Making some Copper (II) Chloride PCB etchant

[wandrson]

So, I have never liked working with Ferric Chloride etchant when making my own PCB’s. I have tried Ammonium Persulfate, but find it a bit of a pain to heat it up to use it (doesn’t work well cold)–in fact I have nearly a kilogram (dry powder) if anyone wants it…

So, after researching, I decided to use Copper Chloride, since it can be made at home and is therefore much cheaper, and frankly easier to dispose of.

I have purchased some Muriatic Acid from Lowes, 31.45% concentration from Lowes. I am going to start with a liter of this, which works out to about 9.25 moles. That means I need about 4.62 moles of copper or about 294 grams. I am going to use about 300 grams so that hopefully all of the HCL is used up.

Now I could heat this mixture up and add some over the counter hydrogen peroxide to speed up the reaction so that it only takes a couple of hours; however, I really don’t like the idea… So I am just bubbling air through the solution. My understanding is that this reaction can take days to ‘start’ and that once started the speed of reaction increases.

So I started the process 24 hours ago. The color of the solution has experienced a slight change (less yellow), and the copper is showing signed of reacting with the HCL. Anyway, I plan to document how long the reaction takes to completion.

Does anyone know what the pH is of a solution of saturated copper chloride is in water?

[wandrson]

Don’t like working with it. Particularly disposing of it. After researching it, I found that Copper chloride can be made safe for disposal fairly easily.

I can use HAAS scrap aluminum to precipitate out the copper from the used up solution. Then I can neutralize the acid with baking soda, and the remaining chemicals are much safer and easier to dispose of.

It is also a cost issue. The purchased HCL is about $8 worth. The copper can be endlessly reused via recyling the used up solution. I need about 3L of etchant for my tank, which for Ferric Chloride is about $30 worth…

[mstovenour]

Careful with the fumes There is a bit of acid vapor given off because of the bubblers. I did a nice patina job on a lot of the tools on my peg board. Now if we had a working fume hood, that would be ideal.

[bpamplin]

I’m gong to start doing a few boards again. Please update this string with progress as you move through the project. If it is successful, a class or at least a link to a good article would be appreciated.

[Webdevel]

I use a Muriatic Acid + Hydrogen Peroxide solution to etch copper and brass. This method is MUCH cheaper than using Ferric Chloride.

I typically have to etch copper for about 45 minutes to get a good depth. My solution doesn’t maintain though. I find that trying to save the acid, even adding more peroxide to start the process again still doesn’t work as well. It’s cheap enough that making a new batch each time I need it is fine though.

The cap on the muriatic acid containers I have vents, to allow gases to escape. It will corrode metal, found this out the hard way FYI.

[mstovenour]

That solution can be regenerated by bubbling air through it for a day or so. The color will change to bright green as it regenerates. No need to dispose of hazardous copper solutions.

[wandrson]

This only works if there is enough copper in the solution. The straight HCL + H2O2 solution will eventually start to create Copper Chloride (II), but it is slow as @Webdevel says. What I am creating is a strong solution of Copper (II) Chloride, which functions as the etchant. It does wear out, but can be replenished by adding more O2 and HCL.

What the O2 on its own does is convert Copper (I) chloride which doesn’t etch to Copper (II) Chloride which does.

Bubbling O2 is slow (as my demonstration is going to show), but is a viable solution. Using H2O2 (peroxide) works quick, and even quicker in a hot solution, by doing the same thing adding O2. The problem is that it also adds H2O (water) which dilutes the solution, reducing its effectiveness in the future.

Now the nice thing is that my intended etchant tank is that it includes an aquarium pump to bubble air through the etchant when etching. This helps regardless of the etchant you use, but for different reasons.

[wandrson]

Theoretically, my approach above will produce a 1L solution with about 4.62 moles of CuCl2, which equates to a little over 520 grams. This should be a nearly saturated solution. There are several other approaches.

1. Purchase CuCl2 powder and create solution directly.  https://www.amazon.com/gp/product/B01BKW5KRY/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1
2. Start with Copper Sulfate, cheaper and more easily obtained, only disadvantage is your etchant will be contaminated with sulfates, but these do not affect its etchant ability, though they do complicate the disposal process.

[wandrson]

So I have just taken a second picture of the reaction after 48 hours. Here it is side by side with yesterdays photo. I am using the same camera, and despite different lighting conditions the camera light balance seems to be taking care of most of the difference as can be seen by the exposure of the background.

So you can see from yesterdays’ photo the solution was starting to turn green, which indicates the presence of Copper Cloride (II), with a darker color today, which indicates a greater concentration of the solution. The large amount of copper in the bottom of the flask indicates that the reaction has a long way to go. I am also thinking that the ambient temps (mid 40 deg F) are slowing the reaction as well.

May replicate this experiment with a controlled temperature environment to see how that effects the reaction rate.

[wandrson]

So day four of the process, the etchant appears to have gotten a little darker, but I am thinking that the day to day changes are getting gradual enough that this isn’t a definitive statement. Sometime early next week, I think I will extract the copper pieces from the jar and weigh them. This will tell how much has been consumed by the reaction.

I have also aquired 100g of reagent grade Copper (II) Chloride. I plan on making several concentrations of the powder in a solution of distilled water to determine how effective it is on its own as an etchant. I also want to measure the pH of those solutions to potentially provide a way to estimate if the home made stuff is water/CuCl2 or mostly HCl

The erlenmyer flask and stopper seems to prevent most of the fuming that @mstovenour had with his setup affecting his tools. Though it is possible that the cool temperatures have helped minimize that as well.

[wandrson]

Day five of the process. Subjectively the solution seems to be a darker green. There still seems to be plenty of copper left in the bottom of the flask. I will retrieve them and weigh them monday.

[wandrson]

Well, this is going much slower then I would have expected…

I drained the liquid in the flask into a beaker, and then placed the copper on an absorbent pad (still has HCL on it). I noticed that a lot of ‘powder’ attached to the absorbant pad.

I then weighed the copper and found I still have 263.15 grams. Which means that the reaction has only consumed (300.32g - 263.15) about 37.17g or a little more then 12% of the original copper in the solution. In addition when I returned the copper to the solution the color of solution turned a much lighter green. It is now possible to ‘see through’ the solution. I will wash and dry the absorbant pad. Recapture the precipitate and weigh it. I will then return it to the solution. At this point I suspect it is copper (I) chloride which is insoluable in this liquid. It also appears to be ‘coating’ the copper and slowing its conversion.

Anyway, the test is working, it is just taking longer then expected.

NOTE: Within 20 minutes of returning the solution to bubbling, the color returned to the dark green of the last few photographs. I suspect that the bubbling is causing all of the sediment to be suspended in the solution.

[mstovenour]

When I did this I stripped about 20 ft of 20ga of stranded wire. I think the surface area helped speed it along.