WO2009017266A1

WO2009017266A1 - Electroless plating process of crosslinked monodisperse polymer particles with a diameter of micron and the plated particles therefrom

Info

Publication number: WO2009017266A1
Application number: PCT/KR2007/003683
Authority: WO
Inventors: Dong Ok Kim; Jeong Hee Jin; Won Il Son; Seok Heon Oh
Original assignee: Hanwha Chemical Corporation
Priority date: 2007-07-31
Filing date: 2007-07-31
Publication date: 2009-02-05

Abstract

Disclosed herein are a method for the electroless metal plating of micron-sized monodisperse crosslinked polymer particles and plated particles prepared thereby. The method is performed using a dropping method, in which a plating solution, divided into a metal salt solution and a reducing salt solution, is continuously added to a plating bath. In the method for electroless metal plating of monodisperse crosslinked polymer particles, plating uniformity, plating reproducibility and dispersion properties are improved by adjusting the pH in the initial stage of the plating reaction, improving a plating solution addition method, adding an intermission, and selecting a suitable stirring method.

Description

[DESCRIPTION] [Invention Title]

ELECTROLESS PLATING PROCESS OF CROSSLINKED MONODISPERSE POLYMER PARTICLES WITH A DIAMETER OF MICRON AND THE PLATED PARTICLES THEREFROM [Technical Field]

The present invention relates to a method for the electroless metal plating of micron- sized monodisperse crosslinked particles and plated particles prepared thereby, and more particularly to a process for the electroless metal plating of micron-sized monodisperse crosslinked particles, which comprises forming a thin continuous metal plating film on micron- sized monodisperse crosslinked particles through electroless plating so as to improve plating uniformity, plating reproducibility and dispersion properties, as well as plated particles prepared thereby.

[Background Art] Recently, in the electronic component packaging industry, a packaging technique with

ACF (anisotropic conductive film), which substitutes for a process such as soldering and underfill encapsulation, can solve both miniaturization and environmental problems. Thus, it is currently used for TCP interconnection and COG (chip-on-glass) and COF (chip-on-film) packaging in flat panel display modules. Also, it has recently been used in FC (flip-chip) mounting. Such ACF is prepared in the form of a film comprising conductive particles dispersed in an adhesive organic material such as epoxy, and is present between a chip and a substrate to provide electrical communication therebetween. Herein, the conductive particles have a double coating structure, in which a conductive metal layer of nickel or copper is plated on insulating core particles (Japanese Patent Laid-Open Publication Nos. Hei 6-96771 and 7-118866 and Japanese Patent No. 2507381), and gold or platinum is additionally plated thereon in order to prevent the oxidation of the metal layer and improve the electrical conductivity of the metal layer (Japanese Patent Laid-Open Publication Nos. Hei 10- 101962 and 11 -329060). As base particles for plating, polymer materials having a given elasticity have recently been emphasized, rather than inorganic materials. This is because, in a process of placing ACF between a chip electrode and a substrate electrode and thermally pressing the resulting structure, the contact area between conductive particles and electrodes can be increased to solve a problem of contact failure and simplify the mounting process. Thus, the technology for plating this core polymer material with a metal layer is considered to be a key technology for the preparation of conductive particles.

However, in the case of electroless plating on crosslinked polymer microparticles, the plating reaction rate is very high due to the very large surface area, unlike electroless plating on other general bases. For this reason, it is difficult to control the pH of a plating bath and the concentration of each component in the plating bath, and the agglomeration between particles is severe. Thus, for stable plating operation, there was developed a dropping method, in which a plating solution, divided into a metal salt and a reducing agent solution, is slowly and continuously added to a plating bath, while the thickness of a plating layer is suitably controlled (Japanese Patent Laid-Open Publication Nos. Hei 6-96771 and 7-118866). The use of this dropping method forms uniform plating surfaces on crosslinked polymer particles and improves the dispersion of plated particles, because it is easy to control the plating rate, the stability of a plating bath, and the like, compared to a method of introducing crosslinked polymer particles into a plating bath at the same time. However, this method leaves room for improvement with respect to plating uniformity and plating reproducibility depending on the feed rate of a plating solution and the pH of a plating bath, and also fails to sufficiently improve the dispersion of plated particles. [Disclosure] [Technical Problem) Accordingly, the present inventors have conducted studies on the electroless metal plating of crosslinked polymer microparticles in order to solve the problems occurring in the prior dropping method. As a result, the present inventors have found that plating rate and dispersion conditions at the initial stage of plating have strong effects on plating uniformity, plating reproducibility and dispersion properties in electroless plating, and that the agglomeration of plated particles, which has a great effect on plating yield and particle surface conditions in the metal plating of crosslinked polymer microparticles, occurs predominantly at the initial state of plating, thereby completing the present invention.

