Conductive Sheet, Wiring Board, and Electronic Device

Abstract

The present disclosure provides: a conductive sheet having a conductive composition which has outstanding metal recycling properties and good adhesive power and conductivity, prevents sticking to protective sheets during storage, and has outstanding protective sheet peeling properties, water droplet evaporation properties, and reworking properties; and a wiring board provided with said conductive composition. The conductive sheet of the present disclosure is a conductive sheet 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), wherein the conductive composition dissolves, so as to leave a residue, when submerged for 24 hours in a specific type of solvent composition (C) at 30°C, the residue includes a metal element, and the peak density Spd of the surface of the conductive composition not facing the protective sheet (D) is 1,000-500,000 / mm2.

Description

Technical Field

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

Background Art

[0002] The printed wiring board mounted inside an electronic device has flexibility, but for connector parts that connect components, a reinforcing plate may be arranged to suppress deformation. Epoxy glass or the like has been used for the reinforcing plate, but a metal plate has come to be used from the viewpoint of imparting an electromagnetic wave noise suppression function. For the connection between the printed wiring board and the metal plate, a conductive composition mainly composed of resin is used as a bonding agent.

[0003] For the purpose of conducting between the metal plate and the printed wiring board or for the purpose of controlling the elastic modulus or the like, a filler may be added to the bonding agent. 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. Further, Patent Document 2 discloses a conductive adhesive sheet containing a thermosetting resin (A), a curing agent (B), conductive fine particles (C), and a compound (D) selected from the group consisting of a silane coupling agent, a silyl compound, phosphoric acid, and a bisphenol S type epoxy resin, which 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 and the like, which comprises a binder of a resin composition containing a resol-type phenol resin having a dimethylene ether bond and a linear polymer having a molecular weight of 1000 or more and compatible with the phenol resin, and metal particles composed of Cu powder coated with Ag. Patent Document 4 discloses a conductive paste containing a polyurethane prepolymer having an NCO value of 12 to 14% and a viscosity of 1000 to 2000 mPa·s.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0006] Electronic devices equipped with printed wiring boards have been discarded without being reused due to the expiration of their useful life or the emergence of new model devices. Also, when using a conductive composition as an adhesive, it is processed into a desired shape and size to fit the shape of the printed wiring board, but a large amount of scrap materials are generated in the process and are also discarded without being reused. In recent years, for the purpose of resource conservation, activities to recover metal resources from these electronic devices and scrap materials during manufacturing have become active. As a method for recovering metal resources, there is a method of burning and carbonizing organic substances at high temperatures (incineration), but this method requires a large amount of energy for incineration, so an alternative and efficient method is required (metal recoverability).

[0007] Incidentally, a conductive sheet having a two-layer structure with a conductive layer / protective sheet is often manufactured in a roll form and stored. When stored in a roll form, there is a problem that a phenomenon called blocking occurs, in which the conductive composition adheres to the back surface of the protective sheet during use (blocking resistance).

[0008] In addition, the conductive sheet is used by adhering a second adherend to the exposed conductive composition after adhering (temporarily pasting) the first adherend and the conductive composition and then peeling off and removing the protective sheet. However, due to insufficient strength of the protective sheet or excessive adhesion of the conductive composition to the protective sheet, peeling defects such as breakage of the protective sheet occur during peeling and removal of the protective sheet (easy peelability).

[0009] Also, when the conductive composition is stored at a high temperature, the reaction of the contained curing agent may proceed and the adhesiveness may decrease. For this reason, the conductive composition may be stored in a refrigerator or freezer. However, the conductive composition taken out from a refrigerated or frozen storage may cause condensation due to moisture in the air. When the pasting operation is performed with water droplets (including fine ones that are not visible to the naked eye) present on the surface of the binder, poor bonding may occur. Therefore, until the moisture volatilizes, the pasting operation to the adherend cannot be carried out, which is a factor reducing the production efficiency (instantaneous property).

[0010] Furthermore, from the viewpoint of reducing environmental impact, technologies for increasing the manufacturing yield of printed wiring boards are required. In the manufacturing process of printed wiring boards, usually, the conductive sheet is temporarily attached to the wiring board and joined by thermocompression bonding. If re-peelability (reworkability) can be ensured at the stage of temporary attachment to the wiring board, the manufacturing yield can be increased. However, when re-peeling, glue residue may remain on the adherend and rework may not be possible. In addition, with the thinning of the wiring board, the wiring board itself tends to be easily damaged, and there is also a problem that it is not easy to ensure reworkability at the stage of temporary attachment.

[0011] The present disclosure aims to provide a conductive sheet having a conductive composition that is excellent in metal recoverability, has high adhesiveness and conductivity, prevents adhesion to a protective sheet during storage, and is excellent in peelability of the protective sheet, evaporability of water droplets, and reworkability, and a wiring board including the conductive composition.

Means for Solving the Problems

[0012] The present disclosure provides the following conductive composition, conductive sheet, wiring board, and electronic device. [1]: The conductive sheet according to the present disclosure is a conductive sheet in which a conductive composition containing metal powder (A) and a binder (B) is disposed on one main surface of a protective sheet (D), when the conductive composition is immersed in a solvent composition (C) at 30 °C for 24 hours, it dissolves and residues remain, and the residues contain metal elements, the peak point density Spd of the surface of the conductive composition on the side non-facing the protective sheet (D) is 1,000 to 500,000 pieces / mm 2 and the solvent composition (C) contains 5 to 40% by mass of a nitrogen-containing organic solvent (c1) with respect to the total mass of the solvent composition (C), and contains 5 to 40% by mass of a basic inorganic compound (c2) with respect to the total mass of the solvent composition (C). [2]: The conductive sheet according to [1], wherein the conductive composition has adhesiveness. [3]: The conductive sheet according to [1] or [2], wherein the binder (B) has one or more 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 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 non-facing the protective sheet (D) is 0.01 to 4. [6]: The maximum value (2) of the storage elastic modulus of the conductive composition at 0 to 30 °C is 0.01 to 100 GPa, 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 elastic 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 value of the storage elastic modulus of the protective sheet (D) at 0 to 30°C is 0.01 to 1000 GPa. [8]: A wiring board including a metal plate, a conductive composition obtained by peeling the protective sheet (D) of the conductive sheet according to any one of [1] to [7], and a wiring circuit board, wherein the metal plate is fixed to the wiring circuit board via the conductive composition. [9]: An electronic device including the wiring board according to [8].

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

[11] : The conductive composition according to

[10] , having adhesiveness.

