JP7572638B2 - 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, etc., but it is known that in such anisotropic conductive films, the conductive particles exist in a linked or aggregated state. For this reason, when anisotropic conductive films are used to connect terminals of IC chips and terminals of wiring boards, which are becoming narrower in pitch as electronic devices become lighter and smaller, there are cases where short circuits occur between adjacent terminals due to the conductive particles existing in a linked or aggregated state in the anisotropic conductive film.

Conventionally, anisotropic conductive films that correspond to such narrow pitches have been proposed in which conductive particles are regularly arranged in a 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 biaxially stretched until the distance between the conductive particles becomes a desired distance to arrange the conductive particles regularly, and then an insulating adhesive base layer that is a component of the anisotropic conductive film is pressed against the conductive particles, and the conductive particles are transferred to the insulating adhesive base layer (Patent Document 1). In addition, an anisotropic conductive film has been proposed in which conductive particles are scattered on a recess-forming surface of a transfer mold having a recess on its surface, the recess-forming surface is squeegeeed to hold the conductive particles in the recess, an adhesive film on which an adhesive layer for transfer is formed is pressed from above, and the conductive particles are primarily transferred to the adhesive layer, and then an insulating adhesive base layer that is a component of the anisotropic conductive film is pressed against the conductive particles attached to the adhesive layer, and the conductive particles are transferred to the insulating adhesive base layer (Patent Document 2). These anisotropic conductive films generally have an insulating adhesive cover layer laminated on the surface of the conductive particles to cover the conductive particles.

WO2005/054388 JP 2010-33793 A

However, because conductive particles tend to aggregate and turn into secondary particles due to static electricity, etc., it is difficult to keep conductive particles present alone as primary particles all the time. For this reason, the techniques of Patent Document 1 and Patent Document 2 have the following problems. That is, in the case of Patent Document 1, it is difficult to densely pack conductive particles in a single layer without defects over the entire surface of the stretchable film, and the conductive particles are packed into the stretchable film in an aggregated state, which can cause short circuits or create unfilled areas (so-called "holes") that can cause poor conductivity. In the case of Patent Document 2, when the recesses of the transfer mold are covered with conductive particles with a large particle diameter, they are subsequently removed by a squeegee, resulting in recesses that do not hold the conductive particles, causing conductive particles to be "lost" in the anisotropic conductive film and resulting in poor conductivity. Conversely, if many small conductive particles are pushed into the recesses, the conductive particles will aggregate when transferred to the insulating adhesive base layer, and since the conductive particles located on the bottom side of the recesses are not in contact with the insulating adhesive base layer, they will be scattered on the surface of the insulating adhesive base layer, damaging the regular arrangement and causing short circuits and poor conductivity.

As such, the reality is that Patent Documents 1 and 2 do not fully consider how to control the "disappearance" and "aggregation" of conductive particles that should be arranged in a regular pattern on an anisotropic conductive film.

The object of the present invention is to solve the problems of the conventional technology described above, and to provide an anisotropic conductive film in which the occurrence of short circuits and poor electrical continuity is greatly suppressed from the viewpoint of "missing" and "aggregation" of conductive particles that should be arranged in a regular pattern.

The inventors discovered that when arranging conductive particles at the lattice points of a planar lattice, the above-mentioned object can be achieved by controlling the "proportion of lattice points where conductive particles are not arranged" and the "proportion of lattice points where conductive particles are arranged in agglomeration" with respect to all lattice points of a planar lattice pattern assumed in any reference region of an anisotropic conductive film, and thus completed the present invention. In addition, the inventors discovered that such an anisotropic conductive film can be manufactured by adhering conductive particles to the tips of columnar convex portions formed on the surface of a transfer body and transferring the conductive particles, rather than arranging conductive particles in the concave portions of the transfer body, and thus 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 at which conductive particles are not arranged to all lattice points of a planar lattice pattern assumed in a reference region 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 arranged in an aggregated manner to the total lattice points of the planar lattice pattern is 15% or less, and the total of the voids and aggregates is less than 20%.

In addition, the present invention provides a method for manufacturing an anisotropic conductive film, the ratio of lattice points at which conductive particles are not arranged to all lattice points of a planar lattice pattern assumed in a reference region of the anisotropic conductive film being less than 5%;
The present invention provides an anisotropic conductive film in which the ratio of lattice points where a plurality of conductive particles are arranged in an aggregated manner to the total lattice points of the planar lattice pattern is more than 10% and less than 15%. In this case, too, the sum of the voids and the aggregates is preferably less than 20%.

