JP2008186760A - Anisotropic conductive film and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an anisotropic conductive film and its manufacturing method capable of improving its conductive performance while a porous membrane formed by making use of waterdrops is used. <P>SOLUTION: The anisotropic conductive film comprises the porous membrane having numerous hole sections arranged in a honeycomb shape and bending an inner wall surface of each hole section in an outward direction, conductive particles retained in the hole sections of the porous membrane, and an adhesive layer formed on one side of the porous membrane. In the anisotropic conductive film, the porous membrane is made of polyvinyl acetal system resin in which an amount of residual hydroxyl group is within a range from more than 22 mol% to less than 30 mol%. The porous membrane is suitably made by making exist a support body casting polymer solution at least including an organic solvent having hydrophobicity and volatility, the polyvinyl acetal system resin, and a surfactant at an ambient atmosphere of 50% or more of relative humidity. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an anisotropic conductive film and a method for producing the same.

  2. Description of the Related Art In recent years, with the increase in functionality and miniaturization of electronic devices, the need to electrically and mechanically connect members having conductors arranged at a narrow pitch has increased. As a case where such a need arises, for example, in the field of liquid crystal display (LCD), a TAB (Tape Automated Bonding) electrode on which a driving IC chip is mounted and a liquid crystal panel electrode are connected. And a case where a bare drive IC chip (bare chip) is directly connected to the electrode of the liquid crystal panel (Chip On Glass: COG).

  In the above connection, generally, an anisotropic conductive film (ACF) showing conductivity in the film thickness direction and insulating in the film surface direction is often used.

  As the anisotropic conductive film, for example, in Patent Document 1 by the present applicant, a support substrate in which a polymer is dissolved in an organic solvent that exhibits hydrophobicity and volatilizes, and this polymer solution is cast is described. An anisotropic conductive film having a three-layer structure in which a porous film is formed by being present under high humidity conditions, conductive particles are filled in the pores of the porous film, and then both surfaces of the film are covered with an adhesive layer Is disclosed.

  According to the method for forming the porous film, water droplets due to condensation are generated on the surface of the liquid film due to the latent heat generated when the organic solvent evaporates. As a result, a porous film having a large number of pores arranged in a honeycomb shape is formed.

International Publication No. WO2005 / 096442 Pamphlet

  However, it has been found that the conventional three-layer anisotropic conductive film has the following points to be improved.

  That is, for example, when an anisotropic conductive film having a three-layer structure is interposed between an IC chip and a circuit pattern, and these are thermocompression bonded, an adhesive layer between a bump that is an electrode of the IC chip and the circuit pattern Is eliminated. In addition, conductive particles are sandwiched between the two. Then, the IC chip and the circuit pattern are bonded together while maintaining this state, whereby the IC chip and the circuit pattern are electrically and mechanically connected.

  However, according to the results of previous research conducted by the present inventors, it has been found that the number of conductive particles trapped between conductors to be connected may be reduced after crimping depending on the crimping conditions and the like. .

  This is considered to be because the porous film collapses with the flow of the adhesive layer, and the conductive particles flow out from the film. This type of phenomenon is likely to occur on the side where there is little space where the adhesive layer is fluidly excluded, such as on the circuit pattern side.

  Therefore, even if an anisotropic conductive film in which conductive particles are regularly arranged is produced, the regularity of the conductive particles is disturbed at the time of pressure bonding, and it is difficult to further improve the conduction performance. .

  Further, when forming a porous film using water droplets, it is necessary to stably generate a group of water droplets due to condensation on the surface of the liquid film in order to stably form regularly arranged pores. For this reason, it has been usual to use a hydrophobic polymer material.

  Therefore, in order to secure an adhesive force with a connected object made of a hydrophilic material such as a glass substrate or a circuit pattern, an adhesive layer has to be formed on both surfaces of the hydrophobic porous film. Therefore, it has been difficult to avoid the above problems while using a porous film formed using water droplets.

  The present invention has been made in view of the above problems, and an anisotropic conductive film that can improve the conduction performance while using a porous film formed by using water droplets, and its It is to provide a manufacturing method.

  In order to solve the above problems, an anisotropic conductive film according to the present invention has a porous film having a large number of holes arranged in a honeycomb shape, and an inner wall surface of the holes is curved outward. , Having conductive particles held in the pores of the porous membrane and an adhesive layer formed on one side of the porous membrane, the porous membrane having a residual hydroxyl group content of more than 22 mol% to 30 mol% The gist is that it is formed from a polyvinyl acetal resin within a range of less than

  Here, the conductive particles are preferably fused to the porous film.

  The conductive particles are preferably present in substantially the same plane.

  The porous membrane is a polymer containing at least a hydrophobic and volatile organic solvent, a polyvinyl acetal resin having a residual hydroxyl amount in the range of more than 22 mol% to less than 30 mol%, and a surfactant. It is preferable that the support formed by casting the solution is formed by being present in an atmosphere having a relative humidity of 50% or more.

  On the other hand, the method for producing an anisotropic conductive film according to the present invention has a large number of holes arranged in a honeycomb shape, the inner wall surface of the holes is curved outward, and the residual hydroxyl group amount is 22 mol. A step of forming a porous film made of a polyvinyl acetal resin in the range of more than% to less than 30 mol%, a step of filling conductive particles in the pores of the porous film, and a filling of the conductive particles And a step of forming an adhesive layer on one side of the film.

  At this time, the formation of the porous film includes at least a hydrophobic and volatile organic solvent, a polyvinyl acetal resin having a residual hydroxyl group content in the range of more than 22 mol% to less than 30 mol%, and a surfactant. It is preferable that the support on which the polymer solution is contained be present in an atmosphere having a relative humidity of 50% or more.

  An anisotropic conductive film according to the present invention has a porous film having a large number of pores arranged in a honeycomb shape, and an inner wall surface of the pores is curved outward, and in the pores of the porous membrane. It has conductive particles held and an adhesive layer formed on one side of the polymer film, and the porous film is formed from a polyvinyl acetal resin having a residual hydroxyl group amount within a specific range. .

  Therefore, the anisotropic conductive film can improve the conduction performance while using a porous film formed using water droplets.

  That is, in the polyvinyl acetal resin forming the porous film, the amount of residual hydroxyl groups is defined by the above upper limit value. In this case, the degree of hydrophilicity of the polyvinyl acetal resin does not become too high, and even if a method for forming a porous film using water droplets is used as a raw material, the film can be stably formed. Therefore, it is possible to employ a porous film having a honeycomb structure formed using water droplets.

  In addition, the polyvinyl acetal resin forming the porous film has a residual hydroxyl amount defined by the lower limit. In this case, the degree of hydrophilicity of the polyvinyl acetal resin does not become too low, and the porous film itself can exhibit good adhesiveness to the connected object. Therefore, it is not necessary to form an adhesive layer on both sides of the porous film, and it is possible to adopt a two-layer structure in which an adhesive layer is formed on one side of the porous film.

  The reason why the conduction performance is improved is that by adopting a two-layer structure, it is possible to suppress the collapse of the porous film due to the flow of the adhesive layer and the outflow of conductive particles due to the flow during the pressure bonding. It is possible to capture more conductive particles between conductors of the connected object while maintaining the original regular arrangement, and the adhesion and adhesion layer of the porous film itself. Thus, it is conceivable that the objects to be connected can be mechanically connected in a state where many conductive particles are sandwiched.

