Several Random E-Scrap Processing Questions for the More Experienced...

[AuggieDog]

First...How much Sn is too much when using AR to digest e-scrap? Another words, if I am digesting 150g of top hat transistors and there is solder residue on the majority of the legs, (that is a tiny amount) am I going to run into trouble with the formation of metastannic acid? Is there a rule of thumb? Or does it have to be NO Sn whatsoever...?

If I am processing large amounts of ceramic IC's with silicon dies mounted on gold solder (is this solder?), does this solder contain Sn...?

If I am processing large amounts of IC's with gold solder but aluminum bonding wires, are there any issues with the Al reacting with AR...?

Finally, if I was to pulverize ceramic IC's to near dust, will it react with HNO3, HCL, or AR...? Is there any risk of contamination or dissolution of the ceramic components?

Thank you!

 

[Yggdrasil]

First...How much Sn is too much when using AR to digest e-scrap? Another words, if I am digesting 150g of top hat transistors and there is solder residue on the majority of the legs, (that is a tiny amount) am I going to run into trouble with the formation of metastannic acid? Is there a rule of thumb? Or does it have to be NO Sn whatsoever...?

If I am processing large amounts of ceramic IC's with silicon dies mounted on gold solder (is this solder?), does this solder contain Sn...?

If I am processing large amounts of IC's with gold solder but aluminum bonding wires, are there any issues with the Al reacting with AR...?

Finally, if I was to pulverize ceramic IC's to near dust, will it react with HNO3, HCL, or AR...? Is there any risk of contamination or dissolution of the ceramic components?

Thank you!

I do not think there is a threshold for this it is just an increasing nuisance.
Removing as much Tin as practical with HCl is the best way for this I believe.

The ceramic ICs with Gold Solder, the Solder may be better described as brazing maybe?
So there may or may not be Tin in it. Test one.
Al is passified by Nitric and dissolved in HCl. so there should not be a big deal.
I can see no reason to pulverize the ceramic, noting in there.

 

[ólom]

Metastannic acid is not produced in AR, but if you only use nitric acid, metastannic acid is produced, which you can dissolve with sulfuric acid, that is, you can put it in suspension.

 

[GoIdman]

First...How much Sn is too much when using AR to digest e-scrap? Another words, if I am digesting 150g of top hat transistors and there is solder residue on the majority of the legs, (that is a tiny amount) am I going to run into trouble with the formation of metastannic acid? Is there a rule of thumb? Or does it have to be NO Sn whatsoever...?

If I am processing large amounts of ceramic IC's with silicon dies mounted on gold solder (is this solder?), does this solder contain Sn...?

If I am processing large amounts of IC's with gold solder but aluminum bonding wires, are there any issues with the Al reacting with AR...?

Finally, if I was to pulverize ceramic IC's to near dust, will it react with HNO3, HCL, or AR...? Is there any risk of contamination or dissolution of the ceramic components?

Thank you!

I would cut off the soldered legs and process those separately if you do not apply the HCl method to dissolve the tin.....but old gold cap transistors or IC were soldered with mostly lead solder combined with tin to be soft and flexible.....todays ROHS solders break like glass and make bad joints in time...

Pulverizing ceramic IC is mostly not feasable, there is nothing inside which is PM, you just waste your time with it...

Search the forum how to recover gold from ceramic IC`s...CPU`s

Pete

 

[kurtak]

Metastannic acid is not produced in AR,

That just flat out is NOT true --- the nitric acid in the AR will MOST CERTAINLY cause any tin put into the AR to turn into metastannic acid

If you haven't already done so - read Hokes book - she explains this FACT very well in her book

It is also why here on this forum it is ALWAYS the recommendation to first remove as much tin as possible (if not all tin) before going to dissolving gold in AR

Tin - also known as the refiners nightmare - because it turns to metastannic acid in both nitric & AR (because of the nitric in the AR)

It is a nightmare because it is a filtering problem - because -------

1) metastannic acid is made up of ULTRA FINE particles of a tin oxide - so fine that some of it is "more then likely" going to go through even the best of filters - which is more then likely going to end up contaminating your gold or silver when you go to drop your gold or silver --- & - it likes to "keep following" the gold or silver even with 2 or 3 re-refines

