JP7348563B2 - Anisotropic conductive film - Google Patents

Description

The present invention relates to an anisotropic conductive film.

Anisotropic conductive films in which conductive particles are dispersed in an insulating resin binder are widely used when mounting electronic components such as IC chips on wiring boards. It is known that conductive particles exist in a connected or aggregated state. For this reason, when an anisotropic conductive film is applied to connect the terminals of an IC chip and the terminals of a wiring board, which are becoming narrower in pitch as electronic devices become lighter and smaller, it is difficult to connect or aggregate them in the anisotropic conductive film. Conductive particles that remain in such a state may cause a short circuit between adjacent terminals.

Conventionally, as an anisotropic conductive film corresponding to such a narrow pitch, a film in which conductive particles are regularly arranged in the film has been proposed. For example, an adhesive layer is formed on a stretchable film, the surface of the adhesive layer is densely packed with a single layer of conductive particles, and then the film is biaxially stretched until the distance between the conductive particles reaches a desired distance. Anisotropic conductivity obtained by arranging conductive particles in an ordered manner, then pressing an insulating adhesive base layer, which is a component of an anisotropic conductive film, against the conductive particles, and transferring the conductive particles to the insulating adhesive base layer. A film has been proposed (Patent Document 1). In addition, conductive particles are sprinkled on the recess-forming surface of a transfer mold that has recesses on the surface, the recess-forming surface is squeegeeed to hold the conductive particles in the recesses, and an adhesive film on which an adhesive layer for transfer is formed is applied. The conductive particles are first transferred to the adhesive layer by pressing, and then an insulating adhesive base layer, which is a component of the anisotropic conductive film, is pressed against the conductive particles attached to the adhesive layer to transfer the conductive particles to an insulating property. An anisotropic conductive film obtained by transfer to an adhesive base layer has also been proposed (Patent Document 2). Regarding these anisotropic conductive films, an insulating adhesive cover layer is generally laminated on the conductive particle side surface so as to cover the conductive particles.

WO2005/054388 Japanese Patent Application Publication No. 2010-33793

However, since conductive particles tend to aggregate due to static electricity or the like and become secondary particles, it is difficult to allow conductive particles to exist alone as primary particles at all times. For this reason, the following problems arise in the techniques of Patent Document 1 and Patent Document 2. That is, in the case of Patent Document 1, it is difficult to densely fill the entire surface of the stretchable film with conductive particles in a single layer without defects, and the conductive particles may be filled in the stretchable film in an aggregated state, causing short circuits. However, there is a problem in that unfilled areas (so-called "dropouts") occur, which may cause poor conduction. In addition, in the case of Patent Document 2, when the recesses of the transfer mold are covered with conductive particles having a large particle diameter, they are removed by a subsequent squeegee, creating recesses that do not hold the conductive particles, and the anisotropic conductive film becomes conductive. Particles may "miss out" and cause poor conductivity, or conversely, if many small conductive particles are pushed into the recesses, they may aggregate when transferred to the insulating adhesive base layer, or Since the conductive particles located at the bottom of the recess are not in contact with the insulating adhesive base layer, they are scattered on the surface of the insulating adhesive base layer, disrupting the regular arrangement and causing short circuits and poor conduction. There was a problem that

As described above, Patent Documents 1 and 2 do not sufficiently explain how to control the "dropout" and "agglomeration" of conductive particles that should be arranged in a regular pattern in an anisotropic conductive film. The reality is that this is not taken into consideration.

The purpose of the present invention is to solve the above-mentioned problems of the conventional technology, and to prevent the occurrence of short circuits and conduction defects from the viewpoint of "dropout" and "agglomeration" of conductive particles that should be arranged in a regular pattern. An object of the present invention is to provide an anisotropic conductive film with greatly suppressed anisotropy.

When arranging conductive particles at the lattice points of a planar lattice, the present inventor has proposed that, when arranging conductive particles at the lattice points of a planar lattice, "lattice points where conductive particles are not placed" are The inventors have discovered that the above object can be achieved by controlling the ratio of lattice points where conductive particles are aggregated and the ratio of lattice points where conductive particles are arranged in agglomerated manner, and have completed the present invention. In addition, such an anisotropic conductive film does not place conductive particles in the recesses of the transfer body, but instead attaches the conductive particles to the tips of the convex parts of the transfer body, which has columnar convex parts formed on the surface. The inventors have discovered that it can be manufactured by performing the transfer process, and have completed the manufacturing method of the present invention.

That is, the present invention provides an anisotropic conductive film having a structure in which conductive particles are arranged at lattice points of a planar lattice pattern on an insulating adhesive base layer,
The ratio of lattice points on which conductive particles are not placed to all lattice points of a planar lattice pattern assumed in the reference area of the anisotropic conductive film is less than 20%,
An anisotropic conductive film in which the ratio of lattice points where a plurality of conductive particles are arranged in agglomeration to all lattice points of the planar lattice pattern is 15% or less, and the total of omissions and aggregation is less than 25%. provide.

The present invention also 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 near the interface thereof at lattice points of a planar lattice pattern. ,
The ratio of lattice points on which conductive particles are not placed to all lattice points of a planar lattice pattern assumed in the reference area of the anisotropic conductive film is less than 20%,
The present invention provides an anisotropic conductive film in which the ratio of lattice points where a plurality of conductive particles are aggregated to all lattice points of the planar lattice pattern is 5% or less. Again, the sum of shedding and agglomeration is preferably less than 25%.

