Have I struck gold?

[bemate]

I came across an old switchboard of some kind that I was able to get pieces off, judging from the overall appearance, it's late 60's, early 70's. There were some old-style circuit boards and a generous amount of gold-coated pins.

The boards have a nice, thich layer of metals on the plated fingers, you can really feel the ridged structure indicating they have a fairly thick coating, consistent with the age. However, I'm more unsure about the covered conductors on the rest of the cards, they are more reddish, but scraping them shows a golden colour underneath a thin top layer (see photos). My question is: does the gold coating from the pins comtimue all across the boards or is that likely copper? If so, how to best test it, just drip HNO3 on and look for a reaction?

 

[jason_recliner]

bemate,
The rest of the board is copper, as you suspected. If you wish you could confirm it with a drop of nitric, as you suspected.

Your hypotheses are running pretty well so far.

 

[goldsilverpro]

Figure about $0.40 for every square inch covered by gold on the fingers.

 

[FrugalRefiner]

The boards have a nice, thich layer of metals on the plated fingers, you can really feel the ridged structure indicating they have a fairly thick coating, consistent with the age.

Most of the thickness you feel is the copper under the gold. Circuit boards start with a solid layer of copper over the whole board. The copper is etched away where it's not wanted, leaving the copper traces you see. The contact areas (fingers) are then plated with about 30 microinches of gold.

Dave

 

[bemate]

Thanks for replying, pretty much as I expected then, better than modern-day RAM-fingers, but not too much value.

Anyway, I have a follow-up question: I saw that some of the cards had some transistors, pried one off and opened it. I pulled out one of the pins going into the transistor and looked at it through a stereo lens. While it looks as though it is fused from an outer part of base metal, or possibly silver, to a more or less solid gold part running through the transistor, I can't quite make myself believe that. Could anyone comment if they have seen anything like this before?

 

[goldsilverpro]

The gold plating on fingers was no thicker in 1972 than it is today. I started in this business in 1966 and the thickness on wear surfaces (connector pins, fingers, etc.) was the same as today - 30 millionths of an inch.

The inside fingers on those DIP legs (last 3 photos) are plated as well, probably about the same thickness. No solid gold on any of this stuff. About the only solid gold on electronics scrap are the bonding wires. With those, there are either 2 miles or 4 miles of wire per troy oz of gold, depending on whether the diameter of the wire used was .001" or .0007",

 

[anachronism]

The gold plating on fingers was no thicker in 1972 than it is today. I started in this business in 1966 and the thickness on wear surfaces (connector pins, fingers, etc.) was the same as today - 30 millionths of an inch.

Chris - do you think from your experience that this is cast in stone regardless of manufacturer, country and application?

 

[g_axelsson]

There have been some really thin plating on some cards, some is hardly gold toned. I used some PCI-cards like that to create thin golden films in water and captured it on a small copper grid. The films were then examined in a transmission electron microscope and you could see the individual crystal areas of the gold film. At least that one was transparent to electrons and that indicated 100-150 nm thickness. Any thicker and it becomes opaque.

So maybe any plating worth using as a contact surface is the same today as for 30 years ago, but some manufacturers have cut corners and ended up with inferior plating that actually can fail in a short time.

I know that as a fact, as the last card I designed used gold flash (ENIG) instead of fully plated fingers. On the other hand I'm using the cards for a private project so I'm not intending to sell it to a customer. :mrgreen:

Göran

 

[goldsilverpro]

The gold plating on fingers was no thicker in 1972 than it is today. I started in this business in 1966 and the thickness on wear surfaces (connector pins, fingers, etc.) was the same as today - 30 millionths of an inch.

Chris - do you think from your experience that this is cast in stone regardless of manufacturer, country and application?

Nothing is cast in stone when it comes to plating and all 3 of those variables can exhibit large thickness differences. When I speak about thickness, I'm talking averages. It's only a guide and an educated guess. We must start someplace. There is no simple way of determining thickness.

We know that Russian electronics are often plated thicker than the Western counterparts. The US manufacturers probably have variations in their thicknesses. Parts used in a rocket are probably plated thicker than those same parts used in a TV.

Were I to set up a refinery, the 1st investment I would make would be in a fire assay setup. If everyone had fire assay, discussions such as this wouldn't exist. As a refiner, I don't ever remember plating thicknesses ever being discussed. The question was always, "What was the assay?"

 

[bemate]

An update for those interested:

I also removed the connector board the cards were slotted into:

While not looking forward to the task of removing them all only to find they were not gold plated, the colour looked slightly too much coppery, I decided to do a small test.

