JPH08271925A - Liquid crystal device - Google Patents

Abstract

(57) Abstract: To improve connection workability between circuit boards and improve connection reliability. An anisotropic conductive adhesive 6 composed of an insulating adhesive layer 8 and conductive fine particles 7 is in a sheet shape before curing, and in this state, a space between a connection circuit 5 and a copper foil pattern 2 is formed. Sandwiched between. Then, the circuit board is heated and pressed by a heater tool, whereby the anisotropic conductive adhesive 6 is cured, and the conductive fine particles 7 come into contact with both the connection circuit 5 and the copper foil pattern 2. Further, the connection circuit 5 is strongly pressed, and finally the connection circuit 5 is provided with a recessed hole corresponding to the shape of the conductive fine particles. The parallelism of the heater tool with respect to the pressed circuit component may be relatively gentle, and the flatness of the surface of the heater tool itself may be relatively gentle, so that the processing difficulty is low and therefore the processing cost can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal device used for a pocket TV, a wall TV, a projection TV, a laptop personal computer, a game machine and the like.

[0002]

2. Description of the Related Art Conventionally, connection terminals such as connection of semiconductors and semiconductor components to liquid crystal panels, connection of integrated circuits to photosensors, connection of surface mount components to various circuit boards, etc. As a connection method in the case where they are lined up relatively at a fine pitch, a method using soldering or conductive paste is widely used. However, in these methods, since the conductive connecting member must be formed only in the conductive circuit portion, it has been difficult to connect a fine circuit with high density and high definition. In recent years, the connection material of the circuit has been studied, and an anisotropic conductive adhesive member layer containing conductive fine particles and adhesive components obtained by metal plating metal particles or plastic particles between the opposing circuits is provided.
A method has been proposed in which pressure, heat pressure, or pressure light curing means is used to electrically connect the circuits and at the same time to provide insulation between the adjacent circuits, while adhering and fixing the circuits that face each other. ing.

As a method of connecting a circuit of a liquid crystal panel and another circuit board using such an anisotropic conductive adhesive,
For example, a circuit pattern of a copper foil is formed on a polyimide tape, and a semiconductor component having an IC mounted thereon is connected to a mounting terminal of a liquid crystal panel, or an IC chip is directly faced down so that a liquid crystal panel There is one that is connected on the connection circuit.

FIG. 6 shows an example of a conventional circuit board connecting method. In FIG. 6, a copper foil pattern 22 as a connecting circuit is formed on a TAB tape material 21 made of polyimide, and the copper foil pattern 22 is tin-plated. On the other hand, a connection circuit 24 is formed on the substrate of the liquid crystal panel 23, and the connection circuit 2
4 and the copper foil pattern 22 are electrically connected via an anisotropic conductive adhesive 25.

[0005]

Here, the anisotropic conductive adhesive 25 is one in which conductive particles 26 in which plastic particles are metal-plated are mixed and dispersed in an insulating adhesive layer. Before curing, it is in sheet form. The anisotropic conductive adhesive 25 is sandwiched between the connection circuit 24 and the copper foil pattern 22 in such a sheet-like state. Then, the conductive fine particles 26 are cured by being heated and pressed by the heater tool from above the circuit board.
Contacts both the connecting circuit 24 and the copper foil pattern 22. As a result, electrical connection between the connection circuit 24 and the copper foil pattern 22 is realized. As is apparent from FIG. 6, conventionally, pressure is applied to the extent that the deformation of the conductive fine particles 26 obtained by metal-plating plastic particles does not exceed its elastic limit.

On the other hand, in the circuit board as shown in FIG. 6, the connection pitch must be kept small, and therefore the size of the plastic particles must be quite small, such as about 5 to 10 μm in diameter. In general,
Polystyrene-based plastic particles are often used for metal plating, but polystyrene-based plastic particles have an extremely small elastic limit of about 5 kgw / cm ² . Therefore, in order to crush plastic particles having a small diameter of about 5 to 10 μm to the extent that the elastic limit is not exceeded, that is, to the extent that plastic particles do not crush or crack, the deformation amount must be suppressed to about 1 to 2 μm. I won't.

