Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-11-15
2003-02-25
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S153000, C349S155000
Reexamination Certificate
active
06525799
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device and a method of manufacturing the same, and more particularly to a liquid crystal display device for use in miniature portable apparatuses such as a cellular phone and an electronic notebook, and a method of manufacturing the same.
2. Prior Art
In recent years, with rapid development of information communication technology, liquid crystal display devices have acquired an increasing importance, not least in the field of miniature portable apparatuses such as a cellular phone and an electronic notebook.
A liquid crystal display device of this kind is comprised of a liquid crystal cell formed by encapsulating liquid crystal in an airtight manner between two glass substrates (first and second glass substrates), and a driving circuit (hereinafter referred to as “driving IC”) arranged on the periphery of the liquid crystal cell, for driving and controlling the liquid crystal cell, the liquid crystal cell and the driving IC together composing a single module.
Conventionally, in the manufacture of a miniature module, a so-called “multi-cell bonding” method has been employed in which a multiplicity of liquid crystal cells are formed on a large-sized glass substrate in a single continuous process by carrying out a multi-cell bonding. Subsequently, driving ICs are directly mounted onto a liquid crystal panel by means of a so-called COG (chip on glass) mounting method. This manufacturing method allows a multiplicity of liquid crystal cells to be obtained in a single process by means of multi-cell bonding, leading to a substantial improvement of productivity, which, in turn, is combined with the adoption of the COG mounting method to reduce the number of manufacturing steps, and allow the manufacture of miniature modules at low costs.
FIG. 16
is a top plan view schematically showing essential parts of a conventional liquid crystal display device of this kind. Specifically, the liquid crystal display device includes a seal
52
in the form of a frame having a liquid crystal injection port
51
and sandwiched between a lower first glass substrate
53
and an upper second glass substrate
54
, both transparent. The injection port
51
, upon injection of liquid crystal
55
therethrough into the interior of the seal, is sealed with a sealant such as an ultraviolet ray-setting resin (hereinafter referred to as “UV-setting resin”) or the like, thereby hermetically encapsulating the liquid crystal
55
with the seal
52
in an airtight manner. A vertical conducting portion
56
is provided in the vicinity of a corner of the seal
52
, for conductive connection between respective transparent conductive films formed on the surfaces of the first and second glass substrates. The seal
52
is formed by screen-printing in a frame pattern a sealant which contains epoxy resin as a primary constituent.
FIG. 17
is a sectional view showing details of the seal
52
. As shown in the figure, the seal
52
contains a multiplicity of spacers
58
and conductive particles
59
mixed and generally evenly dispersed therein. The thickness of the seal
52
is controlled by the spacers
58
, and the conductive connection between the transparent conductive films formed on the surfaces of the first and second glass substrates
53
,
54
is ensured by means of anisotropic conduction obtained with the conductive particles
59
. Although the conductive particles
59
has only to be mixed into the vertical conducting portion
56
alone in order to secure conductive connection between the transparent conductive films, they are generally mixed in the seal
52
uniformly over the entire region thereof in view of production efficiency.
In the modern information society, increasingly refined display patterns on the liquid crystal display are demanded so as to be able to display as much information as possible. To this end, connection wiring
57
connected to the driving IC (see
FIG. 16
) needs to be formed with a narrow line width, especially in the vicinity of the driving IC, where the connection wiring
57
needs to be formed extremely fine with a line width not exceeding 100 &mgr;m.
However, when the connection wiring
57
is formed extremely fine, the wiring resistance becomes so high that if the connection wiring
57
is composed solely of the transparent conductive film, a voltage drop in the connection wiring would become so large as to interfere with the normal operation of the liquid crystal display.
Therefore, it has been a conventional practice to deposit a metal thin film which has small wiring resistance and hence excellent conductivity on the transparent conductive film such that the connection wiring
57
has a two-layered structure composed of a transparent conductive film and a metal thin film.
As described above, the first and second glass substrates
53
,
54
have the transparent conductive film, specifically an indium tin oxide (hereinafter referred to as “ITO”) film, formed on respective surfaces thereof. A transparent insulating film is further laminated on the surface of the ITO film at a portion corresponding to the liquid crystal display portion. Conventionally, this transparent insulating film is used as a mask to perform electroless nickel (Ni)—phosphorus (P) alloy plating and electroless gold (Au) plating on the surface of the transparent conductive film, thereby forming a metal thin film on a specified portion of the ITO film. Desired extremely fine connection wiring
57
can be obtained in this way while preventing the metal thin film from adhering to the liquid crystal display portion.
In the electroless plating, a Ni—P alloy precipitates selectively on the portion where the ITO film is formed, and then Au precipitates by substitution reaction with P on the Ni—P alloy as well as by an autocatalytic reaction of Au ion. Thus, desired extremely fine connection wiring
57
can be obtained without the plated film adhering to the liquid crystal display portion. In this way, a metal precipitates selectively on the ITO film as a transparent conductive film, depositing a metal thin film on the ITO film. Since a metal film is not formed on those portions where the ITO film is not formed, connection wiring
57
composed of a metal thin film can be formed at the desired portion without need for patterning to form the metal thin film.
However, in the conventional liquid crystal display device, as described above, electroless plating is performed using the transparent insulating film as a mask so that the plated film, that is, the metal thin film, deposits also on the transparent conductive film in the vertical conducting portion
56
where no transparent insulating film is coated.
Further, since a multiplicity of liquid crystal cells are, as described earlier, produced at one time by “multi-cell bonding” in a single continuous process, the metal thin film deposits in the vertical conducting portion
56
on the side of the second glass substrate
54
as well as on the side of the first glass substrate
53
.
FIG. 18
is a sectional view taken along line X—X in
FIG. 16
, and
FIG. 19
is a sectional view taken along line XI—XI in FIG.
18
. ITO films
60
,
61
are formed on the opposed surfaces of the first and second glass substrates
53
,
54
, respectively. Since no transparent insulating film is formed on the vertical conducting portion
56
on the first and second glass substrates
53
,
54
, the plating treatment is also performed on portions of the ITO film
60
,
61
of the vertical conducting portion
56
to form metal thin films
62
.
Therefore, if the spacers
58
used in the vertical conducting portion
56
have the same particle diameter as those in portions other than the vertical conducting portion
56
, the thickness of the seal
52
in the vertical conducting portion
56
becomes larger than that in the other portions by the combined film thickness 2×t′ of both metal films
62
on the opposed surfaces of the first and second glass substrates
53
,
54
, t′
Nanox Corporation
Rossi & Associates
Schechter Andrew
Ton Toan
LandOfFree
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