JP2680412B2 - Anisotropic conductive film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a fine circuit such as a connection between an LCD (liquid crystal display) and a flexible printed circuit board and a micro-joint between a semiconductor IC and a circuit board for mounting an IC. The present invention relates to an anisotropic conductive film that can be used for electrical connection of.

[Conventional technology]

With the recent miniaturization and thinning of electronic devices, the need for connecting minute circuits to minute circuits and connecting minute parts to minute circuit boards has increased dramatically. With the progress of joining technology, as a new material,
So-called "elastic connectors", which have striped conductive and insulating parts, and anisotropic conductive adhesives and sheets are beginning to be used. (For example, JP-A-59-120436, 60-
84718, 60-191228, 61-55809, 61-274394, 61-2879
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, the thermosetting resin system takes advantage of its high reliability based on its heat resistance, and the thermoplastic resin system has its workability because its adhesiveness and repeated press-bonding / peeling are possible. It is used for different purposes, and is mainly used for joining fine circuits centering on the joining of liquid crystal display and flexible printed circuit board, and joining of circuits that cannot adopt the soldering joining method due to insufficient heat resistance. . However, there is still no anisotropic conductive film that has all of the above characteristics.
The current situation is that it has become a stumbling block for higher reliability of electronic devices using this.

[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]

100 parts by weight of a solvent-soluble thermoplastic polymer having a melting point of 150 ° C. or less, such as an acrylonitrile / butadiene-based copolymer and a styrene / butadiene-based copolymer, and an epoxy resin and an imidazole-based compound which is solid at room temperature and used to cure the epoxy resin A resin solution in which a total of 25 to 400 parts by weight of a curing agent as a main component is uniformly dispersed and mixed, and an average particle size is 5
~ 15μm, maximum particle size is 25μm or less, minimum particle size is 1μm or more, 50% indium
Conductive particles composed of solder powder having a melting point of 110 ° C. or higher and containing 0.5 to 20% by volume with respect to the solid content of the resin solution are mixed and uniformly dispersed, on a release film. An anisotropic conductive film, which is obtained by casting and drying on a film to form a film having a thickness of 50 μm or less and forming it into a B stage, which can be peeled off again by heat or an organic solvent after thermocompression bonding once. Is.

The thermoplastic elastomer used in the present invention is
Acrylonitrile-butadiene copolymer, styrene-butadiene copolymer, etc., melting point 150
The so-called rubber-based polymer, which has a temperature below ℃ and is soluble in solvents,
A material having a good compatibility with the epoxy resin and the imidazole-based curing agent, which are used singly or in combination of two or more, and which are used at the same time, is appropriately selected.

The epoxy resin may be an bisphenol-based epoxy resin, an aliphatic-based epoxy resin, or a polyfunctional aromatic-based epoxy resin. As the curing agent, from the viewpoint of workability, storability, and reliability, an imidazole-based curing agent, such as 2-methylimidazole, 2-
Phenyl imidazole, 2-phenyl-4 methyl imidazole, 2-phenyl-4,5-dihydroxymethyl imidazole, 2-phenyl-4-methyl-5-hydroxymethyl imidazole, N, N- [2-methyl imidazolyl- (1) -Ethyl] -adiboyldiamide, 2,4-diamino-6- {2'-methylimidazolyl-1 '} ethyl-S-triazine / isocyanuric acid adduct, etc. In addition, 1 type or a mixture of 2 or more types is used, and it has good storage stability when mixed with epoxy resin (3 months or longer at room temperature, 6 months or longer at refrigerated).
And the rapid curing property by heating (120 ° C to 200 ° C for 5 seconds to 1
Compositions that give initial adhesion in minutes) are preferably used. In addition, in order to improve adhesion with conductive fillers such as accelerators, antioxidants, and coupling agents, or with transparent conductive glass circuit boards or flexible circuit boards,
Various additives can be appropriately used in combination.

Epoxy resin and curing agent require bonding conditions such as low-temperature short-time curing, workability such as repairability, compatibility with the thermoplastic elastomer, and further reliability such as heat resistance after pressure bonding / curing and wet heat resistance. It is appropriately selected based on the characteristics. The so-called repairability required for ordinary anisotropic conductive films,
That is, it is an important property that workability is indispensable that the film can be peeled off by heat or an organic solvent or the like after thermocompression bonding once and then realigned using a newly prepared film and bonded.

