Conductive composition, conductive sheet, laminate, connection structure, and method for producing connection structure

Abstract

The present invention provides a conductive composition having improved integration properties with respect to a wiring circuit board. A conductive composition according to an embodiment of the present invention contains solder particles, resin, and flux. The flux contains a carboxylic acid compound. The carboxylic acid compound has a first acid dissociation constant pKa1 of 3.41-4.70 and a second acid dissociation constant pKa2 of 6.34 or less.

Description

Conductive Composition, Conductive Sheet, Laminate, Connection Structure, and Method for Producing Connection Structure

[0001] The present invention relates to a conductive composition, a conductive sheet, a laminate, a connection structure, and a method for producing a connection structure.

[0002] Conventionally, anisotropic conductive compositions have been used for connecting two wiring circuit boards. When heated while disposed between two wiring circuit boards, the anisotropic conductive composition develops conductivity in the lamination direction of the two wiring circuit boards, while ensuring insulating properties in the direction orthogonal to the lamination direction (plane direction).

[0003] As an anisotropic conductive composition, a combination of solder particles and a thermosetting resin is known (for example, Patent Document 1). When this anisotropic conductive composition is heated, the solder particles melt and aggregate between the electrode of one wiring circuit board and the electrode of the other wiring circuit board. Thereafter, the molten solder is cooled and solidified, whereby these electrodes are electrically connected. In regions where no electrodes are present, aggregation of the solder particles does not proceed, and insulation by the resin is maintained. By such a mechanism, anisotropy is developed in which the electrical characteristics differ between the lamination direction and the plane direction of the two wiring circuit boards.

[0004] International Publication No. 2023 / 145487

[0005] Conductive compositions have room for improvement from the viewpoint of integration with wiring circuit boards.

[0006] An object of the present invention is to provide a conductive composition with improved integration for wiring circuit boards.

[0007] [1] A conductive composition according to an embodiment of the present invention is a conductive composition comprising solder particles, a resin, and a flux, wherein the flux comprises a carboxylic acid compound, and the carboxylic acid compound has a first acid dissociation constant pKa1 of 3.41 to 4.70 and a second acid dissociation constant pKa2 of 6.34 or less. [2] In the conductive composition described in [1] above, the second acid dissociation constant pKa2 may be 4.10 or more. [3] In the conductive composition described in [1] or [2] above, the ratio of the weight of the flux to the weight of the oxygen contained in the solder particles may be 0.300 or less. [4] In the conductive composition described in any of [1] to [3] above, the number of carboxyl groups contained in the carboxylic acid compound may be 2 or more. [5] In the conductive composition described in any of [1] to [4] above, the number of carboxyl groups contained in the carboxylic acid compound may be 3. [6] In the conductive composition described in any of [1] to [5] above, the resin may include at least one selected from the group consisting of epoxy resin, (meth)acrylic resin, phenoxy resin, and phenol resin. [7] In the conductive composition described in any of [1] to [6] above, the resin may include epoxy resin. [8] In the conductive composition described in [7] above, the weight-average molecular weight of the epoxy resin may be less than 10,000. [9] In the conductive composition described in [7] or [8] above, the epoxy resin may include repeating units having glycidyl groups.

[10] In the conductive composition described in any of [7] to [9] above, the epoxy resin may have at least one selected from the group consisting of dicyclopentadiene skeleton, biphenyl skeleton, naphthalene skeleton, phenol skeleton, and cresol skeleton.

[11] In the conductive composition described in any of [7] to

[10] above, the conductive composition may include liquid epoxy resin and solid epoxy resin.

[12] In the conductive composition described in any of [7] to

[11] above, the epoxy equivalent of the epoxy resin may be 225 g / eq. or more.

[13] In the conductive composition described in any of [1] to

[12] above, the resin may include a polymer resin having a weight-average molecular weight of 10,000 or more.

[14] In the conductive composition described in

[13] above, the content ratio of the polymer resin in the resin may be 20% by weight or less.

[15] A conductive sheet according to an embodiment of the present invention is made from a conductive composition described in any of [1] to

[14] above.

[16] A laminate according to an embodiment of the present invention comprises a conductive sheet described in

[15] above, and a release liner.

[17] A connecting structure according to an embodiment of the present invention comprises a first substrate on which a first electrode is arranged, a second substrate on which a second electrode is arranged, and a connecting member connecting the first substrate and the second substrate, wherein the connecting member is formed from a conductive composition described in any of [1] to

[14] above.

[18] A method for manufacturing a connecting structure according to an embodiment of the present invention is a method for manufacturing a connecting structure as described in

[17] above, comprising: arranging the conductive composition between the first substrate and the second substrate; and heating the conductive composition to form the connecting member.

[0008] According to embodiments of the present invention, it is possible to provide a conductive composition with improved integration with respect to a wiring circuit board.

[0009] This is a graph illustrating the relationship between temperature and complex viscosity for a conductive composition excluding solder particles. This is a schematic cross-sectional view of a conductive sheet according to one embodiment of the present invention. This is a schematic cross-sectional view of a connecting structure according to one embodiment of the present invention. This is a diagram illustrating the manufacturing method of the connecting structure shown in Figure 3. This is a diagram illustrating the manufacturing method of the connecting structure shown in Figure 3.

[0010] ≪1. Conductive Composition≫ The conductive composition according to the embodiment of the present invention comprises solder particles, a resin, and a flux. The flux comprises a carboxylic acid compound C. The carboxylic acid compound C has a first acid dissociation constant pKa1 of 3.41 to 4.70 and a second acid dissociation constant pKa2 of 6.34 or less. The conductive composition of this embodiment can typically function as an anisotropic conductive composition.

[0011] In this specification, the "acid dissociation constant" is the value in water at 25°C. The first acid dissociation constant pKa1 and the second acid dissociation constant pKa2 of carboxylic acid compound C can be determined by the following method. First, prepare 20 mL of an aqueous solution of carboxylic acid compound C (concentration 0.5 mol / L). Add an aqueous solution of sodium hydroxide (concentration 0.5 mol / L) dropwise to this aqueous solution and perform a neutralization titration. In the neutralization titration, the first hydrogen ion (H) from carboxylic acid compound C is determined. + The acid dissociation constant when ) dissociates can be considered as the first acid dissociation constant pKa1, and the acid dissociation constant when the second hydrogen ion dissociates from the carboxylic acid compound C can be considered as the second acid dissociation constant pKa2. The above neutralization titration is performed under a temperature of 25°C.

[0012] The flux containing the carboxylic acid compound C mentioned above tends to effectively remove oxide films that may be present on the surface of solder particles. This flux also tends to effectively remove oxide films that may be present on the surface of electrodes in contact with a conductive composition when the conductive composition is used to connect two circuit boards. The removal of oxide films and other contaminants from solder particles by the flux tends to improve integration with the circuit board.

[0013] Furthermore, fluxes containing the carboxylic acid compound C mentioned above tend to efficiently remove oxide films and other contaminants from solder particles, even in small amounts. Therefore, this flux makes it easier to adjust the flux content in conductive compositions to a low level. When the flux content is low, corrosion of solder particles due to flux residue tends to be suppressed. Additionally, a low flux content tends to reduce the water absorption of the conductive composition, improving its durability.

[0014] The first acid dissociation constant pKa1 of carboxylic acid compound C is 3.41 to 4.70 as described above, and may be 4.69 or less, 4.66 or less, 4.60 or less, 4.50 or less, 4.40 or less, 4.30 or less, 4.20 or less, 4.10 or less, 4.00 or less, and even 3.95 or less. The lower limit of pKa1 may be 3.45 or more, and may be 3.50 or more, 3.60 or more, 3.70 or more, 3.80 or more, and even 3.90 or more.

