CN102187405B - Conductive powdery material, conductive material containing same, and method for manufacturing conductive particles - Google Patents

Abstract

Provided is a conductive powdery material having excellent dispersibility and conductivity, even though the particle diameter of the conductive powdery material is smaller than the particle diameters of conventional conductive powdery materials. The conductive powdery material is composed of conductive particles each of which has a nickel film or a nickel alloy film formed on the surface of a core particle. The conductive particle has many protruding sections, each of which protrudes from the surface of the film, is formed continuous to the film, and has an aspect ratio of 1 or more. The ratio of the protruding sections having an aspect ratio of 1 or more is 40% or higher with respect to the total number of protruding sections. As for the conductive powdery material, the weight of the primary particles among the conductive particles is 85 wt% or more with respect to the weight of the conductive powdery material.

Description

Conductive powder, conductive material containing the same, and method for producing conductive particles

technical field

The present invention relates to an electroconductive powder and an electroconductive material containing the electroconductive powder. Moreover, this invention relates to the manufacturing method of electroconductive particle.

Background technique

The present applicant has previously proposed a conductive electroless plating powder body having minute protrusions formed of nickel or a nickel alloy on the surface (see Patent Document 1). The electroless plating particles in the powder exhibit good electrical conductivity through the function of their tiny protrusions. The electroless plated particles pass through the electroless plating process (A process) in which the aqueous slurry of the spherical core material is added to an electroless plating bath containing nickel salt, reducing agent, complexing agent, etc., and the aqueous slurry of the spherical core material In the slurry, the constituent components of the electroless plating solution are separated into at least two kinds of liquids, and the electroless plating process (B process) of adding them separately over time is produced. In this production method, in the A step, a nickel coating is formed on the surface of the core material particle, and at the same time, nuclei serving as origins of protrusions are formed. This nucleus grows in step B to form a protrusion. The thus-obtained electroless plated particles can be suitably used, for example, in conductive adhesives, anisotropic conductive films, anisotropic conductive adhesives, and the like for electrically bonding opposing connecting circuits.

In addition to this technology, Patent Document 2 proposes to attach a nickel core substance with a particle diameter of 50 nm to the surface of a core material particle with a particle diameter of 4 μm, followed by electroless plating of nickel to obtain conductive particles having protrusions. method. However, in this method, since the adhesion between the core particle and the nickel core substance is weak, the integrity of the nickel layer covering the surface of the core particle and the protrusions is insufficient, and when pressure is applied to the conductive particles, the protrusions Easy to break. In addition, it is very difficult to uniformly adhere a 50 nm nickel core substance which is very smaller than the particle diameter to the surface of the core material particle with a particle diameter of 4 μm. This is because the aggregation of the nickel core substances occurs more easily than the adhesion of the nickel core substances on the surface of the core material particles. As a result, aggregated particles with a large particle size formed by agglomerating the nickel core substances tend to adhere to the surface of the core material particles, and very large protrusions are likely to be formed.

In addition, as electronic devices have become more miniaturized in recent years, the circuit width and pitch of electronic circuits have become smaller and smaller. Along with this, the electroless plating powder used for the above-mentioned conductive adhesive, anisotropic conductive film, anisotropic conductive adhesive, etc. is required to have a small particle size. However, if the particle size of the particles is reduced, aggregation of the particles tends to occur. Therefore, even if particles with a small particle size are used, the apparent particle size (secondary particle size) increases due to aggregation. In addition, when using particles with a small particle size, it is more difficult to improve conductivity (reduce electrical resistance) than when using large particles.

prior art literature

patent documents

Patent Document 1: Japanese Patent Laid-Open No. 2000-243132

Patent Document 2: Japanese Patent Laid-Open No. 2006-228474

Contents of the invention

The problem to be solved by the invention

Therefore, an object of the present invention is to provide an electroconductive powder having various properties further improved than the above-mentioned conventional electroconductive powder.

Solution to the problem

In order to achieve the above object, the inventors of the present invention conducted intensive research and found that when using conductive particles having the same degree of dispersibility as before and having a smaller particle size than before, the protrusions formed on the surface can The shape is longer than before, which can suppress the decrease of electrical conductivity.

The present invention is based on the above findings, and provides a conductive powder characterized in that the conductive powder is formed of conductive particles coated with nickel or nickel alloy on the surface of the core particle. body, the above-mentioned conductive particles have a plurality of protrusions protruding from the surface of the above-mentioned coating and forming a continuum with the coating with an aspect ratio of 1 or more, and the proportion of the above-mentioned protrusions with an aspect ratio of 1 or more is relative to The number of all protrusions is 40% or more, and in the conductive powder, the weight of the primary particles in the conductive particles is 85% by weight or more with respect to the weight of the conductive powder.

In addition, the present invention provides a method for producing conductive particles, which is characterized in that it includes: Step A, mixing an electroless plating bath containing a dispersant and nickel ions with core material particles on which precious metals are loaded on the surface. When an initial nickel thin film layer is formed on the surface of the material particle, the core material particle is used in an amount whose total surface area is 1 to 15 m ² with respect to the electroless plating bath whose nickel ion concentration is adjusted to 0.0001 to 0.008 mol/liter in 1 liter. and the B process, the aqueous slurry comprising the above-mentioned core material particles with the nickel initial film layer and the above-mentioned dispersant obtained in the A process is maintained at the pH range showing the dispersion effect of the dispersant, and in the aqueous Nickel ions and a reducing agent are added to the slurry in an amount corresponding to a nickel precipitation amount of 25 to 100 nm per hour, and nickel core particles are generated in the aqueous slurry, and the generated core particles are attached to the core On the material particle, the core particle is grown with the attached core particle as a starting point to form a protrusion having an aspect ratio of 1 or more.

The effect of the invention

The conductive powder of the present invention not only has a particle size of conductive particles constituting the conductive powder smaller than conventional ones, but also has good dispersibility and conductivity. Moreover, according to the manufacturing method of this invention, such electroconductive powder can be manufactured easily.

