JP4746116B2 - Conductive powder, conductive material containing the same, and method for producing conductive particles - Google Patents

Description

  The present invention relates to a conductive powder and a conductive material including the same. The present invention also relates to a method for producing conductive particles.

  The present applicant has previously proposed a conductive electroless plating powder having fine protrusions made of nickel or a nickel alloy on its surface (see Patent Document 1). The electroless plating particles in this powder exhibit good conductivity due to the action of the fine protrusions. The electroless plating particles include an electroless plating step (step A) in which an aqueous slurry of a spherical core material is added to an electroless plating bath containing a nickel salt, a reducing agent, a complexing agent, and the like, and an aqueous slurry of a spherical core material The electroless plating solution is manufactured by an electroless plating step (step B) in which the components of the electroless plating solution are separated into at least two solutions and added simultaneously and with time. In this manufacturing method, in step A, a nickel film is formed on the surface of the core material particles, and nuclei that are the starting points for the formation of protrusions are formed. The nucleus grows in the B process, so that a protrusion is formed. The electroless plated particles thus obtained are suitably used for, for example, conductive adhesives, anisotropic conductive films, anisotropic conductive adhesives and the like for conductively bonding opposing connection circuits.

  Apart from this technique, Patent Document 2 discloses a conductive material having a protrusion by attaching a nickel core material having a particle diameter of 50 nm to the surface of a core material particle having a particle diameter of 4 μm and then performing electroless plating of nickel. A method for obtaining a conductive particle has been proposed. However, in this method, since the adhesion between the core material particles and the nickel core material is weak, the nickel layer covering the surface of the core material particles and the protrusions are not integrated, and the pressure is applied to the conductive particles. Protrusions are easily damaged. Further, it is very difficult to uniformly adhere a nickel core material having a particle size of 50 nm, which is much smaller than this, to the surface of the core material particles having a particle size of 4 μm. This is because it is easier for the nickel core materials to agglomerate than the nickel core materials adhere to the surface of the core particles. As a result, aggregated particles having a large particle diameter in which nickel core materials are aggregated often adhere to the surface of the core material particles, and very large protrusions are easily formed.

  By the way, with the further miniaturization of electronic devices in recent years, the circuit width and pitch of electronic circuits are becoming increasingly smaller. Accordingly, electroless plating powders used for the above-mentioned conductive adhesives, anisotropic conductive films, anisotropic conductive adhesives, and the like are required to have a small particle size. However, if the particle size of the particles is reduced, the particles tend to aggregate, and the apparent particle size (secondary particle size) increases due to the aggregation even though particles having a small particle size are used. In addition, when particles having a small particle diameter are used, it is more difficult to increase the conductivity (lower the electrical resistance) than when large particles are used.

JP 2000-243132 A JP 2006-228474 A

  Accordingly, an object of the present invention is to provide a conductive powder having various performances further improved as compared with the conductive powder of the prior art described above.

  As a result of intensive studies by the present inventors to achieve the above object, when conductive particles having a dispersibility comparable to that of the prior art and having a particle size smaller than that of the prior art are used, they are formed on the surface. It has been found that the lowering of the conductivity can be suppressed by making the shape of the protruding protrusions vertically longer than before.

The present invention was made on the basis of the above knowledge, and is a conductive powder comprising conductive particles in which nickel or a nickel alloy film is formed on the surface of core material particles,
The conductive particles protrude from the surface of the coating and are continuous with the coating, and have a large number of protrusions with an aspect ratio of 1 or more,
The ratio of the protrusions having an aspect ratio of 1 or more is 40% or more with respect to the total number of protrusions,
The conductive powder provides a conductive powder characterized in that the weight of the primary particles among the conductive particles is 85% by weight or more based on the weight of the conductive powder. It is.

Further, the present invention mixes an electroless plating bath containing a dispersant and nickel ions and core material particles carrying a noble metal on the surface, and forms a nickel initial thin film layer on the surface of the core material particles. A using the core material particles in such an amount that the total surface area is 1 to 15 m ² with respect to 1 liter of the electroless plating bath whose nickel ion concentration is adjusted to 0.0001 to 0.008 mol / L. Process,
While maintaining the aqueous slurry containing the core particles having the nickel initial thin film layer and the dispersant obtained in the step A in a pH range in which the dispersing effect of the dispersant is expressed, Nickel ions and a reducing agent in an amount corresponding to an amount of nickel deposited per hour of 25 to 100 nm are added over time to generate nickel core particles in the aqueous slurry, and the generated core particles And B process for growing the core particles from the attached core particles as a starting point to form protrusions having an aspect ratio of 1 or more. A method is provided.

  The conductive powder of the present invention has good dispersibility and conductivity even though the particle size of the conductive particles constituting the conductive powder is smaller than the conventional one. Moreover, according to the manufacturing method of this invention, such electroconductive powder can be manufactured easily.

  Hereinafter, the present invention will be described based on preferred embodiments thereof. The conductive powder of the present invention is obtained by forming a nickel film or a nickel alloy film (hereinafter, these films are simply referred to as “nickel film”) on the surface of the core material particles. The conductive powder of the present invention is characterized in that it has a large number of protrusions protruding from the surface of the nickel film. Hereinafter, this protrusion will be described.

  Forming a large number of protrusions on the surface of the conductive powder is a technique well known in the art as described in the background art section of this specification. In contrast to such background art, the present invention is markedly different from conventional conductive powders in that a projection having a specific shape is employed. Specifically, the protrusion in the conductive powder of the present invention is characterized by an aspect ratio of 1 or more. The aspect ratio in the present specification is a value defined by a ratio between the height H of the protrusion and the width D of the protrusion at the base of the protrusion, that is, H / D. As is clear from this definition, the aspect ratio is a measure of the slenderness of the protrusion, and the larger the value, the more the protrusion has an elongated shape.

