Kill App, part II: The PCB burning nuclear LASER-O-DEATH

[Evan]

I declare total victory in the quest for a very simple way to make conventional etched circuit boards using a small CNC hobby mill and a cheap 200 milliwatt laser.

I built a regulated power supply for the laser to run it at maximum power. It greatly increased the output with no apparent ill effects since it is designed for use at 6 volts DC. I also had installed a heat sink to ensure it doesn't overheat.

I have made a video of the operation that shows just how very effective the laser is at burning vinyl. It actually produces a very realistic miniature mushroom cloud when it is switched on the work. I didn't even see it until I reviewed the video. This is a frame from that video. [grin]



The video: 3.5mb

http://ixian.ca/video/laserburn.wmv

The secret of the process is the masking material. It is black sign vinyl which is easily obtained at any sign shop, probably for free if you ask for some scraps. The board is polished and then masked by rubbing down the adhesive vinyl making sure that there are no trapped air bubbles. If you have a bubble lift the film up and rub it back down making sure to NOT to put your grubby fingers on the board or underside of the film.

The laser cuts fast and to avoid overburning the cutting speed must be at least 10 ipm. This will vary depending on laser power and the thickness of the film. The laser must be very carefully focused to the smallest possible point. To interrupt the laser beam during rapids I built a simple adjustable limit switch on the Z axis that senses when the Z moves up to traverse. This activates a solenoid that operates a flag to block the beam. The flag has a small piece of corundum emery paper as the beam stop and is impervious to the laser beam. It also is very non reflective. The video shows how the beam interrupter works.

Here is another nuclear aftermath picture just after the laser finished the board.



Peeling off the vinyl is an easy job if the burn was deep enough, which it was.

This is the board ready to etch. I can't wait to try it on something more complex. I know it will work very well and look forward to making some boards the very easy way.

[dp]

Very cool, Evan. How are you cutting off the beam on "pen up" events? Yikes! Never mind - just saw the solenoid solution. Damn clever!

[alanganes]

Yikes! That is awesome, Evan. Nice work!

Perhaps a similar laser retrofit could be adapted to replace the pen in an old pen plotter for those of us without the neat-O CNC mill. Hmmmmm....

Thanks for posting that.

[chipmaker4130]

Sweet indeed. Perhaps on your next iteration you'll be able to punch the component lead holes as you go!

[dp]

Sweet indeed. Perhaps on your next iteration you'll be able to punch the component lead holes as you go!

Probably no need as the same machine can drill them, too.

[Evan]

Perhaps a similar laser retrofit could be adapted to replace the pen in an old pen plotter for those of us without the neat-O CNC mill. Hmmmmm....

Precisely what I will be doing soon. I have an old HP flat bed plotter and all it needs is a couple of low power stepper drives. Now I have the means to make small but complex boards easily so the plotter project is moving to the front. The laser head on the pen is very small and light and can probably be handled by the plotter pen mechanism unmodified. It will require a lightweight heatsink.

[Evan]

Probably no need as the same machine can drill them, too.

That is the next item to be fitted to the mill. I will be installing a simple laser pointer at a precise offset from the spindle axis. It will be focused to a pinpoint at a specific height from the table so that all I need to do to align a board for drilling later is to line up the laser with a pair of reference marks on the board and input the offsets to the DRO positions.

[dp]

Yikes! That is awesome, Evan. Nice work!

Perhaps a similar laser retrofit could be adapted to replace the pen in an old pen plotter for those of us without the neat-O CNC mill. Hmmmmm....

Thanks for posting that.

Exactly what I was thinking. Here's what a 200mw laser looks like - about 1/4" diameter. It would easily fit in a plotter pen shell.

[Jim Shaper]

Evan, why not dimple a scrap with a sharpened in the machine punch (so it's perfectly centered in the spindle), and then calculate your work offset from lining up the laser from the travel to reach that point?

You'll have the exact travel needed to backtrack to your workpiece coordinate zero.

[tyrone shewlaces]

The success you've been experiencing with this has made you giddy.
I could swear you've rediscovered your sense of humor! You're not at all the crusty PITA we came to know and... well know, hehe.

And for good reason too. This has an extremely high cool factor. What's not to love about it? Two or three (so far) great applications that are extremely economical to pull off. I must tip the metaphorical hat that I'm not actually wearing to you. Good job sir.

Question: would that puddle of thick smoke affect the effectiveness of the laser enough to warrant a vacuum or ventilation of some kind?

Too bad those flatbed plotters aren't sitting around in basements like inkjet printers are. You could whip these things together, make 'em for sale and be a dozennaire!

[Evan]

Unfortunately the exact point of aim of the laser varies with the focus and the height above the table. This is because I have the laser off tram slightly so that a specular reflection doesn't reflect back up it's own snorkel. That could damage the laser chip at this power level. I will need a separate alignment laser as a consistent reference.

[Evan]

I didn't expect that much smoke, a fan is in order. Both to keep the work clear and to prevent the smoke from fogging the laser optics.

As for other applications, it does an excellent job of cutting high density thin gasket foam about 1/16 thick. I am sure it will cut deeper than that as it cuts this stuff as fast as the vinyl. It was a bit too hot for the really fine detail. I should insert some dwell time in the off position.



It also works on chocolate bars. I am certain a chocolate bar maker would be interested as this would only take a millisecond with a high power scanning laser.

[dp]

What kinds of chemistry comprises that smoke cloud, anyway? I'm certain you've already thought about that, but it's worth sharing with the rank and file.

[Evan]

The smoke is the product of pyrolytic non flaming degradation of the thermoplastic. As such it contains very little soot. The white smoke is mainly water vapour with a trace of zinc fume and calcium carbonate reacted with hydrochloric acid. This type of PVC contains a food safe stabilizer made from calcium/zinc. That is present to neutralize the hydrochloric acid formed on heat degradation. The smoke isn't overly toxic although some PVC materials are stabilized with either cadmium or lead. This is not. You can tell by the colour of the fumes. White is zinc, yellow is cadmium and lead is transparent.

[wierdscience]

Nice!