"Gold" plated connectors....When and why?

[george graves]

So what's really going on with these connectors?  We all know that gold doesn't tarnish.  But, on the other hand, it's not the best conductor.  Also, I notice that very few pieces of test equipment has them.  I assume it's a tin coating mix with something - all over brass, steel, or copper? - someone chime in on that....but the bigger question is:

So gold.....Things we all know:

a.) It's a marketing wank thing for consumers.
b.) Oxidation is a real thing
c.) I assume that gold plating is on the micro, thinnest of coating.  So resistance is almost zero between a coated and non-coated contact.

But when and where is a gold coating appropriate?  For sure it's not on the lugs of an 8.5 digit mulitmeter.  So....I'm confused.  I'll just use an example we all know off hand of Dave's ucurrent "GOLD", and the golden lugs he used.  Was there any practical advantage to that?

My last question, is some of the "gold" connectors actually not gold at all?

[VK5RC]

I thought they were used mainly in RF connectors where the skin effect is active and a tarnished surface may be high resistance.

[rs20]

Oh, they're commonly available for non-RF uses as well -- USB & audio cables & plugs, 0.1" pin headers -- I like ordering gold-plated things because they're so damn shiny and gold!

Well-designed, non-RF connectors will scrape through typical corrosion, if it is present. So industrial/marine/RF applications aside (i.e., for my purposes), it's just marketing and shininess as far as I know.

[Zero999]

Contact resistance, especially at very low voltages. With other metals the non-conductive oxide increases the contact resistance. At lower voltages it's even worse because the voltage is too low to breakdown the oxide layer so the resistance is even higher.

Gold doesn't oxidise so even if it's slightly more resistive than copper, the contact resistance will be lower.

I imagine at RF the best possible coating would be a layer of silver (the skin effect means most of the current flows through the outer layer) followed by a layer of gold to protect it but I admit I'm no RF expert.

[PeterFW]

Contact resistance, especially at very low voltages.

I allways wondered why industrial audio connectors are silver plated.

[jpb]

I thought they were used mainly in RF connectors where the skin effect is active and a tarnished surface may be high resistance.

When I worked on GaAs MMICs the test jigs were gold plated brass. I think that there were two reasons, one is to reduce resistive losses and I'd guess also that gold being soft makes a good contact. The pads on the chips themselves were gold and connected with gold bond wires.

But I think when the move was made to microwave wafer probes (which were coplanar 50 ohm line essentially) a different, harder material was used for the contact.

As a young engineer I rather liked using gold plated kit.

The other thing I liked were the vibration resistant tables they used in clean rooms to mount the probe stations on - the tops of these were massive slabs of polished granite or marble.

[coppice]

Contact resistance, especially at very low voltages.

I allways wondered why industrial audio connectors are silver plated.

Industrial audio connectors aren't silver plated. It became a stupid fashion for headphone sockets on consumer equipment, but it corrodes too much for any serious audio use. Cheap industrial connectors are gold plated, and the good ones for small signal things like mics use expensive exotic alloys.

[wraper]

Contact resistance, especially at very low voltages. With other metals the non-conductive oxide increases the contact resistance. At lower voltages it's even worse because the voltage is too low to breakdown the oxide layer so the resistance is even higher.

Rather low current, not voltage. Like in relays with wetting current rating.

[wraper]

I imagine at RF the best possible coating would be a layer of silver (the skin effect means most of the current flows through the outer layer) followed by a layer of gold to protect it but I admit I'm no RF expert.

You cannot plate anything over everything. That's why ENIG on the PCBs consists of gold over nickel. It won't hold on bare copper. The same with connectors, there is nickel layer underneath the gold.

[coppice]

I imagine at RF the best possible coating would be a layer of silver (the skin effect means most of the current flows through the outer layer) followed by a layer of gold to protect it but I admit I'm no RF expert.

Silver is an awful coating for RF connectors, unless you are in a fairly dry location. In high humidity (e.g coastal areas) they blacken in days, and disintegrate in weeks. If you coat gold over silver the gold will be where the skin current flows. It defeats the resistance benefits of the silver.

