PCB etching with HCl and H2O2

As my electronics designs are getting more complex and my patience for soldering air-wires for all connections on a perfboard is decreasing, I started looking into making my own PCBs. Although there are professional PCB fabrication companies that are not very expensive, I am not so confident yet with my Eagle PCB design skills. Hence I decided to start fabricating some simple PCB boards myself to get a better insight in all aspects relevant for PCB boards.

Reading about the different options for etching PCBs, and following a instruction evening organized at the Hackerspace Nijmegen on using a small CNC mill for PCB fabrication, I opted for toner transfer using a laser printer and using HCl and H2O2 as described here.

My first attempt was with 10% HCl from the local hardware store (dat zeg ik, Gamma!) and 3% peroxide from the drugstore. Directly following mixing, etching went OK-ish, but rather slow. It took some 10 minutes for the 1-sided PCB board to be clean. The etchant turned into a nice green color. The second time (a month later) the etchant would not really work any more, and th ePCB only got dark. Rejuvenating the solution with some additional H2O2 as per instruction did not change anything. I guess the concentrations were too low, and after a few hours I abandoned the attempt and took the board out.

For the second attempt I ordered 30% Hcl and 10% peroxide in an online store. Using my old etchant solution, I diluted the H2O2 to approximately 3% and mixed that with the HCl in a 2:1 ratio (adding the acid to the HO2O, to prevent a strong exothermic reaction). I popped in my board (from the previous attempt, which had gotten quite dark). The result was a very nice etching process. The process was clearly visible and there were no bubbles.

You can see that half of the copper of the PCB board has been etched away

The result of the etching is quite nice.

Resulting PCB board. It is about 2×3 cm large and will contain a 6 pin DIP optocoupler with some resistors and a diode to implement a MIDI filter.

I am happy with the result of the etching. The ill-defined traces on the board are due to poor toner transfer; I had to make some corrections with a permanent marker (fine liner) on the board. Measuring the connection between all pads revealed that there was one short-circuit (on the left side of the board). I was able to remove that with an x-acto knife.

The next time I will design the traces in Eagle to be slightly wider and to have more space between them. In the Eagle design rules I used a 6 mil minimum trace width (the default), and a 12 mil clearance. And I have to practice more with the toner transfer… to be continued.

4 thoughts on “PCB etching with HCl and H2O2

    1. Robert Post author

      A permanent marker can be used to “repair” traces that were not transferred properly and for which the toner is a bit thin. By itself, the layer left by a permanent marker is too thin to properly shield the underlying copper from the etchant. But it would be convenient to simply use a marker; if you or someone else knows of a suitable type, please let me know.

  1. richard

    Just a thought ; I watched some youtube video of a desktop CNC router which can easily ‘etch’ a PCB design up to 0,1mm traces. these units cost approx 150,- euro on amazon and would avoid you working with ‘sterk zuur’ altogether 😉 en het is bijna kerst !

    1. Robert Post author

      Yes, agreed! The explorations on etching my own PCBs did not get me that far as I am not comfortable working with these types of chemicals. Furthermore, as I don’t want to mess up the kitchen sink, it has to be done outside. A light CNC router would indeed offer a nice alternative.

      But it was an interesting project to try out, and along the way I learned how to use Eagle for PCB design. I designed one that I got fabricated at JLCPCB; it is beautiful! A dual-sided PCB with vias connecting both sides is much more convenient.


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