Adhesive sheet

Abstract

The present invention provides an adhesive sheet which contains thermally expandable microspheres and can exhibit releasability by heating, and in which a change in thickness and a change in surface roughness are suppressed even at high temperatures at which release of the adhesive sheet is not required.　An adhesive sheet according to one embodiment of the present invention is sequentially provided with a base material, a resin layer, and a first adhesive layer in this order. The first adhesive layer contains thermally expandable microspheres. The thickness deformation starting temperature Tf (°C) of the adhesive sheet as determined by TMA analysis and the gasification starting temperature Tgas (°C) of the thermally expandable microspheres as determined by EGA / MS analysis satisfy the relational expression Tf ≥ Tgas -10.

Description

adhesive sheet

[0001] The present invention relates to a pressure-sensitive adhesive sheet, and more particularly to a pressure-sensitive adhesive sheet that can exhibit easy peelability in response to a thermal stimulus.

[0002] Conventionally, adhesive sheets have been used to fix or temporarily fix workpieces when processing electronic components, etc. For example, adhesive sheets have been used as temporary fixing materials for cutting semiconductor wafers or ceramic sheets, or as temporary fixing materials in processes for encapsulating semiconductor chips with resin (chip size package: CSP or wafer level package: WLP). As one such adhesive sheet, an adhesive sheet has been investigated that has an adhesive layer containing heat-expandable microspheres, and whose adhesive strength decreases when the heat-expandable microspheres expand upon heating.

[0003] In recent years, in the field of FOWLP semiconductor packaging, the expansion of applicable semiconductor devices has led to a demand for high positional accuracy when resin-encapsulating semiconductor chips. Chip shift during the resin-encapsulation process is significantly influenced by the fluidity of the encapsulation resin, and the trend toward higher encapsulation temperatures to reduce chip shift variation is accelerating. When the above-described pressure-sensitive adhesive sheet is used in such a resin-encapsulation process, the increased encapsulation temperature approaches the temperature at which the heat-expandable microspheres expand, causing changes in the thickness and surface roughness of the pressure-sensitive adhesive sheet, thereby worsening chip shift variation.

[0004] Japanese Patent Application Laid-Open No. 2003-201452

[0005] The present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to provide a pressure-sensitive adhesive sheet that contains heat-expandable microspheres and can exhibit peelability upon heating, and that suppresses changes in thickness and surface roughness even at high temperatures where peeling is not required.

[0006] [1] An adhesive sheet according to one embodiment of the present invention comprises a substrate, a resin layer, and a first adhesive layer in this order, wherein the first adhesive layer contains heat-expandable microspheres, and the thickness deformation initiation temperature Tf (°C) of the adhesive sheet as determined by TMA analysis and the gasification initiation temperature Tgas (°C) of the heat-expandable microspheres as determined by EGA / MS analysis satisfy the relationship Tf≧Tgas-10. [2] The adhesive sheet described in [1] above may further comprise a second adhesive layer on the opposite side of the substrate from the resin layer. [3] In the pressure-sensitive adhesive sheet described in [2] above, the ratio (rate of change) of the surface roughness Ra(II) of the second pressure-sensitive adhesive layer surface after heating for 450 seconds in a 160°C environment to the surface roughness Ra(I) of the second pressure-sensitive adhesive layer surface when the pressure-sensitive adhesive sheet is heated in a 130°C environment for 30 minutes and then stored at 25°C / 60%RH for 24 hours may be 130% or less. [4] In the pressure-sensitive adhesive sheet described in any of [1] to [3] above, the gasification onset temperature Tgas of the heat-expandable microspheres may be lower than 180°C. [5] In the pressure-sensitive adhesive sheet described in any of [1] to [3] above, the gasification onset temperature Tgas of the heat-expandable microspheres may be 180°C or higher. [6] In the pressure-sensitive adhesive sheet described in any of [1] to [5] above, the thickness of the first pressure-sensitive adhesive layer may be thinner than the thickness of the resin layer. [7] In the pressure-sensitive adhesive sheet according to any one of [1] to [6] above, the volume filling rate of the heat-expandable microspheres in the first pressure-sensitive adhesive layer may be 21% or less. [8] In the pressure-sensitive adhesive sheet according to any one of [1] to [7] above, the dynamic storage modulus G' of the resin layer at 160°C may be 0.1 MPa or less. [9] In the pressure-sensitive adhesive sheet according to any one of [1] to [8] above, the thickness of the substrate may be 40 μm to 200 μm.

[0007] According to the present invention, it is possible to provide a pressure-sensitive adhesive sheet that contains heat-expandable microspheres and can exhibit peelability upon heating, and in which changes in thickness and surface roughness are suppressed even at high temperatures at which peeling is not required.

[0008] 1 is a schematic cross-sectional view of a pressure-sensitive adhesive sheet according to one embodiment of the present invention.

[0009] A. Overview of the Pressure-Sensitive Adhesive Sheet Fig. 1(a) is a schematic cross-sectional view of a pressure-sensitive adhesive sheet according to one embodiment of the present invention. The pressure-sensitive adhesive sheet 100 comprises, in this order, a substrate 10, a resin layer 20, and a first pressure-sensitive adhesive layer 30. The first pressure-sensitive adhesive layer 30 contains heat-expandable microspheres. Furthermore, as shown in Fig. 1(b), a second pressure-sensitive adhesive layer 40 may be provided on the side of the substrate 10 opposite the resin layer 20.

[0010] The heat-expandable microspheres can be expanded at a predetermined temperature. When the heat-expandable microspheres expand on heating, the first pressure-sensitive adhesive layer containing such heat-expandable microspheres develops unevenness on the adhesive surface (i.e., the surface of the first pressure-sensitive adhesive layer), resulting in a decrease or loss of adhesive strength. For example, when the pressure-sensitive adhesive sheet of the present invention is used as a sheet for temporarily fixing workpieces during the processing of electronic components (e.g., semiconductor chips), the adhesive strength required for temporary fixing is exhibited when the workpieces are subjected to a predetermined processing (e.g., resin sealing), and when the workpieces are to be peeled off after processing, the adhesive strength is reduced or lost by heating, resulting in good peelability.

[0011] In an embodiment of the present invention, the thickness deformation starting temperature Tf (°C) of the PSA sheet determined by TMA analysis and the gasification starting temperature Tgas (°C) of the heat-expandable microspheres determined by EGA / MS analysis satisfy the relationship Tf≧Tgas-10.

[0012] The thickness deformation onset temperature Tf determined by TMA analysis is the temperature at which the thickness of the pressure-sensitive adhesive sheet begins to change upon heating, and is measured from a displacement-temperature curve determined by TMA analysis. Specifically, in this specification, the thickness deformation onset temperature Tf determined by TMA analysis is defined as the temperature at which the displacement amount becomes 15 μm, with the displacement at 40° C. as the reference (0 μm). In one embodiment, the thickness deformation onset temperature Tf determined by TMA analysis is primarily due to the change in thickness of the first pressure-sensitive adhesive layer caused by the behavior of the heat-expandable microspheres. A method for measuring the thickness deformation onset temperature Tf determined by TMA analysis will be described later.

