JP2006331714A - Conductive fine particle and anisotropic conductive material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a conductive fine particle and an anisotropic conductive material capable of preventing defective conduction and lowering of resistance, on a view point that further reduction of the resistance of the conductive fine particle used as a material for the anisotropic conductive material is required according to recent rapid progress and development of electronic device. <P>SOLUTION: The conductive fine particle is composed of fine particle base material and conductive layer composed of nickel formed on the surface of the conductive fine particle. The conductive layer has protrusions on its surface, and at least the protrusion contains aluminum and/or lead. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to conductive fine particles capable of preventing conduction failure and reducing resistance, and an anisotropic conductive material.

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 used to electrically connect circuit boards to each other, for example, in electronic devices such as liquid crystal displays, personal computers, and mobile phones, and to electrically connect small components such as semiconductor elements to the circuit board. For this reason, it is used by being sandwiched between circuit boards and electrode terminals facing each other.

As the conductive fine particles used for such anisotropic conductive materials, conventionally, a metal plating layer is formed as a conductive layer on the surface of non-conductive fine particles such as resin particles having a uniform particle size and appropriate strength. Conductive fine particles are used. However, when the circuit boards are electrically connected using such an anisotropic conductive material, a binder resin or the like is sandwiched between the conductive layer on the surface of the conductive fine particles and the circuit board. In some cases, the connection resistance between them and the like increases. In particular, with the rapid progress and development of electronic devices in recent years, there has been a demand for further reduction in connection resistance between conductive fine particles and circuit boards.

Patent Document 1 discloses conductive fine particles having protrusions on the surface for the purpose of reducing connection resistance. This conductive fine particle ensures that the protrusion and the circuit board are connected by the protrusion breaking through the binder resin or the like existing between the conductive layer on the surface of the conductive fine particle and the circuit board. Thus, the connection resistance between the conductive fine particles and the circuit board or the like is reduced.

However, in the conductive fine particles described in Patent Document 1, since the protrusions are formed by abnormal precipitation of nickel on the surface of the conductive fine particles, the connection resistance can be sufficiently reduced due to the high resistance value of nickel. It could not be said that it was planned.
Japanese Patent Laid-Open No. 7-118866

An object of the present invention is to provide conductive fine particles and an anisotropic conductive material capable of preventing conduction failure and reducing a resistance value in view of the above-described present situation.

The present invention is a conductive fine particle comprising a substrate fine particle and a conductive layer made of nickel formed on the surface of the substrate fine particle, the conductive layer has a protrusion on the surface, and At least the protrusions are conductive fine particles containing aluminum and / or zinc.
The present invention is described in detail below.

As a result of intensive studies, the present inventors have included a conductive layer of conductive fine particles used for electrical connection of a circuit board or the like with nickel and aluminum and / or zinc, which has a lower resistance than nickel, and It is possible to reduce the resistance value of the conductive layer including the protrusion by adding nickel and aluminum and / or zinc to the protrusion portion by dispersing or precipitating aluminum and / or zinc when forming the nickel layer. It has been found that the circuit board and the like can be connected with high reliability without causing poor connection and the like, and the present invention has been completed.

The conductive fine particles of the present invention are composed of substrate fine particles and a conductive layer made of nickel formed on the surface of the substrate fine particles.

The substrate fine particles are not particularly limited, and may be an organic material or an inorganic material as long as it has an appropriate elastic modulus, elastic deformability, and restoration property. Since it is excellent in resilience, it is preferably a resin fine particle made of a resin.

The resin fine particles are not particularly limited. For example, polyolefins such as polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyvinylidene chloride, polytetrafluoroethylene, polyisobutylene, and polybutadiene; acrylic resins such as polymethyl methacrylate and polymethyl acrylate A copolymer resin of acrylate and divinylbenzene, polyalkylene terephthalate, polysulfone, polycarbonate, polyamide, phenol formaldehyde resin, melamine formaldehyde resin, benzoguanamine formaldehyde resin, urea formaldehyde resin, and the like. These resin fine particles may be used independently and 2 or more types may be used together.

