JP4715969B1 - Conductive particles - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide conductive particles that are low in cost, high in conductivity, and excellent in connection reliability between electrodes without causing migration.
SOLUTION: Core particles 11, a palladium layer 12 covering the core particles 11, having a phosphorus concentration of 1% by weight to 10% by weight and a thickness of 20 nm to 130 nm, and a surface of the palladium layer 12 are disposed. And conductive particles 8b comprising insulating particles 1 having a particle size of 20 nm to 500 nm.
[Selection] Figure 2

Description

  The present invention relates to conductive particles.

  The method of mounting the liquid crystal driving IC on the glass panel for liquid crystal display can be roughly divided into two types, COG (Chip-on-Glass) mounting and COF (Chip-on-Flex) mounting.

  In COG mounting, an IC for liquid crystal is directly bonded onto a glass panel using an anisotropic conductive adhesive containing conductive particles. On the other hand, in COF mounting, a liquid crystal driving IC is bonded to a flexible tape having metal wiring, and these are bonded to a glass panel using an anisotropic conductive adhesive containing conductive particles. Anisotropy here means conducting in the pressurizing direction and maintaining insulation in the non-pressurizing direction.

  By the way, with recent high-definition liquid crystal display, bumps, which are circuit electrodes of liquid crystal driving ICs, have narrowed pitch and area, so that anisotropic conductive adhesive conductive particles are between adjacent circuit electrodes. It has become a problem to cause a short circuit.

  In addition, when conductive particles flow out between adjacent circuit electrodes, the number of conductive particles in the anisotropic conductive adhesive captured between the bump and the glass panel decreases, and the connection resistance between the opposing circuit electrodes increases. However, there was a problem of causing poor connection.

  As a method for solving these problems, as exemplified in the following Patent Document 1, by forming an insulating adhesive on at least one surface of the anisotropic conductive adhesive, the bonding quality in COG mounting or COF mounting There are a method for preventing the decrease in the thickness and a method for covering the entire surface of the conductive particles with an insulating film as exemplified in Patent Document 2 below.

  Patent Documents 3 and 4 below show a method of coating polymer polymer core particles coated with a gold layer with insulating child particles. Further, Patent Document 4 below discloses a method of forming a functional group on the gold layer surface by treating the surface of the gold layer covering the core particles with a compound having any of a mercapto group, a sulfide group, or a disulfide group. Yes. Thereby, a strong functional group can be formed on the gold layer.

  Patent Document 5 listed below discloses a method of performing copper / gold plating on resin fine particles as an attempt to improve the conductivity of conductive particles.

  Patent Document 6 below includes a non-metallic fine particle, a metal layer that covers the non-metallic fine particle and contains 50% by weight or more of copper, a nickel layer that covers the metal layer, and a gold layer that covers the nickel layer. Conductive particles are shown, and there is a description that according to the conductive particles, the conductivity is improved as compared with general conductive particles made of nickel and gold.

  The following Patent Document 7 discloses conductive particles having a base particle and a metal coating layer provided on the base particle, wherein the gold content in the metal coating layer is 90 wt% or more and 99 wt%. There is a description of conductive particles characterized in that it is not more than%.

Japanese Patent Laid-Open No. 08-279371 Japanese Patent No. 2779409 Japanese Patent No. 2748705 International Publication No. 03/02955 Pamphlet JP 2006-028438 A JP 2001-155539 A Japanese Patent Laying-Open No. 2005-036265

However, as shown in Patent Document 1, in the method of forming an insulating adhesive on one side of the circuit connection member, when the bump area is narrowed to less than 3000 μm ² , circuit connection is required to obtain a stable connection resistance. It is necessary to increase the number of conductive particles in the member. When the number of conductive particles is increased in this way, there is still room for improvement in insulation between adjacent electrodes.

  In addition, as shown in Patent Document 2, in the method of covering the entire surface of the conductive particles with an insulating coating in order to improve the insulating property between adjacent electrodes, the insulating property between the circuit electrodes is increased. There is a problem that the conductivity of the conductive particles tends to be low.

  Further, as shown in Patent Documents 3 and 4, in the method of covering the surface of the conductive particles with insulating child particles, resin child particles such as acrylic are used because of the problem of adhesion between the child particles and the conductive particles. There is a need. In this case, the resin-made child particles are melted at the time of thermocompression bonding between the circuits, and the conductive particles are brought into contact with both circuits, thereby establishing conduction between the circuits. At this time, if the resin of the molten child particles covers the surface of the conductive particles, the conductivity of the conductive particles may be easily lowered, as in the method of covering the entire surface of the conductive particles with an insulating film. I understand. For these reasons, suitable particles having a relatively high hardness and high melting temperature, such as inorganic oxides, are suitable as the insulating child particles. For example, Patent Document 4 exemplifies a method in which a silica surface is treated with 3-isocyanatopropyltriethoxysilane and silica having an isocyanate group on the surface is reacted with conductive particles having an amino group on the surface.

  However, it is generally difficult to modify the surface of particles having a particle diameter of 500 nm or less with a functional group, and inorganic oxides such as silica are aggregated during centrifugation and filtration performed after the modification with the functional group. Problems are likely to occur. Furthermore, in the method exemplified in Patent Document 4, it is difficult to control the coverage of the insulating child particles.

  In addition, when the metal surface is treated with a compound having either a mercapto group, a sulfide group or a disulfide group, the reaction between the metal and the compound may occur if there is even a base metal such as nickel or an easily oxidizable metal such as copper. Is difficult to progress.

  Furthermore, as has been clarified by the study by the present inventors, when the conductive particles are coated with an inorganic substance such as silica, conductivity is developed by crushing the metal surface on the conductive particles with silica. Accordingly, since the silica is destroyed by the conductive metal, the migration characteristics tend to deteriorate if the conductive metal contains something other than the noble metal.

  In addition, as shown in Patent Document 6, in recent years, conductive particles of a type in which gold plating is performed on a nickel layer are becoming mainstream. However, in such conductive particles, nickel is eluted and migration is caused. There is. Furthermore, the tendency becomes remarkable when the thickness of the gold plating is set to 40 nm or less.

  Moreover, as shown in the said patent document 7, although electrically conductive particle | grains coat | covered with the metal coating layer whose gold content is 90 weight% or more are favorable in terms of reliability, cost is high. Therefore, it is difficult to say that conductive particles including a metal coating layer having a high gold content are practical, and in recent years, there is a tendency to reduce the gold content of the metal coating layer. On the other hand, the electroconductive particle provided with copper plating is excellent on electroconductivity and cost. However, the conductive particles provided with copper plating have a problem in terms of moisture absorption resistance because migration is likely to occur. Attempts have been made to compensate for the shortcomings of both (gold and copper), but none of them are perfect. For example, the method disclosed in Patent Document 5 cannot sufficiently compensate for the shortcomings of both (gold and copper).

  The present invention has been made in view of the above problems, and an object thereof is to provide conductive particles that are low in cost, high in conductivity, and excellent in connection reliability between electrodes without causing migration.

  In order to achieve the above object, the conductive particles according to the first aspect of the present invention cover the core particles (resin fine particles) and the core particles, the phosphorus concentration is 1 wt% or more and 10 wt% or less, and the thickness is 20 nm. And a palladium layer of 130 nm or less. That is, the conductive particle according to the first aspect of the present invention includes resin fine particles and a conductive layer formed on the surface of the resin fine particles, the conductive layer is a palladium layer containing phosphorus, and the phosphorus concentration in the palladium layer is It is 1 to 10% by weight, and the thickness of the palladium layer is 20 to 130 nm. A feature of the present invention is that the palladium layer is directly formed on the surface of the resin fine particles. In other words, in the present invention, it is preferable that a metal other than palladium (for example, nickel) does not exist on the surface of the resin fine particles. Such characteristics of the present invention are indispensable for achieving the following effects of the present invention.

  In the first aspect of the present invention, since the palladium layer has ductility, when connecting a pair of electrodes using the anisotropic conductive adhesive provided with the conductive particles, the palladium layer is palladium even after the conductive particles are compressed. The layer is hard to break. Therefore, it is possible to improve the conductivity of the conductive particles after compression and the connection reliability between the electrodes, and it is possible to prevent migration of palladium due to cracking of the palladium layer. Palladium is inexpensive and practical compared to noble metals such as gold and platinum. Therefore, the conductive particles according to the first aspect of the present invention including the palladium layer are less expensive than the conductive particles using only gold or platinum.

