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OVERVIEW:

This is a simple procedure for preparing 1 liter of cupric chloride etching solution. The tradeoff for the simplicity is a bit of patience as it may take a while to complete the preparation. The value of this patience is that the resulting solution won't be overburdened with hydrochloric acid and thus won't be as smelly and as corrosive to materials around it as some more quickly prepared solutions may tend to be. It also won't have any residual hydrogen peroxide which will result in a very slightly lower tendency to undercut your PCB traces. That last effect is really quite small, but why not? Also, since we won't be depending on the presence of H2O2 once the etching solution is prepared, we don't have to worry about over diluting our solution by trying to regenerate it with the weak 3% H2O2 commonly available in drugstores. We'll be regenerating with an air bubbler, which can serve double duty to agitate the solution when etching.


MATERIALS:

One large (at least 2 liter/0.5 gallon) glass container with a plastic lid. A 1/2 gallon "iced tea" jar with a plastic lid (plastic lid liner or no lid liner) and a small pop open spout would be ideal because you can open the spout to insert a fritted glass bubbler for use in rejuvenating the solution after use. If you need more than 1 liter (1 qt) of solution, consider using a larger container and increase the amounts of materials below accordingly. I suggest the container be only about half full when done. Only partially full plus a small opening in the lid keeps any spray resulting from regeneration by air bubbling inside the glass container.

One small aquarium pump. The cheap vibrating kind is fine.

One fritted glass bubbler, preferably long enough that it can reach the bottom of the large glass container with at least an inch or more of glass tube sticking out - preferably. If you can't find one that long, then your plastic tubing will extend into the container. I don't like that, but that's just me.

Plastic tubing to connect the pump to the fritted glass bubbler. I like enough tubing that I can place my pump higher then the top of my jar. Not likely the solution will syphon out if the pump is lower, but it's 100% impossible if it's higher.

200 grams (7 oz) of copper wire, copper pipe or other pure copper. I used solid copper wire, but stranded copper will dissolve quite a bit faster. Pennies (even the old type) and some misc plumbing or electrical hardware aren't pure copper and are unsuitable. Tarnish (discoloration) is OK, but it must be clean otherwise. 200 gms of copper is about 14 feet of #10 copper wire... 22 feet of #12... 36 feet of #14... 56 feet of #16.

32% - 37% Hydrochloric Acid - also called Muriatic Acid - free of detergent or other additives. READ THE LABEL! This really needs to be 32% - 37% HCl and free of additives, so READ THE LABEL! You can get concrete driveway cleaner that meets these requirements at Home Depot, Lowes and assorted hardware stores. Look until you find 32% - 37%, Hydrochloric Acid or Muriatic Acid free of additives. You'll be sorry if you don't. It should be easy to find in the USA... might require some looking elsewhere.

3% Hydrogen Peroxide. This is readily available at Walmart, a grocery store or the drugstore. You only need a few ounces so forget about stronger solutions that are harder to find and more expensive. If you think stronger is better and manage to hunt down 35% H2O2, please don't bother to tell me... especially if you hurt yourself... perhaps seriously.


SOLUTION PREPARATION:

Pour 1 liter (4-1/4 cups) of water into your container and clearly mark the level on the outside of the container. Pour out the water. This is the level you will want to maintain later after etching and rejuvenating.

Add the copper to the empty glass container.

Carefully pour 0.6 liters (2.5 cups) of hydrochloric acid into the glass container.

Add 0.1 liter (0.5 cup) of hydrogen peroxide. This should be all the hydrogen peroxide you'll ever need.

The copper wire will begin dissolving as evidenced by a green color forming in the solution and bubbles being generated on the surface of the copper wire.

Place the lid on the container, open the spout and insert the fritted glass bubbler connected to the aquarium pump and begin bubbling to mix the solution.

Here's where patience comes in... continue bubbling until the copper wire is completely dissolved. If the solution becomes a brownish/muddy color, add 1 oz of hydrochloric acid and continue bubbling until the wire is completely dissolved AND the solution is a deep emerald green. You really shouldn't need extra HCl, but if it's weaker than the label says you might. If it's a LOT weaker because you bought the wrong stuff... well... you were warned. When the copper is all dissolved, the color will be fairly dark, so hold the solution up to a bright light, or pour a bit into a smaller container, to gauge the color. If the acid you're using is on the slightly weaker side you may need to repeat the addition of a bit (less than an ounce this time) of hydrochloric acid if several days of bubbling doesn't result in a deep emerald green color with no trace of a brownish or muddy color.

Dilute to 1 liter with water and that's it.

Use it as you'd use any solution to etch PCBs and pour the used solution back into the main glass container when done. Inspect for color of the portion you used for etching each time. (It should be easier to gauge the color in the etching tank because you won't be looking thru as much solution.) As long as it's emerald green or only slightly off color, it's good. No harm in bubbling to rejuvenate after every use, but not necessary until it's no longer a pure emerald green.

The amount of excess HCl in the final solution is designed to be quite low. If a lot of excess HCl is present there's no avoiding some of it being driven off by bubbling, possibly resulting in an odor and the release of corrosive gasses. But at very low concentrations that amount is essentially negligible. For those whom I might consider overly concerned about smell and corrosion... you can have the greater peace of mind you desire by avoiding unnecessary rejuvenation... and when HCl must be added because the solution won't fully rejuvenate, you can add it in smaller increments than I recommend until the solution can be rejuvenated to a pure emerald green. An ounce in excess is enough. And for those who are concerned anyhow, you can always store and rejuvenate someplace well ventilated.

At some point you'll find you can't rejuvenate just by bubbling. When that happens, add 1oz (less if maybe overly concerned about corrosive fumes) of hydrochloric acid and bubble until emerald green. If you add less than an ounce, realize you may need to add several smaller amounts before you can fully rejuvenate. Rejuvenation requires oxygen that you get from the air by bubbling, plus an excess of chloride ions from hydrochloric acid. You don't need a large excess of HCl, but you need some. More isn't better.

Maintain the solution level in the glass container at 1 liter - or whatever your initial volume was - by adding water if it falls lower. If you only add HCl very sparingly, and only when needed, you may find the volume of the solution doesn't increase because some water evaporates when bubbling. If you add H2O2 to regenerate because you're impatient, your solution will continue to increase in volume and may become too dilute.

Over time, depending how much etching you do, copper will build up in the solution. When this occurs you can remove a bit of solution (maybe 0.5 - 1 cup), pour it into a pint jar and set it somewhere to evaporate.

If you accumulate any significant amount of copper chloride crystals in this pint jar, you can scrape it into a small freezer baggie and give it to someone who wants to use it to kick start his own smaller batch of etching solution. DO NOT dispose of excess copper chloride down the drain. It's deadly to pretty much all aquatic life.

That's it.

Jim H

P.S. This was originally: /g/homebrewpcbs/message/36051
Some small changes have been added.