Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-08-02
2001-03-06
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S149000, C349S139000
Reexamination Certificate
active
06198522
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device of a “chip-on-glass” (hereinafter referred to as “COG”) type or “chip-on-film” (hereinafter referred to as “COF”) type in which a semiconductor chip is directly mounted on a wiring pattern on a substrate of e.g. glass constituting a liquid crystal panel, or on a film substrate connected directly or through a heat seal to a liquid crystal panel. The present invention is more particularly to a liquid crystal display device capable of making the connecting pressure between each of electrodes pads of the semiconductor chip and a wiring pattern constant so that uniform electric connection therebetween can be obtained.
2. Description of the Related Art
In a liquid crystal display (LC) device, transparent electrode patterns are formed respectively on two glass substrates so that they are opposite to and spaced from each other by a prescribed interval, and a liquid crystal material is sandwiched therebetween. A data signal is supplied to each of segment electrodes (pixel electrodes) so that each segment electrode is on/off controlled to provide a desired display. Traditionally, supply of the data signal to each segment electrode was made in such a manner that each segment electrode is connected to a circuit board and the data signal is directly supplied from a signal processing circuit provided on the circuit board to each segment electrode.
However, an increase in the number of segment electrodes leads to a great increase in the number of connecting wirings. Therefore, in recent years, a COG type display device is used in which a semiconductor chip (IC chip) for signal processing is directly mounted on a glass substrate, or a COF type display device is used in which the IC chip is directly mounted on a wiring pattern of a film substrate electrically connected to a liquid crystal panel.
Meanwhile,
FIG. 6A
is a plan view of a connection portion between a part of an IC chip
2
and wiring patterns
5
. As seen from
FIG. 4
, the interval A between the wiring patterns
5
is as narrow as 50-100 &mgr;m. For this reason, the electric connection between the IC chip and wiring pattern of the COG type and COF type display devices is made by thermal crimping technique. In this technique, as seen from the section shown in
FIG. 6B
, anisotropic conductive adhesive
6
is applied or labelled on the wiring pattern
5
on the film substrate
4
, the IC chip
2
is pressed thereon with constant force F while heating (by thermal compression bonding method), and the adhesive is hardened. The anisotropic conductive adhesive
6
is composed of epoxy resin mixed with metallic conductive particles
6
a
. When the adhesive
6
is pressed by fixed force, the epoxy resin is extruded in a lateral direction. Since the conductive particles
6
a
are sandwiched between an electrode pad
3
of the IC chip
2
and the wiring pattern
5
, the electrode pad
3
and the wiring pattern
5
are electrically connected to each other. On the other hand, in the lateral direction, they are insulated by the epoxy resin.
With a development of the miniaturization and high definition of the liquid crystal display device in recent years, the numbers of output terminals increases and electrode pads of the IC chip
2
to be connected to the wiring patterns
5
have been increased. Where different numbers of the electrode pads
3
are provided on e.g. both opposite sides of the IC chip
2
, the electrode pads
3
each having a prescribed width cannot be provided at regular intervals so that there is a tendency for the electrode pads
3
to have different areas. For example, in
FIG. 6B
, electrode pad C has a large width of 85 &mgr;m whereas electrode pad B has a small width of 47 &mgr;m. In this case, each wiring of the wiring pattern has a width enough to cover any electrode pad
3
. Therefore, the contact area between each electrode pad
3
and each wiring of the wiring pattern
5
is 85 &mgr;m (width)×85 &mgr;m (length) for the electrode pad C and 47 &mgr;m×85 &mgr;m for the electrode pad B. The ratio of contact area between the electrode pads C and B is as large as about 9:5, and difference of the contact area between the electrode pads C and B is large.
As described above, where a plurality of electrode pads of the IC chip are provided, there is a tendency for the electrode pads to have different areas. On the other hand, traditionally, each wiring of the wiring pattern
5
is formed to cover the corresponding electrode pad. Therefore, as the case may be, the areas of the electrode pads of the IC chip and the wiring pattern are different according to different electrode pads. The electrode pads and the corresponding wiring patterns are connected by thermal crimping through application of prescribed pressure using anisotropic conductive adhesive of epoxy resin mixed with conductive particles. Therefore, different contact areas lead to different pressures to be applied to the conductive particles to be in contact with each electrode pad. With different pressures, the conductive particles are not sufficiently crushed at the electrode pad to which low pressure is applied, thereby providing insufficient electrical contact and hence poor contact. Such a tendency is particularly remarkable where the IC chip is mounted on a soft flexible film substrate as in the case of COF type display device.
The present invention has been accomplished in order to solve such a problem.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a reliable liquid crystal display device in which each electrode pad of an IC chip and wiring pattern can be always stably electrically-connected on an unstable wiring pattern like an COF type display device.
In order to attain the above object of the present invention, in accordance with the present invention, there is provided a liquid crystal display device comprising: two substrates constituting a liquid crystal panel, on which electrode patterns are formed and between which a liquid crystal layer is sandwiched; a plurality of wiring patterns located on each substrate or a film substrate electrically connected to the liquid crystal panel; a semiconductor chip having a plurality of electrode pads having different areas and directly mounted on the plurality of wiring patterns so that the electrode pads are electrically connected to the plurality of wiring patterns, wherein the wiring patterns are defined in accordance with the areas of the plurality of electrode pads so that contact areas between the electrode pads and the corresponding wiring patterns are made equal to one another.
The electrode pads refer to areas which permits electrodes of the semiconductor chip to be connected to external wirings, and may have bumps formed thereon. The film substrate is a substrate in which wiring patterns of a metallic film are formed on an insulating film such as a flexible film.
In this configuration described above, the contact areas between the electrode pads and the corresponding wiring patterns are always equal even when the areas of the electrode pads are different. Therefore, when the semiconductor chip is mounted on the wiring patterns using anisotropic conductive adhesive, constant force is always applied to each electrode pad. Thus, even when the semiconductor chip is mounted on an unstable film like a COF type display device, stable connection can be made, thereby providing a reliable liquid crystal display device.
Preferably, each wiring pattern is sized so that each electrode pad has a width larger than that of the corresponding wiring pattern by 10 &mgr;m or larger. In this configuration, even if the semiconductor chip is slightly displaced, a part of the wiring pattern does not extend off the electrode pad, thus keeping the contact area constant.
Preferably, an area of the semiconductor chip other than the area thereof where the electrode pad is to be formed is covered with an insulating film. This prevents the semiconductor chip from being short-circuite
Morgan & Lewis & Bockius, LLP
Rohm & Co., Ltd.
Sikes William L.
Ton Toan
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