PCB photoresist film exposure

[Koskee]

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.

[MegaBlackJoe]

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.

[Stonemull]

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

[Andrew]

all these wierd mixtures to etch cooper board with...OK, BUT, whats wrong with good old ferric chloride?

[Stonemull]

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.

[Stonemull]

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.

[Stonemull]

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