# Stripping solder mask



## Gold Nut (Dec 14, 2008)

Is there somewhere on the forum that says anything about using Draino to strip the solder mask? 
Gold Nut


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## butcher (Dec 14, 2008)

yes there is.
edit: drano can also called sodium hydroxide, caustic soda or lye


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## lazersteve (Dec 14, 2008)

Solid crystal types of Drano also contain Aluminum and sodium nitrate as well as lye and salt.

Drano Data

Steve


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## Golddigger Greg (Jul 23, 2012)

I just stripped 15 or so Sound Blaster cards using Draino and it seemed to work like a charm, but as I was rinsing the last few cards I noticed that there seemed to be a change in color to the gold plating on the second half of the card. I had the cards standing on edge in the solution until one half was stripped, rinsed and scrubbed the mask off that half, flipped it over, and returned the card to the lye bath to strip the other half. 
Is it possible that I lost some of the gold plating to the solution? If so, is it spilled milk, or can I still retrieve it from the saved solution?
Edit: The search tool is a wonderful thing!  I read a post by GSP from March 2009 that said that the Draino will not digest the plating into solution. I'll test the solution after it cools anyway; just to be sure.


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## Geo (Jul 23, 2012)

you cant let that stuff get very hot. not only will you lose some values but it is also very dangerous.


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## Golddigger Greg (Jul 23, 2012)

The solution was kept right at the near-boil point, but perhaps that was enough heat to begin digesting the gold plating on the last few pieces. I haven't tested the solution for values yet, but will as time allows.
And yes, lye solutions are to be respected for their dangers, especially to the eyes.


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## Harold_V (Jul 24, 2012)

Golddigger Greg said:


> And yes, lye solutions are to be respected for their dangers, especially to the eyes.


I had the misfortune of splashing a drop of 68% nitric acid directly in my right eye, many years ago. Within seconds of the splash, the surface of my eye was yellow and was shedding. I was near water, so it was rinsed very quickly. I was alone, so I had to drive myself to an ophthalmologist. I was seen immediately. 

The ophthalmologist told me how lucky I was that I was working with acid and not lye. I was told that the body can neutralize acid and recover, but had the drop of solution been lye, I would have been blinded in that eye. It can not be neutralized, unlike acid. 

Treat lye with considerable respect. 

Harold


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## Golddigger Greg (Jul 24, 2012)

I tested the solution last night for values; negative.
Many years ago, while working construction, I got a healthy blast of caulking into my right eye. I could not imagine if I had to drive myself to help. :shock:


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## maynman1751 (Jul 24, 2012)

How did you test for values....what procedure did you use?


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## Golddigger Greg (Jul 24, 2012)

I placed a drop of the solution on clean white paper, and placed a drop of Stannous Chloride on top of that. No color change at all, no tell-tale rings of color, nothing.
I will not discard the solution until I know two more things; my procedure is correct, and my Stannous Chloride is tested against a standard. I read somewhere that the only certain way to lose values is to throw them away. I'm still pretty green at this so I try to err on the side of caution.


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## butcher (Jul 25, 2012)

Golddigger Greg, 
If I understand the discussion, dissolving the solder mask with Draino brand drain cleaner (sodium hydroxide with other metals involved), and you suspect loss of some gold in solution, my thinking say's the gold would be elemental metal possibly as small flakes and should settle with time, stannous will not detect elemental gold even if the gold is a very fine powder like the precipitated gold, the gold would need to be dissolved into solution (oxidized missing electrons), and then the stannous will reduce (the stannous chloride reduces the gold to a colloidal gold that gives a purple color of the very fine elemental gold metal floating around in solution), the purple of cassius color, if you did have gold in the caustic solution, let solution settle well, then you might try, remove a small portion of the settled material from the bottom of the vessel, neutralize it with HCl acid, and let any powder settle from the salt solution, decant liquid salt water, filter powders, incinerate the filter then dissolve in some HCl with a few drops of bleach in a test tube, heat tube to drive off chlorine and then try the stannous test to see if you had any gold in the reaction.


