Author Topic: PCB photoresist film exposure  (Read 3857 times)

Stonemull

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PCB photoresist film exposure
« on: April 05, 2017, 10:47:28 AM »
Using a 2500mW benbox running grbl 1.1f and latest T2, pcbs designed in Kicad.

I have some new thermal photoresist coming from china atm, currently though I am using Cape Fear Press Puretch film. Probably the same photoresist though I do not know yet.

Getting good results at feed 1000, laser max 26, bidirectional off, I was using 0.05mm resolution but I think it is overkill and takes around 35 minutes per square inch.
So I am just doing my first attempt at 0.1mm.

Most of the testing has just been done with a piece of film with both plastic layers attached, tried it held down with coins on the corner, microslope glass slide or a piece of 1.5mm glass on top and not noticed much difference.

Everything I do is SMD so aiming for at least a 0.5mm track with 0.5 clearance. Close to achieving it, I might have to 'detune' the focus yet or change a few more parameters.

Though this is a negative photoresist, with a laser you need to consider it positive, so isolation routing is of no use, flatcam is out, gerber2pcb is out, inkscape gcodeutils from a dxf source produces odd scaling.

I am using gerbers currently. Hope to try dxf or plt when I can work out how as I have no holes in my through hole pads currently. I would really prefer to vector trace instead of raster scan these.

I joticed in a search that others are using paint options, I will go back and have a read now :)
Just typing this as I am bored waiting for the next test to complete.

Attached a photo of the last few test runs on a piece of plastic to make the film more visible.



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Stonemull

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Re: PCB photoresist film exposure
« Reply #1 on: April 05, 2017, 12:22:56 PM »
Ok I etched the board mentioned above and in general it was a success, I need to up the laser power a little and optimise the board a bit, there was nothing done to that one, I usually increase pad sizes for the through hole headers, vias and IC pads. I failed to do even the most basic checks on that one, I just pumped out a test design .. so the IC footprint is incorrect :)

Photo of a narrow SOIC28  with a match for scale. A couple of the trackes near the match head were improved with a sharpie pre etch as the exposure was pretty minimal and there were a few holes in the tracks in some area.
My photoresist is about 4 years past its use by date too, so it also had visible dark patches that did not etch fully .. very promising though.

Tomorrow, redesign and I might attempt a double sided board.


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Zax

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Re: PCB photoresist film exposure
« Reply #2 on: April 05, 2017, 02:45:51 PM »
It looks like you're making good progress.

I don't know if it will work but you can trace the GBR import result, and now use hatch fill to produce it using vector rather than raster scanning.

Stonemull

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Re: PCB photoresist film exposure
« Reply #3 on: April 05, 2017, 07:49:05 PM »
It looks like you're making good progress.

I don't know if it will work but you can trace the GBR import result, and now use hatch fill to produce it using vector rather than raster scanning.

Oh he** yah, I want this but I cannot seem to find it. Also, I actually need the exact opposite, I need the tracks hatch filled not the background.

Can you run me through the command chain ?
If I import a gbr, then hit 'Trace..' nothing happens, if I hit 'Autotrade..' then I get it traced, does the '..' part indicate I am missing menu options somehow ?
I cannot see a hatch fill option anywhere though ?
Is v1.3y the latest ?

With this I could also use the DXF input, which gives me pad holes.


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Kunaphil

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Re: PCB photoresist film exposure
« Reply #4 on: April 06, 2017, 12:56:37 PM »
Cool,  someone else is trying this.  I'm the one that has been trying the paint method and have had various results.  Let us know your results please.

Philip
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Stonemull

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Re: PCB photoresist film exposure
« Reply #5 on: April 06, 2017, 06:46:05 PM »
Will do, this is basically my note pad for this process.

 late last night I scanned this board at F1000 laser 25, which seemed a bit low on exposure.
Seems that 30 is almost over cooked and 25 is almost undercooked.
So the tracks on this took some damage during developing, I use a finger to remove the unexposed gel.

https://imgur.com/a/xa4F5

I then chucked the board under a mercury lamp for a rew minutes to harden up the tracks.

The pad holes are all supposed to be 0.5mm, every hole is, the vias are 1.5mm dia, T2 is temoving a bit too much copper on them, I think I have a viable solution however.
Far too much laser destroys the etch resist entirely, so I think in future I will be scanning just the gerber and then use the drill file to over expose the pad holes.

Mine fired up the laser on entering laser control (not added the pull down yet) and you can see the result at the zero mark.
So this will do 2 functions, create a pad hole and toughen the surrounding pad, so long as I can get the power right and the resulting expised region is not larger than a small pad.

The large square header pads are all 2x3mm so the pad gap is 0.54mm, the SOIC 28 (1.27 pitch) I went with a 0.65 width pad I think.

Off to bandsaw the board and etch it .. attached, happy with this though it can be improved and still have to work out an alignment method.


« Last Edit: April 06, 2017, 07:12:53 PM by Stonemull »
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Zax

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Re: PCB photoresist film exposure
« Reply #6 on: April 07, 2017, 05:35:05 AM »
Considering the size and how small the details are I think it looks awesome!

I appreciate you taking the time to write up the notes too.

FYI: I've fixed the GBR and PLT import code for kicad format so drill sizes are correct and you don't need to edit them. These changes will be in the next release.

Stonemull

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Re: PCB photoresist film exposure
« Reply #7 on: April 07, 2017, 07:56:11 AM »
Thats great, I look forward to it.


