Conductive sheet, wiring board, and electronic device

Abstract

To provide a conductive sheet having a conductive composition which has excellent metal recycling properties and high adhesive power and conductivity, prevents sticking to protective sheets during storage, and has excellent protective sheet peeling properties, water droplet evaporation properties, and reworking properties; and a wiring board provided with the conductive composition.SOLUTION: There is provided a conductive sheet of the present disclosure in which a conductive composition containing a metal powder (A) and a binder (B) is disposed on only one surface of a protective sheet (D). The conductive composition dissolves and leaves a residue when submerged for 24 hours in a specific type of solvent composition (C) at 30°C. The residue includes a metal element. The peak density Spd of the surface of the conductive composition not facing the protective sheet (D) is 1,000-500,000 pieces / mm2.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a conductive composition containing a metal powder (A) and a binder (B), and also to a conductive sheet, a wiring board, and an electronic device. [Background technology]

[0002] Printed wiring boards installed inside electronic devices are flexible, but reinforcing plates are sometimes used to prevent deformation in connectors that connect components. Epoxy glass and other materials have traditionally been used as reinforcing plates, but metal plates are increasingly being used to suppress electromagnetic noise. A conductive composition primarily composed of resin is used as a bonding agent to connect the printed wiring board and metal plate.

[0003] A filler may be added to the adhesive agent for the purposes of providing electrical continuity between the metal plate and the printed wiring board, controlling the modulus of elasticity, and the like. For example, Patent Document 1 discloses connecting a conductor circuit and a reinforcing plate via a bonding agent layer, and describes using a conductive adhesive containing conductive particles and an adhesive as the bonding agent layer. Patent Document 2 also discloses a conductive adhesive sheet containing a thermosetting resin (A), a curing agent (B), conductive fine particles (C), and a compound (D) that is at least one selected from the group consisting of a silane coupling agent, a silyl compound, phosphoric acid, and a bisphenol S-type epoxy resin, and that has a functional group containing at least one element selected from the group consisting of nitrogen, phosphorus, and sulfur.

[0004] Patent Document 3 discloses a conductive composition for use in electronic components, etc., which comprises a binder of a resin composition containing a resol-type phenolic resin having a dimethylene ether bond and a linear polymer compatible with the phenolic resin and having a molecular weight of 1,000 or more, and metal particles made of Ag-coated Cu powder. Patent Document 4 discloses a conductive paste containing a polyurethane prepolymer having an NCO value of 12 to 14% and a viscosity of 1,000 to 2,000 mPa·s. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-317946 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-185717 [Patent Document 3] Japanese Patent Application Publication No. 8-217955 [Patent Document 4] Chinese Patent Application Publication No. 109943252 Summary of the Invention [Problem to be solved by the invention]

[0006] Electronic devices equipped with printed wiring boards are often discarded without being reused when their useful life expires or new models are introduced. Furthermore, when conductive compositions are used as adhesives, they are processed into the desired shape and size to fit the shape of the printed wiring board. This process generates a large amount of scrap material, which is also discarded without being reused. In recent years, efforts to recover metal resources from scrap materials produced during the manufacturing of electronic devices have become active in order to conserve resources. One method for recovering metal resources is to burn and carbonize organic matter at high temperatures (incineration). However, this method requires a large amount of energy for incineration, so an alternative, more efficient method is needed (metal recovery).

[0007] Conductive sheets with a two-layer structure of a conductive layer and a protective sheet are often manufactured and stored in roll form. When stored in roll form, a problem arises in that the conductive composition adheres to the back surface of the protective sheet during use, a phenomenon known as blocking (blocking resistance).

[0008] Furthermore, the conductive sheet is used by bonding (temporarily attaching) the conductive composition to a first adherend, peeling off the protective sheet, and then bonding the second adherend to the exposed conductive composition. However, due to insufficient strength of the protective sheet or excessive adhesion of the conductive composition to the protective sheet, peeling failures such as damage to the protective sheet occur when the protective sheet is peeled off (easy peelability).

[0009] Furthermore, when a conductive composition is stored at high temperatures, the reaction of the contained curing agent may progress, resulting in a decrease in adhesiveness. For this reason, the conductive composition is sometimes stored in a refrigerator or freezer. However, when the conductive composition is removed from a refrigerator or freezer, condensation may occur due to moisture in the air. If the application work is performed when water droplets (including tiny droplets that are invisible to the naked eye) are present on the surface of the binder, poor adhesion may occur. Therefore, the application work to the adherend cannot be performed until the moisture has evaporated, which is a factor that reduces production efficiency (instantaneousness).

[0010] Furthermore, from the perspective of reducing environmental impact, technology to increase the manufacturing yield of printed wiring boards is needed. In the manufacturing process of printed wiring boards, a conductive sheet is usually temporarily attached to a wiring board and bonded by thermocompression. If re-peelability (reworkability) could be ensured at the stage of temporary attachment to the wiring board, manufacturing yield could be increased. However, re-peelability may leave adhesive residue on the adherend, making rework impossible. Furthermore, as wiring boards become thinner, the wiring boards themselves tend to be more susceptible to damage, which presents a problem: ensuring re-workability at the stage of temporary attachment is not easy.

[0011] The present disclosure aims to provide a conductive sheet having a conductive composition that has excellent metal recovery properties, high adhesive strength and conductivity, prevents adhesion to a protective sheet during storage, and has excellent protective sheet peelability, water droplet evaporation properties, and reworkability, and a wiring board that includes the conductive composition. [Means for solving the problem]

[0012] The present disclosure provides the following conductive composition, conductive sheet, wiring board, and electronic device. [1]: Conductivity according to the present disclosure Sheet is a conductive sheet having a conductive composition containing a metal powder (A) and a binder (B) disposed on one main surface of a protective sheet (D), the conductive composition dissolves and leaves a residue when immersed in a solvent composition (C) at 30°C for 24 hours, the residue containing a metal element; The peak density Spd of the surface of the conductive composition on the side not facing the protective sheet (D) is 1,000 to 500,000 / mm 2 and The solvent composition (C) contains a nitrogen-containing organic solvent (c1) in an amount of 5 to 40 mass % relative to the total mass of the solvent composition (C), and a basic inorganic compound (c2) in an amount of 5 to 40 mass % relative to the total mass of the solvent composition (C). [2]: The conductive sheet according to [1], wherein the conductive composition has adhesive properties. [3]: The conductive sheet according to [1] or [2], wherein the binder (B) has one or more groups selected from the group consisting of an ester group, an imide group, an amide group, a urethane group, and a urea group. [4]: The conductive sheet according to any one of [1] to [3], wherein the binder (B) has two or more groups selected from the group consisting of an ester group, an imide group, an amide group, a urethane group, and a urea group. [5]: The conductive sheet according to any one of [1] to [4], wherein the developed area ratio Sdr of the surface of the conductive composition on the side not facing the protective sheet (D) is 0.01 to 4. [6]: the conductive composition has a maximum storage modulus (2) of 0.01 to 100 GPa at 0 to 30°C; The conductive sheet according to any one of [1] to [5], wherein the value α obtained by dividing the maximum value (2) by the maximum value (1) of the storage modulus of the protective sheet (D) at 0 to 30° C. is 0.01 to 30. [7]: The conductive sheet according to any one of [1] to [6], wherein the maximum storage modulus of the protective sheet (D) at 0 to 30°C is 0.01 to 1000 GPa. [8]: A conductive sheet comprising a metal plate, a conductive composition obtained by peeling off the protective sheet (D) of the conductive sheet according to any one of [1] to [7], and a wiring circuit board; A wiring board in which the metal plate is fixed to the wiring circuit board via the conductive composition. [9]: An electronic device comprising the wiring board according to [8].

[10] : A conductive composition comprising a metal powder (A) and a binder (B), wherein when immersed in a solvent composition (C) containing 5 to 40 mass% of a nitrogen-containing organic solvent (c1) and 5 to 40 mass% of a basic inorganic compound (c2) at 30°C for 24 hours, the conductive composition is partially dissolved and partially insoluble, and the insoluble portion contains a metal element derived from the metal powder (A).

