Adhesive film

Abstract

To provide highly reliable adhesive films. [Solution] An adhesive film comprising: a first adhesive layer containing first conductive particles which are dendrite-shaped conductive particles; and a second adhesive layer containing second conductive particles which are conductive particles other than the first conductive particles, and which have a non-conductive core and a conductive layer provided on the core.

Description

Technical Field

[0001] The present invention relates to an adhesive film.

Background Art

[0002] In recent years, in fields such as semiconductors and liquid crystal displays, various adhesives have been used for fixing electronic components and connecting circuits. In these applications, the density and definition of electronic components, circuits, etc. have been increasing, and higher levels of performance are required for adhesives.

[0003] For example, for the connection between a liquid crystal display and a TCP (Tape Carrier Package), the connection between an FPC (Flexible Printed Circuit) and a TCP, or the connection between an FPC and a printed wiring board, an adhesive in which conductive particles are dispersed is used. In such adhesives, it is required to further enhance conductivity and reliability.

[0004] For example, Patent Document 1 describes a conductive film provided with a conductive film containing predetermined dendrite-shaped silver-coated copper powder particles on a base film, and it is disclosed that sufficient conductive characteristics can be obtained without blending silver powder with such a conductive film.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] An object of the present invention is to provide an adhesive film having excellent reliability.

Means for Solving the Problems

[0007] One aspect of the present invention is an adhesive film comprising: a first adhesive layer containing first conductive particles which are dendritic conductive particles; and a second adhesive layer containing second conductive particles which are conductive particles other than the first conductive particles and which have a non-conductive core and a conductive layer provided on the core.

[0008] The first adhesive layer may further contain second conductive particles. In this case, the volume ratio of the second conductive particles in the first adhesive layer may be smaller than the volume ratio of the second conductive particles in the second adhesive layer. The first adhesive layer may not contain second conductive particles.

[0009] The adhesive film may be an adhesive film having, on another side, the first adhesive layer, the second adhesive layer, and the third adhesive layer in this order, wherein the third adhesive layer contains third conductive particles which are dendrite-shaped conductive particles.

[0010] The third adhesive layer may further contain the second conductive particles. In this case, the volume ratio of the second conductive particles in the third adhesive layer may be smaller than the volume ratio of the second conductive particles in the second adhesive layer. The third adhesive layer does not need to contain the second conductive particles.

[0011] The conductive layer may contain at least one material selected from the group consisting of gold, nickel, and palladium. [Effects of the Invention]

[0012] According to the present invention, a highly reliable adhesive film can be provided. [Brief explanation of the drawing]

[0013] [Figure 1] This is a schematic cross-sectional view showing one embodiment of an adhesive film. [Figure 2] This is a schematic cross-sectional view of a key part illustrating an example of the connection between electronic components. [Figure 3] This is a schematic cross-sectional view showing another embodiment of the adhesive film. [Figure 4] This is a schematic cross-sectional view of a key part illustrating another example of how electronic components are connected. [Figure 5] This is a schematic diagram illustrating the method for fabricating a mounting unit for reliability testing. [Figure 6] This is a schematic diagram illustrating the method for measuring connection resistance in reliability testing. [Modes for carrying out the invention]

[0014] The embodiments of the present invention will be described in detail below with reference to the drawings as appropriate.

[0015] Figure 1 is a schematic cross-sectional view showing one embodiment (first embodiment) of an adhesive film. As shown in Figure 1, the adhesive film 1A according to the first embodiment comprises a first adhesive layer 2 and a second adhesive layer 3 provided on one surface of the first adhesive layer 2. The first adhesive layer 2 contains a first adhesive component 4 and first conductive particles 5 dispersed in the first adhesive component 4. The second adhesive layer 3 contains a second adhesive component 6 and second conductive particles 7 dispersed in the second adhesive component 6.

[0016] The first adhesive component 4 and the second adhesive component 6 may be of the same type or different types, but from the viewpoint of obtaining stable adhesive strength against changes in ambient temperature, they are preferably of the same type. The first adhesive component 4 and the second adhesive component 6 may be the adhesive components described below.

[0017] As the adhesive component, for example, it may be composed of a material that exhibits curability by heat or light, and may be an epoxy-based adhesive, a radical-curing adhesive, a thermoplastic adhesive such as polyurethane or polyvinyl ester, etc. Since the adhesive component is excellent in heat resistance and moisture resistance after adhesion, it may be composed of a crosslinkable material. Among these, an epoxy-based adhesive containing an epoxy resin, which is a thermosetting resin, as a main component is preferably used in terms of being able to cure in a short time, having good connection workability, and excellent adhesiveness. A radical-curing adhesive has characteristics such as being superior in curability at a lower temperature and in a shorter time than an epoxy-based adhesive, and is therefore appropriately used according to the application.

