KR100795309B1 - Method for preparing conductive ball using carbon nano tube - Google Patents

Abstract

A method for preparing conductive balls is provided to improve electroconductivity of conductive balls and to form an ion-bonded multilayer by a self assembled monolayer, thereby preventing crack of a conductive layer causable by a characteristic difference between a polymer and metal. A method for preparing conductive balls includes the steps of: (1) subjecting the surfaces of polymer beads to direct sulfonation to change the surfaces of the polymer beads into sulfone groups; (2) mixing the modified polymer beads(A) with a mixture of a cationic electrolyte solution and a solvent to form a cationic layer(B) on the surface of the modified polymer bead; (3) mixing the cation-stacked polymer beads with a mixture of an anionic electrolyte solution and a solvent to form an anionic layer(C) on the surface of the cation-stacked polymer bead; (4) to form a desired layer, alternately coupling anionic/cationic layers through a repetitive self assembled monolayer comprising the step 2 and step 3, thereby forming a multilayer having a finally cationic layer on the surface of the bead; and (5) mixing the modified polymer beads of the step (4) with surface-modified carbon nanotubes dispersed in a solvent to form polymer beads coated with carbon nanotubes(D).

Description

Method for manufacturing conductive balls using carbon nanotubes {METHOD FOR PREPARING CONDUCTIVE BALL USING CARBON NANO TUBE}

1 is a diagrammatic representation of each layer of conductive balls formed in accordance with the manufacturing method of the present invention:

(A): Polymer beads surface-modified with anions by sulfonation

(B): cation layer laminated by cationic electrolyte solution:

(C): Anion layer laminated by anion electrolyte solution:

(D) modified carbon nanotube (CNT) layer

Figure 2 shows a SEM picture of the conductive ball coated with carbon nanotubes formed according to the manufacturing method of the present invention ((a) 15,000 magnification; (b) 100,000 magnification).

The present invention relates to a method for producing a conductive ball which is a component of an anisotropic conductive film mainly used as a packaging material connecting material of an electronic device.

In general, electronic packaging technology is a very wide variety of system fabrication techniques including all stages from semiconductor devices to final products, and is a very important technique for determining performance, size, price, reliability, etc. of final electronic products.

In recent years, in electronic packaging, the necessity of connecting a large number of narrow-gap electrodes at one time has increased as the circuits have finer gaps and increase in connection density. Accordingly, in the packaging of liquid crystal displays (LCDs), conductive adhesives are used for mechanical and electrical connection between a flexible printed circuit (FPC) and a glass display, and in particular, anisotropic conductive films (Anisotropic) Conductive Film) is mainly used.

The conductive adhesive is largely in the form of anisotropic conductive film, isotropic conductive adhesive (Isotropic Conductive Adhesive), etc., and basically conductive particles such as nickel (Ni), nickel / polymer (Ni), silver (Ag) It is composed of thermosetting and thermoplastic insulating resin.

The anisotropic conductive film is composed of a conductive particle and an insulating adhesive, and as the conductive particles that play an electrically conductive role, carbon fibers were initially used, and then solder balls were used, followed by nickel balls or silver balls. It is used until now.

The reason why silver is used as the conductive particles of the anisotropic conductive film is that it is easy to use as conductive particles due to its low price, high electrical conductivity and good chemical stability, but it is accompanied with the problem of electrical ion migration. In addition, nickel has a low price and relatively good electrical conductivity, but when exposed to high temperature and high humidity, there is a problem such as corrosion or oxidation on the surface. In order to solve this problem, the surface is coated with gold to improve the properties of the conductive particles. However, the above-described gold-coated nickel particles have been developed in the form of coating nickel on a polystyrene ball of divinylbenzene type and coating gold on the outer surface thereof. There is a problem that the elastic force becomes too high to adversely affect the properties of the conductive balls for anisotropic conductive films.

