# Need help on LEDs



## Marcel (Jun 5, 2012)

Well I got this batch of about 250g of SMD LEDs which is crying for getting processed, but I just cannot figure out HOW to concentrate the stuff.


I used them from my own old PCBs and unsused from the reel.



The refiner took the LEDs to the lab and (somehow, dont know how) returned me a 2,4% Au yield.

If you have never examined an LED:



It´s *yummy, yummy! *
Gold, silver and some germanium.
I guess I will only hunt for the gold though.
I have tried:
- to cook them in hot NaOH for hours - no avail unchanged
- "roast" them with heat (400°C), it did not affect the lens

The transparent lens is made of epoxy resin, that is at least what the datasheets say.
If you put them into AP, only the goldplated contacts on the outside will float away, but no internals will be dissolved or attacked.
Any idea on how to get to the core ?
LEDS are becomming mainstream products in households as well. Maybe worth taking a look at...


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## NobleMetalWorks (Jun 5, 2012)

The problem is that you need to figure out what the resin is, is it some type of epoxy resin or maybe nylon resin, since you have already tried NaOH, and it had no affect on the resin that probably means it's not a nylon resin but an epoxy resin. But to make sure you should try other methods. Nitric Acid, Sulfuric Acid, Hydrochloric Acid among others will also dissolve nylon resin, but not epoxy. You might try one of those just to make sure that you are not dealing with nylon resin. You can also try Ethanol, it will also dissolve nylon but not epoxy resin. In short, strong acids, strong bases and ethanol will not dissolve epoxy resins but will nylon. If you try more than one of these, and it doesn't do the job, chances are that you are dealing with an epoxy resin.

You are however in luck, Aqua Regia will dissolve most Epoxy Resins, and Nylon.

Scott


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## Marcel (Jun 5, 2012)

Thank you Scott,
that is a lot of information you gave me.
I had to correct myself, it is expoxy resin that the lenses are made of. I will try to solve it without Aqua Regia and keep on trying.

Marcel


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## NobleMetalWorks (Jun 5, 2012)

If you find something other than Aqua Regia or Incineration, please post here I would like to know myself.

Thanks

Scott


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## tek4g63 (Jun 5, 2012)

This is just a question. Can they be crushed into a powder then dissolved in HCL/CL? I have no experience with things like these awesome looking LED's it's just a question that came to my mind. A coffee grinder(electric) might make short work of them, but it would probably be it's last job. 

They look great, can't wait to see this one get solved!


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## Geo (Jun 5, 2012)

Marcel, you seem to know what you doing and i assume you have all the equipment needed to do what im am about to recommend. this process is not for the beginner as it is very dangerous, even more so than working with noxious fumes.

i would recommend that you try a sample with wet ashing. if you dont know the term or the procedure, do not attempt this until you fully understand the dangers involved in working with hot sulfuric acid.do a small sample on a small scale to see how the reaction works and how long it takes to break down the organics. 

WARNING : hot sulfuric acid will dissolve flesh and bone very quickly. if it comes into contact with bare skin, rinse immediately with a solution of baking soda and water and then with copious amounts of water. wear protective gear, gloves, apron and eye protection. contact of hot sulfuric with the eyes will cause immediate and permanent blindness.

do all testing and processing in lab rated glassware.


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## etack (Jun 5, 2012)

tek4g63 said:


> A coffee grinder(electric) might make short work of them, but it would probably be it's last job.



Sounds like a job for will it blend :lol: http://www.youtube.com/watch?v=oRr7N7A4Wc0&feature=fvwrel

http://www.blendtec.com/Home

Eric


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## Marcel (Jun 5, 2012)

A few hours later cooking *very hard* in NaHO the lenses went off!


Now I have:
- lenses floating around 
- tiny bond wires floating around
- silver which was used as solder for the die is not visible anymore (dissolved)
- dies (with Germanium) are not visible anymore (dissolved?)
- some thinner gold platings seem to have dissolved, copper is visible. Strong hot lye can dissolve gold and other PMs.



