Homebrew PCBs

John,

The cones on our machine were just long enough to accept a screw in 
nozzle that put the gas or air output in the focal plane. The screw 
in nozzle was made of brass and came with different hole sizes but 
the one we used the most was .060 inches. When they wore out I would 
put them in a lathe and bore the hole to a larger size, face off the 
tip and use them again.

The air or gas pressures were not very high, probably around 10 to 20 
psi. You can experiment with this pressure for best results. Your 
cutting speed and edge quality will be greatly improved using the 
compressed air.

Your moving XY table is the best way to go because trying to align 
the beam with the flying optics would be difficult for a hobby setup.
The gantry table allowed a smaller machine footprint but with very 
complicated alignment procedures.

I have never tried any kind of engraving or etching of PCB laminates 
with a laser but your idea would probably work. Some of the big PCB 
lasers use a type of "shadow mask" to drill all of the holes in one 
operation. The mask is kind of like a big negative film or metal 
plate with clear holes where the laser power comes through and burns 
through the laminate. The available laser power is divided across all 
of the openings to form the holes. I saw something like this at the 
NEPCON show several years ago and it was quite expensive, more than 
$600,000.

I would also like to get some high power laser diodes since I have 
several really nice CNC controlled XY tables that could be 
retrofitted. That would be a great machine to have around for cutting 
plastics and wood.

I use dry film photoresist and silk screening for making boards and 
will probably not try the laser method. Most of my boards are short 
runs on photoresist and I always keep some spare coated panels handy 
for a quick job. Any large jobs are run with screen printing.

Tom

--- In Homebrew_PCBs@yahoogroups.com, "John Myszkowski" 
<myszka_us2000@y...> wrote:
> Hi Tom,
> 
> I wouldn't mind the thinner kerf, also the power/area would 
increase 
> as well I suppose. 
> 
> The air funnel idea is a good one. I've been thinking of 
implementing 
> something like that. How much air pressure/flow would you suggest?
> 
> I move my work in the X-Y direction (modified plotter). I want to 
> avoid as many optical paths as possible. In other words, the less 
> bends the better. I have too little power to spare as it is.
> 
> The PCB resist etch idea will probably work fine. All you need to 
do 
> is vapourize the thin resist layer. The copper won't be touched 
(for 
> obvious reasons). An acrylic cage keeps any stray beams inside the 
> work area.
> 
> I would love to get my hands on one of the high power laser diodes. 
> They would be perfect for resist etching. It would keep the overall 
> size of the machine to a desktop size. You could probably retrofit 
> any XY plotter to work with a laser "pen".
> 
> John M...
> ==============