HK1240409B - Anisotropic conductive film - Google Patents

Description

Anisotropic conductive film

Technical Field

The present invention relates to an anisotropic conductive film.

Background Art

Anisotropic conductive films (ACFs) are widely used when mounting electrical components such as IC chips on wiring boards. These films contain conductive particles dispersed in an insulating resin binder. However, it is known that the conductive particles in such ACFs exist in a connected or aggregated state. Consequently, when ACFs are used to connect terminals of IC chips and wiring boards, which are becoming increasingly thinner and smaller as electronic devices become lighter, the connected or aggregated conductive particles in the ACFs can cause short circuits between adjacent terminals.

In the past, anisotropic conductive films have been proposed to cope with such fine pitches, in which conductive particles are regularly arranged in the film. For example, an anisotropic conductive film has been proposed, in which an adhesive layer is formed on a stretchable film, conductive particles are densely packed in a single layer on the surface of the adhesive layer, and the film is then biaxially stretched until the distance between the conductive particles reaches a desired distance, thereby regularly arranging the conductive particles. An insulating adhesive base layer, a component of the anisotropic conductive film, is then pressed against the conductive particles to transfer the conductive particles to the insulating adhesive base layer, thereby obtaining an anisotropic conductive film (Patent Document 1). In addition, an anisotropic conductive film has been proposed, which comprises spreading conductive particles on a concave-forming surface of a transfer mold having concave portions, scraping the concave-forming surface to hold the conductive particles in the concave portions, pressing an adhesive film having an adhesive layer for transfer thereto to transfer the conductive particles to the adhesive layer, and then pressing an insulating adhesive base layer, a component of the anisotropic conductive film, against the conductive particles attached to the adhesive layer to transfer the conductive particles to the insulating adhesive base layer (Patent Document 2). These anisotropic conductive films typically have an insulating adhesive cover layer laminated on the surface of the conductive particles so as to cover the conductive particles.

Prior art literature

Patent Literature

Patent Document 1: WO2005/054388

Patent Document 2: Japanese Patent Application Laid-Open No. 2010-33793

Summary of the Invention

Problems to be solved by the invention

However, conductive particles are easily condensed and transformed into secondary particles due to static electricity, so it is difficult to make conductive particles exist alone as primary particles. Therefore, the technology of patent document 1 and patent document 2 produces the following problems. That is, in the case of patent document 1, it is difficult to densely fill the conductive particles with a single layer without defects on the entire surface of the stretchable film, and there is the following problem: the conductive particles are filled into the stretchable film in a condensed state, which causes a short circuit, or an unfilled area (i.e., "missing") is generated, which causes poor conduction. In addition, in the case of patent document 2, there is the following problem: if the concave portion of the transfer mold is covered with conductive particles with large particle size, it is removed by scraping and sweeping afterwards, resulting in a concave portion that does not retain conductive particles, and the "missing" of conductive particles is generated in the anisotropic conductive film, which causes poor conduction, or conversely, if the concave portion is configured with small conductive particles, then when transferred to the insulating adhesive base layer, the position of the conductive particles to be configured does not overlap with the center of the conductive particles actually configured and a position deviation occurs, resulting in a regular arrangement being destroyed, which causes a short circuit and poor conduction.

As such, in Patent Documents 1 and 2, the current situation is that how to control the “missing” and “displacement” of the conductive particles that are to be arranged in a regular pattern in the anisotropic conductive film has not been fully considered.

The present invention aims to solve the above problems of the prior art and to provide an anisotropic conductive film that significantly suppresses the occurrence of short circuits and poor conduction from the viewpoint of "missing" and "displacement" of conductive particles that are to be arranged in a regular pattern.

Methods for solving problems

The present inventors have discovered that the above-mentioned objectives can be achieved by controlling the proportion of grid points without conductive particles and the deviation of the arrangement of the conductive particles relative to the grid points when arranging conductive particles at the grid points of a planar lattice, relative to all grid points of a hypothetical planar lattice pattern in any reference region of the anisotropic conductive film. The present inventors have thus completed the present invention. Furthermore, the present inventors have discovered that such an anisotropic conductive film can be produced by attaching the conductive particles to the tips of columnar protrusions formed on the surface of a transfer member and transferring the conductive particles, rather than arranging the conductive particles in the concave portions of the transfer member. The present inventors have thus completed the present invention's production method.

That is, the present invention provides an anisotropic conductive film having a structure in which an insulating adhesive base layer and an insulating adhesive cover layer are laminated, and conductive particles are arranged at lattice points of a planar lattice pattern near the interface.

The ratio of the lattice points where no conductive particles are arranged relative to all the lattice points of the plane lattice pattern assumed in any reference region of the anisotropic conductive film is 25% or less.

A portion of the conductive particles arranged at the lattice points of a planar lattice pattern are arranged offset relative to the corresponding lattice points in the length direction of the anisotropic conductive film, and the offset amount defined as the distance between the plane projection center of the offset conductive particles and the corresponding lattice points is less than 50% of the average particle size of the conductive particles.

Furthermore, the present invention provides a manufacturing method for the above-mentioned anisotropic conductive film, comprising the following steps (A) to (E):

<Process (A)>

a step of preparing a transfer member having columnar protrusions corresponding to grid points of a planar grid pattern formed on a surface of the transfer member;

<Process (B)>

a step of forming a slightly adhesive layer on at least the top surface of the convex portion of the transfer body;

<Process (C)>

a step of attaching conductive particles to the slightly adhesive layer on the convex portion of the transfer body;

<Process (D)>

A step of overlapping and pressing an insulating adhesive base layer on the surface of the transfer body on which the conductive particles are attached, thereby transferring the conductive particles to the insulating adhesive base layer; and

<Step (E)>

A step of laminating an insulating adhesive cover layer on the insulating adhesive base layer to which the conductive particles have been transferred, from the side on which the conductive particles have been transferred.