[0007] However, the deformation amount of the plastic particles is 1
A very difficult technique is required to control the thickness to about 2 μm. First, the heating and pressing by the heater tool must be performed with extremely good parallelism with respect to the pressing object, and the flatness of the heater tool itself must be obtained. Normally, the accuracy must be within 1 μm or less, but it is extremely difficult to achieve such high accuracy. Moreover, even if the heater tool is flat-polished at room temperature to maintain the flatness to an accuracy of 1 μm, it is not guaranteed that the flatness is maintained when heated, and the flatness usually decreases.

Further, the plastic particles must be pressed against the connecting circuit of the liquid crystal panel so weakly as not to exceed the elastic limit. In this case, the conductive connection between the conductive fine particles and the connecting circuit 24 of the liquid crystal panel is simply a contact. It is possible that the connection reliability of the connection circuit that is relatively facing is considerably reduced. Especially, when a thin oxide film is formed on the surface of the connecting circuit due to some influence.

In this way, the amount of crushing the plastic particles is made uniform, and the deformation amount of the plastic particles is 1 to
It is quite difficult to suppress the thickness to about 2 μm. Therefore, conventionally, the variation in the amount of deformation of the plastic particles becomes large in places, and in some places, the limit stress is exceeded and the plastic particles are deformed. As a result, the plastic particles are broken halfway, and the connection circuits are in contact with each other at points or in an extremely small area, resulting in considerably low connection reliability.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above-mentioned conventional drawbacks, improve the workability of connection between circuit boards, and improve the reliability of connection.

[0011]

According to the present invention, a liquid crystal is sandwiched between a pair of substrates, and a connection pattern for connecting to another circuit board is formed at an end portion of the board. The circuit board is a liquid crystal device connected through an anisotropic conductive adhesive containing conductive fine particles,
It is characterized in that a part of the connection pattern is formed with a recessed portion which is bitten by the conductive fine particles.

[0012]

1 and 2 show an embodiment of the present invention. FIG. 1 shows an example in which a TAB tape is mounted, and FIG. 2 shows an example in which an IC chip is directly mounted on a mounting terminal surface of a panel by a sectional view of a main part. Further, FIGS. 3, 4, and 5 are sectional views showing the connection portion of FIGS. 1 and 2 as a center and further in detail.
1 to 5, 1 is a TAB tape material, 2 is a copper foil pattern which is a connection circuit, and the copper foil pattern 2 is tin-plated. Reference numeral 3 is a liquid crystal panel, and 5 is a connecting circuit formed on a circuit board. In the figure, 6 is an anisotropic conductive adhesive present between the connection circuit 4 and the copper foil pattern 2, 7 is conductive fine particles, and 8 is an insulating adhesive layer. Further, 9 is an IC chip, and 10 is a gold bump which is a circuit for connecting the IC chip. Also 11, 13, 14
Indicates a conductive thin film layer, and 12 indicates an insulating thin film layer. The insulating thin film layer 12 may be intentionally formed, for example, in a process of forming a circuit pattern of a liquid crystal panel, or may be unconsciously formed when another conductive thin film such as ITO is formed on a metal thin film. It may be formed in.

The anisotropic conductive adhesive 6 composed of the insulating adhesive layer 8 and the conductive fine particles 7 is in the form of a sheet before curing, and in this state, it is placed between the connection circuit 5 and the copper foil pattern 2. It is pinched. Then, the circuit board is heated and pressed by a heater tool, whereby the anisotropic conductive adhesive 6 is cured, and the conductive fine particles 7 come into contact with both the connection circuit 5 and the copper foil pattern 2. Further, the connection circuit 5 is strongly pressed, and finally the connection circuit 5 is provided with a recessed hole corresponding to the shape of the conductive fine particles, and the conductive fine particles 7 are bitten into the connection circuit 5. Also, electrical connection between the connection circuit 5 and the copper foil pattern 2 can be achieved. In general, the insulating adhesive layer 8 uses a thermosetting adhesive as a base material and is made of, for example, a material in which an epoxy-based main material and a curing material are blended. When heating is performed by the heater tool, the coating material sprinkled around the curing material is melted, the main material reacts with the curing material, and the insulating adhesive 8 is cured.

