What is the ideal tool shape for milling PCBs. The copper is about 20 microns thick but you cant expect the PCB to be mounted 100% flat. So I guess a cut depth of about 1/50inch would be OK. The milled path can vary be 0.01 to 0.03inch thick. Due to the thin copper layer, using a flat end mill causes a lot of edge unevenness.

Check out http://www.thinktink.com

Think and Tinker sell bits specifically designed for PCB milling.

Neomiller,

There is no "best" design for an all purpose pcb etching bit. The tool shape depends on the application, the resolution that you are trying to achieve, and how much you want to spend on a bit.

The cheapest hi-resolution bits around are "V" groove engraving cutters. They offer a good combination of tiny tip geometry (typ. 0.125mm), high strength, and reasonable life (50 to 100 meters in 37micron copperclad). Their disadvantage is that they require that either the board be held VERY flat or that you use an engraving machine equipped with some kind of surface following appliance (see LPKF, T-TECH, EverPrecision, MITS, Think & Tinker).

Traditional end-mills that have been tuned for milling copperclad remove the necessity of surface following but at MUCH higher cost (go to: http://www.precisecut.com and look at the PreciseBit non-ferrous end-mills), shorter life, and lower milling speeds.

As far as degree of penetration, you generally want to impact the substrate as little as possible. Just cut deep enough to remove the copper and the underlying adhesive layer (50 microns in 1 ounce copperclad and 33 microns in 1/2 ounce copperclad)