PCB boards, gold traces in middle layers

[olson13]

Hello, I am new to this quest of stripping and refining gold from PCB boards. I have some PCB boards that my work gave me that have gold traces that run through the whole depth of the boards. My question is, what is the best way to get that gold out of the layers? I was thinking about shredding them to a funeral dust, but am unsure if that would work. Any help anyone can give me will be greatly appreciated!
Thank you
Swen

 

[Yggdrasil]

Hello, I am new to this quest of stripping and refining gold from PCB boards. I have some PCB boards that my work gave me that have gold traces that run through the whole depth of the boards. My question is, what is the best way to get that gold out of the layers? I was thinking about shredding them to a funeral dust, but am unsure if that would work. Any help anyone can give me will be greatly appreciated!
Thank you
Swen

Welcome to us.
I have never heard about such boards, where do they come from?

 

[FrugalRefiner]

For gold plated boards, most folks use a copper chloride leach, also known as AP (for Acid Peroxide). Although older posts here suggest using a lot of hydrogen peroxide, we now all agree that only a small amount is needed to start the action.

It will dissolve the copper traces that are underneath the gold plating, releasing the gold plated layer as thin "foils".

You can find a lot of information on the forum about this process.

Dave

 

[Shark]

A very aggressive air bubbler in AP, and given a lot of time, will eventually get under the solder mask where the gold layer is. Scratch through the covering along the gold trace and run them in AP for smaller numbers of boards. The air bubbling hard will break up the gold foils into tiny pieces, but it also aids in releasing those pieces trapped behind the mask covering.

 

[Yggdrasil]

It seem to have slipped by, but he said the Gold layers was through and inside the board, hence my question of what kind of boards.
I have never heard about such boards.
Maybe they are just plated on both sides?

 

[haveagojoe]

what is the best way to get that gold out of the layers?

I think we could do with a little clarity here...
Do you mean these are multilayered boards, where the traces are sandwiched between layers of board, as well as on the surface? If so, it's very unlikely that the internal layer is gold plated.
If you mean traces on the surface, usually only the exposed parts will be gold plated. Sometimes high-end boards will have gold below the solder mask (which is kinda like a layer of paint, usually green), in which case it can be removed with a soak in lye if you really want to, otherwise as Shark says, just normal Copper Chloride etching will get to it eventually.

 

[olson13]

Welcome to us.
I have never heard about such boards, where do they come from?

They come from my job. I work on automated welding machines. I asked the guy who designs our PCB boards, and he did confirm that gold goes through the board. Some of these boards are having high frequency/temps/current going through. So, I believe that is why the boards were designed and made this way.

 

[olson13]

I think we could do with a little clarity here...
Do you mean these are multilayered boards, where the traces are sandwiched between layers of board, as well as on the surface? If so, it's very unlikely that the internal layer is gold plated.
If you mean traces on the surface, usually only the exposed parts will be gold plated. Sometimes high-end boards will have gold below the solder mask (which is kinda like a layer of paint, usually green), in which case it can be removed with a soak in lye if you really want to, otherwise as Shark says, just normal Copper Chloride etching will get to it eventually.

Sorry for the not so good description. It is a single layer boards. But, the traces run in both sides of the board and they follow all the way through the depth of the board. If I could get a good pic I would send it. But, it is so hard to see. I confirmed with the guy in our board room and the gold traces do run through the board. All be it very thin traces.

 

[Yggdrasil]

They come from my job. I work on automated welding machines. I asked the guy who designs our PCB boards, and he did confirm that gold goes through the board. Some of these boards are having high frequency/temps/current going through. So, I believe that is why the boards were designed and made this way.

I'm thinking a direct dissolution in AR might be the thing for this application.

 

[haveagojoe]

I'm still confused, I can't imagine that there is gold between the two surfaces, on the inside of the board. OP I think you need to cut one to confirm.

The only time I've ever seen gold anywhere other than on the surface is with fully plated vias and through-holes, and that's pretty rare. Even then it's still on the "outside" and can be recovered with Copper Chloride etching.

 

[Yggdrasil]

I'm still confused, I can't imagine that there is gold between the two surfaces, on the inside of the board. OP I think you need to cut one to confirm.

The only time I've ever seen gold anywhere other than on the surface is with fully plated vias and through-holes, and that's pretty rare. Even then it's still on the "outside" and can be recovered with Copper Chloride etching.

No I think there is conductors going through the board, as it is not a multi layer bard as the OP says.

They come from my job. I work on automated welding machines. I asked the guy who designs our PCB boards, and he did confirm that gold goes through the board. Some of these boards are having high frequency/temps/current going through. So, I believe that is why the boards were designed and made this way.

