Where the
world gathers for metal finishing
Q&As since 1989


-----

Discoloration Solder Plating and Sn-Bi Plating Solution

2004

Our process is solder plating and Tin-Bismuth plating. After 3 years, Sn2+ were oxidized become Sn4+. The plating colour become turbid. We plan to use reduction agent to reduct Sn4+ become Sn2+. Did you have technical experience how to do it ? Is reduction agent also precipitate other metal, like Pb.

In our Tin Bismuth plating, the solution also become yellow turbid (We difficult to analysed additive). Filter can not make it clear. If we take solution in 10 days, solution become clear and there are precipitation in bottom. Did you have solution to solve this problem?

Rajab Asmara
solder plating engineer - LOBAM, Indonesia

---

Hi Rajab,
1.Based on my understood that Tin-Bismuth plating is one of the solder plating.
2.Sn©‚⁺+O©Õ---> Sn©ã⁺ and Sn©ã⁺ will become sludge which can be remove by precipitation. Keep some of anode ball dip in the solution to prevent Sn©ã⁺. But this method may caused Sn©‚⁺ increase.
3.The color of plating solution should not affect plating quality. Only need to control the very tiny particles ( sludge ) in the solution.
4.the additive can be analysis by extraction-UV, wherever the solution is turbid or clear

Zhou Heng
- Singapore
June 15, 2011

----
Ed. note: Sorry, but the special characters in Zhoh's posting did not survive the trip from his keyboard to the e-mail we received :-(