Therefore, the present invention provides a process for the electroless metal plating of monodisperse crosslinked polymer microparticles using a dropping method, which can improve plating uniformity and plating reproducibility by adjusting pH at the initial stage of plating and improving a plating solution addition method, as well as plated particles prepared thereby.

Also, the present invention provides a process for the electroless metal plating of monodisperse crosslinked polymer microparticles, which can improve the dispersion of plated particles by placing an intermission period, during which the addition of a plating solution is stopped, after the initial stage of plating, carrying out intensive mixing, and then starting the plating reaction again, as well as plated particles prepared thereby. [Technical Solution]

To achieve the above objects, according to one aspect of the present invention, there is provided a method for the electroless metal plating of monodisperse crosslinked polymer microparticles, which improves plating uniformity, plating reproducibility and dispersion properties, the method comprising the steps of: (i) subjecting crosslinked polymer microparticles to a catalytic process (pretreatment process) with SnCl₂ and PdCl₂ to obtain slurry; (ii) adding the slurry to a plating bath, adjusting the pH of the slurry to a value higher than a normal pH level by about 1-3, and continuously adding a plating solution, divided into a metal salt solution and a reducing agent solution, to the slurry, according to a dropping method; (iii) after a point of time at which the color of the slurry turns black, carrying out an initial stage of plating at said adjusted pH for 1/100-1/5 of a total plating time; and (iv) adjusting the pH of the slurry to the normal pH level, and then adding the plating solution to the slurry to perform the remaining stage of plating. According to another aspect of the present invention, there is provided a method for electroless metal plating of micron-sized monodisperse crosslinked polymer particles using a dropping method, the plating method comprising the steps of: (i) subjecting crosslinked polymer microparticles to a catalytic process (pretreatment process) with SnCl₂ and PdCl₂ to obtain slurry; (ii) adding the slurry to a plating bath, adjusting the pH of the slurry to a value higher than a normal pH level by about 1-3, and then simultaneously adding 1/100-1/5 of the amount of metal salt and reducing agent that is to be added over the total plating time; (iii) after a point of time at which the color of the slurry turns black, an initial stage of plating at said adjusted pH for 1/100- 1/5 of the total plating time; and (iv) adjusting the pH of the slurry to the normal pH level, and then adding the plating solution to the slurry to perform the remaining stage of plating. [Advantageous Effects ]

According to the present invention, in a method for the electroless metal plating of crosslinked polymer microparticles using a dropping method, plating uniformity, plating reproducibility and dispersion properties can be improved by: 1) adjusting pH at the initial stage of plating and improving a plating solution addition method, and 2) adding a given intermission time after the initial stage of plating, conducting intensive mixing and then carrying out a plating reaction again. Thus, the present invention can provide high-quality, conductive, electroless- plated particles, which can be used in the formation of fine interconnections, have no problem of electrical capacity when electrically connected, and do not cause a leakage phenomenon. Thus, the present invention will have high industrial applicability. [Description of Drawings ] FIG. 1 is a 10,000-fold enlarged SEM (scanning electron microscope) photograph of the surface of plated particles prepared in Example 1.

FIG. 2 is a 10,000-fold enlarged SEM photograph of the surface of plated particles prepared in Example 2. FIG. 3 is a 10,000-fold enlarged SEM photograph of the surface of plated particles prepared in Example 3.

FIG. 4 is a 10,000-fold enlarged SEM photograph of the surface of plated particles prepared in Example 4.

FIG. 5 is a 10,000-fold enlarged SEM photograph of the surface of plated particles prepared in Comparative Example 1.

