Mike Young wrote:
> ----- Original Message -----
> From: "derekhawkins" <derekhawkins@...>
> To: <Homebrew_PCBs@yahoogroups.com>
> Sent: Wednesday, November 16, 2005 4:37 PM
> Subject: [Homebrew_PCBs] Re: A $500.00 "UV" non-trivial exposure box.....
>
>
>>>The workflow for both the top vs. bottom (or bottom vs. top) are
>>>identical.
>>
>>So if you had to do 5 boards you would have to do the following steps
>>5 times, once for each board;
>
> The same would seem to apply to photo resist. Drill it; align artwork;
> expose/laminate; develop/strip the paper backing. The step-by-step for photo
> would seem to be longer.
It's much easier. You only need to make the front and back printouts ∗once∗.
(I have a draw full of re-useable printouts).
You lay one printout on top of the other and align them and stick them together
with two small pieces of double-sided foam tape (it is commonly 1.6mm which is
the same as the pcb thickness). This is a 30s operation, and easy after the
first time.
From then-on, whenever you want to make a double-sided pcb, just put the
blank into the sandwich, then put that into the lightbox and expose for
90secs. Turn over and do the other side for 90secs. Pull out pcb and remove
cellophane plastic layer from pcb. Put into flat container that has 10g/L
of swimming-pool NaCO3 (sodium carbonate pre-heated in microwave for 30secs
to 25-30degC). Brush developer for 1-2mins until well done, repeating for
both sides. Rinse, then put into flat tray with 10g/L NaOH (sodium hydroxide
garage floor cleaner), and heat in microwave for 1min to 50-60degC. The resist
just wrinkles and falls off. Rinse then dry. No scrubbing or cleaning is needed
anywhere.
> In my mind, photo resist is still coming up short. There are more variables,
> more opportunities for error, more equipment to acquire, maintain, and
> adjust. And more junk in the sewers (not that I lose sleep over what my
> neighbors might be doing or not).
Calibrate the lightbox ∗once∗ to match your pcb. Nothing else needs adjusting.
> All that aside, the quality of the artwork would seem to be paramount. The
> laserjet prints very clean, very crisp edges. Filled areas are very dense
> black and consistent. The Epson 1280 (28800 dpi) only manages a fuzzy edge,
> not crisp at all, and not nearly as dense.
You're obviously using either crap ink, crap transparency or both. Genuine
epson ink and transparency gives a sharpness and density you couldn't fault.
There are certain refill inks and transparency that give acceptable results
too.
> If both are available, I expect
> you would choose the laserjet. And if you're printing on the laserjet
> anyway, why not go straight to the board for the onesie-twosie?
Double-sided pcbs with TT are a pain. Laminators cost a lot more than
building a lightbox. Lightboxes are a lot easier to build than a laminator.
TT can use non-coated pcb. You can spray on positive resist to pcb after
adequate cleaning, but a lot of users don't master the cleaning step.
You can apply your own dry-film resist to pcb, but it's a bit tedious
without the right machine.
> Actually, I didn't intend to seem so polarized. I'm asking it as a question,
> as a newbie with no experience with photo, and only very little with TT.
> What is the advantage of photo-resist compared to toner transfer?