AP + PCB + Solder = Questions!!

[enragedcow]

So, we have ~130 of the boards pictured below. They are 8"x9.5", approximately 25% covered in gold, as an estimate. Assuming they are Class 00 plated, we're looking at 20 microinches thick. Doing the math, that equates to an estimated yield of about .21 grams / board.

..
..

However, that's not happening - not even close. The two batches we've done thus far, 10 boards each, we came out with <1g of "gold", but it's not quite the right color, so I'm sure it's not even pure.

Here's our process:

1 - We depopulate the boards using the toaster oven method. Heat for 5 minutes, bang on a cookie sheet and scrape into a bin. This removes all the SMDs and a fair amount of the solder - however, there is definitely a fair amount left (note: This is pre-RoHS so it's lead/tin).

2 - We break the boards into quarters, to fit nicer in the bucket. Because the gold is so dispersed across both sides, we have to treat the whole board. I realize this is *not* ideal, as it means a lot more copper/solder and other garbage (garbage in = garbage out)

3 - We treat the boards in AP. When they are mostly clean, we scrub them, and filter the liquid. We end up with lots of gold flakes, little bits of green PCB, and a good amount of black powder, which I presume is a bit of precipitated gold, but mostly solder remnants.

4 - We filter, keep AP for re-use, the particulate matter gets HCL and water washed.

5 - After the HCL/Water rinses, we go for the HCL+CL dissolving. That goes fine - most of the black powder remains undissolved, but the HCL+CL takes on more of a reddish hue.

6 - We precipitate the gold with SMB. It pulls down a fair amount of lead (I think it's lead chloride anyway, was it vanishes with a water rinse).

7 - Ultimately, we end up with <.8g of impure gold in the end.


Now, obviously it's not ideal to process the entire board like this. But, assuming we have to do this, I'm curious if anyone has ideas on what we're doing wrong - and maybe address these questions:

1 - The black powder we have after filtering the AP, most of it doesn't dissolve in HCL (hot or otherwise) or HCL-CL... wonder what it could be. My assumption is that we only have lead, tin, gold, and copper present.

2 - I further assume we still have some gold locked up in our AP. However, when I test it, nothing happens - guessing it's because the dissolved tin already in there means I already have stannous chloride in the solution, so adding more won't cause a reaction (our AP is dark green, BTW)

3 - Any other ideas where our Gold could be hiding?


Thanks in advance!!

 

[lazersteve]

Hello,

The boards, as you found out, are total s-crap.

The gold is so thin you can strip it with a toothbrush and AP in a matter of 5-10 minutes. The black stuff is likely a copper compound. The white powder is likely plain old salt (sodium chloride) or copper I chloride.

I think you did really well to get the 0.8 grams of impure gold.

I did a post on the exact board you show in the photo.

Here's the link to the thread:

Telecom Boards

Steve

 

[enragedcow]

Hello,

The boards, as you found out, are total s-crap.

The gold is so thin you can strip it with a toothbrush and AP in a matter of 5-10 minutes. The black stuff is likely a copper compound. The white powder is likely plain old salt (sodium chloride) or copper I chloride.

I think you did really well to get the 0.8 grams of impure gold.

I did a post on the exact board you show in the photo.

Here's the link to the thread:

Telecom Boards

Steve

Thanks Steve!

Funny thing, I'd read that post already (I've read pretty much every post here now I think )

I guess I was confused, in so far as the results don't agree even remotely with the calculation. However, that could be due to my assumption of the plating thickness. I realize the plating here is just to act as contact strips for a static Faraday cage - it's not like these are plated as contacts that will be repeatedly connected/disconnected, as would memory fingers, pins, etc. So, it'd make sense if this gold plate is accordingly quite thin.

This is why I assumed it was class 00, but I suppose it could be even thinner than that - I'm no expert.

I'm just hoping I'm not straight up losing a ton of gold here... I can't imagine a spot in my process where I would be, but I figure it doesn't help to get some third party advice!

 

[enragedcow]

...

I think you did really well to get the 0.8 grams of impure gold.
...

Just to be sure, you don't find it odd that we got less than 1/10th of a gram out of TEN of these boards - i.e. that each board has less than 1/100th of a gram on it?

I realize these are plated really thin, but that seems way low to me still... :?

 

[Rag and Bone]

I'm not surprised.

"Gold is the most malleable and ductile metal; a single gram can be beaten into a sheet of one square meter, or an ounce into 300 square feet. Gold leaf can be beaten thin enough to become translucent." Wiki

 

[lazersteve]

Cow,

Those boards are the lowest yielding I've ever processed. The plating is so thin you can remove it with AP and a toothbrush in a matter of minutes.

