Adhesive sheet

Abstract

Provided is an adhesive sheet that contains thermoexpandable microspheres and is capable of exhibiting hot peelability, wherein the adhesive sheet is capable of reducing adherend damage during peeling and suppressing substrate deformation due to hot peeling.　An adhesive sheet according to one embodiment of the present invention is provided with a substrate and an adhesive agent layer disposed on at least one side of the substrate. This adhesive sheet can be peeled by laser light irradiation and is expandable. The shelf modulus of this adhesive sheet at 0°C is 10 to 500 MPa. The adhesive agent layer contains thermoexpandable microspheres, and the adhesive agent layer is filled with 1 to 28% by volume of the thermoexpandable microspheres.

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, during the manufacture of semiconductor chips, adhesive sheets are sometimes used as temporary fixing materials in an expanding process in which a semiconductor wafer provided with weak spots by stealth dicing or the like is cleaved together with a die attach film by cool expanding to widen the gap between adjacent semiconductor chips. Adhesive sheets used in this manner are required to have expandability, and therefore, an expandable substrate is generally used as the substrate constituting the adhesive sheet.

[0003] Furthermore, methods for imparting releasability during temporary fixing include forming an adhesive layer whose adhesiveness decreases upon curing, and forming an adhesive layer containing heat-expandable microspheres.

[0004] In methods for forming adhesive layers whose adhesiveness decreases upon curing, photocurable adhesive layers are often formed, partly due to the tendency for expandable substrates to have poor heat resistance. Meanwhile, with the recent trend toward smaller and thinner semiconductor packages, the ratio of functional layers to semiconductor chips has increased, resulting in the tendency for semiconductor chips to become more fragile. When a photocurable adhesive sheet is used to temporarily fix such semiconductor chips, the semiconductor chips may break upon peeling. This is because photocurable adhesive sheets have no trigger for peeling, so the semiconductor chip needs to be pushed up from the substrate side with a block or the like.

[0005] In a pressure-sensitive adhesive layer containing heat-expandable microspheres, the heat-expandable microspheres expand upon heating, causing unevenness on the adhesive surface and reducing or eliminating adhesive strength. A pressure-sensitive adhesive sheet comprising such a pressure-sensitive adhesive layer can solve the above-mentioned problems by allowing natural peeling upon heating. However, problems arise, such as deformation of the substrate upon heating; when multiple semiconductor chips are individually peeled after dicing, deformation of the substrate can cause contact between the semiconductor chips; force is applied to chips that do not require peeling, resulting in chip cracking; the chips cannot be maintained horizontally and can no longer be adsorbed by a die bonder; and damage to the semiconductor chips due to heating.

[0006] Japanese Patent Application Laid-Open No. 2003-201452

[0007] The present invention has been made to solve the above-mentioned problems of the conventional art, and an object of the present invention is to provide a pressure-sensitive adhesive sheet that contains heat-expandable microspheres and can exhibit heat-removal properties, thereby reducing damage to the adherend during peeling and suppressing deformation of the substrate due to heat-removal.

[0008] [1] A pressure-sensitive adhesive sheet according to one embodiment of the present invention comprises a substrate and a pressure-sensitive adhesive layer disposed on at least one side of the substrate, and is laser-removable and expandable, wherein the pressure-sensitive adhesive sheet has a storage modulus of 10 MPa to 500 MPa at 0°C, and the pressure-sensitive adhesive layer contains heat-expandable microspheres, the volume filling rate of the heat-expandable microspheres in the pressure-sensitive adhesive layer being 1% to 28%. [2] The pressure-sensitive adhesive sheet described in [1] above may have a breaking elongation at 25°C of 220% to 2500%. [3] In the pressure-sensitive adhesive sheet described in [1] or [2] above, the pressure-sensitive adhesive layer may contain carbon black. [4] In the pressure-sensitive adhesive sheet described in any of [1] to [3] above, the pressure-sensitive adhesive layer may have a light absorptivity of 20% to 100% at a wavelength of 900 nm. [5] In the pressure-sensitive adhesive sheet according to any one of [1] to [4] above, the pressure-sensitive adhesive layer may have an indentation hardness of 0.005 MPa to 0.4 MPa at 25°C as measured by a nanoindentation method. [6] In the pressure-sensitive adhesive sheet according to any one of [1] to [5] above, the pressure-sensitive adhesive layer may not exhibit active energy ray curability. [7] In the pressure-sensitive adhesive sheet according to any one of [1] to [6] above, the thickness of the substrate may be 50 μm to 200 μm. [8] In the pressure-sensitive adhesive sheet according to any one of [1] to [7] above, the substrate may include a layer formed from a polyolefin-based resin layer. [9] In the pressure-sensitive adhesive sheet according to any one of [1] to [8] above, the substrate may have a multilayer structure including a layer formed from a polyolefin-based resin layer and a layer formed from an ethylene-vinyl acetate copolymer resin.

[10] In the pressure-sensitive adhesive sheet according to any one of [1] to [9] above, a die attach film may be used as an adherend.

[11] A laminate according to one embodiment of the present invention comprises the pressure-sensitive adhesive sheet according to any one of [1] to

[10] above and a die attach film.

[12] The melt viscosity at 120°C of the resin constituting the die attach film may be 3,000 Pa·s to 150,000 Pa·s.

[0009] According to the present invention, it is possible to provide a pressure-sensitive adhesive sheet that contains heat-expandable microspheres and can exhibit heat-removal properties, thereby reducing damage to the adherend during peeling and suppressing deformation of the substrate due to heat-removal.

[0010] 1 is a schematic cross-sectional view of a pressure-sensitive adhesive sheet according to one embodiment of the present invention; 2 is a schematic cross-sectional view of a laminate according to one embodiment of the present invention;

[0011] A. Overview of the Pressure-Sensitive Adhesive Sheet Fig. 1 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 a substrate 10 and a pressure-sensitive adhesive layer 20 disposed on at least one side of the substrate 10.