FIG. 6 is a 10,000-fold enlarged SEM photograph of the surface of plated particles prepared in Comparative Example 2. [Best Mode]

Hereinafter, the present invention will be described in further detail. As described above, the present invention provides a method for the electroless metal plating of monodisperse crosslinked polymer microparticles, which can improve plating uniformity, plating reproducibility and dispersion properties, which are problems in the prior process, which includes the use of a dropping method, by 1) adjusting the pH at the initial stage of plating and improving a plating solution addition method at the initial stage of plating, and 2) adding a given intermission after the initial stage of plating, conducting intensive mixing, and then carrying out the plating reaction again, as well as plated particles prepared thereby.

Also, according to the present invention, the dispersion of plated particles can be improved by placing an intermission of 1/100-1/5 of the total plating time, in which the addition of the metal salt and the reducing agent is stopped, after an initial plating stage, then conducting more intensive mixing compared to the initial stage of plating so as to sufficiently disperse plated particles, which are weakly agglomerated in a relatively initial stage of plating, and then adding the plating solution again.

Each step of the inventive process for the electroless plating of polymer microparticles will now be described in detail. In the present invention, there is no particular limitation on the kind of resin that is used as the electroless plating base. Resin that can be used in the present invention, may be one or a mixture of two or more selected from among, for example: polyolefins, such as polyethylene, polyvinyl chloride, polypropylene, polystyrene and polyisobutylene; olefin copolymers, such as styrene- acrylonitrile copolymers and acrylonitrile-butadiene-styrene terpolymers; acrylic acid derivatives, such as poly acrylate, polymethyl methacrylate and polyacrylamide; polyvinyl compounds, such as polyvinyl acetate and polyvinyl alcohol; ether polymers, such as polyacetal, polyethylene glycol, polypropylene glycol and epoxy resin; amino compounds, such as benzoguanamine, urea, thiourea, melamine, acetoguanamine, dicyanamide and anilin; aldehydes, such as formaldehyde, palladium formaldehyde and acetaldehyde; polyurethanes; and polyesters. hi the present invention, the average particle size of the resin microparticles is 0.5-1000 jLfliL If the average particle size is less than 0.5 μm, the resulting conductive particles will not be brought into contact with the electrode surfaces that are to be electrically connected with each other, and thus contact failure will often occur due to the distance between electrodes. On the other hand, if the average particle size is more than 1000 μm, an electrically conductive fine connection cannot be achieved. For these reasons, the average particle size is limited within the above-specified range. The average particle size is preferably 1-100 μm, more preferably 1-20 μm, and most preferably 2-10 μm.

Also, the aspect ratio of the resin microparticles for use in the present invention is less than 2, preferably less than 1.3, and more preferably 1.1. If the aspect ratio is more than 2, there may be a large amount of particles that cannot come into contact with electrode surfaces due to their non-uniform particle size in a process of making electrical contact between electrodes using the resulting conductive particles. For this reason, the aspect ratio is limited within the above- specified range.

The coefficient of variation (Cv) of the resin microparticles for use in the present invention is less than 30%, preferably 20%, and more preferably less than 10%. If the coefficient of variation (Cv) is more than 30%, there can be a large amount of particles that cannot come into contact with electrode surfaces due to their non-uniform particle size in a process of making electrical contact between electrodes using the resulting conductive particles. For this reason, the coefficient of variation (Cv) is limited within the above-specified range. In the present invention, the coefficient of variation (Cv) is defined by the following Math Figure 1 :

Math Figure 1

Cv(%) = ( o /Dn) xiOO

wherein σ is the standard deviation of particle size, and Dn is number-average particle size. The standard deviation and the number-average particle size can be calculated using a particle size analysis system (Accusizer model 780, Particle Sizing Systems, Inc,).

