LOW-Α-EMISSION BISMUTH AND PROCESS FOR PRODUCING LOW-Α-EMISSION BISMUTH

摘要

Bismuth characterized by having an α-ray emission of 0.007 cph/cm² or less; and a process for producing low-α-emission bismuth, characterized by using bismuth having an α-ray emission of 0.15 cph/cm² or less as a starting material, electrolytically producing a bismuth nitrate solution having a bismuth concentration of 5-50 g/L and a pH of 0.0-0.4, adding a 20-60% aqueous solution of sodium hydroxide to the solution to yield a sediment including polonium, separating the resultant mixture into a sediment (1) and a filtrate (1) by filtration, and then subjecting the filtrate (1) to electrowinning to recover the bismuth. Since recent semiconductor devices have a heightened density and an increased capacity, the risks that software errors occur are increasing due to the influence of α rays from materials present around the semiconductor chips. In particular, the solder materials to be used in the close vicinity to semiconductor devices are strongly desired to have a higher purity, and materials reduced in α rays are also desired. Thus, the present invention addresses the problem of obtaining high-purity bismuth which is reduced in α-ray emission and is usable as the demanded materials.