The present invention also provides a method for producing 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 near the interface thereof at lattice points of a planar lattice pattern. The following steps (a) to (e):
<Process (a)>
a step of preparing a transfer body having columnar convex portions formed on its surface corresponding to lattice points of a planar lattice pattern;
<Process (b)>
a step of forming at least the top surface of the convex portion of the transfer body into a slightly adhesive layer;
<Process (c)>
a step of attaching conductive particles to the slightly adhesive layer of the convex portion of the transfer body;
<Process (d)>
A step of transferring the conductive particles to the insulating adhesive base layer by stacking and pressing the insulating adhesive base layer on the surface of the transfer body on which the conductive particles are attached; and <Step (E)>
Provided is a manufacturing method that includes the step of laminating an insulating adhesive cover layer on an insulating adhesive base layer to which conductive particles have been transferred from the side to which the conductive particles have been transferred.

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

In the anisotropic conductive film of the present invention, the ratio of "lattice points on which no conductive particles are arranged" to all the lattice points of the planar lattice pattern assumed in the reference area is set to less than 20%, and "a plurality of conductive The ratio of "lattice points where particles are arranged in agglomerated manner" is set to 15% or less, and the total of omissions and agglomeration is set to less than 25%. Therefore, when the anisotropic conductive film of the present invention is applied to an anisotropic conductive connection, a good initial conduction resistance value and good conduction reliability after aging can be achieved, and the occurrence of short circuits can also be suppressed. Moreover, it is excellent in economical efficiency not only for COG but also for electronic components with sufficiently large bump areas and distances, such as FOG.

In a preferable anisotropic conductive film of the present invention, the ratio of "lattice points on which no conductive particles are arranged" to all the lattice points of the planar lattice pattern assumed in the reference area is set to less than 20%, and "multiple The ratio of lattice points where conductive particles are arranged in agglomerated manner is 5% or less. Therefore, when the anisotropic conductive film of the present invention is applied to an anisotropic conductive connection, a good initial conduction resistance value and good conduction reliability after aging can be achieved, and the occurrence of short circuits can also be suppressed.

In addition, in the method for producing an anisotropic conductive film of the present invention, a transfer body is used in which columnar convex portions corresponding to the lattice points of a planar lattice pattern are formed on the surface, and columnar convex portions are formed on the top surface of the convex portions. After the conductive particles are attached to the slightly adhesive layer, the conductive particles are transferred to the insulating adhesive base layer. For this reason, the ratio of "lattice points where conductive particles are not placed" to all the lattice points of the planar lattice pattern assumed in the reference area of the anisotropic conductive film is less than 20%, and The ratio of "lattice points where a plurality of conductive particles are arranged in agglomerated manner" can be made 5% or less. Therefore, the manufacturing method of the present invention can economically advantageously manufacture an anisotropic conductive film, and by using this anisotropic conductive film, short-circuits and short-circuits can be avoided between narrow pitch IC chips and wiring boards. Anisotropic conductive connections can be made while greatly suppressing the occurrence of conduction failures.

FIG. 1 is a cross-sectional view of the anisotropic conductive film of the present invention. FIG. 2 is a plan perspective view of the anisotropic conductive film of the present invention. FIG. 3A is a process explanatory diagram of the manufacturing method of the present invention. FIG. 3B is a process explanatory diagram of the manufacturing method of the present invention. FIG. 3C is a process explanatory diagram of the manufacturing method of the present invention. FIG. 3D is a process explanatory diagram of the manufacturing method of the present invention. FIG. 3E is a process explanatory diagram of the manufacturing method of the present invention. FIG. 3F is a process explanatory diagram of the manufacturing method of the present invention and a schematic cross-sectional view of the anisotropic conductive film of the present invention.

The anisotropic conductive film of the present invention has a structure in which an insulating adhesive base layer and an insulating adhesive cover layer are laminated, and conductive particles are arranged near the interface thereof at lattice points of a planar lattice pattern. The ratio of lattice points on which conductive particles are not arranged to all lattice points of a planar lattice pattern assumed in the reference area of this anisotropic conductive film is less than 20%, and The ratio of lattice points where conductive particles are arranged in agglomerated manner is 15% or less, and the total of omissions and agglomeration is less than 25%. Hereinafter, the anisotropic conductive film of the present invention will be explained in detail with reference to the drawings.

<Anisotropic conductive film>
As shown in FIG. 1 (cross-sectional view) and FIG. 2 (plane perspective view), the anisotropic conductive film 10 of the present invention has an insulating adhesive base layer 11 and an insulating adhesive cover layer 12 laminated together. It has a structure in which conductive particles 13 are arranged near the interface at lattice points of a planar lattice pattern (dotted lines in FIG. 2). In FIGS. 1 and 2, the planar lattice pattern is assumed to extend along the longitudinal direction of the anisotropic conductive film 10 and the direction perpendicular thereto (short direction); may be assumed to be inclined. Here, arrow A indicates a position where no conductive particles are arranged at a lattice point of the planar lattice, a so-called position where conductive particles are "missing". Note that arrow B indicates a position where conductive particles are in contact with each other and aggregate, and arrow C indicates a position where conductive particles are aggregated without contacting each other. Here, "coagulating without contact" means that the conductive particles are close to each other within a range that does not exceed 25% of the average particle diameter of the conductive particles.

