Abstract:
An X-ray detector, which comprises a gate pad connected to a gate line disposed crosswise in a first direction, a data pad connected to a data line disposed lengthwise in a second direction substantially perpendicular to the first direction, a switching element disposed in the region where the gate line and the data line cross, a storage capacitor connected with the switching element on the same plane, and scanning and data integrated circuit chips for operating the switching element, is produced by a method which includes connecting an X-ray detector panel with the scanning and/or data integration chip by a tape carrier package and/or a chip-on-glass method. According to the invention, closely spaced terminals can be connected, the connection area can be decreased, and the processing time for making the connections can be reduced.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an X-ray detector and methods of fabricating the same, and more particularly to the electrical connection between an X-ray detector panel and an integrated circuit chip of the X-ray detector. 
     2. Discussion of the Related Art 
     In an X-ray detector, a package connecting an external integrated circuit chip with the X-ray detector serves not only for electrical connection, but also for transmission of electrical signals, mechanical support and release of heat generated during operation. The importance of the package is increasing recently because the signal transmission speed of a chip is much higher than that of the package and the signal delay time in the package determines the efficiency of an X-ray detector. 
     The wire bonding method has been employed for packaging an X-ray detector, which is a method wherein a chip and a pad formed in a lead frame are connected by a wire such as Au, Al, etc. The wire bonding method is used, in general, with integrated circuit chips for a wide range of process conditions with good reliability. An example is illustrated in FIG. 1, where a gate line  3  or data line  4  of a TFT (thin film transistor)  2  is connected by a wire  6  with an integrated circuit  5  on an X-ray detector panel  1 , and the integrated circuit  5  is also connected with a printed circuit board  7  by a wire  6 . 
     However, the wire bonding method is a sequential connection method wherein connecting terminals are connected one by one. Therefore, it requires a long time when the number of connecting terminals is large, as in an X-ray detector, and connection is impossible where the distance between connecting terminals is very short. In addition, the connection area is undesirably large owing to the height of the wire loop. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to an X-ray detector and a method of fabricating the same that substantially obviates one or more of the problems due to limitations and disadvantages of the related art. 
     An object of the present invention is to provide a method for fabricating an X-ray detector, whereby the time period required in the process of connecting an X-ray detector panel and a drive integrated circuit is shortened, and whereby a very short connection between connecting terminals becomes possible and the connection area is reduced. 
     Another object of the present invention is to provide an X-ray detector fabricated by such a method. 
     In order to achieve the above objects, the present invention provides in a first aspect, a method for fabricating an X-ray detector comprising a gate pad connected to a gate line disposed crosswise in a first direction, a data pad connected to a data line disposed lengthwise in a second direction substantially perpendicular to the first direction, a switching element disposed in the region where a gate line and a data line cross, a storage capacitor connected with the switching element, scanning and data integrated circuit chips for operating the switching element and a printed circuit board for driving the scanning and data integrated circuit chips, which comprises: 
     forming at least two protruding electrodes, or bumps, on the scanning integrated circuit chip; 
     providing a first polyamide film having an electrode adhered thereto, the electrode having an inner lead and an outer lead; 
     providing a second polyamide film having an electrode adhered thereto, the electrode having an inner lead and an outer lead; 
     bonding the inner leads of the first and the second polyamide films with the bumps, respectively; 
     bonding the outer lead of the first polyamide film to the gate pad with an anisotropic conducting film interposed therebetween; and 
     connecting the outer lead of the second polyamide film to the printed circuit board by soldering. 
     In a second aspect, the present invention provides a method for fabricating an X-ray detector similar to that as described above, which comprises: 
     forming at least two bumps on the data integrated circuit chip; 
     providing a first polyamide film having an electrode adhered thereto, the electrode having an inner lead and an outer lead; 
     providing a second polyamide film having an electrode adhered thereto, the electrode having an inner lead and an outer lead; 
     bonding the inner leads of the first and the second polyamide films with the bumps, respectively; 
     bonding the outer lead of the first polyamide film to the data pad with an anisotropic conducting film interposed therebetween; and 
     connecting the outer lead of the second polyamide film to the printed circuit board by soldering. 
     In the above methods according to a first mode (tape carrier package) of the invention, the switching element is preferably a thin film transistor. 
     The above methods may further comprise encapsulating the integrated circuit chip and the inner leads of the electrodes of the first and second polyamide film with a resin after bonding the inner leads of the first and second lead electrodes with the protruding conductor of the integrated circuit chip. An epoxy resin may be preferably used as the encapsulating resin. 