[0015] The second acid dissociation constant pKa2 of carboxylic acid compound C is 6.34 or less as described above, and may also be 6.30 or less, 6.20 or less, 6.10 or less, 6.00 or less, 5.90 or less, 5.80 or less, 5.70 or less, 5.60 or less, 5.50 or less, 5.40 or less, 5.30 or less, 5.20 or less, 5.10 or less, 5.00 or less, 4.90 or less, 4.85 or less, and even 4.80 or less. The lower limit of the above pKa2 is, for example, 3.50 or more, and may also be 3.60 or more, 3.70 or more, 3.80 or more, 3.90 or more, 4.00 or more, 4.10 or more, 4.20 or more, 4.30 or more, 4.40 or more, 4.50 or more, 4.60 or more, 4.70 or more, and even 4.75 or more. The above pKa2 may be in the range of 4.10 to 5.60.

[0016] <1-1. Solder Particles> As described above, the conductive composition contains solder particles. There may be only one type of solder particle, or there may be two or more types. From the viewpoint of environmental protection, the material of the solder particles is preferably lead-free solder material that does not contain lead.

[0017] The solder particles preferably contain tin (Sn). Solder particles containing tin tend to accelerate the hardening of the resin through metal catalytic action. In the solder particles, tin may exist in elemental form or form an alloy with other metals. Examples of tin alloys include tin-bismuth alloy (Sn-Bi), tin-silver-copper alloy (Sn-Ag-Cu), tin-silver alloy (Sn-Ag), and tin-bismuth-indium alloy (Sn-Bi-In).

[0018] When solder particles contain a tin-silver-copper alloy, the tin content in the tin-silver-copper alloy may be, for example, 90% by weight or more, and may be 95% by weight or more. The silver content in the tin-silver-copper alloy may be, for example, 10% by weight or less, and may be 5% by weight or less. The copper content in the tin-silver-copper alloy may be, for example, 1% by weight or less, and may be 0.5% by weight or less.

[0019] When the solder particles contain a tin-bismuth alloy, the tin content in the tin-bismuth alloy may be, for example, 80% by weight or less, or 50% by weight or less. The bismuth content in the tin-bismuth alloy may be, for example, 20% by weight or more, or 50% by weight or more.

[0020] The shape of the solder particles is not particularly limited as long as they are particulate, and examples include spherical, ellipsoidal, flaky, and fibrous shapes. Spherical solder particles are preferred. The average particle diameter (average primary particle diameter) of the solder particles is, for example, 20 μm or less, and may be 10 μm or less, 8 μm or less, 5 μm or less, or even 3 μm or less. Solder particles with a small average particle diameter are suitable for fabricating miniaturized, low-profile connection structures. The average particle diameter of the solder particles may be, for example, 0.1 μm or more, or 0.5 μm or more. In this specification, the average particle diameter can be specified as the median diameter (D50) in the particle size distribution measured by a laser diffraction particle size distribution analyzer or the like.

[0021] The melting point T0 of solder particles is, for example, 70°C or higher, and may be 100°C or higher, 120°C or higher, 150°C or higher, 180°C or higher, or even 200°C or higher. The melting point T0 of solder particles is, for example, 280°C or lower, and may be 260°C or lower, or even 240°C or lower. The melting point can be measured by differential scanning calorimetry (DSC).

[0022] The content of solder particles in the conductive composition is, for example, 20% by weight or more, and may be 30% by weight or more, 40% by weight or more, 50% by weight or more, or even 60% by weight or more. The above content may be, for example, 80% by weight or less, and may be 70% by weight or less.

[0023] Note that solder particles may have an oxide film formed on their surface, but it is preferable that no oxide film is formed. The oxide film on the solder particles can be removed, for example, by performing an acid treatment on the solder particles before preparing the conductive composition. Details of the method for removing the oxide film will be explained in section 1-6. Method for producing the conductive composition.

[0024] <1-2. Resin> As described above, the conductive composition includes a resin. As the resin, any resin known in the field of anisotropic conductive compositions can be used, such as thermosetting resins and thermoplastic resins. It is preferable that the resin includes a thermosetting resin.

[0025] The resin preferably contains at least one selected from the group consisting of epoxy resin, (meth)acrylic resin, phenoxy resin, and phenolic resin, and is particularly preferably epoxy resin. In this specification, "(meth)acrylic" means "acrylic and / or methacrylic".

[0026] (1-2-a. Epoxy Resins) The epoxy resin may be of one type or two or more types. The epoxy resin described in section (1-2-a. Epoxy Resins) typically has a weight-average molecular weight of less than 10,000 and is not classified as a polymer resin, as will be discussed later.

[0027] Epoxy resins are typically thermosetting. In other words, epoxy resins typically have at least one epoxy group (particularly a glycidyl group) in one molecule. The epoxy equivalent of an epoxy resin is, for example, 100 g / eq. or more, and may be 150 g / eq. or more, 180 g / eq. or more, 200 g / eq. or more, 225 g / eq. or more, 230 g / eq. or more, 250 g / eq. or more, and even 280 g / eq. or more. The above epoxy equivalent is, for example, 3000 g / eq. or less, and may be 2000 g / eq. or less, 1000 g / eq. or less, 800 g / eq. or less, 500 g / eq. or less, 400 g / eq. or less, and even 300 g / eq. or less. Note that epoxy equivalent refers to the molecular weight of the epoxy resin per equivalent of epoxy groups contained in the epoxy resin. If the conductive composition contains two or more types of epoxy resins, the average value of the epoxy equivalents may satisfy the above numerical range.

[0028] The flux contained in the conductive composition of this embodiment tends to accelerate the curing of the epoxy resin. In other words, the presence of the flux may lower the temperature required to cure the epoxy resin (curing temperature). According to the inventors' studies, when the conductive composition contains an epoxy resin with an epoxy equivalent of 225 g / eq. or more, it tends to be easier to adjust the curing temperature of the epoxy resin to an appropriate value, even when combined with the flux mentioned above.

[0029] Epoxy resins preferably contain repeating units having epoxy groups (particularly glycidyl groups) in their molecules. Repeating units having epoxy groups are represented, for example, by the following formula (1).

[0030] In formula (1) above, A is a divalent linking group. Preferably, A includes a ring structure. Examples of ring structures include aliphatic rings such as dicyclopentadiene rings; aromatic rings such as benzene rings, biphenyl rings, and naphthalene rings. The ring structure may or may not have further substituents. The ring structure may be directly bonded to the benzene ring adjacent to A in formula (1), or it may be bonded via a linking group such as an alkylene group.

[0031] As shown in formula (1), the benzene ring adjacent to A has a glycidyl group. This benzene ring may further have other substituents besides the glycidyl group. Examples of other substituents include alkyl groups such as methyl groups.

[0032] Epoxy resins preferably have at least one skeleton selected from the group consisting of a dicyclopentadiene skeleton, a biphenyl skeleton, a naphthalene skeleton, a phenol skeleton, and a cresol skeleton in their molecule, more preferably at least one selected from the group consisting of a dicyclopentadiene skeleton, a biphenyl skeleton, and a naphthalene skeleton, and particularly preferably have a dicyclopentadiene skeleton. Epoxy resins having skeletons such as a dicyclopentadiene skeleton, a biphenyl skeleton, or a naphthalene skeleton are suitable for adjusting the storage modulus of a conductive composition to an appropriate value. These epoxy resins also tend to reduce the water absorption of the conductive composition.

[0033] The dicyclopentadiene skeleton can be represented, for example, by the following formula (2).