  Since the anisotropic conductive film has an adhesive layer on one side, for example, good electrical and electrical connection with a connected object having a relatively high protruding conductor such as a bump of an IC chip. Mechanical connection can be achieved.

  Here, when the conductive particles are fused to the porous film, the adhesion between the conductive particles and the porous film is enhanced. Therefore, at the time of manufacturing the anisotropic conductive film, the conductive particles are difficult to drop off, and the handling property is excellent.

  In addition, when a large number of conductive particles held in the porous film are present in almost the same plane, the conduction in the film thickness direction is ensured without depending on the contact between the stacked conductive particles. can do. Therefore, the contact resistance between the conductive particles is eliminated, which contributes to the improvement of the conduction performance. In addition, the conductive particles stacked at the time of crimping are ejected from between the conductors, and there is no fear of deteriorating insulation.

  On the other hand, the method for producing an anisotropic conductive film according to the present invention has a large number of holes arranged in a honeycomb shape, the inner wall surface of the holes is curved outward, and the residual hydroxyl group amount is 22 mol%. A step of forming a porous film made of a polyvinyl acetal-based resin in a range of ultra to less than 30 mol%, a step of filling conductive particles in the pores of the porous film, and one side of the film filled with the conductive particles Forming an adhesive layer. Therefore, an anisotropic conductive film that exhibits the above-described effects can be obtained.

  The porous film is formed of a polymer containing at least a hydrophobic and volatile organic solvent, a polyvinyl acetal resin having a residual hydroxyl amount in the range of more than 22 mol% to less than 30 mol%, and a surfactant. When the support on which the solution is cast is present in an atmosphere having a relative humidity of 50% or more, the honeycomb structure has a large number of pores formed from water droplets and arranged in a honeycomb shape. Easy to obtain a membrane.

  Hereinafter, the anisotropic conductive film according to the present embodiment (hereinafter also referred to as “the present ACF”). The method for manufacturing the anisotropic conductive film according to the present embodiment (hereinafter referred to as “the present manufacturing method”). This will be described in detail.

1. This ACF
FIG. 1 shows an example of a schematic cross-sectional view of the present ACF. The ACF 10 includes a porous film 12, conductive particles 14, and an adhesive layer 16.

  The ACF 10 has a two-layer structure of a porous film 12 and an adhesive layer 16, and the objects to be connected can be bonded by the adhesive property of the porous film 12 itself and the adhesive layer 16.

(Porous membrane)
In the present ACF, the porous film is formed of a polyvinyl acetal resin.

  The polyvinyl acetal resin is basically a polyvinyl alcohol acetalized with various aldehydes. The porous film may be formed of one or more polyvinyl acetal resins.

  The aldehyde used for the acetalization is not particularly limited, and any aldehyde that can be acetalized, such as formaldehyde, acetaldehyde, butyraldehyde, propylaldehyde, and the like may be used.

  Specific examples of the polyvinyl acetal resin include a polyvinyl butyral resin and a polyvinyl formal resin from the viewpoints of, for example, good adhesion to glass, metal, and the like, and easy availability. Particularly preferred is a polyvinyl butyral resin.

  Here, the polyvinyl acetal resin forming the porous film has a residual hydroxyl amount in the range of more than 22 mol% to less than 30 mol%.

  The polyvinyl acetal resin is basically a hydrophilic material, but the degree of hydrophilicity varies depending on the amount of residual hydroxyl group. In the present ACF, the amount of residual hydroxyl group ensures both the film formability when forming a honeycomb-structured porous film using water droplets, which will be described later, and the adhesion to the connected object when the present ACF is used. It is a physical property involved in

  This ACF is excellent in the balance between the film formability of the porous film and the adhesiveness to the adherend by setting the residual hydroxyl amount of the polyvinyl acetal resin forming the porous film within the above range.

  The lower limit of the residual hydroxyl group is preferably 23 mol% or more, more preferably 24 mol% or more, and even more preferably 24.5 mol% or more, from the viewpoint of improving the adhesiveness.

  On the other hand, the upper limit of the amount of the remaining hydroxyl group is preferably 29.5 mol% or less, more preferably 29 mol% or less, and still more preferably, from the viewpoint of improving the film formability of the porous film using water droplets. Is preferably 28.5 mol% or less.

  When the amount of the residual hydroxyl group is 22 mol% or less, the degree of hydrophilicity is lowered, the adhesiveness is lowered, and a tendency to peel off after press bonding is observed. In addition, when the amount of the remaining hydroxyl group is 30 mol% or more, the degree of hydrophilicity increases, and it tends to be difficult to form a porous film having a well-ordered honeycomb structure using water droplets.

  The amount of residual hydroxyl group was determined by IR measurement in advance with a calibration curve using absorbance for the amount of hydroxyl group derived from vinyl alcohol (mol%) and the amount of acetyl group derived from residual acetyl group (mol%). In addition, an actual sample can be measured and calculated from the calibration curve (based on JISK6728).

  In the present ACF, the porous film has a honeycomb structure in which a large number of holes are arranged in a honeycomb shape, and the inner wall surface of the holes is curved outward.

  Here, the hole may be a through-hole penetrating in the film thickness direction or a non-through hole not penetrating in the film thickness direction. The hole may have both a through hole and a non-through hole. Preferably, it is a non-through hole.

  During production of this ACF, the conductive particles are less likely to drop off and have excellent handling properties. During this ACF press-bonding, it is difficult for the conductive particles to flow out from the side opposite to the adhesive layer forming surface, making it easier to improve the conduction performance. Because there is an advantage of.

  Specific examples of the curved shape of the inner wall surface of the hole include, for example, a substantially spherical shape (including a substantially spherical shape crushed in the thickness direction) and the like.

  The honeycomb structure is usually a structure that is difficult to fabricate using mechanical processing or the like. Therefore, having the honeycomb structure is one of the promising grounds for using a film forming method using water droplets, which will be described later.

  From the standpoint of increasing the reliability of anisotropic conduction, for example, the opening diameter of the hole is smaller than the narrowest of the intervals between the plurality of conductors of the connected object, and the interval between the holes. Is preferably smaller than the narrowest of the widths of a plurality of conductors (for example, bumps of an IC chip, circuit patterns of a printed wiring board, etc.) included in the connected object.

  In this case, it is preferable that the opening diameter of the hole is ½ or less of the narrowest of the intervals between the plurality of conductors of the connected object, and the interval of the hole is a plurality of the number of the connected object. The width of the conductor is preferably 1/2 or less of the narrowest width.

  In addition, the opening diameter of the said hole means the average value of the diameter of each opening part measured about 10 porous parts which observed the porous membrane surface with the laser microscope and was selected arbitrarily. Moreover, the said space | interval of the said hole part observes the porous membrane surface with a laser microscope, and measured the average value of the distance between each opening edge part measured about 10 places between the opening edge parts of the adjacently selected hole part. Say.

  Such a porous membrane is obtained by dissolving the polyvinyl acetal resin in a volatile organic solvent that is not mixed with water and using a method in which a support obtained by casting the polymer solution is present in a high humidity atmosphere. It can form suitably. Details will be described later in the section of this manufacturing method.

  The film thickness of the porous film can be determined in consideration of the particle size of the conductive particles to be filled, the film strength, the handleability during production, and the like.

