Interesting homebrew process from Charles Lohr, who demonstrates it here with a multicolor-LED-controlling capacitive touch sensor that works from the reverse side of the glass, i.e. you can use it without actually touching the copper. No holes are drilled in the glass, so components have to be SMT.
Cool stuff. Charles has promised a dedicated blog post to follow on the topic, but in the meantime, here’s my condensed version of his process:
- Apply glass microscope slide to slightly oversize 1-oz copper PCB foil with UV-curing glue. Press out bubbles.
- Cure adhesive using appropriate UV source, e.g. EPROM eraser. Dab away uncured glue. Cut away excess foil.
- Laser print PCB stencil on toner transfer paper, and apply stencil to copper-glass composite using conventional toner transfer methods. Be cautious when applying pressure, e.g. with an iron, to avoid cracking the glass.
- Etch away the unmasked areas as usual.
- Gently clean away remaining toner with a scrap of steel wool under running water. Dry the board thoroughly with a paper towel.
- Use a toothpick to dab no-clean solder paste onto the pads, and position SMT components as needed using tweezers.
- Carefully and evenly heat the board with a heat gun to melt the solder paste and secure the components. Touch up any bad joints with a soldering iron while the board is still hot.
- Test the board.
- Allow board to cool, then coat copper side with clear polymer overcoat, e.g. polyurethane varnish. This both protects the copper and clarifies the cured UV-adhesive, which has a “frosted” look without it.
I wonder how hard it would be to form the circuit traces without etching at all, e.g. by using a photomask to just cure the UV adhesive in those areas where you want copper, then washing off the uncured glue and mechanically removing the unglued copper, somehow? Could you use gold leaf instead of copper? [via adafruit]