WO2024070281A1

WO2024070281A1 - Display device and display device manufacturing method, and connecting film and connecting film manufacturing method

Info

Publication number: WO2024070281A1
Application number: PCT/JP2023/029363
Authority: WO
Inventors: 俊紀白岩; 怜司塚尾; 大樹野田
Original assignee: デクセリアルズ株式会社
Priority date: 2022-09-28
Filing date: 2023-08-10
Publication date: 2024-04-04
Also published as: JP2024049076A

Abstract

Provided are: a display device and a display device manufacturing method with which it is possible to obtain excellent light transmission and visibility; and a connecting film, and a connecting film manufacturing method. This display device comprises a plurality of light emitting elements (30), a wiring substrate (20), and a cured film (40) of a connecting film that connects the plurality of light emitting elements (30) and the wiring substrate (20), wherein the cured film (40) has a first surface (40a) for which the root mean square height is 3.0×10-1 μm or lower, and the plurality of light emitting elements (30) are mounted on the first surface 40a. This makes it possible to suppress light scattering and to obtain excellent light transmission and visibility.

Description

Display device and method for manufacturing the same, connection film and method for manufacturing the same

This technology relates to a display device in which light-emitting elements are connected and arranged via a connecting film such as an anisotropic conductive film (ACF) or an adhesive film (NCF: Non-Conductive Film), and a method for manufacturing the display device. In particular, this technology relates to a display device in which LED elements such as mini-LEDs (Light Emitting Diodes) and micro-LEDs are connected and arranged, and a method for manufacturing the display device. This application claims priority based on Japanese Patent Application No. 2022-155321, filed in Japan on September 28, 2022, which application is incorporated herein by reference.

The development of mini-LED and micro-LED displays is attracting attention as the next generation of displays. Mini-LED and micro-LED displays are constructed by arranging tiny light-emitting elements on a substrate, which means that the backlight required for LCD displays can be omitted, allowing displays to be made thinner, while also enabling wider color gamuts, higher definition, and lower power consumption.

Patent Document 1 discloses a method of joining LEDs with ACF. In the method described in Patent Document 1, ACF is attached to the entire surface of the element mounting surface of the substrate, so excellent light transmittance and visibility cannot always be obtained.

JP 2017-157724 A

This technology has been proposed in light of the current situation, and provides a display device and a method for manufacturing a display device that can provide excellent light transmittance and visibility, as well as a connection film and a method for manufacturing a connection film.

A display device according to the present technology includes a plurality of light-emitting elements, a wiring board, and a cured film of a connection film that connects the plurality of light-emitting elements and the wiring board, the cured film having a first surface having a root-mean-square height of 3.0× ^10-1 or less, and the plurality of light-emitting elements are mounted on the first surface.

A manufacturing method for a display device according to the present technology includes a placement step of placing a connection film having a first surface with a root-mean-square height of 3.0 × ^10-1 or less at a predetermined position on a wiring board, and a mounting step of mounting a plurality of light-emitting elements on the first surface and mounting the plurality of light-emitting elements on the wiring board.

The connecting film according to the present technology has a first surface having a root mean square height of 3.0×10 ⁻¹ μm or less.

The method for producing a connecting film according to the present technology includes forming a connecting film on a base film having a root mean square height of 3.0×10 ⁻¹ μm or less, and providing a first surface on the base film side having a root mean square height of 3.0×10 ⁻¹ μm or less.

This technology makes it possible to suppress light scattering and achieve excellent light transmittance and visibility.

FIG. 1 is a diagram for explaining an example of a manufacturing method for a connection film (conductive film, anisotropic conductive film) in this embodiment, in which FIG. 1(A) shows a preparation process for preparing a base film, FIG. 1(B) shows a formation process for forming a connection film (conductive film, anisotropic conductive film) on the base film, and FIG. 1(C) shows an attachment process for attaching a cover film onto the connection film (conductive film, anisotropic conductive film). FIG. 2 is a cross-sectional view showing a schematic example of a display device according to the present embodiment. 3A and 3B are diagrams for explaining an example of a manufacturing method for a display device in this embodiment, in which FIG. 3A shows a placement process for placing a connecting film (conductive film, anisotropic conductive film) at a predetermined position on a wiring board, and FIG. 3B shows a mounting process for mounting a light-emitting element on the wiring board.

Hereinafter, embodiments of the present technology will be described in detail with reference to the drawings in the following order.
1. Connecting film 2. Manufacturing method of connecting film 3. Display device 4. Manufacturing method of display device 5. Examples

<1. Connection film>
The connection film (conductive film, anisotropic conductive film) according to the present embodiment has a first surface having a root mean square height equal to or less than a predetermined value. When a light emitting element is mounted using a connection film having such a first surface, a display device having excellent light transmittance and visibility can be obtained.

Here, the root mean square height (Sq: Root Mean Square Height (surface roughness: ISO 25178)) is the root mean square deviation of the roughness profile (Rq: Root Mean Square Deviation of the Roughness Profile (Line Roughness: JIS B 0601)) extended to a surface. The root mean square roughness Rq is the root mean square of the roughness curve Z(x) at the reference length l as shown in formula (1), and the root mean square height Sq corresponds to the standard deviation of the distance from the mean surface and corresponds to the standard deviation of the height as shown in formula (2). The root mean square height Sq can be measured using a three-dimensional non-contact surface roughness measuring device.

The root mean square height of the first surface of the connecting film is preferably 3.0× ¹⁰ μm or less, more preferably 2.0× ¹⁰ μm or less, and even more preferably 1.0× ¹⁰ μm or less. If the root mean square height is large, a lot of light scattering occurs, making it difficult to obtain excellent light transmittance and visibility.

