JPS61215528A - Liquid-crystal display device - Google Patents

Abstract

PURPOSE:To reduce contact resistance and to improve adhesive strength by arranging a flexible wiring board which has two divided connection terminals on one terminal of a transparent electrode for external connection across an anisotropic conductive adhesive, and making an electric connection by thermocompression bonding. CONSTITUTION:Connection terminals 5 of the flexible wiring board 4 are position- matched on the top surface of the transparent electrode 2 for external connection and then pressed against a heat plate, so that they are joined with the anisotropic conductive adhesive 3 by fusion. In this case, almost all the anisotropic conductive adhesive 3 right under the two divided connection terminals is removed to a part where no pressure is applied, i.e. except to the connection terminals 5 and to a recessed part formed of the two divided connection terminals 5. Consequently, conductive particles of the anisotropic adhesive 3 contact one another closely in the gap among the connection terminals 5 and transparent electrode 2 for external connection to decrease the contact resistance. At the same time, no pressure is applied directly to the anisotropic conductive adhesive 3 right under the recessed part of the connection terminals 5, so there is almost no flow of the adhesive, which is confined to the recessed part, thereby maintaining the adhesive strength by forming a reservoir for the adhesive.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a liquid crystal display device featuring highly reliable connection leads.

2. Description of the Related Art In recent years, anisotropic conductive adhesives have been increasingly used to connect liquid crystal display elements and drive circuit boards. Conventionally, the most commonly used connecting material is an elastic connector called zebra rubber, but when configured as a liquid crystal display device, it requires a mechanical pressure-welding mechanism and is susceptible to vibration. Fine-pitch electrodes have drawbacks such as ``positional matching is difficult,'' and as an alternative to this, the use of the above-mentioned anisotropic conductive adhesive has increased.

This anisotropic conductive adhesive is composed of conductive powder of appropriate particle size dispersed in an insulating and hot-melt synthetic resin, and is inserted between connected substrates or between a liquid crystal display element and a flexible wiring board. However, electrical connection can be obtained by thermocompression bonding the side substrates.

FIG. 4 shows a connection state when an anisotropically conductive adhesive is used in this liquid crystal display device. Reference numeral 1a designates one glass plate constituting the liquid crystal display element, on the surface of which a transparent electrode 2 for external connection is formed in the shape of an eave as shown in the figure, and is attached to a flexible wiring board via an anisotropic conductive adhesive 3. 4 is glued. In this case, the connection terminals 6 of the flexible wiring board are also aligned one terminal at a time so as to correspond to each terminal of the transparent electrode 2 for external connection, and connected via the anisotropic conductive adhesive 3. Note that this flexible wiring board is connected to a drive circuit board, and signals are transmitted to the liquid crystal display element.

Problems to be Solved by the Invention The connection using the anisotropic conductive adhesive described above does not require a pressure welding mechanism after connection, and the conductive powder that contributes to the connection is minute, so it can also be used for fine patterns. However, the biggest drawback is that the adhesive strength after thermocompression bonding and the contact resistance between the electrodes are in a contradictory relationship, so if you try to increase the adhesive strength, the contact resistance will also increase. It is. That is, this anisotropic conductive adhesive is removed by thermocompression bonding to areas other than between the upper and lower electrodes that require electrical connection, and electrical connection is obtained via the conductive powder remaining between the electrodes. Taking a liquid crystal display device as an example, when connecting one connecting terminal of a flexible wiring board to one terminal of a transparent electrode for external connection, if the pressure during thermocompression bonding is increased to ensure a secure connection, Most of the adhesive is removed between the two, and the conductive powders are in close contact with each other, resulting in lower contact resistance, but on the other hand, too much adhesive is removed. However, the adhesive strength decreases, which poses a major problem in long-term connection reliability.

The present invention solves these problems and provides high connection reliability that simultaneously reduces contact resistance and improves adhesive strength when a liquid crystal display device is constructed using an anisotropic conductive adhesive. The purpose of the present invention is to provide a liquid crystal display device with high quality.

Means for Solving the Problems In order to solve the above problems, the liquid crystal display device of the present invention uses a flexible wiring having a connection terminal divided into at least two terminals on one terminal of a transparent electrode for external connection. The following is a structure in which the plates are disposed via an anisotropic conductive adhesive and are bonded by thermocompression to obtain electrical connection.