[0012] The pressure-sensitive adhesive sheet 100 has expandability. In this specification, "expandable" means that the storage modulus at 0°C is 500 MPa or less. By configuring the pressure-sensitive adhesive sheet to have expandability, it is possible to provide a pressure-sensitive adhesive sheet that can be preferably used in a manufacturing method that includes a step (so-called expanding step) of ensuring a distance between multiple adherends (e.g., semiconductor chips) arranged on the pressure-sensitive adhesive sheet after dicing before peeling the adherends. Specifically, the pressure-sensitive adhesive sheet is resistant to breaking during the expanding step, and can expand the spacing between multiple arranged semiconductor chips as necessary and sufficiently. A pressure-sensitive adhesive sheet having expandability can be obtained, for example, by using a substrate having expandability or by adjusting the properties (e.g., indentation hardness) of the pressure-sensitive adhesive layer.

[0013] The pressure-sensitive adhesive layer 20 contains heat-expandable microspheres. The heat-expandable microspheres can expand at a predetermined temperature. When the heat-expandable microspheres expand in a pressure-sensitive adhesive layer containing such heat-expandable microspheres, unevenness occurs on the adhesive surface (i.e., the surface of the pressure-sensitive adhesive layer) due to heating, resulting in a decrease or loss of adhesive strength. When the pressure-sensitive adhesive sheet of the present invention is used as a sheet for temporarily fixing workpieces during processing of electronic components (e.g., semiconductor chips), the adhesive strength required for temporary fixing is exhibited when the workpieces are subjected to the predetermined processing, and when the workpieces are to be released after processing, the adhesive strength is reduced or lost by heating, resulting in good releasability. The good releasability allows the adherend to be picked up without the need for operations such as pushing up a block, thereby reducing damage to the adherend.

[0014] In an embodiment of the present invention, the volume filling rate of the heat-expandable microspheres in the pressure-sensitive adhesive layer is 1% to 28%. Within this range, a pressure-sensitive adhesive sheet that exhibits favorable releasability upon laser light irradiation can be obtained. Details will be described later.

[0015] The adhesive strength at 23°C when the adhesive layer of the pressure-sensitive adhesive sheet is applied to polyethylene terephthalate is preferably 0.3 N / 20 mm or more, more preferably 0.4 N / 20 mm to 20 N / 20 mm, even more preferably 0.5 N / 20 mm to 10 N / 20 mm, and even more preferably 0.6 N / 20 mm to 8 N / 20 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 stroke with a 2 kg roller, peel speed (tensile speed): 300 mm / min, peel angle: 180°).

[0016] The adhesive strength of the 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.

[0017] The pressure-sensitive adhesive sheet can be peeled off by irradiation with laser light. More specifically, when the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet is irradiated with laser light, the pressure-sensitive adhesive layer is partially heated, causing the heat-expandable microspheres to expand, resulting in a decrease or loss of adhesive strength, as described above, enabling the pressure-sensitive adhesive sheet to be peeled off. The conditions for laser light irradiation (wavelength, irradiation dose, etc.) are not particularly limited as long as they are conditions that can heat the pressure-sensitive adhesive layer. In one embodiment, infrared laser light is used. The wavelength of the laser light is, for example, 600 nm to 1700 nm, preferably 700 nm to 1200 nm. In one embodiment, laser light with a wavelength of 940 nm is used. The output of the laser light irradiation is, for example, 10 W to 200 W. The irradiation time of the laser light irradiation is, for example, 10 msec to 200 msec. The laser light may be irradiated from the substrate side or the pressure-sensitive adhesive layer side.

[0018] "Releasable by laser light irradiation" means that the adhesive strength to the adherend becomes a predetermined value or less upon laser light irradiation (e.g., the sheet can fall naturally). In one embodiment, the state of "releasable by laser light irradiation" can be a state in which unevenness occurs on the surface of the adhesive layer after the adhesive layer is irradiated with laser light (wavelength: 940 nm, output: 50 W, irradiation time: 40 msec). The surface roughness Sa (arithmetic mean height) of the adhesive layer after the adhesive layer is irradiated with laser light (wavelength: 940 nm, output: 50 W, irradiation time: 40 msec) can be 15 μm or more. Preferably, the pressure-sensitive adhesive sheet is naturally releasable by laser light irradiation. "Naturally releasable" means that a predetermined adherend (e.g., size 3 mm × 3 mm, weight 0.004 g) can be peeled (fallen) by gravity.

[0019] The pressure-sensitive adhesive sheet is releasable by laser light irradiation, and therefore, even when a plurality of minute adherends (e.g., sizes of 4 mm x 12 mm, 3 mm x 3 mm, etc.; thickness of, for example, 30 μm) such as semiconductor chips are arranged, the adherends can be individually released. Furthermore, because the pressure-sensitive adhesive sheet is releasable by laser light irradiation, the heating time can be shortened, and releasability can be achieved by heating within 1 second, for example. Therefore, little heat is transferred to the substrate, and deformation of the substrate due to heat can be suppressed. Such a pressure-sensitive adhesive sheet can preferably achieve heat-releasability even when equipped with a substrate that tends to have low heat resistance (typically, a substrate having expandability).

[0020] In one embodiment, the pressure-sensitive adhesive sheet is used when temporarily fixing a semiconductor chip with a die attachment film. The semiconductor chip with the die attachment film can be configured by arranging the die attachment film so that it faces the adhesive layer of the pressure-sensitive adhesive sheet. In the semiconductor chip manufacturing process, when processing a semiconductor chip with a die attachment film on an adhesive sheet, the semiconductor chip with the die attachment film is required to have expandability in the cool expansion step before picking up (peeling off) the semiconductor chip with the die attachment film; heat-peeling ability during picking up; and suppression of substrate deformation during heating. The pressure-sensitive adhesive sheet is advantageous in that it can satisfy all of these requirements.

[0021] The storage modulus of the pressure-sensitive adhesive sheet at 0°C is preferably 10 MPa to 500 MPa, more preferably 20 MPa to 400 MPa, and even more preferably 30 MPa to 350 MPa. Within this range, the pressure-sensitive adhesive sheet can be suitable as a temporary fixing sheet in the cool-expanding process. If the storage modulus is too high, the pressure-sensitive adhesive sheet may break during cool-expanding. Furthermore, if the storage modulus is too low, the stress during expansion may be too small, making it impossible to cleave the die-attach film during expansion. The storage modulus E' can be measured using a dynamic viscoelasticity measuring device under measurement conditions of a frequency of 1 Hz and a heating rate of 5°C / min. Details will be described later.

