Abstract:
An IC chip includes a built-in semiconductor and a plurality of bumps exposed to the exterior and provided on a surface, the bumps being pressed and bonded to a substrate or the like using an ACF (Aniosotropic Conductive Film). With respect to at least one of the bumps among the plurality of bumps, the height H of the outer portion is determined to be larger than the height H of the inner portion. When the ACF is pressed by the IC chip, conductive particles in the ACF are prevented from outwardly escaping from the bump by the high outer portion. Therefore, a greater number of conductive particles can be trapped around the bump.

Description:
INDUSTRIAL FIELD OF THE INVENTION 
     The present invention relates to an integral circuit (IC) chip in which a plurality of bumps forms an input terminal and an output terminal, and to an IC chip assembly including the IC chip. Furthermore, the present invention relates to a liquid crystal device including the IC chip. Furthermore, the present invention relates to an electric apparatus including the IC chip. 
     DESCRIPTION OF THE RELATED ART 
     Liquid crystal devices are widely used for visual image display units in a variety of electric apparatuses such as mobile phones and video cameras. Such electric apparatus and liquid crystal devices are equipped with a variety of semiconductor components. The “semiconductor component” is an IC chip itself or an IC chip assembly in which an IC chip and a substrate are integrated. 
     With respect to the above-mentioned IC chip, a bare chip IC which is not packaged, an IC which is packaged and has a terminal on the rear surface, and the like have been known. In addition, with respect to the above-mentioned IC assembly, the following has been known: A chip-on-board (COB) or a multi-chip-module (MCM) in which one or a plurality of IC chips is mounted on one substrate, a chip-on-flexible-printed-circuit (COF) in which an IC chip is mounted on a flexible-printed-circuit (FPC), or the like. 
     When the above-mentioned IC chip is conductively connected to an object member to be bonded, such as a wiring substrate, there is a method in which after formation of bumps on an input terminal and an output terminal of the IC chip, a conductive connection is achieved by utilizing the bumps. In this method, an anisotropic conductive adhesive such as an anisotropic conductive film (ACF) is intercalated between the IC chip and the object member to be bonded, and the connection is performed using the anisotropic conductive adhesive. In this state, the bumps of the IC chip are conductively connected to an electrode terminal on the object member to be bonded by conductive particles containing in the anisotropic conductive adhesive. 
     However, as shown in FIG. 10, in a conventional IC chip, out of a plurality of surfaces of bumps  52  which is provided on the active sufrace  51   a  as an input and output terminal, surfaces  52   a  to which is applied an anisotropic conductive adhesive is formed to be plane and approximately parallel to an active surface  51   a  of an IC chip  51 . 
     Generally, when the IC chip  51  is bonded to an object member to be bonded using the anisotropic conductive adhesive, the IC chip  51  is pressed to the object member to be bonded by intercalating the anisotropic conductive adhesive. The pressed anisotropic conductive adhesive is extruded laterally. When the surfaces  52   a  of the bumps  52  are a plane and are parallel to the active surface  51   a  of the IC chip  51  as described above, the anisotropic conductive adhesive, which is pressed by the surface  52   a  of the bump  52 , spreads so as to escape from the bump  52 . Therefore, conductive particles around the surfaces  52   a  of the bumps  52  decrease, so that satisfactory conductivity is not obtained. 
     The present invention is performed in view of the above-described problem. An object of the present invention is to prevent conductive particles in an anisotropic conductive adhesive from escaping from surfaces of bumps of an IC chip, and to retain more numerous conductive particles around the surfaces of the bumps. 
     (1) To this end, an IC chip in accordance with the present invention includes a built-in semiconductor and a plurality of bumps exposed to the exterior, and provided on a surface, the bumps being pressed and bonded to an object member to be bonded using an anisotropic conductive adhesive; wherein a mounting surface of the bump opposed to the object member to be bonded has a larger height in the outward direction of the IC chip than a height in the inward direction thereof. 
     With respect to the IC chip, the height of the outer portion of the bump is larger than the height of the inner portion thereof. Thus, when an anisotropic conductive adhesive is pressed by the IC chip, conductive particles in the anisotropic conductive adhesive are prevented from outwardly moving toward the outside of the IC chip by the high outer portion of the bump. As a result, numerous conductive particles can remain around the bump so that substantial conductivity can be obtained. 
