I made one of these too, out of an old flatbed scanner body, aluminium foil lined on the inside, with two 4Watt insect killer uv lamps, a lot safer on the eyes and skin. The lamps were on special offer too, 2 for 1, both cost only 13quid!
I’m achieving very fine traces using uv sensitive copper board after 15mins exposure, could probably cut that time down too.
The same shop I bought the uv lamps (Maplins) also sell proper uv exposure boxes, upwards of £135!!! Saved a bomb.

this would be good for screen printing. I have another use for this to. thanks for posting. you could also use reptile flourescent lights. they come in several differant spectrums, would be worth experimenting

*pulse=post. Gah! HAD why won’t you allow post editing!?

drill a hole at each end so you can insert clear piping and it could double as part of a portable water purifying system.. for when you are not being a mad scientist of course..

> I always wince when anglophones use French to sound smarter… and fail because they do it wrong.

> Posted at 4:42 pm on Oct 20th, 2010 by Philippe

Français râleur!!!

UV LED’s are usually in the range of 405 nanometers or so, which isn’t even really technically ultaviolet. It’s a bit of a stretch to even call it UVA.

Most etching boxes use industrial grade UVC lights, which DO cause cancer, and you DO want to shield yourself from.

UV LED’s are less dangerous than a black light, wood’s glass peaks somewhere around 380nm. You can take off your welding glasses and SPF100 sunscreen, those LED’s aren’t going to hurt you. It’s not until you encounter light in the sub-200-nanometer range that you have to worry about cancer.

absolutezero: I was under the impression that most silkscreening masks were *light*-sensitive, not necessarily just UV. I recall a girlfriend of mine doing some silkscreening stuff for a university art course, and I’m pretty sure she just used a 100W incandescent bulb. I’m not sure you need UV light for most silkscreening stuff. I’ll agree though, all things considered, that using the toner-transfer method is easier and more straightforward. Unless you’re planning on making hundreds or thousands of boards at a time, I wouldn’t bother with photo etching.

@DA ah, mais je t’emmerde !

guys, rtfm or insert other phrase here

mercury vapor lamps are 350-400nm, so UV LEDs are well within the range of most photoresist cures. the problem with UV LEDs is simply that they cost a shitton for the little amount of UV they put out. UV blacklights are far cheaper for the power you’re getting for this application, even if they don’t sound as cool (which is the only reason anyone wants to do LEDs)

the bigger problem, which i’ve seen in almost all exposure boxes, is the lack of collimation. the light coming out of most exposure boxes here is not well collimated at all–the LEDs spew light out at a crapton of angles. what does that mean? suppose you have a ray of light going at 45 degrees from the normal, which is very reasonable (at these distances, it’s probably even worse). your photoresist thickness is 1-2mil, so you easily get 1-2 mil undercutting on both sides of a traces. 8 mil becomes 4 mil–good luck with that. and it’s probably worse than that in real life. . .

really, just build one of these: http://www.thinktink.com/stack/volumes/voliii/equipment/uvlamp/uvlamp.htm

these guys have been around forever, and are pretty darn legit.

could also be used to test the UV stability of materials. how long will it take for x material to turn yellow?

@threepointone, LEDs usually have fairly narrow viewing angles, and most light comes straight out, not at a “crapton of angles” so actually LEDs are fairly well suited for this application. ( I didn’t even know you could get 140-degree UV leds, so maybe undercutting is a problem here.)

Incidentally, if you do use narrow angle LEDs the light tends to focus in a bunch of circles, so you need to have a good distribution of bulbs as well as make sure you have enough distance between the LEDs and the exposure surface.

I made a box just like this, with 22-degree bulbs and a depth of about 10″ so the light hitting the glass at the top is pretty even.

With 90 410nm leds in an 8×10″ area I can expose silkscreens in 10 mins. It’s my understanding that visible light won’t cure screenprinting emulsion. I still haven’t tried PCBs yet.

@absolutezero
I use pre-sensitized boards because using spray on lacquer is just too complicated: it smells, you have to let it dry, keep it dust free, do special moves to get a uniform thickness. I did start using spray, it was called POSITIV 20. But it expired before i got the chance to finish it and i only found out when the board didn’t come out right. For such small scale the cost difference is worth the trouble.

@hreepointone
I have not noticed any undercutting, though i only made a couple of boards with 10mil tracks. I might check that in the future. What would you suggest as a collimator?
As for your suggestion of 18″ tubes. It defies my needs and purpose: small compact box. Of course it is cheaper to make with tubes. you just can’t make it so small(ok, maybe you could if you could source 2W UV tubes, which i couldn’t).

@nfs maybe you should read the data sheet of the LM317 better. Short answer: it can handle 1.5A. and it is stable at such current if you use it right. The whole box consumes about 1.2A. That three amp diode is the next larger thing i had after 1n4007.
UV light is below 400nm. The leds i use have a peak wavelength at 405nm. It’s safe to say half of the energy they put out is below 405(almost all UV) and half is above, which is visible.

@threepointone

This guy knows what he’s talking about.

Little boxes like these are OK for one-offs, but diffusion will increase problems with narrow traces if you’re doing really narrow traces for surface mount and then etching – especially if the UV exposure was weak.

Old bulb based tanning lamps work pretty well, if you keep a fan on them to keep the heat down and use very thin glass to hold down the artwork. You can set them 6-12″ above the pcb.

PS – An industrial wand style “personal massager” set on jack-hammer mode will do an excellent job of agitating a tray full of etchant. I always meant to try an ultrasonic etchant tray but never got around to building one.

I still remember building a hundred and fifty or so populated PC boards by hand as a kid – from bulk pcb material to test. It was a Tom Sawyer thing, with friends coming over to do the work.

Got them done in a weekend, and I suspect the combined Etchant/Lead/plastic fumes caused permanent damage.

They looked like south china specials, and since I didn’t understand through hole technology or proper bit sizing, I used big drill bits and then used solder – lots and lots of solder – to fill the gaps. Awful, but they worked.

The day I cashed a check for a week’s work that was more than both my parents had made in three months was the day that I decided to become a tech whore. I’m a little played out, but my clientele likes that kind of rough experience. Luckily I have a great Pimp. :)

Don’t do drugs!

i am a native french speaking, and i confirm, it is perfectly ok to use “coup de grâce” here. Even if this sentence is “tombée en désuétude” because we have abolished death penalty a long time ago, it is still used in this exact context.

I like the idea here, and to all those people complaining about the definition of UV or the wavelengths, who cares? This box serves a purpose to expose PCBs, and having used these LEDs for photo resist PCBs myself it works very well.

One thing about the diffuse lighting though, it does create a problem for small traces. You can use a grid made of densely packed black straws cut about 50mm long to “collimate” the light. Ok so it’s not really collimated but it does actually do a very fine job at decreasing stray light and making the rays hit the board perpendicularly.

I want to make a UV LED exposure box for testing UV exposure on cultural materials (museum collections). I am looking for 340nm UV LEDs. Anyone know of a source?