core for electroless plating.

(Anisotropic conductive material)
Next, 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 present invention has the above-described configuration, it is excellent in resin rejection when thermally bonded to an electrode with an anisotropic conductive film or the like, and has improved connection reliability by increasing the connection area with the electrode. Fine particles can be obtained. In addition, it is possible to obtain an anisotropic conductive material using the conductive fine particles that are excellent in resin exclusion properties and have increased connection area with the electrode and improved connection reliability when thermocompression bonded to the electrode. became.

  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
(Electroless plating pretreatment process)
Alkali degreasing with a sodium hydroxide aqueous solution, acid neutralization, and sensitizing in a tin dichloride solution were performed on 10 g of base material fine particles made of a divinylbenzene polymer having an average particle size of 4 μm. Thereafter, an electroless plating pretreatment consisting of activation in a palladium dichloride solution was performed, and after filtering and washing, substrate fine particles having palladium adhered to the particle surfaces were obtained.

(Core material compounding process)
The obtained substrate fine particles were dispersed in 300 ml of deionized water with stirring for 3 minutes, and then 1 g of nickel particles (“2020SUS” manufactured by Mitsui Kinzoku Co., Ltd., average particle diameter 200 nm, Vickers hardness 500) was added to the aqueous solution as a core material. As a result, substrate fine particles to which a core substance was adhered were obtained.

(Electroless nickel plating process)
Next, sulfuric acid was added to an aqueous suspension of 10 g of the substrate fine particles to which the obtained core material was adhered to prepare an aqueous suspension having a pH of 4.

  On the other hand, as a nickel plating solution for the first step, a mixed solution of nickel sulfate 450 g / l, sodium hypophosphite 150 g / l, sodium citrate 116 g / l, and plating stabilizer 6 ml was adjusted to pH 7 with sulfuric acid. 300 ml of this nickel plating solution was added to the aqueous suspension through a metering pump at an addition rate of 40 ml / min. The reaction temperature was set at 40 ° C. Then, it stirred until pH became stable, it confirmed that hydrogen foaming stopped, and the electroless-plating pre-process was performed. It was confirmed that the pH after the first plating step was 5 or less.

  Next, the pH 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 adjusted to 11 with ammonia as a nickel plating solution for the latter stage process. 200 ml of this mixed solution was added through a metering pump at an addition rate of 15 ml / min. The reaction temperature was set at 40 ° C. Thereafter, the mixture was stirred until the pH was stabilized, it was confirmed that hydrogen foaming stopped, and electroless plating was performed at a later stage to obtain conductive fine particles on which a metal plating film was formed. It was confirmed that the pH after the latter plating step was 8 or more.

(Gold plating process)
The obtained conductive fine particles on which the metal plating film was formed were further subjected to substitution gold plating to obtain conductive fine particles on which the gold film was formed on the metal plating film.

(Evaluation of conductive fine particles)
About the obtained electroconductive fine particles, the cross section was cut out with the focused ion beam, and it observed with the 200,000 times transmission electron microscope, and investigated the height and film thickness of the projection part. Further, the contents of nickel and phosphorus in the metal plating film were investigated by the following component measuring method using EDX.
These results are shown in Table 1.

(Component measurement method by EDX)
Using EDX (“Energy Dispersive X-ray Spectrometer”, manufactured by JEOL Datum), the cross-section of the conductive fine particles is cut out with a focused ion beam, and each component in the metal plating film is subjected to component analysis. The detection value of phosphorus was measured. The contents of nickel and phosphorus in the metal plating composition were calculated from the obtained measured values.

(Preparation of anisotropic conductive film)
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, the obtained conductive fine particles are added, After sufficiently mixing using a planetary stirrer, it was applied on a release film so that the thickness after drying was 7 μm, and toluene was evaporated to obtain an adhesive film containing conductive fine particles. 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.