  The aspect ratio of the protrusions in the conventional conductive powder having the protrusions is 1 or more as long as the present inventors know, including Patent Document 1 described in the background art section of this specification. It is not easy to do. The protrusions in the conventional conductive powder have a so-called stubby shape (see, for example, FIG. 2 described later). In contrast, the protrusions in the conductive powder of the present invention are elongated protrusions that extend substantially radially from the surface of the particle, as shown in FIG. The present inventors examined the aspect ratio of the protrusion, and it was found that by setting this value to 1 or more, that is, by making the shape of the protrusion more slender than before, the conductivity becomes very high. . The reason for this is that when conducting the electrode using the conductive powder of the present invention, a thin oxide film is naturally formed on the surface of the electrode, or an oxide film of the electrode is intentionally formed. In some cases, it is considered that this oxide film can be easily broken if the aspect ratio of the protrusion is large. Moreover, when an anisotropic conductive film is formed using conductive powder, if the aspect ratio of the protrusions is large, the resin exclusion property becomes high, so that the conductivity is considered to be high. In view of this, the aspect ratio of the protrusion is considered to be that if this value is excessively large, the protrusion may be damaged. Therefore, the preferred range of the aspect ratio is 1.0 to 4.0, more preferably It is 1.0-3.5, More preferably, it is 1.0-3.0. Such conductive particles having protrusions with a large aspect ratio can be produced by, for example, a method described later.

  When focusing on the individual particles in the conductive powder, it is ideal that the aspect ratios of the protrusions of the individual particles all satisfy the above-mentioned range. However, sufficient conductivity can be obtained when the ratio of the protrusions satisfying the above-mentioned range of the aspect ratio is 40% or more, preferably 45% or more, more preferably 50% or more with respect to the total number of protrusions. Turned out to be.

  The above aspect ratio measurement method is as follows. The individual particles in the conductive powder are magnified and observed with an electron microscope. The length D and height H of the base are measured for at least one protrusion for each particle. In this case, it is important from the viewpoint of accurate measurement of dimensions that the projections present at the periphery of the particles are measured rather than the projections present at the center of the particles in the observed image. Such a measurement is performed on at least 20 different particles. The data of a plurality of aspect ratios thus obtained are arithmetically averaged, and the value is used as the aspect ratio. As shown in FIG. 1 to be described later, since the cross section of the protrusion has a shape with small anisotropy (for example, substantially circular), the value of the length D of the base of the protrusion depends on the observation angle of the particles. There is little concern that will change.

  The aspect ratio of the protrusion is as described above, and the base length D of the protrusion and the height H of the protrusion itself are 0.05 to 0.5 μm for the base length D, In particular, the thickness is preferably 0.1 to 0.4 μm, and the height H is preferably 0.05 to 0.5 μm, particularly preferably 0.1 to 0.4 μm. When the length D of the base of the protrusion and the height H of the protrusion are within this range, the conductivity is further improved.

  The number of protrusions having an aspect ratio of 1 or more in the individual particles of the conductive powder depends on the particle size of the particles. However, as will be described later, when the particle size is 3 μm or less, The number per particle is preferably 2 to 40, particularly 2 to 20 from the viewpoint of further improving the conductivity of the conductive powder.

  The individual protrusions in the conductive powder are continuous with the nickel film covering the core particles. Therefore, the protruding portion is made of nickel or a nickel alloy in the same manner as the nickel coating. The term “continuum” as used herein means that the nickel film and the entire protrusion are made of the same material, the protrusion is formed by a single process, and a seam or the like is formed between the nickel film and the protrusion. It means that there is no part that impairs the sense of unity. Therefore, for example, a nickel film is formed on the surface of the core material particles, core particles for forming the protrusions are adhered thereon, and the protrusions formed using the core particles as a starting point of growth have a single protrusion. Since it is not formed by a process, it is not included in the continuum referred to in the present invention. Since the protrusions are continuous with the nickel film, the strength of the protrusions is ensured, so that the protrusions are not easily damaged even when pressure is applied during use of the conductive powder. As a result, good conductivity can be obtained.

  Regarding the thickness of the nickel coating, if the thickness is too thin, the conductive powder is difficult to exhibit sufficient conductivity, and conversely if it is too thick, the nickel coating is easily peeled off from the surface of the core particles. From these viewpoints, the thickness of the nickel film (thickness at the site where no protrusion is present) is preferably 0.01 to 0.3 μm, and more preferably 0.05 to 0.2 μm. The thickness of the nickel coating can be determined by dissolving nickel from the conductive powder and quantifying the dissolved nickel. In addition, according to this method, not only the nickel film but also the nickel of the protrusion is dissolved, but since the ratio of the protrusion to the entire nickel is very low, the amount of nickel in the protrusion should be ignored. Can do.

  In the conductive powder of the present invention, the shape of each particle is preferably spherical. The particle shape referred to here is the particle shape excluding the protrusions. Due to the spherical shape of the particles and the protrusions, the conductive powder of the present invention has high conductivity.

  In the conductive powder of the present invention, the size of each particle can be appropriately set according to the specific application of the conductive powder. As a result of the study by the present inventors, it has been found that the conductivity of the conductive particles is smaller when the particle size is smaller in relation to the aspect ratio of the protrusion described above. Specifically, the conductive particles preferably have a particle size of 1 to 10 μm, particularly 1 to 5 μm, particularly 1 to 3 μm. The particle size of the conductive particles does not include the height of the protrusions. The particle size of the conductive particles can be measured by observation with an electron microscope. Moreover, the particle diameter of the core material particles and the thickness of the nickel coating can be measured and obtained from these values.

  Conductive particles tend to agglomerate as the particle size decreases. When aggregation occurs, there is an inconvenience that an anisotropic conductive film using conductive particles easily causes a short circuit. Further, when a treatment such as pulverization is performed to loosen the agglomeration, the nickel film is peeled off, which causes a decrease in conductivity. From this viewpoint, it is important to improve the dispersibility of individual particles in the conductive powder of the present invention. Therefore, in the present invention, the weight occupied by the primary particles in the conductive particles is 85% by weight or more, preferably 90% by weight or more, more preferably 92% by weight or more based on the weight of the conductive powder. Yes. In order to improve the dispersibility of the conductive particles, for example, the conductive particles may be produced according to a method described later. The weight occupied by the primary particles is measured by the following method. 0.1 g of conductive powder is placed in 100 mL of water and dispersed with an ultrasonic homogenizer for 1 minute. Next, the particle size distribution is measured by a Coulter counter method. From the result, the weight ratio of the primary particles is calculated.