The haze of the connection film is preferably less than 50%, more preferably less than 45%, and even more preferably less than 40%. Haze can be measured using a HAZEMETER in accordance with a method in accordance with JIS K7136.

The visible light transmittance of the connection film is preferably 30% or more, more preferably 40% or more, and even more preferably 45% or more. The transmittance in the visible light region (380 nm to 780 nm) can be measured, for example, using a UV-Vis spectrophotometer.

The connection film may be provided with a base film having a root mean square height of a predetermined value or less on the first surface side. The root mean square height of the base film is preferably 3.0×10 ⁻¹ μm or less, more preferably 1.5×10 ⁻¹ μm or less, and even more preferably 0.05×10 ⁻¹ μm or less. If the root mean square height of the base film is large, it becomes difficult to obtain a connection film having a small root mean square height. In addition, from the viewpoint of handling, the connection film may be provided with a cover film on the second surface.

The storage modulus of the connection film at 30°C, measured in a tensile mode in accordance with JIS K7244 after curing, is preferably 100 MPa or more, and more preferably 2000 MPa or more. If the storage modulus at 30°C is too low, good conductivity cannot be obtained and connection reliability tends to decrease. The storage modulus at 30°C can be measured in a tensile mode using a viscoelasticity tester (Vibron) in accordance with JIS K7244 under measurement conditions of, for example, a frequency of 11 Hz and a heating rate of 3°C/min.

The binder of the connecting film is not particularly limited as long as it is hardened by energy such as heat or light, and can be appropriately selected from, for example, a thermosetting binder, a light-curing binder, or a binder that is hardened by both heat and light.

Thermosetting binders include, for example, a thermal anionic polymerization type resin composition containing an epoxy compound and a thermal anionic polymerization initiator, a thermal cationic polymerization type resin composition containing an epoxy compound and a thermal cationic polymerization initiator, and a thermal radical polymerization type resin composition containing a (meth)acrylate compound and a thermal radical polymerization initiator. Thermosetting binders include, for example, a photocationic polymerization type resin composition containing an epoxy compound and a photocationic polymerization initiator, and a photoradical polymerization type resin composition containing a (meth)acrylate compound and a photoradical polymerization initiator. Thermosetting and photosetting binders include a mixture of a thermosetting binder and a photosetting binder. The (meth)acrylate compound includes both acrylic monomers (oligomers) and methacrylic monomers (oligomers).

(Thermal Cationic Polymerization Resin Composition)
In the following, as a specific example of the thermosetting binder, a thermal cationic polymerization type resin composition containing a film-forming resin, an epoxy compound, and a thermal cationic polymerization initiator will be described.

The film-forming resin corresponds to a high molecular weight resin having an average molecular weight of, for example, 10,000 or more, and from the viewpoint of film formability, the average molecular weight is preferably about 10,000 to 80,000. Examples of the film-forming resin include various resins such as polyvinyl acetal resin, phenoxy resin, butyral resin, polyester resin, polyurethane resin, polyester urethane resin, acrylic resin, and polyimide resin, which may be used alone or in combination of two or more types. Among these, it is preferable to use polyvinyl acetal resin from the viewpoint of film formation state, connection reliability, etc. The content of the film-forming resin is preferably 20 to 70 parts by mass, more preferably 30 to 60 parts by mass or less, and even more preferably 45 to 55 parts by mass, relative to 100 parts by mass of the thermosetting binder.

The epoxy compound is not particularly limited as long as it is an epoxy compound having one or more epoxy groups in the molecule, and may be, for example, a bisphenol A type epoxy resin, a bisphenol F type epoxy resin, or a urethane-modified epoxy resin. Among these, hydrogenated bisphenol A glycidyl ether can be preferably used. A specific example of hydrogenated bisphenol A glycidyl ether is the product name "YX8000" manufactured by Mitsubishi Chemical Corporation. The content of the epoxy compound is preferably 30 to 60 parts by mass, more preferably 35 to 55 parts by mass or less, and even more preferably 35 to 45 parts by mass, per 100 parts by mass of the thermosetting binder.

As the thermal cationic polymerization initiator, a known initiator for thermal cationic polymerization of epoxy compounds can be used. For example, known iodonium salts, sulfonium salts, phosphonium salts, ferrocenes, etc. can be used, which generate an acid capable of cationic polymerization of a cationic polymerization compound by heat. Among these, aromatic sulfonium salts that show good latency against temperature can be preferably used. A specific example of an aromatic sulfonium salt-based polymerization initiator is "SI-60L" manufactured by Sanshin Chemical Industry Co., Ltd. The content of the thermal cationic polymerization initiator is preferably 1 to 20 parts by mass, more preferably 5 to 15 parts by mass or less, and even more preferably 8 to 12 parts by mass, per 100 parts by mass of the thermosetting binder.

Other additives that may be added to the thermosetting binder, as necessary, include rubber components, inorganic fillers, silane coupling agents, diluting monomers, bulking agents, softeners, colorants, flame retardants, and thixotropic agents.

The rubber component is not particularly limited as long as it is an elastomer with high cushioning properties (shock absorption properties), and specific examples include acrylic rubber, silicone rubber, butadiene rubber, and polyurethane resin (polyurethane-based elastomer). As inorganic fillers, silica, talc, titanium oxide, calcium carbonate, magnesium oxide, and the like can be used. The inorganic fillers may be used alone or in combination of two or more types.

A thermosetting binder with this composition can suppress the hardening reaction when forming individual pieces with laser light, and can quickly harden with heat during thermocompression bonding.

(Connection film)
The connection film may be a conductive film further containing conductive particles. Examples of the conductive film include an isotropic conductive film and an anisotropic conductive film. Hereinafter, an anisotropic conductive film will be described as one form of the conductive film.

