Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2001-09-14
2004-09-14
Crispino, Richard (Department: 1734)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S103000, C156S291000, C156S299000, C100S046000, C100S206000, C100S207000
Reexamination Certificate
active
06790300
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Art
This invention relates to a method and an apparatus, for bonding substrate plates face to face in a predetermined gap relation through an interposed spacer material, and more particularly to a method and apparatus for bonding, for example, upper and lower substrate plates which form a liquid crystal cell of an LCD panel, strictly registering relative positions of the two substrate plates with each other and then pressing the substrate plates toward each other to compress and flatten the interposed sealer material to such a degree as to form a gap of a predetermined width between the upper and lower substrate plates.
2. Prior Art
A liquid crystal cell of an LCD panel is formed by bonding together a couple of substrate plates of transparent synthetic resin material through a sea sealer material which is interposed between and along outer marginal edges of the substrate plates, and filling liquid crystal in a sealed gap space which is formed between the two substrate plates by the sealer material. For instance, in the case of a color TFT type LCD panel, a lower substrate plate constitutes a TFT substrate which has circuit patterns including TFT elements formed thereon in the fashion of a matrix, while an upper substrate constitutes as a filter substrate which has color filters formed thereon A driver IC and a printed circuit board are connected to the TFT substrate of the LCD panel. More particularly, the LCD panel is fabricated in the manner as described below.
Firstly, a sealer material is applied along outer marginal edges of either the TFT substrate or the filter substrate. Then, the two substrate plates are overlapped one on the other, namely, in such a way that the filter substrate comes on top of the TFT substrate. Normally, a sealer material is applied on the side of the lower TFT substrate and in the shape of a rectangular frame which is partly opened by a void portion. The initial thickness of the applied sealer material is larger than the width of a gap space to be ultimately formed between the two substrate plates in a subsequent hot-pressing stage.
In the next place, the two substrate plates are adjusted to a registered position relative to each other and the overlapped substrate plates are pressed and temporarily fixed to each other. At this time, it has been the general practice to apply, for example, an ultraviolet hardening synthetic resin spot-wise and to irradiate ultraviolet ray for temporarily fixing them. Thereafter, the substrate plates are pressed toward each other under heated conditions in such a way as to press and flatten the interposed sealer material for adjusting a gap width between the two substrate plates. In this hot-pressing stage, heat is applied to harden the sealer material. However, the sealer material is hardened only to such a degree as to maintain a certain gap width between the two substrate plates in a stable state. Finally, the temporarily bonded substrate plates are sent to a hot-hardening stage to thermally harden the sealer material completely.
In the above-mentioned hot-pressing stage, a couple of substrate plates are pressed under heated conditions by the use of a press means, which is provided with heated upper and lower press members. However, since the substrate plates of an LCD panel are formed of a relatively fragile material like glass and synthetic resin, they can be easily damaged if hot press members are abutted directly against the respective substrate plates. Therefore, in most cases the abutting faces of the upper and lower pressing members are covered with a cushioning material like a rubber sheet of a predetermined thickness, so that the pressing members are abutted against the substrate plates through a cushioning material.
In this connection, recently there is a strong trend toward high-resolution fine-pitch LCD panels, which require to register and bond substrate plates to each other in an extremely strict and precise manner because a very slight positional deviation of several micrometers or less is impermissible in the case of fine-pitch LCD panels. Therefore, in a substrate bonding stage, positions of substrate plates are adjusted relative to each other very strictly. However, no matter how strictly substrate plates are one on the other before pressing, it cannot guarantee that the bonded substrate plates stay in the registered position without deviations therefrom. The reason for this is that, as the substrate plates are pressed in the hot-pressing stage, a pressing force is applied thereto through a cushioning material which is compressed and flexed under the pressing force. As a cushioning material is compressed and caused to flex, it is difficult to control the direction of flexure, which more or less differ from one cushioning member to another. Namely, in some cases the pressing members fail to press substrate plates in a normal straightforward direction, and, since the interposed sealer material is not yet hardened in the hot-pressing stage, may give rise to a detrimental positional deviation between upper and lower substrates. Although the overlapped two substrate plates are temporarily bonded by an ultraviolet hardening synthetic resin, the bondage by the synthetic resin is strong enough only for preventing deviations of the substrate plates in handling or in the course of transfer. If the overlapped substrate plates are strongly bonded by an ultraviolet hardening synthetic resin, it will become difficult to determine the gap width precisely later in the hot-pressing stage.
No positional deviations occur to the overlapped substrate plate as long as the cushioning members on the upper and lower pressing members of the press means of the same compressive characteristics, namely, as long as the cushioning members on upper and lower pressing members are flexed in the same direction and to the same degree and distorted in the same manner when compressed. On the other hand, for example, in case upper and lower cushioning members are flexed in the opposite directions upon compression in the hot-pressing stage, this difference in compressive characteristics results in amplification of relative movements of upper and lower substrate plates and thus in augmentation of positional deviations of the upper and lower substrate plates.
Accordingly, it is important to carefully select suitable cushioning material to be adhered on the pressing members of the press means to make sure that the cushioning pad members on the upper and lower pressing members have the same compressive characteristics. For this reason, the selection of cushioning material is met by various limitations. In this regard, it is possible to produce a large number of cushioning pad members and select therefrom pairs of matching compressive characteristics for the upper and lower pressing members. However, the pad selection of this sort is very troublesome, in addition to a detrimental drawback that a large amount of material has to be wasted. Besides, there is little possibility of finding a pair of cushioning pads which perfectly match in compressive characteristics. Therefore, it is difficult to cope with the demands for fine-pitch LCD panels of higher grades, simply through selection of cushioning pads. Further, since a pressure is applied on substrate plates under heating conditions, cushioning pads undergo accelerated deteriorations under the influence of heat and need to be replaced after use over a certain period of time. The replacements of cushioning pads involve the same problem as explained above.
Thus, there are great limits to preventing positional deviations of substrate plates in a hot-pressing stage by matching compressive characteristics of cushioning pads to be adhered on upper and lower press members. Regarding methods without using cushioning pads, there have thus far been proposed various methods, for example, a method of pressing substrate plates by the use of a fluid pressure. However, since a pressing method of this sort invariably requires complicate equipments for the supply
Ichikawa Hisayoshi
Kiyomiya Hiroaki
Otsubo Yuji
Sugizaki Shinji
Watanabe Hiroyuki
Hitachi Electronics Engineering Co. Ltd.
Keady, Olds & Maier PLLC
Koch, III George R.
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