HK1242362B - Multilayer adhesive film and connection structure - Google Patents

Description

Multilayer adhesive film and connection structure

Technical Field

The present invention relates to a multilayer adhesive film and a connection structure.

Background Art

In recent years, multilayer adhesive films have been widely used to bond electronic components such as IC chips and liquid crystal panels to substrates and the like in the manufacturing process of electronic devices.

This multilayer adhesive film contains a polymer composition containing an uncured polymer and a curing agent as an adhesive component, and the polymer is cured by thermocompression bonding or the like, thereby bonding the substrate and the electronic component.

When high-temperature thermocompression bonding is required for multi-layer adhesive films, thermal expansion and curing shrinkage can cause deformation of electronic components and substrates, resulting in floating at the bonding interface and reduced bond strength. Therefore, there is a need for multi-layer adhesive films that can bond electronic components to substrates, even at relatively low temperatures.

For example, Patent Document 1 below discloses a thermal cationically polymerizable composition that contains an epoxy polymer compound as an adhesive polymer composition and a thermal cationically polymerizable curing agent as a curing agent, thereby enabling bonding by low-temperature thermocompression bonding.

Furthermore, when the reactivity of the epoxy polymer compound and the curing agent in the multilayer adhesive film is increased to enable bonding by low-temperature thermocompression bonding, the epoxy polymer compound may slowly cure during storage, and the adhesiveness of the multilayer adhesive film may decrease.

Therefore, Patent Document 2 below discloses a curing agent for epoxy polymers that is rendered latent by encapsulating an anionic polymerizable curing agent in microcapsules. This latent curing agent for epoxy polymers can be stably stored at room temperature and rapidly initiates a curing reaction under specified heat, pressure, or other conditions, thereby improving the storage stability of multilayer adhesive films.

Prior art literature

Patent Literature

Patent Document 1: International Publication No. 2013/027541;

Patent Document 2: International Publication No. 2007/037378.

Summary of the Invention

Problems to be solved by the invention

However, the thermally cationically polymerizable composition disclosed in Patent Document 1 described above is subject to polymerization inhibition when the adherend is made of alkali glass or polyimide, resulting in insufficient curing. Consequently, multilayer adhesive films using the thermally cationically polymerizable composition disclosed in Patent Document 1 may have reduced adhesion depending on the material of the adherend.

Furthermore, the multilayer adhesive film using the latent epoxy polymer curing agent disclosed in Patent Document 2 mentioned above is not restricted by the bonded surface, but requires thermocompression bonding at a high temperature to obtain sufficient adhesion.

Therefore, the present invention is made in view of the above-mentioned problems, and the purpose of the present invention is to provide: a new and improved multilayer adhesive film containing an anionic polymerization type epoxy curing agent, having high storage stability and sufficient adhesion even under low-temperature thermal compression; and a connection structure obtained by bonding with the multilayer adhesive film.

Means for solving problems

To solve the above problems, according to one aspect of the present invention, a multilayer adhesive film is provided, comprising: a plurality of epoxy layers containing an uncured epoxy polymer compound and a latent epoxy curing agent; and a curing agent layer containing an anionic polymerization-type non-latent epoxy curing agent sandwiched between the plurality of epoxy layers.

The invention may further include an interface layer formed between each of the epoxy layers and the curing agent layer and containing a cured epoxy polymer compound.

The non-latent epoxy curing agent may be contained in an amount of 10% by mass or more and 50% by mass or less relative to the total mass of the curing agent layer.

The non-latent epoxy curing agent may be an imidazole compound.

The latent epoxy curing agent may be a curing agent that is rendered latent by encapsulating the curing agent in microcapsules.

At least any one of the plurality of epoxy layers and the curing agent layer may contain conductive particles.

The conductive particles may be included in at least any one layer of the plurality of epoxy layers.

The total film thickness of the multilayer adhesive film may be 4 μm or more and 50 μm or less.

Furthermore, in order to solve the above-mentioned problems, according to another aspect of the present invention, there is provided a connection structure in which an electronic component is bonded to another electronic component or a substrate via the above-mentioned multilayer adhesive film.

At least a portion of the bonded surface of the electronic component may be covered with a protective film containing polyimide.

Effects of the Invention

As described above, according to the present invention, during thermocompression bonding, the highly reactive non-latent epoxy curing agent diffuses into the layer containing the uncured epoxy polymer compound. Therefore, even at low-temperature thermocompression bonding, a multilayer adhesive film with sufficient adhesion can be achieved. Furthermore, according to the present invention, since the layer containing the non-latent epoxy curing agent is separated from the layer containing the uncured epoxy polymer compound, a multilayer adhesive film with high storage stability can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view schematically showing a cross section of a multilayer adhesive film according to one embodiment of the present invention cut along its thickness direction.

FIG2 is a cross-sectional view of the multilayer adhesive film shown in FIG1 , in which an interface layer is formed between the epoxy layer and the curing agent layer.

FIG. 3 is a cross-sectional view schematically showing a cross section of a multilayer adhesive film according to a modification of the embodiment when cut along the thickness direction.

DETAILED DESCRIPTION

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that in this specification and the accompanying drawings, components having substantially the same functional configuration are denoted by the same reference numerals to omit repeated description.

＜1. Multilayer Adhesive Film＞

[1.1. Composition of multilayer adhesive film]

First, the structure of a multilayer adhesive film according to one embodiment of the present invention will be described with reference to Figures 1 and 2. Figure 1 is a cross-sectional view schematically showing a cross section of a multilayer adhesive film 100 according to this embodiment, taken along its thickness. Furthermore, Figure 2 is a cross-sectional view of a multilayer adhesive film 100A having interface layers 131 and 132 formed between epoxy layers 111 and 112 and a curing agent layer 120.

