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PCB Etching Problems


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Hey everybody.

I'm trying to make my own homemade PCBs using one layer copper clad PCBs with pre-applied photoresistive film(and protective cover). I'm having problems making the film appear correctly. Here is the process I follow from the begining:

I use 1 15W UV lamp for about 3 mins. I have printed the circuit twice on tranparent paper and place them on top of each other to avoid unwanted gaps.
Then I dip the PCB in worm water (50C-70C, 300ml) with about 1g of Sodium hydroxide (NaOH) and i leave it there for 1 min .

I tried different "UV exposure times" from 1-6 mins and I changed the NaOH amount of the water, 0,5g-2g.

Sometimes once I dip the PCB in the water-NaOH solution the traces appear (blackish) on the board and then they desolve in the water in seconds. Also when I go to the actual etching there is either no traces (all copper gets etched) or the film is intacted (no copper gets etched).Is that because I left the pcb too long under the UV light and it "burned" all the film, or is the solution to strong and disolve all the film?

Once I managed to get good results but I didn't write down the exact "recipe" since then I tried half a dozen of PCBs but nothing. :-\

PS I use a modified scanner with 1 UV lamp, the distance between the glass where I place the PCB and the lamp is about 2cm.

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Not all UV lamps are equal.

Ideally you need a black light, like the type used in insect killers but the short used in discos will do.

Ambient light, including the shorter visible wavelengths (blue and violet) can expose the board. Once exposed, the PCB shouldn't be exposed to any light at all and ideally it needs to be developed in total darkness.

The yellow and red part of the won't expose the board so you can use a photography safe light or make your own with a load of red and yellow LEDs.

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