JP2024022788A - Conductive paste, method for producing conductive paste and connection structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conductive paste that enhances both storage stability and screen printing quality, while facilitating efficient solder particle placement on an electrode.

SOLUTION: A conductive paste according to the present invention includes a thermosetting component, and flux-carrying solder particles. The flux-carrying solder particles each consist of a solder particle, and flux carried on the solder particle. The solder particles have an average particle size of 5.0 μm or less. The flux carried on the solder particle is a carboxylic acid or carboxylate.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to a conductive paste containing solder particles. The present invention also relates to a method of manufacturing a conductive paste containing solder particles, and a connected structure using the conductive paste.

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

The above-mentioned anisotropic conductive material is used to obtain various connected structures. Examples of connections using the anisotropic conductive material include connections between flexible printed circuit boards and glass substrates (FOG (Film on Glass)), connections between semiconductor chips and flexible printed circuit boards (COF (Chip on Film)), and semiconductor Examples include connection between a chip and a glass substrate (COG (Chip on Glass)), connection between a flexible printed circuit board and a glass epoxy substrate (FOB (Film on Board)), and the like.

In recent years, in conductive materials containing conductive particles such as solder particles, the diameter of the conductive particles has been reduced due to the finer pitch of wiring and connectors in printed wiring boards and the like.

Patent Document 1 listed below discloses a conductive paste containing metal particles as a main component with an average particle diameter of 0.4 μm to 2.0 μm. In the conductive paste, the number of metal particles having a particle diameter of 0.2 μm or less is 5% or less out of 100% of the total number of metal particles.

Japanese Patent Application Publication No. 10-134637

When making a conductive connection using a conductive paste containing solder particles, a plurality of upper electrodes and a plurality of lower electrodes are electrically connected to make a conductive connection. The solder particles are preferably placed between the upper and lower electrodes, and desirably not between adjacent lateral electrodes. It is desirable that adjacent horizontal electrodes are not electrically connected.

Generally, a conductive paste containing solder particles is placed at a specific position on a substrate by screen printing or the like, and then heated by reflow or the like before use. When the conductive paste is heated to a temperature higher than the melting point of the solder particles, the solder particles melt and the solder aggregates between the electrodes, thereby electrically connecting the upper and lower electrodes. Flux is sometimes used in conductive pastes to efficiently place solder particles on the electrodes.

Here, when conductive particles with a small particle size are used as in the conductive paste of Patent Document 1, the total surface area of the conductive particles in the conductive paste becomes large, so the conductive particles are placed on the electrode. For efficient placement, large amounts of flux are sometimes incorporated into the conductive paste.

However, when a large amount of liquid flux is blended into the conductive paste, the storage stability (pot life) of the conductive paste may deteriorate. If the storage stability (pot life) of the conductive paste deteriorates, the viscosity of the conductive paste during screen printing will decrease, and the amount of penetration through the screen will increase, causing bleeding or problems during printing. The viscosity of the conductive paste becomes high and the conductive paste clogs the mesh, which may cause scratches.

On the other hand, when a large amount of solid flux is mixed into the conductive paste, the storage stability (pot life) of the conductive paste deteriorates, the viscosity of the conductive paste increases during printing, and the conductive paste clogs the mesh. There are things to do. As a result, the conductive paste may become blurred. With conventional conductive pastes, it may not be possible to uniformly apply the conductive paste to a printed wiring board or the like due to deterioration in storage stability (pot life) of the conductive paste.

An object of the present invention is to provide a conductive paste that can improve storage stability, improve screen printability, and efficiently arrange solder particles on electrodes. Moreover, the objective of this invention is to provide the manufacturing method of the said electrically conductive paste, and the connection structure using the said electrically conductive paste.

According to a broad aspect of the present invention, the present invention includes a thermosetting component and a flux-coated solder particle, the flux-coated solder particle comprising a solder particle and a flux supported on the solder particle; A conductive paste is provided, wherein the average particle diameter is 5.0 μm or less, and the flux supported on the solder particles is a carboxylic acid or a carboxylate salt.

In a particular aspect of the conductive paste according to the present invention, the ratio of the average particle diameter of the flux supported on the solder particles to the average particle diameter of the solder particles is 0.001 or more and 10.0 or less.

In a particular aspect of the conductive paste according to the present invention, the flux supported on the solder particles is a carboxylic acid amine salt.

In a particular aspect of the conductive paste according to the present invention, the viscosity of the conductive paste at 25° C. and 5 rpm immediately after the manufactured conductive paste is stored at 25° C. and 50% RH for 24 hours. The ratio of viscosity of the conductive paste at 25° C. and 5 rpm is 1.5 or less.

According to a broad aspect of the present invention, a step of obtaining fluxed solder particles comprising solder particles and a flux supported on the solder particles, mixing a thermosetting component and the fluxed solder particles, obtaining a conductive paste, the average particle diameter of the solder particles is 5.0 μm or less, and the flux supported on the solder particles is a carboxylic acid or a carboxylate salt. provided.

In a particular aspect of the method for manufacturing a conductive paste according to the present invention, flux is further mixed in the step of obtaining the conductive paste.

According to a broad aspect of the present invention, 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 the first connection target member, a connecting portion connecting the second connection target member, the material of the connecting portion is the above-mentioned conductive paste, and the first electrode and the second electrode are connected to the connecting portion. A connecting structure is provided that is electrically connected by a solder portion therein.

The conductive paste according to the present invention includes a thermosetting component and solder particles with flux, and the solder particles with flux include solder particles and flux supported on the solder particles. In the conductive paste according to the present invention, the average particle diameter of the solder particles is 5.0 μm or less. In the conductive paste according to the present invention, the flux supported on the solder particles is a carboxylic acid or a carboxylate salt. Since the conductive paste according to the present invention has the above configuration, it is possible to improve storage stability, improve screen printability, and efficiently arrange solder particles on electrodes. Can be done.

FIG. 1 is a cross-sectional view schematically showing a connected structure obtained using a conductive paste according to an embodiment of the present invention.

The details of the present invention will be explained below.

(conductive paste)
The conductive paste according to the present invention includes a thermosetting component and solder particles with flux, and the solder particles with flux include solder particles and flux supported on the solder particles. In the conductive paste according to the present invention, the average particle diameter of the solder particles is 5.0 μm or less. In the conductive paste according to the present invention, the flux supported on the solder particles is a carboxylic acid or a carboxylate salt.

Since the conductive paste according to the present invention has the above configuration, it is possible to improve storage stability, improve screen printability, and efficiently arrange solder particles on electrodes. Can be done.

In addition, in the conductive paste according to the present invention, multiple solder particles (solder particles with flux) tend to gather between the upper and lower opposing electrodes during conductive connection between the electrodes, and the multiple solder particles are placed on the electrodes (lines). can be placed. In addition, it is difficult for some of the plurality of solder particles to be placed between horizontal electrodes that should not be connected, and it is possible to considerably reduce the amount of solder particles that are placed between horizontal electrodes that should not be connected. can. As a result, the present invention can effectively increase the continuity reliability between the upper and lower electrodes that should be connected, and can effectively increase the insulation reliability between adjacent lateral electrodes that should not be connected. Can be done.

Furthermore, in the present invention, positional displacement between the electrodes can be prevented. In the present invention, when the second connection target member is superimposed on the first connection target member on which the conductive paste is disposed, the electrodes of the first connection target member and the electrodes of the second connection target member are overlapped. Even in a state where the alignment is misaligned, the misalignment can be corrected and the electrodes can be connected to each other (self-alignment effect).

From the viewpoint of further increasing storage stability and screen printability, the viscosity (η25) at 25° C. and 5 rpm of the conductive paste immediately after preparation is preferably 30 Pa·s or more, more preferably 50 Pa·s. s or more, preferably 250 Pa·s or less, more preferably 200 Pa·s or less. The above viscosity (η25) can be adjusted as appropriate depending on the types and amounts of the ingredients.

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

The viscosity (ηA) at 25° C. and 5 rpm of the conductive paste after storing the conductive paste immediately after preparation for 24 hours at 25° C. and 50% RH is preferably 50 Pa·s or more, more preferably 100 Pa·s. s or more, preferably 400 Pa·s or less, more preferably 300 Pa·s or less. When the viscosity (ηA) is not less than the lower limit and not more than the upper limit, storage stability can be further improved, screen printability can be further improved, and solder particles can be applied on the electrode more efficiently. can be placed. The above viscosity (ηA) can be adjusted as appropriate depending on the types and amounts of the ingredients.

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

The viscosity (ηA) at 25°C and 5 rpm of the above conductive paste after storing the above conductive paste immediately after production at 25 °C and 50% RH for 24 hours, and the viscosity (ηA) at 25 °C and 5 rpm of the above conductive paste immediately after production. The ratio of A to the viscosity (η25) is defined as the ratio (ηA/η25). The ratio (ηA/η25) is preferably 0.6 or more, more preferably 0.7 or more, even more preferably 0.8 or more, particularly preferably 0.9 or more, and most preferably 1.0 or more. The ratio (ηA/η25) is preferably 1.8 or less, more preferably 1.7 or less, even more preferably 1.5 or less, particularly preferably 1.2 or less. When the ratio (ηA/η25) is not less than the lower limit and not more than the upper limit, storage stability can be further improved, screen printability can be further improved, and solder particles can be spread on the electrode more efficiently. It can be placed as follows.

