JP5091416B2 - Conductive fine particles, method for producing conductive fine particles, and anisotropic conductive material - Google Patents

Description

The present invention relates to conductive fine particles that are excellent in resin rejection and capable of reducing resistance, a method for producing conductive fine particles, and an anisotropic conductive material.

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

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

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

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

However, even when conductive fine particles having protrusions on such a surface are used, the size of the protrusions varies due to agglomeration when forming the protrusions, and depending on the size of the protrusions, there is a resin bite between the protrusions. In other words, the protrusion may not be able to break through the binder resin or the like, and thus it cannot be said that the connection resistance between the conductive fine particles and the circuit board is sufficiently reduced.
JP 2000-243132 A

An object of the present invention is to provide conductive fine particles, a method for producing conductive fine particles, and an anisotropic conductive material that are excellent in resin rejection and capable of reducing resistance, in view of the above situation.

The present invention relates to a base material fine particle dispersion containing a dispersing agent in which base material fine particles not subjected to catalyst treatment are dispersed, and a highly dispersible metal nano paste containing metal nanoparticles having an average particle diameter of 5 to 80 nm, And mixing the metal nanoparticles onto the surface of the substrate fine particles by heteroaggregation, and after performing the catalyst treatment, the substrate fine particles to which the metal nanoparticles are adhered by an electroless plating method This is a method for producing conductive fine particles comprising the step 2 of forming a metal plating layer having a thickness of 10 to 500 nm on the surface.
The present invention is described in detail below.

As a result of intensive studies, the present inventors have used conductive fine particles having a low average height of protrusions and a small variation in the height of protrusions as conductive fine particles used for electrical connection of circuit boards and the like. The contact area between the circuit board and the conductive fine particles increases, and the pressure applied to the protrusions is large, so it is easy to break through the resin. Therefore, it is possible to reduce the connection resistance and maintain a stable connection. When producing an anisotropic conductive material by dispersing fine particles in a binder resin or the like, the inventors have found that the dispersibility of the conductive fine particles is excellent, and have completed the present invention.

The conductive fine particles of the present invention are composed of substrate fine particles and a metal plating layer having protrusions with metal nanoparticles having an average particle diameter of 5 to 80 nm formed on the surface of the substrate fine particles.

The substrate fine particles are not particularly limited, and may be an inorganic material or an organic material as long as it has an appropriate elastic modulus, elastic deformability, and restoration property. Since it is easy to control the deformability and the recoverability, resin fine particles made of resin are preferable.

The resin fine particles are not particularly limited. For example, polyolefins such as polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyvinylidene chloride, polytetrafluoroethylene, polyisobutylene, and polybutadiene; acrylic resins such as polymethyl methacrylate and polymethyl acrylate Divinylbenzene polymer resin; divinylbenzene-styrene copolymer, divinylbenzene-acrylic acid ester copolymer, divinylbenzene-methacrylic acid ester copolymer and other divinylbenzene copolymer resins; polyalkylene terephthalate, polysulfone, polycarbonate, Polyamide, phenol formaldehyde resin, melamine formaldehyde resin, benzoguanamine formaldehyde resin, urea formaldehyde resin, etc. Thing, and the like. These resin fine particles may be used independently and 2 or more types may be used together.

Although it does not specifically limit as an average particle diameter of the said base material fine particle, A preferable minimum is 1 micrometer and a preferable upper limit is 20 micrometers. If it is less than 1 μm, for example, it is likely to aggregate when electroless plating is performed, and it may be difficult to form single particles. If it exceeds 20 μm, it exceeds the range used between the substrate electrodes as an anisotropic conductive material. May end up. A more preferable upper limit is 10 μm.

The metal type of the metal nanoparticles is not particularly limited, and examples thereof include low melting point metals such as silver, tin, and silver tin alloy, nickel, palladium, copper, and gold.

The lower limit of the average particle diameter of the metal nanoparticles is 5 nm, and the upper limit is 80 nm. If the thickness is less than 5 nm, the obtained protrusions are too small and sufficient resin-exclusion property cannot be obtained. If the thickness exceeds 80 nm, the obtained protrusions are too large, and when used for connection between circuit boards, The contact area with the protrusion is reduced, and cannot contribute to a decrease in connection resistance. A preferred lower limit is 10 nm and a preferred upper limit is 60 nm.

It does not specifically limit as a metal kind of the said metal plating layer, For example, gold | metal | money, silver, copper, nickel, tin etc. are mentioned.

