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

Abstract

A conductive film according to the present invention includes an insulating high-viscosity resin layer, an insulating low-viscosity resin layer, and conductive particles having an average particle diameter of 13 μm or more. The low-viscosity resin layer is laminated on the high-viscosity resin layer, and the viscosity ratio between the high-viscosity resin layer and the low-viscosity resin layer at 80°C is 7:4 or more. The conductive particles are disposed on the high-viscosity resin layer side from the position at which 2 / 3 of the particle diameter is on the low-viscosity resin layer side from the boundary between the high-viscosity resin layer and the low-viscosity resin layer.

Description

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

[0001] The present invention relates to a conductive film, a method for manufacturing a conductive film, and a method for manufacturing a connection structure, and more particularly to a large-diameter particle-aligned anisotropic conductive film, which is a large-diameter particle-aligned conductive film.

[0002] Anisotropic conductive films (ACFs) are widely used to mount electronic components on circuit boards. In recent years, the increasing density of components in smartphones and other devices has led to space limitations within the case. Camera modules, in particular, are becoming larger and more multi-lens cameras, leading to larger imager boards to improve image accuracy. Meanwhile, connection pads are becoming smaller, necessitating the need to achieve more stable conduction resistance values ​​even with the small connection area required for this application. Ceramic substrates are often used for camera modules, and large-diameter particles are sometimes used in ACFs to address the unevenness and steps of these substrates. Furthermore, with large-diameter particles, dispersed ACFs (hereinafter referred to as dispersed ACFs) face challenges in terms of surface area and shorting, resulting in the need for anisotropic conductive films with regularly arranged conductive particles in a planar view of the film (aligned ACFs).

[0003] For example, Patent Document 1 describes an anisotropic conductive film having a filler-dispersed layer in which a filler is dispersed in a resin layer, and the surface of the resin layer near the filler has a recess with respect to the tangent plane of the resin layer at the center between adjacent fillers. Patent Document 2 also describes an anisotropic conductive film including an insulating adhesive layer and conductive particles regularly arranged in the insulating adhesive layer in a planar view, wherein the conductive particle diameter is 13 μm or more, the film thickness is 1 to 3.5 times the conductive particle diameter, the positional variation of the conductive particles in the thickness direction of the film is less than 10% of the conductive particle diameter, 10 regions each having an area of ​​1 mm × 1 mm are extracted in the longitudinal direction of the anisotropic conductive film, and the difference between the maximum and minimum particle densities measured in the planar view of each region is less than 20% of the average particle density of the regions, and further, an insulating adhesive layer different from the insulating adhesive layer in which the conductive particles are regularly arranged in a planar view is laminated.

[0004] JP 2019-031649 A JP 2019-087536 A

[0005] However, the anisotropic conductive films of Patent Documents 1 and 2 have room for further improvement in terms of stabilizing the number of particles with the minimum connection area captured when large-diameter particles are used. Conductive films also have room for improvement in terms of capturing particles at intended locations.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a conductive film or an anisotropic conductive film that can increase the number of particles captured and that can be used on undulating ceramic substrates and substrates with small connection pads.

[0007] The inventors discovered the following and conceived the present invention. Specifically, in order to maintain a more stable conductive resistance value in a conductive film (anisotropic conductive film), it is desirable to capture a certain number of particles at each terminal (connection pad) and to keep the number of particles captured at each connection pad within a certain range for each connection structure. This is beneficial for the quality stability of the connection structure. However, in the case of a single layer using large-diameter particles, controlling viscosity alone has limitations in improving particle capture. While changing the particle arrangement of regularly arranged conductive particles can be effective in improving particle capture in a single layer, a two-layer product with a viscosity difference is preferable to ensure even higher particle capture. Meanwhile, in camera module substrates using undulating ceramic substrates, it is difficult to use small-diameter particles less than 13 μm to eliminate the elevation differences caused by the undulations. Therefore, it is more desirable to use large-diameter particles of 13 μm or more and form a two-layer product.

[0008] The conductive film of the present invention comprises an insulating high-viscosity resin layer, an insulating low-viscosity resin layer, and conductive particles having an average particle diameter of 13 μm or more, the low-viscosity resin layer being laminated on the high-viscosity resin layer, the viscosity ratio of the high-viscosity resin layer to the low-viscosity resin layer at 80°C being 7:4 or more, and the conductive particles being arranged on the high-viscosity resin layer side from a position where two-thirds of the particle diameter protrudes toward the low-viscosity resin layer from the boundary between the high-viscosity resin layer and the low-viscosity resin layer.

[0009] The method for producing a conductive film of the present invention includes the steps of: attaching regularly arranged conductive particles having an average particle diameter of 13 μm or more to the surface of an insulating high-viscosity resin layer; burying the conductive particles in the high-viscosity resin layer while applying heat and pressure to the surface of the high-viscosity resin layer to which the conductive particles are attached; and disposing and pressing an insulating low-viscosity resin layer on the surface of the high-viscosity resin layer to which the conductive particles are embedded; or attaching regularly arranged conductive particles having an average particle diameter of 13 μm or more to the surface of the insulating low-viscosity resin layer; and applying heat and pressure to the surface of the low-viscosity resin layer to which the conductive particles are attached. The conductive particles are embedded in the low-viscosity resin layer while applying pressure and an insulating high-viscosity resin layer is placed on the surface of the low-viscosity resin layer where the conductive particles are embedded, and the resin is pressed against the surface. The resin includes the high-viscosity resin layer, the low-viscosity resin layer, and the conductive particles, and the low-viscosity resin layer is laminated on the high-viscosity resin layer. The viscosity ratio of the high-viscosity resin layer to the low-viscosity resin layer at 80°C is 7:4 or more, and the conductive particles are placed on the high-viscosity resin layer side at a position where two-thirds of the particle diameter protrudes from the boundary between the high-viscosity resin layer and the low-viscosity resin layer toward the low-viscosity resin layer. Note that the pressure bonding during the manufacturing method of the conductive film is different from the pressure bonding during the connection process. The temperature and pressure do not affect the product life of the conductive film.

