This article was taken from the June 2015 issue of WIRED magazine. Be the first to read WIRED's articles in print before they're posted online, and get your hands on loads of additional content by subscribing online.
Steve Hodges wants to make it easy to prototype electronic devices, so he's found a way to print circuits with an inkjet printer. Hodges, head of the sensors and devices group at Microsoft Research in Cambridge, says the technique could be transformative for the maker community. "It makes electronics more accessible," he says. "We're empowering people to learn about circuits, play with designs, and make their own devices. Ultimately, we hope some people are going to sell these things across a wide range of products."
Hodges worked with, among others, Yoshihiro Kawahara at the University of Tokyo to hack a standard inkjet printer. The trick is to load the printer cartridges with special ink containing silver nanoparticles developed by Mitsubishi Chemical in Japan. When the ink is deposited on to high-quality photo paper or thin plastic film, the silver nanoparticles instantly fuse together -- a process called self-sintering -- to produce a thin layer of pure silver. Crucially, it works at room temperature. "Typically, silver nanoparticle inks require heat treatment," says Hodges. "Until recently you'd need a small team of PhDs in bunny suits in a clean room and a £30,000 printer. Now you can do it at home with a £50 printer."
You also won't need a soldering iron: Hodges and Kawahara have attached electronic components such as resistors, capacitors, sensors and LEDs by using conducting glue. They've also used circuit stickers: components backed with conductive double-sided sticky tape, which can be peeled off and stuck down to matching points on the circuit. Circuit stickers are not yet widely available but they can be purchased from chibitronics.com, a startup founded by Jie Qi at MIT Media Lab in the other (Massachusetts) Cambridge. "We're at a tipping point where it's becoming easy and inexpensive for people with very little experience of electronics to play around with working circuits," says Hodges. Get started by printing this simple circuit to switch on an LED.
What you'll need
- Standard inkjet printer (such as the Brother DCP-J140W)
- High-quality photo paper
- Silver nanoparticle ink supplied by Mitsubishi Paper Mills (NBSIJ-MU01)
- LED sticker
- Coin-cell battery
Design your circuitOpen Microsoft PowerPoint and draw your circuit. "You could use any drawing software that allows you to put black where you want the silver ink to go and white where you don't," says Hodges. Starting in the top-right corner of the document, draw a 6mm-thick line down 10cm, across to the right 5cm, then back up 7cm and across to the left by 3cm. You should have a broken rectangle that looks something like a paper clip. Now make a 1cm gap halfway up the vertical line on the left.
Configure the printerMost standard inkjet printers will do the job, but Hodges and colleagues used the Brother DCP-J140W because Brother nozzles are known to eject higher volumes of ink than other brands. Now optimise the printer settings: media type/other photo paper; print quality/best; colour mode/vivid; enable colour enhancement; colour density/+2; enable improve pattern printing. "We found that these setting result in the right amount of ink to ensure good conductivity," says Hodges.
Fill your cartridgesThe silver nanoparticle ink comes with a syringe and disposable paper filters. Wearing rubber gloves to avoid getting ink on your skin, draw the ink out of the bottle into the syringe. Attach the filter and push the ink into the empty cartridge. "You need third-party cartridges that have not been filled before to avoid contaminants that could result in poor sintering," explains Hodges. Carefully fill all four colour cartridges (C, M, Y and K) and then install them into your printer.
Add paper and print the circuitUse high-quality photo paper such as Kodak Premium. "The chemical coating on this sort of paper means the ink dries out very quickly, avoiding smudges and allowing the silver nanoparticles on the surface to self-sinter," says Hodges. Open your circuit document in PowerPoint and hit "Print". "It will take longer than usual with these printer settings because it prints more carefully and puts down more ink. But in around two or three minutes you'll see your circuit pop out."
Stick on an LED, fold to lightOnce your circuit has dried, place the circuit-sticker LED across the gap on the vertical line on the left of the circuit. Make sure the apex of the triangle points upwards and you press down each end to ensure good contact with the printed silver strips. Place the coin-cell battery negative-side down at the end of the circuit and fold the paper over at the top-right corner so both ends of the circuit are in contact with the battery. The LED will light up. To keep it shining, hold the fold in place with a binding clip.
This article was originally published by WIRED UK