[11] : The conductive composition according to

[10] , which has adhesive properties.

[12] : The conductive composition according to

[10] or

[11] , wherein the binder (B) has one or more groups selected from the group consisting of an ester group, an imide group, an amide group, a urethane group, and a urea group.

[13] : The conductive composition according to any one of

[10] to

[12] , wherein the binder (B) has two or more groups selected from the group consisting of an ester group, an imide group, an amide group, a urethane group, and a urea group. [Effects of the Invention]

[0013] According to the present disclosure, a conductive sheet is provided that has a conductive composition that has excellent metal recovery properties, high adhesive strength and conductivity, prevents adhesion to a protective sheet during storage, and is excellent in protective sheet peelability, water droplet evaporation, and reworkability, thereby providing a wiring board that is easy to recover resources from. DETAILED DESCRIPTION OF THE INVENTION

[0014] The conductive composition, conductive sheet, and wiring board according to the present disclosure will be described below in order. Note that unless otherwise specified, the symbol "to" indicating a range of values ​​includes the lower and upper limits.

[0015] [Conductive composition] The conductive composition of the present disclosure contains a metal powder (A) and a binder (B). When this conductive composition is immersed at 30°C for 24 hours in a solvent composition (C) containing 5 to 40 mass% of a nitrogen-containing organic solvent (c1) and 5 to 40 mass% of a basic inorganic compound (c2), a portion of the conductive composition dissolves and a portion of the composition remains insoluble, with the insoluble portion containing metal elements derived from the metal powder (A). In other words, the conductive composition dissolves and a residue remains. This residue contains metal elements derived from the metal powder (A).

[0016] Here, dissolution in the present disclosure is defined as a phenomenon in which a target article is immersed in the solvent composition (C) to bring the article into contact with the solvent composition (C), and the article dissolves in the solvent composition (C) and loses its original shape. In other words, it is not necessary for the entire article to dissolve in the solvent composition (C), and insoluble matter (residue) may remain.

[0017] When the conductive composition of the present disclosure is dissolved in a solvent composition (C), the metal elements contained in the insoluble matter (residue) include those derived from the metal powder (A). The solvent composition (C) acts on the binder (B). Due to the decomposition action of the solvent in the solvent composition (C), the binder (B) is decomposed and dissolved in the solvent composition (C), and the insoluble metal powder (A) is contained in the residue, allowing the metal powder (A) in the conductive composition to be efficiently recovered. When the conductive layer of the present disclosure is immersed in a solvent composition (C) at 30°C for 24 hours, it dissolves and a residue remains, and this residue includes the metal elements derived from the metal powder (A).

[0018] [Metal powder (A)] The metal powder (A) is used for the purpose of imparting electrical conductivity to the conductive composition. The metal powder (A) is preferably a conductive metal such as gold, platinum, silver, copper, or nickel, or an alloy thereof. Instead of fine particles of a single composition, composite fine particles may be used, each having a core and a coating layer formed from a material with higher conductivity than the core, covering the surface of the core. Composite fine particles are preferred from the viewpoint of reducing costs. The core is preferably a conductive metal or an alloy thereof, more preferably selected from nickel, silica, or copper. The coating layer may be made of any material that is conductive, and is preferably a conductive metal or a conductive polymer. Examples of conductive metals include gold, platinum, silver, tin, manganese, and indium, as well as alloys thereof. Among these, silver is preferred from the viewpoint of conductivity.

[0019] The metal powder (A) may be used alone or in combination of two or more kinds.

[0020] The composite microparticles preferably have a coating layer in a ratio of 1 to 40 parts by mass, more preferably 5 to 30 parts by mass, per 100 parts by mass of the core. Coating with 1 to 40 parts by mass allows for further cost reduction while maintaining conductivity. It is preferable that the coating layer completely covers the core of the composite microparticles. However, in practice, some of the core may be exposed. Even in such cases, conductivity is easily maintained as long as at least 70% of the core surface area is covered with a conductive material.

[0021] The shape of the metal powder (A) is not limited as long as the desired conductivity is obtained. For example, spherical, flake, leaf, dendritic, plate, needle, rod, grape, and irregular mass shapes are suitable. Spherical and dendritic shapes are more preferred for efficiently forming a vertical conductive path between the metal reinforcing plate and the wiring board.

[0022] The average particle diameter of the metal powder (A) is D when the metal powder (A) is spherical, dendritic, needle-like, rod-like, grape-like, or irregularly shaped. 50 The average particle diameter D is preferably 5 to 20 μm, more preferably 5.5 to 15 μm, and even more preferably 6 to 10 μm. 50 The average particle diameter D is 5 to 20 μm, which allows for both adhesive strength and conductivity. 50 can be determined using a laser diffraction / scattering particle size distribution analyzer.

[0023] Furthermore, when the metal powder (A) is spherical, dendritic, needle-like, rod-like, grape-like, or irregularly shaped, D 10 is 1 to 15 μm, and D 90 From the viewpoint of achieving both adhesiveness and conductivity, it is preferable that the thickness is 10 to 30 μm. 10 , D 90 is the average particle diameter D 50 It can be determined by a laser diffraction / scattering particle size distribution measuring device in the same way as above.

[0024] In addition, when the metal powder (A) is spherical, dendritic, needle-like, rod-like, grape-like, or irregularly shaped, D 90 / D 10 is preferably 1.5 to less than 8.0. When the ratio is in this range, the filling state of the metal powder (A) in the conductive composition is optimized, and the conductivity is particularly excellent.

[0025] When the metal powder (A) is in the form of flakes, leaves, or plates, the average particle diameter D of the metal powder (A) 50 The average particle diameter D is preferably 5 to 50 μm, more preferably 6.5 to 30 μm, and even more preferably 8 to 20 μm. 50By having a diameter of 5 to 50 μm, both adhesive strength and conductivity can be achieved.

[0026] Furthermore, when the metal powder (A) is in the form of flakes, leaves, or plates, D 10 is 1 to 25 μm, and D 90 From the viewpoint of achieving both adhesiveness and conductivity, it is preferable that the thickness is 10 to 100 μm.

[0027] In addition, when the metal powder (A) is in the form of flakes, leaves, or plates, D 90 / D 10 is preferably 1.5 to less than 8.0. When the ratio is in this range, the filling state of the metal powder (A) in the conductive composition is optimized, resulting in particularly excellent conductivity.

[0028] The content of the metal powder (A) in the conductive composition is preferably 40 to 90 mass %, more preferably 45 to 80 mass %, and even more preferably 50 to 70 mass %. By adding the metal powder in the above amount, metal recovery, adhesive strength, and conductivity can all be achieved.

[0029] Binder (B) The binder (B) serves as a substrate for the conductive composition and functions to disperse and support the metal powder (A). Since the binder (B) needs to be decomposed by the solvent composition (C), it is preferably an organic material. The binder (B) is not particularly limited in terms of composition, etc., as long as it has the above-mentioned function, but it preferably contains a resin (b-1). The resin (b-1) in the present disclosure is defined as an organic material that is solid, semi-solid, or solidified at room temperature, has a softening or melting range, and has a weight-average molecular weight (Mw) of 5,000 or more.

[0030] The binder (B) can dissolve in the solvent composition (C) by decomposing specific chemical bonds with the solvent composition (C), which has a strong solvent-induced decomposition effect. The binder (B) preferably has one or more groups selected from the group consisting of an ester group, an imide group, an amide group, a urethane group, and a urea group. The conductive composition having the functional groups described above allows for more efficient decomposition by the solvent composition (C), resulting in more finely divided molecular chains of the binder (B). This allows more of the binder (B) to dissolve in the solvent composition (C), thereby reducing the amount of binder (B)-derived components remaining in the residue.

[0031] To obtain the above effects, it is more preferable that the binder (B) has two or more groups selected from the group consisting of ester groups, imide groups, amide groups, urethane groups, and urea groups. By having two or more groups, multiple effects are achieved, and the binder (B) can be decomposed more efficiently. Suitable examples include ester groups, imide groups, and amide groups. and An example is a combination of one or more urea groups with a urethane group.

