[0xFFFF]

Over the last few months I have been uncapping ICs and taking photos of silicon dies. It's fun and educational but I have no idea what chemical processes are taking place.

The process I go through to remove silicon dies from their packaging...

• Physically remove IC from hardware (if required).
• Physically remove legs / pins / excess epoxy from IC package.
• Chemically strip epoxy from IC by placing in a heated beaker containing nitric acid (70%).
• Carbon deposits often stick to the silicon die.
• Clean up the silicon die by placing in a heated beaker containing sulfuric acid (98%).
• Remove and wash the die with distilled water.
• Place die in an ultrasonic cleaner with acetone to clean it up a bit.

What I hope to learn in time:

• Understanding what is actually happening.
• 'Learn how to learn'. I clearly don't have a chemistry background. I don't even know what type of chemistry this is.
• Advice on a free (or close to free) course that can put me on a track to get a better understanding of the above
• Best practice for uncapping integrated circuits.
• Distilling / recovering nitric and sulfuric acid. Waste minimization etc...
• How to recover the gold that is accumulating in my beakers... for fun.

TIA

-Kev

[Arkcon]

Pics?

[0xFFFF]

These pics don't show the procedure I go through.
You can see what I'm getting up to though.
I can post more photos later.

My homemade microscope:

Fully automated (excluding zoom).
I want to upgrade to a metallurgical microscope one day.

Bad sample die shot:
Inside Secure Picopass iCLASS 2K die IC215HA


Other attachments:
3920 - Modified slow cooker. Baking soda to neutralise and spills.
Must've had really bad weather last night. There is dirt all over my bench!
3921 - Beaker with sulfuric acid, copper oxide? and dissolved epoxy. Bits of gold.
3922 - Beaker with copper oxide? and dissolved epoxy. Bits of gold.
3923 - Beaker with nitric acid, dissolved epoxy.

[Borek]

I am afraid the chemistry behind dissolution in nitric acid is either highly complicated - many different reactions occurring at once, or quite simple - relatively strong acid protonating and oxidizing everything it can.

[Enthalpy]

Some elements:

Epoxy is a rather inert polymer. Solvents or normal acids would take very long to remove it. Being an oxidizer, nitric acid does it faster, and heat accelerates it.

Said "epoxy" is filled with a powder of quite pure silica in huge proportion, supposedly by mixing different grain sizes. This stabilizes the dimensions against humidity and temperature to match silicon better. After etching, the silica remains in the acid and thickens it.

This epoxy is very special in that its polymerization or cross-linking releases no HCl - not even that little bit, because HCl catalyses the corrosion by humidity of the ultra-thin metal layers. Long ago, the only plant worldwide burned in Japan and the whole semiconductor industry was in trouble.

There may well be additional passivation layers between the chip and the epoxy, like polyimide, and these layers can react differently to the acids, leaving black residues. Just a hypothesis.

If your chips still use bonding wires, these are of gold (aluminium existed long ago). Untouched by both acids, so the recovery would rather be mechanical. If TAB makes the connections between the chip and the macroscopic contacts (as was the case in chipcards), it usually had gold conductors printed on polyimide.

In case the chips still have aluminium conductors, anything exposed goes bye-bye in the acids. But under the silica or silicon nitride passivation, it can survive.

Please take with mistrust: I left the semiconductors three decades ago, when we made the etchings with flint stone and the ion implantation with a blowpipe.

[0xFFFF]

Thanks for the detailed response.

Heat certainly has a huge impact on the reaction time! I forgot to mention that I'm heating the nitric (and sulfuric) to 100°c. Is there a good range?

Do you think I should physically separate the epoxy, polyimide, etc... and observe those results?

The end results are always pretty. By the end of it all I'm left with little gold pieces and shiny silicone.

I'm pretty sure I managed to dissolve the gold once when I mixed the nitric and sulfuric together. Didn't try going any further.

[Enthalpy]

Temperature range: I dunno. Try and observe.

Separate physically: how? They adhere very well and you don't know how thick they're.

[0xFFFF]

I have boxes of old EEPROMs. I can destroy a few and separate the major components.
I might not be able to separate everything but the exercise and observations will be interesting.

I'll keep the temperature at 100°C for now.

[bubblegumpi]

Thats almost scary you are working with hot 98% sulfuric acid and 70% nitric acid and self admittedly have no idea whats going on. I'm not one of those "you'll shot your eye out!" internet safety police, what you do doesn't affect me. But have you seen what nitric acid does to the blue nitrile lab gloves? If you want to try it out, do it outside because there will be flames. 

