WO2005109448A1

WO2005109448A1 - Insulated conductive ball for anisotropic electric connection and its method of preparation and products using the same

Info

Publication number: WO2005109448A1
Application number: PCT/KR2005/001367
Authority: WO
Inventors: Sang Hun Lee; Kee Ho Chang; Jeong Deok Seo
Original assignee: Microglobe Corp Co., Ltd.
Priority date: 2004-05-12
Filing date: 2005-05-10
Publication date: 2005-11-17
Also published as: JP2007537572A; KR100637763B1; KR20050108521A

Abstract

The present invention relates to insulated conductive particles for anisotropic conductive connection, preparation methods thereof and anisotropic conductive products using the same. In particular, the present invention relates to formation methods of insulation layer of a uniform and sufficient thickness avoiding aggregation of the particles, which is a major cause for connection failure, and the formation of insulation layer that is stable enough to resist undesirable stripping off from the surface of the particle and to minimize dissolution in solvents. In the present invention, as an insulated conductive particle comprising of a conductive particle and an insulation resin layer coated on the surface of the conductive particle for anisotropic conductive connection, an anisotropic insulated conductive particle whose insulation layer is formed by coating insulation resin microparticle containing hetero- element or functional group. The insulated conductive particle of the present invention can be prepared without delicate devices with high yields, and the conductive connection material using the insulated conductive particle ensures production of uniform and excellent products in quality.

Description

Description INSULATED CONDUCTIVE BALL FOR ANISOTROPIC ELECTRIC CONNECTION AND ITS METHOD OF PREPARATION AND PRODUCTS USING THE SAME Technical Field

[1] The present invention relates to insulated conductive ball for anisotropic electric connection, and its method of preparation and products using the same. In particular, the present invention relates to formation methods of insulation layer of a uniform and sufficient thickness avoiding aggregation of the particles, which is a major cause for connection failure, and the formation of insulation layer which is stable enough to resist undesirable stripping off from the surface of the particle and to minimize dissolution in solvents. Background Art

[2] An anisotropic conductive connection method is widely used for electric connection between electronic parts, semiconductor devices and connection terminals of substrate. An anisotropic connection method is generally applied to electrical connections between TCP(tape carrier package) terminals and transparent electric terminals of glass substrate, and between drive I/C and FPC(flexible printed circuit board) terminals or between drive I/C and transparent electric terminals. Especially, in these days the application of anisotropic connection materials is being extended to chip packaging by flip-chip manner as a next generation packaging process in which it can substitute for conventional solder ball packaging medium.

[3] Recently, as electronic parts has been manufactured to be smaller and thinner, the connection terminals have become even finer, and thus it become a major issue to prevent occurrence of a short circuit between the neighboring terminals in an anisotropic conductive connection process. To avoid such a short circuit formation, the use of insulated conductive ball as a conductive medium in anisotropic conductive materials is being extended which is the conductive particle coated with a thin resin layer.

[4] However, insulated conductive balls so far developed have diverse problems in terms of preparation procedure and product characteristics. The type of presently developed insulated conductive balls could be sorted into three categories by the type of insulation resin; that is, thermoplastic resin.

[5] First, when the thermoplastic resin is used as an insulating coating material, it is difficult to obtain a sufficiently thick and uniform coating layer. Actually, the coating processes such as solution dipping and interfacial polymerization have been reported. In solution dipping process, the insulation layer of a certain thickness may be obtained by repeating dipping of conductive particle into a resin solution of a certain concentration and drying. In interfacial polymerization process, once conductive particles are treated with a coupling agent or a surface treatment agent having a particular functionality, then a desired monomer is added and polymerized. However, these processes do not ensure a uniform quality and high yield because many steps of procedure are needed, and furthermore the aggregation of particles during the process can not be avoided intrinsically. As a result, when an anisotropic conductive material using such insulated conductive balls is used in electric connection of electronic devices, those balls may occur connection failure. In addition, when the insulation layer consisted of thermoplastic resin, the layer may be peeled off by the solvent used for preparation of the anisotropic conductive connection material, and thus the solvents which can be used are limited.