  The upper limit of the thickness of the porous membrane is preferably 3/2 or less of the particle size of the conductive particles, more preferably 1 or less of the particle size of the conductive particles, and even more preferably It is good that it is 2/3 times or less the particle size of the conductive particles.

  On the other hand, the lower limit of the thickness of the porous membrane is preferably 1/10 or more times the particle size of the conductive particles, more preferably 1/5 or more times the particle size of the conductive particles, and even more. Preferably, it is 1/3 times or more the particle size of the conductive particles.

  When the film thickness of the porous film is within the above range, the conductive particles are stacked in the film thickness direction and difficult to be filled when the conductive particles are filled. In addition, when a conductor (IC chip bump or the like) included in the connected object crushes the conductive particles, the porous film is unlikely to hinder it. For this reason, the conductive particles are easily captured and the conduction performance in the film thickness direction is easily improved.

(Conductive particles)
In the present ACF, the conductive particles are held in a large number of pores of the porous film.

  Specific examples of the conductive particles include substantially spherical shapes (including those having a substantially elliptical cross section), substantially columnar shapes, spindle shapes, needle shapes, and the like. Preferably, the shape of the conductive particles is substantially spherical from the viewpoint of easily filling the pores with the conductive particles during the production of the present ACF, excellent insulation reliability in the film surface direction, and being easily compressed uniformly. And good.

  The conductive particles only need to have conductivity capable of being electrically connected in the film thickness direction when the ACF is used.

  Specific examples of the conductive particles include, for example, particles that are filled with a conductive substance from the surface to the center thereof, and the surface of the polymer particles that are coated with one or more conductive layers. The particle | grains etc. which can be illustrated can be illustrated.

  The latter particles are preferably used. This is because the particles are easily elastically deformed by the pressurization, so that when the present ACF is used, the contact area with the conductor of the connected object is increased, and it is easy to ensure conductivity in the film thickness direction.

  More specifically, for example, as an example of the former particles, metal particles, carbon particles and the like are used, and as an example of the latter particles, one or two or more metal plating layers (electrolytic plating, Electrolytic plating etc.) and particles having a sputtered layer can be exemplified.

  Specific examples of metals that can be used in the conductive material and conductive layer include gold, silver, white metals (platinum, palladium, ruthenium, rhodium, osmium, iridium), nickel, copper, zinc, and iron. 2 such as lead, tin, aluminum, cobalt, indium, chromium, titanium, antimony, bismuth, germanium, cadmium, etc., tin-lead alloy, tin-copper alloy, tin-silver alloy, tin-lead-silver alloy, etc. Examples include alloys composed of more than one kind of metal. These may be contained alone or in combination of two or more.

  Specific examples of the polymer applicable to the polymer particles include polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyvinylidene chloride, polytetrafluoroethylene, polyisobutylene, polybutadiene, polyalkylene terephthalate, polysulfone, Polycarbonate, polyamide, phenol formaldehyde resin, melamine formaldehyde resin, benzoguanamine formaldehyde resin, urea formaldehyde resin, (meth) acrylic acid ester polymer, divinylbenzene polymer, divinylbenzene-styrene copolymer and divinylbenzene- (meth) acrylic acid Examples thereof include divinylbenzene polymers such as ester copolymers. These may be contained alone or in combination of two or more. In addition, the said (meth) acrylic acid ester may be bridge | crosslinked as needed.

  Preferred are dimethybenzene-based polymers such as (meth) acrylic acid ester polymers, divinylbenzene polymers, divinylbenzene-styrene copolymers and divinylbenzene- (meth) acrylic acid ester copolymers.

Further, in the present ACF, particles in which one or two or more insulating layers made of an insulating oxide such as TiO ₂ or the above polymer are coated on the surface of the conductive particles may be used. However, it is necessary that the insulating layer has a thickness that allows at least a portion in contact with a conductor such as an electrode to be broken and conductive when the ACF is crimped. In the case where such particles are used, the insulating layer is difficult to break in a portion that is not in contact with a conductor such as an electrode, so that it is easy to improve the insulation in the film surface direction.

  The particle size of the conductive particles can be determined in consideration of the opening diameter of the hole of the porous film, the depth of the hole, the width and pitch of the conductor of the connected object, and the like.

  Specifically, the upper limit of the particle size of the conductive particles is preferably 10 μm or less, more preferably 7 μm or less, and even more preferably 5 μm or less.

  On the other hand, the lower limit of the particle size of the conductive particles is specifically preferably 1 μm or more, more preferably 2 μm or more, and even more preferably 3 μm or more.

  In addition, the particle diameter of the said electroconductive particle is an average particle diameter measured with the particle size distribution measuring apparatus (The Seishin company make, "PITA-1"). Further, the present ACF may contain one or more of the above-described conductive particles.

  In the present ACF, the conductive particles may be held in the porous film with a gap between the conductive particles and the porous film, or the conductive particles and the porous film May be held in the porous membrane in a state of being in close contact with each other.

  The conductive particles and the porous film are preferably in close contact with each other from the viewpoint that the conductive particles do not easily fall off during the production of the present ACF and the handling property is excellent. More preferably, the conductive particles and the porous film are preferably fused from the viewpoint of excellent effects.

  The conductive particles may be held in a state in which a part of the conductive particles are exposed on both surfaces of the porous film, or a part of the conductive particles may be on one side of the porous film. It may be held in an exposed state.

  When the conductive particles are exposed, the conductive particles are easily brought into contact with the conductor of the connected object disposed on the exposed surface side. Therefore, it becomes easy to ensure conductivity.

  Preferably, from the viewpoint of excellent effects, the conductive particles may be held in a state in which a part thereof is projected from at least one surface of the porous membrane.

  Further, when the conductive particles are held on the porous film without exposing a part of the conductive particles on the film surface opposite to the adhesive layer forming surface, the conductive particles are produced during the production of the ACF. Since it is difficult to drop off, it is excellent in handling.

  In addition, the said electroconductive particle may be hold | maintained in the state which is not exposed on both surfaces of a porous membrane.

  In the present ACF, a large number of conductive particles are preferably present in substantially the same plane (a plane substantially parallel to the membrane surface of the porous membrane). In this case, a plurality of conductive particles are not stacked in the film thickness direction. Therefore, the contact resistance between the conductive particles is not involved in the conduction in the film thickness direction, and the conduction performance is easily improved. In addition, the conductive particles stacked at the time of crimping are ejected from between the conductors, and there is no fear of deteriorating insulation.

  In addition, the space | interval of the said electroconductive particles is mainly determined by the space | interval of the hole part of the used porous membrane.

(Adhesive layer)
This ACF has an adhesive layer on one side of the porous membrane. This is because it is better to have one adhesive layer from the viewpoint of obtaining a strong mechanical connection.

  Any material can be used as the adhesive layer material as long as it has adhesiveness and insulating properties with respect to the connected object.

  As the adhesive layer material, various thermosetting resins, thermoplastic resins, rubbers, and the like can be used. Specifically, for example, epoxy resin, melamine resin, phenol resin, diallyl phthalate resin, bismaleimide triazine resin, unsaturated polyester resin, polyurethane resin, phenoxy resin, polyamide resin, polyimide resin Resin, thermosetting resin such as cyanate resin, polyamide resin, polyester resin, polycarbonate resin, polyphenylene oxide resin, polyurethane resin, polyacetal resin, polyvinyl acetal resin, polyethylene resin, polypropylene resin, Examples thereof include thermoplastic resins such as polyvinyl resins, rubbers and elastomers containing one or more functional groups such as hydroxyl groups, carboxyl groups, vinyl groups, amino groups, and epoxy groups. These may be contained alone or in combination of two or more.

