Electroconductive resin composition, joined sheet, method for producing electroconductive resin composition, method for producing joined body, and joined body

Abstract

This electroconductive resin composition comprises acid-treated solder particles 5, a resin component, and a flux having carboxyl groups. The maximum Mulliken charge of the carbon in the carboxyl groups of the flux is 0.5850 or less.

Description

Conductive resin composition, bonding sheet, method for manufacturing conductive resin composition, method for manufacturing bonded body, and bonded body

[0001] The present invention relates to a conductive resin composition, a bonding sheet, a method for producing a conductive resin composition, a method for producing a bonded body, and a bonded body, and more particularly to a conductive resin composition, a bonding sheet containing the conductive resin composition, a method for producing a conductive resin composition, a method for producing a bonded body obtained by using the conductive resin composition, and a bonded body including an adhesive layer that is a cured product of the bonding sheet.

[0002] Conventionally, a bonding sheet is used to bond terminals of two wired circuit boards, and the bonding sheet is made of a composition containing solder particles, a curable resin, and a flux.

[0003] The bonding sheet is first placed between two printed circuit boards. Next, the bonding sheet is heated. This softens the curable resin, causing the solder particles to gather and agglomerate between the terminals (self-agglomeration). The curable resin then hardens around the solder. The agglomerated solder solidifies as the temperature is lowered, forming a soldered portion. The curable resin forms a hardened resin portion around the soldered portion.

[0004] Known examples of such joining sheets include conductive materials containing solder particles, a thermosetting compound, and glutaric acid benzylamine salt as a flux (the maximum Mulliken charge of the carbon of the carboxyl group of glutaric acid benzylamine salt is 0.5996) (see, for example, Example 1 of Patent Document 1).

[0005] International Publication No. 2019 / 124512 Pamphlet

[0006] On the other hand, in the conductive material of Patent Document 1, the flux may react with the thermosetting compound. However, the reaction product of the flux and the thermosetting compound is decomposed by the unreacted flux, generating gas. This gas can cause voids.

[0007] The present invention provides a conductive resin composition that suppresses the generation of voids, a bonding sheet containing the conductive resin composition, a method for producing the conductive resin composition, a method for producing a bonded body obtained using the conductive resin composition, and a bonded body including an adhesive layer that is a cured product of the bonding sheet.

[0008] The present invention [1] is a conductive resin composition comprising acid-treated solder particles, a resin component, and a flux having a carboxyl group, wherein the maximum value of the Mulliken charge of carbon in the carboxyl group of the flux is 0.5850 or less.

[0009] The present invention [2] includes the conductive resin composition according to the above [1], in which the content ratio of the flux is 1 part by mass or more and 7 parts by mass or less per 100 parts by mass of the acid-treated solder particles.

[0010] The present invention [3] includes the conductive resin composition according to the above [1] or [2], wherein the flux is a carboxylic acid.

[0011] The present invention [4] includes the conductive resin composition according to the above [3], in which the flux is a dicarboxylic acid.

[0012] The present invention [5] includes a joining sheet containing the conductive resin composition according to any one of the above [1] to [4].

[0013] The present invention [6] is a method for producing a conductive resin composition, comprising a first step of acid-treating solder particles with an acid treating agent, and a second step of mixing the acid-treated solder particles, a resin component, and a flux having a carboxyl group, wherein the maximum value of the Mulliken charge of carbon in the carboxyl group of the flux is 0.585 or less.

[0014] The present invention [7] includes the method for producing a conductive resin composition according to the above [6], wherein the acid treatment agent has a carboxyl group, and the maximum value of the Mulliken charge of the carbon of the carboxyl group exceeds 0.5850.

[0015] The present invention [8] includes a method for manufacturing a bonded body, the method comprising: a third step of preparing a plurality of substrates each having a plurality of electrodes arranged in a planar direction; a fourth step of preparing a bonding sheet by applying the conductive resin composition obtained by the manufacturing method described in the above [6] or [7]; a fifth step of manufacturing a laminate by stacking the two substrates with the bonding sheet sandwiched therebetween so that the electrodes of the two substrates face each other; and a sixth step of heating the laminate to melt the solder particles, thereby forming columnar solder portions so as to electrically connect the electrodes of the two substrates and curing the resin component.

[0016] The present invention [9] includes the method for producing a bonded body according to the above [8], in which the sixth step is carried out in a pressure oven.

[0017] The present invention

[10] provides a bonding sheet comprising: a first substrate having a plurality of first electrodes arranged in a surface direction; a second substrate having a plurality of second electrodes arranged in the surface direction, the first electrodes and the second electrodes being arranged at intervals in a thickness direction perpendicular to the surface direction so that the first electrodes and the second electrodes are opposed to each other; and an adhesive layer interposed between the first substrate and the second substrate, electrically connecting the first electrodes and the second electrodes opposed to each other in the thickness direction and adhering the first substrate to the second substrate; wherein the adhesive layer is a cured product of the bonding sheet according to any one of [1] to [4] above, and the adhesive layer comprises a bonding body including a columnar solder portion and a cured resin that electrically connects the first electrodes and the second electrodes opposed to each other in the thickness direction.

[0018] In addition, in this conductive resin composition, the maximum value of the Mulliken charge of the carbon of the carboxyl group of the flux is 0.5850 or less, which makes it possible to suppress the generation of voids.

[0019] Specifically, in conductive resin compositions, the resin component and the flux may react (e.g., an ester-forming reaction). However, when the reaction product (e.g., an ester bond) between the resin component and the flux is subjected to nucleophilic attack by unreacted flux (anions), it decomposes and generates gas. This gas can cause voids. The likelihood of the nucleophilic attack is determined by the force with which the reaction product between the resin component and the flux attracts the unreacted flux and the amount of protons released by the unreacted flux.

[0020] When the maximum Mulliken charge of the carbon of the carboxyl group of the flux is 0.5850 or less, the reaction product between the resin component and the flux is less susceptible to nucleophilic attack, thereby suppressing void formation. When the maximum Mulliken charge of the carbon of the carboxyl group of the flux is 0.5850 or less, the force with which the reaction product between the resin component and the flux attracts unreacted flux is suppressed. The polarization of the ester bond in the reaction product is reduced, thereby reducing the force with which it attracts unreacted flux (anions). Furthermore, a flux with a maximum Mulliken charge of the carbon of the carboxyl group of the flux being 0.5850 or less releases fewer protons, which act as hydrolysis catalysts. A flux with a small positive Mulliken charge of the carbon atom of the carboxyl group of the flux has a small negative Mulliken charge of the oxygen atom adjacent to the hydrogen atom. In this case, the polarization with the hydrogen atom is small, resulting in less proton release. From the above, the generation of voids can be suppressed by using a flux in which the maximum value of the Mulliken charge of the carbon of the carboxyl group is 0.5850 or less.

[0021] Furthermore, the conductive resin composition of the present invention contains acid-treated solder particles. That is, the solder particles are acid-treated before being mixed with the resin component and flux. This removes most of the oxide film on the surface of the solder particles. When such solder particles are mixed with flux, the flux further removes the oxide film from the solder particles. However, because most of the oxide film has already been removed, the amount of water generated during the oxide film removal can be reduced. As a result, the generation of voids due to water generation can be suppressed.

[0022] The bonding sheet of the present invention contains the conductive resin composition of the present invention, and therefore, the occurrence of voids can be suppressed.

[0023] The method for producing a conductive resin composition of the present invention includes a first step of acid-treating solder particles with an acid treating agent. That is, the conductive resin composition contains acid-treated solder particles. Therefore, this method can produce a conductive resin composition that can suppress the generation of voids.

[0024] Furthermore, the maximum value of the Mulliken charge of the carbon of the carboxyl group of the flux is 0.5850 or less. Therefore, according to this method, it is possible to produce a conductive resin composition that can suppress the generation of voids.

[0025] The method for producing a bonded body of the present invention uses the conductive resin composition of the present invention, and therefore, the generation of voids can be suppressed.

[0026] The bonded structure of the present invention includes an adhesive layer that is a cured product of the bonding sheet of the present invention, and therefore, the occurrence of voids can be suppressed.

