JP2680430B2 - Anisotropic conductive film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to electrical connection between minute circuits, more specifically, connection between an LCD (liquid crystal display) and a flexible circuit board, a semiconductor IC and an IC mounting circuit. The present invention relates to an anisotropic conductive film that can be used for micro joining of substrates.

[Conventional technology]

With the recent miniaturization and thinning of electronic devices, the need for connecting minute circuits to minute circuits, connecting minute parts to minute circuit boards, etc. has increased dramatically. With the progress of joining technology, as a new material,
A so-called "elastic connector", which has a conductive portion and an insulating portion arranged in stripes, and an anisotropic conductive adhesive or sheet have begun to be used. (For example, JP-A-59-120436, 60
-84718, 60-191228, 61-55809, 61-274394, 61-28
However, most of them are basically classified into thermosetting resins or thermoplastic resins, and usage methods utilizing the respective characteristics have been proposed. That is, in the thermosetting resin system, high reliability based on its heat resistance is utilized, and in the thermoplastic resin system, its adhesiveness and peelability by heat or solvent after once pressure-bonding are good, It can be used properly by taking advantage of its excellent workability, mainly for the bonding of fine circuits centering on the bonding of the liquid crystal display and the flexible printed circuit board, and the circuit where the soldering bonding method cannot be adopted due to lack of heat resistance. Used for joining comrades. However, there is still no anisotropic conductive film having all of the above-mentioned characteristics, and it is the present condition that it is a shackle for improving the reliability of electronic devices using the anisotropic conductive film.

Further, with respect to the conductive particles, most of them have conventionally used solder particles, nickel particles, carbon black powder, and the like. When solder particles are used, it is difficult to control the temperature and pressure when connecting electronic circuits. That is, if the temperature is too high, the solder particles may melt and the insulation between adjacent circuits may not be maintained. Further, if the pressure is too high, the solder particles are crushed too much, resulting in poor reliability, and if the pressure is insufficient, sufficient conduction cannot be obtained. Further, the nickel particles and the carbon black powder are hard and do not deform, so that the contact area is small, which is disadvantageous in terms of conductivity. In some cases, examples using thermoplastic beads such as polystyrene (JP-A-61-77279, 61-780) are used.
69, 62-243668), but there is a problem in heat resistance. As a recent trend, heat resistance is especially required,
At present, not only the resin but also the conductive particles have to be considered for heat resistance.

[Problems to be solved by the invention]

The present invention aims to provide a novel anisotropic conductive film having both good workability and high reliability, which were not obtained by the above-mentioned conventional techniques.

[Means for solving the problem]

The present invention, 100 parts by weight of an epoxy resin, 1 to 20 parts by weight of a curing agent containing an imidazole-based compound as a main component for curing the epoxy resin, and good compatibility with an epoxy resin,
Moreover, a resin solution in which 20 to 200 parts by weight of a thermoplastic elastomer soluble in a common solvent with an epoxy resin is uniformly mixed, and an average particle size is in the range of 5 to 15 μm, and a maximum particle size is
0.1 μm to 0.3 μm in the thickness of 25 μm or less and a novolac-based phenolic resin particulate cured product with a minimum particle size of 1 μm or more
1 to 10% by volume of the conductive fine particles coated with nickel or aluminum with respect to the solid content of the resin solution, and mixed, and the mixed solution uniformly dispersed is cast on a release film and dried. The present invention relates to an anisotropic conductive film, which is obtained by forming a film having a thickness of 150 μm or less and forming it into a B stage, and which can be peeled by heat or an organic solvent after thermocompression bonding once.

The epoxy resin used in the present invention may be an bisphenol-based epoxy resin, or an aliphatic or polyfunctional aromatic resin. As a curing agent, from the viewpoint of workability, storability, and reliability, an imidazole-based curing agent 2-methylimidazole, 2-phenylimidazole, 2-phenyl-4
Methyl imidazole, 2-phenyl-4,5-dihydroxymethyl imidazole, 2-phenyl-4-methyl-5
-Hydroxymethylimidazole, N, N- [2-methylimidazolyl- (1) -ethyl] -adivoyldiamide, 2,4-diamino-6- {2'-methylimidazolyl-1 '} ethyl-S-triazine. Mixtures of one or more selected from imidazole compounds that are solid at room temperature, such as isocyanuric acid adducts, are used, and have good storage stability when mixed with an epoxy resin (3 months or more at room temperature, refrigerated at room temperature. 6 months or more) and heat-hardening (120 to 200)
A composition that gives initial adhesion at 5 ° C. for 5 seconds to 1 minute) is preferably used.