  In the first aspect of the present invention, since the palladium layer has a thickness of 20 nm or more, sufficient conductivity can be obtained.

  In the first aspect of the present invention, since the palladium layer contains 1 wt% or more and 10 wt% or less of phosphorus, the conductive film having high hardness and biting into the counter electrode surface and having sufficient strength can be obtained.

  The conductive particles according to the second aspect of the present invention include a core particle, a palladium layer covering the core particle, having a phosphorus concentration of 1 wt% to 10 wt%, and a thickness of 20 nm to 130 nm, and a palladium layer And insulating particles having a particle diameter of 20 to 500 nm.

  When an anisotropic conductive adhesive (anisotropic conductive film) obtained by dispersing a plurality of conductive particles in an adhesive is placed between a pair of electrodes and the pair of electrodes are connected (thermocompression bonding), In the direction (the direction in which the pair of electrodes face each other), the entire conductive particle is compressed by the pair of electrodes. As a result, the insulating particles sink into the core particles from the surface of the palladium layer, and the exposed palladium layer can be brought into contact with the pair of electrodes. That is, the pair of electrodes are electrically connected through the palladium layer of the conductive particles. On the other hand, in the lateral direction (direction perpendicular to the direction in which the pair of electrodes face each other), insulating particles included in each conductive particle are interposed between adjacent conductive particles, and the insulating particles are in contact with each other. Therefore, in the lateral direction, insulation is maintained between the pair of electrodes and the electrodes adjacent thereto.

  In the second aspect of the present invention, since the palladium layer has ductility, it becomes possible to improve the conductivity of the conductive particles after compression and the connection reliability between the electrodes as in the case of the first aspect of the present invention. It becomes possible to prevent migration of palladium. Furthermore, palladium is cheaper and more practical than noble metals such as gold and platinum. Therefore, the conductive particles according to the second aspect of the present invention including the palladium layer are less expensive than the conductive particles using only gold or platinum.

  In the second aspect of the present invention, since the palladium layer having a thickness of 20 nm or more is provided as the conductive layer, sufficient conductivity can be obtained.

  In the first and second aspects of the present invention, the palladium layer is preferably a reduction plating type palladium layer. Thereby, the coverage of the palladium layer with respect to a core particle improves, and it becomes easy to improve the electroconductivity of an electroconductive particle.

  Further, since the palladium layer is a reduction plating type palladium layer, it is possible to form a dense and homogeneous palladium layer on the resin fine particles, and to provide conductive particles with less exposure of the resin fine particle surfaces. Moreover, it is possible to arbitrarily set the thickness of the palladium layer according to the amount of the plating solution. That is, the thickness of the palladium layer can be controlled to a thickness as required.

  In the present invention, the components in the conductive layer (elemental composition and phosphorus concentration of the conductive layer) are preferably qualitatively and quantitatively determined by energy dispersive X-ray spectroscopy (EDX).

  In the first and second aspects of the invention, the insulating particles are preferably silica. Insulating particles made of silica have excellent insulating properties, are easy to control the particle diameter, and are inexpensive. In addition, when silica is dispersed in water to form water-dispersed colloidal silica, it has a hydroxyl group on its surface, so it has excellent binding properties with the palladium layer. Furthermore, the hydroxyl group on the surface of the silica is excellent in the binding property with the functional group formed on the surface of the palladium layer. Therefore, the insulating particles made of silica can be firmly adsorbed on the surface of the palladium layer or the gold layer.

  According to the present invention, it is possible to provide conductive particles that are low in cost, high in conductivity, and excellent in connection reliability between electrodes without causing migration.

FIG. 1 is a schematic cross-sectional view of conductive particles according to the first embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of conductive particles according to the second embodiment of the present invention. FIG. 3 (a) is a schematic cross-sectional view of an anisotropic conductive adhesive provided with conductive particles according to the second embodiment of the present invention, and FIGS. 3 (b) and 3 (c) are anisotropic conductive. It is a schematic sectional drawing for demonstrating the preparation method of the connection structure using an adhesive agent.

  Hereinafter, the best mode for carrying out the invention will be described in detail. However, the present invention is not limited to the following embodiments.

[First embodiment]
(Conductive particles)
As shown in FIG. 1, the conductive particle 8a according to the first embodiment of the present invention covers the core particle 11 and the entire core particle 11, has a thickness of 20 nm to 130 nm, and a phosphorus concentration of 1% by weight or more. And a palladium layer 12 of 10% by weight or less. Hereinafter, the conductive particles 8a according to the first embodiment are sometimes referred to as “mother particles 2a”.

<Core particle 11>
The particle diameter of the core particle 11 used in the present invention is preferably smaller than the minimum distance between the first electrode 5 and the second electrode 7 shown in FIG. Moreover, when the particle size of the core particle 11 varies in the height of the electrodes (interval between the electrodes), it is preferable that the core particle 11 is larger than the variation in the height (maximum interval between the electrodes). For these reasons, the particle size of the core particles 11 is preferably 1 to 10 μm, more preferably 1 to 5 μm, and particularly preferably 2.0 to 3.5 μm.

  The core particle in the conventional conductive particle is either a particle made of only a metal, or a particle made of an organic substance or an inorganic substance, but the core particle 11 in the present embodiment is a resin fine particle made of a resin.

  The organic core particles 11 are not particularly limited, but include acrylic resins such as polymethyl methacrylate and polymethyl acrylate, polyolefin resins such as polyethylene, polypropylene, polyisobutylene, and polybutadiene, polystyrene, divinylbenzene polymer, and divinylbenzene-styrene. Resin particles made of a copolymer, benzoguanamine formaldehyde resin or the like are preferable.

<Palladium layer 12>
Since the palladium layer 12 has ductility, after the conductive particles 8a are compressed, it is difficult for metal cracks to occur, and migration associated with metal cracks is also difficult to occur. Moreover, the palladium layer 12 is excellent in acid resistance and alkali resistance compared with a base metal and copper. Furthermore, since the palladium layer 12 is an alloy containing phosphorus, it is more excellent in acid resistance and alkali resistance. Therefore, it binds stably to a functional group such as a mercapto group, sulfide group, or disulfide group described later. Furthermore, palladium, gold, and platinum have the same tendency in the bondability with these functional groups, but when these noble metals are compared in the same volume, palladium is the cheapest and practical. Further, the palladium layer 12 is excellent in conductivity. For these reasons, the palladium layer 12 is suitable as a metal layer that covers the core particles 11.

  The phosphorus concentration in the palladium layer 12 is from 1% by weight to 10% by weight from the viewpoint of connection resistance, but is preferably from 1% by weight to 8% by weight, and preferably from 1% by weight to 6% by weight. Is more preferable. Moreover, the palladium layer containing phosphorus has high hardness compared with the pure palladium layer which does not contain phosphorus (refer nonpatent literature 1 "surface technology P651, Vol55, No10, 2004"). If the surface of the palladium layer in contact with the electrode has a high hardness, the conductive particles tend to sink into the electrode surface, break the oxidized electrode, and ensure the conduction performance. On the other hand, when the phosphorus content exceeds 10% by weight, the conduction resistance of the palladium layer is too large. When the phosphorus content exceeds 10% by weight, for example, when the palladium layer 12 is formed by plating, the palladium plating is difficult to proceed, and the time required for the plating process becomes long.

  The palladium layer 12 is preferably a reduction plating type palladium layer. Thereby, the coverage of the palladium layer 12 with respect to the core particle 11 improves, and the electroconductivity of the electrically-conductive particle 8a improves more. The reducing agent for eutecting phosphorus and alloying palladium preferably contains at least a reducing agent containing phosphorus such as hypophosphorous acid or a salt thereof, phosphorous acid or a salt thereof. The reducing agent is not particularly limited as long as it contains the phosphorus-containing reducing agent described above, and may contain other reducing agents. Even when other reducing agents are contained, it is known that phosphorus co-deposits in the palladium film from the phosphorus-containing reducing agent.

