The hard requirement on this project is that it use the PCB as the USB contacts. This restricts the total height of the board + components to 2mm. The tallest components are currently the QFN and caps at 0.5mm. There are many PCB houses that will do thin boards (DirtyPCBs will do down to 0.6mm) but I didn't want to wait too long to find out my first pass was broken since this is my first time on KiCAD and using this particular micro.

So for the first board I left the underside of the connector end bare and put the components on a part of the PCB that sits outside the port. I added an edgemount header that brings out SWD, UART, reset, and boot mode select. I also added an LED off a GPIO because "Hello, world" on a micro is better that way. These changes let me get it fabbed at OSHPark which takes just a couple of weeks to get me a 1.7mm thick board. I also ordered a stencil (OSHStencils), paste, and components.

Still need to figure out what I'm going to use to reflow it. Hot air gun? Skillet? Maybe an excuse to make a reflow toaster?