Underfill material for micro-led display element, underfill film, method for producing underfill film, and micro-led display element

Abstract

A purpose of the present invention is to provide an underfill material for making it possible to improve the efficiency of mass transfer and metal bonding of an LED element and improve the quality of an LED display element, the underfill material having a flux function, sufficient adhesive force at room temperature, and thermal yellowing resistance during high-temperature processes, and enabling film formation in only a specific area. Another purpose of the present invention is to provide: an underfill film that is patterned on an array substrate, uses the underfill material, and can improve the efficiency of mass transfer and metal bonding of an LED element; a method for producing the underfill film; and a micro-LED display element provided with the underfill film. A thermosetting adhesive composition contains the following component (A), component (B), component (C), and component (D).　Component (A): an alkali-soluble resin which has a phenolic hydroxyl group and in which the glass transition temperature (Tg) of the polymer is 60°C or less　Component (B): a compound which has an isocyanurate skeleton　Component (C): an aliphatic or alicyclic epoxy compound　Component (D): a solvent.

Description

Underfill material for micro LED display element, underfill film, method for manufacturing underfill film, and micro LED display element

[0001] The present invention relates to an underfill material for a micro LED display element, an underfill film, a method for manufacturing an underfill film, and a micro LED display element, and in particular to an underfill material used in a micro LED display element, a method for manufacturing an underfill film, an underfill film obtained by the manufacturing method, and a micro LED display element using the underfill film.

[0002] Currently, liquid crystal displays (LCDs) and organic light-emitting diode displays (OLEDs) are primarily used in flat panel displays used in mobile phones, monitors, and TVs. While LCDs have well-established mass production technology, they are inexpensive and can be made large. However, the need for a backlight for display results in poor form factor and flexibility. OLEDs, while offering superior flexibility, face the challenge of shortening their lifespan as the brightness of the display increases. To address these drawbacks, micro-LED display elements, which use inorganic light-emitting diodes arranged on each pixel of an array substrate, have been developed in recent years. Because micro-LED display elements use micrometer-sized inorganic light-emitting diodes as light sources, they can achieve higher brightness, higher color purity, and a longer lifespan than LCDs and OLEDs. Furthermore, because LEDs are arranged for each pixel, each pixel can be isolated and the display is highly flexible.

[0003] The LED elements that serve as light sources are supplied as small pieces by epitaxially growing a semiconductor layer on a sapphire substrate, forming electrodes, and then dicing the substrate. Micro LED display elements require the LED elements manufactured in this way to be arranged on an array substrate with high precision. The pick-and-place method, in which each LED element is installed individually, has been considered as a method for arranging LED elements on an array substrate. However, this method requires a significant amount of time to install the LEDs, making it unsuitable for mass production.

[0004] Therefore, in recent years, a stamp method has been proposed in which a large number of LED elements are picked up from a sapphire substrate at once using an adhesive base material (stamp), mass-transferred to an array substrate, and then the LED elements are metal-bonded to the electrodes of the array substrate by thermocompression bonding using a bonding head or by laser heating (Non-Patent Documents 1 and 2).This method is expected to significantly improve throughput compared to the pick-and-place method, as it allows a large number of LED elements to be arranged on the array substrate and bonded to the array substrate at once.

[0005] Adv. Optical Mater. 2015, 3, 1313-1335SID 2017 DIGEST, 257

[0006] In this stamp-based mass-transfer method, the LED elements are mass-transferred from the sapphire substrate to the array substrate due to the difference in adhesiveness between the array substrate and the LED elements and the stamp and the LED elements. Therefore, an adhesive component is required on the array substrate. The adhesive component often serves to bond the LED elements to the substrate electrodes, and is typically a solder paste or conductive paste. However, this method creates space around the electrodes of the LED elements, which can lead to problems such as electrode peeling and corrosion due to external stresses applied to the panel, such as vibrations, or moisture.

[0007] Among the adhesive components, the non-conductive paste and film are expected to alleviate the above-mentioned problems by being expelled from between the LED electrode and the array substrate electrode and remaining as a permanent film around the electrode when the LED element is bonded onto the paste or film and the LED element is joined to the substrate electrode, thereby functioning as an underfill material that protects the area around the electrode from moisture and external stress.

[0008] Another challenge specific to micro LED display elements is the prevention of heat-induced yellowing of the components surrounding the LED element. Because light emitted from the LED element spreads in all directions, not just perpendicular to the substrate, the transparency of the surrounding components is essential to maintain the color purity of the LED element. Furthermore, as mentioned above, high-temperature processes such as thermocompression bonding and laser heating are used to metal-bond the electrodes of the LED element and array substrate. Therefore, the components surrounding the LED element must be heat-resistant and yellow-resistant to maintain high transparency even after this high-temperature process.

[0009] Another issue common to semiconductor-mounted devices, but not unique to micro LED display elements, is the flux treatment process for removing oxide films from the electrodes. In micro LED display elements, if an oxide film forms on the electrodes of the array substrate or LED elements, metal bonding is impaired, resulting in poor electrical continuity. Typically, this oxide film is removed using a flux agent containing volatile small molecules, but if these volatile small molecules remain between the electrodes after flux treatment, electrode corrosion can occur.

[0010] Furthermore, once a functional film is formed over the entire surface of an array substrate or wafer, there is the issue of it being difficult to extract the wiring afterwards. Therefore, there is a demand for underfill materials that are non-volatile and have flux functionality, and that can be used to form a film only in specific areas by patterning using photolithography, inkjet coating, or pattern application using a film sheet.

