Silver plated copper coil

[Joe_Lorenz]

That's a most interesting fact! I would have expected tarnish to make considerable changes i.e. on coils soon. I think I've got some older mil comms gear where huge amounts of laquer were used to protect even silver plated components' surfaces.

And yes: I've seen not-so-cheap audio cartridges, too, where green corrosion had grown between plastic and coils!

[Ceeejay]

Originally Posted by Bazz4CQJ

Does silver-plating change the sound quality? These are my thoughts;

• If tested on some super-sensitive electronic test equipment, some small change might well be detected.
  
• If listened to by 17 year old humans, maybe some small percentage of them might report something.
  
• If listened to by septuagenarians….well, maybe not?

I think our Age Poll is due out soon?
B

I think you missed the most important factors in audiophile HiFi, the price and marketing.

If it costs more and has more buzzwords then it has to make a difference right?

[Bazz4CQJ]

Originally Posted by Radio Wrangler

In RF engineering, we use plenty of silver plated wire. With the skin depths in play, there is enough difference to be worth it,
David

I still have a box full of bits of Pye VHF gear from the late 60's, and much of that is silver plated and most of it still looks very good. In contrast, I have some other silver plated stuff from the same era, and kept in the same conditions, which now looks very tarnished. I very much suspect that plating is one of the dark-arts!

@ceejay, re audiophile Hifi, I find that my beloved Technics Graphics Equaliser solves all problems in the search for "the Closest Approach", as sought by Peter Walker of Quad fame.

B

[kalee20]

Originally Posted by ortek_service

I knew silver oxidises in air, so although Silver is the best conductor the 2nd-best Gold is often preferred as it doesn't easily react with much.

Originally Posted by Radio Wrangler

Gold isn't second. It's nowhere near as good as copper and copper is close to silver.

Absolutely - it's somewhere between copper and aluminium.

However, gold is extremely ductile, so there might be an argument for using gold in a m/c cartridge if drawn to super-fine diameter. Against that, the stuff is quite dense, more than 2 1/2 times as dense as copper, so you have to reduce the diameter quite a lot before bringing the weight of the moving coil back down to what copper would've given - and resistance would then have increased quite a lot, firstly by the use of the less-conductive gold, and secondly by the reduction in gauge.

Apart from the cost, whether the sums add up to give an advantage (the extra resistance increases Johnson noise of course), I don't know. It's just that there might be a justification (and of course it scores high marks amongst the muggles in the pub hi-fi fraternity).

[CambridgeWorks]

Reminds me, I saw that roller coaster recently, the one I mentioned in another thread a while ago about some having solid silver wire that when word got around, the surplus dealers removed the unit for scrap value before selling the radio.
Rob

[m0cemdave]

I came across a WW2 aircraft receiver module some time ago with a rollercoaster in the PTO / VFO that had been ruined by removal of the winding wire.

Careful examination of the remaining stubs indicated that it had been silver plated copper.

Somebody must have been disappointed!

[Julesomega]

Sounds like you had a 78 Set, Dave

[emeritus]

Originally Posted by Craig Sawyers

In space applications gold plating is a no-no. It dissolves in solder to form a brittle intermetallic.

Space-grade parts are received with gold plating (just over bare copper - no nickel) - but this is only to protect the bare wire from slight corrosion that could compromise solderability. So before soldering, the parts are "de-golded", usually in an automated solder bath - so the gold is removed into the bath and replaced by a skin of regular tin-lead solder. The parts are then stored in desiccators before use.

The bath is monitored for the amount of dissolved gold. Beyond a certain gold percentage (I forget what the number is), it 6is drained and new fresh solder added.

Craig

Gold used to be used in some early integrated circuits, but in contact with other metals was found to develop purple inter-metallic compounds, known as the "purple plague" that could cause connections to fail.

[ortek_service]

Originally Posted by emeritus

Gold used to be used in some early integrated circuits, but in contact with other metals was found to develop purple inter-metallic compounds, known as the "purple plague" that could cause connections to fail.

Well Gold was (/ still is?) used for the bond-wires, inside IC-packages / on Chip-On-Board PCB's and substrates.
Although they did often move to Aluminium and later Copper.
I'd originally thought using Copper was for cost-reasons (like Aluminium), but maybe copper gave better performance if higher electrical-conductance than Gold.

Somehow for many decades since School, I'd always believed it was Gold that was second-best to Silver for Electrical (& Thermal) conductivity.
So it was quite a surprise to recently look at the tables and discover Copper was actually better than Gold for both.
That may well explain why switches with Gold-plated contacts are only rated for small-signal use.
- Whereas the same switch with silver-plated contacts is rated at many Amps, for Power-switching.