Description of drawings

FIG. 1 is an SEM image of conductive particles obtained in Example 3. FIG.

FIG. 2 is a SEM image of conductive particles obtained in Comparative Example 1. FIG.

Detailed ways

Hereinafter, it is demonstrated based on preferable embodiment of this invention. The conductive powder of the present invention is a conductive powder in which a nickel coating or a nickel alloy coating (hereinafter these coatings are collectively referred to as "nickel coating") is formed on the surface of the core particle. One of the characteristics of the conductive powder of the present invention is that it has a plurality of protrusions protruding from the surface of the nickel coating. Hereinafter, this protruding portion will be described.

Forming a plurality of protrusions on the surface of an electroconductive powder is a well-known technique in this technical field as described in the background art section of this specification. Against such background art, the present invention is significantly different from conventional conductive powders in that a protrusion having a specific shape is used as the protrusion. Specifically, the protrusions in the conductive powder of the present invention are characterized by having an aspect ratio of 1 or more. The aspect ratio in this specification refers to the ratio of the height H of the protrusion to the width D of the protrusion at the base of the protrusion, that is, it is a value defined by H/D. From this definition, it can be seen that the aspect ratio is a measure of the slenderness of the protrusion, and that the larger the value, the more slender the shape of the protrusion.

The aspect ratio of the protrusions in the conventional conductive powder having protrusions is not easy to manufacture within the limits known to the present inventors, including Patent Document 1 described in the background art section of this specification. become more than 1. The protrusions in the conventional conductive powder have a so-called short and thick shape (for example, refer to FIG. 2 described later). On the other hand, the protrusions in the conductive powder of the present invention are, for example, elongated protrusions extending substantially radially from the particle surface, as shown in FIG. 1 described later. The inventors of the present invention studied the aspect ratio to the protrusion and found that by setting this value to 1 or more, that is, by making the shape of the protrusion more slender than conventional, the conductivity becomes very high. The reason is considered to be that when the conductive powder of the present invention is used to conduct a conductive electrode, when a thin oxide film is naturally formed on the surface of the electrode or an oxide film of the electrode is intentionally formed, if the aspect ratio of the protrusion is large, then It is easy to break through the oxide film. In addition, it is considered that when the anisotropic conductive film is formed using conductive powder, if the aspect ratio of the protrusion is large, the resin repellency becomes high, and thus the conductivity becomes high. For this reason, it is also considered that if the value of the aspect ratio of the protrusion is too large, the protrusion will be damaged, so the preferred range of the aspect ratio is 1.0 to 4.0, more preferably 1.0 to 3.5, and even more preferably 1.0 to 3.0 . The electroconductive particle which has such a protrusion part with a large aspect ratio can be manufactured by the method mentioned later, for example.

When focusing on individual particles in the conductive powder, it is ideal that the aspect ratios of the protrusions of each particle satisfy the above-mentioned range. Sufficient conductivity can be obtained when the number of protrusions is 40% or more, preferably 45% or more, and more preferably 50% or more relative to the total number of protrusions.

The measuring method of the said aspect ratio is as follows. Use an electron microscope to magnify and observe individual particles in the conductive powder. For one particle, the base length D and height H are measured for at least one protrusion. In this case, it is more important to measure the protrusions present in the periphery of the particle rather than the protrusions present in the center of the particle in the observed image, which is important for accurate size measurement. Such determinations are made with at least 20 different particles as objects. The arithmetic mean of the plurality of aspect ratio data obtained in this way is taken as the aspect ratio. In addition, as shown in FIG. 1 described later, since the cross section of the protrusion has a shape with small anisotropy (for example, a substantially circular shape), the numerical value of the base length D of the protrusion is less likely to change depending on the viewing angle of the particle. Small.

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

The number of protrusions with an aspect ratio of 1 or more in each particle of the conductive powder also depends on the particle size. As described later, when the particle size is 3 μm or less, the conductivity of the conductive powder is improved. From the viewpoint of improvement, it is preferable to have 2 to 40 protrusions per particle, and particularly preferably 2 to 20 protrusions.

Each protrusion in the conductive powder and the nickel coating covering the core particles form a continuum. Therefore, the protrusions and the nickel coating are also made of nickel or nickel alloy. Here, the term "continuous body" means that the nickel coating and the protrusions are entirely made of the same material, the protrusions are formed in a single process, and there is no seam between the nickel coating and the protrusions, which impairs the overall feeling. parts. Therefore, for example, a nickel coating is formed on the surface of the core material particle, a core particle for forming a protrusion is attached thereto, and the protrusion formed by using the core particle as a starting point for growth is not formed by a single process. , so it is not included in the continuum mentioned in the present invention. Since the protrusions and the nickel coating are formed as a continuous body, the strength of the protrusions is ensured. Therefore, when using conductive powder, the protrusions will not be damaged even if pressure is applied. As a result, good conductivity can be obtained.

Regarding the thickness of the nickel coating, if it is too thin, it will be difficult for the electroconductive powder to exhibit sufficient conductivity. On the contrary, if it is too thick, it will be easily peeled off from the surface of the core particle. From these viewpoints, the thickness of the nickel coating (the thickness of the portion where the protrusion does not exist) is preferably 0.01 to 0.3 μm, more preferably 0.05 to 0.2 μm. The thickness of the nickel coating can be obtained by dissolving nickel from the conductive powder and quantifying the dissolved nickel. In addition, according to this method, not only the nickel coating but also the nickel in the protrusions are dissolved, but since the ratio of the protrusions to the whole nickel is very low, the amount of nickel in the protrusions can be ignored.

In the conductive powder of the present invention, the shape of each particle is preferably spherical. The particle shape mentioned here refers to the particle shape excluding protrusions. The conductive powder of the present invention has high conductivity because the particles are spherical and have protrusions.