The conductive particles may be appropriately selected from those used in known anisotropic conductive films. Examples of the conductive particles include metal particles such as nickel (melting point 1455°C), copper (melting point 1085°C), silver (melting point 961.8°C), gold (melting point 1064°C), palladium (melting point 1555°C), tin (melting point 231.9°C), nickel boride (melting point 1230°C), ruthenium (melting point 2334°C), and solder, which is a tin alloy. Examples of the conductive particles include metal-coated metal particles in which the surface of the metal particles is coated with a metal such as nickel, copper, silver, gold, palladium, tin, nickel boride, and ruthenium. Examples of the conductive particles include metal-coated resin particles in which the surface of resin particles, such as polymers containing at least one monomer selected from polyamide, polybenzoguanamine, styrene, and divinylbenzene as monomer units, is coated with a metal such as nickel, copper, silver, gold, palladium, tin, nickel boride, and ruthenium. Other examples include metal-coated inorganic particles in which the surfaces of inorganic particles such as silica, alumina, barium titanate, zirconia, carbon black, silicate glass, borosilicate glass, lead glass, soda-lime glass, and alumina silicate glass are coated with metals such as nickel, copper, silver, gold, palladium, tin, nickel boride, and ruthenium. The coated metal layer of the metal-coated resin particles and metal-coated inorganic particles may be a single layer or a multilayer of different metals.

The conductive particles may be coated with insulating particles such as a resin layer, resin particles, or inorganic particles to provide an insulating coating. Here, the particle diameter of the conductive particles does not include the portion that is subjected to the insulating coating. The particle diameter of the conductive particles may be appropriately changed depending on the optical element to be mounted, the electrodes of the wiring board, the area of the bumps, etc., but is preferably 1 to 30 μm, more preferably 1 to 10 μm, and particularly preferably 1 to 3 μm. For example, when used to mount micro LED elements, since the areas of the electrodes and bumps are small, the particle diameter of the conductive particles is preferably 1 to 3 μm, more preferably 1 to 2.5 μm, and particularly preferably 1 to 2.2 μm. The particle diameter can be determined by measuring 200 or more particles under a microscope (optical microscope, metallurgical microscope, electron microscope, etc.) and taking the average value.

In addition, when the conductive particles are metal-coated resin particles or metal-coated inorganic particles in which the aforementioned resin particles or inorganic particles are coated with a metal, the thickness of the metal coating is preferably 0.005 μm or more, more preferably 0.01 μm or more, and preferably 10 μm or less, more preferably 1 μm or less, and even more preferably 0.3 μm or less. When the metal coating is a multi-layer coating, this coating thickness is the thickness of the entire metal coating. When the metal coating thickness is equal to or greater than the above lower limit and equal to or less than the above upper limit, sufficient conductivity is easily obtained, and the conductive particles do not become too hard, making it easy to utilize the properties of the aforementioned resin particles or inorganic particles.

The metal coating thickness can be measured, for example, by observing the cross section of the conductive particle using a transmission electron microscope (TEM). It is preferable to calculate the coating thickness as the average of five arbitrary coating thicknesses as the coating thickness of one conductive particle, and it is more preferable to calculate the average thickness of the entire coating portion as the coating thickness of one conductive particle. The coating thickness is preferably determined by calculating the average coating thickness of each of 10 arbitrary conductive particles.

The conductive particles may have a spherical, ellipsoidal, spike-like, or irregular shape. Among these, spherical conductive particles are preferred because they are easy to control the particle size and particle size distribution. The conductive particles may have protrusions on their surfaces to improve connectivity.

In the anisotropic conductive film, the conductive particles are preferably aligned in the planar direction (regularly arranged in a planar view). By aligning the conductive particles in the planar direction, the particle surface density becomes uniform, and the conductivity and insulation properties can be improved. The state in which the conductive particles are aligned in the planar direction can be, for example, a planar lattice pattern having one or more arrangement axes in which the conductive particles are arranged in a specific direction at a specific pitch, such as an oblique lattice, a hexagonal lattice, a square lattice, a rectangular lattice, and a parallelepiped lattice. The arrangement of the conductive particles in the planar direction can also be random, or the film can have multiple regions with different planar lattice patterns.

The particle surface density of the anisotropic conductive film can be appropriately designed according to the size of the electrode to be connected, and the lower limit of the particle surface density is not particularly limited as long as the performance is not impaired, and can be ³⁰ pieces/ ^mm2 or more, 500 pieces/ ^mm2 or more, 20000 pieces/mm2 or more, 40000 pieces/ ^mm2 or more, or 50000 pieces/ ^mm2 or more, and the upper limit of the particle surface density can be 1500000 pieces/ ^mm2 or less, 1000000 pieces/ ^mm2 or less, 500000 pieces/ ^mm2 or less, or 100000 pieces/ ^mm2 or less. This makes it possible to obtain excellent conductivity and insulation even when the electrode size to be connected is small. Among these, it is preferable that the anisotropic conductive film has an average particle size of the conductive particles of 3.0 μm or less, and the conductive particles are aligned at a particle surface density of 50000 pieces/mm2 or ^more . The particle surface density of the anisotropic conductive film is that of the conductive particles arranged in the film during production. When determining the particle number density from a plurality of pieces, the particle surface density can be calculated from the area obtained by excluding the spaces between the pieces from the area including the pieces and the spaces, and the number of particles.

The thickness of the anisotropic conductive film before connection is preferably 1 μm to 10 μm, more preferably 1 μm to 6 μm, and even more preferably 2 μm to 4 μm. The thickness of the anisotropic conductive film before connection is preferably the average particle size of the conductive particles plus 1 to 4 μm, and particularly preferably 1 to 2 μm, since this tends to make the distance between the film and the electrode side surface of the micro LED approximately the same. It can be measured using a known micrometer or digital thickness gauge. The film thickness can be calculated, for example, by measuring at 10 or more points and averaging them.