The average particle diameter of the substrate fine particles is not particularly limited, but a preferable lower limit is 1 μm and a preferable upper limit is 20 μm. If it is less than 1 μm, it tends to agglomerate when forming a conductive layer, making it difficult to form single particles, and if it exceeds 20 μm, it may exceed the range used between substrate electrodes as an anisotropic conductive material. There is. A more preferable upper limit is 10 μm.

Although the average film thickness of the conductive layer is not particularly limited, the preferable lower limit is 10 nm and the preferable upper limit is 1 μm in consideration of exerting the necessary conductivity as the conductive connection material. If the thickness is less than 10 nm, a portion where the conductive layer is not formed may be formed on the substrate fine particles, or the resistance may be increased. If the thickness exceeds 1 μm, the conductive layer becomes hard and cannot follow the deformation of the substrate fine particles, so that the breakage easily proceeds, the connection electrode is destroyed to prevent the deformation of the substrate fine particles, and the contact area does not increase. In some cases, the connection resistance value is increased or connection failure is likely to occur. A more preferable upper limit is 500 nm.
Here, the average film thickness is a film thickness obtained by measuring 10 randomly selected particles and arithmetically averaging them. In addition, when the film thickness of each conductive fine particle is uneven, the maximum film thickness and the minimum film thickness are measured, and the arithmetic average value is taken as the film thickness.

The conductive layer made of nickel has protrusions on the surface, and at least the protrusions contain aluminum and / or zinc.
Since the resistance value of aluminum and zinc is lower than that of nickel, the presence of aluminum and / or zinc in the conductive layer can further reduce the resistance value of the conductive layer. When forming the nickel layer, protrusions can be formed by dispersing aluminum and / or zinc as fine particles such as metal in the plating solution or by depositing them as metal or metal hydroxide. Nickel and aluminum and / or zinc can be contained. Moreover, since nickel, aluminum, and zinc do not cause migration, they can be stably present in the conductive layer.
Further, since the conductive fine particles of the present invention have protrusions, when the anisotropic conductive material formed using the conductive fine particles of the present invention is sandwiched between the circuit boards and the like and is crimped at the time of conductive connection, The present invention breaks through a binder resin or the like in the anisotropic conductive material existing between the conductive fine particles of the present invention (resin eliminability), and the projections are crushed and the tip is flattened on the surface of the circuit board. The conductive fine particles and the circuit board are in surface contact, and the protrusions also contain nickel and aluminum and / or zinc. In addition to prevention, the resistance value can be reduced.

In the conductive layer of the conductive fine particles of the present invention, it is preferable to form a sea-island structure in which nickel is a sea component and aluminum and / or zinc is an island component. By forming the sea-island structure, the resistance value of the nickel layer can be reduced due to the presence of aluminum and / or zinc, which have a lower resistance value than nickel, and the aluminum and / or zinc is localized in the protrusions. Therefore, it is possible to obtain an effect that the resistance value of the protruding portion can be further reduced as compared with a uniform alloy or the like.
Here, the sea-island structure means that the sea component and the island component exist in a phase-separated state, and the island component is dispersed in the sea component.

Although it does not specifically limit as a dispersed particle diameter of the dispersion state of the said aluminum and / or zinc, A preferable minimum is 0.1 nm. If it is less than 0.1 nm, it may be difficult to obtain the effect of reducing the resistance value due to the presence of aluminum and / or zinc, or it may be difficult to disperse in the conductive layer. A more preferred lower limit is 1 nm. The aluminum and / or zinc dispersed particles may be an aggregate in which two or more dispersed particles are aggregated.
Here, the dispersed particle diameter is determined by measuring the dispersed particle diameters of 50 randomly selected island components such as aluminum and / or zinc, and arithmetically averaging them. At this time, when the dispersed particles of aluminum and / or zinc cannot be regarded as spherical, the major axis and minor axis are measured, and the arithmetic average value is taken as the dispersed particle size.

The average height of the protrusions is not particularly limited, but a preferred lower limit is 0.5% of the particle diameter of the substrate fine particles, and a preferred upper limit is 25% of the particle diameter of the substrate fine particles. If it is less than 0.5%, sufficient resin exclusion may not be obtained, and if it exceeds 25%, the protrusions may be deeply embedded in the circuit board and the like, possibly damaging the circuit board.
Note that the average height of the protrusions is obtained by measuring the heights of the protrusions on 50 conductive layers selected at random, and calculating the average height of the protrusions to obtain the average height of the protrusions. At this time, a projection having a projection of 10 nm or more on the conductive layer was selected as the projection as an effect of providing the projection.