[0034] In formula (2) above, * indicates a bonding site with other structures. Formula (2) specifically represents a dicyclopentadiene ring functioning as a divalent linking group. This dicyclopentadiene ring may or may not have substituents. Examples of epoxy resins having a dicyclopentadiene skeleton include those in which A in the repeating unit of formula (1) above is represented by formula (2).

[0035] Furthermore, examples of epoxy resins having a biphenyl skeleton include those in which A is a biphenyl ring in the repeating unit of formula (1) above. Examples of epoxy resins having a naphthalene skeleton include those in which A is a naphthalene ring in the repeating unit of formula (1) above.

[0036] The epoxy resin included in the conductive composition of this embodiment is not limited to those described above. For example, the conductive composition may include other epoxy resins other than the epoxy resin having the repeating unit of formula (1) described above.

[0037] Specific examples of epoxy resins (thermosetting epoxy resins) include bisphenol-type epoxy resins (e.g., bisphenol A-type epoxy resin, bisphenol F-type epoxy resin, and bisphenol S-type epoxy resin), novolac-type epoxy resins (e.g., phenol novolac-type epoxy resin, cresol novolac-type epoxy resin, and biphenyl-type epoxy resin), naphthalene-type epoxy resin, fluorene-type epoxy resin (e.g., bisarylfluorene-type epoxy resin), triphenylmethane-type epoxy resin (e.g., trishydroxyphenylmethane-type epoxy resin), and dicyclopentadiene-type epoxy resin.

[0038] The conductive composition preferably contains at least one epoxy resin selected from the group consisting of dicyclopentadiene-type epoxy resins, biphenyl-type epoxy resins, and naphthalene-type epoxy resins, and is particularly preferably a dicyclopentadiene-type epoxy resin. However, the conductive composition may also contain other epoxy resins (for example, bisphenol A-type epoxy resins, cresol novolac-type epoxy resins, phenol novolac-type epoxy resins, etc.).

[0039] Commercially available dicyclopentadiene-type epoxy resins include "EPICLON HP-7200HHH" from DIC Corporation and "XD-1000" from Nippon Kayaku Co., Ltd. Commercially available biphenyl-type epoxy resins include "NC-3000" and "NC-3500" from Nippon Kayaku Co., Ltd. Commercially available naphthalene-type epoxy resins include "NC-7000H" from Nippon Kayaku Co., Ltd. Commercially available bisphenol-type epoxy resins include "jER828" from Mitsubishi Chemical Corporation and "NPES907" from Nanya Plastics Co., Ltd. Commercially available cresol novolac-type epoxy resins include "EOCN-1020-70" from Nippon Kayaku Co., Ltd. Commercially available phenol novolac-type epoxy resins include "EPPN-502H" from Nippon Kayaku Co., Ltd.

[0040] The weight-average molecular weight of the epoxy resin is, for example, less than 10,000, and may be 9,000 or less, 8,000 or less, 7,000 or less, 6,000 or less, 5,000 or less, or even 4,000 or less. The weight-average molecular weight is, for example, 100 or more, and may be 300 or more, 500 or more, 800 or more, or even 1,000 or more. The weight-average molecular weight can be measured by GPC (gel permeation chromatography).

[0041] The curing temperature of the epoxy resin is preferably above the melting point T0 of the solder particles, for example, 150°C to 280°C, and may also be 160°C to 260°C, or even 170°C to 250°C.

[0042] In the conductive composition, the epoxy resin may be liquid or solid. The conductive composition of this embodiment preferably contains both liquid epoxy resin and solid epoxy resin. However, the conductive composition may contain only one of the liquid epoxy resin or solid epoxy resin (for example, only solid epoxy resin). In this specification, "liquid" means a substance in a liquid state that can flow at atmospheric pressure (101.325 kPa) and 25°C, and "solid" means a substance in a solid state that does not flow at atmospheric pressure and 25°C.

[0043] The softening point of the solid epoxy resin is preferably lower than the melting point T0 of the solder particles. The above softening point is, for example, 40°C or higher, may be 60°C or higher, or even 80°C or higher. The above softening point is, for example, 200°C or lower, may be 180°C or lower, 150°C or lower, or even 140°C or lower. Note that the softening point can be measured with a thermomechanical analyzer.

[0044] The content of the epoxy resin in the conductive composition is, for example, 10% by weight or more, may be 20% by weight or more, 25% by weight or more, or even 30% by weight or more. The above content is, for example, 60% by weight or less, may be 50% by weight or less, or even 40% by weight or less.

[0045] The content ratio R1 of solid epoxy resin in the resin contained in the conductive composition is, for example, 40% by weight or more, may be 50% by weight or more, 60% by weight or more, 65% by weight or more, or even 70% by weight or more. The content ratio R1 is, for example, 95% by weight or less, may be 90% by weight or less, 85% by weight or less, or even 80% by weight or less.

[0046] (1-2-b. Polymer Resin) The conductive composition preferably contains a polymer resin having a weight average molecular weight of 10,000 or more. The polymer resin is suitable for adjusting the complex viscosity of the conductive composition to an appropriate value. Only one type of polymer resin may be used, or two or more types may be used.

[0047] Examples of the polymer resin include epoxy resins and (meth)acrylic resins having a weight average molecular weight of 10,000 or more. Epoxy resins having a weight average molecular weight of 10,000 or more are sometimes referred to as phenoxy resins.

[0048] The epoxy resin used as a polymer resin may be thermosetting or thermoplastic. A thermosetting epoxy resin typically has at least one epoxy group (particularly a glycidyl group) in one molecule. In this case, the epoxy equivalent of the epoxy resin may be, for example, 3000 g / eq. or more, 5000 g / eq. or more, and even 8000 g / eq. or more. The epoxy equivalent may also be, for example, 50000 g / eq. or less, and 10000 g / eq. or less.

[0049] Specific examples of epoxy resins are those exemplified in section (1-2-a. Epoxy Resins). The epoxy resin used as the polymer resin is preferably a bisphenol-type epoxy resin (particularly bisphenol A-type epoxy resin or bisphenol F-type epoxy resin). Examples of commercially available bisphenol-type epoxy resins used as polymer resins include the product names "jER1256" and "jER4250" manufactured by Mitsubishi Chemical Corporation.

[0050] The (meth)acrylic resin used as the polymer resin is preferably thermoplastic. Examples of commercially available (meth)acrylic resins include "Teisan Resin SG-70L" manufactured by Nagase ChemteX Corporation and "ARUFON UH-2170" manufactured by Toagosei Co., Ltd.

[0051] The weight-average molecular weight of the polymer resin is 10,000 or more, as described above, but may be 20,000 or more, 30,000 or more, or even 40,000 or more. The above weight-average molecular weight may be, for example, 2 million or less, but may be 1 million or less, 500,000 or less, 300,000 or less, or even 100,000 or less.

[0052] The polymer resin may be thermosetting or thermoplastic. If the polymer resin is thermosetting, the curing temperature of the polymer resin is preferably above the melting point T0 of the solder particles, for example, 120°C to 280°C, and may also be 160°C to 260°C, or even 170°C to 250°C.

[0053] In the conductive composition, the polymer resin may be liquid, but it is preferably solid. The glass transition temperature of the solid polymer resin is preferably lower than the melting point T0 of the solder particles. The glass transition temperature is, for example, 50°C to 150°C, and may also be 80°C to 120°C.

[0054] The content of polymer resin in the conductive composition is, for example, 0.1% by weight or more, and may be 0.5% by weight or more, 1.0% by weight or more, 2.0% by weight or more, and even 3.0% by weight or more. The above content is, for example, 20% by weight or less, and may be 15% by weight or less, 10% by weight or less, and even 5.0% by weight or less.