  As described above, the nickel coating and the protrusions on the conductive particles are made of the same material. Specifically, it is composed of metallic nickel or a nickel alloy. The nickel alloy includes, for example, a nickel-phosphorus alloy. The nickel-phosphorus alloy is an alloy produced when sodium hypophosphite is used as a nickel reducing agent in the production of conductive powder described later.

  In the conductive powder of the present invention, the surface of each particle may be made of nickel or a nickel alloy, or the surface of nickel or a nickel alloy may be coated with a noble metal. As the noble metal, it is preferable to use gold or palladium, particularly gold, which is a highly conductive metal. This coating makes it possible to further increase the conductivity of the conductive powder. The thickness of the noble metal coating is generally about 0.001 to 0.5 μm. This thickness can be calculated from the amount of precious metal ions added and chemical analysis.

  Next, the suitable manufacturing method of the electroconductive powder of this invention is demonstrated. In this production method, (1) A step of forming a nickel initial thin film layer on the surface of the core material particles, and (2) B forming the target conductive particles using the particles obtained in step A as raw materials. It is roughly divided into two processes. Hereinafter, each process will be described.

  In step A, an electroless plating bath containing a dispersant and nickel ions is mixed with core material particles having a noble metal supported on the surface to form a nickel initial thin film layer on the surface of the core material particles. There is no restriction | limiting in particular in the kind of core material particle, Both organic substance and an inorganic substance are used. Considering the electroless plating method described later, the core material particles are preferably dispersible in water. Accordingly, the core particles are preferably substantially insoluble in water, and more preferably not dissolved or denatured in acid or alkali. "Dispersible in water" means that a suspension substantially dispersed in water can be formed to such an extent that a nickel film can be formed on the surface of the core particles by a normal dispersing means such as stirring.

  The shape of the core particles greatly affects the shape of the target conductive particles. As described above, since the thickness of the nickel film covering the surface of the core material particles is thin, the shape of the core material particles is almost directly reflected in the shape of the conductive particles. Since it is preferable that the conductive particles have a spherical shape as described above, the shape of the core particles is also preferably a spherical shape.

  When the core material particles are spherical, the particle size of the core material particles greatly affects the particle size of the target conductive particles. As described above, since the thickness of the nickel film covering the surface of the core particle is thin, the particle diameter of the core particle is almost reflected in the particle diameter of the conductive particles. From this viewpoint, the particle diameter of the core particles can be set to be approximately the same as the particle diameter of the target conductive particles. Specifically, it is preferably 1 to 10 μm, particularly 1 to 5 μm, and particularly preferably 1 to 3 μm. The particle diameter of the core particles can be measured by the same method as that of the conductive particles.

There is a range in the particle size distribution of the core powder measured by the method described above. Generally, the width of the particle size distribution of the powder is represented by a coefficient of variation represented by the following formula (1).
Coefficient of variation (%) = (standard deviation / average particle diameter) × 100 (1)
A large coefficient of variation indicates that the distribution is wide, while a small coefficient of variation indicates that the particle size distribution is sharp. In the present invention, it is preferable to use the core particles having a coefficient of variation of 30% or less, particularly 20% or less, particularly 10% or less. This is because, when the conductive particles of the present invention are used as the conductive particles in the anisotropic conductive film, there is an advantage that the effective contribution ratio for connection is increased.

  Specific examples of the core powder include metal (including alloys), glass, ceramics, silica, carbon, metal or non-metal oxides (including hydrates), and metal silicates including aluminosilicates as inorganic substances. Metal carbide, metal nitride, metal carbonate, metal sulfate, metal phosphate, metal sulfide, metal acid salt, metal halide and carbon. Organic materials include natural fibers, natural resins, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polybutene, polyamide, polyacrylate, polyacrylonitrile, polyacetal, ionomer, polyester, and other thermoplastic resins, alkyd resins, phenol resins, urea Examples thereof include resins, melamine resins, benzoguanamine resins, melamine resins, xylene resins, silicone resins, epoxy resins, and diallyl phthalate resins. These may be used alone or in a mixture of two or more.

The other physical properties of the core particles are not particularly limited, but when the core particles are resin particles, the value of K defined by the following formula (2) is 10 kgf at 20 ° C. / Mm ^{2 to} 10000 kgf / mm ² , and the recovery rate after 10% compression deformation is preferably in the range of 1% to 100% at 20 ° C. This is because, by satisfying these physical property values, the electrodes can be sufficiently brought into contact with each other without being damaged when the electrodes are crimped together.

K value (kgf / mm ² ) = (3 / √2) × F × S ^−3/2 × R ^−1/2 (2)
F and S represented by the formula (2) are the load value (kgf) and compression in 10% compression deformation of the microsphere, respectively, when measured with a micro compression tester MCTM-500 (manufactured by Shimadzu Corporation). Displacement (mm), and R is the radius (mm) of the microsphere.

  It is preferable that the surface of the core particle is modified so that the surface thereof has a precious metal ion capturing ability or a precious metal ion capturing ability. The noble metal ions are preferably palladium or silver ions. Having a noble metal ion scavenging ability means that the noble metal ion can be captured as a chelate or salt. For example, when an amino group, an imino group, an amide group, an imide group, a cyano group, a hydroxyl group, a nitrile group, a carboxyl group, or the like is present on the surface of the core particle, the surface of the core particle is capable of capturing noble metal ions. Have In the case of modifying the surface so as to have the ability to trap noble metal ions, for example, a method described in JP-A-61-64882 can be used.