The viscosity (ηmp) of the conductive paste at the melting point of the solder particles is preferably 0.1 Pa·s or more, more preferably 0.5 Pa·s or more, and preferably 50 a·s or less, more preferably 30 Pa·s or less. , more preferably 10 Pa·s or less. When the viscosity (ηmp) is less than or equal to the upper limit, solder particles can be arranged on the electrode even more efficiently. When the viscosity (ηmp) is equal to or higher than the lower limit, voids at the connection portion can be suppressed, and the conductive paste can be prevented from protruding to areas other than the connection portion.

The above viscosity (ηmp) was measured using STRESSTECH (manufactured by REOLOGICA), etc., with strain control of 1 rad, frequency of 1 Hz, temperature increase rate of 20 °C/min, and measurement temperature range of 25 °C to 200 °C (provided that the melting point of the solder particles is 200 °C). ℃, the upper temperature limit is the melting point of the solder particles). From the measurement results, the viscosity of the conductive paste at the melting point of the solder particles is calculated.

Preferably, the conductive paste is an anisotropic conductive paste. The above-mentioned conductive paste is suitably used for electrical connection of electrodes. Preferably, the conductive paste is a circuit connection paste.

The environment in which the conductive paste is used is not particularly limited. The conductive paste may be used in an environment of 25° C. and 50% RH, or in other environments.

Each component contained in the conductive paste will be explained below. In addition, in this specification, "(meth)acrylic" means one or both of "acrylic" and "methacrylic."

(thermosetting component)
The conductive paste according to the present invention contains a thermosetting component. The conductive paste preferably contains a thermosetting compound as a thermosetting component. The conductive paste may or may not contain a thermosetting agent. The conductive paste may contain a thermosetting compound and a thermosetting agent as thermosetting components. When the conductive paste contains a thermosetting compound and a thermosetting agent, the conductive paste can be cured even better.

(Thermosetting component: thermosetting compound)
The above thermosetting compound is not particularly limited. Examples of the thermosetting compound include oxetane compounds, epoxy compounds, episulfide compounds, (meth)acrylic compounds, phenol compounds, amino compounds, unsaturated polyester compounds, polyurethane compounds, silicone compounds, and polyimide compounds. From the viewpoint of further improving the curability and viscosity of the conductive paste, further increasing the conduction reliability, and further increasing the insulation reliability, the thermosetting compound may be an epoxy compound or an episulfide compound. Preferably, epoxy compounds are more preferable. From the viewpoint of further improving the curability and viscosity of the conductive paste, further increasing the continuity reliability, and further increasing the insulation reliability, the thermosetting compound preferably contains an epoxy compound. . The above thermosetting compounds may be used alone or in combination of two or more.

The above epoxy compound is a compound having at least one epoxy group. The above-mentioned epoxy compounds include bisphenol A type epoxy compounds, bisphenol F type epoxy compounds, bisphenol S type epoxy compounds, phenol novolak type epoxy compounds, biphenyl type epoxy compounds, biphenyl novolac type epoxy compounds, biphenol type epoxy compounds, and naphthalene type epoxy compounds. , fluorene type epoxy compound, phenol aralkyl type epoxy compound, naphthol aralkyl type epoxy compound, dicyclopentadiene type epoxy compound, anthracene type epoxy compound, epoxy compound having an adamantane skeleton, epoxy compound having a tricyclodecane skeleton, naphthylene ether type Examples include epoxy compounds and epoxy compounds having a triazine nucleus in their skeleton. Only one kind of the above-mentioned epoxy compound may be used, or two or more kinds thereof may be used in combination.

The epoxy compound is liquid or solid at room temperature (25° C.), and when the epoxy compound is solid at room temperature, the melting temperature of the epoxy compound is preferably equal to or lower than the melting point of the solder particles. By using the preferred epoxy compound described above, the viscosity is high at the stage when the connection target members are bonded together, and when acceleration is applied due to impact such as transportation, the first connection target member and the second connection target member are bonded together. Misalignment with the target member can be suppressed. Furthermore, the heat generated during curing can greatly reduce the viscosity of the conductive paste, allowing the solder particles to coagulate efficiently.

From the viewpoint of improving connection reliability, the epoxy compound preferably includes a phenol novolac type epoxy compound or a bisphenol F type epoxy compound.

The content of the thermosetting component in 100% by weight of the conductive paste is preferably 10% by weight or more, more preferably 15% by weight or more, even more preferably 20% by weight or more, and preferably 90% by weight or less, more preferably It is preferably 85% by weight or less, more preferably 80% by weight or less, particularly preferably 75% by weight or less. When the content of the thermosetting component is not less than the lower limit and not more than the upper limit, the solder particles can be arranged on the electrodes even more efficiently, and the insulation reliability between the electrodes can be further improved. This makes it possible to further improve the reliability of conduction between the electrodes. From the viewpoint of effectively increasing impact resistance, it is preferable that the content of the thermosetting component be as large as possible.

The content of the thermosetting compound in 100% by weight of the conductive paste is preferably 5% by weight or more, more preferably 10% by weight or more, even more preferably 15% by weight or more, and preferably 90% by weight or less, more preferably It is preferably 85% by weight or less, more preferably 80% by weight or less, particularly preferably 75% by weight or less. When the content of the thermosetting compound is not less than the lower limit and not more than the upper limit, the solder particles can be arranged on the electrodes even more efficiently, and the insulation reliability between the electrodes can be further improved. This makes it possible to further improve the reliability of conduction between the electrodes. From the viewpoint of effectively increasing impact resistance, it is preferable that the content of the thermosetting compound be as large as possible.

The content of the epoxy compound in 100% by weight of the conductive paste is preferably 5% by weight or more, more preferably 10% by weight or more, even more preferably 15% by weight or more, and preferably 90% by weight or less, more preferably It is 85% by weight or less, more preferably 80% by weight or less, particularly preferably 75% by weight or less. When the content of the epoxy compound is not less than the lower limit and not more than the upper limit, the solder particles can be arranged on the electrodes even more efficiently, and the insulation reliability between the electrodes can be further improved. The reliability of conduction between the electrodes can be further improved. From the viewpoint of effectively increasing impact resistance, it is preferable that the content of the epoxy compound is as large as possible.

(Thermosetting component: thermosetting agent)
The above thermosetting agent is not particularly limited. The thermosetting agent thermosets the thermosetting compound. Examples of the above-mentioned thermosetting agents include thiol curing agents such as imidazole curing agents, amine curing agents, phenol curing agents, and polythiol curing agents, acid anhydride curing agents, thermal cationic initiators (thermal cationic curing agents), thermal radical generators, etc. can be mentioned. The above thermosetting agents may be used alone or in combination of two or more.

From the viewpoint of enabling the conductive paste to be cured more quickly at low temperatures, the thermosetting agent is preferably an imidazole curing agent, a thiol curing agent, or an amine curing agent. Further, from the viewpoint of improving the storage stability when the thermosetting compound and the thermosetting agent are mixed, the thermosetting agent is preferably a latent curing agent. Preferably, the latent curing agent is a latent imidazole curing agent, a latent thiol curing agent or a latent amine curing agent. Note that the thermosetting agent may be coated with a polymeric substance such as polyurethane resin or polyester resin.

The above imidazole curing agent is not particularly limited. Examples of the imidazole curing agent include 2-methylimidazole, 2-ethyl-4-methylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-phenylimidazolium trimellitate, 2,4-diamino-6 -[2'-Methylimidazolyl-(1')]-ethyl-s-triazine and 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanuric acid addition 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2-phenyl-4-benzyl-5-hydroxymethylimidazole, 2-paratolyl-4-methyl- 5 of 1H-imidazole in 5-hydroxymethylimidazole, 2-metatolyl-4-methyl-5-hydroxymethylimidazole, 2-metatolyl-4,5-dihydroxymethylimidazole, 2-paratolyl-4,5-dihydroxymethylimidazole, etc. Examples include imidazole compounds in which the hydrogen at position is substituted with a hydroxymethyl group, and the hydrogen at position 2 is substituted with a phenyl group or tolyl group.

The above-mentioned thiol curing agent is not particularly limited. Examples of the thiol curing agent include trimethylolpropane tris-3-mercaptopropionate, pentaerythritol tetrakis-3-mercaptopropionate, and dipentaerythritol hexa-3-mercaptopropionate.

The above amine curing agent is not particularly limited. Examples of the amine curing agent include hexamethylene diamine, octamethylene diamine, decamethylene diamine, 3,9-bis(3-aminopropyl)-2,4,8,10-tetraspiro[5.5]undecane, bis(4 -aminocyclohexyl)methane, metaphenylenediamine, and diaminodiphenylsulfone.

The acid anhydride curing agent is not particularly limited. As the acid anhydride curing agent, acid anhydrides used as curing agents for thermosetting compounds such as epoxy compounds can be widely used. The acid anhydride curing agents include phthalic anhydride, tetrahydrophthalic anhydride, trialkyltetrahydrophthalic anhydride, hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylbutenyltetrahydrophthalic anhydride. , anhydrides of phthalic acid derivatives, maleic anhydride, nadic anhydride, methyl nadic anhydride, glutaric anhydride, succinic anhydride, glycerin bis-trimellitic anhydride monoacetate, and difunctional compounds such as ethylene glycol bis-trimellitic anhydride. trifunctional acid anhydride curing agents such as trimellitic anhydride, pyromellitic anhydride, benzophenonetetracarboxylic anhydride, methylcyclohexenetetracarboxylic anhydride, polyazelaic anhydride, etc. Examples include acid anhydride curing agents having four or more functional groups.