The present invention also provides a method for producing the above-mentioned 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 in the vicinity of the interface between them, the method comprising the steps of (a) to (e):
<Step (A)>
A step of preparing a transfer body having a surface on which columnar protrusions corresponding to the lattice points of the planar lattice pattern are formed;
<Step (b)>
a step of forming a weak adhesive layer on at least the top surface of the convex portion of the transfer body;
<Step (C)>
A step of attaching conductive particles to the slightly adhesive layer of the convex portion of the transfer body;
<Step (D)>
a step of placing an insulating adhesive base layer on the surface of the transfer body on which the conductive particles are attached and pressing the insulating adhesive base layer against the surface, thereby transferring the conductive particles to the insulating adhesive base layer; and <step (e)>
The present invention provides a manufacturing method including a step of laminating an insulating adhesive cover layer onto the insulating adhesive base layer onto which the conductive particles have been transferred, from the conductive particle-transferred surface side.

The present invention further 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 where no conductive particles are arranged" to all lattice points of the planar lattice pattern assumed in the reference region is set to less than 20%, the ratio of lattice points where multiple conductive particles are arranged in agglomeration to all lattice points of the planar lattice pattern is set to 15% or less, and the sum of missing and agglomerated particles is set to less than 20%. Therefore, when the anisotropic conductive film of the present invention is applied to an anisotropic conductive connection, good initial conductivity (initial conductive resistance value) and good conductive reliability after aging can be achieved, and the occurrence of short circuits can be suppressed. In addition, it is economical not only for COG, but also for electronic components with sufficiently large bump areas and distances, such as FOG.

In a preferred anisotropic conductive film of the present invention, the ratio of "lattice points where no conductive particles are arranged" to all lattice points of a planar lattice pattern assumed in any reference region is set to less than 5%, and the ratio of "lattice points where multiple conductive particles are arranged in agglomeration" is set to more than 10% and less than 15%. Therefore, when the anisotropic conductive film of the present invention is applied to an anisotropic conductive connection, it is possible to achieve a good initial conductive resistance value and good conductive reliability after aging, and also to suppress the occurrence of short circuits.

In addition, in the manufacturing method of the anisotropic conductive film of the present invention, a transfer body having a surface formed with columnar convex portions corresponding to the lattice points of the planar lattice pattern is used, and conductive particles are attached to a micro-adhesive layer formed on the top surface of the convex portions, and then the conductive particles are transferred to an insulating adhesive base layer. Therefore, the ratio of "lattice points where no conductive particles are arranged" to all lattice points of the planar lattice pattern assumed in any reference region of the anisotropic conductive film can be made less than 5%, and the ratio of "lattice points where multiple conductive particles are arranged in agglomeration" to all lattice points of the planar lattice pattern can be made more than 10% and less than 15%. Therefore, the manufacturing method of the present invention can manufacture an anisotropic conductive film economically, and by using this anisotropic conductive film, an anisotropic conductive connection can be made between a narrow-pitched IC chip and a wiring board while greatly suppressing the occurrence of short circuits and poor conduction.

FIG. 1 is a cross-sectional view of an anisotropic conductive film of the present invention. FIG. 2A is a plan view perspective view of an anisotropic conductive film of the present invention. FIG. 2B is a partially enlarged plan 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 is also 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 at the lattice points of a planar lattice pattern near the interface between them. The ratio of lattice points at which no conductive particles are arranged to all lattice points of the planar lattice pattern assumed in the reference region of this anisotropic conductive film is less than 20%, and the ratio of lattice points at which multiple conductive particles are arranged in an aggregated manner to all lattice points of the planar lattice pattern is 15% or less, and the sum of missing and aggregated particles is less than 20%. The anisotropic conductive film of the present invention will be described in detail below with reference to the drawings.

<Anisotropic Conductive Film>
As shown in FIG. 1 (cross-sectional view) and FIG. 2A and FIG. 2B (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 laminated, and conductive particles 13 are arranged at the lattice points of a planar lattice pattern (dotted lines in FIG. 2A and FIG. 2B) near the interface between them. In FIG. 1, FIG. 2A, and FIG. 2B, the planar lattice pattern is assumed along the longitudinal direction of the anisotropic conductive film 10 and the direction perpendicular thereto (short side direction), but it may be assumed to be inclined as a whole with respect to the longitudinal direction and the short side direction. Here, arrow A indicates a position where a conductive particle is not arranged at the lattice point of the planar lattice, that is, a position where a conductive particle is "missing". Note that arrow B indicates a position where conductive particles are in contact with each other and aggregated (connected), and arrow C indicates a position where conductive particles are aggregated without contact. Here, "aggregated without contact" means that conductive particles are close to each other within a range not exceeding 25% of the average particle diameter of the conductive particles.

