JPH0749731Y2 - Flexible board connection structure - Google Patents

Description

[Detailed Description of the Invention] "Industrial field of application" The present invention relates to a flexible substrate connection structure mainly used for connecting a liquid crystal display dot matrix unit (hereinafter referred to as LCD) and a printed circuit board having an output terminal. Is.

"Conventional technology and its problems" LCD units have been rapidly developed recently, and for example, large LCD units such as 640 x 200 dots, 640 x 400 dots, and 12-inch size were put to practical use. There is. L
While the CD unit becomes larger, the dot pitch is made smaller, and so-called fine pitches such as 0.4 mm pitch and 0.35 mm pitch are adopted.

There is known an anisotropic conductive film connection method in which such an LCD unit and a printed circuit board having an output terminal are connected via an anisotropic conductive film and a flexible substrate.
That is, for example, as shown in FIGS. 4 and 5, the transparent electrode 2 of the LCD unit 1 is connected to the terminal 4 of the flexible substrate 3 via the anisotropic conductive film 5. In addition, the terminals 4 of the other part of the flexible substrate 3 and the output terminals 7 of the printed circuit board 6 are connected via another anisotropic conductive film 8. Gold plating 9 is coated on any of the terminals 4 of the flexible substrate 3, while an intermediate portion thereof is coated with an ink cover lay 10.

However, the anisotropic conductive films 5 and 8 are, for example, those obtained by embedding a conductive material such as nickel particles in a styrene-butadiene-based resin, and are vulnerable to high temperature or high temperature and high humidity.
When the anisotropic conductive films 5 and 8 are connected to the flexible substrate 3, the gold plating 9 cannot be heated sufficiently to melt.
As a result, for example, as shown in FIG. 4, there is a problem in that the gold plating and the conductive particles 5a of the anisotropic conductive film 5 are not well fitted to each other, and the reliability of the connection is anxious.

Therefore, the gold plating 9 on the terminals 4 of the flexible substrate 3 is further subjected to solder plating having a relatively low melting point, and the flexible substrate 3 and the anisotropic conductive film 5 are interposed via the solder plating.
Tried to connect. In this case, the connection between the solder plating and the conductive material 5a of the anisotropic conductive film 5 was good, and the flexible substrate 3 and the anisotropic conductive film 5 could be connected with a predetermined reliability.

Further, in order to compare with the above-mentioned configuration, at the connection portion of the terminals of the flexible board 3 and the printed board 6, the same solder plating as above is applied on the gold plating of the terminals 4 of the flexible board 3, while As a result of attempting to directly solder the flexible substrate 3 and the printed circuit board 6 without using a conductive film, the reliability of the connection between the flexible substrate 3 and the printed circuit board 6 could not be obtained.

However, even in the former configuration, that is, in the configuration in which the flexible substrate 3 and the anisotropic conductive film are connected via gold plating and solder plating, a (gold-solder) alloy is formed at the joint between gold plating and solder plating. It turns out that the organization is so fragile that there are concerns about the stability of the connection.

"Purpose of Invention" The present invention was made in consideration of the above circumstances.
An object of the present invention is to provide a connection structure for a flexible substrate, which has high connection reliability and stability with an anisotropic conductive film.

[Means for Solving Problems] In order to achieve the above object, the present invention provides a terminal of a substrate to be connected through an anisotropic conductive film in which conductive particles are embedded in a synthetic resin. On the premise of the connection structure of the flexible substrate having the connection portion to be connected to, the terminals of the connection portion are covered with solder plating having a film thickness of about 2 μm to about 6 μm, and one of the conductive particles of the anisotropic conductive film is A flexible substrate connection structure is employed in which parts are heated and connected so as to bite into the solder plating.

According to this structure, the solder plating is excellent in bonding strength to the terminals of the flexible substrate and can be melted at a relatively low temperature, so that the synthetic resin forming the anisotropic conductive film is not anisotropically transformed. Can be bonded to a conductive conductive film. Moreover, the melting of the solder plating causes some of the conductive particles in the anisotropic conductive film to bite into the solder plating, thereby firmly bonding the solder plating and the anisotropic conductive film. Will be.

The connected board in the above configuration is exemplified by an LCD unit, a printed board to which the LCD unit is connected, and the like.

In the above, the thickness of the solder plating is about 2 μm to about 6 μm
It was confirmed that the above range is preferable, and such a film thickness does not cause deterioration in reliability due to oxidation of the solder plating. On the contrary, when the thickness of the solder plating is 1 μm or less, the connection reliability with the anisotropic conductive film is drastically reduced, while when the thickness is 8 μm or more, excess solder is generated from the terminals during heating. It is not preferable because it may flow out and cause a short circuit with other terminals.

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

FIG. 1 is a vertical sectional view of an embodiment of the present invention, FIG. 2 is a plan view, and FIG. 3 is an enlarged sectional view of a main part thereof.
In this embodiment, the connected substrate referred to in the present invention is
A printed circuit board to which the D unit and the LCD unit are connected is provided, and the connection structure of the flexible substrate to the LCD unit is shown in FIG.