[6] Meanwhile, when the insulation layer is formed with a thermosetting resin, the problems of thermoplastic resin such as peeling-off and aggregation may be avoidable in some extent, but it is difficult to control the crosslink density of insulation resin layer. If the degree of crosslink is too low the same problem as in thermoplastic resin happens, and if the degree of crosslink is too high, the insulation layer would not get removed from the surface of the conductive particle in the anisotropic connection process so that the electric connection between the terminals would not be made satisfactorily, and when the too high pressure is applied to destroy and remove the insulation layer, it is likely to damage the terminals and even in case of that the pieces of the insulation layer still remains in the surface of the particles to block the reliable electric conduction between the terminals.

[7] To solve such problems, Sony Chemical Corp. has proposed the preparation of insulated conductive balls by coating crosslinked polymer with a predetermined degree of crosslink by physical and mechanical manner(KR 2001-0060234 A). Sony Chemical Corp. claimed that the above problems was overcome by coating the conductive particle in the coating ratio of 50-99% using a resin particle whose gel portion is above 90%. But, Sony's method can not give the uniform coat, and the resultant insulation layer is not entirely crosslinked it is easy to peel off the surface of the particle. Also, dry coating process such as hybridization method results inevitably in agglomeration of particles, which brings a problem of purification.

[8] Disclosure of Invention Technical Problem

[9] The present invention is to provide formation methods of insulation layer of uniform and sufficient thickness on a conductive particle avoiding aggregation of the particles, which is a major cause for connection failure, and the formation of insulation layer which is stable enough to minimize undesirable stripping off the surface of the particle and dissolution in solvents.

[10] In other words, the object of the present invention is to solve the problems of insulated conductive balls so far in which thermoplastic or thermosetting resin, and to provide insulated conductive ball, which is much improved electric conduction and insulation characteristics, and its preparation methods.

[11] Technical Solution

[12] Generally, it is very difficult to coat a resin layer of several ten to hundred nm thick on a microparticle. As a coating process which forms resin-coated microparticles, in JP 96-13076, several methods including interfacial polymerization, in situ polymerization, spray-dry process and vacuum deposition were proposed, and in JP 87-71255, solution dipping method was proposed. However, all of those processes do not allow the uniform layer of several ten to hundred nm thick. In interfacial or in situ polymerizations not only the aggregation of the conductive particles occurs but also the polymerization proceeds in a place other than the surface of the conductive particles. Thus, a uniform and pure products without impurity can not be obtained. Spray-dry and vacuum deposition processes can not avoid the aggregation either. The solution dipping process proposed in JP 87-71255 is not a practical method of preparation of coated microparticles because even repeated dipping-drying can not form a several hundred thick coating layer and after each dipping-drying process it is necessary to break down and separate the aggregated particles to individual particles. In KR 2001-060234 A Sony Chemical Corp. proposed a method in which conductive particles are covered with partially crosslinked polymer particles mechanically in gas phase. The method, as mentioned before, the formation of uniform coat is intrinsically impossible and the binding force between conductive particle and the insulation particle is weak, and as a result mechanical strength and solvent resistance of the insulation layer are not that strong.

[13] The present invention is based on the results of the intensive research carried by the present inventors that when such polymer particles having hetero elements or functional units on the surfaces, which have attractive interaction with metal surfaces of the conductive particles, are used for coating the conductive particles, the above problems can be overcome and uniform and sufficient coating is possible.

[14] Elements such as sulfur and phosphorous are known to make a strong bonding which is close to a covalent bonding with many metals including gold, and nitrogen and oxygen also make a relatively strong bonding with metals via dipole-dipole interaction. Thus, resin particles containing hetero elements such as sulfur, phosphorous, oxygen and nitrogen or functional groups containing the such, which show attractive interaction with metal, recognize the metal surfaces like gold, silver, nickel and copper which consist of conventional conductive particles, and attach and fix on the surface of conductive particles. Therefore, by use of such resin particles it is possible to form a uniform insulation layer on the conductive particles easily and simply, and the resultant insulated conductive balls have superior stability due to the attractive interactions even in solutions which are used in preparation of anisotropic conductive materials.

[15] In addition, by altering the size of the above resin particles, the thickness of insulation layer can be controlled, and by adjusting the concentration of the insulation resin particles uniform coating on the surface of conductive particles, without aggregation is possible.