The thermal cationic initiator is not particularly limited. Examples of the thermal cationic initiator include iodonium-based cationic curing agents, oxonium-based cationic curing agents, and sulfonium-based cationic curing agents. Examples of the iodonium-based cationic curing agent include bis(4-tert-butylphenyl)iodonium hexafluorophosphate. Examples of the oxonium-based cationic curing agent include trimethyloxonium tetrafluoroborate. Examples of the sulfonium-based cationic curing agent include tri-p-tolylsulfonium hexafluorophosphate.

The thermal radical generator described above is not particularly limited. Examples of the thermal radical generator include azo compounds and organic peroxides. Examples of the azo compound include azobisisobutyronitrile (AIBN) and the like. Examples of the organic peroxide include di-tert-butyl peroxide and methyl ethyl ketone peroxide.

The reaction initiation temperature of the thermosetting agent is preferably 50°C or higher, more preferably 60°C or higher, even more preferably 70°C or higher, preferably 250°C or lower, more preferably 200°C or lower, and even more preferably 175°C. The temperature below is particularly preferably 150°C or below. When the reaction start temperature of the thermosetting agent is equal to or higher than the lower limit and lower than the upper limit, solder particles can be arranged on the electrode even more efficiently. It is particularly preferable that the reaction initiation temperature of the thermosetting agent is 70°C or more and 150°C or less.

The reaction start temperature of the thermosetting agent means the temperature at which the exothermic peak starts rising in differential scanning calorimetry (DSC).

The content of the thermosetting agent is not particularly limited. With respect to 100 parts by weight of the thermosetting compound, the content of the thermosetting agent is preferably 0.01 parts by weight or more, more preferably 1 part by weight or more, and preferably 200 parts by weight or less, more preferably The amount is 100 parts by weight or less, more preferably 75 parts by weight or less. When the content of the thermosetting agent is equal to or higher than the lower limit, it is easy to sufficiently cure the conductive paste. When the content of the thermosetting agent is below the above upper limit, it becomes difficult for excess thermosetting agent that did not take part in curing to remain after curing, and the heat resistance of the cured product becomes even higher.

(solder particles with flux)
The conductive paste includes solder particles with flux. The solder particles with flux include solder particles and flux supported on the solder particles.

In the solder particles with flux, the flux is supported on the solder particles (carrier). Here, "supported" means a state in which a substance to be supported is immobilized on a carrier. The supported substance may be placed on the surface of the carrier. The supported substance may be scattered on the surface of the carrier, may be concentrated on the surface of the carrier, or may be coated on the surface of the carrier. In the flux-coated solder particles, the flux may be placed on the surface of the solder particles through a chemical bond or without a chemical bond. In the solder particles with flux, the flux is preferably arranged on the surface of the solder particles without any chemical bond.

The content of the fluxed solder particles in 100% by weight of the conductive paste is preferably 50% by weight or more, more preferably 55% by weight or more, even more preferably 60% by weight or more, and preferably 90% by weight or less, more preferably It is preferably 85% by weight or less, more preferably 80% by weight or less. When the content of the solder particles with flux is at least the above lower limit and below the above upper limit, the solder particles can be arranged on the electrodes even more efficiently, and it is easy to arrange a large amount of solder between the electrodes. Yes, it is possible to further improve conduction reliability. From the viewpoint of further improving conduction reliability, it is preferable that the content of the solder particles with flux is large.

The content of the solder particles with flux is preferably 100 parts by weight or more, more preferably 150 parts by weight or more, even more preferably 200 parts by weight or more, and preferably 400 parts by weight or more, based on 100 parts by weight of the thermosetting component. It is not more than 350 parts by weight, more preferably not more than 300 parts by weight. When the content of the solder particles with flux is at least the above lower limit and below the above upper limit, the solder particles can be arranged on the electrodes even more efficiently, and it is easy to arrange a large amount of solder between the electrodes. Yes, it is possible to further improve conduction reliability. From the viewpoint of further improving conduction reliability, it is preferable that the content of the solder particles with flux is large.

[Solder particles]
The solder particles are carriers in the fluxed solder particles. The flux is supported on the solder particles. From the viewpoint of exhibiting the effects of the present invention even more effectively, it is preferable that the solder particles carry a plurality of the fluxes. From the viewpoint of exhibiting the effects of the present invention even more effectively, it is preferable that a plurality of the above-mentioned fluxes are supported on the above-mentioned solder particles. Preferably, the surfaces of the solder particles are coated with a plurality of the fluxes.

Both the center portion and the outer surface of the solder particles are made of solder. The solder particles described above are particles in which both the center portion and the outer surface are solder. When conductive particles comprising base particles made of a material other than solder and a solder portion disposed on the surface of the base particles are used instead of the solder particles described above, conductive particles can be placed on the electrodes. Particles become difficult to collect. In addition, since the conductive particles described above have low solder bondability between conductive particles, the conductive particles that have moved onto the electrode tend to move out of the electrode, and the effect of suppressing misalignment between the electrodes is also low. tends to be lower.

The average particle diameter of the solder particles is 5.0 μm or less. The average particle diameter of the solder particles is preferably 0.1 μm or more, more preferably 0.5 μm or more, even more preferably 1.0 μm or more, and preferably 4.9 μm or less, more preferably 4.5 μm or less, and Preferably it is 4.0 μm or less. When the average particle diameter of the solder particles is not less than the above lower limit and not more than the above upper limit, the solder particles can be arranged on the electrode much more efficiently. When the average particle diameter of the solder particles is equal to or less than the above upper limit, screen printing properties on fine-pitch substrates and the like can be further improved. In the conductive paste according to the present invention, the smaller the average particle diameter of the solder particles, the more effectively the above effects of the present invention are exhibited. That is, in the conductive paste according to the present invention, the smaller the average particle diameter of the solder particles, the more efficiently the solder particles can be arranged on the electrodes, and the reliability of conduction between the upper and lower electrodes to be connected is improved. can effectively increase the insulation reliability between adjacent horizontal electrodes that should not be connected.

The average particle diameter of the solder particles is preferably a number average particle diameter. The average particle diameter of the above solder particles can be determined, for example, by observing 50 arbitrary solder particles with an electron microscope or optical microscope and calculating the average value of the particle diameter of each solder particle, or by laser diffraction particle size distribution measurement. It is sought after by doing. In observation using an electron microscope or an optical microscope, the particle diameter of each solder particle is determined as the particle diameter in equivalent circle diameter. In observation using an electron microscope or an optical microscope, the average particle diameter of any 50 solder particles in equivalent circle diameter is approximately equal to the average particle diameter in equivalent sphere diameter. In the laser diffraction particle size distribution measurement, 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 by laser diffraction particle size distribution measurement.

The coefficient of variation (CV value) of the particle diameter of the solder particles is preferably 5% or more, more preferably 10% or more, and preferably 40% or less, more preferably 30% or less. When the coefficient of variation of the particle diameter of the solder particles is not less than the above lower limit and not more than the above upper limit, the solder particles can be arranged on the electrodes even more efficiently. However, the CV value of the particle diameter of the solder particles may be less than 5%.

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

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

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

From the viewpoint of arranging the solder particles on the electrodes more efficiently, the specific gravity of the solder particles is preferably 4 or more, more preferably 5 or more, and still more preferably 6 or more.

The specific gravity of the solder particles is determined by, for example, "Accupic II 1340" manufactured by Shimadzu Corporation.

The solder is preferably a metal having a melting point of 450° C. or lower (low melting point metal). The solder particles are preferably metal particles having a melting point of 450° C. or lower (low-melting point metal particles). The low melting point metal particles are particles containing a low melting point metal. The low melting point metal refers to a metal having a melting point of 450° C. or lower. The melting point of the low melting point metal is preferably 300°C or lower, more preferably 260°C or lower. The solder is preferably a low melting point solder having a melting point of less than 250°C.

From the viewpoint of further improving connection reliability, the melting point of the solder particles is preferably 100°C or higher, more preferably 150°C or higher, even more preferably 200°C or higher, and preferably 400°C or lower, more preferably 350°C or higher. The temperature is preferably 300°C or lower, more preferably 300°C or lower.

The melting point of the solder particles can be determined by differential scanning calorimetry (DSC). Examples of the differential scanning calorimetry (DSC) device include "EXSTAR DSC7020" manufactured by SII.

Further, it is preferable that the solder particles contain tin. The content of tin is preferably 30% by weight or more, more preferably 40% by weight or more, still more preferably 70% by weight or more, and particularly preferably 90% by weight or more in 100% by weight of the metal contained in the solder particles. . When the content of tin in the solder particles is equal to or higher than the lower limit, the conduction reliability and connection reliability between the solder portion and the electrode will be further increased.

The above tin content is based on a high-frequency inductively coupled plasma emission spectrometer (for example, "ICP-AES" manufactured by Horiba) or a fluorescent X-ray analyzer (for example, "EDX-800HS" manufactured by Shimadzu Corporation). It can be measured using, etc.

