Conductive paste and connection structure

Abstract

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, a plurality of solder particles, and flux. The solder particles have an average particle size of 5.0 μm or less. The flux has a melting point of 200°C or higher. An absolute value of a difference between the melting point of the solder particles and the melting point of the flux is 50°C or lower.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a conductive paste containing solder particles, and also to a connection structure using the conductive paste. [Background technology]

[0002] Anisotropic conductive materials such as anisotropic conductive pastes and anisotropic conductive films are widely known, in which conductive particles are dispersed in a binder resin.

[0003] The anisotropic conductive material is used to obtain various connection structures. Examples of connections using the anisotropic conductive material include connections between a flexible printed circuit board and a glass substrate (FOG (film on glass)), between a semiconductor chip and a flexible printed circuit board (COF (chip on film)), between a semiconductor chip and a glass substrate (COG (chip on glass)), and between a flexible printed circuit board and a glass epoxy substrate (FOB (film on board)).

[0004] In recent years, in conductive materials containing conductive particles such as solder particles, the particle size of the conductive particles has been decreasing due to finer pitches in wiring and connectors in printed wiring boards and the like.

[0005] Patent Document 1 below discloses a conductive paste containing metal particles with an average particle size of 0.4 μm to 2.0 μm as a main component, in which the number of metal particles with a particle size of 0.2 μm or less is 5% or less out of the total number of the metal particles (100%). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 10-134637 Summary of the Invention [Problem to be solved by the invention]

[0007] When a conductive connection is made using a conductive paste containing solder particles, the upper electrodes are electrically connected to the lower electrodes, and the conductive connection is made. The solder particles are preferably disposed between the upper and lower electrodes, and are preferably not disposed between adjacent lateral electrodes. The adjacent lateral electrodes are preferably not electrically connected.

[0008] 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 equal to or higher than the melting point of the solder particles, the solder particles melt and the solder condenses between the electrodes, electrically connecting the upper and lower electrodes.

[0009] However, in conventional conductive pastes such as that in Patent Document 1, the particle diameter of the solder particles is small, which can deteriorate the storage stability (pot life) of the conductive paste.

[0010] In addition, when a connection structure is produced, after the conductive paste is placed on a connection target member such as a substrate by screen printing or the like, the conductive paste may be left for a certain period of time before being electrically connected. In the conventional conductive paste such as that in Patent Document 1, since it is not possible to enhance storage stability (pot life), for example, when the conductive paste is placed and left for a certain period of time, the conductive paste may thicken, inhibiting the aggregation of the solder particles, and making it impossible to efficiently place the solder particles between the upper and lower electrodes to be connected. As a result, the solder particles contained in the conductive paste may be placed in an area where no electrodes are formed, and the amount of solder particles placed between the upper and lower electrodes to be connected may decrease. This may result in a decrease in the reliability of conduction between the upper and lower electrodes to be connected, or a decrease in the reliability of insulation between adjacent lateral electrodes.

[0011] Furthermore, if the storage stability (pot life) of the conductive paste deteriorates, when screen printing is performed, the viscosity of the conductive paste during printing decreases, increasing the amount of screen transmission, which can cause bleeding, or the viscosity of the conductive paste during printing increases, causing the conductive paste to clog the mesh, resulting in smearing. With conventional conductive pastes, the deterioration of the storage stability (pot life) of the conductive paste can make it impossible to apply the conductive paste uniformly to a printed wiring board or the like.

[0012] An object of the present invention is to provide a conductive paste that can improve storage stability, improve screen printability, and enable efficient arrangement of solder particles on an electrode. Another object of the present invention is to provide a connection structure using the conductive paste. [Means for solving the problem]

[0013] According to a broad aspect of the present invention, there is provided a conductive paste comprising a thermosetting component, a plurality of solder particles, and a flux, wherein the average particle size of the solder particles is 5.0 μm or less, the melting point of the flux is 200° C. or more, and the absolute value of the difference between the melting point of the solder particles and the melting point of the flux is 50° C. or less.

[0014] In a specific aspect of the conductive paste according to the present invention, the flux is a carboxylate amine salt.

[0015] In a specific aspect of the conductive paste according to the present invention, the flux is a trimellitic acid dibenzylamine salt.

[0016] In a specific aspect of the conductive paste according to the present invention, the content of the flux is 10 parts by weight or more and 30 parts by weight or less with respect to 100 parts by weight of the solder particles.

[0017] In a specific aspect of the conductive paste according to the present invention, the ratio of the viscosity of the conductive paste at 25°C and 5 rpm after storing the conductive paste immediately after preparation under conditions of 25°C and 50% RH for 24 hours to the viscosity of the conductive paste immediately after preparation at 25°C and 5 rpm is 1.5 or less.

[0018] According to a broad aspect of the present invention, there is provided a connection structure comprising a first connection target member having a first electrode on its surface, a second connection target member having a second electrode on its surface, and a connection portion connecting the first connection target member and the second connection target member, wherein the material of the connection portion is the above-mentioned conductive paste, and the first electrode and the second electrode are electrically connected by a solder portion in the connection portion. Effect of the Invention

[0019] The conductive paste according to the present invention includes a thermosetting component, a plurality of solder particles, and a flux. In the conductive paste according to the present invention, the average particle size of the solder particles is 5.0 μm or less. In the conductive paste according to the present invention, the melting point of the flux is 200° C. or more. In the conductive paste according to the present invention, the absolute value of the difference between the melting point of the solder particles and the melting point of the flux is 50° C. or less. 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 the solder particles on the electrodes. [Brief description of the drawings]

[0020] [Figure 1] FIG. 1 is a cross-sectional view that illustrates a connection structure obtained by using a conductive paste according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] The present invention will be described in detail below.

[0022] (Conductive paste) The conductive paste according to the present invention includes a thermosetting component, a plurality of solder particles, and a flux. In the conductive paste according to the present invention, the average particle size of the solder particles is 5.0 μm or less. In the conductive paste according to the present invention, the melting point of the flux is 200° C. or more. In the conductive paste according to the present invention, the absolute value of the difference between the melting point of the solder particles and the melting point of the flux is 50° C. or less.

[0023] Since the conductive paste according to the present invention has the above-mentioned configuration, it is possible to improve storage stability, and therefore it is possible to suppress thickening of the conductive paste even if the conductive paste is left for a certain period of time after being placed. Also, since the conductive paste according to the present invention has the above-mentioned configuration, it is possible to improve screen printability and efficiently place solder particles on the electrodes.

[0024] In addition, in the conductive paste according to the present invention, when the electrodes are conductively connected, the multiple solder particles are likely to gather between the upper and lower opposing electrodes, and the multiple solder particles can be arranged on the electrodes (lines). In addition, some of the multiple solder particles are unlikely to be arranged between the horizontal electrodes that should not be connected, and the amount of solder particles arranged between the horizontal electrodes that should not be connected can be significantly reduced. As a result, in the present invention, the conductive reliability between the upper and lower electrodes that should be connected can be effectively increased, and the insulation reliability between adjacent horizontal electrodes that should not be connected can be effectively increased.

[0025] Furthermore, the present invention can prevent misalignment between electrodes. In the present invention, when a second connection target member is superimposed on a first connection target member having a conductive paste disposed on its upper surface, even if the electrodes of the first connection target member and the second connection target member are misaligned, the misalignment can be corrected to connect the electrodes together (self-alignment effect).