  Specifically, as the thermosetting resin, for example, an epoxy resin or the like can be suitably used from the viewpoint of excellent adhesion to an object to be connected.

  The adhesive layer material may be a prepreg obtained by semi-curing the thermosetting resin. In this case, for example, the adhesive layer easily flows out in the gaps between the plurality of conductors of the connected object. Moreover, the adhesiveness with a to-be-connected object also increases.

  The adhesive layer material preferably has an elastic modulus at 85 ° C. (before thermosetting for those that are thermally cured), preferably 1 MPa or more, and more preferably 7 MPa or more. The elastic modulus at 210 ° C. (after thermosetting for those that are thermally cured) is preferably 1.5 MPa or more, and more preferably 2.5 MPa or more.

  If the elastic modulus is within the above range, the holding force of the conductive particles is good, the movement of the porous film is small, and the conductive particles are more difficult to flow out.

  The elastic modulus at 85 ° C. was obtained by preparing a sample (diameter 20 mm, thickness 400 μm) of the polymer and using a stress-controlled rheometer (for example, “AR500” manufactured by TA Instruments Japan Co., Ltd.). Etc.) is used to measure the elastic modulus from 20 ° C. to 180 ° C. under the measurement conditions of a temperature rising rate of 5 ° C./min, a frequency of 1 Hz, and a compression strain of 0.1%. Value.

  On the other hand, the elastic modulus at 210 ° C. is obtained by preparing a sample obtained by thermocompression bonding a sample made of the polymer (width 5 mm, length 30 mm, thickness 2 mm) at 210 ° C. and 5 MPa for 6 minutes. , Manufactured by UBM Co., Ltd., “Rheogel-E4000F” etc. is marketed.), Temperature rising rate 3 ° C./min, frequency 15 Hz, strain 0.05% (automatic adjustment), automatic static load, It is a value obtained by measuring the elastic modulus from 30 ° C. to 230 ° C. under the measurement condition of chuck interval 20 mm.

  The thickness of the adhesive layer takes into account the height of the conductor (IC chip bump, etc.) of the connected object to be bonded to the adhesive layer, and the amount of gap generated between the connected objects (IC chip and circuit pattern, etc.). Can be determined.

  The upper limit of the thickness of the adhesive layer is preferably 3 times or less, more preferably 2 times or less, and even more preferably 1.75 times or less the height of the conductor of the connected object to be bonded to the adhesive layer. Good to have.

  The lower limit of the thickness of the adhesive layer is preferably 1 time or more, more preferably 1.2 times or more, and even more preferably 1.3 times the height of the conductor of the connected object to be bonded to the adhesive layer. It is good to be above.

  At this time, the thickness of the adhesive layer is preferably selected so as to be thicker than the thickness of the porous film from the viewpoint of easily filling a gap generated between the connected objects.

2. This Manufacturing Method This manufacturing method includes a porous film forming step, a particle filling step, and an adhesive layer forming step.

(Porous membrane formation process)
In this production method, the porous film forming step has a large number of holes arranged in a honeycomb shape, and the inner wall surface of the holes is curved outward, and the amount of residual hydroxyl group exceeds 22 mol% to 30 mol. It is a step of forming a porous film made of a polyvinyl acetal resin within a range of less than%.

  Here, the porous membrane is not mixed with water, and uses a method in which the polyvinyl acetal resin is dissolved in a volatile organic solvent and the support obtained by casting the polymer solution is present in a high-humidity atmosphere. Can be suitably formed.

  According to this method, the porous film is spontaneously formed on the basis of the following principle.

  That is, the polymer solution formed in a film shape with a predetermined coating thickness on the surface of the support is deprived of latent heat when the organic solvent in the solution evaporates. Therefore, a group of minute water droplets formed by condensation of water vapor in the atmosphere adheres to the surface of the polymer solution whose temperature has decreased. The adhering water droplets are transported and collected by convection or capillary force generated in the polymer solution by latent heat, and are finally packed most closely. Thereafter, when the closely packed water droplet group evaporates, a porous film having a honeycomb structure is formed using the self-organized water droplet group as a template.

  The porous membrane thus formed basically has the following three-dimensional structure regardless of whether it has through holes or non-through holes. .

  That is, the holes are arranged in a honeycomb shape, and the adjacent holes are separated by the partition walls. In addition, since these holes are formed using water droplets as a mold, the inner wall surface thereof is curved in a substantially spherical shape toward the outer side (because it is derived from the surface of the water droplets, the hole diameter is larger than the opening diameter of the holes). The inner diameter of the part is larger). Therefore, the partition wall has a constricted portion having a thinner thickness than the vicinity of the film surface in the vicinity where the inner wall surfaces of the adjacent hole portions are closest to each other.

  More specifically, the method for forming the porous film is, for example, a support obtained by casting a polymer solution containing at least a hydrophobic and volatile organic solvent, the polyvinyl acetal resin, and a surfactant. A method of allowing the body to exist in an atmosphere having a relative humidity of 50% or more can be suitably used.

  In this case, specific examples of the hydrophobic and volatile organic solvent include halides such as chloroform and methylene chloride, aromatic hydrocarbons such as benzene, toluene and xylene, ethyl acetate, butyl acetate and the like. And ketones such as methyl ethyl ketone (MEK) and acetone. These may be used alone or in combination.

  Since the content of the polyvinyl acetal resin is as described in “1. Present ACF”, it is omitted here, but one or more of them can be used in combination.

  The surfactant is added mainly for the purpose of stabilizing water droplets adhering to the surface of the polymer solution. Basically, it is a compound having both a hydrophobic part and a hydrophilic part.

  As the surfactant, specifically, for example, a polymer having a hydrophilic acrylamide polymer as a main chain skeleton, a dodecyl group as a hydrophobic side chain, a lactose group or a carboxyl group as a hydrophilic side chain, Alternatively, a polyionic complex of an anionic polysaccharide such as heparin or dextran sulfate and a quaternary long chain alkyl ammonium salt can be exemplified. These can be used alone or in combination of two or more.

  The upper limit of the concentration of the polyvinyl acetal resin contained in the polymer solution is preferably 1% by weight or less, more preferably 0.5% by weight or less, and even more preferably, from the viewpoint of retention of water droplets that form condensation. Preferably, it is 0.4 weight% or less.

  On the other hand, the lower limit of the concentration of the polyvinyl acetal resin contained in the polymer solution is preferably 0.01% by weight or more, more preferably 0.1% by weight or more, from the viewpoint of water droplet condensation time, etc. More preferably, it is 0.2% by weight or more.

  In addition, the upper limit of the content of the surfactant is preferably not more than 1 time, more preferably 1/2 times the amount of the polyvinyl acetal resin, from the viewpoint of retention of water droplets that form condensation. In the following, it is even more preferably ¼ or less.

  On the other hand, the lower limit of the content of the surfactant is preferably 1/30 times or more, more preferably 1/20, relative to the amount of polyvinyl acetal resin, from the viewpoint of retention of water droplets that form condensation. Double amount or more, and even more preferably, 1/15 times or more.

