Electrodes on a mounting substrate and a liquid crystal display apparatus including same

Abstract: An electrode wiring (4-5) on a mounting substrate (1) adapted for use in liquid crystal (3) display apparatus (20), the electrode wiring including portions of Mo or Mo alloy (10) to which bumps (7) of an integrated circuit (6) such as LSI is bonded with conductive paste (8).

Description: BACKGROUND OF THE INVENTION 1. Field of the invention: The present invention relates generally to a wiring arrangement, and more particularly to a substrate assembly comprising a pattern of electrode wiring formed on a substrate, the electrode wiring including portions to which bumps of an integrated circuit such as an LSI are connected. The invention relates also to liquid crystal display apparatus incorporating such a substrate assembly. 2. Description of the prior art: As a method of mounting an integrated circuit (IC) or the like on a substrate, a direct bonding in which IC chips are connected face-down to a substrate is well known. In this method, tiny electrodes formed on the IC chips are connected to electrodes on the mounting substrate with conductive paste, etc. This method is particularly suitable when a large scale integration (LSI) with high integration is mounted on the mounting substrate. For connection convenience, electrodes of ICs are projected, which are commonly called bumps, and those projected on the mounting substrate connected to the bumps are called pads because of their pad-like nature. A number of circuit pattern wirings are electrically connected to the pads on the mounting substrate. Japanese Laid-Open Patent Publication No. 60-238817 discloses a method of mounting ICs or the like for driving a liquid crystal by using a glass substrate of a liquid crystal panel as a mounting substrate in the above-mentioned manner. This method makes possible a direct mounting of an IC on the panel for driving a liquid crystal, an LSI, or the like, with the use of an increasing number of pins depending upon a magnification, a high definition, and a minimization of picture element pitches of a liquid crystal display apparatus. This method uses pads made of Au or ITO (Indium Tin Oxide). However, the above-mentioned known method has the following problems: When the pad is made of Au, the connection resistance at a connecting portion between the bumps and pads is low and stable. The formation of such a pad requires a gilding process, thereby complicating the step. In addition, Au is expensive, and the production cost becomes high. When the pads are made of ITO, it is advantageous in that the process of making them can share the process of making transparent electrodes of ITO during the production of a liquid crystal display panel, thereby reducing the number of steps in the process. However, there is a problem that the connection resistance at the connection points between the pad made of ITO and bumps becomes high (5 - 10 Ω). When the connection resistance increases, the voltage applied to the liquid crystal display portion substantially decreases due to a voltage drop at the connection points, so that the quality of the resulting display becomes poor. This is particularly notable in a large-sized or high definition liquid crystal display apparatus. These display apparatus generate a number of outputs per IC so as to drive a liquid crystal with high clock frequency, and a greater power consumption in the ICs and a liquid crystal itself, so that instantaneous passage of a current is difficult through the circuit patterns. This causes a further drop of the voltage applied to the liquid crystal display portion. US-A-4 853 296 relates to an electrode plate for a colour display device and teaches the use of nickel as an essential element in a metal thin film conductor, formed on a transparent electrode, which conductor may have a multi-layer structure, including a layer of molybdenum. SUMMARY OF THE INVENTION In one aspect, this invention provides a substrate assembly, comprising a pattern of electrode wiring formed directly on a mounting substrate, the electrode wiring of said pattern being formed at least partially of two layers, one layer including portions consisting solely of Mo metal to which portions bumps of an integrated circuit such as an LSI are exclusively connected. In another aspect, this invention provides a liquid crystal display apparatus comprising the above substrate assembly and a further substrate which sandwich a layer of liquid crystal therebetween in a display region of the apparatus, said integrated circuit being provided in a region of said mounting substrate outside said display region, for driving the liquid crystal layer. In a preferred embodiment, the portions of Mo metal are connected to the bumps of said integrated circuit through conductive paste, the electrode wiring of said pattern being covered by an insulating material excepting at least said portions connected to the bumps of the integrated circuit. The invention described herein makes possible the objectives of (1) providing an electrode wiring which can be connected to an integrated circuit without the possibility of increasing connection resistance at the connecting portions to the integrated circuit, and (2) providing an electrode wiring which can be connected to an integrated circuit easily and economically. BRIEF DESCRIPTION OF THE DRAWINGS This invention may be better understood and its numerous objects and advantages will become apparent to those skilled in the art by reference to the accompanying drawings as follows: Figure 1 is a sectional view showing an example of the present invention; Figures 2, 3 and 4 are sectional views showing other examples, respectively; and Figures 5 6 and 7 are sectional views showing modifications to the embodiments shown in Figures 1, 2 and 3. DESCRIPTION OF THE PREFERRED EMBODIMENTS Figure 1 shows a main portion of a liquid crystal display panel 20 on which electrodes pads 10 are formed. A liquid crystal 3 is liquid-tightly sandwiched between glass substrates 1 and 2 of the liquid crystal display panel 20 . On the glass substrate 1 there is formed an input circuit pattern wiring 5 and output circuit pattern wiring 4 respectively for a liquid crystal driving LSI 6 . The input circuit pattern wiring 5 is connected to an outside control circuit (not shown). The output circuit pattern wiring 4 is connected to a wiring or an electrode in a liquid crystal cell of a display portion of the liquid crystal display panel 20 . The circuit pattern wirings 4 and 5 can be made of a transparent conductive film such as an ITO, Ni, Cu/Ni, Ti, Ta, W, or Al. The pads 10 are disposed at predetermined positions on the circuit pattern wirings 4 and 5 so as to effect connection between the pattern wirings 4 , 5 , and bumps 7 of the liquid crystal driving LSI 6 . The pads 10 are made of Mo. The liquid crystal driving LSI 6 is connected to the glass substrate 1 of the liquid crystal panel 20 by a face-down bonding method. The bumps 7 of the LSI 6 are connected to the pads 10 , preferably, with conductive paste 8 , and are connected to the input circuit pattern wiring 5 and the output circuit pattern wiring 4 through the pads 10 . The conductive paste 8 of silver or any other conductive substance is applied at least to the top ends of the bumps 7 by use of a dispenser or a transcriber before the LSI 6 is mounted on the glass substrate 1 . In order to protect the pads 10 from being dissolved or eroded by a solvent or the like used in subsequent processes after the LSIs 6 are mounted, the conductive paste 8 may completely cover the pads 10 as shown in Figures 1 to 4, wherein the adjacent conductive pastes 8 are electrically disconnected from each other as with the interposition of a known electrically insulating film which is omitted in Figures 1 to 3. Alternatively, the conductive paste 8 may only cover the top portions of the pads 10 as shown in Figures 5 to 7, that is, the adjacent conductive pastes 8 are arranged at intervals, thereby eliminating the necessity of interposing electrically insulating films therebetween. The interval between one pad 10 and the next is preferably 50 µm but it can be larger than 50 µm, for example, 100 µm. Instead of silver, gold paste, copper paste, or carbon paste may be used as the conductive paste 8. In order to prevent the erosion of the pads 10 , an anti-moisture resin 9 is filled in the spots between the LSI 6 and the glass substrate 1 , and is allowed to harden. As mentioned above, the pads 10 of Mo have the following advantages: The pads 10 made of Mo are stable throughout the subsequent processes of forming the liquid crystal panel. For example, an insulating layer likely to increase connection resistance is prevented from being formed on the surface of the pads 10 even if the subsequent process includes a step at which an oxidation reaction occurs. As a result, the connection resistance at the connecting portions between the pads 10 and the bumps 7 is kept constantly low. In the present example, the connection resistance is several hundreds mΩ. In contrast, in the comparative example using pads made of either Ti, Ta, W, or Al the connection resistance between the pads 10 and the bumps 7 is several Ω to several hundreds Ω. Ti, Ta, W, or Al are metal materials whose specific resistances are as low as that of Mo but they are disadvantageous in that they are likely to form an undesirable insulating layer on the surface of the pads owing to an oxidation reaction during the formation of the panel. In the comparative example, the connection resistance at the connecting points with the bumps 7 is increased because of the presence of this insulating layer. In the illustrated embodiment the pads 10 are made of Mo, which is not liable to an oxidation reaction, and are bonded to the bumps 7 of the IC with conductive paste 8 , so that the connection resistance therebetween is low. Thus, the voltage applied to the liquid crystal display portion is prevented from dropping. Also, the pads 10 covered by the conductive paste 8 are protected against deterioration by a solvent in the course of the subsequent process of forming the panel. As a result, whether it may be a large-sized liquid crystal display apparatus or a high definition liquid crystal display apparatus, desired display conditions and high yield are satisfied. Mo is a relatively cheap material, thereby reducing the production cost. In addition, Mo is used to make wirings