JPH07140480A - Anisotropically conductive and adhesive film - Google Patents

Abstract

PURPOSE:To enhance a resolving power and to improve reliability of connection by uniformly dispersing conductive particulates formed by coating the surfaces of spherical polymer particulates having rugged shapes on surfaces with a metal and specifying the average grain size thereof to a specific range into an insulating adhesive. CONSTITUTION:The conductive particulates 5 having an average grain size of 2 to 20mum formed by coating the spherical polymer particulates having the rugged shapes on the surfaces with the metal are used for the anisotropically conductive and adhesive film formed by uniformly dispersing the conductive particulates 5 into the insulating adhesive 6. The rugged shapes on the surfaces of the particles are preferably such that the specific surface area of these spherical particles is about 1.3 to 5 times the truly spherical particles having the same average grain size. The film of 0.05 to 0.5mum of nickel, etc., is formed by an electroless plating method on such spherical polymer particles. The conductive particulates 5 formed in such a manner are added at 0.1 to 15 pts.wt. to 100 pts.wt. insulating adhesive. As a result, the reliability of connection to counter electrodes 2, 4 per 1 piece of the conductive particulate is enhanced and the anisotropically conductive and adhesive film having high fineness is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anisotropic conductive adhesive film used for connecting and fixing an electrode of a liquid crystal display module or the like and an electrode of a circuit board which is placed opposite to the electrode.

[0002]

2. Description of the Related Art In recent years, electronic parts have become smaller, thinner, and have higher performance, and along with this, economical high-density mounting technology has been actively developed. Since it is difficult to connect these fine circuits with a conventional solder or rubber connector, an anisotropic conductive adhesive film having excellent resolution has been widely used. This method uses a liquid crystal display module (LCD) and a TAB (Tape Automated B).
When connecting fine electrodes such as onding) or FPC (Flexible Print Circuit) substrates, an anisotropic conductive adhesive film made of an adhesive containing a predetermined amount of conductive fine particles is sandwiched between the electrodes, and heated. A plurality of electrodes are collectively connected by applying pressure.

As the conductive fine particles used here, fine metal powders, plastic fine particles coated with metal, and the like have been conventionally used.

The fine metal powder generally has a wide particle size distribution, and there is a problem in connection reliability due to the effects of conductivity, insulation, and connection mechanism. In addition, the conductive fine particles obtained by metal-coating the plastic fine particles can have a narrow particle size distribution, but they have a drawback that they easily aggregate, and the contact area when connecting electrodes is small, and the holding power to both electrodes is also small. Therefore, it is extremely difficult to cope with high definition with an addition amount that does not cause aggregation.

On the other hand, in recent years, liquid crystal display modules have become finer and more reliable, and the conventional electrode pitch is 200 μm.
(5 lines / mm) to 100 μm or less (10 lines / mm
The above) are required, and further higher resolution is required in the future. Along with this, the conductive fine particles added to the anisotropic conductive adhesive film are also required to have improved characteristics in connection reliability between electrodes.

[0006]

The conventional approach to high resolution is to make the particle size of the conductive fine particles smaller than that of the insulating portion between the circuits in order to secure the insulating property with the adjacent circuit.
At the same time, the addition amount was adjusted so that the conductive fine particles did not come into contact with each other, and the conductivity of the circuit connecting portion was obtained. However, when the particle diameter of the conductive fine particles is reduced, the number of particles is remarkably increased and the surface area is increased, so that the particles cause secondary agglomeration and the insulating property from an adjacent circuit cannot be maintained. In addition, if the amount of added particles is reduced, the number of conductive fine particles on the circuit to be connected decreases, so the number of contact points becomes insufficient, and it becomes difficult to obtain conductivity at the circuit connecting portion, so that the connection reliability is maintained. However, it was extremely difficult to increase the resolution.

The present invention has been made in view of the above situation, and has a high resolving power by adding a predetermined amount of conductive fine particles having a large holding area when the electrodes are connected to each other and having a large contact area to the adhesive. It is an object to provide an anisotropic conductive adhesive film having excellent connection reliability.

[0008]

