JPH11135909A - Electronic equipment and flexible wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an offset phenomenon of conductive particles and to enable a joint between a connection target such as an LCD(liquid crystal display) or the like and an FPC(flexible printed circuit board) which are joined together with anisotropic conductive adhesive agent to be improved in adhesive strength and continuity reliability. SOLUTION: A flexible wiring board 3 is equipped with signal transmission connection terminals 4 formed and arranged for external connection transparent electrodes 2 arranged on an LCD and at least a dummy pattern 5 provided between the signal transmission connection terminals 4. The flexible wiring board 3 is arranged on outer connection transparent electrodes 2 through the intermediary of and anisotropic conductive adhesive agent 7, and the outer connection transparent electrodes 2 and the signal transmission connection terminals 4 are bonded together by theremocompression.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for electrically connecting a plurality of connection electrodes provided on a connection object such as a liquid crystal display element (hereinafter, LCD) and connection terminals of a flexible wiring board (hereinafter, FPC). Related to an electronic device connected to the electronic device.

[0002]

2. Description of the Related Art Conventionally, there has been known a method of electrically connecting an LCD and an FPC by thermocompression bonding via an anisotropic conductive adhesive. It is considered that this method makes it easy to obtain high conduction reliability while securing mechanical strength, even when the interval between connection terminals is narrow and there is no room for mounting space.

The anisotropic conductive adhesive has a structure in which conductive particles having a diameter of several microns are dispersed in a thermosetting adhesive usually called a binder.
There are two general forms: a form in which the anisotropic conductive adhesive is coated on the bonding surface of C, and a form in which a film tape-like material is later attached to the bonding surface of the FPC. In any case, electrical connection can be obtained by thermocompression bonding the LCD and the FPC.

[0004] For example, Japanese Patent Publication No. Hei 8-12352 discloses an F: one-to-one correspondence with a transparent electrode for external connection of an LCD.
A technique is described in which a connection terminal surface of a PC is divided into at least two concave portions to increase adhesive strength. Also, Japanese Patent Application Laid-Open No. 2-5
Japanese Patent Publication No. 375 describes a technique for increasing the bonding strength by providing dummy patterns on both outer sides of the connection terminals of the FPC to prevent poor conduction.

[0005]

However, the techniques described in Japanese Patent Publication No. Hei 8-12352 and Japanese Patent Laid-Open Publication No. Hei 2-5375 both improve the adhesive strength and prevent the conduction failure of the connection terminal portion. The conductive particles are not evenly dispersed between the connection terminals, and the conductive particles are arranged as if they were connected in a direction perpendicular to the connection terminals. This prevents short-circuit failure between the connection terminals due to the so-called biasing phenomenon of the conductive particles. I do not consider doing.

An example of the above-described bias phenomenon of the conductive particles will be described with reference to FIGS. 3 and 4. FIG. FIG. 3A shows an LCD and an FP.
A partially enlarged plan view when the joint of C is observed from directly above,
FIG. 3B is a BB cross-sectional view thereof. FIG. 4 shows FIG.
It is CC sectional drawing of (a).

In FIG. 3, a plurality of external connection transparent electrodes 31 (for example, formed as an ITO film) are formed at predetermined positions on the surface of one glass plate 30a constituting the LCD. Similarly, connection terminals 33 at substantially equal intervals corresponding to the transparent electrodes 31 for external connection on a one-to-one basis are exposed on the bonding surface of the FPC 32. Then, an anisotropic conductive adhesive 35 (see FIG. 4) containing conductive particles 34 having a diameter of several microns (shown by black circles in the figure) is coated to a predetermined thickness on the entire surface of the bonding surface of the FPC. . Note that 30b in FIG. 3B is the other glass plate for sandwiching the liquid crystal 36, and 37 is a sealant. Also, when a film tape-shaped anisotropic conductive adhesive is used, the same connection state as described above is obtained.

At this time, between the connection terminals 33, the conductive particles 34 are connected in a horizontal line or in a strip shape (region 3 in the figure).
8). Such connection of the conductive particles causes the conductive particles 34 themselves to be in a state of being in close contact with each other, and as a result, there is a risk of causing a short circuit failure between the adjacent connection terminals 33. In addition, the connection of these conductive particles is likely to occur when the anisotropic conductive adhesive 35 between the connection terminals 33 moves in a narrow gap in a certain direction due to pressure during thermocompression bonding. The gap, the pressure at the time of thermocompression bonding, and the like are considered as the main factors of the generation mechanism.

FIG. 4 is an enlarged cross-sectional view (C in FIG. 3A) of the joint portion between the LCD and the FPC at the time of thermocompression bonding (heated / pressed state).
-C sectional view). In the actual thermocompression bonding, a cushioning material (usually a silicon rubber sheet or a Teflon sheet having a thickness of about several tens to 100 microns) 40 is used so that the pressure of the heating / pressing head 39 is evenly applied to the joint.
Is carried out between the heating / pressing head 39 and the FPC 32.

