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Pitting in Nickel Sulfamate Bath
Q. I am a chemical engineer at a defense and space company working mainly in circuit fabrication. We have been having a lot of problems with pitting in our nickel sulfamate bath. I was wondering if you guys had any additional advice that you could give me.
Here's the scoop. I have tried many of the common solutions to pitting problems. Adding boric acid, providing additional agitation, checking the pH, checking the connections from the rectifier, and adding some hydrogen peroxide. These modifications didn't help, thus, we have replaced the nickel bath twice, since the first replacement didn't provide any difference either. We seem to be having most of the pitting on smaller surface areas.
I am thinking of replacing the anodes or cleaning the anodes that we currently have. What is the best way to clean the nickel s-round anodes? HCl and water?
Any other suggestions that could help solve this mystery?
Thank you very much for your help and advice.
Defense & Space - San Diego, California, USA
A. Does your process use proprietary additives? If so check the levels of brightener and wetting agent (you may need to ask your supplier for advice about how to do this).
Check the surface tension of the solution. If the chemistry of the bath is correct there could be two problems:
1. Pre-cleaning. You haven't told us what the pre-clean cycle is. Any contamination left on the surface will affect the quality of plating (check for waterbreaks before you nickel strike).
2. The parts are not wetting out in the plating bath. By checking the surface tension of the solution you should be able to determine if you have sufficient wetting agent present.
If you are still not getting anywhere you could consider asking your chemical supplier for assistance, they usually have a reasonable idea about the process.
Aerospace - Yeovil, Somerset, UK
A. Check rectifier, electrical contact, Voltage on rectifier and compare with the voltage in anodes and cathode, check water quality, it should be D.I. water.Carlos Carrera
- Miami, Florida, USA
A. Dear Ghee,
- Mexico City, Mexico
A. I note from your information that you have changed the nickel bath without solving the problem. I presume you have done a Hull cell test to make sure your bath is working correctly; if not, this should be your first test before changing anything else. You say you've checked everything, but I see there is no mention of a wetting agent. You will need one that is compatible with your process. Wetting agents are essential to most plating as it reduces the propensity of hydrogen bubbles adhering to the cathodic surface during plating and thereby making pits in the deposit. Nickel deposition is not 100% efficient, so there will always be some hydrogen deposited, but the trick is to prevent it sticking - hence wetting agents. You also do not mention whether the process is proprietary or in-house; if the latter, ask the supplier and if the former, then it's down to you....Other causes of pitting can be operating at too higher current density, inadequate agitation or the wrong pH. The current density is in part connected to the nickel ion concentration, so make sure the two are compatible. Inadequate agitation will allow gas bubble to adhere and the wrong pH will allow excessive hydrogen (too low pH) or nickel hydroxide inclusions (too high pH). I would suggest about 6-8 tank turnovers per hour for common nickel plating and sulphamate nickel should operate at pH 3.6-4.3. It should NEVER operate at over 70 °C as the sulphamate breaks down to sulphate and ammonium ions, causing an increase in stress. If the bath chemistry and operating conditions are OK, then in must be either the plated part (porous substrate?) or the cleaning cycle. Is it possible that the substrate is still contaminated with photoresist materials? It is possible that there is solution contamination due to drag-in, but this is not a common problem in a well run shop. Hope this helps - good luck.
R&D practical scientist
Chesham, Bucks, UK
Thank you everyone for your help.
- San Diego, California
A. It sounds like you are plating at a high CD for the given Chemistry and plating parameters. cut back on current Density say at 50%, see what happen.
- Philadelphia, Pennsylvania
Q. The bath we are using is at a pH of about 3.4 because the technical data sheet from the vendor states that it should be between 2.75-4.5, with an optimal pH of 3.25. The operating temperature is at 50 °C. We use an in-tank filter pump that is connected to a couple of spargers for agitation.
When racking the part using copper wire with two connections to the substrate, the plating comes out pretty good. However, when I try to use the standard rack that we use, which is comprised with a polypro shell with one copper connection, we seem to continue to get pits. Could the rack be adding to the problem? (FYI, the substrates we plate do have photoresist material on them)
Thanks for your help and advice.
- San Diego, California, USA
? How about some pictures of the parts and the racks? It may help....
