Re-did one of my boards that had a section of dense 6/6 traces.
Technically, 6 mil traces on 12.5 mil centers. The last attempt way
over-etched and cut many of the traces; this time I "bloated" all
edges by 1.25 (i.e. 8.5/4 rules) and the undercutting brought all
the traces down to their expected sizes. So far, I've found only one
flaw, a 2 mil gap in one of the traces, easily fixed.
Photos:
http://www.delorie.com/pcb/lab/Today's tips:
To laminate the photofilm, I used 240F and an oversized (9" by 6")
PCB. The board is 4.5" by 5". I cut a 12" by 6.5" film, peeled the
first cover, laid it sticky side UP on a piece of paper and positioned
the PCB copper ∗down∗ on it, leaving 1/2 inch sticking out the top. I
folded that 1/2" over and pressed it flat (no wrinkles!) on the pcb,
where it stuck. Flip over and un-stick the film. Run it through the
laminator, with the paper, stuck edge first of course, holding the
other two corners of the film. Hold the film AWAY from the board!
Up, back, and out. The extra 2.5" of film let me hold the film until
the whole PCB went through the rollers. Run through a second time,
same direction. Use scissors to cut around the PCB, freeing it from
the paper. After noting the bubbles, I trimmed the board to the 5x5
section I wanted and saved the rest (I have an aluminum foil pouch I
store them in) for less critical boards.
Note that I was much more careful about ambient light this time; it's
night (dark) and I unscrewed most of the bulbs in the basement,
leaving only indirect light from distant bulbs. I kept it this way
from when I opened the film tube to when I finished developing. I
don't know if this made that much of a difference, but I didn't see
any significant film webbing between traces, and no shorts.
Exposure and development were as usual; 6 minutes UV, 10 minutes
develop. Etch was as usual too, about 5-8 minutes. For develop and
etch, I used double-sided tape to tape the pcb to a stick so I could
move it around and easily remove it for inspection. These are SS
boards.
To strip I put it in the stripper until the small traces started
coming up, then laid it flat on some PVC I have. After a minute or
so, all the film was bubbled off and I just scraped it off (wearing
gloves, of course) and rinsed. No film in the stripper tank :-)