# Problem with wet ashing of IC's



## AnilSuthar (Nov 17, 2017)

Hello guys, 
I am new to this forum and in this field. I have separated the gold plating from all the pins. But when processing IC's and BGA chips, I tried wet ashing as it is most convenient for me at the time (I don't have anything to incinerate). I now have a mixture of sulfuric acid some metal and lot of black particles. My problem is how to separate the black particles as I can not filter the solution and I don't want to pour the solution and hope that the metals will stick in the bottom. I diluted the solution many times and drained the water but the black particles are still there. Should I use aqua regia directly(after removing base metals) or is there a problem with the black particles?
Note : All of this is on a very small scale, in a 200ml beaker. :? (It was tough due to small size for all the bubbles that came out but I managed to dissolve 100gm chips in it)


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## nickvc (Nov 17, 2017)

Wet asking is really not advised here on the forum due to the real dangers of using hot concentrated sulphuric, it has to be one of the nastiest acids around and can cause severe burns and even the fumes are highly dangerous so I would advise you not to do this again.
For what you have you can filter the solution if as you say it is diluted, a charming plug, toilet paper, or glass fiber insulation caked down should do the trick.


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## AnilSuthar (Nov 17, 2017)

Thank you for the reply and I understand the risks of working with boiling H2So4. My problem is that the black material will not go through the filter paper and it will stick with the gold wires. Is that thing soluble in any acid or anything cheap enough? If not than I can dissolve everything in aqua regia and then filter to get the gold water? 
And to precipitate the gold I need SMB which my chemical supplier says will come after one month when all the schools will order chemicals(He orders in bulk only). Is there anything else by which I can precipitate the gold. 
One more thing, I am using HCL and Calcium Hypochlorite instead of Sodium Hypochlorite (Not using Aqua Regia) So, what else can I use to precipitate?


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## kjavanb123 (Nov 17, 2017)

In your current situation, you should dilute your sulfuric acid solution with water, let it settle for 10 minutes, then decant into container.

You do this until water becomes clear. The residue should be mostly copper and small precious metals.

You can dissolve in nitric, heat it to red hot, to remove nitric from residue, dissolve in AR.


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## AnilSuthar (Nov 17, 2017)

Another question, can I use Sulfuric acid and KNo3 instead of pure nitric acid? (Nitric acid is not available to public here and I dont have apparatus for condensation to make pure nitric acid)


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## AnilSuthar (Nov 19, 2017)

Can anyone please answer my small questions? Please read all my questions and show me a way, not all of them are answered or do I need to ask each question in a separate thread? (That would not be good I think :? )


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## snoman701 (Nov 19, 2017)

Wet ashing is too dangerous and thus is not discussed on this forum. 


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## anachronism (Nov 19, 2017)

snoman701 said:


> Wet ashing is too dangerous and thus is not discussed on this forum.
> 
> 
> Sent from my iPhone using Tapatalk



It's more that most people here don't even follow the safety required for using other more forgiving acids. Given that scenario they would hurt themselves badly using concentrated hot sulphuric, because it's far less forgiving. Now if they did use the correct PPE and safety protocols then it would probably be something to explore, but frankly there are people around that can't be trusted to be safe with water let alone anything corrosive. 8)


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## snoman701 (Nov 19, 2017)

Agreed.

I'm more comfortable using HF than I am concentrated sulfuric at high temperatures. 




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## chemtag (Nov 20, 2017)

What is it about hot sulfuric that causes you such concern? Is it just the combination of a strong acid (H2SO4 has a pka of -3, so its quite strong) and very high temperature (93% has a boiling point of over 300C)? I mean, not to say that a strong acid at over 3x the temperature of boiling water isn't in itself cause for concern!


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## anachronism (Nov 20, 2017)

chemtag said:


> What is it about hot sulfuric that causes you such concern? Is it just the combination of a strong acid (H2SO4 has a pka of -3, so its quite strong) and very high temperature (93% has a boiling point of over 300C)? I mean, not to say that a strong acid at over 3x the temperature of boiling water isn't in itself cause for concern!



It's the fact that one drop in the eye has a completely different result from one drop in the eye of HCl or Nitric.


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## denim (Nov 20, 2017)

Yet they sell it as a drain cleaner for any idiot to use. Seems odd to me that something so dangerous is so readily available to the masses. Maybe if it's cold it's not as bad. I doubt that your typical maintenance guy in some hotel would even bother to use goggles, or gloves for that matter, when unplugging a kitchen drain line with 93% sulfuric acid. In his race to 'save the day' for the kitchen manager he might lose an eye!

Stay safe when using any acid, lye (sodium hydroxide), bleach, and any other chemicals. It only takes a second to 'safety up', and it takes even less time to lose an eye.