The conductive fine particles of the present invention preferably further have a gold layer formed on the surface of the conductive layer. By applying a gold layer to the surface of the conductive layer, it is possible to prevent oxidation of the conductive layer, reduce connection resistance, stabilize the surface, and the like.

The method for forming the gold layer is not particularly limited, and examples thereof include conventionally known methods such as electroless plating, displacement plating, electroplating, reduction plating, and sputtering.

Although it does not specifically limit as thickness of the said gold layer, A preferable minimum is 1 nm and a preferable upper limit is 100 nm. If it is less than 1 nm, it may be difficult to prevent oxidation of the conductive layer, and the connection resistance value may be high. If it exceeds 100 nm, the gold layer erodes the conductive layer, Adhesion with the conductive layer may be deteriorated.

It does not specifically limit as a manufacturing method of the electroconductive fine particles of this invention, For example, the following methods are mentioned.
First, the surface of the substrate fine particles is roughened by etching the substrate fine particles with an alkaline solution such as an aqueous sodium hydroxide solution, and a catalyst is applied to the surface of the substrate fine particles.
Subsequently, aluminum (ion) and / or zinc (ion) is added to an electroless nickel plating solution containing a plating stabilizer and sodium hypophosphite (reducing agent), and aluminum and / or zinc is added at pH 4.5 to This is a method of depositing as a metal or metal hydroxide in 5.0 and forming a projection using this precipitate as a nucleus.
According to this method, since the aluminum and / or zinc is easily taken into the protruding portion, the resistance value of the conductive fine particles of the present invention can be effectively reduced.
Here, as a method for applying the catalyst, for example, acid neutralization and sensitization in a tin dichloride (SnCl ₂ ) solution are performed on the substrate fine particles etched with an alkaline solution, and palladium dichloride (PdCl ₂ ) A method of performing an electroless plating pretreatment step for activating in solution.
Sensitizing is a process in which Sn ²⁺ ions are adsorbed on the surface of an insulating material, and activating is a reaction represented by Sn ²⁺ + Pd ²⁺ → Sn ⁴⁺ + Pd ⁰ on the surface of an insulating material. In this process, palladium is used as a catalyst core for electroless plating.

In addition, for example, the following method can be cited.
The surface of the substrate fine particles is roughened by etching the substrate fine particles with an alkaline solution such as an aqueous sodium hydroxide solution, and after the catalyst is applied to the surface of the substrate fine particles, a plating stabilizer and sodium hypophosphite (reducing agent) Aluminum (metal) and / or zinc (metal) was dispersed and added to the contained electroless nickel plating solution, and the catalyst was applied to the electroless nickel plating bath containing aluminum and / or zinc in a suspended state. This is a method of performing electroless plating by immersing the substrate fine particles. As a result, aluminum and / or zinc is taken into the conductive layer simultaneously with nickel, so that conductive fine particles having a conductive layer in a eutectoid state and having protrusions can be obtained.

An anisotropic conductive material can be produced by dispersing the conductive fine particles of the present invention in a binder resin. Such an anisotropic conductive material is also one aspect of the present invention.

Specific examples of the anisotropic conductive material of the present invention include, for example, anisotropic conductive paste, anisotropic conductive ink, anisotropic conductive adhesive layer, anisotropic conductive film, anisotropic conductive sheet and the like. Is mentioned.

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

In addition to the conductive fine particles of the present invention and the resin binder described above, the anisotropic conductive material of the present invention includes, for example, a bulking agent and a softening agent (if necessary) within a range not impairing the achievement of the present invention. Additives such as plasticizers), adhesive improvers, antioxidants (anti-aging agents), heat stabilizers, light stabilizers, UV absorbers, colorants, flame retardants, organic solvents, etc. Good.

