Summer Family Project: Printed Circuit Boards?!? (part 2)

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HeavyMetal commented on part 1 asking about disposal of the used ferric chloride.  I had promised the next article would be about designing the circuit, but my research into that question found plenty of material for part 2.

Hazardous Waste

Ferric Chloride, by itself, is not a significant environmental problem.  It is used by some municipal sewage and drinking water plants to clarify the water.  However, as soon as we start etching circuit boards the solution becomes loaded with copper ions that are toxic to plants and fish.

Dumping the used solution down the drain is not only illegal, it is bad for the planet.  I recommend calling the local fire department, they will know where you can take your hazardous waste.  Or watch the newspaper, most communities have an annual toxic waste round-up.

I have also heard that you can neutralize the whole mess with baking soda (go slow so it doesn’t fizz).  Once it is slightly basic the copper will precipitate out as copper hydroxide.  The liquid can be poured off, diluted and sent down the drain.  The sludge can be dried, mixed in cement and disposed in a land fill.  I don’t think I would be comfortable doing all this, and will just take it to the haz-mat round-up later this year.

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Acid Cupric Chloride

I also found a great, but slightly less kid friendly, alternative to etching with ferric chloride.  Acid Cupric Chloride is easy to make, and according to "the internet" it can be re-used nearly indefinitely.
You will need some Hydrogen Peroxide, and Muriatic Acid

To mix up a batch, think back to your last chemistry class and observe a few safety rules.  Muriatic Acid will eat your skin, so wear gloves, apron, safety goggles, and anything else that makes you feel safe.  A
full face shield wouldn’t be overkill if you have one.

You will need two small plastic or glass measures.  A larger plastic container for storage.  I used a Rubbermaid food dish with a tight snap on lid so I can both etch and store in the same container.  All of the boards that I am etching are under 1" square so this size works well for me.  You might want a larger dish if you are making larger circuits.

I bought one quart of muriatic acid (31.45%) at Tractor Supply for about $4 and a pint of peroxide (3%) from the pharmacy for $1, making this the cheapest etchant yet. 

My smallest measure was a 1-Cup Pyrex with 50ml as the smallest gradient so that dictated the size of the batch I mixed up.  Add 2 parts peroxide (100ml) to your empty container, then slowly pour
1 part muriatic acid (50ml) into the peroxide.  Remember to pour the acid into the water, not the other way around.  If you are etching larger boards you may need to mix a larger batch and get a larger container.

As you etch more boards, the color will turn to a bright clear emerald green (darker than the photo to left) and become cupric chloride.  You can help it along by adding bits of copper, or just keep etching circuits til you get there.  I found that it etches faster than ferric chloride.  My first board etched in under 2 minutes, subsequent boards took about 10 minutes.  If it becomes dark or murky add some peroxide or bubble air through it to restore the color and clarity.


You Let Your Kids Touch What?

I do not recommend letting smaller children handle this, but with supervision it is not terribly unsafe for the pre-teens.  Make sure your kids wear proper gear, keep a sink and plenty of water on hand to flush anything touched by the acid.  This is a great opportunity for teaching a little chemistry and lab safety.

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