JP7674706B2 - Underfill material for micro LED display element, underfill film, method for producing underfill film, and micro LED display element - Google Patents

Description

The present invention relates to an underfill material for micro LED display elements, 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 micro LED display elements, 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.

Currently, liquid crystal display elements (LCD) and organic light-emitting diode display elements (OLED) are mainly used in flat panel displays used in mobile phones, monitors, and TVs. LCDs have already been fully mass-produced, and are inexpensive and can be made large. However, they are inferior in form factor and flexibility because they require the use of a backlight for display. OLEDs are also excellent in flexibility, but they have the problem that their lifespan is shortened when the brightness of the display element is increased. As a display element that can solve these shortcomings, micro LED display elements have been developed in recent years, which display by arranging inorganic light-emitting diodes on each pixel of an array substrate. Micro LED display elements use inorganic light-emitting diodes of micrometer size as the light source, so they can achieve higher brightness than LCDs and OLEDs, have high color purity, and have a long lifespan. In addition, because LEDs are arranged for each pixel, each pixel can be made independent, and they are also excellent in flexibility.

The LED elements that are the light source are supplied as small pieces by epitaxially growing a semiconductor layer on a sapphire substrate, forming electrodes, and then dicing. Micro LED display elements require LED elements manufactured in this way to be arranged on an array substrate with high precision. Until now, the pick-and-place method, in which each LED element is installed one by one, has been considered as a method for arranging LED elements on an array substrate. However, this method is not suitable for mass production because it takes a huge amount of time to install the LEDs.

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) and mass-transferred to an array substrate, after which the LED elements are bonded to the electrodes of the array substrate by thermocompression bonding using a bonding head or by metal bonding using 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 at once and bonded to the array substrate.

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

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 adhesion between the array substrate and the LED elements and between the stamp and the LED elements, so an adhesive component is required on the array substrate. The adhesive component often serves to bond the LED elements to the substrate electrodes, so solder paste or conductive paste is usually used. However, in this case, spaces are created around the electrodes of the LED elements, which can cause problems such as peeling and corrosion of the electrodes due to external stresses applied to the panel, such as vibrations, or moisture.

Among the adhesive components, the non-conductive paste and film are expected to alleviate the problems described above by being expelled from between the LED electrode and the array substrate electrode and remaining as a permanent film around the electrodes 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 electrodes from moisture and external stress.

Another issue specific to micro LED display elements is the prevention of heat-resistant yellowing of the components surrounding the LED element. Since light emitted from the LED element spreads in all directions, not just perpendicular to the substrate, the transparency of the surrounding components is required 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. For this reason, the components surrounding the LED element are required to be heat-resistant and yellowing-resistant in order to maintain high transparency even after this high-temperature process.

Next, a common issue for semiconductor mounted devices, but not unique to micro LED display elements, is the flux treatment process for removing the oxide film on the electrodes. In micro LED display elements, if an oxide film is formed on the electrodes of the array substrate or LED elements, metal bonding is not possible and poor conductivity occurs. Normally, 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, there is an issue of electrode corrosion.

In addition, once a functional film is formed over the entire surface of an array substrate or wafer, there is the issue that it can be difficult to remove the wiring thereafter. Therefore, there is a demand for an underfill material that is non-volatile and has flux functionality, and that can form a film only in specific areas using methods such as photolithography patterning, inkjet coating, and pattern application using a film sheet.

Therefore, an object of the present invention is to provide an underfill material having the following functions in order 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) exhibiting sufficient adhesive strength at room temperature; (3) suppressing heat yellowing in high-temperature processes; and (4) forming a film only in a specific area. Another object of the present invention is to provide an underfill film patterned on an array substrate using the underfill material, which enables efficient mass transfer and metal bonding of LED elements.

Furthermore, the present invention aims to provide a method for manufacturing an underfill film using the underfill material, which enables efficient mass transfer and metal bonding of LED elements.

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.