According to the present invention, a metal coaling film is formed on the crosslinked polymer microparticles having the above-described properties. The method of forming the metal coating film consists broadly of 1) a pretreatment process (catalytic process) for bases and 2) an electrolysis plating process. In the pretreatment process, a conventional catalytic process, consisting of a sensitization process using SnCl₂ (tin chloride) and an activation process using PdCl₂ (palladium chloride), is carried out. In the electroless plating process, a given amount of the crosslinked polymer microparticles, subjected to the pretreatment process, are added to a temperature- and pH-controlled plating bath at a concentration of 1-10 g/l, and are thoroughly dispersed therein. At this time, a given amount of a dispersing agent may also be added to the plating bath in order to promote the dispersion of the base particles. As the dispersing agent, one or more selected from among polyethylene glycol (molecular weight of 200-20,000), polyalkylene alkyl ether, polyalkylene alkyl ethyl and polyvinyl pyrrolidone (molecular weight of 500-400,000) may be used. The dispersing agent is added to the plating bath at concentrations of 0.1-10000 ppm, and preferably 1-1000 ppm.

Moreover, an ultrasonic stirrer, a general stirrer, a high-speed stirrer or a homogenizer may also be used for the purpose of facilitating the dispersion of the base particles, and can continue to be used during a plating reaction. Then, the plating reaction is carried out using a dropping method, in which a plating solution, divided into a metal salt solution and a reducing agent, is continuously added to the temperature- and pH-controlled plating bath.

The metal salt solution in the plating solution is prepared at a concentration of 1-3 moles from a salt that is generally widely used in electroless plating, for example, nickel chloride, nickel sulfate, copper sulfate, copper acetate, cobalt sulfate, palladium chloride, gold cyanide or gold chloride. The reducing agent solution is prepared at a concentration 1-5 times the concentration of the relative metal salt solution using, for example, sodium hypophosphite (NaH₂PO₂), a borohydride compound or hydrazine. In the present invention, electroless plating is carried out according to the dropping method, in which each of these two solutions is continuously added at a constant flow rate. To such a metal salt solution, reducing agent solution and plating bath, various compounds that promote electroless plating, for example, a pH adjuster, a pH buffer, a complexing agent, a promoter, a stabilizer, etc., may, if necessary, be added according to a conventional method known to those skilled in the art.

However, in the present invention, in order to solve problems of plating uniformity, plating reproducibility and dispersion properties, which are the problems of the prior known dropping method (in which the flow rate of a plating solution, pH, stirring rate, etc., are maintained constant throughout a plating process), electroless plating is carried out in the following manner. In the case where plating is initiated using the dropping method, the initial stage of plating is carried out for 1/100-5/1 (preferably 1/50-1/10) of the total plating time, after the pH of the plating bath is adjusted to a value higher than the normal pH level by 1-3. Alternatively, instead of initiating the plating process using the dropping method, the initial stage of plating is carried out for 1/100-5/1 (preferably, 1/50-1/10) of the total plating time by simultaneously adding 1/100-1/5 (preferably 1/20-1/5) of the amount of each of metal salt and reducing agent, which is to be added throughout the plating process, and then the plating solution is added according to the dripping method to continue to carry out the plating reaction.

Herein, if the difference of the raised pH from the normal pH level is less than 1, plating uniformity and reproducibility will be reduced, and if it is more than 3, the stability of the plating bath will be reduced. Also, if the time of the initial stage of the plating reaction is excessively short, plating uniformity and plating reproducibility will not be improved, and if it is excessively long, the plating reaction will stop. For this reason, the rate of the initial plating reaction is set at a relatively high level in order to solve problems of plating uniformity and reproducibility, which can occur in the dropping method due to the low plating rate at the initial stage of the plating process.

Also, in a process of plating a conductive metal on particles such as crosslinked polymer microparticles, the agglomeration of plated particles, which is a serious problem with plated particles, in addition to problems of plating uniformity and reproducibility, occurs. This phenomenon acts as the main cause of either reduced plating yield or the production of plated particles having a non-coated surface resulting from the decomposition of agglomerated plated particles.

The present inventors have found that this agglomeration of plated particles occurs predominantly at the initial stage of plating reaction. In order to solve this problem, the dispersion of plated particles can be improved by placing an intermission of 1/100-1/5 (preferably 1/50-1/10) of the total plating time, in which the addition of the metal salt and the reducing agent is stopped, at the time of completion of the initial plating stage, carrying out more intensive mixing than in the initial plating stage after the intermission period, so as to sufficiently disperse the plated particles, which have been weakly agglomerated in an earlier stage of plating, and then starting to add the plating solution again. Herein, if the intermission time is excessively short, no improvement in the dispersion of plated particles will be obtained, and if it is excessively long, the plating reaction will stop.

