Homebrew PCBs

Mike Young wrote:
> ----- Original Message ----- 
> From: "Russell Shaw" <rjshaw@...>
> 
>>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.
> 
> I like that. Simple is good. Seems to me I have room for a small lightbox on 
> the worktable. What would you suggest?

A box with four 15Watt flouros (tubes about 20cm long), and 10-20cm from glass
where PCBs lie. Because i haven't used a flouro box for a while, there's a
chance that exposure may be too quick and you'll have to use less tubes.
Paint the inner sides of the box matt black, and have a good flat white
reflective surface behind the tubes. You can use long parabolic reflectors
if you can get them, and that they don't put out extra bright spots on your pcb
(reflectors are best if you want long distance like 20cm or more).

>>>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.
> 
> Actually, it's very expensive ink, and better in the Epson than the Epson 
> ink.

It doesn't matter how expensive it is, if it's not compatible with the
transparency. I've seen replacement ink that's supposed to give equal
results on photo quality inkjet paper, but it doesn't work on the
epson transparency.

Unlike other transparencies that are just a rough sandpapery surface,
the epson stuff has a gelatine absorbing coating. Print heavy in epson
ink and you'll see the droplets absorb and sink into it. Other ink just
sits on top.

Certain combinations of refill ink and transparency can give adequate
resolution, but take longer to dry, and may not be as dark (still dark
enough tho).

If you use expensive epson transparency and ink, do a quick rough printout
on normal paper, then stick down a piece of transparency the right size,
and feed back thru for a final print. A packet of transparency lasts a
lot longer then. I only use the epson stylus 400 color (720dpi) for pcbs,
so the ink lasts a long time. I also only do negative printouts and have
large copper fills, so minimal ink is used for large boards. It would be
better to use a later model epson because the ink is cheaper and you get
1440 or 2880dpi (720dpi is adequate tho).

 > I fancy myself a photographer in other moments. Granted, everything
> seen through a 50x microscope looks flawed. The LJ is just less flawed than 
> the inkjet.

Non-linear dimensional warming of paper in a laser printer is a problem for
cnc and doing larger double-sided PCBs.

>>>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.
> 
> My laminator cost $50. Even with a lightbox, I would still want to use it 
> for panels.
> 
>>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.
> 
> And expensive, at least at Think and Tinker's prices. Committing to 50 sq. 
> ft. of material is asking quite a bit.