Conductive film and method for manufacturing same, and connection structure and method for manufacturing same

Abstract

This conductive film achieves high capturability and stable conduction characteristics of conductive particles having a large particle diameter and suppresses resin protrusion and blocking even when slitted. The conductive film has a structure in which conductive particles having an average particle diameter of 10 µm or more are disposed in a laminate of a first insulating resin layer and a second insulating resin layer. In this conductive film, 90% or more of the conductive particles on a number basis are arranged so as to be separated from each other, and a resin flow amount difference between the first insulating resin layer and the second insulating resin layer is 0.07-0.09, and / or the viscosity ratio at 80°C of the first insulating resin layer and the second insulating resin layer is less than 2.

Description

Conductive Film, Method for Producing the Same, Connection Structure, and Method for Producing the Same

[0001] The present invention relates to an anisotropic conductive film useful when mounting an electronic component on a circuit board, particularly a conductive film typified by an anisotropic conductive film using large-particle-size conductive particles.

[0002] In recent years, in electronic devices such as smartphones, the density of components has been increasing, and space constraints have occurred within the case. Particularly in camera modules, the size and number of cameras have been increasing, and the size of the imager substrate has been increasing in order to improve image accuracy. On the other hand, since the connection pads of the substrate are becoming smaller, when mounting an electronic component on a circuit board using an anisotropic conductive film, in order to obtain more stable conduction characteristics with a small connection area, it is necessary to capture conductive particles on the connection pads more than before. <00,00014>Therefore, in order to suppress the unintentional movement of conductive particles caused by resin flow during mounting using an anisotropic conductive film and enhance the captureability of conductive particles, it has been proposed to configure the anisotropic conductive film such that conductive particles are sandwiched between two insulating resin layers adjusted so that the ratio of the minimum melt viscosities is 2 or more (Patent Document 1).

[0004] In addition, in camera modules, since a ceramic substrate having unevenness and steps on the surface is used, in order to suppress the destabilization of conduction characteristics due to the unevenness and steps on the substrate surface, it has been proposed to use conductive particles having a large particle size, for example, a particle size of 10 μm or more, in the anisotropic conductive film and increase the thickness of the insulating resin layer (Patent Document 2).

[0005] Therefore, in an anisotropic conductive film for camera modules using ceramic substrates, when the aim is to suppress the instability of conductivity characteristics due to irregularities and steps on the substrate surface, and at the same time suppress the unintended movement of conductive particles due to resin flow during mounting and improve the capture ability of conductive particles, attempts have been made to construct an anisotropic conductive film in which conductive particles with a particle size of 10 μm or more are sandwiched between two insulating resin layers, adjusted so that the ratio of 80°C viscosity, which is easier to measure than the minimum melt viscosity, is 2 or more, instead of the ratio of the minimum melt viscosity. Such attempts have been made not only when using ceramic substrates, but also when anisotropic conductive connections are made for components with relatively high terminal heights.

[0006] Japanese Patent Publication No. 2019-031649, Japanese Patent Publication No. 6504307

[0007] In recent years, the miniaturization and increased density of camera components have led to changes in the structure of camera modules (center shift), resulting in narrower mounting areas and smaller connection areas. Therefore, there is a demand for anisotropic conductive films for camera modules that can be slit into narrow strips. Consequently, there is also a requirement to prevent resin overflow and blocking during slitting of the raw material and processing into windings.

[0008] In response to these requirements, when the aforementioned anisotropic conductive film (a film in which conductive particles having a particle diameter of 10 μm or more are sandwiched between two insulating resin layers adjusted so that the viscosity ratio at 80°C is 2 or more) created considering the disclosures in Patent Documents 1 and 2 is applied, it is possible to suppress the instability of conductivity characteristics due to irregularities and steps on the substrate surface, and at the same time, to suppress the unintended movement of conductive particles due to resin flow during mounting and improve the capture ability of conductive particles. However, there was a problem that the risk of resin overflow and blocking occurred during slitting and processing into a winding body increased.

[0009] The object of the present invention is to achieve high particle capture and stable conductivity even when the structure of a conductive film, such as an anisotropic conductive film, is configured by laminating two insulating resin layers and arranging conductive particles with a large particle diameter of 10 μm or more in the laminate, in order to control the influence of resin flow and improve particle capture. Furthermore, the object of the present invention is to provide a conductive film in which resin overflow and blocking during slitting are suppressed to a level that does not hinder the practical use of the conductive film.

[0010] The present inventors have found that a conductive film having a first insulating resin layer, a second insulating resin layer laminated thereon, and conductive particles with an average particle diameter of 10 μm or more, increases the proportion of conductive particles spaced apart from each other in the conductive film, which increases the possibility of achieving good particle capture and good conductivity. They also found that the flow of the resin due to heating and pressurizing during the mounting of the conductive film is closely related to the degree of deformation of the film before and after such heating and pressurizing (difference in resin flow rate). Furthermore, they discovered that this difference in resin flow rate is closely related to the 80°C viscosity ratio of the laminated insulating resin layers constituting the conductive film, thus completing the present invention.

[0011] In other words, the present invention provides a conductive film having a first insulating resin layer, a second insulating resin layer laminated thereon, and conductive particles with an average particle diameter of 10 μm or more, wherein 90% or more of the conductive particles are arranged in the conductive film spaced apart from each other on a number basis, and the difference in resin flow amount between the first insulating resin layer and the second insulating resin layer is 0.07 or more and 0.09 or less, or / or the 80°C viscosity ratio between the first insulating resin layer and the second insulating resin layer is less than 2.

[0012] In the conductive film of the present invention, the preferred viscosity ratio at 80°C is 10 / 7 or more and 7 / 4 or less. Within this range, it is possible to mount relatively thick films at low pressure and to suppress excessive flow of the resin.

[0013] Furthermore, the present invention provides a method for manufacturing a conductive film in which the difference in resin flow amount between a first insulating resin layer and a second insulating resin layer is 0.07 or more and 0.09 or less, or / or the 80°C viscosity ratio between the first insulating resin layer and the second insulating resin layer is less than 2, characterized in that conductive particles with an average particle diameter of 10 μm or more are arranged in the first insulating resin layer such that 90% or more are individually spaced apart on a number basis, and the second insulating resin layer is laminated on the first insulating resin layer. In this case, it is preferable to laminate the second insulating resin layer on the surface of the first insulating resin layer on the side where the conductive particles are arranged.