As described above, when the conductive fine particles 7 are pressed into the connection circuit 5 of the liquid crystal panel in a simple and complete pressing direction until they are pressed, when the heater tool is pressed from above the TAB tape as the circuit board, the pressing is performed. The parallelism of the heater tool with respect to the circuit components used may be relatively gentle, and the flatness of the surface of the heater tool itself may be relatively gentle. Since the processing accuracy may be relatively gentle, the processing difficulty is low, and therefore the processing cost can be reduced.

Furthermore, recently, there has been a remarkable progress in liquid crystal panels, and in particular, there has been a remarkable progress in the development of active matrix panels such as MIM and TFT. Unlike a simple matrix panel such as STN, an active matrix panel is generally a multilayer wiring having two or more wiring patterns. For example, M
On the substrate on which the MIM element of the IM panel is formed, a tantalum thin film is formed in the lowermost layer, tantalum pentoxide which is a tantalum oxide film is formed in the second layer, and Cr and ITO are formed thereon. Of these layers, those constituting the mounting terminals are slightly different depending on the size of the panel, the purpose for which it is aimed, etc., but the tantalum (conductive thin film 11) and I as shown in FIG.
2 layer structure of TO (conductive thin film 13), 3 layer structure of tantalum (conductive thin film 11), tantalum pentoxide (insulating thin film 12), ITO (conductive thin film 13) as shown in FIG. 4, FIG. Tantalum (conductive thin film 11), tantalum pentoxide (insulating thin film 12), Cr (conductive thin film 13),
A four-layer structure of ITO (conductive thin film 14) can be considered. T
Similarly, in the FT substrate, the mounting terminal is composed of a plurality of thin film layers.

Of these, a mounting terminal structure having a three-layer structure of tantalum 11, tantalum pentoxide 12, and ITO 13 shown in FIG. 4 and tantalum 11, tantalum pentoxide 12, C shown in FIG.
In the four-layer structure mounting terminal structure of r13 and ITO14, since an insulating oxide film is formed between a plurality of conductive thin films, the presence of pinholes between the conductive thin film layers above and below the oxide film, etc. As a result, the resistance between the outermost surface and the lowermost layer varies greatly depending on the terminal. The more pinholes, the lower the resistance between the outermost surface and the lowermost layer, and the less pinholes, the higher the resistance. Here, as can be seen from FIG. 1 and FIG.
The connection circuit 2 of the TAB tape 1 and the gold bumps 10 of the IC chip 9 mounted face down are connected to the outermost surfaces (ITOs 13 and 14) of the mounting terminals, while the pixels inside the panel are connected. The bottom layer (tantalum 11) of the mounting terminals of the panel is often connected to the portion. In such a case, the signal from the external circuit or the drive IC is supplied from the outermost surface of the mounting terminal. Then, between the connection circuit 2 or the gold bumps 10 and the internal pattern of the panel, there is a resistance between the conductive thin film on the outermost surface and the conductive thin film on the lowermost layer of the connection circuit 5, which is a mounting terminal of the panel. In addition, the resistance between the uppermost conductive thin film and the lowermost conductive thin film will be greatly different depending on the terminal. However, the image quality of the liquid crystal panel is greatly affected by the resistance between the outermost conductive thin film and the lowermost conductive thin film of the panel connection circuit 5, so that if the resistance varies greatly, The image quality is significantly degraded, and in the worst case, it becomes a line defect. It is desirable to suppress such variations as much as possible by reducing the number of pinholes, but it is impossible to eliminate pinholes between thin films owing to the principle of sputtering and other thin film forming methods.

