Methods of depopulating PCB's

Gold Refining Forum

Help Support Gold Refining Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

badastro

Well-known member
Joined
Jul 7, 2007
Messages
94
Location
Indiana
Printed circuit boards contain a variety of items that contain values. In order to obtain those values, the first step is to remove them from the board. In addition, the some boards might even have gold plated traces eg. cell phone boards.

Of the common methods to depopulate the boards, they fall into three categories: mechanical, thermal, and chemical.

Mechanical

Method 1: Manual extraction
Manual extraction involves using hand tools to remove items of values.

Examples: Using a sharp blade to extract "flatpacks" by running the blade across the legs of the package as shown in lazersteve's tutorial video. Using hammers, pliers, levers, metal shears for fingers, or chisels to smash or pry out components are also methods.

Pro: Method 1 is easy to implement with minimal resources.
Con: This method is very labor intensive, has low productivity, and can put particulate matter into the air. A mask is recommended.


Method 2: Powered tool extraction
This method involves using power tools to aid in extraction of items.

Examples: Using an air chisel to buzz off parts. Using saws to cut off fingers.

Pro: Fast and relatively productive.
Con: Not everyone has the required tools. It can be very messy as parts fly everywhere. Hazardous dust is produced, a mask is required.


Method 3: Milling
This method involves using hammer mills, ball mills, or other mills to crush and grind boards to dust.

Pro: It is the most productive of mechanical methods. It can be configured to batch or continuous processes.
Con: It is a considerable investment. It is very noisy and very dirty.


Thermal

Method 4: Heat gun
A heat gun is used to melt the solder to allow components to fall off the boards.

Pro: This method is easy to implement and very selective for clean removals.
Con: Toxic fumes can be produced. Over heating of the boards is possible. This method has low productivity and uses a lot of electricity which costs money. Other components are likely to fall off, especially smaller surface mount components. It also takes significant time for the solder to heat up.


Method 5: Sand in a pan
This method was suggested by one of our members. It involves filling an electric pan with .25"-.5" of play sand and resting the boards on the sand. The heat melts the solder allowing the components to be picked off.

Pro: This method is easy to implement and can have higher productivity than the heat gun. The solder will pool under the sand and can be recovered and processed for values.
Con: This method is still time consuming and produces hazardous fumes.

Method 6: Vibrating oven
This method involves placing board in an oven with some mechanism to vibrate the boards so the components can fall into a collection pan.

Example 1: Place boards vertically in an old oven outside the house. Have a pan under the boards. Give the boards a good shake when the solder has melted or rig up some mechanical shaker.

Example 2: Build a rotating heated cage where boards can be fed in one end and come out the other. The rotation knocks off components which fall down out of the cage into a collection pan.

Pro: High productivity
Con: It requires an investment to implement. It also produces toxic fumes. Not all components can be shaken off. It requires a lot of energy.


Method 7: Forbidden
Pro: Highest productivity
Con: You could make yourself and others very sick and go to jail.


Chemical

Method 8: Acid peroxide
Remove ferrous materials and dip boards into an acid peroxide bath.

Pro: This method is easy to do in small scales. It produces less fumes than other methods.
Con: It takes a long time to process boards--low productivity. It generates a lot of waste solution, which may have to be processed for values. AP is indiscriminate in what it will dissolve and is thus inefficient for depopulating boards.


Method 9: Hot acid bath
Remove ferrous materials. Place boards in a bath of straight or diluted muriatic acid in a crock pot. Do not boil and keep it covered. The acid will attack all solder and leave gold and copper intact. The process should be over in less than an hour.

Pro: Method 9 is fast and efficient. It only dissolves the solder leaving behind components, a clean board, and dirty acid solution. Some people crock pot pins anyway...
Con: It can produce acid fumes. Hot acid is dangerous. The spent acid is very toxic. It is difficult of an average person to scale up.


Method 10: Thermal depolymerization
This method involves taking whole boards (or loosely ground up boards) and converting the plastics into oil, gas, and other useful components.

Pro: Scaling is unlimited. This process does not produce unmanageable toxic gases. It is the most efficient and productive. It will accept all wastes, even sewage, and convert it to oil.
Con: This method is unavailable to the average person.

comments meow?
 
Astro,

Great post!

It's nice to have everything spelled out in black and white for each method. I really like the pros and cons section for each. :wink:

AP can be a selective depopulation tool if it is used in a shallow dish. I've actually used it to 'desolder' components from boards thru chemical means. It's not exactly the cleanest or fastest process, but it does work.


Steve
 
badastro said:
Method 3: Milling
This method involves using hammer mills, ball mills, or other mills to crush and grind boards to dust.

Pro: It is the most productive of mechanical methods. It can be configured to batch or continuous processes.
Con: It is a considerable investment. It is very noisy and very dirty.

So instead of purchasing a ball mill, build one from an old tire and a couple of steel rolls, or steel rods on pillow block bearings a pulley and a couple of casters to keep the tire straight, use plywood to cover the center hole, cut a door in the thing and power the unit with an old electric motor of a horse or less.

www.acc.umu.se/~widmark/bigtumbler.pdf gives the details and such to make a unit that will handle about 50 pounds inside, and probably can be bilt for under $50 if you have a few parts laying around the laboratory/shop a far cry from the $800 or about for what the commercial units will set back the hobbyists such as the Lortone commercial units like the double 20pound drum http://www.lortone.com/commercial_tumblers

anyhow it is an option for some folks, especially for those of us who have limited funds to operate on.

William
Central Idaho
 
Badastro,

Excellent post!

blueduck,

The tire is a grinder that takes forever, It's not a crusher, with big balls that drop and crush the parts. I don't think it would work for most of our stuff. Interesting and cheap idea, though. Would probably work for a few certain items.

Ralph.

Now you're talking! There's so much of this kind of equipment laying around rusty in yards (scrap, surplus, etc.) that can be bought for a song (much for near iron scrap value) and put back into service. Do they still print "Used Equipment", Ralph. Everything in that mag. is negoitable.

Transportation, bearings (sometimes), electrical, paint, etc. is all you usually need. All equipment is out there used. It's out there. You just have to find it.
 
Do they still print "Used Equipment", Ralph.

I think they do. The market for items that scrap recyclers use ( Junk-scrap yard ) Is way over saturated. You can find items for nearly any application when it come to just tearing and shredding the shit out of it.
These can be drug out of a field and put back into service for pennies on the dollar.

I use to get some good leads and items from :arrow: :arrow: http://www.rossmach.com/


The lab sales ? I to have my eye on some items. The redstone arsenal , in huntsville, al. It's about 70 mile n of me. They sell some goooood army and space command materials from their inventory. They do space research and the home of the United States Army Aviation and Missile Command to ( they are one of two groups of people who push the button on your ass. ) . I have seen everthing on their base web site that is for sale. You would not believe what materials you can lay your hands on. It's scary.

Their are many science research companies in the area who support the base and the space command. When the deals are to be had, go to where their is a surplus of that item and you will find the lowest cost.


:)
 
I did some work a while back on a method depopulating circuit boards by heating them gently on a large hot plate as a basis for removing components.

Take a hotplate and place on top a thin piece of steel plate to increase surface area. The plate can be anywhere from 8 inches to well over a foot in length and width but needs to be at least 1/4 inch in thickness. When you place a circuit board on the hotplate on low heat it will take up to 15 mins or longer to heat the solder up to allow components to be flipped or picked off from the board. This is of course slow so I had to figure out how to get the right amount of heat immediately to the entire surface area of the bottom of the circuit board without burning everything up. What actually slows the heating up of the bottom of the board is the component legs and solder sticking thru the board bottom which creates an air pocket between the circuit board and the hot plate surface. No instant heat. So what I did was put the circuit board in a vise or holding clamp and run a hand held grinder over the bottom to knock of the legs sticking thru. You have to wear a full face mask and gloves for tiny pieces of hot metal fly everywhere! I then took the board and run it for a minute or two on a belt driven sander to further flaten the botton of the board and get it smooth. Here gloves and a face mask are necessary to not breathe metal dust. When I put the bottom surface flattened circuit board back on the hot plate it heated up very rapidly, under a minute easily. I think most of the ones I tried were about thirty seconds. You had to use a fume hood on this step to not breathe the fumes. You can pick the components off the board on the hot plate or what I did was turn the board over and very gently tap them into a plastic bucket. With the components off but not the heated solder I then tapped the circuit board very hard on a large piece of glass. The heated solder will fly off, cool immediately on the glass, and then you simply scrap it off into a bucket for collection.

This method has its pros and cons like all the others listed here. You are hand processing the boards so you are exposed to fumes, heated surfaces, and flying metal pieces. You can though rapidly go thru a lot of circuit boards in a day if you desire and get all the steps down smoothly. I do use a band saw to cut larger circuit boards down to size to fit more easily on the hot plate. Here again cutting fingers off is a danger.

Regards, Chris.
 
I know it's an old thread, but...