[0026] In order to more effectively exert the effects of the present invention, the viscosity (η25) of the conductive paste immediately after preparation at 25°C and 5 rpm is preferably 30 Pa s or more, more preferably 50 Pa s or more, and preferably 250 Pa s or less, more preferably 200 Pa s or less. The viscosity (η25) can be appropriately adjusted by the types and amounts of the blended components.

[0027] The viscosity (η25) can be measured, for example, using an E-type viscometer under conditions of 25° C. and 5 rpm. Examples of the E-type viscometer include “TVE22L” manufactured by Toki Sangyo Co., Ltd.

[0028] The conductive paste immediately after preparation has been stored at 25°C and 50% RH for 24 hours and then has a viscosity (ηA) at 25°C and 5 rpm of preferably 50 Pa·s or more, more preferably 100 Pa·s or more, and preferably 400 Pa·s or less, more preferably 300 Pa·s or less. When the viscosity (ηA) is equal to or more than the lower limit and equal to or less than the upper limit, the effects of the present invention can be more effectively exhibited. The viscosity (ηA) can be appropriately adjusted by the types and amounts of the components.

[0029] The viscosity (ηA) can be measured, for example, using an E-type viscometer under conditions of 25° C. and 5 rpm. Examples of the E-type viscometer include “TVE22L” manufactured by Toki Sangyo Co., Ltd.

[0030] The ratio of the viscosity (ηA) of the conductive paste at 25°C and 5 rpm after storing the conductive paste immediately after preparation under conditions of 25°C and 50% RH for 24 hours to the viscosity (η25) of the conductive paste immediately after preparation at 25°C and 5 rpm 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, and particularly preferably 1.2 or less. When the ratio (ηA / η25) is equal to or more than the lower limit and equal to or less than the upper limit, the effect of the present invention can be more effectively exhibited.

[0031] 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 Pa·s or less, more preferably 30 Pa·s or less, and even more preferably 10 Pa·s or less. When the viscosity (ηmp) is equal to or less than the upper limit, the solder particles can be arranged on the electrodes more efficiently. When the viscosity (ηmp) is equal to or more than the lower limit, voids in the connection portion can be suppressed, and the conductive paste can be suppressed from spilling out of the connection portion.

[0032] The above viscosity (ηmp) can be measured using STRESSTECH (manufactured by REOLOGICA) or the like under the conditions of strain control 1 rad, frequency 1 Hz, heating rate 20°C / min, and measurement temperature range 25°C to 200°C (however, if the melting point of the solder particles exceeds 200°C, the upper temperature limit is set to 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.

[0033] The conductive paste is preferably an anisotropic conductive paste. The conductive paste is suitably used for electrical connection of electrodes. The conductive paste is preferably a circuit connection paste.

[0034] 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.

[0035] Each component contained in the conductive paste will be described below. In this specification, "(meth)acrylic" means either or both of "acrylic" and "methacrylic".

[0036] (thermosetting component) The conductive paste according to the present invention includes a thermosetting component. The conductive paste preferably includes a thermosetting compound as the thermosetting component. The conductive paste may or may not include a thermosetting agent. The conductive paste may include a thermosetting compound and a thermosetting agent as the thermosetting component. When the conductive paste includes a thermosetting compound and a thermosetting agent, the conductive paste can be cured even better.

[0037] (Thermosetting component: thermosetting compound) The 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 is preferably an epoxy compound or an episulfide compound, and more preferably an epoxy compound. 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, it is preferable that the thermosetting compound contains an epoxy compound. Only one type of the thermosetting compound may be used, or two or more types may be used in combination.

[0038] The epoxy compound is a compound having at least one epoxy group. Examples of the epoxy compound include bisphenol A type epoxy compounds, bisphenol F type epoxy compounds, bisphenol S type epoxy compounds, phenol novolac type epoxy compounds, biphenyl type epoxy compounds, biphenyl novolac type epoxy compounds, biphenol type epoxy compounds, naphthalene type epoxy compounds, fluorene type epoxy compounds, phenol aralkyl type epoxy compounds, naphthol aralkyl type epoxy compounds, dicyclopentadiene type epoxy compounds, anthracene type epoxy compounds, epoxy compounds having an adamantane skeleton, epoxy compounds having a tricyclodecane skeleton, naphthylene ether type epoxy compounds, and epoxy compounds having a triazine nucleus in the skeleton. The epoxy compounds may be used alone or in combination of two or more.

[0039] 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, the viscosity is high at the stage of bonding the connection target members, and when acceleration is applied due to an impact from transportation, etc., it is possible to suppress misalignment between the first connection target member and the second connection target member. Furthermore, the viscosity of the conductive paste can be significantly reduced by the heat during curing, and the aggregation of the solder particles can be efficiently promoted.

[0040] From the viewpoint of improving connection reliability, the epoxy compound preferably contains a phenol novolac type epoxy compound or a bisphenol F type epoxy compound.

[0041] In 100% by weight of the conductive paste, the content of the thermosetting component 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 85% by weight or less, even more preferably 80% by weight or less, and particularly preferably 75% by weight or less. When the content of the thermosetting component is equal to or more than the lower limit and equal to or less than the upper limit, the solder particles can be arranged on the electrodes more efficiently, the insulation reliability between the electrodes can be further improved, and the conduction reliability between the electrodes can be further improved. From the viewpoint of effectively improving the impact resistance, the content of the thermosetting component is preferably large.

[0042] In 100% by weight of the conductive paste, the content of the thermosetting compound 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 85% by weight or less, even more preferably 80% by weight or less, and particularly preferably 75% by weight or less. When the content of the thermosetting compound is equal to or more than the lower limit and equal to or less than the upper limit, the solder particles can be arranged on the electrodes more efficiently, the insulation reliability between the electrodes can be further improved, and the conduction reliability between the electrodes can be further improved. From the viewpoint of effectively improving the impact resistance, the content of the thermosetting compound is preferably large.

[0043] In 100% by weight of the conductive paste, the content of the epoxy compound 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 85% by weight or less, even more preferably 80% by weight or less, and particularly preferably 75% by weight or less. When the content of the epoxy compound is equal to or more than the lower limit and equal to or less than the upper limit, the solder particles can be arranged on the electrodes more efficiently, the insulation reliability between the electrodes can be further improved, and the conduction reliability between the electrodes can be further improved. From the viewpoint of effectively improving the impact resistance, the content of the epoxy compound is preferably high.

[0044] (Thermosetting component: thermosetting agent) The heat curing agent is not particularly limited. The heat curing agent thermally cures the heat curing compound. Examples of the heat curing agent include imidazole curing agents, amine curing agents, phenolic curing agents, thiol curing agents such as polythiol curing agents, acid anhydride curing agents, thermal cationic initiators (thermal cationic curing agents), and thermal radical generators. The heat curing agent may be used alone or in combination of two or more.

[0045] From the viewpoint of enabling the conductive paste to be cured more quickly at low temperatures, the heat curing agent is preferably an imidazole curing agent, a thiol curing agent, or an amine curing agent. Also, from the viewpoint of improving storage stability when the thermosetting compound and the heat curing agent are mixed, the heat curing agent is preferably a latent curing agent. The latent curing agent is preferably a latent imidazole curing agent, a latent thiol curing agent, or a latent amine curing agent. The heat curing agent may be coated with a polymeric substance such as a polyurethane resin or a polyester resin.

