Nickel plating of aluminum for good EMC still ok?

A good catch by Tim. But, if the electronics are RoHS, the whisker potential there remains. Shorter gaps mean whiskers on the pcb will cause shorts before whiskers from the case-to-pcb interface area ever could.

Meanwhile Joerg's Ni-plating all around sounds reasonable, unless the real experts know something better.

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Cheers,
James Arthur

Thanks, Joseph. Then tin is mega-out because this stuff will be used in nearly any climate zone on the planet.

Yes, I'd like to hear from experts on this one. I know it was a good process in the 80's but lots of stuff has been placed on the boo-boo list by regulatory folks.

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Regards, Joerg

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If you want to hear from experts then why are you posting here instead of calling a few plating shops and discussing it with them, or posting on sci.engr.metallurgy?

Sci.engr.metallurgy has only a few true experts who semi-routinely answer questions, but they might point you at the Nickel Institute as a good place to start a search for Ni plating info, such as:

Try Thomas Register for the closest plating shops that specialize in electroless Ni? Check with a few in Arizona where there are no environmental restrictions? (just kidding...)

Ni plating on steel (over a copper flash plating) or on any copper alloy is extremely easy, requiring nothing more dangerous than battery acid. I used to do it at home in a plastic bucket with a battery charger on a variac as the power supply. Never done Ni over Al, it is definitely not compatible with sulphuric acid and IIRC an electroless nickel?phosphorus is normally used, not pure Ni, and that the process is still readily available and economical even if not suitable for use at home in the kitchen sink. The properties of the plating (ductility, hardness, resistance to peeling) can be varied quite a bit with changes in phosphorous content, various plating parameters and surface preparation, so I suggest using a shop with experience in applications similar to yours to minimize the chance of problems due to a plating optimized for some other use.

I should also mention that I am not an expert on this subject and you probably ought to find one at a plating shop or two :-).

BTW I once spoke with the president of a company that sold a system of plating process and chemicals called "Zerpol" (not sure if it is still around) who claimed that with sufficient understanding and control of plating bath chemistry it is possible to continuosly regenerate all plating baths for any plating process, and recover essentially all chemicals from rinse water, thus producing zero pollution at the same time as economical operation (not throwing away expensive chemicals with "depleted" plating baths and rinse water compensating extra control and rinse distillation cost). Very few platers adopted it then (~15 years ago) "because they are a bunch of clueless luddites" to paraphrase a bit, but IMO the availability of plating is not likely to be affected by stricter environmental regulations (only the price).

Regards, Glen

I'll leave the nitty gritty to my client since they also have to make decisions about the cosmetics. I was just thinking that I can't be the only one in this EE group who runs into such plating issues.

No joke, it happened: Suggested a zinc-plated steel chassis to a client and they liked the idea. Unit ended up being a whole lot more robust, cheaper, better EMI and so on. Then the shop in California threw the hands into the air, they weren't allowed to do it anymore. So we had to go out of state, found a shop in Colorado, and from then on an

18-wheeler would roll from Colorado to northern California and back on a regular basis. Now that makes perfect environmental sense, doesn't it?

Well, I know Ni over Al works. But we'll make sure to talk this over with a plating shop. What surprised me was that board fab houses found it highly unusual when I asked for nickel-only plating and not the usual nickel-gold. So is nobody doing that anymore? Hard to believe. Guys?

Price would not be a big issue in this case, as long as reasonable (as in "a few Dollars more").

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Regards, Joerg

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"James Arthur" wrote in message news:V40_l.2919$ snipped-for-privacy@nwrddc01.gnilink.net...

You do not buy "active" stainless steels. Because they are alloys with distinct crystal phases, stainless steels are far more complex in their corrosion than are simple metals. Stainless steels can be both passive and active with respect to itself. In other words, a piece of stainless can selectively undergo galvanic corrosion in certain areas while other areas are protected. The work history (machining), the temperature history, and the strain the part is subjected to determine whether stainless is active or passive and whether stress corrosion cracking occurs.

People often buy stainless exhaust systems for their vehicles because they are tired of the conventional components rusting away. But they are usually wasting their money. Stainless steels have poor resistance to chloride attack so if your exhaust system is rusting away because your state salts the roads in winter, they will still corrode away - just a little slower. The much higher price of stainless in these areas is virtually never recovered by longer life.

For chloride and other halide exposure, the alloys of choice are the Hastelloy alloys. Not only are they extremely expensive, they require extreme care in machining as they work harden. When you consider that stellite machine tools are made from similar alloys, this makes more sense.

By the way, the galvanic series referenced in your post contains a number of typographical errors, especially in regard to the stainless alloys. 430 SST should only appear twice, once as active and once as passive.

Nickel plating copper is easy. Plating nickel over aluminum requires that the aluminum surface must be free of oxidation. But as soon as the piece is lifted from the etch tank, it oxidizes again. Generally the aluminum is cleaned in a slightly acidic solution containing zinc salts. This produces a very thin layer of zinc that protects the aluminum during the transfer. The nickel is then plated over the zinc to any desired thickness. I think that the peeling referred to above is with electroless nickel. I have had aluminum waveguides nickel plated for abrasion resistance and I never saw the plating peel off, even when gouged with a screwdriver. Electroless nickel can be applied over plastics (like buttons) but with no true metallic bonding. I once visited a startup company that was doing nickel coatings via the thermal decomposition of gaseous nickel tetracarbonyl. Because of the extreme toxicity of Ni(CO)4, I would avoid this process completely. The OSHA permissible exposure limit for nickel tetracarbonyl is one part per billion. This is 50,000 times lower than carbon monoxide. [If you do get a stainless exhaust system for your automobile, carbon monoxide in your exhaust will slowly corrode the nickel out of the stainless forming nickel tetracarbonyl. At International Nickel, I saw pieces of stainless tubing and stainless fittings that had been eaten through by carbon monoxide flowing through them.]

I have a number of files on galvanic corrosion including a few that specifically discuss stainless steels and marine environments. Email me if you would like copies of them.

Barry snipped-for-privacy@charter.net

I imagined "active" just meant stainless steel that hadn't been passivated, e.g.:

Joerg's the guy with the requirement, and he's decided to leave the final choices up to his customer. Nonetheless, that was a very interesting treatment of several related questions.

Thanks!

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Cheers,
James Arthur