JPH03184023A - Joint structure of liquid crystal panel and joining method thereof - Google Patents

Abstract

PURPOSE:To largely relieve a thermal stress and to improve a reliability characteristic by electrically joining an electrode and a joining electrode positioned in an overhang part via an anisotropic conductive adhesive. CONSTITUTION:The anisotropic conductive adhesive is applied or stuck on the electrode formed at the substrate end of a liquid crystal panel and the joining electrode 11 consisting of a conductive layer is formed on a film base material. The joining electrode 11 positioned in the overhang part 15 exposed with the joining electrode 11 exclusive of a part of the film base material is registered with the electrode and the electrodes are pressurized and joined by a heating means from above the joining electrode 11, by which the electrodes are electrically connected. A heating tool 16 directly presses the joining electrode 11 from above and imposes the rear surface of electrode glass 9 onto a tool rest and, therefore, the joining electrode 11 is strongly pressed to the anisotropic conductive adhesive 10 and the metallic particles (many) coexisting in the anisotropic conductive adhesive 10 are deformed or gnawed into the rear surface of the joining electrode 11. Thus, the sure electrical connection is executed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for bonding electrode groups of a mounted body having a large number of electrodes (electrode groups) in a mounted body such as a display panel using liquid crystal or EL. The present invention relates to a joining structure and a joining method thereof.

[Conventional technology]

With reference to FIGS. 2 to 5, a conventional configuration will be explained using a liquid crystal display panel as an example. The mounting of the driving ICI on the liquid crystal display panel is as shown in Figure 2.
The AB tape 2 is bonded using a well-known TAB (tape automatic bonding) method, as shown in FIG. 4, using a well-known bonding agent 3. Regarding the bonding agent 3, solder, anisotropic conductive adhesive, etc. have been put into practical use, but recently, insulating adhesives (for example, U
Examples of V-curing adhesives, thermosetting adhesives, and instant adhesives have been reported.

(IEICE Technical Report Vol. 1.85.tt35 (1986
, 3)) This is based on the idea of fixing the contact continuity between the electrode groups with an adhesive.

Another method is to mount the driving ICI on the printed circuit board 4 by wire bonding, as shown in FIG.
As shown in FIG. 5, the flexible printed wiring board 6 was bonded in the same manner as described above.

[Problem to be solved by the invention]

Recently, there has been a rapid increase in the number of devices that display text or images using display panels that utilize liquid crystals or EL. This is simply because these display panels have the excellent characteristics of being able to be made thinner and moreover, have the potential to be made at low cost.

However, in order to achieve clearer images and higher definition, it is necessary to increase the number of scanning lines formed on these display panels. Increasing the number of scanning lines is
This means that the number of drive electrodes in the display panel also increases proportionally. An increase in the number of drive electrodes results in an increase in the number of drive ICs for driving the display panel.

Therefore, when considering the improvement of the performance of liquid crystal display panels, etc., the number of bonding points between the drive IC and the display panel inevitably increases, and the pitch of the bonding electrode group becomes smaller, which reduces the reliability of the bonding. Not only is this decreasing, but it also has a large impact on implementation costs, which is a major barrier to practical application.

When we investigated the factors that prevented us from improving the performance of display panels using conventional methods, we found the following as the biggest factor. In other words, the organic film 8 used in the flexible printed wiring board 6 used for connection or the tape 2 for TAB (tape automatic bonding)
and electrode glass 9 used in display panels.
This was found to be due to the large difference in thermal expansion between the two. The electrode glass 9 has a thermal expansion coefficient of αc-4. oxto-', and the organic film 8 has αt =2.2xio-'. Since the minus digit of this coefficient is also different, the thermal stress applied to the electrical junction is large, and is beyond the range of stress that can be withstood by a structure in which conduction is achieved through mere contact. Furthermore, in order to improve performance, the bonding pitch has become narrower, and the contact area per wire has become smaller.

