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Ductile Nickel Plating

December 11, 2009

We have electrical contacts plated with Low Stress Sulfamate Nickel (IAW SAE-AMSQQN290 Class 2), 50-150 microinches thick over copper over Brass 360 base metal. The contacts are finished with 20 microinches minimum Gold, Type III, Grade A, per MIL-DTL-45204.

These contacts are .020" in diameter and get bent to 90 degrees. We have been experiencing micro cracking of the nickel plate.

My question is, " Is Low Stress Sulfamate Nickel the most ductile Nickel plate I can get and be in accordance with SAE-AMSQQN290 Class 2?"

Jeff Lesiczka
Mechanical Engineer - Hudson, New Hampshire

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First of two simultaneous responses --

Yes, as long as it really is "low stress" nickel. Have you been monitoring the actual hardness and internal stress level? If you have and found it to be in accordance, a thickness reduction of the copper substrate might be required. In order to maintain their current carrying capacity conductors that bend are generally designed thin but wide.

Guillermo Marrufo
Monterrey, NL, Mexico
December 14, 2009

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Second of two simultaneous responses -- December 14, 2009

Several parameters affect the stress and ductility of the sulfamate nickel deposit: temperature, pH, anode activity, Sn breakdown into ammonia ⇦ this on eBay or Amazon [affil links] ion, current density, overall purity, halogen content. If your sulfamate vendor cannot or will not help you get a 90 degree bend, then come back and we will get into details.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

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First off, control the nickel thickness at the low end of the spec. Yes, sulfamate is a good choice for maximum ductility, but there are many parameters which influence the ductility - temperature, current density, bath composition, pH, sulfamate decomposition products, additives and contaminants. Your chemical supplier should be able to help.

Jeffrey Holmes, CEF
Spartanburg, South Carolina
December 15, 2009

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Using nickel sulphamate is an excellent start - this will usually give you the best low stress nickel, but you must not use any additives, or these can increase your stress. You do not say what your bath formulation is, so we don't know what you are using. Also, keep the current density down - say 20 ASF or slightly less. Also, do not run at a temperature above 60 °C or you run the risk of the bath starting to break down. Keep the bath between pH 3.8-4.2 and make sure you have adequate boric acid in it (35 g/l). This will help keep hydrogen codeposition and any embrittlement down.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
December 21, 2009

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First of two simultaneous responses --

Years ago, I had curves for sulfamate nickel that I got from then Allied Kelite that had Barretts's and Inco information.
Talk to Inco and to a couple of the leaders in providing sulfamate nickel to see if you can get copies.

James Watts
- Navarre, Florida
December 21, 2009

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Second of two simultaneous responses -- December 21, 2009

There is much confusion between stress and hardness (or ductility). Low stress is important if you are trying to replicate a surface or plating on one side of a flexible substrate. Hardness and ductility are important if you want to bend or form a part that is overall plated without any orange peel or cracking of the surface.

Parts plated from a watts bath without any additives is the most ductile nickel. A part plated from a sulfamate nickel bath will always contain some sulfur (since it is low stress) and be less ductile than a watts nickel.

Pat Mentone
St Paul, Minnesota

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Consider as well as the chloride content should be well monitored and in an low range. Watch out of the additives, which are mostly grain refiners, they have nice working effects, but getting pretty ugly when it is overdosed. How often you have to make pH-Adjustments and what are you using for?

Regards and Happy New Year!

Dominik Michalek
- Sydney, Australia
December 25, 2009