[0014] Furthermore, the present invention provides a connection structure in which a first electronic component and a second electronic component are electrically joined via the conductive film of the present invention described above, and a method for manufacturing a connection structure in which the first electronic component and the second electronic component are electrically joined via the conductive film of the present invention described above.

[0015] The conductive film of the present invention is a conductive film having a first insulating resin layer, a second insulating resin layer laminated thereon, and conductive particles with an average particle diameter of 10 μm or more. In this conductive film, 90% or more of the conductive particles are spaced apart from each other on a numerical basis. Therefore, the possibility of controlling the effect of resin flow and realizing good particle capture and good conductivity is increased. Furthermore, for the first insulating resin layer and the second insulating resin layer, the difference in resin flow amount between the two layers (the value obtained by subtracting the smaller resin flow amount from the larger resin flow amount), which is an indicator of the degree of deformation of the film before and after heating and pressurizing, is set to 0.07 or more and 0.09 or less, or / or the 80°C viscosity ratio of the two layers (the value obtained by dividing the higher 80°C viscosity by the lower 80°C viscosity) is set to less than 2. This makes it possible to suppress the risk of resin overflow and blocking during slitting or processing into a winding body without impairing good particle capture and good conductivity. The definition of resin flow amount will be described later.

[0016] This is a plan view of the conductive film of the present invention (e.g., an anisotropic conductive film). This is a cross-sectional view of the conductive film of the present invention (e.g., anisotropic conductive film) along line A-A. This is a schematic diagram showing temporary bonding during pressure bonding.

[0017] The conductive film of the present invention will be described in detail below with reference to the drawings. In each figure, the same reference numerals represent the same or equivalent components.

[0018] <Overall Structure of the Conductive Film> Figure 1 is a plan view of the conductive film 1 of the present invention, and Figure 2 shows a cross-sectional view along line A-A. Hereafter, the conductive film 1 may be described using an anisotropic conductive film as an example.

[0019] Figure 1 is a plan view of a conductive film 1 according to an embodiment of the present invention. The conductive film 1 has a first insulating resin layer 11, a second insulating resin layer 12 laminated thereon, and conductive particles 20 with an average particle diameter of 10 μm or more. The laminated first insulating resin layer 11 and the second insulating resin layer 12 may sometimes be simply referred to as the insulating resin layer 10. Figure 2 is a cross-sectional view of the conductive film 1 along the line A-A passing through the center of the conductive particles 20 in Figure 1.

[0020] (Separated arrangement of conductive particles) In the conductive film 1 of the present invention, 90% or more, more preferably 95% or more, of the conductive particles 20 are arranged at a distance from each other based on the number of particles. This increases the possibility of achieving good particle capture and good conductivity. Furthermore, being arranged at a distance from each other means that any conductive particle 20 is arranged independently in a plan view of the film without coming into contact with other conductive particles 20.

[0021] (Distance between the centers of adjacent conductive particles) Regarding the lower limit of the spacing distance of the conductive particles 20 (i.e., the distance between the centers of adjacent conductive particles 20), there is a concern that short circuits may occur if the distance between the centers of adjacent conductive particles 20 is too short. Therefore, it is preferable to set the distance between the centers of the closest adjacent conductive particles 20 to at least 1.2 times, more preferably 1.5 times, the average particle diameter. When the conductive particles 20 are arranged in a regular pattern and multiple conductive particles 20 are connected to form a unit, the "distance between the centers of adjacent conductive particles" can be considered as the "distance between the centers of adjacent units (for example, the distance between the centroids of the units)." Furthermore, regarding the upper limit of the spacing distance of the conductive particles 20, there is no particular restriction on the distance between the centers of adjacent conductive particles, as the required conductivity performance differs depending on the bump layout (shape, area, dimensions, distance between bumps, etc.), the type of electronic component, and the intended use of the connected object. From the viewpoint of cost benefits such as reduction of conductive particles, a longer distance is preferable. Furthermore, if the distance between the centers of adjacent conductive particles is excessively long, there is a concern that the number of conductive particles captured by the terminal will be insufficient, resulting in insufficient conductivity. Therefore, in practical terms, the distance between the centers of the closest adjacent conductive particles should be preferably 100 times or less, more preferably 80 times or less, the average particle diameter. The average particle diameter of conductive particles can be calculated by measuring 10,000 or more particles using a commercially available particle size analyzer, particularly an image-type particle size analyzer (FPIA-3000, Malvern Panalytical Co., Ltd.). If the conductive particles are spherical, it can also be calculated by measuring at least 200 conductive particles by observation using an electron microscope such as a SEM in a planar view of the film.

[0022] (Random and regular arrangement of conductive particles) Conductive particles may be randomly arranged as long as they are spaced apart from each other. However, in order to accommodate components with relatively large differences in terminal height, if a portion of the conductive particles with a low particle density is placed on the terminal during connection, the conductive particles on that terminal will flow, further reducing the particle density in that portion, which reduces the number of conductive particles that can be captured at the terminal and may cause poor conductivity (insufficient conductive performance). Therefore, a regular arrangement is preferable. This is because a regular arrangement makes it easier for conductive particles to be captured at the terminal even if there are undulations or differences in height on the connection surface where the terminal is formed, significantly reducing the occurrence of poor conductivity and short circuits. A preferred embodiment of the regular arrangement is one in which the conductive particles are regularly arranged between the laminated first insulating resin layer 11 and the second insulating resin layer 12. When regularly arranged, the particles may be intentionally in contact with each other to form a unit. Specific examples of regular arrangements include configurations in which conductive particles are arranged at the grid points of a lattice arrangement (e.g., a hexagonal lattice arrangement, a square lattice arrangement, a rectangular lattice arrangement, etc.), but there are no particular restrictions as long as there is regularity.

