TWI888361B - Anisotropic conductive film, connection structure, and method for manufacturing same - Google Patents

Abstract

An anisotropic conductive film suitable for anisotropically conductively connecting electronic parts with bumps such as image display elements or driver IC chips to a flexible plastic substrate formed with transparent electrodes and wiring has at least an insulating resin layer and a conductive particle dispersion layer composed of conductive particles dispersed in the insulating resin layer. The anisotropic conductive film satisfies the following conditions: condition (1): the 20% compression modulus of the conductive particles is not less than 6000 N/ ^mm2 and not more than 15000 N/ ^mm2 ; condition (2): the compression recovery rate of the conductive particles is not less than 40% and not more than 80%; condition (3): the average particle size of the conductive particles is not less than 1 μm and not more than 30 μm; condition (4) the minimum melt viscosity of the insulating resin layer is not more than 4000 Pa･s; and condition (5): the number density of the conductive particles is not less than 6000/ ^mm2 and not more than 36000/ ^mm2 .

Description

Anisotropic conductive film, connection structure, and method for manufacturing the connection structure

The present invention relates to an anisotropic conductive film.

In response to the requirements of lightweight or curved image display panels, flexible plastic substrates are used as substrates for mounting electronic components such as image display elements or driver IC chips. As a representative example of such plastic substrates, from the perspective of preventing thermal deformation and reflection, the "plastic substrate 24 having a structure formed by laminating a polyethylene terephthalate film 20 and a polyimide film 22 having a transparent electrode 21 using an urethane adhesive layer 23" as shown in FIG. 7 can be cited (Patent Document 1). [Prior Technical Document] [Patent Document]

Patent document 1: Japanese Patent Application Publication No. 2016-54288

[The problem that the invention wants to solve]

However, the bumps of the IC chip are generally connected to the electrodes of the flexible plastic substrate by anisotropic conductive connection as shown in FIG7 through an anisotropic conductive film in which conductive particles are dispersed in an insulating resin adhesive. In this case, a plurality of bumps are arranged at a fine pitch on the IC chip, and an oxide film is formed on the electrode surface of the plastic substrate. Therefore, in order to reliably connect the bumps to the electrodes after the bumps of the IC chip penetrate the oxide film on the electrode surface of the plastic substrate, the IC chip is pressed into the plastic substrate with a relatively large pressure.

Therefore, since the rigidity of the IC chip is much higher than that of the plastic substrate, there is a concern that the deformation of the plastic substrate side may increase due to the pressure during connection, resulting in problems such as "disconnection of the wiring on the plastic substrate side" or "insufficient pressing of particles". Specifically, as shown in FIG8 , when heating and pressurizing are performed to anisotropically conduct the bump B of the IC chip and the electrode 21 of the plastic substrate 24 via the anisotropic conductive film ACF, there is a possibility that the adhesive layer 23 of the plastic substrate 24 is excluded to the outside of the bump B of the IC chip, thereby generating a phenomenon of forming an inverted dome-shaped thin portion 25 (doming phenomenon). If such a bulge occurs, there is a concern that cracks may occur near the shoulder 26 on the wiring 21a extending from the electrode 21. Furthermore, in order to evaluate the conduction reliability of the anisotropic conductive connection, the indentations formed by the conductive particles sandwiched between the electrode 21 and the bump B were observed and evaluated from the polyethylene terephthalate film 20 side. With respect to the conductive particles 27a sandwiched between the bump B and the electrode 21 near the edge E of the pressing surface of the bump, indentations showing good connection were observed. However, with respect to the conductive particles 27b sandwiched between the bump B and the electrode 21 near the center C of the pressing surface of the bump B, there was concern that indentations showing good connection (in other words, the clamping state of the conductive particles) might be difficult to observe. When such indentation is not observed, there is a problem that even if good conduction is achieved, the evaluation results of conduction characteristics (initial conduction, conduction reliability, etc.) have to be lowered.

In order to eliminate such concerns, it is considered to start from the perspective of, for example, (a) adjusting the conditions of anisotropic conductive connection, (b) adjusting the structure or characteristics of the plastic substrate, (c) adjusting the structure or characteristics of the IC chip, and (d) adjusting the structure or characteristics of the anisotropic conductive film. However, when starting from the perspective of (a), it is necessary to modify the manufacturing equipment or introduce new manufacturing equipment, and when starting from the perspectives of (b) and (c), it is necessary to change the specifications of the electronic parts that are the objects of anisotropic conductive connection. Therefore, it is required to start from the perspective of (d) without modifying or installing new manufacturing equipment and changing the specifications of the electronic parts that are the objects of anisotropic conductive connection.

The purpose of the present invention is to solve the above known problems, in particular to provide an anisotropic conductive film which is suitable for anisotropically conductively connecting electronic parts with bumps such as image display elements or driver IC chips to a flexible plastic substrate having electrodes (for example, metal electrodes such as Ti, Ti/AL, etc., metal oxide electrodes such as ITO, or metal oxide electrodes oxidized on the surface of the above metal electrodes). During the anisotropic conductive connection, no cracks are generated in the wiring of the plastic substrate, and an indentation showing a good anisotropic conductive connection is formed, thereby achieving higher conduction reliability. [Technical means for solving the problem]

The inventors of the present invention have found that, when an anisotropic conductive film having at least an insulating resin layer and a conductive particle dispersion layer composed of conductive particles dispersed in the insulating resin layer is used for anisotropic conductive connection, the conductive particles are subjected to compressive force in the thickness direction of the film, and the conductive particles are subjected to compressive force in the thickness direction of the film. In order to meet the purpose of the present invention, the 20% compression elastic modulus, compression recovery rate, average particle size, number density of the conductive particles, and the minimum melt viscosity of the insulating resin layer are controlled within specific numerical ranges, thereby achieving the purpose of the present invention and completing the present invention.

That is, the present invention provides an anisotropic conductive film having at least an insulating resin layer and a conductive particle dispersion layer composed of conductive particles dispersed in the insulating resin layer, and satisfying the following conditions (1) to (5).

<Condition (1)> The 20% compression modulus of the conductive particles is not less than 6000 N/ ^mm2 and ^not more than 15000 N/mm2; <Condition (2)> The compression recovery rate of the conductive particles is not less than 40% and not more than 80%; <Condition (3)> The average particle size of the conductive particles is not less than 1 μm and not more than 30 μm; <Condition (4)> The minimum melt viscosity of the insulating resin layer is not more than 4000 Pa･s; and <Condition (5)> The number density of the conductive particles is not less than 6000 particles/ ^mm2 and not more than 36000 particles/ ^mm2 .

In addition, the present invention provides a manufacturing method, which is a manufacturing method of the anisotropic conductive film of the present invention, and has a step of forming a conductive particle dispersion layer by pressing conductive particles into an insulating resin layer. As a preferred embodiment of the step, the following embodiments can be cited: the conductive particles are maintained on the surface of the insulating resin layer in a prescribed arrangement, and the conductive particles are pressed into the insulating resin layer by a flat plate or a roller, thereby forming a conductive particle dispersion layer; or the conductive particles are filled in a transfer mold, and the conductive particles are transferred to the insulating resin layer, thereby maintaining the conductive particles on the surface of the insulating resin layer in a prescribed configuration.