[16] Thus, one aspect of the present invention provide a method of formation insulation layer of uniformity and controlled thickness, which solves the problems found in case that thermoplastic or thermosetting resin are used as insulation materials as well as the case that round microparticle is used for the insulation(KR 2001-060234 A)

[17] Another aspect of the present invention is about the methods of preparation of insulation resin particles which is used as an insulation material for conductive ball.

[18] A further aspect of the present invention is about anisotropic conductive connection materials and connection structures.

[19] The other objectives and advantages of the present invention will be described and will be more clearly understood by reference to the detailed description of the preferred embodiment.

[20] In the present invention, as an insulated conductive ball comprising of a conductive particle and an insulation resin layer coated on the surface of the conductive particle for anisotropic conductive connection, an anisotropic insulated conductive particle whose insulation layer is formed by coating insulation resin microparticle containing hetero element or functional group.

[21] It is desirable that the above hetero- element or functional group is a hetero element such as sulfur, phosphorous, nitrogen or oxygen, or a chemical group which contains such an element or elements more than one.

[22] The above insulation resin microparticle can be a uncrosslinked olefin polymer whose molecular weight is a range of 100,000 ~ 1,000,000; a copolymer; condensation thermoplastic copolymer; or a crosslinked resin.

[23] Since the desirable average thickness of the above insulation resin layer is 10 nm ~ 1 μm, the desirable average diameter of the insulation resin microparticle is 10 ~ 1,000 nm.

[24] The glass transition temperature of the above insulation resin is -30 ~ 200°C, desirably.

[25] The anisoptopic insulation conductive ball of the present invention can be prepared by coating conductive particle uniformly with insulation resin microparticle which contains hetero- element or functional group on the surface and thus has binding force with metal.

[26] The coating of insulation resin microparticle can be simply carried out by putting the above conductive particle into an aqueous or an organic suspension (or solution) of the insulation resin particle and stirring the mixture. As a result the insulation resin microparticle attachs and fixes the surface of the conductive particle. Then the resultant product is obtained by filtration, isolation and drying. However, the formation method of insulation layer is not limited by the above, rather so-called hybridization is possible, in which dried powder of insulation resin microparticle is bound to the surface of conductive particle by means of mechanical and thermal manner.

[27] The thickness of insulation layer can be controlled by altering the size of the insulation resin microparticle, and the uniform coating can be achieved by adjusting concentration of the insulation resin microparticle in the suspension (or solution).

[28] Also, after coating like the above, by maintaining the insulated conductive particle at temperature higher than glass transition temperature of insulation layer, the surface of the insulation resin layer can be more smooth.

[29] In an example of the present invention, the above insulation resin microparticle is prepared by radical polymerization in which monomer or functional group containing hetero elements having interaction forces with metal, other monomers, radical initiator, and surface active agent are mixed, and the mixture is polymerized.

[30] In an example of the present invention, insulation resin microparticle which contains sulfur on the surface is prepared by polymerizing isothiuronium salt and the following hydrolysis of the salt to mercaptan.

[31] Also, in the present invention anisotropic connection material and connection structure using it is provided which comprised of insulated adhesives and insulated conductive balls of the present invention uniformly dispersed in the adhesives.

[32] In the present application, the term "hetero element or functional group having binding forces with metal" means any hetero element or functional unit which can attach to metal surface either by covalent bond or by polar linkage or affinity for metal.

[33] In the present application, the term "conductive particle" means any metal microparticle such as nickel, copper, gold, silver, or metal-coated polymer or ceramic microparticle, either used at present or not, either spherical shape or irregular shape.

[34] Advantageous Effects

[35] According to the present invention, it is possible to form insulation resin layer of a uniform and sufficient thickness on the surface of conductive balls easily and simply. Particularly, the insulated conductive particle of the present inventin can be prepared without delicate devices with high yields. The insulated conductive balls of the present invention avoid aggregation of the balls and have superior stability in solutions. The insulated conductive balls of this invention exhibits excellent current feed and insulation characteristics improving the drawbacks of conventional conductive balls for anisotropic electric connection coated by thermoplastic or thermosetting resin. The conductive connection material using the insulated conductive balls ensure production of uniform and excellent products in quality.

[36] Brief Description of the Drawings

[37] FIG. 1 is a schematic sectional view of an insulated conductive particle for anisotropic conductive connection, according to the present invention.

[38] FIG. 2 is a schematic view of the structure of an insulation resin microparticle which composes the insulation resin layer.

