JP7509179B2 - Conductive particles, circuit connecting material, connection structure and method for producing same - Google Patents

Description

This disclosure relates to a method for selecting conductive particles, a circuit connection material, a connection structure and a method for manufacturing the same, and conductive particles.

A driving IC is mounted on glass panels for liquid crystal and OLED (Organic Light-Emitting Diode) displays. The mounting method can be broadly divided into two types: COG (Chip-on-Glass) mounting and COF (Chip-on-Flex) mounting. In COG mounting, the driving IC is directly bonded to the glass panel using an anisotropic conductive adhesive containing conductive particles. On the other hand, in COF mounting, the driving IC is bonded to a flexible tape with metal wiring, and these are then bonded to the glass panel using an anisotropic conductive adhesive containing conductive particles. Anisotropy here means that it is conductive in the direction of pressure and maintains insulation in the direction of no pressure. The anisotropic conductive adhesive containing conductive particles may be formed into a film in advance, and such a film is called an anisotropic conductive film.

Until now, ITO (Indium Tin Oxide) wiring has been the mainstream for wiring on glass panels, but it is being replaced by IZO (Indium Zinc Oxide) wiring in order to improve productivity and smoothness. Furthermore, in recent years, electrodes formed by laminating multiple layers of Cu, Al, Ti, etc. on glass panels, as well as composite multi-layer electrodes in which ITO or IZO is further formed on the top surface, have been developed. It is necessary to obtain stable connection resistance for such electrodes that are highly flat and use high-hardness materials such as Ti.

Patent Document 1 discloses a method for producing conductive microparticles having a core microparticle and a conductive film formed on the surface of the core microparticle, the conductive film having protrusions on the surface. According to this document, conductive microparticles having a conductive film with protrusions are said to have excellent conductive reliability.

Patent Document 2 discloses conductive particles having a base particle and a nickel-boron conductive layer provided on the surface of the base particle. According to this document, the nickel-boron conductive layer has a suitable hardness, so that when connecting electrodes, the oxide film on the surface of the electrodes and conductive particles can be sufficiently removed, thereby lowering the connection resistance.

Patent document 3 discloses conductive particles having resin particles, an electroless metal plating layer covering the surface of the resin particles, and a metal sputter layer other than Au that forms the outermost layer. According to this document, by coating the resin particle surface with electroless metal plating, adhesion to the resin particle surface is improved, and by forming the outermost layer as a metal sputter layer, good connection reliability is obtained.

Japanese Patent No. 4563110 JP 2011-243455 A JP 2012-164454 A

Conventionally, for conductive particles or anisotropic conductive films containing them used in the manufacturing process of displays, panel manufacturers have selected from a wide variety of types that are suitable for the material of the electrode surface. For example, circuits with titanium on the surface, which are used in organic EL displays, have titanium oxide formed on the top surface to make them non-conductive, so conductive particles with a harder plating layer are used compared to conventional ones. As a result, when the conductive particles are pressed together, they penetrate the non-conductive film on the top surface and come into contact with the conductor part inside the electrode, achieving low resistance. However, when conductive particles improved by such physical methods are applied to electrodes of ITO film, for example, there are cases where the conductive particles before improvement show lower resistance, and there is a problem of lack of versatility.

Recently, the rapid commoditization of display-related products has led to intensifying competition among panel manufacturers. Some panel manufacturers are working to standardize their anisotropic conductive film varieties in order to improve their cost competitiveness. However, the reality is that standardizing anisotropic conductive film varieties is difficult for the following reasons:

First, the electrode circuits of liquid crystal displays and organic electroluminescence displays are not uniform. For example, in liquid crystal displays, oxide-based transparent conductive films (ITO, IZO, IGZO, IGO, ZnO, etc.) are mainly used. On the other hand, in organic electroluminescence displays, electrode materials mainly composed of metals such as titanium, chromium, aluminum, and tantalum are mainly used. In addition, for the purpose of protecting the electrode part or increasing its reliability, the electrode surface may be coated with organic materials such as acrylic resin, or inorganic materials such as SiNx and SiOx. Furthermore, examples of electrode circuits other than display substrates include FPCs (Flexible Printed Circuits) and ICs (Integrated Circuits), and various metals such as gold, copper, and nickel are used for the electrodes of these displays.

The present disclosure has been made in consideration of the above-mentioned circumstances, and aims to provide a method for selecting conductive particles that are sufficiently versatile for the circuit electrodes of the circuit components to be connected. The present disclosure also aims to provide conductive particles, a circuit connection material using the conductive particles, and a connection structure and a method for manufacturing the same.

The present disclosure relates to a method for selecting conductive particles, the method comprising the steps of determining whether a metal constituting an outermost layer of a conductive particle satisfies a first condition below, and determining whether the conductive particle satisfies a second condition below, and judging a conductive particle that satisfies both the first and second conditions as good.
First condition: Electrical conductivity at 20° C. is 40×10 ⁶ S/m or less. Second condition: Volume resistivity when a load of 2 kN is applied is 15 mΩcm or less.

By adopting conductive particles that satisfy both the first and second conditions, it is possible to reduce the resistance of the contact interface between the conductive particles and the electrode surface for circuit electrodes with various surface compositions (such as oxide-based transparent conductive films such as ITO and metal electrodes such as Ti), and good connection resistance can be obtained. The inventors have found that the second condition is particularly useful for selecting conductive particles that can achieve good connection resistance and are highly versatile. A load of 2 kN is presumed to be a state in which the conductive particles are hardly flattened. Therefore, it is considered that the resistance value of the conductive particle surface can be detected with good sensitivity compared to when the load is large. In addition, in an actual connection portion, conductive particles with different flatness are mixed between a pair of opposing electrodes due to the variation in the particle size of the conductive particles or the fine unevenness of the electrode surface. In other words, some of these conductive particles are hardly flattened. As described above, the conductive particles selected by the method according to the present disclosure can contribute greatly to reducing the resistance of the connection portion even if they are only slightly flattened, and a good connection resistance can be obtained overall. In contrast, conductive particles that do not satisfy either the first or second condition contribute little to reducing the resistance of the connection if they are only slightly flattened. Note that "facing" in this specification means that a pair of components face each other.

