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
The course itself is very self sufficient, and on top of that you have the community behind it. People are happy to help and review your work. I would definitely recommend the course!