[39] * The description of the codes about major parts of the FIG.'s

[40] 10: insulated conductive particle

[41] 11: conductive particle

[42] 12: insulation resin layer

[43] 20: insulation resin microparticle

[44] 22: heteroatom on the surface of the insulation resin microparticle

[45] Best Mode for Carrying Out the Invention

[46] As illustrated in FIG. 1, an insulated conductive particle 10 for anisotropic conductive connection of the present invention is composed of conductive particle 11 and insulation resin layer 12 which coats the surface of the conductive particle.

[47] Although a conductive particle 11 of this invention is not specially limited, generally a particle of 2~10D diameter can be used. The thickness (average thickness) of insulation resin layer 12 is preferably lOnm ~ ID. When the thickness of insulation resin layer is too high current feed characteristics may become poor. In addition, because the fraction of insulation rein in an anisotropic conductive connection material using the insulated conductive particle becomes large, after connection the properties such as heat-resistance and adhesion become inferior. On the contrary, when the layer is too thin the insulation characteristics may not be satisfactory. The appearance of surface of insulation layer can be smooth and of uniform thickness or rough and of irregular thickness according to composition of insulation resin microparticle and process condition of insulation coating.

[48] Insulation resin layer, according to characteristics of insulation resin microparticle (FIG. 2), is composed of usual thermoplastic resin or crosslinked polymer of suitable crosslink density. Preferably, the above insulation resin microparticle is comprised of one of such polymers whose molecular weights are 100,000-1,000,000 as un- crosslinked olefin polymer, copolymer, condensation thermoplastic resin, and crosslinked polymer.

[49] Softening point of insulation resin layer is preferably higher than the heating temperature of anisotropic conductive connection process. When the softening point is lower than the heating temperature, insulation characteristics tends to deteriorate. However, when softening temperature is too higher than the heating temperature, the insulation resin layer can not be easily removed from the surface of the conductive particle when the insulated conductive particle is pressed between bumps, and as a result, current feed characteristics may become poor. In preparation of resin particle (FIG 2) of the present invention, by using various monomers and a appropriate amount of multifunctional monomers, many properties of insulation resin layer including heat resistance, mechanical strength, and rheological properties can be adjusted as desired.

[50] The important properties required in insulation resin layer are suitable mechanical strength, solvent resistance and heat resistance. Insulation resin layer should be remained safe during preparation of anisotropic conductive connection materials against mechanical agitation and mixing with solvent, resin, curing agent, coupling agent and etc. Generally used solvents in the preparation of anisotropic conductive connection materials are ketones such as acetone, methyl ethyl ketone (MEK) and methyl isobutyl ketone (MIBK),or hydrocarbon solvents such as toluene, benzene and xylene, as well as common industrial solvents including THF. Therefore, unless there is a special attractive or binding forces to metal surface of conductive particle as an insulation layer of the present invention, dissolution or peeling-off can not be avoidable.

[51]

[52] Whatever the composition of bulk 21 is, the insulation resin microparticle 20, which is used as an insulation material in the present invention, has hetero- elements 22 on the surface such as sulfur, phosphorous, nitrogen and oxygen, or functional groups containing such elements (FIG 2). Because those heteroatoms show binding force with metal, they attach and fix firmly to the surface of conductive particle and the insulation resin layer formed in such manner does not only peel off by physical impact but also has excellent solvent resistance so that it does not deform and dissolve during the process of preparation. [53] Insulation resin layer should not flow even upon heating if no pressure is applied. Otherwise in an anisotropic conductive connection process a flow of insulation resin layer can bring phase separation in adhesive matrix and aggregation of conductive particle, and resultant occurrence of a short circuit. Therefore softening point or glass transition temperature of insulation resin layer is preferably same as or slightly higher than the anisotropic conductive connection temperature. However, recently device assembly companies demand anisotropic conductive connection materials which can be processed at lower temperature and pressure for better productivity and security of connection process on a flexible board or film. In other words, because insulation resin layer should be removed at low temperature within a short time for the 'low temperature-rapid cure' anisotropic conductive connection process, in this case the softening point of insulation resin layer is preferable to be lower than heating temperature. However, insulated conductive particles developed to date in which softening point of insulation resin layer is lower than heating temperature do not satisfy low temperature-rapid cure connection process since phase separation occur. On the contrary, the insulated conductive particle of the present invention is different from those developed so far since there is binding force between insulation resin particle and the surface of conductive particle, and thus even if the softening point of insulation resin layer is lower than the heating temperature phase separation does not occur and the connection process is accomplished. In the present invention glass transition temperature of insulation resin layer is preferably -30 ~ 200°C, and it may be generally higher than the heating temperature, but it may be lowered below the heating temperature for low temperature-rapid cure process.