(Loss of conductive particles)
In the anisotropic conductive film of the present invention, the ratio of "lattice points where no conductive particles are arranged" (A in FIG. 2A) (the ratio of lattices where conductive particles are missing) to all lattice points of a planar lattice pattern assumed in any reference region of the anisotropic conductive film is set to less than 5%, preferably 4% or less, and more preferably 1% or more and 4% or less. As a result, when the anisotropic conductive film of the present invention is applied to an anisotropic conductive connection, good initial conductive resistance and good conductive reliability after aging can be achieved, and the occurrence of short circuits can also be suppressed.

(Plane grid pattern)
Examples of planar lattice patterns include an oblique lattice, a hexagonal lattice, a square lattice, a rectangular lattice, and a parallelepiped lattice. Among these, a hexagonal lattice that allows closest packing is preferred.

Here, it is possible to select the entire surface of the anisotropic conductive film as the reference region of the anisotropic conductive film, but it is usually preferable to select as the reference region a substantially rectangular region consisting of sides X and Y in the planar central portion of the anisotropic conductive film that satisfies the following relational formula (A), preferably relational formula (1) and relational formulas (2) and (3).

When applied to c-connection, which allows for a relatively large connection area, it is possible to reduce the amount of conductive particles in the film. In such cases, as shown below, it is preferable to increase the values of X and Y, preferably to 20D or more, and the value of "X+Y" is also preferably between 100D and about 400D, ultimately to 400D.

In the formulas (A) and (1) to (3), 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 also be measured by surface observation. 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. 2A), 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 or approximate to the shape of the bump against which the conductive particles are pressed, and as a result, the allowable range of deviation of the conductive particles from the planar lattice pattern can be increased, making it possible to economically and stably perform anisotropic conductive connection. In other words, by making the smallest side of this reference area at least five times the conductive particle diameter, even if the conductive particles are misaligned, missing, or close to each other within this range, they will be captured by one of the bumps and will not excessively aggregate in the space between the bumps, so that anisotropic conductive connection can be reliably performed.

The reason why the minimum side is set to 5 times or more the conductive particle diameter is that, in general, at least one side of the bump connected by anisotropic conductive connection needs to be larger than the average particle diameter of the conductive particles to ensure capture, and the space between the bumps also needs to be preferably at least twice the average particle diameter of the conductive particles to prevent short circuits. In other words, when focusing on a circular conductive particle as a standard, if no unexpected defects occur within a concentric circle whose diameter is the average particle diameter D of the conductive particles plus four times the length (4D) of that diameter (i.e., 5D), the above requirement can be met. Also, 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)
In the anisotropic conductive film of the present invention, the ratio of the lattice points (arrows B and C in FIG. 2A) where a plurality of conductive particles are arranged in an aggregated manner to all the lattice points of the planar lattice pattern is preferably 15% or less, and may be more than 10% but less than 15%, and there is no practical problem if it is 11% or more and 14% or less. If the ratio of the aggregated arrangement lattice points is within this range, even when the anisotropic conductive film of the present invention is applied to an anisotropic conductive connection, better initial conductivity and conductive reliability after aging can be realized, and the occurrence of short circuits can be further suppressed. Here, the state in which conductive particles are aggregated together includes not only the case where they are directly connected as shown by arrow B in FIG. 2A, but also the case where conductive particles are not directly connected to each other but are very close to each other as shown by arrow C in FIG. 2A. The distance between the conductive particles is preferably within 25% of the average particle diameter of the conductive particles. In addition, the degree of aggregation of conductive particles at one lattice point may be such that more than two conductive particles are connected in a chain shape, but from the viewpoint of suppressing short circuits, it is preferable that the aggregation is small, and it is preferable that more than two conductive particles do not aggregate.

In the present invention, the direction of aggregation of the conductive particles arranged in an aggregated state (usually the direction of a line connecting the centers of gravity of each of the two aggregated conductive particles) is shifted in the thickness direction, and is inclined toward the plane direction of the anisotropic conductive film, as shown by arrows B and C in Figure 1. The degree of inclination is preferably 5 to 45 degrees, more preferably 10 to 40 degrees, so as not to hinder the pushing when connecting. The reason for this inclination is that if the conductive particles are present at the end of the bump when connecting, they can be captured on at least one side (if they overlap without being inclined, it will affect the pushing). There is no particular problem if the aggregation is horizontal.

(Arrangement of Conductive Particles)
The conductive particles are preferably arranged in a continuous array of 11 or more particles in a direction perpendicular to the longitudinal direction of the film, and more preferably arranged in a continuous array of 13 or more particles. This is because if conductive particles are missing in the longitudinal direction of the bump, this may cause problems with the anisotropic conductive connection. In this case, it is preferable that the above condition be satisfied in all three consecutive rows along the longitudinal direction of the film, and more preferably that the above condition be satisfied in all five rows. This allows the number of conductive particles captured by the bump to be greater than or equal to a certain level, and a stable anisotropic conductive connection can be achieved.

