Direct exposure on photosensitive PCB?

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Is it possible to build/modify a plotter and reliably expose a PCB directly?

I know that plotters are used to expose photo-masks for production PCB runs, are they more sensitive to exposure then the PCBs?

I would consider building a plotter and use a UV LED to expose the PCB.

Its for hobby work, so if it takes a while to expose the board, its not such a big deal

Anyone have any thoughts on this?

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I think it would take too long time to be of any practical use, except very small boards. Perhaps use the plotter to print resist on the board instead.

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Nice idea ! You'd need some optics though for focus. And if you need small tracks/ smd's like SOIC and TQFP, you need very good optics :) That will be the challenge I guess.

There is a group on Yahoo for homebrewed PCB's

I use a inkjet-printer to print on calque paper, and then expose the pcb using 72 UV-leds. Other freaks here have good results with laserprinters. The use heat to transfer the toner to the bare pcb.

If you do a search in the OffTopic, you'll find a thread (or more) on this subject.

Nard

A GIF is worth a thousend words   She is called Sylvia (2018), lives at Mint18.3 https://www.linuxmint.com/

Dragon broken ? http://aplomb.nl/TechStuff/Dragon/Dragon.html for how-to-fix tips

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CountZero wrote:
I think it would take too long time to be of any practical use, except very small boards. Perhaps use the plotter to print resist on the board instead.

Plons wrote:
I use a inkjet-printer to print on calque paper, and then expose the pcb using 72 UV-leds. Other freaks here have good results with laserprinters. The use heat to transfer the toner to the bare pcb.

Though I wouldn't know where to find that/those threads, these things have been discussed several times - as recently as Q1 of 2007,

In that thread, I proposed a plotter that would print resist directly onto the copper clad. I haven't made any progress on it yet. Heck, I haven't even considered starting on it yet.

If you do start on something along these lines, keep us posted as to your progress.

You can avoid reality, for a while.  But you can't avoid the consequences of reality! - C.W. Livingston

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A UV LED doesn't produce anything like enough power to do that in a reasonable amount of time. A UV laser might work, though.

Leon

Leon Heller G1HSM

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I think there are some people at the local university electronics club that have experimented with plotter and a LED. But that was before there were UV leds available, heck, it might have been even blue leds were available.

- Jani

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For an example of direct plotting see this: http://web.telia.com/~u85920178/...

Also, on cnczone.com there is an extensive thread on modifying inkjet printers to print on copper clad boards.

Edit and here is the link: http://www.cnczone.com/forums/sh...

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I have done both laser on paper to be ironed onto the PCB, and laser transparency films for sensitized PCB.

Using the plotter to draw the resist occured to me, but I wasn't sure if the markers would stand up to the length of time it would take to draw the board.

Plons: how long is your exposure time with 72 LEDs?

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Quote:
Plons: how long is your exposure time with 72 LEDs?
13 minutes. Link follows .... (updating webpage)

Done. Start of the story
http://www.aplomb.nl/TechStuff/PCB_s/UVsource_PCB.html

and the 72LED-version:
http://www.aplomb.nl/TechStuff/PCB_s/PCB2/PCB2.html

A GIF is worth a thousend words   She is called Sylvia (2018), lives at Mint18.3 https://www.linuxmint.com/

Dragon broken ? http://aplomb.nl/TechStuff/Dragon/Dragon.html for how-to-fix tips

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I think PCB photoresist is way too slow for a direct photoplotter. If it takes 13 minutes to expose a whole board, then even though light focussed on a small point will be more intense, it's still going to take a very long time. Photoplotters use litho film, which is pretty slow by film standards, but would be fully exposed by 5-10 seconds of normal room lighting. The plotters use a seriously bright halogen lamp, 50 watts or more - the brightness is synced to the plotting speed, for constant exposure. A bright blue or white LED would do, but it would be very slow by comparison. Plotters also use an aperture wheel, like a carousel of ready-made shapes, rather than writing directly on the film with a small spot. That's how they handle fine detail. The apertures are plotted on litho film, several times actual size, in a separate operation, then loaded on the carousel for the main job. The light shines through the aperture and the plotter optics reduce the image to actual size on the film. It's quite complicated.

Here's a link to a tutorial on Gerber files, the industry standard photoplotter language. Strangely enough, Gerber doesn't make PCB plotters any more, but their original plotter language is still the standard after more than 40 years.

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Nobody uses photo-plotters any more! They all use laser-plotters these days - much faster and no aperture wheels are needed. They mostly use Gerber files, still, although ODB+ is getting popular and has lots of advantages over Gerbers.

Leon

Leon Heller G1HSM

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Quote:
Nobody uses photo-plotters any more!

I thought not, as I couldn't find a picture of one. You could hardly get same-day turn round on a PCB job when it took half a day just to prepare the aperture wheel. They still want the aperture file, though. The laser still plots on film, right? Not directly on the PCB?

I had actual hands-on with a Gerber photoplotter when I was at college, but I haven't been inside a PCB shop now in more than 15 years.

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Yes, they plot on film. There are a few systems (LDI) that plot directly on the PCB.

Leon

Leon Heller G1HSM