[0013] The gasification onset temperature Tgas of heat-expandable microspheres determined by EGA / MS analysis is the temperature at which the heat-expandable microspheres begin to foam upon heating. Specifically, in this specification, the gasification onset temperature Tgas of heat-expandable microspheres determined by EGA / MS analysis is defined as the temperature at which the peak intensity at mass m / z = 57 in EGA / MS analysis of a pressure-sensitive adhesive sheet is 2% of the maximum gas generation peak intensity.

[0014] In the present invention, by satisfying the above-mentioned relationship between the thickness deformation onset temperature Tf and the gasification onset temperature Tgas of the heat-expandable microspheres, a pressure-sensitive adhesive sheet can be obtained that exhibits minimal changes in surface condition (e.g., changes in shape and roughness associated with thickness changes) at high temperatures that do not require peeling. Use of such a pressure-sensitive adhesive sheet can suppress variations in chip shift at high temperatures that do not require peeling when temporarily fixing electronic components such as semiconductor chips on the pressure-sensitive adhesive sheet. In one embodiment, changes in the surface condition of the pressure-sensitive adhesive sheet on the side opposite the outer surface of the first pressure-sensitive adhesive layer (e.g., the substrate, the second pressure-sensitive adhesive layer) are suppressed. Preferably, the thickness deformation onset temperature Tf (°C) determined by TMA analysis and the gasification onset temperature Tgas (°C) of the heat-expandable microspheres determined by EGA / MS analysis satisfy the relationship Tf ≧ Tgas −7, preferably Tf ≧ Tgas −5, and more preferably Tf ≧ Tgas −2. Such a relationship enhances the above-mentioned effects. In one embodiment, the upper limit of Tf is Tgas + 15°C.

[0015] In one embodiment, the thickness deformation starting temperature Tf determined by TMA analysis is preferably 140°C to 300°C, and more preferably 160°C to 250°C.

[0016] The adhesive strength at 23°C (also referred to as normal adhesive strength X) of the first adhesive layer of the pressure-sensitive adhesive sheet when adhered to polyethylene terephthalate is preferably 0.5 N / 20 mm or more, more preferably 1 N / 20 mm to 30 N / 20 mm, even more preferably 2 N / 20 mm to 20 N / 20 mm, and even more preferably 3.5 N / 20 mm to 15 N / mm. Within these ranges, a pressure-sensitive adhesive sheet useful as a temporary fixing sheet for use in the manufacture of electronic components can be obtained. In this specification, the adhesive strength refers to the adhesive strength in a state where there is no decrease in adhesive strength due to the expansion of the heat-expandable microspheres, and refers to the adhesive strength in a state where the sheet has not been subjected to a thermal history of 40°C or higher. The adhesive strength refers to the adhesive strength measured according to JIS Z 0237:2009 (lamination conditions: one reciprocal movement with a 2 kg roller, peel speed (tensile speed): 300 mm / min, peel angle: 180°).

[0017] The adhesive strength of the first adhesive layer of the pressure-sensitive adhesive sheet when attached to polyethylene terephthalate is preferably reduced to 0.3 N / 20 mm or less (preferably 0.2 N / 20 mm or less, more preferably 0.1 N / 20 mm or less) by heating. The heating temperature is preferably 150°C to 300°C, more preferably 170°C to 280°C. In one embodiment, the heating temperature may be the gasification initiation temperature Tgas.

[0018] The adhesive strength Y at (gasification initiation temperature Tgas-10)°C when the first adhesive layer of the pressure-sensitive adhesive sheet is attached to polyethylene terephthalate is preferably 0.6 N / 20 mm to 40 N / 20 mm, more preferably 1.5 N / 20 mm to 30 N / 20 mm, and even more preferably 3 N / 20 mm to 20 N / mm.

[0019] The ratio (Y / X) of the adhesive strength Y at (gasification initiation temperature Tgas-10)°C when the first adhesive layer of the pressure-sensitive adhesive sheet is attached to polyethylene terephthalate, to the normal adhesive strength X of the first adhesive layer, is preferably 0.6 or more, more preferably 0.8 or more, and even more preferably 0.9 or more. Within this range, a pressure-sensitive adhesive sheet can be obtained that exhibits little change in surface condition (e.g., change in shape or change in roughness due to change in thickness) at high temperatures that do not require peeling. In one embodiment, the upper limit of Y / X is 1. In another embodiment, the upper limit of Y / X is 1.2.

[0020] The thickness of the pressure-sensitive adhesive sheet is preferably 10 μm to 400 μm, more preferably 20 μm to 200 μm, and even more preferably 30 μm to 150 μm.

[0021] B. First Pressure-Sensitive Adhesive Layer The first pressure-sensitive adhesive layer contains heat-expandable microspheres as described above. The first pressure-sensitive adhesive layer may further contain a pressure-sensitive adhesive.

[0022] Examples of adhesives constituting the first adhesive layer include acrylic adhesives, rubber adhesives, and silicone adhesives. Among these, acrylic adhesives are preferably used. Furthermore, an active energy ray-curable acrylic adhesive (hereinafter referred to as an active energy ray-curable adhesive) may be used as the adhesive. Details of the adhesive are described in, for example, JP 2015-168711 A. The description of this publication is incorporated herein by reference.

[0023] (Acrylic Pressure-Sensitive Adhesive) In one embodiment, an acrylic pressure-sensitive adhesive is used as the pressure-sensitive adhesive. Examples of the acrylic pressure-sensitive adhesive include acrylic pressure-sensitive adhesives having, as a base polymer, an acrylic polymer (homopolymer or copolymer) using one or more (meth)acrylic acid alkyl esters as monomer components.

[0024] Specific examples of the (meth)acrylic acid alkyl esters include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, ) C1-20 alkyl (meth)acrylates such as nonyl acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate. Among these, preferred are (meth)acrylic acid alkyl esters having a linear or branched alkyl group having 4 to 20 carbon atoms (more preferably 6 to 20, and particularly preferably 8 to 18), more preferably 2-ethylhexyl (meth)acrylate.