[0018] The epoxy-based adhesive contains, for example, a thermosetting material such as an epoxy resin and a curing agent, and may further contain a thermoplastic resin, a coupling agent, a filler, etc. as required.

[0019] Examples of the epoxy resin include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, phenol novolak type epoxy resin, cresol novolak type epoxy resin, bisphenol A novolak type epoxy resin, bisphenol F novolak type epoxy resin, alicyclic epoxy resin, glycidyl ester type epoxy resin, glycidyl amine type epoxy resin, hydantoin type epoxy resin, isocyanurate type epoxy resin, aliphatic chain epoxy resin, etc. These epoxy resins may be halogenated, hydrogenated, or may have a structure in which an acryloyl group or a methacryloyl group is added to the side chain. These epoxy resins are used alone or in combination of two or more.

[0020] The curing agent is not particularly limited as long as it can cure the epoxy resin, and examples include an anion-polymerizable catalyst type curing agent, a cation-polymerizable catalyst type curing agent, an addition polymerization type curing agent, etc. The curing agent is preferably an anion or cation-polymerizable catalyst type curing agent in terms of being excellent in fast curing property and not requiring chemical equivalent consideration.

[0021] Anionic or cationic polymerization type catalytic curing agents may be, for example, imidazole-based, hydrazide-based, boron trifluoride - amine complexes, onium salts (such as aromatic sulfonium salts, aromatic diazonium salts, aliphatic sulfonium salts, etc.), amine imides, diaminomaleonitrile, melamine and its derivatives, salts of polyamines, dicyandiamide, etc., and may also be modified products thereof. Examples of polyaddition type curing agents include polyamines, polymercaptans, polyphenols, acid anhydrides, etc.

[0022] Potential curing agents obtained by coating these curing agents with polymer substances such as polyurethane-based and polyester-based, metal thin films such as nickel and copper, and inorganic substances such as calcium silicate and microencapsulating them are preferable because the pot life can be extended. The curing agent is used alone or in combination of two or more.

[0023] The content of the curing agent may be 0.05 to 20 parts by mass with respect to 100 parts by mass of the total amount of the thermosetting material and the thermoplastic resin blended as required.

[0024] Radical curing type adhesives contain, for example, a radical polymerizable material and a radical polymerization initiator (also called a curing agent), and may further contain a thermoplastic resin, a coupling agent, a filler, etc. as required.

[0025] As the radical polymerizable material, any substance having a functional group that polymerizes by radicals can be used without particular limitation. Specifically, the radical polymerizable material may be, for example, radical polymerizable substances such as acrylate (including the corresponding methacrylate; the same applies hereinafter) compounds, acryloxy (including the corresponding methacryloxy; the same applies hereinafter) compounds, maleimide compounds, citraconimide resins, nadimide resins, etc. These radical polymerizable substances may be in the state of a monomer or an oligomer, or may be in the state of a mixture of a monomer and an oligomer.

[0026] Examples of acrylate compounds include methyl acrylate, ethyl acrylate, isopropyl acrylate, isobutyl acrylate, ethylene glycol diacrylate, diethylene glycol diacrylate, trimethylolpropane triacrylate, tetramethylolmethane tetraacrylate, 2-hydroxy-1,3-diacryloxypropane, 2,2-bis[4-(acryloxymethoxy)phenyl]propane, 2,2-bis[4-(acryloxypolyethoxy)phenyl]propane, dicyclopentenyl acrylate, tricyclodecanyl acrylate, tris(acryloyloxyethyl)isocyanurate, urethane acrylate, and phosphate ester diacrylate.

[0027] Radical polymerizable substances such as acrylate compounds may be used together with polymerization inhibitors such as hydroquinone and methyl ether hydroquinone, if necessary. From the viewpoint of improving heat resistance, radical polymerizable substances such as acrylate compounds preferably have at least one substituent such as a dicyclopentenyl group, a tricyclodecanyl group, or a triazine ring. As radical polymerizable substances other than acrylate compounds, for example, compounds described in International Publication No. 2009 / 063827 can be suitably used. Radical polymerizable substances may be used individually or in combination of two or more.

[0028] As a radical polymerization initiator, any compound that decomposes upon heating or irradiation with light to generate free radicals can be used without particular limitations. Specifically, radical polymerization initiators may be, for example, peroxide compounds, azo compounds, etc. These compounds are appropriately selected depending on the desired connection temperature, connection time, pot life, etc.

