Solder paste, metal-coated particles for solder paste, and connection structure

Abstract

The present invention provides a solder paste which does not easily wet and expand in an unintended area at a time of connection, easily maintains a shape of a connection portion formed by the solder paste in a connection structure after the connection, and is capable of maintaining a high connection strength even if the connection structure after the connection is subjected to a thermal shock or a physical impact.　A solder paste according to the present invention includes a plurality of solder particles and a plurality of metal-coated particles. The metal-coated particle has a specific gravity of 6.0 or less and includes a base material particle and a metal portion disposed on a surface of the base material particle. The metal portion includes metal capable of forming an intermetallic compound with solder, includes metal capable of performing melt-bonding with solder, or includes metal capable of diffusing with solder.

Description

[Technical Field]

[0001] The present invention relates to a solder paste containing a plurality of solder particles and a plurality of particles different from the solder particles. The present invention also relates to metal-coated particles used in the solder paste. The present invention also relates to a connection structure using the solder paste or the metal-coated particles. [Background technology]

[0002] Anisotropic conductive materials containing solder are known, and the content of solder particles in the anisotropic conductive materials is, for example, 80 wt % or less.

[0003] On the other hand, solder joint materials containing a large amount of solder are known, such as solder paste, and the solder particle content in the solder joint material exceeds 80 wt %, for example.

[0004] The solder bonding materials are used to obtain various connection structures, such as a connection between a flexible printed circuit board and a glass substrate (FOG (Film on Glass)), a connection between a semiconductor chip and a flexible printed circuit board (COF (Chip on Film)), a connection between a semiconductor chip and a glass substrate (COG (Chip on Glass)), a connection between a flexible printed circuit board and a glass epoxy substrate (FOB (Film on Board)), and a connection between an electronic component, a module, or a package thereof and a rigid printed circuit board (SMT (Surface mount technology)).

[0005] When electrically connecting electrodes, the solder joint material is selectively applied to the electrodes, which are the soldered portions of a circuit board or the like, by, for example, screen printing. Next, a semiconductor chip or the like is stacked, and the solder is melted and then solidified. The solidified solder electrically connects the electrodes.

[0006] Patent Document 1 below discloses a solder paste in which a plurality of solder particles are dispersed in a thermosetting resin composition. The solder paste may contain high-melting-point metal particles having a melting point higher than that of the solder particles.

[0007] Patent Document 2 below discloses a conductive paste containing tin-coated copper powder, a resin, and a solvent. In the tin-coated copper powder, the surfaces of copper particles are coated with tin or a tin alloy. The amount of the tin or tin alloy coated is 1% by mass to 33% by mass of the entire tin-coated copper powder. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-220466 [Patent Document 2] Japanese Patent Application Publication No. 2018-131666 Summary of the Invention [Problem to be solved by the invention]

[0009] Conventional solder pastes can spread to unintended areas during connection.

[0010] Furthermore, in a solder paste containing high-melting-point metal particles as described in Patent Document 1, the high-melting-point metal particles may not be uniformly dispersed in the solder paste. As a result, the shape of the connection formed by the solder paste may not be sufficiently maintained in the connection structure after connection. Tin-coated copper powder as described in Patent Document 2 may also not be uniformly dispersed in the solder paste after connection.

[0011] Furthermore, when a conventional solder paste is used, if the connected structure is subjected to thermal or physical shock, cracks or peeling may occur in the connection formed by the solder paste, which may result in a decrease in connection strength.

[0012] An object of the present invention is to provide a solder paste and metal-coated particles for a solder paste that are less likely to wet and spread to unintended areas during connection, that are more likely to maintain the shape of the connection formed by the solder paste in the connection structure after connection, and that are able to maintain high connection strength even when the connection structure after connection is exposed to thermal shock or physical shock. Another object of the present invention is to provide a connection structure using the solder paste or the metal-coated particles for a solder paste. [Means for solving the problem]

[0013] According to a broad aspect of the present invention, there is provided a solder paste comprising a plurality of solder particles and a plurality of metal-coated particles, the metal-coated particles having a specific gravity of 6.0 or less, the metal-coated particles having a base particle and a metal portion disposed on a surface of the base particle, the metal portion comprising a metal capable of forming an intermetallic compound with the solder, a metal capable of melt-bonding with the solder, or a metal capable of diffusing into the solder.

[0014] According to a broad aspect of the present invention, there is provided metal-coated particles for solder paste (hereinafter, sometimes referred to as "metal-coated particles") having a specific gravity of 6.0 or less, comprising a base particle and a metal portion disposed on the surface of the base particle, wherein the metal portion contains a metal capable of forming an intermetallic compound with solder, a metal capable of melt-bonding with solder, or a metal capable of diffusing into solder.

[0015] In a specific aspect of the solder paste and metal-coated particles according to the present invention, the base particles are resin particles or organic-inorganic hybrid particles.

[0016] In certain aspects of the solder paste and metal-coated particles according to the present invention, the metal portion includes, at the outer surface portion of the metal portion, a metal capable of forming an intermetallic compound with the solder, a metal capable of melt-bonding with the solder, or a metal capable of diffusing into the solder.

[0017] In a specific aspect of the solder paste and metal-coated particles according to the present invention, the metal portion includes nickel, gold, tin, or an alloy containing tin on an outer surface portion of the metal portion.

[0018] In a specific aspect of the solder paste and metal-coated particles according to the present invention, the metal portion contains tin or an alloy containing tin on an outer surface portion of the metal portion.

[0019] In a specific aspect of the solder paste and metal-coated particles according to the present invention, the ratio of the average thickness of the metal portion to the particle diameter of the base particle is 0.005 or more.

[0020] In a specific aspect of the solder paste and metal-coated particles according to the present invention, the metal-coated particles have a rust inhibitor or flux on the outer surface of the metal portion.

[0021] In a specific aspect of the solder paste according to the present invention, the solder paste further includes at least one of an organic solvent and a flux.

[0022] In a specific aspect of the solder paste according to the present invention, the content of the solder particles is 50% by weight or more in 100% by weight of the solder paste.

[0023] In a specific aspect of the solder paste according to the present invention, the total content of the solder particles and the metal-coated particles is 51% by weight or more in 100% by weight of the solder paste.

[0024] According to a broad aspect of the present invention, there is provided a connection structure comprising a first connection target member having a first connection area on its surface, a second connection target member having a second connection area on its surface, and a connection portion connecting the first connection target member and the second connection target member, wherein the connection portion is formed from the above-mentioned solder paste, and the first connection area and the second connection area are electrically or physically connected by solder derived from the solder particles.

[0025] According to a broad aspect of the present invention, there is provided a connection structure comprising a first connection target member having a first connection area on its surface, a second connection target member having a second connection area on its surface, and a connection portion connecting the first connection target member and the second connection target member, wherein the connection portion is formed from a solder paste containing a plurality of solder particles and a plurality of metal-coated particles, the metal-coated particles being the metal-coated particles described above, and the first connection area and the second connection area being electrically or physically connected by solder derived from the solder particles. [Effects of the Invention]

[0026] The solder paste according to the present invention comprises a plurality of solder particles and a plurality of metal-coated particles, the metal-coated particles having a specific gravity of 6.0 or less, and the metal-coated particles having a base particle and a metal portion disposed on the surface of the base particle. In the solder paste according to the present invention, the metal portion contains a metal capable of forming an intermetallic compound with the solder, a metal capable of melt-bonding with the solder, or a metal capable of diffusing into the solder. Because the solder paste according to the present invention has the above-described configuration, it is less likely to wet and spread to unintended areas during connection, the shape of the connection formed by the solder paste in the connected connection structure is easily maintained, and the connected connection structure can maintain high connection strength even when exposed to thermal shock or physical shock.

