JPH04215209A - Anisotropic conductive film - Google Patents

Abstract

PURPOSE:To obtain the anisotropic conductive film having a small residual stress (distortion) after hardening of the resin, a large adhesive strength, the excellent reliability and the excellent workability such as storage stability and hardenability or the like by compounding the solvent and conductive particles to the resin component which consists of epoxy resin, silicone modified epoxy resin and potential hardening agent. CONSTITUTION:Epoxy resin and potential hardening agent are dissolved in the solvent of silicone modified epoxy resin, and conductive particles are dispersed therein evenly to obtain the mixture. This mixture is flowed over the film, to which mold releasing processing is performed, and is dried to obtain the anisotropic conductive film.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is applicable to electrical connection between minute circuits, more specifically, for connection between an LCD (liquid crystal display) and a flexible 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 various purposes.

0002

[Background Art] With the recent miniaturization and thinning of electronic devices, the need for connections between minute circuits, connections between minute components and minute circuits, etc. has increased dramatically. Anisotropic conductive adhesives and films are beginning to be used. (For example, JP-A-59-120436, 6
0-191228, 61-274394, 61-287
974, 62-244142, 63-153534, 6
3-305591, 64-47084, 64-8187
8, Japanese Unexamined Patent Publication No. 1-46549, 1-251787, various publications)

[0003] In this method, between the 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, electrical connections are made between circuits while at the same time ensuring insulation between adjacent circuits. It is something.

Conventionally, this anisotropically conductive adhesive or anisotropically conductive film can be roughly divided into a thermoplastic type that uses a thermoplastic resin as an adhesive component, and a thermosetting type that uses a thermosetting resin as an adhesive component. It is rapidly being adopted for applications that connect a large number of minute circuit terminals at once, including the connection between an LCD panel driver IC and an LCD board.

[0005] Recently, as LCD panels have become more colored and larger, thermosetting type anisotropic conductive films, mainly made of epoxy resins, which offer higher reliability, are increasingly being used instead of thermoplastic types. be.

Thermoplastic types include SBS (styrene-butadiene-styrene), SIS (styrene-isoprene-styrene), and SEBS (styrene-ethylene-styrene).
Styrenic copolymers such as (butadiene-styrene) have been mainly used, but the method of using these thermoplastic types is basically a melt-fusion method, and the workability generally depends on the selection of conditions. Compared to thermosetting types, it can be applied at relatively low temperatures and in a short time, and is considered to be good. It is becoming impossible to meet the demands.

On the other hand, regarding the workability of thermosetting type products, there is an upper limit to the heating temperature based on the heat resistance of the adherend (LCD panel, substrate, etc.), and there are also improvements in work efficiency such as shortening cycle time. Due to strong requirements, it must be cured in about 30 seconds or less at a temperature of 200° C. or less. At the same time, under normal usage conditions, it is required to have storage stability of 3 months or more at room temperature.

[0008] Anisotropic conductive films that meet these required characteristics are already on the market, but as adherends such as LCD panels and printed circuit boards become larger, the hardening during the thermosetting reaction of anisotropic conductive films becomes more difficult. A new problem has arisen in which adherends are damaged (for example, cracks and warpage of substrates) due to shrinkage and distortion stress of the resin itself in various atmospheres.

[0009] In other words, the current situation is that a thermosetting type anisotropic conductive film that has fast curing, long life, and small residual strain in the bonded portion, and therefore has high reliability over a long period of time, has not yet been obtained. .

0010

[Problems to be Solved by the Invention] Anisotropic conductive films are mainly used to connect a large number of fine circuit terminals all at once, but as the size of the adherend (liquid crystal display panel, etc.) increases, As a result, the connecting portion also becomes longer and larger, and the strain remaining in the joint portion also increases in proportion to this.

Therefore, even when bonding is performed under predetermined heating and pressurizing conditions, the substrate (for example, a glass substrate) may warp or
Cracks occur all over the board (panel), including small defects on the edge of the board. To prevent this, measures have been taken to reduce the total amount of stress by narrowing the joint width, but although this reduces distortion due to stress concentration, it ends up reducing joint reliability. There is.

[0012] In addition to long-term reliability, the properties required for an anisotropic conductive film include film-forming properties, appropriate fluidity when heated and pressurized, appropriate adhesion to adherends, Properties such as adhesion to the carrier film and releasability from the carrier film must be satisfied.

[0013] In addition to these basic properties, the present invention aims to provide a highly reliable anisotropic conductive film with extremely low strain (stress), which has not been available with conventional thermosetting types. .

[0014]

[Means for solving the problem] Conventional thermosetting type anisotropic conductive films contain epoxy resin as a main component, mixed with a latent curing agent, a solvent, and conductive particles, and are used to create films with good mold releasability, such as It is produced by casting and drying onto a fluororesin film or a silicone-treated polyester film.

