Light/Exposure
The optimal wavelength for photoresist exposure is usually 350nm which is near UV (400nm is visible purple). The 'blacklight' lamps output maximum here. However, The Gxxx lamps emit far UV light, useful for erasing EPROMs bugs and your eyes, but have enough emission at 350nm to expose photoresist (not to mention that they are about 5 times more efficient than blacklight lamps and that photoresist is also sensitive down to to 253nm).
Look for fluorescent bulbs with markings that start with G = germicidal/bare glass, uv transparent (this is what you want for boards). Danger: these emit short-wave UV which can cause eye and skin damage. For example, H-G4T20BLB(3) is a UV light (G) with (4) watt capacity and (T20) means four pins, two at each end, 20mm apart from each other which is the standard.
The exposure of the photosensitive stock is the most difficult part of the process to predict. Differing sensitivities of photoresist and lights of different strengths will require experimenting with the exposure and development until a reliable result is obtained.
Test Exposure: Every setup will be different, do an exposure test with a scrap before trying with the real thing. Cover all but one end of the PCB with a shade and then move the shade back, exposing more and more of the PCB at regular intervals (e.g. 30 seconds to 2 minutes depending on how strong a light you think you have). When the last bit has been exposed for the interval you choose, stop and develop the scrap.
Examples: (your times will vary, do an exposure test first):
* 500W mercury vapor lamp (standard lightning lamp), getting around 18 minutes at a distance of 20cm. Or a mercury vapor yard lamp with the outer frosted glass envelope removed, leaving only the inner quartz bulb.
* 500W Gxxx lamp for 2.5 minutes at 18"
* A pair of 9W Tropical Aquarium "Blue" bulbs for 12 minutes at 6"
Please see post #84.snip
Incidentally, some years ago, I tried the 4w blacklight tubes that are commonly found in small handheld units for checking banknotes...no results even after 1 hour exposure time.
I'm working on modifying an inkjet printer to print directly to a pcb.So far, in all these 14 pages, I have seen no mention of the alternative way of "exposing" boards by laser printing (or even ink jet printing, according to a couple of references I have see on the net) the layout onto "Press n Peel" film, ironing this on to very clean, blank printed board, cleaning away the excess, and then etching.
I found an excellent step-by-step description located on an Australian web site a few weeks ago (alas, did not bookmark it), which looks like it might be worth investigating.