Now I renewed the lye, but keept the fully white one. Some white sediment is visible.



OMG! Now I am in trouble and need real chemists pros: Where did all the nice stuff go? I have no experience on how to recover PMs from a lye. I can see all the gurus of this forum jumping on me: "Why the hell then did you do that?"
I just wanted to remove the expoxy resin....

@Geo: Thanks for the safety advice. One cannot say that often enough. Would be sad to learn that someone has sacrificed his health for a little bit of money. In my case, I stay away from AR and other nictric stuff. If I cannot do it with AP, mechanical, thermal etc. I leave it to the pros. I have family and I even recommend anyone new and non-pro without lab to stay away from this stuff.


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## goldenchild (Jun 5, 2012)

If you did somehow dissolve metals with lye simply acidify it with HCL and drop out with copper. Zinc if you want to get everything. Lye is a very strong base so you might need a good amount of HCL depending on how much lye you used.

P.S. wouldn't your basic paint strippers dissolve the epoxy?


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## Marcel (Jun 5, 2012)

The solution is still on the hot plate. Took some samples and looked at them through a microscope. So far the lye has separated the lenses from the mini PCB. The lenses are getting dull and disintegrate very slowly. The bondwire is stuck in there as well as the die. I will have to continue to heat until the lens fully falls apart. I then should have a mini PCB that is gold plated, loose bond wires and dies that carry the germanium (very tiny) and the silver which has turned black meanwhile.
Goldplating is getting thinner and thinner and going away on many LED substrates. Copper is visible. Maybe it was only flash gold. But some keept their golden color.
@goldenchild: Thanks for the hint. I will collect the lye and try to do what you said later. As for paint remover: I have some here, maybe I try that also.


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## patnor1011 (Jun 5, 2012)

I did sample last year. However my method was more crude/brute/force :lol: 
I simply reduced everything to powder, hot nitric wash and AR.


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## NobleMetalWorks (Jun 5, 2012)

patnor1011 said:


> I did sample last year. However my method was more crude/brute/force :lol:
> I simply reduced everything to powder, hot nitric wash and AR.



Did you reduce them to powder in a ball mill?

Scott


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## qst42know (Jun 5, 2012)

The gold wires are still in the lens. 

Incinerate hotter, burn it to ash. The ceramic from surface mounts may be robbing some heat but the legged leds turn to soft dust when hot enough. All epoxies have a limit you need to overcome.


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## patnor1011 (Jun 6, 2012)

It was more Stone age like method Scott. Hollow pipe with cap on one end and solid about 7-8 kg heavy steel rod. Like oversized mortar and pestle. I think that there is a picture of it in my flatpacks pdf - http://goldrefiningforum.com/phpBB3/download/file.php?id=11479
In this thread: http://goldrefiningforum.com/phpBB3/viewtopic.php?f=52&t=11827&start=40


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## greeneye (Jul 22, 2012)

Hi, First post here. Thanks to all of you for this fantastic forum! I'm new to refining - just getting set up now and doing research, aiming to put my chemistry and engineering background to good use.

Glad to see that the epoxy came off in NaOH.
Another option to remove various epoxies and plastics is NMP (N-methyl-2-pyrrolidone), which can be found in grout remover, some paint strippers, or for example masterbond industrial epoxy remover MB6A.


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## NoIdea (Jul 23, 2012)

goldenchild said:


> P.S. wouldn't your basic paint strippers dissolve the epoxy?



Just be careful with caustic soda based paint strippers as they may have a non-flamible solvent called methylene chloride, awsum solvent by the way, butt it has a very low boiling point, somewhere around 32deg. C, so do not heat. 

Methylene chloridebelongs to the chloroform and carbon tetrachloride family, tho it is non-carcinogenic, well so far anyway, give it another 10 years and they will find something wrong with it :roll: 

Deano


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