The connection film is not limited to the anisotropic conductive film described above, but may be a laminate of a conductive particle-containing layer that contains conductive particles, an adhesive layer that does not contain conductive particles, a pressure-sensitive adhesive layer, etc., and the number of layers and lamination surfaces can be appropriately selected according to the target and purpose.

2. Method for manufacturing connecting film
The manufacturing method of the connection film (conductive film, anisotropic conductive film) according to the present embodiment is to form the connection film on a base film having a root mean square height equal to or less than a predetermined value, and obtain a connection film having a first surface on the base film side. This allows the surface condition of the base film to be reflected on the first surface of the connection film, and a first surface having a small root mean square height can be obtained.

Below, we will explain a method for manufacturing anisotropic conductive film as one form of a method for manufacturing a connection film.

FIG. 1 is a diagram for explaining an example of a method for manufacturing an anisotropic conductive film in this embodiment, where FIG. 1(A) shows a preparation process for preparing a base film, FIG. 1(B) shows a formation process for forming an anisotropic conductive film on the base film, and FIG. 1(C) shows an attachment process for attaching a cover film onto the anisotropic conductive film.

(Preparation process)
1A, a base film 11 is prepared having a first surface 11a whose root mean square height is equal to or less than a predetermined value. The root mean square height of the base film 11 is preferably equal to or less than 3.0×10 ⁻¹ μm, more preferably equal to or less than 1.5×10 ⁻¹ μm, and even more preferably equal to or less than 0.05×10 ⁻¹ μm. If the root mean square height of the base film 11 is large, it becomes difficult to obtain an anisotropic conductive film with a small root mean square height.

The base film 11 is not particularly limited as long as it can support the anisotropic conductive film 12 and can be peeled off from the anisotropic conductive film 12 at the desired timing. Materials for the base film 11 may include, for example, polyesters such as polyethylene terephthalate (PET), polyolefins such as polypropylene (PP), plastic materials such as poly-4-methylpen-1 (PMP) and polytetrafluoroethylene (PTFE), and glass substrates such as quartz glass. The base film 11 may also have a release layer on the surface on the side that is bonded to the anisotropic conductive film 12, and the release layer may contain a release agent such as silicone resin or polyolefin resin.

The thickness of the base film 11 is not particularly limited, but from the viewpoint of efficiently forming a long film roll, it is preferably 100 μm or less, more preferably 80 μm or less, even more preferably 60 μm or less, and even more preferably 50 μm or less. The lower limit of the thickness of the base film 11 is not particularly limited, but from the viewpoint of handleability during the production of the connection film, during slitting, and during winding onto the core, it is preferably 8 μm or more.

(Forming process)
Next, as shown in Fig. 1 (B), an anisotropic conductive film 12 is formed on the first surface 11a of the base film 11. Examples of methods for forming the anisotropic conductive film 12 include a method of applying a solution of a conductive adhesive onto the base film 11 and drying it, and a method of forming an adhesive layer that does not contain conductive particles on the base film 11 and fixing conductive particles to the obtained adhesive layer. The conductive particles may be regularly arranged or randomly arranged when viewed from above. The regularly arranged particles may be arranged by any known method as long as it does not impair the effects of the invention.

For example, a binder is applied onto the base film 11, dried to form a resin film, the resin film is attached to an array sheet on which conductive particles are aligned in a predetermined array at a predetermined particle density, and the conductive particles are pressed into the resin film to transfer it, thereby forming the anisotropic conductive film 12. As a result, the first surface of the anisotropic conductive film 12 reflects the surface condition of the first surface 11a of the base film 11, and a root-mean-square height of 3.0×10 ⁻¹ or less can be obtained.

(Attachment process)
Next, as shown in FIG. 1C, a cover film 13 is attached onto the second surface of the anisotropic conductive film 12 to prepare a film laminate. The cover film 13 is not particularly limited as long as it can be peeled off from the second surface of the anisotropic conductive film 12 at a predetermined timing. The material of the cover film 13 may be the same as that of the base film 11. Similarly to the base film 11, the cover film 13 may also have a peeling layer on the surface on the side that is bonded to the anisotropic conductive film 12. The thickness of the cover film 13 is not particularly limited, but is preferably smaller than that of the base film 11.

According to such a method for producing a connecting film, the surface condition of the base film is reflected on the first surface of the connecting film, and a root mean square height of 3.0×10 ⁻¹ or less can be obtained.

[Modification]
The anisotropic conductive film may be a piece of a predetermined unit, such as one pixel unit (one pixel unit) of one set of RGB, for example, when used in a micro LED. The shape of the piece is not particularly limited and can be appropriately set according to the dimensions of the electronic component to be connected. When forming the piece using a laser lift-off (LLO) device, the shape of the piece is preferably at least one selected from a polygon having obtuse angles, a polygon having rounded corners, an ellipse, an oval, and a circle in order to suppress the occurrence of curling or chipping.

The dimensions of the pieces (length x width) are set appropriately according to the dimensions of the electronic component or electrode to be connected, and the ratio of the area of the pieces to the area of the electronic component or electrode is preferably 2 or more, more preferably 4 or more, and even more preferably 5 or more. Even in the case of individual pieces, if the anisotropic conductive film is exposed from the outer shape of the micro-LED, it is considered that this aspect of the present invention is necessary to suppress the influence of optical characteristics. In addition, the thickness of the individual pieces is the average particle size of the conductive particles plus preferably 1 to 4 μm, particularly preferably 1 to 2 μm, like the thickness of the anisotropic conductive film, and is preferably 1 μm to 10 μm, more preferably 1 μm to 6 μm, and even more preferably 2 μm to 4 μm.

