JPH04362104A - Method for coating metallic particle with polymer - Google Patents

Abstract

PURPOSE:To completely coat the surfaces of metallic particles with a polymer relating to the formation of a conductive adhesive and more specifically a microcapsule type conductive filler. CONSTITUTION:This method consists in the procedure subjecting the metallic particles 1 to a surface treatment with a coupling agent, then dispersing the metallic particles 1 into an org. solvent dissolving a monomer to form a homopolymer and a polymn. initiator to form an oil phase, adding this oil phase to a water phase consisting of an emulsifier and thickener dissolved in water to form a suspension, and acting heat and/or catalyst on this suspension to polymerize the monomer thereby forming the homopolymer films 2 on the surfaces of the metallic particles, or subjecting the metallic particles 1 to the surface treatment with the coupling agent, then dispersing the metallic particles 1 into the org. solvent dissolving a monomer A to form the copolymer to form an oil phase, adding this oil phase to the water phase consisting of another monomer B, an emulsifier and thickener dissolved in the water to form the suspension, and acting the heat and/or catalyst on this suspension to polymerize the monomer, thereby forming the copolymer films on the surface of the metallic particles 1.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for producing a microcapsule type conductive filler. In recent years, there has been an increasing demand for conductive adhesives in which metal particles are dispersed in adhesive resin as a bonding technique to replace solder bonding. Among these, various benefits can be expected if microcapsule-type conductive filler, in which the surface of metal fine particles is coated with an insulating resin, is used instead of metal particles.

[0002] If a conductive adhesive, which is an organic and inorganic composite consisting of a binder mainly made of synthetic resin and a conductive filler mainly made of metal powder, is used, the adhesive method, applicable materials, usage methods, etc. It has wide applicability in For example, applicable materials include conductive adhesion of plastics such as epoxy resins and phenolic resins that cannot be soldered in the past, adhesion of Nesa glass used in liquid crystal display tubes, adhesion of phosphor bronze and carbon brushes used in micro motors, and crystal vibration. It is an indispensable material for bonding lead wires, etc.

Recent developments in the semiconductor industry in particular have been remarkable, with ICs and LSIs being developed and mass-produced one after another. Traditionally, Au-Si eutectic was used to bond these semiconductor chips to lead frames, but in order to reduce costs and improve productivity, conductive adhesives made by mixing silver powder into epoxy resin have been used. has become widely used.

[0004] Epoxy resin is generally used as the resin binder of this conductive adhesive, but other resins such as polyimide, phenol, and polyester are also used in some cases. On the other hand, conductive fillers include gold, silver,
Fine powder of metals such as copper, amorphous carbon, and graphite powder are used, and in some cases, metal oxides are also used. However, silver powder is most commonly used due to its price, reliability, and track record.

Although conductive adhesives have various advantages over conventional soldering and welding, they are not without problems. For example, consider a case where this conductive adhesive is used between an IC or LSI chip and a pattern on a substrate. As shown in the graph of FIG. 5, as the amount of conductive fine particles in the conductive adhesive increases, the insulation resistance decreases and the possibility that adjacent patterns are electrically connected increases. vice versa,
When the amount of conductive fine particles decreases, the conductivity between the chip and the pattern becomes unsatisfactory. That is, the amount of conductive fine particles used in the conductive adhesive must be strictly controlled. To solve this problem, a microcapsule-type conductive filler, which is made by coating the surface of conductive particles with an insulating resin, is dispersed in an adhesive, and this is applied to the substrate, either to the size of the chip or to the entire surface of the substrate. , pressure is applied between the chip and the pattern to break the coating layer of the capsule and establish continuity, and between the patterns that are not pressed by the chip, encapsulated conductive particles remain, so insulation can be maintained. can.

[0006] As described above, the microcapsule type conductive filler has great advantages, and the insulating resin used may be thermoplastic or thermosetting. However, in the spray-drying method currently used to coat fine metal particles, resin is dissolved in a solvent and then spray-dried, but this method cannot completely coat the surface of fine metal particles, and only thermoplastic resins can be used. The problem is that it cannot be used.