The present inventors have conducted intensive research to solve the above problems and have come up with the present invention.
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): a compound having an isocyanurate skeleton, Component (C): an aliphatic or alicyclic epoxy compound, 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) having a homopolymer Tg of 0° C. or lower.
3. The adhesive composition according to 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 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):

式中、Ｐは（メタ）アクリル基、（メタ）アクリルアミド基、Ｎ－メチル（メタ）アクリルアミド基、またはマレイミド基を表し、ｂ_１は単結合、または炭素数１～１２の直鎖、分岐、もしくは環状、およびその組み合わせからなるアルキレン基を表し、ｃ_１は単結合、－Ｏ－、－ＣＯＯ－、または－ＯＣＯ－を表し、ｄ_１は置換または非置換のヒドロキシフェニル基を表す。
５．前記単独重合体のＴｇが０℃以下となるモノマー（Ａ２）が、下記式（２）で表される化合物である３に記載の接着性組成物。

In the formula, 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; c ₁ represents a single bond, -O-, -COO-, or -OCO-; and d ₁ represents a substituted or unsubstituted hydroxyphenyl group.
5. The adhesive composition according to 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):

式中、Ｒ_２は水素原子またはメチル基を表し、ａ_２は酸素原子または硫黄原子を表し、ｂ_２は炭素数２～２０の直鎖、分岐、もしくは環状、およびその組み合わせからなるアルキレン基を表し、該アルキレン基中の－ＣＨ_２－は、互いに隣り合わないことを条件に、酸素原子に置き換えられても良い。ｃ_２は単結合、－Ｏ－、－ＣＯＯ－、または－ＯＣＯ－を表し、ｄ_２は水素原子または水酸基を表す。
６．（Ａ）成分の１００質量部に対して、（Ｂ）成分が２０～１００質量部である１～５のいずれかに記載の接着性組成物。（イソシアヌレート成分の最適量）
７．（Ａ）成分の１００質量部に対して、（Ｃ）成分が１０～１００質量部である１～５のいずれかに記載の接着性組成物。（その他エポキシ成分の最適量）
８．（Ｅ）成分として、界面活性剤を更に（Ａ）成分の１００質量部に対して０．０１～１．０質量部含有する、１～５のいずれかに記載の接着性組成物。
９．（Ｆ）成分として、無機フィラーをさらに含む、１～５のいずれかに記載の接着性組成物。
１０．１～５のいずれかに記載の接着性組成物の両面を剥離基材でラミネートした接着性シート。
１１．１～５のいずれかに記載の接着性組成物を硬化してなる硬化膜。
１２．１１に記載の硬化膜をアンダーフィル材として有するＬＥＤ表示素子。

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

The adhesive composition of the present invention has excellent flux properties, adhesion, and heat yellowing resistance, and has excellent film transparency, making it possible to 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 necessary parts of the array substrate.

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 and 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 Component (D): a solvent

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

In the present invention, 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 that contains a carbon-carbon double bond in its structure.

The resin of component (A) is not particularly limited in terms of the main chain skeleton and type of side chain of the polymer constituting the acrylic polymer.

If the resin of component (A) has a weight average molecular weight less than 20,000, the peelability from the release substrate when the sheet is produced is likely to deteriorate, while if the weight average molecular weight is more than 150,000, the flexibility of the film is impaired and the resin repulsion during flip chip bonding is deteriorated. 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.

The resin of component (A) can be synthesized simply by copolymerizing a monomer mixture containing monomer (A1) having a phenolic hydroxyl group and a polymerizable unsaturated group, and monomer (A2) whose homopolymer has a Tg of 0°C or less. Here, the homopolymer refers to a polymer of monomer (A2) alone, and is obtained by polymerization reaction at a temperature of 50 to 110°C in a solvent in which a polymerization initiator, etc. is optionally present, or by polymerization reaction by irradiation with ultraviolet light in the presence of monomer (A2) and a photoradical generator, etc., with a weight average molecular weight of 3000 or more.

Details regarding the constituent monomers of component (A) are provided below.