The distance between the pieces on the base film is preferably 3 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more. The upper limit of the distance between the pieces is preferably 3000 μm or less, more preferably 1000 μm or less, and even more preferably 500 μm or less. If the distance between the pieces is too small, it becomes difficult to transfer the pieces by LLO, and if the distance between the pieces is large, a method of attaching the pieces is preferable. The distance between the pieces can be measured using a microscope (optical microscope, metallographic microscope, electron microscope, etc.).

The pieces may be formed by slitting or half-cutting, or may be formed using a laser lift-off device. When forming the pieces using an LLO device, the substrate film may be any material that is transparent to laser light, and is preferably quartz glass, which has high light transmittance across all wavelengths.

When forming individual pieces using an LLO device, an anisotropic conductive film provided on a base film is irradiated with laser light from the base film side, and the irradiated areas of the anisotropic conductive film are removed, thereby forming individual pieces of a predetermined shape made of anisotropic conductive film on the base film.

For example, a mask with a rectangular opening window is used to remove unnecessary portions of the anisotropic conductive film from the base film, allowing individual pieces of a predetermined shape to be formed from the remaining portions of the anisotropic conductive film. Also, for example, a mask with a predetermined shaped light-shielding portion formed in the opening window is used to remove unnecessary portions of the anisotropic conductive film around the individual pieces from the base film, allowing individual pieces of a predetermined shape to be formed from the remaining portions of the anisotropic conductive film.

In addition, when the pieces are produced using a laser lift-off device, the reaction rate of the pieces is 25% or less, preferably 20% or less, and more preferably 15% or less. This allows for excellent transferability. The reaction rate of the curable resin film before laser irradiation and the pieces obtained after laser irradiation can be measured by, for example, the reduction rate of the reactive group using FT-IR. For example, in the case of a curable resin film utilizing the reaction of an epoxy compound, the sample is irradiated with infrared rays to measure the IR spectrum, and the peak heights of the methyl group (near 2930 cm ⁻¹ ) and the epoxy group (near 914 cm ⁻¹ ) in the IR spectrum are measured, and the ratio of the peak height of the epoxy group to the peak height of the methyl group before and after the reaction (for example, before and after laser irradiation) can be calculated as shown in the following formula.

Reaction rate (%) = {1 - (a/b)/(A/B)} x 100
In the above formula, A is the peak height of the epoxy group before the reaction, B is the peak height of the methyl group before the reaction, a is the peak height of the epoxy group after the reaction, and b is the peak height of the methyl group after the reaction. If the epoxy group peak overlaps with another peak, the peak height of the completely cured sample (reaction rate 100%) may be set to 0%.

<3. Display device>
The display device according to the present embodiment includes a plurality of light-emitting elements, a wiring board, and a cured film of a connection film that connects the plurality of light-emitting elements and the wiring board, and the cured film has a root mean square height of The light-emitting element has a first surface having a refractive index of 3.0×10 ⁻¹ or less, and a plurality of light-emitting elements are mounted on the first surface. In the case where the electrode of the light-emitting element has a flat bottom surface, an adhesive layer that does not contain conductive particles can be used as the connection film. Also, for example, in the case where the electrode of the light-emitting element has a flat bottom surface, an anisotropic conductive film can be used as the connection film.

FIG. 2 is a cross-sectional view showing a schematic example of a display device according to the present embodiment. As shown in FIG. 2, the display device includes a plurality of light-emitting elements 30, a wiring board 20 on which the plurality of light-emitting elements 30 are arranged, and a cured film 40 of an anisotropic conductive film that connects the plurality of light-emitting elements 30 to the wiring board 20. Note that, although light is transmitted from the wiring board 20 side in FIG. 2, light is also transmitted from the cured film 40 side, providing visibility. In other words, the direction of light in FIG. 2 may be reversed.

The wiring board 20 has a circuit pattern for a first conductivity type and a circuit pattern for a second conductivity type on a base material, and has a first electrode and a second electrode at positions corresponding to the first conductivity type electrode on the p side and the second conductivity type electrode on the n side, respectively, so that the light-emitting elements 30 are arranged in units of subpixels that make up one pixel. The wiring board 20 also forms circuit patterns such as data lines and address lines of the matrix wiring, and enables the light-emitting elements corresponding to each subpixel that makes up one pixel to be turned on and off. One pixel may be composed of, for example, three subpixels of R (red), G (green), and B (blue), four subpixels of RGBW (white) and RGBY (yellow), or two subpixels of RG and GB.

When the display device is a transparent display, the wiring substrate 20 is preferably a light-transmitting substrate, and the base material is preferably glass, PET (Polyethylene Terephthalate), or the like. The first electrode 22 and the second electrode 23 are preferably transparent conductive films such as ITO (Indium-Tin-Oxide), IZO (Indium-Zinc-Oxide), ZnO (Zinc-Oxide), and IGZO (Indium-Gallium-Zinc-Oxide).

The light-emitting element 30 includes a body, a first-conductivity-type electrode, and a second-conductivity-type electrode, and has a horizontal structure in which the first-conductivity-type electrode and the second-conductivity-type electrode are arranged on the same surface side. The body includes a first-conductivity-type clad layer made of, for example, n-GaN, an active layer made of, for example, an In _x Al _y Ga _1-x-y N layer, and a second-conductivity-type clad layer made of, for example, p-GaN, and has a so-called double heterostructure. The first-conductivity-type electrode is formed on a part of the first-conductivity-type clad layer by a passivation layer, and the second-conductivity-type electrode is formed on a part of the second-conductivity-type clad layer. When a voltage is applied between the first-conductivity-type electrode and the second-conductivity-type electrode, carriers are concentrated in the active layer and recombined to generate light emission.