[0023] (Regular arrangement of conductive particles in the conductive film of Figure 1) In the conductive film 1 of Figure 1, the conductive particles 20 are regularly arranged in the insulating resin layer 10 in a plan view. That is, they are arranged in a square grid (quadrilateral grid) in a plan view. It is preferable that the conductive particles 20 are regularly arranged in the conductive film 1 in this way because there is no variation in the density of the conductive particles 20 in the planar arrangement. For example, it is preferable that the difference between the maximum and minimum values ​​of the particle density when 10 areas of area 1 mm × 1 mm are extracted in the longitudinal direction X of the film and the particle density of conductive particles in each area is less than 20% of the average particle density of each area. To this end, the conductive particles 20 may be arranged at grid points such as an orthorhombic grid, a rectangular grid, or a hexagonal grid, in addition to a square grid (quadrilateral grid). When arranged regularly, conductive particles are more easily captured by the terminals even if there are undulations on the connection surface where the terminals are formed, and the occurrence of poor conductivity and short circuits can be significantly reduced.

[0024] As mentioned above, in the conductive film 1 of Figure 1, the conductive particles 20 are arranged in a grid, and the grid axis B of this arrangement intersects the longitudinal direction X from the viewpoint of stabilizing particle capture. For example, when the conductive film 1 is an anisotropic conductive film for fine pitch, the angle θ between the longitudinal direction X of the conductive film 1 and the grid axis B is preferably set to 10° to 40°. The grid axis B may also be parallel to the longitudinal direction X and the short direction Y of the conductive film 1, and can be determined according to the terminal width, terminal pitch, etc.

[0025] (Arrangement of conductive particles in the film thickness direction) In the insulating resin layer 10 of the conductive film 1 of the present invention, the conductive particles 20 may be arranged in the film thickness direction Z so as to be pressed into the exposed surface of the first insulating resin layer 11 or the exposed surface of the second insulating resin layer 12. However, as shown in Figure 2, it is preferable to arrange them between the first insulating resin layer 11 and the second insulating resin layer 12 so as to be sandwiched between them (boundary C). This prevents the resin from flowing and reducing the ability to capture conductive particles when the conductive film 1 is pressed during connection. Therefore, the conductive film 1 can increase the number of particles it can capture and can accommodate wavy ceramic substrates and substrates with small connection pads. Note that, as long as the conductive particles 20 are arranged at the boundary C between the first insulating resin layer 11 and the second insulating resin layer 12, it is acceptable for more than half of the particle diameter to be embedded in one of the layers.

[0026] The fact that the conductive particles 20 are positioned at specific locations in the film thickness direction Z can be confirmed, for example, by cutting the conductive film 1 along the line A-A in Figure 1 and observing the cross-section with an electron microscope (see Figure 2).

[0027] (Resin flow rate difference, 80°C viscosity ratio) The conductive film 1 of the present invention is characterized in that the resin flow rate difference (the value obtained by subtracting the smaller resin flow rate (usually the first insulating resin layer 11) from the larger resin flow rate (usually the second insulating resin layer 12)) between the first insulating resin layer 11 and the second insulating resin layer 12, which is an indicator of the degree of deformation of the film before and after heating and pressurizing, is 0.07 or more and 0.09 or less. If the resin flow rate difference falls below 0.07, the resin flow becomes too small, making it difficult to fill the gaps between the bumps, which may make low-pressure mounting difficult. If it exceeds 0.09, the resin flow becomes large, but there is a concern that conductive particles will move more easily. These concerns are also affected by the viscosity of the entire film, so in the present invention, the viscosity of the entire film is considered to be the viscosity at 80°C, which is the temperature before resin flow begins during the main bonding process. The viscosity of the entire film is taken into consideration when designing the first and second insulating resin layers. Here, "resin flow rate" in this invention is a numerical value defined as follows. A larger resin flow rate means that the resin flows more easily when heated and pressurized. In other words, it means that the melt viscosity at 80°C is lower.

[0028] (Definition of Resin Flow Amount) The conductive film is slit to a width of 2.0 mm or less, preferably 2.0 mm. The slit conductive film is sandwiched between two 1.1 mm thick non-alkali glass sheets. Then, using a 2.0 mm wide heat tool, pressure is applied from above the non-alkali glass, directly above the conductive film, under heating and pressurizing conditions of 140°C / 2 MPa / 6 seconds. The width of the conductive film before and after pressurizing is measured, and the value calculated using the following formula (1) is defined as the resin flow amount. If the conductive film is composed of a laminate of multiple insulating resin layers, the resin flow amount can be calculated for each insulating resin layer. Conductive films with a film width of less than 2.0 mm can be used for resin flow amount measurement without slitting. As mentioned above, a certain correlation can be assumed between "resin flow rate" and "80°C viscosity." Therefore, for example, if a film width of less than 2.0 mm affects the measurement of the resin flow rate, the "80°C viscosity ratio" characteristic described later can be adopted instead of the "resin flow rate difference" characteristic of the conductive film of the present invention, although this is on a case-by-case basis. The choice of which to adopt can be appropriately selected depending on the object to be connected, the mounting area, and the film width when measuring the resin flow rate. The heating and pressing conditions are set based on the same considerations as the 80°C viscosity described above, as conditions under which resin flow for this bonding can occur. Although the present invention focuses on controlling viscosity and resin fluidity with temperature, it is not limited to the formulations described in the specification.

[0029]

[0030] Furthermore, the numerical values ​​of the "resin flow rate" of the first insulating resin layer 11 and the second insulating resin layer 12 should be greater than 1.05, more preferably 1.06 or higher, and even more preferably 1.08 or higher, because if it is too small, connection at low pressure becomes difficult (because the resistance to pushing increases due to the thickness of the resin layer). If it is too large, the fluidity of the resin becomes too great, making capture difficult, so it should be less than 1.32, and more preferably less than 1.30. Thus, the characteristic of the "resin flow rate" in the present invention is that one of the objectives of the invention is to control the effect of resin flow, and this differs from the technique of simply designing the melt viscosity to be low, as is the case with general conductive particle-free layers, in order to achieve such an objective. In the case of general conductive particle-free layers, the resin flow rate is considered to be greater than 1.35.

[0031] Regarding the indicator of the degree of deformation of the film before and after heating and pressurizing, the difference in resin flow rate has been explained, but from another perspective, in the conductive film 1 of the present invention, the 80°C viscosity ratio of the first insulating resin layer 11 and the second insulating resin layer 12 (the value obtained by dividing the higher 80°C viscosity (usually the 80°C viscosity of the first insulating resin layer 11) by the lower 80°C viscosity (usually the 80°C viscosity of the second insulating resin layer 12)) is less than 2, preferably between 10 / 7 and 7 / 4. If the 80°C viscosity ratio is 2 or more, the fluidity of the resin at connection becomes too large, and in some cases (such as when the film width is relatively narrow), slitting tends to become difficult. Furthermore, the 80°C viscosity ratio can be understood as functioning as a means to satisfy the resin flow rate ratio. In the conductive film 1 of the present invention, it is preferable to satisfy both the "resin flow rate difference" and the "80°C viscosity ratio" described above, but it is preferable to satisfy them simultaneously in order to balance the behavior of resin flow and the workability of slitting.