and electrodes in the display portions of the liquid crystal display panel 20 . Therefore, when the wirings and the electrodes are to be made of Mo, the pads 10 can be made in the same process. As a result, the step of forming the pads 10 is reduced, thereby saving time and money in production. Figure 2 shows another example. In this example, the wiring 12 made of Mo is formed in one piece with the pad 10 on the circuit pattern wirings 4 and 5 . A current flows through the circuit pattern wirings 4 and 5 and the wiring 12 at the same time, thereby reducing the wiring resistance as a whole. Figure 3 shows a further example. In this example, the input circuit pattern wiring 15 and output circuit pattern wiring 14 are made of Mo in one piece with the pads 10 of Mo. The pads 10 , the circuit pattern wirings 14 and 15 are formed in a single process, thereby reducing the production steps. Another wiring 13 made of a conductive material other than Mo is mounted on the circuit pattern wirings 14 and 15 of Mo. The wiring 13 is situated at positions other than those at which the bumps 7 of the LSI 6 are connected to the circuit pattern wirings 14 and 15 , and at the predetermined position the pads 10 of Mo are bonded to the bumps 7 of the LSI 6 with conductive paste 8 . The wiring resistance is reduced. Figure 4 shows another example in which a protective film 16 made of SiO₂, SiN or the like is formed on the circuit pattern wirings 4 and 5 against deterioration of the circuit pattern wirings 4 and 5 not only during the formation of the panel but also after the panel is formed. Thus, the production yield and reliability of the liquid crystal display apparatus is enhanced. In the illustrated examples, the circuit pattern wirings 4 and 5 are made in single layers of ITO, Ni, Cu/Ni, Ti, Ta, W, or Al. It is of course possible to make the wirings in multi-layers. The pads 10 are made of Mo in a single layer, but as long as the portions of the pads 10 bonded to the bumps 7 of the liquid crystal driving LSI 6 are made of Mo, the pads 10 can be multi-layered if the top layers are made of Mo. The glass substrate 1 of the liquid crystal display panel 20 is used as a mounting substrate, but the material for the mounting substrates is not limited to glass. Various materials can be used. Therefore, because of the adoption of a variety of material, the electrodes of the present invention are applicable to computers and any other electronic apparatus. As is evident from the foregoing, the present invention reduces processing steps, thereby saving time and money of the production. The connection resistance at the connecting portions between the electrodes on the mounting substrate and the bumps of the integrated circuit becomes low, thereby preventing the voltage applied to drive the liquid crystal from dropping. Since the electrode wiring on the substrate of a liquid crystal display panel is connected to the bumps of an integrated circuit such as an LSI for driving a liquid crystal through Mo layers, the connection resistance therebetween is advantageously reduced, thereby preventing the voltage applied to the liquid crystal display portion from undesirably dropping. Because of this advantage, whether it may be a large-sized liquid crystal display apparatus or a high definition liquid crystal display apparatus, satisfactory display conditions and production yields can be obtained. Moreover, when wirings and electrodes are made of Mo for the liquid crystal display portion, the production process is simplified with a reduced number of steps. This reduces the production cost.

Claims: A substrate assembly, comprising a pattern of electrode wiring formed directly on a mounting substrate (1), the electrode wiring of said pattern being formed at least partially of two layers, one layer including portions (10) consisting solely of Mo metal to which portions bumps (7) of an integrated circuit (6) such as an LSI are exclusively connected. A substrate assembly according to claim 1, wherein the portions (10) of Mo metal are connected to the bumps (7) of said integrated circuit (6) through conductive paste (8), the electrode wiring of said pattern being covered by an insulating material (9) excepting at least said portions (10) connected to the bumps of the integrated circuit. A liquid crystal display apparatus (20) comprising a substrate assembly according to claim 1 and a further substrate (2) which sandwich a layer of liquid crystal (3) therebetween in a display region of the apparatus, said integrated circuit (6) being provided in a region of said mounting substrate (1) outside said display region, for driving the liquid crystal layer (3). A liquid crystal display apparatus according to claim 3, wherein the portions (10) of Mo metal are connected to the bumps (7) of said integrated circuit (6) through conductive paste (8), the electrode wiring of said pattern being covered, in said region of the mounting substrate (1), by an insulating material (9) excepting at least said portions (10) connected to the bumps of the integrated circuit.

Inventors: YOSHIDA HIROKAZU, YOSHIDA, HIROKAZU
Applicants: SHARP KK, SHARP KABUSHIKI KAISHA
Application year: 1990
Main classification: H01L21
IPC codes: H01L25, G02F1, H01L21