JP7733583B2 - Conductive particles, sockets, conductive materials and connection structures - Google Patents

Description

The present invention relates to conductive particles in which a conductive portion is disposed on the surface of a base particle. The present invention also relates to sockets, conductive materials, and connection structures using the conductive particles.

Anisotropic conductive materials such as anisotropic conductive pastes and anisotropic conductive films are widely known. In these anisotropic conductive materials, conductive particles are dispersed in a binder.

The anisotropic conductive material is used to electrically connect electrodes of various connection target components, such as flexible printed circuit boards (FPCs), glass substrates, glass epoxy substrates, and semiconductor chips, to obtain connection structures. Furthermore, the conductive particles may be conductive particles having a base particle and a conductive portion disposed on the surface of the base particle.

In recent years, with the expansion of markets for IoT, 5G communications, VR, AR, artificial intelligence, and autonomous driving systems, the amount of information has increased and communication speeds have increased, placing an even greater demand on processors in data servers, PCs, mobile devices, and other devices to process information faster.

One method for processing large amounts of information at high speed is to improve the processing power of the CPU (Central Processing Unit). To improve CPU processing power, the metal terminals (metal pins) of the socket (CPU socket) that connects the CPU to the motherboard are becoming more and more multi-pin and with narrower pitches.

An example of a socket using metal terminals (metal pins) is disclosed in Patent Document 1 below. Patent Document 1 below discloses an electronic component socket that is interposed between an electronic component, such as a semiconductor element or semiconductor device, and a mounting board to detachably mount the electronic component and electrically connect the electronic component to the mounting board. In this electronic component socket, a connection terminal is provided on the mounting surface side of a socket body made of resin. This connection terminal is formed by a conductive film coated on the outer surface of a resin bump that is integral with the socket body and protrudes from the socket body. In this electronic component socket, the connection terminal is provided with a base end joined to the inner surface of the conductive film, and the base end side is embedded and sealed in the resin bump and the socket body. The tip side of this connection terminal is formed in a bent shape extending from the side opposite the mounting surface of the socket body.

Japanese Patent Application Laid-Open No. 2003-297507

With conventional sockets such as those described in Patent Document 1, it is extremely difficult to process fine metal terminals (metal pins) to accommodate increased pin counts and narrower pitches. Furthermore, miniaturizing metal terminals (metal pins) reduces their strength, which can lead to connection failures due to the metal terminals (metal pins) breaking or bending when connecting to a CPU, etc. With sockets that use conventional metal terminals (metal pins), it is difficult to accommodate increased pin counts and narrower pitches, making it difficult to achieve faster information processing speeds.

An object of the present invention is to provide conductive particles that can maintain high connection reliability even when compressed over a long period of time. Another object of the present invention is to provide a conductive material and a connection structure using the conductive particles.

After extensive research into the above-mentioned problems, the inventors discovered that the above-mentioned problems can be solved by using specific conductive particles instead of metal terminals (metal pins).

According to a broad aspect of the present invention, there is provided a conductive particle comprising a base particle and a conductive portion disposed on the surface of the base particle, wherein the conductive particle has a compression recovery rate of 85% or more after being held in a 20% compressed state for 168 hours.

In a particular aspect of the conductive particle of the present invention, the conductive portion has a first conductive layer, the material of the first conductive layer includes a ductile metal, and the ratio of the particle diameter of the conductive particle to the thickness of the first conductive layer is 50 or more and 1000 or less.

In a particular aspect of the conductive particles of the present invention, the compressive deformation rate when the conductive particles are compressed under a load of 1000 mN is 10% or more.

In a particular aspect of the conductive particles of the present invention, when the base particle is loaded to 1961 mN at a loading rate of 14.12 mN/sec and then unloaded at an unloading rate of 14.12 mN/sec, the ratio of the compressive displacement at a compressive load of 500 mN during loading to the compressive displacement at a compressive load of 500 mN during unloading is 0.7 or more, and the ratio of the compressive displacement at a compressive load of 1000 mN during loading to the compressive displacement at a compressive load of 1000 mN during unloading is 0.7 or more.

In a particular aspect of the conductive particles of the present invention, the material of the base particle contains a polyfunctional (meth)acrylate having a polyether skeleton, and the content of the polyfunctional (meth)acrylate having a polyether skeleton in 100% by weight of the material of the base particle is 5% by weight or more.

In a particular aspect of the conductive particles of the present invention, the particle diameter of the conductive particles is 100 μm or more and 1000 μm or less.

In a particular aspect of the conductive particle of the present invention, the conductive portion has a laminated structure of two or more layers, and the material of the outer surface of the conductive portion is gold, silver, copper, tin, zinc, nickel, beryllium, cobalt, palladium, platinum, rhodium, ruthenium, iridium, or an alloy thereof.

In one particular aspect of the conductive particles of the present invention, the conductive particles are used to obtain a socket or connector.

According to a broad aspect of the present invention, there is provided a socket comprising a socket body and the above-mentioned conductive particles, the conductive particles constituting connection terminals.

According to a broad aspect of the present invention, there is provided a conductive material comprising the conductive particles described above and a binder.

According to a broad aspect of the present invention, there is provided a connection structure comprising a first connection target member having a first electrode on its surface, a second connection target member having a second electrode on its surface, and a connection portion having an insulating member and conductive particles, wherein the conductive particles are the conductive particles described above, and the first electrode and the second electrode are electrically connected by the conductive particles.

The conductive particles of the present invention comprise a base particle and a conductive portion disposed on the surface of the base particle. The conductive particles of the present invention have a compression recovery rate of 85% or more after being held in a 20% compressed state for 168 hours. Because the conductive particles of the present invention have the above configuration, they can maintain high connection reliability even when compressed for a long period of time.

FIG. 1 is a cross-sectional view showing a conductive particle according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view showing a conductive particle according to a second embodiment of the present invention. FIG. 3 is a cross-sectional view showing a conductive particle according to a third embodiment of the present invention. FIG. 4 is a front cross-sectional view that schematically shows a connection structure using conductive particles according to the first embodiment of the present invention. FIG. 5 is a front cross-sectional view schematically showing another example of a connection structure using conductive particles according to the first embodiment of the present invention.

The details of the present invention are described below.

(Conductive particles)
The conductive particle according to the present invention includes a base particle and a conductive portion disposed on the surface of the base particle, and has a compression recovery rate of 85% or more after being held in a 20% compressed state for 168 hours.

The conductive particles of the present invention have the above-mentioned configuration, so they can maintain high connection reliability even when compressed for a long period of time.

Furthermore, when using conductive particles instead of metal terminals (metal pins), conventional conductive particles are only designed to temporarily increase connection reliability, and do not take into consideration maintaining high connection reliability even after being subjected to a compressive load for an extended period of time (e.g., about a week). When conventional conductive particles are used in place of metal terminals (metal pins), there is an issue in that connection reliability decreases when the particles are subjected to a compressive load for an extended period of time (e.g., about a week).

After extensive research into the above-mentioned issues, the inventors discovered that when conventional conductive particles are used in connection structures and subjected to a compressive load over an extended period of time by components to be connected, the conductive particles may be damaged, or may remain deformed and not fully recover their shape even after the load is removed. In other words, connection structures using conventional conductive particles may experience poor conductivity the next time they are connected after extended use (compression of the conductive particles).

On the other hand, the conductive particles of the present invention have the above-mentioned configuration, so they can maintain high connection reliability even when compressed for a long period of time. In the present invention, the use of specific conductive particles greatly contributes to achieving the above-mentioned effects.

The compression recovery rate of the conductive particles after holding them in a 20% compressed state for 168 hours is 85% or more. The compression recovery rate of the conductive particles after holding them in a 20% compressed state for 168 hours is preferably 90% or more, more preferably 95% or more, even more preferably 97% or more, and most preferably 100%. When the compression recovery rate of the conductive particles after holding them in a 20% compressed state for 168 hours is above the lower limit, the conductive particles are less likely to be damaged over long periods of time. As a result, high connection reliability can be maintained even more effectively, even when the conductive particles are compressed for long periods of time.

The compression recovery rate after holding the above conductive particles in a 20% compressed state for 168 hours can be measured using the following compression test A.

<Compression Test A>
Conductive particles are dispersed on the surface of a first glass slide, and a second glass slide is then laminated thereon to obtain a laminate. The laminate is then clamped using a micrometer, and a load is applied at 25°C until the particle diameter of the conductive particles is compressed by 20%. After holding the conductive particles in a 20% compressed state for 168 hours, the conductive particles are removed and observed using an electron microscope or optical microscope to measure the particle diameter of the conductive particles. The compression recovery rate after holding the conductive particles in a 20% compressed state for 168 hours is calculated using the following formula. It is preferable to measure 50 random conductive particles and calculate the average particle diameter of the conductive particles. The particle diameter of the conductive particles before compression test A is the particle diameter of the conductive particles before compression in the compression direction in the subsequent compression. The particle diameter of the conductive particles after compression test A is the particle diameter of the conductive particles after compression in the compression direction. The particle diameter of the conductive particles after compression test A is the particle diameter measured 30 minutes after removing the conductive particles. An example of the micrometer is the "MDC-25PXT" manufactured by Mitutoyo Corporation. The particle diameters of the conductive particles before and after compression test A can be measured, for example, using a diameter measurement function of software attached to an optical microscope. An example of the optical microscope is the "Digital Microscope VHX Series" manufactured by Keyence Corporation.

