Yes, I have to agree with you that sellers of potentaially hazardous chemicals should also act responsibly by giving information about disposal of waste products.
I did some digging and found the MSDS for the 2 most common etchants; Ferric Chloride
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Ammonium Persulphate
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Recycling of Ferric Chloride etchant can be done but is really only economical in large quantities as indicated by this item
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This paper
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indicates several techniques for re-utilisinf Ferric Chloride but again, none of these methods would be available to the hobby or small pcb manufacturer.
This University of Wisconsin page recommends that up to 5lbs of Ammonium Persulphate is safe to dispose of via the sewer
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I suppose that all of this really highlights the fact that in most cases hobby pcb manufacturers are almost forced to dispose of our waste etchant down the sewer. I dare say that eventually it will come back to bite us on the bum.
What exposure lamps did you use? It seems like they didn't expose long enough to get thru the resist. Try repositioning your layout and re-exposing again. What type of artwork did you use?
I looked at the replies and your answers, and I think you said the board was 5" away from your light source. Did you use a piece of glass to hold the layout against the board? If you did, and you used just any old piece, it may have had lead in it. This will impede the uv which exposes the resist. Get a piece of
6mm no lead content plate glass from your local glass house and try again.
I use F15T8BL uv lamps or the latest eqv in cheap fluroscent holders I buy from Home Depot. I remove the plastic cover, replace their lamp. I built a box big enough to hold 4 holders, with 6" high sides and rabbitted a groove on the top inside edge, for the glass to sit in. With the holders 3" apart, I can expose a 12" x 12" board without problems. Since my lamps are 15 years old, I expose 5 minutes and can easily do .01" traces. I have used MG boards and resist for years, but now they don't supply resist. I coat my own boards with positive resist and use MG418 developer mixed .1part dev, to 6 parts water. This is my "stock" solution. When I need developer, I mix 1 part stock to 1 part water. It can be cold and put it in a glass dish. I watch the resist change color, and remove the board when it is quite dark. I wash it off and put it back into the tray to finish developing, then wash and etch. The developer can be reused until it get too dark to see the board. Keep the used developer in a different bottle.
If you need any assistance please c>I have tried my first positive photo resist etch. The light exposure /
___ I tried looking for some positive photoresist at MG, but couldn't find any. Where can you get it? Any special tips or tricks about applying it to the boards?
Positive photo resist has not been available to us users for three years or so. At least not in Canada where I am. I bought 5 gallons from the company who made the original resist that MG sold. Now due to WHMIS and all those regulations, it's difficult to send it in liquid. The fines are disgusting. I had thought that a way to do it would be to coat boards and sell them. There would be a learning curve to be able to coat them in quantity for resale. I usually coat a 36" x 12" piece and cut when and as needed. This works for me.
I coat the boards by first wiping the copper with a paper towel soaked in some acetone. This removes the surface grease and allows the resist to coat quite nicely. I pour some resist into a glass or metal tray, hold the board vertical and use a fine foam brush to "paint" a layer of resist over it. Excess resist will run down into the tray, for use again, then when most of the excess is off, I take the board into my darkroom and place it upright and onto a pad of paper towel to sop up the resist drips. Then pour the tray resist back into the bottle.
The new resist I have is quite forgiving, it doesn't matter if there are run lines, making some areas thicker than others, (within reason). I just expose a little longer and these runs develop out and I get a etchable board.
Resist is green and exposed resist turns red in the developer making it easy to see areas needing to be developed longer. As I said previously, I take the board out of the developer just after it turns red and wash the developed resist off, then back in for more develop time.
Bill Jenkins wrote of spray cans of positive resist:
Others will probably mention them, if they are still available. But I'm just wondering how hard it is to make one's own spray cans for this purpose. People do home canning and people use CO2 cartridges to make their own seltzer and several decades ago, in lieu of canned bug sprays, people had DIY bug spray using some clumsy mechanical contraption that came with the liquid insecticide. So maybe it is possible to improvise.
I'm no good at practical stuff like this, although I succeed occasionally, but what would be wrong with an arrangement using a CO2 cartridge and positive resist in a seltzer bottle and a suitable kind of nozzle to shape the spray better, just as some kinds of shower heads do?
Ignorantly, Allan Adler snipped-for-privacy@zurich.ai.mit.edu
I think your new agitator will quickly tell you whether it is depleted etchant. I'm lucky that there was a stirring hotplate in my lab when I got there. A pyrex baking dish, a teflon-coated magnet (stirred by the magnet clutch of the hotplate), and some ceramic blocks to elevate the PCB make life easy.
CadSoft USA (divison of a German company)
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has a nice PCB layout package called EAGLE (Easily Applicable Graphical Layout Editor). The free version does 100mm x 80mm double-sided (4" x ~3"). It will output Gerber; many PCB houses also take native EAGLE files. Like anything else, it has its quirks but it is very popular. The upgrade path is also reasonable. There is a user's newsgroup and a factory-guys newsgroup (caution: Tilmann doesn't suffer fools lightly).
There's no need to go throught that effort, at least in the US. Your local hardware store, or at least a local home center such as Home Depot carries Preval units. These come with compressed cartridges and a small glass sjar and are made specifically for for the purpose of making your own spray "cans". They are cheap (under 10 USD) and widely available-at least in the US.
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