How do you know how to work with this stuff if you don't "have any idea what sort of chemistry this is"? But I'm glad you want to learn. I guess its just hard for me to understand because before I do anything that can seriously main or kill me I want to know everything about it. Plus nitric acid is hard for me to get, so I would have to make it at home which require knowing alot about it.

To make gold at home see "codyslab" or "nileRed" on you tube he shows exactly how to do this, and goes over the bit of safety and most importantly how to process the waste so you are not just dumping chemicals down the drain.

[Enthalpy]

It's scary but that's how a good part of the semiconductor industry works, because it demands many skills that aren't available from straight chemists, so you meet in a semiconductor lab people with very different backgrounds, who have to use chemicals not really benign. I know no good solution for that.

You mentioned nitric acid. While I'm not sure that here 70% concentration ignites something, I did hear of the contact ignition of some ethanolamine by concentrated nitric acid within a cleanroom, yes. The colleague hadn't expected this at all, he was shocked.

But if you're scared of nitric acid, it's only because you don't know what else is used there. Gaseous hydrogen fluoride and hydrazine, phosphine, arsine, silane, pretty strong hydrogen peroxide, and so on and so forth. Very few users have a notion of what might go wrong and how.

[0xFFFF]

I was kind of expecting the concerned or condemning posts to appear eventually

Almost scary? I'd say it is scary but as long as you give it the respect it deserves and execute everything with caution... nothing can posibli go wrong.
Before doing anything, I did some research and I discussed what I was going to do with a scientist.
All of the work I do is outside in a very well ventilated area. I use latex gloves (did the research 1st).
I also have a full face mask with a positive air flow coming from a compressor.

I'll have to go through the "codyslab" and "nileRed" videos again. I have seen some videos on recycling but nothing mentioning nitric or sulfuric.

Not sure if I want to set gloves on fire. I watched a few YouTube videos instead.

As time goes by I hope to continue learning more about the chemistry involved.
Making Nitric acid would be an interesting goal. I'm sure I'm a long way off attempting something like that.

[0xFFFF]

I only just discovered pretty blue crystals in the bottom of one of my beakers?!

This is the first time that this has occurred so I'm a little unsure as to why or how this has occurred. I believe what I have is Copper Sulfate. The Copper Sulfate crystals have formed as a result of the copper and nitric acid.
The solution had a more noticeable blue colour to it rather than the usual green I'm used to seeing.

What I did:
I placed a small audio amplifier module in a beaker with nitric acid. The audio amplifier module has an aluminium back plate with copper heat sinks attached. The copper traces were bonded to the back plate presumably using an epoxy layer underneath and a silkscreen on top.
There are multiple silicon dies, bond wires (aluminium?) and resistors (carbon?).

The beaker as far as I can tell contains:
Nitric acid
Carbon
Epoxy resin
Aluminium - No apparent reaction. The crystals were mostly 'hanging' off the end of it and some in the bottom of the beaker.
Copper
Silicon


My 'lab' is somewhat dependant on natural light so I can't take a good photo until the earth has rotated.

Based on the description above would I be correct in saying that I've produced Copper Sulfate?
Am I correct in saying that the Copper Sulfate crystals formed as a result of the copper and nitric acid?
I'm assuming that this has only occurred once because I usually attempt to keep the copper down to an absolute minimum.

[Borek]

No source of sulfates, so it is more likely you have copper nitrate.

[0xFFFF]

Ahhh ok. Thank you.

A little searching led me to these two sites:
http://www.chem.uiuc.edu/webfunchem/Redox/RedoxIndex.htm
https://practicum.melscience.com/experiments/reaction-of-copper-with-nitric-acid.html

So I didn't have a dry beaker after washing it or water somehow got in to the beaker.

[Enthalpy]

[...] water somehow got in to the beaker.

You told the nitric acid is 70% concentrated, so you have an obvious source of water.

Which is an excellent thing, because pure nitric acid would ignite many compounds, maybe the epoxy of your integrated circuits, or your gloves.

You wrote that you can escape swiftly any toxic gas, didn't you? Toxic emanations can occur with nitric acid.

Aluminium, or alumina (which is a white aluminium oxide), in the amplifier module?

The blue crystals could possibly have only a blue surface.