According to the present disclosure, a method for selecting conductive particles that are sufficiently versatile for the circuit electrodes of the circuit components to be connected is provided. In addition, according to the present disclosure, conductive particles, a circuit connection material using the conductive particles, and a connection structure and a method for manufacturing the same are provided.

FIG. 1(a) is a schematic cross-sectional view showing an enlarged view of a connection portion of a connection structure manufactured using conductive particles selected by the method disclosed herein, and FIG. 1(b) is a schematic cross-sectional view showing an enlarged view of a connection portion of a connection structure manufactured using conductive particles that do not satisfy either the first or second condition. FIG. 2 is a graph showing an example of the measurement results of volume resistivity. 3(a) to 3(c) are cross-sectional views that typically show one example of a method for producing a connection structure.

The following describes in detail the embodiments of the present disclosure. However, the present invention is not limited to the following embodiments.

<Conductive particle selection method>
The conductive particle selection method according to this embodiment includes a step of determining whether the metal constituting the outermost layer of a conductive particle satisfies the following first condition, and a step of determining whether the conductive particle satisfies the following second condition, and a conductive particle that satisfies both the first condition and the second condition is judged to be good.
First condition: Electrical conductivity at 20° C. is 40×10 ⁶ S/m or less. Second condition: Volume resistivity when a load of 2 kN is applied is 15 mΩcm or less.

By using conductive particles that satisfy both the first and second conditions, it is possible to reduce the resistance of the contact interface between the conductive particles and the electrode surface for circuit electrodes with various surface compositions (such as oxide-based transparent conductive films such as ITO and metal electrodes such as Ti), and to obtain good connection resistance.

Figure 1(a) is a schematic cross-sectional view showing an enlarged view of a connection part of a connection structure manufactured using conductive particles selected by the method according to this embodiment. The conductive particles 1 (conductive particles 1a, 1b) shown in the figure satisfy both the first and second conditions. Figure 1(b) is a schematic cross-sectional view showing an enlarged view of a connection part of a connection structure manufactured using conductive particles 2 (2a, 2b) that do not satisfy either the first or second condition. In these figures, the thickness of the arrows indicates the ease with which current flows.

1(a), in the connection portion of the connection structure 10, due to the variation in the particle size of the conductive particles 1, conductive particles 1 with different flatness are mixed between the circuit electrodes 3a, 4a of the pair of opposing circuit members 3, 4. As shown in FIG. 1(a), of the three conductive particles 1a, 1b, 1a, two conductive particles 1a, 1a are hardly flattened. Even if the conductive particles 1 (conductive particles 1a, 1b) are only slightly flattened, they contribute greatly to reducing the resistance of the connection portion, so that a good connection resistance can be obtained overall. In contrast, the conductive particles 2 (2a, 2b) shown in FIG. 1(b) contribute little to reducing the resistance of the connection portion when they are only slightly flattened. Here, a case where conductive particles with different flatness are mixed due to the variation in the particle size of the conductive particles is illustrated, but even if the particle size of the conductive particles is sufficiently uniform, the degree of flatness of the conductive particles may change depending on the unevenness of the surfaces of the circuit electrodes 3a, 4a.

The electrical conductivity of the metal of the outermost layer according to the first condition can be measured, for example, using a conductivity measuring device (device name: SIGMATEST, manufactured by Nippon Forster Co., Ltd.). However, conductive particles are generally very small, and it is difficult to measure them with the same device. Therefore, instead of measuring the electrical conductivity using such a device, the elements constituting the outermost layer may be analyzed, and the electrical conductivity may be determined from the type of the elements. From the viewpoint of lowering the connection resistance at the connection part of the connection structure, the first condition (electrical conductivity of the metal layer at 20° C.) may be 1×10 ⁶ to 40×10 ⁶ S/m, or 5×10 ⁶ to 40×10 ⁶ S/m.

The volume resistivity related to the second condition can be measured, for example, using a powder resistivity measurement system (device name: PD51, manufactured by Mitsubishi Chemical Analytech Co., Ltd.). Specifically, 2.5 g of conductive particles can be put into a dedicated cell of the above device, and the volume resistivity of the conductive particles can be measured when a load of 2 kN is applied using the above device. Note that the amount of conductive particles put in should be 0.5 g or more, as it is sufficient to fill the bottom of the dedicated cell. The measurement load can also be changed as desired.

Figure 2 is a graph showing an example of the results of measuring the volume resistivity. The results in Figure 2 were measured at loads of 2 kN to 20 kN, with measurements being taken at 2 kN increments. In this embodiment, the volume resistivity at 2 kN is used as the index. From the viewpoint of lowering the connection resistance at the connection portion of the connection structure and obtaining a more versatile circuit connection material, the second condition (volume resistivity when a load of 2 kN is applied) may be set to 10 mΩcm or less, or 7.5 mΩcm or less, or 5 mΩcm or less.

<Conductive particles>
The conductive particles are not particularly limited as long as they have compressibility, and examples thereof include core-shell particles having a core particle made of a resin material and a metal layer covering the core particle. The metal layer does not need to cover the entire surface of the core particle, and may be a mode in which only a part of the surface of the core particle is covered with the metal layer. The metal layer may have a single layer structure or a multilayer structure.

The particle size of the conductive particles is generally smaller than the minimum distance between the electrodes of the circuit components to be connected. If there is variation in the height of the electrodes to be connected, it is preferable that the average particle size of the conductive particles is larger than the variation in height. From this perspective, the average particle size of the conductive particles is preferably 1 to 50 μm, more preferably 1 to 20 μm, even more preferably 2 to 10 μm, and particularly preferably 2 to 6 μm. In addition, the "average particle size" referred to in this specification means a value obtained by observation with a differential scanning electron microscope. That is, one particle is arbitrarily selected, and observed with a differential scanning electron microscope to measure its maximum and minimum diameters. The square root of the product of the maximum and minimum diameters is defined as the particle size of the particle. In this method, the particle sizes of 50 arbitrarily selected particles are measured, and the average value is calculated to obtain the average particle size of the particles.