In this embodiment, the LCD unit 1 has a flexible substrate 3a.
~ 3e while connecting one side, each flexible board 3a ~
The other end of 3e is connected to predetermined printed boards 6a to 6c, respectively.

The LCD unit 1 has a well-known structure and is formed by laminating a pair of glass substrates 1a and 1b via a micro space (not shown) in which a liquid crystal for display is sealed. In addition, each of the above glass substrates 1
The a and 1b are cut so that the vertical and horizontal dimensions are different, and thereby, for example, in a region of each glass substrate 1a (1b) protruding from the end of the other glass substrate 1b (1a), for example, oxidized. The horizontal scanning electrodes 2 and the vertical scanning electrodes (not shown because they appear on the lower surface side) formed of a transparent thin film made of indium (ITO) appear as terminals connected to the flexible substrates 3a to 3e.

The horizontal scanning electrode 2 is formed on the upper left side of the glass substrate 1b at a position corresponding to the left vertical side of the LCD unit 1, while the vertical scanning electrode is at a position corresponding to both upper and lower horizontal sides. It is formed on the lower surface side of the glass substrate 1a.

Further, the printed boards 6a, 6b, 6c are arranged so as to face the three sides of the LCD unit 1, and Cu electroless and electrolytic plating is performed on a substrate made of glass / epoxy resin.
A lead wire having a predetermined pattern is formed by a method of etching or electrolytic plating of solder, and an output terminal to be connected to the LCD unit 1 on the peripheral edge of the printed circuit boards 6a, 6b, 6c so as to be connected to the lead wire. 7 is appearing. The lead wire portion is covered and protected by a resist 13 except the output terminal 7.

Further, in each of the flexible boards 3a to 3e, a Cu foil or the like is adhered (adhered) to the base material 3 made of, for example, a polyimide resin, and a required number of terminals 4 are formed at both ends by a method such as etching or electrolytic plating. Each terminal 4 is covered with an ink cover lay 10 except both ends thereof.

The present invention is applied to all the connection structures of the flexible substrates 3a to 3e having such a configuration, and the connection structure between the flexible substrate 3e and the horizontal scanning electrodes 2 of the LCD unit 1 will be described as an example (first). (See Figure 3).

That is, the surface of the terminal 4 as the connecting portion of the flexible substrate 3e is solder-plated with a film thickness of about 2 μm to about 6 μm.
An anisotropic conductive film 5 having a structure in which conductive particles 5a are embedded in a synthetic resin is laminated on the solder plating 11 as in the conventional case.

As shown in FIG. 3, the solder plating 11 and the anisotropic conductive film 5 are formed by a part of the conductive particles 5a in the anisotropic conductive film 5.
It is connected to the solder plating 11 so as to penetrate into the solder plating 11. Such a configuration can be achieved by melting the solder plating 11 with a heating means such as infrared heating while closely contacting the solder plating 11 and the anisotropic conductive film 5.

According to the above configuration, generally solder plating 11 having a relatively melting point is used.
Since it is connected to the anisotropic conductive film 5, the solder plating 11 and the terminal 4 can be firmly bonded to each other without changing the synthetic resin component of the anisotropic conductive film 5 during the heating. This makes it possible to obtain excellent connection reliability.

Further, in the past, in order to secure reliability for connection for 1000 hours in a stored state, a temperature of 40 ° C. and a humidity of 90% were required, but in the above-mentioned embodiment, a temperature of 55 ° C. and a humidity more severe than this.
We were able to secure the reliability of the required connections even after 1000 hours under 95% conditions.

[Advantage of Invention] As described above, according to the flexible board connection structure of the present invention, the terminal surface of the connection portion formed on the flexible board is coated with the solder plating having a film thickness of about 2 μm to about 6 μm. Compared to the conventional flexible board where the terminal surface is plated with gold, it can be more firmly connected to the anisotropic conductive film,
The reliability of the connection and the stability of the connection can be improved.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of an embodiment of the present invention, FIG. 2 is a plan view thereof, FIG. 3 is an enlarged vertical sectional view schematically showing a connecting mechanism of an LCD unit and a flexible substrate, and FIG. FIG. 5 is a vertical cross-sectional view showing a connection structure of a conventional flexible substrate and a connecting portion of an LCD unit and a printed circuit board, and FIG. 5 is an enlarged cross-sectional view schematically showing a connection mechanism between the LCD unit and the conventional flexible substrate. In the figure, 1 ... LCD unit (connection target substrate), 4 ... Terminal (connection part), 5 ... Anisotropic conductive film, 5a ... Conductive particles, 6 ... Printed circuit board (connection target substrate) ), 11 ... Solder plating.

Claims (1)

[Scope of utility model registration request] 1. A flexible substrate connection structure having a connection portion connected to a terminal of a substrate to be connected through an anisotropic conductive film having conductive particles embedded in a synthetic resin. Connection structure of a flexible substrate in which the terminals are covered with solder plating having a film thickness of about 2 μm to about 6 μm, and some of the conductive particles of the anisotropic conductive film are heat-connected so as to bite into the solder plating. .