[0046] The 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 adduct, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxyimidazole, and 2-phenyl-4-methyl-5-hydroxyimidazole. Examples of imidazole compounds include imidazole compounds in which the hydrogen at the 5-position of 1H-imidazole is substituted with a hydroxymethyl group and the hydrogen at the 2-position is substituted with a phenyl group or a toluyl group, such as 2-phenyl-4-benzyl-5-hydroxymethylimidazole, 2-para-toluyl-4-methyl-5-hydroxymethylimidazole, 2-meta-toluyl-4-methyl-5-hydroxymethylimidazole, 2-meta-toluyl-4,5-dihydroxymethylimidazole, and 2-para-toluyl-4,5-dihydroxymethylimidazole.

[0047] The thiol curing agent is not particularly limited, and examples of the thiol curing agent include trimethylolpropane tris-3-mercaptopropionate, pentaerythritol tetrakis-3-mercaptopropionate, and dipentaerythritol hexa-3-mercaptopropionate.

[0048] The amine curing agent is not particularly limited, and examples of the amine curing agent include hexamethylenediamine, octamethylenediamine, decamethylenediamine, 3,9-bis(3-aminopropyl)-2,4,8,10-tetraspiro[5.5]undecane, bis(4-aminocyclohexyl)methane, metaphenylenediamine, and diaminodiphenylsulfone.

[0049] The acid anhydride curing agent is not particularly limited. The acid anhydride curing agent can be widely used as an acid anhydride used as a curing agent for thermosetting compounds such as epoxy compounds. The acid anhydride curing agent can be phthalic anhydride, tetrahydrophthalic anhydride, trialkyltetrahydrophthalic anhydride, hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylbutenyltetrahydrophthalic anhydride, anhydrides of phthalic acid derivatives, maleic anhydride, nadic anhydride, methylnadic anhydride, glutaric anhydride, succinic anhydride, glycerin bistrimellitic anhydride monoacetate, and ethylene glycol bistrimellitic anhydride, bifunctional acid anhydride curing agents such as trimellitic anhydride, and tetrafunctional or more acid anhydride curing agents such as pyromellitic anhydride, benzophenonetetracarboxylic anhydride, methylcyclohexenetetracarboxylic anhydride, and polyazelaic anhydride.

[0050] The thermal cationic initiator is not particularly limited. The thermal cationic initiator may include an iodonium cationic curing agent, an oxonium cationic curing agent, and a sulfonium cationic curing agent. The iodonium cationic curing agent may include bis(4-tert-butylphenyl)iodonium hexafluorophosphate. The oxonium cationic curing agent may include trimethyloxonium tetrafluoroborate. The sulfonium cationic curing agent may include tri-p-tolylsulfonium hexafluorophosphate.

[0051] The thermal radical generator is not particularly limited. Examples of the thermal radical generator include azo compounds and organic peroxides. Examples of the azo compounds include azobisisobutyronitrile (AIBN). Examples of the organic peroxides include di-tert-butyl peroxide and methyl ethyl ketone peroxide.

[0052] The reaction initiation temperature of the heat curing agent is preferably 50° C. or higher, more preferably 60° C. or higher, even more preferably 70° C. or higher, and is preferably 250° C. or lower, more preferably 200° C. or lower, even more preferably 175° C. or lower, and particularly preferably 150° C. or lower. When the reaction initiation temperature of the heat curing agent is equal to or higher than the lower limit and equal to or lower than the upper limit, the solder particles are more efficiently arranged on the electrodes. The reaction initiation temperature of the heat curing agent is particularly preferably 70° C. or higher and 150° C. or lower.

[0053] The reaction initiation temperature of the heat curing agent means the temperature at which the rise of an exothermic peak begins in differential scanning calorimetry (DSC).

[0054] The content of the heat curing agent is not particularly limited. The content of the heat curing 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 100 parts by weight or less, and even more preferably 75 parts by weight or less, relative to 100 parts by weight of the heat curing compound. When the content of the heat curing agent is equal to or more than the lower limit, it is easy to sufficiently cure the conductive paste. When the content of the heat curing agent is equal to or less than the upper limit, the excess heat curing agent that is not involved in the curing is unlikely to remain after curing, and the heat resistance of the cured product is further increased.

[0055] (solder particles) The solder particles are formed of solder at both the center and the outer surface. The solder particles are particles in which both the center and the outer surface are solder. When conductive particles having a base particle formed of a material other than solder and a solder portion arranged on the surface of the base particle are used instead of the solder particles, the conductive particles are less likely to gather on the electrode. In addition, the conductive particles have low solder bonding between the conductive particles, so that 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 also tends to be low.

[0056] 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, even more preferably 4.0 μm or less. When the average particle diameter of the solder particles is equal to or greater than the lower limit and equal to or less than the upper limit, the solder particles can be arranged on the electrodes more efficiently. When the average particle diameter of the solder particles is equal to or less than the upper limit, the screen printability on the fine-pitched substrate 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-mentioned effects of the present invention are exerted. That is, in the conductive paste according to the present invention, the smaller the average particle diameter of the solder particles, the more effectively the solder particles can be arranged on the electrodes, the more effectively the reliability of the conduction between the upper and lower electrodes that should be connected can be improved, and the insulation reliability between adjacent lateral electrodes that should not be connected can be effectively improved.

[0057] The average particle size of the solder particles is preferably a number average particle size. The average particle size of the solder particles is obtained, for example, by observing 50 arbitrary solder particles with an electron microscope or an optical microscope and calculating the average particle size of each solder particle, or by performing laser diffraction particle size distribution measurement. In the observation with an electron microscope or an optical microscope, the particle size of each solder particle is obtained as a particle size of a circle equivalent diameter. In the observation with an electron microscope or an optical microscope, the average particle size of 50 arbitrary solder particles with a circle equivalent diameter is almost equal to the average particle size of a sphere equivalent diameter. In the laser diffraction particle size distribution measurement, the particle size of each solder particle is obtained as a particle size of a sphere equivalent diameter. The average particle size of the solder particles is preferably calculated by laser diffraction particle size distribution measurement.

[0058] 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 is preferably 40% or less, more preferably 30% or less. When the coefficient of variation of the particle diameter of the solder particles is equal to or more than the lower limit and equal to or less than the upper limit, the solder particles can be arranged on the electrode more efficiently. However, the CV value of the particle diameter of the solder particles may be less than 5%.

[0059] The coefficient of variation (CV value) can be measured as follows.

[0060] CV value (%) = (ρ / Dn) × 100 ρ: Standard deviation of solder particle diameter Dn: Average particle size of solder particles

[0061] The shape of the solder particles is not particularly limited, and may be spherical, may be a shape other than spherical, or may be flat or the like.

[0062] From the viewpoint of more efficiently disposing the solder particles on the electrodes, the specific gravity of the solder particles is preferably 4 or more, more preferably 5 or more, and further preferably 6 or more.

[0063] The specific gravity of the solder particles is determined, for example, by using "AccuPic II 1340" manufactured by Shimadzu Corporation.