As described above, the volume resistivity of the conductive particles to be selected when a load of 2 kN is applied is 15 mΩcm or less. From the viewpoint of lowering the connection resistance at the connection part of the connection structure and obtaining a more versatile circuit connection material, the volume resistivity is preferably 0.1 to 10 mΩcm, more preferably 0.1 to 7.5 mΩcm, and even more preferably 0.1 to 5 mΩcm or less.

The compressive elastic modulus (20% K value) of the conductive particles when displaced by 20% compression at 25°C (at 20% compression) is preferably 0.5 to 15 GPa, and more preferably 1.0 to 10 GPa. The compression hardness K value is an index of the softness of the conductive particles, and by having the 20% K value in the above range, the conductive particles flatten appropriately between the electrodes when connecting opposing electrodes, making it easier to ensure the contact area between the electrodes and the particles, which tends to further improve connection reliability.

The 20% K value of a conductive particle is determined by the following method using a Fischerscope H100C (manufactured by Fischer Instruments). One conductive particle dispersed on a glass slide is compressed at a speed of 0.33 mN/sec. This produces a stress-strain curve, from which the 20% K value is determined. Specifically, the 20% K value can be determined from the following formula K=E/(1-σ 2 )=(3/2 1/2 )×F×(S -3/2 )×(R -1/2 ) using the compression formula for an elastic sphere F=(2 ^1/2 /3)×(S ^3/2 )×(E×R ^1/2 )/(1-σ ² ), where F is the load (N), S is the displacement (mm), R is the particle radius ( ^mm ), E is the ^elastic modulus ( ^Pa ), ^and σ is the Poisson's ratio. Furthermore, if the deformation rate is X (%) and the diameter of the sphere is D (μm), the K value at any deformation rate can be calculated by the following formula: K = 3000F/( ^D2 × X3 ^/2 ) × ^106. The deformation rate X is calculated by the following formula: X = (S/D) × 100. The maximum test load in the compression test is set to, for example, 50 mN.

(Core Particle)
As described above, the conductive particles in this embodiment are core-shell type particles and contain a core particle. The conductive particles having a core particle greatly expand the range of designing the physical properties of the conductive particles themselves, and the size uniformity of the conductive particles is improved compared to metal powders, etc., making it easier to optimize the conductive particles when connecting various members together.

Specific examples of core particles include various plastic particles. Examples of plastic particles include those formed from at least one resin selected from the group consisting of acrylic resins such as polymethyl methacrylate and polymethyl acrylate, polyolefin resins such as polyethylene, polypropylene, polyisobutylene, and polybutadiene, polystyrene resins, polyester resins, polyurethane resins, polyamide resins, epoxy resins, polyvinyl butyral resins, rosin resins, terpene resins, phenol resins, guanamine resins, melamine resins, oxazoline resins, carbodiimide resins, and silicone resins. The plastic particles may be composites of these resins and inorganic substances such as silica.

From the viewpoint of ease of control of the compression recovery rate and the compression hardness K value, the plastic particles may be plastic particles made of a resin obtained by polymerizing one type of polymerizable monomer having an ethylenically unsaturated group, or plastic particles made of a resin obtained by copolymerizing two or more types of polymerizable monomers having an ethylenically unsaturated group. When obtaining a resin by copolymerizing two or more types of polymerizable monomers having an ethylenically unsaturated group, the compression recovery rate and the compression hardness K value of the plastic particles can be easily controlled by using a non-crosslinkable monomer and a crosslinkable monomer in combination and appropriately adjusting the copolymerization ratio and type thereof. As the non-crosslinkable monomer and the crosslinkable monomer, for example, the monomers described in JP-A-2004-165019 can be used.

The average particle size of the plastic particles is preferably 1 to 50 μm. From the viewpoint of high-density mounting, the average particle size of the plastic particles is more preferably 1 to 20 μm. Furthermore, from the viewpoint of maintaining a more stable connection state when there is variation in the unevenness of the electrode surface, the average particle size of the plastic particles is even more preferably 2 to 10 μm.

(Metal Layer)
In this embodiment, the outermost layer of the conductive particles is composed of a metal layer having an electrical conductivity of 40×10 ⁶ S/m or less at 20° C. By adopting such a configuration, good connection reliability can be obtained. The outermost layer here means a range within 50 nm from the surface of the metal layer. The electrical conductivity of the metal constituting the outermost layer at 20° C. is 40×10 ⁶ S/m or less, preferably 1×10 ⁶ to 40×10 ⁶ S/m, and more preferably 5×10 ⁶ to 20×10 ⁶ S/m.

The metal layer may be made of a single metal or an alloy. Examples of metals having an electrical conductivity of 40×10 ⁶ S/m or less include Al, Ti, Cr, Fe, Co, Ni, Zn, Zr, Mo, Pd, In, Sn, W, and Pt. The metal layer is preferably formed of at least one metal selected from the group consisting of Ni, Ni/Au (an embodiment in which an Au layer is provided on a Ni layer; the same applies below), Ni/Pd, Ni/W, Cu, and NiB. The metal layer may be formed by a general method such as plating, vapor deposition, or sputtering, and may be a thin film. In addition, when forming a metal layer on plastic particles by plating, the metal layer preferably contains Ni, Pd, or W from the viewpoint of plating properties on plastic. Furthermore, the metal layer preferably contains Ni, since the removal of resin between the electrode and the particles during compression is effective and a lower resistance can be obtained. Ni has excellent resin removal properties during compression bonding, and is also advantageous in that it has superior plating properties and corrosion resistance compared to Au, Cu, and Ag, which have high electrical conductivity, and is also excellent in terms of supply stability and price.