The present invention further provides a connection structure, in which a first electronic component (such as an IC chip or an IC module) and a second electronic component (such as a flexible plastic substrate) are anisotropically conductively connected via the anisotropic conductive film of the present invention. [Effect of the invention]

The anisotropic conductive film of the present invention has a conductive particle dispersion layer composed of at least an insulating resin layer and conductive particles dispersed in the insulating resin layer. In the anisotropic conductive film of the present invention, conductive particles retained in the conductive particle dispersion layer are used whose 20% compression modulus, compression recovery rate and average particle size are respectively within specific numerical ranges, and the insulating resin layer retaining such conductive particles is used whose minimum melt viscosity is below a specific numerical value, and the degree of retaining conductive particles in such insulating resin layer (in other words, number density) is set within a specific range. Therefore, when an electronic component with bumps such as an image display element or a driver IC chip is anisotropically conductively connected to a flexible plastic substrate with electrodes and wiring formed thereon through the anisotropic conductive film of the present invention, cracks in the wiring of the plastic substrate can be prevented. In addition, an indentation showing a good anisotropic conductive connection can be produced, and a good conduction reliability evaluation can be obtained during the anisotropic conductive connection.

The anisotropic conductive film of the present invention has a conductive particle dispersion layer composed of at least an insulating resin layer and conductive particles dispersed in the insulating resin layer. The conductive particles retained in the conductive particle dispersion layer are set to have specific numerical value ranges for the conditions (1): "20% compression elastic modulus", the condition (2): "compression recovery rate", and the condition (3): "average particle size", respectively. The insulating resin layer retaining the conductive particles is set to have a specific range for the condition (4): "minimum melt viscosity", and the condition (5): "number density" is set to a specific range as the degree of retaining the conductive particles in the insulating resin layer. Hereinafter, an example of the anisotropic conductive film of the present invention will be described in detail with reference to the drawings. In the following drawings, the same symbols represent the same or equivalent components.

<Overall structure of anisotropic conductive film> Figure 1A is a top view illustrating the particle arrangement of an anisotropic conductive film 10A of an embodiment of the present invention, and Figure 1B is a cross-sectional view taken along line X-X of Figure 1A. In addition, Figures 2, 3 and 4 are cross-sectional views of anisotropic conductive films 10B, 10C and 10D of an embodiment of the present invention, respectively. The anisotropic conductive film of the present invention is not limited to the embodiments disclosed in these figures.

The anisotropic conductive film 10A may be in the form of a strip film having a length of 5 m or more, or may be in the form of a roll wound around a core.

The anisotropic conductive film 10A is composed of a conductive particle dispersion layer 3, in which the conductive particles 1 and the insulating resin layer 2 are in a non-contact state. It is preferred that the conductive particles 1 are regularly arranged in a state where the conductive particles 1 are exposed on one side of the insulating resin layer 2. When the film is viewed from above, the conductive particles 1 are not in contact with each other, and the conductive particles 1 do not overlap each other in the film thickness direction. It is preferred that the conductive particle layer is a single layer in which the conductive particles 1 are positioned in the film thickness direction in a consistent manner. Furthermore, the ratio of conductive particles in a non-contact state (based on the number of particles) is preferably 95% or more, and more preferably 98% or more.

The surface 2a of the insulating resin layer 2 around each conductive particle 1 may also form a concave portion 2b relative to the cross section 2p of the insulating resin layer 2 at the center between adjacent conductive particles (FIG. 1B, FIG. 2). Furthermore, as shown in FIG. 2, the top portion 1a of the conductive particle 1 may also be flush with the surface 2a of the insulating resin layer 2. In this case, compared with the case of FIG. 1B, the movement of the conductive particles caused by the flow of the resin during anisotropic conductive connection can be alleviated. Furthermore, as described below, in the anisotropic conductive film of the present invention, a recess 2c may be formed on the surface of the insulating resin layer just above the conductive particle 1 embedded in the insulating resin layer 2 (FIG. 3, FIG. 4). In the case of FIG. 3, a point on the top 1a of the conductive particle 1 may also be exposed from the insulating resin layer.

<Conductive particles> Conductive particles 1 can be appropriately selected from conductive particles used in known anisotropic conductive films and can be metal-coated resin particles having a metal layer formed on the surface of a resin core particle. As such metal-coated resin particles, those having been subjected to an insulating coating treatment (e.g., insulating microparticle attachment treatment, insulating resin coating treatment, etc.) can also be used. Two or more metal-coated resin particles can also be used in combination. Furthermore, conductive particles having conductive protrusions on the surface can also be used as conductive particles 1. For example, the following methods may be used: insulating particles that form the core material of the protrusions are attached to the surface of the resin core particles, and the entire conductive particles are covered with a conductive layer; the surface of such conductive particles is further covered with another conductive layer; or insulating particles that form the core material of the protrusions are attached to the surface of the resin core particles covered with a conductive layer, and the entire conductive particles are further covered with a conductive layer. The conductive layer may be 2 layers or more. The protrusions may also exist between the conductive layers. Such a conductive layer may be formed, for example, on the surface of the resin core particles by known film-forming methods such as electroless plating, electroplating, and sputtering. Furthermore, as long as there is a method for attaching conductive microparticles, the conductive particles satisfy the following conditions and can satisfy the conduction performance, there is no particular limitation. In addition, the surface of the conductive layer may be subjected to a known insulating treatment. In this case, the size of the conductive particle is the size minus the thickness of the insulating layer formed by the insulating treatment.

The conductive particles 1 used in the present invention meet the following conditions (1) to (3).

<Condition (1)> From the viewpoint that even if an oxide film is formed on the surface of an electrode or terminal of an electronic component, the oxide film can be penetrated by the conductive particles, the lower limit of the 20% compressive elastic modulus (K) of the conductive particles used in the present invention is 6000 N/ ^mm2 or more, preferably 10000 N/ ^mm2 or more. Here, the 20% compressive elastic modulus can be calculated by measuring the compression variation of the conductive particles when a compressive load is applied to the conductive particles using a micro compression tester (e.g., Fischerscope H-100 manufactured by Fischer Corporation) (e.g., when the conductive particles are compressed at a compression rate of 2.6 mN/sec and a maximum test load of 10 gf using a smooth indenter end face of a cylinder (diameter 50 μm, made of diamond) and applying the measured value to the following formula (1).

In formula (1), F is the load value (N) when the conductive particle is compressed and deformed by 20%, S is the compression displacement (mm) when the conductive particle is compressed and deformed by 20%, and R is the radius of the conductive particle (mm).

<Condition (2)> In addition, the conductive particles used in the present invention are required to penetrate the oxide film formed on the surface of the electrode or terminal of the electronic component as described above, so that a corresponding pressure is applied to the conductive particles during connection. As a result, it is expected that the conductive particles will be flattened. Therefore, it is required that "after the pressure of the connection is released, the conductive particles are sufficiently ensured to have a contact area with the opposite electrode or terminal surface, and then recover after compression." From this point of view, the lower limit of the compression recovery rate (X) is 40% or more, preferably 55% or more. In addition, if the upper limit is too high, there is a risk of hindering the maintenance of the connection state maintained by the cured or polymerized resin, and it is not expected to be too high. The upper limit is 80% or less, preferably 75% or less. Here, the compression recovery rate can be calculated by using the above-mentioned micro compression tester to compress the conductive particles with the end surface of a smooth compression head of a cylinder (diameter 50 μm, made of diamond), measuring the displacement (L2) from the initial load (load 0.4 mN) to the load reversal (load 5 mN), and the displacement (L1) from the load reversal to the final load (load 0.4 mN), and applying the measured values to the following formula (2).

<Condition (3)> From the perspective of corresponding to the deviation of wiring height, the lower limit of the average particle size of the conductive particles 1 used in the present invention is 1 μm or more, preferably 2.5 μm or more, and from the perspective of suppressing the increase of on-resistance and suppressing the occurrence of short circuits, the upper limit is 30 μm or less, preferably 9 μm or less. Here, the average particle size can be obtained using a general particle size distribution measuring device (for example, FPIA-3000 (Malvern-Panalytical)). The number of samples to be measured is preferably 1000 or more. In addition, the average particle size D of the conductive particles in the anisotropic conductive film can be obtained using an electron microscope such as SEM. In this case, it is preferred to set the number of samples to be measured to 200 or more. Furthermore, when using conductive particles having insulating particles attached to their surface, the average particle size of the conductive particles of the present invention refers to the average particle size excluding the insulating particles on the surface.

