Homebrew PCBs

PPC wrote:
> The 2 KW UV plate exposure machine is  a commercial type used in offset 
> plate exposure. The lamp is a Philip halogen lamp enclosed in a simple 
> reflector. Distance between plate and lamp is about 36".
> 
> Actually, for home hobby use, I believe there were discussions here on how 
> to make a black light box. The black light flourescent lamp will give you 
> the correct UV range to expose most photoresist materials. Using a simple 
> box with glass top, black light, incorporate a vacuum pump (we use old 
> discarded refrigerator compressor or even car aircon compressor), you can 
> come up with a reasonably good exposure box though exposure time will be 
> much longer.

I made a UV lightbox with 125Watt HID lamp 24" from the glass, and in
a cylindrical parabolic reflector (lamp lays horizontal). 90%+ exposure
happens in 30secs, and i found a good optimum to use is 90secs for
pre-coated negative pcb. The pcb is held against the glass by the lid
that has a layer of sponge.