The present invention aims to solve these problems, and its purpose is to provide a liquid crystal panel bonding structure and its structure that can greatly alleviate this thermal stress and greatly improve reliability characteristics. The purpose is to provide a joining method.

[Means to solve the problem]

(1) The bonding structure of the liquid crystal panel of the present invention includes an electrode formed on the edge of the substrate of the liquid crystal panel, and a bonding electrode made of a conductive layer on the film base material, and the edge of the film base material is formed on the edge of the film base material. The bonding electrode has an overhang portion in which the bonding electrode is exposed with a portion remaining, and the electrode and the bonding electrode located in the overhang portion are electrically bonded via an anisotropic conductive adhesive. do.

(2) The method for bonding a liquid crystal panel of the present invention involves coating or pasting an anisotropic conductive adhesive on the electrodes formed on the edge of the substrate of the liquid crystal panel, and applying a bonding electrode made of a conductive layer on a film base material. is formed, and the bonding electrode is positioned at the overhang part where the bonding electrode is exposed, leaving a part of the edge of the film base material, and the bonding electrode is aligned, and pressure is applied from above the bonding electrode by heating means. It is characterized by being bonded and electrically connected.

(3) Furthermore, in the method for bonding liquid crystal panels of the present invention, a bonding electrode made of a conductive layer is formed on a film base material, and an overhang where the bonding electrode is exposed is formed by leaving a part of the edge of the film base material. An anisotropic conductive adhesive is applied or pasted on the bonding electrode located at the edge of the substrate, and the bonding electrode is aligned with the electrode formed on the edge of the substrate of the liquid crystal panel, and heating means is applied from above the bonding electrode. It is characterized by pressure bonding and electrical bonding.

[For production]

The effect was analyzed in detail using an anisotropic conductive adhesive and will be explained below.

When an anisotropic conductive adhesive is used, it is bonded to the electrode glass 9, which is the substrate of the liquid crystal display panel, using a thermocompression bonding method. Since the thermal expansion coefficients of the film 8 and the electrode glass 9, such as soda-based glass or quartz glass, are significantly different, distortion occurs in the bonded portion during thermocompression bonding.

This strain remains in the joint as residual stress even after joining, and
Decreases reliability. Regarding this residual stress, the maximum stress applied to the joint was estimated using a model sample using the finite element method. The results are shown in Figure 6.

It can be seen that there is a large difference depending on the thickness of the organic film 8 of the TAB tape 2, and it can be seen that the thinner the organic film 8, the smaller the residual stress. At the same time, it can also be inferred that the residual stress at the joint without the organic film 8 is extremely small. It is thought that similar stress is added even more during times of cold or heat.

We also investigated how the reliability of the bonding resistance with the electrode glass 9 changes depending on the thickness of the organic film 8. The test method was a cold/hot cycle test, and the thickness of the organic film 8 was 75μ and 25μ, and O in the diagram of FIG.
What is indicated by μ is the above-mentioned overhang portion, the details of which are shown in FIG. This TAB
The film 8 used for the tape 2 has a thickness of 125μ. The results are shown in FIG.

As can be seen from FIG. 7, the thickness of the organic film 8 is Oμ
(The overhang portion, that is, the state where the bonding electrode 11 protrudes from the organic film 8) has the most stable bonding resistance. It can be seen that the overhang structure is the best structure.

Next, we investigated how well this overhang structure and other structures could withstand stress and how strong they were.

As an evaluation method, strain was generated by applying bending stress to the joint portion. 1.6m thick glass
A flexible printed circuit board made by applying gold plating to the entire surface of an epoxy copper-clad laminate and applying tin plating to this,
The TAB tape 2 on the overhang part is joined with an anisotropic conductive adhesive 10, and pressure is applied as shown in FIG. gives distortion to. Then, the change in junction resistance at point A was observed, and the amount of strain when the junction resistance became 10 times or more of the initial value (open) was measured. The results were as shown in Figure 8.

