JPH02288019A - Anisotropic conductive film - Google Patents

Abstract

PURPOSE:To make a connecting material for a microcircuit have high workability and reliability by pouring a solution containing a specific elastomer, an epoxy resin, and a conductive powder upon a separation-type film to give a film and making the film become in B-stage so as to peel the film by heat or an organic solvent. CONSTITUTION:A solvent-soluble and thermally elastic polymer with <=150 deg.C of melting point, an epoxy resin, and their hardening agent are mixed with acrylonitrile-butadiene-based copolymer. A conductive powder of a solder powder having average grain size of 5-15mum, the largest grain size of <=25mum, the smallest grain size >=1mum, and 110 deg.C of melting point, and containing >=50% of indium in a specified amount is added to the mixed solution. The resulting mixed solution is poured upon a separation-type film and dried to give a film with <=50mum thickness which is then made to become in B-stage. By this way, a connecting material having high workability and durability and able to be peeled off by heat or an organic solvent is obtained.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is applicable to fine circuits such as connection between an LCD (liquid crystal display) and a flexible printed circuit board, and micro-bonding 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 between devices.

[Conventional technology]

With the recent miniaturization and thinning of electronic equipment, the need to connect microcircuits to microcircuits and to connect microcomponents to microcircuit boards has increased dramatically. With the advancement of solder bonding technology, new materials such as so-called "elastic connectors" in which conductive and insulating parts are arranged in a striped pattern, and anisotropic conductive adhesives and sheets are beginning to be used. 59-120436.
60-84718.60-191228.61-558
09.61-274394.61-287974, etc.) However, most of them are basically classified as thermosetting resins or thermoplastic resins, and methods of use that take advantage of the characteristics of each have been proposed. In other words, thermosetting resins take advantage of their high reliability based on their heat resistance, while thermoplastic resins have good workability due to their adhesiveness and the ability to be repeatedly bonded and peeled. You can use it to your advantage.

It is mainly used for joining microcircuits, such as joining liquid crystal displays and flexible printed circuit boards, and for joining circuits where soldering cannot be used due to lack of heat resistance. However, there is still no anisotropic conductive film that has all of the above characteristics, and this is currently hindering efforts to improve the reliability of electronic devices using this film.

[Problem to be solved by the invention]

The present invention aims to provide a novel anisotropic conductive film that has both good workability and high reliability that could not be obtained with the prior art.

[Means to solve the problem]

Acrylonitrile/butadiene copolymer styrene/
100 ffi parts of a thermoplastic polymer having a melting point below 150'C and soluble in a solvent, such as a butadiene copolymer;
and a hardening agent whose main components are an epoxy resin and an imidazole compound that is solid at room temperature and used to harden it.
A resin solution in which 5 to 400 parts by weight are uniformly dispersed and mixed, the average particle size is in the range of 5 to 15 μm, the maximum particle size is 25 μm or less, and the minimum particle size is lIJm or more,
A mixed solution in which conductive particles made of solder powder containing 50% or more of indium and having a melting point of 110°C or more are added and mixed in an amount of 0.5 to 20% by volume based on the solid content of the resin solution and uniformly dispersed. is casted and dried on a release film to form a film with a thickness of 50 μm or less and B-staged, and is characterized in that it can be peeled off again by heat or an organic solvent after being bonded by heat once. The present invention relates to a conductive film.

The thermoplastic elastomer used in the present invention is selected from acrylonitrile-butadiene copolymers, styrene-butadiene copolymers, etc., and has a melting point of 150°C.
A so-called rubber-based polymer which is soluble in a solvent is used alone or in combination, and a material having good compatibility with the epoxy resin and imidazole curing agent used at the same time is appropriately selected.

As the epoxy resin, in addition to the usual bisphenol type, an aliphatic type or a polyfunctional aromatic type may be used.

As the curing agent, from the viewpoint of workability, storage stability, and reliability, imidazole-based curing agents, such as 2-methylimidazole, 2-phenylimidazole, 2-phenyl-4methylimidazole, 2-phenyl-45-dihydroxy Methylimidazole, 2-phenyl-4methyl-5-hydroxymethylimidazole, N,N[2-methylimidazolyl-(1)-ethyl]-adipoyldiamide, 2.
4-diamino-6-(2'-methylimidazolyl-1"
) Ethyl-3-) selected from imidazole compounds that are solid at room temperature, such as riazine/isocyanuric acid adducts,
One type or a mixture of two or more types is used, and when mixed with epoxy resin, it has good storage stability (3 months or more at room temperature, 6 months or more when refrigerated), and has fast curing property (120°C ~2
A composition that provides initial adhesion in 5 seconds to 1 minute at 00°C is preferably used. In addition, various additives are used in combination as appropriate to improve adhesion with conductive fillers such as accelerators, antioxidants, and coupling agents, or to improve adhesion with Tongmei conductive glass circuit boards and flexible circuit boards. I can do things.

