# Getting rid of tin and/or lead



## bswartzwelder (Dec 20, 2013)

I know that I can put computer pins in either hydrochloric acid or nitric acid to get rid of the tin and/or lead that's in the solder. I also know they will cause HCl to give off chlorine gas as it reacts with them. I have a gallon jug of HCl where I've used some of it for making AP. If I put the pins in this jug and then put on the cap, will containing the chlorine gas in the jug help the reaction?


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## jonn (Dec 20, 2013)

There is post from Palladium, where he uses a 5 gallon bucket with a lid and a pin hole in the lid. Maybe give that a try?


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## rickbb (Dec 20, 2013)

I don't think the gas will have much effect, maybe some free chlorine in solution will help oxidize the material. But I doubt you will need it. HCL will digest the tin/lead quite well on it's own. It may take longer if the used AP is well used and the concentration is low, but should still do the job.

PS. I don't think it's wise to cap a bottle of acid under a reaction process that is evolving a toxic gas. It concentrates the gas and builds up pressure, 2 things you really don't want to do.


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## butcher (Dec 20, 2013)

Let's look at what we have with tin metal (Sn) dissolved in hydrochloric acid (HCl).

Sn (s) + 2 HCl (aq) → SnCl2 (aq) + H2 (g)

In the above reaction, we have no chlorine gas (Cl2), but we do form hydrogen gas, and stannous chloride in the reaction.

Of coarse you will have other metals in solution also, if you will check your reactivity series of metals chart, you will see most of the base metals are above hydrogen on the chart, so these metals will also act similar, displacing hydrogen from the acid in the reaction.

In the reaction above the HCl acid is reduced to chlorides (by the tin metal), as the tin or other metal are oxidized to ions (by the acid), leaving both the tin and chloride ions in this solution.
The acid contains water even if you did not dilute the acid,32 % HCl is 68% water.
The tin metal forming the tin cation, the acid forming the chloride anion, and these Ions in solution forming a dissolved salt of tin chloride or stannous chloride SnCl2 in solution.
The Hydrogen gas (H2) escapes the solution as vapors

We do not want to seal this vessel, and leave that hydrogen gas with no escape route, which could blow our container under the pressure this gas would form in a closed sealed vessel.

If the reaction was run to completion (no metal left to oxidize, or no free acid left to be reduced, or both) then we could seal the vessel as the stannous chloride would not build pressure in the vessel as the Hydrogen gas would no longer be forming in the tin salt solution.


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## sharkhook (Dec 20, 2013)

Thanks, butcher. Your replies make a lot of sense and are easy to understand.


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## FrugalRefiner (Dec 21, 2013)

bswartzwelder said:


> I know that I can put computer pins in either hydrochloric acid or nitric acid to get rid of the tin and/or lead that's in the solder.


If you have tin present, you don't want to use nitric acid. You'll create metastannic acid (tin paste) that will complicate your recovery.

Dave


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## bswartzwelder (Dec 21, 2013)

Thank you to everyone who responded. Yes, I knew the bottle would build up pressure, but most plastic bottles are strong enough to withstand a drop of several feet without bursting. At any rate, I was going to place the bottle inside a 5 gallon bucket and then either invert another 5 gallon bucket over top of that (taping the seam) or else put a lid on it (with a hole in the lid) and have a weight on top of the lid. I didn't want to have to deal with an acid explosion. 

I wasn't sure if keeping the chlorine (under pressure) would help the reaction or not. I also didn't want to just dump the pins in my AP bucket because I knew it would destroy the AP for further use. But, since I would be using fresh HCl anyway, I could just use my old AP and then make up a fresh batch when needed.

Plan now is to just dump the pins into the HCl bottle without the cap and place that inside of a 5 gallon bucket with a lid on it. In a usage such as this, I usually poke a small hole in the bucket (not the lid) to allow for pressure to release. I also have several buckets I use to dry things out. I have anywhere from 1 to 4 small holes in the bottom and put a Band Aid with the pad over the hole. It allows water and gasses to escape but keeps anything solid inside the bucket. I have to make sure that the buckets I use for liquids don't have holes in them. I picked up a bucket with a hole in it one time when I needed a solid bucket. Fortunately, I was only using it with water.

I thought I had read somewhere on the forum that Nitric acid could be used to get rid of solder. It would not have been my first choice anyhow because it is much more expensive than HCl.


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## Harold_V (Dec 21, 2013)

bswartzwelder said:


> I thought I had read somewhere on the forum that Nitric acid could be used to get rid of solder. It would not have been my first choice anyhow because it is much more expensive than HCl.


You are always well served to avoid using nitric where tin is involved. 