Therefore, it is necessary to positively increase the number of pinholes to similarly reduce the resistance between the outermost thin film layer and the lowermost thin film layer of the connection circuit 5. The present invention positively forms from the outside what corresponds to such a pinhole. That is, the conductive fine particles 7 present in the anisotropic conductive adhesive 6 positively strongly press the outermost surface layer of the connecting circuit 5, which is a mounting terminal on the panel, and pierce the oxide film to thereby break the connecting circuit 5. It is possible to uniformly reduce the resistance between the outermost thin film layer and the lowermost thin film layer.

As described above, the conductive fine particles are used to break through the oxide film layer of the connection circuit 5, so that when connecting a large number of TAB tapes 1 and IC chips 9, TAB is connected.
Variations in connection resistance between the tapes 1 or between the IC chips 9 are reduced, and as a result, reduction in image quality can be prevented. In addition, it is possible to easily write the image signal into the liquid crystal panel, which also improves the image quality. It is possible. Furthermore, by uniformly reducing the resistance between the outermost thin film layer and the lowermost thin film layer of the connection circuit 5, it is possible to significantly improve the connection reliability.

[0019]

As described above, according to the present invention, a liquid crystal is sandwiched between a pair of substrates, and a connection pattern for connecting to another circuit board is formed at an end portion of the board, and the connection terminals and A liquid crystal device, which is connected to the other circuit board via an anisotropic conductive adhesive containing conductive fine particles, wherein a part of the connection pattern is a recess depressed by the conductive fine particles. By forming the above, the image quality of the liquid crystal panel can be improved and the connection reliability of the connection circuit can be improved.

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part showing an embodiment of the present invention.

FIG. 2 is a cross-sectional view of an essential part showing an embodiment of the present invention.

FIG. 3 is a detailed cross-sectional view of a connection portion according to the embodiment of the present invention.

FIG. 4 is a detailed cross-sectional view of a connection portion according to the embodiment of the present invention.

FIG. 5 is a detailed cross-sectional view of a connection portion according to the embodiment of the present invention.

FIG. 6 is a sectional view of a main part showing a conventional technique.

[Explanation of symbols]

 1,21 TAB tape 2,22 Connection circuit on TAB tape 3,23 Liquid crystal panel 5,24 Connection circuit on liquid crystal panel 6,25 Anisotropic conductive adhesive 7,26 Conductive fine particles 8 Insulating adhesive Layer 9 IC chip 10 Gold bump 11 Conductive thin film 12 Insulating thin film 13 Conductive thin film 14 Conductive thin film

Claims (4)

[Claims] 1. A liquid crystal is sandwiched between a pair of substrates, a connection pattern for connecting to another circuit board is formed at an end of the substrate, and the connection pattern and the other circuit board are made of conductive fine particles. A liquid crystal device which is connected via an anisotropic conductive adhesive containing, wherein a part of the connection pattern is formed with a recess depressed by the conductive fine particles. Liquid crystal device. 2. The liquid crystal device according to claim 1, wherein the connection pattern has a laminated structure of at least two layers. 3. The connection pattern has a laminated structure in which an insulating layer is formed on a first conductive layer, and a second conductive layer is further formed on the insulating layer. 2. The recessed part which is bitten by the conductive fine particles is formed in a part of the second conductive layer.
The liquid crystal device described. 4. The connection pattern has an insulating layer formed on a first conductive layer, a second conductive layer formed on the insulating layer, and a second conductive layer formed on the second conductive layer. 3 has a laminated structure in which the conductive layer is formed, and the insulating fine layer, the second conductive layer, and a part of the third conductive layer are formed with a recessed portion which is cut into by the conductive fine particles. The liquid crystal device according to claim 1, wherein