In general, conductive balls are plated with plastic beads plated in the order of Pd, Ni, and Au, and dispersed in the main body part or the resin part, and serve to make electrical connections. In particular, the most important characteristics of conductive balls are connection resistance, reliability, and fairness. Through the research process up to now, these characteristics can be improved. During the process of forming the conductive portion in the contact portion by adhering to each other, cracking of the metal layer occurs due to the difference in the modulus of the polymer bead and the metal layer, resulting in poor conductivity.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method of manufacturing a conductive ball coated with carbon nanotubes having improved surface conductivity as a solution to the above-mentioned conventional problems.

It is also an object of the present invention to provide a conductive ball with improved surface conductivity produced by the production method of the present invention.

In order to achieve the above object, the present invention provides a method for producing a conductive ball coated with carbon nanotubes.

More specifically, the present invention,

Direct sulfonation of the polymer bead surface to modify the surface of the polymer bead with a sulfone group (step 1);

Mixing the modified polymer beads with a mixture of a cationic electrolyte and a solvent to deposit cations on the surface of the modified polymer beads (step 2);

Mixing the cation-laminated polymer beads with a mixture of anionic electrolyte solution and a solvent to deposit anion on the surface of the cation-laminated polymer beads (step 3);

Alternately combining anion / cationic layers through a self assembled monolayer consisting of steps 2 and 3 to form a desired layer to form a multilayer film laminated with final cations on the surface of the polymer beads ( Step 4); And

Mixing the modified polymer beads obtained in step 4 with surface modified carbon nanotubes dispersed in a solvent to form carbon nanotube coated polymer beads (step 5). to provide.

Hereinafter, each step will be described in more detail.

Step 1 produces polymer beads whose surface is modified with sulfone groups.

Polymer beads whose surface has been modified with sulfone groups are formed through the sulfonation process directly on the polymer surface in the form of beads. More specifically, the surface modified polymer beads are obtained by reacting the polymer beads in a solvent for 1 to 24 hours and then centrifuging. At this time, usable solvents include chlorosulfonic acid, sulfonic acid, acetic sulfide, preferably chlorosulfonic acid. The polymers in the form of beads usable in the present invention may include all polymers usable in the art, and their sizes are also conventionally deformable to all available sizes. Preferably, the polymer beads may include polystyrene beads having several micro sizes in a single process through dispersion polymerization.

In step 2, cations are deposited on the surface modified polymer beads.

More specifically, the surface prepared under a specific pH in step 1 is mixed with a sulfone group-modified polymer beads with a mixture of a cationic electrolyte and a solvent to induce ionic bonds of cations from the sulfone groups and cationic electrolyte formed on the surface. The cationic electrolyte that can be used is capable of generating a compound having a terminal group as a cation, more preferably a compound having a terminal group with an amine group (NH ³⁺ ), for example poly (diallyldimethylammonium chloride), Acrylamide, poly (ethyleneamine), poly (allylamine hydrochloride), poly (methyl-vinylpyridinium), poly (butanylbiologen), poly (vinylbenzeneyltrimethylammonium chloride) and the like. In addition, usable solvents are C ₁ to C ₆ linear or branched alcohols, preferably ethanol, methanol, isopropanol. Particularly, in this step, the pH is adjusted to a range of 7.5 to 11 by mixing with a basic solution or the like in a solvent to more smoothly and strongly adsorb the bond between the sulfone group-modified surface and the cation to facilitate stacking of cations on the modified surface. Can be. At this time, the reaction is carried out for 10 minutes to 24 hours to be sufficiently bonded to the modified surface, which may vary depending on the type of cationic electrolyte used and the pH of the solvent to be mixed.

Then, the excess charged cationic electrolyte is removed and washed, for example, separated by centrifugation and washed several times with distilled water.

In step 3, anions are deposited on the surface of the polymer beads on which cations are deposited.

More specifically, the polymer beads formed in step 2 are mixed with an anionic electrolyte with a solvent to induce ionic bonds of anions from cations and anionic electrolytes already formed on the surface. Used herein capable of generating an anionic electrolyte is a compound capable of anionic terminal groups, groups and more preferably the terminal COOH ^-, OH ^- will capable of generating a compound, SO ^3-, poly (acrylic acid), poly As an example ( Sodium styrene) and the like. In addition, usable solvents are C ₁ to C ₆ linear or branched alcohols, preferably ethanol, methanol, isopropanol. In particular, in this step, the pH is adjusted to the range of 1.0 to 7.5 by mixing with a hydrochloric acid, sulfuric acid, etc. in a solvent to more smoothly and strongly adsorb the ionic bond of the cation-modified surface and the anion obtained in the step 2 to the modified surface Lamination of anions can be made easier. At this time, the reaction is carried out for 10 minutes to 24 hours to be sufficiently adsorbed on the modified surface, which may vary depending on the type of the anion electrolyte used and the pH of the solvent mixed.