[0011] Therefore, the present invention aims to provide an underfill material that has the following functions to improve the efficiency of mass transfer and metal bonding of LED elements and to enable high-quality LED display elements: (1) Having flux function (2) Demonstrating sufficient adhesive strength at room temperature (3) Suppressing heat yellowing in high-temperature processes (4) Forming a film only in specific areas Another aim of the present invention is to provide an underfill film patterned on an array substrate using the underfill material, which enables the efficiency of mass transfer and metal bonding of LED elements.

[0012] Another object of the present invention is to provide a method for manufacturing an underfill film using the underfill material, which enables efficient mass transfer and metal bonding of an LED element.

[0013] The present invention aims to provide a micro LED display element having an underfill film that enables efficient mass transfer and metal bonding of the LED element.

[0014] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result have discovered the present invention. Specifically, the present invention relates to the following: 1. An adhesive composition containing the following components (A), (B), (C), and (D): Component (A): an alkali-soluble resin having a phenolic hydroxyl group, the polymer of which has a glass transition temperature (Tg) of 60°C or lower; Component (B): a compound having an isocyanurate skeleton; Component (C): an aliphatic or alicyclic epoxy compound; and Component (D): a solvent. 2. The adhesive composition according to 1, wherein the component (A) is a polymer containing a structural unit derived from a monomer (A2) that gives a homopolymer having a Tg of 0°C or lower. 3. The adhesive composition according to 2, wherein the component (A) is an acrylic polymer containing, as structural components, a monomer (A1) having a phenolic hydroxyl group and a polymerizable unsaturated group, and a structural unit derived from a monomer (A2) that gives a homopolymer having a Tg of 0°C or lower. 4. 4. The adhesive composition according to 3, wherein the monomer (A1) having a phenolic hydroxyl group and a polymerizable unsaturated group is selected from the group consisting of p-hydroxystyrene, m-hydroxystyrene, α-methyl-p-hydroxystyrene, and compounds represented by the following formula (1):

[0015] In the formula, P represents a (meth)acrylic group, a (meth)acrylamide group, an N-methyl(meth)acrylamide group, or a maleimide group; １ represents a single bond, or a linear, branched, or cyclic alkylene group having 1 to 12 carbon atoms, or a combination thereof; １ represents a single bond, —O—, —COO—, or —OCO—; d １represents a substituted or unsubstituted hydroxyphenyl group. 5. The adhesive composition according to 3 or 4, wherein the monomer (A2) that gives a homopolymer having a Tg of 0°C or less is a compound represented by the following formula (2):

[0016] In the formula, R ２ represents a hydrogen atom or a methyl group; ２ represents an oxygen atom or a sulfur atom, b ２ represents a linear, branched, or cyclic alkylene group having 2 to 20 carbon atoms, or a combination thereof, and —CH ２ - may be replaced by an oxygen atom, provided that they are not adjacent to each other. ２ represents a single bond, —O—, —COO—, or —OCO—; d ２ represents a hydrogen atom or a hydroxyl group. 6. The adhesive composition according to any one of 1 to 5, wherein the amount of component (B) is 20 to 100 parts by mass per 100 parts by mass of component (A). (Optimum amount of isocyanurate component) 7. The adhesive composition according to any one of 1 to 6, wherein the amount of component (C) is 10 to 100 parts by mass per 100 parts by mass of component (A). (Optimum amount of other epoxy component) 8. The adhesive composition according to any one of 1 to 7, further comprising a surfactant as component (E) in an amount of 0.01 to 1.0 part by mass per 100 parts by mass of component (A). 9. The adhesive composition according to any one of 1 to 8, further comprising an inorganic filler as component (F). 10. An adhesive sheet obtained by laminating both sides of the adhesive composition according to any one of 1 to 9 with a release material. 11. A cured film obtained by curing the adhesive composition according to any one of 1 to 9. 12. An LED display element having the cured film according to 11 as an underfill material.

[0017] The adhesive composition of the present invention has excellent flux properties, adhesion, and heat yellowing resistance, and has excellent film transparency, and can form an underfill material that enables efficient mass transfer and metal bonding of LED elements. Furthermore, in the form of a film sheet, it is possible to form an underfill film only on the required areas on an array substrate.

[0018] The adhesive composition of the present invention contains the following components (A), (B), (C), and (D): Component (A): a resin having a phenolic hydroxyl group, the polymer of which has a glass transition temperature (Tg) of 60°C or lower, Component (B): a compound having an isocyanurate skeleton, Component (C): an epoxy compound having an aliphatic or alicyclic skeleton, and Component (D): a solvent.

[0019] Each component will be described in detail below. <Component (A)> Component (A) is a resin having a phenolic hydroxyl group and a glass transition temperature (Tg) of the polymer of 60°C or lower, and specifically, is an alkali-soluble resin. The alkali-soluble resin is preferably an acrylic polymer.

[0020] In the present invention, the acrylic polymer refers to a polymer obtained using a monomer having a polymerizable unsaturated group, such as an acrylic acid ester, a methacrylic acid ester, styrene, or maleimide, i.e., a polymerizable group containing a carbon-carbon double bond in the structure.

[0021] The resin of component (A) is not particularly limited with respect to the type of main chain skeleton and side chains of the polymer constituting the acrylic polymer.

[0022] If the resin of component (A) has a weight-average molecular weight that is too low, less than 20,000, the sheet tends to be poorly releasable from the release material when produced, while if the weight-average molecular weight is too high, more than 150,000, the flexibility of the film is impaired and the resin repulsion during flip-chip bonding is impaired. From these viewpoints, the weight-average molecular weight of the resin is preferably in the range of 20,000 to 150,000, more preferably in the range of 30,000 to 100,000.

