JPH0532799A - Anisotropic conductive film - Google Patents

Abstract

PURPOSE:To obtain an anisotropic conductive film having excellent storage stability at ordinary temperature, having high adhesion and high reliability in a wide range of temperature and small residual stress as well as moisture resistance and repair properties and suitable for connection between LCD and a flexible circuit board. CONSTITUTION:A mixture solution containing a reactive elastomer (e.g. carboxyl group-containing styrene-butadiene copolymer) in which a silane coupling agent is uniformly mixed, epoxy resin, solvent (e.g. acetone) for dissolving these compounds, encapsulated imidazole derivative and 3-10vol.% conductive particles (e.g. nickel) having 5-10mum particle diameter is cast onto a mold-releasable carrier film and dried and formed into film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrical connection between minute circuits, more specifically, a connection between an LCD (liquid crystal display) and a flexible circuit board, and a micro connection between a semiconductor IC and an IC mounting circuit board. The present invention relates to a directional conductive film.

[0002]

2. Description of the Related Art With the recent miniaturization and thinning of electronic devices, the necessity of connecting minute circuits to each other, connecting minute parts to minute circuits, etc. has been dramatically increasing. Anisotropic conductive adhesives and films are beginning to be used. (For example, JP-A-59-120436, 60-191228,
61-274394, 61-287974, 62-244142, 63-153534, 63
-305591, 64-47084, 64-81878, Flat 1-446549, 1
− 251787 Bulletins, etc.)

According to this method, an adhesive or film containing a predetermined amount of conductive particles is sandwiched between the circuits to be connected, and thermocompression bonding is performed at a predetermined temperature, pressure and time to establish electrical connection between the circuits. At the same time, the insulation is secured between adjacent circuits.

Conventionally, this anisotropic conductive adhesive or anisotropic conductive film is roughly classified into a thermoplastic type having a thermoplastic resin as an adhesive component and a thermosetting type having a thermosetting resin as an adhesive component. Panel driver IC and LC
Adoption is rapidly advancing in applications such as connecting D substrates, in which a large number of minute circuit terminals are connected together.

Recently, with the colorization and size increase of LCD panels, instead of the thermoplastic type, the adoption of a thermosetting type anisotropic conductive film centering on an epoxy resin, which is more reliable, is increasing. ..

For the thermoplastic type, styrene-butadiene-styrene, styrene-isoprene-styrene,
Styrene-based copolymers such as styrene-ethylene-butadiene-styrene have been mainly used, but the method of using these thermoplastic types is basically a heat fusion method, and the workability thereof is generally the If it is selected, it can be applied at a relatively low temperature for a short time, but it is no longer possible to meet the demands for high reliability such as heat resistance, thermal shock resistance, and adhesive strength required for the joint part in the future. ..

On the other hand, regarding the thermosetting type, there is an upper limit of the heating temperature based on the heat resistance of the adherend (LCD panel, substrate, etc.) in terms of workability, and the cycle time is shortened to improve work efficiency. Due to strong demand, usually 150-20
It should be cured at about 0 ° C. for about 30 seconds or less. At the same time, under normal use conditions, storage stability at room temperature for 3 months or more (up to 6 months) is required, and after connection, it must be excellent in reliability such as moisture resistance.

Further, in the connection work between the circuits using the anisotropic conductive film, it is possible to peel and re-press the connected members once they have been connected without damaging or damaging them (so-called "repair") due to misalignment or the like. The adherend is damaged (for example, the glass substrate used in LCDs) based on the requirement of being able to do so, the curing shrinkage during the thermosetting reaction of the anisotropic conductive film, and the strain stress of the resin itself in various atmospheres. Problems such as cracks in the substrate and warpage of the substrate) are occurring. That is, there is a strong demand for a highly reliable thermosetting anisotropic conductive film having fast curing, long life, repairability, moisture resistance, and low distortion.

