I just posted a note in comp.robotics.misc about using 4 mil
single-matte mylar for this purpose. Print the pads and traces on the
shiny(non-matte) side. Placing the shiny side in contact with the copper
foil, iron the mylar until it turns from translucent to almost
transparent. I was set to "wool" and it took about 10 minutes. When the
mylar is peeled off the traces remain on the copper foil. I was able to
duplicate a 5 mil line with this process.

Thanks for having this archive. It is great.

Dr. Spiff


========================


later:

I've done a couple of boards now using single-matte mylar as the transfer
medium and can report that it seems to work well. For more efficient etching
I built a new tank and apparatus. 

The tank is a CD case glued shut on 3 sides and open on the top. This gives
me a vertical etching tank that holds about 3 oz. of etchant and will
accomodate a PCB about 4.5" square. I RTV'd a holder for this tank onto a
small aquarium air pump and piped the air into a small manifold in the base
of the tank. This give me a 60hz agitation as well as bubbles to flake off
the excess copper. A 50 watt quartz-halogen light mounted normal to the tank
and about 6" away raises the etchant temp to about 55 degrees C. 

My etchant is Ferric Chloride cut 50% with water. This allows me to see the
progress of the board. I just finished a 2" by 2" board in 7 minutes with
this setup. 

I hope this info helps those of you embarking on the quest for the "perfect
board".

Dr. Spiff