(“Escape” of conductive particles)
In the anisotropic conductive film of the present invention, the ratio of "lattice points where conductive particles are not arranged" (A in FIG. 2) to all the lattice points of the planar lattice pattern assumed in the reference area of the anisotropic conductive film (Percentage of lattices where conductive particles are missing) is set to less than 20%, preferably 18% or less, more preferably 10 to 18%. As a result, when the anisotropic conductive film of the present invention is applied to an anisotropic conductive connection, good initial conductivity and good conduction reliability after aging can be achieved, and the occurrence of short circuits can also be suppressed.

(Plane grid pattern)
Planar lattice patterns include orthorhombic lattice, hexagonal lattice, square lattice, rectangular lattice, and parallel body lattice. Among these, a hexagonal lattice that allows close packing is preferred.

Here, it is possible to select the entire surface of the anisotropic conductive film as the reference area of the anisotropic conductive film, but usually, the following relational expression (A) at the center of the plane of the anisotropic conductive film is preferably selected. It is preferable to select a substantially rectangular area consisting of side X and side Y that satisfies relational expression (1) and relational expressions (2) and (3) as the reference area.

In addition, when applying to FOG connection which allows a relatively large connection area, it is possible to reduce the amount of conductive particles in the film, and in such a case, as shown below, it is possible to reduce the amount of conductive particles in the film. It is preferable to make the values of Y and Y larger, preferably 20D or more, and it is preferable that the value of "X+Y" is also a value in the vicinity of 100D to 400D, and finally 400D.

In formulas (A) and (1) to (3), and the above formulas, D is the average particle diameter of the conductive particles. The average particle diameter of the conductive particles can be measured using an image-type particle size distribution analyzer. It may be measured by surface observation. Further, side Y is a straight line within a range of less than ±45° with respect 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 area in this way, it is possible to make the reference area similar to or approximate the shape of the bump on which the conductive particles are pressed, and as a result, the tolerance range for deviation from the planar lattice pattern of the conductive particles is increased. This makes it possible to economically and stably perform anisotropic conductive connections. In other words, by setting the minimum side of this reference area to at least 5 times the diameter of the conductive particles, even if the conductive particles are misaligned, missing, or close to each other within the range assumed within this range, either Since the particles are captured by the bumps and do not aggregate excessively in the spaces between the bumps, anisotropic conductive connections can be made reliably.

The reason why the smallest side is made to be 5 times or more the diameter of the conductive particle is that it is generally made larger than the average particle diameter of the conductive particle in order to ensure capture on at least one side of the bump to be anisotropically conductively connected. Moreover, it is necessary to provide a space between bumps that is preferably twice or more the average particle diameter of the conductive particles in order to prevent short circuits. In other words, when focusing on a circular conductive particle that serves as a reference, the diameter is the sum of the average particle diameter D of this conductive particle and four times the length (4D) of the diameter (that is, 5D). This is because it is considered that the above requirements can be met if no unexpected defects occur within the concentric circles. This is also because the minimum distance between bumps in the case of fine pitch is, for example, less than four times the conductive particle diameter.

(Agglomeration of conductive particles)
Further, in the anisotropic conductive film of the present invention, the ratio of lattice points (B and C in FIG. 2) where a plurality of conductive particles are aggregated to all lattice points of the planar lattice pattern is preferably 15 % or less, more preferably 5% or less. Since 0% is theoretically most preferable, it may be less than 0.1%. If the ratio of aggregated lattice points is 5% or less, even when the anisotropic conductive film of the present invention is applied to anisotropic conductive connections, better initial conductivity and continuity reliability after aging can be achieved. This makes it possible to further suppress the occurrence of short circuits. Here, the degree of aggregation of conductive particles with respect to one lattice point is preferably small from the viewpoint of suppressing short circuits, and preferably does not exceed two. In addition, when the aggregated conductive particles are not in contact with each other as shown in C of FIG. 2, the interval between them is preferably within 25% of the average particle diameter of the conductive particles, and more preferably within 15%. be.

(Arrangement of conductive particles)
It is preferable that 11 or more conductive particles are consecutively arranged in a direction perpendicular to the longitudinal direction of the film, and more preferably that 13 or more conductive particles are arranged continuously. This is because if conductive particles are missing in the longitudinal direction of the bump, there is a risk that the anisotropic conductive connection will be impaired. In this case, it is preferable that all three consecutive rows along the longitudinal direction of the film satisfy the above condition, and it is more preferable that all five columns satisfy the above condition. Thereby, the number of conductive particles captured by the bump can be increased to a certain level or more, and stable anisotropic conductive connection can be performed.

When the conductive particles are aggregated, the number of pairs of two connected conductive particles is preferably 3 or less, more preferably 2 or less, and even more preferably 1, around the two aggregated conductive particles. less than or equal to one. This is because if two agglomerated conductive particles exist closely together, it becomes a cause of short circuit occurrence.