Various studies were conducted on the compounding amount of the epoxy resin and the curing agent with respect to 100 parts by weight of the thermoplastic elastomer, and when the compounding amount was 25 parts by weight or less, the resin matrix after pressure bonding was formed by the thermoplastic elastomer, and The epoxy resin distributed in a shape hardly contributes to the adhesion strength. For this reason, the adhesive strength with the adherend is centered on the tackiness of the thermoplastic elastomer, and the high adhesive strength with the adherend originally possessed by the epoxy resin and the high reliability cannot be obtained. In addition, when the amount is 400 parts by weight or more, the resin matrix after pressure bonding is formed with a mesh structure of epoxy resin, and high adhesion strength and high reliability backed by heat resistance are expected, but resin curing progresses during pressure bonding work. As a result, the adhesive strength was developed by one-time pressure bonding, and the pressure-bonded adherend could not be peeled off without damage and the repairability was lost. Therefore, the compounding amount of the epoxy resin and the curing agent mixture with respect to 100 parts by weight of the thermoplastic elastomer is 25 parts by weight or more and 400 parts by weight or less, and more preferably 4 parts by weight or less.
It is preferable that the range is from 0 parts by weight to 150 parts by weight.

Anisotropic conductive films are mainly used for joining liquid crystal panels and flexible printed circuit boards,
A transparent conductive glass substrate to be adhered, that is, indium-
Adhesion to a glass substrate on which a tin-based oxide film is formed is one of the essential characteristics. Therefore, as a result of various studies on the conductive particles, the content of indium is 50% or more,
Moreover, it has been found that a low melting point solder composed of two or more kinds of metals having a melting point of 110 ° C. or higher exhibits excellent connection stability.

As a method of obtaining a low melting point solder, in addition to indium, for example, a method of adding bismuth, cadmium, etc. to a tin / lead system is known, but bismuth system and cadmium system have low strength in a peeling test after pressure bonding, On the other hand, when the indium-based material was used, the solder powder was cohesively broken and remained on the surface of the glass plate after peeling, resulting in high strength. In addition,
The bismuth type also lacks the reliability of electrical connection after joining, and it is preferable to avoid using the cadmium type due to its toxicity.

When the content of indium is 50% or less, the effect of adding it is small in adhesion and reliability. Indium content is 50
% Or more, if the melting point is 110 ° C or less, the heat resistance after crimping will be insufficient, and the solder will melt during crimping, causing agglomeration of the solder particles and insulation reliability between adjacent circuits. Sex will be reduced. Although the melting point of the solder powder can be freely changed depending on its composition, it is preferably 110 ° C. or higher, more preferably 120 ° C. or higher and 160 ° C. or lower.

The size of the solder powder as conductive particles has a suitable range depending on the pattern accuracy of the circuit to be bonded and the conductive mechanism, but the current circuit width / circuit interval = 0.1 / 0.1mm used for bonding. To fit,
The maximum particle size is 25 μm or less and the minimum particle size is 1 μm or more, and the average particle size must be 5 to 15 μm. If the particle size is 25 μm or more, adjacent circuits may be short-circuited when particles are aggregated or crushed 2-3 times during pressure bonding. If it is less than 1 μm,
Aggregation of particles becomes remarkable, and the dielectric properties of the anisotropic conductive film as a whole are affected. 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.
The amount added to the resin solid content is 0.5% by volume.
Below, conductivity cannot be obtained, and above 20%, insulation reliability between adjacent circuits is poor.

 Hereinafter, the present invention will be described based on examples.

[Examples 1 to 5] Acrylonitrile / butadiene copolymer (NBR) 15 parts (parts by weight, the same applies hereinafter) (manufactured by Nippon Synthetic Rubber Co., Ltd.) was dissolved in 85 parts of methyl ethyl ketone to prepare a solution having a concentration of 15%. . Similarly, styrene-butadiene copolymer (SB
For R), a 15% strength toluene solution was prepared.