When the bonding portion is strongly pressed by the heating / pressing head 39 at the time of thermocompression bonding, the FPC 32 in the portion where the connection terminal 33 is not provided is provided with the buffer material 40 and the external connection transparent electrode 31 on the LCD. It sinks concavely near the surface of the glass plate 30a.

At this time, the anisotropic conductive adhesive 35 between the connection terminals 33 that has been softened by being heated at the same time as the pressing is applied.
Is discharged out of the joint through a slight gap between the FPC 32 and the glass plate 30a. However, when the FPC 32 sinks near the surface of the glass plate 30a, the conductive particles 34 having a diameter of several microns are not discharged, and as a result, the conductive particles 34 stay along the boundary of the sink.

The present invention prevents the biasing phenomenon of the conductive particles, which is considered to be caused by such a mechanism, and makes it possible to connect a connection object such as an LCD connected by using an anisotropic conductive adhesive.
It is an object of the present invention to provide an electronic device having improved bonding strength and conduction reliability of a connection portion with a PC, and a flexible wiring board used for the electronic device.

[0013]

In order to achieve the above object, an electronic apparatus according to a first aspect of the present invention comprises a plurality of connection electrodes arranged on a plurality of connection electrodes arranged on a connection target. At least one provided between the connection terminal and each of the above connection terminals
Flexible wiring board having dummy patterns
The connection electrode was connected via an anisotropic conductive adhesive.

According to this, the sinking of the flexible wiring board can be reliably reduced at least by the thickness of the dummy pattern by the dummy pattern provided between the connection terminals of the flexible wiring board. As a result, the excess anisotropic conductive adhesive is smoothly discharged to the outside of the joint due to the heating and pressurization during thermocompression bonding, the stagnation of the conductive particles can be eliminated, and the conductive reliability can be improved. In addition, since the bonding area increases by adding the dummy pattern, the bonding strength can be improved at the same time.

Here, the connection targets are those that are electrically connected to the flexible wiring board, such as substrates such as rigid boards and flexible wiring boards, liquid crystal display elements, ICs, and the like.
Although the present invention is not particularly limited to electronic components such as LSI and various modules such as a distance measuring module and a photometric module, the present invention provides a liquid crystal display element having a narrow interval between connection electrodes as described in claim 2. Is particularly effective when is a connected member.

According to a third aspect of the present invention, there is provided the flexible wiring board, wherein at least one dummy pattern is provided between the plurality of connection terminals arranged for the plurality of connection electrodes arranged for connection. Was provided.

In this flexible wiring board, since at least one dummy pattern is provided between each connection terminal, when connecting to an object to be connected by thermocompression bonding via an anisotropic conductive adhesive, a sink is formed. Is prevented.

The dummy pattern is an invalid wiring pattern irrelevant to signal transmission, and may have a function of promoting the flow of the anisotropic conductive adhesive during thermocompression bonding. The size, thickness, shape, and the like are limited. Not done.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of the present invention will be described with reference to the drawings, taking as an example a case where a flexible wiring board (FPC) is electrically connected to a liquid crystal display element (LCD) to be connected. I do.

FIG. 1 is a partially enlarged plan view when the joint between the LCD and the FPC is observed from directly above. FIG.
FIG. 1 shows an enlarged cross-sectional view (cross-sectional view taken along the line AA in FIG. 1) of a bonding portion between the LCD and the FPC at the time of thermocompression bonding (heated / pressed state).

In FIG. 1, the LCD has two glass plates 1
A transparent electrode 2 for external connection is formed on a surface of one glass plate 1a (corresponding to 30a in FIG. 3) at a predetermined position. Similarly,
On the bonding surface of the FPC 3, connection terminals 4 at substantially equal intervals corresponding to the respective patterns of the transparent electrode for external connection 1 on a one-to-one basis, and a dummy pattern 5 having a predetermined width at a substantially intermediate position between the connection terminals 4. Is provided. Furthermore, conductive particles 6 having a diameter of several microns (shown by black circles in the figure) are formed on the entire surface of the bonding surface.
Is coated to a predetermined thickness.

In FIG. 2, the heating / pressing head 8 is thermocompression-bonded via a cushioning material 9 so that pressure is evenly applied to the joining surface. Here, when the bonding surface is strongly pressed by the heating / pressing head 8, the FPC 3 where the dummy pattern 5 is provided sinks in a concave shape toward the glass plate 1 a of the LCD together with the cushioning material 9. However, since the dummy pattern 5 serves as a support for the glass plate 1 a, sinking is surely restricted by at least the thickness of the dummy pattern 5. Thus, the dummy pattern 5
Is provided, the conductive particles 6 in the anisotropic conductive adhesive 7 are uniformly dispersed without staying at one place and being connected. Therefore, since no stagnation of the conductive particles occurs, the LCD
And the conduction reliability of the FPC can be improved.