Compression recovery rate (%) = (H2/H1) x 100
H1: Particle diameter of conductive particles before compression test A H2: Particle diameter of conductive particles after compression test A

In addition, from the viewpoint of improving initial connection reliability, the compression recovery rate of the above-mentioned conductive particles when compressed by 20% (compression recovery rate measured without maintaining the compressed state) is preferably 90% or more, more preferably 95% or more, even more preferably 97% or more, and most preferably 100%.

The compression recovery rate of the above conductive particles when compressed by 20% (compression recovery rate measured without maintaining the compressed state) can be measured using the following compression test B.

<Compression Test B>
In the above-mentioned compression test A, the conductive particles are held in a 20% compressed state for 5 minutes, and then removed and observed under an electron microscope or optical microscope to measure the particle diameter of the conductive particles. The compression recovery rate of the conductive particles when compressed 20% (compression recovery rate measured without holding the compressed state) is calculated using the following formula. It is preferable to measure 50 random conductive particles and calculate the average particle diameter of the conductive particles. The particle diameter of the conductive particles before compression test B is the particle diameter of the conductive particles before compression in the compression direction in the subsequent compression. The particle diameter of the conductive particles after compression test B is the particle diameter of the conductive particles after compression in the compression direction. The particle diameter of the conductive particles after compression test B is the particle diameter measured 30 minutes after the conductive particles were removed.

Compression recovery rate (%) = (J2/J1) x 100
J1: Particle diameter of conductive particles before compression test B J2: Particle diameter of conductive particles after compression test B

The compressive deformation ratio of the conductive particles when compressed under a load of 1000 mN is preferably 10% or more, more preferably 15% or more, even more preferably 20% or more, and preferably 50% or less, more preferably 45% or less, and even more preferably 40% or less. When the compressive deformation ratio of the conductive particles when compressed under a load of 1000 mN is above the lower limit and below the upper limit, the conductive particles are less likely to be damaged over an extended period of time. As a result, high connection reliability can be more effectively maintained even when the conductive particles are compressed over an extended period of time. The compressive deformation ratio indicates the ratio (%) of the particle diameter of the conductive particles in the compression direction after compression to the particle diameter of the conductive particles before compression.

The compressive modulus of elasticity when compressed by 10% (10% K value) of the conductive particles is preferably 10 N/ ^mm2 or more, more preferably 50 N/ ^mm2 or more, and preferably 1000 N/mm2 or ^less , more preferably 500 N/ ^mm2 or less. When the 10% K value is equal to or greater than the above lower limit and equal to or less than the above upper limit, the initial connection reliability can be improved.

The compressive modulus of elasticity when compressed by 20% (20% K value) of the conductive particles is preferably 10 N/ ^mm2 or more, more preferably 50 N/ ^mm2 or more, and preferably 1000 N/mm2 or ^less , more preferably 500 N/ ^mm2 or less. When the 20% K value is equal to or greater than the lower limit and equal to or less than the upper limit, the initial connection reliability can be improved.

The above compressive modulus (10% K value and 20% K value) of the above conductive particles can be measured as follows.

Using a micro-compression testing machine, one conductive particle is compressed with the end face of a cylindrical (2 mm diameter, BeCu/Au on stainless steel) smooth indenter at 25°C, a compression speed of 0.3 mN/sec, and a maximum test load of 20 mN. The load value (N) and compression displacement (mm) at this time are measured. From the obtained measured values, the compressive elastic modulus can be calculated using the following formula. An example of a micro-compression testing machine that can be used is the Nordson 4000Plus Bond Tester.

10% K value or 20% K value (N/mm ² ) = (3/2 ^1/2 )·F·S ^-3/ 2·R ^-1/2
F: Load value (N) when the conductive particles are compressed and deformed by 10% or 20%
S: Compression displacement (mm) when the conductive particles are compressed and deformed by 10% or 20%
R: Radius of conductive particle (mm)

The above compressive modulus universally and quantitatively represents the hardness of conductive particles. By using the above compressive modulus, the hardness of conductive particles can be quantitatively and unambiguously represented.

The resistance value (R1) of the conductive particles when compressed by 20% is preferably 0.1 mΩ or more, more preferably 1 mΩ or more, and preferably 100 mΩ or less, more preferably 50 mΩ or less, even more preferably 25 mΩ or less, and particularly preferably 20 mΩ or less. When the resistance value (R1) is above the lower limit and below the upper limit, initial connection reliability can be improved.

The resistance value (R2) of the conductive particles after holding them in a 20% compressed state for 168 hours is preferably 0.1 mΩ or more, more preferably 1 mΩ or more, and preferably 100 mΩ or less, more preferably 50 mΩ or less, even more preferably 25 mΩ or less, and particularly preferably 20 mΩ or less. When the resistance value (R2) is above the lower limit and below the upper limit, high connection reliability can be more effectively maintained even when the conductive particles are compressed for a long period of time.

The above resistance value (R1) and the above resistance value (R2) can be measured as follows.

Using a micro-compression testing machine, a load is applied at 25°C with the end face of a smooth cylindrical indenter (2 mm diameter, made of BeCu/Au on stainless steel) toward the center of the conductive particle until the conductive particle is compressed by 20%. The electrical resistance is measured when the conductive particle is compressed by 20%, and this is the resistance value (R1). The electrical resistance is also measured after the conductive particle has been held in the 20% compressed state for 168 hours, and this is the resistance value (R2). Examples of the micro-compression testing machine that can be used include the Nordson 4000Plus Bond Tester.

The particle diameter of the conductive particles is preferably 100 μm or more, more preferably 150 μm or more, even more preferably 300 μm or more, and preferably 1000 μm or less, more preferably 800 μm or less, and even more preferably 700 μm or less. When the particle diameter of the conductive particles is equal to or greater than the above-mentioned lower limit and equal to or less than the above-mentioned upper limit, the effects of the present invention can be more effectively exerted. Furthermore, the conductive particles can be suitably used to obtain sockets or connectors.

The particle diameter of the conductive particles is preferably an average particle diameter, and more preferably a number-average particle diameter. The particle diameter of the conductive particles can be determined, for example, by observing 50 random conductive particles with an electron microscope or optical microscope and calculating the average particle diameter of each conductive particle, or by using a particle size distribution analyzer. When observed with an electron microscope or optical microscope, the particle diameter of each conductive particle is determined as the particle diameter in equivalent circle diameter. When observed with an electron microscope or optical microscope, the average particle diameter of 50 random conductive particles in equivalent circle diameter is approximately equal to the average particle diameter in equivalent sphere diameter. When observed with a particle size distribution analyzer, the particle diameter of each conductive particle is determined as the particle diameter in equivalent sphere diameter. The average particle diameter of the conductive particles is preferably calculated using a particle size distribution analyzer.

The coefficient of variation (CV value) of the particle size of the conductive particles is preferably 10% or less, more preferably 5% or less. When the coefficient of variation of the particle size of the conductive particles is below the upper limit, the contact area between the conductive particles and the electrode can be sufficiently large.

The above coefficient of variation (CV value) can be measured as follows.

CV value (%) = (ρ/Dn) × 100
ρ: Standard deviation of particle diameter of conductive particles Dn: Average particle diameter of conductive particles

The shape of the conductive particles is not particularly limited. The conductive particles may be spherical or may have a shape other than spherical, such as a square pillar, a cylindrical shape, or a flat shape.

The present invention will now be described in detail with reference to the drawings.

Figure 1 is a cross-sectional view showing a conductive particle according to a first embodiment of the present invention.

The conductive particle 1 shown in Figure 1 has a base particle 2 and a conductive portion 3. The conductive portion 3 is arranged on the surface of the base particle 2. In the conductive particle 1, the conductive portion 3 is in contact with the surface of the base particle 2. The conductive particle 1 is a coated particle in which the surface of the base particle 2 is coated with the conductive portion 3.

In the conductive particle 1, the conductive portion 3 is a single-layer conductive layer. In the conductive particle, the conductive portion may cover the entire surface of the base particle, or the conductive portion may cover only a portion of the surface of the base particle. In the conductive particle, the conductive portion may be a single-layer conductive layer, or a multi-layer conductive layer composed of two or more layers.

Conductive particle 1, unlike conductive particle 11 described below, does not have a core substance. Conductive particle 1 does not have protrusions on its surface. Conductive particle 1 is spherical. Conductive portion 3 does not have protrusions on its outer surface. Thus, the conductive particle of the present invention may not have protrusions on the surface of the conductive portion and may be spherical.