Using such core material particles, a noble metal is supported on the surface. Specifically, the core material particles are dispersed in a dilute acidic aqueous solution of a noble metal salt such as palladium chloride or silver nitrate. This traps noble metal ions on the surface of the particles. The concentration of the noble metal salt is sufficiently in the range of 1 × 10 ⁻⁷ to 1 × 10 ⁻² mol per 1 m ² of the particle surface area. The core particles in which the noble metal ions are captured are separated from the system and washed with water. Subsequently, the core material particles are suspended in water, and a reducing agent is added to the suspension so that noble metal ions are reduced. As a result, the noble metal is supported on the surface of the core particles. Examples of the reducing agent include sodium hypophosphite, sodium boron hydroxide, potassium borohydride, dimethylamine borane, hydrazine, formalin and the like.

  Before capturing the noble metal ions on the surface of the core material particles, a sensitization treatment for adsorbing the tin ions on the surface of the particles may be performed. In order to adsorb the tin ions on the surface of the particles, for example, the surface-treated core material particles may be put into an aqueous solution of stannous chloride and stirred for a predetermined time.

  The core material particles pretreated in this way are mixed with an electroless plating bath containing a dispersant and nickel ions. The electroless plating bath is a solution using water as a medium, and examples of the dispersant contained therein include nonionic surfactants, zwitterionic surfactants, and water-soluble polymers. As the nonionic surfactant, polyoxyalkylene ether surfactants such as polyethylene glycol, polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, and the like can be used. As the zwitterionic surfactant, a betaine surfactant such as alkyldimethylacetic acid betaine, alkyldimethylcarboxymethylacetic acid betaine, and alkyldimethylaminoacetic acid betaine can be used. As the water-soluble polymer, polyvinyl alcohol, polyvinyl pyrrolidinone, hydroxyethyl cellulose and the like can be used. The amount of the dispersant used is generally 0.5 to 30 g / L based on the volume of the liquid (electroless plating bath) although it depends on the type. In particular, the amount of the dispersant used is preferably in the range of 1 to 10 g / L with respect to the volume of the liquid (electroless plating bath) from the viewpoint of improving the adhesion of the nickel film.

  For nickel ions contained in the electroless plating bath, a water-soluble nickel salt is used as the nickel source. As the water-soluble nickel salt, nickel sulfate or nickel chloride can be used, but is not limited thereto. The concentration of nickel ions contained in the electroless plating bath is preferably 0.0001 to 0.008 mol / liter, particularly preferably 0.0001 to 0.005 mol / liter.

In addition to the above components, the electroless plating bath can contain a reducing agent. As the reducing agent, those similar to those used for the reduction of the noble metal ions described above can be used. The concentration of the reducing agent in the electroless plating bath is preferably 4 × 10 ^{−4 to} 2.0 mol / liter, particularly 2.0 × 10 ^{−3 to} 0.2 mol / liter.

  The electroless plating bath may further contain a complexing agent. By containing the complexing agent, an advantageous effect that the decomposition of the plating solution is suppressed is exhibited. Examples of the complexing agent include organic carboxylic acids or salts thereof such as citric acid, hydroxyacetic acid, tartaric acid, malic acid, lactic acid or gluconic acid, or alkali metal salts or ammonium salts thereof. These complexing agents can be used alone or in combination of two or more. The concentration of the complexing agent in the electroless plating bath is preferably 0.005 to 6 mol / liter, particularly preferably 0.01 to 3 mol / liter.

  There is no particular limitation on the method of mixing the pretreated core material particles and the electroless plating bath. For example, the electroless plating bath can be heated to a temperature at which nickel ions can be reduced, and the pretreated core material particles can be put into the electroless plating bath under this state. By this operation, nickel ions are reduced, and nickel produced by the reduction forms an initial thin film layer on the surface of the core material particles. The initial thin film layer is preferably formed to have a thickness of 0.1 to 10 nm, particularly 0.1 to 5 nm. At this point, the protrusion has not yet been formed.

An important point in the step A is the relationship between the amount of nickel ions contained in the electroless plating bath and the amount of core material particles to be introduced. Specifically, the total surface area for 1 liter of electroless plating bath whose nickel ion concentration is adjusted to 0.0001 to 0.008 mol / liter, preferably 0.0001 to 0.005 mol / liter. Is used in an amount of 1 to 15 m ² , particularly 2 to 8 m ² . Thereby, the initial thin film layer having the above-described thickness can be easily formed. In addition, by making the relationship between the amount of nickel ions and the amount of core material particles as described above, aggregation of the core material particles on which the initial thin film layer is formed can be effectively prevented. This is particularly effective when the particle diameter of the core material particles is small, for example, when the particle diameter is 3 μm or less.

  When the reduction of nickel ions is completed, the process B is then performed. The B process is performed after the A process, and the operation such as separation of the core particles having the nickel initial thin film layer obtained in the A process from the liquid is not performed. Therefore, the dispersant added in the step A remains in the aqueous slurry containing the core particles having the nickel initial thin film layer. In step B, nickel ions and a reducing agent are added over time to the aqueous slurry containing the core material particles having the nickel initial thin film layer obtained in step A and the dispersant used in step A. “Adding over time” is intended to exclude adding nickel ions and a reducing agent all at once, and adding nickel ions and a reducing agent continuously or intermittently over a certain period of time. Intended. In this case, the timing of adding the nickel ions and the reducing agent may be completely the same, or the addition of nickel ions may precede and the addition of the reducing agent may follow. The reverse is also possible. Further, at the end point of addition, the end of the addition of nickel ions may precede, and the end of the addition of the reducing agent may follow. The reverse is also possible.

  As the nickel source of nickel ions used in the B process, the same nickel source as used in the A process can be used. The same applies to the reducing agent.

  In step B, by reducing nickel ions, first, fine nickel core particles are generated in the liquid, and the core particles are attached to the surface of the core material particles having the nickel initial thin film layer obtained in step A. This is grown from the adhering core particles as a starting point to form a protrusion. By adopting this method, aggregation of particles can be effectively prevented, and a projection having an aspect ratio of 1 or more can be easily formed. On the other hand, in Patent Document 1 described in the background art section of the present specification, first, a nickel film is formed on the surface of the core material particles, and a nucleus that is a starting point of the formation of the protrusion is formed (No. 1). Then, the projection is formed by growing the nucleus in the next step (second step). In this method, since the concentration of nickel ions in the first step needs to be relatively high, particle aggregation tends to occur due to this. In addition, it is difficult to form a protrusion with a high aspect ratio.