In the conductive powder of the present invention, the size of each particle can be appropriately set according to the specific use of the conductive powder. As a result of studies conducted by the inventors of the present invention, it has been determined that conductive particles having a smaller particle size have higher conductivity due to the relationship of the aspect ratio of the above-mentioned protrusions. Specifically, the particle size of the conductive particles is preferably 1 to 10 μm, particularly preferably 1 to 5 μm, and especially preferably 1 to 3 μm. In addition, the particle diameter of electroconductive particle does not include the height of a protrusion. The particle diameter of electroconductive particle can be measured by electron microscope observation. In addition, it is also possible to measure the particle diameter of the core particle and the thickness of the nickel coating, respectively, and obtain it from these values.

When the particle diameter of electroconductive particle is small, it exists in the tendency which aggregates easily. If aggregation occurs, the anisotropic conductive film using conductive particles has a disadvantage that short circuits are likely to occur. In addition, when treatment such as pulverization is performed to loosen the aggregation, the nickel coating is peeled off, which causes a decrease in electrical conductivity. From this point of view, 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 of 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. In order to improve the dispersibility of electroconductive particle, what is necessary is just to manufacture electroconductive particle by the method mentioned later, for example. The weight occupied by the primary particles is measured according to the method described below. Add 0.1 g of conductive powder to 100 mL of water, and disperse for 1 minute using an ultrasonic homogenizer. Next, the particle size distribution was measured by the Coulter counter method. From this result, the weight ratio of the primary particles was calculated.

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

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

Next, a suitable production method of the conductive powder of the present invention will be described. This production method is roughly divided into two steps: (1) A step of forming an initial thin film layer of nickel on the surface of the core particle, and (2) a step B of forming the target conductive particles using the particles obtained in A step as a raw material. process. Hereinafter, these steps will be described respectively.

In the step A, an electroless plating bath containing a dispersant and nickel ions is mixed with core particles having noble metals supported on their surfaces to form a primary nickel thin film layer on the surfaces of the core particles. The type of core particles is not particularly limited, and either organic or inorganic can be used. In consideration of the electroless plating method described later, the core particles are preferably water-dispersible particles. Therefore, the core particles are preferably substantially insoluble in water, and more preferably insoluble or denatured by acid and alkali. The term "water-dispersible" means that a suspension that can be substantially dispersed in water can be formed by ordinary 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 coating covering the surface of the core particle is thin, the shape of the core particle almost directly reflects the shape of the conductive particle. Since the conductive particles are preferably spherical as described above, the shape of the core particles is also preferably spherical.

When the core particle is spherical, the particle diameter of the core particle has a great influence on the particle diameter of the target conductive particle. As mentioned above, since the thickness of the nickel film covering the surface of the core particle is relatively thin, the particle size of the core particle basically directly reflects the particle size of the conductive particle. From this point of view, the particle diameter of the core particle may be about the same as the particle diameter of the target conductive particle. Specifically, it is preferably 1 to 10 μm, particularly preferably 1 to 5 μm, and especially preferably 1 to 3 μm. The particle size of the core particle can be measured by the same method as the particle size of the conductive particle.

The particle size distribution of the core material powder measured by the above method has a certain width. In general, the width of the powder particle size distribution is represented by a coefficient of variation represented by the following formula (1).

Coefficient of variation (%) = (standard deviation / average particle size) × 100 ... (1)

A large coefficient of variation indicates a broad distribution, while a small coefficient of variation indicates a sharp particle size distribution. In the present invention, as the core particle, it is preferable to use a material whose coefficient of variation is 30% or less, particularly preferably 20% or less, and especially preferably 10% or less. The reason for this is that when the conductive particles of the present invention are used as the conductive particles in the anisotropic conductive film, there is an advantage of increasing the ratio of effective participation in connection.

Specific examples of core material powders include metals (including alloys), glass, ceramics, silicon dioxide, carbon, metal or nonmetal oxides (including hydrates), and aluminosilicates as inorganic substances. Salts of metal silicates, metal carbides, metal nitrides, metal carbonates, metal sulfates, metal phosphates, metal sulfides, metal salts, metal halides and carbon, etc. Examples of organic substances include natural fibers, natural resins, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polybutene, polyamide, polyacrylate, polyacrylonitrile, polyacetal, ionomer, polyester Such as thermoplastic resin, alkyd resin, phenolic resin, urea resin, melamine resin, benzoguanamine resin, melamine resin, xylene resin, silicone resin, epoxy resin or diallyl phthalate resin, etc. . These may be used individually or as a mixture of 2 or more types.

In addition, other physical properties of the core particles are not particularly limited, but when the core particles are resin particles, the K value defined by the following formula (2) is preferably in the range of 10kgf/mm ² to 10000kgf/mm ² at 20°C , and the recovery rate after 10% compression deformation is preferably in the range of 1% to 100% at 20°C. By satisfying these physical property values, when the electrodes are crimped together, the electrodes can be sufficiently contacted without damaging the electrodes.

F and S shown in formula (2) are the load values (kgf) at the time of 10% compression deformation of the microspheres when measured using a micro-compression testing machine MCTM-500 (manufactured by Shimadzu Corporation). and compression displacement (mm), R is the radius (mm) of the microsphere.

The core particle is preferably a particle having a noble metal ion capturing ability on its surface, or a particle whose surface has been modified so as to have a noble metal ion capturing ability. The noble metal ion is preferably an ion of palladium or silver. Having the ability to capture noble metal ions means that noble metal ions can be captured as chelates or salts. For example, when there are amino groups, imino groups, amide groups, imide groups, cyano groups, hydroxyl groups, nitro groups, carboxyl groups, etc. on the surface of the core particle, the surface of the core particle has the ability to capture noble metal ions. When modifying the surface to have the ability to capture noble metal ions, for example, the method described in JP-A-61-64882 can be used.

