DJ Delorie <
dj@...> writes:
> That's my next test. So far, I've tested my system with the LEDs,
> glass, transparencies, and film I'll be using. The only thing
> missing was the ink, but that's how you calibrate the system - no
> ink.
>
> Now, to see how far ∗past∗ "ideal" the ink will hold, I increase my
> exposure 16x, or 8 steps (2^(8/2) = 16). Now we're at 80 minutes.
I did one of these tests. I used 8x the "ideal" time, because my
timer only goes to 60 minutes. So I ran for 44 minutes. Here's a
scan of the board which may help explain my recent ramblings:
http://www.delorie.com/pcb/dryfilm2.htmlRemember, this is a negative film, so ink = no cure = no copper, and
clear = cure = copper.
Since I'm exposing for 8x the time, that means everything is shifted
by 6 steps (2^(6/2) = 8). Step 14 is partially cured even through the
clear parts of the pattern, that corresponds to step 8 at the ideal
time. So far so good (the data sheet says to expose to steps 7-9).
Step 7 is what the board will actually see. The results at step 7
look reasonable. Mind you, I didn't try too hard to get a good print
- I just printed a test pattern at whatever the printer was set for,
with no attempt to calibrate the edges.
Step 6 is still OK, but starting to hint at overexposure. Step 5 is
definitely overexposed, and step 4 is almost completely shorted.
So if I was forced to use this ink and print settings, I might think
about reducing the exposure a step or two to give myself more margin
against overexposing through the ink. Midway between "too much" and
"too little" is step 9, which would mean exposing for two steps less
than ideal, or about half the ideal exposure time (~3 minutes for me).
However, at step 9 the copper is narrower than it should be (probably
due to ink bleeding near the edges of the print and blocking some UV),
so I'd need to make my copper a bit thicker than my spaces to
compensate.
But I haven't played with the other color inks yet, nor have I
experimented with heavier coats or edge adjustments.
Notes: The other imperfections in the etch are due to poor results
laminating the film. This is my first try. The blob at step 20 is
where the clip held the board in the developer. The stripes are 12
mil wide, 12 mil between.