[laxguy28]

So long story short I have a project in a class of mine regarding RTD's (Resistance Temperature Devices)...there essentially the same as thermo-couples but I'm working on the manufacturing process that goes into these RTD's.

They get held into place by these "clamps" currently made of oxygen free copper with a pure silver coating where contact is made with the RTD's...problem is, I want to make the resistance lower so I can calibrate the RTD's better.

My thought:  Keep the oxygen free copper contacts and use a gold coating (rather than silver) where it touches the RTD's in hopes to lower the resistance.

My question: Will the gold coating adhere to the oxygen free copper or do I have to use a medium such as nickel? 

ANY advice would be GREATLY appreciated! 

Thanks in advance!!!

[curiouscat]

I've seen gold plated audio connectors. So I think it can be done.

Look up those items; I think they even make HDTV connectors in gold / silver plated versions.

[eazye1334]

You will need a nickel layer. There is somewhat of an adherence problem,but most seriously is the alloy problem: the gold will diffuse into the copper layer and create a gold-copper alloy over time. Thus the copper on the outside oxidizes and ruins the contacts.

I've never done it personally, but I do work in an electroplating/electroforming shop. I found this paper that may help you out.

[Arkcon]

I've seen gold plated audio connectors. So I think it can be done.

Look up those items; I think they even make HDTV connectors in gold / silver plated versions.

curiouscat:, like eazye1334: said, the "gold plated contacts" used in precision electronics (more like the O.P's application), generally require an under-plating of another metal, to prevent diffusion and other deleterious effects.

http://en.wikipedia.org/wiki/Gold_plating#Electronics

 Audio-visual equipment connectors likewise often have an underlayer, to save costs.  In some ways, the only thing "gold-plated" about those high-priced audio-visual connectors is the name.

[curiouscat]

@Arkon

Thanks! I didn't know that.

[laxguy28]

Hey everyone!,

I wanted to thank you guys for all the replys and had a quick followup question if you had a second to answer.

What I'm wondering is if you guys had any suggestions for the "under-plated" metal...I had just assumed nickel would work but does that have the lowest resistance? 

Also, is there a specific process for adhering these together or can you point me in the direction to research this?

Thank you in advance.

[eazye1334]

Nickel is typically used for electronics, I wouldn't really consider anything else as an underplating.

However, before getting into actually doing, can I ask why you're trying to replace silver with gold? Silver already has the lowest resistance. You wouldn't be gaining anything except better corrosion resistance. The only way the gold can possibly have lower electrical resistance than the silver is if you have incredibly pure gold, which I'm guessing you won't have access to.  I just don't see how this will help you if you're only worried about the electrical characteristics.

[Enthalpy]

Replacing silver is absolutely correct.

Not because of the resistivity of bulk silver, but because contact quality depends essentially on surface cleanliness and oxidation. Silver develops a semiconductive oxide layer. Not only in books and on tea pots: older computer memory modules had silvered contacts and did work unreliably.

Gold is THE proper choice for contacts. That's why the electronics industry is the second consumer of gold. Many people tried alternatives but failed. Well, rhodium and platinum would fit also... 

Nickel is THE standard affordable barrier against diffusion that gets easily wetted by molten metals; at high (many MHz) frequencies, where nickel's magnetic permeability increases losses by skin effect, palladium replaces it.

Nickel might also bring some mechanical strength to contacts, which neither copper nor gold do, and this should improve the endurance for repetitive connections. Only a hypothesis from me.

To know if nickel is commonly used as a barrier, take an old component (say, a computer memory module) and abrade its contacts gently with fine sand paper. Look for a white metal at the transition between remaining gold and apparent copper.

[eazye1334]

Trust me when I say nickel is used as the most common underplate between copper and gold.

While what Enthalpy is saying is true, to get those benefits you need very pure gold. Resistivity of precious metals increases substantially with small amounts of impurities or alloys. So if all you're doing is stripping the silver layer to plate it with impure gold, I'm not sure you're going to see any improvement.

If you're still interested in doing it yourself, considering the small amount you would be using, I would look into small home kits. Caswell Plating is one place that I know of that has what you would need. I would suggest for the nickel layer an electroless deposition as the electrolytic process is likely to be much more involved than what you'll want to do. After that, the "plug-and-plate" system for gold would be the next step. These will adhere well enough.

As you can see though, this process will not be cheap. I have no idea where you live, but you may want to look into finding an electroplating shop. They are used to doing small pieces and jobs like yours and the cost may be much more effective this way. There are even some that could ship them the parts to do the plating. This way you also don't have to worry about hazardous chemical disposal or anything like that. If you were planning on doing this more often than your posting implies, then I would maybe suggest the home kits. But for now, for just these pieces, my first suggestion would definitely be to let an expert do it if at all possible.