(Although I'm a little puzzled why Gold-sheets are used for heat reflection, in space etc applications - Maybe it is stronger than copper or silver sheets would be?)

I knew that soldering to gold can be tricky, so why PCB's had a nickel barrier underneath the Gold plating to stop 'leaching' when hand-soldering / may have been needed for Gold-wire bonding to pads.
Although bare Gold was often used on Alumina substrates (even for RF, when it seems Copper / Silver would be better).
However, I believe in Space applications there are issues with 'Out-gassing' / reaction with 'Atomic-Oxygen' with silver etc. so maybe Gold is better there if not in contact with solder to cause issues with that?

[Bazz4CQJ]

Originally Posted by ortek_service

(Although I'm a little puzzled why Gold-sheets are used for heat reflection, in space etc applications - Maybe it is stronger than copper or silver sheets would be?)

Isn't much of the thermal protection actually Mylar (polymer) sheet coated with gold (or at least, something that looks like gold)? Titanium nitride looks very much like gold, and can be sputter-plated on to metal to make it wear-resistant (and perhaps on to polymers to make them reflective?).

B

[Radio Wrangler]

Gold wire bonds inside ICs, both to the leadframe and occasionally point-to point on the substrate are normally attached by welds at each end, not by soldering. The usual machine used was a ball-wedge bonder.

The purple plague I remember with ICs was a problem with mostly CMOS but applied to other low power dissipation things as well. Moisture ingress would leach phosphorus from the glass protection layer over the die. The leachate was acidic and corroded the aluminium metallisation layer. Under a microscope it looked purple. CMOS unless running fast had very low power dissipation, close to zero if static! Other IC families dissipated much more power and tended to drive out moisture. In industry we discovered a bad reliability problem with this family and troubles were compounded on finding that parts held in stock had been quietly degrading as well. Changes to passivation layers on CMOS happened, moisture absorbers and sealed bags for stock storage and distribution came in. There may, of course, be other plagues of the same hue, but that's the big one I remember. Under a microscope, the bad joints we had from gold-saturated solder looked ordinarily dry, with a matt-silver surface.

Our stolen scrap solder was indeed contaminated with dissolved gold, the aforementioned intermetallics and the problem it gave was the rate of bad joints on wave soldered boards found in production. Downstream, there wasn't a bad joint problem found in the field, but around the time we had a major campaign on reducing warranty failures in the field, we also switched to pre-tinned SMOBC and the gold had gone away. Consequently, there may have been a background level gold contamination problem, but it wasn't large enough to see with the earlier level of scrutiny.

Silver seems to be much better behaved with solder!

It's not terribly expensive, so it's feasible to buy new wire to restore roller inductors which have been harvested by the hopeful. The London Wire company under their various trade names are a source. Be sure to buy real silver-on-copper wire for electronics. They also sell silver plated wire for the jewellery market and it has thin silver over nickel and skin effect makes it rather lossy.

David

[kalee20]

Originally Posted by ortek_service

I'd always believed it was Gold that was second-best to Silver for Electrical (& Thermal) conductivity.
So it was quite a surprise to recently look at the tables and discover Copper was actually better than Gold for both.
That may well explain why switches with Gold-plated contacts are only rated for small-signal use.
- Whereas the same switch with silver-plated contacts is rated at many Amps, for Power-switching.

That's not quite the right reason, it's nothing to do with the electrical resistance of gold contacts against silver.

Gold is used as a plating because it doesn't tarnish. You get a good metal-metal contact every time, which is important when you are switching millivolts and milliamps (or less).

If you put volts and amps on the switch, then at the instant of switching, you get a small spark or arc. That quickly removes the gold plating. The switch becomes unreliable for very small-signals thereafter - the contact base metal (which is frequently silver anyway) then needs several volts to punch-through any tarnish on the surface.

[GrimJosef]

Originally Posted by Bazz4CQJ

...Isn't much of the thermal protection actually Mylar (polymer) sheet coated with gold (or at least, something that looks like gold)? ...

It's Kapton. For the James Webb telescope it was aluminised and two of the five sheets also had silicon coated onto them. NASA give a wealth of detail here https://science.nasa.gov/mission/webb/webbs-sunshield/#Sunshield-Material.

Metalising Mylar can be quite challenging (I once looked into it for an entirely different application). Thermal changes during the deposition process cause the thin film to bend or even wrinkle once it's settled back down to room temperature. Perhaps that problem could be solved with a big enough budget but we didn't have that.

Cheers,

GJ

[Radio Wrangler]

Thin gold plating (dictated financially!) is very prone to pinhole defects, so if done over copper, sulphurous solutions can get in from the atmosphere and react with the copper surface, this then works along under the gold and creates a right mess. So the economical solution was to stick a good thick nickel plate layer over the copper and then do thin gold over that.

