Tuesday, 2 April 2013

Etching PCB resist with an LS3020 laser cutter

This time we tried making a PCB with no "filled plane" between traces. Normally we flood fill all the spaces between traces, just so that the ferric doesn't have as much exposed copper to etch away. But out of interest, we made up a PCB with no ground plane to see how it would laser (as compared to the press-n-peel method).

As ever, our designs were drawn in ExpressPCB and we stuck with the usual 0.5mm traces. Then printed to CutePDF and loaded the pdf into Inkscape. Finally, exported from Inkscape as a png at 600dpi.

(remember we'll be cutting away any non-white areas)

The PCB in the top left of the board (in the photo below) is the resulting etch:

The resulting PCB was a nicely etched board. But the traces looked a little thinner than we'd normally get if we used the press-n-peel method. Maybe the laser strength was too high? Who knows - but the resulting traces were - although perfectly serviceable - noticeably thinner than we'd expected.

So we loaded the png into PaintShop Pro, selected all the white areas and expanded by 3 pixels all round. The resulting etch is the board in the top right hand part of the board

This time the traces were just that little bit too thick and in places, despite the image having a pixel or two gap between pads and traces, some traces appeared merged together.
The boards in the bottom half of the copper board were created by taking the original png image, selecting all white areas and expanding by two pixels. The end result looks very similar to the type of board we'd expect using our toner-transfer (press-n-peel) approach with 0.5mm traces.

So with three good boards, we're going to try immersion and sponge/contact etching with ferric chloride to see which gives the best results. Time to get yellow fingers again.....