The present invention has been made to achieve the above object. In order to solve this subject, the present inventors examined in detail the connection mechanism by an anisotropic conductive adhesive film. Currently, the anisotropic conductive adhesive film that has been actually tested is obtained by dispersing spherical conductive particles having a relatively smooth surface of about 5 to 10 μm in a resin such as an epoxy resin having a film thickness of about 20 μm. There are many things. After sandwiching this between a thin film electrode (ITO, Al, etc.) formed on a substrate such as a liquid crystal display module and an electrode of a circuit substrate such as TAB, FPC, etc., the electrodes of both substrates are aligned, The process of thermocompression bonding is common. At this time, as an electrode of the circuit board, a copper foil having a thickness of about 18 to 35 μm plated with tin or the like is often used. Figure 1
FIG. 2 shows an explanatory diagram of a connecting method when the anisotropic conductive adhesive film of the present invention is used and FIG. 2 is a conventional anisotropic conductive adhesive film. 1A and 2A are respectively the anisotropic conductive adhesive film of the present invention (FIG. 1A).
2 shows a state in which a conventional anisotropic conductive adhesive film ((a) in FIG. 2) is sandwiched between a circuit board and a display module board. During thermocompression bonding of the anisotropic conductive film in which the conductive fine particles 5 are dispersed in the adhesive 6, pressurization proceeds and the circuit board 3
When the distance between the electrode portion 4 of the and the thin film electrode 2 on the display module substrate 1 becomes the same as the particle diameter of the conductive fine particles 5, the conductive fine particles 5 are applied between the electrodes (2, 4) due to the pressure applied between the electrodes. Retained. 1B and 2B show this state, and FIG. 1C and FIG. 2C show
FIG. 3 is a partially enlarged view of FIG. 1B and FIG. 2B, respectively. At this time, in the case of spherical conductive fine particles having a relatively smooth surface which has been conventionally used, a good contact state cannot be expected because the conductive fine particles do not bite into both electrodes, and contact per conductive fine particle Since the area is also small, it became clear that it is difficult to achieve high resolution while maintaining connection reliability. Therefore, the present inventors have found that a desired purpose can be achieved by incorporating a predetermined amount of conductive fine particles having an uneven surface on the insulating adhesive, and have completed the present invention.

That is, the present invention provides an anisotropic conductive adhesive film in which conductive fine particles are uniformly dispersed in an insulating adhesive, and an average particle size of a spherical polymer fine particle having irregularities on the particle surface coated with a metal. 2 to 20 μm of conductive fine particles are used to provide an anisotropic conductive adhesive film.

As a method for obtaining spherical polymer fine particles having irregularities on the particle surface, spherical particles having a relatively smooth surface synthesized by suspension polymerization, emulsion polymerization, dispersion polymerization, seed polymerization, etc. are mechanically or chemically treated. Although it is also possible to extremely roughen the surface by a method, it is difficult to arbitrarily determine the particle shape and the manufacturing cost is high.Therefore, use a manufacturing method in which the surface of the spherical polymer particles has an uneven shape during the production of the polymer particles. Is preferred. For example, seed polymer particles dispersed in an aqueous dispersion medium, absorb the oil-soluble unsaturated monomer mixed with a non-crosslinkable unsaturated monomer and a crosslinkable unsaturated monomer, oil-soluble polymerization initiator In the method for producing monodisperse particles in which an oil-soluble unsaturated monomer is polymerized in the presence of, the weight of the oil-soluble unsaturated monomer added is 0.5 to 8 times the weight of the seed polymer particles. Thus, the target particles can be obtained. The shape of the particles can be controlled by changing the weight of the oil-soluble unsaturated monomer added at this time and the mixing ratio of the non-crosslinkable unsaturated monomer and the crosslinkable unsaturated monomer.

The irregular shape of the particle surface is not particularly limited, but preferably the specific surface area of spherical particles having irregularities is 1.3 times the specific surface area of the true spherical particles having the same average particle diameter. It is preferably about 5 times.

The thus-obtained spherical polymer fine particles having an uneven surface are coated with a metal by plating or the like to obtain conductive fine particles having an average particle diameter of 2 to 20 μm. Examples of the plating method include an electroless plating method and the like, and a coating film of nickel, gold, copper or the like can be easily formed. The thickness of the coating is preferably 0.05 μm to 0.5 μm.

An anisotropic conductive adhesive film can be obtained by uniformly dispersing the conductive fine particles thus obtained in an insulating adhesive material. The amount of conductive fine particles is 100
It is preferably 0.1 to 15 parts by weight with respect to parts by weight. The thickness of the anisotropic conductive adhesive film is preferably 70 μm or less, and is 15 to 35 in order to obtain good connection reliability.
As the insulating adhesive, thermoplastic materials used for insulating sheets and materials curable by heat or light can be widely applied as the insulating adhesive, but the heat resistance and moisture resistance after connection are high. It is preferable to use a curable material because of its excellent properties. Among them, the epoxy adhesive is preferably applied because it has a feature that it can be cured in a short time, has good workability in connection, and has excellent adhesiveness due to its molecular structure.

Epoxy adhesives are mainly composed of polymer epoxy, solid epoxy and liquid epoxy, phenoxy resin and liquid epoxy, epoxy mixed with urethane, polyester, NBR and the like, and a latent curing agent and a coupling agent. It is generally composed of a system to which various modifying agents such as agents and catalysts are added. .

[0015]

EXAMPLES The present invention will now be described in more detail based on examples.

Example 1 An average particle size of about 2.5 μm prepared by dispersion polymerization
Cross-linked polystyrene seed particles 10 parts by weight, H₂ O 4
00 parts by weight, sodium lauryl sulfate as a surfactant
Mix 0.3 parts by weight and apply ultrasonic vibration to the seed polymer.
-The particles were dispersed. Furthermore, 3% by weight of polyvinyl
Aqueous alcohol solution is used as a particle coagulation inhibitor at 550 weights.
A part was added. Add 15 parts by weight of styrene monomer to this solution.
And 2 parts by weight of 55% by weight divinylbenzene are mixed and started.
A solution prepared by dissolving 1 part by weight of benzoyl peroxide as an agent
N₂The mixture was added in the atmosphere and stirred at 30 ° C. for 1 hour. So
After that, the temperature was raised to 70 ° C. and polymerization was carried out for 8 hours. Particles obtained
Has unevenness on the surface of spherical particles as shown in FIG.
It was. The particle size distribution of this particle is
When measured with an Iser (manufactured by Coulter), the average diameter is 5.
The particle size distribution was 0 μm and the particle size distribution was 4.0 to 6.0 μm. Change
In addition, the specific surface area of these particles was determined by GEMINI 2360 (Shimadzu
2.2 × 10 when measured by the factory)^Fourcm²/ G
Met.

