JPH0645024A - Anisotropic conductive adhesive film - Google Patents

Abstract

PURPOSE:To prevent short-circuiting between adjacent circuits by providing, on either surface of an anisotropic conductive film, adhesive layers each having a fusing viscosity relatively lower than that of an insulative resin. CONSTITUTION:An adhesive layer 6 including a conductive particle and an adhesive layer 7 are laminated on a thin film electrode 2 on a display module substrate 1. A circuit substrate electrode 4 is mounted on a circuit substrate 3, to be positioned with respect to the thin film electrode 2, followed by thermal press-fitting. Heat is transmitted to the adhesive in contact with the electrode 4 of the circuit substrate 3 in thermally press-fitting so that the adhesive is fused. The adhesive, which is fused under pressure, flows into a cavity 5 of the circuit substrate together with the conductive particle. When the fluidation proceeds and a distance between the electrodes 2, 4 becomes equal to a diameter of the conductive particle, the particle is held between the electrodes by pressurizing force. Accordingly, only the adhesive layer 7 flows into the cavity 5. At this time, the thickness of an anisotropic conductive film becomes approximately equal to a diameter of the conductive particle. Consequently, it is possible to prevent short-circuiting between the adjacent circuits so as to provide the anisotropic conductive film which can be connected at high accuracy.

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. For example, when connecting fine electrodes such as a liquid crystal display module (LCD) and a TAB (Tape Automated Bonding) or FPC (Flexible Printed Circuit) substrate, an anisotropic conductive adhesive film is sandwiched between the electrodes, and heated. A method of collectively connecting a plurality of electrodes by applying pressure is being used.

[0003]

In recent years, as the definition of liquid crystal display modules has become higher and higher, the conventional electrode pitch is 200 μm.
From about (5 lines / mm) to 100 μ or less (10 lines / mm or more) is required. Along with this, the anisotropic conductive adhesive film is required not only to have conventional electrical connection and adhesion between electrodes but also to have improved characteristics against short circuit between electrodes due to aggregation of conductive fine particles. In the conventional method, the resin layer containing conductive particles under the electrodes of the circuit board is melted by the heat and pressure at the time of connection and flows into the space between the electrodes of the circuit board, and the electrodes of the liquid crystal display module and the electrodes of the circuit board. However, the conductive particles contained in the adhesive that flowed into the space between the electrodes on the circuit board aggregated especially in the resin pool or the flow front, which caused a short circuit between the electrodes. There was a problem of doing.

[0004]

The present invention has been made to solve the above problems. The present inventors have studied in detail the connection process using an anisotropic conductive adhesive film in order to solve this problem. Many of the anisotropic conductive adhesive films that are actually tested at present are ones in which conductive fine particles of about 5 to 10 μm are dispersed in an epoxy resin or the like having a film thickness of about 20 μm. 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 on both substrates are aligned, The process of thermocompression bonding is common. At this time, the electrode of the circuit board is about 1
A copper foil having a thickness of 8 to 35 μm plated with tin or the like is often used, but the copper foil is etched out between the electrodes to form a cavity. FIG. 2 shows an outline of the case of the conventional example. At the time of thermocompression bonding, heat is first transferred to the adhesive which contacts the electrode portion 4 of the circuit board 3 and melts. The pressure-sensitive adhesive melts into the cavity 5 of the circuit board together with the conductive particles contained therein. When the pressure is increased and the distance between the electrode portion 4 of the circuit board and the thin film electrode 2 on the substrate 1 of the display module becomes the same as the particle diameter of the conductive fine particles, the particles are held between the electrodes due to the pressure applied between the electrodes. Only the adhesive flows into the interelectrode cavity 5 of the circuit board.