[0023] A simple method for synthesizing the resin of component (A) is to copolymerize a monomer mixture containing a monomer (A1) having a phenolic hydroxyl group and a polymerizable unsaturated group, and a monomer (A2) that provides a homopolymer with a Tg of 0° C. or less. Here, the homopolymer refers to a polymer of the monomer (A2) alone, and is a polymer having a weight-average molecular weight of 3,000 or more that can be obtained by polymerizing the monomer (A2) alone at a temperature of 50 to 110° C. in a solvent optionally containing a polymerization initiator or the like, or by polymerizing the monomer (A2) in the presence of a photoradical generator or the like by irradiating it with ultraviolet light.

[0024] The constituent monomers of component (A) will be described in detail below.

[0025] Monomer (A1) is a monomer having a phenolic hydroxyl group and a polymerizable unsaturated group, and is preferably at least one monomer selected from p-hydroxystyrene, m-hydroxystyrene, α-methyl-p-hydroxystyrene, and a compound represented by the following formula (1):

[0026] In formula (1), P represents a (meth)acrylic group, a (meth)acrylamide group, an N-methyl(meth)acrylamide group, or a maleimide group, and is preferably a (meth)acrylic group. １ represents a single bond, or a linear, branched, or cyclic alkylene group having 1 to 12 carbon atoms, or a combination thereof, and is preferably a single bond or a linear alkylene group having 1 to 6 carbon atoms. １ represents a single bond, —O—, —COO—, or —OCO—, and is preferably a single bond or —O—. １ represents a substituted or unsubstituted hydroxyphenyl group, preferably a p-hydroxyphenyl group. Substituents on the hydroxyphenyl group include halogen atoms, alkyl groups having 1 to 3 carbon atoms, alkenyl groups having 2 to 3 carbon atoms, alkoxy groups having 1 to 3 carbon atoms, fluoroalkyl groups having 1 to 3 carbon atoms, fluoroalkenyl groups having 2 to 3 carbon atoms, fluoroalkoxy groups having 1 to 3 carbon atoms, alkyloxycarbonyl groups having 2 to 3 carbon atoms, cyano groups, and nitro groups. The presence of these hydroxyphenyl groups allows component (A) to exhibit fluxing properties.

[0027] Examples of the monomer (A1) include p-hydroxystyrene, α-methyl-p-hydroxystyrene, N-(p-hydroxyphenyl)maleimide, N-(p-hydroxyphenyl)acrylamide, N-(p-hydroxyphenyl)methacrylamide, p-hydroxyphenyl acrylate, and p-hydroxyphenyl methacrylate, which can be used alone or in combination of two or more. Among these, monomers selected from p-hydroxyphenyl acrylate and p-hydroxyphenyl methacrylate are preferred.

[0028] Monomer (A2) is a monomer that gives a homopolymer having a Tg of 0° C. or less, and is preferably a compound represented by the following formula (2).

[0029] In formula (2), R ２ represents a hydrogen atom or a methyl group. ２ represents an oxygen atom or a sulfur atom, and is preferably an oxygen atom. ２ represents a linear, branched, or cyclic alkylene group having 2 to 20 carbon atoms, or a combination thereof, preferably a linear, branched, or cyclic alkylene group having 2 to 12 carbon atoms, or a combination thereof, more preferably a linear or branched alkylene group having 2 to 12 carbon atoms. ２ -CH in the alkylene group ２ - may be replaced by an oxygen atom, provided that they are not adjacent to each other. ２ represents a single bond, —O—, —COO—, or —OCO—, and preferably represents a single bond or —O—. ２ represents a hydrogen atom or a hydroxyl group.

[0030] Specific examples of the monomer (A2) include ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, tert-butyl acrylate, n-pentyl acrylate, n-hexyl acrylate, n-hexyl methacrylate, n-heptyl acrylate, n-heptyl methacrylate, n-octyl acrylate, n-octyl methacrylate, nonyl acrylate, nonyl methacrylate, isononyl acrylate, isononyl methacrylate, lauryl acrylate, lauryl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, 2-hydroxyethyl acrylate, 3-hydroxypropyl ... Examples of the acrylate include propyl acrylate, 4-hydroxybutyl acrylate, ethyl carbitol acrylate, glycidyl acrylate, methoxytriethylene glycol acrylate, methoxytriethylene glycol methacrylate, 2-methoxyethyl acrylate, 2-methoxyethyl methacrylate, 2-ethoxyethyl acrylate, 2-ethoxyethyl methacrylate, tetrahydrofurfuryl acrylate, 3-methoxybutyl acrylate, 3-methoxybutyl methacrylate, diethylene glycol monoacrylate, and diethylene glycol monomethacrylate, which may be used alone or in combination of two or more, but are not limited to these.

[0031] From the viewpoint of suitably achieving the effects of the present invention, the constituent units derived from monomer (A1) in component (A) preferably account for 10 to 50 mass% of the total of the constituent units derived from monomer (A1) and the constituent units derived from monomer (A2), and the constituent units derived from monomer (A2) in component (A) preferably account for 50 to 90 mass% of the total of the constituent units derived from monomer (A1) and the constituent units derived from monomer (A2).

[0032] In the present invention, when obtaining the acrylic polymer of component (A), other monomers copolymerizable with the above-mentioned monomers (A1) and (A2) can be used in combination. Specific examples of the other monomers include acrylic acid ester compounds, methacrylic acid ester compounds, maleimides, acrylamide compounds, acrylonitrile, styrene compounds, and vinyl compounds. Specific examples of the other monomers are listed below, but are not limited to these.

[0033] Examples of the acrylic acid ester compound include methyl acrylate, cyclohexyl acrylate, isobornyl acrylate, 2-methyl-2-adamantyl acrylate, anthryl acrylate, anthrylmethyl acrylate, 2,2,2-trifluoroethyl acrylate, 2-aminoethyl acrylate, 2-propyl-2-adamantyl acrylate, caprolactone 2-(acryloyloxy)ethyl ester, and poly(ethylene glycol) ethyl ether acrylate.

