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
I’d absolutely recommend this course even if you've never done hardware design. We all have a phone with a couple of gigahertz worth of compute power in our hands but I don't think many people know exactly how that works.
Fran Gonzalez (digital course)