Conductive film, connection structure and manufacturing method for the same

Abstract

The conductive film 100 of the present invention has an insulating resin layer having a first resin layer 10, a second resin layer 20, and a third resin layer 30 sequentially stacked. During conductive or anisotropic conductive connections, the conductive film 100 can suppress short circuits by inhibiting the movement of conductive particles accompanying resin flow, thereby improving the connection reliability of the connection structure. The lowest melt viscosity of each layer, from highest to lowest, is the second resin layer 20, the first resin layer 10, and the third resin layer 30. A plurality of conductive particles 40 are dispersed in the insulating resin layer and are held at least by the first resin layer 10 and the second resin layer 20. When the thickness of the first resin layer 10 is set to Tt, the thickness of the second resin layer 20 is set to Tc, and the average particle size of the conductive particles 40 is set to D, the conductive film 100 satisfies the relationship of equation (1): [Equation 1].

Description

Technical Field

[0001] This invention relates to a conductive film, a connection structure using the conductive film, and a method for manufacturing the same. Prior Technology

[0002] Conductive films, obtained by dispersing a large number of conductive particles in an insulating resin layer, are widely used in the packaging of electronic components such as IC chips or micro LEDs. These conductive films include those with conductive directions not limited to a specific direction and those with conductive directions limited to a fixed direction; the latter, i.e., those with conductive directions limited to a fixed direction, are known as anisotropic conductive films. In conductive films, conductive particles are dispersed at a high density in the insulating resin layer to cope with high packaging density. However, increasing the number density of conductive particles, especially in the case of anisotropic conductive films, can become a significant cause of short circuits.

[0003] To ensure the reliability of anisotropic conductive connections and suppress short circuits, it is proposed to carry conductive particles in an insulating resin layer with a multilayered structure. For example, an anisotropic conductive film is proposed in which conductive particles are arranged in a monolayer on one side of a photopolymerizable resin layer, and the conductive particles are fixed to the photopolymerizable resin by irradiation with ultraviolet light. Then, an intermediate insulating resin layer is placed around the fixed conductive particles as a stress-relieving layer applied to the conductive particles, and a polymerizable resin layer polymerized by heat or light is deposited on top of it (Patent Document 1).

[0004] Furthermore, an anisotropic conductive film is proposed, which is composed of an insulating substrate layer, an intermediate layer, and an adhesive layer, so that the conductive particles are retained in either the adhesive layer or the intermediate layer, and the melt viscosity of the intermediate layer and the adhesive layer is higher than the melt viscosity of the insulating substrate layer, and the elastic modulus of the anisotropic conductive film after thermal polymerization is higher than a specific value (Patent Document 2). [Previous Technical Documents] [Patent Literature]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2015-147823 [Patent Document 2] Japanese Patent Application Publication No. 2017-22017 Summary of the Invention

[0006] [The problem that the invention aims to solve]

[0007] When using conductive films for conductive connections, heating and pressurization can cause relatively large resin flow in the insulating resin layer. Conductive particles can easily move along the direction of this resin flow, potentially reducing the reliability of the connection structure. Even when the conductive particles are neatly arranged in anisotropic conductive films, the arrangement can be disrupted by the resin flow. Furthermore, conductive particles can enter between adjacent protruding electrodes (hereinafter sometimes referred to as "bumps") as the resin flows, causing short circuits and further reducing the reliability of the connection structure.

[0008] While patent documents 1 and 2, as prior art, also noted the influence of resin flow during anisotropic conductive connections, the primary purpose of the intermediate insulating resin layer in patent document 1 was to alleviate stress on conductive particles, and the intermediate layer in patent document 2 similarly did not adequately address the function of suppressing conductive particles from entering between adjacent bumps.

[0009] Furthermore, in recent years, connections have become more diverse, and there are situations where terminal configurations cannot be considered anisotropic conductive connections. For example, even if a conductive film is attached to a terminal, the distance between the terminals may be very close. Therefore, in such cases, there are concerns about issues such as short circuits or poor conductivity between terminals, which are the same problems as with anisotropic conductive films.

[0010] Therefore, the purpose of this invention is to provide a conductive film that can suppress the occurrence of short circuits by inhibiting the movement of conductive particles accompanying resin flow during conductive connection, thereby improving the connection reliability of the connection structure. [Technical means to solve the problem]

[0011] The inventors have discovered that by constructing an insulating resin layer as a laminated structure having at least three layers, including a first resin layer, a second resin layer, and a third resin layer, and by making the second resin layer, which is located in the middle, a high-viscosity layer with a relatively high minimum melt viscosity, the total thickness (Tt+Tc) of the first and second resin layers is within a specific range in relation to the average particle size of the conductive particles. As a result, even if resin flow occurs during conductive connection, the influence of resin flow is mitigated by the second resin layer, and the movement of conductive particles can be suppressed, thus completing the present invention.

[0012] That is, the present invention provides a conductive film and an anisotropic conductive film, the conductive film and the anisotropic conductive film comprising: an insulating resin layer having a laminated structure in which a first resin layer, a second resin layer and a third resin layer are sequentially stacked; and conductive particles dispersed in the insulating resin layer. Furthermore, in the present invention, the conductive film includes anisotropic conductive films; however, even the same conductive film may sometimes be considered as a conductive film exhibiting isotropic conductivity, and sometimes as an anisotropic conductive film exhibiting anisotropic conductivity, depending on the object being connected. Also, it should be noted that, considering the technological advancements in recent years regarding the increasing complexity of electrode configurations or arrangements in electronic components, it may be difficult to strictly distinguish between these.

[0013] In the conductive film of this invention, the lowest melt viscosity of each layer in the insulating resin layer, from highest to lowest, is: second resin layer > first resin layer > third resin layer, and the lowest melt viscosity of the second resin layer is in the range of 1500 Pa·s to 80000 Pa·s. By making the lowest melt viscosity of the second resin layer the highest, it is possible to prevent conductive particles present on the second and first resin layer sides from moving towards or being entrained by the third resin layer, which has the lowest melt viscosity, during pressing.

[0014] Furthermore, in the conductive film of the present invention, the conductive particles are held by at least the first resin layer and the second resin layer. When the thickness of the first resin layer is set to Tt, the thickness of the second resin layer is set to Tc, and the average particle size of the conductive particles is set to D, the following relationship (1) is satisfied.

[0015]

[0016] Furthermore, the present invention provides a method for manufacturing a connection structure and a connection structure thereof. The method for manufacturing the connection structure is a method for manufacturing a connection structure for conductive connection between a first electronic component and a second electronic component. The invention is characterized in that: a first electronic component and a second electronic component are electrically connected by pressing together the aforementioned conductive film; the manufacturing method of this connection structure is particularly a method for manufacturing a connection structure in which the conductive connection is anisotropic and the conductive film is anisotropic; the connection structure system of the first electronic component and the second electronic component electrically connected by the aforementioned connection structure system is characterized in that: it is formed by electrically connecting the first electronic component and the second electronic component through the aforementioned conductive film; the connection structure is particularly a connection structure in which the conductive connection is anisotropic and the conductive film is anisotropic. [Effects of the Invention]

[0017] According to the conductive film of the present invention, the phenomenon of conductive particles moving with the resin flow during conductive bonding, especially the phenomenon of conductive particles entering between adjacent bumps, can be effectively suppressed. Therefore, the connection structure obtained by conductive bonding using the conductive film of the present invention can suppress the occurrence of short circuits and improve connection reliability. The effect of this invention is particularly good in connection structures obtained by using anisotropic conductive films for anisotropic conductive bonding. Since even with a conductive film, unnecessary movement of conductive particles does not occur during crimping, the advantage of high-precision particle position control within the electrode can be expected. Simple Explanation of the Diagram

[0018] [Figure 1] is a cross-sectional view of a conductive (anisotropic conductive) film according to one embodiment of the present invention. [Figure 2] is a cross-sectional view of a conductive (anisotropic conductive) film according to another embodiment of the present invention. [Figure 3] is a cross-sectional view of a conductive (anisotropic conductive) film according to another embodiment of the present invention. [Figure 4] is a cross-sectional view of a conductive (anisotropic conductive) film according to another embodiment of the present invention. [Figure 5] is a cross-sectional view illustrating the state before anisotropic conductive connection is made using a conventional anisotropic conductive film. [Figure 6] is a cross-sectional view of the connection structure obtained by connecting using a conventional anisotropic conductive film. [Figure 7] is a cross-sectional view illustrating the state before anisotropic conductive connection is performed using the anisotropic conductive film of the present invention. [Figure 8] is a cross-sectional view of the connection structure obtained by connecting using the anisotropic conductive film of the present invention. Implementation

[0019] Hereinafter, embodiments of the present invention will be described with appropriate reference to the drawings. Although the description pertains to anisotropic conductive films, it can also be applied to conductive films.

