Homebrew PCBs

I bought a used UV Exposure unit off EBay for $75.
Its pretty big, but works excellent.
I think it was for exposing printer plates.


--- In Homebrew_PCBs@yahoogroups.com, Adam Seychell <a_seychell@...> wrote:
>
> jcarlosmor wrote:
> >  
> 
> > And by the way, as someone stated, UV Leds are not used for UV curing or 
> > imaging of PCB processes. If you want to build a real-use UV 
> > photoimaging box, do not waste money on UV leds. Use blacklight 
> > fluorescent tubes. They are cheaper, and provide real results. In fact, 
> > they are used widely in PCB making (However, for fast batch use, there 
> > is no substitute for high power mercury arc lamps).
> > 
> 
> After experience with both 395nm UV LED and BL tube (spectral peak 
> 365nm) light sources, I would totally agree. The major problem with LEDs 
> is light non-uniformity and inadequate intensity for solder mask and 
> positive resists. Only the negative dry film photoresists seem to be 
> sensitive enough. For some reason, extending the exposure time with LEDs 
> does not work on these materials.
> 
> One would expect excessive light undercut from the relatively wide angle 
> radiation pattern emitted by an array of BL tubes. In my experience, 
> 0.2mm (0.008") line/spaces are easily achievable. It is critical the ink 
> side of transparency makes contact with the photoresist. I found the 
> ratio of maximum/minimum exposure time can be high as 1.5 while still 
> maintaining an acceptable deviation in line & space widths.
> 
> The limit to minimum line & space is not the exposure source, but that 
> of inkjet printer resolution.
> 
> Adam
>