Plating Electroless nickel directly onto aluminum

A. I have seen electroless nickel applied directly to aluminum--without a zincate treatment!--for connector housings. Reports were that it was satisfactory, but I never saw lab work verifying the adhesion, etc.

Zincate followed by electroless nickel seems to be the common & correct approach. I don't know what the advantage of an intermediary layer of copper is supposed to be. We have a few electronics plating gurus hanging around here, and hopefully one of them will chime in on that.

A. We always use zincate followed by electroless Ni with controlled P.
By the way, MIL-26074 has been canceled. We now use AMS2404.

A. Gordy, does your customer object to the use of nickel in the product because of its magnetic properties, or is the customer just unaware of common plating practice? Sometimes you have to spend a bit of time to educate them. Although there are methods to apply copper directly to aluminum--see Durney, Electroplating Engineering Handbook [on AbeBooks or eBay or Amazon affil links] . They require uncommon chemistry and a bit of experience to be successful. If the problem is magnetics, you may be stuck trying to find a process supplier. If not, then take time to educate your customer on common aluminum finishing methods.
Good Luck,

A. In addition to the traditional generic zincate, Atotech offers their 'Alstan' tin-bearing pretreatment for aluminum, and Gumm offers their 'Bondal' process. Presumably these companies will be able to present quantitative data supporting their processes as being better than zincate.

Ed. note: Fred Gumm Chemical Co. no longer exists, but the process perhaps can be found at MacDermid.

A. Gordy,
At this location we also double zincate aluminum prior to electroless nickel. I do remember that in one application we followed zincate with a copper strike which had a matching effect on the difference in coefficients of thermal expansion which sound like your customer's concern. I think we looked at it as a cushioning layer. I don't remember the specifics, but I remember doing it. We spoke last year about your zinc phosphate application question.

A. You may use a high pH electroless on double zincate, prior to ordinary electroless with PH about 4.8. This high pH EN plates a thin layer, protects zincate and gives very good adhesion. Sara

A. As some people know, I sometimes find an answer looking for a question. I may have found one here.

I was just reading "pretreatment for plating on aluminum using the Stannate process by Jongkind and Seyb, aluminum finishing seminar, vol II, Proc. Conf., St Louis MO, 30 mar-1apr 1982, aluminum assoc. 818 Connecticut Ave, NW, Washington DC USA Met A, 8303-72-0144, 539-549.

It says that improved corrosion might be found by having tin next to the aluminum rather than zinc.

Maybe this would interest you.

A. If your customer is really serious about this, do some comparative thermal cycling of both products. I doubt if you can beat the alkaline strike that Sara mentioned followed by an EN selected for its ductility and its ability to maintain it for the bath life. Most EN vendors probably will not want to spend a lot of time unless it is a lot of plating. I have seen papers from two vendors that address at least ductility and turnovers. I will put a cup of coffee on an alkaline EN followed by most any EN beating copper.
PS copper migration can cause real problems.