[0064] The solder is preferably a metal having a melting point of 450°C or less (low melting point metal). The solder particles are preferably metal particles having a melting point of 450°C or less (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 less. The melting point of the low melting point metal is preferably 300°C or less, more preferably 260°C or less. The solder is preferably a low melting point solder having a melting point of less than 250°C.

[0065] 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 lower, even more preferably 300°C or lower.

[0066] The melting point of the solder particles can be determined by differential scanning calorimetry (DSC), such as the "EXSTAR DSC7020" manufactured by SII Corporation.

[0067] The solder particles preferably contain tin. The tin content of the solder particles is preferably 30% by weight or more, more preferably 40% by weight or more, even more preferably 70% by weight or more, and particularly preferably 90% by weight or more, based on 100% by weight of the metal contained in the solder particles. When the tin content in the solder particles is equal to or greater than the lower limit, the electrical continuity reliability and connection reliability between the solder portion and the electrode are further increased.

[0068] The tin content can be measured using a high-frequency inductively coupled plasma optical emission spectrometer (e.g., "ICP-AES" manufactured by Horiba, Ltd.) and a fluorescent X-ray analyzer (e.g., "EDX-800HS" manufactured by Shimadzu Corporation).

[0069] By using the solder particles, the solder melts and bonds to the electrodes, and the solder portion conducts electricity between the electrodes. For example, the solder portion and the electrodes are easily in surface contact rather than point contact, so that the connection resistance is reduced. In addition, the use of the solder particles increases the bonding strength between the solder portion and the electrodes, so that the solder portion and the electrodes are less likely to peel off, and the reliability of the electrical continuity and the reliability of the connection are further improved.

[0070] 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. The alloy may be tin-silver alloy, tin-copper alloy, tin-silver-copper alloy, tin-bismuth alloy, tin-zinc alloy, tin-indium alloy, and tin-antimony alloy. Since the low melting point metal has excellent wettability with respect to the electrode, it is preferable that the low melting point metal is tin, tin-silver alloy, tin-silver-copper alloy, tin-bismuth alloy, tin-indium alloy, or tin-antimony alloy, and more preferably tin-silver-copper alloy, tin-bismuth alloy, tin-indium alloy, or tin-antimony alloy.

[0071] In order to further increase the bonding strength between the solder part and the electrode, the solder particles may contain metals such as nickel, copper, antimony, aluminum, zinc, iron, gold, titanium, phosphorus, germanium, tellurium, cobalt, bismuth, manganese, chromium, molybdenum, and palladium. In order to further increase the bonding strength between the solder part and the electrode, the solder particles preferably contain nickel, copper, antimony, aluminum, or zinc. In order to further increase the bonding strength between the solder part and the electrode, the content of these metals in the solder particles to increase the bonding strength is preferably 0.0001% by weight or more, and preferably 1% by weight or less, based on 100% by weight of the metal contained in the solder particles.

[0072] In the conductive paste (100% by weight), the content of the solder particles is preferably 50% by weight or more, more preferably 55% by weight or more, even more preferably 60% by weight or more, particularly preferably 65% ​​by weight or more, and most preferably 70% by weight or more. In the conductive paste (100% by weight), the content of the solder particles is preferably 90% by weight or less, more preferably 85% by weight or less, even more preferably 80% by weight or less, and particularly preferably 75% by weight or less. When the content of the solder particles is equal to or more than the lower limit and equal to or less than the upper limit, the solder particles can be arranged on the electrodes more efficiently, it is easy to arrange a large amount of solder between the electrodes, and the electrical reliability is further improved. From the viewpoint of further improving the electrical reliability, the content of the solder particles is preferably large.

[0073] (Flux) In the conductive paste, the melting point (activation temperature) of the flux is 200° C. or higher. The melting point (activation temperature) of the flux is preferably 201° C. or higher, more preferably 210° C. or higher, and even more preferably 220° C. or higher, and is preferably 300° C. or lower, more preferably 280° C. or lower, and even more preferably 260° C. or lower. When the melting point of the flux is equal to or higher than the lower limit, the storage stability can be further improved. When the melting point of the flux is equal to or lower than the upper limit, the connection reliability can be further improved.

[0074] The melting point of the flux may be the same as or different from the melting point of the solder particles. The melting point of the flux may be higher or lower than the melting point of the solder particles. From the viewpoint of further improving storage stability, the melting point of the flux is preferably higher than the melting point of the solder particles.

[0075] The absolute value of the difference between the melting point of the solder particles and the melting point of the flux is 50°C or less. The absolute value of the difference between the melting point of the solder particles and the melting point of the flux is preferably 49°C or less, more preferably 45°C or less, and even more preferably 40°C or less. When the absolute value of the difference between the melting point of the solder particles and the melting point of the flux is equal to or less than the upper limit, the connection reliability can be further improved. The lower limit of the absolute value of the difference between the melting point of the solder particles and the melting point of the flux is not particularly limited. The absolute value of the difference between the melting point of the solder particles and the melting point of the flux may be 0°C, 3°C or more, 5°C or more, or 10°C or more.

[0076] The melting point of the flux can be determined by differential scanning calorimetry (DSC). An example of a DSC device is "EXSTAR DSC7020" manufactured by SII Corporation.

[0077] Examples of the flux include zinc chloride, a mixture of zinc chloride and an inorganic halide, a mixture of zinc chloride and an inorganic acid, a molten salt, an organic phosphorus compound, an organic halide, hydrazine, an amine compound, an organic acid, a salt of an organic acid, and rosin. Only one type of the flux may be used, or two or more types may be used in combination.

[0078] The molten salt may, for example, be ammonium chloride.

[0079] Examples of the organic phosphorus compound include organic phosphonium salts, organic phosphoric acids, organic phosphoric acid esters, organic phosphonic acids, organic phosphonic acid esters, organic phosphinic acids, and organic phosphinic acid esters.

[0080] Examples of the amine compound include cyclohexylamine, dicyclohexylamine, benzylamine, benzhydrylamine, imidazole, benzimidazole, phenylimidazole, carboxybenzimidazole, benzotriazole, and carboxybenzotriazole.

[0081] The rosin is a rosin containing abietic acid as a main component, and examples of the rosin include abietic acid and acrylic modified rosin.

[0082] The salt of the organic acid may be a neutralization reaction product (salt) of an organic acid and a basic compound. The salt of the organic acid is preferably a salt produced by a neutralization reaction between an organic acid and a basic compound. The conditions for the neutralization reaction are preferably a heating temperature of 25°C to 150°C and a heating time of 5 minutes to 30 minutes. The organic acid preferably has an effect of cleaning the surface of a metal, and the basic compound preferably has an effect of neutralizing the organic acid.

[0083] The organic acid is preferably an organic compound (carboxylic acid) having a carboxyl group. Examples of the organic acid 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 acids include cyclohexyl carboxylic acid and 1,4-cyclohexyl dicarboxylic acid. Examples of the aromatic carboxylic acids include isophthalic acid, terephthalic acid, trimellitic acid, and ethylenediaminetetraacetic acid. From the viewpoint of more efficiently disposing the solder particles on the electrodes, improving the insulation reliability, and more effectively improving the conduction reliability, the organic acid is preferably trimellitic acid, glutaric acid, cyclohexyl carboxylic acid, or adipic acid, and more preferably trimellitic acid.