[0020] [Anisotropic conductive film] Figure 1 is a cross-sectional view of an anisotropic conductive film according to one embodiment of the conductive film of the present invention. Figures 2-4 are cross-sectional views of an anisotropic conductive film according to another embodiment of the present invention. The anisotropic conductive film 100 illustrated in Figures 1-4 has an insulating resin layer, which has a structure in which a first resin layer 10, a second resin layer 20, and a third resin layer 30 are sequentially stacked. A plurality of conductive particles 40 are carried in a dispersed state within the insulating resin layer. Specifically, the conductive particles 40 are held at least by the first resin layer 10 and the second resin layer 20.

[0021] <Location of Conductive Particles> Regarding the position of the conductive particles 40 in the thickness direction of the first resin layer 10, the conductive particles 40 are preferably carried on both the first resin layer 10 and the second resin layer 20, as illustrated in Figures 1-4, rather than being buried in either the first resin layer 10 or the second resin layer 20. That is, the conductive particles 40 are preferably embedded in both the first resin layer 10 and the second resin layer 20. If the conductive particles 40 are buried in either the first resin layer 10 or the second resin layer 20, the conduction resistance of the connection structure obtained by anisotropically conductively connecting electronic components may become high. In particular, when the conductive particles 40 are buried in the first resin layer 10, the reliability of the connection after anisotropic conductive connection may be reduced due to the high viscosity of the second resin layer 20, as described later.

[0022] On the other hand, if the conductive particles 40 are embedded too deeply into the second resin layer 20, the effect of the second resin layer 20 in keeping the conductive particles 40 stationary will be weakened. This raises concerns that the conductive particles 40 may move with the resin flow during anisotropic conductive connections, reducing the capture rate of the conductive particles 40 by the bumps, or that the conductive particles may enter between adjacent bumps, causing a short circuit. Therefore, the degree to which the conductive particles 40 are embedded in the second resin layer 20 is preferably within the range of 10% to 50% of the average particle size D of the conductive particles 40, and more preferably within the range of 20% to 40%.

[0023] Therefore, the conductive particles 40 can be embedded and held in the first resin layer 10 and the second resin layer 20, as shown in FIG1. ​​Furthermore, although the conductive particles 40 are held in FIG1 with approximately equal embedment in the first resin layer 10 and the second resin layer 20, the degree of embedment in the first resin layer 10 and the second resin layer 20 can be different.

[0024] Alternatively, the conductive particles 40 may penetrate the first resin layer 10, as shown in FIG2. In this case, the conductive particles 40 may protrude from the exposed surface of the first resin layer 10 (the surface opposite to the surface in contact with the second resin layer 20).

[0025] Furthermore, as shown in Figure 3, conductive particles 40 can penetrate the second resin layer 20, with a portion of the conductive particles 40 embedded in the third resin layer 30. However, if the degree to which the conductive particles 40 are embedded in the third resin layer 30 is too great, there is a concern that the conductive particles 40 may move with the resin flow during anisotropic conductive connections, reducing the capture rate of the conductive particles 40 by the bumps, or causing a short circuit. Therefore, the degree to which the conductive particles 40 are embedded in the third resin layer 30 is preferably within the range of 0% (unembedded) to 10% of the average particle size of the conductive particles 40, and more preferably within the range of 0% to 5%. Here, it is preferable that at the interface between the first and second resin layers, the average particle size of the conductive particles is 50% or more, more preferably 55% or more, and even more preferably 60% or more.

[0026] Furthermore, although the illustration is omitted, the conductive particles 40 can penetrate both the first resin layer 10 and the second resin layer 20. That is, the conductive particles are exposed from the first resin layer 10.

[0027] Furthermore, as shown in Figure 4, the conductive particles 40 may not reach the interface between the second resin layer 20 and the third resin layer 30. In this case, the average particle size D of the conductive particles 40 may not reach the sum of the thicknesses of the first resin layer 10 and the second resin layer 20. The relationship between the average particle size of the conductive particles 40 and the thickness of each layer is as follows.

[0028] <Relationship between average particle size of conductive particles and layer thickness> When the thickness of the first resin layer 10 is set to Tt, the thickness of the second resin layer 20 is set to Tc, and the average particle size of the conductive particles 40 is set to D, the anisotropic conductive film 100 satisfies the following relationship (1).

[0029]

[0030] When the relationship in equation (1) is not satisfied, and the sum of the thicknesses of the first resin layer 10 and the second resin layer 20 (Tt+Tc) is more than 4 / 3 times D, the conductivity after anisotropic conductive connection becomes unreliable, and the connection reliability is reduced. Based on the same point of view, it is preferable to satisfy the relationship in equation (2) below, and even more preferable to satisfy the relationship in equation (3) below.

[0031]

[0032] Furthermore, when the sum of the thicknesses (Tt+Tc) of the first resin layer 10 and the second resin layer 20 is too small, the holding force of the first resin layer 10 and the second resin layer 20 on the conductive particles 40 is weakened, and it may not be possible to sufficiently suppress the positional changes of the conductive particles 40 as the resin flows with the third resin layer 30. Therefore, the lower limit of the sum of the thicknesses (Tt+Tc) of the first resin layer 10 and the second resin layer 20, with the average particle size D of the conductive particles 40 as a reference, is used as the minimum total thickness that will exhibit the effect of suppressing the positional changes of the conductive particles 40 caused by resin flow, even considering the range of the lowest melt viscosity of the second resin layer 20 or the range of the average particle size D of the conductive particles 40. For example, it is preferably set to be more than 0.8 times the average particle size D of the conductive particles 40. That is, it is preferably to satisfy the relationship of the following equation (4).

[0033]

[0034] To reliably maintain the conductive particles 40 in the state of the anisotropic conductive film 100, the ratio of the thickness Tt of the first resin layer 10 to the average particle size D of the conductive particles 40 [(Tt / D)×100] is preferably in the range of 50% to 90%, more preferably in the range of 50% to 80%. In this case, it is preferable that more than half of the conductive particles are embedded in the thickness Tt of the first resin layer 10.

[0035] The ratio of the thickness Tc of the second resin layer 20 to the average particle size D of the conductive particles 40 [(Tc / D)×100] is preferably in the range of 10% to 50%, more preferably in the range of 20% to 50%, and even more preferably in the range of 15% to 40%. If this ratio [(Tc / D)×100] is less than 10%, the effect of suppressing the positional changes of the conductive particles 40 caused by resin flow may not be fully realized. If it is greater than 50%, the insertion of the conductive particles may be insufficient, and the conductivity after anisotropic conductive connection may be impaired due to the high viscosity of the second resin layer 20.

[0036] Furthermore, the relationship between the thickness Tt of the first resin layer 10 and the thickness Tc of the second resin layer 20 only needs to be Tt ≥ Tc, preferably Tt > Tc. If the thickness Tt of the first resin layer 10 is less than the thickness Tc of the second resin layer 20, the function of maintaining the conductive particles 40 may be reduced, or the conductivity after anisotropic conductive connection may be impaired due to the high viscosity of the second resin layer 20.

[0037] Furthermore, the lower limit of the thickness Tc of the second resin layer 20 is a minimum thickness that, even considering the range of the lowest melt viscosity of the second resin layer 20 or the range of the average particle size D of the conductive particles 40, will exhibit the effect of suppressing the positional changes of the conductive particles 40 caused by resin flow. It is preferably 0.1 μm or more, more preferably 1.2 μm or more, and even more preferably 2.0 μm or more. These are defined based on the relationship with particle size, and for certain particle sizes, it may sometimes only cover the apex of the particles. It does not necessarily need to be consistent with the above definition based on the relationship between particle size and thickness. Due to the influence of particle size and the thickness of the third resin layer, or resin flow factors such as the lowest melt viscosity, sometimes the inventive effect can be achieved simply by covering the apex of the particles.