[0027] FIGS. 1A and 1B show one embodiment of a method for manufacturing a bonding sheet. FIG. 1A shows a preparation step for preparing a release liner. FIG. 1B shows an arrangement step for placing a bonding sheet on one thickness-wise surface of the release liner. FIGS. 2A to 2E show one embodiment of a method for using a bonding sheet (a method for manufacturing a bonded body). FIG. 2A shows a third step for preparing two substrates each having a plurality of electrodes arranged in the surface direction. FIG. 2B shows a fourth step for preparing a bonding sheet by applying a conductive resin composition. FIG. 2C shows a fifth step for manufacturing a laminate by stacking a first substrate and a second substrate with the bonding sheet sandwiched between them so that the electrodes of the two substrates face each other. FIG. 2D shows a sixth step for thermocompression bonding the first substrate and the second substrate to the bonding sheet. FIG. 2E shows a sixth step for forming an adhesive layer for solder-bonding the first substrate and the second substrate to the bonding sheet. Fig. 3 is a graph showing the results of the removal rate of the oxide film on the surface of the solder particle by the acid treatment agent. Fig. 4 is an explanatory diagram explaining the observation position in observing the accumulation state of the solder and evaluating the occurrence of voids.

[0028] 1. Conductive Resin Composition The conductive resin composition contains acid-treated solder particles, a resin component, and a flux.

[0029] <Acid-Treated Solder Particles> Acid-treated solder particles are obtained by acid-treating solder particles with an acid treating agent.

[0030] [Acid Treatment Agent] The acid treatment agent is a component for removing the oxide film on the surface of the solder particles.

[0031] The acid treating agent has a carboxyl group. Examples of such an acid treating agent include a carboxylic acid treating agent. Examples of the carboxylic acid treating agent include a monocarboxylic acid treating agent, a dicarboxylic acid treating agent, and a trifunctional or higher functional carboxylic acid treating agent.

[0032] Examples of monocarboxylic acid treating agents include aliphatic monocarboxylic acid treating agents and aromatic monocarboxylic acid treating agents.

[0033] Aliphatic monocarboxylic acid treating agents include, for example, acetic acid (0.5554), propionic acid (0.5755) and butyric acid (0.5738).

[0034] Aromatic monocarboxylic acid treating agents include, for example, benzoic acid (0.5364), 2-phenoxybenzoic acid (0.5413), and diphenylacetic acid (0.5930).

[0035] Examples of dicarboxylic acid treating agents include aliphatic dicarboxylic acid treating agents and aromatic dicarboxylic acid treating agents.

[0036] Examples of aliphatic dicarboxylic acid treating agents include glutaric acid (0.5761), pimelic acid (0.5789), adipic acid (0.5785), 3,3-dimethylglutaric acid (0.5807), 2-methyladipic acid (0.5827), malonic acid (0.5864), succinic acid (0.5963), malic acid (0.6092), suberic acid (0.5790), sebacic acid (0.5769), methylmalonic acid (0.5979), ethylmalonic acid (0.6062), and phenylmalonic acid (0.6119).

[0037] An example of an aromatic dicarboxylic acid treatment agent is phthalic acid (0.5245).

[0038] Examples of tri- or higher functional carboxylic acid treating agents include tri- or higher functional aliphatic carboxylic acid treating agents and tri- or higher functional aromatic carboxylic acid treating agents.

[0039] An example of a tri- or higher functional aliphatic carboxylic acid treating agent is citric acid (0.5930).

[0040] Examples of tri- or higher functional aromatic carboxylic acid treating agents include trimellitic acid (0.5496) and pyromellitic acid (0.5357).

[0041] The acid treating agent is preferably a dicarboxylic acid treating agent, more preferably an aliphatic dicarboxylic acid treating agent, and even more preferably malic acid.

[0042] In the acid treatment agent, the value in parentheses indicates the maximum value of Mulliken charge, which will be described later.

[0043] The maximum value of the Mulliken charge (described later) of the acid treatment agent is, for example, 0.5700 or more, and from the viewpoint of increasing the speed at which the oxide film on the surface of the solder particles is removed, it preferably exceeds 0.5850, more preferably 0.5900 or more, and even more preferably 0.6000 or more, and is, for example, 0.6200 or less.

[0044] The acid treating agents can be used alone or in combination of two or more kinds.

[0045] [Solder Particles] From the viewpoint of environmental friendliness, the solder material forming the solder particles may be a solder material that does not contain lead (lead-free solder material). Specific examples of the solder material include tin and tin alloys. Examples of tin alloys include tin-bismuth alloys (Sn—Bi), tin-silver-copper alloys (Sn—Ag—Cu), and tin-silver alloys (Sn—Ag). Preferred examples of the solder material include tin-bismuth alloys (Sn—Bi) and tin-silver-copper alloys (Sn—Ag—Cu).

[0046] The tin content in the tin-silver-copper alloy is, for example, 90% by mass or more, preferably 95% by mass or more. The silver content in the tin-silver-copper alloy is, for example, 10% by mass or less, preferably 5% by mass or less. The copper content in the tin-silver-copper alloy is, for example, 1% by mass or less, preferably 0.5% by mass or less.

[0047] The tin content in the tin-bismuth alloy is, for example, 80 mass % or less, or preferably 50 mass % or less, and the bismuth content in the tin-bismuth alloy is, for example, 20 mass % or more, or preferably 50 mass % or more.

[0048] The melting point of the solder material (i.e., the melting point of the solder particles) is higher than the softening point of the solid resin described below, and is, for example, 100° C. to 260° C., preferably 135° C. to 235° C., and more preferably 185° C. to 220° C. The melting point can be determined by differential scanning calorimetry (DSC) (the same applies hereinafter).

[0049] The shape of the solder particles is not particularly limited, and examples thereof include a spherical shape, a plate shape, and a needle shape. A preferred shape of the solder particles is a spherical shape.

[0050] From the viewpoint of miniaturization and low profile, the average primary particle diameter of the solder particles is, for example, 10 μm or less, preferably 7 μm or less, more preferably 5 μm or less, and for example, 0.1 μm or more, preferably 0.5 μm or more. The average primary particle diameter can be measured using a laser diffraction particle size distribution analyzer.

[0051] The solder particles can be used alone or in combination of two or more kinds.

[0052] [Manufacturing of Acid-Treated Solder Particles] The acid-treated solder particles are obtained by acid-treating solder particles with an acid treating agent. Specifically, the manufacturing method of the acid-treated solder particles includes a preparation step of preparing an aqueous solution of the acid treating agent, an immersion step of immersing the solder particles in the aqueous solution of the acid treating agent, a cleaning step of cleaning the solder particles, and a solvent removal step of removing the solvent.

[0053] (Preparation Step) In the preparation step, an aqueous solution of the acid treating agent is prepared. To prepare the aqueous solution of the acid treating agent, the acid treating agent is diluted with water to prepare the aqueous solution of the acid treating agent.

[0054] The molar concentration of the aqueous solution of the acid treating agent is, for example, 0.5 mol / L to 3.0 mol / L.

[0055] (Immersion Step) In the immersion step, the solder particles are immersed in an aqueous solution of an acid treatment agent at room temperature (10° C. to 30° C.), and the solution is stirred as necessary.

[0056] The immersion time is, for example, 1 to 60 minutes, preferably 5 to 30 minutes.

[0057] (Washing Process) In the washing process, the solder particles are washed. Specifically, after the solder particles have naturally settled, the supernatant is removed, and a solvent (e.g., ethanol or acetone) is added and stirred. Note that washing can be performed multiple times.

[0058] (Solvent Removal Step) In the solvent removal step, the solvent is removed by, for example, vacuum drying in a vacuum oven.

[0059] In vacuum drying, the drying temperature is, for example, 20° C. to 50° C. The drying time is, for example, 0.5 to 12 hours, preferably 1 to 6 hours.

[0060] As a result, the solder particles are acid-treated with the acid treating agent, and acid-treated solder particles are produced.

[0061] The solder particles are subjected to an acid treatment to remove most of the oxide film on the surface of the solder particles. Specifically, the thickness of the oxide film is, for example, 5 nm or less, preferably 3 nm or less, more preferably 1 nm or less, even more preferably 0.5 nm or less, and typically 0.1 nm or more.