[0010] In addition, the method for manufacturing a connection structure of the present invention includes a joining step of electrically joining a first electronic component and a second electronic component with a conductive film, wherein the conductive film includes an insulating high-viscosity resin layer, an insulating low-viscosity resin layer, and conductive particles having an average particle diameter of 13 μm or more, the low-viscosity resin layer being laminated on the high-viscosity resin layer, the viscosity ratio of the high-viscosity resin layer to the low-viscosity resin layer at 80°C being 7:4 or more, and the conductive particles are arranged on the high-viscosity resin layer side from a position where 2 / 3 of the particle diameter protrudes toward the low-viscosity resin layer from the boundary between the high-viscosity resin layer and the low-viscosity resin layer.

[0011] The conductive film of the present invention is a particle-arrayed ACF using large-diameter particles, and is a two-layer film with a viscosity difference, which allows the conductive film of the present invention to increase the number of particles captured and is compatible with undulating ceramic substrates and substrates with small connection pads.

[0012] FIG. 1 is a plan view of an anisotropic conductive film (conductive film) of an embodiment; FIG. 2 is a cross-sectional view of an anisotropic conductive film (conductive film) of an embodiment; FIG. 3 is a diagram schematically showing temporary attachment during pressure bonding; FIG. 4 is a cross-sectional view of an anisotropic conductive film (conductive film) of Example 3; FIG. 5 is a cross-sectional view of an anisotropic conductive film (conductive film) of Comparative Example 2.

[0013] Modes (embodiments) for carrying out the present invention will be described in detail. The present invention is not limited to the contents described in the following embodiments. Furthermore, the components described below include those that can be easily imagined by a person skilled in the art and those that are substantially the same. Furthermore, the configurations described below can be combined as appropriate. Furthermore, various omissions, substitutions, or modifications of the configuration can be made without departing from the gist of the present invention. The following description of the present invention will focus on anisotropic conductive films, but it can also be considered to be applicable to conductive films.

[0014] Specifically, the configuration, characteristics, and manufacturing method of the anisotropic conductive film of the embodiment are described below. These configurations, characteristics, and manufacturing methods can be considered to be applicable to conductive films as well. The term "conductive film" encompasses both anisotropic conductive films and isotropic conductive films. However, even the same conductive film can be considered as an anisotropic conductive film exhibiting anisotropic conductivity, depending on the connection object, or as a conductive film (conductive particle-containing adhesive film, bonding film). Furthermore, given the recent demand for increasingly complex configurations (various dimensions) and layouts of electrodes (terminals, connection pads, pads) of electronic components, it can be difficult to clearly distinguish between them. Furthermore, a method for manufacturing a connection structure of the embodiment using the above-mentioned anisotropic conductive film is described below. This manufacturing method can be considered to be applicable even when the above-mentioned conductive film is used.

[0015] Fig. 1 is a plan view of an anisotropic conductive film according to an embodiment, and Fig. 2 is a cross-sectional view of the anisotropic conductive film according to an embodiment. The anisotropic conductive film 1 includes an insulating resin layer 10, which includes an insulating high-viscosity resin layer 11 and an insulating low-viscosity resin layer 12, and conductive particles 20, with the low-viscosity resin layer 12 laminated on the high-viscosity resin layer 11. Fig. 2 is a cross-sectional view taken along line A-A in Fig. 1. The cross-sectional view taken along line A-A passes through the center of the conductive particles 20. The anisotropic conductive film according to an embodiment can be in the form of a long film, for example, 5 m or longer, and can also be wound around a core to form a wound body.

[0016] As shown in FIG. 1 , in the anisotropic conductive film 1, the conductive particles 20 are regularly arranged in the resin layer 10 in a planar view. That is, they are arranged in a square lattice (tetragonal lattice) in a planar view. Thus, the regular arrangement of the conductive particles 20 in the anisotropic conductive film 1 is preferably regular so as to prevent variations in the planar arrangement of the conductive particles 20. For example, ten regions each having an area of ​​1 mm × 1 mm are extracted in the longitudinal direction X of the film, and the particle density of the conductive particles in each region is measured. It is preferable that the difference between the maximum and minimum particle densities be less than 20% of the average particle density of each region. To this end, the conductive particles 20 may be arranged in a square lattice (tetragonal lattice), an oblique lattice, a rectangular lattice (rectangular lattice), a hexagonal lattice, or other lattice. Regular arrangement makes it easier for the conductive particles to be captured by the terminals even if the connection surface on which the terminals are formed is uneven, significantly reducing the occurrence of poor conductivity and short circuits.

[0017] Furthermore, if the conductive particles are randomly dispersed, when a low particle density portion of the conductive particles is placed on a terminal located on a convex portion of the undulations of the module substrate during an anisotropic conductive connection, the conductive particles on that terminal will flow, further lowering the particle density in that portion, reducing the number of conductive particles captured on the terminal and potentially causing poor conductivity (inadequate conductive performance).