I snipped off a piece of one pin and made a small setup in a fume hood:


I added 1 ml MQ-water (18,2 MOhm) and 1 ml 65% HNO3. The reaction was immediate and a clear blue colour emerged:

(Edit: The test tube on the right is the transistor legs from my previous post in the same solution, note the lack of blue colour...)
After about an hour I was left with a bright blue solution and tiny gold flakes, disproving my fear that the pins were solid copper rather than plated:


Happy that my pins contain gold, I started quantifying the board, and after prying out a single pin, i weighed it and found a single pin to be 353mg, with 30 pins per connector, some of them double rows, I calculated there are a bit more than 600 grams of cleaned pins. But, as can be seen in the first picture, there are wires all over the place, luckily only a few are soldered, the rest are wound around the pins, but still a mammoth task to clean them.

So, the question is then: any useful ideas on how to free the pins before further processing? Burning the plastics away is probably the easiest solution, that would likely take care of a good portion of the solder as well, but are there any other creative ideas? I thought maybe sticking a piece in the freezer to try and make the plastic brittle would help a bit, then I could just hammer away and sort through the debris for the pins...

Edited to add picture comment about test tube No.2.

 

[bemate]

There was not room for all the pictures in my last post, just some details on the connectors and pins:

 

[Barren Realms 007]

Try putting them in the freezer overnight then take out one or two and see if they become brittle enough to break apart when hitting them with a hammer.

 

[Topher_osAUrus]

Those kindof look like ones i had, where i could fit a screwdriver under the bottom part and pry it so it split open.

Some were troublesome and didnt split well... So i left them outside on a cold winter night, then the next morning beat them to death with a hammer, as Barren suggested. Worked well (to remove the pins AND relieve stress 8) )

Edit to fix where to were..grammar matters!

 

[bemate]

I'll give the freezer a go then, might be even better in the -80 freezer. Hopefully that will work. I've only cleared a quarter of the pins so far, but I'll post an update next week when I can try it out.

Thanks a lot for the input guys, I really appreciate you taking the time to help a newbie out.

 

[g_axelsson]

I'll give the freezer a go then, might be even better in the -80 freezer. Hopefully that will work. I've only cleared a quarter of the pins so far, but I'll post an update next week when I can try it out.

Thanks a lot for the input guys, I really appreciate you taking the time to help a newbie out.

Nope, the -80 freezer is a bad idea, you would freeze the nitric acid too.
http://nitrogen.atomistry.com/physical_properties_nitric_acid.html
The idea is to lower the solubility of the sulfate and then to pour off a nitric acid low in dissolved sulfate salt.

Göran

 

[bemate]

You misunderstood my intent Gøran, I'm talking about freezing the unprocessed connectors to make the plastic brittle. Then I can (hopefully) smash them with a hammer to break apart the connectors and free the pins. No chemicals at this stage, the setup I tried was just the snipped ends off of two pins to look for gold foils. :wink:

 

[g_axelsson]

My bad, must have read a post about making nitric acid by the cold method from nitrates and sulfuric acid and then read your post and mixing the threads together.

For smashing plastic it will probably work like a charm... and I think protective goggles and well isolated gloves is a must, but coming from Norway I know the cold won't be a problem for you.

Göran

 

[bemate]

My bad, must have read a post about making nitric acid by the cold method from nitrates and sulfuric acid and then read your post and mixing the threads together.

For smashing plastic it will probably work like a charm... and I think protective goggles and well isolated gloves is a must, but coming from Norway I know the cold won't be a problem for you.

Göran

Haha, no that won't be a problem. I'll grab my skiing goggles and wool mittens... :lol:

Or i could just wait a few months and leave them outside, that should work just as well.

 

[bemate]

I did a rough estimate on the surface area of the pins, measuring them to 45mm in length, about 1,7mm wide and between 0,5 and 1mm in thickness. Rounding down to err on the side of caution, I estimate each pin to have a surface area of about 200mm2.

With 58 rows of 30 pins, that gives me a total surface area of about 3500 cm2. Calculating for 30 microinches, or 0,76 micrometers, that gives a total volume of about 0,27cm3, with gold at 19,3gm per cm3 should give about 5 grams of gold.

Does that sound reasonable for 600 grams of pure pins, not counting in the weight of wires, solder etc?

Also, I tried putting a couple of connectors in the -80 freezer for a couple of hours. It did make the plastic brittle, but the connectors are very thick plastic, so smashing them with a hammer did not help too much. I'll keep looking at possible ways, just trying small scale until I settle upon a method I like.

 

[jason_recliner]

5g in 600g = 120:1 = 0.8%, and sounds conceivable for plated pins.
I expect that one's processing method would affect the final yield as much as would the originating material. If you would be so kind, share with us your own final result.