[0027] The metal-coated particles for solder paste according to the present invention have a specific gravity of 6.0 or less and include a base particle and a metal portion disposed on the surface of the base particle. In the metal-coated particles for solder paste according to the present invention, the metal portion includes a metal capable of forming an intermetallic compound with solder, a metal capable of fusion bonding with solder, or a metal capable of diffusing into solder. Because the metal-coated particles for solder paste according to the present invention have the above-described configuration, they are suitable for use in solder paste. A solder paste containing the metal-coated particles for solder paste according to the present invention is less likely to wet and spread to unintended areas during connection, is more likely to maintain the shape of the connection formed by the solder paste in the connected connection structure, and can maintain high connection strength even when the connected connection structure is exposed to thermal shock or physical shock. [Brief explanation of the drawings]

[0028] [Figure 1] FIG. 1 is a cross-sectional view showing a metal-coated particle according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view showing a metal-coated particle according to a second embodiment of the present invention. [Figure 3] FIG. 3 is a cross-sectional view showing a metal-coated particle according to a third embodiment of the present invention. [Figure 4] FIG. 4 is a cross-sectional view that schematically shows a connection structure that uses a solder paste that includes the metal-coated particles shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0029] The present invention will be described in detail below.

[0030] (Metal coated particles for solder paste) The metal-coated particles for solder paste according to the present invention (hereinafter sometimes referred to as "metal-coated particles") have a specific gravity of 6.0 or less. The metal-coated particles according to the present invention have a base particle and a metal portion disposed on the surface of the base particle. In the metal-coated particles according to the present invention, the metal portion contains a metal capable of forming an intermetallic compound with solder, a metal capable of melt-bonding with solder, or a metal capable of diffusing into solder.

[0031] The metal coated particles according to the present invention have the above-mentioned features and can therefore be suitably used in solder paste.

[0032] The solder paste containing the metal-coated particles according to the present invention is less likely to spread to unintended areas during connection. This is because the metal-coated particles have a base particle and a metal portion disposed on the surface of the base particle, and the metal-coated particles have a specific gravity of 6.0 or less. The metal-coated particles are easily dispersed uniformly in the solder paste, making it less likely for the solder paste to spread to unintended areas during connection.

[0033] Furthermore, in the solder paste containing the metal-coated particles according to the present invention, the shape of the connection formed by the solder paste in the connection structure after connection is easily maintained. This is because the metal-coated particles have a base particle and a metal portion disposed on the surface of the base particle, and the metal-coated particles have a specific gravity of 6.0 or less. Furthermore, in the metal-coated particles, the metal portion contains a metal capable of forming an intermetallic compound with the solder, a metal capable of fusion bonding with the solder, or a metal capable of diffusing into the solder.

[0034] Furthermore, the solder paste containing the metal-coated particles according to the present invention can maintain high connection strength even when the connected connection structure is exposed to thermal shock or physical shock. This is because the solder paste contains the metal-coated particles. The connection portion of the connection structure contains the metal-coated particles or the base particles. The metal-coated particles or the base particles effectively prevent cracking and peeling at the connection portion. As a result, the connected connection structure can maintain high connection strength even when exposed to thermal shock or physical shock.

[0035] The present invention will be specifically described below with reference to the drawings. Note that different parts in Fig. 1 and the figures described below can be interchanged with each other.

[0036] FIG. 1 is a cross-sectional view showing a metal-coated particle according to a first embodiment of the present invention.

[0037] The metal-coated particle 1 shown in FIG. 1 has a base particle 2 and a metal portion 3. The metal portion 3 is disposed on the surface of the base particle 2. In the first embodiment, the metal portion 3 is in contact with the surface of the base particle 2, and the metal portion 3 has a layered shape. The metal-coated particle 1 is a coated particle in which the surface of the base particle 2 is coated with the metal portion 3. The entire surface of the base particle 2 is coated with the metal portion 3.

[0038] In the metal-coated particle 1, the metal portion 3 is a single metal layer. In the metal-coated particle, the metal portion may cover the entire surface of the base particle, or the metal portion may cover only a portion of the surface of the base particle. The metal portion may or may not be in contact with the surface of the base particle. A layer other than the metal portion may be disposed between the base particle and the metal portion. From the viewpoint of more effectively exerting the effects of the present invention, it is preferable that the metal portion be in contact with the surface of the base particle.

[0039] FIG. 2 is a cross-sectional view showing a metal-coated particle according to a second embodiment of the present invention.

[0040] The metal-coated particle 1A shown in FIG. 2 has a base particle 2A and a metal portion 3A. The metal portion 3A is disposed on the surface of the base particle 2A. In the second embodiment, the metal portion 3A is in contact with the surface of the base particle 2A, and the metal portion 3A has a layered shape. The metal-coated particle 1A is a coated particle in which the surface of the base particle 2A is coated with the metal portion 3A. The entire surface of the base particle 2A is coated with the metal portion 3A.

[0041] The metal part 3A has a first metal part 3AA as an inner layer and a second metal part 3AB as an outer layer. The first metal part 3AA is disposed on the surface of the base particle 2A. The second metal part 3AB is disposed on the outer surface of the first metal part 3AA.

[0042] In the metal-coated particle, the metal portion may be a single metal layer or a multi-layer metal layer composed of two or more layers. The first metal portion and the second metal portion may be formed as metal portions having different compositions or may be formed as metal portions having the same composition.

[0043] FIG. 3 is a cross-sectional view showing a metal-coated particle according to a third embodiment of the present invention.

[0044] The metal-coated particle 1B shown in FIG. 3 comprises a base particle 2B and a metal portion 3B disposed on the surface of the base particle 2B. The metal portion 3B has a first metal portion 3BA, which is an inner layer, and a second metal portion 3BB outside the inner layer. In a third embodiment, the metal portion 3B is in contact with the surface of the base particle 2B, the first metal portion 3BA has a layered shape, and the second metal portion 3BB has a convex shape. The metal-coated particle 1B is a coated particle in which the surface of the base particle 2B is coated with the metal portion 3B. The entire surface of the base particle 2B is coated with the metal portion 3B. The metal portion 3BB is a convex portion. The second metal portion 3BB is a protrusion. The outer surface of the first metal portion 3BA is partially coated with the second metal portion 3BB.

[0045] In the metal-coated particle, the metal portion may be composed of one metal portion or two or more metal portions. The first metal portion and the second metal portion may be formed as metal portions having different compositions or may be formed as metal portions having the same composition.

[0046] In the metal-coated particles, the base particle may or may not be completely coated with the metal portion. The base particle may have a portion that is not coated with the metal portion. The metal portion that is the inner layer may or may not be completely coated with the outer metal portion. The metal portion that is the inner layer may have a portion that is not coated with the outer metal portion.

[0047] The specific gravity of the metal-coated particles is 6.0 or less. The specific gravity of the metal-coated particles is preferably 5.5 or less, more preferably 5.0 or less, even more preferably 4.5 or less, even more preferably 4.0 or less, and even more preferably 3.5 or less. When the specific gravity of the metal-coated particles is below the upper limit, the metal-coated particles are more easily dispersed uniformly in the solder paste. Therefore, the shape of the connection formed by the solder paste in the connection structure after connection is more easily maintained. The specific gravity of the metal-coated particles may be 1.1 or more, or may be 1.5 or more.

[0048] The specific gravity of the metal-coated particles can be measured using a pycnometer or an electronic pycnometer. It is particularly preferable to measure the specific gravity of the metal-coated particles using an electronic pycnometer. Examples of the electronic pycnometer include the "EW-300SG" manufactured by Alpha Mirage.

[0049] In the metal-coated particles, the area of ​​the portion where the metal portion is present (the coverage rate by the metal portion) of the total surface area of ​​the base particle (100%) is preferably 5% or more, more preferably 10% or more, even more preferably 30% or more, even more preferably 50% or more, particularly preferably 70% or more, and most preferably 80% or more. Of the total surface area of ​​the base particle (100%), the area of ​​the portion where the metal portion is present is preferably 100% or less. When the area of ​​the portion where the metal portion is present is not less than the above lower limit, the effects of the present invention are more effectively exhibited.

[0050] The area of ​​the portion where the metal portion is present relative to the total surface area (100%) of the base particle can be calculated by subjecting a cross section of the conductive particle to SEM-EDX analysis to elemental mapping and analyzing the image.