[0029] More specifically, the radical polymerization initiators preferably include diacyl peroxides, peroxydicarbonates, peroxyesters, peroxyketals, dialkyl peroxides, hydroperoxides, and silyl peroxides. Among these, peroxyesters, dialkyl peroxides, hydroperoxides, and silyl peroxides are preferred, with peroxyesters being more preferred from the viewpoint of obtaining high reactivity. As these radical polymerization initiators, for example, compounds described in International Publication No. 2009 / 063827 can be suitably used. The radical polymerization initiators can be used individually or in combination of two or more.

[0030] The amount of radical polymerization initiator may be 0.1 to 10 parts by mass per 100 parts by mass of the total amount of the radical polymerizable material and the thermoplastic resin, if necessary.

[0031] Thermoplastic resins, which may be added as needed in epoxy adhesives and radical-curing adhesives, can, for example, facilitate the imparting of excellent film moldability to the adhesive. Examples of thermoplastic resins include phenoxy resins, polyvinyl formal resins, polystyrene resins, polyvinyl butyral resins, polyester resins, polyamide resins, xylene resins, polyurethane resins, polyester urethane resins, phenolic resins, and terpene phenolic resins. For example, compounds described in International Publication No. 2009 / 063827 can be suitably used as thermoplastic resins. Phenoxy resins are preferred because they have excellent adhesion, compatibility, heat resistance, and mechanical strength. Thermoplastic resins can be used individually or in combination of two or more.

[0032] When incorporated into epoxy adhesives, the thermoplastic resin content may be 5 to 80 parts by mass per 100 parts by mass of the total amount of thermoplastic resin and thermosetting material. When incorporated into radical-curing adhesives, the thermoplastic resin content may be 5 to 80 parts by mass per 100 parts by mass of the total amount of thermoplastic resin and radical polymerizable material.

[0033] Other examples of adhesive components include a thermoplastic resin, a radical polymerizable material containing a liquid radical polymerizable substance at 30°C, and a radical polymerization initiator. The thermoplastic radical-curable adhesive has a lower viscosity than the adhesive components described above. The content of the radical polymerizable substance in the thermoplastic radical-curable adhesive is preferably 20 to 80 parts by mass, more preferably 30 to 80 parts by mass, and even more preferably 40 to 80 parts by mass, based on 100 parts by mass of the total amount of thermoplastic resin and radical polymerizable substance.

[0034] The adhesive component may be an epoxy adhesive containing a thermoplastic resin, a thermosetting material containing a liquid epoxy resin at 30°C, and a curing agent. In this case, the epoxy resin content in the epoxy adhesive is preferably 20 to 80 parts by mass, more preferably 40 to 80 parts by mass, and even more preferably 30 to 80 parts by mass, based on 100 parts by mass of the total amount of thermoplastic resin and thermosetting material.

[0035] When adhesive film 1A is used to connect an IC chip to a glass substrate, a flexible printed circuit board (FPC), etc., the adhesive composition preferably further contains a component that exhibits an internal stress-relaxing effect, from the viewpoint of suppressing warping of the substrate caused by the difference in the coefficient of thermal expansion between the IC chip and the substrate. Specific examples of such components include acrylic rubber and elastomer components. Alternatively, the adhesive composition may be a radical-curing adhesive as described in International Publication No. 98 / 44067.

[0036] The content of the first adhesive component 4 in the first adhesive layer 2 (the volume ratio of the first adhesive component 4 in the first adhesive layer 2) may be 75% by mass or more, or 85% by volume or more, and 98% by volume or less, or 92% by volume or less, based on the total volume of the first adhesive layer 2.

[0037] The content of the second adhesive component 6 in the second adhesive layer 3 (the volume ratio of the second adhesive component 6 in the second adhesive layer 3) may be 80% by mass or more, or 90% by mass or more, and 98% by volume or less, or 95% by volume or less, based on the total volume of the second adhesive layer 3.

[0038] The first adhesive layer 2 contains the first conductive particles 5. The first conductive particles 5 have a dendritic (also called tree-like) shape and consist of a single main axis and a plurality of branches that branch out two-dimensionally or three-dimensionally from the main axis. The first conductive particles 5 may be made of a metal such as copper or silver, and may be silver-coated copper particles, for example, copper particles coated with silver.

[0039] The first conductive particle 5 may be a known material, specifically available as, for example, ACBY-2 (Mitsui Mining & Smelting Co., Ltd.) or CE-1110 (Fukuda Metal Foil & Powder Industry Co., Ltd.). Alternatively, the first conductive particle 5 may be manufactured by a known method (for example, the method described in Patent Document 1 above).

