The present invention relates to an anisotropically electroconductive connection body, in which two elements, each having electrodes on a confronting face, are connected with each other, as well as to a method for forming such a connection body by interposing between the elements a connecting material containing a binder component comprising a thermosetting resin.
A connecting material constituted predominantly of a thermosetting resin has been used for establishing electrical connection between opposing electrodes disposed on two elements to be bonded with each other. For example, in a liquid crystal display (LCD), such a connection is realized between an indium tin oxide film (ITO film) on a substrate glass plate and an IC chip of a driver IC or a tape carrier package (TCP). Also in the assemblage of semiconductors, such as IC and LSI, on a substrate circuit board, it has been practiced to build up electrical connection between bear chips of the semiconductors and the circuit board directly using a connecting material. The connection between the circuit board and these elements to be connected is performed by holding them in a posture in which the electrodes or terminals disposed on the chips and on the circuit board are in a correspondingly confronting relationship with each other, while interposing the connecting material between these elements, whereupon the material is caused to harden to attain mechanical firm fixation and electrical connection therebetween simultaneously.
In such a connecting material, a thermosetting resin is used as the main component. The connecting material is interposed between the elements to be connected, for example, IC chips and substrate circuit boards, and these elements are held in such a posture that the electrodes or terminals to be electrically connected together disposed on them are in a correspondingly confronting relationship, whereupon the elements are heat-pressed onto each other by pressing them together with heating to cause the thermosetting resin to set to thereby build up the connection body. Here, the mechanical bonding between the elements is secured by the adhesive strength of the resin and the electrical connection between the corresponding electrodes or terminals is attained by a pressed friction contact of them secured by the heat setting of the resin. This electrical connection by frictional press contact between the elements may be attained by direct contact of the electrodes or the terminals with each other or under intermediation with electroconductive particles contained in the connecting material in a dispersed state.
The connection body formed in this manner is held in an electrically conductive condition with respect to the connected electrodes or terminals by direct or intermediate electroconductive contact of them, while the connection body is held in an insulated condition between the adjacent connected electrodes or terminals with each other, by isolation of them and due to isolation of each electroconductive particle by the electroinsulating resin mass surrounding them. Thus, the resulting assembly serves as an anisotropically electroconductive connection body.
The elements to be connected are put together and the connecting material is interposed therebetween in such a manner that a part of the material is caused to protrude from the periphery of one of the elements on the other element to form an extraneous portion of the material on the other element in order to contribute to the positioning of the elements and in order to exclude the occurrence of defects in the connection between the elements.
The connection body having such a protruded portion obtained in this manner was found, however, to be still subject to the occurrence of defective electric continuity. Examination of the reason for this problem had led to the discovery that the connecting material in the protruded portion mentioned above is not subjected to heat setting sufficiently and is in a state in which hardened resin and uncured mass are present therein in a mixed form. In general, the heat-set resin contained in the connection body may often be contaminated by impurities. For example, an epoxy resin commonly used as a thermosetting resin often contains impurities, including chloride ions originating from its raw material, epichlorohydrin. In some cases, impurities, such as chloride ions, sodium ions, etc., may also be introduced from the elements to be bonded together or from contamination through the processing steps.
These impurities will not usually cause any hazard of galvanic corrosion at the heat-pressed contact portion, since the impurities are confined within the heat-set resin in the heat-pressed portion of the connection material. The uncured resin mass has, however, a high hygroscopic ability and may have a considerable moisture content, causing the ionic impurities to become associated with the contained water, resulting in an increase in the electroconductivity of the resin mass. Since the electrodes and terminals of the elements to be bonded are laid passing through the above-mentioned protruding extraneous part of the bonding mass, therefore, the electrodes and terminals are brought into contact with the higher water content region. When the assemblage containing these elements is actuated by impressing a voltage, aluminum constituting the material of the electrode and terminal, ITO and so on may be subjected to a galvanic corrosion, resulting eventually in the occurrence of a defective electroconductivity in the above-mentioned extraneous portion of the resin mass.
The object of the present invention is to provide an anisotropically electroconductive connection body formed between two elements to be connected together, each provided on a confronting face with a plurality of electrodes, which can avoid the occurrence of defective electroconductivity under prevention of galvanic corrosion of the electrodes and terminals inside the connecting material, as well as to provide a method for attaining such a connection body by interposing between the elements to be connected together a connecting material containing an adhesive component comprising a thermosetting resin.
The above object of the present invention is attained according to the present invention. Thus, the present invention consists of an anisotropically electroconductive connection body and a method for forming such a connection body, as given below:
(1) An anisotropically electroconductive connection body, in which two elements, each having electrodes on a confronting face, are connected with each other, comprising
a connecting material containing an adhesive component comprising a thermosetting resin, which is interposed between the two elements to be connected, and
an extraneous portion of the connecting material protruding from the periphery of one of the elements on the other one of the elements,
wherein the degree of hardening of the thermosetting resin in the connecting material in the extraneous portion is at least 60%.
(2) The connection body as defined in the above (1), wherein the saturation limit of moisture absorption of the connecting material in the extraneous portion at 85xc2x0 C. and at a relative humidity of 85% is 3% or less.
(3) A method for forming an anisotropically electroconductive connection body, in which two elements, each having electrodes on confronting faces, are connected with each other, comprising
interposing between the elements to be connected with each other a connecting material containing an adhesive component comprising a thermosetting resin so as to form an extraneous portion of the connecting material protruding from the periphery of one of the elements on the other one of the elements, while holding these elements in a posture in which the electrodes on the confronting face of each of the elements are in a correspondingly confronting relationship with each other,
heat-pressing the two elements onto each other to harden the thermosetting resin and
heating the extraneous portion of the connecting material simultaneously with or after the heat-pressing to effect hardening of the thermosetting resin of this portion up to a degree of hardening of at least 60%.
(4) The method as defined in the above (3), wherein the heating of the extraneous portion is effected by blowing a hot gas onto the extraneous portion.
(5) The method as defined in the above (3), wherein the heating of the extraneous portion is effected by heating the other one of the elements.
(6) The method as defined in the above (3), wherein the hardening of the thermosetting resin in the extraneous portion of the connecting material is effected by heating the connection body totally after the heat-pressing.