[0051] The particle diameter of the metal-coated particles is preferably 1 μm or more, more preferably 3 μm or more, and is preferably 100 μm or less, more preferably 30 μm or less. When the particle diameter of the metal-coated 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 are more effectively exhibited.

[0052] The particle diameter of the metal-coated particles is preferably an average particle diameter, and more preferably a number-average particle diameter. The particle diameter of the metal-coated particles can be determined, for example, by observing 50 randomly selected metal-coated particles with an electron microscope or optical microscope and calculating the average particle diameter of each metal-coated particle, or by using a particle size distribution analyzer. When observed with an electron microscope or optical microscope, the particle diameter of each metal-coated 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 randomly selected metal-coated 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 metal-coated particle is determined as the particle diameter in equivalent sphere diameter. The average particle diameter of the metal-coated particles is preferably calculated using a particle size distribution analyzer.

[0053] The coefficient of variation (CV value) of the particle diameter of the metal-coated particles is preferably 10% or less, more preferably 5% or less. When the coefficient of variation of the particle diameter of the metal-coated particles is equal to or less than the upper limit, the metal-coated particles are more easily dispersed uniformly in the solder paste.

[0054] The coefficient of variation (CV value) can be measured as follows.

[0055] CV value (%) = (ρ / Dn) × 100 ρ: Standard deviation of particle size of metal-coated particles Dn: average particle size of metal-coated particles

[0056] The shape of the metal-coated particles is not particularly limited, and may be spherical, or may be a shape other than spherical, such as flat.

[0057] The ratio of the average thickness of the metal portion to the particle diameter of the base particle (average thickness of the metal portion / particle diameter of the base particle) is preferably 0.0001 or more, more preferably 0.001 or more, even more preferably 0.005 or more, and particularly preferably 0.01 or more. When this ratio is equal to or greater than the lower limit, the effects of the present invention are more effectively exhibited. The ratio (average thickness of the metal portion / particle diameter of the base particle) is preferably 1 or less, more preferably 0.5 or less. When this ratio is equal to or less than the upper limit, the specific gravity is easily reduced.

[0058] The average thickness of the metal portion only takes into account the regions on the base particle where the metal portion is present, and does not take into account the regions on the base particle where the metal portion is not present. When the metal portion is partially disposed on the surface of the base particle, the thickness of the region where the metal portion has no thickness (i.e., zero) is not taken into account when determining the average thickness of the metal portion.

[0059] The average thickness of the metal portion can be measured by observing the cross section of the metal-coated particle using, for example, a transmission electron microscope (TEM). The average thickness of the metal portion is preferably determined by calculating the average thickness of the metal portion of 50 randomly selected metal-coated particles.

[0060] From the viewpoint of further effectively exerting the effects of the present invention, the metal-coated particles preferably contain a rust inhibitor or flux on the outer surface of the metal part. The metal-coated particles may contain a rust inhibitor or flux on the outer surface of the metal part.

[0061] Base material particles: The material of the base particle is not particularly limited. The material of the base particle may be an organic material or an inorganic material. Examples of base particles formed only from the organic material include resin particles. Examples of base particles formed only from the inorganic material include inorganic particles other than metals. Examples of base particles formed from both the organic material and the inorganic material include organic-inorganic hybrid particles. From the viewpoint of further reducing the specific gravity of the metal-coated particles and more effectively exhibiting the effects of the present invention, the base particle is preferably a resin particle or an organic-inorganic hybrid particle, and more preferably a resin particle.

[0062] Examples of 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, divinylbenzene polymer, and divinylbenzene copolymer. Examples of the divinylbenzene copolymer include divinylbenzene-styrene copolymer and divinylbenzene-(meth)acrylic acid ester copolymer. From the viewpoint of more effectively exerting the effects of the present invention, the material of the base particle is preferably a polymer obtained by polymerizing one or more polymerizable monomers having an ethylenically unsaturated group.

[0063] When the base particle is 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.

[0064] Examples of the non-crosslinkable monomer 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; and (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 suitable (meth)acrylate compounds include alkyl (meth)acrylate compounds such as (meth)acrylate and isobornyl (meth)acrylate; oxygen-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)acrylate compounds 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.

[0065] Examples of the crosslinkable monomer include vinyl compounds such as vinyl monomers like divinylbenzene, 1,4-divinyloxybutane, and divinylsulfone; (meth)acrylic compounds such as polyfunctional (meth)acrylate compounds like 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, polypropylene glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, and 1,4-butanediol di(meth)acrylate; and allyl compounds. Examples of silane compounds include triallyl (iso) cyanurate, triallyl trimellitate, diallyl phthalate, diallyl acrylamide, and diallyl ether; examples of silane compounds include silane alkoxide compounds such as tetramethoxysilane, tetraethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, isopropyltrimethoxysilane, isobutyltrimethoxysilane, cyclohexyltrimethoxysilane, n-hexyltrimethoxysilane, n-octyltriethoxysilane, n-decyltrimethoxysilane, phenyltrimethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, diisopropyldimethoxysilane, trimethoxysilylstyrene, γ-(meth)acryloxypropyltrimethoxysilane, 1,3-divinyltetramethyldisiloxane, methylphenyldimethoxysilane, and diphenyldimethoxysilane;Examples of suitable silane alkoxides include polymerizable double bonds such as vinyltrimethoxysilane, vinyltriethoxysilane, dimethoxymethylvinylsilane, dimethoxyethylvinylsilane, diethoxymethylvinylsilane, diethoxyethylvinylsilane, ethylmethyldivinylsilane, methylvinyldimethoxysilane, ethylvinyldimethoxysilane, 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 single-end-modified silicone oil, double-end-modified silicone oil, and side-chain silicone oil; and carboxyl group-containing monomers such as (meth)acrylic acid, maleic acid, and maleic anhydride.

[0066] Examples of the inorganic material include silica, alumina, barium titanate, zirconia, carbon black, silicate glass, borosilicate glass, lead glass, soda-lime glass, and alumina silicate glass.

[0067] 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. The inorganic material is preferably 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 firing as necessary. Examples of the organic-inorganic hybrid particles include organic-inorganic hybrid particles formed from a crosslinked alkoxysilyl polymer and an acrylic resin.

[0068] 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.

[0069] Examples of the material for the organic core include the organic materials described above.

[0070] Examples of materials for the inorganic shell include the inorganic substances listed as materials for the base particle described above. The material for the inorganic shell is preferably silica. The inorganic shell is preferably formed by forming a shell-like substance from a metal alkoxide on the surface of the core by a sol-gel method and then firing the shell-like substance. The metal alkoxide is preferably a silane alkoxide. The inorganic shell is preferably formed from a silane alkoxide.

[0071] Metal parts: The metal portion includes a metal capable of forming an intermetallic compound with the solder, a metal capable of fusion bonding with the solder, or a metal capable of diffusing into the solder. The metal portion may include a metal capable of forming an intermetallic compound with the solder, a metal capable of fusion bonding with the solder, or a metal capable of diffusing into the solder. The metal portion may further include a metal that does not correspond to any of a metal capable of forming an intermetallic compound with the solder, a metal capable of fusion bonding with the solder, or a metal capable of diffusing into the solder.

[0072] From the viewpoint of exerting the effects of the present invention more effectively, it is preferable that the metal part contains, on the outer surface portion of the metal part, a metal that can form an intermetallic compound with the solder, a metal that can be fused and bonded with the solder, or a metal that can diffuse into the solder.

[0073] A metal that can form an intermetallic compound with solder is a metal that can form an intermetallic compound with tin in a metal equilibrium diagram. A metal that can melt and bond with solder is a metal that melts when heated and can bond with solder. A metal that can diffuse into solder is a metal that does not melt when heated but diffuses into the solder when the solder melts.

[0074] From the viewpoint of more effectively exerting the effects of the present invention, the metal capable of forming an intermetallic compound with the solder is preferably nickel, gold, palladium, indium, silver, copper, tin, or an alloy containing tin, more preferably nickel, gold, tin, or an alloy containing tin, and even more preferably tin or an alloy containing tin. From the viewpoint of more effectively exerting the effects of the present invention, the metal capable of fusion bonding with the solder is preferably indium, tin, or an alloy containing tin, and even more preferably tin or an alloy containing tin. From the viewpoint of more effectively exerting the effects of the present invention, the metal capable of diffusing into the solder is preferably nickel, gold, palladium, silver, or copper, and even more preferably nickel or gold.