2) if you create a lot of it (because you don't remove it in the first place) at the beginning of filtering - some will most certainly go through the filter - but then the filter will become "plugged" with the metastannic acid & it will take FOREVER to finish filtering the solution --- a solution that is still contaminated with the ULTRA FINE metastannic acid that went through the filter when you first started filtering

I don't mean to be rude here - but - saying that metastannic acid is not produced in AR is not only bad advice - but is IN FACT WRONG advice

Kurt

 

[kurtak]

Finally, if I was to pulverize ceramic IC's to near dust,

You absolutely do NOT want to do that

It will create two BIG problems

1) It will create a "clay" like mud that is impossible to filter because it will plug/seal the filter - kind of like clay is used to plug/seal ponds to prevent a pond from leaking/draining

2) because it becomes a clay like mud it is impossible to wash out all of gold dissolved in your leach solution

This is called "diminishing" returns --- each time you wash the mud (to wash out the leach solution) you get "some" of the dissolved gold ions to come out in the wash water - BUT - you will NEVER get all of them to come out in the wash water - some of the dissolved gold ions will ALWAYS stay "tied up" in the MUD

Kurt

 

[kurtak]

If I am processing large amounts of IC's with gold solder but aluminum bonding wires, are there any issues with the Al reacting with AR...?

No - the aluminum (in this case) is not a problem at all

It is a VERY small amount of aluminum - which dissolves in the AR - & it stays dissolved in the AR when you precipitate the gold

Kurt

 

[AuggieDog]

You absolutely do NOT want to do that

It will create two BIG problems

1) It will create a "clay" like mud that is impossible to filter because it will plug/seal the filter - kind of like clay is used to plug/seal ponds to prevent a pond from leaking/draining

2) because it becomes a clay like mud it is impossible to wash out all of gold dissolved in your leach solution

This is called "diminishing" returns --- each time you wash the mud (to wash out the leach solution) you get "some" of the dissolved gold ions to come out in the wash water - BUT - you will NEVER get all of them to come out in the wash water - some of the dissolved gold ions will ALWAYS stay "tied up" in the MUD

Kurt

Ok, it seems that I have nearly 100 pounds of early 1970's - @1985 ceramic IC's. These are just basic IC's *SEPARATE* from any with gold caps, legs, or some which I have that are entirely gold plated. The ones I am referring to are the type that a small love tap with a hammer will split right in half. There you can see the die was brazed with gold solder and I also noted mostly aluminum bond wires. I have read that some formulas of this braze were AU & Si based and others were gold with tin & other ingredients. I was going to dissolve the legs on these, crush them, and then process them for the gold braze. I have a rock crusher but it doesn't allow for much control, and I figured the only way to be sure the die area is exposed on all of them would be to basically pulverize them into dust. I guess this isn't a great idea. So, do I tap a hundred thousand of these ICs in half or is there a better way? Anyone even know if the yield is worth the trouble...?

 

[Yggdrasil]

Ok, it seems that I have nearly 100 pounds of early 1970's - @1985 ceramic IC's. These are just basic IC's *SEPARATE* from any with gold caps, legs, or some which I have that are entirely gold plated. The ones I am referring to are the type that a small love tap with a hammer will split right in half. There you can see the die was brazed with gold solder and I also noted mostly aluminum bond wires. I have read that some formulas of this braze were AU & Si based and others were gold with tin & other ingredients. I was going to dissolve the legs on these, crush them, and then process them for the gold braze. I have a rock crusher but it doesn't allow for much control, and I figured the only way to be sure the die area is exposed on all of them would be to basically pulverize them into dust. I guess this isn't a great idea. So, do I tap a hundred thousand of these ICs in half or is there a better way? Anyone even know if the yield is worth the trouble...?

Do not pulverize anything ceramic.
It will be a nightmare to filter.
Crush to largeish pieces and leach with AR.
The AR will penetrate all in time.

