WO2023238253A1

WO2023238253A1 - Buffer sheet, method for mounting electronic component, and method for manufacturing electronic component device

Info

Publication number: WO2023238253A1
Application number: PCT/JP2022/023007
Authority: WO
Inventors: 一尊本田; 昌貴西田; 佑太郎高松; 栄作石川
Original assignee: 株式会社レゾナック
Priority date: 2022-06-07
Filing date: 2022-06-07
Publication date: 2023-12-14

Abstract

This buffer sheet comprises a thermally cured layer and a non-thermally cured layer, wherein the thickness of the non-thermally cured layer is 10 μm or less.

Description

Buffer sheet, electronic component mounting method, and electronic component device manufacturing method

The present disclosure relates to a buffer sheet, a method for mounting electronic components, and a method for manufacturing an electronic component device.

Conventionally, displays using LEDs (Light Emitting Diodes) have mainly used LED packages (chip LEDs) with a size of about 1 mm or more, which are manufactured by mounting LEDs on a substrate by wire bonding. In recent years, from the viewpoint of achieving higher pixel density and response speed, a method of directly mounting small LEDs called mini LEDs, micro LEDs, etc. on a substrate by flip-chip bonding is being adopted.

In addition to display peripheral components such as LEDs, package forms such as FO-WLP (Fan Out Wafer Level Package) and FI-WLP (Fan In Wafer Level Package), and discrete semiconductors that perform a single function such as capacitors will become widespread. Accordingly, the size of electronic components mounted on boards is becoming smaller. Since it takes a lot of time to individually mount miniaturized electronic components onto a board, there is a trend toward a method of mounting multiple electronic components at once in order to improve productivity.

As a method for mounting multiple electronic components on a board at once, multiple electronic components are placed on the board via a connecting material such as solder, and a member is heated to a temperature that melts the connecting material. There is a method (thermo-compression bonding) in which electronic components are pressed onto a board using a method called thermocompression bonding. With this method, if the shape, height, etc. of the electronic component is not constant, or if the surface of the heated member that contacts the electronic component is tilted, the pressure will be applied evenly to the electronic component (especially the connection part with the board). Otherwise, a connection failure may occur. As a measure to apply pressure evenly to LED chips arranged on a substrate, for example, Patent Document 1 discloses that a sheet in which cured layers of a silicone rubber composition are laminated on both sides of a heat-resistant resin film is used to apply heat. It has been proposed to perform crimping.

Japanese Patent Application Publication No. 2015-170690

As electronic components become smaller, there is an increasing possibility that connection failures will occur due to slight unevenness in thermocompression bonding conditions. In addition, as the density of electronic components increases, the distance between electronic components arranged on a substrate tends to become narrower. For this reason, existing sheets cannot be sufficiently deformed to accommodate the narrower spacing between electronic components, and as a result, a sufficient contact area with electronic components cannot be obtained, resulting in cases where good pressure buffering effects cannot be obtained. ing.

In view of the above circumstances, the present disclosure provides a buffer sheet that enables good mounting of electronic components on a board, a method for mounting electronic components using this buffer sheet, and a method for manufacturing an electronic component device using this buffer sheet. The task is to do so.

Means for solving the above problems include the following embodiments.
<1> A buffer sheet comprising a thermosetting layer and a non-thermosetting layer, the thickness of the non-thermosetting layer being 10 μm or less.
<2> The buffer sheet according to <1> for use in the process of mounting electronic components on a board.
<3> The buffer sheet according to <2>, wherein the electronic component includes a micro LED.
<4> The buffer sheet according to <2> or <3>, wherein the non-thermosetting layer is disposed on a side facing the electronic component.
<5> The buffer sheet according to any one of <1> to <4>, wherein the thermosetting layer has a thickness of 10 μm to 100 μm.
<6> The buffer sheet according to any one of <1> to <5>, wherein the thermosetting layer contains a (meth)acrylate compound.
<7> The buffer sheet according to any one of <1> to <6>, wherein the thermosetting layer contains a polymer component.
<8> The buffer sheet according to any one of <1> to <7>, comprising the non-thermosetting layer, the thermosetting layer, and the cover layer in this order.
<9> A step of thermocompression bonding an electronic component and a board using a heating member, and the thermocompression bonding includes any one of <1> to <8> between the heating member and the electronic component. A method for mounting electronic components with the buffer sheet described in section 2.
<10> A step of thermocompression bonding an electronic component and a board using a heating member, and the thermocompression bonding includes any one of <1> to <8> between the heating member and the electronic component. A method for manufacturing an electronic component device, which is carried out in a state in which the buffer sheet described in 1.