When the conductive particles are agglomerated, it is preferable that there are no more than three pairs of connected conductive particles around each pair of agglomerated conductive particles, more preferably no more than two, and even more preferably no more than one. This is because if two agglomerated conductive particles are present in a dense arrangement, this can cause a short circuit. It is preferable that there are no more than three agglomerated conductive particles in a row in one direction of the arrangement, while still satisfying the above conditions.

It is also preferable that four or more consecutive conductive particle voids in the longitudinal direction of the film do not intersect with four or more consecutive conductive particle voids in a direction perpendicular to the longitudinal direction of the film, and it is more preferable that any of the four or more consecutive voids are not adjacent to one another via conductive particles that form one or more lattice points, and it is even more preferable that any of the four or more consecutive voids are not adjacent to one another via conductive particles that form two or more lattice points. There is no problem if up to three rows of such voids intersect simultaneously with voids in one direction. If the voids are not continuous beyond this, they will be captured by the bump by the conductive particles nearby.

It is generally not desirable to have multiple areas where consecutive gaps intersect in the vicinity, but as long as there is an arrangement of conductive particles equal to or greater than the number of gaps, there will be no problem with the stability of the anisotropic conductive connection.

Furthermore, as shown in FIG. 2B, it is preferable that the distance L between the lattice point P1 at which the aggregated conductive particles 13 are arranged and the center P2 of the circle inscribed in the aggregated conductive particles 13 be 25% or less of the average particle diameter of the conductive particles in terms of preventing short circuits.

(Particle Area Occupancy Rate)
Furthermore, the particle area occupancy rate of all conductive particles present in an arbitrary reference region of the anisotropic conductive film is usually 0.15% or more, preferably 0.35% or more, and more preferably 1.4% or more, when the bump size and the distance between the bumps are relatively large, such as in FOG connection. In this case, the upper limit is preferably 35% or less, more preferably 32% or less. In addition, when the bump size and the distance between the bumps are relatively small (for example, COG connection), it is more preferably 15 to 35%, particularly preferably 20 to 25%. Within this range, even when the anisotropic conductive film of the present invention is applied to an anisotropic conductive connection, better initial conductivity and conductivity reliability after aging can be achieved, and the occurrence of short circuits can be further suppressed. Here, the particle area occupancy rate is the ratio of the area occupied by all conductive particles present in an arbitrary reference region to the area S of the reference region. The area occupied by all 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.

Incidentally, when the average particle diameter of the conductive particles is 2 μm, the number density is 500/ ^mm2 (0.0005/ ^μm2 ), X=Y=200D, and X+Y=400D, the calculated particle area occupancy is 0.157%. When the average particle diameter of the conductive particles is 3 μm, the number density is 500/ ^mm2 (0.0005/ ^μm2 ), X=Y=200D, and X+Y=400D, the calculated particle area occupancy is 0.35325%. When the average particle diameter of the conductive particles is 3 μm, the number density is 2000/ ^mm2 (0.002/ ^μm2 ), X=Y=200D, and X+Y=400D, the calculated particle area occupancy is 1.413%. Furthermore, when the average particle diameter of the conductive particles is 30 μm, the particle 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)
The conductive particles may be appropriately selected from those used in known anisotropic conductive films. Examples include metal particles such as nickel, copper, silver, gold, and palladium, and metal-coated resin particles in which the surfaces of resin particles such as polyamide and polybenzoguanamine are coated with a metal such as nickel. The average particle size is preferably 1 to 30 μm, more preferably 1 to 10 μm, and particularly preferably 2 to 6 μm, from the viewpoint of ease of handling during production. The average particle size can be measured by an image-type or laser-type particle size distribution meter, 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 usually 300 to 40,000 particles/mm ² .

(distance between adjacent lattice points)
Furthermore, the distance between adjacent lattice points in a planar lattice pattern assumed for the anisotropic conductive film is preferably greater than 0.5 times the average particle size of the conductive particles, more preferably at least 1 time, and even more preferably from 1 to 20 times. Within this range, even when the anisotropic conductive film of the present invention is applied to an anisotropic conductive connection, better initial conductivity and conductive reliability after aging can be achieved, and the occurrence of short circuits can be further 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 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 the like, or a cured resin layer thereof can be used. In addition, these resin layers can contain appropriately selected silane coupling agents, pigments, antioxidants, ultraviolet absorbers, etc., as necessary.