[54]

[55] Preparation of insulation resin layer

[56] In the present invention, insulation resin particle satisfying all the above required characteristics can be prepared by various methods. For the polymerization methods, it is preferable to use polymerization techniques such as dispersion polymerization, suspension polymerization, micro-suspension polymerization, and emulsion polymerization, in which products are obtained as particles. This is because obtained particle suspension can be directly used in coating process, and furthermore the particle size can be controlled. The preferable diameter of insulation resin microparticle is 10~l,000nm since the desirable average thickness of insulation resin layer is 10 nm~lμm.

[57] An example of preparation method of insulation resin microparticle for the present invention is as follows. After a monomer or a few monomers, which will be main components of the microparticle, are placed in dispersion medium like water and alcohol, a monomer containing hetero-atom such as sulfur, phosphorous, nitrogen and oxygen are added to the mixture along with an appropriate amount of radical initiator and surfactant. The mixture is heated and stirred to give resin microparticles which have hetero-atom on the surface. In this case the monomer containing a hetero-atom is placed on the surface of the resultant resin microparticle because the monomer is relatively hydrophilic.

[58] In dispersion polymerization, according to hydrophilicity of monomer having hetero-atom, pure water or a mixture of water and alcohol can be used as a dispersion solvent. But, suspension polymerization is not suitable for highly hydrophilic monomers such as acrylamide and acylic acid. For an example, suspension copoly- merization of acrylamide, styrene and methyl methacrylate probably results in a heterogeneous product, which is a mixture of poly (strene-co-methyl methacrylate) resin particle containing almost no acrylamide in it and polyacrylamide that is dissolved in water phase.

[59] The diameter, thermal and mechanical properties, as well as composition and characteristics of the surface can be controlled by adjusting type and amount of each reactant, temperature and agitation speed, etc. The insulation resin layer is formed of the resin microparticle attached to surface of conductive particle via binding force between the two. Therefore, most of properties of the insulation resin layer are determined by the size and characteristics of the microparticle.

[60] In an example of the present invention, a resin particle containing hetero-atoms on the surface is prepared by multi-step reactions. As mentioned before, multi-step reaction is desirable in order to attach sulfur or phosphorous to surface of particle, which is different case from hydrophilic monomers such as acrylamide and acrylic acid. In particular, a sulfur-containing monomer like 4-methylmercaptostyrene is not such a hydrophilic monomer that it is not expectable to locate at the surface of particle in dispersion polymerization, and furthermore mercaptan or thiol compound participate chain transfer reaction in radical polymerization and hinder the polymerization itself.

[61] Therefore, for preparation of particle containing hetero-elements at the surface it is preferable that a particle containing reactive group at the surface such as epoxy is synthesized first, then a desired element is added through the reaction of the surface of the particle and a suitable reactant. In case of particle containing sulfur, particularly a isothiuronium salt can be polymerized as a precursor, followed by hydrolysis of the salt on the surface of particle to mercaptan.

[62] Composition of insulation resin particle is not necessarily a polymer which is made by addition of a olefin monomer. That is a condensation polymer microparticle such as polyester, polyamide and polyurethane. In this case particle itself shows adhesion force superior to olefin polymer particle, but by modification of the surface coating efficiency can be improved. [63] Meanwhile, it is not necessary for insulation resin particle to be round in shape. An irregular powder prepared by bulk or solution polymerization followed by pulverization can be used as an insulation material for the present invention as long as it contains some amount of hetero-atom such as sulfur or nitrogen.

[64]

[65] Preparation of insulated conductive particle

[66] The conventional insulation coating processes including solution dipping, interfacial polymerization, in situ polymerization, spray-dry process and vacuum deposition, physical-mechanical hybridization can hardly give uniform and sufficiently thick insulation layer. On the contrary, in the present invention insulation coating can be achieved simply by putting a conductive particle in an aqueous suspension of microparticle followed by mixing, filtration and drying.