[0055] The content ratio R2 of the polymer resin in the resin contained in the conductive composition is, for example, 30% by weight or less, and may be 25% by weight or less, 20% by weight or less, 15% by weight or less, or even 10% by weight or less. The content ratio R2 is, for example, 0.1% by weight or more, and may be 0.5% by weight or more, 1.0% by weight or more, 5.0% by weight or more, or even 8.0% by weight or more.

[0056] (1-2-c. Other Resins) The conductive composition may contain other resins besides those described above. Examples of other resins include urea resin, melamine resin, diallyl phthalate resin, silicone resin, polyester resin (e.g., polyethylene terephthalate), polyimide resin, polyurethane resin, polyolefin (e.g., polyethylene, polypropylene, ethylene-propylene copolymer), polyvinyl acetate, ethylene-vinyl acetate copolymer, polyvinyl chloride, polystyrene, polyacrylonitrile, polyamide, polycarbonate, polyacetal, polyphenylene oxide, polyphenylene sulfide, polysulfone, polyethersulfone, polyetheretherketone, polyallylsulfone, polyaminobismaleimide, polyamideimide, polyetherimide, bismaleimide triazine resin, polymethylpentene, fluorinated resin, liquid crystal polymer, olefin-vinyl alcohol copolymer, ionomer, polyarylate, acrylonitrile-ethylene-styrene copolymer, acrylonitrile-butadiene-styrene copolymer, acrylonitrile-styrene copolymer, butadiene-styrene copolymer, and the like.

[0057] The content of other resins in the conductive composition may be, for example, 10% by weight or less, 5% by weight or less, 1% by weight or less, or even 0.1% by weight or less. The conductive composition may be substantially free of other resins.

[0058] <1-3. Flux> As described above, the conductive composition includes a flux. The carboxylic acid compound C contained in the flux is not particularly limited as long as pKa1 and pKa2 are within the above range. There may be only one carboxylic acid compound C or two or more.

[0059] Carboxylic acid compound C is a compound containing at least one carboxyl group. The number of carboxyl groups in carboxylic acid compound C is, for example, two or more. The upper limit of the number of carboxyl groups is, for example, five or less, and may be four or less, or even three or less. It is preferable that the number of carboxyl groups in carboxylic acid compound C is three. In other words, it is preferable that carboxylic acid compound C is a tricarboxylic acid compound. However, carboxylic acid compound C may also be a dicarboxylic acid compound having two carboxyl groups.

[0060] Tricarboxylic acid compounds tend to react more efficiently with oxide films that may be present on the surface of solder particles compared to dicarboxylic acid compounds. Furthermore, even after the dissociation of hydrogen ions from the first carboxyl group, tricarboxylic acid compounds exhibit a large imbalance in electron density within the molecule due to the inductive effect of other carboxyl groups. Therefore, hydrogen ions are more easily dissociated from the second carboxyl group, resulting in a tendency towards high reactivity. When tricarboxylic acid compounds react with resins such as epoxy resins, they can also form branched crosslinked structures. The formation of these crosslinked structures during integration into wiring circuit boards tends to result in connection structures with high heat resistance and mechanical properties.

[0061] Carboxylic acid compound C may contain functional groups other than carboxyl groups (e.g., hydroxyl groups), but it is preferable that it does not. In particular, when carboxylic acid compound C without hydroxyl groups is used, gas is less likely to be generated from the conductive composition during the fabrication of the connecting structure, and the generation of voids (bubbles) caused by such gas tends to be suppressed.

[0062] The carboxylic acid compound C is preferably an aliphatic compound having a carboxyl group. The number of carbon atoms in this aliphatic compound is, for example, 1 to 10, 3 to 9, and even 5 to 8. The aliphatic compound may be linear or branched. The aliphatic compound is preferably an aliphatic saturated compound that does not have any unsaturated groups other than the carboxyl group. However, the aliphatic compound may be an aliphatic unsaturated compound. The carboxylic acid compound C may, in some cases, be an aromatic compound having a carboxyl group.

[0063] Examples of carboxylic acid compound C include dicarboxylic acid compounds such as 3-methyladipic acid; and tricarboxylic acid compounds such as 1,3,5-pentanetricarboxylic acid and tricarbaryl acid. Carboxylic acid compound C preferably contains at least one selected from the group consisting of 1,3,5-pentanetricarboxylic acid and tricarbaryl acid, and preferably contains 1,3,5-pentanetricarboxylic acid.

[0064] The flux may further contain other acids (especially organic acids) besides the carboxylic acid compound C mentioned above, but it is preferable that it does not contain other acids.

[0065] The flux content in the conductive composition is, for example, 0.1 parts by weight or more, and may be 0.5 parts by weight or more, or even 1 part by weight or more, per 100 parts by weight of solder particles. As described above, the flux containing the carboxylic acid compound C above tends to efficiently remove oxide films and the like from solder particles even in small amounts. Therefore, this flux makes it easy to adjust the flux content in the conductive composition to a low value. The above content is, for example, 20 parts by weight or less, and may be 10 parts by weight or less, 8 parts by weight or less, 5 parts by weight or less, or even 3 parts by weight or less, per 100 parts by weight of solder particles.

[0066] Furthermore, in this embodiment, it is preferable that the ratio P of the weight of flux to the weight of oxygen contained in the solder particles is adjusted to an appropriate range. The ratio P is, for example, 0.300 or less, and may be 0.280 or less, 0.250 or less, 0.230 or less, 0.200 or less, 0.180 or less, 0.173 or less, 0.150 or less, and even 0.130 or less. The ratio P is, for example, 0.050 or more, and may be 0.080 or more, and even 0.100 or more. The ratio P may be between 0.100 and 0.300.

[0067] The above ratio P can be determined by the following method. First, solder particles are prepared before the conductive composition is made (i.e., before the oxide film is removed). These solder particles are subjected to quantitative analysis by inert gas fusion-infrared absorption spectroscopy. This determines the oxygen content R in the solder particles. The oxygen in the solder particles originates from the oxide film contained in the solder particles. Based on the solder particle content W1 (g), flux content W2 (g), and the above content R (weight %) in the conductive composition, the ratio P can be calculated using the following formula: Ratio P = Content W2 / (Content W1 × Content R / 100)

[0068] <1-4. Curing Agent> The conductive composition may further contain a curing agent. The curing agent can react with a resin component, such as epoxy resin, to accelerate its curing. There may be only one type of curing agent, or two or more types.

[0069] Examples of curing agents include acid anhydride-based curing agents, amine-based curing agents, phenol-based curing agents, cationic initiators, imidazole catalysts, and DICY (dicyandiamide).

[0070] The amount of curing agent in the conductive composition is, for example, less than 20 parts by weight per 100 parts by weight of the resin component, and may be less than 10 parts by weight, less than 5 parts by weight, less than 3 parts by weight, or even less than 1 part by weight. The conductive composition does not need to contain a curing agent.

[0071] <1-5. Other Additives> The conductive composition may further contain other additives in addition to the components described above. Other additives include solvents and curing aids. Examples of solvents include organic solvents such as methyl ethyl ketone.

[0072] The content of other additives in the conductive composition may be, for example, 10% by weight or less, 5% by weight or less, 1% by weight or less, or even 0.1% by weight or less. The conductive composition may be substantially free of other additives. If the conductive composition contains a solvent, the solid content concentration of the conductive composition may be, for example, 50% by weight to 80% by weight, or 60% by weight to 75% by weight.