[0084] The basic compound is preferably an organic compound (amine compound) having an amino group. Examples of the basic compound include diethanolamine, triethanolamine, methyldiethanolamine, ethyldiethanolamine, cyclohexylamine, dicyclohexylamine, benzylamine, benzhydrylamine, 2-methylbenzylamine, 3-methylbenzylamine, 4-tert-butylbenzylamine, N-methylbenzylamine, N-ethylbenzylamine, N-phenylbenzylamine, N-tert-butylbenzylamine, N-isopropylbenzylamine, N,N-dimethylbenzylamine, imidazole compounds, and triazole compounds. From the viewpoint of more efficiently disposing the solder particles on the electrode, improving the insulation reliability, and more effectively improving the conduction reliability, the basic compound is preferably benzylamine.

[0085] From the viewpoint of more efficiently disposing the solder particles on the electrodes, the flux is preferably a salt of an organic acid, more preferably an amine carboxylate, such as dibenzylamine trimellitate (melting point: 260°C).

[0086] From the viewpoint of further improving the storage stability, it is particularly preferable that the flux is a trimellitic acid dibenzylamine salt.

[0087] The flux may be dispersed in the conductive paste, or may be attached to the surface of the solder particles.

[0088] The shape of the flux is not particularly limited. The flux may be spherical, may be a shape other than spherical, or may be flat or the like. From the viewpoint of further improving screen printability, the flux is preferably spherical.

[0089] The particle size of the flux is preferably 0.1 μm or more, more preferably 0.5 μm or more, and even more preferably 1.0 μm or more, and is preferably 30 μm or less, more preferably 25 μm or less, and even more preferably 20 μm or less.

[0090] The particle size of the flux is preferably an average particle size, and more preferably a number average particle size. The average particle size of the flux is obtained, for example, by observing 50 arbitrary fluxes with an electron microscope or an optical microscope, and calculating the average particle size of each flux, or by performing laser diffraction particle size distribution measurement. In the observation with an electron microscope or an optical microscope, the particle size of each flux is obtained as a particle size of a circle equivalent diameter. In the observation with an electron microscope or an optical microscope, the average particle size of each arbitrary 50 fluxes with a circle equivalent diameter is almost equal to the average particle size of each sphere equivalent diameter. In the laser diffraction particle size distribution measurement, the particle size of each flux is obtained as a particle size of a sphere equivalent diameter. The average particle size of the flux is preferably calculated by laser diffraction particle size distribution measurement.

[0091] The ratio of the average particle size of the flux to the average particle size of the solder particles (average particle size of flux / average particle size of solder particles) is preferably 0.01 or more, more preferably 0.1 or more, even more preferably 0.2 or more, and is preferably 15.0 or less, more preferably 10.0 or less, and even more preferably 5.0 or less. When the ratio (average particle size of flux / average particle size of solder particles) is equal to or more than the lower limit and equal to or less than the upper limit, the flux can be effectively brought into contact with the solder particles, and the flux performance during heating can be further improved.

[0092] In order to more effectively exert the effects of the present invention, it is preferable that the flux does not have water absorption properties, and it is more preferable that the flux does not have hygroscopic properties.

[0093] The content of the flux in 100% by weight of the conductive paste is preferably 1% by weight or more, more preferably 5% by weight or more, and is preferably 30% by weight or less, more preferably 25% by weight or less. When the content of the flux is equal to or more than the lower limit and equal to or less than the upper limit, it becomes more difficult for an oxide film to be formed on the surfaces of the solder particles and the electrodes, and further, the oxide film formed on the surfaces of the solder particles and the electrodes can be removed more effectively.

[0094] The content of the flux is preferably 1 part by weight or more, more preferably 5 parts by weight or more, and preferably 30 parts by weight or less, more preferably 25 parts by weight or less, relative to 100 parts by weight of the thermosetting component. When the content of the flux is equal to or more than the lower limit and equal to or less than the upper limit, it becomes even more difficult for an oxide film to be formed on the surfaces of the solder particles and the electrodes, and further, the oxide film formed on the surfaces of the solder particles and the electrodes can be removed more effectively.

[0095] The content of the flux is preferably 1 part by weight or more, more preferably 5 parts by weight or more, and even more preferably 10 parts by weight or more, and is preferably 30 parts by weight or less, and more preferably 25 parts by weight or less, relative to 100 parts by weight of the solder particles. When the content of the flux is equal to or more than the lower limit and equal to or less than the upper limit, it becomes even more difficult for an oxide film to be formed on the surfaces of the solder particles and the electrodes, and further, the oxide film formed on the surfaces of the solder particles and the electrodes can be more effectively removed.

[0096] (Other ingredients) The conductive paste may contain various additives, as necessary, such as a thixotropic agent, a filler, an extender, a softener, a plasticizer, a leveling agent, a polymerization catalyst, a curing catalyst, a colorant, an antioxidant, a heat stabilizer, a light stabilizer, an ultraviolet absorber, a lubricant, an antistatic agent, and a flame retardant.

[0097] From the viewpoint of favorably supporting the flux performance and more efficiently disposing the solder particles on the electrode, the conductive paste preferably contains a thixotropic agent. The thixotropic agent may be used alone or in combination of two or more kinds.

[0098] In the conductive paste (100% by weight), the content of the thixotropic agent is preferably 0.005% by weight or more, more preferably 0.01% by weight or more, and even more preferably 0.05% by weight or more, and is preferably 2% by weight or less, more preferably 1% by weight or less, and even more preferably 0.5% by weight or less. When the content of the thixotropic agent is equal to or more than the lower limit and equal to or less than the upper limit, the flux performance is favorably supported, and the solder particles can be arranged on the electrodes more efficiently.

[0099] 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, and is preferably 2 parts by weight or less, more preferably 1 part by weight or less, and even more preferably 0.7 parts by weight or less, relative to 100 parts by weight of the solder particles. When the content of the thixotropic agent is equal to or more than the lower limit and equal to or less than the upper limit, the flux performance is favorably supported, and the solder particles can be arranged on the electrodes more efficiently.

[0100] 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, more preferably 3 parts by weight or less, relative to 100 parts by weight of the thermosetting component. When the content of the thixotropic agent is equal to or more than the lower limit and equal to or less than the upper limit, the flux performance is favorably supported, and the solder particles can be more efficiently arranged on the electrodes.

[0101] 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, more preferably 3 parts by weight or less, based on 100 parts by weight of the thermosetting compound. When the content of the thixotropic agent is equal to or more than the lower limit and equal to or less than the upper limit, the flux performance is favorably supported, and the solder particles can be more efficiently arranged on the electrodes.

[0102] The thixotropic agent is preferably (A) a thixotropic agent that is liquid at 25° C. and has a hydroxyl group, or (B) a thixotropic agent that is solid at 25° C. and exhibits a weight increase rate of 0.2% by weight or more when the thixotropic agent is left for 24 hours at 25° C. and 50% RH. When the thixotropic agent is in the above preferred embodiment, it can favorably support the flux performance and more efficiently arrange the solder particles on the electrodes.

[0103] Weight increase rate (weight%) = (W2-W1) x 100 / W1 W1: Weight of the thixotropic agent before standing W2: Weight of the thixotropic agent after standing

[0104] The thixotropic agent may be (A) a thixotropic agent that is liquid at 25° C. and has a hydroxyl group (hereinafter, may be referred to as “thixotropic agent A”). The thixotropic agent may be (B) a thixotropic agent that is solid at 25° C. and has a weight increase rate of 0.2% by weight or more (hereinafter, may be referred to as “thixotropic agent B”). The thixotropic agent is preferably the thixotropic agent A or the thixotropic agent B.