[0032] For the 80°C viscosity, a rotary rheometer (TA Instruments) was used to measure the melt viscosity under the following conditions: heating rate of 10°C / min, constant measurement pressure of 5g, and plate diameter of 8mm. The viscosity at 80°C was read, and the resulting value was defined as the 80°C viscosity.

[0033] Furthermore, the 80°C viscosity of the first insulating resin layer 11 and the second insulating resin layer 12 themselves is preferably 1000 Pa·s or more, more preferably 2000 Pa·s or more, more preferably 30000 Pa·s or less, and more preferably 10000 Pa·s or less, respectively, in order to make them applicable to low-temperature, low-pressure anisotropic conductive connection conditions (for example, 190°C or less, 2 MPa or less).

[0034] The viscosity at 80°C of the insulating resin layer 10, which is formed by laminating a first insulating resin layer 11 and a second insulating resin layer 12 exhibiting such an 80°C viscosity value, basically depends largely on the second insulating resin layer 12, which exhibits a relatively low 80°C viscosity. If it is too low, the fluidity during connection decreases, and if it is too high, defects in the slits are likely to occur depending on the slit width. Therefore, the lower limit is preferably 2000 Pa·s or more, more preferably 4000 Pa·s or more, and even more preferably 5000 Pa·s or more, and the upper limit is preferably less than 10000 Pa·s, and more preferably 8500 Pa·s or less.

[0035] (First insulating resin layer, second insulating resin layer) As the first insulating resin layer 11 and the second insulating resin layer 12, known insulating resin layers applied to conductive films such as known anisotropic conductive films can be appropriately adopted. For example, a photoradical polymerization type resin layer containing an acrylate compound and a photoradical polymerization initiator, a thermal radical polymerization type resin layer containing an acrylate compound and a thermal radical polymerization initiator, a thermal cationic polymerization type resin layer containing an epoxy compound and a thermal cationic polymerization initiator, a thermal anionic polymerization type resin layer containing an epoxy compound and a thermal anionic polymerization initiator, etc. can be used. Furthermore, these resin layers may be polymerized resin layers as needed. For example, in the case of a thermal radical polymerization type resin layer, it is preferable to use a thermal radical polymerization initiator in an amount of preferably 2 parts by mass or more and 60 parts by mass or less, more preferably 5 parts by mass or more and 40 parts by mass or less, per 100 parts by mass of the acrylate compound.

[0036] The first insulating resin layer 11 and the second insulating resin layer 12 preferably further contain a film-forming resin and a silane coupling agent. Examples of film-forming resins include phenoxy resin, epoxy resin, unsaturated polyester resin, saturated polyester resin, urethane resin, butadiene resin, polyimide resin, polyamide resin, and polyolefin resin. Two or more film-forming resins can be used in combination. Among these, phenoxy resin is preferably used from the viewpoint of film-forming properties, processability, and connection reliability. Examples of silane coupling agents include epoxy-based silane coupling agents and acrylic-based silane coupling agents. These silane coupling agents are mainly alkoxysilane derivatives. The first insulating resin layer 11 and the second insulating resin layer 12 may also contain insulating fillers such as silica fine particles, alumina, and aluminum hydroxide as needed. For example, in the case of a thermal radical polymerization type resin layer, it is preferable to use an insulating filler in an amount of 5 to 50 parts by mass per 100 parts by mass of the acrylate compound. Furthermore, the first insulating resin layer 11 and the second insulating resin layer 12 may contain, in addition to the insulating filler described above, fillers, softeners, accelerators, antioxidants, colorants (pigments, dyes), organic solvents, ion catchers, and the like.

[0037] From the viewpoint of the ease of temporarily attaching the conductive film 1 to the substrate, the thickness of the first insulating resin layer 11 and the thickness of the second insulating resin layer 12 are preferably at least 2 / 3 of the average particle diameter of the conductive particles 20. Furthermore, the sum of the thicknesses of the first insulating resin layer 11 and the second insulating resin layer 12 is usually 3.5 times or less the average particle diameter of the conductive particles 20. As can be understood from the description in paragraph 0025, either the first insulating resin layer 11 or the second insulating resin layer 12 can be recognized as a so-called conductive particle-containing layer, and when conductive particles are placed at the interface between the two layers, the layer in which the conductive particles are more deeply embedded can be recognized as the conductive particle-containing layer. Also, if conductive particles are embedded to a similar extent in both layers, both can be recognized as conductive particle-containing layers (the laminated layers together may be considered as a conductive particle-containing layer).

[0038] (Conductive Particles) As the conductive particles 20 constituting the conductive film 1 of the present invention, those used in known conductive films such as anisotropic conductive films can be appropriately selected and used. For example, metal particles such as nickel, cobalt, silver, copper, gold, and palladium, and metal-coated resin particles obtained by coating core resin particles with metal can be mentioned. Two or more of these can also be used in combination. Here, the metal coating of the metal-coated resin particles can be formed using known metal film formation methods such as electroless plating and sputtering. The core resin particles may be formed of only resin. The particles are preferably spherical, but may be protrusion particles having protrusions formed on the surface of the particles. The surface of the conductive particles 20 may be subjected to insulation treatment by known techniques.

[0039] From the point of ensuring stable conduction even when the surface has undulations like a ceramic substrate used in a camera module, etc., the average particle diameter of the conductive particles 20 is 10 μm or more. Also, from the perspective of the risk of short circuit, it is preferably 30 μm or less. As described above, this average particle diameter can be calculated by measuring 10,000 or more particles using a commercially available particle size distribution meter, particularly an image type particle size distribution meter (FPIA - 3000, Malvern Panalytical Ltd.).