  By using reduction plating, it is easy to control the plating thickness of the palladium layer 12. For example, since the plating thickness after deposition can be calculated in advance from the concentration of palladium ions contained in the plating solution to be used, wasteful palladium and reagents are not used, and the cost can be reduced.

  Although the thickness of the palladium layer 12 is 20 nm or more and 130 nm or less, it is preferably 20 nm or more and 100 nm or less, and more preferably 20 nm or more and 80 nm or less. When the thickness of the palladium layer is less than 20 nm, sufficient conductivity cannot be obtained. On the other hand, if the thickness of the palladium layer 12 exceeds 130 nm, the elasticity of the entire core particle 11 tends to decrease. When the elasticity of the whole mother particle 2a is lowered, when the conductive particle 8a is sandwiched between a pair of electrodes and crushed in the longitudinal direction, the palladium layer 12 is sufficiently pressed against the electrode surface by the elasticity of the mother particle 2a. It becomes difficult to obtain. Therefore, the contact area between the palladium layer 12 and both electrodes tends to be small, and the effect of the present invention that improves the connection reliability between the electrodes tends to be small. In addition, the thicker the palladium layer 12, the higher the cost, which is not economically preferable, and the conductive layer of the conductive particles 8a sandwiched between the pair of electrodes and crushed in the vertical direction when being mounted and pressure-bonded, that is, The palladium layer 12 may be cracked, and the connection resistance between the electrodes tends to increase.

(Analysis of plating layer)
An atomic absorption photometer can be used for component analysis of the palladium layer 12 covering the surface of the core particle 11. For example, there is a method in which a solution obtained by dissolving the palladium layer 12 with an acid or the like is analyzed using an atomic absorption photometer to measure and calculate the metal ion concentration. Further, the palladium layer 12 may be analyzed using an ICP emission analyzer. When an ICP emission analyzer is used, phosphorus can be quantified simultaneously with qualitative analysis. Moreover, the phosphorus concentration in the palladium layer 12 can also be quantified using EDX. In addition, since EDX measurement at a low magnification obtains information from a plurality of particles, EDX measurement at a high magnification is preferable.

[Second Embodiment]
Next, the electroconductive particle which concerns on 2nd embodiment of this invention, and the manufacturing method of an electroconductive particle are demonstrated. In the following, only the differences between the first embodiment and the second embodiment described above will be described, and description of matters common to both will be omitted.

(Conductive particles)
As shown in FIG. 2, the conductive particle 8 b according to the second embodiment includes not only the core particle 11 and the palladium layer 12 but also a plurality of insulating particles 1 disposed on the surface of the palladium layer 12. It differs from the conductive particles 8a according to one embodiment.

<Insulating particle 1>
The insulating particle 1 is preferably an inorganic oxide. If the insulating particles 1 are an organic compound, the insulating particles 1 are deformed in the anisotropic conductive adhesive manufacturing process, and the properties of the anisotropic conductive adhesive obtained tend to change. .

As the inorganic oxide constituting the insulating particle 1, an oxide containing at least one element selected from the group consisting of silicon, aluminum, zirconium, titanium, niobium, zinc, tin, cerium, and magnesium is preferable. These oxides can be used alone or in admixture of two or more. As the inorganic oxide, water-dispersed colloidal silica (SiO ₂ ) having excellent insulating properties and controlled particle diameter is most preferable among oxides containing the above-described elements.

  Examples of commercially available insulating particles composed of such inorganic oxides (hereinafter referred to as “inorganic oxide fine particles”) include, for example, Snowtex, Snowtex UP (manufactured by Nissan Chemical Industries, Ltd.), Quatron PL series. (Manufactured by Fuso Chemical Industry Co., Ltd.).

  The particle diameter of the inorganic oxide fine particles is preferably smaller than the resin fine particles. Specifically, the average particle diameter of the inorganic oxide fine particles is 20 to 500 nm, preferably 30 to 400 nm, and more preferably 40 to 350 nm. The particle diameter of the inorganic oxide fine particles is measured by the specific surface area conversion method by the BET method or the X-ray small angle scattering method. If the particle diameter is less than 20 nm, the inorganic oxide fine particles adsorbed on the mother particle 2a do not act as an insulating film and tend to cause a short circuit between a part of the electrodes. On the other hand, when the particle diameter exceeds 500 nm, the electrode and the conductive layer (palladium layer 12) of the conductive particles 8b are difficult to contact when mounted and pressure-bonded, so that the connection resistance between the electrodes increases and good conductivity is obtained. There is a tendency not to be able to.

(Method for producing conductive particles)
The manufacturing method of the conductive particles 8 a according to the first embodiment of the present invention includes the step (S 1) of forming the palladium layer 12 on the surfaces of the core particles 11. In the method for producing the conductive particles 8b according to the second embodiment of the present invention, after the step S1, the surface of the palladium layer 12 is treated with a compound having any of a mercapto group, a sulfide group, or a disulfide group, and the palladium layer A step (S2) of forming a functional group on the surface of 12, a step (S3) of treating the surface of the palladium layer on which the functional group is formed with a polymer electrolyte, and a treatment with the polymer electrolyte in which the functional group is formed A step (S4) of fixing the insulating particles 1 to the surface of the palladium layer 12 by chemical adsorption. Hereinafter, the case where the insulating particles 1 are inorganic oxide fine particles having hydroxyl groups formed on the surface will be described.

<S1>
First, the palladium layer 12 is formed on the surface of the core particle 11 to obtain the mother particle 2a (the conductive particle 8a according to the first embodiment). Specific examples of the method include plating with palladium. In this plating step, the surface of the core particle 11 is degreased with an alkali or the like and then neutralized with an acid to adjust the surface of the core particle 11. Thereafter, a palladium catalyst is applied, and reduction-type electroless palladium plating is preferably performed using the phosphorus-containing reducing agent described above. The composition of the reduced electroless palladium plating solution is preferably (1) a water-soluble palladium salt such as palladium sulfate, (2) a reducing agent, (3) a complexing agent, and (4) a pH adjusting agent. . As a method of adjusting the phosphorus concentration in the palladium layer 12 to 1 wt% or more and 10 wt% or less, for example, a method of adjusting the components shown in (1) to (4) constituting the palladium plating solution shown above. Is used. In particular, a method for controlling the phosphorus concentration in the palladium plating solution, such as a method for selecting a reducing agent containing phosphorus, a method for adjusting the amount of the reducing agent, a method for controlling the pH of the plating reaction, and a method for adjusting the plating temperature. Etc. The phosphorus concentration can also be adjusted by adjusting the type and concentration of the complexing agent. Especially, since it is excellent in reaction control, the method of controlling the pH of plating reaction is used suitably. The methods shown above may be used alone, but when they are combined, the phosphorus concentration can be easily adjusted and the stability of the plating solution can be easily controlled.

<S2>
When the conductive particles 8b according to the second embodiment are formed, the surface of the palladium layer 12 is further made of a compound having any of a mercapto group, a sulfide group, or a disulfide group that forms a coordinate bond with palladium. To process. Thereby, a functional group is formed on the surface of the palladium layer 12.

  Specific examples of the compound used for the surface treatment of the palladium layer 12 include mercaptoacetic acid, 2-mercaptoethanol, methyl mercaptoacetate, mercaptosuccinic acid, thioglycerin, and cysteine. Examples of the functional group formed on the surface of the palladium layer 12 treated with these compounds include a hydroxyl group, a carboxyl group, an alkoxyl group, or an alkoxycarbonyl group.

  Palladium easily reacts with thiol groups (mercapto groups), whereas base metals such as nickel hardly react with thiol groups. Therefore, the palladium particles of the present embodiment (core particles 11 coated with the palladium layer 12) react with thiol groups compared to conventional nickel / gold particles (core particles coated with the nickel layer and the gold layer). Cheap. The nickel / gold particles tend to have a high nickel ratio on the particle surface when the gold thickness is 30 nm or less.

  As a specific method for treating the surface of the palladium layer 12 with the above compound, for example, in a liquid obtained by dispersing about 10 to 100 mmol / l of a compound such as mercaptoacetic acid in an organic solvent such as methanol or ethanol, A method of dispersing palladium particles can be mentioned.

<S3, S4>
Next, the surface of the palladium layer 12 on which the functional group is formed is treated with a polymer electrolyte, and then the insulating particles 1 are chemically adsorbed on the surface of the palladium layer 12.

