Benbox Laser Machines/CO2 Lasers/3D Printers

General Category => Projects => Topic started by: Stonemull on April 05, 2017, 10:47:28 AM

Title: PCB photoresist film exposure
Post by: Stonemull 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.



Title: Re: PCB photoresist film exposure
Post by: Stonemull 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.


Title: Re: PCB photoresist film exposure
Post by: Zax 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.
Title: Re: PCB photoresist film exposure
Post by: Stonemull 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.


Title: Re: PCB photoresist film exposure
Post by: Kunaphil 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
Title: Re: PCB photoresist film exposure
Post by: Stonemull 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.


Title: Re: PCB photoresist film exposure
Post by: Zax 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.
Title: Re: PCB photoresist film exposure
Post by: Stonemull on April 07, 2017, 07:56:11 AM
Thats great, I look forward to it.


Title: Re: PCB photoresist film exposure
Post by: Stonemull 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

Title: Re: PCB photoresist film exposure
Post by: nottingham82 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!
Title: Re: PCB photoresist film exposure
Post by: Kunaphil on April 08, 2017, 08:30:33 PM
I'm impressed also!
Title: Re: PCB photoresist film exposure
Post by: Kunaphil on April 09, 2017, 04:46:26 PM
Excellent!
Title: Re: PCB photoresist film exposure
Post by: Stonemull 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

Title: Re: PCB photoresist film exposure
Post by: Stonemull 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.

Title: Re: PCB photoresist film exposure
Post by: Stonemull 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.








Title: Re: PCB photoresist film exposure
Post by: Zax on April 20, 2017, 10:28:43 AM
The roundness of the dot depends a lot on the optics, when I was testing different lenses I noticed the 3 element was far superior which probably explains how it burns better despite all measuring the same output (overall power was no different, just the density in an area increased). Some lasers use a diode array which is always going to be a line.
Title: Re: PCB photoresist film exposure
Post by: Stonemull on April 20, 2017, 10:38:22 AM
Yeh I get its a line, more concerned with it appears to be bouncing off the threads inside the lens when focusing at that range and when I go a shorter range, I cannot get a tight focus at all.

This is the dot I am using currently, that is as fine as I can focus and the dot appears a lot larger, however the camera I guess is clipping the brighter spot in the middle of it, like it is a lot more of a gausssian distibution than it appears.
if I expose with that at 0.1mm raster I ended up with distinct lines on the film, pretty much 50:50 of the 0.1 pitch, so I ended up defocusing slightly and going to 0.05mm raster.

Probably a moot point anyway, I am sourcing a smaller 50mW 405nm laser to try and use for exposing and will keep the 2500 for heavier duty work. As long as I can get it to work I am a happy chappy.
If that works out well I probably try and fit it to my old plotter body which has 600 step steppers. lighter carriage and smaller pitch pulleys with cable drive, l ran that at 20000mm/min and 132 steps/mm.


Title: Re: PCB photoresist film exposure
Post by: Stonemull on May 09, 2017, 07:36:57 AM
My new laser turned up today, a 404nm 50mW 5V device. Good news, it exposes the film no problem at any speed I have tried so far.
Though I purchased a 'dot' laser they sent me a damn line version so I am using the lens off the 2500mW currently.
It has a built in driver, 2 wires only so it is not keen on being pwm'ed.
I am running it from the +5v on servo (centre pin) and Gnd from the motor connector (pin closest to laser output), so setting power to 255, it seems to take a few milliseconds to turn on, bidirectional mode is pretty much out as all vertical lines zig zag.
I am running at feed 2000 currently, just did a 0.1mm resolution expose and it is pretty good however the lines are too far apart, just doing a 0.05mm version now..
So I reckon the exposure is a lot better than the 2500mW...
Will document on imgur with some microscope images shortly.

hmm, I am just listening to my scanning pausing, stopped for a split second then had a longer pause of around a half second a few seconds later, not sure what that is about.


ok, imgur album http://imgur.com/a/QRURn

When i posted the above I had not tried developing the film, it is pretty apparent that it is being overexposed even at feed 3000, 0.05mm is a lot worse than 0.1mm so I might try a unidirectional feed 3000 at 0.1mm, also have a look and see if I can improve the laser focus. I do not have goggles suitable for this wavelength at all and I suspect 405nm is a lot worse than 445nm, I also cannot currently use a "low level" on this laser, so as fine a focus as I could manage was done through arc welding goggles, there was a lot of guesswork involved.
Over exposing is better than under, means I have enough power in this 50mW to expose fully at full speed, I can always reduce it .. add a chucnk of ND film inside the laser or after the lens even, add a collimating assembly etc.

so I think it is time I joined the laserpointer forums and get some info about hacking the driver modules in these little lasers, it appears to have a switch mode internally, at 2v it draws more current than at 5v, it just seems to take 12mS to turn on and there is evidence on the film that it takes longer to turn on the longer it has been off. So not an ideal driver for what I want to do. In fact I think a big resistor off the 12v rail would do a better job.

