In this video tutorial, the presenter is removing epoxy packaging from chips to expose the die or in simple words decapping some chips. This involves using fuming nitric acid.
The process starts by milling a precise pocket into the IC using a CNC machine. Carbide tooling is used to cut the glass fiber/epoxy material. A couple of drops of the acid are placed in the pocket, and the temperature is raised to about 100°C. The acid dissolves the epoxy packaging as it sort of “dries”. More acid is added to the pocket every few minutes. After about 10 minutes, the IC is washed in acetone and the acid is reapplied to check if there was still material left on the die. Eventually, it was all cleared away resulting in a nice decapped IC.