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I have a positive acting presensitized UV-curable PCB board (link). I'm using the manufacturer-provided developer.

Supposedly, the parts that get exposed will get washed away by the developer. However, I observed that my traces are always the ones that get exposed no matter what arrangement I do. It seems like the "minority" always gets exposed.

What am I doing wrong? Is this the normal behavior for photoresist PCBs? I'm always using the same developer all cases.

enter image description here Please ignore the scratches and blurry impressions. These are test runs. Left is first run, right is second run.

EDIT: added included pamphlet enter image description here

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    \$\begingroup\$ No, that doesn't make any sense. It seems like you have one negative and one positive board and managed to invert your printed layout exactly to the matching board to get the same result. \$\endgroup\$ – Arsenal Jul 25 '18 at 14:44
  • \$\begingroup\$ So far, I've tried it on 5 boards \$\endgroup\$ – PNDA Jul 25 '18 at 14:44
  • \$\begingroup\$ @pandalion98 And you got the same result everytime regardless of which printed layout you used? \$\endgroup\$ – Arsenal Jul 25 '18 at 14:47
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    \$\begingroup\$ @pandalion98 that would mean if you only inverted half of it, it would still produce the same circuit, but I haven't heard of intelligent photo resist which does always that what the user doesn't want. \$\endgroup\$ – Arsenal Jul 25 '18 at 14:52
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    \$\begingroup\$ @pandalion98 oh, so they mean you can do either A exposure box or B fluorescent light. I'm really bad at reading manuals these days... \$\endgroup\$ – Arsenal Jul 25 '18 at 15:11
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There are at least two curing mechanics known to me - first is UV light and second is heat. You may notice that traces on left PCB is much more accurate - that's an appropriate result for an UV curing. Right PCB, however, is ugly. It looks like heat traveled from traces outward and cured away photoresist. Also, film is really important - semi-transparent film is bad and soaked up paper is trash. You wont get any thin traces with that.

I would recommend moving exposure lamp away from PCB and increasing exposure time proportionally. That would help to reduce heat

UV curable photoresist really helps in creation of tiny traces and double-sided PCBs, however, with such huge trace width, tonetransfer technique would be superior

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