Homebrew PCBs

I did a little more testing of UV LEDs this weekend. The LEDs are
plugged into a solderless breadboard and driven with a variable
external power supply I tried a 3x3 grid with 1 inch and .5 inch
spacing. The LEDs were run at 20mA and pulled about 10V.

The 1 inch spacing at 1.25 inches above the board showed too much
variation in exposure. I would get areas of overexposure while other
areas would not get enough exposure. I tried times of 1,5 and 10
minutes. 10 minutes was way over exposed, 5 not so bad and 1 left some
areas okay, but other areas underexposed.

I then did tests with .5 inch spacing with the LEDs at 1.25 inches
above the board. Uniformity of exposure was much better. I tried an
exposure time of 1 minute. I think I can drop that down to 45 seconds
as I still saw a little extra exposure in areas directly below the LEDs.

So I think for me .5 inch LED spacing is what I am going to use to get
uniformity. I will do a few more tests of increasing the distance to 2
inches above the board to see how that works.

--- In Homebrew_PCBs@yahoogroups.com, "javaguy11111"
<javaguy11111@...> wrote:
>
> I just did a quick test with my UV LEDs using a step pattern going
> from 10/10 spacing down to 1/1 spacing in thousands of an inch. This
> test pattern was printed by an Epson 2400 printer using Pictorico
> transparency.
> 
> The leds were 1 1/4 inches above the board with a .5 inch spacing. I
> tested with 4 LED's running 2 in series and then 2 of those in
> parallel running 20ma at 6.6V. 
> Exposure time was 60 seconds. 
> 
> After developing in sodium carbonate, I got good lines down to  3/3
> spacing. The 2/2 looked pretty good as well, but was a bit jagged.
> Possibly due to the 1440 dpi resolution of the printer. The 1/1 lines
> were all merged together. 
> 
> I will try 3/4 inch and 1 inch spacing over the weekend to see how
> those work, before I commit to a spacing. I will post the results of
> those tests as well.
>