[0034] Examples of the methacrylic acid ester compound include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, tert-butyl methacrylate, n-pentyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, 2-methyl-2-adamantyl methacrylate, 2-hydroxyethyl methacrylate, glycidyl methacrylate, tetrahydrofurfuryl methacrylate, anthryl methacrylate, anthrylmethyl methacrylate, 2,2,2-trifluoroethyl methacrylate, 2-aminomethyl methacrylate, γ-butyrolactone methacrylate, 2-propyl-2-adamantyl methacrylate, caprolactone 2-(methacryloyloxy)ethyl ester, and poly(ethylene glycol) ethyl ether methacrylate.

[0035] Examples of the acrylamide compound include N-methylacrylamide, N-methylmethacrylamide, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N-methoxymethylacrylamide, N-methoxymethylmethacrylamide, N-butoxymethylacrylamide, and N-butoxymethylmethacrylamide.

[0036] Examples of the vinyl compound include methyl vinyl ether, benzyl vinyl ether, cyclohexyl vinyl ether, vinyl naphthalene, vinyl anthracene, vinyl carbazole, allyl glycidyl ether, 3-ethenyl-7-oxabicyclo[4.1.0]heptane, 1,2-epoxy-5-hexene, and 1,7-octadiene monoepoxide.

[0037] Examples of the styrene compound include styrenes having no hydroxy group, such as styrene, α-methylstyrene, chlorostyrene, and bromostyrene.

[0038] The method for obtaining the alkali-soluble resin used in the present invention is not particularly limited, but it can be obtained, for example, by polymerizing the monomer (A1) and the monomer (A2), the other monomers described above, and optionally a polymerization initiator, etc., in a solvent at a temperature of 50 to 110°C. The solvent used in this case is not particularly limited as long as it dissolves the monomers constituting the resin and the resin. Specific examples include the solvents described below in the section on (D) solvent.

[0039] The resin thus obtained (hereinafter also referred to as the specific copolymer) is usually in the form of a solution dissolved in a solvent.

[0040] In addition, the solution of the specific copolymer obtained as described above can be reprecipitated by adding diethyl ether, water, or the like under stirring, and the resulting precipitate can be filtered and washed, and then dried at room temperature or by heating under normal or reduced pressure to obtain a powder of the specific copolymer.By such an operation, the polymerization initiator and unreacted monomers coexisting with the specific copolymer can be removed, and as a result, a powder of the purified specific copolymer can be obtained.If the specific copolymer cannot be sufficiently purified by a single operation, the obtained powder can be redissolved in a solvent and the above operation can be repeated.

[0041] In the present invention, the powder of the specific copolymer may be used as it is, or the powder may be redissolved in the solvent (D) described below and used in the form of a solution.

[0042] In the present invention, the resin of component (A) may be a mixture of multiple types of specific copolymers.

[0043] <Component (B)> The component (B) of the present invention is a compound having an isocyanurate skeleton. By including an isocyanurate skeleton in the composition, high adhesion to metals can be achieved at room temperature. From the viewpoint of curability, a compound having two or more polymerizable unsaturated double bonds in the isocyanurate skeleton is preferred. Preferred skeletons of the component (B) are exemplified by formula (4A) and formula (4B) (also simply referred to as formula (4)).

[0044]

[0045]

[0046] The content of the component (B) in the composition of the present invention is preferably 20 to 100 parts by mass, and more preferably 30 to 90 parts by mass, per 100 parts by mass of the component (A).

[0047] <Component (C)> Component (C) is an epoxy compound having an aliphatic or alicyclic skeleton. If the epoxy compound serving as the crosslinking component in the composition has an aromatic or aminoglycidyl group, yellowing of the film is easily caused by high-temperature heating, and therefore an aliphatic or alicyclic skeleton is preferred.

[0048] A preferred skeleton of the component (C) is represented by formula (5) or formula (6).

[0049] (In formula (5), k is an integer of 2 to 10, m is an integer of 0 to 4, and X ５ represents a k-valent organic group that does not contain an aromatic ring. Multiple m's may be the same or different.

[0050] (In formula (6), k is an integer of 2 to 10, and X ６ represents a k-valent organic group that does not contain an aromatic ring.

[0051] Specific examples of the compound having a cycloalkene oxide structure represented by formula (5) include Epolead GT-401, GT-403, GT-301, GT-302, PB4700, Celloxide 2021, Celloxide 2081, and Celloxide 3000 (trade names manufactured by Daicel Corporation), Epocalic DE-102, and DE-103 (all manufactured by ENEOS Corporation), and the like.

[0052] Specific examples of the compound represented by formula (6) include an alicyclic epoxy compound EHPE3150 (trade name, manufactured by Daicel Corporation), hydrogenated glycidyl ether epoxy compounds Denacol EX-252 (trade name, manufactured by Nagase Chemtex Corporation), ST-3000, ST-4000D (trade names, manufactured by Nippon Steel Chemical & Material Co., Ltd.), EPOTEC YDH184, EPOTEC YDH3000 (trade names, manufactured by Tomoe Engineering Co., Ltd.), Rikaresin HBE-100 (trade name, manufactured by New Japan Chemical Co., Ltd.), aliphatic ester structure EPOTEC RD107, RD111, 114, 130, 113, 129 (trade names, manufactured by Tomoe Engineering Co., Ltd.), and Showfree PETG (trade name, manufactured by Resonac Corporation).

[0053] The content of the component (C) in the composition of the present invention is preferably 10 to 100 parts by mass, and more preferably 30 to 90 parts by mass, per 100 parts by mass of the component (A).