[0073] <1-6. Method for Producing Conductive Compositions> Conductive compositions according to embodiments of the present invention can be prepared, for example, by stirring and mixing the solder particles, resin, flux, and, if necessary, a solvent as described above. After preparing the conductive composition, the solvent may be removed from the conductive composition by heat treatment or the like.

[0074] Before preparing the conductive composition, the oxide film formed on the surface of the solder particles may be removed beforehand. The oxide film can be removed, for example, by acid treatment, in which the solder particles are brought into contact with an acid treatment agent. The acid treatment agent may be one type or two or more types.

[0075] The acid treatment agent is preferably a carboxylic acid treatment agent having a carboxyl group. Examples of carboxylic acid treatment agents include monocarboxylic acid treatment agents, dicarboxylic acid treatment agents, and trifunctional or more carboxylic acid treatment agents, with dicarboxylic acid treatment agents being preferred. The dicarboxylic acid treatment agent is preferably an aliphatic dicarboxylic acid treatment agent, and is particularly preferably malic acid. In this embodiment, the step of removing the oxide film beforehand may be omitted.

[0076] <1-7. Physical Properties of Conductive Compositions> It is preferable that the minimum value V1 of the complex viscosity determined by the following test is 10 Pa·s or less for the conductive composition. Test: The conductive composition, excluding solder particles, is heated from 25°C to a temperature 30°C higher than the melting point T0 of the solder particles (T0 + 30°C) at a heating rate of 10°C / min. The complex viscosity of the conductive composition, excluding solder particles, is measured from 25°C to the temperature (T0 + 30°C), and its minimum value is identified.

[0077] The minimum value V1 of the complex viscosity can be measured in detail by the following method. First, a measurement sample is prepared, consisting of a conductive composition from which solder particles have been removed. Note that the conductive composition from which solder particles have been removed is simply a resin composition and does not strictly exhibit conductivity, but for convenience, it is referred to as a "conductive composition" in this specification. The measurement sample is disc-shaped, with a base diameter of 25.0 mm and a thickness of 500 ± 50 μm. The measurement sample is preferably in a dry state. "Dry state" means that the solvent content remaining in the measurement sample is 1000 wt ppm or less, preferably 500 wt ppm or less. It is preferable that the measurement sample is substantially solvent-free. The measurement sample may also be a disc-shaped cutout of a laminate of multiple conductive sheets made using a conductive composition from which solder particles have been removed. Next, dynamic viscoelasticity measurement is performed on the measurement sample under the following measurement conditions. Measurement conditions: Measurement environment: atmospheric atmosphere; Strain value: 0.5%; Measurement frequency: 1 Hz; Temperature range: 25°C to 300°C; Heating rate: 10°C / min; Shape: Parallel plate, 25.0 mm diameter

[0078] From the results of the dynamic viscoelasticity measurements described above, a temperature-complex viscosity profile (e.g., Figure 1) is created. Based on this profile, the minimum value V1 of the complex viscosity can be identified in the range from 25°C to a temperature 30°C higher than the melting point T0 of the solder particles (T0 + 30°C).

[0079] Figure 1 is a graph illustrating the relationship between temperature and complex viscosity for a conductive composition excluding solder particles (i.e., the measurement sample described above). This graph schematically shows the relationship between temperature and complex viscosity and does not limit the physical properties of the conductive composition. As can be seen from the graph in Figure 1, when the measurement sample is heated and its temperature rises, it is preferable that the complex viscosity gradually decreases. At temperature T1, the complex viscosity reaches its minimum value V1. Furthermore, when the measurement sample is heated to a temperature higher than T1, it is preferable that its complex viscosity increases.

[0080] The minimum value V1 of the complex viscosity is preferably 10 Pa·s or less, as described above, but may also be 5.0 Pa·s or less, 3.0 Pa·s or less, 2.0 Pa·s or less, 1.0 Pa·s or less, or even 0.5 Pa·s or less. The smaller the minimum value V1, the easier it is for solder particles (or molten solder) to move through the conductive composition. Therefore, when a conductive composition is used to connect two wiring circuit boards, for example, solder is more likely to aggregate between the electrodes of one wiring circuit board and the electrodes of the other wiring circuit board, thereby obtaining a connection structure with high electrical reliability. The lower limit of the minimum value V1 is, for example, 0.01 Pa·s or more, and may also be 0.03 Pa·s or more.

[0081] Furthermore, the temperature T1 at which the complex viscosity reaches its minimum value V1 is preferably lower than the melting point T0 of the solder particles. Also, the difference between temperature T1 and the melting point T0 |T1-T0| is, for example, 0°C to 50°C, and may be 5°C to 30°C.

[0082] ≪2. Conductive Sheet≫ The conductive sheet according to the embodiment of the present invention is composed of the conductive composition described above. More specifically, the conductive sheet has the same composition as the conductive composition, except that it does not contain a solvent (or has a low solvent content). However, the conductive sheet may contain a small amount of solvent derived from the conductive composition. When the conductive composition contains a thermosetting resin, the thermosetting resin is typically present in an uncured state in the conductive sheet. The conductive sheet of this embodiment can typically function as an anisotropic conductive sheet.

[0083] <2-1. Structure of the Conductive Sheet> An example of a conductive sheet according to an embodiment of the present invention is shown in Figure 2. Figure 2 shows the conductive sheet 1 placed on the release liner 15. Another aspect of the present invention is to provide a laminate 150 comprising the conductive sheet 1 and the release liner 15. When the conductive sheet 1 is used, the release liner 15 is peeled off from the conductive sheet 1.

[0084] As shown in Figure 2, the conductive sheet 1 has, for example, a matrix 3 and solder particles 5 dispersed in the matrix 3. More specifically, the matrix 3 surrounds the solder particles 5. In the matrix 3, the solder particles 5 may be spaced apart from each other or partially aggregated. In this embodiment, it is preferable that the matrix 3 contains the above-mentioned resin.

[0085] As the release liner 15, the release liner described in section 2-2, "Method for Manufacturing Conductive Sheets," can be used. In the example shown in Figure 2, the conductive sheet 1 is placed on one release liner 15. However, the conductive sheet 1 may be placed between two release liners 15.

[0086] <2-2. Method for Manufacturing a Conductive Sheet> A conductive sheet according to an embodiment of the present invention can be manufactured, for example, by the following method. First, the above-mentioned conductive composition is prepared. Next, the conductive composition is applied to a release liner to form a coating film. A conductive sheet can be formed by drying the coating film. The drying conditions for the coating film are not particularly limited, and for example, the drying temperature is 40°C to 100°C and the drying time is 1 minute to 60 minutes.

[0087] Known materials can be used as the release liner. Examples of the base material for the release liner (hereinafter referred to as "liner base material") include resin films. Examples of resins that make up the resin film include polyester such as polyethylene terephthalate, acetate resin, polyethersulfone, polycarbonate, polyamide, polyimide, polyolefin, (meth)acrylic resin, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyvinyl alcohol, polyarylate, and polyphenylene sulfide. Preferably, the resin that makes up the resin film is polyester such as polyethylene terephthalate. The thickness of the release liner is, for example, 1 μm to 100 μm.

[0088] The peel-off liner may include layers other than the liner substrate. The peel-off liner may include a release layer. For example, the peel-off liner includes a liner substrate and a release layer formed on one side of the liner substrate. In the peel-off liner, the release layer may be on the side of the coating film.

[0089] <2-3. Physical Properties of Conductive Sheets> The thickness of the conductive sheet is, for example, 50 μm or less, and may be 25 μm or less, 15 μm or less, or even 10 μm or less. The thickness of the conductive sheet is, for example, 1 μm or more.