  While the material of the support for casting the polymer solution does not affect the formation of a liquid film by the polymer solution, it is altered or corroded by an organic solvent or various additives contained in the solution. The material is not particularly limited as long as it is a non-destructive material. Specific examples of the material for the support include inorganic materials such as glass, metal, and silicon wafers, polymer materials such as polypropylene, polyethylene, polyetherketone, and fluororesin, and liquids such as water and liquid paraffin. It can be illustrated.

  The shape of the support is not particularly limited as long as it can stably hold the liquid film formed of the polymer solution on the surface thereof. Usually, for example, a planar shape such as a plate shape or a film shape can be suitably used.

  The coating thickness when casting the polymer solution on the support is such that, for example, the concentration of the polyvinyl acetal resin, the viscosity of the solution, etc. are taken into account so that the water droplet group can form through holes and non-through holes. It can be adjusted as appropriate.

  The support on which the polymer solution is cast is desirably present in a gas atmosphere having a relative humidity of 50% or more, preferably 50% to 95%. This is because if the relative humidity is within the above range, sufficient condensation is likely to occur.

  At this time, the polymer solution may be cast on a support in an atmosphere having a relative humidity of 50% or more, or the support on which the polymer solution has been cast in advance is placed in an atmosphere having a relative humidity of 50% or more. Also good. Alternatively, a gas having a relative humidity of 50% or more may be blown onto the polymer solution from above or from an oblique direction.

  Specific examples of the gas in the atmosphere and the gas to be sprayed include inert gases such as argon gas and nitrogen gas, and air. These may be contained alone or in combination of two or more. Preferably, air (atmosphere) advantageous in cost is used.

  In this method, it is possible to form both through-holes and non-through-holes by appropriately adjusting the film formation conditions. Specific examples of conditions for forming a film that determines penetration or non-penetration include, for example, the coating thickness (cast amount) of the polymer solution, the concentration of the resin contained in the polymer solution, and the relative humidity. it can.

  More specifically, for example, adjustments such as increasing (increasing) the coating thickness (cast amount) of the polymer solution, increasing the concentration of the resin contained in the polymer solution, and decreasing the relative humidity are performed. For example, non-through holes are easily formed. If the reverse adjustment is performed, the through hole is easily formed.

  Among these, the conditions for determining penetration / non-penetration simply and effectively are the coating thickness (cast amount) of the polymer solution and the concentration of the resin contained in the polymer solution.

  In order to confirm whether the formed porous membrane has through-holes or non-through-holes, the surface of the membrane is observed to confirm whether the support is exposed in the pores. The film may be peeled off from the support and the back surface of the film may be observed.

In the method for forming a porous film, heating is performed within a range that does not affect the formation of the porous film, if necessary, in order to promote the evaporation of the organic solvent and the evaporation of water droplets during film formation. Drying or the like may be performed.

(Particle filling process)
In this production method, the particle filling step is a step of filling the conductive particles described above into the pores of the porous membrane.

  In this step, it is preferable to fill the conductive particles so that the conductive particles are not stacked in the hole depth direction. In other words, it is preferable to fill the pores with the conductive particles so that they are substantially in the same plane. More preferably, from the viewpoint of making the conductive particles separated from each other one by one, the conductive particles may be filled one by one for each hole.

  Specifically, as the method for filling the conductive particles, for example, (1) after spreading the conductive particles themselves or a dispersion thereof on the surface of the porous film, scraping with a brush, brush, blade, etc. (2) After spreading the conductive particles themselves or a dispersion thereof on the surface of the porous film, applying magnetic force or vibration from the outside to put the conductive particles in the pores A method, (3) a method of immersing the porous membrane in the dispersion, (4) a plate-like member arranged at a certain distance from the surface of the porous membrane, and the dispersion in the formed gap And a method of slidably moving the porous membrane and / or the plate-like member, a combination thereof, and the like.

  Since the conductive particles are physically pushed into the pores, it is preferable to use the method (1) from the viewpoint of easy filling of the conductive particles more reliably and a relatively short time required for filling. Is good. More preferably, from the viewpoint of being able to carry out by a dry method, it is preferable to use powdered conductive particles themselves in the method (1). More preferably, in the method (1), the conductive particles are attracted to the porous film by a magnetic force from the side opposite to the side where the conductive particles are spread, from the viewpoint that the conductive particles are easily introduced into the pores. On the other hand, it is good to scrape off by a scraping means. In this case, the conductive particles may be those having conductivity and magnetism.

(Adhesive layer forming process)
In this manufacturing method, the adhesive layer forming step is a step of forming an adhesive layer on one side of the film filled with conductive particles.

  At this time, when both surfaces of the film holding the conductive particles have adhesiveness, an adhesive layer may be formed on any surface. Moreover, when one side of the film holding the conductive particles has adhesiveness, an adhesive layer is formed on the surface opposite to the surface.

  As the method for forming the adhesive layer, specifically, for example, a coating liquid prepared so that the adhesive layer material has an appropriate solid content and viscosity is applied using a known coating means such as a coater. Examples thereof include a method of drying as necessary, and a method of laminating and bonding a film-like adhesive layer prepared in advance.

  This manufacturing method may have one or two or more additional steps described below in addition to the above steps.

(Heat treatment process)
The present manufacturing method includes a porous membrane between at least one of the porous membrane forming step and the particle filling step, between the particle filling step and the adhesive layer forming step, and after the adhesive layer forming step. A step of heat-treating the porous film at a temperature of about a glass transition temperature to a glass transition temperature + 100 ° C. of the polyvinyl acetal resin that forms the film may be included.

  According to the method for forming a porous film using water droplets, the partition located between adjacent pores is formed by a polymer solution that has entered a gap between adjacent water droplets.

  Therefore, especially in the vicinity of the constricted portion where the water droplet and the water droplet are closest, the partition wall tends to be thin. In some cases, there may be a communication hole in the constriction that communicates adjacent holes.

  However, when the heat treatment step is performed, the narrow constricted portion of the porous membrane partition is softened and melted quickly, and the communication hole that may exist in the constricted portion is crushed. Therefore, the independence between adjacent holes can be increased. In addition, the strength of the partition can be improved. Then, if the conductive particles are filled in the pores of the porous film in which the independence between the pores is improved, the insulation reliability in the film surface direction of the obtained anisotropic conductive film can be improved.

  At this time, the time for heating the porous film can be appropriately adjusted in consideration of the above temperature range and the like. If the heating time is too long, the porous film may be deformed. On the other hand, when the heating time is too short, the tendency to improve the independence of the hole is insufficient. Therefore, when heating a porous membrane, it is good to pay attention to these.

  The method for heating the porous membrane may be either a contact type or non-contact type heating method, and is not particularly limited.

  Specifically, as the heating method, for example, a method of bringing the heating source adjusted to the above temperature and the porous membrane into contact with each other for a certain period of time directly or via a member capable of conducting heat, etc. A method of bringing the heating source and the porous film close to each other can be exemplified.

  More specifically, for example, a method of placing the porous film on a heating source such as a hot plate adjusted to a predetermined temperature via a glass substrate for a predetermined time can be exemplified.

  Here, the heat treatment step may be a heat / pressure treatment step accompanied by pressurization of the porous film in the film thickness direction.

  In the method for forming a porous film using water droplets, water droplets condensed on the surface of the polymer solution are concentrated in a floating island shape. When the water droplet groups densely packed in a floating island shape are transported and accumulated, a step or unevenness in the film thickness direction tends to occur near the boundary where the water droplet groups collide with each other.

