Both Cornelius & myself have what’s known as the $400-ish ‘eBay 40W laser’: https://www.google.com.au/search?q="ebay+40w+laser"&tbm=isch that have a bed size of roughly an A4 piece of paper, aka the 3020 laser (3020 = 30cm x 20cm).
I got my first one about 5 years ago, there’s plenty of info on the ‘net about these now.
I’ve also got the next size up which is the 50W version with a 700x500mm bed.
Both are CO2 lasers that output infrared light, these will cut organics (wood, plastic etc) but not metal. They operate at the wrong frequency to cut metal, you need what’s called a YAG laser that has a shorter wavelength (still IR).
That’s why they’ll burn the paint, but not the copper. One of my machine actually has mirrors made from copper in it, copper is very good at reflecting IR.
As mentioned depending on how much power you output, the paint will either vaporise exposing the metal underneath, or burn leaving a black mark on the metal, as per these links: currency: https://dl.dropboxusercontent.com/u/31090134/Laser/2016-02-04%2008.50.28.jpg, https://dl.dropboxusercontent.com/u/31090134/Laser/2016-02-04%2008.53.59.jpg, https://dl.dropboxusercontent.com/u/31090134/Laser/2016-02-04%2008.51.42.jpg.
I did do some business card holders where I left them painted black and vaporised the paint, so shiny lettering on a black background, but I never took any photos of those. That’s what you’d do for PCBs.
I doesn’t have to paint, lots of stuff will work but paint is cheap and easily available.
I don’t have any experience with UV or visible light laser diodes in the 2W range you often see people playing with.
Tony
when you say "burn it off with a laser' what laser are you using?
maybe a cnc machine?
dave
You don’t need high temp paint, I think anything will work. I recall reading a recommendation to use water-based polyurethane (clear top coat) as it apparently burns off without leaving a residue. I’ll give that a try one of these days.
There’s no problem repainting the board after etching and using that as a solder mask, all depends in how enthusiastic you want to be. You’d need to prepare another image so the laser can clear the pads.
One page (or maybe Youtube video) that I can’t find did talk about using the laser to drill the holes after etching. The conclusion was that it wasn’t worth the effort as the holes were of poor quality. Pretty sure that was in FR4. And of course that’s another image you’ll need to prepare.
Surface mount means you don’t need many holes anyway, but a solder mask would still be handy. You could burn the component layout into it as well.
Might need to try this one of these days.
Tony
Hang on... I don't think everyone understand the idea here, which is already working just fine for at least some members (who I would REALLY love to see pictures from, BTW Tony).
1. Clean PCB blank and spray with high temp black / dark paint.
2. Laser at low power / high speed to burn away paint around traces (isolation) or raster for removal of larger areas.
4. Leave the paint / melt in place over the traces (as soldermask) and Laser again at higher power, to burn away paint / melt from solder pads. In fact... spray the etched board again with green paint (or whatever color) and laser that clear off the pads.
5. If you etched out a hole in the center of each through hole pad, and have a high enough power laser, you might be able to laser cut your holes through the FR4.
Now you have a nicely protected PCB. Don't tell me the paint can't manage the solder heat because there are very high temp paints.
This REALLY sounds to me like something worth trying.