[0032] [Resin (b-1)] The resin (b-1) is not particularly limited in terms of composition, molecular structure, etc., other than the weight average molecular weight (Mw) described above, but is preferably a resin having one or more chemical bonds selected from the group consisting of an imide bond, an amide bond, a urethane bond, and a urea bond. Furthermore, from the viewpoint of exhibiting the function of dispersing and supporting the metal powder (A), the resin (b-1) is preferably a thermosetting resin, a thermoplastic resin, a photocurable resin such as an ultraviolet-curable resin, a natural resin, or an elastomer, and from the viewpoint of imparting excellent adhesiveness to the conductive composition, the resin (b-1) is preferably a thermosetting resin (b-2).

[0033] [Thermosetting resin (b-2)] The thermosetting resin (b-2) is a resin (b-1) that has thermosetting properties. Thermosetting is defined as "a state in which heat causes polymerization and / or crosslinking reactions, resulting in an irreversible increase in elastic modulus."

[0034] When the thermosetting resin (b-2) has reactive functional groups, the above-mentioned thermosetting property may be exhibited by a reaction between the reactive functional groups, or may be exhibited by a reaction between reactive functional groups incorporated in the thermosetting resin (b-2) and the curing agent (H) described later.

[0035] Examples of thermosetting resins (b-2) include epoxy resins, phenolic resins, polyacrylic resins, polyester resins, polyurethane resins, polyamide resins, polyimide resins, polyamideimide resins, urea resins, polyurethaneurea resins, melamine resins, and polyolefin resins. Among these, it is preferable that the thermosetting resin (b-2) has one or more groups selected from the group consisting of ester groups, imide groups, amide groups, urethane groups, and urea groups. The imide bond, amide bond, urethane bond, and urea bond can achieve strong adhesive strength by interacting with the adherend through the unshared electron pair of the nitrogen atom contained in the bond. When the thermosetting resin (b-2) has two or more groups selected from the group consisting of ester groups, imide groups, amide groups, urethane groups, and urea groups, the aforementioned effect of improving adhesiveness can be further enhanced.

[0036] The binder (B) may further contain a curing agent (H). In the present disclosure, the curing agent (H) is a substance that accelerates or regulates the curing reaction and is defined as a substance having a molecular weight or weight-average molecular weight (Mw) of less than 5,000. The curing reaction is defined as "polymerizing and / or crosslinking a prepolymer or polymer composition by means of heat, radiation, catalyst, or the like, thereby irreversibly increasing the elastic modulus." From the viewpoint of forming polymerization and / or crosslinking in the binder (B) by stimuli such as heat, and thereby exhibiting strong adhesiveness to the conductive composition, the binder (B) of the present disclosure preferably contains a curing agent (H). The curing agent (H) may be appropriately selected from known compounds that exhibit curing properties when combined with the thermosetting resin (b). Examples of the curing agent (H) include epoxy compounds, oxetane compounds, episulfide compounds, aziridine compounds, isocyanate compounds, amine compounds, imidazole compounds, and acid anhydrides.

[0037] Examples of epoxy compounds include glycerol, Shiji ether type epoxy compound, glycol Shiji Preferred are amine-type epoxy compounds, glycidyl ester-type epoxy compounds, and cycloaliphatic (alicyclic) epoxy compounds.

[0038] Examples of the glycidyl ether type epoxy compound include bisphenol A type epoxy compounds, bisphenol F type epoxy compounds, bisphenol S type epoxy compounds, bisphenol AD ​​type epoxy compounds, cresol novolac type epoxy compounds, phenol novolac type epoxy compounds, α-1-naphthol novolac type epoxy compounds, bisphenol A type novolac type epoxy compounds, dicyclopentadiene type epoxy compounds, tetrabromobisphenol A type epoxy compounds, brominated phenol novolac type epoxy compounds, tris(glycidyloxyphenyl)methane, and tetrakis(glycidyloxyphenyl)ethane.

[0039] Examples of the glycidylamine type epoxy compound include tetraglycidyldiaminodiphenylmethane, triglycidyl paraaminophenol, triglycidyl meta-aminophenol, and tetraglycidyl meta-xylylenediamine.

[0040] Examples of the glycidyl ester type epoxy compound include diglycidyl phthalate, diglycidyl hexahydrophthalate, and diglycidyl tetrahydrophthalate.

[0041] Examples of the cyclic aliphatic (alicyclic) epoxy compounds include epoxycyclohexylmethyl-epoxycyclohexanecarboxylate and bis(epoxycyclohexyl)adipate.

[0042] Examples of the oxetane compound include 1,4-bis{[(3-ethyloxetan-3-yl)methoxy]methyl}benzene, 3-ethyl-3-{[(3-ethyloxetan-3-yl)methoxy]methyl}oxetane, 1,3-bis[(3-ethyloxetan-3-yl)methoxy]benzene, 4,4'-bis[(3-ethyl-3-oxetanyl)methoxymethyl]biphenyl, an ester compound of (2-ethyl-2-oxetanyl)ethanol and terephthalic acid, an ether compound of (2-ethyl-2-oxetanyl)ethanol and phenol novolac resin, and an ester compound of (2-ethyl-2-oxetanyl)ethanol and a polycarboxylic acid compound.

[0043] Examples of the episulfide compound include bis(1,2-epithioethyl) sulfide, bis(1,2-epithioethyl) disulfide, bis(2,3-epithiopropyl) sulfide, bis(2,3-epithiopropylthio)methane, bis(2,3-epithiopropyl) disulfide, bis(2,3-epithiopropyldithio)methane, bis(2,3-epithiopropyldithio)ethane, bis(6,7-epithio-3,4-dithiaheptyl) sulfide, Examples of suitable bis(2,3-epithiopropyldithiomethyl)benzene include 1,6-bis(2,3-epithiopropyldithiomethyl)-2-(2,3-epithiopropyldithioethylthio)-4-thiahexane and 1,2,3-tris(2,3-epithiopropyldithio)propane.

[0044] Examples of the aziridine compound include trimethylolpropane-tri-a-2-aziridinylpropionate, tetramethylolmethane-tri-a-2-aziridinylpropionate, N,N'-diphenylmethane-4,4'-bis(1-aziridinecarboxamide), and N,N'-hexamethylene-1,6-bis(1-aziridinecarboxamide).

[0045] Examples of the amine compound include diethylenetriamine, triethylenetetramine, methylenebis(2-chloroaniline), methylenebis(2-methyl-6-methylaniline), 1,5-naphthalene diisocyanate, and n-butylbenzylphthalic acid.

[0046] Examples of the isocyanate compound include tolylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, dicyclohexylmethane diisocyanate, 1,5-naphthalene diisocyanate, tetramethylxylylene diisocyanate, and trimethylhexamethylene diisocyanate.

[0047] Examples of the imidazole compound include 2-methylimidazole, 2-heptadecylimidazole, 2-phenyl-4-methylimidazole, and 1-cyanoethyl-2-undecylimidazolium trimellitate.

[0048] Examples of the acid anhydride include tetrahydrophthalic anhydride, dodecenyl succinic anhydride, methylnadic anhydride, trimellitic anhydride, and pyromellitic anhydride.

[0049] The content of the curing agent (H) is preferably 1 to 70 parts by mass, more preferably 3 to 50 parts by mass, and even more preferably 3 to 30 parts by mass, based on 100 parts by mass of the thermosetting resin (b-2). By including the curing agent (H) in an amount of 1 part by mass or more, the conductive composition can be brought into a B-stage cured state. B-stage curing is a method in which the conductive composition is heated at a predetermined temperature for a predetermined time, thereby partially inducing a curing reaction of the contained curing agent (H). By carrying out B-stage curing, the strength of the conductive composition can be increased while maintaining its adhesive strength, and the blocking resistance can be improved by increasing the elasticity of the conductive composition. Furthermore, by including the curing agent (H) in an amount of 70 parts by mass or less, the formation of an excessive crosslinked structure when the conductive composition is cured can be suppressed, and the solubility of the binder (B) in the solvent composition (C) can be increased.

