# Depopulating with air hammer



## Bluebloomer (Jun 29, 2018)

I've been depopulating some 100+ motherboards with an air hammer. Bought a new powerfull compressor to do so, and I depopulate in 3 steps; first I take of the low grade pins like PCI and Memory slots, collect it in a bin and then I move on the full plated IDE pins and some of the big chips, and lastly I remove the MLCC's, flatpacks and Ta caps with a chisel by hand.
Works realy well despite the extra work, but this way I don't have to sort as much, and much less waste.

However, after air hammering off the PCI and Memory slots pins I'end up with a lot of powder mixed in with the pins. I think it is mostly Tin but i could also be crushed MLCC's and some of the gold plating.

I think here is some value in the 'dust' mixed up with the pins, but since I want to recover the gold with the sulfuric acid cell I need to separate the powder from the pins but so far I can't find a good way to do so without having to pluck 100's of pins out from the dust.

The dust is not very welcome in the sulfuric acid cell, so does anybody have an idea or technique to separate the pins from the dust ?
The finest steel sieve I can find still allows PCI pins to fall thru if I shake the sieve. Even a magnet still takes on way too much fines when I release the pins.


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## snoman701 (Jun 29, 2018)

Do you really think it's worthwhile? 

I depopulate a small amount, but I have the following rules:

1) Whatever I take off has to have a value of at least $25/lb
2) Whatever I take off cannot lower the overall grade of my board.  

Further, I can't tell you the last time I removed anything other than a couple tantalum caps off a motherboard. 

As for your problem, find a finer sieve, if there are still pins making it through at that point, just digest in HCl without oxidizer. The tin solder, if attached to gold, will collect minute amounts of gold anyway. This isn't something you have to actively do, just toss it in a bucket with HCl, and process it once a year or something.


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## Geo (Jun 29, 2018)

Have you tried gravity separation with water? I imagine that the small particles will move better in a stream of water as apposed to the metal pins.


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## Bluebloomer (Jun 30, 2018)

> Do you really think it's worthwhile?



Yes I think it is. Once all motherboards are processed this way I think It will double the 7 pounds of pins allready collected. Estimating at 0.1 - 1 % Au per kilogram of pins it might yield a troy ounce of gold.

Then I move on to full plated pins, MLCC's (5 Lbs so far) and 25 kg of mixed chips and cpu sockets of around 300 motherboards. I just collect all he material and want to process it in bulk minimizing loss.



Geo said:


> Have you tried gravity separation with water?



I was thinking about it, just not sure how to approach it. I have to make a bluebowl anyway for incinerated chips and flatpacks, and I have these polyester 'bubble bags' ranging from 25 micron to 220 micron. (25, 73, 120, 160,, 220 micron) 
Could it work to fill a sieve or bubble bag and flush the finer particles out with a stream of water ?

Any other idea's are welcom.. :wink:


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## Geo (Jun 30, 2018)

Put the material in a large bowl or pan and fill with water. Give it a few good swirls and while the lighter stuff is still suspended, pour the water into a bucket. Keep doing it until all the lighter material is washed from the pins. Low tech but it should work.


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## Geo (Jun 30, 2018)

Also, with the bowl filled with water, reach in and pick the pins up by hand and the heavier, smaller particles, like solder balls, will stay in the bottom. You should be able to get most of the pins separated in this way.


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