In step 4, a multilayer film laminated with final cations is formed through a self-assembled monolayer.

The self-assembled monolayer membrane is a monolayer membrane composed of the cation of step 2 and the anion of step 3, which is ionic and can form repetitive self-assembly between cations and anions. This repeats the method of steps 2 and 3, whereby the cation / anion layers are combined alternately. The specific method is the same as described in steps 2 and 3 above. At this time, the number of multilayer films can be laminated from three layers to 20 layers, and the thickness at this time includes 0.1 to 1000 nm. In the case of lamination in a single layer, the uniformity of the thickness cannot be secured due to the formation of a missing layer of the ion layer, whereas in the case of lamination in the multilayer, a neutral layer is formed in the middle of alternating anion membrane and cationic membrane to strengthen the bonding strength of each membrane. do. This phenomenon may cause problems when the final carbon nanotubes are laminated due to the lack of a neutral layer when forming a single layer film.

The surface of the multilayer film thus obtained is made to form a final cation, preferably an amine group (NH ³⁺ ).

In step 5, the polymer beads having the surface of the multilayer film are coated with carbon nanotubes.

More specifically, the multilayer film obtained in step 4 is formed and the polymer beads having the final cationic surface are mixed with the surface modified carbon nanotubes dispersed in the solvent to form the carbon nanotube coated polymer beads.

The carbon nanotubes cannot be directly coated on the surface of the multilayer film, so that the surface and / or the ends thereof are modified with a carboxyl group or a butyl group. Carbon nanotubes that can be used in the present invention is not particularly limited, such as multi, single, and can be used by purchasing a commercially available product or by using a conventional method. As a method for modifying the carboxyl group, any method commonly used in the art may be used, and for example, carbon nanotubes are sintered at 300 to 500 ° C. or higher to remove organic and inorganic materials, and then strong acid (preferably nitric acid). After a sonication for 20 to 26 hours, preferably 24 hours using a solution of a sulfuric acid and a solution of sulfuric acid, a method of diluting with distilled water and centrifugation may be used.

The carboxyl group-modified carbon nanotubes thus formed are dispersed and used in a solvent. Solvents that can be used include distilled water, isopropyl alcohol, ethanol, methanol, butyl alcohol, chloroform, diethyl ether, hexane, cyclohexane, propylene glycol monomethyl ether acetate, cyclotetrahydrofuran, methyl ethyl ketone, and the like. Or it can mix and use.

The conductive balls produced by the present invention can improve the electrical conductivity of the conductive balls by coating carbon nanotubes having excellent electrical conductivity on the surface, which is advantageous for micropattern applications, and is a multilayer film ion-bonded by a self-assembled monolayer film. By forming it, it is possible to prevent the crack of the conductive film caused by the characteristic difference between the polymer and the metal, and to simplify the manufacturing process.

The conductive balls produced by the present invention can improve the electrical conductivity of the conductive balls by coating carbon nanotubes having excellent electrical conductivity on the surface, which is advantageous for micropattern applications, and is a multilayer film ion-bonded by a self-assembled monolayer film. By forming it, it is possible to prevent the crack of the conductive film caused by the characteristic difference between the polymer and the metal, it is possible to simplify the manufacturing process.

Hereinafter, the present invention will be described in more detail based on the following examples. The following examples are intended to illustrate the invention and are not intended to limit the invention. All documents disclosed in the present invention are incorporated by reference.

<Example>

Example 1 Preparation of Conductive Balls of the Present Invention

First, the polymer beads were prepared as follows.

