Homebrew PCBs

When you print to a laser printer, the paper gets heated causing the paper
to expand. The moisture also gets driven out, which I believe causes the
paper to shrink. Net expansion probably depends on the relative humidity of
where you live. Depending on the grain of the paper, it will probably
expand/shrink more in one dimension than the other.

Running some pages through the printer immediately before prior to printing
on them will help. You may need to print something along the edges to get
the wire to heat up.

You can really see this effect on duplexing laser printers, where the first
side imaged has a sometimes dramatically different size (up to 1/8") than
the second side imaged.

I believe that with transparencies, the expansion is more uniform. Because
the media is expanded while being printed, it causes your image to shrink
once the media cools down.

With ink jet printers, you're adding moisture to the page, which causes it
to expand. Here, the amount of ink makes a difference (more ink = more
expansion). The grain of the paper will cause different amounts of expansion
in either dimension. Things should shrink back up a bit once the ink is
completely dried.

I wouldn't expect transparencies to be affected on an ink-jet (except for
heating effects, which should be much less than a laser printer).

Dave Hylands

> -----Original Message-----
> From: Steve Greenfield [mailto:alienrelics@...]
> Sent: Tuesday, April 02, 2002 12:54 PM
> To: Homebrew_PCBs@yahoogroups.com
> Subject: Re: [Homebrew_PCBs] Printing PCB boards
> 
> 
> --- JanRwl@... wrote:
> > In a message dated 02-Apr-02 05:36:45 Central Standard Time, 
> > derryck@... writes:
> > 
> > 
> > > Print your layouts using the right transparent medium for your
> > printer
> > > (laser or inkjet) and use that to expose the board under UV
> > 
> > 
> > But this assumes the PRINTER will make an exact "1:1" duplicate
> > of the 
> > artwork you "draw" on the screen!  Without a special plotter
> > DESIGNED for 
> > that, how can this really happen?  Just how accurate ARE these
> > ink-jet 
> > printers?
> 
> I used to use a Canon 610, it was not symmetrical and printed
> slightly smaller than it was supposed to. Haven't tested my Canon
> 6000 to any high degree of precision, I seem to recall measuring an
> 8x10 print once and it was within a 1/16".
> 
> Back in the days when I used copy machines to make business cards
> and photo layouts, I had to use one particular copy machine. At
> 102%, it would print out very close to 100%. I had it worked out to
> blow up a PCB or business card pattern to a particular percentage,
> then I'd clean it up, then shrink it down by a particular
> percentage. By the math, it wouldn't work out, but because of the
> copy machine it would work out.
> 
> Steve Greenfield