[0009]

The anisotropic conductive film connecting portion is often bonded to an ultraviolet curable resin or a silicone rubber adhesive for the purpose of preventing a decrease in adhesive strength due to moisture absorption and for reinforcement to increase mechanical strength. It is used by applying the agent and the like so as to cover it from the FPC side. If the high adhesive strength is maintained in a wide temperature range and the adhesive strength is not lowered due to moisture absorption, such a process and equipment related thereto are not necessary.

As described above, the anisotropic conductive film is used for collectively connecting a large number of fine circuit terminals, but due to the increase in size of the adherend (liquid crystal display panel, etc.),
The number of joining terminals is also increasing, the connecting portion is also lengthening, and the shrinkage due to thermosetting of the anisotropic conductive film applied to the whole and the distortion under various environments are also proportionally increased.

For this reason, the substrate (for example, a glass substrate) may be warped even when bonded under a predetermined heating and pressurizing condition.
Small scratches on the edge of the substrate trigger cracks on the entire surface of the substrate (panel). As a method to prevent this, measures such as narrowing the joint width to reduce the total stress amount, eliminating the joining of continuous long parts, and joining the connected parts divided by short films individually are taken. However, although the strain due to the stress is reduced, the joint reliability is eventually lowered.

[0012] Therefore, as a result of various studies to reduce the original curing strain (stress) of the resin, the strain after bonding is extremely small and the moisture resistance of the film is extremely low without impairing various properties required for the film. We have found an anisotropic conductive film.

That is, the present invention has excellent storage stability at room temperature, which was not obtained by the conventional thermosetting type, and was excellent in a wide temperature range (-40 to 100 ° C.) after being cured by heating and pressing. Thermosetting anisotropic conductive film that has adhesive strength, has extremely small strain (stress) remaining at the joint, and can be peeled and re-bonded by heating the pressure-bonded product once above a specified temperature. Is provided.

[0014]

According to the present invention, a reactive elastomer and an epoxy resin in which a silane coupling agent is uniformly mixed, a solvent for dissolving them, a mixture solution containing a microencapsulated imidazole derivative and conductive particles are used as a carrier film. An anisotropic conductive film formed by casting and drying on top.

In the case of the thermosetting epoxy resin alone, the stress after curing due to curing shrinkage is large, and as a residual strain, for example, an LCD glass substrate and a flexible circuit substrate were bonded under a normal condition with a size of 3 mm × 50 mm. Case 294.
A stress of 1-1470.7 N / cm ² is applied to the bonded glass portion. As a method of reducing this, mixing of various plasticizers, additives, etc. can be considered, but curability, storability,
A part of properties such as tackiness is impaired, and as a result, a highly reliable film has not been obtained. Therefore, in order to reduce the stress due to curing shrinkage of the resin, various studies were conducted from the resin prescription side, and the residual stress was extremely small when the anisotropic conductive film was cured by the combination of the reactive elastomer, the epoxy resin, and the microencapsulated imidazole derivative. Found.

Further, they have found that when the reactive elastomer is uniformly mixed with a silane coupling agent in advance and then mixed with an epoxy resin, the moisture resistance is extremely improved, and the present invention has been completed.

In the present invention, the compounding ratio of the reactive elastomer determines the residual stress. The higher the amount, the lower the residual stress, but the thermosetting properties are impaired, and if too small, the residual stress-reducing hardening cannot be obtained. As a result of various studies, the compounding ratio of the reactive elastomer is 20 to 50% by weight, preferably 25 to 4% by weight based on the total amount of the resin.
Used in the range of 0% by weight.

The above-mentioned reaction elastomer is a carboxyl group-containing styrene-butadiene copolymer, a carboxyl group-containing styrene-isoprene copolymer, a carboxyl group-containing styrene-butadiene saturated copolymer, a carboxyl group-containing styrene-isoprene saturated copolymer. Carboxyl group-containing styrene-ethylene-butene-styrene copolymer, carboxyl group-containing styrene-ethylene-butene-
Styrene saturated copolymer, carboxylic acid-terminated acrylonitrile-butadiene copolymer, carboxylic acid-modified acrylonitrile-butadiene copolymer, hydrogenated carboxylic acid-modified acrylonitrile-butadiene copolymer, carboxylic acid-modified acrylic rubber, polyvinyl butyral resin, polyvinyl acetal Resin, urethane resin, cellulose derivative, amino group-modified polyol resin, amino group-modified phenoxy resin,
Examples include hydroxy-terminated saturated copolyester resin, carboxy-terminated copolyester resin, etc., and select a resin that is reactive with the epoxy groups of the epoxy resin and that has good compatibility and is uniformly soluble in a common solvent. Used. You may use these elastomers individually or in mixture of 2 or more types.