[0050] The step of heating the conductive composition to adhere it to the adherend is preferably a hot press. The addition of pressure improves adhesion to the adherend. The hot press conditions can be appropriately selected depending on the composition of the conductive composition and the material, size, and shape of the adherend. For example, a temperature of 130 to 200°C, 1 to 10 MPa, and 3 to 60 minutes are preferred.

[0051] The content of the binder (B) is preferably 10 to 60 mass % of the total solid content of the conductive composition, from the viewpoint of excellent adhesion to metal plates and wiring circuit boards.

[0052] The conductive composition of the present disclosure preferably has voids. The presence of voids in the conductive composition promotes penetration of the solvent composition (C) and improves metal recovery. Any known means can be used to determine the presence or absence of voids and to adjust the porosity, but voids can be formed relatively easily by using dendritic metal powder as the metal powder (A).

[0053] The porosity of the conductive composition is preferably 0.5 to 60%. By setting the porosity to 0.5% or more, the penetration of the solvent composition (C) is promoted, improving metal recovery, and the evaporation of condensation that occurs when the conductive composition is removed from a freezer is promoted, thereby improving instantaneous properties. Furthermore, by setting the porosity to 60% or less, the accumulation of excessive condensation can be suppressed, improving instantaneous properties. The porosity is more preferably 1.0 to 30%.

[0054] In this specification, "porosity" refers to the percentage of the area of ​​voids derived from a microscopic image of a cross section of a conductive composition. The specific calculation method is as follows: The cross section of the conductive composition is observed using a microscope such as a scanning electron microscope (SEM) or a laser microscope. When the cross section is observed vertically with the microscope, a contrast difference occurs between the conductive composition and the voids, allowing the shape of the voids to be recognized. The cross section image of the conductive composition is binarized into black and white using the image analysis software "GIMP 2.10.6," with the conductive composition and voids binarized into black and white. The number of black and white pixels is then counted, and the percentage of the area of ​​voids is calculated from the ratio of the pixel counts.

[0055] The porosity of the conductive composition can be controlled by any known method, such as using a foaming agent that foams and generates voids when triggered by heat or other triggers. However, it is particularly preferable to control the porosity by adjusting the shape and content of the metal powder (A). When the metal powder (A) is particularly bulky and dendritic, voids that exhibit the effects of the present disclosure are easily formed, making it more suitable than other metal powders. Furthermore, the amount of voids tends to increase as the content of the metal powder (A) increases.

[0056] [Solvent composition (C)] The solvent composition (C) of the present disclosure contains a nitrogen-containing organic solvent (c1) and a basic inorganic compound (c2). To efficiently utilize the solubility effect of the solvent composition (C) on the binder (B), the solvent composition (C) contains 5 to 40 mass% of the nitrogen-containing organic solvent (c1) relative to the total mass of the solvent composition (C). The content of the nitrogen-containing organic solvent (c1) is more preferably 10 to 30 mass%. The nitrogen-containing organic solvent (c1) can be any organic solvent containing a nitrogen atom in its molecule without any particular limitations. Specifically, N-methyl-2-pyrrolidone, normal propyl bromide, γ-butyrolactone, monoethanolamine, diethanolamine, triethanolamine, etc. can be used, and the type can be appropriately selected depending on the components of the binder (B) to be dissolved.

[0057] In order to render the solvent composition (C) basic and promote decomposition of the binder (B) by the solvent, the solvent composition (C) contains a basic inorganic compound (c2) in an amount of 5 to 40 mass % based on the total mass of the solvent composition (C). Any substance that exhibits the above-mentioned functions may be used without particular limitation. Examples of the basic inorganic compound (c2) include at least one selected from the group consisting of sodium hydroxide, potassium hydroxide, ammonium hydroxide, sodium bicarbonate, sodium dihydrogen phosphate, disodium phosphate, trisodium phosphate, potassium dihydrogen phosphate, and tripotassium phosphate. In order to impart suitable solubility to the solvent composition (C), the content of the basic inorganic compound (c2) is more preferably 10 to 30 mass %.

[0058] To the solvent composition (C), an organic solvent for dilution or an additive for promoting decomposition of the binder (B) may be appropriately added in order to impart fluidity. From the viewpoint of facilitating the handling of the solvent composition (C), it is preferable to use low-volatility glycerin.

[0059] [Conductive sheet] The conductive sheet according to this embodiment is a conductive sheet in which a conductive composition containing a metal powder (A) and a binder (B) is disposed on one main surface (only one surface) of a protective sheet (D). In other words, this conductive sheet is a sheet-like article having a conductive composition on a protective sheet (D). The conductive composition provided in the conductive sheet is a non-fluid solid at room temperature and forms a layer of a certain thickness, also referred to as a conductive layer. This conductive layer dissolves when immersed in a solvent composition (C) at 30°C for 24 hours, leaving a residue, the residue containing a metal element.

[0060] Protective Sheet The protective sheet (D) can be any film that has been treated with a release agent on one or both sides. Examples of the substrate for the protective sheet (D) include plastic sheets such as polyethylene terephthalate, polyethylene naphthalate, polyvinyl fluoride, polyvinylidene fluoride, rigid polyvinyl chloride, polyvinylidene chloride, nylon, polyimide, polystyrene, polyvinyl alcohol, ethylene-vinyl alcohol copolymer, polycarbonate, polyacrylonitrile, polybutene, flexible polyvinyl chloride, polyethylene, polypropylene, polyurethane, ethylene-vinyl acetate copolymer, and polyvinyl acetate; papers such as glassine paper, wood-free paper, kraft paper, and coated paper; various nonwoven fabrics, synthetic paper, metal foil, and composite films combining these. Among these, polyethylene terephthalate and polyethylene naphthalate are preferred from the viewpoint of enhancing ease of peeling.

[0061] The surface of the protective sheet (D) may be subjected to a matte treatment, if necessary, such as sand matte, etching matte, coating matte, chemical matte, or kneaded matte.

[0062] The protective sheet (D) can be obtained, for example, by applying a release agent to a substrate. Examples of release agents that can be used include hydrocarbon resins such as polyethylene and polypropylene, higher fatty acids and their metal salts, higher fatty acid soaps, waxes, animal and vegetable oils, mica, talc, silicone surfactants, silicone oils, silicone resins, fluorine-based surfactants, fluorine resins, fluorine-containing silicone resins, melamine resins, and acrylic resins. The release agent can be applied by any of the conventional methods known in the art, such as gravure coating, kiss coating, die coating, lip coating, comma coating, blade coating, roll coating, knife coating, spray coating, bar coating, spin coating, and dip coating.

[0063] The maximum storage modulus (1) of the protective sheet (D) at 0 to 30° C. is preferably 0.01 to 1000 GPa, and more preferably 0.1 to 100 GPa. When the maximum storage modulus (1) of the protective sheet (D) at 0 to 30° C. is 0.01 to 1000 GPa, the protective sheet (D) can be easily peeled off from the conductive composition after thermal lamination without stretching or breaking.

[0064] The maximum storage modulus (2) of the conductive composition (conductive layer) at 0 to 30°C is preferably 0.01 to 100 GPa, more preferably 1 to 10 GPa. When the maximum storage modulus (2) of the conductive composition at 0 to 30°C is within this range, the protective sheet (D) can be easily peeled off from the conductive composition after thermal lamination without stretching or breaking. The storage moduli of the conductive composition and the protective sheet (D) can be determined using a dynamic viscoelasticity measuring device.

[0065] The value α obtained by dividing the maximum storage modulus (2) of the conductive composition (conductive layer) at 0 to 30°C by the maximum storage modulus (1) of the protective sheet (D) at 0 to 30°C is preferably 0.01 to 30, and more preferably 0.1 to 15. When α is 0.01 to 30, the protective sheet (D) can be easily peeled from the conductive composition after thermal lamination.