In Fig. 8, the thickness of the organic film 8 is 25μ and the thickness of Oμ (overhang part) includes an open junction resistance due to bending breakage of the glass epoxy.
The oven distortion values are also close. However, if the breaking strain of the glass epoxy resin had been larger, the difference between 25μ and the overhang portion would have been more significant.

In addition, in this bending stress, as shown in FIGS. 15 and 16, the overhang structure relieves the stress applied to the joint by bending the joining electrode 11 on the TAB tape 2 side. FIG. 15 and FIG. 16 are sample sketch diagrams.

This is because the thinner the bonding pitch, the greater the effect of stress relaxation (because the bonding electrode 11 becomes thinner, the bending strength becomes weaker). See FIG. 16.

Furthermore, the plane spacing between the electrode glass 9 and the organic film 8 (FIGS. 15A and 16B) is important as it plays a role in relieving stress, but this size depends on the thickness and width of the bonding electrode 11. is greatly related to.

When the bonding electrode 11 is a TAB tape of 35μ thick copper foil, which can be made larger if it is thicker or smaller if it is thinner,
If A and B are 0.5 m or more, there will be almost no problem and reliability can be ensured.

〔Example〕

Next, examples will be described. The electrode 12 (see FIG. 1) on the electrode glass 9 of the liquid crystal display panel is
The film thickness is approximately 500 (actually 100 to 5000 is possible) and the sheet resistance is approximately 500.
It is ΩO.

On the other hand, in the TAB tape 2 on which the drive-like ICI is inner-lead bonded, the organic film 8 is a polyimide (Kapton) film with a thickness of 125 μm, and the copper foil pattern 14 as a conductive layer is 35 μm thick. is 0.5
It has a μ-thick sparrow. Further, the bonding electrode 11, which is an extension of the copper foil pattern 14, forms an overhang portion and is exposed to the left side of the film 8 in FIG.

Next, the procedure will be explained briefly using FIG. The anisotropic conductive adhesive 10 is bonded or applied to the electrode 12 on the electrode glass 9 using a roll or press.

Next, the bonding electrode 11 of the TAB tape 2 is aligned with the electrode 12. When the alignment is completed, pressure bonding is performed using a heating tool 16 that has been subjected to a non-adhesive treatment.

As shown in FIG. 1, the heating tool 16 directly presses the bonding electrode 11 from above, and the lower surface of the electrode glass 9 is placed on the tool holder, so the bonding electrode 11 is strongly pressed against the anisotropic conductive adhesive 10 and causes abnormality. Since the metal particles (a large number) mixed in the directional conductive adhesive 10 are deformed or embedded into the lower surface of the bonding electrode 11, the electrical connection is ensured.

Next, press out is performed after waiting for time for the anisotropic conductive adhesive 10 to flow sufficiently. After being pressed out, strong adhesion is completed by natural cooling.

The surface of the bonding electrode 11 is covered with semi-old plating, semi-old plating,
I considered gold plating, but the results were similar. Furthermore, regarding the bonding of the anisotropic conductive adhesive 10, there are two methods: one method is to bond it to the electrode glass 9 side, and the other is to bond it to the TAB tape 2 side, but the results were the same in both cases. .

Furthermore, the bonding pitch of each electrode is 0.3, 0.
Three types, 25 mm and 0.19 am, were examined, and similar trends were found.

A reliability test was carried out using TAB tape 2 made of a 125 μm polyimide film to form an overhang structure at the joint with the panel 7, and the reliability of the panel module was evaluated by changing the connection resistance. The results are shown in Figure 10~
It is shown in Figure 13.