The surfaces of the polymer fine particles thus obtained were plated with Ni and Au to obtain conductive fine particles having an average particle size of 5.3 μm.

The conductive fine particles were added to an epoxy adhesive varnish containing a latent curing material in an amount of 2% by volume based on the solid content of the varnish.
An adhesive film with a thickness of 20 μm prepared by mixing
An anisotropic conductive adhesive film was produced by casting on a release film.

This anisotropic conductive adhesive film is used as a glass substrate.
The upper ITO electrode and a copper layer with a pitch of 50 μm and a thickness of 35 μm
170 ° C- sandwiched between the tinned FPCs
20 kgf / cm² Connection was made under thermocompression bonding conditions of -20 seconds.

The connection resistance of this circuit was measured by applying a constant voltage of a measuring current of 1 mA between adjacent circuits. The insulation resistance was measured by applying a voltage of 100 V between adjacent circuits. As a reliability test, -40 ° C / 30 minutes, 25 ° C / 5 minutes, 80 ° C
After conducting a temperature cycle test of / 30 minutes and 25 ° C / 5 minutes for 250 cycles, the connection resistance between adjacent circuits was measured. The results obtained are shown in Table 1.

Example 2 An anisotropic conductive adhesive film was prepared and evaluated in the same manner as in Example 1 except that the conductive fine particles were mixed at a solid volume ratio of 1%. The results obtained are shown in Table 1.

Comparative Example 1 200 parts by weight of a styrene monomer and 16 parts by weight of 55% by weight divinylbenzene were mixed and 14 parts by weight of benzoyl peroxide were dissolved as a polymerization initiator, and 350 parts by weight of H ₂ O and a dispersion stabilizer were prepared. The mixture was added to a mixture of 350 parts by weight of a 10% by weight tricalcium phosphate aqueous solution, and the mixture was subjected to high-speed shearing with a homomixer to atomize the monomer droplets. After keeping it at 70 ° C for 1 hour, it was transferred to a polymerization tank.
Polymerization was carried out at 0 ° C for 7 hours. The obtained particles were spherical particles having a smooth surface as shown in FIG.

This is classified at 4.0 to 6.0 μm,
Particles having an average diameter of 5.0 μm were obtained. Furthermore, the specific surface area of the particles was measured and found to be 1.3 × 10 ⁴ cm ² / g. Ni and Au plating was performed on the surface of the fine particles to obtain conductive fine particles having an average diameter of 5.3 μm.

An anisotropic conductive adhesive film was prepared and evaluated in the same manner as in Example 1 using the conductive fine particles. The results obtained are shown in Table 1.

Comparative Example 2 The procedure of Example 1 was repeated except that the conductive fine particles prepared in Comparative Example 1 were blended at a ratio of 1% in terms of solid volume ratio of varnish.
An anisotropic conductive adhesive film was produced and evaluated.
The results obtained are shown in Table 1.

Comparative Example 3 The procedure of Example 1 was repeated, except that the conductive fine particles prepared in Comparative Example 1 were blended at a varnish solid volume ratio of 4%.
An anisotropic conductive adhesive film was produced and evaluated.
The results obtained are shown in Table 1.

[0027]

[Table 1]

[0028]

According to the present invention, by adding a predetermined amount of spherical conductive fine particles having irregularities on the surface of the particles to the insulating adhesive, the connection reliability of the conductive fine particles to the facing electrode can be improved. It becomes possible to provide a highly precise and highly reliable anisotropic conductive adhesive film without increasing the amount of particles added to the anisotropic conductive adhesive film.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a state in which a connection is made using the anisotropic conductive film of the present invention.

FIG. 2 is an explanatory diagram showing a state in which a conventional anisotropically conductive film is used for connection.

FIG. 3 is an electron micrograph showing a particle structure of a conductive fine particle core used as an example of the present invention.

FIG. 4 is an electron micrograph of a particle structure of a conductive fine particle core used as a comparative example of a conventional method.

[Explanation of symbols]

 1 Display Module Board 2 Thin Film Electrode 3 Circuit Board 4 Circuit Board Electrode 5 Conductive Fine Particles 6 Adhesive

Claims (1)

[Claims] 1. An anisotropic conductive adhesive film in which conductive fine particles are uniformly dispersed in an insulating adhesive, wherein spherical polymer fine particles having irregularities on the particle surface are coated with a metal to have an average particle size of 2 to 2. An anisotropic conductive adhesive film characterized by using conductive fine particles of 20 μm.