# Separation of precious metals - are fine particles of any value?



## CorinneEllis (Sep 8, 2021)

I've got a small jar with some metal dust that came from grinding up some of the black squares found on circuit boards. (The example pictured here is from an IPhone circuit board)Not sure what kind of metals it could contain, or how to separate them. I'm wondering if it is even of any value this way, or should I just cut the squares off the circuit board and set them aside for later. 

Any help is greatly appreciated.


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## Martijn (Sep 8, 2021)

Welcome to the forum.
If you scratched that shiny chip you probably just loosened some epoxy or silica from the chip.
Integrated Circuits or IC's contain tiny gold bonding wires to connect the legs or pads to the silicon chip.
It's a long study to be able to get the gold out without harming yourself with toxic dust or chemicals and deadly vapors.
You need a lot of electronic scrap to get a bit of gold. A couple of phones wil not give even enough gold to be able to melt and weigh it.
If you're interested, start with plated contact fingers.
After you've searched the forum and study.
A place to start:
Welcome to All Newbies
And some interesting reading about chips:
My results of specific types of IC chips, flatpacks and BGA
CM Hoke's refining book: from FrugalRefiner' signature.
Screen Readable Version of Hoke's Book
Martijn.


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## kurtak (Sep 10, 2021)

CorinneEllis said:


> I've got a small jar with some metal dust that came from grinding up some of the black squares found on circuit boards.



Per the underlined - there are NO metals IN the "black square" - that is the "silicon die" - the silicon die is what dose the data processing in your computer/phone - that silicon die is other wise known as the IC chip

Silicon is highly purified glass

However - you will see that the die/chip (in that pic) is sitting on top of (molded to) an epoxy layer (which you also see around the edges of the die/chip

Inside of that epoxy is where you will find the gold bonding wires

The gold bonding wires are what make the connection from the die/chip to the circuit board

So - after you remove the chip from the board - you can incinerate (burn) the epoxy to turn it to carbon &/or ash

once the epoxy is turned to carbon/ash you can crush it (because it has become soft) & then recover the gold bonding wires from the carbon/ash

You can read more about processing chips for the gold bonding wires here

:arrow: Gold inside chips (black, flatpacks - not CPU)

And here

:arrow: My results of specific types of IC chips, flatpacks and BGA

The chip in your picture will pay between 2 - 4 grams per pound of chips (not all chips are created equal)

it takes A LOT of chips to get a pound of them

Kurt


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## g_axelsson (Sep 10, 2021)

Kurt is mostly correct, but that chip contains virtually no gold, it's a flip-chip and attached to the substrate with solder bumps, no bond wires there. The ones you are looking for is where the silicon die is covered in epoxy. Often called "Gold cornered bga chip".

Göran


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## kurtak (Sep 11, 2021)

g_axelsson said:


> but that chip contains virtually no gold, it's a flip-chip and attached to the substrate with solder bumps, no bond wires there.
> 
> Göran



If that is a flip chip there will be no gold bonding wires

I just spent a couple hours searching for images of flip chips (including a search for "identify the flip chips in an iphone") & could not find a pic of a flip chip like that one

Most all the pics of flip chips I found have the chip sitting on a board with a glue (called the "underfill") around the edge of the chip 

Kind of like the pic from wiki (found pics of flip chips from very small to large but they all had that "underfill" glue around the edge of the silico die)

:arrow: Flip chip - Wikipedia

So - I just don't know about the chip pictured in the OP of this thread (meaning you could very well be right that there are on bonding wires)

However -----



> The ones you are looking for is where the silicon die is covered in epoxy.



Per the underlined - the silicon die of an IC chip does not have to be "covered" with epoxy for it to have gold bonding wires - the silicon die can be exposed & still have bond wires

Here is an example I posted about back in 2018

:arrow: RAM "Bus" IC chips

Those RAM bus chips definitely have bonding wires

Also - I have incinerated other "single" chips - with exposed silicon dies - to check/test them for bond wire & found them to have bond wires

in other words - an "exposed" silicon die is not an absolute indication of no bond wires - nor is a full epoxy covered IC chip an indication of bonding wires 

As I said - not all IC chips created equal 

But you are right - it is an assumption on my part that the pic of the chip in the OP has bond wires - I have never incinerated "one" of those chips & tested it for bond wires 

Kurt


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## g_axelsson (Sep 12, 2021)

You are right Kurt, in this case the old saying that for every rule there is an exception applies here.

The Apple die on the picture above is so large that it covers almost all of the substrate board. The underfill is covering the little space left of the substrate.

I agree, the "exposed die" is just a broad rule, the ram chips are the exception. But the bond wires needs protection and in that case the bond wires are located in the dark epoxy string in the middle of the chip.

When a chip is connected via bonding wires it is mounted in three basic steps.
- The die is attached to the substrate. (fiber board, lead frame or ceramic capsule)
- The electrical connections are added by bond wires between conductors on the substrate and the die.
- The bond wires are given a physical protection. (Adding a lid or embedded in epoxy)

So a better rule would be exposed backside of the die and no epoxy then there are no bond wires... maybe. :wink: 

Göran


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