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## nickvc (Nov 21, 2017)

The real danger of sulphuric especially concentrated is that it is water hungry, we advise to cover the container when using a sulphuric stripping cell because it will draw water from the air even cold, now the human body is mainly water so add sulphuric and heat and you can figure the rest....


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## chemtag (Nov 21, 2017)

anachronism said:


> chemtag said:
> 
> 
> > What is it about hot sulfuric that causes you such concern? Is it just the combination of a strong acid (H2SO4 has a pka of -3, so its quite strong) and very high temperature (93% has a boiling point of over 300C)? I mean, not to say that a strong acid at over 3x the temperature of boiling water isn't in itself cause for concern!
> ...



I was always under the impression that a drop of strong acid (HCl, HNO3, H2SO4, etc.) in your eye was going to give the same result (partial or complete blindness). Is it just that lab grade "concentrated" sulfuric acid is so much higher weight% of the acid (93/98% for sulfuric versus 65/70% for Nitric, and 32/36% for HCl)? Again, I apologize for my ignorance, I am just surprised to hear that sulfuric is uniquely dangerous.


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## snoman701 (Nov 21, 2017)

Concentrated sulfuric is extremely hygroscopic. Add the 300+ degrees you need to have and you end up having a hygroscopic mist capable of denaturing proteins by dehydrating and by pyrolizing carbohydrates through the dehydration. 

Also, chemistry at that temperature should be using thick walled glass, with no scratches, etc. 

Breaking a beaker or flask at wet ashing temperatures is likely going to be ugly even in a university lab.


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## cuchugold (Nov 22, 2017)

AnilSuthar said:


> Another question, can I use Sulfuric acid and KNo3 instead of pure nitric acid? (Nitric acid is not available to public here and I dont have apparatus for condensation to make pure nitric acid)


Yes you can. You are effectively making nitric acid + K2SO4 when you do your mix.


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## Rougemillenial (Dec 3, 2017)

AnilSuthar said:


> Hello guys,
> I am new to this forum and in this field. I have separated the gold plating from all the pins. But when processing IC's and BGA chips, I tried wet ashing as it is most convenient for me at the time (I don't have anything to incinerate). I now have a mixture of sulfuric acid some metal and lot of black particles. My problem is how to separate the black particles as I can not filter the solution and I don't want to pour the solution and hope that the metals will stick in the bottom. I diluted the solution many times and drained the water but the black particles are still there. Should I use aqua regia directly(after removing base metals) or is there a problem with the black particles?
> Note : All of this is on a very small scale, in a 200ml beaker. :? (It was tough due to small size for all the bubbles that came out but I managed to dissolve 100gm chips in it)


 I wouldn't recommend this process at all. The acid is being reduced to toxic sulfur oxides the process of the reducing agents like the epoxy


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## LT_golden (Oct 31, 2018)

What about wet ashing at a lower temperature, around 70-80 deg. C, as the “Archimedes Channel” and Bohemia Graman have suggested and performed on YouTube? I’d still be pretty afraid about it as one appears to be a professional (Archimedes Channel) and the other seems to be doing it inside his/her house, but am just curious if it’s a little safer at those relatively lower temperatures?


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## nickvc (Oct 31, 2018)

Concentrated sulphuric is nasty cold and gets more progressively nasty as it heats up so my advice is to find a safer more forgiving method to accomplish your goals.


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## kurtak (Oct 31, 2018)

LT_golden said:


> What about wet ashing at a lower temperature, around 70-80 deg. C, as the “Archimedes Channel” and Bohemia Graman have suggested and performed on YouTube? I’d still be pretty afraid about it as one appears to be a professional (Archimedes Channel) and the other seems to be doing it inside his/her house, but am just curious if it’s a little safer at those relatively lower temperatures?



NO :!: :!: :!: 

Let me put it this way --- 


Just because some idiot puts a video on You Tube about running in front of a speeding car & he doesn't get run over by the car --- does not mean you should go out & run in front of speeding cars to :!: :!: :!: 

Kurt


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## galenrog (Oct 31, 2018)

YouTube can kill.

Time for more coffee.


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## patnor1011 (Nov 6, 2018)

As far as I can see you did it wrong. 
Wet ashing is where hot sulfuric is used to dissolve IC body and this thick black solution is poured off as it does not contain anything of value.
Value remains on the bottom in a mix of other metals. 

What you did is that you dissolved IC body but instead of pouring off this junk, diluting your solution made it all come down on your values and the rest. 

I do not have any idea if redoing your stuff with fresh concentrated hot sulfuric can put that junk back in solution. It is not worth it in my opinion. 100g of IC will have enough of gold to cover expenses you had already with time included. 

If you do have means to fool around with hot sulfuric I honestly can't see how incineration can be a problem. 
Drain your mess, pour off as much as you can and wash with water. Then incinerate your concentrate and wash ashes off.
Stay safe.


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