The intensive mixing can be performed either by increasing the stirring speed of the stirrer (including a high-speed stirrer) used in the initial plating stage or by increasing stirring force using a high-speed stirrer instead of a general stirrer used in the initial plating stage. However, when the intensive mixing is excessive, the plating reaction can stop. Specifically, the intensity of stirring for the intensive mixing can be experimentally determined in consideration of the size of a plating bath, the size of working volume, the concentration of solids, etc.

The above-described electroless plating method can form a single-layer coating film or a multilayer coating film made of more than two materials. Preferably, an Ni coating film or an Ni-Au double-layer coating film is formed. The Ni coating film can provide an electroless plating layer that has good adhesion to the base resin particles and good peel resistance. Also, it is easy to form an Au layer on the Ni coating film, and the Ni coating layer can ensure a firm bond with a coating layer plated thereon. Moreover, the formation of the Ni-Au double-layer coating film has an advantage in that it can increase the conductive performance compared to that of a single-layer coating film. The thickness of the coating film formed on the base particles is 10- 500 ran for a single-layer coating film and 10-1000 ran for a double-layer coating film, but the scope of the present invention is not limited thereto.

As described above, the conductive particles prepared according to the present invention are high-quality, conductive, electroless-plated particles, which have excellent plating uniformity, plating reproducibility and dispersion properties, can be used in the formation of fine interconnections, have no problem of limited electrical capacity in electrical connection, and do not cause a leakage phenomenon.

[Mode for Invention] Hereinafter, the inventive method for preparing the conductive particles having excellent plating uniformity, plating reproducibility and particle dispersion will be described in further detail with reference to examples, but the scope of the present invention is not limited thereto. Preparation Example: Process for pretreatment of crosslinked polymer particles Acrylic particles, having an average particle size of 3.6 p, a Cγ of 5% and an aspect ratio of 1.06, were used. 5 g of the particles were dispersed in a chromic acid-sulfuric acid mixture solution (CrO₃: H₂SO₄ = 1: 50) and treated with an ultrasonic cleaner for 30 minutes. After the treatment, the dispersion was maintained at 60 ^°C for 10 minutes and then washed with deionized water. After washing, the particles were immersed in an aqueous solution of SnCl₂ (1.0 g/€) for 3 minutes. Then, the particles were washed with cold deionized water. Then, the particles were immersed in an aqueous solution of PdCl₂ (0.1 g/£) for 3 minutes, and then washed several times with cold deionized water, thus obtaining slurry. Example 1

1 liter of ion-exchanged water was placed in a plating bath, and said slurry was added thereto, while the temperature was raised to 50 ^°C , and stirring was performed. A small amount of ammonia water was added to adjust the pH of the plating bath to 6.5, and then, a plating solution, divided into a metal salt solution (containing 1 mole of nickel chloride) and a reducing agent solution (containing 2.5 moles of sodium hypophosphite), was added slowly to the plating bath at a rate of 1 ι\ύ/mkι using a metering pump. As a result, the plating reaction took place at the same time as the addition of the two solutions. During the plating reaction, the plating bath was maintained at a pH of 6.5. Then, the metal salt solution and the reducing agent solution were continuously added to the plating bath, until the color of the slurry turned black. For 3 minutes after the point of time at which the slurry turned black, the initial stage of plating was performed while the pH was maintained at 6.5. Then, the pH of the plating bath was adjusted to a set value of 5, and an additional plating reaction was carried out, such that the total plating time was 120 minutes. At this time, in order to promote the dispersion of the plated particles in the plating bath, ultrasonic waves of 40 kHz were applied to the plating bath using an ultrasonic dispersion device (BRANSON model 5210).

