Homebrew PCBs

In practice, the laser is always focused to do work. Otherwise the 
beam is too weak to burn through much. 
I tried to burn through styrofoam with and without focusing. The 
focused beam has a "waist" where it is focused to a tiny spot with 
extremely high energy/area ratio.
The unfocused beam has enough power to go through the foam, but it is 
slow and dirty. Instead simply vaporizing the material, it melts it 
and gives off a LOT of noxious fumes (even with ventilation). It is 
slow. It is not even because of the foam's density variations. Sort 
of like cutting through wood, but worse (faster).
While the beam melts through the denser pellets in the foam, it 
generates localized hot spots that melt surrounding material.

The only way to do it is to use a focused bem with a LONG focal 
point. The longer the FP, the longer the waist part that does all the 
cutting.

With the YAG, you could cut copper by pulsing and checking the light 
return (feedback or reflection) from the material during the pulse. 
There is always scattered light from the point where the laser 
impacts. When much lower scattered light (reflection) is detected, 
then you are through the copper layer. Just move to the next point 
and start popping the copper.

I think the best use of laser would be to vapourize the resist, which 
could simply be a varnish or paint. That way you could easily use a 
low power CO2 laser.

An even easier, (and cheaper) application of lasers would be to 
expose the photoresist directly with a low power UV laser or even 
better (and MUCH MUCH cheaper) is to use a focused UV LED. Just place 
the PCB material on the pen plotter. Replace the pen with an LED and 
go fo it!...


John Myszkowski...
=========================



> didn't know you would have problems with beam dispersion
>   over such a short run hadn't heard that before.
> 
> I was thinking it might not be possible because of the
> depth of the cut and the way the material vaporizes. Thats
> really all the hot wire does is vaporize the material area
> immediately around the wire.
> 
> Oh well learn something everyday.
> 
> Thanks
> 
> Dave