By using the above-mentioned solder particles, the solder melts and joins to the electrodes, and the solder portion establishes conduction between the electrodes. For example, since the solder portion and the electrode tend to make surface contact rather than point contact, the connection resistance becomes low. Furthermore, the use of the solder particles increases the bonding strength between the solder part and the electrode, making it even more difficult for the solder part to separate from the electrode, resulting in even higher conduction reliability and connection reliability.

The low melting point metal constituting the solder particles is not particularly limited. The low melting point metal is preferably tin or an alloy containing tin. Examples of the alloy include tin-silver alloy, tin-copper alloy, tin-silver-copper alloy, tin-bismuth alloy, tin-zinc alloy, tin-indium alloy, and tin-antimony alloy. The low melting point metal is preferably tin, tin-silver alloy, tin-silver-copper alloy, tin-bismuth alloy, tin-indium alloy, and tin-antimony alloy, since they have excellent wettability to the electrode. More preferably, it is a tin-silver-copper alloy, a tin-bismuth alloy, a tin-indium alloy, or a tin-antimony alloy.

The solder particles are preferably filler metals whose liquidus line is 450° C. or less based on JIS Z3001: Welding terminology. Examples of the composition of the solder particles include metal compositions containing zinc, gold, silver, lead, copper, tin, bismuth, indium, and the like. Preferred are tin-indium (117° C. eutectic) or tin-bismuth (139° C. eutectic) which have a low melting point and are lead-free. That is, the solder particles preferably do not contain lead, and preferably contain tin and indium, or tin and bismuth.

In order to further increase the bonding strength between the solder part and the electrode, the solder particles include nickel, copper, antimony, aluminum, zinc, iron, gold, titanium, phosphorus, germanium, tellurium, cobalt, bismuth, manganese, chromium, It may also contain metals such as molybdenum and palladium. Moreover, from the viewpoint of further increasing the bonding strength between the solder part and the electrode, it is preferable that the solder particles contain nickel, copper, antimony, aluminum, or zinc. From the viewpoint of further increasing the bonding strength between the solder part and the electrode, the content of these metals for increasing the bonding strength is preferably 0.0001% by weight or more based on 100% by weight of the metal contained in the solder particles, Preferably it is 1% by weight or less.

[flux]
The solder particles with flux include flux (hereinafter sometimes referred to as "flux X") supported on the solder particles. The flux X is supported on the solder particles.

In the conductive paste, the flux (flux X) supported on the solder particles is a carboxylic acid or a carboxylate salt. The flux X may be a carboxylic acid or a carboxylate.

A carboxylic acid is an organic compound having one or more carboxyl groups. The carboxylic acid may have one carboxyl group, two carboxyl groups, two or more carboxyl groups, or three carboxyl groups. or three or more carboxyl groups. The carboxylic acid may have 10 or less carboxyl groups, may have 8 or less carboxyl groups, or may have 5 or less carboxyl groups.

Examples of the carboxylic acids include aliphatic carboxylic acids, alicyclic carboxylic acids, and aromatic carboxylic acids. Examples of the aliphatic carboxylic acids include malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, citric acid, and malic acid. Examples of the alicyclic carboxylic acid include cyclohexylcarboxylic acid and 1,4-cyclohexyldicarboxylic acid. Examples of the aromatic carboxylic acids include isophthalic acid, terephthalic acid, trimellitic acid, and ethylenediaminetetraacetic acid. From the viewpoint of arranging solder particles on the electrode more efficiently, the carboxylic acid is preferably glutaric acid, cyclohexylcarboxylic acid, or adipic acid.

Examples of the above-mentioned carboxylic acid salt include neutralization reaction products (salts) of the above-mentioned carboxylic acid and a basic compound. The carboxylic acid salt is preferably a salt produced by a neutralization reaction between a carboxylic acid and a basic compound. The conditions for the neutralization reaction are preferably a heating temperature of 25° C. to 60° C. and a heating time of 5 minutes to 30 minutes. The carboxylic acid preferably has the effect of cleaning the surface of the metal, and the basic compound preferably has the effect of neutralizing the carboxylic acid.

The basic compound is preferably an organic compound having an amino group (amine compound). The above basic compounds 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 arranging solder particles on the electrode more efficiently, the basic compound is preferably benzylamine.

From the viewpoint of arranging solder particles on the electrode more efficiently, the carboxylic acid salt is preferably a carboxylic acid amine salt. Examples of the carboxylic acid amine salt include glutaric acid benzylamine salt, adipic acid benzylamine salt, and malic acid benzylamine salt.

From the viewpoint of arranging the solder particles on the electrode more efficiently, the flux More preferred is an acid benzylamine salt.

It is preferable that the flux X is solid at 25°C. Specifically, it is preferable that the flux X is solid at 25° C. when supported on the solder particles and not mixed with the thermosetting component (solder particles with flux alone). .

Further, it is preferable that the flux X is solid at 25° C. before being supported on the solder particles. It is preferable that the flux before being supported on the solder particles is solid at 25°C. That is, it is preferable that the flux alone is solid at 25°C.

Note that whether or not the flux X is solid at 25° C. in the state of a single fluxed solder particle can be determined by differential scanning calorimetry (DSC). Examples of the differential scanning calorimetry (DSC) device include "EXSTAR DSC7020" manufactured by SII.

Note that whether or not the flux (flux alone) is solid at 25° C. before being supported on the solder particles can be determined as follows. In this specification, a flux that is not liquid at 25°C is defined as a flux that is solid at 25°C, and a flux that maintains its shape when left standing for 5 minutes at 25°C and 50% RH. A flux that does not retain its shape when left standing for 5 minutes at 50% RH is defined as a semi-solid flux at 25°C. Further, a flux that is semi-solid at 25°C is not included in a flux that is solid at 25°C.

The shape of the flux X is not particularly limited. The flux X may be spherical, may have a shape other than spherical, or may have a flat shape or the like. From the viewpoint of further improving screen printability, the shape of the flux X is preferably spherical.

The particle size of the flux be.

The particle size of the flux X is preferably an average particle size, more preferably a number average particle size. The average particle diameter of the above flux X can be determined, for example, by observing 50 arbitrary fluxes X with an electron microscope or optical microscope and calculating the average value of the particle diameter of each flux X, or by performing laser diffraction particle size distribution measurement. It is required by In observation using an electron microscope or an optical microscope, the particle diameter of each flux X is determined as the particle diameter in equivalent circle diameter. In observation using an electron microscope or an optical microscope, the average particle diameter of any 50 fluxes X in equivalent circle diameter is approximately equal to the average particle diameter in equivalent sphere diameter. In the laser diffraction particle size distribution measurement, the particle diameter of each flux X is determined as the particle diameter in equivalent sphere diameter. The average particle diameter of the flux X is preferably calculated by laser diffraction particle size distribution measurement.

When measuring the particle diameter of the flux X in the flux-coated solder particles, for example, it can be measured as follows.

Fluxed solder particles are added to "Technovit 4000" manufactured by Kulzer Co., Ltd. to a content of 30% by weight, and dispersed to produce an embedded resin body for inspecting fluxed solder particles. Using an ion milling device (“IM4000” manufactured by Hitachi High-Technologies), cut out a cross section of the fluxed solder particles so as to pass through the center of the flux X in the fluxed solder particles dispersed in the embedded resin body for inspection. Then, using a field emission scanning electron microscope (FE-SEM), set the image magnification to 50,000 times, randomly select 50 fluxes X, measure the particle diameter of each flux The particle size of flux X is determined by taking the arithmetic mean of

The ratio of the average particle diameter of the flux (flux or more, preferably 10.0 or less, more preferably 5.0 or less, even more preferably 4.0 or less. When the above ratio (average particle diameter of flux X/average particle diameter of solder particles) is above the above lower limit and below the above upper limit, flux Performance can be further improved.

The melting point (activation temperature) of the flux below ℃. When the melting point of the flux X is greater than or equal to the lower limit and less than or equal to the upper limit, solder particles can be disposed on the electrode even more efficiently.

The melting point of the flux X can be determined by differential scanning calorimetry (DSC). Examples of the differential scanning calorimetry (DSC) device include "EXSTAR DSC7020" manufactured by SII.

From the viewpoint of arranging the solder particles on the electrodes more efficiently, the melting point of the flux X is preferably lower than the melting point of the solder particles. From the viewpoint of arranging the solder particles on the electrodes more efficiently, the melting point of the flux X is more preferably 5° C. or more lower than the melting point of the solder particles, and even more preferably 10° C. or more lower.

Examples of the method for supporting flux on the solder particles (method for producing solder particles with flux) include the following method. A method in which solder particles are immersed in a solvent in which flux is dissolved. A method in which solder particles are immersed in a solvent and flux is generated in the solvent through a chemical reaction. A method of solid phase mixing of solder particles and flux.

As a method for confirming that the flux-coated solder particles carry the flux There are methods to confirm that peaks are expressed in each. Examples of the differential scanning calorimetry (DSC) device include "EXSTAR DSC7020" manufactured by SII.

From the viewpoint of arranging the solder particles on the electrodes more efficiently, the proportion of the surface area on which the flux X is supported (coverage rate by flux X) is preferably 10% of the 100% surface area of the solder particles. More preferably, it is 20% or more, preferably 90% or less, and more preferably 80% or less.