From the viewpoint of balancing electrical conductivity and cost, the thickness of the metal layer is preferably 10 to 1000 nm, more preferably 20 to 500 nm, and even more preferably 50 to 250 nm.

From the viewpoint of improving the insulation between adjacent electrodes, the conductive particles may have an attachment layer formed by attaching a layer of insulating material (e.g., an organic film) or insulating fine particles (e.g., organic fine particles or inorganic fine particles) to the outside of the metal layer. The thickness of the attachment layer is preferably about 50 to 1000 nm. The attachment layer is preferably formed on conductive particles that have been confirmed to satisfy the first and second conditions. The thickness of the metal layer and the attachment layer can be measured, for example, by a scanning electron microscope (SEM), a transmission electron microscope (TEM), an optical microscope, etc. Furthermore, the metal layer may have protrusions formed on the surface. By having the metal layer have protrusions, the resin can be effectively removed during compression, the contact points with the electrode are increased, and the conductive particles can be more easily contacted with the inside of the electrode, thereby achieving even lower resistance.

<Circuit connecting materials>
The circuit connecting material according to the present embodiment is used for bonding circuit members together and electrically connecting circuit electrodes (e.g., connection terminals) of the respective circuit members together. This circuit connecting material contains an adhesive component that is cured by light or heat, and conductive particles dispersed in the adhesive component, and the conductive particles satisfy both the first and second conditions.

The circuit connecting material is prepared by dispersing conductive particles in the adhesive component. As the circuit connecting material, a paste-like adhesive composition may be used as is, or an anisotropic conductive film obtained by molding the paste into a film may be used. From the viewpoint of achieving a good balance between the conductivity between opposing electrodes and the insulation between adjacent electrodes, the amount of conductive particles is preferably 0.1 to 30 parts by volume, more preferably 0.5 to 15 parts by volume, and even more preferably 1 to 7.5 parts by volume, when the total volume of the circuit connecting material is taken as 100 parts by volume.

The amount of adhesive component is preferably 10 to 90 parts by mass, more preferably 20 to 80 parts by mass, and even more preferably 30 to 70 parts by mass, based on the viewpoint of easily ensuring the strength and elastic modulus required to maintain the gap between the electrodes during and after circuit connection and provide excellent connection reliability, when the total mass of the circuit connecting material is taken as 100 parts by mass.

The adhesive component is not particularly limited, but for example, a composition containing an epoxy resin and a latent curing agent for the epoxy resin (hereinafter referred to as the "first composition"), a composition containing a radically polymerizable substance and a curing agent that generates free radicals when heated (hereinafter referred to as the "second composition"), or a mixed composition of the first composition and the second composition are preferred.

Epoxy resins contained in the first composition include bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol S type epoxy resins, phenol novolac type epoxy resins, cresol novolac type epoxy resins, bisphenol A novolac type epoxy resins, bisphenol F novolac type epoxy resins, alicyclic epoxy resins, glycidyl ester type epoxy resins, glycidyl amine type epoxy resins, hydantoin type epoxy resins, isocyanurate type epoxy resins, aliphatic chain epoxy resins, etc. These epoxy resins may be halogenated or hydrogenated. Two or more of these epoxy resins may be used in combination.

The latent curing agent contained in the first composition may be any agent capable of curing an epoxy resin. Examples of such latent curing agents include anionic polymerization catalyst-type curing agents, cationic polymerization catalyst-type curing agents, polyaddition-type curing agents, etc. These may be used alone or as a mixture of two or more types. Of these, anionic or cationic polymerization catalyst-type curing agents are preferred because they have excellent fast curing properties and do not require consideration of chemical equivalents.

Examples of anionic or cationic polymerizable catalyst-type curing agents include imidazole-based curing agents, hydrazide-based curing agents, boron trifluoride-amine complexes, sulfonium salts, aminimides, diaminomaleonitrile, melamine and its derivatives, polyamine salts, dicyandiamide, etc., and modified products of these can also be used. Examples of polyaddition-type curing agents include polyamines, polymercaptans, polyphenols, acid anhydrides, etc.

When tertiary amines, imidazoles, etc. are blended as anionically polymerizable catalytic hardeners, the epoxy resin is hardened by heating at a medium temperature of about 160°C to 200°C for about tens of seconds to several hours. This allows for a relatively long pot life. As a cationic polymerizable catalytic hardener, for example, a photosensitive onium salt (aromatic diazonium salt, aromatic sulfonium salt, etc.) that hardens the epoxy resin by irradiation with energy rays is preferable. In addition to energy rays, aliphatic sulfonium salts and the like are also used as agents that are activated by heating to harden the epoxy resin. This type of hardener is preferable because it has the characteristic of being fast curing.

These latent curing agents are preferably microencapsulated by coating with a polyurethane or polyester polymer, a thin metal film such as nickel or copper, or an inorganic material such as calcium silicate, since this extends the usable time. The amount of latent curing agent contained in the first composition is preferably 20 to 80 parts by mass, more preferably 30 to 70 parts by mass, per 100 parts by mass of the epoxy resin and the film-forming material added as needed.