[67] Insulated conductive particle in the present invention can be prepared as follows. After putting conductive particle in an emulsion or suspension of insualtion resin microparticle, then stirring the mixture for a certain time to attach the resin particle to surface of the conductive particle, filtering and isolating followed by drying to give the final product. In the drying step of this case vacuum may be applied, but common air- circulation drying oven is enough. Insulation microparticle as an insulation material of the present invention contains hetero-atom or functional group. Therefore, simply agitating a mixture of aqueous dispersion of microparticle and conductive particle makes microparticle attach and fix to surface of conductive particle to form a insulation layer.

[68] In this process, the uniform coating of insulation resin on the surface of conductive particle without aggregation of the particles can be achieved by adjusting the concentration of insulation resin in the dispersion.

[69] The shape and surface roughness of insulation resin layer depends on work-up conditions. If insulated conductive particle is placed at a temperature higher than the softening point, an insulation layer of more uniform thickness and smooth surface could be obtained. In this case, if particles coagulate each other due to stickiness of the surface it is usable to put the insulated conductive particle in a non-solvent whose boiling point is higher than the softening point of insulation layer, and heat it.

[70] Also, besides the above methods as a way of coating a conductive particle with an insulation resin microparticle, a mechanical-thermal binding of dry powdery insulation resin microparticle to the surface of conductive particle is possible.

[71]

[72] Anisotropic conductive connection material and connection structure.

[73] An anisotropic conductive connection material can be obtained in the shape of film or paste by uniformly dispersing the anisotropic insulated conductive particle of this invention into an insulating adhesive using a conventional technique. In this case, common adhesives can be used as an insulating adhesive.

[74] In addition, a connection structure, which shows good conductive and insulating properties, can be obtained by an anisotropic conductive connection material of this invention as above is placed between the confronting two connection objectives (semiconductor, circuit board to package the semiconductor, flexible circuit board, transparent electrode array, etc.), and heat and press it.

[75]

[76] The more detail of the present invention is illustrated as follows by specific examples.

[77]

[78] Example 1

[79] Preparation of insulation resin microparticle

[80] Chloromethylstyrene(7.0g) and thiourea(3.7g) were added to methanol(15mL), and mixed well. To the mixture t-butylcathecol(0.20g) was added and followed by stirring for 10 hours at 48°C. The mixture was poured into ether to give precipitate which was filtered and dried under reduced pressure. The resultant isothiuronium salt(2.0g) was dissoved in distilled water(80mL), and styrene(20.0g), butyl acrylate(60.0g) and K S O 8 (0.25g) were added. The mixture was heated and stirred for 20 hours at 70°C. To the reactants PVA(lg) and KOH(2M, 5.0mL) were added, and the mixture was agitated for 5 hours at room temperature. The obtained particle was purified by centrifuge and washing with ethanol, finally by dried under reduced pressure.

[81]

[82] Example 2

[83] Preparation of insulation resin microparticle

[84] In a 250-mL flask, styrene(8.0g), butyl acrylate(2.0g) and deionized water(lθθg) were placed and mixed. PVP(2.0g) and K S O (0.20g) were added to the mixture and stirred for 12 hours at 70°C. To the mixture glycidyl methacrylate(2.0g), PVA(l.Og) and deionized water(20g) were added and stirred strongly for 12 hours at 70°C. To the obtained product hexamethylenediamine(2.0g) was added and the mixture was stirred for 24 hours at 50°C. The obtained microparticle was isolated by centrifuge and washed with water and ethanol. Analysis show that the average diameter of the particle was about 150 nm.

[85]

[86] Example 3

[87] Preparation of insulation resin microparticle

[88] Styrene(7.0g), butyl acrylate(3.0g), acrylamide(l.Og), K S O (0.5g) and ethanol(70g) were placed and mixed in a 100-mL flask, and a mixture of deionized water(40g) and PVP(2.0g) was put into the flask. The temperature of the reactants was raised to 90°C and stirred for 24 hours at that temperature. The prepared particle was isolated, washed and observed by SEM. The average diameter of particle was around 105nm.

[89]

[90] Example 4

[91] Preparation of insulation resin microparticle

[92] The insulation resin microparticle was prepared by the same way except a mixture of butyl acrylate(59g) and hexamethylenediamine(lg) was used instead of butyl acrylate(60g).