[0062] If the thickness of the oxide film is equal to or less than the above upper limit, it is possible to suppress the generation of voids due to the removal of the oxide film, which will be described later.

[0063] The thickness of the oxide film can be measured using a transmission electron microscope (TEM).

[0064] In addition, in the production of the acid-treated solder particles, a part or all of the resin component described below may be blended in advance. In such a case, a part or all of the resin component is blended after the cleaning step and before the solvent removal step.

[0065] The content of the acid-treated solder particles relative to the conductive resin composition is, for example, 40% by mass to 70% by mass, preferably 50% by mass to 65% by mass, and more preferably 55% by mass to 60% by mass.

[0066] <Resin Component> The resin component is not particularly limited, but preferably contains a solid resin and a liquid resin. When the resin component contains a solid resin and a liquid resin, the bonding sheet (described later) has excellent formability and adhesive strength.

[0067] The mass ratio of the solid resin to the liquid resin in the resin component is, for example, 0.5 to 1.5, preferably 0.7 to 1.3, and more preferably 0.9 to 1.1.

[0068] A solid resin does not flow and has no viscosity at 25° C. A liquid resin includes liquids and fluids at 25° C. and has viscosity.

[0069] As the solid resin and the liquid resin, a thermoplastic resin and a curable resin are selected.

[0070] [Thermoplastic Resin] Examples of thermoplastic resins include thermoplastic epoxy resins, thermoplastic phenolic resins, phenoxy resins, polyolefins (e.g., polyethylene, polypropylene, ethylene-propylene copolymers, etc.), thermoplastic acrylic resins, thermoplastic polyesters, polyvinyl acetate, ethylene-vinyl acetate copolymers, polyvinyl chloride, polystyrene, polyacrylonitrile, polyamide (Nylon (registered trademark)), polycarbonate, polyacetal, polyethylene terephthalate, polyphenylene oxide, polyphenylene sulfide, polysulfone, polyether sulfone, polyether ether ketone, polyallylsulfone, thermoplastic polyimide, thermoplastic polyurethane, polyaminobismaleimide, polyamideimide, polyetherimide, bismaleimide triazine resin, polymethylpentene, fluorinated resins, liquid crystal polymers, olefin-vinyl alcohol copolymers, ionomers, polyarylates, acrylonitrile-ethylene-styrene copolymers, acrylonitrile-butadiene-styrene copolymers, acrylonitrile-styrene copolymers, and butadiene-styrene copolymers.

[0071] The thermoplastic resins can be used alone or in combination of two or more kinds.

[0072] The content of the thermoplastic resin relative to 100 parts by mass of the resin component is, for example, 50 parts by mass or less, preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 0 part by mass. In other words, the resin component more preferably does not contain a thermoplastic resin.

[0073] [Curable Resin] Examples of the curable resin include thermosetting resins. Examples of the thermosetting resin include thermosetting epoxy resins, urea resins, melamine resins, diallyl phthalate resins, silicone resins, phenolic resins, thermosetting acrylic resins, thermosetting polyesters, thermosetting polyimides, and thermosetting polyurethanes. Preferred examples of the curable resin include thermosetting epoxy resins and phenolic resins.

[0074] Examples of thermosetting epoxy resins include thermosetting bisphenol-type epoxy resins (e.g., thermosetting bisphenol A-type epoxy resins, thermosetting bisphenol F-type epoxy resins, and thermosetting bisphenol S-type epoxy resins), thermosetting novolac-type epoxy resins (e.g., thermosetting phenol novolac-type epoxy resins, thermosetting cresol novolac-type epoxy resins, and thermosetting biphenyl-type epoxy resins), thermosetting naphthalene-type epoxy resins, thermosetting fluorene-type epoxy resins (e.g., thermosetting bisarylfluorene-type epoxy resins), and thermosetting triphenylmethane-type epoxy resins (e.g., thermosetting trishydroxyphenylmethane-type epoxy resins). A preferred example of the thermosetting epoxy resin is a thermosetting bisphenol-type epoxy resin. A more preferred example of the thermosetting epoxy resin is a thermosetting bisphenol A-type epoxy resin.

[0075] Examples of the phenolic resin include novolac-type phenolic resins and dicyclopentadiene-type phenolic resins. Examples of the novolac-type phenolic resin include phenol novolac resins and cresol novolac resins. A preferred example of the phenolic resin is novolac-type phenolic resin. A more preferred example of the phenolic resin is phenol novolac resin.

[0076] These thermosetting resins may be in either a solid or liquid state at room temperature (25° C.).

[0077] As the thermosetting resin, a solid thermosetting resin and a liquid thermosetting resin are preferably used in combination.

[0078] The curing temperature of the thermosetting resin is equal to or higher than the melting point of the solder particles, for example, 100°C to 260°C, preferably 135°C to 235°C, and more preferably 185°C to 220°C.

[0079] The curable resins may be used alone or in combination of two or more.

[0080] The content of the curable resin relative to 100 parts by mass of the resin component is, for example, 50 parts by mass or more, preferably 80 parts by mass or more, more preferably 90 parts by mass or more, and even more preferably 100 parts by mass. In other words, the resin component is more preferably made of a curable resin.

[0081] The resin component preferably comprises a thermosetting resin as a solid resin and a thermosetting resin as a liquid resin.

[0082] The content of the thermosetting resin as a solid resin is, for example, 30 parts by mass to 80 parts by mass, preferably 30 parts by mass to 60 parts by mass, more preferably 30 parts by mass to 50 parts by mass, and even more preferably 35 parts by mass to 45 parts by mass.

[0083] Specifically, the content of the thermosetting resin as a solid resin is, from the viewpoint of suppressing the generation of voids due to the removal of the oxide film described later, for example, 30 parts by mass or more, preferably 35 parts by mass or more, and from the viewpoint of suppressing the generation of voids due to the removal of the oxide film described later, for example, 80 parts by mass or less, preferably 60 parts by mass or less, more preferably 50 parts by mass or less, and even more preferably 45 parts by mass or less.

[0084] The content ratio of the thermosetting resin as the liquid resin is, for example, 20 parts by mass to 70 parts by mass, preferably 40 parts by mass to 70 parts by mass, more preferably 50 parts by mass to 70 parts by mass, and even more preferably 55 parts by mass to 65 parts by mass.

[0085] Specifically, the content of the thermosetting resin as the liquid resin is, from the viewpoint of suppressing the occurrence of voids due to the removal of the oxide film described later, for example, 20 parts by mass or more, preferably 40 parts by mass or more, more preferably 50 parts by mass or more, and even more preferably 55 parts by mass or more, and from the viewpoint of suppressing the occurrence of voids due to the removal of the oxide film described later, for example, 70 parts by mass or less, preferably 65 parts by mass or less.

[0086] The softening point of the solid resin is lower than the melting point of the solder particles. More specifically, in order to soften the solid resin without melting the solder particles in the thermocompression bonding in the sixth step described later, the softening point of the solid resin is lower than the melting point of the solder particles. The softening point of the solid resin is, for example, 40°C to 200°C, preferably 60°C to 150°C.

[0087] The softening point can be measured using a thermomechanical analyzer.

[0088] Alternatively, the resin component may be blended with a known solvent to prepare a varnish containing the resin component. The solid content of the varnish containing the resin component is, for example, 30% by mass to 80% by mass, preferably 40% by mass to 70% by mass.

[0089] The content of the resin component relative to the conductive resin composition is, for example, 20% by mass to 60% by mass, preferably 30% by mass to 50% by mass, and more preferably 33% by mass to 45% by mass.

[0090] <Flux> The flux is a component for further removing the oxide film on the surface of the acid-treated solder particles, and also for removing the oxide film on the surface of the metal electrodes (specifically, the first electrode and the second electrode described below) to enable solder bonding.

[0091] The flux has a carboxyl group. From the viewpoint of further removing the oxide film on the surface of the solder particles, for example, a carboxylic acid can be used as the flux. Examples of the carboxylic acid include monocarboxylic acids, dicarboxylic acids, and trifunctional or higher functional carboxylic acids.

[0092] Examples of monocarboxylic acids include aliphatic monocarboxylic acids and aromatic monocarboxylic acids.

