Eric Sorensen

Step Five: Etching

Now you are finally ready to prepare the acid and etch your board! At this point personal safety becomes more of a concern. This process produces potentially harmful fumes, so it is best done in a well ventilated environment. I recommend using rubber gloves when handling acid because you don’t want this stuff on your hands. And once again- DO NOT get this acid on anything metal. It WILL eat through most metals it comes in contact with. Measure and store the acid in a glass or plastic enclosure. In all honesty, I don’t wear safety glasses but it would probably be wise to do so.

I should also note I am NOT a chemist. Please take my advice with a grain of salt. While I have used this method of etching many times I make no guarantees. I won’t be held responsible if you injure yourself, burn your house down, or kill your family pet. You’ve been warned.

At this point I’d like to credit the site where I originally read about this etching method, here. If I am not clear about any steps, or if you’d like more information about the chemical process being used, I highly encourage you to reference his guide. You can also check out his source, here, if you want more in depth information.

1. Mix the acid

While it is always important to perform each of these steps in a well ventilated area, it is particularly important the first time you mix the solutions and use them to etch. Take the hydrogen peroxide and the muriatic acid outside! Muriatic acid comes in two standard concentrations, 5M and 10M. If you have 5M, mix it with the peroxide in a 2:1 ratio (two parts acid to one part peroxide). Since the 10M acid is twice as strong, mix it in a 1:1 ratio. When mixing the acid and the peroxide, you should treat the peroxide as water- which means you should add the acid to the peroxide instead of the other way around. Adding the peroxide to the acid can cause the mixture to explode!

Ad this point, your solution should be clear (it won’t be green like the above picture.. yet. ) Drop in your board and get ready for the fastest etch of your life. Depending on the size of your board the first etch can proceed in as few as 1-5 minutes. Throughout the etching, the solution will strip away copper from your board, turning the solution to a bright green color. This is the process of converting your solution from HCl and H202, to copper (ii) chloride, and eventually copper chloride. See the referenced links if you are curious about how how this process works chemically.

The etching proceeds much faster if you agitate the solution by moving your board around in the solution. I use a wooden or plastic stick for this.  Don’t worry if the etching takes longer than five minutes! In a cool environment large boards can take awhile to etch. Just continue to agitate the solution and check up on the progress periodically. In my experience the corners of the copper board completely dissolve first. Once they start to disappear, the rest of the copper has been thinned significantly and quickly follows suit.

When all of the copper has been removed from the board, remove it from the acid (using gloves!) and toss it under some running water for at least a minute. DO NOT throw away the etching solution. This solution can be used over and over again- exactly as you used it this time. As soon as you drop a copper board into it it’ll start etching away any exposed copper. After etching a few boards you will notice the solution getting darker. Once the solution is sufficiently dark (nearly black), it is saturated and will no longer work. There are two easy ways to rejuvenate it- you can either pour in a little more hydrogen peroxide (a cap full should be enough!), or leave it sitting out exposed for a few hours. Exposure to the oxygen in the air will bring the solution back to a functional state. The latter option is preferred if you have the time because it has the side benefit of evaporating some of the excess liquid in the solution.

This is what your board will look like after drying it off. The toner is masking the copper traces so in order to use the board you’ll need to remove it. The easiest way to do so is with a work rag and some acetone. Pour a small amount of acetone onto the rag and wipe it over the traces- the toner should come off easily. If are having to scrub hard you should use more acetone.

If your board looks something like this, congratulations! You are ready for the last step!

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Tags: howto, howto etch circuit guide