  The surface potential (zeta potential) of the palladium layer 12 having a functional group such as a hydroxyl group, a carboxyl group, an alkoxyl group, or an alkoxycarbonyl group is usually negative when the pH is in a neutral region. On the other hand, since the surface of the insulating particle 1 to be adsorbed on the surface of the palladium layer 12 in the subsequent step is made of an inorganic oxide having a hydroxyl group, the surface potential of the insulating particle 1 is usually negative. As described above, the insulating particles 1 having a negative surface potential tend not to be adsorbed around the palladium layer 12 having a negative surface potential. Therefore, the surface of the palladium layer 12 is easily coated with the insulating particles 1 by treating the surface of the palladium layer 12 with the polymer electrolyte.

As a method for adsorbing the insulating particles 1 on the surface of the palladium layer 12 after the treatment with the polymer electrolyte, a method of alternately laminating the polymer electrolyte and the inorganic oxide on the surface of the palladium layer 12 is preferable. More specifically, by performing the following steps (1) and (2) in sequence, a mother surface partially coated with an insulating coating film in which a polymer electrolyte and inorganic oxide fine particles are laminated. The particles 2a, that is, the conductive particles 8b can be manufactured.
Step (1): Step of rinsing the mother particle 2a after dispersing the mother particle 2a having a functional group on the surface of the palladium layer 12 in the polymer electrolyte solution and adsorbing the polymer electrolyte on the surface of the palladium layer 12. .
Step (2): The mother particles 2a after rinsing are dispersed in a dispersion solution of inorganic oxide fine particles, the inorganic oxide fine particles are adsorbed on the surface (palladium layer 12) of the mother particles 2a, and then the mother particles 2a are rinsed. Process.

  That is, in the step (1), a polymer electrolyte thin film is formed on the surface of the mother particle 2a, and in the step (2), inorganic oxide fine particles are fixed to the surface of the mother particle 2a by chemical adsorption through the polymer electrolyte thin film. Turn into. By using this polymer electrolyte thin film, the surface of the mother particle 2a can be uniformly coated with inorganic oxide fine particles without defects. When the circuit electrodes are connected using the anisotropic conductive adhesive using the conductive particles obtained through the steps (1) and (2), insulation is ensured even when the circuit electrode interval is narrow. Therefore, the connection resistance is low and good between the electrodes connected to each other.

  The method having the above steps (1) and (2) is referred to as an alternating lamination method (Layer-by-Layer assembly). The alternate lamination method is described in G.H. This is a method of forming an organic thin film published by Decher et al. In 1992 (see Thin Solid Films, 210/211, p831 (1992)).

  In this alternate lamination method, a polymer adsorbed on a substrate by electrostatic attraction by alternately immersing the substrate in an aqueous solution of a polymer electrolyte having a positive charge (polycation) and a polymer electrolyte having a negative charge (polyanion). A combination of a cation and a polyanion is laminated to obtain a composite film (alternate laminated film).

  In the alternating layering method, the film is grown by attracting the charge of the material formed on the substrate and the material having the opposite charge in the solution by electrostatic attraction, so that the adsorption proceeds and the charge is neutralized. When this occurs, no further adsorption occurs. Therefore, when reaching a certain saturation point, the film thickness does not increase any more.

  Lvov et al. Applied the alternate lamination method to fine particles and reported a method of laminating a polymer electrolyte having a charge opposite to the surface charge of the fine particles by using the fine particle dispersions of silica, titania and ceria. (See Langmuir, Vol. 13, (1997) p6195-6203).

  By using this method, by alternately laminating silica fine particles having a negative surface charge and polydiallyldimethylammonium chloride (PDDA) or polyethyleneimine (PEI) which are polycations having the opposite charge, It is possible to form a fine particle laminated thin film in which silica fine particles and polymer electrolyte are alternately laminated.

  In the manufacturing method of the conductive particles 8b according to the second embodiment, the mother particle 2a is immersed in a polymer electrolyte solution or a dispersion of inorganic oxide fine particles, and then immersed in a fine particle dispersion or polymer electrolyte solution having an opposite charge. Before the cleaning, it is preferable to wash away the excess polymer electrolyte solution or the dispersion of inorganic oxide fine particles from the mother particles 2a by rinsing with only a solvent.

  Since the polymer electrolyte and inorganic oxide fine particles adsorbed on the mother particle 2a are electrostatically adsorbed on the surface of the mother particle 2a, they are not separated from the surface of the mother particle 2a in this rinsing step. However, if excessive polymer electrolyte or inorganic oxide fine particles that are not adsorbed on the mother particle 2a are brought into a solution having a charge opposite to them, cations and anions are mixed in the solution, and the polymer electrolyte and the inorganic oxide are mixed. Aggregation and precipitation of fine particles may occur. Such a malfunction can be prevented by rinsing.

  Solvents used for rinsing include water, alcohol, acetone, etc. Usually, ions having a specific resistance value of 18 MΩ · cm or more are easy in that excessive polymer electrolyte solutions or inorganic oxide fine particle dispersions can be easily removed. Exchange water (so-called ultrapure water) is used.

  The polymer electrolyte solution is obtained by dissolving a polymer electrolyte in water or a mixed solvent of water and a water-soluble organic solvent. Examples of water-soluble organic solvents that can be used include methanol, ethanol, propanol, acetone, dimethylformamide, acetonitrile, and the like.

  As the polymer electrolyte, a polymer that is ionized in an aqueous solution and has a charged functional group in the main chain or side chain can be used. In this case, a polycation is preferably used.

  The polycation generally has a positively charged functional group such as polyamines such as polyethyleneimine (PEI), polyallylamine hydrochloride (PAH), polydiallyldimethylammonium chloride (PDDA). , Polyvinyl pyridine (PVP), polylysine, polyacrylamide, and a copolymer containing at least one of them can be used.

  Among polyelectrolytes, polyethyleneimine has a high charge density and a strong binding force. Among these polymer electrolytes, alkali metal (Li, Na, K, Rb, Cs) ions, alkaline earth metal (Ca, Sr, Ba, Ra) ions, halide ions are used to avoid electromigration and corrosion. Those not containing (fluorine ion, chloride ion, bromine ion, iodine ion) are preferred.

  These polymer electrolytes are either water-soluble or soluble in a mixture of water and an organic solvent, and the molecular weight of the polymer electrolyte is generally determined depending on the type of polymer electrolyte used. Although it cannot be determined, generally about 500 to 200,000 is preferable. In general, the concentration of the polymer electrolyte in the solution is preferably about 0.01 to 10% by weight. The pH of the polymer electrolyte solution is not particularly limited.

  The coverage of the inorganic oxide fine particles can be controlled by adjusting the type, molecular weight, or concentration of the polymer electrolyte thin film that covers the mother particles 2a.

  Specifically, when a polymer electrolyte thin film having a high charge density such as polyethyleneimine is used, the coverage of the inorganic oxide fine particles tends to be high, and a polymer electrolyte having a low charge density such as polydiallyldimethylammonium chloride. When a thin film is used, the coverage of inorganic oxide fine particles tends to be low.

  Further, when the molecular weight of the polymer electrolyte is large, the coverage of the inorganic oxide fine particles tends to be high, and the inorganic oxide fine particles can be firmly adsorbed to the palladium layer 12. From the viewpoint of bonding strength, the molecular weight of the polymer electrolyte is preferably 10,000 or more. On the other hand, when the molecular weight of the polymer electrolyte is small, the coverage of the inorganic oxide fine particles tends to be low.

  Furthermore, when the polymer electrolyte is used at a high concentration, the coverage of the inorganic oxide fine particles tends to be high, and when the polymer electrolyte is used at a low concentration, the coverage of the inorganic oxide fine particles tends to be low. is there. When the coverage of the inorganic oxide fine particles is high, the insulation tends to be high and the conductivity tends to be poor. When the coverage of the inorganic oxide fine particles is low, the conductivity tends to be high and the insulation is poor.

  Only one layer of the inorganic oxide fine particles is preferably coated. Multi-layer stacking makes it difficult to control the stacking amount. The coverage of the surface of the palladium layer 12 with inorganic oxide fine particles is preferably in the range of 20 to 100%, and more preferably in the range of 30 to 60%.