[0022] The breaking elongation of the pressure-sensitive adhesive sheet at 25°C is preferably 50% or more, more preferably 220% to 2500%, even more preferably 300% to 2200%, and particularly preferably 400% to 2000%. Within these ranges, the pressure-sensitive adhesive sheet can be suitable as a temporary fixing sheet in a cool expanding process. The breaking elongation can be measured in accordance with JIS K7113.

[0023] 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.

[0024] B. Pressure-sensitive adhesive layer As described above, the pressure-sensitive adhesive layer contains heat-expandable microspheres. The pressure-sensitive adhesive layer may further contain a pressure-sensitive adhesive. In one embodiment, the pressure-sensitive adhesive layer has photothermal conversion ability. A pressure-sensitive adhesive layer having photothermal conversion ability can generate heat, for example, by absorbing laser light of a predetermined wavelength. This heat generation can cause the heat-expandable microspheres to expand and foam. By exerting releasability using laser light, minute adherends can be selectively released. This effect is particularly remarkable, coupled with the ability to form a pressure-sensitive adhesive layer with excellent smoothness. As the laser light, IR laser light, UV laser light, etc. are used. IR laser light is preferred.

[0025] The arithmetic surface roughness Ra of the 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. Within this range, a pressure-sensitive adhesive sheet having excellent adhesion to an adherend can be obtained. Furthermore, a pressure-sensitive adhesive sheet capable of adhering to an adherend with good positional accuracy can be obtained.

[0026] The thickness of the pressure-sensitive adhesive layer is preferably 5 μm to 40 μm, more preferably 7 μm to 35 μm, and even more preferably 20 μm to 35 μm.Within such a range, a pressure-sensitive adhesive sheet containing heat-expandable microspheres can be obtained that has excellent smoothness, high adhesion, and excellent stress transmission properties.

[0027] The indentation hardness of the pressure-sensitive adhesive layer at 25°C, as measured by the nanoindentation method, is preferably 0.005 MPa to 0.4 MPa, more preferably 0.010 MPa to 0.3 MPa, and even more preferably 0.015 MPa to 0.2 MPa. Within these ranges, a pressure-sensitive adhesive sheet with appropriate adhesiveness, releasability, and expandability can be obtained. If the indentation hardness is too high, the initial adhesion to the adherend (e.g., die attach film) will be high, and the heat-expandable microspheres may sink into the adherend even after expansion, preventing release. The indentation hardness measured by the nanoindentation method refers to the modulus of elasticity determined from the load-indentation depth curve obtained by continuously measuring the load and indentation depth when an indenter is pressed into a sample, both during loading and unloading. In this specification, the indentation hardness measured by the nanoindentation method refers to the modulus of elasticity measured by a single indentation method at a predetermined temperature (25°C) using a nanoindenter (for example, Triboindenter TI-950 manufactured by Hysitron Inc.) under the measurement conditions of an indentation speed of about 300 nm / sec, an extraction speed of about 300 nm / sec, and an indentation depth of about 1300 nm.

[0028] The optical absorptance of the pressure-sensitive adhesive layer at a wavelength of 900 nm is preferably 20% to 100%, more preferably 30% to 95%, and even more preferably 40% to 95%. Within this range, a pressure-sensitive adhesive layer having photothermal conversion ability can be formed, which preferably generates heat upon irradiation with IR laser light and exhibits excellent releasability with heat-expandable microspheres. Furthermore, by ensuring a light absorptance at a wavelength of 900 nm of 20% or more, damage to the adherend (semiconductor chip) caused by light transmitted through the pressure-sensitive adhesive sheet during laser light irradiation can be suppressed. The optical absorptance of the adhesive layer at a wavelength of 900 nm may be 0%. In this case, the semiconductor chip absorbs the IR laser light, and heat from the semiconductor chip is transferred to the pressure-sensitive adhesive layer, potentially causing expansion of the heat-expandable microspheres.

[0029] In one embodiment, the pressure-sensitive adhesive layer does not exhibit active energy ray curability. By configuring the pressure-sensitive adhesive layer in this manner, a pressure-sensitive adhesive sheet with excellent expandability can be obtained.

[0030] (Adhesive) Any appropriate adhesive can be used as the adhesive constituting the adhesive layer, as long as the effects of the present invention can be obtained. Examples of adhesives include acrylic adhesives, rubber adhesives, and silicone adhesives. Of these, acrylic adhesives can be preferably used. Details of adhesives are described in, for example, JP 2015-168711 A. The description of this publication is incorporated herein by reference.

[0031] In one embodiment, the pressure-sensitive adhesive is an acrylic pressure-sensitive adhesive, such as an acrylic pressure-sensitive adhesive having, as a base polymer, an acrylic polymer (homopolymer or copolymer) using one or more (meth)acrylic acid alkyl esters as a monomer component.

[0032] 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.

[0033] 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; glycol-based acrylic ester monomers such as polyethylene glycol (meth)acrylate, polypropylene glycol (meth)acrylate, methoxyethylene glycol (meth)acrylate, and methoxypolypropylene glycol (meth)acrylate; p) acrylic acid ester monomers having a heterocycle, a halogen atom, a silicon atom, or the like, such as tetrahydrofurfuryl acrylate, fluorine (meth)acrylate, and silicone (meth)acrylate; 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 ... Polyfunctional monomers such as erythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, epoxy acrylate, polyester acrylate, and urethane acrylate; olefin-based monomers such as isoprene, butadiene, and isobutylene; vinyl ether-based monomers such as vinyl ether; isocyanate group-containing monomers such as (meth)acryloyl isocyanate, 2-(meth)acryloyloxyethyl isocyanate, and m-isopropenyl-α,α-dimethylbenzyl isocyanate;These monomer components may be used alone or in combination of two or more. Among the above, a carboxyl group-containing monomer (particularly preferably acrylic acid) or a hydroxyl group-containing monomer (particularly preferably hydroxyethyl (meth)acrylate) is more preferred. In this specification, (meth)acrylic means acrylic and / or methacrylic.

[0034] 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 adjusters, softeners, surfactants, flame retardants, and antioxidants.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] (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.

[0040] 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.

[0041] 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.