Such core material particles are used so that noble metals are supported on the surface. Specifically, core particles are dispersed in a dilute acidic aqueous solution of a noble metal salt such as palladium chloride or silver nitrate. Thereby, noble metal ions are captured on the surface of the particles. The concentration of the noble metal salt is sufficient to be in the range of 1×10 ^-7 to 1×10 ^-2 mol per 1 m ² of particle surface area. The core particles that have captured the noble metal ions are separated from the system and washed with water. Next, the core material particles are suspended in water, and a reducing agent is added thereto to perform reduction treatment of noble metal ions. Thus, the noble metal is supported on the surface of the core particle. As the reducing agent, for example, sodium hypophosphite, sodium borohydride, potassium borohydride, dimethylamine borane, hydrazine, formalin or the like can be used.

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

The core particle thus pretreated is mixed with an electroless plating bath containing a dispersant and nickel ions. The electroless nickel plating bath is a solution in which water is used as a medium, and examples of the dispersant contained therein include nonionic surfactants, zwitterionic surfactants, and/or water-soluble polymers. As the nonionic surfactant, polyoxyalkylene ether-based surfactants such as polyethylene glycol, polyoxyethylene alkyl ether, and polyoxyethylene alkylphenyl ether can be used. As the zwitterionic surfactants, surface-active surfactants of betalines such as alkyldimethylcarboxymethylacetate, alkyldimethylaminoacetic acid betaine, etc., can be used. agent. As the water-soluble polymer, polyvinyl alcohol, polyvinylpyrrolidone, hydroxyethylcellulose and the like can be used. The usage-amount of a dispersant depends on its kind, but generally, it is 0.5-30 g/L with respect to the volume of liquid (electroless nickel plating bath). In particular, when the usage-amount of a dispersing agent is the range of 1-10 g/L with respect to the volume of liquid (electroless nickel plating bath), since the adhesiveness of a nickel coating improves, it is preferable from this point.

The nickel ions contained in the electroless nickel plating bath can use a water-soluble nickel salt as its 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 nickel plating bath is preferably 0.0001 to 0.008 mol/liter, particularly preferably 0.0001 to 0.005 mol/liter.

In the electroless plating bath, a reducing agent may be contained in addition to the above components. As the reducing agent, the same reducing agent as that used for the reduction of the above-mentioned noble metal ion 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 preferably 2.0×10 ^-3 to 0.2 mol/liter.

In the electroless nickel plating bath, a complexing agent may be further contained. By containing a complexing agent, it can exert the beneficial effect of suppressing the decomposition of the plating solution. As complexing agents, organic carboxylic acids or salts thereof such as citric acid, glycolic acid, tartaric acid, malic acid, lactic acid or gluconic acid or alkali metal or ammonium salts thereof may be cited. These complexing agents can be used 1 type or 2 or more types. 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.

The method of mixing the pretreated core particle and the electroless nickel plating bath is not particularly limited. For example, the electroless nickel plating bath can be heated in advance to a temperature at which nickel ions can be reduced, and in this state, pretreated core material particles can be put into the electroless nickel plating bath. Through this operation, the nickel ions are reduced, and the reduced nickel forms an initial thin film layer on the surface of the core particle. The initial thin film layer is preferably formed to have a thickness of 0.1 to 10 nm, particularly preferably 0.1 to 5 nm. At this time, the protrusion has not yet been formed.

The key point in the A step is the relationship between the amount of nickel ions contained in the electroless plating bath and the amount of core material particles to be charged. Specifically, an electroless nickel plating bath whose nickel ion concentration is adjusted to 0.0001 to 0.008 mol/liter, preferably 0.0001 to 0.005 mol/liter relative to 1 liter of nickel ion, uses a total surface area of 1 to 15 m ² , preferably 2 to 8m ² of core material particles. Thereby, an initial thin film layer having the above thickness can be easily formed. Furthermore, by setting the relationship between the amount of nickel ions and the amount of core material particles as described above, it is possible to effectively prevent the aggregation of the core material particles forming the initial thin film layer. This is particularly effective when the particle size of the core material particles is small, for example, 3 μm or less.

After the reduction of nickel ions is completed, the B step is performed next. The B step is carried out following the A step, and operations such as separating the core material particles having the initial nickel thin film layer obtained in the A step from the liquid are not performed. Therefore, the dispersant added in the A step remains in the aqueous slurry including the core particles having the initial nickel thin film layer. In the B step, nickel ions and a reducing agent are added over time to the aqueous slurry containing the core particle having the nickel primary thin film layer obtained in the A step and the dispersant used in the A step. "Adding over time" does not mean adding nickel ions and reducing agent all at once, and means adding nickel ions and reducing agent continuously or intermittently over a certain period of time. At this time, the timing of adding the nickel ions and the reducing agent can be exactly the same, or the nickel ions can be added first, and then the reducing agent can be added. The reverse order is also possible. In addition, when the addition is completed, the addition of the nickel ions may be terminated first, and then the addition of the reducing agent may be terminated. The reverse order is also possible.

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

In the B process, through the reduction of nickel ions, first generate tiny nickel core particles in the liquid, and make the core particles adhere to the surface of the core particle with the initial nickel thin film layer obtained in the A process, and the attached The core particle is used as a starting point to grow and form a protrusion. By adopting this method, aggregation of particles can be effectively prevented, and protrusions having an aspect ratio of 1 or more can be easily formed. In contrast, in Patent Document 1 described in the background art section of this specification, first, a coating is formed on the surface of the core material particle, and at the same time, a nucleus as a starting point for the formation of protrusions is formed (first step), and then by making This nucleus grows in a subsequent step to form a protrusion (second step). In this method, since it is necessary to increase the nickel ion ratio in the first step, particle aggregation is likely to occur due to this. In addition, it is difficult to form protrusions with high aspect ratios.

