My old and rusty PCB exposure unit gave up so I had to build a new one. Can’t believe how expensive pre-built units can be.. but atleast it is not that hard or expensive to build your own. The enclosure from older flatbed scanners are almost designed for this very purpose.
I began by getting hold on a lot of UV leds, enough to cover two 160×100 mm boards. Each board contains 96 leds and is powered by a 12 volts power supply. On each board there are multiple strings of 3 leds and one resistor, and those strings are wired in parallell. The two boards are then controlled by the main controller board (basically just a timer). I think the specs for the leds were something like this:
Size: 5 mm
Peak wave length (nm): 395 ~ 405
Forward voltage (V): 3.2 ~3.8
Max continuous forward current (mA): 20
Luminous intensity (mcd): 3000 (typ) ~ 5000 (max)
Viewing angle: 20~25 degree
An exposure time of 4 minutes and 30 seconds seems to be the sweet spot for this setup.