[0042] The heat-expandable microspheres may be formed using inorganic or organic blowing agents, such as ammonium carbonate, ammonium bicarbonate, sodium bicarbonate, ammonium nitrite, sodium boron hydroxide, and various azides. Examples of organic blowing agents include fluorinated alkane compounds such as trichloromonofluoromethane and dichloromonofluoromethane; azo compounds such as azobisisobutyronitrile, azodicarbonamide and barium azodicarboxylate; hydrazine compounds such as paratoluenesulfonylhydrazide, diphenylsulfone-3,3'-disulfonylhydrazide, 4,4'-oxybis(benzenesulfonylhydrazide) and allylbis(sulfonylhydrazide); semicarbazide compounds such as p-toluylenesulfonylsemicarbazide and 4,4'-oxybis(benzenesulfonylsemicarbazide); triazole compounds such as 5-morpholyl-1,2,3,4-thiatriazole; and N-nitroso compounds such as N,N'-dinitrosopentamethylenetetramine and N,N'-dimethyl-N,N'-dinitrosoterephthalamide.

[0043] 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.

[0044] 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.

[0045] The expansion initiation temperature of the heat-expandable microspheres is preferably 80°C to 250°C, more preferably 80°C to 230°C, even more preferably 80°C to 200°C, still more preferably 80°C to 150°C, particularly preferably 80°C to 120°C, and most preferably 80°C to 100°C. In this specification, the expansion initiation temperature of heat-expandable microspheres refers to the lowest temperature at which the thickness of the pressure-sensitive adhesive layer increases by 5% or more from the thickness at room temperature. For example, the expansion initiation temperature may correspond to the temperature at which the adhesive strength of the pressure-sensitive adhesive tape decreases to 1.0 N / 20 mm or less and to 50% or less of the initial adhesive strength.

[0046] The content of the heat-expandable microspheres in the pressure-sensitive adhesive layer can be appropriately set depending on the desired reduction in adhesive strength, etc. The content of the heat-expandable microspheres is, for example, 1 to 30 parts by weight, preferably 3 to 25 parts by weight, more preferably 5 to 25 parts by weight, even more preferably 5 to 20 parts by weight, and particularly preferably 10 to 20 parts by weight, relative to 100 parts by weight of the base polymer forming the pressure-sensitive adhesive layer.

[0047] As described above, the volume filling rate of the heat-expandable microspheres in the pressure-sensitive adhesive layer is 1% to 28%, more preferably 3% to 25%, even more preferably 5% to 20%, and particularly preferably 10% to 20%. Within these ranges, the expansion rate of the heat-expandable microspheres can be controlled even by heating via laser light irradiation. As a result, a pressure-sensitive adhesive sheet can be obtained that exhibits favorable releasability and is capable of suppressing substrate deformation due to heating. The method for measuring the volume filling rate of the heat-expandable microspheres will be described later.

[0048] The heat-expandable microspheres can be produced by any suitable method. In one embodiment, the heat-expandable microspheres are obtained by suspension polymerization. Suspension polymerization is typically carried out by dispersing a monomer (shell-forming material) and an organic solvent in an aqueous dispersion medium containing a dispersant, and polymerizing the monomer in the presence of the organic solvent. A dispersion stabilizer may also be used to stabilize the dispersion. Examples of the dispersion stabilizer in the aqueous dispersion medium include inorganic fine particles such as silica, magnesium hydroxide, calcium phosphate, and aluminum hydroxide. Examples of dispersion stabilizing aids that may be used include condensation products of diethanolamine and aliphatic dicarboxylic acids, polyvinylpyrrolidone, methylcellulose, polyethylene oxide, polyvinyl alcohol, and various emulsifiers.

[0049] The properties of heat-expandable microspheres, such as particle size and organic solvent content, can be controlled by adjusting the polymerization conditions for the suspension polymerization and the types and amounts of the mixed components. For example, heat-expandable microspheres with large particle sizes can be obtained by reducing the amount of dispersant added or slowing the stirring speed during polymerization. Heat-expandable microspheres with thick shells can be obtained by increasing the amount of monomers added or slowing the stirring speed during polymerization.

[0050] (IR absorbent) In one embodiment, the pressure-sensitive adhesive layer contains an IR absorbent. The pressure-sensitive adhesive layer containing the IR absorbent can exhibit peelability by irradiation with IR laser light. Examples of IR absorbents that can be used include carbon black, cesium tungsten oxide, lanthanum hexaboride, tin-doped indium oxide, antimony-doped tin oxide, cyanine compounds, phthalocyanine compounds, dithiol metal complexes, naphthoquinone compounds, diimmonium compounds, and azo compounds. Of these, carbon black is preferred.

[0051] The content of the IR absorber is preferably 0.05 to 30 parts by weight, more preferably 0.1 to 20 parts by weight, based on 100 parts by weight of the base polymer.

[0052] 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.

[0053] In one embodiment, the substrate comprises a polyolefin resin, preferably a polypropylene resin. By using a substrate formed from a polyolefin resin, a PSA sheet having excellent expandability and useful as a temporary fixing material in an expanding process can be obtained.

[0054] In one embodiment, a substrate having a multilayer structure (e.g., a three-layer structure) including a layer formed from a polyolefin resin (preferably polypropylene) and a layer formed from an ethylene-vinyl acetate copolymer resin is used. By using such a substrate, a PSA sheet having excellent expandability and useful as a temporary fixing material in an expanding process can be obtained. Furthermore, by using a multilayer structure and separating the functions of each layer, it is possible to easily achieve both expandability and heat resistance during thermal foaming.

[0055] The thickness of the substrate is preferably 200 μm or less, more preferably 50 μm to 200 μm, even more preferably 60 μm to 180 μm, and particularly preferably 70 μm to 150 μm. Within these ranges, a PSA sheet can be obtained that exhibits excellent expandability and that can suppress substrate deformation due to heating. This can contribute to improved liner releasability, and can provide a substrate that exhibits excellent strength, flexibility, suppleness, buckling resistance, and the like.

[0056] The storage modulus of the substrate at 0° C. is preferably 10 MPa to 800 MPa, more preferably 20 MPa to 400 MPa, and even more preferably 30 MPa to 350 MPa. Within such ranges, a pressure-sensitive adhesive sheet suitable as a temporary fixing sheet in a cool expanding step can be obtained.