[0025] The acrylic polymer may contain, as necessary, units corresponding to other monomer components copolymerizable with the alkyl (meth)acrylate, for the purpose of modifying properties such as cohesive strength, heat resistance, and crosslinkability. Examples of such monomer components include carboxyl group-containing monomers such as acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid; acid anhydride monomers such as maleic anhydride and itanoic anhydride; hydroxyl group-containing monomers such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, hydroxyhexyl (meth)acrylate, hydroxyoctyl (meth)acrylate, hydroxydecyl (meth)acrylate, hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)methyl methacrylate; sulfonic acid group-containing monomers such as styrenesulfonic acid, allylsulfonic acid, 2-(meth)acrylamido-2-methylpropanesulfonic acid, (meth)acrylamidopropanesulfonic acid, sulfopropyl (meth)acrylate, and (meth)acryloyloxynaphthalenesulfonic acid; (N-substituted) amide monomers such as methylol (meth) acrylamide, N,N-dimethyl (meth) acrylamide, N-butyl (meth) acrylamide, N-methylol (meth) acrylamide, and N-methylol propane (meth) acrylamide; aminoalkyl (meth) acrylate monomers such as aminoethyl (meth) acrylate, N,N-dimethylaminoethyl (meth) acrylate, and t-butylaminoethyl (meth) acrylate; alkoxyalkyl (meth) acrylate monomers such as methoxyethyl (meth) acrylate and ethoxyethyl (meth) acrylate; maleimide monomers such as N-cyclohexyl maleimide, N-isopropyl maleimide, N-lauryl maleimide, and N-phenyl maleimide; itaconimide monomers such as N-methyl itaconimide, N-ethyl itaconimide, N-butyl itaconimide, N-octyl itaconimide, N-2-ethylhexyl itaconimide, N-cyclohexyl itaconimide, and N-lauryl itaconimide;succinimide-based monomers such as N-(meth)acryloyloxymethylene succinimide, N-(meth)acryloyl-6-oxyhexamethylene succinimide, and N-(meth)acryloyl-8-oxyoctamethylene succinimide; vinyl-based monomers such as vinyl acetate, vinyl propionate, N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, N-vinylcarboxylic acid amides, styrene, α-methylstyrene, and N-vinylcaprolactam; cyanoacrylate monomers such as acrylonitrile and methacrylonitrile; epoxy group-containing acrylic monomers such as glycidyl (meth)acrylate; polyethylene glycol (meth)acrylate, polypropylene glycol (meth)acrylate, and methoxyethyl (meth)acrylate. glycol-based acrylic ester monomers such as ethylene glycol and methoxypolypropylene glycol (meth)acrylate; acrylic ester monomers having a heterocycle, a halogen atom, a silicon atom, or the like, such as tetrahydrofurfuryl (meth)acrylate, fluorine (meth)acrylate, and silicone (meth)acrylate; polyfunctional monomers such as hexanediol di(meth)acrylate, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, epoxy acrylate, polyester acrylate, and urethane acrylate; olefin-based monomers such as isoprene, butadiene, and isobutylene;Examples of suitable monomers include vinyl ether-based monomers such as vinyl ether. These monomer components may be used alone or in combination of two or more. Among the above, more preferred are carboxyl group-containing monomers (particularly preferably acrylic acid) or hydroxyl group-containing monomers (particularly preferably hydroxyethyl (meth)acrylate). The content of the structural units derived from the carboxyl group-containing monomer is preferably 0.1 wt % to 10 wt %, more preferably 0.5 wt % to 5 wt %, and particularly preferably 1 wt % to 4 wt %, based on the total structural units constituting the acrylic polymer. The content of the structural units derived from the hydroxyl group-containing monomer is preferably 0.1 wt % to 20 wt %, more preferably 0.5 wt % to 10 wt %, and particularly preferably 1 wt % to 7 wt %, based on the total structural units constituting the acrylic polymer. In this specification, (meth)acrylic means acrylic and / or methacrylic.

[0026] The acrylic pressure-sensitive adhesive may contain any suitable additives as needed, such as crosslinkers, tackifiers, plasticizers (e.g., trimellitate ester plasticizers, pyromellitate ester plasticizers, etc.), pigments, dyes, fillers, antioxidants, conductive materials, antistatic agents, UV absorbers, light stabilizers, release modifiers, softeners, surfactants, flame retardants, and antioxidants.

[0027] Examples of the crosslinking agent contained in the acrylic pressure-sensitive adhesive include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, melamine-based crosslinking agents, peroxide-based crosslinking agents, as well as urea-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, carbodiimide-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, and amine-based crosslinking agents. Of these, isocyanate-based crosslinking agents and epoxy-based crosslinking agents are preferred.

[0028] Specific examples of the isocyanate-based crosslinking agent contained in the acrylic pressure-sensitive adhesive include lower aliphatic polyisocyanates such as butylene diisocyanate and hexamethylene diisocyanate; alicyclic isocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate and isophorone diisocyanate; aromatic isocyanates such as 2,4-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate and xylylene diisocyanate; and isocyanate adducts such as trimethylolpropane / tolylene diisocyanate trimer adduct (manufactured by Nippon Polyurethane Industry Co., Ltd., trade name "Coronate L"), trimethylolpropane / hexamethylene diisocyanate trimer adduct (manufactured by Nippon Polyurethane Industry Co., Ltd., trade name "Coronate HL"), and isocyanurate of hexamethylene diisocyanate (manufactured by Nippon Polyurethane Industry Co., Ltd., trade name "Coronate HX"). The content of the isocyanate-based crosslinking agent can be set to any appropriate amount depending on the desired adhesive strength, and is typically 0.1 to 20 parts by weight, and more preferably 0.5 to 10 parts by weight, per 100 parts by weight of the base polymer.

[0029] Examples of the epoxy crosslinking agent contained in the acrylic pressure-sensitive adhesive include N,N,N',N'-tetraglycidyl-m-xylenediamine, diglycidylaniline, 1,3-bis(N,N-glycidylaminomethyl)cyclohexane (manufactured by Mitsubishi Gas Chemical Company, Inc., trade name "Tetrad C"), 1,6-hexanediol diglycidyl ether (manufactured by Kyoeisha Chemical Co., Ltd., trade name "Epolite 1600"), neopentyl glycol diglycidyl ether (manufactured by Kyoeisha Chemical Co., Ltd., trade name "Epolite 1500NP"), and the like. ), ethylene glycol diglycidyl ether (manufactured by Kyoeisha Chemical Co., Ltd., trade name "Epolite 40E"), propylene glycol diglycidyl ether (manufactured by Kyoeisha Chemical Co., Ltd., trade name "Epolite 70P"), polyethylene glycol diglycidyl ether (manufactured by NOF Corporation, trade name "Epiol E-400"), polypropylene glycol diglycidyl ether (manufactured by NOF Corporation, trade name "Epiol P-200"), sorbitol polyglycidyl ether (manufactured by Nagase ChemteX Corporation, trade name "Denacol") Examples of suitable crosslinking agents include glycerol polyglycidyl ether (manufactured by Nagase ChemteX Corporation, trade name "Denacol EX-314"), pentaerythritol polyglycidyl ether, polyglycerol polyglycidyl ether (manufactured by Nagase ChemteX Corporation, trade name "Denacol EX-512"), sorbitan polyglycidyl ether, trimethylolpropane polyglycidyl ether, adipic acid diglycidyl ester, o-phthalic acid diglycidyl ester, triglycidyl tris(2-hydroxyethyl)isocyanurate, resorcinol diglycidyl ether, bisphenol-S-diglycidyl ether, and epoxy resins having two or more epoxy groups in the molecule. The content of the epoxy crosslinking agent can be set at any appropriate amount depending on the desired adhesive strength, and is typically 0.01 to 10 parts by weight, and more preferably 0.03 to 5 parts by weight, per 100 parts by weight of the base polymer.

[0030] The tackifier contained in the acrylic pressure-sensitive adhesive may be any appropriate tackifier, such as a tackifying resin. Specific examples of the tackifying resin include rosin-based tackifying resins (e.g., unmodified rosin, modified rosin, rosin phenol-based resins, rosin ester-based resins, etc.), terpene-based tackifying resins (e.g., terpene-based resins, terpene phenol-based resins, styrene-modified terpene-based resins, aromatic-modified terpene-based resins, hydrogenated terpene-based resins), hydrocarbon-based tackifying resins (e.g., aliphatic hydrocarbon resins, aliphatic cyclic hydrocarbon resins, aromatic hydrocarbon resins (e.g., styrene-based resins, xylene-based resins, etc.), aliphatic / aromatic petroleum resins, aliphatic / alicyclic petroleum resins, hydrogenated hydrocarbon resins, coumarone-based resins, coumarone-indene resins, etc.), phenol-based tackifying resins (e.g., alkylphenol-based resins, xylene-formaldehyde-based resins, resol, novolac, etc.), ketone-based tackifying resins, polyamide-based tackifying resins, epoxy-based tackifying resins, and elastomer-based tackifying resins. Among these, rosin-based tackifying resins, terpene-based tackifying resins, and hydrocarbon-based tackifying resins (such as styrene-based resins) are preferred. These tackifiers may be used alone or in combination of two or more. The amount of the tackifier added is preferably 5 to 100 parts by weight, more preferably 10 to 50 parts by weight, per 100 parts by weight of the base polymer.

