JPH0521094A - Anisotropic electric conductive adhesive agent - Google Patents

Abstract

PURPOSE:To provide an anisotropic electric conductive adhesive agent capable of connecting a circuit excellent in reliability of connection and whose circuit connection part can be easily repaired with a general purpose solvent in the case of occurrence of a failure. CONSTITUTION:An adhesive agent is composed mainly of acrylate resin having a carboxyl group, a reactive adhesive agent, a potential curing agent and electric conductive particles. This adhesive agent after curing can be removed from a bonding surface with a solvent of a SP value 8.0-12.0.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is, for example, formed between electrodes of two circuit boards in a liquid crystal panel or the like, heated and pressed to bond the two circuit boards, and electrically connect both electrodes. The present invention relates to an anisotropic conductive adhesive.

[0002]

2. Description of the Related Art While bonding two circuit boards together,
For the adhesive to provide electrical continuity between these electrodes, conductive particles are used in thermosetting substances such as styrene-based, urethane-based, polyester-based, acrylic-based thermoplastics, epoxy-based, silicone-based, etc. Various blended substances are known (JP-A-55-104007,
JP-A-55-59889).

In the connection with these adhesives, if the electrical connection is defective or the electronic parts or circuits become defective after the connection, the circuits are separated by peeling and the adhesive is removed with a solvent or the like. After that, a method of connecting non-defective products with the above adhesive again is used. In this case, it is as important as the reliability after connection that the adhesive on the fine circuit can be removed quickly and easily by using a general-purpose solvent (for example, toluene, acetone, alcohol, etc.).
Especially in the mass production process, this ease of repair is essential in terms of workability.

When used for an epoxy type thermosetting adhesive, the repairing method is generally a method of removing the adhesive with a so-called epoxy stripping agent using a solution in which a small amount of acid or the like is mixed with methylene chloride. Is.

[0005]

Considering the connection reliability of the circuit connecting portion, that is, heat resistance and moisture resistance, it is effective to use a thermosetting resin such as an epoxy resin as the reactive adhesive. However, as mentioned above, the repair method in this case is generally a method using methylene chloride mixed with an acid, and due to the occurrence of circuit corrosion or electrolytic corrosion due to the effect of acid or halide on the reconnection part, Connection reliability is insufficient. On the other hand, when a thermoplastic resin that can be easily repaired with a general-purpose solvent is used for the adhesive, the heat resistance is poor and a problem occurs in connection reliability. The present invention aims at satisfying both of these situations, and provides an anisotropic conductive adhesive having a highly reliable connection portion and easily repairable by a solvent.

[0006]

DISCLOSURE OF THE INVENTION The present invention is an anisotropic conductive material which retains the connection reliability of a circuit connecting portion, peels off between the circuits in the case of a poor connection, and can easily remove the remaining adhesive with a solvent. As a result of diligent examination of a water-soluble adhesive, it was found that the above objects can be achieved by using a special acrylic resin,
The present invention has been completed based on this finding.

That is, the present invention is an adhesive containing a carboxyl group-containing acrylic resin, a reactive adhesive, a latent curing agent and conductive particles as main components, and the cured adhesive has an SP value of 8. An anisotropic conductive adhesive characterized in that it can be removed from an adhesive surface with a solvent of 0 to 12.0.

The present invention will be described in detail below. The acrylic resin used in the present invention is not particularly limited as long as it has a carboxyl group in the resin, but acrylic acid ester, methacrylic acid ester or acrylonitrile is used as the main monomer component, and the main monomer component and the main monomer component are 100 parts by weight. On the other hand, it is a copolymer obtained by copolymerizing 0.5 parts by weight or more of acrylic acid and / or methacrylic acid. Among them, acrylic acid and / or methacrylic acid are preferably used. Having a carboxyl group is essential for repairing with the above-mentioned solvent,
The appropriate amount is 0.5 with respect to 100 parts by weight of the main monomer component.
Is preferably 5 to 5 parts by weight, more preferably 1.5 to 3 parts by weight. If the amount of acrylic acid and / or methacrylic acid is small, the removability by a general-purpose solvent after curing will be insufficient, and if it is too large, the storability of the adhesive will be reduced.