Polymer production method can be largely prepared by dispersion polymerization, emulsion polymerization, suspension polymerization. In the case of suspension polymerization, polymer beads of uniform size cannot be prepared. In the case of emulsion polymerization, beads of very uniform size can be made, but several micro-sized beads are prepared through various stepwise methods. Therefore, in this experiment, uniform polymer beads having several micro sizes were prepared in a single process through dispersion polymerization.

As the polymer beads, polymers such as polymethylmethacrylate and polystyrene may be made, but in this experiment, polymer beads of polystyrene were synthesized. Initiator (benzoyl peroxite, AIBN), dispersant (polyvinylpyrrolidone, polyvinylacetate, hydroxypropyl-cellulose butyl acrylate), styrene monomer, divinyl in a solvent such as ethanol, isopropyl alcohol, distilled water, toluene, methanol Benzene was separately mixed and dissolved in a constant ratio and reacted at a reaction temperature of 50 to 70 ° C. for 12 to 24 hours. The polystyrene beads thus prepared had a uniform size of 500 nm to 10 μm. The polystyrene beads thus obtained were washed several times with ethanol, methanol and distilled water, and dried using a centrifuge and a lyophilizer to obtain polystyrene beads.

Step 1: sulfonation step

After adding chlorosulfonic acid, sulfonic acid, and acetic sulfide solution to each of the three reactors, polystyrene beads were added to each reactor and reacted at a stirring speed of 10 to 150 rpm. The reaction temperature at this time was kept at 0-90 degreeC. After reacting for 5 hours, the mixture was neutralized with ethanol, methanol, and distilled water to obtain polystyrene beads in which the surface of the beads was modified with sulfone groups.

In case of sulfonation using an acetic sulfide solution and sulfonic acid, deformation of polystyrene beads was observed, and in the case of using chlorosulfonic acid, it was confirmed that sulfonation was successful without changing the shape of polystyrene beads.

Steps 2 to 4: cation and anion deposition step

The surface-modified polystyrene beads in the reactor were dispersed in 0.5M NaCl aqueous solution, and impregnated for 24 hours by adding poly (diallyldimethylammonium chloride, 0.05M) and anionic electrolyte poly (sodium styrene, 0.05M) as a cationic electrolyte. When the cation was laminated, the pH was adjusted to 7.5 to 11 using sodium hydroxide solution and the reaction temperature was maintained at 20 to 75 ° C. to stack the cation electrolyte on the surface. In addition, the anion electrolyte solution was laminated by adjusting the pH to 1.0 to 7.5 with sulfuric acid and hydrochloric acid when anion was deposited, and the reaction temperature was adjusted to 20 to 75 ° C. and impregnated for 24 hours.

Carbon Nanotube Modification and Dispersion Process

-Preparation of carbon nanotubes surface-modified with carboxyl groups

Carbon nanotubes were put in a sintering furnace and sintered at 300 to 500 ° C. or higher to remove organics and inorganics. The obtained carbon nanotubes were sonicated for 24 hours with the ratio of nitric acid (HNO ₃ ): sulfuric acid (H ₂ SO ₄ ) solution 3: 1 and washed several times with distilled water, followed by carbon nanoparticles using a 0.2 μm filter. A tube was obtained. 1 to 2.5% by weight carbon nanotubes were dispersed in a solution (70 ml) of distilled water and ethanol at a ratio of 80:20 for 24 hours using an ultrasonic apparatus.

-Carbon nanotubes surface-modified with butyl group

As a method of modifying the butyl group, 20 mg of MWNT (Multi-Wall Nanotube) was dissolved in DMF (30 ml) and dispersed in an ultrasonic wave for 3 hours. Iodo-butane (4 mmol) and benzoyl peroxide (1.6 mmol) were added thereto and reacted at 75 ° C. for 24 hours under argon atmosphere. After completion of the reaction, the reaction mixture was diluted with 100 ml of DMF, filtered, and placed in the same amount of DMF and sonicated for 20 minutes. After repeating the process twice, and washed with acetone and methanol, and dried for 12 hours in a vacuum oven at 80 ℃ to obtain a carbon nanotube surface-modified butyl group. 1 to 2.5% by weight carbon nanotubes were dispersed in a solution (70 ml) of distilled water and ethanol at a ratio of 80:20 for 24 hours using an ultrasonic apparatus.