[0031] (Heat-Expandable Microspheres) Any suitable heat-expandable microspheres can be used as long as they are capable of expanding or foaming upon heating. Typical examples of heat-expandable microspheres include microspheres in which a substance that gasifies upon heating and readily expands is encapsulated within an elastic shell. Such heat-expandable microspheres can be produced by any suitable method, such as coacervation or interfacial polymerization.

[0032] Examples of substances that gasify and easily expand when heated include liquids such as propane, propylene, butene, normal butane, isobutane, isopentane, neopentane, normal pentane, normal hexane, isohexane, heptane, octane, petroleum ether, methane halides, and tetraalkylsilane; and azodicarbonamide, which gasifies when thermally decomposed.

[0033] Examples of materials constituting the shell include polymers composed of nitrile monomers such as acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile, and fumaronitrile; carboxylic acid monomers such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, and citraconic acid; vinylidene chloride; vinyl acetate; (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, isobornyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, and β-carboxyethyl acrylate; styrene monomers such as styrene, α-methylstyrene, and chlorostyrene; and amide monomers such as acrylamide, substituted acrylamide, methacrylamide, and substituted methacrylamide. Polymers composed of these monomers may be homopolymers or copolymers. Examples of such copolymers include vinylidene chloride-methyl methacrylate-acrylonitrile copolymer, methyl methacrylate-acrylonitrile-methacrylonitrile copolymer, methyl methacrylate-acrylonitrile copolymer, and acrylonitrile-methacrylonitrile-itaconic acid copolymer.

[0034] In one embodiment, a liquid containing isooctane is used as the substance that gasifies and expands easily when heated. The liquid containing isooctane may contain other liquids (e.g., isopentane, n-octane). By using a liquid containing isooctane, the gasification onset temperature Tgas of the heat-expandable microspheres is high (e.g., 180°C or higher), making it possible to form a first PSA layer with excellent heat resistance, and to easily obtain a PSA sheet with minimal changes in surface condition (e.g., changes in shape and roughness due to changes in thickness) at high temperatures that do not require peeling.

[0035] The gasification onset temperature Tgas of heat-expandable microspheres is preferably 140° C. to 250° C., more preferably 150° C. to 240° C., and even more preferably 160° C. to 230° C. The gasification onset temperature Tgas of heat-expandable microspheres can be adjusted by the boiling point of the substance (liquid) that expands easily upon heating, the composition of the substance (liquid) that expands easily upon heating (e.g., the mixing ratio of different types of substances (liquids)), the composition of the polymer constituting the shell, the glass transition temperature of the polymer constituting the shell, the molecular weight of the polymer constituting the shell, the shell thickness, etc.

[0036] In one embodiment, the heat-expandable microspheres have a gasification initiation temperature Tgas of less than 180°C.

[0037] In another embodiment, the gasification onset temperature Tgas of the heat-expandable microspheres is equal to or higher than 180° C. When Tgas is within this range, a first pressure-sensitive adhesive layer having excellent heat resistance can be formed, and a pressure-sensitive adhesive sheet can be easily obtained that undergoes minimal changes in surface condition (e.g., changes in shape and roughness associated with changes in thickness) at high temperatures that do not require peeling.

[0038] The particle size of the heat-expandable microspheres before heating is preferably 0.5 to 80 μm, more preferably 5 to 45 μm, even more preferably 10 to 20 μm, and particularly preferably 10 to 15 μm. Therefore, the average particle size of the heat-expandable microspheres before heating is preferably 6 to 45 μm, more preferably 15 to 35 μm. The particle size and average particle size are values ​​determined by particle size distribution measurement using a laser scattering method.

[0039] The heat-expandable microspheres preferably have an appropriate strength so that they do not burst until their volumetric expansion rate reaches at least 5 times, more preferably at least 7 times, and even more preferably at least 10 times. When such heat-expandable microspheres are used, their adhesive strength can be efficiently reduced by heat treatment.

[0040] The content of the heat-expandable microspheres in the first pressure-sensitive adhesive layer can be appropriately set depending on the desired adhesive strength reduction, etc. The content of the heat-expandable microspheres is, for example, 1 to 150 parts by weight, preferably 10 to 130 parts by weight, and more preferably 15 to 100 parts by weight, relative to 100 parts by weight of the base polymer forming the first pressure-sensitive adhesive layer.

[0041] The volume filling rate of the heat-expandable microspheres in the first pressure-sensitive adhesive layer is preferably 28% or less, more preferably 24% or less, and even more preferably 21% or less. Within this range, a pressure-sensitive adhesive sheet can be obtained that exhibits minimal changes in surface condition (e.g., changes in shape and roughness associated with thickness changes) at high temperatures that do not require peeling. In one embodiment, changes in the surface condition of the pressure-sensitive adhesive sheet on the side opposite the outer surface of the first pressure-sensitive adhesive layer (e.g., the substrate or the second pressure-sensitive adhesive layer) are suppressed. The effect of setting the volume filling rate of the heat-expandable microspheres within this range is particularly effective when the gasification onset temperature Tgas of the heat-expandable microspheres is less than 180°C. The volume filling rate of the heat-expandable microspheres in the first pressure-sensitive adhesive layer is preferably 10% or more, more preferably 15% or more.

[0042] The arithmetic surface roughness Ra of the first pressure-sensitive adhesive layer before the expansion of the heat-expandable microspheres (i.e., before heating) is preferably 500 nm or less, more preferably 400 nm or less, and even more preferably 300 nm or less. The arithmetic surface roughness Ra can be measured in accordance with JIS B 0601.

[0043] The thickness of the first pressure-sensitive adhesive layer is preferably 5 μm to 70 μm, more preferably 10 μm to 60 μm, even more preferably 10 μm to 50 μm, and most preferably 10 μm to 40 μm. Within this range, a pressure-sensitive adhesive sheet can be obtained that exhibits excellent liner peeling operability, application operability, adhesiveness, smoothness, and deformability upon heating. In one embodiment, the thickness of the first pressure-sensitive adhesive layer is 20 μm or less. Within this range, a pressure-sensitive adhesive sheet can be obtained that exhibits minimal changes in surface condition (e.g., changes in shape and roughness associated with thickness changes) at high temperatures that do not require peeling. In one embodiment, changes in the surface condition of the pressure-sensitive adhesive sheet on the side opposite the outer surface of the first pressure-sensitive adhesive layer (e.g., the substrate, the second pressure-sensitive adhesive layer) are suppressed. This effect is particularly effective when the gasification initiation temperature (Tgas) of the heat-expandable microspheres is less than 180°C.