According to the present disclosure, a buffer sheet that enables good mounting of electronic components on a board, a method for mounting electronic components using this buffer sheet, and a method for manufacturing an electronic component device using this buffer sheet are provided.

FIG. 2 is a schematic diagram showing an example of the configuration of a buffer sheet. It is a schematic diagram showing an example of a thermocompression bonding process using a buffer sheet. It is a schematic diagram showing an example of a thermocompression bonding process using a buffer sheet. It is a schematic diagram showing an example of a thermocompression bonding process using a buffer sheet. It is a schematic diagram showing an example of a thermocompression bonding process using a buffer sheet.

Hereinafter, embodiments according to the present disclosure will be described in detail. However, the present disclosure is not limited to the following embodiments.
In the following embodiments, the constituent elements (including elemental steps and the like) are not essential unless otherwise specified. The same applies to numerical values and their ranges, and they do not limit the present invention.
In this disclosure, the term "step" includes not only a step that is independent from other steps, but also a step that cannot be clearly distinguished from other steps, as long as the purpose of the step is achieved. .
In the present disclosure, numerical ranges indicated using "~" include the numerical values written before and after "~" as minimum and maximum values, respectively.
In the numerical ranges described step by step in this disclosure, the upper limit or lower limit described in one numerical range may be replaced with the upper limit or lower limit of another numerical range described step by step. . Furthermore, in the numerical ranges described in this disclosure, the upper limit or lower limit of the numerical range may be replaced with the values shown in the Examples.
In the present disclosure, each component may contain multiple types of corresponding substances. If there are multiple types of substances corresponding to each component in the composition, the content rate or content of each component is the total content rate or content of the multiple types of substances present in the composition, unless otherwise specified. means quantity.

<Buffer sheet>
The buffer sheet of the present disclosure includes a thermosetting layer and a non-thermosetting layer, and the thickness of the non-thermosetting layer is 10 μm or less.
In the present disclosure, the term "buffer sheet" refers to a material used to reduce uneven pressure applied to an object when pressing one object onto another object.
In the present disclosure, the term "thermosetting layer" refers to a layer that has the property of being hardened by heating.
In the present disclosure, a "non-thermosetting layer" means a layer that does not have the property of being hardened by heating.

The buffer sheet of the present disclosure is used, for example, in the process of mounting electronic components on a board. By using the buffer sheet having the above configuration, it is possible to successfully mount electronic components onto a board. In particular, the occurrence of connection failures can be effectively suppressed even when small electronic components are mounted at high density. The reason for this is thought to be as follows.

The thermosetting layer included in the buffer sheet is deformed to match the shape of the electronic component by pressure applied from a member (hereinafter also referred to as a heating member) that applies heat and pressure to the electronic component placed on the substrate. , is cured by heat applied from a heating member. That is, the thermosetting layer is cured in a deformed state that conforms to the shape of the electronic component, so that the deformed state is maintained.

The non-thermosetting layer included in the buffer sheet deforms in response to deformation of the thermosetting layer depending on the shape of the electronic component. When the thickness of the non-thermosetting layer is 10 μm or less, it is possible to sufficiently follow the deformation of the thermosetting layer even when the distance between electronic components is narrow (for example, 100 μm or less).
As a result, a sufficient contact area of the buffer sheet with respect to the electronic component can be ensured, and the effect of buffering the pressure applied to the electronic component can be satisfactorily exhibited.

It is preferable that the buffer sheet has a non-thermosetting layer having a thickness of 10 μm or less on the side that comes into contact with electronic components in the thermocompression bonding process.
By having a non-thermosetting layer with a thickness of 10 μm or less on the side where the buffer sheet contacts electronic components during the thermocompression bonding process, a sufficient contact area of the buffer sheet with the electronic components during thermocompression bonding can be ensured, reducing the pressure applied to the electronic components. The buffering effect is well exhibited. Furthermore, the buffer sheet can be removed from the electronic component after the thermocompression bonding process is completed without the thermosetting layer adhering to the electronic component.

From the viewpoint of ensuring a sufficient contact area between the buffer sheet and the electronic component, it is preferable that the thermosetting layer is temporarily softened by the heat applied in the thermocompression bonding process, and then hardened.

From the viewpoint of avoiding adhesion of the non-thermo-cured layer to electronic components, it is preferable that the melting point of the components contained in the non-thermo-cured layer is higher than the temperature of the heat applied in the thermocompression bonding process. For example, when the component contained in the non-thermosetting layer is a thermoplastic resin, its melting point is preferably 30°C or more higher than the temperature of the heat applied in the thermocompression bonding process, and more preferably 50°C or more higher. , more preferably 70°C or more.
When the component contained in the non-thermosetting layer is a metal, its melting point is preferably 30°C or more higher than the temperature of the heat applied in the thermocompression bonding process, more preferably 50°C or more higher, and 70°C or more higher. It is even more preferable.
In the present disclosure, the glass transition temperature of the thermoplastic resin is measured using a differential scanning calorimeter (DSC, manufactured by PerkinElmer, Model DSC-7) at a sample amount of 10 mg, a heating rate of 5°C/min, and a measurement atmosphere. : Value measured under air conditions.