[0105] The thixotropic agent A is liquid at 25° C. and has a hydroxyl group (—OH group).

[0106] The thixotropic agent A is liquid at 25° C. Specifically, the thixotropic agent A (thixotropic agent A alone) is liquid at 25° C. when not mixed with the thermosetting component, the plurality of solder particles, and the flux.

[0107] In the above conductive paste, the thixotropic agent A is preferably in a liquid state in the conductive paste at 25° C. In the above conductive paste, the thixotropic agent A is preferably present in a liquid state in the conductive paste at 25° C.

[0108] 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 hydroxyl groups, three or more hydroxyl groups, or four or more hydroxyl groups. 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 the volatilization of the conductive paste and further improving the screen printability, the thixotropic agent A preferably has two or more hydroxyl groups, and more preferably has three or more hydroxyl groups. From the viewpoint of preventing the volatilization of the conductive paste and further improving the 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.

[0109] Examples of the thixotropic agent A include methanol, ethanol, propanol, N-oleoyl sarcosine, propylene glycol, propanediol, diethylene glycol, glycerol (glycerin), trimethylolpropane, 1,2,4-butanetriol, diglycerin, and polyglycerin.

[0110] From the viewpoint of preventing volatilization of the conductive paste and further improving screen printability, the thixotropic agent A is preferably glycerol (glycerin), N-oleoyl sarcosine, or 1,2,4-butanetriol, and more preferably glycerol (glycerin).

[0111] The thixotropic agent B is solid at 25° C., and when the thixotropic agent is left to stand at 25° C. and 50% RH for 24 hours, the following weight increase rate is 0.2% by weight or more.

[0112] Weight increase rate (weight%) = (W2-W1) x 100 / W1 W1: Weight of the thixotropic agent before standing W2: Weight of the thixotropic agent after standing

[0113] The thixotropic agent B is a solid at 25° C. Specifically, the thixotropic agent B (thixotropic agent B alone) is a solid at 25° C. when not mixed with the thermosetting component, the plurality of solder particles, and the flux.

[0114] In the above conductive paste, the thixotropic agent B is preferably in a solid state in the conductive paste at 25° C. In the above conductive paste, the thixotropic agent B is preferably present in a solid state in the conductive paste at 25° C.

[0115] Whether or not the above thixotropic agent B (thixotropic agent B alone) is solid at 25°C can be determined as follows. In this specification, with respect to thixotropic agent B that is not liquid at 25°C, thixotropic agent B that maintains its shape when thixotropic agent B alone is left to stand for 5 minutes at 25°C and 50% RH is defined as thixotropic agent B that is solid at 25°C. Furthermore, thixotropic agent B that does not maintain its shape when thixotropic agent B alone is left 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 that is semisolid at 25°C is not included in thixotropic agent B that is solid at 25°C.

[0116] Whether or not the thixotropic agent B is solid in the conductive paste at 25°C can be determined as follows. In this specification, with respect to the thixotropic agent B that is not liquid at 25°C, the thixotropic agent B that maintains its shape when the conductive paste containing the thixotropic agent B is left to stand for 5 minutes at 25°C and 50% RH is defined as the thixotropic agent B that is solid at 25°C. In addition, the thixotropic agent B that does not maintain its shape when the conductive paste containing the thixotropic agent B is left to stand for 5 minutes at 25°C and 50% RH is defined as the thixotropic agent B that is semi-solid at 25°C. The thixotropic agent B that is semi-solid at 25°C is not included in the thixotropic agent B that is solid at 25°C.

[0117] The weight of the thixotropic agent B increases when it is left at 25° C. and 50% RH for 24 hours. When the thixotropic agent B is left at 25° C. and 50% RH for 24 hours, the weight of the thixotropic agent B after being left is greater than the weight of the thixotropic agent B before being left.

[0118] From the viewpoint of favorably supporting the flux performance and more efficiently disposing the solder particles on the electrode, the thixotropic agent B is preferably water-absorbent or hygroscopic, and more preferably hygroscopic. From the viewpoint of favorably supporting the flux performance and more efficiently disposing the solder particles on the electrode, the thixotropic agent B is even more preferably hygroscopic at 25° C. and 50% RH.

[0119] 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 8% by weight or less, and even more preferably 5% by weight or less. When the weight increase rate of the thixotropic agent B is equal to or greater than the lower limit, the flux performance is favorably supported, and the solder particles can be arranged on the electrode more efficiently. When the weight increase rate of the thixotropic agent B is equal to or less than the upper limit, the screen printability can be further improved. From the viewpoint of favorably supporting the flux performance and more efficiently arranging the solder particles on the electrode, it is particularly preferable that the thixotropic agent B is a thixotropic agent that is solid at 25° C. and has a weight increase rate of 1% by weight or more.

[0120] The weight increase rate of the thixotropic agent B can be measured by the following method: 10 g (W1) of thixotropic agent B is taken out of the desiccator at 25° C. and 0% RH, and left at 25° C. and 50% RH for 24 hours, and the weight (W2) of the thixotropic agent B after leaving it is measured.

[0121] Examples of the thixotropic agent B include boron trifluoride-monoethylamine complex, pentaerythritol, sorbitol, mannitol, sorbitan, dipentaerythritol, sucrose, glucose, mannose, fructose, and methyl glucoside.

[0122] From the viewpoint of more efficiently disposing the solder particles on the electrode, the thixotropic agent B is preferably a boron trifluoride-monoethylamine complex or glucose, and more preferably a boron trifluoride-monoethylamine complex.

[0123] (Connection structure) The connection structure according to the present invention comprises a first connection target member having a first electrode on its surface, a second connection target member having a second electrode on its surface, and a connection part connecting the first connection target member and the second connection target member. In the connection structure according to the present invention, the material of the connection part is the conductive paste described above. In the connection structure according to the present invention, the first electrode and the second electrode are electrically connected by a solder part in the connection part.

[0124] The thickness of the solder 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.

[0125] The method for producing the connection structure is not particularly limited. One example of the method for producing the connection structure is a method in which the conductive paste is placed between a first connection target member and a second connection target member, a laminate is obtained, and then the laminate is heated. 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 equal to or lower than the upper limit, the electrical conductivity reliability and the insulation reliability between the electrodes can be further improved. During the heating, pressure may or may not be applied.

[0126] Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.

[0127] FIG. 1 is a cross-sectional view that illustrates a connection structure obtained by using a conductive paste according to one embodiment of the present invention.

[0128] The connection structure 1 shown in Fig. 1 includes a first connection target member 2, a second connection target member 3, and a connection portion 4 connecting the first connection target member 2 and the second connection target member 3. The connection portion 4 is formed of the above-mentioned conductive paste. In this embodiment, the conductive paste includes a thermosetting component, a plurality of solder particles, and flux. The thermosetting component includes a thermosetting compound and a thermosetting agent.

[0129] The connection portion 4 has a solder portion 4A in which a plurality of solder particles are gathered and joined together, and a cured portion 4B in which a thermosetting compound is thermally cured.