  The concentration of alkali metal ions and alkaline earth metal ions in the dispersion of the inorganic oxide fine particles is preferably 100 ppm or less. Thereby, it becomes easy to improve the insulation reliability between adjacent electrodes. As the inorganic oxide fine particles, inorganic oxide fine particles produced by a hydrolysis reaction of metal alkoxide, so-called sol-gel method, are suitable.

In particular, the inorganic oxide fine particles are preferably water-dispersed colloidal silica (SiO ₂ ). Since the water-dispersed colloidal silica has a hydroxyl group on the surface, it is suitable for inorganic oxide fine particles in that it has excellent binding properties with the mother particles 2a, is easily aligned in particle diameter, and is inexpensive.

  In general, a hydroxyl group is known to form a strong bond with a hydroxyl group, a carboxyl group, an alkoxyl group, or an alkoxycarbonyl group. Specific examples of the bond between the hydroxyl group and these functional groups include covalent bond by dehydration condensation and hydrogen bond. Accordingly, the inorganic oxide fine particles having a hydroxyl group on the surface thereof are strongly adsorbed to the palladium layer 12 (the surface of the mother particle 2a) on which a functional group such as a hydroxyl group, a carboxyl group, an alkoxyl group, or an alkoxycarbonyl group is formed. Is possible.

  The hydroxyl group on the surface of the inorganic oxide fine particles can be modified to an amino group, a carboxyl group or an epoxy group with a silane coupling agent or the like, but it is difficult when the particle size of the inorganic oxide is 500 nm or less. is there. Therefore, it is desirable to coat the mother particles 2a with the inorganic oxide fine particles without modifying the functional group.

  The bonding between the insulating particles 1 and the mother particles 2a can be further strengthened by heating and drying the conductive particles 8b completed as described above. The reason why the bonding force increases is, for example, a chemical bond between a functional group such as a carboxyl group on the surface of the palladium layer 12 and a hydroxyl group on the surface of the insulating particle 1, or a carboxyl group on the surface of the palladium layer 12 and the insulating particle 1. It is mentioned that the dehydration condensation of the amino group on the surface is promoted. In addition, it is preferable to perform heating in vacuum from the viewpoint of preventing rust of the metal. Even when the outermost surface of the mother particle is a gold layer, as in the case of the palladium layer 12, the bonding between the insulating particles and the mother particle can be further strengthened by heating and drying.

  The drying temperature is preferably 60 to 200 ° C., and the heating time is preferably 10 to 180 minutes. When the temperature is less than 60 ° C. or when the heating time is less than 10 minutes, the insulating particles 1 are easily peeled off from the mother particles 2a, and when the temperature exceeds 200 ° C. or the heating time exceeds 180 minutes, It is not preferable because the particles 2a are easily deformed.

  (Observation of Particles) A scanning electron microscope (SEM, Scanning Electron Microscope) can be used for observing the plating film (palladium layer) covering the resin fine particles and the insulating particles disposed on the plating film. . From the image, it is possible to confirm the plating film surface, the position and number of insulating fine particles, and the like.

(Anisotropic conductive adhesive)
As shown in FIG. 3A, the anisotropic conductive adhesive 40 is obtained by dispersing the conductive particles 8 b produced as described above in the adhesive 3. A method for producing the connection structure 42 using the anisotropic conductive adhesive 40 is shown in FIGS. 3A, 3B, and 3C, the conductive particles 8b are referred to as conductive particles 8. In addition, the palladium layer 12 included in the conductive particles 8 is omitted for simplification of the drawing.

  As shown in FIG.3 (b), the 1st board | substrate 4 and the 2nd board | substrate 6 are prepared, and the anisotropic conductive adhesive 40 is arrange | positioned among them. At this time, the first electrode 5 included in the first substrate 4 and the second electrode 7 included in the second substrate 6 are opposed to each other. Thereafter, the first substrate 4 and the second substrate 6 are stacked while being heated under pressure in the direction in which the first electrode 5 and the second electrode 7 face each other, and the connection structure shown in FIG. A body 42 is obtained.

  When the connection structure 42 is produced in this way, in the longitudinal direction, the insulating particles 1 are embedded in the base particles 2, and the first electrode 5 and the second electrode 7 pass through the surface (palladium layer) of the base particles 2. Conductivity is maintained, and in the lateral direction, insulation is maintained by interposing the insulator particles 1 between the mother particles.

  In recent years, anisotropic conductive adhesives for COG are required to have insulation reliability at a narrow pitch of 10 μm level. However, if the anisotropic conductive adhesive 40 according to this embodiment is used, a narrow pitch of 10 μm level is used. It is possible to improve the insulation reliability in the case.

  As the adhesive 3 used for the anisotropic conductive adhesive 40, a mixture of a heat-reactive resin and a curing agent is used, and specifically, a mixture of an epoxy resin and a latent curing agent is preferable.

  Epoxy resins include bisphenol type epoxy resins derived from epichlorohydrin and bisphenol A, F, AD, etc., epoxy novolac resins derived from epichlorohydrin and phenol novolac and cresol novolac, and naphthalene type epoxy resins having a skeleton containing a naphthalene ring. , Various epoxy compounds having two or more glycidyl groups in one molecule such as glycidylamine, glycidyl ether, biphenyl, and alicyclic can be used alone or in admixture of two or more.

These epoxy resins, impurity ions ^(Na +, Cl ^-, etc.) and, it is preferable to use a high purity which is reduced to 300ppm or less hydrolyzable chlorine and the like. This makes it easier to prevent electromigration.

  Examples of the latent curing agent include imidazole series, hydrazide series, boron trifluoride-amine complex, sulfonium salt, amine imide, polyamine salt, dicyandiamide, and the like. In addition, an energy ray curable resin such as a mixture of a radical reactive resin and an organic peroxide or ultraviolet rays is used for the adhesive.

  The adhesive 3 can be mixed with butadiene rubber, acrylic rubber, styrene-butadiene rubber, silicone rubber or the like in order to reduce the stress after bonding or to improve the adhesion.

  The adhesive 3 is a paste or film. In order to make the adhesive into a film, it is effective to blend a thermoplastic resin such as a phenoxy resin, a polyester resin, or a polyamide resin. These film-forming polymers are also effective in stress relaxation when the reactive resin is cured. In particular, when the film-forming polymer has a functional group such as a hydroxyl group, the adhesiveness is improved, which is more preferable.

  The film is formed by dissolving or dispersing an adhesive composition composed of epoxy resin, acrylic rubber, latent curing agent, and film-forming polymer in an organic solvent, and applying it onto a peelable substrate. And by removing the solvent below the activation temperature of the curing agent. The organic solvent used at this time is preferably an aromatic hydrocarbon-based and oxygen-containing mixed solvent in terms of improving the solubility of the material.

  The thickness of the anisotropic conductive adhesive 40 is relatively determined in consideration of the particle size of the conductive particles 8 and the characteristics of the anisotropic conductive adhesive 40, but is preferably 1 to 100 μm. If it is less than 1 μm, sufficient adhesion cannot be obtained, and if it exceeds 100 μm, a large amount of conductive particles are required to obtain conductivity, which is not realistic. For these reasons, the thickness is more preferably 3 to 50 μm.

  Examples of the first substrate 4 or the second substrate 6 include a glass substrate, a tape substrate such as polyimide, a bare chip such as a driver IC, and a rigid package substrate.

  As mentioned above, although preferred embodiment of the electroconductive particle which concerns on this invention, and the manufacturing method of electroconductive particle were described in detail, this invention is not limited to the said embodiment. For example, the conductive particles 8a according to the first embodiment include resin fine particles 11, a palladium layer 12 that covers the surface of the resin fine particles 11, and another conductive layer (for example, a gold layer) that covers the surface of the palladium layer 12. May be provided. In addition, the conductive particles 8b according to the second embodiment include resin fine particles 11, a palladium layer 12 that covers the surface of the resin fine particles 11, and another conductive layer (for example, a gold layer) that covers the surface of the palladium layer 12. And a plurality of insulating particles 1 disposed on the surface of the conductive layer.

  Hereinafter, the present invention will be described by way of examples.

