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topic 25279

Low Contact Resistance Plating. Alternatives to gold plating?



A discussion started in 1995 & continuing through 2017

(1995)

Q. I would like to replace the gold plating of an electrical spring contact with another material to save money. Currently we use two gold plated surfaces that are electrically connected by a gold wire spring which makes surface contact with the two gold pads. The spring is in place to compensate for expansion and contraction driven by temperature changes. I really do not know of any need to replace the spring but would like to replace the plating on the two contact surfaces. The processing problems associated with plating the gold on the contact surfaces is the main driver for change. Currently they are brush plated and this will not facilitate the production volumes anticipated. The intent of the package is to function for a minimum of twenty years and will be hermetic. The current subcontractor for the two contact surfaces has suggested replacement by simple solder plate (Pb/Sn). I am concerned that this would be unreliable due to migration or dendrites or something. I have never seen Pb/Sn used as a contact surface. Could carbon be used when applied by a thick film process? Would Palladium work? Would it be any cheaper? Any other ideas?

Gordy S [last name deleted for privacy by Editor]
Honeywell Inc.


(1995)

A. IC's with tin or solder plated leads (I don't know how much lead they use) are commonly used both in zero-insertion-force sockets and conventional spring sockets, even for low-voltage DC circuits. On the other hand I've seen circuit boards with tin or solder plated fingers used in control systems in bad environments, and the experience was miserable. I can't count how many times I pulled boards out and reinserted them so that the scraping action would present a clean contact surface so they would work again.

I suspect that if the contacts are sealed, and the application is not very low voltage, that it probably would work for 20 years. But this is based on the anecdotal evidence of my very limited observations, and I hope that somebody who really knows what they're talking about pipes in.

Electroless nickel is very widely used, but perhaps for somewhat higher voltages (the battery charging contacts on almost everything these days use nickel plated or electroless nickel contacts).

As for palladium, that should be a satisfactory substitute for gold. It's somewhat lighter and somewhat cheaper per pound, roughly halving the cost. AT&T Nassau Metals division used to market a plating process, but with the constant changes in corporate structures these days, I wouldn't know offhand how to locate a supplier of proven palladium plating processes.

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



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(2001)

Q. I am a mechanical design engineer for a firm that manufactures a line of electro-mechanical switches. The non-moving contact is kovar (within a header) and is currently plated with matte sulfamate nickel a minimum of 100 microinches thick followed by a cobalt hardened gold plate 50 microinches thick. The moving contact is brass and is currently plated with electro-deposited nickel a minimum of 50 microinches thick, followed by a minimum of 50 microinches of gold. Contacts are normally open, resistance is 10 ohms maximum, rating is 50ma at 12vdc. Excellent conductivity and corrosion resistance are paramount.

The question is: Are there any other plating(or combination of plating) that would yield the same or reasonably the same characteristics from what is currently being used? Cost savings are also desired with any alternative plating process. Quantities of each are equal and are currently plated in lots of 10,000.

Arthur H. Nintzel
- West Sayville, New York


(2001)

A. Palladium is widely used as a substitute for gold on electrical contacts, Arthur. Talk to your supplier about installing such a bath. Recognize that all non-precious metals tarnish, so at very low signal levels they won't work. But you'll often see electroless nickel plating on the power circuits and earphone adapters of a device like a cell phone while gold plating is used on the digital circuits of the same device.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



To minimize searching and offer multiple viewpoints, we've combined multiple threads into the dialog you're viewing. Please forgive any resultant repetition or failures of chronological order.



(2003)

Q. I have a phosphor bronze (ASTM B103) contact we designed and solder into a battery cell holder. We measure extremely (uA) low currents in all type of batteries and contact resistance is of extreme importance to us. I have a "oxidation problem" reported by my customers. I am considering plating these with an undercoating of nickel and top coating of gold. Is this the best method or is there another solution available?

Randy Gordon
Battery test equipment - Tulsa, Oklahoma


(2003)

A. Precious metals don't tarnish or oxidize. I believe that when contact resistance is critical, precious metal plating is the only alternative. An under layer of nickel is a very good idea, if not a requirement, to prevent diffusion of copper into the gold. There may be slightly less expensive alternatives to gold though, like palladium, and you might look into that. Good luck.

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


Alternative to gold plating for conductivity

July 18, 2017 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Dear all,
I do gold plating on brass components (Pins). Kindly suggest any other plating to increase conductivity. Our focus is not decoration but conduction.

Regards,

Iftikhar Ali
employee - Karachi, Pakistan


July 2017

A. Hi Iftikhar. We appended your inquiry to a thread which discusses your issues. Nickel plating or electroless nickel plating are widely used for low contact resistance ... but not super low. Precious metals are the only non-tarnishing conductive materials. Good luck.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"


July 20, 2017

Q. Dear Ted,

Thanks, but can you elaborate it extensively.

Regards

Iftikhar Ali
PIA - Karachi, Pakistan


July 2017

thumbs up sign Sorry cousin, but no. Extensive elaboration about generalities is a subject for books, not a public forum.

But if you elaborate your own exact situation -- what these pins are, what voltage & amperage they are expected to carry, whether they are for one-time soldering or wire wrapping vs. millions of insertion cycles, anticipated lifecycle, environmental exposure situation, etc., additional help may certainly be possible.

Meanwhile, a great way to learn is to try to help others with their problems (and it's your turn). You very quickly find out what you know, don't know, and thought you knew but actually didn't :-)

Thanks, and regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"


July 19, 2017

A. Cobalt can also be used as substitute as it's more conductive than nickel.

Marvin Sevilla
- Managua Nicaragua



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