  However, when the porous film is heated and pressurized after the film formation, the steps or irregularities generated on the surface of the porous film are made uniform. Thereafter, in the particle filling step, the holes are easily filled with conductive particles. Further, the communication hole in the film surface direction that may exist in the constricted portion is also easily crushed by pressurization. Therefore, it becomes easy to achieve independence between the adjacent holes described above.

  As a method for pressurizing the porous membrane, specifically, for example, the porous membrane is sandwiched by a plate-like member having a flat surface, and while maintaining this state, the intervening member is directly or by a known pressurizing device. For example, a method of indirectly pressurizing the pressure can be exemplified.

  Further, the pressure for pressurizing the porous film may be variously adjusted in consideration of the hardness of the resin forming the film, the thickness of the constricted portion, the heating time of the film, and the like. That is, any pressure may be used as long as the level difference generated in the film formation process can be made flat. When the porous membrane is excessively pressurized, the three-dimensional structure of the membrane may be broken. On the other hand, if the pressure applied to the porous film is too small, it is difficult to flatten the step. Therefore, when pressurizing the porous membrane, these should be noted.

  Further, when pressurizing the porous membrane, this pressurization may be performed almost simultaneously with the heating of the porous membrane, or even if the pressurized porous membrane is heated, the heated porous membrane is pressurized. Also good. That is, pressurization may be performed at any timing as long as at least desired heat and pressure are applied to the porous membrane.

3. Method of using the present ACF The present ACF can be used, for example, as follows.

  As shown in FIG. 2, for example, the ACF 10 is placed between the IC chip 22 and the circuit pattern 26 formed on the substrate 24, and thermocompression bonding is performed at a temperature at which the adhesive layer 16 flows as shown in FIG. . As a result, the adhesive layer 16 between the bumps 28 of the IC chip 22 and the circuit pattern 26 is fluidly eliminated. Further, the conductive particles 14 are sandwiched between the bumps 28 and the circuit pattern 26. Then, the IC chip 22 and the circuit pattern 26 are bonded to each other while the conductive particles 14 are sandwiched between the adhesive property of the porous film 12 and the adhesive layer 16. Thereby, the IC chip 22 and the circuit pattern 26 are electrically and mechanically connected.

  Here, in the present ACF, the adhesive layer forming surface side is preferably used as the pressure side, and the film surface opposite to the adhesive layer forming surface is preferably used as the non-pressurizing side.

  For example, when connecting an IC chip and a circuit pattern, as described above, the IC chip side is usually the pressure side and the circuit pattern side is often the non-pressure side.

  The circuit pattern side has less space for the adhesive layer to flow than the IC chip side having bumps. For this reason, the absence of an adhesive layer on this side makes it easier to prevent the porous film from collapsing and the outflow of the conductive particles, and to facilitate the connection while maintaining the original arrangement of the conductive particles.

  Further, if an object to be connected having a relatively high conductor such as an IC chip having bumps is brought into contact with the adhesive layer side, the gap between the conductors can be easily filled with the adhesive layer. Therefore, it becomes easy to improve mechanical connectivity.

  Hereinafter, the present invention will be described in detail using examples.

1. Selection of porous membrane material First, the following simple evaluation was performed in order to select a porous membrane material.

(Film formability evaluation)
Several types of polyvinyl butyral resins having different residual hydroxyl amounts and polybutadiene rubber were prepared, and using these, a porous film was formed using water droplets, and the film formability was evaluated.

Here, the polyvinyl butyral resin and polybutadiene rubber used are as follows.
-Polyvinyl butyral resin having a residual hydroxyl content of 20 mol% (Sekisui Chemical Co., Ltd., "S-Rec BL5")
-Polyvinyl butyral resin having a residual hydroxyl content of 22 mol% (Sekisui Chemical Co., Ltd., "S-Rec BL-S")
-Polyvinyl butyral resin having a residual hydroxyl content of 25 mol% (Sekisui Chemical Co., Ltd., "S-REC KS-3Z")
-Polyvinyl butyral resin having a residual hydroxyl content of 28 mol% (Sekisui Chemical Co., Ltd., "S-Rec BL-10")
-Polyvinyl butyral resin having a residual hydroxyl group content of 30 mol% (Sekisui Chemical Co., Ltd., "S-REC BH-6")
-Polyvinyl butyral resin having a residual hydroxyl group content of 33 mol% (Sekisui Chemical Co., Ltd., "ESREC BX-3")
-Polyvinyl butyral resin having a residual hydroxyl content of 36 mol% (Sekisui Chemical Co., Ltd., "S-Rec BL-2")
・ Polybutadiene rubber (manufactured by JSR Corporation, “RB820”)

  In addition, the amount of residual hydroxyl groups of each polyvinyl butyral resin is a value calculated based on the above measurement method.

  Moreover, the porous membrane was produced in the following procedures. That is, a copolymer of dodecylacrylamide and caproic acid as a surfactant is added to a solution obtained by dissolving the predetermined polyvinyl butyral resin in chloroform to a concentration of 0.26 wt% with respect to the polyvinyl butyral resin. 0.026 wt% was added to prepare a polymer solution.

  Next, 7 ml of the polymer solution was cast on a petri dish having a diameter of 90 mm (outer diameter) in an atmosphere at a temperature of 22 ° C. and a relative humidity of 57%. Thereafter, air having the same temperature and humidity as described above (flow rate 2 L / min) was continuously blown onto the liquid surface from an angle of 20 ° using an air pump.

  After 30 minutes, the formed film was observed with a microscope (450 times magnification). Then, the area ratio (%) of the part having good regularity of the hole and the hole diameter with respect to the total area of the bottom of the petri dish (hereinafter, sometimes referred to as “the area ratio of the good film forming part”) was obtained.

(Adhesion evaluation)
Next, by bonding each porous film obtained in the above film formability evaluation and the adhesive layer prepared in substantially the same manner as described later, without filling the pores with conductive particles, Each simulated membrane was prepared.

  Next, each simulated film is interposed between a glass substrate on which a circuit pattern made of ITO is formed and an IC chip having gold bumps, and these are bonded under the conditions of a temperature of 210 ° C., a pressing force of 80 MPa, and a pressing time of 60 seconds. Each sample was made. At this time, an IC chip was disposed on the adhesive layer forming surface side of each simulated film.

  Next, the initial state of each sample and the state of peeling after heating at 80 ° C. for 24 hours were confirmed with a microscope (450 magnifications).

  Then, arbitrary five points were photographed, and the area where white haze in the photographed surface increased compared to the initial and after processing was measured, and the ratio of the area of the white haze to the photographing area was calculated. . Based on this, the area ratio (%) of the portion without white haze seen at the time of peeling with respect to the total area of the IC chip (hereinafter, sometimes referred to as “the area ratio of the non-peeled portion”) was obtained.

  FIG. 4 shows the relationship between the amount of residual hydroxyl groups (mol%) of the used polyvinyl butyral resin, the area ratio (%) of the non-peeled part (adhesiveness), and the area ratio of the good film forming part (film forming property). Indicates.

  According to FIG. 4, there is a trade-off relationship between adhesiveness and film formability, but when the amount of residual hydroxyl group is in the range of more than 22 mol% to less than 30 mol%, there is a relationship between adhesiveness and film formability. It was confirmed that the balance between the two was excellent.