<Insulating resin layer 2> In the anisotropic conductive film of the present invention, the insulating resin layer 2 that holds the conductive particles 1 and functions as a base layer of the anisotropic conductive film can be formed of a curable resin composition as described below and satisfies the following condition (4).

<Condition (4)> The minimum melt viscosity of the insulating resin layer 2 constituting the anisotropic conductive film of the present invention has an upper limit of 4000 Pa·s or less, preferably 3000 Pa·s or less, from the viewpoint of reducing the pressure during connection, suppressing deformation, especially when the substrate is plastic, and being able to press the conductive particles well. Furthermore, from the perspective of suppressing deformation during connection, especially in a plastic substrate, the lower limit is ideally lower, and therefore, there is no particular restriction and it can be appropriately adjusted. However, from the perspective of preventing the conductive particles 1 that should be sandwiched between the terminals from excessively running away due to the flow of the resin during anisotropic conductive connection, and preventing the overflow of the resin when forming a winding, it is preferably 200 Pa·s or more, and more preferably 400 Pa·s or more. Here, the minimum melt viscosity can be determined, for example, by using a rotational rheometer (manufactured by TA Instruments) with a measuring plate of 8 mm in diameter kept fixed at a measuring pressure of 5 g. More specifically, it can be determined by setting the temperature range to 30 to 200°C, the heating rate to 10°C/min, the measuring frequency to 10 Hz, and the load change on the measuring plate to 5 g.

Furthermore, in the case where the conductive particle dispersion layer 3 of the anisotropic conductive film 10A is formed by pressing the conductive particles 1 into the insulating resin layer 2, the insulating resin layer 2 when the conductive particles 1 are pressed into the insulating resin layer 2 is set to be a high viscosity viscous body as follows: when the conductive particles 1 are pressed into the insulating resin layer 2 in such a manner that the conductive particles 1 are exposed from the insulating resin layer 2 with an exposed diameter Lc, the insulating resin layer 2 is formed to have a high viscosity. The insulating resin layer 2 is plastically deformed to form a recess 2b in the insulating resin layer 2 around the conductive particle 1 (Fig. 1B, Fig. 2); or, when the conductive particle 1 is pressed into the insulating resin layer 2 so that the conductive particle 1 is not exposed from the insulating resin layer 2 but embedded in the insulating resin layer 2, a recess 2c is formed on the surface of the insulating resin layer 2 directly above the conductive particle 1 (Fig. 3, Fig. 4). Therefore, it is preferable to set the viscosity of the insulating resin layer 2 at 60°C to 3000-20000 Pa·s. This measurement can be performed by the same measurement method as the minimum melt viscosity, and the value at a temperature of 60°C is selected.

The specific viscosity of the insulating resin layer 2 when the conductive particles 1 are pressed into the insulating resin layer 2 can be determined by referring to the description of Patent No. 6187665 (Paragraph 0054).

As described above, by forming the recessed portion 2b around the conductive particle 1 exposed from the insulating resin layer 2 (FIG. 1B, FIG. 2), during anisotropic conductive connection, the resistance received by the insulating resin due to "flattening of the conductive particle 1 generated when the conductive particle 1 is sandwiched between the terminals" is reduced compared to the case where there is no recessed portion 2b, so that the conductive particle can be easily sandwiched between the terminals, thereby improving the conductive performance and the capturing property.

Furthermore, by forming a recess 2c (FIG. 3 and FIG. 4) on the surface of the insulating resin layer 2 directly above the embedded conductive particle 1 that is not exposed from the insulating resin layer 2, the pressure during anisotropic conductive connection is easily concentrated on the conductive particle 1, and the conductive particle 1 is easily clamped by the terminal, thereby improving the capture property and the conductive performance.

(Thickness of insulating resin layer) In the anisotropic conductive film of the present invention, the ratio of the thickness La of the insulating resin layer 2 to the average particle size D of the conductive particles 1 (La/D) is sufficient if there is a resin amount that can hold the conductive particles, so it is sufficient to be 0.3 or more, preferably 0.6 or more, and more preferably 1.0 or more. If La/D is less than 0.3, it is difficult to precisely maintain the conductive particles 1 in a predetermined particle dispersion state or predetermined arrangement by the insulating resin layer 2. Here, the average particle size D is defined as the size of the metal-coated resin particles (including the size of the resin core particles and the conductive layer on their surface). If the thickness La of the insulating resin layer 2 is too large relative to the conductive particles, the conductive particles are easily misplaced during anisotropic conductive connection, and the capture of the conductive particles in the terminal is reduced. Therefore, the upper limit of La/D is preferably 8.0 or less, and more preferably 6.0 or less.

(Composition of insulating resin layer) The insulating resin layer 2 can be formed of a curable resin composition, for example, a thermopolymerizable composition containing a thermopolymerizable compound and a thermopolymerizable initiator. The thermopolymerizable composition can also contain a photopolymerizable initiator as needed.

When a thermal polymerization initiator and a photopolymerization initiator are used together, a compound that also functions as a photopolymerizable compound may be used as the thermal polymerization compound, or the photopolymerizable compound may be contained separately from the thermal polymerization compound. It is preferred to contain the photopolymerizable compound separately from the thermal polymerization compound. For example, a cationic polymerization initiator is used as the thermal polymerization initiator, an epoxy resin is used as the thermal polymerization compound, a photoradical polymerization initiator is used as the photopolymerization initiator, and an acrylate compound is used as the photopolymerizable compound.

As photopolymerization initiators, multiple types that react to light of different wavelengths may be included. This allows for different wavelengths to be used for photocuring of the resin that forms the insulating resin layer when manufacturing anisotropic conductive films and for photocuring of the resin that connects electronic components when making anisotropic conductive connections.

In the photocuring when manufacturing the anisotropic conductive film, all or part of the photopolymerizable compound contained in the insulating resin layer can be photocured. By this photocuring, the arrangement of the conductive particles 1 in the insulating resin layer 2 is maintained or fixed, which is expected to suppress short circuits and improve the capture performance. In addition, the viscosity of the insulating resin layer in the process of manufacturing the anisotropic conductive film can also be appropriately adjusted by this photocuring.

The amount of the photopolymerizable compound in the insulating resin layer is preferably 30% by mass or less, more preferably 10% by mass or less, and even more preferably less than 2% by mass. The reason for this is that if the amount of the photopolymerizable compound is too much, the thrust required for press-fitting during connection increases.

Examples of thermally polymerizable compositions include: thermally free radical polymerizable acrylate compositions containing a (meth)acrylate compound and a thermally free radical polymerization initiator, thermally cationic polymerizable epoxy compositions containing an epoxy compound and a thermally cationic polymerization initiator, etc. A thermally anionic polymerizable epoxy composition containing a thermally anionic polymerization initiator may be used instead of a thermally cationic polymerizable epoxy composition containing a thermally cationic polymerization initiator. In addition, if no special obstacles are brought about, multiple polymerizable compositions may be used in combination. As examples of combination, the combination of a thermally cationic polymerizable composition and a thermally free radical polymerizable composition may be cited.

Here, as the (meth)acrylate compound, a conventionally known heat-polymerizable (meth)acrylate monomer can be used, for example, a monofunctional (meth)acrylate monomer or a difunctional or higher polyfunctional (meth)acrylate monomer can be used.

Examples of the thermal radical polymerization initiator include organic peroxides and azo compounds. In particular, organic peroxides that do not generate nitrogen gas, which causes bubbles, are preferably used.

