Gold loss removing solder mask?? HELP PLEASE a NEWBE

[dan63]

Loss of Gold in NaOH… Please help… I’VE SEARCHED AND READ… but have not seen anything related to what I’m seeing. I have over 100 printed circuit boards some of them are solid gold plate on one side (30 square inches) and gold plated traces on the other plus the typical gold fingers. I have removed the solder mask using a 20% solution of NaOH (500ml of H2O and 125g of NaOH flakes). I boiled at a slow boil for about 5 minutes. The solder mask came off ok… BUT…
Here is the problem: some of the large areas that were gold in color are now silver. HELP…. One of two things is happening; either I’m getting some form of tin/lead plating or I’m losing my thin layer of gold and exposing a layer of tin below? From my limited knowledge for Chem. NaOH is”looking” for another H ion, and will form some type of salt and water. NaOH should have no effect on Gold. So if I’m losing the gold into solution why???? is it due to heat and a very thin layer???? I processed several batches, the first three or four batches the solder mask came off easily after that each batch was a little less effective. But ALL batches of boards have some amount of silver where there had once been gold… this may have gotten a little worse with each batch???? Hard to say.
If this is just a platting issue it will be dealt with in the AP process and should not be a problem BUT if I’m losing Gold into the solution of NaOH then I have a worse problem… I did take a bit of HCl and rubbed it over some of the “silver areas”(in hopes of removing the tin/lead) however I did NOT see the gold color return so I thinking I’m losing my Gold into the solution of NaOH… I don’t think I can use stannous chloride on the solution of NaOH right???? any ideas????
Maybe I should use a different approach all together, I could first remove what I can of the exposed gold using HCL/CL or AP then treat the boards with NAOH to get at the Gold under the solder mask and then go back to HCL/CL or AP ?????? What are your thought folks?????? And thanks so much for your help!!!

 

[etack]

Why do you think that you have gold under you solder mask?

did you scratch off some or are you seeing gold color.

lye wont eat your gold most likey you didn't have any.

Post a pick of your boards.

Eric

 

[dan63]

these boards are a little unusual. many have full gold fields on one side and have the traces on the other. the solder mask is also in many cases only on one side. and Yes I have scratched the solder mask off and verified that the gold is also under the solder mask. in most cases the areas that have turned silver are only portions of a gold "field". I'm very puzzled by this. is there a possibility that there is some chemical in the solder mask that could attack the gold?? I know NaOH can not. or is there a chance that some of the tin in residual solder is plating areas of the gold. I'll post some pics in the am. thanks for your help.

 

[Geo]

unlikely. strong bases will discolor gold if you let the temperature get too high. it doesnt really dissolve it at all. take a rough piece of cloth and give the discolored spot a good rub. if the gold doesnt show back up, you can always apply a drop of nitric acid. ive seen cards that had gold traces showing on many spots only to remove the solder mask and find copper under the mask. the gold traces will still be there, but the areas under the solder mask would be bright red.

good luck.

 

[dan63]

Ya I've see that too, mostly on newer boards esp. Ram cards where the fingers are gold and the pads that the parts are soldered to are gold but the ares under the soldermask are copper.... I've been in the electronic industry for 30 years... worked for HP for 20, The boards I have are full gold plated under the solder mask..

I was thinking about this last night while trying to sleep... lol Is there a possibility that the field around the burner is setting up eddy currents in the foil and causing a reverse electroplating??? It really looks like I've lost a lot of Gold... I sure hope that you are correct and it has just discolored but it is a nice bright shinny silver where it once was Gold. I'm thinking I've exposed a nickle or tin layer between the Gold and Copper. OK looking forward to replies I'll sit back here and not get too worked up LOL and continue reading.

Does anyone have an idea how many boards I can process in 500 ml of 20% NaOH the boards are roughly 3.5X10 and most only have solder mask on one side?? can I keep running batches unit is no longer effective or am I reaching considerations of some chemical that is causing me grief at higher temps????? thanks so much for your time!!!!!!!

 

[maynman1751]

I don't understand why either, but I have lost gold while removing mask also. I was removing mask from ram sticks and when they came out the gold that was visible before was pretty much gone! I wondered if perhaps I left it in the solution too long, like overnight.
I've also had gold removed while soaking ram sticks in warm HCl to remove the chips. This is not supposed to happen either! :?:

 

[goldsilverpro]

Have you ever had success getting gold from under the mask on ram sticks?

 

[Palladium]

What may be happening is you are not using a high enough concentration of sodium hydroxide. Tin will dissolve in NaOH and then plate back out on your gold. If left to long it will make the gold traces start to release the foils. Did you do a pre wash in hcl first? Ammonium should clean up any tin that has precipitated on the gold The process does not take long and should not be left over night. You need the solution hot for it to work fast before it starts too cause trouble. Add the boards first then water that has already been premixed with NaOh being careful not to splash it on you or your skin, especially your eyes, then heat. Use fresh NaOh for each new batch. Hot NaOh is nothing to play with!