Now we have 80 microsteps/mm or 0.0125mm / ustep, so 0.05 is 4 usteps or quarter of a full step and 0.1mm is a full step.
So, can I assume that if I set T2 to 0.1mm resolution and hit laser control I have always had only sequences of exactly 8 pulses every time, I want to use precise full step and half steps each time.
Going to try locating laser to origin and just before lasering, turn 12v off and back on, this should reset the motor drivers to a full step position.


Cool, it just unscrewed easily, I tried before and it didn't move.
Ok, we have a control pot internally. added pics to imgur album too ..

ok searched google images and this is basically the driver circuit.
https://www.aliexpress.com/item/3-5-5V-Power-Supply-Driver-for-1-250mw-405nm-Violet-Blue-Laser-Diode-Module/32279684822.html

Ok worked out how to add TTL to this little guy and it will work at 8Khz a doddle, up to a few hundred kilohertz if I remove one little cap.
details in imgur..






Title: Re: PCB photoresist film exposure
Post by: Stonemull on May 09, 2017, 10:52:30 PM
Added TTL mod to the laser and it works perfectly at all output settings, also dropped the power (turn pot ACW .. increase resistance, decreases base current) since full power was too much at any speed.
I can  now set power to 1 and focus (even power 2 is too bright to see spot detail)
I measured the boost supply on the laser module (laser on so under load) at 6.2V
Laser voltage was 5.37V at turn on but was slowly dropping over time, did not measure current.

Added a DTC114ET bias transistor, sometimes drawn as a 3 terminal inverter. The ET variant has both resistors 10K. One track needed to be cut, the one connecting the low side of the power pot to the ground track, transistor goes across that point basically.
These are different than regular transistors as the have a series base resistor and a base emitter resistor, I bought 100 of these 5 years ago and still have like 80 left, great for doing mods like this as you can tuck them between connector pins etc, they are an SOT416 package which is about half the size of a SOT23, so a pain to solder but they fit anywhere.

The base is connected to the currently unused third pin on the module, so I now have a true 3 pin module with +5, gnd and TTL .. so added a 3 wire twisted cable and it plugs straight into the servo connector.

Now to try the test image..




Title: Re: PCB photoresist film exposure
Post by: Stonemull on May 09, 2017, 11:25:05 PM
Well I also found the original line lens is fine and better performing than the 2500mW 3 element lens, it can be unscrewed and the front line element removed easily.


The first photo is the best dot I could get with the 2500mW lens, the second image is the result with the line lens with line element removed.
Power is on 2/255 and the grid is 0.1mm resolution (came with the USB microscope).


I am excite !.



Title: Re: PCB photoresist film exposure
Post by: Stonemull on May 10, 2017, 06:54:43 AM
Mucked around for a while with different focus options and get speed and power ideal, laser cut some card apertures to fit inside the laser before the lens to try and make a square dot, fail. Ended up with a larger dot than before somehow.
Laser is better a few inches above the board, further away is larger dot no matter how much you refocus. also had to increase my motor currents again. I was getting gaps in the Y and X deviations
between passes.

Ended up with 255/2500/0.05 unidirectional with the modded 50mW 405nm.

Results speak for themselves, bloody awesome. No tracks to fix, no gaps bridged. This is 0.5mm tracks and will be the servo conversion board for the pcb drill, takes a PIC 10F220.
4:25 to expose, took ages to etch in the etching tank though, probably half an hour plus, I have not got the hang of hydrochloric acid/ hydrogen peroxide yet. i will try heating it next time.

Title: Re: PCB photoresist film exposure
Post by: Zax on May 10, 2017, 07:40:09 AM
Wow, yeah that's a super clean result. Awesome!
Title: Re: PCB photoresist film exposure
Post by: Stonemull on May 31, 2017, 11:35:13 AM
Latest video using a 50mW 405nm laser on an old plotter retrofitted with a Ramps board, running off 20V, laser mount attached to top of pen solenoid.
This is bidirectional 6000/255/0.05 and took only 5 minutes, awesome. Motor currents have a lot of room to increase, I would probably go unidirectional and I spent 30 seconds getting the focus rough enough, it is actually a mm or two lower than what I focused on, just a piece of the film exposed under glass and not yet developed.
The device in the photo is a TSSOP8 package which is 3 x 4.5mm and a 0.65mm pin pitch, the only common finer pitch is 0.5mm but I very rarely use them, so this is looking frigging great.

