Dummy plating copper from nickel sulfamate bath
Q. I am looking for a starting point for setting up a plate out cell to remove low levels of Cu (10-20 ppm) from a nickel sulfamate plating solution. We are setting up a cell with a cathode, anode, and rectifier to pump solution through that we can use to remove Cu while we continue to plate in the main plating cells. Obviously we will plate Ni on the corrugated dummy cathode while we are removing Cu. What I am looking for is either the proper voltage setting, or current density to reduce the amount of Ni plated out while preferentially plating Cu. With a corrugated dummy panel we will have a current density range, I am looking for a place to center the range. Is there any reference material on this?Rich Reifenheiser
- Fountain Inn, South Carolina
A. There isn't really a rule, Mr. Reifenheiser, because it depends on what current density you are electroforming at. The principle that is in play here is simply that the lower the current density, the more it will favor copper. So if you are electroforming at 20-50 ASF, then dummy at, say 5 ASF. But I know of one application that is electroformed at 1 ASF, such that dummying at even 1 ASF would be much too high. And some electroforming is done at 400 ASF or more, where dummying could probably be successfully done at as high as 10 ASF.
Ted Mooney, P.E.
Pine Beach, New Jersey
A. If you do not want to plate out a lot of your nickel, dummy at the lowest amperage that will do the trick. 2 - 3 ASF removes very little nickel relative to the amount of trash metals removed. If you can get by with continuous dummy, try 1 ASF.James Watts
- Navarre, Florida
February 26, 2013
Q. Dear all,
We are doing Ni/Au barrel plating for pogo pin connectors.
Our Nickel sulfamate plating bath consists of 270L PP tank and 2 anodes with 5 kg INCO R-Rounds Electrolytic Nickel in each 12*12*2 inch Ti basket.
There is something we can't understand: Bath Voltage when we do dummy plating using a 28dm^2 dummy plating cathode.
First bath voltage is ~0.8V, when current density is 0.1ASD. Then bath voltage will slowly increase from 0.8V to 2.5V. We don't know why. What is the mechanism in this situation. Is it any anode passivation, capacitance effects or something?
Thanks a lot for your help.
- Taipei, Taiwan
March 2, 2013
A. Hello Clark,
As you may know higher voltage = increased resistance. It is odd that you only experience this in dummy plating and not in your production barrel plating. First I would check all anode and cathode connections, and make sure they are getting good contact. Inspect your dummy plating cathode rack. I set a meter for ohm resistance (continuity) and attach one lead to the rack / cathode connection point then the other at the bottom of the cathode dummy. Your continuity should not exceed 0.5 ohms. Make sure anode and cathode bars are clean. I assume that your rectifier cabling is adequate for the current density that you are using. You can also use a clamp meter set at DC amps. Check your current on both the cabling before the anode and cathode connections. Both readings should be similar. If space allows I also like to check the current around the anode hooks with the clamp meter. Hope this helps.
Process Engineer - Mesa, Arizona USA
How long have you plated with this anode basket? Are they full up to level? I'm not sure about that. Have you checked the nickel anodes that this does not contain some copper? Has your titanium anode a twisted hook?
3rd Generation in Plating
Consultant - Arvika, Sweden
A. Hello Clark,
I meant to say measure amp readings with the clamp meter around the cabling before the anode and cathode bars and around the anode and cathode bars. The readings you get should be similar. I apologize for the confusion.
Process Engineer - Mesa, Arizona, USA
May 11, 2013
A. Hi: If you really want to get the copper out of your bath, use the lowest current that you can get on your rectifier. Set your dummy panel in the bath; set your rectifier to zero; and move your knob to increase power very, very slowly, when you see a minimal movement around your panel, you are good to go.
Dummy for 24 hours, and next day all you will see is only copper and no nickel. You can go as low as half volt.
- New York, New York
September 3, 2014
Hello, I came across this site while searching some info on plating solution.
I read all the answers about dummying of copper. Some was suggesting to plate the solution in low current in order to remove copper.
So, my question is why do we need to use low current in order to dummy copper?
I really appreciate your opinion.
- Johor, Malaysia
A. Hi Atiqah. Picture keeping the current very low, and thus having just a few excess electrons present on a dummy cathode sheet sitting in a nickel plating solution that is contaminated with copper. Those sparse electrons have many positively charged ions of nickel and copper around them to choose from, and they will reduce only a few of them. For reasons that I partially understand but don't fully understand, the copper ions are hungrier to mate with the electrons than the nickel ions are; consequently, the copper will plate out onto the dummy sheet in preference to the nickel.
Now, turn the current way up so there is an abundance of excess electrons on the dummy sheet clamoring to mate with positively charged ions and reduce them to metal. At any small given area the copper ions will rapidly be used up, and there will be no more immediately available there, so the hungry electrons, which must be satisfied, will neutralize and plate out nickel ions as nickel metal -- but your objective was not to remove nickel from the solution.
Thus, it is not so much the case that "low current is needed to remove copper" as it is that high current will remove the copper but will also wastefully remove nickel.
Ted Mooney, P.E.
Pine Beach, New Jersey
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