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'[EE] Plotting an image via laser onto photoresist '
2007\05\01@054648 by Picbits Sales

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Heres the theory .......

While browsing some other forums I came across someone who stripped a dvd recorder and found the laser head could put out around 250mw of power - enough to melt plastic/burn paper. Further investigation showed these laser diodes are good for between 80mw and 250mw output depending on the dvd burner.

The optics on these allow a fine focus

If photoresist boards can be "influenced" by these high powered lasers then it could be a cheapish way of "printing" directly onto PCBs.

Thoughts are to either have a rotary indexed table or maybe reverse engineer a cheap laser printer and pass the board through using the printer optics to raster print the image onto the board.

Anyone know what happens to photoresist under a moderate power laser beam ?

Dom

2007\05\01@063846 by Tony Smith

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{Quote hidden}

The resists are UV sensitive, what wavelength are DVD lasers?  Aren't they
infrared?

I guess you might be able to burn the resist off, but that's not quite what
you want.

The alternative is to use the laser directly onto film, develop & use that
as the mask.  This has been done forever, I used to make barcode masters for
printers like this, the laser was controlled by a BBC Micro, of all things.

As far as mechanicals, the usual method is to bounce the laser off a mirror.
I've seen film wrapped around a drum and rotated, with a mechanically
scanned laser (basically what you've suggested), or an X-Y table with the
laser fixed overhead.

The mirror method is the best.  Mirrors don't have much mass, so the 'scan
rate' is fast, and the amount of movement is tiny.  Bit tricky to get
accuracy though.

Tony

2007\05\01@101436 by Neil Baylis

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> If photoresist boards can be "influenced" by these high powered lasers then it could be a cheapish way of "printing" directly onto PCBs.
>
> Thoughts are to either have a rotary indexed table or maybe reverse engineer a cheap laser printer and pass the board through using the printer optics to raster print the image onto the board.
>
> Anyone know what happens to photoresist under a moderate power laser beam ?
>

The laser from a DVD burner most likely won't have any effect on the
resist. It's wavelength is about 650 nm, whereas the resist is
sensitive to UV. You may have luck if you were to use the laser from a
Blu-Ray burner, but that will set you back many hundreds of dollars.

The guts from a laser printer won't cut it either, because they use a
much lower power laser, and it's 780 nm, which is even further from
the seisitivity of the PCB resist. In addition, the spot from the
laser printer moves very fast across the surface, so will never stay
in one place long enough to affect the resist, unless you were to
write the same scan line many thousands of times before stepping on.
It might be possible to istall the laser from a Blu-ray burner into a
laser printer.. but then all the optics would be wrong and the beam
would need to be refocussed and realigned somehow.

I think a more promising route is to use a much higher powered laser,
and find a positive acting resist that hardens with heat, or use a
resist that the laser selectively ablates. I'm building such a system
at the moment, using a CO2 laser, but it won't be functional for a few
more months.

2007\05\01@105618 by Mike Harrison

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On Tue, 1 May 2007 07:14:21 -0700, you wrote:

{Quote hidden}

Why bother ? I can't see any benefit in doing this - printing artwork on tracing paper on a laser
printer and using a conventional UV exposure box will always be so much quicker and cheaper.
Plenty of info here : http://www.electricstuff.co.uk/pcbs.html

2007\05\01@114650 by Robert Rolf

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What is so difficult about printing the pattern onto clear film
(overhead transparencies) and make a contact print exposure of the resist?
It would be FAR simpler and cheapper I would think. (and faster if you need multiple
boards).
The sun is a free source of sufficient power UV light.

Robert


Neil Baylis wrote:

{Quote hidden}

2007\05\01@114721 by Neil Baylis

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>
> Why bother ? I can't see any benefit in doing this - printing artwork on tracing paper on a laser
> printer and using a conventional UV exposure box will always be so much quicker and cheaper.

Two reasons, as far as I can tell: Firstly, because it's interesting.
Secondly, using a laser has the potential of higher precision, because
it eliminates the step of making a mask for the photoresist.

2007\05\01@121901 by Picbits Sales

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I actually use an inkjet printer with transparencies with very very good
results at the moment - it was just a bit of a mad idea I suddenly had as
I've been looking at building a 3 axis PCB drilling machine and this could
easily be bolted on.

Obviously exposing a whole board by laser would be a nightmare - the
distance the head would have to travel would be lengthy.

But ..... if you left most of the copper on the board and only exposed
places where you definitely don't want copper then it becomes more feasible.

Dom
{Original Message removed}

2007\05\01@121902 by Mike Harrison

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On Tue, 1 May 2007 08:47:20 -0700, you wrote:

>>
>> Why bother ? I can't see any benefit in doing this - printing artwork on tracing paper on a laser
>> printer and using a conventional UV exposure box will always be so much quicker and cheaper.
>
>Two reasons, as far as I can tell: Firstly, because it's interesting.

Fine. No problem with that, as long as it's regarded as a learning excercise and not something
likely to be better/cheaper/more useful than simpler methods...

>Secondly, using a laser has the potential of higher precision, because
>it eliminates the step of making a mask for the photoresist.

Precision ( accuracy) isn't usually a big deal - laser printers are easilya dequate in this respect.
Resolution may be theoretically better, however I think the limits of the resist itself, plus the
home etching process mean you wouldn't get much improvement in what would be achievable.
In theory, direct laser might me more accurate & have teh potential for more resolution, but
building laser optics to work better than what can be achieved with a print+expose method would be
pretty tricky.

You can reliably get 50 tracks/inch with 1200dpi laser on tracing paper and a simple
(non-collimated) UV box.  
It's unlikely you would be doing PCBs that need more than that density which didn't also need proper
vias & resists, therefore best left to proper fab houses.


2007\05\01@122456 by Neil Baylis

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> What is so difficult about printing the pattern onto clear film
> (overhead transparencies) and make a contact print exposure of the resist?

I don't think anyone said the masking step is difficult. The reason to
avoid this step is not because it's a difficult step, but because it's
an extra step. Every step in a process has the potential for
introducing error.

> It would be FAR simpler and cheapper I would think. (and faster if you need multiple
> boards).

I don't think it's simpler if it involves an extra step. If you can
expose the board directly with a laser, you completely eliminate the
step of making the mask.

Furthermore, if the laser can ablate (i.e., remove) the resist, you
would also eliminate the step of developing the resist image. However,
doing so would probably take more time than its worth, because you
would need to expose a much greater area.

> The sun is a free source of sufficient power UV light.

Not sure how that's relevant.

2007\05\01@123009 by Robert Young

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>
> I actually use an inkjet printer with transparencies with
> very very good
> results at the moment - it was just a bit of a mad idea I
> suddenly had as
> I've been looking at building a 3 axis PCB drilling machine
> and this could
> easily be bolted on.
>
> Obviously exposing a whole board by laser would be a nightmare - the
> distance the head would have to travel would be lengthy.
>
> But ..... if you left most of the copper on the board and
> only exposed
> places where you definitely don't want copper then it becomes
> more feasible.
>
> Dom

LPKF already does this with both mechanical and laser ablading.

Not cheap equipment though.

The laser based machines can do some spiffy flex circuit boards.

Rob

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