[0007]

[Problems to be Solved by the Invention] An object of the present invention is to provide a metal particle whose surface can be completely coated with an insulating resin, and which can also be coated with either a thermoplastic resin or a thermosetting resin. An object of the present invention is to provide a method for coating fine particles.

[0008]

[Means for Solving the Problem] The above object is to treat the surface of fine metal particles with a coupling agent, and then disperse the fine metal particles in an organic solvent in which a monomer and a polymerization initiator to form a homopolymer are dissolved. This oil phase is added to an aqueous phase in which an emulsifier and a thickener are dissolved in water to form an emulsion in which fine metal particles are suspended, and this emulsion is subjected to heat and/or a catalyst. A method for coating metal fine particles is characterized in that the monomer is polymerized to form a homopolymer film on the surface of the metal fine particles, and after the metal fine particles are surface-treated with a coupling agent, the metal fine particles are coated with a copolymer to form a copolymer. Dispersing monomer A in an organic solvent to form an oil phase,
This oil phase is added to an aqueous phase in which other monomer B, an emulsifier, and a thickener are dissolved in water to form an emulsion in which fine metal particles are suspended, and this emulsion is heated and/or catalyzed. This problem can be solved by a method for coating metal fine particles, which is characterized by polymerizing monomers by causing a copolymer to form a copolymer film on the surface of the metal fine particles.

[0009]

[Function] If one type or multiple types of monomer is uniformly present on the surface of metal fine particles that have been subjected to coupling treatment in advance, and this is polymerized into a homopolymer or copolymer, the metal fine particles can be completely covered, and moreover, the monomer Depending on the selection, it can be coated with either thermoplastic resin or thermosetting resin, and the above problem can be solved. For example, when an acrylic monomer is radically polymerized on the surface of a metal particle, a thermoplastic resin is obtained, and when an epoxy monomer and an amine are reacted, a thermosetting resin is obtained.

When polymerizing a homopolymer using one type of monomer, an oil phase in which fine metal particles surface-treated with a coupling agent are dispersed in an organic solvent in which the monomer and an initiator are dissolved is mixed with an emulsifier. An emulsion is prepared by dropping the mixture into an aqueous phase in which a thickener is dissolved. By applying heat or the like to this emulsion, the monomer is polymerized on the surface of the metal fine particles on the spot, thereby coating the metal fine particles. In addition, when using two types of monomers, one monomer is dissolved in an organic solvent,
An emulsion is prepared by dropping an oil phase in which fine metal particles surface-treated with a coupling agent are dispersed into an aqueous phase in which other monomers, an emulsifier, and a thickener are dissolved. By applying heat or the like to this emulsion, the two monomers can be interfacially polymerized on the surface of the metal fine particles to coat the metal fine particles.

[0011] If the particle size of the metal fine particles is less than 0.1 μm, the fine particles tend to aggregate, and if it exceeds 30 μm, they will settle and separate. Therefore, even if the fine particles aggregate, they should not become particles larger than 30 μm. If the weight of the coupling agent is less than 0.1% by weight of the metal fine particles, the coupling effect will not be sufficient, and if it exceeds 4% by weight, the coupling agent will not form a monomolecular layer and the monomer will be removed from the surface of the fine particles. It becomes easier to leave. Regarding the aqueous phase, if the viscosity is less than 20 cps, the metal fine particles will settle and coagulate, and large aggregates will be coated as they are. Moreover, if it exceeds 5000 cps, stirring becomes difficult and separation of fine particles after polymerization becomes difficult. Further, when an emulsifier is not added to the aqueous phase, emulsification between the metal fine particles and the oil phase containing the organic solvent is not performed, so that a complete coating layer is not formed on the metal fine particles.