Therefore, in the conventional method, the agglomeration of the conductive fine particles that have flowed into the interelectrode cavity of the circuit board from the initial stage of pressure bonding until the distance between both electrodes becomes equal to the particle diameter of the conductive fine particles causes a short circuit between the electrodes. I understand that. In particular, since there is a large amount of this aggregation at the flow tips of the inter-electrode cavities, etc., the conductive fine particles contained in the initial stage of pressing, in other words, in the portion in contact with the circuit board side of the anisotropic conductive adhesive film is a problem. It became clear. Therefore, the present inventors have found that a desired object can be achieved by using an anisotropic conductive adhesive film having a two-chamber structure in which the side in contact with the circuit board is an adhesive layer containing no conductive fine particles. At this time, it is important that the adhesive layer containing no conductive fine particles has a lower melt viscosity at the temperature of connection than the melt viscosity of the anisotropic conductive film body. This is because in order to achieve the present invention, the adhesive layer containing no conductive fine particles must first flow into the inter-electrode space of the circuit board at the time of connection. If the anisotropic conductive film body has a lower melt viscosity, flow from the side in contact with the display substrate occurs, which is not preferable. Further, if the thickness of the anisotropic conductive film body is made substantially equal to the particle diameter of the conductive fine particles by the above connection mechanism, there is no inflow of the conductive fine particles into the pace between the electrodes of the circuit board, and the distance between the electrodes is initially Since the dispersed state of the conductive fine particles of the film is maintained, the present invention can be completely carried out. Note that it is clear from the point of view of the present invention that the type of adhesive, the diameter and type of conductive particles are not limited to those used in the above description.

[0006]

EXAMPLE An adhesive film having a thickness of 10 μ and containing 2 vol% of plastic particles plated with Ni and Au having an average particle size of 10 μm as conductive fine particles on an epoxy adhesive A is cast on a release film. Then, an epoxy-based adhesive B containing no conductive fine particles was cast thereon to a thickness of 15 μm to form a two-layer anisotropic conductive adhesive film. When the viscosities of the adhesive A and the adhesive B at 160 ° C. were measured without the curing agent, the adhesive A was 1.8 times the viscosity of the adhesive B.
A display substrate having ITO electrodes formed on a glass substrate at a pitch of 70 μm and a 25 μm copper foil (Sn plated product) electrode on a 75 μm polyimide film are provided so that the adhesive A is disposed on the display substrate side. It is sandwiched between FPC circuit boards formed with a 70 μm pitch, 160 ° C., 20 kg / c
m ² Connection was performed under thermocompression bonding conditions of 20 sec.

For comparison, an adhesive film having a thickness of 25 μ containing 2 vol% of plastic particles plated with Ni and Au having an average particle size of 10 μm as fine particles at 0 ° C. is applied to a release film as a fine particle on the epoxy adhesive A. It was stretched, sandwiched between the display substrates used in the examples, and connected under the same conditions as the examples. Example, Comparative Example, Substrate 5 with 160 Electrodes Each
When the connection resistance and the short circuit between the circuits were measured for each of the sheets, the connection resistance was the same level of 1.
Although it was 6Ω, the short circuit between the circuits was 0 in the example, but in the comparative example, a short circuit was observed at 20 to 50 places in all of the five substrates.

[0006]

According to the present invention, a high-definition liquid crystal display module and a circuit board can be connected without fear of a short circuit.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a state at the time of connection according to the present invention.

FIG. 2 is a schematic diagram showing a connection state in the case of a conventional example shown for comparison.

[Explanation of symbols]

 1 Display Module Substrate 2 Thin Film Electrode on Display Substrate 3 Circuit Board 4 Electrode on Circuit Board 5 Cavity between Electrodes on Circuit Board 6 Adhesive Layer Containing Conductive Fine Particles 7 Adhesive Layer Not Containing Conductive Fine Particles 8 Conductivity Fine particles

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tatsuo Ito 1150 Gozamiya, Shimodate City, Ibaraki Prefecture Gotomiya Plant, Hitachi Chemical Co., Ltd.

Claims (2)

[Claims] 1. An anisotropic conductive film having conductive fine particles uniformly dispersed in an insulating resin, wherein at least one surface of the anisotropic conductive film has a melt viscosity relatively lower than that of the insulating resin. An anisotropic conductive adhesive film having an adhesive layer having the above. 2. The anisotropic conductive adhesive film according to claim 1, wherein the thickness of the anisotropic conductive film is substantially the same as the particle size of the conductive fine particles.