The radical polymerizable substance contained in the second composition is a substance having a functional group that polymerizes by radicals. Examples of such radical polymerizable substances include acrylate (including the corresponding methacrylate; the same applies below) compounds, acryloxy (including the corresponding methacryloxy; the same applies below) compounds, maleimide compounds, citraconic imide resins, and nadimide resins. The radical polymerizable substance may be used in the form of a monomer or oligomer, and it is also possible to use a combination of a monomer and an oligomer. Specific examples of the acrylate compound include methyl acrylate, ethyl acrylate, isopropyl acrylate, isobutyl acrylate, ethylene glycol diacrylate, diethylene glycol diacrylate, trimethylolpropane triacrylate, tetramethylolmethane tetraacrylate, 2-hydroxy-1,3-diacryloxypropane, 2,2-bis[4-(acryloxymethoxy)phenyl]propane, 2,2-bis[4-(acryloxypolyethoxy)phenyl]propane, dicyclopentenyl acrylate, tricyclodecanyl acrylate, tris(acryloyloxyethyl)isocyanurate, and urethane acrylate. These can be used alone or in combination of two or more. If necessary, a polymerization inhibitor such as hydroquinone or methyl ether hydroquinones may be appropriately used. Furthermore, from the viewpoint of improving heat resistance, it is preferable that the acrylate compound has at least one substituent selected from the group consisting of a dicyclopentenyl group, a tricyclodecanyl group, and a triazine ring. As the radical polymerizable substance other than the above acrylate compound, for example, the compounds described in International Publication No. 2009/063827 can be suitably used. These are used alone or in combination of two or more types.

It is also preferable to use a radical polymerizable substance having a phosphate ester structure represented by the following formula (I) in combination with the above radical polymerizable substance. In this case, the adhesive strength to inorganic surfaces such as metals is improved, making it suitable for bonding circuit electrodes together.

［式中、ｎは１～３の整数を示す。］

[In the formula, n represents an integer of 1 to 3.]

Radically polymerizable substances having a phosphate ester structure can be obtained by reacting phosphoric anhydride with 2-hydroxyethyl (meth)acrylate. Specific examples of radically polymerizable substances having a phosphate ester structure include mono(2-methacryloyloxyethyl) acid phosphate, di(2-methacryloyloxyethyl) acid phosphate, etc. These can be used alone or in combination of two or more.

The amount of the radical polymerizable substance having the phosphate ester structure represented by the above formula (I) is preferably 0.01 to 50 parts by mass, and more preferably 0.5 to 5 parts by mass, per 100 parts by mass of the total of the radical polymerizable substance and the film-forming material added as necessary.

The above radical polymerizable substance can also be used in combination with allyl acrylate. In this case, the amount of allyl acrylate is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 5 parts by mass, per 100 parts by mass of the total of the radical polymerizable substance and the film-forming material that is added as necessary.

The curing agent contained in the second composition that generates free radicals when heated is a curing agent that decomposes when heated to generate free radicals. Examples of such curing agents include peroxides and azo-based compounds. Such curing agents are appropriately selected depending on the intended connection temperature, connection time, pot life, and the like. From the viewpoint of high reactivity and improved pot life, organic peroxides having a 10-hour half-life temperature of 40°C or higher and a 1-minute half-life temperature of 180°C or lower are preferred, and organic peroxides having a 10-hour half-life temperature of 60°C or higher and a 1-minute half-life temperature of 170°C or lower are more preferred.

When the connection time is 25 seconds or less, the amount of the curing agent is preferably 2 to 10 parts by mass, and more preferably 4 to 8 parts by mass, per 100 parts by mass of the radical polymerizable substance and the film-forming material that is added as needed. This allows a sufficient reaction rate to be obtained. When the connection time is not limited, the amount of the curing agent is preferably 0.05 to 20 parts by mass, and more preferably 0.1 to 10 parts by mass, per 100 parts by mass of the radical polymerizable substance and the film-forming material that is added as needed.

Specific examples of the curing agent contained in the second composition that generates free radicals when heated include diacyl peroxides, peroxydicarbonates, peroxyester peroxyketals, dialkyl peroxides, hydroperoxides, and silyl peroxides. From the viewpoint of suppressing corrosion of the circuit electrodes, a curing agent containing chlorine ions and organic acids at a concentration of 5000 ppm or less is preferred, and a curing agent that generates less organic acid after thermal decomposition is more preferred. Specific examples of such curing agents include peroxyesters, dialkyl peroxides, hydroperoxides, and silyl peroxides, and a curing agent selected from peroxyesters that provide high reactivity is more preferred. The above curing agents can be used in appropriate mixtures.

Peroxy esters include cumyl peroxy neodecanoate, 1,1,3,3-tetramethylbutyl peroxy neodecanoate, 1-cyclohexyl-1-methylethyl peroxy neodecanoate, t-hexyl peroxy neodecanodate, t-butyl peroxy pivalate, 1,1,3,3-tetramethylbutyl peroxy 2-ethylhexanoate, 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane, 1-cyclohexyl-1-methylethyl peroxy 2-ethylhexanoate, t-hexyl peroxy 2-ethylhexanoate, t- Examples of the curing agent that generates free radicals by heating other than the above peroxy esters include, for example, compounds described in International Publication No. 2009/063827. These may be used alone or in combination of two or more.

These curing agents can be used alone or in combination of two or more kinds, and may be used in combination with a decomposition accelerator, decomposition inhibitor, etc. Furthermore, these curing agents may be microencapsulated by coating with a polyurethane or polyester polymeric substance, etc. Microencapsulated curing agents are preferred because they have an extended pot life.

The circuit connecting material of this embodiment may be used by adding a film-forming material as necessary. The film-forming material is a material that, when the liquid is solidified to form the constituent composition into a film shape, makes the film easy to handle under normal conditions (room temperature and pressure) and imparts mechanical properties to the film, such as preventing it from easily tearing, cracking, or becoming sticky. Examples of film-forming materials include phenoxy resin, polyvinyl formal resin, polystyrene resin, polyvinyl butyral resin, polyester resin, polyamide resin, xylene resin, polyurethane resin, and the like. Among these, phenoxy resin is preferred because of its excellent adhesion, compatibility, heat resistance, and mechanical strength.