[0018] In the anisotropic conductive film 1, the conductive particles 20 are arranged in a lattice pattern, and the lattice axis B of the arrangement intersects with the longitudinal direction X in order to stabilize particle capture. For example, in the case of an anisotropic conductive film for fine pitch applications, the angle θ between the longitudinal direction X of the anisotropic conductive film 1 and the lattice axis B is preferably set to 10° to 40°. The lattice axis B may also be parallel to the longitudinal direction X or the lateral direction Y of the anisotropic conductive film 1, and can be determined depending on the terminal width, terminal pitch, etc.

[0019] The particle density of the conductive particles 20 is set to 20 particles / mm from the viewpoint of electrical conduction reliability. 2 It is preferable that the number of particles is 40 or more per mm. 2 More preferably, the number is 150 / mm or more. 2 From the viewpoint of electrical conductivity reliability, the particle density of the conductive particles 20 is preferably 2000 particles / mm 2 It is preferable that the number of particles is 1500 or less per mm. 2 More preferably, the number is 850 or less per mm 2 It is even more preferable that the particle density (number density) of the conductive particles 20 is determined by the method described in Patent Document 1, for example.

[0020] Regarding the regular arrangement of the conductive particles 20, if the center-to-center distance between adjacent conductive particles is too short, short circuits are more likely to occur, while if it is too long, the number of conductive particles captured by the terminals will be insufficient, resulting in insufficient conductive connection. Therefore, it is necessary to achieve both short-circuit prevention and stable conductive connection. From the viewpoint of ensuring a certain number of captured particles and improving conductive stability, the center-to-center distance between the closest adjacent conductive particles 20 is preferably 1.2 times or more, and more preferably 1.5 times, the average particle diameter. Furthermore, from the viewpoint of preventing short circuits, which may occur when conductive particles join together and cause conduction between terminals, the center-to-center distance between the closest adjacent conductive particles 20 is preferably 100 times or less, and more preferably 80 times or less, the average particle diameter. The center-to-center distance may be appropriately selected based on the conditions of the objects to be connected, such as the electrode configuration and layout.

[0021] The average particle diameter of the conductive particles 20 is 13 μm or more in order to ensure stable conduction even when the surface is undulated, such as in a ceramic module substrate. Furthermore, from the viewpoint of the risk of short circuits, it is preferably 30 μm or less. The average particle diameter is determined by measuring 10,000 or more particles using a particle size distribution analyzer. It is preferable to measure using an imaging particle size distribution analyzer. Furthermore, when the conductive particles are spherical, the average diameter may be determined by measuring 200 or more particles in a planar view of the film.

[0022] The structure of the conductive particles 20 themselves can be appropriately selected from those used in known anisotropic conductive films. Examples include metal particles such as nickel, cobalt, silver, copper, gold, and palladium, and metal-coated resin particles in which core resin particles are metal-coated. Two or more types of conductive particles 20 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 solely from resin. The particles are preferably spherical, but may also be protruding particles with protrusions formed on the surface of the particles. The surfaces of the conductive particles may be subjected to an insulating treatment using known techniques.

[0023] In the anisotropic conductive film 1, the viscosity ratio between the high-viscosity resin layer 11 and the low-viscosity resin layer 12 at 80°C (viscosity of the high-viscosity resin layer 11 at 80°C: viscosity of the low-viscosity resin layer 12 at 80°C) is 7:4 or more, preferably 4:1 or more. This prevents the resin from flowing and reducing its ability to capture conductive particles when pressed during anisotropic conductive connection. Furthermore, the viscosity ratio between the high-viscosity resin layer 11 and the low-viscosity resin layer 12 is preferably 30:1 or less, more preferably 10:1 or less. The above viscosity ratio can be expressed as follows: In the anisotropic conductive film 1, the viscosity of the high-viscosity resin layer 11 at 80°C / the viscosity of the low-viscosity resin layer 12 at 80°C is 7 / 4 or more, preferably 4 / 1 or more. Furthermore, the viscosity of the high-viscosity resin layer 11 at 80°C / the viscosity of the low-viscosity resin layer 12 at 80°C is preferably 30 / 1 or less, more preferably 10 / 1 or less.

[0024] The viscosity of the high-viscosity resin layer 11 is preferably 30,000 Pa·s or less. Because the module substrate is equipped with an image sensor and a lens, the anisotropic conductive connection is typically performed under low-temperature, low-pressure conditions of a temperature of 190°C or less and a pressure of 2 MPa or less. When the viscosity of the high-viscosity resin layer 11 is within the above range, the anisotropic conductive connection can be performed suitably even under low-temperature, low-pressure conditions. In the anisotropic conductive film 1 in which the high-viscosity resin layer 11 and the low-viscosity resin layer 12 are laminated, the viscosity at 80°C is preferably 30,000 Pa·s or less. Furthermore, in the anisotropic conductive film 1 in which the high-viscosity resin layer 11 and the low-viscosity resin layer 12 are laminated, the lower limit of the viscosity at 80°C is preferably 1,000 Pa·s or more, and more preferably 2,000 Pa·s or more.

[0025] The viscosity of the high-viscosity resin layer 11 is measured using a rotational rheometer (manufactured by TA Instruments) under conditions of a temperature rise rate of 10°C / min, a constant measurement pressure of 5 g, and a measurement plate diameter of 8 mm, and the viscosity is read at 80°C. The viscosity of the low-viscosity resin layer 12 can also be measured and read in the same way. The viscosity ratio between the high-viscosity resin layer 11 and the low-viscosity resin layer 12 can then be determined from these values.

[0026] From the viewpoint of the ability to temporarily attach the anisotropic conductive film to a substrate, the thickness of the high-viscosity resin layer 11 and the thickness of the low-viscosity resin layer 12 are each preferably at least two-thirds the average particle diameter of the conductive particles 20. In addition, the total thickness of the high-viscosity resin layer 11 and the low-viscosity resin layer 12 is usually no more than 3.5 times the average particle diameter of the conductive particles 20.