[PeterFW]

Industrial audio connectors aren't silver plated.

I knew i should have phrased that differently, let me try again.

I allways wondered why the thounsands of dynamic microphone and balanced signal xlr connectors i soldered and used in the past 20 years were mostly silver plated.
Ranging from wannabe dj, over band touring equipment to small small tv broadcasting stuff.

I only noticed that they go for gold plating in the past... maybe 5 years.
Until then most of the rugged, solid, expensive, water resitant stuff from name brand big time companies was silver plated.
At least the stuff i bought, was given or came across.

But yes, the Harting, Socapex and other high densitiy stuff was mostly nickel(?) or gold.

[max_torque]

I imagine at RF the best possible coating would be a layer of silver (the skin effect means most of the current flows through the outer layer) followed by a layer of gold to protect it but I admit I'm no RF expert.

You cannot plate anything over everything. That's why ENIG on the PCBs consists of gold over nickel. It won't hold on bare copper. The same with connectors, there is nickel layer underneath the gold.

Pure gold is also too soft to withstand the mechnical loadings in a connector contact set, hence it's normally a gold alloy, thinly plated over a thicker base layer, often as you say, of Nickel.

[splin]

This AMP white paper 'Golden Rules: Guidelines For The Use Of Gold On Connector Contacts' is useful:

http://www.te.com/documentation/whitepapers/pdf/aurulrep.pdf

Summary: Gold plated contacts have excellent properties with some exceptions:

1) Hot make and break circuits
2) High contact force connections where the relatively soft gold suffers physical damage.
3) Gold contacts should not be mated with tin contacts due to fretting corrosion

As you may expect, the details are important including the materials alloyed with the gold to harden it, the quality of the underplating (usually nickel) and the thickness of the gold. Cheap unbranded gold plated connectors probably have very thin (possibly soft) gold plating and thus may not be durable and may allow corrosion of the underlying copper due to the porosity of the gold plating.

An important issue not mentioned in the white paper is that when gold plated metals are soldered, the resulting solder/gold alloy joint can be embrittled if sufficient gold is present reducing the reliability of the joints. This could be a particular problem for connectors where the solder joints will be stressed when the connectors are mated and seperated.

Thin plating (such as sometimes used as a surface coting on bare PCBs) isn't a problem, but in the telecommunications manufacturer I worked at, gold in soldered joints was forbidden - to the point that the gold plating had to be removed from components which came with gold plated leads as standard - such as some TO-18 metal can transistors including BC109s etc.

And as for the skin effect for RF applications, whilst the resistivity of gold is approx 45% higher than copper, this is ameliorated by the fact that the skin depth is proportional to the square root of the resistivity. Thus gold will have approx 20% more resistance than copper or 24% more than silver at high frequencies. 

Splin

[Siwastaja]

I knew i should have phrased that differently, let me try again.

I allways wondered why the thounsands of dynamic microphone and balanced signal xlr connectors i soldered and used in the past 20 years were mostly silver plated.
Ranging from wannabe dj, over band touring equipment to small small tv broadcasting stuff.

I have never seen a silver plated audio or video connector, and I have worked with audio/video connectors quite a bit. Either they are something relatively recent, or you have some weird-ass niche source of those connectors, or, as I suspect, you have just been mistaking something else as "silver" for those 20 years - probably nickel, which, alongside gold, is the most common plating in audio connectors. Gold plating started appear more in the late 90's. Both are good. Silver plating would kinda suck, as already stated by others, that's why it's not normally used in audio connectors. It's like copper, it oxidizes too easily and forms a semi-conductive oxide.

Material DC or AC resistance has nothing to do with this. Any of those materials, gold, silver, copper or even nickel has good enough resistance for practically every purpose. It's only about corrosion and mechanical durability.

[PeterFW]

I have never seen a silver plated audio or video connector, and I have worked with audio/video connectors quite a bit.

Take a look in the datasheets, amphenol, neutrik, hicon or switchcraft.
It says "silver" in the datasheet, not "silvery metal".
It looks like silver on the connector.
The tarnish looks like silver.