Furthermore, the present invention provides a connection structure in which a terminal of a first electric component and a terminal of a second electric component are anisotropically conductively connected via the anisotropic conductive film of the present invention.

Effects of the Invention

In the anisotropic conductive film of the present invention, the ratio of "grid points without conductive particles" to the total grid points of a hypothetical planar grid pattern in any reference area is set to 25% or less. Furthermore, a portion of the conductive particles arranged at the grid points of the planar grid pattern are offset relative to the corresponding grid points in the longitudinal direction of the anisotropic conductive film. The "conductive particle offset," defined as the distance between the center of the offset conductive particles and the corresponding grid point, is set to less than 50% of the average particle size of the conductive particles. This longitudinal offset is a deviation along one direction of the longitudinal direction. Therefore, when the anisotropic conductive film of the present invention is used in anisotropic conductive connections, it is possible to achieve good initial on-resistance and good conduction reliability after aging, while also suppressing the occurrence of short circuits.

Furthermore, in the method for manufacturing an anisotropic conductive film of the present invention, a transfer member having columnar protrusions formed on its surface corresponding to the lattice points of a planar lattice pattern is used. After conductive particles are attached to a slightly adhesive layer formed on the top surface of the protrusions, the conductive particles are transferred to an insulating adhesive base layer. Consequently, the ratio of "grid points without conductive particles" relative to the total number of grid points of a hypothetical planar lattice pattern in any reference region of the anisotropic conductive film can be kept at 25% or less. Furthermore, when a portion of the conductive particles arranged at the grid points of the planar lattice pattern are offset in the longitudinal direction of the anisotropic conductive film relative to the corresponding grid points, the "conductive particle offset," defined as the distance between the center of the offset conductive particle and the corresponding grid point, is less than 50% of the average particle size of the conductive particles. Consequently, the anisotropic conductive film obtained by the manufacturing method of the present invention enables anisotropic conductive connection between fine-pitch IC chips and wiring substrates, significantly suppressing the occurrence of short circuits and poor conduction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a cross-sectional view of an anisotropic conductive film according to the present invention.

FIG2 is a perspective plan view of an anisotropic conductive film according to the present invention.

FIG. 3A is a process diagram illustrating the manufacturing method of the present invention.

FIG3B is a process diagram illustrating the manufacturing method of the present invention.

FIG3C is a process diagram illustrating the manufacturing method of the present invention.

FIG3D is a process diagram illustrating the manufacturing method of the present invention.

FIG. 3E is a process diagram illustrating the manufacturing method of the present invention.

3F is a process explanatory diagram of the manufacturing method of the present invention and is also a schematic cross-sectional view of the anisotropic conductive film of the present invention.

DETAILED DESCRIPTION

Hereinafter, the anisotropic conductive film of the present invention will be described in detail with reference to the accompanying drawings.

<Anisotropic Conductive Film>

As shown in Figures 1 (cross-sectional view) and 2 (planar perspective view), the anisotropic conductive film 10 of the present invention has a structure in which an insulating adhesive base layer 11 and an insulating adhesive cover layer 12 are stacked, and near their interface, conductive particles 13 are arranged at the grid points of a planar lattice pattern (dashed line in Figure 2). In Figures 1 and 2, the planar lattice pattern is assumed to be along the length direction of the anisotropic conductive film 10 and the direction perpendicular thereto (width direction), but it can also be assumed that the entire structure is tilted relative to the length direction and width direction. Here, arrow A shows the position where the conductive particles are not arranged at the grid points of the planar lattice, that is, the position where the conductive particles are "missing". Arrow B shows the conductive particles arranged offset relative to the corresponding grid points in the length direction of the anisotropic conductive film. Here, considering the regular arrangement, the deviation, defined as the distance between the center of the offset conductive particles (specifically, the center of gravity of the image of the conductive particles projected onto the plane) and the corresponding grid points, is less than 50% of the average particle size of the conductive particles. It should be noted that this deviation is caused by the manufacturing method and occurs only with respect to the length direction of the film. The conductive particles deviate within a specified range in this way, resulting in an effect that the conductive particles are easily captured by the bump during anisotropic conductive connection. With respect to the width direction of the bump (a direction perpendicular to the length direction of the film), even if the conductive particles are located at the end of the bump, due to the moderate deviation, compared to the case where the conductive particles are arranged along a lattice line, that is, in a direction roughly parallel to the length direction of the film, if they are arranged in a manner where the outer lines of the conductive particles are not consistent, any particle becomes easily captured, and the effect of stabilizing the number of captured particles can be expected. This effect is particularly effective in the case of fine pitch.

It is to be noted that the maximum value of the deviation amount of the conductive particles arranged so as to be deviated from the lattice points in the longitudinal direction of the anisotropic conductive film is preferably larger than the deviation amount in the direction perpendicular to the longitudinal direction.

In addition, from the viewpoint of connection stability, the proportion of lattice points at which the conductive particles are arranged deviatingly in the length direction of the anisotropic conductive film is preferably 90% or more relative to all lattice points at which the conductive particles are arranged. In other words, the number of conductive particles that are close to each other at a distance less than 50% of the particle size is less than 10% of the number of conductive particles. For example, in the case of FIG2 , the deviation becomes the direction (right side) leaning towards one side of the length direction. Since more than 90% lean towards one side, the arrangement distance of more than 1 times the particle size can be maintained as a whole. Therefore, the conductive particles that are close are less than 10% of the total number. As a result, almost all the conductive particles deviate within a specified range in one direction, so the lattice shape is maintained, and aggregation, which is the cause of the short circuit, does not occur. In this way, there is a tendency for the regularity along the length direction of the film to be higher than the regularity along the direction orthogonal to the length direction of the film. This means that, for example, in the case of FIG2 , the conductive particles tend to gather in a straight line in the length direction of the film, and tend to fall off easily in the direction orthogonal to the length direction. Furthermore, in detail, the particles in the membrane plane direction deviate as a whole toward one side of the membrane's length direction, which means that the center points of the particles are observed to deviate mainly toward the membrane's length direction relative to the arrangement lattice points. In addition, they are observed to be winding in a direction orthogonal to the membrane's length direction.