In the reduction of nickel ions in the B step, it is important to maintain the aqueous slurry within the pH range where the dispersant added in the A step (this dispersant remains in the B step) exhibits a dispersing effect. Thereby, aggregation of particles can be effectively prevented. The pH can be adjusted by adding acids such as various inorganic acids or alkalis such as sodium hydroxide to the aqueous slurry while monitoring the pH of the aqueous slurry. The adjustment range of pH should just take an appropriate value according to the dispersing agent used. When using, for example, a nonionic surfactant as a dispersant, it is preferable to maintain the pH of the aqueous slurry in a range of 5-10. When using a zwitterionic surfactant as a dispersant, it is preferable to maintain the pH of the aqueous slurry in a range of 5-8. Also when using a water-soluble polymer as a dispersant, it is preferable to maintain the pH of the aqueous slurry in the range of 5-8.

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

When adding nickel ions and reducing agent, the aqueous slurry can be heated to a specified temperature, so that the reduction of nickel ions through the reducing agent can proceed smoothly. When adding nickel ions and reducing agent, the aqueous slurry can also be stirred first to make the reduced nickel evenly generated.

In this way, the desired conductive particles can be obtained. The conductive particles may be post-treated as needed. As post-processing, an electroless gold plating process or an electroless palladium plating process is mentioned. By applying this step, a gold-plated layer or a palladium-plated layer is formed on the surface of the conductive particles. The formation of the gold plating layer can be performed according to a conventionally known electroless plating method. For example, a gold plating layer can be formed by adding an electroless plating solution containing tetrasodium edetate, disodium citrate, and potassium gold cyanide to an aqueous suspension of conductive particles and adjusting the pH with sodium hydroxide. .

In addition, the formation of the palladium plating layer can be performed according to a conventionally known electroless plating method. For example, adding water-soluble palladium compounds such as palladium chloride to the aqueous suspension of conductive particles; reducing agents such as hypophosphorous acid, phosphorous acid, formic acid, acetic acid, hydrazine, boron hydride, aminoborane compounds or their salts And complexing agent and other commonly used non-electrolytic palladium plating solution, and then add dispersant, stabilizer, pH buffering agent as needed. Then, the pH is adjusted with an acid such as hydrochloric acid or sulfuric acid, or an alkali such as sodium hydroxide, and reduction electroless plating is performed to form a palladium plating layer. As another method, a palladium ion source such as tetraammine palladium salt, a complexing agent and, if necessary, a dispersing agent are added to an aqueous suspension of conductive particles, and displacement-type non-electrolytic electrolysis is performed by a displacement reaction between palladium ions and nickel ions. Plating, palladium plating can also be formed.

In addition, the above-mentioned palladium plating layer does not substantially contain phosphorus or the palladium plating layer whose content is reduced to 3% by weight or less is preferable from the viewpoint of excellent electrical conductivity and electrical reliability. In order to form such a plated layer, for example, when performing displacement type electroless plating or performing reduction type electroless plating, a non-phosphorus-containing reducing agent (such as formic acid) can be used.

As the dispersant used in reduction electroless plating or displacement electroless plating, the same dispersant as that exemplified in the above step A can be used. In addition, as a commonly used non-electrolyte palladium plating solution, for example, commercial products available from Kojima Chemicals Co., Ltd., Nippon Kanisen Co., Ltd., Chuo Chemical Industry Co., Ltd., etc. can be used.

As another post-treatment, the conductive particles may be subjected to a pulverization step using a grinder such as a ball mill. By providing this pulverization step, the weight of the primary particles relative to the weight of the conductive powder can be set within the above-mentioned range in combination with the above-mentioned reduction conditions of the nickel ions.

The conductive particles of the present invention thus obtained can be favorably used as, for example, an anisotropic conductive film (ACF), a heat seal connector (HSC), a circuit for connecting electrodes of a liquid crystal display panel to an LSI chip for driving Conductive materials used on the substrate, etc. In particular, the conductive powder of the present invention can be suitably used as a conductive filler of a conductive adhesive.

The above-mentioned conductive adhesive can be preferably used as an anisotropic conductive adhesive that is placed between two substrates forming the conductive base material, and the conductive base material is bonded and electrically connected by heating and pressing. . This anisotropic conductive adhesive contains the electroconductive particle and adhesive resin of this invention. The binder resin can be used without particular limitation as long as it is insulating and can be used as a material of the binder resin. It may be any of a thermoplastic resin and a thermosetting resin, and is preferably a substance that exhibits adhesive properties by heating. Such adhesive resins include, for example, thermoplastic types, thermosetting types, ultraviolet curable types, and the like. In addition, there are so-called semi-thermosetting types exhibiting intermediate properties between thermoplastic types and thermosetting types, composite types of thermosetting types and ultraviolet curable types, and the like. These adhesive resins can be appropriately selected in consideration of the surface properties of the circuit board to be bonded, etc., or the form of use. In particular, an adhesive resin composed of a thermosetting resin is preferable in that it has excellent material strength after bonding.

As the binder resin, specifically, ethylene-vinyl acetate copolymer, carboxy-modified ethylene-vinyl acetate copolymer, ethylene-isobutyl acrylate copolymer, polyamide, polyimide , polyester, polyvinyl ether, polyvinyl butyral, polyurethane, SBS block copolymer, carboxyl modified SBS copolymer, SIS copolymer, SEBS copolymer, maleic acid modified SEBS copolymer, polybutylene Diene rubber, chloroprene rubber, carboxy-modified chloroprene rubber, styrene-butadiene rubber, isobutylene-isoprene copolymer, acrylonitrile-butadiene rubber (hereinafter referred to as NBR), Carboxy-modified NBR, amine-modified NBR, epoxy resin, epoxy ester resin, acrylic resin, phenolic resin, or silicone resin, or a combination of two or more of them as the main ingredient Material. Among these, styrene-butadiene rubber, SEBS, and the like are preferable because they are excellent in reworkability as thermoplastic resins. As a thermosetting resin, epoxy resin is preferable. Among them, epoxy resins are most preferable because of their high adhesive strength, excellent heat resistance and electrical insulation properties, low melt viscosity, and connection at low pressure.