Harold


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## Pantherlikher (Dec 22, 2013)

When I have excess or overused AP, I pour most into another container for base metals and then to desolder. I leave some AP and add HCL. No need for peroxide to get the AP running again.
Before putting anything into AP:
I soak in old AP bath solution
Then I soak in fresh HCL just to be sure no solder is present. 
Rinsing with water between soaks
A seperate, marked bucket or container for each.

I couldn't see any reason for pressurizing the bucket. Just a small hole in the lid to allow gas to escape.

B.S.


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## Sharding757 (Feb 6, 2014)

I'm kinda at a loss here on this one. I have a few circuit boards that under the solder mask it's gold plated. To avoid complicated recovery, I've read the forums and everyone says to use HCL (some say HCL diluted with water) to remove solder and tin. As an experiment, I had a small board from a cell phone and a ISA Soundcard. So I used just enough HCL to cover the boards and diluted with about 1/3 of water. Now I was under the impression that the GOLD would be untouched as long as I didnt kick start the process with H202 and the solder would be removed along with some surface mount components i have not removed. 24 hours later, I see the gold has disappeared from the fingers and now the solution is attacking the copper where the gold once was. Also the solder is being attacked by the HCL as well but the process is slow. Am I missing something? My goal was to clean the boards of any solder, then remove all the solder mask then use the AP method to lift the gold traces. Obviously I will continue to search for answers but can someone point me in the right direction? The experiment was to understand each step of the process when it comes to gold plated circuit boards. I understand that I should have removed the gold fingers and processed them separately but again this was an experiment to just remove the tin and solder prior to experimenting with step two of lifting the gold using AP and not having to worry about the Tin/Lead. Thanks in Advance. Sam


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## butcher (Feb 6, 2014)

Copper and gold are below hydrogen in the reactivity series, they will not be attacked by HCl alone without an oxidizer, gold will not dissolve in HCl alone, copper will not dissolve in HCl, copper if oxidized to copper oxide will easily dissolve in HCl, or gold if oxidized will dissolve into solution as chlorides of these metals, gold needing a stronger oxidizer than copper as it is a less reactive or more noble metal...

Air in solution can act as an oxidizer for copper, or copper if exposed to the air can form copper carbonates especially if damp from acids...

Another thought is with city water you may have some dissolved chlorine used as water treatment, to kill the bacteria of the sewer water in the river from the town up river from your city.
I doubt there would be enough chlorine in the water to dissolve much gold but it may dissolve some which would quickly plate back out of solution with remaining base metals or a powder...

Once the copper does dissolve into HCl it can form CuCl2 that can also attack copper as long as there is some oxidizer or air dissolved in solution.

Gold can be plated so thin, even though it does not dissolve it may appear to, the gold may fall off as fine powder, or could also be coated over with other powders in solution...


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## Sharding757 (Feb 7, 2014)

Thanks for the reply Butcher. I live on a farm outside of town so chlorine in the water isnt an issue. I did however use this same HCL as a last wash after the AP process of another batch (before HCL/Clorox) but after using water which is most likely the issue. It was a last wash and appeared clean so I figured I'd reuse it. I understand all the points you made which was why i was stumped at the time as to why the gold was coming off. I guess it was oxygenated more than i suspected it to be. More than likely new HCL should be used for this process alone. Is it good practice to dilute it with water or will just pure HCL handle the situation? I just dont want to contaminate the rest of the process. Once the tin/lead solder is removed, I'll remove the solder masks then go outright with the ap process like i would with fingers. Moving forward in baby steps....Thanks again for the reply.


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## butcher (Feb 7, 2014)

Just my opinion.

I would not dilute the HCl acid, it is only 32% HCl (g) and 68% water to begin with, stannous chloride (tin dissolved in HCl) will form a hydroxide of tin when diluted, the stannous chloride in water hydrolysis occurs making a basic insoluble salt of tin, not the soluble stannous chloride. 

Sn (s) + 2HCl (aq) --> SnCl2 (aq) + H2 (g)
SnCl2 (aq) + H2O (l) --> Sn(OH)Cl (s) + HCl (aq)


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## Sharding757 (Feb 7, 2014)

Opinions are always welcome! Thanks again Butcher!


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## kurtak (Feb 8, 2014)

Sharding757 said:


> More than likely new HCL should be used for this process alone. Is it good practice to dilute it with water or will just pure HCL handle the situation?



No you don't need to dilute the HCL when using HCL to de-populate boards but yes you should start with new HCL - that way you know its not contaminated with an oxidizer which can/will dissolve gold

I use HCL to de-populate my ram - it takes more HCL to cover the boards then is needed to remove the solder - so the HCL can be reused a couple more times for de-populating - I get about 3 or 4 runs out of my HCL before it is saturated with tin & stops working (last run might require the addition of a little more HCL to complete process)

I simply pour the HCL back into its jug (after each run ) the mark the jug HCL + tin / used /// each hash mark after the word used represents the number of times it has been used 

Kurt


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## rewalston (Feb 8, 2014)

Kurt, what do you do with the HCl after the last run, as in disposal wise?

