Adhesive sheet for printed wiring board, metal-clad laminate, printed wiring board, and electronic device

Abstract

The purpose of the present disclosure is to provide: an adhesive sheet for a printed wiring board, which realizes printed wiring having stable impedance characteristics, has no generation of puddling, is excellent in thermal cycle resistance, enables formation of an opening with good appearance during laser machining and drilling, and has high adhesion of a base material during lamination; a metal-clad laminate using the sheet; a printed wiring board; and an electronic device.　Said problem is solved by an adhesive sheet for a printed wiring board, which has a release film laminated on at least one surface of an adhesive layer, and in which the adhesive layer contains 5-15,000 ppm of toluene on a mass basis, and is used as a member for interlayer adhesion of the printed wiring board.

Description

Adhesive sheet for printed wiring boards, metal-clad laminate, printed wiring board, and electronic device

[0001] The present disclosure relates to an adhesive sheet for printed wiring boards, a metal-clad laminate, a printed wiring board, and an electronic device.

[0002] In recent years, the electronics field has seen remarkable development, and there is a demand for high-speed processing of large amounts of information. As a result, the frequency band of signals used in printed wiring boards used in electronic devices, communication devices, etc. is shifting from the MHz band to the GHz band. Therefore, printed wiring boards will be required to have material suitability over a wide range of high-frequency bands in the future.

[0003] It is known that electrical signal transmission loss is generally composed of dielectric loss due to the dielectric properties of the insulating layer surrounding the wiring, and conductor loss due to the shape of the conductor, skin resistance, characteristic impedance, etc. However, in the case of high-frequency circuits, the influence of dielectric loss is usually greater. Here, dielectric loss increases in proportion to the product of the square root of the relative dielectric constant of a material and the dielectric loss tangent of the material. Therefore, in order to reduce dielectric loss, it is necessary to use materials with low relative dielectric constant and dielectric loss tangent for printed wiring boards.

[0004] Furthermore, in the case of high-frequency circuits, it is important to match the impedance of the transmission line and the circuit to suppress transmission delays. If the impedance between the transmission line and the connected circuit differs, the signal will be reflected at the interface between the transmission line and the circuit, generating a wave in the opposite direction. This reflected wave causes signal loss and distortion, which can degrade circuit performance, so it is necessary to match the impedance of each component in the circuit.

[0005] Patent Document 1 discloses a metal-clad laminate having an insulating resin layer, an adhesive layer, and a metal layer, in which the adhesive layer contains a polyimide containing specific amounts of tetracarboxylic acid residues and specific diamine residues.

[0006] JP 2018-140544 A

[0007] Here, printed wiring boards are fabricated by etching a metal-clad laminate, which is a laminate consisting of a metal plate or a resin layer and an adhesive layer, to form a signal line pattern. In multilayer printed wiring boards, a dielectric adhesive layer may be laminated on one of the signal lines to create a laminated structure. The impedance characteristics of the signal line may vary depending on the dielectric characteristics and thickness of the nearby dielectric. When manufacturing such multilayer printed wiring boards, the adhesive layer is bonded to other layers using a heat press process. However, if the adhesive layer contains a large amount of low-molecular-weight components such as residual solvents, their evaporation upon heating can change the thickness of the adhesive layer, causing the impedance characteristics of the signal line to vary from the original design, potentially hindering circuit design.

[0008] Furthermore, in the process of manufacturing the aforementioned multilayer printed wiring board, a process of laminating (temporarily attaching) a printed wiring board adhesive sheet to an adherend, followed by a heat pressing process, is common. However, in this lamination process, air can get trapped between the printed wiring board adhesive sheet and the adherend (air entrapment), resulting in poor appearance (puddling).

[0009] In addition, with the recent global spread of electronic devices such as smartphones and tablets, reliability over a wide temperature range from low to high is required. Conventional printed wiring boards have sometimes experienced peeling between the adhesive layer and the adjacent layer when exposed to extreme temperature changes. For this reason, adhesive layers are required to have long-term stability in both low- and high-temperature environments (hereinafter also referred to as thermal cycling resistance).

[0010] Furthermore, in recent years, new concepts such as space saving and circuit design have led to demands for excellent processability that does not cause defects in appearance such as gouging of the adhesive layer or burrs when using processing methods such as lasers and drills to form vias and through holes in printed wiring boards.

[0011] The present disclosure has been made in view of the above-mentioned problems, and aims to provide an adhesive sheet for printed wiring boards that realizes printed wiring with stable impedance characteristics, is free from puddling, has excellent thermal cycle resistance, can form openings with good appearance when laser processing or drilling is performed, and has high adhesion to substrates when laminating. Another aim of the present disclosure is to provide a metal-clad laminate, a printed wiring board, and an electronic device that use the adhesive sheet for printed wiring boards.

[0012] The present inventors have conducted extensive research and have found that the problems of the present disclosure can be solved in the following aspects, leading to the completion of the present disclosure. [1]: An adhesive sheet for printed wiring boards, comprising a release film laminated on at least one surface of an adhesive layer, the adhesive layer containing 5 to 15,000 ppm of toluene by mass, and the adhesive layer being used as an adhesive layer for joining layers of a printed wiring board. [2]: The adhesive sheet for printed wiring boards according to [1], wherein the release film is laminated on one surface A of the adhesive layer, and surface B of the adhesive layer opposite surface A has an arithmetic mean roughness Sa of 0.05 to 2.0 μm as determined in accordance with ISO 25178-2:2012. [3]: The adhesive sheet for printed wiring boards according to [1], wherein the storage modulus at 25°C (Er ２５ ) and the storage modulus at 250 °C (Er ２５０ ) and the absolute value of the difference |Er ２５ -Er ２５０ The adhesive sheet for printed wiring boards according to [1] or [2], wherein | is 0.10 to 100,000 MPa. [4]: ​​The adhesive sheet for printed wiring boards according to any of [1] to [3], wherein the cured layer obtained by heating the adhesive layer at 180°C for 60 minutes has an elongation at break of 50 to 1,000%. [5]: A metal-clad laminate having a cured layer of the adhesive layer according to any of [1] to [4]. [6]: A printed wiring board having the metal-clad laminate according to [5]. [7]: An electronic device having the printed wiring board according to [6].

[0013] The present disclosure provides an adhesive sheet for printed wiring boards that realizes printed wiring with stable impedance characteristics, is free from puddling, has excellent thermal cycle resistance, can form openings with good appearance when laser processing or drilling is performed, and has high adhesion to substrates when laminating. The present disclosure also provides a metal-clad laminate, a printed wiring board, and an electronic device that use the adhesive sheet for printed wiring boards.

[0014] Fig. 1 is a schematic plan view of the main surface side of a wiring board having a coplanar circuit according to an example and a comparative example; Fig. 2 is a schematic plan view of the back surface side of a wiring board having a coplanar circuit according to an example and a comparative example; Fig. 3 is a schematic plan view of the main surface side of a wiring board having a coplanar circuit with an electromagnetic wave shielding sheet according to an example and a comparative example; Fig. 4 is a schematic view showing an example of a cross section near a blind via portion formed by laser processing of a printed wiring board; Fig. 5 is a schematic view showing an example of a cross section near a through-hole portion formed by drilling of a printed wiring board;

[0015] The adhesive sheet for printed wiring boards, metal-clad laminates, printed wiring boards, and electronic devices according to the present disclosure will be described below in order. In this specification, the "to" symbol indicating a numerical range includes the upper and lower limits unless otherwise specified. In the numerical ranges described in stages in this specification, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in the numerical ranges described in this specification, the upper or lower limit of that numerical range may be replaced with a value shown in the examples. Furthermore, the drawings have been simplified as appropriate for clarity of explanation. Furthermore, the scale of each component in the drawings may vary significantly for illustrative purposes.

[0016] <<Adhesive Sheet for Printed Wiring Boards>> The adhesive sheet for printed wiring boards of the present disclosure (hereinafter also referred to as the present adhesive sheet) is an adhesive sheet in which a release film is laminated on at least one surface of an adhesive layer, and is used as an adhesive bonding member for printed wiring boards. That is, in the present adhesive sheet, a release film may be laminated on one surface of the adhesive layer, or release films may be laminated on both surfaces of the adhesive layer.

[0017] In this adhesive sheet, the adhesive layer contains 5 to 15,000 ppm of toluene by mass. A toluene content of 5 ppm or more in the adhesive layer enhances temporary adhesion to the substrate and suppresses poor transfer of the sheet to the substrate. On the other hand, a toluene content of 15,000 ppm or less in the adhesive layer suppresses the reduction in film thickness associated with thermal evaporation of low-molecular-weight components during hot pressing, resulting in stable impedance characteristics. The toluene content in the adhesive layer is preferably 10 to 10,000 ppm, and more preferably 50 to 5,000 ppm. The toluene content in the adhesive layer can be calculated, for example, from the peak area in a chart obtained by gas chromatography.

[0018] As disclosed in, for example, JP 2014-114373 A, toluene is one of the general-purpose organic solvents widely used in the production of adhesives in the electrical field, including printed wiring boards according to the present disclosure. In the aforementioned electrical field, it is preferable to use a highly hydrophobic organic solvent to avoid problems such as short circuits caused by moisture. Therefore, toluene, which does not have a polar group in its molecule and has high solubility, is particularly frequently used in the process of producing adhesive layers for adhesive sheets for printed wiring boards (adhesive resin sheets for printed wiring boards). Therefore, toluene often remains in the adhesive layer even after the adhesive layer is formed, and the above-mentioned effects can be best achieved by controlling the toluene content.