The coverage by the flux X can be measured by the following method. By observing 20 solder particles with flux using a scanning electron microscope (SEM), the ratio of the total area (projected area) of the part carrying the above flux X to 100% of the surface area of the solder particles was determined. Calculate.

In one flux-coated solder particle, the content of the flux X is preferably 0.01 parts by weight or more, more preferably 0.1 parts by weight or more, still more preferably 1 part by weight, based on 100 parts by weight of the solder particles. The amount is at least 30 parts by weight, more preferably at most 20 parts by weight, even more preferably at most 10 parts by weight. When the content of the flux X is not less than the lower limit and not more than the upper limit, solder particles can be arranged on the electrodes even more efficiently, and it is easy to arrange a large amount of solder between the electrodes, Continuity reliability can be further improved.

The conductive paste may contain a flux different from the flux X in the flux-coated solder particles (hereinafter sometimes referred to as "flux Y"). The conductive paste may contain a flux other than the flux X (flux Y). From the viewpoint of arranging solder particles on the electrodes more efficiently, the conductive paste preferably contains a thermosetting component, solder particles with flux, and flux (flux Y). It is preferable that the flux Y is not supported on the solder particles in the conductive paste. The flux Y may be the same as or different from the flux X. The flux Y may be solid or liquid.

The above flux Y includes zinc chloride, a mixture of zinc chloride and an inorganic halide, a mixture of zinc chloride and an inorganic acid, a molten salt, an organic phosphorus compound, an organic halide, hydrazine, an amine compound, an organic acid, and an organic acid. Examples include salt, pine resin, and the like. The above flux Y may be used alone or in combination of two or more.

Examples of the molten salt include ammonium chloride.

Examples of the organic phosphorus compounds include organic phosphonium salts, organic phosphoric acids, organic phosphoric esters, organic phosphonic acids, organic phosphonic esters, organic phosphinic acids, and organic phosphinic esters.

Examples of the amine compounds include cyclohexylamine, dicyclohexylamine, benzylamine, benzhydrylamine, imidazole, benzimidazole, phenylimidazole, carboxybenzimidazole, benzotriazole, and carboxybenzotriazole.

The above-mentioned pine resin is a rosin whose main component is abietic acid. Examples of the rosins include abietic acid and acrylic modified rosin.

Examples of the above-mentioned organic acids and salts of the above-mentioned organic acids include the above-mentioned carboxylic acids and carboxylic acid salts.

From the viewpoint of arranging solder particles on the electrodes more efficiently, the flux Y is preferably the same as the flux X.

With respect to 100 parts by weight of the flux X, the content of the flux Y is preferably 10 parts by weight or more, more preferably 30 parts by weight or more, even more preferably 50 parts by weight or more, and preferably 1000 parts by weight or less, more preferably Preferably it is 800 parts by weight or less, more preferably 500 parts by weight or less. When the content of the flux Y is equal to or higher than the lower limit, solder particles can be arranged on the electrodes even more efficiently. When the content of the above-mentioned flux Y is below the above-mentioned upper limit, storage stability and screen printability can be further improved.

The content of the flux Y in 100% by weight of the conductive paste is preferably 1% by weight or more, more preferably 5% by weight or more, and preferably 30% by weight or less, more preferably 25% by weight or less. When the content of flux Y is at least the above lower limit, solder particles can be arranged on the electrodes even more efficiently. When the content of the above-mentioned flux Y is below the above-mentioned upper limit, storage stability and screen printability can be further improved.

With respect to 100 parts by weight of the thermosetting component, the content of the flux Y is preferably 1 part by weight or more, more preferably 5 parts by weight or more, still more preferably 10 parts by weight or more, and preferably 35 parts by weight. The amount is more preferably 30 parts by weight or less, still more preferably 25 parts by weight or less. When the content of the flux Y is equal to or higher than the lower limit, solder particles can be arranged on the electrodes even more efficiently. When the content of the above-mentioned flux Y is below the above-mentioned upper limit, storage stability and screen printability can be further improved.

The content of the flux Y is preferably 1 part by weight or more, more preferably 3 parts by weight or more, still more preferably 5 parts by weight or more, and preferably 35 parts by weight with respect to 100 parts by weight of the solder particles with flux. The amount is more preferably 30 parts by weight or less, still more preferably 25 parts by weight or less. When the content of the flux Y is equal to or higher than the lower limit, solder particles can be arranged on the electrodes even more efficiently. When the content of the above-mentioned flux Y is below the above-mentioned upper limit, storage stability and screen printability can be further improved.

(other ingredients)
The above conductive paste may contain, if necessary, for example, a thixotropic agent, a filler, an extender, a softener, a plasticizer, a leveling agent, a polymerization catalyst, a curing catalyst, a coloring agent, an antioxidant, a heat stabilizer, and a light stabilizer. It may contain various additives such as a UV absorber, a lubricant, an antistatic agent, and a flame retardant.

From the viewpoint of favorably assisting flux performance and arranging solder particles on the electrodes more efficiently, the conductive paste preferably contains a thixotropic agent. The above-mentioned thixotropic agents may be used alone or in combination of two or more.

The content of the thixotropic agent in 100% by weight of the conductive paste is preferably 0.005% by weight or more, more preferably 0.01% by weight or more, even more preferably 0.05% by weight or more, and preferably It is 2% by weight or less, more preferably 1% by weight or less, even more preferably 0.5% by weight or less. When the content of the thixotropic agent is not less than the above lower limit and not more than the above upper limit, flux performance can be favorably assisted and solder particles can be arranged on the electrode more efficiently.

The content of the thixotropic agent is preferably 0.003 parts by weight or more, more preferably 0.005 parts by weight or more, and even more preferably 0.01 parts by weight or more with respect to 100 parts by weight of the solder particles with flux. The amount is preferably 2 parts by weight or less, more preferably 1 part by weight or less, even more preferably 0.7 parts by weight or less. When the content of the thixotropic agent is not less than the above lower limit and not more than the above upper limit, flux performance can be favorably assisted and solder particles can be arranged on the electrode more efficiently.

The content of the thixotropic agent is preferably 0.1 parts by weight or more, more preferably 0.3 parts by weight or more, and preferably 5 parts by weight or less, based on 100 parts by weight of the thermosetting component. Preferably it is 3 parts by weight or less. When the content of the thixotropic agent is not less than the above lower limit and not more than the above upper limit, flux performance can be favorably assisted and solder particles can be arranged on the electrode more efficiently.

The content of the thixotropic agent is preferably 0.1 parts by weight or more, more preferably 0.3 parts by weight or more, and preferably 5 parts by weight or less, based on 100 parts by weight of the thermosetting compound. Preferably it is 3 parts by weight or less. When the content of the thixotropic agent is not less than the above lower limit and not more than the above upper limit, flux performance can be favorably assisted and solder particles can be arranged on the electrode more efficiently.

The thixotropic agent is (A) a thixotropic agent that is a liquid at 25°C and has a hydroxyl group, or (B) a thixotropic agent that is a solid at 25°C and the thixotropic agent is 50% It is preferable that the thixotropic agent has the following weight increase rate of 0.2% by weight or more when left at RH for 24 hours. When the above-mentioned thixotropic agent is in the above-mentioned preferred embodiment, it can favorably assist the flux performance and arrange the solder particles on the electrode much more efficiently.

Weight increase rate (weight%) = (W2-W1) x 100/W1
W1: Weight of the above thixotropic agent before standing W2: Weight of the above thixotropic agent after standing

The thixotropic agent may be (A) a thixotropic agent that is liquid at 25° C. and has a hydroxyl group (hereinafter sometimes referred to as "thixotropic agent A"). Further, the above-mentioned thixotropic agent is (B) a thixotropic agent that is solid at 25°C and has the above-mentioned weight increase rate of 0.2% by weight or more (hereinafter sometimes referred to as "thixotropic agent B") It may be. The thixotropic agent is preferably the thixotropic agent A or the thixotropic agent B.

The thixotropic agent A is liquid at 25° C. and has a hydroxyl group (—OH group).

The thixotropic agent A is liquid at 25°C. Specifically, the thixotropic agent A (thixotropic agent A alone) is a liquid at 25° C. in a state where it is not mixed with the thermosetting component and the fluxed solder particles.

In the conductive paste, it is preferable that the thixotropic agent A is a liquid in the conductive paste at 25°C. In the conductive paste, the thixotropic agent A is preferably present in liquid form in the conductive paste at 25°C.

The thixotropic agent A has at least one hydroxyl group. The thixotropic agent A may have one hydroxyl group, two hydroxyl groups, two or more hydroxyl groups, three or more hydroxyl groups, or three or more hydroxyl groups. or four or more. The thixotropic agent A may be a monohydric alcohol or a polyhydric alcohol. The thixotropic agent A may be a dihydric alcohol, a trihydric alcohol, or a tetrahydric alcohol. From the viewpoint of preventing volatilization of the conductive paste and further improving screen printability, the thixotropic agent A preferably has two or more hydroxyl groups, more preferably three or more. From the viewpoint of preventing volatilization of the conductive paste and further improving screen printability, the thixotropic agent A is preferably a polyol compound (polyhydric alcohol). The thixotropic agent A may have 10 or less hydroxyl groups, or may have 7 or less hydroxyl groups.