[0090] ≪3. Connection Structure≫ <3-1. Configuration of the Connection Structure> An example of a connection structure according to an embodiment of the present invention is shown in Figure 3. The connection structure 100 shown in Figure 3 comprises a first substrate 20, a second substrate 30, and a connecting member 10. A first electrode 21 is arranged on the first substrate 20, and a second electrode 31 is arranged on the second substrate 30. The connecting member 10 is formed from the conductive composition described above and connects the first substrate 20 and the second substrate 30. The first substrate 20, the connecting member 10, and the second substrate 30 are arranged in this order in the stacking direction Y.

[0091] The first substrate 20 is typically a wiring circuit board. The first substrate 20 has, for example, a flat plate shape and a pair of main surfaces (the surfaces of the first substrate 20 that have the largest surface area). Of the pair of main surfaces, the first electrode 21 is arranged on the main surface facing the connecting member 10.

[0092] Examples of materials for the first substrate 20 include insulating materials and semiconductor materials. The thickness of the first substrate 20 is, for example, 5 μm to 1000 μm.

[0093] The first electrodes 21 are arranged in a pattern on the first substrate 20, for example. For example, the first electrodes 21 may be arranged in a dot pattern. In this case, the shape of the first electrodes 21 is typically columnar (such as cylindrical or prismatic). In this embodiment, a plurality of columnar first electrodes 21 may be arranged in an evenly aligned plane direction X perpendicular to the stacking direction Y. Figure 3 shows an example in which two first electrodes 21 are arranged on the first substrate 20.

[0094] Examples of materials for the first electrode 21 include metals such as gold, copper, and nickel.

[0095] The thickness of the first electrode 21 is, for example, 0 μm to 20 μm, and may be 0.001 μm to 5 μm. At least a portion of the first electrode 21 may be embedded in the first substrate 20. In this case, the thickness of the portion of the first electrode 21 that protrudes from the first substrate 20 is considered to be the thickness of the first electrode 21. That is, if the first electrode 21 does not protrude from the first substrate 20 and the surface of the first electrode 21 coincides with the surface of the first substrate 20, the thickness of the first electrode 21 is 0 μm.

[0096] When the first electrode 21 is cylindrical, the diameter of the first electrode 21 in plan view is, for example, 1 μm to 200 μm, and may be 1 μm to 100 μm, 1 μm to 50 μm, or even 1 μm to 20 μm.

[0097] The distance (pitch) between two adjacent first electrodes 21 in the planar direction X is, for example, 3 μm to 400 μm, and may be 5 μm to 200 μm, 7 μm to 100 μm, or even 10 μm to 40 μm.

[0098] The second substrate 30 is typically a wiring circuit board. However, the second substrate 30 may also be a chip component such as a mini / micro LED. The second substrate 30 has, for example, a flat plate shape and a pair of main surfaces. The second electrode 31 is placed on the main surface of the pair of main surfaces that faces the connecting member 10.

[0099] The material and thickness of the second substrate 30 are as described above for the first substrate 20.

[0100] The second electrodes 31 are arranged in a pattern on the second substrate 30, for example. For example, the second electrodes 31 may be arranged in a dot pattern. In this case, the shape of the second electrodes 31 is typically columnar (such as cylindrical or prismatic). In this embodiment, a plurality of columnar second electrodes 31 may be arranged evenly aligned in the planar direction X. Figure 3 shows an example in which two second electrodes 31 are arranged on the second substrate 30.

[0101] The material and dimensions, such as thickness, of the second electrode 31 are as described above for the first electrode 21.

[0102] Preferably, the distance (pitch) between two adjacent second electrodes 31 in the planar direction X is the same as the distance (pitch) between two adjacent first electrodes 21 in the planar direction X. In other words, it is preferable that the second electrodes 31 face the first electrodes 21, and that these electrodes 21 and 31 are aligned along the stacking direction Y. More specifically, it is preferable that the second electrodes 31 overlap the first electrodes 21 in a plan view.

[0103] The connecting member 10 has a conductive portion 6 and an insulating portion 7. The conductive portion 6 is in direct contact with the first electrode 21 arranged on the first substrate 20 and the second electrode 31 arranged on the second substrate 30, and electrically connects them. The conductive portion 6 makes it possible to exhibit conductivity in the stacking direction Y.

[0104] It is preferable that the conductive portion 6 overlaps the first electrode 21 and the second electrode 31 in a plan view. If the first electrode 21 and the second electrode 31 are arranged in a pattern, it is preferable that the conductive portion 6 is also arranged in a pattern. For example, the conductive portion 6 may be arranged in a dot pattern. In this case, the shape of the conductive portion 6 is typically columnar (such as cylindrical or prismatic). In this embodiment, a plurality of columnar conductive portions 6 may be arranged evenly aligned in the planar direction X. Figure 3 shows an example in which two conductive portions 6 are arranged within the connecting member 10.

[0105] The conductive portion 6 is formed by the melting and aggregation of solder particles, as described later. Therefore, the conductive portion 6 typically contains material derived from solder particles.

[0106] The insulating portion 7 surrounds the conductive portion 6 and fills the space between the first substrate 20 and the second substrate 30 where the conductive portion 6 is not present. The insulating portion 7 is in direct contact with the surface of the first substrate 20 where the first electrode 21 is not placed, and with the surface of the second substrate 30 where the second electrode 31 is not placed. The insulating portion 7 can function as an adhesive portion that adheres to the first substrate 20 and the second substrate 30, respectively. The insulating portion 7 ensures insulation in the plane direction X.

[0107] The insulating portion 7 is formed by the curing of a resin such as epoxy resin, as described later. Therefore, the insulating portion 7 typically contains material derived from the matrix of the conductive sheet.

[0108] The thickness of the connecting member 10 is, for example, 50 μm or less, and may be 25 μm or less, 15 μm or less, or even 5 μm or less. The thickness of the connecting member 10 is, for example, 1 μm or more.

[0109] <3-2. Method for Manufacturing a Connecting Structure> A method for manufacturing a connecting structure 100 according to an embodiment of the present invention includes, for example, placing a conductive composition (typically a conductive sheet 1 composed of the conductive composition) between a first substrate 20 and a second substrate 30, and heating the conductive composition to form a connecting member 10.

[0110] The connecting structure 100 can be manufactured in detail by the following method. First, as shown in Figure 4A, a conductive sheet 1 made of a conductive composition is placed between the first substrate 20 and the second substrate 30. At this time, it is preferable that the conductive sheet 1 is in contact with both the first electrode 21 and the second electrode 31.

[0111] Next, the conductive sheet 1 is heated. It is preferable to heat the conductive sheet 1 by first heating and second heating. In the first heating, the conductive sheet 1 is heated to a temperature above the softening point of the resin in the conductive sheet 1 (for example, solid epoxy resin or solid polymer resin) and below the melting point T0 of the solder particles 5. With the first heating, the conductive sheet 1 softens and the first electrode 21 and the second electrode 31 each become embedded in the conductive sheet 1 (Figure 4B). As a result, the first electrode 21 and the second electrode 31 each become embedded in the conductive sheet 1. The conductive sheet 1 comes into contact with the surface of the first substrate 20 where the first electrode 21 is not placed and the surface of the second substrate 30 where the second electrode 31 is not placed.

[0112] The heating temperature in the first heating stage is, for example, 180°C or lower, and may be 100°C or lower, 80°C or lower, or even 70°C or lower. The above heating temperature is, for example, 40°C or higher.

[0113] In the first heating stage, pressure may be applied to the laminate of the first substrate 20, the conductive sheet 1, and the second substrate 30 in the stacking direction Y to cause them to be pressed together (thermocompressed). The pressure applied to the laminate in the first heating stage may be, for example, 0.001 MPa to 10 MPa, 0.005 MPa to 5 MPa, or even 0.01 MPa to 1 MPa.

