I isolation route quite a few PCB's. The copper is pretty soft stuff and will, if given half the chance, make incredible burrs. I have found that the RPM needs to be as high as possible and the depth of cut shallow. I only use moderate to slow feedrates and machine dust.
But the most important thing by far is that the tool is sharp. If there is any shiny reflection from the cutting edge when viewed with an eye glass then the the tool is dull and needs replacing.
I use solid carbide 30 degree points and they don't last long, especially after they have been into fiberglass.