Examples of the thixotropic agent A include methanol, ethanol, propanol, N-oleoylsarcosine, propylene glycol, propanediol, diethylene glycol, glycerol (glycerin), trimethylolpropane, 1,2,4-butanetriol, diglycerin, and polyglycerin.

From the viewpoint of preventing volatilization of the conductive paste and further improving screen printability, the thixotropic agent A is preferably glycerol (glycerin), N-oleoylsarcosine, or 1,2,4-butanetriol. , glycerol (glycerin) is more preferred.

The thixotropic agent B is solid at 25° C., and has the following weight increase rate of 0.2% by weight or more when the thixotropic agent is left at 25° C. and 50% RH for 24 hours.

Weight increase rate (weight%) = (W2-W1) x 100/W1
W1: Weight of the above thixotropic agent before standing W2: Weight of the above thixotropic agent after standing

The thixotropic agent B is solid at 25°C. Specifically, the thixotropic agent B (thixotropic agent B alone) is solid at 25° C. without being mixed with the thermosetting component and the fluxed solder particles.

In the conductive paste, the thixotropic agent B is preferably solid in the conductive paste at 25°C. In the conductive paste, the thixotropic agent B is preferably present in solid form in the conductive paste at 25°C.

Note that whether or not the thixotropic agent B (thixotropic agent B alone) is solid at 25° C. can be determined as follows. In this specification, regarding thixotropic agent B that is not a liquid at 25°C, thixotropic agent B that maintains its shape when thixotropic agent B alone is allowed to stand for 5 minutes at 25°C and 50% RH is referred to as thixotropic agent B that is not liquid at 25°C. Defined as solid thixotropic agent B. In addition, thixotropic agent B that does not maintain its shape when thixotropic agent B alone is allowed to stand for 5 minutes at 25° C. and 50% RH is defined as thixotropic agent B that is semisolid at 25° C. Note that thixotropic agent B, which is semi-solid at 25°C, is not included in thixotropic agent B, which is solid at 25°C.

Note that whether the thixotropic agent B is solid in the conductive paste at 25° C. can be determined as follows. In this specification, regarding thixotropic agent B that is not liquid at 25°C, thixotropic agent B that maintains its shape when a conductive paste containing thixotropic agent B is left standing for 5 minutes at 25°C and 50% RH, Thixotropic agent B is defined as solid at 25°C. Further, thixotropic agent B that does not retain its shape when a conductive paste containing thixotropic agent B is allowed to stand for 5 minutes at 25° C. and 50% RH is defined as thixotropic agent B that is semi-solid at 25° C. Note that thixotropic agent B, which is semi-solid at 25°C, is not included in thixotropic agent B, which is solid at 25°C.

The thixotropic agent B increases in weight when left for 24 hours at 25° C. and 50% RH. When the thixotropic agent B is left for 24 hours at 25° C. and 50% RH, the weight of the thixotropic agent B after being left is greater than the weight of the thixotropic agent B before being left.

From the viewpoint of favorably assisting flux performance and arranging solder particles on the electrode more efficiently, the thixotropic agent B preferably has water absorption or hygroscopicity, and more preferably has hygroscopicity. preferable. From the viewpoint of favorably assisting flux performance and arranging solder particles on the electrode more efficiently, it is more preferable that the thixotropic agent B has hygroscopicity at 25° C. and 50% RH.

The weight increase rate of the thixotropic agent B is 0.2% by weight or more. The weight increase rate of the thixotropic agent B is preferably 0.3% by weight or more, more preferably 0.5% by weight or more, even more preferably 1% by weight or more, and preferably less than 10% by weight, more preferably is 8% by weight or less, more preferably 5% by weight or less. When the weight increase rate of the thixotropic agent B is equal to or higher than the lower limit, the flux performance can be favorably assisted and the solder particles can be arranged on the electrode more efficiently. When the weight increase rate of the thixotropic agent B is below the above upper limit or below the above upper limit, screen printability can be further improved. From the viewpoint of favorably assisting flux performance and arranging solder particles on the electrode more efficiently, the thixotropic agent B is solid at 25° C. and has a weight increase rate of 1% by weight or more. Particularly preferred are certain thixotropic agents.

The weight increase rate of the thixotropic agent B can be measured by the following method. Take out 10 g (W1) of thixotropic agent B from a desiccator at 25° C. and 0% RH, and leave it for 24 hours at 25° C. and 50% RH. The weight (W2) of thixotropic agent B after standing is measured.

Examples of the thixotropic agent B include boron trifluoride-monoethylamine complex, pentaerythritol, sorbitol, mannitol, sorbitan, dipentaerythritol, sucrose, glucose, mannose, fructose, and methyl glucoside.

From the viewpoint of arranging solder particles on the electrode more efficiently, the thixotropic agent B is preferably a boron trifluoride-monoethylamine complex or glucose, and a boron trifluoride-monoethylamine complex. It is more preferable that there be.

(Method for manufacturing conductive paste)
The method for producing a conductive paste according to the present invention includes a step of obtaining fluxed solder particles comprising solder particles and a flux supported on the solder particles, and a step of mixing a thermosetting component and the fluxed solder particles. and obtaining a conductive paste. In the method for manufacturing a conductive paste according to the present invention, the average particle diameter of the solder particles is 5.0 μm or less. In the method for manufacturing a conductive paste according to the present invention, the flux supported on the solder particles is a carboxylic acid or a carboxylate salt.

Since the method for manufacturing a conductive paste according to the present invention has the above-mentioned configuration, it is possible to improve the storage stability of the conductive paste obtained, improve screen printability, and to apply solder on the electrode. Particles can be efficiently arranged.

In addition, in the conductive paste according to the present invention, multiple solder particles (solder particles with flux) tend to gather between the upper and lower opposing electrodes during conductive connection between the electrodes, and the multiple solder particles are placed on the electrodes (lines). can be placed. In addition, it is difficult for some of the plurality of solder particles to be placed between horizontal electrodes that should not be connected, and it is possible to considerably reduce the amount of solder particles that are placed between horizontal electrodes that should not be connected. can. As a result, the present invention can effectively increase the continuity reliability between the upper and lower electrodes that should be connected, and can effectively increase the insulation reliability between adjacent lateral electrodes that should not be connected. Can be done.

Furthermore, in the present invention, positional displacement between the electrodes can be prevented. In the present invention, when the second connection target member is superimposed on the first connection target member on which the conductive paste is disposed, the electrodes of the first connection target member and the electrodes of the second connection target member are overlapped. Even in a state where the alignment is misaligned, the misalignment can be corrected and the electrodes can be connected to each other (self-alignment effect).

In the method for producing a conductive paste according to the present invention, the fluxed solder particles and the thermosetting component are preferably the fluxed solder particles and the thermosetting component described above.

Examples of the method for supporting flux on the solder particles (method for producing solder particles with flux) include the following method. A method in which solder particles are immersed in a solvent in which flux is dissolved. A method in which solder particles are immersed in a solvent and flux is generated in the solvent through a chemical reaction. A method of solid phase mixing of solder particles and flux.

In the step of mixing the thermosetting component and the solder particles with flux to obtain a conductive paste, the method of mixing the thermosetting component and the solder particles with flux is not particularly limited. Examples of methods for dispersing the fluxed solder particles in the thermosetting component include the following method. A method in which the fluxed solder particles are added to the thermosetting component and then kneaded and dispersed using a planetary mixer or the like. A method in which the solder particles with flux are uniformly dispersed in water or an organic solvent using a homogenizer or the like, and then added to the thermosetting component and kneaded and dispersed using a planetary mixer or the like. A method of diluting the thermosetting component with water or an organic solvent, adding the fluxed solder particles, and kneading and dispersing with a planetary mixer or the like.

From the viewpoint of arranging solder particles on the electrodes more efficiently, it is preferable to further mix flux in the step of obtaining the conductive paste. That is, in the step of obtaining a conductive paste, it is preferable to mix the thermosetting component, the solder particles with flux, and the flux. The flux that is mixed with the thermosetting component and the solder particles with flux is a flux that is mixed separately from the flux contained in the solder particles with flux. The above-mentioned flux is preferably the above-mentioned flux Y. The order of mixing the thermosetting component, the solder particles with flux, and the flux is not particularly limited. The above-mentioned flux may be used in combination when mixing the above-mentioned thermosetting component and the above-mentioned solder particles with flux. It may also be used by mixing it into a mixture. Preferably, the fluxed solder particles are prepared before being mixed with the thermosetting component (and optionally the flux).

(connection structure)
The 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 the first connection target member, and a connecting portion connecting the second connection target member. In the connected structure according to the present invention, the material of the connection portion is the conductive paste described above. In the connected structure according to the present invention, the first electrode and the second electrode are electrically connected by a solder part in the connecting part.

The thickness of the solder portion between the electrodes is preferably 10 μm or more, more preferably 20 μm or more, and preferably 100 μm or less, more preferably 80 μm or less. The solder wetted area on the surface of the electrode (the area in contact with the solder out of 100% of the exposed area of the electrode) is preferably 50% or more, more preferably 70% or more, and preferably 100% or less.

The method for manufacturing the above-mentioned connected structure is not particularly limited. An example of a method for manufacturing a connected structure includes a method in which the conductive paste is placed between a first member to be connected and a second member to be connected, a laminate is obtained, and then the laminate is heated. can be mentioned. The heating temperature is preferably 230°C or higher, more preferably 250°C or higher, and preferably 350°C or lower, more preferably 300°C or lower. When the heating temperature is equal to or higher than the lower limit and lower than the upper limit, the reliability of conduction and insulation between the electrodes can be further improved. At the time of the heating, pressurization may or may not be applied.

Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a cross-sectional view schematically showing a connected structure obtained using a conductive paste according to an embodiment of the present invention.

The connection structure 1 shown in FIG. 1 includes a first connection target member 2, a second connection target member 3, and a connection connecting the first connection target member 2 and the second connection target member 3. 4. The connecting portion 4 is formed of the above-mentioned conductive paste. In this embodiment, the conductive paste includes a thermosetting component and solder particles with flux. The solder particles with flux include solder particles and flux supported on the solder particles. The thermosetting component includes a thermosetting compound and a thermosetting agent.

The connecting portion 4 includes a solder portion 4A in which a plurality of solder particles (solder particles with flux) are gathered and bonded to each other, and a cured material portion 4B in which a thermosetting compound is thermoset.

The first connection target member 2 has a plurality of first electrodes 2a on its surface (upper surface). The second connection target member 3 has a plurality of second electrodes 3a on the front surface (lower surface). The first electrode 2a and the second electrode 3a are electrically connected by a solder portion 4A. Therefore, the first connection target member 2 and the second connection target member 3 are electrically connected by the solder portion 4A. Note that, in the connecting portion 4, no solder particles are present in a region different from the solder portion 4A gathered between the first electrode 2a and the second electrode 3a (cured material portion 4B portion). In a region different from the solder portion 4A (cured material portion 4B portion), there are no solder particles separated from the solder portion 4A. Note that solder particles may be present in a region different from the solder portion 4A gathered between the first electrode 2a and the second electrode 3a (cured material portion 4B portion) as long as the amount is small.

As shown in FIG. 1, in the connection structure 1, a plurality of solder particles (solder particles with flux) gather between the first electrode 2a and the second electrode 3a, and after the plurality of solder particles are melted, The solder portion 4A is formed by solidifying the melted solder particles after wetting and spreading the surface of the electrode. Therefore, the contact area between the solder portion 4A and the first electrode 2a and between the solder portion 4A and the second electrode 3a becomes large. That is, by using solder particles, the solder portion 4A and the first electrode 2a, as well as the solder portion 4A and the The contact area with the second electrode 3a becomes larger. This also increases the conduction reliability and connection reliability in the connection structure 1. Note that the above-mentioned flux is generally gradually deactivated by heating.

In the connection structure 1, when looking at the portion where the first electrode 2a and the second electrode 3a face each other in the stacking direction of the first electrode 2a, the connection portion 4, and the second electrode 3a, the first It is preferable that the solder portion 4A in the connecting portion 4 is disposed on 50% or more of the 100% area of the opposing portion of the electrode 2a and the second electrode 3a. When the solder portion 4A in the connection portion 4 satisfies the above-mentioned preferable aspects, the continuity reliability can be further improved.

When looking at the opposing portions of the first electrode and the second electrode in the stacking direction of the first electrode, the connecting portion, and the second electrode, the first electrode and the second electrode It is preferable that the solder portion in the connection portion is disposed on 50% or more of the 100% area of the portion facing the second electrode. When looking at the opposing portions of the first electrode and the second electrode in the stacking direction of the first electrode, the connecting portion, and the second electrode, the first electrode and the second electrode It is more preferable that the solder portion in the connection portion is disposed on 60% or more of the 100% area of the portion facing the second electrode. When looking at the opposing portions of the first electrode and the second electrode in the stacking direction of the first electrode, the connecting portion, and the second electrode, the first electrode and the second electrode It is more preferable that the solder part in the connection part is disposed on 70% or more of the 100% area of the part facing the second electrode. When looking at the opposing portions of the first electrode and the second electrode in the stacking direction of the first electrode, the connecting portion, and the second electrode, the first electrode and the second electrode It is particularly preferable that the solder portion in the connection portion is disposed on 80% or more of the 100% area of the portion facing the second electrode. When looking at the opposing portions of the first electrode and the second electrode in the stacking direction of the first electrode, the connecting portion, and the second electrode, the first electrode and the second electrode It is most preferable that the solder part in the connection part is disposed on 90% or more of the 100% area of the part facing the second electrode. When the solder portion in the connection portion satisfies the preferred embodiments described above, conduction reliability can be further improved.

When the opposing portions of the first electrode and the second electrode are viewed in a direction perpendicular to the stacking direction of the first electrode, the connection portion, and the second electrode, the first It is preferable that 60% or more of the solder portion in the connection portion is disposed at the portion where the electrode and the second electrode face each other. When the opposing portions of the first electrode and the second electrode are viewed in a direction perpendicular to the stacking direction of the first electrode, the connection portion, and the second electrode, the first More preferably, 70% or more of the solder portion in the connection portion is disposed in a portion where the electrode and the second electrode face each other. When the opposing portions of the first electrode and the second electrode are viewed in a direction perpendicular to the stacking direction of the first electrode, the connection portion, and the second electrode, the first It is further preferable that 90% or more of the solder portion in the connection portion be disposed at a portion where the electrode and the second electrode face each other. When the opposing portions of the first electrode and the second electrode are viewed in a direction perpendicular to the stacking direction of the first electrode, the connection portion, and the second electrode, the first It is particularly preferable that 95% or more of the solder portion in the connection portion is disposed at the portion where the electrode and the second electrode face each other. When the opposing portions of the first electrode and the second electrode are viewed in a direction perpendicular to the stacking direction of the first electrode, the connection portion, and the second electrode, the first It is most preferable that 99% or more of the solder portion in the connecting portion is disposed at the portion where the electrode and the second electrode face each other. When the solder portion in the connection portion satisfies the preferred embodiments described above, conduction reliability can be further improved.

The first and second connection target members are not particularly limited. Specifically, the first and second connection target members include semiconductor chips, semiconductor packages, LED chips, LED packages, electronic components such as capacitors and diodes, resin films, printed circuit boards, flexible printed circuit boards, and flexible Examples include electronic components such as flat cables, rigid-flexible boards, circuit boards such as glass epoxy boards, and glass boards. It is preferable that the first and second connection target members are electronic components.

It is preferable that at least one of the first connection target member and the second connection target member is a resin film, a flexible printed circuit board, a flexible flat cable, or a rigid flexible circuit board. It is preferable that the second connection target member is a resin film, a flexible printed circuit board, a flexible flat cable, or a rigid flexible circuit board. Resin films, flexible printed circuit boards, flexible flat cables, and rigid-flexible circuit boards have the properties of being highly flexible and relatively lightweight. When a conductive film is used to connect such connection target members, solder particles tend to be difficult to collect on the electrodes. On the other hand, by using a conductive paste, even if a resin film, flexible printed circuit board, flexible flat cable, or rigid-flex board is used, the solder particles can be efficiently collected on the electrodes, ensuring continuity between the electrodes. You can fully enhance your sexuality. When using resin films, flexible printed circuit boards, flexible flat cables, or rigid-flex circuit boards, the reliability of conduction between electrodes can be improved by not applying pressure, compared to when using other connection objects such as semiconductor chips. The improvement effect can be obtained even more effectively.

Examples of the electrodes 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 member to be connected is a flexible printed circuit board, the electrode is preferably a gold electrode, a tin electrode, a silver electrode, or a copper electrode. When the member to be connected is a glass substrate, the electrode is preferably a copper electrode or a silver electrode. In addition, when the said electrode is an aluminum electrode, it may be an electrode formed only with aluminum, and the electrode may be an electrode in which an aluminum layer is laminated|stacked on the surface of a metal oxide layer. Examples of the material 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 elements include Sn, Al, and Ga.

In the connected structure according to the present invention, it is preferable that the first electrode and the second electrode are arranged in an area array or a peripheral. The effects of the present invention are even more effectively exhibited when the first electrode and the second electrode are arranged in an area array or peripherally. The above-mentioned area array is a structure in which electrodes are arranged in a grid pattern on the surface of the connection target member on which the electrodes are arranged. The above-mentioned peripheral refers to a structure in which electrodes are arranged on the outer periphery of a member to be connected. In the case of a structure in which the electrodes are arranged in a comb shape, the solder particles only need to aggregate along the direction perpendicular to the comb, whereas in the above area array or peripheral structure, the solder particles aggregate on the entire surface on the surface where the electrodes are arranged. It is necessary for the solder particles to coagulate uniformly. Therefore, in the conventional method, the amount of solder tends to be uneven, whereas in the method of the present invention, solder particles can be uniformly aggregated over the entire surface.

Hereinafter, the present invention will be specifically explained with reference to Examples and Comparative Examples. The invention is not limited only to the following examples.

