PCB photoresist film exposure

[Zax]

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.

[Stonemull]

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.

[Stonemull]

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..

[Stonemull]

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..

[Stonemull]

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 !.

[Stonemull]

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.

[Zax]

Wow, yeah that's a super clean result. Awesome!

[Stonemull]

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

[Koskee]

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.

[Stonemull]

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.

[ThothLoki]

When I watch pcbs I use the muratic acid and peroxide mix at a 2:1 ratio. Works well.

[ggallant571]

A strong solution of H2O2 will eat your lungs very nicely. We use a powerful UV lamp to reduce the H2O2 to water & oxygen.

[Kunaphil]

I use the same recipe as Thoth.  It works pretty good, but make sure to have plenty of ventilation.

[Stonemull]

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..

[Kunaphil]

My recipe turns green.  It seems to get stronger each time you use it.