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Article: The black and white of immersion tin: keeping an eye on cupric ions can eliminate black tin.(LAB BENCH)
- Article from:
- Printed Circuit Design & Fab
- Article date:
- July 1, 2009
- Author:
CopyrightCOPYRIGHT 2009 UP Media Group, Inc. This material is published under license from the publisher through the Gale Group, Farmington Hills, Michigan. All inquiries regarding rights should be directed to the Gale Group. (Hide copyright information)
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Every immersion tin plating operation faces the same problem during the immersion tin bath. Eventually, the bath will begin to plate black tin, and until recently, there has been no way to predict when the bath would begin to plate black tin. You might ask, "Why does this happen?"
When immersion tin plates onto the copper, two atoms of copper dissolve for every atom of tin that plates out. The copper metal goes into solution as copper one (also known as cuprous ions, or [Cu.sup.+]). Copper in this form is well tolerated by most immersion tin plating solutions, and at reasonable levels, it has no effect. However, cuprous ions can react with atmospheric oxygen. ...