JP3046081B2 - Anisotropic conductive film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for electrical connection between fine circuits, more specifically, for connection between an LCD (Liquid Crystal Display) and a flexible circuit board, and micro-joining 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.

[0002]

2. Description of the Related Art With the recent miniaturization and thinning of electronic devices, the necessity of connection between minute circuits, connection between minute components and minute circuits, etc. has been dramatically increased. Anisotropic conductive adhesives and films have begun to be used. (For example, see JP-A-59-120436, 6
0-191228, 61-274394, 61-287
974, 62-244142, 63-153534, 6
3-3055591, 64-47084, 64-8187
8, JP-A-1-46549, 1-251787, each gazette)

[0003] In this method, between circuits to be connected,
By sandwiching an adhesive or film containing a predetermined amount of conductive particles and thermocompression bonding at a predetermined temperature, pressure, and time, an electrical connection between the circuits is made and at the same time insulation between adjacent circuits is ensured. Things.

Conventionally, this anisotropic conductive adhesive or anisotropic conductive film is roughly classified into a thermoplastic type using a thermoplastic resin as an adhesive component and a thermosetting type using a thermosetting resin as an adhesive component. For example, the connection between a driver IC of an LCD panel and an LCD substrate, and the use of connecting a large number of fine circuit terminals at once are rapidly increasing.

In recent years, with the increase in color and size of LCD panels, the use of thermosetting anisotropic conductive films centered on epoxy resins, which provide higher reliability, has been increasing in place of thermoplastic types. is there.

For the thermoplastic type, SBS (styrene-butadiene-styrene), SIS (styrene-isoprene-styrene), SEBS (styrene-ethylene-styrene) are used.
Styrene-based copolymers such as (butadiene-styrene) have been mainly used. However, these thermoplastic types are basically used in a melt-fusion type, and the workability is generally selected by selecting conditions. It can be applied at a relatively low temperature and in a short time compared with the thermosetting type, and it is considered to be good. It is no longer meeting demands.

On the other hand, in the case of the thermosetting type as well, the workability has an upper limit of the heating temperature based on the heat resistance of the adherend (LCD panel, substrate, etc.). Due to strong demands, curing must usually be performed at a temperature of 200 ° C. or less for about 30 seconds or less. At the same time, under normal use conditions
Requires storage stability for more than a month.

Although anisotropic conductive films satisfying these required characteristics are already on the market, as an adherend such as an LCD panel or a printed circuit board increases in size, curing of the anisotropic conductive film during a thermosetting reaction. A new problem has arisen in that the adherend is damaged (eg, cracks or warp of the substrate) based on shrinkage and strain stress of the resin itself in various atmospheres.

That is, in addition to rapid curing and long life, a thermosetting anisotropic conductive film which has a small distortion remaining at a joint portion and therefore has high reliability for a long time has not yet been obtained. .

[0010]

The anisotropic conductive film is mainly used for connecting a large number of fine circuit terminals at once, but the number of bonding terminals is increased due to an increase in the size of an adherend (such as a liquid crystal display panel). Therefore, the connection portion becomes longer and larger, and the distortion remaining at the connection portion becomes proportionally larger.

Therefore, even when bonding is performed under predetermined heating and pressing conditions, the substrate (for example, a glass substrate) warps,
Cracks occur on the entire surface of the substrate (panel), including small defects on the end surface of the substrate. As a method to prevent this, measures such as reducing the total stress amount by reducing the joint width have been taken.However, although the distortion due to the stress concentration is reduced, the joint reliability is eventually reduced. I have.

The properties required for the anisotropic conductive film include, in addition to long-term reliability, film forming properties (film forming properties), appropriate fluidity at the time of heating and pressing, moderate adhesiveness to an adherend, Characteristics such as adhesion to the carrier film and releasability from the carrier film must be satisfied.

The present invention is to provide a highly reliable anisotropic conductive film having extremely small distortion (stress), which cannot be obtained by the conventional thermosetting type, in addition to these basic characteristics. .