Figure 2 is a cross-sectional view showing a conductive particle according to a second embodiment of the present invention.

The conductive particle 11 shown in Figure 2 has a base particle 2, a conductive portion 12, and multiple core materials 13. The conductive portion 12 is arranged on the surface of the base particle 2 so as to be in contact with the base particle 2.

In the conductive particle 11, the conductive portion 12 is a single-layer conductive layer. In the conductive particle, the conductive portion may cover the entire surface of the base particle, or the conductive portion may cover only a portion of the surface of the base particle. In the conductive particle, the conductive portion may be a single-layer conductive layer, or a multi-layer conductive layer composed of two or more layers.

The conductive particle 11 has multiple protrusions 11a on the surface of the conductive portion. The conductive portion 12 has multiple protrusions 12a on its outer surface. Multiple core materials 13 are arranged on the surface of the base particle 2. The multiple core materials 13 are embedded within the conductive portion 12. The core materials 13 are arranged inside the protrusions 11a, 12a. The conductive portion 12 coats the multiple core materials 13. The outer surface of the conductive portion 12 is raised by the multiple core materials 13, forming the protrusions 11a, 12a.

Figure 3 is a cross-sectional view showing a conductive particle according to a third embodiment of the present invention.

The conductive particle 21 shown in Figure 3 has a base particle 2 and a conductive portion 23. The conductive portion 23 as a whole has a first conductive layer 23A on the base particle 2 side and a second conductive layer 23B on the opposite side to the base particle 2 side.

The only difference between conductive particle 1 and conductive particle 21 is the conductive portion. That is, conductive particle 1 has a single-layer conductive portion 3, while conductive particle 21 has a two-layer conductive portion 23 (first conductive layer 23A and second conductive layer 23B). The first conductive layer 23A and second conductive layer 23B are formed as separate conductive portions.

The first conductive layer 23A is disposed on the surface of the base particle 2. The first conductive layer 23A is disposed between the base particle 2 and the second conductive layer 23B. The first conductive layer 23A is in contact with the base particle 2. The second conductive layer 23B is in contact with the first conductive layer 23A. Therefore, the first conductive layer 23A is disposed on the surface of the base particle 2, and the second conductive layer 23B is disposed on the surface of the first conductive layer 23A.

Conductive particle 21, unlike conductive particle 11, does not have a core material. Conductive particle 21 does not have protrusions on its surface. Conductive particle 21 is spherical. Conductive portion 23 does not have protrusions on its outer surface.

Further details of the conductive particles are described below.

(Base material particles)
The material of the base particles is not particularly limited.

The material of the base particles may be either an organic material or an inorganic material. Examples of base particles formed solely from the organic material include resin particles. Examples of base particles formed solely from the inorganic material include inorganic particles excluding metals. Examples of base particles formed from both the organic material and the inorganic material include organic-inorganic hybrid particles. From the perspective of improving both the flexibility and compression characteristics of the base particles, the base particles are preferably resin particles or organic-inorganic hybrid particles, and more preferably resin particles.

The organic materials include polyolefin resins such as polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyvinylidene chloride, polyisobutylene, and polybutadiene; acrylic resins such as polymethyl methacrylate and polymethyl acrylate; polycarbonate, polyamide, phenol-formaldehyde resin, melamine-formaldehyde resin, benzoguanamine-formaldehyde resin, urea-formaldehyde resin, phenolic resin, melamine resin, benzoguanamine resin, urea resin, epoxy resin, unsaturated polyester resin, saturated polyester resin, polyethylene terephthalate, polysulfone, polyphenylene oxide, polyacetal, polyimide, polyamide-imide, polyether ether ketone, polyether sulfone, and divinylbenzene polymer. The vinylbenzene polymer may be a divinylbenzene copolymer. Examples of the divinylbenzene copolymer include divinylbenzene-styrene copolymer and divinylbenzene-(meth)acrylic acid ester copolymer. The material of the base particle is preferably a polymer obtained by polymerizing one or more polymerizable monomers having an ethylenically unsaturated group, since the compression characteristics of the base particle can be easily controlled within a suitable range.

The base particles can be obtained by polymerizing the polymerizable monomer having the ethylenically unsaturated group. The polymerization method is not particularly limited, and examples include known methods such as radical polymerization, ionic polymerization, polycondensation (condensation polymerization, polycondensation), addition condensation, living polymerization, and living radical polymerization. Another polymerization method is suspension polymerization in the presence of a radical polymerization initiator.

When the above base particles are obtained by polymerizing a polymerizable monomer having an ethylenically unsaturated group, the polymerizable monomer having an ethylenically unsaturated group may be a non-crosslinkable monomer or a crosslinkable monomer.

The above-mentioned non-crosslinkable monomers include vinyl compounds such as styrene monomers, α-methylstyrene, and chlorostyrene; vinyl ether compounds such as methyl vinyl ether, ethyl vinyl ether, and propyl vinyl ether; acid vinyl ester compounds such as vinyl acetate, vinyl butyrate, vinyl laurate, and vinyl stearate; halogen-containing monomers such as vinyl chloride and vinyl fluoride; (meth)acrylic compounds such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, and cyclohexyl (meth)acrylate. Examples of the compound include alkyl (meth)acrylate compounds such as silyl (meth)acrylate and isobornyl (meth)acrylate; oxygen atom-containing (meth)acrylate compounds such as 2-hydroxyethyl (meth)acrylate, glycerol (meth)acrylate, polyoxyethylene (meth)acrylate and glycidyl (meth)acrylate; nitrile-containing monomers such as (meth)acrylonitrile; halogen-containing (meth)acrylates such as trifluoromethyl (meth)acrylate and pentafluoroethyl (meth)acrylate; α-olefin compounds such as diisobutylene, isobutylene, linearene, ethylene and propylene; and conjugated diene compounds such as isoprene and butadiene.

Examples of the crosslinkable monomer include vinyl compounds such as vinyl monomers like divinylbenzene, 1,4-divinyloxybutane, and divinylsulfone; (meth)acrylic compounds such as tetramethylolmethane tetra(meth)acrylate, polytetramethylene glycol diacrylate, tetramethylolmethane tri(meth)acrylate, tetramethylolmethane di(meth)acrylate, trimethylolpropane tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol penta(meth)acrylate, glycerol tri(meth)acrylate, glycerol di(meth)acrylate, polyethylene glycol di(meth)acrylate, and polypropylene. Polyfunctional (meth)acrylates such as pyrene glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, and 1,4-butanediol di(meth)acrylate; allyl compounds such as triallyl (iso)cyanurate, triallyl trimellitate, diallyl phthalate, diallyl acrylamide, and diallyl ether; silane compounds such as tetramethoxysilane, tetraethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, isopropyltrimethoxysilane, isobutyltrimethoxysilane, cyclohexyltrimethoxysilane, n-hexyltrimethoxysilane, and n-octyltriethoxysilane. Silane alkoxide compounds such as silane, n-decyltrimethoxysilane, phenyltrimethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, diisopropyldimethoxysilane, trimethoxysilylstyrene, γ-(meth)acryloxypropyltrimethoxysilane, 1,3-divinyltetramethyldisiloxane, methylphenyldimethoxysilane, and diphenyldimethoxysilane; vinyltrimethoxysilane, vinyltriethoxysilane, dimethoxymethylvinylsilane, dimethoxyethylvinylsilane, diethoxymethylvinylsilane, diethoxyethylvinylsilane, ethylmethyldivinylsilane, methylvinyldimethoxysilane, and ethylvinyldimethoxysilane; Examples of the silane alkoxides include silane alkoxides containing a polymerizable double bond, such as silane, methylvinyldiethoxysilane, ethylvinyldiethoxysilane, p-styryltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, and 3-acryloxypropyltrimethoxysilane; cyclic siloxanes such as decamethylcyclopentasiloxane; modified (reactive) silicone oils such as one-end-modified silicone oil, both-ends silicone oil, and side-chain silicone oil; and carboxyl group-containing monomers such as (meth)acrylic acid, maleic acid, and maleic anhydride.

When the base particle is obtained by polymerizing a polymerizable monomer having an ethylenically unsaturated group, the polymerizable monomer having an ethylenically unsaturated group preferably includes a crosslinkable monomer, more preferably a polyfunctional crosslinkable monomer. The polymerizable monomer having an ethylenically unsaturated group more preferably includes polypropylene glycol di(meth)acrylate, and particularly preferably includes a monomer represented by the following formula (1). From the perspective of more effectively achieving the effects of the present invention, the material for the base particle preferably includes a polyfunctional (meth)acrylate, more preferably a polyfunctional (meth)acrylate having a polyether skeleton. From the perspective of more effectively achieving the effects of the present invention, the material for the base particle more preferably includes a polyfunctional (meth)acrylate having a polyalkylene glycol skeleton, particularly preferably polypropylene glycol di(meth)acrylate, and most preferably includes a monomer represented by the following formula (1) (hereinafter sometimes referred to as "monomer X"). From the viewpoint of more effectively exerting the effects of the present invention, the number of carbon atoms in the alkylene group of the polyalkylene glycol skeleton is preferably at least 2, preferably at most 4, and more preferably at most 3. When the material of the base particle contains the above-mentioned preferred monomer X, the compression recovery rate after the conductive particle is held in a 20% compressed state for 168 hours can be more effectively increased, and the effects of the present invention can be more effectively exerted.