[0093] Aliphatic monocarboxylic acids include, for example, acetic acid (0.5554), propionic acid (0.5755) and butyric acid (0.5738).

[0094] Aromatic monocarboxylic acids include, for example, benzoic acid (0.5364) and 2-phenoxybenzoic acid (0.5413).

[0095] The dicarboxylic acid may be, for example, an aliphatic dicarboxylic acid.

[0096] Examples of aliphatic dicarboxylic acids include glutaric acid (0.5761), pimelic acid (0.5789), adipic acid (0.5785), 3,3-dimethylglutaric acid (0.5807), and 2-methyladipic acid (0.5827).

[0097] Examples of tri- or higher functional carboxylic acids include tri- or higher functional aromatic carboxylic acids.

[0098] Examples of the tri- or higher functional aromatic carboxylic acid include trimellitic acid (0.5496) and pyromellitic acid (0.5357).

[0099] In addition, the numerical values ​​in parentheses for the flux indicate the maximum value of the Mulliken charge, which will be described later.

[0100] Furthermore, a salt of the above-mentioned carboxylic acid can also be used as the flux.

[0101] As the flux, from the viewpoint of further removing the oxide film on the surface of the solder particles, preferably, a dicarboxylic acid is used. As the flux, more preferably, an aliphatic dicarboxylic acid is used. As the flux, even more preferably, glutaric acid, pimelic acid, adipic acid, and 3,3-dimethylglutaric acid are used. As the flux, from the viewpoint of improving the integration of the solder described below, particularly preferably, glutaric acid is used.

[0102] The maximum value of the Mulliken charge of the carbon of the carboxyl group of the flux is 0.5850 or less, preferably 0.5800 or less, more preferably 0.5790 or less, even more preferably 0.5770 or less, and usually 0.5000 or more.

[0103] The maximum value of the Mulliken charge of the carboxyl carbon of the flux is an index showing the positive charge of the carbon atom, and as the value decreases, the positive charge decreases, and as will be described in detail later, the reactivity of the nucleophilic attack by the anion tends to decrease. As a result, the decomposition of the reaction product between the resin component and the flux, which will be described later, can be suppressed, and the generation of voids can be suppressed.

[0104] On the other hand, if the maximum value of the Mulliken charge exceeds the upper limit, it is not possible to suppress decomposition of the reaction product between the resin component and the flux, which will be described later, and it is not possible to suppress the generation of voids.

[0105] The Mulliken charge is calculated by calculating the average distribution of electrons from an electronic state calculation and then calculating the charge distribution occurring in each atom. The Mulliken charge can be calculated, for example, using the general-purpose quantum chemistry calculation program Gaussian 16 (Gaussian). The Mulliken charge can be calculated for each atom in a molecule and takes positive or negative values. A positive or negative Mulliken charge value means that the atom has a positive or negative charge. In more detail, the method for calculating the maximum Mulliken charge will be described in detail in the Examples below.

[0106] Preferably, the maximum value of the Mulliken charge in the acid treatment agent is adjusted to be larger than the maximum value of the Mulliken charge in the flux. Specifically, the maximum value of the Mulliken charge in the acid treatment agent is adjusted to exceed 0.5850, while the maximum value of the Mulliken charge in the flux is adjusted to be 0.5850 or less.

[0107] More specifically, the ratio of the maximum Mulliken charge in the acid treatment agent to the maximum Mulliken charge in the flux (maximum Mulliken charge in the acid treatment agent / maximum Mulliken charge in the flux) is adjusted to, for example, more than 1.00, preferably 1.02 or more, more preferably 1.04 or more, and even more preferably 1.05 or more, for example, 1.50 or less.

[0108] This increases the speed at which the acid treatment agent removes the oxide film on the surface of the solder particles, and also suppresses the occurrence of voids (the occurrence of voids caused by the decomposition of the reaction product between the resin component and the flux, as described below).

[0109] The fluxes can be used alone or in combination of two or more kinds.

[0110] Alternatively, the flux may be mixed with a known solvent (e.g., ethanol) to prepare a solution of the flux. The solid content of the flux solution is, for example, 10% by mass to 50% by mass, preferably 20% by mass to 40% by mass.

[0111] The content of the flux is, for example, 0.5 to 10 parts by mass, preferably 1 to 10 parts by mass, and more preferably 5 to 7 parts by mass, per 100 parts by mass of the acid-treated solder particles.

[0112] Specifically, the content of the flux is, for example, 0.5 parts by mass or more, preferably 1 part by mass or more, more preferably 5 parts by mass or more, relative to 100 parts by mass of the acid-treated solder particles, from the viewpoint of further removing the oxide film on the surface of the solder particles, and is, for example, 10 parts by mass or less, and preferably 7 parts by mass or less, from the viewpoint of suppressing the occurrence of voids due to the removal of the oxide film on the solder particles, as described below.

[0113] The content of the flux relative to the conductive resin composition is, for example, 0.5% by mass to 10% by mass, preferably 1% by mass to 10% by mass, and more preferably 3% by mass to 5% by mass.

[0114] <Additives> The conductive resin composition may contain additives (for example, a curing agent, a curing accelerator, and a silane coupling agent) in an appropriate ratio, if necessary.

[0115] 2. Manufacturing of Conductive Resin Composition The manufacturing method of the conductive resin composition includes a first step of acid-treating solder particles with an acid treating agent, and a second step of mixing the acid-treated solder particles with a resin component and a flux.

[0116] In the first step, the solder particles are subjected to an acid treatment using an acid treatment agent to produce acid-treated solder particles. Specifically, the acid-treated solder particles are produced in accordance with the method for producing the acid-treated solder particles described above.

[0117] <Second Step> In the second step, the acid-treated solder particles, the resin component, and the flux are mixed. Specifically, the acid-treated solder particles, the resin component, the flux, and optional additives are mixed and stirred as necessary. This produces a conductive resin composition.

[0118] Alternatively, the conductive resin composition may be blended with a known solvent to prepare a varnish of the conductive resin composition. The solid content of the varnish of the conductive resin composition is, for example, 50% by mass to 80% by mass, preferably 60% by mass to 75% by mass.

[0119] Next, the bonding sheet obtained using this conductive resin composition will be described in detail.

[0120] 3. Bonding Sheet The bonding sheet is formed into a sheet shape from a conductive resin composition. That is, the bonding sheet contains a conductive resin composition.

[0121] An embodiment of a method for manufacturing a bonding sheet will be described in detail with reference to FIGS. 1A and 1B.

[0122] 1A and 1B, the up-down direction of the paper surface is the up-down direction (thickness direction). The upper side of the paper surface is the upper side (one side in the thickness direction), and the lower side of the paper surface is the lower side (the other side in the thickness direction). The left-right direction and the depth direction of the paper surface are surface directions perpendicular to the up-down direction. Specifically, they conform to the directional arrows in each figure.

[0123] The method for manufacturing the bonding sheet includes a preparation step of preparing a release liner 10 and a placement step of placing the bonding sheet 1 on one surface of the release liner 10 in the thickness direction.

[0124] [Preparation Step] In the preparation step, a release liner 10 is prepared as shown in FIG. 1A.

[0125] The release liner is a support for supporting the bonding sheet 1. The release liner 10 has a film shape.

[0126] The release liner 10 is, for example, a plastic substrate (plastic film). Examples of plastic substrates include polyester sheets (polyethylene terephthalate (PET) sheets), polyolefin sheets (e.g., polyethylene sheets and polypropylene sheets), polyvinyl chloride sheets, polyimide sheets, and polyamide sheets (nylon sheets). The surface of the release liner 10 (one surface in the thickness direction) may be subjected to a surface treatment such as silicone treatment.

[0127] The thickness of the release liner 10 is, for example, 1 μm to 100 μm.

[0128] [Placement Step] In the placement step, as shown in FIG. 1B, the bonding sheet 1 is placed on one surface of the release liner 10 in the thickness direction.

[0129] To place the bonding sheet 1 on one surface of the release liner 10 in the thickness direction, a conductive resin composition (a varnish of the conductive resin composition) is applied to one surface of the release liner 10 in the thickness direction, and then dried if necessary.