As shown in FIG. 1 , the multilayer adhesive film 100 according to the present embodiment has a laminated structure in which a curing agent layer 120 is sandwiched between a plurality of epoxy layers 111 and 112 .

It should be noted that a release sheet (not shown) is provided on either side of the multilayer adhesive film 100 to support the multilayer adhesive film 100. The release sheet is made by coating a release agent such as silicone onto a sheet of PET (Poly Ethylene Terephthalate), OPP (Oriented Polypropylene), PMP (Poly-4-methylpentene-1), or PTFE (Polytetrafluoroethylene). It prevents the multilayer adhesive film 100 from drying out and maintains its shape. This release sheet can be used appropriately when forming each layer of the multilayer adhesive film 100.

(Epoxy layer)

The epoxy layers 111 and 112 contain a film-forming component, an uncured epoxy polymer compound, and a latent epoxy curing agent.

The film-forming component is a resin or the like that forms the film shape of the epoxy layers 111 and 112, and functions as a binder that holds the uncured epoxy polymer compound and the latent epoxy curing agent. The film-forming component may be, for example, a polymer resin having an average molecular weight of 10,000 or greater. From the perspective of film-forming properties, a polymer resin having an average molecular weight of approximately 10,000 to 80,000 is preferred.

Specifically, various resins such as epoxy resins, phenoxy resins, polyesterurethane resins, polyester resins, polyurethane resins, acrylic resins, polyimide resins, and butyral resins can be used as the film-forming component. These resins can be used alone or in combination of two or more. It should be noted that, in order to achieve good film-forming properties and adhesion reliability, a phenoxy resin is preferably used as the film-forming component.

To obtain good film strength and adhesion reliability, for example, the epoxy layers 111 and 112 preferably contain film-forming components at 10% to 55% by mass, and more preferably at 10% to 30% by mass, relative to the total mass of the epoxy layers 111 and 112 .

The uncured epoxy polymer compound is a compound, oligomer, or prepolymer having one or more epoxy groups within its molecule. The multilayer adhesive film 100 cures by polymerizing during thermal compression bonding, thereby bonding adherends. The uncured epoxy polymer compound undergoes a polymerization reaction upon mixing with a curing agent. Any curable material can be solid or liquid.

As solid epoxy polymer compound, for example, various modified epoxy resins of bisphenol A type epoxy resin, bisphenol F type epoxy resin, novolac type epoxy resin, rubber and urethane etc. or their prepolymer etc. can be used. In addition, as liquid epoxy polymer compound, for example, bisphenol type epoxy resin, naphthalene type epoxy resin, biphenyl type epoxy resin, phenol novolac type epoxy resin, stilbene type epoxy resin, trisphenol methane type epoxy resin, dicyclopentadiene type epoxy resin, triphenylmethane type epoxy resin or their prepolymer etc. can be used. It should be noted that, uncured epoxy polymer compound can use these compounds alone, also can use two or more combinations.

In order to obtain good film strength and bonding reliability, for example, the uncured epoxy polymer compound is preferably contained in an amount of 15 mass % or more and 65 mass % or less relative to the total mass of the epoxy layers 111 and 112, and more preferably in an amount of 30 mass % or more and 50 mass % or less.

Latent epoxy curing agents are latent curing agents that selectively initiate a polymerization reaction with uncured epoxy polymer compounds during, for example, thermocompression bonding. Specifically, latent epoxy curing agents are curing agents that, while unreactive with epoxy polymer compounds at room temperature (e.g., 25°C), rapidly become reactive with epoxy polymer compounds and cure them under specified conditions such as heat, light, or pressure. In other words, "latent" means that the curing agent is inactive under storage conditions such as room temperature but becomes activated under specified conditions.

Examples of such latent epoxy curing agents include: a latent epoxy curing agent encapsulated in microcapsules, which is activated by destroying the microcapsules with heat or pressure (such as NOVACURE manufactured by Asahi Kasei E-materials); and a latent epoxy curing agent in which an amine compound that functions as a curing agent is passivated by forming an adduct or salt, which is then decomposed and activated by heating (such as Amicure manufactured by Ajinomoto Fine Techno Co., Ltd. and Fujicure manufactured by Fuji Chemical Industries, Ltd.).

However, in order to improve storage stability and obtain good adhesion even at low-temperature pressure bonding, it is preferable to use a microcapsule-type latent epoxy curing agent (such as NOVACURE manufactured by Asahi Kasei E-materials) as the latent epoxy curing agent.

It should be noted that the latent epoxy curing agent is an anionic polymerizable epoxy curing agent. By using an anionic polymerizable latent epoxy curing agent, the multilayer adhesive film 100 of this embodiment exhibits excellent adhesion even to adherends that would be inhibited by a cationic polymerizable epoxy curing agent. Examples of adherends that would be inhibited by a cationic polymerizable epoxy curing agent include alkaline glass and polyimide.

In order to obtain good storage stability and adhesion, for example, the latent epoxy curing agent is preferably contained in an amount of 10 mass % to 50 mass % relative to the total mass of the epoxy layers 111 and 112 , and more preferably in an amount of 20 mass % to 40 mass % relative to the total mass of the epoxy layers 111 and 112 .

It should be noted that the epoxy layers 111 and 112 may contain silane coupling agents, inorganic fillers, colorants, antioxidants, and rust inhibitors as other additives.

