JPH0812352B2 - Liquid crystal display - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device having highly reliable connection leads.

2. Description of the Related Art In recent years, anisotropic conductive adhesives have been increasingly used for connecting a liquid crystal display element and a drive circuit board. Conventionally, the most commonly used connection material is an elastic connector called zebra rubber, but when it is configured as a liquid crystal display device, it requires a mechanical pressure contact mechanism and is weak against vibration. Fine pitch electrodes have drawbacks such as difficulty in position alignment, and the use of the above anisotropic conductive adhesive has been increasing as an alternative. This anisotropic conductive adhesive has a structure in which conductive powder having an appropriate particle size is 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. Then, an electrical connection can be obtained by thermocompressing both substrates.

FIG. 4 shows a connection state when an anisotropic conductive adhesive is used in this liquid crystal display device. Reference numeral 1a is one glass plate constituting a liquid crystal display element, on the surface of which a transparent electrode 2 for external connection is formed in an eaves-shaped portion as shown in the figure, and a flexible wiring board with an anisotropic conductive adhesive 3 interposed therebetween. 4 is glued. In this case, the connection terminals 5 of the flexible wiring board are also aligned one by one so as to correspond to each terminal of the transparent electrode 2 for external connection, and are connected through the anisotropic conductive adhesive 3. The flexible wiring board is connected to the 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 since the conductive powder that contributes to the connection is minute, 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 electrodes are in a reciprocal relationship, so if you try to increase the adhesive strength, the contact resistance also increases. Is. That is, this anisotropic conductive adhesive is removed by thermocompression bonding except between the upper and lower electrodes that require electrical connection,
An electrical connection is obtained through the conductive powder remaining between the electrodes,
As described above, taking the liquid crystal display device as an example, in order to securely connect the external connection transparent electrode 1 terminal to the connection terminal 1 terminal of the flexible wiring board,
When the pressure during thermocompression bonding is increased, most of the adhesive is removed between the two, and the conductive powder particles come into close contact with each other, resulting in a reduction in contact resistance. On the other hand, since the adhesive is excessively removed, the adhesive strength is lowered, which causes a serious problem in long-term connection reliability.

The present invention solves such a problem and has a high connection reliability that simultaneously achieves reduction of the adhesive resistance and improvement of the adhesive strength when a liquid crystal display device is configured by using an anisotropic conductive adhesive. It is an object of the present invention to provide a liquid crystal display device having high performance.

Means for Solving the Problems In order to solve the above problems, the liquid crystal display device of the present invention has at least two terminals on one terminal of a transparent electrode for external connection.
A flexible wiring board having connection terminals divided into terminals is arranged via an anisotropic conductive adhesive and thermocompression bonded to obtain an electrical connection.

Function According to this configuration, the anisotropic conductive adhesive is trapped in the recessed portions of the divided connection terminals of the flexible wiring board during thermocompression bonding, and remains as a "pump" of the adhesive in the recessed portions. As a result, the adhesive strength can be improved. Further, at this time, the anisotropic conductive adhesive can be surely confined in the recessed portion because the removable volume of the adhesive increases because the connection terminal has the recessed portion. For this reason, between the connection terminals that are in direct contact with the transparent electrode, the conductive powder particles are in close contact with each other, and as a result, the contact resistance can be reduced.

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

1 and 2 are cross-sectional views of an embodiment of the present invention, in which 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 on its surface. Are formed and exposed like eaves. Reference numeral 3 is an anisotropic conductive adhesive in which conductive powder is dispersed in a hot melt type adhesive, and the transparent electrode 2 for external connection is previously formed on the eaves of the glass plate 1a.
Is formed so as to cover the surface of the. Reference numeral 4 denotes a flexible wiring board in which a connection terminal 5 divided into two terminals is formed in advance for one terminal in the transparent electrode 2 for external connection. The connection terminal 5 of the flexible wiring board 4 is aligned with the upper surface of the transparent electrode 2 for external connection, and is then pressure-welded by a hot plate to be fused through the anisotropic conductive adhesive 3.
In this case, the anisotropic conductive adhesive 3 directly below the connection terminal 5 divided into two terminals comes out from a portion where no pressure is applied, that is, outside the connection terminal 5 or from the connection terminal 5 divided into two terminals. Almost all of the anisotropic conductive connecting agent 3 was removed in the recessed portion, and the conductive powders in the anisotropic conductive adhesive 3 closely contacted each other in the gap between the connection terminal 5 and the transparent electrode 2 for external connection. The state can be established and the contact resistance can be reduced. at the same time,
Anisotropic conductive adhesive 3 directly below the concave portion of the connection terminal 5
Since the pressure is not directly applied, the adhesive hardly flows and is confined in the concave portion, and the adhesive strength can be maintained by forming a “pump” of the adhesive. Although the adhesive terminal 5 is divided into two terminals in the embodiment of the present invention, the connection terminal 5 is divided into two or more terminals as long as it is within the same width as the transparent electrode 2. By using, it is possible to achieve connection with higher adhesive strength and lower contact resistance. In addition, 6 is a liquid crystal and 7 is a sealant.

FIG. 3 compares the relationship between the number of connection terminals, the contact resistance, and the adhesive strength (peeling strength) in the embodiment of the present invention with the conventional example. As is clear from FIG. By dividing the terminal into two or more terminals,
It is possible to significantly improve the adhesive strength and reduce the contact resistance as compared with the terminal connection.

EFFECTS OF THE INVENTION The liquid crystal display device of the present invention configured as described above has a flexible wiring board that electrically connects a liquid crystal display element and a circuit board, and when an external stress is applied, a "pump" of the adhesive causes It is of great industrial value that the adhesive strength can be increased by dispersing the stress elsewhere, and the long-term connection reliability can be maintained because of reliable connection with multiple terminals.

[Brief description of drawings]

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

Claims (1)

[Claims] 1. A flexible wiring board having connection terminals divided into at least two terminals is arranged on one terminal of a transparent electrode for external connection via an anisotropic conductive adhesive, and thermocompression-bonded to electrically. A liquid crystal display device characterized by being connected.