[0130] As drying conditions, the drying temperature is, for example, 40° C. to 100° C. The drying time is, for example, 1 minute to 60 minutes.

[0131] In this manner, it is possible to manufacture the bonding sheet 1 disposed on one surface in the thickness direction of the release liner 10. In the bonding sheet 1, the solder particles 5 are dispersed in the resin component.

[0132] From the viewpoint of miniaturization and low profile, the thickness of the bonding sheet 1 is, for example, 50 μm or less, preferably 25 μm or less, more preferably 15 μm or less, and even more preferably 10 μm or less, and for example, 1 μm or more.

[0133] Next, a method for using the bonding sheet 1 (a method for manufacturing a bonded body) will be described in detail.

[0134] 4. Method of Using the Bonded Sheet (Method of Manufacturing a Bonded Body) One embodiment of a method of using the bonded sheet (method of manufacturing a bonded body) will be described in detail with reference to FIGS. 2A to 2E.

[0135] A method for using the bonding sheet (a method for manufacturing a bonded body) includes a third step of preparing a plurality of substrates each having a plurality of electrodes arranged in the surface direction; a fourth step of preparing a bonding sheet 1 by applying a conductive resin composition; a fifth step of manufacturing a laminate 6 by stacking two substrates with the bonding sheet 1 sandwiched therebetween so that the electrodes of the two substrates face each other; and a sixth step of heating the laminate 6 and melting the solder particles 5 to form columnar solder portions 15 so as to electrically connect the electrodes of the two substrates and harden the resin component.

[0136] [Step 3] In step 3, a plurality of substrates each having a plurality of electrodes aligned in the surface direction are prepared. This method will be described in detail with respect to the case where two substrates each having a plurality of electrodes aligned in the surface direction are prepared. Specifically, as shown in FIG. 2A, a first substrate 2 and a second substrate 4 are prepared.

[0137] The first substrate 2 has a flat plate shape.

[0138] The first substrate 2 includes a first wired circuit board 11 and a plurality of first electrodes 12 arranged in the surface direction of the first wired circuit board 11. In other words, the first substrate 2 includes the first wired circuit board 11 and a plurality of first electrodes 12 provided on the surface (one surface in the thickness direction) of the first wired circuit board 11.

[0139] The first wired circuit board 11 is made of, for example, an insulating material and a semiconductor material.

[0140] The thickness of the first wired circuit board 11 is, for example, 5 μm to 1000 μm.

[0141] The first electrode 12 is made of a metal.

[0142] The first electrodes 12 are arranged on the first substrate 2 in, for example, a dot pattern.

[0143] More specifically, the first electrodes 12 have a circular shape in a plan view, and the first electrodes 12 are aligned and disposed evenly in the surface direction.

[0144] The thickness of the first electrode 12 is, for example, 0 μm to 20 μm, or preferably 0.001 μm to 5 μm. When the surface of the first substrate 2 and the surface of the first electrode 12 are flush with each other, the thickness of the first electrode 12 is 0 μm.

[0145] The diameter of the first electrode 12 is, for example, 1 μm to 200 μm, preferably 1 μm to 100 μm, more preferably 1 μm to 50 μm, and even more preferably 1 μm to 20 μm.

[0146] The distance (pitch) between adjacent first electrodes 12 in the surface direction is, for example, 3 μm to 400 μm, preferably 5 μm to 200 μm, more preferably 7 μm to 100 μm, and even more preferably 10 μm to 40 μm.

[0147] The second substrate 4 has a flat plate shape.

[0148] The second substrate 4 includes a second wired circuit board 13 and a plurality of second electrodes 14 arranged in the surface direction of the second wired circuit board 13. In other words, the second substrate 4 includes the second wired circuit board 13 and a plurality of second electrodes 14 provided on the surface (the other surface in the thickness direction) of the second wired circuit board 13.

[0149] The second wired circuit board 13 is made of, for example, an insulating material or a semiconductor material.

[0150] The thickness of the second wired circuit board 13 is, for example, 5 μm to 1000 μm.

[0151] The second electrode 14 is made of a metal.

[0152] The second electrodes 14 are arranged on the second substrate 4 in, for example, a dot pattern.

[0153] More specifically, the second electrodes 14 have a circular shape in a plan view, and the second electrodes 14 are aligned and disposed evenly in the surface direction.

[0154] The thickness of the second electrode 14 is, for example, 0 μm to 20 μm, or preferably 0.001 μm to 5 μm. When the surface of the second substrate 4 and the surface of the second electrode 14 are flush with each other, the thickness of the second electrode 14 is 0 μm.

[0155] The diameter of the second electrode 14 is, for example, 1 μm to 2100 μm, preferably 1 μm to 100 μm, more preferably 1 μm to 50 μm, and even more preferably 1 μm to 20 μm.

[0156] Furthermore, the distance (pitch) between adjacent second electrodes 14 in the surface direction is the same as the distance (pitch) between adjacent first electrodes 12 in the surface direction described above.

[0157] [Fourth Step] In the fourth step, the bonding sheet 1 is prepared as shown in Fig. 2B. Specifically, the bonding sheet 1 is prepared in accordance with the above-described method for manufacturing the bonding sheet.

[0158] 2C , the two substrates are laminated with the bonding sheet 1 sandwiched therebetween so that the electrodes of the two substrates face each other, thereby producing the laminate 6. Specifically, the first substrate 2 and the second substrate 4 are laminated with the bonding sheet 1 sandwiched therebetween so that the first electrode 12 of the first substrate 2 and the second electrode 14 of the second substrate 4 face each other, thereby producing the laminate 6.

[0159] Specifically, first, the first substrate 2 and the second substrate 4 are brought close to the bonding sheet 1, and the first substrate 2 and the second substrate 4 are brought into contact with the bonding sheet 1. More specifically, one thickness-wise surface of the first substrate 2 is brought into contact with the other thickness-wise surface of the bonding sheet 1, and the other thickness-wise surface of the second substrate 4 is brought into contact with one thickness-wise surface of the bonding sheet 1, so that the first electrode 12 and the second electrode 14 face each other in the thickness direction.

[0160] In this way, the laminate 6 is manufactured.

[0161] [Step 6] In step 6, the laminate 6 is heated to melt the solder particles 5, thereby forming columnar solder portions 15 that electrically connect the electrodes of the two substrates and hardening the resin component.

[0162] Specifically, first, as shown in FIG. 2D, the first substrate 2, the second substrate 4, and the bonding sheet 1 are thermocompression bonded to each other.

[0163] Specifically, while the laminate 6 is heated, the first substrate 2 and the second substrate 4 are pressed (thermocompression bonded) against the bonding sheet 1 .

[0164] The thermocompression bonding temperature is equal to or higher than the softening point of the thermoplastic resin and lower than the melting point of the solder particles 5. That is, in this process, the thermoplastic resin is softened without melting the solder particles. Specifically, the thermocompression bonding temperature is, for example, 180°C or lower, preferably 100°C or lower, more preferably 80°C or lower, and, for example, 40°C or higher. The thermocompression bonding pressure is, for example, 0.001 MPa to 10 MPa, preferably 0.005 MPa to 5 MPa, more preferably 0.01 MPa to 1 MPa.

[0165] As a result, the resin component softens, and the first electrode 12 of the first substrate 2 becomes embedded in the bonding sheet 1, and one thickness-wise surface of the first substrate 2 comes into contact with the bonding sheet 1. Also, the second electrode 14 of the second substrate 4 becomes embedded in the bonding sheet 1, and the other thickness-wise surface of the second substrate 4 comes into contact with the bonding sheet 1.

[0166] 2E, the laminate 6 is heated. Preferably, the laminate 6 is heated in a pressure oven 25. The pressure oven 25 is an apparatus capable of applying pressure while heating in an enclosed space, and examples thereof include an automatic heating and pressure treatment apparatus, a pressure oven, a voidless pressure oven, an autoclave, and a vacuum pressure reflow apparatus.

[0167] When the laminate 6 is heated, volatile substances may volatilize due to the heating. Such volatile substances may impair electrical connections in the laminate 6. On the other hand, when the laminate 6 is heated using the pressure oven 25, the generation of the volatile substances can be suppressed by applying pressure. As a result, the above-mentioned impediment can be suppressed.

