I may try that if I will end up building another one, but hey mine -
with aparently the worest placement (20mmx20mm square) works perfectly.
Sometimes this group is surprizing me for searching to solve problems
which in reality do not exist... :-)
SCNR
Markus
Donald H Locker schrieb:
>
> I hope someone is experimenting with hexagonal placement of the UV
> LEDs. A
> square pattern is guaranteed to have the greatest non-uniformity for
> the number
> of LEDs used.
>
> Donald.
>
> Homebrew_PCBs@yahoogroups.com <mailto:Homebrew_PCBs%40yahoogroups.com>
> wrote:
> > There are 17 messages in this issue.
>
> [snip]
>
> > 1d. Re: buying LED's for a exposure box
> > Posted by: "Adam Seychell" a_seychell@...
> <mailto:a_seychell%40yahoo.com.au> a_seychell
> > Date: Thu Feb 14, 2008 2:43 pm ((PST))
> >
> > Markus Zingg wrote:
> >>
> >> Adam,
> >>
> >> I do have a 20mm grid spacing, and I'm so far satisfied. Even though it
> >> never formed a problem of any kind, one can SEE the grid on the
> >> resulting exposed laminate. It's seen like kind of darker and lighter
> >> circular shaped areas on the exposed resist. Again, developping the
> >> result always worked excellent with no irritations in the result
> whatsoever.
> >
> > That's good to hear it works despite the visible pattern. What is your
> > space between the LED and PCB ? I guess the larger the distance the
> > greater the light overlap of adjacent LED's and possibly better
> uniformity.
> >
> >> At the very surprisingly low prices of these LEDs, I would consider
> >> using an even more narrow grid. My box (kingbright leds, with what I
> >> understand only 160mcd typical) result in a one minute exposure time.
> >
> > The BestHongKong ebay seller Tom pointed out had the better specs
> > (tighter spectrum tolerance, polar plot). Interestingly , some LEDs are
> > rated in mcd while others rated in mW. BestHongKong 5mm UV LED's are
> all
> > 11mW 20 degree. I think I'll get these. But might also get $11 ones
> from
> > Winsome House Store just for fun.
> >
> > >.... I would spend the time to build a complete exposure unit to make
> >> sure they work.
> >
> > For sure. Some preliminary testing will soon give me estimate of
> > exposure times vs grid spacing and test non-uniformity.
> >
> > I'll be sure to let others know how it goes.
> >
> > Adam Seychell
>
> [snip]
>
>