[0066] [Mountain peak density Spd and development area ratio Sdr] The conductive sheet of the present disclosure has a peak density Spd of 1,000 to 500,000 peaks / mm on the surface of the conductive composition (conductive layer) that is not facing the protective sheet (D) (non-facing side). 2 By keeping the peak apex density Spd of the surface within this range, the contact points with the adherend are kept within an appropriate range, and excessive adhesion to the adherend is suppressed, thereby improving reworkability. The peak apex density Spd is 10,000 to 300,000 / mm 2 It is preferable that the number of particles is 25,000 to 250,000 particles / mm 2 It is more preferable that:

[0067] The interface peak density Spd (hereinafter sometimes simply referred to as Spd) is defined in ISO 25178-2:2012 and represents the number of peaks per defined region (unit area).

[0068] In the conductive sheet of the present disclosure, it is preferable that the developed surface area ratio Sdr of the surface of the conductive composition (conductive layer) on the non-facing surface that does not face the protective sheet (D) is 0.01 to 4, from the viewpoint of achieving both adhesiveness and blocking resistance. The conductive sheet is stored or transported in a rolled state. When the conductive sheet is unwound from the roll, a blocking phenomenon may occur in which the conductive sheet adheres to the back surface of the protective sheet (D). By setting the Sdr of the conductive layer surface within the above-mentioned specific range, it is possible to make the irregularities per defined area denser. This makes it possible to reduce the contact area between the surface of the conductive composition and the back surface of the protective sheet (D) in the rolled product, thereby achieving both adhesiveness and blocking resistance.

[0069] The developed surface area ratio Sdr (hereinafter simply referred to as Sdr) of an interface is defined in ISO 25178-2:2012 and is an index that indicates how much the developed surface area (surface area) of a defined region increases relative to the area of ​​the defined region. Note that the Sdr of a flat surface is 0 (zero).

[0070] In this disclosure, the peak density Spd and the developed area ratio Sdr are values ​​measured in accordance with ISO 25178-2:2012. Specifically, measurement data is acquired using a laser microscope (Keyence Corporation, VK-X100), and the acquired measurement data is imported into analysis software (Keyence Corporation's VK-H1XA analysis application equipped with the ISO 25178-2:2012 surface texture measurement module VK-H1XR), and the values ​​can be calculated by performing ISO 25178-2:2012 surface texture measurement.

[0071] The present inventors further found that water droplets evaporate easily when the developed area ratio Sdr of the surface of the conductive composition that is not facing the protective sheet (D) is 0.01 to 4.0. The easy evaporation of water droplets can shorten the waiting time for evaporation of condensation that occurs when the composition is removed from a freezer, for example. As a result, the waiting time for application to the adherend can be shortened (hereinafter also referred to as instantaneous property), and work efficiency can be improved. From the viewpoint of improving instantaneous property, the developed area ratio Sdr is preferably 0.1 to 3.0, more preferably 0.25 to 2.0.

[0072] [Spd, Sdr control method] The method for controlling the peak density Spd and developed area ratio Sdr of the conductive sheet surface of the present disclosure can be any conventional method for adjusting the surface shape of an object. Different methods for Spd and Sdr can be used, or a common method can be used. Examples include polishing the surface using a coated abrasive; shot blasting, which uses compressed air to spray an abrasive onto the surface of the conductive composition; forming a conductive composition on a film having a predetermined peak density Spd and developed area ratio Sdr, laminating a protective sheet, and then removing the film to transfer the film surface irregularities; pressing a film having a predetermined peak density Spd and developed area ratio Sdr and a conductive composition together to transfer the film surface irregularities; and controlling the surface irregularities by adding particulate matter to the conductive composition.

[0073] The thickness of the conductive composition (conductive layer) in the conductive sheet is preferably 5 to 200 μm, more preferably 10 to 100 μm, and even more preferably 30 to 70 μm, from the viewpoint of achieving both thin film properties and conductivity.

[0074] [Conductive sheet manufacturing method] The conductive sheet of the present disclosure can be obtained, for example, by coating the conductive composition on a protective sheet (D), drying, and, if necessary, B-stage curing. The coating method may be appropriately selected from known methods, taking into consideration the film thickness of the bonding agent, etc. Specific examples of coating methods include gravure coating, kiss coating, die coating, lip coating, comma coating, blade coating, roll coating, knife coating, spray coating, bar coating, spin coating, and dip coating.

[0075] [Manufacturing method for wiring boards] One example of a method for manufacturing a wiring board includes laminating a wiring circuit board for a printed wiring board, a conductive composition, and a metal plate, bonding them together by pressure, and then mounting electronic components on the substrate. An example of a method for manufacturing a wiring board is described below.

[0076] First, a conductive composition varnish is applied to a protective sheet (D) and dried to prepare a conductive sheet (step a). Next, the exposed surface of the conductive layer (the surface of the conductive layer not facing the protective sheet (D)) is brought into contact with a metal plate and thermally laminated to laminate the conductive sheet onto the metal plate (step b). Next, the protective sheet (D) is peeled off (step c), and the exposed conductive composition is brought into contact with a wiring circuit board and thermally laminated (step d). Thereafter, the conductive composition is cured by a heat press or the like to obtain a wiring board in which the metal plate is fixed to the wiring circuit board via the conductive composition (step e).

[0077] [Electronic equipment] The wiring board can be applied to any conventionally known product that uses a printed wiring board. Specifically, it can be applied to electronic devices such as mobile phones, smartphones, laptops, digital cameras, and liquid crystal displays. It can also be suitably used in transportation equipment such as automobiles, trains, ships, and aircraft. [Example]

[0078] The present disclosure will be specifically described below using examples and comparative examples, but the present disclosure is not limited to these examples. The blending ratios are expressed as solid content values ​​except for the solvent. Furthermore, "parts" represent "parts by mass."

[0079] [Metal powder (A) D 10、 D 50、 D 90 Average particle size] D 50 The average particle size was measured using a laser diffraction / scattering particle size distribution analyzer LS13320 (manufactured by Beckman Coulter). The value was obtained by measuring the conductive filler using a Tornado dry powder sample module, and is the particle size at which the cumulative value in the particle size cumulative distribution is 50%. The refractive index was set to 1.6. 10、 D 90 is the average particle size at 10% and 90% cumulative values ​​in the particle size cumulative distribution, and was measured in the same manner as above.

[0080] [Acid value of thermosetting resin (b-2)] The acid value (mgKOH / g) was calculated by converting the measured value into solids in accordance with the neutralization titration method of JIS K 0070. Approximately 1 g of sample was precisely weighed into a stoppered Erlenmeyer flask, and 100 mL of a tetrahydrofuran / ethanol (volume ratio: tetrahydrofuran / ethanol = 2 / 1) mixture was added and dissolved. Phenolphthalein test solution was added as an indicator, and the solution was titrated with 0.1 N alcoholic potassium hydroxide solution. The endpoint was determined when the indicator retained a pale pink color for 30 seconds. The acid value was calculated using the following formula (unit: mgKOH / g). Acid value (mgKOH / g)=(5.611×a×F) / S however, S: Amount of sample collected (g) a: Amount of 0.1N alcoholic potassium hydroxide solution consumed (mL) F: Potency of 0.1N alcoholic potassium hydroxide solution

[0081] [Weight average molecular weight (Mw) of thermosetting resin (b-2)] Mw was measured using a GPC (gel permeation chromatograph) "HPC-8020" (manufactured by Tosoh Corporation). GPC is a liquid chromatograph that separates and quantifies substances dissolved in a solvent (THF: tetrahydrofuran) based on differences in their molecular size. This measurement was performed using two "LF-604" columns (manufactured by Showa Denko: GPC column for rapid analysis: 6 mm ID x 150 mm size) connected in series, at a flow rate of 0.6 mL / min and a column temperature of 40°C. Mw was determined in polystyrene equivalent.

[0082] <Preparation of conductive composition> The raw materials used to prepare each conductive composition are shown below.