("Missing" conductive particles)

In the anisotropic conductive film of the present invention, the ratio of "grid points without conductive particles" (A in FIG. 2 ) (the ratio of grid points with missing conductive particles) relative to all grid points in a hypothetical planar lattice pattern in any reference region of the anisotropic conductive film is set to 25% or less, preferably 10 to 25%. Consequently, when the anisotropic conductive film of the present invention is used in an anisotropic conductive connection, good initial on-resistance and good conduction reliability after aging can be achieved, while also suppressing the occurrence of short circuits.

It should be noted that from the perspective of initial on-resistance and on-reliability, the lattice points where the conductive particles are "missing" are preferably discontinuous in the planar direction of the anisotropic conductive film, but in practical applications, more than 9 lattice points where the conductive particles are "missing" can be discontinuous.

(Flat lattice pattern)

Examples of the planar lattice pattern include a rhombus lattice, a hexagonal lattice, a square lattice, a rectangular lattice, and a parallelogram lattice. Among them, a hexagonal lattice that allows for closest packing is preferred.

Here, as the reference area of the anisotropic conductive film, the entire surface of the anisotropic conductive film can be selected, but it is usually preferred to select a roughly square area in the center of the plane of the anisotropic conductive film composed of sides X and Y that satisfy the following relationship (A), preferably relationship (1), and relationships (2) and (3) as the reference area.

100D≤X+Y≤400D (A)

X+Y＝100D (1)

X≥5D (2)

Y≥5D (3)

It should be noted that when applied to FOG connections with a larger connection area, the amount of conductive particles in the film can be reduced. In such a case, as shown below, it is preferred to make the values of X and Y large, preferably set to 20D or more, and the value of "X+Y" is also a value from 100D to around 400D, and finally preferably set to 400D.

X+Y＝400D

X≥20D

Y≥20D

In formula (A) and (1) to (3), D is the average particle size of the conductive particles. The average particle size of the conductive particles can be measured using an imaging particle size distribution analyzer. Furthermore, side Y is a straight line within a range of less than ±45° relative to the longitudinal direction of the anisotropic conductive film (see FIG. 2 ), and side X is a straight line perpendicular to side Y.

By defining the reference region in this way, the shape of the reference region and the bumps that press the conductive particles can be made similar or approximate. As a result, the permissible range of deviation from the planar lattice pattern of the conductive particles can be widened, enabling economical and stable anisotropic conductive connection. In other words, by setting the minimum side of the reference region to be at least five times the conductive particle diameter, even if the conductive particles are misaligned, missing, or close together within this assumed range, they can be captured by any bump, and there is no excessive aggregation in the gaps between the bumps, thus ensuring reliable anisotropic conductive connection.

It should be noted that the reason for setting the minimum side to more than 5 times the conductive particle diameter is because, in general, in order to reliably capture at least one side of the bump of the anisotropic conductive connection, it is necessary to set the minimum side to be larger than the average particle diameter of the conductive particles, and from the perspective of preventing short circuits in the gaps between the bumps, it is necessary to set it to a size preferably more than 2 times the average particle diameter of the conductive particles. In other words, it is believed that when focusing on a circular conductive particle as a benchmark, if no unintended defects occur within a concentric circle having a diameter of a length (i.e., 5D) obtained by adding the average particle diameter D of the conductive particle to 4 times the length (4D) of the particle diameter, then it is considered that the above requirements can be met. In addition, the minimum distance between bumps when set to fine pitch can also be less than 4 times the conductive particle diameter as an example.

(Configuration of Conductive Particles)

The conductive particles are preferably arranged in a continuous manner in a direction perpendicular to the length direction of the film in a number of 6 or more, more preferably in a continuous manner in a number of 8 or more. This is because if a lack of conductive particles occurs relative to the length direction of the bump, there is concern that the anisotropic conductive connection may malfunction. In this case, preferably 3 of the 7 columns continuous along the length direction of the film meet the above conditions, and more preferably 5 of the 7 columns meet the above conditions. Thus, the number of conductive particles captured by the bump can be made to be more than a certain number, and a stable anisotropic conductive connection can be achieved.

Furthermore, regarding defects in the conductive particles, it is preferred that four or more consecutive defects in the longitudinal direction of the film and four or more consecutive defects in the direction perpendicular to the longitudinal direction of the film do not intersect. It is more preferred that four or more consecutive defects are separated by one or more conductive particles that serve as grid points and are not adjacent to each other. It is even more preferred that four or more consecutive defects are separated by two or more conductive particles that serve as grid points and are not adjacent to each other. Regarding the intersection of such defects, there is no problem even if up to three rows of defects in one longitudinal direction intersect simultaneously. This is because, as long as there are no more than three rows of defects, the conductive particles nearby will be trapped by the bumps.

In practical applications, defects in conductive particles along the film length are not a problem as long as they total no more than 12 in any consecutive 50 grid points. Defects can also be counted midway through a film as long as there are no defects in any adjacent rows with consecutive defects.