In the above formula (1), n represents an integer of 5 or more and 20 or less. In the above formula (1), n is preferably 7 or more, more preferably 10 or more, and preferably 17 or less, more preferably 15 or less.

The content of the polyfunctional (meth)acrylate having a polyether skeleton, based on 100% by weight of the material of the base particle, is preferably 5% by weight or more, more preferably 10% by weight or more, even more preferably 30% by weight or more, and preferably 100% by weight or less, more preferably 90% by weight or less, even more preferably 80% by weight or less, and particularly preferably 60% by weight or less. When the content of the polyfunctional (meth)acrylate having a polyether skeleton is above the above-mentioned lower limit and below the above-mentioned upper limit, the effects of the present invention can be more effectively achieved. Based on 100% by weight of the material of the base particle, the content of the polyfunctional (meth)acrylate having a polyether skeleton may be 100% by weight (total amount).

The content of the polyfunctional (meth)acrylate having a polyalkylene glycol skeleton, based on 100% by weight of the base particle material, is preferably 5% by weight or more, more preferably 10% by weight or more, even more preferably 30% by weight or more, and preferably 100% by weight or less, more preferably 90% by weight or less, even more preferably 80% by weight or less, and particularly preferably 60% by weight or less. When the content of the polyfunctional (meth)acrylate having a polyalkylene glycol skeleton is above the above-mentioned lower limit and below the above-mentioned upper limit, the effects of the present invention can be more effectively achieved. Based on 100% by weight of the base particle material, the content of the polyfunctional (meth)acrylate having a polyalkylene glycol skeleton may be 100% by weight (total amount).

The content of the monomer X in 100% by weight of the material of the base particle is preferably 5% by weight or more, more preferably 10% by weight or more, even more preferably 30% by weight or more, and preferably 100% by weight or less, more preferably 90% by weight or less, even more preferably 80% by weight or less, and particularly preferably 60% by weight or less. When the content of the monomer X is above the above lower limit and below the above upper limit, the effects of the present invention can be more effectively achieved. The content of the monomer X in 100% by weight of the material of the base particle may be 100% by weight (total amount).

The material of the base particle may contain a monomer other than the monomer X. Examples of such a monomer other than the monomer X include styrene, divinylbenzene, methyl (meth)acrylate, polytetramethylene glycol di(meth)acrylate, and 1,9-nonanediol di(meth)acrylate. The monomer other than the monomer X is preferably polytetramethylene glycol di(meth)acrylate or 1,9-nonanediol di(meth)acrylate, and more preferably polytetramethylene glycol di(meth)acrylate. When the monomer other than the monomer X is one of the preferred monomers, the compression recovery rate of the conductive particles after holding them in a 20% compressed state for 168 hours is further increased, thereby enabling the effects of the present invention to be more effectively achieved.

From the viewpoint of reducing the viscosity of the base particle material and improving the moldability of the base particle, the content of monomers other than the monomer X in 100% by weight of the base particle material is preferably 10% by weight or more, more preferably 20% by weight or more, even more preferably 40% by weight or more, and preferably 95% by weight or less, more preferably 90% by weight or less, even more preferably 70% by weight or less.

Examples of the inorganic materials include silica, alumina, barium titanate, zirconia, carbon black, silicate glass, borosilicate glass, lead glass, soda-lime glass, and alumina silicate glass.

The base particles may be organic-inorganic hybrid particles. The base particles may be core-shell particles. When the base particles are organic-inorganic hybrid particles, examples of inorganic materials for the base particles include silica, alumina, barium titanate, zirconia, and carbon black. It is preferable that the inorganic material is not a metal. The base particles formed from silica are not particularly limited, but examples include base particles obtained by hydrolyzing a silicon compound having two or more hydrolyzable alkoxysilyl groups to form crosslinked polymer particles, followed by calcination as necessary. Examples of the organic-inorganic hybrid particles include organic-inorganic hybrid particles formed from a crosslinked alkoxysilyl polymer and an acrylic resin.

The organic-inorganic hybrid particles are preferably core-shell organic-inorganic hybrid particles having a core and a shell disposed on the surface of the core. The core is preferably an organic core. The shell is preferably an inorganic shell. The base particle is preferably an organic-inorganic hybrid particle having an organic core and an inorganic shell disposed on the surface of the organic core.

Examples of materials for the organic core include the organic materials mentioned above.

The inorganic shell may be made of any of the inorganic materials listed above as the base particle material. Preferably, the inorganic shell is made of silica. The inorganic shell is preferably formed by forming a shell-like material from a metal alkoxide on the surface of the core using a sol-gel method, and then firing the shell-like material. The metal alkoxide is preferably a silane alkoxide. The inorganic shell is preferably formed from a silane alkoxide.

When the base particle is loaded to 1961 mN at a loading rate of 14.12 mN/s and then unloaded at a unloading rate of 14.12 mN/s, the ratio (L1/L2) of the compressive displacement (L1) at a compressive load of 500 mN during loading to the compressive displacement (L2) at a compressive load of 500 mN during unloading preferably satisfies the following range: That is, the ratio (L1/L2) is preferably 0.6 or greater, more preferably 0.7 or greater, even more preferably 0.8 or greater, and particularly preferably 0.9 or greater. When the ratio (L1/L2) is equal to or greater than the lower limit, the effects of the present invention can be more effectively achieved. There is no particular upper limit for the ratio (L1/L2). The ratio (L1/L2) may be 1.0 or less, or may be less than 1.0.

Furthermore, when the base particle is loaded to 1961 mN at a loading rate of 14.12 mN/s and then unloaded at a unloading rate of 14.12 mN/s, the ratio (L3/L4) of the compressive displacement (L3) at a compressive load of 1000 mN during loading to the compressive displacement (L4) at a compressive load of 1000 mN during unloading preferably satisfies the following range: That is, the ratio (L3/L4) is preferably 0.6 or greater, more preferably 0.7 or greater, even more preferably 0.8 or greater, and particularly preferably 0.9 or greater. When the ratio (L3/L4) is equal to or greater than the lower limit, the effects of the present invention can be more effectively achieved. There is no particular upper limit for the ratio (L3/L4). The ratio (L3/L4) may be 1.0 or less, or may be less than 1.0.

From the viewpoint of more effectively achieving the effects of the present invention, it is preferable that the ratio (L1/L2) of the base particle is 0.7 or greater and the ratio (L3/L4) of the base particle is 0.7 or greater. From the viewpoint of more effectively achieving the effects of the present invention, it is preferable that the ratio of the compressive displacement under load to the compressive displacement upon unloading is 0.7 or greater over the entire range of compressive loads under load from 500 mN to 1000 mN. From the viewpoint of more effectively achieving the effects of the present invention, it is preferable that the ratio of the compressive displacement under load to the compressive displacement upon unloading is 1.0 or less over the entire range of compressive loads under load from 500 mN to 1000 mN.

The above compression displacement (L1), the above compression displacement (L2), the above compression displacement (L3), and the above compression displacement (L4) can be measured using the following compression test C.

<Compression Test C>
Base material particles are scattered on a sample stage. For each scattered base material particle, a load of 1961 mN (reversed load value) is applied in the direction of the center of the base material particle using a micro-compression tester at a loading rate of 14.12 mN/sec. Then, the load is unloaded to the origin load value (20.2 mN) at an unloading rate of 14.12 mN/sec. The load-compression displacement during this period is measured, and a compression displacement-compression load curve (compression displacement curve) is created. The compression displacement (L1) at a compressive load of 500 mN during loading, the compression displacement (L2) at a compressive load of 500 mN during unloading, the compression displacement (L3) at a compressive load of 1000 mN during loading, and the compression displacement (L4) at a compressive load of 1000 mN during unloading are determined. Examples of the micro-compression tester include the "Micro Autograph MST-I" manufactured by Shimadzu Corporation. The above-mentioned compression displacement (L1), compression displacement (L2), compression displacement (L3), and compression displacement (L4) are all based on the compression displacement at the origin load value (20.2 mN).

