laserable coating for PCB etching

[brian257]

I need to etch some prototype P.C. boards this weekend and I am looking for some type of coating I can put on the boards to selectively laser off as an etch resist. I have tried a few different types of thin tape and other coatings with not great results. Seems everything leaves some type of residue on the board even though it looks like the laser took it off cleanly so the boards do not etch well. So far my best results were from a few thin coats of engine enamel, but it is still not perfect. A varnish might work good, but will be hard to see if I got the laser power settings correct since it would be clear.

Yes, I realize I can use ceremark or other specialty types of coatings made for lasering, but I need something I can find at a local hardware store. Any suggestions?

[jgecik]

I've never used the cutter for this application, but you could try contact paper. Cover the board with contact paper, laser out your circuit on low power/high speed (just enough to cut the paper) and peel off the little bits where you cut. There may be some residue, but some light wiping with Windex and a paper towel should take care of it.

[Rob_hoppe]

Did you try plastidip?

Rob

[parsifaldruddle]

I keep seeing posts about how well auto lacquer works. 2 pretty light coats - just enough to block the etchant - and maybe a small radiative heat source to cure it. I think the guys with the best results are curing - not just drying - the paint.

*** I must mention that copper is an excellent reflector of 10.6u wavelength radiation and is used in CO2 laser optics as mirrors to good effect ***. Granted, the work you seek to accomplish requires low power, but it is low, focused power directed at (for it's wavelength) a highly reflective surface. Don't do it.

Use your laser printer, transparencies and photosensitive pcbs, use your laser printer, transfer paper and a t-shirt press, even get yourself a UV diode laser and stick it on the side of your laser head and use that on photosentive pcbs, but do not shine a CO2 laser beam at a shiny-yet-masked Cu surface.

A diode laser in one of the 2030 or 4060 lite stages & uv sensitive pcbs would be very handy, I think. Couple-few guys on the interweb barkin' about it - sounds like it's gonna be peachy. Me, I started doing boards in '82 - vellum, tape, camera, UV box, carbon-tet vapor tank & ferric, so I am partial to photoetch. But I've had good results with the toner transfer - I just bought a 9x12 heat press to start back up again.

Seems to me by the time folks are done waiting for paint to dry properly, lasering it, etc - laser printer and heat press might be faster - like under 4 minutes from print to press to ready for cleaning and tinning. Laminators require more time to build heat in the copper due to limited contact area and I don't like multiple passes that can skew the transfer - meh - tried it, found it annoying. Heat presses gotta be warmed up, but then it's like 60 seconds to get the toner to transfer (did a couple tests transferring to alu can while waiting for the blank bds to arrive - worked fine).

[brian257]

Thanks Pars. I agree with most of what you said, but these boards are thermalclad for high power LEDs so they are a very thin insulator between the copper and a thick aluminum backing. Tried the toner transfer, but board too thick to go through laminator and iron did a dismal job. I don't have any sensitizer and developer to photo etch the board and the chemicals can't air ship so looking for a fast solution.

I did wind up trying with the blue engine enamel. It works good on thick traces, but not so much on the very thin traces on this SMT board. I already have a proto on FR4 PCB, but I need to test with all driver electronics mounted and getting hot on the final board before ordering a few thousand dollars worth and prototype quantities on the thermalclad are over $500 and at least a week lead time.

[parsifaldruddle]

Gotcha - just be careful.