[12] : The conductive composition according to

[10] or

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

[0013] According to the present disclosure, there is provided a conductive sheet having a conductive composition that is excellent in metal recoverability, has high adhesive strength and conductivity, prevents adhesion to a protective sheet during storage, and is excellent in peelability of the protective sheet, evaporation of water droplets, and reworkability. Thereby, a wiring board that facilitates resource recovery can be provided. [Embodiments for Carrying Out the Invention]

[0014] Hereinafter, the conductive composition, conductive sheet, and wiring board according to the present disclosure will be described in order. Note that "~" indicating a numerical range includes the lower limit value and the upper limit value thereof unless otherwise specified.

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

[0016] Here, dissolution in the present disclosure is defined as a phenomenon in which an article to be treated is immersed in the solvent composition (C) to bring the article into contact with the solvent composition (C), and a part of the article dissolves in the solvent composition (C) and the original shape is not maintained. That is, it is not necessary for all of the corresponding article to dissolve in the solvent composition (C), and insoluble matter (residue) may be present.

[0017] The metal element contained in the insoluble matter (residue) when the conductive composition of the present disclosure is dissolved in the solvent composition (C) includes those derived from the metal powder (A). What the solvent composition (C) acts on is the binder (B). By the decomposition action of the solvent or the like of 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, so that the metal powder (A) in the above conductive composition can be efficiently recovered. The conductive layer of the present disclosure dissolves and a residue remains when immersed in the solvent composition (C) at 30°C for 24 hours, and this residue contains a metal element derived from the metal powder (A).

[0018] [Metal Powder (A)] The metal powder (A) is used for the purpose of imparting conductivity to the conductive composition. The metal powder (A) is preferably a conductive metal such as gold, platinum, silver, copper, and nickel, and alloys thereof. Instead of fine particles of a single composition, composite fine particles having a core body and a coating layer covering the surface of the core body formed of a material having higher conductivity than the core body may be used. The composite fine particles are preferable from the viewpoint of cost reduction. The core body is preferably a conductive metal and alloys thereof, and more preferably selected from nickel, silica, and copper. The coating layer may be any material having conductivity, and a conductive metal or a conductive polymer is preferable. Examples of the conductive metal include gold, platinum, silver, tin, manganese, and indium, and alloys thereof. Among these, silver is preferable from the viewpoint of conductivity.

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

[0020] The composite fine particles preferably have a coating layer in a proportion of 1 to 40 parts by mass with respect to 100 parts by mass of the core body, and more preferably 5 to 30 parts by mass. Coating with 1 to 40 parts by mass can reduce costs while maintaining conductivity. It is preferable that the coating layer completely covers the core body in the composite fine particles. However, in practice, a part of the core body may be exposed. Even in such a case, if the conductive substance covers 70% or more of the surface area of the core body, it is easy to maintain conductivity.

[0021] The shape of the metal powder (A) is not particularly limited as long as the desired conductivity can be obtained. For example, spherical, flake-like, leaf-like, dendritic (dendrite-like), plate-like, needle-like, rod-like, grape-like, and irregular lump-like are suitable. Spherical and dendritic shapes are more preferable for efficiently forming a longitudinal conduction path between the metal reinforcing plate and the wiring board.

[0022] When the metal powder (A) is spherical, dendritic, needle-like, rod-like, grape-like, or irregular lump-like, the average particle diameter D of the metal powder (A) 50 is preferably 5 to 20 μm, more preferably 5.5 to 15 μm, and still more preferably 6 to 10 μm. When the average particle diameter D 50 is in the range of 5 to 20 μm, both adhesion and conductivity can be achieved. Note that the average particle diameter D50 can be determined by a laser diffraction / scattering particle size distribution measuring device.

[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 electrical conductivity, it is preferable that the thickness is 10 to 30 μm. 10 , D 90 is the average particle size D 50 It can be determined by a laser diffraction / scattering particle size distribution measuring device in the same manner 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 from 1.5 to less than 8.0. By being 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) is 50 The average particle diameter D is preferably 5 to 50 μm, more preferably 6.5 to 30 μm, and further preferably 8 to 20 μm. 50 A thickness of 5 to 50 μm ensures both adhesive strength and electrical conductivity.

[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 electrical 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 from 1.5 to less than 8.0. By being 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 ratio of the metal powder (A) is preferably 40 to 90% by mass, more preferably 45 to 80% by mass, and still more preferably 50 to 70% by mass in the conductive composition. By setting the addition amount as described above, it is possible to achieve both metal recoverability, adhesive strength, and conductivity.

[0029] [Binder (B)] The binder (B) serves as the base of the conductive composition and has a function of dispersing and supporting the metal powder (A). Since the binder (B) needs to be decomposed by the solvent composition (C), an organic substance is preferable. The composition of the binder (B) is not particularly limited as long as it has the above-described 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 coagulated at normal 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 be decomposed by a solvent composition (C) having a decomposition action by a strong solvent, and the specific chemical bond is decomposed by the solvent and can dissolve in the solvent composition (C). It is preferable that the binder (B) has one or more selected from the group consisting of an ester group, an imide group, an amide group, a urethane group, and a urea group. When the conductive composition has the above-described functional groups, the decomposition by the solvent composition (C) is performed more efficiently, the molecular chain of the binder (B) is more subdivided, more of the binder (B) dissolves in the solvent composition (C), and the components derived from the binder (B) contained in the residue can be reduced.

[0031] For the above effects, it is more preferable that the binder (B) has two or more selected from the group consisting of an ester group, an imide group, an amide group, a urethane group, and a urea group. By having two or more kinds, multiple effects are exhibited, and the binder (B) can be decomposed more efficiently. As a preferred example, a combination of one or more selected from an ester group, an imide group, an amide group, a urea group, and an ester group and a urethane group can be exemplified.

[0032] [Resin (b-1)] 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 a resin having at least one chemical bond selected from the group consisting of imide bonds, amide bonds, urethane bonds, and urea bonds is preferred. Furthermore, from the viewpoint of expressing 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. 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) having thermosetting properties. Thermosetting is defined as "causing a polymerization and / or crosslinking reaction by heat and irreversibly increasing the elastic modulus".

[0034] The above-described thermosetting properties may be exhibited by the reaction of reactive functional groups with each other when the thermosetting resin (b-2) has reactive functional groups, or may be exhibited by the reaction of reactive functional groups incorporated in each of the thermosetting resin (b-2) and the curing agent (H) described below.