[0075] From the viewpoint of more effectively exerting the effects of the present invention and more effectively improving connection reliability, the metal part preferably contains nickel, gold, palladium, indium, silver, copper, tin or an alloy containing tin, more preferably contains nickel, gold, tin or an alloy containing tin, and even more preferably contains tin or an alloy containing tin.

[0076] From the viewpoint of more effectively exerting the effects of the present invention and more effectively improving connection reliability, the metal part preferably contains nickel, gold, palladium, silver, copper, tin, or an alloy containing tin, and more preferably contains nickel, gold, palladium, indium, tin, or an alloy containing tin, at the outer surface of the metal part. From the viewpoint of more effectively exerting the effects of the present invention and more effectively improving connection reliability, it is even more preferable that the metal part contains nickel, gold, tin, or an alloy containing tin, at the outer surface of the metal part.

[0077] The tin content, based on 100% by weight of the metal part, is preferably 0.1% by weight or more, more preferably 1% by weight or more, and preferably 100% by weight or less, more preferably 90% by weight or less. The tin content may be 80% by weight or less, 60% by weight or less, 40% by weight or less, 20% by weight or less, or 10% by weight or less. When the tin content is equal to or greater than the lower limit and equal to or less than the upper limit, the effects of the present invention are more effectively exhibited.

[0078] When the metal part is multi-layered, the tin content of 100% by weight of the tin-containing layers is preferably 0.1% by weight or more, more preferably 1% by weight or more, and preferably 100% by weight or less, more preferably 90% by weight or less. The tin content may be 80% by weight or less, 60% by weight or less, 40% by weight or less, 20% by weight or less, or 10% by weight or less. When the tin content is equal to or greater than the lower limit and equal to or less than the upper limit, the effects of the present invention are more effectively exhibited.

[0079] The metal portion is preferably formed of solder, and more preferably, the outer surface of the metal portion is formed of solder.

[0080] The solder is preferably a metal (low melting point metal) with a melting point of 450°C or less, based on JIS Z3001: Welding Terminology. The low melting point metal refers to a metal with a melting point of 450°C or less. The melting point of the low melting point metal is preferably 300°C or less. The solder also contains tin. In 100% by weight of the metals contained in the solder, the tin content is preferably 30% by weight or more, more preferably 40% by weight or more, even more preferably 70% by weight or more, and particularly preferably 90% by weight or more. When the tin content in the solder is equal to or greater than the lower limit, the effects of the present invention are even more effectively exhibited.

[0081] The content of various metals in the metal part or the metal-containing layer can be measured using a high-frequency inductively coupled plasma atomic emission spectrometer ("ICP-AES" manufactured by Horiba, Ltd.) or a fluorescent X-ray analyzer ("EDX-800HS" manufactured by Shimadzu Corporation).

[0082] The low-melting-point metal constituting the solder is not particularly limited. The low-melting-point metal is preferably tin or an alloy containing tin. Examples of such alloys include tin-silver alloy, tin-copper alloy, tin-silver-copper alloy, tin-bismuth alloy, tin-zinc alloy, and tin-indium alloy. Because of their excellent wettability with respect to the components to be connected, the low-melting-point metal is preferably tin, tin-silver alloy, tin-silver-copper alloy, tin-bismuth alloy, or tin-indium alloy. A tin-bismuth alloy or tin-indium alloy is more preferred.

[0083] To further increase the connection strength, the solder may contain metals such as nickel, copper, antimony, aluminum, zinc, iron, gold, titanium, phosphorus, germanium, tellurium, cobalt, bismuth, manganese, chromium, molybdenum, and palladium. Furthermore, from the viewpoint of further increasing the connection strength, the solder preferably contains nickel, copper, antimony, aluminum, or zinc. To further increase the connection strength, the content of these metals is preferably 0.0001% by weight or more, and preferably 1% by weight or less, based on 100% by weight of the solder.

[0084] The metal part may be formed of one layer. The metal part may be formed of multiple layers. That is, the metal part may have a laminated structure of two or more layers. From the viewpoint of more effectively improving the conduction reliability, it is preferable that the metal part has a laminated structure of two or more layers.

[0085] The method for forming the metal portion on the surface of the base particle is not particularly limited. Examples of methods for forming the metal 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 metal 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 Manufacturing Co., Ltd.).

[0086] Rust inhibitor: The outer surface of the metal part may be treated with a rust inhibitor for rust prevention, and the metal-coated particle may have an anti-rust film formed on the outer surface of the metal part by the rust inhibitor.

[0087] The rust inhibitor may be a compound having an alkyl group having 6 to 22 carbon atoms (hereinafter, may be referred to as compound A). The rust inhibitor may be a compound that does not contain phosphorus. The rust inhibitor may be an alkyl phosphate compound or an alkyl thiol. The rust inhibitor may be used alone or in combination of two or more kinds.

[0088] When the alkyl group of the compound A has 6 or more carbon atoms, rust is more unlikely to form on the metal part. When the alkyl group of the compound A has 22 or less carbon atoms, the conductivity is high. The alkyl group of the compound A preferably has 16 or less carbon atoms. The alkyl group may have a linear structure or a branched structure. The alkyl group preferably has a linear structure.

[0089] The compound A is not particularly limited as long as it has an alkyl group having 6 to 22 carbon atoms. The compound A is preferably a phosphate ester or a salt thereof having an alkyl group having 6 to 22 carbon atoms, a phosphite ester or a salt thereof having an alkyl group having 6 to 22 carbon atoms, or an alkoxysilane having an alkyl group having 6 to 22 carbon atoms. The compound A is preferably an alkylthiol having an alkyl group having 6 to 22 carbon atoms, or a dialkyldisulfide having an alkyl group having 6 to 22 carbon atoms. The compound A having an alkyl group having 6 to 22 carbon atoms is preferably a phosphate ester or a salt thereof, a phosphite ester or a salt thereof, an alkoxysilane, an alkylthiol, or a dialkyldisulfide. The use of these preferred compounds A can make the metal part even more resistant to rust. From the viewpoint of making it even more resistant to rust, the compound A is preferably the phosphate ester or a salt thereof, the phosphite ester or a salt thereof, or an alkylthiol, and more preferably the phosphate ester or a salt thereof, or the phosphite ester or a salt thereof. The compound A may be used alone or in combination of two or more.

[0090] The compound A preferably has a reactive functional group capable of reacting with the outer surface of the metal part. The rust inhibitor is preferably chemically bonded to the metal part. The presence of the reactive functional group and the chemical bond makes the rust inhibitor less likely to peel off, thereby making it even more difficult for rust to form on the metal part.

[0091] Examples of the phosphoric acid ester or salt thereof having an alkyl group having 6 to 22 carbon atoms include hexyl phosphate, heptyl phosphate, monooctyl phosphate, monononyl phosphate, monodecyl phosphate, monoundecyl phosphate, monododecyl phosphate, monotridecyl phosphate, monotetradecyl phosphate, monopentadecyl phosphate, monohexyl phosphate monosodium salt, monoheptyl phosphate monosodium salt, monooctyl phosphate monosodium salt, monononyl phosphate monosodium salt, monodecyl phosphate monosodium salt, monoundecyl phosphate monosodium salt, monododecyl phosphate monosodium salt, monotridecyl phosphate monosodium salt, monotetradecyl phosphate monosodium salt, and monopentadecyl phosphate monosodium salt. Potassium salts of the above phosphoric acid esters may also be used.