     In addition, “an anisotropic conductive adhesive” is a conductive adhesive including conductive particles, and is not limited to a particular adhesive material in practice. An anisotropic conductive film (ACF) which has the overall form of a film, an anisotropic conductive adhesive which has the overall form of a paste and the like are exemplified. 
     In addition, “an object to be bonded” is an arbitrary member to which an IC chip is mounted. A variety of members such as a hard wiring substrate, a soft wiring substrate, a flexible wiring substrate, and a transmissive substrate for a liquid crystal panel are exemplified. 
     (2) With respect to the above-described IC chip, a difference (H-h) between the outward height H of the bump and the inward height h thereof is preferably smaller than a diameter of a conductive particle in the anisotropic conductive adhesive. Thus, numerous conductive particles can be trapped around the bump. 
     (3) With respect to the above—described IC chip, the bump may be formed so as to include a concave portion on a mounting surface opposed to the object member to be bonded. With this form, conductive particles can remain in the concave portion, so that a greater number of conductive particles can be trapped around the bump. 
     (4) An IC assembly in accordance with the present invention includes an IC chip and a substrate for mounting the IC chip using an anisotropic conductive adhesive; wherein the IC chip is an IC chip according to any one of the paragraphs (1) to (3) above. With this IC assembly, numerous conductive particles can remain around the bump in the same way as described above in paragraphs (1) to (3), which explain the IC chip. Therefore, substantial conductivity can be obtained. 
     (5) Next, a liquid crystal device in accordance with the present invention includes a liquid crystal panel including a pair of substrates containing a liquid crystal sandwiched therebetween, and an IC for driving the liquid crystal directly or indirectly connected to the liquid crystal panel using an anisotropic conductive adhesive; wherein the IC for driving the liquid crystal is composed of the IC chip according to any one of the paragraphs (1) to (3). With this liquid crystal, numerous conductive particles can be retained around the bump in the same way as described above in paragraphs (1) to (3), which explain the IC chip. Therefore, substantial conductivity can be obtained. 
     In addition, “a direct connection of the IC for driving the liquid crystal to the liquid crystal panel” means that after mounting the IC for driving the liquid crystal to an intermediate substrate other than the liquid crystal panel, the IC for driving the liquid crystal is connected to the liquid crystal panel by connecting the intermediate substrate to the liquid crystal panel. 
     (6) Next, an electric apparatus in accordance with the present invention includes an IC chip wherein the IC chip is an IC chip according to any one of paragraphs (1) to (3). With this electric apparatus, numerous conductive particles can be retained around the bump in the same way as described above in paragraphs (1) to (3), which explain the IC chip. Therefore, substantial conductivity can be obtained. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an perspective view of an IC chip according to an embodiment of the present invention. 
     FIG. 2 is a cross-sectional view of the IC chip shown in FIG.  1 . 
     FIG. 3 is an perspective view of an IC assembly according to an embodiment of the present invention. 
     FIG. 4 is an enlarged cross-sectional view of an essential part of the IC assembly shown in FIG.  3 . 
     FIG. 5 is a cross-sectional view of a bump according to a modified embodiment of the present invention. 
     FIG. 6 is a cross-sectional view of a bump according to another modified embodiment of the present invention. 
     FIG. 7 is an perspective view of a liquid crystal device according to an embodiment of the present invention. 
     FIG. 8 is an perspective view of assembly of an electronic apparatus according to an embodiment of the present invention. 
     FIG. 9 is a block diagram showing an example of an electric control system used for the electronic apparatus shown in FIG.  8 . 
     FIG. 10 is a front view of an example of a conventional IC chip. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows an IC chip according to an embodiment of the present invention. A circuit which is arranged so as to perform a predetermined function is built into an IC chip  1 . 
     The IC chip  1  is formed as an IC for driving a liquid crystal in a liquid crystal device or the like. A plurality of bumps  2  is provided on an active surface la of the IC chip  1  as an input terminal or an output terminal of the internal circuit. 
     With respect to the IC chip  1  shown in FIG. 2, for example, aluminum electrodes  3  are formed at appropriate areas of a surface of a chip body  1   b . Passivation films  4  are provided on the surface of the chip body  1   b  other than the aluminum electrodes  3  in such a manner that the aluminum electrodes  3  are open. Then, bumps  2  are formed on the aluminum electrodes  3  by selective plating of gilding. In FIGS. 1 and 2, the bumps  2  are illustrated enlarged compared with the size of the IC chip  1  in order to clearly show the configuration of the bump  2  or the like. 