[0040] Also, the particle density of the conductive particles 20 is not particularly limited, but generally, from the point of conductive reliability, it is preferably 20 particles / mm ２ or more, more preferably 40 particles / mm ２ or more, even more preferably 150 particles / mm ２ or more, and preferably 7000 particles / mm ２ or less, more preferably 2000 particles / mm ２ or less, even more preferably 1500 particles / mm ２ or less, and particularly preferably 850 particles / mm ２ or less. The particle density (number density) of the conductive particles 20 can be determined, for example, by the method described in JP-A-2019-031649.

[0041] <Method for Manufacturing Conductive Film> The conductive film 1 of the present invention is manufactured by arranging conductive particles 20 having an average particle diameter of 10 μm or more in the first insulating resin layer 11 so that 90% or more of them are individually separated on a number basis, and laminating the second insulating resin layer 12 on the first insulating resin layer 11 in which the conductive particles 20 are arranged. In this case, it is preferable to laminate the second insulating resin layer 12 on the surface of the first insulating resin layer 11 on the side where the conductive particles 20 are arranged. More specifically, the conductive film 1 can be manufactured, for example, as follows.

[0042] <Specific Manufacturing Example of Conductive Film> First, a mold having convex portions corresponding to the arrangement of the conductive particles 20 is produced on a flat metal plate by methods such as machining, laser processing, or photolithography. Next, a curable resin is filled into the mold and cured to produce a resin mold with reversed concavities and convexities. The conductive particles 20 are placed in the concave portions of this resin mold, and the first insulating resin layer 11 formed in advance is placed thereon, and the first insulating resin layer 11 is peeled off in a state where the conductive particles 20 adhere to the surface.

[0043] While applying heat and pressure to the surface of the peeled first insulating resin layer 11 to which the conductive particles 20 adhere, the conductive particles 20 are pushed into the first insulating resin layer 11 so that a part of them is exposed. The second insulating resin layer 12 formed in advance is placed on the surface of the first insulating resin layer 11 on the side where the conductive particles 20 are pushed in, and by pressure bonding, the conductive film 1 as shown in FIG. 2 is obtained.

[0044] The conductive film 1 of the present invention obtained in this way can be preferably used as an anisotropic conductive film. Preferably, it is slit into a narrow width of 0.5 mm or more and preferably 10.0 mm or less, and can be made into a wound body of 5 m or more. Here, the wound body is obtained by winding a conductive film around a core provided with side plates (flanges). Not only when slit in this way but also when made into a wound body, the conductive film 1 of the present invention can achieve good particle capturing properties and good conduction characteristics, and can suppress the risk of resin protrusion and blocking, and can also be applied to a wavy ceramic substrate or a substrate with small connection pads.

[0045] <Connection structure and method for manufacturing the same> The conductive film 1 of the present invention is useful for manufacturing a connection structure that exhibits stable conductivity characteristics. Specifically, a connection structure in which a first electronic component and a second electronic component are electrically joined via the conductive film 1 of the present invention, and a method for manufacturing a connection structure in which the first electronic component and the second electronic component are electrically joined via the conductive film 1 of the present invention are also part of the present invention.

[0046] Here, the first electronic component may be a flexible printed circuit board (FPC), and the second electronic component may be a ceramic substrate. Furthermore, components with relatively high bump heights, such as flexible printed circuit boards (FPCs) or semiconductor elements, can also be used as the second electronic component. From the standpoint of obtaining the effects of the present invention, it is preferable that the second electronic component is a substrate with "undulations" rather than being smooth, as will be described later. The ceramic substrate may have a camera module mounted or incorporated on it. When the second electronic component is a ceramic substrate, it usually has undulations of 20 μm or more, specifically 20 to 50 μm. The undulations of the ceramic substrate can be measured using a surface roughness meter (SurfCorder SE-400, Kosaka Laboratory Co., Ltd.). Specifically, the stylus of the surface roughness meter is scanned in the direction of the terminal arrangement on the ceramic substrate to obtain a surface surface roughness profile, and the undulations are determined from the difference between the maximum and minimum heights in this profile. Measurement may also be performed in the same manner as described in Japanese Patent Publication No. 6425382. Furthermore, it is preferable to place the first insulating resin layer 11, which has a relatively high viscosity at 80°C, on the side of the second electronic component.

[0047] According to the manufacturing method of the connection structure of the present invention, by using the conductive film 1 of the present invention described above, the first electronic component and the second electronic component are suitably electrically connected, and a connection structure having stable conductivity characteristics can be obtained.

[0048] In particular, when the second electronic component is a substrate (ceramic substrate) that has a non-smooth "undulation," both the terminals on the convex and concave parts of this undulation are well electrically connected to the opposing terminals. This can be explained as follows: During (anisotropic) conductive connection, the resin forming the insulating resin layers (first insulating resin layer and second insulating resin layer) melts and flows. However, in the conductive film 1 described above, the average particle size of the conductive particles is within a specific range, and the insulating resin layers are composed of a first insulating resin layer and a second insulating resin layer having a specific resin flow rate difference or a specific 80°C viscosity ratio. Therefore, even when the resin melts and flows, conductive particles on the terminals on the convex parts of the undulation are less likely to flow, increasing the number of captured particles and achieving a good conductive connection.

[0049] When manufacturing the connecting structure, the conductive film 1 of the present invention is temporarily attached to the first or second electronic component and then permanently bonded. Typical conditions for temporary attachment include a temperature of 40°C to 60°C, a pressure of 0.5 MPa to 1.5 MPa, and a time of 1 second to 2 seconds. Typical conditions for permanent bonding include a temperature of 140°C to 200°C, a pressure of 1 MPa to 6 MPa, and a time of 3 seconds to 60 seconds.

[0050] Incidentally, in this invention, the resin flow rate of the conductive film 1 is measured at 140°C, which corresponds to the lower limit temperature under the actual bonding conditions. Even if the binder composition of the conductive film 1 of this invention were designed to be suitable for bonding at 200°C, the resin would still flow once it reached 140°C, making it a suitable method for determining the resin flow rate. This invention is based on a binder design suitable for such mounting conditions. Therefore, it is not limited to the binder design disclosed in the specification.

[0051] Furthermore, when checking the 80°C viscosity ratio of a conductive film in which multiple insulating resin layers are laminated, it is possible to confirm that there are slight differences in the melt viscosity of each laminated layer by sandwiching the conductive film between glass under the mounting conditions (temperature / pressure / time) of this crimping method and measuring the resin flow rate.

