Silver vs. gold switch contacts

The problem occurs when the contacts are open. If there is a DC bias voltage between them and the humidity is high, the silver will migrate and eventually cause a short. Usually this happens between adjacent contacts as the silver forms dendrites. Gold is unlikely to do this. Tin will also migrate; you can actually see the whiskers form. I have seen the tin bridge air gaps. The higher the humidity and the voltage, the faster the effect takes place.

Al

There is a app note from Tyco/Pandbrelays.com called "relay contact life" that goes through many contact formulation. Dont have the URL, the app note *may* be called IH/12-00

worth a read if you can find it

martin

Found it easily thanks to Google...

Thanks for the info.

What kind of moron would use silver? Do they expect you to get out the silver polish every two weeks to remove the tarnish?

Are you confusing some other silvery metal with silver?

Silver, element Ag, the one that tarnishes is used all over the place in electronics. And I often wonder why since it tarnishes like crazy. Of course, it also has many desirable features.

What really bugs me is BNC and other connectors and switches with solder lugs that after sitting in a drawer for a while are impossible to solder. Have to wire brush them with a dremel tool. Very time consuming.

But silver is indispensible it seems in contacts rated for carrying significant amounts of current. Low level stuff though, clearly needs all gold.

One good reason is that silver oxide is a metal. Tarnish is ugly but hardly affects the contact resistance.

Cheers,

Phil Hobbs

On Wed, 05 Apr 2006 17:59:03 GMT, AZ Nomad Gave us:

Most switch contacts are gold or platinum plated.

Just so you know Silver Oxide in pure form is a better conductor than silver itself is. There is none better, in fact.

Elementally speaking, the best conductor is Silver. With respect to compounds, however, Silver Oxide is the best conductor known to man, short of superconducting media.

Very interesting! Howcome this isnt more widely known?

But isnt the black stuff on silver more likely to be silver sulfide?

Silver oxide is more a brownish color I think,, the crud on silver is usually brown to black.

But isn't much of silver tarnish silver sulfide, rather than oxide? Silver in a non-sulfurous environment remains free of tarnish for quite a long time. The tarnish I see on most stuff is black, which I think is mostly silver sulfide. It is not at all conducive to soldering, but I suppose usually doesn't cause too much trouble with contact resistance, as it probably gets scraped away sufficiently during wiping action.

Seems to be reiterated here:

Haven't heard of platinum plated contacts either. Can you link to a vendor that has any such beasts? This document speaks of using palladium in relay contacts:

Silver sulphide is a good conductor too, although not as good as silver oxide.

Cheers,

Phil Hobbs

Phil, Any info on the conductivity of silver hydroxide, AgOH? In fact, if you have any info on AgOH, such as decomposition temperature, I'd sure appreciate it!

Thanks,

Mike Monett

"Phil Hobbs"

........ Phil

Er, silver oxide is a compound. If it were a metal, it wouldn't be a compound, period! LOL

(Sure, lots of intermetallic alloys look like compounds, though.. MgAl vs. PbS vs. pure Si, etc...)

Tim

Ha. Ha ha.

So, smarty pants, got a cite to share with us?

Tim

"Phil Hobbs"

Silver plated switch contacts INSULATE the circuit if they become tarnished with silver sulphide.

Low current silver plated switches are normally designed to be "self cleaning" - ie the contact surfaces wipe each other during switching.

Silver oxide does not exist on metallic silver under normal conditions.

....... Phil

I'd be interested in how it compares to other metalic oxides. AFAIK, they're all lousy conductors.

Yeah, Silicon oxide is a horrible conductor, and its as common as sand. ;-)

Bull.-)-)-) I have made lots of skin electrodes with silversulfide layer on silver ,and they conducted fine,one funny property was that the layer was photo sensitive,you had to grow the layer in total darkness.Conduction was oke in both cases but the layer grown exposed to light tended to drop off the silver.

This will get you kick started.

Wrong topic .....

......... Phil