[0092] Examples of the phosphite ester or salt thereof having an alkyl group having 6 to 22 carbon atoms include hexyl phosphite, heptyl phosphite, monooctyl phosphite, monononyl phosphite, monodecyl phosphite, monoundecyl phosphite, monododecyl phosphite, monotridecyl phosphite, monotetradecyl phosphite, monopentadecyl phosphite, monohexyl phosphite monosodium salt, monoheptyl phosphite monosodium salt, monooctyl phosphite monosodium salt, monononyl phosphite monosodium salt, monodecyl phosphite monosodium salt, monoundecyl phosphite monosodium salt, monododecyl phosphite monosodium salt, monotridecyl phosphite monosodium salt, monotetradecyl phosphite monosodium salt, and monopentadecyl phosphite monosodium salt. Potassium salts of the above phosphites may also be used.

[0093] Examples of the alkoxysilane having an alkyl group having 6 to 22 carbon atoms include hexyltrimethoxysilane, hexyltriethoxysilane, heptyltrimethoxysilane, heptyltriethoxysilane, octyltrimethoxysilane, octyltriethoxysilane, nonyltrimethoxysilane, nonyltriethoxysilane, decyltrimethoxysilane, decyltriethoxysilane, undecyltrimethoxysilane, undecyltriethoxysilane, dodecyltrimethoxysilane, dodecyltriethoxysilane, tridecyltrimethoxysilane, tridecyltriethoxysilane, tetradecyltrimethoxysilane, tetradecyltriethoxysilane, pentadecyltrimethoxysilane, and pentadecyltriethoxysilane.

[0094] Examples of the alkyl thiol having an alkyl group having 6 to 22 carbon atoms include hexyl thiol, heptyl thiol, octyl thiol, nonyl thiol, decyl thiol, undecyl thiol, dodecyl thiol, tridecyl thiol, tetradecyl thiol, pentadecyl thiol, and hexadecyl thiol. The alkyl thiol preferably has a thiol group at the end of the alkyl chain.

[0095] Examples of the dialkyl disulfides having an alkyl group having 6 to 22 carbon atoms include dihexyl disulfide, diheptyl disulfide, dioctyl disulfide, dinonyl disulfide, didecyl disulfide, diundecyl disulfide, didodecyl disulfide, ditridecyl disulfide, ditetradecyl disulfide, dipentadecyl disulfide, and dihexadecyl disulfide.

[0096] Flux: The outer surface of the metal part may be treated with a flux. The use of the flux can prevent oxidation of the metal in the metal part and remove foreign matter and oxide films. The flux is not particularly limited. A flux commonly used for soldering or the like can be used as the flux.

[0097] Examples of the flux include zinc chloride, a mixture of zinc chloride and an inorganic halide, a mixture of zinc chloride and an inorganic acid, a molten salt, phosphoric acid, a derivative of phosphoric acid, an organic halide, hydrazine, an amine compound, an organic acid, and pine resin. Only one type of the flux may be used, or two or more types may be used in combination.

[0098] Examples of the molten salt include ammonium chloride. Examples of the organic acid include lactic acid, citric acid, stearic acid, glutamic acid, and glutaric acid. Examples of the rosin include activated rosin and non-activated rosin. The flux is preferably an organic acid having two or more carboxyl groups or rosin. The flux may be an organic acid having two or more carboxyl groups or rosin. The use of an organic acid or rosin having two or more carboxyl groups further increases connection strength and electrical reliability.

[0099] Examples of the organic acid having two or more carboxyl groups include succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid.

[0100] Examples of the amine compound include cyclohexylamine, dicyclohexylamine, benzylamine, benzhydrylamine, imidazole, benzimidazole, phenylimidazole, carboxybenzimidazole, benzotriazole, and carboxybenzotriazole.

[0101] The rosin is a rosin containing abietic acid as a main component. Examples of the rosin include abietic acid and acrylic-modified rosin. The flux is preferably a rosin, and more preferably abietic acid. The use of this preferred flux further enhances the flux effect.

[0102] The activation temperature (melting point) of the flux is preferably 50° C. or higher, more preferably 70° C. or higher, even more preferably 80° C. or higher, and is preferably 200° C. or lower, more preferably 190° C. or lower, even more preferably 160° C. or lower, even more preferably 150° C. or lower, and even more preferably 140° C. or lower. When the activation temperature of the flux is equal to or higher than the lower limit and equal to or lower than the upper limit, the flux effect is further enhanced.

[0103] The melting point of the flux can be determined by differential scanning calorimetry (DSC). Examples of DSC devices include the "EXSTAR DSC7020" manufactured by SII Corporation.

[0104] The boiling point of the flux is preferably 200°C or lower.

[0105] The flux is preferably a flux that releases cations when heated, which further increases connection strength and electrical reliability.

[0106] The flux that releases cations when heated includes the above-mentioned thermal cationic initiator (thermal cationic curing agent).

[0107] From the viewpoint of further enhancing the flux effect, the flux is preferably a salt of an acid compound and a basic compound.

[0108] The acid compound is preferably an organic compound having a carboxyl group. Examples of the acid compound include aliphatic carboxylic acids such as malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, citric acid, and malic acid, alicyclic carboxylic acids such as cyclohexylcarboxylic acid and 1,4-cyclohexyldicarboxylic acid, and aromatic carboxylic acids such as isophthalic acid, terephthalic acid, trimellitic acid, and ethylenediaminetetraacetic acid. From the viewpoint of more effectively increasing connection strength and more effectively increasing conduction reliability, the acid compound is preferably glutaric acid, cyclohexylcarboxylic acid, or adipic acid.

[0109] The basic compound is preferably an organic compound having an amino group. Examples of the basic compound include diethanolamine, triethanolamine, methyldiethanolamine, ethyldiethanolamine, cyclohexylamine, dicyclohexylamine, benzylamine, benzhydrylamine, 2-methylbenzylamine, 3-methylbenzylamine, 4-tert-butylbenzylamine, N-methylbenzylamine, N-ethylbenzylamine, N-phenylbenzylamine, N-tert-butylbenzylamine, N-isopropylbenzylamine, N,N-dimethylbenzylamine, imidazole compounds, and triazole compounds. From the viewpoint of more effectively increasing connection strength and more effectively increasing conduction reliability, the basic compound is preferably benzylamine.

[0110] (solder paste) The solder paste according to the present invention includes a plurality of solder particles and a plurality of metal-coated particles. The solder paste according to the present invention is a solder paste containing metal-coated particles. The above-described metal-coated particles can be used in the solder paste according to the present invention. The metal-coated particles included in the solder paste according to the present invention have a specific gravity of 6.0 or less. The metal-coated particles included in the solder paste according to the present invention have a base particle and a metal portion disposed on the surface of the base particle. In the metal-coated particles included in the solder paste according to the present invention, the metal portion includes a metal capable of forming an intermetallic compound with the solder, a metal capable of fusion bonding with the solder, or a metal capable of diffusing into the solder.

[0111] The term "solder paste" includes a solder joint material that is in a paste form, melts when heated, and connects components to be connected.

[0112] The ratio of the particle size of the solder particles to the particle size of the base particle (particle size of the solder particles / particle size of the base particle) is preferably 0.1 or more, more preferably 0.5 or more, even more preferably 1 or more, and particularly preferably 1.5 or more. The ratio (particle size of the solder particles / particle size of the base particle) is preferably 20 or less, more preferably 15 or less, even more preferably 10 or less, and particularly preferably 8 or less. When the ratio is equal to or greater than the lower limit and equal to or less than the upper limit, the effects of the present invention are even more effectively exhibited.

[0113] The content of the solder particles in the solder paste is preferably 20% 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. The content of the solder particles in the solder paste is preferably 99.99% by weight or less, more preferably 99.90% by weight or less, even more preferably 99.00% by weight or less, and particularly preferably 98.00% by weight or less. When the content of the solder particles is equal to or greater than the lower limit and equal to or less than the upper limit, the effects of the present invention are more effectively exhibited.

[0114] The content of the metal-coated particles in the solder paste is preferably 0.01 wt% or more, more preferably 0.10 wt% or more, even more preferably 0.50 wt% or more, and particularly preferably 1.00 wt% or more. The content of the metal-coated particles in the solder paste is preferably 70 wt% or less, more preferably 50 wt% or less, even more preferably 30 wt% or less, and particularly preferably 20 wt% or less. When the content of the metal-coated particles is equal to or greater than the lower limit and equal to or less than the upper limit, the effects of the present invention are more effectively exhibited.