[0027] The high-viscosity resin layer 11 and the low-viscosity resin layer 12 can be appropriately selected from insulating resin layers used in known anisotropic conductive films. That is, they can be appropriately selected so that the viscosity ratio between the high-viscosity resin layer 11 and the low-viscosity resin layer 12 falls within the above-mentioned range. For example, a photoradical polymerization resin layer containing an acrylate compound and a photoradical polymerization initiator, a thermal radical polymerization resin layer containing an acrylate compound and a thermal radical polymerization initiator, a thermal cationic polymerization resin layer containing an epoxy compound and a thermal cationic polymerization initiator, or a thermal anionic polymerization resin layer containing an epoxy compound and a thermal anionic polymerization initiator can be used. Furthermore, these resin layers may be polymerized resin layers as needed. In the case of a thermal radical polymerization resin layer, the thermal radical polymerization initiator is preferably used in an amount of 2 to 60 parts by weight, more preferably 5 to 40 parts by weight, per 100 parts by weight of the acrylate compound.

[0028] The high-viscosity resin layer 11 and the low-viscosity 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 types of film-forming resins can be used in combination. Among these, phenoxy resin is preferred from the viewpoints of film-forming ability, 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 primarily alkoxysilane derivatives. The high-viscosity resin layer 11 and the low-viscosity 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 resin layer, it is preferable to use 5 to 50 parts by weight of insulating filler per 100 parts by weight of acrylate compound. Furthermore, the high-viscosity resin layer 11 and the low-viscosity resin layer 12 may contain, in addition to the insulating filler described above, a filler, a softener, an accelerator, an antioxidant, a colorant (pigment, dye), an organic solvent, an ion catcher agent, etc.

[0029] The conductive particles 20 are arranged closer to the high-viscosity resin layer 11 than a position where two-thirds of the particle diameter protrudes toward the low-viscosity resin layer from the boundary C between the high-viscosity resin layer 11 and the low-viscosity resin layer 12. In this way, in the anisotropic conductive film 1, the conductive particles 20 are arranged at specific positions in the thickness direction Z, which prevents the resin from flowing and reducing the conductive particle capture ability when the anisotropic conductive film 1 is pressed in for anisotropic conductive connection. From the perspective of conductive particle capture ability, the conductive particles 20 are preferably arranged at a position where one-half of the particle diameter protrudes toward the low-viscosity resin layer 12 from the boundary C between the high-viscosity resin layer 11 and the low-viscosity resin layer 12, or are arranged closer to the high-viscosity resin layer 11 than a position where one-half of the particle diameter protrudes toward the low-viscosity resin layer 12. The conductive particles 20 may not protrude from the boundary C between the high-viscosity resin layer 11 and the low-viscosity resin layer 12, and may be entirely arranged on the high-viscosity resin layer 11 side. In other words, the conductive particles 20 are embedded in the high-viscosity resin layer by more than one-third of their particle diameter relative to the boundary C between the high-viscosity resin layer 11 and the low-viscosity resin layer 12. Preferably, the conductive particles 20 are embedded in the high-viscosity resin layer by at least half of their particle diameter relative to the boundary C. More preferably, the conductive particles 20 are embedded in the high-viscosity resin layer by at least two-thirds of their particle diameter relative to the boundary C. Alternatively, the conductive particles 20 may be entirely embedded in the high-viscosity resin layer relative to the boundary C.

[0030] The fact that the conductive particles 20 are arranged at specific positions in the thickness direction Z can be confirmed, for example, as follows: The anisotropic conductive film 1 is cut at a cross section passing through line A-A in Figure 1, and the cross section is observed with an electron microscope to confirm the positions of the conductive particles 20.

[0031] In the anisotropic conductive film 1, the variation in the positions of the conductive particles 20 in the thickness direction Z is preferably less than 10% of the average particle diameter. This variation is measured as the variation in the distance L between either surface of the anisotropic conductive film 1 and each conductive particle 20. More specifically, first, 100 conductive particles 20 are consecutively selected in the longitudinal direction X of the anisotropic conductive film 1, and the difference ΔL between the maximum and minimum distances L measured for each conductive particle 20 is obtained. Next, the variation can be calculated as the ratio of ΔL to the average particle diameter.

[0032] As described above, the anisotropic conductive film 1 has specific ranges for the average particle size of the conductive particles 20, the viscosity ratio between the high-viscosity resin layer 11 and the low-viscosity resin layer 12, and the position of the conductive particles 20 in the thickness direction Z. This prevents the resin from flowing and reducing the ability to capture conductive particles when pressed during anisotropic conductive connection. Therefore, the anisotropic conductive film 1 can increase the number of captured particles and is compatible with undulating ceramic substrates and substrates with small connection pads.