[0052] The present invention will be specifically described below with reference to examples. First, the preparation of insulating resin films A to D for forming the first insulating resin layer and the second insulating resin layer will be described, and then the preparation of resin molds used to arrange conductive particles in these films will be described. Next, the preparation of anisotropic conductive films as conductive films for examples and comparative examples using these films will be described.

[0053] <Preparation of insulating resin films> Insulating resin films A to D were prepared with a thickness of 16 μm from four types of compositions, a to d, shown in Table 1. Note that the formulations in Table 1 are the amounts of each component excluding the solvent.

[0054] For the four types of insulating resin films A to D that were fabricated, the melt viscosity was measured using a rotary rheometer (manufactured by TA Instruments) under the following conditions: heating from room temperature, heating rate of 10°C / min, constant measurement pressure of 5g, and measurement plate diameter of 8mm. The viscosity at 80°C was read as the 80°C viscosity. These results are also shown in Table 1.

[0055]

[0056] <Preparation of resin mold> Density 600 pcs / mm ２ The mold was then fabricated by machining a nickel plate to create a mold with a four-sided grid pattern in the convex portion. A resin mold was formed by pouring molten pellets of a known transparent resin into the mold and then cooling and solidifying it to create a mold in which the recessed portion has the same pattern as the convex portion.

[0057] Example 1 Conductive particles with an average particle size of 20 μm (Micropearl®, manufactured by Sekisui Chemical Co., Ltd.) were filled into the recess of the resin mold prepared above, and an insulating resin film A (viscosity 10,000 Pa·s at 80°C) was placed on top of them. The insulating resin film A was peeled off with the conductive particles still attached to the surface. Heat and pressure were applied to the conductive particles attached to the insulating resin film A, and the conductive particles were pressed into the insulating resin film A so that half of the particle size of the conductive particles was embedded in the insulating resin film A. Next, an insulating resin film B (viscosity 7,000 Pa·s at 80°C), which had been previously formed on a base film (a 50 μm thick release-treated PET film), was placed on the surface of the insulating resin film A on the side where the conductive particles were pressed, and the film was pressed together and cured by irradiation with ultraviolet light to produce the anisotropic conductive film of Example 1 (see Figure 2). Insulating resin film A, which exhibits a high viscosity at 80°C, corresponds to the first insulating resin layer, and insulating resin film B corresponds to the second insulating resin layer. The viscosity at 80°C of the laminate of insulating resin film A (corresponding to the first insulating resin layer) and insulating resin film B (corresponding to the second insulating resin layer) was 8100 Pa·s.

[0058] Furthermore, a cover film was attached to the exposed insulating resin film A surface of the anisotropic conductive film obtained in Example 1, slit to a width of 0.8 mm, peeled off the cover film, and 100 m of the anisotropic conductive film was wound onto a winding core (100 mm in diameter) equipped with a flange (side plate) so that the base film was on the outside, thereby producing a winding body of the anisotropic conductive film of Example 1.

[0059] Example 2 An anisotropic conductive film of Example 2 was prepared by repeating the same procedure as in Example 1, except that insulating resin film B (80°C viscosity 7000 Pa·s) and insulating resin film C (80°C viscosity 4000 Pa·s) were used instead of insulating resin film A and insulating resin film B (see Figure 2). Insulating resin film B, which exhibits a high 80°C viscosity, corresponds to the first insulating resin layer, and insulating resin film C corresponds to the second insulating resin layer. Furthermore, a winding of the anisotropic conductive film of Example 2 was prepared in the same manner as in Example 1. The 80°C viscosity of the laminate of insulating resin film B, which corresponds to the first insulating resin layer, and insulating resin film C, which corresponds to the second insulating resin layer, was 5300 Pa·s.

[0060] Comparative Example 1 An anisotropic conductive film of Comparative Example 1 was prepared by repeating the same procedure as in Example 1, except that two insulating resin films A (80°C viscosity 10,000 Pa·s) were used instead of insulating resin film A and insulating resin film B (see Figure 2). In the anisotropic conductive film of Comparative Example 1, the 80°C viscosity of the first insulating resin layer and the second insulating resin layer are equal. Furthermore, a winding of the anisotropic conductive film of Comparative Example 1 was prepared in the same manner as in Example 1. The 80°C viscosity of the laminate of insulating resin film A corresponding to the first insulating resin layer and another insulating resin film A corresponding to the second insulating resin layer was 10,000 Pa·s.

[0061] Comparative Example 2 An anisotropic conductive film of Comparative Example 2 was prepared by repeating the same procedure as in Example 1, except that insulating resin film C (80°C viscosity 4000 Pa·s) and insulating resin film D (80°C viscosity 1000 Pa·s) were used instead of insulating resin film A and insulating resin film B (see Figure 2). Insulating resin film C, which exhibits a high 80°C viscosity, corresponds to the first insulating resin layer, and insulating resin film D corresponds to the second insulating resin layer. Furthermore, a winding of the anisotropic conductive film of Comparative Example 2 was prepared in the same manner as in Example 1. The 80°C viscosity of the laminate of insulating resin film C, which corresponds to the first insulating resin layer, and insulating resin film D, which corresponds to the second insulating resin layer, was 1800 Pa·s.

[0062] Comparative Example 3 An anisotropic conductive film of Comparative Example 3 was prepared by repeating the same procedure as in Example 1, except that conductive particles with an average particle diameter of 3 μm (Micropearl®, manufactured by Sekisui Chemical Co., Ltd.) were used instead of conductive particles with an average particle diameter of 20 μm (see Figure 2). Insulating resin film A, which exhibits a high viscosity at 80°C, corresponds to the first insulating resin layer, and insulating resin film B corresponds to the second insulating resin layer. Furthermore, a winding of the anisotropic conductive film of Comparative Example 3 was prepared in the same manner as in Example 1. The viscosity at 80°C of the laminate of insulating resin film A, which corresponds to the first insulating resin layer, and insulating resin film B, which corresponds to the second insulating resin layer, was 8100 Pa·s.

[0063] <Evaluation> The anisotropic conductive films and their windings in the examples and comparative examples were tested and evaluated as follows: "80°C viscosity ratio," "resin flow rate and resin flow rate difference," "conductive particle capture rate and conductivity characteristics," "interparticle distance and resin flow before and after crimping," "overflow in the winding," and "blocking in the winding."