In addition, it is preferable that four or more conductive particles consecutive in the longitudinal direction of the film and four or more consecutive conductive particles in the direction perpendicular to the longitudinal direction of the film do not intersect, and that none of four or more consecutive conductive particles are missing. It is more preferable that the missing portions are not adjacent to each other through conductive particles that become one or more lattice points, and any of four or more consecutive missing holes are not adjacent to each other through conductive particles that become two or more lattice points. Even more preferably, they are not adjacent to each other. There is no problem in intersecting such omissions even if up to three columns intersect simultaneously for omissions in one direction. This is because if the missing parts are not more continuous, they will be captured by the bumps by the nearby conductive particles.

It should be noted that it is generally undesirable for there to be multiple areas in the vicinity where consecutive missing areas intersect in this way, but the stability of the anisotropic conductive connection can be improved if there is an arrangement of conductive particles with the same number or more as the missing areas. There is no problem.

(particle area occupancy)
Furthermore, the particle area occupancy of all the conductive particles present in the area of the reference area of the anisotropic conductive film with respect to the area of the reference area is, for cases where the bump size and distance between bumps are relatively large, such as FOG connection. is usually 0.15% or more, preferably 0.35% or more, more preferably 1.4% or more. In this case, the upper limit is preferably 35% or less, more preferably 32% or less. Further, when the bump size or distance between bumps is relatively small (for example, COG connection), the ratio is more preferably 15 to 35%, particularly preferably 16 to 20%. Within this range, even when the anisotropic conductive film of the present invention is applied to anisotropic conductive connections, better initial conductivity and continuity reliability after aging can be achieved, and the occurrence of short circuits can be further reduced. It can be suppressed. Here, the particle area occupancy rate is the ratio of the area occupied by all conductive particles existing in the reference region to the area S of the reference region. The area occupied by all the conductive particles is expressed as (R/2) ² ×π×n, where R is the average particle diameter of the conductive particles and n is the number of conductive particles. Therefore, the particle area occupancy rate (%) is expressed as [{(R/2) ² ×π×n}/S]×100.

By the way, when the average particle diameter 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, the calculated particle area occupancy is as follows. It becomes 0.157%. When the average particle diameter 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, the calculated particle area occupancy is 0. It becomes 35325%. When the average particle diameter 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, the calculated particle area occupancy is 1. It becomes 413%. Furthermore, when the average particle diameter 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: It becomes 35.325%.

(conductive particles)
As the conductive particles, those used in known anisotropic conductive films can be appropriately selected and used. Examples include metal particles such as nickel, copper, silver, gold, and palladium, and metal-coated resin particles in which the surface of resin particles such as polyamide and polybenzoguanamine is coated with a metal such as nickel. Further, the average particle diameter of the conductive particles is preferably 1 to 30 μm, more preferably 1 to 10 μm, particularly preferably 2 to 6 μm, from the viewpoint of ease of handling during production. The average particle diameter can be measured using an image-type particle size distribution meter, as described above. It may be measured by surface observation.

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 diameter of the conductive particles, and is usually 300 to 40,000 particles/mm ² .

(distance between adjacent grid points)
Further, the distance between adjacent lattice points in the planar lattice pattern assumed for the anisotropic conductive film is preferably larger than 0.5 times, more preferably 1 time or more, and even more preferably 1 to 1 times the average particle diameter of the conductive particles. It is 20 times more. Within this range, even when the anisotropic conductive film of the present invention is applied to anisotropic conductive connections, better initial conductivity and continuity reliability after aging can be achieved, and the occurrence of short circuits can be further reduced. It can be suppressed.

(Insulating adhesive base layer)
As the insulating adhesive base layer 11, those used as insulating adhesive base layers in known anisotropic conductive films can be appropriately selected and used. For example, a photoradical polymerizable resin layer containing an acrylate compound and a photoradical polymerization initiator, a thermally radically polymerizable resin layer containing an acrylate compound and a thermal radical polymerization initiator, a thermally radical polymerizable resin layer containing an epoxy compound and a thermal cationic polymerization initiator, A cationic polymerizable resin layer, 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. Moreover, these resin layers can contain a silane coupling agent, a pigment, an antioxidant, an ultraviolet absorber, etc., which are appropriately selected, as necessary.

Note that the insulating adhesive base layer 11 is formed by forming a coating composition containing the resin as described above by a coating method and drying it, further curing it, or by forming it into a film in advance by a known method. can do.

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

(Insulating adhesive cover layer)
As the insulating adhesive cover layer 12, those used as insulating adhesive cover layers in known anisotropic conductive films can be appropriately selected and used. Furthermore, a layer made of the same material as the insulating adhesive base layer 11 described above can also be used.

The insulating adhesive cover layer 12 can be formed by forming a coating composition containing the resin as described above by a coating method and drying it, by further curing it, or by forming it into a film in advance by a known method. can do.

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

Furthermore, insulating filler such as silica fine particles, alumina, aluminum hydroxide, etc. may be added to the insulating adhesive base layer 11 and the insulating adhesive cover layer 12 as necessary. The amount of the insulating filler to be blended is preferably 3 to 40 parts by weight based on 100 parts by weight of the resin constituting these layers. Thereby, even if the insulating adhesive layer 10 melts during anisotropic conductive connection, unnecessary movement of the conductive particles 2 by the melted resin can be suppressed.