[0083] <Raw materials> Metal powder (A) A1: Silver coated copper powder: D 50 = 5.7 μm, D 10 = 2.1 μm, D 90 =12.8μm, dendritic (Mitsui Mining & Smelting Co., Ltd.) A2: Silver coated copper powder: D 50 = 31.2 μm, D10 = 12.9 μm, D 90 =44.6μm, dendritic (Mitsui Mining & Smelting Co., Ltd.) A3: Silver coated copper powder: D 50 = 10.8 μm, D 10 = 3.2 μm, D 90 =29.5μm, spherical (Showa Denko Materials) A4: Silver coated copper powder: D 50 = 7.5 μm, D 10 = 1.5 μm, D 90 =11.3μm, spherical (Showa Denko Materials) A5: Silver coated copper powder: D 50 = 11.3 μm, D 10 = 3.8 μm, D 90 =29.5μm, flakes (manufactured by DOWA Holdings) Binder (B) Thermosetting resin (b-2) P1: Polyester resin (thermosetting resin with ester groups): acid value 36 mg KOH / g, Mw = 27,000 (manufactured by Toyochem) P2: Polyimide resin (thermosetting resin with imide groups): acid value = 22 mg KOH / g, Mw = 55,000 (manufactured by Toyochem) P3: Polyamide resin (thermosetting resin with amide groups): acid value = 28 mg KOH / g, Mw = 49,000 (manufactured by Toyochem) P4: Polymaleimide resin (thermosetting resin with imide groups): acid value = 13 mg KOH / g, Mw = 98,000 (manufactured by Toyochem) P5: Polyurethane imide resin (thermosetting resin having urethane and imide groups): acid value = 11 mg KOH / g, Mw = 100,000 (manufactured by Toyochem) P6: Polyacrylic resin (a thermosetting resin having no ester, imide, amide, urethane, or urea groups): acid value = 17 mg KOH / g, Mw = 120,000 (manufactured by Toyochem) P7: Polyolefin resin (thermosetting resin having no ester group, imide group, amide group, urethane group, or urea group): acid value = 26 mg KOH / g, Mw = 85,000 (manufactured by Toyochem) Hardener (H) H1: Bisphenol A epoxy compound (jER834, molecular weight = 470, manufactured by Mitsubishi Chemical) Protective sheet (D) D1: A protective sheet made of 50 μm PET (polyethylene terephthalate) film that has been sandblasted to give it a matte finish and coated with a silicone release agent. D2: A protective sheet made of 50 μm PEN (polyethylene naphthalate) film that has been sandblasted to give it a matte finish and coated with a silicone release agent. D3: A protective sheet made of 38 μm PP (polypropylene) film that has been sandblasted to give it a matte finish and coated with a silicone release agent.

[0084] <Preparation of conductive composition and conductive sheet> [Example 1] 100 parts by mass of polyurethaneimide resin (P5) as thermosetting resin (b-2), 225 parts by mass of dendritic metal powder (A1) as metal powder (A) were placed in a container, 20 parts by mass of epoxy compound (H1) as curing agent (H) was added, and MEK (methyl ethyl ketone) was added and mixed so that the nonvolatile content concentration was 45% by mass. The mixture was stirred for 10 minutes with a stirrer to prepare a conductive composition varnish.

[0085] Next, the conductive composition varnish prepared above was applied using a doctor blade onto the release-treated surface (one side only) of the protective sheet (D1) so that the thickness of the conductive composition (conductive layer) after drying would be 60 μm, and the coated sheet was dried in an electric oven at 120°C for 2 minutes to obtain a conductive sheet (protective sheet (D1) / conductive layer laminate sheet).

[0086] [Examples 2 to 27 and Comparative Examples 1 to 3] Conductive sheets of Examples 2 to 27 and Comparative Examples 1 to 3 were obtained in the same manner as in Example 1, except that the types and amounts of each component to be blended were as shown in Tables 1 to 4. However, for Examples 16 to 21, Spd and Sdr were adjusted to the desired values ​​by buffing the surface of the conductive composition after drying in an electric oven.

[0087] <How to check solubility> The following method was used to confirm whether the conductive composition (conductive layer) dissolved in the solvent composition (C) and whether the residue contained metal (solubility). The conductive sheet was cut into a size of 45 mm wide and 100 mm long, and the protective sheet (D) was peeled off to obtain a conductive composition. The resulting composition was immersed in 100 g of solvent composition (C) (containing 20% ​​by mass of monoethanolamine as a nitrogen-containing organic solvent (c1), 15% by mass of potassium hydroxide as a basic inorganic compound (c2), and 65% by mass of glycerin) at 30°C, followed by ultrasonic treatment for 2 hours and leaving to stand for 22 hours. If the conductive composition was broken down into smaller pieces compared to its shape before immersion, it was judged to have "dissolved," and whether the insoluble portion (residue) contained metal was confirmed. If the shape remained unchanged from before immersion, it was judged to have "not dissolved." If no change in shape was apparent to the naked eye, the mass of the sample before and after immersion was compared, and if the mass loss was less than 5%, it was judged to have "not dissolved."

[0088] Whether or not the residue contained metal was confirmed by qualitative analysis using an ICP optical emission spectrometer ("SPECTRO ARCOS (registered trademark): FHS12" manufactured by AMETEK Corporation). In the above analysis, whether or not the residue contained metal elements was confirmed, and if the residue contained metal elements, it was determined to be "contained."

[0089] <Method for measuring peak density Spd and developed area ratio Sdr> The peak density Spd and the developed area ratio Sdr of the conductive composition (conductive layer) on the surface opposite to the protective sheet (D) were measured using the following method. The surface of the conductive composition was measured using a laser microscope (Keyence Corporation, VK-X100) to obtain measurement data. The obtained measurement data was then imported into analysis software (the analysis application "VK-H1XA" equipped with the ISO 25178-2:2012 surface texture measurement module "VK-H1XR", both manufactured by Keyence Corporation), and ISO 25178-2:2012 surface texture measurement was performed. The conditions were S-filter: 1 μm, L-filter: 0.2 mm.

[0090] <Measurement of the maximum storage modulus of the conductive composition (conductive layer) and protective sheet (D) at 0 to 30°C> The maximum storage modulus of each of the conductive composition and protective sheet (D) at 0 to 30° C. was measured by the following method. The thickness of the conductive layer was 60 μm, and the thickness of the protective sheet was the value listed in the raw materials. First, a measurement sample measuring 5 mm in width and 30 mm in length was prepared. This sample was placed in a dynamic viscoelasticity measuring device (DVA-200 dynamic viscoelasticity measuring device, manufactured by IT Measurement & Control Co., Ltd.) and subjected to dynamic viscoelasticity measurement under the conditions of a heating rate of 10°C / min, a measuring frequency of 1 Hz, and a strain of 0.08%. From the obtained dynamic viscoelasticity curve, the storage modulus E' at 0 to 30°C was read and the maximum value was determined.

[0091] <Evaluation> The obtained conductive compositions were evaluated for metal recovery, adhesive strength, conductivity, blocking resistance, peelability, instantability, and reworkability according to the following methods. The evaluation results are shown in Table 5.

[0092] [Metal recovery] Metal recovery is evaluated by the ratio of the metal component (M1) remaining after the conductive composition (conductive layer) is exposed to high temperatures to carbonize and decompose the binder (B), to the residue (M2) obtained after the conductive composition (conductive layer) is immersed in a solvent composition (C) to decompose the binder (B). The conductive sheets prepared in each example and comparative example were cut into a size of 45 mm wide and 100 mm long, and the protective sheet (D) was peeled off to obtain a conductive composition. The conductive composition was then left to stand in an electric furnace at 600°C for 10 hours, and after removal, the mass of the metal component (M1) was measured. Similarly, the conductive sheet was cut into a size of 45 mm wide and 100 mm long, and the protective sheet (D) was peeled off to obtain a conductive composition. The conductive composition was then immersed in 100 g of a solvent composition (C) (containing 20% ​​by mass of monoethanolamine as a nitrogen-containing organic solvent (c1), 15% by mass of potassium hydroxide as a basic inorganic compound (c2), and 65% by mass of glycerin) at 30 ° C., followed by ultrasonic treatment for 2 hours and standing for 22 hours to allow the residue to settle. The supernatant solvent composition (C-1) was then replaced with isopropanol, and the mixture was again stood for 5 hours. The supernatant was then removed, and the residue (M2) was air-dried for 3 days and the mass was measured. The value obtained by dividing M1 by M2 was calculated, and the metal recovery was evaluated according to the following criteria. +++: Very good (M1 / M2 0.95 or higher). ++: Excellent (M1 / M2 is 0.80 or more and less than 0.95). +: Practical (M1 / M2 is 0.50 or more and less than 0.80). NG: Impractical (M1 / M2 less than 0.50).