Even heavily "corroded" silver contacts still work fine, even with dynamic microphones that pick up a fart from the fly on the wall.

[dannyf]

"Gold" plated connectors....When and why?

to help you part with more of your money more quickly.

[Siwastaja]

Take a look in the datasheets, amphenol, neutrik, hicon or switchcraft.
It says "silver" in the datasheet, not "silvery metal".
It looks like silver on the connector.
The tarnish looks like silver.

OK, my bad - then, this is a thing now. I mostly use cheap connectors.

Even heavily "corroded" silver contacts still work fine, even with dynamic microphones that pick up a fart from the fly on the wall.

Of course they work - because audio is not critical. That's how the audiofool business works; you can sell anything as high-tech. They will tarnish, increase contact resistance and possibly cause heavy distortion. But people will be fine. Increased resistance doesn't show up, and if there ever is distortion, people will juggle the connectors or just buy a new cable. No big deal. Getting rid of bad cables and jiggling the contacts is everyday life even in professional audio. Everybody knows the scratching sound of bad contacts. We are just so used to it that we don't complain. It's only a source of nuisance. If it was a real security issue, the connectors would just work. This would mainly happen by physical design, correct plating being secondary. (For example, the XLRs work much better regardless of plating, whereas 1/4" instruments plugs are always a PITA, more or less, but still "ok enough" so we live with them.)

And, to be fair, I have seen silver-plated connectors - but they have all been a lot older than 20 years, something from the 70's.

But, this thread is kind of theoretically discussing about plating and whether it makes sense to gold plate or not. And to answer that, yes, gold plating really actually makes some sense, it's not merely a marketing trick (as anyone designing a PCB card edge connector knows!). But I guess silver plating is a marketing trick, even more than gold plating ever was, because unlike gold plating, silver plating doesn't make sense, or at least I can't see it. I might be wrong.

And, in professional installations, I have only seen nickel and gold - and no tarnish. But I haven't seen much of the scene in the last 10 years or so.

[SeanB]

Rhodium gold contacts are very common in low current low voltage precision relays, though there you typically also are using them inside a sealed glass reed relay enclosure. Gold flash over German silver ( a silver copper alloy used for contact material) is also common, though there the gold flash is there for the use of the relay in low signal use, the flash will evaporate leaving the silver slug under it if you pass more than 10ma at over 20v through it. Silver contacts are used in wiping applications as they are soft yet durable, the wiping as the contacts are mated or the relay closes ensures good contact with impurities becoming embedded in the coating rather than forming an insulating film.

[PeterFW]

OK, my bad - then, this is a thing now. I mostly use cheap connectors.

That is not a new thing...

Even heavily "corroded" silver contacts still work fine, even with dynamic microphones that pick up a fart from the fly on the wall.

Of course they work - because audio is not critical. That's how the audiofool business works;

This has nothing to do with audio voodoo...
Why dit i say that?
I have seen nickel, chrome or brass connectors that looked as bad as the silver see fail were the silver plated still worked.
Why dit i say dynamic microphone? Because they tend to have a output in the mV range.

Edit: If you say "audio is not critical" you should do some reading... it may be that you put a bunch of stuff that is considered industrial audio into the realm of voodoo.

[Siwastaja]

Silver plating can work very well if the connector has enough spring pressure and the mechanical design is self-cleaning. The idea is that the silver contacts scrape against each other, removing any surface tarnish, and provide kind of a "cold weld" - an almost continuous metal from one connector to another. This works because silver is soft, so this is kind of the opposite of how a gold plated contact works (it's not soft gold - it's a hard alloy).

The limitation here is the durability in contacts that are frequently reconnected, and the usage outside of proper connector types where this scheme works (i.e., not enough pressure or incorrect insertion path). Also, sometimes the tarnishing can be bad enough that the self-wiping action is not enough.

I have seen any type of surface plating fail, too.

[PeterFW]

The limitation here is the durability in contacts that are frequently reconnected,

Just to be clear, i dont want to say "silver is better".
But silver will work in some cases and is cheaper.

