JPS60120772A - Anisotropically conductive adhesive - Google Patents

Abstract

PURPOSE:To provide the titled adhesive suitable for use in connecting narrow pitch electrode groups to each other, by shaping a thermoplastic resin compsn. contg. electrically conductive power dispersed therein into a thin film of 10- 100mm. in length. CONSTITUTION:A thermoplastic resin such as high-molecular polyester resin (which may be used together with a thermosetting resin such as phenolic resin) is dissolved in an org. solvent and electrically conductive powder (e.g. carbon black having a particle size of 0.1mu) is dispersed therein. A release paper 2 is coated with the resulting compsn. and predried to form an anisotropically conductive adhesive 1 of 10-100mu in thickness. When a metal oxide such as (antimony-doped) tin oxide or indium oxide is used as the electrically conductive powder, a light-transmissible adhesive can be obtd. Hence, in forming a liquid crystal panel, etc., an electrode to be connected on a drive circuit side is visible from a glass electrode sheet side and positioning between electrodes can be easily made.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an anisotropically conductive adhesive that can be used to connect circuit boards to each other or to connect circuit boards to circuit components.

Conventional configurations and their problems Conventionally, when electrically connecting the corresponding electrodes of a plurality of circuit boards, the method for doing so is, for example, to form the corresponding electrodes in the same shape and to make them face each other. There is a method to obtain a connection by sandwiching a so-called elastic connector between both electrodes and applying pressure.

However, this type of elastic connector always requires a pressurized state, there are limits to the dimensions of the elastic connector itself, which limits the distance between the two circuit boards, and the electrodes have an extremely narrow pitch.

For example, it has a drawback that it cannot be used with a pitch of 100 μm or the like.

Another method is to use a sheet-like anisotropic conductive film in which a fibrous conductor is contained in an adhesive. That is, this sheet is sandwiched between opposing electrodes, and then hot pressed to bring the fibrous conductor into contact with the electrodes to obtain continuity. In this case as well, the fibrous conductor has a length of 50 to 1000 μm. Since it uses carbon fiber, it has the disadvantage that it cannot be used for narrow pitch electrodes.

Furthermore, as another method, there is a method in which a conductive ink and a non-conductive ink having thermocompression adhesive properties are alternately printed in stripes on an insulating film, and then thermocompression sorting is used. In other words, this type of Atagawa-made sheet is printed to match the shape of the electrode to be connected, and when used, the conductive part of the striped printed pattern is aligned with the electrode on the circuit board, and then heat pressed to make it conductive. This is a method of obtaining electrical connections between corresponding electrodes by performing a process on each circuit board to obtain electrical connections between corresponding electrodes. However, this thermocompression bonded sheet also has a limitation in fine pattern printing, so it has the drawback that it cannot be used for narrow pitch electrodes.

OBJECTS OF THE INVENTION The present invention aims to eliminate the above-mentioned drawbacks and provide an anisotropically conductive adhesive that can be used also for narrow pitch electrodes.

Structure of the Invention In order to achieve this object, the anisotropically conductive adhesive of the present invention has a conductive powder dispersed in a thermoplastic resin or a mixture of a thermoplastic resin and a thermosetting resin, and has a conductive powder of 10 to 10 μm.
It is characterized by being formed into a thick thin film. The anisotropically conductive adhesive configured in this way is fixed onto the electrode to be connected on the first circuit board to be bonded, and the electrode to be connected on the second circuit board to be bonded is fixed to the electrode to be connected on the second circuit board to be bonded. The conductive powder is fixed between the pair of electrodes to be connected by the hardened resin by applying pressure while applying heat, then reducing the pressure and cooling the conductive powder, thereby making it possible to obtain an electrical connection. At this time, the anisotropic conductive adhesive of the present invention has 1
Since it is formed in the form of a thin film of 0 to 100 μm, it can be easily fixed by placing it on one of the electrodes to be connected and applying heat and pressure, so there is no need to use means such as screen printing. The reason why the film is formed with a thickness of 10 to 100 μm is that if it is less than 10 μm, the adhesive strength is insufficient;
This is because if the thickness exceeds μm, conduction failure will occur. still,
By selecting the particle size of the conductive powder sufficiently small, the particle size of 100μ
It can be used even with electrodes with a narrow pitch of less than m without generating interelectrode pitch.