     In addition, the arrangement of the bumps on the IC chip is not limited to the arrangement shown in FIG.  1 . The bumps may be provided along two edges of the IC chip, or may have a staggered arrangement. 
     FIG. 3 shows an embodiment of the use of the IC chip  1 , that is, a chip-on-board (CC)B) type IC assembly  6 . The IC chip  1  is bonded to a predetermined region for mounting the IC chip A on a printed substrate  7 , which is an object member to be bonded, using an anisotropic conductive film (ACF)  8  as an anisotropic conductive adhesive, so that the IC assembly  6  is formed. As shown in FIG. 3, circuit parts  9  such as a chip resistor or a chip capacitor are arranged around the IC chip  1 , if necessary. 
     When the adhesive which forms ACF  8  includes a thermosetting resin, the IC chip  1  is bonded to the printed substrate  7  by inserting the ACF  8  between the IC chip  1  and the printed substrate  7 , by heating them, and by pressing them. As shown in FIG. 4, the bumps  2  under the IC chip  1  are conductively connected to electrode terminals  8   a  and  8   b  on the printed substrate  7  by conductive particles  11  in the ACF  8 . 
     As shown in FIG. 4, in the present embodiment, the height H of the outer portion of the bump  2  is larger than the heights of the inner portion thereof. Thus, when the ACF  8  is pressed to the printed substrate  7  by the IC chip  1 , substantial amount of resin in the adhesive which forms the ACF  8  are pushed outwardly of the IC chip  1 . However, the conductive particles  11 , which tend to be moved toward the outside of the region in which the IC chip  1  is mounted, are prevented from flowing out by an interior wall  17  of the outer portion of the bump  2  having a large height. Therefore, numerous conductive particles  11  included in the ACF  8  remain between the bump  2  and the electrode  8   a  or between the bump  2  and the electrode  8   b . Thus, superior conductivity can be obtained. 
     The difference between the height of the outer portion of the bump  2  and the height of the inner portion thereof (H-h) is preferably smaller than the diameter of the conductive particle  11  in the ACF  8 . When the difference (H-h) is larger the diameter of the conductive particle  11 , a gap between the bump  2  and the electrode  8   a  or between the bump  2  and the electrode  8   b  becomes larger than the diameter of the conductive particle  11 . Thus, the bump  2  cannot satisfactorily trap the particles  11 . 
     FIG. 5 shows a bump  2  according to a modified embodiment of the present invention. With respect to the bump  2 , a concave portion  5  is formed on a surface to which an ACF  8  is attached and to which an electrode  8   a  or an electrode  8   b  is opposed as an object member to be bonded to the bump  2 . The concave portion  5  can prevent the conductive particles  11  from flowing out at an interior wall  17  of the outer portion of the bump  2  having a large height. Further, numerous conductive particles  11  can remain and accumulate around the bump  2  due to a dimple  15  at the concave portion  5 ; therefore, superior conductivity can be obtained. 
     FIG. 6 shows a bump  2  according to another modified embodiment of the present invention. With respect to the bump  2 , a surface to which an ACF  8  is attached and to which an electrode  8   a  or an electrode  8   b , which is an object member to be bonded, is opposed to the bump  2  is outwardly convexed. Numerous conductive particles  11  can remain around the inner portions of the bump  2  having a small height due to a taper portion  18  of the convex portion; therefore, superior conductivity can be obtained. 
     FIG. 7 shows a liquid crystal device as another embodiment of an IC assembly using an IC chip shown in FIG.  1 . The liquid crystal device  12  includes a pair of transmissive substrates  13   a  and  13   b , which are opposed to each other. A seal member  14  is printed to be a rectangular frame configuration on one of these substrates  13   a  and  13   b . The substrates  13   a  and  13   b  are bonded together by the seal member  14 . Liquid crystal is filled in a gap between the substrate  13   a  and the substrate  13   b , that is, in a cell gap. In addition, a plurality of linear transmissive electrodes  16   a  is formed on the inner surface of the substrate  13   a  by a photolithography process. On the other hand, a plurality of linear transmissive electrodes  16   b  is formed on the inner surface of the substrate  13   b  by a photolithography process. 
     Thus, a liquid crystal panel in which a pair of the substrate  13   a  and  13   b  containing liquid crystal sandwiched therebetween is formed. With respect to the liquid crystal panel, the substrate  13   a  is longer than the substrate  13   b  to form a stretched portion. Regions for mounting IC chips A are provided on the stretched portion in order to mount ICs for driving the liquid crystal  21 , which are IC chips. 
