Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-11-23
2002-03-12
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S150000, C257S698000
Reexamination Certificate
active
06356333
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a conductive adhesive used to mount an electronic component on a substrate or the like, and more particularly, to a conductive adhesive comprising an adhesive resin and a plurality of conductive particles mixed in the adhesive resin. The present invention also relates to a mounting structure formed using such a conductive adhesive. The present invention also relates to a liquid crystal device formed using such a mounting structure. The present invention also relates to an electronic device formed using such a liquid crystal device. The present invention also relates to a method of producing a mounting structure, a liquid crystal device, and an electronic device.
2. Description of the Related Art
Liquid crystal devices are widely used in various electronic devices such as a portable telephone, a portable electronic terminal, etc. In many cases, liquid crystal devices are used to display information in the form of a character, a numeral, or a graphical image.
In general, a liquid crystal device includes a pair of liquid crystal substrates and a liquid crystal disposed between the pair of liquid crystal substrates wherein an electrode is formed on the inner surface of each substrate. The alignment of the liquid crystal is controlled by varying the voltage applied across the liquid crystal thereby modulating light incident on the liquid crystal. To control the voltage applied to the liquid crystal, it is required to use a liquid crystal driving integrated circuit, that is, a semiconductor chip, which is connected to the liquid crystal substrate directly or indirectly via a mounting structure.
In the case where the liquid crystal driving integrated circuit is connected indirectly to the liquid crystal substrate via the mounting structure, the mounting structure is formed, for example, by mounting the liquid crystal driving integrated circuit on a base substrate on which an interconnection pattern and electrode terminals are formed, and the resultant mounting structure is connected to the substrate of the liquid crystal device. In this case, when the liquid crystal driving integrated circuit is mounted on the base substrate, the liquid crystal driving integrated circuit may be connected to the base substrate using a conductive adhesive such as an ACF (anisotropic conductive film). More specifically, the liquid crystal driving integrated circuit and the base substrate are adhesively fixed to each other using an adhesive resin contained in the ACF such that bumps or terminals of the liquid crystal driving integrated circuit are electrically connected to electrode terminals on the base substrate via conductive particles contained in the ACF.
In some cases, when a semiconductor chip such as a liquid crystal driving integrated circuit is mounted on a base substrate, a passive electronic component such as a capacitor or a resistor or other electronic components such as a connector are also mounted on the base substrate via solder or the like, separately from the liquid crystal driving integrated circuit. Soldering for this purpose is generally performed using a solder reflow technique.
In the solder reflow technique, a solder pattern is first formed on a base substrate, at a predetermined location, by means of printing, dispensing, or the like, and a chip component such as the passive electronic component is placed on the solder pattern. The base substrate with the chip component placed thereon is then placed in a high-temperature furnace so as to melt the solder thereby soldering the chip component to the base substrate. In this process, the temperature of the heating furnace is set within the range of 200° C. to 250° C. The base substrate is exposed in a high-temperature region in this heating furnace for a short time. After completion of heating, the base substrate is cooled.
The conventional conductive adhesives such as an ACF used to mount a semiconductor chip include conductive particles formed of a synthesis resin such as polyester which is poor in heat resistance. Therefore, it is impossible to perform solder reflow processing after mounting a semiconductor chip on the base substrate using a conventional conductive adhesive. Thus, in conventional techniques, soldering of a chip component is first performed, and then the semiconductor chip is mounted using an ACF or the like.
In view of the above, it is an object of the present invention to provide a conductive adhesive which can withstand solder reflow processing. It is another object of the present invention to provide a mounting structure using such a conductive adhesive, a liquid crystal device using such a mounting structure, an electronic device using such a liquid crystal device. It is still another object of the present invention to provide a method of producing a mounting structure, a liquid crystal device, and an electronic device, using a simplified process.
SUMMARY OF THE INVENTION
1. According to an aspect of the invention, to achieve the above objects, there is provided a conductive adhesive comprising an adhesive resin and a plurality of conductive particles mixed in the adhesive resin, wherein: (1) each conductive particle comprises a core formed of a synthetic resin and a conductive material covering the core; and (2) the synthetic resin forming the core has a thermal deformation temperature higher than the thermal deformation temperature of the adhesive resin.
In this conductive adhesive, as described above, cores of the respective conductive particles contained in the conductive adhesive are made of a synthetic resin so that when two objects to be connected are brought into contact with each other via the conductive particles, the conductive particles are elastically deformed to a proper degree thereby achieving a stable contact between the two objects and thus achieving a stable electric connection between the two objects.
Furthermore, because the cores of the respective conductive particles contained in the conductive adhesive are formed using a synthetic resin having a high thermal deformation temperature, the conductive adhesive has high heat resistance. As a result, the conductive adhesive can withstand a solder reflow process in which the entire objects to be soldered are placed in a high temperature furnace. Therefore, it becomes possible to solder a chip component such as a capacitor to a base substrate by means of solder reflow processing after mounting a semiconductor chip on the base substrate using the conductive adhesive.
In the conductive adhesive described above, the adhesive resin may be a thermosetting resin such as an epoxy resin, a urethane resin, or an acrylic resin, wherein they have a thermal deformation temperature about 100° C. below which no deformation occurs. The conductive material covering the cores of the conductive adhesive may be, for example, nickel or carbon.
2. In the conductive adhesive described above, the synthetic resin forming the cores preferably has a thermal deformation temperature (18.6 kg/cm
2
) equal to or higher than 120° C. as measured according to the measuring method defined in the ASTM (American Society of Testing Materials) standard D648. This allows the conductive adhesive to have higher heat resistance which ensures that the conductive adhesive withstands solder reflow processing.
3. The synthetic resin having a thermal deformation temperature higher than 120° C. as measured according to the ASTM-D648 standard may be selected from the group consisting of polyphenylene oxide, polysulfone, polycarbonate, polyacetal, and polyethylene terephthalate. If the cores of the conductive adhesive are formed using one of the synthetic resins described above, the conductive adhesive has high heat resistance which allows the conductive adhesive to withstand solder reflow processing. The characteristics of the respective synthetic resins described above are summarized in Table 1.
TABLE 1
Thermal
Deformation
Linear
Tensile
Temperature
Expansion
Specific
Strength
(° C.)
Coefficient
Gravity
(
Chowdhury Tarifur R.
Harness & Dickey & Pierce P.L.C.
Seiko Epson Corporation
Sikes William L.
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