     In a third aspect, the present invention provides a method for fabricating an X-ray detector comprising first and second gate pads connected to first and second gate lines, respectively, each disposed crosswise in a first direction, first and second data pads connected to first and second data lines, respectively, each disposed lengthwise in a second direction substantially perpendicular to the first direction, a switching element disposed in a region where one of the gate lines and one of the data lines cross, a storage capacitor connected on a same plane with the switching element, and scanning and data integrated circuit chips for operating the switching element, which comprises: 
     providing a flexible printed circuit board for operating the scanning integrated circuit chip; 
     providing an anisotropic conductive film; 
     forming on the scanning integrated circuit chip first and second protruding conductors; 
     bonding the first gate pad with the first protruding conductor on the scanning integrated circuit chip; 
     bonding the second gate pad with the second protruding conductor on the scanning integrated circuit chip; and 
     bonding the flexible printed circuit board with the second gate pad by the anisotropic conductive film. 
     In a fourth aspect, the present invention also provides a method for fabricating an X-ray detector as described above, which comprises: 
     providing a flexible printed circuit board for operating a data integrated circuit chip; 
     providing an anisotropic conductive film; 
     forming on the data integrated circuit chip first and second protruding conductors; 
     bonding the first data pad with the first protruding conductor on the data integrated circuit chip; 
     bonding the second data pad with the second protruding conductor on the data integrated circuit chip; and 
     bonding the flexible printed circuit board with the second data pad by the anisotropic conductive film. 
     In the above methods according to a second mode of the invention (chip-on-glass method), the switching element is preferably a thin film transistor. 
     In a fifth aspect, the present invention also provides an X-ray detector fabricated according to the first and second modes set forth above. 
     Additional features and advantages of the invention will be set forth in the description, which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. 
     In the drawings: 
     FIG. 1 is a cross-sectional view of an enlarged scale illustrating the Wire Bonding method, where an X-ray detector panel and an integrated circuit are connected each other by a wire. 
     FIG. 2 is a cross-sectional view of an enlarged scale illustrating one embodiment of the present invention wherein an X-ray detector panel and an integration circuit are connected each other according to first mode (tape carrier package) of the present invention. 
     FIG. 3 is a plan view of an enlarged scale illustrating a marginal section of an X-ray detector containing a gate pad and data pad. 
     FIG. 4 is a cross-sectional view of an enlarged scale illustrating another embodiment of the present invention wherein an X-ray detector panel and an integrated circuit are connected to each other according to a second mode (chip-on-glass method) of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the invention will be described in detail hereinafter, referring to FIGS. 2 to  4 . 
     A first mode of the present invention adapts the tape carrier package method to the process of manufacturing an X-ray detector. Tape carrier packaging was generally introduced initially by General Electric Co., in the U.S. in the 1960s and has been greatly developed after the 1980s. According to this method, a chip is electrically and mechanically connected to a panel using a tape with fine circuit lines. The method includes an inner lead bonding process, an encapsulation process and an outer lead bonding process. As shown in FIG. 2, the tape carrier used in this method includes first and second polyamide films  20   a  and  20   b  each having an inner lead and an outer lead attached thereto. 
     In the inner lead bonding process, heat energy and pressure bond the chip and the inner lead of the tape carrier. The encapsulation process forms a film of an epoxy-type resin that protects the chip and the inner lead from the surrounding environment, after the inner lead bonding process. The outer lead bonding process connects the outer lead to a pad formed on a printed circuit board, after an electrical test following the encapsulation process. 
     FIG. 2 illustrates a partial cross-section of an X-ray detector fabricated using the tape carrier package method in accordance with the first mode of the present invention. 
     As illustrated in FIG. 2, a plurality of copper foils  100  in a striped pattern are adhered to each of two polyamide films  20   a  and  20   b , each foil having an inner lead  17  and an outer lead  18 . The inner lead  17  is provided for connection to a scanning integrated circuit chip  14  or a data integrated circuit chip  15 . The outer lead  18  is provided for connection to a gate pad  12  or a data pad  13  on the X-ray detector panel  10 , or for connection to a printed circuit board  23 . 
     Before connecting the inner lead  17  to the chip  14  or  15 , it is necessary to form a protruding electrode or bump  16  on the chip  14  or  15  in advance. 
     The inner lead  17  and the bump  16  are bonded with pressure and heat, and the inner lead  17  and the chip  14  or  15  are encapsulated with a resin protective film  24 . 
     An anisotropic conducting film  21  is used to connect the outer lead  18  to the gate pad  12  or data pad  13  on the X-ray detector panel  10 . A soldering contact  22  is used to connect the outer lead  18  to the printed circuit board  23 . 
     FIG. 3 shows a gate line  30 , gate electrode  31 , data line  32 , source electrode  33 , drain electrode  34 , common electrode  36  and pixel electrode  37 , gate pad  40  and its contact hole  41 , and data pad  38  and its contact hole  39 . 