[0038] Furthermore, when the thickness of the third resin layer 30 is set to Tn, in order to ensure the filling between the bumps and the insulation after the connection during the anisotropic conductive connection, Tn is preferably sufficiently greater than either Tt or Tc, and more preferably, for example, the relationship Tn>Tc+Tt holds.

[0039] <Minimum Melt Viscosity> When the minimum melt viscosity of the first resin layer 10 is set to Vt, the minimum melt viscosity of the second resin layer 20 is set to Vc, and the minimum melt viscosity of the third resin layer 30 is set to Vn, the relationship between the minimum melt viscosities of each layer in the insulating resin layer is Vc>Vt>Vn. That is, regarding the minimum melt viscosity of each layer, the second resin layer 20 has the highest, followed by the first resin layer 10, and the third resin layer 30 has the lowest. By setting the minimum melt viscosity Vc of the second resin layer 20 to the highest, the influence of the resin flow of the third resin layer 30 on the positional change of the conductive particles 40 during anisotropic conductive connections can be effectively suppressed.

[0040] That is, even if resin flow occurs in the third resin layer 30, which has the lowest minimum melt viscosity during anisotropic conductive bonding, the presence of the high-viscosity second resin layer 20 makes it easier to keep the conductive particles 40 stationary, thus suppressing their movement. Therefore, based on the viewpoint of suppressing the effect of resin flow on the conductive particles 40 during anisotropic conductive bonding, the minimum melt viscosity Vc of the second resin layer 20 is preferably 1500 Pa·s or higher, more preferably 20000 Pa·s or higher, especially preferably 40000 Pa·s or higher, and preferably within the range of 80000 Pa·s or lower. If Vc is less than 1500 Pa·s, the effect of suppressing the movement of conductive particles 40 during anisotropic conductive bonding may not be fully realized; on the other hand, if Vc exceeds 80000 Pa·s, the conductivity after anisotropic conductive bonding may be impaired.

[0041] Furthermore, the minimum melt viscosity Vc of the second resin layer 20 is preferably at least 1.5 times (Vc ≥ 1.5 × Vt) ​​of the minimum melt viscosity Vt of the first resin layer 10, more preferably at least 20 times (Vc ≥ 20 × Vt), further preferably at least 40 times (Vc ≥ 40 × Vt), and most preferably more than 40 times (Vc > 40 × Vt). By ensuring that Vc is sufficiently higher than Vt in this manner, the positional change of the conductive particles 40 due to the resin flow of the third resin layer 30 during anisotropic conductive bonding can be effectively suppressed. The upper limit of the ratio of Vc to Vt should not be particularly limited, but in practical use, it is preferably less than 80 times (Vc ≤ 80 × Vt). Moreover, when Vc is less than 40 times Vt, it is preferable that Vc is 40,000 Pa·s or more, more preferably more than 40,000 Pa·s.

[0042] The minimum melt viscosity Vt of the first resin layer 10 is preferably in the range of 800 Pa·s to 2000 Pa·s, and more preferably in the range of 1000 Pa·s to 1500 Pa·s.

[0043] To ensure filling between bumps during anisotropic conductive connections, the minimum melt viscosity Vn of the third resin layer 30 is preferably in the range of 300 Pa·s to 800 Pa·s, and more preferably in the range of 300 Pa·s to 500 Pa·s.

[0044] Furthermore, when heating is involved in anisotropic conductive bonding, the temperature at which the minimum melt viscosity of the first resin layer 10, the second resin layer 20, and the third resin layer 30 is preferably lower than the heating temperature at this time. Moreover, the temperature at which the minimum melt viscosity is reached is measured using a rotational rheometer (TA Instruments) under the following conditions: a heating rate of 10°C / min, a constant measuring pressure of 5 g, a measuring plate diameter of 8 mm, and a measuring temperature preferably within a range of 30°C to 250°C. The measuring temperature range can also be appropriately adjusted according to the adhesive conditions.

[0045] <First Resin Layer> The first resin layer 10 may be formed of a curable resin composition. For example, it is preferably formed of a thermally polymerizable composition containing a thermally polymerizable compound and a thermally polymerizable initiator.

[0046] Examples of thermopolymerizable compositions include: thermopolymerizable acrylate compositions containing (meth)acrylate compounds and thermopolymerizable initiators, and thermopolymerizable epoxy compositions containing epoxy compounds and thermopolymerizable cationic initiators (here, (meth)acrylate includes both acrylates and methacrylates). Thermopolymerizable anionic epoxy compositions containing thermopolymerizable anionic initiators can also be used instead of thermopolymerizable cationic epoxy compositions containing thermopolymerizable cationic initiators. Furthermore, multiple polymerizable compositions can be used in combination unless there are particular obstacles. Examples of parallel use include the combined use of thermopolymerizable cationic compositions and thermopolymerizable compositions.

[0047] Here, as a (meth)acrylate compound, a previously known thermopolymerizable (meth)acrylate monomer can be used. For example, a monofunctional (meth)acrylate monomer or a difunctional or more polyfunctional (meth)acrylate monomer can be used.

[0048] Examples of initiators for thermal free radical polymerization include organic peroxides and azo compounds. In particular, nitrogen-based organic peroxides, which do not generate bubbles, are preferred.

[0049] If too little thermal free radical polymerization initiator is used, it will lead to poor curing; if too much is used, it will lead to a reduced product life. Therefore, it is preferable to use more than 2 parts by mass and less than 60 parts by mass relative to 100 parts by mass of (meth)acrylate compound, and more preferably more than 5 parts by mass and less than 40 parts by mass.

[0050] Examples of epoxy compounds include: bisphenol A type epoxy resin, bisphenol F type epoxy resin, phenolic varnish type epoxy resin, modified epoxy resins of the above, alicyclic epoxy resins, etc., and two or more of these can be used in combination. Furthermore, in addition to epoxy compounds, oxetane compounds can also be used in combination.

[0051] As a thermal cationic polymerization initiator, those known as thermal cationic polymerization initiators for epoxy compounds can be used, such as monazite salts, strontium salts, phosphorus salts, ferrocene salts, etc., which generate acids by heat. Aromatic strontium salts, which exhibit good potential for temperature-dependent polymerization, are particularly preferred.

[0052] If the amount of thermal cationic polymerization initiator used is too small, there is a tendency for poor curing; if it is too large, there is a tendency for the product life to be reduced. Therefore, relative to 100 parts by mass of epoxy compound, it is better to use more than 2 parts by mass and less than 60 parts by mass, and more preferably more than 5 parts by mass and less than 40 parts by mass.

[0053] The thermopolymerizable composition preferably contains a film-forming resin or a silane coupling agent. Examples of film-forming resins include: phenoxy resins, epoxy resins, unsaturated polyester resins, saturated polyester resins, polyurethane resins, butadiene resins, polyimide resins, polyamide resins, and polyolefin resins. Two or more of these can be used in combination. From the viewpoints of film-forming properties, processability, and bonding reliability, phenoxy resins are preferably used. The weight-average molecular weight of the film-forming resin is preferably 10,000 or more. Examples of silane coupling agents include: epoxy-based silane coupling agents and acrylic-based silane coupling agents. These silane coupling agents are primarily alkoxysilane derivatives.

[0054] The thermopolymerizable composition may also contain insulating fillers to adjust the melt viscosity. Examples of insulating fillers include silica powder or alumina powder. The size of the insulating filler is preferably 20 nm to 1000 nm. Furthermore, the amount of insulating filler incorporated varies depending on the viscosity range, and is preferably 5 to 50 parts by mass relative to 100 parts by mass of the thermopolymerizable compound such as the epoxy compound.

[0055] Furthermore, the thermopolymerizable composition may also contain fillers, softeners, accelerators, anti-aging agents, colorants (pigments, dyes), organic solvents, ion scavengers, etc., which are different from the insulating fillers mentioned above.