[0093] [Adhesive strength] The conductive sheets prepared in each Example and Comparative Example were cut to a size of 25 mm wide and 100 mm long, and the conductive sheets were laminated on a SUS plate (a commercially available SUS304 plate with a thickness of 0.2 mm and a nickel layer with a thickness of 2 μm) with a width of 30 mm and a length of 150 mm so that the surface with the exposed conductive composition (conductive layer) was in contact with the SUS plate. Next, using a roll laminator, the conductive sheets were laminated at 130°C and 3 kgf / cm 2 The conductive sheet and the SUS plate were roll-laminated under the conditions of 130°C, 3 kgf / cm , and 0.5 m / min, and then the protective sheet (D) was peeled off, and gold-plated copper foil (gold-plated copper foil with a thickness of 25 μm) was placed on the surface where the conductive composition was exposed, and the laminate was then roll-laminated using a roll laminator at 130°C, 3 kgf / cm 2 The conductive composition and gold-plated copper foil were roll-laminated at a speed of 0.5 m / min to obtain a pre-press laminate. The pre-press laminate was then hot-pressed at 150°C and 2 MPa, and then left to stand (cure) in an atmosphere of 180°C for 30 minutes to obtain a sample for evaluation (SUS plate with conductive adhesive).

[0094] Next, using a tensile tester (small tabletop tester EZ-TEST, manufactured by Shimadzu Corporation) at a pulling rate of 50 mm / min, the adhesive strength of the conductive composition to the gold-plated surface of the evaluation sample in a 90° peel test was used as an index to evaluate the adhesive strength according to the following evaluation criteria. +++: Very good (adhesive strength of 3N / cm or more). ++: Excellent (adhesion strength is 2N / cm or more and less than 3N / cm). +: Practical (adhesive strength is 1N / cm or more and less than 2N / cm). NG: Impractical (adhesion strength less than 1 N / cm).

[0095] [Conductive] The conductive sheet (20 mm wide, 20 mm long) prepared in each Example and Comparative Example was laminated on a 20 mm wide, 20 mm long SUS plate (a commercially available SUS304 plate with a thickness of 0.1 mm and a nickel layer of 2 μm thick formed on the surface) so that the surface on which the conductive composition was exposed was in contact with the SUS plate. Next, using a roll laminator, the conductive sheet was laminated on a SUS plate at 90°C and 3 kgf / cm. 2 The conductive sheet and the SUS plate were roll-laminated under the condition of 1 m / min, to obtain a SUS plate with a conductive sheet.

[0096] Next, the protective sheet (D) was peeled off from the SUS plate with the conductive sheet, and the plate was punched into a square with a side of 10 mm using a punching machine. Thus, a SUS plate with a conductive composition (hereinafter referred to as "SUS plate with conductive composition") was obtained. Next, the surface of the SUS plate with the conductive composition exposed (the surface of the conductive composition not facing the SUS plate) was placed on a separately prepared wiring circuit board (flexible printed wiring board), and the surface was laminated using a roll laminator at 130°C and 3 kgf / cm. 2The SUS plate with the conductive composition and the flexible printed wiring board were attached at a speed of 1 m / min. Then, they were thermocompressed at 170°C, 2 MPa, and 5 minutes, and then heated in an electric oven at 160°C for 60 minutes to obtain a sample for evaluation. The wiring circuit board described above had a 75 μm thick polyimide film with a copper foil circuit formed on each side with a thickness of 32 μm, and a square with a side of 0.7 mm and an opening area of ​​0.49 mm on the copper foil circuit. 2 A 37.5 μm thick insulating cover film with adhesive and a through-hole (opening) is laminated on the other copper foil circuit. In addition, a 37.5 μm thick insulating cover film with adhesive and no through-hole is laminated on the other copper foil circuit (the copper foil circuit and cover film are arranged symmetrically with respect to the polyimide film to prevent the wiring circuit board from warping).

[0097] Next, using a resistance meter and a BSP probe (model number: MCP-TP05P, manufactured by Mitsubishi Chemical Analytech), the electrical resistance (connection resistance value) between the SUS plate and the copper foil circuit of the evaluation sample was measured, and the conductivity was evaluated using this measurement value as an index according to the following evaluation criteria. +++: Good (connection resistance less than 20 mΩ). ++: Practical (connection resistance is 20 mΩ or more and less than 100 mΩ). +: Practical (connection resistance is 100mΩ or more and less than 300mΩ). NG: Impractical (connection resistance is 300 mΩ or more).

[0098] [Blocking resistance] Two conductive sheets (50 mm wide, 50 mm long) were prepared for each example and comparative example. The conductive sheets were then stacked so that the surface of one conductive sheet on which the conductive composition was exposed was in contact with the surface of the other conductive sheet on which the protective sheet (D) was exposed (i.e., the surface not coated with a release agent). A 2 kg weight was placed on each sheet, and the sheets were left standing at 40°C and atmospheric pressure for 3 days. The weight was then removed, and the conductive sheets were separated. The area of ​​the conductive composition transferred to the protective sheet (D) was used as an index to evaluate blocking resistance according to the following evaluation criteria. +++: Good (transferred area is less than 5%). ++: Practical (transferred area is 5% or more and less than 10%). +: Practical (transferred area is 10% or more but less than 20%). NG: Impractical (transferred area is 20% or more).

[0099] [Easy peelability] The conductive sheets prepared in each Example and Comparative Example were cut to a size of 25 mm wide and 100 mm long, and the conductive sheets were laminated on a SUS plate (a commercially available SUS304 plate with a thickness of 0.2 mm and a nickel layer with a thickness of 2 μm) with a width of 30 mm and a length of 150 mm so that the surface on which the conductive composition was exposed was in contact with the SUS plate. Next, using a roll laminator, the conductive sheets were laminated on a SUS plate with a thickness of 130°C and a pressure of 3 kgf / cm. 2 The conductive sheet and the SUS plate were roll-laminated under the conditions of 0.5 m / min to obtain a sample for evaluation.

[0100] Next, using a tensile tester (small tabletop tester EZ-TEST, manufactured by Shimadzu Corporation) at a pulling rate of 50 mm / min, the peel strength of the protective sheet (D) to the conductive composition of the evaluation sample in a 90° peel test was used as an index to evaluate the ease of peeling according to the following evaluation criteria. +++: Very good (peel strength less than 50g / 50mm). ++: Excellent (peel strength is 50g / 50mm or more and less than 100g / 50mm). +: Practical (peel strength is 100g / 50mm or more and less than 400g / 50mm). NG: Impractical (peel strength is 400 g / 50 mm or more).

[0101] [Instantness] The conductive sheets prepared in each example and comparative example were cut into a size of 25 mm wide and 100 mm long, and left to stand in a freezer (-15°C) for 10 hours, then removed and left to stand in an environment of 23°C and 50% RH for 3 minutes. Next, the conductive sheets were laminated on a SUS plate (a commercially available SUS304 plate with a thickness of 0.2 mm and a nickel layer of 2 μm thick formed on the surface) with the exposed surface of the conductive composition (conductive layer) in contact with the SUS plate with a width of 30 mm and a length of 150 mm. Next, using a roll laminator, the conductive sheets were laminated on a SUS plate with a thickness of 90°C and a pressure of 3 kgf / cm. 2 The conductive sheet and the SUS plate were roll-laminated under conditions of 0.5 m / min, and then the protective sheet was peeled off from the conductive sheet to obtain a SUS plate with a conductive layer.

