Recently, I've been working on setting up my lab for decapping ICs for the purpose of reverse engineering and future invasive attacks. Here are some notes from my initial round of using sulfuric acid to perform the decap.

DISCLAIMER: I am not trained as a chemist. This experiment is dangerous. Perform your own risk assessment before repeating. Repeat this experiment at your own risk.

Materials

• Glass beakers (one 50mL, one 250mL, and one 1000mL)
• Watch glass
• Sulfuric acid drain cleaner. I used "Liquid Lightning" brand which was purchased at a local Walmart. This product is a clear liquid with no dyes. It is thick and viscous and probably at least 90% concentration. I have not attempted to determine the exact composition (including possible inhibitors).
• A cheap kitchen hotplate with no stirring capability, purchased from Amazon

That's it! There is actually very little equipment needed if you only want to completely dissolve the plastic package on a chip and leave only a bare die. However, the following additional items are recommended:

• Sand
• Baking soda
• Type-K thermocouple
• Beaker tongs

And finally, the following safety equipment is required:

• A cheap box fan used to exhaust fumes.
• A full face respirator. These two items are used in lieu of having a proper fume hood.
• Chemical-resistant gloves

Procedure

1. Prepare the 1000mL beaker by filling it with about 250mL of tap water. We will need this later.
2. Place the chips to be decapped into the 50mL beaker. Caution: If the chip package is physically very large, it is strongly recommended to mechanically trim it to just the material around the die. I currently have not tried this, but others have recommended either carefully grinding until bond wires are visible or grinding the back side of the package until the paddle the die is attached to is visible.
3. Pour some sulfuric acid drain cleaner into the beaker. Caution: Do not fill the beaker more than one-quarter with acid. Otherwise there will be a large risk of the acid bubbling over and overflowing out of the beaker.

4. VERY VERY IMPORTANT: Place the 50mL beaker containing the ICs and acid inside the 250mL beaker. Optionally place some sand into the large beaker to improve thermal transfer.

   If you do not do this, you run the risk of hot sulfuric acid overflowing out of the beaker and landing on the surface of the hotplate. Because this cheap hotplate is intended for the kitchen, this hot acid will instantly react with some plastic coating on the hotplate and produce a huge cloud of probably-toxic white smoke. This will leave a detectable odor even after several days of blowing air through the room with fans. Depending on your living situation, this will also escalate the problems with that one other housemate that you are not on speaking terms with.

5. Place the two nested beakers slightly off the center of the hotplate. Cover with a watch glass.

6. Ensure the fume exhausting box fan is turned to max speed. Turn the hotplate temperature to "MAX" and turn the hotplate on. Occasionally monitor the temperature using a thermocouple. I was monitoring the temperature by poking a thermocouple into the gap between the beaker and the hotplate (which probably overestimates the actual temperature of the solution).
7. Initially, not much will appear to be happening. However, as the acid nears its boiling point (with the hotplate temperature almost at 400 degrees C), the mixture will suddenly begin bubbling vigorously. If it looks to be going out of control, immediately shut of the heating. Otherwise, leave the mixture heating for about five minutes. During this process, white fumes are emitted. These are likely sulfur trioxide. Avoid coming into contact with them. At this point, you must be absolutely sure that the respirator is properly sealed against your face and that the box fan is blowing the fumes away. If you somehow determine that this is not the case, abort the experiment and run away as fast as you can.

8. Once the chips look sufficiently dissolved, shut off the hotplate. Wait for the apparatus to cool.

   If you are in a hurry, you can remove the beakers from the hotplate once touching the top of the large beaker no longer burns your fingers. This will make cooling slightly faster because the surface of the hotplate has quite a bit of thermal mass. Absolutely do not attempt to do this unless the hotplate temperature is below about 100 degrees C.

9. Once everything is sufficiently cooled, carefully pull the small beaker out of the large beaker. You should definitely use beaker tongs for this. If like me you do not, you risk spilling the contents of the beaker onto the carpet because you did not get a good grip on the beaker. If this happens, quickly pour baking soda on it to neutralize it.

   Very slowly pour out the spent acid into the 1000mL beaker that was filled with water. Make sure to avoid any splashes. Because we are pouring a concentrated acid into water, use a huge beaker with a huge amount of water (but still significantly less than the maximum volume of the beaker).

10. Because the waste water and acid solution is still acidic, it is recommended to neutralize it with baking soda. If you do this, make sure to add the baking soda slowly or else the solution will spill out of the beaker. (This is another reason why this waste beaker is 1000mL.) However, if you have an antagonistic relationship with your landlords like me, you might skip this step and just pour the waste solution down the drain with the tap turned on to further dilute.

11. It should now be possible to rinse out the small 50mL beaker with water and search for the freed silicon dies. If for some reason some dies did not get freed, repeat the decap procedure until they are.

Results