[0114] The second heating is typically performed after the first heating. In the second heating, the conductive sheet 1 is heated to a temperature above the melting point T0 of the solder particles 5. Due to the second heating, the solder particles 5 in the conductive sheet 1 melt and aggregate (self-aggregate) between the first electrode 21 and the second electrode 31. This forms a conductive portion 6 that electrically connects the first electrode 21 and the second electrode 31. At this time, the resin constituting the matrix 3 of the conductive sheet 1 hardens while surrounding the conductive portion 6, thereby forming an insulating portion 7. In this way, the connecting member 10 is formed from the conductive sheet 1 by the first and second heating, and a connecting structure 100 (Figure 3) can be obtained.

[0115] The heating temperature for the second heating step is, for example, 70°C or higher, and may be 100°C or higher, 120°C or higher, 130°C or higher, 150°C or higher, or even 200°C or higher. The above heating temperature is, for example, 300°C or lower, and may be 280°C or lower, or even 270°C or lower.

[0116] The second heating step may be performed using a pressure oven. A pressure oven allows the conductive sheet 1 to be heated under pressure in a sealed space. This tends to suppress the volatilization of some of the components of the conductive sheet 1 and the generation of voids. Examples of pressure ovens include automatic heating and pressurizing equipment, pressurizing ovens, voidless pressurizing ovens, autoclaves, and vacuum pressurizing reflow apparatus.

[0117] The present invention will be specifically described below with reference to examples, but the present invention is not limited in any way to these examples. Where "parts" is mentioned, it means "parts by weight" unless otherwise specified, and where "%" is mentioned, it means "percent by weight" unless otherwise specified.

[0118] (Example 1) First, a varnish (solid content concentration 40% by weight) was prepared by dissolving a dicyclopentadiene type epoxy resin (DIC Corporation, trade name "EPICLON HP-7200HHH", epoxy equivalent 280-292 g / eq, solid (25°C)) as a solid epoxy resin in methyl ethyl ketone.

[0119] Next, 175 parts by weight of solder particles (manufactured by DUKSAN Hi-Metal, trade name "Aurora SAC305 EN (0-3 μm)", Sn 96.5% by weight, Ag 3.0% by weight, Cu 0.5% by weight, melting point 218°C, spherical shape, average primary particle diameter 1 μm), 20 parts by weight of bisphenol A type epoxy resin as a liquid epoxy resin (manufactured by Mitsubishi Chemical Corporation, trade name "jER828", epoxy equivalent 184-194 g / eq, liquid (25°C)), and 70 parts by weight (in terms of solid content) of the above varnish as a solid epoxy resin, and high A conductive composition of Example 1 was obtained by mixing 10 parts by weight (in terms of solid content) of a varnish (manufactured by Mitsubishi Chemical Corporation, trade name "jER1256B40", solid content concentration 40% by weight) obtained by dissolving a bisphenol A type epoxy resin (weight-average molecular weight 45,000, epoxy equivalent 8,500 g / eq, solid (25°C)) as a molecular resin in methyl ethyl ketone with 10 parts by weight of 3-methyladipic acid as a flux and stirring.

[0120] (Examples 2-22) Conductive compositions of Examples 2-22 were obtained by the same method as in Example 1, except that the types and contents of the materials used were changed as shown in Tables 1-3. In Examples 2-22, solid epoxy resins, polymer resins, fluxes, etc., were, if necessary, dissolved in a solvent such as methyl ethyl ketone beforehand to prepare a varnish, and the conductive composition was prepared by mixing the varnish with the other materials.

[0121] <Oxygen Content in Solder Particles> The oxygen content of the solder particles used in each example was measured by the following method. First, solder particles were prepared before the conductive composition was made (i.e., before the oxide film was removed). These solder particles were quantitatively analyzed by inert gas fusion-infrared absorption spectroscopy. An oxygen, nitrogen, and hydrogen simultaneous analyzer (LECO TCH600) was used for the quantitative analysis.

[0122] Furthermore, based on the oxygen content in the solder particles and the content of the solder particles and flux, the ratio P of the flux weight to the weight of oxygen contained in the solder particles was calculated using the above formula.

[0123] <Average Epoxy Equivalent Weight> For each epoxy resin used in the example, the average epoxy equivalent weight was calculated based on the epoxy equivalent weight of each epoxy resin and its content.

[0124] <Acid Dissociation Constants of Flux> For the flux used in each example, the acid dissociation constants were determined by the following method. First, the flux (carboxylic acid compound) was dissolved in deionized water to prepare 20 mL of an aqueous solution of the flux (concentration 0.5 mol / L). To this aqueous solution, an aqueous solution of sodium hydroxide with a concentration of 0.5 mol / L (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product name: 0.5 mol / L sodium hydroxide solution) was added dropwise, and a neutralization titration was performed. The neutralization titration was performed under temperature conditions of 25°C. During the neutralization titration, the acid dissociation constants (first acid dissociation constant pKa1 and second acid dissociation constant pKa2) were determined using a pH meter (manufactured by AS ONE, pH meter (pen type), Code No: 1-062-01, Model: AS600).

[0125] <Integration Test> Using the conductive compositions of each example, connection structures were fabricated using the following method, and the solder integration properties were evaluated. Note that solder integration properties are an indicator of the reliability of electrical connections in connection structures.

[0126] (Fabrication of connecting structure) First, a conductive composition was applied to the release surface of a release liner (manufactured by Mitsubishi Chemical Corporation, product name "MRA50") using an applicator to form a coating film. The release liner was a polyethylene terephthalate (PET) liner with a thickness of 50 μm. A conductive sheet with a thickness of 10 μm was fabricated by drying the coating film at 60°C for 5 minutes using a constant temperature bath.

[0127] Next, the release liner was peeled off the fabricated conductive sheet, and the conductive sheet was bonded to a dummy wafer with Au electrodes (10 mm x 10 mm, electrode square 50 μm, electrode end-to-end distance 50 μm). In this state, a pressure of 0.3 MPa was applied for 2 seconds at a temperature of 65°C. Furthermore, alkali-free glass (10 mm x 10 mm) was bonded to the exposed surface of the conductive sheet, and a pressure of 0.3 MPa was applied for 2 seconds at a temperature of 65°C (first heating). This resulted in a laminate in which the dummy wafer, conductive sheet, and alkali-free glass were stacked in this order.

[0128] Next, the laminate was placed in a vacuum pressure reflow apparatus (SST Vacuum Reflow System, product name "Model1200 Table Top Furnace") and vacuuming was performed. Subsequently, it was pressurized to 4.5 atmospheres with nitrogen and heat treatment (second heating) was performed under the conditions of a heating rate of 100°C / min, a maximum temperature of 260°C, and a holding time of 15 minutes. As a result, connecting members were formed from the conductive sheets, and a connecting structure was obtained.

[0129] (Evaluation of solder integration) The solder integration of the fabricated connection structure was evaluated using the following method. First, the connection structure was observed from the alkali-free glass side using an optical microscope (digital microscope, manufactured by Keyence Corporation, product name "VHX-8000"). The connection structure was observed at a magnification of 500x in three different field-of-view areas.

[0130] Next, for the 35 electrodes within the observation field, electrodes that were completely covered with solder were evaluated as pass, and those with part or all of their surface exposed were evaluated as fail. The ratio of electrodes evaluated as pass was considered the solder density, and evaluation was performed based on the following criteria: • Evaluation Criteria 4: Solder density is 95% or higher. 3: Solder density is 90% or higher but less than 95%. 2: Solder density is 80% or higher but less than 90%. 1: Solder density is less than 80%.