  In the reduction of nickel ions in step B, it is important to maintain the aqueous slurry in a pH range in which the dispersing effect of the dispersant added in step A (this dispersant remains in step B) is exhibited. is there. Thereby, aggregation of particles can be effectively prevented. To adjust the pH, an acid such as various mineral acids or an alkali such as sodium hydroxide may be added to the aqueous slurry while monitoring the pH of the aqueous slurry. The pH adjustment range may be an appropriate value depending on the dispersant used. For example, when a nonionic surfactant is used as the dispersant, it is preferable to maintain the pH of the aqueous slurry in the range of 5 to 10. When using a zwitterionic surfactant as the dispersant, it is preferable to maintain the pH of the aqueous slurry in the range of 5-8. Even when a water-soluble polymer is used as the dispersant, it is preferable to maintain the pH of the aqueous slurry in the range of 5 to 8.

  In the reduction of nickel ions in step B, the amount of nickel ions and the amount of reducing agent added to the aqueous slurry are also important. As a result, it is possible to successfully form a projection having a high aspect ratio. As specific conditions, nickel ions and a reducing agent in an amount corresponding to the amount of precipitation of nickel per hour of 25 to 100 nm, preferably 40 to 60 nm are added to the aqueous slurry over time. By adopting such an addition condition, nickel precipitates preferentially occur in the core particles rather than the initial thin film layer, and a protrusion having a high aspect ratio is easily formed.

  In the addition of nickel ions and a reducing agent, the aqueous slurry may be heated to a predetermined temperature so that the reduction of nickel ions by the reducing agent proceeds smoothly. In the addition of nickel ions and a reducing agent, the aqueous slurry may be stirred so that the reduced nickel adheres uniformly.

  In this way, desired conductive particles are obtained. The conductive particles can be further subjected to post-treatment as necessary. Examples of the post-treatment include an electroless gold plating step or an electroless palladium plating step. By applying this step, a gold plating layer or a palladium plating layer is formed on the surface of the conductive particles. The gold plating layer can be formed according to a conventionally known electroless plating method. For example, by adding an electroless plating solution containing tetrasodium ethylenediaminetetraacetate, disodium citrate, and potassium gold cyanide and adjusted to pH with sodium hydroxide to an aqueous suspension of conductive particles, A plating layer can be formed.

  Moreover, formation of a palladium plating layer can be performed in accordance with a conventionally well-known electroless plating method. For example, reduction of water-soluble palladium compounds such as palladium chloride; hypophosphorous acid, phosphorous acid, formic acid, acetic acid, hydrazine, borohydride, amine borane compounds, or salts thereof into an aqueous suspension of conductive particles A conventional electroless palladium plating solution containing an agent; and a complexing agent, and a dispersant, a stabilizer, and a pH buffering agent are added as necessary. Then, while adjusting the pH with an acid such as hydrochloric acid or sulfuric acid or a base such as sodium hydroxide, reduction type electroless plating can be performed to form a palladium plating layer. Alternatively, a palladium ion source such as tetraamminepalladium salt, a complexing agent and, if necessary, a dispersing agent are added to an aqueous suspension of conductive particles, and substitution is performed using a substitution reaction between palladium ions and nickel ions. A palladium electroplating layer may be formed by performing mold electroless plating.

  In addition, it is preferable that the palladium plating layer does not substantially contain phosphorus or has a content reduced to 3% by weight or less from the viewpoint of excellent conductivity and electrical reliability. In order to form such a plating layer, for example, when substitutional electroless plating is performed or when reducing electroless plating is performed, a phosphorus-free reducing agent (for example, formic acid) may be used.

  As the dispersant used in the reduction-type electroless plating or the displacement-type electroless plating, the same dispersants as those exemplified in the aforementioned step A can be used. Moreover, as a common electroless palladium plating solution, you may use the commercial item available from Kojima Chemical Co., Ltd., Nippon Kanisen Co., Ltd., Chuo Chemical Industrial Co., Ltd., etc., for example.

  As another post-treatment, the conductive particles can be subjected to a pulverization step using a media mill such as a ball mill. By subjecting to this pulverization step, the weight occupied by the primary particles with respect to the weight of the conductive powder can be more easily set within the above-mentioned range in combination with the above-mentioned nickel ion reduction conditions.

  The conductive particles of the present invention thus obtained are, for example, conductive for connecting the electrodes of anisotropic conductive film (ACF), heat seal connector (HSC), and liquid crystal display panel to the circuit board of the driving LSI chip. It is suitably used as a material. In particular, the conductive powder of the present invention is suitably used as a conductive filler of a conductive adhesive.

  The conductive adhesive is preferably used as an anisotropic conductive adhesive that is disposed between two substrates on which a conductive base material is formed, and adheres and conducts the conductive base material by heating and pressing. . This anisotropic conductive adhesive contains the conductive particles of the present invention and an adhesive resin. Any adhesive resin can be used without particular limitation as long as it is insulative and used as an adhesive resin. Either a thermoplastic resin or a thermosetting resin may be used, and those that exhibit adhesive performance by heating are preferred. Examples of such an adhesive resin include a thermoplastic type, a thermosetting type, and an ultraviolet curing type. In addition, there are so-called semi-thermosetting types that exhibit intermediate properties between thermoplastic types and thermosetting types, combined types of thermosetting types and ultraviolet curing types, and the like. These adhesive resins can be appropriately selected according to the surface characteristics and usage pattern of the circuit board or the like to be attached. In particular, an adhesive resin including a thermosetting resin is preferable from the viewpoint of excellent material strength after bonding.