[0040] The content of the first conductive particles 5 in the first adhesive layer 2 (the volume ratio of the first conductive particles 5 in the first adhesive layer 2) may be 2% by volume or more, or 8% by volume or more, and may be 25% by volume or less, or 15% by volume or less, based on the total volume of the first adhesive layer 2.

[0041] The thickness of the first adhesive layer 2 may be, for example, 5 μm or more, 7 μm or more, or 10 μm or more, and may be 30 μm or less, 25 μm or less, or 20 μm or less.

[0042] The second adhesive layer 3 contains second conductive particles 7, which are conductive particles other than the first conductive particles 5. The second conductive particles 7 have a non-conductive core and a conductive layer provided on the core. The core is made of a non-conductive material such as glass, ceramic, or resin, and is preferably made of resin. Examples of resins include acrylic resin, styrene resin, silicone resin, polybutadiene resin, or copolymers of monomers constituting these resins. The average particle size of the core may be, for example, 2 to 30 μm.

[0043] The conductive layer is formed of, for example, gold, silver, copper, nickel, palladium, or an alloy thereof. From the viewpoint of excellent conductivity, the conductive layer preferably contains at least one selected from gold, nickel, and palladium, more preferably gold or palladium, and even more preferably gold. The conductive layer is formed, for example, by plating the above metal onto a core body. The thickness of the conductive layer may be, for example, 10 to 400 nm.

[0044] The average particle size of the second conductive particles 7 is preferably 30 μm or less, more preferably 25 μm or less, and even more preferably 20 μm or less, from the viewpoint of being able to suitably thin the adhesive film 1A. The average particle size of the second conductive particles 7 may be, for example, 1 μm or more. The average particle size of the second conductive particles 7 is measured by a particle size distribution analyzer using laser diffraction and scattering (Microtrac (product name, Nikkiso Co., Ltd.)).

[0045] The content of the second conductive particles 7 in the second adhesive layer 3 (the volume ratio of the second conductive particles 7 in the second adhesive layer 3) may be 2% by volume or more, or 5% by volume or more, and may be 20% by volume or less, or 10% by volume or less, based on the total volume of the second adhesive layer 3.

[0046] The thickness of the second adhesive layer 3 may be, for example, 5 μm or more, 7 μm or more, or 10 μm or more, and may be 30 μm or less, 25 μm or less, or 20 μm or less.

[0047] In the first embodiment, the first adhesive layer 2 contains only the first conductive particles 5 as conductive particles, and the second adhesive layer 3 contains only the second conductive particles 7 as conductive particles. However, the first adhesive layer may further contain other conductive particles such as the second conductive particles 7, and the second adhesive layer may further contain other conductive particles such as the first conductive particles 5.

[0048] If the first adhesive layer further contains the second conductive particles 7, the volume ratio of the second conductive particles 7 in the first adhesive layer is preferably smaller than the volume ratio of the second conductive particles 7 in the second adhesive layer, from the viewpoint of obtaining an adhesive film with even greater reliability. The content of the second conductive particles 7 in the first adhesive layer may be, for example, 10% by volume or less, 5% by volume or less, or 2% by volume or less, based on the total volume of the first adhesive layer. From a similar viewpoint, the first adhesive layer preferably does not contain the second conductive particles 7, as in the first embodiment.

[0049] The adhesive film 1A is obtained, for example, by separately forming a first adhesive layer 2 and a second adhesive layer 3, and then laminating them. The first adhesive layer 2 and the second adhesive layer 3 are obtained, for example, by applying a paste-like adhesive composition to a resin film such as a PET (polyethylene terephthalate) film and drying it. The paste-like adhesive composition is obtained, for example, by heating or dissolving a mixture containing adhesive components 4 and 6 and a first conductive particle 5 or a second conductive particle 7 in a solvent. As the solvent, for example, a solvent with a boiling point of 50 to 150°C at atmospheric pressure is used.

[0050] The adhesive film 1A according to the first embodiment can be used as an adhesive to bond similar adherends together, and can also be used as an adhesive to bond different adherends together (for example, adherends with different coefficients of thermal expansion). The adhesive film 1A is suitably used for connecting electronic components together.

[0051] Figure 2 is a schematic cross-sectional view of a key part illustrating an example of the connection between electronic components. First, as shown in Figure 2(a), an adhesive film 1A is placed between a first electronic component 10, which comprises a first substrate 8 and a first electrode 9 formed on substantially the entire surface of the main surface of the first substrate 8, and a second electronic component 13, which comprises a second substrate 11 and a second electrode 12 formed on substantially the entire surface of the main surface of the second substrate 11, to form a laminate 14A.