[0056] <Second Resin Layer> The second resin layer 20 is a high-viscosity resin layer, which has the function of suppressing the influence of the resin flow of the third resin layer 30 on the positional change of the conductive particles 40 during anisotropic conductive connection. That is, even when the resin of the third resin layer 30 flows during anisotropic conductive connection, the high-viscosity second resin layer 20 can keep the conductive particles 40 stationary, and their movement is suppressed.

[0057] The second resin layer 20 may be composed of the same composition as the thermopolymerizable composition constituting the first resin layer 10. In the anisotropic conductive film 100 of the present invention, it is preferable that the resins constituting the first resin layer 10, the second resin layer 20, and the third resin layer 30 are all thermopolymerizable resins.

[0058] Furthermore, this second resin layer 20 can be formed by photocuring the surface of the first resin layer 10 or the third resin layer 30 (described later) to a specific thickness. In this case, it is preferable that the thermopolymerizable composition used to form either the first resin layer 10 or the third resin layer 30 contains a photopolymerization initiator. When using both a thermopolymerization initiator and a photopolymerization initiator, a composition having the functions of both a thermopolymerizable compound and a photopolymerizable compound can be used, or it can contain both a thermopolymerizable compound and a photopolymerizable compound separately, preferably separately. For example, a thermocationic polymerization initiator can be used as the thermopolymerization initiator, an epoxy compound can be used as the thermopolymerizable compound, a photoradical polymerization initiator can be used as the photopolymerization initiator, and an acrylate compound can be used as the photopolymerizable compound.

[0059] As the acrylate compound that forms the acrylate unit, previously known photopolymerizable acrylate monomers can be used. For example, monofunctional (meth)acrylate monomers and difunctional or more polyfunctional (meth)acrylate monomers can be used. As a photopolymerization initiator, photoradical polymerization initiator can be used, for example. More specifically, examples include acetophenone-based photopolymerization initiators, benzil ketal-based photopolymerization initiators, and phosphorus-based photopolymerization initiators. If the amount of photopolymerization initiator used is too small, photopolymerization cannot be carried out sufficiently; if it is too large, it will cause a decrease in rigidity. Therefore, relative to 100 parts by mass of the acrylate compound, it is preferable to be 0.1 parts by mass to 25 parts by mass, and more preferably 0.5 parts by mass to 15 parts by mass.

[0060] <Third Resin Layer> The third resin layer 30 is a layer used to impart good adhesion to the anisotropic conductive film 100. This third resin layer 30 may be composed of a layer of the same composition as the thermopolymerizable composition constituting the first resin layer 10.

[0061] <Conductive particles> The conductive particles 40 can be appropriately selected from those used in known conductive films or anisotropic conductive films. Preferred examples of conductive particles 40 include: metal particles such as nickel, cobalt, silver, copper, gold, and palladium; alloy particles such as solder; and metal-coated resin particles. Two or more of these can also be used together. Among these, metal-coated resin particles repel each other after connection, thereby easily maintaining contact with the terminals, which is superior in terms of stable conductivity. Furthermore, the surface of the conductive particles 40 can be treated with an insulating process that does not impede conductivity characteristics using known techniques.

[0062] While the average particle size D of the conductive particles 40 can be appropriately selected based on the type of object being connected, if it is too small, it may fail to absorb deviations in wiring height, leading to increased resistance; if it is too large, it may cause short circuits. Therefore, in order to cope with deviations in wiring height and suppress the increase in conduction resistance and the occurrence of short circuits, the average particle size D is preferably 1 μm or more, more preferably 2.5 μm or more, more preferably 30 μm or less, and more preferably 9 μm or less. The particle size of the conductive particles 40 dispersed before the insulating resin layer can be measured using a conventional particle size distribution measuring device, and the average particle size D can also be determined using a particle size distribution measuring device. As an example of a measuring device, the FPIA-3000 (Malvern Panalytical) can be used. The N number is 1000 or more, preferably 5000 or more. The particle size of the conductive particles 40 in the anisotropic conductive film 100 can be determined by observation using an electron microscope such as SEM. In this case, it is ideal to set the number of samples for measuring the particle size of conductive particles 40 to be 200 or more.

[0063] The particle size deviation of the conductive particles 40 constituting the anisotropic conductive film 100 of the present invention is preferably CV value (standard deviation / average) of 20% or less. By ensuring a CV value of 20% or less, the particles are easily and evenly pressed during clamping, especially in the case of arranged particles, preventing pressure concentration in certain areas and improving conductivity stability. Furthermore, the connection status can be evaluated with high precision using indentation after connection. Specifically, the connection status can be accurately confirmed using indentation for both larger terminal sizes (FOG, etc.) and smaller terminal sizes (COG, etc.). Therefore, inspection after anisotropic conductive connection becomes easier, and the productivity of the connection process is expected to improve.

[0064] Here, the deviation in particle size of the conductive particles 40 can be calculated using an image-based particle size analyzer. For example, the particle size of the conductive particles 40, which are raw material particles for the anisotropic conductive film 100 and are not disposed within it, can be determined using a wet flow particle size / shape analyzer FPIA-3000 (Malvern Panalytical). In this case, measuring 1000 or more, preferably 3000 or more, and more preferably 5000 or more conductive particles 40 is sufficient to accurately determine the deviation of individual conductive particles 40. When the conductive particles 40 are disposed within the anisotropic conductive film 100, the deviation can be determined using planar or cross-sectional images.

[0065] Furthermore, the conductive particles 40 are preferably approximately spherical. By using approximately spherical particles as the conductive particles 40, for example when manufacturing an anisotropic conductive film 100 with the conductive particles 40 arranged using a transfer mold, the conductive particles 40 can be precisely filled into specific positions on the transfer mold because they will roll smoothly on the mold. Therefore, the conductive particles 40 can be accurately positioned. Here, approximately spherical means refers to a sphericity calculated by the following formula that is in the range of 70 to 100.

[0066]

[0067] In the formula, So is the area of ​​the circumcircle of the conductive particle 40 in the planar image of the conductive particle 40, and Si is the area of ​​the incircle of the conductive particle 40 in the planar image of the conductive particle 40.

[0068] In this calculation method, it is preferable to take planar images of the conductive particles 40 from the surface view and cross-section of the anisotropic conductive film 100. In each planar image, for any conductive particle 40, the areas of the circumscribed circles and inscribed circles of 100 or more (preferably 200 or more) are measured, and the average area of ​​the circumscribed circles and the average area of ​​the inscribed circles are calculated. These average areas of the circumscribed circles and the average areas of the inscribed circles are used as the aforementioned So and Si. Furthermore, it is preferable that the sphericity of either the surface view or the cross-section is within the aforementioned range. The difference in sphericity between the surface view and the cross-section is preferably within 20, more preferably within 10. Since the inspection of the anisotropic conductive film 100 during production is mainly based on the surface view, and the detailed quality judgment after the anisotropic conductive connection is performed using both the surface view and the cross-section, the difference in sphericity is preferably small. If it is a single particle, the true sphericity can also be determined using the aforementioned wet flow particle size / shape analyzer FPIA-3000 (Malvern Panalytical).

[0069] The conductive particles 40 can be dispersed randomly or in a regularly arranged manner. In either case, in terms of the stability of the bumps in capturing the conductive particles 40, it is preferable that the positions of the anisotropic conductive film 100 are uniform in the film thickness direction.

[0070] Furthermore, regarding the balance between the ability of the bumps to capture the conductive particles 40 and the suppression of short circuits, the conductive particles 40 are preferably arranged regularly when viewed from above the anisotropic conductive film 100. The arrangement pattern depends on the configuration of the terminals and bumps, and is therefore not particularly limited. For example, it can be arranged in a square grid when viewed from above. In addition, as a regular arrangement pattern of conductive particles 40, rectangular grids, rhomboid grids, hexagonal grids, triangular grids, etc., can be listed. It can also be a pattern composed of multiple grids of different shapes. The regular arrangement is not limited to the grid arrangement mentioned above. For example, the conductive particles 40 can also be arranged in a straight line at specific intervals to form a particle column with specific intervals. By making the conductive particles 40 non-contacting and forming a regular grid pattern, pressure can be uniformly applied to each conductive particle 40 during anisotropic conductive connection, thereby reducing the unevenness of conduction resistance. The regular arrangement can be confirmed, for example, by observing whether a specific particle configuration repeats along the length of the anisotropic conductive film 100. When the conductive particles 40 are arranged regularly, if the arrangement has a lattice axis or arrangement axis, the lattice axis or arrangement axis can be parallel to or orthogonal to the length direction of the anisotropic conductive film 100, or it can intersect the length direction of the anisotropic conductive film 100, depending on the width of the terminals to be connected, the terminal spacing, and the configuration. Furthermore, the conductive particles 40 are preferably arranged regularly when viewed from above the anisotropic conductive film 100, and their positions are neat along the film thickness direction, in order to balance capture stability and short-circuit suppression.