If the amount of the thermal free radical polymerization initiator is too small, the curing will be poor, and if it is too large, the product life will be reduced. Therefore, it is preferably 2 to 60 parts by mass, and more preferably 5 to 40 parts by mass, relative to 100 parts by mass of the (meth)acrylate compound.

Examples of epoxy compounds include bisphenol A type epoxy resins, bisphenol F type epoxy resins, novolac type epoxy resins, modified epoxy resins thereof, and aliphatic epoxy resins, and two or more of these may be used in combination. In addition to epoxy compounds, cyclohexane compounds may also be used in combination.

As the thermal cationic polymerization initiator, a known thermal cationic polymerization initiator of an epoxy compound can be used. For example, iodonium salts, coronium salts, phosphonium salts, ferrocenes, etc. that generate an acid by heat can be used. In particular, aromatic coronium salts that show good potential for temperature can be preferably used.

If the amount of the thermal cationic polymerization initiator used is too small, the curing tends to be poor, and if it is too large, the life of the product tends to be reduced. Therefore, it is preferably 2 to 60 parts by mass, more preferably 5 to 40 parts by mass, relative to 100 parts by mass of the epoxy compound.

The heat-polymerizable composition preferably contains a film-forming resin or a silane coupling agent. Examples of the film-forming resin include phenoxy resins, epoxy resins, unsaturated polyester resins, saturated polyester resins, amine resins, butadiene resins, polyimide resins, polyamide resins, polyolefin resins, and the like, and two or more of these resins may be used in combination. Among these, phenoxy resins may be preferably used from the viewpoints of film-forming properties, processability, and connection reliability. The weight average molecular weight is preferably greater than 10,000. Also, examples of the silane coupling agent include epoxy-based silane coupling agents, acrylic-based silane coupling agents, and the like. The silane coupling agents are mainly alkoxysilane derivatives.

In order to adjust the melt viscosity, the heat-polymerizable composition may also contain an insulating filler. Examples of the insulating filler include silicon dioxide powder and aluminum oxide powder. The size of the insulating filler is preferably 20 to 1000 nm in particle size, and the blending amount is preferably 5 to 50 parts by mass relative to 100 parts by mass of the heat-polymerizable compound (and photopolymerizable compound) such as epoxy compound.

Furthermore, it may also contain fillers different from the above-mentioned insulating fillers, softeners, promoters, anti-aging agents, colorants (pigments, dyes), organic solvents, ion scavengers, etc.

<Degree of retention of conductive particles by the insulating resin layer> The insulating resin layer 2 showing the minimum melt viscosity retains the conductive particles 1 as described above, and the degree of retention can be evaluated using the number density as an index. That is, in the anisotropic conductive film of the present invention, the number density of the conductive particles 1 satisfies the following condition (5).

<Condition (5)> If the number density of the conductive particles in the anisotropic conductive film of the present invention is too small when viewed from above, there is a concern that the number of particles captured may decrease and the on-resistance may increase. Therefore, the lower limit is 6000 or more/ ^mm2 , preferably 7500 or more/ ^mm2 . If the number density is too large, there is a need to increase the pressure during connection, and there is a concern that the substrate may deform when it is made of plastic. Therefore, in order not to excessively increase the pressure during connection, the upper limit is 36000 or less/ ^mm2 , preferably 30000 or less/ ^mm2 . Here, the number density of the conductive particles can be obtained by observing and calculating using a metal microscope, or by measuring and observing the image using image analysis software (WinROOF, Mitani Shoji Co., Ltd., etc.). The observation method or measurement method is not limited to the above.

Furthermore, as the measurement area of the number density of the conductive particles, it is preferred to set a rectangular area with a side of 100 μm or more at a plurality of locations (preferably 5 locations or more, and more preferably 10 locations or more), and set the total area of the measurement area to 2 ^mm2 or more. The size or number of each area can be appropriately adjusted according to the state of the number density. As an example of a relatively large number density for micro-pitch use, the number density is measured at 200 locations (2 ^mm2 ) of an area of 100 μm×100 μm arbitrarily selected from the anisotropic conductive film 10A using an observation image obtained using a metal microscope, etc., and the average is taken to obtain the "number density of conductive particles in a top view" in the above formula. The area of 100 μm × 100 μm is the area where one or more bumps exist in the connection object with the interval between bumps being 50 μm or less and L/S (line width/interval) being 1 or less.

<Dispersion state of conductive particles in insulating resin layer> The dispersion state of conductive particles 1 in the conductive particle dispersion layer 3 of the anisotropic conductive film of the present invention includes a state where the conductive particles 1 are randomly dispersed and a state where they are dispersed in a regular configuration. In either case, in terms of capture stability, it is preferred that the positions of the conductive particles 1 in the film thickness direction are consistent. Here, the consistency of the positions of the conductive particles 1 in the film thickness direction is not limited to alignment at a single depth in the film thickness direction, but also includes the state where conductive particles exist at or near the interfaces of the front and back surfaces of the insulating resin layer 2.

Furthermore, in terms of suppressing short circuits, the conductive particles 1 are preferably arranged regularly when viewed from above the film. The arrangement pattern depends on the layout of the terminals and bumps, so there is no particular limitation. For example, they can be arranged in a square lattice as shown in FIG1A when viewed from above the film. In addition, as patterns of regular arrangement of conductive particles, rectangular lattices, rhombic lattices, hexagonal lattices, triangular lattices, and the like can be cited. Grids of different shapes can also be combined in multiples. Furthermore, the conductive particles can also be arranged in parallel at specified intervals in a row of particles arranged in a straight line at specified intervals. By making the conductive particles 1 non-contacting each other and arranging them in a regular lattice shape, pressure can be uniformly applied to each conductive particle 1 during anisotropic conductive connection, thereby reducing the deviation of the on-resistance.

Furthermore, in order to take into account both capture stability and short circuit suppression, it is more preferable that the conductive particles are regularly arranged when viewed from above the film and their positions in the film thickness direction are consistent.

On the other hand, in the case where the terminals of the connected electronic parts are wide and short circuits are not likely to occur, the conductive particles can be arranged irregularly and randomly dispersed. In the case of dispersion, when viewed from above, each conductive particle is preferably arranged in a non-contact manner (each conductive particle does not touch and exists independently). Since it depends on the terminal layout, the number ratio can be, for example, 75% or more, preferably 90% or more, more preferably 95% or more, and even more preferably 98% or more.

When the conductive particles are arranged regularly, the lattice axis or arrangement axis of the arrangement may be parallel to the long side direction of the anisotropic conductive film or a direction orthogonal to the long side direction, or may cross the long side direction of the anisotropic conductive film, and may be determined according to the width of the connected terminal, the terminal pitch, etc. For example, in the case of a fine-pitch anisotropic conductive film, it is preferred that the lattice axis A of the arrangement of the conductive particles 1 is oblique to the long side direction of the anisotropic conductive film 10A as shown in FIG. 1A, and the angle θ formed by the long side direction (the short side direction of the film) of the terminal 200 connected by the anisotropic conductive film 10A and the lattice axis A is set to be greater than 6° and less than 84°, preferably greater than 11° and less than 74°.

Furthermore, the interparticle distance of the conductive particles 1 is appropriately determined according to the size of the terminals connected by the anisotropic conductive film or the terminal distance. Generally, from the perspective of preventing short circuits, the lower limit of the closest interparticle distance (i.e., the distance between the closest particles) is preferably 50% or more of the average particle size D of the conductive particles or 0.2 μm or more, whichever is longer. The upper limit is not particularly limited if it can meet the number density condition. For example, it is preferably less than 30 μm of the maximum diameter of the average particle size D of the conductive particles, or when the average particle size D is relatively small, it is preferably less than 10 times the average particle size D.