[0052] Next, while heating the laminate 14A, pressurization is applied in the direction indicated by arrow A in Figure 2(a), thereby electrically connecting the first electronic component 10 and the second electronic component 13 to each other via the circuit connection material 15A, as shown in Figure 2(b), to obtain the connection structure 16A. The heating temperature is, for example, 50 to 190°C. The pressurization pressure is, for example, 0.1 to 30 MPa. These heating and pressurization steps are performed for, for example, 0.5 to 120 seconds.

[0053] The first substrate 8 and the second substrate 11 may each be substrates formed from glass, ceramic, polyimide, polycarbonate, polyester, polyethersulfone, etc. The first electrode 9 and the second electrode 12 may each be electrodes formed from gold, silver, copper, tin, aluminum, ruthenium, rhodium, palladium, osmium, iridium, platinum, indium tin oxide (ITO), etc.

[0054] The circuit connection material 15A contains first conductive particles 5, second conductive particles 7, and a cured product 17A of adhesive components 4 and 6. In other words, the circuit connection material 15 is formed by curing the adhesive film 1A described above.

[0055] The adhesive film 1A according to the first embodiment allows for suitable connection of electronic components 10 and 13 even when the first electrode 9 is made of a material that easily forms an oxide film on its surface (e.g., copper, aluminum). This is thought to be due to the use of both the first conductive particles 5 and the second conductive particles 7 in the adhesive film 1A. That is, as shown in Figure 2(b), the second conductive particles 7 form the main conductive path that connects the first electrode 9 and the second electrode 12, while the first conductive particles 5 assist in the electrical connection between the second conductive particles 7 and the first electrode 9, thereby achieving a suitable connection.

[0056] More specifically, the inventors surmise that because the first conductive particles 5 are dendritic conductive particles, even when an oxide film is formed on the surface of the first electrode 9, the first conductive particles 5 can penetrate the oxide film and come into contact with the first electrode 9, thereby enabling a suitable connection between the second conductive particles 7 and the first electrode 9. Therefore, the adhesive film 1A according to the first embodiment is considered to be more reliable than an adhesive film using only one of the first or second conductive particles, that is, it is capable of maintaining the desired conductivity against changes in ambient temperature.

[0057] Furthermore, the adhesive film 1A according to the first embodiment comprises a first adhesive layer 2 containing first conductive particles 5 and a second adhesive layer 3 containing second conductive particles 7, which enables even more favorable connection between electronic components 10 and 13. Specifically, when connecting electronic components 10 and 13, the first adhesive layer 2 containing the first conductive particles 5 is adhered to the first electrode 9 of the first electronic component 10, causing the first conductive particles 5 in the first adhesive layer 2 to come into contact with the first electrode 9, and in that state, the second conductive particles 7 in the second adhesive layer 3 come into contact with the first conductive particles 5. As a result, even when an oxide film is formed on the surface of the first electrode 9, the first conductive particles 5 can come into stronger contact with the first electrode 9, and it is believed that an even more stable connection can be achieved.

[0058] Therefore, the adhesive film 1A according to the first embodiment is considered to offer even greater reliability compared to an adhesive film consisting of a single layer containing both the first conductive particles 5 and the second conductive particles 7. Furthermore, the adhesive film 1A according to the first embodiment makes it possible to reduce the content of the first conductive particles 5 compared to an adhesive film consisting of a single layer containing both the first conductive particles 5 and the second conductive particles 7, while ensuring a suitable connection between the electronic components 10 and 13.

[0059] In another embodiment, the adhesive film may further comprise a third adhesive layer. Figure 3 is a schematic cross-sectional view showing another embodiment (second embodiment) of the adhesive film. As shown in Figure 3, the adhesive film 1B according to the second embodiment comprises a first adhesive layer 2, a second adhesive layer 3, and a third adhesive layer 18 in this order. The first adhesive layer 2 contains a first adhesive component 4 and first conductive particles 5 dispersed in the first adhesive component 4. The second adhesive layer 3 contains a second adhesive component 6 and second conductive particles 7 dispersed in the second adhesive component 6. The third adhesive layer 18 contains a third adhesive component 19 and third conductive particles 20 dispersed in the third adhesive component 19.

[0060] The first adhesive component 4, the second adhesive component 6, and the third adhesive component 19 may be of the same type or different types, but from the viewpoint of obtaining stable adhesive strength against changes in ambient temperature, they are preferably of the same type. The third adhesive component 19 may be the adhesive component described above.