[0071] Furthermore, when the spacing between the terminals of the electronic components to be connected is relatively wide and short circuits are less likely to occur, the conductive particles 40 can be randomly dispersed rather than arranged in a regular manner without hindering conduction.

[0072] The interparticle distance of the conductive particles 40 can be appropriately determined based on the size of the terminals connected by the anisotropic conductive film 100 or the terminal spacing. For example, when the anisotropic conductive film 100 is used with micro-pitch COG (Chip On Glass), in order to prevent short circuits, it is preferable to set the closest interparticle distance to be at least 0.5 times the average particle size D of the conductive particles 40, and more preferably greater than 0.7 times. On the other hand, in terms of the capture ability of the conductive particles 40, it is preferable to set the closest interparticle distance to be at least 4 times the average particle size D of the conductive particles 40, and more preferably at least 3 times.

[0073] Furthermore, there is no particular limitation on the area occupancy of the conductive particles 40, but it is preferably 35% or less, and more preferably 0.3% to 30%. In the anisotropic conductive film 100, this area occupancy can be calculated by the following formula.

[0074]

[0075] Furthermore, there is no particular limitation on the number density of conductive particles. In practical applications, if the number density is too low, the number of conductive particles captured by the bumps will decrease, making conductive connections for micro LEDs or anisotropic conductive connections for IC chips difficult. If the number density is too high, there is a risk of short circuits. Therefore, the preferred number density is 50 particles / mm² or higher, more preferably 150 particles / mm² or higher, even more preferably 200 particles / mm², and most preferably 6000 particles / mm² or higher. The upper limit is 360,000 particles / mm² or lower, preferably 250,000 particles / mm² or lower, and even more preferably 100,000 particles / mm² or lower. In the case of COG or COP (Chip On Plastic), 12,000 to 30,000 particles / mm² is preferred.

[0076] Here, the number density of conductive particles 40 can be measured by microscopic observation. For example, it can be preferably performed as follows: In the anisotropic conductive film 100, arbitrarily select a plurality of rectangular regions (preferably 5 or more, more preferably 10 or more) with one side of 100 μm or more as observation areas, so that the total area of ​​the measurement areas is 2 mm² or more. The size or number of each region can be adjusted appropriately according to the number density. As an example of micro-pitch applications where the number density is relatively large, the "number density of conductive particles under top view" in the above formula can be obtained as follows: for 200 regions (2 mm²) arbitrarily selected from the anisotropic conductive film 100 with an area of ​​100 μm × 100 μm, measure the number density using observation images obtained by a metallographic microscope or the like, and average the results. A region of 100 μm × 100 μm refers to a region in which there is one or more bumps in a connected object with a spacing of less than 50 μm between bumps.

[0077] The number density of conductive particles 40 can be determined not only by observation using a metallographic microscope as described above, but also by measuring the observed image using image analysis software (such as WinROOF manufactured by Mitani Corporation). The observation methods and measurement techniques are not limited to those described above.

[0078] Furthermore, the average top-view area of ​​a conductive particle (40) was determined by measuring images of the film surface obtained using metallographic microscopy or electron microscopy such as SEM. Image analysis software can also be used. The observation methods and measurement techniques are not limited to those described above.

[0079] [Manufacturing method of anisotropic conductive film 100] As one form of the conductive film of the present invention, the anisotropic conductive film 100 shown in Figures 1 to 4 can be manufactured, for example, by the following method: a second resin layer 20 separately fabricated is disposed on one side of a first resin layer 10 composed of a thermopolymerizable composition on which conductive particles 40 are held on the surface; and a third resin layer 30 separately fabricated is disposed on the side of the second resin layer 20 opposite to the side of the first resin layer 10 that is in contact with it, and the whole is bonded together.

[0080] Here, as a method for retaining the conductive particles 40 in the first resin layer 10, previously known methods can be used. For example, the conductive particles 40 can be retained in the first resin layer 10 by directly dispersing the conductive particles 40 into the film that forms the first resin layer 10. Alternatively, the conductive particles 40 can be retained in the first resin layer 10 by attaching the conductive particles 40 in a monolayer form to an adhesive film for stretching, followed by biaxial stretching, pressing the first resin layer 10 onto the stretched film, thereby transferring the conductive particles 40 onto the first resin layer 10. Furthermore, a transfer mold can also be used to retain the conductive particles 40 in the first resin layer 10. Here, an example of using a transfer mold to manufacture the anisotropic conductive film 100 of the present invention will be described.

[0081] When using a transfer mold, for example, an anisotropic conductive film 100 can be obtained by the following steps A to E.

[0082] (Step A) First, conductive particles 40 are added to the recesses of a transfer mold having a plurality of recesses.

[0083] (Step B) Subsequently, a thermally polymerizable composition containing a thermally polymerizable compound, a thermally polymerizable initiator, and an insulating filler as needed is pressed onto the conductive particles 40 in a transfer mold. The transfer mold is then removed, thereby forming a first resin layer 10 with the conductive particles 40 transferred onto it.

[0084] (Step C) Subsequently, a second resin layer 20 is formed by forming a film of a thermally polymerizable composition containing a thermally polymerizable compound and a thermally polymerizable initiator separately from the first resin layer 10.

[0085] (Step D) Similarly, a third resin layer 30 is formed by forming a film of a thermally polymerizable composition containing a thermally polymerizable compound and a thermally polymerizable initiator.

[0086] (Step E) Then, the second resin layer 20 is disposed on the transfer surface of the conductive particles 40 in the first resin layer 10, and the third resin layer 30 is disposed on the second resin layer 20. The whole is then pressed together to obtain an anisotropic conductive film 100.

[0087] Furthermore, by adjusting the pressing pressure in step B, the degree to which the conductive particles 40 are embedded in the first resin layer 10 can be changed. By increasing the pressing pressure, the degree to which the conductive particles 40 are embedded in the first resin layer 10 can be increased.

[0088] Furthermore, by adjusting the pressure during the pressing in step E, the degree to which the conductive particles 40 are embedded in the second resin layer 20 can be changed. By increasing the pressure, the degree to which the conductive particles 40 are embedded in the second resin layer 20 can be increased.

[0089] As for the transfer mold used, for example, a known opening-forming method such as photolithography can be used to form an opening in inorganic materials such as silicon, various ceramics, glass, and stainless steel, or organic materials such as various resins. Furthermore, the transfer mold can be made into shapes such as plate or roller.

[0090] Examples of the shape of the recesses in the transfer mold include cylindrical, prismatic, and other cylindrical shapes; and conical shapes such as frustums of cones, truncated pyramids, cones, and pyramids. The arrangement of the recesses can be appropriately set as a grid pattern, serrated grid pattern, etc., depending on the arrangement of the conductive particles 40. Regarding the balance between improving transferability and maintaining conductive particle retention, the ratio of the average particle size D of the conductive particles 40 to the depth of the recess (= average particle size D of the conductive particles 40 / depth of the recess) is preferably 0.4 to 3.0, more preferably 0.5 to 1.5. Furthermore, the diameter and depth of the recesses in the transfer mold can be measured using a laser microscope.

[0091] In terms of balancing the ease of receiving the conductive particles 40 and the ease of pressing the insulating resin, the ratio of the opening diameter of the recess to the average particle size D of the conductive particles 40 (= opening diameter of the recess / average particle size D of the conductive particles 40) is preferably 1.1 to 2.0, more preferably 1.3 to 1.8. Furthermore, when the bottom diameter of the recess is smaller than its opening diameter, it is preferable to set the bottom diameter to be 1.1 times or more but less than 2 times the particle size of the conductive particles 40, and to set the opening diameter to be 1.3 times or more but less than 3 times the particle size of the conductive particles 40.