The particle diameter of the base particle is preferably 30 μm or more, more preferably 100 μm or more, even more preferably 200 μm or more, and particularly preferably 300 μm or more, and is preferably 2000 μm or less, more preferably 1000 μm or less, and even more preferably 600 μm or less. When the particle diameter of the base particle is above the above-mentioned lower limit and below the above-mentioned upper limit, the conductive particles can be more suitably used to obtain sockets or connectors. When the particle diameter of the base particle is above the above-mentioned lower limit and below the above-mentioned upper limit, the contact area between the conductive particle and the electrode can be sufficiently increased, and agglomerated conductive particles are less likely to form when forming the conductive portion, making it less likely that the conductive portion will peel off from the surface of the base particle.

It is particularly preferable that the particle diameter of the base particle is 100 μm or more and 1000 μm or less. When the particle diameter of the base particle is within the range of 100 μm or more and 1000 μm or less, the conductive particles are less likely to aggregate when forming a conductive portion on the surface of the base particle, making it difficult for agglomerated conductive particles to form. Furthermore, when the particle diameter of the base particle is within the range of 100 μm or more and 800 μm or less, the conductive particles can be used even more preferably to obtain a socket or connector.

The particle size of the above-mentioned base particles indicates the diameter if the base particles are spherical, and if the base particles are not spherical, indicates the diameter when assumed to be a perfect sphere of equivalent volume.

The particle diameter of the base particles refers to the number-average particle diameter. The particle diameter of the base particles can be determined by observing 50 random base particles with an electron microscope or optical microscope and calculating the average particle diameter of each base particle, or by using a particle size distribution analyzer. When observed with an electron microscope or optical microscope, the particle diameter of each base particle is determined as the particle diameter in equivalent circle diameter. When observed with an electron microscope or optical microscope, the average particle diameter in equivalent circle diameter of 50 random base particles is approximately equal to the average particle diameter in equivalent sphere diameter. When observed with a particle size distribution analyzer, the particle diameter of each base particle is determined as the particle diameter in equivalent sphere diameter. The average particle diameter of the base particles is preferably calculated using a particle size distribution analyzer. When measuring the particle diameter of the base particles in conductive particles, it can be measured, for example, as follows.

Conductive particles are added to Kulzer's Technovit 4000 so that the content is 30% by weight, and dispersed to prepare an embedding resin for conductive particle inspection. An ion milling device (Hitachi High-Technologies Corporation's IM4000) is used to cut out a cross section of the conductive particles (preferably base particles) dispersed in the embedding resin, passing through the vicinity of the center of each particle. Then, 50 conductive particles are randomly selected using a field emission scanning electron microscope (FE-SEM), and the base particle of each conductive particle is observed. The particle diameter of the base particle for each conductive particle is measured, and the arithmetic average of these measurements is used to determine the particle diameter of the base particle.

(Conductive part)
The conductive particle according to the present invention includes a base particle and a conductive portion disposed on the surface of the base particle. The conductive portion preferably contains a metal. The metal constituting the conductive portion is not particularly limited.

Examples of metals constituting the conductive portion include gold, silver, palladium, copper, platinum, zinc, iron, tin, lead, aluminum, cobalt, indium, nickel, chromium, titanium, antimony, beryllium, rhodium, ruthenium, iridium, bismuth, thallium, germanium, cadmium, silicon, tungsten, molybdenum, and alloys thereof. Examples of metals constituting the conductive portion include tin-doped indium oxide (ITO) and solder. Only one type of metal may be used to constitute the conductive portion, or two or more types may be used in combination.

From the viewpoint of more effectively reducing the connection resistance and improving the compression characteristics of the base particles and conductive particles, it is preferable that the conductive portion contains a ductile metal. The ductile metal has ductility. Examples of the ductile metal include copper, zinc, tin, aluminum, nickel, gold, silver, lead, platinum, titanium, and alloys thereof.

From the viewpoint of more effectively reducing the connection resistance, it is preferable that the conductive portion contains nickel, gold, palladium, beryllium, cobalt, tin, silver, or copper, and it is more preferable that it contains nickel, gold, or copper.

The conductive portion preferably has a first conductive layer. The first conductive layer is preferably disposed on the surface of the base particle. The first conductive layer is preferably in contact with the base particle.

The first conductive layer preferably contains a metal. Examples of materials for the first conductive layer include the metals described above. From the viewpoint of more effectively reducing connection resistance, the material for the first conductive layer preferably contains a ductile metal, more preferably contains nickel, gold, or copper, and even more preferably contains copper. From the viewpoint of suppressing cracks in the conductive portion and suppressing connection defects, it is even more preferable that the material for the first conductive layer is copper.

The conductive portion may be formed of one layer. The conductive portion may be formed of multiple layers. The conductive portion may have a two-layer laminate structure, a two or more layer laminate structure, a three-layer laminate structure, or a three or more layer laminate structure. From the perspective of suppressing cracks in the conductive portion and suppressing connection failures, it is preferable that the conductive portion have a two or more layer laminate structure.

When the conductive portion has a laminated structure of two or more layers, the material of the outer surface of the conductive portion is preferably gold, silver, copper, tin, zinc, nickel, beryllium, cobalt, palladium, platinum, rhodium, ruthenium, iridium, or an alloy thereof, and more preferably gold, copper, or an alloy thereof. When the material of the outer surface of the conductive portion is one of these preferred metals, oxidation of the first conductive portion can be suppressed, thereby making the effects of the present invention even more effective.

The method for forming the conductive portion on the surface of the base particle is not particularly limited. Examples of methods for forming the conductive portion include electroless plating, electroplating, physical collision, mechanochemical reaction, physical vapor deposition or physical adsorption, and coating the surface of the base particle with a metal powder or a paste containing a metal powder and a binder. The method for forming the conductive portion is preferably electroless plating, electroplating, or physical collision. Examples of physical vapor deposition methods include vacuum deposition, ion plating, and ion sputtering. Examples of physical collision methods include a Sheeter Composer (manufactured by Tokuju Kosakusho Co., Ltd.).

The thickness of the conductive portion is preferably 0.2 μm or more, more preferably 1 μm or more, and preferably 15 μm or less, more preferably 10 μm or less, even more preferably 8 μm or less, and particularly preferably 7 μm or less. The thickness of the conductive portion refers to the thickness of the entire conductive portion when the conductive portion has a laminated structure of two or more layers. When the thickness of the conductive portion is equal to or greater than the above lower limit and equal to or less than the above upper limit, cracking of the conductive portion can be suppressed, and poor connection can be suppressed. Furthermore, sufficient conductivity can be obtained and the conductive particles can be prevented from hardening.

The thickness of the first conductive layer is preferably 0.2 μm or more, more preferably 1 μm or more, and preferably 15 μm or less, more preferably 10 μm or less, and even more preferably 8 μm or less. When the thickness of the first conductive layer is equal to or greater than the above-mentioned lower limit and equal to or less than the above-mentioned upper limit, the compression recovery rate after the conductive particles are held in a 20% compressed state for 168 hours can be more effectively increased, thereby more effectively achieving the effects of the present invention.

When the conductive portion has a laminated structure of two or more layers, the thickness of the conductive portion of the outermost layer is preferably 0.001 μm or more, more preferably 0.01 μm or more, and preferably 10 μm or less, more preferably 7 μm or less. When the thickness of the conductive portion of the outermost layer is above the above-mentioned lower limit and below the above-mentioned upper limit, the coating by the conductive portion of the outermost layer becomes uniform, and corrosion resistance can be effectively improved. Furthermore, when the metal constituting the outermost layer is gold, the thinner the thickness of the outermost layer, the lower the cost.

The thickness of the conductive portion can be measured by observing the cross section of the conductive particle using, for example, a scanning electron microscope (SEM). It is preferable to calculate the thickness of the conductive portion by averaging the thickness of five arbitrary conductive portions, and it is more preferable to calculate the average thickness of the entire conductive portion as the thickness of the conductive portion of one conductive particle. It is preferable to determine the thickness of the conductive portion by calculating the average thickness of the conductive portion of each of 10 arbitrary conductive particles.

The ratio of the particle diameter of the conductive particles to the thickness of the first conductive layer (particle diameter of conductive particles/thickness of first conductive layer) is preferably 40 or more, more preferably 50 or more, even more preferably 100 or more, and preferably 1500 or less, more preferably 1000 or less, and even more preferably 800 or less. When the ratio (particle diameter of conductive particles/thickness of first conductive layer) is equal to or greater than the above lower limit and equal to or less than the above upper limit, the compression recovery rate after holding the conductive particles in a 20% compressed state for 168 hours can be more effectively increased, thereby more effectively achieving the effects of the present invention.

The ratio of the particle diameter of the conductive particles to the thickness of the conductive portion (particle diameter of conductive particles/thickness of conductive portion) is preferably 5 or more, more preferably 10 or more, and even more preferably 20 or more, and is preferably 800 or less, more preferably 650 or less, and even more preferably 300 or less. When the ratio (particle diameter of conductive particles/thickness of conductive portion) is equal to or greater than the above lower limit and equal to or less than the above upper limit, the compression recovery rate of the conductive particles can be further increased, and the effects of the present invention can be more effectively exerted.