(Evaluation of conductivity of anisotropic conductive film)
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 180 ° C., and then the resistance value between the electrodes was measured.
Moreover, after performing the reliability test (80 degreeC, 95% RH high temperature high-humidity environment hold | maintained for 1000 hours) with respect to the produced test piece, the resistance value between electrodes was measured.
The evaluation results are shown in Table 1.

(Example 2)
In the core material compounding step in Example 1, instead of 1 g of nickel particles (Mitsui Kinzoku "2020SUS", average particle diameter 200 nm, Vickers hardness 500), nickel particles (Mitsui Kinzoku "2007SUS", average particle diameter) Conductive fine particles were obtained in the same manner as in Example 1 except that 1 g of 50 nm and Vickers hardness 500) was used.
The obtained conductive fine particles were evaluated in the same manner as in Example 1.
Further, for the obtained conductive fine particles, an anisotropic conductive film was prepared in the same manner as in Example 1, and the conductivity of the anisotropic conductive film was evaluated.
The evaluation results are shown in Table 1.

(Comparative Example 1)
In the electroless nickel plating step in Example 1, the pH was adjusted to 9.3 instead of the pH 7 of the nickel plating solution for the previous process, the pH was adjusted to 12 instead of the pH 11 of the nickel plating solution for the latter process, and the previous period Conductive fine particles were obtained in the same manner as in Example 1 except that the reaction temperature in the step and the latter step was both set to 27 ° C.
The obtained conductive fine particles were evaluated in the same manner as in Example 1.
Further, for the obtained conductive fine particles, an anisotropic conductive film was prepared in the same manner as in Example 1, and the conductivity of the anisotropic conductive film was evaluated.
The evaluation results are shown in Table 1.

(Comparative Example 2)
Conductive fine particles were obtained in the same manner as in Example 1 except that the core material combining step in Example 1 was not performed.
The obtained conductive fine particles were evaluated in the same manner as in Example 1.
Further, for the obtained conductive fine particles, an anisotropic conductive film was prepared in the same manner as in Example 1, and the conductivity of the anisotropic conductive film was evaluated.
The evaluation results are shown in Table 1.

  From Table 1, the conductive fine particles of the example are wrapped in the conductive film because the conductive film containing the metal plating film is soft when the phosphorus content in the metal plating film is 10% by weight or more. It can be seen that the connection reliability is improved by the protrusions.

According to the present invention, when thermocompression bonding to an electrode with an anisotropic conductive film or the like, conductive fine particles that are excellent in resin rejection and can increase connection area with the electrode and improve connection reliability, And an anisotropic conductive material using the conductive fine particles.

Claims (8)

The surface of the substrate fine particles is coated with a multi-layered conductive film having a metal plating film layer containing nickel and phosphorus and the outermost surface being a gold layer, and the conductive film has conductive protrusions having protrusions raised on the surface. Because
The metal plating film contains 10% by weight or more of phosphorus,
Conductive fine particles, wherein the raised protrusions on the surface of the conductive film have a conductive substance as a core substance.   The conductive fine particles according to claim 1, wherein the metal plating film has a thickness of 40 to 150 nm.   In the metal plating film, the metal plating composition contains 10 to 20% by weight of phosphorus in the region of 20% or less of the metal plating film thickness from the substrate fine particle side, and the metal plating film thickness from the metal plating film surface side. The conductive fine particles according to claim 1 or 2, wherein the metal plating composition contains 1 to 10% by weight of phosphorus in an area of 10% or less.   The conductive fine particles according to any one of claims 1 to 3, wherein a hardness ratio of the conductive film to the core material according to Vickers hardness is 0.2 to 0.7.   5. The conductive fine particle according to claim 1, wherein the core substance is made of at least one metal selected from nickel, copper, gold, silver, and zinc.   The conductive fine particles according to claim 1, wherein the substrate fine particles are resin fine particles.   7. The conductive fine particle according to claim 1, wherein an average height of the protruding protrusion is 0.5% or more of an average particle diameter of the conductive fine particle.   An anisotropic conductive material, wherein the conductive fine particles according to claim 1 are dispersed in a resin binder.