[0130] 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 its surface (lower surface). The first electrode 2a and the second electrode 3a are electrically connected by the 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. In the connection portion 4, there are no solder particles in a region (hardened portion 4B) different from the solder portion 4A gathered between the first electrode 2a and the second electrode 3a. In a region (hardened portion 4B) different from the solder portion 4A, there are no solder particles separated from the solder portion 4A. In addition, if the amount is small, there may be solder particles in a region (hardened portion 4B) different from the solder portion 4A gathered between the first electrode 2a and the second electrode 3a.

[0131] As shown in FIG. 1, in the connection structure 1, a plurality of solder particles gather between the first electrode 2a and the second electrode 3a, and after the plurality of solder particles melt, the molten solder particles wet and spread over the surface of the electrodes, and then solidify to form the solder portion 4A. 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 is increased. That is, by using the solder particles, the contact area between the solder portion 4A and the first electrode 2a, and between the solder portion 4A and the second electrode 3a is increased compared to the case where conductive particles whose outer surface is a metal such as nickel, gold, or copper are used. This also increases the conduction reliability and connection reliability in the connection structure 1. In addition, the above-mentioned flux is generally gradually deactivated by heating.

[0132] In the connection structure 1, when the opposing portion of the first electrode 2a and the second electrode 3a is viewed in the stacking direction of the first electrode 2a, the connection portion 4, and the second electrode 3a, it is preferable that the solder portion 4A in the connection portion 4 is disposed in 50% or more of the 100% area of ​​the opposing portion of the first electrode 2a and the second electrode 3a. When the solder portion 4A in the connection portion 4 satisfies the above-mentioned preferable aspects, the electrical conductivity reliability can be further improved.

[0133] When the portion where the first electrode and the second electrode face each other is viewed in the stacking direction of the first electrode, the connection portion, and the second electrode, the solder portion in the connection portion is preferably arranged in 50% or more of the 100% area of ​​the portion where the first electrode and the second electrode face each other. When the portion where the first electrode and the second electrode face each other is viewed in the stacking direction of the first electrode, the connection portion, and the second electrode, the solder portion in the connection portion is more preferably arranged in 60% or more of the 100% area of ​​the portion where the first electrode and the second electrode face each other. When the portion where the first electrode and the second electrode face each other is viewed in the stacking direction of the first electrode, the connection portion, and the second electrode, the solder portion in the connection portion is further preferably arranged in 70% or more of the 100% area of ​​the portion where the first electrode and the second electrode face each other. It is particularly preferable that the solder portion in the connection portion is disposed in 80% or more of the 100% area of ​​the facing portion of the first electrode and the second electrode when the facing portion of the first electrode and the second electrode is viewed in the stacking direction of the first electrode, the connection portion, and the second electrode. It is most preferable that the solder portion in the connection portion is disposed in 90% or more of the 100% area of ​​the facing portion of the first electrode and the second electrode when the facing portion of the first electrode and the second electrode is viewed in the stacking direction of the first electrode, the connection portion, and the second electrode. When the solder portion in the connection portion satisfies the above-mentioned preferable aspects, the electrical connection reliability can be further improved.

[0134] When the portion where the first electrode and the second electrode face each other is viewed in a direction perpendicular to the stacking direction of the first electrode, the connection portion, and the second electrode, it is preferable that 60% or more of the solder portion in the connection portion is disposed in the portion where the first electrode and the second electrode face each other. It is more preferable that 70% or more of the solder portion in the connection portion is disposed in the portion where the first electrode and the second electrode face each other when the portion where the first electrode and the second electrode face each other is viewed in a direction perpendicular to the stacking direction of the first electrode, the connection portion, and the second electrode. It is even more preferable that 90% or more of the solder portion in the connection portion is disposed in the portion where the first electrode and the second electrode face each other when the portion where the first electrode and the second electrode face each other is viewed in a direction perpendicular to the stacking direction of the first electrode, the connection portion, and the second electrode. It is particularly preferable that 95% or more of the solder in the connection part is disposed in the portion where the first electrode and the second electrode face each other when the portion where the first electrode and the second electrode face each other is viewed in a direction perpendicular to the stacking direction of the first electrode, the connection part, and the second electrode. It is most preferable that 99% or more of the solder in the connection part is disposed in the portion where the first electrode and the second electrode face each other when the portion where the first electrode and the second electrode face each other is viewed in a direction perpendicular to the stacking direction of the first electrode, the connection part, and the second electrode. When the solder in the connection part satisfies the above-mentioned preferable aspect, the electrical connection reliability can be further improved.

[0135] The first and second connection target members are not particularly limited. Specific examples of the first and second connection target members include electronic components such as semiconductor chips, semiconductor packages, LED chips, LED packages, capacitors, and diodes, as well as electronic components such as resin films, printed circuit boards, flexible printed circuit boards, flexible flat cables, rigid flexible boards, glass epoxy boards, and glass boards. The first and second connection target members are preferably electronic components.

[0136] At least one of the first connection target member and the second connection target member is preferably a resin film, a flexible printed circuit board, a flexible flat cable, or a rigid flexible substrate. The second connection target member is preferably a resin film, a flexible printed circuit board, a flexible flat cable, or a rigid flexible substrate. Resin films, flexible printed circuit boards, flexible flat cables, and rigid flexible substrates 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 not to gather on the electrodes. In contrast, by using a conductive paste, even if a resin film, a flexible printed circuit board, a flexible flat cable, or a rigid flexible substrate is used, solder particles can be efficiently gathered on the electrodes, thereby sufficiently improving the conduction reliability between the electrodes. When a resin film, a flexible printed circuit board, a flexible flat cable, or a rigid flexible substrate is used, the effect of improving the conduction reliability between the electrodes by not applying pressure can be obtained more effectively than when other connection target members such as semiconductor chips are used.

[0137] Examples of the electrodes provided on the connection target members include metal electrodes such as gold electrodes, nickel electrodes, tin electrodes, aluminum electrodes, copper electrodes, molybdenum electrodes, silver electrodes, SUS electrodes, and tungsten electrodes. When the connection target members are flexible printed circuit boards, the electrodes are preferably gold electrodes, tin electrodes, silver electrodes, or copper electrodes. When the connection target members are glass substrates, the electrodes are preferably copper electrodes or silver electrodes. When the electrodes are aluminum electrodes, they may be electrodes made of aluminum only, or may be electrodes in which an aluminum layer is laminated on the surface of a metal oxide layer. Examples of materials for the metal oxide layer include indium oxide doped with a trivalent metal element and zinc oxide doped with a trivalent metal element. Examples of the trivalent metal element include Sn, Al, and Ga.

[0138] In the connection structure according to the present invention, the first electrode and the second electrode are preferably arranged in an area array or peripheral arrangement. When the first electrode and the second electrode are arranged in an area array or peripheral arrangement, the effect of the present invention is more effectively exerted. The area array is a structure in which the electrodes of the connection target member are arranged in a lattice shape on the surface on which the electrodes are arranged. The peripheral is a structure in which the electrodes are arranged on the outer periphery of the connection target member. In the case of a structure in which the electrodes are arranged in a comb shape, it is sufficient that the solder particles are aggregated along a direction perpendicular to the comb, whereas in the area array or peripheral structure, the solder particles need to be uniformly aggregated over the entire surface on which the electrodes are arranged. Therefore, while the amount of solder is likely to be non-uniform in the conventional method, the method of the present invention can uniformly aggregate the solder particles over the entire surface.