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):

式（１）中、Ｐは（メタ）アクリル基、（メタ）アクリルアミド基、Ｎ－メチル（メタ）アクリルアミド基、またはマレイミド基を表し、好ましくは（メタ）アクリル基である。ｂ_１は単結合、または炭素数１～１２の直鎖、分岐、もしくは環状、およびその組み合わせからなるアルキレン基を表し、好ましくは単結合、または炭素数１～６の直鎖状アルキレン基である。ｃ_１は単結合、－Ｏ－、－ＣＯＯ－、または－ＯＣＯ－を表し、好ましくは単結合または－Ｏ－である。ｄ_１は置換または非置換のヒドロキシフェニル基を表し、好ましくはｐ－ヒドロキシフェニル基である。該ヒドロキシフェニル基への置換基としては、ハロゲン原子、炭素数１～３のアルキル基、炭素数２～３のアルケニル基、炭素数１～３のアルコキシ基、炭素数１～３のフルオロアルキル基、炭素数２～３のフルオロアルケニル基、炭素数１～３のフルオロアルコキシ基、炭素数２～３のアルキルオキシカルボニル基、シアノ基、ニトロ基等が挙げられる。これらヒドロキシフェニル基を有することにより、（Ａ）成分がフラックス性を発現する。

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. _{b 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. c ₁ represents a single bond, -O-, -COO-, or -OCO-, and is preferably a single bond or -O-. _{d 1} represents a substituted or unsubstituted hydroxyphenyl group, and is preferably a p-hydroxyphenyl group. Examples of the substituent on the hydroxyphenyl group include a halogen atom, an alkyl group having 1 to 3 carbon atoms, an alkenyl group having 2 to 3 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, a fluoroalkyl group having 1 to 3 carbon atoms, a fluoroalkenyl group having 2 to 3 carbon atoms, a fluoroalkoxy group having 1 to 3 carbon atoms, an alkyloxycarbonyl group having 2 to 3 carbon atoms, a cyano group, a nitro group, etc. By having these hydroxyphenyl groups, component (A) exhibits flux properties.

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

Monomer (A2) is a monomer having a homopolymer Tg of 0°C or less, and is preferably a compound represented by the following formula (2):

式（２）中、Ｒ_２は水素原子またはメチル基を表す。ａ_２は酸素原子または硫黄原子を表し、好ましくは酸素原子である。ｂ_２は炭素数２～２０の直鎖、分岐、もしくは環状、およびその組み合わせからなるアルキレン基を表し、好ましくは炭素数２～１２の直鎖、分岐、または環状、およびその組み合わせからなるアルキレン基であり、より好ましくは炭素数２～１２の直鎖または分岐のアルキレン基である。なお、ｂ_２の該アルキレン基中の－ＣＨ_２－は、互いに隣り合わないことを条件に、酸素原子に置き換えられても良い。ｃ_２は単結合、－Ｏ－、－ＣＯＯ－、または－ＯＣＯ－を表し、好ましくは単結合または－Ｏ－を表す。ｄ_２は水素原子または水酸基を表す。

In formula (2), R ₂ represents a hydrogen atom or a methyl group. a ₂ represents an oxygen atom or a sulfur atom, preferably an oxygen atom. b 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. Note that -CH ₂ - in the alkylene group of b ₂ may be replaced by an oxygen atom, provided that they are not adjacent to each other. c ₂ represents a single bond, -O-, -COO-, or -OCO-, preferably a single bond or -O-. d ₂ represents a hydrogen atom or a hydroxyl group.

Specific examples of 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 acrylates 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, diethylene glycol monomethacrylate, and the like, which may be used alone or in combination of two or more thereof, but are not limited thereto.

From the viewpoint of optimally obtaining 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).

In addition, in the present invention, when obtaining the acrylic polymer of component (A), other monomers copolymerizable with the above monomers (A1) to (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.

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

Examples of the methacrylic acid ester compounds 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, anthryl methyl 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.

Examples of the acrylamide compounds include N-methylacrylamide, N-methylmethacrylamide, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N-methoxymethylacrylamide, N-methoxymethylmethacrylamide, N-butoxymethylacrylamide, and N-butoxymethylmethacrylamide.

Examples of the vinyl compounds 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.

Examples of the above styrene compounds include styrenes that do not have a hydroxy group, such as styrene, α-methylstyrene, chlorostyrene, and bromostyrene.

The method for obtaining the alkali-soluble resin used in the present invention is not particularly limited, but for example, it can be obtained by carrying out a polymerization reaction at a temperature of 50 to 110°C in a solvent in which the monomer (A1) and monomer (A2), as well as the other monomers described above, and optionally a polymerization initiator, etc. are coexistent. The solvent used in this case is not particularly limited as long as it dissolves the monomers that constitute the resin and the resin. Specific examples include the solvents described in (D) Solvent below.

