Cleaning circuit boards before refining

[masonwebb]

Hello! I recently purchased 20 lbs of scrap from ebay, I have just finished manual depopulation of every board with pliers and exact-o knife. ( Will be using a blow torch to remove all ceramic capacitors and other small surface mounted devices). I plan on using the Acid/Peroxide method to remove the gold plating on the boards that have it. Now my question is ; will using HCL to help remove some base metals before A/P be beneficial? If so how would I go about cleaning with Hcl?
-Here is another sub question - what exactly is a solder mask? Is it the green coating on the boards?

Thank you!

Edited*-I yielded around 2lbs of flat black chips and around 200 grams of pins from the lot

 

[butcher]

HCl will break down the solder, tin goes into solution the lead falls out of solution as a white solid powder lead chloride.
HCl without an oxidizer will not dissolve copper, so your gold should remain on the undissolved copper traces of the circuit board.

HCl and 3% hydrogen peroxide which forms the copper II chloride leach many call acid peroxide will also break down the solder just like HCl alone, but here we also dissolve copper, which could put gold powder or foils mixed with lead and other insoluble materials.

I say HCl would be best alone to remove solder before moving on to the copper II chloride leach, just because it is easier to deal with, but either will work as long as you understand how to deal with them.

The solder removal can be a little slow, it is no problem if your patient or have other things to work on while the acid is working on the solder, an old tooth brush and rubber gloves a can help, speed it up a little (brushing off the lead chloride every once in a while), it will work without brushing a good stir every now and then can help also.

 

[Captobvious]

Just a side note, I would highly advise not trying to use a torch to remove surface mounted devices and use something like a heat gun instead. the fumes those boards make when scorched ain't no joke! In the end you'll end up with a mostly charred PCB with all those surface mounted devices still stuck to it. Heat gun goes MUCH faster, I personally like the Ryobi models over at Home Depot, as they can put up with a decent amount of abuse.

 

[masonwebb]

OK thanks guys! I will pick up a heat gun when I can. It must be a little slower than a torch, correct?
I figured the HCL would help keep the HCL/ peroxide solution a little cleaner. Because it gets quite dark.

Does the solder that is used on the boards contain silver? I have searched online but can't find any info

 

[butcher]

Lead/tin is the solder you will find most often on circuit boards, although lead free solder such as tin/silver is becoming more popular, tin in these solders is one of our biggest problems when in solutions, although it can be helpful to break down the lead in the solder when using acids or bases to break the solder down chemically.

http://en.wikipedia.org/wiki/Solder

 

[masonwebb]

Lead/tin is the solder you will find most often on circuit boards, although lead free solder such as tin/silver is becoming more popular, tin in these solders is one of our biggest problems when in solutions, although it can be helpful to break down the lead in the solder when using acids or bases to break the solder down chemically.

http://en.wikipedia.org/wiki/Solder

Thanks Butcher!

 

[hatemelborai]

Lead/tin is the solder you will find most often on circuit boards, although lead free solder such as tin/silver is becoming more popular, tin in these solders is one of our biggest problems when in solutions, although it can be helpful to break down the lead in the solder when using acids or bases to break the solder down chemically.

http://en.wikipedia.org/wiki/Solder

Dear Butcher
I have used hcl to remove the solder, but hcl affect on PCI plastic, a contaminates foam appear on solution, how can I cancel this foam

thanks
Hatem

 

[butcher]

Some plastics are broken down, or a portion of them may actually dissolve into the halide acid solution, these types of plastics can get gooey in solution, and are best kept out of solution, about the only way I can think of to eliminate this is to not introduce the plastic in the first place.

If these plastics end up with valuable powders or foils, incineration will burn off the plastic, but I suspect the gases formed in the reaction could also carry gold in these fumes, besides the dangers of the fumes created.

I know very little about all of the different types of plastics, and the chemical makeup of them, some of the softer plastics are the ones that seem to decompose in the acids, once you recognize the types that do break down, you can separate them from the harder plastics that do not seem to be affected by the acids.

 

[cableman]

Just like butcher said, pick up a heat gun and I use a big metal bowl and turn the circuit board or mother board upside down on top of the bowl and pull the trigger on that heat gun. You will be surprised how fast components start falling off. Also you never want to burn a circuit board because of all the toxic fumes. You will end up with terminal lung problems and besides, with the heat gun you are not having to keep paying for gas and oxygen or propane or whatever you are using to heat up with. The only time I burn a flame is when I melt my gold using my handheld propane torch but I have one that uses MAPP gas so it gets hotter and it has auto ignite just pull the trigger and adjust the flame. You can pick one up from Lowe's and even has a tank of MAPP gas included for fifty bucks. As for the heat gun I got mine for about twenty bucks from Harbor Freight and it has a low and high setting. I forget how hot it gets exactly but after you start heating up the board you will have to have gloves because it gets real hot and once you start the whole thing stays hot and it doesn't take long to clean off the materials. Most of the time I use a small sharp chisel and just rake it across the legs of the flat packs where they meet the board and they just drop off, the I use the heat gun for the rest. That still leaves the problem of the solder. I did know the name of a chemical you can get and you just add a tablespoon or so to water in a pan and heat it on a hot plate then after it cools you can just pour cold water over the board and wipe whatever is left on the board off. It cleans all the solder off so you don't have to deal with it in your solutions. I found the name of the chemical here on the forum using the search and I guess I will have to find it again because I have some really good gold plated boards but I need the solder off. I can't get any solder in my solution and I really want to see what the yield is on these boards. They are not off of a computer but some kind of communication equip. Anyway, you can't go wrong with the heat gun, especially if you are stripping off the plated pins and such. They will just start falling off. I couldn't believe the time it saved.

 

[Ronald Stricklett]

Hello! I recently purchased 20 lbs of scrap from ebay, I have just finished manual depopulation of every board with pliers and exact-o knife. ( Will be using a blow torch to remove all ceramic capacitors and other small surface mounted devices). I plan on using the Acid/Peroxide method to remove the gold plating on the boards that have it. Now my question is ; will using HCL to help remove some base metals before A/P be beneficial? If so how would I go about cleaning with Hcl?
-Here is another sub question - what exactly is a solder mask? Is it the green coating on the boards?

Thank you!

Edited*-I yielded around 2lbs of flat black chips and around 200 grams of pins from the lot

Hello can you tell me do I need to remove every thing off boards

 

[Yggdrasil]

Hello can you tell me do I need to remove every thing off boards

Welcome.
Usually there are two methods.
Heating with air gun or other means and then scrape, pick or bump off the components.
Or a chisel.
There are some chemical means but they are often inefficient or too expensive.

 

[Martijn]

Hello can you tell me do I need to remove every thing off boards

Welcome to the forum.
No you don't don't. You need to remove and separate the big basemetal parts and best yield parts and sell the boards as scrap.
Your skills will determine which parts are worth collecting for you. You can separate high yield parts that you can't or won't refinne yourself and get a better price by stripping and separating.