[0057] The breaking elongation of the substrate at 25°C is preferably 50% or more, more preferably 220% to 2500%, even more preferably 300% to 2200%, and particularly preferably 400% to 2000%. Within such ranges, a PSA sheet suitable as a temporary fixing sheet in a cool expanding step can be obtained.

[0058] The elastic modulus of the substrate, as measured by nanoindentation at 25° C., is preferably 500 MPa to 5000 MPa, more preferably 500 MPa to 4000 MPa, and even more preferably 700 MPa to 4000 MPa. Within these ranges, a pressure-sensitive adhesive sheet can be obtained that exhibits excellent expandability and is capable of suppressing substrate deformation due to heating.

[0059] 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.

[0060] D. Resin Layer In one embodiment, the pressure-sensitive adhesive sheet further comprises a resin layer disposed between the pressure-sensitive adhesive layer and the substrate. The presence of a resin layer allows for a pressure-sensitive adhesive sheet with excellent conformability to the adherend. Furthermore, when a pressure-sensitive adhesive layer containing heat-expandable microspheres is heated, the heat-expandable microspheres expand, causing deformation in the thickness direction. However, the resin layer suppresses deformation in the direction toward the substrate, thereby improving peelability. Furthermore, by favorably adjusting the properties of the resin layer (e.g., by increasing flexibility), a pressure-sensitive adhesive sheet with minimal changes in surface condition (e.g., changes in shape and roughness associated with thickness changes) can be obtained at high temperatures that do not require peeling.

[0061] 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 adhesive layer.

[0062] 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.

[0063] 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.

[0064] E. Method for Producing Pressure-Sensitive Adhesive Sheet The pressure-sensitive adhesive sheet can be produced by any suitable method, including, for example, a method of directly coating a substrate with a pressure-sensitive adhesive layer-forming composition (pressure-sensitive adhesive + heat-expandable microspheres), or a method of coating any suitable substrate with a pressure-sensitive adhesive layer-forming composition to form a coating layer, and then transferring the resulting coating layer to the substrate.

[0065] 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.

[0066] 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.

[0067] F. 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, a laminate (e.g., a dicing die bond film) is provided that is constructed by laminating the pressure-sensitive adhesive sheet and a die attach film. FIG. 2 is a schematic cross-sectional view of a laminate according to one embodiment of the present invention. Laminate 200 comprises pressure-sensitive adhesive sheet 100 and die attach film 30 disposed on one side of pressure-sensitive adhesive sheet 100. The die attach film is an adhesive film that is used by being attached to a semiconductor chip before die bonding during semiconductor chip manufacturing; it is attached to a chip in wafer form and can be separated into individual chips together with the wafer during expansion.

[0068] As the die attach film, a die attach film known in the art can be used, and therefore a detailed description of its configuration will be omitted. The die attach film can function, for example, as a curable (e.g., thermosetting) adhesive. The die attach film can include any suitable thermosetting resin. Examples of thermosetting resins include epoxy resins, phenolic resins, amino resins, unsaturated polyester resins, polyurethane resins, silicone resins, and thermosetting polyimide resins. A thermoplastic resin may also be used in the die attach film. Examples of thermoplastic resins include natural rubber, butyl rubber, isoprene rubber, chloroprene rubber, ethylene-vinyl acetate copolymers, ethylene-acrylic acid copolymers, ethylene-acrylic acid ester copolymers, polybutadiene resins, polycarbonate resins, thermoplastic polyimide resins, polyamide resins such as 6-nylon and 6,6-nylon, phenoxy resins, acrylic resins, saturated polyester resins such as PET and PBT, polyamide-imide resins, and fluororesins.

[0069] The melt viscosity at 120°C of the resin constituting the die attach film is preferably 3,000 Pa·s to 150,000 Pa·s, more preferably 4,000 Pa·s to 125,000 Pa·s, and even more preferably 5,000 Pa·s to 100,000 Pa·s. Within these ranges, the pressure-sensitive adhesive sheet does not become too flexible when heated, preventing the pressure-sensitive adhesive layer from sinking into the die attach film when the heat-expandable microspheres expand, thereby favorably exhibiting releasability of the pressure-sensitive adhesive sheet. The melt viscosity can be measured by laminating a 300 μm die attach film and punching it into a circular shape with an 8 mm diameter punch to prepare a measurement sample. This measurement sample can be measured at 120°C using an 8 mm diameter measurement jig under conditions of a gap of 250 μm, a heating rate of 10°C / min, a frequency of 1 Hz, and a strain of 5%. As the measuring device, for example, a product name "HAAKE MARSIII" manufactured by Thermo Scientific Corporation is used.

[0070] 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.

[0071] [Production Example 1] Production of Base Polymer A 89 parts by weight of 2-ethylhexyl acrylate (2EHA) and 11 parts by weight of 2-hydroxyethyl acrylate (HEA) were added to toluene, and 0.2 parts by weight of t-butylperoxy-2-ethylhexanoate (manufactured by NOF Corporation, trade name: Perbutyl O (registered trademark)) was further added as a polymerization initiator. The mixture was subjected to a polymerization reaction treatment in a nitrogen stream at 62°C for 6 hours and then at 75°C for 2 hours, thereby obtaining an acrylic copolymer intermediate. Next, 12 parts by weight of 2-methacryloyloxyethyl isocyanate (MOI) and 0.03% by mass of dibutyltin dilaurate relative to the MOI were added as a reaction catalyst to the liquid containing the obtained acrylic copolymer intermediate. Thereafter, an addition reaction treatment was performed in an air stream at 50°C for 12 hours, thereby obtaining a toluene solution of Polymer A (weight average molecular weight: 460,000).

[0072] [Production Example 2] Production of Base Polymer B To ethyl acetate were added 70 parts by weight of ethyl acrylate (EA), 30 parts by weight of 2-ethylhexyl acrylate (2EHA), 5 parts by weight of methyl methacrylate (MMA), and 4 parts by weight of 2-hydroxyethyl acrylate (HEA), and then 0.4 parts by weight of t-butylperoxy-2-ethylhexanoate (manufactured by NOF Corporation, trade name: PERBUTYL O (registered trademark)) was added as a polymerization initiator, and the mixture was stirred at 80 to 90°C for 12 hours to obtain an ethyl acetate solution of Polymer C (glass transition temperature Tg: -32.5°C) with a solids concentration of 40%.