In FIG. 1, an end portion 8a of the film 8 is provided at the tip of each bonding electrode 11 to connect the bonding electrodes. This end portion 8a may be connected to the film 8 (right end side in FIG. 1) through the side, or may be separated and become a separate body. It is arranged on a plane away from the adhesive 1o. 15 and 16 show the overhang portion 15, and the lower end thereof is not provided with the end portion 8a as in FIG. 1, but the joint 1
The i-pole 11 may be extended downward, and the end portion 8a of the film 8 may be formed at the lower end of the i-pole 11. In that case, the end portion 8a may be connected to the film 8 above on both sides, or may be separated. In this case, 8a shall be formed below the anisotropic conductive adhesive 1o so as not to overlap in plane.

〔Effect of the invention〕

With conventional methods, reliability tests, such as thermal and thermal tests, lasted only about 100 cycles (in the module state), but now they can last three times as many as 300 cycles, significantly increasing the reliability of panel modules. improved.

FIG. 14 shows a comparison between the conventional method and the method according to the present invention in terms of junction resistance. As we will see, there is a clear difference.

In FIG. 14, to further explain the difference between the conventional method and the method of the present invention, in the present invention, the bonding electrode 11 is directly pressed with a pressure bonding tool, whereas in the conventional method, Since the organic film 8 is present between the bonding electrode 11 and the pressure bonding tool, the metal particles in the anisotropic conductive adhesive lo are not crushed under sufficient pressure.

In the method of the present invention, the electrode glass 9 is sufficiently crushed, and the distance between the electrode glass 9 and the bonding electrode 11 is narrow, for example, 4μ or less, and setting it to 4μ or less improves the reliability of bonding. This is also one of the reasons why.

[Brief explanation of drawings]

FIG. 1: A diagram of an electrode bonding structure using TAB of the present invention. FIGS. 2 to 5: Joint structure diagrams illustrating the prior art. FIGS. 6 to 8 are explanatory diagrams of the actions leading up to the present invention. FIG. 9: A diagram showing the procedure for implementing the present invention. Figures 10 to 12: Reliability characteristic diagrams of the present invention. FIG. 13: Reliability diagram of a module using the present invention. FIG. 14: A diagram showing an example of reliability comparison between the present invention and the prior art. Fig. 15, Fig. 16... Diagrams showing the state of stress relaxation in the present invention. 1... Drive IC 2... TAB tape 3... Adhesive 4... Printed circuit board 5... Bonding wire 6... Flexible printed wiring board 7... Panel 8... Organic system Film (film) 9... Electrode glass 10... Anisotropic conductive adhesive 11... Bonding electrode 12... Electrode 13... Molding agent 14... Copper foil pattern 15... Over Above the hang part

Claims (3)

[Claims] (1) An electrode formed at the edge of a substrate of a liquid crystal panel and a bonding electrode made of a conductive layer formed on a film base material, and an overlay where the bonding electrode is exposed, leaving a portion of the edge of the film base material. What is claimed is: 1. A bonding structure for a liquid crystal panel, comprising a hang portion, and wherein the electrode and a bonding electrode located in the overhang portion are electrically bonded via an anisotropic conductive adhesive. (2) An anisotropic conductive adhesive is applied or pasted on the electrode formed on the edge of the substrate of the liquid crystal panel, and a bonding electrode consisting of a conductive layer is formed on the film base material, and the bonding electrode is formed on the film base material. Aligning the electrode with the bonding electrode located in the overhang part where the bonding electrode is exposed, leaving a part of the end portion, and pressurizing and bonding with heating means from above the bonding electrode,
A method for joining liquid crystal panels characterized by electrical connection. (3) A bonding electrode made of a conductive layer is formed on a film base material, and an anisotropic conductive layer is formed on the bonding electrode located in an overhang part where the bonding electrode is exposed, leaving a part of the edge of the film base material. Applying or pasting an adhesive, aligning the electrode formed on the edge of the substrate of the liquid crystal panel with the bonding electrode, and bonding the bonding electrode under pressure using heating means from above the bonding electrode to electrically bond the bonding electrode. A method for bonding liquid crystal panels characterized by: