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

I have been away for awhile and noticed several recent posts investigating various printers and inks for making really dark transparencies for photo exposure masks.

I have been using the positive photoresist method for more than 10 years. Initially, I used an HP inkjet on a high quality (expensive) transparency medium produced for commerical artists. That worked well, but infrequent use led to dried ink cartridges and all the problems associated with that.

More recently, I simply make my transparencies with a laserjet (HP 4101). It doesn't print particularly dark. I use 3M transparency CG3300. That probably doesn't matter. After printing, I let the transparency cool and then go over the entire image with a black, dry erase marker. I use Expo brand. Try to do it with single, overlapping strokes. The solvents in the marker will soften the toner image slightly. Don't scrub the marker back and forth over the transparency. Let it dry thoroughly (10 minutes), then I use folded facial tissue (Kleenex brand) to remove the dry erase. I usually make a first couple of swipes to remove the bulk of the excess, then open a clean surface and remove the rest. The dry erase sticks in the crevices and areas between toner particles, but removes cleanly from the clear areas. You can rub pretty hard to remove last little bits that might be stuck around thermals or other very fine details. In my experience, colored dry erase will not work, as the dyes used in them are not as easily removed.

I will try to upload a picture of a recent board I did for a QFN package. Traces on the QFN sub-board are 16 mil. On the main board they are 24 mil, and you can see that the letters in my name and date are considerable smaller.

John