Although it does not specifically limit as thickness of the said metal plating layer, A preferable minimum is 10 nm and a preferable upper limit is 500 nm. If the thickness is less than 10 nm, desired conductivity may not be obtained. If the thickness exceeds 500 nm, the metal plating layer may be easily peeled off due to the difference in thermal expansion coefficient between the substrate fine particles and the metal plating layer. is there.

The lower limit of the average height of the protrusions having the metal nanoparticles as a core is 20 nm, and the upper limit is 150 nm. If the thickness is less than 20 nm, sufficient resin exclusion effect cannot be obtained. If the thickness exceeds 150 nm, the contact between the circuit board and the plating film is inhibited by the protrusion when used for connection between the circuit boards. Resin remains between the protrusions, and as a result, the contact area becomes small and cannot contribute to the decrease in connection resistance. A preferred lower limit is 40 nm and a preferred upper limit is 130 nm.

As a method for measuring the height of the protrusion, for example, a scanning electron microscope (SEM) is used. As the magnification, an easily observable magnification may be selected. Specifically, for example, the observation is performed at 4000 times.
In the present specification, it is assumed that the effect of providing protrusions is obtained, and those having a size of 10 nm or more are selected as protrusions, and the average height of protrusions is about 50 randomly selected particles. Measured and arithmetically averaged.

In the conductive fine particles of the present invention, the preferable lower limit of the average outer diameter of the protrusions is 50 nm, and the preferable upper limit is 180 nm. If the thickness is less than 50 nm, the contact area between the electrode and the projection is small and may not contribute to the reduction in connection resistance. If the thickness exceeds 180 nm, the area per projection is too large, and the pressure applied to each projection is too high. It may become small and the sufficient resin exclusion effect may not be acquired. A more preferred lower limit is 60 nm, and a more preferred upper limit is 150 nm.

As a method for measuring the outer diameter of the protrusion, for example, a scanning electron microscope (SEM) is used. As the magnification, an easily observable magnification may be selected. Specifically, for example, the observation is performed at 4000 times.
In this specification, the outer diameter of the protrusion is the longest outer diameter that appears as a protrusion from the reference surface that forms the outermost surface of the protrusions that are almost entirely observed among the many protrusions that have been confirmed. To do. At this time, it is assumed that a projection having a size of 10 nm or more is selected as a projection that provides the effect of imparting the projection. Further, the average outer diameter of the protrusions is obtained by measuring 50 randomly selected particles and arithmetically averaging them.

In the conductive fine particles of the present invention, the ratio of protrusions having a height of 200 nm or more with respect to all protrusions is 5% or less. If it exceeds 5%, a stable connection cannot be maintained when a circuit board or the like is connected using the conductive fine particles of the present invention.
Further, the ratio of the protrusions having a height of 200 nm or more to the total protrusions is 5% or less, which means that the metal nanoparticles overlap each other on the surface of the base particle or the metal nanoparticles are the base particle. It is almost never lifted up without contact.

The conductive fine particles of the present invention have a CV value of the height of the protrusion (value obtained by dividing the standard deviation of the height distribution of the protrusion by the average of the protrusion height as a percentage) of 20% or less. It is preferable. Since the CV value is 20% or less, when the circuit board or the like is connected using the conductive fine particles of the present invention, the variation in the contact area between the circuit board and the conductive fine particles is reduced and stable. You can stay connected.

The method for producing the conductive fine particles of the present invention is not particularly limited. For example, the base fine particle dispersion containing a dispersant and the highly dispersible metal nano particles containing metal nanoparticles having an average particle size of 5 to 80 nm. A step 1 of mixing the paste and attaching the metal nanoparticles to the surface of the substrate fine particles by hetero-aggregation; and a step 2 of forming a metal plating layer on the surface of the substrate fine particles to which the metal nanoparticles are attached. And the like, and the like.
Such a method for producing conductive fine particles is also one aspect of the present invention.
Below, the manufacturing method of this electroconductive fine particle is explained in full detail.

The method for producing conductive fine particles of the present invention comprises mixing a base material fine particle dispersion containing a dispersant and a highly dispersible metal nanopaste containing metal nanoparticles having an average particle size of 5 to 80 nm, It has the process 1 which makes the said metal nanoparticle adhere to the surface of base-material microparticles | fine-particles by heteroaggregation.
Such heteroaggregation can be caused by appropriately setting the surface potential difference.
Thus, in the case of heteroaggregation, the metal nanoparticles adhere to the surface of the substrate fine particles uniformly and without overlapping.