As the silane coupling agent, any known silane coupling agent can be used, including epoxy, amino, mercapto/sulfide, and ureide-based silane coupling agents. Addition of these silane coupling agents can improve adhesion to inorganic substrates such as glass substrates. Inorganic fillers such as silica, talc, titanium oxide, calcium carbonate, and magnesium oxide can be used. Addition of these inorganic fillers can control the fluidity of the epoxy layers 111 and 112 and improve film strength.

In order to sufficiently fill the epoxy polymer compound for bonding the electronic component to the substrate, etc., the film thickness of the epoxy layers 111 and 112 is preferably 1 μm to 20 μm, and more preferably 2 μm to 15 μm.

(Curing agent layer)

Curing agent layer 120 contains a film-forming component and an anionic polymerization-type non-latent epoxy curing agent (hereinafter referred to as a non-latent epoxy curing agent). It should be noted that curing agent layer 120 does not contain uncured epoxy polymer compounds. This is to prevent uncured epoxy polymer compounds from reacting with the non-latent epoxy curing agent during storage, thereby curing the epoxy polymer compounds.

The film-forming component is a resin or the like that forms the film shape of curing agent layer 120, and functions as a binder to retain the anionic polymerization-type, non-latent epoxy curing agent. Specifically, the film-forming component can be the same polymer resin as that contained in epoxy layers 111 and 112. To achieve excellent film-forming properties and bonding reliability, a phenoxy resin is preferably used. Furthermore, the film-forming component contained in curing agent layer 120 can be the same polymer resin as that contained in epoxy layers 111 and 112, or a different polymer resin.

In order to obtain good film strength and adhesion reliability, for example, the curing agent layer 120 preferably contains film-forming components at 10 mass % or more and 95 mass % or less, and more preferably at 50 mass % or more and 90 mass % or less, relative to the total mass of the curing agent layer 120 .

Anionic polymerization-type non-latent epoxy curing agents are curing agents that do not exhibit latency and initiate anionic polymerization with epoxy polymer compounds. Specifically, anionic polymerization-type non-latent epoxy curing agents refer to curing agents other than latent epoxy curing agents among anionic polymerization-type epoxy curing agents, such as amine compounds, imidazole compounds, and polyamide compounds. Furthermore, anionic polymerization-type non-latent epoxy curing agents may also refer to curing agents that are not encapsulated in microcapsules or the like, thereby imparting latency.

In the multilayer adhesive film 100 according to this embodiment, since the non-latent epoxy curing agent is anionic polymerizable, it has good adhesion even to adherends such as alkali glass and polyimide, which are inhibited by cationic polymerizable epoxy curing agents.

The anionic polymerization type non-latent epoxy curing agent may include any of the above compounds alone or in combination of two or more. However, in this embodiment, the anionic polymerization type non-latent epoxy curing agent preferably includes an imidazole compound. In this case, the multilayer adhesive film 100 can achieve a lower temperature for thermal compression bonding during bonding, while also achieving a stronger bond.

In the multilayer adhesive film 100 according to this embodiment, during thermocompression bonding, epoxy layers 111 and 112 are squeezed to sandwich curing agent layer 120. This allows the non-latent epoxy curing agent in curing agent layer 120 to diffuse into epoxy layers 111 and 112. Consequently, during thermocompression bonding, the epoxy polymer compound in epoxy layers 111 and 112 undergoes a polymerization reaction with the more reactive non-latent epoxy curing agent in addition to the latent epoxy curing agent, allowing it to cure at a higher cure rate. Therefore, the multilayer adhesive film 100 according to this embodiment can fully cure the epoxy polymer compound even during thermocompression bonding at lower temperatures, thereby achieving sufficient adhesion.

Furthermore, in the multilayer adhesive film 100 according to this embodiment, the curing agent layer 120 containing a highly reactive non-latent epoxy curing agent and the epoxy layers 111 and 112 containing uncured epoxy polymer compounds are formed separately. Therefore, the highly reactive non-latent epoxy curing agent does not come into direct contact with the uncured epoxy polymer compounds except during thermocompression bonding, thus suppressing the polymerization reaction of the epoxy polymer compounds during storage. Consequently, the multilayer adhesive film 100 according to this embodiment can exhibit high storage stability.

In addition, relative to the gross mass of curing agent layer 120, preferably with more than 10 mass % and below 50 mass % containing anionic polymerization type non-latent epoxy curing agent.When the content of non-latent epoxy curing agent is less than 10 mass %, there is the possibility that the cure rate of epoxy layer 111,112 reduces, the adhesiveness reduces, therefore not preferably.In addition, when the content of non-latent epoxy curing agent is more than 50 mass %, when thermocompression bonding, the interface of epoxy layer 111,112 and curing agent layer 120 solidifies rapidly, becomes difficult to fully extrude multilayer adhesive film 100, therefore not preferably.Particularly, as described later, when using multilayer adhesive film 100 as anisotropic conductive film, due to the insufficient extrusion of multilayer adhesive film 100, there is the possibility that can not form definite anisotropic conductive connection, therefore not preferably.

It should be noted that the curing agent layer 120 may contain a silane coupling agent, an inorganic filler, a colorant, an antioxidant, a rust preventive, and the like as other additives, similarly to the epoxy layers 111 and 112 .

In order to sufficiently fill the anionic polymerization type non-latent epoxy curing agent in bonding the electronic component to the substrate, etc., the film thickness of the curing agent layer 120 is preferably 1 μm to 15 μm, and more preferably 2 μm to 10 μm.

Here, as shown in FIG. 2 , the multilayer adhesive film 100A according to this embodiment may also have interface layers 131 and 132 formed between the epoxy layers 111 and 112 and the curing agent layer 120 .