The thickness (total thickness) of the buffer sheet is not particularly limited, and can be selected depending on the thermocompression bonding method, the condition of the object to be thermocompression bonded, etc.
From the viewpoint of ensuring a sufficient pressure buffering effect, the thickness of the buffer sheet is preferably 20 μm or more, more preferably 40 μm or more, and even more preferably 60 μm or more.
From the viewpoint of ensuring sufficient thermal conductivity, the thickness of the buffer sheet is preferably 150 μm or less, more preferably 125 μm or less, and even more preferably 100 μm or less.

(Thermosetting layer)
The thermosetting layer contains, for example, a curable component. Examples of the curable component include (meth)acrylate compounds, epoxy resins, bismaleimide compounds, cyanate compounds, and phenol compounds. The curable component may be a combination of a base agent and a curing agent.

From the viewpoint of the viscosity before the curing reaction of the thermosetting layer and the coefficient of thermal expansion after the curing reaction, the curable component is at least one selected from the group consisting of (meth)acrylate compounds, epoxy resins, bismaleimide compounds, and phenol compounds. (meth)acrylate compounds are preferred, at least one selected from the group consisting of (meth)acrylate compounds, epoxy resins, and bismaleimide compounds is more preferred, and (meth)acrylate compounds are even more preferred from the viewpoint of curing speed. The thermosetting layer may contain only one type of curable component or a combination of two or more types.
In the present disclosure, "(meth)acrylate" means acrylate or methacrylate.

When the thermosetting layer contains a (meth)acrylate compound, the (meth)acrylate compound is not particularly limited and can be appropriately selected from commonly used (meth)acrylate compounds. The (meth)acrylate compound may be a monofunctional (meth)acrylate compound or a bifunctional or more (meth)acrylate compound. Specifically, the (meth)acrylate compounds include erythritol-type poly(meth)acrylate compounds, glycidyl ether-type (meth)acrylate compounds, bisphenol A-type di(meth)acrylate compounds, cyclodecane-type di(meth)acrylate compounds, and methylol-type di(meth)acrylate compounds. (meth)acrylate compounds, dioxane type di(meth)acrylate compounds, bisphenol F type (meth)acrylate compounds, dimethylol type (meth)acrylate compounds, isocyanuric acid type di(meth)acrylate compounds, isocyanuric acid type tri(meth)acrylates compounds, trimethylol type tri(meth)acrylate compounds, and the like. Among them, trimethylol type tri(meth)acrylate compounds, isocyanuric acid type di(meth)acrylate compounds, isocyanuric acid type tri(meth)acrylate compounds, bisphenol F type (meth)acrylate compounds, cyclodecane type di(meth)acrylate compounds, and glycidyl ether type (meth)acrylate compounds.

From the viewpoint of the curing rate and the strength of the cured product after the curing reaction, the (meth)acrylate compound is preferably a difunctional or more functional (meth)acrylate compound.
From the viewpoint of suppressing reaction inhibition (meaning a phenomenon in which all functional groups do not react sufficiently) caused by the large number of functional groups in (meth)acrylate compounds, (meth)acrylate compounds are difunctional (meth)acrylates. A compound or a trifunctional (meth)acrylate compound is preferable.
The number of (meth)acrylate compounds contained in the thermosetting layer may be one or two or more.

When the thermosetting layer contains a (meth)acrylate compound, it may contain a polymerization initiator to promote the polymerization reaction of the (meth)acrylate compound. Examples of the polymerization initiator include compounds that generate radicals by heat (thermal radical polymerization initiators).

Examples of thermal radical polymerization initiators include azo compounds and organic peroxides. From the viewpoint of handleability and storage stability, organic peroxides are preferred.

Examples of the thermal radical polymerization initiator include ketone peroxide, hydroperoxide, diacyl peroxide, dialkyl peroxide, peroxyketal, alkyl perester (alkyl peroxy ester), and peroxy carbonate.
Thermal radical polymerization initiators may be used alone or in combination of two or more.

Specific examples of ketone peroxide include methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide, acetylacetone peroxide, cyclohexanone peroxide, and methyl cyclohexanone peroxide.