[0061] The content of the third adhesive component 19 in the third adhesive layer 18 (the volume ratio of the third adhesive component 19 in the third adhesive layer 18) may be 75% or more by volume, or 85% or more by volume, and 98% or less by volume, or 92% or less by volume, based on the total volume of the third adhesive layer 18.

[0062] The third adhesive layer 18 contains third conductive particles 20, which are dendrite-shaped conductive particles. The details of the third conductive particles 20 are the same as those of the first conductive particles 5 described above, and therefore redundant explanations are omitted here. The third conductive particles 20 may be the same type as the first conductive particles 5 or different types, but from the viewpoint of obtaining stable adhesive strength against changes in ambient temperature, they are preferably the same type.

[0063] The content of the third conductive particles 20 in the third adhesive layer 18 (the volume ratio of the third conductive particles 20 in the third adhesive layer 18) may be 2% by volume or more, or 8% by volume or more, and may be 25% by volume or less, or 15% by volume or less, based on the total volume of the third adhesive layer 18.

[0064] The thickness of the third adhesive layer 18 may be, for example, 5 μm or more, 7 μm or more, or 10 μm or more, and may be 30 μm or less, 25 μm or less, or 20 μm or less.

[0065] In the second embodiment, the third adhesive layer 18 contains only the third conductive particles 20 as conductive particles, but the third adhesive layer may further contain other conductive particles such as the second conductive particles 7.

[0066] If the third adhesive layer further contains the second conductive particles 7, the volume ratio of the second conductive particles 7 in the third adhesive layer is preferably smaller than the volume ratio of the second conductive particles 7 in the second adhesive layer, from the viewpoint of obtaining an adhesive film with even greater reliability. The content of the second conductive particles 7 in the third adhesive layer may be, for example, 10% by volume or less, 5% by volume or less, or 2% by volume or less, based on the total volume of the third adhesive layer. From a similar viewpoint, the third adhesive layer preferably does not contain the second conductive particles 7, as in the second embodiment.

[0067] The adhesive film 1B according to the second embodiment is obtained, for example, by separately forming the first adhesive layer 2, the second adhesive layer 3, and the third adhesive layer 18, and then laminating them together. The third adhesive layer 18 is obtained by the same method as the method for forming the first adhesive layer 2 and the second adhesive layer 3 described above.

[0068] The adhesive film 1B according to the second embodiment can also be used as an adhesive to bond similar adherends together, as well as to bond different adherends together (for example, adherends with different coefficients of thermal expansion), and is particularly suitable for connecting electronic components.

[0069] Figure 4 is a schematic cross-sectional view of a key part illustrating another example of the connection between electronic components. The following explanation will omit any details that overlap with the example of connection between electronic components shown in Figure 2. In this example, as shown in Figure 4(a), the adhesive film 1B according to the second embodiment is placed between the first electronic component 10 and the second electronic component 13 to form a laminate 14B.

[0070] Next, as described above, the laminate 14B is heated and pressurized in the direction indicated by arrow A in Figure 4(a), thereby electrically connecting the first electronic component 10 and the second electronic component 13 to each other via the circuit connection material 15B, as shown in Figure 4(b), to obtain the connection structure 16B. The circuit connection material 15B contains the first conductive particles 5, the second conductive particles 7, the third conductive particles 20, and the cured adhesive component 17B. In other words, the circuit connection material 15B is obtained by curing the adhesive film 1B described above.

[0071] The adhesive film 1B according to the second embodiment allows for suitable connection of electronic components 10 and 13 even when the second electrode 12 is made of a material that easily forms an oxide film on its surface (e.g., copper, aluminum), in addition to the first electrode 9. This is because the third conductive particles 20 are dendrite-shaped conductive particles, and therefore, even when an oxide film is formed on the surface of the second electrode 12, the third conductive particles 20 can penetrate the oxide film and come into contact with the second electrode 12. Accordingly, the adhesive film 1B according to the second embodiment is considered to have superior reliability compared to an adhesive film using only one of the first or second conductive particles, that is, it is considered to be able to maintain the desired conductivity with respect to changes in ambient temperature.

[0072] Furthermore, the adhesive film 1B according to the second embodiment comprises a first adhesive layer 2 containing first conductive particles 5, a second adhesive layer 3 containing second conductive particles 7, and a third adhesive layer 18 containing third conductive particles 20, in this order, which makes it possible to connect electronic components 10 and 13 even more effectively. Specifically, even when an oxide film is formed on the surface of the second electrode 12 in addition to the first electrode 9, when connecting electronic components 10 and 13, the first conductive particles 5 in the first adhesive layer 2 can be brought into contact with the first electrode 9 preferentially over the second conductive particles 7 in the second adhesive layer 3, and the third conductive particles 20 in the third adhesive layer 18 can be brought into contact with the second electrode 12 preferentially over the second conductive particles 7 in the second adhesive layer 3.

