Edge effects in nickel sulphamate electroplating
Q. We are plating a flat surface with sharp corners in a nickel sulphamate solution. The desired plate thickness is 8-10 mils (0.008"). Unfortunately, the deposit tends to build up to 12-14 mils at the edges, as a result of the higher current density there. We need to eliminate this excess build-up.
Due to the part geometry and other requirements changes in the masking are not allowed.
I need to identify a chemical additive to the nickel-sulphamate bath which would eliminate the edge effects.
I am guessing that the desired additive would have to reduce the current exchange density (i.e. make the surface more passive) in order to make diffusion the rate-limiting step.
The surface to be plated is flat and the aspect ratio is zero.
A. Hi Chris. I hope you WANT to eliminate the excess buildup rather than NEED to! After all, virtually everyone wants uniform plating thickness, and virtually nobody gets it.
If you can't mask the parts, then racking them in a self-shielding fashion or using non-conductive shields or even current thieves will help some. Proprietary brighteners will work *to some extent* via the mechanism you mention.
In general, you want your plating conditions to limit ion mobility in order to starve the high current density areas, as well. Usually this means plate fast, keep the temperature low, the concentration low, and minimize agitation--but these are just the theoretical directions and may not always represent practical solutions.
Ted Mooney, P.E. RET
Pine Beach, New Jersey
A. Using low PH (3.8-4), agitation, at least 55 °C and a proprietary additive has to solve your problem. (Is your Ni conc. in the solution high enough?) Sara
chemical process supplier
A. Butadiene Diol is an excellent additive for your problem.
I also recommend to give a spin motion to the part if is possible and conform the anode to avoid build up in the corner.
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