[0168] The heating temperature is equal to or higher than the melting point of the solder particles 5. Specifically, the heating temperature is, for example, 100°C or higher, preferably 130°C or higher, more preferably 200°C or higher, and for example, 300°C or lower, preferably 280°C or lower, more preferably 270°C or lower.

[0169] Such heating melts the solder particles 5. The melted solder particles 5 gather (self-aggregate) between the first electrode 12 and the second electrode 14 that face each other in the thickness direction, forming columnar solder portions 15 that electrically connect the first electrode 12 and the second electrode 14. Meanwhile, the resin component in the bonding sheet 1 is expelled by the self-aggregating solder particles 5 and moves to the periphery of the columnar solder portions 15. Thereafter, the thermosetting resin in the resin component is thermally cured to become a cured resin 16 that bonds the first substrate 2 and the second substrate 4 together.

[0170] As a result, an adhesive layer 3 containing the columnar solder portions 15 and the cured resin 16 is formed between the two base materials (the first substrate 2 and the second substrate 4) from the bonding sheet 1. In other words, the adhesive layer 3 is a cured product of the bonding sheet 1 (conductive resin composition).

[0171] From the viewpoint of miniaturization and low profile, the thickness of the adhesive layer 3 is less than 50 μm, preferably 25 μm or less, more preferably less than 15 μm, even more preferably 5 μm or less, and for example, 1 μm or more.

[0172] In this manner, the bonded body 20 is manufactured.

[0173] The bonded structure 20 includes a first substrate 2, a second substrate 4 disposed at an interval in the thickness direction (thickness direction perpendicular to the surface direction), and an adhesive layer 3 interposed between the first substrate 2 and the second substrate 4. In other words, the bonded structure 20 includes the first substrate 2, the adhesive layer 3, and the second substrate 4, arranged in this order toward one side in the thickness direction. More specifically, the bonded structure 20 includes the first substrate 2, the adhesive layer 3 disposed directly on the upper surface (one surface in the thickness direction) of the first substrate 2, and the second substrate 4 disposed directly on the upper surface (one surface in the thickness direction) of the adhesive layer 3.

[0174] The adhesive layer 3 bonds the first substrate 2 and the second substrate 4. Specifically, the adhesive layer 3 adheres to the surface of the first substrate 2 excluding the first electrode 12. The adhesive layer 3 also adheres to the surface of the second substrate 4 excluding the second electrode 14.

[0175] The adhesive layer 3 (more specifically, the columnar solder portion 15 in the adhesive layer 3) electrically connects the first electrode 12 and the second electrode 14 that face each other in the thickness direction. The columnar solder portion 15 has a columnar shape (more specifically, a cylindrical shape), and is disposed between the first electrode 12 and the second electrode 14 and in contact with them.

[0176] <Effects> The conductive resin composition contains the acid-treated solder particles 5. Therefore, the generation of voids can be suppressed.

[0177] More specifically, from the viewpoint of promoting the self-aggregation of the molten solder particles 5 in the sixth step, it is considered to remove the oxide film on the surface of the solder particles 5 .

[0178] On the other hand, when a flux is mixed with the solder particles 5 to remove the oxide film on the surface of the solder particles 5, water is generated when the flux removes the oxide film on the surface of the solder particles 5. Then, the water volatilizes due to the heating in the fifth and sixth steps, which causes voids to be generated (in other words, voids are generated due to the removal of the oxide film).

[0179] In contrast, the conductive resin composition contains acid-treated solder particles 5. That is, the solder particles 5 are acid-treated before being mixed with the resin component and flux. This removes most of the oxide film on the surface of the solder particles 5. When such solder particles 5 are mixed with flux, the flux further removes the oxide film from the solder particles 5. However, because most of the oxide film has been removed in advance, the amount of water generated when removing the oxide film can be reduced. As a result, the generation of voids due to the removal of the oxide film can be suppressed.

[0180] In addition, in this conductive resin composition, the maximum value of the Mulliken charge of the carbon of the carboxyl group of the flux is 0.5850 or less, which makes it possible to suppress the generation of voids.

[0181] Specifically, in conductive resin compositions, the resin component and the flux may react (e.g., an ester-forming reaction). However, when the reaction product (e.g., an ester bond) between the resin component and the flux is subjected to nucleophilic attack by unreacted flux (anions), it decomposes and generates gas. This gas can cause voids. The likelihood of the nucleophilic attack is determined by the force with which the reaction product between the resin component and the flux attracts the unreacted flux and the amount of protons released by the unreacted flux.

[0182] When the maximum Mulliken charge of the carbon of the carboxyl group of the flux is 0.5850 or less, the reaction product between the resin component and the flux is less susceptible to nucleophilic attack, thereby suppressing void formation. When the maximum Mulliken charge of the carbon of the carboxyl group of the flux is 0.5850 or less, the force with which the reaction product between the resin component and the flux attracts unreacted flux is suppressed. The polarization of the ester bond in the reaction product is reduced, thereby reducing the force with which it attracts unreacted flux (anions). Furthermore, a flux with a maximum Mulliken charge of the carbon of the carboxyl group of the flux being 0.5850 or less releases fewer protons, which act as hydrolysis catalysts. A flux with a small positive Mulliken charge of the carbon atom of the carboxyl group of the flux has a small negative Mulliken charge of the oxygen atom adjacent to the hydrogen atom. In this case, the polarization with the hydrogen atom is small, resulting in less proton release. Therefore, by using a flux in which the maximum value of the Mulliken charge of the carbon of the carboxyl group is 0.5850 or less, the generation of voids can be suppressed.

[0183] As described above, the conductive resin composition can suppress the occurrence of voids by using the acid-treated solder particles 5 in combination with a predetermined flux.

[0184] The bonding sheet 1 contains a conductive resin composition, which can suppress the occurrence of voids.

[0185] The method for producing a conductive resin composition includes a first step of acid-treating solder particles 5 with an acid treating agent. That is, the conductive resin composition contains acid-treated solder particles 5. Therefore, this method makes it possible to produce a conductive resin composition that can suppress the generation of voids.

[0186] Furthermore, the maximum value of the Mulliken charge of the carbon of the carboxyl group of the flux is 0.5850 or less. Therefore, according to this method, it is possible to produce a conductive resin composition that can suppress the generation of voids.

[0187] The method for producing a bonded body uses the conductive resin composition, which can suppress the occurrence of voids.

[0188] The bonded body 20 includes an adhesive layer 3 that is a cured product of the bonding sheet 1. Therefore, the generation of voids can be suppressed.

[0189] <Modifications> In the modification examples, the same components and steps as those in the first embodiment are denoted by the same reference numerals, and detailed descriptions thereof will be omitted. Furthermore, the modification examples can achieve the same effects as those in the first embodiment unless otherwise specified. Furthermore, the first embodiment and the modification examples can be combined as appropriate.

[0190] Furthermore, in the above description, the first electrodes 12 and the second electrodes 14 are arranged in a dot pattern, but the arrangement of the first electrodes 12 and the second electrodes 14 is not limited to this.

[0191] Furthermore, in the above description, the first electrode 12 and the second electrode 14 have a circular shape when viewed from above, but the shapes of the first electrode 12 and the second electrode 14 are not limited to this and may be, for example, a square shape when viewed from above.

[0192] Furthermore, in the above description, the second substrate 4 has a flat plate shape, but the shape of the second substrate 4 is not limited to this and may be, for example, the shape of a chip component (e.g., a mini / micro LED).

[0193] Next, the present invention will be described based on examples and comparative examples, but the present invention is not limited to the following examples. Note that "parts" and "%" are by mass unless otherwise specified. Furthermore, specific numerical values ​​such as blending ratios (content ratios), physical property values, parameters, etc. used in the following description can be substituted with the corresponding upper limit values ​​(numeric values ​​defined as "equal to or less than") or lower limit values ​​(numeric values ​​defined as "equal to or more than" or "exceeding") of the blending ratios (content ratios), physical property values, parameters, etc. described in the above "Modes for Carrying Out the Invention."