Interface layers 131 and 132 contain a cured epoxy polymer compound. The cured epoxy polymer compound contained in interface layers 131 and 132 is a compound obtained by a polymerization reaction between the uncured epoxy polymer compound in epoxy layers 111 and 112 and the non-latent epoxy curing agent in curing agent layer 120, resulting in a cured compound. Interface layers 131 and 132 containing the cured epoxy polymer compound function as a barrier layer between epoxy layers 111 and 112 and curing agent layer 120, thereby suppressing the diffusion of the non-latent epoxy curing agent in curing agent layer 120 into epoxy layers 111 and 112 during storage. Consequently, the storage stability of the multilayer adhesive film 100 formed with interface layers 131 and 132 is further improved.

In order to suppress the diffusion of the non-latent epoxy curing agent into the epoxy layers 111 and 112, the curing rate of the epoxy polymer compound in the interface layers 131 and 132 is preferably 60% or higher, and more preferably 80% or higher. The curing rate of the epoxy polymer compound can be calculated, for example, by measuring the ratio of epoxy groups in the uncured epoxy polymer compound and the ratio of epoxy groups in the cured epoxy polymer compound using infrared spectroscopy (IR), and then calculating the extent to which the number of epoxy groups is reduced due to curing.

In order to obtain good storage stability and adhesion in the multilayer adhesive film, the thickness of the interface layers 131 and 132 is preferably 0.1 μm to 0.6 μm, and more preferably 0.2 μm to 0.5 μm, for example.

As described above, in the multilayer adhesive film 100 according to this embodiment, high storage stability and good adhesion can be achieved by separately forming the curing agent layer 120 containing a highly reactive non-latent epoxy curing agent and the epoxy layers 111 and 112 containing an uncured epoxy polymer compound.

In order to obtain good film strength and adhesion reliability, the total film thickness of the multilayer adhesive film 100 according to the present embodiment is preferably 4 μm or more and 50 μm or less.

[1.2. Method for preparing multilayer adhesive film]

The multilayer adhesive film 100 according to the present embodiment described above can be produced, for example, as follows.

First, a film-forming component, an epoxy polymer compound, and a latent epoxy curing agent are mixed in a suitable solvent at a predetermined ratio. The mixture is uniformly mixed using a known mixing method to prepare an epoxy layer-forming composition. The composition is then applied to a release sheet using a known coating method to a predetermined dry thickness. The composition is then dried at 60°C to 80°C for 2 to 8 minutes to form epoxy layers 111 and 112, respectively.

Similarly, the film-forming component and the anionic polymerization type non-latent epoxy curing agent are mixed in a suitable solvent in a prescribed proportion to prepare a curing agent layer forming composition, which is then applied to another peeling sheet in a manner to form a prescribed dry thickness and dried to form a curing agent layer 120.

Furthermore, the formed epoxy layers 111 and 112 and the curing agent layer 120 are laminated in the order of epoxy layer 111 , curing agent layer 120 , and epoxy layer 112 by a known method, thereby preparing the multilayer adhesive film 100 according to this embodiment.

The method for producing the multilayer adhesive film 100 according to this embodiment is not limited to the method described above. For example, rather than forming the epoxy layers 111 and 112 and the curing agent layer 120 separately and laminating them together, the curing agent layer 120 and the epoxy layer 112 may be sequentially coated on the epoxy layer 111. Furthermore, the multilayer adhesive film 100 may be produced by combining coating and lamination to laminate the epoxy layers 111 and 112 and the curing agent layer 120.

<2. Modifications of Multilayer Adhesive Films>

Next, a multilayer adhesive film 100B according to a modification of the present embodiment will be described with reference to Fig. 3. Fig. 3 is a cross-sectional view schematically showing a cross section of the multilayer adhesive film 100B according to the modification of the present embodiment when cut along the thickness direction.

As shown in FIG3 , a multilayer adhesive film 100B according to a modified example of this embodiment includes conductive particles 140 in at least one of the epoxy layers 111 and 112 and the curing agent layer 120, thereby enabling use as an anisotropic conductive film. It should be noted that in order for the multilayer adhesive film 100B to function as an anisotropic conductive film capable of more reliably performing anisotropic conductive connection, it is preferable that the conductive particles 140 be included in at least one of the epoxy layers 111 and 112.

Conductive particles 140 are, for example, metal particles or metal-coated resin particles. Specifically, conductive particles 140 may be particles of metals such as nickel, cobalt, copper, silver, gold, or palladium. Alternatively, conductive particles 140 may be particles formed by coating the surface of core resin particles such as styrene-divinylbenzene copolymer, benzoguanamine resin, cross-linked polystyrene resin, acrylic resin, or styrene-silica composite resin with a metal such as nickel, copper, gold, or palladium. Furthermore, the surface of conductive particles 140 may be formed with a gold or palladium thin film, or a thin insulating resin film that is thin enough to be destroyed during crimping.

When the multilayer adhesive film 100B is subjected to thermocompression bonding, for example, the conductive particles 140 melt and connect to each other, thereby electrically connecting the terminals of the electronic component and the terminals of the substrate, etc., bonded by the multilayer adhesive film 100B. Furthermore, because the conductive particles 140 form electrical connections only in areas where higher pressure is applied, such as between protruding terminals on the electronic component and the substrate, the insulation properties of the multilayer adhesive film 100B are maintained in the film's in-plane direction. In other words, the multilayer adhesive film 100B according to this variation of the present embodiment can be used as an anisotropic conductive film.

To achieve reliable anisotropic conductive connection, the average particle size (number average of the particle diameters) of the conductive particles 140 is preferably 1 μm to 10 μm, more preferably 2 μm to 5 μm. The average particle size of the conductive particles 140 can be measured, for example, by laser diffraction scattering.