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 are mixed and dispersed uniformly. A method of using a conductive paste, anisotropic conductive ink, anisotropic conductive adhesive, etc., adding the conductive fine particles of the present invention in an insulating resin binder and uniformly dissolving (dispersing), or , Heat-dissolve, and apply to the release treatment surface of the release material such as release paper and release film to have a predetermined film thickness, and perform drying and cooling as necessary, for example, anisotropic For example, an appropriate manufacturing method may be employed in accordance with the type of anisotropic conductive material to be manufactured.
Moreover, it is good also as an anisotropic conductive material by using separately, without mixing an insulating resin binder and the electroconductive fine particles of this invention.

According to the present invention, it is possible to provide conductive fine particles and anisotropic conductive material capable of preventing conduction failure and reducing the resistance value.

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)
10 g of substrate fine particles made of a copolymer resin of tetramethylolmethane tetraacrylate and divinylbenzene having an average particle diameter of 3 μm were subjected to alkali degreasing with an aqueous sodium hydroxide solution, acid neutralization, and sensitizing in a tin dichloride solution. 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.

(Electroless nickel plating process)
The obtained substrate fine particles were further diluted with 1200 mL of water, and after adding 4 mL of plating stabilizer, nickel sulfate 450 g / L, sodium hypophosphite 150 g / L, sodium citrate 116 g / L, plating stability 120 mL of 6 mL of the plating mixture solution was added through a metering pump at an addition rate of 81 mL / min. At the same time, 120 mL of 450 g / L aqueous solution of aluminum sulfate adjusted to pH 3.5 was added through the metering pump at an addition rate of 81 mL / min. did. At that time, the pH in the plating system was kept at 4.5 to 5.0. Thereafter, it was confirmed that hydrogen foaming stopped, and the first electroless plating step was performed.

Subsequently, 650 mL of a mixed solution of 450 g / L of nickel sulfate, 150 g / L of sodium hypophosphite, 116 g / L of sodium citrate, and 35 mL of a plating stabilizer was added through a metering pump at an addition rate of 27 mL / min. At that time, the pH in the plating system was maintained at 7.5 to 8.0. Thereafter, it was confirmed that hydrogen foaming stopped, and an electroless plating late step was performed.

Next, the plating solution was filtered, and the filtrate was washed with water and then dried with a vacuum dryer at 80 ° C. to obtain conductive fine particles.
Thereafter, the surface was further plated with gold by a displacement plating method to obtain conductive fine particles.

The obtained conductive fine particles were observed with a transmission electron microscope (TEM) manufactured by JEOL Datum Co., Ltd., and had protrusions containing nickel and aluminum. The cross section had a sea-island structure with nickel as a sea component and aluminum as an island component, and was a protrusion formed by agglomeration of aluminum.

(Example 2)
The electroless plating pretreatment step was performed in the same manner as in Example 1.
The obtained substrate fine particles were further diluted with 1200 mL of water, and after adding 4 mL of plating stabilizer, nickel sulfate 450 g / L, sodium hypophosphite 150 g / L, sodium citrate 116 g / L, plating stability 6 mL of the agent and 120 mL of the plating mixed solution added with aluminum fine powder having a particle diameter of 40 nm were added through a metering pump at an addition rate of 81 mL / min. At that time, the pH in the plating system was maintained at 7.5 to 8.0. Thereafter, it was confirmed that hydrogen foaming stopped, and the first electroless plating step was performed.

Subsequently, 650 mL of a mixed solution of 450 g / L of nickel sulfate, 150 g / L of sodium hypophosphite, 116 g / L of sodium citrate, and 35 mL of a plating stabilizer was added through a metering pump at an addition rate of 27 mL / min. At that time, the pH in the plating system was maintained at 7.5 to 8.0. Thereafter, it was confirmed that hydrogen foaming stopped, and an electroless plating late step was performed.

Next, the plating solution was filtered, and the filtrate was washed with water and then dried with a vacuum dryer at 80 ° C. to obtain conductive fine particles.
Thereafter, the surface was further plated with gold by a displacement plating method to obtain conductive fine particles.

The obtained conductive fine particles were observed with a transmission electron microscope (TEM) manufactured by JEOL Datum Co., Ltd., and had protrusions containing nickel and aluminum. The cross section had a sea-island structure with nickel as a sea component and aluminum as an island component, and was a protrusion formed by agglomeration of aluminum.