[0033] The anisotropic conductive film 1 can be manufactured by adhering regularly arranged conductive particles having an average particle diameter of 13 μm or more to the surface of the insulating high-viscosity resin layer, applying heat and pressure to the surface of the high-viscosity resin layer to which the conductive particles are attached, thereby embedding the conductive particles in the high-viscosity resin layer, and then placing and pressing the low-viscosity resin layer on the surface of the high-viscosity resin layer where the conductive particles are embedded. More specifically, the anisotropic conductive film 1 can be manufactured, for example, as follows. First, a mold having protrusions corresponding to the arrangement of the conductive particles 20 is fabricated from a flat metal plate by machining, laser processing, photolithography, or other methods. Next, a curable resin is filled into the mold and cured to create a resin mold with an inverted pattern. This resin mold is used as a microcavity for conductive particles, and the conductive particles 20 are placed in the recesses. A pre-formed high-viscosity resin layer 11 is then placed on top of the conductive particles. The high-viscosity resin layer 11 is then peeled off with the conductive particles 20 attached to the surface. The conductive particles 20 are embedded in the high-viscosity resin layer 11 to a desired position while applying heat and pressure to the surface of the high-viscosity resin layer 11 to which the conductive particles 20 are attached. A pre-formed low-viscosity resin layer 12 is then placed and pressure-bonded to the surface of the high-viscosity resin layer 11 with the embedded conductive particles 20. In this manner, an anisotropic conductive film 1 as shown in FIGS. 1 and 2 is obtained. By appropriately adjusting the applied heat and pressure when embedding the conductive particles 20 in the high-viscosity resin layer 11, the positions of the conductive particles 20 in the thickness direction Z can be controlled within a specific range. Alternatively, the anisotropic conductive film 1 may be manufactured by attaching and embedding the conductive particles 20 on the surface of a pre-formed low-viscosity resin layer 12, and then pressure-bonding the high-viscosity resin layer 11 to the surface of the embedded conductive particles 20. That is, the anisotropic conductive film 1 may be manufactured by adhering regularly arranged conductive particles having an average particle diameter of 13 μm or more to the surface of the insulating low-viscosity resin layer, applying heat and pressure to the surface of the low-viscosity resin layer to which the conductive particles are adhered, thereby embedding the conductive particles in the low-viscosity resin layer, and then placing and pressing the high-viscosity resin layer on the surface of the low-viscosity resin layer to which the conductive particles are embedded.

[0034] <Method for Manufacturing Connection Structure> The method for manufacturing a connection structure according to an embodiment includes a bonding step of electrically bonding a first electronic component and a second electronic component using the anisotropic conductive film described above. Specifically, this step results in an anisotropic conductive connection between the connection terminal of the first electronic component and the connection terminal of the second electronic component. The width (short side) of a terminal (connection pad) suitable for anisotropic conductive connection is preferably 12 μm or more. The upper limit of the width is preferably 500 μm or less. The length (long side) of the terminal (connection pad) is preferably 20 μm or more, more preferably 50 μm or more. The upper limit of the length is preferably 1000 μm or less, more preferably 240 μm or less. The height of the terminal (connection pad) is preferably 6 μm or more for both the terminal on the first electronic component side and the terminal on the second electronic component side. The upper limit of the height is preferably 35 μm or less. The terminals (connection pads) preferably have a pitch of 40 μm or more. The upper limit of the pitch is preferably 1500 μm or less. The bonding step is specifically a step of placing the high-viscosity resin layer on the second electronic component side and bonding it.

[0035] Examples of the first electronic component include a flexible substrate, and examples of the second electronic component include a ceramic substrate. As described below, the second electronic component is a substrate that is not smooth but has "undulations," which is suitable for the conductive film and anisotropic conductive film of the present invention. The ceramic substrate may be equipped with or incorporate a camera module. When the second electronic component is a ceramic substrate, it typically has a waviness of 20 μm or more, specifically, 20 to 50 μm. The waviness of the ceramic substrate can be measured using a surface roughness meter (Kosaka Laboratory Co., Ltd., Surfcorder SE-400). Specifically, the stylus of the surface roughness meter is scanned in the direction of the terminal arrangement on the ceramic substrate to obtain a profile of the surface irregularities, and the waviness is determined from the difference between the maximum and minimum heights in this profile. Measurements may be performed in the same manner as in Japanese Patent No. 6,425,382.

[0036] The conductive film and anisotropic conductive film of the present invention are required when the second electronic component has "waviness," when electrodes (terminals, connection pads) are provided at a height greater than a predetermined height on a substrate that is not smooth, such as a conventionally used glass or plastic substrate, and when the first electronic component has electrodes at a height greater than a predetermined height, such as a conventionally used FPC. When objects to be connected have such a configuration and are placed opposite each other, the presence of "waviness" on at least one side makes it difficult to sandwich conductive particles between the opposing electrodes. Therefore, the particle diameter must be set to 13 μm or greater, and the design must take into account the fluidity of the laminated resin layer to stabilize the number of conductive particles captured. This is the premise underlying the design concept of the present invention.

[0037] According to the embodiment of the method for manufacturing a connection structure, by using the above-mentioned anisotropic conductive film, the first electronic component and the second electronic component are suitably anisotropically conductively connected, and a connection structure having a stable conductive resistance value is obtained.

[0038] In particular, when the second electronic component is a substrate (ceramic substrate) that is not smooth and has "undulations," both terminals on the convex portions of the undulations and terminals on the concave portions are electrically connected to their respective opposing terminals. This is thought to be due to the following: During anisotropic conductive connection, the resin forming the insulating resin layer (high-viscosity resin layer and low-viscosity resin layer) melts and flows. However, in the above-mentioned anisotropic conductive film, the average particle diameter of the conductive particles is within a specific range, the insulating resin layer is composed of high-viscosity resin layer and low-viscosity resin layer having a specific viscosity ratio, and the position of the conductive particles in the thickness direction is within a specific range. Therefore, even when the resin melts and flows, the conductive particles on the terminals on the convex portions of the undulations are less likely to flow, making it possible to increase the number of particles captured and achieving an excellent electrically connected connection.

[0039] The bonding step may be a step of placing the low-viscosity resin layer on the second electronic component side and bonding them together. In this case, too, the resulting connection structure exhibits a stable conduction resistance value. From the viewpoint of the particle capture number, the bonding step is preferably a step of placing the high-viscosity resin layer on the second electronic component side and bonding them together.

