I had a go at it with a flat end mill and am satisfied with the end result. (You can hardly call it a pcb, but therefor also a good small test project 
(size of the part is 20mm x 15mm)
The one in the middle was my first attempt with a 1mm flat end mill. it looks like the feed speed set by flatcam isn’t really honored, or something is a bit wrong with it. Either way, it went too fast and the bit broke (yay).
Second try was on the bottom right: In this case the traces went fine and I just wanted to go for it with a .5mm bit. Went really well and when I loaded the second file to cut it out, the work origin shifted for some reason. And I was too late to stop it so the traces were damaged already. Don’t understand why, will have to have a better look at the gcode files as to what caused it. maybe it was just an error on my side that I didn’t only adjust the z-height for the new bit but also the origin. But I think it’s something with the gcode generated by flatcam that throws the snapmaker off.
Third one worked well and appeared to be a succes.(yay). In this case I did copy the cnc code for the traces and the cutout in one file and ran it as a single job.
Did the last ones with a .04mm stepdown (yes, really that small) .4mm stepdown broke the 1mm bit, but in that job I didn’t notice the speed was way too high as well. I did reduce the speed for the jobs with the smaller bit.
Oh, and flatcam isn’t the most intuitive piece of software for a first time user. The files it produces are not fully compatible with the snapmaker. Doing a run boundary does crash the machine every time.
What software did you use to generate the cnc gcode for the PCB?