Function According to this configuration, during thermocompression bonding, the anisotropic conductive adhesive is trapped within the recessed portions of the divided connection terminals of the 7-lexiple wiring board, and a “pool” of the adhesive is formed within the recessed portions. By remaining as an adhesive, the adhesive strength can be improved.

Further, at this time, the anisotropically conductive adhesive can be reliably confined within the recessed portion because the recessed portion of the connection terminal increases the volume that can be removed by the adhesive. Therefore, between the connection terminals that are in direct contact with the transparent electrode, the conductive powder is in close contact with each other, resulting in a reduction in contact resistance.

Example An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 and FIG. 2 are cross-sectional views of one embodiment of the main body,
1a and 1b are two glass plates constituting a liquid crystal display element, and the glass plate 1a has a transparent electrode 2 for external connection formed on its surface and is exposed in the shape of an eave.

Reference numeral 3 denotes an anisotropic conductive adhesive in which conductive powder is dispersed in a hot-melt type adhesive, and is formed in advance on the eave-shaped portion of the glass plate 1a so as to cover the surface of the transparent electrode 2 for external connection. There is. Reference numeral 4 denotes a flexible wiring board on which a connection terminal 6 divided into two terminals is formed in advance for one terminal in the transparent electrode 2 for external connection. After the connection terminals 6 of the flexible wiring board 4 are aligned with the upper surface of the external connection transparent electrode 2, they are fused together via the anisotropic conductive adhesive 3 by pressure contacting them with a hot plate. In this case, the anisotropically conductive adhesive 3 directly below the connecting terminal 6 divided into two terminals is placed in a part where no pressure is applied, that is, outside the connecting terminal 6 or in the recess that comes out from the connecting terminal 5 divided into two terminals. Most of the anisotropically conductive connecting agent 3 is removed from the area, and the conductive powder in the anisotropically conductive adhesive 3 is in close contact with each other in the gap between the connecting terminal 6 and the transparent electrode 2 for external connection. None, contact resistance can be reduced. At the same time, since no direct pressure is applied to the anisotropic conductive adhesive 3 directly below the concave portion of the connection terminal 5, there is almost no flow of the adhesive, and it is confined within the concave portion, causing adhesive "pools". By creating a bond, the adhesive strength can be maintained. In one embodiment of the present invention, the connecting terminal 5 is divided into two terminals, but as long as it is within the same width as the transparent electrode 2, the connecting terminal 5 can be divided into two or more terminals. By using , it is possible to connect with higher adhesive strength and lower contact resistance. Note that 6 is a liquid crystal and 7 is a sealant.

FIG. 3 compares the relationship between the number of connection terminals, contact resistance, and adhesive strength (bealling strength) in the embodiment of the present invention with that of the conventional example. By dividing 5 into two or more terminals, it is possible to significantly improve adhesive strength and reduce contact resistance compared to conventional one-terminal connections.

Effects of the Invention The liquid crystal display device of the present invention configured as described above is capable of preventing damage due to adhesive "accumulation" when external stress is applied to the flexible wiring board that electrically connects the liquid crystal display element and the circuit board. By dispersing stress elsewhere, adhesive strength can be increased, and since the connection is reliable with multiple terminals, long-term connection reliability can be maintained, making it an industrial value.

[Brief explanation of the drawing]

FIG. 1 is a partial cross-sectional view showing the connection state of a flexible wiring board of a liquid crystal display device according to an embodiment of the present invention, FIG. 2 is a cross-sectional view of the main part of the same device, and FIG. A comparison diagram of the number of connection terminals, contact resistance value, and beering strength of a conventional flexible wiring board, and FIG. 4 is a partial cross-sectional view showing a connection state of a flexible wiring board in a conventional liquid crystal display device. 1a, 1b...Glass plate, 2...Transparent electrode for external connection, 3...Anisotropic conductive adhesive, 4...
...Flexible wiring board, 5...Connection terminal, 6...Liquid crystal.

Claims (1)

[Claims] A flexible wiring board having a connection terminal divided into at least two terminals is disposed on one terminal of a transparent electrode for external connection via an anisotropic conductive adhesive, and electrically connected by thermocompression bonding. A liquid crystal display device.