Epoxy resins and curing agents are based on bonding conditions such as low-temperature short-time curing, workability such as repairability, compatibility with thermoplastic elastomers, and required reliability characteristics such as heat resistance after bonding and curing, moisture resistance, etc. Is appropriately selected.

As the thermoplastic elastomer, polyamide resin, modified acrylic rubber, ethylene-vinyl acetate copolymer and the like are applied. In addition, an antioxidant, an antioxidant, an accelerator, a cross-linking agent, a coupling agent, a tackifier, etc. may be appropriately used in combination.

The so-called repairability required for ordinary anisotropic conductive films, that is, the important characteristic that when the material is misaligned after thermocompression bonding, it can be peeled off by heat or solvent without damaging the adherend, is essential. It cannot be done.

When various studies were conducted on the blending amount of the thermoplastic elastomer with respect to 100 parts by weight of the epoxy resin, when the blending amount of the thermoplastic elastomer was 20 parts by weight or less with respect to 100 parts by weight of the epoxy resin, the thermoplastic elastomer was contained in the matrix of the epoxy resin. It is formed in a fine mesh shape and gives impact resistance to the epoxy resin, and it is expected that the epoxy resin will have high adhesion and high reliability backed by heat resistance.
After pressure bonding, it was impossible to peel the adherend without damaging it. In addition, when the amount is 200 parts by weight or more, the resin matrix is formed of the thermoplastic elastomer, and the epoxy resin distributed in an island shape hardly participates in the adhesion strength. Therefore, the adhesiveness (tackiness) of the thermoplastic elastomer plays a central role. The original adhesion strength with the adherend and high reliability were not obtained. Therefore, it is preferable to use the thermoplastic elastomer in an amount of 20 parts by weight or more and 200 parts by weight or less based on 100 parts by weight of the epoxy resin.

When attempting to secure the connection between circuits through an anisotropic conductive film, it is of course necessary to secure the insulation between adjacent circuits between fine lines with fine pitch, but on the circuit, conductive particles The larger the contact area, the more stable conductivity can be obtained. The conductive particles used in the present invention can be deformed without being excessively crushed under a wide range of pressure bonding conditions, and can have a large contact area with a circuit. The conductive particles are obtained by emulsion-polymerizing a novolac-based phenol resin and further cured by heating.
μm, maximum particle size of 25 μm, minimum particle size of 1 μm or more, phenol beads are classified by metal such as nickel and aluminum that is stable against oxidation to 0.1-0.3 μm thickness by electroless plating or physical or chemical method. Is a spherical conductor coated with. Although it depends on the pattern accuracy of the circuit to be joined, the particle size is 1 in order to meet the current circuit width / circuit spacing = 0.1 / 0.1mm used for joining.
If it is less than μm, the cohesion of the particles becomes remarkable, and the dielectric properties of the film as a whole are affected.

Also, if the maximum particle size is 25 μm or more, a smooth adhesive surface that fits the adherend cannot be obtained due to the relationship with the thickness of the resin adhesive layer, and at the same time, conductive particles gather between adjacent circuits after pressure bonding. There is a risk of short circuit. This also relates to the blending amount and dispersity of the conductive particles with respect to the resin adhesive, and in the present invention, the blending amount is preferably 1 to 10% by volume, more preferably 3 to 7% by volume with respect to the resin solid content. If the content of the conductive particles is 1% by volume or less, stable conductivity reliability cannot be obtained, and if it is 20% by volume or more, the insulation reliability between adjacent circuits is poor.

Regarding the average particle size, it is desirable that the particles are electrically bonded by a single particle in the thickness direction from the conduction mechanism by cross-section observation, and the most stable bonding state is shown in the case of 5 to 15 μm.

[Examples 1 to 4] An epoxy resin (EP-1001 manufactured by Yuka Shell Co., Ltd.) was dissolved in methyl ethyl ketone to prepare a 20 wt% solution, and a carboxylic acid-modified acrylonitrile-butadiene copolymer (Nippon Synthetic Chemical Co., Ltd.) was prepared. Rubber (XNBR) manufactured by Rubber Co., Ltd. was also dissolved in methyl ethyl ketone to prepare a 15 wt% solution.

