Sunday, May 01, 2005


First Successful Silver Paint Circuit

The first working circuit has been constructed using technniques similar to PCB construction but with only EVA hot-melt glue and conductive silver paint as materials.

The circuit shown below (click here for a larger image) shows a working soil moisture detector; it is shown here detecting a moistened thumb. A report will appear on the site in the near future.

Are the ripples due to the manufacturing process or when the circuit was soldered? Come to think of it, did you solder the components or was some other technique used?

On a more tangential note, there are a couple of halfbakery ideas that are at least peripherally related to this project:

Low-melting-temperature Plastic Construction Kit, Hot Glue Fabricator and Conductor Transfer Paper
The low-temp plastic is what we call Polymorph, I'm pretty sure. See the blog for 6 April.

I like the hot glue fabricator - that's essentially what Vik's working on. Incidentally, I've found that it's easy to drill & tap the nozle of a glue gun, screw in a short piece of studding, and lock it with a nut. If you put the studding in a lathe you can drill an 0.5 mm hole down it and taper the end to a cone. The result puts out a very fine stream of glue.

I also like the conductor transfer paper. But the problem with copper powder in this context is that the oxide that forms on it can inhibit conduction between particles. Silver is a lot better, but a bit pricey, of course.

- Adrian
Yes, it looks like Polymorph is the same type of plastic. Interesting that its melting temperature is about the same as that of Wood's metal. You could, in theory, use the same type of head to deposite either one, then.

Found a comparison chart of various fusible alloys: Alchemy Castings. Looks like the Low 158 category is equivalent to Wood's Metal.

It'd be handy to find a source for this stuff in glue gun compatible sticks.
The ripples in the plastic are due to my uneven manual movement of the X-Y table - I've not built the automated controls yet. The ripples are a pain as they provide convenient fracture points for the sliver paint to flake along. This should be eliminated when a more solid substrate layer such as polymorph or ABS is added.

The components are not soldered. They are held in place by the layer of plastic through which they are pushed, and blobs of conductive silver paint complete the circuit to the tracks.

I'll publish a full write-up.
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