Rusty


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## kurtak (Feb 8, 2014)

rewalston said:


> Kurt, what do you do with the HCl after the last run, as in disposal wise?
> 
> Rusty



I drop the tin out with hydroxide (which is what I do with all my waste - except copper which I cement out with iron) filter out the hydroxide which becomes a hydroxide cake - adjust the filtered liquid back to zero which is evaporated off in a evaporator pan I have set up (should be able to just dump the water but I evaporate just make sure I got all the nasty's)

The hydroxide cake - this I am not sure if it can just be dumped in the garbage or not (I've heard it can) I've never really looked into that because I am able to take mine over to a big aluminum anodizing plant that's not far from me & throw it in their dumpster of tin/aluminum hydroxide

I am able to do this because over the years I have done a lot of contract work for them so I know the people at the top of the company very well 

In fact I just got done building a couple of new motor control panels to run the pumps for a new tank they just added to one of their anodize lines - the old motor control panel was in the way of where the rectifier for the new tank had to go so the new panels were built as an up grade to control all pumps for all tanks on that line 

guess who got the old motor control center & wire pulled out from relocating the new control center :mrgreen: --- you gota love those big mag disconnects 

Sorry I got a bit carried away there - but that's how I am able to deal with my waste - they have a filter press that's about half the size of a semi trailer for filtering out there hydroxides so my throwing a couple buckets of hydroxide into there dumpster every once in awhile is no problem & they usually have scrap for me to haul away when I stop to dump my hydroxide

Kurt


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## rewalston (Feb 8, 2014)

Thanks for the reply Kurt, looks like I need to buy some more NaOH


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## velimasamatti (Feb 13, 2014)

Sharding757 said:


> I'm kinda at a loss here on this one. I have a few circuit boards that under the solder mask it's gold plated. To avoid complicated recovery, I've read the forums and everyone says to use HCL (some say HCL diluted with water) to remove solder and tin. As an experiment, I had a small board from a cell phone and a ISA Soundcard. So I used just enough HCL to cover the boards and diluted with about 1/3 of water. Now I was under the impression that the GOLD would be untouched as long as I didnt kick start the process with H202 and the solder would be removed along with some surface mount components i have not removed. 24 hours later, I see the gold has disappeared from the fingers and now the solution is attacking the copper where the gold once was. Also the solder is being attacked by the HCL as well but the process is slow. Am I missing something? My goal was to clean the boards of any solder, then remove all the solder mask then use the AP method to lift the gold traces. Obviously I will continue to search for answers but can someone point me in the right direction? The experiment was to understand each step of the process when it comes to gold plated circuit boards. I understand that I should have removed the gold fingers and processed them separately but again this was an experiment to just remove the tin and solder prior to experimenting with step two of lifting the gold using AP and not having to worry about the Tin/Lead. Thanks in Advance. Sam



Sam,
Sounds similar to what happened to me. I was depopulating boards with HCL and the gold seemed to be gone, but it wasn't. Some of the gold pads just got really "dirty", there was some sort of contaminant build-up during the process. Funnily enough there could be two pads side by side one completely clean and the other completely covered by contaminant. I'm thinking a nano plating cell was created while in acid by of the components or the board layout thus the contamination. Anyway, additional acid wash removed the contaminant and the gold was revealed. 
Secondly, modern cell phone boards may not have gold plating at all at solder pads. They use OSP (organic solder protection - if I remember the acronym correct). The gold may be only selectively applied to some pads/card edge fingers and one may think all pads are therefore plated. They are not. It may be hard to detect OSP board depending on the design and if the soldering process has been perfect. Look at the via's (small holes through the layers). If those are copper color suspect an OSP board, if gold color you may be lucky. But just maybe. Board makers are pinching pennies nowadays, OSP is naturally cheap and it works great. Hope this helps.
Cheers, Matti.


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## Sharding757 (Feb 26, 2014)

Yeah youre right. Once i removed the boards and used a pencil eraser on the pads and the gold revealed itself.


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## resabed01 (Feb 26, 2014)

The only reason some of us, myself included, suggest adding water to dilute the HCl is to increase the volume of the solution. And increasing the volume of the solution may make your process work better for you. The trade off for diluting your HCl is it will work slower. Full strength HCl works best but then there are times when 1 gallon of HCl isn't enough to cover all the material you want to remove solder from.

It's your call.


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## Sharding757 (Feb 26, 2014)

Thanks for clearing that up. I can understand the necessity in what you're saying. Before reading what you wrote, I would read different posts here and there and have conflicting thoughts on the matter as to why. Thanks again. Everyone has been very helpful.


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