Having determined that decapsulating integrated circuit packages by resin works but is very time-consuming and energy-intensive, not to mention difficult to clean up after, I decided to investigate two other techniques: ceramic package decapping by heat, and plastic package decapping by hot sulfuric acid.
Also I should note that the techniques I've explored are not suitable for live die analysis. These techniques (possibly the heat decapsulation but definitely the hot sulfuric acid) break the bond wires. I am only interested in dead dies because I like to photograph and reverse-engineer them.
Adventure #2: Heat decapsulation of ceramic packages
This turned out to be almost trivially easy. I also made a video about it.
The equipment needed is:
- A vise with no plastic or paint on it. I used a toolmaker's vise ([HFS Precision Toolmakers Vise 2-1/2"], Amazon, US $61) because I needed it for other machining projects, but you can get any cheap uncoated vise.
- MAPP gas torch (Bernzomatic TS8000KC Premium Torch Kit, Home Depot, US $51). MAPP gas reaches 2000 deg C in air, so is beefy, and better than the crappy little propane torches I tried. The refills are also pretty cheap.
- A piece of aluminum preferably 0.3 inches by 0.6 inches to act as a support for the chip.
Place the chip straddling the aluminum, then clamp its pins in the vise. You should be able to take the pliers and grab the top of the chip firmly. Now (taking away your pliers!) fire up the torch and using the very tip of the flame (not the hot inner part), heat the chip for 20 seconds, moving the flame around to cover the whole top. If the pins glow red, that's fine.
Now quickly turn off the torch, grab the top of the chip with the pliers and just flip it over. That's all it takes.
However, this technique does not work with plastic packages, only with ceramic packages. And, it may not work so well with packages that have windows in them, such as for EPROMs and other UV-erasable devices, since the glass may melt onto the die. In that case, you might try just whacking the seam with a chisel and hoping.
Adventure #3: Hot sulfuric acid decapsulation of plastic packages
Now, you don't have to do it the way I did. You [can do it] with just sulfuric acid, a test tube, and a heat gun.
For this, you will need:
- The [DIY fume chamber] I posted about earlier (US $320 or so, including a fan and ducts).
- 98% sulfuric acid (Duda Diesel, 950 mL, US $13 + 10 shipping). Order this well in advance. Because reasons, this chemical ships FedEx ground, and it took 10 days to reach me.
- Acetone. You can pick this up at the hardware store (US $13/gallon = $3.50/L). It doesn't have to be high-quality. I bought mine from Duda Diesel (because I was buying from them anyway, $8/L 99.5% purity).
- Some flasks and beakers of different sizes. I used a 50 mL flask, a 150 mL flask with a glass stopper, and 50, 100, and 200 mL beakers. I found a set of 5 Pyrex beakers of different sizes from eBay (US $30 shipped) and the flasks I got in a set of 5 of different sizes from Amazon ([213B2 Karter Scientific Glass Erlenmeyer Flask 5 Piece Set], US $17). The glass stopper was from a large kit, but it was a 24/40 stopper and you can get [five for US $12].
- Two 1000mL safety wash bottles, one for distilled water, and one for acetone. ([eBay, Karter Scientific 217H1], US $6 each).
- A bag of 3mL plastic pipettes ([eBay], US $6.50/100).
- A laboratory hotplate capable of at least 300 deg C (eBay, US $60 shipped).
- A glass thermometer capable of at least 250 deg C (eBay, US $40 shipped).
- A box of disposable nitrile gloves (hardware store, US $8/25 pair).
- Tongs for holding hot flasks. I used a test tube clamp ([Amazon], US $7) but I'd prefer something with a little more grip.
- Baking soda for spills.
The procedure I followed was this:
1. Put the entire chip in the 50 mL flask and place the flask in the fume chamber. Do the rest of this in the fume chamber until I tell you to stop :)
2. With a pipette, add 20 mL sulfuric acid.
3. Put the flask on the hotplate and add thermometer. Turn the hotplate on high.
4. Watch the thermometer. At around 90 deg C you will see some black come off the chip. As the temperature rises, the contents will become more and more black. At around 130 deg C you will see fumes in the flask. At this point, lift the flask with the tongs and swirl gently, then put back on the hot plate.
5. When the temperature reaches 200 deg C, lift the flask and swirl gently. Don't put the flask back on the hotplate until the temperature dips a few degrees below 200 deg C.
6. Wait for the temperature to reach 200 deg C again, and repeat for ten minutes.
7. After ten minutes of doing this, remove the flask and set it down to cool. Turn off the hotplate.
8. When the solution has cooled to around 70 deg C, remove the thermometer and slowly decant into the 50 mL beaker. The dregs left in the flask will contain metal bits (pins and lead frame) and the die.
9. Pour the contents of the 50 mL beaker into the 150 mL flask. Stopper it. This is your used acid collection. It can be used a few times.
10. Add about 20 mL of distilled water to the flask. Try to get the sides of the flask also. Swirl it around. Slowly decant into the 200 mL beaker. This is your very dilute acid collection.
11. Repeat the above step: a second washing.
12. You should now have a bunch of metal bits and a die in the flask. You can now take the flask out of the fume chamber.
13. Add about 10 mL of acetone to the flask. Try to get the sides of the flask also. Swirl it around. Slowly decant into the 100 mL beaker.
14. Repeat the above step: a second washing.
15. Pour the acetone from the 100 mL beaker back into the flask, then dump out the flask briskly back into the beaker. The die should go with it. The only reason to do this is to make it easy for you to use tweezers to pick out the die.
Above is my setup in the fume chamber. Approximately from left to right: hotplate, 50 mL flask and thermometer, 150 mL flask and stopper with used acid, bottle of sulfuric acid, test tube tongs, 200 mL beaker of watery acid with some used pipettes, 50 mL transfer beaker, an aborted experiment involving a Buchner filter, wash bottle with distilled water, and baking soda for spills.
I haven't covered a few things. For example, you could put the die in an ultrasonic cleaner and clean it. That involves putting some acetone with the die in a resealable plastic bag and running the ultrasonic cleaner for a few minutes. This gets rid of dust and specks and stubborn bits of plastic.
I also haven't covered disposal. To the watery acid, you can add baking soda carefully until the pH is neutral, then pour down the sink. I'm not sure what to do with the used acid, but I am going to try to distill it back to usable acid again. The acetone can probably be diluted and poured down the drain, or just set outside to evaporate.
Now that I have the capacity of decapping dies from both ceramic and plastic packages, I'm starting [The 54/74 Project]. This will involve collecting and decapping many different kinds of 54xx and 74xx series logic chips, and photographing and reverse engineering the dies. The project page is on the siliconpr0n site, possibly with alternate pages at the Internet Archive.