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

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

(Insulating Adhesive Cover Layer)
The insulating adhesive cover layer 12 may be appropriately selected from those used as insulating adhesive cover layers in known anisotropic conductive films, and may be made of the same material as the insulating adhesive base layer 11 described above.

The insulating adhesive cover layer 12 can be formed by applying a coating composition containing the resin described above and drying or curing the composition, or by forming the composition into a film using a known method.

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

Furthermore, insulating fillers such as silica fine particles, alumina, and aluminum hydroxide may be added to the insulating adhesive base layer 11 and the insulating adhesive cover layer 12 as necessary. The amount of insulating filler is preferably 3 to 40 parts by mass per 100 parts by mass of the resin that constitutes these layers. This makes it possible to prevent the conductive particles 2 from moving unnecessarily due to the molten resin, even if the insulating adhesive layer 10 melts during anisotropic conductive connection.

(Lamination of insulating adhesive base layer and insulating adhesive cover layer, embedding of conductive particles)
In addition, when the insulating adhesive base layer 11 and the insulating adhesive cover layer 12 are laminated with the conductive particles 13 sandwiched therebetween, this can be done by a known method. In this case, the conductive particles 13 are present near the interface between these layers. Here, "present near the interface" means that a part of the conductive particles is embedded in one layer, and the remaining part is embedded in the other layer. The conductive particles may also be embedded in the insulating adhesive base layer. In this case, it can be formed without laminating the insulating adhesive cover layer.

<Production of anisotropic conductive film>
Next, a method for producing an anisotropic conductive film of the present invention having a structure in which an insulating adhesive base layer and an insulating adhesive cover layer are laminated and conductive particles are arranged at the lattice points of a planar lattice pattern near the interface between them will be described. This production method includes the following steps (a) to (e). Each step will be described in detail with reference to the drawings. Note that the present invention is not particularly limited to this production method.

(Step (A))
First, as shown in FIG. 3A, a transfer body 100 is prepared on the surface of which are formed columnar convex portions 101 corresponding to the lattice points of a planar lattice pattern. The columnar shape includes a cone. It is preferably a cylindrical shape. The height of the convex portion 101 can be determined according to the terminal pitch to be anisotropically conductively connected, the terminal width, the space width, the average particle diameter of the conductive particles, etc., and is preferably 2 times or more and less than 4 times the average particle diameter of the conductive particles used. In addition, the width of the convex portion 101 (width at half height) is preferably 1.4 times or more and 3.6 times or less than the average particle diameter of the conductive particles. If the height and width are within these ranges, the effect of not excessively dropping out and only sporadic dropping out can be obtained.

Furthermore, the protrusion 101 has a substantially flat top surface to which the conductive particles can be stably attached.

*Specific examples of the transfer body The transfer body to be prepared in this step (a) can be produced using a known method, for example, by processing a metal plate to produce a master, applying a curable resin to it, and curing it. Specifically, a transfer body master in which recesses corresponding to the protrusions are formed is also produced by cutting a flat metal plate, and the resin composition constituting the transfer body is applied to the recessed surface of this master, cured, and then separated from the master to obtain the transfer body.

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

*Weakly adhesive layer of transfer body The weakly adhesive layer 102 is a layer that exhibits an adhesive force capable of temporarily holding the conductive particles until the conductive particles are transferred to the insulating adhesive base layer constituting the anisotropic conductive film, and is formed on at least the top surface of the convex portion 101. Therefore, the entire convex portion 101 may be weakly adhesive. The thickness of the weakly adhesive layer 102 can be appropriately determined according to the material of the weakly adhesive layer 102, the particle diameter of the conductive particles, etc. In addition, "weakly adhesive" means that the adhesive force is weaker than that of the insulating adhesive base layer when the conductive particles are transferred to the insulating adhesive base layer.

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

(Step (C))
3C, conductive particles 103 are attached to the weak adhesive layer 102 of the convex portions 101 of the transfer body 100. Specifically, the conductive particles 103 are dispersed from above the convex portions 101 of the transfer body 100, and the conductive particles 103 that do not adhere to the weak adhesive layer 102 are blown away with a blower. In this case, in some of the convex portions 101, the conductive particles adhere to the side surfaces due to the action of static electricity or the like with a certain frequency, and furthermore, it occurs that the conductive particles cannot be removed by the blower.

It is also possible to reverse the direction of the surface from FIG. 3C and attach the top surfaces of the protrusions to the surface that is covered with conductive particles. This is to avoid applying unnecessary stress to the conductive particles. By attaching only the conductive particles necessary for placement to the top surfaces of the protrusions in this way, the conductive particles can be easily recovered and reused, and this is more economical than a method in which conductive particles are filled into an opening and then removed. However, when filling conductive particles into an opening and then removing them, there is a concern that unnecessary stress may be applied to the conductive particles that are not filled.