[0092] Furthermore, although the above manufacturing method describes a method of holding a plurality of conductive particles 40 on the first resin layer 10, followed by the deposition of the second resin layer 20 and the third resin layer 30, it is also possible to hold a plurality of conductive particles 40 in the second resin layer 20, followed by the deposition of the first resin layer 10 and the third resin layer 30. In this case, by placing the first resin layer 10 on the transfer surface of the conductive particles 40 in the second resin layer 20, and then placing the third resin layer 30 on the other side of the second resin layer 20, and pressing the entire assembly together, an anisotropic conductive film 100 can be obtained. The deposition conditions can be performed according to the conditions described in Japanese Patent No. 6187665.

[0093] Next, referring to Figures 5-8, the effect of the second resin layer 20 in the anisotropic conductive film 100 of the present invention will be explained. Figure 5 shows the state before the first electronic component 300 and the second electronic component 400 are anisotropically conductively connected using a conventional two-layer anisotropic conductive film 200, and Figure 6 shows a cross-section of an important part of the connection structure after the anisotropic conductive connection. On the other hand, Figure 7 shows the state before the first electronic component 300 and the second electronic component 400 are anisotropically conductively connected using the anisotropic conductive film 100 of the present invention, and Figure 8 shows a cross-section of the main part of the connection structure after the anisotropic conductive connection. Furthermore, in Figures 5 to 8, the surface direction of the anisotropic conductive film is set as an XY plane formed by the X-axis and Y-axis directions that are orthogonal to each other, and the pressing direction of the first electronic component and the second electronic component (the moving direction of the protruding electrode, i.e., the bump 310) perpendicular to the XY plane is set as the Z-axis direction.

[0094] First, as shown in FIG5, the conventional anisotropic conductive film 200 has a structure in which a particle-supporting layer 110 and an insulating substrate layer 120 are stacked. The particle-supporting layer 110 supports a plurality of conductive particles 40 arranged on the same plane. The insulating substrate layer 120 is stacked on the particle-supporting layer 110 and does not support conductive particles 40.

[0095] During anisotropic conductive bonding, resin flow occurs in the insulating substrate layer 120, which has a lower viscosity. Specifically, as the bumps 310 of the first electronic component 300 insert into the insulating substrate layer 120 of the anisotropic conductive film 200, the resin in the insulating substrate layer 120 is squeezed out by the bumps 310 and flows along the XY plane. In particular, during thermoforming with heating, a greater amount of resin flow occurs in the insulating substrate layer 120 constituting the anisotropic conductive film 200 due to heating.

[0096] Furthermore, through the pressing of the first electronic component 300 and the second electronic component 400, a force in the Z-axis direction is applied to the resin between the pressing surface 310a of the bump 310 and the second electronic component 400. Therefore, the resin constituting the particle carrier layer 110 is squeezed out by the pressing surface 310a of the bump 310 and flows towards the insulating substrate layer 120. That is, resin flow also occurs in the direction shown by the arrow in Figure 6, which is obliquely upward (the direction formed by the combination of the XY plane direction and the Z-axis direction). With this resin flow in the particle carrier layer 110, the conductive particles 40 carried in the particle carrier layer 110 also easily move in the obliquely upward direction shown by the arrow in Figure 6. As a result, a portion of the conductive particles 40, which should have been crushed and held between the pressing surface 310a of the bump 310 and the electrode 410 of the second electronic component 400 to ensure conductivity, move into the insulating substrate 120 on the side of the first electronic component 300 (wherein, the resin of both the insulating substrate 120 and the particle carrier layer 110 sometimes melts and mixes at the interface between the insulating substrate 120 and the particle carrier layer 110) between adjacent bumps 310. The conductive particles 40 (represented by symbol 40A in FIG. 6) that enter between adjacent bumps 310 in this manner not only fail to contribute to the conductivity between the first electronic component 300 and the second electronic component 400, but also become the cause of electrical short circuits between adjacent bumps 310.

[0097] Furthermore, another part of the conductive particles 40 (represented by symbol 40B in Figure 6) that should be trapped between the crimping surface 310a of the bump 310 and the electrode 410 of the second electronic component 400 may detach from the crimping surface 310a of the bump 310 and be in a state of insufficient trapping, thereby reducing the stability of conduction.

[0098] The same known problems also exist when the viscosity and thickness of each layer are not considered in a laminated structure consisting of three or more layers of insulating resin.

[0099] On the other hand, the anisotropic conductive film 100 of the present invention, as shown in FIG. 7, has the following structure: a second resin layer 20 with relatively high viscosity is disposed between the first resin layer 10 and the third resin layer 30, and the conductive particles 40 are carried by both the first resin layer 10 and the second resin layer 20. Therefore, in the case of anisotropic conductive connection, even if a large resin flow occurs in the third resin layer 30 with lower viscosity, the influence of resin flow can be mitigated by the second resin layer 20 with higher viscosity, which has the function of keeping the conductive particles 40 stationary, thereby restricting the movement of the conductive particles 40.

[0100] That is, the anisotropic conductive film 100, which is one form of the conductive film of the present invention, has a unique structural feature that the conductive particles 40 are embedded in the openings or recesses of the high-viscosity second resin layer 20. Therefore, the conductive particles 40 are less likely to move in the XY plane and Z axis directions. This can greatly reduce the probability that the conductive particles 40 move between adjacent protrusions 310 or move to a position that is detached from the pressing surface 310a of the protrusion 310 and is in a state of not being fully captured.

[0101] Furthermore, since the total thickness (Tt+Tc) of the first resin layer 10 and the second resin layer 20 of the present invention has the relationship with the average particle size D of the conductive particles 40 as shown in the above formula (1), the conductivity of the conductive particles 40 is not hindered by the high viscosity of the second resin layer 20.

[0102] Therefore, as shown in Figure 8, a plurality of conductive particles 40 can be connected to the bump 310 while maintaining a roughly neat arrangement, thereby suppressing the occurrence of short circuits and improving the reliability of the anisotropic conductive connection between the first electronic component 300 and the second electronic component 400.

[0103] Furthermore, Figure 7 illustrates an anisotropic conductive film 100 with a structure similar to that in Figure 1, and the same applies when using the anisotropic conductive film 100 shown in Figures 2 to 4.

[0104] [Connection Structure] The conductive film of the present invention can be preferably applied to the case of mounting micro LEDs on a substrate, or as an anisotropic conductive film. For example, when anisotropically conductively connecting a first electronic component 300 such as a known semiconductor element, IC chip, IC module, optical semiconductor element, or FPC to a second electronic component 400 such as an FPC, glass substrate, rigid substrate, or ceramic substrate, the anisotropic conductive film 100 can be preferably used.

[0105] As a method for connecting electronic components using the anisotropic conductive film 100, for example, as shown in FIG7, the anisotropic conductive film 100 is temporarily attached from the first resin layer 10 side to a second electronic component 400 such as a substrate, and a first electronic component 300 such as an IC chip is mounted on the temporarily attached anisotropic conductive film 100 and then pressed together. That is, the first electronic component 300 and the second electronic component 400 are pressed together via the anisotropic conductive film 100. The pressing is preferably a hot pressing with heating. In this manner, the connection structure of the present invention illustrated in FIG8 can be manufactured.

[0106] The connection structure 500 of the present invention comprises: a first electronic component 300; a second electronic component 400, which is anisotropically conductively connected to the first electronic component 300; and an insulating resin layer 510, which is disposed between the first electronic component 300 and the second electronic component 400 and dispersed therewith a plurality of conductive particles 40. Furthermore, the insulating resin layer 510 is derived from the resin layers of the first resin layer 10, the second resin layer 20, and the third resin layer 30.