[0019] The method for controlling the toluene content of the adhesive layer is not particularly limited as long as it can adjust the content to the desired value. However, the toluene content of the adhesive layer can be controlled, for example, by the solid content (non-volatile content) and viscosity of the resin composition (hereinafter also referred to as the coating solution), the drying temperature and time of the coating film, and even the thickness of the coating film. The specific drying temperature and time will be described later in the method for producing the adhesive sheet.

[0020] <Adhesive Layer> The adhesive layer in the present disclosure can be obtained by coating an adhesive composition on a release film and drying it. The adhesive layer can be a non-flowable solid at room temperature (e.g., 25°C) and can form a layer of a certain thickness. The thickness of the adhesive layer in the present adhesive sheet is preferably 5 to 200 μm, more preferably 10 to 100 μm, and even more preferably 15 to 70 μm, from the viewpoint of achieving both embeddability and thin film formation for signal lines. The adhesive layer in the present disclosure can be (fully) cured by heating to become the cured layer described below. That is, the present adhesive sheet has an adhesive layer containing a specific amount of toluene, in other words, an adhesive layer before (fully) curing. Here, "before curing" can include uncured (uncured) and semi-cured (cured but not completely cured) adhesives, and can refer to anything before fully cured.

[0021] The adhesive layer preferably contains a binder (A), a filler (B), a solvent (at least toluene), and other optional components.

[0022] [Binder (A)] The binder (A) serves as a base for the adhesive layer and has the function of dispersing and supporting the filler (B) and other additives. The composition of the binder (A) is not particularly limited as long as it has the above-mentioned functions, but it is preferable that the binder (A) contains the resin (a-1) described below.

[0023] The content of the binder (A) in the adhesive layer is preferably 50 to 97% by mass or less, more preferably 60 to 90% by mass, and particularly preferably 64 to 85% by mass, relative to the total mass of the adhesive layer. By containing 50% by mass or more of the binder (A), the elastic modulus of the adhesive layer can be easily set within a suitable range, and the occurrence of cracks in the adhesive layer during drilling can be easily suppressed. Furthermore, by setting the content of the binder (A) to 97% by mass or less, the elastic modulus of the adhesive layer can be appropriately increased, and the occurrence of side etching during laser processing can be easily suppressed.

[0024] Resin (a-1) in the present disclosure can be defined as an organic material that is typically solid, semi-solid, or solidified, has a softening or melting range, and has a weight-average molecular weight (Mw) of 5,000 or more. While the Mw of resin (a-1) is not particularly limited, it is preferably 15,000 or more, more preferably 20,000 or more, from the viewpoint of improving the insulation reliability of the cured product after a heat cycle test. The upper limit of the Mw of resin (a-1) is not particularly limited, and can be appropriately set within a range that achieves the effects of the present disclosure. One type of binder (A) may be used alone, or multiple types may be used in combination. In addition to resin (a-1), binder (A) may contain a curing agent (a-2), which will be described later. Resin (a-1) does not contain curing agent (a-2), and curing agent (a-2) does not contain resin (a-1); the two are different substances.

[0025] (Resin (a-1)) The resin (a-1) is not particularly limited in composition, molecular structure, etc., other than the weight average molecular weight (Mw) described above, but it is also possible to select a suitable resin depending on the properties of the resin. From the viewpoint of exerting adhesive properties by applying a thermal stimulus to the adhesive layer, the resin (a-1) is preferably a thermosetting resin or a thermoplastic resin having the above-mentioned specific Mw. One type of resin (a-1) may be used alone, or multiple types may be used in combination.

[0026] Thermosetting resins are resins that have the ability to be thermoset, which can be defined as "capable of being transformed into a substantially infusible and insoluble product when cured by heat or other means such as radiation, catalysts, etc."

[0027] When the thermosetting resin has a reactive functional group such as an acidic group, the thermosetting property may be exhibited by a reaction between the reactive functional groups. Alternatively, the thermosetting property may be exhibited by a reaction between reactive functional groups incorporated in the thermosetting resin and the curing agent (a-2) described below.

[0028] Examples of resin (a-1) include acrylic resins, polyester resins, polyurethane resins, polyurethane-polyurea resins, polyamide resins, polyimide resins, polycarbonate resins, polyphenylene ether resins, styrene-based elastomers, fluororesins, and styrene-maleic anhydride resins. These may be appropriately selected and used alone or in combination. Among these, the following are preferred from the viewpoints of high insulating properties and dielectric properties due to their high hydrophobicity, and high heat resistance due to their low thermal decomposition point. From this viewpoint, it is preferable to use styrene-based elastomers, polyphenylene ethers, polyimides, polyamides, and polyurethanes as resin (a-1). From the same viewpoint, it is more preferable to use styrene-based elastomers, polyimides, polyamides, and polyurethanes as resin (a-1). The styrene-based elastomers are block copolymers in which a portion composed of styrene and a portion composed of butadiene, isoprene, ethylene, or the like form "blocks."

[0029] When a thermosetting resin is used as the resin (a-1), the resin (a-1) preferably has a reactive functional group capable of reacting with a metal chelate or functional group such as an epoxy group, maleimide group, isocyanate group, or carbodiimide group possessed by the curing agent (a-2) described below. Examples of the reactive functional group include a carboxyl group, an acid anhydride group, a hydroxyl group (alcoholic hydroxyl group, phenolic hydroxyl group), an amino group, a cyanate group, an isocyano group, a cyanato group, an isocyanato group, an imidazole group, a pyrrole group, an acetal group, an acryloyl group, a methacryloyl group, a vinyl group, an aldehyde group, a hydrazide group, a hydrazone group, and a phosphate group. Among these, from the viewpoint of the storage stability (sheet life) of the sheet, the reactive functional group is preferably selected from the group consisting of a carboxyl group, an acid anhydride group, a hydroxyl group (alcoholic hydroxyl group, phenolic hydroxyl group), and an amino group. One resin (a-1) may contain two or more types of reactive functional groups.

[0030] When the resin (a-1) has a carboxyl group, the acid value of the resin (a-1) is preferably 0.5 to 30 mg / KOH, more preferably 1.0 to 20 mg / KOH. By adjusting the acid value to 0.5 to 30 mg / KOH, the dielectric properties can be improved and the thermal cycle resistance can be further improved.

[0031] Thermoplastic resins are resins that have thermoplastic properties. Thermoplasticity can be defined as "the ability to repeatedly soften by heating and harden by cooling over a temperature range specific to plastics, and to repeatedly mold, extrude, or form articles by flowing in the softened state to a desired shape." When a thermoplastic resin is used as resin (a-1), it can be appropriately selected from conventionally known thermoplastic resins having the above-mentioned specific Mw, and is not particularly limited.

[0032] (Curing Agent (a-2)) The curing agent (a-2) in the present disclosure can be a substance that accelerates or regulates the curing reaction, and can be defined as a substance having a molecular weight or weight average molecular weight (Mw) of less than 5,000. The curing reaction can be defined as "polymerizing and / or crosslinking a prepolymer or polymer composition by heating or other means such as radiation, a catalyst, etc., to irreversibly increase the elastic modulus." From the viewpoint of forming polymerization and / or crosslinking in the binder (A) by stimulation such as heat, and thereby exhibiting strong adhesiveness in the adhesive layer, it is preferable that the binder (A) contains a curing agent (a-2). One type of curing agent (a-2) may be used alone, or multiple types may be used in combination.

[0033] The curing reaction may be a self-reaction between curing agents (a-2) themselves, or may be a reaction with other components in the binder (A), such as the resin (a-1). When the resin (a-1) and the curing agent (a-2) undergo a curing reaction, the resin (a-1) is preferably a thermosetting resin, from the viewpoint of efficiently carrying out the reaction.

[0034] From the viewpoint of preventing the curing reaction from proceeding during storage and causing the curing reaction to occur only upon heating, it is preferable to select a combination of the thermosetting resin and the curing agent (a-2) that does not undergo a crosslinking reaction at 50° C. but accelerates the curing reaction at 120° C. to 200° C. In addition, the crosslink density of the adhesive layer in each temperature range may be controlled by appropriately combining two or more curing agents that have different curing reaction initiation temperatures.

[0035] The curing agent (a-2) can be any curing agent that can adjust the crosslink density of the adhesive layer within a suitable range. Among these, the curing agent (a-2) is preferably at least one selected from the group consisting of an epoxy group-containing compound (epoxy compound), a maleimide group-containing compound (maleimide compound), an isocyanate group-containing compound, a metal chelate compound, and a carbodiimide group-containing compound.

[0036] Epoxy Group-Containing Compound The epoxy group-containing compound is not particularly limited as long as it has an epoxy group in the molecule. However, the epoxy group-containing compound is preferably one having an average of two or more epoxy groups per molecule. As the epoxy group-containing compound, for example, an epoxy resin such as a glycidyl ether type epoxy resin, a glycidyl amine type epoxy resin, a glycidyl ester type epoxy resin, or a cyclic aliphatic (alicyclic) epoxy resin can be used.