[0054] <Component (D)> The solvent (D) used in the present invention dissolves the components (A), (B), and (C), and also dissolves various components that are added as desired. There are no particular limitations on the type or structure of the solvent, as long as it is a solvent that has such dissolving ability.

[0055] Examples of such solvents (D) include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, methyl cellosolve acetate, ethyl cellosolve acetate, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, propylene glycol, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, propylene glycol propyl ether acetate, toluene, xylene, methyl ethyl ketone, cyclopentanone, cyclohexanone, 2-butanone, 3-methyl-2-pentanone, 2- Examples of the solvent include pentanone, 2-heptanone, γ-butyrolactone, ethyl 2-hydroxypropionate, ethyl 2-hydroxy-2-methylpropionate, ethyl ethoxyacetate, ethyl hydroxyacetate, methyl 2-hydroxy-3-methylbutanoate, methyl 3-methoxypropionate, ethyl 3-methoxypropionate, ethyl 3-ethoxypropionate, methyl 3-ethoxypropionate, methyl pyruvate, ethyl pyruvate, ethyl acetate, butyl acetate, ethyl lactate, butyl lactate, N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone.

[0056] Among these (D) solvents, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, 2-heptanone, propylene glycol propyl ether, propylene glycol propyl ether acetate, ethyl lactate, butyl lactate, and the like are preferred from the viewpoints of good film-forming properties and high safety.

[0057] Furthermore, for the purpose of improving the wettability to the substrate, adjusting the surface tension of the solvent, adjusting the polarity, adjusting the boiling point, etc., other solvents may be mixed in an amount of 1 to 90% by mass, preferably 1 to 50% by mass, of the total solvents used in the varnish.

[0058] Examples of such solvents include, but are not limited to, methanol, ethanol, isopropyl alcohol, diisoamyl ether, methyl salicylate, etc. These solvents can be used singly or in combination of two or more.

[0059] <Component (E)> The component (E) is a surfactant. The composition of the present invention may further contain a surfactant for the purpose of improving the coatability of the composition, as long as the effect of the present invention is not impaired.

[0060] The surfactant of component (E) is not particularly limited, but examples thereof include fluorine-based surfactants, silicone-based surfactants, and nonionic surfactants. Commercially available surfactants of this type are available from manufacturers such as 3M Japan Ltd., DIC Corporation, and AGC Seimi Chemical Co., Ltd. These commercially available products are convenient because they are readily available. Specific examples include Polyfox PF-136A, 151, 156A, 154N, 159, 636, 6320, 656, and 6520 (manufactured by Omnova), Megafac R30, R08, R40, R41, R43, F251, F477, F552, F553, F554, F555, F556, F557, F558, F559, F560, and F56. 1, F562, F563, F565, F567, F570 (manufactured by DIC Corporation), FC4430, FC4432 (manufactured by 3M Japan Ltd.), Asahiguard AG710, Surflon S-386, S-611, S-651 (manufactured by AGC Seimi Chemical Co., Ltd.), Ftergent FTX-218, DFX-18, 220P, 251, 212M, 215M fluorine-based surfactants such as BYK-300, 302, 306, 307, 310, 313, 315, 320, 322, 323, 325, 330, 331, 333, 342, 345, 346, 347, 348, 349, 370, 377, 378, 3455 (manufactured by BYK Japan Co., Ltd.), SH3746, SH3749, SH377 Examples of silicone surfactants include silicone surfactants such as SH8400, SH8410, SH8700, and SF8428 (manufactured by Dow Corning Toray Silicone Co., Ltd.), and KF-351, KF-352, KF-353, KF-354L, KF-355A, KF-615A, KF-945, KF-618, KF-6011, and KF-6015 (manufactured by Shin-Etsu Chemical Co., Ltd.).

[0061] The surfactant of component (E) can be used alone or in combination of two or more.

[0062] When a surfactant is used, its content is usually 0.01 to 1.0 part by mass, and preferably 0.02 to 0.8 part by mass, based on 100 parts by mass of component (A).

[0063] <Component (F)> The component (F) is an inorganic filler. The composition of the present invention may further contain an inorganic filler for the purpose of improving the transparency of the film and the hardness of the cured film, as long as the effects of the present invention are not impaired.

[0064] The surfactant of component (F) is not particularly limited, but examples thereof include sols of silica, aluminum nitride, boron nitride, zirconia, alumina, etc., each having a particle diameter of 1 nm or more and 700 nm or less. The particles contained in the inorganic filler may be surface-treated with a silane coupling agent or the like.

[0065] When an inorganic filler is used, the content thereof is usually 10 to 90 parts by mass, and preferably 20 to 80 parts by mass, per 100 parts by mass of the total solid content.

[0066] <Adhesive Sheet> The adhesive composition of the present invention can be applied onto a release substrate (for example, a PET film coated with a silicone release layer) used as a base film by bar coating, slit coating, inkjet coating, or the like, and then pre-dried in an oven or the like to form a coating film.

[0067] The conditions for this heat treatment are, for example, a heating temperature and a heating time selected appropriately from the ranges of 70 to 160°C and 0.3 to 60 minutes, respectively. The heating temperature and heating time are preferably 80 to 140°C and 0.5 to 10 minutes.

[0068] Thereafter, a release material for the protective film is laminated onto the coating film of the composition to obtain an adhesive sheet. Using a manual or automatic laminating roller, the coating film and the protective film are pressed together in a certain direction so as to prevent air bubbles from being trapped between them, thereby obtaining an adhesive sheet.