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## maynman1751 (Jul 25, 2012)

butcher said:


> Golddigger Greg,
> If I understand the discussion, dissolving the solder mask with Draino brand drain cleaner (sodium hydroxide with other metals involved), and you suspect loss of some gold in solution, my thinking say's the gold would be elemental metal possibly as small flakes and should settle with time, stannous will not detect elemental gold even if the gold is a very fine powder like the precipitated gold, the gold would need to be dissolved into solution (oxidized missing electrons), and then the stannous will reduce (the stannous chloride reduces the gold to a colloidal gold that gives a purple color of the very fine elemental gold metal floating around in solution), the purple of cassius color, if you did have gold in the caustic solution, let solution settle well, then you might try, remove a small portion of the settled material from the bottom of the vessel, neutralize it with HCl acid, and let any powder settle from the salt solution, decant liquid salt water, filter powders, incinerate the filter then dissolve in some HCl with a few drops of bleach in a test tube, heat tube to drive off chlorine and then try the stannous test to see if you had any gold in the reaction.


This is why I asked how you tested and what procedure you used. I was pretty sure that you couldn't test with stannous from an alkaline solution. Thanks Richard for explaining that!


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## Golddigger Greg (Jul 25, 2012)

Thanks for outlining the procedure Butcher, I'll do that as well.


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## g_axelsson (Jul 29, 2012)

A couple of years ago I experimented with removing the solder mask from some gold plated boards. As I was going to process the whole board I never bothered with removing the gold fingers along the edge. Neither was I in a hurry so the boards was lying in the sodium hydroxide solution for a while until I checked them.
When I came back a couple of gold fingers had changed color and was tin white. I'm quite sure that the gold hadn't gone into solution, it was probably tin that had gone into solution and been plated back again on the gold fingers.

A circuit board contains a lot of different metals, some in contact with each other, other parts isolated. When we add an electrolyte (electrically conductive liquid, the sodium hydroxide solution) we create a lot of potential electric cells, metals that normally wouldn't dissolve can both be dissolved and plated down on other surfaces.

Golddigger Greg, if you still have the card with the changed color you could try to wash it with hydrochloric acid to see if you get the golden surface back. then it was probably something that had plated out from the used solution.

/Göran


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## Golddigger Greg (Jul 29, 2012)

g_axelsson said:


> Golddigger Greg, if you still have the card with the changed color you could try to wash it with hydrochloric acid to see if you get the golden surface back. then it was probably something that had plated out from the used solution.
> 
> /Göran


Too late. The rinsed, depopulated boards are in an AP bath! That is the same conclusion I came up with after re-acidifying the solution and testing it, as well as the solids from the dish as per Butcher's post.


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## NobleMetalWorks (Jul 30, 2012)

I use Lye for all kinds of things, it is very very nasty stuff to splash on yourself. I keep a 1 gallon plastic container of vinegar close at hand in case I do splash any lye on me. When I deal with Lye, I gear up, an apron, face shield, elbow length gloves.

When I was 16 I worked in a restaurant that used Lye to clean the stainless steel parts of a broiler. I was working in front of a huge vat of Lye when another guy threw in another stainless steel piece, it splashed onto my forearm from my wrist almost to my elbow, on the inside of my arm. A manager heard me yelling, ran over and poured vinegar on my forearm, and although I was scarred, it faded over the next 10 years or so. Today, 28 years later, you can barely see the scar. I have no idea what the outcome might have been if the manager didn't pour vinegar on my arm, and ever since, whenever dealing with Lye, I keep vinegar close at hand.

To minimize splashing, I usually turn my solution of Lye into a kind of thick paste, it's far more safe to deal with in this form, and if you do get it on you, it's does it's damage a little bit slower.

Scott


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## craigmotyka (Jun 19, 2013)

I findi it much easier to depopulate all components by hand and scrap the mask off I do these in bulk 30 pound lots at a clip


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