[0044] The thickness of the first pressure-sensitive adhesive layer is preferably thinner than that of the resin layer. By adjusting the thicknesses of both layers in this manner, a pressure-sensitive adhesive sheet can be obtained that exhibits minimal changes in surface condition (e.g., changes in shape and roughness associated with thickness changes) at high temperatures that do not require peeling. In one embodiment, changes in the surface condition of the pressure-sensitive adhesive sheet on the side opposite the outer surface of the first pressure-sensitive adhesive layer (e.g., the substrate or the second pressure-sensitive adhesive layer) are suppressed. The effect of setting the volume filling rate of the heat-expandable microspheres within the above range is particularly effective when the gasification onset temperature Tgas of the heat-expandable microspheres is less than 180°C. The difference in thickness between the first pressure-sensitive adhesive layer and the resin layer is preferably 5 μm or more, more preferably 6 μm to 40 μm, and even more preferably 8 μm to 30 μm.

[0045] The modulus of elasticity of the first pressure-sensitive adhesive layer measured by nanoindentation at 25°C is preferably less than 100 MPa, more preferably 0.1 MPa to 50 MPa, and even more preferably 0.1 MPa to 10 MPa. Within this range, a pressure-sensitive adhesive sheet with appropriate adhesive strength can be obtained. The modulus of elasticity measured by nanoindentation refers to the modulus of elasticity determined by continuously measuring the load and indentation depth on an indenter when the indenter is pressed into a sample, both during loading and unloading, and then determining the modulus from the resulting load-indentation depth curve. In this specification, the modulus of elasticity measured by nanoindentation refers to the modulus of elasticity measured using a nanoindenter (e.g., a Triboindenter TI-950 manufactured by Hysitron Inc.) by a single indentation method at a predetermined temperature (25°C) under the following measurement conditions: an indentation speed of approximately 500 nm / sec, an extraction speed of approximately 500 nm / sec, and an indentation depth of approximately 3000 nm.

[0046] C. Substrate The substrate can be made of any appropriate material. The substrate can be, for example, a plastic film, a plastic sheet, or various sheet-like materials such as paper, cloth, nonwoven fabric, metal foil, or plastic laminates thereof, or laminates of plastics. Among these, plastic films and plastic sheets (hereinafter referred to as plastic films) are most preferable from the standpoints of handleability and cost. The material of the plastic film can be selected as needed from the standpoints of strength, heat resistance, and the like. Examples of suitable materials include olefin-based resins containing α-olefins as monomer components, such as polyethylene (PE), polypropylene (PP), ethylene-propylene copolymer, and ethylene-vinyl acetate copolymer (EVA); polyesters such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polybutylene terephthalate (PBT); polyvinyl chloride (PVC); polyphenylene sulfide (PPS); amide-based resins such as polyamide (nylon) and wholly aromatic polyamide (aramid); polyether ether ketone (PEEK), polyimide, polyetherimide, polystyrene, and acrylic resin. These materials can be used alone or in combination of two or more. The plastic film may be any of an unstretched film, a uniaxially oriented film, and a biaxially oriented film. These films may be laminated films consisting of two or more film layers, or, from the viewpoint of ease of handling, films containing a lubricant such as inert particles may be used.

[0047] The thickness of the substrate is preferably 200 μm or less, more preferably 1 μm to 200 μm, even more preferably 5 μm to 200 μm, particularly preferably 10 μm to 200 μm, particularly preferably 20 μm to 200 μm, and most preferably 30 μm to 200 μm. A thickness within this range can contribute to improved liner releasability, and can provide a substrate that is excellent in strength, flexibility, suppleness, buckling resistance, etc.

[0048] In one embodiment, the thickness of the substrate is 40 μm to 200 μm. Within this range, a PSA sheet can be obtained that exhibits minimal changes in surface condition (e.g., changes in shape and roughness associated with thickness changes) at high temperatures that do not require peeling. In one embodiment, changes in the surface condition of the PSA sheet on the side opposite the outer surface of the first PSA layer (e.g., the substrate and the second PSA layer) are suppressed. This effect is particularly pronounced when the gasification initiation temperature (Tgas) of the heat-expandable microspheres is lower than 180°C.

[0049] The ratio (rate of change) of the surface roughness Ra(ii) of the second adhesive layer surface after heating for 450 seconds in an environment at 160°C to the surface roughness Ra(i) of the second adhesive layer surface when the pressure-sensitive adhesive sheet is heated in an environment at 130°C for 30 minutes and then stored at 25°C / 60% RH for 24 hours is preferably 130% or less, more preferably 101% to 128%, and even more preferably 102% to 120%. Within these ranges, a pressure-sensitive adhesive sheet can be obtained in which, in an environment that does not require peeling, the shape change of the side opposite the first pressure-sensitive adhesive layer is small and variation in tip shift can be preferably suppressed.

[0050] The elastic modulus of the substrate at 25° C. as measured by nanoindentation is preferably 500 MPa to 5000 MPa, more preferably 500 MPa to 4000 MPa, and even more preferably 700 MPa to 4000 MPa.

[0051] The substrate may be subjected to a surface treatment, such as corona treatment, chromic acid treatment, ozone exposure, flame exposure, high-voltage shock exposure, ionizing radiation treatment, or coating with a primer.

[0052] D. Resin Layer As described above, the pressure-sensitive adhesive sheet further includes a resin layer disposed between the first pressure-sensitive adhesive layer and the substrate. The presence of the resin layer allows for a pressure-sensitive adhesive sheet with excellent conformability to the adherend. Furthermore, when heated, a pressure-sensitive adhesive layer containing heat-expandable microspheres tends to expand in the thickness direction as the heat-expandable microspheres expand, causing deformation. However, the resin layer suppresses deformation toward the substrate, thereby improving releasability. Furthermore, by favorably adjusting the properties of the resin layer (e.g., by increasing flexibility), a pressure-sensitive adhesive sheet can be obtained that exhibits minimal changes in surface condition (e.g., changes in shape and roughness associated with thickness changes) at high temperatures that do not require peeling. In one embodiment, changes in the surface condition of the pressure-sensitive adhesive sheet on the side opposite the outer surface of the pressure-sensitive adhesive layer (e.g., the substrate, the second pressure-sensitive adhesive layer) are suppressed.

[0053] In one embodiment, the resin layer may contain any appropriate adhesive. Examples of adhesives constituting the resin layer include acrylic adhesives, rubber adhesives, and silicone adhesives. Among these, acrylic adhesives may be preferably used. Furthermore, an active energy ray-curable acrylic adhesive (hereinafter referred to as an active energy ray-curable adhesive) may be used as the adhesive. Preferably, the adhesive constituting the resin layer is the same as the adhesive constituting the first adhesive layer.

[0054] The thickness of the resin layer is preferably 1 μm to 60 μm, more preferably 5 μm to 50 μm, and even more preferably 10 μm to 40 μm. In one embodiment, the thickness of the resin layer is 20 μm or more (preferably 25 μm or more). Within this range, a PSA sheet can be obtained that exhibits minimal changes in surface condition (e.g., changes in shape and roughness associated with thickness changes) at high temperatures that do not require peeling. In one embodiment, changes in the surface condition of the PSA sheet on the side opposite the outer surface of the first PSA layer (e.g., the substrate and the second PSA layer) are suppressed. This effect is particularly effective when the gasification initiation temperature (Tgas) of the heat-expandable microspheres is less than 180°C.

[0055] The elastic modulus of the resin layer at 25° C. as measured by nanoindentation is preferably 0.001 MPa to 10 MPa, more preferably 0.01 MPa to 8 MPa, and even more preferably 0.5 MPa to 5 MPa.