Thermosetting component (thermosetting compound):
Phenol novolac type epoxy compound (“DEN431” manufactured by DOW)
Bisphenol F type epoxy compound (“DER354” manufactured by DOW)

Solder particles with flux:
Fluxed solder particles 1 (produced according to Synthesis Example 1 below)
Fluxed solder particles 2 (produced according to Synthesis Example 2 below)
Fluxed solder particles 3 (produced according to Synthesis Example 3 below)

(Synthesis example 1)
SnAgCu solder particles (“Sn96.5Ag3.0Cu0.5 ST-3” manufactured by Mitsui Kinzoku Co., Ltd., average particle diameter: 3.0 μm, melting point: 220°C, specific gravity: 7.4) and flux (“Sn96.5Ag3.0Cu0.5 ST-3” manufactured by Mitsui Kinzoku Co., Ltd., average particle diameter: 3.0 μm, melting point: 220°C, specific gravity: 7.4) Adipic acid benzylamine salt, solid at 25°C, average particle size: 10 μm, melting point: 180°C) was prepared. By immersing SnAgCu solder particles in a solution in which benzylamine adipate salt was dissolved, fluxed solder particles 1 comprising solder particles and flux X supported on the solder particles were obtained. The ratio (average particle diameter of flux X/average particle diameter of solder particles) in solder particles 1 with flux was 3.3.

(Synthesis example 2)
SnBi solder particles ("Sn42Bi58 ST-3" manufactured by Mitsui Kinzoku Co., Ltd., average particle diameter: 3.0 μm, melting point: 138 ° C., specific gravity: 8.6) and flux ("Adipate benzylamine salt" manufactured by Showa Chemical Industry Co., Ltd.) , solid at 25°C, average particle size: 10 μm, melting point: 180°C). By immersing SnBi solder particles in a solution in which benzylamine adipate salt was dissolved, solder particles 2 with flux comprising solder particles and flux X supported on the solder particles were obtained. The ratio (average particle diameter of flux X/average particle diameter of solder particles) in solder particles 2 with flux was 3.3.

(Synthesis example 3)
SnAgCu solder particles (“Sn96.5Ag3.0Cu0.5 ST-3” manufactured by Mitsui Kinzoku Co., Ltd., average particle size: 3.0 μm, melting point: 220°C, specific gravity: 7.4) and flux (“Glutaric acid” manufactured by Wako Co., Ltd.) ", solid at 25°C, average particle size: 10 μm, melting point: 98°C) was prepared. By immersing SnAgCu solder particles in a solution in which glutaric acid was dissolved, fluxed solder particles 3 including solder particles and flux X supported on the solder particles were obtained. The ratio (average particle diameter of flux X/average particle diameter of solder particles) in solder particles 3 with flux was 3.3.

Solder particles:
Solder particle 1 (SnAgCu solder particle, (Mitsui Kinzoku Co., Ltd. "Sn96.5Ag3.0Cu0.5 ST-3", average particle diameter: 3.0 μm, melting point: 220 ° C., specific gravity: 7.4)
Solder particles 2 (SnAgCu solder particles, "Sn96.5Ag3.0Cu0.5 DS10" manufactured by Mitsui Kinzoku, average particle diameter: 10.0 μm, melting point: 220 ° C., specific gravity: 7.4)

Flux (flux not supported by solder particles):
Adipic acid benzylamine salt (“Adipate benzylamine salt” manufactured by Showa Kagaku Kogyo Co., Ltd., solid at 25°C, average particle size: 10 μm, melting point: 180°C)
Oleic acid (Oleic acid manufactured by Fujifilm Wako Pure Chemical Industries, liquid at 25℃, boiling point: 223℃)

Other ingredients:
Glycerol (“Glycerol” manufactured by Nacalai Tesque, liquid at 25°C, number of hydroxyl groups: 3, boiling point: 290°C)
N-oleoylsarcosine (“N-oleoylsarcosine” manufactured by TCI, liquid at 25°C, number of hydroxyl groups: 1, boiling point: 197°C)
Boron trifluoride-monoethylamine complex (“Boron trifluoride-monoethylamine complex” manufactured by TCI, solid at 25°C, hygroscopic at 25°C and 50% RH, melting point: 85°C)

(Measurement of weight increase rate)
Regarding "Boron trifluoride-monoethylamine complex" manufactured by TCI, when left for 24 hours at 25°C and 50% RH, the weight of the boron trifluoride-monoethylamine complex after standing was compared to the trifluoride before standing. The weight increase rate with respect to the weight of the boron-monoethylamine complex was measured by the method described above. The weight increase rate of the boron trifluoride-monoethylamine complex was 1.0% to 2.0% by weight.

(Examples 1 to 8 and Comparative Examples 1 to 4)
(1) Preparation of conductive paste (anisotropic conductive paste) The components shown in Tables 1 to 3 below are mixed in the amounts shown in Tables 1 to 3 below to obtain a conductive paste (anisotropic conductive paste). Ta.

(2) Preparation of connection structure As the first connection target member, a glass epoxy substrate (material: FR- 4. Thickness: 0.6 mm) was prepared.

As the second connection target member, a flexible printed circuit board (material: polyimide, thickness: 0.1 mm) with copper electrodes (electrode length: 3 mm, electrode thickness: 12 μm) with L/S = 50 μm/50 μm on the surface is prepared. did.

A conductive paste (anisotropic conductive paste) immediately after preparation was applied to a thickness of 100 μm on the upper surface of the glass epoxy substrate to form a conductive paste (anisotropic conductive paste) layer. Next, a flexible printed circuit board was laminated on the upper surface of the conductive paste (anisotropic conductive paste) layer so that the electrodes faced each other. The weight of the flexible printed circuit board is added to the conductive paste (anisotropic conductive paste) layer. From this state, the conductive paste (anisotropic conductive paste) layer was heated so that the temperature reached the melting point of the solder particles 10 seconds after the start of temperature rise. Furthermore, 15 seconds after the start of temperature rise, the conductive paste (anisotropic conductive paste) layer is heated to a temperature of 250°C to harden the conductive paste (anisotropic conductive paste) layer, and the connected structure is formed. Obtained. No pressure was applied during heating.

(evaluation)
(1) Storage stability The viscosity (η25) at 25°C and 5 rpm of the above conductive paste immediately after preparation, and the viscosity (η25) of the above conductive paste after storing the above conductive paste immediately after preparation at 25°C and 50% RH for 24 hours. The viscosity (ηA) at 25° C. and 5 rpm was measured by the method described above, and the ratio (ηA/η25) was calculated. Storage stability was determined based on the following criteria.

[Criteria for storage stability]
○○: Ratio (ηA/η25) is 1.2 or less ○: Ratio (ηA/η25) is more than 1.2 and 1.5 or less ×: Ratio (ηA/η25) is more than 1.5

(2) Screen printing property The obtained conductive paste (anisotropic conductive paste) was screen printed on a glass slide using a metal mask with dimensions of 20 μm x 50 μm per opening and a thickness of 20 μm. Ta. For the 50 printed patterns, the printed surface immediately after printing was observed with a laser microscope, the volume of the conductive paste applied to the slide glass was calculated, and the opening of the metal mask was calculated based on the volume of the conductive paste applied to the slide glass. The ratio X (%) to the volume per part was calculated. Screen printability was evaluated based on the following criteria.

[Criteria for determining screen printability]
○○: Proportion X is 50% or more ○: Proportion X is 30% or more and less than 50% ×: Proportion X is less than 30%

(3) Accuracy of placement of solder particles In the obtained connected structure, the portion where the first electrode and the second electrode face each other was observed in the stacking direction of the first electrode, the connecting portion, and the second electrode. At the same time, the ratio Y of the area where the solder part in the connection part is arranged to 100% of the area of the opposing part of the first electrode and the second electrode was evaluated. The placement accuracy of solder particles was judged based on the following criteria.

[Criteria for determining solder particle placement accuracy]
○○: Proportion Y is 70% or more ○: Proportion Y is 50% or more and less than 70% ×: Proportion Y is less than 50%

The results are shown in Tables 1 to 3 below.

1... Connection structure 2... First connection target member 2a... First electrode 3... Second connection target member 3a... Second electrode 4... Connection part 4A... Solder part 4B... Cured material part

Claims (7)

Contains a thermosetting component and solder particles with flux,
The solder particles with flux include solder particles and a flux supported on the solder particles,
The average particle diameter of the solder particles is 5.0 μm or less,
A conductive paste, wherein the flux supported on the solder particles is a carboxylic acid or a carboxylate salt. The conductive paste according to claim 1, wherein the ratio of the average particle diameter of the flux supported on the solder particles to the average particle diameter of the solder particles is 0.001 or more and 10.0 or less. The conductive paste according to claim 1 or 2, wherein the flux supported on the solder particles is a carboxylic acid amine salt. The viscosity of the conductive paste at 25 °C and 5 rpm after storing the conductive paste immediately after production for 24 hours at 25 °C and 50% RH versus the viscosity at 25 °C and 5 rpm of the conductive paste immediately after production The conductive paste according to any one of claims 1 to 3, wherein the ratio is 1.5 or less. obtaining fluxed solder particles comprising solder particles and flux supported on the solder particles;
a step of mixing a thermosetting component and the fluxed solder particles to obtain a conductive paste,
The average particle diameter of the solder particles is 5.0 μm or less,
A method for producing a conductive paste, wherein the flux supported on the solder particles is a carboxylic acid or a carboxylate salt. The method for manufacturing a conductive paste according to claim 5, further comprising mixing flux in the step of obtaining the conductive paste. a first connection target member having a first electrode on its surface;
a second connection target member having a second electrode on its surface;
comprising a connection part connecting the first connection target member and the second connection target member,
The material of the connection part is the conductive paste according to any one of claims 1 to 4,
A connection structure in which the first electrode and the second electrode are electrically connected by a solder part in the connection part.

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