Next, 33 parts of a solid epoxy resin (EP-1001 manufactured by Yuka Shell Epoxy Co., Ltd.) and 2 parts of an imidazole-based curing agent (2-phenyl-4-methylimidazole) are dissolved in 65 parts of methyl ethyl ketone to prepare an epoxy resin. A resin solution was prepared. In addition, as a liquid epoxy resin at room temperature, a bisphenol epoxy resin (made by Yuka Shell Epoxy Co., Ltd.)
EP-828), 96 parts of dicyandiamide, 15 parts of methyl cellosolve solution dissolved in 1.5 parts, and 25 parts of methyl ethyl ketone solution dissolved in 2.5 parts of 2-phenyl-4-methylimidazole were added and mixed to prepare a uniform resin solution. .

The thermoplastic elastomer solution of and and the epoxy resin solution of and were mixed at the ratios shown in Table 1 while changing the ratio.

Next, in the resin mixture solution thus obtained, indium alloy particles (In65 wt%, Pb20 wt%, Sn15 wt%, average particle diameter 13 μm, maximum particle diameter 17 μm, minimum particle diameter 2 μ
m) was added and mixed at 5% by volume with respect to the resin solid content, and mixed by an agitating mixer for 10 minutes. This product was cast on a release film (polyethylene terephthalate film, thickness 25 μm) using an applicator so that the film thickness after drying would be 20 μm, and dried at 80 ° C. for 5 minutes to obtain an anisotropic conductive film. Got

Using the obtained anisotropic conductive film, indium-
After aligning the circuit terminals with the transparent conductive circuit formed with tin oxide circuit and the flexible printed circuit board (polyimide 25 μm, copper foil 18 μm, circuit width 0.1 mm, pitch 0.1 mm), thermocompression bonding at 150 ° C. for 30 seconds Connected by. For the test pieces connected in this way,
The characteristics were compared after the treatment at 1000 ° C. for 1000 hours. The results are as shown in Table 1.

[Comparative Examples 1 to 3] Resin solutions shown in Examples to and ordinary 6/4 solder as conductive particles (Sn60%, Pn40%, 500 mess pass)
Other than the above, a test piece was prepared in the same manner as in the other examples, and the reliability was evaluated. The resin composition and the evaluation results are shown in Table 1.

All of the examples showed excellent repairability. That is,
After pressure bonding at 150 ° C. for 30 seconds, microscopic observation revealed that the test piece having a gap between the terminals of the adherend was heated again and immediately peeled off, and the film could be peeled off without breakage. The flexible printed circuit board was peeled off from the test piece that had undergone the reliability test, and the surface of the transparent conductive glass was observed with a microscope.As a result, traces of cohesive failure of metal particles on the glass surface were observed, and excellent adhesion was observed. Was confirmed. From the results of the measurement of the adhesion strength, the strengths after the treatments were slightly increased, and the resistance values were also slightly increased.

On the other hand, in Comparative Example 1, excellent adhesion strength and resistance value stability were exhibited, but there was no repairability at all, and when pressure was applied once and peeling was attempted, the flexible printed circuit board broke. Further, as the blending ratio of the thermoplastic elastomer to the epoxy resin increased, the initial value and the adhesion strength after the treatment were both low, and resistance value stability could not be obtained.

〔The invention's effect〕

The anisotropic conductive film of the present invention has excellent reliability such that adhesiveness to a circuit board, connection resistance, and other properties are stable even after a long-time heat treatment, and can be easily peeled off by reheating. It has excellent repairability, workability, and high reliability and is useful as a connecting material for minute circuits.

Claims (1)

(57) [Claims] 1. A total of 25 parts by weight of 100 parts by weight of a thermoplastic elastomer which has a melting point of 150 ° C. or less and is soluble in a solvent, and an epoxy resin and a curing agent mainly composed of an imidazole compound which is solid at room temperature and used for curing the same. A resin solution in which 400 parts by weight are uniformly dispersed and mixed, and an average particle size is in the range of 5 to 15 μm, a maximum particle size is 25 μm or less, a minimum particle size is 1 μm or more, and indium is contained in 50% or more. Melting point
Conductive particles consisting of solder powder having a temperature of 110 ° C or higher, 0.5 to 20% by volume with respect to the solid content of the resin solution, mixed and uniformly dispersed, and cast on a release film.
An anisotropic conductive film obtained by being dried and formed into a film having a thickness of 50 μm or less, and being B-staged, which can be peeled by heat or an organic solvent after thermocompression bonding once.