Furthermore, in order to achieve reliable anisotropic conductive connection, for example, the conductive particles 140 are preferably contained at 5 mass % to 30 mass % inclusive, and more preferably at 5 mass % to 20 mass % inclusive, relative to the total mass of the layer containing the conductive particles 140 .

(Method for preparing a connected structure)

When the multilayer adhesive film 100B according to the modification of the present embodiment is used as an anisotropic conductive film, for example, the terminals of an electronic component and the terminals of a substrate can be anisotropically conductively connected by the following method.

First, the multilayer adhesive film 100B according to the modified example of this embodiment is temporarily attached to the terminal of the substrate so that the layer containing the conductive particles 140 faces the terminal side of the substrate. The temporary attachment method and conditions can be known methods and conditions, but for example, the multilayer adhesive film 100B can also be temporarily attached by heating and pressurizing it to a level that does not fully cure.

Next, the electronic component is placed on the temporarily attached multilayer adhesive film 100B so that its terminals face the terminals of the substrate and is temporarily fixed. The temporary fixing method and conditions can be known methods and conditions. For example, the substrate, multilayer adhesive film 100B, and electronic component can be temporarily fixed by heating and pressurizing the multilayer adhesive film 100B until it is not fully cured.

Next, the temporarily fixed substrate, multilayer adhesive film 100B, and electronic component are heated and pressed by a heating and pressing member to form a thermocompression bond. This allows anisotropic conductive connection between the substrate terminals and the electronic component terminals, forming a connected structure. The thermocompression bonding method and conditions can be performed using a known thermocompression bonding device.

According to the above method, the multilayer adhesive film 100B according to the modification of the present embodiment has sufficient adhesiveness regardless of the materials of the adhered surfaces of the substrate and the electronic component, and can form a connection structure having anisotropic conductive connection.

Example

<3. Examples>

The multilayer adhesive film according to the present embodiment will be described in more detail below with reference to examples and comparative examples. It should be noted that the following examples are merely examples for demonstrating the feasibility and effectiveness of the multilayer adhesive film according to the present embodiment, and the present invention is not limited to the following examples.

[3.1. Preparation and evaluation of multilayer adhesive films]

First, a multilayer adhesive film according to the present embodiment was prepared and its adhesiveness was evaluated.

(Example 1)

An epoxy layer-forming composition was prepared by mixing 20% by mass of a phenoxy resin (YP50, manufactured by Nippon Steel Chemical Co., Ltd.), 40% by mass of a liquid epoxy resin (EP828, manufactured by Mitsubishi Chemical Corporation), 10% by mass of a solid epoxy resin (YD-014, manufactured by Nippon Steel Chemical Co., Ltd.), and 30% by mass of a latent epoxy curing agent (NOVACURE 3941HP, manufactured by Asahi Kasei E-materials Co., Ltd.). This epoxy layer-forming composition was then applied to a release sheet (38 μm thick silicone-treated PET sheet, the same applies hereinafter) to a film thickness of 6 μm after drying and dried to form an epoxy layer.

Next, a curing agent layer-forming composition was prepared by mixing 90% by mass of a phenoxy resin (YP50, manufactured by Nippon Steel Chemical Co., Ltd.) and 10% by mass of an imidazole compound (2-methylimidazole, manufactured by Shikoku Chemicals Co., Ltd.). This curing agent layer-forming composition was then applied to a release sheet to a film thickness of 6 μm after drying and dried to form a curing agent layer.

Furthermore, each layer was peeled from the release sheet and bonded together so that the curing agent layer was sandwiched between the two epoxy layers, thereby preparing a multilayer adhesive film according to Example 1 (total film thickness: 18 μm).

(Comparative Example 1)

An adhesive film-forming composition was prepared by mixing 20% by mass of a phenoxy resin (YP50, manufactured by Nippon Steel Chemical Co., Ltd.), 40% by mass of a liquid epoxy resin (EP828, manufactured by Mitsubishi Chemical Corporation), 10% by mass of a solid epoxy resin (YD-014, manufactured by Nippon Steel Chemical Co., Ltd.), and 30% by mass of a cationic polymerization-type epoxy curing agent (SI-60L, manufactured by Sanshin Chemical Co., Ltd.). The adhesive film-forming composition was then applied to a release sheet to a film thickness of 18 μm after drying and dried to prepare the adhesive film (total film thickness of 18 μm) according to Comparative Example 1.

(Evaluation methods and evaluation results)

Connected structures were produced using the adhesive films of Example 1 and Comparative Example 1. Specifically, a 0.1 mm thick polyimide film, the adhesive film of Example 1 or Comparative Example 1, and a 0.1 mm thick PET (polyethylene terephthalate) film were sequentially laminated and then thermocompressed at 150°C, 1 MPa, and 5 seconds to produce the connected structures.

The peel strength of the produced connection structure was measured by a T-type peel strength test (in accordance with JIS K6853-3) using a Tensilon universal testing machine (manufactured by Orientec).

[Table 1]

(Table 1)

Example 1 Comparative Example 1 Peel strength [N] 13 3

The results in Table 1 show that Example 1 exhibits higher peel strength and higher adhesion than Comparative Example 1. In particular, in Comparative Example 1, peeling occurs at the interface between the polyimide film and the adhesive film, indicating that the cationic polymerization curing agent is inhibited by the polyimide, resulting in insufficient curing and reduced adhesion.

Therefore, it can be seen that the multilayer adhesive film according to the present embodiment exhibits high adhesiveness regardless of the material of the adhered surface.