[0056] The dynamic storage modulus G' of the resin layer at 160°C is preferably 0.5 MPa or less, more preferably 0.2 MPa or less, and even more preferably 0.1 MPa or less. A PSA sheet can be obtained that exhibits minimal changes in surface condition (e.g., changes in shape and roughness associated with thickness changes) at high temperatures that do not require peeling. In one embodiment, changes in the surface condition of the PSA sheet on the side opposite the outer surface of the first PSA layer (e.g., the substrate and the second PSA layer) are suppressed. This effect is particularly effective when the gasification initiation temperature Tgas of the heat-expandable microspheres is less than 180°C. The lower limit of the dynamic storage modulus G' of the resin layer at 160°C is, for example, 0.01 MPa. The storage modulus can be measured using a dynamic viscoelasticity measuring device (e.g., "ARES-G2" manufactured by TA Instruments) under measurement conditions of a frequency of 1 Hz and a heating rate of 5°C / min.

[0057] E. Second Pressure-Sensitive Adhesive Layer Examples of pressure-sensitive adhesives constituting the first pressure-sensitive adhesive layer include acrylic pressure-sensitive adhesives, rubber pressure-sensitive adhesives, and silicone pressure-sensitive adhesives. Among these, acrylic pressure-sensitive adhesives are preferably used. Furthermore, an active energy ray-curable acrylic pressure-sensitive adhesive (hereinafter referred to as an active energy ray-curable pressure-sensitive adhesive) may be used as the pressure-sensitive adhesive. Details of the pressure-sensitive adhesive are described, for example, in JP 2015-168711 A. The disclosure of this publication is incorporated herein by reference. In one embodiment, the second pressure-sensitive adhesive layer contains the acrylic pressure-sensitive adhesive described in Section B. As described above, the acrylic pressure-sensitive adhesive contains an acrylic polymer as a base polymer.

[0058] The thickness of the second pressure-sensitive adhesive layer is preferably 1 μm to 50 μm, more preferably 2 μm to 60 μm, even more preferably 3 μm to 35 μm, and most preferably 5 μm to 35 μm. Within these ranges, a pressure-sensitive adhesive sheet can be obtained that exhibits excellent liner peeling operability, adhesion operability, adhesiveness, and smoothness. Furthermore, a pressure-sensitive adhesive sheet can be obtained that exhibits minimal changes in surface condition (e.g., changes in shape and roughness associated with thickness changes) at high temperatures that do not require peeling.

[0059] The second pressure-sensitive adhesive layer preferably has a modulus of elasticity measured by a nanoindentation method at 25° C. of 0.001 MPa to 10 MPa, more preferably 0.01 MPa to 8 MPa. Within this range, a pressure-sensitive adhesive sheet having excellent operability, adhesiveness, and smoothness when applied can be obtained.

[0060] The ratio (rate of change) of the surface roughness Ra(II) of the second adhesive layer surface after heating for 450 seconds in a 160°C environment to the surface roughness Ra(I) of the second adhesive layer surface when the pressure-sensitive adhesive sheet comprising the second pressure-sensitive adhesive layer is heated in a 130°C environment for 30 minutes and then stored at 25°C / 60% RH for 24 hours is preferably 130% or less, more preferably 101% to 128%, and even more preferably 102% to 120%. Within these ranges, a pressure-sensitive adhesive sheet can be obtained that exhibits minimal change in the shape of the second adhesive layer surface and can favorably suppress variations in tip shift in an environment that does not require peeling. Heating and storage during Ra(I) measurement can be performed with a SUS plate attached to the surface of the second adhesive layer.

[0061] F. Method for Producing Pressure-Sensitive Adhesive Sheet The pressure-sensitive adhesive sheet can be produced by any appropriate method. Examples of methods for producing a pressure-sensitive adhesive sheet include a method in which a resin layer-forming composition is applied directly onto a substrate to form a resin layer, and then a first pressure-sensitive adhesive layer-forming composition (pressure-sensitive adhesive + heat-expandable microspheres) is applied onto the resin layer, or a method in which the first pressure-sensitive adhesive layer-forming composition is applied to any appropriate substrate, and the resulting coating layer is transferred to a substrate / resin layer laminate. When the pressure-sensitive adhesive sheet includes the second pressure-sensitive adhesive layer, the second pressure-sensitive adhesive layer can be formed by applying a second pressure-sensitive adhesive layer-forming composition (pressure-sensitive adhesive) to the surface of the substrate opposite the resin layer.

[0062] Examples of the coating method for each of the above compositions include coating methods using a die coater, a comma coater, a gravure coater, etc. As a drying method, heat drying is preferably adopted. For example, drying can be carried out by placing the pressure-sensitive adhesive coating layer for a desired period of time in a dryer equipped with a blower that can forcibly circulate air at a predetermined temperature.

[0063] The drying temperature is preferably 55°C or higher and lower than 100°C, more preferably 60°C to 90°C, and even more preferably 65°C to 90°C. The drying time can be any appropriate time. The drying time is, for example, 1 minute to 10 minutes. Within this range, a pressure-sensitive adhesive layer or the like can be formed efficiently.

[0064] G. Applications The pressure-sensitive adhesive sheet can be preferably used as a temporary fixing sheet when processing any appropriate member (e.g., electronic components such as semiconductor chips). In one embodiment, the pressure-sensitive adhesive sheet can be used as a temporary fixing sheet in the field of semiconductor packaging for FOWLP (Fan Out Wafer Level Package). In one embodiment, a plurality of semiconductor chips as workpieces can be arranged on the surface of the pressure-sensitive adhesive sheet opposite the first pressure-sensitive adhesive layer (e.g., the second pressure-sensitive adhesive layer surface). The pressure-sensitive adhesive sheet on which the semiconductor chips are arranged is subjected to a predetermined resin encapsulation process. The pressure-sensitive adhesive sheet is less likely to undergo changes in surface shape (such as changes in shape or surface roughness due to thickness changes) even when subjected to high temperatures in the resin encapsulation process, making it possible to reduce variations in chip shift of semiconductor chips.

[0065] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the examples, "parts" and "%" are by weight unless otherwise specified.

[0066] [Production Example 1] Production of base polymer 1 To a toluene solvent, 30 parts by weight of 2-ethylhexyl acrylate (EHA), 70 parts by weight of ethyl acrylate (EA), 5 parts by weight of methyl methacrylate (MMA), and 4 parts by weight of 2-hydroxyethyl acrylate (HEA) were added, and 0.5 parts by weight of t-butylperoxy-2-ethylhexanoate (manufactured by NOF Corporation, trade name: Perbutyl O (registered trademark)) as a polymerization initiator was further added, and the mixture was stirred at 80 to 90°C for 12 hours to obtain a toluene solution of polymer 1 with a solids concentration of 40%.

[0067] [Production Example 2] Production of adhesive layer-forming composition 1 (adhesive + heat-expandable microspheres) A ​​toluene solution of polymer 1 (polymer 1: 100 parts by weight), 1.4 parts by weight of an isocyanate-based crosslinking agent (manufactured by Mitsui Chemicals, Inc., trade name "Takenate D101A"), 10 parts by weight of a tackifier resin (manufactured by Sumitomo Bakelite Co., Ltd., trade name "Sumilite PR12603"), 30 parts by weight of heat-expandable microspheres (manufactured by Sekisui Chemical Co., Ltd., trade name "Advancell EM504", average particle size: 19 μm), and 0.05 parts of dioctyltin dilaurate were mixed to prepare adhesive layer-forming composition 1.