[0069] By processing the adhesive sheet to a desired size, it is possible to form a film of the adhesive composition only in the required locations on the array substrate. After processing to a desired size, the protective film is peeled off, the peeled surface is attached to the desired location, and the base film is peeled off, thereby transferring the adhesive composition film onto the substrate. Transferring under pressure is also effective in increasing the adhesion between the composition film and the substrate.

[0070] In order to successfully peel the protective film from the coating surface, it is necessary that the peel strength of the protective film is small and that of the base film is large. The peel strength of the protective film is preferably 80 N / 25 mm or less, and the peel strength of the base film is preferably 160 N / 25 mm or more.

[0071] <Cured Film> Subsequently, the pattern-forming film is post-baked for thermal curing, specifically by heating using a hot plate, an oven, or the like, to obtain a film having excellent heat resistance, transparency, flattening properties, low water absorption, chemical resistance, and the like, and having a good pattern.

[0072] Post-baking is generally performed at a heating temperature selected from the range of 140 to 270° C. for 5 to 30 minutes on a hot plate or for 30 to 90 minutes in an oven.

[0073] Thus, by such post-baking, it is possible to obtain a cured film having the desired good pattern shape.

[0074] The film obtained from the adhesive composition of the present invention has flux and adhesive properties, and can be processed as desired to form a film only in required areas on an array substrate.

[0075] After mass-transferring the LED elements onto an array substrate with an adhesive composition film, the array electrodes and LED element electrodes are bonded by thermocompression bonding using a flip-chip bonder (the heating temperature is usually in the range of 250 to 350°C to melt the solder electrodes). During thermocompression bonding, the composition film is in an uncured state, so it melts when heated, and when pressure is applied, the composition film is expelled from between the array electrodes and the LED element electrodes, so it does not interfere with the bonding between the electrodes. The composition film expelled around the electrodes is then thermally cured, and functions as an underfill material that protects the area around the electrodes from air and moisture.

[0076] The adhesive composition of the present invention is highly transparent and does not easily turn yellow even when subjected to high-temperature processes such as flip-chip bonding, and therefore does not easily impair the color purity of LED elements.

[0077] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The abbreviations of the compounds used, the release substrates, and the methods for measuring the various physical properties are as follows.

[0078] (Monomers) HQMA: p-hydroxyphenyl methacrylate HEMA: 2-hydroxyethyl methacrylate BA: n-butyl acrylate (Radical polymerization initiators) AIBN: α,α'-azobisisobutyronitrile (Isocyanurate compound) I1: NK Ester A-9300 (Shin-Nakamura Chemical Co., Ltd.) I2: TEPIC-VL (Nissan Chemical Industries, Ltd.) (Epoxy compounds) E1: Epocalic DE-102 (ENEOS Corporation) E2: EHPE 3150 (Daicel Corporation) E3: jER152 (Mitsubishi Chemical Corporation) E4: Epolead GT-401 (butanetetracarboxylic acid tetra(3,4-epoxycyclohexylmethyl) modified ε-caprolactone, Daicel Corporation) E5: Celloxide 2021P (manufactured by Daicel Corporation) E6: Denacol EX-851 (manufactured by Nagase ChemteX Corporation) E7: Showfree BATG (manufactured by Resonac Corporation) (inorganic filler) F1: Organosilica sol MEK-AC-5140Z (manufactured by Nissan Chemical Industries, Ltd.) (solvent) PGME: Propylene glycol monomethyl ether IPA: Isopropyl alcohol (release substrate) Base film: PET film coated with a silicone release layer and having a peel strength of 380 N / 25 mm (manufactured by Nippa Corporation) Protective film: PET film coated with a silicone release layer and having a peel strength of 40 N / 25 mm (manufactured by Nippa Corporation)

[0079] <Measurement of Molecular Weight> The molecular weight of the polymer was measured using a room temperature gel permeation chromatography (GPC) apparatus (GPC-101) (manufactured by Showa Denko K.K.) and a column (KD-803, KD-805 in series) (manufactured by Showa Denko K.K.) as follows: Column temperature: 50°C Eluent: N,N-dimethylformamide (with lithium bromide monohydrate (LiBr.H) as an additive). ２o-Phosphoric acid) at 30 mmol / L, anhydrous crystalline o-phosphate (o-phosphoric acid) at 30 mmol / L, tetrahydrofuran (THF) at 10 mL / L) Flow rate: 1.0 ml / min Standard samples for preparing a calibration curve: TSK standard polyethylene oxide (molecular weight: approximately 900,000, 150,000, 100,000, and 30,000) (manufactured by Tosoh Corporation) and polyethylene glycol (molecular weight: approximately 12,000, 4,000, and 1,000) (manufactured by Polymer Laboratory Co., Ltd.).

[0080] <Measurement of Glass Transition Temperature (Tg)> The Tg of the polymer obtained in the synthesis examples was measured using a differential scanning calorimetry (DSC) DSC1 (manufactured by METTLER TOREDO) under the following conditions: Heating rate: 10°C / min, Measurement temperature: -20°C to 200°C, Number of measurements: 2. Tg was calculated from the result of the second heating run.