[0037] Examples of glycidyl ether type epoxy resins include bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol S type epoxy resins, bisphenol AD ​​type epoxy resins, cresol novolac type epoxy resins, phenol novolac type epoxy resins, α-naphthol novolac type epoxy resins, bisphenol A type novolac type epoxy resins, dicyclopentadiene type epoxy resins, tetrabromobisphenol A type epoxy resins, brominated phenol novolac type epoxy resins, tris(glycidyloxyphenyl)methane, and tetrakis(glycidyloxyphenyl)ethane.

[0038] Examples of glycidylamine type epoxy resins include tetraglycidyldiaminodiphenylmethane, triglycidyl paraaminophenol, triglycidyl meta-aminophenol, and tetraglycidyl meta-xylylenediamine.

[0039] Examples of glycidyl ester type epoxy resins include diglycidyl phthalate, diglycidyl hexahydrophthalate, and diglycidyl tetrahydrophthalate.

[0040] Examples of cyclic aliphatic (alicyclic) epoxy resins include epoxycyclohexylmethyl-epoxycyclohexanecarboxylate and bis(epoxycyclohexyl)adipate.

[0041] As the epoxy group-containing compound, one of the above-mentioned compounds may be used alone, or two or more may be used in combination. As the epoxy group-containing compound, from the viewpoint of high adhesiveness, it is preferable to use bisphenol A type epoxy resin, cresol novolac type epoxy resin, phenol novolac type epoxy resin, tris(glycidyloxyphenyl)methane, tetrakis(glycidyloxyphenyl)ethane, or tetraglycidyl metaxylylenediamine. Furthermore, as the epoxy group-containing compound, from the viewpoint of heat resistance, it is more preferable to use one containing three or more epoxy groups.

[0042] Maleimide Group-Containing Compound The maleimide group-containing compound is not particularly limited as long as it has a maleimide group in the molecule. However, the maleimide group-containing compound is preferably one having an average of two or more maleimide groups per molecule.

[0043] Specific examples of the maleimide group-containing compound include o-phenylene bismaleimide, m-phenylene bismaleimide, p-phenylene bismaleimide, 4-methyl-1,3-phenylene bismaleimide, N,N'-(toluene-2,6-diyl)bismaleimide, 4,4'-diphenylmethane bismaleimide, bisphenol A diphenyl ether bismaleimide, 3,3'-dimethyl-5,5'-diethyl-4,4'-diphenylmethane bismaleimide, 4,4'-diphenyl ether bismaleimide, and 4,4'-diphenylsulfone bismaleimide. amide, 1,3-bis(3-maleimidophenoxy)benzene, 1,3-bis(4-maleimidophenoxy)benzene, polyphenylmethane maleimide (CASNO: 67784-74-1, reaction product of a polymer of formaldehyde and aniline with maleic anhydride), N,N'-ethylene bismaleimide, N,N'-trimethylene bismaleimide, N,N'-propylene bismaleimide, N,N'-tetramethylene bismaleimide, N,N'-pentamethylene bismaleimide, N,N'-(1,3-pentanediyl)bis(maleinimide), N ,N'-hexamethylenebismaleimide, N,N'-(1,7-heptanediyl)bismaleimide, N,N'-(1,8-octanediyl)bismaleimide, N,N'-(1,9-notanediyl)bismaleimide, N,N'-(1,10-decanediyl)bismaleimide, N,N'-(1,11-undecanediyl)bismaleimide, N,N'-(1,12-dodecanediyl)bismaleimide, N,N'-[(1,4-phenylene)bismethylene]bismaleimide, N,N'-[(1,2-phenylene)bismethylene]bismaleimide, N,N' -[(1,3-phenylene)bismethylene]bismaleimide, 1,6'-bismaleimide-(2,2,4-trimethyl)hexane, N,N'-[(methylimino)bis(4,1-phenylene)]bismaleimide, N,N'-(2-hydroxypropane-1,3-diylbisiminobiscarbonylbisethylene)bismaleimide, N,N'-(dithiobisethylene)bismaleimide, N,N'-[hexamethylenebis(iminocarbonylmethylene)]bismaleimide, N,N'-carbonylbis(1,4-phenylene)bismaleimide, N,N',N''-[nitrilotris(ethylene)]trismaleimide, N,N',N''-[nitrilotris(4,1-phenylene)]trismaleimide, N,N'-[p-phenylenebis(oxy-p-phenylene)]bismaleimide, N,N'-[methylenebis(oxy)bis(2-methyl-1,4-phenylene)]bismaleimide, N,N'-[methylenebis(oxy-p-phenylene)]bis(maleimide)N,N'-[dimethylsilylenebis[(4,1-phenylene)(1,3,4,-oxadiazole-5,2-diyl)( 4,1-phenylene)]]bismaleimide, N,N'-[(1,3-phenylene)bisoxybis(3,1-phenylene)]bismaleimide, 1,1'-[3'-oxospiro[9H-xanthene-9,1'(3'H)-isobenzofuran]-3,6-diyl]bis(1H-pyrrole-2,5-dione), N,N'-(3,3'-dichlorobiphenyl-4,4'-diyl)bismaleimide, N,N'-(3,3'-dimethylbiphenyl-4,4'-diyl)bismaleimide, N,N'-(3,3'-dimethoxybiphenyl-4,4' -diyl)bismaleimide, N,N'-[methylenebis(2-ethyl-4,1-phenylene)]bismaleimide, N,N'-[methylenebis(2,6-diethyl-4,1-phenylene)]bismaleimide, N,N'-[methylenebis(2-bromo-6-ethyl-4,1-phenylene)]bismaleimide, N,N'-[methylenebis(2-methyl-4,1-phenylene)]bismaleimide, N,N'-[ethylenebis(oxyethylene)]bismaleimide, N,N'-[sulfonylbis(4,1-phenylene)bis(oxy)bis(4 ,1-phenylene)]bismaleimide, N,N'-[naphthalene-2,7-diylbis(oxy)bis(4,1-phenylene)]bismaleimide, N,N'-[p-phenylenebis(oxy-p-phenylene)]bismaleimide, N,N'-[(1,3-phenylene)bisoxybis(3,1-phenylene)]bismaleimide, N,N'-(3,6,9-trioxaundecane-1,11-diyl)bismaleimide, N,N'-[isopropylidenebis[p-phenyleneoxycarbonyl(m-phenylene)]]bismaleimide, N,N'-[isopropylidenebis[p-phenyleneoxycarbonyl(p-phenylene)]]bismaleimide, N,N'-[isopropylidenebis[(2,6-dichlorobenzene-4,1-diyl)oxycarbonyl(p-phenylene)]]bismaleimide, N,N'-[(phenylimino)bis(4,1-phenylene)]bismaleimide, N,N'-[azobis(4,1-phenylene)]bismaleimide, N,N'-[1,3,4-oxadiazole-2,5-diylbis( 4,1-phenylene)]bismaleimide, 2,6-bis[4-(maleimido-N-yl)phenoxy]benzonitrile, N,N'-[1,3,4-oxadiazole-2,5-diylbis(3,1-phenylene)]bismaleimide, N,N'-[bis[9-oxo-9H-9-phospha(V)-10-oxaphenanthrene-9-yl]methylenebis(p-phenylene)]bismaleimide, N,N'-[hexafluoroisopropylidenebis[p-phenyleneoxycarbo N,N'-[carbonylbis[(4,1-phenylene)thio(4,1-phenylene)]]bismaleimide, N,N'-carbonylbis(p-phenyleneoxyp-phenylene)bismaleimide, N,N'-[5-tert-butyl-1,3-phenylenebis[(1,3,4-oxadiazole-5,2-diyl)(4,1-phenylene)]]bismaleimide, N,N'-[cyclohexylidenebis(4,1-phenylene)]bis Maleimide, N,N'-[methylenebis(oxy)bis(2-methyl-1,4-phenylene)]bismaleimide, N,N'-[5-[2-[5-(dimethylamino)-1-naphthylsulfonylamino]ethylcarbamoyl]-1,3-phenylene]bismaleimide, N,N'-(oxybisethylene)bismaleimide, N,N'-[dithiobis(m-phenylene)]bismaleimide, N,N'-(3,6,9-trioxaundecane-1,11-diyl)bismaleimide, N,Examples of polyfunctional maleimides include N'-(ethylenebis-p-phenylene)bismaleimide, BMI-689, BMI-1500, BMI-1700, BMI-3000, BMI-5000, and BMI-9000 manufactured by Designer Molecules, and ODA-BMI and BAF-BMI manufactured by JFE Chemical Corporation.

[0044] Furthermore, examples of the maleimide group-containing compound include polyfunctional maleimides obtained by reacting polyfunctional amines with maleic anhydride. Examples of polyfunctional amines include isophorone diamine, dicyclohexylmethane-4,4'-diamine, and Huntsman Corporation's Jeffamine D-230, HK-511, D-400, XTJ-582, D-2000, XTJ-578, XTJ-509, XTJ-510, T-403, and T-5000 having a terminally aminated polypropylene glycol backbone, and XTJ-500, XTJ-501, XTJ-502, XTJ-504, XTJ-511, XTJ-512, and XTJ-590 having a terminally aminated ethylene glycol backbone, and XTJ-542, XTJ-533, XTJ-536, XTJ-548, and XTJ-559 (all trade names) having a terminally aminated polytetramethylene glycol backbone.

