Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

Hi.

I have been printing artwork for making PCB's using negative photo resist. The first problem I ran into was the lack of opacity of the toner. It looks nice and dark until I hold it up to a light, then it's easy to see how translucent it really is.

I tried using the whiteboard marker method mentioned on this list before, but had problems getting it to work consistently. Usually I can't removed the marker from the clear part of the foil without also removing some of the toner.

I have tried dipping the foil in acetone or xylene. The toner looks much better, but is only marginally more opaque.

Heating the foil gives basically the same result as the solvents, but somewhat more opaque.

I tried spraying the foil with clear paint. Doesn't help at all, but it looks very nice. Might be useful for other purposes like panels.

The method I found to work best us to bond an opaque powder to the toner.

I used a very fine cerium oxide powder, normally used for polishing telescope mirrors. I will try aluminium oxide when I remember where I put it. I also tried powdered graphite, but it did not work nearly as well as the cerium oxide.

I put a clothes iron upside down and the put the foil on top of it, with the non-printed side touching the iron. I then brush CeO2 powder on it until no more powder will stick. After it has cooled for a few seconds I wash it with water and detergent. The result looks gray but is very opaque. It took some experimenting to find the correct temperature setting so that the toner would bond to the powder while not shrinking, but there seems to be a wide range that works.

I also tried mixing the CeO2 with xylene and dip the foil in it before leaving it to dry. After it was dry I washed off the excess powder. This works, but the result was less consistent and not as opaque as the melting method.


Emil