[0014]

Means for Solving the Problems A conventional thermosetting type anisotropic conductive film contains an epoxy resin as a main component, a latent curing agent, a solvent, and conductive particles, and is mixed with a film having good releasability. It is manufactured by casting and drying on a fluororesin-based film or a silicon-treated polyester film.

However, in these systems, stresses due to curing shrinkage and thermal expansion coefficient after curing are large, and as residual strain, for example, an LCD substrate and a glass epoxy resin circuit board on which a driver IC is mounted are 3 mm.times. 0.5 to 2.0 kg / mm ² when joining with a size of 50 mm
Is applied to the bonded glass portion, and this stress reduces reliability. As a method of reducing this, mixing of various plasticizers, additives and the like can be considered, but curability, preservability, adhesive strength, a part of properties such as adhesiveness are impaired, and as a result, good reliability is obtained. No film is obtained.

According to the present invention, various studies are made from the viewpoint of resin formulation in order to reduce the stress caused by the curing shrinkage of the resin and the difference in the coefficient of thermal expansion between the resin and the adherend. It has been found that an anisotropic conductive film prepared by blending a solvent and conductive particles with the resin component as a resin component has a lower elastic modulus after curing of the resin and an extremely lower residual stress than conventional films.

Further, the proportion of the silicon-modified epoxy resin determines the amount of the residual stress. As the proportion of the silicon-modified epoxy resin increases, the residual stress decreases, but the adhesion and other thermosetting properties are reduced. If some of the properties are impaired and too little, the effect of reducing the residual stress is small. It has been found that when the blending amount of the silicon-modified epoxy resin is 20 to 50% by weight, more preferably 25 to 40% by weight, the residual stress is greatly reduced while maintaining various properties, and the present invention has been reached.

As the silicon-modified epoxy resin in the present invention, an epoxy resin having at least two or more epoxy groups and a siloxane structure in one molecule is used. As a specific example, a bisphenol A type epoxy resin in which polysilanol and a methoxysilane derivative of a crosslinking agent are heated and stirred to disperse a bridged silicone phase in the epoxy resin, or a bisphenol A type epoxy resin Silanol polydimethylsiloxane at both ends, a silane coupling agent as a cross-linking agent, and a catalyst with heating and stirring, or an RTV silicone rubber dispersed in an epoxy resin using polyether-modified silicone oil as a compatibilizer And the like, alone or as a mixture of two or more. The silicon modification rate can be used up to about 50% (% by weight, the same applies hereinafter). However, in order to obtain a film having a good balance with respect to all properties such as resin solubility, compatibility and stress, 5 to 20% is required. A range of% modification is preferably used.

As the latent curing agent, any of those widely used as a latent curing agent for epoxy resins, such as dicyandiamide and its derivatives, boron trifluoride amine complex, imidazole and its derivatives, can be used. Imidazole and its derivative compounds are preferably used in view of workability such as properties and storage stability.

The imidazole compound includes imidazole, 2-methylimidazole, 2-ethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2 -Methylimidazole, 1-benzyl-2-ethylimidazole, 1-benzyl-2-
Ethyl-5-methylimidazole, 2-phenyl-4-
Methyl-5-hydroxymethylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 2-
Methylimidazole azine, 2-heptadecylimidazole, 2-undecylimidazole, 2,4-diamino-6 {2'-methylimidazole- (1) '} ethyl-
S-triazine / isocyanuric acid adduct, N, N'-
{2-methylimidazolyl- (1) -ethyl} dodecandioyldiazide, N, N '-{2-methylimidazolyl- (1) -ethyl} -aconsandioildiazide and the like can be used, and these imidazoles can be used. The reaction product of epoxy resin and epoxy resin can also be used as a latent curing agent for epoxy resin.

The reaction product of the imidazole and the epoxy compound is commercially available as a fine powder. In addition, some are mixed with isocyanate compounds or microencapsulated to increase storage stability and are used as latent curing agents.However, storage stability of compounds with epoxy resins and rapid curing in a short time Since microcapsulation is possible, microencapsulated products are preferably used.

