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I have attempted to make this board below at home. Applied negative photoresist paint, left to dry for about 4 hours each side over a radiator, applied a double layer tracing paper with the artwork on each side (4 sheets of tracing paper total), exposed it outside for 25 minutes for each side (cloudy winter day in Europe), developed with washing soda + water, etched with an unknown ratio solution of HCl + H2O2.

At first the solution was 2 : 1 of HCl 37% : H2O2 3%. I have etched a PCB in it fine, loosely put a lid on its opaque container and let it sit for a week. Then I have attempted to reuse the same solution about one week later but it would not etch. Poured some H2O2, nothing, poured some HCl, still would not etch, then poured a bit more H2O2 and it did its thing, but slower than the original solution.

In the picture below the is missing copper and some of the copper is a bit stained.

enter image description here

In this second photo the far side looks OK, but the near side has lots of missing traces (towards the middle of the board).

enter image description here

Any clues on what might need changing ?

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  • \$\begingroup\$ Did you clean the board before applying photoresist paint? \$\endgroup\$ – Long Pham Jan 9 at 9:17
  • \$\begingroup\$ @LongPham Yes. With soap & water, and then alcohol & lint free tissues. \$\endgroup\$ – kellogs Jan 9 at 10:18
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It's hard to get the process to work if you have many variables creating uncertainty:

exposed it outside for 25 minutes for each side (cloudy winter day in Europe)

Use a consistent light source, and experiment with different exposure times. I mount a cheap 10W 395nm LED COB 20cm from the PCB, and expose for 30 seconds per side.

Applied negative photoresist paint

Are you sure that the paint is applied evenly and without defects? Is the thickness repeatable? Dry film photoresist is easier to apply. Presensitized boards are even better.

etched with an unknown ratio solution of HCl + H2O2

The peroxide decomposes on its own, as you have noticed. I use ferric chloride, as it's still usable after months.


tracing paper

I've tried that too. It works, but the edges lack definition compared to transparencies.

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