[0040] The present invention will be described in more detail below with reference to the following examples. <A: Preparation of insulating adhesive layer> Insulating adhesive films A to D were prepared with a thickness of 16 μm from four types of compositions, formulations A to D, shown in Table 1. The formulations in Table 1 are the amounts of the components excluding the solvent.

[0041] The four types of insulating adhesive films A to D thus produced were heated from room temperature using a rotational rheometer (manufactured by TA Instruments), and the melt viscosity was measured under conditions of a temperature rise rate of 10°C / min, a constant measurement pressure of 5 g, and a measurement plate diameter of 8 mm, and the viscosity was read at 80°C. The results are also shown in Table 1.

[0042]

[0043] <B: Preparation of resin mold> Density 600 pcs / mm 2 A mold with a tetragonal lattice pattern of convex portions was fabricated by cutting a nickel plate. Melted pellets of a known transparent resin were poured into the mold and cooled to solidify, forming a resin mold with concave portions in the same pattern as the convex portions.

[0044] Example 1 An anisotropic conductive film as shown in FIGS. 1 and 2 was produced. The recesses of the resin mold obtained in <B: Production of Resin Mold> were filled with conductive particles (average particle diameter 20 μm, manufactured by Sekisui Chemical Co., Ltd., product name: Micropearl (registered trademark)), and an insulating adhesive film A was then placed on top of them. The insulating adhesive film A was then peeled off with the conductive particles still attached to the surface. Heat and pressure were applied to the surface of the insulating adhesive film A to embed the conductive particles in the insulating adhesive film A to the desired position. A pre-formed insulating adhesive film D was then placed on the surface of the insulating adhesive film A with the embedded conductive particles and pressure-bonded to the surface. In the produced anisotropic conductive film A, the insulating adhesive film A constituted the high-viscosity resin layer, and the insulating adhesive film D constituted the low-viscosity resin layer. The conductive particles were positioned so that half of their particle diameter protruded from the boundary between the high-viscosity resin layer and the low-viscosity resin layer toward the low-viscosity resin layer. The anisotropic conductive film A had a thickness of 35 μm and a width (short direction): 1 mm. As shown in FIG. 3 , the prepared anisotropic conductive film A (anisotropic conductive film 1) was temporarily attached to an alumina ceramic substrate 2 so that the high-viscosity resin 11 layer was on the alumina ceramic substrate 2 side. Next, a flexible printed circuit board 3 was placed on top and pressure-bonded at 140°C for 6 seconds at 2 MPa to prepare a pressure-bonded sample A. The flexible printed circuit board (FPC) 3 had copper wiring: line / space = 100 μm / 100 μm, terminal 31 height: 12 μm, and polyimide thickness: 25 μm. The alumina ceramic substrate (PWB) 2 had tungsten wiring: line / space = 100 μm / 100 μm, terminal (wiring) 21 height: 10 μm, substrate thickness: 0.4 mm, and waviness = 20 μm. The particle capture rate of the pressure-bonded sample A was calculated to be 50%. Furthermore, the conductive connection of the prepared crimped sample A was measurable in all channels (30 / 30ch).

[0045] [Example 2] An anisotropic conductive film B was produced in the same manner as in Example 1, except that insulating adhesive film C was used instead of insulating adhesive film A. In the produced anisotropic conductive film B, insulating adhesive film C constituted the high-viscosity resin layer, and insulating adhesive film D constituted the low-viscosity resin layer. A pressure-bonded sample B was produced in the same manner as in Example 1, except that anisotropic conductive film B was used instead of anisotropic conductive film A. The particle capture rate for pressure-bonded sample B was calculated to be 48%. Furthermore, the conductive connection of the produced pressure-bonded sample B could be measured in all channels (30 / 30ch).

[0046] Example 3 An anisotropic conductive film as shown in FIGS. 1 and 4 was produced. FIG. 4 is a cross-sectional view of the anisotropic conductive film of Example 3, taken along line A-A in FIG. 1 . The recesses of the resin mold obtained in <B: Production of Resin Mold> were filled with conductive particles (average particle diameter 20 μm, manufactured by Sekisui Chemical Co., Ltd., product name: Micropearl (registered trademark)), and insulating adhesive film B was then placed on top of them. With the conductive particles still attached to the surface, insulating adhesive film B was peeled off. Heat and pressure were applied to the surface of insulating adhesive film B to which the conductive particles had been attached, and the conductive particles were embedded in insulating adhesive film B until they reached the desired position. A previously formed insulating adhesive film C was placed on the surface of insulating adhesive film B with the embedded conductive particles and pressure-bonded to it. In the produced anisotropic conductive film C, insulating adhesive film B constituted the high-viscosity resin layer, and insulating adhesive film C constituted the low-viscosity resin layer. The conductive particles were positioned at a position where one-third of the particle diameter protruded from the boundary between the high-viscosity resin layer and the low-viscosity resin layer toward the low-viscosity resin layer. The anisotropic conductive film C had a thickness of 35 μm and a width (short direction): 1 mm. The prepared anisotropic conductive film C was temporarily attached to an alumina ceramic substrate so that the high-viscosity resin layer was facing the alumina ceramic substrate. Next, a flexible printed circuit board was placed on top and pressure-bonded at 140°C for 6 seconds at 2 MPa to prepare a pressure-bonded sample C. The flexible printed circuit board (FPC) had copper wiring: line / space = 100 μm / 100 μm, terminal height: 12 μm, and polyimide thickness: 25 μm. The alumina ceramic substrate (PWB) had tungsten wiring: line / space = 100 μm / 100 μm, terminal (wiring) height: 10 μm, substrate thickness: 0.4 mm, and waviness = 20 μm. The particle capture rate of the bonded sample C was calculated to be 46%. Furthermore, the conductive connection of the prepared bonded sample C was measurable in all channels (30 / 30ch).