[93]

[94] Examples of practice 1-8

[95] Conductive particle, which is a Ni/Au plated hexamethylenediacrylate polymer of 4D diameter, was coated with insulation resin particles dispered in water which were synthesized as above examples of preparation under the condition as Table 1 to give insulated conductive particles for anisotropic conductive connection. The coating process is as follows.

[96] Microparticle dispersed solution whose solid content was 5% was prepared by adding microparticle powder to water(or ethanol, or other organic solvent) and stirring with ultrasonication. To the solution(50mL) conductive particle(1.0g, Sekisui Chemical Co., Micropearl AUL704) was added, and the mixture was stirred for 30 minutes at 50°C. The resultant particle was isolated by ultracentrifuge and washed with ethanol several times and dried under reduced pressure. SEM pictures showed that the conductive particle was covered with microparticle with 200~300nm thickness. The insulated conductive particle was placed in 50-mL beaker and the beaker was placed into a oven for 5 minutes at 100°C. From the SEM pictures it is found that the particle shape of the insulated conductive particle surface was almost disappeared and smooth insulation layer was formed. The obtained insulated conductive particle, by TGA analysis, was found that it had a insulation layer of 150nm thickness.

[97] Coating fraction(%) and average thickness of insulation resin layer(nm) according to each example of practice is given in Table 1. In Table 1, coating fraction was determined by calculation the area which was covered with microparticle upon 50 conductive balls which were chosen at random on the SEM picture.

[98] Table 1

[99]

[100] Examples of comparison 1-6

[101] Conductive particle, which is a Ni/Au plated hexamethylenediacrylate polymer of 4D diameter, was coated with insulation resin particles(styrene/butyl acrylate copolymer, 180nm diameter) by the same way as above examples of practice under the condition of Table 2 (Examples of comparison 1-3)

[102] Obtained insulated conductive balls were anylized by SEM and TGA after broken down by rubber bar. Analysis show that the aggregation formed and that the average thickness of insulation resin layer was about 12 nm.

[103] [104] Also, insulation coating was accomplished by solution dipping method in which the solution was made by dissolving the above insulation resin particle in toluene(or THF)(Examples of comparison 1-4). In solution dipping method, the conductive particle(2g) was added to a solution which was prepared by dissolving styrene/butyl acrylate copolymer(10g)(styrene/butyl acrylate=7:3 by weight, diameter 180nm) in toluene(lθθg), and the mixture was stirred for 30 minutes at 30°C. After completion of stirring, the conductive ball was filtered, washed twice with ethanol and dried in vacuum oven under reduced pressure.

[105] For each obtained conductive particle, coating fraction(%) and average thickness of insulation resin layer(nm) are shown in Table 2.

[106] [107] Table 2

[108]

[109] Example of practice 9 [HO] The insulated conductive particle obtained from the above example of practice 1-8 and example of comparison was added to a mixture of a Bisphenol-A liquid epoxy resin (60 weight parts, YDF-128, Gookdo Chemical Co.), a latent curing agent (40 weight parts, H-3842, Gookdo Chemical Co.) and methyl ethyl ketone(70 weight parts). The mixture was mixed throughly to make a 20 weight % solution. An anisotropic conductive connection film was prepared by coating a polyimide film treated with a silicone with the above mixture in order that the thickness of the coating layer is 25 D.

[111] The above anisotropic conductive connection film was placed between 50 micron pitch of a semiconductor device(bump size 35x80 D, bump interval 15 D, bump height 20 D) and a glass substrate provided with 50 D pitch of ITO(wire width 35 D, wire interval 15 D), and compressed at 180°C under 3kgf/cmfor 10 seconds, to obtain a connection structure.

[112] The connection structure was measured for current feed characteristics and insulation characteristics. The results are given in Table 3.