Specific examples of hydroperoxides include 1,1,3,3-tetramethylbutyl hydroperoxide, cumene hydroperoxide, t-butyl hydroperoxide, p-menthane hydroperoxide, and diisopropylbenzene hydroperoxide. Can be mentioned.

Specific examples of diacyl peroxide include diisobutyryl peroxide, bis-3,5,5-trimethylhexanoyl peroxide, dilauroyl peroxide, dibenzoyl peroxide, m-toluylbenzoyl peroxide, and succinic acid peroxide. can be mentioned.

Specific examples of dialkyl peroxide include dicumyl peroxide, 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane, 1,3-bis(t-butylperoxyisopropyl)hexane, t-butyl Cumyl peroxide, di-t-butyl peroxide, di-t-hexyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3, and di(t-butyl peroxide) Diisopropylbenzene is mentioned.

Specific examples of peroxyketals include 1,1-bis(t-hexylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-hexylperoxy)cyclohexane, and 1,1-bis(t-hexylperoxy)-3,3,5-trimethylcyclohexane. -butylperoxy)-2-methylcyclohexane, 1,1-bis(t-butylperoxy)cyclohexane, 2,2-bis(t-butylperoxy)butane, and 4,4-bis[(t-butyl)peroxy] Butyl pentanoate is mentioned.

Specific examples of alkyl peresters (alkyl peroxy esters) include 1,1,3,3-tetramethylbutylperoxyneodecanoate, α-cumylperoxyneodecanoate, and t-butylperoxyneodecanoate. , t-hexylperoxyneodecanoate, t-butylperoxyneoheptanoate, t-hexylperoxypivalate, t-butylperoxypivalate, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexa Noate, t-amylperoxy-2-ethylhexanoate, t-butylperoxy-2-ethylhexanoate, t-butylperoxyisobutyrate, di-t-butylperoxyhexahydroterephthalate, 1,1,3 , 3-tetramethylbutylperoxy-3,5,5-trimethylhexanoate, t-amylperoxy-3,5,5-trimethylhexanoate, t-butylperoxy-3,5,5-trimethylhexanoate, t-Butylperoxyacetate, t-butylperoxybenzoate, dibutylperoxytrimethyladipate, 2,5-dimethyl-2,5-di-2-ethylhexanoylperoxyhexane, t-hexylperoxy-2-ethylhexanoate, t -hexylperoxyisopropyl monocarbonate, t-butylperoxylaurate, t-butylperoxyisopropyl monocarbonate, t-butylperoxy-2-ethylhexyl monocarbonate, and 2,5-dimethyl-2,5-di-benzoylperoxyhexane Can be mentioned.

Specific examples of peroxycarbonates include di-n-propylperoxydicarbonate, diisopropylperoxycarbonate, di-4-t-butylcyclohexylperoxycarbonate, di-2-ethylhexylperoxycarbonate, di-sec-butylperoxycarbonate, and di-sec-butylperoxycarbonate. -3-methoxybutyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, diisopropyloxydicarbonate, t-amylperoxyisopropyl carbonate, t-butylperoxyisopropyl carbonate, t-butylperoxy-2-ethylhexyl carbonate, 1,6 -bis(t-butylperoxycarboxyloxy)hexane.

From the viewpoint of reaction rate and storage stability, the polymerization initiators include 1,1-bis(t-butylperoxy)cyclohexane, di(t-butylperoxide)diisopropylbenzene, dicumyl peroxide, and 2,5-dimethyl. -2,5-di(t-butylperoxy)hexane, t-butylcumyl peroxide, and di-t-butyl peroxide are preferred.

When the thermosetting layer contains a polymerization initiator, the content thereof is preferably 0.1 to 20 parts by mass, and 1 to 10 parts by mass, based on 100 parts by mass of the curable component contained in the thermosetting layer. It is more preferably 2 parts by mass to 5 parts by mass.

The thermosetting layer may contain a polymer component from the viewpoint of adjusting film-forming properties and viscosity before the curing reaction, mechanical properties after the curing reaction, etc.

Examples of the polymer component contained in the thermosetting layer include thermoplastic resins such as acrylic resin, styrene resin, butadiene resin, imide resin, and amide resin.
The thermosetting layer may contain only one type of polymer component or a combination of two or more types.

The polymer component can be produced, for example, by radical polymerizing polymerizable monomers. Examples of the polymerizable monomer include (meth)acrylic acid; (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, and benzyl (meth)acrylate; diacetone (meth)acrylamide; (meth)acrylamides such as; styrene or styrene derivatives such as styrene, vinyltoluene, and α-methylstyrene; ethers of vinyl alcohols such as vinyl-n-butyl ether; maleic acid; monomaleic acids such as monomethyl maleate and monoethyl maleate; Esters; fumaric acid; cinnamic acid; itaconic acid; and crotonic acid. These polymerizable monomers may be used alone or in combination of two or more. The polymer component may be an acrylic block copolymer obtained by block copolymerization using at least one selected from the above-mentioned (meth)acrylate compounds as a polymerization component as a curable component.
In the present disclosure, "(meth)acrylic acid" means acrylic acid or methacrylic acid, and "(meth)acrylamide" means acrylamide or methacrylamide.

