Direct PCB laser printing - a different approach

Recently I've rather gone off the whole direct toner to PCB approach. Just doesn't seem to be robust enough. Having recently fabricated some PCBs in the Chemistry department I've seen some of the insane artwork they use. The artwork is (or was, before it was outsourced) produced in the university printing studio. The artwork is staggeringly good - incredibly black. High resolution too.

The process is as follows:

PC outputs postscript to a imagesetter machine. This is basically a high precision scanning laser that writes to photographic film. The film is sensitive to IR, so the laser is cheap. The film is cheap at £60 for a 30m roll,300mm wide, from these guys
Film is then developed and fixed
Job done, the film is transparent and black enough to be used for PCB artwork.

I really can't stress enough how black the artwork is! So I started thinking about modifying a laser printer to be an imagesetter for this film stuff.

At lunch Rob and I started talking about it, and came to the conclusion that we really want to just image straight onto the PCB photoresist. However, there is a serious problem here - PCB photoresist is sensitive to UV light, not IR. UV lasers are horribly expensive.

Ok, so what about an LED printer? I didn't really know how they worked, but it seemed likely that you could mod them to change the LED wavelength. Unfortunately this is not the case. They are actually a line of LEDs, one per pixel! So for a printer with a horizontal resolution of 600dpi there's a line of LEDs in the printer that's 600 LEDs/inch over 9 inches of paper width. Of course these can't just be SMT LEDs on a board! So something horribly complex is at work, and they cannot be replaced with UV ones. Also, 1200dpi ones don't really exist for reasonable amounts of money.

So we're stuck with modifying a laser printer to fit a UV laser. So I started looking for UV laser prices. They barely exist - certainly no UV laser pointers around yet. Then I remembered the DIY air (nitrogen) laser - the only laser you can build at home for a finite amount of money. Almost no money in fact, just an HV supply and a pile of aluminium and acetate. It emits at 337.1nm UV. Awesome.

But one problem - it's pulsed, and the pulsing is built into the laser physics. The guy says the laser pulse lasts <10ns, but doesn't state the recovery time between pulses. This would presumably be reduced by actually using a nitrogen atmosphere rather than air.

So is the pulsing speed sufficiently fast to not bugger up the raster scan of a laser printer? Lets say imaging an A4 page takes around 1s. That's 1200dpi * 11.7" = 14040 lines/page. So one line takes something like 1/14040=71.2us. If we assume a 50% duty cycle on our air laser then that gives us 71.2us/20ns=3560 laser pulses per line, or 3 laser pulses per pixel. So it's sketchy, but possibly doable.

We also don't know whether the amount of energy delivered by the beam is sufficient to expose the board, but I guess we can just pump more nitrogen/current into this laser to address that. Assuming we don't want an enormous reverse engineering excercise we're stuck with the a fixed scan/print speed.

Submitted by jeff on Tue, 08/07/2007 - 14:05. categories [

PCB manufacture

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Very interesting

Submitted by Daniel (not verified) on Wed, 02/27/2008 - 11:20.

Very interesting considerations.
I was looking too at this solution and I have seen a nice introductory article at http://www.circuitree.com/CDA/Articles/Web_Only_Editorial/fd4a33c4318d70...
I have understood that argon laser it is very similar to co2 kind, but it is a little too much for a amateur.
I am very curious about your next steps.

Video of using a laser

Submitted by Ouroborus (not verified) on Sat, 11/22/2008 - 14:55.

Video of using a laser etching system to remove paint from a copper clad pcb.

http://www.flickr.com/photos/macetech/2735223162/

Seems like a good idea, similar to the OP. The manufacturers of such machines claim around 1000dpi.

UV mods

Submitted by EllisGL (not verified) on Thu, 08/13/2009 - 02:05.

Thinking about it, how about using an array of UV LED's in a mirror box that ended up feeding a small fiber optic. Make a printer control board that would turn off and off and on the LED's while it was scanning across?

406 nm, 20 mW, Sharp BLUE Laser Diode

Submitted by Carlos (not verified) on Tue, 08/25/2009 - 20:46.

