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Hydrogen Peroxide and Muriatic acid as an Etchant.

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LAN_403

ConKbot of Doom

Sat Feb 24 2007, 02:05AM

Registered Member #509 Joined: Sat Feb 10 2007, 07:02AM
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I plan to start making my own circuit boards soon using toner transfer, and 1 part muriatic acid, and 2 parts 3% H2O2.

I'm trying to figure out what is going on chemically, so I know the mechanism by which the etchant is working...

I found out that
H2O2 + H2SO4 <--- ---> H2SO5 + H2O
and that the resulting compound is persulfuric acid, or Caro's acid...

Unfortunately that leaves me a bit confused about whats going to be going on when I add the board into the solution, with hydrogen peroxide, sulfuric acid, and persulfuric acid all in the same container.

After that is finished Etching, I'm sure it will be a nice mix of some of the original etchant, CuSO4, and possibly CuSO5?

Also, for safe disposal, what should I be doing?Preferabally how can I make it safe to put down the drain. Neutralizing any remaining acid with baking soda, and diluting it? I know CuSO4 isnt exactly the best thing to be dumping, could I possibly electroplate out the copper after neutralizing the remaining acid? What would be the best anode material to use, since there wouldnt be much point in replacing one nasty thing with another.

Thanks

Hazmatt_(The Underdog)

Sat Feb 24 2007, 03:33AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
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Muriatic acid is HCl

Sulphuric acid is H2SO4

HCl + H2O2 + Cu (on the board) ----> CuCl2 + H2O + O2 (unbalanced)

CuCl2 is poisonous and should not be dumped down the drain.

You can reduce it with iron by use of a nail or rod:

Fe + CuCl2 ----> FeCl2 + Cu ppt., then

FeCl2 + NaOH ----> Fe(OH)2 + NaCl (unbalanced)

When left to dehydrate, the Iron II Hydroxide will in sorts 'loose its water of hydration' and become Iron Oxide, which then can be dumped in the trash can if you like.

OR what you could do, to save a big mess is get a 5 gal. or 3 gal. poly bucket for painting, a fish tank heater and FeCl3 for etching, which dramatically cuts down on waste effluent. I did this a while ago and it cuts down my waste to almost nothing. I rinse the board off into the tank which cuts down effluent and it saves me the trouble of cleaning up all the time.

Hope that helps a bit.

ConKbot of Doom

Sat Feb 24 2007, 04:12AM

Registered Member #509 Joined: Sat Feb 10 2007, 07:02AM
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Haha oops, I should have double checked what muriatic acid was... (I like chemical names better for a reason :p ) What is the purpose of the H2O2 in the etching, in the equation it looks like all it does is decompose.

Hazmatt_(The Underdog)

Sat Feb 24 2007, 06:10AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
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The Peroxide helps to oxidize the copper. HCl by itself will not attack copper. It will however attack the oxides on the surface of the copper, a very useful bit of information if you need to clean your board before etching.

Matt

ConKbot of Doom

Sat Feb 24 2007, 08:31AM

Registered Member #509 Joined: Sat Feb 10 2007, 07:02AM
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Hazmatt_(The Underdog) wrote ...

The Peroxide helps to oxidize the copper. HCl by itself will not attack copper. It will however attack the oxides on the surface of the copper, a very useful bit of information if you need to clean your board before etching.

Matt

Ok, thanks, I'll be going with this method for now since I can get all my supplies locally, if I can find a good source of FeCl online, I may use that eventually.

...

Sat Feb 24 2007, 09:01AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
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not to threadjack, but I have found ammonium persulfate to work pretty good (although don't even try to use it with board with >2oz copper). Using 1/2oz copper I managed to get traces to work with the microscopic ucc chips

Not sure if you are in the US or not, but

persulfate

ferric chloride

Also, I believe that persulfate (being a dry powser till its mixed with warm water) doesn't need a hazmat to ship

ConKbot of Doom

Sat Feb 24 2007, 03:18PM

Registered Member #509 Joined: Sat Feb 10 2007, 07:02AM
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The persulfate says it will make 4 liters of etchant, sounds like a good bit, or does it get exhausted quickly?

I'll have to consider that, because 4l for $27 looks pretty good.

What ucc chips you using, mosfet drivers?

I got plenty of those in DIP, though the fairchild ones in SOIC at the top are 600v rated high/low side half bridge drivers, so they are easier to use for h-bridge stuff.

...

Sat Feb 24 2007, 04:54PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
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the powerpad msop ones, I think the pins are on a .15" spacing.

As to the persulfate; I mix it up in little batches as I go. Take a tray with 100ml of water, microwave it to get it boiling, add 50g of persulfate, add board, let etch. It only works when it is hot (above 130f) so letting it on a hotplate or something helps a lot.

ragnar

Sun Feb 25 2007, 02:46AM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
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I hope this doesn't stray away from the subject of the thread, but I'm sure some guys with expertise will be reading here who can perhaps help me.

When etching boards with ammonium persulphate, I generally do it in a hand-agitated tray rather than a vertical bubble-agitated vessel; and so it cools off very quickly with such a large surface area.

I have a gas stove. Are any metals "OK" to put the etchant in, on the gas, to keep it hot (with fume extractor on, of course?)

Pyrex glass and ceramics would be pretty inert to the etchant... but are there any metals I can use?

...

Sun Feb 25 2007, 03:19AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

Could you just use some normal metal, but spray it with a nice thick layer of polyurethane or something?

Heck, just looking at the time it takes for boards to etch, you would probably be fine with a copper pot ;)

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