The silane coupling agent in the present invention may be a commercially available general one, but it is not a substance that dissolves the microcapsulated imidazole described below or elutes the reaction components in the microcapsules. I won't.

The mixing amount is preferably 0.2 to 5% with respect to the total amount of the reactive elastomer and the epoxy resin. 0.2%
If it is less than 5%, the effect cannot be obtained, and if it exceeds 5%, the tackiness, the hardness of the film and the adhesion to the carrier film are affected. Specific examples include γ-methacryloxypropyltrimethoxysilane, β- (3,4epoxycyclohexyl) ethyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropyltrimethoxysilane, N- β (aminoethyl) γ-
Aminopropyltrimethoxysilane, N-β (aminoethyl) γ-aminopropylmethyldimethoxysilane, γ
-Aminopropyltriethoxysilane, N-phenyl-
γ-aminopropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane, γ-ureidopropyltriethoxysilane and the like can be mentioned, and they can be used alone or in admixture of two or more.

The epoxy resin used in the present invention is an epoxy resin having at least two epoxy groups in one molecule. Specific examples include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin,
Dimer acid diglycidyl ester, phthalic acid diglycidyl ester, tetrabromobisphenol A diglycidyl ether, bisphenol hexafluoroacetone diglycidyl ether, triglycidyl isocyanurate,
Tetraglycidyl diaminodiphenylmethane and the like can be mentioned, and they can be used alone or in admixture of two or more.

As the solvent, any solvent can be used as long as it dissolves both the above-mentioned reactive elastomer and epoxy resin and does not dissolve or decompose the microcapsules of the microencapsulated imidazole derivative, or it takes a long time to dissolve or decompose. Is. Specifically, acetone,
Methyl ethyl ketone, methyl isobutyl ketone, benzene, toluene, xylene, methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butyl alcohol, methyl cellosolve, ethyl cellosolve, diacetone ether, methyl cellosolve acetate, ethyl cellosolve acetate, butyl carbitol acetate, etc. One of them may be used alone, or two or more thereof may be mixed in consideration of solubility and workability. Butyl carbitol acetate is preferred.

The imidazole derivative is an adduct of an imidazole compound and an epoxy compound, and examples of the imidazole compound include imidazole, 2-methylimidazole, 2-ethylimidazole, 2-ethyl-4-methylimidazole and 2-phenyl. Imidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-
Methyl imidazole, 1-benzyl-2-ethyl imidazole, 1-benzyl-2-ethyl-5-methyl imidazole, 2-phenyl-4-methyl-5-hydroxymethyl imidazole, 2-phenyl-4,5-dihydroxymethyl imidazole Etc.

Further, as the epoxy compound, for example,
Glycidyl ether type epoxy resins such as bisphenol A, phenol novolac, bisphenol F, brominated bisphenol A, dimer acid diglycidyl ester, phthalic acid diglycidyl ester, etc. can all be used, but they can be stored as a resin mixture or in a film state. In consideration of the properties, an adduct of an imidazole compound and a bisphenol A type epoxy resin is preferably used.

The reaction product of the imidazole derivative and the epoxy compound is commercially available as a fine powder and is applicable. However, it is further mixed with an isocyanate compound to improve the storage stability, or a microencapsulated product. Is also available and applicable. In order to achieve both fast curing and long-term storage stability, microcapsules of these types are preferable. However, it is necessary to appropriately select and use these compounds in combination with solvent stability and reactive elastomer and epoxy resin which are other resin main components.