The resin obtained in this manner (hereinafter also referred to as the specific copolymer) is usually in the form of a solution dissolved in a solvent.

The solution of the specific copolymer obtained as described above can be reprecipitated by adding it to 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.

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

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

<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 at room temperature can be achieved. 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)).

The content of 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 component (A).

<Component (C)>
The component (C) is an epoxy compound having an aliphatic or alicyclic skeleton. When the epoxy compound serving as the crosslinking component in the composition has an aromatic group or an aminoglycidyl group, the film is easily yellowed by high-temperature heating, so an aliphatic or alicyclic skeleton is preferred.

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

（式（５）中、ｋは２～１０の整数であり、ｍは０～４の整数であり、Ｘ_５は芳香族環を含まないｋ価の有機基を表す。複数個のｍは互いに同じであっても異なっていてもよい。）

(In formula (5), k is an integer of 2 to 10, m is an integer of 0 to 4, and _X5 represents an organic group having a valence of k that does not contain an aromatic ring. The multiple m's may be the same or different.)

（式（６）中、ｋは２～１０の整数であり、Ｘ_６は芳香族環を含まないｋ価の有機基を表す）

(In formula (6), k is an integer of 2 to 10, and _X6 represents an organic group having a valence of k that does not contain an aromatic ring.)

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

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

The content of 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 component (A).

<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. As long as the solvent has such dissolving ability, there are no particular limitations on the type and structure of the solvent.

Examples of such (D) solvents 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 alkyl ester 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.

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, etc. are preferred from the viewpoint of good coating properties and high safety.

Furthermore, other solvents can be mixed in at a ratio of 1 to 90% by mass, preferably 1 to 50% by mass, of the total solvents used in the varnish for purposes such as improving wettability to the substrate, adjusting the surface tension of the solvent, adjusting the polarity, adjusting the boiling point, etc.

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

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

The surfactant of component (E) is not particularly limited, but examples thereof include fluorine-based surfactants, silicone-based surfactants, and nonionic surfactants. As this type of surfactant, for example, commercially available products manufactured by 3M Japan Ltd., DIC Corporation, AGC Seimi Chemical Co., Ltd., etc. can be used. These commercially available products are convenient because they are easily available. Specific examples thereof include Polyfox PF-136A, 151, 156A, 154N, 159, 636, 6320, 656, 6520 (manufactured by Omnova), Megafac R30, R08, R40, R41, R43, F251, F477, F552, F553, F554, F555, F556, F557, F558, F559, F560, F56 1, F562, F563, F565, F567, F570 (DIC Corporation), FC4430, FC4432 (3M Japan Ltd.), Asahiguard AG710, Surflon S-386, S-611, S-651, (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 SH8400, SH8410, SH8700, SF8428 (manufactured by Dow Corning Toray Silicone Co., Ltd.), 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.).

The surfactant component (E) may be used alone or in combination of two or more.

When a surfactant is used, its content is typically 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).

<Component (F)>
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 effect of the present invention is not impaired.

The inorganic filler 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.

When inorganic filler is used, its content is typically 10 to 90 parts by mass, and preferably 20 to 80 parts by mass, per 100 parts by mass of the total solid content.

<Adhesive sheet>
The adhesive composition of the present invention can be applied onto a release substrate (e.g., 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.

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

Then, a release substrate for a protective film is laminated onto the coating of the composition to obtain an adhesive sheet. Using a manual or automatic laminating roller, the coating and the protective film are pressed together in a certain direction so as not to trap air bubbles between them, to obtain an adhesive sheet.

By processing the adhesive sheet to the desired size, the adhesive composition can be applied to form a film only in the required locations on the array substrate. After processing to the desired size, the protective film is peeled off, the peeled surface is attached to the desired location, and the base film is peeled off, 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.

In order to peel the protective film well 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. It is preferable that the peel strength of the protective film is 80 N/25 mm or less, and that of the base film is 160 N/25 mm or more.

<Cured film>
Subsequently, the pattern-forming film is post-baked for thermal curing, specifically by heating using a hot plate, 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.

