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Activation of Kovar for nickel electroplate

We are a captive plating shop that electroplates sulfamate nickel followed by high-purity gold (99.9+ %, < 90 knoop hardness) over a Kovar substrate. The parts also contain glass hermetic seals so fluorides in metal activation step must be avoided or kept to a minimum. Does anyone know of a good cleaning/activation process for plating electrolytic nickel directly over Kovar? We currently do not use a Woods nickel strike but go directly from a 50 vol% hydrochloric acid activation step live into sulfamate nickel electroplate. The process works much of the time, but we often get adhesion failure of nickel off kovar.

Thanks,

Steven Carsberg
plating shop - Phoenix, Arizona, USA
2004

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Hot HCl then cold HCl then Nickel Chloride Strike 2#/gal Nickel Chloride plus 1 quart per gallon HCl then straight into the sulfamate live. Metal builds in the strike and it gradually switches from a low efficiency plating bath (definition of a strike) to a high efficiency plating bath (definition of a plating solution), so use Rolled Depolarized nickel ovals (because they dissolve more slowly) and take the anodes out when not in use. If the metal climbs anyway, then switch to bagged carbon anodes and ventilate like hell to take out the poison chlorine gas.

Chloride dragged into the sulfamate will raise the tensile stress and further contribute to peeling.

Let us know what happens.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

2004

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2004

The following process works very well to plate bondable gold on Kovar.

1. soak clean
2. electroclean
3. rinse
4. cyanide activate
5. rinse
6. gold strike
7. gold plate

Pat Mentone
St Paul, Minnesota

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You may wish to try a Wood's Nickel Strike in your preplate operations. When you do, please make sure that the Hydrochloric Acid is over 12% b.v. I have seen strikes that were between 11.8% and under, that did little for adhesion. When the acid was raised, adhesion improved markedly. The Nickel Chloride is 32 oz/gallon in all cases.

Ed Budman [dec]
- Pennsylvania
With deep sadness we advise that our good friend Ed passed away Nov. 24, 2018
2004

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Steve,

You already had excellent advises but something isn't clear to me. You use a 50% vol HCl activation and straight to the sulfamate nickel live, but you don't specify if it is immersion only or electrolytic activation. Obviously, immersion treatments of high alloys do not produce enough hydrogen evolution or none at all to reduce tenacious oxides on the surface. Electrolytic forward polarity treatments do and may work with HCl alone (as in your case), but there is a high tendency of a HCl solution to dissolve (and plate out) unwanted positively charged ions. A properly balanced Woods strike has enough HCl for oxide reduction and a good amount of nickel chloride to limit further dissolution of other metals.

Guillermo Marrufo
Monterrey, NL, Mexico
2004

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2004

Thank you readers, for your advice. A Woods nickel strike simultaneous activation/strike seems to be the consensus for my question. [Guillermo: No, our current 50% HCl activation step is only an immersion activation step, with ultrasonics-- not an electrolytic step, which is followed by live entry into the electrolytic nickel sulfamate bath at a pH of 3.2-3.5.

Regarding the Woods Nickel Strike activation step, I have been seeing many ranges quoted for cathodic treatment during the Woods nickel strike. (anywhere from 20-200 ASF is quoted in ASTM standards and Metal Finishing Guidebook and Directory recommendations) We are plating very small barrel loads of <<5 ft^2. We don't currently have ability for an anodic treatment in the Wood's Nickel Strike. (only cathodic) Will a 20-30 ASF cathodic treatment in a Woods' Nickel Strike be sufficient for these small barrel loads, without an anodic pre-treatment in the Woods Nickel Strike?

Thanks again to all of you who responded.

Steven Carsberg
Plating Shop - Phoenix, Arizona, USA