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Build laser plotter to cure UV paint and photosensitive film for PCB?

bearer

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While waiting for my 3D printer I'm thinking I'll do some research into making a laser plotter to cure UV paint to form solder mask and silk screen layers on PCBs and maybe also expose a photosensitive film for PCB manufacture.

I've read up a bit already and there seems to be people doing this, but some of the details are lacking.

I keep coming back to Hacking the PHR-803T | Diyouware.com which use a blue-ray pickup sled complete with the autofocus circutry, and it has a really short focal distance.

Their solution has 150mW 405nm laser available, and this is more than sufficient for the photosensitive films used in PCBs. This guy use a 25mW laser pointer https://www.youtube.com/watch?v=va0taOtdYPQ And I suspect its also sufficient for the UV paint as a few minutes in sunlight cures the paint.

So are there better (i.e. easier or cheaper) solutions than the PHR-803T pickup sled to make a focusable dot with a very short focal length? A few millimeters?

Ideal solution would be able to adjust dot size from 1.0mm down to 0.2 or maybe 0.1mm. If a fixed dot size is the only economical solution, then anything below 0.3mm will work for now. I can make PCBs on a mill, so maybe laser only need to handle UV paint for silk screen and solder mask.

And if ending up with a 150mW or less, 405nm laser, OD3 goggles should be sufficient?

If there are similar topics here, please point me in that direction, I've tried browsing all the results I could find for 'UV curing'.
 



Benm

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It sounds entirely feasible to use this to expose PCB photoresist. The wavelength surely is short enough to do that quite effectively.

A fixed focus design that gives a spot small enough to render your smalles detail seems like the most practical approach. If you want to etch away lager areas just make some exposures side by side.

More power means you can do the exposure faster, but in a dark environment you can take as long as is practical. I'd recommend leaving most of the copper on the board (e.g. as groundplane) since that minimizes exposure time as well as amount of etchant used for a given circuit.

A focus spot of 0.2 mm (about 8 mills) would be ideal for fine work (running tracks between 50/100 mill spaced component leads etc). If you're doing strictly through hole work with pin pitches of 100 mills something like 0.3 mm would be okay since you could easily route a track between pins if need be.

One thing to look out for is over-exposure though, if you go too slowly or apply too much power the light will probably bleed a bit risking narrow tracks to be etched away. This is made worse by under-etching in the actual chemical process where the etchant also attacks thin traces from the sides - somehting pretty much unavoidable.

Smart software can mitigate those problems to some degree rescuing sharp turns from being etched under, but those options are limited.
 

bearer

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Slow progress as with most of my projects.

In a weak moment I purchased a cheap Chinese laser engraver, which I've had plenty time to regret and try to get usable.

In any case I've made some exposures on both cheap UV soldermask, and photosensitive PCBs and trying to tweak feeds, and power levels.

FlatCAMs latest development version has functions for importing gerber data, tracing contours and filling in ares as an alternative to rasterising and scanning across the entire board. Although with leaving as much copper fills as possible I'm not sure its much faster, if at all. But it seems to have better edge definition due to the contour. (Leaving out copper fills for now as I don't plan to etch the samples)

Grbl 1.1 has now gotten a laser mode, and a constant power mode that really helps with over-exposure so with some more tweaking I think this should work rather well. My biggest unkown is how to improve the laser host, and focus to get the sharpest dot possible, at reasonably sort distances. Is it possible to achieve a good focus without breaking the bank for a 20mW laser - or is my best bet to adapt a blue-ray pickup sled?

Eagle or KiCad + FlatCAM + Grbl is a software stack that is more than capable of achieving what I want, the two last need features that is not yet in the stable releases, but it works fairly well.

Under is a comparison of Grbl 1.1d with and without the constant power feature:
2016-11-13%2003.07.48.jpg
 

diachi

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Can you post some pictures of the laser? Chances are you'll be able to adjust the built in focusing lens to do what you need? That or possibly change it for something with a shorter FL.

I'm interested in this project, I'd like to do something similar. Have you considered using a more powerful laser and black paint? You etch the paint off with the laser to form the traces.
 

bearer

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The laser engraver as a while is a 2.5W "benbox" thing from Banggood.com (although would not reccomend them due to lacking customer service, 2 months and they still haven't replaced the DOA laser module)
2.5W Desktop DIY Violet Laser Engraver Engraving Machine Picture CNC Printer Assembling Kits Sale - Banggood.com

I knew 2.5W would be major overkill for UV curing so I also bought a 50mW module with TTL driver from aliexpress.com
https://www.aliexpress.com/item/405...le-12V-TTL-long-time-working/32659243565.html

The 50mW module died almost imediately, and I suspect the driver was set to much too high power output and toasted the diode after a few seconds. So I tried finding a 3.8mm replacement diode, but ended up with a 5.6mm 50mW diode in the host from Aliexpress. The issue I'm having is that I can adjust the focus, but it is extremely sensitive. 1/4 turn moves it from quite unfocused to focus and way out of focus again. I can adjust the distance from the diode to the lens, and the distance from the lens to the PCB if I have to. The sensitve focus seems to be an issue with even the slightest unevenness in the PCB, and the dot is never quite round as far as I can tell.