[0107] The first electronic component 300 and the second electronic component 400 face each other and have a plurality of protruding electrodes, namely bumps 310, which are generally rectangular (short strip-shaped) when viewed from above. The plurality of bumps 310 are preferably arranged parallel to each other at specific intervals along their short sides. In this case, a radial arrangement at specific intervals along the short sides is also possible. Furthermore, there are also cases where the bumps are distributed in groups. In the connecting structure 500, the bumps 310 of the first electronic component 300 and the electrodes 410 of the second electronic component 400 are electrically connected via conductive particles 40.

[0108] Here, in the connecting structure 500, the height of the protrusion of the protrusion 310 from the first electronic component 300 is defined as the protrusion height H. Furthermore, the imaginary plane (i.e., the plane passing through the pressing surface 310a of the protrusion 310) that connects the plurality of protrusions 310 between the first electronic component 300 and the second electronic component 400 is defined as the connecting surface P.

[0109] Then, regarding the connecting structure 500, it is preferable that when observing the following cross section, the number of conductive particles 40 (refer to symbol 40A in Figure 6; hereinafter sometimes referred to as "particles intruding between bumps") located between adjacent bumps 310 is two or less. This cross section is orthogonal to the connecting surface P, parallel to the short side direction of any two adjacent bumps 310, and passes through the midpoint of the length of the bump 310 in the length direction.

[0110] Furthermore, regarding cross-sectional observation, it is preferable to use observation methods such as SEM (scanning electron microscope) to observe cross-sections at multiple points (e.g., any 20 points) of the connected structure, and to calculate the average number of particles present between the intruding bumps obtained from each observation, such that the average number is 2 or less. [Example]

[0111] The present invention will now be specifically described through examples. Furthermore, the melt viscosity was measured using a rotational rheometer (TA Instruments) under the following conditions: a heating rate of 10°C / min, a fixed measuring pressure of 5 g, a measuring plate diameter of 8 mm, and a measuring temperature of 80°C.

[0112] [Example 1] (Formation of the first resin layer) A mold with a raised pattern corresponding to a square or hexagonal grid is made. Known transparent resin particles are melted and poured into the mold, then cooled and solidified. This creates a resin transfer mold with recessed areas featuring a grid pattern and a particle density of 28,000 conductive particles / mm². Conductive particles (Sekisui Chemicals Co., Ltd., average particle size 3.2 μm) are then filled into the recessed areas of the transfer mold.

[0113] On the other hand, a thermopolymerizable composition was prepared, comprising, as shown in Table 1 (parts by mass), phenoxy resin (Nippon Steel Chemical Materials Co., Ltd., YP-50), silica filler (Aerosil Co., Ltd., Aerosil R805), liquid epoxy resin (Mitsubishi Chemical Co., Ltd., jER828), thermopolymerizable initiator (Sanshin Chemical Industry Co., Ltd., SI-60L), and silane coupling agent (Shin-Etsu Chemical Industry Co., Ltd., KBM-403). Using a rod coater, the thermopolymerizable composition was coated onto a 50 μm thick PET film and dried in an oven at 80°C for 5 minutes, forming a first adhesive resin layer on the PET film with the thickness shown in Table 2. Using an elastic roller, the first resin layer is pressed onto the conductive particle receiving surface of the transfer mold at a temperature of 50°C and a pressing pressure of 0.5 MPa, thereby forming a first resin layer with transferred conductive particles. The first resin layer is then peeled off from the transfer mold. The minimum melt viscosity of the first resin layer is also shown in Table 2.

[0114] (Formation of the second resin layer) The following thermopolymerizable composition was prepared, comprising, as shown in Table 1 (parts by mass), phenoxy resin (Nippon Steel Chemical Materials Co., Ltd., YP-50), silica filler (Aerosil Co., Ltd., Aerosil R805), liquid epoxy resin (Mitsubishi Chemical Co., Ltd., jER828), thermo-cationic polymerization initiator (Sanshin Chemical Industry Co., Ltd., SI-60L), and silane coupling agent (Shin-Etsu Chemical Industry Co., Ltd., KBM-403). Using a rod coater, the thermopolymerizable composition was coated onto a 50 μm thick PET film and dried in an oven at 80°C for 5 minutes, forming a high-viscosity second resin layer on the PET film with the thickness shown in Table 2. The minimum melt viscosity of this second resin layer is also shown in Table 2.

[0115] (Formation of the third resin layer) The following thermopolymerizable composition was prepared, comprising, as shown in Table 1 (parts by mass), phenoxy resin (Nippon Steel Chemical Materials Co., Ltd., YP-50), silica filler (Aerosil Co., Ltd., Aerosil R805), liquid epoxy resin (Mitsubishi Chemical Co., Ltd., jER828), thermo-cationic polymerization initiator (Sanshin Chemical Industry Co., Ltd., SI-60L), and silane coupling agent (Shin-Etsu Chemical Industry Co., Ltd., KBM-403). Using a rod coater, the thermopolymerizable composition was coated onto a 50 μm thick PET film and dried in an oven at 80°C for 5 minutes, forming a third resin layer with adhesive properties as shown in Table 2. The minimum melt viscosity of this third resin layer is also shown in Table 2. The thickness of the third resin layer was adjusted to achieve an overall layer thickness of approximately 13-14 μm.

[0116] (Layering of the first resin layer, the second resin layer, and the third resin layer) The conductive particle transfer surfaces of the second resin layer and the first resin layer are aligned, and the opposite sides of the opposing surfaces of the second and first resin layers are aligned. The layers are then bonded together under conditions equal to a pressing temperature of 50°C and a pressing pressure of 0.2 MPa, thereby creating an anisotropic conductive film.

[0117] [Examples 2-7] and [Comparative Examples 1-3, Reference Examples 1-3] Using a thermopolymerizable composition having the formulation shown in Table 1, a first resin layer, a second resin layer, and a third resin layer having the thickness and minimum melt viscosity shown in Table 2 are formed. Otherwise, an anisotropic conductive film is manufactured in the same manner as in Example 1.

[0118] The formulation composition of each layer of the anisotropic conductive film constituting the embodiments, reference examples, and comparative examples is shown in Table 1, and the evaluation results of the structure, thickness, physical properties, and characteristics of each layer of the anisotropic conductive film are shown in Table 2.

[0119] [Table 1] (Unit: parts by weight) Comparative example Reference Example Example 1 2 3 1 2 3 1 2 3 4 5 6 7 3rd resin layer phenoxy resin 40 40 40 40 40 40 40 40 40 40 40 40 40 Silica filler 10 10 5 5 5 5 5 5 5 5 5 5 5 Liquid epoxy resin 50 50 55 55 55 55 55 55 55 55 55 55 55 Thermal cationic polymerization initiator 4 4 4 4 4 4 4 4 4 4 4 4 4 Silane coupling agent 1 1 1 1 1 1 1 1 1 1 1 1 1 Second resin layer phenoxy resin 40 40 20 - 40 10 40 40 40 20 20 20 15 Silica filler 10 7 45 - 7 60 10 10 10 45 45 45 50 Liquid epoxy resin 50 53 35 - 53 20 50 50 50 35 35 35 25 Thermal cationic polymerization initiator 4 4 4 - 4 4 4 4 4 4 4 4 4 Silane coupling agent 1 1 1 - 1 1 1 1 1 1 1 1 1 First resin layer phenoxy resin 40 40 40 40 40 40 40 40 40 40 40 40 40 Silica filler 7 10 7 7 7 7 7 7 7 7 7 7 7 Liquid epoxy resin 53 50 53 53 53 53 53 53 53 53 53 53 53 Thermal cationic polymerization initiator 4 4 4 4 4 4 4 4 4 4 4 4 4 Silane coupling agent 1 1 1 1 1 1 1 1 1 1 1 1 1

[0120] [Table 2] Comparative example Reference Example Example unit Each floor 1 2 3 1 2 3 1 2 3 4 5 6 7 Bump height μm - 12 Thickness of each layer μm Third resin layer (Tn) 10 10 7 12 10 10 10 10 10 10 10 10 10 Second resin layer (Tc) 1.60 1.60 3.20 - 1.60 1.60 1.60 1.00 0.60 1.60 1.50 2.00 1.60 First resin layer (Tt) 1.60 1.60 3.20 1.60 1.60 1.60 1.60 2.20 2.60 1.60 1.50 2.00 1.60 Tt+Tc 3.20 3.20 6.40 1.60 3.20 3.20 3.20 3.20 3.20 3.20 3.00 4.00 3.20 Particle size μm - 3.20 Minimum melt viscosity Pa·s 3rd resin layer 1500 1500 500 500 500 500 500 500 500 500 500 500 500 Second resin layer 1500 1000 40000 - 1000 100000 1500 1500 1500 40000 40000 40000 80000 First resin layer 1000 1500 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 Characteristic evaluation immobility D C C B B A A A A A A A A conductivity A A C A A B A A A A A A A adhesion A A A B A A A A A A A A A

[0121] <Characteristic Evaluation> Using the anisotropic conductive films prepared in Examples 1-7, Comparative Examples 1-3 and Reference Examples 1-3, the evaluation IC and the glass substrate are anisotropically conductively connected by thermoforming to form an evaluation connection structure.