 

[dan63]

@ goldsilverpro
I have never seen any gold under the mask on RAM sticks the only place I've seen this is high end test equipment from the 70s and early 80s by the 90s any gold plate under solder mask is so thin the AP process may not be the best way to go at it.

with very thin gold plate it may be better to use HCL/CL or AG... I never done this but it just seems like there is less chance of lost valuables if you are dealing with a solution and are not trying to deal with small flakes... I'm just thinking that with VERY thin Gold plate even in AP some of it goes into solution and if the gold plate is thin enough you may not have any visible flakes to work with????????? does any one have any experience with this????? would love to hear from experience rather than my theory!!!!!

 

[BAMGOLD]

I'm pretty sure I have at-least 1 ram stick with Gold Traces out of 100 sticks or so.

 

[Palladium]

I ran several lbs of gold plated ram here awhile back. The gold plating thickness under the mask is almost not worth it in a way unless i had some serious weight. Now the fingers were pretty good as i remember. Matter of fact the gold under the mask started releasing from the boards during the NaOh phase on me and i had to change my whole process around. I used NaOh as a type of ap i guess. Then i run them for a soak in warm ammonia, wash, then dissolve the foils. Comes out fairly darn clean on the first drop. Of course i ran everything pretty much twice. I figure the coating of gold is released because it is so thin and the NaOh dissolves the layer of gold it's plated on. That's my theory anyway! Don't know what type they were, where they came from or where they were headed but some old gentleman drug them up and brought them to me.

 

[maynman1751]

Have you ever had success getting gold from under the mask on ram sticks?

Hey Chris! My intent was to remove the mask to try to release the tiny 'tubes' that would be solder points on the ram. I've had some success. I know that it is not a large amount of gold retrieved by this, I just wanted to see. I figured that I may have left it too long in solution. Also, I was using potassium hydroxide. I don't know if that makes any difference, but it does basically the same thing. This was a first for me......live and learn. And yes I know this is some bad--- stuff!

 

[Geo]

if you remove the solder mask and run material through AP, filter all solids (even boards if its ram), rinse well and place in a glass container. add a little hcl making sure all material is wet with hcl. add bleach and cover. the chlorine gas will dissolve any gold (even in the little holes)put a lid on and give it a few good shakes.filter solution and rinse solids. add rinse to the filter. of coarse it will be dirty, but you didnt lose any gold. the trick is to make sure all the base metal is gone. of coarse test the solution with stannous chloride before proceeding. a negative result means base metal is still present and the gold cemented out. even with a positive, i would still give it one more rinse with hcl/Cl just to be sure.

 

[artart47]

Hi.
I've had the same thing happen. They are cell boards other items with very thin gold and it just disintegrated.
I left the bucket sit and all the liquid has evaporated leaving a mas of lye crysals solder mask debris and has a dingy color.
The gold is in there!
When I get a chance, I'm going to slowly drip HCl into it to get rid of the lye HCl+NaOH----> NaCl+H2O. I should be able to wash it with water to disolve the salt andlet the solids settle. They sold contain any gold. then boil in HCl and a little sulfuric acid to rid it of base metals.
Just remember that these type of pieces have very little gold even though it looks like alot and you may barely be able to see the gold even after it's recovered. I was thinking of continuing to use my lye bucket untill it contains alot more gold before attempting to recover it.
Also! If you search my posts I had some responces from others on this problem.
Hope this helps!
artart47

 

[dan63]

I'd like to post some pics so you all can see what I'm seeing... I did a search on how to post pics on this sight but not much came up... can someone let me know how to post pics... do you up load them directly or do I need to upload them to some other server and just provide a link/URL????
thanks

 

[Geo]

when you "Post Reply" theres an option below the box your typing in that says "If you wish to attach one or more files enter the details below" click "Choose File" to find the picture or file on your device and then click "add the file".

 

[maynman1751]

if you remove the solder mask and run material through AP, filter all solids (even boards if its ram), rinse well and place in a glass container. add a little hcl making sure all material is wet with hcl. add bleach and cover. the chlorine gas will dissolve any gold (even in the little holes)put a lid on and give it a few good shakes.filter solution and rinse solids. add rinse to the filter. of coarse it will be dirty, but you didnt lose any gold. the trick is to make sure all the base metal is gone. of coarse test the solution with stannous chloride before proceeding. a negative result means base metal is still present and the gold cemented out. even with a positive, i would still give it one more rinse with hcl/Cl just to be sure.

