Control of Lead-Tin Fluoborate Plating Bath and Analysis of the Deposit

Abstract

Each component in the lead-tin fluoborate plating bath would be quantitatively analyzed by the following procedures simply and correctly.
Pb: After the excess of EDTA being added to the bath, Sn⁺⁺ was oxidized with H₂O₂. Then, the solution was masked with triethanolamine and back titrated with Zn⁺⁺ at pH=10 using BT as indicator.
Sn⁺⁺: After Pb was precipitated with H₂SO₄, titrated by iodometry.
Free HBF₄ and Free H₃BO₃: After Pb was precipitated with Na₂SO₄, free HBF₄ was determined by alkaline titration with pH-meter to pH=3.5 as the end point. Then, pH was made to 7.0, mannite was added to it, and free H₃BO₃ was determined by alkaline titration to pH=8.0 as the end point.
Hydroquinone: Precipitate was filtered off from the solution after the determination of HBF₄ and H₃BO₃ and titrated with Ce⁺⁴ using ferroin as indicator after made acidic with H₂SO₄.
Lead and tin in the deposit could be determined by the following procedures.
Pb: Lead-tin plated layer was dissolved by a remover such as Enstrip TL and the excess of EDTA was added to the solution. Then, tin was masked with triethonolamine and back titrated with Zn at pH=10.
Sn: The above solution wa made acidic with HCl and back titrated with Zn at pH=5 in the warm state using PV as indicator to determine Sn+Pb. Then, Sn was calculated.