  In addition, from this result, it can be said that the amount of residual hydroxyl groups is closely related to the adhesiveness and film formability, and also for polyvinyl acetal resins such as polyvinyl formal resins, which are the same series of resins as polyvinyl butyral resins. It is presumed that they have similar properties.

2. Production of Anisotropic Conductive Film According to Examples and Comparative Examples An anisotropic conductive film was actually produced based on the knowledge obtained by the simple evaluation in “1. Selection of porous film material”.

(Example 1)
First, a polyvinyl butyral resin (Sekisui Chemical Co., Ltd., “ESREC KS-3Z”) having a residual hydroxyl group content of 25 mol% was dissolved in chloroform to a concentration of 0.26 wt%. As an activator, a copolymer of dodecylacrylamide and caproic acid was added in an amount of 0.026 wt% to the polyvinyl butyral resin to prepare a polymer solution.

  Next, the polymer solution was cast on a glass substrate with an applied film thickness of 1100 μm in an atmosphere at a temperature of 22 ° C. and a relative humidity of 57%. Thereafter, using an air pump, air having the same temperature and humidity as described above (flow rate 2 L / min) was continuously blown onto the coating liquid surface for 30 minutes from an angle of 20 °.

  As a result, a group of water droplets due to condensation adheres to the polymer solution surface along with the volatilization of chloroform, and after this close-packed, the water droplet group evaporates, resulting in a large number of holes arranged in a honeycomb shape (non-through holes). A porous film (film thickness 5 μm) made of polyvinyl butyral resin in which the inner wall surface of the hole is curved outward is obtained.

  In addition, about the obtained porous membrane, the distance between the opening diameter of a hole part, the depth of a hole part, and the opening center of an adjacent hole part is measured with a laser microscope (ultra-depth color 3D shape measurement microscope, Keyence Corporation "VK. -9500 "). As a result, they were 5 μm, 4 μm, and 6 μm, respectively.

  Next, resin plating particles having an average particle diameter of 4 μm (Sekisui Chemical Co., Ltd., “Micropearl AU-204”) are obtained by sequentially coating the surface of particles made of divinylbenzene-based crosslinked resin with a Ni plating layer and an Au plating layer. ") Was spread on the pore-forming surface of the porous membrane.

  Next, with a permanent magnet installed on the side opposite to the hole forming surface (manufactured by Seiko Sangyo Co., Ltd., ferrite magnet, 1000 gauss), the surface is scraped off with a brush while attracting resin plating particles to the porous film, Resin plating particles were introduced into the holes.

  Resin plating particles adhering to the porous membrane surface where no hole is formed, or resin plating particles adhering to the resin plating particle introduced into the hole due to electrostatic force, etc. It is removed by using a slightly adhesive tape (manufactured by Kimoto Co., Ltd., “Bieful EP50”).

  Thereby, a porous film in which resin plating particles were filled in the pores was prepared. The resin plating particles were substantially filled one by one for each hole. The resin-plated particles are slightly protruded from the particle introduction surface of the porous membrane, and the membrane is not exposed on the back surface (surface opposite to the particle introduction surface) of the membrane. Had been filled.

  Next, 90 parts by weight of a dicyclopentadiene type epoxy resin (Dainippon Ink Co., Ltd., “Epiclon HP7200HH”) and 10 parts by weight of nitrile rubber (NBR) (manufactured by Nippon Zeon Co., Ltd., “Nipol 1072J”) 187 parts by weight of a curing agent (manufactured by Asahi Kasei Chemicals Corporation, “Novacure HXA3932HP”) was diluted with toluene so that the solid content was 42% to prepare an adhesive solution.

  Next, the above adhesive solution was applied to the release surface of a continuously supplied base substrate (polyethylene terephthalate, thickness 38 μm, “PET38C” manufactured by Lintec Corporation) using a comma coater.

  Subsequently, this coating layer was dried at 110 ° C. for 90 seconds to form an adhesive layer (thickness 20 μm). Then, the release surface of the separator (polyethylene terephthalate, thickness 38 μm, manufactured by Lintec Corporation, “PET38B”) was put on the surface of the adhesive layer and wound up.

  Thus, an adhesive layer sandwiched between the base substrate and the separator was prepared.

  Next, the surface of the adhesive layer exposed by peeling the separator was overlapped with the surface of the porous film filled with resin plating particles (particle introduction surface side), and these were bonded together.

  As described above, an adhesive layer was formed on one side of the film filled with the resin plating particles.

  As described above, a porous material made of polyvinyl acetal resin (residual hydroxyl group content ratio 25 mol%) having a large number of pores arranged in a honeycomb shape and the inner wall surface of the pores being curved outward. An anisotropic conductive film according to Example 1 having a film, resin plating particles held in the pores of the porous film, and an adhesive layer formed on one surface of the porous film was produced. The porous film itself has adhesiveness.

(Example 2)
In the preparation of the anisotropic conductive film according to Example 1, a polyvinyl butyral resin having a residual hydroxyl amount of 28 mol% (instead of the polyvinyl butyral resin having a residual hydroxyl content of 25 mol%) at the time of preparing the polymer solution ( The anisotropic conductive film according to Example 2 was manufactured in the same manner except that a porous film (film thickness 5 μm) having a honeycomb structure was formed using “S-LEC BL-10” manufactured by Sekisui Chemical Co., Ltd. Produced.

  In addition, the opening diameter of the hole part of the obtained porous membrane, the depth of a hole part, and the distance between the opening centers of an adjacent hole part were 5 micrometers, 4 micrometers, and 6 micrometers, respectively.

(Comparative Example 1)
A copolymer of dodecylacrylamide and caproic acid as a surfactant in a solution obtained by dissolving polybutadiene rubber (manufactured by JSR, “RB820”) at a concentration of 0.1 wt% in chloroform is 0.01 wt% with respect to the polybutadiene rubber. This was added to prepare a polymer solution.

  Next, this polymer solution was cast at a coating film thickness of 1800 μm on a glass substrate onto which air having a relative humidity of 50% was continuously blown to volatilize chloroform.

  As a result, a porous film (film thickness: 5 μm) made of polybutadiene rubber having a large number of holes (non-through holes) arranged in a honeycomb shape was obtained. At this time, the opening diameter of the hole portion, the depth of the hole portion, and the distance between the opening centers of the adjacent hole portions were 5 μm, 4 μm, and 6 μm, respectively.

  And in preparation of the anisotropic conductive film which concerns on Example 1, it replaced with the porous film made from a polyvinyl butyral resin, the point which used the said porous film made from polybutadiene rubber, resin plating particle | grains at the time of adhesive layer formation In the same manner as in Comparative Example 1 except that adhesive layers (20 μm on the particle introduction surface side and 2 μm on the opposite surface side) were formed on both surfaces of the porous film filled with An anisotropic conductive film was produced.

  The anisotropic conductive film according to Comparative Example 1 has a conventional three-layer structure in which resin plating particles are filled in the pores of a porous film made of polybutadiene rubber, and an adhesive layer is coated on both surfaces of the film. It is.

(Comparative Example 2)
In the production of the anisotropic conductive film according to Comparative Example 1, the anisotropic conductive film according to Comparative Example 2 was produced in the same manner except that the side opposite to the introduction surface of the resin plating particles was not covered with the adhesive layer. did.

  At this time, the opening diameter of the hole portion, the depth of the hole portion, and the distance between the opening centers of the adjacent hole portions were 5 μm, 4 μm, and 6 μm, respectively.