However, in these systems, the stress caused by curing shrinkage and the coefficient of thermal expansion after curing is large, and residual strain occurs, for example, when the LCD board and the glass epoxy resin circuit board mounted with the driver IC are 3mm x 3mm under normal conditions. 0.5 to 2.0 kg/mm2 when joining with a size of 50 mm
stress is applied to the bonded glass portion, and this stress reduces reliability. One possible way to reduce this is to mix various plasticizers, additives, etc., but some of the properties such as curing, preservability, adhesive strength, and tackiness are lost, resulting in poor reliability. No film available.

[0016] In order to reduce the stress caused by curing shrinkage of the resin and the difference in coefficient of thermal expansion with the adherend, the present invention conducted various studies from the viewpoint of resin formulation, and developed a combination of an epoxy resin, a silicone-modified epoxy resin, and a latent curing agent. It has been found that an anisotropically conductive film prepared by blending the resin component with a solvent and conductive particles has a lower elastic modulus and extremely small residual stress after the resin is cured than conventional films.

[0017] The blending ratio of the silicone-modified epoxy resin determines the amount of residual stress. As the blending ratio of the silicone-modified epoxy resin increases, the residual stress decreases, but the adhesion and other thermosetting properties Some of the properties will be lost, and if it is too small, the effect of reducing residual stress will be small. The present invention has been achieved by discovering that residual stress can be significantly reduced while maintaining various properties when the amount of silicone-modified epoxy resin is 20 to 50% by weight, more preferably 25 to 40% by weight.

The silicon-modified epoxy resin used in the present invention is an epoxy resin having at least two epoxy groups and a siloxane structure in one molecule. Specific examples include those in which polysilanol and a methoxysilane derivative as a crosslinking agent are heated and stirred in a bisphenol A epoxy resin, and the crosslinked silicone phase is dispersed in the epoxy resin; Both terminal silanol polydimethylsiloxane, a silane coupling agent as a crosslinking agent, and a catalyst are added and heated and stirred, or RTV silicone rubber is dispersed in an epoxy resin using polyether-modified silicone oil as a compatibilizer. etc., and may be used alone or in combination of two or more. It is possible to use a silicone modification rate up to about 50% (weight%, the same applies hereinafter), but in order to obtain a film with a good balance in all properties such as resin solubility, compatibility, and stress, it is necessary to use a silicone modification rate of 5 to 20%. A range of percent modification is preferably used.

The latent curing agent can be 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, but mainly for curing. Imidazole and its derivative compounds are preferably used from the viewpoint of workability such as stability and storage stability.

The imidazole compounds include 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-
Methylimidazoleazine, 2-heptadecylimidazole, 2-undecylimidazole, 2,4-diamino-6{2'-methylimidazole-(1)'}ethyl-
S-triazine/isocyanuric acid adduct, N,N'-
{2-methylimidazolyl-(1)-ethyl}dodecanedioyldiazide, N,N'-{2-methylimidazolyl-(1)-ethyl}-eikonsandioyldiazide, etc. can be used, and these imidazoles The reaction products of epoxy resins and epoxy resins can also be used as latent hardeners for epoxy resins.

The reaction product of imidazole and epoxy compound is commercially available as a fine powder. Furthermore, some are mixed with isocyanate compounds or microencapsulated to increase storage stability and are used as latent curing agents, but formulations with epoxy resins have excellent storage stability and rapid curing in a short time. Microcapsules are preferably used because they are possible.

Any solvent can be used as long as it dissolves the silicone-modified epoxy resin and the epoxy resin and forms 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 , methyl cellosolve acetate, ethyl cellosolve acetate, dimethyl formamide, dimethyl acetamide, etc.
They are used alone or in combination of two or more in consideration of workability.

[0024] As the conductive particles, metals such as nickel, iron, copper, aluminum, tin, lead, chromium, cobalt, silver, and gold, metal oxides, alloys including solder, carbon, graphite, glass, etc. ceramic,
Examples include conductive particles in which a core material such as plastic is coated with metal by a method such as plating. From the viewpoint of weather resistance and reliability, it is preferable to use a metal coating such as gold, nickel, or solder alloy.

The diameter of the conductive particles used in the present invention needs to be changed depending on the precision of the circuits to be joined, but in order to ensure insulation between adjacent circuits and reliability of connection, , is required to be in the range of 1 to 10 μm, and more preferably in the range of 3 to 8 μm, with a sharp particle size distribution showing better reliability.

The content of the conductive particles is preferably 3 to 10% by volume, 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 deteriorated, which is not preferable.

[0027] As described above, an anisotropic conductive film is produced using the selected and prepared resin material and conductive particles.
Furthermore, various surfactants, antifoaming agents, and stabilizers may be added as appropriate to improve 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 conductive particles are weighed into the mixture and sufficiently stirred and mixed until they are uniformly dispersed in the resin solution. Furthermore, various additives are added as necessary 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 onto a polyester film or a fluororesin film that has been subjected to a mold release treatment, and is dried to a thickness of 20 to 50 mm after drying.
A μm-sized anisotropic conductive film is obtained.