Furthermore, the area occupancy of the conductive particles in the top view of the anisotropic conductive film of the present invention is an indicator of the thrust of the pressing jig required to hot-press the anisotropic conductive film to the electronic components. If the area occupancy is too large, the thrust will also increase accordingly, and it will become a factor of deformation when the substrate is plastic or other easily deformed materials. Therefore, the upper limit of the area occupancy of the conductive particles is preferably less than 30%, more preferably less than 26%, and further preferably less than 23%. Furthermore, when the area occupancy is too small, there is a risk that it will become unable to cope with fine pitches. Therefore, it is preferably more than 3%, more preferably more than 6%, and further preferably more than 9%. Here, the area occupancy rate [%] of the conductive particles can be calculated by the following formula.

Here, as the measurement area for the number density and area occupancy of the conductive particles, as described in the description of paragraph 0052, it is preferred to set a rectangular area with a side of 100 μm or more at a plurality of locations (preferably 5 locations or more, more preferably 10 locations or more), and set the total area of the measurement area to be 2 ^mm2 or more. The size or number of each area can be appropriately adjusted according to the state of the number density.

<Position of conductive particles in the thickness direction of insulating resin layer> In the anisotropic conductive film of the present invention, the position of conductive particles 1 in the thickness direction of insulating resin layer 2 is as described above. Conductive particles 1 may be exposed from insulating resin layer 2 or may not be exposed but embedded in insulating resin layer 2. Preferably, the ratio of the distance Lb of the deepest part of the conductive particle to the "cross section 2p of the central part between adjacent conductive particles on the surface 2a of the insulating resin layer where recesses 2b and 2c are formed" (hereinafter referred to as the embedding amount) to the particle size D of the conductive particle 1 [(Lb/D)×100] (hereinafter referred to as the embedding rate) is 60% or more and 105% or less.

By setting the embedding rate to 60% or more, the insulating resin layer 2 can maintain the conductive particles 1 in a predetermined particle dispersion state or a predetermined arrangement. Furthermore, by setting it to 105% or less, the amount of resin in the insulating resin layer that causes the conductive particles between the terminals to flow unnecessarily during anisotropic conductive connection can be reduced.

Furthermore, in the present invention, the embedding rate value refers to the embedding rate (Lb/D) value being 80% or more of the number of all conductive particles contained in the anisotropic conductive film, preferably 90% or more, and more preferably 96% or more as the embedding rate (Lb/D) value. Therefore, an embedding rate of 60% or more and 105% or less means that an embedding rate of 80% or more, preferably 90% or more, and more preferably 96% or more of the number of all conductive particles contained in the anisotropic conductive film is 60% or more and 105% or less. In this way, by making the embedding rate (Lb/D) of all conductive particles consistent, the pressure load can be evenly applied to the conductive particles, so that the capture state of the conductive particles in the terminal is good and the stability of conduction is improved.

The embedding rate can be obtained by randomly selecting 10 or more areas with an area of 30 ^mm2 or more from the anisotropic conductive film, observing a portion of the film cross section with a SEM image, and measuring a total of 50 or more conductive particles. In order to further improve the accuracy, more than 200 conductive particles can also be measured to obtain the embedding rate.

In addition, the embedding rate can be measured by adjusting the focus in the plane view image, and a certain degree of number can be obtained at the same time. Alternatively, a laser discrimination displacement sensor (manufactured by KEYENCE, etc.) can also be used to measure the embedding rate.

<Deformation of the anisotropic conductive film> (Second insulating resin layer) The anisotropic conductive film of the present invention may also be a second insulating resin layer 4 (functioning as an insulating bonding layer) having a lower bulk minimum melt viscosity than the insulating resin layer 2 on the side of the conductive particle dispersion layer 3 where the conductive particles 1 are retained (in other words, the side of the insulating resin layer 2 where the recessed portion 2c is formed) as in the anisotropic conductive film 10E shown in FIG. 5 . In addition, as in the anisotropic conductive film 10F shown in FIG6 , a second insulating resin layer 4 (functioning as an insulating bonding layer) having a minimum melt viscosity lower than that of the insulating resin layer 2 may be laminated on the side of the conductive particle dispersion layer 3 where the conductive particles 1 are not retained (in other words, the side of the insulating resin layer 2 where the recessed portion 2c is not formed). By laminating the second insulating resin layer 4, when the anisotropic conductive film is used to anisotropically conduct and connect electronic components, the space formed by the electrodes or bumps of the electronic components can be filled, thereby improving the bonding property. Furthermore, when the second insulating resin layer 4 is laminated, regardless of whether the second insulating resin layer 4 is located on the surface where the recess 2c is formed, the second insulating resin layer 4 is preferably located on the side of the electronic component such as the IC chip to be pressed by the tool (in other words, the insulating resin layer 2 is located on the side of the electronic component such as the substrate mounted on the mounting table). This can prevent the accidental movement of the conductive particles and improve the capture performance.

The greater the difference between the minimum melt viscosity of the insulating resin layer 2 and the second insulating resin layer 4, the easier it is for the space formed by the electrode or bump of the electronic component to be filled with the second insulating resin layer 4, and the effect of improving the adhesion between the electronic components can be expected. In addition, the greater the difference, the smaller the amount of migration of the insulating resin layer 2 in the conductive particle dispersion layer 3, and the easier it is to improve the capture of the conductive particles in the terminal. In terms of practicality, the minimum melt viscosity ratio of the insulating resin layer 2 to the second insulating resin layer 4 (i.e., [minimum melt viscosity of the insulating resin layer 2]/[minimum melt viscosity of the second insulating resin layer 4]) is preferably 2 or more, more preferably 5 or more, and further preferably 8 or more. On the other hand, if the ratio is too large, there is a risk of resin overflow or blocking when the long anisotropic conductive film is made into a roll. Therefore, in terms of practicality, the minimum melt viscosity ratio is preferably 15 or less. The preferred minimum melt viscosity of the second insulating resin layer 4 can be determined by referring to the specification of Patent No. 6187665 (Paragraph 0091).

Furthermore, the second insulating resin layer 4 can be formed by adjusting the viscosity of the same resin composition as the insulating resin layer.

In the anisotropic conductive films 10E and 10F, the thickness of the second insulating resin layer 4 is preferably 4 μm or more and 20 μm or less. Alternatively, it is preferably 1 to 8 times the diameter of the conductive particles.

The lowest melt viscosity of the anisotropic conductive film 10E, 10F formed by combining the insulating resin layer 2 and the second insulating resin layer 4 is preferably 200 Pa·s or more and 4000 Pa·s or less. Furthermore, the lowest melt viscosity of the second insulating resin layer 4 itself is preferably 2000 Pa·s or less, and more preferably 100 to 2000 Pa·s, provided that the above-mentioned lowest melt viscosity ratio is satisfied.

(Third insulating resin layer) A third insulating resin layer may be provided on the opposite side of the second insulating resin layer 4 via the insulating resin layer 2. For example, the third insulating resin layer or the insulating adhesive layer may function as an adhesive layer. Similar to the second insulating resin layer, it may be provided to fill the space formed by the electrode or bump of the electronic component.

The resin composition, viscosity and thickness of the third insulating resin layer may be the same as or different from those of the second insulating resin layer. The minimum melt viscosity of the anisotropic conductive film composed of the insulating resin layer 2, the second insulating resin layer 4 and the third insulating resin layer is not particularly limited and can be set to 200 to 4000 Pa･s.