http://www.youtube.com/watch?v=yAgH7mTnmCc





Title: Re: PCB photoresist film exposure
Post by: Koskee on August 14, 2017, 11:10:59 AM
I've got something you may wish to try.
I've been etching  with 1 part H2O2 (peroxide,  3% I think?) mixed with one part ascetic acid (regular kitchen white vinegar, 5% Im guessing), and table salt (about a teaspoon or 2) and then keep wiping off the orangey-brown gunk that forms on the copper with a foam craft brush.
If the reaction slows down, add more salt is what I was told, but I had better results adding more peroxide. It's by no means an aggressive reaction, and uses the cheapest materials imaginable, but I don't think it took me more than about 20 or 30 mins start to finish. Granted I try to leave as much copper on the board as possible in the form of a ground plane, so I'm not removing as much as you are quite likely.
Im also just spraying on black paint for resist, it seems to be extremely durable, especially if you can let it dry overnight.

Resources:
http://quinndunki.com/blondihacks/?p=835 (etchant recipe & good advice overall)
https://m.youtube.com/watch?v=EWoorkFEOmY (for real speed.. This guy is fuckin nuts tho)

One thing I was wondering about, is when you were using your big blue laser, how were you dealing with reflections off of the copper? I'm concerned because the copper is likely shiny enough once I get through the paint that if the board is sitting exactly perpendicular, and the laser is firing exactly vertical, then in theory the laser would be directed back at the diode, possibly causing damage/excess heat to the diode. Especially since i'm not sure if they have any sort of feedback protection or anything to shut down the later should the temperature spike, incorporated in those super cheap modules.
Title: Re: PCB photoresist film exposure
Post by: Stonemull on August 16, 2017, 11:00:32 PM
Problem is, I simply cannot get cheap peroxide, I have only 2 options currently, 3% or 6% at $5 per 100ml from a pharmacy, it seems to hardly do anything sonetimes. Or 5 litres of 50% from a chemical supply house $50, I think, they do not sell single litres as the bottles tend to outgas and explode.
50% will catch fire if it touches wood or paper, I just don't want a big bottle of it lying around.

So I am currently using hydrochloric acid (muriatic acid 35%) ... added some peroxide and copper to get the reaction started, bubble air through it, after a few hours it eats the copper and eventually turns from brown to green (copper chloride) it now eats copper damn fast, just need to use an air bubbler to give it ixygen, no more need for H202 .. the chemistry gets stronger over time and you need to dilute it with more acid or just water depending on its pH.

Reflections arent a problem, the beam will never head straight back up in the exact direction and spread, it will never make it back through the lens system, a laser works by bouncing light to and fro, so even if 100% of it made it back it would likely interfere with the laser phase and upset the lasing function.
Think of how the lens system operates and what a reflection spread would be, multi lens systems like telescopes etc do not work well backwards, they expand the light instead of focusing it.
Title: Re: PCB photoresist film exposure
Post by: ThothLoki on August 17, 2017, 07:35:43 AM
When I watch pcbs I use the muratic acid and peroxide mix at a 2:1 ratio. Works well.
Title: Re: PCB photoresist film exposure
Post by: ggallant571 on August 17, 2017, 10:20:23 AM
A strong solution of H2O2 will eat your lungs very nicely. We use a powerful UV lamp to reduce the H2O2 to water & oxygen.
Title: Re: PCB photoresist film exposure
Post by: Kunaphil on August 17, 2017, 11:07:53 AM
I use the same recipe as Thoth.  It works pretty good, but make sure to have plenty of ventilation.
Title: Re: PCB photoresist film exposure
Post by: Stonemull on August 17, 2017, 07:22:15 PM
It does work well with good peroxide, using it here I have to use 2 parts peroxide to 1 hcl and it still takes 1.5 hours with agitation..pharmacy peroxide has stabilisers added.
Also I assume you ae discarding the solution after a while ? there is no need.
Does it turn green or start off green ? You can achieve the same thing without any peroxide by using an air bubbler.
Australian muriatic or peroxide, not sure which, seems to have iron contaminants, mine goes brown instantly if I mix them, that is just the hcl from a hardware store..

Title: Re: PCB photoresist film exposure
Post by: Kunaphil on August 18, 2017, 12:19:12 PM
My recipe turns green.  It seems to get stronger each time you use it.
Title: Re: PCB photoresist film exposure
Post by: Koskee on August 19, 2017, 03:22:43 PM
The vinegar, peroxide and salt comes off the board brown, but in solution it appears blue. It also doesn't take much longer than 20 mins or so when etching a small board as long as you keep wiping away the brown sludge every minute or so. I don't need to prime the solution, and I normally will toss it every time.