[0047] [Example 4] Anisotropic conductive film D was produced in the same manner as in Example 1, except that insulating adhesive film B was used instead of insulating adhesive film A and insulating adhesive film C was used instead of insulating adhesive film D. In the produced anisotropic conductive film D, insulating adhesive film B constituted the high-viscosity resin layer, and insulating adhesive film C constituted the low-viscosity resin layer. Except that anisotropic conductive film D was used instead of anisotropic conductive film A, pressure-bonded sample D was produced in the same manner as in Example 1. The particle capture rate for pressure-bonded sample D was calculated to be 40%. Furthermore, the conductive connection of the produced pressure-bonded sample D was measurable in all channels (30 / 30ch).

[0048] Example 5 An anisotropic conductive film E was prepared in the same manner as in Example 1, except that insulating adhesive film C was used instead of insulating adhesive film A. In the prepared anisotropic conductive film E, insulating adhesive film C constituted the high-viscosity resin layer, and insulating adhesive film D constituted the low-viscosity resin layer. The prepared anisotropic conductive film E was temporarily attached to a flexible printed circuit board (FCB) so that the high-viscosity resin layer was facing the flexible printed circuit board. An alumina ceramic substrate was then placed on top and pressure-bonded at 140°C for 6 seconds at 2 MPa to prepare a pressure-bonded sample E. The flexible printed circuit board (FPC) had copper wiring: line / space = 100 μm / 100 μm, terminal height: 12 μm, and polyimide thickness: 25 μm. The alumina ceramic substrate (PWB) had tungsten wiring: line / space = 100 μm / 100 μm, terminal (wiring) height: 10 μm, substrate thickness: 0.4 mm, and waviness = 20 μm. The particle capture rate of the bonded sample E was calculated to be 43%. Furthermore, the conductive connection of the prepared bonded sample E was measurable in all channels (30 / 30ch).

[0049] [Comparative Example 1] Anisotropic conductive film F was produced in the same manner as in Example 1, except that insulating adhesive film A was used instead of insulating adhesive film D. Bonded sample F was produced in the same manner as in Example 1, except that anisotropic conductive film F was used instead of anisotropic conductive film A. The particle capture rate for bonded sample F was calculated to be 35%. Furthermore, the conductive connection of the produced bonded sample F could be measured in all channels (30 / 30ch).

[0050] Comparative Example 2 Anisotropic conductive films as shown in FIGS. 1 and 5 were produced. FIG. 5 is a cross-sectional view of the anisotropic conductive film of Comparative Example 2, taken along line A-A in FIG. 1 . The recesses of the resin mold obtained in <B: Production of Resin Mold> were filled with conductive particles (average particle diameter 20 μm, manufactured by Sekisui Chemical Co., Ltd., product name: Micropearl (registered trademark)), and insulating adhesive film D was then placed on top of them. The insulating adhesive film D was peeled off with the conductive particles still attached to the surface. Heat and pressure were applied to the surface of the insulating adhesive film D to which the conductive particles had been attached, and the conductive particles were embedded in the insulating adhesive film D until they reached the desired position. A previously formed insulating adhesive film A was placed on the surface of the insulating adhesive film D with the embedded conductive particles, and the insulating adhesive film A was then pressure-bonded. In the produced anisotropic conductive film G, the insulating adhesive film A constituted the high-viscosity resin layer, and the insulating adhesive film D constituted the low-viscosity resin layer. The conductive particles were positioned at a position where two-thirds of the particle diameter protruded from the boundary between the high-viscosity resin layer and the low-viscosity resin layer toward the low-viscosity resin layer. The anisotropic conductive film G had a thickness of 35 μm and a width (short direction): 1 mm. The prepared anisotropic conductive film G was temporarily attached to an alumina ceramic substrate so that the high-viscosity resin layer was facing the alumina ceramic substrate. Next, a flexible printed circuit board (FPC) was placed on top and pressure-bonded at 140°C for 6 seconds at 2 MPa to prepare a pressure-bonded sample G. The flexible printed circuit board (FPC) had copper wiring: line / space = 100 μm / 100 μm, terminal height: 12 μm, and polyimide thickness: 25 μm. The alumina ceramic substrate (PWB) had tungsten wiring: line / space = 100 μm / 100 μm, terminal (wiring) height: 10 μm, substrate thickness: 0.4 mm, and waviness = 20 μm. The particle capture rate of the compressed sample G was calculated to be 28%. Furthermore, the conductive connection of the prepared compressed sample G was measurable in all channels (30 / 30ch).

[0051] Comparative Example 3 Anisotropic conductive film H was prepared in the same manner as in Example 1, except that conductive particles (average particle diameter 3 μm, manufactured by Sekisui Chemical Co., Ltd., product name: Micropearl) were used instead of conductive particles (average particle diameter 20 μm, manufactured by Sekisui Chemical Co., Ltd., product name: Micropearl). In the prepared anisotropic conductive film H, insulating adhesive film A constituted the high-viscosity resin layer, and insulating adhesive film D constituted the low-viscosity resin layer. Bonded sample H was prepared in the same manner as in Example 1, except that anisotropic conductive film H was used instead of anisotropic conductive film A. In bonded sample H, the small-diameter particles were unable to accommodate the waviness of the ceramic substrate, making it difficult to calculate the particle capture rate. Furthermore, due to the influence of the ceramic waviness, the conductive connection of the prepared bonded sample H could not be measured except for two channels of measurement terminals at the edge, resulting in poor conductivity (4 / 30 channels). Table 2 shows the evaluation results for the anisotropic conductive films obtained in each example and comparative example. In the anisotropic conductive films obtained in each of the Examples and Comparative Examples, the variation in the position of the conductive particles in the thickness direction was less than 10% of the average particle diameter.