  Specific examples of the adhesive resin include ethylene-vinyl acetate copolymer, carboxyl-modified ethylene-vinyl acetate copolymer, ethylene-isobutyl acrylate copolymer, polyamide, polyimide, polyester, polyvinyl ether, polyvinyl butyral, and polyurethane. , SBS block copolymer, carboxyl-modified SBS copolymer, SIS copolymer, SEBS copolymer, maleic acid-modified SEBS copolymer, polybutadiene rubber, chloroprene rubber, carboxyl-modified chloroprene rubber, styrene-butadiene rubber, isobutylene- Isoprene copolymer, acrylonitrile-butadiene rubber (hereinafter referred to as NBR), carboxyl-modified NBR, amine-modified NBR, epoxy resin, epoxy ester resin, acrylic resin, phenol resin or Those obtained by one or more combinations selected from such recone resins those prepared as main agent. Of these, as the thermoplastic resin, styrene-butadiene rubber, SEBS, and the like are preferable because of their excellent reworkability. As the thermosetting resin, an epoxy resin is preferable. Of these, epoxy resins are most preferred because of their advantages of high adhesive strength, excellent heat resistance and electrical insulation, low melt viscosity, and connection at low pressure.

  As the epoxy resin, a generally used epoxy resin can be used as long as it is a polyvalent epoxy resin having two or more epoxy groups in one molecule. Specific examples include novolak resins such as phenol novolak and cresol novolak, polyhydric phenols such as bisphenol A, bisphenol F, bisphenol AD, resorcin, and bishydroxydiphenyl ether, ethylene glycol, neopentyl glycol, glycerin, and trimethylolpropane. Obtained by reacting polychlorohydric alcohols such as polypropylene glycol, polyamino compounds such as ethylenediamine, triethylenetetramine, and aniline, polycarboxyl compounds such as adipic acid, phthalic acid, and isophthalic acid with epichlorohydrin or 2-methylepichlorohydrin. A glycidyl type epoxy resin is exemplified. Moreover, aliphatic and alicyclic epoxy resins such as dicyclopentadiene epoxide and butadiene dimer epoxide are listed. These can be used alone or in admixture of two or more.

  In addition, it is preferable from the viewpoint of prevention of ion migration that the various adhesive resins described above use high-purity products in which impurity ions (such as Na and Cl) and hydrolyzable chlorine are reduced.

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

  In addition to the above-described conductive particles and adhesive resin, the anisotropic conductive adhesive can be blended with known additives in the technical field, and the blending amount is also known in the technical field. Can be within range. Other additives include, for example, tackifiers, reactive auxiliaries, epoxy resin curing agents, metal oxides, photoinitiators, sensitizers, curing agents, vulcanizing agents, deterioration inhibitors, heat resistant additives, heat Examples thereof include a conductivity improver, a softener, a colorant, various coupling agents, or a metal deactivator.

  Examples of the tackifier include rosin, rosin derivatives, terpene resins, terpene phenol resins, petroleum resins, coumarone-indene resins, styrene resins, isoprene resins, alkylphenol resins, xylene resins and the like. Examples of the reactive assistant, that is, the crosslinking agent include polyols, isocyanates, melamine resins, urea resins, utropines, amines, acid anhydrides and peroxides. As an epoxy resin hardening | curing agent, if it has two or more active hydrogens in 1 molecule, it can be especially used without a restriction | limiting. Specific examples include polyamino compounds such as diethylenetriamine, triethylenetetramine, metaphenylenediamine, dicyandiamide, and polyamideamine; organic acid anhydrides such as phthalic anhydride, methyl nadic anhydride, hexahydrophthalic anhydride, and pyromellitic anhydride. Products: novolak resins such as phenol novolac and cresol novolak. These can be used alone or in admixture of two or more. Moreover, you may use a latent hardening | curing agent as needed and a use. Examples of latent curing agents that can be used include imidazole series, hydrazide series, boron trifluoride-amine complexes, sulfonium salts, amine imides, polyamine salts, dicyandiamide, and the like and modified products thereof. These can be used alone or as a mixture of two or more.

  The anisotropic conductive adhesive is usually prepared by using a manufacturing apparatus widely used among those skilled in the art, and blends the conductive particles and adhesive resin of the present invention and, if necessary, curing agents and various additives, In the case where the adhesive resin is a thermosetting resin, by mixing in an organic solvent, in the case of a thermoplastic resin, at a temperature equal to or higher than the softening point of the adhesive resin, specifically preferably about 50 to 130 ° C, More preferably, it is produced by melt-kneading at about 60 to 110 ° C. The anisotropic conductive adhesive thus obtained may be applied or applied in the form of a film.

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

[Examples 1 to 4]
(1) Process A Spherical styrene-silica composite resin (trade name: Soliostar, manufactured by Nippon Shokubai Co., Ltd.) having a particle size shown in Table 1 and a true specific gravity of 1.1 was used as the core material particles. 40 g of the solution was added to 400 mL of an aqueous conditioner solution (“Cleaner Conditioner 231” manufactured by Rohm and Haas Electronic Materials) with stirring. The concentration of the conditioner aqueous solution was 40 ml / L. Subsequently, the core material particles were surface-modified and dispersed by stirring for 30 minutes while applying ultrasonic waves at a liquid temperature of 60 ° C. The aqueous solution was filtered, and the core particles washed once with repulp water were made into 200 mL of slurry. 200 ml of stannous chloride aqueous solution was added to this slurry. The concentration of this aqueous solution was 5 × 10 ⁻³ mol / L. The mixture was stirred at room temperature for 5 minutes to carry out a sensitization treatment for adsorbing tin ions on the surface of the core material particles. Subsequently, the aqueous solution was filtered and washed once with repulp water. The core particles were then made into 400 ml slurry and maintained at 60 ° C. While stirring the slurry using ultrasonic waves, 2 mL of a 0.11 mol / L palladium chloride aqueous solution was added. The state of stirring as it was was maintained for 5 minutes, and an activation treatment for capturing palladium ions on the surface of the core particles was performed.

  Next, 20 g / L sodium tartrate, 5.4 g / L sodium hypophosphite, nickel sulfate hexahydrate having the concentrations shown in Table 1, and an aqueous solution in which the dispersants having the types and concentrations shown in the table were dissolved. The temperature of 3 liters of the electroless plating bath was raised to 70 ° C., and core particles carrying palladium were added to the electroless plating bath in the amount shown in the table, and the process A was started. The specific contents of the dispersant shown in Table 1 are as shown in Table 2. After stirring for 5 minutes, it was confirmed that hydrogen bubbling stopped and Step A was completed.