Further, by using a metal oxide such as tin oxide, antimony-doped tin oxide, or indium oxide as the conductive powder, it is possible to impart translucency to the product of the present invention. For example, in the case of connecting a liquid crystal display panel and a drive circuit, the recent trend is to increase the size of the liquid crystal panel and increase the number of electrodes and the density of the extraction electrodes, and alignment of the positions of the connected electrodes on both sides becomes a problem during the connection process. It may happen.

When the above-mentioned anisotropically conductive adhesive with transparency of the present invention is used to connect these two, a liquid crystal panel is formed after installing the anisotropically conductive adhesive between both electrodes to be connected. By visually observing the part to be aligned from the glass side, the connected electrodes on the drive circuit board side can be observed through the transparent anisotropic conductive adhesive, making it easier to align the positions with the transparent electrodes on the glass. This means that it is possible to do this.

Description of examples An embodiment of the present invention will be described below.

First, as a resin component of the adhesive of the present invention, 30 parts by weight of Epikote #828 (manufactured by Shell Chemical Co., Ltd., USA) as a thermoplastic resin and 40 parts by weight of a thermoplastic high molecular weight polyester resin (manufactured by Japan Synthetic Rubber Industry Co., Ltd.) , 30 parts by weight of a phenolic resin (manufactured by Matsushita Electric Works Co., Ltd.) as a thermosetting resin was dissolved in methyl ethyl ketone to form a solution with a solid content of approximately 30%, and carbon black with a particle size of 0.1 μm was prepared as a conductive powder. (Lamp Plack, manufactured by Tegusa, West Germany) was used and dispersed in the mixture to prepare an anisotropically conductive adhesive.

Next, as shown in FIG. 1, the adhesive layer was formed by coating the adhesive 1 of the composition on a release paper 2 to a thickness of 30 μm.
It was prepared by drying with 6o molecules at °C. (At this time, another method for creating the adhesive layer is to apply the adhesive of the present composition directly onto the substrate by screen printing or the like, which will be described later, and pre-dry it.

) And as a connection test board, I used a 35μm copper foil board based on a glass epoxy material with a thickness of 1.6? A 6μm thick polyimide base and a 35μm@foil flexible board are used, and both have a line width on the copper foil surface.

Line spacing: 126 μm each, total 250 μm, 160 at equal intervals in bis and chis.
Lines of books formed a pattern.

Next, as shown in FIG. 2, the adhesive 1 formed in the form of a thin film on the release paper 2 as described above is cut into an appropriate size and placed on the connected electrode 4 of the flexible substrate 3. Temporary fixing was performed with the adhesive side facing the electrode 4 side. This temporary fixing was carried out at a temperature of 110"C and a pressure of 6 F'y/crl. After the temporary fixing, the release paper 2 was removed and both substrates 3, 3
After aligning the positions of the corresponding electrodes 4° 4a on the electrodes 4a, the main crimping was performed. This actual crimping is carried out at a temperature of 140"C and 40Kl.
/ct! Both substrates 3 and 3a were bonded together by applying a temperature and pressure of . FIG. 3 shows the state after the main pressure bonding, and 1a is the adhesive layer that flowed during the pressure bonding. As an evaluation method, the surface insulation resistance of the adhesive 1 itself after coating with a thickness of 30 μm and the contact resistance between the conductor patterns and 40′”C,96
The contact resistance after being left in ZRH for 48 hours and the short circuit occurrence rate at 160 connection points were measured.

The table below shows the measured values when the amount of carbon black dispersed in Adhesive 1 was varied.

Below margin *・・・This is a comparative example and is outside the scope of the claims.

Here, the contact resistance is a contact area of 0.15×3. The values were measured in 0 mm, and the characteristics of sample flow 6 were measured under similar conditions with a conventional product using carbon fiber as a conductor.

As is clear from the above table, even when a carbon blank is added to the product of the present invention, the surface insulation shows a value that is sufficient for practical use, and the contact resistance is almost as low as that of the conventional product shown in sample A; s. Furthermore, the contact resistance due to being left in humidity is suppressed to a slight increase.

