--- In
Homebrew_PCBs@yahoogroups.com, DJ Delorie <dj@...> wrote:
>
>
> James Arthur writes:
> > I don't think that's super critical for signal traces--as long as the
> > trace exists & survives etching without breaking; we don't care if
> > it's a little wavy.
>
> I was thinking that less waviness in the print gives you more leniency
> elsewhere. At least, my prints don't have a definite "edge", it's
> more of a 3 thou wide blur. So I can't tell in advance where the edge
> of the copper will be.
We have to distinguish between sharply defined dots in staggered
positions (staggered due to aliasing, for example), from smudged dots.
Angling the printouts 45 degrees might fill in gaps via improved
interpolation.
My 600dpi laser prints on magazine paper are razor-sharp to the eye,
but close-ups reveal a 1-to-1.5 mil-wide scalloping, sloping,
spattered transition at each edge/border. (I'm not sure how to
quantify it better.)
There are also a surprising number of defects in the black areas,
something I hadn't noticed.
From the above estimates of the "sharpness" of my prints on paper, I
suppose that factor would limit me to no better than 6/6 with this
paper (giving traces that, with worst-case defects on both sides,
would be 3 mils, and in danger of etching through).
If the toner is smearing on your paper, it's also poosible the paper's
absorbing and spreading the toner a bit. I've seen papers do that.
If the image is sharp on the paper, it could be smearing during
transfer to the PCB. That's definitely a danger when using a clothes
iron, and could be a problem with multiple passes through a laminator.
The artwork is bound to creep a little each time through.
Passing a gridded test pattern through the laminator multiple times,
keeping the same orientation each time, should reveal any creepage.
> But if the mask is the issue, wouldn't inkjet+photomask be able to be
> done at finer resolution? Or do they still have issues with "fuzzy"
> edges?
Dunno. I haven't used my inkjet since the first cartridge dried up,
virtually unused. That was years ago, and I was too irritated to
replace it.
Whatever the inkjets' resolutions, one could always print the artwork
2x, then reduce it photographically or with lenses.
> > > ∗ Thinner copper?
> >
> > Maybe, but why? (for high currents?) Could electroless plate it up
> > afterwards--that's not hard.
>
> I'm thinking less side-etch, allowing you more time (relatively) to
> over-etch everything else. What I mean is, "in the time it takes you
> to go 150% of the copper etch time, the side etch is still much less
> than with thicker copper."
>
> For example, when I etch 5 thou brass, I can't do a 5 mil space
> between pads because the sides etch all the way across under the
> resist.
Yes, definitely--thinner copper will reduce undercutting. I somehow
read that as "thicker" copper instead of "thinner." Sorry.
> > I've just done my first experiments with magazine paper at 0.010"
> > traces and spaces. I found it transfers and releases ∗much∗ better /
> > more completely than the inkjet paper I had been using.
>
> I'm using Pulsar's paper, which transfers just fine, but the original
> has a "fuzzy" edge, which results in variations in line widths. The
> 2550N has a number of software knobs to fiddle with, but I haven't
> been able to get any of them to make any noticable changes in the
> actual print.
>
> > (Preliminary reason seems to be, in part, the magazine paper is
> > thinner, allowing better heating of the coppper foil underneath it
> > when passing through my laminator. A hot air gun also helps keep
> > everything at temperature.)
>
> I often pass the board alone through the laminator a few times to warm
> it up. I have some 8 and 16 thou SS on order for some
> experimentation, I know I can't get a good transfer with 62 thou
> phonelic as it sucks up too much heat from the laminator.
I preheat by putting the board part-way in. There the laminator's
heaters clamp down and heat the board, but the board is short of the
feed rollers. When the board's good and hot--judged by feel, and the
laminator's "Ready" light staying on--I give the board a push & let it
feed. I then also pass the board through the laminator a few times,
simultaneously adding extra heat to the copper clad with a small heat gun.
More convenient and possibly better, I think, would be to preheat the
board with a heater of some sort (halogen torchiere lamp bulb?), and /
or to slow the laminator's feedrate. One pass might then be enough
for a good transfer.
> I've never tried magazine paper. I suppose that's at least free to
> try, but the TT paper releases so well...
I think the way to achieve finer lines is to go step-by-step in tuning
the process. For toner-transfer, first get hi-res prints. Next,
concentrate on hi-res transfers to the copper-clad. I believe thin
copper and the "float" etch technique I referenced (post #14965) will
suffice for etching to 6/6, maybe better.
James Arthur