[0073] [Production Example 3] Production of Base Polymer C To ethyl acetate were added 30 parts by weight of 2-ethylhexyl acrylate (2EHA), 70 parts by weight of methyl acrylate (MA), and 10 parts by weight of acrylic acid (AA), and then 0.4 parts by weight of t-butylperoxy-2-ethylhexanoate (manufactured by NOF Corporation, trade name: Perbutyl O (registered trademark)) was added, and the mixture was stirred at 80 to 90°C for 12 hours to obtain an ethyl acetate solution of polymer C (weight average molecular weight: 1,100,000) with a solids concentration of 40%.

[0074] [Production Example 4] Production of base polymer D To ethyl acetate, 95 parts by weight of butyl acrylate (BA), 5 parts by weight of acrylic acid (AA), and 3 parts by weight of 2-hydroxyethyl acrylate (HEA) were added, and 0.2 parts by weight of azobisisobutyronitrile was further added, followed by stirring at 80 to 90°C for 12 hours to obtain an ethyl acetate solution of polymer D (weight average molecular weight: 650,000) with a solids concentration of 40%.

[0075] [Production Example 5] Production of Base Material A A two-layer base material was obtained by co-extrusion molding using an extrusion T-die molding machine. The extrusion temperature was 190°C. The layer thickness and resin composition of each layer were as follows. Layer Thickness PP-containing Layer 1: 80 μm PP-containing Layer 2: 15 μm PP-containing Layer 1: Melting point: 124°C, Tensile modulus (90°C): 24.7 [MPa] Main component: Polypropylene resin 1 Other component: Polymer-type antistatic agent PP-containing Layer 2: Melting point: 92°C, Tensile modulus (90°C): 1.92 [MPa] Main component: Polypropylene resin 1 (70 parts by weight) Other component: Ethylene-vinyl acetate copolymer (EVA1) (30 parts by weight) EVA1: Melting point: 88°C, Tensile modulus (90°C): 1.01 [MPa]

[0076] [Production Example 6] Production of substrate B Using a two-kind three-layer extrusion T-die molding machine, a three-layer structure of A layer / B layer / C layer (a three-layer structure in which B layer is the central layer and A layer and C layer are laminated on both sides of B layer as outer layers) was produced. EVA resin (trade name: EVAFlex V1010, manufactured by Mitsui DuPont Chemical Co., Ltd.) was used as the resin for A layer and C layer, and 20% by mass of an antistatic agent was added to the EVA resin. EVA resin (trade name: EVAFlex V1010, manufactured by Mitsui DuPont Chemical Co., Ltd.) was used as the resin for B layer. The extrusion molding was performed at a die temperature of 190°C. That is, A layer, B layer, and C layer were extruded at 190°C. The thickness of the substrate obtained by extrusion molding was 125 μm. The thickness ratio (layer thickness ratio) of A layer, B layer, and C layer was A layer:B layer:C layer = 1:10:1.

[0077] [Production Example 7] Production of substrate C Using a T-die molding machine (manufactured by Placo Corporation, set temperature: 230°C), a stretchable substrate 1 (thickness: 40 μm) was produced from an olefin-based thermoplastic elastomer (propylene-ethylene copolymer, propylene component 86 mol% / ethylene component 14 mol%, manufactured by Mitsubishi Chemical Corporation, trade name "Zelas 7053"). One surface of the stretchable substrate 1 was subjected to a corona treatment.

[0078] [Production Example 8] Substrate D As substrate D, a polyester film (Lumirror #38 S27 (manufactured by Toray Industries, Inc.), thickness: 100 μm) was prepared.

[0079] Example 1 (Preparation of Resin Layer / Substrate Laminate) A mixed solution B was prepared by mixing an ethyl acetate solution of polymer B (polymer B: 100 parts by weight), 1.5 parts by weight of an isocyanate-based crosslinking agent (manufactured by Mitsui Chemicals, Inc., trade name "Takenate D-101A"), and 0.05 parts by weight of dioctyltin dilaurate. The mixed solution B was applied to one surface of substrate A using an applicator so that the thickness after solvent evaporation (drying) was 20 μm. Thereafter, a forced convection hot air drying oven was used to evaporate the solvent (dry) at 70°C for 1 minute, thereby obtaining a resin layer / substrate laminate. (Preparation of MRF38 (liner) / adhesive layer (containing heat-expandable microspheres) laminate) A pressure-sensitive adhesive (mixed solution B) was prepared by mixing a toluene solution of polymer A (polymer A: 100 parts by weight), 1.5 parts by weight of an isocyanate crosslinking agent (manufactured by Mitsui Chemicals, Inc., trade name "Takenate D-101A"), 15 parts by weight (filling rate: 4.8%) of heat-expandable microspheres (manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd., trade name "FN-100S", foaming initiation temperature: 125°C, average particle size: 15 µm), and 5 parts by weight (addition rate: 4.5% by weight) of carbon black (manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd., trade name "ATDN101 Black"). The pressure-sensitive adhesive (mixed solution B) 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. The solvent was then evaporated (dried) at 65°C for 5 minutes using a forced convection hot air drying oven, yielding an MRF38 (liner) / pressure-sensitive adhesive layer (containing heat-expandable microspheres) laminate. (Preparation of MRF38 (liner) / pressure-sensitive adhesive layer (containing heat-expandable microspheres) / resin layer / substrate laminate) The MRF38 (liner) / pressure-sensitive adhesive layer (containing heat-expandable microspheres) and the resin layer / substrate laminate were bonded together so that the pressure-sensitive adhesive layer (containing heat-expandable microspheres) faced the resin, yielding a pressure-sensitive adhesive sheet consisting of the MRF38 (liner) / pressure-sensitive adhesive layer (containing heat-expandable microspheres) / resin layer / substrate laminate. The volume filling rate of the heat-expandable microspheres was determined by the following method. i) Before heating, the sample is fixed to a holder with the first adhesive layer of the adhesive sheet facing upward, and 1601 continuous transmission images are taken from 0 to 180° using an X-ray CT scanner.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) The obtained total transmission image was reconstructed to produce a tomographic image, and a three-dimensional reconstructed image (TIF stack image) and a reconstructed cross-sectional image (three-view image) were created using the analysis software ImageJ. iii) The obtained three-dimensional reconstructed image (TIF stack image) was subjected to image processing to identify the thermally expandable microspheres. From the identification results, the volume filling rate in the thickness direction was calculated. The thickness of the adhesive layer of each sample was measured by SEM cross-section observation, and the filling rate was calculated as the total volume excluding the air bubble portion.