In this embodiment, an LCD glass plate 1a
Although one dummy pattern 5 is provided between each connection terminal 4 of the FPC opposed to each pattern of the external connection transparent electrode 2 provided on the surface of the above, the present invention is not limited to this, and is not limited to thermocompression bonding or connection. The size, shape, number, position, and the like of the dummy patterns may be appropriately adjusted in accordance with the terminal interval, and may be optimally adjusted so that the stagnation of the conductive particles does not occur. In addition, one end of the dummy pattern may be connected to one end of an adjacent connection terminal in consideration of heat radiation of a bonding surface during thermocompression bonding. The dummy pattern may be formed on a glass plate of the LCD. Furthermore, the idea of the present invention is that the LCD and the F
It goes without saying that the present invention can be applied not only to the combination of the PC but also to the combination of the ordinary circuit board such as a rigid board and the FPC.

Further, the present invention embodied by the above-described embodiments can be variously modified without departing from the gist of the present invention. As described above, the present invention has been described based on the embodiments, but the present invention includes the following inventions. That is, (1) at least a plurality of signal transmission connection terminals arranged and formed in substantially the same shape with respect to the plurality of external connection transparent electrodes arranged on the liquid crystal display element, and at least a portion between the signal transmission connection terminals. A liquid crystal display device, wherein a flexible wiring board provided with one dummy pattern is disposed on the transparent electrode for external connection via an anisotropic conductive adhesive and electrically connected by thermocompression bonding. . (2) A plurality of signal transmission connection terminals arranged at substantially the same interval with respect to the plurality of external connection electrodes arranged as a connection target, and at least one of the plurality of signal transmission connection terminals provided between the signal transmission connection terminals. An electronic device (flexible wiring board), wherein a flexible wiring board having a dummy pattern is disposed on the external connection electrode via an anisotropic conductive adhesive and electrically connected by thermocompression bonding. Connection method). (3) The connection target is a substrate such as a rigid board or a flexible wiring board, an electronic component such as a liquid crystal display element, an IC or an LSI, and various modules such as a distance measuring module or a photometric module. Wiring board connection method). (4) Anisotropic conductive bonding between a connection object in which a plurality of connection electrodes are arranged and a flexible wiring board having a plurality of signal transmission connection terminals arranged and formed at substantially the same intervals with respect to the connection electrodes. An electronic device electrically connected by thermocompression bonding via an agent, wherein a flow promoting portion of the anisotropic conductive adhesive is formed between each signal transmission connection terminal of the flexible wiring board. . (5) The electronic device according to (4), wherein the flow promoting unit is an invalid wiring pattern irrelevant to signal transmission.

[0025]

According to the electronic apparatus of the present invention having the above-described structure, a dummy pattern is provided between a plurality of signal transmission connection terminals of a flexible wiring board electrically connected to a connection target such as an LCD. The excess anisotropic conductive adhesive is smoothly discharged out of the joint by heating and pressurizing during thermocompression bonding, so that the retention of conductive particles does not occur and the bonding area increases as the number of dummy patterns increases. Thus, high reliability can be ensured.

[Brief description of the drawings]

FIG. 1 is a partially enlarged plan view when a joint in an embodiment of the present invention is observed from directly above.

FIG. 2 is an enlarged cross-sectional view (cross-sectional view taken along the line AA in FIG. 1) of the above-mentioned joint portion between the LCD and the FPC at the time of thermocompression bonding (heating / pressing state) in the embodiment of the present invention.

FIG. 3 (a) is a partially enlarged plan view when a joint in the related art is observed from directly above, and FIG.
It is BB sectional drawing.

4 is an enlarged cross-sectional view (a cross-sectional view taken along the line CC in FIG. 3A) of the above-described joint between the LCD and the FPC at the time of thermocompression bonding (heated / pressurized state) in a conventional technique.

[Explanation of symbols]

 1a, 1b glass plate 2 transparent electrode for external connection 3 flexible wiring board 4 connection terminal 5 dummy pattern 6 conductive particles 7 anisotropic conductive adhesive

Claims (3)

[Claims] 1. A flexible wiring board having a plurality of connection terminals arranged and formed for a plurality of connection electrodes arranged in a connection target and at least one dummy pattern provided between the connection terminals, An electronic device, wherein the electronic device is connected to the connection electrode via an anisotropic conductive adhesive. 2. The electronic device according to claim 1, wherein the connection target is a liquid crystal display element. 3. A flexible wiring board, wherein at least one dummy pattern is provided between a plurality of connection terminals arranged for a plurality of connection electrodes arranged for connection.