[0035] Examples of the thermosetting resin (b-2) include epoxy resins, phenol 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 at least one selected from the group consisting of ester groups, imide groups, amide groups, urethane groups, and urea groups. In imide bonds, amide bonds, urethane bonds, and urea bonds, a strong adhesive force can be realized by the interaction of the non-bonding electron pairs of nitrogen atoms contained in the bond with the adherend. By having two or more selected from the group consisting of ester groups, imide groups, amide groups, urethane groups, and urea groups in the thermosetting resin (b-2), the above-described effect of improving adhesiveness can be further enhanced.

[0036] The binder (B) may further contain a curing agent (H). The curing agent (H) in the present disclosure is a substance that promotes 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 polymerization composition by means such as heating, radiation, a catalyst, etc., and irreversibly increasing the elastic modulus". In the binder (B), from the viewpoint of forming polymerization and / or crosslinking by stimuli such as heat and expressing strong adhesiveness to the conductive composition, it is preferable that the binder (B) of the present disclosure contains a curing agent (H). The curing agent (H) may be appropriately selected from known compounds that exhibit curability in combination with the thermosetting resin (b). Examples of the curing agent (H) include epoxy compounds, oxetane compounds, episulfide compounds, aziridine compounds, isocyanate compounds, amine compounds, isocyanate compounds, imidazole compounds, and acid anhydrides.

[0037] As the epoxy compound, for example, glycidyl ether type epoxy compounds, glycidyl amine type epoxy compounds, glycidyl ester type epoxy compounds, and cyclic aliphatic (alicyclic) epoxy compounds are preferable.

[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 novolak type epoxy compounds, phenol novolak type epoxy compounds, a-1-naphthol novolak type epoxy compounds, bisphenol A type novolak type epoxy compounds, dicyclopentadiene type epoxy compounds, tetrabromobisphenol A type epoxy compounds, brominated phenol novolak type epoxy compounds, tris(glycidyloxyphenyl)methane, and tetrakis(glycidyloxyphenyl)ethane.

[0039] Examples of the glycidylamine type epoxy compound include tetraglycidyl diaminodiphenylmethane, triglycidyl para-aminophenol, triglycidyl meta-aminophenol, and tetraglycidyl metaxylylene diamine.

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

[0041] Examples of the alicyclic (cycloaliphatic) epoxy compound 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 esterified product of (2-ethyl-2-oxetanyl)ethanol and terephthalic acid, an ether compound of (2-ethyl-2-oxetanyl)ethanol and phenol novolak resin, and an esterified product of (2-ethyl-2-oxetanyl)ethanol and a polyvalent carboxylic acid compound.

[0043] Episulfide compounds include, for example, 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, bis(6,7-epithio-3,4-dithiaheptyl) disulfide, 1,4-dithiane-2,5-bis(2,3-epithiopropyldithiomethyl), 1,3-bis(2,3-epithiopropyldithiomethyl) benzene, 1,6-bis(2,3-epithiopropyldithiomethyl)-2-(2,3-epithiopropyldithioethylthio)-4-thiahexane, 1,2,3-tris(2,3-epithiopropyldithio) propane.

[0044] Aziridine compounds include, for example, trimethylolpropane-tri-a-2-aziridinylpropionate, tetramethylolmethane-tri-a-2-aziridinylpropionate, N,N'-diphenylmethane-4,4'-bis(1-aziridinecarboxamide), N,N'-hexamethylene-1,6-bis(1-aziridinecarboxamide).

[0045] Amine compounds include, for example, diethylenetriamine, triethylenetetramine, methylenebis(2-chloroaniline), methylenebis(2-methyl-6-methylaniline), 1,5-naphthalenediisocyanate, n-butylbenzyl phthalate.

[0046] Isocyanate compounds include, for example, tolylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, dicyclohexylmethane diisocyanate, 1,5-naphthalenediisocyanate, tetramethylxylylene diisocyanate, trimethylhexamethylene diisocyanate.

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

[0048] Examples of acid anhydrides include tetrahydrophthalic anhydride, dodecenyl succinic anhydride, methyl nadic anhydride, trimellitic anhydride, and pyromellitic anhydride.

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

[0050] The step of heating the conductive composition and adhering it to the adherend is preferably a hot press. By applying a pressing treatment, the adhesiveness to the adherend is improved. The conditions of the hot press can be appropriately selected according to the composition of the conductive composition, the material, size, and shape of the adherend. For example, 130 to 200 °C, 1 to 10 MPa, and 3 to 60 minutes are preferable.

[0051] The content ratio of the binder (B) is preferably 10 to 60% by mass in the total solid content of the conductive composition from the viewpoint of excellent adhesiveness to the metal plate and the wiring circuit board.

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

[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, the metal recoverability is improved, the evaporation of dew condensation occurring when taken out from the freezer is promoted, and the instantaneity can be improved. Further, by setting the porosity to 60% or less, the accumulation of excessive dew condensation can be suppressed, and the instantaneity can be improved. The porosity is more preferably 1.0 to 30%.

[0054] In this specification, the "porosity" means the ratio of the area of voids derived from a microscopic image of the cross-section of the conductive composition. The specific calculation method is as follows. Observe the cross-section of the conductive composition using a microscope such as a scanning electron microscope (SEM) or a laser microscope as appropriate. When the cross-section is observed with a microscope from the vertical direction, a contrast difference occurs between the conductive composition and the voids, and the shape of the voids can be recognized. Using the image analysis software "GIMP2.10.6", the cross-sectional image of the conductive composition cut is binarized into black and white for the part of the conductive composition and the part of the voids. Then, by counting the number of black and white pixels, the ratio of the area of the voids is calculated from the ratio of the number of pixels.

[0055] The porosity of the conductive composition can be appropriately adjusted by using a known method such as using a foaming agent that foams by an arbitrary trigger such as heat to generate voids, but it is particularly preferable to control it according to the shape and content of the metal powder (A). When the metal powder (A) is particularly bulky and dendritic (dendritic), the effect of the present disclosure is that voids are easily formed, which is preferable compared to other metal powders. Also, as the content of the metal powder (A) increases, the voids tend to increase.

[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). From the viewpoint of efficiently acting on the binder (B) the solubility effect of the solvent composition (C), the solvent composition (C) contains the nitrogen-containing organic solvent (c1) in an amount of 5 to 40% by mass based on the total mass of the solvent composition (C). The content of the nitrogen-containing organic solvent (c1) is more preferably 10 to 30% by mass. The nitrogen-containing organic solvent (c1) can be used without particular limitation as long as it is an organic solvent containing a nitrogen atom in the molecule. 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 content of the binder (B) to be dissolved.