(2) Step B Using a 224 g / L nickel sulfate aqueous solution and a mixed aqueous solution containing 210 g / L sodium hypophosphite and 80 g / L sodium hydroxide, 300 mL each, and using these in step A, the core material obtained The particle slurry was continuously fractionated and added by a metering pump, and the electroless plating B process was started. The addition rate was 2.5 mL / min. Specific conditions of this step are shown in Table 3. After all the liquid was added, stirring was continued for 5 minutes while maintaining the temperature at 70 ° C. Next, the liquid was filtered, and the filtrate was washed three times, and then dried with a vacuum dryer at 100 ° C. to obtain conductive particles having a nickel-phosphorus alloy film. A scanning electron microscope (SEM) image of the conductive particles obtained in Example 3 is shown in FIG. As is clear from the figure, the nickel coating and the protrusions on the conductive particles are continuous.

[Examples 5 to 23]
Conductive particles were obtained in the same manner as in Example 1 except that Step A and Step B were performed under the conditions shown in Tables 1 and 3. However, in B process of Example 19, the addition amount of nickel sulfate aqueous solution and the mixed aqueous solution containing sodium hypophosphite and sodium hydroxide was 230 mL, respectively. Moreover, in B process of Example 20, the addition amount of nickel sulfate aqueous solution and the mixed aqueous solution containing sodium hypophosphite and sodium hydroxide was 390 mL, respectively. Moreover, the addition amount and dropping rate of the aqueous nickel sulfate solution of Examples 21 to 23 and the mixed aqueous solution containing sodium hypophosphite and sodium hydroxide were 150, 225, 600 mL, 1.3, 1.9, and 5.0 mL, respectively. / Min. Thus, conductive particles having a nickel-phosphorus alloy film were obtained.

Example 24
An electroless gold plating solution consisting of 10 g / L EDTA-4Na, 10 g / L citric acid-2Na and 2.9 g / L potassium gold cyanide (2.0 g / L as Au) was prepared. 2 g of this gold plating solution was heated to 79 ° C., and 10 g of conductive particles obtained in Example 2 were added while stirring the solution. Thus, electroless plating treatment was performed on the surface of the particles. The processing time was 20 minutes. After completion of the treatment, the liquid was filtered and the filtrate was repulped three times. Subsequently, it dried with the 110 degreeC vacuum dryer. In this way, a gold plating coating treatment was performed on the nickel-phosphorus alloy film.

[Examples 25 to 27]
10 g / L EDTA-2Na, 10 g / L 2 Na citrate and 20 g / L tetraamminepalladium hydrochloride (Pd (NH ₃ ) 4 Cl ₂ ) solution (2 g / L as palladium), carboxymethylcellulose (molecular weight 250,000, etherification) Degree 0.9) An electroless palladium plating solution consisting of 100 ppm was prepared. In this example, 0.65 liters (Example 25), 1.3 liters (Example 26 ) and 2.6 liters (Example 27) of this palladium plating solution were heated to 70 ° C. and stirred. 10 g of the obtained conductive particles were added. As a result, a substitutional electroless plating treatment was performed on the surface of the particles. The processing time was 60 minutes. After completion of the treatment, the liquid was filtered and the filtrate was repulped three times. Subsequently, it dried with the 110 degreeC vacuum dryer. In this way, the palladium plating coating treatment was performed on the nickel-phosphorus alloy film. The palladium film contained no phosphorus.

[Comparative Examples 1 to 7]
Conductive particles having a nickel-phosphorus alloy film were obtained in the same manner as in Example 1 except that Step A and Step B were performed under the conditions shown in Tables 1 and 3. However, in B process of the comparative example 3, the addition amount of nickel sulfate aqueous solution and the mixed aqueous solution containing sodium hypophosphite and sodium hydroxide was 230 mL, respectively. Moreover, the addition amount and dropping rate of the aqueous nickel sulfate solution of Comparative Examples 5 to 6 and the mixed aqueous solution containing sodium hypophosphite and sodium hydroxide were 38, 1200 mL, 0.3, 10.0 mL / min, respectively. An SEM image of the conductive particles obtained in Comparative Example 1 is shown in FIG.

[Comparative Example 8]
The conductive particles produced in Comparative Example 2 were subjected to the same gold plating coating treatment as in Example 24.

〔Evaluation of the physical properties〕
The particle diameter of the conductive particles, the thickness of the nickel coating, the thickness of the gold coating, the thickness of the palladium coating, the surface state, the adhesion of the nickel coating, and the conductivity were measured and evaluated, respectively. Further, the gold plating was evaluated for the gold film, and the palladium plating was evaluated for the palladium film. Each physical property evaluation was performed by the following method. Further, the aspect ratio of the protrusions, the ratio of the protrusions having an aspect ratio of 1 or more, the ratio of the primary particles in the conductive powder, and the particle diameter of the conductive particles were measured by the methods described above. The results are shown in Tables 4 and 5.

[Thickness of nickel coating]
The conductive particles were immersed in aqua regia to dissolve the nickel film, the film components were analyzed by ICP or chemical analysis, and the thickness of the nickel film was calculated from the following formulas (1) and (2).
A = [(r + t) ³ −r ³ ] d ₁ / r ³ d ₂ (1)
A = W / (100-W) (2)
In the formula, r is the radius (μm) of the core particles, t is the thickness of the nickel coating, d ₁ is the specific gravity of the nickel coating, d ₂ is the specific gravity of the core particles, and W is the nickel content (% by weight).