[0012] To prepare the emulsion, 1000 to 100
It is preferable to add the organic solution dropwise while stirring at 50 to 250 rpm, and it is preferable to carry out the polymerization reaction while stirring the emulsion at 50 to 250 rpm. Further, it is preferable that the amount of the monomer used be at least an amount that can form a film of 0.05 μm on the surface of the metal fine particles.

[0013] The present invention will be explained below with reference to Examples, but the present invention is not limited thereto.

[Example] Example 1 1. Materials for preparing microcapsule type conductive filler Metal fine particles: Silver powder (particle size 0.3 to 0.5 μm, manufactured by Fukuda Metals) Coupling agent: Titanate coupling agent (manufactured by Ajinomoto) Monomer A: Bisphenol A type epoxy resin (BPA) ,
Monomer B: Tetraethylene pentamine (TEPA, manufactured by Wako Pure Chemical Industries) Emulsifier: Polyoxyethylene alkyl phenyl ether (manufactured by Kao) Thickener: Polyvinyl alcohol (PVA, manufactured by Wako Pure Chemical Industries)

2. Preparation of microcapsule-type conductive filler 2.1 Coupling agent treatment of silver powder Add 0.0 ml of titanate coupling agent to 70 ml of ethanol.
1 g of silver powder and 5 g of silver powder were added thereto, and the mixture was stirred with a stirrer for 10 minutes. Next, the surface of the metal fine particles was treated with a coupling agent by heating this solution to 60° C. and drying the ethanol. 2.2 Preparation of oil phase 10 g of monomer BPA was dissolved in 15 ml of dichloroethane, and 5 g of the above silver powder was added to prepare an oil phase. 2.3 Dispersion of silver powder The oil phase was irradiated with ultrasonic waves at 25 to 45 Hz for 10 minutes to fully disperse the silver powder. 2.4 Preparation of aqueous phase 370ml water, 1.5g emulsifier, thickener PVA25
g, 10 g of monomer TEPA was dissolved to prepare an aqueous phase. 2.5 Preparation of emulsion Prepare the aqueous phase using a homogenizer (manufactured by Fritsch Japan) at 70°C.
While stirring at 00 rpm, the oil phase was gradually added dropwise to prepare an emulsion. 2.6 Interfacial Polymerization Reaction This suspension was heated to 60° C. while stirring at 150 rpm using a three-one motor, and the reaction was continued for 7 hours. 2.7 minutes The microcapsule-type conductive filler was filtered and separated from the weaning emulsion, and its cross section was observed to have a diameter of 0.1 μm as shown in Figure 1.
It was confirmed that a somewhat thin polymer layer was formed.

3. Preparation and application of conductive adhesive 3.1
Add 5g of insulating microcapsule type conductive filler to adhesive resin.
A conductive adhesive was prepared by dispersing it in 3.5 g of BPA. As shown in Figure 2, this conductive adhesive is applied between two glass plates provided with indium tin oxide (ITO) conductive films, and the two glass plates are lightly sandwiched together to generate a DC voltage of 5V between the two ITO conductive films. was applied, it showed an insulation of 1011 Ωcm.

3.2 Conductivity Two glass plates coated with the above conductive adhesive were subjected to a surface pressure of 4
When the coating layer of the microcapsules was destroyed by adding 1.5 kg, conduction was established between the glass plates. Furthermore, when the surface condition of the cross section between the glass plates was observed using a scanning electron microscope, it was confirmed that the coating layer of the microcapsules was destroyed and the metal and ITO were bonded together, as shown in Figure 3. .

Example 2 The same materials and methods were used as in Example 1, except that the silver powder in Example 1 was replaced with copper fine particles (average particle size 4 to 8 μm, manufactured by Tanaka Kikinzoku Co., Ltd.) whose surface was coated with silver in advance. Metal fine particles were coated and used to test conductivity. The same results as in Example 1 were obtained, and it was confirmed that the metal fine particles were coated with an insulating resin.