Furthermore, in the method for producing conductive fine particles according to the present invention, the base fine particles and the metal nanoparticles are firmly bonded by the interaction between the dispersant on the surface of the base fine particles and the dispersant on the surface of the metal nanoparticles. Therefore, when the metal plating is performed on the surface, the core material is not peeled off or lifted up from the surface of the substrate fine particles, and thus a protrusion having a uniform height can be obtained.

When the dispersing agent is used in the step of preparing the base material fine particles, the base material fine particle dispersion is not isolated from the prepared base material fine particles, and the prepared base material fine particle dispersion is used as it is. If the dispersant is not used in the process of preparing the above-mentioned base particles, or if the base particles are isolated, the base particles are dispersed in an appropriate solution, and the dispersant is added. It may be what you did.

The dispersant is not particularly limited, and examples thereof include polyvinyl alcohol, polyvinyl acetal, polyvinyl pyrrolidone, fatty acids such as stearic acid, sodium hexametaphosphate, and the like.

In the present specification, the metal nano paste means a material in which metal nanoparticles are dispersed in a solution containing a dispersant.
The dispersant is not particularly limited, and the same dispersant as that described above may be used.

The manufacturing method of the electroconductive fine particles of this invention has the process 2 which forms a metal plating layer on the surface of the base-material fine particles to which the said metal nanoparticle adhered.

In the method for producing conductive fine particles of the present invention, since the metal nanoparticles surround the surface of the substrate fine particles like a core-shell, a conventional catalyst such as palladium is required in the case of electroless plating. In addition, metal plating can be performed using metal nanoparticles as a base point.

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

In the method for producing conductive fine particles of the present invention, when the melting point of the metal nanoparticles is lower than the melting point of the metal plating, the conductive fine particles are more than the melting point of the metal nanoparticles and the melting point of the metal plating. It is preferable to perform the process 3 heated at the following temperatures. As a result, the metal nanoparticles are melted, and the melted metal nanoparticles are in close contact with the surface of the base particle, so that the adhesion between the base particle and the protrusion can be improved, and the protrusion can be prevented from falling off. .

Since the conductive fine particle of the present invention has the above-described configuration, the height of the protrusion is low and the variation in height is small. Therefore, when the conductive fine particle of the present invention is used for connection between substrates, In the connection between the conductive fine particles and the substrate, the contact area of the plating film of the conductive fine particles is not hindered from increasing and the contact area is increased, and the variation in the contact area is small, so that stable connection can be maintained. Furthermore, since the outer diameter of the protrusion is small, the pressure applied to each protrusion is large and the resin is easily pierced, so that a stable connection can be maintained.

Further, an anisotropic conductive material can be produced by dispersing the conductive fine particles of the present invention in a binder resin. Such an anisotropic conductive material is also one aspect of the present invention.
Since the conductive fine particles of the present invention have small protrusions, they are excellent in dispersibility with respect to the binder resin.

Specific examples of the anisotropic conductive material of the present invention include, for example, anisotropic conductive paste (ACP), anisotropic conductive ink, anisotropic conductive adhesive layer, anisotropic conductive film (ACF), An anisotropic conductive sheet etc. are mentioned.

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

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

The method for producing the anisotropic conductive material of the present invention is not particularly limited. For example, the conductive fine particles of the present invention are added to an insulating resin binder, and are mixed and dispersed uniformly. A method of using a conductive paste, anisotropic conductive ink, anisotropic conductive adhesive, etc., adding the conductive fine particles of the present invention in an insulating resin binder and uniformly dissolving (dispersing), or , Heat-dissolve, apply to the release treatment surface of the release material such as release paper and release film so that it has a predetermined film thickness, perform drying and cooling as necessary, for example, anisotropic For example, an appropriate manufacturing method may be employed in accordance with the type of anisotropic conductive material to be manufactured.
Moreover, it is good also as an anisotropic conductive material by using separately, without mixing an insulating resin binder and the electroconductive fine particles of this invention.