<Manufacturing method of anisotropic conductive film> The anisotropic conductive film of the present invention can be manufactured by a manufacturing method having the following steps: forming a conductive particle dispersion layer by pressing conductive particles into an insulating resin layer. As a preferred embodiment of the step, the following embodiments can be cited: the conductive particles are maintained on the surface of the insulating resin layer in a prescribed arrangement, and the conductive particles are pressed into the insulating resin layer by a flat plate or a roller, thereby forming a conductive particle dispersion layer; or the conductive particles are filled in a transfer mold, and the conductive particles are transferred to the insulating resin layer, thereby maintaining the conductive particles on the surface of the insulating resin layer in a prescribed configuration. In addition, the following aspects can also be listed: the conductive particles 1 are directly scattered and maintained in the insulating resin layer 2; or a single layer of the conductive particles 1 is attached to a biaxially stretchable film, the film is biaxially stretched, the insulating resin layer 2 is pressed against the stretched film, and the conductive particles are transferred to the insulating resin layer 2, thereby maintaining the conductive particles 1 in the insulating resin layer 2.

In the case of forming a conductive particle dispersion layer by pressing conductive particles into an insulating resin layer, the minimum melt viscosity of the insulating resin layer can be determined with reference to the description of Patent No. 6187665 (Paragraph 0097). Thus, the conductive particles can be pressed into the insulating resin layer in such a manner that the surface of the insulating resin layer forming the surface of the conductive particle dispersion layer has a concave portion relative to the cross section of the insulating resin layer at the center between adjacent conductive particles.

Furthermore, when manufacturing an anisotropic conductive film with an embedding rate exceeding 100%, it can also be pressed in with a pressing plate in a manner having protrusions corresponding to the arrangement of the conductive particles.

Furthermore, when the conductive particles 1 are held in the insulating resin layer 2 using a transfer mold, the transfer mold may be, for example, a material in which an opening is formed on an inorganic material such as silicon, various ceramics, glass, stainless steel or other metal, or an organic material such as various resins by a known opening forming method such as photoetching; or a material in which a printing method is applied. Furthermore, the transfer mold may be in a plate shape, a roll shape or the like. Furthermore, the present invention is not limited to the above methods.

Furthermore, a second insulating resin layer having a lower bulk viscosity than that of the insulating resin layer may be provided on the surface of the insulating resin layer having the conductive particles pressed therein, or on the opposite surface thereof, on the side on which the conductive particles are pressed.

In order to use anisotropic conductive films to economically connect electronic components, the anisotropic conductive films are preferably strips of a certain degree of length. Here, the anisotropic conductive film is preferably set to a length of more than 5 m. It can also be determined by referring to the description of Patent No. 6187665 (Paragraph 0103). In addition, when the anisotropic conductive film is actually used, it is realistic to wind it on a reel to form a roll. However, when a roll is made in this way, there is the following situation: if the resin viscosity (i.e., substantially proportional to the minimum melt viscosity of the film) is too low, problems such as overflow or agglomeration will occur during continuous connection. Therefore, it is preferable that the minimum melt viscosity of the anisotropic conductive film be 200 Pa·s or more. This also applies when a second insulating resin layer or a third insulating resin layer is laminated.

<Usage of anisotropic conductive film> The anisotropic conductive film of the present invention can be particularly preferably applied to the case where the first electronic component (the side heated by the tool) is an IC chip, IC module, etc., which has relatively high rigidity (for example, a semiconductor component made of a wafer similar to a general IC chip can be cited), and the second electronic component (mounted on the side of the mounting table) is a flexible material such as a plastic substrate. Furthermore, it is not excluded that the combination of the first electronic component such as a semiconductor component, IC chip, IC module, FPC, etc. and the second electronic component such as FPC, glass substrate, plastic substrate, rigid substrate, ceramic substrate, etc. is used for anisotropic conductive connection. In addition, the anisotropic conductive film of the present invention can also be used to stack IC chips or wafers for multi-layering. Furthermore, the electronic components connected by the anisotropic conductive film of the present invention are not necessarily limited to the above-mentioned electronic components. In recent years, it can be used for a variety of electronic components. For example, when an IC chip or FPC is used as the first electronic component, an OLED plastic substrate can be used as the second electronic component. In particular, when the first electronic component is set as an IC chip and the second electronic component is set as a plastic substrate in a COP structure, the present invention is particularly effective. Therefore, the present invention includes "a connection structure in which a first electronic component and a second electronic component are anisotropically conductively connected via the anisotropic conductive film of the present invention", and also includes "a method for manufacturing a connection structure in which a first electronic component and a second electronic component are anisotropically conductively connected via the anisotropic conductive film of the present invention".

As a method for connecting electronic components using an anisotropic conductive film, when the anisotropic conductive film is composed of a single layer of a conductive particle dispersion layer 3, the second electronic component such as various substrates can be temporarily attached and temporarily pressed from the side where the conductive particles 1 of the anisotropic conductive film are embedded in the surface, and the first electronic component such as an IC chip is attached to the side of the temporarily pressed anisotropic conductive film where the conductive particles 1 are not embedded in the surface, and then thermally pressed to produce. When the insulating resin layer of the anisotropic conductive film contains not only a thermal polymerization initiator and a thermal polymerizable compound, but also a photopolymerization initiator and a photopolymerizable compound (which may be the same as the thermal polymerizable compound), a pressing method using both light and heat can also be used. In this way, the accidental movement of the conductive particles can be suppressed to a minimum. In addition, the side without the embedded conductive particles can be temporarily attached to the second electronic component for use. Furthermore, the first electronic component can be temporarily attached with the anisotropic conductive film instead of the second electronic component, and then aligned and connected.

Furthermore, when the anisotropic conductive film is formed by a laminate of the conductive particle dispersion layer 3 and the second insulating resin layer 4 (functioning as an insulating bonding layer), the conductive particle dispersion layer 3 is temporarily attached and temporarily pressed to a second electronic component such as various substrates, and a first electronic component such as an IC chip is aligned and placed on the second insulating resin layer 4 side of the temporarily pressed anisotropic conductive film, and thermally pressed. Alternatively, the second insulating resin layer 4 side of the anisotropic conductive film may be temporarily attached to the first electronic component. Furthermore, the conductive particle dispersion layer 3 can be temporarily attached to the first electronic component for use. Example

The present invention will be described in more detail below by way of examples. Examples 1 to 8, Comparative Example 1, Reference Example 1 (1) Preparation of resin composition for forming insulating resin layer and insulating adhesive layer Resin compositions for forming an insulating resin layer, a second insulating resin layer, and an insulating adhesive layer were prepared using the components shown in Table 1. By using a rotational rheometer (manufactured by TA Instruments), the measuring pressure is kept fixed at 5 g, a measuring plate with a diameter of 8 mm is used, and the temperature range is 30-200°C, the heating rate is set to 10°C/min, the measuring frequency is 10 Hz, and the load change on the above measuring plate is 5 g, the minimum melt viscosity of the obtained composition is obtained. The obtained results are shown in Table 1. In addition, composition B, composition C and composition D are resin compositions used in the present invention. Composition A and composition E are resin compositions used in comparative examples.

(2) Preparation of conductive particles Metal-coated resin particles (Au/Ni plated, average particle size 3 μm) manufactured by Sekisui Chemical Industry Co., Ltd. were prepared as conductive particles 1 to 4 in Table 2. Here, the 20% compression modulus and compression recovery rate were measured using a micro compression tester (Fischerscope H-100, manufactured by Fischer Corporation) as described below.

<20% compression elastic modulus> The compression displacement of the conductive particles was measured by using a micro compression tester to compress the conductive particles with a smooth indenter end surface of a cylinder (diameter 50 μm, made of diamond) at a compression rate of 2.6 mN/s and a maximum test load of 10 gf. The measured value was applied to the following formula (1) to calculate.

20% compression modulus of elasticity (K) {[N/mm ² ]) = 3/2 ^{1/ 2} ）・F・S ^-3/2・R ^-1/2 （1）

In formula (1), F is the load value (N) when the conductive particle is compressed and deformed by 20%, S is the compression displacement (mm) when the conductive particle is compressed and deformed by 20%, and R is the radius of the conductive particle (mm).

