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How to overcome compressive stress?

2004

Hi, Dear all,

Some background first: My e-forming originally gave me tensile stress. Then, I took someone suggestion here to add about 0.8 g/L saccharin salt and it became compressive now. I guess I use too much of the additives. I tried to clean the tank with activated carbon. But, compressive stress still remained. Here are my e-forming conditions: Nickel sulfamate bath (Ni: 76 g/L, H3BO3 33g/L, pH 4.1). Current density: 15 ASF, temperature 135 °F.

I tried to adjust current density and temperature. But, could not get near zero stress. Can anyone give me suggestion and help me out here.

Thank you very much in advance.

Paul Chen
optoelectronics - Santa Rosa, California, USA

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Once you put the saccharin in you got compressive stress. saccharin is not removed by carbon. The solution will forever be compressive. Make-up a new solution.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

2004

Can Saccharin be oxidized by H2O2, then removed by Carbon treatment?

What temperature should I use, high or low in e-forming in order to reduce compressive stress.

What current should I use to reduce compressive stress, lower or higher?

Paul Chen
- Santa Rosa, California, USA
2004

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First of two simultaneous responses --

The answers to your last questions show that you need more information about chemical reactions occurring in your process. First, a sulfur compound like saccharin will not be oxidized by peroxide; second, even if it was, carbon treatment is not effective to remove oxides but organic contaminants. So, unfortunately the advise given by Mr. Probert remains.

Guillermo Marrufo
Monterrey, NL, Mexico
2004

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Second of two simultaneous responses --

Lower temperature = Lower compressive stress Higher current density= Lower compressive stress

Russell Richter
- Danbury, Connecticut, USA
2004

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2004

Paul,

I would not consider dumping your bath just yet as I think your problem is resolveable.

Firstly, as Russell Richter says, compressive stress can be negated by increasing the cathodic current density and/or by reducing the bath temperature. Personally I prefer the current density route, but since you are electroforming, this may not be a good idea for you. I reckon plating at 35 A/dm2 at 60 °C should give you an approximately neutral stress, assuming you have 0.8 g/l saccharin. Further information on stress in sulphamate baths can be got from NiDI; they published some excellent papers by Dr S. Alec Watson on nickel electroplating and electroforming.

Secondly, I am not sure Robert Probert is correct about carbon treatment. I have never had any problems removing (sodium) saccharin from nickel plating baths by using an active carbon treatment; if you had used NTS it would have been a completely different story!

Thirdly, you will need to have good analytical backup for saccharin analysis, it is not easy to get accurate reproducible results. Nevertheless, you must have good backup to maintain a useable bath. Fourthly, saccharin is consumed during the electrodeposition of nickel, so the bath should become more tensile with use.

Finally, it may be worth talking with your supply house to ascertain whether they have any tensile stress inducing additives that may be suitable; this may be a long shot, as the high compressive stress will be a short term thing.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK

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First of two simultaneous responses -- 2004

Thank you all so much. I am trying to take some of your suggestion to deal with stress.

I also use shadow box in uniformity control. It seems stress change with shadow box in electroforming. Does anyone have idea in this?

Appreciate all your help.

Paul Chen
- Santa Rosa

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Second of two simultaneous responses -- 2004

I did not see Bob Probert's answer, but he is correct in saying that saccharin cannot effectively be removed by simple carbon treatment. Multiple peroxide-carbon treatments can lower the saccharin content somewhat. A permanganate- carbon treatment will lower the content some also. Extreme low current density will also remove some of the saccharin.

As long as there is some left the deposit may remain compressive. This is not particularly harmful unless the deposit is to be exposed to very high temperatures. The saccharin will char and the deposit will loose tensile strength

Don Baudrand
Consultant - Poulsbo, Washington
(Don is co-author of "Plating on Plastics" [on Amazon or AbeBooks affil links]
           and "Plating ABS Plastics" [on Amazon or eBay or AbeBooks affil links])

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Paul, what is a shadow box?

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2004