The conductive particles include metals such as nickel, iron, copper, aluminum, tin, lead, chromium, cobalt, silver and gold, metal oxides, alloys including solder, carbon, and the like.
Examples of the conductive particles include graphite, or a core material such as glass, ceramic, or plastic coated with a metal by a method such as plating. In terms of reliability,
Gold, nickel, solder alloy, indium alloy and the like are preferable.

The diameter of the conductive particles used in the present invention is preferably 5 to 10 μm in order to secure insulation between adjacent circuits and to secure high reliability of connection. Further, the compounding amount of the conductive particles is preferably 3 to 10% by volume. If it is less than 3% by volume, stable conduction reliability cannot be obtained, and if it exceeds 10% by volume, the insulation reliability between adjacent circuits is deteriorated.

As described above, an anisotropic conductive film is produced using the resin material and the conductive particles that have been selected and prepared.
Further, various surfactants, antifoaming agents and stabilizers may be appropriately added in order to improve the stability / compatibility of the resin solution and the dispersibility of the conductive particles.

The anisotropic conductive film is produced by the following method. That is, an elastomer having a group reactive with an epoxy resin and a silane coupling agent are dissolved in a solvent to prepare an elastomer solution. Similarly, the epoxy resin is also dissolved to prepare a resin solution. These resin solutions are uniformly mixed at a predetermined mixing ratio, and the conductive particles which have been surface-treated in advance are weighed therein, and sufficiently stirred and mixed until uniformly dispersed in the resin solution. Next, the microencapsulated imidazole derivative is added and mixed, and if necessary, various additives are added and adjusted with a solvent to prepare a resin solution for an anisotropic conductive film having a solid content of 20 to 30%. Next, this resin solution is cast and dried on a polyester film or a Teflon film which has been subjected to a mold release treatment to obtain an anisotropic conductive film having a thickness after drying of 20 to 50 μm.

[0030]

The present invention will be described in detail below with reference to examples.

Example 1 50 parts by weight of a carboxylic acid-modified acrylonitrile-butadiene copolymer (all addition amounts below are parts by weight) was dissolved in 200 parts of butyl carbitol acetate, and 1 part of γ-mercaptopropyltrimethoxysilane was dissolved. The mixture was added and stirred. To 100 parts of this solution, 50 parts of bisphenol A type epoxy resin (epoxy equivalent: 900 g / eq) dissolved in 50 parts of toluene was mixed and stirred. 80 g of solder atomized powder having an average particle size of 10 μm, a maximum particle size of 20 μm, and a minimum particle size of 2 μm was uniformly dispersed therein.
Thereto, 30 parts of the microencapsulated imidazole derivative was mixed and uniformly dispersed. A coating film was formed on a polyethylene terephthalate film subjected to a mold release treatment with this resin solution so that the thickness after drying was 25 μm, and dried at 50 ° C. for 1 hour to obtain the anisotropic conductive film.

Example 2 Degree of acetylation of 3 mol% or less, Degree of acetalization of 75 mo
Bisphenol A was prepared by mixing 250 parts of a 20% solution obtained by dissolving 1% of polyvinyl acetal resin in toluene and 1 part of γ-aminopropyltriethoxysilane.
50 parts of a 50% toluene solution of epoxy resin of epoxy type (epoxy equivalent 900 g / eq), 80 parts of bisphenol A type epoxy resin (epoxy equivalent of 200 g / eq) and 30 parts of microencapsulated imidazole derivative are rapidly mixed with stirring, and To the same solder atomized powder as in Example 1
Add 0 g, disperse evenly, and then add toluene,
An anisotropic conductive film was obtained by casting and drying on an EP (tetrafluoroethylene-6 fluoropropylene copolymer) film so that the thickness after drying was 25 μm.

Comparative Example 1 15 parts of a carboxylic acid-modified acrylonitrile-butadiene copolymer was dissolved in 40 parts of butyl carbitol acetate, and other coupling agents and resins were mixed and stirred in the same manner as in Example 1 to prepare a solder atomized powder. Dispersed in 40 g, and similarly microencapsulated imidazole derivative 30
Parts were mixed and dispersed. This was cast and dried in the same manner as in Example 1 so that the thickness after drying was 25 μm to obtain an anisotropic conductive film.