The cured film 40 is the cured anisotropic conductive film 12 described above. The cured film 40 may be formed, for example, over the entire display area of the wiring board 20, or may be formed in individual pieces of a predetermined unit in a part of the display area, such as one pixel unit (one picture element unit) of one set of RGB.

The root mean square height of the first surface of the cured film 40 on which the light emitting element 30 is mounted is preferably 3.0×10 ⁻¹ μm or less, more preferably 2.0×10 ⁻¹ μm or less, and even more preferably 1.0×10 ⁻¹ μm or less. If the root mean square height is large, a lot of light scattering occurs, making it difficult to obtain excellent light transmittance and visibility.

The haze of the cured film 40 is preferably less than 50%, more preferably less than 45%, and even more preferably less than 40%. Haze can be measured using a HAZEMETER in accordance with a method in accordance with JIS K7136.

The visible light transmittance of the cured film 40 is preferably 30% or more, more preferably 40% or more, and even more preferably 45% or more. The transmittance in the visible light region (380 nm to 780 nm) can be measured, for example, using a UV-Vis spectrophotometer.

The cured film 40 is preferably arranged with conductive particles in the surface direction, similar to the anisotropic conductive film described above. The particle surface density of the cured film can be appropriately designed according to the electrode size of the light-emitting element 30, and the lower limit of the particle surface density is not particularly limited as long as it does not impair performance, and can be 30 pieces/mm ² or more, 500 pieces/mm ² or more, 20000 pieces/mm ² or more, 40000 pieces/mm ² or more, or 50000 pieces/mm ² or more, and the upper limit of the particle surface density can be 1500000 pieces/mm ² or less, 1000000 pieces/mm ² or less, 500000 pieces/mm ² or less, or 100000 pieces/mm ² or less. This allows excellent conductivity and insulation to be obtained even when the electrode size of the light-emitting element 30 is small.

The particle surface density of the cured film 40 is that of the conductive particles when formed into a film during production. This is the same whether the measurement is for a randomly arranged portion or an arranged portion. When determining the particle number density of an individual piece of the cured film 40 formed in a specified unit, the particle surface density can be calculated from the area including the individual pieces and spaces, excluding the spaces between the pieces, and the number of particles. There are cases where it is inappropriate to express the individual pieces in terms of number density, and there are cases where it is appropriate to express them in terms of the particle area ratio in one piece, particle diameter, inter-particle center distance, and number.

When the binder contains conductive particles, the thickness of the cured film 40 is preferably 1 to 4 μm, and particularly preferably 1 to 2 μm, added to the average particle size of the conductive particles. This makes it possible to reduce the difference between the height Ha of the first surface of the cured film 40 between the light-emitting elements 30 and the height Hb of the bottom surface of the body of the light-emitting element 30. The height Hb of the bottom surface of the body of the light-emitting element 30 is the height from the bottom surface excluding the electrodes, and if there is a step on the bottom surface, it can be taken as the average value of the bottom surface with the step.

The difference between the height Ha of the first surface of the cured film 40 between the light-emitting elements 30 and the height Hb of the bottom surface of the body of the light-emitting element 30 is preferably 1 μm or less, more preferably 0.8 μm or less, and even more preferably 0.6 μm or less. By reducing the difference between the height Ha of the first surface of the cured film 40 and the height Hb of the bottom surface of the body of the light-emitting element 30, it is possible to suppress the occurrence of wrinkles on the first surface of the cured film 40 and to suppress light scattering.

In such a display device, the first surface of the cured film 40 on which the light-emitting element 30 is mounted is optically flat, suppressing light scattering and providing excellent light transmittance and visibility that could not be achieved with conventional connections using ACP, ACF, NCF, etc.

[Connection structure]
In the above-described embodiment, a display device as a display in which light-emitting elements 30 are arranged has been given as an example, but the present technology can also be applied to a connection structure in which a first electronic component and a second electronic component are connected. That is, the connection structure includes a first electronic component, a second electronic component, and a cured film that connects the first electronic component and the second electronic component, the cured film has a first surface having a root-mean-square height of 3.0×10 ⁻¹ or less, and the first electronic component is mounted on the first surface.

Examples of the first electronic component and the second electronic component include light-emitting elements, ICs (Integrated Circuits), flexible printed circuits (FPCs), LCD (Liquid Crystal Display) panels, transparent substrates for flat panel display (FPD) applications such as organic electroluminescence (OLED), touch panel applications, and printed wiring boards (PWBs). The material of the printed wiring board is not particularly limited, and may be, for example, glass epoxy such as FR-4 base material, or plastics such as thermoplastic resins and ceramics. The transparent substrate is not particularly limited as long as it is highly transparent, and examples include glass substrates and plastic substrates. The second electronic component may be provided with, for example, a silicone rubber layer.

<4. Manufacturing method of display device>
The manufacturing method of the display device according to the present embodiment includes a placement step of placing a connection film having a first surface with a root mean square height of a predetermined value or less at a predetermined position on a wiring board, and a mounting step of mounting a plurality of light emitting elements on the first surface and mounting the plurality of light emitting elements on the wiring board. Here, for example, when the electrode of the light emitting element has a cone-shaped protrusion, an adhesive layer that does not contain conductive particles can be used as the connection film. Also, for example, when the electrode of the light emitting element has a flat bottom surface, an anisotropic conductive film can be used as the connection film.

FIG. 3 is a diagram for explaining an example of a manufacturing method for a display device in this embodiment, where FIG. 3(A) shows a placement process for placing an anisotropic conductive film at a predetermined position on a wiring board, and FIG. 3(B) shows a mounting process for mounting a light-emitting element on the wiring board. Here, the anisotropic conductive film 12, wiring board 20, and light-emitting element 30 are the same as those described above for the connection film and display device, so they are given the same reference numerals and their description is omitted.

