WLCSP
This package is very small and cheap to produce. It also has benefits due to the lack of bond wires. Bond wires increase parasitic inductance, and can be a problem for high speed designs.

The downside is that they are very tiny!

The last 5 layers of the Skywater PDK define the layers necessary to build the WLCSP package.
Course feedback
Anybody who wants to learn about ASIC design who's never done it, this was a great introduction. I really enjoyed the course, this has been a great learning experience.
Tom Gwozdz (digital course)