(core substance)
The conductive particles may have protrusions on the outer surface of the conductive portion. The conductive particles may have protrusions on the surface of the conductive portion. Preferably, there are multiple protrusions. An oxide film is often formed on the surface of the electrode that contacts the conductive particles. When conductive particles having protrusions on the surface of the conductive portion are used, the oxide film can be effectively removed by pressing the conductive particles and the electrode together. This ensures more reliable contact between the electrode and the conductive portion, sufficiently increasing the contact area between the conductive particles and the electrode, and more effectively reducing the connection resistance. Furthermore, when the conductive particles are dispersed in a binder and used as a conductive material, the protrusions of the conductive particles can more effectively remove the binder between the conductive particles and the electrode. This allows the contact area between the conductive particles and the electrode to be sufficiently increased, and more effectively reducing the connection resistance.

Methods for forming the protrusions include a method in which a core material is attached to the surface of a base particle and then a conductive portion is formed by electroless plating, and a method in which a conductive portion is formed on the surface of a base particle by electroless plating, then a core material is attached, and then a conductive portion is formed by electroless plating. It is also possible to form the protrusions without using the core material.

Other methods for forming the protrusions include adding a core material during the process of forming conductive portions on the surface of the base particle. Alternatively, to form the protrusions, a method may be used in which, without using the core material, conductive portions are formed on the base particle by electroless plating, and then protrusion-like plating is deposited on the surface of the conductive portions, and then conductive portions are formed by further electroless plating.

Methods for attaching core substances to the surfaces of base particles include adding the core substance to a dispersion of base particles and allowing the core substance to accumulate and adhere to the surfaces of the base particles through van der Waals forces, and adding the core substance to a container containing base particles and allowing the core substance to adhere to the surfaces of the base particles through mechanical action such as rotating the container. From the perspective of controlling the amount of core substance to be attached, the method for attaching core substances to the surfaces of base particles preferably involves allowing the core substance to accumulate and adhere to the surfaces of the base particles in the dispersion.

Materials constituting the core material include conductive and non-conductive materials. Examples of conductive materials include conductive non-metals such as metals, metal oxides, and graphite, as well as conductive polymers. Examples of conductive polymers include polyacetylene. Examples of non-conductive materials include silica, alumina, titanium oxide, and zirconia. From the perspective of more effectively removing the oxide coating, it is preferable that the core material be hard. From the perspective of more effectively reducing the connection resistance between electrodes, it is preferable that the core material be a metal.

The metal is not particularly limited. Examples of the metal include gold, silver, copper, platinum, zinc, iron, lead, tin, aluminum, cobalt, indium, nickel, chromium, titanium, antimony, bismuth, germanium, and cadmium, as well as alloys composed of two or more metals, such as tin-lead alloys, tin-copper alloys, tin-silver alloys, tin-lead-silver alloys, and tungsten carbide. From the perspective of more effectively reducing the connection resistance between electrodes, the metal is preferably nickel, copper, silver, or gold. The metal may be the same as or different from the metal constituting the conductive portion (conductive layer).

The shape of the core substance is not particularly limited. The core substance is preferably in the form of a mass. Examples of the core substance include particulate masses, aggregates formed by the aggregation of multiple microparticles, and amorphous masses.

The particle diameter of the core material is preferably 0.001 μm or more, more preferably 0.05 μm or more, and preferably 0.9 μm or less, more preferably 0.2 μm or less. When the particle diameter of the core material is equal to or greater than the lower limit and equal to or less than the upper limit, the connection resistance between electrodes can be reduced more effectively.

The particle size of the core material above indicates the diameter if the core material is spherical, and if the core material is not spherical, indicates the diameter when assumed to be a perfect sphere of equivalent volume.

The particle size of the core substance is preferably the average particle size, and more preferably the number average particle size. The particle size of the core substance can be determined by observing 50 random core substances with an electron microscope or optical microscope and calculating the average particle size of each core substance, or by using a particle size distribution analyzer. When observed with an electron microscope or optical microscope, the particle size of each core substance is determined as the particle size in equivalent circle diameter. When observed with an electron microscope or optical microscope, the average particle size of 50 random core substances in equivalent circle diameter is approximately equal to the average particle size in equivalent sphere diameter. When observed with a particle size distribution analyzer, the particle size of each core substance is determined as the particle size in equivalent sphere diameter. The average particle size of the core substance is preferably calculated using a particle size distribution analyzer.

The number of protrusions per conductive particle is preferably 3 or more, more preferably 5 or more. There is no particular upper limit to the number of protrusions. The upper limit can be selected appropriately taking into account factors such as the particle diameter of the conductive particles. If the number of protrusions is equal to or greater than the lower limit, the connection resistance between electrodes can be reduced even more effectively.

The number of protrusions can be calculated by observing any conductive particle with an electron microscope or optical microscope. Preferably, the number of protrusions is determined by observing 50 conductive particles with an electron microscope or optical microscope and calculating the average number of protrusions on each conductive particle.

The height of the protrusions is preferably 0.001 μm or more, more preferably 0.05 μm or more, and preferably 0.9 μm or less, more preferably 0.2 μm or less. When the height of the protrusions is equal to or greater than the above-mentioned lower limit and equal to or less than the above-mentioned upper limit, the connection resistance between the electrodes can be reduced even more effectively.

The height of the protrusions can be calculated by observing the protrusions on any conductive particle using an electron microscope or optical microscope. It is preferable to calculate the height of the protrusions by taking the average of the heights of all the protrusions per conductive particle as the height of the protrusions on one conductive particle. It is preferable to determine the height of the protrusions by calculating the average height of the protrusions on 50 random conductive particles.

The conductive particles are preferably used to obtain sockets or connectors. The conductive particles are preferably used in place of metal terminals (metal pins) to obtain sockets or connectors. The conductive particles are preferably used in socket or connector applications, and are particularly preferably used in socket applications. The conductive particles are preferably used in place of metal terminals (metal pins) in socket or connector applications. Using the conductive particles in place of metal terminals (metal pins) enables even narrower pitches to be achieved, effectively suppressing connection failures during CPU connection, etc. Examples of such sockets include CPU sockets, IC sockets, DIP sockets, PGA sockets, SiP sockets, LGA sockets, CSP sockets, QFN sockets, QFP sockets, SOP sockets, and BGA sockets. Note that the DIP socket, PGA socket, SiP socket, LGA socket, CSP socket, QFN sockets, QFP sockets, SOP sockets, and BGA sockets may each be part of an IC socket. Examples of the connector include an FPC connector, a board-to-board connector, a narrow pitch connector, a DIN connector, a compression connector, a one-piece connector, and a card edge connector.

(socket)
The socket according to the present invention comprises a socket body and the conductive particles, the conductive particles constituting connection terminals. In other words, the socket according to the present invention comprises a socket body and connection terminals, the connection terminals being composed of the conductive particles. Because the socket according to the present invention has the above configuration, it can maintain high connection reliability even if the conductive particles are compressed over a long period of time. The connection terminals are preferably disposed on the surface of the socket body. The conductive particles are preferably disposed on the surface of the socket body.

In the above socket, the conductive particles are preferably connection terminals. The above socket is suitable for use with electronic components. The above socket is preferably a socket for electronic components.

(Conductive materials)
The conductive particles are preferably dispersed in a binder and used as a conductive material. The conductive material includes the conductive particles and a binder. The conductive particles are preferably dispersed in a binder and used as a conductive material, and are preferably dispersed in a binder and used as a conductive material. The conductive material is preferably used for electrical connection between electrodes. Since the conductive material uses the conductive particles described above, the connection resistance between electrodes can be more effectively reduced and the occurrence of aggregation between conductive particles can be more effectively suppressed. Since the conductive material uses the conductive particles described above, the occurrence of connection defects can be more effectively suppressed.

The binder is not particularly limited. Known insulating resins and solvents can be used as the binder. The binder preferably contains a thermoplastic component (thermoplastic compound) or a curable component, and more preferably contains a curable component. Examples of the curable component include a photocurable component and a thermosetting component. The photocurable component preferably contains a photocurable compound and a photopolymerization initiator. The thermosetting component preferably contains a thermosetting compound and a thermosetting agent.

Examples of the binder include vinyl resins, thermoplastic resins, curable resins, thermoplastic block copolymers, elastomers, and solvents. Only one type of binder may be used, or two or more types may be used in combination.

Examples of the vinyl resin include vinyl acetate resin, acrylic resin, and styrene resin. Examples of the thermoplastic resin include polyolefin resin, ethylene-vinyl acetate copolymer, and polyamide resin. Examples of the curable resin include epoxy resin, urethane resin, polyimide resin, and unsaturated polyester resin. The curable resin may be a room temperature curable resin, a thermosetting resin, a photocurable resin, or a moisture curable resin. The curable resin may be used in combination with a curing agent. Examples of the thermoplastic block copolymer include styrene-butadiene-styrene block copolymer, styrene-isoprene-styrene block copolymer, hydrogenated styrene-butadiene-styrene block copolymer, and hydrogenated styrene-isoprene-styrene block copolymer. Examples of the elastomer include styrene-butadiene copolymer rubber and acrylonitrile-styrene block copolymer rubber.