[0057] From the viewpoint of making the solvent composition (C) basic and promoting the decomposition of the binder (B) by the solvent, the solvent composition (C) contains the basic inorganic compound (c2) in an amount of 5 to 40% by mass based on the total mass of the solvent composition (C). Any substance that exhibits the above-mentioned function may be used without particular limitation, but the basic inorganic compound (c2) is, for example, at least one selected from the group consisting of sodium hydroxide, potassium hydroxide, ammonium hydroxide, sodium hydrogen carbonate, sodium dihydrogen phosphate, disodium phosphate, trisodium phosphate, potassium dihydrogen phosphate, and tripotassium phosphate. From the viewpoint of imparting suitable solubility to the solvent composition (C), the content of the basic inorganic compound (c2) is more preferably 10 to 30% by mass.

[0058] To the solvent composition (C), an organic solvent for dilution or an additive that promotes the decomposition of the binder (B) may be appropriately added from the viewpoint of imparting 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 metal powder (A) and a binder (B) is disposed on one main surface (only one side) of a protective sheet (D). In other words, this conductive sheet is a sheet-like article having a conductive composition on the protective sheet (D). Note that the conductive composition provided in the conductive sheet is a solid that is non-fluid at room temperature and forms a layer with a certain thickness, which is also referred to as a conductive layer. When this conductive layer is immersed in a solvent composition (C) at 30°C for 24 hours, it dissolves and a residue remains, and the residue contains a metal element.

[0060] [Protective sheet (D)] The protective sheet (D) can be appropriately used as long as it is a film having a release treatment on one side or both sides. Examples of the base material of 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, soft polyvinyl chloride, polyvinylidene fluoride, polyethylene, polypropylene, polyurethane, ethylene-vinyl acetate copolymer, and polyvinyl acetate; papers such as glassine paper, high-quality paper, kraft paper, and coated paper; various non-woven fabrics, synthetic papers, metal foils, and composite films combining these. Among these, polyethylene terephthalate and polyethylene naphthalate are preferable from the viewpoint of enhancing peelability.

[0061] The surface of the protective sheet (D) may be subjected to a matting treatment as necessary. Examples of the matting treatment include sand matting, etching matting, coating matting, chemical matting, and incorporated matting.

[0062] The protective sheet (D) can be obtained, for example, by applying a release agent to a base material. As the release agent, hydrocarbon resins such as polyethylene and polypropylene, higher fatty acids and their metal salts, higher fatty acid soaps, waxes, animal and vegetable oils and fats, mica, talc, silicone-based surfactants, silicone oils, silicone resins, fluorine-based surfactants, fluorine resins, fluorine-containing silicone resins, melamine resins, acrylic resins, etc. are used. As the method for applying the release agent, a conventionally known method, for example, a gravure coating method, a kiss coating method, a die coating method, a lip coating method, a comma coating method, a blade coating method, a roll coating method, a knife coating method, a spray coating method, a bar coating method, a spin coating method, a dip coating method can be used.

[0063] The maximum value (1) of the storage elastic modulus 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 value (1) of the storage elastic modulus of the protective sheet (D) at 0 to 30°C is in the range of 0.01 to 1000 GPa, the protective sheet (D) can be easily peeled off without stretching or breaking when peeling off and removing the protective sheet (D) from the conductive composition after thermal lamination.

[0064] The maximum value (2) of the storage elastic modulus of the conductive composition (conductive layer) at 0 to 30°C is preferably 0.01 to 100 GPa, and more preferably 1 to 10 GPa. When the maximum value (2) of the storage elastic modulus of the conductive composition at 0 to 30°C is in this range, the conductive composition can be easily peeled off without stretching or breaking when peeling off and removing the protective sheet (D) from the conductive composition after thermal lamination. The storage elastic modulus 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 value (2) of the storage modulus of the conductive composition (conductive layer) at 0 to 30 °C by the maximum value (1) of the storage modulus of the protective sheet (D) at 0 to 30 °C is preferably from 0.01 to 30, more preferably from 0.1 to 15. When α is from 0.01 to 30, the protective sheet (D) is likely to peel off from the conductive composition after thermal lamination.

[0066] [Peak point density Spd and developed area ratio Sdr] In the conductive sheet of the present disclosure, the peak point density Spd of the surface of the conductive composition (conductive layer) on the side not facing the protective sheet (D) (non-facing side) is 1,000 to 500,000 per mm 2 By having the peak point density Spd of the surface within this range, the contact points with the adherend are within an appropriate range, and excessive adhesion to the adherend is suppressed, thereby improving the reworkability. The peak point density Spd is preferably from 10,000 to 300,000 per mm 2 and more preferably from 25,000 to 250,000 per mm 2

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

[0068] In the conductive sheet of the present disclosure, the developed area ratio Sdr of the surface of the conductive composition (conductive layer) on the non-facing surface not facing the protective sheet (D) is preferably from 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 unrolled from the rolled conductive sheet, 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 specific range, the unevenness per unit area can be made dense. Thereby, the contact area between the surface of the conductive composition and the back surface of the protective sheet (D) in the rolled body can be reduced, and both adhesiveness and blocking resistance can be achieved.

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

[0070] In the present disclosure, the peak point density Spd and the developed area ratio Sdr shall use the values measured in accordance with ISO 25178-2:2012. Specifically, measurement data is acquired using a laser microscope (manufactured by Keyence Corporation, VK-X100), and the acquired measurement data is imported into analysis software (both the analysis application "VK-H1XA" and the ISO 25178-2:2012 surface property measurement module "VK-H1XR", both manufactured by Keyence Corporation), and can be calculated by performing ISO 25178-2:2012 surface property measurement.

[0071] The present inventor further found that when the developed area ratio Sdr of the surface of the conductive composition, which is the non-facing surface of the protective sheet (D), is 0.01 to 4.0, water droplets are likely to evaporate. Since the water droplets are likely to evaporate, for example, the evaporation waiting time of the dew condensation that occurs when taken out of a freezer can be shortened. As a result, the waiting time for the pasting operation onto the adherend can be shortened (hereinafter also referred to as instantaneity), and the working efficiency can be improved. From the viewpoint of improving instantaneity, the developed area ratio Sdr is preferably 0.1 to 3.0, and more preferably 0.25 to 2.0.

[0072] [Method for Controlling Spd and Sdr] As a method for controlling the peak point density Spd and the developed area ratio Sdr of the surface of the conductive sheet of the present disclosure, a conventionally known method can be applied as a method for adjusting the surface shape of an object. Different methods may be applied for Spd and Sdr respectively, or a common method may be applied. For example, a method of polishing the surface using abrasive paper, a shot blasting method of spraying an abrasive onto the surface of the conductive composition with compressed air, forming a conductive composition on a film having a predetermined peak point density Spd and developed area ratio Sdr, laminating a protective sheet, and then removing the film to transfer the unevenness of the film surface, a method of pressure-bonding a film having a predetermined peak point density Spd and developed area ratio Sdr and a conductive composition to transfer the unevenness of the film surface, and a method of controlling the surface unevenness by including particulate matter in the conductive composition can be mentioned.

