JP4086296B2 - Lead electrode connection structure - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a connection structure of the lead electrodes, and more particularly, to a technique for preventing corrosion due to moisture counterpart substrate of the lead electrodes which are connected to the flexible wiring board.
[0002]
[Prior art]
Since flexible wiring boards are flexible, they are often used as relay boards for connecting electrical components or electrical circuits. In the field of liquid crystal display elements, TCP (tape carrier package), COF (chip on film), and the like are used as a flexible wiring board for connecting a display panel such as a liquid crystal panel or an organic EL panel and its drive circuit board.
[0003]
Flexible wiring board connection methods include mechanical connection methods using connectors, soldering methods, and connection methods using conductive bonding means. When connecting a flexible wiring board to a display panel, a large number of lead electrodes must be connected to each other. A connection method using a conductive adhesive means that can be connected in a batch is preferably employed.
[0004]
An example thereof will be described with reference to FIG. FIG. 3 is a cross-sectional view showing the electrode connection portion of the flexible wiring board 10 and the electrode connection portion of the display panel 20 separately. The lead electrode 12 on the flexible wiring board 10 side is formed on the base film 11 and is displayed. The lead electrode 22 on the panel 20 side is formed on a terminal portion 21 made of a glass substrate.
[0005]
In order to connect the lead electrode 12 on the flexible wiring board 10 side and the lead electrode 22 on the display panel 20 side through conductive adhesive means, for example, an anisotropic conductive film (ACF: As conductive adhesive means) between them. Anisotropic Conductive Film) 30 is placed and thermocompression bonded with a heater bar (not shown).
[0006]
By this thermocompression bonding, the conductive particles contained in the anisotropic conductive film 30 electrically connect the lead electrodes 12 and 22, and the flexible wiring substrate 10 and the liquid crystal panel 20 are bonded by the adhesive action of the synthetic resin of the film material. The terminal portion 21 is mechanically connected.
[0007]
By the way, the lead electrode 22 on the display panel 20 side is made of ITO (indium tin oxide) like the transparent electrode, and has a specific resistance of 200 μΩcm and a film thickness of about 100 nm. Therefore, its sheet resistance is about 20Ω / □. . On the other hand, the lead electrode 12 on the flexible wiring board 10 side is made of a copper foil, which is a metal layer, and has a specific resistance of 2.5 μΩcm and a film thickness of about 25 μm. It is.
[0008]
As described above, when two lead electrodes 12 and 22 having greatly different sheet resistances are connected via the anisotropic conductive film 30, current concentrates on the connection surface side of the copper foil having a small electric resistance. Such uneven distribution of current is not preferable because it reduces the reliability of the electrode connecting portion and promotes deterioration.
[0009]
For example, the conductive particles contained in the anisotropic conductive film 30 are burned out with a current of about 5 mA per particle. Therefore, it becomes a serious problem when a current of about 5 mA or more flows per particle.
[0010]
In the case of a voltage-driven liquid crystal panel, the amount of current flowing through the connecting portion of the lead electrode by the anisotropic conductive film 30 is on the order of several tens of μA. Since the large current flows into the connecting portion of the lead electrode by the anisotropic conductive film 30, it becomes a big problem.
[0011]
For example, when an organic EL panel having a pixel size of 300 μm □ and 100 anodes is driven at a duty of 1/64, assuming that the light emission efficiency is 0.5 cd / A, when lighting with an average luminance of 300 cd / m ² In the selection period, the current flowing into the cathode is 345.6 mA. When such a large current is passed through the connecting portion of the lead electrode by the anisotropic conductive film 30, the current is concentrated on a part and the conductive particles are burned out.
[0012]
In that case, since the burned conductive particles have a high electrical resistance, the portion where the current easily flows gradually moves inside the connection. However, since the current is localized there, the conductive particles still burn out. In this way, the increase in electrical resistance of the anisotropic conductive film 30 propagates inside, and if a large current continues to flow, the electrical connection by the anisotropic conductive film 30 is eventually lost.