(Particle area occupancy)

Furthermore, with respect to the area of any reference region of the anisotropic conductive film, the particle area occupancy of all conductive particles present in the area is generally effective for cases where the bump size and the distance between bumps are large, such as FOG connections, for example. The upper limit of this case is preferably 35% or less, more preferably 32% or less. In addition, for cases where the bump size and the distance between bumps are small (such as COG connections), it is further preferably 10 to 35%, and particularly preferably 14 to 32%. If within this range, when the anisotropic conductive film of the present invention is applied to anisotropic conductive connections, better initial conductivity and conduction reliability after aging can be achieved, and the occurrence of short circuits can be further suppressed. Here, the particle area occupancy is the ratio of the area occupied by all conductive particles present in the reference region relative to the area S of any reference region. The area occupied by all conductive particles is represented by (R/2) ² ×π×n when the average particle size of the conductive particles is R and the number of conductive particles is n. Therefore, it can be expressed as particle area occupancy (%)=[{(R/2) ² ×π×n}/S]×100.

Incidentally, the calculated particle area occupancy when the average particle size of the conductive particles is 2 μm, the number density is 500 particles/mm ² (0.0005 particles/μm ² ), X=Y=200D, and X+Y=400D is 0.157%. The calculated particle area occupancy when the average particle size of the conductive particles is 3 μm, the number density is 500 particles/mm ² (0.0005 particles/μm ² ), X=Y=200D, and X+Y=400D is 0.35325%. The calculated particle area occupancy when the average particle size of the conductive particles is 3 μm, the number density is 2000 particles/mm ² (0.002 particles/μm ² ), X=Y=200D, and X+Y=400D is 1.413%. Furthermore, when the average particle size of the conductive particles is 30 μm, the number density is 500 particles/mm ² (0.0005 particles/μm ² ), X=Y=200D, and X+Y=400D, the calculated particle area occupancy is 35.325%.

(Conductive particles)

Conductive particles used in known anisotropic conductive films can be appropriately selected and used as the conductive particles. For example, metal particles such as nickel, copper, silver, gold, and palladium, and metal-coated resin particles obtained by coating the surface of resin particles such as polyamide and polybenzoguanamine with a metal such as nickel can be mentioned. In addition, from the perspective of operability during production, the average particle size of the conductive particles is preferably 1 to 30 μm, more preferably 1 to 10 μm, and particularly preferably 2 to 6 μm. The average particle size can be measured using an image-type particle size distribution analyzer as described above.

The amount of conductive particles present in the anisotropic conductive film depends on the lattice pitch of the planar lattice pattern and the average particle size of the conductive particles, and is generally 300 to 40,000 particles/mm ² .

(distance between adjacent grid points)

Furthermore, the distance between adjacent lattice points in a hypothetical planar lattice pattern in the anisotropic conductive film is preferably at least 0.5 times the average particle size of the conductive particles, more preferably at least 1 time, and even more preferably at least 1 time but no more than 20 times. Within this range, when the anisotropic conductive film of the present invention is used in an anisotropic conductive connection, better initial conductivity and post-aging conductivity reliability can be achieved, and the occurrence of short circuits can be further suppressed.

(Insulating adhesive base layer)

As the insulating adhesive base layer 11, a layer used as an insulating adhesive base layer in a known anisotropic conductive film can be appropriately selected and used. For example, a photo-radical polymerizable resin layer containing an acrylate compound and a photo-radical polymerization initiator, a thermal-radical polymerizable resin layer containing an acrylate compound and a thermal-radical polymerization initiator, a thermal-cationic polymerizable resin layer containing an epoxy compound and a thermal-cationic polymerization initiator, a thermal-anionic polymerizable resin layer containing an epoxy compound and a thermal-anionic polymerization initiator, or a cured resin layer thereof can be used. In addition, these resin layers can be appropriately selected to contain a silane coupling agent, a pigment, an antioxidant, a UV absorber, etc., as needed.

The insulating adhesive base layer 11 can be formed by forming a film of a coating composition containing the above-mentioned resin by a coating method and drying or further curing the film, or by forming a film by a known method.

The thickness of the insulating adhesive base layer 11 is preferably 1 to 30 μm, more preferably 2 to 15 μm.

(Insulating adhesive cover)

A layer used as an insulating adhesive cover layer in a known anisotropic conductive film can be appropriately selected and used as the insulating adhesive cover layer 12. Alternatively, a layer made of the same material as the insulating adhesive base layer 11 described above can be used.

The insulating adhesive cover layer 12 can be formed by forming a film of a coating composition containing the above-mentioned resin by a coating method and drying or further curing the film, or by forming a film by a known method.

The thickness of the insulating adhesive cover layer 12 is preferably 1 to 30 μm, more preferably 2 to 15 μm.

Furthermore, insulating fillers such as silica particles, alumina, and aluminum hydroxide may be added to the insulating adhesive base layer 11 and the insulating adhesive cover layer 12 as needed. The amount of insulating filler blended is preferably 3 to 40 parts by mass per 100 parts by mass of the resin constituting these layers. This prevents unwanted movement of the conductive particles 13 due to the molten resin, even if the insulating adhesive base layer 11 melts during anisotropic conductive connection.

(Lamination of Insulating Adhesive Base Layer and Insulating Adhesive Cover Layer)

It should be noted that the insulating adhesive base layer 11 and the insulating cover layer 12 can be laminated with the conductive particles 13 interposed therebetween using known methods. In this case, the conductive particles 13 are present near the interface between these layers. Here, "present near the interface" means that some of the conductive particles penetrate into one layer, while the remaining portion penetrates into the other layer.

<Manufacturing of Anisotropic Conductive Film>

Next, a method for producing an anisotropic conductive film of the present invention, comprising a laminated insulating adhesive base layer and an insulating adhesive cover layer, wherein conductive particles are arranged at the lattice points of a planar lattice pattern near their interface, is described. This method comprises the following steps (A) to (E). Each step is described in detail with reference to the accompanying drawings.

(Process (A))

First, as shown in Figure 3A, prepare a transfer body 100, which is formed with a columnar convex portion 101 equivalent to the lattice points of a plane lattice pattern on the surface. Here, columnar refers to cylindrical or prismatic (triangular prism, quadrangular prism, hexagonal prism, etc.). It is preferably cylindrical. The height of the convex portion 101 can be determined based on the terminal spacing, terminal width, gap width, average particle size of the conductive particles to be anisotropically conductively connected, and is preferably more than 2.5 times and less than 5 times the average particle size of the conductive particles used, more preferably more than 2.5 times and less than 3.5 times. In addition, the width of the convex portion 101 (width at half the height) is preferably more than 0.6 times and less than 1.3 times the average particle size of the conductive particles, more preferably more than 0.6 times and less than 1.1 times. As long as the height and width are within these ranges, the effect of avoiding falling off and missing continuous occurrence can be obtained.

Furthermore, the protrusions 101 have top surfaces that are substantially flat to the extent that the conductive particles can be stably attached.

＊Specific examples of transfer media

The transfer body prepared in step (A) can be produced using known methods, for example, by processing a metal plate into a master disc, applying a curable resin thereto, and curing the curable resin. Specifically, a flat metal plate is cut to form a transfer body master disc having recesses corresponding to the protrusions. A resin composition constituting the transfer body is applied to the surface of the master disc where the recesses are formed, and after curing the resin composition, the transfer body is pulled out from the master disc to obtain the transfer body.

(Process (B))

Next, as shown in FIG. 3B , a slightly adhesive layer 102 is formed on at least the top surface of the convex portions 101 of the transfer body 100 having a plurality of convex portions 101 formed in a planar lattice pattern on its surface.

＊Micro-adhesive layer of the transfer body

The slightly adhesive layer 102 exhibits adhesive strength, temporarily retaining the conductive particles until they are transferred to the insulating adhesive base layer that constitutes the anisotropic conductive film. The slightly adhesive layer 102 is formed on at least the top surface of the protrusion 101. Therefore, the entire protrusion 101 can be slightly adhesive. The thickness of the slightly adhesive layer 102 can be appropriately determined based on the material of the slightly adhesive layer 102, the particle size of the conductive particles, and other factors. Furthermore, the term "slightly adhesive" means that when the conductive particles are transferred to the insulating adhesive base layer, the adhesive strength is weaker than that of the insulating adhesive base layer.

The slightly adhesive layer 102 can be a known slightly adhesive layer used in anisotropic conductive films, for example, by applying a silicone adhesive composition and an adhesive layer made of the same material as the insulating adhesive base layer or the insulating adhesive cover layer to the top surface of the protrusion 101 and drying the adhesive layer.

(Process (C))

Next, as shown in FIG3C , conductive particles 103 are attached to the slightly adhesive layer 102 of the convex portions 101 of the transfer body 100. Specifically, conductive particles 103 are sprinkled from above the convex portions 101 of the transfer body 100, and air is used to blow away the conductive particles 103 not attached to the slightly adhesive layer 102. In this case, the following situation may occur: on some convex portions 101, the conductive particles adhere to the side surfaces thereof with a certain degree of frequency due to static electricity, etc., and cannot be removed by air blowing.

When using air blasting to disperse the conductive particles, the amount of conductive particle "missing" can be controlled by varying the number of air blasts. For example, increasing the number of air blasts increases the amount of conductive particle "missing." Increasing the amount of conductive particle "missing" reduces the amount of conductive particles used, thereby reducing the manufacturing cost of the anisotropic conductive film.

It should be noted that, starting from FIG3C , the direction of the surface is flipped so that the surface covered with conductive particles on one side is attached to the top surface of the protrusion. This is to avoid applying unnecessary stress to the conductive particles. In such a configuration, only the necessary conductive particles are attached to the top surface of the protrusion, thereby making it easy to recycle and reuse the conductive particles. Compared with the method of filling the conductive particles into the opening and taking them out, the economic efficiency is also excellent. It should be noted that, in the case of the method of filling the conductive particles into the opening and taking them out, there is a concern that unnecessary stress is easily applied to the conductive particles that are not filled.

(Process (D))

Next, as shown in FIG3D , the insulating adhesive base layer 104 that will constitute the anisotropic conductive film is placed over and pressed against the surface of the transfer body 100 on which the conductive particles 103 are attached, thereby transferring the conductive particles 103 to one side of the insulating adhesive base layer 104 ( FIG3E ). In this case, it is preferable to place the transfer body 100 over and press it against the insulating adhesive base layer 104 with its protrusions 101 facing downward. This is because blowing air downward makes it easier to remove conductive particles that are not attached to the top surface of the protrusions.

(Process (E))

3F, an insulating adhesive cover layer 105 is laminated from the conductive particle transfer surface side onto the insulating adhesive base layer 104 to which the conductive particles 103 are transferred.

<Connection structure>

The anisotropic conductive film of the present invention is arranged between the terminal (e.g., bump) of a first electrical component (e.g., IC chip) and the terminal (e.g., bump, pad) of a second electrical component (e.g., wiring board), and is formally cured by thermal compression bonding from the side of the first electrical component or the second electrical component to perform anisotropic conductive connection, thereby providing a connection structure such as a so-called COG (chip on glass) or FOG (film on glass) in which short circuits and poor conduction are suppressed.

Example

Hereinafter, the present invention will be described in detail.

Example 1

A 2 mm thick nickel plate was prepared, and cylindrical recesses (3 μm inner diameter, 10 μm depth) were formed in a square lattice pattern as a transfer master. The center-to-center distance between adjacent recesses was 8 μm, resulting in a recess density of 16,000/mm ² .