[3.2. Preparation and evaluation of anisotropic conductive films]

Next, a multilayer adhesive film according to a modified example of the present embodiment was prepared, and the adhesiveness, storage stability, conductivity, and the like when used as an anisotropic conductive film were evaluated.

(Example 2)

First, an ACF (anisotropic conductive film) layer-forming composition was prepared by mixing 20% by mass of a phenoxy resin (YP50, manufactured by Nippon Steel Chemical), 30% by mass of a liquid epoxy resin (EP828, manufactured by Mitsubishi Chemical Corporation), 10% by mass of a solid epoxy resin (YD-014, manufactured by Nippon Steel Chemical), 30% by mass of a latent epoxy curing agent (NOVACURE 3941HP, manufactured by Asahi Kasei E-materials), and 10% by mass of conductive particles (AUL-704, manufactured by Sekisui Chemical). The ACF layer-forming composition was then applied to a release sheet to a film thickness of 6 μm after drying and dried to form an ACF layer.

Next, a composition for forming an NCF (nonconductive film) layer was prepared by mixing 20% by mass of a phenoxy resin (YP50, manufactured by Nippon Steel Chemical Co., Ltd.), 40% by mass of a liquid epoxy resin (EP828, manufactured by Mitsubishi Chemical Corporation), 10% by mass of a solid epoxy resin (YD-014, manufactured by Nippon Steel Chemical Co., Ltd.), and 30% by mass of a latent epoxy curing agent (NOVACURE 3941HP, manufactured by Asahi Kasei E-materials Co., Ltd.). The NCF layer-forming composition was then applied to a release sheet to a film thickness of 6 μm after drying and dried to form an NCF layer.

Next, a curing agent layer-forming composition was prepared by mixing 90% by mass of a phenoxy resin (YP50, manufactured by Nippon Steel Chemical Co., Ltd.) and 10% by mass of an imidazole compound (2-methylimidazole, manufactured by Shikoku Chemicals Co., Ltd.). This curing agent layer-forming composition was then applied to a release sheet to a film thickness of 6 μm after drying and dried to form a curing agent layer.

Furthermore, the layers were peeled off from the release sheet and laminated so that the curing agent layer formed above was sandwiched between the ACF layer and the NCF layer, thereby preparing a multilayer adhesive film according to Example 2 (total film thickness: 18 μm).

(Example 3)

A multilayer adhesive film (total film thickness 18 μm) according to Example 3 was prepared in the same manner as in Example 2 except that 60% by mass of a phenoxy resin (YP50, manufactured by Nippon Steel Chemical Co., Ltd.) and 40% by mass of an imidazole compound (2-methylimidazole, manufactured by Shikoku Chemical Co., Ltd.) were mixed to prepare a curing agent layer-forming composition.

(Example 4)

A multilayer adhesive film (total film thickness 18 μm) according to Example 4 was prepared in the same manner as in Example 2 except that 50% by mass of a phenoxy resin (YP50, manufactured by Nippon Steel Chemical Co., Ltd.) and 50% by mass of an imidazole compound (2-methylimidazole, manufactured by Shikoku Chemical Co., Ltd.) were mixed to prepare a curing agent layer-forming composition.

(Example 5)

A multilayer adhesive film (total film thickness 18 μm) according to Example 5 was prepared in the same manner as in Example 2 except that 40% by mass of a phenoxy resin (YP50, manufactured by Nippon Steel Chemical Co., Ltd.) and 60% by mass of an imidazole compound (2-methylimidazole, manufactured by Shikoku Chemical Co., Ltd.) were mixed to prepare a curing agent layer-forming composition.

(Comparative Example 2)

A multilayer adhesive film (total thickness 18 μm) according to Comparative Example 2 was prepared in the same manner as in Example 2 except that the NCF layer had a thickness of 12 μm and only the ACF layer and NCF layer were peeled off from the release sheet and bonded together.

(Comparative Example 3)

An ACF layer-forming composition was prepared by mixing 20% by mass of a phenoxy resin (YP50, manufactured by Nippon Steel Chemical), 20% by mass of a liquid epoxy resin (EP828, manufactured by Mitsubishi Chemical Corporation), 10% by mass of a solid epoxy resin (YD-014, manufactured by Nippon Steel Chemical), 30% by mass of a latent epoxy curing agent (NOVACURE 3941HP, manufactured by Asahi Kasei E-materials), 10% by mass of conductive particles (AUL-704, manufactured by Sekisui Chemical), and 10% by mass of an imidazole compound (2-methylimidazole, manufactured by Shikoku Chemicals). The ACF layer-forming composition was then applied to a release sheet to a film thickness of 6 μm after drying and dried to form an ACF layer.

The NCF layer-forming composition was adjusted to the same composition as in Example 2 so that the film thickness after drying would be 12 μm. The composition was applied onto a release sheet and dried to form an NCF layer.

Furthermore, the ACF layer and the NCF layer were peeled off from the release sheet and bonded together to prepare a multilayer adhesive film (total film thickness: 18 μm) according to Comparative Example 3.

(Comparative Example 4)

The ACF layer-forming composition was adjusted to the same composition as in Example 2 so as to have a film thickness of 6 μm after drying. The composition was applied onto a release sheet and dried to form an ACF layer.

An NCF layer-forming composition was prepared by mixing 20% by mass of a phenoxy resin (YP50, manufactured by Nippon Steel Chemical Co., Ltd.), 30% by mass of a liquid epoxy resin (EP828, manufactured by Mitsubishi Chemical Corporation), 10% by mass of a solid epoxy resin (YD-014, manufactured by Nippon Steel Chemical Co., Ltd.), 30% by mass of a latent epoxy curing agent (NOVACURE 3941HP, manufactured by Asahi Kasei E-materials Co., Ltd.), and 10% by mass of an imidazole compound (2-methylimidazole, manufactured by Shikoku Chemicals Co., Ltd.). The NCF layer-forming composition was then applied to a release sheet to a film thickness of 12 μm after drying and dried to form an NCF layer.