As the epoxy resin, generally used epoxy resins can be used as long as they are multi-component epoxy resins having two or more epoxy groups in one molecule. As a specific example, novolak resins such as phenol novolac resin and cresol novolac resin can be exemplified; polyhydric phenols such as bisphenol A, bisphenol F, bisphenol AD, resorcinol, and bishydroxydiphenyl ether, Ethylene glycol, neopentyl glycol, glycerin, trimethylolpropane, polypropylene glycol and other polyols, ethylenediamine, triethylenetetramine, aniline and other polyamino compounds, adipic acid, phthalic acid, Glycidyl-type epoxy resin obtained by reacting polycarboxylic compounds such as isophthalic acid with epichlorohydrin or 2-methylepichlorohydrin. In addition, aliphatic and alicyclic epoxy resins such as dicyclopentadiene epoxide and butadiene dimer diepoxide, and the like may be mentioned. These epoxy resins can be used individually or in mixture of 2 or more types.

In addition, it is preferable to use high-purity products with reduced impurity ions (Na, Cl, etc.) and hydrolyzable chlorine for the above-mentioned various adhesive resins from the viewpoint of preventing ion migration.

The usage-amount of the electroconductive particle of this invention in an anisotropic conductive adhesive is 0.1-30 weight part normally with respect to 100 weight part of adhesive resin components, Preferably it is 0.5-25 weight part, More preferably, it is 1 to 20 parts by weight. When the usage-amount of electroconductive particle falls within this range, increase of connection resistance and melt viscosity can be suppressed, connection reliability can be improved, and connection anisotropy can fully be ensured.

In the above-mentioned anisotropic conductive adhesive, in addition to the above-mentioned conductive particles and adhesive resin, known additives in the technical field may be blended, and the compounding amount may be within a range known in the technical field. Examples of other additives include tackifiers, reactive additives, epoxy resin curing agents, metal oxides, photoinitiators, sensitizers, curing agents, vulcanizing agents, anti-deterioration agents, heat-resistant additives, heat-conducting Accelerators, softeners, colorants, various coupling agents or metal deactivators, etc.

Examples of tackifiers include rosin, rosin derivatives, terpene resins, terpene phenol resins, petroleum resins, coumarone-indene resins, styrene resins, isoprene resins, alkylphenol resins, xylene resin, etc. As a crosslinking agent which is a reactive auxiliary agent, a polyhydric alcohol, isocyanate, a melamine resin, a urea resin, a urotropic substance, an amine, an acid anhydride, a peroxide, etc. are mentioned, for example. The epoxy resin curing agent can be used without particular limitation as long as it has two or more active hydrogens in one molecule. As a specific curing agent, for example, polyamine compounds such as diethylenetriamine, triethylenetetramine, m-phenylenediamine, dicyandiamide, polyamidoamine; phthalic anhydride, methyl nadic anhydride, hexahydrogenated Organic acid anhydrides such as phthalic anhydride and pyromellitic anhydride; novolac resins such as phenol novolak resins and cresol novolak resins, etc. These curing agents may be used alone or in combination of two or more. In addition, a latent curing agent can also be used depending on the use and need. As latent curing agents that can be used, for example, imidazoles, hydrazides, boron trifluoride-amine complexes, permeic acid salts, amine imides, polyamine salts, dicyandiamide, etc., and their modifications sex. These curing agents can be used alone or as a mixture of two or more.

The above-mentioned anisotropic conductive adhesive is usually prepared using a production device widely used by those skilled in the art, and the conductive particles of the present invention, the adhesive resin, and if necessary, a curing agent and various additives are mixed, and when adhesive When the adhesive resin is a thermosetting resin, it is produced by mixing in an organic solvent, and when it is a thermoplastic resin, it is produced at a temperature above the softening point of the adhesive resin, specifically about 50 to 130° C., More preferably, it is produced by melt-kneading at about 60 to 110°C. The thus-obtained anisotropic conductive adhesive can be used as a coating or as a film.

Example

Hereinafter, the present invention will be described in more detail by way of examples. However, the scope of the present invention is not limited by these examples.

[Embodiments 1 to 4]

(1) A process

A spherical styrene-silica composite resin [manufactured by Nippon Shokubai Co., Ltd., trade name Sorioster] having the particle diameter shown in Table 1 and a true specific gravity of 1.1 was used as the core particle. While stirring, 40 g of this was poured into 400 mL of an aqueous conditioner solution ("CLEANER-CONDITIONER 231" manufactured by Rohm and Haas Electronic Materials). The concentration of the conditioner aqueous solution is 40ml/L. Next, while applying ultrasonic waves at a liquid temperature of 60° C., stirring was performed for 30 minutes to perform surface modification and dispersion treatment of the core material particles. The aqueous solution was filtered, and 200 mL of slurry was formed from the core material particles washed with water for repulping once. 200 ml of stannous chloride aqueous solution was thrown into this slurry. The concentration of the aqueous solution was 5×10 ^-3 mol/L. Stirring at room temperature for 5 minutes was performed to perform sensitization treatment for adsorbing tin ions on the surface of the core particle. Continue to filter the aqueous solution, and carry out 1 repulping water washing. Next, the core material particles were formed into a slurry of 400 ml and maintained at 60°C. While stirring the slurry with ultrasonic waves, 2 mL of 0.11 mol/L palladium chloride aqueous solution was added. This stirring state was kept as it is for 5 minutes, and an activation treatment was performed to trap palladium ions on the surface of the core particle.