(Base particle 1)
3 g of crosslinked polystyrene particles (resin fine particles) having an average particle size of 3.5 μm were neutralized with an acid after alkali degreasing. The resin fine particles were added to 100 ml of the cationic polymer solution adjusted to pH 6.0, stirred at 60 ° C. for 1 hour, filtered through a membrane filter (manufactured by Millipore) having a diameter of 3 μm, and washed with water. After adding resin fine particles after washing with water to 100 mL of palladium-catalyzed liquid containing 8% by weight of Atotech Neneogant 834 (trade name, manufactured by Atotech Japan Co., Ltd.), which is a palladium catalyst, and stirring at 35 ° C. for 30 minutes, The solution was filtered through a membrane filter (manufactured by Millipore) having a diameter of 3 μm and washed with water. Resin fine particles were repeatedly added to the palladium catalyst solution to give a sufficient amount of palladium catalyst to the surface of the resin fine particles. The “palladium catalyst” is a catalyst for forming a palladium layer on the surface of the resin fine particles, and is not the palladium layer itself in the present invention.

  Next, the resin fine particles after washing with water were added to a 3 g / L sodium hypophosphite solution adjusted to pH 6.0 to obtain resin fine particles (resin core particles) whose surfaces were activated. Thereafter, resin fine particles whose surface was activated were immersed in distilled water and ultrasonically dispersed.

  The above solution is filtered through a membrane filter (made by Millipore) with a diameter of 3 μm, and the surface is activated on APP (Ishihara Pharmaceutical Co., Ltd., trade name) which is an electroless palladium plating solution at 50 ° C. The resin fine particles soaked were subjected to electroless Pd plating of 20 nm on the surface of the resin fine particles. APP, which is an electroless palladium plating solution, is known to contain a phosphorus-containing substance such as hypophosphorous acid or a salt thereof, phosphoric acid or a salt thereof as a main component.

  Thereafter, the mixture was filtered with a membrane filter having a diameter of 3 μm (manufactured by Millipore), and washed with water three times. After vacuum drying at 40 ° C. for 7 hours, aggregation was broken by pulverization to produce mother particles 1 having a 20 nm thick palladium layer on resin fine particles.

(Mother particle 2)
Instead of performing electroless Pd plating using the above electroless palladium plating solution APP, the surface is activated on Melplate Pal 6700 (product name, manufactured by Meltex Co., Ltd.), which is an electroless palladium plating solution, at 50 ° C. The mother particles 2 having a 40 nm-thick palladium layer on the resin core particles were produced in the same manner as the mother particles 1 except that the resin fine particles were immersed and electroless palladium plating was performed at pH 8. It is known that Melplate Pal 6700 which is an electroless palladium plating solution contains, as a main component, a phosphorus-containing substance such as hypophosphorous acid or a salt thereof as a reducing agent, phosphoric acid or a salt thereof.

(Mother particle 3)
80 nm thick on the resin core particle in the same manner as the mother particle 2 except that sodium hypophosphite was added to the above electroless palladium plating solution Melplate Pal 6700 (product name, manufactured by Meltex Co., Ltd.). A mother particle 3 having a palladium layer was prepared.

(Base particle 4)
In the same manner as the mother particles 1, a palladium catalyst was applied and activated resin fine particles were dispersed in a 70 ° C. bath in which 50 g / L of sodium citrate was dissolved. Then, using a metering pump, plating solution a and plating solution b were added simultaneously and in parallel at 10 ml / min, and electroless palladium plating was performed on the resin fine particles. As the plating solution a, a solution prepared by mixing palladium: 20 g / L, sodium citrate: 50 g / L, and ethylenediamine 20 g / L and adjusting the pH to 6.0 was used. In the plating solution a, palladium is dissolved in an ion or complex state, and the amount of palladium “20 g / L” is a weight-converted value as metallic palladium. As the plating solution b, a solution prepared by mixing sodium hypophosphite: 1.2 mol / L and adjusting the pH to 6.0 with sodium hydroxide was used. The thickness of the electroless palladium layer formed on the surface of the resin fine particles was adjusted by analyzing the sampled particles with an atomic absorption photometer. When the thickness of the electroless palladium layer reached 130 nm, the addition of the electroless plating solution was stopped. After the addition was completed, it was waited for the generation of bubbles to stop, followed by filtration and washing with water. When the reaction stopped, the pH was 6.0. By the above method, mother particles 4 having an electroless palladium layer having a thickness of 130 nm on resin core particles were produced. The obtained mother particle 4 was gray.

(Mother particle 5)
In the same manner as the mother particles 1, a palladium catalyst was applied and activated resin fine particles were dispersed in a 70 ° C. bath in which 50 g / L of sodium citrate was dissolved. Then, using a metering pump, plating solution c and plating solution d were added simultaneously and in parallel at 4 ml / min, and electroless palladium plating was performed on the resin fine particles. As the plating solution c, a solution prepared by mixing palladium: 20 g / L, sodium citrate: 80 g / L, ethylenediamine: 20 g / L and adjusting the pH to 5.0 was used. As the plating solution d, a solution in which sodium hypophosphite: 2.4 mol / L was mixed and adjusted to pH = 5.0 with sodium hydroxide was used. The thickness of the electroless palladium layer formed on the surface of the resin fine particles was adjusted by analyzing the sampled particles with an atomic absorption photometer. When the thickness of the electroless palladium layer reached 80 nm, the addition of the electroless plating solution was stopped. After the addition was completed, it was waited for the generation of bubbles to stop, followed by filtration and washing with water. When the reaction stopped, the pH was 4.8. By the above method, mother particles 5 having an electroless palladium layer having a thickness of 80 nm on resin core particles were produced. The obtained mother particle 5 was gray.

(Base particle 6)
In the same manner as the mother particles 1, a palladium catalyst was applied and activated resin fine particles were dispersed in a 70 ° C. bath in which 20 g / L of sodium tartrate was dissolved. Then, using a metering pump, the plating solution e and the plating solution f were added simultaneously and in parallel at 15 ml / min, and additive electroless nickel plating was performed on the resin fine particles. As the plating solution e, a solution obtained by mixing nickel: 224 g / L and sodium tartrate: 20 g / L was used. As the plating solution f, a solution in which sodium hypophosphite: 226 g / L and sodium hydroxide: 85 g / L were mixed was used. The nickel film thickness was adjusted by analyzing the sampled particles with an atomic absorption photometer. When the nickel film thickness reached 40 nm, the addition of the electroless plating solution was stopped. After the addition was completed, it was waited for the generation of bubbles to stop, followed by filtration and washing with water. When the reaction stopped, the pH was 6.2 and the fine particles were gray. Next, the resin fine particles after electroless nickel plating were immersed in APP (Ishihara Pharmaceutical Co., Ltd., trade name) which is an electroless palladium plating solution at 50 ° C. to perform electroless palladium plating. .

  The above solution was filtered with a membrane filter (manufactured by Millipore) having a diameter of 3 μm, and washed with water three times. Thereafter, vacuum drying was performed at 40 ° C. for 7 hours, and aggregation was broken by crushing. Thus, mother particles 6 having resin fine particles, a 40 nm-thick electroless nickel layer covering the surface of the resin fine particles, and a 40 nm electroless palladium layer covering the surface of the electroless nickel layer were obtained.

(Mother particle 7)
In place of electroless palladium plating, HGS-500 (product name, manufactured by Hitachi Chemical Co., Ltd.), which is an electroless gold plating solution, is used in the same manner as in the case of the mother particles 6 in a solution bathed at 80 ° C. The formed nickel-plated resin fine particles were immersed, subjected to displacement gold plating, and filtered and washed with water. Thereafter, the particles were immersed in a solution obtained by bathing HGS-2000 (product name, manufactured by Hitachi Chemical Co., Ltd.), which is an electroless gold plating solution, at 60 ° C., followed by filtration and washing with water. Except for these matters, the resin fine particles, a 40 nm-thick nickel layer covering the resin fine particles, and a 40 nm-thick Au layer covering the nickel layer surface are obtained by processing in the same manner as the mother particles 6. The mother particle 7 having was prepared.

(Insulation coating treatment)
Next, conductive particles 1 to 7 were produced using the mother particles 1 to 7 obtained above. The insulating coating treatment for adsorbing silica fine particles, which are insulating particles, on the surface of the mother particles was performed by a method disclosed in Japanese Patent Application Laid-Open No. 2008-120990. In the examples, for convenience of explanation, the mother particles having insulating particles on the surface are referred to as “conductive particles” and distinguished from the mother particles not having insulating particles on the surface. 5 and conductive particles 1 to 5 described later correspond to the conductive particles according to the present invention.