[0064] (80°C Viscosity Ratio) The 80°C viscosity ratio was calculated by dividing the 80°C viscosity of the first insulating resin layer by the 80°C viscosity of the second insulating resin layer. The results are shown in Table 2. The 80°C viscosity of the first and second insulating resin layers combined is also shown in Table 2.

[0065] (Resin flow rate and resin flow rate difference) The fabricated anisotropic conductive film was slit to a width of 2.0 mm, and the slit anisotropic conductive film was sandwiched between two sheets of non-alkali glass (thickness 1.1 mm). Then, using a 2.0 mm wide heat tool, the anisotropic conductive film was pressed from above the non-alkali glass under heating and pressing conditions of 140°C, 2 MPa, and 6 seconds. The width of the anisotropic conductive film before and after pressing (for each of the first and second insulating resin layers) was measured, and the resin flow rate was calculated by applying the anisotropic conductive film width to the conductive film width using the following formula (1). In addition, the resin flow rate difference was calculated by subtracting the resin flow rate of the first insulating resin layer from the resin flow rate of the second insulating resin layer. The obtained results are shown in Table 2.

[0066]

[0067] Regarding the evaluation of resin flow rate, a larger resin flow rate increases the overall fluidity of the insulating resin layer, while a smaller flow rate makes slitting easier even with large differences in resin flow rate, resulting in a highly practical anisotropic conductive film. Furthermore, since resin flow rate is inversely proportional to melt viscosity, eliminating this difference (using the same material) makes it impossible to design the resin flow. However, by introducing a slight difference, it is possible to maintain fluidity while avoiding problems such as resin overflow and blocking during winding, especially in electronic components with relatively large terminal heights that require the use of conductive particles with a particle size of 10 μm or more.

[0068] (Conductive Particle Capture Rate and Conductivity Characteristics) Anisotropic conductive films of the examples and comparative examples were temporarily attached to an alumina ceramic substrate from the side with the first insulating resin layer, and a flexible printed circuit board was placed on the side with the second insulating resin layer. A connection structure sample was then prepared by pressing the films together under the conditions of 140°C, 2 MPa, and 6 seconds. During the preparation of this sample, the number of conductive particles (n0) on the connection terminals was counted by a conventional method after temporary attachment to the alumina ceramic substrate. After pressing the flexible printed circuit board, the number of conductive particles (n1) remaining on the connection terminals when the flexible printed circuit board was peeled off was counted, and the conductive particle capture rate was calculated using the following formula (2). The obtained results are shown in Table 2. For practical purposes, a conductive particle capture rate of 40% or more is desirable.

[0069]

[0070] The conductivity characteristics of the connection structure samples were measured using a digital multimeter (34401A, manufactured by Agilent Technologies, Inc.) for 30 channels, applying a current of 1 mA using the four-terminal method and measuring the conductivity resistance. A resistance value of 2 Ω or less was considered acceptable, and a value exceeding 2 Ω was considered unacceptable. The results obtained (number of acceptable channels / 30 channels) are shown in Table 2.

[0071] The following alumina ceramic substrates and flexible printed circuit boards were used to prepare the connection structure samples.

[0072] <Alumina ceramic substrate> Tungsten wiring: Line / space = 100 μm / 100 μm Terminal (wiring) height: 10 μm Substrate thickness: 0.4 mm Wavy: 20 μm

[0073] <Flexible Printed Circuit Board (FPC)> Copper wiring: Line / space = 100 μm / 100 μm Terminal height: 12 μm Polyimide thickness: 25 μm

[0074] (Interparticle distance and resin flow before and after crimping) As shown in Figure 3, the anisotropic conductive film 1 of the example and comparative example was temporarily attached to an alumina ceramic substrate 2 having terminals 21 so that the first insulating resin layer 11 faced it, and an FPC 3 (Cu wiring: L / S = 100 μm / 100 μm, terminal 31 height: 12 μm, polyimide thickness: 25 μm) was placed on top of it and crimped under the conditions of 140°C, 2 MPa, and 6 seconds. During this crimping, after temporary attachment to the ceramic substrate, one conductive particle P0 on the connection terminal was selected, and the nearest conductive particle Px in the X direction and the nearest conductive particle Py in the Y direction relative to conductive particle P0 were selected, and the interparticle distances in the X and Y directions (distance between particle centers of P0 and Px, distance between particle centers of P0 and Py) before and after crimping were measured. From the obtained results, the particle migration distance due to resin flow in the X and Y directions was calculated, and their average values ​​were obtained. When the average distance traveled by the resin flow is small, capture is good. However, if it is too large, concerns arise such as insufficient capture, variations in the number of captured particles between terminals of the same component, and difficulty in maintaining a constant number of captured particles between terminals in continuous connections. Furthermore, if the resin flow is too small, it may not be suitable for low-voltage mounting. The obtained results are shown in Table 2.

[0075] (Overhang in the winding) For the windings of the anisotropic conductive film of the examples and comparative examples, the quality of the overhang was evaluated based on the amount of overhang of the insulating resin layer from the side surface of the anisotropic conductive film winding, as shown in paragraph 0013 of Japanese Patent Application Publication No. 2017-137188. Specifically, the fabricated anisotropic conductive film winding was attached to the fixing rod of the overhang test jig as shown in Figure 3 of Japanese Patent Application Publication No. 2017-137188, the rotation of the winding core was fixed, and a weight was attached to the end of the anisotropic conductive film that had been drawn out to a predetermined length from the film winding to apply a static load. The test conditions were as follows.

[0076] Joint angle α (the angle with fewer turns of anisotropic conductive film): 90° Length of anisotropic conductive film pulled out from the film winding assembly: 30 cm Weight of the counterweight: 50 g Test ambient temperature: 30°C Test time: 6 hours

[0077] After the overhang test, the joints on the outer circumference of the core of the winding assembly of the anisotropic conductive film were observed using a digital microscope. For example, if the anisotropic conductive film sandwiched the base film and adhered to the anisotropic conductive film one layer above, it was defined as one layer overhang and evaluated according to the following criteria. The evaluation results are shown in Table 2.

[0078] Rank: Evaluation Criteria A: Less than 1 overhanging layer B: 1 or more but less than 2 overhanging layers C: 2 or more overhanging layers D: Could not be evaluated

[0079] (Blocking in the winding) After the protrusion test, the anisotropic conductive film was pulled out from the winding and evaluated as blocking if it could not be pulled out and used due to the protrusion of the insulating resin layer, according to the following criteria.