Phenoxy resin is a resin obtained by reacting bifunctional phenols with epihalohydrin until they are polymerized, or by polyaddition of bifunctional epoxy resin with bifunctional phenols. For example, phenoxy resin can be obtained by reacting 1 mole of bifunctional phenols with 0.985 to 1.015 moles of epihalohydrin in a non-reactive solvent at a temperature of 40 to 120°C in the presence of a catalyst such as an alkali metal hydroxide. In addition, from the viewpoint of the mechanical and thermal properties of the resin, it is preferable to use a phenoxy resin obtained by polyaddition reaction in an organic solvent such as an amide, ether, ketone, lactone, or alcohol solvent with a boiling point of 120°C or higher, heated to 50 to 200°C under conditions of 50% by mass or less of reaction solid content, in which the blending equivalent ratio of bifunctional epoxy resin and bifunctional phenol is epoxy group/phenol hydroxyl group = 1/0.9 to 1/1.1 in the presence of a catalyst such as an alkali metal compound, an organic phosphorus compound, or a cyclic amine compound. Phenoxy resins may be used alone or in combination of two or more types.

The bifunctional epoxy resins include bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol AD type epoxy resins, bisphenol S type epoxy resins, biphenyl diglycidyl ether, methyl-substituted biphenyl diglycidyl ether, etc. Bifunctional phenols have two phenolic hydroxyl groups. Bifunctional phenols include, for example, hydroquinones, bisphenol A, bisphenol F, bisphenol AD, bisphenol S, bisphenol fluorene, methyl-substituted bisphenol fluorene, dihydroxybiphenyl, methyl-substituted dihydroxybiphenyl, and other bisphenols. The phenoxy resin may be modified (e.g., epoxy-modified) with a radically polymerizable functional group or other reactive compound.

The amount of the film-forming material is preferably 10 to 90 parts by mass, and more preferably 20 to 60 parts by mass, when the total mass of the circuit connecting material is 100 parts by mass.

The circuit connecting material of this embodiment may further contain a polymer or copolymer containing at least one of acrylic acid, acrylic acid ester, methacrylic acid ester, and acrylonitrile as a monomer component. Here, the circuit connecting material preferably contains a copolymer-based acrylic rubber containing glycidyl acrylate and/or glycidyl methacrylate containing a glycidyl ether group in combination, because such a copolymer has excellent stress relaxation properties. The weight-average molecular weight of such an acrylic rubber is preferably 200,000 or more in order to increase the cohesive strength of the adhesive composition.
The circuit connecting material of the present embodiment may further contain rubber fine particles, fillers, softeners, accelerators, antioxidants, colorants, flame retardants, thixotropic agents, coupling agents, phenolic resins, melamine resins, isocyanates, and the like.

It is preferable that the rubber microparticles have an average particle size that is no more than twice the average particle size of the conductive particles to be mixed, and a storage modulus at room temperature (25°C) that is no more than half the storage modulus at room temperature of the conductive particles and the adhesive composition. In particular, when the material of the rubber microparticles is silicone, acrylic emulsion, SBR, NBR, or polybutadiene rubber, it is preferable to use them alone or in a mixture of two or more types. These three-dimensionally crosslinked rubber microparticles have excellent solvent resistance and are easily dispersed in the adhesive composition.

The filler can improve the connection reliability of the electrical properties between the circuit electrodes. For example, a filler whose average particle size is half or less than the average particle size of the conductive particles can be used. When non-conductive particles are used in combination, any filler whose average particle size is equal to or less than the average particle size of the non-conductive particles can be used. The amount of filler to be blended is preferably 5 to 60 parts by mass per 100 parts by mass of the adhesive composition. By blending an amount of 60 parts by mass or less, the effect of improving connection reliability tends to be more fully obtained, while on the other hand, by blending an amount of 5 parts by mass or more, the effect of adding the filler tends to be fully obtained.

As coupling agents, compounds containing amino groups, vinyl groups, acryloyl groups, epoxy groups or isocyanate groups are preferred as they improve adhesion.

The circuit connection material melts and flows during connection to obtain a connection between opposing circuit electrodes, and then hardens to maintain the connection, and the fluidity of the circuit connection material is an important factor. Examples of indicators that indicate this include the following. That is, when a 5 mm x 5 mm circuit connection material with a thickness of 35 μm is sandwiched between two 15 mm x 15 mm glass plates with a thickness of 0.7 mm and heated and pressed at 170°C, 2 MPa, and for 10 seconds, the value of fluidity (B)/(A), expressed using the area (A) of the main surface of the circuit connection material before heating and pressing and the area (B) of the main surface after heating and pressing, is preferably 1.3 to 3.0, and more preferably 1.5 to 2.5. A value of 1.3 or more indicates favorable fluidity and tends to make it easier to obtain good connections, and a value of 3.0 or less tends to make it more difficult for bubbles to form and tends to provide better reliability.

The elastic modulus of the circuit connecting material at 40°C after curing is preferably 100 to 3000 MPa, and more preferably 500 to 2000 MPa. The elastic modulus of the circuit connecting material after curing can be measured, for example, using a dynamic viscoelasticity measuring device (DVE, DMA, etc.).

The circuit connection material of this embodiment is suitable for use in COG connections (chip on glass), FOB (flex on board) connections, FOG (flex on glass) connections, FOF (flex on flex) connections, FOP (flex on polymer) connections, COP (chip on polymer) connections, COF (chip on flex) connections, etc.

The COG connection is, for example, a method of connecting an IC to an organic EL panel or an LCD panel, and refers to the connection between circuit electrodes formed on the IC and circuit electrodes formed on the glass substrate that constitutes the organic EL panel or the LCD panel.
The FOB connection refers to the connection between a circuit electrode formed on a flexible substrate, such as TCP (Tape Carrier Package), COF, and FPC, and a circuit electrode formed on a printed wiring board. The FOG connection refers to the connection between a circuit electrode formed on a flexible substrate, such as TCP, COF, and FPC, and a circuit electrode formed on a glass substrate constituting an organic EL panel or LCD panel. The FOF connection refers to the connection between a circuit electrode formed on a flexible substrate, such as TCP, COF, and FPC, and a circuit electrode formed on a flexible substrate. The FOP connection refers to the connection between a circuit electrode formed on a flexible substrate and a circuit electrode formed on a polymer substrate constituting an organic EL panel or LCD panel. The COP connection refers to the connection between a circuit electrode formed on an IC and a circuit electrode formed on a plastic substrate. The COF connection refers to the connection between a circuit electrode formed on an IC and a circuit electrode formed on a flexible substrate.