[0081] <Synthesis of Acrylic Polymer> (Synthesis Example 1) HQMA (6.0 g), HEMA (4.0 g), and BA (10.0 g) were used as monomer components constituting the acrylic polymer, and AIBN (0.2 g) was used as a radical polymerization initiator. These were polymerized in a solvent PGME (47.1 g) at a temperature of 60 ° C. to obtain a solution P1 (acrylic polymer concentration: 30.0 mass%) of an acrylic polymer component having Mn (number average molecular weight): 24,700 and Mw (weight average molecular weight): 111,900. This solution P1 was applied to a 5 cm × 5 cm glass substrate using a spin coater, and then prebaked on a hot plate at a temperature of 100 ° C. for 120 seconds to obtain a dried film of the acrylic polymer. The Tg of the obtained acrylic polymer was 31 ° C. (Synthesis Example 2) HQMA (10.0 g) and BA (10.0 g) were used as monomer components constituting the acrylic polymer, and AIBN (0.06 g) was used as a radical polymerization initiator. These were polymerized in PGME (46.8 g) as a solvent at 60° C. to obtain acrylic polymer P2 (acrylic polymer concentration: 30.0% by mass) having a molecular weight and Tg shown in Table 1. (Synthesis Example 3) HQMA (14.0 g) and BA (6.0 g) were used as monomer components constituting the acrylic polymer, and AIBN (0.2 g) was used as a radical polymerization initiator. These were polymerized in PGME (37.5 g) as a solvent at 60° C. to obtain acrylic polymer P3 (acrylic polymer concentration: 35.0% by mass) having a molecular weight and Tg shown in Table 1.

[0082]

[0083] <Preparation of Adhesive Composition> (Example 1-1) As a resin solution, 0.375 g of an isocyanurate compound I1, 0.375 g of an epoxy compound E1, and solvents PGME (2.683 g) and IPA (2.400 g) were added to 4.167 g of the acrylic polymer solution (P1) obtained in Synthesis Example 1 above, and the mixture was stirred at room temperature for 2 hours to prepare Adhesive Composition V1 having the composition shown in Table 2.

[0084] (Examples 1-2 to 1-5) and (Comparative Examples 1-1 to 1-4) The types and amounts of resin solution, isocyanurate compound, epoxy compound, and solvent were changed as shown in Table 2 and added, and then stirred at room temperature for 2 hours to prepare positive photosensitive adhesive compositions V2 to V5 and RV1 to RV4 having the compositions shown in Table 2.

[0085] (Examples 1-6) To the acrylic polymer resin solution (P2) (2.857 g), an isocyanurate compound I2 (0.623 g), an epoxy compound E2 (0.623 g), an inorganic filler F1 (2.144 g), and a solvent PGME (3.752 g) were added, and the mixture was stirred at room temperature for 2 hours to prepare an adhesive composition V6 having the composition shown in Table 2.

[0086]

[0087] Example 2-1 <Adhesion Strength Evaluation> The adhesive composition V1 prepared in Example 1-1 was applied to a 5 cm x 5 cm glass substrate using a spin coater, and then prebaked on a hot plate at 100°C for 120 seconds to form a prebaked film with a thickness of 3 μm. The peel strength of the coating surface was then measured at room temperature (23°C) using a texture analyzer manufactured by Stable Micro Systems, using a probe ball (diameter: 25 mm, material: SUS), a compression speed of 1 mm / sec, a tensile speed of 1 mm / sec, a compression load of 200 g, and a compression hold time of 2 sec. A peel strength of 1.0 g or more was considered to indicate good adhesion, and a peel strength of less than 1.0 g was considered to indicate poor adhesion. The results are shown in Table 3.

[0088] <Transmittance Evaluation> The adhesive composition V1 prepared in Example 1-1 was applied to a 4 cm x 4 cm quartz substrate using a spin coater, and then prebaked on a hot plate at 100°C for 120 seconds to form a prebaked film with a thickness of 3 μm. This prebaked film was heated on a hot plate at 300°C for 60 seconds, simulating the heat applied to the organic film during flip-chip bonding. This was then postbaked on a hot plate at 230°C for 30 minutes to form a cured film. The transmittance of the resulting cured film was measured, and a transmittance of 95% or more in the visible range (wavelength 400 nm to 800 nm) was evaluated as good, and a transmittance of less than 95% was evaluated as poor. The results are shown in Table 3.

[0089] (Examples 2-2 to 2-6 and Comparative Examples 2-1 to 2-4) Using adhesive compositions V2 to V6 and RV1 to RV4 prepared in Examples 1-2 to 2-6 and Comparative Examples 1-1 to 1-4, the adhesion and transparency were evaluated in the same manner as in Example 2-1. Note that the pre-baking conditions were changed as appropriate to a temperature of 100 to 140°C and a time of 2 to 10 minutes.

[0090] The results are shown in Table 3.

[0091]

[0092] As shown in Table 3, all of the adhesive compositions of the Examples exhibited good adhesion and transparency. In contrast, when an adhesive composition using an acrylic polymer with a glass transition temperature (Tg) of 100°C or higher was used (Comparative Example 2-3), or when no isocyanurate compound was used (Comparative Example 2-2), the adhesiveness was insufficient. Furthermore, when the epoxy compound used had an aromatic ring (Comparative Examples 2-1 and 2-4), the transparency was insufficient.

[0093] (Example 3-1) <Preparation and Evaluation of Film Sheet> The adhesive composition V1 prepared in Example 1-1 was applied to an A4-sized base film using a bar coater, and then prebaked in an oven at a temperature of 100°C for 120 seconds to form a prebaked film with a thickness of 3 μm. A protective film was then laminated onto the prebaked film using a roller to prepare an adhesive sheet S1. Thereafter, the peelability of the protective film was evaluated. After peeling the protective film, if there was no film remaining on the protective film side, it was judged as good, and if a portion of the adhesive composition remained on the protective film side, it was judged as bad. Next, the transferability from the base film to the substrate was evaluated. A glass substrate measuring 5 cm x 5 cm and 1 mm thick was used as the substrate. After peeling the base film, if there was no film remaining on the base film side and the adhesive sheet was transferred to the substrate without wrinkles, it was judged as good. If a portion of the adhesive composition remained on the base film side or wrinkles occurred in the adhesive sheet after transfer, it was judged as bad. Finally, the peel strength of the coating surface was measured at room temperature (23°C) using a texture analyzer manufactured by Stable Micro Systems, using a probe ball (diameter: 25 mm, material: SUS), a compression speed of 1 mm / sec, a tensile speed of 1 mm / sec, a compression load of 200 g, and a compression hold time of 2 sec. A peel strength of 1.0 g or more was judged to be good adhesion, and a peel strength of less than 1.0 g was judged to be poor adhesion. The results are shown in Table 4.

