Silver vs. gold switch contacts

Hi:

I am planning to make a switched gain transimpedance amp, switched gain voltage amp, as well as a switched bandwidth filter based on op-amps and rotary switches. I'd like to use ITT MA00L1NCQD or Grayhill

56DP36-01-1-AJN from DigiKey.

Both of these have silver contacts for the rotor. The ITT has silver stationary contacts as well. While at least the Grayhill has gold plated stationary contacts. In fact, even when ordering the "G" contact type from ITT, the rotor I think is still silver.

Alternatively, there is a bit more expensive ITT 50DP36-01-1-AJN which has all gold contacts.

Is silver unacceptable for circuits in which practically no current flows, such as an op-amp's feedback loop?

Thanks for input.

Good day!

--
_____________________
Christopher R. Carlen
 Click to see the full signature
Reply to
CC
Loading thread data ...

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

Reply to
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

Reply to
martin griffith

Found it easily thanks to Google...

formatting link

Thanks for the info.

--
Good day!

________________________________________
 Click to see the full signature
Reply to
Chris Carlen

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?

Reply to
AZ Nomad

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.

--
Good day!

________________________________________
 Click to see the full signature
Reply to
Chris Carlen

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

Cheers,

Phil Hobbs

Reply to
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.

Reply to
Roy L. Fuchs

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.

Reply to
Ancient_Hacker

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:

formatting link

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:

formatting link

--
Good day!

________________________________________
 Click to see the full signature
Reply to
Chris Carlen

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

Cheers,

Phil Hobbs

Reply to
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

Reply to
mike Monett

"Phil Hobbs"

** Huh ???

** What nonsense.

........ Phil

Reply to
Phil Allison

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

--
Deep Fryer: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
Reply to
Tim Williams

Ha. Ha ha.

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

Tim

--
Deep Fryer: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
Reply to
Tim Williams

"Phil Hobbs"

** Silver sulphide is an INSULATOR !!

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

Reply to
Phil Allison

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

Reply to
AZ Nomad

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

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
 Click to see the full signature
Reply to
Michael A. Terrell

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.

Reply to
Sjouke Burry

** Know anything AT ALL about elctrical contact issues ??

This will get you kick started.

formatting link

** Yawn.

Wrong topic .....

......... Phil

Reply to
Phil Allison

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.