[0068] [Production Examples 3 to 7] Production of Pressure-Sensitive Adhesive Layer-Forming Compositions 2 to 6 Compositions 2 to 6 for forming pressure-sensitive adhesive layers were produced in the same manner as in Production Example 2, except that the types and amounts of heat-expandable microspheres were as shown in Table 1. <Thermal-expandable microspheres> F-230D: Matsumoto Yushi Pharmaceutical Co., Ltd., trade name "Matsumoto Microsphere F-230D", average particle size: 23 μm F-2800D: Matsumoto Yushi Pharmaceutical Co., Ltd., trade name "Matsumoto Microsphere F-2800D", average particle size: 28 μm

[0069]

[0070] [Production Example 8] Production of resin layer-forming composition 1 A toluene solution of polymer 1 (polymer 1: 100 parts by weight) and 3 parts by weight of an isocyanate-based crosslinking agent (manufactured by Mitsui Chemicals, Inc., trade name "Takenate D101A") were mixed to produce resin layer-forming composition 1.

[0071] [Production Example 9] Production of resin layer-forming composition 2 A resin layer-forming composition 2 was produced in the same manner as in Production Example 9, except that the amount of isocyanate-based crosslinking agent (manufactured by Mitsui Chemicals, Inc., trade name "Takenate D101A") was changed to 1 part by weight.

[0072] [Production Example 10] Production of adhesive 7 Adhesive 7 was produced by mixing a toluene solution of polymer 1 (polymer 1: 100 parts by weight), 1.5 parts by weight of an isocyanate-based crosslinking agent (manufactured by Mitsui Chemicals, Inc., trade name "Takenate D101A"), 5 parts by weight of a tackifying resin (manufactured by Sumitomo Bakelite Co., Ltd., trade name "Sumilite PR12603"), and 0.05 parts of dioctyltin dilaurate.

[0073] Example 1 (Preparation of Resin Layer / Substrate Laminate) The resin layer-forming composition 1 was applied to one surface of a PET substrate (thickness: 38 μm) using an applicator so that the thickness after solvent evaporation (drying) would be 13 μm. Subsequently, the solvent was evaporated (dried) at 150°C for 1 minute using a forced convection hot air drying oven to obtain a resin layer / substrate laminate. (Preparation of MRF38 (liner) / first pressure-sensitive adhesive layer (containing heat-expandable microspheres) laminate) The pressure-sensitive adhesive layer-forming composition 1 was applied to the release-treated surface of a liner (PET film, manufactured by Mitsubishi Plastics, Inc., product name "MRF-38") coated with a silicone-based release agent so that the thickness after solvent evaporation (drying) would be 20 μm. Subsequently, the solvent was evaporated (dried) at 65°C for 5 minutes using a forced convection hot air drying oven to obtain an MRF38 (liner) / first pressure-sensitive adhesive layer (containing heat-expandable microspheres) laminate. (Preparation of MRF38 (liner) / first pressure-sensitive adhesive layer (containing heat-expandable microspheres) / resin layer / substrate laminate) The MRF38 (liner) / first pressure-sensitive adhesive layer (containing heat-expandable microspheres) and the resin layer / substrate laminate were bonded together so that the first pressure-sensitive adhesive layer (containing heat-expandable microspheres) faced the resin layer, yielding an MRF38 (liner) / pressure-sensitive adhesive layer (containing heat-expandable microspheres) / resin layer / substrate laminate. (Preparation of MRF50 (liner) / second pressure-sensitive adhesive layer laminate) The pressure-sensitive adhesive 7 was applied to the release-treatment-coated surface of a liner (PET film, manufactured by Mitsubishi Plastics, Inc., product name "MRF-38") coated with a silicone-based release agent, so that the thickness after solvent evaporation (drying) was 5 μm. The resulting laminate was then subjected to solvent evaporation (drying) at 150°C for 1 minute using a forced convection hot air drying oven, yielding an MRF50 (liner) / second pressure-sensitive adhesive layer laminate. (Preparation of liner-attached pressure-sensitive adhesive sheet) An MRF38 (liner) / first pressure-sensitive adhesive layer (containing heat-expandable microspheres) / resin layer / substrate laminate and an MRF50 (liner) / second pressure-sensitive adhesive layer laminate were bonded together so that the substrate and the second pressure-sensitive adhesive layer faced each other, to obtain a liner-attached pressure-sensitive adhesive sheet (MRF38 (liner) / first pressure-sensitive adhesive layer (containing heat-expandable microspheres) / resin layer / substrate / second pressure-sensitive adhesive layer / MRF50 (liner)).

[0074] [Examples 2 to 9, Comparative Examples 1 to 3] Liner-attached PSA sheets were obtained in the same manner as in Example 1, except that the PSA layer-forming composition used to form the first PSA layer, the thickness of the first PSA layer, the resin layer-forming composition used to form the resin layer, the thickness of the resin layer, and the thickness of the substrate were as shown in Table 2 or Table 3.

[0075] <Evaluation> After peeling off the liners from the liner-attached PSA sheets obtained in the Examples and Comparative Examples, the PSA sheets were subjected to the following evaluations. The results are shown in Table 2 or Table 3.

[0076] (1) Volume Filling Fraction of Heat-Expandable Microspheres i) Before heating, a sample was fixed in a holder with the first adhesive layer of the pressure-sensitive adhesive sheet facing upward, and 1601 consecutive transmission images were taken from 0 to 180° using X-ray CT. X-ray CT was performed using a ZEISS Xradia 520 Versa with a tube voltage of 40 kV, a tube current of 73 μA, and a pixel size of 0.3 μm / pixel. ii) A tomographic image was generated by reconstructing the obtained total transmission images, and a three-dimensional reconstructed image (TIF stack image) and a reconstructed cross-sectional image (three-view view) were created using analysis software ImageJ. iii) The obtained three-dimensional reconstructed image (TIF stack image) was subjected to image processing to identify the heat-expandable microspheres. From the identification results, the volume filling fraction in the thickness direction was calculated. The thickness of the adhesive layer of each sample was measured by cross-sectional observation using SEM, and the filling fraction was calculated as the total volume excluding air bubbles. (2) Gasification Onset Temperature (Tgas) of Thermally Expandable Microspheres: Approximately 0.5 mg of a pressure-sensitive adhesive sheet sample was placed in a furnace-type pyrolyzer, and a mass chromatogram was obtained by EGA-MS analysis, in which the components volatilized by heating were analyzed by mass spectrometry. The sample was heated from 40°C to 500°C at a heating rate of 10°C / min using a furnace-type pyrolyzer (manufactured by Frontier Labs, trade name "PY2020iD"), and the maximum gas generation peak intensity was measured from the mass chromatogram at m / z = 57 using a GC / MS analyzer (manufactured by JEOL, trade name "JMS-T100GCV"). The gasification onset temperature is defined as the temperature at which the peak intensity reaches 2% of the maximum gas generation peak intensity in the EGA / MS chromatogram obtained from the EGA analysis. (3) Normal Adhesion Strength (X): The pressure-sensitive adhesive sheets obtained in the Examples and Comparative Examples were cut to a size of 20 mm wide and 140 mm long. A polyethylene terephthalate film (trade name "Lumirror S-10" manufactured by Toray Industries, Inc.; thickness: 25 μm, width: 30 mm) was attached to the first adhesive layer side of the PSA sheet as an adherend, with 5 mm of the film protruding from the left and right in the width direction, by rolling a 2 kg roller back and forth once in accordance with JIS Z 0237: 2009. The second adhesive layer side was attached to a metal plate (SUS304 plate, thickness: 3 mm) via double-sided tape (trade name "No. 500" manufactured by Nitto Denko Corporation) to prepare a measurement sample.The load when the adherend was peeled off from the adhesive sheet in the lengthwise direction under the conditions of a peel angle of 180° and a peel speed (tensile speed) of 300 mm / min was measured, and the maximum load (maximum load excluding the peak top at the initial stage of measurement) was determined, and the adhesive strength (N / 20 mm width) was determined by dividing this maximum load by the tape width. The above operation was carried out in an atmosphere at a temperature of 23°C.