[0131] <Solder connection evaluation> Using the conductive compositions of Examples 1, 2, and 6, connection structures were fabricated using the following method, and solder connection evaluation was performed.

[0132] First, a conductive composition was applied to the release surface of a release liner (manufactured by Mitsubishi Chemical Corporation, product name "MRA50") using an applicator to form a coating film. The release liner was a polyethylene terephthalate (PET) liner with a thickness of 50 μm. A conductive sheet with a thickness of 10 μm was prepared by drying the coating film at 60°C for 5 minutes using a constant temperature bath.

[0133] Next, two dummy wafers with Au electrodes (10 mm x 10 mm, electrode square 10 μm, electrode end-to-end distance 10 μm) were prepared. Then, the release liner was peeled off the fabricated conductive sheet, and the conductive sheet was placed between the two dummy wafers. At this time, a high-precision die bonding device (Finetech, product name "FINEPLACER lambda 2") was used to adjust the position of the electrodes of the opposing wafers so that they were aligned via the conductive sheet.

[0134] Next, the laminate was placed in a vacuum pressure reflow apparatus (SST Vacuum Reflow System, product name "Model1200 Table Top Furnace"), and then vacuum was applied. Subsequently, it was pressurized to 4.5 atmospheres with nitrogen and heated under the conditions of a heating rate of 200°C / min, a maximum temperature of 260°C, and a holding time of 60 seconds. As a result, connecting members were formed from the conductive sheets, and a connecting structure was obtained.

[0135] The obtained connection structures were embedded in resin, and the laminated cross-section was exposed by mechanical polishing. The laminated cross-section was observed with an optical microscope (name "VHX-7000", manufactured by Keyence Corporation), and the solder connection between opposing electrodes was evaluated based on the following criteria: • Evaluation Criteria 2: Solder connection between opposing electrodes was observed. 1: Solder connection between opposing electrodes was not observed.

[0136]

[0137]

[0138]

[0139] The abbreviations used in Tables 1-3 are as follows:SAC305 type10: Manufactured by DUKSAN Hi-Metal, product name "Aurora SAC305 EN (0-3μm)", Sn 96.5 wt%, Ag 3.0 wt%, Cu 0.5 wt%, melting point 218℃, spherical shape, average primary particle diameter 1μm SAC305 ST-3: Manufactured by Mitsui Mining & Smelting Co., Ltd., product name "SAC305 ST-3", Sn 96.5 wt%, Ag 3.0 wt%, Cu 0.5 wt%, melting point 218℃, spherical shape, average primary particle diameter 3μm SAC305 STC-7: Manufactured by Mitsui Mining & Smelting Co., Ltd., product name "SAC305 STC-7", Sn 96.5 wt%, Ag 3.0 wt%, Cu 0.5 wt%, melting point 218℃, spherical shape, average primary particle diameter 8μm SnBi58 ST-7: Manufactured by Mitsui Mining & Smelting Co., Ltd., product name "Sn42Bi58 ST-7", Sn42 wt%, Bi58 wt%, melting point 139°C, spherical shape, average primary particle size 7 μm jER828: Bisphenol A type epoxy resin (manufactured by Mitsubishi Chemical Corporation, product name "jER828", epoxy equivalent 184-194 g / eq, liquid (25°C)) HP7200HHH: Dicyclopentadiene type epoxy resin (manufactured by DIC Corporation, product name "EPICLON HP-7200HHH", epoxy equivalent 280-292 g / eq, solid (25°C)) XD1000: Dicyclopentadiene type epoxy resin (manufactured by Nippon Kayaku Co., Ltd., product name "XD-1000", epoxy equivalent 245-260 g / eq, solid (25°C)) NC3500: Biphenyl type epoxy resin (manufactured by Nippon Kayaku Co., Ltd., product name "NC-3500", epoxy equivalent 209 g / eq, solid (25°C)) EOCN102070: Cresol novolac type epoxy resin (manufactured by Nippon Kayaku Co., Ltd., product name "EOCN-1020-70", epoxy equivalent 191-207 g / eq, solid (25°C)) jER1256: A varnish made by dissolving bisphenol A type epoxy resin (weight-average molecular weight 45,000, epoxy equivalent 8,500 g / eq, solid (25°C)) in methyl ethyl ketone (manufactured by Mitsubishi Chemical Corporation, product name "jER1256B40", solid content concentration 40% by weight). UH2170: (meth)acrylic resin (manufactured by Toagosei Co., Ltd., product name "ARUFON UH-2170", weight-average molecular weight 14,000, solid (25°C)). Note that the content of each component listed in Tables 1 to 3 is the value excluding the solvent (solid content equivalent).

[0140] As can be seen from Tables 1 to 3, the conductive composition of the example, which contains a carboxylic acid compound C as a flux having a first acid dissociation constant pKa1 of 3.41 to 4.70 and a second acid dissociation constant pKa2 of 6.34 or less, showed improved integration with the wiring circuit board compared to the comparative example.

[0141] The conductive composition of the present invention can be used for connecting wiring circuit boards.

Claims

1. A conductive composition comprising solder particles, a resin, and a flux, wherein the flux comprises a carboxylic acid compound, and the carboxylic acid compound has a first acid dissociation constant pKa1 of 3.41 to 4.70 and a second acid dissociation constant pKa2 of 6.34 or less.

2. The conductive composition according to claim 1, wherein the second acid dissociation constant pKa2 is 4.10 or greater.

3. The conductive composition according to claim 1, wherein the ratio of the weight of the flux to the weight of the oxygen contained in the solder particles is 0.300 or less.

4. The conductive composition according to claim 1, wherein the number of carboxyl groups contained in the carboxylic acid compound is two or more.

5. The conductive composition according to claim 1, wherein the number of carboxyl groups contained in the carboxylic acid compound is 3.

6. The conductive composition according to claim 1, wherein the resin comprises at least one selected from the group consisting of epoxy resin, (meth)acrylic resin, phenoxy resin, and phenolic resin.

7. The conductive composition according to claim 1, wherein the resin comprises an epoxy resin.

8. The conductive composition according to claim 7, wherein the weight-average molecular weight of the epoxy resin is less than 10,000.

9. The conductive composition according to claim 7, wherein the epoxy resin comprises repeating units having glycidyl groups.

10. The conductive composition according to claim 7, wherein the epoxy resin has at least one selected from the group consisting of a dicyclopentadiene skeleton, a biphenyl skeleton, a naphthalene skeleton, a phenol skeleton, and a cresol skeleton.

11. The conductive composition according to claim 7, wherein the conductive composition comprises a liquid epoxy resin and a solid epoxy resin.

12. The conductive composition according to claim 7, wherein the epoxy equivalent of the epoxy resin is 225 g / eq. or more.

13. The conductive composition according to claim 1, wherein the resin comprises a polymer resin having a weight-average molecular weight of 10,000 or more.

14. The conductive composition according to claim 13, wherein the content of the polymer resin in the resin is 20% by weight or less.

15. A conductive sheet comprising a conductive composition according to any one of claims 1 to 14.

16. A laminate comprising the conductive sheet described in claim 15 and a release liner.

17. A connecting structure comprising: a first substrate on which a first electrode is disposed; a second substrate on which a second electrode is disposed; and a connecting member connecting the first substrate and the second substrate, wherein the connecting member is formed from a conductive composition according to any one of claims 1 to 14.

18. A method for manufacturing a connecting structure according to claim 17, comprising: arranging the conductive composition between the first substrate and the second substrate; and heating the conductive composition to form the connecting member.

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