A thermosetting resin composition containing 60 parts by mass of a phenoxy resin (YP-50, Nippon Steel & Sumikin Chemical Co., Ltd.), 40 parts by mass of an epoxy resin (jER828, Mitsubishi Chemical Co., Ltd.) and 2 parts by mass of a cationic curing agent (SI-60L, Sanshin Chemical Industry Co., Ltd.) was applied to the obtained transfer body original disc in such a manner that the dry thickness became 30 mm, and the resultant was heated at 80°C for 5 minutes to prepare a transfer body.

The transfer body is peeled off from the original disk and wound around a stainless steel roller with a diameter of 20 cm in such a manner that the protrusions are on the outside. The roller is rotated while contacting an adhesive sheet, which is an adhesive sheet made by impregnating a non-woven fabric with a micro-adhesive composition containing 70 parts by mass of an epoxy resin (jER828, Mitsubishi Chemical Corporation) and 30 parts by mass of a phenoxy resin (YP-50, Nippon Steel & Sumikin Chemical Corporation). The micro-adhesive composition is attached to the top surface of the protrusion to form a micro-adhesive layer with a thickness of 1 μm to obtain a transfer body.

Conductive particles (nickel-plated resin particles (AUL704, Sekisui Chemical Co., Ltd.)) having an average particle size of 4 μm were sprinkled on the surface of the transfer member, and then the conductive particles not adhering to the slightly adhesive layer were removed by air blowing.

The transfer body to which the conductive particles were attached was pressed from its conductive particle attachment surface onto a 5 μm thick sheet-shaped thermosetting insulating adhesive film (a film formed from an insulating adhesive composition containing 60 parts by mass of a phenoxy resin (YP-50, Nippon Steel & Sumikin Chemical Co., Ltd.), 40 parts by mass of an epoxy resin (jER828, Mitsubishi Chemical Co., Ltd.), 2 parts by mass of a cationic curing agent (SI-60L, Sanshin Chemical Co., Ltd.), and 20 parts by mass of silica particles (Aerosil RY200, Japan Aerosil Co., Ltd.)) serving as an insulating adhesive base layer at a temperature of 50°C and a pressure of 0.5 MPa, thereby transferring the conductive particles to the insulating adhesive base layer.

On the conductive particle-attached surface of the resulting insulating adhesive base layer, another 15 μm-thick insulating adhesive film (a film formed from a thermosetting resin composition containing 60 parts by mass of a phenoxy resin (YP-50, Nippon Steel & Sumikin Chemical Co., Ltd.), 40 parts by mass of an epoxy resin (jER828, Mitsubishi Chemical Corporation), and 2 parts by mass of a cationic curing agent (SI-60L, Sanshin Chemical Industry Co., Ltd.)) was stacked at a temperature of 60°C and a pressure of 2 MPa. This produced an anisotropic conductive film.

Example 2

An anisotropic conductive film was obtained by repeating Example 1 except that the number of air blowing for removing the conductive particles not attached to the slightly adhesive layer was set to three times that of Example 1.

Example 3

An anisotropic conductive film was obtained by repeating Example 1 except that the inner diameter of the concave portion of the transfer base was 2 μm, the depth of the concave portion was 9 μm, the center-to-center distance between adjacent concave portions was 6 μm, the density of the concave portions was 28,000/mm ² , and conductive particles having an average particle size of 3 μm (AUL703, Sekisui Chemical Co., Ltd.) were used instead of conductive particles having an average particle size of 4 μm.

Example 4

An anisotropic conductive film was obtained by repeating Example 3 except that the number of air blowing for removing the conductive particles not attached to the slightly adhesive layer was set to three times that of Example 3.

Comparative Example 1

An anisotropic conductive film was obtained by repeating Example 1 except that the number of air blowing for removing the conductive particles not attached to the slightly adhesive layer was set to 10 times that of Example 1.

Comparative Example 2

An anisotropic conductive film was obtained by repeating Example 3 except that the number of air blowing for removing the conductive particles not attached to the slightly adhesive layer was set to 10 times that of Example 3.

<Evaluation>

("Missing" and "Deviation" of Conductive Particles)

For the anisotropic conductive films of Examples 1 to 4 and Comparative Examples 1 to 2, an optical microscope (MX50, Olympus Corporation) was used to observe a 1 cm square area from the side of the transparent insulating adhesive cover layer to investigate the ratio of grid points to which conductive particles were not attached relative to all grid points in the assumed planar lattice pattern (missing points [%]). The results are shown in Table 1. In addition, the amount of deviation of the conductive particles arranged at the grid points of the assumed planar lattice pattern from the grid points was measured. The maximum value obtained is shown in Table 1. It should be noted that, other than missing points, no significant failures in the connection were observed.

It should be noted that the conductive particles in the anisotropic conductive films of Examples 1 to 4 and Comparative Examples 1 and 2 were offset in one direction along the longitudinal direction of the anisotropic conductive film. Furthermore, the proportion of lattice points where the conductive particles were offset by less than 50% of their particle diameter in one direction along the longitudinal direction of the anisotropic conductive film relative to the total number of lattice points where the conductive particles were arranged was 4% in Example 1, 10% in Example 2, 5% in Example 3, 10% in Example 4, 15% in Comparative Example 1, and 17% in Comparative Example 2. Large offsets make it difficult to position the conductive particles at the desired locations, which can easily lead to defective terminals.

(Particle area occupancy)

The particle area occupancy was calculated from the average particle size of the conductive particles and the concave density of the transfer master (=convex density of the transfer body), taking into account the "missing" portion of the conductive particles.

(Initial on-resistance)

Using the anisotropic conductive films of the examples and comparative examples, an IC chip with gold bumps having a 12μm inter-bump gap, a height of 15μm, and a diameter of 30×50μm was anisotropically conductively connected to a glass substrate with wiring having a 12μm gap at 180°C, 60MPa, and 5 seconds to obtain a connection structure. The initial on-resistance value of the obtained connection structure was measured using a resistance meter (digital multimeter, Yokogawa Electric Corporation). The results are shown in Table 1. It is desirable to be 0.5Ω or less.