[0013]
Therefore, in order to prevent such localization of current, particularly in an organic EL panel, as shown in FIG. 5, a metal electrode 23 having a small electric resistance is formed on a lead electrode 22 made of ITO on the display panel 20 side. Thus, the difference in sheet resistance with the lead electrode 12 on the flexible wiring board 10 side is made as small as possible.
[0014]
As the metal electrode 23, Al or Al alloy, Mo or Mo alloy, Cr or Cr alloy, Ag alloy, or the like is used. However, in some models of not only organic EL panels but also voltage-driven liquid crystal panels, A metal electrode 23 is formed on the lead electrode 22 made of ITO on the display panel 20 side to reduce the wiring resistance from the electrode connection portion by the anisotropic conductive film 30 to the display portion.
[0015]
[Problems to be solved by the invention]
However, as the metal electrode 23 is formed on the lead electrode 22 on the display panel 20 side, another problem arises, that is, the metal electrode 23 is corroded by moisture.
[0016]
The cause is on the flexible wiring board 10 side. Since the flexible wiring board 10 is required to have heat resistance, a polyimide film having good heat resistance is usually used for the base film 11, but the polyimide film has high moisture permeability. Incidentally, the moisture permeability of the polyimide film is 0.1 mm, and the measured value according to JIS-Z0208 is about 20 g / m ² · 24 hr.
[0017]
For this reason, moisture enters the connecting portion of the lead electrode through the base film 11, thereby causing the metal electrode 23 to be corroded. In some cases, the lead electrode 22 made of ITO may also be corroded. This electrode corrosion causes an increase in connection resistance and, in the worst case, disconnection. This problem is particularly serious in an organic EL panel that is a current-driven display element in which a large current flows through the connection portion of the lead electrode.
[0018]
Therefore, an object of the present invention is to prevent moisture from penetrating into the connecting portion of the lead electrode from the side of the flexible wiring board when the flexible wiring board is connected to the counterpart substrate via the conductive adhesive means.
[0019]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention provides a first lead electrode made of a metal layer exposed at an electrode connection portion of a flexible wiring board, a second lead electrode exposed at an electrode connection portion of a counterpart substrate, In the connection structure of the lead electrode to connect through the conductive adhesive means,
A moisture permeation preventing material is formed along both sides of the first lead electrode so as to be wider than the width of the second lead electrode, and the second lead electrode is viewed from the base film side of the flexible wiring board. The lead electrode is present in the projection plane on the first lead electrode side including the moisture permeation preventive material .
[0020]
The moisture permeability of the moisture permeation preventive material used in the present invention is preferably 10 g / m ² · 24 hr or less as measured by JIS-Z0208.
[0021]
Moreover, in this invention, there is no restriction | limiting in particular in the other party board | substrate connected with a flexible wiring board, and its lead electrode. That is, the present invention has a remarkable effect when the counterpart substrate is a current-driven organic EL panel and has a metal electrode, but the counterpart substrate is a voltage-driven liquid crystal display element or other circuit board. Moreover, the lead electrode of the counterpart substrate may be either an ITO electrode or a metal electrode.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
First, a reference embodiment of the present invention will be described with reference to FIG . FIG. 1 is an enlarged cross-sectional view of the main part showing the electrode connection portion of the flexible wiring board 10 and the electrode connection portion of the display panel 20 separately as in FIG. 3 described above.
[0023]
The basic configuration may be the same as that of the conventional example of FIG. 3 , and the lead electrode 12 on the flexible wiring board 10 side is made of a copper foil pattern formed on a base film 11 made of polyimide, and the display panel A metal electrode 23 is formed on the lead electrode 22 made of ITO at the electrode connecting portion 20.
[0024]
Te this reference embodiment smell, the width of the display panel 20 side of the metal electrode 23 with the lead electrodes 22 and W1, the width of the flexible wiring board 10 side of the lead electrode 12 as W2, the metal width W2 of the lead electrode 12 It is made to be wider than the width W1 with electrode 23 of the lead electrode 22 (W2> W1).