Relay and switch contacts used for very low signal currents suffer from surface contamination and this can make them high resistance when closed... sometimes very high resistance. There are several solutions. Telephone systems suffered from this in some relays, and their solution was to apply a little DC to blast the contaminant out (on a microscopic scale) on contact closure. Higher power circuits didn't need any such help. Another evasion of contaminant was to make contacts wipe a little on closure, mechanically scraping the grot off. This leads to wear and limited life, plus debris will gravitate automatically to whatever it will most effectively disrupt. The other counter to contamination was gold contacts because they don't react with anything going around, and then being very carefup to keep oils and greases away.

Mankind has used an immense number of switch and relay contacts. A lot has been learned. There are books form SDS Relais as well as Omron and many makers and there's a lot you can learn from them.

On the test gear front at HP I had to handle attenuators reucung signals right down to receiver noise floors as well as noise figure gear measuring noise sources at around 290 Kelvin. Gold contact and scrupulous cleanliness territory! Our telecomms division sharing the site did autotest gear to go in phone exchanges and had to be right up to date on high reliability relays.

David

[ortek_service]

Yes, I do recall some of those inter-locking multi-gang push switches, that had silver-plated contacts, were apparently 'self-wiping' in order to help keep surface contamination at bay.


One surprising thing with gold-plated contacts I'd recently learnt, is that apparently you shouldn't mate them with tin-plated contacts as that was actually worse than using tin-plated contacts against other tin-plated contacts.

So with edge-connectors, if PCB-edge was only tin-plated then you should only really use tin-plated edge-connectors.
But many third-party peripheral manufacturers did frequently use gold-plated edge connectors, when only a few manufacturers of the main units (Like Commodore computers, and HP etc. Test equipment) had used gold-plated edge-connectors.
Maybe the opposite with PC's, where most ISA cards had Gold-plated fingers, but most motherboards only had tin-plated ISA-bus edge connectors.

With many Molex connector series, they sell both the headers and the socket-housing contacts in both Tin and Gold plated versions.
- So should really use the same version for both ends of the mating connectors.

Silver-plated contacts on connectors aren't too-common - Mostly older RF connectors, with smaller more-recent types usually all Gold-plated (even if it isn't the best for RF - particularly if there's a thick-layer of an even-worse material like Nickel underneath).
Stainless-steel was also often used for precision connectors, even if that isn't particularly low-loss (So might have been plated).

The cheapest RF connectors often seemed to look very-shiny, so had maybe been Chrome-plated, which also probably isn't too good for RF compared with Silver.

[Bazz4CQJ]

Originally Posted by ortek_service

The cheapest RF connectors often seemed to look very-shiny, so had maybe been Chrome-plated, which also probably isn't too good for RF compared with Silver.

How does nickel perform with RF? More ecologically friendly than chromium, and quite easy to do (can be plated in an electroless process).

B

[smiler411]

Silver is susceptible to migration in areas of higher humidity, this can result in short circuits or low resistance paths across insulators. Copper gold tin etc do not do this, so using silver in any circuits of higher impedance where there may be high humidity should be avoided. I have seen Opto isolators that turned on incorrectly due to this migration of silver from their internal construction

[ortek_service]

Originally Posted by smiler411

Silver is susceptible to migration in areas of higher humidity, this can result in short circuits or low resistance paths across insulators. Copper gold tin etc do not do this
>>

I thought that Tin did have migration issues - Known as 'Tin whiskers' (which happened inside many AF117 etc 4pin with shield Metal-cased Germanium transistors).
Plus semiconductor manufacturers carried on making non Lead-free parts for use in safety-critical Automotive & Aerospace/Military etc. applications (Although they have now seemingly accepted modern Lead-free parts as being reliable enough)
And was also one of the reasons why Lead was originally added to Solder
- Although Lead-free solder now replaces the Lead with Copper and Silver, so two element that have migration issues? (But maybe the alloy of the three elements does now overcome the migration problems).

[Craig Sawyers]

Older Tektronix scopes - the valved ones - used ceramic strips with notches into which components are soldered. The notches were originally silver plated, to provide a location in which to place component leads prior to soldering.

I have an old 545A which originally had some obscure faults. Examination of the contacts showed a ghostly metallization between the notches.

The silver plating had migrated - possibly due to dampness at some point. After scaping the migrated silver away with a scalpel, everything started working as it ought.

Craig

[m0cemdave]

Interesting.
I used to have a 545A, and I remember it had a small roll of special solder (Tin-Lead-Silver, I think) for use on those strips.