(Comparative Example 1)
In the electroless nickel plating process, the aluminum sulfate aqueous solution was not added, and the pH in the plating system was maintained at 7.5 to 8.0 instead of 4.5 to 5.0. Except that, conductive fine particles were obtained in the same manner as in Example 1.

The obtained conductive fine particles were observed with a transmission electron microscope (TEM) manufactured by JEOL Datum, and had a smooth nickel layer.

(Comparative Example 2)
In the electroless nickel plating step, the aluminum sulfate aqueous solution was not added, the pH in the plating system was kept at 4.5 to 5.0 instead of 4.5 to 5.0, and Conductive fine particles were obtained in the same manner as in Example 1 except that 1 mL of plating stabilizer was used instead of 4 mL of plating stabilizer added first, and thereafter no plating stabilizer was added. In the electroless nickel plating process, the plating solution self-decomposed.

When the obtained electroconductive fine particles were subjected to cross-sectional observation using a transmission electron microscope (TEM) manufactured by JEOL Datum, the nickel layer had protrusions due to abnormal precipitation of nickel.

<Evaluation>
The following evaluation was performed about the electroconductive fine particles obtained in Examples 1-2 and Comparative Examples 1-2. The results are shown in Table 1.

(1) Measurement of connection resistance value An anisotropic conductive material was produced by the following method using the obtained conductive fine particles, and the connection resistance value between the electrodes was measured.
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 resin binder resin are sufficiently mixed using a planetary stirrer. Then, it was applied on the release film so that the thickness after drying was 10 μm, and toluene was evaporated to obtain an adhesive film.
Subsequently, 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 resin binder resin were obtained. After adding fine particles and mixing well using a planetary stirrer, it is coated on a release film so that the thickness after drying is 7 μm, and toluene is evaporated to form an adhesive film containing conductive fine particles Got. In addition, the compounding quantity of electroconductive fine particles was made for the content in a film to be 50,000 piece / cm < ² >.
By laminating the obtained adhesive film and an adhesive film containing conductive fine particles at room temperature, an anisotropic conductive film having a two-layer structure and a thickness of 17 μm was obtained.
The obtained anisotropic conductive film was cut into a size of 5 × 5 mm. After affixing this to approximately the center of 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 having a lead wire for resistance measurement, a glass substrate having an ITO electrode is obtained. After aligning the electrodes so that they overlap each other, they were bonded together.
The bonded portion of this glass substrate was thermocompression bonded under pressure bonding conditions of 10N and 100 ° C., and then the connection resistance value between the electrodes was measured.
In addition, a reliability test (held at 80 ° C. in a high-temperature and high-humidity environment of 95% RH for 1000 hours) was performed on the prepared test piece, and then the connection resistance value between the electrodes was measured.

(2) Average height of protrusions The obtained conductive fine particles were observed with a scanning electron microscope (SEM) manufactured by Hitachi High-Technologies Corporation at a magnification of 10,000 to examine the height of the protrusions.
The height of the protrusion was measured by measuring the height appearing as a protrusion from the reference surface of the conductive layer forming the outermost surface of the conductive fine particles.
The average height of the protrusions was measured for 20 confirmed protrusions, and the average of the protrusions was calculated as the average height of the protrusions.

According to the present invention, it is possible to provide conductive fine particles and anisotropic conductive material capable of preventing conduction failure and reducing the resistance value.

Claims (5)

Conductive fine particles comprising substrate fine particles and a conductive layer made of nickel formed on the surface of the substrate fine particles, wherein the conductive layer has protrusions on the surface, and at least the protrusions Conductive fine particles characterized by containing aluminum and / or zinc. 2. The conductive fine particles according to claim 1, wherein the conductive layer has a sea-island structure in which nickel is a sea component and aluminum and / or zinc is an island component. The conductive fine particles according to claim 1 or 2, wherein the average height of the protrusions is 0.5 to 25% of the average particle diameter of the substrate fine particles. 4. The conductive fine particles according to claim 1, wherein a gold layer is formed on the surface of the conductive layer. An anisotropic conductive material, wherein the conductive fine particles according to claim 1, 2, 3 or 4 are dispersed in a resin binder.