Homebrew PCBs

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 wrote:
> There are 17 messages in this issue.

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> 1d. Re: buying LED's for a exposure box
>     Posted by: "Adam Seychell" a_seychell@... 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

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