"Safety concerns" about various chemicals

[gijim]

Hi everyone,

It's been a while since high school chemistry class, so I wanted to get your input on some things...

I read on the net about a new "cheap" way to etch PC boards. What you do is you mix 1 part Hydrochloric acid (the 30% pool supply stuff) with 2 parts Hydrogen Peroxide (the 3% disinfectant). Then you just add your copper board and watch as it dissolves.

Now I have several questions... First, how dangerous is 30% Hydrochloric acid? Back in high school, somebody wet their arm and put lye on it to make a paste, and it took some 20 minutes to a half hour before there was any noticable change. That quite literally changed my life, because I figure if it can burn me - I have 20 minutes to wash it off. Is 30% hydrochloric acid more dangerous than lye? (I wear gloves and eye protection, but I want to know what I'm dealing with here)

Second, when it is mixed with the 3% H2O2, it is dilluted significantly. How much "less" dangerous is it then?

Third, if I understand the process right, it turns copper into copper chloride. Is that solution any more/less dangerous than what it started as?

Thanks in advance,

 

[insult2injury]

That is the same mixture that metalographers use to etch their copper/brass specimens. I'm not an expert but It usually doesn't etch the copper to a large extent. I believe that it must be mixed fresh about every 20 minutes or else too much of the solution has reacted to accomplish the etching. Maybe check a metalography handbook and it would have safety information.

I2I

 

[gijim]

The wierd part that I've been reading, is that it can be "regenerated" with an air bubbler.

I guess I don't understand the chemistry well enough to understand how it works, but it sounds like the copper chloride reacts again with the copper or something?

 

[insult2injury]

the copper cloride is formed when the acid reacts with the copper.

I2I

 

[bimr]

Here is information on hydrochloric acid:

http://en.wikipedia.org/wiki/Hydrochloric_acid

 

[epoisses]

Pls ask a vendor for an MSDS. You will want to apply proper handling guidelines and find out how dangerous it is beforehand, not afterwards...

 

[moltenmetal]

Ferric chloride isn't cheap enough for you? It's nothing but old Camaros and hydrochloric acid- how much cheaper can it get? And it eats copper for breakfast...

What you want to make sure of is that the etchant you use is compatible with (i.e. resisted by) the etch resist you are using. No use to you whatsoever if it etches everything except the substrate!

 

[ScottyUK]

Cupric chloride is a common industrial PCB etchant, or was a few years ago. When used in a well-controlled process it can produce better trace geometry and can etch finer traces accurately when compared to iron III chloride.


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Sometimes I only open my mouth to swap feet...

 

[gijim]

FeCl isn't all that cheap. Because I usually buy small quantities locally, I end up shopping at radioshack, which ends up charging me something like $7 a pint. HCL and H2O2 etchant are about $10 a gallon - for literally a lifetime supply. It can be regenerated by bubbling air through it.

There IS no MSDS for the HCl/H2O2/CuCl/water mix, which is what I'm most concerned about.

I understand the HCl is nasty stuff. Just taking the lid off and it starts "steaming" fumes/vapors. However, once it is mixed and dilluted with H2O2, and a portion of the HCl is converted into CuCl, I'm curious what the danger is then.

 

[kenvlach]

First, this bit of mis-information needs corrections:
"Back in high school, somebody wet their arm and put lye on it to make a paste, and it took some 20 minutes to a half hour before there was any noticable change. That quite literally changed my life, because I figure if it can burn me - I have 20 minutes to wash it off."*
WRONG!
Lye (sodium hydroxide), even as dilute as 5 wt%, is sticky and difficult to wash off. It causes painful, deep, long-lasting burns that may take months to heal. Fortunately, it has negligible vapor pressure, so it is safe to use if wearing simple PPE (plastic gloves, apron, eye protection).

Hydrochloric acid is dangerous on contact. But, maybe more insidious due to its high vapor pressure -- about 1 atm at 40% aqueous solution. HCl vapor can cause serious burning of eyes, lungs, etc. The 30% stuff is still seriously dangerous. For your DIY etching solution, work outside, stay on the upwind side and remember the 'pour acid into water (the 3% peroxide solution) rule.' At 10%, the vapor pressure is much reduced, as given in the Wikipedia article, but still neeeds ventilation.

Bubbling air into acidic solutions creates acidic mist, so be careful of yourself & ventilation equipment. PVC ducts resist HCl mist, but not stainless steel.

The oxygen from the air oxidizes Cu[sup]+1[/sup] to Cu[sup]+2[/sup] and Fe[sup]+2[/sup] to Fe[sup]+3[/sup]; a change of valence from '-ous' to '-ic' state. The acidity keeps the metal hydroxides from precipitating out of solution (eventually will reach a pH-dependent saturation limit).

Hope this helps. Be careful out there!

* Maybe the high school experiment was a re-creation of colonists' soapmaking, wherein extremely dilute caustic solution is generated by leaching wood ashes.

 

[gijim]

Painful - no.
Deep and longlasting - oh yeah.

(slightly O/T) I was in classes with him throughout the day, and he was giving me the play by play as the lye ate through his skin... He said he didn't feel a thing. After his skin started to turn clear a la lutefisk, he washed it off. It was a nasty looking burn, and as I recall he now has a permanent scar.

Back on topic, the vapors that I see pouring out of the container of HCl when I open it up - is that what it means to be "fuming"? Like when you hear people saying, "use fuming sulfuric acid"...

Once the acid is dilluted with the peroxide, would it be safe to etch indoors then? The only danger seems to be the acid fumes, which are reduced to zero once dilluted...

 

[kenvlach]

Re "Painful - no."
-- One doesn't feel an immediate burning with sodium hydroxide solution. But, the burn goes through all the layers of skin, into the flesh. The pain lasts for weeks or months while skin regrows from the edges (like tree bark does after pruning a large branch).

The fuming seen with most acids is the invisible vapor reacting with humidity in the air. With some highly concentrated acids, the reaction of humid air at the acid surface is so exothermic that it creates an acid mist.

Even diluted to 10%, HCl vapor can cause health & corrosion problems if used indoors w/o proper ventilation. It will etch stainless, dissolve concrete, etc.