[0194] <Details of Components> The trade names and abbreviations of the components used in each example and each comparative example are described in detail below. Solder particles (1): Sn 96.5% by mass, Ag 3.0% by mass, Cu 0.5% by mass, melting point 217-219°C, spherical shape, average primary particle diameter 3 μm, trade name "SAC305 ST-3", manufactured by Mitsui Mining & Smelting Co., Ltd. Solder particles (2): Sn 96.5% by mass, Ag 3.0% by mass, Cu 0.5% by mass, melting point 217-219°C, spherical shape, average primary particle diameter 7 μm, trade name "SAC305 ST-7", manufactured by Mitsui Mining & Smelting Co., Ltd. Solder particles (3): Sn 96.5% by mass, Ag 3.0% by mass, Cu 0.5% by mass, melting point 217-219°C, spherical shape, average primary particle diameter 8 μm, trade name "SAC305 STC-7", manufactured by Mitsui Mining & Smelting Co., Ltd. Solder particle (4): Sn42% by mass, Bi58% by mass, melting point 138 to 140°C, spherical shape, average primary particle diameter 3 μm, trade name "Sn42Bi58 ST-3", manufactured by Mitsui Mining & Smelting Co., Ltd. Glutaric acid: manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Pimelic acid: manufactured by Tokyo Chemical Industry Co., Ltd. Adipic acid: manufactured by Tokyo Chemical Industry Co., Ltd. 3,3-dimethylglutaric acid: manufactured by Merck KCaA 2-methyladipic acid: manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Malonic acid: manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Succinic acid: manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Malic acid: manufactured by Tokyo Chemical Industry Co., Ltd. Benzylamine glutaric acid: manufactured by Showa Chemical Co., Ltd. YD-017: bisphenol A type epoxy resin, epoxy equivalent 1650 to 2050, solid at 25°C, thermosetting resin, softening point 128°C, manufactured by Nippon Steel Chemical Co., Ltd. NPES907: bisphenol A type epoxy resin, epoxy equivalent 1500 to 1600 g / eq, solid at 25°C, thermosetting resin, softening point 120 to 130°C, manufactured by Nanya Plastics Co., Ltd. J-DPP-115: dicyclopentadiene type phenolic resin, thermosetting resin, softening point 107 to 116°C, manufactured by JFE Chemical Corporation MEH-7851-H: phenol novolac resin, thermosetting resin, softening point 64 to 85°C, manufactured by UBE Corporation jER828: bisphenol A type epoxy resin, epoxy equivalent 184 to 194 g / eq, liquid at 25°C, thermosetting resin, manufactured by Mitsubishi Chemical Corporation

[0195] <Production of Acid-Treated Solder Particles> Production Example 1 (Production of Malic Acid-Treated Solder Particles (1)) [Preparation Step] Malic acid as an acid treatment agent was dissolved in distilled water to a concentration of 1 mol / L, and the dissolved gas was replaced with nitrogen by bubbling with nitrogen, thereby preparing an aqueous solution of the acid treatment agent.

[0196] [Immersion Step] 50 g of an aqueous solution of an acid treatment agent was added to 50 g of the solder particles (1), and the container was closed with a lid, followed by stirring for 20 minutes.

[0197] [Cleaning Step] After waiting for the solder particles (1) to settle naturally, the supernatant was removed, ethanol was added, and the mixture was stirred until it became homogeneous. Then, the same procedure was repeated once more.

[0198] Next, the solder particles (1) were allowed to settle naturally, the supernatant was removed, acetone was added, and the mixture was stirred until it became homogeneous.

[0199] Next, after waiting for the solder particles (1) to settle naturally and removing the supernatant, jER828 was added according to the formulations shown in Tables 1 to 3, and the mixture was stirred until homogenous.

[0200] [Solvent Removal Step] Vacuum drying was carried out in a vacuum oven at 25° C. for 2 hours, thereby producing acid-treated solder particles (malic acid-treated solder particles (1)).

[0201] Production Example 2 (Production of Glutaric Acid-Treated Solder Particles (1)) Acid-treated solder particles (glutaric acid-treated solder particles (1)) were produced based on the same procedure as in Production Example 1. However, the acid treatment agent was changed to glutaric acid.

[0202] Production Example 3 (Production of Malic Acid-Treated Solder Particles (2)) Acid-treated solder particles (glutaric acid-treated solder particles) were produced based on the same procedure as in Production Example 1. However, the solder particles were changed to solder particles (2).

[0203] Production Example 4 Acid-treated solder particles (malic acid-treated solder particles) were produced based on the same procedure as in Production Example 1. However, the solder particles were changed to solder particles (3).

[0204] Production Example 5 Acid-treated solder particles (malic acid-treated solder particles) were produced based on the same procedure as in Production Example 1. However, the solder particles were changed to solder particles (4).

[0205] <Production of Conductive Resin Composition> Examples 1 to 24 and Comparative Examples 1 to 9 [Step 1] In Step 1, solder particles were acid-treated with an acid treating agent. Specifically, malic acid-treated solder particles (1) of Production Example 1, glutaric acid-treated solder particles (1) of Production Example 2, malic acid-treated solder particles (2) of Production Example 3, malic acid-treated solder particles (3) of Production Example 4, and malic acid-treated solder particles (4) of Production Example 5 were prepared.

[0206] [Second Step] The acid-treated solder particles, resin component, and flux were mixed according to the formulations shown in Tables 1 to 3. Then, acetone was added and the mixture was stirred until homogenous, thereby producing a varnish of the conductive resin composition (solid content concentration: 70% by mass).

[0207] YD-017 was dissolved in methyl ethyl ketone in advance to prepare a varnish (solid content concentration: 60% by mass). Flux was dissolved in ethanol in advance to prepare a flux solution (solid content concentration: 30% by mass). The values ​​of each component listed in Tables 1 to 3 are the solid content values.

[0208] <Production of Test Joint> [Third Step] In Examples 1 to 14, 16 to 24, and Comparative Examples 1 to 9, two substrates were prepared: a dummy wafer with Ni electrodes (size 10 mm × 10 mm, electrode φ 15 μm, distance between electrode edges 15 μm) and alkali-free glass (10 mm × 10 mm). In Example 15, two substrates were prepared: a dummy wafer with Au electrodes (size 10 mm × 10 mm, electrode φ 30 μm, distance between electrode edges 30 μm) and alkali-free glass (10 mm × 10 mm). In Example 23, two dummy wafers with Au electrodes (silicon wafer substrate, size 10 mm × 10 mm, electrode φ 30 μm, distance between electrode edges 30 μm) were prepared. In Example 24, two FPC boards (electrodes φ100 μm, distance between electrode ends 200 μm) were prepared as the two boards.

[0209] [Step 4] The conductive resin composition of each example and comparative example was applied to a release liner using an applicator and dried for 5 minutes at 60° C. In this way, a bonding sheet (thickness 5 μm) was prepared.

[0210] [Fifth Step] A dummy wafer with a Ni electrode or an Au electrode, a bonding sheet, and alkali-free glass were bonded together in this order in a vacuum at 50° C. The release liner was removed during the bonding process, thereby producing a laminate.

[0211] The resulting laminate was observed with an optical microscope (VHX-8000, KEYENCE) to confirm that no air bubbles were trapped.

[0212] [Step 6] The laminate was placed in a vacuum pressure reflow machine (Model 1200 Table Top Furnace, SST International), and after evacuation, the machine was pressurized to 4.5 atmospheres with nitrogen. Thereafter, heating was performed under the conditions of a temperature increase rate of 100°C / min, a maximum temperature of 260°C, and a holding time of 15 minutes. In this way, a test bonded body was produced.

[0213] <Evaluation> [Maximum Value of Mulliken Charge] The maximum value of Mulliken charge was calculated for each flux using the general-purpose quantum chemistry calculation program Gaussian 16 (Gaussian).

[0214] The initial structure was created and drawn using the molecular editor software Avogadro (Avogadro Chemistry).

[0215] For the bimolecular complex, the initial structure was set up so that intermolecular interactions occurred only between the additional molecule and the carboxyl group of the fluxing agent.

[0216] For benzylamine glutaric acid (complex), two types of simulations were performed: one with a benzene ring and a carboxyl group interaction, and the other with a primary amine and a carboxyl group interaction, and the results for the structure with the lowest energy were adopted.