In FIG. 3C, the width of the weak adhesive layer 102 of the left half of the convex portion 101 is adjusted to be narrower than that of the weak adhesive layer 102 of the right half of the convex portion 101. As a result, as shown in FIG. 3C, there may be differences in the aggregation state of the conductive particles 103 between the left half and the right half.

(Step (D))
Next, as shown in Fig. 3D, the insulating adhesive base layer 104 that is to constitute the anisotropic conductive film is placed on the surface of the transfer body 100 on which the conductive particles 103 are attached and pressed, thereby transferring the conductive particles 103 to one side of the insulating adhesive base layer 104 (Fig. 3E). In this case, it is preferable to place the transfer body 100 on the insulating adhesive base layer 104 and press it so that the convex parts 101 face downward. By blowing with the transfer body facing downward, it is possible to easily remove the conductive particles that are not attached to the top surface of the convex parts.

(Step (E))
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 conductive particle transfer surface side, thereby obtaining an anisotropic conductive film 200 of the present invention.

<Connection structure>
The anisotropic conductive film of the present invention is disposed between a terminal (e.g., a bump) of a first electronic component (e.g., an IC chip) and a terminal (e.g., a bump, pad) of a second electronic component (e.g., a wiring board), and is fully cured by thermocompression bonding from the first or second electronic component side to form an 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 conductivity are suppressed.

The present invention will be described in detail below.

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

A photopolymerizable resin composition containing 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 2 parts by mass of photopolymerization initiator (IRGACURE184, BASF Japan Ltd.) was applied to the resulting transfer master on a PET (polyethylene terephthalate) film to a dry thickness of 30 μm, and the resulting film was dried at 80°C for 5 minutes, after which it was irradiated with 1000 mJ of light from a high-pressure mercury lamp to create a transfer master.

The transfer body was peeled off from the master and wound around a stainless steel roll with a diameter of 20 cm so that the convex parts were on the outside. While rotating the roll, a weak adhesive composition containing 70 parts by mass of epoxy resin (jER828, Mitsubishi Chemical Corporation) and 30 parts by mass of phenoxy resin (YP-50, Nippon Steel & Sumikin Chemical Co., Ltd.) was brought into contact with the adhesive sheet impregnated into the nonwoven fabric, and the weak adhesive composition was attached to the top surface of the convex parts, forming a weak adhesive layer with a thickness of 1 μm to obtain the transfer body.

Conductive particles (nickel-plated resin particles (AUL704, Sekisui Chemical Co., Ltd.)) with an average particle size of 4 μm were sprayed onto the surface of this transfer body, and then the conductive particles that were not attached to the slightly adhesive layer were removed by blowing.

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

On the conductive particle transfer surface of the obtained insulating adhesive base layer, another insulating adhesive film in sheet form having a thickness of 15 μm was layered as a transparent insulating adhesive cover layer (a film formed from an insulating adhesive composition containing 60 parts by mass of phenoxy resin (YP-50, Nippon Steel & Sumikin Chemical Co., Ltd.), 40 parts by mass of epoxy resin (jER828, Mitsubishi Chemical Co., Ltd.), and 2 parts by mass of cationic curing agent (SI-60L, Sanshin Chemical Industry Co., Ltd.)), and laminated 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 amount of conductive particles dispersed and the number of blower cycles were doubled compared to Example 1.

Example 3
An anisotropic conductive film was obtained by repeating the procedure of Example 1, except that the cylindrical recesses of the transfer body master had an inner diameter of 4.5 μm and a depth of 7.5 μm, the distance between the centers of adjacent recesses was 6 μm, the density of the recesses ^was 28,000 pieces/mm2, and conductive particles having an average particle diameter of 3 μm (AUL703, Sekisui Chemical Co., Ltd.) were used instead of the conductive particles having an average particle diameter of 4 μm.

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

Comparative Example 1
An anisotropic conductive film was obtained by repeating Example 1, except that the depth of the recesses in the transfer master was 4.4 μm, the inner diameter of the recesses was 4.8 μm, the distance between the centers of adjacent recesses was 5.6 μm, and the density of the recesses was 32,000 pcs/ ^mm2 .

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

<Evaluation>
(Disappearance and aggregation of conductive particles)
For the anisotropic conductive films of Examples 1 to 4 and Comparative Examples 1 and 2, a 1 cm square area was observed from the transparent insulating adhesive cover layer side with an optical microscope (MX50, Olympus Corporation), and the ratio of lattice points to all lattice points to which no conductive particles were attached (missing points [%)) in an assumed planar lattice pattern, and the ratio of lattice points to all lattice points to which two or more conductive particles were aggregated, were examined. The results are shown in Table 1.