Step 5: stacking carbon nanotubes

Polystyrene beads (1 g) having an anion / cationic layer laminated thereon were added to a solvent in which surface-modified carbon nanotubes were dispersed, and then lamination was performed at a stirring speed of 10 rpm for 24 hours.

Experimental Example 1: Confirmation of the shape of the conductive ball of the present invention

The shape of the conductive beads prepared through a field emission scanning electron microscope (SEM, JEOL. JSM 890) was confirmed.

The results are shown in FIG. As can be seen in Figure 2, the carbon nanotubes are well bonded to the polystyrene beads formed as the final cation film, the carbon nanotubes laminated on the surface were well bonded to each other to form a carbon nanotube film was confirmed that .

As described above, the conductive balls manufactured by the present invention can improve the electrical conductivity of the conductive balls by coating carbon nanotubes having excellent electrical conductivity on the surface, which is advantageous for the application of fine patterns, and also a self-assembled monolayer film. By forming the multi-layer film ion-bonded by, it is possible to prevent the crack of the conductive film caused by the characteristic difference between the polymer and the metal, and to simplify the manufacturing process.

Although the above has been described with reference to a preferred embodiment of the present invention, those skilled in the art will be variously modified and changed without departing from the spirit and scope of the invention described in the claims below I can understand that you can.

Claims (12)

Direct sulfonation of the polymer bead surface to modify the surface of the polymer bead with a sulfone group (step 1); Mixing the modified polymer beads with a mixture of a cationic electrolyte and a solvent to deposit cations on the surface of the modified polymer beads (step 2); Mixing the cation-laminated polymer beads with a mixture of anionic electrolyte solution and a solvent to deposit anion on the surface of the cation-laminated polymer beads (step 3); Alternately combining anion / cationic layers through a self assembled monolayer consisting of steps 2 and 3 to form a desired layer to form a multilayer film laminated with final cations on the surface of the polymer beads ( Step 4); And Mixing the modified polymer beads obtained in step 4 with surface modified carbon nanotubes dispersed in a solvent to form carbon nanotube coated polymer beads (step 5). The method of claim 1 wherein step 1 is characterized in that the polymer beads are reacted in chlorosulfonic acid, sulfonic acid, or acetic sulfide for 1 to 24 hours to form polymer beads whose surface is modified with sulfone groups. The method of claim 1 wherein step 1 is carried out in chlorosulfonic acid using polystyrene as polymer beads. The method according to claim 1, wherein the cationic electrolyte is selected from poly (diallyldimethylammonium chloride), acrylamide, poly (ethyleneamine), poly (allylamine hydrochloride), poly (methyl-vinylpyridinium), and poly (butanylbiol). Gen), or poly (vinylbenzeneyltrimethylammonium chloride). The method of claim 1 wherein the anionic electrolyte is poly (acrylic acid) or poly (sodium styrene). The method of claim 1 wherein the solvent used in steps 2 to 4 is a C ₁ to C ₆ alcohol. The method of claim 1, wherein the solvent used in step 5 is distilled water, isopropyl alcohol, ethanol, methanol, butyl alcohol, chloroform, diethyl ether, hexane, cyclohexane, propylene glycol monomethyl ether acetate, cyclotetrahydrofuran, methyl And one or a mixture thereof selected from the group consisting of ethyl ketones. The method of claim 1, wherein the surface-modified carbon nanotubes are carbon nanotubes surface-modified with carboxyl groups or carbon nanotubes surface-modified with butyl groups. The method of claim 1 wherein each stack is formed by ionic bonding by cation-anions formed on the surface. A process according to claim 1, characterized in that the end of the cation consists of an amine group (NH ³⁺ ) and the end of the anion consists of COOH ⁻ , OH ⁻ or SO ^{3 −} . The method of claim 1 wherein the cation deposition is performed at pH 7.5 to 11 and the anion deposition is performed at pH 1.0 to 7.5. A conductive ball coated with carbon nanotubes prepared by the method of any one of claims 1 to 11.

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