The weight average molecular weight of the polymer component is preferably from 5,000 to 1,000,000, more preferably from 20,000 to 500,000, from the viewpoint of film formability and fluidity.
The weight average molecular weight of the polymer component in the present disclosure is a value measured by gel permeation chromatography (GPC) and converted using a calibration curve prepared using standard polystyrene. The conditions for GPC are shown below.
Pump: L-6000 type (manufactured by Hitachi, Ltd., product name)
Column: Gelpack GL-R420 + Gelpack GL-R430 + Gelpack GL-R440 (3 columns in total) (manufactured by Showa Denko Materials Co., Ltd., product name)
Eluent: Tetrahydrofuran (THF)
Measurement temperature: 40℃
Flow rate: 2.05 mL/min Detector: L-3300 RI (manufactured by Hitachi, Ltd., trade name)

When the thermosetting layer contains a curable component and a polymer component, the content of the polymer component is, for example, preferably 1 part by mass to 500 parts by mass, and 10 parts by mass, based on 100 parts by mass of the curable component. It is more preferably from 100 parts to 300 parts by weight, and even more preferably from 100 parts to 300 parts by weight.
When the content of the polymer component is 1 part by mass or more per 100 parts by mass of the curable component, film formability tends to improve. When the content of the polymer component is 500 parts by mass or less based on 100 parts by mass of the curable component, the curability of the thermosetting layer is sufficiently ensured and a sufficient pressure buffering effect tends to be obtained.

The thermoset layer may contain an inorganic filler. Examples of inorganic fillers include silica such as fused silica and crystalline silica, calcium carbonate, clay, alumina, silicon nitride, silicon carbide, boron nitride, calcium silicate, potassium titanate, aluminum nitride, beryllia, zirconia, zircon, and phosphatide. Examples include inorganic materials such as stellite, steatite, spinel, mullite, titania, and glass.
Examples of the shape of the inorganic filler include particles, beads made of spherical particles, fibers, and the like.
The thermosetting layer may contain only one type of inorganic filler or a combination of two or more types.

When the inorganic filler is a particle, the volume average particle diameter is preferably in the range of 0.01 μm to 15.0 μm, more preferably in the range of 0.3 μm to 5.0 μm, for example. When the volume average particle diameter of the inorganic filler is 0.01 μm or more, the addition of the inorganic filler can sufficiently provide effects such as adjusting the viscosity of the thermoset layer. When the volume average particle size of the inorganic filler is 15.0 μm or less, the hardenability of the thermoset layer and the elastic modulus after curing can be effectively controlled without impairing the conformability of the thermoset layer to the shape of electronic components. .
In the present disclosure, the "volume average particle diameter" is measured by a laser diffraction scattering method. Specifically, in a volume-based particle size distribution curve obtained using a laser diffraction type particle size distribution measuring device, the particle size (D50) when the accumulation from the small diameter side is 50% is defined as the volume average particle size.

When the thermosetting layer contains an inorganic filler, the content of the inorganic filler is, for example, preferably 5% to 90% by mass, and 20% to 80% by mass of the total nonvolatile content contained in the thermosetting layer. It is more preferably 60% to 75% by mass, and even more preferably 60% to 75% by mass.
When the content of the inorganic filler is 5% by mass or more of the total nonvolatile content contained in the thermoset layer, the effect of reducing the coefficient of thermal expansion of the thermoset layer tends to be large, and the moisture resistance reliability is improved. There is a tendency. When the content of the inorganic filler is 90% by mass or less of the total nonvolatile content contained in the thermoset layer, the effects of addition of the inorganic filler such as deterioration of moldability of the thermoset layer and powder falling off tend to be suppressed. be.

The thermosetting layer may contain components other than those mentioned above, if necessary. Other components include polymerization inhibitors, curing accelerators, coupling agents, colorants, surfactants, ion trapping agents, and the like.

From the viewpoint of improving the formation of the thermosetting layer, the material used for forming the thermosetting layer may contain a solvent. For example, if the material used to form the thermosetting layer contains a solvent (varnish-like), the thermosetting layer with a desired thickness can be formed with high precision.
Examples of the solvent include methyl ethyl ketone, xylene, toluene, acetone, ethylene glycol monoethyl ether, cyclohexanone, ethyl ethoxypropionate, N,N-dimethylformamide, N,N-dimethylacetamide, and the like.
The number of solvents contained in the material used to form the thermosetting layer may be one type or a combination of two or more types.
The proportion of the solvent contained in the material used to form the thermosetting layer is not particularly limited, and can be adjusted according to the conditions for producing the thermosetting layer.