Comparative Example 2 As in Example 2, 170 parts of polyvinyl acetal was made into a 20% solution of toluene, and other coupling agents, resins and microencapsulated imidazole derivative were stirred and mixed in the same manner as in Example 2. 105 g of the same solder atomized powder as in Example 1 was uniformly dispersed and cast and dried on FEP so that the thickness after drying was 25 μm to obtain an anisotropic conductive film.

Comparative Example 3 An anisotropic conductive film was obtained in the same manner as in Example 1 except that 1 part of the silane coupling agent γ-mercaptopropyltrimethoxysilane was not added.

The anisotropic conductive film of the test pieces used in the above Examples and Comparative Examples had a thickness of 25 μm, and the adherend was a flexible circuit in which 35 μm of copper foil was plated with 5 μm of nickel and 0.5 μm of gold. A substrate (pitch: 0.2 mm, number of terminals: 250) and a full-face electrode ITO glass having a surface resistance of 30 Ω were used.

Storage stability was evaluated at room temperature and 40
After being left at ℃ for 3 months, it was confirmed that it melted on a hot plate at 120 ℃, and after thermocompression bonding to the adherend under specified conditions, the connection resistance between adjacent terminals was measured. If all terminals had a resistance of 2Ω or less, it was rated as ◯.

As a reliability test, -30 ° C./30 minutes →
The connection resistance between adjacent terminals was measured after 300 cycles of the temperature cycle test with 25 ° C./5 minutes → 85 ° C./30 minutes → 25 ° C./5 minutes as one cycle.

The adhesive strength was measured by fixing the ITO glass of the adherend, which was thermocompression-bonded, horizontally, and pulling the flexible circuit board in the direction perpendicular to the ITO glass at a pulling speed of 50 mm.
A 90 ° peel test of peeling off at a speed of / min was performed. As a humidity resistance test, a high temperature and high humidity test of 85 ° C and 85% is 1000
After performing Hr, the adhesive strength was similarly measured.

For measuring the residual stress, a glass epoxy copper clad laminate (thickness 0.2 mm, copper foil 35 μm, pitch 0.
25mm, 350 terminals) thickness 1.1mm x 30mm x 1
A test piece was obtained by pressure-bonding to 50 mm ITO glass.
Light is incident on the vicinity of the center of the crimping portion from the end face of the glass, and the optical path difference is measured by an automatic ellipsometer DVA-36LS (Co., Ltd.).
(Mizojiri Optical Industry Co., Ltd.).

The above results are shown in Table 1.

[0042]

[Table 1]

[0043]

EFFECTS OF THE INVENTION According to the present invention, the thermosetting type film has the high adhesive strength and high reliability which are the features of the film, and further, the extremely small residual stress which cannot be obtained by the conventional thermosetting type film is realized. In addition, the anisotropic conductive film of the present invention, which also has moisture resistance, repairability, and good storage stability, connects large glass substrates such as liquid crystal display panels to drive circuit substrates (flexible circuit substrates, glass epoxy substrates, etc.). It provides excellent anisotropic conductive film that has good reliability and workability even if a large number of minute circuit terminals are connected at once, and also eliminates cracks and breaks in the glass substrate after connection and improves yield. is there.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁵ Identification number Internal reference number FI Technical indication C08L 63/00 NKU 8416-4J NLC 8416-4J H01B 5/16 7244-5G // B29K 63:00 105: 16 B29L 7:00 4F C08L 63:00

Claims (1)

Claim: What is claimed is: 1. A reactive elastomer in which a silane coupling agent is uniformly mixed, an epoxy resin, a solvent for dissolving the reactive elastomer, a mixture solution containing a microencapsulated imidazole derivative and conductive particles, on a carrier film. Casted on
An anisotropic conductive film characterized by being dried and formed into a film.