I have considered paint (but basically soldermask UV Sensitive paint) for use when etching as well, but I think I find that the photosensitive film is easier to apply than paint. Also not sure if the 50mW laser is sufficient for anything other than curing UV stuff for now.
 

Benm

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Those etch resists don't look too bad. You will need to get the focus exactly right though, if you etch it without the drill holes removed it will be a pain to get the holes drilled.

The best way to test things it to actually etch them though. On small boards like that you can do that as-is... the copper fill is mainly there to save etchant and provide groundplanes for some applications, but for small test runs of the actual etching process it doesn't matter that much.

A good test would be to put something like a DIP16 package on there and snake a track between all of the pads. If you get it to etch such that the track is not shorting to the pads, not broken at its corners, and the holes a drillable you're probably okay for this scale of work.
 

bearer

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Getting the focus right seems to the biggest issue - not sure what to do to get "more resolution" on the adjusting of the focus to enable optimal spot size and sharpness

The g-code used for testing doesn't have drill holes for now; leaning towards maybe drilling on the cnc router - but I also wanted to avoid getting fiberglass on the router. But I will definitively make sure to have guides for drill holes when hand drilling!

For now I'm just trying different power levels and feed rates to see what works best, the whole machine isn't running straight, the picture below was supposed to be squares on a grid; but some of the wheels are a bit wobbly so everything gets distorted. And trying to get any other response than "we offer you 200 Banggood points" from Banggoods customer service is actually painful! So regretting where I bought the laser more than having bought it.
2016-11-14%2001.04.33.jpg
 

bearer

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First etch!

SOP to DIP adapter, looks like there is potential. Soldemask was a failure, but I think it should be doable.

Traces still came out too thick, and I think the laser dot is quite oval seeing tracks seem thicker in one direction than the other.

2016-11-17%2007.04.04.jpg
 

diachi

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First etch!

SOP to DIP adapter, looks like there is potential. Soldemask was a failure, but I think it should be doable.

Traces still came out too thick, and I think the laser dot is quite oval seeing tracks seem thicker in one direction than the other.

2016-11-17%2007.04.04.jpg


That looks pretty decent! Not perfect, but certainly good for a first run. :beer:
 

bearer

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There has been *a lot* of unetched photoresist washed away, so its not quite the first run :D

But yeah, seems most parameter except the beam size/sharpness is under control now. And this is "good enough" to get most of the pending projects done while I try to figure out the beam stuff.
 

diachi

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There has been *a lot* of unetched photoresist washed away, so its not quite the first run :D

But yeah, seems most parameter except the beam size/sharpness is under control now. And this is "good enough" to get most of the pending projects done while I try to figure out the beam stuff.


Something that may help adjusting the focus; wrap some teflon tape (Same stuff plumbers use) around the threads on the lens holder. It'll make the lens less wobbly, easier to adjust and will stop it from slipping out of focus.

Be careful not to get any on the diode of course. :beer:
 

bearer

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Already applied teflon tape as suggested in one of the many threads I've combed through here. It made it a lot smoother, but not realy any easier to fine adjust.

This seems to be the limit with the current setup, its a lot better already, but I think I will try to buy a new laser module and avoid China stuff.
2016-11-18%2011.15.46.jpg


And order a blue-ray pick-up and start messing with that, now that I have something thats usable I can go down that route which is likely to take a while :)

Edit:
Used about 30-40mW laser. 30-50% power and feed 2500-3000mm/min seemed to work best for the dry film photoresist. And 100% power two-three passes at 2000min/min for the solder mask. Might try getting a bigger laser and see if its doable to get the solder masking in one pass; but it seems the dot "bleeds" quite a lot at higher powers.
 
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bearer

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Did a tqfp32 with just random traces and a 0805 with a trace running under it just to see. Seems at this scale the oval shape of the dot is an issue as my vertical lines are thicker than my horizontal lines.

But I think with a little more tweaking it should be possible to do 0.8mm pitch on tqfp or maybe even 0.5 pitch, but it sure requires more TLC on the developing and etching side.

But this is with the cheap ready to go laser engravers from China, so better than expected. (Pardon the partial green solder mask, was not a success..)
Cus10002-002.JPG
 




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