Homebrew PCBs

On Wed, Jan 5, 2011 at 1:23 PM, Les Newell <les.newell@...> wrote:
>
>
>
> To remove paint you just need to up the voltage - say 10kV or more. This
> could be generated by a simple car ignition coil driven from an
> oscillator. I have no idea how much paint would be removed on each
> spark. It would definitely be a case of trial and error.
>

Having spent a great deal of time dealing with HV, commonly over a 75
KV, I can tell you that you are likely to have a huge problem with the
selectivity of the spark that breaks the paint/insulation.  Like
lightning, it seeks the easiest path to complete the circuit and with
any variation in the thickness of the paint at all it will tend to
wander around where you're trying to target based on a number of
variables like the thickness, air flow, the electrode shape/wear, and
so forth.  Then there's the issue of current supplied: you must supply
enough current to vaporize paint, not knock tiny holes in it as it
breaks down, but actually remove a significant amount of it.  The more
current expended, the larger the diameter of the spark, which
accentuates your inaccuracy in targeting a specific point.  The
process at best would be inaccurate and slow since if you go too fast
your electrode will heat significantly, pre-ionizing the air within
the gap and adding another variable to the problem; go fast enough and
you get an arc-welder :-)

It's an interesting idea but I believe the amount of time to even get
any kind of result (The setup for routing pulsed HV down to a point
within a plotter would be hazardous to the electronics as it is) is
somewhat daunting.  I would really think skipping the HV part and
doing the resist-scratch-removal process would be faster, easier, and
far more precise.

Larry