[0080] Examples 2 to 6, Example 8, Comparative Examples 1 to 4 Liner-attached PSA sheets were obtained in the same manner as in Example 1, except that the base polymers shown in Table 1 were used to form the PSA layers and resin layers, and the content (filling rate) of heat-expandable microspheres, the amount of carbon black added, the thickness of each layer, and the type of substrate were set as shown in Table 1.

[0081] Example 7 (Preparation of MRF38 (liner) / adhesive layer (containing thermally expandable microspheres) laminate) A pressure-sensitive adhesive was prepared by mixing a toluene solution of polymer A (polymer A: 100 parts by weight), 1.5 parts by weight of an isocyanate-based crosslinking agent (manufactured by Mitsui Chemicals, Inc., trade name "Takenate D-101A"), 15 parts by weight (filling rate: 14.4%) of thermally expandable microspheres (manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd., trade name "FN-100S", foaming initiation temperature: 125°C, average particle size: 15 μm), and 2.8 parts by weight (addition rate: 2.5% by weight) of carbon black (manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd., trade name "ATDN101 Black") The pressure-sensitive adhesive was applied to the release-treated surface of a liner (PET film, manufactured by Mitsubishi Plastics, Inc., trade name "MRF-38") coated with a silicone-based release agent, so that the thickness after solvent evaporation (drying) would be 30 μm. The solvent was then evaporated (dried) in a forced convection hot air drying oven at 65°C for 5 minutes to obtain an MRF38 (liner) / adhesive layer (containing heat-expandable microspheres) laminate. (Preparation of MRF38 (liner) / adhesive layer (containing heat-expandable microspheres) / resin layer / substrate laminate) The MRF38 (liner) / adhesive layer (containing heat-expandable microspheres) and substrate A were bonded together to obtain a pressure-sensitive adhesive sheet consisting of MRF38 (liner) / adhesive layer (containing heat-expandable microspheres) / substrate.

[0082] Comparative Example 5 A mixed solution was prepared by mixing 100 parts of the ethyl acetate solution of polymer D prepared in Production Example 4 (polymer D), 0.5 parts of an epoxy crosslinker (manufactured by Mitsubishi Gas Chemical Company, Inc., trade name "Tetrad C"), 30 parts of a terpene phenol resin (manufactured by Yasuhara Chemical Co., Ltd., trade name "YS Polystar U130") as a tackifier, 50 parts of thermally expandable microspheres (manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd., trade name "FN-100S", foaming initiation temperature: 125°C, average particle size: 15 μm), 25 parts of an active energy ray reactive oligomer (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "Shikou 7620EA", urethane acrylate oligomer), and 6 parts by weight of an energy ray polymerization initiator (manufactured by BASF Japan Ltd., trade name "Irgacure 184"). The same solvent (toluene) as the solvent in the mixed solution was further added to adjust the viscosity to a level that was easy to apply. This mixture was applied using an applicator to a polyethylene terephthalate film (thickness: 50 μm) with a silicone release agent-treated surface so that the thickness after solvent evaporation (drying) would be 40 μm, and then dried to form an adhesive layer. This adhesive layer was then bonded to the corona-treated surface of the above-mentioned substrate C (Production Example 7) to obtain an adhesive sheet.

[0083] <Evaluation> After the liners were peeled off 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 1.

[0084] The composition of the die attach film used in the evaluation was as follows: 35 parts by mass (solid content) of acrylic polymer (product name "SG-P3", manufactured by Nagase ChemteX Corporation, glass transition temperature 12°C, containing epoxy groups), 30 parts by mass (solid content) of acrylic polymer (acrylic resin solution prepared by dissolving a copolymer of ethyl acrylate, butyl methacrylate, and glycidyl methacrylate in methyl ethyl ketone: weight average molecular weight Mw = 70,000 / epoxy equivalent = 444 (g / eq) / glass transition temperature Tg = 11°C), 6 parts by mass of phenolic resin (product name "MEHC-7851SS", manufactured by Meiwa Chemical Industry Co., Ltd.), 27 parts by mass of silica filler (product name "SE2050-MCV", manufactured by Admatechs Co., Ltd.), and 2 parts by mass of silane coupling agent (product name "KBM-403", manufactured by Shin-Etsu Chemical Co., Ltd.).

[0085] (1) Laser Removability A semiconductor chip (3 mm x 3 mm, 100 μm thick, made from a silicon mirror wafer) was placed on the die attach film and bonded using a thermocompression film laminator manufactured by MCK (MRK-600A modified) at a bonding pressure of 0.3 MPa, a bonding temperature of 80°C, and a bonding speed of 1.0 m / min. The bonded semiconductor chip with die attach film was cut into 3 mm x 3 mm pieces, and the die attach film side was placed on the adhesive layer side of the adhesive sheet. The pieces were then bonded again using a thermocompression film laminator manufactured by MCK (MRK-600A modified) at a bonding pressure of 0.3 MPa, a bonding temperature of 80°C, and a bonding speed of 1.0 m / min to obtain a laser irradiation sample. Then, IR laser light (wavelength: 940 nm) was irradiated from the substrate side of the adhesive sheet. The peelability of the adherend (die attach film / semiconductor chip laminate) from the adhesive layer was evaluated. After irradiation with IR laser light, if the adherend peeled off naturally (if it peeled off (dropped) due to gravity), it was judged as pass (◯), and if it did not peel off naturally, it was judged as fail (×). Evaluation equipment: L13920-611 laser irradiation diameter 6.4 mmφ (manufactured by Hamamatsu Photonics) Evaluation conditions: output 50 W, irradiation time: 40 msec

