Wednesday, 3 April 2013

Laser etching PCBs update. Don't bother!

We've made about half a dozen different PCBs using our laser etching and laser cutting methods for creating the etch-resistant mask. And while creating the actual mask is relatively straightforward - compared with press-n-peel or exposing photo-sensitive boards to UV - lasering the mask seems to create all manner of other work around it.

For example, when you've laser etched paint off a board, the exposed copper could have a sticky coating over it (from where the paint has been vapourised by the laser). You need to remove every trace of this before etching (else it forms a transparent barrier which also acts as an etch-resist, but just looks like the copper isn't reacting to the ferric).

You need to remember to flip the design so that the through-hole parts are mounted the right way round on the final board (the act of using toner-transfer automatically flips the pcb design so the ExpressPCB design can be used without further editing). We've already made a couple of useless boards by forgetting to do this first!

We found that the original bitmap/png created a board with very narrow traces - to prepare the image so that it etched with nice chunky 0.5mm traces (as designed in ExpressPCB) involved quite a bit of extra image manipulation before sending to the laser cutter.

You need to remember to turn the laser cutter power down so that it doesn't destroy the image (or in a worst case, the copper board itself). But too low and the laser only marks rather than cuts the paint. Too high and too much paint is removed, making your traces much thinner than required - far too high and the copper board gets ruined!

But even when we've done all this extra work, got an etch-mask we were happy with and cleaned our latest boards thoroughly, they took an unusually long time to etch (using both the heated immersion method, and sponge/contact method of etching)

Although we're etching away more material than usual (we deliberately left the filled planes off this design to see how the laser would cope with etching away large sections) it still took longer than we'd hoped, to complete these boards. And when we finally scoured the etch-resist away, there were still a few areas which hadn't etched completely:

At first we were really excited about the idea of laser etching PCBs - it seemed such a cool and easy way to make the boards. And while getting the mask etched was relatively simple (once the laser settings had been worked out, the image amended and mirrored correctly), all the extra work around making the PCB actually workable after taking the board out of the laser cutter, has lead us to admit - albeit begrudgingly - that maybe press-n-peel isn't such a bad way to make PCBs after all.

We're off to PC World this evening to pick up a cheap b&w laser printer so we can create these boards again using the Old Blue Stuff and compare the results.

But our experience with laser-etching PCB masks to date has been - don't.

Maybe we're just really good at press-n-peel (some people hate the stuff) or maybe we're just unusually rubbish at using our laser cutter (Steve swears by it for making pcbs) but for us, the total amount of time taken to get a working PCB is far less if we stick to press-n-peel (not counting the time it takes to drive to PC World and buy a laser printer!)