[0102] Next, the gold-plated surface of an electroless gold-plated sheet (manufactured by Taiyo Kogyo Co., Ltd.) cut to a width of 30 mm and a length of 200 mm was attached to the exposed surface of the conductive layer of the SUS plate, and roll-laminated under the same conditions as above. These were then thermocompressed at 170°C, 2 MPa, and 3 minutes, and subsequently heated in an electric oven at 160°C for 60 minutes to obtain evaluation samples. The area where the conductive layer was present on the obtained evaluation samples was observed from the electroless gold-plated sheet side, and the degree of appearance defect (blistering due to evaporation of water droplets on the conductive layer) was graded from a to d (blistering evaluation). a: The area of ​​the bulge is 5% or more and less than 10% of the area of ​​the conductive layer. b: The area of ​​the bulge is 10% or more and less than 15% of the area of ​​the conductive layer. c: The area of ​​the bulge is 15% or more and less than 20% of the area of ​​the conductive layer. d: The area of ​​the bulge is less than 5% of the area of ​​the conductive layer.

[0103] Each of the evaluation samples obtained above was subjected to a tensile test using a small tabletop tester (EZ-TEST, manufactured by Shimadzu Corporation). The part where the SUS plate was not attached was attached to the tensile tester, and the adhesive strength of the conductive layer to the electroless gold-plated surface of the evaluation sample was measured in a 180° peel test under the condition of a pulling speed of 50 mm / min, and the results were ranked from a to d (adhesion strength). a: Adhesive strength is 6N / cm or more. b: Adhesive strength is 3N / cm or more and less than 6N / cm. c: Adhesive strength is 1N / cm or more but less than 3N / cm. d: Adhesion strength is less than 1 N / cm.

[0104] Furthermore, using each result as an index, the adhesive strength was evaluated according to the following evaluation criteria. +++: Both swelling rating and adhesive strength are A (very good). ++: Either the blister rating or adhesive strength is a and the other is b, or both are b (excellent) +: Either the blister rating or adhesive strength is C, but not D (practical) NG: Either the swelling rating or the adhesive strength or both are d (not practical).

[0105] [Reworkability] Reworkability was evaluated by the area and arithmetic mean height of the adhesive residue of the conductive layer when the conductive layer temporarily attached to the polyimide was peeled off. The exposed surface of the conductive layer of a conductive sheet cut to a width of 50 mm and a length of 50 mm was attached to a polyimide film (Kapton 300H) cut to a width of 70 mm and a length of 70 mm, and the laminate was then laminated using a roll laminator (transport speed: 1 m / min, temperature: 90°C, pressure: 3 kgf / cm). 2) and temporary bonding was performed. The conductive layer in the resulting temporarily bonded laminate was peeled off from the edge, and the area of ​​the conductive layer remaining on the polyimide was divided by the area of ​​the conductive layer before bonding to calculate the adhesive residue rate. Next, five randomly selected points from the adhesive residue area were measured using a laser microscope (Keyence VK-X100) to obtain measurement data. The obtained measurement data was imported into analysis software (VK-H1XA analysis application equipped with the ISO 25178 surface texture measurement module VK-H1XR, both manufactured by Keyence), and ISO 25178 surface texture measurement was performed to calculate the arithmetic mean height (conditions: S-filter: 1 μm, L-filter: 0.2 mm). The adhesive residue rate and arithmetic mean height obtained were evaluated according to the following criteria. +++: The adhesive residue rate is 5% or less, and if there is adhesive residue, the arithmetic mean height is less than 20% of the adhesive layer thickness. Very good. ++: The adhesive residue rate is more than 5% and 15% or less, and the arithmetic mean height is less than 20% of the adhesive layer thickness. Good. +: The adhesive residue rate is 15% or less, and the arithmetic mean height of the adhesive residue is 20-50% of the adhesive layer thickness. Suitable for practical use. NG: The adhesive residue rate is greater than 15% and / or the arithmetic mean height of the adhesive residue is greater than 50% of the adhesive layer thickness. Not suitable for practical use.

[0106] [Table 1]

[0107] [Table 2]

[0108] [Table 3]

[0109] [Table 4]

[0110] [Table 5]

[0111] Comparative Example 1, which did not dissolve in the solvent composition (C), had problems with metal recovery. Furthermore, Comparative Examples 2 and 3, which had Spd outside the range of 1,000 to 500,000, had problems with reworkability. In contrast, the conductive sheets of Examples 1 to 27, which had Spd in the range of 1,000 to 500,000 particles / mm2, dissolved in the solvent composition (C), and had a conductive layer in which the residue contained a metal element, were confirmed to have excellent metal recovery, adhesive strength, conductivity, blocking resistance, easy peelability, instant property, and reworkability.

Claims

1. A conductive sheet having a conductive composition containing metal powder (A) and a binder (B) arranged on one main surface of a protective sheet (D), The conductive composition dissolves when immersed in a solvent composition (C) at 30°C for 24 hours, leaving a residue, the residue containing a metal element. The peak density Spd on the surface of the conductive composition on the non-facing side of the protective sheet (D) is 1,000 to 500,000 particles / mm². ２ And, The solvent composition (C) contains 5 to 40% by mass of a nitrogen-containing organic solvent (c1) relative to the total mass of the solvent composition (C), and also contains 5 to 40% by mass of a basic inorganic compound (c2) relative to the total mass of the solvent composition (C). A conductive sheet wherein the conductive composition has voids, and the void ratio is 1.0 to 30%.

2. The conductive sheet according to claim 1, wherein the conductive composition has adhesive properties.

3. The conductive sheet according to claim 1, wherein the binder (B) has one or more selected from the group consisting of ester groups, imide groups, amide groups, urethane groups, and urea groups.

4. The conductive sheet according to claim 1, wherein the binder (B) comprises a thermosetting resin (b-2) selected from epoxy resin, phenolic resin, polyacrylic resin, polyester resin, polyurethane resin, polyamide resin, polyimide resin, polyamide-imide resin, urea resin, polyurethane-urea resin, melamine resin, and polyolefin resin.

5. The conductive sheet according to claim 1, wherein the Sdr ratio of the unfolded area of ​​the protective sheet (D) to the surface of the conductive composition on the non-facing side is 0.01 to 4.

6. The maximum storage modulus (2) of the conductive composition at 0 to 30°C is 0.01 to 100 GPa. The conductive sheet according to claim 1, wherein the value α obtained by dividing the above-mentioned maximum value (2) by the maximum value (1) of the storage modulus of the protective sheet (D) at 0 to 30°C is 0.01 to 30.

7. The conductive sheet according to claim 1, wherein the maximum value (1) of the storage modulus of the protective sheet (D) at 0 to 30°C is 0.01 to 1000 GPa.

8. The metal powder (A) is in the form of a sphere, dendritic, needle-shaped, rod-shaped, grape-shaped, or amorphous lump, The conductive sheet according to claim 1, wherein the ratio D90 / D10 of the average particle diameter D90 to the average particle diameter D10 of the metal powder (A) is 1.5 or more and less than 8.

0.

9. The metal powder (A) is spherical, dendritic, needle-shaped, rod-shaped, grape-shaped, and amorphous lumps, The conductive sheet according to claim 1, wherein the average particle size D10 of the metal powder (A) is 1 to 15 μm, and the average particle size D90 is 10 to 30 μm.

10. The conductive sheet according to claim 1, wherein the maximum value (2) of the storage modulus of the conductive composition at 0 to 30°C is 1 to 100 GPa.

11. The conductive sheet according to claim 1, further comprising a curing agent (H) having a molecular weight or weight-average molecular weight of less than 5,000.

12. The conductive sheet according to claim 1, wherein the conductive composition does not contain any silane coupling agent, silyl compound, phosphoric acid, or bisphenol S type epoxy resin.

13. The material comprises a metal plate, a conductive composition obtained by peeling off the protective sheet (D) of the conductive sheet according to any one of claims 1 to 12, and a wiring circuit board. A wiring board in which the metal plate is fixed to the wiring circuit board via the conductive composition.

14. An electronic device comprising the wiring board described in claim 13.