Next, an electroless plating solution formed by dissolving 3 L of sodium tartrate at 20 g/L, sodium hypophosphite at 5.4 g/L, nickel sulfate hexahydrate shown in Table 1, and a dispersant of the type and concentration shown in Table 1 The temperature of the bath was raised to 70° C., and the amount of palladium-loaded core material particles shown in Table 1 was thrown into the electroless plating bath, and the A step was started. Wherein, the specific content of the dispersant shown in Table 1 is shown in Table 2. Stir for 5 minutes, confirm that the generation of hydrogen bubbles ceases, and end the A process.

(2) B process

Use 300mL 224g/L nickel sulfate aqueous solution and the mixed aqueous solution that contains 210g/L sodium hypophosphite and 80g/L sodium hydroxide respectively, and use metering pump to add them continuously respectively to the slurry of the core material particle obtained in A process In the material, start the electroless plating B process. The addition rate was all 2.5 mL/min. The specific conditions of this process are shown in Table 3. After all the liquid had been added, stirring was continued for 5 minutes while maintaining a temperature of 70°C. Next, the liquid was filtered, and the filtrate was washed three times, and then dried in a vacuum dryer at 100° C. to obtain conductive particles having a nickel-phosphorus alloy coating. A scanning electron microscope (SEM) image of the conductive particles obtained in Example 3 is shown in FIG. 1 . As can be seen from this figure, the nickel coating and the protrusions in the electroconductive particles form a continuous body.

[Example 5-23]

Except having performed A process and B process under the conditions shown in Table 1 and Table 3, it carried out similarly to Example 1, and obtained the electroconductive particle. However, in the B process of Example 19, the addition amount of the mixed aqueous solution containing nickel sulfate aqueous solution, sodium hypophosphite, and sodium hydroxide was each 230 mL. Moreover, in the B process of Example 20, the addition amount of the mixed aqueous solution containing nickel sulfate aqueous solution, sodium hypophosphite, and sodium hydroxide was made into 390 mL each. In addition, the addition amount and the dropping rate of the mixed aqueous solution containing nickel sulfate aqueous solution, sodium hypophosphite and sodium hydroxide in Examples 21 to 23 were 150, 225, 600 mL; 1.3, 1.9, 5.0 mL/min. In this manner, conductive particles having a nickel-phosphorus alloy coating were obtained.

[Example 24]

An electroless gold plating solution consisting of 10 g/L of EDTA-4Na, 10 g/L of citrate-2Na, and 2.9 g/L of potassium gold cyanide (2.0 g/L as Au) was prepared. 2 liters of this gold plating solution was heated to 79° C., and 10 g of the electroconductive particles obtained in Example 2 were added thereto while stirring. Electroless plating treatment is thus performed on the surface of the particles. The processing time was 20 minutes. At the end of the treatment, the liquid was filtered and the filtrate was reslurried 3 times. Next, it dried with the vacuum dryer of 110 degreeC. In this manner, gold plating was applied to the nickel-phosphorus alloy film.

[Example 25-27]

Prepare a solution (2 g/L as palladium) of 10 g/L of EDTA-2Na, 10 g/L of citric acid 2Na and 20 g/L of tetraammine palladium hydrochloride (Pd(NH ₃ ) ₄ Cl ₂ ), 100 ppm An electroless palladium plating solution composed of carboxymethyl cellulose (molecular weight: 250,000, degree of etherification: 0.9). 0.65 liters of this palladium plating solution (embodiment 25), 1.3 liters of this palladium plating solution (embodiment 16), and 2.6 liters of this palladium plating solution (embodiment 27) were heated to 70° C., and 10 g was added while stirring. Conductive particles obtained in Example 2. Thus, a displacement type electroless plating treatment is performed on the surface of the particles. The processing time was 60 minutes. At the end of the treatment, the liquid was filtered and the filtrate was reslurried 3 times. Next, it dried with the vacuum dryer of 110 degreeC. In this manner, palladium plating was applied to the nickel-phosphorus alloy film. Phosphorus is not contained in the palladium coating.

[Comparative examples 1 to 7]

Except having performed A process and B process under the conditions shown in Table 1 and Table 3, it carried out similarly to Example 1, and obtained the electroconductive particle which has a nickel-phosphorus alloy coating. However, in the B process of the comparative example 3, the addition amount of the mixed aqueous solution containing nickel sulfate aqueous solution, sodium hypophosphite, and sodium hydroxide was each made into 230 mL. In addition, the addition amount and the dropping rate of the mixed aqueous solution containing nickel sulfate aqueous solution, sodium hypophosphite, and sodium hydroxide in Comparative Examples 5 to 6 were respectively 380, 1200 mL; 0.3, 10.0 mL/min. The SEM image of the electroconductive particle obtained in the comparative example 1 is shown in FIG.

[Comparative Example 8]

The same gold plating coating treatment as in Example 24 was applied to the conductive particles produced in Comparative Example 2.

[Physical evaluation]

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 and the conductivity of the nickel coating obtained in Examples and Comparative Examples were measured and evaluated, respectively. sex. In addition, the adhesion of the gold coating was also evaluated for the particles with gold plating, and the adhesion of the palladium coating was also evaluated for the particles with palladium plating. Each physical property evaluation was performed by the following method. In addition, the aspect ratio of the protrusions, the proportion of protrusions with an aspect ratio of 1 or more, the proportion of primary particles in the conductive powder, and the particle diameter of the conductive particles were measured by the methods described above. These results are shown in Table 4 and Table 5.

[Thickness of Nickel Coating]

The conductive particles were immersed in aqua regia to dissolve the nickel coating, and the components of the coating were subjected to ICP analysis or chemical analysis, and the thickness of the nickel coating was calculated from the following (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 particle, t is the thickness of the nickel coating, _d1 is the specific gravity of the nickel coating, _d2 is the specific gravity of the core particle, and W is the nickel content (weight %) .