 

[ólom]

That just flat out is NOT true --- the nitric acid in the AR will MOST CERTAINLY cause any tin put into the AR to turn into metastannic acid

If you haven't already done so - read Hokes book - she explains this FACT very well in her book

It is also why here on this forum it is ALWAYS the recommendation to first remove as much tin as possible (if not all tin) before going to dissolving gold in AR

Tin - also known as the refiners nightmare - because it turns to metastannic acid in both nitric & AR (because of the nitric in the AR)

It is a nightmare because it is a filtering problem - because -------

1) metastannic acid is made up of ULTRA FINE particles of a tin oxide - so fine that some of it is "more then likely" going to go through even the best of filters - which is more then likely going to end up contaminating your gold or silver when you go to drop your gold or silver --- & - it likes to "keep following" the gold or silver even with 2 or 3 re-refines

2) if you create a lot of it (because you don't remove it in the first place) at the beginning of filtering - some will most certainly go through the filter - but then the filter will become "plugged" with the metastannic acid & it will take FOREVER to finish filtering the solution --- a solution that is still contaminated with the ULTRA FINE metastannic acid that went through the filter when you first started filtering

I don't mean to be rude here - but - saying that metastannic acid is not produced in AR is not only bad advice - but is IN FACT WRONG advice

Kurt

Hoke describes in his book that tin dissolves in AR and the precipitant pulls it off in the form of metastannic acid, sulfur dioxide gas is less likely to pull the tin off.

 

[orvi]

First...How much Sn is too much when using AR to digest e-scrap? Another words, if I am digesting 150g of top hat transistors and there is solder residue on the majority of the legs, (that is a tiny amount) am I going to run into trouble with the formation of metastannic acid? Is there a rule of thumb? Or does it have to be NO Sn whatsoever...?

If I am processing large amounts of ceramic IC's with silicon dies mounted on gold solder (is this solder?), does this solder contain Sn...?

If I am processing large amounts of IC's with gold solder but aluminum bonding wires, are there any issues with the Al reacting with AR...?

Finally, if I was to pulverize ceramic IC's to near dust, will it react with HNO3, HCL, or AR...? Is there any risk of contamination or dissolution of the ceramic components?

Thank you!

I never had a problem regarding solder in AR. In AR, everything is nicely dissolved into solution without any residues of insoluble tin compounds. Bigger culprit can be lead - because lead chloride isn´t extraordinarily soluble even in heavy chloride solutions like base-metals saturated AR. I processed heavily soldered pins many many times, where the weight of the solder was more than 10-15 % of weight (assuming typical SnPb40 solder, or even more leaded types used in industry to cut costs), and even in lots of more than 10 kilograms or more, I never experienced any precipitated tin compounds. Tin is nicely dissolved into various tin chlorides and hydroxyclorides/oxychlorides. Unless you do not forcefully reduce acidity of the mixture (eg by ading base), they hardly hydrolyze at all = it will all stay nicely liquid. That is why I like AR processing, as there simply isn´t any unwanted precipitate formation and AR is also not "picky", and will process mixed scrap of copper-based and ferrous-based pins/CPUs/etc. while nitric won´t do well with ferrous scrap.

Yup, it is brazing alloy typically consisting of gold and tin, but there are variety of different alloys. You just need to be sure that AR can access the silicon wafer - so that there aren´t any lids, silicone or varnish on top of that. It can take day or two macerating in the AR, but gold will be eaten from under the silicon chip.
With material like larger CPUs, where silicon die is relatively large, it is beneficial to break the ceramic into several pieces - just to make it easier for the acid. Never crush the ceramic finer, or even pulverize cerams... There is simply no benefit of doing this and I am quite shocked how many people in YT videos or even here on the forum still do it. There is no gold inside the cermic.

Ceramic won´t dissolve in regular acids we use for refining. It is typically alumina ceramic, or in some more exotic instances even beryllium-containing ceramic (usually white). If you are to process ceramic stuff like CPUs, gold plated ceramic DIP IC´s or halved EPROMs, do it in straight AR. There is no benefit in any nitric leaching for this type of scrap.