[0086] (2) Expandability A die attach film and a semiconductor wafer (stealth diced) were placed in this order on the adhesive layer of the adhesive sheet, and cleavage was attempted under the following conditions. If the adhesive sheet could be expanded without breaking, it was rated as pass (◯), and if the adhesive sheet broke, it was rated as fail (×). Evaluation equipment: DDS (manufactured by Disco Corporation) Chip size: 4 mm x 13 mm x 30 μmt Chip material: Silicon Evaluation conditions: Ambient temperature -15°C Cool expand push-up height: 13 mm Cool expand push-up speed: 100 mm / sec

[0087] (3) Substrate deformation (surface roughness of substrate after laser light irradiation) A die attach film and a semiconductor wafer (stealth diced, made of silicon, 4 mm x 4 mm x 100 μmt) were placed in this order on the adhesive layer of the adhesive sheet, and laser light was irradiated under the same conditions as in (1) above. The surface roughness (arithmetic mean height Sa) of the side opposite the adhesive layer of the substrate (back surface) was measured. When the arithmetic mean height Sa was 60 μm or less, it was judged as pass (◯), and when the arithmetic mean height Sa was more than 60 μm, it was judged as fail (×). The arithmetic mean height Sa was measured by setting the substrate after laser irradiation in an Olympus "LEXT-OLS-5000" and measuring it in a 2 cm x 2 cm area with a lens magnification of 20 times. The lowest measured value among three measurements was adopted.

[0088] (4) Arithmetic mean height Sa of adhesive layer after laser light irradiation A die attach film and a semiconductor wafer (stealth diced, silicon, 4 mm x 4 mm x 100 μmt) were placed in this order on the adhesive layer of the adhesive sheet, and laser light was irradiated under the same conditions as in (1) above. The surface roughness (arithmetic mean height Sa) of the adhesive layer was then measured. A surface roughness of 15 μm or more was deemed pass (◯), and a surface roughness of 15 μm or less or the adherend did not peel naturally was deemed fail (×). The arithmetic mean height Sa was measured by setting the substrate after laser irradiation in an Olympus "LEXT-OLS-5000" and measuring it over a 2 cm x 2 cm area with a lens magnification of 20x. The lowest measured value among three measurements was used.

[0089] (5) Storage Modulus of Pressure-Sensitive Adhesive Sheet at 0°C Using a dynamic viscoelasticity measuring device (manufactured by TA Instruments under the trade name "RSA-G2"), the storage modulus E' of the pressure-sensitive adhesive sheet was measured under the measurement conditions of a frequency of 1 Hz, a temperature rise rate of 5°C / min, and a measurement temperature of 0°C. The sample size was 20 mm x 70 mm, and the jig gap during measurement was 20 mm.

[0090] (6) Breaking Elongation of Pressure-Sensitive Adhesive Sheet at 25°C A pressure-sensitive adhesive sheet test piece (10 mm wide x 70 mm long) was cut out. A tensile test was then performed on the pressure-sensitive adhesive sheet test piece using a tensile tester, and the breaking elongation of the tape test piece stretched at a predetermined tensile speed was measured. In the tensile test, the initial chuck distance was 50 mm, the temperature condition was 25°C, and the tensile speed was 300 mm / min.

[0091] (7) Indentation Hardness of Pressure-Sensitive Adhesive Layer at 25°C Using a nanoindenter (Triboindenter TI-950 manufactured by Hysitron Inc.), the indentation hardness of the pressure-sensitive adhesive layer at 25°C was measured by a single indentation method under the following measurement conditions: indenter used: Berkovich (triangular pyramid), indentation speed: 300 nm / sec, pull-out speed: 300 nm / sec, indentation depth: 1300 nm.

[0092] (8) IR Absorbance of Pressure-Sensitive Adhesive Layer The IR (wavelength: 900 nm) absorbance of the pressure-sensitive adhesive layer was measured using a spectrophotometer, model "SOLID SPEC-3700" manufactured by Shimadzu Corporation. The measurement conditions were: measurement wavelength range 280 nm to 2500 nm, scan speed: medium speed, sampling pitch: 1 nm.

[0093]

[0094] REFERENCE SIGNS LIST 10: Substrate 20: Adhesive layer 30: Die attach film 100: Adhesive sheet 200: Laminate

Claims

1. A pressure-sensitive adhesive sheet comprising a substrate and a pressure-sensitive adhesive layer disposed on at least one side of the substrate, which is peelable by irradiation with laser light and has expandability, wherein the pressure-sensitive adhesive sheet has a storage modulus at 0°C of 10 MPa to 500 MPa, the pressure-sensitive adhesive layer contains heat-expandable microspheres, and the volume filling rate of the heat-expandable microspheres in the pressure-sensitive adhesive layer is 1% to 28%.

2. The pressure-sensitive adhesive sheet according to claim 1, having a breaking elongation at 25°C of 220% to 2500%.

3. The pressure-sensitive adhesive sheet according to claim 1, wherein the pressure-sensitive adhesive layer contains carbon black.

4. The pressure-sensitive adhesive sheet according to claim 1, wherein the pressure-sensitive adhesive layer has a light absorptivity of 20% to 100% at a wavelength of 900 nm.

5. The pressure-sensitive adhesive sheet according to claim 1, wherein the pressure-sensitive adhesive layer has an indentation hardness of 0.005 MPa to 0.4 MPa at 25°C as measured by a nanoindentation method.

6. The pressure-sensitive adhesive sheet according to claim 1, wherein the pressure-sensitive adhesive layer does not exhibit active energy ray curability.

7. The pressure-sensitive adhesive sheet according to claim 1, wherein the thickness of the substrate is 50 μm to 200 μm.

8. The pressure-sensitive adhesive sheet according to claim 1, wherein the substrate includes a layer formed from a polyolefin-based resin layer.

9. The pressure-sensitive adhesive sheet according to claim 1, wherein the substrate has a multilayer structure including a layer formed from a polyolefin resin layer and a layer formed from an ethylene-vinyl acetate copolymer resin.

10. The pressure-sensitive adhesive sheet according to claim 1, wherein the adherend is a die attach film.

11. A laminate comprising the pressure-sensitive adhesive sheet according to claim 1 and a die attach film.

12. The laminate according to claim 11, wherein the resin constituting the die attach film has a melt viscosity at 120°C of 3,000 Pa·s to 150,000 Pa·s.

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