- Apr 01.2014, 15:37:00
In a pinch, I have had to make a pcboard literally from a cardboard cigar box lid. A cigar box lid has no conductive surface to etch, so you're going to have to add conductors. There are several ways to do that, and of course you don't have to make it on a cigar box. One way is point to point wiring. Another is to use conductive paint. Yet another is to use copper donut pads and foil tape. That's what we'll look at here. They used to be commonly available, but are harder to find now. One source is Datak. Their web page is a little bit 1990's, but the donuts and tape catalog page is there. CF-2 for the donuts, and CF-3 for the foil. I haven't found a source for it other than Surplus Traders in Vermont, and Circuit Specialists in Arizona. You'll need to search for them by part number.
The method is simple:
Use a component layout pattern to drill holes in the substrate.
Lightly sand the substrate if required to remove burrs.
Stick donuts to the substrate and burnish.
Connect the dots using foil tape and burnish.
Lightly solder the tape onto the pads.
Solder the components into their places.
The tricky part is...well, it's all tricky. You have to get the pads and tape burnished onto the substrate, and they don't want to stay. Then you have to solder the tape to the pads, because the adhesive is the best insulator known to man. The adhesive is also thermally reactive, so once heated it loses it's sticky. To be fair, it was not intended to be used to create PC boards, it was made to make minor repairs to existing circuits. Old fashioned circuits, with really big traces. It serves that purpose well enough.
Newer foil tape, which comes in various widths and is widely available, can be handy for RF circuits. An example of this copper foil tape RF application can be found at the HP Archive. The tape is also good for shielding. This "modern" tape generally has conductive adhesive, so you must use mylar packing tape or similar to insulate where traces cross.