     The transmissive electrodes  16   a , which are formed on the substrate  13   a , are directly elongated to the stretched portion of the substrate  13   a , and end portions thereof form land in the regions for mounting IC chips A. In addition, the transmissive electrode  16   b  formed on the substrate  13   b  is connected to a conductive line on the stretched portion of the substrate  13   a  via a conductive member (not shown), which is provided between the substrate  13   a  and the substrate  13   b . The end portion of the conductive line forms a land in the regions for mounting the IC chips A. In the present embodiment, the stretched portion of the transmissive substrate  13   a  is an object member to be bonded for bonding the ICs for driving the liquid crystal  21 , that is, the IC chips. 
     After mounting the ICs for driving the liquid crystal  21  on the regions for mounting IC chips A, polarizing plates  12   a  are bonded to the outer surface of the transmissive substrate  13   a  and the outer surface of the transmissive substrate  13   b . In addition, a backlight is provided at the outside of any one of the transmissive substrate  13   a  and the transmissive substrate  13   b , if necessary. The IC for driving the liquid crystal  21  is a semiconductor device, which has a function of transmitting a scanning signal and a data signal to the transmissive electrode  16   a  and the transmissive electrode  16   b . A plurality of bumps  2  is provided on active surfaces  21   a  (lower surfaces shown in FIG. 7) in order to transmit or receive signals to or from an external circuit, or in order to receive a voltage applied from an external source. With respect to the bump  2  shown in FIG. 4, the height H of the outer portion of the bump  2  is larger than the height h of the inner portion thereof. Therefore, when heating and compression is performed to an ACF  8  by the IC for driving the liquid crystal  21 , conductive particles  11  included in the ACF  8  are prevented from moving outwardly from the periphery of the bump  2 . Thus, numerous conductive particles  11  can remain between the bumps  2  and the lands in the regions for mounting the IC chips A. 
     FIG. 8 shows a mobile phone according to an embodiment of the present invention, which is an electronic apparatus including an IC chip in accordance with the present invention. The mobile phone includes an upper housing  26  and a lower housing  27 . The upper housing  26  includes an antenna  28  for transmission and reception, a keyboard  29 , and a microphone  32 . The lower housing  27  includes a liquid crystal device  12  shown in FIG. 7, for example, a speaker  33  and a circuit substrate  34 . 
     As shown in FIG. 9, a receiving unit  38  connected to the input terminal of the speaker  33 , a transmitting unit  37  connected to the output terminal of the microphone  32 , a controlling unit  36  having a central processing unit (CPU), and a power supply unit  39  which applies electric power to each unit are provided on the circuit substrate  34 . The controlling unit  36  reads signals of the transmitting unit  37  and the receiving unit  38 , and based on it, the controlling unit  36  transmits information to the ICs for driving the liquid crystal  21 , so that visible information is displayed on the effective display area of the liquid crystal device  12 . 
     While the present invention has been described with respect to what is at present considered to be the preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. The invention covers various modifications and equipment arrangements included within the spirit and scope of the invention disclosed in the claims. 
     For example, an IC chip in accordance with the present invention may have an arbitrary configuration other than the configuration shown in FIG.  1 . An IC assembly in accordance with the present invention is not limited to the COB type semiconductor assembly shown in FIG. 3, but may be a chip-on-flexible-printed-substrate (COF) type assembly. Furthermore, the IC assembly is not limited to the liquid crystal device shown in FIG. 7, but may be another arbitrary assembly to which an IC chip having a bump is bonded by an anisotropic conductive adhesive. In addition, a liquid crystal device in accordance with the present invention is not limited to the COG type liquid crystal device shown in FIG. 7 in which an IC for driving a liquid crystal is directly mounted on a liquid crystal panel substrate, but may have a variety of configurations. Furthermore, although FIG. 8 shows a mobile phone as one example of an electric apparatus, the present invention can obviously be applied to a variety of electric apparatuses such as a video camera. 
     With respect to an IC chip, an IC assembly, a liquid crystal device, and an electronic apparatus in accordance with the present invention, the height of the outer portion of a bump is larger than the height of the inner portion thereof. Therefore, when an anisotropic conductive adhesive is pressed by the IC chip, conductive particles in the anisotropic conductive adhesive can be prevented from moving outwardly from the region for mounting the IC chip by the high outer portion of the bump. Thus, numerous conductive particles can remain around the bump, so that substantial conductivity can be obtained.