[0094] (Example 3-2) Using the adhesive composition V2 prepared in Example 1-2, an adhesive sheet S2 was produced in the same manner as in Example 3-1, and the peelability of the protective film, the transferability to the substrate, and the adhesiveness of the sheet were evaluated. The results are shown in Table 4.

[0095]

[0096] (Examples 4-1 and 4-2) <Flip Chip Bonding Test> As a mounting sample, a TEG (Test Element Group) chip (5.1 mm × 5.1 mm × 700 μm thick) having 1,700 electrodes with an electrode area of ​​20 μm × 20 μm and an electrode height of 5.5 μm (SnAg solder height: 2.3 μm, copper post electrode height: 3.2 μm) and a TEG substrate (15 mm × 15 mm × 700 μm thick) on which copper electrodes were wired in a daisy chain with the electrodes of the TEG chip were prepared. The adhesive sheets prepared in Examples 3-1 and 3-2 were transferred onto the TEG substrate, respectively, to form an underfill film. Next, using a Panasonic Corporation flip chip bonder, the TEG chip was flip chip bonded to the TEG substrate with the underfill film at a stage temperature of 60°C, a head temperature of 370°C for 60 seconds, and a head pressure of 150 N. Thereafter, post-baking (post-curing) was performed at 230°C for 30 minutes to obtain a bonded body. The obtained bonded body was evaluated for the presence or absence of peeling of the TEG chip (no peeling: ◯, peeling: ×) and the electrical resistance value (less than 100Ω: ◯, 100Ω or more: ×). The results are shown in Table 5.

[0097] (Comparative Example 4-1) A bonded assembly was formed in the same manner as in Example 4-1, except that instead of using an adhesive sheet as an underfill film, the TEG chip and TEG substrate were washed with a 5% by mass aqueous solution of sulfuric acid before flip-chip bonding to remove the surface oxide film, and the presence or absence of peeling of the TEG chip was confirmed and the conduction resistance value was measured. The results are shown in Table 5.

[0098]

[0099] As shown in Table 5, the TEG assembly using the adhesive sheet of the example as the underfill film did not experience peeling of the TEG chip and had good electrical resistance values. In contrast, when no underfill film was used, peeling of the TEG chip increased significantly, and it was not possible to measure the resistance value reproducibly (Comparative Example 4-1).

Claims

1. An adhesive composition comprising the following components (A), (B), (C), and (D): Component (A): an alkali-soluble resin having a phenolic hydroxyl group and a glass transition temperature (Tg) of the polymer of 60° C. or lower Component (B): Compound having an isocyanurate skeleton Component (C): Aliphatic or alicyclic epoxy compound Component (D): Solvent

2. 2. The adhesive composition according to claim 1, wherein the component (A) is a polymer containing a structural unit derived from a monomer (A2) that gives a homopolymer having a Tg of 0° C. or lower.

3. 3. The adhesive composition according to claim 2, wherein the component (A) is an acrylic polymer containing, as constituent components, constituent units derived from a monomer (A1) having a phenolic hydroxyl group and a polymerizable unsaturated group, and a monomer (A2) having a homopolymer Tg of 0°C or less.

4. The adhesive composition according to claim 3, wherein the monomer (A1) having a phenolic hydroxyl group and a polymerizable unsaturated group is selected from the group consisting of p-hydroxystyrene, m-hydroxystyrene, α-methyl-p-hydroxystyrene, and a compound represented by the following formula (1): 【Chemistry 1】 In formula (1), P represents a (meth)acrylic group, a (meth)acrylamide group, an N-methyl(meth)acrylamide group, or a maleimide group; b １ represents a single bond, or a linear, branched, or cyclic alkylene group having 1 to 12 carbon atoms, or a combination thereof; １ represents a single bond, -O-, -COO-, or -OCO-; d １ represents a substituted or unsubstituted hydroxyphenyl group.

5. The adhesive composition according to claim 3 , wherein the monomer (A2) that gives a homopolymer having a Tg of 0° C. or less is a compound represented by the following formula (2): 【Chemistry 2】 (In formula (2), R ２ represents a hydrogen atom or a methyl group; ２ represents an oxygen atom or a sulfur atom, b ２ represents a linear, branched, or cyclic alkylene group having 2 to 20 carbon atoms, or a combination thereof, and —CH ２ - may be replaced with an oxygen atom, provided that they are not adjacent to each other. ２ represents a single bond, -O-, -COO-, or -OCO-; d ２ represents a hydrogen atom or a hydroxyl group.)

6. 6. The adhesive composition according to claim 1, wherein the amount of the component (B) is 20 to 100 parts by mass per 100 parts by mass of the component (A).

7. 6. The adhesive composition according to claim 1, wherein the amount of the component (C) is 10 to 100 parts by mass per 100 parts by mass of the component (A).

8. The adhesive composition according to any one of claims 1 to 5, further comprising, as component (E), 0.01 to 1.0 part by mass of a surfactant per 100 parts by mass of component (A).

9. The adhesive composition according to any one of claims 1 to 5, further comprising an inorganic filler as a component (F).

10. 6. An adhesive sheet comprising the adhesive composition according to claim 1 laminated on both sides with a release substrate.

11. A cured film obtained by curing the adhesive composition according to any one of claims 1 to 5.

12. An LED display element comprising the cured film according to claim 11 as an underfill material.

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