(Conduction reliability)

The connection structure used in the initial on-resistance measurement was placed in an aging tester set at 85°C and 85% humidity. The on-resistance after 500 hours was measured in the same manner as for the initial on-resistance. The results are shown in Table 1. It is desirable to have an on-resistance of 5Ω or less.

(Defective conduction rate)

The same connection structure as that used for the initial on-resistance measurement was prepared, and the conduction failure rate of the terminals was measured. The obtained results are shown in Table 1.

[Table 1]

As can be seen from the results in Table 1, the connection structures using the anisotropic conductive films of Examples 1 to 4 showed good results in the evaluation items of initial on-resistance, conduction reliability, and conduction failure rate.

On the other hand, in the case of the anisotropic conductive films of Comparative Examples 1 and 2, the ratio of "missing" conductive particles was high, the initial on-resistance value was higher than that of the example, and the conduction failure rate was not 0%.

Example 5

A transfer body was produced in the same manner as in Example 2, except that the center-to-center distance between adjacent recesses was adjusted to accommodate a transfer master with a recess density of 500/ ^mm² . Furthermore, an anisotropic conductive film was produced. The resulting anisotropic conductive film was measured for the "missing" and "deviation" amounts of conductive particles in the same manner as in Example 2, and the particle area occupancy was calculated. The results showed that the "missing" amount of conductive particles was comparable to that of Example 2. The "deviation" amount also matched the results of Example 2. Furthermore, the particle area occupancy was 0.5%.

The resulting anisotropic conductive film was sandwiched between a glass substrate (ITO solid-state electrode) and a flexible wiring substrate (bump width: 200 μm, L(line)/S(space) = 1, wiring height 10 μm) with a connection bump length of 1 mm. Anisotropic conductive connection was performed at 180°C, 80 MPa, and 5 seconds to produce a connection structure for evaluation. The resulting connection structure was evaluated for its initial on-resistance and conduction reliability after 500 hours in a thermostat at 85°C and 85% RH. The on-resistance was measured using a digital multimeter (34401A, manufactured by Agilent Technologies) using a four-terminal method at a current of 1 A. For the initial on-resistance, values of 2 Ω or less were evaluated as good, while values exceeding 2 Ω were evaluated as poor. For the conduction reliability, values of 5 Ω or less were evaluated as good, while values exceeding 5 Ω were evaluated as poor. As a result, all the connection structures of this example were evaluated as “good.” Furthermore, the “conductivity failure rate” was measured in the same manner as in Example 2, and similarly to Example 2, good results were obtained.

Example 6

A transfer body was produced in the same manner as in Example 2, except that the center-to-center distance between adjacent recesses was adjusted to accommodate the use of a transfer master with a recess density of 2000/ ^mm² . Furthermore, an anisotropic conductive film was produced. The resulting anisotropic conductive film was measured for the "missing" and "deviation" of conductive particles in the same manner as in Example 2, and the particle area occupancy was calculated. The results showed that the "missing" and "deviation" of conductive particles were comparable to those in Example 2. The results for "deviation" also matched those in Example 2. Furthermore, the particle area occupancy was 1.9%.

The obtained anisotropic conductive film was sandwiched between a glass substrate and a flexible wiring substrate in the same manner as in Example 5 to achieve anisotropic conductive connection, thereby producing a connection structure for evaluation. The obtained connection structure was evaluated for "initial on-resistance," "conduction reliability," and "conduction failure rate" in the same manner as in Example 5, with good results obtained.

Example 7

A transfer body was produced in substantially the same manner as in Example 1, except that the recess size and center-to-center distance of adjacent recesses were adjusted to change the conductive particle size from 4 μm to 10 μm and to achieve a recess density of 4,400 particles/ ^mm² using a master printing plate similar to Example 1. Furthermore, an anisotropic conductive film was produced in the same manner as in Example 1, except that the conductive particle size was changed to 10 μm, the thickness of the insulating adhesive base layer was changed to 12 μm, and the thickness of the insulating adhesive cover layer was changed to 12 μm. The resulting anisotropic conductive film was measured for the "missing" and "deviated" amounts of conductive particles in the same manner as in Example 1, and the particle area occupancy was calculated. The results showed that the "missing" amount of conductive particles was comparable to that of Example 1. The "deviated amount" also matched the results of Example 1. The particle area occupancy was 30.7%.

The resulting anisotropic conductive film was sandwiched between a glass substrate (ITO solid-state electrode) and a flexible wiring substrate (bump width: 100 μm, L(line)/S(space) = 1, wiring height 19 μm) with a connection bump length of 1 mm. Anisotropic conductive connection was performed at 180°C, 80 MPa, and 5 seconds to produce a connection structure for evaluation. The resulting connection structure was evaluated for its initial on-resistance and conduction reliability after 500 hours in a thermostat at 85°C and 85% RH. The on-resistance was measured using a digital multimeter (34401A, manufactured by Agilent Technologies) using a four-terminal method at a current of 1 A. For the initial on-resistance, values of 2 Ω or less were evaluated as good, while values exceeding 2 Ω were evaluated as poor. For the conduction reliability, values of 5 Ω or less were evaluated as good, while values exceeding 5 Ω were evaluated as poor. As a result, all the connection structures of this example were evaluated as “good.” Furthermore, the “conductivity failure rate” was measured in the same manner as in Example 1, and similarly to Example 1, good results were obtained.