  The anisotropic conductive film according to Comparative Example 2 has a two-layer structure in which resin plating particles are filled in the pores of a polybutadiene rubber porous film, and an adhesive layer is covered on one side of the film. .

3. Evaluation of Each Anisotropic Conductive Film With respect to the anisotropic conductive films according to Examples and Comparative Examples prepared above, the conducting performance in the film thickness direction and the insulating performance in the film surface direction were evaluated.

(Preparation of evaluation sample)
That is, first, an anisotropic conductive film is placed on a circuit pattern (material ITO, pattern pitch 30 μm, pattern width 20 μm) formed on the surface of a 0.7 mm thick glass substrate, and the temperature is 120 ° C. on the circuit pattern. Temporary pressure bonding was performed on the bonded anisotropic conductive film under the conditions of a pressure of 0.25 MPa and a pressure bonding time of 5 seconds.

  Next, after separating the temporarily-bonded anisotropic conductive film separator, an IC chip (bump pitch 30 μm, bump width 20 μm) having an Au bump is placed on the separator so that the circuit pattern and the Au bump face each other. Placed on.

  Next, in this state, the main pressure bonding was performed under the conditions of a temperature of 210 ° C., a pressure of 80 MPa, and a pressure bonding time of 60 seconds. After the main pressure bonding, cooling was subsequently performed under the conditions of a temperature of 50 ° C., a pressure of 80 MPa, and a time of 30 seconds.

  Thus, Sample 1 to Sample 2 and Comparative Sample 1 to Comparative Sample 2 were prepared. Note that the numbers of the sample and the comparative sample correspond to the numbers of the example and the comparative example.

(Evaluation of conduction performance in the film thickness direction)
With respect to each of the obtained samples, the electric resistance between the circuit pattern and the Au bump that face each other was measured by a four-terminal four-probe method using a resistivity meter (“Loresta GP” manufactured by Dia Instruments). The number of each sample was N = 10 [pieces], and an average value was calculated by arithmetic average, and this was taken as the electric resistance in the film thickness direction.

(Evaluation of insulation performance in the film surface direction)
About each obtained sample, the electrical resistance between adjacent circuit patterns was measured using tester T2 (the product made by AND, "AD5522"). Note that the number of each sample was N = 10 [pieces], and the ratio of the electrical resistance to 10 ⁸ Ω or more = insulation securing ratio (%) was determined.

(Evaluation results)
Table 1 summarizes the evaluation results of the anisotropic conductive films according to Examples and Comparative Examples.

(Discussion)
A relative comparison of Table 1 shows the following.

  That is, the anisotropic conductive film according to Comparative Example 1 has a conventional three-layer structure. For this reason, the electrical resistance in the film thickness direction is larger than the others.

  This is because the flow of the adhesive layer on the circuit pattern side causes the porous film to collapse and the resin plating particles to flow out of the holes, disturbing the initial regular arrangement and trapping between the circuit pattern and the bumps. This is presumably because the resin plating particles that should have been reduced.

  Further, the anisotropic conductive film according to Comparative Example 2 uses a porous film made of polybutadiene rubber, which is a hydrophobic material, as in Comparative Example 1, but has one adhesive layer. Therefore, the surface of the porous film on the side opposite to the adhesive layer forming surface has no adhesiveness. Therefore, in a state where the resin plating particles are compressed and sandwiched between the circuit pattern and the bumps, the two cannot be mechanically connected, and the electric resistance in the film thickness direction is extremely large, indicating insulation.

  Here, in Example 1 and Example 2, in forming a porous film using water droplets, a conventional hydrophobic polymer was used using a polyvinyl butyral resin that is a hydrophilic material. It can be said that it is remarkable that a porous film having a honeycomb structure can be formed in substantially the same manner as in the case. As a result, in the present invention, it is possible to utilize a regular arrangement of pores of the porous membrane having the honeycomb structure.

  And the anisotropic conductive film which concerns on Example 1 and Example 2 can also improve conduction | electrical_connection performance compared with the anisotropic conductive film which concerns on the comparative example 1 of the conventional 3 layer structure. I understand.

  The reason for this is that by adopting a two-layer structure, it is possible to prevent the porous film from collapsing due to the flow of the adhesive layer at the time of crimping, and to suppress the outflow of resin plating particles accompanying this. Many resin-plated particles due to the fact that the particles could be captured between the circuit pattern and the bump while maintaining the original regular arrangement, and the adhesion and adhesive layer of the porous film itself. For example, the circuit pattern and the IC chip can be mechanically connected in a state where the pin is sandwiched.

  Therefore, from these results, according to the anisotropic conductive film and the method for manufacturing the same according to the present invention, it is possible to improve the conduction performance while using the porous film formed using water droplets. It was confirmed that there was.

  Although one embodiment and one example of the present invention have been described above, the present invention is not limited to the above embodiment and example, and various modifications can be made without departing from the spirit of the present invention. is there.

It is an example of the typical sectional view of the anisotropic conductive film concerning this embodiment. It is the figure which showed typically the state which interposed the anisotropic conductive film which concerns on this embodiment between IC chip and a circuit pattern. It is the figure which showed typically the state from which the IC chip and the circuit pattern were connected by the anisotropic conductive film which concerns on this embodiment. It is the figure which showed the relationship between the amount of residual hydroxyl groups (mol%) of a polyvinyl butyral resin, the area ratio (%) (adhesiveness) of the said non-peeling part, and the area ratio (film forming property) of a film-forming favorable part. .

Explanation of symbols

10 ACF
12 Porous film 14 Conductive particles 16 Adhesive layer 22 IC chip 24 Substrate 26 Circuit pattern 28 Bump

Claims (6)

A porous membrane having a large number of pores arranged in a honeycomb shape, and an inner wall surface of the pores being curved outward;
Conductive particles held in the pores of the porous membrane;
An adhesive layer formed on one side of the porous membrane,
The anisotropic conductive film, wherein the porous film is formed of a polyvinyl acetal resin having a residual hydroxyl group content in the range of more than 22 mol% to less than 30 mol%.   The anisotropic conductive film according to claim 1, wherein the conductive particles are fused to the porous film.   The anisotropic conductive film according to claim 1, wherein the conductive particles exist in substantially the same plane.   The porous membrane comprises a polymer solution containing at least a hydrophobic and volatile organic solvent, a polyvinyl acetal resin having a residual hydroxyl amount in the range of more than 22 mol% to less than 30 mol%, and a surfactant. 4. The anisotropic conductive film according to claim 1, wherein the anisotropic conductive film is formed by allowing a cast support to exist in an atmosphere having a relative humidity of 50% or more. A polyvinyl acetal resin having a large number of holes arranged in a honeycomb shape, the inner wall surface of which is curved outward, and the amount of residual hydroxyl group is in the range of more than 22 mol% to less than 30 mol% Forming a porous film comprising:
Filling the pores of the porous membrane with conductive particles;
Forming an adhesive layer on one side of the film filled with the conductive particles;
A method for producing an anisotropic conductive film, comprising:   The porous film is formed by a polymer containing at least a hydrophobic and volatile organic solvent, a polyvinyl acetal resin having a residual hydroxyl amount in the range of more than 22 mol% to less than 30 mol%, and a surfactant. 6. The method for producing an anisotropic conductive film according to claim 5, wherein the support on which the solution is cast is present in an atmosphere having a relative humidity of 50% or more.

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