Now, though, thanks to some brilliant minds at the UIUC Materials Research Laboratory, you can make your own decent conductive ink!
This ink seems to address many of the problems that other inks have. It’s particle free (won’t clog print heads!), is easy to make, and anneals to the conductivity of bulk silver at only 90 degrees Centigrade (194 degrees Fahrenheit).
After I stumbled upon this paper last month, I decided that I absolutely had to make some.
I am not a chemist, nor have I done any chemistry since high school, so I ended up having to buy both the glassware as well as the chemicals. Even after buying everything that I needed (and some stuff that I probably didn’t), I only spent around $150.
For those of you who want to repeat the process, here’s my list of purchases:
GLASSWARE AND TOOLS:
TOTAL: $109.86 (plus shipping)
After receiving the materials and reviewing the proper MSDS sheets (1,2,3) I got to work.
NOTE: Please don’t do this at home unless you understand the risks and dangers and know how to avoid them. In fact, it’s best that you have a chemist or someone experienced with how to handle chemicals properly help you.
Ammonium hydroxide is nasty stuff. Formic Acid is even worse (It’s basically liquid pain. It’s the chemical in ant bites and bee stings that makes them hurt). Please respect this stuff.
(All of the instructions I have listed here were extrapolated from the journal article from UIUC.)
USING AND ANNEALING THE INK:
The first thing I tried was silver acetate on regular printer paper.
It didn’t work. I’m guessing the paper is too porous, while the silver is coating the paper fibers, the individual particles are too far apart to conduct electricity between each other. Even after 3 coats, I was unable to get the paper to conduct. More experiments are pending…
The second thing I tried was thread. Again, this didn’t work. I’m thinking the reason is similar to the paper.
The third thing I tried was glass. This worked!
The resulting traces were a bit low in conductivity for ink. The first reading I got was about 9 Ohms over a centimeter. (Your mileage may vary)
I was able to light up an LED using the traces.
Then I tried stenciling it by applying masking tape and then laser cutting the stencil into the tape.
I then applied the ink over the tape, and annealed it. Unfortunately, the tape didn’t quite stick so well, so some of the ink flowed underneath it…
I tried again, heating up the tape pattern and making sure it was thoroughly stuck to the tape.
Better, but there was still one problem; the ink scraped off quite easily. If I wanted to use the ink for anything practical, I’d have to fix it.
Since it was 3am, and I was finally tired enough to try anything, I laser etched a piece of glass into the shape of the trace that I wanted. My reasoning was that the rough surface of the etched glass would help the silver stick to the glass, and also provide a “trench” for the silver to be deposited into.
The first attempt didn’t work… but after the second coating, it worked! I’m guessing that the rough surface of the engraving had too many little peaks and valleys which kept the silver from forming a uniform surface.
The other benefit of the laser-etching method was that I didn’t need a stencil anymore. The trench allowed me to wipe the excess solder from around the trace without removing the silver deposited in the etching.
I wasn’t able to solder directly to the silver surface, but I did have a Circuit Writer silver-based pen. I coated the pads in the Circuit Writer ink, and after it solidified (about 10 minutes) I was able to solder components directly to the pad.
This is my first finished circuit on a glass substrate.
I’m pretty satisfied with it.
There are plenty more things to try, and methods to apply, and I’ll continue to document them on this blog, so stay tuned! Of primary importance is increasing the conductivity, which should be possible by thinning it with alcohols.
If any of you make your own ink, please let me know! I’d love to hear about other people’s work.
Special thanks to Sacha De’Angeli, @IdeaPDish, and Steve Finkelman for their advice! Also thanks to Pumping Station: One, where I did all of this work!