The maximum distance between the aggregated conductive particles (aggregation distance) was also measured and is shown in Table 1. Note that the "aggregation" direction was the horizontal direction of the anisotropic conductive film in all cases.

(Particle Area Occupancy Rate)
The particle area occupancy was calculated from the average particle diameter of the conductive particles and the concave density of the transfer body master (=convex density of the transfer body), taking into consideration the "dropout" and "aggregation" of the conductive particles. The obtained results are shown in Table 1.

(Initial Conduction Resistance)
Using the anisotropic conductive films of the examples and comparative examples, an IC chip having gold bumps of 15 μm height and 30 μm×50 μm with a bump spacing of 12 μm was anisotropically conductively connected to a glass substrate having wiring spaced 12 μm apart at 180° C., 60 MPa, and 5 seconds to obtain a connection structure. The initial conduction resistance of the connection structure obtained was measured using a resistance measuring device (digital multimeter 7565, Yokogawa Electric Corporation). The results are shown in Table 1. It is desirable that the resistance be 0.5Ω or less.

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

(Short circuit occurrence rate)
The same connection structure as that used for the initial conductive resistance was fabricated, and the occurrence of short circuits between adjacent wirings was examined. The results are shown in Table 1. It is desirable that the rate of occurrence of short circuits is 50 ppm or less.

The results in Table 1 show that the connection structures using the anisotropic conductive films of Examples 1 to 4 showed good results in the evaluation items of initial conductive resistance, conductive reliability, and short circuit occurrence rate.

On the other hand, in the case of the anisotropic conductive films of Comparative Examples 1 and 2, although the rate of "missing" conductive particles was low, the rate of "aggregation" was too high, resulting in a short circuit occurrence rate that far exceeded 50 ppm.

Example 5
A transfer body was produced 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/ ^mm2 , and an anisotropic conductive film was also produced. For the obtained anisotropic conductive film, the "missing" and "aggregation" of 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 "aggregation" of conductive particles were found to be the same as in Example 2. In addition, the particle area occupancy was 0.7%.

The anisotropic conductive film obtained was sandwiched between a glass substrate (ITO solid electrode) and a flexible wiring substrate (bump width: 200 μm, L (line) / S (space) = 1, wiring height 10 μm), and anisotropic conduction was performed under conditions of 180 ° C, 80 MPa, and 5 seconds so that the connection bump length was 1 mm, to obtain a connection structure for evaluation. The "initial conduction resistance value" of the obtained connection structure and its "conductivity reliability" after being placed in a thermostatic chamber at a temperature of 85 ° C and a humidity of 85% RH for 500 hours were measured by a four-terminal method with a digital multimeter (34401A, manufactured by Agilent Technologies, Inc.) at a current of 1 A. In the case of the "initial conduction resistance value," a measured value of 2 Ω or less was evaluated as good, and a value exceeding 2 Ω was evaluated as bad. In the case of the "conductivity reliability," a measured value of 5 Ω or less was evaluated as good, and a value of 5 Ω or more was evaluated as bad. As a result, all of the connection structures in Example 5 were evaluated as "good." In addition, when the "short circuit occurrence rate" was measured in the same manner as in Example 2, good results were obtained, similar to Example 2.

Example 6
A transfer body was produced 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/ ^mm2 , and an anisotropic conductive film was also produced. For the obtained anisotropic conductive film, the "missing" and "aggregation" of 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 "aggregation" of conductive particles were found to be equivalent to those in Example 2. In addition, the particle area occupancy was 2.7%.

The resulting anisotropic conductive film was sandwiched between a glass substrate and a flexible wiring substrate in the same manner as in Example 5 to form an anisotropic conductive connection, thereby obtaining a connection structure for evaluation. The resulting connection structure was evaluated for "initial conductive resistance value," "conductivity reliability," and "short circuit occurrence rate" in the same manner as in Example 5, and good results were obtained in all cases.

In a preferred anisotropic conductive film of the present invention, the ratio of "lattice points where no conductive particles are arranged" to all lattice points of a planar lattice pattern assumed in any reference region is set to less than 5%, and the ratio of "lattice points where multiple conductive particles are arranged in agglomeration" to all lattice points of a planar lattice pattern is more than 10% and less than 15%. Therefore, when the anisotropic conductive film of the present invention is applied to an anisotropic conductive connection, good initial conductivity and good conductive reliability after aging can be achieved, and the occurrence of short circuits can be suppressed, making it useful when anisotropically conductively connecting a narrow-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 Slightly adhesive layer A Position where no conductive particles are arranged at the lattice points (position where no conductive particles are arranged)
B: Position where conductive particles are in contact with each other and aggregated. C: Position where conductive particles are not in contact with each other and aggregated. P1: Lattice point where aggregated conductive particles are arranged. P2: Center of circle inscribed in aggregated conductive particles. L: Distance between P1 and P2.

