In the production process of semiconductor integrated circuit devices, after a great number of integrated circuits are formed on a wafer composed of, for example, silicon, a probe test for sorting defective integrated circuits is generally conducted as to each of these integrated circuit, by inspecting basic electrical properties. This probe test is conducted under a temperature environment of, for example, 85° C. This wafer is then cut, thereby forming semiconductor chips. Such semiconductor chips are contained and sealed in respective proper packages. Each of the packaged semiconductor integrated circuit devices is further subjected to a burn-in test that electrical properties thereof are inspected under a high-temperature environment of, for example, 125° C., thereby sorting semiconductor integrated circuit devices having latent defects.
In such electrical inspection of integrated circuits, such as probe test or burn-in test, a probe member is in use for electrically connecting each of electrodes to be inspected in an object of inspection to a tester. As such a probe member, is known a member composed of a circuit board for inspection, on which inspection electrodes have been formed in accordance with a pattern corresponding to a pattern of electrodes to be inspected, and an anisotropically conductive elastomer sheet arranged on this circuit board for inspection.
As such anisotropically conductive elastomer sheets, those of various structures have heretofore been known. For example, the following Prior Art. 1 or the like discloses an anisotropically conductive elastomer sheet (hereinafter referred to as “dispersion type anisotropically conductive elastomer sheet”) obtained by dispersing conductive particles in an elastomer in a state oriented so as to align in a thickness-wise direction of the elastomer, and the following Prior Art. 2 or the like discloses an anisotropically conductive elastomer sheet (hereinafter referred to as “uneven distribution type anisotropically conductive elastomer sheet”) obtained by unevenly distributing conductive particles in an elastomer in a state oriented so as to align in a thickness-wise direction of the elastomer, thereby forming a great number of conductive parts extending in the thickness-wise direction and an insulating part for mutually insulating them. Further, the following Prior Art. 3 or the like discloses an uneven distribution type anisotropically conductive elastomer sheet with a difference in level defined between the surface of the conductive part and an insulating part.
In the uneven distribution type anisotropically conductive elastomer sheet, since the conductive parts are formed in accordance with a pattern corresponding to a pattern of electrodes to be inspected of an integrated circuit to be inspected, it is advantageous compared with the dispersion type anisotropically conductive elastomer sheet in that electrical connection between electrodes can be achieved with high reliability even to an integrated circuit small in the arrangement pitch of electrodes to be inspected, i.e., center distance between adjacent electrodes to be inspected.
In such an anisotropically conductive elastomer sheet, since the conductive particles are oriented by application of a magnetic field so as to align in the thickness-wise direction upon the production of this anisotropically conductive elastomer sheet, it is necessary to use particles exhibiting magnetism as the conductive particles. In order to provide an anisotropically conductive elastomer sheet having high conductivity and permitting the conductivity to be retained for a long period of time, it is essential for the conductive particles to have high conductivity by themselves and be chemically stable over a long period of time. From such a point of view, particles obtained by forming a coating layer formed of gold on the surfaces of core particles composed of ferromagnetic substance such as nickel are used as the conductive particles.
By the way, in a probe test conducted for integrated circuits formed on a wafer, a method that a probe test is collectively performed on a group of integrated circuits composed of, for example, 16 or 32 integrated circuits among a great number of integrated circuits formed on a wafer, and the probe test is successively performed on other groups of integrated circuits has heretofore been adopted.
In recent years, there has been a demand for collectively performing a probe test on, for example, 64 or 128 integrated circuits among a great number of integrated circuits formed on a wafer, or all the integrated circuits for the purpose of improving inspection efficiency and reducing inspection cost.
In such a probe test, an anisotropically conductive elastomer sheet used in a probe member for conducting the probe test is required to have durability capable of withstanding repeated use of, for example, at least 50,000 times when wafers that are an object of inspection are mass-produced products.
In a conventional anisotropically conductive elastomer sheet, however, the conductivity of conductive parts thereof has been markedly deteriorated when it has been used in the probe test repeatedly, for example, 20,000 times or more, so that it has been unable to be used in subsequent tests, and so it has been required to be replaced by new one.
In a burn-in test on the other hand, it takes a long time to individually conduct electrical inspection of a great number of integrated circuit devices because each integrated circuit device, which is an object of inspection, is fine, and its handling is inconvenient, whereby inspection cost becomes considerably high. From such reasons, there has been proposed a WLBI (Wafer Level Burn-in) test in which the burn-in test is collectively performed on a great number of integrated circuits formed on a wafer in the state of the wafer.
In such a WLBI test, an anisotropically conductive elastomer sheet used in a probe member for conducting the WLBI test is required to have durability capable of withstanding repeated use of, for example, at least 500 times when wafers that are an object of inspection are mass-produced products.
In a conventional anisotropically conductive elastomer sheet, however, the conductivity of conductive parts thereof has been markedly deteriorated when it has been used in the WLBI test repeatedly, for example, 200 times or more, so that it has been unable to be used in subsequent tests, and so it has been required to be replaced by new one.
In, for example, a flip chip mounting method, semiconductor chips, in which a semi-spherical projected electrode composed of eutectic solder, lead-free solder, high-temperature solder (lead-rich solder) or the like has been formed on surface electrodes, are used. In order to obtain such semiconductor chips at high efficiency, it is conducted to form a projected electrode on electrodes in respective integrated circuits in a state of a wafer.
Thus, an anisotropically conductive elastomer sheet used in the probe test of a wafer is also required to have durability capable of withstanding repeated use over a great number of times even when the wafer, which is an object of inspection, has projected electrodes to be inspected.
In a conventional anisotropically conductive elastomer sheet, however, the conductivity of conductive parts thereof has been markedly deteriorated when it has been used in the probe test of wafers having projected electrodes to be inspected repeatedly, for example, 10,000 times or more, so that it has been unable to be used in subsequent tests, and so it has been required to be replaced by new one.
Prior Art. 1: Japanese Patent Application Laid-Open No. 93393/1976;
Prior Art. 2: Japanese Patent Application Laid-Open No. 147772/1978;
Prior Art. 3: Japanese Patent Application Laid-Open No. 250906/1986.