The epoxy resin and curing agent are determined by bonding conditions such as low-temperature and short-time curing, workability such as repairability, compatibility with the thermoplastic elastomer, and reliability such as heat resistance and moist heat resistance after crimping and curing. The so-called repairability required for normal anisotropic conductive films, that is, the film is peeled off with heat or an organic solvent after being bonded under heat once, and a new one is prepared. The ability to reposition and bond using the film that has been prepared is an important characteristic that is essential for workability.

We conducted various studies on the blending amount of the mixture of epoxy resin and curing agent with respect to 100 parts by weight of the thermoplastic elastomer, and found that if the blending amount is 25 parts by weight or less, the resin matrix after pressure bonding will be formed by the thermoplastic elastomer, resulting in islands. The epoxy resin distributed in a shape has almost no effect on adhesion strength.

For this reason, the adhesion strength with the adherend is mainly due to the tackiness of the thermoplastic elastomer, and the high adhesive strength with the adherend and high convertibility that epoxy resins inherently have 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 network structure of epoxy resin,
High adhesion strength and high reliability backed by heat resistance are expected, but the resin hardens too much during the crimping process, resulting in the adhesive strength being developed with just one crimping process and damaging the crimped adherend. It was impossible to remove the film without causing damage, and the repairability was lost. Therefore, the amount of the epoxy resin and curing agent mixture based on 100 parts by weight of the thermoplastic elastomer is 25 parts by weight or more and 400 parts by weight or less, more preferably 4 parts by weight.
It is preferably in the range of 0 parts by weight or more and 150 parts by weight or less.

Anisotropic conductive films are mainly used for bonding liquid crystal panels and flexible printed circuit boards, and are applied to transparent conductive glass substrates as adherends, that is, glass substrates on which indium-tin oxide films are formed. Adhesion with the material is one of the essential characteristics. For this reason, as a result of various studies on conductive particles, we found that they contain more than 50% indium,
Furthermore, it has been found that a low melting point solder made of two or more metals having a melting point of 110° C. or higher exhibits excellent connection stability.

A known method for obtaining low melting point solder is to add indium, for example, bismuth, cadmium, etc. to tin/lead based solders, but bismuth and cadmium based solders have low strength in peel tests after crimping. On the other hand, when indium was used, solder powder remained on the surface of the glass plate after peeling due to cohesive failure, and the strength was also high. Furthermore, the bismuth type is insufficient in electrical connection reliability after bonding,
It is preferable to avoid using cadmium based materials due to their toxicity.

If the indium content is less than 50%, the effect of adding it on adhesion and reliability is small.
Even if the melting point is 0% or more, if the melting point is 110°C or less, not only will the heat resistance after crimping be insufficient, but the solder will melt during crimping, causing agglomeration of solder particles, and causing damage between adjacent circuits. This will lower the insulation chain properties. The melting point of the solder powder can be freely changed depending on its composition, but it is preferably in the range of 110°C or higher, more preferably 120°C or higher and 160''C or lower.

The size of solder powder as a conductive particle depends on the pattern accuracy of the circuit to be joined and the conductive mechanism.
Each has a suitable range, but in order to comply with the circuit width/circuit spacing = 0.110°1 used for current bonding, the maximum particle diameter should be in the range of 25 μm or less and the minimum particle diameter of 1 μm or more. It is necessary that the average particle diameter is 5 to 15 μm.

If the particle size is 25 μm or more, there is a risk that adjacent circuits may be short-circuited when the particles aggregate or are crushed 2 to 3 times in size during crimping. Furthermore, if the particle size is 1 μm or less, agglomeration of particles becomes significant, and the dielectric properties of the anisotropic conductive film as a whole are affected. Regarding the average particle diameter, it is desirable that the particles be electrically bonded as a single particle in the thickness direction, based on the conductive mechanism observed in the cross section.
The most stable bonding state is obtained when the thickness is 5 to 15 μm.