Post-baking generally involves heating the film at a temperature selected from the range of 140-270°C for 5-30 minutes on a hot plate or 30-90 minutes in an oven.

Thus, by such post-baking, a cured film having the desired good pattern shape can be obtained.

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

After mass-transferring the LED elements onto an array substrate having 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 250-350°C to melt the solder electrodes). During thermocompression bonding, the composition film is in an uncured state, so it becomes molten 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 impede the bonding between the electrodes. The composition film that has been 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.

Furthermore, the adhesive composition of the present invention is highly transparent and does not yellow easily even during the high-temperature process of flip-chip bonding, so it does not easily impair the color purity of LED elements.

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:

(monomer)
HQMA: p-hydroxyphenyl methacrylate HEMA: 2-hydroxyethyl methacrylate BA: n-butyl acrylate (radical polymerization initiator)
AIBN: α,α'-azobisisobutyronitrile (isocyanurate compound)
I1: NK Ester A-9300 (manufactured by Shin-Nakamura Chemical Co., Ltd.)
I2: TEPIC-VL (Nissan Chemical Industries, Ltd.)
(Epoxy Compound)
E1: Epocalic DE-102 (manufactured by ENEOS Corporation)
E2: EHPE 3150 (manufactured by Daicel Corporation)
E3: jER152 (manufactured by Mitsubishi Chemical Corporation)
E4: Epolead GT-401 (butanetetracarboxylic acid tetra(3,4-epoxycyclohexylmethyl) modified ε-caprolactone, manufactured by Daicel Corporation)
E5: Celoxide 2021P (manufactured by Daicel Corporation)
E6: Denacol EX-851 (manufactured by Nagase ChemteX Corporation)
E7: Showfree BATG (manufactured by Resonac Co., Ltd.)
(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, with a peel strength of 40N/25mm (manufactured by Nippa Corporation)

<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 KK) and a column (KD-803, KD-805 in series) (manufactured by Showa Denko KK) as follows.
Column temperature: 50°C
Eluent: N,N-dimethylformamide (additives: lithium bromide monohydrate (LiBr.H ₂ O) 30 mmol/L (liter), phosphoric acid anhydrous crystal (o-phosphoric acid) 30 mmol/L, tetrahydrofuran (THF) 10 mL/L)
Flow rate: 1.0 ml/min. Standard samples for preparing a calibration curve: TSK standard polyethylene oxide (molecular weight: about 900,000, 150,000, 100,000 and 30,000) (manufactured by Tosoh Corporation) and polyethylene glycol (molecular weight: about 12,000, 4,000 and 1,000) (manufactured by Polymer Laboratory Co., Ltd.).

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

<Synthesis of Acrylic Polymer>
(Synthesis Example 1)
As monomer components constituting the acrylic polymer, HQMA (6.0 g), HEMA (4.0 g), and BA (10.0 g) were used, 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 subjected to a polymerization reaction in a solvent of PGME (46.8 g) at a temperature of 60° C., to obtain an acrylic polymer P2 (acrylic polymer concentration: 30.0 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 subjected to a polymerization reaction in a solvent of PGME (37.5 g) at a temperature of 60° C., to obtain an acrylic polymer P3 (acrylic polymer concentration: 35.0 mass%) having a molecular weight and Tg shown in Table 1.

<Preparation of adhesive composition>
(Example 1-1)
As a resin solution, isocyanurate compound I1 (0.375 g), epoxy compound E1 (0.375 g), and solvents PGME (2.683 g) and IPA (2.400 g) were added to the acrylic polymer solution (P1) (4.167 g) 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.

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

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

(Example 2-1)
<Adhesive 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 a temperature of 100 ° C. for 120 seconds to form a prebaked film with a thickness of 3 μm. Thereafter, 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), compression speed: 1 mm / sec, tensile speed: 1 mm / sec, compression load: 200 g, and compression holding time: 2 sec. If the peel strength was 1.0 g or more, the adhesion was judged to be good, and if it was less than 1.0 g, the adhesion was judged to be poor. The results are shown in Table 3.

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

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

The results are shown in Table 3.

