As I tried to point out, my LED's were from a cheapass store, which means it would be of the lowest quality you could probably get, so those expensive LEDs from RS should work much better... just remember you need alot of LED's and the costs mounts quickly... I think that 9 buck e-bay auction, could be just the number... with so many LEDS' you could easily up the density of LEDS on our board to even make up for weaker LEDS...
I've recently been doing a lot of work with UV leds for curing glue. Cree make some lovely 400nm ones. They will deliver 200mW at 350mA, but you can push them to 800mA and get 400mW, if you put a good heatsink on them. They're not to badly priced, at A$11 each from Cutter electronics . Its the Cree XL7090 series leds.
I've also played with some of the Nichia 100mW 365nm leds, but they're really expensive (US$100 each
)
For cheap 5mm UV leds you can try Best Hongkong
I've also played with some of the Nichia 100mW 365nm leds, but they're really expensive (US$100 each
)For cheap 5mm UV leds you can try Best Hongkong
I have build UV LED lightbox using old flatbed scanner and 40 Kingbright L-7113UVC LEDs. These LEDs have narrow ray (+-10 degrees), it helps to get sharp shadow on photoresist even if photomask is not cling to the PCB very tight. LEDs mounted on carriage moved by stepper motor (scanner's mechanics reused), so 40 LEDs are enough to expose up to A4/Letter PCBs. LEDs mounted close to each other, so it provide well distributed light even with small deepness of box. Exposure adjusted by changing linear speed of the carriage.
Sapa,
3rd attempt to reply, ARHAA!
Sapa, very nice job!
What exposure times do you acheive using your exposure unit?
Does the carriage that holds the LESs make several passes back and forth or just one?
Does the carriage that hold the LEDs have an adjustable setting so that when doing smaller board the carriage does not travel the full distance?
Nice twist to the UV exposure unit. I like it may have to try this one myself
Thanks
3rd attempt to reply, ARHAA!
Sapa, very nice job!
What exposure times do you acheive using your exposure unit?
Does the carriage that holds the LESs make several passes back and forth or just one?
Does the carriage that hold the LEDs have an adjustable setting so that when doing smaller board the carriage does not travel the full distance?
Nice twist to the UV exposure unit. I like it may have to try this one myself
Thanks
Photoresist used by me (Cramolin POSITIV spray) well exposed with carriage speed = 2 cm/min.
Only one pass.
No adjustable settings (except speed), but when I think that expose is done and carriage moved beyond the PCB, I press the button and carriage returned to start and LEDs turned off.
Unfortunately UV LEDs produce long wave ultraviolet (350-410nm) that good for photoresist exposure, but can't erase EEPROMs.
I now have a real UV box that's made for the purpose due to the fact that I make a lot of PCB's, but back when I just needed the occasional board every now and then, I simply went across the street to one of those tan centers. For like 3 uds you can expose like a 10 square feet of double sided PCB, both sides in one operation. Now all that was good if it wasnt for people wondering why that pale guy went for a tan THAT often....and remained pale 
Magura
Magura
SAPA,
2 cm/minute, that is pretty good. Currently I'm using a F15T8BL fluorescent with an exposure of 10 minutes. However it will not do anywhere near an A$ size pcb that yours does. For this reason I very interested in your exposure/scanner approach.
You stated that when you think the board is done you press a button and the LEDs go off and the carriage goes home.
Well, someone always want to try and improve on someone elses idea, so here is mine...
What if you pressed and held your button while the carriage quickly moved towards the end of your board. When you release the button the carriage stops. Press the button again and the UV LEDs come on and the carriage moves 2 cm/minute back towards home. When the carriage reaches home it shuts off itself.
Thanks
2 cm/minute, that is pretty good. Currently I'm using a F15T8BL fluorescent with an exposure of 10 minutes. However it will not do anywhere near an A$ size pcb that yours does. For this reason I very interested in your exposure/scanner approach.
