Solder Masks and Pea Soup?

[Astraveller]

Now we have an AP process that works we have been looking at what else we can strip before we move on to the Clorox process and beyond. You can see from the photo that the plastic sieve (right) contains various bits and pieces being dunked in AP. We discovered that a few of the pc boards we have appear to be gold plated quite well so we decided to have a go at these. The only problem is they are covered in green solder mask.

The first thing we did was to depopulate a couple of boards using hot sand and a good thump. Then we dipped one in caustic soda (left hand dish) – after an hour nothing! I thought it would be a good idea to burn off the green stuff on another bit of gold plated board with a blow torch, which we did. Man that stuff stinks! And is definitely toxic! But it revealed some gold so we put it into the AP to see what would happen.

In the meanwhile I had washed the caustic soda board a few times, to examine it, in clean water (center dish). Also as some of the bits and pieces from the experimental AP dish were being dissolved I rinsed them in the rinse dish (centre). After a short time I noticed that the rinse dish was turning into pea soup. (Homer – “Hmmm, Pea Soup!)

What is this pea soup? A better question might be – How do we get rid of green solder mask?

TIA,

Linton.

 

[tamerakshar]

- you must heat your sodium hydroxide solution to get rid of solder mask, try to jig saw your boards to weaken the green layer and to make it fit into your container which helps you to deal with more boards simultaneously.
- warning:
your sieve looks like metal thing, don't dump it in AP and i recommend not to use it at all.

 

[Astraveller]

Thanks for the input tamerakshar, I thought my post had developed a cloak of invisibility.

The sieve is plastic! I have already figured out that the AP process should only contain copper and gold – what you are seeing is a small test dish that we are using to test what other bits of computers we can use with the AP but thanks for your warning and confirmation.

After posting this thread, I did a bit of digging and found that I should heat the caustic soda but it is a dangerous thing and that there is a solvent that will do it but that it might not financially worth it. (I can’ remember the name or the post, but I have it bookmarked)

Either way, we have enough of these boards to consider trying to give it a go – I guess I was hoping that someone would say “it’s easy, do this and this and this”

We have a good supply of computers (so we are lucky there!) but are ‘feeling our way’ as how to process them. It took a long time just to get the AP process to work because we only used bleach instead of acid, - duh!

http://goldrefiningforum.com/phpBB3/viewtopic.php?t=4249

Thanks tamerakshar,

Linton,

 

[nicknitro]

Hi all,

Just expanding on this topic a little. Sorry for intrusion, but is it common for boards to contain this much plating under the solder mask? I thought most were copper laminates, until I recently "unconfirmed" found an old accessory board from a PC that appears to have gold wires under the solder mask. The solder mask was very dark-green and where the wires are running it is more blackish.

Any thoughts Appreciated,
Nick

 

[goldsilverpro]

Unless things have changed, all-gold traces under the mask are not that common. Often, they LOOK like gold but aren't. Looking through the mask, they look like gold. Sometimes, when the mask is removed, they will have a yellowish cast, but this isn't gold. For what purpose would the traces be all-gold plated, anyhow? Before I spent all that time and effort removing the mask, I would absolutely make sure there is gold underneath it.

 

[nicknitro]

Will do Chris, I have a few of the wires soaking in Nitric right now to clean them up a bit, as I kinda pulled/peeled them off the board, and they have some mask / crap attached to them. Once cleaned I will wash and desolve them in AR and test with Stannic. Post results tomorrow night?
As well as source if it is positive. I can find more of these boards if it proves to be worthwhile.

Nick :roll:

 

[daveerf]

To be redundant, I agree with Chris that gold plated traces on circuit boards is RARE. Extremely rare.

You will only find that on one out of a million of different types of circuit boards. It may not even be worth your time to find out which ones do have that because you will end up testing for hundreds of hours and chances are you will never find even one with gold plated traces.

 

[oldtimmer]

Having worked in the electronics industry for 35 years, it is not uncommon to see some boards that do have gold plating under the solder mask. In the 70's and 80's you could find it more common that what you will find today. I have never seen a computer mother board with gold traces. It is not needed. Where I work we do a lot of RF testing and all of our boards have 100% gold plating on all of the copper runs. And yes if the solder mask is of a lighter green color, when used over the copper, you get an appearance almost that of there being a gold plating under the solder mask. This is very commonly seen on memory cards where the pads that are solder to are gold plated but the other runs are only copper. I am currently processing around 500 memory cards and I do a scratch the solder mask to see if the runs are gold plated. I have found only 2 out of around 250 that actually have gold plated runs. Both of these are older memory sticks probably from the 70's and 80.s.

 

[lazersteve]

I have seen and posses many PCBs with fully gold plated runs under the green solder mask. A common card that comes to mind is the Ensoniq sound PCI cards. Another card that commonly has gold plated over copper traces under the solder mask are early 1990's ISA slot sound card plus modem and cdrom controller combo boards made by Creative.

Here' a photo of a box of boards with confirmed gold plated copper traces under the solder mask:

[img:668:765]http://www.goldrecovery.us/goldrecovery/images/goldplatedtraces.jpg[/img]

A short list of manufacturers of some of the cards are :

Kingston, Ensoniq, S3 Video, HP, and Creative.