[0217] When performing calculations with Gaussian 16, values ​​obtained by structural optimization calculations using B3LYP as the functional and 6-31+G(d) as the basis set were used.

[0218] In this calculation, dispersion force correction was performed using the D3 method of Grimme et al.

[0219] The calculated Mulliken charge was used for molecules with multiple carboxyl groups. The results are shown in Tables 1 to 3.

[0220] [Removal Rate of Oxide Film on the Surface of Solder Particles by Acidizing Agent] Malic acid (acidizing agent) was dissolved in distilled water and stirred to give a concentration of 1 mol / L to prepare an aqueous solution of malic acid.

[0221] Next, 10 g of the solder particles (1) were immersed in 10 g of an aqueous solution of malic acid and stirred.

[0222] After that, 1 cc of the solution was taken after 1, 3, 5 and 10 minutes, and centrifuged (15,000 rpm x 1 minute) to separate the solder particles (1) from the supernatant.

[0223] The supernatant was then filtered using a syringe filter with a pore size of 0.45 μm to obtain a filtrate. Approximately 100 mg of the filtrate was then weighed out and placed in a container (hereinafter referred to as the sample amount), and acid was added thereto, followed by sealing.

[0224] The sealed container was then irradiated with microwaves (UltraWAVE, Milestone) and subjected to acid decomposition under pressure at a maximum temperature of 250°C.

[0225] Then, ultrapure water was added to make the volume 50 mL, and this was used as a measurement solution. Sn quantitative analysis (analysis wavelength 189.989 nm) was performed using ICP-AES (SPS-3520UV, Hitachi High-Tech Science) to measure the Sn ion concentration in the measurement solution.

[0226] In order to confirm the reproducibility of the preparation of the measurement solution and the measurement, sampling was carried out with n=2, and the average value was calculated.

[0227] Separately, the Sn ion concentration in the operation blank was measured. Specifically, the Sn quantitative analysis was performed on ultrapure water in the same manner as above. Thus, the Sn ion concentration in the operation blank was measured.

[0228] The Sn concentration was then calculated according to the following formula. The results are shown in Table 4 and FIG. 3. It can be seen that the higher the Sn concentration, the faster the removal rate of the oxide film on the surface of the solder particle (1) by the acid treatment agent. Furthermore, the acid treatment agent was changed to glutaric acid, and the Sn concentration was calculated using the same procedure. The results are shown in Table 4 and FIG. 3. Sn ion concentration [mass %] = (Sn ion concentration in measurement solution [ng / mL] - Sn ion concentration in operation blank [ng / mL]) × volume of measurement solution [mL] / (amount of sample collected [mg] × 10,000)

[0229] FIG. 3 shows that malic acid has a faster oxide film removal rate than glutaric acid.

[0230] [Observation of solder accumulation state] For the test joints of each example and comparative example, seven locations (more specifically, (1) to (7) shown in FIG. 4) were observed at a magnification of 500x using an optical microscope (VHX-8000, KEYENCE) within an area of ​​630 μm × 500 μm. The solder accumulation state was evaluated based on the following criteria. The results are shown in Tables 1 to 3. {Criteria} Level 4 (◎): The solder covered 95% or more of the electrode. Level 3 (◯): The solder covered 90% or more but less than 95% of the electrode. Level 2 (△): The solder covered 80% or more but less than 90% of the electrode. Level 1 (×): The solder covered less than 80% of the electrode.

[0231] [Void occurrence] For the test bonded bodies of each Example and Comparative Example, the occurrence of voids was observed at seven locations (more specifically, (1) to (7) shown in FIG. 4) within an area of ​​630 μm × 500 μm at 500x magnification using an optical microscope (VHX-8000, KEYENCE). The occurrence of voids was evaluated based on the following criteria. The results are shown in Tables 1 to 3. {Criteria} Level 3 (◯): The area of ​​the portion containing bubbles was less than 5% of the visual field. Level 2 (△): The area of ​​the portion containing bubbles was 5% or more but less than 20% of the visual field. Level 1 (×): The area of ​​the portion containing bubbles was 20% or more of the visual field.

[0232] [Evaluation of Electrical Connection] After the test connection structure of Example 23 was embedded in resin, the laminate cross section was exposed by mechanical polishing, and the electrical connection of the counter electrodes was evaluated using an optical microscope (name "VHX-8000", manufactured by Keyence Corporation) according to the following criteria. The results are shown in Table 3. {Criteria} Level 2: Connection of the counter electrodes by solder was observed. Level 1: Connection of the counter electrodes by solder was not observed.

[0233] Furthermore, for the test connection structure of Example 24, the electrical resistance value between the opposing electrodes was evaluated using a digital multimeter (name "PC500a", manufactured by Sanwa Electric Measurement Co., Ltd.). The electrical connection of the opposing electrodes was evaluated according to the following criteria. The results are shown in Table 3. {Criteria} Level 2: The electrical resistance value was a positive value (a value exceeding 0). Level 1: The electrical resistance value was 0 or less.

[0234]

[0235]

[0236]

[0237]

[0238] The above invention is provided as an exemplary embodiment of the present invention, but this is merely an example and should not be interpreted as limiting. Modifications of the present invention that are obvious to those skilled in the art are intended to be included in the scope of the following claims.

[0239] The conductive resin composition, bonding sheet, method for producing a conductive resin composition, method for producing a bonded body, and bonded body of the present invention are suitably used in the production of electronic devices, for example.

[0240] REFERENCE SIGNS LIST 1 Bonding sheet 2 First substrate 4 Second substrate 5 Solder particles 6 Laminate 12 First electrode 14 Second electrode 15 Columnar solder portion 20 Bonded body 25 Pressure oven

Claims

1. A conductive resin composition comprising acid-treated solder particles, a resin component, and a flux having a carboxyl group, the maximum value of the Mulliken charge of carbon of the carboxyl group of the flux being 0.5850 or less.

2. The conductive resin composition according to claim 1, wherein the content of said flux is from 1 part by mass to 7 parts by mass with respect to 100 parts by mass of said acid-treated solder particles.

3. The conductive resin composition according to claim 1, wherein the flux is a carboxylic acid.

4. The conductive resin composition according to claim 3, wherein the flux is a dicarboxylic acid.

5. A bonding sheet comprising the conductive resin composition according to any one of claims 1 to 4.

6. A method for producing a conductive resin composition, comprising: a first step of acid-treating solder particles with an acid treating agent; and a second step of mixing the acid-treated solder particles, a resin component, and a flux having a carboxyl group, wherein the maximum value of the Mulliken charge of the carbon of the carboxyl group of the flux is 0.585 or less.

7. The method for producing a conductive resin composition according to claim 6, wherein the acid treating agent has a carboxyl group, and the maximum value of the Mulliken charge of the carbon of the carboxyl group exceeds 0.5850.

8. A method for producing a joint body, comprising: a third step of preparing a plurality of substrates each having a plurality of electrodes arranged in a planar direction; a fourth step of preparing a joint sheet by applying a conductive resin composition obtained by the manufacturing method described in claim 6 or 7; a fifth step of stacking the two substrates with the joint sheet sandwiched therebetween so that the electrodes of the two substrates face each other, to produce a laminate; and a sixth step of heating the laminate and melting the solder particles to form columnar solder portions so as to electrically connect the electrodes of the two substrates, and hardening the resin component.

9. The method for producing a bonded body according to claim 8, wherein the sixth step is carried out in a pressure oven.

10. A bonded body comprising: a first substrate having a plurality of first electrodes aligned in a surface direction; a second substrate having a plurality of second electrodes aligned in the surface direction, the second substrate being spaced apart in a thickness direction perpendicular to the surface direction such that the first electrodes and the second electrodes face each other; and an adhesive layer interposed between the first substrate and the second substrate, electrically connecting the first electrodes and the second electrodes facing each other in the thickness direction and bonding the first substrate and the second substrate together, the adhesive layer being a cured product of the bonding sheet according to any one of claims 1 to 4, and the adhesive layer including columnar solder portions and cured resin that electrically connect the first electrodes and the second electrodes facing each other in the thickness direction.

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