[113] [114] Current feed characteristics [115] Rank: Criterion [116] O : initial resistance of connected 100 pins of 5 ohm or less [117] Δ : initial maximum resistance of connected 100 pins exceeding 5 ohm while being less than 10 ohm

[118] x: initial maximum resistance of connected 100 pins exceeding 10 ohm [119] [120] Insulation Characteristics [121] Rank: Criterion [122] O : resistance of non-connected 100 pins of 10 ohm or more [123] Δ : minimum resistance of non-connected 100 pins of 10 ohm or more [124] x : minimum resistance of non-connected 100 pins less than 10 ohm [125] [126] Table 3

[127] As apparent from Tables 1-3, in particular, Table 3, the insulated conductive particle coated with resin particle containing elements on the surface that exert binding force to metal has superior current feed an insulation characteristics to those coated with common resin particle or resin solution.

[128] Further, the insulated conductive particles is not damaged upon agitation in toluene or MEK for 3 hours at room temperature. Therefore, the insulated conductive particle of the present invention provide with excellent stability in preparation of anisotropic conductive connection materials, and the anisotropic conductive connection materials prepared by such manner provide outstanding anisotropic connection characteristics in anisotropic connection process.

[129] Industrial Applicability

[130] The insulated conductive particle of the present invention exhibits excellent current feed characteristics and insulation characteristics. It can be widely used for anisotropic conductive connections in electronic device and semiconductor industries, for examples, between TCP terminals and transparent terminals of glass substrate in preparation of flat panel display, driver IC and FPC(flexible printed circuit) terminals, driver IC and transparent terminals. In particular, it can be used for electronic devices which recently become smaller and thinner.

[131]

Claims

[I] An insulated conductive ball for anisotropic conductive connection having a conductive particle and an insulating resin layer coated on the surface of the conductive particle, wherein the insulating resin layer is formed of insulating resin microparticles containing hetero element or functional group on the surface, which has binding force to metal. [2] The insulated conductive ball of claim 1, wherein the hetero element or the functional group is selected from the group consisting of sulfur; phosphorous; nitrogen; oxygen and chemical groups containing one or more of these elements. [3] The insulated conductive ball of claim 1 or 2, wherein the insulating resin microparticle comprises the polymer selected from the group consisting of an un- crosslinked olefin polymer; copolymer; thermoplastic condensation resin and crosslinked polymer. [4] The insulated conductive ball of claim 1 or 2, wherein the diameter of the insulating resin microparticle is 10~l,000nm. [5] The insulated conductive ball of claim 1 or 2, wherein the glass transition temperature of the insulating resin layer is -30~200°C. [6] A method of preparing an anisotropic insulated conductive ball comprising: coating a conductive particle uniformly with insulating resin microparticles containing hetero element or functional group on the surface, which has binding force to metal. [7] The method of claim 6, wherein the insulating resin microparticle comprises the polymer selected from the group consisting of an uncrosslinked olefin polymer; copolymer; thermoplastic condensation resin and crosslinked polymer. [8] The method of claim 6, wherein the insulating resin microparticle is olefin addition polymer having molecular weight of 100,000-1,000,000 which is prepared by radical polymerization where a mixture of dispersion solvent; one or more monomers; a monomer containing hetero element or functional group; a radical initiator; and a surfactant is heated. [9] The method of any of claims 6-8, wherein the hetero element or the functional group is selected from the group consisting of sulfur; phosphorous; nitrogen; oxygen and chemical groups containing one or more of these elements. [10] The method of any of claims 6-8, wherein the insulating resin microparticle is prepared by polymerization of isothiuronium salt followed by hydrolysis of the salt located on the surface to mercaptan.

[II] The method of any of claims 6-8, wherein adjusting the size of the insulating resin microparticle controls the thickness of the formed insulating resin layer. [12] The method of any of claims 6-8, wherein the coating comprises dispersing or dissolving insulating resin microparticles in water or an organic solvent to form a suspension or solution; combining the suspension or solution with the conductive particles to form a mixture; and filtration, isolation and drying of the mixture to form anisotropic insulated conductive ball. [13] The method of claim 12, wherein the insulating resin microparticles are uniformly coated on the surface of the conductive particle by adjusting the concentration of insulating resin microparticles in the suspension or solution. [14] The method of claim 12, wherein the coating further comprises maintaining the formed ball at temperature higher than softening temperature of the insulating resin microparticle in order to obtain the smooth surface. [15] An anisotropic conductive connection material in which the insulated conductive balls of claim 1 are uniformly dispersed in an insulating adhesive. [16] A connection structure comprising two target objects facing each other to be connected by placing the anisotropic conductive connection material of claim 15 between the two, and heated and compressed.