As the solvent, any solvent can be used as long as it dissolves the silicon-modified epoxy resin and the epoxy resin and becomes a uniform solution when mixed with the latent curing agent.

Specifically, acetone, methyl ethyl ketone, methyl isobutyl ketone, benzene, toluene, xylene, methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butyl alcohol, ethyl acetate, tetrahydrofuran, methyl cellosolve, ethyl cellosolve, diacetone ether And methyl cellosolve acetate, ethyl cellosolve acetate, dimethylformamide, dimethylacetamide, etc., and these are used alone or in combination of two or more in consideration of solubility and workability.

The conductive particles include metals such as nickel, iron, copper, aluminum, tin, lead, chromium, cobalt, silver, and gold, metal oxides, alloys such as solder, carbon, graphite, glass, and the like. ceramic,
Conductive particles obtained by coating a core material such as plastic with a metal by plating or the like can be used. From the viewpoints of weather resistance and reliability, those coated with a metal such as gold, nickel, or a solder alloy are preferable.

Although the diameter of the conductive particles used in the present invention must be changed depending on the precision of the circuit to be joined, in order to ensure insulation between adjacent circuits and to ensure reliability of connection. It is necessary that the particle size is in the range of 1 to 10 μm, and more preferably, the one having a sharp particle size distribution in the range of 3 to 8 μm shows better reliability.

The compounding amount of the conductive particles is preferably 3 to 10% by volume, more preferably 4 to 6%. If the amount is less than 3% by volume, stable conduction reliability after bonding cannot be obtained, and if it is more than 10% by volume, insulation reliability between adjacent circuits may be inferior.

As described above, an anisotropic conductive film is produced by using the resin material and the conductive particles selected and prepared.
Further, various surfactants, defoaming agents, and stabilizers may be appropriately added for improving the stability and compatibility of the resin solution and the dispersibility of the conductive particles.

The anisotropic conductive film is produced by the following method. First, a silicon-modified epoxy resin and an epoxy resin are dissolved in a solvent to prepare a uniform resin solution. Next, a latent curing agent is added and mixed, and the conductive particles are weighed and sufficiently stirred and mixed until uniformly dispersed in the resin solution. Further, 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-based film or a fluororesin-based film subjected to a release treatment, and the thickness after drying is 20 to 50.
A μm anisotropic conductive film is obtained.

[0029]

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

Example 1 A bisphenol A-type epoxy resin having an epoxy equivalent of 340, a silanol polydimethylsiloxane having an average molecular weight of 2,500 at both ends, and a silane coupling agent and a catalyst as a crosslinking agent were added. Heat and stir 1
A 60% solution of 5% silicon-modified epoxy resin was prepared. 100 parts by weight of this resin solution (hereinafter, all added amounts represent parts by weight), 40 parts of a bisphenol A type epoxy resin having an epoxy equivalent of 340, and 12 parts of 2-undecylimidazole as a latent curing agent were mixed.

Next, as the conductive particles, solder atomized powder 6 having an average diameter of 10 μm, a maximum diameter of 20 μm, and a minimum diameter of 2 μm.
5 g, and the total solid content was 2 by MEK.
It was diluted to 2% to obtain a resin solution. A coating film is formed on a polyethylene terephthalate film which has been subjected to a release treatment with a silicone resin so that the thickness after drying becomes 25 μm, and dried at 50 ° C. for 1 hour (with a carrier film) to form an anisotropic conductive film. Obtained.

Example 2 In the same manner as in Example 1, a bisphenol A type epoxy resin having an epoxy equivalent of 195, a terminal silanol polydimethylsiloxane having an average molecular weight of 3,200, a silane coupling agent and a catalyst were added, and toluene was added. Heat reaction was performed at 100 ° C. for 3 hours to obtain a silicon-modified epoxy resin having a modification rate of 7%, and toluene was further added to prepare a 65% resin solution. An epoxy equivalent of 195 was added to 100 parts of the resin solution.
35 parts of a bisphenol A type epoxy resin, and a bisphenol A type epoxy resin having an epoxy equivalent of 195 and N,
N '-{2-methylimidazolyl- (1) -ethyl}-
55 parts of the reaction product with eicosandioildiazide are mixed and uniformly dispersed.