[0073] From the viewpoint of achieving both thin film properties and conductivity, 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 still more preferably 30 to 70 μm.

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

[0075] [Method for manufacturing a wiring board] As an example, the method for manufacturing this wiring board includes a method of laminating a wiring circuit board for a printed wiring board, a conductive composition, and a metal plate, pressure-bonding and joining them, and then mounting electronic components on the board. An example of the method for manufacturing a wiring board will be described below.

[0076] First, a conductive composition varnish is applied onto a protective sheet (D) and dried to prepare a conductive sheet (step a). Next, thermal lamination is performed in a state where the exposed surface of the conductive layer (the surface of the conductive layer not facing the protective sheet (D)) is in contact with a metal plate, and the conductive sheet is laminated on the metal plate (step b). Next, the protective sheet (D) is peeled off (step c), and thermal lamination is performed in a state where the exposed conductive composition is in contact with a wiring circuit board (step d). Then, the conductive composition is cured by heating press or the like, and a wiring board in which the metal plate is fixed to the wiring circuit board via the conductive composition is obtained (step e).

[0077] [Electronic device] This wiring board can be applied to all conventionally known products where printed wiring boards are used. Specifically, it can be applied to electronic devices such as mobile phones, smartphones, notebook PCs, digital cameras, and liquid crystal displays. It can be preferably used for transportation equipment such as automobiles, trains, ships, and airplanes.

Examples

[0078] Examples and comparative examples are given below to specifically explain the present disclosure, but the present disclosure is not limited to these examples. The mixing ratios show values in terms of solid content except for the solvent. Also, "parts" represents "parts by mass".

[0079] [D of metal powder (A) 10、 D 50、 D 90 [Average particle size] D 50 The average particle size was measured by a laser diffraction / scattering particle size distribution measuring device LS13320 (manufactured by Beckman Coulter). It is a value obtained by measuring the conductive filler with a Turbula 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. D 10、 D 90 are the average particle sizes at which the cumulative values in the particle size cumulative distribution are 10% and 90%, and were measured in the same manner as above.

[0080] [Acid value of thermosetting resin (b-2)] Based on the neutralization titration method of JIS K 0070, it was determined by converting the measured acid value (mgKOH / g) to solid content. Approximately 1 g of the sample was precisely weighed into a conical flask with a stopper, and 100 mL of a mixed solution of tetrahydrofuran / ethanol (volume ratio: tetrahydrofuran / ethanol = 2 / 1) was added and dissolved. To this, phenolphthalein test solution was added as an indicator, and titrated with 0.1N alcoholic potassium hydroxide solution. The end point was determined when the indicator maintained a light pink color for 30 seconds. The acid value was determined by the following formula (unit: mgKOH / g). Acid value (mgKOH / g) = (5.611 × a × F) / S However, S: Sampling amount of the sample (g) a: Consumption of 0.1N alcoholic potassium hydroxide solution (mL) F: Normality of 0.1N alcoholic potassium hydroxide solution

[0081] [Weight average molecular weight (Mw) of thermosetting resin (b-2)] The measurement of Mw was carried out by GPC (gel permeation chromatography) "HPC-8020" (manufactured by Tosoh Corporation). GPC is a liquid chromatograph that separates and quantifies substances dissolved in a solvent (THF: tetrahydrofuran) based on the difference in their molecular sizes. In this measurement, two "LF-604" (manufactured by Showa Denko KK: GPC column for rapid analysis: 6 mm ID × 150 mm size) columns were connected in series and used. The measurement was carried out under the conditions of a flow rate of 0.6 mL / min and a column temperature of 40°C. The determination of Mw was carried out in terms of polystyrene conversion.

[0082] [Preparation of conductive composition] The raw materials used for the preparation of 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 = 12.8 μm, dendritic (manufactured by Mitsui Mining & Smelting Co., Ltd.) A2: Silver-coated copper powder: D 50 = 31.2 μm, D10 = 12.9 μm, D 90 = 44.6 μm, dendritic (manufactured by Mitsui Mining & Smelting Co., Ltd.) A3: Silver-coated copper powder: D 50 = 10.8 μm, D 10 = 3.2 μm, D 90 = 29.5 μm, spherical (manufactured by Showa Denko Materials Co., Ltd.) A4: Silver-coated copper powder: D 50 = 7.5 μm, D 10 = 1.5 μm, D 90 = 11.3 μm, spherical (manufactured by Showa Denko Materials Co., Ltd.) A5: Silver-coated copper powder: D 50 = 11.3 μm, D 10 = 3.8 μm, D 90 = 29.5 μm, flake-shaped (manufactured by DOWA Holdings Co., Ltd.) Binder (B) Thermosetting resin (b-2) P1: Polyester resin (thermosetting resin having an ester group): Acid value 36 mgKOH / g, Mw = 27,000 (manufactured by Toyochem Co., Ltd.) P2: Polyimide resin (thermosetting resin having an imide group): Acid value = 22 mgKOH / g, Mw = 55,000 (manufactured by Toyochem Co., Ltd.) P3: Polyamide resin (thermosetting resin having an amide group): Acid value = 28 mgKOH / g, Mw = 49,000 (manufactured by Toyochem Co., Ltd.) P4: Polymaleimide resin (thermosetting resin having an imide group): Acid value = 13 mgKOH / g, Mw = 98,000 (manufactured by Toyochem Co., Ltd.) P5: Polyurethaneimide resin (thermosetting resin having a urethane group and an imide group): Acid value = 11 mgKOH / g, Mw = 100,000 (manufactured by Toyochem Co., Ltd.) P6: Polyacrylic resin (thermosetting resin having none of an ester group, an imide group, an amide group, a urethane group, and a urea group): Acid value = 17 mgKOH / g, Mw = 120,000 (manufactured by Toyochem Co., Ltd.) P7: Polyolefin resin (thermosetting resin having none of an ester group, an imide group, an amide group, a urethane group, and a urea group): Acid value = 26 mgKOH / g, Mw = 85,000 (manufactured by Toyochem Co., Ltd.) Hardener (H) H1: Bisphenol A type epoxy compound (jER834, molecular weight = 470, manufactured by Mitsubishi Chemical) Protective sheet (D) D1: A protective sheet obtained by subjecting a 50 μm PET (polyethylene terephthalate) film to a matting treatment by sandblasting and applying a silicone release agent D2: A protective sheet obtained by subjecting a 50 μm PEN (polyethylene naphthalate) film to a matting treatment by sandblasting and applying a silicone release agent D3: A protective sheet obtained by subjecting a 38 μm PP (polypropylene) film to a matting treatment by sandblasting and applying a silicone release agent

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

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

[0086] [Examples 2 to 27 and Comparative Examples 1 to 3] The same operations as in Example 1 were carried out except that the types and amounts of the respective components to be blended were as described in Tables 1 to 4, and conductive sheets of Examples 2 to 27 and Comparative Examples 1 to 3 were obtained. However, for Examples 16 to 21, Spd and Sdr were adjusted to desired values by buff-polishing the surface of the conductive composition after drying in an electric oven.

