Q. I cannot achieve uniform adhesion of either Wood’s nickel or cyanide copper on C14500, tellurium-bearing copper. I clean using reverse current followed by 11 percent HCl, a Wood’s nickel strike and a silver strike. After stripping the failed plate and repeating the process, I sometimes have much better adhesion. Is this due to the aggressive etch provided by the stripping process or better oxide removal provided by the process? T.I.
A. Plating on beryllium- and tellurium-containing alloys always gives platers problems. The formation of oxides on the surface prevents good adhesion. The stripping of the defective plate likely gives you a better, cleaner surface for plating.
The procedure below gives successful results in many situations.
- Anodic alkaline electroclean
- Dip for 20-60 sec in 50 percent by volume HCl solution
- Rinse at once in cold water and immediately go into
- Alkaline coppper strike bath*
- Plate in an alkaline copper plating bath for approximately five minutes**
- Plate and finish as desired
*Classically, a copper cyanide strike bath was used, but non-cyanide alkaline copper strike will work as well. Use of a non-cyanide strike avoids the possible problem of forming messing complexes with any tellurium remaining on the surface.
**Again, a Rochelle copper plating bath was used, but an alkaline copper plating bath will work as well.