Abstract
Analysis of Cu(I) in copper sulfate electroplating solution was conducted by absorption of a chelate of Cu(I) with bathocuproinedisulfonic acid, disodium salt (BCS). Although the absorption of new copper sulfate electroplating solutions was negligible, the absorption of operating solutions was clear. The difference of new solutions and operating solutions was also verified using an electrochemical method for detection of Cu(I). We concluded that the Cu(I) ions are measurable using this chelate reagent. The absorption increased quickly in a few minutes after mixing with the chelate reagent and subsequently continued to increase slowly. To clarify this phenomenon, the organic compounds in the plating solutions were analyzed and Cu(I)-PEG (polyethylene glycol) complexes with different chain lengths were detected using MALDI-MS. Results show that Cu(I) ions exist in the plating solutions not only as small complexes with small organic compounds but also as large complexes with PEG. Small complexes of Cu(I) can react quickly with BCS and cause the rapid increase of the absorption in a few minutes after mixing. Cu(I)-PEG complexes prevent the chelating reaction of Cu(I) with BCS by steric hindrance of PEG, which explains the subsequent slow increase of the absorption. Using this chelate method, we monitored quantities of Cu(I) in copper sulfate electroplating production lines, detected the variation of Cu(I) quantities, and found the increase during the resting state of the lines.
