Etching Idea

[rockgardenlove]

So, I recently got into T-shirt silk screening, and I'm using this photo emulsion stuff to make my shirt.  Basically, you put the photo emulsion goop on your printing screen, put a positive printed on acetate over it, and expose it to light.  The part exposed to the UV in the light hardens, so when you wash out the screen, the parts you covered up (with the positive) wash away to leave you with a stencil.  The resolution is really excellent and precise.

But to get back to pedals, I was thinking:
Photo emulsified boards already exist, obviously.  What if you put silk screening photo emulsion goop on your PCB board, made a negative, laid that on top of the board, and then exposed that?  Basically, just homebrew photosensitive PCBs.
The clear parts in your acetate (traces) cause the photo emulsion harden up and stick to the board.  The rest of the photo emulsion (uncured part under black of transparency) washes off with water.  After you etch, the photo emulsion washes off with bleach easily.

A bottle of photo emulsion for silkscreen is pretty cheap.  Like 8 bucks for a ton o' boards worth.  This is of course assuming that the photo emulsion will resist acid, but I'd guess it would. 

Has anybody tried this?  So far as I know, and after a Google search, it's never been done...

Cheers!

[tranceracer]

Interesting topic!
I actually did some research in my quest to find an etch method that works for me.  I did look at the silk screen technique and went as far as even buying all the lights and emulsion, embroidery hoops.  I even went to some of these diy craft sites that shows how to make your own silk screen using panty hose and embroidery hoop found on this site:
http://www.instructables.com/id/D.I.Y.-Screen-Printing/
(the video is pretty lame)

I was going to try silk screening the trace on the board and do the emulsion technique you mentioned here's what I found.

1. It's a challenge to get an even coating of the emulsion on the board
2. you have to wait for the emulsion to dry
3. not sure how the emulsion will stick to the Cu so may have to "touch up after washing the non trace areas off.
3a. not sure how much detail I could get from the "panyhose" screen because I noticed that the netting was kind of big (about 0.5mm).
4. like you mentioned I wasn't sure how the emulsion will react to the etchant (feric or peroxide/muric solution)
5. A good method would be to just silkscreen the trace onto the board then etch.
6. I've since settled on just using laser printer on avery sticker backing.  No drying time and instant gratification.  I really like the pre-sensitized board method but the boards are (as you may expect) more expensive than the plain Cu.

It would be really cool if you can perfect and share the technique, there's potential to make some really nice labels for your boxes and boards! 

I haven't the time to pursue and follow up to see if the panty-hose silk screen technique can produce acceptable results but I will post an update if I get satisfactory results.

[R.G.]

It's been done. Back in the 1960s and 1970s, many low resolution boards were done this way. It's cheap, fast and easy way to resist many boards.

The disadvantages, and why it's not done now are
- it suffers from needing lots of prep time to make a screen and then clean up afterwards
- you have to let the inks dry after screening
- resolution is limited. As a practical matter, you usually cannot get one trace between IC pads, which is a big deal in dense board, no issue at all in simple boards.

It's best for simple, low resolution boards in 100's and up.

[sean k]

I get what your saying.
You want to put emulsion onto the copper then when it dries off the artwork, in negative and on a clear acetate, is taped to the Circuit board and exposed under uv light. What you're doing is taking away the printing onto a screen and using the negative cured emulsin to resist the etch. Good idea!
My brother and friends did the screen printing thing back in the 80's using the UV affected cure emulsion and they did their artworks with .5mm rotring pens and with double layer acetates were able to acheive the same detail after curing and printing.

If you can get that emulsion on even onto the copper and it resists the etch then your home free. Try it out and see what happens.