Process for producing high-purity tin

摘要

High purity tin and tin alloy are provided in which the respective contents of U and Th are 5 ppb or less, the respective contents of Pb and Bi are 1 ppm or less, and the purity is 5N or higher, provided that this excludes the gas components of O, C, N, H, S and P. A cast ingot of the tin or alloy has an α ray count of 0.001 cph/cm2 or less. Since recent semiconductor devices are densified and of large capacity, there is risk of a soft error occurring due to α ray from materials in the vicinity of the semiconductor chip. Thus, there are demands for purifying soldering material used in the vicinity of semiconductor devices, and materials with fewer α rays. The disclosed tin, alloy, and method reduce α dose of tin so as to be adaptable as the foregoing material.

主权项

1. A method of manufacturing a high purity tin, consisting of the steps of:
leaching a raw material tin with an acid to obtain a tin leachate, the raw material tin having a purity of 2N to 3N level, while suspending in the tin leachate one or more adsorbents selected from the group consisting of titanium oxide, aluminum oxide, tin oxide, activated carbon and carbon to adsorb impurities and make the tin leachate a purified electrolyte, performing electrolysis at a temperature of 10-80° C. with a current density of 0.1-50 A/dm2 by using the purified electrolyte and an anode of a raw material tin having a purity of 2N to 4N level, and obtaining an electrolytically-refined tin having a purity of 5N or higher excluding gas components of O, C, N, H, S and P, a content of each of U and Th of 5 ppb or less, and a content of each of Pb and Bi of 1 ppm or less, melting, which is followed by casting, the electrolytically-refined tin at a temperature of 250 to 500° C., to form an ingot, and keeping the ingot in an inert gas atmosphere or in vacuum for 6 months or longer to obtain a high purity tin having an α ray count of 0.001 cph/cm2 or less.