[0025]
When connecting the electrode connection portion of the flexible wiring board 10 and the electrode connection portion of the display panel 20 via, for example, the anisotropic conductive film 30, the lead electrode 12 and the lead electrode 22 with the metal electrode 23 are in the center. Are aligned to match.
[0026]
When connected in this aligned state, the lead electrode 22 with the metal electrode 23 on the liquid crystal panel 20 side is present in the projection plane of the lead electrode 12 when viewed from the base film 11 side of the flexible wiring board 10. Will do.
[0027]
The lead electrode 12 is made of a copper foil, and its moisture permeability is a value that cannot be measured and hardly allows moisture to pass through. Therefore, the penetration of moisture into the lead electrode connection portion from the flexible wiring board 10 side is prevented, and corrosion of the metal electrode 23 and the lead electrode (ITO electrode) 22 is prevented. In addition, since the lead electrode 12 on the flexible wiring substrate 10 side is usually plated with gold, there is no possibility that the lead electrode 12 is also corroded.
[0028]
It will now be described implementation form of the present invention by FIG. In implementation form of this, in a manner different from that described above referential embodiment, to prevent the penetration of moisture to the read electrode connection portion from the flexible wiring board 10 side.
[0029]
That is, the width of the lead electrode 12 on the flexible wiring board 10 side may be the same width as or narrower than the width W1 of the lead electrode 22 with the metal electrode 23 on the display panel 20 side. The moisture permeation preventing materials 13 and 13 are formed along both sides of the electrode 12 so that the entire width W2 on the lead electrode 12 side including the moisture permeation preventing materials 13 and 13 satisfies W2> W1.
[0030]
In the present invention, the moisture permeability of the moisture permeation preventing materials 13 and 15 is preferably 10 g / m ² · 24 hr or less as measured by JIS-Z0208 (40 ° C., relative humidity 90%).
[0031]
Examples of moisture permeation prevention materials that satisfy this condition include polyethylene terephthalate (5.5 g / m ² · 24 hr), polypropylene (1.5 g / m ² · 24 hr), polyethylene (5.0 g / m ² · 24 hr), poly An example is vinylidene chloride (1.0 g / m ² · 24 hr) (all thicknesses are 0.1 mm thick).
[0032]
【The invention's effect】
As described above, according to the present invention, in order to connect with the counterpart substrate through a conductive adhesive means a flexible wiring board, opposing counterpart substrate moisture permeation prevention member on either side of the full Rekishiburu wiring board side of the lead electrode by the Ruco be formed to be wider than the width of the lead electrode, since the moisture penetration from the flexible wiring board side to connecting portions of the lead electrodes is prevented, it is possible to prevent corrosion of the counter lead electrode due to moisture, A reliable connection state can be obtained.
[Brief description of the drawings]
FIG. 1 is an enlarged cross-sectional view of a main part showing a reference embodiment according to a lead electrode connection structure of the present invention.
[Figure 2] enlarged sectional view showing the implementation form engagement Ru connection structure of the lead electrode of the present invention.
FIG. 3 is an enlarged sectional view showing a conventional lead electrode connection structure;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10, 10A, 10B Flexible wiring board 11 Base film 12 Lead electrode 13, 15 Moisture permeable prevention material 20 Display panel 21 Terminal part 22 Lead electrode 23 Metal electrode 30 Anisotropic conductive film

Claims (2)

A lead electrode for connecting a first lead electrode made of a metal layer exposed at the electrode connection portion of the flexible wiring board and a second lead electrode exposed at the electrode connection portion of the counterpart substrate through a conductive adhesive means In the connection structure of
A moisture permeation preventing material is formed along both sides of the first lead electrode so as to be wider than the width of the second lead electrode, and the second lead electrode is viewed from the base film side of the flexible wiring board. A lead electrode connection structure, wherein the lead electrode is present in a projection plane on the first lead electrode side including the moisture permeation preventing material. The lead electrode connection structure according to claim 1 , wherein the moisture permeability preventing material has a moisture permeability of 10 g / m ² · 24 hr or less.

Images