(Lamination of insulating adhesive base layer and insulating adhesive cover layer, embedding of conductive particles)
Note that when the insulating adhesive base layer 11 and the insulating cover layer 12 are laminated with the conductive particles 13 in between, a known method can be used. In this case, the conductive particles 13 are present near the interface between these layers. Here, "existing near the interface" indicates that a part of the conductive particles bites into one layer and the rest bites into the other layer. Also, conductive particles may be embedded in the insulating adhesive base layer. In this case, it can be formed without laminating an insulating adhesive cover layer.

<Manufacture of anisotropic conductive film>
Next, an insulating adhesive base layer and an insulating adhesive cover layer are laminated, and conductive particles are arranged near the interface thereof at lattice points of a planar lattice pattern. Explain. This manufacturing method includes the following steps (a) to (e). Each step will be explained in detail with reference to the drawings. Note that the present invention is not particularly limited to this manufacturing method.

(Process (a))
First, as shown in FIG. 3A, a transfer body 100 having columnar convex portions 101 formed on its surface corresponding to lattice points of a planar lattice pattern is prepared. Here, the columnar shape means a columnar shape or a prismatic shape (triangular prism, square prism, hexagonal prism, etc.). This columnar shape includes a cone. Preferably it is cylindrical. The height of the convex portion 101 can be determined depending on the terminal pitch to be anisotropically conductively connected, the terminal width, the space width, the average particle diameter of the conductive particles, etc. Preferably it is 1.2 times or more and less than 2 times. Further, the width (width at half height) of the convex portion 101 is preferably 0.7 times or more and 1.3 times or less of the average particle diameter of the conductive particles. If the height and width are within these ranges, it is possible to avoid the continuous occurrence of falling off and coming off.

Furthermore, the convex portion 101 has a flat top surface that allows conductive particles to stably adhere thereto.

*Specific example of transfer body The transfer body to be prepared in this step (a) can be created using a known method. For example, a master is created by processing a metal plate, and a hardening resin is applied to it. It can be created by coating and curing. Specifically, a transfer body master is also prepared by cutting a flat metal plate to form concave portions corresponding to the convex portions, and a resin composition constituting the transfer body is applied to the concave portion forming surface of this master, After curing, a transfer body is obtained by separating it from the master.

(Process (b))
Next, as shown in FIG. 3B, at least the top surface of the convex portions 101 of the transfer body 100, on which a plurality of convex portions 101 are formed in a planar lattice pattern, is made into a slightly adhesive layer 102.

*Slightly adhesive layer of transfer body The slightly adhesive layer 102 is a layer that exhibits adhesive strength that can temporarily hold conductive particles until they are transferred to the insulating adhesive base layer that constitutes the anisotropic conductive film. It is formed on at least the top surface of the convex portion 101. Therefore, the entire convex portion 101 may be slightly adhesive. The thickness of the slightly adhesive layer 102 can be appropriately determined depending on the material of the slightly adhesive layer 102, the particle size of the conductive particles, and the like. Moreover, "slight adhesion" means that the adhesive force is weaker than that of the insulating adhesive base layer when conductive particles are transferred to the insulating adhesive base layer.

As such a slightly adhesive layer 102, a slightly adhesive layer used in known anisotropic conductive films can be applied. For example, it can be formed by applying a silicone adhesive composition or an adhesive layer made of the same material as the insulating adhesive base layer and the insulating adhesive cover layer to the top surface of the convex portion 101 .

(Process (c))
Next, as shown in FIG. 3C, conductive particles 103 are attached to the slightly adhesive layer 102 of the convex portion 101 of the transfer body 100. Specifically, the conductive particles 103 may be scattered from above the convex portions 101 of the transfer body 100, and the conductive particles 103 that have not adhered to the slightly adhesive layer 102 may be blown away using a blower. Alternatively, the direction of the surface may be reversed from FIG. 3C, and the top surface of the protrusion may be attached to the surface covered with conductive particles. This is to avoid applying unnecessary stress to the conductive particles. In this way, by attaching only the conductive particles necessary for the arrangement to the top surface of the protrusion, it becomes easier to collect and reuse the conductive particles, and it is also more economical than the method of filling the opening with conductive particles and taking them out. Become. In addition, in the case of the method of filling the opening with conductive particles and taking them out, there is a concern that unnecessary stress is likely to be applied to the conductive particles that are not filled.

In addition, in FIG. 3C, the width of the convex portion 101 on the left half is adjusted to be narrower than the width of the convex portion 101 on the right half. As a result, as shown in FIG. 3C, there may be a difference in the manner of aggregation of the conductive particles 103 between the left half and the right half.

(Process (d))
Next, as shown in FIG. 3D, the surface of the transfer body 100 on which the conductive particles 103 are attached is pressed with an insulating adhesive base layer 104 that is to form an anisotropic conductive film. Conductive particles 103 are transferred onto one side of adhesive base layer 104 (FIG. 3E). In this case, it is preferable that the transfer body 100 is pressed against the insulating adhesive base layer 104 so that the convex portion 101 thereof faces downward. This is to make it easier to remove conductive particles that are not attached to the top surface of the convex portion by blowing downward.