When the conductive fine particles of the present invention use conductive fine particles having a low average height of protrusions and little variation in the height of the protrusions, the conductive fine particle coating film is formed in the connection between the conductive fine particles and the substrate. Since the contact area increases without being obstructed from contacting the substrate and the contact area is less varied, a stable connection can be maintained. Furthermore, since the outer diameter of the protrusion is small, the pressure applied to each protrusion is large and the resin is easily pierced, so that a stable connection can be maintained.
Further, when an anisotropic conductive material is produced by dispersing the conductive fine particles in a binder resin or the like, the dispersibility of the conductive fine particles is excellent.
ADVANTAGE OF THE INVENTION According to this invention, it can provide the conductive fine particle which is excellent in resin exclusion property, and can reduce resistance value, the manufacturing method of conductive fine particle, and an anisotropic conductive material.

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

Example 1
(1) Core material compounding step After 10 g of substrate fine particles made of divinylbenzene polymerized resin having an average particle size of 4 μm are dispersed in 300 mL of deionized water for 3 minutes by stirring, nickel nanopaste (average particles) is used as the core material in the aqueous solution. 3 g (diameter 40 nm, CV value 10%) were added to obtain substrate fine particles to which a core substance was adhered.
Thereafter, alkali degreasing with an aqueous sodium hydroxide solution, acid neutralization, and sensitizing in a tin dichloride solution were performed. Thereafter, an electroless plating pretreatment consisting of activation in a palladium dichloride solution was performed, and after filtering and washing, substrate fine particles having palladium adhered to the particle surfaces were obtained.

(2) Electroless nickel plating step After further diluting the obtained particles with 1200 mL of water and adding 4 mL of plating stabilizer, nickel sulfate 450 g / L, sodium hypophosphite 150 g / L, sodium citrate 116 g / L, 120 mL of a mixed solution of 6 mL of plating stabilizer was added through a metering pump at an addition rate of 81 mL / min. Then, it stirred until pH became stable, it confirmed that hydrogen foaming stopped, and the electroless-plating pre-process was performed.
Subsequently, 650 mL of a mixed solution of 450 g / L nickel sulfate, 150 g / L sodium hypophosphite, 116 g / L sodium citrate, and 35 mL plating stabilizer was added through a metering pump at an addition rate of 27 mL / min. Then, it stirred until pH became stable, it confirmed that hydrogen foaming stopped, and the electroless-plating late process was performed.
Next, the plating solution was filtered, and the filtrate was washed with water, and then dried with a vacuum dryer at 80 ° C. to obtain nickel-plated fine particles.

(3) Gold plating step Further, conductive fine particles were obtained by performing gold plating on the surface by a displacement plating method.

(Example 2)
Conductive fine particles were produced in the same manner as in Example 1 except that 3 g of nickel nanopaste (average particle size 80 nm, CV value 16%) was used as the core material.

(Comparative Example 1)
(1) Electroless Plating Pretreatment Step 10 g of substrate fine particles made of divinylbenzene polymer resin having an average particle size of 4 μm were subjected to alkali degreasing with an aqueous sodium hydroxide solution, acid neutralization, and sensitizing in a tin dichloride solution. Thereafter, an electroless plating pretreatment consisting of activation in a palladium dichloride solution was performed, and after filtering and washing, substrate fine particles having palladium adhered to the particle surfaces were obtained.

(2) Core material complexing step After the obtained base material fine particles were dispersed with 300 mL of deionized water for 3 minutes by stirring, 3 g of nickel particles (average particle size 200 nm, CV value 23%) were added to the aqueous solution as a core material. Substrate fine particles to which a core substance was adhered were added.

(3) Electroless nickel plating process After further diluting the obtained substrate fine particles with 1200 mL of water and adding 4 mL of plating stabilizer, nickel sulfate 450 g / L, sodium hypophosphite 150 g / L, citric acid 120 mL of a mixed solution of 116 g / L sodium and 6 mL plating stabilizer was added through a metering pump at an addition rate of 81 mL / min. Then, it stirred until pH became stable, it confirmed that hydrogen foaming stopped, and the electroless-plating pre-process was performed.
Subsequently, 650 mL of a mixed solution of 450 g / L nickel sulfate, 150 g / L sodium hypophosphite, 116 g / L sodium citrate, and 35 mL plating stabilizer was added through a metering pump at an addition rate of 27 mL / min. Then, it stirred until pH became stable, it confirmed that hydrogen foaming stopped, and the electroless-plating late process was performed.
Next, the plating solution was filtered, and the filtrate was washed with water, and then dried with a vacuum dryer at 80 ° C. to obtain nickel-plated fine particles.