[0087] <Method for Confirming Solubility> Regarding whether the conductive composition (conductive layer) dissolves in the solvent composition (C) and whether the residue contains metal (solubility), it was confirmed by the following method. The conductive sheet was cut into a size of 45 mm in width and 100 mm in length, and the conductive composition obtained by peeling off the protective sheet (D) was immersed in 100 g of the solvent composition (C) at 30 °C (containing 20% by mass of monoethanolamine as the nitrogen-containing organic solvent (c1), 15% by mass of potassium hydroxide as the basic inorganic compound (c2), and 65% by mass of glycerin), then ultrasonic-treated for 2 hours, and left standing for 22 hours. If the conductive composition was fragmented compared to its shape before immersion, it was judged as "dissolved", and it was confirmed whether the insoluble matter (residue) contained metal. If there was no change in the shape before immersion, it was judged as "not dissolved". In addition, when the shape change was not obvious visually, the mass of the sample before and after immersion was compared, and when the mass loss was less than 5%, it was judged as "not dissolved".

[0088] To confirm whether the residue contained metal, qualitative analysis using an ICP emission spectrometer (SPECTRO ARCOS (registered trademark): FHS12 manufactured by AMETEK) was performed on the residue. In the above-mentioned analysis, it was confirmed whether it contained metal elements, and if it contained metal elements, it was judged as "containing".

[0089] <Method for Measuring Peak Point Density Spd and Spread Area Ratio Sdr> The peak point density Spd and spread area ratio Sdr of the non-opposing surface of the conductive composition (conductive layer) and the protective sheet (D) were measured by the following method. After using a laser microscope (VK-X100 manufactured by Keyence) to measure the surface of the conductive composition and obtain measurement data, the obtained measurement data was imported into analysis software (the analysis application "VK-H1XA" and the ISO 25178-2:2012 surface texture measurement module "VK-H1XR", both manufactured by Keyence), and ISO 25178-2:2012 surface texture measurement was executed. The conditions were S-filter: 1 μm and L-filter: 0.2 mm.

[0090] <Measurement of the maximum value of the storage modulus of the conductive composition (conductive layer) and the protective sheet (D) at 0 to 30 °C> The maximum value of the storage modulus of each of the conductive composition and the 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 described in the raw materials. First, a measurement sample with a width of 5 mm and a length of 30 mm was prepared, and this sample was set in a dynamic viscoelasticity measuring device (Dynamic Viscoelasticity Measuring Device DVA - 200, manufactured by IT Measurement & Control Co., Ltd.). Dynamic viscoelasticity measurement was performed under the conditions of a heating rate of 10 °C / min, a measurement 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 obtained.

[0091] <Evaluation> For each of the obtained conductive compositions, the metal recoverability, adhesive strength, conductivity, blocking resistance, peelability, instant property, and reworkability were evaluated according to the following methods. The evaluation results are shown in Table 5.

[0092] [Metal recoverability] The metal recoverability is evaluated by the ratio of the metal component (M1) remaining after exposing the conductive composition (conductive layer) to high temperature to carbonize and decompose the binder (B), and the residue (M2) obtained after immersing the conductive composition (conductive layer) in the solvent composition (C) to decompose the binder (B). The conductive sheets prepared in each of the examples and comparative examples were cut into a size of 45 mm in width and 100 mm in length. After peeling off the protective sheet (D), the obtained conductive composition was left standing in an electric furnace at 600 °C for 10 hours. After taking it out, the mass of the metal component (M1) was measured. Also, a conductive sheet was cut into a size of 45 mm in width and 100 mm in length, and the conductive composition obtained by peeling off the protective sheet (D) was immersed in 100 g of a solvent composition (C) at 30 °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), then ultrasonic-treated for more than 2 hours, allowed to stand for 22 hours, and the residue was allowed to settle. Thereafter, the supernatant solvent composition (C-1) was replaced with isopropanol, allowed to stand again for 5 hours, then the supernatant was removed, and after air-drying for 3 days, the mass of the residue (M2) obtained was measured. The value obtained by dividing M1 by M2 was determined, and the metal recoverability was evaluated according to the following criteria. +++: Extremely excellent (M1 / M2 is 0.95 or more). ++: Excellent (M1 / M2 is 0.80 or more and less than 0.95). +: Practicable (M1 / M2 is 0.50 or more and less than 0.80). NG: Impracticable (M1 / M2 is less than 0.50).

[0093] [Adhesive strength] The conductive sheets prepared in each example and comparative example were cut into a size of 25 mm in width and 100 mm in length, and the conductive sheet was overlaid on the SUS plate such that the surface on which the conductive composition (conductive layer) was exposed contacted 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 formed on its surface) having a width of 30 mm and a length of 150 mm. Next, using a roll laminator, under the conditions of 130 °C, 3 kgf / cm 2 and 0.5 m / min, the conductive sheet and the SUS plate were roll-laminated. After that, the protective sheet (D) was peeled off, and a gold-plated copper foil (a copper foil with a thickness of 25 μm plated with gold) was overlaid on the exposed surface of the conductive composition. Using a roll laminator, under the conditions of 130 °C, 3 kgf / cm 2 and 0.5 m / min, the conductive composition and the gold-plated copper foil were roll-laminated to obtain a pre-press laminate. Thereafter, the pre-press laminate was subjected to hot pressing under the conditions of 150 °C and 2 MPa, and then allowed to stand (cure) for 30 minutes in an atmosphere of 180 °C to obtain an evaluation sample (SUS plate with a conductive adhesive).

[0094] Next, using a tensile testing machine (EZ-TEST, a small desktop testing machine manufactured by Shimadzu Corporation), under the condition of a pulling speed of 50 mm / min, taking the adhesive strength of the conductive composition against the gold-plated surface of the evaluation sample in a 90° peel test as an index, the adhesive force was evaluated according to the following evaluation criteria. +++: Extremely excellent (adhesive strength is 3 N / cm or more). ++: Excellent (adhesive strength is 2 N / cm or more and less than 3 N / cm). +: Practically applicable (adhesive strength is 1 N / cm or more and less than 2 N / cm). NG: Not practically applicable (adhesive strength is less than 1 N / cm).