Examples of the solvent include water and organic solvents. Organic solvents are preferred because they are easily removable. Examples of the organic solvent include alcohol compounds such as ethanol; ketone compounds such as acetone, methyl ethyl ketone, and cyclohexanone; aromatic hydrocarbon compounds such as toluene, xylene, and tetramethylbenzene; glycol ether compounds such as cellosolve, methyl cellosolve, butyl cellosolve, carbitol, methyl carbitol, butyl carbitol, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol diethyl ether, and tripropylene glycol monomethyl ether; ester compounds such as ethyl acetate, butyl acetate, butyl lactate, cellosolve acetate, butyl cellosolve acetate, carbitol acetate, butyl carbitol acetate, propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl ether acetate, and propylene carbonate; aliphatic hydrocarbon compounds such as octane and decane; and petroleum-based solvents such as petroleum ether and naphtha.

In addition to the conductive particles and binder, the conductive material may contain various additives such as fillers, extenders, softeners, plasticizers, polymerization catalysts, curing catalysts, colorants, antioxidants, heat stabilizers, light stabilizers, UV absorbers, lubricants, antistatic agents, and flame retardants.

The method for dispersing the conductive particles in the binder can be any conventionally known dispersion method and is not particularly limited. Examples of methods for dispersing the conductive particles in the binder include the following: A method in which the conductive particles are added to the binder and then kneaded and dispersed using a planetary mixer or the like; A method in which the conductive particles are uniformly dispersed in water or an organic solvent using a homogenizer or the like, then added to the binder and then kneaded and dispersed using a planetary mixer or the like; A method in which the binder is diluted with water or an organic solvent or the like, then the conductive particles are added, and then kneaded and dispersed using a planetary mixer or the like.

The viscosity (η25) of the conductive material at 25°C is preferably 30 Pa·s or more, more preferably 50 Pa·s or more, and preferably 400 Pa·s or less, more preferably 300 Pa·s or less. When the viscosity of the conductive material at 25°C is above the above lower limit and below the above upper limit, the conductive material can be applied more uniformly to the connection target components, and the occurrence of connection failures can be more effectively suppressed. The viscosity (η25) can be adjusted as appropriate by changing the types and amounts of the blended components.

The above viscosity (η25) can be measured, for example, using an E-type viscometer ("TVE22L" manufactured by Toki Sangyo Co., Ltd.) at 25°C and 5 rpm.

The conductive material can be used as a conductive paste, a conductive film, etc. When the conductive material is a conductive film, a film that does not contain conductive particles may be laminated on a conductive film that contains conductive particles. The conductive paste is preferably an anisotropic conductive paste. The conductive film is preferably an anisotropic conductive film.

The content of the binder in 100% by weight of the conductive material is preferably 10% by weight or more, more preferably 30% by weight or more, even more preferably 50% by weight or more, and particularly preferably 70% by weight or more, and is preferably 99.99% by weight or less, more preferably 99.9% by weight or less. When the content of the binder is equal to or greater than the above-mentioned lower limit and equal to or less than the above-mentioned upper limit, the conductive particles are efficiently arranged on the connection target components, and the occurrence of connection defects can be more effectively suppressed.

The content of the conductive particles in 100% by weight of the conductive material is preferably 0.01% by weight or more, more preferably 0.1% by weight or more, and preferably 80% by weight or less, more preferably 60% by weight or less, even more preferably 40% by weight or less, particularly preferably 20% by weight or less, and most preferably 10% by weight or less. When the content of the conductive particles is above the above lower limit and below the above upper limit, the conductive particles are efficiently arranged on the connection target components, preventing the occurrence of connection failures.

(Connection structure)
A connection structure according to the present invention includes a first connection-target member having a first electrode on its surface, a second connection-target member having a second electrode on its surface, and a connection portion having an insulating member and conductive particles. In the connection structure according to the present invention, the conductive particles are the conductive particles described above. In the connection structure according to the present invention, the first electrode and the second electrode are electrically connected by the conductive particles.

It is preferable that the above-mentioned connection portion is a socket portion formed by a socket or a connector portion formed by a connector.

Figure 4 is a front cross-sectional view schematically showing an example of a connection structure using conductive particles according to the first embodiment of the present invention.

The connection structure 51 shown in Figure 4 comprises a first connection target member 52, a second connection target member 53, and a connection portion 54. The first connection target member 52 has a plurality of first electrodes 52a on its surface (upper surface). The second connection target member 53 has a plurality of second electrodes 53a on its surface (lower surface). The connection portion 54 has conductive particles 1, an insulating member 31, a solder paste portion 32, an electrode 33, and a solder ball 34. The connection portion 54 is a socket portion. The insulating member 31 has a through-hole 31a that penetrates from the upper surface to the lower surface.

A solder ball 34 is disposed on the first electrode 52a. An insulating member 31 is disposed on the solder ball 34. An electrode 33 is disposed on the insulating member 31. A solder paste portion 32 is disposed on the electrode 33. Conductive particles 1 are disposed on the solder paste portion 32. A second electrode 53a is disposed on the conductive particles 1. A conductive via-fill paste is disposed inside the through-hole 31a.

Each first electrode 52a is electrically connected to one solder ball 34, one electrode 33, one solder paste portion 32, one conductive particle 1, and one second electrode 53a. Therefore, in the connection structure 51, the first electrode 52a and the second electrode 53a are electrically connected by the conductive particle 1.

In Figure 4, conductive particle 1 is shown schematically for convenience of illustration. Other conductive particles such as conductive particles 11 and 21 may be used instead of conductive particle 1.

The connection structure uses the conductive particles described above, so it can maintain high connection reliability even if the conductive particles are compressed over a long period of time. This allows it to be used in place of metal terminals (metal pins), enabling even narrower pitches to be accommodated. It can also effectively prevent connection failures when connecting a CPU, etc.

Examples of materials for the insulating member include ceramic and resin. Examples of resins include fluororesin, phenolic resin, epoxy resin, and polyimide resin. Examples of substrates on which the insulating member is provided include FR-1, FR-2, FR-3, FR-4, FR-5, XPC, CEM-1, CEM-3, glass polyimide substrates, glass PPO substrates, and BT substrates.

Figure 5 is a front cross-sectional view schematically showing another example of a connection structure using conductive particles according to the first embodiment of the present invention.

The connection structure 81 shown in Figure 5 comprises a first connection target member 82, a second connection target member 83, and a connection portion 84 connecting the first connection target member 82 and the second connection target member 83. The connection portion 84 is formed from a conductive material containing conductive particles 1.

The first connection target member 82 has a plurality of first electrodes 82a on its surface (upper surface). The second connection target member 83 has a plurality of second electrodes 83a on its surface (lower surface). The first electrodes 82a and second electrodes 83a are electrically connected by one or more conductive particles 1.

In Figure 5, conductive particle 1 is shown schematically for convenience of illustration. Other conductive particles such as conductive particles 11 and 21 may be used instead of conductive particle 1.

The first and second connection target members are not particularly limited. Examples of the first connection target member include a motherboard. Examples of the second connection target member include a semiconductor chip, an IC package, a CPU, etc.

Examples of the electrodes provided on the first and second connection target components include metal electrodes such as gold electrodes, nickel electrodes, tin electrodes, aluminum electrodes, copper electrodes, molybdenum electrodes, silver electrodes, SUS electrodes, and tungsten electrodes. When the electrodes are aluminum electrodes, they may be formed solely from aluminum, or may be electrodes in which an aluminum layer is laminated on the surface of a metal oxide layer. Examples of materials for the metal oxide layer include indium oxide doped with a trivalent metal element and zinc oxide doped with a trivalent metal element. Examples of the trivalent metal element include Sn, Al, and Ga.

The present invention will be specifically explained below with reference to examples and comparative examples. The present invention is not limited to the following examples.

The following materials were prepared for the base particles.

(Monomer X)
Polypropylene glycol #700 diacrylate ("APG-700" manufactured by Shin-Nakamura Chemical Co., Ltd., n=12)
Polypropylene glycol #400 diacrylate ("APG-400" manufactured by Shin-Nakamura Chemical Co., Ltd., n=7)

(Monomers other than monomer X)
Monomer A: Polytetramethylene glycol diacrylate ("Light Acrylate PTMGA-250" manufactured by Kyoeisha Chemical Co., Ltd.)
Monomer B: Styrene ("St" manufactured by NS Styrene Monomer Co., Ltd.)
Monomer C: Divinylbenzene (DVB)

Example 1
Preparation of conductive particles:
Base particles (particle diameter 500 μm) formed from a copolymer resin of polypropylene glycol #700 diacrylate (monomer X) and polytetramethylene glycol diacrylate (monomer A) were prepared. The base particles were electrolytically copper plated to form a copper plating layer (first conductive layer) with an average thickness of 5.0 μm on the surface of the base particles. Next, electrolytic gold plating was performed on the outer surface of the copper plating layer to form a gold plating layer (second conductive layer) with an average thickness of 0.5 μm. In this way, conductive particles having a two-layer laminate structure of a copper plating layer and a gold plating layer were obtained as the conductive portion.