Regarding the amount added to the resin solid content, if it is less than 0.5% by volume, conductivity cannot be obtained, and if it is more than 20%, the insulation conductivity between adjacent circuits is poor.

The present invention will be explained below based on Examples.

[Examples 1 to 5] Acrylonitrile-butadiene copolymer (NBR) 15
(parts by weight, the same applies hereinafter) (manufactured by Nippon Synthetic Rubber (■)) was dissolved in 85 parts of methyl ethyl ketone to prepare a solution (2) with a concentration of 15 parts. Similarly, a 15 parts toluene solution (2) of styrene-butadiene copolymer (SBR) was prepared.

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

The thermoplastic elastomer solutions (1) and (2) and the epoxy resin solutions (2) and (2) were mixed at different ratios as shown in Table 1.

Next, indium alloy particles (In65 wt%, Pb2O wt%, 5n15
(wt%, average particle size 13 μm, maximum particle size 17 μm, minimum particle size 2 μm) was added in an amount of 5% by volume based on the resin solid content, and mixed for 10 minutes using an agitating mixer. This material was cast onto a release film (polyethylene terephthalate film, thickness 25 μm) using an applicator so that the film thickness after drying was 20//m.
Dry at 0°C for 5 minutes to obtain an anisotropic conductive film.Using the obtained anisotropic conductive film, a transparent conductive circuit formed of indium-tin oxide and a flexible printed circuit board (polyimide 25 μm, copper foil 1Bμm, 0.
After aligning the circuit terminal portions (1 mm, pitch 0.1 mrs), they were connected by thermocompression bonding at 150° C. for 30 seconds. For the test pieces connected in this way, the initial characteristics and the characteristics after being treated at 150° C. for 1000 hours were compared. The results were as shown in Table 1.

[Comparative Examples 1 to 3] Resin solutions 1 to 3 shown in Examples and ordinary 68 solder (60% Sn, 40% Pn, 500% Pn) as conductive particles
Mess Pass) was used to prepare a test piece in exactly the same manner as in the Example except for the test piece, and reliability evaluation was performed. The resin formulation and evaluation results are shown in Table 1.

All of the examples showed excellent pairability.

That is, after 30 seconds of pressure bonding at 150°C, as a result of microscopic observation,
When a test piece in which misalignment occurred between the terminals of the adherend was heated again and immediately peeled off, the film was able to be peeled off without any breakage. In addition, after the reliability test was completed, the flexible printed circuit board was peeled off from the test piece, and the surface of the transparent conductive glass was observed under a microscope. As a result, traces of cohesive failure of metal particles on the glass surface were observed, indicating excellent adhesion. I was able to confirm the gender. The results of adhesion strength measurement also showed that the strength after treatment increased slightly, and the increase in resistance value was also slight.

On the other hand, Comparative Example 1 showed excellent adhesion strength and resistance value stability, but had no repairability at all, and when attempting to peel it off after being crimped once, the flexible printed circuit board broke. Furthermore, as the blending ratio of the thermoplastic elastomer to the epoxy resin increases, the adhesion strength both at the initial value and after treatment decreases, and resistance value stability cannot be obtained.

〔Effect of the invention〕

The anisotropic conductive film of the present invention has stable characteristics such as adhesive strength and connection resistance to a circuit board even after long-term heat treatment, and has excellent reliability, and can be easily peeled off by reheating. It has excellent repairability and is useful as a connection material for microcircuits with excellent workability and high reliability.

Claims (1)

[Claims] (1) 100 parts by weight of a thermoplastic elastomer with a melting point of 150°C or lower and soluble in a solvent, and a curing agent whose main components are an epoxy resin and an imidazole compound that is solid at room temperature and is used to cure this, totaling 25 to 400 parts by weight. and a resin solution in which the average particle size is in the range of 5 to 15 μm, the maximum particle size is 25 μm or less, the minimum particle size is 1 μm or more, contains 50% or more of indium, and has a melting point. Conductive particles made of solder powder having a temperature of 110°C or higher are added in an amount of 0.5 to 20% by volume based on the solid content of the resin solution.
A mixed solution that has been added and mixed and uniformly dispersed is cast on a release film and dried to form a film with a thickness of 50 μm or less and B-staged. After once thermocompression bonding,
An anisotropic conductive film characterized in that it can be peeled off again using heat or an organic solvent.