(UV) Laser for pcb photoresist exposure

Hi, I'm new here, i just wanted to share an idea that came to me, while browing the RepRap wiki.
Maybe it's not novel at all, but i ether got lots of noise or no matches at all when searching for it on the forum.

So, here goes: the idea is to use a laser to define the traces on a standard photoresist-covered PCB-laminate.
On way would be to use a UV-laser (with suitable wavelength) to expose a positive photoresist, and then develop and etch the board the usual way. An option to a laser might be to use a high powered UV-diode with focusing optics to make a small enough dot of light to be useful.

Alternatively, a higher powered laser could be used to cut traces directly into the photoresist, and then etch the board directly (developing not needed). This variant could use either negative or positive resist. The negative would just have to be pre-exposed.

The advantages compared to conventional techniques would (hopefully) be higher precision, very thin traces possible, no (or very little) tool wear, no burr, no need for very powerful laser.

The laser could possibly even be reprapped (http://photonics.tfp.uni-karlsruhe.de/1/a-homemade-uv-laser.html), but it's a bit beyound my current knowledge to say if this feasible. And it's quite dangerous too, not for the faint of heart.

I'm basically throwing this out there to see if it's feasible...

Some questions that i haven't really researched yet:
How much power would it take to expose/cut the photoresist in a reasonable time?
What would a laser (or diode/optics arrangement) with sufficient power cost?
Could a dvd-writer diode be used?

Any thoughts on this is appreciated.

/Andreas

This guy was playing with it for awhile. I don't think he ever managed to tweak it though.

http://reonarudo.info/blog/

anwe79 Wrote:
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> Some questions that i haven't really researched yet:
> How much power would it take to expose/cut the
> photoresist in a reasonable time?

... some ten years ago i've used green LED's with a conic black coated tip, opened at the tip to 0.1 - 0.2mm width as 'light-pen' in a plotter for exposing positive photo-films.

- Here you can use modern UV-LED's
- or BluRay-diodelasers with 50-200mW for positive/negative films
- or 445nm(blue)-diodelaser with 1Watt max. power for exposing and/or cutting/engraving
- or 808nm/975nm-IR-diodelasers with powers of some Watts to some ten Watts of power for cutting/engraving


> What would a laser (or diode/optics arrangement)
> with sufficient power cost?

- UV-LED with driver - some cents
- (salvaged) BluRay-diode with optics driver - some ten $/€
- 445nm-diodelaser with optics and driver - maybe 50 - 100 $
- IR-diodelaser with optics and driver - maybe 200 - 1500 $ (power-dependant)

> Could a dvd-writer diode be used?

- maybe ...

---

Viktor
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I had the same idea about fixing the photoresist with a reprap today, which lead me here and to this post. I think using a small lens and an led would be perfect. I tried a lens from a cd player (high power lens) so the distance between the lens and the board is small but that's ok. I could make a very tiny spot of light on a surface using the lens and LED. These lenses are normally used to make spots the size of a bit on a cd so we know the points of light are small.

My previous experience with making circuit boards is spending lots of time and effort for poor quality transfers to the copper from wax paper or photo paper. I don't have experience with transparencies but I can guess it's not much better. With a printer and a very tiny spot of uv light, I think we could expect amazing board quality. I love the idea of not having to get out a marker or paint to touch up a transfer.

There is probably an opportunity to improve the top to bottom lineup of the board as well. Maybe even a head with a top and bottom light that is already aligned and you print both sides as you go. Just thinking outside the box.

I have yet to build my first reprap but I am sure I will by working on this topic when I finish my first one.

Eric

If the head had a drill built in, the board could be done quickly and with good alignment. I'm not sure about drilling before etching though.

Might need a way to match up the alignment from fixing the photoresist and drilling after the etch, to drill with a reprap too.

Eric