(Placement process)
3(A), in the placement step, the anisotropic conductive film 12 formed on the base film 11 is placed at a predetermined position on the wiring board 20. Specifically, in the film laminate shown in FIG. 1(C), the cover film 13 is peeled off from the anisotropic conductive film 12, the second surface of the anisotropic conductive film 12 is placed in contact with the wiring board 20, the base film 11 is peeled off from the anisotropic conductive film 12, and the first surface of the anisotropic conductive film 12 is used as the mounting surface.

The anisotropic conductive film 12 may be disposed, for example, over the entire display area of the wiring board 20, or may be disposed in individual pieces of a predetermined unit in part of the display area, such as one pixel unit (one picture element unit) of one set of RGB.

The method of arranging the anisotropic conductive film 12 on the wiring board 20 is not particularly limited. For example, when arranging the anisotropic conductive film 12 over the entire surface of the display section, a lamination method can be used. Also, when arranging individual pieces of the anisotropic conductive film 12 on a portion of the display section, a method of directly transferring and arranging the individual pieces from the base film 11 to the wiring board 20 using an LLO device, or a method of using a transfer material (stamp material) to which the individual pieces have been previously adhered, and transferring and arranging the individual pieces from the transfer material to the wiring board 20 can be used.

(Mounting process)
3B, in the mounting process, the light emitting element 30 is mounted on the first surface of the anisotropic conductive film 12 arranged at a predetermined position on the wiring board 20. The method of arranging the light emitting element in the mounting process is not particularly limited. For example, there is a method of arranging the light emitting element on the wiring board using an LLO device, a method of using a transfer material (stamp material) to which the light emitting element has been previously adhered, and a method of arranging the light emitting element from the transfer material to the wiring board.

The light-emitting element 30 can be connected to the wiring board 20 by any suitable method, such as thermocompression bonding, photocompression bonding, or thermo-photocompression bonding, which are all used in known anisotropic conductive films. If the conductive particles are solder particles, they may be connected by reflow. Connection conditions include, for example, a temperature of 150°C to 260°C, a pressure of 1 MPa to 60 MPa, and a time of 5 seconds to 300 seconds. As the anisotropic conductive film hardens, a hardened film is formed, allowing the light-emitting element 30 to be anisotropically connected to the wiring board 20.

[Method of manufacturing the connection structure]
In addition, in the above-described embodiment, the manufacturing method of the display device as a display is given as an example, but the present technology is not limited thereto, and can be applied to, for example, a manufacturing method of a light-emitting device as a light source. Also, the present technology can be applied to a manufacturing method of a connection structure that connects a first electronic component and a second electronic component. That is, the manufacturing method of the connection structure includes a placement step of placing a connection film having a first surface whose root mean square height is a predetermined value or less at a predetermined position of the first electronic component, and a mounting step of mounting a plurality of second electronic components on the first surface and mounting the plurality of second electronic components on the first electronic component. Examples of the first electronic component and the second electronic component include those similar to the connection structure described above.

5. Examples
In this example, an anisotropic conductive film was produced and evaluated for Sq (root mean square height), haze, and visible light transmittance. Note that the present technology is not limited to these examples.

[Sq (root mean square height) measurement]
The Sq of the base film and the Sq of the surface of the sample facing the base film were measured using a three-dimensional non-contact surface roughness measuring device manufactured by Zygo.

[Haze measurement]
The haze of the sample was measured using a HAZEMETER (HM-150, manufactured by Murakami Color Research Laboratory) according to a method in accordance with JIS K7136. The haze was evaluated according to the haze (%) on both the plain glass side and the anisotropic conductive film side of the sample, according to the following criteria. The haze is preferably evaluated as B or higher.
A: Less than 40% B: Between 40% and 50% C: 50% or more

[Visible light transmittance measurement]
The transmittance of the sample in the visible light region (380 nm to 780 nm) was measured using an ultraviolet-visible spectrophotometer (V-560 manufactured by JASCO Corporation). The visible light transmittance was evaluated according to the following criteria according to the visible light transmittance (%) of both the plain glass side and the anisotropic conductive film side of the sample. The visible light transmittance is preferably evaluated as B or higher.
A: 45% or more B: 30% or more but less than 45% C: less than 30% [Example 1]

(Preparation of anisotropic conductive film)
A binder was prepared by mixing 50 wt % of polyvinyl acetal resin (product name: KS-10, manufactured by Sekisui Chemical Co., Ltd.), 40 wt % of high-purity hydrogenated epoxy resin (product name: YX8000, manufactured by Mitsubishi Chemical Corporation), and 10 wt % of a cationic polymerization initiator (product name: SI-60L, manufactured by Sanshin Chemical Industry Co., Ltd.).

The binder was applied to a PET (Poly Ethylene Terephthalate) film (product name: SP3040ASCR, manufactured by Toyo Cross Co., Ltd.) having a root mean square height (Sq) of 1.2×10 ⁻³ and a thickness of 50 μm as a base film, and dried to form a resin film. Next, an arrangement sheet in which conductive particles (average particle size ^2.2 μm, resin core metal-coated fine particles, Ni plating 0.1 μm thick, manufactured by Sekisui Chemical Co., Ltd.) with a particle density of 58000 pcs/mm 2 were arranged in a hexagonal lattice shape was attached to the resin film, and the conductive particles were pressed into the resin film to be transferred. Next, a PET (Poly Ethylene Terephthalate) film (product name: RSP3030FA2S, manufactured by Toyo Cross Co., Ltd.) having a thickness of 25 μm was attached to the transfer surface of the conductive particles as a cover film, and an anisotropic conductive film in which conductive particles were aligned to a thickness of 4 μm was produced.

Then, the cover film was peeled off from the anisotropic conductive film measuring 30 mm x 40 mm and 4 μm thick, and the conductive particle transfer surface was attached to plain glass measuring 40 mm x 70 mm and 0.4 mm thick, after which the base film was peeled off to produce a sample with the first surface of the anisotropic conductive film on its surface. The bonding conditions were a temperature of 50°C, a vacuuming time of 10 seconds, a pressure time of 10 seconds, and a pressure of 0.1 MPa.

As shown in Table 1, the sample of Example 1 had an Sq of 6.0×10 ⁻² μm, a haze rating of A, and a visible light transmittance rating of A.

[Example 2]
An anisotropic conductive film was produced using a PET film with a root mean square height (Sq) of 1.1×10 ⁻¹ μm and a thickness of 50 μm as the base film, and a sample was produced in the same manner as in Example 1, except that the film was cured at a temperature of 200° C. for 10 minutes.

As shown in Table 1, the sample of Example 2 had an Sq of 8.0×10 ⁻² μm, a haze rating of A, and a visible light transmittance rating of A.

[Example 3]
A sample was prepared in the same manner as in Example 1, except that a PET film having a root mean square height (Sq) of 1.1×10 ⁻¹ μm and a thickness of 50 μm was used as the substrate film.

As shown in Table 1, the sample of Example 3 had an Sq of 9.0×10 ⁻² μm, a haze rating of A, and a visible light transmittance rating of B.

[Example 4]
A sample was prepared in the same manner as in Example 1, except that a PET film having a root-mean-square height (Sq) of 2.8×10 ⁻¹ μm and a thickness of 50 μm was used as the substrate film.

As shown in Table 1, the sample of Example 4 had an Sq of 2.6×10 ⁻¹ μm, a haze rating of B, and a visible light transmittance rating of B.

[Comparative Example 1]
A sample was prepared in the same manner as in Example 1, except that a PET film having a root mean square height (Sq) of 5.0×10 ⁻¹ μm or more and a thickness of 50 μm was used as the base film.

As shown in Table 1, the sample of Comparative Example 1 had an Sq of 5.0×10 ⁻¹ μm or more, a haze rating of C, and a visible light transmittance rating of C.

[Comparative Example 2]
A sample was prepared in the same manner as in Example 1, except that a PET film having a root mean square height (Sq) of 7.0×10 ⁻¹ μm or more and a thickness of 50 μm was used as the base film.

As shown in Table 1, the sample of Comparative Example 2 had an Sq of 7.0×10 ⁻¹ μm or more, a haze rating of C, and a visible light transmittance rating of C.

As shown in Table 1, in Comparative Example 1 and Comparative Example 2, the root mean square height of the first surface of the anisotropic conductive film exceeded 3.0×10 ⁻¹ μm, and therefore good haze evaluation and visible light transmittance evaluation could not be obtained.

On the other hand, in Examples 1 to 4, the root mean square height of the first surface of the anisotropic conductive film was 3.0×10 ⁻¹ μm or less, so good haze evaluations and visible light transmittance evaluations could be obtained, and it was found that it was possible to improve the light transmittance and visibility of the display device. Also, in Examples 1 to 3, the root mean square height of the first surface of the anisotropic conductive film was 1.0×10 ⁻¹ μm or less, so the haze could be made less than 40%. Also, as a result of comparing Example 2 with Example 3, it was found that the visible light transmittance was improved by curing the anisotropic conductive film.

REFERENCE SIGNS LIST 11 Base film, 11a First surface, 12 Connection film, 12a First surface, 13 Cover film, 20 Wiring board, 30 Light emitting element, 40 Hardened film, 40a First surface

Claims

A light-emitting element comprising: a plurality of light-emitting elements; a wiring board; and a cured film of a connection film that connects the plurality of light-emitting elements and the wiring board;
the cured film has a first surface having a root mean square height of 3.0×10 −1 μm or less;
A display device in which the plurality of light-emitting elements are mounted on the first surface.
The display device according to claim 1, wherein the haze of the cured film between the light-emitting elements is less than 50%, and the visible light transmittance of the cured film between the light-emitting elements is 30% or more.
The display device according to claim 1, wherein the cured film contains conductive particles, and the thickness of the cured film is the average particle size of the conductive particles plus 1 to 2 μm.
The conductive particles have an average particle size of 3.0 μm or less,
4. The display device according to claim 3, wherein the conductive particles are aligned at a particle surface density of 50,000 particles/ mm2 or more.
The display device according to claim 4, wherein the difference in height between the first surface of the cured film between the light-emitting elements and the bottom surface of the body of the light-emitting element is 1 μm or less.
a placement step of placing a connection film having a first surface with a root mean square height of 3.0×10 −1 μm or less at a predetermined position on a wiring board;
a mounting step of mounting a plurality of light-emitting elements on the first surface and mounting the plurality of light-emitting elements on a wiring board.
A connecting film having a first surface with a root mean square height of 3.0×10 −1 μm or less.
The connection film according to claim 7, which has a haze of less than 50% and a visible light transmittance of 30% or more.
The connection film according to claim 7, which contains conductive particles and has a thickness that is the average particle size of the conductive particles plus 1 to 2 μm.
The conductive particles have an average particle size of 3.0 μm or less,
The connecting film according to claim 9 , wherein the conductive particles are aligned at a particle surface density of 50,000 particles/mm 2 or more.
8. The connection film according to claim 7, further comprising a base film having a root mean square height of 3.0×10 −1 μm or less on the first surface side.
forming a connection film on a base film having a root mean square height of 3.0×10 −1 μm or less;
A method for producing a connecting film, the connecting film having a first surface on the base film side, the first surface having a root mean square height of 3.0×10 −1 μm or less.