In this embodiment, connection between printed circuit boards has been described, and next, an embodiment of connection between a liquid crystal panel and a drive circuit board will be described. First, the same resin composition as in the previous example was used as the binder for the adhesive, and antimony-doped tin oxide powder (T-1 manufactured by Mitsubishi Metals Corporation) was added to the resin composition in an amount of 100% by weight as the conductive powder. An adhesive was prepared by dispersing the adhesive in 3 parts by weight per part and coating it on a release paper to a thickness of 30 μm as shown in FIG. This adhesive is temporarily fixed onto the electrode to be connected on the flexible substrate.

This temporary fixing was carried out at a temperature of 110° C. and a pressure of 6 Kp/crl. Next, we removed the release paper and aligned the position with the transparent electrode to be connected on the glass plate of the liquid crystal panel.
At this time, as shown in FIG. 4, since the anisotropically conductive adhesive 7 of this embodiment is translucent, by observing from the glass plate 5 side of the liquid crystal panel, it is possible to see that the transparent electrode 6 and the flexible Positional alignment with the electrode 4 on the substrate 3 could be performed extremely easily.

At this time, when carbon black is used as the conductive powder, it is difficult to observe the electrode 4 because the adhesive is opaque. Then, the main crimping was done at 140°゛C140//c
After pressure bonding, the contact resistance between the transparent electrode 6 and the electrode 4 on the flexible substrate 3 was measured.
22Q/-, which was a sufficient value for connection between a high impedance liquid crystal panel and a drive circuit. Therefore, the antimony-doped tin oxide powder used as the conductive powder in this example has excellent translucency and conductivity, and is a conductive powder for use in an anisotropically conductive adhesive having translucency. This is particularly effective.

In the above example, a case was explained in which a mixture of a thermoplastic resin and a thermosetting resin was used as a binder, but the same effect as described above can be obtained even when a thermoplastic resin alone is used as a binder. It was confirmed that

Effects of the Invention As described above, the anisotropically conductive adhesive of the present invention is formed by dispersing conductive powder in a resin composition and forming it into a thin film having a thickness of 10 to 100 μm. By using this adhesive, objects to be connected are always bonded with the optimum amount of adhesive, resulting in a reliable connection with low contact resistance and high environmental resistance.

However, by appropriately selecting the particle size of the conductive powder, a reliable connection can be obtained even with narrow-pitch electrodes without the occurrence of cirquets. Furthermore, since no mechanical auxiliary pressure welding means is required after connection, there is an advantage that no restrictions are placed on the structure of the objects to be connected. By using conductive metal oxide powder such as tin oxide doped with antimony as the conductive powder, it is possible to provide an anisotropically conductive adhesive with translucency, and it is possible to provide a narrow-pitch and multi-layer conductive adhesive. This has the effect of greatly simplifying the positional matching work for connecting the pins to the liquid crystal panel and the drive circuit. Furthermore, the anisotropically conductive adhesive of the present invention can be used not only to connect circuit boards to each other or to connect liquid crystal display panels to drive circuit boards, but also to reduce the cost of products by using the adhesive in areas that were conventionally soldered. Excellent effects such as cost reduction and reliability improvement can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a state in which a release paper is coated with an anisotropic conductive adhesive according to an embodiment of the present invention, and FIGS. 2 and 3 are a state in which substrates are connected to each other using the adhesive of the present invention. FIG. 4 is a cross-sectional view showing a state in which a liquid crystal panel and a drive circuit board are connected using the adhesive of the present invention. 1.7. Anisotropic conductive adhesive, 1a-. Adhesive layer,
2...Release paper, 3...Flexible substrate, 3a
... Substrate, 4.4a... Electrode, 6 - Glass plate, 6... Transparent electrode.

Claims (2)

[Claims] (1) Conductive powder is dispersed in a thermoplastic resin or in a mixture of a thermoplastic resin and a thermosetting resin, and the conductive powder is 10 to 100μ
An anisotropic conductive adhesive characterized by being formed into a thin film with a thickness of m. (2) The anisotropic conductive adhesive according to claim C, characterized in that a conductive metal oxide powder is used as the conductive powder.