<Compression recovery rate> The conductive particles were compressed by the end face of a smooth cylindrical indenter (50 μm in diameter, made of diamond) using a micro compression tester. The displacement (L2) from the initial load (load 0.4 mN) to the load reversal (load 5 mN) and the displacement (L1) from the load reversal to the final load (load 0.4 mN) were measured. The measured values were applied to the following formula (2) to calculate.

Compression recovery rate (X[%]) = (L1/L2) × 100   (2)

Furthermore, conductive particles 1, 3, and 4 are conductive particles used in the present invention, and conductive particle 2 is a conductive particle used in a comparative example.

(3) Formation of insulating resin layer, second insulating resin layer and insulating adhesive layer The resin composition for forming the insulating resin layer, the second insulating resin layer or the insulating adhesive layer (see Table 1) was applied to a PET film having a film thickness of 50 μm using a bar coater and dried in an oven at 80°C for 5 minutes to form an insulating resin layer having a thickness as shown in Table 3 on the PET film. Similarly, the second insulating resin layer or the insulating adhesive layer was formed on another PET film with a thickness as shown in Table 3.

[Table 1] (Mass) Composition A Composition B Composition C Composition D Composition E Insulating resin layer (AE) Special phenoxy resin (FX-293, Nippon Steel Chemical Materials Co., Ltd.) 30 Phenoxy resin (YP-50, Nippon Steel Chemical Materials Co., Ltd.) 5 15 30 55 25 Phenoxy resin (FX-316ATM55, Nippon Steel Chemical Materials Co., Ltd.) 50 40 25 Difunctional acrylate (A-DCP, Shin-Nakamura Chemical Industry Co., Ltd.) 20 20 20 20 20 Difunctional urethane acrylate oligomer (UN-9200A, Negami Industries Co., Ltd.) 25 35 35 35 25 Silane coupling agent (A-187, Maitu High-tech Materials Co., Ltd.) 1 1 1 1 1 Methacrylate phosphate (KAYAMER PM-2, Nippon Kayaku Co., Ltd.) 1 1 1 1 1 Benzoyl peroxide (Nyper-BW, NOF Corporation) 5 5 5 5 5 Condition (4) Minimum melt viscosity [Pa･s] 200 1000 2000 4000 8000

[Table 2] Conductive particle properties Unit conductive particles 1 2 3 4 Condition (1) 20% compression modulus of elasticity [N/mm ² ] 13000 4000 6000 10000 Condition (2) Compression recovery rate [%] 72 35 68 71 Condition (3) Average particle size [μm] 3 3 3 3

(4) Preparation of resin transfer master A mold was prepared in the following manner: the conductive particles 1 were arranged in a square lattice as shown in FIG. 1A when viewed from above, the distance between the particles was equal to the average particle size of the conductive particles, and the number density of the conductive particles was the value shown in Table 3. That is, a mold was prepared in which the convex pattern of the mold was arranged in a square lattice, the distance between the convex portions in the lattice axis was twice the average conductive particle size, and the angle θ between the lattice axis and the short side direction of the anisotropic conductive film was 15°. Particles of a known transparent resin were flowed into the mold in a molten state, and the resin transfer master was formed by cooling and solidifying. Thus, a resin transfer master with concave portions arranged in the pattern shown in FIG. 1A was formed.

(5) Preparation of anisotropic conductive film The conductive particles shown in Table 2 were filled in the concave portions of a resin mold having the number of concave portions corresponding to the number density of the conductive particles shown in Table 3, and the insulating resin layer was coated thereon, and the layers were bonded by pressing at 60°C and 0.5 MPa. Then, the insulating resin layer was peeled off from the mold, and the conductive particles on the insulating resin layer were pressed into the insulating resin layer by applying pressure (pressing conditions: 60-70°C, 0.5 MPa), thereby preparing an anisotropic conductive film composed of a single layer of a conductive particle dispersion layer (Examples 1-5, Comparative Example 1, and Reference Example 1). The embedding state of the conductive particles is controlled by the pressing conditions (mainly pressure and temperature).

In addition, a two-layer anisotropic conductive film was prepared by laminating a second insulating resin layer on a conductive particle dispersion layer prepared in the same manner (Examples 6 and 7). Furthermore, a three-layer anisotropic conductive film was prepared by laminating an insulating adhesive layer having adhesive properties on the side of the conductive particle dispersion layer of the two-layer anisotropic conductive film prepared in the same manner (Example 8).

(6) Evaluation The anisotropic conductive films of the examples and comparative examples prepared in (5) were measured or evaluated in the following manner: (a) initial on-resistance, (b) conduction reliability, (c) indentation, and (d) particle capture. The results are shown in Table 3.

(a) Initial on-resistance The anisotropic conductive film of each embodiment and comparative example was sandwiched between an IC for conducting characteristic evaluation and a plastic substrate, and heated and pressed (180°C, 60 MPa, 5 seconds) to obtain each evaluation connection, and the on-resistance of the obtained evaluation connection was measured. The initial on-resistance is preferably 2 Ω or less in terms of practicality.

Here, regarding the evaluation IC and the plastic substrate, the terminal patterns thereof correspond to each other and the sizes are as follows. Also, when connecting the evaluation IC and the plastic substrate, the long side direction of the anisotropic conductive film is aligned with the short side direction of the bump.

IC for evaluating conduction characteristics Appearance   1.8×20.0 mm Thickness   0.5 mm Bump specifications   Size 30×85 μm, bump spacing 50 μm, bump height 15 μm

Plastic substrate (ITO wiring) Substrate material   Polyethylene terephthalate base film/polyurethane adhesive/polyimide film (PET/PU/PI substrate) Appearance   30×50 mm Thickness   0.5 mm Electrode   ITO wiring

(b) On-resistance The on-resistance of the evaluation connection made in (a) was measured in the same manner as the initial on-resistance after being placed in a constant temperature bath at 85°C and 85%RH for 500 hours. For practical purposes, the on-resistance is preferably 5 Ω or less, and more preferably 2 Ω or less.

(c) Indentation Observe the evaluation connector made in (a) from the plastic substrate side with a metal microscope to check whether an indentation is observed in the center of the bump end. If an indentation is observed, it is evaluated as good, and if it is not observed, it is evaluated as poor.

(d) Particle capture performance Using an IC for particle capture performance evaluation, the alignment between the IC and the plastic (PET/PU/PI) substrate (ITO wiring) corresponding to the terminal pattern was offset by 6 μm, and heat and pressurized (180°C, 60 MPa, 5 seconds). The number of conductive particles captured was measured for 100 6 μm×66.6 μm areas where the bumps of the IC and the terminals of the substrate overlapped. The minimum number of captured particles was obtained and evaluated based on the following criteria. In terms of practicality, B or above is preferred.