Thanks Geo! That's basically what I was doing although I tried spraying the 'tubes' out with my spray bottle and that worked relatively well. It was more labor intensive, but I wanted to see how much I could recover and if it was worth it. Some of those ram sticks have quite a bit of gold that most people don't bother with! To me, with my limited resources, I find it rewarding to ferrit out every bit I can. It's just a hobby.....and it's fun. I don't plan on making any real profits.......maybe someday.
Thanks Again Buddy!

 

[Marcel]

1. Hot NaOH can dissolve Gold (but very unlike unless you don´t take it to the top concerning heat, NaOH concentration,time)
2. Hot NaOH will dissolve basemetals such as tin oder Pb.
3. These dissolved basemetals will be cemented back onto gold plated areas and make them appear in a different color ( usually black)
HCl + a bit H2=2 should remove this layer.

But in addition to that, many areas that lie underneath the solderresist look golden because of the color that is in the solderresist. Once removed it is only copper.
Green(Solderresist)+Red(Copper)= Yellow/Golden.....
it is called additive color.
http://en.wikipedia.org/wiki/Additive_color

I have been tricked by this effect several times.

 

[dan63]

Wow thanks so much for all the feed back
I have found out a bit more as I've experimented:

first I'm more sure it is Gold loss and not plating over the gold... and I think the reason for it is evaporation of H2O as I run boards through the solution of NaOH... should have been obvious to me...

The concentration of the NaOH is approaching 30-35% by the time I run 6 or 7 boards through at roughly 5 minutes/board. I know not all the loss of solution is due to evaporation but there is enough water loss that my concentration has to be rising as I run batches. I've been using a large flat glass baking dish to accommodate the size of the printed circuit boards... this provides a lot of surface area for evaporation. I never see this gold loss with new batches of NAOH it is only after I've run several batches. I'll have a chance to verify this with my next batch. If I can prevent Gold loss by adding a bit of H2O it will pretty much settle the question in my mind.

but that does lead to this question: does anyone know at what concentration levels of NaOH Gold will go into solution?

as for the question of gold plating under the solder mask... the boards I'm working with HAVE gold plating under the solder mask. I know now days this is not a common practice but when I first started working in the aerospace electronics industry it was a common practice for several manufacturers. at the time it was considered "best practice" although time and technology would change all that!!! lol

Geo thanks for the file upload info not sure why I didn't see it!! ... Pics to follow!

 

[dan63]

OK it seems I've worked through my trouble with NaOH. following are some suggestions to prevent problems:

1. as Steve indicates, a 20% solutions works well on most types of solder mask. There is one type of solder mask I found... it is a blue green color, comes off after about 10-15 seconds in hot 20% NaOH and makes a mess of the solution. I found that a 10% solution works best with this type of Solder Mask, and it only takes about a minute before you can easily rinse it off with water. there is a another type of solder mask that is a clear yellow green that turns into about 1/8 inch of slim and makes a real mess... not easy to get off... may not be worth your time!! it has a very unique look to it and out of more than 100 boards there were only 2.

2. the smaller the board size the better, this minimizes the size of container you have to use to heat the NaOH and reduces evaporation. I found it best to cut larger boards down to a 3x5 inch size.

3. try to keep the temp just below boiling. 210 F seemed to work very well, however a few boards took 7+ minutes at this slightly lower temp.

4. if the solution of NaOH becomes thick with dissolved solder mask it is PAST time to start a fresh batch. it really seems to me that the more solder mask in solution the more trouble I had with Gold loss. I don't have an explanation for this. I also think that this is secondary, and the primary problem was an increase in the concentration of NaOH due to evaporation of water. I'm also not convinced that fields set-up by the electric burner inducing eddy currents in the foil were not in part to blame. I say this because of the pattern of gold loss on the boards. I plan to try a gas burner and see if that changes anything.

5. I can not stress enough the need for ventilation when working with this stuff!!!!! I worked outside and even set a fan in place to move fumes away. But a hood really is what should be used!!

As I'm typing I'm also realizing that this may not be very useful info to most people... it is not often that you find boards with gold plated traces under solder mask.

my next step is to run the AP process on a few of these boards!!! wish me luck!!!!!

I did a search of the sight in advance as I'm afraid of losing more Gold in solution. I did not see much specifics on what to do with Gold in AP solution... I know most won't go into solution, but I've already lost a bunch, so I'm more concerned and given my luck so far... I want to do what I can to avoid this...

In Steve's video on the AP process, he states that some of His gold went into solution and that he would have to use SMB to precipitate it. later he stated that the "copper pushed the gold out of solution. Is this pretty much always the case? Or only the case with AP that has been in use for a while and has higher levels of copper chloride in solution?? There is something I'm missing here... I'll do a review of lit. I'll for sure test with stannous chloride... but if I have a gallon to gallon and half and I end up with gold in solution what is the "best practice" steps to recovery. OK OK maybe I should not even give it a second thought and cross that bridge when/if I come to it.

thanks again everyone I'm learning a lot, and hope to one day provide useful info to other beginners.