The Photo-Positive Process - Notes, And A Few Questions

[smallbearelec]

I'm close to ready to publish my tutorial. I have confirmed that making the positive on Avery #53212 Window Decal Stock eliminates the need for a contact printer or even a glass cover; the adhesive back ensures good contact with the board. I'm doing the experiment now to see if the photoresist is compatible with a Sodium Persulfate etch. A few questions:

--Lye works fine for making the developer, but of course it is caustic. From my Gilbert Chemistry Set days, I recall that they supplied Sodium Carbonate (washing soda) to create an alkaline solution. Can anyone confirm that that will/will not work with the positive resist chemistry? I'll do the experiment if need be.

--Does anyone know of a safe way to dispose of spent lye developer solution? I added white vineger to neutralize the NaOH, and I see that the resist has formed a blue precipitate. I figure to wait till the water mostly evaporates, mop up the remains with a paper towel in a gloved hand, let that dry out and trash. Comment?

--The product of the Sodium Persulfate etch is copper sulfate. Is there a known good disposal method for that?

Regards
SD

[Nasse]

I used drain pipe cleaner as developer, the stuff is mainly sodium hydroxide, and is made to be poured to the pipe so I was not thinkin about it, because it was only a small amount, less than 1 liter ready mix with water added. Dunno if neutralising makes it to some kind of salt which may have problems like corrosion and pollution later where it goes. Quess doing only small boards now and then does not make much harm, when you think how much all kind of other bad stuff goes down there. Maybe it could be combusted in the back yard with leaves and such.

[Nasse]

I have been wondering if plastic (acrylic or polycarbonate or other) does dampen UV rays less than glass. I used clear CD box cover for small pcbs

I quit using spray-on positive photo resist after failures when tryin to spray even film on copper, but it is good when you are lucky

Some shops have special treatments for photocopy/laser prints that make it more black. I used black water based drawing ink (engineers and architects used it in the old days) and it worked quite well imho, I just put few drops on laser print on overhead polyester film, wipe off with soft paper, seems to stick on laser print.

[R.G.]

If you ever get serious enough to do photo positive, you'll never go back to what you used to do.

I personally like the pre-sensitized boards. I could never get the spray stuff to work consistently. And in all photo-chemical processes, consistency is the fundamental worry. Anyone who has ever printed photos with enlarger and trays has no trouble with photo PCB processes - which, of  course, means that it's as common a skill these days as knapping flint for arrowheads. 

Get a good process for positive film, exposure, time, and developing, and FOLLOW IT EVERY TIME and you'll get resolution sufficient to print 8-mil traces.

[defaced]

I have been wondering if plastic (acrylic or polycarbonate or other) does dampen UV rays less than glass. I used clear CD box cover for small pcbs

Depends on the UV spectrum you need for exposure. 

UVA goes through most anything clear.  It definitely passes through glass.  This and UVB are big in the reptile/amphibian hobbies, which is an old stomping ground of mine.  Actylic, polycarb and glass are used pretty much interchangeable when all you care about is UVA. 
UVB is sensitive to composition, but there are plastics that allow it to pass (OP4).  Glass blocks UVB. 
UVC, I have never played with.

I am really looking forward to this.  I have never been successful with the toner transfer methods.

[smallbearelec]

Another question answered:

At least with the resist on the boards I have in stock, Sodium Persulfate works fine for the etchant.

SD

[jonnyeye]

This website indicates that sodium carbonate is an acceptable developer for photoresist.  Sodium carbonate is a good choice if it works, as the spent developer and spent persulphate etchant can simply be mixed together to precipitate out the copper (as a carbonate) for disposal - copper carbonate being quite insoluble in water.  Copper hydroxide is insoluble too, but tends to gel a bit (adding carbonate will help it along).  Working with colder solutions helps too.  Filter and dry the precipitate and dispose in your local landfill.

Do not add vinegar to neutralize any copper solution you intend to precipitate out - copper acetate is soluble in water.  You'll need to evapourate any copper and vinegar solutions.  Hydrochloric acid or sulphuric acid are better for this, and even low concentrations will work ok.

[DiscoVlad]

If you end up with copper hydroxide: leave it overnight so that it breaks down into copper oxide, which is also insoluble and can be filtered out.

[smallbearelec]

Tutorial is posted:

http://www.smallbearelec.com/HowTos/PhotoPCBoards/PhotoPCBoards.htm

and kit and materials are available on the Stock List. Comments welcome.

Regards
SD

[toneman]

Hey SD,

Nice tutorial   

Does the photo-positive pcb come in sizes other than 3" x 5" (bigger, say 5x9)??

thanx
T

[Meanderthal]

as common a skill these days as knapping flint for arrowheads.

Sure, who doesn't prefer obsidian nowdays...

I really like the idea of diy photoetching. Seems less crude than Iron ons and sharpies, might be easier to acheive more professional looking(in an old school way) results. Might give it a try if I ever get back into this...

[trjones1]

I really like the idea of diy photoetching. Seems less crude than Iron ons and sharpies, might be easier to acheive more professional looking(in an old school way) results. Might give it a try if I ever get back into this...

Once you go photo, you'll never go back.

[therecordingart]

I always had consistency issues with MG Chemicals sodium hydroxide as a developer. I'd either under develop or over develop most of the time. I switched to sodium metasilicate crystals which work great!

My setup was a few fluorescent black light bulbs, transparencies, sodium metasilicate, and FeCl.

[smallbearelec]

Does the photo-positive pcb come in sizes other than 3" x 5" (bigger, say 5x9)??

I can get any size I want. However, to get it at a kick-butt price, I have to bring it in on the boat with other stuff from Taiwan. Remembering also that it has a shelf life, I don't want to get stuck with material that I can't sell or that creates unhappy customers. So I will buy more small ones as the market (I hope) grows, and buy some larger pieces.

[Meanderthal]

 

Does anyone know of a safe way to dispose of spent lye developer solution?

How spent is it? Can ya still make soap with it?

[PRR]

> dispose of spent lye developer solution? .... I figure to wait till the water mostly evaporates, mop up the remains with a paper towel in a gloved hand, let that dry out and trash. Comment?

This turns dilute alkali into CONCENTRATED alkali.

The total damage potential is similar either way. But dilute stuf tends to do small damage over a large area, concentrated make heavy damage in a small area. With lye in plumbing, this can be the difference bewteen 50 feet of softened scum, and one inch through-the-pipe. In the trash, you have a concentrated "bomb" which can probably sit in a landfill, if it does not get ripped and spilled or dampened on its way there. Remember: "never add water to a mass of the powder".

Why mop it up? Can you find a STRONG capped disposable container? Laundry detergent jugs are pretty sturdy.

In many towns, the only legal disposal is via the Hazardous Waste program.

[smallbearelec]

Cat litter is ground clay...would that work?