[0073] Therefore, according to the adhesive film 1B of the second embodiment, reliability is considered to be further improved compared to an adhesive film consisting of a single layer containing, for example, the first conductive particles 5 (third conductive particles 20) and the second conductive particles 7. Furthermore, according to the adhesive film 1B of the second embodiment, while ensuring suitable connection between electronic components 10 and 13, it is possible to reduce the content of the first conductive particles 5 (third conductive particles 20) compared to an adhesive film consisting of a single layer containing, for example, the first conductive particles 5 (third conductive particles 20) and the second conductive particles 7. [Examples]

[0074] The present invention will be described in more detail below based on examples, but the present invention is not limited to the following examples.

[0075] (Preparation of Solution A1) 50 g of phenoxy resin (manufactured by Union Carbide Co., Ltd., product name: PKHC, weight-average molecular weight: 45000) was dissolved in a mixed solvent of toluene (boiling point: 110.6°C) and ethyl acetate (boiling point: 77.1°C) (toluene:ethyl acetate = 1:1 by mass ratio) to obtain a phenoxy resin solution with a solid content of 40% by mass. To this phenoxy resin solution, urethane acrylate (manufactured by Negami Kogyo Co., Ltd., product name: UN7700) and phosphate ester dimethacrylate (manufactured by Kyoeisha Chemical Co., Ltd., product name: Light Ester P-2M) as radical polymerizable substances, and 1,1-bis(t-hexylperoxy)-3,3,5-trimethylcyclohexane (manufactured by Nippon Oil & Fats Co., Ltd., product name: Perhexa TMH) as a curing agent were added in a solid mass ratio of phenoxy resin:urethane acrylate:phosphate ester dimethacrylate:curing agent = 10:10:3:2 to obtain solution A1.

[0076] As conductive particle B1 (first conductive particle), dendrite-shaped conductive particles (silver-coated copper particles, manufactured by Mitsui Mining & Smelting Co., Ltd., product name: ACBY-2) were used.

[0077] (Production of the core (resin particles)) A polymerization reaction was carried out by adding benzoyl peroxide as a polymerization initiator to a mixed solution of divinylbenzene, styrene monomer, and butyl methacrylate, and heating it while uniformly stirring at high speed to obtain a fine particle dispersion. This fine particle dispersion was filtered and dried under reduced pressure to obtain blocks, which are aggregates of fine particles. Furthermore, these blocks were pulverized to produce core bodies (resin particles) with an average particle size of 20 μm and different crosslinking densities.

[0078] (Preparation of conductive particles C1) A palladium catalyst (Muromachi Technos Co., Ltd., product name: MK-2605) was supported on the surface of the above-mentioned core body, and the core body was activated using an accelerator (Muromachi Technos Co., Ltd., product name: MK-370). This core body was placed in a mixture of nickel sulfate aqueous solution, sodium hypophosphite aqueous solution, and sodium tartrate aqueous solution heated to 60°C to perform the electroless plating pre-process. This mixture was stirred for 20 minutes, and it was confirmed that hydrogen foaming had stopped. Next, a mixed solution of nickel sulfate, sodium hypophosphite, sodium citrate, and a plating stabilizer was added, and the mixture was stirred until the pH stabilized, and the electroless plating post-process was performed until hydrogen foaming stopped. Subsequently, the plating solution was filtered, the filtrate was washed with water, and then dried in a vacuum dryer at 80°C to produce nickel-plated conductive particles C1 (second conductive particles).

[0079] [Example 1] <Film formation of adhesive compositions> A mixed solution was obtained by dispersing 45 volumes of conductive particles B1 in 100 volumes of solution A1. The obtained mixed solution was applied to a fluororesin film with a thickness of 80 μm, and the solvent was removed by hot air drying at 70°C for 10 minutes to obtain a 10 μm thick film-like adhesive composition (first adhesive layer) formed on the fluororesin film.

[0080] Next, 5 volumes of conductive particles C1 were dispersed in 100 volumes of solution A1 to obtain a mixed solution. The obtained mixed solution was applied to an 80 μm thick fluororesin film, and the solvent was removed by hot air drying at 70°C for 10 minutes to obtain a 20 μm thick adhesive composition on the fluororesin film (second adhesive layer). The first adhesive layer was laminated onto the second adhesive layer, and the fluororesin film was peeled off to obtain an adhesive film with a thickness of 30 μm.

