Weird PCB etching behavior

[twospoons]

You should probably be using something like this:
https://www.aliexpress.com/i/4000351290401.html
The best thing about 405nm LEDs is they only emit light at 405nm. There are no other  more dangerous wavelengths to deal with. They are also super easy to drive, very efficient compared to fluoro tubes and the strips make it easy to produce an even illumination.

[tooki]

You should probably be using something like this:
https://www.aliexpress.com/i/4000351290401.html
The best thing about 405nm LEDs is they only emit light at 405nm. There are no other  more dangerous wavelengths to deal with. They are also super easy to drive, very efficient compared to fluoro tubes and the strips make it easy to produce an even illumination.

I thought that UV LEDs had not yet caught up with the efficiency of UV fluorescent tubes?

And as far as even illumination goes, fluorescent is better, as it doesn’t make the hotspots LEDs tend to.

[twospoons]

If you look at the mercury emission spectrum it is spread across a number of UV and visible lines that are not useful in this case and wasting power, whereas the LED has a single emission line. 

https://www.nature.com/articles/s41438-020-0283-7#:~:text=A%20violet%20LED%20with%20a,increase%20as%20current%20density%20decreases.

At 25 °C and 350 mA, UV-B and UV-C LEDs are only ~3% efficient31, but these photons can have large biological effects in small quantities. At 25 °C and 700 mA, the efficiency of UV-A LEDs increases from 50 to 60% as the wavelength increases from 370 to 395 nm32. A violet LED with a peak between 402 and 408 nm is ~65% efficient, and has 15–30% of its photons below 400 nm. Efficiency will increase as current density decreases.

https://www.waveformlighting.com/tech/top-4-things-to-consider-before-buying-uv-blacklights

As a rough ballpark estimate, fluorescent blacklights have an efficiency value of 5-15%. In other words, for every 100 Watts of electrical energy consumed, the blacklight will emit 5-15W of useful UV light energy.

As for even illumination - the OP only had a single tube, so covering an area with led strip is going to be better. Add standoff height ~10x led spacing and the result becomes pretty even.

[ali6x944]

All you need is simple UV-A, like used for disco blacklights, counterfeit money detection, bug zappers, and curing UV gel fingernail polish. For PCB exposure, it doesn't matter whether it's the kind that filters visible light (like disco blacklights and counterfeit money detection) or lets it out (like bug zappers).

i think i found it, something like Philips Actinic BL TL-D 15W:
https://www.lighting.philips.com/api/assets/v1/file/Signify/content/928024801029_EU.en_AA.PROF.FP/Localized_commercial_leaflet_928024801029_en_AA.pdf

[jpanhalt]

That's probably identical to the lamps I used.  They were GE F15T8BL "Backlight" 15W made in Hungary.

[Sagar]

I also worked with Fecl3 but it was not that bad 26 hours!! No, I have etched mine in just 40-50 minutes and my design is also have same complexicities. Try 60 degree 60 min technique and keep moving the solution after each 5 minutes. Or you should go with an alternate option of professional PCB from any chinese manufacturer, rather cheap $2.

[ali6x944]

That's probably identical to the lamps I used.  They were GE F15T8BL "Backlight" 15W made in Hungary.

i ordered some from ebay because i didn't find them locally, i will however attempt the etching the pattern again since i can still do it just with longer exposure times, this time i will use the notes given by @tooki and @jpanhalt to make sure i got proper developed boards that are clean of photoresist and i will also make sure the etchant is hot to ensure fast etching, will also redo it when the new tubes arrive, will report all soon.