A nicely implemented project, and performance seems fine according to the project forum (and Google Translate) – “time highlighting the 2-2.5min and thus develop very quickly for about half a minute in 10% NaOH solution.”
I wonder if there’s a way to make the exposure more even without adding more bulbs (not that it’s a problem for smaller boards)?

Posted at 9:22 am on Nov 10th, 2009 by Ben Ryves

Those are definitely CFL’s, possibly mogul base or standard. Lights like those might be a few hundred lumen each. Mylar is better than foil, as it gives a more even reflection.

Posted at 9:24 am on Nov 10th, 2009 by Skitchin

Could always go for an over-sized bulb http://www.buylighting.com/z200-Watt-Compact-Fluorescent-5000K-Full-Spectrum-p/fe-iiib-200w-50k.htm

Posted at 9:30 am on Nov 10th, 2009 by Skitchin

That’s pretty fast, I use blacklight bulbs and I have to expose my boards for at least 6 minutes for them to come clean quickly.

I was thinking of using the same flat bed scanner but just use UV leds.

Posted at 9:34 am on Nov 10th, 2009 by jcdillin

there are cfl uv light sources, you can get them at the pet store for terrariums. they sometimes come in two varieties, “tropical” and “desert” depending on how much uvb you need. apparently some? reptiles need uv to process vit d for sth with calcium to make strong bones or what have you. they put out a hell of a lot more uv than you’ll get from any led, that’s for sure.

Posted at 9:37 am on Nov 10th, 2009 by g3

Those are not just cfl lamps. They are ultraviolet reptile lamps. About 30% of the light they output is UVB. 30% uva. and 40% white light.

you can get them at petsmart. I just used one when i made some retr0brite to clean up a radio.

Posted at 10:09 am on Nov 10th, 2009 by googfan

If the scanner bed is glass it will block the UV.
I’m pretty sure glass is opaque to UV.

Posted at 10:21 am on Nov 10th, 2009 by Fallen

Ordinary glass is partially transparent to UVA but is opaque to shorter wavelengths while Silica or quartz glass, depending on quality, can be transparent even to vacuum UV wavelengths. Ordinary window glass passes about 90% of the light above 350 nm, but blocks over 90% of the light below 300 nm (Source: Wikipedia)

Posted at 10:27 am on Nov 10th, 2009 by Boudico

I have build a similar box a long time ago, a double sided one, so I could do both sides of the PCB at once, eliminating the possibility of shifting the masks when turning around the PCB.
Some hints:
-make the box 1.5 times as deep as it is wide.
-use a cardboard template to form the aluminum foil in a parabolic shape, for an even distribution.
-make the insides of the box black, or at least don’t put the foil there. (Light from the wrong direction is worse than a slightly longer processing time!)

The trick is to get the light distribution very even over the whole surface, and to get the light perpendicular to the surface as much as possible. That makes it much easier to get a sharp image.

I have successfully make double-sided PCB’s with 0.2mm traces on a 0.5mm pitch using that box.

Posted at 11:59 am on Nov 10th, 2009 by jwstolk

Great build! In the same vane I’ve got an old EPROM eraser kicking around. Apart from the health risks of exposure to short wavelength UV, would this light source work for photoresist PCB etching?

My eraser is large enough to accept a decent size PCB and has a nice little timer built into the light-tight enclosure.

Posted at 12:39 pm on Nov 10th, 2009 by Lobo

@Lobo: usualy photoresist is mostly sensitive to UVA, you can expose it even with regular lumnescent lamps (think office lamp with an U-shaped bulb). Chip eraser is more likely to be a quartz lamp in harsher UV range, which calls for using protective goggles and probably not very efficient for resist exposure.

http://sensi.org/~svo/spdifpcb/dsc01711.html

This is how I used to expose my PCB’s before I learned that you need longer wavelengths :) It worked, but much worse than little screw-in blacklight bulb I’m using now.

Posted at 3:06 pm on Nov 10th, 2009 by svofski

I thought fluorescent lamps and blacklight lamps were the same thing, the difference being that blacklight are coated to filter visible light, and fluorescent are coated to filter the UV?

Posted at 3:51 pm on Nov 10th, 2009 by GSV Ethics Gradient

@Fallen, @Boudico – it depends on what’s actually *in* the glass. Glass isn’t just ‘glass’. There are many variations in composition, so you’d have to measure the amount of attenuation..

Wikipedia really is a relatively poor source of information…

Posted at 6:45 pm on Nov 10th, 2009 by medix

You could build some kind of scintillometer to measure relative UV attenuation in a real ballpark way. take a light tight project enclosure, cut a window, add a camera style UV bandpass filter over the window, inside add a piece of material coated in uv reactive dye or something, and use a the photoresistive circuit of your choice to measure how much the UV reactive material glows. establish a baseline reading using a uv source of known intensity shone through the window, then measure with the material to be analyzed between the uv source and the window.

just an idea

Posted at 6:56 pm on Nov 10th, 2009 by Ashley

@GSV Ethics Gradient:

Fluorescent lamps convert (most of) the UV light produced by the tube to visible with a phosphor coating. Blacklight tubes (i.e. not the regular incandescent ones) either use a different phosphor chemistry to produce specific wavelengths or just a filter to keep in the (more?) harmful shorter wavelengths (I don’t know which). There might even be a different gas/gases inside the envelope, too.

And then there are the germicidal ones that have no coating of any kind (I have a “burnt-out” one on my desk right now). These are the ones that hurt/blind people and break down DNA in microbes.

Posted at 7:02 pm on Nov 10th, 2009 by Amos