(Examples 2 to 13 and Comparative Examples 1 to 3)
Conductive particles were obtained by setting the type, content, and particle diameter of the material of the base particle, and the material and thickness of the conductive portion as shown in the following Tables 1 to 4. In Example 12, a first conductive layer, a second conductive layer, and a third conductive layer were formed in this order.

(evaluation)
(1) Thickness of the conductive part of the conductive particles The obtained conductive particles were added to "Technovit 4000" manufactured by Kulzer so as to have a content of 30 wt % and dispersed to prepare an embedding resin for testing. A cross section of the conductive particles was cut out using an ion milling machine ("IM4000" manufactured by Hitachi High-Technologies Corporation) so as to pass through the vicinity of the center of the conductive particles dispersed in the embedding resin.

Using a field emission scanning electron microscope (FE-SEM) (Hitachi High-Technologies Corporation, model S-4800), the image magnification was set to 15,000x, and 10 conductive particles were randomly selected to observe the conductive portion of each conductive particle. The thickness of the conductive portion and the thickness of each conductive layer in each conductive particle were measured, and the arithmetic mean was calculated to determine the thickness of the conductive portion and the thickness of each conductive layer.

(2) Particle diameter of conductive particles The particle diameter of the obtained conductive particles was calculated using a particle size distribution analyzer (Beckman Coulter's "Multisizer 4"). Specifically, the particle diameter of approximately 100,000 conductive particles was measured and the average value was calculated. Furthermore, from the obtained results, the ratio of the particle diameter of the conductive particles to the thickness of the first conductive layer (particle diameter of conductive particles/thickness of the first conductive layer) was calculated.

(3) Compression recovery rate of conductive particles (Compression test A and Compression test B)
The obtained conductive particles were subjected to the above-mentioned compression test A and compression test B, and the compression recovery rate after the conductive particles were held in a 20% compressed state for 168 hours, and the compression recovery rate when the conductive particles were compressed by 20% (the compression recovery rate measured without holding the compressed state) were measured.

(4) Compression test of base particles (compression test C)
The obtained base particle was subjected to the above-mentioned compression test C, and the compression displacement (L1) at a compressive load of 500 mN when loaded, the compression displacement (L2) at a compressive load of 500 mN when unloaded, the compression displacement (L3) at a compressive load of 1000 mN when loaded, and the compression displacement (L4) at a compressive load of 1000 mN when unloaded were determined. In addition, the ratios (L1/L2) and (L3/L4) were calculated.

(5) Initial connection reliability and long-term connection reliability For the obtained conductive particles, the resistance value (R1) of the conductive particles when compressed by 20% and the resistance value (R2) of the conductive particles after being held in a 20% compressed state for 168 hours were measured using the method described above.

Initial connection reliability and long-term connection reliability were judged using the following criteria.

[Initial connection reliability criteria]
○ ○: Resistance value (R1) is 0 mΩ or more and less than 20 mΩ ○: Resistance value (R1) is 20 mΩ or more and less than 50 mΩ ×: Resistance value (R1) is 50 mΩ or more

[Criteria for determining long-term connection reliability]
○ ○: Resistance value (R2) is 0 mΩ or more and less than 20 mΩ ○: Resistance value (R2) is 20 mΩ or more and less than 50 mΩ ×: Resistance value (R2) is 50 mΩ or more

(6) State of Conductive Particles in Connection Structure Using the obtained conductive particles, a connection structure (a connection structure having the structure shown in FIG. 4) was produced as follows.

A BGA substrate was prepared in which solder balls and metal pads (hereinafter referred to as LANS) were electrically connected via through-holes. Conductive via-fill paste was placed inside the through-holes of this BGA substrate.

The BGA substrate was installed in a package receiving unit equipped with a package fixing unit for fixing the IC package. Next, solder paste was applied to the LAND on the top surface of the BGA substrate using a dispenser. The obtained conductive particles were placed on the applied solder paste using a ball mounter. Next, it was heated in a reflow oven at 280°C for 3 minutes in a nitrogen atmosphere. In this way, an IC socket was obtained in which the LAND and conductive particles were bonded via solder, and the bottom of the BGA substrate installed in the package receiving unit was bonded via solder to an electric circuit board (motherboard).

To mount an IC package (CPU) on the resulting IC socket, the lever on the package fixing unit was raised to open the pressure cover, and the IC socket was set in the package receiving unit so that the LAND portion at the bottom of the IC package came into contact with the conductive particles arranged on the BGA substrate. With the pressure cover lowered, the lever was pushed down, causing the pressure cover to press down on the IC package from above, applying a vertical load to the IC package toward the contacts, resulting in a connection structure.

The resulting connection structure was operated continuously for 168 hours and then unloaded. Using an optical microscope (Keyence Corporation's "Digital Microscope VHX Series") set to an image magnification of 200x, 50 conductive particles were randomly selected and the total number of damaged conductive particles and conductive particles whose shape had not recovered was counted. The condition of the conductive particles in the connection structure was evaluated according to the following criteria.

[Criteria for determining the state of conductive particles in a connection structure]
〇〇: The number of damaged or deformed conductive particles is less than 3. ○: The number of damaged or deformed conductive particles is 3 or more but less than 6. ×: The number of damaged or deformed conductive particles is 6 or more.

The results are shown in Tables 1 to 4 below.

REFERENCE SIGNS LIST 1...Conductive particle 2...Base particle 3...Conductive portion 11...Conductive particle 11a...Protrusion 12...Conductive portion 12a...Protrusion 13...Core substance 21...Conductive particle 23...Conductive portion 23A...First conductive layer 23B...Second conductive layer 31...Insulating member 31a...Through hole 32...Solder paste portion 33...Electrode 34...Solder ball 51, 81...Connection structure 52, 82...First connection target member 52a, 82a...First electrode 53, 83...Second connection target member 53a, 83a...Second electrode 54, 84...Connection portion

Claims (11)

A conductive particle comprising a base particle and a conductive portion disposed on a surface of the base particle,
Conductive particles, wherein in compression test A, in which the conductive particles are held in a 20% compressed state for 168 hours, the following compression recovery rate after the conductive particles are held in a 20% compressed state for 168 hours is 85% or more.
Compression recovery rate (%) = (H2/H1) x 100
H1: Particle diameter of conductive particles before compression test A
H2: Particle diameter of conductive particles after compression test A the conductive portion has a first conductive layer,
the material of the first conductive layer comprises a ductile metal;
The conductive particles according to claim 1 , wherein a ratio of a particle diameter of the conductive particles to a thickness of the first conductive layer is 50 or more and 1000 or less. The conductive particles according to claim 1 or 2, wherein the compressive deformation rate when compressed under a load of 1000 mN is 10% or more. When the base particle was loaded to 1961 mN at a loading rate of 14.12 mN/s and then unloaded at an unloading rate of 14.12 mN/s,
The ratio of the compressive displacement when a compressive load of 500 mN is applied to the compressive displacement when a compressive load of 500 mN is applied and released is 0.7 or more;
4. The conductive particles according to claim 1, wherein the ratio of the compressive displacement when a compressive load of 1000 mN is applied to the compressive displacement when a compressive load of 1000 mN is applied and released is 0.7 or more. the material of the base particle contains a polyfunctional (meth)acrylate having a polyether skeleton,
The conductive particle according to any one of claims 1 to 4, wherein the content of the polyfunctional (meth)acrylate having a polyether skeleton is 5% by weight or more in 100% by weight of the material of the base particle. The conductive particles according to any one of claims 1 to 5, wherein the particle diameter of the conductive particles is 100 μm or more and 1000 μm or less. the conductive portion has a laminated structure of two or more layers,
The conductive particle according to any one of claims 1 to 6, wherein the material of the outer surface of the conductive portion is gold, silver, copper, tin, zinc, nickel, beryllium, cobalt, palladium, platinum, rhodium, ruthenium, iridium, or an alloy thereof. The conductive particles according to any one of claims 1 to 7 are used to obtain a socket or connector. A socket body and the conductive particles according to any one of claims 1 to 8,
The socket, wherein the conductive particles form connection terminals. A conductive material comprising the conductive particles according to any one of claims 1 to 8 and a binder. a first connection target member having a first electrode on a surface thereof;
a second connection target member having a second electrode on its surface;
a connecting portion having an insulating member and conductive particles;
The conductive particles are the conductive particles according to any one of claims 1 to 8,
A connection structure in which the first electrode and the second electrode are electrically connected by the conductive particles.