Example 3 In the preparation of the aqueous phase in Example 1, the monomer TEPA was not added, and in the preparation of the oil phase, 10 g of homomonomer methyl methacrylate (manufactured by Wako Pure Chemical Industries, Ltd.) was used instead of the monomer BPA.
and polymerization initiator benzoyl peroxide (manufactured by Wako Pure Chemical Industries, Ltd.) 0.1
A microcapsule type conductive filler was produced in the same manner as in Example 1 except that g was added. The same results as in Example 1 were obtained.

Comparative Example 1 When coating with metal fine particles was attempted in the same manner as in Example 1 except that no coupling agent was used, there were uncovered portions as shown in FIG.

Comparative Example 2 When an attempt was made to coat fine metal particles in the same manner as in Example 1, except that no thickener was used, the particles settled and agglomerated, and coating as fine particles could not be achieved.

Comparative Example 3 An attempt was made to coat fine metal particles in the same manner as in Example 1, except that no emulsifier was used, but sufficient coating could not be achieved because the oil layer and water phase did not emulsify. .

[0022]

Effects of the Invention According to the method of the present invention, the microcapsule-type conductive filler coated with a polymer resin layer is dispersed in an adhesive resin, applied between a chip and a pattern, and pressed to form a capsule shell. The polymer coating layer to be formed is destroyed to create electrical continuity between the chip and the pattern.
On the other hand, insulation between adjacent patterns can be maintained. And since it is based on emulsion polymerization, just select the monomer,
Metal fine particles can be coated with either thermosetting or thermoplastic resin.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a microcapsule-type conductive filler coated according to the present invention.

FIG. 2 is a cross-sectional view showing a state in which an adhesive in which microcapsule-type conductive filler is dispersed is applied between two conductive substrates.

FIG. 3 is a cross-sectional view of the microcapsule-type conductive filler shown in FIG. 2 in a conductive state.

FIG. 4 is a cross-sectional view of an incompletely coated microencapsulated conductive filler.

FIG. 5: The amount of uncoated conductive fine particles
It is a graph showing the relationship between insulation resistance and conductivity.

[Explanation of symbols]

1...Metal fine particles 2...Polymer coating layer 3...Adhesive resin 4...ITO conductive film 5...Glass plate

Claims (6)

[Claims] Claim 1: After surface-treating fine metal particles with a coupling agent, the fine metal particles are dispersed in an organic solvent in which monomers to form a homopolymer and a polymerization initiator are dissolved to form an oil phase. , an emulsifier and a thickener are added to an aqueous phase in which an emulsifier and a thickener are dissolved in water to form an emulsion in which fine metal particles are suspended;
A method for coating fine metal particles, which comprises applying heat and/or a catalyst to the emulsion to polymerize a monomer to form a homopolymer film on the surface of the fine metal particles. 2. After surface-treating the metal fine particles with a coupling agent, the metal fine particles are dispersed in an organic solvent in which monomer A to form a copolymer is dissolved to form an oil phase, and this oil phase is mixed with other monomers. B, an emulsifier, and a thickener are added to an aqueous phase in which an emulsifier and a thickener are dissolved in water to form an emulsion in which fine metal particles are suspended;
A method for coating fine metal particles, which comprises applying heat and/or a catalyst to the emulsion to polymerize a monomer, thereby forming a copolymer film on the surface of the fine metal particles. [Claim 3] The particle size of the metal fine particles is 0.1 to 30 μm.
3. The method according to claim 1 or 2, wherein the method is within the range of . 4. Claim 1 or 2, wherein the amount of the coupling agent is in the range of 0.1 to 4% by weight based on the weight of the metal fine particles.
Method described. [Claim 5] The viscosity of the aqueous phase to which the thickener has been added is 20 to 5.
3. The method according to claim 1 or 2, wherein the range is 000 cps. 6. The method according to claim 1 or 2, wherein no metal fine particle aggregates of 30 μm or more are present.