Originally posted on my Instagram account, copied here as backup
🌟Chip photography 🌟
🔶 Getting rid of the epoxy – failures 🔶
I can’t mention enough times that getting rid of epoxy is absurdly difficult. This material withstands bathing in acetone, dichloromethane or chloroform even after a month. It can stay in a jar of concentrated sulfuric acid or concentrated nitric acid or concentrated hydrochloric acid or even a mixture of them for weeks – or until the lid of the jar corrodes from the fumes. Nothing. And it’s not that the acids are bad. The paint might fall off but the epoxy is like new. They should start building houses, floors, etc from epoxy – it will last anything.
Mecanical pressure is impossible since silicon is actually quite brittle and harsh handling would leaves you with shards. A painfully slow process would be use sand paper to grind it away. It would take hours. As a bonus, one needs some special diamond lapping films that are so fine that the beautiful silicon doesn’t get ground away, too. Once, after several hours of grinding, two of us taking turns, we reached a bit too far… On another occasion we were more careful and managed to remove most of the epoxy, while the silicon was intact. The problem is that by doing the back-and-forth grinding motion, the pressure applied on the chip is not even and you end up grinding away the corners while in the middle there are still leftovers of the copper plate which the chip lies on.
In the picture there is a chip of a controller of an SD card. The thing is really tiny, less than a centimetre. Some of the bond wires connecting the chip to the rest of the components on the circuit board are missing. I can’t remember how it was opened but most likely with boiling sulfuric acid.
This should give a hint about the problems. But given that I can show so many photos of chips, then there has been success, too. That will come tomorrow.(originally posted on 30.9.2020 on my Instagram profile)