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Electrical conductivity of plating materials

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I'm working on a fishing device that detects when a fish bites. It operates off a 1.5 volt battery. The device activates when a metal rod (.6" length X .03" dia.) comes in and out of contact with 2 gold plated pins (the kind used in computer cable assemblies). For my prototypes I have been using paper clips to produce the rod. These work fine but unfortunately I can not get the MSDS sheet to tell me what they are made/plated with. I have now had a company send me some stainless steel rods for production but when tested they do not perform as well. Because of the small amount of pressure from the fishing line that causes the rod to come in and out of contact with the pins, the stainless steel rods seem to not allow the electric current to flow as easily, which causes the buzzer to sound 'scratchy'. My question is what would be the best type of plating for the stainless steel rods that would allow 1. excellent electrical conductivity. 2. good corrosion resistance (will be exposed to rain and water). 3. good durability. The rods are extremely small so I do not believe material cost will be a factor i.e.: if gold plating is suggested. Also, stainless steel does not need to be used for the rod if another magnetic metal could be used that would hold the plating better.

P.S. I have no experience with metals and platings so any suggestions would be extremely helpful. Thank you in advance.

Andy Corbiere
Inventor - Milton, Vermont, USA


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Precious metals like gold are best for critical resistance issues because they do not tarnish, whereas all other metals develop--to a larger or smaller degree--a non-conductive oxide tarnish. If you look at your cell phone and other micro electronic devices, you'll see that critical communication ports are gold plated. Some precious metals are harder and more wear resistant than others. Gold can be plated from very soft to quite hard. Rhodium is especially hard.

However, if the application doesn't need super low resistance, electroless nickel is an ideal plating for this application. If you look at a cordless phone and other devices which use a "drop-in" battery charger, those battery contacts are usually electroless nickel plated.

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Ted Mooney, P.E. RET
finishing.com
Brick, New Jersey

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I have read on your answer (and in some other places) that precious metals are very good for resistivity or conductivity related needs, therefore the gold plated electronic devices. But reviewing tables which state the conductivity values of those precious metals, I saw that Silver or Copper have higher values on conductivity. Why is gold still considered the best for this application ?

Francisco C Garcia
Manufacturing - Monterrey, NL, Mexico


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You are correct that copper has excellent conductivity. That is why it is used for wiring and bus bars. But copper tarnishes, that is, an oxide film grows on it. That tarnish is a thin electrical insulating layer that prevents good electrical contact. In high voltage applications it doesn't matter, but in low voltage applications it can interrupt the current flow. Precious metal like gold do not tarnish so they do not grow this insulating layer, so their surface conductivity is excellent even for low voltage applications.

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Ted Mooney, P.E. RET
finishing.com
Brick, New Jersey


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I am looking for information related to the electrical conductivity, corrosive and mechanical characteristics of various metal platings. I would like to find rather specific information in the form of measurement values for these properties. Could be in the form of data sheets or tables. Most of what I have found so far is rather qualitative and vague. Can you point me in the right direction please?

Regards,

Chris Sandmeyer
- Christchurch, New Zealand


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Hi, Chris. The type of quantitative data you seek -- although probably not every piece of data you would like -- can be found in Safranek's Properties of Electrodeposited Metals and Alloys [link is to info about book at Amazon]. Good luck.

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Brick, New Jersey



July 21, 2011

Hi all, I work in a metal finishing company and we do gold plating but recently we have a problem with hard gold plating and its electrical conductivity. Our customer does electrical conductivity test for gold plated parts and he says the parts gold plated doesn't have sufficient electrical performance. We recently made a new hard gold tank but still have same problem even though they said it has better electrical performance. Do you guys have any idea what can cause this problem or any advice how to fix it?
thank you

Onur Bakirman
- Gilroy, California, USA

First of two simultaneous responses -- July 25, 2011

The gold is probably not thick enough - IF- the substrate material is significantly less conductive, like stainless steel.

James Watts
- Navarre, Florida

misc. plating stuff
For Sale cheap



Second of two simultaneous responses -- July 25, 2011

So-called "hard gold" contains other metals in it to make it hard - usually cobalt or nickel, but indium has been used as well. The addition of these metals provides better wear characteristics than pure gold plating but they also reduce the electrical conductivity. Usually, the gold purity of the hard gold ranges from 99.0% - 99.9%, depending mainly on the amount of nickel or cobalt salts contained in the bath. In general, the lower the gold purity, the worse the conductivity. To get improved conductivity, I would say that you'll have to have a bath that will produce a higher purity gold. However, by doing this, you will sacrifice some hardness.

Chris Owen
- Nevada, Missouri, USA

July 27, 2011

You say you just made a new gold bath, well, what's in it? Only he who knows may be able to tell you for sure.
G. Marrufo-Mexico

Guillermo Marrufo
Monterrey, NL, Mexico

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