(Conductive particles 1)
A reaction liquid was prepared by dissolving 8 mmol of mercaptoacetic acid in 200 ml of methanol.

  Next, 1 g of the mother particle 1 was added to the reaction solution, and the mixture was stirred with a three-one motor and a stirring blade having a diameter of 45 mm at room temperature (25 ° C.) for 2 hours. After washing with methanol, the mother particles 1 having a carboxyl group on the surface were obtained by filtering the mother particles 1 with a membrane filter (manufactured by Millipore) having a diameter of 3 μm.

  Next, a 30% polyethyleneimine aqueous solution (manufactured by Wako Pure Chemical Industries, Ltd.) having a molecular weight of 70,000 was diluted with ultrapure water to obtain a 0.3 wt% polyethyleneimine aqueous solution. 1 g of the mother particle 1 having a carboxyl group was added to a 0.3 wt% polyethyleneimine aqueous solution and stirred at room temperature for 15 minutes.

  Thereafter, the mother particles 1 were filtered with a membrane filter (manufactured by Millipore) having a diameter of 3 μm, put in 200 g of ultrapure water, and stirred at room temperature for 5 minutes. Further, the mother particle 1 is filtered through a membrane filter (made by Millipore) having a diameter of 3 μm, and washed twice with 200 g of ultrapure water on the membrane filter, so that polyethyleneimine not adsorbed on the mother particle 1 is obtained. Removed.

  Next, a dispersion of colloidal silica, which is insulating particles (mass concentration 20%, manufactured by Fuso Chemical Industry Co., Ltd., product name: Quatron PL-3, average particle size 35 nm) is diluted with ultrapure water to obtain a 0. A 1% by weight silica dispersion was obtained. The mother particles 1 after the treatment with polyethyleneimine were placed in a 0.1 wt% silica dispersion solution and stirred at room temperature for 15 minutes.

  Next, the mother particles 1 were filtered with a membrane filter (manufactured by Millipore) having a diameter of 3 μm, put in 200 g of ultrapure water, and stirred at room temperature for 5 minutes. Further, the base particle 1 is filtered through a membrane filter (Millipore) having a diameter of 3 μm, and the silica not adsorbed on the base particle 1 is removed by washing twice with 200 g of ultrapure water on the membrane filter. did. Thereafter, drying was performed at 80 ° C. for 30 minutes, and heating drying was performed at 120 ° C. for 1 hour, whereby conductive particles 1 in which silica (child particles) were adsorbed on the surfaces of the mother particles 1 were produced.

(Conductive particles 2)
The mother particle 2 is used in place of the mother particle 1, and the colloidal silica dispersion is PL-7 instead of PL-3 (mass concentration 20%, manufactured by Fuso Chemical Industry Co., Ltd., product name: Quatron PL-7, average A conductive particle 2 was produced in the same manner as the conductive particle 1 except that a particle diameter of 75 nm) was used.

(Conductive particles 3)
The mother particle 3 is used in place of the mother particle 1, and the colloidal silica dispersion is PL-13 instead of PL-3 (mass concentration 20%, manufactured by Fuso Chemical Industry Co., Ltd., product name: Quatron PL-13, average A conductive particle 3 was produced in the same manner as the conductive particle 1 except that the particle diameter was 130 nm.

(Conductive particles 4)
The mother particle 4 is used instead of the mother particle 1, and the colloidal silica dispersion is PL-20 (mass concentration 20%, manufactured by Fuso Chemical Industry Co., Ltd., product name: Quatron PL-20, average instead of PL-3. A conductive particle 4 was produced in the same manner as the conductive particle 1 except that the particle diameter was 200 nm.

(Conductive particles 5)
The mother particle 5 is used in place of the mother particle 1, and the colloidal silica dispersion is PL-50 instead of PL-3 (mass concentration 20%, manufactured by Fuso Chemical Industry Co., Ltd., product name: Quatron PL-50, average A conductive particle 5 was produced in the same manner as the conductive particle 1 except that the particle diameter was 500 nm.

(Conductive particles 6)
Conductive particles 6 were produced in the same manner as the conductive particles 3 except that the mother particles 6 were used instead of the mother particles 3.

(Conductive particles 7)
Conductive particles 7 were produced in the same manner as the conductive particles 3 except that the mother particles 7 were used instead of the mother particles 3.

Example 1
<Preparation of adhesive solution>
10 g of phenoxy resin (Union Carbide, trade name: PKHC) and 7.5 g of acrylic rubber (40 parts of butyl acrylate, 30 parts of ethyl acrylate, 30 parts of acrylonitrile, 3 parts of glycidyl methacrylate, molecular weight: 850,000) Dissolve in 30 g of ethyl acetate to obtain a 30 wt% solution.

  Next, 30 g of liquid epoxy (epoxy equivalent 185, manufactured by Asahi Kasei Epoxy Co., Ltd., trade name: NovaCure HX-3941) containing a microcapsule type latent curing agent was added to this solution and stirred to prepare an adhesive solution. .

  4 g of the conductive particles 1 prepared above were dispersed in 10 g of ethyl acetate.

  The particle dispersion is dispersed in an adhesive solution so that the conductive particles 1 are 37% by weight based on the adhesive, and this solution is applied to a separator (silicone-treated polyethylene terephthalate film, thickness 40 μm) with a roll coater. The film was dried at 90 ° C. for 10 minutes to prepare an anisotropic conductive adhesive film having a thickness of 25 μm.

  Next, using the produced anisotropic conductive adhesive film, a chip (1.7 × 17 mm, thickness: 0.5 mm) with gold bumps (area: 30 × 90 μm, space: 10 μm, height: 15 μm, bump number: 362) A connection structure sample of a glass substrate with ITO circuit (thickness: 0.7 mm) was prepared by the following method.

First, an anisotropic conductive adhesive film (2 × 19 mm) was attached to a glass substrate with an ITO circuit at 80 ° C. and 0.98 MPa (10 kgf / cm ² ), the separator was peeled off, and the chip bump and the ITO circuit glass The substrate was aligned. Next, heating and pressurization were performed from above the chip under conditions of 190 ° C. for 5 seconds, and this connection was made to obtain a sample.

(Example 2)
The conductive particles 2 are used in place of the conductive particles 1, and the adhesive is used so that the number of conductive particles dispersed per unit area of the anisotropic conductive adhesive film produced in Example 2 is the same as in Example 1. A sample was prepared in the same manner as in Example 1 except that the ratio of the conductive particles 2 to be added was adjusted.

(Example 3)
A sample was prepared in the same manner as in Example 2 except that the conductive particles 3 were used instead of the conductive particles 2.

Example 4
A sample was prepared in the same manner as in Example 2 except that the conductive particles 4 were used instead of the conductive particles 2.

(Example 5)
A sample was prepared in the same manner as in Example 2 except that the conductive particles 5 were used instead of the conductive particles 2.

(Comparative Example 1)
A sample was prepared in the same manner as in Example 2 except that the conductive particles 6 were used instead of the conductive particles 2.

(Comparative Example 2)
A sample was prepared in the same manner as in Example 2 except that the conductive particles 7 were used instead of the conductive particles 2.

(Metal film thickness measurement)
In the measurement of each film thickness of Pd, Ni, and Au, each particle was dissolved in 50% by volume aqua regia, and then resin fine particles and solids were removed by filtration with a membrane filter (manufactured by Millipore) having a diameter of 3 μm. After measuring the amount of each metal with a photometer S4700 (product name, manufactured by Hitachi, Ltd.), the thickness was converted.

(Component analysis in plating film)
In component analysis in the plating film, each particle was dissolved in 50% by volume aqua regia, and then the resin was removed by filtration with a membrane filter (manufactured by Millipore) having a diameter of 3 μm. The ICP (inductively coupled plasma) emission spectrometer P4010 ( Hitachi, Ltd. product name) was used.

(Child particle coverage)
The coverage of the child particles (insulating particles) was calculated by taking an electron micrograph of each conductive particle and analyzing the image. For the electron microscope, S4700 (product name, manufactured by Hitachi, Ltd.) was used, and observation was performed at 5000 times or more.