(Process (e))
As shown in FIG. 3F, an insulating adhesive cover layer 105 is laminated on the insulating adhesive base layer 104 to which the conductive particles 103 have been transferred from the side to which the conductive particles have been transferred. As a result, the anisotropic conductive film 200 of the present invention is obtained.

Note that in this anisotropic conductive film 200, a plurality of conductive particles may be arranged in agglomerated manner in contact with each other in the horizontal direction or in close proximity to each other at one lattice point of the planar lattice pattern. This is because when attaching the conductive particles to the slightly adhesive layer on the convex part of the transfer body, the width of the convex part (width of the slightly adhesive layer) and the average particle diameter of the conductive particles are approximately the same size. Although it is difficult to imagine that multiple conductive particles exist on one convex part, excess conductive particles may adhere to the edges of the slightly adhesive layer, or fall off from the convex part and not be completely blown away by the blower. This is because there may be cases where it remains.

<Connection structure>
The anisotropic conductive film of the present invention is provided between a terminal (e.g. bump) of a first electronic component (e.g. IC chip) and a terminal (e.g. bump, pad) of a second electronic component (e.g. wiring board). So-called COG (chip on glass) and FOG (film on glass).

The present invention will be specifically explained below.

Example 1
A nickel plate with a thickness of 2 mm was prepared, and a cylindrical recess (inner diameter 5 μm, depth 6 μm) was formed in a square lattice pattern to serve as a transfer master. The distance between the centers of adjacent recesses was 8 μm. Therefore, the density of the recesses was 16,000/mm2.

To the obtained transfer master, 60 parts by mass of phenoxy resin (YP-50, Nippon Steel & Sumikin Chemical Co., Ltd.), 29 parts by mass of acrylate resin (M208, Toagosei Co., Ltd.), and a photopolymerization initiator (IRGCUR184, BASF Japan) were added. Co., Ltd. A photopolymerizable resin composition containing 2 parts by mass was applied onto a PET (polyethylene terephthalate) film to a dry thickness of 30 μm, dried at 80°C for 5 minutes, and then exposed to a high-pressure mercury lamp. A transfer body was created by irradiating with 1000 mJ of light.

The transfer body is peeled off from the master disc, wrapped around a stainless steel roll with a diameter of 20 cm so that the convex portion faces outward, and the roll is coated with 70 parts by mass of epoxy resin (jER828, Mitsubishi Chemical Corporation) and phenoxy resin while rotating. (YP-50, Nippon Steel & Sumikin Chemical Co., Ltd.) A slightly adhesive composition containing 30 parts by mass is brought into contact with an adhesive sheet impregnated with nonwoven fabric, and the slightly adhesive composition is attached to the top surface of the convex portion. A transfer body was obtained by forming a slightly adhesive layer with a thickness of 1 μm.

After scattering conductive particles (nickel-plated resin particles (AUL704, Sekisui Chemical Co., Ltd.)) with an average particle diameter of 4 μm on the surface of this transfer body, blowing is performed to prevent the conductive particles from adhering to the slightly adhesive layer. was removed.

The transfer body to which the conductive particles are attached is coated with a sheet-like thermosetting insulating adhesive film (phenoxy resin (YP-50), Nippon Steel & Sumikin Chemical Co., Ltd. Co., Ltd.) 60 parts by mass, epoxy resin (jER828, Mitsubishi Chemical Corporation) 40 parts by mass, cationic curing agent (SI-60L, Sanshin Chemical Industry Co., Ltd.) 2 parts by mass, and silica fine particles (Aerosil RY200, Conductive particles were transferred to the insulating adhesive base layer by pressing a film formed from an insulating adhesive composition containing 20 parts by mass of Nippon Aerosil Co., Ltd. at a temperature of 50 ° C. and a pressure of 0.5 MPa. Ta.

Another 15 μm thick sheet-shaped insulating adhesive film (phenoxy resin (YP-50, Nippon Steel & Sumikin Chemical Co., Ltd. )) 60 parts by mass, 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.). (films formed from the above) were overlapped and laminated at a temperature of 60° C. and a pressure of 2 MPa. As a result, an anisotropic conductive film was obtained.

Example 2
An anisotropic conductive film was obtained by repeating Example 1 except that the amount of conductive particles sprinkled and the number of times of blowing were doubled compared to Example 1.

Example 3
The inner diameter of the concave portion of the transfer master was 3.6 μm, the distance between the centers of adjacent concave portions was 6 μm, the density of the concave portion was 28,000 pieces/mm2, and conductive particles with an average particle diameter of 3 μm (AUL703) were used instead of conductive particles with an average particle diameter of 4 μm. An anisotropic conductive film was obtained by repeating Example 1, except for using the following method (Sekisui Chemical Co., Ltd.).

Example 4
An anisotropic conductive film was obtained by repeating Example 3 except that the amount of conductive particles sprinkled and the number of blowers were doubled compared to Example 3.

Comparative example 1
Example 1 is repeated except that the depth of the recess of the transfer master is 4.4 μm, the inner diameter of the recess is 4.8 μm, the distance between the centers of adjacent recesses is 5.6 μm, and the density of the recess is 32000 pieces/ ^mm2 . As a result, an anisotropic conductive film was obtained.