[0095] [Conductivity] Using the conductive sheets (width 20 mm, length 20 mm) prepared in each example and comparative example, the conductive sheet was overlapped on the SUS plate such that the surface where the conductive composition was exposed contacted the SUS plate (a commercially available SUS304 plate with a thickness of 0.1 mm and a nickel layer with a thickness of 2 μm formed on the surface) with a width of 20 mm and a length of 20 mm. Then, using a roll laminator, under the conditions of 90°C, 3 kgf / cm 2 , 1 m / min, the conductive sheet and the SUS plate were roll laminated to obtain a SUS plate with a conductive sheet.

[0096] Next, after peeling off the protective sheet (D) from the SUS plate with the conductive sheet, it was punched into a square with a side length of 10 mm using a punching machine. And a SUS plate with a conductive composition (hereinafter referred to as "SUS plate with a conductive composition") was obtained. Then, the surface where the conductive composition of the SUS plate with the conductive composition was exposed (the non-opposing surface of the conductive composition to the SUS plate) was overlapped on a separately prepared wiring circuit board (flexible printed wiring board), and using a roll laminator at 130°C, 3 kgf / cm 2, under the condition of 1 m / min, the SUS plate with the conductive composition and the flexible printed wiring board were pasted together. Then, they were thermocompression bonded under the conditions of 170 °C, 2 MPa, and 5 minutes, and subsequently, an evaluation sample was obtained by heating at 160 °C for 60 minutes using an electric oven. The above-mentioned wiring circuit board has copper foil circuits with a thickness of 32 μm formed on both sides of a polyimide film with a thickness of 75 μm. On the copper foil circuit, an insulating cover film with an adhesive and a thickness of 37.5 μm having a through hole (opening) in the shape of a square with a side length of 0.7 mm and an opening area of 0.49 mm 2 is laminated. Also, on the other copper foil circuit, an insulating cover film with an adhesive and a thickness of 37.5 μm without a through hole is laminated (the copper foil circuit and the cover film are symmetrically arranged with respect to the polyimide film so that the wiring circuit board does not warp).

[0097] Next, using a resistance measuring instrument 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 according to the following evaluation criteria using this measured value as an index. +++: Good (connection resistance value is less than 20 mΩ). ++: Practically applicable (connection resistance value is 20 mΩ or more and less than 100 mΩ). +: Practically applicable (connection resistance value is 100 mΩ or more and less than 300 mΩ). NG: Not practically applicable (connection resistance value is 300 mΩ or more).

[0098] [Blocking Resistance] Two conductive sheets (width: 50 mm, length: 50 mm) prepared in each of the examples and comparative examples were prepared. Then, the conductive sheets were overlapped such that the surface where the conductive composition of one conductive sheet was exposed and the surface where the protective sheet (D) of the other conductive sheet was exposed (i.e., the surface where the release agent was not applied) were in contact. After placing a 2 kg weight on them, they were left standing for 3 days under the conditions of 40 °C and atmospheric pressure. Then, after removing the weight and separating each conductive sheet, the blocking resistance was evaluated according to the following evaluation criteria using the area of the surface of the protective sheet (D) onto which the conductive composition was transferred as an index. +++: Good (transferred area is less than 5%). ++: Practically applicable (transferred area is 5% or more and less than 10%). +: Practically applicable (transferred area is 10% or more and less than 20%). NG: Not practically applicable (transferred area is 20% or more).

[0099] [Easiness of peeling] The conductive sheets prepared in each of the examples and comparative examples were cut into a size of width 25 mm and length 100 mm, and the conductive sheets were overlapped on the SUS plate such that the surface where the conductive composition was exposed was in contact with the SUS plate (a commercially available SUS304 plate with a thickness of 0.2 mm and a nickel layer with a thickness of 2 μm formed on its surface) having a width of 30 mm and a length of 150 mm. Then, using a roll laminator, the conductive sheet and the SUS plate were roll laminated under the conditions of 130 °C, 3 kgf / cm 2 and 0.5 m / min to obtain a sample for evaluation.

[0100] Next, using a tensile tester (small bench-top tester EZ-TEST, manufactured by Shimadzu Corporation), the peel strength of the protective sheet (D) with respect to the conductive composition of the sample for evaluation in a 90° peel test was used as an index under the condition of a pulling speed of 50 mm / min, and the easiness of peeling was evaluated according to the following evaluation criteria. +++: Very excellent (peel strength is less than 50 g / 50 mm). ++: Excellent (peel strength is 50 g / 50 mm or more and less than 100 g / 50 mm). +: Practical (peel strength is 100 g / 50 mm or more and less than 400 g / 50 mm). NG: Not practical (peel strength is 400 g / 50 mm or more).

[0101] [Instantaneous property] The conductive sheets prepared in each of the examples and comparative examples were cut into a size of 25 mm in width and 100 mm in length, left standing in a freezer (-15 °C) for 10 hours, then taken out and left standing in an environment of 23 °C and 50% RH for 3 minutes. Next, the conductive sheet was overlapped on the SUS plate so that the surface on which the conductive composition (conductive layer) was exposed contacted the SUS plate (a commercially available SUS304 plate with a thickness of 0.2 mm and a nickel layer with a thickness of 2 μm formed on the surface) having a width of 30 mm and a length of 150 mm. Next, using a roll laminator, under the conditions of 90 °C, 3 kgf / cm 2 , 0.5 m / min, the conductive sheet and the SUS plate were roll laminated, 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 nickel plating sheet (manufactured by Taiyo Kogyo Co., Ltd.) cut to a width of 30 mm and a length of 200 mm was pasted on the surface of the SUS plate with the conductive layer exposed, and roll lamination was performed under the same conditions as above. Then, these were thermocompression bonded under the conditions of 170 °C, 2 MPa, and 3 minutes, and then heated in an electric oven at 160 °C for 60 minutes to obtain a sample for evaluation. The location where the conductive layer of the obtained sample for evaluation existed was observed from the side of the electroless nickel plating sheet, and the degree of appearance defect (swelling caused by evaporation of water droplets on the conductive layer) was graded from a to d (swelling evaluation). a: The area of the swelling is 5% or more and less than 10% with respect to the area of the conductive layer. b: The area of the swelling is 10% or more and less than 15% with respect to the area of the conductive layer. c: The area of the swelling is 15% or more and less than 20% with respect to the area of the conductive layer. d: The area of the swelling is less than 5% with respect to the area of the conductive layer.