[0122] Evaluation using IC: Dimensions: 1.8 mm × 20 mm × 0.2 mm; Gold bump dimensions: 12 μm (height) × 15 μm (width) × 100 μm (length) (gap between bumps is 15 μm)

[0123] Glass substrate with ITO-coated wiring: Dimensions = 30 mm × 50 mm × 0.5 mm

[0124] Hot-press connection conditions: From the IC chip side, perform hot pressing at 150°C and 80 MPa for 5 seconds.

[0125] For the constructed evaluation connection structure, the following methods were used to evaluate (a) the immobility of conductive particles, (b) conductivity, and (c) adhesion. The results are shown in Table 2.

[0126] (a) The immobility of conductive particles The self-evaluation connection structure was used to create cross-sections, which were then observed using a scanning electron microscope (SEM). The number of conductive particles that moved due to resin flow was counted to determine the immobility of the particles. The cross-sectional observation was performed on the following cross-section: when the height of the protrusion of the IC used for bump self-evaluation is defined as the bump height H, and the imaginary plane connecting the height H of the plurality of bumps between the evaluation IC and the glass substrate (i.e., the plane passing through the pressure surface of the bumps) is defined as the connection surface P (see Figure 8), the cross-section is orthogonal to the connection surface P, parallel to the short side direction of any two adjacent bumps, and passes through the midpoint of the length direction of the bumps. Through cross-sectional observation, conductive particles located between adjacent bumps that are entirely closer to the evaluation IC than the connection surface P are called "particles intruding between bumps." The number of these particles is counted, and the average value is calculated when observing any 20 cross-sections. The evaluation criteria are as follows.

[0127] (Evaluation Criteria) A (Excellent): 0 particles intruding between bumps (None) B (Good): 1 to 2 particles intruding between bumps C (Defect): More than 2 but less than 3 particles intruding between bumps D (Extremely Undesirable): More than 3 particles intruding between bumps

[0128] (b) Conductivity Using a digital multimeter and the four-terminal method, the on-resistance (initial on-resistance) of the evaluation connection structure was measured when a current of 2 mA was applied. In practical use, it is desirable to measure a resistance value of less than 2 Ω. Therefore, a resistance value less than 1.5 Ω is classified as A (Good), a resistance value between 1.5 and 2 Ω is classified as B (Acceptable), and a resistance value exceeding 2 Ω is classified as C (Fail).

[0129] (c) Adhesion Using a commercially available ACF application device (Shibaura Mechatronics Co., Ltd., model TTO-1794M), an anisotropic conductive film was applied to a glass substrate in a size of 2 mm × 5 cm. The film was temporarily applied at a pressure of 1 MPa, with the temperature reaching 60°C to 80°C after 1 second. When the glass substrate was flipped, the anisotropic conductive film was visually observed to determine whether it peeled off or bulged from the glass substrate, and the following criteria were used for evaluation.

[0130] (Evaluation Criteria) A (Good): Can be temporarily applied at 60℃. B (Normal): Situations where temporary adhesion is not possible at 60℃ but is possible at 80℃. C (Defect): Unable to adhere temporarily at 80℃.

[0131] As shown in Table 2, in the anisotropic conductive films of Examples 1-7, by having a second resin layer with relatively high viscosity interposed between the first and third resin layers, and by ensuring that the total thickness (Tt+Tc) of the first and second resin layers satisfies the relationship of Equation (1) with respect to the average particle size D of the conductive particles 40, good results were observed in any of the evaluation items: (a) immobility of conductive particles, (b) conduction resistance, and (c) adhesion. In contrast, in Comparative Example 1, where the relationship between the minimum melt viscosity of each layer was inappropriate, and in Comparative Example 2, where the minimum melt viscosity of the second resin layer was less than 1500 Pa·s, the immobility of the conductive particles 40 was "poor" or "extremely poor". Furthermore, in Comparative Example 3, where the total thickness (Tt+Tc) of the first resin layer and the second resin layer does not satisfy the relationship of Equation (1) with respect to the average particle size D of the conductive particles 40, the immobility of the conductive particles 40 is "poor" and the conductivity is also "poor". [Industrial Applicability]

[0132] The conductive film of this invention can be used to make conductive or anisotropic conductive connections between electronic components such as IC chips or micro LEDs and wiring substrates.

[0133] The embodiments of the present invention have been described in detail above for illustrative purposes, but the present invention is not limited to the above embodiments.

[0134] 10: First resin layer 20: Second resin layer 30: Third resin layer 40, 40A, 40B: Conductive particles 100: Conductive (anisotropic conductive) film 110: Particle-supported layer 120: Insulating base layer 200: Anisotropic conductive film (common knowledge) 300: First Electronic Component 310: Bump (protruding electrode) 310a: Press-fit surface 400: Second electronic component 410: Electrode 500: Connection Structure 510: Insulating resin layer H: Bump height P: Imaginary connecting surface

Claims

1. A conductive film comprising: an insulating resin layer having a laminated structure in which a first resin layer, a second resin layer, and a third resin layer are sequentially laminated; and conductive particles dispersed in the insulating resin layer, wherein the minimum melt viscosity of each layer in the insulating resin layer is in descending order as the second resin layer > the first resin layer > the third resin layer, and the minimum melt viscosity of the second resin layer is in the range of 1500 Pa·s to 80000 Pa·s, and the conductive particles are held at least by the first resin layer and the second resin layer, wherein when the thickness of the first resin layer is set to Tt, the thickness of the second resin layer is set to Tc, and the average particle size of the conductive particles is set to D, the following equation (1) is satisfied.

2. The conductive film of Request 1 satisfies the following equation (4): .

3. The conductive film as claimed in claim 1, wherein, When the minimum melt viscosity of the second resin layer is set as Vc and the minimum melt viscosity of the first resin layer is set as Vt, Vc is more than 1.5 times Vt.

4. The conductive film as claimed in claim 1, wherein, When the minimum melt viscosity of the second resin layer is set as Vc and the minimum melt viscosity of the first resin layer is set as Vt, Vc is more than 40 times that of Vt.

5. As in claim 1, the conductive film, when the thickness of the third resin layer is set to Tn, is in the relationship that Tn > Tc + Tt.

6. The conductive film as claimed in claim 1, wherein, The resins constituting the first and second resin layers are thermopolymerizable resins.

7. The conductive film as claimed in claim 1, wherein, The conductive particles are arranged in a regular lattice pattern.

8. The conductive film of any one of claims 1 to 7 is used as an anisotropic conductive film.

9. A method for manufacturing a connecting structure, which is a method for manufacturing a connecting structure for conductive connection between a first electronic component and a second electronic component, characterized in that: the first electronic component and the second electronic component are conductively connected by pressing together a conductive film according to any one of claims 1 to 7.

10. A method for manufacturing a connection structure, comprising a method for manufacturing the connection structure of claim 9 having an anisotropic conductive connection, wherein the method comprises performing anisotropic conductive connection by pressing a first electronic component and a second electronic component together via the aforementioned conductive film.

11. A connection structure for electrically connecting a first electronic component and a second electronic component, characterized in that: the first electronic component and the second electronic component are electrically connected via a conductive film of any one of claims 1 to 7.

12. A connection structure, which is the connection structure of claim 11, wherein the conductive connection is anisotropic, the connection structure system is formed by anisotropically conductively connecting a first electronic component and a second electronic component via the aforementioned conductive film.

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