After completion of the plating process, the obtained nickel-plated particles were washed three times with ion-exchanged water, washed with methanol, and then dried in a vacuum, thus obtaining nickel-plated particles. The formed nickel plating layer had a thickness of about 120 nm. A scanning electron microscope (SEM) photograph of the surface of the obtained plated particles is shown in FIG. 1. Example 2 In this Example, the slurry prepared in Preparation Example was thoroughly dispersed, as in Example 1. However, unlike Example 1 , in which the initial stage of plating was carried out by adding the plating solution according to the dropping method, 10 ml of each of a metal salt solution (containing 1 mole of nickel sulfate) and a reducing agent solution (containing 2.5 moles of sodium hypophosphite) was added to a plating bath having a temperature of 50 ^°C and a pH of 6.5, and thus the plating reaction took place. Then, the color of the slurry immediately turned black, and for 10 minutes after that point in time, the initial stage of plating was performed while the pH was maintained at 6.5. Then, the pH of the plating bath was adjusted to 5 and, at the same time, each of the solutions was added to the plating bath at a rate of 1 iniVmin to carry out an additional plating reaction. The total plating time was 120 minutes.

After completion of the plating process, the obtained nickel-plated particles were washed three times with ion-exchanged water, washed with methanol and then dried in a vacuum, thus obtaining nickel-plated particles. The formed nickel plating layer had a thickness of about 120 ran. A scanning electron microscope photograph of the surface of the obtained plated particles is shown in FIG. 2.

Example 3 The process of Example 1 was repeated, except that the initial stage of plating was followed by an intermission of 5 minutes, during which the addition of the plating solution was interrupted, and then the stirring speed of the stirrer was increased by 50% and the plating reaction was carried out.

After completion of the plating process, the obtained nickel-plated particles were washed three times with ion-exchanged water, washed with methanol and then dried in a vacuum, thus obtaining nickel-plated particles. The formed nickel plating layer had a thickness of about

120 ran. A scanning electron microscope photograph of the surface of the obtained plated particles is shown in FIG. 3.

Example 4 The process of Example 2 was repeated, except that the initial stage of plating was followed by an intermission of 5 minutes, during which the addition of the plating solution was interrupted, and then the stirring speed of the stirrer was increased by 50% and the plating reaction was carried out.

After the completion of the plating process, the obtained nickel-plated particles were washed three times with ion-exchanged water, washed with methanol, and then dried in a vacuum, thus obtaining nickel-plated particles. The formed nickel plating layer had a thickness of about

120 ran. A scanning electron microscope photograph of the surface of the obtained plated particles is shown in FIG. 4.

Example 5 The process of Example 1 was repeated, except that the initial stage of plating was followed by an intermission of 5 minutes, during which the addition of the plating solution was interrupted, and then the stirrer was replaced with a high-speed stirrer, and the plating reaction was carried out.

After the completion of the plating process, the obtained nickel-plated particles were washed three times with ion-exchanged water, washed with methanol, and then dried in a vacuum, thus obtaining nickel-plated particles. The formed nickel plating layer had a thickness of about 120 ran.

Example 6

The process of Example 2 was repeated, except that the initial stage of plating was followed by an intermission of 5 minutes, during which the addition of the plating solution was interrupted, and then the stirrer was replaced with a high-speed stirrer, and the plating reaction was carried out.

After completion of the plating process, the obtained nickel-plated particles were washed three times with ion-exchanged water, washed with methanol, and then dried in a vacuum, thus obtaining nickel-plated particles. The formed nickel plating layer had a thickness of about 120 ran.

Comparative Example 1

The process of Example 1 was repeated, except that the entire plating process, including the initial stage of plating, was carried out at a pH of 5. After completion of the plating process, the obtained nickel-plated particles were washed three times with ion-exchanged water, washed with methanol, and then dried in a vacuum, thus obtaining nickel-plated particles. The formed nickel plating layer had a thickness of about 110 ran. A scanning electron microscope photograph of the surface of the obtained plated particles is shown in FIG. 5. Comparative Example 2 The process of Example 2 was repeated, except that the amount of each of the solutions added at the initial stage of plating was 2 ml.

After completion of the plating process, the obtained nickel-plated particles were washed three times with ion-exchanged water, washed with methanol, and then dried in a vacuum, thus obtaining nickel-plated particles. The formed nickel plating layer had a thickness of about

100 nm. A scanning electron microscope photograph of the surface of the obtained plated particles is shown in FIG. 6.