Epoxy resin solid content 10
A uniform mixture of 4 kinds of 20 parts by weight, 50 parts by weight, 100 parts by weight, and 200 parts by weight of elastomer solid content was prepared with respect to 0 part by weight. Further, the imidazole-based curing agent and the dicyandiamide were added to each of the four resin solutions so as to be 2% by weight with respect to the solid content of the epoxy resin, and mixed uniformly.

Next, nickel is added to the resin mixed solution thus obtained.
Electroless plated phenol beads with a thickness of 0.1 μm (average particle size 10 μm, maximum particle size 22 μm, minimum particle size 2
μm) was added to the resin solid content in an amount of 5% by volume, and mixed by an agitating mixer for 1 hour. Using an applicator, cast this on a release film (25 μm thick polyethylene terephthalate) so that the thickness after drying will be 20 μm, dry at 80 ° C for 5 minutes, then heat at 100 ° C for 5 minutes. An anisotropic conductive film was obtained. Using the obtained anisotropic conductive film, a transparent conductive circuit circuit formed of indium / tin oxide and a flexible printed circuit board (copper foil 18 μm,
After the circuit terminals were aligned, a circuit width of 0.1 mm and polyimide 25 μm) were connected, and then thermocompression bonding was performed for 20 seconds at 150 ° C.

For the test pieces connected in this way,
The characteristics were compared after treatment at 150 ° C for 1000 hours. The results are shown in Table 1.

[Comparative Examples 1 and 2] As a comparative example, a solution obtained by mixing 10 parts by weight (comparative example 1) and 250 parts by weight (comparative example 2) of the elastomer with respect to the epoxy resin solid content was prepared in the same manner as in the example. A sample was prepared and evaluated. The results are also shown in Table 1.

From the above results, it was confirmed that Examples 1 to 4 exhibited excellent heat resistance. Also, after crimping,
When heated at 180 ° C. and immediately peeled off, the adherend could be peeled off without damage.

[Comparative Examples 3 to 4] Next, a resin solution having the same compounding ratio as that of the example was mixed with 5% by volume of solder powder based on the resin solid content and styrene beads plated with 0.1 μm of nickel. A similar test piece was prepared and the change in connection resistance after heating at 150 ° C. for 1000 hours was measured. Table 2 shows the results. The solder powder and the styrene beads used were spherical, and those having a particle size distribution similar to those of the phenol beads used in Examples 1 to 4 were used.

[Example 5] [Comparative Examples 5 to 6] Using the anisotropic conductive films prepared in Example 2 and Comparative Examples 3 and 4, pressure under pressure bonding conditions was changed in the range of ²⁰ to 50 kg / cm ² , The connection resistance at the time of crimping at 150 ° C. for 20 seconds and the crimping state with a microscope were observed. The evaluation results are shown in Table 3 as Example 5 and Comparative Examples 5 and 6, respectively.

From the above results, it was confirmed that phenol beads can be a core material for conductive particles having both heat resistance and workability.

〔The invention's effect〕

The anisotropic conductive film of the present invention is obtained by uniformly mixing a thermoplastic elastomer having good compatibility with an epoxy resin in a wide range with the epoxy resin, thereby providing the epoxy resin with heat resistance and high adhesion and By combining the repairability with eliminating the brittleness of the epoxy resin and using phenol resin beads as the core material of the conductive particles, stable heat resistance and other reliability can be obtained, and the pressure bonding conditions A wide range of pressure, which is an important factor, can be selected, it has a wide contact area with a good crushing condition, and stable connection reliability can be obtained, which is useful as a material for connecting minute circuits and components. .

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Claims (1)

(57) [Claims] 1. An epoxy resin of 100 parts by weight, 1 to 20 parts by weight of a curing agent containing an imidazole compound as a main component for curing the epoxy resin, and good compatibility with the epoxy resin,
Also, a resin solution in which 20 to 200 parts by weight of a thermoplastic elastomer soluble in a common solvent with an epoxy resin is uniformly mixed, and an average particle diameter is in the range of 515 μm and a maximum particle diameter is 25
Conductive microparticles coated with nickel or aluminum having a thickness of 0.1 to 0.3 μm on a particle-like cured product of a novolac-based phenol resin having a particle diameter of 1 μm or less and a minimum particle diameter of 1 μm or more is 1 with respect to the solid content of the resin solution. ~ 10% by volume added and mixed, and the mixed solution uniformly dispersed is cast on a release film, dried to form a film having a thickness of 150 µm or less, which is obtained by B-stage, and thermocompression-bonded once. An anisotropic conductive film, which can be subsequently peeled off by heat or an organic solvent.