<Connection structure>
The circuit connection structure of this embodiment has a first circuit member having a first circuit electrode, a second circuit member having a second circuit electrode, and a connection part made of the cured product of the above-mentioned circuit connection material interposed between the first circuit member and the second circuit member. In this embodiment, the material of the circuit electrode can be Ti, Al, Mo, Co, Cu, Cr, Sn, Zn, Ga, In, Ni, Au, Ag, V, Sb, Bi, Re, Ta, Nb, W, etc. From the viewpoint of balancing the connection resistance and the price, the thickness of the circuit electrode is preferably 100 to 5000 nm, more preferably 100 to 2500 nm. The lower limit can also be set to 500 nm.

The circuit connection structure of this embodiment can be produced by arranging a first circuit member having a first circuit electrode and a second circuit member having a second circuit electrode so that the first circuit electrode and the second circuit electrode face each other, interposing a circuit connection material between the opposed first and second circuit electrodes, and applying heat and pressure to electrically connect the first and second circuit electrodes. In this way, the circuit connection material of this embodiment is useful as a material for bonding electrical circuits together.

More specifically, examples of circuit components include chip components such as semiconductor chips, resistor chips, and capacitor chips, and substrates such as printed circuit boards. These circuit components are usually provided with a large number of the above-mentioned circuit electrodes (or in some cases, a single circuit electrode). At least some of these circuit electrodes are arranged opposite each other, a circuit connection material is interposed between the oppositely arranged circuit electrodes, and at least one set of circuit components is heated and pressurized to electrically connect the oppositely arranged circuit electrodes. At this time, the oppositely arranged circuit electrodes are electrically connected to each other via the conductive particles contained in the circuit connection material, while insulation between adjacent circuit electrodes is maintained. In this way, the circuit connection material of this embodiment exhibits anisotropic conductivity.

One embodiment of a method for manufacturing a circuit connection structure will be described with reference to Figures 3(a) to 3(c). Figure 3(a) is a cross-sectional view of the process before circuit members are connected to each other, Figure 3(b) is a cross-sectional view of the process when circuit members are connected to each other, and Figure 3(c) is a cross-sectional view of the process after circuit members are connected to each other.

First, as shown in FIG. 3(a), a circuit member 20 having a circuit electrode 21a and a circuit board 21b provided on an organic EL panel 21, and a circuit member 30 having a circuit electrode 31a provided on a board 31 are prepared. Then, a circuit connection material 5 formed into a film is placed on the circuit electrode 21a.

Next, as shown in FIG. 3(b), the substrate 31 on which the circuit electrode 31a is provided is placed on the circuit connection material 5 while aligning the circuit electrodes 21a and 31a so that they face each other, and the circuit connection material 5 is interposed between the circuit electrodes 21a and 31a. The circuit electrodes 21a and 31a have a structure (not shown) in which multiple electrodes are arranged in the depth direction. The circuit connection material 5 is in the form of a film, and is therefore easy to handle. Therefore, the circuit connection material 5 can be easily interposed between the circuit electrodes 21a and 31a, and the connection work between the circuit members 20 and 30 can be facilitated.

Next, the circuit connection material 5 is pressed in the direction of arrow A in FIG. 3(b) through the organic EL panel 21 and the substrate 31 while being heated, to perform a curing process. This results in a circuit connection structure 50 in which the circuit members 20, 30 are connected to each other through the cured product 5a of the circuit connection material, as shown in FIG. 3(c). As a method of curing, either or both of heating and light irradiation can be adopted depending on the adhesive composition used.

The present disclosure will be explained in more detail below with reference to examples. However, the present invention is not limited to these examples.

(1) Preparation of conductive particles Eleven types of conductive particles A to K shown in Table 1 below were prepared. All of these conductive particles are core-shell particles composed of a core made of a plastic particle and a shell made of a metal layer (nickel layer) covering the core particle. The electrical conductivity of nickel is 14.5 x 10 ⁶ S/m. Of the conductive particles A to K, conductive particles A to E and conductive particles H and J satisfied both the first and second conditions.

Example 1
(2) Preparation of anisotropic conductive film (preparation of phenoxy resin solution)
50 g of phenoxy resin (product name: PKHC, manufactured by Union Carbide Corporation, weight average molecular weight: 5000) was dissolved in a mixed solvent of toluene/ethyl acetate = 50/50 (mass ratio) to prepare a phenoxy resin solution with a solid content of 40 mass %.

(Synthesis of urethane acrylate)
A 2L (liter) four-neck flask equipped with a thermometer, a stirrer, an inert gas inlet and a reflux condenser was charged with 4000 parts by mass of polycarbonate diol (manufactured by Aldrich, number average molecular weight Mn = 2000), 238 parts by mass of 2-hydroxyethyl acrylate, 0.49 parts by mass of hydroquinone monomethyl ether and 4.9 parts by mass of tin catalyst to prepare a reaction liquid. 666 parts by mass of isophorone diisocyanate (IPDI) was uniformly dropped over 3 hours into the reaction liquid heated to 70 ° C. to react. After completion of the dropwise addition, the reaction was continued for 15 hours, and the time when the NCO% (NCO content) became 0.2% by mass or less was regarded as the end of the reaction, and a urethane acrylate was obtained. The NCO% was confirmed by a potentiometric automatic titrator (product name: AT-510, manufactured by Kyoto Electronics Manufacturing Co., Ltd.). As a result of GPC analysis, the weight average molecular weight of the urethane acrylate was 8,500 (standard polystyrene equivalent). The GPC measurement conditions are shown in Table 2.