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Stonemull

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Re: PCB photoresist film exposure
« Reply #8 on: April 08, 2017, 05:10:12 AM »
Board assembled and code ported from the little 18f1220 I was using.
I had quite a few shorts to sort out, microscopic copper hairs, I think I was a bit slack with the etching as the under developed tracks concerned me, scaling is good though, no issue with footprint for micro.

https://imgur.com/a/WU1jJ

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nottingham82

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Re: PCB photoresist film exposure
« Reply #9 on: April 08, 2017, 07:51:03 PM »
OMG thats cool.  This is a project I will not be doing but it is soo cool seeing it can be done!
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Kunaphil

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Re: PCB photoresist film exposure
« Reply #10 on: April 08, 2017, 08:30:33 PM »
I'm impressed also!
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Kunaphil

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Re: PCB photoresist film exposure
« Reply #11 on: April 09, 2017, 04:46:26 PM »
Excellent!
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Stonemull

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Re: PCB photoresist film exposure
« Reply #12 on: April 14, 2017, 01:04:02 PM »
So I played with thermal paper which has more similar attributes to ohotoresist film then burning things, ie it can be used at high speed. Also backed off the carriage tensions and tweaked belt tensions.
This helped me dial in much better settings than the 25/1000 that was used earlier and I can now use bidirectonal mode at 45/3500 so 3.5 times quicker and both directions means an etch is now 7 times quicker than originally with similar results.

I have a dual layer method sorted but not needed it yet, practiced it on thermal paper. I will upload my how-to reminder text file later.

Only made 2 simple boards for actual use so far, both needed cleanup, a few minor shorts, the second one probably woukd have been fine but I touched what appeared to be a soggy bit of film after develiopment, what do you know, it was soggy and sort of smeared the film a little, it was also a bitch of a board for a non plate through board being just 2x40 pin headers. They suck to get a sufficiient, drillable pad size and still allow a track between pads. Using a lot of rectangular pads, they come out with rounded corners anyway, I may have a go at refocusing later.

Also used old headers I probably have had for 10 years, they did not like taking solder 10 years sgo and they are even more of a mongrel now. So if you wonder why the soldering seriously sucks on the header board, thats why, despite fluxing the pads and headers, desoldering and resoldering 3 or 4 tines in some pins, gah, still not wetting properly. Must buy new headers..
Since so much drilling on that one, made the pad holes at 0.5mm and loaded the drill file to get decent drill guide dots.

Still using 0.1mm scan so trying to align everything on a 0.1mm grid and using say 0.4mm tracks instead of 0.5mm, as I want to avoid things that need 0.05mm resolution.
Track clearances are easier to keep vertically than they are horizontally, so align SMD ic's so the footprint is vertical.

I have had some board outlines come out quite well, they are a single 0.1mm line, so it is quite possible with a lot of tuning to get that resolution with this method I think, not that I have any intention of trying it except for experimenting.

https://imgur.com/a/LK1Sy

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Stonemull

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Re: PCB photoresist film exposure
« Reply #13 on: April 19, 2017, 09:04:26 AM »
My new aliexpress photoresist film arrived today, test results are that this stuff is good !
At least with the basics, not tried etching with it yet.

I cut a small square and okaced ut hext to my old film and plotted a gerber across the pair at 45/3500
The image came iut a LOT darker after exposure and before developing, looks like I need to drop laser power again for this stuff.
Then developed the same as my usual method (10g/litre sodium carbonate solution), I was pretty rough with it giving it a good finger rubbing while developing.

Then I gave half of both films a few minutes under a UV source to see if further exposure would harden it more. My ipad did not like taking a photo under UV..

Results are ...
photo 1 post laser
photo 2 post developing and extra UV result.

question, is attaching photos here ok or woukd admin prefer i use imgur ?
not sure who is wearing the costs for hosting this.

« Last Edit: April 19, 2017, 09:06:10 AM by Stonemull »
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Stonemull

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Re: PCB photoresist film exposure
« Reply #14 on: April 20, 2017, 10:11:09 AM »
Last update for a little while, not sure how many are interested anyway.

After struggling with belt tension and a cruisy X axis after yesterdays dismantling to check out a Z axis addition, I have dropped the attempts at doing it as quickly as possible, it is an issue of diminishing returns, I can expose a board in under 10 minutes or 1 hour however if the quality is such that I need to spend a while looking for shorts and repairing broken tracks then there is no time saved, I may as well let the laser do its thing for a bit longer and have a result I can use with very little touchup.

The first image is from yesterday and is about the best part of a 40/3500/0.1mm bidirectional run trying to tune in on a good laser power (that was 40 I believe), other parts exhibited shorts where the laser scans in different directions merge the areas together. Overall, useable, just with probably a dozen areas needing repair.

The second image is the worst part of first attempt tonight at a 32/2500/0.05mm unidirectional  run, this took 62 minutes instead of 8 minutes, (slower, one direction and double the resolution) but I can use it as is and I have not even tried increasing the exposure slightly. The only issue is the 3 tracks there that look like they will probably need a cleanup with a scalpel to separate them.
They have a 0.25mm clearance, perhaps a bit longer in the developer would fix it too.
The IC pads there are a 1.27mm pitch.

This should be my last test exposure as I reckon I can tune it in during use from now on, yet to try etching any of this new film but so far it is looking far better than my old  Puretch film, also a lot cheaper and far easier to use.

I am going to make so much more stuff now.


edit: I forgot to mention, I looked at the laser focus last night, either with a microscope on the dot or imaging it out of focus onto paper, the distance  I using I can get a small spot however it looks like a galaxy on its side, the bright spot rotates with the lens focus and is off centre, after mucking around for an hour or so I ended up dropping the whole laser so I am now exposing at about 2.5 inches instead of 5 inches. At this area I get a larger but rounder dot, I still had many of the same issues as yesterday though with mechanical backlash.
Attached the old dot, I think was causing the slightly exposed perimeters in one direction which tended to short out.








« Last Edit: April 20, 2017, 10:16:44 AM by Stonemull »
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