[0103] Using a tensile testing machine (EZ-TEST, a small desktop testing machine manufactured by Shimadzu Corporation) for each of the evaluation samples obtained above, attach the part where the SUS plate is not attached to the tensile tester, and under the condition of a pulling speed of 50 mm / min, measure the adhesion strength of the conductive layer to the electroless gold plating surface of the evaluation sample in the 180° peel test, and grade the results from a to d (adhesion strength). a: The adhesion strength is 6 N / cm or more. b: The adhesion strength is 3 N / cm or more and less than 6 N / cm. c: The adhesion strength is 1 N / cm or more and less than 3 N / cm. d: The adhesion strength is less than 1 N / cm.

[0104] Furthermore, using each result as an index, the adhesive force was evaluated according to the following evaluation criteria. +++: In terms of bulge evaluation and adhesion strength, both are a (very excellent). ++: In terms of bulge evaluation and adhesion strength, either one is a and the other is b, or both are b (excellent). +: In terms of bulge evaluation, either one of the adhesion strengths is c and there is no d (practicable). NG: In terms of bulge evaluation, either one or both of the adhesion strengths are d (impracticable).

[0105] [Reworkability] The reworkability was evaluated by the adhesive residue area and the arithmetic mean height of the conductive layer when the conductive layer temporarily adhered to the polyimide was peeled off. The surface where the conductive layer of the conductive sheet cut out to a width of 50 mm and a length of 50 mm was exposed was bonded to a polyimide film (Kapton 300H) cut out to a width of 70 mm and a length of 70 mm, and a roll laminator (conveying speed: 1 m / min, temperature: 90°C, pressure: 3 kgf / cm 2) was passed through to perform temporary bonding. The conductive layer in the obtained temporarily bonded laminate was peeled off from the end, and the paste residue rate was calculated by dividing the area of the conductive layer remaining on the polyimide by the area of the conductive layer before bonding. Next, five arbitrary points were selected from the paste residue portion, and the surface was measured using a laser microscope (Keyence Corporation, VK-X100) to obtain measurement data. The obtained measurement data was imported into analysis software (analysis application "VK-H1XA" equipped with ISO 25178 surface property measurement module "VK-H1XR", both manufactured by Keyence Corporation), and ISO 25178 surface property measurement was executed to calculate the arithmetic mean height (conditions: S-filter: 1 μm, L-filter: 0.2 mm). Using the paste residue rate and arithmetic mean height thus obtained, evaluation was performed according to the following criteria. +++: When the paste residue rate is 5% or less and there is a paste residue portion, the arithmetic mean height thereof is less than 20% of the adhesive layer thickness. It is extremely good. ++: The paste residue rate exceeds 5% and is 15% or less, and the arithmetic mean height thereof is less than 20% of the adhesive layer thickness. It is good. +: The paste residue rate is 15% or less, and the arithmetic mean height of the paste residue portion is 20 - 50% of the adhesive layer thickness. It is practical. NG: The paste residue rate is greater than 15% and / or the arithmetic mean height of the paste residue portion is greater than 50% of the adhesive layer thickness. It is not practical.

[0106]

Table 1

[0107]

Table 2

[0108]

Table 3

[0109]

Table 4

[0110]

Table 5

[0111] In Comparative Example 1, which did not dissolve in the solvent composition (C), there was a problem with metal recoverability. Also, Comparative Examples 2 and 3, in which Spd was outside the range of 1000 to 500,000, had problems with reworkability. On the other hand, according to the conductive sheets of Examples 1 to 27, in which Spd was in the range of 1,000 to 500,000 pieces / mm2, dissolved in the solvent composition (C), and had a conductive layer with a residue containing metal elements, it was confirmed that they were excellent in metal recoverability, adhesion, conductivity, blocking resistance, easy peelability, instantaneity, and reworkability.

[0112] This application claims the priority based on Japanese Patent Application No. 2022-70493 filed on April 22, 2022, and incorporates all of its disclosure herein.

Claims

1. On one main surface of a protective sheet (D), there is disposed a conductive composition containing metal powder (A), a binder (B), and a curing agent (H) having a molecular weight or weight average molecular weight of less than 5,000, and not containing any of a silane coupling agent, a silyl compound, phosphoric acid, and a bisphenol S type epoxy resin, wherein the binder (B) contains a thermosetting resin (b-2) selected from a polyimide resin, a polyamide resin, a polymaleimide resin, a polyurethaneimide resin, and a polyacrylic resin, the conductive composition is one that dissolves and has a residue remaining when immersed in a solvent composition (C) at 30 °C for 24 hours, and the residue contains a metal element, The peak point density Spd of the surface of the protective sheet (D) and the conductive composition on the non-opposing side is 1,000 to 500,000 pieces / mm ２ and and the solvent composition (C) contains 5 to 40% by mass of a nitrogen-containing organic solvent (c1) based on the total mass of the solvent composition (C), and 5 to 40% by mass of a basic inorganic compound (c2) based on the total mass of the solvent composition (C). A conductive sheet.

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

3. The conductive sheet according to claim 1, wherein the binder (B) has one or more 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 claim 1, wherein the binder (B) has two or more 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 claim 1, wherein the developed area ratio Sdr of the surface of the conductive composition on the side non-opposite to the protective sheet (D) is 0.01 to 4.

6. The maximum value (2) of the storage modulus of the conductive composition at 0 to 30 °C is 0.01 to 100 GPa, and 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. The conductive sheet according to claim 1.

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

8. The conductive sheet according to claim 1, wherein the conductive composition has voids and the porosity is 1.0 to 30%.

9. The metal powder (A) is any one of spherical, dendritic, needle-shaped, rod-shaped, grape-shaped, and irregular massive, The average particle diameter D of the metal powder (A) １０ is 1 to 15 μm, and the average particle diameter D ９０ is 10 to 30 μm, and D ９０ / D １０ is 1.5 or more and less than 8.

0. The conductive sheet according to claim 8

10. The peak point density Spd of the surface of the conductive composition on the non-opposing side to the protective sheet (D) is 25,000 to 500,000 pieces / mm ２ and The conductive sheet according to claim 9, wherein the maximum value (2) of the storage elastic modulus of the conductive composition at 0 to 30 °C is 1 to 100 GPa.

11. A wiring board including a metal plate, a conductive composition obtained by peeling a protective sheet (D) of the conductive sheet according to any one of claims 1 to 10, and a wiring circuit board, wherein the metal plate is fixed to the wiring circuit board via the conductive composition.

12. An electronic device comprising the wiring board according to claim 11.

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