(Preparation of adhesive composition-containing liquid)
The phenoxy resin solution was weighed out so as to contain 50 g of solids from the above phenoxy resin solution, and 30 g of the above urethane acrylate, 15 g of isocyanurate-type acrylate (product name: M-215, manufactured by Toagosei Co., Ltd.), 1 g of phosphate-type acrylate, and 4 g of benzoyl peroxide (product name: Nyper BMT-K40, manufactured by NOF Corporation) as a free radical generator were mixed together to prepare an adhesive composition-containing liquid.

(Preparation of anisotropic conductive film)
A circuit connecting material-containing liquid was prepared by dispersing 5 parts by mass of conductive particles A in 100 parts by mass of the adhesive composition-containing liquid. This circuit connecting material-containing liquid was applied to a 50 μm-thick polyethylene terephthalate (PET) film with one surface-treated side using a coating device, and then dried with hot air at 70° C. for 3 minutes. As a result, an anisotropic conductive film with a thickness of 20 μm was obtained on the PET film. When the total mass of this anisotropic conductive film was 100 parts by volume, the contents of the adhesive component and the conductive particles were 97 parts by volume and 3 parts by volume, respectively.

(3) Fabrication of connection structure (top electrode surface: titanium)
The anisotropic conductive film with the PET film was cut to a predetermined size (width 1.5 mm x length 3 cm). The surface on which the anisotropic conductive film was formed (adhesive surface) was transferred onto a glass substrate (thickness 0.7 mm) coated with titanium (film thickness 50 nm) and aluminum (film thickness 250 nm) in that order from the outermost surface. The transfer conditions were 70 ° C., 1 MPa, and 2 seconds. After peeling off the PET film, a flexible circuit board (FPC) having 600 tin-plated copper circuits with a pitch of 50 μm and a thickness of 8 μm was temporarily fixed on the anisotropic conductive film. The temporary fixing conditions were 24 ° C., 0.5 MPa, and 1 second. Next, this was placed in the main pressure bonding device, and a silicone rubber sheet with a thickness of 200 μm was used as a cushioning material, and the FPC side was heated and pressed with a heat tool at 170 ° C., 3 MPa, and 6 seconds to connect over a width of 1.5 mm. This resulted in a connection structure.

(4) Preparation of connection structure (top electrode surface: ITO)
A connection structure was obtained in the same manner as above, except that a glass substrate coated with ITO (film thickness 100 nm) on the outermost surface was used instead of the above glass substrate coated with titanium and aluminum in that order from the outermost surface.

(5) Preparation of connection structure (top electrode surface: IZO)
A connection structure was obtained in the same manner as described above, except that a glass substrate coated with IZO (film thickness 100 nm), Cr (film thickness 50 nm), and aluminum (film thickness 200 nm) in that order from the outermost surface was used instead of the above glass substrate coated with titanium and aluminum in that order from the outermost surface.

(6) Measurement of Connection Resistance The connection resistance of the two types of connection structures obtained above was measured as follows. The resistance value between adjacent circuits of the FPC including the connection part of the connection structure was measured with a multimeter (device name: TR6845, manufactured by Advantest Corporation). The resistance between 40 adjacent circuits was measured and the average value was calculated, which was used as the connection resistance. The results are shown in Table 3.

<Examples 2 to 5 and Comparative Examples 1 and 2>
Three types of connection structures were produced and their connection resistances were measured in the same manner as in Example 1, except that conductive particles B to K were used instead of conductive particles A. The results are shown in Table 3.

According to the present disclosure, a method for selecting conductive particles that are sufficiently versatile for the circuit electrodes of the circuit components to be connected is provided. In addition, according to the present disclosure, conductive particles, a circuit connection material using the conductive particles, and a connection structure and a method for manufacturing the same are provided.

1, 1a, 1b...conductive particles; 3, 4, 20, 30...circuit members; 3a, 4a, 21a, 31a...circuit electrodes; 5...circuit connecting material; 5a...cured product of the circuit connecting material; 10, 50...connection structure

Claims (10)

A metal layer having an electrical conductivity of 1×10 ⁶ S/m or more and 40×10 ⁶ S/m or less at 20° C. is provided;
The volume resistivity when a load of 2 kN is applied is 0.1 mΩcm or more and 15 mΩcm or less ,
Further comprising core particles made of a resin material,
A conductive particle , wherein the metal layer is formed on the surface of the core particle . A metal layer including Ni is provided,
Conductive particles having a volume resistivity of 0.1 mΩcm or more and 15 mΩcm or less when a load of 2 kN is applied. Further comprising core particles made of a resin material,
The conductive particle according to claim 2 , wherein the metal layer is formed on the surface of the core particle. The conductive particles according to any one of claims 1 to 3 , which are used for connecting a circuit electrode whose outermost surface is made of Ti or IZO. A circuit connecting material used for bonding circuit members together and electrically connecting circuit electrodes of the respective circuit members together, comprising:
an adhesive component that hardens when exposed to light or heat;
The conductive particles according to any one of claims 1 to 4 , which are dispersed in the adhesive component;
A circuit connecting material comprising: 6. The circuit connecting material according to claim 5 , wherein the adhesive component comprises a phenoxy resin, a urethane acrylate, an isocyanurate-type acrylate, and a phosphoric acid ester-type acrylate. A pair of circuit members disposed opposite each other;
a connection part made of the cured product of the circuit connecting material according to claim 5 or 6 , which is interposed between the pair of circuit members and bonds the circuit members together so that circuit electrodes of the respective circuit members are electrically connected to each other;
A connection structure comprising: The connection structure according to claim 7 , wherein the outermost surface of the circuit electrode is made of Ti or IZO. A step of interposing the circuit connecting material according to claim 5 or 6 between a pair of circuit members arranged opposite to each other;
forming a connection portion made of a cured product of the circuit connecting material by applying heat and pressure, the connection portion being interposed between the pair of circuit members and bonding the circuit members together so that circuit electrodes of the respective circuit members are electrically connected to each other;
A method for manufacturing a connection structure comprising: The method for producing a connection structure according to claim 9 , wherein the outermost surface of the circuit electrode is made of Ti or IZO.

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