[0045] Isocyanate Group-Containing Compound The isocyanate group-containing compound is not particularly limited as long as it is a compound having an isocyanate group in the molecule. Specific examples of the isocyanate group-containing compound having one isocyanate group per molecule include n-butyl isocyanate, isopropyl isocyanate, phenyl isocyanate, benzyl isocyanate, (meth)acryloyloxyethyl isocyanate, 1,1-bis[(meth)acryloyloxymethyl]ethyl isocyanate, vinyl isocyanate, allyl isocyanate, (meth)acryloyl isocyanate, and isopropenyl-α,α-dimethylbenzyl isocyanate. Examples of isocyanate group-containing compounds include 1,6-diisocyanatohexane, isophorone diisocyanate, 4,4'-diphenylmethane diisocyanate, polymeric diphenylmethane diisocyanate, xylylene diisocyanate, 2,4-tolylene diisocyanate, toluene diisocyanate, 2,4-toluene diisocyanate, hexamethylene diisocyanate, 4-methyl-m-phenylene diisocyanate, naphthylene diisocyanate, paraphenylene diisocyanate, tetramethylxylylene diisocyanate, Compounds obtained by reacting equimolar amounts of diisocyanate compounds such as cyclohexylmethane diisocyanate, hydrogenated xylylene diisocyanate, cyclohexyl diisocyanate, tolidine diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, m-tetramethylxylylene diisocyanate, p-tetramethylxylylene diisocyanate, and dimer acid diisocyanate with hydroxyl group-, carboxyl group-, or amide group-containing vinyl monomers can also be used.

[0046] Specific examples of the isocyanate group-containing compound having two isocyanate groups in one molecule include aromatic diisocyanates such as 1,3-phenylene diisocyanate, 4,4'-diphenyl diisocyanate, 1,4-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-toluidine diisocyanate, 2,4,6-triisocyanate toluene, 1,3,5-triisocyanate benzene, dianisidine diisocyanate, 4,4'-diphenyl ether diisocyanate, and 4,4',4"-triphenylmethane triisocyanate; Aliphatic diisocyanates such as trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, dodecamethylene diisocyanate, and 2,4,4-trimethylhexamethylene diisocyanate; aromatic aliphatic diisocyanates such as ω,ω'-diisocyanate-1,3-dimethylbenzene, ω,ω'-diisocyanate-1,4-dimethylbenzene, ω,ω'-diisocyanate-1,4-diethylbenzene, 1,4-tetramethylxylylene diisocyanate, and 1,3-tetramethylxylylene diisocyanate; Examples of the diisocyanate include alicyclic diisocyanates such as 3-isocyanatemethyl-3,5,5-trimethylcyclohexyl isocyanate (also known as isophorone diisocyanate), 1,3-cyclopentane diisocyanate, 1,3-cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), 1,3-bis(isocyanatemethyl)cyclohexane, and 1,4-bis(isocyanatemethyl)cyclohexane.

[0047] Specific examples of the isocyanate group-containing compound having three isocyanate groups in one molecule include aromatic polyisocyanates, aliphatic polyisocyanates such as lysine triisocyanate, araliphatic polyisocyanates, and alicyclic polyisocyanates, as well as the trimethylolpropane adducts of the diisocyanates described above, biuret products obtained by reaction with water, and trimers having an isocyanurate ring.

[0048] As the isocyanate group-containing compound, blocked isocyanate group-containing compounds in which the isocyanate groups in the various isocyanate group-containing compounds exemplified above are protected with ε-caprolactam, MEK oxime, or the like can also be used. Specific examples include compounds in which the isocyanate groups of the isocyanate group-containing compounds are blocked with ε-caprolactam, methyl ethyl ketone (hereinafter referred to as MEK) oxime, cyclohexanone oxime, pyrazole, phenol, or the like. In particular, hexamethylene diisocyanate trimer, which has an isocyanurate ring and is blocked with MEK oxime or pyrazole, is highly preferred because it exhibits excellent heat resistance when used in the adhesive sheet. Furthermore, from the standpoint of heat resistance, it is preferable that the isocyanate group-containing compound have a tri- or higher functional isocyanate group.

[0049] Metal Chelate Compounds Metal chelate compounds are organometallic compounds composed of a metal and an organic substance, and can react with the reactive functional groups of the binder resin (A) to form crosslinks. The type of organometallic compound is not particularly limited, but examples include organoaluminum compounds, organotitanium compounds, and organozirconium compounds. Furthermore, the bond between the metal and the organic substance may be a metal-oxygen bond, and is not limited to a metal-carbon bond. Additionally, the bond between the metal and the organic substance may be a chemical bond, a coordinate bond, or an ionic bond. Furthermore, it is preferable that the metal chelate compound be trifunctional or more from the viewpoint of heat resistance.

[0050] The organoaluminum compound is preferably an aluminum metal chelate compound, such as ethyl acetoacetate aluminum diisopropylate, aluminum tris(ethyl acetoacetate), alkyl acetoacetate aluminum diisopropylate, aluminum monoacetylacetonate bis(ethyl acetoacetate), aluminum tris(acetylacetate), aluminum monoacetylacetate bis(ethyl acetoacetate), aluminum di-n-butoxide monomethyl acetoacetate, aluminum diisobutoxide monomethyl acetoacetate, aluminum di-sec-butoxide monomethyl acetoacetate, aluminum isopropylate, monosec-butoxyaluminum diisopropylate, aluminum sec-butylate, and aluminum ethylate.

[0051] The organic titanium compound is preferably a titanium metal chelate compound, such as titanium acetylacetonate, titanium tetraacetylacetonate, titanium ethylacetoacetate, titanium octylene glycolate, titanium ethylacetoacetate, titanium-1,3-propanedioxybis(ethylacetoacetate), polytitanium acetylacetylacetonate, tetraisopropyl titanate, tetra-n-butyl titanate, butyl titanate dimer, tetraoctyl titanate, dashalyamyl titanate, tetratertiarybutyl titanate, tetrastearyl titanate, titanium isostearate, tri-n-butoxytitanium monostearate, di-i-propoxytitanium distearate, titanium stearate, di-i-propoxytitanium diisostearate, and (2-n-butoxycarbonylbenzoyloxy)tributoxytitanium.

[0052] The organic zirconium compound is preferably a zirconium metal chelate compound. Examples of the zirconium metal chelate compound include zirconium tetraacetylacetonate, zirconium tributoxyacetylacetonate, zirconium monobutoxyacetylacetonate bis(ethylacetoacetate), zirconium dibutoxybis(ethylacetoacetate), zirconium tetraacetylacetonate, normal propyl zirconate, normal butyl zirconate, zirconium stearate, and zirconium octylate. Among these, organic titanium compounds and organic zirconium compounds are preferred in terms of thermosetting reactivity.

[0053] Carbodiimide Group-Containing Compound The carbodiimide group-containing compound is not particularly limited as long as it has a carbodiimide group in the molecule. Examples of the carbodiimide group-containing compound include Carbodilite V-01, V-03, V-05, V-07, and V-09 (all trade names, Nisshinbo Chemical Inc.), and cyclic carbodiimide (Teijin Limited). From the viewpoint of heat resistance, the carbodiimide group-containing compound is preferably one having an average of three or more carbodiimide groups per molecule.

[0054] The curing agent (a-2) is preferably contained in a total amount of 1 to 30 parts by mass, more preferably 1 to 20 parts by mass, and even more preferably 1 to 10 parts by mass, per 100 parts by mass of the binder (A). By adding 1 to 30 parts by mass of the curing agent (a-2), the content of polar groups derived from the curing agent (a-2) contained in the adhesive sheet can be reduced, and the dielectric loss tangent can be easily reduced. Furthermore, by controlling the amount of this curing agent (a-2) added, the Tg of the adhesive layer can be easily controlled within a preferred range, and both high flexibility and low dielectric loss tangent can be easily achieved.

[0055] The functional group equivalent of the curing agent (a-2) component is preferably 50 to 1,000 g / eq, more preferably 50 to 500 g / eq, and even more preferably 50 to 300 g / eq. By setting the functional group equivalent to 50 to 1,000 g / eq, sufficient crosslink density is achieved, a decrease in storage modulus at high temperatures is easily prevented, and side etching (gouging) during laser processing can be easily suppressed. Furthermore, by setting the functional group equivalent within the above range, the content of polar groups derived from the curing agent (a-2) contained in the adhesive sheet can be easily controlled, and the dielectric loss tangent can be easily reduced.

[0056] In addition, from the viewpoint of increasing heat resistance and improving thermal cycle resistance, it is preferable that the curing agent (a-2) has an aromatic structure in its structure.

[0057] The curing agent (a-2) may be used alone or in combination of two or more. The curing agent (a-2) preferably has a molecular weight or weight average molecular weight of 100 or more, from the viewpoint of adjusting the storage modulus and glass transition temperature of the conductive composition.