[0115] The total content of the solder particles and the metal-coated particles in the solder paste is preferably 21% by weight or more, more preferably 31% by weight or more, even more preferably 51% by weight or more, and particularly preferably 71% by weight or more. The total content of the solder particles and the metal-coated particles in the solder paste is preferably 100% by weight or less, more preferably 99.9% by weight or less, even more preferably 99.0% by weight or less, and particularly preferably 98.0% by weight or less. When the total content of the solder particles and the metal-coated particles is equal to or greater than the lower limit and equal to or less than the upper limit, the effects of the present invention are more effectively exhibited.

[0116] The solder paste according to the present invention may contain at least one of an organic solvent and a flux. The solder paste according to the present invention may contain an organic solvent or a flux. Furthermore, the solder paste according to the present invention may contain an additive such as a thixotropic agent or a surfactant, as necessary.

[0117] Solder particles: The particle diameter of the solder particles is preferably 0.1 μm or more, more preferably 1 μm or more, and is preferably 100 μm or less, more preferably 50 μm or less. When the particle diameter of the solder particles is equal to or greater than the above lower limit and equal to or less than the above upper limit, the effects of the present invention are more effectively exhibited.

[0118] The particle diameter of the solder particles is preferably an average particle diameter, and more preferably a number-average particle diameter. The particle diameter of the solder particles can be determined, for example, by observing 50 random solder particles with an electron microscope or optical microscope and calculating the average particle diameter of each solder particle, or by using a particle size distribution analyzer. When observed with an electron microscope or optical microscope, the particle diameter of each solder 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 solder 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 solder particle is determined as the particle diameter in equivalent sphere diameter. The average particle diameter of the solder particles is preferably calculated using a particle size distribution analyzer.

[0119] The coefficient of variation (CV value) of the particle diameter of the solder particles is preferably 15% or less, and more preferably 10% or less. When the coefficient of variation of the particle diameter of the solder particles is equal to or less than the upper limit, the solder particles tend to be dispersed more uniformly in the solder paste.

[0120] The coefficient of variation (CV value) can be measured as follows.

[0121] CV value (%) = (ρ / Dn) × 100 ρ: Standard deviation of solder particle diameter Dn: Average particle diameter of solder particles

[0122] The shape of the solder particles is not particularly limited, and may be spherical, may be a shape other than spherical, or may be flat or the like.

[0123] The solder is preferably a metal (low melting point metal) with a melting point of 450°C or less, based on JIS Z3001: Welding Terminology. The low melting point metal refers to a metal with a melting point of 450°C or less. The melting point of the low melting point metal is preferably 300°C or less. The solder also contains tin. In 100% by weight of the metals contained in the solder, the tin content is preferably 30% by weight or more, more preferably 40% by weight or more, even more preferably 70% by weight or more, and particularly preferably 90% by weight or more. When the tin content in the solder is equal to or greater than the lower limit, the effects of the present invention are even more effectively exhibited.

[0124] The content of various metals in the solder particles can be measured using a high-frequency inductively coupled plasma atomic emission spectrometer ("ICP-AES" manufactured by Horiba, Ltd.) or a fluorescent X-ray analyzer ("EDX-800HS" manufactured by Shimadzu Corporation).

[0125] The low-melting-point metal constituting the solder is not particularly limited. The low-melting-point metal is preferably tin or an alloy containing tin. Examples of such alloys include a tin-silver alloy, a tin-copper alloy, a tin-silver-copper alloy, a tin-bismuth alloy, a tin-zinc alloy, and a tin-indium alloy. From the viewpoint of more effectively increasing connection strength and more effectively increasing conduction reliability, the low-melting-point metal is preferably tin, a tin-silver alloy, a tin-silver-copper alloy, a tin-gold alloy, a tin-antimony alloy, a tin-lead alloy, a tin-bismuth alloy, or a tin-indium alloy.

[0126] To further increase the connection strength, the solder may contain metals such as nickel, copper, antimony, aluminum, zinc, iron, gold, titanium, phosphorus, germanium, tellurium, cobalt, bismuth, manganese, chromium, molybdenum, and palladium. Furthermore, from the viewpoint of further increasing the connection strength, the solder preferably contains nickel, copper, antimony, aluminum, or zinc. To further increase the connection strength, the content of these metals is preferably 0.0001% by weight or more, and preferably 1% by weight or less, based on 100% by weight of the solder.

[0127] From the viewpoint of more effectively exerting the effects of the present invention, the solder particles are preferably Sn—Ag—Cu particles (SAC particles), Sn—Bi particles, or Pb—Sn particles, more preferably Sn—Ag—Cu particles (SAC particles) or Sn—Bi particles, and even more preferably Sn—Ag—Cu particles (SAC particles). The solder particles may be Sn—Ag—Cu particles (SAC particles), Sn—Bi particles, or Pb—Sn particles.

[0128] Flux: The use of the flux can prevent oxidation of the metal in the solder particles, metal-coated particles, and electrodes, and can remove foreign matter and oxide films. Examples of the flux in the solder paste include the fluxes described in the section describing the metal-coated particles.

[0129] When the solder paste contains the flux, the content of the flux in 100% by weight of the solder paste is preferably 0.01% by weight or more, more preferably 0.1% by weight or more, even more preferably 0.5% by weight or more, and is preferably 30% by weight or less, more preferably 25% by weight or less. When the content of the flux is equal to or more than the lower limit and equal to or less than the upper limit, oxide films are less likely to form on the surfaces of the solder and electrodes, and further, oxide films formed on the surfaces of the solder and electrodes can be removed more effectively.

[0130] Organic solvents: The use of the organic solvent can improve the handleability of the solder paste and adjust the viscosity of the solder paste. Examples of the organic solvent in the solder paste 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 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.

[0131] When the solder paste contains the organic solvent, the content of the organic solvent in 100% by weight of the solder paste is preferably 0.01% by weight or more, more preferably 0.1% by weight or more, even more preferably 0.5% by weight or more, and is preferably 30% by weight or less, more preferably 25% by weight or less. When the content of the organic solvent is equal to or more than the lower limit and equal to or less than the upper limit, the handleability of the solder paste can be improved, and voids are less likely to occur in the connection after connection.

[0132] Other Ingredients: The solder paste may contain, as other components, vinyl resin, thermoplastic resin, curable resin, thermoplastic block copolymer, elastomer, and the like.

[0133] 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, a hydrogenated product of styrene-butadiene-styrene block copolymer, and a hydrogenated product of styrene-isoprene-styrene block copolymer. Examples of the elastomer include styrene-butadiene copolymer rubber and acrylonitrile-styrene block copolymer rubber.

[0134] (Connection structure) The connection structure according to the present invention comprises a first connection target member having a first connection area on its surface, a second connection target member having a second connection area on its surface, and a connection portion connecting the first connection target member and the second connection target member. In the connection structure according to the present invention, the connection portion is formed from the solder paste. The connection portion includes solder derived from the solder particles and the metal-coated particles or particles derived from the metal-coated particles. In the connection structure according to the present invention, the first connection area and the second connection area are electrically connected by the solder derived from the solder particles.

[0135] In the connection portion, the metal portion of the metal-coated particle preferably forms an intermetallic compound with the solder, is bonded to the solder, or is diffused with the solder.

[0136] In the connection structure, the metal-coated particles or particles derived from the metal-coated particles do not have to be in contact with both the first connection area and the second connection area, but may be in contact with only one of the first connection area and the second connection area.

[0137] The average thickness of the connection portion is preferably greater than the particle diameter of the metal-coated particles or particles derived from the metal-coated particles.

[0138] FIG. 4 is a cross-sectional view that schematically shows a connection structure that uses a solder paste that includes the metal-coated particles shown in FIG.

[0139] 4 includes a first member to be connected 22, a second member to be connected 23, and a connection portion 24 connecting the first member to be connected 22 and the second member to be connected 23. The connection portion 24 is formed from a solder paste containing a plurality of solder particles and metal-coated particles 1.

[0140] The connection portion 24 includes solder 24a derived from a plurality of solder particles, and particles 24b derived from the metal-coated particles 1.