Further, coexistence of hydroxyethyl methacrylate as a monomer component used in the above-mentioned copolymer is more preferable because the adhesive force is improved.

Methyl acrylate, ethyl acrylate, butyl acrylate, octyl acrylate and the like can be applied as acrylic acid ester which is a monomer component of the above copolymer, and methyl methacrylate and the like can be applied as methacrylic acid ester. These may be used in combination.

The above-mentioned acrylic acid ester and methacrylic acid ester are soft components (glass transition point: Tg is 0 ° C. or lower) constituting an acrylic resin, and styrene or the like is used as a hard component (Tg is 20 ° C. or higher) in addition to acrylonitrile. Can also be used. That is, Tg of copolymerized acrylic resin
Is preferably 0 ° C. or lower, more preferably −10 ° C. or lower.

In consideration of heat resistance, the molecular weight of the acrylic resin used in the present invention is 200,000 to 100 in terms of the weight average molecular weight of the above copolymer (styrene conversion value by GPC method).
It is preferably about 10,000, more preferably about 500,000 to 800,000. When the molecular weight is low, the cohesive force of the adhesive system decreases and it becomes difficult to handle. When the molecular weight is too high, the fluidity decreases at the time of connection and the contact between the conductive particles and the circuit becomes insufficient. As the reactive adhesive used in the present invention, various substances having reactivity with the curing agent are used. Of these, epoxy resin is preferably used. The epoxy resin is a compound having two or more epoxy groups in one molecule, and all generally known epoxy resins can be applied. Typical examples are polyglycidyl ethers of polyhydric phenols such as bisphenol type epoxy resins derived from epichlorohydrin and bisphenol A or bisphenol F, and epoxy novolac resins derived from epichlorohydrin and phenol novolac or cresol novolac. In addition, there are polyglycidyl esters of polycarboxylic acids, alicyclic epoxy resins, polyglycidyl ethers of polyhydric alcohols, polyglycidyl compounds of polyhydric amines, etc. These can be used alone or in combination of two or more. .

The latent curing agent used in the present invention includes imidazole type, organic acid hydrazide type, boron trifluoride type
Amine complex, diaminomaleonitrile, amine imide,
There are polyamine salts, dicyandiamide and the like and modified products thereof, and these can be applied alone or as a mixture of two or more kinds. As a preferred embodiment of the present invention in which the contradictory properties of long-term storability and fast curing property are required to be satisfied, these curing agents are used as cores, and polymer materials such as polyurethane and polystyrene, and metal thin films such as Ni and Cu are used. It is preferable to use a microcapsule-type curing agent coated with a shell as the shell, or to use a molecular sieve method to reduce the chance of contact between the curing agent and the reactive component such as epoxy.

A point to be noted when using a microcapsule type curing agent applicable as a more preferable form of the present invention is that a particle size smaller than the thickness of the connecting member prevents capsule destruction during storage. It is preferable to use a solvent in which the shell material is not easily corroded in the production by the solvent system.

The compounding ratio of the reactive adhesive and the latent curing agent is not particularly specified because it can be set arbitrarily. When the epoxy resin is used as the reactive adhesive, the compounding ratio (weight ratio) of the curing component (epoxy resin and latent curing agent) and the acrylic resin is preferably 90/10 to 20/80, 70
/ 30 to 35/65 is more preferable. If the ratio of the curing components is large, the removability with respect to a general-purpose solvent is lowered, and if the ratio of the acrylic resin is large, the heat resistance is lowered. For the curing reaction, a usual method using heat or light can be applied.

The conductive particles used in the present invention are metal particles such as Ni, Cr, Co, Al, Sb, Mo and P.
Examples thereof include b, Cu, Ag, Pt, Au, Sn, Ta, and the like, and glass, ceramics, plastics, and the like that do not exhibit conductivity may be coated with these metals. These can be used as simple substances, alloys, composites and mixtures. Among the above, those having a thin metal layer formed on the surface of the plastic particles or solder particles are preferably used because the connection reliability is improved because the contact area to the circuit that exhibits deformability at the time of connection and increases, Among them, particles in which a thin metal layer is formed on the surface of plastic particles do not exhibit a specific melting point like solder particles, and therefore, the range of conditions (particularly temperature) at the time of connection can be set broadly, and thus are more preferable. The content of these conductive particles in the adhesive is 0.1 to 20% by volume,
A preferable anisotropic conductivity is obtained by preferably adjusting the content to 0.5 to 15% by volume.