[0029]

EXAMPLES The present invention will be explained in detail below using examples.

[Example 1] A bisphenol A epoxy resin with an epoxy equivalent of 340 and a double-terminated silanol polydimethylsiloxane with an average molecular weight of 2,500 were added with a silane coupling agent and a catalyst as a crosslinking agent, and the mixture was heated in MEK at 80°C. Heat and stir, 1
A 60% solution of 5% silicon-modified epoxy resin was prepared. 100 parts by weight of this resin solution (all amounts added hereinafter 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 conductive particles, solder atomized powder 6 having an average diameter of 10 μm, a maximum particle diameter of 20 μm, and a minimum particle diameter of 2 μm was used.
5g was uniformly dispersed, and further the total solid content was reduced to 2 by MEK.
A resin solution was obtained by diluting the resin to a concentration of 2%. A coating film was formed on a polyethylene terephthalate film that had been subjected to mold release treatment with silicone resin so that the thickness after drying would be 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 with an epoxy equivalent of 195, a terminal silanol polydimethylsiloxane with an average molecular weight of 3200, a silane coupling agent and a catalyst were added, and the mixture was dissolved in toluene. A heating reaction was carried out at 100° C. for 3 hours to obtain a silicone-modified epoxy resin with a modification rate of 7%, and toluene was further added to prepare a 65% resin solution. 100 parts of this resin solution also has an epoxy equivalent of 195
35 parts of bisphenol A epoxy resin, bisphenol A epoxy resin with an epoxy equivalent of 195, and N,N
55 parts of the reaction product with '-{2-methylimidazolyl-(1)-ethyl}-eicosandioyldiazide are mixed and uniformly dispersed.

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

[Comparative Example 1] Instead of the silicone-modified epoxy resin of Example 1, a bisphenol A type epoxy resin with an epoxy equivalent of 340 was used.
An anisotropic conductive film was produced in exactly the same manner except that the following was used.

[Comparative Example 2] Anisotropic conduction was carried out in the same manner as in Example 2, except that 65 g of bisphenol A type epoxy resin with an epoxy equivalent of 195 was used instead of the silicone-modified epoxy resin used in Example 2. A film was produced.

[0036] The four types of anisotropic conductive films obtained as described above were used in test patterns (substrate thickness 0.5 mm, copper foil thickness 18 μm, circuit width 0.1 mm, circuit spacing 0.1 m).
m, the pattern surface is temporarily fixed to a size of 3 mm x 50 mm (Ni/Au [5/1 μ] plating), and after peeling off the carrier film, an ITO film (indium/tin oxide film) is formed on the entire surface. 1 on the surface of a 1.1 mm glass plate.
Pressure bonding was carried out at 50° C. for 1 minute. Next, using a photoelasticity experiment device, light was incident on the crimped portion of the circuit board from the end surface of the glass, and the optical path difference was measured using a compensator, and the stress value applied to the crimped surface was measured. Table 1 shows the results.
Shown below.

Table 2 shows the evaluation results of workability and reliability, which are the basic properties required of an anisotropic conductive film.

[0038]

[Table 1]

[0039]

[Table 2]

As shown in Table 1, the anisotropic conductive film according to the present invention can reduce the stress value remaining at the adhesive interface after curing by using a silicone-modified epoxy resin in place of the conventional epoxy resin alone. , about 1 compared to conventional products
It was possible to significantly reduce the size to 1/3 to 1/4.

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

[0042] As for the curing properties, 1 at 150°C.
Good properties are obtained when cured within minutes.

Regarding the adhesive strength, 90°C peeling (
When the peel strength was 500 g/cm or more, it was marked as ○, and when it was 300 g/cm or less, it was marked as ×.

Regarding the reliability test, in TC (temperature cycle test, -30°C ⇔ RT ⇔ 80°C), the conventional film failed (conductivity failure) after less than 100 cycles, whereas the film according to the present invention failed after less than 100 cycles. When using film 5
It was stable up to 00 cycles or more.

Furthermore, when we conducted a temperature cycle test under the conditions of -65°C⇔RT⇔150°C, we found that the conventional product
While the connection resistance value increases by more than 50% after ~10 cycles, when the film according to the present invention is used, the initial resistance value only changes by less than 10% even after 30 cycles.
Good results were obtained.

[0046]

[Effects of the Invention] As described above, the anisotropic conductive film according to the present invention has small residual stress (strain) after curing.
It not only has high adhesive strength and excellent reliability, but also has excellent working properties such as storage stability and curing properties, making it suitable for connection applications such as fine circuit terminals that require increasingly high reliability. It is something that

Claims (1)

[Claims] 1. An anisotropic conductive film comprising a silicon-modified epoxy resin, a mixture containing the epoxy resin, a latent curing agent, a solvent for dissolving these, and conductive particles.