From the viewpoint of ensuring a sufficient pressure buffering effect, the thickness of the thermosetting layer is preferably 10 μm or more, more preferably 20 μm or more, and even more preferably 30 μm or more.
From the viewpoint of ensuring sufficient thermal conductivity, the thickness of the thermoset layer is preferably 100 μm or less, more preferably 80 μm or less, and even more preferably 60 μm or less.

(Non-thermosetting layer)
The material of the non-thermosetting layer is not particularly limited and can be selected in consideration of heat resistance to heat during thermocompression bonding, releasability from electronic components after the thermocompression bonding process, etc.
From the viewpoint of conformability to the shape of the electronic component and peelability from the electronic component, the non-thermosetting layer preferably has thermoplasticity (a property of softening when heated and hardening when cooled).

The non-thermosetting layer may be a layer containing, for example, a thermoplastic resin, a metal such as copper or aluminum, an inorganic oxide, or the like.
Specifically, thermoplastic resins include polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate, polyvinyl chloride, polycarbonate, polyimide, ABS (acrylonitrile-butadiene-styrene) resin, and AS ( Examples include acrylonitrile-styrene) resin, acrylic resin, polyamide, and polyamideimide.
The number of thermoplastic resins contained in the non-thermosetting layer may be one or two or more.

When the non-thermosetting layer contains a thermoplastic resin, polyethylene terephthalate and polyimide are preferable as the thermoplastic resin from the viewpoint of heat resistance and processability (external shape processing, thickness adjustment, etc.).

The non-thermosetting layer may be a single layer or a stack of multiple layers. For example, the non-thermosetting layer may be a laminated state of a layer containing a thermoplastic resin and a layer containing a metal.

From the viewpoint of conformability to the shape of the electronic component, the thickness of the non-thermosetting layer is preferably 9 μm or less, more preferably 8 μm or less, and even more preferably 7 μm or less.
From the viewpoint of avoiding defects such as tearing during thermocompression bonding, the thickness of the non-thermosetting layer is preferably 1 μm or more, more preferably 2 μm or more, and even more preferably 3 μm or more.

(cover layer)
If necessary, the buffer sheet may have a cover layer on the opposite side of the thermosetting layer to the side facing the non-thermosetting layer. That is, the buffer sheet may have a non-thermosetting layer, a thermosetting layer, and a cover layer in this order.
The cover layer plays the role of, for example, protecting the surface of the thermosetting layer of the buffer sheet, and facilitating the peeling of the buffer sheet from the heating member after the thermocompression bonding process.

The material of the cover layer is not particularly limited and can be selected depending on the desired function. For example, it may be a layer containing a resin, a metal such as copper, aluminum, an inorganic oxide, or the like. The resin may be the curable component exemplified as the curable component contained in the thermosetting layer, the thermoplastic resin exemplified as the thermoplastic resin contained in the non-thermosetting layer, or the like.

The thickness of the cover layer is not particularly limited and can be selected depending on its function. For example, it may be in the range of 1 μm to 50 μm. From the viewpoint of ensuring sufficient strength, the thickness of the cover layer is preferably 10 μm or more. From the viewpoint of ensuring sufficient thermal conductivity, the thickness of the cover layer is preferably 50 μm or less.

A specific example of the buffer sheet of the present disclosure and a thermocompression bonding process using the buffer sheet will be described with reference to the drawings. However, the present disclosure is not limited to this specific example.

FIG. 1 is a schematic diagram showing an example of the configuration of a buffer sheet. The buffer sheet 1 shown in FIG. 1 has a cover layer 1-a, a thermosetting layer 1-b, and a non-thermosetting layer 1-c in this order.

2 to 5 are schematic diagrams showing an example of a thermocompression bonding process using a buffer sheet.
As shown in FIG. 2, the electronic component 2 is placed on the substrate 5 so that the bumps 3 of the electronic component 2 face the pads or wiring 4 on the substrate 5. The bump 3 and the pad or wiring 4 are made of a metal material such as solder that melts with the heat of thermocompression bonding.

Next, as shown in FIG. 3, the heating member 6 is used to press the electronic component 2 toward the substrate 5 side. At this time, the buffer sheet 1 is placed between the heating member 6 and the electronic component 2. The buffer sheet 1 shown in FIG. 3 is arranged so that the non-thermosetting layer 1-c is in contact with the electronic component 2.

