Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-11-30
2002-07-23
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S150000, C349S151000, C349S152000
Reexamination Certificate
active
06424400
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a display panel having an image display function, and a printed circuit board mounted on the display panel.
BACKGROUND ART
Owing to the recent advancement in ultrafine processing technology, liquid crystal material technology, and mounting technology, liquid crystal panels capable of displaying various images such as television images at a practically satisfactory level in diagonal size of 5 to 50 cm are presented on a commercial base.
Besides, color display is easily realized by forming an RGB coloring layer in one of the two glass substrates for composing a liquid crystal panel.
In particular, in a so-called active type liquid crystal panel incorporating switching elements in every pixel, an image of high contrast ratio is obtained in high speed response with less crosstalk.
Such liquid crystal panels are generally composed in a matrix comprising 100 to 1000 scanning lines and 200 to 2000 signal lines, and lately both large screen and high definition are promoted simultaneously in relation to the increase in the display capacity.
FIG. 6
is a perspective view of an active type liquid crystal panel, in which the active type liquid crystal panel is composed of an active substrate
2
, a confronting counter substrate
9
, and liquid crystal filled between them.
The active substrate
2
has a plurality of scanning lines formed on a principal surface of a transparent insulating substrate, and a plurality of signal lines substantially orthogonal to the scanning lines formed at least across one insulating layer, and at least one switching element and at least one pixel electrode are disposed at every intersection of scanning line and signal line, and a terminal electrode group of the scanning lines and signal lines is disposed outside of the image display region.
The counter substrate
9
is composed of a glass substrate which is a transparent insulating substrate having a transparent conductive counter electrode.
The active substrate
2
and counter substrate
9
are formed across a specific distance of several microns by way of a spacer such as resin fiber or beads, and their gap is a closed space sealed by sealing material and filling material made of organic resin on the peripheral edge of the counter substrate
9
, and this closed space is filled with liquid crystal.
In the case of color display, the closed space side of the counter substrate
9
is coated with a coloring layer containing either a dye or a pigment or both, as an organic thin film of about 1 to 2 &mgr;m in thickness, so that a color display function is provided. In this case, the glass substrate
9
is also called a color filter.
Depending on the properties of the liquid crystal material, a polarizing plate is adhered to either the upper surface of the counter substrate
9
or the lower surface of the glass substrate
2
, or on both sides, so that the liquid crystal panel
1
functions as an electro-optical element.
In the majority of panels, at the present, the Twisted Nematic (TN) system is used in the liquid crystal, and it requires two polarizing plates.
In thus constituted liquid crystal panel, outside the image display region of the active substrate
2
, for example, on the terminal electrode group
6
of scanning lines, a semiconductor integrated circuit chip
3
for supplying drive signals is mounted by direct connecting Chip-On-Glass (COG) system, whereas on the terminal electrode group
5
of signal lines, a Tape-Carrier-Package (TCP) film
4
is mounted by the TCP system of connecting and fixing with a conductive adhesive.
The TCP film
4
has a terminal of copper foil (not shown) of gold plating or solder plating, for example, formed on a polyimide resin thin film of about 0.1 mm in thickness.
Two mounting methods are shown herein, but actually either method is properly selected.
The image display unit of the liquid crystal panel
1
, and the terminal electrode groups
5
,
6
of signal lines and scanning lines are connected by means of wiring lines
7
,
8
, but the wiring lines
7
,
8
are not always required to be composed of same conductive material as the terminal electrode groups
5
,
6
.
In this liquid crystal panel, liquid crystal cells are composed of transparent conductive pixel electrodes formed on the active substrate
2
, transparent conductive counter electrodes formed on the counter substrate
9
, and liquid crystal filled between the two glass substrates.
In the recently developed In-Plain-Switching (IPS ) type liquid crystal panel capable of expanding the viewing field angle, the liquid crystal cells are composed of a pair of comb electrodes formed on one glass substrate (active substrate) and the liquid crystal filled between the two glass substrates, and hence the transparent electrode (counter electrode) is not needed on the color filter, but the detail is omitted herein.
To display an image on the liquid crystal panel, an electric signal must be given to the terminal electrodes of the scanning lines and signal lines by TCP or COG mounting as mentioned above. Recently, to save the mounting cost, or to enhance the mounting reliability by decreasing the number of connecting positions, the COG mounting tends to be preferred.
FIG. 7
is a magnified view of essential parts by COG mounting of a driving integrated circuit chip
3
on the active substrate
2
, and in the COG mounting, since systems of power source line, input signal line, and clock line scanning to a plurality of driving integrated circuit chips cannot be supplied in each chip as in the TCP mounting, it is needed to form about 20 to 40 conductive bus lines
10
on the peripheral edge of the active substrate
2
, but in the digitized signal system, in order to be applicable to high image quality, henceforth, the number of bits tends to increase rapidly.
To form active elements, it is also needed to form scanning lines and signal lines, and these wiring lines can be formed simultaneously with the active elements, which is more rational.
Forming places of wiring lines
10
can be easily insulated by forming an insulation layer on the surface, and, for example, by utilizing the space effectively by disposing wiring lines
10
beneath the integrated circuit chip
3
, it may contribute to narrowing of peripheral margin of the liquid crystal panel.
In the COG mounting, however, in the screen diagonal size of 6 (15 cm) or more at which the resistance value of the wiring line
10
is high, as shown in
FIG. 8
, it is required to use together with a bus flexible film
11
.
The bus flexible film
11
is similar to the TCP film
4
, that is, a wiring line
12
made of a conductive thick film is formed on a flexible film. Its length is as long as 20 to 50 cm, and the wiring line connecting between parallel lines crosses orthogonally with the parallel lines, and hence it requires several or more multiple layers, which is very expensive, and it is difficult to lower the cost.
Inevitably, however, the bus flexible film
11
is used as explained below.
When manufacturing a active liquid crystal panel, since the film thickness of the conductive lines such as scanning lines and signal lines is about 0.5 &mgr;m, the resistance value of the conductive lines cannot be lowered sufficiently, and the resistance of the wiring lines
10
increases due to the shape effect (ratio of length/width of wiring pattern), and a sufficient current cannot be passed by the bus wiring lines
10
alone. More specifically, for example, by using an aluminum film of about 0.3 &mgr;m in thickness in the wiring line material, if a surface resistance of 0.1 &OHgr;/cm
2
is obtained, in the case of wiring width of 50 &mgr;m and wiring length of 25 &mgr;m, the resistance value of the wiring lines reaches as much as 500&OHgr;, and it is hence difficult to use in the power source lines of mA unit or higher.
Similarly, in the input signal and clock lines, such wiring resistance is added to the input resistance of the semiconductor integrated circuit, and in the case of high speed transfer of signal (more than hundreds of
Chowdhury Tarifur R.
Parkhurst & Wendel LLP
Sikes William L.
LandOfFree
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