I use the old reliable method.
I place 3 fiducials on the board for alignment holes near the corners
of the board. Two are for alignment and the third is a check point.
They should be near 3 of the 4 corners on the pcb. These can be actual
fiducials or they can be mounting holes or component holes near the
corners as well.
I carefully poke a hole through the center of the alignment holes on
the images for both layers with a pin (fiducials have a cross hair to
make this easy to do).
Take one layer and lay it on the copper board and mark through each of
the 3 holes with a small sharp center punch (accuracy depends on how
well these holes are marked and drilled.
Drill each hole carefully with a small bit (I use a #75).
Place the top layer image on the copper board and align it by placing
pins through the hole in the image and the pcb in two opposite
corners, the 3rd hole can be used to verify alignment is good or can
be used for alignment if one of the other holes are bad for some reason.
With the image aligned on the pcb, tack it down with an iron being
carefully that the image is pressed flat to the pcb and doesn't move
while tacking.
Remove the pins and Iron the image thoroughly to the board. Let board
cool and repeat on the other side (if the board is hot, the image will
start to stick before being aligned).
After both sides are done, soak & remove the paper. This has worked
perfectly for me every time. All of my boards are double sided with
usually 10/10 rules. Vias are a little larger to make drilling easier.
Phil (KA0HBG)
--- In Homebrew_PCBs@yahoogroups.com, "awakephd" <a_wake@...> wrote:
> 2) Both of my recent efforts with TT have been double-sided layouts.
> The first time, I tried to align using the edges of the board; the
> second time, I thought I had gotten smart (based on something I read
> here or elsewhere), and I lined up the two prints using a bright
> backlight, then stapled them together to make a "pocket" into which I
> inserted the board. Both methods gave me boards that were usable, but
> not as closely aligned as I had hoped -- the second was marginally
> better, but still off in some places by maybe .010" - .020". What's
> the secret to getting a perfectly aligned double-sided board?
>