[0058] The curing agent (a-2) is preferably blended in an amount of 0.1 to 70 parts by mass, more preferably 10 to 20 parts by mass, per 100 parts by mass of the resin (a-1). By adding 0.1 parts by mass or more of the curing agent (a-2), the density of the crosslinked structure of the cured layer is optimized, heat resistance is increased, and thermal cycle resistance is further improved, while a decrease in the elastic modulus of the adhesive layer at high temperatures can be easily suppressed. By adding 70 parts by mass or less of the curing agent (a-2), excessive hardening of the cured layer can be easily prevented, stress relaxation at low temperatures can be increased, and thermal cycle resistance can be further improved.

[0059] [Filler (B)] The filler (B) used in the present adhesive sheet will now be described in detail. The adhesive layer in the present disclosure preferably contains a filler (B) to achieve a modulus of elasticity within a desired range.

[0060] The filler (B) is not particularly limited, and examples of its shape include spherical, powdery, fibrous, needle-like, and scale-like shapes. Examples of the filler (B) include fluorine-based fillers such as polytetrafluoroethylene powder and modified products thereof, tetrafluoroethylene-perfluoroalkyl vinyl ether powder, tetrafluoroethylene-ethylene powder, tetrafluoroethylene-hexafluoropropylene powder, tetrafluoroethylene-vinylidene fluoride powder, tetrafluoroethylene-hexafluoropropylene-perfluoroalkyl vinyl ether powder, polychlorotrifluoroethylene powder, chlorotrifluoroethylene-ethylene powder, chlorotrifluoroethylene-vinylidene fluoride powder, polyvinylidene fluoride powder, and polyvinyl fluoride powder.Polymer fillers such as polyethylene powder, polyacrylate powder, epoxy resin powder, polyamide powder, polyimide powder, polyurethane powder, liquid crystal polymer beads, polysiloxane powder, etc., as well as multilayer core-shell fillers using silicone, acrylic, styrene-butadiene rubber, butadiene rubber, etc.; (poly)phosphate compounds such as melamine phosphate, melamine polyphosphate, guanidine phosphate, guanidine polyphosphate, ammonium phosphate, ammonium polyphosphate, ammonium amide phosphate, ammonium amide polyphosphate, carbamate phosphate, and carbamate polyphosphate, organic phosphate ester compounds, phosphazene compounds, phosphonic acid compounds, phosphinic acid compounds such as aluminum diethylphosphinate, aluminum methylethylphosphinate, aluminum diphenylphosphinate, aluminum ethylbutylphosphinate, aluminum methylbutylphosphinate, and aluminum polyethylenephosphinate, phosphine oxide compounds, phosphorus-based fillers such as phosphorus oxide compounds, phosphorus compounds, phosphorus amide compounds; Nitrogen-based fillers such as benzoguanamine, melamine, melam, melem, melon, melamine cyanurate, cyanuric acid compounds, isocyanuric acid compounds, triazole compounds, tetrazole compounds, diazo compounds, and urea; and inorganic fillers such as silica, hollow silica, porous silica, mica, talc, kaolin, clay, hydrotalcite, wollastonite, xonotlite, silicon nitride, boron nitride, aluminum nitride, calcium hydrogen phosphate, calcium phosphate, glass flakes, hydrated glass, calcium titanate, sepiolite, magnesium sulfate, aluminum hydroxide, magnesium hydroxide, zirconium hydroxide, barium hydroxide, calcium hydroxide, titanium oxide, tin oxide, aluminum oxide, magnesium oxide, zirconium oxide, zinc oxide, molybdenum oxide, antimony oxide, nickel oxide, zinc carbonate, magnesium carbonate, calcium carbonate, barium carbonate, zinc borate, and aluminum borate.

[0061] From the viewpoint of reducing the coefficient of linear expansion (CTE) of the adhesive layer, it is preferable to use a fluorine-based filler, boron nitride, liquid crystal polymer, silica, or phosphorus-based filler as the filler (B). From the same viewpoint, it is more preferable to use a fluorine-based filler, boron nitride, phosphorus-based filler, or silica as the filler (B). Because these fillers have a strong crystalline structure, they have small molecular vibrations even in high frequency bands and excellent dielectric loss tangents. In this adhesive sheet, these fillers (B) may be used alone or in combination.

[0062] The content of the filler (B) in the adhesive layer is preferably 3 to 50% by mass, more preferably 10 to 40% by mass, and particularly preferably 15 to 36% by mass, based on the total mass of the adhesive layer. By including 3% or more by mass of the filler (B) in the adhesive layer, the elastic modulus of the adhesive layer can be appropriately increased, and side etching during laser processing can be easily suppressed. Furthermore, the filler (B) has the effect of lowering the dielectric loss tangent. Furthermore, by including 50% or less by mass of the filler (B), the elastic modulus of the adhesive layer can be easily kept within a suitable range, and cracking of the adhesive layer during drilling can be easily suppressed.

[0063] From the viewpoint of the dielectric loss tangent, the filler (B) preferably has a dielectric loss tangent at 10 GHz of 0.005 or less, more preferably 0.004 or less, and even more preferably 0.003 or less.

[0064] Average particle diameter D of filler (B) ５０ The average particle diameter D of the filler (B) is preferably 0.1 to 25 μm, and more preferably 1 to 10 μm. ５０ By setting the thickness of the coating agent to 0.1 to 25 μm, further improvement in coating properties can be expected.

[0065] The method for adding the filler (B) is not particularly limited, and any conventionally known method may be used. Specific examples of the method for adding the filler (B) include adding the filler (B) to the polymerization reaction liquid before or during the polymerization of the resin (a-1), kneading the filler (B) with the binder (A) using a three-roll mill, and preparing a dispersion containing the filler (B) and mixing it with the binder (A). Furthermore, in order to disperse the filler (B) well and stabilize the dispersion state, a dispersant, a thickener, or the like may be used within a range that does not affect the physical properties of the adhesive layer.

[0066] [Solvent] The adhesive layer may contain a solvent containing at least a specific amount of toluene. In addition to toluene, other solvents that may be contained in the adhesive layer include, for example, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, ethyl acetate, butyl acetate, cellosolve acetate, propylene glycol monomethyl ether acetate, carbitol acetate, cellosolve, methyl carbitol, butyl carbitol, xylene, dimethylformamide, dimethylacetamide (hereinafter also referred to as "DMAc"), N-methylpyrrolidone (hereinafter also referred to as "NMP"), diethylene glycol dimethyl ether, and propylene glycol monomethyl ether. From the viewpoints of impedance matching and solder heat resistance, the total content of these solvents in the adhesive layer is preferably 5 ppm to 15,000 ppm by mass. As mentioned above, the adhesive layer in this adhesive sheet contains 5 to 15,000 ppm of toluene by mass.

[0067] [Other Additives] The adhesive sheet may further contain optional components such as energy ray absorbers, dyes, pigments, antioxidants, polymerization inhibitors, defoamers, leveling agents, ion scavengers, moisturizers, viscosity modifiers, preservatives, antibacterial agents, antistatic agents, antiblocking agents, infrared absorbers, and electromagnetic wave shielding agents, provided that the intended purpose is not impaired. To improve laser processability, it is preferable to incorporate an energy ray absorber, such as a UV absorber, as an additive. The amount of these additives added can be appropriately set within a range that achieves the effects of the present disclosure and is not particularly limited.

[0068] <Arithmetic mean roughness Sa> In this specification, the arithmetic mean roughness Sa is defined in ISO 25178-2:2012. The arithmetic mean roughness Sa is one of the parameters that represent three-dimensional surface properties, and is a parameter that extends the arithmetic mean roughness (Ra) evaluated on a straight line to a surface. The arithmetic mean roughness Sa represents the average of the absolute values ​​of the height differences of each point with respect to the average plane of the surface.

[0069] In the present disclosure, the arithmetic mean roughness Sa of the adhesive layer on the side B opposite to the side A on which the release film is laminated is preferably 0.05 to 2.0 μm. When the arithmetic mean roughness Sa of side B is 0.05 μm or more, air escape during lamination is further improved, and puddling can be easily suppressed. On the other hand, when Sa is 2.0 μm or less, adhesion to the adherend during lamination is further improved, and lifting that causes puddling can be easily suppressed. From the same viewpoint, the arithmetic mean roughness Sa of side B is more preferably 0.15 to 1.0 μm, and even more preferably 0.3 to 0.5 μm.

[0070] <Method for controlling arithmetic mean roughness Sa> The method for controlling the arithmetic mean roughness Sa of the B side of the adhesive layer can be a conventionally known method for adjusting the surface shape of an object. Different methods can be applied to each adhesive sheet, or a common method can be applied. Specific examples of the control method include a method of polishing the surface using an abrasive cloth, a shot blasting method in which an abrasive is sprayed onto the surface of the adhesive layer using compressed air, a method of forming an adhesive layer on a film having a predetermined arithmetic mean roughness Sa, laminating a protective sheet, and then removing the film to transfer the unevenness of the film surface, a method of pressing a film having a predetermined arithmetic mean roughness Sa and the adhesive layer together to transfer the unevenness of the film surface, and a method of containing particulate matter in the adhesive layer to control the surface unevenness.

[0071] <Cured Layer> The adhesive layer in the present disclosure is preferably cured by a stimulus such as heat or active energy rays such as ultraviolet rays. The adhesive layer after (complete) curing is referred to as a cured layer. A conventionally known method can be applied as a method for curing the adhesive layer, and can be appropriately selected depending on the type of curing agent used. When the adhesive layer is thermosetting, it is preferable because strong interlayer adhesion can be achieved by contacting both surfaces of the adhesive layer with adherends and performing heat pressing.