[0052]

[0053] <Evaluation Method> (Position and Variation of Conductive Particles in the Thickness Direction) The anisotropic conductive film was cut along the line A-A in Figure 1, and the cross section was observed using an electron microscope to determine the position and variation of conductive particles in the thickness direction. Specifically, the position of 50 conductive particles cut along the cross section so as to pass through the center of the conductive particle sphere was measured in the thickness direction, and the average value was calculated. The variation was calculated according to the description in the specification. (Particle Capture Rate) After temporary attachment, the number of particles on the connection terminal of the alumina ceramic substrate was counted and recorded as "Number of particles on terminal before crimping (a)." Next, a flexible printed circuit board was crimped, and after peeling the flexible printed circuit board, the number of particles (b) remaining on the connection terminal was counted and recorded as "Number of particles on terminal after crimping (b)." The particle capture rate was then calculated using the following formula (1). Particle Capture Rate (%) = Number of Particles on Terminals After Crimping (b) ÷ Number of Particles on Terminals Before Crimping (a) × 100 (1) However, in Example 5, after temporary attachment, the number of particles on the connection terminals of the flexible printed circuit board was counted and defined as "Number of Particles on Terminals Before Crimping (a)." Next, an alumina ceramic substrate was crimped, and after the alumina ceramic substrate was peeled off, the number of particles (b) remaining on the connection terminals was counted and defined as "Number of Particles on Terminals After Crimping (b)." (Conduction Resistance) The conductivity resistance of the crimped sample was measured using a digital multimeter (34401A, manufactured by Agilent Technologies Inc.) by a four-terminal method, passing a current of 1 mA. A measured resistance value of 2Ω or less was considered pass, and a value exceeding 2Ω was considered fail. 30 channels were measured, and the number of pass channels was determined. (Overall Evaluation) A sample was considered pass if the particle capture rate was 40% or more and the conductivity resistance was pass for all 30 channels measured. Furthermore, a case where the particle capture rate was less than 40% or where the conduction resistance did not pass all of the 30-channel measurements was judged to be unacceptable.

[0054] REFERENCE SIGNS LIST 1 anisotropic conductive film 10 insulating resin layer 11 high-viscosity resin layer 12 low-viscosity resin layer 20 conductive particles 2 alumina ceramic substrate 3 flexible printed circuit board 21, 31 terminal

Claims

1. A conductive film comprising an insulating high-viscosity resin layer, an insulating low-viscosity resin layer, and conductive particles having an average particle diameter of 13 μm or more, the low-viscosity resin layer being laminated on the high-viscosity resin layer, the viscosity ratio of the high-viscosity resin layer to the low-viscosity resin layer at 80°C being 7:4 or more, and the conductive particles being arranged on the high-viscosity resin layer side at a position where 2 / 3 of the particle diameter protrudes toward the low-viscosity resin layer side from the boundary between the high-viscosity resin layer and the low-viscosity resin layer.

2. Adhering regularly arranged conductive particles having an average particle diameter of 13 μm or more to the surface of an insulating high-viscosity resin layer, applying heat and pressure to the surface of the high-viscosity resin layer to which the conductive particles are attached, while burying the conductive particles in the high-viscosity resin layer, and disposing an insulating low-viscosity resin layer on the surface side of the high-viscosity resin layer where the conductive particles are embedded, and pressing the layer against the surface; or Adhering regularly arranged conductive particles having an average particle diameter of 13 μm or more to the surface of an insulating low-viscosity resin layer, applying heat and pressure to the surface of the low-viscosity resin layer to which the conductive particles are attached, while burying the conductive particles in the low-viscosity resin layer, and pressing the layer against the surface side of the low-viscosity resin layer where the conductive particles are embedded, A method for manufacturing a conductive film comprising the high-viscosity resin layer, the low-viscosity resin layer, and the conductive particles, the low-viscosity resin layer being laminated on the high-viscosity resin layer, a viscosity ratio between the high-viscosity resin layer and the low-viscosity resin layer at 80°C being 7:4 or more, and the conductive particles being arranged on the high-viscosity resin layer side at a position where 2 / 3 of the particle diameter protrudes toward the low-viscosity resin layer from the boundary between the high-viscosity resin layer and the low-viscosity resin layer.

3. A method for manufacturing a connection structure, comprising a bonding step of electrically bonding a first electronic component and a second electronic component with a conductive film, the conductive film comprising an insulating high-viscosity resin layer, an insulating low-viscosity resin layer, and conductive particles having an average particle diameter of 13 μm or more, the low-viscosity resin layer being laminated on the high-viscosity resin layer, the viscosity ratio of the high-viscosity resin layer to the low-viscosity resin layer at 80°C being 7:4 or more, and the conductive particles being arranged on the high-viscosity resin layer side from a position where 2 / 3 of the particle diameter protrudes toward the low-viscosity resin layer side from the boundary between the high-viscosity resin layer and the low-viscosity resin layer.

4. The method for manufacturing a connection structure according to claim 3, wherein the joining step is a step of placing the high-viscosity resin layer on the second electronic component side and joining the high-viscosity resin layer to the second electronic component side.

5. The method for manufacturing a connection structure according to claim 3 or 4, wherein the second electronic component is a substrate having a waviness of 20 μm or more.

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