[0081] [Example 2] A first adhesive layer and a second adhesive layer were prepared in the same manner as in Example 1. A third adhesive layer identical to the first adhesive layer was also prepared. In the same manner as in Example 1, the first adhesive layer was laminated onto the second adhesive layer, the fluororesin film on the second adhesive layer was peeled off, the third adhesive layer was laminated onto the side of the second adhesive layer opposite to the first adhesive layer, and the fluororesin film was peeled off to obtain an adhesive film with a thickness of 40 μm.

[0082] [Comparative Example 1] A mixed solution was obtained by dispersing 15 volumes of conductive particles C1 in 100 volumes of solution A1. The obtained mixed solution was applied to an 80 μm thick fluororesin film, and the solvent was removed by hot air drying at 70°C for 10 minutes to obtain a 40 μm thick film-like adhesive composition formed on the fluororesin film.

[0083] [Comparative Example 2] A mixed solution was obtained by dispersing 30 volumes of conductive particles C1 in 100 volumes of solution A1. The obtained mixed solution was applied to an 80 μm thick fluororesin film, and the solvent was removed by hot air drying at 70°C for 10 minutes to obtain a 40 μm thick film-like adhesive composition formed on the fluororesin film.

[0084] [Reference example 1] A mixed solution was obtained by dispersing 45 volumes of conductive particles B1 and 15 volumes of conductive particles C1 in 100 volumes of solution A1. The obtained mixed solution was applied to an 80 μm thick fluororesin film, and the solvent was removed by hot air drying at 70°C for 10 minutes to obtain a 30 μm thick film-like adhesive composition formed on the fluororesin film.

[0085] The reliability of each adhesive film (film-like adhesive composition) obtained in the examples, comparative examples, and reference examples when used as a circuit connection material was evaluated by the reliability tests described below. The results are shown in Tables 1 and 2.

[0086] <Reliability Testing> As shown in Figures 5(a) and (b), an adhesive film 21 cut to 6 mm x 6 mm was placed approximately in the center of a 6 mm x 50 mm copper foil 22, and attached by heating and pressing (50°C, 0.5 MPa, 2 seconds) using a BD-07 manufactured by Ohashi Seisakusho Co., Ltd. Subsequently, as shown in Figures 5(c) and (d), a 50 mm x 6 mm aluminum foil 23 was prepared and placed on top of the laminate of copper foil 22 and adhesive film 21 so as to cover the adhesive film 21, and a mounting body for reliability testing was obtained by heating and pressing (150°C, 0.5 MPa, 10 seconds) using a BD-07 manufactured by Ohashi Seisakusho Co., Ltd. As shown in Figure 6, an ammeter and a voltmeter were connected to the obtained mounting, and the connection resistance (initial) was measured using the four-terminal method. In addition, a heat cycle test was performed on the mounting using an ESPEC TSA-43EL, in which the heat cycle consisted of holding at -20°C for 30 minutes, raising the temperature to 100°C over 10 minutes, holding at 100°C for 30 minutes, and cooling down to -20°C over 10 minutes, repeated 500 times. After this, the connection resistance (after the heat cycle test) was measured in the same manner as described above.

[0087] [Table 1]

[0088] [Table 2] [Explanation of symbols]

[0089] 1A, 1B...Adhesive film, 2...First adhesive layer, 3...Second adhesive layer, 5...First conductive particles, 7...Second conductive particles, 18...Third adhesive layer, 20...Third conductive particles.

Claims

1. A first adhesive layer containing first conductive particles which are dendritic conductive particles, An adhesive film comprising: a second adhesive layer containing a second conductive particle, which is a conductive particle other than the first conductive particle, and which has a non-conductive core and a conductive layer provided on the core.

2. The first adhesive layer further contains the second conductive particles, The adhesive film according to claim 1, wherein the volume ratio of the second conductive particles to the first adhesive layer is smaller than the volume ratio of the second conductive particles to the second adhesive layer.

3. The adhesive film according to claim 1, wherein the first adhesive layer does not contain the second conductive particles.

4. The first adhesive layer, the second adhesive layer, and the third adhesive layer are provided in this order. The adhesive film according to any one of claims 1 to 3, wherein the third adhesive layer contains third conductive particles which are dendritic conductive particles.

5. The third adhesive layer further contains the second conductive particles, The adhesive film according to claim 4, wherein the volume ratio of the second conductive particles in the third adhesive layer is smaller than the volume ratio of the second conductive particles in the second adhesive layer.

6. The adhesive film according to claim 4, wherein the third adhesive layer does not contain the second conductive particles.

7. The adhesive film according to any one of claims 1 to 6, wherein the conductive layer contains at least one selected from the group consisting of gold, nickel, and palladium.

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