Homebrew PCBs

Ross McKenzie wrote:
> Twelve months ago I bought 50 UV leds from an ebay seller in Homg Kong
> for US$1.99 plusd US$11 postage. One was dead on arrival but the others
> were perfect. My UV light box with 7 strings each of 7 leds in series
> spaced at 20 mm works perfectly for me. But you do need a diffuser to
> get an even light (no hot spots). Believe it or not, I used two sheets
> of baking paper. Lovely even glow. Ten minute exposure times at 60 mm
> above the leds. I mount my sensitied board and the photoartwork inside a
> slide in photoframe with a single sheet of glass in front. Very tight
> package. No undercutting.
> 

Thanks Ross. It looks like ebay is the best to get LEDs for this 
project. Diffusers only undermine light undercut. When I'm pushing the 
limits out of what my inkjet printer can produce, I need minimum 
undercut. I've tried banks of fluorescent tubes in the past with dismal 
results. I'm using large HID mercury lamp for the time being.

I had the idea of mounting the LEDs in an array of 5mm diameter holes 
drilled through a 18mm (3/4") thick MDF particle board. This will 
guarantee a maximum +-8 degree from each LED. As Markus Zingg, suggested 
I'd need to experiment a bit until I find optimum layout.

I know that all LEDs aren't made equal. From experimenting with normal 
colour LEDs I notice some manufactures have fairly poor uniformity or 
patterns of rings when shined on a white surface.

Adam Seychell