Steve

 

[enragedcow]

I'm not surprised.

"Gold is the most malleable and ductile metal; a single gram can be beaten into a sheet of one square meter, or an ounce into 300 square feet. Gold leaf can be beaten thin enough to become translucent." Wiki

I'd seen that actually, but forgotten about it.

It sort of makes sense - based on the size of the boards, it could take as many as ~14 to get a gram, so that actually plays out reasonably close.

Cow,

Those boards are the lowest yielding I've ever processed. The plating is so thin you can remove it with AP and a toothbrush in a matter of minutes.

Steve

Okay good, I just wanted to make sure I wasn't missing something horribly obvious.

In retrospect, it does make sense that it'd be extremely thin. It's just there to be non-corroding contacts to create a Faraday cage around the components. Since it doesn't get rubbed/scraped during insertion or removal, like fingers do, it need only be thick enough to cover the copper. Therefore, it makes sense that it'd be the thinnest flash plate possible.

Alrighty, thanks for the help guys. The impression I'm getting thus far is that these aren't even worth the time/effort. Bummer! Good thing I didn't have to pay for them

 

[eagle2]

One thing, about the testing for Gold in used AP solutions. Since your pcb plating is so thin, more than usual amounts of Gold likely have dissolved into solution.

Trying to test for Gold in used AP solution will still give negative results, when there is heavy contamination of Copper and other base metals.

I found the best process to use is just do a simple Zinc precip as a matter of course, without bothering to test for Gold.

Zinc cementation produces a lot of very fine and colloidal Gold, so give it a couple of days to settle. You will get everthing there is that way, including most PGM`s, without wondering if you missed something.

Zinc cementation dosen`t work well if there is a lot of acid. The starting Ph should be about 1-2. If you get a white/off white precip along with the Copper, Gold, Pd, etc. this is probably Tin Chloride and you had too little acid to start with, or added too much Zinc and used up the acid. You will have to do some careful washing in order to keep the Fine Gold mixed in from dissolving again. With the right amount of acid and not excess Zinc you will get a clean precip. I use about a teaspoonful of Zinc dust to 4 liters of warm solution, with a lot of stirring. Zinc knocks down some Copper too, but that also helps cement out all the PM`s.

Any excess Zinc dissolves and doesn`t bother the re-use of the solution.

Al

 

[warrendya]

Trying to test for Gold in used AP solution will still give negative results, when there is heavy contamination of Copper and other base metals.

I found the best process to use is just do a simple Zinc precip as a matter of course, without bothering to test for Gold.

Zinc cementation produces a lot of very fine and colloidal Gold, so give it a couple of days to settle. You will get everthing there is that way, including most PGM`s, without wondering if you missed something.

Wouldn't adding zinc bring down the copper as well? That was my interpretation of the list at http://goldrefiningforum.com/phpBB3/viewtopic.php?t=2259&highlight=electrochemical+potential

 

[eagle2]

All the metals lower in the series precip out preferentially before Copper.

Some sponge Copper does precip out. This is no problem, since all your trying to do is get all the PM`s. They will be separated from the vast majority of the used solution.

Most of the copper precip and excess zinc are dissolved with the washing procedure, anyway.

Collect these precips until you have enough to work in the next step. You can dissolve them in HCl + Cl and drop out the gold with SMB, if you want to do it that way.

Al

 

[saly255]

Hello,

The boards, as you found out, are total s-crap.

The gold is so thin you can strip it with a toothbrush and AP in a matter of 5-10 minutes. The black stuff is likely a copper compound. The white powder is likely plain old salt (sodium chloride) or copper I chloride.

I think you did really well to get the 0.8 grams of impure gold.

I did a post on the exact board you show in the photo.

Here's the link to the thread:

Telecom Boards

Steve

well this thread that you post is dead any possible way to get it back,i know its old one
thanks

 

[jimdoc]

This may be the link?

http://goldrefiningforum.com/phpBB3/viewtopic.php?p=20215#20215

Jim

 

[saly255]

thanks jim
i have allmost the boards so your reply was helpfull.
:mrgreen: :mrgreen:

 

[jimdoc]

Any link you find like this;
http://goldrefiningforum.com/phpBB2/viewtopic.php?p=20215#20215

Change the BB2 to BB3 and then it should work.

http://goldrefiningforum.com/phpBB3/viewtopic.php?p=20215#20215

Jim

 

[lazersteve]

I fixed the original broken link in my original post.

Thanks for pointing it out.

Steve