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Comment by pjbk | Hacker News Reader

Don't use a marker. I use 2-3 layers of TPU filament or Ninjaflex over copper treated with washable adhesive. Works wonderfully. As always, clean the copper very well with isopropyl before anything. You can also do flex PCBs this way:

- https://www.instructables.com/id/Make-Flexible-Circuit-Board...

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Nice! My first thought when I saw this post was that extruded filament of some sort would probably be more precise, and easier to set up.

Why TPU or Ninjaflex? Does that make it easier to eventually remove the mask? Or is it that other materials would break down in the etchant?

Adherence. Normal PLA/ABS or other plastic filaments will shrink when they cool down, and cause the thin layer of material to pull and separate from the copper. TPU is rubber-like and will have less inner stress to pull the material off. Also PLA absorbs humidity and will tend to change volume in a solution, with the same propensity to separate from the copper during the etching. TPU has more impermeability.

I have also tried using adhesion glues and hair sprays. Sometimes a thin application of hair spray (removed with a quick spray of isopropyl before the etching) helps a bit to define the edge traces. However I found that cleaning the copper very well, having a clean chamber in the printer and controlling well the etching temperature to reduce the etching time has the same effect and is less burdensome.

Have you tried PETG? I know loves to adhere to glass (if rather aggressively) - maybe it'd work here too?

It'd be cool if it does because PETG is a lot easier to print because of its rigidity (especially in bowden drives)

Good question. Not yet. When I carried out the tests (3+ years ago) I didn't have PETG filament around. Then TPU worked well for me and I have been sticking with it. I have a couple of PETG spools now so I will certainly try it next time!

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