[0141] The first member to be connected 22 has a single or multiple first connection areas 22a on its surface (upper surface). The second member to be connected 23 has a single or multiple second connection areas 23a on its surface (lower surface). The first connection areas 22a and the second connection areas 23a are electrically or physically connected by solder 24a derived from the solder particles. Therefore, the first member to be connected 22 and the second member to be connected 23 are electrically or physically connected by the solder 24a.

[0142] The method for manufacturing the connection structure is not particularly limited. One example of the method for manufacturing the connection structure is a method in which the solder paste is placed between the first member to be connected and the second member to be connected, a laminate is obtained, and then the laminate is heated and pressurized. By heating and pressurizing, the solder particles contained in the solder paste melt, and the connection areas are electrically or physically connected by the solder derived from the solder particles. The pressure of the pressurization is 9.8 × 10 4 Pa~4.9×10 6 Pa. The heating temperature is 120°C to 220°C.

[0143] The first and second connection target members are not particularly limited. Specific examples of the first and second connection target members include electronic components such as semiconductor chips, semiconductor packages, LED chips, LED packages, capacitors, and diodes, as well as electronic components such as resin films, printed circuit boards, flexible printed circuit boards, flexible flat cables, rigid-flexible boards, glass epoxy boards, and glass boards. The first and second connection target members are preferably electronic components.

[0144] The connection area may be an electrode.

[0145] Examples of the electrode provided on the connection target member 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 connection target member is a flexible printed circuit board, the electrode is preferably a gold electrode, nickel electrode, tin electrode, silver electrode, or copper electrode. When the connection target member is a glass substrate, the electrode is preferably an aluminum electrode, copper electrode, molybdenum electrode, silver electrode, or tungsten electrode. When the electrode is an aluminum electrode, it may be an electrode made of aluminum alone, or an electrode 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.

[0146] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0147] The following particles were prepared as base particles.

[0148] Resin particles 1: Sekisui Chemical Co., Ltd. "Micropearl SP-220" (resin particles formed from divinylbenzene copolymer, particle diameter 20 μm)

[0149] Resin particles 2: Sekisui Chemical Co., Ltd. "Micropearl SP-210" (resin particles formed from divinylbenzene copolymer, particle diameter 10 μm)

[0150] Resin particles 3: Sekisui Chemical Co., Ltd. "Micropearl SP-295" (resin particles formed from divinylbenzene copolymer, particle diameter 5 μm)

[0151] Organic-inorganic hybrid particles 1: Organic-inorganic hybrid particles having an organic core formed from an acrylic resin and an inorganic shell formed from a crosslinked alkoxysilyl polymer (prepared according to Synthesis Example 1 below, particle diameter 20 μm)

[0152] <Synthesis Example 1> A 500 mL reaction vessel equipped with a stirrer and thermometer was charged with 300 g of a 0.13 wt % aqueous ammonia solution. Next, a mixture of 4.1 g of methyltrimethoxysilane, 19.2 g of vinyltrimethoxysilane, and 0.7 g of silicone alkoxy oligomer (X-41-1053, manufactured by Shin-Etsu Chemical Co., Ltd.) was slowly added to the aqueous ammonia solution in the reaction vessel. After the hydrolysis and condensation reactions were allowed to proceed with stirring, 2.4 mL of a 25 wt % aqueous ammonia solution was added. Particles were isolated from the aqueous ammonia solution and the resulting particles were heated under an oxygen partial pressure of 100°C. -17 The mixture was then calcined at 350°C for 2 hours under atmospheric pressure to obtain organic-inorganic hybrid particles.

[0153] Nickel particle 1: particle diameter 20 μm

[0154] Copper particle 1: particle size 10μm

[0155] Example 1 Preparation of metal-coated particles: Metal-coated particles were obtained by forming a metal layer, which had an inner nickel layer and an outer tin layer, on the outer surface of the resin particles 1 by electroless plating. The metal portion of the obtained metal-coated particles was layer-like.

[0156] Preparation of solder paste containing metal coated particles: 2.0 parts by weight of the obtained metal-coated particles were mixed with 98.0 parts by weight of SAC paste (solder paste containing SAC particles, "M705-RGS800" manufactured by Senju Metal Industry Co., Ltd., particle diameter of SAC particles: 20 μm) and stirred using a planetary mixer at 1200 rpm, 120 seconds and 0.2 kPa to obtain a solder paste containing metal-coated particles.

[0157] Examples 2 and 3 Metal-coated particles were obtained in the same manner as in Example 1, except that the types of base particles were set as shown in the following Table 1. A solder paste containing metal-coated particles was obtained in the same manner as in Example 1, except that the obtained metal-coated particles were used.

[0158] Example 4 Metal-coated particles were obtained by forming a metal portion having a nickel inner layer and tin protrusions on the outer surface of resin particles 1 by electroless plating. The metal portion of the obtained metal-coated particles had a protrusion-like outer surface, with tin protrusions partially formed on the nickel layer. A solder paste containing metal-coated particles was obtained in the same manner as in Example 1, except that the obtained metal-coated particles were used.

[0159] Example 5 The metal-coated particles of Example 1 were prepared. The outer surfaces of these particles were treated with flux (rosin) to obtain metal-coated particles. A solder paste containing metal-coated particles was obtained in the same manner as in Example 1, except that the obtained metal-coated particles were used.

[0160] Example 6 Metal-coated particles were obtained by forming a metal layer, which had an inner layer of nickel and an outer layer of a tin-silver alloy, on the outer surfaces of resin particles 1 by electroless plating. A solder paste containing metal-coated particles was obtained in the same manner as in Example 1, except that the obtained metal-coated particles were used.

[0161] ( reference Example 7) Metal-coated particles were obtained by forming a metal layer having an inner nickel layer and an outer gold layer by electroless plating on the outer surfaces of resin particles 1. A solder paste containing metal-coated particles was obtained in the same manner as in Example 1, except that the obtained metal-coated particles were used.

[0162] Example 8 Except for changing the thickness of the metal layer, metal-coated particles were obtained in the same manner as in Example 1. Except for using the obtained metal-coated particles, a solder paste containing metal-coated particles was obtained in the same manner as in Example 1.

[0163] Example 9 Metal-coated particles were obtained by forming a nickel metal layer by electroless plating on the outer surfaces of the resin particles 1. A solder paste containing metal-coated particles was obtained in the same manner as in Example 1, except that the obtained metal-coated particles were used.

[0164] Examples 10 and 11 The metal-coated particles of Example 1 were prepared. Solder pastes containing metal-coated particles were obtained in the same manner as in Example 1, except that the content of the metal-coated particles was changed as shown in Table 1 below.

[0165] Example 12 Metal-coated particles were prepared for Example 1. A solder paste containing metal-coated particles was obtained in the same manner as in Example 1, except that the type of solder paste was changed from SAC paste to SnBi paste (solder paste containing Sn—Bi particles, “L20-BLT-T7F” manufactured by Senju Metal Industry Co., Ltd., particle diameter of Sn—Bi particles: 20 μm).

[0166] ( reference Example 13) Metal-coated particles were obtained by forming a metal layer having an inner nickel layer and an outer gold layer by electroless plating on the outer surface of resin particles 1. A solder paste containing metal-coated particles was obtained in the same manner as in Example 1, except that the obtained metal-coated particles were used and the type of solder paste was changed from SAC paste to SnBi paste (solder paste containing Sn—Bi particles, “L20-BLT-T7F” manufactured by Senju Metal Industry Co., Ltd., particle size of Sn—Bi particles: 20 μm).

[0167] Example 14 Metal-coated particles were prepared for Example 1. A solder paste containing metal-coated particles was obtained in the same manner as in Example 1, except that the type of solder paste was changed from SAC paste to Pb—Sn paste (solder paste containing Pb—Sn particles, “OZ 295-162F-50-8” manufactured by Senju Metal Industry Co., Ltd., particle diameter of Pb—Sn particles: 20 μm).