(4) Gold plating step Further, conductive fine particles were produced by performing gold plating on the surface by a displacement plating method.

(Comparative Example 2)
Conductive fine particles were produced in the same manner as in Example 1 except that 3 g of gold nanopaste (average particle diameter 8 nm, CV value 10%) was used as the core substance.

(Comparative Example 3)
Conductive fine particles were produced in the same manner as in Comparative Example 1 except that 3 g of copper particles (average particle size 100 nm, CV value 16%) were used as the core substance.

<Evaluation>
The following evaluation was performed about the electroconductive fine particles obtained in Examples 1-2 and Comparative Examples 1-3. The results are shown in Table 1.

(1) Measurement of average height of protrusions and average outer diameter For conductive fine particles obtained in Examples and Comparative Examples, particles were observed with a scanning electron microscope (SEM) manufactured by Hitachi High-Technologies Corporation, and conductive fine particles The average outer diameter of the protrusions, the average height of the protrusions, the ratio of protrusions having a height of 200 nm or more to the total protrusions, and the CV value of the height of the protrusions were examined.
Further, the SEM photograph of Example 1 is shown in FIG. 1, the SEM photograph of Example 2 is shown in FIG. 2, and the SEM photograph of Comparative Example 1 is shown in FIG.

(2) Evaluation of anisotropic conductive material An anisotropic conductive material was produced by the following method using the conductive fine particles obtained in Examples and Comparative Examples, and the resistance value between the electrodes was evaluated.
As a resin binder resin, 100 parts by weight of an epoxy resin (“Epicoat 828” manufactured by Yuka Shell Epoxy Co., Ltd.), 2 parts by weight of trisdimethylaminoethylphenol, and 100 parts by weight of toluene were sufficiently mixed using a planetary stirrer. Then, it apply | coated so that the thickness after drying might be set to 10 micrometers on a release film, and toluene was evaporated, and the adhesive film was obtained.
Next, 100 parts by weight of an epoxy resin (“Epicoat 828” manufactured by Yuka Shell Epoxy Co., Ltd.), 2 parts by weight of trisdimethylaminoethylphenol, and 100 parts by weight of toluene as a resin binder resin were obtained. And then thoroughly mixed using a planetary stirrer, and then coated on the release film so that the thickness after drying is 7 μm, and the adhesive film containing conductive fine particles is evaporated by evaporating toluene. Obtained. The blending amount of the conductive fine particles was such that the content in the film was 40,000 pieces / cm ² .
By laminating the obtained adhesive film and an adhesive film containing conductive fine particles at room temperature, an anisotropic conductive film having a two-layer structure and a thickness of 17 μm was obtained.
The obtained anisotropic conductive film was cut into a size of 5 × 5 mm. After affixing this to approximately the center of an aluminum electrode having a width of 200 μm, a length of 1 mm, a height of 0.2 μm, and an L / S of 20 μm having a lead wire for resistance measurement, a glass substrate having an ITO electrode is obtained. After aligning the electrodes so that they overlap each other, they were bonded together.
The bonded portion of this glass substrate was thermocompression bonded under a pressure bonding condition of 9N and 140 ° C., and then the resistance value between the electrodes was evaluated.

ADVANTAGE OF THE INVENTION According to this invention, it can provide the conductive fine particle which is excellent in resin exclusion property, and can reduce resistance value, the manufacturing method of conductive fine particle, and an anisotropic conductive material.

2 is a SEM photograph of conductive fine particles obtained in Example 1. 4 is a SEM photograph of conductive fine particles obtained in Example 2. 3 is a SEM photograph of conductive fine particles obtained in Comparative Example 1.

Claims (2)

A base material fine particle dispersion containing a dispersing agent in which base material fine particles not subjected to catalyst treatment are dispersed is mixed with a highly dispersible metal nano paste containing metal nanoparticles having an average particle size of 5 to 80 nm. Step 1 for attaching the metal nanoparticles to the surface of the substrate fine particles by heteroaggregation;
After conducting the catalyst treatment, the method comprises the step 2 of forming a metal plating layer having a thickness of 10 to 500 nm on the surface of the substrate fine particles to which the metal nanoparticles are adhered by an electroless plating method. A method for producing fine particles. The method for producing conductive fine particles according to claim 1, further comprising a step 3 of heating the conductive fine particles at a temperature not lower than the melting point of the metal nanoparticles and not higher than the melting point of the metal plating.