Furthermore, the ACF layer and the NCF layer were peeled off from the release sheet and then bonded together to prepare a multilayer adhesive film (total film thickness: 18 μm) according to Comparative Example 4.

(Comparative Example 5)

First, an ACF layer-forming composition was prepared by mixing 20% by mass of a phenoxy resin (YP50, manufactured by Nippon Steel Chemical), 30% by mass of a liquid epoxy resin (EP828, manufactured by Mitsubishi Chemical Corporation), 10% by mass of a solid epoxy resin (YD-014, manufactured by Nippon Steel Chemical), 30% by mass of a cationic polymerization-type epoxy curing agent (SI-60L, manufactured by Sanshin Chemical Co., Ltd.), and 10% by mass of conductive particles (AUL-704, manufactured by Sekisui Chemical Co., Ltd.). The ACF layer-forming composition was then applied to a release sheet to a film thickness of 6 μm after drying and dried to form the ACF layer.

Next, an NCF layer-forming composition was prepared by mixing 20% by mass of a phenoxy resin (YP50, manufactured by Nippon Steel Chemical Co., Ltd.), 40% by mass of a liquid epoxy resin (EP828, manufactured by Mitsubishi Chemical Co., Ltd.), 10% by mass of a solid epoxy resin (YD-014, manufactured by Nippon Steel Chemical Co., Ltd.), and 30% by mass of a cationic polymerization-type epoxy curing agent (SI-60L, manufactured by Sanshin Chemical Co., Ltd.). This NCF layer-forming composition was then applied to a release sheet to a film thickness of 12 μm after drying and dried to form an NCF layer.

Furthermore, the ACF layer and the NCF layer were peeled off from the release sheet and then bonded together to prepare a multilayer adhesive film (total film thickness: 18 μm) according to Comparative Example 5.

(Confirmation of interface layer)

First, in the multilayer adhesive films of Examples 2 to 5, interfacial layers were confirmed to form between the curing agent layer and the ACF and NCF layers. Specifically, in Examples 2 to 5, the curing rates of the ACF and NCF layers near the interface with the curing agent layer were calculated separately along the thickness direction, confirming the formation of interfacial layers containing a cured epoxy polymer compound.

It should be noted that the cure rate was calculated by calculating the ratio of epoxy groups using IR measurement. Specifically, the ratio of epoxy groups to methyl groups in the ACF layer and the ratio of epoxy groups to methyl groups in the measurement area were measured using IR measurement. The reduction ratio of the epoxy group ratio in the measurement area was used to calculate the cure rate.

The calculated curing rates are shown in Table 2. It should be noted that no significant difference was observed in the calculated changes in the curing rates in the thickness direction among Examples 2 to 5.

[Table 2]

(Table 2)

The results in Table 2 confirmed that an interface layer containing a cured epoxy polymer compound having a curing rate of 80% or more was formed within a range of 0 μm to 0.2 μm from the interface with the curing agent layer in both the ACF layer and the NCF layer.

Furthermore, when the distance from the interface with the curing agent layer is greater than 0.5 μm, the curing rate is less than 3%. This is believed to be because the interface layer functions as a barrier layer, inhibiting the diffusion of the non-latent epoxy curing agent into the ACF and NCF layers, thereby suppressing the curing of the ACF and NCF layers. Therefore, the thickness of the interface layer is believed to be approximately 0.4 μm in both the ACF and NCF layers.

(Evaluation method and evaluation results)

Using the anisotropic conductive films of Examples 2-4 and Comparative Examples 2-4, connection structures were fabricated. Specifically, a polyimide substrate with a Ti/Al coating and a thickness of 0.3 mm and an IC (Integrated Circuit) chip with a planar area of 1.8 mm × 20 mm and a thickness of 0.3 mm and gold-plated bumps with a height of 15 μm and a planar area of 30 μm × 85 μm were thermocompressed together using the anisotropic conductive films of Examples 2-4 and Comparative Examples 2-4. The thermocompression bonding conditions were set to 190°C, 60 MPa, and 5 seconds (high temperature conditions) or 150°C, 60 MPa, and 5 seconds (low temperature conditions).

In addition, the produced connection structures were evaluated according to the following evaluation methods.

The curing rate was evaluated as follows: using infrared spectroscopy (IR), the ratio of epoxy groups to methyl groups in the ACF layer before and after thermocompression bonding was measured, and the reduction ratio of the epoxy group ratio before and after thermocompression bonding was calculated as the curing rate.

The warpage amount was evaluated by measuring the surface roughness of the substrate side after thermocompression bonding using a surface roughness measuring instrument (manufactured by Kosaka Laboratory Co., Ltd.).

On-resistance was evaluated by measuring the resistance between the polyimide substrate and the IC chip using a digital multimeter (manufactured by Yokogawa Electric Co., Ltd.). To evaluate reliability, on-resistance was measured immediately after crimping and after 500 hours in an environment with a temperature of 85°C and a humidity of 85%.

Floating at the bonding interface was visually inspected, with those with floating rated as poor (B) and those without floating rated as good (A). Furthermore, to evaluate reliability, floating at the bonding interface was evaluated both immediately after pressure bonding and after 500 hours in an environment with a temperature of 85°C and a humidity of 85%.