[0072] The heating temperature is preferably 150 to 200° C., more preferably 160 to 180° C. The heating time is preferably 10 to 120 minutes, more preferably 30 to 60 minutes.

[0073] The pressure applied when the adhesive layer is cured using a hot press is preferably 1 to 5 MPa, more preferably 2 to 3 MPa. The temperature and time are the same as those described above.

[0074] <|Er ２５ -Er ２５０ |> The storage modulus at 25°C (Er ２５ ) and the storage modulus at 250 °C (Er ２５０ ) absolute value of the difference |Er ２５ -Er ２５０ | is preferably 0.10 to 100,000 MPa. ２５ -Er ２５０ When |Er is 0.10 MPa or more, crack generation can be easily suppressed by stress relaxation when the temperature is raised from a low temperature, and the thermal cycle resistance can be further improved. ２５ -Er ２５０ When |Er is 100,000 MPa or less, moisture in the air is captured when the temperature is lowered, and poor appearance (foaming) due to moisture evaporation when the temperature is raised again is easily suppressed, and the resistance to thermal cycles can be further improved. ２５ -Er ２５０ From the same viewpoint, | is more preferably 1.0 to 10,000 MPa, and even more preferably 10 to 1,000 MPa.

[0075] The storage modulus of the cured layer can be adjusted to a desired value, for example, by adjusting the molecular weight of the resin in the adhesive layer, adjusting the amount of curing agent contained in the adhesive layer, or even by changing the skeleton of the resin in the adhesive layer.

[0076] <Elongation at Break> The elongation at break of the cured layer obtained by heating the adhesive layer in the present disclosure at 180°C for 60 minutes is preferably 50 to 1,000%. With an elongation at break of 50% or more, the cured layer can adequately relax stress and easily suppress the occurrence of cracks when drilling a printed wiring board. On the other hand, with an elongation at break of 1,000% or less, the occurrence of burrs (curling of the cured layer) during drilling can be easily suppressed. The elongation at break is more preferably 80 to 500%, and even more preferably 100 to 300%.

[0077] The breaking elongation of the cured layer can be adjusted to a desired value by, for example, adjusting the amount of filler contained in the adhesive layer or by using a resin with lower elasticity.

[0078] <Release Film> The release film serves as a support for the adhesive layer in the adhesive sheet, and also serves to protect the adhesive layer from damage and contamination.

[0079] Examples of release films 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, polyvinylidene fluoride, 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, plastic sheets are preferred because the storage modulus can be easily adjusted by blending the material components. Furthermore, among these, polyethylene terephthalate and polyethylene naphthalate, which combine rigidity and flexibility, are more preferred.

[0080] The surface of the release film may be subjected to a matte treatment as required, for example, by sand matte, etching matte, coating matte, chemical matte, or kneading matte.

[0081] The release film may be coated with a release agent to improve its releasability from the adhesive layer. Examples of the release agent include 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 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 a conventional method, such as gravure coating, kiss coating, die coating, lip coating, comma coating, blade coating, roll coating, knife coating, spray coating, bar coating, spin coating, or dip coating.

[0082] The thickness of the release film is not particularly limited, but is preferably 10 μm or more from the viewpoint of providing the release film with appropriate rigidity (toughness) and suppressing breakage of the release film during peeling, and is preferably 100 μm or less from the viewpoint of thinning.

[0083] <<Method for Producing an Adhesive Sheet for Printed Wiring Boards>> The method for producing this adhesive sheet can include, for example, the following steps. First, a coating solution containing the above-described resin (a-1), curing agent (a-2), filler (B), other optional components, and a solvent (at least toluene) is applied to one side of a release film. Subsequently, the liquid medium, such as an organic solvent, contained in the coating film is removed and dried, typically by heating at 40 to 150°C for 30 seconds to 10 minutes. The drying conditions are such that the specific amount of toluene described above remains in the adhesive layer. This results in an adhesive sheet with a single-sided release film, in which an adhesive layer is formed on one side of the release film. Next, a separate release film is laminated on the surface of this adhesive sheet, more specifically, on the surface of the adhesive layer not covered by the release film, to obtain an adhesive sheet with a double-sided release film. Laminating both sides with release films prevents surface contamination of the adhesive sheet. The adhesive sheet (only the adhesive layer) can then be isolated by peeling off the release film. The two release films can be the same or different types. By using release films with different release properties, it is possible to vary the peel strength, making it easier to peel them off in order. Note that this adhesive sheet may be the adhesive sheet with a single-sided release film described above, an adhesive sheet with double-sided release films, or an adhesive sheet after peeling off the release film on one side of an adhesive sheet with double-sided release films.

[0084] <Metal-clad laminate> The metal-clad laminate according to the present disclosure (hereinafter also referred to as the present metal-clad laminate) has a cured layer of the present adhesive layer. The present metal-clad laminate can also be one in which a metal foil and an insulating film are laminated via a cured layer, which is a cured product of the present adhesive layer. Such a metal-clad laminate can be obtained, for example, by the following procedure. That is, first, after peeling off the release film, a metal foil is placed on one side of the adhesive layer of the printed wiring board adhesive sheet, and an insulating film is placed on the other side (this process is sometimes referred to as temporary bonding). Next, the resulting sheet is subjected to a heating or heat-pressing process to thermally cure the adhesive layer between the metal foil and the insulating film, thereby obtaining a metal-clad laminate. The present metal-clad laminate may have metal foil on both outermost layers, such as metal foil / cured layer / insulating film / cured layer / metal foil, or an inner layer of metal foil may be provided. When metal foils or insulating films are laminated using multiple adhesive layers, multiple temporary bonding processes may be performed, followed by heat curing of multiple adhesive layers at once.

[0085] <Printed Wiring Board> The printed wiring board according to the present disclosure (hereinafter also referred to as the present printed wiring board) includes the present metal-clad laminate. The present printed wiring board can be obtained, for example, by processing the metal foil in the present metal-clad laminate by etching or the like to form signal circuits and ground circuits. By attaching the adhesive layer of the present adhesive sheet to the circuit surface and heat-curing it, the signal circuit can be protected or it can be used as a substrate for further multilayering. The following method, for example, can be used to provide signal circuits and ground circuits on the present metal-clad laminate. That is, first, a photosensitive etching resist layer is formed on the metal foil in the present metal-clad laminate, and then exposed to light through a mask film having a circuit pattern, curing only the exposed areas. Next, the unexposed metal foil is removed by etching, and then the remaining resist layer is peeled off, thereby forming a conductive circuit from the metal foil.

[0086] Electronic Device An electronic device according to the present disclosure (hereinafter also referred to as the present electronic device) includes the present printed wiring board. The present printed wiring board can be used to manufacture various electronic devices such as smartphones, tablet devices, personal computers, televisions, and cameras.

[0087] Hereinafter, the present disclosure will be described in more detail with reference to examples and comparative examples, but the present disclosure is not limited to the following examples. Note that the "parts" and "%" below are values ​​based on "parts by mass" and "% by mass", respectively. In addition, the acid value and weight average molecular weight (Mw) of resin (a-1), and the D of filler (B) ５０ The average particle size was measured by the following method.

[0088] <Acid Value of Resin (a-1)> The acid value (mg KOH / g) was calculated by converting the measured acid 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 titration was performed with 0.1 N alcoholic potassium hydroxide solution. The endpoint was determined when the indicator maintained a pale pink color for 30 seconds. The acid value was calculated using the following formula (unit: mg KOH / g): Acid value (mg KOH / g) = (5.611 × a × F) / S, where each symbol is as follows: S: sample amount (g); a: amount of 0.1 N alcoholic potassium hydroxide solution consumed (mL); F: titer of 0.1 N alcoholic potassium hydroxide solution.

[0089] <Weight-average molecular weight (Mw) of resin (a-1)> Measurement of Mw was carried out using a GPC (gel permeation chromatograph) "HPC-8020" (trade name, 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 carried out using two "LF-604" (trade name, manufactured by Showa Denko KK: GPC column for rapid analysis: 6 mm ID x 150 mm size) columns 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 terms.

[0090] <D of filler (B) ５０ Average particle diameter>D ５０ The average particle size was measured using a laser diffraction / scattering particle size distribution analyzer LS13320 (trade name, manufactured by Beckman Coulter, Inc.). 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.

[0091] <Raw Materials> [Binder (A)] Resins (a-1) (a-1)-1: Polyamide resin, acid value 10 mg KOH / g, weight average molecular weight 21,000, Tg 55°C (manufactured by Toyochem Co., Ltd.) (a-1)-2: Styrene-based elastomer, trade name: FG1901GT (maleic acid-modified styrene-based elastomer), acid value 10 mg KOH / g, weight average molecular weight 95,000, Tg 80°C (manufactured by Kraton Co., Ltd.) (a-1)-3: Polyurethane resin, acid value 10 mg KOH / g, weight average molecular weight 12,0000, Tg 25°C (manufactured by Toyochem Co., Ltd.) (a-1)-4: Polyester resin, trade name: Vylon 637, polyester resin with acid value 5 mg KOH / g, weight average molecular weight 30,000, Tg 21°C (manufactured by Toyobo Co., Ltd.) (a-1)-5: Trade name: Umex 1001 (maleic acid-modified polypropylene), acid value 26 mg KOH / g (manufactured by Sanyo Chemical Industries, Ltd.) (a-1)-6: Polyimide resin, acid value 9 mg KOH / g, weight average molecular weight 45,000, Tg 50°C (manufactured by Toyochem Co., Ltd.)