Claims (14)

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 at which conductive particles are not arranged to all lattice points of a planar lattice pattern assumed in a reference region of the anisotropic conductive film is less than 20%;
the ratio of lattice points where a plurality of conductive particles are arranged in an aggregated manner to all lattice points of the planar lattice pattern is 15% or less, and the sum of the voids and the aggregates is less than 20%,
When the conductive particles are aggregated, the number of pairs of two connected conductive particles around two aggregated conductive particles is three or less;
In each of three consecutive rows along the longitudinal direction of the anisotropic conductive film in a planar grid pattern, 11 or more conductive particles are consecutively arranged in a direction perpendicular to the longitudinal direction of the film,
The reference region is a region at the center of the plane of the anisotropic conductive film that satisfies the following relations (A), (2), and (3):

wherein D is the average particle diameter of the conductive particles, side Y is a straight line within a range of less than ±45° with respect to the longitudinal direction of the anisotropic conductive film, and side X is a straight line perpendicular to side Y. 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 at which conductive particles are not arranged to all lattice points of a planar lattice pattern assumed in any reference region of the anisotropic conductive film is less than 5%;
a ratio of lattice points at which a plurality of conductive particles are arranged in an aggregated manner to all lattice points of the planar lattice pattern is more than 10% and less than 15%;
When the conductive particles are aggregated, the number of pairs of two connected conductive particles around two aggregated conductive particles is three or less;
In each of three consecutive rows along the longitudinal direction of the anisotropic conductive film in a planar grid pattern, 11 or more conductive particles are consecutively arranged in a direction perpendicular to the longitudinal direction of the film,
The reference region is a region at the center of the plane of the anisotropic conductive film, and the region satisfies the following relations (A), (2), and (3):

wherein D is the average particle diameter of the conductive particles, side Y is a straight line within a range of less than ±45° with respect to the longitudinal direction of the anisotropic conductive film, and side X is a straight line perpendicular to side Y. 3. The anisotropic conductive film according to claim 1, wherein the sum of X and Y is 100D. 4. The anisotropic conductive film according to claim 1 , wherein the particle area occupancy rate of all conductive particles present in an arbitrary reference region of the anisotropic conductive film is 15 to 35% of the area of the reference region. 5. The anisotropic conductive film according to claim 1 , wherein the conductive particles have an average particle size of 1 to 10 μm, and the distance between adjacent lattice points in the planar lattice pattern is greater than 0.5 times the average particle size of the conductive particles. 6. The anisotropic conductive film according to claim 1 , wherein the direction of aggregation of the conductive particles arranged in an aggregated state is inclined with respect to the planar direction of the anisotropic conductive film. 7. The anisotropic conductive film according to claim 1, wherein the distance between the lattice points at which the agglomerated conductive particles are arranged and the center of a circle inscribed in the agglomerated conductive particles is 25% or less of the average particle diameter of the conductive particles. 4. The anisotropic conductive film according to claim 1, wherein the particle area occupancy rate of all conductive particles present in an arbitrary reference region of the anisotropic conductive film is 0.15% or more with respect to the area of the reference region. 9. The anisotropic conductive film according to claim 8 , wherein the conductive particles have an average particle size of 1 to 30 μm, and the distance between adjacent lattice points in the planar lattice pattern is greater than 0.5 times the average particle size of the conductive particles. 10. The anisotropic conductive film according to claim 1, further comprising an insulating adhesive cover layer laminated on the insulating adhesive base layer. 11. The anisotropic conductive film according to claim 10 , wherein conductive particles are arranged at lattice points of a planar lattice pattern in the vicinity of the interface between the insulating adhesive base layer and the insulating adhesive cover layer. An anisotropic conductive film according to any one of claims 1 to 11, wherein, when conductive particles are missing, four or more consecutive missing particles in the longitudinal direction of the anisotropic conductive film do not intersect with four or more consecutive missing particles in a direction perpendicular to the longitudinal direction of the anisotropic conductive film. A connection structure in which a terminal of a first electrical component and a terminal of a second electrical component are anisotropically conductively connected by the anisotropic conductive film according to any one of claims 1 to 12 . A method for manufacturing a connection structure, comprising: disposing the anisotropic conductive film according to any one of claims 1 to 12 between a terminal of a first electrical component and a terminal of a second electrical component; and bonding the two together by pressure bonding to form an anisotropic conductive connection.

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