As shown in FIG. 4, when the electronic component 2 is pressed toward the substrate 5 using the heating member 6, the thermosetting layer 1-b of the buffer sheet 1 is deformed to match the shape of the electronic component 2. At this time, the non-thermosetting layer 1-c also deforms in accordance with the shape of the thermosetting layer 1-b.
In the buffer sheet of the present disclosure, since the thickness of the non-thermosetting layer 1-c is 10 μm or less, the non-thermosetting layer 1-c has excellent ability to follow the deformation of the thermosetting layer 1-b. Therefore, a sufficient contact area between the buffer sheet 1 and the electronic component 2 is ensured.
The heat applied from the heating member 6 hardens the thermosetting layer 1-b, and the metal material contained in the bumps 3 and pads or wirings 4 melts and joins them together.

After the thermocompression bonding process is completed, the release sheet 1 is removed from the electronic component 2, as shown in FIG. Since the buffer sheet 1 has the non-thermosetting layer 1-c on the side in contact with the electronic component 2, the buffer sheet 1 can be removed from the electronic component 2 without the thermosetting layer 1-b adhering to the electronic component 2. Can be removed.

<Method for mounting electronic components and method for manufacturing electronic component devices>
The electronic component mounting method of the present disclosure includes a step of thermocompression bonding the electronic component and the board using a heating member, and the thermocompression bonding includes the above-mentioned buffer sheet between the heating member and the electronic component. This is a mounting method for electronic components that is performed with the

A method for manufacturing an electronic component device according to the present disclosure includes a step of thermocompression bonding an electronic component and a board using a heating member, and the thermocompression bonding includes the above-mentioned buffer between the heating member and the electronic component. This is a method of manufacturing an electronic component device, which is performed with sheets arranged.

Hereinafter, the electronic component mounting method of the present disclosure and the electronic component device manufacturing method of the present disclosure may be collectively referred to as the "method of the present disclosure."
According to the method of the present disclosure, electronic components can be mounted on a board in good condition. It is particularly suitable for mounting a plurality of electronic components on a board. For example, even when small electronic components are mounted at high density, the occurrence of connection failures can be effectively suppressed.

The method of the present disclosure may be a method of mounting electronic components on a substrate with high density (ie, the distance between adjacent electronic components is small).
For example, the distance between adjacent electronic components (or the minimum value if the distance is not constant) may be 300 μm or less, 200 μm or less, 100 μm or less, or 50 μm or less. It's okay. The lower limit of the distance between adjacent electronic components (or the minimum value if the distance is not constant) is not particularly limited, but may be 10 μm or more.

In the method of the present disclosure, conditions for carrying out thermocompression bonding are not particularly limited. For example, the temperature of the heating member may be within the range of 25°C to 400°C.
From the viewpoint of obtaining a good pressure buffering effect, the temperature of the heating member is preferably such that the buffer sheet becomes deformable.
From the viewpoint of avoiding adhesion of the buffer sheet to electronic components, the temperature of the heating member is preferably such that the components contained in the buffer sheet do not melt.
The time during which the heating member is in contact with the electronic component (thermocompression bonding time) may be within the range of 1 second to 600 seconds.

The type of electronic component used in the method of the present disclosure is not particularly limited. Examples include semiconductor elements such as diodes, transistors, and thyristors, and various parts used in electronic component devices.
The type of semiconductor element is not particularly limited, and can be selected from LEDs, elemental semiconductors such as silicon and germanium, and compound semiconductors such as gallium arsenide and indium phosphide.

In some embodiments, the disclosed method uses micro-LEDs as electronic components. Micro LEDs are LEDs that are smaller than conventional LEDs (for example, the maximum diameter is less than 1000 μm), and are used in direct backlights of liquid crystal screens, etc. In order to achieve high definition images, there is a tendency for micro-LEDs to be mounted on a substrate at high density (that is, the intervals between micro-LEDs are narrow). According to the method of the present disclosure, high-density packaging of micro-LEDs can be performed satisfactorily.

The material of the bumps of the electronic component used in the method of the present disclosure is not particularly limited. Examples include gold, silver, copper, solder, tin, nickel, indium tin oxide (ITO), and indium. Examples of the solder include alloys whose main components are tin-silver, tin-lead, tin-bismuth, tin-copper, and the like. The bumps may be made of one type of material or a combination of two or more types. The bump may have a structure in which multiple types of metals are laminated.

The material of the substrate used in the method of the present disclosure is not particularly limited. Examples include glass, glass epoxy, polyester, ceramic, epoxy, bismaleimide triazine, polyimide, and the like.

