Photographic PCBs?

I was just reading: http://e-gizmo.com/blog/pcb/diypcb.html
Can a presensitized pcb be used in a photographic process? They seem cheap.
I've heard that you can develop them in the sun, but I doubt that would transfer to the idea of using one in-camera since the exposure time would be extra long.
What are the differences between this copper presensitized pcb and a glass presensitized pcb?
What exactly is coated? I know nothing.

jsmoove said:

What are the differences between this copper presensitized pcb and a glass presensitized pcb?
What exactly is coated? I know nothing.

Click to expand...

The photosensitive part is lacquer coating on copper foil. The foil in turn is bonded to a sturdy base material like an epoxy glass composite (not transparent, think fiberglass). Areas of the lacquer exposed to light become soluble (in water? I forget) and are washed away. Actual PCB etching is done by immersing board into a solution of ferric chloride, which dissolves any copper not still coated with lacquer. The process normally doesn't allow for any real tonality, but perhaps you could etch halftone images in this manner.

After UV Exposure it is developed in NaOH solution. I don't remember which part is dissolved, the UV exposed or the unexposed.

Where the layer had dissolved the underlying copper can be etched away with FeCl3 or persulfate.

Look up polymer photogravure.

There are several different kinds of photoresists.

The precoated boards you can buy from Bungard etc. are "photopositive". Areas exposed to UV light will be washed away during the development process. So the copper traces, pads, texts usw are black on the film. Everything else is transparent.
I did a lot of PCB boards using that technique. (With inkjet printer on special foil)
Usually NaOH solution is used. Strength can be looked up in datasheets and tutorials.

The company "Kontakt Chemie" offers a spray-on positive lacquer that works the same but can be sprayed on boards/materials that have no coating. It is called Positive 20 and i also used it for RF boards where the base substrate is not available with coating.

Industrially, a negative tenting-resist is used. Thats a thin photosensitive foil that is hot-rolled on the already drilled and plated-through board. There the whole thing is inverted. The UV light hardens the parts that should remain after developing.
I also used this resist for my later boards. There may be other techniques in industrial PCB manufacturing, but i do not know all of them.

I do not think it is possible to create tonal transitions with those resists. Either it stays on the board or it is removed.

But i think one could print out the films with half-tone patterns and etch them in copper

Ah yes, "back in the day" I made many PC boards with photographic processes -- but in those days I used a negative resist lacquer (made by Kodak, no less) -- a rather aromatic solvent was used for developer. However, anything resembling a continuous tone was purely accidental. I did occasionally etch some images of line drawings, and even less occasionally some using a halftone screen pattern, or a grate of parallel lines. A neighbor who worked for a manufacturer of the copper laminated glass-epoxy board got me some thick material with a nice blue color to play with for interesting effect. I also tried deep etching a brass plate and filling the etched parts with India ink -- there's no limit to what can find to do to avoid what he's supposed to be doing ...

Yes I was looking at these ones: http://www.acdcshop.gr/photosensitivepcb-c-88_91_122-bungard-f-77_en.html
But yeah if there is no tonal possibility, then I guess that wouldn't work so well.
Thanks all for the info, cool stuff!

@nmp these things? https://www.toyobo-global.com/products/xk/lineup/printight/index.html
I've never seen this before....very interesting....I wonder what the exposure times are.

Can any photo gravure process be used in camera?

Found an example of the Toyobo plates: https://www.impactprintmaking.com/wp-content/uploads/2020/11/Figure5_e-1536x485.jpg
From: https://www.impactprintmaking.com/article/light-emitting-prints-on-glass_autumn_2020/