[Gold film / palladium film thickness]
The conductive particles were immersed in aqua regia to dissolve the gold or palladium film and the nickel film, and the film components were analyzed by ICP or chemical analysis. And the thickness of the gold | metal | money or palladium membrane | film | coat was computed from the following (3) and (4).
B = [(r + t + u) ³ − (r + t) ³ ] d ₃ / (r + t) ³ d ₄ (3)
B = X (100-X) (4)
In the formula, u is the thickness of the gold or palladium film, d ₃ is the specific gravity of the gold or palladium film, d ₄ is the specific gravity of the Ni product, and X is the content (% by weight) of gold or palladium. Here, the specific gravity d ₄ of the Ni product is calculated using a calculation formula. The specific gravity was calculated using the following formula (5).
d ₄ = 100 / [(W / d ₁ ) + (100−W) / d ₂ ] (5)
In the formula, d ₁ is the specific gravity of the nickel coating, d ₂ is the specific gravity of the core particles, and W is the nickel content (% by weight).

〔Surface condition〕
Using SEM, the conductive particles were magnified 30000 times, 10 fields of view were observed, and the average value of the number of protrusions of one conductive particle was calculated. 10 to 100 pieces were evaluated as ◯, and 10 or less as △. In addition, the case where nickel was abnormally deposited was marked as x. Abnormal precipitation refers to, for example, the case where nickel does not precipitate on the surface of the core material particles but separates in the liquid.

[Coating adhesion]
In a 100 mL beaker, 2 g of conductive particles and 90 g of zirconia beads having a diameter of 1 mm were added, and further 10 mL of toluene was added. After stirring for 10 minutes with a stirrer, the zirconia beads and the slurry were separated and dried. The dried conductive particles were magnified 2000 times using SEM, 10 fields were observed, and the average value of the number of peeled pieces generated by stirring was calculated. The number of peeled pieces of less than 10 was evaluated as ◯, 10-30 as Δ, and more than 30 as X.

〔Conductivity〕
100 parts of epoxy resin, 150 parts of curing agent, and 70 parts of toluene were mixed to prepare an insulating adhesive. This was mixed with 15 parts of conductive particles to obtain a paste. This paste was applied onto a silicone-treated polyester film and dried using a bar coater. Using the obtained coated film, connection was made between glass whose surface was vapor-deposited with aluminum and a polyimide film substrate having a copper pattern formed on a 50 μm pitch. And the electroconductivity of electroconductive particle was evaluated by measuring the conduction | electrical_connection resistance between electrodes. In the evaluation, a resistance value of 2Ω or less was evaluated as ◯, 2-5Ω was evaluated as Δ, and 5Ω or more was evaluated as ×. In addition, the presence or absence of short circuit is also shown in the table.

  As is clear from the results shown in Tables 4 and 5, the conductive powder obtained in each example (the product of the present invention) has an aspect ratio of protrusions compared to the conductive powder obtained in the comparative example. It can be seen that the ratio of primary particles is high. Moreover, it turns out that the electroconductive powder obtained by each Example has high electroconductivity and the adhesiveness of a nickel membrane | film | coat compared with the electroconductive powder obtained by the comparative example.

4 is a SEM image of conductive particles obtained in Example 3. 3 is a SEM image of conductive particles obtained in Comparative Example 1.

Claims (7)

Conductive powder composed of conductive particles in which nickel or a nickel alloy film is formed on the surface of the core material particles,
The conductive particles protrude from the surface of the coating and are continuous with the coating, and have a large number of protrusions with an aspect ratio of 1 or more,
The aspect ratio is a value defined by the ratio H / D between the height H of the protrusion and the width D of the protrusion at the base of the protrusion,
The ratio of the protrusions having an aspect ratio of 1 or more is 40% or more with respect to the total number of protrusions,
Wherein in the conductive powder, of the conductive particles, the weight occupied primary particles is state, and are 85 wt% or more based on the weight of the conductive powder,
The weight ratio occupied by the primary particles was calculated from the results obtained by placing 0.1 g of the conductive powder in 100 mL of water and dispersing with an ultrasonic homogenizer for 1 minute, then measuring the particle size distribution by the Coulter counter method. electrically conductive powder, wherein Monodea Rukoto.   The conductive powder according to claim 1, wherein the core particles have an average particle size of 1 to 3 μm.   The conductive powder according to claim 1 or 2, wherein the surface of the coating including the protrusion is coated with gold or palladium.   A conductive material comprising the conductive powder according to claim 1 and an insulating resin. When the electroless plating bath containing a dispersant and nickel ions is mixed with the core material particles having a noble metal supported on the surface, and the nickel initial thin film layer is formed on the surface of the core material particles, the concentration of nickel ions is Step A using the core material particles in such an amount that the total surface area is 1 to 15 m ² with respect to 1 liter of the electroless plating bath adjusted to 0.0001 to 0.008 mol / liter;
While maintaining the aqueous slurry containing the core particles having the nickel initial thin film layer and the dispersant obtained in the step A in a pH range in which the dispersing effect of the dispersant is expressed, Nickel ions and a reducing agent in an amount corresponding to the amount of nickel deposited per hour corresponding to a nickel film thickness of 25 to 100 nm are added over time to produce nickel core particles in the aqueous slurry. And the B step of attaching the produced core particles to the core material particles, growing the core particles starting from the attached core particles, and forming a protrusion having an aspect ratio of 1 or more ,
The aspect ratio is a value defined by the ratio H / D between the height H of the protrusion and the width D of the protrusion at the base of the protrusion,
The thickness of the nickel coating, the conductive particles are immersed in aqua regia to dissolve the nickel coating, the coating ingredients ICP or chemical analysis, Ru der those calculated from the following equation (1) and (2) The manufacturing method of the electroconductive particle characterized by the above-mentioned.
A = [(r + t) ³ −r ³ ] d ₁ / r ³ d ₂ (1)
A = W / (100-W) (2)
(Wherein, r is the radius (μm) of the core material particles, t is the thickness of the nickel film, d ₁ is the specific gravity of the nickel film, d ₂ is the specific gravity of the core material particles, and W is the nickel content (% by weight)). .)   The manufacturing method of Claim 5 which performs A process so that the thickness of a nickel initial stage thin film layer may be set to 0.1-10 nm.   The production method according to claim 5 or 6, wherein a nonionic surfactant, an amphoteric surfactant or a water-soluble polymer is used as the dispersant.