Industrial availability

In the anisotropic conductive film of the present invention, the ratio of "grid points without conductive particles arranged" relative to all grid points of a plane lattice pattern assumed in any reference region is set to 25% or less, and a portion of the conductive particles arranged at the grid points of the plane lattice pattern are offset relative to the corresponding grid points in the longitudinal direction of the anisotropic conductive film, with the offset amount, defined as the distance between the center of the offset conductive particles and the corresponding grid point, being less than 50% of the average particle size of the conductive particles. Therefore, when the anisotropic conductive film of the present invention is used in anisotropic conductive connections, it can achieve excellent initial conductivity and good conductivity reliability after aging, and can also suppress the occurrence of short circuits. Therefore, it is useful for anisotropic conductive connections between fine-pitch IC chips and wiring substrates.

Explanation of symbols

10, 200: anisotropic conductive film; 11, 104: insulating adhesive base layer; 12, 105: insulating adhesive covering layer; 13, 103: conductive particles; 100: transfer body; 101: protrusion; 102: micro-adhesion layer; A: a position where the conductive particles are not arranged at the grid point (a position where the conductive particles are missing); B: conductive particles arranged in a deviated manner in the length direction of the anisotropic conductive film.

Claims (13)

1. An anisotropic conductive film comprising a laminated insulating adhesive substrate layer and an insulating adhesive capping layer, wherein conductive particles are disposed at grid points of a planar lattice pattern near the interface between the insulating adhesive substrate layer and the insulating adhesive capping layer. Compared to all the lattice points of a hypothetical planar lattice pattern in an arbitrary reference region of an anisotropic conductive film, the proportion of lattice points without conductive particles is less than 25%. When a portion of the conductive particles disposed at grid points in a planar lattice pattern are offset from their corresponding grid points only along the length of the anisotropic conductive film, the offset amount, defined as the distance between the center of the offset conductive particle and its corresponding grid point, is less than 50% of the average particle size of the conductive particles. Compared to all the lattice points where conductive particles are arranged, the proportion of lattice points where conductive particles are arranged in a direction deviated from the length direction of the anisotropic conductive film is more than 90%, and the agglomeration that is the cause of short circuits does not occur. 2. The anisotropic conductive film according to claim 1, wherein the reference region is a roughly square region in the central part of the plane of the anisotropic conductive film, formed by sides X and Y satisfying the following relationships (A), (2) and (3). 100D≤X+Y≤400D (A) X≥5D (2) Y≥5D (3) Here, D is the average particle size of the conductive particles, Y is a straight line within a range of less than ±45° relative to the length direction of the anisotropic conductive film, and X is a straight line perpendicular to Y. 3. The anisotropic conductive film according to claim 1, wherein the reference region is a roughly square region in the central part of the plane of the anisotropic conductive film, formed by sides X and Y satisfying the following relationships (1) to (3). X+Y＝100D (1) X≥5D (2) Y≥5D (3) Here, D is the average particle size of the conductive particles, Y is a straight line within a range of less than ±45° relative to the length direction of the anisotropic conductive film, and X is a straight line perpendicular to Y. 4. The anisotropic conductive film according to claim 1, wherein the particle area occupancy of all conductive particles present in any reference region of the anisotropic conductive film is 10-35% relative to the area of the reference region of the anisotropic conductive film. 5. The anisotropic conductive film according to claim 1, wherein the average particle size of the conductive particles is 1 to 10 μm, and the distance between adjacent grid points of the planar grid pattern is more than 0.5 times the average particle size of the conductive particles. 6. In any one of claims 1 to 5, the maximum value of the deviation of conductive particles disposed off-center from the lattice points along the length direction of the anisotropic conductive film is greater than the deviation in a direction orthogonal to the length direction. 7. The anisotropic conductive film according to claim 1, wherein the reference region is a roughly square region in the central part of the plane of the anisotropic conductive film, formed by sides X and Y satisfying the following relationship. X+Y＝400D X≥20D Y≥20D Here, D is the average particle size of the conductive particles, Y is a straight line within a range of less than ±45° relative to the length direction of the anisotropic conductive film, and X is a straight line perpendicular to Y. 8. The anisotropic conductive film according to claim 7, wherein the particle area occupancy of all conductive particles present in any reference region of the anisotropic conductive film is 0.15% or more. 9. The anisotropic conductive film according to claim 7 or 8, wherein the average particle size of the conductive particles is 1 to 30 μm, and the distance between adjacent grid points of the planar grid pattern is more than 0.5 times the average particle size of the conductive particles. 10. The method for manufacturing the anisotropic conductive film according to claim 1, comprising the following steps (A) to (E): <Process (A)> The process of preparing the transfer body, which has columnar protrusions on its surface that correspond to a grid pattern of planar dots; <Process (B)> The process of forming a micro-adhesive layer on at least the top surface of the raised portion of the transfer body; <Process (C)> The process of attaching conductive particles to the micro-adhesive layer on the protrusion of the transfer body; <Process (D)> The process of overlapping and pressing an insulating adhesive base layer onto the surface of the transfer body on the side where the conductive particles are attached, thereby transferring the conductive particles to the insulating adhesive base layer; and <Process (E)> For an insulating adhesive substrate layer to which conductive particles have been transferred, the process of laminating an insulating adhesive capping layer from the conductive particle transfer surface side. 11. The manufacturing method according to claim 10, wherein the transfer body used in step (A) is a base plate made by processing a metal plate, coating the base plate with a curable resin and curing it. 12. In the manufacturing method according to claim 10 or 11, the height of the protrusion of the transfer body in step (A) is more than 2.5 times and less than 5 times the average particle size of the conductive particles, and the width of the protrusion is more than 0.6 times and less than 1.3 times the average particle size of the conductive particles. 13. A connection structure, wherein the terminals of a first electrical component and the terminals of a second electrical component are anisotropically conductively connected by an anisotropic conductive film according to any one of claims 1 to 9.