[0092] Curing Agent (a-2) (a-2)-1: Epoxy group-containing compound, trade name: Denacol EX-614B (manufactured by Nagase ChemteX Corporation, sorbitol polyglycidyl ether, tetrafunctional, functional group equivalent weight 173 g / eq.)

[0093] [Filler (B)] B-1: UF-310 (trade name, manufactured by Tokuyama Corporation, silica, average particle diameter D ５０ ; 3.5 μm)

[0094] [UV absorber (C)] C-1: Tinuvin 326 (trade name, manufactured by BASF Japan, benzotriazole-containing compound)

[0095] <Production of Adhesive Sheet for Printed Wiring Boards> [Example 1] 100 parts of binder resin (a-1)-1, 20 parts of curing agent (a-2)-1, 15 parts of filler B-1, and 2 parts of UV absorber C-1 were charged into a container in terms of solid content. Next, a mixed solvent (toluene:MEK=9:1 (weight ratio)) was added to the container so that the nonvolatile content concentration was 30%, and the mixture was stirred with a disper for 10 minutes to obtain a resin composition (coating liquid). The obtained coating liquid was applied to a 50 μm thick release film (polyethylene terephthalate (PET) film coated with a release agent) using a doctor blade so that the thickness after drying was 25 μm. Then, the mixture was dried at 120 ° C. for 2 minutes to obtain an adhesive sheet for printed wiring boards.

[0096] [Examples 2 to 46, Comparative Examples 1 and 2] As shown in Tables 1 to 6, the amounts of binder (A) (resin (a-1) and curing agent (a-2)) and filler (B) and various conditions (e.g., drying conditions) were changed, and the same procedures were followed as in Example 1 to obtain adhesive sheets for printed wiring boards of Examples 2 to 46 and Comparative Examples 1 and 2. The arithmetic mean roughness Sa of surface B of the adhesive layer opposite surface A on which the release film was laminated was adjusted by polishing the surface with an abrasive cloth.

[0097] <Measurement of Toluene Content in Adhesive Layer> The adhesive sheet obtained in each example was cut into a piece 1 cm wide and 5 cm long and placed in a vial as a test piece. The toluene content in the adhesive layer was then measured by headspace chromatography (HS-GC) using a GC system (Nexis GC-2030 (trade name), manufactured by Shimadzu Corporation). The toluene content was obtained by measuring the peak area assigned to toluene in a chart obtained when the vial was heated at 200°C for 30 minutes.

[0098] <Measurement of arithmetic mean roughness Sa of surface B> The arithmetic mean roughness Sa of surface B was measured by observing surface B of the adhesive layer opposite surface A on which the release film was laminated, of the adhesive sheet obtained in each example, using a confocal microscope (manufactured by Lasertec, product name: OPTELICS HYBRID+, objective lens 20x). More specifically, measurements were taken at five arbitrary locations in accordance with ISO 25178, and then the arithmetic mean roughness Sa was calculated by analysis using data analysis software (product name: LMeye8).

[0099] <Measurement of Storage Modulus of Cured Layer> The storage modulus of the cured layer was measured by the DMA method. The adhesive sheet obtained in each example was heated at 180°C for 60 minutes, and the release film was then peeled off to obtain a cured layer. A test piece was then cut into a width of 5 mm and a length of 30 mm. Using a dynamic viscoelasticity measuring device "DVA200" (trade name, manufactured by IT Measurement Control Co., Ltd.), the test piece was cooled to 0°C, then heated to 300°C at a rate of 10°C / min, and the viscoelasticity was measured at a vibration frequency of 10 Hz. The storage modulus at each temperature (25°C and 250°C) was determined from the resulting viscoelastic curve. Furthermore, the absolute value of the difference between the storage modulus at 25°C and the storage modulus at 250°C was calculated for the cured layer.

[0100] <Measurement of Breaking Elongation> The adhesive sheet obtained in each example was heated at 180°C for 60 minutes, and then the release film was peeled off to obtain a cured layer, which was then cut into a size of 20 mm wide x 50 mm long to prepare a measurement sample. A tensile test (test speed 50 mm / min) was carried out on the measurement sample using a small tabletop testing machine EZ-TEST (trade name, manufactured by Shimadzu Corporation) under conditions of a temperature of 25°C and a relative humidity of 50%. The breaking elongation (%) of the cured layer was calculated from the obtained S-S curve (stress-strain curve).

[0101] <Evaluation> The adhesive sheets obtained in each example were evaluated for impedance matching, puddling, thermal cycle resistance, and processability according to the methods described below. The evaluation results are shown in Tables 1 to 6. FIG. 1 is a schematic plan view of the main surface of a wiring board having a coplanar circuit according to each example, and FIG. 2 is a schematic plan view of the back surface of the wiring board. FIG. 3 is a schematic plan view of the main surface of a wiring board having a coplanar circuit with an electromagnetic shielding sheet according to each example. FIG. 4 is a schematic view showing an example of a cross section of a printed wiring board near a blind via formed by laser processing. FIG. 5 is a schematic view showing an example of a cross section of a printed wiring board near a through-hole formed by drilling.

[0102] [Impedance Matching] Impedance matching was evaluated using a printed wiring board 100 having an electromagnetic wave shielded coplanar circuit in which electromagnetic wave shielding sheets were laminated on both sides, as shown in FIG.

[0103] Schematic plan views of the main surface and back surface of a (flexible) printed wiring board 90 having a coplanar circuit used in the measurements are shown in FIGS. 1 and 2, respectively. Specifically, a double-sided CCL "R-F775" (trade name, manufactured by Panasonic Corporation) was prepared, consisting of a 50 μm-thick polyimide film 1 laminated with 12 μm-thick rolled copper foil on both sides. Six through-holes 2 (0.1 mm diameter) were then drilled near each of the four rectangular corners. Note that only two through-holes 2 are shown in the figure for ease of illustration. Next, electroless plating was performed, followed by electrolytic plating to form a 10 μm-thick copper plating film 3. Electrical continuity between the main surface and back surface was ensured via the copper plating film 3 formed in the through-holes 2. Thereafter, as shown in FIG. 1 , two 10 cm long signal wires 4 were formed on the main surface of the polyimide film 1, and a ground wire 5 was formed on the outside of the signal wires 4 in parallel with the signal wires 4, and a ground pattern 6 was formed in an area extending from the ground wire 5 and including the through-hole 2 in the short direction of the polyimide film 1.

[0104] Thereafter, the copper foil formed on the back surface of the polyimide film 1 was etched to obtain a back surface ground pattern 7 as shown in Figure 2 at a position corresponding to the ground pattern 6. The inspection specifications for the circuit appearance and tolerance were in accordance with the JPCA standard (JPCA-DG02).

[0105] Next, a polyimide film (thickness 12.5 μm) and the exposed surface of the adhesive layer of the printed wiring board adhesive sheet of Example 1 were bonded together and vacuum laminated. The resulting laminate was attached to the main surface of polyimide film 1, and then hot-pressed at 180° C. and 2 MPa for 60 minutes to obtain printed wiring board 90 having a coplanar circuit equipped with cover coat layer 10. Thereafter, the copper foil pattern exposed from cover coat layer 10 was nickel-plated (not shown), and then gold-plated (not shown).

[0106] 1 , an electromagnetic wave shielding sheet 20 (manufactured by Toyochem Co., Ltd., product name: LIOELM TSS210) consisting of a laminate of a conductive layer and an insulating layer was prepared, and a release-treated sheet (not shown) provided on the conductive adhesive layer of the electromagnetic wave shielding sheet 20 was peeled off. Then, with the conductive adhesive layer of the electromagnetic wave shielding sheet 20 facing inward, the electromagnetic wave shielding sheet 20 was attached to a wiring board 90 having a coplanar circuit so that the signal wiring 4 on the main surface side of the printed wiring board 90 was covered with a cover coat layer 10 and the electromagnetic wave shielding sheet 20 contacted areas on the ground wiring 5 where the cover coat layer 10 was not present. By attaching the electromagnetic wave shielding sheet 20 to these areas, electrical conduction was established between the electromagnetic wave shielding sheet 20 and the ground wiring 5. 3, an electromagnetic wave shielding sheet 20 (manufactured by Toyochem Co., Ltd., product name: LIOELM TSS210) consisting of a laminate of a conductive layer and an insulating layer was prepared, and a release-treated sheet (not shown) provided on the conductive adhesive layer of the electromagnetic wave shielding sheet 20 was peeled off. Then, with the conductive adhesive layer of the electromagnetic wave shielding sheet 20 facing inward, the sheet was pressure-bonded to the entire rear surface of a printed wiring board 90 having a coplanar circuit under conditions of 170°C, 2.0 MPa, and 30 minutes, thereby obtaining a printed wiring board 100 having a coplanar circuit with an electromagnetic wave shield. In FIG. 3, the rear-side ground pattern 7 is shown in a perspective view.