An affordable near UV laser diode:
http://www.thorlabs.com/thorproduct.cfm?partnumber=GH04020B2A $344.80

500mW laser diode for 405nm

Submitted by gyurma (not verified) on Mon, 07/18/2011 - 22:11.

Hi!

I also thought of modding an old laserjet to make laser direct imaging. First I was enthusiastic because I found a 100mW 405nm laser on ebay.
With this and a beam focus point diameter of around 20um I needed to slow down to 2 cm/s imaging speed. The laserjet scanned _much_ faster.
Also the complex scanner optics were not suitable of focusing the 405nm light, they were tuned and developed to perfectly focus a 780nm light beam. The point is, that the focus would be on a perfect line as a sharp moving focus point with a 780nm source, but the blue is almost half wavelength, and the perfect line gets missaligned. The collimating lens does not fit, and the object lenses seem to make either horizontal line foci, or vertical line foci depending on object placement.

The latter moved me to a complete self made design, made of a laser scanner galvo kit from ebay. But the most important is this: SF-BW512P. This part has a 500mW diode in it.
Also it has all the collimator optics needed. You need to remove a lot of unnecessary stuff. I hope i get mine soon.

Why I am not looking for UV? Because the maximum sensitivity of the Bungard resists is around 405nm :D

500mW with 20um diameter makes 10cm/s...

Glad you experimented with a

Submitted by jeff on Wed, 07/20/2011 - 15:57.

Glad you experimented with a laser scanning module. I'm interested to hear about the wavelength effects; I don't know much about optics.

Do you have any more results/info on your build?

Cheers
Jeff

via connections and solder mask

Submitted by EBo (not verified) on Tue, 01/11/2011 - 09:15.

I just saw your uber cool video and noticed that you mentioned needing a solution for connecting via's. One technique I used in the past is to bend a piece of bare copper wire into an L and solder it into the hole. If you are careful, the solder will wick through and fill the hole - establishing a good connection.

Also, I worked at an industrial PCB manufacturing plant for awhile (I should also add, that was 20 years ago). The soldermask technique we used was not a photo-resist process, but was a direct print via silk screen. We used the same technique for printing the legend and art work.

Also, your idea of pre-drilling holes and using alignment pins is exactly right. I do not know where you can buy them but we used paper thin spring steel shims with with little nubs on them that we could tape down to the silk screen tables for alignment. Once down and aligned the nubs allow us to quickly load up new boards. The same technique can be used with a backer sheet that has a known geometry.

As for optical alignment, take a look at the vinyl cutters. I remember seeing one recently CraftRobo or something. It actually has a camera which looks for 4 registration marks printed in the corners. Something similar would be trivial for you.

Again I really want to say how much I like your work, and I really want to build one of these things! Contact me off list and let me know how I can help! BTW, I served an apprenticeship with a tool and die machinist, and previously worked as an instrumentation engineer.

oops... I think I replied to the wrong post

Submitted by EBo (not verified) on Tue, 01/11/2011 - 09:25.

Bouncing back and forth between browsers I thought I was commenting on a post to the following video:

http://blog.makezine.com/archive/2011/01/printing_circuit_boards_lecture...

The wax printing is what I am really interested in...

Wax printing

Submitted by Sir Athos (not verified) on Tue, 02/15/2011 - 09:24.

You may want to look at this link. It documents what to use and how to achieve wax printing for etching purposes. The only drawback is, it uses a thin copper coated film to print on instead of a regular thickness PCB.
http://www.instructables.com/id/DIY-Flexible-Printed-Circuits/

Thanks, EBo, some

Submitted by jeff on Tue, 01/18/2011 - 23:09.

Thanks, EBo, some interesting contributions. Hoping to get back to the project soon, but in the mean time I have to attend to my work for a while instead! Keep watching this space...

What about 405nm Laser Diodes?

Submitted by Gyurma's Electronics (not verified) on Mon, 07/18/2011 - 21:59.

Hi!

Why I am not looking for UV? Because the maximum sensitivity of the Bungard resists is around 405nm :D

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