[0139] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0140] Thermosetting component (thermosetting compound): Phenol novolac type epoxy compound (DOW "DEN431") Bisphenol F type epoxy compound (DOW "DER354")

[0141] Solder particles: Solder particles 1 (SnAgCu solder particles, Mitsui Kinzoku Co., Ltd. "Sn96.5Ag3.0Cu0.5 ST-3", average particle size: 3.0 μm, melting point: 220°C, specific gravity: 7.4) Solder particles 2 (SnSb solder particles, "Sn95Sb5" manufactured by Senju Metals, average particle size: 5.0 μm, melting point: 240°C, specific gravity: 7.3) Solder particles 3 (SnAgCu solder particles, Mitsui Kinzoku Co., Ltd. "Sn96.5Ag3.0Cu0.5 DS10", average particle size: 10.0 μm, melting point: 220°C, specific gravity: 7.4) Solder particles 4 (SnBi solder particles, Mitsui Kinzoku Co., Ltd. "Sn42Bi58 ST-3", average particle size: 3.0 μm, melting point: 138°C, specific gravity: 8.6)

[0142] Flux: Trimellitic acid dibenzylamine salt (solid at 25°C, average particle size: 10 μm, melting point: 260°C) Benzylamine adipate ("Benzylamine adipate" manufactured by Showa Chemical Industry Co., Ltd., solid at 25°C, average particle size: 10 μm, melting point: 180°C)

[0143] Other Ingredients: Glycerol (Nacalai Tesque's "Glycerol", liquid at 25°C, number of hydroxyl groups: 3, boiling point: 290°C) N-Oleoyl Sarcosine (TCI "N-Oleoyl Sarcosine", 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)

[0144] (Weight gain measurement) The boron trifluoride-monoethylamine complex manufactured by TCI was left at 25°C and 50% RH for 24 hours, and the weight increase rate of the boron trifluoride-monoethylamine complex after being left to stand relative to the weight of the boron trifluoride-monoethylamine complex before being left to stand was measured by the method described above. The weight increase rate of the boron trifluoride-monoethylamine complex was 1.0% by weight to 2.0% by weight.

[0145] (Examples 1 to 4 and Comparative Examples 1 to 4) (1) Preparation of conductive paste (anisotropic conductive paste) The components shown in Tables 1 and 2 below were mixed in the amounts shown in Tables 1 and 2 below to obtain a conductive paste (anisotropic conductive paste).

[0146] (2) Fabrication of connection structure As the first connection target member, a glass epoxy board (material: FR-4, thickness: 0.6 mm) having copper electrodes (electrode length: 3 mm, electrode thickness: 12 μm) with L / S=50 μm / 50 μm on its surface was prepared.

[0147] As the second connection target member, a flexible printed circuit board (material: polyimide, thickness: 0.1 mm) having copper electrodes (electrode length: 3 mm, electrode thickness: 12 μm) with L / S=50 μm / 50 μm on its surface was prepared.

[0148] The conductive paste (anisotropic conductive paste) immediately after preparation was applied to the upper surface of the glass epoxy board to a thickness of 100 μm 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 was added to the conductive paste (anisotropic conductive paste) layer. From that state, the conductive paste (anisotropic conductive paste) layer was heated so that the temperature of the conductive paste (anisotropic conductive paste) layer reached the melting point of the solder particles 10 seconds after the start of the temperature rise. Furthermore, 15 seconds after the start of the temperature rise, the conductive paste (anisotropic conductive paste) layer was heated so that the temperature of the conductive paste (anisotropic conductive paste) layer reached 250° C., the conductive paste (anisotropic conductive paste) layer was hardened, and a connection structure was obtained. No pressure was applied during heating.

[0149] (evaluation) (1) Storage stability The viscosity (η25) of the conductive paste immediately after preparation at 25°C and 5 rpm and the viscosity (ηA) of the conductive paste immediately after preparation at 25°C and 50% RH for 24 hours were measured by the method described above, and the ratio (ηA / η25) was calculated. The storage stability was evaluated according to the following criteria.

[0150] [Criteria for storage stability] ○○: Ratio (ηA / η25) is 1.5 or less ○: The ratio (ηA / η25) is greater than 1.5 and less than 1.8 ×: The ratio (ηA / η25) exceeds 1.8

[0151] (2) Screen printability The obtained conductive paste (anisotropic conductive paste) was screen printed on a glass slide using a metal mask with dimensions of 20 μm × 50 μm per opening and a thickness of 20 μm. For 50 printed patterns, the printed surface immediately after printing was observed with a laser microscope, the volume of the conductive paste applied to the glass slide was calculated, and the ratio X (%) of the volume of the conductive paste applied to the glass slide to the volume of each opening of the metal mask was calculated. The screen printability was evaluated according to the following criteria.

[0152] [Criteria for Screen Printability] ○○: The percentage of X is 60% or more ○: Proportion X is 40% or more but less than 60% ×: Proportion X is less than 40%

[0153] (3) Accuracy of solder particle placement In the obtained connection structure, when the portion where the first electrode and the second electrode face each other in the lamination direction of the first electrode, the connection portion, and the second electrode is viewed, the ratio Y of the area where the solder portion in the connection portion is arranged to the area of ​​the portion where the first electrode and the second electrode face each other (100%) was evaluated. The arrangement accuracy of the solder particles was evaluated according to the following criteria.

[0154] [Criteria for solder particle placement accuracy] ○○: Proportion Y is 70% or more ○: Proportion Y is 50% or more but less than 70% ×: Proportion Y is less than 50%

[0155] The results are shown in Tables 1 and 2 below.

[0156] [Table 1]

[0157] [Table 2] [Explanation of symbols]

[0158] 1...Connection structure 2...First connection target member 2a...First electrode 3...Second connecting member 3a...Second electrode 4…Connection 4A…Solder part 4B…Cured product part

Claims

1. A conductive paste comprising a thermosetting component, a plurality of solder particles, and a flux, wherein an average particle diameter of the solder particles is 5.0 μm or less, a melting point of the flux is 200°C or higher, and an absolute value of a difference between a melting point of the solder particles and a melting point of the flux is 50°C or less.

2. The conductive paste according to claim 1, wherein the flux is a carboxylic acid amine salt.

3. The conductive paste according to claim 2, wherein the flux is a dibenzylamine salt of trimellitic acid.

4. The conductive paste according to any one of claims 1 to 3, wherein a content of the flux is 10 parts by weight or more and 30 parts by weight or less with respect to 100 parts by weight of the solder particles.

5. The conductive paste according to any one of claims 1 to 3, wherein a ratio of a viscosity of the conductive paste at 25°C and 5 rpm after storing the conductive paste immediately after production under conditions of 25°C and 50% RH for 24 hours to a viscosity of the conductive paste at 25°C and 5 rpm immediately after production is 1.5 or less.

6. A first connection target member having a first electrode on a surface thereof, a second connection target member having a second electrode on a surface thereof, and a connection portion connecting the first connection target member and the second connection target member, wherein a material of the connection portion is the conductive paste according to any one of claims 1 to 3, and the first electrode and the second electrode are electrically connected by a solder portion in the connection portion.

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