[Thickness of Gold Coating - Palladium Coating]

Immerse conductive particles in aqua regia, dissolve gold or palladium coatings and nickel coatings, and perform ICP analysis or chemical analysis of coating components. Then, the thickness of the gold or palladium coating was calculated 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 coating, d ₃ is the specific gravity of the gold or palladium coating, d ₄ is the specific gravity of Ni products, and X is the content rate (% by weight) of gold or palladium. Here, the specific gravity _d4 of the Ni product is calculated using a calculation formula. The specific gravity was calculated using the calculation formula of the following (5).

d ₄ =100/[(W/d ₁ )+(100-W)/d ₂ ] (5)

In the formula, _d1 is the specific gravity of the nickel coating, _d2 is the specific gravity of the core particle, and W is the nickel content (% by weight).

[surface condition]

The electroconductive particle was magnified 30000 times using SEM, 10 fields of view were observed, and the average number of objects of the protrusion part which one electroconductive particle has was computed. The evaluation of 10 to 100 pieces was ◯, and the evaluation of 10 or less was △. In addition, the case where nickel was deposited abnormally was evaluated as x. Abnormal precipitation refers to, for example, the case where nickel is not precipitated on the surface of the core particle, but is precipitated alone in the liquid.

[Adhesion of film]

2 g of conductive particles and 90 g of zirconia beads with a diameter of 1 mm were added to a 100 mL beaker, and 10 mL of toluene was added. After stirring for 10 minutes with a stirring device, the zirconia beads and the slurry were separated and dried. The dried electroconductive particles were magnified 2000 times using SEM, 10 fields of view were observed, and the average value of the number of peeled pieces generated by stirring was calculated. When the number of release sheets was less than 10, it was evaluated as ◯, when it was 10 to 30, it was evaluated as △, and when it was more than 30, it was evaluated as ×.

[conductivity]

Mix 100 parts of epoxy resin, 150 parts of curing agent, and 70 parts of toluene to prepare an insulating adhesive. 15 parts of conductive particles were mixed therein to obtain a paste. Using a bar coater, the paste was coated on a silicone-treated polyester film and allowed to dry. The obtained coating film was used to connect glass whose entire surface was vapor-deposited with aluminum and a polyimide film substrate on which copper patterns were formed at a pitch of 50 μm. Then, the electrical conductivity of the electroconductive particles was evaluated by measuring the conduction resistance between electrodes. A resistance value of 2Ω or less was evaluated as ◯, a resistance value of 2 to 5Ω was evaluated as Δ, and a resistance value of 5Ω or more was evaluated as ×. In addition, the presence or absence of a short circuit is also recorded in the table.

[Table 1] A process

[Table 2]

A polyethylene glycol B   Polyoxyethylene alkyl ether C Polyoxyethylene alkylphenol ether D. Alkyl dimethyl carboxymethyl betaine acetate E. Alkyl dimethyl betaine acetate f Betaine Alkyl Dimethylaminoacetate G polyvinyl alcohol h Polyvinylpyrrolidone I Hydroxyethyl cellulose

[Table 3] B process

※The range of pH is the transition from the start of dropping to the end of dropping

As can be seen from the results shown in Table 4 and Table 5, compared with the conductive powder obtained in the comparative example, the conductive powder obtained in each example (the product of the present invention) was judged to have a longer diameter of the protrusion than the conductive powder obtained in the comparative example. The ratio is high, and the proportion of primary particles is high. Moreover, compared with the electroconductive powder obtained in the comparative example, the electroconductive powder obtained by each Example also judged that electroconductivity is high and the adhesiveness of a nickel coating is high.

Industrial availability

The conductive powder of the present invention not only has a particle diameter of conductive particles constituting the conductive powder smaller than conventional ones, but also has good dispersibility and conductivity. Moreover, according to the manufacturing method of this invention, such electroconductive powder can be manufactured easily.

Claims (7)

1. electric conduction powder is characterized in that:

It is to be formed with the electric conduction powder that the conductive particle by nickel or nickel alloy overlay film forms on the surface of core material particles,

Described conductive particle have a plurality of surfaces from described overlay film outstanding and and this overlay film draw ratio of forming non-individual body be 1.0～4.0 jut, draw ratio is that the ratio of 1.0～4.0 described jut is more than 40% with respect to the quantity of whole juts, in described electric conduction powder, the shared weight of primary particle is more than 85 % by weight with respect to the weight of electric conduction powder in the described conductive particle.

2. electric conduction powder as claimed in claim 1 is characterized in that:

The average grain diameter of described core material particles is 1～3 μ m.

3. electric conduction powder as claimed in claim 1 or 2 is characterized in that:

The surface that comprises the described overlay film of described jut with gold or palladium.

4. conductive material is characterized in that:

Comprise each described electric conduction powder and insulative resin in the claim 1～3.

5. the manufacture method of a conductive particle is characterized in that, comprising:

The A operation; the electroless plating bath that will comprise dispersant and nickel ion has the core material particles of noble metal to mix with the upper load in surface; when the surface of this core material particles formation nickel initial stage thin layer; nickel ion concentration with respect to 1 liter is adjusted to this electroless plating of 0.0001～0.008 mol/L and bathes, and using the surface area summation is 1～15m ²This core material particles of amount; With

The B operation, the resulting water paste that comprises the described core material particles with nickel initial stage thin layer and contain described dispersant in the A operation is maintained the pH scope of the dispersion effect that shows this dispersant, and in this water paste, add nickel ion and reducing agent that to be equivalent to the nickel amount of separating out hourly be the amount of 25～100nm through time ground, the nuclear particle of generating nickel in this water paste, and the nuclear particle that makes generation is attached on the described core material particles, as starting point this nuclear particle is grown up with the nuclear particle that adheres to, the formation draw ratio is the jut more than 1.

6. manufacture method as claimed in claim 5 is characterized in that:

So that becoming the mode of 0.1～10nm, the thickness of nickel initial stage thin layer carries out operation A.

7. such as claim 5 or 6 described manufacture methods, it is characterized in that:

As described dispersant, use non-ionic surface active agent, zwitterionic surfactant or water soluble polymer.

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