Circuit board etching

[Bern]

Thanks to all, on my other topics. You all have been a big help. Now I need to make some circuits boards. Question: Buying circuit board kits can get expensive. I have double sided raw board material. What can be used for a cheap etchant? As I recall, several years ago as I was around a circuit board shop, they used lots of ammonia. Can a person buy ammonia in a store that is strong enough to etch boards? Even if it took quite a bit longer, will it work? Is there something else that can be used, that is readably available?

[Dean Huster]

Ferric chloride is probably the least inexpensive of the commonly-available etchants, but it sure is messy. Irreversibly stains anything it touches. And it's difficult to see through to check on the progress of the PCB without lifting the PCB out of the soup. It's available as a premixed liquid or as a powder.<p>Ammonium persulfate is the preferred etchant, in my opinion. It's pretty much transparent, etches about as quickly and isn't as nasty as the ferric chloride. It's available as a powder.<p>Both etchants work much better if they're heated to around 130 or 140° or so and both work lots better if you agitate the solution somehow. Bubblers placed in the bottom of the tank do well, but does cool the solution off surprisingly quickly.<p>Harry Lythall (you have to spin that one through Google because I've lost the URL for his site) likes to use a combination of hydrochloric acid and hydrogen peroxide, but a peroxide that's in a concentration that isn't easily available. Overall, it may be the cheapest etchant, but it also stands to pose a lot of serious safety hazards, so I don't recommend it at all.<p>Clean the bare copper on the board really well before you lay out the traces. I like to use 3M Scotchbrite pads (those green pads in the grocery section), but don't get sucked in on anything but the 3M brand. The "clones", although cheaper, aren't nearly as agressive. If you get to doing this a lot, Sams sells big stacks of big Scotchbrite pads for a very reasonable price.<p>There are a lot of resists that can be used to cover the traces on the bare board that you want to remain behind. Doing it by hand is a good way if you're starting out with a simple board. Some folks like to use black Sharpie felt-tip pens. I don't have the best of luck with those other than for repair of lifts on the toner transfer method. But if you try it, use a new pen that has a sloppy amount of ink on the tip. There are lacquers available for that purpose also. I've always had good luck with Testor's #1103 red model paint. The other colors, for some reason, don't work as well, at least in ferric chloride. You can use a thin artist's brush to apply the paint or lacquer, but I've had the best luck using one of those old split nib inking pens that came in old drafting instrument sets.<p>Just be sure to rinse the board off really well when you're done etching.<p>Dean

[haklesup]

Nitric acid diluted to desired etch rate<p>or if you don't like acid<p>10ml Amonium hydroxide (oven cleaner maybee), 10ml 3% hydrogen peroxide, 100ml water<p>or if you want something you can actually get and won't burn you instantly<p>Ferric Chloride available at places that sell bare boards. <p>I don't think Hydrochloric acid works which is too bad because you can get it in the dollar store as toilet cleaner. I can't think of a household or automotive product with nitric acid in it. That's probably a good thing because mixing with organic compounds often produces unstable stuff (like nitro-glycerine)<p>There are others I can't think of but I'm sure someone else will add to the list.

[jwax]

Stay safe with ferric chloride- off the shelf at Radio Shack. Use aluminum foil on a table, then etch in a shallow pan that's inside an empty old pan, or cookie sheet to catch any splashes. Glass or plastic containers will work, and use plastic tongs for handling the board. Use gloves and eye protection! Etching is faster at warm temperatures, but until you figure out a safe way to heat the etchant, room temp will do. Fresh air ventilation needed- anyway you do it.

[Mike]

how i heat the ferric chloride is heat some water on the stove, dump it into an old butter container, and place the bottle of etchant in there.<p>In my experiences, sharpie doesn't work at all, the etchant eats right through it. The best way to do it that I have done is design the board on the computer with software such as Eagle (free at I think [url=http://www.cadsoft-usa.com)]www.cadsoft-usa.com)[/url] then print it using a laser printer onto the thick glossy laser paper that the people at kinkos will sell to you by the sheet. If you do not have a laser, print it on an inkjet and have kinkos copy it onto that paper.<p>Then, using an iron, heat the board for 30 seconds, place the design face down to the board and iron on for 2 minutes. Place the board in boiling water for 30 seconds then take it out and peel off the paper. Then, use VERY fine sandpaper and lightly sand off the remaining paper. be careful not to sand off the traces.<p>Then, etch in the solution until all copper is gone, then using sandpaper (or, even better, steel wool) and rubbing alcohol, clean off the toner, drill the holes with a small drill bit (ACE hardware has a nice selection of them) and solder.