[0077] (4) Adhesive Strength Y after Heating at (Tgas-10)°C The adhesive strength at (Tgas-10)°C was measured in accordance with the method described in (1) above.

[0078] (5) Adhesion Strength After Heating at (Tgas+15)°C The adhesion strength at (Tgas+15)°C was measured in accordance with the method in (1) above.

[0079] (6) Storage Modulus of Resin Layer Using a dynamic viscoelasticity measuring device (manufactured by TA Instruments, trade name "ARES-G2"), the storage modulus G' was measured at a measurement frequency of 1 Hz, a strain of 0.05%, and 160°C. Specifically, it was measured by the following method. Using the same resin layer as the resin layer used in each example and comparative example, a resin layer having a thickness of 50 μm was formed, and the resin layer was laminated to obtain a sample having a thickness of 1 mm or more. The obtained sample was punched out to a φ8 mm size and set on the probe of the "ARES-G2". The temperature was raised from -50°C to 260°C at a heating rate of 5°C / min, and the value of the storage modulus G' at 160°C was obtained.

[0080] (7) Thickness deformation start temperature Tf by TMA analysis Using a TMA Q400 (manufactured by TA-instrument), a Φ3.0 mm probe was used, and the displacement-temperature curve of the pressure-sensitive adhesive sheet was measured in expansion mode under the following conditions: nitrogen gas flow rate: 50.0 ml / min, indentation load: 0.0196 N, measurement temperature range: 40 ° C to 260 ° C, temperature rise rate: 5 ° C / min. The thickness deformation start temperature Tf by TMA analysis is defined as the temperature at which the displacement at 40 ° C is 15 μm, with the displacement at 40 ° C as the reference (0 μm). Measurements were performed with N = 5, and the average value of N = 3, excluding the maximum and minimum values, was taken as the thickness deformation start temperature Tf of the sample.

[0081] (8) Variation in Chip Shift The first adhesive layer of the pressure-sensitive adhesive sheets obtained in the Examples and Comparative Examples was bonded to a SUS substrate (0.8 mm thick, 12 inches in diameter) using a laminator. During bonding, the bonding speed was 0.5 m / min, the temperature was room temperature, and the pressure was 0.3 MPa. Next, 25 silicon chips (400 μm thick, 7 mm square) were radially arranged on the pressure-sensitive adhesive sheet, eight chips each at positions 25 mm, 50 mm, and 100 mm from the center chip, and the chips were bonded at a pressure of 0.2 MPa for a bonding time of 1.0 second. Next, the initial position of each chip on the pressure-sensitive adhesive sheet was measured using a CNC (Computer Numerical Control) image measuring device (trade name "Quickvision PRO", manufactured by Mitutoyo Corporation). Next, the SUS substrate with the silicon chip attached to the adhesive sheet was preheated in a dryer at 130°C for 30 minutes and then stored in a thermo-hygrostat set at 25°C / 60% RH for 24 hours. The resulting sample was placed in a compression molding machine (manufactured by TOWA Corporation, product name "CPM1080") and resin-sealed using a sealing resin (manufactured by Sumitomo Bakelite Co., Ltd., product name "Sumikon EME-G750") at a sealing temperature of 160°C, a pressure of 50 tons, and a sealing time of 450 seconds. Next, using a drying oven, the resin-sealed sample was heated at 200-240°C for 5 minutes to reduce the adhesive strength of the first adhesive layer (heat-foamable adhesive layer) of the adhesive sheet, and the adhesive sheet and sealing resin substrate were then thermally peeled from the SUS substrate. Furthermore, the sealing resin substrate was heated on a hot plate preheated to 150°C, and the second adhesive layer of the adhesive sheet was peeled off. The obtained encapsulating resin substrate was observed using a CNC image measuring machine (trade name "Quickvision PRO", manufactured by Mitutoyo Corporation), and the position of each chip in the encapsulating resin substrate after encapsulation was measured. Based on the obtained position information of the silicon chip, the relative distance from the center chip to each chip at the initial position and the position after encapsulation was calculated, and the change in relative distance from the initial position to the position after encapsulation (chip shift) was measured. For eight silicon chips arranged at a position 100 mm from the center chip, the maximum and minimum values ​​of chip shift were read, and the difference between them was defined as the chip shift variation.

[0082]

[0083]

[0084] 10: Substrate 20: Resin layer 30: First adhesive layer 40: Second adhesive layer 100, 200: Adhesive sheet

Claims

1. An adhesive sheet comprising, in this order, a substrate, a resin layer, and a first adhesive layer, the first adhesive layer containing heat-expandable microspheres, wherein a thickness deformation starting temperature Tf (°C) of the adhesive sheet as determined by TMA analysis and a gasification starting temperature Tgas (°C) of the heat-expandable microspheres as determined by EGA / MS analysis satisfy the relationship Tf≧Tgas-10.

2. The pressure-sensitive adhesive sheet according to claim 1, further comprising a second pressure-sensitive adhesive layer on the opposite side of the substrate to the resin layer.

3. The adhesive sheet according to claim 2, wherein the ratio (rate of change) of the surface roughness Ra(II) of the second adhesive layer surface after heating for 450 seconds in an environment of 160°C after storage to the surface roughness Ra(I) of the second adhesive layer surface when the adhesive sheet is heated in an environment of 130°C for 30 minutes and then stored at 25°C / 60% RH for 24 hours is 130% or less.

4. The pressure-sensitive adhesive sheet according to claim 1, wherein the gasification initiation temperature Tgas of the heat-expandable microspheres is lower than 180°C.

5. The pressure-sensitive adhesive sheet according to claim 1, wherein the gasification initiation temperature Tgas of the heat-expandable microspheres is 180° C. or higher.

6. The pressure-sensitive adhesive sheet according to claim 1, wherein the thickness of said first pressure-sensitive adhesive layer is thinner than the thickness of said resin layer.

7. The pressure-sensitive adhesive sheet according to claim 1, wherein the volumetric filling rate of the heat-expandable microspheres in the first pressure-sensitive adhesive layer is 21% or less.

8. The pressure-sensitive adhesive sheet according to claim 1, wherein the resin layer has a dynamic storage modulus G' at 160° C. of 0.1 MPa or less.

9. The pressure-sensitive adhesive sheet according to claim 1, wherein the thickness of the substrate is 40 μm to 200 μm.

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