Comparative Example 3

The process of Example 2 was repeated, except that the temperature of the plating bath at the initial stage of plating was room temperature.

95 nm. A scanning electron microscope photograph of the surface of the obtained plated particles is shown in FIG. 6.

The plated particles prepared in Examples 1-6 and Comparative Examples 1-3 above were measured for the following items, and the test results are shown in Table 1 below.

1. Measurement of plating uniformity

The surfaces of about 1,000 plated particles, prepared in each of the above Examples and Comparative Examples, were observed with a scanning electron microscope (SEM) at 5,000- 10,000x magnification, and the number of particles having non-uniform surfaces was counted.

2. Measurement of plating reproducibility

The above-described plating reaction was repeated 20 times, the surfaces of 500 plated particles for each batch were observed with an SEM, and the number of batches having defects on plated surfaces was counted. 3. Measurement of dispersion of plated particles

The dispersion of the plated particles was measured by dispersing 10 g of the plated particles, having plating uniformity observed as described above, in ultrapure water, classifying the particle solution through an electroformed sieve having 5-μm pores, measuring the amount of particles recovered relative to the amount of particles introduced, and calculating the degree of dispersion according to Math Equation 2 below on the basis of the measurement results.

Math Equation 2

Degree of dispersion (%) = amount of particles recovered/amount of particles introduced X 100 TABLE 1

As can be seen in Table 1 above, in Examples 1 and 2, plated particles having improved uniformity and reproducibility compared to the case of using the prior dropping method could be obtained, and in Examples 3-6, plated particles having improved uniformity, reproducibility and dispersion properties could be obtained.

Claims

[CLAIMS] [Claim 1 ]

A method for electroless metal plating of micron-sized monodisperse crosslinked polymer particles using a dropping method, the plating method comprising the steps of: (i) subjecting crosslinked polymer microparticles to a catalytic process (pretreatment process) with SnCl₂ and PdCl₂ to obtain slurry;

(ii) adding the slurry to a plating bath, adjusting the pH of the slurry to a value higher than a normal pH level by about 1-3, and continuously adding a plating solution, divided into a metal salt solution and a reducing agent solution, to the slurry, according to a dropping method; (iii) after a point of time at which the color of the slurry turns black, carrying out an initial stage of plating at said adjusted pH for 1/100-1/5 of a total plating time; and

(iv) adjusting the pH of the slurry to the normal pH level, and then adding the plating solution to the slurry to perform the remaining stage of plating. [Claim 2] A method for electroless metal plating of micron-sized monodisperse crosslinked polymer particles using a dropping method, the plating method comprising the steps of:

(i) subjecting crosslinked polymer microparticles to a catalytic process (pretreatment process) with SnCl₂ and PdCl₂ to obtain slurry;

(ii) adding the slurry to a plating bath, adjusting the pH of the slurry to a value higher than a normal pH level by about 1-3, and then simultaneously adding 1/100-1/5 of the amounts of metal salt and reducing agent that are to be added over a total plating time;

(iii) after a point of time at which the color of the slurry turns black, an initial stage of plating at said adjusted pH for 1/100-1/5 of the total plating time; and

(iv) adjusting the pH of the slurry to the normal pH level, and then adding the plating solution to the slurry to perform the remaining stage of plating. [Claim 3]

The method of Claim 1 or 2, wherein the crosslinked polymer microparticles have an average particle diameter of 0.5-1000 μm, an aspect ratio of less than 2, and a coefficient of variation (Cv) of particle size of less than 30%. [Claim 4]

The method of Claim 1 or 2, further comprising, after the step (iv), a step (v) of washing and vacuum-drying the plated particles. [Claim 5]

The method of Claim 1 or 2, wherein the initial plating of step (iii) is followed by an intermission of about 1/100-1/5 of the total plating time, in which addition of the metal salt and the reducing agent is completely stopped, and after completion of the intermission, more intensive mixing compared to the initial plating stage is carried out at the same time as the step (iv). [Claim 6]

Micron-sized monodisperse crosslinked polymer particles comprising an electroless plating layer formed thereon according to the method of Claim 1 or 2, the particles having a plating layer thickness of 10-1000 ran and a degree of dispersion of 65-95%.