Here, 80 parts of the same solder atomized powder as in Example 1 was added, uniformly dispersed, and toluene was further added to obtain a 22% solution. This resin solution was cast and dried on a 50 μm-thick FEP (tetrafluoroethylene-6-fluoropropylene copolymer) film to obtain a 25 μm-thick anisotropic conductive film.

Comparative Example 1 Instead of the silicon-modified epoxy resin of Example 1, a bisphenol A type epoxy resin 60 having an epoxy equivalent of 340 was used.
An anisotropic conductive film was produced in exactly the same manner except that parts were used.

Comparative Example 2 Anisotropically conducting in exactly the same manner as in Example 2 except that 65 g of bisphenol A type epoxy resin having an epoxy equivalent of 195 was used instead of the silicon-modified epoxy resin used in Example 2. A film was prepared.

The four types of anisotropic conductive films obtained as described above were tested with a test pattern (substrate thickness 0.5 mm, copper foil thickness 18 μm, circuit width 0.1 mm, circuit interval 0.1 m).
m, the pattern surface is temporarily fixed on Ni / Au [5 / 1μ] plating to a size of 3 mm × 50 mm, and after the carrier film is peeled off, the thickness of the ITO film (indium / tin oxide film) formed on the entire surface 1.1 mm on a glass plate surface
Crimping was performed at 50 ° C. for 1 minute. Next, these test pieces were measured for the optical path difference with a compensator by applying light from the glass end face to the crimped portion of the circuit board using a photoelasticity tester, and the stress applied to the crimped face was measured. Table 1 shows the results.
Shown in

Table 2 shows workability and reliability evaluation results, which are basic characteristics required for an anisotropic conductive film.

[0038]

[Table 1]

[0039]

[Table 2]

As shown in Table 1, in the anisotropic conductive film according to the present invention, after curing, the stress value remaining at the bonding interface can be determined by using a silicon-modified epoxy resin in combination with the conventional epoxy resin alone. However, the size was reduced to about 1/3 to 1/4 of that of the conventional product.

In Table 2, regarding the storage stability, the film was stored in an atmosphere of 20 to 25 ° C. and 50 to 55%, and after 3 months, the same bonding characteristics as the initial performance (conductive resistance, adhesive strength, etc.) Was evaluated, and showed good storage stability.

Regarding the curability, all of them were 1 at 150 ° C.
Good properties are obtained when cured within minutes.

Regarding the adhesive strength, when the peel strength at 90 ° C. when the FPC and the glass substrate are bonded to a size of 3 × 30 mm is 500 g / cm or more, it is regarded as Δ, and when it is 300 g / cm or less, And

Regarding the reliability test, in the TC (temperature cycle test, −30 ° C.⇔RT⇔80 ° C.), according to the present invention, a defect (conduction defect) occurred in less than 100 cycles of the conventional film. Case 5 with film
It was stable up to 00 cycles or more.

Further, a temperature cycle test was performed under the condition of -65 ° C.⇔RT⇔150 ° C.
While the connection resistance value increases by 50% or more in 10 cycles to 10 cycles, the initial resistance value of the film according to the present invention changes by 10% or less even when the cycle exceeds 30 cycles,
Good results were obtained.

[0046]

As described above, the anisotropic conductive film according to the present invention has a small residual stress (strain) after curing,
Not only has high bonding strength and excellent reliability, but also excellent work characteristics such as storage stability and curability, and is suitable for connection applications of fine circuit terminals etc. that require increasingly higher reliability. It is a thing.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01B 5/16 H01R 11/01 H05K 3/32 H05K 3/36

Claims (1)

(57) [Claims] 1. A mixture comprising 20 to 50% by weight of a silicon-modified epoxy resin , an epoxy resin, a latent curing agent, a solvent for dissolving them, and conductive particles having a particle size in the range of 1 to 10 μm. An anisotropic conductive film, comprising: