Methods of depopulating PCB's

curtis.a

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thanks steve ive been reading the forum for some time i was refuring to the powder from grinding the whole board HCl first for lead and tin nitric for silver, palladium, copper and AR for gold and platinum
 

cejohnsonsr

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Thank you, Geo. I remember you mentioning the fumes & the fan in the video. I promise I'll set it up with positive airflow to move the fumes away from me & NOT toward anyone else. So about 400 degrees should do the trick I think. That helps a lot. Now all I have to do is decide on a heat source. Thanks again!

Ed
 

butcher

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Thanks steve I have been reading the forum for some time I was Referring
to the powder from grinding the whole board HCl first for lead and tin nitric for silver, palladium, copper and AR for gold and platinum


curtis.a,
I am not sure what your question is about, but processing whole circuit boards is a bad idea.
When you say HCl first for lead and tin, you do understand lead will form insoluble salts of lead chloride, tin will form a gel that can hold fine gold, make filtering almost impossible, and if this was mixed with ground up circuit boards would just form one big mess.
Then you speak of using nitric acid; here you will just make a bigger mess dissolving your gold into solution (you would still have the chlorides involved).

Just making one big toxic deadly mess.

Grinding whole boards can be a process used industrially, but then you would have to treat them prior to using acids, by some other means such as gravity and mechanical separation, or adding a lot of copper and melting to impure copper bars or some other means.

You cannot just take one statement here (like grinding whole boards to powder) and use some other processes you read about to recovery or refine it using methods meant to refine other types of materials.

Begin with reading Hokes book, get an understanding of how to separate and process the many different types of materials, work on the getting acquainted experiments, to get a good understanding of how different metals react in solution, study the forum to learn how to separate your material and treat it with the several different processes needed (do not try and take one process and recover or refine it with a different process.

Study the forum and learn the processes used for each material, and the steps needed to do each process in recovery, and the following processes needed to refine the materials.

Start with the guided tour in the guide to the forum, and reading the welcome to new members found in the general reaction section.

Also study dealing with waste in the safety section, the safety and understanding this is the most important thing you need to understand.
What good will it do to get a gram of gold if you killed yourself trying to get it?
 

curtis.a

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[/Grinding whole boards can be a process used industrially, but then you would have to treat them prior to using acids, by some other means such as gravity and mechanical separationquote]

thanks butcher that is the info i was looking for im not doing it just researching I don't do anything till ive done a good bit of research on the subject.
curtis
 

butcher

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I believe industrially they separate mechanically as much as possible, and melt with scrap copper making impure copper anode bars (95% or greater in copper content) then ship these to the copper refiner's who electro win the copper to fairly pure copper cathode sheets, in huge copper refining cells, taking very large amounts of electricity, and current, to run these copper cells, precious metals end up as anode mud or slimes to be further processed for their values.
 

Pantherlikher

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I've been kicking the idea of using a George Forman type burger grill with sand.
The large grill is big enough for mother boards and has raised ,grill like, surface witch sand can fill for a flat surface. It's also slightly tilted forward so solder sinking through the sand can flow out and into a catch pan. I'm not sure how hot they get but should be hot enough for solder.

I also had a wild thought of mylar grilling in this as the melted mylar would drain off leaving the silver traces. But not sure if it would melt or just burn the mylars causing bad fumes.

BS.
Gotta love the cold winter as it puts off great experiments...
 

Geo

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Pantherlikher said:
I've been kicking the idea of using a George Forman type burger grill with sand.
The large grill is big enough for mother boards and has raised ,grill like, surface witch sand can fill for a flat surface. It's also slightly tilted forward so solder sinking through the sand can flow out and into a catch pan. I'm not sure how hot they get but should be hot enough for solder.

I also had a wild thought of mylar grilling in this as the melted mylar would drain off leaving the silver traces. But not sure if it would melt or just burn the mylars causing bad fumes.

BS.
Gotta love the cold winter as it puts off great experiments...

most types of heating elements like that only reach around 400 degrees F. if you add sand, it may not warm hot enough to melt solder but its worth a shot. who knows, it could be a "knock out". :lol:
 

butcher

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Make sure you have some type of fume evacuation system so those fumes do not knock you out.
 

Buster

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Hey Pantherlikher, let me know if this works for you, I might give it a go too if it does.
 

g_axelsson

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The solder will not drain away, it is held in place by surface tension.
And the idea of leaving silver after melting off mylars doesn't work either, the silver is just a powder that crumbles when the plastic melts and mixes in with the plastic. It is actually silver paint made up of many small grains so it has no mechanical strength what so ever.

Göran
 

MMFJ

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g_axelsson said:
The solder will not drain away, it is held in place by surface tension.

In my experience (with soldering copper pipes and uncountable wires and electrical connections), it seems that any excess solder will 'flow' if kept hot enough, however, there will first be a layer of 'waste' (in this instance - perhaps 'unrecoverable' might be a better word?) which will coat the tray first, then the excess that is hot enough will flow away if the angle of the tray is high enough.

I'm not saying this is a useful concept (although very interesting, if it worked), simply that the excess solder would flow away (how much 'waste' would depend on the material the tray is made of - as stainless is hard to solder, there may not be any waste, though traces would always be there and any other attempts at recovery with the same tray would have contamination).

And, while I consider the concept potentially interesting, it is impractical as the vast majority of 'excess' solder has already been trimmed from the boards in the original manufacturing process, which typically uses a capillary type action to draw UP the solder from a tray bath and therefore, doesn't lend itself to removal in the same manner (with the parts oriented on top).

Perhaps, with enough agitation, some solder would come off enough to then remove the parts, but there will be parts that continue to hold on, etc. - using even more time later in processing by hand.

The (MUCH) simpler idea is to take the board into an 'oven', upside down (where the parts will fall as they heat enough to melt the solder) - agitating along the way (my vision is a pizza type oven with a 'cobble-stone road' (something to cause as much bouncing around as possible - could be oblong wheels, a board full of screws/nails at different heights - anything to make it shake as it goes through).

The board should come out clean - other than some transformers, etc. that have parts/pins folded over, which will have to be physically removed.

One challenge here is that the parts will have hot solder on the legs and may want to stick to other pieces. My thought on this is to keep a moving belt (more like a series of small trays that are close enough to touch when under the boards and then dump the contents as they pass the end and turn upside down upon return) going in the opposite direction - that should eliminate that problem. However, it should first be proven this is an issue - it may be that simply keeping a collection tray low enough to allow for cooling will keep the parts from sticking too much (I tend to over-engineer things and then test alternatives before building the 'ultimate' contraption!)

g_axelsson said:
And the idea of leaving silver after melting off mylars doesn't work either, the silver is just a powder that crumbles when the plastic melts and mixes in with the plastic. It is actually silver paint made up of many small grains so it has no mechanical strength what so ever.

Göran

I've also experimented with mylars, melting them slowly, and did find silver there, in 'solid' form. I followed the method http://goldrefiningforum.com/phpBB3/viewtopic.php?p=6388#p6438 - however, I believe (though have not tried it) that a diluted nitric wash (also discussed in that thread) is a better idea.
 

gold4mike

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MMFJ,

I like your "pizza oven" idea and have used a smaller more manual version of it. I use a small electric grill to heat the bottom of the board until I can move parts around on top. I grip the board with pliers, turn it over and thump it on the edge of a large porcelain/metal baking pan. Most of the parts come off and some of the smaller MLCC's and such do, as you mentioned, get stuck in some of the solder that comes off as well.

I'm thinking of building a shear using something similar to a wood splitter as a basis. I envision a large piece of metal with a precise 90 degree angle edge, resting on the surface of the board, then shoving it along the surface, plowing off all the parts into a catch pan at the end.

The board would rest against a stop at the far end of the duty cycle of the ram and lie flat on a heavy steel plate. The distance between the plate and the ram with the metal block would have to be able to be increased or decreased to compensate for the different board thicknesses and the length of the portion of pins that stick through the board on the bottom.
 

mjgraham

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I have been depopulating boards today and I ended up using a convection oven ( not for food again ) goes to 550F about 5 min in and good slap, something I made for the MLCCs and such was to take some 1" Al flat bar and build a frame that had a gap that the board would fit through and while it is hot slide it though it, gets the rest off or go at it with a scraper while hot, working pretty good. Better than the heat gun , while it works much slower.
 

butcher

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Remember the tin in solder will dissolve gold into it, making an almagam of tin and gold, even at temperatures as low as the melting point of the solder.

Free melted solder will also solder to other (unsoldered metals) before it will drip off.
 

mjgraham

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Oh yea I have a mess of parts , but sorted the chips ,tantalum caps, and the other into piles (solder, MLCCs and other small parts) , of course I have removed non PM stuff already, and I guess I should say any electrolytic caps get tore off before the heat. I guess getting the parts off is the easy , fast part the rest is slow and steady and hopefully not sad in the end. Most of these boards were gold plated so now there a soldery smeary mess that gets some HCl for a while.
 

Geo

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gold4mike said:
MMFJ,

I like your "pizza oven" idea and have used a smaller more manual version of it. I use a small electric grill to heat the bottom of the board until I can move parts around on top. I grip the board with pliers, turn it over and thump it on the edge of a large porcelain/metal baking pan. Most of the parts come off and some of the smaller MLCC's and such do, as you mentioned, get stuck in some of the solder that comes off as well.

I'm thinking of building a shear using something similar to a wood splitter as a basis. I envision a large piece of metal with a precise 90 degree angle edge, resting on the surface of the board, then shoving it along the surface, plowing off all the parts into a catch pan at the end.

The board would rest against a stop at the far end of the duty cycle of the ram and lie flat on a heavy steel plate. The distance between the plate and the ram with the metal block would have to be able to be increased or decreased to compensate for the different board thicknesses and the length of the portion of pins that stick through the board on the bottom.


https://www.google.com/url?q=http://goldrefiningforum.com/~goldrefi/phpBB3/viewtopic.php%3Ff%3D60%26t%3D10822%26view%3Dprevious&sa=U&ei=Tb4SUdbMMrG_2QXnrYG4DQ&ved=0CAcQFjAA&client=internal-uds-cse&usg=AFQjCNHYWqUgTMdGh9p_KkRe_H1F2TMNAw
 

butcher

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HCl + Tin = Stannous Chloride
HCl + Tin + Gold in Solution = Colloidal Gold
Keep the oxidizers out.

I have always like that idea of the hydraulic Shear to remove parts from the boards.
 

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