Part of the draw to this reaction,  for me, was the fact that I can simply head to the grocery store and grab everything I need (and I actually had everything on hand without making a trip) Plus, the fact that they're all extremely inexpensive, it seemed perfect. Our peroxide is only 3% as well, available in the  first aid section, and is about $2.50 for around 8 or 900ml, so by no means expensive.

It occurs to me that when designing my boards I generally will keep as much copper on the board as possible through the use of ground planes and arranging components such that I'm not removing large areas of copper, so this could possibly make a difference.

I suppose it is labour intensive  in the sense that you have to "babysit" the reaction, continuously agitating, but I'd prefer that because i wouldn't have an opportunity to forget about it and thus over etch. Undercutting doesn't seem to be a problem neither.
Title: Re: PCB photoresist film exposure
Post by: MegaBlackJoe on October 09, 2017, 12:37:17 PM
Sir, could you please share the link to the laser and photoresist?

I have Eleksmaker A5 2500mW laser engraver and I would like to use it to expose a photoresist. I have a green laser but as far as I understand I need to replace a laser head since photoresist reacts to UV and green laser doesn't have the right spectrum. So violet laser from aliexpress works better since it provides more UV spectrum and green laser won't work on normal photoresist. Am I right?

Could you please  tell which photoresist are you using - the negative or positive one?

Thank you very much in advance.
Title: Re: PCB photoresist film exposure
Post by: Stonemull on October 18, 2017, 08:27:56 AM
https://www.banggood.com/405nm-50mW-Focusable-Violet-Dot-Laser-Module-Laser-Generator-Diode-p-960448.html

https://www.banggood.com/30cm-Photosensitive-Dry-Film-Replace-Thermal-Transfer-PCB-Board-Longth-1M-p-947764.html




Title: Re: PCB photoresist film exposure
Post by: Andrew on October 19, 2017, 11:59:51 AM
all these wierd mixtures to etch cooper board with...OK, BUT, whats wrong with good old ferric chloride?
Title: Re: PCB photoresist film exposure
Post by: Stonemull on October 19, 2017, 09:35:17 PM
Nothing, I am thinking of going back to Ferric chloride :)
Its dirty and half of my jeans and T shirts have nice sh*t coloured stains on them, you can't see through it so need to keep checking the board, works best heated so need to heat in a microwave which increases risk, it also gets used up .. I think.. you also end up with solids in the etchant unlike the acid etches. It is also tricky to dispose of properly. Done well though the HCl brew will etch fasterr than unheated FeCl imo and you end up with a stronger solution, there is a reason that every single pro fab house does not use FeCl..

What I did not realise till recently is that the FeCl is not doing the actual etching, it creates CuCl the same as the HCl,H2O2 mixes .. everyone discards the ferric when its 'used up' but it is likely that addition of peroxide or bubbling air through it for a bunch of hours will regenerate it.
Title: Re: PCB photoresist film exposure
Post by: Stonemull on November 09, 2017, 05:33:52 AM
Been using the plotter with 50mW laser (255 power, 5000 feed, bidirectional, 0.05mm .. takes <2 minutes or so for a 1" x 1" board) and been knocking out quite a few boards lately, I ran out of single sided copper for these little surface mount boards and found that double sided works fine, peel the resist, drop the board onto it and wrap it around, the resist sticks to itself, snip off the exposed edges, feed through laminator.
Use magnets on edge of extra resist to hold onto plotter, then snip close to the edges and peel off the film once both sides are exposed. Etching in HCl brew with air bubbler is taking about 5 minutes currently at room temp, it is getting faster each time, I had to dilute it down with more HCl acid so now I have more etchant that is stronger each time I use it.
Instead of making entire projects on a board I have started making just little boards about an inch square with a single chip.
Big 4x4mm surface mount pads for interconnects and keep a standard position for 5v and ground.
So this was yesterdays prototype for an isolation test for a pH probe, I have a buffer on the left board and left the coppper on the back for a ground plane (femto ohm input impedance measuring micro volts) .. the right board is an SOT23-6 18 bit i2c ADC and on the back of the right board is a 12f675 bit banging the i2c and a 9600 baud serial port outputting data. Then I can repurpose them later when this job is done.
Taking a break atm hence browsing, but pH probe is sitting in a pH 7.00 buffer solution and my rough uncalibrated, no offset adjustment probe is measuring between 6.992xxx and 6.993xxx, so .. yay.


Title: Re: PCB photoresist film exposure
Post by: Stonemull on December 11, 2017, 08:35:45 AM
I just knocked up a board and decided to document it in a little more detail showing software used and chemical strengths etc.
too many photos in one lump to add here so stuck it up on imgur in an album. did a couple of vis too but not uploaded them yet .. will do shortly.

https://imgur.com/a/KgKBY