[0080] Rank: Evaluation Criteria A: No blocking occurred B: Blocking occurred C: Could not be evaluated

[0081]

[0082] <Evaluation Results> (Example 1) In the case of the anisotropic conductive film of Example 1, the resin flow rate of the second insulating resin layer that protruded beyond the first insulating resin layer was 1.17 times the width of the anisotropic conductive film before pressurization, confirming that it was a two-layer structure. Furthermore, when the difference in resin flow rate was calculated, it was found to be 0.09, the viscosity ratio at 80°C was 1.43 (10 / 7), and the average migration distance of conductive particles due to resin flow after pressurization was 17.2 μm, indicating that both particle capture and resin flow were achieved. This can be understood by comparing it with Comparative Example 1. In addition, the conductive particle capture rate was 40%, and no problems occurred with the conductivity characteristics in all 30 channels. No problems occurred with overhang or blocking of the winding.

[0083] (Example 2) In the case of the anisotropic conductive film of Example 2, the resin flow rate of the second insulating resin layer that protruded beyond the first insulating resin layer was 1.29 times the width of the anisotropic conductive film before pressurization, confirming that it was a two-layer structure. Furthermore, when the difference in resin flow rate was calculated, it was found to be 0.07, the viscosity ratio at 80°C was 1.75 (7 / 4), and the average migration distance of conductive particles due to resin flow after pressurization was 16.2 μm, indicating that both particle capture and resin flow were achieved. This can be understood by comparing it with Comparative Example 1 and Example 1. The conductive particle capture rate was 43%, and furthermore, no problems occurred in the conductivity characteristics of all 30 channels. Although the overhang of the winding was rated C, the blocking was rated B, and no practical problems occurred.

[0084] (Comparative Example 1) In the case of the anisotropic conductive film of Comparative Example 1, the resin flow rate of both the first insulating resin layer and the second insulating resin layer was 1.16 times, confirming that it is a two-layer structure. Furthermore, when the difference in resin flow rate was calculated, it was 0.0, and the viscosity ratio at 80°C was 1.0 (1 / 1). In addition, the average migration distance of conductive particles due to resin flow after pressurization was 18.1 μm. Although no problems occurred in the conductivity characteristics of all 30 channels, the conductive particle capture rate was 35%. Furthermore, the overhang and blocking of the winding body were also rated A. In other words, no problems occurred in actual use, so Comparative Example 1 can be considered as a reference example. As mentioned above, it is inferior in performance compared to Examples 1 and 2, but it can be considered as an indicator that makes it easier to understand the effects of the present invention.

[0085] (Comparative Example 2) In the case of the anisotropic conductive film of Comparative Example 2, the resin flow rate of the second insulating resin layer that protruded beyond the first insulating resin layer was 1.38 times the width of the anisotropic conductive film before pressurization, confirming that it had a two-layer structure. Furthermore, when the difference in resin flow rate was calculated, it was found to be 0.06, the viscosity ratio at 80°C was 4.0 (4 / 1), and the average migration distance of conductive particles due to resin flow after pressurization was less than 15 μm, indicating that both particle capture and resin flow were achieved. The conductive particle capture rate was 45% or more, and no problems were observed in the conductivity characteristics of all 30 channels. However, the overhang of the winding was rated D, and the blocking was rated C, indicating that it is unsuitable for winding, and therefore it is difficult to use it in a shipping form as a winding on a reel.

[0086] (Comparative Example 3) In the case of the anisotropic conductive film of Comparative Example 3, it is the same as in Example 1 except that the conductive particles were changed to 3 μm, so there are no problems as a wound body. However, since the conductive particle diameter has decreased from 20 μm to 3 μm, it is clear that it is not suitable for connecting electronic components to which the present invention is intended.

[0087] 1 Conductive film (anisotropic conductive film) 10 Insulating resin layer 11 First insulating resin layer 12 Second insulating resin layer 20 Conductive particles 2 Alumina ceramic substrate 3 Flexible printed circuit board 21, 31 Terminals B Lattice axis C Boundary X Longitudinal direction Y Shortitudinal direction Z Film thickness direction

Claims

1. A conductive film comprising a first insulating resin layer, a second insulating resin layer laminated thereon, and conductive particles with an average particle diameter of 10 μm or more, wherein 90% or more of the conductive particles are arranged in the conductive film spaced apart from each other, and the difference in resin flow amount between the first insulating resin layer and the second insulating resin layer is 0.07 or more and 0.09 or less.

2. The conductive film according to claim 1, wherein the viscosity ratio at 80°C of the first insulating resin layer and the second insulating resin layer is less than 2.

3. A conductive film comprising a first insulating resin layer, a second insulating resin layer laminated thereon, and conductive particles with an average particle diameter of 10 μm or more, wherein 90% or more of the conductive particles are arranged in the conductive film spaced apart from each other, and the 80°C viscosity ratio of the first insulating resin layer and the second insulating resin layer is less than 2.

4. The conductive film according to claim 1 or 3, wherein the viscosity at 80°C of the laminate of the first insulating resin layer and the second insulating resin layer is 2,000 Pa·s or more and less than 10,000 Pa·s.

5. The conductive film according to claim 2 or 3, wherein the viscosity ratio at 80°C is 10 / 7 or more and 7 / 4 or less.

6. The conductive film according to claim 1 or 3, wherein conductive particles are regularly arranged between a first insulating resin layer and a second insulating resin layer.

7. The conductive film according to claim 1 or 3, in the form of a rolled-up body.

8. A method for manufacturing a conductive film according to claim 1 or 3, comprising: arranging conductive particles with an average particle diameter of 10 μm or more in a first insulating resin layer such that 90% or more of them are individually spaced apart on a number basis; and laminating a second insulating resin layer onto the first insulating resin layer.

9. The manufacturing method according to claim 8, wherein a second insulating resin layer is laminated on the surface of the first insulating resin layer on the side where conductive particles are arranged.

10. A connection structure in which a first electronic component and a second electronic component are electrically joined via a conductive film according to claim 1 or 3.

11. A method for manufacturing a connecting structure, comprising electrically joining a first electronic component and a second electronic component via a conductive film according to claim 1 or 3.

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