     Although only part of a panel is illustrated and total line distribution cannot be seen, FIG. 3 shows that a gate line  30  is disposed crosswise and a gate electrode  31  is connected to each gate line, and in the upper position, a data line  32  is disposed lengthwise and a source electrode  33  is connected to each data line. A drain electrode  34  is disposed facing the source electrode  33  to constitute a thin film transistor. 
     The drain electrode  34  has a contact hole  35  to connect with the common electrode  36 , and a pixel electrode  37  is disposed in the upper position of the TFT to constitute a storage capacitor together with the common electrode  36 . 
     The storage capacitor receives X-ray radiation and collects electron-hole pairs produced in a photosensitive material (not illustrated) and stores them in the pixel electrode  37 . A scanning integrated circuit chip (not illustrated) transmits a scanning signal to the gate line  30  thereby to sequentially apply a voltage on a gate electrode  31 . A data integrated circuit chip (not illustrated) applies a voltage on a data line  32  crossing the selected gate electrode  31 , enabling the charges stored in the storage capacitor to flow outside through the contact hole  35  of the drain electrode  34 . 
     In order to transmit a scanning signal to the gate line  30  and make electric charges stored in the storage capacitor flow to an external data integrated circuit chip, preferably a gate pad  40  for the gate line  30  and the scanning integration circuit  14  are connected with each other according to the method shown in FIG. 2, and a data pad  38  for the data line  32  is connected with the data integrated circuit chip  15  by the same method. Alternatively, either of the connections may be accomplished by the chip-on-glass method disclosed below. 
     For the alignment and connection of a data pad  38  connected to the data line  32  according to the first mode described above, description is not given here because it is substantially the same as explained above. 
     Now, the second mode of the present invention, which adapts the chip-on-glass method to attach an integrated circuit to an X-ray panel, is described. 
     While in the tape carrier package method, an integrated circuit chip is mounted on a film, in the chip-on-glass method an external scanning integrated circuit chip or data integrated circuit chip is mounted directly on a panel to form a connection therebetween. 
     According to this method, a protruding electrode or conductor called a “bump” in the form of a hemisphere is formed on the aluminum electrode part of an integrated circuit chip, and then the integrated circuit chip is placed such that the bump faces the connecting terminal of a panel, and both are connected with each other by heating with pressure. With this method, it is possible to form a plurality of bumps on the total surface of a chip and to establish all of the connections at the same time irrespective of the number of bumps, which enables high-density connection and mounting in a short time. Automation of this method is easy because the bump tends to place itself in a correct position by the action of surface tension when the bump is melted by heating. 
     Referring to FIG. 4, a bump  16  is shown which has been formed on a scanning integrated circuit chip  14  to connect it with the X-ray detector panel  10 . The bump  16  is aligned with a gate pad  12  connected to a gate line  30  on the X-ray detector panel  10 , and the bump  16  and gate pad  12  are adhered by heating. The scanning integrated circuit chip  14  may have a plurality of bumps  16 , which may all be connected with a plurality of gate lines  30  on the X-ray detector panel  10  in this way. The integrated circuit chip  14  is thus connected to the X-ray detector panel  10  and therefore any other accessory, such as a tape carrier package, is not necessary in this method. 
     Also, the data integrated circuit chip  15  can be connected by the same method as the scanning integrated circuit chip  14 , for the alignment and connection of data pad  13  connected to data line  32  via the chip-on-glass method is substantially the same as described above and is therefore not repeated. 
     After the connection of the integrated circuit chip  14  or  15 , a flexible printed circuit board  25  is connected to the X-ray detector panel  10  by means of an anisotropic conductive film  21 . The anisotropic conductive film  21  is a kind of thermosetting resin film containing conductive particles, and can establish an electrical connection in the vertical direction when heated with pressure after aligning the panel  10 , flexible printed circuit board  25  and gate pad  12  or data pad  13 . 
     As described in detail heretofore, the present invention employs the tape carrier package or chip-on-glass method in connecting together an X-ray detector panel and a scanning or data integrated circuit chip. According to the invention, a reduction in processing time and a productivity improvement are obtained. 
     In particular, the tape carrier package method can produce a light, thin and small package because it produces a package by connecting a scanning or data integration chip on a polymer film. Also, it can be used in extremely narrow pitch for high resolution and preciseness, and products made by it can be repaired easily. 
     The chip-on-glass method provides a stable connection and fine pitch connection because it mounts an integrated circuit chip directly on a detector panel and requires no additional components. Accordingly, cost reduction and a light product can be obtained, as well as good reliability. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the x-ray detector and method of fabricating the same of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.