Locally, in a 500km radius, when i see a XLR connector, it will most likely be a Neutrik.
They are extremely popular, they mostly have silver plated contacts, they can take a beating and get plugged in and out of the socket on a daily baisis during a road show.
Yes, they do sell gold ones, they are very slightly more expensive.
But once there was a huge price gap between gold and silver.

But we are running in circles, i am out now...

[splin]

Ok. Here is TE Connectivitie's white paper on when silver plated contacts are appropriate and their characteristics:

http://www.te.com/documentation/whitepapers/pdf/Ag_use_connectors_503-1016.pdf

A large part of what drives making contact finish choices is cost. What limits contact finish choice is performance requirements and manufacturing concerns. The finish appropriate for any connector application is determined not only by performance requirements, but also lifetime exposures under which it will have to function. Silver has a long history of performing well in the tarnished state in power applications and certain appropriate signal applications.

Characteristics of silver as a contact finish:
Positives:
Silver has a unique combination of material properties such as the highest thermal and electrical conductivity of any metal and a relatively low hardness. Theory and experience show how these aspects lead to very low CR values for mated clean silver surfaces [5, 6, 7, 8]. Current passing through a clean silver-to-silver contact interface sees a relatively large conducting area (less constriction) made up of adhesively bonded metal-to-metal asperity junctions. This unique combination of properties results in relatively low CR, superior thermal-rise performance, and excellent vibrational stability. The attributes make it attractive for use in power applications.

Silver also has good solderability characteristics, even if the silver is somewhat tarnished. If the level of tarnish is excessive, a more active flux may be required. Immersion silver is widely used as a solderable finish on board applications but can have limited shelf life if the silver is exposed to the environment.

With any changes away from traditional finish choices comes the risk of unintentional finish combinations. Generally, it is recommended to mate ‘like on like’, that is to say, mating a silver plug to a silver receptacle. Fortunately, silver can be an appropriate choice for mating to either gold based or tin finishes. Performance levels and costs of such combinations will fall somewhere between the two different finishes. For example, if you are mating silver to tin, you will not appreciably improve durability and fretting failure could still be a risk; all at the higher cost of silver [9]. General rankings of the galvanic corrosion susceptibility of different contacting material combinations show that silver-to-gold and silver-to-tin are satisfactory combinations in many environments; with silver-to-tin presenting the most risk in harsher environments [10,11, 12]. Therefore, a combination may have to be tested to determine its viability in more severe environment applications.

Potential Issues:
Unfortunately, silver has some less favorable contact performance attributes. Silver does not have the ‘noble’ character of gold and will form surface tarnish films when exposed to some reducible sulfur bearing atmospheres. Silver has a high Coefficient of Friction (COF) (high insertion forces) and poor wear characteristics (poor durability). Silver may be susceptible to electro-migration failures under specific conditions. 

A history of using silver finished contacts has shown that low and stable CR is maintained in many applications using tarnished silver contact surfaces – even with films on the order of a thousand angstroms in thickness [17]. If the quality and level of silver tarnish is not excessive and wipe and sufficient normal loads are incorporated into the connector design, silver tarnish typically will not cause contact performance problems (Figure 5). The films can even lead to durability and insertion force improvements.

[dom0]

I never heard of a XLR connector electrically failing. Mechanical failure (i.e. hit with a large bolt, sledge or beam, because you can't really destroy them otherwise), yeah, happens, rarely. But contact failure? Nahh...

[SeanB]

I have had them melt, mostly because they were used as speaker connections and the solder joints came loose inside the backshell, arced and cooked the lot together.

[TimFox]

Gold-plated connections (binding posts and banana jacks) are used in precision DC applications due to the low thermal emf (about 0.5 uV/K) against copper.  Many "silvery" connectors (such as standard banana plugs) are nickel plated, which has a higher thermal emf against copper (about 10 uV/K).  Actual silver against copper is similar to gold against copper, but silver surfaces in normal urban/industrial environments react with atmospheric sulfur to get the familiar "tarnish" (not oxidation under normal conditions at room temperature).