In the adhesive composition, for example, tackifiers, plasticizers and other tackiness regulators, interface strengtheners, film formers, silica and other fillers, isocyanates and melamines and other crosslinking agents, solvents and polymerizations. Inhibitors, coupling agents and the like can be contained as necessary.

The adhesive of the present invention must be removable from the adhesive surface by a solvent having a solubility parameter after curing (hereinafter referred to as SP value) in the range of 8.0 to 12.0. . The SP value here is Adhesion Handbook No. 2 published by Nikkan Kogyo Shimbun.
Edition, pages 107-109. Examples of typical solvents together with SP values shown in () include cyclohexane (8.2), toluene (8.9), ethyl acetate (9.1), methyl ethyl ketone (9.3), acetone (10.0). ), Propyl alcohol (11.5-1)
1.9) and the like, and may be a mixture of ligroin and the like. If the SP value is less than 8.0, the solubility or swellability of the cured adhesive will be insufficient, and if it exceeds 12.0, the peripheral materials of the circuit will be adversely affected and the reliability will be reduced.

As a method of removing the adhesive after curing using these solvents, for example, after removing the connected circuit, the unnecessary adhesive portion may be rubbed with a cloth impregnated with the solvent and washed. Peeling is easy when heating is also used, and the connecting portion may be immersed in the solvent without peeling.

[0020]

The anisotropic conductive adhesive obtained by mixing the acrylic resin having a carboxyl group of the present invention with the reactive adhesive, the latent curing agent, and the conductive particles has a connection reliability superior to that of the conventional one. Given that it dissolves and / or swells with a general-purpose solvent having an SP value of 8.0 to 12.0, repairs with these solvents became possible. As described above, the above function is exhibited because the carboxyl group in the acrylic resin has an affinity for the metal (for example, copper or tin) or metal oxide (usually indium oxide) used on the electrode surface as described above. It is considered that this is because the adhesive strength at the time of connection is improved because it is high, and since the acrylic resin is soluble in the solvent (toluene, acetone, etc.) after the connection, the swelling property of the adhesive with the solvent is improved. .

[0021]

EXAMPLES The present invention will now be described in detail based on examples, but the present invention is not limited thereto. Examples 1 to 11 and Comparative Examples 1 to 2 (1) Acrylic resin: butyl acrylate, ethyl acrylate, and acrylonitrile as main monomer components, and acrylic acid, methacrylic acid, and hydroxyethyl methacrylate as other monomer components are shown in Table 1. An acrylic copolymer obtained by polymerizing monomers in a weight ratio by a pearl polymerization method was dissolved in toluene to obtain a solution having a solid content of 15% by weight.

【table 1】

(2) Reactive adhesive Epicoat 1001 (bisphenol type solid epoxy resin, trade name of Yuka Shell Epoxy Co., Ltd.) was prepared in a toluene solvent to a solid concentration of 50% by weight.

(3) Conductive Particles The surface of the particles having polystyrene as the core is coated with nickel in a thickness of 0.2 μm, and the outside of the nickel layer is further covered with a thickness of 0.
Treated with 02 μm gold, average particle size 10 μm, specific gravity 2.0
Particles were used.

(4) Latent curing agent Novacure HX-3741 (trade name, manufactured by Asahi Chemical Industry Co., Ltd., microcapsule type latent curing agent, particle size of about 5 μm) was used.

(5) Preparation of Anisotropic Conductive Adhesive The above (1) to (4) were blended in a weight ratio as shown in Table 2, and this solution was coated on a Teflon film of 80 μm,
Blast drying was performed at 80 ° C. to obtain an anisotropic conductive adhesive having a thickness of 25 μm.

