For those of you who may not know, “decapping an IC” refers to removing the epoxy package that insulates and protects the sensitive microelectronics inside so that you can see what’s actually going on under the hood. For years, I worked with electronics and ICs while having no idea what was actually going on inside of those mysterious little black monoliths with feet.
I thought it would be interesting to try decapping some chips. This involves using fuming nitric acid, which also seemed fun, so I thought I would give it a go. The process starts by milling a precise pocket into the IC using my CNC machine. I used carbide tooling to cut the glass fiber/epoxy material. I then put a drop or two of the acid into the pocket, and raised the temperature to about 100*C. The acid dissolves the epoxy packaging as it sort of “dries”. I added more acid to the pocket every few minutes. After about 10 minutes, I washed the IC in acetone, then reapplied acid if there was still material left on the die. Eventually, it was all cleared away, and I had a nice decapped IC.
Once he had decapped the chip, Ben was anxious to look at it under a scanning electron microscope. He decapped common 555 timer chips. With a relatively long time constant on the oscillations of the chip, he thought it’d give him a better chance to actually see visual evidence of the circuit in action.
Back in 2009, on Collin’s Lab, Collin took a stab at decapping through the more common brute force method of torching the package. You obviously don’t end up with a circuit that you can probe, but you at least get a chance to see the teeny electronics hidden on the die inside.