I just came from the local Goodwill store with an indoor electric grill. It takes about 3-4 minutes to get a motherboard hot enough to melt the solder and is large enough to heat approximately half the board at a time. I heat it up, turn it over and thump it on the edge of my wife's old turkey roasting pan. Almost everything falls off the board with one thump. The longer slots (PCI, ISA, AGP, RAM) are easily plucked off with a pair of needle nose pliers. The grill has a sloped two pan design that lets anything that falls off the bottom of the board drop under the top pan, keeping it from getting overheated by the element.

This thing cost me $2.99 and I stripped 15 motherboards in less than 2 hours after work yesterday.

They also had a nice Pyrex casserole dish with lid for $1.00. The lab is coming together nicely!
 
Hey guys I know of another method.Its pretty easy to do,its extremely economical,super easy to obtain,and its even portable.Its a porpane camp heater.The one I am referring to is a directional heater that looks like a vertical stainless mixing bowl that sits on top of the small propane tanks.The dish and tanks are available at pretty much any walmart,or just about any type of camping or outdoor store.What I do is place a board in my bench vise and position the heater up against the board,but not too close or youll start burning the board before the solder starts to melt.You can see when the solder starts melting,so while holding the board with something(I use visegrips) that can keep your fingers away from the heat,you just hit the arm on the vise to release the board and tap it on something to pop the components off.If you try this methd I can save you a little time by telling you to make sure the board is not positioned directly over your vise,unless you are into the shiny silver plated vise look.Also if you place a device under the board to recover the solder make sure you move it before you take the board out of the vise or you may end up dropping components into your solder.


Johnny
 
I forgot to add something to to the blueprints for the tumbler from blueduck.Instead of a switch,to supply the power I would use a reostat,like an adjustable output for a ceiling fan.That way the rpm could be fine tuned to the most effective rate.

Johnny
 
I use an old toaster oven I paid $5 for at the flea market. You can get them at Goodwill real cheap.

Just let it heat a minute and pick the board out with needlenose pliers and give it a whack on the inside of a 5 gallon bucket or something similar (I use a square cat litter bucket that's perfect) and then scrape off the monolithics and anything that doesn't fall right off with a putty knife. If you time it right you can use channellocks to pull the plastic PCI and memory slots off and leave all the pins still on the board, than heat a little more and the pins all fall off next ready to go right in the cell.

One thing I do for safety is pull the cylinder capacitors off that contain oil. When the oil inside them heats up it tends to smoke and I'd rather not breathe in those fumes if I can avoid it. It only adds a minute to the proccess but I think its worth it. I also only do this outside for ventalation.

One nice thing is you can do this while you're doing something else while the boards heat up. Just don't forget to check the oven every minute or so or you can end up with a mess.

Steve
 
What about using a very hot blowdryer/ hairdryer to melt the solder, would it get hot enough... I don't think so but maybe it's worth a try. I do like the oven methods, I will have to look for a toaster oven.
 
i dont recomend hairdryer as most of them are fitted with overheating auto-disconnect switch. better option is heat gun. I was usin this but when depopulating with heatgun you are exposed to some fumes if board is overheated, also plastic connectors can melt and there is still solder left on your pins. tin can give you headache later when processing with acids. if you are doing it as hobby in spare time why not to use precicion snipers, and cut pins out. it is time consuming, sometimes you can get blisters but for start as perfect as anything else. when and if you will move to bigger amounts and more experience you can consider some other method which will suit you better. btw i am still cutting pins with knipex precision snipers...
 
Sound like a plan. Yeah I kinda figure my regular house-hold scissors wouldn't cut it, lol pun intended. I have alot of old NES games too I don't play, I might as well throw those in as well. Now next will be finding something to dissolve the green film that cover the other trace metals on the board...
 
jevaud said:
Now next will be finding something to dissolve the green film that cover the other trace metals on the board...

not worth, as there is mostly copper and if gold then only traces.
 
I know this thread might be dead but I am curious as to what method 7 is. Is it using a foundry furnace to melt everything?
 
badastro said:
Method 9: Hot acid bath
Remove ferrous materials. Place boards in a bath of straight or diluted muriatic acid in a crock pot. Do not boil and keep it covered. The acid will attack all solder and leave gold and copper intact. The process should be over in less than an hour.

Pro: Method 9 is fast and efficient. It only dissolves the solder leaving behind components, a clean board, and dirty acid solution. Some people crock pot pins anyway...
Con: It can produce acid fumes. Hot acid is dangerous. The spent acid is very toxic. It is difficult of an average person to scale up.

I am interested in using this method to depopulate tons of boards, but what does ths person mean it will be difficult to "scale up?"
 
Back
Top