Storage stability was evaluated by measuring the epoxy group to methyl group ratio of the ACF layer by the above method after a 12-hour accelerated curing test at 50°C and calculating the reduction ratio of the epoxy group to methyl group ratio of the ACF layer immediately after thermocompression bonding.

Table 3 shows the above evaluation results.

[Table 3]

In Table 3, "High Temperature" in the "Conditions" column indicates that thermocompression bonding was performed under high temperature conditions of 190°C, 60 MPa, and 5 seconds, and "Low Temperature" indicates that thermocompression bonding was performed under low temperature conditions of 150°C, 60 MPa, and 5 seconds.

The results in Table 3 show that Examples 2-5 exhibit high cure rates even when thermocompression bonding is performed under low-temperature conditions of 150°C, 60 MPa, and 5 seconds, with no floating at the bond interface. Furthermore, even after an accelerated curing test at 50°C for 12 hours, Examples 2-5 maintain a cure rate below 8%, demonstrating excellent storage stability.

Furthermore, it can be seen that Examples 2-4 also have low on-resistance values, indicating that a suitable anisotropic conductive connection is formed between the substrate and the IC. However, in Example 5, where the content of the non-latent epoxy curing agent, i.e., the imidazole compound, is 60% by mass, the curing of the curing agent layer, the ACF layer, and the NCF layer is rapid, and insufficient compression during thermocompression bonding occurs. This results in a high on-resistance value and an inability to form a suitable anisotropic conductive connection. Therefore, it can be seen that the content of the non-latent epoxy curing agent in the curing agent layer is preferably 10% to 50% by mass relative to the total mass of the curing agent layer.

On the other hand, since no curing agent layer was formed in Comparative Example 2, the curing rate decreased when thermocompression bonding was performed under low-temperature conditions of 150°C, 60 MPa, and 5 seconds, and floating was observed at the bonded interface. It should be noted that in Comparative Example 2, thermocompression bonding under high-temperature conditions of 190°C, 60 MPa, and 5 seconds showed a sufficient curing rate, but the amount of warpage increased, making it undesirable.

It is found that in Comparative Examples 3 and 4, since the ACF layer or NCF layer contains the non-latent epoxy curing agent, ie, the imidazole compound, the curing rate exceeds 30% in the accelerated curing test at 50° C. for 12 hours, and the storage stability is low.

In Comparative Example 5, since a cationic polymerization-type epoxy curing agent was used, polymerization was inhibited by the polyimide on the bonded surface, resulting in a reduced cure rate. Furthermore, floating was observed at the bonded interface after standing. Therefore, it can be seen that in Comparative Example 5, the adhesiveness was reduced depending on the material of the bonded surface.

As described above, in the multilayer adhesive film 100 according to this embodiment, during thermocompression bonding, the epoxy polymer compound can undergo a polymerization reaction not only with the latent epoxy curing agent but also with the more reactive non-latent epoxy curing agent. Therefore, the multilayer adhesive film 100 according to this embodiment can exhibit sufficient adhesion even during thermocompression bonding at low temperatures.

Furthermore, in the multilayer adhesive film 100 according to this embodiment, the curing agent layer 120 containing a highly reactive non-latent epoxy curing agent and the epoxy layers 111 and 112 containing uncured epoxy polymer compounds are formed separately. Therefore, the multilayer adhesive film 100 according to this embodiment can have high storage stability.

Furthermore, the multilayer adhesive film 100 according to the present embodiment can be suitably used as an anisotropic conductive film by including conductive particles in any of the layers.

While preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to the embodiments described above. A person having ordinary knowledge in the technical field to which the present invention pertains will readily conceive of various variations and modifications within the scope of the technical concepts set forth in the claims, and these variations and modifications are understood to fall within the technical scope of the present invention.

Explanation of symbols

100, 100A, 100B Multilayer adhesive film

111, 112 Epoxy layer

120　　　　 Curing agent layer

131, 132　　 Interface layer

140　　　　 Conductive particles

Claims (10)

1. A multilayer adhesive film, which has the following characteristics: Multiple epoxy layers are formed using uncured epoxy polymer compounds and latent epoxy curing agents; and A curing agent layer sandwiched between the plurality of epoxy layers, the curing agent layer being formed using an anionic polymeric non-latent epoxy curing agent. 2. The multilayer adhesive film according to claim 1, further comprising: An interface layer is formed between each of the epoxy layers and the curing agent layer, the interface layer comprising a cured epoxy polymer compound. 3. The multilayer adhesive film according to claim 1 or 2, wherein the non-latent epoxy curing agent is contained in an amount of 10% by mass or more and 50% by mass or less relative to the total mass of the curing agent layer. 4. The multilayer adhesive film according to claim 1 or 2, wherein the non-latent epoxy curing agent is an imidazole compound. 5. The multilayer adhesive film according to claim 1 or 2, wherein the latent epoxy curing agent is a curing agent that is endowed with latent properties by encapsulating the curing agent in microcapsules. 6. The multilayer adhesive film of claim 1 or 2, wherein at least any one of the plurality of epoxy layers and the curing agent layer comprises conductive particles. 7. The multilayer adhesive film of claim 6, wherein the conductive particles are contained in at least any one of the plurality of epoxy layers. 8. The multilayer adhesive film according to claim 1 or 2, wherein the total thickness of the multilayer adhesive film is 4 μm or more and 50 μm or less. 9. A connecting structure, wherein electronic components are bonded to other electronic components or a substrate by means of a multilayer adhesive film according to any one of claims 1 to 8. 10. The connection structure of claim 9, wherein at least a portion of the bonding surface of the electronic component is covered with a protective film comprising polyimide.