Comparative example 2
The depth of the recess of the transfer body master is 3.3 μm, the inner diameter of the recess is 3.6 μm, the distance between the centers of adjacent recesses is 4.2 μm, the density of the recess is 57,000 pieces/ ^mm2 , and conductive particles have an average particle diameter of 4 μm. An anisotropic conductive film was obtained by repeating Example 1, except that conductive particles (AUL703, Sekisui Chemical Co., Ltd.) having an average particle diameter of 3 μm were used instead.

<Evaluation>
(“Shedding” and “agglomeration” of conductive particles)
Regarding the anisotropic conductive films of Examples 1 to 4 and Comparative Examples 1 to 2, a 1 cm square area was observed from the transparent insulating adhesive cover layer side using an optical microscope (MX50, Olympus Corporation), and the expected In the planar lattice pattern, the ratio of lattice points to which conductive particles are not attached to all lattice points (missing [%]) and the ratio of lattice points to which two or more conductive particles are aggregated to all lattice points are investigated. Ta. The results obtained are shown in Table 1.

In addition, the maximum distance between agglomerated conductive particles (aggregation distance) was measured and is also shown in Table 1. In addition, the "agglomeration" direction was the horizontal direction of the anisotropic conductive film in all cases.

(particle area occupancy)
The particle area occupancy rate was calculated from the average particle diameter of the conductive particles and the density of the concave portions of the transfer material master (=density of convex portions of the transfer material), taking into account "missing" and "agglomeration" of the conductive particles. . The results obtained are shown in Table 1.

(Initial conduction resistance)
Using the anisotropic conductive films of Examples and Comparative Examples, an IC chip having gold bumps of 30 x 50 μm with an inter-bump space of 12 μm and a height of 15 μm, and a glass substrate provided with wiring with a 12 μm space were fabricated. Anisotropic conductive connection was performed under the conditions of 180° C., 60 MPa, and 5 seconds to obtain a connected structure. The initial conduction resistance value of the obtained connected structure was measured using a resistance measuring device (Digital Multimeter 7565, Yokogawa Electric Corporation). The results obtained are shown in Table 1. It is desired that the resistance is 0.5Ω or less.

(Continuity reliability)
The connected structure used to measure the initial conduction resistance value was placed in an aging tester set at a temperature of 85°C and humidity of 85%, and the conduction resistance value after being left for 500 hours was measured in the same manner as the initial conduction resistance. It was measured. The results obtained are shown in Table 1. It is desirable that the resistance be 5Ω or less.

(Short occurrence rate)
A connection structure similar to that used for the initial conduction resistance was created, and the occurrence of shorts between adjacent wirings was investigated. The results obtained are shown in Table 1. It is desired that the short circuit occurrence rate be 50 ppm or less.

From the results in Table 1, it can be seen that the connected structures using the anisotropic conductive films of Examples 1 to 4 showed good results in each evaluation item of initial conduction resistance, conduction reliability, and short circuit occurrence rate. Recognize.

On the other hand, in the case of the anisotropic conductive films of Comparative Examples 1 and 2, the rate of "dropout" of conductive particles was low, but the rate of "agglomeration" was too high, so the evaluation of the incidence of short circuits was low.

Example 5
A transfer body was created in the same manner as in Example 2, except that the distance between the centers of adjacent recesses was adjusted in order to use a transfer master with a recess density of 500 pieces/ ^mm2 , and an anisotropic conductive film was also created. . Regarding the obtained anisotropic conductive film, the "dropout" and "agglomeration" of the conductive particles were measured in the same manner as in Example 2, and the particle area occupancy was calculated. As a result, the "missing" and "agglomeration" of the conductive particles were the same as in Example 2. Further, the particle area occupancy was 0.6%.

In addition, the obtained anisotropic conductive film was placed between a glass substrate (ITO solid electrode) and a flexible wiring board (bump width: 200 μm, L (line)/S (space) = 1, wiring height 10 μm). Anisotropic conduction was carried out under the conditions of 180° C., 80 MPa, and 5 seconds so that the length of the connection bump was 1 mm, and a connected structure for evaluation was obtained. For the resulting connected structure, its "initial conduction resistance value" and "continuity reliability" after being placed in a constant temperature bath at a temperature of 85°C and a humidity of 85% RH for 500 hours were measured using a digital multimeter (34401A, Agilent・Measure the continuity resistance using the 4-terminal method at a current of 1A using a device manufactured by Technology Co., Ltd. For the "initial continuity resistance value", if the measured value is 2Ω or less, it is considered good, and if it exceeds 2Ω, it is considered good. In the case of "continuity reliability," a measured value of 5Ω or less was evaluated as good, and a measured value of 5Ω or more was evaluated as poor. As a result, all the connected structures of Example 5 were evaluated as "good." Further, when the "short circuit occurrence rate" was measured in the same manner as in Example 2, good results were obtained as in Example 2.

Example 6
A transfer body was created in the same manner as in Example 2, except that the distance between the centers of adjacent recesses was adjusted in order to use a transfer master with a recess density of 2000 pieces/ ^mm2 , and an anisotropic conductive film was also created. . Regarding the obtained anisotropic conductive film, the "dropout" and "agglomeration" of the conductive particles were measured in the same manner as in Example 2, and the particle area occupancy was calculated. As a result, the "missing" and "agglomeration" of the conductive particles were the same as in Example 2. Further, the particle area occupancy was 2.4%.

