Homebrew PCBs

> And while discussing methods of putting holes in boards, don't forget
> that you can laser thru the top copper, all the fiberglass and down
> TO, but NOT THRU the bottom copper.  Makes cool blind thru holes.
>
>

That laser thing is really fascinating... bit expensive though...

How do they know where they are? i guess the reflection from copper/fr4 is 
different?
and how does it work to cut through glass / epoxy?
i mean that are quite different materials, how can you blow a hole in 
there with a laser?

ST