I would not go as far as to say the cards are common, but they certainly are not rare between 1990 and 1997. Prior to 1990 the gold plated copper traces were even more common.

I've learned to quickly recognize the cards by the lighter colored edge traces that the fingers have. The gold plating (across the entire card) on them is actually thinner than the very common fingers that have a more rich golden color to the finger edge. The deep yellow fingers are typically the ones with only copper under the mask. The brighter, shiny almost white fingers are typically the ones with gold plating over copper traces under the solder mask. I'm guessing the function of this complete plating is possibly for added radio frequency shielding.

The exceptions I have seen to the lighter colored traces have been old laptop (386-486) power boards and very old HP plotter and test equipment boards. These types have a nice rich yellow color to them across all of the copper traces under the solder mask.

Steve

 

[nicknitro]

Thanks For all the responses guys,

My results were from a hard drive controller board of an early 90's IBM P/S2 XT 70 computer. The wires I peeled away from the board were completely dissolved in nitric, so I would have to report a nil value.

Steve, Maybe a sticky of the boards for treasure hunters?

Thanks again
Nick

 

[Astraveller]

I thought some might be interested to see what we discovered today. At the beginning of this tread I took a picture of three dishes – the one on the left was a gold plated circuit board in caustic soda – we just left it there. 10 days later TonyD took another look and although it didn’t look any different he gave it a prod with a spatula and noticed that the green solder mask fell away revealing the gold plate underneath.

We fished it out, cleaned it off with fresh water and put it through the AP process which stripped it in an hour or so. The yield was low, the plating must be very thin but the process is cheap and as I have been reminded a few times ‘gold is gold’

This is great!! if we have got it right – no hot caustic – no expensive chemicals – just patience – and the process is easily ‘up scaled’.

Comments gratefully appreciated.

Linton.

Photos below.

 

[nicknitro]

Nice Job,

I really appreciate the update. Quick question. Lye is relatively easy to find. What was your source, chem manufacturer or store bought.

Great knowledge for future refining.

Nick

 

[lamp]

I have a question , would any PM's be left behind in the caustic soda solution? If so what would be the best way to remove it?

 

[oldtimmer]

In one of the post, I saw a mention of adding salt to the hot sodium hydroxide solution to help in the removal of the solder mask. I could not find any mention of how much to add.

Can someone provide any more information?

Thanks

 

[Astraveller]

Nicknitro - We bought caustic soda at the local DIY store.

Lamp – I do not think any PMs are left in solution but this question is best answered by others with more experience.

Oldtimmer – I don’t know about adding salt to the solution but the caustic soda we used was not heated at all. Here in the UK it’s quite cold at the moment, all we did was to leave a pc board in caustic soda for 10 days – and that was out of laziness rather than a scientific experiment. I’m hoping the big guns will show up and will ratify/explain/condemn or commend this observation.

Linton.

 

[g_axelsson]

Astraveller, that is a great result. Do you have any idea about what concentration of caustic soda you used?

I have twice tried to treat some cards I got but never got a good result. I have a couple of kilos of clean boards with gold plate under the solder mask. It is enough to be a nuisance to store and too good looking to sell as scrap. Time to do something about it.

Thanks for sharing!

 

[nicknitro]

Brand Name then?

We have many similar brands out my way, however, I just wonder if yours had any additives>?


Must be further direction in your process Old Timmer


= dumb answer

 

[Astraveller]

Hi, g_axelsson and Nick,

As I write this I am at home in the evening so do not have the bottle of caustic in front of me but I will double check the info and post a pic tomorrow if necessary. We bought a plastic bottle – the equivalent to about 250 to 500 ml (if it had been a liquid) of 99% Caustic Soda. It had ‘Caustic Soda’ in big letters on the label - please do not think I being sarcastic, I am not. There was a brand name which I can’t remember and it is probably not that relevant anyway.

The legend on the back was for two types drain clearing dilutions, we choose the stronger.

Since the variables are:- Dilution, Temperature and Time and since hot caustic is best avoided it would seem the best advice would be – get the strongest caustic you can, ‘dilute’ it to saturation point (that doesn’t make sense but you know what I mean) and see how long it takes.

The thing is that is does seem to work.

Since my last post I have put some more boards into the caustic solution, which I beefed up a bit, and some of them have cleaned already – two days – some of the others show signs of stripping and the rest are a bit more stubborn – but they will be mine! Oh yes, they will be mine! GOLD! GOLD! I TELL YOU!!

Ahmm, sorry about that!

Hope this helps.

Linton.

 

[goldsilverpro]

The saturation point of NaOH is above 100 av.oz./gallon = 6.25 #/gal = 750 gm/l. It's available in that strength in drums as 50% caustic soda - 50% water and 50% caustic soda, by weight. It's like syrup and can be nasty to work with. It's like H2SO4, as it gets hot when you dilute it. Being already liquid, though, it's mighty handy. Caustic can etch glass. Use SS instead of pryex. You'll really screw your beakers up.

 

[bmgold]

Caustic can etch glass. Use SS instead of pryex. You'll really screw your beakers up.

Thanks goldsilverpro. Little bits of knowledge like that makes it worth reading every post.