Sorry for the not so good description. It is a single layer boards. But, the traces run in both sides of the board and they follow all the way through the depth of the board. If I could get a good pic I would send it. But, it is so hard to see. I confirmed with the guy in our board room and the gold traces do run through the board. All be it very thin traces.

 

[haveagojoe]

No I think there is conductors going through the board, as it is not a multi layer bard as the OP says.

Maybe I am having a dysfunction of imagination... all I can picture is vias. I can't see how manufacturers could produce a slot filled with gold. If it exists, it would be very costly... and very desirable as escrap!

 

[haveagojoe]

Perhaps OP means tented gold plated vias? If so, it's just solder mask covering the via; after a lye bath to remove the mask, all the gold should be accessible.

Edit: ...unless perhaps they are epoxy-filled

 

[GoIdman]

Sorry for the not so good description. It is a single layer boards. But, the traces run in both sides of the board and they follow all the way through the depth of the board. If I could get a good pic I would send it. But, it is so hard to see. I confirmed with the guy in our board room and the gold traces do run through the board. All be it very thin traces.

Through my experience i have seen similar boards, those had gold plating on surface and then the through holes had gold plating to, usually, high power boards have almost 1 mm holes which are bridges that go through the board to link the traces between them from one side to another and back, and even for components that are not surface mounted....(usually these power board have little to no surface mounted components, the old ones)

Usually have better yields than normal 0.1-0.3 mm through holes on modern boards.

Those (the holes) act similar to traces and have probably thicker plating then the surface layers, also the copper in these holes are thicker.

It is my opinion that the op is talking about these boards.

Please confirm if this is the case so the members here can help you out with the best process to recover the gold.

The solder mask can be removed with hot sodium hydroxide, although i do not recommend it since its very dangerous.

You can burn it to ash (takes a lot of time and stinks like hell) and use a grinder to grind it to dust (much like the IC chips method), then wash it out and then treat it with acid. Labor intensive since you have to grind as small particles as you can. (I have tried with depopulated RAM boards to recover the copper and remaining gold traces, not worth the effort if you are not doing it in large, for experiment it was ok, but financially was not worth it)

No matter what process you will use there are advantages and disadvantages to it...

I hope this helps.

Pete.

 

[haveagojoe]

bridges that go through the board to link the traces between them from one side to another

Yea those are vias. They can be open or tented, or if the hole is large they may be epoxy filled and tented.
https://albapcb.com/wp-content/uploads/2020/10/viafilling_news_post.jpg
If they are epoxy filled the board may need to be shredded to get all the gold, but otherwise it should be accessible with the board intact.
If the board is multilayered, there may be buried vias which again would require shredding to recover.

 

[MareNextDoor]

another way to remove solder mask that is less dangerous than hot NaOH is pure propylene glycol with ~3M of NaOH in solution. this solution is nice in that propylene glycol does not evaporate quickly at all, and catalyzes the breakdown of the soldermask in a day or two with no heating necessary.

 

[haveagojoe]

Well, apparently solid gold-filled vias do exist, news to me: https://www.thinfilm.com/vias_solid.html

 

[4metals]

I have a hard time justifying a dual recovery process for this type of material, it simply cannot justify the labor to go back and granulate and grind the material after it is first treated with an AP or similar leach method. The minuscule quantity of gold left in those little nooks and crannies may not even be visible once dropped from anything short of a large processing quantity. This is exactly why large processors will use one method to properly expose all of the values for their chosen method to work.

Personally I'm a smelting advocate. I do remember when we first started the smelting thread I thought that the thread would be to expose members to methods used on a larger scale. But as it turned out we had members here who processed small quantities of e-scrap using the process successfully. I remember one member, although I cannot remember who it was, posting photos of his cast copper based bullion anodes that were cast in a cast iron corn-bread cooking pan. So even smaller processors can do it in a way to maximize yields with one consistent process.

 

[Shark]

I remember one member, although I cannot remember who it was, posting photos of his cast copper based bullion anodes that were cast in a cast iron corn-bread cooking pan. So even smaller processors can do it in a way to maximize yields with one consistent process.

That would be me. Later I made them in a small cast iron skillet. The skillet made an anode roughly 5.5 inches in diameter could be up to 1.25 inches thick.

 

[4metals]

That would be me. Later I made them in a small cast iron skillet.

Wow, that was then and look at you now, you have been upgraded (I am truly not sure if that upgraded is the appropriate term) to a moderator. I do remember those corn on the cob anodes!