[0107] The width of the ground wiring 5 was 100 μm, and the distance between the ground wiring 5 and the signal wiring 4 was 1 mm.

[0108] A network analyzer E5071C (trade name, manufactured by Agilent Japan) was connected to the exposed signal wiring 4 of a printed wiring board 100 having a coplanar circuit with an electromagnetic shielding sheet, and a 15 GHz sine wave was input. The maximum width at which the difference from the reference impedance was greatest was measured, and the impedance matching was evaluated based on the following criteria. The reference impedance was defined as the impedance when no connection to the signal wiring was taken as 100 Ω. Evaluation criteria: A: The maximum width of the characteristic impedance difference is less than 40 Ω. Very good. B: The maximum width of the characteristic impedance difference is 40 Ω or more but less than 50 Ω. Good. C: The maximum width of the characteristic impedance difference is 50 Ω or more but less than 60 Ω. Usable. D: The maximum width of the characteristic impedance difference is 60 Ω or more. Unusable.

[0109] [Puddling] First, a double-sided copper-clad laminate (TAS124500, manufactured by DuPont) was prepared, which was composed of 12 μm copper foil laminated on both sides of a polyimide film. The uneven surface of the adhesive sheet obtained in each example was temporarily bonded to the copper foil on one side of the double-sided copper-clad laminate using a vacuum laminator (a small pressure-type vacuum laminator V-130 (product name) manufactured by Nikko Materials Co., Ltd.) to prepare a sample. The obtained samples were then visually evaluated for the presence or absence of appearance defects such as lifting or bubbling at the adhesive layer / copper foil interface based on the following criteria. Thirty samples were used in each example. Evaluation criteria: A: Two or fewer samples showed appearance defects. An extremely good result. B: Three or more but five or fewer samples showed appearance defects. A good result. C: Six or more but eight or fewer samples showed appearance defects. This is within the practical range. D: Nine or more samples showed appearance defects. Not practical.

[0110] [Cold-heat cycle resistance] (Sample preparation) The adhesive layer of the adhesive sheet obtained in each example was attached to the copper foil on one side of a double-sided copper-clad laminate consisting of a 50 μm polyimide film and a 12 μm copper foil laminated on both sides, and the laminate was temporarily bonded using a vacuum laminator. Next, the release film was peeled off, and the polyimide film side of a single-sided copper-clad laminate consisting of a 50 μm polyimide film and a 12 μm copper foil laminate was temporarily bonded to the exposed adhesive layer using a vacuum laminator. The laminate was then thermally cured in a heat press at 180 ° C for 1 hour at 2 MPa to obtain an evaluation sample with a laminate structure of copper foil / polyimide film / copper foil / cured layer / polyimide film / copper foil. (Evaluation) The above samples were used to evaluate their cold-heat cycle properties. The treatment conditions were 15 minutes at -30°C and 15 minutes at 150°C, with one cycle consisting of 15 minutes. After 2000 cycles, the cross section was observed with a laser microscope (Keyence VK-X100) at a magnification of approximately 20 to 500 times. 30 samples were evaluated. The thermal cycle resistance was evaluated based on the following criteria. Evaluation criteria A: Peeling occurred in 2 or fewer samples. Extremely good results. B: Peeling occurred in 3 to 5 samples. Good results. C: Peeling occurred in 6 to 8 samples. Within the practical range. D: Peeling occurred in 9 or more samples. Not suitable for practical use.

[0111] [Processability] The processability was evaluated by testing laser processability and drill processability separately, and the test results were used to comprehensively evaluate the processability.

[0112] As shown in Figure 4, an evaluation sample 40 was prepared, which had a laminated structure of copper foil 31 / polyimide film 30 / cured product of adhesive layer (cured layer) 32 / copper foil 31 / polyimide film 30 / copper foil 31. A UV-YAG laser (trade name, Model 5335, manufactured by ESI) was used to irradiate the sample from the upper side of the paper in Figure 4, thereby forming a blind via with a diameter of 100 µm up to the boundary between the cured product 32 of the adhesive layer and the double-sided copper-clad laminate (the upper side of the paper in Figure 4 of the third layer (copper foil 31) from the bottom). The cross section of the blind via portion 34 was then observed with a laser microscope (manufactured by Keyence Corporation, trade name: VK-X100) at a magnification of approximately 20 to 500 times, and the maximum length of side etching 33 (abrasion in the horizontal direction exceeding the designed opening diameter) occurring in the cured product 32 of the adhesive layer was measured, and the evaluation was performed according to the following criteria. Evaluation criteria: A: 5 μm or less B: 5 μm or more and 7 μm or less C: 7 μm or more and 10 μm or less D: More than 10 μm

[0113] Drilling Processability An evaluation sample 40 having a laminated structure of copper foil 31 / polyimide film 30 / cured product of adhesive layer (cured layer) 32 / copper foil 31 / polyimide film 30 / copper foil 31 shown in FIG. 5 was prepared. Next, a printed circuit board drilling machine NB-1S212 (trade name, manufactured by Via Mechanics) was used to drill a 100 μm diameter through-hole from the top of the page in FIG. 5 to the boundary between the cured product 32 of the adhesive layer and the double-sided copper-clad laminate (the bottom layer (copper foil 31) on the bottom side of the page in FIG. 5). Next, when the cross section of the through-hole portion 35 was observed with a laser microscope (manufactured by Keyence Corporation, trade name: VK-X100) at a magnification of approximately 20 to 500 times, the number of samples in which cracks occurred in the cured product 32 of the adhesive layer was counted, and evaluation was performed based on the following criteria. The total number of samples used for evaluation was 30. Evaluation criteria: A: Less than 10% of samples had cracks. B: 10% to less than 20% of samples had cracks. C: 20% to less than 30% of samples had cracks. D: 30% or more of samples had cracks.

[0114] Based on the above results of laser processability and drill processability, the processability of each example was evaluated based on the following criteria. Evaluation criteria A: Both laser processability and drill processability were rated A. Extremely good. B: Either laser processability or drill processability was rated A, and the other was rated B or C. Good results. C: Both laser processability and drill processability were rated B or C. Within the practical range. D: Either laser processability or drill processability was rated D. Not practical.

[0115] [Temporary Adhesion (Substrate Adhesion)] The adhesive layer of the adhesive sheet obtained in each example was attached to the copper foil on one side of a double-sided copper-clad laminate consisting of a 50 μm polyimide film with 12 μm copper foil laminated on both sides, and the adhesive was temporarily bonded using a vacuum laminator to prepare an evaluation sample. Next, when the release film was peeled off, the adhesive layer was visually observed to determine whether it had been transferred to the copper foil without lifting or peeling, and the substrate adhesion was evaluated based on the following criteria. Thirty evaluation samples were used. Evaluation Criteria A: The number of samples with poor transfer was 2 or less. This is an extremely good result. B: The number of samples with poor transfer was 3 or more but not more than 5. This is a good result. C: The number of samples with poor transfer was 6 or more but not more than 8. This is within the practical range. D: The number of samples with poor transfer was 9 or more. This is not practical.

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[0122] The present disclosure is not limited to the above-described embodiment, and can be appropriately modified without departing from the spirit and scope of the present disclosure. Furthermore, the present disclosure may be implemented by appropriately combining the above-described embodiment and examples thereof.

[0123] This application claims priority based on Japanese Patent Application No. 2023-212876, filed December 18, 2023, the disclosure of which is incorporated herein by reference in its entirety.

[0124] REFERENCE SIGNS LIST 1 Polyimide film 2 Through hole 3 Copper plating film 4 Signal wiring 5 Ground wiring 6 Ground pattern 7 Back surface ground pattern 10 Cover coat layer 20 Electromagnetic wave shielding sheet 30 Polyimide film 31 Copper foil 32 Cured product of adhesive layer (cured layer) 33 Side etching 34 Blind via portion 35 Through hole portion 40 Evaluation sample 90 Printed wiring board having a coplanar circuit 100 Printed wiring board having a coplanar circuit with electromagnetic wave shielding

Claims

1. An adhesive sheet for printed wiring boards, comprising an adhesive layer having a release film laminated on at least one surface thereof, the adhesive layer containing 5 to 15,000 ppm toluene by mass, and the adhesive layer being used as an adhesive for bonding layers of a printed wiring board.

2. The adhesive sheet for printed wiring boards according to claim 1, wherein the release film is laminated to one surface A of the adhesive layer, and a surface B of the adhesive layer opposite to the surface A has an arithmetic mean roughness Sa of 0.05 to 2.0 μm as determined in accordance with ISO 25178-2:2012.

3. The storage modulus (Er ２５ ) and the storage modulus at 250°C (Er ２５０ ) Absolute value of the difference |Er ２５ -Er ２５０ The adhesive sheet for printed wiring boards according to claim 1 or 2, wherein | is 0.10 to 100,000 MPa.

4. The adhesive sheet for printed wiring boards according to any one of claims 1 to 3, wherein the cured layer obtained by heating the adhesive layer at 180°C for 60 minutes has a breaking elongation of 50 to 1,000%.

5. A metal-clad laminate having a cured layer of the adhesive layer according to any one of claims 1 to 4.

6. A printed wiring board comprising the metal-clad laminate according to claim 5.

7. An electronic device having the printed wiring board according to claim 6.

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