The substrate may have a wiring pattern on its surface. The wiring pattern is formed by etching away unnecessary parts of the metal layer formed on the surface of the substrate, by plating metal on the surface of the substrate, and by printing a conductive substance on the surface of the substrate. Examples include things.
The material of the wiring pattern is not particularly limited, and examples include gold, silver, copper, solder, tin, nickel, indium tin oxide (ITO), and indium. Examples of the solder include alloys whose main components are tin-silver, tin-lead, tin-bismuth, tin-copper, and the like. The wiring pattern may be made of only one material or a combination of two or more materials. The wiring pattern may have a structure in which multiple types of metals are laminated.

The substrate may have a connection portion called a pad on its surface. Pads can be formed by etching away unnecessary parts of the metal layer formed on the surface of the substrate, pads formed by plating metal on the surface of the substrate, or pads formed by printing a conductive material on the surface of the substrate. etc.
The material of the pad is not particularly limited, and examples include gold, silver, copper, solder, tin, nickel, indium tin oxide (ITO), and indium. Examples of the solder include alloys whose main components are tin-silver, tin-lead, tin-bismuth, tin-copper, and the like. The material of the pad may be one type or a combination of two or more types. The pad may have a structure in which multiple types of metals are laminated.

The electronic component device obtained by the method of the present disclosure is not particularly limited. For example, it may be an electronic component device having an image display function such as a computer, a television, a game machine, a mobile phone, or a car navigation system.
Since the method of the present disclosure allows small electronic components to be mounted on a substrate at high density, it can also be suitably used for manufacturing an image display device equipped with a direct backlight.

Hereinafter, the present disclosure will be specifically described based on Examples, but the present disclosure is not limited to these Examples.

(Preparation of composition for thermosetting layer)
In a flask equipped with a stirrer, 4 g of an acrylic block copolymer (manufactured by Kuraray Co., Ltd., trade name "LA4285") was added as a polymer component, and tris (2-acryloyloxyethyl) isocyanurate (Showa) was added as a curable component. 2 g of Denko Materials Co., Ltd., trade name "FA731A") was added, and 0.08 g of dicumyl peroxide (manufactured by NOF Corporation, trade name "Perc Mill D") was added as a polymerization initiator, and as an inorganic filler. 16.7 g of silica particles (manufactured by Admatec Co., Ltd., trade name "SE2050", volume average particle diameter: 0.5 μm) and 12.8 g of methyl ethyl ketone as a solvent were added. These were stirred and mixed to obtain a varnish-like composition for a thermosetting layer.

(Preparation of buffer sheet)
The obtained thermosetting layer composition was coated on a polyimide film (manufactured by DuPont-Toray Co., Ltd., trade name "Kapton 100H", thickness: 25 μm) as a cover layer, and dried in a dryer at 70°C. It was dried by heating for 10 minutes to form a thermoset layer with a thickness of 50 μm on the polyimide film.
A polyethylene terephthalate film (manufactured by Toray Industries, Inc., thickness: 6 μm) as a non-thermoset layer is layered on the thermoset layer, and heated at 100°C, 0.5MPa, and 1.0m/min using a hot roll laminator. By bonding them together, a buffer sheet having a cover layer, a thermosetting layer, and a non-thermosetting layer in this order was obtained.

All documents, patent applications, and technical standards mentioned herein are incorporated by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference. Incorporated herein by reference.

Claims

A buffer sheet comprising a thermosetting layer and a non-thermosetting layer, the thickness of the non-thermosetting layer being 10 μm or less.
The buffer sheet according to claim 1, for use in the process of mounting electronic components on a board.
The buffer sheet according to claim 2, wherein the electronic component includes a micro LED.
The buffer sheet according to claim 2 or 3, wherein the non-thermosetting layer is arranged on a side facing the electronic component.
The buffer sheet according to any one of claims 1 to 4, wherein the thermosetting layer has a thickness of 10 μm to 100 μm.
The buffer sheet according to any one of claims 1 to 5, wherein the thermosetting layer contains a (meth)acrylate compound.
The buffer sheet according to any one of claims 1 to 6, wherein the thermosetting layer contains a polymer component.
The buffer sheet according to any one of claims 1 to 7, comprising the non-thermosetting layer, the thermosetting layer, and the cover layer in this order.
The method according to any one of claims 1 to 8, further comprising the step of thermocompression bonding an electronic component and a substrate using a heating member, and the thermocompression bonding is performed between the heating member and the electronic component. A method for mounting electronic components with a buffer sheet in place.
The method according to any one of claims 1 to 8, further comprising the step of thermocompression bonding an electronic component and a substrate using a heating member, and the thermocompression bonding is performed between the heating member and the electronic component. A method of manufacturing an electronic component device in which a buffer sheet is placed.