Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1998-10-27
2003-06-24
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S149000
Reexamination Certificate
active
06583834
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an adhesive, and more particularly, to an anisotropic conductive adhesive comprising electrically conductive particles. In addition, it relates to a liquid crystal device using the anisotropic conductive adhesive for connection between a liquid crystal panel and an external circuit substrate or a semiconductor element, and to a process for manufacturing the same. Further, it relates to electronic equipment composed of the aforementioned liquid crystal device as a display part.
BACKGROUND ART
For connection between fine pitch terminals, such as the connection between an input terminal held on a glass substrate of a liquid crystal panel and a terminal of a TCP (Tape Carrier Package) (a bump is sometimes formed on the terminal), anisotropic conductive adhesives are used.
Conventional anisotropic conductive adhesives are composed of a thermosetting or thermoplastic insulating adhesive material such as an epoxy resin, and plural electrically conductive particles disposed in the adhesives. Since such an insulating adhesive material adheres to both adherends, i.e., the glass substrate and the TCP formed of polyimide, a versatile adhesive is employed in order to adhere to any of these adherends including those made of different materials with a given adhesiveness.
Although such a versatile adhesive can adhere to adherends formed of various materials with adhesiveness of a constant level, when the adhesiveness to one adherend is increased to a given level or higher, the adhesiveness to the other adherend decreases, and, as a result, adhesiveness of a constant level as a whole can not be obtained.
In particular, when a glass substrate is used for a liquid crystal panel and is connected to a polymer substrate as an external circuit substrate, they both may have markedly different adhesive properties. Therefore, failures caused by peeling of the adhesive tend to occur in only one of the glass substrate or the polymer substrate.
It is an object of the present invention to provide an anisotropic conductive adhesive which can enhance adhesiveness to each of the adherends even when it is applied to two kinds of adherends composed of different materials, and a liquid crystal device which is safe from connection failures, and a process for manufacturing the liquid crystal device.
SUMMARY OF THE INVENTION
The adhesive of the present invention is an adhesive for adhering a first adherend and a second adherend composed of a different material from that of the first adherend, wherein the adhesive has a first adhesive layer having adhesive properties suitable for the first adherend and a second adhesive layer having adhesive properties suitable for the second adherend.
For adhesion between the first adherend and the second adherend using the adhesive of the present invention, the first adhesive layer can be in contact with the first adhered, and the second adhesive layer can be in contact with the second adherend. This achieves adhesion of one adherend to the other with appropriate adhesion properties suitable for each of the adherends, and thereby enhances strong adhesion between the adherends.
In another aspect, the invention provides the aforementioned adhesive, wherein the first adhesive layer comprises a first insulating adhesive material and a plurality of electrically conductive particles, and the second adhesive layer comprises a second insulating adhesive material.
When electrical connections are required between the first adherend and the second adherend, electrically conductive particles may be incorporated into the first adhesive layer, as is in the present invention. The electrically conductive particles can also naturally be incorporated into the second adhesive layer. In general, however, when the first and second adherends are electrically connected to each other, the first and second adherends are pressed against each other and thereby adhere together. Therefore, if the electrically conductive particles are only incorporated into the first adhesive layer, electrical connections can be achieved.
Incorporation of the electrically conductive particles only in the first adhesive layer achieves easy control of the number and distribution of the electrically conductive particles and hence provides easy production of an anisotropic conductive adhesive. In this embodiment, since the second adhesive layer should only be used for the adhesion to the second adherend, the thickness of the second adhesive layer can be reduced as compared with that of the first adhesive layer.
The first adherend and the second adherend can also be electrically connected to each other by forming, interposed between the first and second adhesive layers, an electrically conductive layer containing an insulating adhesive material and a plurality of electrically conductive particles.
In this case, since the electrically conductive layer which contains the electrically conductive particles does not directly contact the adherend, selection of its raw material depending on the adherend is not required. Accordingly, even when the adhesive is adhered with any adherend, the adhesive properties of the first and second adhesive layers have only to be determined depending on each of the adherends, and the insulating adhesive material of the electrically conductive layer can be used in common. This embodiment hence enhances manufacturing efficiency and reduces the cost in the manufacture of the anisotropic conductive adhesive having a variety of adhesive properties.
As concrete measures for adjusting the adhesive properties of the first and second adhesive layers, there may be mentioned as follows:
(1) To use different primary ingredients in the insulating adhesive materials between the first adhesive layer and the second adhesive layer respectively;
(2) to add different coupling agents to each of the first adhesive layer and the second adhesive layer; and
(3) to use different primary ingredients and different coupling agents between the first adhesive layer and the second adhesive layer.
When the same insulating adhesive material is employed in the first and second adhesive layers, and a first coupling agent suitable for the first adherend is added to the first adhesive layer and a second coupling agent suitable for the second adherend is added to the second adhesive layer, only modification of the species of the coupling agents can alter the properties of the adhesives. Therefore, this embodiment can reduce the species of insulating adhesive materials to be used, enhance the manufacturing efficiency and lower the cost.
The present invention also provides, in another aspect, a liquid crystal device comprising a liquid crystal panel having a pair of substrate, a liquid crystal encapsulated between the substrates and an electrode terminal formed on at least one of the substrates, and a circuit substrate having an electrode terminal formed thereon and connected to the one substrate on which the electrode terminal is formed, wherein the aforementioned one substrate and the circuit substrate are connected by an adhesive comprising a first adhesive layer having adhesive properties suitable for one of the one substrate or the circuit substrate, and a second adhesive layer having adhesive properties suitable for the other.
According to the above-mentioned liquid crystal device of the present invention, a substrate for a liquid crystal panel (principally, a glass substrate) is connected to a circuit substrate (principally, a polymer substrate) by using an adhesive comprising a plurality of adhesive layers each having adhesive properties suitable for each of the substrate. As a result, adhesion forces of both substrates are uniformly enhanced, and hence connection reliability can be improved.
In an additional aspect, the invention provides the liquid crystal device, wherein the electrode terminal formed on the one substrate and the electrode terminal formed on the circuit substrate are different in their thickness, the first adhesive layer contains a first insulating adhesive material an
Kim Robert H.
Nguyen Dung
Seiko Epson Corporation
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