(Particle boiling test)
1 g of any one of the conductive particles 1 to 7 was collected and dispersed in 50 g of pure water. Next, the sample was put into a 60 ml pressure vessel and left at 100 ° C. for 10 hours.

  Thereafter, the dispersion solvent of the conductive particles was filtered with a 0.2 μm filter, and each metal ion in the filtrate was measured with an atomic absorption photometer. The amount of boiled out (measured ion value) was determined by the following formula.

(Component analysis)
Each mother particle before the insulating coating treatment was spread on a conductive tape (Cat No 7311 manufactured by Nissin EM Co., Ltd.) fixed to the sample stage, and the sample stage was inverted and shaken to drop excess conductive particles. Next, using the EDX analyzer attached to the scanning electron microscope S4700 (product name, manufactured by Hitachi, Ltd.): EMAX EX-300 (product name, manufactured by Horiba, Ltd.), the surface of the mother particle enlarged by 30,000 times The conductive layer was analyzed and qualified. The phosphorus concentration in palladium was calculated from the average value obtained by measuring 10 base particles. Further, a thin piece of the conductive layer portion of the conductive particles was cut out with a focused ion beam. Using a transmission electron microscope HF-2200 (product name, manufactured by Hitachi, Ltd.), the flakes were observed at a magnification of 100,000 times or more, and component analysis of each region of the conductive layer was performed using NORAN EDX attached to the apparatus. . The concentration of nickel, palladium and phosphorus in each region was calculated from the obtained values.

(Insulation resistance test and conduction resistance test)
The insulation resistance test (insulation reliability test) and conduction resistance test of the samples produced in Examples 1 to 5 and Comparative Examples 1 and 2 were performed. It is important that the anisotropic conductive adhesive film has high insulation resistance between the chip electrodes and low conduction resistance (connection resistance) between the chip electrode and the glass electrode.

  The insulation resistance between the chip electrodes was measured for 20 samples, and the minimum value was measured. Regarding the insulation resistance, the minimum value of the result before and after the bias test (durability test with humidity 60%, 90 ° C., 20V DC voltage) is shown. In addition, 100 hours, 300 hours, 500 hours, and 1000 hours shown in Table 1 mean the time of the bias test.

  Moreover, the average value of 14 samples was measured regarding the conduction | electrical_connection resistance between a chip electrode / glass electrode. For the conduction resistance, an initial value and a value after a hygroscopic heat resistance test (left for 1000 hours under conditions of a temperature of 85 ° C. and a humidity of 85%) were measured.

(result)
The measurement results of Examples 1 to 5 and Comparative Examples 1 and 2 are shown in Table 1.

  As shown in Table 1, in the conductive particles of Examples 1 to 5 which do not use nickel at all, there is almost no metal elution as shown in the boiling test results.

  On the other hand, in Comparative Examples 1 and 2 using nickel as the base, nickel tends to elute as compared with Examples 1-5. Therefore, it is safer not to use nickel in a narrow pitch COG substrate.

  Note that palladium, which is a noble metal, has almost no elution. The results of the insulation reliability test mostly depend on the elution amount of nickel. It is clear that the example with little nickel elution shows good results, and the comparative example with much elution of nickel has low insulation reliability.

  Palladium is relatively inexpensive and practical among noble metals, but it is still more expensive than nickel, which is used in large numbers as conductive particles for anisotropic conductive films, so it is desirable to reduce the amount of palladium used as much as possible. On the other hand, it is necessary to bite into the electrode without breaking the palladium layer on the surface of the conductive particles when in contact with the electrode. In addition, the palladium layer is required to have sufficient strength that does not cause cracking or peeling due to an external force during the conductive particle creation process. Palladium is ductile but inferior in hardness to nickel.

  In the present invention, a phosphate-based electroless palladium plating solution such as hypophosphorous acid or phosphorous acid is used as the reducing agent, and phosphorus is precipitated in the palladium layer, resulting in high hardness and corrosion resistance. It is possible to provide a conductive particle excellent in the above.

  When components in each of the plating films of Examples 1 to 5 were qualitatively analyzed using an ICP (inductively coupled plasma) emission spectrometer P4010 (product name, manufactured by Hitachi, Ltd.), palladium and phosphorus were the main components. The element was not detected within the detection error range.

(Example 6)
Instead of using the conductive particles 1, the mother particles 2 are used, and the amount of the mother particles 2 is adjusted so as to be half the number of conductive particles dispersed per unit area of the anisotropic conductive adhesive film produced in Example 1. A sample was prepared in the same manner as in Example 1 except that.

(Comparative Example 3)
Instead of using the conductive particles 1, the mother particles 7 are used, and the amount of the mother particles 7 is adjusted so as to be half the number of conductive particles dispersed per unit area of the anisotropic conductive adhesive film produced in Example 1. A sample was prepared in the same manner as in Example 1 except that.

  In the same manner as in Examples 1 to 5, the particle boiling test and the conduction resistance test in Example 6 and Comparative Example 3 were performed.

  The test results of Example 6 and Comparative Example 3 are shown in Table 2.

(Evaluation of particles not subjected to insulation coating treatment)
As shown in Table 2, the connection resistance of Example 6 was good, but the connection resistance of Comparative Example 3 increased with time. This is because the gold layer of Comparative Example 3 was not soft, so it was difficult to bite into the electrode and could not follow the displacement of the electrode position that occurred over time.

  When the sample was observed from the glass surface side with an optical microscope, a larger amount of particle aggregation was observed in Comparative Example 3. When the mother particle 7 of Comparative Example 3 was subjected to EDX analysis, the phosphorus concentration in nickel was as low as 2% by weight. Therefore, in Comparative Example 3, it was considered that the mother particles 7 were aggregated due to magnetism.

  As shown in Table 2, in Example 6 including only the palladium layer as the metal layer, only a small amount of palladium was eluted in the boiling test, but in Comparative Example 3, a large amount of nickel was eluted. The eluted nickel causes short-circuit failure due to migration or forms an oxide film on the palladium surface, thus reducing the conduction resistance. It should be avoided to use a metal (for example, nickel) that may cause elution.

  As a method of electroless palladium plating for forming a palladium layer on resin fine particles, in this embodiment, a method of immersing resin fine particles activated by applying a catalyst in an electroless palladium plating solution that has been built and a catalyst are used. The method of adding the electroless palladium plating solution sequentially while immersing the applied fine resin particles in warm distilled water and dispersing by stirring was used. However, the palladium plating method is limited to these methods. Not. In addition, in the method of sequentially adding the electroless palladium plating solution described above, the electroless plating solution that has already been erected may be dropped, and the components of the electroless palladium plating solution are divided into at least two, and these are simultaneously performed. And they may be added in parallel. As a method of dividing the components of the electroless palladium plating solution, for example, there is a method of adding palladium ions and a palladium complex component and a reducing agent component as separate solutions.

  As described above, according to the present invention, it is possible to provide conductive particles that are low in cost, high in conductivity, and excellent in connection reliability between electrodes without causing migration.

  DESCRIPTION OF SYMBOLS 1 ... Insulating particle, 2, 2a ... Mother particle, 3 ... Adhesive, 4 ... 1st board | substrate, 5 ... 1st electrode, 6 ... 2nd board | substrate 7 ... second electrode 8, 8a8b ... conductive particles, 11 ... core particles, 12 ... palladium layer, 40 ... anisotropic conductive adhesive, 42 ... connection structure body.

Claims (5)

Comprising resin fine particles and a conductive layer formed on the surface of the resin fine particles,
The conductive layer is a palladium layer containing phosphorus;
The phosphorus concentration in the palladium layer is 1 wt% or more and 10 wt% or less,
The palladium layer has a thickness of 20 nm to 130 nm,
Conductive particles. Insulating particles disposed on the surface of the palladium layer and having a particle size of 20 to 500 nm,
The conductive particles according to claim 1. The palladium layer is a reduction plating type palladium layer,
The conductive particles according to claim 1 or 2. The components in the conductive layer are characterized and quantified by energy dispersive X-ray spectroscopy.
The electroconductive particle as described in any one of Claims 1-3. The conductive particles according to any one of claims 1 to 4 are dispersed in an adhesive.
Anisotropic conductive adhesive.

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