[Table 2]

(6) Evaluation Using this anisotropically conductive adhesive, a line width of 100 μm,
A flexible circuit board (FPC) having 250 copper circuits with a pitch of 200 μm and a thickness of 35 μm, and a thin layer of indium oxide (ITO) on the entire surface (surface resistance 30 Ω /
□) Connection condition with a glass plate having a thickness of 1.1 mm 170 ° C-
20 kg / m ² -20 seconds heating / pressurizing connection width 3 mm
I was connected with. At this time, after attaching the adhesive surface of the anisotropic conductive adhesive on the FPC in advance, 80 ° C.-5 kg / cm ² −
Temporary connection was performed for 5 seconds, and then the separator (Teflon film) was peeled off to connect with ITO. Table 3 shows the evaluation results of the circuit-connected products obtained as described above.

[0027]

[Table 3]

In Table 3, the connection resistance is FP including the connection portion.
The resistance value of the adjacent circuit of C was measured with a multimeter and displayed as the maximum value (Max) with the average value (x). In addition, the reliability test after connection considers changes in temperature and humidity at the same time.
It was carried out under an environmental cycle of 30 ° C / 2h ← → 70 ° C-90% RH / 2h. Further, in Table 3, if repair with a solvent is impossible, remove the FPC of the above connection from the ITO and
Apply a certain area (20 × 3mm ² ) of adhesive remaining on the top
The average time required for wiping off with a cotton swab dipped in a solvent having a P value of 8.0 to 12.0 (toluene, acetone) was evaluated.

In each of Examples 1 to 11, the reliability test and the solvent repair test were good. On the other hand, Comparative Examples 1 and 2 are difficult to repair with a solvent.
Almost no residue of the adhesive could be removed even after a second. In each of Examples 1, 3 to 8 and 11, the content of the carboxyl group in the acrylic resin and the weight average molecular weight of the acrylic resin are both in the optimum range, and reliability and repairability by a solvent are all present. Was well balanced.

Further, as a comparison, the same evaluation was performed using polyester and polyurethane instead of the acrylic resin, but none having good reliability was obtained.

The elastic modulus and dielectric loss tangent of the cured anisotropic conductive adhesives shown in Examples 1 to 11 and Comparative Examples 1 and 2 were measured (using Rheospectra DVE-4 manufactured by Rheology Co., Ltd.,
The temperature was raised in the tension mode at a frequency of 10 Hz and 5 ° C./min).

As a result, each of the examples has a higher elastic modulus near room temperature than the comparative example, the two maximum values of tan δ on the low temperature side and the high temperature side are small, and the peak positions are close to each other. The examples suggest that the epoxy resin and the acrylic resin have good compatibility.

As typical examples of these, the graphs shown in FIGS. 1 and 2 were measured for Example 7 and Comparative Example 2.

[0034]

As described above in detail, according to the present invention, it is possible to connect a circuit having excellent connection reliability and to easily repair a general-purpose solvent when a defect occurs in the circuit connecting portion. It was possible to obtain a very useful anisotropic conductive adhesive.

[Brief description of drawings]

FIG. 1 is a graph showing the temperature dependence of elastic modulus and tan δ of a cured adhesive of Example 7 of the present invention.

FIG. 2 shows the elastic modulus and tan δ of the cured adhesive of Comparative Example 2.
It is a graph which shows the temperature dependence of.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Kyohisa Ota, inventor             Hitachi Chemical, 1500 Ogawa, Shimodate City, Ibaraki Prefecture             Shimodate Research Institute, Industry Co., Ltd. (72) Inventor Yutaka Yamaguchi             Hitachi Chemical, 1500 Ogawa, Shimodate City, Ibaraki Prefecture             Shimodate Research Institute, Industry Co., Ltd.

Claims (3)

[Claims] 1. An acrylic resin having a carboxyl group,
An adhesive containing a reactive adhesive, a latent curing agent, and conductive particles as main components, the cured adhesive having an SP value of 8.
An anisotropic conductive adhesive characterized by being removable from an adhesive surface with a solvent of 0 to 12.0. 2. The acrylic resin contains acrylic acid ester, methacrylic acid ester or acrylonitrile as a main monomer component, and 0.5 to 5 parts by weight of acrylic acid and / or meta is used with respect to 100 parts by weight of the main monomer component. The anisotropic conductive adhesive according to claim 1, which is a copolymer obtained by copolymerizing acrylic acid. 3. The anisotropic conductive adhesive according to claim 1, wherein the acrylic resin has a weight average molecular weight of 200,000 or more.