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topic 18316

Sulfamate Nickel Strike Problems


2002

Q. We are using the Barrett Nickel Sulfamate Strike process to plate a two circuit SSt-copper laminant panel. We run 75 g/L Ni, 30 g/L boric, pH 1.2-1.5 and [Cl-]=1.4% by volume. Temperature is 30 degrees C (86 F) and our plating time is 2.5 to 5 minutes. We get good adhesion of the strike to the SSt and copper circuit of the panel. The other circuit on the panel is copper only and we DO NOT plate it with the strike (but it does get exposed to the chemistry for the entire strike time). We then follow up the strike bath with a quick spray rinse and a nickel sulfamate plate. The problem is that we get blistering on the copper that does NOT get nickel strike. Anybody have any ideas what is possibly going on here? Our metallic contamination of the strike bath is very low (< 2 ppm in Cu and Cr).

John Hutchison
- Eau Claire, Wisconsin


First of two simultaneous responses -- 2002

A. Obviously, the strike bath is deleteriously affecting the unplated copper; the question is how or why. My suspicion would probably be that the unplated areas are becoming bipolar anodes such that they are partly nickel plated under poor conditions on one side and partly made anodic and passive on the other side.

You could run some parts through the strike bath with the current off to see if my wild guess has validity, or if mere exposure to the solution is the problem.

In the worst case you'd have to mask the unplated area; in the best case your rack could have some simple shield pieces that would stop the bipolar action.

Just a wild, sight-unseen guess :-)

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"


Second of two simultaneous responses -- 2002

A. Dick Crane or Jim Will should be able to handle this problem.

Meanwhile, here is a long shot. If the Barrett Strike is very old, then at that pH most of the sulfamate radical has broken down into ammonia and sulfate and the sulfate is attaching to the uncharged bare copper, Perhaps a mechanical wipe with Scotch Brite and another hit electrolytically this time in the strike might prepare the surface to receive plating without blistering.

OR, make up a 5 gallon brand new strike and see if the same thing happens. This will confirm my theory about the breakdown into sulfate.

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina
Editor's note: Mr. Probert is the author of Aluminum How-To / Aluminio El Como
and co-author of The Sulfamate Nickel How-To Guide


2002

Q. More questions for Ted's response:

1) If it is a bipolar effect (Cu-only circuit acting as an anode while the SSt-Cu Laminant circuit is the cathode) why don't we see similar blistering when we expose the parts to a standard sulfamate nickel bath? Does pH have an influence on the bipolar effect? What is the anodic reaction of the copper that would cause poor adhesion?
2) Does it make sense to lower the current density to minimize the bipolar effect?
3) Earlier testing at higher current densities showed that we would get a very thin deposit of Ni on the copper-only circuit ... even though it was isolated from the SSt-Cu laminant circuit.

Thanks,

John Hutchison
- Eau Claire, Wisconsin


2002

A. John, the bipolar effect I'm speaking of is not the same thing as a galvanic effect; it doesn't depend on the difference in materials, it depends on their orientation between the anode and the cathode, as shown in the exaggerated picture below:

18316

The bipolar effect in your case would be much less, but can account for the nickel you see deposited on the copper. A portion of the copper which is not connected to anything will be anodic, and will have a small amount of copper dissolving from them; and a portion will be cathodic and will have nickel depositing on them.

The effect is probably more dependent on voltage applied than on pH.

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"



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