R&D practical scientist
Chesham, Bucks, UK
A. IF YOU ARE GETTING PITTING YOU MIGHT WANT TO TRY TWO THINGS REPLACED YOUR ANNODE BAGS WITH FRESH ONES A HEAVY POLY NAP IS REAL GOOD IT IS A LITTLE MORE EXPENSIVE BUT THEY WILL LAST ABOUT 10 TIMES LONGER AND BE CHEAPER IN THE LONG RUN ALSO YOU MIGHT WANT TO TRY SNAP L WETTER WE USE THIS AND IT SEEMS TO CLEAR UP THE PITTING WE HAVE. IF THAT DOES NOT WORK YOU MAY NEED TO FILTER YOUR NICKEL BATH OR CHECK IT FOR POSSIABLE CONTAMINATION.DOUG THOMPSON
- ERIE, PENNSYLVANIA, USA
February 3, 2017 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread
Q. I'm having major pitting problems in a new nickel sulfamate bath. The tank was remade a few months back before I started at this facility. This tank is not continuously used and sometimes a week or two will pass between use. The pitting is inconsistent and sometimes one side of a part will have it and the other comes out good. Here is what I have done to fix the problem:
1.) Analysis of bath each time it is used and weekly if not.
pH: 4.3 Range: 3.6-4.5
Nickel: 12.2 oz/gal Range: 9-12 oz/gal
Additive "A" .76 oz/gal Range: .4-1.2 oz/gal this is a chloride salt corrosion aid
Boric Acid: 5.2 oz/gal Range: 5.0-6.5 oz/gal
Snap A/M: .32%/V Range: .1 -.4 %/V Surface tension adjuster
Outside Analysis confirms that metal contaminates are below 1 PPM.
The bath is Barret SN. The ranges come from Macdermid Inc. [a finishing.com supporting advertiser].
2.) Checked agitation. The tank is 1100 gallons and the air agitation is moderately vigorous.
3.) Changed Anode Bags.
4.) Verified pre-cleaning procedures. Aluminium 80 grit blast. Then we use a wax to cover areas that don't require plating and use solvents to remove its residue followed by scrubbing and rinsing.
I have pictures I can post but I'm not sure how to. Any help would be greatly appreciated.
Plating Manager - US
Ed. note: This is one of several threads about "nickel sulfamate pitting"; use that term in the search engine to read the others.
February 7, 2017
Q. When the part was ground down it was found the pitting started about 10 thousands into the deposit. This makes me believe I am having an issue with hydrogen bubbles or pH related. So I have done the following:
1.) Increased to boric acid to stay between 6.0-6.5 oz/gal
2.) Enforced a strict pH range of 3.9-4.1
3.) Changed the placement of the air lines to get better agitation through out the tank.
I'll give another update after our next run.
- Cleveland, Ohio USA
February 10, 2017
A. You did not mention temperature, regardless of the data sheet, the boric acid solubility is a function of temp. If the temp drops during the plating process, then the boric acid comes down, if it lays on the horizontal surface, the pits form right there and grow with the thickness build. Over the weekend the boric acid drops into the corners of the tank and will not go back in unless stirred and heated. Low boric acid causes random pitting. You did not mention filtering, but a teny tiny leak in the filter pipping/hosing will make an air bubble that causes pitting (different from normal blower air agitation), so tighten down all the hose clamps and look for where the filter might be sucking air. You did not mention electrolytic purification (dummying), the S-rounds are loaded with copper which must be dummied out, if not the copper contamination lowers the efficiency and causes hydrogen bubbles to start. And how about organic contamination, a real blaster to efficiency and guaranteed to start the hydrogen bubbles - so carbon treat a small batch, maybe in the Hull Cell, and see if you get less pitting. I do not charge for "homework", call me
Robert H Probert Technical Services
Garner, North Carolina
February 15, 2017
Q. The tank is maintained at 130 °F. I have verified it is fully calibrated. The heater is not turned off over the weekend so the boric should not be dropping out. After some research I found that the boric is supposed to be around 6.25 oz/gallon for 130 °F.
Filtration is accomplished by an over the side Flo King pump so no air should be getting into the solution from there. I'm used to much stronger pumps with multiple turn overs per hour but for now its all we have. The filters at 15 micro 20" depth wound cartridges. There is no present continuous carbon treatment so I have changed our filters to carbon 20" cartridges and have been keeping a close eye on the Snap-AM wetter we use in case (not sure if the carbon will mess with it but I've seen other products have issues)
I have started dummying the tank on a regular basis before parts are ran to remove any possible metallic contamination.
The last collar we ran came out without any pitting. Hopefully I can keep it that way. Here are the things I think that helped the most:
1.) Higher boric acid concentration up to 6.25-6.5 oz/gal
2.) Stricter pH range (3.8-4.2)
3.) Increased and adjusted the air agitation placement
4.) Regular carbon treatment and dummying of tank
5.) Soaking the nickel S-rounds in 2-4% sulfamate acid to clean before use in our home made anodes for these collars
- Cleveland, Ohio USA