| 摘要 |
PURPOSE:To provide a plating soln. giving a solder film in which the occurrence of memory errors is remarkably suppressed, by reducing alpha-radioactivity of a plating soln. contg. a specified arom. sulfonic acid, their lead and tin salts thereof to below a specified value. CONSTITUTION:This plating soln. contains an arom. sulfonic acid represented by the formula, the lead and tin salts thereof and has <20ppm radioisotope content and <0.1CPH/cm<2> counted number of radioactive alpha-particles. In the formula, each of R1 and R2 is H, OH, lower alkyl or sulfone. In order to prepare the plating soln., lead and tin each having >=99.99% purity are dissolved in high purity nitric acid and the concn. of free nitric acid in the resulting soln. is regulated to 5-10mol. with pure water. The soln. is treated with an ion exchange resin to adsorb and remove U and Th, the above-mentioned arom. sulfonic acid is added and neutralization is carried out to produce the lead and tin salts of the arom. sulfonic acid. The prepd. aq. soln. contg. the arom. sulfonic acid, the lead and tin salts thereof and generating a small dose of alpha-rays is used as an electrolytic soln.
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