[0168] Example 15 Metal-coated particles were obtained in the same manner as in Example 1, except that the types of base particles were set as shown in the following Table 1. A solder paste containing metal-coated particles was obtained in the same manner as in Example 1, except that the obtained metal-coated particles were used.

[0169] (Comparative Example 1) SAC paste (solder paste containing SAC particles, "M705-RGS800" manufactured by Senju Metal Industry Co., Ltd., particle diameter of SAC particles: 20 μm) itself was prepared as the solder paste.

[0170] (Comparative Example 2) Resin particles 1 were prepared. A resin particle-containing solder paste was obtained in the same manner as in Example 1, except that resin particles 1 were used instead of the metal-coated particles.

[0171] (Comparative Example 3) Nickel particles 1 were prepared. A solder paste containing metal particles was obtained in the same manner as in Example 1, except that the metal-coated particles were changed to nickel particles 1.

[0172] Comparative Example 4 Metal-coated particles having a metal layer with an inner nickel layer and an outer tin layer were obtained in the same manner as in Example 1, except that the types of base particles were set as shown in Table 2. Metal particle-containing solder pastes were obtained in the same manner as in Example 1, except that the obtained metal-coated particles were used.

[0173] (Comparative Example 5) Copper particles 1 were prepared. A metal particle-containing solder paste was obtained in the same manner as in Example 1, except that the metal-coated particles were changed to copper particles 1.

[0174] (evaluation) The connection structure A was obtained as follows.

[0175] A copper plate (approximately square with sides of 10.0 mm and a height of 0.1 mm) was prepared as the first member to be connected. A silicon chip (approximately square with sides of 2.0 mm and a height of 0.1 mm) was prepared as the second member to be connected. The obtained solder paste was screen-printed onto the first member to be connected using a metal mask with a length of 2.5 mm, a width of 2.5 mm and a height of 100 μm. After printing, the second member to be connected was layered on top of it to obtain a laminate. The obtained laminate was reflow-treated with an average heating temperature of 1.2°C / sec and a peak temperature of the melting point of the solder particles + 8°C to obtain connection structure A.

[0176] The connection structure B was obtained as follows.

[0177] A copper plate (approximately square with sides of 50.0 mm and a height of 0.1 mm) was prepared as the connection target component. Using a metal mask measuring 2000 μm in length, 500 μm in width, and 120 μm in height, the resulting solder paste was screen-printed onto the connection target component. The printed copper plate was reflow-treated at an average temperature rise rate of 1.2°C / sec and a peak temperature of the melting point of the solder particles + 8°C, yielding connection structure B.

[0178] (1) Initial shear strength The shear strength of the connection structure A obtained immediately after the reflow treatment was measured. The shear strength was measured at the time of break using a Nordson Dage4000.

[0179] (2) Shear strength after aging A connection structure A was prepared after measuring the initial shear strength. A TCT test was performed 1,000 times, with one cycle consisting of a low-temperature condition of -45°C for 30 minutes and a high-temperature condition of 125°C for 30 minutes, to obtain a connection structure after aging. (1) The shear strength after aging was measured in the same manner as in the measurement of the initial shear strength.

[0180] (3) Dispersibility A cross-section of the connection structure A obtained immediately after reflow was observed. The solder connection was divided into an upper and lower section along a line at half the height, and the number of particles present in each section was counted. The ratio was calculated as a percentage and used as an index of dispersibility (e.g., upper 6 / lower 4). The closer the ratio between the upper and lower sections, the higher the dispersibility was judged to be.

[0181] (4) Bleed In the production stage of connection structure A, the area of ​​the solder paste printed portion was measured before reflow. Then, the planar area of ​​the connection portion of connection structure A obtained immediately after the reflow treatment was evaluated. The percentage increase in the planar area of ​​the connection portion after reflow relative to the planar area before reflow was evaluated. The planar area before reflow was set to 100%, and the increased area (%) was taken as the bleed value. The planar area was measured using a "VHX" manufactured by KEYENCE Corporation.

[0182] (5) Short The connection structures B (5 in total) obtained immediately after the reflow treatment were evaluated for the presence or absence of short circuits between the electrodes.

[0183] The details and results are shown in Tables 1 to 3 below.

[0184] [Table 1]

[0185] [Table 2]

[0186] [Table 3] [Explanation of symbols]

[0187] 1,1A,1B…metal coated particles 2,2A,2B…Base material particles 3,3A,3B…Metal part 3AA...First metal part 3AB...Second metal part 3BA...First metal part 3BB...Second metal part 21...Connection structure 22...First connection target member 22a...First connection area 23...Second connecting member 23a...Second connecting area 24...Connection 24a...Solder 24b…particle

Claims

1. a plurality of solder particles and a plurality of metal-coated particles; the metal-coated particles have a specific gravity of 6.0 or less; The metal-coated particle has a base particle and a metal portion disposed on a surface of the base particle, the metal part has a laminated structure of two or more layers, and the metal part has a nickel layer as an inner layer and a layer containing nickel, tin, or an alloy containing tin as an outer layer; the metal portion contains nickel, tin, or an alloy containing tin on an outer surface portion of the metal portion, A solder paste, wherein the outer surface portion of the outer layer of the metal part is the outer surface portion of the metal part.

2. The solder paste according to claim 1 , wherein the base particles are resin particles or organic-inorganic hybrid particles.

3. The metal part has a layer containing tin or an alloy containing tin as the outer layer, The solder paste according to claim 1 or 2, wherein the metal portion contains tin or an alloy containing tin on an outer surface portion of the metal portion.

4. 4. The solder paste according to claim 1, wherein the ratio of the average thickness of the metal portion to the particle diameter of the base particles is 0.005 or more.

5. 5. The solder paste according to claim 1, wherein the metal-coated particles have a rust inhibitor or flux on the outer surface of the metal portion.

6. 6. The solder paste according to claim 1, further comprising at least one of an organic solvent and a flux.

7. 7. The solder paste according to claim 1, wherein the content of said solder particles is 50% by weight or more in 100% by weight of the solder paste.

8. 8. The solder paste according to claim 1, wherein the total content of said solder particles and said metal-coated particles is 51% by weight or more in 100% by weight of the solder paste.

9. A method for producing a solder paste containing a plurality of solder particles and a plurality of metal-coated particles, the method comprising the steps of: having a specific gravity of 6.0 or less, A substrate particle and a metal portion disposed on a surface of the substrate particle, the metal part has a laminated structure of two or more layers, and the metal part has a nickel layer as an inner layer and a layer containing nickel, tin, or an alloy containing tin as an outer layer; the metal portion contains nickel, tin, or an alloy containing tin on an outer surface portion of the metal portion, The metal-coated particle for solder paste, wherein the outer surface portion of the outer layer of the metal portion is the outer surface portion of the metal portion.

10. The metal-coated particles for solder paste according to claim 9 , wherein the base particles are resin particles or organic-inorganic hybrid particles.

11. The metal part has a layer containing tin or an alloy containing tin as the outer layer, The metal coated particle for solder paste according to claim 9 or 10, wherein the metal portion contains tin or an alloy containing tin on an outer surface portion of the metal portion.

12. 12. The metal coated particle for solder paste according to claim 9, wherein the ratio of the average thickness of the metal portion to the particle diameter of the base particle is 0.005 or more.

13. The metal coated particle for solder paste according to any one of claims 9 to 12, wherein the metal part has an anti-rust agent or flux on the outer surface thereof.

14. a first connection target member having a first connection area on a surface thereof; a second connection target member having a second connection area on its surface; a connection portion connecting the first connection target member and the second connection target member, The connection portion is formed from the solder paste according to any one of claims 1 to 8, A connection structure in which the first connection area and the second connection area are electrically or physically connected by solder derived from the solder particles.

15. a first connection target member having a first connection area on a surface thereof; a second connection target member having a second connection area on its surface; a connection portion connecting the first connection target member and the second connection target member, the connection portion is formed of a solder paste containing a plurality of solder particles and a plurality of metal-coated particles, The metal-coated particles are the metal-coated particles according to any one of claims 9 to 13, A connection structure in which the first connection area and the second connection area are electrically or physically connected by solder derived from the solder particles.

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