As shown in Table 3, all of the adhesive compositions of the examples showed 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 adhesion was insufficient. Furthermore, when the epoxy compound used had an aromatic ring (Comparative Examples 2-1 and 2-4), the transparency was insufficient.

(Example 3-1)
<Production and evaluation of film sheets>
The adhesive composition V1 prepared in Example 1-1 was applied onto 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. The protective film was then laminated onto the prebaked film using a roller to prepare an adhesive sheet S1. The peelability of the protective film was then evaluated. After the protective film was peeled off, it was judged to be good if there was no film remaining on the protective film side, and bad if a part of the adhesive composition remained on the protective film side. Next, the transferability from the base film to the substrate was evaluated. A glass substrate with a size of 5 cm×5 cm and a thickness of 1 mm was used as the substrate. After the base film was peeled off, it was judged to be good if there was no film remaining on the base film side and the adhesive sheet was transferred to the substrate without wrinkles, and bad if a part of the adhesive composition remained on the base film side or wrinkles occurred on the adhesive sheet after transfer. Finally, the peel strength of the coating surface was measured at room temperature (23°C) using a texture analyzer manufactured by Stable Micro Systems, with a probe ball (diameter: 25 mm, material: SUS), compression speed: 1 mm/sec, tensile speed: 1 mm/sec, compression load: 200 g, and compression hold time: 2 sec. If the peel strength was 1.0 g or more, the adhesion was judged to be good, and if it was less than 1.0 g, the adhesion was judged to be poor. The results are shown in Table 4.

(Example 3-2)
Using the adhesive composition V2 prepared in Example 1-2, an adhesive sheet S2 was prepared 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.

(Examples 4-1 and 4-2)
<Flip chip bonding test>
As a mounting sample, a TEG (Test Element Group) chip (5.1 mm x 5.1 mm x thickness 700 μm) having 1700 electrodes with an electrode area of 20 μm x 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 x 15 mm x thickness 700 μm) in which copper electrodes were wired to form 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 having 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 conductive resistance value (less than 100Ω: ◯, 100Ω or more: ×). The results are shown in Table 5.

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

As shown in Table 5, the TEG assembly using the adhesive sheet of the embodiment as an underfill film did not experience peeling of the TEG chip and had good conductive resistance values. In contrast, when no underfill film was used, peeling of the TEG chip increased significantly and resistance measurements could not be performed reproducibly (Comparative Example 4-1).

Claims (10)

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 60 ° C. or lower, the acrylic polymer containing, as constituent components, a constituent unit derived from a monomer (A1) having a phenolic hydroxyl group and a polymerizable unsaturated group, and a constituent unit derived from a monomer (A2) having a homopolymer with a Tg of 0° C. or lower.
Component (B): A compound having a (meth)acrylic group or an epoxy group and an isocyanurate skeleton. Component (C): A polyfunctional aliphatic or alicyclic epoxy compound. Component (D): A solvent. 2. The adhesive composition according to claim 1, 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 ):

(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; c ₁ represents a single bond, -O-, -COO-, or -OCO-; and d ₁ represents a substituted or unsubstituted hydroxyphenyl group.) 2. The adhesive composition according to claim 1, wherein the monomer (A2) which gives a homopolymer having a Tg of 0° C. or lower is a compound represented by the following formula (2):

(In formula (2), R ₂ represents a hydrogen atom or a methyl group, a ₂ represents an oxygen atom or a sulfur atom, b ₂ represents an alkylene group having 2 to 20 carbon atoms which is linear, branched or cyclic, or a combination thereof, and -CH ₂ - in the alkylene group may be replaced by an oxygen atom, provided that they are not adjacent to each other, c ₂ represents a single bond, -O-, -COO- or -OCO-, and d ₂ represents a hydrogen atom or a hydroxyl group.) 4. 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). 4. 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). The adhesive composition according to any one of claims 1 to 3 , 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). The adhesive composition according to any one of claims 1 to 3 , further comprising an inorganic filler as a component (F). An adhesive sheet comprising the adhesive composition according to any one of claims 1 to 3 laminated on both sides with a release substrate. A cured film obtained by curing the adhesive composition according to any one of claims 1 to 3 . An LED display element comprising the cured film according to claim 9 as an underfill material.