You stated that when you think the board is done you press a button and the LEDs go off and the carriage goes home.
Well, someone always want to try and improve on someone elses idea, so here is mine...
What if you pressed and held your button while the carriage quickly moved towards the end of your board. When you release the button the carriage stops. Press the button again and the UV LEDs come on and the carriage moves 2 cm/minute back towards home. When the carriage reaches home it shuts off itself.
Thanks
I built a UV box just like the one in Elektor but bigger (I think I made it 7" x 5" or so, and two-sided for dual-layered boards). I got the UV LEDs from a place called LSDiodes. I didn't see anyone post about this place above (my apologies if it's been mentioned).
The 3mm diodes are around 395nm wavelength, with an intensity of 500mcd. They've worked phenomenally, and they are pretty cheap at $0.60 USD compared to what I've seen elsewhere. On top of a good price, you get bonus LEDs with your order and a wicked "Robots WILL kill you" sticker with each order as well.
LSDiodes
The 3mm diodes are around 395nm wavelength, with an intensity of 500mcd. They've worked phenomenally, and they are pretty cheap at $0.60 USD compared to what I've seen elsewhere. On top of a good price, you get bonus LEDs with your order and a wicked "Robots WILL kill you" sticker with each order as well.
LSDiodes
$0.60 for usual 3mm UV LED? Too expensive. Also, 5mm ones are more effective. For example:
http://cgi.ebay.com/Lot-of-100-X-5m...ryZ66951QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
http://cgi.ebay.com/100-UV-Ultra-Vi...ryZ66951QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
http://cgi.ebay.com/Lot-of-100-X-5m...ryZ66951QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
http://cgi.ebay.com/100-UV-Ultra-Vi...ryZ66951QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
Hey, can someone plz let me know what im doing wrong.
I have a UV box I built a while ago and used it first time yesterday, Its a scanner with UV fluorescent tubes. First few times I used it i tried to determine the exposure time and realised my tubes were too far apart cos it was under exposed in a stripe down the board, I added more tubes and now whenever I try to develope the boards after exposing them the resist seems to almost "flake" off in small bits rather than disolve away into the NaOH like it used to.
I'm getting frustrated, been trying to get this stupid thing to work for the last 2 days now. Its almost as if the exposure time changes everytime i do it. How thick must the positiv 20 be on the board? getting it to be evenly spread seems to be an issue, whenever the spray hits it it leaves circles that kind of even out but not totally. Can someone run through everything and please let me know if im doing anything wrong, i cant even get to the etching stage cos I cant get past the development stage.
I have a UV box I built a while ago and used it first time yesterday, Its a scanner with UV fluorescent tubes. First few times I used it i tried to determine the exposure time and realised my tubes were too far apart cos it was under exposed in a stripe down the board, I added more tubes and now whenever I try to develope the boards after exposing them the resist seems to almost "flake" off in small bits rather than disolve away into the NaOH like it used to.
I'm getting frustrated, been trying to get this stupid thing to work for the last 2 days now. Its almost as if the exposure time changes everytime i do it. How thick must the positiv 20 be on the board? getting it to be evenly spread seems to be an issue, whenever the spray hits it it leaves circles that kind of even out but not totally. Can someone run through everything and please let me know if im doing anything wrong, i cant even get to the etching stage cos I cant get past the development stage.
I don't know if that's the same type of positive photoresist I've used, but I found that baking it in a toaster oven (NOT an oven you use for cooking) at a low temperature helped harden the resist. (wait for it to flow out smooth first, in a dark place of course.)
Also, I got fairly poor results using a spray can. Using liquid resist, thinned 50% and spread with a foam brush, then allowed to "flow out" smooth before baking worked pretty well.
Also, I got fairly poor results using a spray can. Using liquid resist, thinned 50% and spread with a foam brush, then allowed to "flow out" smooth before baking worked pretty well.
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