IC for evaluating particle capture performance Appearance   1.6×29.8 mm Thickness   0.3 mm Bump specifications   Size 12×66.6 μm, bump pitch 22 μm (L/S＝12 μm/10 μm), bump height 12 μm

Particle capture evaluation criteria A   5 or more B   3 or more but less than 5 C   Less than 3

[Table 3] Embodiment 1 Embodiment 2 Embodiment 3 Comparative example 1 Embodiment 4 Embodiment 5 Reference Example 1 Embodiment 6 Embodiment 7 Embodiment 8 conductive particles 1 1 1 1 3 4 2 1 1 1 Insulating resin layer composition/thickness (La) [μm] B/16 C/16 D/16 E/16 C/16 C/16 C/16 C/4 C/4 E/2.5 Second insulating resin layer/thickness [μm] - - - - - - - B/12 B/12 B/12 Insulating adhesive layer/thickness [μm] - - - - - - - - - A/1.5 Correspondence Schema 10C 10C 10C 10B 10C 10C 10C 10F 10E 3 layers Condition (5) Number density [pcs/mm ² ] 20000 20000 20000 20000 20000 20000 20000 20000 20000 20000 Embedment amount Lb [μm] 3.1 3.1 3 2.6 3.1 3.1 3.1 3.1 3 - Particle exposure diameter Lc [μm] - - - 2.4 - - - - - - La/D 5.3 5.3 5.3 5.3 5.3 5.3 5.3 5.3 5.3 - Embedment rate [(Lb/D)×100] [%] 103 103 100 87 103 103 103 103 100 - (a) Initial on-resistance [Ω] 0.2 0.2 0.2 0.6 0.3 0.2 0.4 0.2 0.2 0.2 (b) Conductivity reliability [Ω] 0.6 0.4 0.6 6.1 0.8 0.6 2.6 0.4 0.4 0.4 (c) Indentation good good good poor good good good good good good (d) Particle capture B B B B B B B A A A

(Investigation) According to the results in Table 3, the following conditions (1) to (5) are satisfied: <Condition (1)> The 20% compression modulus of the conductive particles is 6000 N/ ^mm2 or more and 15000 N/mm2 or ^less ; <Condition (2)> The compression recovery rate of the conductive particles is 40% or more and 80% or less; <Condition (3)> The average particle size of the conductive particles is 1 μm or more and 30 μm or less; <Condition (4)> The minimum melt viscosity of the insulating resin layer is 4000 Pa･s or less; and <Condition (5)> The number density of the conductive particles is 6000 particles/mm2 or more and 36000 particles/mm2 or ^less . ² The anisotropic conductive films of Examples 1 to 8 below have good results in terms of (a) initial on-resistance, (b) conduction reliability, (c) indentation, and (d) particle capture properties, which are above the level of having no practical problems.

On the other hand, the anisotropic conductive film of Comparative Example 1, which exceeds the numerical range of condition (4), has problems with "conduction reliability". Furthermore, there are problems with "stamping". In addition, the anisotropic conductive film of Reference Example 1, which is slightly below the numerical range of conditions (1) and (2), has a slightly higher initial on-resistance or conduction reliability resistance value than the anisotropic conductive film of Examples 1 to 8, but it is not to the extent that it causes problems in practical use. Among them, if the connection conditions during manufacturing are changed, it is better to have a low initial on-resistance or conduction reliability resistance value as in Examples 1 to 8. [Industrial Applicability]

In the anisotropic conductive film of the present invention, conductive particles are retained in the conductive particle dispersion layer using a 20% compressive elastic modulus, a compression recovery rate, and an average particle size that are respectively within specific numerical ranges, and an insulating resin layer that retains such conductive particles using a minimum melt viscosity that is below a specific numerical value, and the degree to which such an insulating resin layer retains conductive particles (in other words, the number density) is set within a specific range. Therefore, when an electronic component with bumps such as an image display element or a driver IC chip is anisotropically conductively connected to a flexible plastic substrate formed with electrodes and wiring through the anisotropic conductive film of the present invention, cracks in the wiring of the plastic substrate can be prevented. In addition, an indentation showing a good anisotropic conductive connection can be produced, and a good conduction reliability evaluation can be obtained during the anisotropic conductive connection. Therefore, the anisotropic conductive film of the present invention is useful for anisotropically conductively connecting electronic components (especially IC chips) not only to glass substrates but also to plastic substrates.

1: Conductive particle 1a: Top of conductive particle 2: Insulating resin layer 2a: Surface of insulating resin layer 2b: Concave part 2c: Concave part 2p: Cut surface 3: Conductive particle dispersion layer 4: Second insulating resin layer 10A, 10B, 10C, 10D, 10E, 10F: Anisotropic conductive film of embodiment 2 00: Terminal A: Grid axis of conductive particles D: Average particle size of conductive particles La: Thickness of insulating resin layer Lb: Embedment amount (distance between the deepest part of conductive particles and the center section of adjacent conductive particles) Lc: Exposure diameter θ: Angle between the long side of the terminal and the grid axis of conductive particles

FIG. 1A is a top view showing the arrangement of conductive particles of an anisotropic conductive film 10A of an embodiment. FIG. 1B is a cross-sectional view of an anisotropic conductive film 10A of an embodiment. FIG. 2 is a cross-sectional view of an anisotropic conductive film 10B of an embodiment. FIG. 3 is a cross-sectional view of an anisotropic conductive film 10C of an embodiment. FIG. 4 is a cross-sectional view of an anisotropic conductive film 10D of an embodiment. FIG. 5 is a cross-sectional view of an anisotropic conductive film 10E of an embodiment. FIG. 6 is a cross-sectional view of an anisotropic conductive film 10F of an embodiment. FIG. 7 is a schematic cross-sectional view of a plastic substrate. FIG. 8 is an explanatory view of a case where an IC chip is anisotropically conductively connected to a plastic substrate.

Claims (13)

An anisotropic conductive film comprises at least an insulating resin layer and a conductive particle dispersion layer composed of conductive particles dispersed in the insulating resin layer, and satisfies the following conditions (1) to (5): <Condition (1)> the 20% compressive elastic modulus of the conductive particles is ^not less than 6000 N/mm2 and not more than 15000 N/ ^mm2 ; <Condition (2)> the compression recovery rate of the conductive particles is not less than 40% and not more than 80%; <Condition (3)> the average particle size of the conductive particles is not less than 1 μm and not more than 30 μm; <Condition (4)> the minimum melt viscosity of the insulating resin layer is 4000 Pa. s or less; and <Condition (5)> the number density of the conductive particles is not less than 6000/ ^mm2 and not more than 36000/ ^mm2 , the conductive particles are arranged in a non-contact manner in the insulating resin layer, and the closest inter-particle distance of the conductive particles is not less than 50% of the average particle size of the conductive particles or not less than 0.2 μm, whichever is longer. The anisotropic conductive film as described in claim 1, wherein the minimum melt viscosity of the insulating resin layer is 200 Pa.s or more. An anisotropic conductive film as described in claim 1, wherein the conductive particles are regularly arranged when viewed from above. The anisotropic conductive film as described in claim 1 or 2, wherein a second insulating resin layer is laminated on the side of the conductive particle dispersion layer on which the conductive particles are retained. The anisotropic conductive film as described in claim 1 or 2, wherein a second insulating resin layer is laminated on the side of the conductive particle dispersion layer on which the conductive particles are not retained. An anisotropic conductive film as described in claim 4, wherein the minimum melt viscosity of the second insulating resin layer is lower than the minimum melt viscosity of the insulating resin layer. The anisotropic conductive film as described in claim 4, wherein the minimum melt viscosity ratio of the insulating resin layer to the second insulating resin layer is greater than 2. A method for manufacturing an anisotropic conductive film as described in claim 1, comprising the step of forming a conductive particle dispersion layer by pressing conductive particles into an insulating resin layer. A manufacturing method as described in claim 8, wherein the conductive particles are maintained in a prescribed arrangement on the surface of the insulating resin layer, and the conductive particles are pressed into the insulating resin layer using a flat plate or a roller, thereby forming a conductive particle dispersion layer. A manufacturing method as described in claim 9, wherein conductive particles are filled into a transfer mold and the conductive particles are transferred to an insulating resin layer, thereby maintaining the conductive particles on the surface of the insulating resin layer in a prescribed configuration. A connection structure, wherein a first electronic component and a second electronic component are anisotropically conductively connected via the anisotropic conductive film described in any one of claims 1 to 7. The connection structure as described in claim 11, wherein the first electronic component is an IC chip or an IC module, and the second electronic component is a plastic substrate. A method for manufacturing a connection structure, wherein a first electronic component and a second electronic component are anisotropically conductively connected via the anisotropic conductive film described in any one of claims 1 to 7.

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