Further, the obtained anisotropic conductive film was sandwiched between a glass substrate and a flexible wiring board in the same manner as in Example 5, and anisotropic conductive connection was performed to obtain a connected structure for evaluation. The resulting connected structure was evaluated for "initial conduction resistance", "conduction reliability", and "short circuit occurrence rate" in the same manner as in Example 5, and good results were obtained in all of them.

In the preferred anisotropic conductive film of the present invention, the ratio of "lattice points on which conductive particles are not arranged" to all the lattice points of the plane lattice pattern assumed in the reference area is set to less than 20%, and the plane lattice pattern is The ratio of "lattice points where a plurality of conductive particles are arranged in agglomerated manner" to all the lattice points of the pattern is 5% or less. Therefore, when the anisotropic conductive film of the present invention is applied to anisotropic conductive connections, good initial conductivity and good continuity reliability after aging can be achieved, and the occurrence of short circuits can be suppressed. It is useful when making anisotropic conductive connection between a pitched IC chip and a wiring board.

10, 200 Anisotropic conductive film 11, 104 Insulating adhesive base layer 12, 105 Insulating adhesive cover layer 13, 103 Conductive particles 100 Transfer body 101 Convex portion 102 Slight adhesive layer A Grid points where conductive particles are missing B Conductive Lattice points where particles are in contact with each other and aggregate C Lattice points where conductive particles are separated from each other and aggregate

Claims (10)

An anisotropic conductive film having a structure in which conductive particles are arranged at lattice points of a planar lattice pattern on an insulating adhesive base layer,
A lattice point where no conductive particles are arranged is defined as a "missing" lattice point, a lattice point where multiple conductive particles are arranged in an agglomerated manner is defined as an "aggregated" point, the average particle diameter of the conductive particles is D, and any conductive particle is When the area within the concentric circle with a diameter of 5D centered on the area is taken as the reference area of the anisotropic conductive film,
The ratio of missing lattice points , which are lattice points where conductive particles are not placed, to all lattice points of a planar lattice pattern assumed in the reference area of the anisotropic conductive film is less than 20%,
Anisotropy in which the ratio of agglomeration, which is a lattice point where a plurality of conductive particles are arranged in agglomeration, to all lattice points of the planar lattice pattern is 15% or less, and the total of omissions and aggregation is less than 25%. conductive film. It has a structure in which an insulating adhesive cover layer is further laminated on the insulating adhesive base layer, and conductive particles are arranged at the lattice points of a planar lattice pattern near the interface between them. 2. The anisotropic conductive film according to claim 1, wherein the ratio of voids to all lattice points of the planar lattice pattern is less than 20%, and the ratio of aggregation to all lattice points of the planar lattice pattern is 5% or less. The reference area is the following relational expressions (A), (2) and (3) at the center of the plane of the anisotropic conductive film:

It is a substantially rectangular region consisting of side X and side Y that satisfy the following conditions, where D is the average particle diameter of the conductive particles, and side Y is a region within a range of less than ±45° with respect to the longitudinal direction of the anisotropic conductive film. The anisotropic conductive film according to claim 1 or 2, which is a straight line, and the side X is a straight line perpendicular to the side Y. The reference area is the following relational expressions (1) to (3) at the center of the plane of the anisotropic conductive film:

It is a substantially rectangular region consisting of side X and side Y that satisfy the following conditions, where D is the average particle diameter of the conductive particles, and side Y is a region within a range of less than ±45° with respect to the longitudinal direction of the anisotropic conductive film. The anisotropic conductive film according to claim 1 or 2, which is a straight line, and the side X is a straight line perpendicular to the side Y. The anisotropic conductive film according to any one of claims 1 to 4, wherein the particle area occupation ratio of all the conductive particles present in the area of the reference region of the anisotropic conductive film is 15 to 35%. Anisotropy according to any one of claims 1 to 5, wherein the conductive particles have an average particle diameter of 1 to 10 μm, and the distance between adjacent lattice points of the planar lattice pattern is greater than 0.5 times the average particle diameter of the conductive particles. conductive film. The following relational expression where the reference area is the center of the plane of the anisotropic conductive film:

It is a substantially rectangular region consisting of side X and side Y that satisfy the following conditions, where D is the average particle diameter of the conductive particles, and side Y is a region within a range of less than ±45° with respect to the longitudinal direction of the anisotropic conductive film. The anisotropic conductive film according to claim 1 or 2, which is a straight line, and the side X is a straight line perpendicular to the side Y. 8. The anisotropic conductive film according to claim 7, wherein the particle area occupancy of all the conductive particles present in the area of an arbitrary reference region of the anisotropic conductive film is 0.15% or more. The anisotropic conductive film according to claim 7 or 8, wherein the conductive particles have an average particle diameter of 1 to 30 μm, and the distance between adjacent lattice points of the planar lattice pattern is 0.5 times or more the average particle diameter of the conductive particles. . A connection structure in which a terminal of a first electronic component and a terminal of a second electronic component are anisotropically conductively connected by the anisotropic conductive film according to any one of claims 1 to 9.

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